Non-aqueous lithium battery cells

Abstract

The present invention provides a non-aqueous lithium storage element, which comprises a positive electrode, a negative electrode, a separator and a non-aqueous electrolyte, wherein the positive electrode comprises a positive electrode collector and a positive electrode active material layer, the positive electrode active material layer comprises activated carbon, and has the following constitution (1) and / or (2): (1) the negative electrode comprises a negative electrode collector and a negative electrode active material layer, the negative electrode active material layer comprises a carbon material, and in a binary image of a SEM image taken of the surface of the negative electrode active material layer, for all pixels in a bright field area, a set of maximum inscribed circles enclosed by each pixel is obtained. When expressed in the form of a frequency distribution of each diameter, the area ratio Z1 of the total area of ​​the largest inscribed circle with a diameter less than 100 nm in the total area of ​​the largest inscribed circle is 3.5 to 25.5%; (2) the non-aqueous electrolyte contains: (A) LiPF6 and / or LiBF4, (B) an imide-based lithium salt, and (C) an oxalic acid complex-based lithium salt, and the mass of the (C) component in the non-aqueous electrolyte relative to the total mass of the (A) component and the (B) component is 1.0 to 10.0 mass%.

Description

Technical Field

[0001] The present invention relates to a non-aqueous lithium storage device. Background Art

[0002] In recent years, from the perspective of effectively utilizing energy to protect the global environment and conserve resources, wind power generation power stabilization systems and midnight power storage systems, household distributed power storage systems based on solar power generation technology, and power storage systems for electric vehicles have attracted attention.

[0003] The primary requirement for batteries used in these power storage systems is high energy density. As a powerful alternative to high-energy-density batteries that can meet this requirement, the development of lithium-ion batteries has been actively promoted.

[0004] The second requirement is high output performance. For example, in a combination of a high-efficiency engine and a power storage system (e.g., a hybrid electric vehicle), or a combination of a fuel cell and a power storage system (e.g., a fuel cell electric vehicle), the power storage system is required to have high output discharge characteristics during acceleration.

[0005] Currently, electric double layer capacitors and nickel-metal hydride batteries are being developed as high-output power storage devices.

[0006] Among electric double-layer capacitors, those using activated carbon as electrodes have an output characteristic of approximately 0.5 to 1 kW / L. These electric double-layer capacitors also have high durability (cycle characteristics and high-temperature storage characteristics) and are considered to be the best devices for the aforementioned fields requiring high output. However, their energy density is only approximately 1 to 5 Wh / L. Therefore, there is a need to further improve the energy density.

[0007] Meanwhile, nickel-metal hydride batteries currently used in hybrid electric vehicles have high output comparable to electric double-layer capacitors and an energy density of approximately 160 Wh / L. However, there is a demand for further improvements in energy density and output, as well as enhanced durability (particularly stability at high temperatures), and research is actively underway to achieve these goals.

[0008] In addition, in lithium-ion batteries, research has also been conducted towards high output. For example, a lithium-ion battery with a high output of more than 3kW / L when the depth of discharge (a value indicating the state of how much percentage of the discharge capacity of the storage element has been discharged) is 50% has been developed. However, its energy density is less than 100Wh / L, and the high energy density, which is the biggest feature of lithium-ion batteries, is deliberately suppressed by the design. In terms of its durability (cycle characteristics and high-temperature storage characteristics), it is inferior to that of double-layer capacitors. Therefore, in order to have practical durability, it is used in a range narrower than the range of 0-100% depth of discharge. Since the capacity that can be actually used will become smaller, research to further improve durability is actively carried out.

[0009] As mentioned above, there is a strong demand for the practical application of energy storage devices that combine high energy density, high output characteristics, and durability. However, existing energy storage devices have both strengths and weaknesses. Therefore, there is a need for new energy storage devices that fully meet these technical requirements. As a promising alternative, energy storage devices known as lithium-ion capacitors are attracting attention and are being actively developed.

[0010] A lithium-ion capacitor is a type of storage element (non-aqueous lithium storage element) that uses a non-aqueous electrolyte solution containing a lithium salt. This storage element is charged and discharged by performing a non-Faradaic reaction at the positive electrode at approximately 3V or above, based on the adsorption and desorption of anions, similar to an electric double-layer capacitor, and a Faradaic reaction at the negative electrode, based on the absorption and release of lithium ions, similar to a lithium-ion battery.

[0011] Summarizing the aforementioned electrode materials and their characteristics, when materials such as activated carbon are used for the electrodes and charging and discharging are performed by adsorption and desorption of ions on the activated carbon surface (non-Faradaic reactions), high output and high durability can be achieved, but the energy density is reduced (for example, by 1 times). On the other hand, when oxides or carbon materials are used for the electrodes and charging and discharging is performed by faradaic reactions, the energy density is increased (for example, 10 times that of non-Faradaic reactions using activated carbon), but there are problems with durability and output characteristics.

[0012] As a combination of these electrode materials, the electric double layer capacitor is characterized in that activated carbon (energy density is 1 times) is used for the positive and negative electrodes, and both the positive and negative electrodes are charged and discharged by non-Faradaic reactions. It has the following characteristics: although it has high output and high durability, the energy density is low (1 times the positive electrode × 1 times the negative electrode = 1).

[0013] Lithium-ion secondary batteries are characterized by using a lithium transition metal oxide for the positive electrode (10 times the energy density) and a carbon material for the negative electrode (10 times the energy density). Both the positive and negative electrodes are charged and discharged through the Faradaic reaction. While they offer high energy density (10 times the positive electrode x 10 times the negative electrode = 100), they suffer from issues with output characteristics and durability. To meet the high durability requirements of hybrid electric vehicles and other applications, the depth of discharge must be limited, and lithium-ion secondary batteries can only use 10-50% of their energy.

[0014] Among the batteries (storage elements) used in the aforementioned energy storage systems, lithium-ion capacitors are characterized by using activated carbon (1x the energy density) for the positive electrode and a carbon material (10x the energy density) for the negative electrode. The positive electrode charges and discharges via a non-Faradaic reaction, while the negative electrode charges and discharges via a Faradaic reaction. This is a novel asymmetric capacitor that combines the characteristics of both an electric double-layer capacitor and a lithium-ion secondary battery. Despite high output and durability, it boasts a high energy density (1x the positive electrode x 10x the negative electrode = 10), eliminating the need for depth-of-discharge restrictions common to lithium-ion secondary batteries.

[0015] Various studies have been conducted to further increase the output and durability of the lithium ion capacitors described above (Patent Documents 1 to 10).

[0016] Patent Document 1 proposes a lithium ion secondary battery that uses lithium bis(oxalato)borate as a lithium salt and contains acrylonitrile as a solvent, thereby achieving high output characteristics.

[0017] Patent Document 2 proposes a lithium ion secondary battery using LiPF6, LiBF4, and lithium difluorooxalatoborate as fluorine-containing lithium salts, and having excellent corrosion resistance and long-term stability of the Al current collector.

[0018] Patent Document 3 proposes a lithium ion secondary battery that includes a negative electrode active material having a particle size of 3 μm or less and uses an oxalatoborate-type compound and a difluorophosphate compound in the electrolyte, achieving a good balance between input characteristics and storage durability.

[0019] Patent Document 4 proposes a lithium ion capacitor using a lithium salt electrolyte having an imide structure and a binder containing a polymer whose solubility in the electrolyte is suppressed. The capacitor can maintain its capacity in a high temperature environment of 85° C. with minimal increase in internal resistance.

[0020] Patent Document 5 proposes a lithium ion secondary battery using a non-aqueous electrolyte containing an oxalatoborate-type compound, which can suppress an increase in film thickness and thereby suppress an increase in negative electrode resistance.

[0021] Patent Document 6 proposes a non-aqueous electrolyte solution containing specific amounts of a bismaleimide compound and fluoroethylene carbonate, respectively, which can maintain capacity in an environment of 60°C.

[0022] Patent Document 7 proposes a lithium-ion secondary battery that uses a non-aqueous electrolyte solution containing a lithium salt electrolyte having an imide structure and one or more additives selected from the group consisting of lithium difluorooxalatophosphate, trimethylsilylpropyl phosphate, 1,3-propylene sultone, and vinyl sulfate, and that can maintain capacity in an environment of 60°C.

[0023] Patent Document 8 discloses a negative electrode for achieving high output of a lithium ion capacitor. The negative electrode active material has a coating composed of carbon nanotubes and carboxymethyl cellulose formed on the surface of the negative electrode active material. The mixing ratio of carbon nanotubes and carboxymethyl cellulose is 1.5 to 7.0 by mass.

[0024] Patent Document 9 proposes a positive electrode precursor having high capacity and high output, which promotes the decomposition of an alkali metal compound contained in the positive electrode precursor.

[0025] Patent Document 10 discloses a carbon composite comprising carbon particles as cores and fibrous carbon having a graphene structure formed on the surfaces of the carbon particles in order to improve energy density and achieve higher output.

[0026] It should be noted that, in this specification, the mesopore amount is calculated by the BJH method, and the micropore amount is calculated by the MP method.

[0027] The BJH method is proposed in Non-Patent Document 1.

[0028] The MP method is a method for determining the pore volume, pore area, and pore distribution using the "t-plot method" (Non-Patent Document 2), and this method is described in Non-Patent Document 3.

[0029] In addition, regarding the Thickness of BoneJ in this specification, it is as shown in Non-Patent Document 4.

[0030] Prior art literature

[0031] Patent Literature

[0032] Patent Document 1: Japanese Patent Application Laid-Open No. 2016-192377

[0033] Patent Document 2: Japanese Patent Application Laid-Open No. 2018-60689

[0034] Patent Document 3: International Publication No. 2014 / 002939

[0035] Patent Document 4: Japanese Patent Application Laid-Open No. 2017-17299

[0036] Patent Document 5: Japanese Patent Application Laid-Open No. 2011-34893

[0037] Patent Document 6: Japanese Patent Application Publication No. 2019-186222

[0038] Patent Document 7: International Publication No. 2015 / 065093

[0039] Patent Document 8: Japanese Patent Application Laid-Open No. 2015-156293

[0040] Patent Document 9: Japanese Patent Application Laid-Open No. 2013-73526

[0041] Patent Document 10: Japanese Patent Application Laid-Open No. 2008-66053

[0042] Non-patent literature

[0043] Non-patent document 1: EP Barrett, LG Joyner and P. Halenda, J. Am. Chem. Soc., 73, 373 (1951)

[0044] Non-patent document 2: BC Lippens, JH de Boer, J. Catalysis, 4319 (1965)

[0045] Non-patent document 3: R. S. Mikhail, S. Brunauer, E. E. Bodor, J. Colloid Interface Sci., 26, 45 (1968)

[0046] Non-patent document 4: T. Hildebrand, P. Ruesgsegger, J. of Microscopy, 185 (1996) 67-75. Summary of the Invention

[0047] Problems to be solved by the invention

[0048] In view of the above-mentioned situation, an object of the present invention is to provide a non-aqueous lithium battery element having excellent input and output and high durability against storage at high temperatures of 80° C. or higher.

[0049] Means for solving problems

[0050] The above-mentioned problems are solved by the following technical means. That is, the present invention is as follows.

[0051] <Method 1> A non-aqueous lithium storage element comprising a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte containing lithium ions, wherein:

[0052] The positive electrode comprises a positive electrode current collector and a positive electrode active material layer provided on one or both surfaces of the positive electrode current collector and containing a positive electrode active material.

[0053] The positive electrode active material comprises activated carbon, and

[0054] Having at least one of the following structures (1) and (2):

[0055] (1) The negative electrode comprises a negative electrode current collector and a negative electrode active material layer on one or both sides of the negative electrode current collector.

[0056] The negative electrode active material layer comprises a negative electrode active material, carbon nanotubes and a dispersant.

[0057] The negative electrode active material comprises a carbon material.

[0058] In a binary SEM image of the surface of the negative electrode active material layer, when a set of maximum inscribed circles enclosed by each pixel is expressed as a frequency distribution of each diameter for all pixels in a bright field area, an area ratio Z1 of the total area of ​​the largest inscribed circles having a diameter of less than 100 nm to the total area of ​​the largest inscribed circles is not less than 3.5% and not more than 25.5%;

[0059] (2) The non-aqueous electrolyte solution contains:

[0060] (A) at least one lithium salt selected from LiPF6 and LiBF4,

[0061] (B) a lithium salt having an imide structure, and

[0062] (C) a lithium salt having an oxalic acid complex as an anion, and

[0063] In the non-aqueous electrolyte solution, the ratio of the mass of the component (C) to the sum of the mass of the component (A) and the mass of the component (B) is 1.0 mass % or more and 10.0 mass % or less.

[0064] [Aspect 2] The non-aqueous lithium storage element according to aspect 1, wherein the non-aqueous electrolyte contains (B) a lithium salt having an imide structure, and the component (B) is a lithium salt having an imide structure represented by the following formula (a):

[0065] [Chemistry 1]

[0066]

[0067] {In formula (a), R 1 and R 2 are independently a hydrogen atom, a halogen atom, an alkyl group or a haloalkyl group, R 1 and R 2 At least one of them is a halogen atom or a halogenated alkyl group.

[0068] <<Method 3>> The non-aqueous lithium storage element as described in Method 1, wherein the above-mentioned (B) lithium salt having an imide structure is a lithium salt selected from the group consisting of lithium bis(fluorosulfonyl)imide and lithium bis(trifluoromethane)sulfonylimide.

[0069] [Method 4] A non-aqueous lithium storage element as described in any one of Methods 1 to 3, wherein the non-aqueous electrolyte contains (C) a lithium salt with an oxalic acid complex as an anion, and the component (C) is one or more lithium salts selected from the group consisting of lithium bis(oxalatoborate), lithium fluorooxalatoborate and lithium difluorooxalatoborate.

[0070] <<Method 5>> A non-aqueous lithium storage element as described in any one of Methods 1 to 4, wherein the non-aqueous electrolyte contains one or more nitrile compounds in a range of 0.1 mol / L to 5 mol / L.

[0071] [Method 6] A non-aqueous lithium storage element as described in any one of Methods 1 to 5, wherein the non-aqueous electrolyte contains one or more trinitrile compounds selected from the group consisting of 2-amino-1,1,3-tricyano-1-propene, 1-butyl-3-methylimidazolium tricyanomethane and lithium tricyanomethane in a range of 0.1 mol / L to 5 mol / L.

[0072] [Aspect 7] The non-aqueous lithium storage element according to any one of aspects 1 to 6, wherein the negative electrode active material layer has a solid electrolyte interface (SEI) material on its surface.

[0073] The solid electrolyte interface (SEI) material includes lithium oxalate represented by the following formula (b).

[0074] [Chemistry 2]

[0075]

[0076] "Method 8" A non-aqueous lithium storage element as described in any one of Methods 1 to 7, wherein, in the X-ray photoelectron spectroscopy (XPS) of the above-mentioned negative electrode active material layer, the ratio I1 / I2 of the intensity I1 of the peak P1 observed in the range of 289 eV to 290 eV to the intensity I2 of the peak P2 observed in the range of 284 eV to 285 eV is greater than 0.1.

[0077] [Method 9] A non-aqueous lithium storage element as described in any one of Methods 1 to 8, wherein the non-aqueous electrolyte contains one or more ether compounds selected from the group consisting of 1,2-dimethoxyethane, 1,2-diethoxyethane, tetrahydrofuran, 1.3-dioxane, 1.4-dioxane and 2-methyltetrahydrofuran in a range of not less than 1 mol / L and not more than 10 mol / L.

[0078] [Method 10] A non-aqueous lithium storage element as described in any one of Methods 1 to 9, wherein in a binary image of an SEM image of the surface of the negative electrode active material layer, a 1,000 nm 2 Above 5,000nm 2 The total area of ​​the following regions is 1,000nm 2 Above 20,000nm 2 The area ratio Z2 of the total area of ​​the following regions is 63.0% or more and 92.0% or less.

[0079] <<Mode 11>> The non-aqueous lithium storage element according to any one of Modes 1 to 10, wherein the total content concentration of Fe atoms and Ni atoms in the negative electrode active material layer is 1 ppm to 500 ppm.

[0080] "Method 12" A non-aqueous lithium storage element as described in any one of methods 1 to 11, wherein, in an XRD (X-ray diffraction) spectrum measured for the above-mentioned negative electrode active material layer, it has a peak Y1 having a peak top in the range of 2θ being greater than 26.2° and less than 26.5°, and the half-value width of the above-mentioned peak Y1 is greater than 0.1° and less than 0.5°.

[0081] "Method 13" A non-aqueous lithium storage element as described in any one of Methods 1 to 12, wherein the dispersant in the negative electrode active material layer is two or more selected from the group consisting of carboxymethyl cellulose, polycarboxylic acid, polycarboxylate, polyvinyl pyrrolidone, polyvinyl alcohol and surfactant.

[0082] <<Aspect 14>> The non-aqueous lithium storage element according to any one of aspects 1 to 13, wherein the average fiber diameter of the carbon nanotubes is 2 nm or more and less than 100 nm.

[0083] <Aspect 15> The non-aqueous lithium battery element according to any one of aspects 1 to 14, wherein

[0084] The positive electrode active material layer further comprises carbon nanotubes and an alkali metal compound other than the positive electrode active material.

[0085] When the mass ratio of the alkali metal compound to the total mass of the positive electrode active material layer of the positive electrode is C2 (mass %), 0.1≤C2≤7.0,

[0086] In a binary image of a 1,280×890 pixel (1 pixel = 9.96 nm) SEM image of the surface of the positive electrode active material layer of the positive electrode taken at a magnification of 10,000 times, when the set of the largest inscribed circles enclosed in each pixel for all pixels in the bright field area is represented in the form of a frequency distribution of each diameter, the area ratio Z'2 of the total area of ​​the largest inscribed circles with a diameter less than 100 nm in the total area of ​​the largest inscribed circles is greater than 7.5% and less than 35.0%.

[0087] "Method 16" A non-aqueous lithium storage element as described in Method 15, wherein, in an XRD (X-ray diffraction) spectrum measured for the above-mentioned positive electrode active material layer, there is a peak X2 in the range of 2θ being greater than 25.7° and less than 27.0°, and the half-peak width of the above-mentioned peak X2 is greater than 0.1° and less than 0.5°.

[0088] <<Mode 17>> A non-aqueous lithium storage element as described in Mode 15 or 16, wherein the total content concentration of Fe atoms and Ni atoms in the above-mentioned positive electrode active material layer is 1 ppm to 500 ppm.

[0089] [Aspect 18] The non-aqueous lithium battery element according to any one of aspects 15 to 17, wherein

[0090] The positive electrode active material layer further contains a dispersant,

[0091] The dispersant is two or more selected from the group consisting of carboxymethyl cellulose, polycarboxylic acid, polycarboxylate, polyvinyl pyrrolidone, polyvinyl alcohol, and surfactants.

[0092] <<Mode 19>> The non-aqueous lithium storage element according to any one of Modes 15 to 18, wherein the alkali metal compound is one or more selected from the group consisting of lithium carbonate, sodium carbonate, and potassium carbonate.

[0093] <<Mode 20>> The non-aqueous lithium storage element according to any one of Modes 15 to 19, wherein the average fiber diameter of the carbon nanotubes is 2 nm or more and less than 100 nm.

[0094] [Aspect 21] The nonaqueous lithium battery device according to any one of aspects 15 to 20, wherein

[0095] The positive electrode active material further comprises a lithium transition metal oxide,

[0096] The lithium transition metal oxide is selected from Lix Ni a Co b Al (1-a-b) O2 (where a, b, and x satisfy 0.02 < a < 0.97, 0.02 < b < 0.97, and 0 ≤ x ≤ 1 respectively), Li x Ni c Co d Mn (1-c-d) O2 (where c, d, and x satisfy 0.02 < c < 0.97, 0.02 < d < 0.97, and 0 ≤ x ≤ 1 respectively), Li x CoO2 (where x satisfies 0 ≤ x ≤ 1), Li x Mn2O4 (where x satisfies 0 ≤ x ≤ 1), Li x FePO4 (where x satisfies 0 ≤ x ≤ 1), Li x MnPO4 (where x satisfies 0 ≤ x ≤ 1) and Li z At least one selected from the group consisting of V2(PO4)3 (where z satisfies 0 ≤ z ≤ 3).

[0097] <<Mode 22>> The non-aqueous lithium storage element according to any one of Modes 15 to 21, wherein when the average particle diameter of the activated carbon contained in the positive electrode active material layer is X1,

[0098] 3.0 μm ≤ X1 ≤ 7.0 μm,

[0099] In the Raman spectrum of the activated carbon, when the peak intensity I1 of the maximum value appearing near the Raman shift of 1,590 cm -1 and the peak intensity I2 of the minimum value appearing near the Raman shift of 1,470 cm -1 are such that the ratio I1 / I2 is Y1,

[0100] 2.0 ≤ Y1 ≤ 5.5,

[0101] The product X1Y1 of the above X1 and the above Y1 is

[0102] 10 ≤ X1Y1 ≤ 28, and

[0103] The amount of functional groups Z1 of the activated carbon is

[0104] 0.80 mmol / g ≤ Z1 ≤ 2.5 mmol / g.

[0105] <<Mode 23>> The non-aqueous lithium storage element according to Mode 22, wherein 4.0 μm ≤ X1 ≤ 6.0 μm for the above X1.

[0106] <<Mode 24>> The non-aqueous lithium storage element according to Mode 22 or 23, wherein the product X1Y1 of the above X1 and the above Y1 is 13 ≤ X1Y1 ≤ 26.

[0107] <Aspect 25> A power storage module comprising the non-aqueous lithium power storage element according to any one of aspects 1 to 24.

[0108] [Method 26] The storage module as described in Method 25 is assembled into a system selected from the group consisting of a power regeneration auxiliary system, a power load balancing system, an uninterruptible power supply system, a contactless power supply system, an energy harvesting system, a storage system, a solar power generation storage system, an electric power steering system, an emergency power supply system, a hub motor system, an idle stop system, an electric vehicle, a plug-in hybrid vehicle, a hybrid vehicle, an electric two-wheeled vehicle, a fast charging system and a smart grid system.

[0109] Method 27: A power storage system comprising:

[0110] The energy storage device according to any one of aspects 1 to 24; and

[0111] Lead batteries, nickel-metal hydride batteries, lithium-ion secondary batteries, or fuel cells.

[0112] Effects of the Invention

[0113] According to the present invention, a non-aqueous lithium battery device having both high-temperature durability and input performance can be provided. BRIEF DESCRIPTION OF THE DRAWINGS

[0114] Figure 1 This is a SEM image of the negative electrode active material layer of negative electrode 20 obtained in Example 13.

[0115] Figure 2 yes Figure 1 Binarized image of the SEM image.

[0116] Figure 3 is Figure 2 Frequency distribution of the diameters of the largest inscribed circle obtained from the binarized image.

[0117] Figure 4 This is a SEM image of the negative electrode active material layer of negative electrode 21 obtained in Comparative Example 9.

[0118] Figure 5 yes Figure 4 Binarized image of the SEM image.

[0119] Figure 6 is Figure 5 Frequency distribution of the diameters of the largest inscribed circle obtained from the binarized image.

[0120] Figure 7 This is a SEM image of the positive electrode active material layer of the positive electrode precursor 36 obtained in Example 84.

[0121] Figure 8 yes Figure 7 Binarized image of the SEM image.

[0122] Figure 9 is Figure 8 Frequency distribution of the diameters of the largest inscribed circle obtained from the binarized image.

[0123] Figure 10 This is a SEM image of the positive electrode active material layer of the positive electrode precursor 37 obtained in Comparative Example 42.

[0124] Figure 11 yes Figure 10 Binarized image of the SEM image.

[0125] Figure 12 is Figure 11 Frequency distribution of the diameters of the largest inscribed circle obtained from the binarized image. DETAILED DESCRIPTION

[0126] Hereinafter, an embodiment of the present invention (hereinafter referred to as "this embodiment") will be described in detail for the purpose of illustration, but the present invention is not limited to this embodiment. In this specification, the upper limit and lower limit of each numerical range can be arbitrarily combined.

[0127] Non-aqueous lithium battery elements

[0128] A non-aqueous lithium battery cell generally comprises a positive electrode, a negative electrode, a separator, and an electrolyte solution as its main components. The electrolyte solution used is a non-aqueous electrolyte solution containing an organic solvent and an electrolyte containing a lithium salt dissolved in the organic solvent.

[0129] The non-aqueous lithium-type energy storage device of the present invention is a non-aqueous lithium-type energy storage device comprising a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte solution containing lithium ions, wherein:

[0130] The positive electrode comprises a positive electrode current collector and a positive electrode active material layer provided on one or both surfaces of the positive electrode current collector and containing a positive electrode active material.

[0131] The positive electrode active material comprises activated carbon, and

[0132] Having at least one of the following structures (1) and (2):

[0133] (1) The negative electrode comprises a negative electrode current collector and a negative electrode active material layer on one or both surfaces of the negative electrode current collector, wherein the negative electrode active material layer comprises a negative electrode active material, carbon nanotubes, and a dispersant.

[0134] The negative electrode active material comprises a carbon material.

[0135] In a binary SEM image of the surface of the negative electrode active material layer, when a set of maximum inscribed circles enclosed by each pixel is expressed as a frequency distribution of each diameter for all pixels in a bright field area, an area ratio Z1 of the total area of ​​the largest inscribed circles having a diameter of less than 100 nm to the total area of ​​the largest inscribed circles is not less than 3.5% and not more than 25.5%;

[0136] (2) The non-aqueous electrolyte solution contains:

[0137] (A) at least one lithium salt selected from LiPF6 and LiBF4,

[0138] (B) a lithium salt having an imide structure, and

[0139] (C) a lithium salt having an oxalic acid complex as an anion, and

[0140] In the non-aqueous electrolyte solution, the ratio of the mass of the component (C) to the sum of the mass of the component (A) and the mass of the component (B) is 1.0 mass % or more and 10.0 mass % or less.

[0141] The elements constituting the non-aqueous lithium-type electricity storage device of the present invention will be described in detail below.

[0142] <Positive electrode>

[0143] As described below, in the present embodiment, it is preferred to pre-dope the negative electrode with alkali metal ions in the storage element assembly process. As the pre-doping method, it is preferred to assemble the storage element using a positive electrode precursor, a negative electrode, a separator, an outer body and a non-aqueous electrolyte containing an alkali metal compound, and then apply a voltage between the positive electrode precursor and the negative electrode. In this case, the alkali metal compound can be contained in the positive electrode precursor in any manner. For example, the alkali metal compound can be present between the positive electrode collector and the positive electrode active material layer, can be present on the surface of the positive electrode active material layer, or can be present in the positive electrode active material layer. The alkali metal compound is preferably contained in the positive electrode active material layer formed on the positive electrode collector of the positive electrode precursor. In such a manner, as the alkali metal ions pre-dope the negative electrode, pores are formed in the positive electrode active material layer, and the effective area of ​​the positive electrode active material layer increases.

[0144] In this specification, the positive electrode before the alkali metal doping step is defined as a "positive electrode precursor", and the positive electrode after the alkali metal doping step is defined as a "positive electrode".

[0145] The positive electrode in this embodiment includes a positive electrode current collector and a positive electrode active material layer provided on one or both surfaces thereof. The positive electrode active material layer in this embodiment includes the positive electrode active material and carbon nanotubes, and may also include an alkali metal compound other than the positive electrode active material.

[0146] [Positive Electrode Active Material Layer of Positive Electrode]

[0147] The positive electrode active material layer of the positive electrode contains a positive electrode active material and carbon nanotubes, and may also contain an alkali metal compound other than the positive electrode active material. In the non-aqueous lithium-type storage element of this embodiment, the positive electrode active material layer of the positive electrode precursor preferably contains an alkali metal compound other than the positive electrode active material. However, the alkali metal compound is consumed during the pre-doping of the negative electrode, forming pores in the positive electrode active material layer of the positive electrode. Alkali metal compounds other than the positive electrode active material may or may not remain in the positive electrode active material layer of the resulting positive electrode.

[0148] When an alkali metal compound other than the positive electrode active material remains in the positive electrode active material layer of the positive electrode, for example, by applying a voltage between the positive electrode and the negative electrode during charging, the alkali metal compound in the positive electrode decomposes to release cations, and the cations are reduced at the negative electrode, thereby pre-doping the negative electrode.

[0149] The decomposition of the alkali metal compound is an oxidative decomposition reaction. To properly carry out this reaction, it is necessary to appropriately control the reaction area between the positive electrode and the non-aqueous electrolyte and the electronic conductivity of the positive electrode.

[0150] The positive electrode active material layer may contain, in addition to the positive electrode active material, carbon nanotubes, and an alkali metal compound other than the positive electrode active material, optional components described below as needed.

[0151] [Positive electrode active material]

[0152] The positive electrode active material includes activated carbon, and may further include graphene, a conductive polymer, a lithium transition metal oxide, and the like in addition to the activated carbon.

[0153] In the positive electrode precursor of the present embodiment, the positive electrode active material in the positive electrode active material layer preferably contains activated carbon and a lithium transition metal oxide.

[0154] When activated carbon is used as the positive electrode active material, there is no particular restriction on the type of activated carbon and its raw materials. In order to achieve both high input-output characteristics and high energy density, it is preferable to optimally control the pores of the activated carbon. Specifically, the diameter calculated by the BJH method is above Let the mesopore volume of the following fine pores be V1 (cc / g), and when the micropore volume from the fine pores with a diameter less than is set as V2 (cc / g),

[0155] (1) In order to obtain high input / output characteristics, it is preferable to satisfy 0.3 < V1 ≤ 0.8 and 0.5 ≤ V2 ≤ 1.0, and the specific surface area measured by the BET method is 1,500 m 2 / g or more and 3,000 m 2 / g or less of activated carbon (hereinafter also referred to as activated carbon 1); or

[0156] (2) In order to obtain high energy density, it is preferable to satisfy 0.8 < V1 ≤ 2.5 and 0.8 < V2 ≤ 3.0, and the specific surface area measured by the BET method is 2,300 m 2 / g or more and 4,000 m 2 / g or less of activated carbon (hereinafter also referred to as activated carbon 2).

[0157] Activated carbon having the above characteristics can be obtained, for example, using the raw materials and treatment methods described below.

[0158] [[ID=二十二]]In this embodiment, the carbon source used as the raw material of the activated carbon is not particularly limited. For example, plant-based raw materials such as wood, wood powder, coconut shell, by-products during pulp manufacturing, sugarcane residue, molasses, etc.; fossil-based raw materials such as peat, sub-bituminous coal, lignite, bituminous coal, anthracite, petroleum distillation residue components, petroleum pitch, coke, coal tar, etc.; various synthetic resins such as phenolic resin, vinyl chloride resin, vinyl acetate resin, melamine resin, urea resin, resorcinol resin, celluloid, epoxy resin, polyurethane resin, polyester resin, polyamide resin, etc.; synthetic rubbers such as polybutene, polybutadiene, polychloroprene, etc.; other synthetic woods, synthetic pulps, etc. and their carbides. Among these raw materials, from the aspects of coping with mass production and cost, plant-based raw materials such as coconut shell and wood powder and their carbides are preferred, and coconut shell carbide is particularly preferred.

[0159] As the method for carbonization and activation for making these raw materials into the above-mentioned activated carbon, known methods such as fixed bed method, moving bed method, fluidized bed method, slurry method, rotary kiln method, etc. can be adopted. [[ID=二十七]]

[0160] As the carbonization method of these raw materials, a method of firing for about 30 minutes to 10 hours at 400 to 700 °C (preferably 450 to 600 °C) using inert gases such as nitrogen, carbon dioxide, helium, argon, xenon, neon, carbon monoxide, combustion exhaust gas, or a gas in which these inert gases are the main component and mixed with other gases can be cited.

[0161] Methods for activating carbides include a gas activation method in which carbides are fired using an activation gas such as steam, carbon dioxide, or oxygen; and an alkali metal activation method in which carbides are mixed with an alkali metal compound and then subjected to a heat treatment.

[0162] In the method using activation gas, it is preferred to supply the activation gas at a rate of 0.5 to 3.0 kg / h (preferably 0.7 to 2.0 kg / h) and simultaneously heat the obtained carbide to 800 to 1,000° C. for activation over 3 to 12 hours.

[0163] However, it is speculated that when activated at high temperatures using an activating gas, not only the amorphous portion of the activated carbon is activated, but also the crystalline portion, and the amount of functional groups may be reduced, which may have a negative impact on the durability of the energy storage device. Therefore, in order to obtain highly crystalline activated carbon, activation is performed at a low temperature of approximately 200-600°C for a short time of approximately 3-5 hours. This allows for sufficient activation without compromising the crystallinity and functional group content of the activated carbon.

[0164] In the method using an alkali metal compound, carbide and an alkali metal compound such as KOH or NaOH are mixed in a mass ratio of 1:1 or more (the amount of the alkali metal compound is the same as or greater than the amount of the carbide), and then heated in an inert gas atmosphere at 600 to 900°C for 0.5 to 5 hours. The alkali metal compound is then washed with acid and water to remove the alkali metal compound, and then dried.

[0165] In the case of alkali activation, alkali metal ions are inserted into the interlayers of the carbon structure during activation, which has an adverse effect on crystallinity. Therefore, it is speculated that gas activation is effective in obtaining activated carbon with high crystallinity.

[0166] To increase micropores without increasing mesopores, the amount of carbide mixed with KOH can be increased during activation. To increase both micropores and mesopores, the amount of KOH can be increased. Furthermore, to primarily increase mesopores, it is preferable to perform steam activation after alkali activation.

[0167] The carbide may be activated once before the activation treatment described above. This activation is preferably performed by firing the carbon material at a temperature below 900°C using an activation gas such as steam, carbon dioxide, or oxygen.

[0168] By appropriately combining the firing temperature and firing time in the carbonization method described above with the activation gas supply amount, heating rate, and maximum activation temperature in the activation method, activated carbon that can be used in this embodiment can be produced. Regarding the activation conditions of the activated carbon, it is preferably steam activation at 200-600°C for 3-5 hours, more preferably steam activation at 400-600°C for 4-5 hours, and even more preferably steam activation at 500-550°C for 4-5 hours.

[0169] The average particle size X1 of the activated carbon is preferably 3.0 μm or more and 7.0 μm or less (i.e., 3.0 μm ≤ X1 ≤ 7.0 μm). When the average particle size X1 is 3.0 μm or more, the density of the active material layer is high, so the electronic conductivity between the particles increases, and the effective surface area during the reaction can be increased, thereby promoting the oxidation reaction of the alkali metal compound. It should be noted that if the average particle size X1 is small, it may lead to disadvantages such as low durability, but if the average particle size X1 is 3.0 μm or more, it is not easy to produce such disadvantages. On the other hand, if the average particle size X1 is 7.0 μm or less, side reactions other than the oxidation reaction of the alkali metal compound are suppressed. The average particle size X1 of the activated carbon is more preferably 4.0 μm or more and 6.0 μm or less, and further preferably 4.2 μm or more and 6.3 μm or less.

[0170] The activated carbon of this embodiment has a Raman shift of 1590 cm in its spectroscopic measurement. -1 The peak intensity and Raman shift near the maximum value of 1470 cm -1 The peak intensity of the minimum value appearing near 1600nm is used as a feature. In this embodiment, the intensity G1 of the G band and the intensity D1 of the D band of the activated carbon are values ​​obtained by the following method. Peak separation is performed on the spectrum obtained by Raman spectrometry at an excitation wavelength of 532nm (hereinafter referred to as the "Raman spectrum"), and the maximum peak intensity near 1600nm is used as G1, and the maximum peak intensity near 1300nm is used as D1. Baseline correction is performed during peak separation to reduce the peaks to only two peaks, namely the G band and the D band.

[0171] In this specification, the Raman spectrum refers to a spectrum obtained by measuring using inVia Reflex manufactured by Renishaw as a Raman spectroscopic analysis device.

[0172] In carbon materials, the Raman shift is 1590 cm -1 The nearby frequency band is called the G band, which is caused by the graphene structure (sp 2 bonding); Raman shift 1360cm -1 The nearby frequency band is called the D band, which originates from the diamond structure (sp 3 bonding). The intensity ratio of the G band to the D band is generally related to the crystallinity of the carbon material (sp2 However, it does not take into account the half-peak width of the band that also represents crystallinity, and is therefore insufficient as a definition. The half-peak width here refers to the width of the Raman shift when the relative intensity relative to the intensity of the maximum value of the spectrum is 50%. It can be said that the smaller the half-peak width of the G band, the higher the crystallinity. Therefore, by defining crystallinity as the intensity I1 of the G band and the Raman shift of 1470 cm -1 The ratio of the peak intensity I2 of the minimum value near the peak value I1 / I2(Y1) can take into account not only the peak intensity but also the half-peak width. Here, I1 and I2 are the intensities after baseline correction. Baseline correction means that the peak intensity is adjusted from 500 cm -1 to 2200cm -1 Within the Raman shift range, the baseline of the spectrum is approximated to a straight line, and the distance from the straight line is used as the peak intensity to correct the slope of the baseline. Since the wavenumbers of the extreme values ​​of the Raman spectrum may vary slightly due to differences in the microstructure of the activated carbon, the term "near" is used.

[0173] The Y1 of activated carbon is preferably 0.40 or more and 0.50 or less (i.e., 2.0≤Y1≤5.5, 2.0≤I1 / I2≤5.5). When Y1 is 2.0 or more, the activated carbon has high crystallinity and high electron conductivity, which is beneficial for the decomposition reaction of the positive electrode precursor or the alkali metal compound in the positive electrode. In addition, as the positive electrode deteriorates, the sp 2 The performance is reduced, so it can be achieved by using high sp 2 On the other hand, when Y1 is 5.5 or less, the side reactions caused by excessively high electron conductivity can be suppressed, which is beneficial for the decomposition reaction of the positive electrode precursor or the alkali metal compound in the positive electrode.

[0174] Y1 is more preferably 2.5 or more and 5.0 or less, and even more preferably 2.8 or more and 4.5 or less.

[0175] The product X1Y1 of X1 and Y1 described above is a parameter representing the size of the reaction field and the electron conductivity, indicating the ease with which the chemical reaction occurs. In the present embodiment, X1Y1 is preferably greater than 10 and less than 28 (i.e., 10≤X1Y1≤28, 10≤X1I1 / I2≤28). When X1Y1 is greater than 10, the decomposition reaction of the alkali metal compound in the positive electrode precursor or the positive electrode proceeds smoothly. When X1Y1 is less than 28, side reactions other than the oxidation reaction of the alkali metal compound can be suppressed. From the same aspect, X1Y1 is more preferably greater than 13 and less than 27.

[0176] The activated carbon in this embodiment is characterized by its functional group content. The functional group content Z1 of the activated carbon in this embodiment is determined by the following method. Specifically, the functional group content Z1 is determined by heating a sample from 50°C to 1000°C, determining the composition of the decomposition gas generated using a mass spectrometer, and integrating this with the temperature at which the gas is generated to quantify the surface functional groups.

[0177] The functional group amount measurement in this specification refers to the functional group amount measured under the following conditions.

[0178] FRONTIER LAB Py3030D was used as the thermal decomposition apparatus.

[0179] The heating temperature conditions were as follows: the sample was held at 50° C. for 20 minutes, the temperature was increased at 20° C. / min, and then the sample was held at 1000° C. for 30 minutes.

[0180] The temperature of the heating furnace was 250°C.

[0181] The heating atmosphere was He gas.

[0182] Agilent MSD5975 was used as a gas chromatography / mass spectrometer (GC / MS), Agilent FS Deactivated was used as a column, the injection port and GC oven temperature were 250°C, ions generated by electron ionization at 230°C were used as the ion source, and 3 mg of sample was used.

[0183] The functional group amount Z1 of the activated carbon is preferably 0.80 mmol / g or more and 2.5 mmol / g or less (i.e., 0.80 ≤ Z1 (mmol / g) ≤ 2.5). When the functional group amount Z1 is 0.80 mmol / g or more, the wettability of the electrode is improved, thereby allowing sufficient penetration of the electrolyte, which plays a beneficial role in the decomposition reaction of the alkali metal compound. When the functional group amount Z1 is 2.5 mmol / g or less, side reactions derived from the functional groups are suppressed. The functional group amount Z1 of the activated carbon is more preferably 0.90 mmol / g or more and 2.1 mmol / g.

[0184] The BET specific surface area, mesopore content, micropore content, and average pore diameter of the active material in this embodiment are values ​​calculated using the following methods. A sample is vacuum-dried at 200°C overnight, and an adsorption / desorption isotherm is measured using nitrogen as the adsorbate. Using the adsorption isotherm obtained in this manner, the BET specific surface area is calculated using the BET multipoint method or the BET single-point method, the mesopore content is calculated using the BJH method, and the micropore content is calculated using the MP method.

[0185] The BJH method is a calculation method generally used in the analysis of mesopores, and was proposed by Barrett, Joyner, Halenda et al. (Non-Patent Document 1).

[0186] The MP method is a method for determining pore volume, pore area, and pore distribution using the "t-plot method" (Non-Patent Document 2), and is a method designed by RS Mikhail, Brunauer, and Bodor (Non-Patent Document 3).

[0187] The average pore diameter is a value obtained by dividing the total pore volume per unit mass of a sample by the BET specific surface area, as measured at liquid nitrogen temperature for each equilibrium adsorption amount of nitrogen gas at each relative pressure.

[0188] (How to use activated carbon)

[0189] The activated carbon may be a single type of activated carbon or a mixture of two or more types of activated carbon, and the mixture as a whole may exhibit the above-mentioned property values.

[0190] The positive electrode active material may include materials other than activated carbon (eg, activated carbon not having the specific mesopore volume V1 and / or micropore volume V2 described above, or materials other than activated carbon (eg, conductive polymers)).

[0191] In the illustrated manner,

[0192] When the mass ratio of the activated carbon content in the positive electrode active material layer is A1, or

[0193] When the positive electrode active material of the positive electrode contains a conductive filler, a binder, a dispersion stabilizer, etc., and the total amount of activated carbon and these materials is A1,

[0194] A1 is preferably 15 mass % to 65 mass %, more preferably 20 mass % to 50 mass %.

[0195] When Al is 15% by mass or greater, the contact area between the highly conductive carbon material and the alkali metal compound increases, thereby promoting the oxidation reaction of the alkali metal compound during the pre-doping step and enabling pre-doping to be completed in a shorter time. When Al is 65% by mass or less, the packing density of the positive electrode active material layer increases, enabling higher capacity.

[0196] (Lithium transition metal oxide)

[0197] The positive electrode active material preferably further comprises a lithium transition metal compound. By comprising a lithium transition metal oxide, the non-aqueous lithium storage element can achieve a high capacity. The lithium transition metal oxide comprises a transition metal oxide that can absorb and release lithium. The transition metal oxide used as the positive electrode active material is not particularly limited. As the transition metal oxide, for example, an oxide comprising at least one element selected from the group consisting of cobalt, nickel, manganese, iron, vanadium and chromium can be cited. As the transition metal oxide, specifically, a compound represented by the following formula can be cited:

[0198] Li x CoO2{where x satisfies 0≤x≤1},

[0199] Li x NiO2{where x satisfies 0≤x≤1},

[0200] Li x Ni y M (1-y) O2{wherein, M is at least one element selected from the group consisting of Co, Mn, Al, Fe, Mg and Ti, x satisfies 0≤x≤1, and y satisfies 0.05 <y<0.97}、

[0201] Li x Ni 1 / 3 Co 1 / 3 Mn 1 / 3 O2{where x satisfies 0≤x≤1},

[0202] Li x MnO2{where x satisfies 0≤x≤1},

[0203] α-Li x FeO2{where x satisfies 0≤x≤1},

[0204] Li x VO2{where x satisfies 0≤x≤1},

[0205] Li x CrO2{where x satisfies 0≤x≤1},

[0206] Li x FePO4{where x satisfies 0≤x≤1},

[0207] Li x MnPO4{where x satisfies 0≤x≤1},

[0208] Li z V2(PO4)3{where z satisfies 0≤z≤3},

[0209] Li xMn2O4 {where x satisfies 0 ≤ x ≤ 1},

[0210] Li x M y Mn (2-y) O4 {where M is at least one element selected from the group consisting of Co, Mn, Al, Fe, Mg, and Ti, x satisfies 0 ≤ x ≤ 1, and y satisfies 0.05 < y < 0.97},

[0211] Li x Ni a Co b Al (1-a-b) O2 {where x satisfies 0 ≤ x ≤ 1, and a and b satisfy 0.02 < a < 0.97 and 0.02 < b < 0.97},

[0212] Li x Ni c Co d Mn (1-c-d) O2 {where x satisfies 0 ≤ x ≤ 1, and c and d satisfy 0.02 < c < 0.97 and 0.02 < d < 0.97}.

[0213] Among these, from the aspects of high capacity, low resistance, cycle characteristics, suppression of the decomposition of alkali metal compounds, and shedding of the positive electrode active material during pre-doping, it is preferably at least one compound selected from the group consisting of the above formula Li x Ni a Co b Al (1-a-b) O2 (where a, b, and x satisfy 0.02 < a < 0.97, 0.02 < b < 0.97, and 0 ≤ x ≤ 1), Li x Ni c Co d Mn (1-c-d) O2 (where c, d, and x satisfy 0.02 < c < 0.97, 0.02 < d < 0.97, and 0 ≤ x ≤ 1), Li[[ID=�1]] x CoO2 (where x satisfies 0 ≤ x ≤ 1), Li x Mn2O4 (where x satisfies 0 ≤ x ≤ 1), Li x FePO4 (where x satisfies 0 ≤ x ≤ 1), Li x MnPO4 (where x satisfies 0 ≤ x ≤ 1) and Li z V2(PO4)3 (where z satisfies 0 ≤ z ≤ 3).

[0214] In this embodiment, if the positive electrode precursor contains an alkali metal compound different from the positive electrode active material, then during pre-doping, the alkali metal compound becomes a dopant source of alkali metal and can be pre-doped into the negative electrode. Therefore, even if the transition metal compound does not contain lithium ions in advance (i.e., even if x=0 or z=0), it can be electrochemically charged and discharged as a non-aqueous lithium storage element.

[0215] The content of the lithium transition metal oxide in the positive electrode active material layer of the positive electrode is preferably 10.0% by mass or more and 50.0% by mass or less. When the content of the lithium transition metal oxide in the positive electrode active material layer of the positive electrode is 10.0% by mass or more, the non-aqueous lithium battery device can achieve a high capacity. When this value is 50.0% by mass or less, the non-aqueous lithium battery device can achieve a low resistance.

[0216] It should be noted that the content of the lithium transition metal oxide in the positive electrode active material layer of the positive electrode precursor is preferably 8.0% by mass or more and 30.0% by mass or less. When the content of the lithium transition metal oxide in the positive electrode active material layer of the positive electrode precursor is 8.0% by mass or more, the non-aqueous lithium storage element can achieve a high capacity. When this value is 30.0% by mass or less, the non-aqueous lithium storage element can achieve a low resistance.

[0217] (Carbon Nanotubes)

[0218] The positive electrode active material layer contains carbon nanotubes.

[0219] Multilayered carbon nanotubes are preferably used as the carbon nanotubes included in the positive electrode active material layer. The average fiber diameter of the carbon nanotubes is preferably 2 nm or more and less than 100 nm, more preferably 3 nm or more and 80 nm or less. An average fiber diameter of 2 nm or more improves the dispersibility of the carbon nanotubes. An average fiber diameter of less than 100 nm allows for higher output.

[0220] The carbon nanotubes of this embodiment can be synthesized by an appropriate method such as chemical vapor deposition, arc discharge, or laser evaporation.

[0221] The carbon nanotube content in the positive electrode active material layer of the positive electrode is preferably 6.0% by mass or more and 33.0% by mass or less, and more preferably 7.0% by mass or more and 30.0% by mass or less, based on the total mass of the positive electrode active material layer of the positive electrode as 100% by mass. A value of 6.0% by mass or more enables higher output of the energy storage device. A value of 33.0% by mass or less enables increased energy density of the energy storage device.

[0222] It should be noted that the carbon nanotube content in the positive electrode active material layer of the positive electrode precursor is preferably 5.0% by mass or more and 20.0% by mass or less, and more preferably 6.0% by mass or more and 19.0% by mass or less, when the total mass of the positive electrode active material layer of the positive electrode precursor is 100% by mass. When this value is 5.0% by mass or more, the decomposition of the alkali metal compound can be promoted, and a high-output storage element can be obtained. When this value is 20.0% by mass or less, the energy density can be increased.

[0223] The total content ratio of activated carbon and carbon nanotubes in the positive electrode active material layer of the positive electrode can be 60.0 mass % or more and 90.0 mass % or less, when the total mass of the positive electrode active material layer of the positive electrode is 100 mass %.

[0224] It should be noted that the combined content ratio of activated carbon and carbon nanotubes in the positive electrode active material layer of the positive electrode precursor is preferably 55.0% by mass or greater and 85.0% by mass or less, based on the total mass of the positive electrode active material layer of the positive electrode precursor being 100% by mass. When this ratio is 55.0% or greater, the electron conductivity in the positive electrode precursor is improved, which can promote the decomposition of the alkali metal compound. When this ratio is 85.0% or less, the porosity after the decomposition of the alkali metal compound is increased, which can improve ion diffusivity and achieve high output of the resulting energy storage device.

[0225] The carbon nanotubes are preferably uniformly dispersed on the surface of the positive electrode active material.

[0226] By uniformly dispersing carbon nanotubes on the surface of the positive electrode active material, the electron conductivity and binding properties between the positive electrode active material particles can be improved, and the amount of binder mixed can be reduced. Binders slowly decompose in high-temperature environments above 80°C. Therefore, reducing the amount of binder mixed can improve durability in high-temperature environments above 80°C.

[0227] The quantitative evaluation of the dispersion state is as follows.

[0228] (Alkali Metal Compounds)

[0229] The positive electrode active material layer of the positive electrode precursor of this embodiment contains an alkali metal compound. The alkali metal compound decomposes in the positive electrode precursor to release cations, which are reduced at the negative electrode, thereby pre-doping the negative electrode.

[0230] The alkali metal compound contained in the positive electrode active material layer of the positive electrode precursor may or may not remain in the positive electrode active material layer of the positive electrode. When the alkali metal compound remains in the positive electrode active material layer of the positive electrode, its preferred content is as follows.

[0231] The alkali metal compound contained in the positive electrode active material layer of the positive electrode precursor is as follows.

[0232] (Other components of the positive electrode active material layer)

[0233] The positive electrode active material layer of the positive electrode in the present invention may contain, in addition to the positive electrode active material, carbon nanotubes and alkali metal compound, optional components such as a dispersant, a conductive filler, a binder, one or more atoms selected from Fe atoms and Ni atoms, and a pH adjuster as needed.

[0234] (Dispersant)

[0235] The dispersant is not particularly limited, and for example, one or more selected from carboxymethyl cellulose, polycarboxylic acids, polycarboxylates, polyvinyl pyrrolidone, polyvinyl alcohol, and surfactants can be suitably used. In particular, by using two or more of these dispersants, both the dispersibility of the carbon nanotubes and the stability of the coating solution can be achieved. A particularly preferred dispersant is, for example, carboxymethyl cellulose and one or more selected from polyvinyl pyrrolidone and polyvinyl alcohol.

[0236] The total amount of the dispersion stabilizer is preferably 1.0 parts by mass or more and 7.0 parts by mass or less relative to 100 parts by mass of the solid content in the positive electrode active material layer. When the amount of the dispersion stabilizer is 7.0 parts by mass or less, the ingress and egress and diffusion of ions in the positive electrode active material are not hindered, thereby exhibiting high input-output characteristics.

[0237] (Conductive filler)

[0238] The conductive filler is preferably composed of a conductive carbonaceous material having a higher conductivity than the positive electrode active material. Such conductive fillers are preferably selected from one or more of carbon black, graphite, graphene, and mixtures thereof. Examples of carbon black include Ketjen black and acetylene black. Examples of graphite include flake graphite. Carbon black is particularly suitable as the conductive filler.

[0239] The amount of the conductive filler mixed in the positive electrode active material layer of the positive electrode is preferably in the range of 0 to 20 parts by mass, more preferably 1 to 15 parts by mass relative to 100 parts by mass of the positive electrode active material. From the perspective of high input, it is preferred to mix as much conductive filler as possible. However, if the mixing amount exceeds 20 parts by mass, the content ratio of the positive electrode active material in the positive electrode active material layer is reduced, and thus the energy density per unit volume of the positive electrode active material layer is reduced, which is not preferred.

[0240] (Binder)

[0241] As the binder, for example, polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE), fluororubber, polyimide, latex, styrene-butadiene copolymer, acrylic copolymer, etc. can be used. The amount of the binder used in the positive electrode active material layer is preferably 0 to 20 parts by mass, more preferably 0.1 to 15 parts by mass, relative to 100 parts by mass of the positive electrode active material.

[0242] In this embodiment, since the carbon nanotubes cover the surface of the positive electrode active material, crosslinking the positive electrode active material particles, the amount of binder used can be 0 parts by mass. This improves the diffusivity of ions in the positive electrode active material layer, thereby enabling high-output storage devices. When the amount of binder is 20 parts by mass or less, the amount of binder on the surface of the positive electrode active material is not excessive, thereby promoting the diffusion of ions within the pores of the active material.

[0243] (one or more atoms selected from Fe atoms and Ni atoms)

[0244] The positive electrode active material layer may contain one or more atoms selected from Fe atoms and Ni atoms. In this case, based on the total mass of the positive electrode active material layer, the total concentration of Fe atoms and Ni atoms is preferably 1 ppm or more and 500 ppm or less. More preferably, it is 2 ppm or more and 300 ppm or less, and further preferably 3 ppm or more and 200 ppm or less. When the concentration of Fe or Ni atoms is 1 ppm or more, Fe or Ni atoms can promote the decomposition of alkali metal compounds in a catalytic manner. When the concentration of Fe or Ni atoms is 500 ppm or less, the non-aqueous lithium storage element can be made high-voltage by suppressing the decomposition of the solvent.

[0245] (pH adjuster)

[0246] When water is used as a solvent in the coating solution for forming the positive electrode active material layer, the coating solution may become alkaline due to the addition of an alkali metal compound. Therefore, a pH adjuster may be added to the coating solution for forming the positive electrode active material layer as needed.

[0247] There are no particular restrictions on the pH adjuster, and examples thereof include hydrogen halides such as hydrogen fluoride, hydrogen chloride, and hydrogen bromide; halogen oxygen acids such as hypochlorous acid, chlorous acid, and chloric acid; carboxylic acids such as formic acid, acetic acid, citric acid, oxalic acid, lactic acid, maleic acid, and fumaric acid; sulfonic acids such as methanesulfonic acid, benzenesulfonic acid, and p-toluenesulfonic acid; and acids such as nitric acid, sulfuric acid, phosphoric acid, boric acid, and carbon dioxide.

[0248] (Preferred Embodiments of Positive Electrode Active Material Layer)

[0249] In the non-aqueous lithium storage element of this embodiment, it is planned to pre-dope the negative electrode with alkali metal ions. As a pre-doping method, it is preferred to assemble the storage element using a positive electrode precursor containing an alkali metal compound, a negative electrode, a separator, an outer body, and a non-aqueous electrolyte, and then apply a voltage between the positive electrode precursor and the negative electrode. By applying this voltage, the alkali metal compound in the positive electrode precursor decomposes and releases cations, which are reduced at the negative electrode, thereby pre-doping the negative electrode.

[0250] The decomposition of the alkali metal compound is an oxidative decomposition reaction. To properly carry out this reaction, it is necessary to appropriately control the reaction area between the positive electrode precursor and the non-aqueous electrolyte and the electronic conductivity of the positive electrode precursor.

[0251] The positive electrode precursor of the present embodiment becomes a positive electrode by undergoing such an alkali metal doping step of the negative electrode.

[0252] In the positive electrode active material layer of the positive electrode that has undergone the alkali metal doping step for the negative electrode, pores are formed due to the decomposition of the alkali metal compound, thereby increasing the effective area of ​​the positive electrode active material layer. However, alkali metal that was not consumed in the alkali metal doping step for the negative electrode may remain in the positive electrode active material layer.

[0253] The positive electrode of this embodiment is preferably the following positive electrode:

[0254] It comprises a positive electrode current collector and a positive electrode active material layer on one or both sides of the positive electrode current collector.

[0255] The positive electrode active material layer contains a positive electrode active material, carbon nanotubes, and an alkali metal compound other than the positive electrode active material.

[0256] The positive electrode active material includes activated carbon,

[0257] When the mass ratio of the alkali metal compound to the total mass of the positive electrode active material layer of the positive electrode is C2 (mass %), 0.1≤C2≤7.0,

[0258] In a binary image of a 1,280×890 pixel (1 pixel = 9.96 nm) SEM image of the surface of the positive electrode active material layer of the positive electrode taken at a magnification of 10,000 times, when the set of the largest inscribed circles enclosed in each pixel for all pixels in the bright field area is represented in the form of a frequency distribution of each diameter, the area ratio Z'2 of the total area of ​​the largest inscribed circles with a diameter less than 100 nm in the total area of ​​the largest inscribed circles is greater than 7.5% and less than 35.0%.

[0259] Since the alkali metal compound in the positive electrode active material layer of the positive electrode precursor is used as a doping source for the negative electrode in the alkali metal doping process, the alkali metal compound content in the positive electrode active material layer of the positive electrode that has undergone the alkali metal doping process is less than the alkali metal compound content in the positive electrode active material layer of the positive electrode precursor.

[0260] The mass ratio C2 (mass %) of the alkali metal compound relative to the total mass of the positive electrode active material layer of the positive electrode is 0.1≤C2≤7.0, preferably 0.5≤C2≤6.0, more preferably 1.0≤C2≤5.0, and further preferably 1.5≤C2≤4.5.

[0261] The alkali metal element in the positive electrode active material layer of the positive electrode can be quantitatively determined by ICP-AES, atomic absorption spectrometry, fluorescent X-ray spectrometry, neutron radiation spectrometry, ICP-MS, or the like.

[0262] In the positive electrode of this embodiment, in a binary SEM image of the surface of the positive electrode active material layer, when the set of the largest inscribed circles enclosed by each pixel for all pixels in the bright field region is represented as a frequency distribution of each diameter, the area ratio Z'2 of the largest inscribed circles having a diameter of less than 100 nm is 7.5% to 35.0%. This area ratio Z'2 is 7.5% to 35.0%, preferably 7.7% to 33.0%, more preferably 8.0% to 30.0%, and even more preferably 10.0% to 25.0%.

[0263] The area ratio Z'2 of the total area of ​​the largest inscribed circles having a diameter less than 100 nm to the total area of ​​the largest inscribed circles can be calculated by the following method using an SEM image of the surface of the positive electrode active material of the positive electrode.

[0264] SEM images of the surface of the positive electrode active material layer were captured at a magnification of 10,000x with a resolution of 1,280 × 960 pixels. The images were then cropped to 1,280 × 890 pixels, excluding the captions below the images, and processed using ImageJ (open-source, publicly available image processing software) under the following conditions.

[0265] The SEM image was binarized using a median filter (radius set to 2.0 pixels) with a value of 1 nm = 0.1004 pixels. The bright field region of the resulting binarized image was extracted for analysis. It is known that this bright field region contains a large number of carbon nanotubes covering the surface of the positive electrode active material layer. On the other hand, the dark field region often corresponds to shadows in the surface irregularities of the positive electrode active material layer and can therefore be ignored.

[0266] For all pixels in the bright field grayscale area, a maximum inscribed circle is assumed within each pixel, and the set of assumed maximum inscribed circles is expressed as a frequency distribution of diameters.

[0267] In this case, if there are multiple overlapping maximum inscribed circles, each of the overlapping maximum inscribed circles is assumed to have the following area. The area is divided by the area of ​​the maximum inscribed circle as a full circle, and the resulting value is counted as the number of the maximum inscribed circles:

[0268] (1) When the diameters of the repeated maximum inscribed circles are equal, the area of ​​the repeated part is proportionally distributed to the area of ​​the other maximum inscribed circles; and

[0269] (2) When the diameters of the repeated maximum inscribed circles are different, the area of ​​the repeated portion belongs to the maximum inscribed circle with the largest diameter, and the area of ​​the maximum inscribed circle with a smaller diameter is the area of ​​the portion that does not overlap with other maximum inscribed circles with larger diameters.

[0270] Through the above processing, the total area of ​​the largest inscribed circles is adjusted to coincide with the area of ​​the bright field region.

[0271] By performing the above operation, the frequency distribution of the diameters of the largest inscribed circle can be obtained. Then, the area ratio Z'2 of the largest inscribed circle with a diameter less than 100 nm can be calculated based on this frequency distribution.

[0272] In actual operation, the Thickness of BoneJ (which is an ImageJ plug-in) is implemented for the area extracted by the binary image to obtain the frequency distribution of each diameter of the maximum inscribed circle for all pixels, and Z'2 is calculated using it. This operation is implemented for any 10 fields of view of the SEM image of the surface of the positive active material, and the average value of the 10 fields of view is used as Z'2.

[0273] (X-ray Diffraction Measurement of Positive Electrode Active Material Layer of Positive Electrode)

[0274] In the positive electrode of the present embodiment, it is further preferred that in the XRD (X-ray diffraction) spectrum measured for the positive electrode active material layer, there is a peak X1 having a peak top in the range of 2θ being 25.7° or more and 27.0° or less, and the half-peak width of the peak X1 is 0.1° or more and 0.5° or less. It is known that when the 2θ of the peak X1 is 25.7° or more, a state in which ions easily diffuse between the positive electrode active material particles is formed, and high output can be achieved by increasing the ion diffusion in the positive electrode active material layer. It is known that when the 2θ of the peak X1 is 27.0° or less, the carbon nanotubes are uniformly coated on the surface of the positive electrode active material, and high output can be achieved by increasing the electron conductivity in the positive electrode active material.

[0275] [Positive Electrode Active Material Layer of Positive Electrode Precursor]

[0276] The positive electrode precursor in this embodiment includes a positive electrode current collector and a positive electrode active material layer provided on one or both surfaces thereof and containing a positive electrode active material. The positive electrode active material layer in this embodiment includes a positive electrode active material, carbon nanotubes, and an alkali metal compound other than the positive electrode active material, and may also include optional components other than these.

[0277] The positive electrode active material, carbon nanotubes, and optional components contained in the positive electrode active material layer of the positive electrode precursor are the same as those contained in the positive electrode active material layer of the positive electrode.

[0278] Here, the alkali metal compound other than the positive electrode active material that is essential to the positive electrode active material layer of the positive electrode precursor of this embodiment will be described.

[0279] (Alkali metal compounds other than positive electrode active materials)

[0280] As the alkali metal compound contained in the positive electrode active material layer of the positive electrode precursor in the present embodiment, for example, oxides such as M2O in which M is one or more selected from Li, Na, K, Rb, and Cs; hydroxides such as MOH; halides such as MF and MCl; carboxylates such as RCOOM (wherein R is H, alkyl, or aryl), more than one of which can be used. As the alkali metal compound, specifically, for example, lithium carbonate, sodium carbonate, potassium carbonate, rubidium carbonate, cesium carbonate, lithium oxide, lithium hydroxide, etc. can be cited. As the alkali metal compound, it is suitable to use one or more alkali metal carbonates selected from lithium carbonate, sodium carbonate, potassium carbonate, rubidium carbonate, and cesium carbonate, more preferably lithium carbonate, sodium carbonate, or potassium carbonate. From the aspect of high capacity per unit mass, lithium carbonate is particularly suitable.

[0281] The positive electrode precursor of this embodiment may contain at least one alkali metal compound.

[0282] The positive electrode precursor of this embodiment may contain one or more carbonates, oxides, hydroxides, halides and carboxylates of alkaline earth metals (selected from the group consisting of Be, Mg, Ca, Sr and Ba) instead of the above-mentioned alkali metal compounds or together with the above-mentioned alkali metal compounds.

[0283] The alkali metal compound and, when an alkaline earth metal compound is used, the alkaline earth metal compound is preferably in the form of fine particles.

[0284] In this embodiment, the average particle size of the alkali metal compound is preferably 0.1 μm or more and 10 μm or less. When the average particle size is 0.1 μm or more, the dispersibility in the positive electrode precursor is excellent. When the average particle size is 10 μm or less, the surface area of ​​the alkali metal compound increases, thereby allowing the decomposition reaction to proceed efficiently.

[0285] The average particle size of the alkali metal compound is preferably smaller than the average particle size of the activated carbon described above. If the average particle size of the alkali metal compound is smaller than the average particle size of the activated carbon, the electron conductivity of the positive electrode active material layer is improved, thereby contributing to lower resistance of the electrode body or storage element.

[0286] The method for measuring the average particle size of the alkali metal compound in the positive electrode precursor is not particularly limited and can be calculated based on SEM images and SEM-EDX images of the positive electrode cross section. Regarding the method for forming the positive electrode cross section, BIB processing can be used, in which an Ar beam is irradiated from the top of the positive electrode and a smooth cross section is produced along the end of a shielding plate placed directly above the sample.

[0287] The alkali metal compound can be finely divided using various methods, for example, a pulverizer such as a ball mill, a bead mill, a ring mill, a jet mill, or a rod mill can be used.

[0288] Regarding the content ratio of the alkali metal compound contained in the positive electrode active material layer of the positive electrode precursor, when the total mass of the positive electrode active material is 100 mass%, the content ratio is preferably 15.0 mass% or more and 45.0 mass% or less. When this value is 15.0 mass% or more, a sufficient amount of alkali metal ions can be pre-doped into the negative electrode to increase the capacity of the non-aqueous lithium storage element. When this value is 45.0 mass% or less, the electron conduction in the positive electrode precursor can be improved, thereby effectively decomposing the alkali metal compound.

[0289] When the positive electrode precursor contains two or more alkali metal compounds or alkaline earth metal compounds in addition to the alkali metal compound, the total amount of the alkali metal compound and the alkaline earth metal compound is preferably within the above range.

[0290] The alkali metal elements and alkaline earth metal elements can be quantitatively determined by ICP-AES, atomic absorption spectrometry, fluorescent X-ray analysis, neutron radiation analysis, ICP-MS, or the like.

[0291] [Positive electrode current collector]

[0292] The material constituting the positive electrode current collector of this embodiment is not particularly limited as long as it has high electron conductivity and does not degrade due to dissolution in the electrolyte or reaction with the electrolyte or ions. Metal foil is preferred. Aluminum foil is more preferred as the positive electrode current collector in the non-aqueous lithium storage element of this embodiment.

[0293] The metal foil may be a normal metal foil without projections and depressions or through-holes, or a metal foil with projections and depressions subjected to embossing, chemical etching, electrolytic deposition, sandblasting, or the like, or a metal foil with through-holes such as expanded metal, punched metal, or etched foil.

[0294] From the viewpoint of the pre-doping treatment described later, a non-porous aluminum foil is more preferred, and an aluminum foil having a roughened surface is particularly preferred.

[0295] The thickness of the positive electrode current collector is not particularly limited as long as the shape and strength of the positive electrode can be sufficiently maintained, but is preferably 1 to 100 μm, for example.

[0296] An anchor layer composed of a conductive material, such as graphite, flake graphite, carbon nanotubes, graphene, Ketjen black, acetylene black, or vapor-grown carbon fiber, is preferably provided on the surface of the metal foil. The anchor layer improves electrical conduction between the positive electrode current collector and the positive electrode active material layer, thereby reducing electrical resistance. The thickness of the anchor layer is preferably 0.1 μm to 5 μm per side of the positive electrode current collector.

[0297] [Manufacturing of positive electrode precursor]

[0298] In the present embodiment, the positive electrode precursor constituting the positive electrode of the non-aqueous lithium storage element can be manufactured by the manufacturing technology of the electrode in known lithium ion batteries, double electric layer capacitors, etc. For example, the positive electrode active material and the alkali metal compound and other optional components used as needed can be dispersed or dissolved in water or an organic solvent to prepare a slurry coating liquid, and the coating liquid is applied to the single or double sides on the positive electrode collector to form a coating film, which is dried to obtain a positive electrode precursor. The obtained positive electrode precursor can also be further pressed to adjust the film thickness or bulk density of the positive electrode active material layer.

[0299] Preparation of the coating liquid for forming the positive electrode active material layer, application of the coating liquid to the positive electrode current collector, drying of the coating film, and pressing can be performed according to the methods described later in the production of the negative electrode.

[0300] The thickness of the positive electrode active material layer of the positive electrode precursor of this embodiment is preferably 10 μm to 200 μm on each single side of the positive electrode collector. The thickness of the positive electrode active material layer is more preferably 20 μm to 100 μm on each single side, and further preferably 30 μm to 80 μm. When the thickness is 10 μm or more, sufficient charge and discharge capacity can be exhibited. On the other hand, when the thickness is 200 μm or less, the ion diffusion resistance in the electrode can be maintained very low. Therefore, sufficient output characteristics can be obtained and the battery cell volume can be reduced, thereby increasing the energy density.

[0301] When the positive electrode current collector has through holes or irregularities, the thickness of the positive electrode active material layer refers to the average thickness per single side of the portion of the positive electrode current collector that does not have through holes or irregularities.

[0302] As described above, the carbon nanotubes are preferably uniformly dispersed on the surface of the positive electrode active material.

[0303] As a method for uniformly dispersing carbon nanotubes on the surface of the positive electrode active material, for example, a method of preparing a dispersion of carbon nanotubes in advance, adding the positive electrode active material to the dispersion, and mixing the mixture can be exemplified.

[0304] The dispersion preferably contains carbon nanotubes and a solvent and also contains a dispersant. Examples of the solvent include water and NMP. The dispersant can be appropriately selected from the above-mentioned components that can be included in the positive electrode active material layer. Suitable dispersants include one or more selected from carboxymethyl cellulose, polycarboxylic acids, polycarboxylates, polyvinyl pyrrolidone, polyvinyl alcohol, and surfactants. It is particularly preferred to use a dispersant containing carboxymethyl cellulose and one or more selected from polyvinyl pyrrolidone and polyvinyl alcohol.

[0305] The carbon nanotube dispersion can be prepared by any method. For example, it can be prepared by dissolving a dispersant in a solvent, mixing carbon nanotubes in the resulting solution, and dispersing the carbon nanotubes using an appropriate dispersing method. Examples of dispersing methods include ultrasonic treatment, a ball mill, and a bead mill. The carbon nanotube dispersion can also contain a compound that provides one or more atoms selected from Fe and Ni atoms (e.g., iron (II) oxide, zinc oxide, etc.).

[0306] The positive electrode active material, the alkali metal compound, and other optional components as needed are added to the thus obtained carbon nanotube dispersion, mixed, and dispersed to obtain a coating solution for forming a positive electrode active material layer containing the positive electrode active material with carbon nanotubes uniformly dispersed on the surface.

[0307] By uniformly dispersing carbon nanotubes on the surface of the positive electrode active material, the electron conductivity and binding properties between the positive electrode active material particles can be improved, and the amount of binder mixed can be reduced. Since binders slowly decompose in high-temperature environments above 80°C, reducing the amount of binder mixed can improve high-temperature durability above 80°C.

[0308] The preparation method of the coating liquid for forming the positive electrode active material layer is not particularly limited, and can be suitably carried out using a disperser such as a homogeneous disperser, a multi-axis disperser, a planetary mixer, a thin film gyratory high-speed mixer. In order to obtain a coating liquid with a good dispersion state, it is preferred to disperse the coating liquid at a peripheral speed of 1 m / s or more and 50 m / s or less. When the peripheral speed is 1 m / s or more, various materials can be well dissolved or dispersed, and thus it is preferred. When the peripheral speed is 50 m / s or less, various materials will not be destroyed by the heat or shear force generated by the dispersion, and reaggregation can be suppressed, and thus it is preferred.

[0309] The dispersion of the coating liquid, as measured by a particle size analyzer, is preferably between 0.1 μm and 100 μm. The upper limit of the dispersion is more preferably 80 μm or less, and even more preferably 50 μm or less. Within this particle size range, the material is not crushed during preparation of the coating liquid, which prevents nozzle clogging and the formation of coating film streaks during coating, allowing for stable coating.

[0310] The viscosity (ηb) of the coating liquid is preferably from 1,000 mPa·s to 20,000 mPa·s, more preferably from 1,500 mPa·s to 10,000 mPa·s, and even more preferably from 1,700 mPa·s to 5,000 mPa·s. A viscosity (ηb) of 1,000 mPa·s or higher suppresses dripping during film formation, allowing for good control of the film width and thickness. Furthermore, a viscosity of 20,000 mPa·s or lower reduces pressure loss in the coating liquid flow path during use in a coater, enabling stable coating and easier control of the film thickness.

[0311] The TI value (thixotropic index) of the coating liquid is preferably 1.1 or greater, more preferably 1.2 or greater, and even more preferably 1.5 or greater. When the TI value is 1.1 or greater, the coating film width and thickness can be well controlled.

[0312] There is no particular limitation on the formation of the coating of the positive electrode active material layer, and a coating machine such as a die coater, a comma coater, a knife coater, or a gravure coater can be suitably used. The coating film can be formed by single-layer coating or by multi-layer coating. In the case of multi-layer coating, the coating liquid composition can be adjusted so that the content of the components in each layer of the coating film is different.

[0313] When the coating film is applied to the positive electrode current collector, multiple lines of coating may be applied, intermittent coating may be applied, or multiple lines of intermittent coating may be applied.

[0314] When forming the positive electrode active material layer on both sides of the positive electrode current collector, the coating can be performed sequentially, with coating and drying performed on one side of the positive electrode current collector, followed by coating and drying on the other side. Alternatively, the coating can be performed simultaneously on both sides of the positive electrode current collector. In this case, the difference in thickness between the positive electrode active material layer on the front and back sides of the positive electrode current collector is preferably less than 10% of the average thickness of the two layers. The closer the mass ratio and film thickness ratio of the positive electrode active material layer on the front and back sides are to 1.0, the less the charge and discharge load is concentrated on one side, thereby improving high-load charge and discharge cycle characteristics.

[0315] After forming a coating film of the positive electrode active material layer on the positive electrode current collector, the coating film is dried.

[0316] The coating of the positive electrode precursor is preferably dried by a suitable drying method such as hot air drying, infrared (IR) drying, and more preferably by far infrared, near infrared or hot air. Regarding the drying of the coating, it can be dried at a single temperature or by changing the temperature in multiple stages. It is also possible to dry by combining two or more drying methods.

[0317] The drying temperature is preferably 25°C to 200°C, more preferably 40°C to 180°C, and even more preferably 50°C to 160°C. A drying temperature of 25°C or higher allows for sufficient volatilization of the solvent in the coating. On the other hand, a drying temperature of 200°C or lower can suppress cracking of the coating due to rapid solvent volatilization, segregation of the binder due to migration, and oxidation of the positive electrode current collector or positive electrode active material layer.

[0318] When the total mass of the positive electrode active material layer is 100 mass%, the water content in the dried positive electrode active material layer is preferably 0.1 mass% to 10 mass%. A water content of 0.1 mass% or more can suppress degradation of the binder due to overdrying, thereby achieving low resistance. A water content of 10 mass% or less can suppress deactivation of alkali metal ions, thereby achieving high capacity.

[0319] When N-methyl-2-pyrrolidone (NMP) is used to prepare the coating solution, the NMP content in the dried positive electrode active material layer is preferably 0.1 mass % to 10 mass % based on the total mass of the positive electrode active material layer being 100%.

[0320] The water content in the positive electrode active material layer can be measured by, for example, Karl Fischer titration (JIS 0068 (2001) "Determination of water content in chemical products").

[0321] The amount of NMP contained in the positive electrode active material layer can be quantified as follows: the positive electrode active material layer is immersed in ethanol with a mass 50 to 100 times the mass of the positive electrode active material layer at 25°C for 24 hours to extract NMP, which is then measured by GC / MS and quantified based on a pre-prepared calibration curve.

[0322] The positive electrode active material layer can be pressed using a suitable press such as an oil press, a vacuum press, or a roller press. The film thickness, bulk density, and electrode strength of the positive electrode active material layer can be adjusted by the pressing pressure, the gap between the pressing rollers, and the surface temperature of the pressing portion, which will be described later. The pressing pressure is preferably 0.5 kN / cm to 20 kN / cm, more preferably 1 kN / cm to 10 kN / cm, and further preferably 2 kN / cm to 7 kN / cm. When the pressing pressure is 0.5 kN / cm or more, the electrode strength can be fully improved. On the other hand, when the pressing pressure is 20 kN / cm or less, the positive electrode precursor will not bend or wrinkle, and the positive electrode active material layer can be adjusted to a desired film thickness or bulk density.

[0323] When a roll press is used for pressing, the gap between the pressing rolls can be set to an appropriate value so that the positive electrode active material layer has a desired thickness and bulk density.

[0324] The pressing speed can be set to an appropriate speed that does not cause bending and wrinkling of the positive electrode precursor.

[0325] The surface temperature of the pressed portion may be room temperature or heated as needed. When heated, the lower limit of the surface temperature of the pressed portion is preferably a temperature equal to or higher than the melting point of the adhesive used minus 60°C, more preferably a temperature equal to or higher than the melting point of the adhesive minus 45°C, and even more preferably a temperature equal to or higher than the melting point of the adhesive minus 30°C. On the other hand, when heated, the upper limit of the surface temperature of the pressed portion is preferably a temperature equal to or lower than the melting point of the adhesive used plus 50°C, more preferably a temperature equal to or lower than the melting point of the adhesive plus 30°C, and even more preferably a temperature equal to or lower than the melting point of the adhesive plus 20°C.

[0326] For example, when polyvinylidene fluoride (melting point 150°C) is used as the binder, the press part is preferably heated to 90°C to 200°C, more preferably 105°C to 180°C, and even more preferably 120°C to 170°C. Furthermore, when a styrene-butadiene copolymer (melting point 100°C) is used as the binder, the press part is preferably heated to 40°C to 150°C, more preferably 55°C to 130°C, and even more preferably 70°C to 120°C.

[0327] The melting point of the binder can be determined from the position of the endothermic peak in DSC (Differential Scanning Calorimetry). For example, using a Perkin Elmer differential scanning calorimeter "DSC7," 10 mg of a sample resin is placed in a measuring cell and the temperature is raised from 30°C to 250°C at a rate of 10°C / minute in a nitrogen atmosphere. The endothermic peak temperature during the heating process is the melting point.

[0328] Pressing may be performed multiple times while changing the conditions of press pressure, gap, speed, and surface temperature of the press portion.

[0329] When the positive electrode active material layer is applied in multiple strips, it is preferably cut longitudinally before pressing. If the positive electrode precursor is pressed without cutting the positive electrode active material layer applied longitudinally, excessive stress will be applied to the portion of the positive electrode current collector not coated with the positive electrode active material layer, potentially causing wrinkles. The positive electrode active material layer can be cut longitudinally again after pressing.

[0330] (SEM Analysis of the Positive Electrode Active Material Layer of the Positive Electrode Precursor)

[0331] In the positive electrode precursor of this embodiment, in the binary image of the SEM image obtained by photographing the surface of the positive electrode active material layer, when the set of the maximum inscribed circles enclosed in each pixel for all pixels in the bright field area is represented in the form of a frequency distribution of each diameter, the area ratio Z'1 of the total area of ​​the maximum inscribed circles with a diameter less than 100 nm in the total area of ​​the maximum inscribed circles is greater than 5.9% and less than 28.0%.

[0332] In the positive electrode precursor of this embodiment, the carbon nanotubes are preferably uniformly distributed throughout the positive electrode active material layer. Specifically, the carbon nanotubes preferably uniformly cover at least the surface of the positive electrode active material and uniformly cover the spaces between the positive electrode active material and the alkali metal compound particles.

[0333] In a binary SEM image of the surface of the positive electrode active material layer, if the area ratio Z'1 of the largest inscribed circle with a diameter less than 100 nm is 5.9% or more, it can be evaluated that the carbon nanotubes are uniformly distributed throughout the entire positive electrode active material layer. In this case, it is considered that the carbon nanotubes with a fiber diameter less than 100 nm are in a state where they uniformly cover both the surface of the positive electrode active material and the spaces between the particles of the positive electrode active material and the alkali metal compound. When the positive electrode active material layer is in such a state, the decomposition of the alkali metal compound can be promoted, which can suppress the capacity reduction and resistance increase of the storage element in a high temperature environment. When the area ratio Z'1 of the largest inscribed circle with a diameter less than 100 nm is 28.0% or less, the diffusion rate of ions in the positive electrode active material layer is increased, and the positive electrode can achieve low resistance.

[0334] By uniformly dispersing carbon nanotubes on the surface of the positive electrode active material, the electron conductivity and binding properties between the positive electrode active material particles can be improved, and the amount of binder mixed can be reduced. Binders slowly decompose in high-temperature environments above 80°C or high-voltage environments above 4.1V. Therefore, by reducing the amount of binder mixed, high-temperature durability above 80°C and high-voltage durability above 4.1V can be achieved.

[0335] The area ratio Z'1 can be calculated from the SEM image of the positive electrode active material layer of the positive electrode precursor by the same method as the calculation of the area ratio Z'2 of the largest inscribed circle with a diameter less than 100 nm from the SEM image of the positive electrode active material layer of the positive electrode.

[0336] In the cathode precursor of the present invention, the value of Z'1 determined by such a procedure is 5.9% to 28.0%. This Z'1 value is preferably 6.0% to 26.0%, more preferably 8.0% to 24.0%, further preferably 8.5% to 22.0%, and particularly preferably 10.0% to 20.0%.

[0337] <Negative electrode>

[0338] The negative electrode of the present invention includes a negative electrode current collector and a negative electrode active material layer present on one or both surfaces of the negative electrode current collector.

[0339] [Negative Electrode Active Material Layer]

[0340] The negative electrode active material layer contains a negative electrode active material, carbon nanotubes, and a dispersant, and may also contain optional components such as a conductive filler, a binder, and a metal compound as needed.

[0341] (Negative electrode active material)

[0342] The negative electrode active material may be a material capable of absorbing and releasing alkali metal ions, and specifically, carbon materials, titanium oxides, silicon, silicon oxides, silicon alloys, silicon compounds, tin, and tin compounds can be used.

[0343] The negative electrode active material of this embodiment includes a carbon material. The content of the carbon material is preferably 50% by mass or more, more preferably 70% by mass or more, relative to the total amount of the negative electrode active material. The content of the carbon material may be 100% by mass, but from the perspective of achieving the desired effect of combining with other materials, it is preferably 95% by mass or less, and may be 90% by mass or less, for example. The upper and lower limits of the carbon material content range may be arbitrarily combined.

[0344] In addition, the carbon material contained in the negative electrode active material is characterized by the D band (1,360 cm -1 The peak intensity Id of the peak Pd near the G band (1,580 cm -1 The R value represented by the ratio Id / Ig of the peak intensity Id of the peak Pg (near ) is 0.6 or less.

[0345] The non-aqueous lithium-type storage element of the present embodiment can exert excellent high-temperature storage characteristics by using a negative electrode active material comprising a carbon material having an R value of less than 0.6 in the Raman spectrum. The principle is not yet clear, but it is speculated that by adjusting the R value to less than 0.6, the decomposition reaction of the non-aqueous electrolyte on the negative electrode surface can be suppressed, thereby improving the high-temperature storage characteristics under high voltage. In particular, when the positive electrode precursor contains a lithium compound, the lithium compound is usually decomposed by applying a high voltage, the protective coating (SEI) on the negative electrode surface is destroyed, and gas is easily generated at high temperatures. However, it is speculated that when a negative electrode active material comprising a carbon material showing an R value of less than 0.6 is used, the decomposition of the lithium compound on the negative electrode surface is suppressed, and as a result, excellent high-voltage and high-temperature storage characteristics can be exhibited.

[0346] The R value of the carbon material in the Raman spectrum is preferably 0.05 to 0.5, more preferably 0.1 to 0.45, further preferably 0.15 to 0.4, particularly preferably 0.2 to 0.35.

[0347] The Raman spectrum of the carbon material is measured by, for example, micro-Raman spectroscopy using laser light with a wavelength of 532 nm.

[0348] Examples of the carbon material included in the negative electrode active material include difficult-to-graphitize carbon materials; easily graphitizable carbon materials; carbon black; carbon nanoparticles; activated carbon; artificial graphite; natural graphite; graphitized mesocarbon microbeads; graphite whiskers; amorphous carbonaceous materials such as polyacene-based materials; carbonaceous materials obtained by heat-treating a carbonaceous material precursor; thermal decomposition products of furfuryl alcohol resins or novolac resins; fullerenes; carbon nanofibers; and composite carbon materials thereof. The carbonaceous material precursor is not particularly limited as long as it is a material that forms a carbonaceous material by heat treatment. Examples include petroleum-based pitch, coal-based pitch, mesocarbon microbeads, coke, and synthetic resins (e.g., phenolic resins).

[0349] Among these, from the perspective of reducing the resistance of the negative electrode, it is preferred to heat-treat the coexistence of one or more graphite materials (selected from artificial graphite, natural graphite, graphitized mesophase carbon microbeads, graphite whiskers, high specific surface area graphite, etc.) and one or more carbonaceous material precursors (petroleum-based pitch, coal-based pitch, mesophase carbon microbeads, coke, synthetic resins (such as phenolic resins, etc.), so as to form a composite carbon material composed of the graphite material and the carbonaceous material from the carbonaceous material precursor.

[0350] The carbonaceous material precursor is not particularly limited as long as it is a substance that can be converted into a carbonaceous material by heat treatment, but petroleum-based pitch or coal-based pitch is particularly preferred.

[0351] Before heat treatment, the graphite material and the carbonaceous material precursor may be mixed at a temperature higher than the melting point of the carbonaceous material precursor. The heat treatment temperature is preferably a temperature at which the components produced by volatilization or thermal decomposition of the carbonaceous material precursor used become carbonaceous materials, preferably 400°C to 2,500°C, more preferably 500°C to 2,000°C, and even more preferably 550°C to 1,500°C. The atmosphere for heat treatment is not particularly limited, but a non-oxidizing atmosphere is preferred.

[0352] The BET specific surface area of ​​the composite carbon material is preferably 1 m 2 / g above 50m 2 / g or less, more preferably 1.5m 2 / g above 40m 2 / g or less, more preferably 2m 2 / g above 25m 2 / g or less. The BET specific surface area of ​​the composite carbon material is 1m 2 When the carbon composite material has a BET specific surface area of ​​50 m 2When the content is 1.5747kJ / g or less, the charge and discharge efficiency of lithium ions can be improved, and the reductive decomposition of the non-aqueous electrolyte during charge and discharge can be suppressed, thereby exhibiting high high-load charge and discharge cycle characteristics.

[0353] The average pore diameter of the composite carbon material is preferably 1.5 nm to 25 nm, more preferably 2 nm to 22 nm, further preferably 3 nm to 20 nm, and particularly preferably 3.5 nm to 18 nm. When the average pore diameter of the composite carbon material is 1.5 nm or more, the number of pores larger than the size of the solvated lithium ions in the non-aqueous electrolyte (about 0.9 nm to 1.2 nm) increases, so the diffusion of the solvated lithium ions in the composite carbon material is good, and the non-aqueous lithium-type storage element using the composite carbon material can show high input-output characteristics. On the other hand, when the average pore diameter of the composite carbon material is 25 nm or less, the packing density of the negative electrode active material layer using the composite carbon material can be sufficiently increased, so that a high energy density can be shown.

[0354] The composite carbon material may be in a granular form, and its average particle size is preferably 1 μm or more and 10 μm or less, more preferably 2 μm or more and 8 μm or less, and even more preferably 3 μm or more and 6 μm or less. When the average particle size of the composite carbon material is 1 μm or more, the charge and discharge efficiency of lithium ions can be improved, and high high-load charge and discharge cycle characteristics can be exhibited. When the average particle size of the composite carbon material is 10 μm or less, the number of reaction sites with lithium ions in the non-aqueous electrolyte can be increased, thereby exhibiting high input-output characteristics.

[0355] The mass ratio of the carbonaceous material in the composite carbon material relative to the graphite material is preferably 1% by mass or more and 20% by mass or less, more preferably 1.2% by mass or more and 15% by mass or less, further preferably 1.5% by mass or more and 10% by mass or less, and further preferably 2% by mass or more and 5% by mass or less. When the mass ratio of the carbonaceous material is 1% by mass or more, the reaction sites with the lithium ions in the non-aqueous electrolyte can be fully increased by the carbonaceous material, and the desolvation of the lithium ions can also be easily performed, so that high input-output characteristics can be shown. When the mass ratio of the carbonaceous material is 20% by mass or less, the solid diffusion of the lithium ions between the carbonaceous material and the graphite material can be well maintained, so that high input-output characteristics can be shown. In addition, the charge and discharge efficiency of the lithium ions can be improved, so that high high-load charge and discharge cycle characteristics can be shown.

[0356] The lithium ion doping amount per unit mass of the composite carbon material is preferably 50 mAh / g to 700 mAh / g, more preferably 70 mAh / g to 650 mAh / g, further preferably 90 mAh / g to 600 mAh / g, and even more preferably 100 mAh / g to 550 mAh / g.

[0357] Lithium ion doping reduces the negative electrode potential. Therefore, when a negative electrode comprising a composite carbon material doped with lithium ions is combined with a positive electrode, the voltage of the non-aqueous lithium-type energy storage device increases, while the usable capacity of the positive electrode increases. Consequently, the resulting non-aqueous lithium-type energy storage device has increased capacity and energy density.

[0358] When the lithium ion doping rate per unit mass of the composite carbon material is 50 mAh / g or higher, lithium ions can be effectively doped even at irreversible sites within the composite carbon material where lithium ions cannot be released once inserted, thereby achieving high energy density. A higher doping rate reduces the negative electrode potential, improving input-output characteristics, energy density, and durability.

[0359] When the lithium ion doping amount per unit mass of the composite carbon material is 700 mAh / g or less, adverse effects such as lithium metal precipitation are less likely to occur.

[0360] The BET specific surface area of ​​the graphite material used in the composite carbon material is preferably 0.5 m 2 / g above 80m 2 / g or less, more preferably 1m 2 / g above 70m 2 / g or less, more preferably 1.5m 2 / g above 60m 2 When the BET specific surface area of ​​the graphite material used in the composite carbon material is within the above range, the BET specific surface area of ​​the composite carbon material can be adjusted to the above range.

[0361] The graphite material used in the composite carbon material may be in a granular form, and its average particle size is preferably from 1 μm to 10 μm, and more preferably from 2 μm to 8 μm. When the average particle size of the graphite material used in the composite carbon material is within the range of from 1 μm to 10 μm, the average particle size of the composite carbon material can be adjusted to the above range.

[0362] The carbonaceous material precursor used as the raw material of composite carbon material refers to the solid, liquid or organic material soluble in the solvent that can make carbonaceous material and graphite material composite by being heat-treated.As this carbonaceous material precursor, for example, pitch, mesophase carbon microbeads, coke and synthetic resin (such as phenolic resin) etc. can be enumerated.In these carbonaceous material precursors, from the aspect of manufacturing cost, preferably use cheap pitch.Pitch can be roughly divided into petroleum-based pitch and coal-based pitch.As petroleum-based pitch, for example, can illustrate the distillation residue of crude oil, mobility contact decomposition residue (clarified oil etc.), derive from the residual oil of thermal cracking, the ethylene tar obtained when naphtha cracking etc.

[0363] The negative electrode active material is preferably in a granular form.

[0364] The content of the negative electrode active material in the negative electrode active material layer of the negative electrode precursor is preferably 70% by mass or more, more preferably 80% by mass or more, based on the total mass of the negative electrode active material layer.

[0365] (Carbon Nanotubes)

[0366] Multiwalled carbon nanotubes are suitable for use as the carbon nanotubes in this embodiment. The average fiber diameter of the carbon nanotubes is preferably 2 nm or greater and less than 100 nm, more preferably 3 nm or greater and 80 nm or less. An average fiber diameter of 2 nm or greater improves the dispersibility of the carbon nanotubes. An average fiber diameter of less than 100 nm allows for higher output.

[0367] The carbon nanotubes of this embodiment can be synthesized by an appropriate method such as chemical vapor deposition, arc discharge, or laser evaporation.

[0368] When the total mass of the negative electrode active material layer is 100 mass %, the content of the carbon nanotubes in the negative electrode active material layer is preferably 5.0 mass % to 30.0 mass %, more preferably 6.0 mass % to 25.0 mass %.

[0369] When the total mass of the negative electrode active material layer is 100 mass%, the total content of the carbon material and the carbon nanotubes in the negative electrode active material layer is preferably 60.0 mass% or more and less than 100.0 mass%, more preferably 70 mass% or more and 99.0 mass% or less, and even more preferably 80 mass% or more and 98.0 mass%.

[0370] The carbon nanotubes are preferably uniformly dispersed on the surface of the negative electrode active material.

[0371] By uniformly dispersing carbon nanotubes on the surface of the negative electrode active material, the electronic conductivity and binding properties between the negative electrode active material particles can be improved, and the amount of binder mixed can be reduced. Binders slowly decompose in high-temperature environments above 80°C. Therefore, reducing the amount of binder mixed can improve durability in high-temperature environments above 80°C.

[0372] The quantitative evaluation of the dispersion state is as follows.

[0373] (Dispersant)

[0374] The dispersant is not particularly limited, and for example, one or more selected from carboxymethyl cellulose, polycarboxylic acids, polycarboxylates, polyvinyl pyrrolidone, polyvinyl alcohol, and surfactants can be suitably used. In particular, by using two or more of these dispersants, both the dispersibility of the carbon nanotubes and the stability of the coating solution can be achieved. A particularly preferred dispersant is, for example, carboxymethyl cellulose and one or more selected from polyvinyl pyrrolidone and polyvinyl alcohol.

[0375] The total amount of the dispersion stabilizer used is preferably 1.0 parts by mass or more and 7.0 parts by mass or less relative to 100 parts by mass of the solid content in the negative electrode active material layer. When the amount of the dispersion stabilizer is 7.0 parts by mass or less, the entry, exit, and diffusion of ions in the negative electrode active material are not hindered, thereby exhibiting high input-output characteristics.

[0376] (Other components of the negative electrode active material layer)

[0377] The negative electrode active material layer of the present embodiment may contain, in addition to the negative electrode active material, optional components such as a binder and a conductive filler as needed.

[0378] Examples of the binder include polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE), fluororubber, polyimide, latex, styrene-butadiene copolymer, and acrylic copolymer. The amount of the binder used in the negative electrode active material layer is preferably in the range of 0 to 20 parts by mass, more preferably in the range of 0.1 to 15 parts by mass, relative to 100 parts by mass of the negative electrode active material.

[0379] In this embodiment, since the carbon nanotubes cover the surface of the negative electrode active material and cross-link the negative electrode active material particles, the amount of binder used can be 0 parts by mass. This can improve the diffusivity of ions in the negative electrode active material layer, thereby enabling the storage element to achieve high output. On the other hand, in the case where the negative electrode active material layer does not substantially contain carbon nanotubes, or in a state where the carbon nanotubes are not broken but agglomerated, as long as the amount of binder is 0.1 parts by mass or more, the adhesion between the negative electrode collector and the negative electrode active material layer can be fully improved, and the interface resistance between the collector and the active material layer can be reduced. On the other hand, when the amount of binder is 20 parts by mass or less, the amount of binder on the surface of the negative electrode active material will not be excessive, which can promote the diffusion of ions in the pores of the active material.

[0380] The conductive filler is preferably composed of a conductive carbonaceous material having a higher conductivity than the negative electrode active material. Such conductive fillers are preferably one or more selected from carbon black, graphite, graphene, and mixtures thereof. Examples of carbon black include Ketjen black and acetylene black. Examples of graphite include flake graphite. Carbon black is particularly suitable as the conductive filler.

[0381] The amount of the conductive filler mixed in the negative electrode active material layer is preferably 25 parts by mass or less, and more preferably in the range of 5% to 20 parts by mass, relative to 100 parts by mass of the negative electrode active material. To achieve higher input, the conductive filler is preferably mixed in the negative electrode active material layer. To maintain the energy density per unit volume of the storage element, the amount is preferably controlled to 25 parts by mass or less.

[0382] In order to uniformly disperse the carbon nanotubes, the negative electrode active material layer may contain a metal compound.

[0383] The metal compound is suitably a compound containing one or more atoms selected from Fe atoms and Ni atoms. As such a compound, for example, oxides, hydroxides, hydrides, sulfides, halides, porphyrin derivatives, cyclopentadiene derivatives, etc. containing one or more atoms selected from Fe atoms and Ni atoms can be cited. Among them, an oxide containing one or more atoms selected from Fe atoms and Ni atoms is preferred, and iron (II) oxide or nickel oxide is more preferred.

[0384] The content of the metal compound in the negative electrode active material layer is preferably 1 ppm to 500 ppm, more preferably 2 ppm to 300 ppm, and even more preferably 3 ppm to 200 ppm, in terms of the ratio of metal atoms to the total mass of the negative electrode active material layer (ppm by mass).

[0385] [SEI substance]

[0386] The negative electrode active material layer has a solid electrolyte interface (SEI) material on its surface. The SEI material preferably contains, for example, lithium oxalate represented by the following formula (b).

[0387] [Chemistry 3]

[0388]

[0389] The lithium oxalate serving as the SEI material in the negative electrode active material layer of this embodiment can be adjusted using any of the components of the negative electrode active material layer. It is preferably prepared as a decomposition product of a non-aqueous electrolyte. For example, lithium oxalate can be prepared by dissolving a compound such as a lithium salt containing an oxalic acid complex as an anion in a non-aqueous electrolyte and doping the negative electrode with lithium ions.

[0390] (SEM analysis of negative electrode active material layer)

[0391] In the negative electrode of this embodiment, in the binary image of the SEM image obtained by taking a picture of the surface of the negative electrode active material layer, when the set of the maximum inscribed circles enclosed in each pixel for all pixels in the bright field area is represented in the form of a frequency distribution of each diameter, the area ratio Z1 of the total area of ​​the maximum inscribed circles with a diameter less than 100 nm in the total area of ​​the maximum inscribed circles is greater than 3.5% and less than 25.5%.

[0392] In the negative electrode of this embodiment, the carbon nanotubes are preferably uniformly distributed throughout the negative electrode active material layer. Specifically, the carbon nanotubes preferably uniformly cover at least the surface of the negative electrode active material and uniformly cover the spaces between the particles of the negative electrode active material.

[0393] In a binary SEM image of the negative electrode active material layer surface, if the area ratio Z1 of the largest inscribed circle with a diameter less than 100 nm is 3.5% or greater, it can be evaluated that the carbon nanotubes are uniformly distributed throughout the negative electrode active material layer. In this case, it is considered that the carbon nanotubes with a fiber diameter less than 100 nm are uniformly covering both the surface of the negative electrode active material and the spaces between the particles of the negative electrode active material. When the negative electrode active material layer is in this state, the electronic conductivity between the negative electrode active material particles can be improved, achieving high output, and the decomposition of the electrolyte on the surface of the negative electrode active material can be suppressed, thereby suppressing capacity reduction and resistance increase in high temperature environments. When the area ratio Z1 of the largest inscribed circle with a diameter less than 100 nm is 25.5% or less, the diffusion of lithium ions in the negative electrode active material layer is improved, which can achieve low resistance.

[0394] The area ratio Z1 of the total area of ​​the largest inscribed circles having a diameter smaller than 100 nm to the total area of ​​the largest inscribed circles can be calculated by the following method using an SEM image of the surface of the negative electrode active material.

[0395] SEM images of the surface of the negative electrode active material layer were captured at a magnification of 10,000x at a resolution of 1,280 × 960 pixels. The images were then cropped to 1,280 × 890 pixels, excluding the captions below the images, and processed using ImageJ (open-source, publicly available image processing software) under the following conditions.

[0396] The SEM image was binarized using a median filter (radius set to 2.0 pixels) with a value of 1 nm = 0.1004 pixels. The bright field region of the resulting binarized image was extracted for analysis. This bright field region is known to contain a large number of carbon nanotubes in the negative electrode active material layer. The dark field region, on the other hand, often corresponds to shadows in the surface irregularities of the negative electrode active material layer and can therefore be ignored.

[0397] For all pixels in the bright field grayscale area, a maximum inscribed circle is assumed within each pixel, and the set of assumed maximum inscribed circles is expressed as a frequency distribution of diameters.

[0398] In this case, if there are multiple overlapping maximum inscribed circles, each of the overlapping maximum inscribed circles is assumed to have the following area. The area is divided by the area of ​​the maximum inscribed circle as a full circle, and the resulting value is counted as the number of the maximum inscribed circles:

[0399] (1) When the diameters of the repeated maximum inscribed circles are equal, the area of ​​the repeated part is proportionally distributed to the area of ​​the other maximum inscribed circles; and

[0400] (2) When the diameters of the repeated maximum inscribed circles are different, the area of ​​the repeated portion belongs to the maximum inscribed circle with the largest diameter, and the area of ​​the maximum inscribed circle with a smaller diameter is the area of ​​the portion that does not overlap with other maximum inscribed circles with larger diameters.

[0401] Through the above processing, the total area of ​​the largest inscribed circles is adjusted to coincide with the area of ​​the bright field region.

[0402] By performing the above operation, the frequency distribution of the diameters of the largest inscribed circle can be obtained. Then, the area ratio Z1 of the largest inscribed circle with a diameter less than 100 nm can be calculated based on this frequency distribution.

[0403] In actual operation, the Thickness of BoneJ (which is an ImageJ plug-in) is implemented for the area extracted by the binary image, and the frequency distribution of each diameter of the maximum inscribed circle for all pixels is obtained, and Z1 is calculated using it. This operation is implemented for any 10 fields of view of the SEM image of the negative electrode active material surface, and the average value of the 10 fields of view is used as Z1.

[0404] In the negative electrode of the present invention, the Z1 value determined by such a procedure is 3.5% to 25.5%, preferably 4.0% to 23.0%, more preferably 4.5% to 20.0%, and even more preferably 5.0% to 18.0%.

[0405] In the negative electrode of the present embodiment, in a binary image of a 1,280×890 pixel (1 pixel = 9.96 nm) SEM image of the negative electrode active material layer surface obtained by taking the image at a magnification of 10,000 times in the same manner as above, the 1,000 nm in the dark field region is 2 Above 5,000nm 2 The total area of ​​the following regions is 1,000nm 2 Above 20,000nm 2 The area ratio Z2 of the total area of ​​the following regions is preferably 63.0% or more and 92.0% or less. When this area ratio Z2 is 63.0% or more, a large number of microscopic voids (thin gaps between adjacent carbon nanotubes) exist on the surface of the negative electrode active material, through which lithium ions can diffuse, enabling the non-aqueous lithium battery element to achieve higher output. When the area ratio Z2 is 92.0% or less, the contact area between the negative electrode active material and lithium ions increases, thereby enabling higher output of the battery element.

[0406] About finding 1,000nm 2 Above 5,000nm 2 The method of the area ratio Z2 of the following region, up to the step of taking the SEM image of the negative electrode active material layer and binarization, can be carried out in the same manner as the evaluation of the area ratio Z1 of the largest inscribed circle less than 100nm. After the binarization process, the dark field area is extracted from the obtained binarized image for analysis. At this time, the bright field area is mostly a convex portion corresponding to the carbon nanotubes dispersed on the surface of the negative electrode active material, which has nothing to do with the tiny gaps on the surface of the negative electrode active material and can be ignored. In addition, even for the dark field area, 20,000nm 2 In the region with the above area, the probability that carbon nanotubes do not exist on the surface of the negative electrode active material is also very high, and therefore can be ignored.

[0407] Next, the 1,000 nm region in the extracted dark field was 2 Above 20,000nm 2 The following regions are expressed in the form of frequency distribution of each area.

[0408] Then, the frequency distribution of each area can be used to determine the 1,000nm 2 Above 5,000nm 2 The total area of ​​the following regions is 1,000nm 2 Above 20,000nm 2 The area ratio Z2 in the total area of ​​the following regions.

[0409] In actual operation, Analyze Particles (which is an ImageJ plug-in) is used to calculate the area and number of all dark field areas extracted from the binary image, obtain the area distribution, and calculate Z2. At this time, the area connected to the outer frame of the image is not included. This operation is performed for any 10 fields of view of the SEM image of the negative electrode active material surface, and the average value of the 10 fields of view is used as Z2.

[0410] In the negative electrode of the present invention, the value of Z2 determined by such a procedure is preferably 63.0% to 92.0%, more preferably 64.0% to 85.0%, and even more preferably 65.5% to 80.0%.

[0411] (X-ray Diffraction Measurement of Negative Electrode Active Material Layer)

[0412] In the negative electrode of this embodiment, it is further preferred that the XRD (X-ray diffraction) spectrum measured for the negative electrode active material layer has a peak Y1 with a peak top in the range of 2θ being greater than or equal to 26.2° and less than or equal to 26.5°, and the half-peak width of the peak Y1 is preferably greater than or equal to 0.1° and less than or equal to 0.5°. It is known that when the 2θ of the peak Y1 is greater than or equal to 26.2°, a state in which ions easily diffuse between the particles of the negative electrode active material exists, and high output can be achieved by improving ion diffusion within the negative electrode active material layer. It is known that when the 2θ of the peak Y1 is less than or equal to 26.5°, a state in which carbon nanotubes uniformly cover both the surface of the negative electrode active material and the spaces between the particles of the negative electrode active material, and high output can be achieved by improving the electronic conductivity within the negative electrode active material.

[0413] [Negative electrode current collector]

[0414] The material constituting the negative electrode current collector of this embodiment is preferably a material having high electron conductivity and being resistant to dissolution in the electrolyte or degradation due to reaction with the electrolyte or ions. For example, metal foil may be used. Such metal foil is not particularly limited, and examples thereof include aluminum foil, copper foil, nickel foil, and stainless steel foil. Copper foil is preferably used as the negative electrode current collector in the non-aqueous lithium battery element of this embodiment.

[0415] The metal foil used as the negative electrode current collector can be a conventional metal foil without concave-convex or through-holes, or a metal foil with concave-convex that has been subjected to embossing, chemical etching, electrolytic deposition, sandblasting, etc., or a metal foil with through-holes such as metal plate mesh, punched metal, or etched foil.

[0416] The thickness of the negative electrode current collector is not particularly limited as long as the shape and strength of the negative electrode can be sufficiently maintained, and is, for example, 1 to 100 μm.

[0417] [Manufacturing of negative electrode]

[0418] The negative electrode is composed of a negative electrode active material layer on one or both sides of a negative electrode current collector. In a typical embodiment, the negative electrode active material layer is fixed to the negative electrode current collector.

[0419] The negative electrode can be manufactured using known techniques for manufacturing electrodes in lithium-ion batteries, double-layer capacitors, and the like. For example, various materials comprising the negative electrode active material can be dispersed or dissolved in water or an organic solvent to prepare a slurry-like coating solution, which is then applied to one or both sides of the negative electrode current collector to form a coating film, which is then dried to obtain the negative electrode. The obtained negative electrode can also be further pressed to adjust the film thickness or bulk density of the negative electrode active material layer.

[0420] As described above, the carbon nanotubes are preferably uniformly dispersed on the surface of the negative electrode active material.

[0421] As a method for uniformly dispersing carbon nanotubes on the surface of the negative electrode active material, for example, a method of preparing a dispersion of carbon nanotubes in advance, adding the negative electrode active material to the dispersion, and mixing them can be exemplified.

[0422] The dispersion preferably contains carbon nanotubes and a solvent, and also contains a dispersant. Examples of the solvent include water and NMP. The dispersant can be appropriately selected from the above-mentioned components that can be included in the negative electrode active material layer, and one or more selected from carboxymethyl cellulose, polycarboxylic acids, polycarboxylates, polyvinyl pyrrolidone, polyvinyl alcohol, surfactants, etc. are preferably used. It is particularly preferred to use a dispersant containing carboxymethyl cellulose and one or more selected from polyvinyl pyrrolidone and polyvinyl alcohol.

[0423] The carbon nanotube dispersion can be prepared by any method. For example, it can be prepared by dissolving a dispersant in a solvent, mixing the carbon nanotubes in the resulting solution, and dispersing the carbon nanotubes using an appropriate dispersing means. Examples of such dispersing means include ultrasonic treatment, a ball mill, and a bead mill.

[0424] The negative electrode active material layer-forming coating liquid can be prepared by adding other components such as the negative electrode active material to the above-mentioned carbon nanotube dispersion liquid as needed.

[0425] In the negative electrode active material layer formed using this coating solution, carbon nanotubes are uniformly dispersed on the surface of the negative electrode active material and between the particles, uniformly coating them. This improves the electronic conductivity and binding properties between the negative electrode active material particles, thereby reducing the amount of binder incorporated into the negative electrode active material layer. Binders slowly decompose in high-temperature environments above 80°C, so reducing the amount of binder incorporated can enhance high-temperature durability above 80°C.

[0426] The preparation method of the coating liquid for forming the negative electrode active material layer is not particularly limited, and can be suitably carried out using a disperser such as a homogenizer, a multi-axis disperser, a planetary mixer, a thin film gyratory high-speed mixer, etc. In order to obtain a coating liquid with a good dispersion state, it is preferred to disperse the coating liquid at a peripheral speed of 1 m / s or more and 50 m / s or less. When the peripheral speed is 1 m / s or more, various materials can be well dissolved or dispersed, and thus it is preferred. When the peripheral speed is 50 m / s or less, various materials will not be destroyed by the heat or shear force generated by the dispersion, and reaggregation can be suppressed, and thus it is preferred.

[0427] The dispersion of the coating liquid, as measured by a particle size analyzer, is preferably between 0.1 μm and 100 μm. The upper limit of the dispersion is more preferably 80 μm or less, and even more preferably 50 μm or less. Within this particle size range, the material is not crushed during preparation of the coating liquid, which prevents nozzle clogging and the formation of coating film streaks during coating, allowing for stable coating.

[0428] The viscosity (ηb) of the coating liquid is preferably from 1,000 mPa·s to 20,000 mPa·s, more preferably from 1,500 mPa·s to 10,000 mPa·s, and even more preferably from 1,700 mPa·s to 5,000 mPa·s. A viscosity (ηb) of 1,000 mPa·s or higher suppresses dripping during film formation, allowing for good control of the film width and thickness. Furthermore, a viscosity of 20,000 mPa·s or lower minimizes pressure loss in the coating liquid flow path during use in a coater, enabling stable coating and easier control of the film thickness.

[0429] The TI value (thixotropic index) of the coating liquid is preferably 1.1 or greater, more preferably 1.2 or greater, and even more preferably 1.5 or greater. When the TI value is 1.1 or greater, the coating film width and thickness can be well controlled.

[0430] There are no particular limitations on the formation of the coating film of the negative electrode active material layer. A coating machine such as a die coater, a comma coater, a knife coater, or a gravure coater can be used as appropriate. The coating film can be formed by single-layer coating or multi-layer coating. In the case of multi-layer coating, the coating liquid composition can be adjusted so that the content of the components in each layer of the coating film is different.

[0431] When applying the coating film on the negative electrode current collector, multiple coating lines may be applied, intermittent coating may be applied, or multiple intermittent coating lines may be applied.

[0432] When forming the negative electrode active material layer on both sides of the negative electrode current collector, the coating can be performed sequentially, with coating and drying performed on one side, followed by coating and drying on the other side. Alternatively, the coating can be performed simultaneously, with the coating solution applied and dried on both sides. In this case, the thickness difference between the negative electrode active material layers on the front and back sides of the negative electrode current collector is preferably no more than 10% of the average thickness of the two layers. The closer the mass ratio and thickness ratio of the negative electrode active material layers on the front and back sides are to 1.0, the less the charge and discharge load is concentrated on one side, thereby improving high-load charge and discharge cycle characteristics.

[0433] After forming a coating film of the negative electrode active material layer on the negative electrode current collector, the coating film is dried.

[0434] The coating of the negative electrode precursor is preferably dried by a suitable drying method such as hot air drying or infrared (IR) drying, more preferably by far infrared, near infrared, or hot air. The coating may be dried at a single temperature or by varying the temperature in multiple stages. Drying may also be performed by combining two or more drying methods.

[0435] The drying temperature is preferably 25°C to 200°C, more preferably 40°C to 180°C, and even more preferably 50°C to 160°C. A drying temperature of 25°C or higher allows for sufficient volatilization of the solvent in the coating film. On the other hand, a drying temperature of 200°C or lower can suppress cracking of the coating film due to rapid solvent volatilization, segregation of the binder due to migration, and oxidation of the negative electrode current collector or negative electrode active material layer.

[0436] The water content of the dried negative electrode active material layer is preferably 0.1% to 10% by mass, based on the total mass of the negative electrode active material layer being 100% by mass. A water content of 0.1% or more by mass can suppress deterioration of the binder due to excessive drying, thereby achieving lower resistance. A water content of 10% or less by mass can suppress deactivation of alkali metal ions, thereby achieving higher capacity.

[0437] When N-methyl-2-pyrrolidone (NMP) is used to prepare the coating solution, the NMP content in the negative electrode active material layer after drying is preferably 0.1 mass % to 10 mass % based on the total mass of the negative electrode active material layer being 100%.

[0438] The water content in the negative electrode active material layer can be measured by, for example, Karl Fischer titration (JIS 0068 (2001) “Determination of water content in chemical products”).

[0439] The amount of NMP contained in the negative electrode active material layer can be quantified by immersing the negative electrode active material layer in ethanol at a mass 50 to 100 times the mass of the negative electrode active material layer at 25°C for 24 hours to extract NMP, followed by GC / MS measurement and quantification based on a pre-prepared calibration curve.

[0440] The negative electrode active material layer can be pressed using a suitable press such as an oil press, a vacuum press, or a roller press. The film thickness, bulk density, and electrode strength of the negative electrode active material layer can be adjusted by the pressing pressure, the gap between the pressing rollers, and the surface temperature of the pressing portion, which will be described later. The pressing pressure is preferably 0.5 kN / cm to 20 kN / cm, more preferably 1 kN / cm to 10 kN / cm, and even more preferably 2 kN / cm to 7 kN / cm. When the pressing pressure is 0.5 kN / cm or more, the electrode strength can be sufficiently improved. On the other hand, when the pressing pressure is 20 kN / cm or less, the negative electrode will not bend or wrinkle, and the negative electrode active material layer can be adjusted to the desired film thickness or bulk density.

[0441] When a roll press is used for pressing, the gap between the pressing rolls can be set to an appropriate value so that the negative electrode active material layer has a desired thickness and bulk density.

[0442] The pressing speed can be set to an appropriate speed that does not cause bending and wrinkling of the negative electrode.

[0443] The surface temperature of the pressed portion may be room temperature or heated as needed. When heated, the lower limit of the surface temperature of the pressed portion is preferably a temperature equal to or higher than the melting point of the adhesive used minus 60°C, more preferably a temperature equal to or higher than the melting point of the adhesive minus 45°C, and even more preferably a temperature equal to or higher than the melting point of the adhesive minus 30°C. On the other hand, when heated, the upper limit of the surface temperature of the pressed portion is preferably a temperature equal to or lower than the melting point of the adhesive used plus 50°C, more preferably a temperature equal to or lower than the melting point of the adhesive plus 30°C, and even more preferably a temperature equal to or lower than the melting point of the adhesive plus 20°C.

[0444] For example, when polyvinylidene fluoride (melting point 150°C) is used as the binder, the press part is preferably heated to 90°C to 200°C, more preferably 105°C to 180°C, and even more preferably 120°C to 170°C. Furthermore, when a styrene-butadiene copolymer (melting point 100°C) is used as the binder, the press part is preferably heated to 40°C to 150°C, more preferably 55°C to 130°C, and even more preferably 70°C to 120°C.

[0445] The melting point of the binder can be determined from the position of the endothermic peak in DSC (Differential Scanning Calorimetry). For example, using a Perkin Elmer differential scanning calorimeter "DSC7," 10 mg of a sample resin is placed in a measuring cell and the temperature is raised from 30°C to 250°C at a rate of 10°C / minute in a nitrogen atmosphere. The endothermic peak temperature during the heating process is the melting point.

[0446] Pressing may be performed multiple times while changing the conditions of press pressure, gap, speed, and surface temperature of the press portion.

[0447] If the negative electrode active material layer is applied in multiple strips, it is preferably cut longitudinally before pressing. If the negative electrode is pressed without cutting the negative electrode active material layer applied longitudinally, excessive stress will be applied to the negative electrode current collector where the negative electrode active material layer is not applied, potentially causing wrinkles. The negative electrode active material layer can be cut longitudinally again after pressing.

[0448] The thickness of the negative electrode active material layer per single side is preferably 10 μm to 70 μm, more preferably 20 μm to 60 μm. A thickness of 10 μm or greater allows for excellent charge and discharge capacity. On the other hand, a thickness of 70 μm or less allows for a smaller battery cell volume, thereby increasing energy density.

[0449] When the negative electrode current collector has pores, the thickness of the negative electrode active material layer refers to the average value of the thickness per single side of a portion of the negative electrode current collector that does not have pores.

[0450] Non-aqueous electrolyte

[0451] In the non-aqueous lithium battery element of this embodiment, the electrolyte is a non-aqueous electrolyte. That is, the electrolyte contains an organic solvent (non-aqueous solvent) and substantially no water. The non-aqueous electrolyte contains a lithium salt electrolyte. That is, the non-aqueous electrolyte contains lithium ions derived from the lithium salt electrolyte as an electrolyte.

[0452] [Lithium salt]

[0453] The non-aqueous electrolyte solution contains, as a lithium salt electrolyte:

[0454] (A) at least one lithium salt selected from LiPF6 and LiBF4,

[0455] (B) a lithium salt having an imide structure, and

[0456] (C) a lithium salt having an oxalic acid complex as an anion, and

[0457] In the above-mentioned non-aqueous electrolyte, the ratio of the mass of component (C) to the total mass of component (A) and component (B) is in the range of 1.0% by mass or more and 10.0% by mass or less. When this ratio is 1.0% by mass or more, the ability of the solid electrolyte interface (SEI) substance to form on the surface of the negative electrode can be effectively exerted, thereby obtaining a non-aqueous lithium storage element with excellent durability at high temperatures. Among them, if the amount of lithium salt (C) with oxalic acid complex as anion is too much, the resistance of the electrolyte increases and the input characteristics deteriorate. In this regard, if the ratio of the mass of component (C) to the total mass of component (A) and component (B) is 10.0% or less, the resistance of the electrolyte can be maintained at a low level and the input characteristics will not be reduced.

[0458] The electrolyte solution of this embodiment contains at least one lithium salt of LiPF6 and LiBF4 as component (A).

[0459] The lithium salt having an imide structure as the component (B) contained in the electrolyte solution of this embodiment is preferably a lithium salt having an imide structure represented by the following formula (a):

[0460] [Chemistry 4]

[0461]

[0462] {In formula (a), R 1 and R 2 independently of one another, a hydrogen atom, a halogen atom, an alkyl group or a haloalkyl group, at least one of which is a halogen atom or a haloalkyl group.

[0463] When the lithium salt having an imide structure is a lithium salt selected from the group consisting of lithium bis(fluorosulfonyl)imide and lithium bis(trifluoromethane)sulfonylimide, excellent input-output characteristics can be obtained, which is preferred.

[0464] In the electrolyte of the present embodiment, as component (C), a lithium salt having an oxalic acid complex as an anion is contained. As lithium salts having an oxalic acid complex as an anion, for example, lithium bis(oxalatoborate), lithium fluorooxalatoborate, lithium difluorooxalatoborate, etc. can be cited, and one or more selected from them can be used. Thus, an electrolyte film is formed at the negative electrode interface, effectively exerting the ability to form a protective film (SEI film) composed of a solid electrolyte interface (SEI) substance on the negative electrode surface, thereby achieving excellent high-temperature durability.

[0465] Based on the total amount of the non-aqueous electrolyte, the total concentration of the lithium salt electrolyte in the non-aqueous electrolyte is preferably 0.5 mol / L or more, more preferably in the range of 0.5 mol / L or more and 2.0 mol / L or less. When the concentration of the lithium salt electrolyte is 0.5 mol / L or more, the anions are sufficiently present, and thus the capacity of the storage element can be sufficiently increased. When the concentration of the lithium salt electrolyte is 2.0 mol / L or less, it is possible to prevent undissolved lithium salt from precipitating into the non-aqueous electrolyte and prevent the viscosity of the electrolyte from becoming too high, without reducing the conductivity or the output characteristics, and thus is preferred.

[0466] Examples of the non-aqueous solvent contained in the non-aqueous electrolyte solution of the present embodiment include cyclic carbonates and chain carbonates.

[0467] Examples of the cyclic carbonate include alkylene carbonate compounds represented by ethylene carbonate, propylene carbonate, butylene carbonate, etc. Alkylene carbonate compounds are typically unsubstituted compounds.

[0468] As chain carbonates, for example, dialkyl carbonate compounds represented by dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, dipropyl carbonate, dibutyl carbonate, etc. can be cited. Dialkyl carbonate compounds are typically non-substituted compounds. Among them, from the perspective of durability under high temperature storage, it is preferred not to use dimethyl carbonate, which has a low boiling point and poor heat resistance. In addition, ethylene carbonate forms an SEI coating on the negative electrode surface after reductive decomposition, which can obtain a non-aqueous lithium storage element with excellent durability under high temperature and high voltage, and is therefore preferred. Propylene carbonate has a low melting point and is therefore not prone to solidification of the non-aqueous electrolyte or precipitation of the non-aqueous solvent component under low temperature conditions, and is therefore preferred. When ethylene carbonate and propylene carbonate are mixed for use, since ethylene carbonate can effectively exert the SEI coating forming ability on the negative electrode surface, it is preferred to have a higher content of ethylene carbonate than propylene carbonate.

[0469] The nonaqueous solvent in this embodiment preferably contains both cyclic carbonate and chain carbonate. From the perspective of dissolving a desired concentration of lithium salt and exhibiting high lithium ion conductivity, it is advantageous for the nonaqueous electrolyte to contain cyclic carbonate and chain carbonate.

[0470] Based on the total mass of the non-aqueous electrolyte, the total content of cyclic carbonate and linear carbonate is preferably more than 50 mass %, more preferably more than 65 mass %, preferably less than 95 mass %, more preferably less than 90 mass %. When the total content of cyclic carbonate and linear carbonate is more than 50 mass %, it is easy to dissolve the lithium salt of the desired concentration and can show high lithium ion conductivity; when it is less than 95 mass %, the electrolyte is easy to further contain additives described later. The upper and lower limits of the scope of the above-mentioned total concentration can be arbitrarily combined.

[0471] [additive]

[0472] The non-aqueous electrolyte solution of the present embodiment may further contain an additive selected from nitrile compounds, ether compounds, and the like.

[0473] The number of cyano groups in the nitrile compound is preferably 1 or more and 6 or less, more preferably 1 or more and 4 or less, further preferably 1 or more and 3 or less, and even more preferably 3 or less.

[0474] The nitrile compound may be a molecular compound or may be in the form of a salt.

[0475] Examples of molecular nitrile compounds having one cyano group include the following formula (Cy1):

[0476] [Chemistry 5]

[0477]

[0478] A compound represented by {in formula (Cy1), a is 0 or 1, and b is an integer of 1 to 6}. b is preferably an integer of 1 to 4, more preferably 1 or 2. Specific examples of the compound represented by formula (Cy1) include acetonitrile (a=0, b=1), methoxyacetonitrile (a=1, b=1), and 3-methoxypropionitrile (a=1, b=2).

[0479] Examples of molecular nitrile compounds having two cyano groups include the following formula (Cy2):

[0480] [Chemistry 6]

[0481]

[0482] A compound represented by {in formula (Cy2), c is an integer of 1 to 8}. c is preferably an integer of 1 to 6, more preferably an integer of 2 to 4. Specific examples of the compound represented by formula (Cy2) include succinonitrile (c = 2), glutaronitrile (c = 3), and adiponitrile (c = 4).

[0483] Examples of the molecular nitrile compound having three cyano groups include 2-amino-1,1,3-tricyano-1-propene.

[0484] Examples of nitrile compounds in the form of salts include salts composed of tricyanomethanide anions, 4,5-dicyano-2-(perfluoroalkyl)imidazolium anions, and their countercations. The perfluoroalkyl group in the 4,5-dicyano-2-(perfluoroalkyl)imidazolium anion is preferably a perfluoroalkyl group having 1 to 6 carbon atoms, more preferably 1 to 4 carbon atoms, and even more preferably 1 to 3 carbon atoms, and may be, for example, a trifluoromethyl group, a pentafluoroethyl group, a hexafluoropropyl group, or a hexafluoroisopropyl group.

[0485] Examples of the counter cation in the nitrile compound in the form of a salt include lithium ions and the following formula (Im1):

[0486] [Chemistry 7]

[0487]

[0488] A cation represented by {in formula (Im1), each R is independently a hydrogen atom or an alkyl group having 1 to 6 carbon atoms}. The alkyl group of R in formula (Im1) is preferably an alkyl group having 1 to 4 carbon atoms, and specific examples thereof include a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, an isobutyl group, and a tert-butyl group. Preferred examples of the cation represented by formula (Im1) include a 1-ethyl-3-methylimidazolium cation, a 1-butyl-3-methylimidazolium cation, a 1-ethyl-3,4,5-trimethylimidazolium cation, and a 1-butyl-3,4,5-trimethylimidazolium cation.

[0489] Specific examples of the nitrile compound in the form of a salt include 1-ethyl-3-methylimidazolium tricyanomethane, 1-butyl-3-methylimidazolium tricyanomethane, 1-ethyl-3,4,5-trimethylimidazolium tricyanomethane, 1-butyl-3,4,5-trimethylimidazolium tricyanomethane, and lithium tricyanomethane.

[0490] The nitrile compound in the present invention is preferably one or more selected from the group consisting of acetonitrile, methoxyacetonitrile, 3-methoxypropionitrile, succinonitrile, glutaronitrile, adiponitrile, 2-amino-1,1,3-tricyano-1-propene, 1-butyl-3-methylimidazolium tricyanomethane, 4,5-dicyano-2-(trifluoromethyl)imidazolium lithium and lithium tricyanomethane.

[0491] The trinitrile compound in the present invention is preferably at least one selected from the group consisting of 2-amino-1,1,3-tricyano-1-propene, 1-butyl-3-methylimidazolium tricyanomethanide, and lithium tricyanomethanide.

[0492] When the non-aqueous electrolyte solution contains such a nitrile compound, a storage device exhibiting excellent storage characteristics can be obtained. The content of the nitrile compound in the non-aqueous electrolyte solution is preferably 5 mol / L or less, more preferably 0.1 mol / L or more and 5 mol / L or less.

[0493] Examples of ether compounds include 1,2-dimethoxyethane, 1,2-diethoxyethane, tetrahydrofuran, 1,3-dioxane, 1,4-dioxane, and 2-methyltetrahydrofuran. When a non-aqueous electrolyte solution contains these ether compounds, a storage device exhibiting excellent input / output characteristics can be obtained. The content of the ether compound in the non-aqueous electrolyte solution is preferably from 1 mol / L to 10 mol / L.

[0494] (Moisture)

[0495] The non-aqueous electrolyte of this embodiment contains substantially no water. The non-aqueous electrolyte containing substantially no water means that the water content in the non-aqueous electrolyte is 200 ppm or less. The water content in the non-aqueous electrolyte may be 100 ppm or less, 50 ppm or less, or 10 ppm or less, or may contain no water at all.

[0496] Partition

[0497] The positive electrode precursor and the negative electrode are stacked with a separator interposed therebetween, or are stacked and wound to form an electrode stack or an electrode wound body including the positive electrode precursor, the separator, and the negative electrode.

[0498] As the separator, separators used in lithium ion secondary batteries, electric double layer capacitors, lithium ion capacitors, and the like can be preferably used.

[0499] [Materials for the separator]

[0500] The separator in the present embodiment is preferably a separator containing at least one selected from the group consisting of polyolefin, cellulose, and aramid resin.

[0501] As one aspect of this embodiment, a separator comprising a coating layer containing an aramid resin or inorganic particles is preferred. Separators comprising these materials are less likely to shrink even when maintained at high temperatures (e.g., above 85°C), can maintain the liquid retention of the non-aqueous electrolyte, and can maintain the low resistivity of the non-aqueous lithium storage element, and are therefore preferred.

[0502] As preferred separators in this embodiment, for example, there can be exemplified a separator comprising a polyolefin microporous membrane, a separator as a laminate having a coating comprising inorganic microparticles on at least one side of a polyolefin microporous membrane, a separator as a laminate having a coating comprising an aromatic polyamide resin on at least one side of a polyolefin microporous membrane, a separator comprising cellulose nonwoven paper, and the like.

[0503] Examples of the polyolefin include polyethylene and polypropylene. The aramid resin may be a para-substituted aramid resin or a meta-substituted aramid resin.

[0504] The polyolefin microporous membrane, the coating layer containing inorganic fine particles, the coating layer containing an aramid resin, and the cellulose nonwoven paper may each be a single layer or a laminate composed of multiple layers.

[0505] Organic or inorganic fine particles may be contained inside the separator.

[0506] [Thickness of the partition]

[0507] The separator thickness is preferably from 5 μm to 35 μm. A separator thickness of 5 μm or greater is preferred because it tends to reduce self-discharge caused by internal micro-short circuits. A separator thickness of 35 μm or less is preferred because it tends to improve the input-output characteristics of the non-aqueous lithium battery element. The separator thickness is more preferably from 10 μm to 30 μm, and even more preferably from 15 μm to 25 μm.

[0508] In addition, when the separator has a coating layer, the thickness of the separator is the thickness of the entire separator including the coating layer.

[0509] [Exterior body]

[0510] As the outer body, for example, a metal can, a laminated packaging material, etc. can be used. As the metal can, an aluminum metal tube is preferred. As the laminated packaging material, a film formed by laminating a metal foil and a resin film is preferred, and a film having a three-layer structure consisting of an outer resin film / metal foil / inner resin film can be exemplified. The outer resin film is used to prevent the metal foil from being damaged due to contact, etc., and resins such as nylon and polyester can be suitably used. The metal foil is used to prevent the permeation of moisture and gas, and foils such as copper, aluminum, and stainless steel can be suitably used. The inner resin film is used to protect the metal foil from being damaged by the non-aqueous electrolyte contained inside, and is also used to perform melt sealing when heat-sealing the outer body, and polyolefins, acid-modified polyolefins, etc. can be suitably used.

[0511] Method for manufacturing non-aqueous lithium storage device

[0512] The non-aqueous lithium battery element of this embodiment can be manufactured by, for example, housing an electrode stack or an electrode wound body together with a non-aqueous electrolyte in an outer casing, followed by sequential lithium doping, aging, and exhaust. An exemplary method for manufacturing a non-aqueous lithium battery element is described below.

[0513] 〈Assembly〉

[0514] [Electrode laminate or electrode wound body]

[0515] In the assembly process, typically, the positive electrode precursor cut into single sheets and the negative electrode are stacked with a separator interposed therebetween to form an electrode stack, and the positive and negative electrode terminals are connected to the electrode stack. Alternatively, the positive electrode precursor and the negative electrode are stacked and wound with a separator interposed therebetween to form an electrode wound body, and the positive and negative terminals are connected to the electrode wound body. The electrode wound body can be cylindrical or flat.

[0516] The method for connecting the electrode laminate or electrode wound body to the positive electrode terminal and the negative electrode terminal is not particularly limited, and resistance welding, ultrasonic welding, or the like can be used.

[0517] [Storage in the outer body]

[0518] The dried electrode stack or electrode wound body is preferably housed in an outer package, such as a metal can or laminated packaging material, and sealed with only one opening. The outer package is not particularly limited in sealing method; when a laminated packaging material is used, heat sealing, impulse sealing, or other methods can be used.

[0519] [dry]

[0520] The electrode laminate or wound electrode body housed in the outer casing is preferably dried to remove any residual solvent. The drying method is not limited and vacuum drying, for example, may be employed. The residual solvent content is preferably 1.5% by mass or less per unit mass of the positive electrode active material layer or negative electrode active material layer. A residual solvent content of 1.5% by mass or less is preferred because it is less likely to degrade self-discharge characteristics and cycle characteristics.

[0521] <Liquid injection, impregnation, and sealing>

[0522] A non-aqueous electrolyte is injected into an outer casing containing a dried electrode laminate or electrode wound body. Preferably, after injection, the positive electrode precursor, the negative electrode, and the separator are fully impregnated with the non-aqueous electrolyte. If at least a portion of the positive electrode precursor, the negative electrode, and the separator is not impregnated with the non-aqueous electrolyte, the doping may be uneven in the lithium doping step described later, which may increase the resistance of the resulting non-aqueous lithium storage element or reduce its durability, which is not preferred.

[0523] The impregnation method is not particularly limited. For example, the following method can be used: the non-aqueous lithium battery element after injection is placed in a reduced pressure chamber with the outer casing open, the chamber is reduced in pressure using a vacuum pump, and then the pressure is restored to atmospheric pressure. After impregnation, the outer casing is sealed while the pressure is reduced in the open state, thereby achieving airtightness.

[0524] [Lithium doping process]

[0525] In the lithium doping step, preferably, a voltage is applied between the positive electrode precursor and the negative electrode to decompose the lithium compound in the positive electrode precursor to release lithium ions, which are then reduced at the negative electrode to pre-dope the negative electrode active material layer with lithium ions.

[0526] During the lithium doping process, the oxidative decomposition of the lithium compound in the positive electrode precursor generates gases such as CO2. Therefore, when a voltage is applied, it is preferable to employ a method for releasing the generated gas to the exterior of the outer casing. Examples of such methods include: applying the voltage while leaving a portion of the outer casing open; applying the voltage while pre-installing a suitable gas release mechanism, such as a vent valve or gas-permeable membrane, in a portion of the outer casing; and so on.

[0527] <aging>

[0528] After lithium doping, the nonaqueous lithium storage element is preferably aged. During aging, the organic solvent in the nonaqueous electrolyte decomposes at the negative electrode, forming a lithium ion permeable solid electrolyte interface (SEI) film on the negative electrode surface.

[0529] The aging method for effectively forming a good SEI material is described below.

[0530] <exhaust>

[0531] After aging, it is preferable to further vent the electrolyte to reliably remove any remaining gas in the non-aqueous electrolyte, positive electrode, and negative electrode. Residual gas in at least a portion of the non-aqueous electrolyte, positive electrode, and negative electrode hinders ion conduction, potentially increasing the resistance of the resulting non-aqueous lithium battery element.

[0532] The exhaust method is not particularly limited. For example, a method of placing the nonaqueous lithium battery element in a reduced-pressure chamber with its outer casing opened and reducing the pressure in the chamber using a vacuum pump may be used.

[0533] 《Characteristics Evaluation of Non-aqueous Lithium Storage Devices》

[0534] A method for evaluating the characteristics of the non-aqueous lithium battery device according to this embodiment will be described below.

[0535] C-ratio

[0536] The C-rate of current hereafter refers to a relative value of 1C when a constant current discharge is performed from an upper limit voltage to a lower limit voltage, with the current value required to complete the discharge in 1 hour being regarded as the current value.

[0537] Discharge capacity

[0538] In this specification, the discharge capacity Q is a value obtained by the following method.

[0539] First, the battery cell corresponding to the non-aqueous lithium battery element was charged at a constant current of 20C in a thermostat set at 25°C until it reached Vmax. This was followed by constant voltage charging at Vmax for a total of 30 minutes. This was followed by constant current discharge at a current of 2C until it reached Vmin. The discharge capacity at this point was referred to as the discharge capacity Q (mAh) in this embodiment.

[0540] (Electrostatic Capacitance)

[0541] In this specification, the electrostatic capacitance F (F) is a value obtained by the following method.

[0542] First, the battery cell corresponding to the non-aqueous lithium battery element was charged at a constant current of 2C in a thermostatic chamber set at 25°C until it reached Vmax. This was followed by constant voltage charging, where a constant voltage of Vmax was applied for a total of 30 minutes. This was followed by constant current discharge at a current of 2C to Vmin, with the capacity at that point being referred to as Q. The capacitance F is calculated using the Q obtained here, using the formula: capacitance F = Q / (Vmax - Vmin).

[0543] Internal resistance at room temperature discharge

[0544] In this specification, the room temperature discharge internal resistance Ra (Ω) is a value obtained by the following method.

[0545] First, for the battery cell corresponding to the non-aqueous lithium storage element, a constant current charge is performed at a current value of 20C in a constant temperature chamber set at 25°C until Vmax is reached, followed by a constant voltage charge with a constant voltage of Vmax applied for a total of 30 minutes. Next, the sampling interval is set to 0.05 seconds, and a constant current discharge is performed at a current value of 20C until Vmin is reached, and a discharge curve (time-voltage) is obtained. In this discharge curve, the voltage values ​​at the moment of discharge time 1 second and 2 seconds are extrapolated with a straight line approximation. When the voltage at the obtained discharge time = 0 seconds is set as Eo, the value obtained by reducing the voltage ΔE = Vmax - Eo and Ra = ΔE / (20C (current value A)) is calculated, and the value obtained is the internal resistance of the room temperature discharge.

[0546] From the perspective of exhibiting sufficient charge and discharge capacity for a large current, Ra (Ω) is preferably 3.0 (mΩ) or less. When Ra (Ω) is equal to or less than the upper limit, excellent output characteristics can be obtained.

[0547] (Electric Energy)

[0548] In this specification, electric energy E (Wh) is a value obtained by the following method.

[0549] This means using the capacitance F (F) calculated by the above method to calculate the capacitance by the mathematical formula: F×(Vmax 2 -Vmin 2 ) / 2 / 3,600.

[0550] (volume)

[0551] The volume V (L) of the energy storage element refers to the volume of the portion of the outer casing that houses the electrode laminate or the electrode wound body.

[0552] For example, in the case of an electrode stack or an electrode wound body housed in a laminate film, typically, the region where the positive electrode active material layer and the negative electrode active material layer exist in the electrode stack or the electrode wound body is housed in the cup-molded laminate film. x ) Using the outer dimension length of the cup forming part (l x ) and outer dimension width (w x ) and the thickness of the storage element including the laminate film (t x ) According to the mathematical formula: V x =l x ×w x ×t x Perform calculations.

[0553] In the case of an electrode stack or an electrode winding housed in a square metal can, the volume of the energy storage element is calculated based on the outer dimensions of the metal can. That is, the volume of the energy storage element (V y ) Use the outer length of the square metal can (l y ) and outer dimension width (w y ), outer dimension thickness (t y ) According to the mathematical formula: V y =l y ×w y ×t y Perform calculations.

[0554] In the case of an electrode winding body housed in a cylindrical metal can, the outer dimension volume of the metal can is used as the volume of the storage element. That is, the volume of the storage element (V z ) Use the outer radius (r) and outer length (l) of the bottom or top surface of a cylindrical metal can. z ) According to the mathematical formula: V z =3.14×r×r×l z Perform calculations.

[0555] <High temperature storage test>

[0556] In this specification, the internal resistance increase rate during room temperature discharge after the high-temperature storage test is measured by the following method.

[0557] First, the room-temperature internal resistance (Ra) of a battery cell corresponding to a non-aqueous lithium storage element was measured in a thermostat set at 25°C, with Vmax = 3.8V and Vmin = 2.2V. The battery cell was then subjected to constant-current charging at a current value of 100C until it reached an arbitrary voltage of 4.0V. This was followed by constant-voltage charging, where a constant voltage of 4.0V was applied for 10 minutes. The battery cell was then stored in an 85°C environment. Once a week, the battery cell was removed from the 85°C environment, charged to 4.0V using the above charging procedure, and then stored in an 85°C environment again. This procedure was repeated for a specific period of time to conduct a high-temperature storage test.

[0558] For battery cells after the high-temperature storage test, the resistance value obtained using the same measurement method as for the room-temperature discharge internal resistance is defined as the room-temperature discharge internal resistance Rb after the high-temperature storage test. The internal resistance increase rate after the high-temperature storage test relative to the room-temperature discharge internal resistance Ra before the start of the high-temperature storage test is calculated as Rb / Ra.

[0559] In this specification, the discharge capacity after the high-temperature storage test is measured by the following method.

[0560] First, for a battery cell corresponding to a non-aqueous lithium storage element, the discharge capacity Qa at Vmax = 3.8V and Vmin = 2.2V was measured in a thermostatic chamber set at 25°C. The battery cell was then subjected to constant current charging at a current value of 100C until it reached an arbitrary voltage of 4.0V, followed by constant voltage charging with a constant voltage of 4.0V applied for 10 minutes. The battery cell was then stored in an 85°C environment. Every week, the battery cell was removed from the 85°C environment, charged to 4.0V using the above charging procedure, and then stored in an 85°C environment again. This operation was repeated for a specific period of time to conduct a high-temperature storage test.

[0561] For the battery cell after the high-temperature storage test, the capacity obtained using the same measurement method as the discharge capacity is defined as the discharge capacity Qb after the high-temperature storage test. The discharge capacity remaining ratio after the high-temperature storage test relative to the discharge capacity Qa before the start of the high-temperature storage test is calculated as Qb / Qa.

[0562] [X-ray photoelectrometry (XPS)]

[0563] The electronic state can be analyzed by XPS, thereby determining the binding state of the lithium compound.

[0564] Examples of measurement conditions include the following.

[0565] X-ray source: monochromated AlKα

[0566] X-ray beam diameter: 100μmΦ (25W, 15kV)

[0567] Pass energy: narrow scan, 58.70eV

[0568] Charge neutralization: Yes

[0569] Scan number: Narrow scan, 10 times (carbon, oxygen)

[0570] Energy step: narrow scan, 0.25eV

[0571] Before XPS measurement, the surface of the sample (e.g., the positive electrode) is preferably cleaned by sputtering. For example, the sputtering conditions may be an acceleration voltage of 1.0 kV, a 2 mm x 2 mm area, and a duration of 1 minute (1.25 nm / min in terms of SiO2).

[0572] The peaks of the obtained XPS spectrum can be assigned, for example, as follows.

[0573] <Li1s Peak>

[0574] Peak with binding energy of 50-54 eV: LiO2 or Li-C bond

[0575] Peaks of 55-60 eV: LiF, Li2CO3, Li x PO y F z (wherein x, y, and z are integers from 1 to 6);

[0576] <C1s Peak>

[0577] Peak with binding energy of 285 eV: C-C bond

[0578] Peak at 286 eV: CO bond

[0579] Peak at 288eV: COO

[0580] Peak at 289.5: COO-

[0581] Peak at 290-292 eV: CO3 2- , CF key;

[0582] O1s Peak

[0583] Peak with binding energy of 527-530 eV: O 2- (Li2O)

[0584] Peaks at 531-532 eV: CO, CO3, OH, PO x (wherein x is an integer from 1 to 4), SiO x (where x is an integer from 1 to 4)

[0585] 533eV peak: CO, SiO x (wherein x is an integer from 1 to 4);

[0586] F1s Peak

[0587] Peak with binding energy of 685 eV: LiF

[0588] Peak at 687eV: CF bond, Li x PO y F z (wherein x, y, and z are integers from 1 to 6), PF6 - ;

[0589] P2p Peak

[0590] Peak with binding energy of 133 eV: PO x (where x is an integer from 1 to 4)

[0591] Peak at 134-136 eV: PF x (wherein x is an integer from 1 to 6);

[0592] Si2p Peak

[0593] Peak with binding energy of 99 eV: Si, silicide

[0594] Peak at 101-107 eV: Si x O y (where x and y are arbitrary integers)

[0595] In the case of peak overlap in the obtained spectrum, it is preferable to separate the peaks using a Gaussian function or a Lorentzian function and assign the spectrum. The lithium compound present can be identified based on the obtained electronic state measurement results and the results of the element ratio.

[0596] [Solid Electrolyte Interface (SEI) Materials]

[0597] In this specification, a solid electrolyte interface (SEI) material composed of decomposition products of the non-aqueous electrolyte, such as the non-aqueous electrolyte, is formed on the negative electrode surface to suppress decomposition of the non-aqueous electrolyte and improve high-temperature durability. This SEI material lacks electrical (electronic) conductivity but has lithium ion conductivity, and its formation is known to suppress electrolyte decomposition.

[0598] The solid electrolyte interface (SEI) material can be formed on the surface of the negative electrode by subjecting the manufactured energy storage element to an aging treatment under specific conditions.

[0599] The above-mentioned aging treatment can be carried out, for example, as follows: constant current discharge is performed at 1.0 A in an environment of 25°C until the voltage reaches 3.0V, and then the voltage is adjusted to 3.0V by constant voltage discharge at 3.0V for 1 hour, and then the obtained non-aqueous lithium storage element is stored in a constant temperature bath at 60°C for 60 hours to perform aging treatment.

[0600] Examples of the solid electrolyte interface (SEI) material include lithium oxalate, lithium fluoride, lithium carbonate, lithium oxide, organic lithium compounds, and organic polymers. Among these, lithium oxalate is preferred from the perspective of suppressing decomposition of the electrolyte solution.

[0601] The formation of a solid electrolyte interface (SEI) material (eg, lithium oxalate) on the surface of the negative electrode can be confirmed by X-ray photoelectron spectroscopy (XPS) based on a peak in the range of 289 eV to 290 eV.

[0602] <Iron Quantification Method ICP-MS>

[0603] The sample to be measured is subjected to acid decomposition using a strong acid such as concentrated nitric acid, concentrated hydrochloric acid, or aqua regia, and the resulting solution is diluted with pure water to an acid concentration of 2% to 3% by mass. During the acid decomposition, the sample may be heated or pressurized as appropriate.

[0604] The resulting dilution is used as a test sample and analyzed by ICP-MS. In this case, it is preferred to add a known amount of an element as an internal standard. If the iron element of the measurement object exceeds the upper limit of the measurement concentration, it is preferred to further dilute the dilution while maintaining the acid concentration of the dilution.

[0605] The obtained measurement results can be used to quantify the iron element based on a calibration curve prepared in advance using a standard solution for chemical analysis.

[0606] In this specification, the content of iron in the positive electrode precursor is measured using ICP-MS. A portion of the obtained positive electrode precursor is vacuum dried at 180°C for 20 hours, and the positive electrode active material layer is collected from the positive electrode precursor in a dry air environment with a dew point below -40°C and weighed. Using the collected sample, the content of iron contained in the positive electrode active material layer of the positive electrode precursor is measured by ICP-MS, and the content is divided by the mass of the positive electrode active material layer of the positive electrode precursor used in the measurement, thereby calculating the content of iron per unit mass of the positive electrode active material layer of the positive electrode precursor.

[0607] [XRD (X-ray diffraction)]

[0608] In the negative electrode of this embodiment, the spectrum of the negative electrode active material layer measured using XRD (X-ray diffraction) preferably has a peak Y1 with a peak top in the range of 2θ from 26.2° to 26.5°, and the half-peak width of this peak Y1 is from 0.1° to 0.5°. When the half-peak width of peak Y1 is 0.1° or more, it can be evaluated that the diffusivity of ions in the negative electrode active material layer is improved, and it can be considered that low resistance of the negative electrode is achieved. When the half-peak width of peak Y1 is 0.5° or less, the carbon nanotubes are uniformly dispersed on the surface of the negative electrode active material, and it can be considered that the capacity reduction and resistance increase in high temperature environments can be suppressed.

[0609] In addition, the peak X1 in XRD (X-ray diffraction) measured on the positive electrode active material layer is as described above.

[0610] [Raman spectroscopy analysis of negative electrode active material layer]

[0611] Raman spectroscopic analysis was performed using a microscopic Raman spectrometer, trade name "inViaReflex," manufactured by Renishaw Ltd. The excitation light had a laser wavelength of 532 nm, and a 100x objective lens was used to focus the light at a power of approximately 0.1 mW at the sample position.

[0612] For the surface of the negative electrode active material layer, a Raman spectrum was obtained for a measurement area of ​​40 μm×40 μm.

[0613] To remove spike noise, we used the "Cosmic ray removal" feature included with the analysis software "WiRE" manufactured by Renishaw Ltd. For principal component analysis to remove noise, we used the "Noise filter" included with the analysis software "WiRE" and reconstructed the spectra of the top 12 components with the highest scores.

[0614] In the obtained Raman spectrum, the wavelength from 1,000 cm -1 To 1,800cm -1 The baseline of the straight line is 1,350±15cm. -1 The peak intensity Id of the observed D-band peak Pd is similar to that at 1,585±15 cm -1 The peak intensity Ig of the peak Pg of the G band that appears is used to determine its intensity ratio Id / Ig. The R value is the average value of 8 measurements.

[0615] It should be noted that Raman spectroscopic analysis of the positive electrode active material layer was performed by the method described in Examples below.

[0616] BET surface area, average pore diameter, mesopore volume, and micropore volume

[0617] In this specification, the BET specific surface area, average pore diameter, mesopore content, and micropore content are values ​​calculated using the following methods. A sample was vacuum-dried at 200°C overnight, and adsorption / desorption isotherms were measured using nitrogen as the adsorbate. Using the adsorption isotherm obtained here, the BET specific surface area was calculated using the BET multi-point method or the BET single-point method. The average pore diameter was calculated by dividing the total pore volume per unit mass by the BET specific surface area. The mesopore content was calculated using the BJH method, and the micropore content was calculated using the MP method.

[0618] The BJH method is a calculation method generally used in mesopore analysis and was proposed by Barrett, Joyner, Halenda et al. (EP Barrett, LG Joyner and P. Halenda, J. Am. Chem. Soc., 73, 373 (1951)) (Non-Patent Document 1).

[0619] The MP method refers to a method of calculating the pore volume, pore area, and pore distribution using the "t-plot method" (BC Lippens, JH de Boer, J. Catalysis, 4319 (1965) (non-patent document 2)). It is a method designed by M. Mikhail, Brunauer, and Bodor (RS Mikhail, S. Brunauer, EE Bodor, J. Colloid Interface Sci., 26, 45 (1968) (non-patent document 3)).

[0620] Average particle size

[0621] In this specification, the average particle size refers to the particle size at the point where the cumulative curve reaches 50% (i.e., the 50% diameter (median diameter)) when the particle size distribution is measured using a particle size distribution analyzer, with the total volume being 100%. The average particle size can be measured using a commercially available laser diffraction particle size analyzer.

[0622] <Applications of Non-aqueous Lithium Storage Devices>

[0623] The storage module can be made by connecting a plurality of non-aqueous lithium storage elements of the present embodiment in series or in parallel. In addition, the non-aqueous lithium storage element and the storage module of the present embodiment can take into account both high input-output characteristics and safety at high temperatures. Therefore, the non-aqueous lithium storage element and the storage module of the present embodiment can be assembled into a power regeneration auxiliary system, a power load balancing system, an uninterruptible power supply system, a contactless power supply system, an energy collection system, a storage system, a solar power generation storage system, an electric power steering system, an emergency power supply system, a wheel hub electrode system, an idling stop system, a fast charging system, a smart grid system, etc. for use.

[0624] Energy storage systems are suitable for natural power generation such as solar and wind power, power load balancing systems for microgrids, and uninterruptible power supply systems for factory production equipment. In contactless power supply systems, non-aqueous lithium storage elements are suitable for balancing and storing voltage fluctuations such as those caused by microwave transmission or electric field resonance. In energy harvesting systems, non-aqueous lithium storage elements are suitable for utilizing electricity generated by vibration power generation, for example.

[0625] In a power storage system, a plurality of nonaqueous lithium storage elements are connected in series or in parallel as a battery stack, or a nonaqueous lithium storage element is connected in series or in parallel with a lead battery, a nickel-hydrogen battery, a lithium-ion secondary battery, or a fuel cell.

[0626] Furthermore, the non-aqueous lithium battery element of this embodiment combines high input-output characteristics with safety at high temperatures, and can therefore be incorporated into vehicles such as electric vehicles, plug-in hybrid vehicles, hybrid electric vehicles, and electric two-wheeled vehicles. The aforementioned power regeneration assist system, electric power steering system, emergency power supply system, in-wheel motor system, and idle stop system, or combinations thereof, are suitable for incorporation into vehicles.

[0627] Example

[0628] <Examples 1 to 13 and Comparative Examples 1 to 9>

[0629] The following examples and comparative examples will be used to specifically describe the embodiments of the present invention. However, the present invention is not limited to the following examples and comparative examples.

[0630] <Preparation of Carbon Nanotube Dispersion>

[0631] 8.0 mass% of commercially available multi-walled carbon nanotubes (average fiber diameter 40 nm, average fiber length 12 μm), 1.0 mass% of carboxymethyl cellulose (CMC) and 91.0 mass% of distilled water as dispersant 1, and Fe2O3 as a metal compound (equivalent to 10 ppm in terms of iron atoms) were mixed and dispersed at a speed of 100 rpm for 120 minutes using a planetary ball mill to prepare a carbon nanotube dispersion (CNT dispersion).

[0632] <Manufacturing Example 1 of Negative Electrode>

[0633] 84.0 parts by mass of artificial graphite with an average particle size of 4.5 μm, 100 parts by mass of the above-mentioned carbon nanotube dispersion (equivalent to 8.0 parts by mass of carbon nanotubes and 1.0 parts by mass of carboxymethyl cellulose), 3.0 parts by mass of acetylene black (AB), 1.0 part by mass of PVP (polyvinyl pyrrolidone) as dispersant 2, 3.0 parts by mass of styrene butadiene rubber (SBR) as a binder, and an additional component of Fe2O3 as a metal compound (equivalent to 10 ppm in terms of iron atoms) and distilled water are mixed to obtain a mixture with a solid content ratio of 36.5% by mass.

[0634] The obtained mixture was dispersed using an autorotating and orbiting mixer "Awatori Rentaro (registered trademark)" manufactured by Thinky Co., Ltd. at a rotation speed of 2,000 rpm for 20 minutes to obtain a negative electrode coating liquid.

[0635] The viscosity (ηb) and TI value of the obtained negative electrode coating liquid were measured using an E-type viscometer TVE-35H manufactured by Toki Sangyo Co., Ltd. The viscosity (ηb) was 1,970 mPa·s and the TI value was 3.3.

[0636] The negative electrode coating solution was applied to one side of an 8 μm thick electrolytic copper foil using a doctor blade and dried for 10 minutes on a hot plate heated to 50°C. The foil was then pressed using a roller press at a pressure of 5 kN / cm and a surface temperature of 25°C to produce negative electrode 1.

[0637] The total thickness of negative electrode 1 was measured at 10 random locations using a thickness meter "Linear Gauge Sensor GS-551" manufactured by Ono Keiki Co., Ltd., and the thickness of the negative electrode active material layer was determined by subtracting the thickness of the electrolytic copper foil from the average value. The thickness of the negative electrode active material layer of negative electrode 1 was 31 μm.

[0638] <Negative Electrode Manufacturing Examples 2 to 17, 19, and 20>

[0639] A carbon nanotube dispersion (CNT dispersion) was prepared in the same manner as in <Example 1 for the manufacture of a negative electrode>, except that the average fiber diameter and average fiber length of the multi-walled carbon nanotubes (CNTs), the amount of CNTs used in preparing the CNT dispersion, and the type of metal compound and its amount converted to metal atoms were as described in Table 1.

[0640] Negative electrodes 2 to 17, 19, and 20 were produced in the same manner as in <Negative Electrode Production Example 1> except that the types and amounts of the components were adjusted as shown in Table 2, respectively, using these CNT dispersions.

[0641] <Manufacturing Example 18 of Negative Electrode>

[0642] 84.0 parts by mass of artificial graphite with an average particle size of 4.5 μm, 8.0 parts by mass of commercially available multi-walled carbon nanotubes (average fiber diameter of 40 nm, average fiber length of 12 μm), 3.0 parts by mass of acetylene black, 1.0 part by mass of carboxymethyl cellulose, 1.0 part by mass of PVP (polyvinyl pyrrolidone), 3.0 parts by mass of styrene butadiene rubber, Fe2O3 (equivalent to 20 ppm in terms of iron atoms) and distilled water are mixed to obtain a mixture with a solid content ratio of 36.5% by mass.

[0643] The resulting mixture was dispersed using an Awatori Rentaro (registered trademark) autorotating mixer manufactured by Thinky Co., Ltd. at a rotation speed of 2,000 rpm for 20 minutes to obtain a negative electrode coating solution. The same procedures as in Negative Electrode Preparation Example 1 were followed to measure the viscosity (ηb) of the coating solution to 1,370 mPa·s and the TI value to 6.3.

[0644] A negative electrode 18 having a negative electrode active material layer with a thickness of 32 μm was obtained in the same manner as in Production Example 1 of the negative electrode except that the obtained mixture was used.

[0645] <Manufacturing Example 21 of Negative Electrode>

[0646] A negative electrode 21 was produced in the same manner as in Production Example 18 of the negative electrode, except that the types and amounts of the components were as described in Table 2.

[0647] [Table 1]

[0648] Table 1.

[0649]

[0650] [Table 2]

[0651] Table 2.

[0652]

[0653] <Preparation of Positive Electrode Active Material>

[0654] Crushed coconut shell carbide was placed in a small carbonization furnace and carbonized at 500°C for 3 hours under a nitrogen atmosphere to obtain carbide. The obtained carbide was placed in an activation furnace, and steam heated in a preheating furnace was introduced into the activation furnace at a rate of 1 kg / h. The temperature was raised to 900°C over 8 hours for activation. The activated carbide was removed and cooled under a nitrogen atmosphere to obtain activated activated carbon. The obtained activated activated carbon was washed with water for 10 hours to remove moisture, dried in an electric dryer maintained at 115°C for 10 hours, and then pulverized in a ball mill for 1 hour to obtain activated carbon 1.

[0655] The average particle size of activated carbon 1 was measured using a laser diffraction particle size distribution analyzer (SALD-2000J) manufactured by Shimadzu Corporation and was found to be 5.5 μm. Furthermore, the pore distribution of activated carbon 1 was measured using a pore distribution analyzer (AUTOSORB-1AS-1-MP) manufactured by Yuasa Ionics. The BET specific surface area was 2360 m 2 / g, the mesopore volume (V1) is 0.52cc / g, the micropore volume (V2) is 0.88cc / g, and V1 / V2=0.59.

[0656] <Preparation of Carbon Nanotube Dispersion>

[0657] 8.0 parts by mass of commercially available multi-walled carbon nanotubes (average fiber diameter 40 nm, average fiber length 50 μm), 1.0 parts by mass of carboxymethyl cellulose (CMC) as dispersant 1, 91.0 parts by mass of distilled water, and Fe2O3 (equivalent to 10 ppm in terms of iron atoms) were mixed and dispersed at a speed of 100 rpm for 120 minutes using a planetary ball mill to prepare a carbon nanotube dispersion for forming a positive electrode active material layer.

[0658] <Production Example 1 of Positive Electrode Precursor>

[0659] Activated carbon 1 (56.0 parts by mass), carboxymethyl cellulose (CMC) 1.5 parts by mass, lithium carbonate 30.0 parts by mass, acetylene black (AB) 3.0 parts by mass and acrylic latex (LTX) 4.5 parts by mass, PVP (polyvinyl pyrrolidone) 5.0 parts by mass, and distilled water having a solid content of 46.5% by mass were mixed, and the mixture was dispersed at a rotation speed of 2000 rpm for 30 minutes using an autorotational mixer "Awatori Rentaro (registered trademark)" manufactured by Thinky to obtain a positive electrode coating solution.

[0660] The viscosity (ηb) and TI value of the resulting positive electrode coating solution were measured using a TVE-35H E-type viscometer from Toki Sangyo Co., Ltd. The viscosity (ηb) was 3,650 mPa·s and the TI value was 5.1. Furthermore, the dispersion of the resulting positive electrode coating solution was measured using a particle size analyzer manufactured by Yoshimitsu Seiki Co., Ltd. The particle size was 33 μm.

[0661] The positive electrode coating liquid was applied to one side of a 15 μm thick aluminum foil using a doctor blade, dried on a hot plate heated to 50° C. for 10 minutes, and then pressed using a roll press at a pressure of 6 kN / cm and a surface temperature of 25° C. to obtain a positive electrode precursor 1.

[0662] The total thickness of the obtained positive electrode precursor 1 was measured at 10 random locations using a Linear Gauge Sensor GS-551 manufactured by Ono Keiki Co., Ltd. The thickness of the positive electrode active material layer was calculated by subtracting the thickness of the aluminum foil from the average value. The thickness of the positive electrode active material layer of the positive electrode precursor 1 was 61 μm.

[0663] <Production Example 2 of Positive Electrode Precursor>

[0664] Using activated carbon 1 (53.0 parts by mass), 100 parts by mass of the carbon nanotube dispersion for forming the above-mentioned positive electrode active material layer (equivalent to 8.0 parts by mass of carbon nanotubes and 1.0 parts by mass of carboxymethyl cellulose), 30.0 parts by mass of lithium carbonate, 3.0 parts by mass of acetylene black (AB), 1.5 parts by mass of PVP (polyvinyl pyrrolidone) and 3.5 parts by mass of acrylic latex (LTX), a positive electrode coating liquid was prepared in the same manner as in Example 1 of the preparation of the positive electrode precursor, and the positive electrode precursor 2 was prepared using the same.

[0665] <Preparation Example 1 of Electrolyte Solution>

[0666] A mixed solvent of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) = 33:67 (volume ratio) was used as an organic solvent, and the electrolyte salt was dissolved in such a manner that the concentration ratio of LiPF6 to LiFSI was 1:1 and the total concentration was 1.2 mol / L, thereby obtaining a non-aqueous electrolyte solution 1.

[0667] <Preparation Example 2 of Electrolyte Solution>

[0668] A mixed solvent of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) = 33:67 (volume ratio) was used as the organic solvent, and electrolyte salts were dissolved in a concentration ratio of LiPF6, LiFSI and LiBOB of 5:6:1 and a total concentration of 1.2 mol / L to obtain a non-aqueous electrolyte solution 2.

[0669] Example 1

[0670] <Manufacturing of Non-aqueous Lithium Storage Devices>

[0671] The obtained positive electrode precursor 1 is cut into a piece according to the size of 4.4cm×9.4cm for the positive electrode active material layer. Then, the negative electrode 1 is cut into a piece according to the size of 4.5cm×9.5cm for the negative electrode active material layer. In addition, a 4.7cm×9.8cm polyethylene separator (manufactured by Asahi Chemical, with a thickness of 15μm) is prepared. Using these components, the positive electrode active material layer and the negative electrode active material layer are stacked opposite each other with the separator sandwiched therebetween in the order of the positive electrode precursor 1, the separator and the negative electrode 1 to obtain an electrode laminate. The positive terminal and the negative terminal are ultrasonically welded to the obtained electrode body, which is then placed in an outer body formed of an aluminum laminate packaging material, and the three sides containing the electrode terminal portion are sealed by heat sealing.

[0672] Under atmospheric pressure, in a dry air environment with a temperature of 25°C and a dew point below -40°C, approximately 2.5g of non-aqueous electrolyte solution 1 was injected into the outer casing containing the electrode stack. Next, the outer casing containing the electrode stack and the non-aqueous electrolyte was placed in a decompression chamber, depressurized from atmospheric pressure to -87kPa, then returned to atmospheric pressure and allowed to stand for 5 minutes. This process was then repeated four times, with the outer casing in the chamber depressurized from atmospheric pressure to -87kPa and then returned to atmospheric pressure. The chamber was then allowed to stand at atmospheric pressure for 15 minutes. Through these steps, the non-aqueous electrolyte solution 1 was impregnated into the electrode stack.

[0673] Thereafter, the electrode laminate impregnated with the non-aqueous electrolyte solution 1 was placed in a vacuum sealer and sealed at a pressure of 0.1 MPa at 180° C. for 10 seconds under a reduced pressure of −95 kPa to seal the outer package.

[0674] [Alkali Metal Doping Process]

[0675] The sealed electrode laminate was charged at a temperature of 40°C and a current of 50 mA until the voltage reached 4.5 V, and then charged at a constant voltage of 4.5 V for 2 hours. This method was used for initial charging and alkali metal doping was performed on the negative electrode.

[0676] [Aging process]

[0677] The alkali metal-doped electrode laminate was removed from the drying oven and discharged at a constant current of 50 mA at 25°C until the voltage reached 4.0 V. The voltage was then adjusted to 4.0 V by performing constant current discharge at 4.0 V for 1 hour. The electrode assembly was then stored in a thermostatic chamber at 60°C for 12 hours.

[0678] [Exhaust process]

[0679] After aging, the outer casing was partially opened in a dry air environment at 25°C and a dew point of -40°C, and the electrode stack was removed. The removed electrode stack was placed in a decompression chamber and depressurized from atmospheric pressure to -80 kPa over 3 minutes using a diaphragm pump. This process was then repeated a total of three times, followed by a 3-minute return to atmospheric pressure. The electrode stack was then placed back into the outer casing, depressurized to -90 kPa using a vacuum sealer, and then sealed at 0.1 MPa for 10 seconds at 200°C to produce a non-aqueous lithium battery cell.

[0680] A plurality of non-aqueous lithium storage devices having the same structure are manufactured through the above steps.

[0681] <Evaluation of Non-aqueous Lithium Storage Devices>

[0682] [Measurement of capacitance Qa and internal resistance Ra]

[0683] The capacitance Qa and internal resistance Ra of one of the resulting non-aqueous lithium storage elements were measured using a charge-discharge device (5 V, 10 A) manufactured by Asuka Electronics Co., Ltd. in a thermostatic chamber set at 25°C using the above method. The results showed that Qa was 9.04 mAh and Ra was 88.3 mΩ. These values ​​are shown in Table 3 as the initial capacitance Qa and initial internal resistance Ra.

[0684] [High voltage and high temperature storage test]

[0685] Another of the resulting non-aqueous lithium storage elements was subjected to a high-voltage, high-temperature storage test using the aforementioned method. After the test, the capacitance Qb and internal resistance Rb were measured; Qb was 8.14 mAh and Rb was 97.3 mΩ. These values ​​are shown in Table 3 as capacitance Qb and internal resistance Rb after high-voltage, high-temperature storage.

[0686] <Analysis of Negative Electrode>

[0687] [SEM image capture]

[0688] For another one of the obtained nonaqueous lithium storage devices, the outer casing was partially opened in a dry air environment at a temperature of 25° C. and a dew point of −40° C., the electrode laminate was taken out, and the negative electrode was collected.

[0689] Gold was sputtered onto the negative electrode active material layer in a vacuum of 10 Pa, thereby coating the surface with a gold film having a thickness of several nanometers. SEM images of the negative electrode active material layer surface were then taken under atmospheric exposure under the following conditions.

[0690] (SEM measurement conditions)

[0691] Measurement device: Field emission scanning electron microscope S-4700 manufactured by Hitachi High-Technologies Corporation

[0692] Accelerating voltage: 1kV

[0693] Emission current: 10μA

[0694] ·Measurement magnification: 10000 times

[0695] Detector: Secondary electron detector

[0696] Electron beam incident angle: 90°

[0697] During the imaging, the brightness and contrast were adjusted so that there were no pixels with the maximum brightness value in the SEM image and the average brightness value fell within the range of 40% to 60% of the maximum brightness value.

[0698] Using the captured SEM images, the area ratio Z1 of the largest inscribed circle with a diameter less than 100 nm in the bright field area and the area ratio Z2 of the largest inscribed circle with a diameter less than 100 nm in the dark field area were calculated by the above method. 2 Above 5,000nm 2 The total area of ​​the following regions is 1,000nm 2 Above 20,000nm 2 The area ratio Z2 of the following regions in the total area was 4.1% for Z1 and 64.1% for Z2.

[0699] [XRD (X-ray diffraction) measurement]

[0700] As described above, the negative electrode taken out from the non-aqueous lithium storage element was cut into 1 cm 2 The size of the sample was 1 cm × 1 cm and used as the sample for XRD.

[0701] The obtained XRD sample was subjected to XRD measurement under the following conditions.

[0702] Equipment used: Rigaku Ultima IV

[0703] Detector: D / teX Ultra

[0704] Tube: CuKα

[0705] Tube voltage: 40kV

[0706] Tube current: 40mA

[0707] Sampling interval: 0.01° / point

[0708] Scanning speed: 5° / min

[0709] Measuring angle range: 5 to 90°

[0710] Divergence slit (DS): 1°

[0711] Divergence limit: 10mm

[0712] Anti-scatter slit (SS): open

[0713] Receiving slit (RS): Open

[0714] In the obtained XRD spectrum, the peak top position and half-value width of peak Y1 having a peak top in the range of 2θ of 26.2° to 26.5° were examined, and the peak top position was 26.47° and the half-value width was 0.12°.

[0715] Examples 2 to 13, Comparative Examples 1 to 9

[0716] A nonaqueous lithium storage device was produced and evaluated in the same manner as in Example 1 except that the materials listed in Table 3 were used as the negative electrode, positive electrode precursor, and nonaqueous electrolyte.

[0717] The evaluation results are shown in Table 3.

[0718] The results of SEM analysis of the negative electrode active material layers of the negative electrode 20 of Example 13 and the negative electrode 21 of Comparative Example 9 are shown in FIG. Figures 1 to 6 .

[0719] Figure 1 is an SEM image of the negative electrode active material layer of the negative electrode 20 obtained in Example 13; Figure 2 yes Figure 1 Binarized image of the SEM image; Figure 3 is Figure 2 Frequency distribution of the diameters of the largest inscribed circle obtained from the binarized image.

[0720] Figure 4 is an SEM image of the negative electrode active material layer of negative electrode 21 obtained in Comparative Example 9; Figure 5 yes Figure 4 Binarized image of the SEM image; Figure 6 is Figure 5 Frequency distribution of the diameters of the largest inscribed circle obtained from the binarized image.

[0721]

[0722]

[0723]

[0724]

[0725] <Examples 14 to 47 and Comparative Examples 10 to 18>

[0726] <Crushing of lithium carbonate>

[0727] The lithium carbonate is pulverized by causing brittle fracture at a temperature of -196°C while preventing thermal modification.

[0728] 200 g of lithium carbonate with an average particle size of 53 μm was placed in a pulverizer (liquid nitrogen bead mill LNM) manufactured by IMEX, cooled to -196°C with liquid nitrogen, and then pulverized using dry ice beads at a peripheral speed of 10.0 m / s for 9 minutes. The average particle size of the obtained lithium carbonate was 2.26 μm.

[0729] Preparation of positive electrode active material

[0730] [Preparation of activated carbon 2]

[0731] The crushed coconut shell carbide was carbonized in a small carbonization furnace at 500°C for 3 hours under a nitrogen atmosphere to obtain carbide. The obtained carbide was placed in an activation furnace, and 1 kg / h of water vapor heated in a preheating furnace was introduced into the activation furnace. The temperature was raised to 900°C over 8 hours for activation. The activated carbide was taken out and cooled in a nitrogen atmosphere. The obtained activated carbon was washed with water for 10 hours to remove moisture. The washed and dehydrated activated carbon was dried in an electric dryer maintained at 115°C for 10 hours, and then pulverized in a ball mill for 1 hour to obtain activated carbon 2.

[0732] The average particle size of activated carbon 2 was measured using a laser diffraction particle size distribution analyzer (SALD-2000J) manufactured by Shimadzu Corporation, and the result was 4.2 μm. Furthermore, the pore distribution of activated carbon 1 was measured using a pore distribution analyzer (AUTOSORB-1AS-1-MP) manufactured by Yuasa Ionics, and the BET specific surface area was 2,360 m 2 / g, the mesopore volume (V1) is 0.52cc / g, and the micropore volume (V2) is 0.88cc / g, V1 / V2=0.59.

[0733] [Preparation of activated carbon 3]

[0734] Phenolic resin was carbonized in a calcining furnace at 600°C for 2 hours under a nitrogen atmosphere, then pulverized and classified using a ball mill to obtain a carbide with an average particle size of 7.0 μm. This carbide was mixed with KOH at a mass ratio of 1:5 and activated by heating at 800°C for 1 hour in a calcining furnace under a nitrogen atmosphere. The mixture was then stirred and washed in dilute hydrochloric acid adjusted to a concentration of 2 mol / L for 1 hour, then boiled and washed with distilled water until the pH stabilized between 5 and 6, and then dried to obtain activated carbon 3.

[0735] The average particle size of activated carbon 3 measured in the same manner as activated carbon 1 was 7.1 μm, and the BET specific surface area was 3,627 m 2 / g, the mesopore volume (V1) is 1.50cc / g, and the micropore volume (V2) is 2.28cc / g, V1 / V2=0.66.

[0736] <Cathode Precursor 3>

[0737] [Preparation of lithium compounds containing iron]

[0738] 100 parts by mass of lithium carbonate as a lithium compound and 2.3 parts by mass of ferric chloride (FeCl3·6H2O) were added to distilled water to prepare an aqueous solution with a concentration of 0.5% by mass of lithium carbonate. The obtained aqueous solution was stirred for 1 hour using a homogenizer while being heated to 60°C in an oil bath. The liquid temperature was then raised to 100°C to evaporate the water and precipitate lithium carbonate powder containing an iron element. The obtained lithium carbonate powder containing an iron element was placed in an alumina container, which was placed in a muffle furnace and heated at 300°C for 10 hours while blowing a nitrogen / hydrogen mixed gas. After dechlorination treatment, the mixture was pulverized using a jet mill to obtain lithium carbonate powder 1 containing an iron element having a specific particle size. The average particle size of the lithium carbonate powder 1 containing an iron element was measured using a laser diffraction particle size distribution measuring device manufactured by Shimadzu Corporation, and the result was 0.8 μm.

[0739] [Manufacturing of Positive Electrode Precursor 3]

[0740] As the positive electrode active material, the activated carbon 2 (58.5 parts by mass) obtained in the above-mentioned [Preparation of Activated Carbon 2] was used, and the lithium compound and the conductive filler other than the positive electrode active material of the type and amount described in Table 4 were mixed. 1.5 parts by mass of PVP (polyvinyl pyrrolidone), 8.0 parts by mass of PVDF (polyvinylidene fluoride) and NMP (N-methylpyrrolidone) were further mixed in the obtained mixture, and dispersed under the condition of a circumferential speed of 17 m / s using a thin film gyratory high-speed mixer "FILMIX (registered trademark)" manufactured by PRIMIX to obtain a coating liquid. The above-mentioned coating liquid was applied to one or both sides of an aluminum foil having a thickness of 15 μm and no through-holes as a positive electrode collector at a coating speed of 1 m / s using a die coater manufactured by Toray Engineering Co., Ltd., and dried at a drying temperature of 100°C to obtain a positive electrode precursor. The obtained positive electrode precursor was pressed using a roll press under the conditions of a pressure of 4 kN / cm and a surface temperature of a pressing portion of 25°C.

[0741] Hereinafter, a positive electrode precursor coated only on one side of a positive electrode current collector may be referred to as a “single-sided positive electrode precursor,” and a positive electrode precursor coated on both sides of a positive electrode current collector may be referred to as a “double-sided positive electrode precursor.”

[0742] After a portion of the obtained positive electrode precursor was vacuum dried at 180 ° C for 20 hours, a portion of the positive electrode active material layer was collected as a measurement sample under a dry air environment with a dew point of -40 ° C or less, and weighed. The content of iron contained in the sample was quantified by ICP-MS analysis of the collected sample, and the obtained value was divided by the mass of the sample (positive electrode active material layer of the positive electrode precursor) used in the measurement, thereby calculating the content of iron per unit mass of the positive electrode active material layer of the positive electrode precursor. The results are shown in Table 4.

[0743] [Manufacturing of Positive Electrode Precursors 4 to 9]

[0744] In addition to making the amount of ferric chloride (FeCl3·6H2O) and the type and amount of conductive filler in [Preparation of lithium compounds containing iron elements] as described in Table 4, various lithium carbonate powders containing iron elements were prepared using the same method as positive electrode precursor 3, and used to manufacture positive electrode precursors.

[0745]

[0746] The abbreviations of the components in Table 4 have the following meanings.

[0747] [Lithium compounds other than positive electrode active materials]

[0748] Fe-carbonate Li1: Iron-containing lithium carbonate powder 1 with an average particle size of 0.8 μm obtained in the above-mentioned "Preparation of the lithium compound containing iron"

[0749] Fe-carbonates Li2-4: Iron-containing lithium carbonate powders 2-4 having an average particle size of 0.8 μm were prepared in the same manner as the iron-containing lithium carbonate powder 1 except that the amount of ferric chloride used was changed.

[0750] KB: Ketjen Black

[0751] <Preparation of Carbon Nanotube Dispersion>

[0752] 8.0 mass% of commercially available multi-walled carbon nanotubes (average fiber diameter 40 nm, average fiber length 12 μm), 1.0 mass% of carboxymethyl cellulose (CMC) and 91.0 mass% of distilled water as dispersant 1, and Fe2O3 as a metal compound (equivalent to 10 ppm in terms of iron atoms) were mixed and dispersed at a speed of 100 rpm for 120 minutes using a planetary ball mill to prepare a carbon nanotube dispersion (CNT dispersion).

[0753] Negative Electrode Manufacturing

[0754] <Manufacturing Example 22 of Negative Electrode>

[0755] 84.0% by mass of artificial graphite having an average particle size of 4.5 μm, 10.0% by mass of acetylene black, 3.0% by mass of carboxymethyl cellulose, 3.0% by mass of styrene butadiene rubber, and distilled water having a solid content of 36.5% by mass were mixed, and the mixture was dispersed at a rotation speed of 2,000 rpm for 10 minutes using an autorotating and orbiting mixer "Awatori Rentaro (registered trademark)" manufactured by Thinky Co., Ltd. to obtain a negative electrode coating solution.

[0756] The viscosity (ηb) and TI value of the obtained negative electrode coating liquid were measured using a TVE-35H E-type viscometer manufactured by Toki Sangyo Co., Ltd. The viscosity (ηb) was 1,840 mPa·s and the TI value was 3.1.

[0757] The negative electrode coating liquid was applied to both sides of an 8μm thick electrolytic copper foil serving as a negative electrode current collector using a doctor blade, and dried for 10 minutes on a hot plate heated to 50°C to obtain a negative electrode. Pressing was performed using a roller press at a pressure of 5kN / cm and a surface temperature of 25°C at the pressing portion. The total thickness of the pressed negative electrode was measured using a Linear GaugeSensor GS-551 manufactured by Ono Keiki Co., Ltd. at 10 randomly set locations on the negative electrode surface. The thickness of the negative electrode current collector was subtracted from the average value, and the resultant value was multiplied by 1 / 2. The resulting value was used as the thickness of each single side of the negative electrode active material layer. According to the measurement results obtained, the thickness of the negative electrode active material layer of the negative electrode was 30μm per single side.

[0758] <Manufacturing Example 23 of Negative Electrode>

[0759] 84.0 parts by mass of artificial graphite with an average particle size of 4.5 μm, 100 parts by mass of the above-mentioned carbon nanotube dispersion (equivalent to 8.0 parts by mass of carbon nanotubes and 1.0 parts by mass of carboxymethyl cellulose), 3.0 parts by mass of acetylene black (AB), 1.0 part by mass of PVP (polyvinyl pyrrolidone) as dispersant 2, 3.0 parts by mass of styrene butadiene rubber (SBR) as a binder, Fe2O3 as an additional component of a metal compound (equivalent to 10 ppm in terms of iron atoms), and distilled water are mixed to obtain a mixture with a solid content ratio of 36.5% by mass.

[0760] The obtained mixture was dispersed using an autorotating and orbiting mixer "Awatori Rentaro (registered trademark)" manufactured by Thinky Co., Ltd. at a rotation speed of 2,000 rpm for 20 minutes to obtain a negative electrode coating liquid.

[0761] The viscosity (ηb) and TI value of the obtained negative electrode coating liquid were measured using a TVE-35H E-type viscometer manufactured by Toki Sangyo Co., Ltd. The viscosity (ηb) was 1,970 mPa·s and the TI value was 3.3.

[0762] The negative electrode coating liquid was applied to one side of an 8 μm thick electrolytic copper foil using a doctor blade and dried for 10 minutes on a hot plate heated to 50°C. The foil was then pressed using a roller press at a pressure of 5 kN / cm and a surface temperature of 25°C to produce the negative electrode 23.

[0763] The total thickness of the negative electrode 23 was measured at 10 random locations using a thickness meter "Linear Gauge Sensor GS-551" manufactured by Ono Keiki Co., Ltd. The thickness of the negative electrode active material layer was calculated by subtracting the thickness of the electrolytic copper foil from the average value. The thickness of the negative electrode active material layer of the negative electrode 23 was 31 μm.

[0764] <Preparation of non-aqueous electrolyte solutions 3 to 18>

[0765] A mixed solvent of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) = 33:67 (volume ratio) was used as an organic solvent, and electrolyte salts of the types and concentrations listed in Table 5 were dissolved in the organic solvent to obtain non-aqueous electrolyte solutions 3 to 18, respectively.

[0766] <Preparation of Non-aqueous Electrolyte Solutions 19-34>

[0767] A mixed solvent of ethylene carbonate (EC): ethyl methyl carbonate (EMC) = 33:67 (volume ratio) was used as the organic solvent, and the electrolyte salts of the types and concentrations described in Table 6 were dissolved in the organic solvent, and the nitrile compounds and / or ether compounds of the types and concentrations described in Table 6 were further mixed to obtain non-aqueous electrolyte solutions 19 to 34, respectively.

[0768]

[0769]

[0770] The abbreviations of the components in Tables 5 and 6 have the following meanings.

[0771] [(A) component] at least one lithium salt selected from LiPF6 and LiBF4

[0772] LiBF4: lithium tetrafluoroborate

[0773] LiPF6: lithium hexafluorophosphate

[0774] [Component (B)] Lithium salt having an imide structure

[0775] LiN(SO2F)2:Lithium bis(fluorosulfonyl)imide

[0776] LiN(CF3SO2)2: Lithium bis(trifluoromethanesulfonyl)imide

[0777] LiN(CF3CF2SO2)2: Lithium bis(pentafluoroethanesulfonyl)imide

[0778] [Component (C)] Lithium salt with oxalic acid complex as anion

[0779] LiBOB: lithium bis(oxalatoborate) salt

[0780] LiFOB: lithium fluorooxalatoborate

[0781] LiDFOB: lithium difluorooxalatoborate

[0782] [Nitrile compounds]

[0783] AcCN: acetonitrile

[0784] ScCN: succinonitrile

[0785] MeOAcCN: methoxyacetonitrile

[0786] ATCNP: 2-amino-1,1,3-tricyano-1-propene

[0787] IM-TCNM: 1-butyl-3-methylimidazolium tricyanomethane

[0788] Li-DCNIM: Lithium 4,5-dicyano-2-(trifluoromethyl)imidazolium

[0789] Li-TCNM: 1-butyl-3-methylimidazolium tricyanomethane

[0790] [Ether compounds]

[0791] DMEt: 1,2-dimethoxyethane

[0792] DIOX: 1,3-dioxane

[0793] "-" in Tables 5 and 6 means that the ingredient in that column was not used.

[0794] Example 14

[0795] <Manufacturing of non-aqueous lithium battery cells>

[0796] [Assembly]

[0797] In Example 14, a two-layer separator was used in which a 5 μm-thick coating layer containing boehmite (AlOOH) fine particles was formed on one surface of a 15 μm-thick polyethylene (PE) microporous membrane.

[0798] 21 pieces of double-sided negative electrodes, 20 pieces of double-sided positive electrode precursors 3 and 2 pieces of single-sided positive electrode precursors 3 were cut into 10 cm × 10 cm (100 cm 2 A single-sided positive electrode precursor 3 was used at the top and bottom, with the positive electrode active material layer positioned inward. Twenty-one sheets of double-sided negative electrodes 22 and twenty sheets of double-sided positive electrode precursor 3 were alternately used in between. Microporous membrane separators were sandwiched between adjacent negative and positive electrode precursors along the stacking direction. The negative and positive terminals were ultrasonically welded to the negative and positive electrode precursors, respectively, and then vacuum dried at 80°C, 50 Pa, and 60 hours to produce an electrode laminate.

[0799] The dried electrode stack is placed in an outer casing made of aluminum laminate packaging material in a dry environment with a dew point of -45°C, and the three sides of the outer casing, including the positive and negative electrode terminals and the bottom, are heat-sealed under the conditions of a temperature of 180°C, a sealing time of 20 seconds, and a sealing pressure of 1.0 MPa.

[0800] [Injection, impregnation and sealing]

[0801] In a dry air environment with a temperature of 25°C and a dew point below -40°C, about 80g of non-aqueous electrolyte 1 is injected into an electrode laminate contained in an aluminum laminate packaging material at atmospheric pressure to form a non-aqueous lithium storage element before lithium doping treatment. Next, the non-aqueous lithium storage element is placed in a decompression chamber, decompressed from normal pressure to -87kPa, restored to normal pressure, and allowed to stand for 5 minutes. Repeat the operation of decompressing from normal pressure to -87kPa and then restoring to normal pressure 4 times, and then let it stand at normal pressure for 15 minutes. Further decompress from normal pressure to -91kPa, and then restore to normal pressure. Similarly, the operation of decompressing and restoring to normal pressure is repeated a total of 7 times (at this time, the pressure is reduced from normal pressure to -95, -96, -97, -81, -97, -97, and -97kPa respectively). Through the above steps, the non-aqueous electrolyte 1 is impregnated into the electrode laminate of the non-aqueous lithium storage element.

[0802] The outer body containing the electrode stack impregnated with the non-aqueous electrolyte 3 is placed in a reduced pressure sealing machine, and sealed at 180°C and a pressure of 0.1 MPa for 10 seconds under a reduced pressure of -95 kPa to seal the aluminum laminate packaging material, thereby obtaining a non-aqueous lithium storage element (lithium ion capacitor).

[0803] [Lithium doping]

[0804] The obtained non-aqueous lithium storage element was charged with a constant current of 50 mA at 25°C using a charge and discharge device (TOSCAT-3100U) manufactured by Toyo Systems Corporation until the voltage reached 4.5 V. The element was then charged with a constant voltage of 4.5 V for 72 hours. This method was used for initial charging and lithium doping was performed in the negative electrode.

[0805] [aging]

[0806] The lithium-doped non-aqueous lithium storage element was discharged at a constant current of 1.0 A at 25°C until the voltage reached 3.0 V, and then discharged at a constant voltage of 3.0 V for 1 hour to adjust the voltage to 3.0 V. The non-aqueous lithium storage element was stored in a thermostatic chamber at 60°C for 60 hours for aging.

[0807] [exhaust]

[0808] In a dry air environment at a temperature of 25°C and a dew point of -40°C, the aluminum laminate packaging material of the aged non-aqueous lithium storage element was partially unsealed. Next, the partially unsealed non-aqueous lithium storage element of the aluminum laminate packaging material was placed in a decompression chamber and decompressed from normal pressure to -80 kPa in 3 minutes using a diaphragm pump (N816.3KT.45.18) manufactured by KNF. This operation was repeated a total of 3 times. The non-aqueous lithium storage element was placed in a decompression sealer, decompressed to -90 kPa, and then sealed at a temperature of 200°C and a pressure of 0.1 MPa for 10 seconds to seal the aluminum laminate packaging material (resealed).

[0809] The non-aqueous lithium battery device was evaluated through the above-mentioned procedures.

[0810] [Measurement of Discharge Capacity Q at Vmax = 3.8 V, Vmin = 2.2 V]

[0811] The discharge capacity Q of the storage element was measured using Vmax = 3.8V and Vmin = 2.2V. The resulting non-aqueous lithium storage element was charged at a constant current of 20C to 3.8V using a charge-discharge device (5V, 360A) manufactured by Fujitsu Telecom Networks Co., Ltd. in a thermostatic chamber set at 25°C. This was followed by constant voltage charging at a constant voltage of 3.8V for a total of 30 minutes. The discharge capacity Q was then measured by constant current discharge at a current of 2C to 2.2V.

[0812] In the non-aqueous lithium battery element of Example 14, the discharge capacity Q at Vmax=3.8V and Vmin=2.2V was 952.3 mAh.

[0813] [Calculation of the internal resistance Ra during normal temperature discharge when Vmax = 3.8V and Vmin = 2.2V]

[0814] The initial room-temperature discharge internal resistance Ra of the storage element was measured, assuming Vmax = 3.8 V and Vmin = 2.2 V. The resulting non-aqueous lithium storage element was subjected to initial charge and discharge operations in a thermostatic chamber set at 25°C using a charge and discharge device (5 V, 360 A) manufactured by Fujitsu Telecom Network Works Co., Ltd., according to the following procedure.

[0815] First, constant current charging is performed at a current value of 20C until it reaches 3.8V, followed by constant voltage charging with a constant voltage of 3.8V for a total of 30 minutes. Then, constant current discharge is performed at a current value of 20C until it reaches 2.2V, completing the initial charge and discharge operation. In the discharge curve (time-voltage) obtained during this constant current discharge, the voltage values ​​at the discharge time of 1 second and 2 seconds are extrapolated using a straight line approximation. The voltage at the discharge time = 0 second is obtained as E0, and the normal temperature discharge internal resistance Ra is calculated by reducing the voltage ΔE = 3.8-E0 and R = ΔE / (20C (current value A)).

[0816] The room temperature discharge internal resistance Ra of the non-aqueous lithium storage device of Example 14 after initial charge and discharge was 1.01 mΩ.

[0817] [Calculation of Rb and Rb / Ra after high-temperature storage test]

[0818] The obtained nonaqueous lithium battery device was subjected to the above-mentioned high-temperature storage test.

[0819] For non-aqueous lithium storage elements, in a thermostatic chamber set at 25°C, a charge and discharge device (5V, 360A) manufactured by FUJITSU TELECOMNETWORKS Co., Ltd. was used to perform constant current charging at a current value of 100C until it reached 4.0V, followed by constant voltage charging with a constant voltage of 4.0V applied for a total of 10 minutes. The storage element was then stored in an 85°C environment, taken out from the 85°C environment every week, and the battery cell voltage was charged to 4.0V through the same charging operation. The battery cell was then returned to the 85°C environment for continued storage. This operation was repeated for 500 hours to perform a high-temperature storage test of the non-aqueous storage element. For the storage element after the high-temperature storage test, the normal temperature discharge internal resistance Rb after the high-temperature storage test was calculated in the same manner as above [Calculation of normal temperature discharge internal resistance Ra when Vmax = 3.8V, Vmin = 2.2V]. The ratio Rb / Ra was calculated by dividing Rb (Ω) by the normal temperature discharge internal resistance Ra (Ω) obtained before the high temperature storage test at Vmax = 3.8 V and Vmin = 2.2 V. The ratio Rb / Ra was 4.19.

[0820] [Calculation of Qb and Qb / Qa after high-temperature storage test]

[0821] The obtained nonaqueous lithium battery device was subjected to the above-mentioned high-temperature storage test.

[0822] For non-aqueous lithium storage elements, in a thermostatic chamber set at 25°C, a charge and discharge device (5V, 360A) manufactured by FUJITSU TELECOMNETWORKS Co., Ltd. was used to perform constant current charging at a current value of 100C until it reached 4.0V, followed by constant voltage charging with a constant voltage of 4.0V applied for a total of 10 minutes. The storage element was then stored in an 85°C environment, taken out of the 85°C environment every week, and the battery cell voltage was charged to 4.0V using the same charging operation. The battery cell was then returned to the 85°C environment and continued to be stored. This operation was repeated for 500 hours to perform a high-temperature storage test of the non-aqueous storage element. For the storage element after the high-temperature storage test, the discharge capacity Qb after the high-temperature storage test was calculated in the same manner as above [Calculation of discharge capacity Qa when Vmax = 3.8V, Vmin = 2.2V]. This Qb (mAh) was divided by the discharge capacity Qa (mAh) obtained above at Vmax = 3.8 V and Vmin = 2.2 V before the high-temperature storage test to calculate the ratio Qb / Qa, which was 0.70.

[0823] [Confirmation of SEI (lithium oxalate) formation]

[0824] The resulting non-aqueous lithium storage element was disassembled in an Ar box maintained at a dew point below -90°C and an oxygen concentration below 1 ppm in a room at 23°C, and the negative electrode was removed. The negative electrode was cleaned with a dimethyl carbonate (DMC) solution. The surface of the negative electrode active material layer of the negative electrode was analyzed using X-ray photoelectron spectroscopy (XPS) (Versa Probe II, manufactured by ULVAC-PHI Co., Ltd.) under the following conditions without exposure to the atmosphere.

[0825] Excitation source: monochromated AlKα

[0826] X-ray beam diameter: 100μmΦ (25W, 15kV)

[0827] Pass energy: narrow scan, 46.95eV

[0828] Charge neutralization: Yes

[0829] Number of scans: Narrow scan 10 times

[0830] Energy step: narrow scan, 0.25eV

[0831] The formation of lithium oxalate was confirmed by the presence of a peak (carbon peak) in the range of 289 eV to 290 eV.

[0832] [Confirmation of the presence of Al corrosion]

[0833] The obtained nonaqueous lithium battery device was subjected to the above-mentioned high-temperature storage test.

[0834] For non-aqueous lithium storage elements, in a thermostatic chamber set at 25°C, a charge and discharge device (5V, 360A) manufactured by FUJITSU TELECOMNETWORKS Co., Ltd. was used to perform constant current charging at a current value of 100C until it reached 4.0V, followed by constant voltage charging with a constant voltage of 4.0V applied for a total of 10 minutes. The storage element was then stored in an 85°C environment, taken out of the 85°C environment every week, and the battery cell voltage was charged to 4.0V using the same charging operation. The battery cell was then returned to the 85°C environment and continued to be stored. This operation was repeated for 500 hours to conduct a high-temperature storage test of the non-aqueous storage element. The storage element after the high-temperature storage test was disassembled in an Ar box set in a room at 23°C with a dew point below -90°C and an oxygen concentration below 1ppm, and the surface of the positive electrode collector was visually confirmed. As a result, no blackening characteristic of Al corrosion was observed on the surface of the positive electrode current collector, indicating that no Al corrosion occurred.

[0835] Examples 15 to 47 and Comparative Examples 10 to 18

[0836] Non-aqueous lithium storage devices were produced in the same manner as in Example 14 except that the positive electrode precursor, negative electrode, and non-aqueous electrolyte were as shown in Tables 7 to 9, respectively, and various evaluations were performed.

[0837] The evaluation results of the obtained non-aqueous lithium storage device are shown in Tables 7 to 9.

[0838]

[0839]

[0840]

[0841]

[0842] The above examples demonstrate that the non-aqueous lithium battery element of the present invention exhibits high capacity, excellent initial output characteristics, and excellent high-temperature storage durability. In particular, even after high-temperature storage at 85°C and 4.0V, the discharge capacity residual ratio Qb / Qa remains at least 0.70, and the internal resistance increase ratio Rb / Ra is no more than 5.0, demonstrating excellent high-temperature durability.

[0843] The excellent high-temperature durability of the non-aqueous lithium battery element of this embodiment is believed to be a synergistic effect of the following effects:

[0844] (1) The lithium compound contained in the positive electrode other than the positive electrode active material is converted into a protective film of the positive electrode during charge and discharge;

[0845] (2) The iron element in the positive electrode active material layer functions as a catalyst, improving the ability to form a protective film from lithium compounds other than the positive electrode active material; and

[0846] (3) The non-aqueous electrolyte solution contains three specific lithium salts (A) to (C) at specific ratios.

[0847] It is understood that the non-aqueous lithium battery elements of Examples 46 and 47 have particularly excellent high-temperature durability.

[0848] This is considered a synergistic effect of:

[0849] The carbon nanotubes in the negative electrode prevent the electrode from swelling and maintain the negative electrode structure;

[0850] The non-aqueous electrolyte contains three specific lithium salts (A) to (C) in specific ratios; and

[0851] The non-aqueous electrolyte solution contains a specific trinitrile compound at a specific ratio.

[0852] In the non-aqueous lithium storage device of Comparative Example 12, corrosion was observed in the Al positive electrode current collector after high-temperature storage. This is believed to be due to insufficient formation of aluminum fluoride, which inhibits Al corrosion.

[0853] <Examples 48 to 67 and Comparative Examples 19 to 27>

[0854] <Crushing of lithium carbonate>

[0855] The lithium carbonate is pulverized by causing brittle fracture at a temperature of -196°C while preventing thermal modification.

[0856] 200 g of lithium carbonate with an average particle size of 53 μm was placed in a pulverizer (liquid nitrogen bead mill LNM) manufactured by IMEX, cooled to -196°C with liquid nitrogen, and then pulverized using dry ice beads at a peripheral speed of 10.0 m / s for 9 minutes. The average particle size of the obtained lithium carbonate was 2.26 μm.

[0857] Preparation of positive electrode active material

[0858] [Preparation of activated carbon 4]

[0859] The crushed coconut shell carbide was carbonized in a small carbonization furnace at 500°C for 3 hours under a nitrogen atmosphere to obtain carbide. The obtained carbide was placed in an activation furnace, and 1 kg / h of water vapor heated in a preheating furnace was introduced into the activation furnace. The temperature was raised to 900°C over 8 hours for activation. The activated carbide was taken out and cooled in a nitrogen atmosphere. The obtained activated carbon was washed with water for 10 hours to remove moisture. The activated carbon after washing and dehydration was dried in an electric dryer maintained at 115°C for 10 hours, and then pulverized in a ball mill for 1 hour to obtain activated carbon 4.

[0860] The average particle size of activated carbon 4 was measured using a laser diffraction particle size distribution analyzer (SALD-2000J) manufactured by Shimadzu Corporation, and the result was 4.2 μm. Furthermore, the pore distribution of activated carbon 1 was measured using a pore distribution analyzer (AUTOSORB-1AS-1-MP) manufactured by Yuasa Ionics, and the BET specific surface area was 2,360 m 2 / g, the mesopore volume (V1) is 0.52cc / g, and the micropore volume (V2) is 0.88cc / g, V1 / V2=0.59.

[0861] <Cathode Precursor 4>

[0862] [Preparation of lithium compounds containing iron]

[0863] 100 parts by mass of lithium carbonate as a lithium compound and 2.3 parts by mass of ferric chloride (FeCl3·6H2O) were added to distilled water to prepare an aqueous solution having a concentration of 0.5% by mass of lithium carbonate. The obtained aqueous solution was stirred for 1 hour using a homogenizer while being heated to 60°C in an oil bath. The liquid temperature was then raised to 100°C to evaporate the water and precipitate lithium carbonate powder containing an iron element. The obtained lithium carbonate powder containing an iron element was placed in an alumina container, which was placed in a muffle furnace and heated at 300°C for 10 hours while blowing a nitrogen / hydrogen mixed gas. After dechlorination treatment, the mixture was pulverized using a jet mill to obtain lithium carbonate powder 5 containing an iron element having a specific particle size. The average particle size of the lithium carbonate powder 5 containing an iron element was measured using a laser diffraction particle size distribution measuring device manufactured by Shimadzu Corporation, and the result was 0.8 μm.

[0864] [Manufacturing of Positive Electrode Precursor 4]

[0865] As the positive electrode active material, activated carbon 4 (58.5 parts by mass) obtained in the above-mentioned [Preparation of Activated Carbon 4] was used, and the types and amounts of lithium compounds other than the positive electrode active material and the conductive fillers described in Table 1 were mixed. 1.5 parts by mass of PVP (polyvinyl pyrrolidone), 8.0 parts by mass of PVDF (polyvinylidene fluoride) and NMP (N-methylpyrrolidone) were further mixed in the obtained mixture, and dispersed under the conditions of a circumferential speed of 17 m / s using a thin film gyratory high-speed mixer "FILMIX (registered trademark)" manufactured by PRIMIX to obtain a coating liquid. The above-mentioned coating liquid was applied to one or both sides of an aluminum foil having a thickness of 15 μm and no through-holes as a positive electrode collector at a coating speed of 1 m / s using a die coater manufactured by Toray Engineering Co., Ltd., and dried at a drying temperature of 100°C to obtain a positive electrode precursor. The obtained positive electrode precursor was pressed using a roll press under the conditions of a pressure of 4 kN / cm and a surface temperature of a pressing portion of 25°C.

[0866] Hereinafter, a positive electrode precursor coated only on one side of a positive electrode current collector may be referred to as a “single-sided positive electrode precursor,” and a positive electrode precursor coated on both sides of a positive electrode current collector may be referred to as a “double-sided positive electrode precursor.”

[0867] [Manufacturing of Positive Electrode Precursors 5 to 10]

[0868] Positive electrode precursors 5 to 10 were prepared by the same method as that for positive electrode precursor 4, except that the types and amounts of the lithium compound and the conductive filler other than the positive electrode active material were as described in Table 10, respectively.

[0869] [Table 14]

[0870] Table 10.

[0871]

[0872] The abbreviations of the components in Table 10 have the following meanings.

[0873] [Lithium compounds other than positive electrode active materials]

[0874] Fe-carbonate Li5: Iron-containing lithium carbonate powder 5 with an average particle size of 0.8 μm obtained in the above <Preparation of iron-containing lithium compound>

[0875] Lithium hydroxide: lithium hydroxide with an average particle size of 2.4 μm

[0876] [Conductive filler]

[0877] KB: Ketjen Black

[0878] <Manufacturing of Composite Carbon Material 1>

[0879] The average particle size of the substrate was 9.7 μm and the BET specific surface area was 1.2 m 2 200g of artificial graphite (10000 t / g) was placed in a stainless steel mesh basket and placed on a stainless steel plate containing 60g of coal-based pitch (softening point: 65°C), a carbonaceous material precursor. Both were placed in an electric furnace (effective furnace dimensions: 300mm × 300mm × 300mm). Under a nitrogen atmosphere, the temperature was raised to 1,110°C over 8 hours and maintained at this temperature for 4 hours to allow a thermal reaction to occur, yielding Composite Carbon Material 1. The resulting Composite Carbon Material 1 was cooled to 60°C by natural cooling and then removed from the furnace.

[0880] The obtained composite carbon material 1 was subjected to Raman spectroscopic analysis by micro-Raman spectroscopy using a laser beam with a wavelength of 532 nm according to the above method. -1 The intensity of the peak Pg near Ig is similar to that at 1,360 cm -1 The ratio Id / Ig of the intensity Id of the nearby peak Pd is 0.59.

[0881] (Manufacturing of Composite Carbon Materials 2 to 8)

[0882] Composite carbon materials 2 to 8 were produced in the same manner as in the above-mentioned <Production of Composite Carbon Material 1> except that the types and amounts of the substrate and carbonaceous material precursor, and the heating temperature were as described in Table 11, respectively.

[0883] The results of the same Raman spectroscopic analysis as above are also shown in Table 11.

[0884] [Table 15]

[0885] Table 11.

[0886]

[0887] <Manufacturing of Negative Electrode 24>

[0888] The above-obtained composite carbon material 1:84.0 mass %, acetylene black 10.0 mass %, carboxymethyl cellulose 3.0 mass % and styrene butadiene rubber 3.0 mass % as the negative electrode active material, and distilled water with a solid content of 36.5% were mixed, and the mixture was dispersed at a rotation speed of 2,000 rpm for 10 minutes using an autorotating and orbiting mixer "Awatori Rentaro (registered trademark)" manufactured by Thinky Company to obtain a negative electrode coating liquid.

[0889] The viscosity (ηb) and TI value of the obtained negative electrode coating liquid were measured using a TVE-35H E-type viscometer manufactured by Toki Sangyo Co., Ltd. The viscosity (ηb) was 1,840 mPa·s and the TI value was 3.1.

[0890] The negative electrode coating liquid was applied to both sides of an 8μm thick electrolytic copper foil, which served as the negative electrode current collector, using a doctor blade. The negative electrode was dried for 10 minutes on a hot plate heated to 50°C to obtain a negative electrode. A roller press was used to press the negative electrode 24 under the conditions of a pressure of 5kN / cm and a surface temperature of 25°C at the pressing part. The total thickness of the negative electrode 24 obtained was measured at 10 randomly set points on the negative electrode surface using a Linear Gauge Sensor GS-551 manufactured by Ono Keiki Co., Ltd. The thickness of the negative electrode current collector was subtracted from the average value, and the resultant value was multiplied by 1 / 2. The resulting value was used as the thickness of the negative electrode active material layer per single side. According to the obtained measurement results, the thickness of the negative electrode active material layer of the negative electrode 24 was 30μm per single side.

[0891] (Manufacturing of Negative Electrodes 25 to 31)

[0892] Negative electrodes 25 to 31 were produced in the same manner as in the above-mentioned <Production of Negative Electrode 24> except that the composite carbon materials listed in Table 12 were used as negative electrode active materials.

[0893] [Table 16]

[0894] Table 12.

[0895]

[0896] <Preparation of Non-aqueous Electrolyte 35-50>

[0897] A mixed solvent of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) = 33:67 (volume ratio) was used as an organic solvent, and electrolyte salts of the types and concentrations listed in Table 13 were dissolved in the organic solvent to obtain non-aqueous electrolyte solutions 35 to 50, respectively.

[0898]

[0899] The abbreviations of the components in Table 13 have the following meanings.

[0900] [(A) component] at least one lithium salt selected from LiPF6 and LiBF4

[0901] LiBF4: lithium tetrafluoroborate

[0902] LiPF6: lithium hexafluorophosphate

[0903] [Component (B)] Lithium salt having an imide structure

[0904] LiN(SO2F)2:Lithium bis(fluorosulfonyl)imide

[0905] LiN(CF3SO2)2: Lithium bis(trifluoromethanesulfonyl)imide

[0906] LiN(CF3CF2SO2)2: Lithium bis(pentafluoroethanesulfonyl)imide

[0907] [Component (C)] Lithium salt with oxalic acid complex as anion

[0908] LiBOB: lithium bis(oxalatoborate) salt

[0909] LiFOB: lithium fluorooxalatoborate

[0910] LiDFOB: lithium difluorooxalatoborate

[0911] "-" in Table 13 indicates that the component in that column was not used.

[0912] Example 48

[0913] <Manufacturing of non-aqueous lithium battery cells>

[0914] [Assembly]

[0915] In Example 48, a two-layer separator was used in which a 5 μm-thick coating layer containing boehmite (AlOOH) fine particles was formed on one surface of a 15 μm-thick polyethylene (PE) microporous membrane.

[0916] 21 pieces of double-sided negative electrodes, 20 pieces of double-sided positive electrode precursors 1 and 2 pieces of single-sided positive electrode precursors 1 were cut into 10 cm × 10 cm (100 cm 2 A single-sided positive electrode precursor 1 was used at the top and bottom, with the positive electrode active material layer positioned inward. Twenty-one sheets of double-sided negative electrodes and twenty sheets of double-sided positive electrode precursor 1 were alternately used in between. Microporous membrane separators were sandwiched between adjacent negative and positive electrode precursors along the stacking direction. The negative and positive terminals were ultrasonically welded to the negative and positive electrode precursors, respectively. The electrodes were then vacuum-dried at 80°C, 50 Pa, and 60 hours of drying time to produce an electrode laminate.

[0917] The dried electrode stack is placed in an outer casing made of aluminum laminate packaging material in a dry environment with a dew point of -45°C, and the three sides of the outer casing, including the positive and negative electrode terminals and the bottom, are heat-sealed under the conditions of a temperature of 180°C, a sealing time of 20 seconds, and a sealing pressure of 1.0 MPa.

[0918] [Injection, impregnation and sealing]

[0919] In a dry air environment with a temperature of 25°C and a dew point below -40°C, about 80g of non-aqueous electrolyte 1 is injected into an electrode laminate contained in an aluminum laminate packaging material at atmospheric pressure to form a non-aqueous lithium storage element before lithium doping treatment. Next, the non-aqueous lithium storage element is placed in a decompression chamber, decompressed from normal pressure to -87kPa, restored to normal pressure, and allowed to stand for 5 minutes. Repeat the operation of decompressing from normal pressure to -87kPa and then restoring to normal pressure 4 times, and then let it stand at normal pressure for 15 minutes. Further decompress from normal pressure to -91kPa, and then restore to normal pressure. Similarly, the operation of decompressing and restoring to normal pressure is repeated a total of 7 times (at this time, the pressure is reduced from normal pressure to -95, -96, -97, -81, -97, -97, and -97kPa respectively). Through the above steps, the non-aqueous electrolyte 35 is impregnated into the electrode laminate of the non-aqueous lithium storage element.

[0920] The outer body containing the electrode stack impregnated with the non-aqueous electrolyte 35 is placed in a reduced pressure sealing machine, and sealed at 180°C and a pressure of 0.1 MPa for 10 seconds under a reduced pressure of -95 kPa to seal the aluminum laminate packaging material, thereby obtaining a non-aqueous lithium storage element (lithium ion capacitor).

[0921] [Lithium doping]

[0922] The obtained non-aqueous lithium storage element was charged with a constant current of 50 mA at 25°C using a charge and discharge device (TOSCAT-3100U) manufactured by Toyo Systems Corporation until the voltage reached 4.5 V. The element was then charged with a constant voltage of 4.5 V for 72 hours. This method was used for initial charging and lithium doping was performed in the negative electrode.

[0923] [aging]

[0924] The lithium-doped non-aqueous lithium storage element was discharged at a constant current of 1.0 A at 25°C until the voltage reached 3.0 V, and then discharged at a constant voltage of 3.0 V for 1 hour to adjust the voltage to 3.0 V. The non-aqueous lithium storage element was stored in a thermostatic chamber at 60°C for 60 hours for aging.

[0925] [exhaust]

[0926] In a dry air environment at a temperature of 25°C and a dew point of -40°C, the aluminum laminate packaging material of the aged non-aqueous lithium storage element was partially unsealed. Next, the partially unsealed non-aqueous lithium storage element of the aluminum laminate packaging material was placed in a decompression chamber and decompressed from normal pressure to -80 kPa in 3 minutes using a diaphragm pump (N816.3KT.45.18) manufactured by KNF. This operation was repeated a total of 3 times. The non-aqueous lithium storage element was placed in a decompression sealer, decompressed to -90 kPa, and then sealed at a temperature of 200°C and a pressure of 0.1 MPa for 10 seconds to seal the aluminum laminate packaging material (resealed).

[0927] The non-aqueous lithium battery device was evaluated through the above-mentioned procedures.

[0928] [Measurement of Discharge Capacity Q at Vmax = 3.8 V, Vmin = 2.2 V]

[0929] The discharge capacity Q of the storage element was measured using Vmax = 3.8V and Vmin = 2.2V. The resulting non-aqueous lithium storage element was charged at a constant current of 20C to 3.8V using a charge-discharge device (5V, 360A) manufactured by Fujitsu Telecom Networks Co., Ltd. in a thermostatic chamber set at 25°C. This was followed by constant voltage charging at a constant voltage of 3.8V for a total of 30 minutes. The discharge capacity Q was then measured by constant current discharge at a current of 2C to 2.2V.

[0930] In the non-aqueous lithium battery element of Example 1, the discharge capacity Q at Vmax=3.8V and Vmin=2.2V was 917 mAh.

[0931] [Calculation of the internal resistance Ra during normal temperature discharge when Vmax = 3.8V and Vmin = 2.2V]

[0932] The initial room-temperature discharge internal resistance Ra of the storage element was measured, assuming Vmax = 3.8 V and Vmin = 2.2 V. The resulting non-aqueous lithium storage element was subjected to initial charge and discharge operations in a thermostatic chamber set at 25°C using a charge and discharge device (5 V, 360 A) manufactured by Fujitsu Telecom Network Works Co., Ltd., according to the following procedure.

[0933] First, constant current charging was performed at a current value of 20C until it reached 3.8V, followed by constant voltage charging with a constant voltage of 3.8V applied for a total of 30 minutes. Then, constant current discharge was performed at a current value of 20C until it reached 2.2V, completing the initial charge and discharge operation. In the discharge curve (time-voltage) obtained during this constant current discharge, the voltage values ​​at the discharge time of 1 second and 2 seconds were extrapolated using a straight line approximation. The voltage at the discharge time of 0 seconds was taken as E0, and the normal temperature discharge internal resistance Ra was calculated by reducing the voltage ΔE = 3.8-E0 and R = ΔE / (20C (current value A)).

[0934] The room temperature discharge internal resistance Ra of the non-aqueous lithium storage device of Example 1 after initial charge and discharge was 1.97 mΩ.

[0935] [Calculation of Rb and Rb / Ra after high-temperature storage test]

[0936] The obtained nonaqueous lithium battery device was subjected to the above-mentioned high-temperature storage test.

[0937] For non-aqueous lithium storage elements, in a thermostatic chamber set at 25°C, a charge and discharge device (5V, 360A) manufactured by FUJITSU TELECOMNETWORKS Co., Ltd. was used to perform constant current charging at a current value of 100C until it reached 4.0V, followed by constant voltage charging with a constant voltage of 4.0V for a total of 10 minutes. The storage element was then stored in an 85°C environment, taken out of the 85°C environment every week, and the battery cell voltage was charged to 4.0V using the same charging operation. The battery cell was then returned to the 85°C environment and continued to be stored. This operation was repeated for 500 hours to perform a high-temperature storage test of the non-aqueous storage element. For the storage element after the high-temperature storage test, the normal temperature discharge internal resistance Rb after the high-temperature storage test was calculated in the same manner as above [Calculation of normal temperature discharge internal resistance Ra when Vmax = 3.8V, Vmin = 2.2V]. The ratio Rb / Ra was calculated by dividing Rb (Ω) by the normal temperature discharge internal resistance Ra (Ω) obtained before the high temperature storage test at Vmax = 3.8 V and Vmin = 2.2 V. The ratio Rb / Ra was 1.65.

[0938] [Calculation of Qb and Qb / Qa after high-temperature storage test]

[0939] The obtained nonaqueous lithium storage device was subjected to the above-mentioned high-temperature storage test.

[0940] For non-aqueous lithium storage elements, in a thermostatic chamber set at 25°C, a charge and discharge device (5V, 360A) manufactured by FUJITSU TELECOMNETWORKS Co., Ltd. was used to perform constant current charging at a current value of 100C until it reached 4.0V, followed by constant voltage charging with a constant voltage of 4.0V applied for a total of 10 minutes. The storage element was then stored in an 85°C environment, taken out of the 85°C environment every week, and the battery cell voltage was charged to 4.0V using the same charging operation. The battery cell was then returned to the 85°C environment and continued to be stored. This operation was repeated for 500 hours to perform a high-temperature storage test of the non-aqueous storage element. For the storage element after the high-temperature storage test, the discharge capacity Qb after the high-temperature storage test was calculated in the same manner as above [Calculation of discharge capacity Qa when Vmax = 3.8V, Vmin = 2.2V]. This Qb (mAh) was divided by the discharge capacity Qa (mAh) obtained above at Vmax = 3.8 V and Vmin = 2.2 V before the high-temperature storage test to calculate the ratio Qb / Qa, which was 0.83.

[0941] [Confirmation of SEI (lithium oxalate) formation]

[0942] The resulting non-aqueous lithium storage element was disassembled in an Ar box maintained at a dew point below -90°C and an oxygen concentration below 1 ppm in a room at 23°C, and the negative electrode was removed. The negative electrode was cleaned with a dimethyl carbonate (DMC) solution. The surface of the negative electrode active material layer of the negative electrode was analyzed using X-ray photoelectron spectroscopy (XPS) (Versa Probe II, manufactured by ULVAC-PHI Co., Ltd.) under the following conditions without exposure to the atmosphere.

[0943] Excitation source: monochromated AlKα

[0944] X-ray beam diameter: 100μmΦ (25W, 15kV)

[0945] Pass energy: narrow scan, 46.95eV

[0946] Charge neutralization: Yes

[0947] Number of scans: Narrow scan 10 times

[0948] Energy step: narrow scan, 0.25eV

[0949] The formation of lithium oxalate was confirmed by the presence of a peak P1 (carbon peak) in the range of 289 eV to 290 eV.

[0950] [Confirmation of SEI (lithium oxalate) formation amount]

[0951] In XPS of the negative electrode active material layer, the ratio I1 / I2 of the intensity I1 of the peak P1 observed in the range of 289 eV to 290 eV to the intensity I2 of the peak P2 observed in the range of 284 eV to 285 eV was 0.17.

[0952] [Confirmation of the presence of Al corrosion]

[0953] The obtained nonaqueous lithium battery device was subjected to the above-mentioned high-temperature storage test.

[0954] For non-aqueous lithium storage elements, in a thermostatic chamber set at 25°C, a charge and discharge device (5V, 360A) manufactured by FUJITSU TELECOMNETWORKS Co., Ltd. was used to perform constant current charging at a current value of 100C until it reached 4.0V, followed by constant voltage charging with a constant voltage of 4.0V applied for a total of 10 minutes. The storage element was then stored in an 85°C environment, taken out of the 85°C environment every week, and the battery cell voltage was charged to 4.0V using the same charging operation. The battery cell was then returned to the 85°C environment and continued to be stored. This operation was repeated for 500 hours to conduct a high-temperature storage test of the non-aqueous storage element. The storage element after the high-temperature storage test was disassembled in an Ar box set in a room at 23°C with a dew point below -90°C and an oxygen concentration below 1ppm, and the surface of the positive electrode collector was visually confirmed. As a result, no blackening characteristic of Al corrosion was observed on the surface of the positive electrode current collector, indicating that no Al corrosion occurred.

[0955] Examples 49 to 67 and Comparative Examples 19 to 27

[0956] Non-aqueous lithium storage devices were produced in the same manner as in Example 48 except that the types of the positive electrode precursor, negative electrode, and non-aqueous electrolyte used were as shown in Tables 14 to 17, respectively, and various evaluations were performed.

[0957] The evaluation results of the obtained non-aqueous lithium storage device are shown in Tables 14 to 17.

[0958]

[0959]

[0960]

[0961]

[0962] The above examples demonstrate that the non-aqueous lithium battery element of the present invention exhibits high capacity, excellent initial output characteristics, and excellent high-temperature storage durability. In particular, even after high-temperature storage at 85°C and 4.0V, the discharge capacity residual ratio Qb / Qa remains at least 0.70, demonstrating excellent high-temperature durability.

[0963] <Examples 68 to 84 and Comparative Examples 28 to 42>

[0964] <Preparation of Positive Electrode Active Material>

[0965] The crushed coconut shell carbide was placed in a small carbonization furnace and carbonized at 500°C for 3 hours under a nitrogen atmosphere to obtain carbide. The obtained carbide was placed in an activation furnace, and steam heated in a preheating furnace was introduced into the activation furnace at a rate of 1 kg / h. The temperature was raised to 900°C over 8 hours for activation. The activated carbide was removed and cooled under a nitrogen atmosphere to obtain activated activated carbon. The obtained activated activated carbon was washed with water for 10 hours to remove moisture, dried in an electric dryer maintained at 115°C for 10 hours, and then pulverized in a ball mill for 1 hour to obtain activated carbon 5.

[0966] The average particle size of activated carbon 5 was measured using a laser diffraction particle size distribution analyzer (SALD-2000J) manufactured by Shimadzu Corporation and was found to be 5.5 μm. Furthermore, the pore distribution of activated carbon 1 was measured using a pore distribution analyzer (AUTOSORB-1AS-1-MP) manufactured by Yuasa Ionics. The BET specific surface area was 2,360 m 2 / g, the mesopore volume (V1) is 0.52cc / g, the micropore volume (V2) is 0.88cc / g, and V1 / V2=0.59.

[0967] <Preparation of Carbon Nanotube Dispersion>

[0968] 8.0 parts by mass of commercially available multi-walled carbon nanotubes (CNTs) (average fiber diameter 40 nm, average fiber length 50 μm), 1.0 parts by mass of carboxymethyl cellulose (CMC) as dispersant 1, 91.0 parts by mass of distilled water, and 10 ppm of Fe2O3 relative to the total mass of CNTs and CMC were mixed and dispersed at a speed of 100 rpm for 120 minutes using a planetary ball mill to prepare a carbon nanotube dispersion (CNT dispersion).

[0969] <Production Example 10 of Positive Electrode Precursor>

[0970] Activated carbon 5 (53.0 parts by mass) as a positive electrode active material, 100 parts by mass of the above-mentioned carbon nanotube dispersion (equivalent to 8.0 parts by mass of carbon nanotubes and 1.0 parts by mass of carboxymethyl cellulose), 30.0 parts by mass of lithium carbonate as an alkali metal compound, 3.0 parts by mass of acetylene black (AB) as a conductive filler, 1.5 parts by mass of PVP (polyvinyl pyrrolidone) as a dispersant 2, 3.5 parts by mass of acrylic latex (LTX) as a binder, and distilled water with a solid content of 26.5% were mixed, and the mixture was dispersed at a rotation speed of 2,000 rpm for 10 minutes using an autorotating and revolving mixer "Awatori Rentaro (registered trademark)" manufactured by Thinky Co., Ltd. to obtain a positive electrode coating liquid.

[0971] The viscosity (ηb) and TI value of the resulting positive electrode coating solution were measured using a TVE-35H E-type viscometer from Toki Sangyo Co., Ltd. The viscosity (ηb) was 1,650 mPa·s and the TI value was 4.5. The dispersion of the resulting positive electrode coating solution was also measured using a particle size analyzer manufactured by Yoshimitsu Seiki Co., Ltd. The particle size was 20 μm.

[0972] The positive electrode coating liquid was applied to one side of a 15 μm thick aluminum foil using a doctor blade, dried on a hot plate heated to 50° C. for 10 minutes, and then pressed using a roll press at a pressure of 6 kN / cm and a surface temperature of 25° C. to produce a positive electrode precursor 10 .

[0973] The total thickness of the obtained positive electrode precursor 10 was measured at 10 random locations using a Linear Gauge Sensor GS-551 manufactured by Ono Keiki Co., Ltd. The thickness of the positive electrode active material layer was calculated by subtracting the thickness of the aluminum foil from the average value. The thickness of the positive electrode active material layer of the positive electrode precursor 10 was 60 μm.

[0974] <Production Examples 11 to 30, 32, 34, and 36 of Positive Electrode Precursors>

[0975] A carbon nanotube dispersion (CNT dispersion) was prepared in the same manner as in <Production Example 10 of Positive Electrode Precursor> except that the types and amounts of the components used were as shown in Table 18.

[0976] These CNT dispersions were used to produce positive electrode precursors 11 to 30, 32, 34, and 36 in the same manner as in <Production Example 5 of Positive Electrode Precursor> except that the types and amounts of the components were as described in Table 19.

[0977] <Production Example 31 of Positive Electrode Precursor>

[0978] Activated carbon 5 (53.0 parts by mass) as a positive electrode active material, 8.0 parts by mass of commercially available multiwalled carbon nanotubes (average fiber diameter 40 nm, average fiber length 50 μm), 1.5 parts by mass of carboxymethyl cellulose (CMC) as a dispersant 1, 30.0 parts by mass of lithium carbonate as an alkali metal compound, 3.0 parts by mass of acetylene black (AB) as a conductive filler, 4.5 parts by mass of acrylic latex (LTX) as a binder, 20 ppm of Fe2O3 relative to the total mass of these components, and distilled water with a solid content ratio of 26.5% were mixed, and the mixture was dispersed using an autorotating and orbiting mixer "Awatori Rentaro (registered trademark)" manufactured by Thinky at a rotation speed of 2,000 rpm for 10 minutes to obtain a positive electrode coating liquid.

[0979] The viscosity (ηb) and TI value of the resulting positive electrode coating solution were measured using a TVE-35H E-type viscometer from Toki Sangyo Co., Ltd. The viscosity (ηb) was 780 mPa·s and the TI value was 7.5. Furthermore, the dispersion of the resulting positive electrode coating solution was measured using a particle size analyzer manufactured by Yoshimitsu Seiki Co., Ltd. The particle size was 35 μm.

[0980] The positive electrode coating liquid was applied to one side of a 15 μm thick aluminum foil using a doctor blade, dried on a hot plate heated to 50° C. for 10 minutes, and then pressed using a roll press at a pressure of 6 kN / cm and a surface temperature of 25° C. to produce a positive electrode precursor 31 .

[0981] The total thickness of the obtained positive electrode precursor 31 was measured at 10 random locations using a Linear Gauge Sensor GS-551 manufactured by Ono Keiki Co., Ltd. The thickness of the positive electrode active material layer was calculated by subtracting the thickness of the aluminum foil from the average value. The thickness of the positive electrode active material layer of the positive electrode precursor 31 was 61 μm.

[0982] <Production Examples 33, 35, and 37 of Positive Electrode Precursors>

[0983] Positive electrode precursors 33, 35, and 37 were produced in the same manner as in <Production Example 31 of Positive Electrode Precursor> except that the types and amounts of the components were as described in Table 19.

[0984] [Table 22]

[0985] Table 18.

[0986]

[0987] (Table 18. Continuation)

[0988] [Table 23]

[0989] Table 18. (Continued)

[0990]

[0991] (Table 18. End)

[0992]

[0993]

[0994] <Manufacturing Example 32 of Negative Electrode>

[0995] 84.0 parts by mass of artificial graphite having an average particle size of 4.5 μm, 10.0 parts by mass of acetylene black (AB), 3.0 parts by mass of carboxymethyl cellulose (CMC), 3.0 parts by mass of styrene butadiene rubber (SBR), and distilled water were mixed to obtain a mixture having a solid content of 36.5% by mass.

[0996] The obtained mixture was dispersed using an autorotating and orbiting mixer "Awatori Rentaro (registered trademark)" manufactured by Thinky Co., Ltd. at a rotation speed of 2,000 rpm for 10 minutes to obtain a negative electrode coating liquid.

[0997] The viscosity (ηb) and TI value of the obtained negative electrode coating liquid were measured using a TVE-35H E-type viscometer manufactured by Toki Sangyo Co., Ltd. The viscosity (ηb) was 1,840 mPa·s and the TI value was 3.1.

[0998] The negative electrode coating liquid was applied to one side of an 8 μm thick electrolytic copper foil using a doctor blade and dried for 10 minutes on a hot plate heated to 50°C. The foil was then pressed using a roller press at a pressure of 5 kN / cm and a surface temperature of 25°C to produce the negative electrode 32.

[0999] The total thickness of negative electrode 1 was measured at 10 random locations using a thickness meter "Linear Gauge Sensor GS-551" manufactured by Ono Keiki Co., Ltd. The thickness of the negative electrode active material layer was calculated by subtracting the thickness of the electrolytic copper foil from the average value. The thickness of the negative electrode active material layer of negative electrode 32 was 30 μm.

[1000] <Manufacturing Example 33 of Negative Electrode>

[1001] 96.0 parts by mass of artificial graphite having an average particle size of 4.5 μm, 100 parts by mass of the above-mentioned carbon nanotube dispersion (equivalent to 8.0 parts by mass of carbon nanotubes and 1.0 parts by mass of carboxymethyl cellulose), 3.0 parts by mass of acetylene black (AB) and further 2.0 parts by mass of carboxymethyl cellulose, and distilled water are mixed to obtain a mixture having a solid content ratio of 36.5% by mass.

[1002] The obtained mixture was dispersed using an autorotating and orbiting mixer "Awatori Rentaro (registered trademark)" manufactured by Thinky Co., Ltd. at a rotation speed of 2,000 rpm for 10 minutes to obtain a negative electrode coating liquid.

[1003] A negative electrode 33 was produced in the same manner as in Production Example 32 of the negative electrode, except that the obtained negative electrode coating solution was used.

[1004] <Preparation Example 51 of Electrolyte Solution>

[1005] A mixed solvent of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) = 33:67 (volume ratio) was used as an organic solvent, and the electrolyte salt was dissolved in such a manner that the concentration ratio of LiPF6 to LiFSI was 1:1 and the total concentration was 1.2 mol / L, thereby obtaining a non-aqueous electrolyte solution 51.

[1006] <Preparation Example 52 of Electrolyte Solution>

[1007] A mixed solvent of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) = 33:67 (volume ratio) was used as an organic solvent, and electrolyte salts were dissolved in such a manner that the concentration ratio of LiPF6, LiFSI and LiBOB was 5:6:1 and the total concentration was 1.2 mol / L, thereby obtaining a non-aqueous electrolyte solution 52.

[1008] Example 68

[1009] <Manufacturing of Non-aqueous Lithium Storage Devices>

[1010] The obtained positive electrode precursor 10 is cut into a piece according to the size of the positive electrode active material layer of 4.4cm×9.4cm. Then, the negative electrode 32 is cut into a piece according to the size of the negative electrode active material layer of 4.5cm×9.5cm. In addition, a 4.7cm×9.8cm polyethylene separator (manufactured by Asahi Chemical, with a thickness of 15μm) is prepared. Using these components, the positive electrode active material layer and the negative electrode active material layer are stacked opposite each other with the separator sandwiched therebetween in the order of the positive electrode precursor 10, the separator and the negative electrode 32 to obtain an electrode laminate. The positive terminal and the negative terminal are ultrasonically welded to the obtained electrode body, which is placed in an outer body formed of an aluminum laminate packaging material, and the three sides containing the electrode terminal portion are sealed by heat sealing.

[1011] Under atmospheric pressure, in a dry air environment with a temperature of 25°C and a dew point below -40°C, approximately 2.5g of non-aqueous electrolyte 51 was injected into the outer casing containing the electrode stack. Next, the outer casing containing the electrode stack and the non-aqueous electrolyte was placed in a decompression chamber, depressurized from atmospheric pressure to -87kPa, then returned to atmospheric pressure and allowed to stand for 5 minutes. This process was then repeated four times, with the outer casing in the chamber depressurized from atmospheric pressure to -87kPa and then returned to atmospheric pressure. The chamber was then allowed to stand at atmospheric pressure for 15 minutes. Through the above process, the non-aqueous electrolyte 51 was impregnated into the electrode stack.

[1012] Thereafter, the electrode laminate impregnated with the nonaqueous electrolyte 51 was placed in a vacuum sealer and sealed at a pressure of 0.1 MPa at 180° C. for 10 seconds under a reduced pressure of −95 kPa to seal the outer package.

[1013] [Alkali Metal Doping Process]

[1014] The sealed electrode laminate was charged at a temperature of 40°C and a current of 50 mA until the voltage reached 4.5 V, and then charged at a constant voltage of 4.5 V for 2 hours. This method was used for initial charging and alkali metal doping was performed on the negative electrode.

[1015] [Aging process]

[1016] The alkali metal-doped electrode laminate was removed from the drying oven and discharged at a constant current of 50 mA at 25°C until the voltage reached 4.0 V. The voltage was then adjusted to 4.0 V by performing constant current discharge at 4.0 V for 1 hour. The electrode assembly was then stored in a thermostatic chamber at 60°C for 12 hours.

[1017] [Exhaust process]

[1018] After aging, the outer casing was partially opened in a dry air environment at 25°C and a dew point of -40°C, and the electrode stack was removed. The removed electrode stack was placed in a decompression chamber and depressurized from atmospheric pressure to -80 kPa over 3 minutes using a diaphragm pump. This process was then repeated a total of three times, followed by a 3-minute return to atmospheric pressure. The electrode stack was then placed back into the outer casing, depressurized to -90 kPa using a vacuum sealer, and then sealed at 0.1 MPa for 10 seconds at 200°C to produce a non-aqueous lithium battery cell.

[1019] A plurality of non-aqueous lithium storage devices having the same structure are manufactured through the above steps.

[1020] <Evaluation of Non-aqueous Lithium Storage Devices>

[1021] [Measurement of capacitance Qa and internal resistance Ra]

[1022] The capacitance Qa and internal resistance Ra of one of the resulting non-aqueous lithium storage elements were measured using a charge-discharge device (5 V, 10 A) manufactured by Asuka Electronics Co., Ltd. in a thermostatic chamber set at 25°C using the above method. The results showed that Qa was 8.75 mAh and Ra was 86.5 mΩ. These values ​​are shown in Table 20 as the initial capacitance Qa and initial internal resistance Ra.

[1023] [High voltage and high temperature storage test]

[1024] Another of the resulting non-aqueous lithium storage elements was subjected to a high-voltage, high-temperature storage test using the aforementioned method. After the test, the capacitance Qb and internal resistance Rb were measured; Qb was 8.04 mAh and Rb was 98.2 mΩ. These values ​​are shown in Table 20 as capacitance Qb and internal resistance Rb after high-voltage, high-temperature storage.

[1025] In addition, the change rates of electrostatic capacitance and internal resistance before and after the high-voltage, high-temperature storage test were calculated as indicators of high-voltage, high-temperature storage resistance. The results showed that the electrostatic capacitance change rate Qb / Qa was 0.92 and the resistance change rate Rb / Ra was 1.14, both of which were good.

[1026] <Analysis of Positive Electrode Precursor and Positive Electrode>

[1027] The positive electrode precursor and the positive electrode active material layer of each positive electrode were subjected to SEM analysis and XRD measurement, and the positive electrode active material layer of the positive electrode was further subjected to ICP-MS analysis.

[1028] The positive electrode precursor was taken out from the nonaqueous lithium battery element immediately after the assembly. The positive electrode was taken out from the assembled nonaqueous lithium battery element after adjusting the voltage to 3.5 V.

[1029] [SEM image capture]

[1030] For the non-aqueous lithium storage element having the above-mentioned positive electrode precursor or positive electrode, a portion of the outer body is unsealed in an argon box, the electrode laminate is taken out, and the positive electrode precursor or positive electrode is collected. The positive electrode precursor or positive electrode is made into a cut piece of 1 cm square size. The cut piece is washed twice with ethyl methyl carbonate, air-dried, and then moved out of the argon box. Then, the cut piece is immersed in distilled water at 25°C for 24 hours, and then dried under reduced pressure at 80°C and -97kPa for 12 hours.

[1031] Gold was sputtered onto the positive electrode active material layer of the dried cut sheet in a vacuum of 10 Pa, thereby coating the surface with a gold film several nanometers thick. SEM images of the positive electrode active material layer surface were then taken under the following conditions while exposed to the atmosphere.

[1032] (SEM measurement conditions)

[1033] Measurement device: Field emission scanning electron microscope S-4700 manufactured by Hitachi High-Technologies Corporation

[1034] Accelerating voltage: 1kV

[1035] Emission current: 10μA

[1036] ·Measurement magnification: 10000 times

[1037] Detector: Secondary electron detector

[1038] Electron beam incident angle: 90°

[1039] During the imaging, the brightness and contrast were adjusted so that there were no pixels with the maximum brightness value in the SEM image and the average brightness value fell within the range of 40% to 60% of the maximum brightness value.

[1040] Using an SEM image of the positive electrode active material layer of the positive electrode precursor, the area ratio Z'1 of the largest inscribed circle having a diameter less than 100 nm in the bright field region was determined by the above method. The result was 5.9%.

[1041] Furthermore, the area ratio Z'2 in the bright field region was determined by the above-mentioned method using an SEM image of the positive electrode active material layer of the positive electrode. The result was that Z'2 was 7.7%.

[1042] [XRD (X-ray diffraction) measurement]

[1043] The positive electrode precursor or positive electrode taken out from the non-aqueous lithium storage element was cut into 1 cm pieces in the same manner as above. 2 The size of the sample was 1 cm × 1 cm and used as the sample for XRD.

[1044] XRD was performed on the obtained XRD sample under the following conditions.

[1045] Equipment used: Rigaku Ultima IV

[1046] Detector: D / teXUltra

[1047] Tube: CuKα

[1048] Tube voltage: 40kV

[1049] Tube current: 40mA

[1050] Sampling interval: 0.01° / point

[1051] Scanning speed: 5° / min

[1052] Measuring angle range: 5 to 90°

[1053] Divergence slit (DS): 1°

[1054] Divergence limit: 10mm

[1055] Anti-scatter slit (SS): open

[1056] Receiving slit (RS): Open

[1057] In the XRD spectrum obtained for the positive electrode active material layer of the positive electrode precursor, the half-value width of the peak X1 having a peak top in the range of 2θ of 25.7° to 27.0° was examined and found to be 0.15°.

[1058] In the XRD spectrum obtained for the positive electrode active material layer of the positive electrode, the half-value width of the peak X2 having a peak top in the range of 2θ of 25.7° to 27.0° was examined and found to be 0.14°.

[1059] [ICP-MS analysis]

[1060] The positive electrode active material layer of the positive electrode taken out from the nonaqueous lithium storage element in the same manner as above was subjected to ICP-MS analysis to quantify the content of the alkali metal compound.

[1061] A portion of the positive electrode active material layer was scraped off with a spatula, accurately weighed, and then acid-decomposed with aqua regia. The resulting solution was diluted with pure water to an acid concentration of about 2% by mass. An internal standard solution (10 μg / mL) containing yttrium as an internal standard element was added to the resulting dilution, and this was used as the measurement sample.

[1062] The measurement sample was subjected to ICP-MS analysis, and the amount of alkali metal compound in the sample was quantified based on a calibration curve prepared using a standard solution. The concentration of the alkali metal compound relative to the total mass of the positive electrode active material layer was calculated by dividing by the original sample mass. The result showed that the concentration of the alkali metal compound was 3.5% by mass.

[1063] Examples 69 to 84 and Comparative Examples 28 to 42

[1064] A nonaqueous lithium storage device was produced and evaluated in the same manner as in Example 68 except that the components listed in Table 20 were used as the negative electrode, positive electrode precursor, and nonaqueous electrolyte.

[1065] The evaluation results are shown in Table 20.

[1066] The results of SEM analysis of the positive electrode active material layers of the positive electrode precursor 36 of Example 84 and the positive electrode precursor 37 of Comparative Example 42 are shown in FIG. Figures 7 to 12 .

[1067] Figure 7 This is an SEM image of the positive electrode active material layer of the positive electrode precursor 36 obtained in Example 84;

[1068] Figure 8 for Figure 7 Binarized image of the SEM image;

[1069] Figure 9 for the reason Figure 2 Frequency distribution of the diameters of the largest inscribed circle obtained from the binarized image.

[1070] Figure 10 This is an SEM image of the positive electrode active material layer of the positive electrode precursor 37 obtained in Comparative Example 42;

[1071] Figure 11 for Figure 10 Binarized image of the SEM image;

[1072] Figure 12 for the reason Figure 11 Frequency distribution of the diameters of the largest inscribed circle obtained from the binarized image.

[1073]

[1074]

[1075]

[1076]

[1077] As shown in Table 20, high capacity was confirmed when the mass ratio C2 of the alkali metal compound was 0.1≤C2≤7.0. In addition, excellent durability was confirmed for the examples with an area ratio Z'2 of 7.5% to 35.0%.

[1078] Furthermore, it is expected that by combining a negative electrode containing carbon nanotubes and a non-aqueous electrolyte containing an additive selected from nitrile compounds, even more excellent input-output characteristics and high-temperature durability can be exhibited.

[1079] <Examples 85 and 86 and Comparative Examples 43 to 57>

[1080] <Preparation of Positive Electrode Active Material>

[1081] The following activated carbon was used: The average particle size was measured using a laser diffraction particle size distribution analyzer (SALD-2000J) manufactured by Shimadzu Corporation.

[1082] (1) Activated carbon 6 (Example 85) with a particle size of 4.8 μm, using coconut shell as the raw material and heated to 500° C. for 3 hours and then steam activated

[1083] (2) Activated carbon 7 (Example 86) with a particle size of 6.1 μm, using charcoal as a raw material and heated to 500° C. for 3 hours and then steam activated

[1084] (3) Activated carbon 8 with a particle size of 8.2 μm, which was prepared by heating coconut shell to 500° C. over 3 hours and then alkali-activating (Comparative Example 43)

[1085] (4) Activated carbon 9 (Comparative Example 44) using coconut shell as a raw material and heating to 800°C for 9 hours and then steam-activated

[1086] (5) Activated carbon 10 with a particle size of 4.9 μm, which was steam activated by heating sawdust to 500° C. over 3 hours (Comparative Example 45)

[1087] (6) Activated carbon 11 with a particle size of 3.5 μm, which was alkali-activated by heating to 900° C. over 7 hours using phenol resin as a raw material (Comparative Example 46)

[1088] (7) Activated carbon 12 with a particle size of 2.8 μm, which was alkali-activated by heating coal to 900° C. over 8 hours (Comparative Example 47)

[1089] (8) Activated carbon 13 with a particle size of 5.0 μm, which was prepared by heating rice hulls to 800° C. over 7 hours and then alkali-activated (Comparative Example 48)

[1090] (9) Activated carbon 14 with a particle size of 5.0 μm, which was prepared by heating rice hulls to 800° C. over 9 hours and then alkali-activated (Comparative Example 49)

[1091] (10) Activated carbon 15 with a particle size of 5.0 μm, which was prepared by heating rice hulls to 800° C. for 5 hours and then alkali-activated (Comparative Example 50)

[1092] (11) Activated carbon 16 with a particle size of 3.8 μm, which was alkali-activated by heating to 1000° C. over 6 hours using sawdust as a raw material (Comparative Example 51)

[1093] (12) Activated carbon 17 with a particle size of 3.8 μm, which was alkali-activated by heating sawdust to 1000° C. over 4 hours (Comparative Example 52)

[1094] (13) Activated carbon 18 with a particle size of 3.8 μm, which was alkali-activated by heating to 1000° C. over 8 hours using sawdust as a raw material (Comparative Example 53)

[1095] (14) Activated carbon 19 with a particle size of 4.2 μm, using coconut shell as the raw material and heated to 900°C for 8 hours and then steam activated (Comparative Example 54)

[1096] (15) Activated carbon 20 with a particle size of 7.0 μm, which was alkali-activated by heating to 800° C. for 1 hour using phenol resin as a raw material (Comparative Example 55)

[1097] (16) Activated carbon 21 with a particle size of 5.3 μm, which was alkali-activated by heating to 900° C. over 8 hours using phenol resin as a raw material (Comparative Example 56)

[1098] (17) Activated carbon 22 with a particle size of 5.3 μm, which was alkali-activated by heating to 900° C. over 4 hours using phenol resin as a raw material (Comparative Example 57)

[1099] <Production of positive electrode precursor>

[1100] The above-mentioned activated carbon 6 was used as the positive electrode active material to produce a positive electrode precursor. Activated carbon 6 (56.8% by mass), lithium carbonate 31.8% by mass, acetylene black 4.2% by mass, CMC (carboxymethyl cellulose) 1.5% by mass, PVP (polyvinyl pyrrolidone) 1.8% by mass, and acrylic latex 4.0% by mass were mixed with distilled water to a solid content ratio of 34.1%. The mixture was dispersed for 4 minutes using a rotary mixer (manufactured by THINKY) at a peripheral speed of 2,000 times / minute to obtain a positive electrode coating solution.

[1101] The positive electrode coating liquid was applied to one side of a 15 μm thick aluminum foil using a power coater (manufactured by Imoto Seisakusho) and dried on a hot plate at 50°C to obtain a positive electrode precursor. The obtained positive electrode precursor was pressed using a 2-ton mechanical roller press (manufactured by ThankMetal) at a surface temperature of 25°C on the pressing section.

[1102] <Manufacturing of negative electrode>

[1103] 82.8 mass% of artificial graphite, 4.3 mass% of porous carbon, 8.7 mass% of acetylene black, 2.0 mass% of CMC (carboxymethyl cellulose) and 2.2 mass% of SBR (styrene butadiene rubber) latex, and distilled water with a solid content of 34.0% were mixed, and the mixture was dispersed at a peripheral speed of 2000 times / min for 4 minutes using a rotary mixer (manufactured by THINKY) to obtain a negative electrode coating liquid.

[1104] The negative electrode coating liquid was applied to one side of an 8 μm thick copper foil using a power coater (manufactured by Imoto Seisakusho) and dried on a hot plate at 50°C to obtain a negative electrode. The obtained negative electrode was pressed using a 2-ton mechanical roller press (manufactured by Thank Metal Co., Ltd.) at a surface temperature of 25°C on the press section.

[1105] <Fabrication of Metal Lithium Counter Electrode>

[1106] Cut the copper foil into 4.6cm×9.6cm(44cm 2 ) size, and a rectangular-shaped metal lithium foil was stacked on it. The lithium foil was then pressed onto the copper foil using a hand roller to obtain a metal lithium counter electrode.

[1107] <Preparation of Electrolyte>

[1108] A mixed solvent of ethylene carbonate (EC): ethyl methyl carbonate (EMC): dimethyl carbonate (DMC) = 34:22:44 (volume ratio) was used as an organic solvent, and the electrolyte salt was dissolved in such a way that the concentration ratio of LiPF6 to LiFSI was 3:1 and the total concentration was 1.2 mol / L to prepare a non-aqueous electrolyte.

[1109] <Fabrication of Non-aqueous Lithium Storage Device>

[1110] The obtained positive electrode precursor was sized to 4.3 cm × 9.5 cm (41 cm 2 ) size, and cut the negative electrode into 4.6 cm × 9.6 cm (44 cm 2 ) size. Also prepare 4.8cm×9.8cm(47cm 2 A polyolefin separator (manufactured by Asahi Kasei Corporation, 15 μm thick) was stacked in this order, forming an electrode laminate. The positive electrode precursor, separator, and negative electrode were ultrasonically welded to the resulting electrode laminate. The resulting electrode laminate was then placed in a container made of aluminum laminate packaging material, and the three sides including the electrode terminals were sealed by heat sealing.

[1111] At atmospheric pressure, in an argon environment at a temperature of 25°C and a dew point of -60°C, approximately 3g of a non-aqueous electrolyte was injected into the electrode stack contained within an aluminum laminate packaging material. The aluminum laminate packaging material containing the electrode stack and the non-aqueous electrolyte was then placed in a decompression chamber. The pressure was reduced from atmospheric pressure to -87kPa, then restored to atmospheric pressure and allowed to stand for 5 minutes. This process of reducing the pressure of the packaging material in the chamber from atmospheric pressure to -87kPa and then returning to atmospheric pressure was repeated four times, followed by a 15-minute stand. Through these steps, the non-aqueous electrolyte was impregnated into the electrode stack.

[1112] Thereafter, the aluminum laminate packaging material containing the electrode stack impregnated with the non-aqueous electrolyte is placed in a reduced pressure sealing machine, and sealed at a pressure of 0.1 MPa at 180°C for 10 seconds under a reduced pressure of -95 kPa, thereby sealing the aluminum laminate packaging material to form a non-aqueous lithium storage element.

[1113] [Alkali Metal Doping Process]

[1114] Next, the non-aqueous lithium battery element was placed in a thermostat set at 45° C. A charge-discharge device manufactured by Asuka Electronics Co., Ltd. was used, and the current value per unit electrode area of ​​the positive electrode was 1.2 mA / cm 2 Constant current charging was performed until the voltage reached 4.5 V, and then constant voltage charging at 4.5 V was continued for 3 hours. This method was used to perform initial charging and alkali metal doping.

[1115] Thereafter, a charge-discharge cycle consisting of the following discharge step and charge step was repeated 5 times. In the discharge step, the current value per unit electrode area of ​​the positive electrode was 1.2 mA / cm 2 The battery was discharged at a constant current from 4.0V to 2.0V, and then discharged at a constant voltage of 2.0V for 10 minutes. During this charging process, the current value per unit electrode area of ​​the positive electrode was 1.2mA / cm 2 The battery was charged at a constant current from 2.0 V to 4.0 V, and then charged at a constant voltage of 2.0 V for 10 minutes.

[1116] [Aging process]

[1117] The non-aqueous lithium storage element after the alkali metal doping step was placed in a thermostat set at 60°C and the current value per unit electrode area of ​​the positive electrode was 1.2 mA / cm 2 After constant current charging to 4.0V, constant voltage charging at 4.0V was performed for 16 hours.

[1118] Thereafter, a charge-discharge cycle consisting of the following discharge step and charge step was repeated 5 times. In the discharge step, the current value per unit electrode area of ​​the positive electrode was 1.2 mA / cm 2The battery was discharged at a constant current from 4.0V to 2.0V, and then discharged at a constant voltage of 2.0V for 10 minutes. During this charging process, the current value per unit electrode area of ​​the positive electrode was 1.2mA / cm 2 The battery was charged at a constant current from 2.0 V to 4.0 V, and then charged at a constant voltage of 2.0 V for 10 minutes.

[1119] [Exhaust process]

[1120] For the non-aqueous lithium storage element after the aging process, a portion of the aluminum laminate packaging material was opened in an argon environment with a temperature of 25°C and a dew point of -60°C. Next, the partially opened aluminum laminate packaging material containing the electrode stack was placed in a decompression chamber, and a diaphragm pump was used to reduce the pressure from atmospheric pressure to -80kPa over 3 minutes, and then it took 3 minutes to return to atmospheric pressure. This process was repeated a total of 10 times. Thereafter, the partially opened aluminum laminate packaging material containing the electrode stack was placed in a decompression sealer, and after the pressure was reduced to -90kPa, it was sealed at a pressure of 0.1MPa at 200°C for 10 seconds. In this way, the aluminum laminate packaging material was sealed to produce a non-aqueous lithium storage element.

[1121] [Calculation of initial battery cell capacity and battery cell life]

[1122] The prepared non-aqueous lithium storage element was placed in an environment with a temperature of 25°C and a current value of 10 mA / cm per unit electrode area of ​​the positive electrode. 2 A constant current discharge from 3.8V to 2.2V was performed, and the initial cell capacity was calculated to be 6.9mAh.

[1123] The non-aqueous lithium storage element was further stored in an environment with a temperature of 65°C. The time until the battery cell capacity reached 3.0 mAh measured under the above conditions was 2.2×10 3 Hour.

[1124] <Fabrication of Positive Electrode Monopolar Battery Cell>

[1125] The positive electrode precursor was cut so that the positive electrode active material layer was 4.3 cm × 9.5 cm (41 cm 2 ) size. Also prepare 4.8cm×9.8cm(47cm 2 ) polyolefin separator (manufactured by Asahi Kasei Corporation, thickness 15 μm) and 4.8 cm × 9.8 cm (47 cm 2 ) glass filter. Subsequently, the positive electrode precursor, separator, glass filter, and metallic lithium counter electrode are layered in this order to obtain an electrode laminate. The positive and negative electrode terminals are ultrasonically welded to the resulting electrode laminate, which is then placed in a container made of aluminum laminate packaging material, and the three sides including the electrode terminals are sealed by heat sealing.

[1126] Under atmospheric pressure, in an argon environment at a temperature of 25°C and a dew point of -60°C, approximately 6g of a non-aqueous electrolyte was injected into the electrode stack contained in an aluminum laminate packaging material. Next, the aluminum laminate packaging material containing the electrode stack and the non-aqueous electrolyte was placed in a decompression chamber. After the pressure was reduced from atmospheric pressure to -87kPa, the pressure was returned to atmospheric pressure, and the packaging material was allowed to stand for 5 minutes. This process was then repeated four times, with the packaging material in the chamber being decompressed from atmospheric pressure to -87kPa and then returned to atmospheric pressure. The packaging material was then allowed to stand for 15 minutes. Through the above process, the non-aqueous electrolyte was impregnated into the electrode stack.

[1127] Thereafter, the aluminum laminate packaging material containing the electrode stack impregnated with the non-aqueous electrolyte was placed in a vacuum sealer and sealed at a pressure of 0.1 MPa at 180°C for 10 seconds under a reduced pressure of -95 kPa to obtain a positive electrode monopolar battery cell.

[1128] <Evaluation of Positive Electrode Monopolar Battery Cell>

[1129] [Calculation of Alkali Metal Doping Reaction Efficiency]

[1130] The sealed positive electrode monopolar battery cell was placed in a thermostat set at 45°C. A charge and discharge device manufactured by Toyo System Co., Ltd. was used to charge and discharge the positive electrode at a current value of 0.49 mA / cm per electrode area. 2 After constant current charging to a voltage of 4.5 V, constant voltage charging at 4.5 V was continued for 3 hours to perform initial charging and alkali metal doping. The alkali metal doping reaction efficiency η was calculated to be 81%.

[1131] [Raman spectroscopy of activated carbon]

[1132] For the activated carbon, Raman spectroscopy was performed under the following conditions.

[1133] Equipment used: inVia Reflex manufactured by Renishaw

[1134] Excitation wavelength: 532nm

[1135] Excitation light intensity: 5%

[1136] Objective lens: 50 times

[1137] ·Measurement method: Confocal

[1138] Diffraction grating: 1800gr / mm

[1139] Exposure time: 30 seconds

[1140] Number of points: 8 times

[1141] As a result, Y1 was calculated to be 2.9.

[1142] In addition, Y1 is at a Raman shift of 1,590 cm -1 The peak intensity I1 appears to be at its maximum near the Raman shift of 1,470 cm -1 The ratio I1 / I2 of the peak intensity I2 of the minimum value appearing near Y1 is (Y1=I1 / I2).

[1143] [Determination of functional group content of activated carbon]

[1144] The amount of functional groups in the activated carbon was measured by thermal decomposition GC / MS analysis under the following conditions.

[1145] Thermal decomposition device: FRONTIER LAB Py3030D

[1146] Heating temperature: After maintaining at 50°C for 20 minutes, increase the temperature at 20°C / min and maintain at 1000°C for 30 minutes

[1147] IF temperature: 250℃

[1148] Heating atmosphere: He gas

[1149] GC / MS device: Agilent MSD5975

[1150] Column: Agilent FSDeactivated

[1151] Column temperature: 250°C

[1152] Inlet temperature: 250℃

[1153] Ion source: electron bombardment ionization method, temperature 230℃, I / F 250℃

[1154] Sample volume: about 3 mg

[1155] As a result, it was calculated that the functional group amount of activated carbon 6 used in Example 85 was 2.1 mmol / g.

[1156] <Example 86 and Comparative Examples 43 to 57>

[1157] The non-aqueous lithium battery element was produced according to the configuration and production conditions shown in Table 21, and various evaluations were performed.

[1158] It should be noted that the capacity (F / g) of various activated carbons was calculated based on the evaluation of the positive electrode single-electrode battery cell, and the basis weight (g / cm 2 ) is adjusted so that the positive electrode capacity of the battery cell is the same in all activated carbons.

[1159]

[1160] As shown in Table 21, highly crystalline activated carbon was obtained by steam activation at 500°C for 3 hours. Furthermore, for examples with an average particle size X1 of 3.0 μm to 7.0 μm and a Y1 of 2.5 or greater, high doping reaction efficiency and a long life were confirmed.

Claims

1. A non-aqueous lithium storage element comprising a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte containing lithium ions, wherein: The positive electrode comprises a positive electrode current collector and a positive electrode active material layer provided on one or both surfaces of the positive electrode current collector and containing a positive electrode active material. The positive electrode active material comprises activated carbon, The positive electrode active material layer further comprises carbon nanotubes and an alkali metal compound other than the positive electrode active material, wherein the alkali metal compound is one or more selected from the group consisting of lithium carbonate, sodium carbonate, and potassium carbonate. The mass ratio of the alkali metal compound relative to the total mass of the positive electrode active material layer of the positive electrode is set to C2, and when the unit of C2 is mass %, 0.1≤C2≤7.0, and Having at least one of the following structures (1) and (2): (1) The negative electrode comprises a negative electrode current collector and a negative electrode active material layer on one or both sides of the negative electrode current collector. The negative electrode active material layer comprises a negative electrode active material, carbon nanotubes and a dispersant. The negative electrode active material comprises a carbon material, In a binary SEM image of the surface of the negative electrode active material layer, when a set of maximum inscribed circles enclosed by each pixel is expressed as a frequency distribution of each diameter for all pixels in a bright field area, an area ratio Z1 of the total area of ​​the largest inscribed circles having a diameter of less than 100 nm to the total area of ​​the largest inscribed circles is not less than 3.5% and not more than 25.5%; (2) The non-aqueous electrolyte contains: (A) at least one lithium salt selected from LiPF6 and LiBF4, (B) a lithium salt having an imide structure, and (C) a lithium salt having an oxalic acid complex as an anion, and In the non-aqueous electrolyte solution, the ratio of the mass of the component (C) to the sum of the mass of the component (A) and the mass of the component (B) is 1.0 mass % or more and 10.0 mass % or less.

2. The non-aqueous lithium storage element according to claim 1, wherein The non-aqueous electrolyte solution contains (B) a lithium salt having an imide structure, wherein the component (B) is a lithium salt having an imide structure represented by the following formula (a): [Chemistry 1] In formula (a), R 1 and R 2 are independently a hydrogen atom, a halogen atom, an alkyl group or a haloalkyl group, R 1 and R 2 At least one of them is a halogen atom or a halogenated alkyl group.

3. The non-aqueous lithium storage element according to claim 1, wherein The (B) lithium salt having an imide structure is a lithium salt selected from the group consisting of lithium bis(fluorosulfonyl)imide and lithium bis(trifluoromethane)sulfonylimide.

4. The nonaqueous lithium storage device according to any one of claims 1 to 3, wherein The non-aqueous electrolyte solution contains (C) a lithium salt having an oxalic acid complex as an anion, wherein the component (C) is one or more lithium salts selected from the group consisting of lithium bisoxalatoborate, lithium fluorooxalatoborate, and lithium difluorooxalatoborate.

5. The nonaqueous lithium storage device according to any one of claims 1 to 3, wherein The non-aqueous electrolyte solution contains one or more nitrile compounds in a range of 0.1 mol / L to 5 mol / L.

6. The nonaqueous lithium storage device according to any one of claims 1 to 3, wherein The non-aqueous electrolyte contains one or more trinitrile compounds selected from the group consisting of 2-amino-1,1,3-tricyano-1-propene, 1-butyl-3-methylimidazolium tricyanomethanide, and lithium tricyanomethanide in a range of 0.1 mol / L to 5 mol / L.

7. The nonaqueous lithium storage device according to any one of claims 1 to 3, wherein The negative electrode active material layer has a solid electrolyte interface (SEI) material on the surface, The solid electrolyte interface (SEI) material includes lithium oxalate represented by the following formula (b): [Chemistry 2] 8. The nonaqueous lithium storage device according to any one of claims 1 to 3, wherein In X-ray photoelectron spectroscopy (XPS) of the negative electrode active material layer, a ratio I1 / I2 of an intensity I1 of a peak P1 observed in the range of 289 eV to 290 eV to an intensity I2 of a peak P2 observed in the range of 284 eV to 285 eV is 0.1 or more.

9. The nonaqueous lithium storage device according to any one of claims 1 to 3, wherein The non-aqueous electrolyte solution contains one or more ether compounds selected from the group consisting of 1,2-dimethoxyethane, 1,2-diethoxyethane, tetrahydrofuran, 1,3-dioxane, 1,4-dioxane, and 2-methyltetrahydrofuran in a range of 1 mol / L to 10 mol / L.

10. The nonaqueous lithium storage device according to any one of claims 1 to 3, wherein In the binary image of the SEM image of the surface of the negative electrode active material layer, the 1,000 nm 2 Above 5,000nm 2 The total area of ​​the following regions is 1,000nm 2 Above 20,000nm 2 The area ratio Z2 of the total area of ​​the following regions is 63.0% or more and 92.0% or less.

11. The nonaqueous lithium storage device according to any one of claims 1 to 3, wherein The total content concentration of Fe atoms and Ni atoms in the negative electrode active material layer is 1 ppm to 500 ppm.

12. The nonaqueous lithium storage device according to any one of claims 1 to 3, wherein An XRD (X-ray diffraction) spectrum measured for the negative electrode active material layer includes a peak Y1 having a peak top in the range of 2θ of 26.2° to 26.5°, and a half-value width of the peak Y1 is 0.1° to 0.5°.

13. The nonaqueous lithium storage device according to any one of claims 1 to 3, wherein The dispersant in the negative electrode active material layer is two or more selected from the group consisting of carboxymethyl cellulose, polycarboxylic acid, polycarboxylate, polyvinyl pyrrolidone, polyvinyl alcohol, and surfactant.

14. The nonaqueous lithium storage device according to any one of claims 1 to 3, wherein The average fiber diameter of the carbon nanotubes contained in the negative electrode active material layer is greater than or equal to 2 nm and less than 100 nm.

15. The nonaqueous lithium storage device according to any one of claims 1 to 3, wherein In a binary image of a 1,280×890 pixel SEM image of the surface of the positive electrode active material layer of the positive electrode taken at a magnification of 10,000 times, when the set of the largest inscribed circles enclosed in each pixel for all pixels in the bright field area is represented in the form of a frequency distribution of each diameter, the area ratio Z'2 of the total area of ​​the largest inscribed circles with a diameter less than 100 nm to the total area of ​​the largest inscribed circles is greater than 7.5% and less than 35.0%, where 1 pixel = 9.96 nm.

16. The nonaqueous lithium storage device according to claim 15, wherein An XRD (X-ray diffraction) spectrum measured for the positive electrode active material layer has a peak X2 in a range of 2θ of 25.7° to 27.0°, and a half-value width of the peak X2 is 0.1° to 0.5°.

17. The nonaqueous lithium storage element according to claim 15, wherein The total content concentration of Fe atoms and Ni atoms in the positive electrode active material layer is 1 ppm to 500 ppm.

18. The non-aqueous lithium storage device according to claim 15, wherein The positive electrode active material layer further comprises a dispersant, The dispersant is two or more selected from the group consisting of carboxymethyl cellulose, polycarboxylic acid, polycarboxylate, polyvinyl pyrrolidone, polyvinyl alcohol, and surfactant.

19. The non-aqueous lithium storage element according to claim 15, wherein The average fiber diameter of the carbon nanotubes contained in the positive electrode active material layer is greater than or equal to 2 nm and less than 100 nm.

20. The non-aqueous lithium storage device according to claim 15, wherein The positive electrode active material further comprises a lithium transition metal oxide, The lithium transition metal oxide is at least one selected from the group consisting of: Li x Ni a Co b Al (1-a-b) O2, where a, b, and x satisfy 0.02 < a < 0.97, 0.02 < b < 0.97, and 0 ≤ x ≤ 1, respectively; Li x Ni c Co d Mn (1-c-d) O2, where c, d, and x satisfy 0.02 < c < 0.97, 0.02 < d < 0.97, and 0 ≤ x ≤ 1, respectively; Li x CoO2, where x satisfies 0 ≤ x ≤ 1; Li x Mn2O4, where x satisfies 0 ≤ x ≤ 1; Li x FePO4, where x satisfies 0 ≤ x ≤ 1; Li x MnPO4, where x satisfies 0 ≤ x ≤ 1; and Li z V2(PO4)3, where z satisfies 0 ≤ z ≤ 3.

21. The nonaqueous lithium storage device according to claim 15, wherein When the average particle size of the activated carbon contained in the positive electrode active material layer is X1, 3.0μm≤X1≤7.0μm, In the Raman spectrum of the activated carbon, the Raman shift of 1,590 cm -1 The peak intensity I1 appears to be at its maximum near the Raman shift of 1,470 cm -1 When the ratio I1 / I2 of the minimum peak intensity I2 appearing near is Y1, 2.0≤Y1≤5.5， The product X1Y1 of X1 and Y1 is 10≤X1Y1≤28, and The functional group amount Z1 of the activated carbon is 0.80mmol / g≤Z1≤2.5mmol / g.

22. The non-aqueous lithium storage element according to claim 21, wherein The X1 is 4.0 μm≤X1≤6.0 μm.

23. The nonaqueous lithium storage element according to claim 21 or 22, wherein The product X1Y1 of X1 and Y1 is 13≤X1Y1≤26.

24. The nonaqueous lithium storage device according to any one of claims 1 to 3, wherein The activated carbon contained in the positive electrode active material layer is calculated by the BJH method. above The following pore volume is defined as V1, and the mesopore volume calculated by the MP method is from the pores with a diameter less than When the pore volume of the pores is set to V2, the units of V1 and V2 are cc / g, Satisfying 0.3 < V1 ≤ 0.8 and 0.5 ≤ V2 ≤ 1.0, and having a specific surface area measured by the BET method of 1,500 m 2 / g or more and 3,000 m 2 / g or less; or Satisfying 0.8 < V1 ≤ 2.5 and 0.8 < V2 ≤ 3.0, and having a specific surface area measured by the BET method of 2,300 m 2 / g or more and 4,000 m 2 / g or less.

25. The non-aqueous lithium storage element according to claim 21, wherein The Y1 is 2.5 or more and 4.5 or less.

26. The nonaqueous lithium storage element according to claim 21, wherein The functional group amount Z1 of the activated carbon is greater than or equal to 0.90 mmol / g and less than or equal to 2.5 mmol / g.

27. The nonaqueous lithium storage device according to claim 15, wherein The carbon nanotubes in the positive electrode active material layer are multi-layer carbon nanotubes.

28. The nonaqueous lithium storage device according to claim 15, wherein The positive electrode active material layer further includes a conductive filler and / or a binder.

29. The nonaqueous lithium storage device according to claim 18, wherein The dispersant in the positive electrode active material layer includes carboxymethyl cellulose and one or more selected from polyvinyl pyrrolidone and polyvinyl alcohol.

30. The nonaqueous lithium storage device according to any one of claims 1 to 3, wherein The alkali metal compound is lithium carbonate.

31. The nonaqueous lithium storage element according to claim 15, wherein In the binary image of the SEM image obtained by photographing the surface of the positive electrode active material layer, when the set of the largest inscribed circles enclosed in each pixel for all pixels in the bright field area is expressed in the form of a frequency distribution of each diameter, the area ratio Z'1 of the total area of ​​the largest inscribed circles with a diameter less than 100 nm to the total area of ​​the largest inscribed circles is greater than 5.9% and less than 28.0%.

32. The nonaqueous lithium storage device according to any one of claims 1 to 3, wherein In the carbon material contained in the negative electrode active material, the Raman spectrum at 1,360 cm -1 The peak intensity Id of the D-band peak Pd near 1,580 cm -1 The R value represented by the ratio Id / Ig of the peak intensity Ig of the peak Pg of the nearby G band is 0.6 or less.

33. The nonaqueous lithium storage element according to any one of claims 1 to 3, wherein The negative electrode contains a composite carbon material formed by combining a graphite material and a carbonaceous material derived from a carbonaceous material precursor.

34. The nonaqueous lithium storage device according to any one of claims 1 to 3, wherein The dispersant in the negative electrode active material layer includes carboxymethyl cellulose and one or more selected from polyvinyl pyrrolidone and polyvinyl alcohol.

35. The nonaqueous lithium storage element according to any one of claims 1 to 3, wherein The negative electrode active material layer further includes a conductive filler and / or a binder.

36. The nonaqueous lithium storage device according to any one of claims 1 to 3, wherein The Z1 is not less than 4.0% and not more than 24.1%.

37. The nonaqueous lithium storage device according to any one of claims 1 to 3, wherein In the non-aqueous electrolyte solution, the ratio of the mass of the component (C) to the sum of the mass of the component (A) and the mass of the component (B) is 1.4 mass % or more and 9.1 mass % or less.

38. The nonaqueous lithium storage device according to any one of claims 1 to 3, wherein The non-aqueous electrolyte solution includes a non-aqueous solvent selected from the group consisting of cyclic carbonates and chain carbonates.

39. The nonaqueous lithium storage element according to claim 38, wherein The nonaqueous solvent contains both a cyclic carbonate and a chain carbonate. 40 . A power storage module comprising the non-aqueous lithium power storage element according to claim 1 .

41. The power storage module as described in claim 40 is assembled into a system selected from the group consisting of a power regeneration auxiliary system, a power load balancing system, an uninterruptible power supply system, a contactless power supply system, an energy harvesting system, a power storage system, a solar power generation and storage system, an electric power steering system, an emergency power supply system, a hub motor system, an idle stop system, an electric vehicle, a hybrid vehicle, an electric two-wheeled vehicle, a fast charging system and a smart grid system.

42. A power storage system comprising: The energy storage element according to any one of claims 1 to 39; and Lead batteries, nickel-metal hydride batteries, lithium-ion secondary batteries, or fuel cells.

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