Non-aqueous lithium storage element

Abstract

The present disclosure provides a nonaqueous lithium power storage element in which the positive electrode active substance layer contains lithium iron phosphate and a carbon material containing activated carbon as the positive electrode active substance. When the content of carbon material in the positive electrode active substance layer is X1 (mass%) and the lithium iron phosphate content is X2 (mass%), the lithium iron phosphate mass ratio (X2 / (X1+X2)) is 0.40 to 0.85. The total pore volume of the positive electrode active substance layer is 0.29 cc / g to 0.70 cc / g, the void diameter D25 of the positive electrode active substance layer is 0.34 μm to 0.64 μm, the void diameter D75 of the positive electrode active substance layer is 0.10 μm to 0.20 μm, and the difference between the void diameter D25 and the void diameter D75 (D25-D75) is 0.20 μm to 0.45 μm.

Description

[Technical Field]

[0001] The present disclosure relates to a nonaqueous lithium energy storage element, etc. This international application claims priority to Japanese Patent Application No. 2023-023607 filed on February 17, 2023, Japanese Patent Application No. 2023-039941 filed on March 14, 2023, Japanese Patent Application No. 2023-023750 filed on February 17, 2023, Japanese Patent Application No. 2023-024515 filed on February 20, 2023, and Japanese Patent Application No. 2023-022538 filed on February 16, 2023, the entire contents of which are incorporated herein by reference. [Background technology]

[0002] In recent years, from the perspective of protecting the global environment and effectively utilizing energy to conserve resources, attention has been drawn to wind power generation power smoothing systems or late-night power storage systems, distributed home energy storage systems based on solar power generation technology, and energy storage systems for electric vehicles.

[0003] The first requirement for batteries used in these energy storage systems is a high energy density. Lithium-ion secondary batteries are being vigorously developed as a promising candidate for a high-energy density battery that can meet this requirement. The second requirement is high output characteristics. For example, in a combination of a highly efficient engine and an energy storage system (e.g., a hybrid electric vehicle) or a combination of a fuel cell and an energy storage system (e.g., a fuel cell electric vehicle), an energy storage system that exhibits high output discharge characteristics during acceleration is required. Currently, electric double-layer capacitors, lithium-ion capacitors, and the like are being developed as high-output energy storage devices. Since these requirements are being studied from various angles, the background art is described below.

[0004] <Background technology 1> Among lithium-ion capacitors, those that use activated carbon as the positive electrode active material have output characteristics of approximately 20 kW / L. This lithium-ion capacitor not only has high output characteristics, but also high durability (cycle characteristics and high-temperature storage characteristics), and has been considered the optimal device for the fields that require high output as mentioned above. However, since its energy density is only approximately 20 Wh / L, further increases in capacity, i.e., improvements in energy density, are necessary.

[0005] Research into increasing the output of lithium-ion secondary batteries is also underway. For example, lithium-ion secondary batteries have been developed that can achieve high output of over 3 kW / L at a discharge depth of 50% (i.e., the ratio (%) of the discharge amount to the discharge capacity of the storage element). However, their energy density is 100 Wh / L or less, a design that deliberately suppresses the high capacity characteristic that is the greatest feature of lithium-ion secondary batteries. Furthermore, their durability (cycle characteristics and high-temperature storage characteristics) is inferior to that of lithium-ion capacitors, so such lithium-ion secondary batteries are used within a discharge depth range narrower than the range of 0 to 100% in order to ensure practical durability. Since the capacity of lithium-ion secondary batteries that can be used in practice will become even smaller, research is being actively conducted to further improve their durability.

[0006] Various studies have been conducted to further increase the capacity and energy density of the lithium ion capacitor, and for example, a technique has been disclosed in which activated carbon and lithium iron phosphate are used in combination as a positive electrode active material (Patent Documents 1 to 3).

[0007] Patent Document 1 aims to provide a nonaqueous lithium storage element that has high capacity and low resistance and in which decomposition of the lithium compound in the positive electrode precursor is promoted, and describes a nonaqueous lithium storage element that has a positive electrode containing activated carbon and lithium iron phosphate (LiFePO4) as the positive electrode active material.

[0008] Patent Document 2 aims to provide an electricity storage device with little deterioration in electrical characteristics, and describes a capacitor positive electrode in which a positive electrode active material layer disposed on one side of the positive electrode contains activated carbon and a positive electrode active material layer disposed on the other side contains lithium iron phosphate.

[0009] Patent Document 3 aims to provide a lithium ion capacitor with a long life and large capacity, and describes a lithium ion capacitor having a positive electrode containing activated carbon and lithium iron phosphate (LiFePO4) as the positive electrode active material.

[0010] <Background technology 2> As the above-mentioned high-power storage devices, electric double layer capacitors, nickel-metal hydride batteries, etc. have been developed.

[0011] Among electric double layer capacitors, those that use activated carbon for the electrodes have output characteristics of approximately 0.5 to 1 kW / L. These electric double layer capacitors not only have high output characteristics but also high durability (cycle characteristics and high-temperature storage characteristics), and have been considered to be the optimal device for the above-mentioned fields that require high output. However, their energy density is only approximately 1 to 5 Wh / L, so further improvement in energy density is necessary.

[0012] On the other hand, nickel-metal hydride batteries, which are currently commonly used in hybrid electric vehicles, have high output equivalent to that of electric double-layer capacitors and an energy density of about 160 Wh / L. However, there is a demand for further improvements in their energy density and output characteristics, as well as durability (especially stability at high temperatures), and research into this is being actively pursued.

[0013] As described above, there is a strong demand for practical application of energy storage elements that combine high energy density, high output characteristics, and high durability. However, the existing energy storage elements described above each have their own advantages and disadvantages, and new energy storage elements that satisfy these technical requirements are needed. A lithium-ion capacitor is a type of energy storage element that has attracted attention as a promising candidate, and active development is underway. A lithium-ion capacitor is a type of energy storage element that uses a non-aqueous electrolyte solution containing lithium salt (hereinafter also referred to as a "nonaqueous lithium energy storage element"). At approximately 3 V or higher, the positive electrode undergoes a non-Faradic reaction involving the adsorption and desorption of anions, similar to that of an electric double-layer capacitor, and the negative electrode undergoes a Faradic reaction involving the absorption and release of lithium ions, similar to that of a lithium-ion secondary battery.

[0014] To summarize the electrode materials commonly used in the above-mentioned energy storage elements and their characteristics, generally, when materials such as activated carbon are used for the electrodes and charging and discharging is performed by the adsorption and desorption of ions on the surface of the activated carbon (non-Faradaic reaction), high output and high durability are obtained, but the energy density is low (for example, 1x). On the other hand, when oxide or carbon materials are used for the electrodes and charging and discharging is performed by the Faradaic reaction, the energy density is high (for example, 10x that of non-Faradaic reaction using activated carbon), but there are issues with durability and output characteristics.

[0015] As a combination of these electrode materials, electric double layer capacitors use activated carbon (energy density 1x) for the positive and negative electrodes, and are characterized by charging and discharging through non-Faradic reactions at both the positive and negative electrodes.As a result, they have high output and high durability, but are characterized by low energy density (positive electrode 1x x negative electrode 1x = 1).

[0016] Lithium-ion secondary batteries use lithium transition metal oxides (10 times the energy density) for the positive electrode and carbon materials (10 times the energy density) for the negative electrode, and are characterized by charging and discharging via the Faraday reaction at both the positive and negative electrodes. Therefore, they have a high energy density (10 times the positive electrode × 10 times the negative electrode = 100), but they have issues with output characteristics and durability. Furthermore, to meet the high durability required for 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.

[0017] Lithium-ion capacitors use activated carbon (energy density 1x) for the positive electrode and carbon material (energy density 10x) for the negative electrode, and are characterized by charging and discharging via a non-Faradaic reaction at the positive electrode and a Faradic reaction at the negative electrode, making them asymmetric capacitors that combine the features of electric double-layer capacitors and lithium-ion secondary batteries. Lithium-ion capacitors are characterized by high output and durability, as well as a high energy density (1x positive electrode x 10x negative electrode = 10), and by the absence of the need to limit the depth of discharge as with lithium-ion secondary batteries.

[0018] As described above, the structural features of electric double layer capacitors, lithium ion capacitors, and lithium ion secondary batteries have been described. However, various studies are still being conducted to further increase the energy density of lithium ion capacitors or secondary batteries (Patent Documents 1, 3, and 4).

[0019] Patent Document 3 discloses a long-life, large-capacity lithium ion capacitor that uses activated carbon and lithium iron phosphate as the positive electrode active material.

[0020] Patent Document 1 discloses a positive electrode precursor that contains a carbon material, a lithium transition metal oxide, and an alkali metal compound, has high capacity and low resistance, and can be pre-doped into a negative electrode in a short time by promoting the decomposition of the alkali metal compound.

[0021] Patent Document 4 discloses a non-aqueous electrolyte secondary battery that uses two types of positive electrode active materials with different particle sizes, and has high energy density and excellent cycle characteristics.

[0022] <Background technology 3> The third requirement is long-term stable use. For example, in the combination of a high-efficiency engine and a power storage system (e.g., hybrid electric vehicles) or a combination of a fuel cell and a power storage system (e.g., fuel cell electric vehicles), a power storage system that exhibits excellent output characteristics (low resistance), high-temperature durability, and vibration resistance is required. In particular, as electric vehicles become more widespread worldwide in response to demands from a society striving for carbon neutrality, it is expected that there will be an increase in off-road travel on underdeveloped roads, and in areas with harsh climatic conditions such as tropical regions. This will likely result in demands for higher high-temperature durability and vibration resistance than ever before.

[0023] Furthermore, electric double layer capacitors, lithium ion capacitors, and the like are currently being developed as high-power, high-durability electricity storage devices. Electric double layer capacitors use activated carbon as the active material for the positive and negative electrodes, while lithium ion capacitors use activated carbon as the active material for the positive electrode, and charge and discharge are carried out by the adsorption and desorption of ions on the surface of the activated carbon (non-Faraday reaction), thereby achieving high-power (low resistance) performance and high durability. Therefore, when activated carbon is used as the active material, aluminum foil coated with a conductive undercoat layer (hereinafter referred to as anchor foil), or etched foil, expanded foil, punched foil, or the like, in which the aluminum surface has been subjected to a fine processing treatment, has traditionally been used as the current collector (Patent Documents 5 and 6).

[0024] Various studies have been conducted to improve the output and durability of capacitors using activated carbon electrodes. For example, Patent Document 7 discloses a technology for improving output performance by adding carbon nanotubes. Patent Document 8 discloses a technology for improving vibration resistance by supporting each component housed in a metal case with insulating resin. Patent Document 9 discloses a technology for improving input / output characteristics and durability by reducing aggregates in activated carbon electrodes.

[0025] <Background technology 4> Furthermore, in the development of higher output, Patent Document 10 discloses a technique for pre-doping the negative electrode by adding an alkali metal compound to the positive electrode precursor and a technique for improving cycle durability at room temperature. Patent Document 11 discloses a technique for promoting the decomposition of the alkali metal compound in the positive electrode precursor and pre-doping the negative electrode by applying pressure and heat, and a technique for improving cycle durability at high temperatures.

[0026] <Background technology 5> Lithium iron phosphate (LiFePO4: hereinafter sometimes abbreviated as "LFP") is widely used as a positive electrode active material containing iron as the main component. Lithium iron phosphate as a positive electrode active material is characterized by high thermal stability, but it has the property of causing a sudden rise in voltage at the end of charging and a sudden change in potential at the end of discharging. Patent Document 1 discloses a technology that attempts to gently control the voltage rise of a battery by incorporating a positive electrode active material that has a charge / discharge capacity at a higher voltage than lithium iron phosphate.

[0027] Lithium iron phosphate has a lower voltage plateau (hereinafter sometimes referred to as "plateau") than the above-mentioned ternary positive electrode active materials, and therefore tends to have a relatively low energy density. For this reason, Patent Document 13 discloses a technique that attempts to increase the plateau by substituting manganese for some of the iron in lithium iron phosphate, thereby increasing the energy density of lithium-ion secondary batteries. On the other hand, Patent Document 14 discloses a technique that attempts to increase the energy density of lithium-ion secondary batteries by oxidatively decomposing a lithium compound, such as lithium carbonate, contained in a positive electrode and pre-doping the resulting lithium ions into a negative electrode. Furthermore, Patent Document 15 discloses a technique that attempts to improve the large-current discharge characteristics of lithium-ion secondary batteries by using a positive electrode active material that is a mixture of lithium iron phosphate and electrolytic manganese dioxide. [Prior art documents] [Patent documents]

[0028] [Patent Document 1] International Publication No. 2019 / 098197 [Patent Document 2] Japanese Patent Application Laid-Open No. 2009-141181 [Patent Document 3] Japanese Patent Application Laid-Open No. 2012-89825 [Patent Document 4] Japanese Patent Application Laid-Open No. 2007-335318 [Patent Document 5] Japanese Patent Application Publication No. 57-84120 [Patent Document 6] Japanese Patent Application Publication No. 11-283871 [Patent Document 7] International Publication No. 2021 / 066174 [Patent Document 8] Japanese Patent Application Laid-Open No. 2012-104571 [Patent Document 9] Japanese Patent Application Publication No. 2020-140889 [Patent Document 10] International Publication No. 2017 / 126693 [Patent Document 11] Japanese Patent Publication No. 2020-167343 [Patent Document 12] International Publication No. 2011 / 096469 [Patent Document 13] Japanese Patent Application Laid-Open No. 2008-243662 [Patent Document 14] International Publication No. 2017 / 126682 [Patent Document 15] Japanese Patent Application Laid-Open No. 2009-170106 [Non-patent literature]

[0029] [Non-Patent Document 1] EP Barrett, LG Joyner, and P. Halenda, "The Determination of Pore Volume and Area Distributions in Porous Substances", J.Am.Chem.Soc., (1951), 73, pp.373-380 [Non-patent document 2] BCLippens, and JHde Boer, "Studies on pore Systems in Catalysis V. The t Method", J.Catalysis, (1965), 4, pp.319-323 [Non-patent document 3] RSMikhail, S.Brunauer, and EEBodor, "Investigations of a Complete Pore Structure Analysis", J.Colloid Interface Sci., (1968), 26, pp.45-53 Summary of the Invention [Problem to be solved by the invention]

[0030] The present disclosure aims to provide a positive electrode precursor, a negative electrode, and an energy storage device using the same, which can improve one or more of the problems in the following first to fifth embodiments. Further problems and advantages of the present disclosure will be presented below and in the detailed description of the invention.

[0031] In a first embodiment, the present disclosure aims to provide a nonaqueous lithium energy storage element and the like that is excellent in low-temperature power density, suppression of micro-short circuits during low-temperature cycle testing, and durability in high-power cycles from low to high temperatures.

[0032] In a second embodiment, the present disclosure aims to provide a positive electrode precursor that has high capacity and low resistance and can be pre-doped into a negative electrode in a short time, and a nonaqueous lithium storage element using the same.

[0033] In a third embodiment, the present disclosure aims to provide an energy storage element or the like that has low resistance and excellent vibration resistance and high-temperature durability.

[0034] In a fourth embodiment, the present disclosure provides a nonaqueous lithium storage element or the like that suppresses micro-short circuits in a pre-doping step, has low internal resistance, and is excellent in cycle durability over a wide temperature range, and also provides a negative electrode for producing the same.

[0035] In a fifth embodiment, the present disclosure aims to provide a nonaqueous lithium storage element and the like that has excellent discharge capacity and energy density per unit voltage in a low voltage region and can suppress an increase in resistance in a high-temperature environment. [Means for solving the problem]

[0036] First Embodiment Examples of the first embodiment of the present disclosure are listed in the following items [1] to [8]. [1] A non-aqueous lithium storage element comprising: a positive electrode including a positive electrode active material layer disposed on a positive electrode current collector; a negative electrode including a negative electrode active material layer disposed on a negative electrode current collector; a separator; and a non-aqueous electrolyte solution containing lithium ions, the positive electrode active material layer contains a carbon material including activated carbon as a positive electrode active material, and lithium iron phosphate; When the content of the carbon material in the positive electrode active material layer is X1 (mass%) and the content of lithium iron phosphate is X2 (mass%), the mass ratio of lithium iron phosphate (X2 / (X1+X2)) is 0.40 or more and 0.85 or less, a total pore volume of the positive electrode active material layer based on the weight of the positive electrode active material layer is 0.29 cc / g or more and 0.70 cc / g or less, the positive electrode active material layer has a pore diameter D25 of 0.34 μm or more and 0.64 μm or less, as measured by a mercury porosimeter; The pore diameter D75 of the positive electrode active material layer, measured by mercury porosimetry, is 0.10 μm or more and 0.20 μm or less, and A non-aqueous lithium storage element in which the difference between pore diameters D25 and D75 (D25-D75) is 0.20 μm or more and 0.45 μm or less. [2] Item 2. The nonaqueous lithium storage element according to item 1, wherein the mass ratio of the lithium iron phosphate is 0.70 or more and 0.80 or less. [3] 3. The nonaqueous lithium storage element according to item 1 or 2, wherein the positive electrode active material layer has a total pore volume of 0.31 cc / g or more and 0.50 cc / g or less. [4] 4. The nonaqueous lithium storage element according to any one of items 1 to 3, wherein the positive electrode active material layer has a pore diameter D25 of 0.36 μm or more and 0.52 μm or less. [5] 5. The nonaqueous lithium storage element according to any one of items 1 to 4, wherein the positive electrode active material layer contains 0.01 mass % to 5.0 mass % of lithium carbonate based on the total mass of the positive electrode active material layer. [6] 6. The nonaqueous lithium storage element according to any one of items 1 to 5, wherein the positive electrode active material layer has a volume resistivity of 1.5 Ωcm or more and 8.0 Ωcm or less. [7] 1000 μm of the surface of the positive electrode active material layer 2 More than 10000μm 2 Aggregate frequency of 0.5 particles / cm or less 2 7. The nonaqueous lithium storage element according to any one of items 1 to 6, wherein: [8] 8. The nonaqueous lithium storage element according to any one of items 1 to 7, wherein the nonaqueous lithium storage element is discharged at a constant current of 18 A from 4.0 V to 2.8 V at 5°C, the discharge is paused, and the voltage change (ΔV) 10 seconds after the discharge is paused is divided by 18 A to obtain a value R1 (Ω) as the 5°C 10-second current-paused resistance, and R2 (Ω) as the 25°C 10-second current-paused resistance, and the same procedure is repeated at 25°C to obtain a value R2 (Ω) as the 25°C 10-second current-paused resistance. The ratio (R1 / R2) of the 5°C 10-second current-paused resistance R1 (Ω) to the 25°C 10-second current-paused resistance R2 (Ω) is 1.05 or more and 1.90 or less.

[0037] Second Embodiment Examples of the second embodiment of the present disclosure are listed below. [1] A positive electrode precursor having a positive electrode current collector and a positive electrode active material layer disposed on the positive electrode current collector, wherein the positive electrode active material layer contains a carbon material containing at least activated carbon, a lithium transition metal oxide, and an alkali metal compound, wherein a mass ratio A1 of the carbon material in the positive electrode active material layer is 38 mass% or more and 60 mass% or less, a mass ratio A2 of the lithium transition metal oxide in the positive electrode active material layer is 15 mass% or more and 45 mass% or less, A1+A2 is 74 mass% or more and 93 mass% or less, A2 / A1 is 0.30 or more and 1.20 or less, and a specific surface area B of the lithium transition metal oxide measured by a BET method is 7.5 m 2 / g or more 11.0m 2 / g or less, and the D of the lithium transition metal oxide 10 C1, the lithium transition metal oxide D 90where C2 is C2 / C1, the positive electrode precursor has a value of 10 or more and 25 or less. [2] Item 2. The positive electrode precursor according to item 1, wherein the alkali metal compound is lithium carbonate and the lithium transition metal oxide is an olivine-based compound. [3] 3. The positive electrode precursor according to item 1 or 2, wherein the lithium transition metal oxide is lithium iron phosphate. [4] A non-aqueous lithium storage element including a positive electrode having a positive electrode current collector and a positive electrode active material layer disposed on the positive electrode current collector, a negative electrode, a separator, and a non-aqueous electrolyte solution containing lithium ions, The positive electrode active material layer contains a carbon material containing at least activated carbon, a lithium transition metal oxide, and an alkali metal compound, wherein a mass ratio X1 of the carbon material in the positive electrode active material layer is 43 mass% or more and 74 mass% or less, a mass ratio X2 of the lithium transition metal oxide in the positive electrode active material layer is 23 mass% or more and 55 mass% or less, X2 / X1 is 0.30 or more and 1.20 or less, and X1+X2 is 92.5 mass% or more and 99.3 mass% or less, and a specific surface area Y of the lithium transition metal oxide measured by a BET method is 7.5 m 2 / g or more 11.0m 2 / g or less, and D of the lithium transition metal oxide 10 Z1, the lithium transition metal oxide D 90 where Z2 is the total mass of the non-aqueous lithium storage element, and Z2 / Z1 is 10 or more and 25 or less. [5] 5. The nonaqueous lithium storage element according to item 4, wherein the alkali metal compound is lithium carbonate and the lithium transition metal oxide is lithium iron phosphate. [6] Item 6. At least one storage module selected from the group consisting of a power regeneration assist system, a power load leveling 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, an in-wheel motor system, an idling stop system, an electric vehicle, a plug-in hybrid vehicle, a hybrid vehicle, an electric motorcycle, a quick charging system, and a smart grid system, comprising the nonaqueous lithium storage element according to Item 4 or 5. [7] Item 6. An electricity storage system comprising the nonaqueous lithium electricity storage element according to item 4 or 5 connected in series or in parallel with a lead battery, a nickel-metal hydride battery, a lithium ion secondary battery, a sodium ion secondary battery, a zinc ion secondary battery, a fluoride ion secondary battery, or a fuel cell.

[0038] Third Embodiment Examples of the third embodiment of the present disclosure are listed below. [1] An electric storage element including: a positive electrode including a positive electrode active material layer disposed on a positive electrode current collector; a negative electrode including a negative electrode active material layer disposed on a negative electrode current collector; a separator; and an electrolytic solution, the positive electrode current collector is a non-porous aluminum foil, there is no undercoat layer on the positive electrode current collector, and the positive electrode active material layer is formed directly on the positive electrode current collector; the positive electrode active material layer contains activated carbon as a positive electrode active material, The electric storage element is disassembled and removed, and the interface resistance between the positive electrode active material layer and the positive electrode current collector of the positive electrode is 0.05 Ωcm 2 More than 5.00Ωcm 2 is less than or equal to, and The storage element was disassembled and removed, and the positive electrode surface was measured to obtain a 1000 μm 2 More than 10000μm 2 The aggregate frequency is less than 0.5 particles / cm 2 The following is a storage element. [2] The lithium ion is doped in the negative electrode active material layer, and the electrolytic solution is a non-aqueous electrolytic solution containing lithium ions, for the power storage element according to item 1. [3] The positive electrode active material layer contains a lithium transition metal oxide as a positive electrode active material, for the power storage element according to item 1 or 2. [4] The lithium transition metal oxide is represented by the following formula: Li x Ni a Co b Al (1-a-b) O2 {where x satisfies 0 ≦ x ≦ 1, and a and b satisfy 0.2 < a < 0.97 and 0.2 < b < 0.97.} Li x Ni c Co d Mn (1-c-d) O2 {where x satisfies 0 ≦ x ≦ 1, and c and d satisfy 0.2 < c < 0.97 and 0.2 < d < 0.97.} 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.}, or Li z V2(PO4)3 {where z satisfies 0 ≦ z ≦ 3.}, for the power storage element according to item 3. [5] The lithium transition metal oxide is lithium iron phosphate, for the power storage element according to item 3 or 4. [6] The lithium transition metal oxide is lithium iron phosphate, and the ratio of the 3.4 - 3.0V capacity (mAh) to the 4.0 - 2.0V capacity (mAh) of the power storage element is 25 - 82%, for the power storage element according to any one of items 3 - 5. [7] 6. The energy storage element according to any one of items 3 to 5, wherein the lithium transition metal oxide is lithium iron phosphate, and the ratio of the 3.4-3.0 V capacity (mAh) to the 4.0-2.0 V capacity (mAh) of the energy storage element is 50 to 70%. [8] The interface resistance between the positive electrode active material layer of the positive electrode and the positive electrode current collector is A [Ωcm 2 8. The energy storage element according to any one of items 1 to 7, wherein A / B is 0.02 to 250, where B [mmol / g] is the concentration of lithium fluoride contained in the negative electrode relative to the weight of the negative electrode active material layer. [9] The interface resistance between the positive electrode active material layer of the positive electrode and the positive electrode current collector is A [Ωcm 2 8. The electric storage element according to any one of items 1 to 7, wherein A / B is 0.07 to 5.5, where B [mmol / g] is the concentration of lithium fluoride contained in the negative electrode relative to the weight of the negative electrode active material layer.

[10] 10. The electricity storage element according to any one of items 1 to 9, wherein the positive electrode contains 0.01 to 5.0% by mass of lithium carbonate.

[11] the negative electrode active material layer contains activated carbon, and the interface resistance between the negative electrode active material layer and the negative electrode current collector of the negative electrode obtained by disassembling and removing the electricity storage element is 0.05 Ωcm 2 More than 5.00Ωcm 2 Item 2. The energy storage element according to item 1, wherein:

[0039] Fourth Embodiment Examples of the fourth embodiment of the present disclosure are listed below. [1] A negative electrode comprising a negative electrode current collector and a negative electrode active material layer on one or both surfaces of the negative electrode current collector, the negative electrode active material layer comprising graphite capable of absorbing and desorbing lithium ions, (1) to (4) below: (1) The average thickness of the material constituting the negative electrode active material layer is 0.2 μm or more and 1.0 μm or less; (2) The pore size of the negative electrode active material layer is 0.15 μm or more and 0.70 μm or less. (3) The negative electrode active material layer has a specific surface area of ​​8 m2 calculated based on the mass of the negative electrode active material layer. 2 / g or more 40m 2 / g or less, and (4) The frequency of aggregates on the surface of the negative electrode is 0 pieces / cm 2 More than 1.0 pieces / cm 2 The negative electrode satisfies all of the following requirements. [2] Item 2. The negative electrode according to item 1, wherein 1.0≦(1.35−p) / t≦2.8 is satisfied, where t (μm) is an average thickness of a material constituting the negative electrode active material layer and p (μm) is a pore diameter of the negative electrode active material layer. [3] The void volume of the negative electrode active material layer is 0.5 cm 3 / g or more 1.2cm 3 / g or less. [4] 4. The negative electrode according to any one of items 1 to 3, wherein the material constituting the negative electrode active material layer has an average thickness of 0.3 μm or more and 0.8 μm or less. [5] 5. The negative electrode according to any one of items 1 to 4, wherein the negative electrode active material layer has a pore size of 0.20 μm or more and 0.60 μm or less. [6] The negative electrode active material layer has a specific surface area of ​​12 m2 calculated based on the mass of the negative electrode active material layer. 2 / g or more 30m 2 6. The negative electrode according to any one of items 1 to 5, wherein the negative electrode has a densitometric value of 0.1 / g or less. [7] The frequency of agglomerates on the surface of the negative electrode is 0.2 pieces / cm 2 7. The negative electrode according to any one of items 1 to 6, wherein: [8] The void volume of the negative electrode active material layer is 0.6 cm 3 / g or more 1.1cm 3 8. The negative electrode according to any one of items 1 to 7, wherein the negative electrode has a densitometric value of 0.1 / g or less. [9] A non-aqueous lithium storage element, in which a non-aqueous electrolyte solution containing the negative electrode according to any one of items 1 to 8, a positive electrode, a separator, and lithium ions is housed in an exterior body.

[0040] <Fifth Embodiment> Examples of the fifth embodiment of the present disclosure are listed below. [1] A non-aqueous lithium storage element including a positive electrode, a negative electrode, and a non-aqueous electrolyte containing lithium ions, where the positive electrode has a positive electrode current collector and a positive electrode active material layer provided on one or both sides of the positive electrode current collector, the positive electrode active material layer includes a positive electrode active material and a transition metal oxide represented by MO2 {where M is one or more selected from the group consisting of Co, Ni, and Mn.}, the positive electrode active material is Li x Mn (1-y) Fe y and includes a compound represented by PO4 {where x satisfies 0 ≦ x ≦ 1 and y satisfies 0 < y ≦ 1.}, the negative electrode has a negative electrode current collector and a negative electrode active material layer provided on one or both sides of the negative electrode current collector, when the discharge capacity per unit area of the positive electrode is A1 (mAh / cm 2 ) and the charge capacity per unit area of the negative electrode is B1 (mAh / cm 2 ), it satisfies 0.71 ≦ A1 / B1 ≦ 0.96, a non-aqueous lithium storage element. [2] The non-aqueous lithium storage element according to item 1, wherein the positive electrode active material layer further includes activated carbon. [3] When based on the total mass of the negative electrode active material layer, the non-aqueous lithium storage element according to item 1 or 2, wherein the negative electrode active material layer contains a carbon material in a proportion of 50 parts by mass or more and 98 parts by mass or less as the negative electrode active material. [4] When based on the total mass of the negative electrode active material layer, the non-aqueous lithium storage element according to any one of items 1 to 3, wherein the negative electrode active material layer contains one or more selected from the group consisting of silicon, silicon compounds, tin, and tin compounds in a proportion of 5 parts by mass or more and 3 parts by mass or less as the negative electrode active material. [5] The proportion of the MO2 contained in the positive electrode is 1 part by mass or more and 20 parts by mass or less based on the total mass of the positive electrode active material layer, and the non-aqueous lithium storage element according to any one of items 1 to 4. [6] When the total mass of the negative electrode active material layer is used as a reference, the negative electrode active material layer contains a carbon material as the first negative electrode active material at a ratio of 50 parts by mass or more and 95 parts by mass or less, contains at least one of silicon and silicon compounds as the second negative electrode active material at a ratio of 5 parts by mass or more and 30 parts by mass or less, and the non-aqueous lithium storage element according to any one of items 1 to 5. [7] A power storage module including the non-aqueous lithium storage element according to any one of items 1 to 6. [8] The power storage module is incorporated into at least one system selected from the group consisting of a power regeneration assist system, a power load leveling system, an uninterruptible power supply system, a non-contact power supply system, an energy harvesting system, an electric vehicle, a plug-in hybrid vehicle, a hybrid vehicle, an electric motorcycle, and a rapid charging system, and the power storage module according to item 7. [9] A non-aqueous lithium storage element precursor including a positive electrode precursor, a negative electrode precursor, and a non-aqueous electrolyte containing lithium ions, The positive electrode precursor has a positive electrode current collector and a positive electrode active material layer provided on one or both sides of the positive electrode current collector, The positive electrode active material layer contains a positive electrode active material and a lithium compound composite, The positive electrode active material is Li x Mn (1-y) Fe y PO4 {where x satisfies 0 ≦ x ≦ 1 and y satisfies 0 < y ≦ 1.}, and contains a compound represented by The lithium compound composite is a composite of a lithium compound and a transition metal oxide represented by MO2 {where M is one selected from the group consisting of Co, Ni, and Mn.}, the negative electrode precursor includes a negative electrode current collector and a negative electrode active material layer provided on one or both surfaces of the negative electrode current collector, The charge capacity per unit area of ​​the positive electrode precursor is defined as A2 (mAh / cm 2 ), and the discharge capacity per unit area of ​​the positive electrode precursor is defined as A3 (mAh / cm 2 ), and the charge capacity per unit area of ​​the negative electrode precursor is defined as B2 (mAh / cm 2 ), the relationship 0.65≦A3 / A2≦0.93 is satisfied and the relationship 1.03≦B2 / A3≦1.26 is satisfied. Non-aqueous lithium storage element precursor.

[10] 10. A method for producing a nonaqueous lithium storage element, comprising a pre-doping step of applying a voltage of 4.2 V or more to the nonaqueous lithium storage element precursor according to Item 9 at a temperature of 20° C. or higher and 60° C. or lower to decompose the lithium compound.

[0041] <Combination of the first to fifth embodiments> Examples of combinations of the first to fifth embodiments of the present disclosure are listed in the following items [1] to

[22] . [1] A non-aqueous lithium storage element comprising: a positive electrode including a positive electrode active material layer disposed on a positive electrode current collector; a negative electrode including a negative electrode active material layer disposed on a negative electrode current collector; a separator; and a non-aqueous electrolyte solution containing lithium ions, the positive electrode active material layer contains a carbon material including activated carbon as a positive electrode active material, and lithium iron phosphate; When the content of the carbon material in the positive electrode active material layer is X1 (mass%) and the content of lithium iron phosphate is X2 (mass%), the mass ratio of lithium iron phosphate (X2 / (X1+X2)) is 0.40 or more and 0.85 or less, a total pore volume of the positive electrode active material layer based on the weight of the positive electrode active material layer is 0.29 cc / g or more and 0.70 cc / g or less, the positive electrode active material layer has a pore diameter D25 of 0.34 μm or more and 0.64 μm or less, as measured by a mercury porosimeter; The pore diameter D75 of the positive electrode active material layer, measured by mercury porosimetry, is 0.10 μm or more and 0.20 μm or less, and A non-aqueous lithium storage element in which the difference between pore diameters D25 and D75 (D25-D75) is 0.20 μm or more and 0.45 μm or less. [2] 2. The nonaqueous lithium storage element according to item 1, wherein the positive electrode active material layer contains 0.01% by mass or more and 5.0% by mass or less of lithium carbonate based on the total mass of the positive electrode active material layer. [3] 3. The nonaqueous lithium storage element according to item 2, wherein the volume resistivity of the positive electrode active material layer is 1.5 Ωcm or more and 8.0 Ωcm or less. [4] 1000 μm of the surface of the positive electrode active material layer 2 More than 10000μm 2 Aggregate frequency of 0.5 particles / cm or less 2 Item 3. The nonaqueous lithium storage element according to item 2, wherein: [5] Item 1. A positive electrode precursor for use in the energy storage element according to item 1, the positive electrode precursor having a positive electrode current collector and a positive electrode active material layer disposed on the positive electrode current collector, the positive electrode active material layer including a carbon material containing at least activated carbon, a lithium transition metal oxide, and an alkali metal compound, wherein a mass ratio A1 of the carbon material in the positive electrode active material layer is 38% by mass or more and 60% by mass or less, a mass ratio A2 of the lithium transition metal oxide in the positive electrode active material layer is 15% by mass or more and 45% by mass or less, A1+A2 is 74% by mass or more and 93% by mass or less, A2 / A1 is 0.30 or more and 1.20 or less, and a specific surface area B of the lithium transition metal oxide measured by a BET method is 7.5 m 2 / g or more 11.0m 2 / g or less, and the D of the lithium transition metal oxide 10 C1, the lithium transition metal oxide D 90 2. A positive electrode precursor for use in an electric storage device according to item 1, wherein C2 / C1 is 10 or more and 25 or less, where C2 is C2. [6] 6. The positive electrode precursor according to item 5, wherein the alkali metal compound is lithium carbonate and the lithium transition metal oxide is lithium iron phosphate. [7] A non-aqueous lithium storage element including a positive electrode having a positive electrode current collector and a positive electrode active material layer disposed on the positive electrode current collector, a negative electrode, a separator, and a non-aqueous electrolyte solution containing lithium ions, The positive electrode active material layer contains a carbon material containing at least activated carbon, a lithium transition metal oxide, and an alkali metal compound, wherein a mass ratio X1 of the carbon material in the positive electrode active material layer is 43 mass% or more and 74 mass% or less, a mass ratio X2 of the lithium transition metal oxide in the positive electrode active material layer is 23 mass% or more and 55 mass% or less, X2 / X1 is 0.30 or more and 1.20 or less, and X1+X2 is 92.5 mass% or more and 99.3 mass% or less, and a specific surface area Y of the lithium transition metal oxide measured by a BET method is 7.5 m 2 / g or more 11.0m 2 / g or less, and D of the lithium transition metal oxide 10 Z1, the lithium transition metal oxide D 90 2. The nonaqueous lithium storage element according to item 1, wherein Z2 / Z1 is 10 or more and 25 or less, where Z2 is Z2 / Z1. [8] 8. The nonaqueous lithium storage element according to item 7, wherein the alkali metal compound is lithium carbonate and the lithium transition metal oxide is lithium iron phosphate. [9] An electric storage element including: a positive electrode including a positive electrode active material layer disposed on a positive electrode current collector; a negative electrode including a negative electrode active material layer disposed on a negative electrode current collector; a separator; and an electrolytic solution, the positive electrode current collector is a non-porous aluminum foil, there is no undercoat layer on the positive electrode current collector, and the positive electrode active material layer is formed directly on the positive electrode current collector; the positive electrode active material layer contains activated carbon as a positive electrode active material, The electric storage element is disassembled and removed, and the interface resistance between the positive electrode active material layer and the positive electrode current collector of the positive electrode is 0.05 Ωcm 2 More than 5.00Ωcm2 is as follows, and 1000 μm to 10000 μm on the surface of the positive electrode obtained by disassembling and taking out the storage battery element 2 or more 2 The following aggregate frequency is 0.5 pieces / cm 2 or less, the non-aqueous lithium storage battery element according to item 1.

[10] The positive electrode active material layer contains a lithium transition metal oxide as a positive electrode active material, and the lithium transition metal oxide has the following formula: Li x Ni a Co b Al (1-a-b) O2 {where x satisfies 0 ≦ x ≦ 1, and a and b satisfy 0.2 < a < 0.97 and 0.2 < b < 0.97.}, Li x Ni c Co d Mn (1-c-d) O2 {where x satisfies 0 ≦ x ≦ 1, and c and d satisfy 0.2 < c < 0.97 and 0.2 < d < 0.97.}, 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.}, or Li z V2(PO4)3 {where z satisfies 0 ≦ z ≦ 3.}, the non-aqueous lithium storage battery element according to item 9.

[11] The positive electrode active material layer contains a lithium transition metal oxide as a positive electrode active material, and the lithium transition metal oxide is lithium iron phosphate, the non-aqueous lithium storage battery element according to item 9 or 10.

[12] Item 12. The nonaqueous lithium storage element according to item 11, wherein the lithium transition metal oxide is lithium iron phosphate, and the ratio of the 3.4-3.0 V capacity (mAh) to the 4.0-2.0 V capacity (mAh) of the nonaqueous lithium storage element is 25 to 82%.

[13] The interface resistance between the positive electrode active material layer of the positive electrode and the positive electrode current collector is A [Ωcm 2 and a concentration of lithium fluoride contained in the negative electrode relative to the weight of the negative electrode active material layer is B [mmol / g], A / B is 0.02 to 250.

[14] A negative electrode for use in the nonaqueous lithium storage element according to item 1, the negative electrode comprising a negative electrode current collector and a negative electrode active material layer on one or both surfaces of the negative electrode current collector, the negative electrode active material layer comprising a negative electrode active material made of graphite capable of absorbing and desorbing lithium ions, (1) to (4) below: (1) The average thickness of the material constituting the negative electrode active material layer is 0.2 μm or more and 1.0 μm or less; (2) The pore size of the negative electrode active material layer is 0.15 μm or more and 0.70 μm or less. (3) The negative electrode active material layer has a specific surface area of ​​8 m2 calculated based on the mass of the negative electrode active material layer. 2 / g or more 40m 2 / g or less, and (4) The frequency of aggregates on the surface of the negative electrode is 0 pieces / cm 2 More than 1.0 pieces / cm 2 A negative electrode for use in a nonaqueous lithium storage element according to item 1, which satisfies all of the following conditions:

[15] Item 15. The negative electrode according to item 14, wherein 1.0≦(1.35−p) / t≦2.8 is satisfied, where t (μm) is an average thickness of a material constituting the negative electrode active material layer and p (μm) is a pore diameter of the negative electrode active material layer.

[16] The void volume of the negative electrode active material layer is 0.5 cm 3 / g or more 1.2cm 3 / g or less.

[17] Regarding the negative electrode active material layer, the specific surface area calculated based on the mass of the negative electrode active material layer is 12 m 2 / g or more and 30 m 2 / g or less, and the negative electrode according to item 14 or 15.

[18] A non-aqueous lithium storage element according to item 1, comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte containing lithium ions, wherein the positive electrode has a positive electrode current collector and a positive electrode active material layer provided on one or both sides of the positive electrode current collector, the positive electrode active material layer contains a positive electrode active material and a transition metal oxide represented by MO2 {where M is at least one selected from the group consisting of Co, Ni, and Mn.}, the positive electrode active material is Li x Mn (1-y) Fe y and contains a compound represented by PO4 {where x satisfies 0 ≦ x ≦ 1 and y satisfies 0 < y ≦ 1.}, the negative electrode has a negative electrode current collector and a negative electrode active material layer provided on one or both sides of the negative electrode current collector, when the discharge capacity per unit area of the positive electrode is A1 (mAh / cm 2 ) and the charge capacity per unit area of the negative electrode is B1 (mAh / cm 2 ), it satisfies 0.71 ≦ A1 / B1 ≦ 0.96, the non-aqueous lithium storage element according to item 1.

[19] the non-aqueous lithium storage element according to item 18, wherein the positive electrode active material layer further contains activated carbon.

[20] Regarding the negative electrode active material layer, when based on the total mass of the negative electrode active material layer, the non-aqueous lithium storage element according to item 18 or 19, which contains at least one selected from the group consisting of silicon, silicon compounds, tin, and tin compounds as the negative electrode active material in a proportion of 5 parts by mass or more and 30 parts by mass or less.

[21] Regarding the negative electrode active material layer, when based on the total mass of the negative electrode active material layer, contains a carbon material as the first negative electrode active material in a proportion of 50 parts by mass or more and 95 parts by mass or less, The non-aqueous lithium storage element according to item 18 or 19, which contains at least one of silicon and silicon compounds as the second negative electrode active material in a proportion of 5 parts by mass or more and 30 parts by mass or less.

[22] A non-aqueous lithium storage element precursor used for the non-aqueous lithium storage element according to item 1, wherein the non-aqueous lithium storage element precursor includes a positive electrode precursor, a negative electrode precursor, and a non-aqueous electrolyte containing lithium ions. The positive electrode precursor has a positive electrode current collector and a positive electrode active material layer provided on one or both sides of the positive electrode current collector. The positive electrode active material layer contains a positive electrode active material and a lithium compound composite. The positive electrode active material is Li x Mn (1-y) Fe y PO4 {where x satisfies 0 ≦ x ≦ 1 and y satisfies 0 < y ≦ 1.} and includes a compound represented by The lithium compound composite is a composite of a lithium compound and a transition metal oxide represented by MO2 {where M is one selected from the group consisting of Co, Ni, and Mn.} The negative electrode precursor has a negative electrode current collector and a negative electrode active material layer provided on one or both sides of the negative electrode current collector. When the charge capacity per unit area of the positive electrode precursor is A2 (mAh / cm 2 ), the discharge capacity per unit area of the positive electrode precursor is A3 (mAh / cm 2 ), and the charge capacity per unit area of the negative electrode precursor is B2 (mAh / cm 2 ), then 0.65 ≦ A3 / A2 ≦ 0.93 is satisfied, and 1.03 ≦ B2 / A3 ≦ 1.26 is satisfied. Non-aqueous lithium storage element precursor. [Advantages of the Invention]

[0042] According to the present disclosure, a positive electrode precursor, a negative electrode, and a storage element using these are provided, which can improve one or more of the problems in the following first to fifth embodiments.

[0043] According to the first embodiment of the present disclosure, it is possible to provide a nonaqueous lithium storage element and the like that has excellent low-temperature power density, suppression of micro-short circuits during low-temperature cycle tests, and durability in high-power cycles from low to high temperatures.

[0044] According to the second embodiment of the present disclosure, it is possible to provide a positive electrode precursor that has high capacity and low resistance and can be pre-doped into a negative electrode in a short time, and a nonaqueous lithium storage element using the same.

[0045] According to the third embodiment of the present disclosure, it is possible to provide an energy storage element or the like that has low resistance and excellent vibration resistance and high-temperature durability.

[0046] According to the fourth embodiment of the present disclosure, it is possible to provide a nonaqueous lithium storage element or the like that suppresses micro-short circuits in a pre-doping step, has low internal resistance, and is excellent in cycle durability over a wide temperature range, and also to provide a negative electrode for producing the same.

[0047] According to the fifth embodiment of the present disclosure, it is possible to provide a nonaqueous lithium storage element and the like that has excellent discharge capacity and energy density per unit voltage in a low voltage region and can suppress an increase in resistance in a high-temperature environment. DETAILED DESCRIPTION OF THE INVENTION

[0048] Examples of embodiments of the present disclosure will be described in detail below, but the present disclosure is not limited to the following embodiments. The upper and lower limits of each numerical range in the present disclosure can be arbitrarily combined to form any numerical range.

[0049] Summary of the Disclosure In the present disclosure, in order to improve one or more characteristics required of an energy storage element, the configuration of each member constituting the energy storage element has been approached according to the following first to fifth embodiments. Note that, since the first to fifth embodiments all relate to the configuration of each member constituting the energy storage element, these configurations can be combined in any manner.

[0050] First Embodiment In the first embodiment, the mass fraction, pore volume, and pore size of the positive electrode active material layer containing activated carbon and an alkali transition metal oxide (particularly, iron phosphate oxide) are adjusted within specific ranges. This improves low-temperature power density and suppresses micro-short circuits during low-temperature cycle testing, even though the inclusion of lithium iron phosphate can lead to poor low-temperature performance. Furthermore, it improves high-power cycle durability over a wide temperature range, from low to high temperatures. This enables nonaqueous lithium energy storage devices with the same electrode and cell specifications to be shipped in tropical and cold regions, leading to increased productivity. This is primarily because the charge / discharge reaction within the electrode proceeds more uniformly, thereby suppressing deterioration and micro-short circuits caused by uneven charge / discharge reactions. Previously, there had been no examples focusing on suppressing deterioration and micro-short circuits caused by uneven charge / discharge reactions within the electrode when the positive electrode active material layer contains activated carbon and lithium iron phosphate. Therefore, it was unexpected that the first embodiment leads to improvements in low-temperature power density, micro-short circuits during low-temperature cycle testing, and high-power cycle durability over a wide temperature range.

[0051] Second Embodiment In a second embodiment, the composition ratio of a positive electrode active material layer containing activated carbon, a lithium transition metal oxide, and an alkali metal compound, the specific surface area of ​​the lithium transition metal compound, and the particle size of the lithium transition metal oxide are adjusted to specific ranges. This allows for a high-capacity, low-resistance positive electrode precursor that can be pre-doped into a negative electrode in a short time, and a nonaqueous lithium storage element using the same. In the past, there was no idea of ​​providing a positive electrode precursor that can be pre-doped into a negative electrode in a short time by promoting the decomposition of the alkali metal compound in a positive electrode precursor containing activated carbon, a lithium transition metal oxide, and an alkali metal compound. In fact, no such technology has been disclosed. Therefore, it is unexpected that pre-doping can be performed in a short time using this configuration.

[0052] Third Embodiment In a third embodiment, a non-porous positive electrode current collector without an undercoat layer is used to adjust the interface resistance between the positive electrode active material layer and the positive electrode current collector and the frequency of aggregates on the positive electrode surface within specific ranges. This allows for the provision of an energy storage device with low resistance, excellent vibration resistance, and high-temperature durability. The purpose of using aluminum foil with an undercoat layer or special processing (e.g., conductive undercoat, etching, expanding, punching, etc.) is thought to be to improve electrical contact between the current collector foil interface and the composite layer, thereby enhancing the high-output performance of the activated carbon electrode, and to maintain electrical contact between the positive electrode current collector and the positive electrode active material layer even after long-term use, thereby maintaining the high durability of the activated carbon electrode. However, there has been no technology to simultaneously improve low resistance, vibration resistance, and high-temperature durability in an energy storage device with an activated carbon electrode that uses aluminum foil without special processing as a current collector. Furthermore, the use of these special aluminum foils complicates the current collector manufacturing process and increases the cost of the energy storage device. In this regard, the inventors have noticed for the first time that low resistance performance, high temperature durability performance, and vibration resistance can be achieved without using special aluminum foil.

[0053] Fourth Embodiment In a fourth embodiment, the average thickness of the material constituting the negative electrode active material layer, the pore size of the negative electrode active material layer, the specific surface area, and the frequency of aggregates on the negative electrode surface are adjusted within specific ranges. This makes it possible to provide a negative electrode that can suppress micro-short circuits during the pre-doping process and provide a nonaqueous lithium storage element with low internal resistance and excellent cycle durability over a wide temperature range. The inventors have found that conventional nonaqueous lithium storage elements aimed at achieving high output are lacking in practicality, and more specifically, that there is room for improvement in micro-short circuits during the pre-doping process, internal resistance, and cycle durability over a wide temperature range. They have focused for the first time on improving these issues through the above-described configuration of the negative electrode.

[0054] Fifth Embodiment In a fifth embodiment, the positive electrode active material layer includes a positive electrode active material containing lithium manganese iron phosphate (LMFP) and / or lithium iron phosphate (LFP), and a transition metal oxide. The ratio of the positive electrode discharge capacity to the negative electrode charge capacity is adjusted to a specific range. This allows for the provision of a nonaqueous lithium storage battery element or the like that exhibits excellent discharge capacity and energy density per unit voltage in the low-voltage region and suppresses resistance increases in high-temperature environments. While prior art has been disclosed that aims to improve battery characteristics, accurately determining the amount of electricity that can be discharged and / or charged from a lithium-ion secondary battery is essential for the safe use of such a battery. Therefore, a technology for accurately estimating the state of charge (hereinafter sometimes abbreviated as "SOC") is required. A commonly used technology for estimating the SOC is the "OCV method," which measures the open circuit voltage (hereinafter sometimes abbreviated as "OCV") of a lithium-ion secondary battery and calculates the SOC based on the correlation between the SOC and the OCV. In lithium-ion secondary batteries containing lithium manganese iron phosphate (hereinafter sometimes abbreviated as "LMFP") or lithium iron phosphate as a positive electrode active material, the plateau voltage is flat and the voltage change in response to SOC changes at the end of discharge is steep, making SOC estimation using the OCV method difficult. Furthermore, the steep voltage drop in response to SOC changes at the end of discharge can lead to large errors in SOC estimation, which can lead to situations such as the device's battery running out without the user noticing. Therefore, the inventors focused for the first time on suppressing this rapid voltage drop at the end of discharge, thereby improving the accuracy of SOC estimation using the OCV method.

[0055] <Non-aqueous lithium storage element> In the present disclosure, the term "nonaqueous lithium storage element" (also simply referred to as "storage element") encompasses electric double layer capacitors (e.g., lithium ion capacitors), lithium ion secondary batteries, and the like. In general, nonaqueous lithium storage elements mainly comprise a positive electrode, a negative electrode, a separator, and an electrolyte. The electrolyte uses an organic solvent containing lithium ions (hereinafter also referred to as a "nonaqueous electrolyte"). Furthermore, electric double layer capacitors mainly comprise a positive electrode containing activated carbon, a negative electrode containing activated carbon, a separator, and an electrolyte. The components that make up these storage elements are described below.

[0056] <Positive electrode> The positive electrode precursor and positive electrode have a positive electrode current collector and a positive electrode active material layer containing a positive electrode active material disposed thereon (more specifically, disposed on one or both surfaces thereof). The positive electrode active material layer preferably contains a carbon material including activated carbon and lithium iron phosphate. The positive electrode active material layer may be formed directly on the positive electrode current collector or on an undercoat layer disposed on the positive electrode current collector. As described below, it is preferable to pre-dope the negative electrode with lithium ions during the energy storage device assembly process. A preferred pre-doping method involves assembling an energy storage device using a positive electrode precursor containing an alkali metal compound, a negative electrode, a separator, an outer casing, and a non-aqueous electrolyte solution, and then applying a voltage between the positive electrode precursor and the negative electrode. The alkali metal compound may be contained in the positive electrode precursor in any manner. For example, the alkali metal compound may be present between the positive electrode current collector and the positive electrode active material layer, or on the surface of the positive electrode active material layer. The alkali metal compound is preferably contained in a positive electrode active material layer formed on a positive electrode current collector of the positive electrode precursor. In the present disclosure, the positive electrode before the lithium doping step is defined as a "positive electrode precursor," and the positive electrode after the lithium doping step is defined as a "positive electrode."

[0057] (Cathode active material layer) The positive electrode active material layer preferably contains a carbon material containing activated carbon as the positive electrode active material and a lithium transition metal oxide or the like. The positive electrode active material layer may further contain optional components such as a conductive filler, a binder, a dispersion stabilizer, and a pH adjuster as necessary. Further, it is preferable that the positive electrode active material layer of the positive electrode precursor or the surface of the positive electrode active material layer further contains a lithium compound other than the positive electrode active material. If a lithium compound different from the positive electrode active material is contained in the positive electrode precursor, the lithium compound can serve as a dopant source of lithium ions in the pre-doping step, and lithium ions can be pre-doped into the negative electrode. A part of the lithium compound may remain in the positive electrode active material layer of the positive electrode or on the surface of the positive electrode active material layer.

[0058] ·Positive electrode active material The positive electrode active material includes a carbon material containing activated carbon and a lithium transition metal oxide such as lithium iron phosphate. The positive electrode active material may contain one or more types of carbon materials or the like in addition to activated carbon. As this carbon material, it is preferable to use carbon nanotubes, conductive polymers, or porous carbon materials, and more preferably activated carbon. One or more types of carbon materials may be mixed and used in the positive electrode active material.

[0059] ··Activated carbon There are no particular restrictions on the type of activated carbon and its raw material, but 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, when the mesopore volume derived from pores with a diameter of 20 Å or more and 500 Å or less calculated by the BJH method is V1 (cc / g) and the micropore volume derived from pores with a diameter of less than 20 Å calculated by the MP method is V2 (cc / g), (1) for high input / output characteristics, 0.3 < V1 ≤ 0.8 and 0.5 ≤ V2 ≤ 1.0 are satisfied, 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) is preferable. Also, (2) in order to obtain high energy density, 0.8 < V1 ≤ 2.5 and 0.8 < V2 ≤ 3.0 are satisfied, and the specific surface area measured by the BET method is 2,300 m 2 / g or more and 4,000 m2 / g or less (hereinafter also referred to as activated carbon 2) is preferred.

[0060] The BET specific surface area, mesopore volume, micropore volume, and average pore diameter of a positive electrode active material are determined by the following methods. A sample is vacuum-dried overnight at 200°C, and adsorption / desorption isotherms are measured using nitrogen as the adsorbate. Using the resulting adsorption isotherms, the BET specific surface area is calculated by the multipoint BET method or the single-point BET method, the mesopore volume by the BJH method, and the micropore volume by the MP method. The BJH method is a calculation method commonly used to analyze mesopores and was proposed by Barrett, Joyner, Halenda, et al. (Non-Patent Document 1). The MP method is a method for determining micropore volume, micropore area, and micropore distribution using the "t-plot method" (Non-Patent Document 2), and was devised by RS Mikhail, Brunauer, and Bodor (Non-Patent Document 3). The average pore diameter refers to the total pore volume per mass of a sample, which is obtained by measuring the equilibrium adsorption amounts of nitrogen gas at liquid nitrogen temperature under various relative pressures, divided by the BET specific surface area. Note that, except for the case where V1 is the upper limit and V2 is the lower limit, any combination of the upper and lower limits may be used. Below, the above (1) activated carbon 1 and (2) activated carbon 2 will be explained individually and in order.

[0061] ···Activated carbon 1 The mesopore volume V1 of the activated carbon 1 is preferably greater than 0.3 cc / g in order to improve the input / output characteristics when the positive electrode material is incorporated into an energy storage device. V1 is preferably 0.8 cc / g or less in order to prevent a decrease in the bulk density of the positive electrode. V1 is more preferably 0.35 cc / g or more and 0.7 cc / g or less, and even more preferably 0.4 cc / g or more and 0.6 cc / g or less.

[0062] The micropore volume V2 of the activated carbon 1 is preferably 0.5 cc / g or more to increase the specific surface area of ​​the activated carbon and the capacity. V2 is preferably 1.0 cc / g or less to reduce the bulk of the activated carbon, increase the density as an electrode, and increase the capacity per unit volume. V2 is more preferably 0.6 cc / g or more and 1.0 cc / g or less, and even more preferably 0.8 cc / g or more and 1.0 cc / g or less.

[0063] The ratio of mesopore volume V1 to micropore volume V2 (V1 / V2) is preferably in the range of 0.3≦V1 / V2≦0.9. That is, from the viewpoint of increasing the ratio of mesopore volume to micropore volume to an extent that can suppress a decrease in output characteristics while maintaining high capacity, V1 / V2 is preferably 0.3 or more. On the other hand, from the viewpoint of increasing the ratio of micropore volume to mesopore volume to an extent that can suppress a decrease in capacity while maintaining high output characteristics, V1 / V2 is preferably 0.9 or less. A more preferable range for V1 / V2 is 0.4≦V1 / V2≦0.7, and an even more preferable range for V1 / V2 is 0.55≦V1 / V2≦0.7.

[0064] The average pore diameter of activated carbon 1 is preferably 17 Å or more, more preferably 18 Å or more, and even more preferably 20 Å or more, from the viewpoint of maximizing the output of the resulting energy storage element. Furthermore, from the viewpoint of maximizing the capacity, the average pore diameter of activated carbon 1 is preferably 25 Å or less. The BET specific surface area of ​​activated carbon 1 is 1,500 m 2 / g or more 3,000m 2 / g or less, and 1,500m 2 / g or more 2,500m 2 / g or less is more preferable. 2 / g or more, a good energy density is easily obtained, while a BET specific surface area of ​​3,000 m 2 When the electrode has a capacitance of 0.15 or less, it is not necessary to add a large amount of binder to maintain the strength of the electrode, and therefore the performance per volume of the electrode is improved.

[0065] Activated carbon 1 having the above-described characteristics can be obtained, for example, using the raw materials and processing methods described below. The carbon source used as the raw material for activated carbon 1 is not particularly limited. Examples include plant-based raw materials such as wood, wood flour, coconut shells, pulp manufacturing by-products, bagasse, and blackstrap molasses; fossil-based raw materials such as peat, lignite, brown coal, bituminous coal, anthracite, petroleum distillation residue components, petroleum pitch, coke, and coal tar; various synthetic resins such as phenolic resins, vinyl chloride resins, vinyl acetate resins, melamine resins, urea resins, resorcinol resins, celluloid, epoxy resins, polyurethane resins, polyester resins, and polyamide resins; synthetic rubbers such as polybutylene, polybutadiene, and polychloroprene; other synthetic woods, synthetic pulps, and carbonized versions of these. Among these raw materials, plant-based raw materials such as coconut shells and wood flour, and carbonized versions of these, are preferred from the standpoints of mass production and cost, with coconut shell carbonized versions being particularly preferred.

[0066] As a method for carbonizing and activating these raw materials to produce the activated carbon 1, known methods such as a fixed bed method, a moving bed method, a fluidized bed method, a slurry method, a rotary kiln method, etc. can be used.

[0067] Examples of carbonization methods for these raw materials include a method of firing them at about 400 to 700°C (preferably 450 to 600°C) for about 30 minutes to 10 hours using an inert gas such as nitrogen, carbon dioxide, helium, argon, xenon, neon, carbon monoxide, or combustion exhaust gas, or a mixed gas containing these inert gases as the main component.

[0068] The carbonized material obtained by the carbonization method described above is preferably activated by a gas activation method in which the carbonized material is fired using an activation gas such as steam, carbon dioxide, or oxygen. Of these, the method using steam or carbon dioxide as the activation gas is preferred. In this activation method, the carbonized material is preferably activated by heating the carbonized material to 800 to 1,000°C over 3 to 12 hours (preferably 5 to 11 hours, more preferably 6 to 10 hours) while supplying the activation gas at a rate of 0.5 to 3.0 kg / h (preferably 0.7 to 2.0 kg / h).

[0069] Furthermore, prior to the activation treatment of the carbonized material described above, the carbonized material may be subjected to primary activation in advance. In this primary activation, a method of gas activation in which the carbon material is fired at a temperature of less than 900°C using an activation gas such as water vapor, carbon dioxide, or oxygen is preferably employed.

[0070] The activated carbon 1 can be produced by appropriately combining the calcination temperature and calcination time in the carbonization method described above with the activation gas supply amount, temperature rise rate, and maximum activation temperature in the activation method.

[0071] The average particle diameter of the activated carbon 1 is preferably 2 to 20 μm. If the average particle diameter is 2 μm or more, the density of the active material layer is high, and therefore the capacity per electrode volume tends to be high. Note that a small average particle diameter may result in the drawback of low durability, but if the average particle diameter is 2 μm or more, such a drawback is unlikely to occur. On the other hand, if the average particle diameter is 20 μm or less, it tends to be more suitable for high-speed charging and discharging. The average particle diameter of the activated carbon 1 is more preferably 2 to 15 μm, and even more preferably 3 to 10 μm.

[0072] ···Activated carbon 2 The mesopore volume V1 of the activated carbon 2 is preferably greater than 0.8 cc / g from the viewpoint of increasing the output characteristics when the positive electrode material is incorporated into an energy storage device. V1 is preferably 2.5 cc / g or less from the viewpoint of suppressing a decrease in the capacity of the energy storage device. V1 is more preferably 1.00 cc / g or more and 2.0 cc / g or less, and even more preferably 1.2 cc / g or more and 1.8 cc / g or less.

[0073] The micropore volume V2 of activated carbon 2 is preferably greater than 0.8 cc / g to increase the specific surface area of ​​the activated carbon and increase its capacity. V2 is preferably 3.0 cc / g or less to increase the density of the activated carbon as an electrode and increase its capacity per unit volume. V2 is more preferably greater than 1.0 cc / g and less than 2.5 cc / g, and even more preferably 1.5 cc / g or more and less than 2.5 cc / g.

[0074] The activated carbon 2 having the above-mentioned mesopores and micropores has a higher BET specific surface area than activated carbons used in conventional electric double layer capacitors or lithium ion capacitors. The specific value of the BET specific surface area of ​​the activated carbon 2 is 2,300 m 2 / g or more 4,000m 2 / g or less, and 2 / g or more 4,000m 2 / g or less is more preferable, and 3,200m 2 / g or more 3,800m 2 / g or less. 2 / g or more, a good energy density is easily obtained, and the BET specific surface area is 4,000 m 2 When the electrode has a capacitance of 0.15 or less, it is not necessary to add a large amount of binder to maintain the strength of the electrode, and therefore the performance per volume of the electrode is improved.

[0075] The activated carbon 2 having the above-described characteristics can be obtained, for example, using the raw materials and processing methods described below. The carbonaceous material used as the raw material for the activated carbon 2 is not particularly limited as long as it is a carbon source typically used as an activated carbon raw material, and examples thereof include plant-based raw materials such as wood, wood flour, and coconut shells; fossil-based raw materials such as petroleum pitch and coke; and various synthetic resins such as phenolic resin, furan resin, vinyl chloride resin, vinyl acetate resin, melamine resin, urea resin, and resorcinol resin. Among these raw materials, phenolic resin and furan resin are particularly preferred because they are suitable for producing activated carbon with a high specific surface area.

[0076] Methods for carbonizing these raw materials or heating methods during activation treatment include known methods such as fixed bed, moving bed, fluidized bed, slurry, and rotary kiln. The atmosphere used during heating is an inert gas such as nitrogen, carbon dioxide, helium, or argon, or a gas mixture containing these inert gases as the main component with other gases. Carbonization is generally performed at a temperature of about 400 to 700°C for about 0.5 to 10 hours.

[0077] Methods for activating carbides include gas activation, which involves calcining using an activation gas such as steam, carbon dioxide, or oxygen, and alkali metal activation, which involves mixing with a lithium compound and then heat-treating. The alkali metal activation method is preferred for producing activated carbon with a high specific surface area. For example, this activation method involves mixing the carbide with an alkali metal compound such as KOH or NaOH in a mass ratio of 1:1 or more (the amount of the alkali metal compound is equal to or greater than the amount of the carbide), followed by heating in an inert gas atmosphere at 600 to 900°C for 0.5 to 5 hours. The alkali metal compound is then removed by washing with acid and water, followed by drying.

[0078] To increase the micropore volume without increasing the mesopore volume, it is recommended to mix a larger amount of carbide with KOH during activation. To increase both the micropore volume and the mesopore volume, it is recommended to use a larger amount of KOH. Furthermore, to mainly increase the mesopore volume, it is preferable to perform steam activation after alkali activation treatment.

[0079] The average particle size of the activated carbon 2 is preferably 2 μm or more and 20 μm or less, and more preferably 3 μm or more and 10 μm or less.

[0080] Use of activated carbon Activated carbons 1 and 2 may each be a single type of activated carbon, or a mixture of two or more types of activated carbons that exhibit the aforementioned characteristic values ​​as a whole mixture. The activated carbons 1 and 2 may be used by selecting either one of them, or by mixing both. The positive electrode active material may include a material other than activated carbons 1 and 2 (e.g., an activated carbon that does not have the specific V1 and / or V2 described above, or a material other than activated carbon (e.g., a conductive polymer, etc.)).

[0081] In an exemplary embodiment, when the content of activated carbon 1, the content of activated carbon 2, or the combined content of activated carbons 1 and 2 in the positive electrode active material layer of the positive electrode precursor, i.e., the mass proportion of the carbon material in the positive electrode active material layer, is A1, A1 is 38% by mass or more and 60% by mass or less, preferably 40% by mass or more and 60% by mass or less, and more preferably 45% by mass or more and 60% by mass or less. When A1 is 38% by mass or more, the contact area between the highly electrically conductive carbon material and the alkali metal compound increases, thereby accelerating the oxidation reaction of the alkali metal compound in the pre-doping step and enabling pre-doping to be completed in a short time. When A1 is 60% by mass or less, the bulk density of the positive electrode active material layer increases, resulting in a high capacity.

[0082] When the content of activated carbon 1, the content of activated carbon 2, or the total content of activated carbons 1 and 2 in the positive electrode active material layer of the positive electrode, i.e., the mass proportion of the carbon material in the positive electrode active material layer, is designated as X1, X1 is preferably 43% by mass or more and 74% by mass or less. When X1 is 43% by mass or more, the area for ion adsorption and desorption during charge and discharge is increased, thereby enabling low resistance. When X1 is 74% by mass or less, high capacity can be achieved.

[0083] Lithium transition metal oxides The positive electrode active material may contain one or more lithium transition metal oxides as the positive electrode active material. The lithium transition metal oxide includes a transition metal oxide capable of occluding and releasing lithium. There is no particular limitation on the transition metal oxide used as the positive electrode active material. Examples of the transition metal oxide include oxides containing at least one element selected from the group consisting of cobalt (Co), nickel (Ni), manganese (Mn), iron (Fe), vanadium (V), titanium (Ti), and chromium (Cr). Of course, the examples of the transition metal oxide are not limited thereto.

[0084] By using a lithium transition metal oxide as the positive electrode active material in admixture, the adhesion at the interface between the positive electrode current collector and the positive electrode active material layer can be further enhanced, and low resistance performance can be provided even after vibration conditions. As the lithium transition metal oxide, a transition metal oxide represented by the following formula is preferable, and lithium iron phosphate is more preferable.

[0085] Specifically, as the transition metal oxide, the following formula: Li x CoO2 {where x satisfies 0 ≦ x ≦ 1.}, Li x NiO2 {where x satisfies 0 ≦ x ≦ 1.}, Li x Ni y M (1-y) O2 {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 0.2 < y < 0.97.}, Li x Ni 1 / 3 Co 1 / 3 Mn 1 / 3 O2 {where x satisfies 0 ≦ x ≦ 1.}, Li x MnO2 {where x satisfies 0 ≦ x ≦ 1.}, α-Li x FeO2 {where x satisfies 0 ≦ x ≦ 1.}, Li x VO2 {where x satisfies 0 ≦ x ≦ 1.}, Li xCrO2{where x satisfies 0≦x≦1.} Li x FePO4{where x satisfies 0≦x≦1.} Li x MnPO4{where x satisfies 0≦x≦1.} Li z V2(PO4)3{where z satisfies 0≦z≦3.} Li x Mn2O4{where x satisfies 0≦x≦1.} 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.} Li x Ni a Co b Al (1-a-b) O2{where x satisfies 0≦x≦1, and a and b satisfy 0.05 < a < 0.97 and 0.2 < b < 0.97.} Li x Ni c Co d Mn (1-c-d) O2{where x satisfies 0≦x≦1, and c and d satisfy 0.05 < c < 0.97 and 0.05 < d < 0.97.} Li x Mn e Fe (1-e) PO4{where x satisfies 0≦x≦1, and e satisfies 0.05 < e < 0.97.} Li x Mn (1-y) Fe y PO4{where x satisfies 0≦x≦1, and y satisfies 0 < y ≦ 1.} Compounds represented by the formula etc. may be mentioned.

[0086] Among these, from the viewpoints of high capacity, low resistance, cycle characteristics, decomposition of alkali metal compounds, and suppression of loss of the positive electrode active material during pre-doping, the above formula Li x Ni a Co b Al (1-a-b)O2, Li x Ni c Co d Mn (1-c-d) O2, Li x CoO2, Li x Mn2O4, Li x FePO4, Li x MnPO4, Li x Mn e Fe (1-e) PO4 or Li z Compounds represented by V2(PO4)3 are preferred.

[0087] If the positive electrode precursor contains an alkali metal compound different from the positive electrode active material, the alkali metal compound serves as a dopant source for the alkali metal during pre-doping, and the negative electrode can be pre-doped. Therefore, even if the transition metal compound does not contain lithium ions in advance (i.e., even if x = 0 or z = 0 in the above formula), the positive electrode precursor can be used as a non-aqueous lithium storage element for electrochemical charging and discharging.

[0088] The average particle size of the lithium transition metal oxide is preferably 0.1 to 20 μm. When the average particle size is 0.1 μm or more, the density of the active material layer is high, and therefore the capacity per electrode volume tends to be high. A small average particle size can result in the drawback of low durability, but when the average particle size is 0.1 μm or more, such a drawback is unlikely to occur, that is, the durability of the nonaqueous lithium energy storage element is easily ensured. When the average particle size is 20 μm or less, the element tends to be more suitable for high-rate charge and discharge. The average particle size of the lithium transition metal oxide is more preferably 0.5 to 15 μm, and even more preferably 1 to 10 μm.

[0089] Furthermore, it is preferable that the average particle size of the lithium transition metal oxide is smaller than that of the carbon material described above. If the average particle size of the lithium transition metal oxide is small, the lithium transition metal oxide can be arranged in the voids formed by the carbon material having a large average particle size, thereby reducing the resistance.

[0090] Regarding the structure of the lithium transition metal oxide, from the viewpoints of high capacity, low resistance, cycle characteristics, decomposition of the alkali metal compound, suppression of capacity degradation of the lithium transition metal oxide during pre-doping, and suppression of loss of the positive electrode active material during pre-doping, the lithium transition metal oxide is preferably at least one selected from the group consisting of layered compounds, spinel compounds, and olivine compounds, more preferably an olivine compound, and even more preferably lithium iron phosphate. If a lithium compound different from the positive electrode active material is contained in the positive electrode precursor, the lithium compound becomes a dopant source for lithium ions during pre-doping, and the negative electrode can be pre-doped.

[0091] Lithium iron phosphate The lithium transition metal oxide is preferably lithium iron phosphate (LiFePO4). By further including lithium iron phosphate as the positive electrode active material in addition to a carbon material containing activated carbon, high capacity characteristics can be provided in addition to the high output characteristics of the carbon material. That is, there is a tendency to provide an electricity storage device that combines high output characteristics such as an electric double layer capacitor or a lithium ion capacitor with high capacity characteristics such as a lithium ion secondary battery.

[0092] The average particle size of lithium iron phosphate is preferably 0.1 to 20 μm. When the average particle size of lithium iron phosphate is 0.1 μm or more, the density of the active material layer is high, which tends to increase the capacity per electrode volume, and also makes it easier to ensure the durability of the nonaqueous lithium storage element. When the average particle size of lithium iron phosphate is 20 μm or less, it tends to be more suitable for high-speed charging and discharging. The average particle size of lithium iron phosphate is more preferably 0.5 to 15 μm, and even more preferably 1 to 10 μm. The average particle size of lithium iron phosphate is preferably smaller than the average particle size of the carbon material described above. If the average particle size of lithium iron phosphate is small, lithium iron phosphate can be arranged in the voids formed by the carbon material with a large average particle size, thereby reducing the resistance.

[0093] Furthermore, when the positive electrode active material layer contains lithium iron phosphate as the lithium transition metal oxide, it is desirable to coat the surface of the lithium iron phosphate with carbon in order to reduce resistance. When the positive electrode active material layer contains lithium iron phosphate as the lithium transition metal oxide, the ratio of the discharge capacity (mAh) from 3.4 V to 3.0 V to the discharge capacity (mAh) at a 1C rate from 4.0 V to 2.0 V of the nonaqueous lithium energy storage element is preferably adjusted to 25% to 82%, more preferably 50% to 70%. The upper and lower limits can be arbitrarily combined. When the ratio is 25% to 82%, the internal resistance of the completed cell can be reduced, the initial low resistance can be maintained even when used in a vibration environment, and gas generation in a high-temperature environment can be suppressed. The principle behind this effect is not entirely clear, but is presumed to be as follows.

[0094] If the ratio of the 3.4-3.0V capacity (mAh) to the 4.0-2.0V capacity (mAh) of the energy storage element is 25% or more, the higher ratio of rigid lithium iron phosphate compared to activated carbon destroys the aluminum oxide layer on the aluminum surface, making it easier to establish conductivity with the aluminum, reducing the internal resistance when the cell is completed and maintaining the initial low resistance even after exposure to vibration. Furthermore, because there is less activated carbon in the positive electrode active material layer, gas generation due to solvent oxidation reactions on the positive electrode activated carbon that occurs at high temperatures can be suppressed.

[0095] If the ratio of the 3.4-3.0V capacity (mAh) to the 4.0-2.0V capacity (mAh) of the energy storage element is 82% or less, a conductive network between the lithium iron phosphates is formed via the highly electrically conductive activated carbon, reducing the internal resistance of the completed cell and maintaining the initial low resistance even after exposure to vibration. Furthermore, because a certain amount of activated carbon is present in the positive electrode active material, a protective film is formed on the surface of the lithium iron phosphate through a reaction between the functional groups of the activated carbon and the electrolyte solvent, suppressing gas generation due to solvent oxidation on the lithium iron phosphate.

[0096] Mass ratio of lithium iron phosphate When the content of the carbon material in the positive electrode active material layer is X1 (mass%) and the content of lithium iron phosphate is X2 (mass%), the lower limit of the mass proportion of lithium iron phosphate (X2 / (X1+X2)) is preferably 0.40 or more, more preferably 0.70 or more, and the upper limit of the mass proportion of lithium iron phosphate is preferably 0.85 or less, more preferably 0.80 or less.

[0097] When the mass fraction of lithium iron phosphate is 0.40 or more, the presence of sufficient lithium iron phosphate increases the electrode density and improves the low-temperature power density per volume. Furthermore, the increased electrode density and thinner electrode thickness shorten the diffusion path of electrolyte ions, allowing reactions during low-temperature charge and discharge to proceed uniformly, thereby improving low-temperature cycle durability and suppressing micro-short circuits after cycling. Furthermore, the low activated carbon ratio suppresses electrolyte decomposition side reactions initiated by functional groups on the activated carbon at high temperatures, thereby improving high-temperature cycle durability. When the mass fraction of lithium iron phosphate is 0.95 or less, the proportion of carbon material containing activated carbon with excellent low-temperature input / output characteristics increases, thereby improving the low-temperature power density per volume. Furthermore, the increased proportion of carbon material containing activated carbon with excellent low-temperature input / output characteristics reduces low-temperature cycle durability and micro-short circuits after low-temperature cycle testing. Furthermore, during high-rate cycles, the load is concentrated on the carbon material containing activated carbon rather than on the lithium iron phosphate. However, the sufficient amount of carbon material containing activated carbon mitigates current concentration on the activated carbon particles during high-temperature cycles. This suppresses electrolyte decomposition side reactions initiated by the functional groups of the activated carbon at high temperatures, improving high-temperature cycle durability.

[0098] The mass proportion of lithium iron phosphate can be controlled, for example, by adjusting the composition of the carbon material containing activated carbon and lithium iron phosphate when preparing the positive electrode coating liquid.

[0099] By including a lithium transition metal oxide containing a lithium iron phosphate compound in the positive electrode active material, the adhesion at the interface between the positive electrode current collector and the positive electrode active material layer is further enhanced, and low resistance performance can be provided even after vibration conditions. As the lithium transition metal oxide, known materials used in lithium ion batteries can be used. One or more lithium transition metal oxides may be mixed and used in the positive electrode active material. As the lithium transition metal oxide, a compound represented by the formula described later and / or lithium iron phosphate is preferable.

[0100] ···Combined use of LFP and / or LMFP and activated carbon The above Li x Mn (1-y) Fe y PO4 {where x satisfies 0 ≦ x ≦ 1 and y satisfies 0 < y ≦ 1.} By using lithium iron phosphate (LFP) and / or lithium manganese iron phosphate (LMFP) represented by the formula and activated carbon in combination, the output characteristics of the positive electrode may be improved. In addition, in activated carbon, there is a proportional relationship between SOC and voltage. Therefore, by using activated carbon in combination, it becomes easier to suppress a rapid voltage drop at the end of discharge of the non-aqueous lithium storage element. In addition to this, in the voltage range excluding the plateau region of LFP and / or LMFP, it is also possible to estimate the SOC from the cell voltage of the non-aqueous lithium storage element.

[0101] ···BET specific surface area of lithium transition metal oxide When the BET specific surface area of the lithium transition metal oxide in the positive electrode precursor is B and the BET specific surface area of the lithium transition metal oxide in the positive electrode is Y, the specific surface area B or Y is preferably 7.5 m 2 / g or more and 11.0 m 2 / g or less, and more preferably 7.5 m 2 / g or more and 10 m 2 / g or less. If B or Y is 7.5 m 2 / g or more, the contact area between the lithium transition metal oxide and the carbon material increases, so the resistance can be reduced. When the specific surface area B or Y is 11.0 m 2If the carbon content is 0.01g or less, the carbon material required to maintain the conductivity of the lithium transition metal oxide can be reduced, and good contact between the highly conductive carbon material and the alkali metal compound can be maintained. Therefore, the oxidation reaction of the alkali metal compound is promoted in the pre-doping step, and pre-doping can be completed in a short time.

[0102] D of lithium transition metal oxides in the cathode precursor 10 (μm) and D 90 (μm) are C1 and C2, respectively, and the D of the lithium transition metal oxide in the positive electrode 10 (μm) and D 90 When Z1 and Z2 (μm) are used, respectively, C2 / C1 or Z2 / Z1 is preferably 10 or more and 25 or less, more preferably 10 or more and 23 or less, and even more preferably 10 or more and 20 or less. When C2 / C1 or Z2 / Z1 is 10 or more, the contact between the lithium transition metal oxides is improved, thereby reducing the amount of carbon material required to maintain electronic conductivity between the lithium transition metal oxides. Therefore, the proportion of lithium transition metal oxide in the positive electrode active material layer can be increased, resulting in higher capacity. When C2 / C1 or Z2 / Z1 is 25 or less, it tends to be more suitable for high-speed charge and discharge.

[0103] The average particle size of the lithium transition metal oxide is preferably 0.1 to 20 μm. If the average particle size is 0.1 μm or more, the density of the active material layer is high, and therefore the capacity per electrode volume tends to be high. If the average particle size is small, durability may be a drawback, but if the average particle size is 0.1 μm or more, such a drawback is unlikely to occur. If the average particle size is 20 μm or less, it tends to be more suitable for high-speed charge and discharge. The average particle size of the lithium transition metal oxide is more preferably 0.5 to 15 μm, and even more preferably 1 to 10 μm.

[0104] Furthermore, it is preferable that the average particle size of the lithium transition metal oxide is smaller than that of the activated carbon described above. If the average particle size of the lithium transition metal oxide is small, the lithium transition metal oxide can be arranged in the voids formed by the activated carbon having a large average particle size, thereby reducing the resistance.

[0105] where D 10 , D 90 The average particle size and the average particle diameter are the 10%, 90%, and 50% particle diameters on a volume basis measured by laser diffraction (ISO13320:2009), respectively.

[0106] Use of lithium transition metal oxides The lithium transition metal oxide may be one kind, or a mixture of two or more kinds of materials, each of which exhibits the above-mentioned characteristic values ​​as a whole mixture.

[0107] The positive electrode active material may contain a material other than the lithium transition metal oxide (e.g., a conductive polymer, etc.). In an exemplary embodiment, when the content of the lithium transition metal oxide in the positive electrode active material layer of the positive electrode precursor is A2, A2 is preferably 15% by mass or more and 45% by mass or less, more preferably 20% by mass or more and 45% by mass or less. When A2 is 15% by mass or more, the bulk density of the positive electrode active material layer increases, thereby enabling a high capacity. When A2 is 45% by mass or less, the contact area between the carbon material with high electrical conductivity and the alkali metal compound increases, thereby accelerating the oxidation reaction of the alkali metal compound in the pre-doping step and enabling pre-doping to be completed in a short time.

[0108] Furthermore, when the content of lithium transition metal oxide in the positive electrode active material layer of the positive electrode is X2, it is preferable that X2 is 23% by mass or more and 55% by mass or less. If X2 is 23% by mass or more, high capacity can be achieved. If X2 is 55% by mass or less, the area for ion adsorption and desorption becomes large, resulting in low resistance.

[0109] Mass fraction of lithium transition metal oxide The ratio A2 / A1 of the mass proportion A2 of the lithium transition metal oxide to the mass proportion A1 of the carbon material in the positive electrode precursor is preferably 0.30 to 1.20, more preferably 0.40 to 1.20, and even more preferably 0.40 to 1.15. When A2 / A1 is 0.30 or greater, the bulk density of the positive electrode active material layer can be increased, resulting in high capacity. When A2 / A1 is 1.20 or less, the electronic conduction between the activated carbon is enhanced, resulting in low resistance, and the contact area between the activated carbon and the alkali metal compound is increased, resulting in accelerated decomposition of the alkali metal compound. Furthermore, A1+A2 is preferably 74% to 93% by mass, more preferably 75% to 90% by mass, and even more preferably 77% to 90% by mass. When A1+A2 is 74% by mass or greater, the proportion of active material in the positive electrode precursor increases, resulting in high capacity due to the sufficient amount of lithium transition metal oxide, and low resistance due to the sufficient amount of activated carbon. When A1+A2 is 93 mass% or less, the positive electrode precursor can contain a sufficient amount of alkali metal compound, allowing a sufficient amount of alkali metal ions to be pre-doped into the negative electrode, thereby increasing the capacity of the nonaqueous lithium storage element.

[0110] Furthermore, the ratio X2 / X1 of the mass proportion X2 of the lithium transition metal oxide to the mass proportion X1 of the carbon material in the positive electrode is preferably 0.30 or more and 1.20 or less. When X2 / X1 is 0.30 or more, the bulk density of the positive electrode active material layer can be increased, resulting in high capacity. When X2 / X1 is 1.20 or less, the conductivity between the carbon materials is increased, resulting in low resistance. Furthermore, X1+X2 is preferably 92.5% by mass or more and 99.3% by mass or less. When X1+X2 is 92.5% by mass or more, the active material is sufficiently present in the positive electrode, resulting in high capacity and low resistance of the nonaqueous lithium storage battery element. When X1+X2 is 99.3% by mass or less, a nonaqueous lithium storage battery element with high electrode strength and excellent durability can be provided.

[0111] Average particle size of the positive electrode active material The average particle diameter of the positive electrode active material is preferably 0.5 to 20 μm. If the average particle diameter of the positive electrode active material is 1 μm or more, the density of the active material layer is high, and therefore the capacity per electrode volume tends to be high. If the average particle diameter of the positive electrode active material is small, durability may be reduced, but if the average particle diameter is 1 μm or more, durability is less likely to be reduced. If the average particle diameter of the positive electrode active material is 20 μm or less, it tends to be more suitable for high-speed charging and discharging. The average particle diameter of the positive electrode active material is more preferably 1 to 15 μm, and even more preferably 2 to 10 μm.

[0112] The average particle diameter of the positive electrode active material refers to the particle diameter at the point where the cumulative curve is 50% when the particle size distribution is measured using a particle size distribution analyzer and the total volume is taken as 100% (i.e., the 50% diameter (Median diameter)). This average particle diameter can be measured using a commercially available laser diffraction particle size distribution analyzer.

[0113] Positive electrode active material content The content of the positive electrode active material in the positive electrode active material layer is preferably 50 parts by mass or more and 97 parts by mass or less, based on the total mass of the positive electrode active material layer. The lower limit of the content of the positive electrode active material is more preferably 60 parts by mass or more, and even more preferably 70 parts by mass or more. The upper limit of the content of the positive electrode active material is more preferably 97 parts by mass or less. By having the content of the positive electrode active material in the positive electrode active material layer be 50 parts by mass or more and 97 parts by mass or less, favorable charge / discharge characteristics are exhibited.

[0114] Alkali metal compounds The positive electrode active material layer in the positive electrode precursor preferably contains an alkali metal compound, preferably a lithium compound. The positive electrode active material layer of the positive electrode after the doping process may also contain an alkali metal compound. The lithium compound is not particularly limited as long as it can decompose at the positive electrode during the lithium doping process described below and release lithium ions. The lithium compound is preferably at least one selected from the group consisting of lithium carbonate, lithium oxide, lithium hydroxide, lithium fluoride, lithium chloride, lithium oxalide, lithium iodide, lithium nitride, lithium oxalate, and lithium acetate. Among these, lithium carbonate, lithium oxide, and lithium hydroxide are more suitable, and lithium carbonate is even more preferred from the viewpoints of ease of handling in air and low hygroscopicity. Such lithium compounds decompose upon application of voltage, function as a dopant source for lithium doping into the negative electrode, and form pores in the positive electrode active material layer, thereby forming a positive electrode with excellent electrolyte retention and ionic conductivity.

[0115] Various methods can be used to microparticulate the lithium compound. For example, grinders such as a ball mill, bead mill, ring mill, jet mill, and rod mill can be used. The average particle size of the lithium compound is preferably 0.1 μm or more and 10 μm or less. An average particle size of 0.1 μm or more provides excellent dispersibility in the positive electrode precursor. An average particle size of 10 μm or less increases the surface area of ​​the lithium compound, allowing the decomposition reaction to proceed efficiently. Furthermore, the average particle size of the lithium compound is preferably smaller than the average particle size of the carbon material described above. If the average particle size of the lithium compound is smaller than the average particle size of the carbon material, the electronic conductivity of the positive electrode active material layer is enhanced, which can contribute to reducing the resistance of the electrode body or the energy storage device.

[0116] The positive electrode active material in the positive electrode precursor preferably contains two lithium compounds with different average particle sizes. For example, the positive electrode active material in the positive electrode precursor preferably contains a first lithium compound with an average particle size of more than 1 μm and not more than 10 μm and a second lithium compound with an average particle size of 0.1 μm or more and not more than 1 μm. By containing two lithium compounds with different average particle sizes and adjusting the average particle size and composition, the pore size of the positive electrode active material layer can be appropriately adjusted.

[0117] The positive electrode precursor and the positive electrode coating fluid may contain one alkali metal compound or two or more alkali metal compounds. The positive electrode precursor and the positive electrode coating fluid may contain at least one alkali metal compound, where M is one or more selected from lithium (Li), sodium (Na), potassium (K), rubidium (Rb), and cesium (Cs). The positive electrode precursor and the positive electrode coating fluid may contain one or more oxides such as MO, hydroxides such as MOH, halides such as MF and MCl, and carboxylates such as RCOOM (where R is H, an alkyl group, or an aryl group). The alkali metal compound may be one or more alkaline earth metal carbonates, alkaline earth metal oxides, alkaline earth metal hydroxides, alkaline earth metal halides, or alkaline earth metal carboxylates selected from the group consisting of BeCO, MgCO, CaCO, SrCO, and BaCO.

[0118] Mass proportion of alkali metal compounds The mass proportion A3 of the alkali metal compound contained in the positive electrode active material layer of the positive electrode precursor is preferably 10 mass% or more and 30 mass% or less. If A3 is 10 mass% or more, a sufficient amount of alkali metal ions can be pre-doped into the negative electrode, thereby increasing the capacity of the nonaqueous lithium storage battery element. If A3 is 30 mass% or less, electronic conductivity in the positive electrode precursor can be increased, thereby efficiently decomposing the alkali metal compound.

[0119] The mass proportion X3 of the alkali metal compound contained in the positive electrode active material layer of the positive electrode is preferably 0.6 mass% or more and 7.5 mass% or less. When X3 is 0.6 mass% or more, fluorine ions generated during high-load charge-discharge cycles can be adsorbed, improving the high-load charge-discharge cycle characteristics. When X3 is 7.5 mass% or less, gas generation due to decomposition of the alkali metal compound can be suppressed, improving the high-load charge-discharge cycle characteristics.

[0120] When the positive electrode precursor contains two or more of the above alkali metal compounds or alkaline earth metal compounds in addition to the alkali metal compound, the positive electrode precursor is preferably prepared so that the total amount of the alkali metal compounds and alkaline earth metal compounds is 10% by mass or more and 30% by mass or less in the positive electrode active material layer per side of the positive electrode precursor.

[0121] When the positive electrode coating fluid contains two or more of the above alkali metal compounds or alkaline earth metal compounds in addition to the alkali metal compound, the positive electrode coating fluid is preferably prepared so that the total amount of the alkali metal compounds and alkaline earth metal compounds is 10 mass % or more and 30 mass % or less with respect to the total solid content in the positive electrode coating fluid.

[0122] When the positive electrode contains two or more of the above alkali metal compounds or alkaline earth metal compounds in addition to the alkali metal compound, the total amount of the alkali metal compounds and alkaline earth metal compounds is preferably 0.6% by mass or more and 7.5% by mass or less in the positive electrode active material layer per one side of the positive electrode.

[0123] The mass proportion of the lithium compound, preferably lithium carbonate, contained in the positive electrode precursor is preferably 5% by mass or more and 40% by mass or less. If the mass proportion of the lithium compound is 5% by mass or more, a sufficient amount of lithium ions can be pre-doped into the negative electrode, increasing the capacity of the nonaqueous lithium-type storage element. If the mass proportion of the lithium compound is 40% by mass or less, electronic conductivity in the positive electrode precursor can be increased, allowing the lithium compound to be decomposed efficiently.

[0124] The content of the lithium compound, preferably lithium carbonate, in the positive electrode active material layer of the positive electrode is preferably 0.01% by mass or more and 5.0% by mass or less, based on the total mass of the positive electrode active material layer. A lithium compound content of 0.01% by mass or more can capture acids such as HF generated by decomposition of the electrolyte salt under high-temperature, high-voltage conditions, thereby suppressing gas generation due to decomposition of the electrolyte solvent under high-temperature conditions. Furthermore, the rigid lithium carbonate destroys the aluminum oxide layer on the aluminum surface and penetrates into the aluminum, thereby improving the vibration resistance of the interface and preserving the initial low resistance even under vibration conditions. A lithium compound content of 5.0% by mass or less can suppress gas generation associated with oxidative decomposition of the lithium compound under high-temperature conditions. Since the lithium compound is unlikely to interfere with the conductive network of the activated carbon, the internal resistance of the completed cell can be reduced, and the initial low resistance can be maintained even under vibration conditions. The lithium carbonate content in the positive electrode active material layer can be adjusted by the amount of lithium carbonate added to the positive electrode precursor, the temperature conditions of pre-doping, etc. The amount of lithium carbonate in the positive electrode active material layer can be determined by the method for determining lithium carbonate in a positive electrode, which will be described later.

[0125] Improved high-load charge / discharge characteristics using alkali metal compounds When a non-aqueous lithium-ion battery element is charged and discharged, alkali metal ions and anions in the electrolyte move and react with the active material. The activation energies for the ion insertion and desorption reactions into the active material are different. Therefore, particularly under heavy charge-discharge loads, the ions cannot keep up with the changes in charge and discharge and accumulate in the active material. As a result, the electrolyte concentration in the bulk electrolyte decreases, resulting in an increase in the resistance of the non-aqueous lithium-ion battery element.

[0126] However, when an alkali metal compound is contained in the positive electrode precursor, the alkali metal compound is oxidized and decomposed to release alkali metal ions for pre-doping the negative electrode, and good pores capable of retaining the electrolyte are formed inside the positive electrode. Since ions are constantly supplied from the electrolyte in the pores formed near the active material to the positive electrode during charge and discharge, it is thought that the high-load charge and discharge cycle characteristics are improved.

[0127] The alkali metal compound contained in the positive electrode precursor undergoes oxidative decomposition upon application of a high voltage when a nonaqueous lithium storage element is formed, releasing alkali metal ions, which are then reduced at the negative electrode, thereby progressing the pre-doping process. Therefore, by promoting the oxidation reaction, the pre-doping process can be completed in a short time. To promote the oxidation reaction, it is important to ensure electronic conductivity by bringing the alkali metal compound, which is an insulator, into contact with the positive electrode active material, and to diffuse the cations released by the reaction into the electrolyte. Therefore, it is important that the alkali metal compound adequately covers the surface of the positive electrode active material.

[0128] Various methods can be used to microparticulate the alkali metal compound and alkaline earth metal compound, for example, using a grinder such as a ball mill, a bead mill, a ring mill, a jet mill, or a rod mill.

[0129] The amounts of the alkali metal elements and alkaline earth metal elements can be determined by ICP-AES, atomic absorption spectrometry, X-ray fluorescence spectrometry, neutron activation analysis, ICP-MS, or the like.

[0130] Average particle size of alkali metal compounds The average particle size of the alkali metal compound is preferably 0.1 μm or more and 10 μm or less. If the average particle size is 0.1 μm or more, the alkali metal compound has excellent dispersibility in the positive electrode precursor. If the average particle size is 10 μm or less, the surface area of ​​the alkali metal compound increases, allowing the decomposition reaction to proceed efficiently.

[0131] Furthermore, it is preferable that the average particle size of the alkali metal compound is smaller than that of the carbon material described above. If the average particle size of the alkali metal compound is smaller than that of the carbon material, the electron conductivity of the positive electrode active material layer is increased, which can contribute to lowering the resistance of the electrode body or the electricity storage element.

[0132] The method for measuring the average particle diameter of the alkali metal compound in the positive electrode precursor is not particularly limited, but it can be calculated from the SEM image of the positive electrode cross-section and the SEM-EDX image. Regarding the method for forming the positive electrode cross-section, BIB processing can be used, in which an Ar beam is irradiated from the upper part of the positive electrode to produce a smooth cross-section along the edge of a shielding plate installed directly above the sample. Above, the optimum conditions when attempting to expand the positive electrode active material from lithium iron phosphate to a lithium transition metal oxide were explained.

[0133] · Transition metal oxide as a decomposition catalyst As the positive electrode active material, Li x Mn (1-y) Fe y When using LFP and / or LMFP represented by PO4 {where x satisfies 0 ≤ x ≤ 1 and y satisfies 0 < y ≤ 1}, since these positive electrode active materials have low electron conductivity, simply mixing the positive electrode active material and the lithium compound makes it difficult for the oxidative decomposition of the lithium compound in the positive electrode precursor to proceed, and therefore, it is difficult for pre-doping into the negative electrode precursor to proceed. Therefore, it is preferable that the positive electrode active material layer further contains a transition metal oxide represented by MO2 described later. The transition metal oxide represented by the MO2 is considered to be able to promote the oxidative decomposition reaction of the lithium compound by functioning as a decomposition catalyst for the lithium compound, and efficiently perform pre-doping into the negative electrode precursor. The transition metal oxide represented by MO2 may be in the form of a composite of a lithium compound and a transition metal oxide represented by MO2 {where M is one selected from the group consisting of Co, Ni, and Mn} (hereinafter referred to as "lithium compound composite"). The mixing ratio of the lithium compound in the lithium compound composite is preferably 25 parts by mass or more and 85 parts by mass or less based on the total mass of the lithium compound composite. If the mixing ratio of the lithium compound is 25 parts by mass or more, the mixing ratio of the lithium compound composite in the positive electrode precursor can be reduced, thereby making it easier to increase the energy density. If the mixing ratio of the lithium compound is 85 parts by mass or less, the decomposition of the lithium compound can be carried out under relatively mild conditions.

[0134] The mixing ratio of the lithium compound composite contained in the positive electrode precursor is preferably 5 parts by mass or more and 25 parts by mass or less, based on the total mass of the positive electrode active material layer, and the upper limit is preferably less than 25 parts by mass. When the mixing ratio of the lithium compound composite is 5 parts by mass or more, the charge capacity per unit area A2 (mAh / cm) of the positive electrode precursor described later can be reduced. 2 When the mixed proportion of the lithium compound composite is 25 parts by mass or less (preferably less than 25 parts by mass), the mass ratio of the positive electrode active material increases, making it easier to achieve a high energy density.

[0135] The transition metal oxide represented by MO2 (wherein M is one or more selected from the group consisting of Co, Ni, and Mn) contained in the positive electrode active material layer of the positive electrode may be MO2 remaining in the positive electrode as a result of decomposition of the lithium compound from the lithium compound complex in the positive electrode precursor. When a nonaqueous lithium storage device is stored in a high-temperature environment, a solid electrolyte interphase (also sometimes abbreviated as "SEI") is formed on the positive electrode due to the decomposition reaction of the electrolyte. This SEI inhibits the reaction between the positive electrode active material and lithium ions, resulting in an increase in resistance as the SEI grows. Therefore, by including a transition metal oxide represented by MO2 in the positive electrode active material layer, MO2 acts as a decomposition catalyst for the SEI, thereby suppressing an increase in resistance in a high-temperature environment. The mixing ratio of MO2 contained in the positive electrode is preferably 1 part by mass or more and 20 parts by mass or less, based on the total mass of the positive electrode active material layer. When the mixing ratio of MO2 is 1 part by mass or more, it is easy to suppress an increase in resistance in a high-temperature environment. When the mixing ratio of MO2 is 20 parts by mass or less, it is easy to achieve a high energy density. The transition metal oxide contained in the positive electrode active material layer may be one type or two or more types.

[0136] Other components of the positive electrode active material layer The positive electrode active material layer of the positive electrode precursor may contain optional components such as a conductive filler, a binder, a dispersion stabilizer, and a pH adjuster, in addition to the positive electrode active material and the lithium compound, as needed. Examples of the conductive filler include conductive carbonaceous materials with higher conductivity than the positive electrode active material. Examples of such conductive fillers include carbon black, vapor-grown carbon fiber, graphite, flake graphite, carbon nanotubes, graphene, and mixtures thereof. The amount of conductive filler mixed in the positive electrode active material layer of the positive electrode precursor is preferably 0 to 20 parts by mass, more preferably 1 to 15 parts by mass, per 100 parts by mass of the positive electrode active material. Mixing a conductive filler is preferable from the viewpoint of high input power. On the other hand, a mixed amount of 20 parts by mass or less increases the proportion of the positive electrode active material in the positive electrode active material layer, thereby improving the energy density per volume of the positive electrode active material layer, which is preferable. The amount of conductive filler used is preferably 0 to 3.0% by mass per 100% by mass of the positive electrode active material. If the amount of the conductive filler is 3.0% by mass or less, the content of the positive electrode active material in the positive electrode active material layer is increased, thereby enabling an increase in capacity.

[0137] The binder is not particularly limited, and examples thereof include PVdF (polyvinylidene fluoride), PTFE (polytetrafluoroethylene), polyimide, acrylic latex, styrene-butadiene copolymer, fluororubber, and acrylic copolymer. The amount of binder used is preferably 1 to 30 parts by mass per 100 parts by mass of the positive electrode active material. More preferably, it is 3 to 27 parts by mass, and even more preferably, it is 5 to 25 parts by mass. If the amount of binder is 1% by mass or more, the electrode strength is improved. On the other hand, if the amount of binder is 30 parts by mass or less, the ingress and egress of ions into and diffusion from the positive electrode active material are not hindered, and the input / output characteristics are improved.

[0138] The dispersion stabilizer is not particularly limited, but examples thereof include PVP (polyvinylpyrrolidone) and PVA (polyvinyl alcohol). The amount of the dispersion stabilizer used is preferably 0 to 10 parts by mass relative to 100 parts by mass of the positive electrode active material. When the amount of the dispersion stabilizer is 10 parts by mass or less, the ingress and egress of ions into and from the positive electrode active material and the diffusion thereof are not hindered, improving the input / output characteristics.

[0139] The dispersant is not particularly limited, but may be at least one selected from the group consisting of carboxymethyl cellulose, methyl cellulose, ethyl cellulose, cellulose acetate phthalate, hydroxymethyl cellulose, hydroxypropyl methyl cellulose, hydroxyethyl methyl cellulose, hydroxypropyl methyl cellulose phthalate, polyvinyl pyrrolidone, polyvinyl alcohol, and polyvinyl acetal. The amount of dispersant used is preferably 0 to 10 parts by mass, more preferably 0 to 10 parts by mass, per 100 parts by mass of the positive electrode active material. When the amount of dispersant is 10 parts by mass or less, the ingress and egress of ions into and diffusion from the positive electrode active material are not inhibited, improving input / output characteristics.

[0140] As the dispersion solvent for the positive electrode coating liquid, water, N-methyl-2-pyrrolidone, a mixture thereof, or the like can be used.

[0141] When an organic solvent other than water is used as the dispersion solvent for the coating liquid, the water content in the dispersion solvent is preferably 0% by mass or more and 10% by mass or less. If the water content is 0% by mass or more (especially if the water content exceeds 0% by mass), a small amount of alkali metal compound dissolves, increasing the contact between the positive electrode active material and the conductive material and the alkali metal compound, and promoting pre-doping. If the water content is 10% by mass or less, the basicity of the coating liquid does not become too high, and denaturation of the binder can be suppressed. Examples of methods for suppressing the water content to 10% by mass or less include adding a dehydrating agent such as magnesium sulfate or zeolite. When water is used as the solvent for the coating liquid, adding a lithium compound may make the coating liquid alkaline, so a pH adjuster may be added to the coating liquid as needed. The pH adjuster is not particularly limited, and examples thereof include hydrogen halides such as hydrogen fluoride, hydrogen chloride, and hydrogen bromide; halogen oxoacids 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.

[0142] Total pore volume of the positive electrode active material layer The lower limit of the total pore volume of the positive electrode active material layer based on the weight of the positive electrode active material layer is preferably 0.29 cc / g or more, more preferably 0.31 cc / g or more, and the upper limit of the total pore volume is preferably 0.70 cc / g or less, more preferably 0.50 cc / g or less.

[0143] When the total pore volume is 0.29 cc / g or more, sufficient electrolyte is retained within the positive electrode active material layer, resulting in excellent electrolyte ion diffusion and improved output at low temperatures. Furthermore, reactions during low-temperature charge / discharge proceed uniformly, improving low-temperature cycle durability and suppressing micro-short circuits after cycling. Furthermore, sufficient electrolyte retention within the electrode allows charge / discharge reactions to proceed uniformly during high-temperature charge / discharge cycles, preventing localized electrolyte decomposition reactions and improving durability. When the total pore volume is 0.70 cc / g or less, the positive electrode active material layer does not contain excessive voids, providing sufficient active material density, resulting in high low-temperature input / output density per volume. Furthermore, sufficient active material density allows sufficient contact between active materials, allowing reactions during low-temperature charge / discharge to proceed uniformly within the active material layer, improving low-temperature cycle durability and suppressing micro-short circuits after cycling. Furthermore, because the amount of electrolyte retained within the electrode is not excessive, electrolyte decomposition reactions are less likely to proceed during high-temperature charge / discharge cycles, improving durability. The total pore volume of the positive electrode active material layer can be obtained by mercury porosimeter measurement, which will be described later.

[0144] The total pore volume of the positive electrode active material layer can be controlled by adjusting the amount of lithium carbonate mixed in the positive electrode active material layer and decomposing the lithium carbonate in the pre-doping step. However, in a system in which the mass ratio of lithium iron phosphate in the positive electrode active material layer is high as in the present disclosure, Fe generated from lithium iron phosphate placed in an alkaline environment by a lithium compound such as lithium carbonate during the production of the positive electrode coating solution. 3+ This crosslinking of the binder and thickener tends to cause aggregation of the activated carbon and conductive material. As a result, the decomposition reaction of lithium carbonate in the pre-doping process is difficult to proceed, making it difficult to generate pores in the positive electrode active material layer. Therefore, a preferred method for controlling the total pore volume of the positive electrode active material layer is to suppress aggregation of the activated carbon and conductive material in the positive electrode in an alkaline environment by adjusting the temperature during dispersion of the positive electrode coating liquid. It has been found that this allows the decomposition reaction of lithium carbonate to proceed sufficiently, generating pores and controlling the total pore volume, even when the ratio of lithium iron phosphate is high.

[0145] Pore ​​diameter of the positive electrode active material layer The pore diameters D25 and D75 of the positive electrode active material layer are obtained by measuring the positive electrode with a mercury porosimeter, which will be described later. The lower limit of the pore diameter D25 of the positive electrode active material layer is preferably 0.34 μm or more, and more preferably 0.36 μm or more. The upper limit of the pore diameter D25 of the positive electrode active material layer is preferably 0.64 μm or less, and more preferably 0.52 μm or less. The lower limit of the pore diameter D75 of the positive electrode active material layer is 0.10 μm or more. The upper limit of the pore diameter D75 of the positive electrode active material layer is 0.20 μm or less. The lower limit of the difference between the pore diameters D25 and D75 (D25 - D75) is 0.20 μm or more. The upper limit of D25 - D75 is 0.45 μm or less.

[0146] For lithium iron phosphate, which has a high capacity density, retention of the electrolyte in large pore pores is desirable to fully utilize its charge / discharge performance, particularly input / output and cycle durability at low temperatures. On the other hand, for activated carbon, in which ions are adsorbed and desorbed on the surface of fine pores, retention of the electrolyte in small pore pores is desirable to fully utilize its charge / discharge performance, particularly input / output and cycle durability at low temperatures. When D25, D75, and D25-D75 satisfy the above ranges, a good balance is maintained between large and small pore pores, improving the low-temperature input / output and cycle durability and suppressing the micro-short circuit rate after low-temperature cycling of a positive electrode containing a mixture of lithium iron phosphate and activated carbon.

[0147] As a method for controlling the pore size of the positive electrode active material layer, lithium carbonate of a plurality of particle sizes may be mixed into the positive electrode active material layer and adjusted by decomposing the lithium carbonate in a pre-doping process. However, in a system in which the mass ratio of lithium iron phosphate in the positive electrode active material layer is high as in the present disclosure, Fe generated from lithium iron phosphate placed in an alkaline environment by a lithium compound such as lithium carbonate during the production of the positive electrode coating solution. 3+This crosslinking of the binder and thickener tends to cause aggregation of the activated carbon and conductive material. As a result, the decomposition reaction of lithium carbonate in the pre-doping process is difficult to proceed, making it difficult to generate pores in the positive electrode active material layer. Therefore, a preferred method for controlling the pore size of the positive electrode active material layer is to suppress aggregation of the activated carbon and conductive material in the positive electrode in an alkaline environment by adjusting the temperature during dispersion of the positive electrode coating liquid. It has been found that this method can sufficiently promote the decomposition reaction of lithium carbonate, generate pores, and adjust the pore size, even when the ratio of lithium iron phosphate is high.

[0148] Volume resistivity of the positive electrode active material layer The volume resistivity of the positive electrode active material layer in the positive electrode is preferably 1.5 Ωcm or more and 8.0 Ωcm or less. If the volume resistivity of the positive electrode active material layer is 1.5 Ωcm or more, an appropriate amount of binder is present in the positive electrode active material layer, providing sufficient strength. Therefore, even if lithium insertion / extraction into / from the negative electrode or expansion / shrinkage due to temporary lithium precipitation and loss occurs during low-temperature charge / discharge cycling, the positive electrode active material layer will not peel off, thereby reducing the micro-short circuit rate after low-temperature cycling. If the volume resistivity of the positive electrode active material layer is 8.0 Ωcm or less, sufficient electrical conductivity within the active material layer allows the charge / discharge reaction to proceed uniformly within the positive electrode active material layer during charge / discharge cycling, preventing low-temperature lithium precipitation due to localized overvoltage increases, thereby reducing the micro-short circuit rate after cycling.

[0149] The method for controlling the volume resistivity of the positive electrode active material layer is not particularly limited, and for example, it can be adjusted by the mass ratio of lithium iron phosphate. In a system in which the mass ratio of lithium iron phosphate in the positive electrode active material layer is high as in the present disclosure, the volume resistivity of the positive electrode active material layer can be adjusted by adjusting the mass ratio of lithium iron phosphate. 3+This crosslinking of the binder and thickener tends to cause the lithium iron phosphate to aggregate. As a result, it is difficult to build a sufficient conductive network. A preferred method for controlling the volume resistivity of the positive electrode active material layer is to suppress the aggregation of lithium iron phosphate in the positive electrode in an alkaline environment by adjusting the temperature during storage of the positive electrode coating solution. It has been found that this makes it possible to form a conductive network and control the volume resistivity even when the ratio of lithium iron phosphate is high. The method for measuring the volume resistivity of the positive electrode active material layer will be described later.

[0150] Thickness of the positive electrode active material layer The thickness of the positive electrode active material layer is preferably 40 μm or more and 200 μm or less per side of the positive electrode current collector. The thickness of the positive electrode active material layer is more preferably 50 μm or more and 150 μm or less per side, and even more preferably 60 μm or more and 130 μm or less. A thickness of 40 μm or more improves charge / discharge capacity. On the other hand, a thickness of 200 μm or less can maintain low ion diffusion resistance within the electrode. Therefore, sufficient output characteristics can be obtained, and the cell volume can be reduced, thereby increasing the energy density. Note that when the current collector has through-holes or irregularities, the thickness of the positive electrode active material layer refers to the average thickness per side of the current collector in the portion that does not have through-holes or irregularities.

[0151] ·Bulk density of the positive electrode active material layer The bulk density of the positive electrode active material layer is preferably 1.0 g / cm 3 More preferably, 1.2 g / cm 3 More than 4.5g / cm 3 The bulk density of the positive electrode active material layer is 1.2 g / cm or less. 3 If the bulk density of the positive electrode active material layer is 4.5 g / cm or more, a high energy density is easily achieved, and therefore, it is easy to achieve a miniaturization of the electricity storage element. 3 If the thickness is equal to or less than this, the electrolyte solution will diffuse sufficiently in the pores in the positive electrode active material layer, and high output characteristics will be easily obtained.

[0152] Peel strength of the positive electrode active material layer The peel strength of the positive electrode active material layer of the positive electrode precursor is preferably 0.02 N / cm or more and 3.00 N / cm or less. If the peel strength is 0.02 N / cm or more, it is possible to suppress the loss of the positive electrode active material layer due to gas generation in the pre-doping process and to suppress micro-short circuits. If the peel strength is 3.00 N / cm or less, this means that there is no excess binder or the like in the positive electrode active material layer, improving the diffusibility of the electrolyte and reducing resistance. The peel strength of the positive electrode active material layer is preferably 0.02 N / cm or more and 2.40 N / cm or less.

[0153] (Positive electrode current collector) The material for the positive electrode current collector is not particularly limited as long as it has high electronic conductivity and is not susceptible to degradation due to elution in the electrolyte or reaction with the electrolyte or ions, but metal foil is preferred. Aluminum foil is more preferred as the positive electrode current collector because it is less susceptible to degradation due to elution in the electrolyte or reaction with the electrolyte or ions. The aluminum foil is preferably non-porous, and more preferably smooth. "Smooth" means that the surface is not subjected to surface treatments (e.g., embossing, etching, blasting, laser processing, expanding, punching) to create irregularities or through-holes.

[0154] The metal foil may be a normal metal foil without irregularities or through holes, or may be a metal foil with irregularities obtained by embossing, chemical etching, electrolytic deposition, blasting, etc., or may be a metal foil with through holes such as expanded metal, punched metal, etched foil, etc. From the viewpoint of the pro-dope treatment described later, non-porous aluminum foil is more preferred, and it is particularly preferred that the surface of the aluminum foil is roughened.

[0155] The thickness of the positive electrode current collector is not particularly limited as long as it can sufficiently maintain the shape and strength of the positive electrode, but is preferably 1 to 100 μm, for example.

[0156] It is preferable to provide an undercoat layer (also referred to as an anchor layer or conductive coating layer) containing a conductive material such as graphite, flake graphite, carbon nanotubes, graphene, carbon black, or vapor-grown carbon fiber on the surface of the metal foil. The undercoat layer improves electrical conductivity between the positive electrode current collector and the positive electrode active material layer, thereby reducing resistance. The thickness of the undercoat layer is preferably 0.1 μm or more and 5 μm or less per side of the positive electrode current collector.

[0157] (Interfacial resistance between the positive electrode active material layer and the positive electrode current collector) It is also preferable that the positive electrode current collector does not have an undercoat layer, and the positive electrode active material layer is formed directly on the positive electrode current collector. In this case, the interface resistance between the positive electrode active material layer of the positive electrode and the positive electrode current collector is 0.05 Ω cm 2 More than 5.00Ωcm 2 Preferably, it is 0.08 Ωcm or less. 2 More than 0.11Ωcm 2 It is more preferable that the interfacial resistance is 0.05 Ωcm or less. The upper and lower limits can be combined arbitrarily. As described above, the positive electrode is the positive electrode after the cell is completed, so the above interfacial resistance can be obtained for the positive electrode taken out by disassembling the energy storage element. 2 More than 5.00Ωcm 2 If the thickness is less than or equal to the thickness of the undercoat layer, the internal resistance of the completed cell can be reduced, micro-short circuits can be suppressed even when used in a vibration environment, the initial low resistance can be maintained, and gas generation can be suppressed in high-temperature environments. More specifically, for example, it is expected that the increase in internal resistance due to poor contact at the interface between the aluminum foil and the positive electrode active material layer can be suppressed, the increase in resistance due to vibration conditions such as when used in a vehicle traveling on rough roads can be suppressed, and gas generation can be suppressed under high-temperature conditions such as when used in a vehicle in a tropical region or in an energy storage system (ESS). Furthermore, the absence of an undercoat layer has the advantage of simplifying the current collector manufacturing process, leading to cost reductions for energy storage elements. The principle behind this effect is unclear, but it is speculated as follows.

[0158] The interface resistance between the positive electrode active material layer of the positive electrode and the positive electrode current collector is 5.00 Ω cm 2If the thickness is less than this, there are a sufficient number of contact points between the positive electrode active material and the positive electrode current collector, thereby reducing the internal resistance of the completed cell. Furthermore, even in a vibration environment, interfacial peeling between the positive electrode active material layer and the positive electrode current collector is suppressed, improving vibration resistance and suppressing micro-short circuits and resistance increases associated with active material peeling during vibration. Furthermore, interfacial peeling can be prevented even when the volume of the positive electrode current collector aluminum foil changes in a high-temperature environment, thereby reducing decomposition reactions of the electrolyte solvent associated with exposure of the active interface of activated carbon, which is the positive electrode active material, and thereby suppressing gas generation.

[0159] The interface resistance between the positive electrode active material layer and the positive electrode current collector is 0.05 Ωcm 2 If the above conditions are met, the positive electrode active material layer and the positive electrode current collector can be sufficiently bound by the binder in the positive electrode active material layer, thereby reducing the internal resistance of the completed cell. Furthermore, even in a vibration environment, interfacial peeling between the positive electrode active material layer and the positive electrode current collector is suppressed, improving vibration resistance and suppressing micro-short circuits and resistance increases associated with active material peeling during vibration. Furthermore, interfacial peeling can be prevented even when the volume of the positive electrode current collector aluminum foil changes in a high-temperature environment, thereby reducing decomposition reactions of the electrolyte solvent associated with exposure of the active interface of activated carbon, which is the positive electrode active material, and suppressing gas generation.

[0160] This section describes a method for controlling interfacial resistance. When smooth aluminum foil is used as the positive electrode current collector, peeling occurs more easily at the interface between the aluminum foil and the active material layer than when the aluminum foil has been subjected to surface processing (embossing, etching, blasting, laser processing, expanding, punching, etc.) such as unevenness or through-holes. Interfacial peeling occurs during the assembly, injection, and lithium doping processes (in the case of non-aqueous lithium storage elements) after the electrode is completed (for example, after coating, or after pressing if pressing is performed), and the interfacial resistance cannot be controlled when the cell is completed. Therefore, by reducing the decompression rate in a high-vacuum state during impregnation, the interfacial resistance between the positive electrode active material layer and the positive electrode current collector after the cell is completed can be reduced to 0.05 Ω cm. 2 More than 5.00Ωcm 2 The following control methods were found, the details of which are described in the sections for each process.

[0161] When positive electrode active material layers are provided on both surfaces of the positive electrode current collector, it is sufficient that the interfacial resistance is within the above range on at least one surface of the positive electrode active material layer, and it is more preferable that the interfacial resistance is within the above range on both surfaces of the positive electrode active material layer.

[0162] (Frequency of aggregates on the positive electrode surface) The positive electrode has a surface thickness of 1000 μm. 2 More than 10000μm 2 The aggregate frequency is preferably 1.5 / cm 2 Less than or equal to 1.0 particles / cm 2 Less than or equal to 0.8 particles / cm, more preferably 0.8 particles / cm 2 More preferably, 0.5 particles / cm or less 2 Less than 0.15 particles / cm is particularly preferable. 2 The aggregates on the positive electrode surface are 1000 μm or less. 2 More than 10000μm 2 Aggregate frequency of 1.5 particles / cm or less 2 If the frequency is less than 0, the distance between the positive electrode and the negative electrode becomes uniform, which is preferable because it can suppress the occurrence of micro-short circuits that are caused by lithium deposition on the negative electrode surface during low-temperature charge-discharge cycles due to non-uniform charge-discharge reactions. 2 or more, e.g., 0 pieces / cm 2 It can be super.

[0163] In addition, the above aggregate frequency is 0.5 pieces / cm 2 If the thickness is less than 1000 μm, the internal resistance of the completed cell can be reduced, micro-short circuits can be suppressed even when used in a vibrating environment, the initial low resistance can be maintained, and gas generation in a high-temperature environment can be suppressed. The principle of this effect is not clear, but it is speculated as follows. That is, if the aggregates on the positive electrode surface are 1000 μm or less, the internal resistance of the completed cell can be reduced, micro-short circuits can be suppressed even when used in a vibrating environment, the initial low resistance can be maintained, and gas generation in a high-temperature environment can be suppressed. 2 More than 10000μm 2 Aggregate frequency of 0.5 particles / cm or less 2If the distance between the positive electrode and the negative electrode is equal to or less than this, the ion transport resistance of the electrolyte can be reduced, and the internal resistance of the completed cell can be reduced. Furthermore, interfacial peeling between the positive electrode active material layer and the positive electrode current collector due to cracks in the positive electrode active material layer originating from aggregates in a vibration environment is suppressed, improving vibration resistance, thereby suppressing micro-short circuits and resistance increases associated with active material peeling during vibration. Furthermore, even in a high-temperature environment, volume changes in the positive electrode current collector aluminum foil can be prevented, preventing interfacial peeling between the positive electrode active material layer and the positive electrode current collector due to cracks in the positive electrode active material layer originating from aggregates. This reduces decomposition reactions of the electrolyte solvent associated with exposure of the active interface of activated carbon, which is the positive electrode active material, and suppresses gas generation.

[0164] The method for controlling the agglomerates is not particularly limited. In a system in which the mass ratio of lithium iron phosphate in the positive electrode active material layer is high, the agglomerates are generated from lithium iron phosphate placed in an alkaline environment by a lithium compound such as lithium carbonate in the produced positive electrode coating liquid. 3+ The binder and thickener are crosslinked by the crosslinking agent, which tends to cause the lithium iron phosphate to aggregate. A preferred method for controlling the aggregation is to suppress the aggregation of lithium iron phosphate in the positive electrode in an alkaline environment by adjusting the temperature during storage of the positive electrode coating solution. Furthermore, the generation of aggregates on the positive electrode surface can be suppressed by reducing the amount of minute gases generated in the positive electrode coating solution containing activated carbon, which causes the generation of aggregates, depending on the conditions for producing the positive electrode coating solution. The frequency of aggregates on the positive electrode surface can be measured for positive electrodes removed by disassembling a completed energy storage device. The method for measuring the frequency of aggregates on the positive electrode surface will be described later.

[0165] <Negative electrode> The negative electrode has a negative electrode current collector and a negative electrode active material layer present on one or both sides of the negative electrode current collector. In an electric double layer capacitor, the positive electrode and the negative electrode may be the same, so the negative electrode constituent material of the electric double layer capacitor according to the present disclosure can be the same material composition as the positive electrode described above, and can include activated carbon.

[0166] (Negative electrode active material layer) The negative electrode active material layer contains a negative electrode active material capable of absorbing and releasing lithium ions, including graphite. In addition, optional components such as a conductive filler, a binder, and a dispersion stabilizer may be contained as necessary. Specific examples include carbon materials, titanium oxides, silicon, silicon oxides, silicon alloys, silicon compounds, tin, and tin compounds. The carbon material content relative to the total amount of the negative electrode active material is preferably 50% by mass or more, and more preferably 70% by mass or more. While the carbon material content may be 100% by mass, from the viewpoint of obtaining the desired effect of the combined use of other materials, it is preferably 90% by mass or less, and may be 80% by mass or less, for example. The upper and lower limits of the range of the carbon material content can be arbitrarily combined.

[0167] ·Negative electrode active material The negative electrode active material may be a material capable of absorbing and releasing lithium ions. Specific examples include carbon materials, titanium oxides, silicon, silicon oxides, silicon alloys, silicon compounds, tin, and tin compounds. The content of the carbon material relative to the total amount of the negative electrode active material is preferably 50% by mass or more, and more preferably 70% by mass or more. While the content of the carbon material may be 100% by mass, from the viewpoint of obtaining the desired effect of the combined use of other materials, it is preferably 90% by mass or less, and may be 80% by mass or less, for example. The upper and lower limits of the range of the carbon material content can be combined arbitrarily.

[0168] Carbon materials Examples of carbon materials include non-graphitizable carbon materials; graphitizable carbon materials; carbon black; carbon nanoparticles; activated carbon; artificial graphite; natural graphite; graphitized mesophase carbon microspheres; graphite whiskers; amorphous carbonaceous materials such as polyacene-based substances; carbonaceous materials obtained by heat-treating carbon precursors such as petroleum-based pitch, coal-based pitch, mesocarbon microbeads, coke, and synthetic resins (e.g., phenolic resins); pyrolysates of furfuryl alcohol resins or novolac resins; fullerenes; carbon nanophones; and composite carbon materials thereof.

[0169] The BET specific surface area of ​​the composite carbon material is 100m 2 / g or more 350m 2 / g or less, and more preferably 150m 2 / g or more 300m 2 / g or less. BET specific surface area is 100m 2 / g or more, the amount of alkali metal ions pre-doped can be made sufficiently large, allowing the negative electrode active material layer to be thin. 2 If the average molecular weight is 1 / g or less, the coating property of the negative electrode active material layer is excellent.

[0170] The composite carbon material was used with lithium metal as the counter electrode, and the current value was 0.5 mA / cm at a measurement temperature of 25°C. 2 After constant current charging was performed until the voltage reached 0.01 V, the current was increased to 0.01 mA / cm 2 The initial charge capacity when constant-voltage charging is performed until the initial charge capacity reaches 100 mAh / g is preferably 300 mAh / g or more and 1,600 mAh / g or less, more preferably 400 mAh / g or more and 1,500 mAh / g or less, and even more preferably 500 mAh / g or more and 1,450 mAh / g or less per unit mass of the composite carbon material. If the initial charge capacity is 300 mAh / g or more, the amount of alkali metal ions pre-doped can be sufficiently large, so that high output characteristics can be obtained even when the negative electrode active material layer is thinned. Furthermore, if the initial charge capacity is 1,600 mAh / g or less, swelling and shrinkage of the composite carbon material when alkali metal ions are doped and undoped into the composite carbon material is reduced, and the strength of the negative electrode is maintained.

[0171] From the viewpoint of obtaining a good internal resistance value, the above-mentioned negative electrode active material is particularly preferably a composite porous material that satisfies the following conditions (1) and (2). (1) Mesopore volume (the amount of pores with a diameter of 2 nm to 50 nm) Vm1 (cm) calculated using the BJH method 3 / g) satisfies the condition 0.01≦Vm1<0.10. (2) Micropore volume (volume of pores with a diameter of less than 2 nm) Vm2 (cm) calculated using the MP method described above 3 / g) satisfies the condition 0.01≦Vm2<0.30.

[0172] ··Particle size of negative electrode active material The negative electrode active material is preferably in particulate form. The particle diameter of silicon, silicon oxide, silicon alloy, and silicon compound, as well as tin and tin compound, is preferably 0.1 μm or more and 30 μm or less. If the particle diameter is 0.1 μm or more, the contact area with the electrolyte increases, thereby reducing the resistance of the nonaqueous lithium energy storage element. Furthermore, if the particle diameter is 30 μm or less, the swelling and shrinkage of the negative electrode caused by the doping and dedoping of lithium ions into and from the negative electrode during charging and discharging is reduced, thereby maintaining the strength of the negative electrode.

[0173] Silicon, silicon oxides, silicon alloys and silicon compounds, as well as tin and tin compounds, can be finely divided by pulverizing them using a jet mill with a built-in classifier, an agitator ball mill, etc. The pulverizer is equipped with a centrifugal classifier, and the fine particles pulverized in an inert gas environment such as nitrogen or argon can be collected with a cyclone or dust collector.

[0174] Negative electrode active material content The content of the negative electrode active material in the negative electrode active material layer of the negative electrode precursor is preferably 70 mass % or more, and more preferably 80 mass % or more, based on the total mass of the negative electrode active material layer.

[0175] Use of graphite The negative electrode active material may contain graphite, and such graphite is preferably artificial graphite or natural graphite. The graphite content relative to the total amount of the negative electrode active material is preferably 50% by mass (e.g., 50.0% by mass) or more, and more preferably 70% by mass (e.g., 70.0% by mass) or more. The carbon material content may be 100% by mass (e.g., 100.0% by mass). From the viewpoint of obtaining a good effect by using other materials in combination, it is preferably, for example, 92% by mass (e.g., 92.0% by mass) or less. The upper and lower limits of the range of the graphite content can be combined arbitrarily.

[0176] The graphite is preferably particulate. The average particle size is preferably 1.0 μm or more and 9.0 μm or less, more preferably 1.5 μm or more and 7.0 μm or less, and particularly preferably 2.0 μm or more and 5.0 μm or less. If the average particle size is 1.0 μm or more, the bulk density increases when the graphite is made into an electrode, making it easier to achieve sufficient energy density. If the particle size is 9.0 μm or less, the particle surface area per weight increases, making it easier to increase the contact area between the electrolyte and the graphite surface. This reduces the reaction resistance of lithium ion insertion and desorption, making it easier to reduce the resistance of nonaqueous lithium storage elements.

[0177] The specific surface area of ​​graphite is 10m 2 / g or more 45m 2 / g or less (e.g., 10.0m 2 / g or more 45.0m 2 / g or less) is preferable. 2 If the solubility is 45m / g or more, the contact area between the electrolyte and the graphite surface is likely to increase, which reduces the reaction resistance of the lithium ion insertion and desorption, making it easier to reduce the resistance of the non-aqueous lithium storage element. 2 If the surface area is 0.05 to 0.15 μm, the surface area of ​​contact with the electrolyte can be reduced, and the formation of a coating due to decomposition of the electrolyte during long-term use can be easily suppressed.

[0178] The negative electrode active material may contain, in addition to graphite, a substance capable of absorbing and releasing lithium ions. Specific examples include carbon materials other than graphite, titanium oxide, silicon, silicon oxide, silicon alloys, silicon compounds, tin, and tin compounds. Examples of carbon materials other than graphite include non-graphitizable carbon materials, graphitizable carbon materials, carbon black, carbon nanoparticles, activated carbon, graphitized mesophase carbon microspheres, graphite whiskers, amorphous carbonaceous materials such as polyacene-based substances, carbonaceous materials obtained by heat-treating carbon precursors such as petroleum-based pitch, coal-based pitch, mesocarbon microbeads, coke, and synthetic resins (e.g., phenolic resins), pyrolyzates of furfuryl alcohol resins or novolac resins, fullerenes, carbon nanophones, and composite carbon materials thereof. Silicon, silicon oxide, silicon alloys, and silicon compounds, as well as tin and tin compounds, can be finely divided by pulverization using a jet mill with a built-in classifier, an agitation ball mill, or the like. The pulverizer is equipped with a centrifugal classifier, and the fine particles pulverized in an inert gas environment such as nitrogen or argon can be collected with a cyclone or dust collector.

[0179] The content of the negative electrode active material in the negative electrode active material layer of the negative electrode precursor is preferably 70 mass % or more, and more preferably 80 mass % or more, based on the total mass of the negative electrode active material layer.

[0180] ··Combined use of carbon materials and alloy-based active materials The negative electrode active material may include a carbon material as a first negative electrode active material and one or more selected from the group consisting of silicon, silicon compounds, tin, and tin compounds as a second negative electrode active material. The second negative electrode active material can form an alloy with lithium. Therefore, the second negative electrode active material is also called an "alloy-based active material."

[0181] The negative electrode active material preferably includes a carbon material as the first negative electrode active material. Examples of carbon materials include amorphous or microcrystalline carbon materials, nanocarbons, and crystalline carbon materials. Examples of amorphous or microcrystalline carbon materials include non-graphitizable carbon materials and graphitizable carbon materials; examples of nanocarbons include carbon nanoparticles, fullerenes, and graphene; and examples of crystalline carbon materials include graphite. Examples of graphite include artificial graphite, natural graphite, graphitized mesophase carbon microspheres, graphite whiskers, and composite carbon materials thereof. Among these carbon materials, graphite is preferred from the viewpoint of increasing the capacity of non-aqueous lithium storage elements. Preferably, one or more selected from artificial graphite, natural graphite, graphitized mesophase carbon microspheres, graphite whiskers, and composite carbon materials thereof are used.

[0182] The negative electrode active material preferably further contains, as a second negative electrode active material, one or more selected from the group consisting of silicon, silicon compounds, tin, and tin compounds. In particular, the negative electrode active material preferably contains, as a second negative electrode active material, at least one of silicon and silicon compounds. Among these, the silicon compound is preferably silicon oxide, and SiO x {wherein x satisfies 0.01≦x≦2.} is more preferable. The tin compound is preferably tin oxide, and more preferably tin dioxide (SnO2). The second negative electrode active material may be in the form of a composite material in which it is combined with carbon or a carbonaceous material.

[0183] The alloy-based active material as the second negative electrode active material allows the charge / discharge reaction of lithium ions to proceed at a higher potential and with a more gradual potential fluctuation than, for example, the graphite as the first negative electrode active material. Since the voltage of a nonaqueous lithium storage element is expressed as the difference between the positive electrode potential and the negative electrode potential, the inclusion of an alloy-based active material with a gradual potential fluctuation as the negative electrode active material facilitates gradual voltage fluctuation at the end of discharge of the nonaqueous lithium storage element.

[0184] The ratio of carbon material to alloy-based active material The proportion of the first negative electrode active material is preferably 50 parts by mass to 99 parts by mass, more preferably 50 parts by mass to 98 parts by mass, even more preferably 60 parts by mass to 98 parts by mass, and even more preferably 65 parts by mass to 95 parts by mass, based on the total mass of the negative electrode active material layer. From the viewpoint of increasing the capacity of the nonaqueous lithium storage element, it is particularly preferable to use graphite as the first negative electrode active material and to set the concentration of the graphite contained in the negative electrode active material layer to the above proportion, based on the total mass of the negative electrode active material layer. The proportion of the second negative electrode active material is preferably 1 part by mass to 50 parts by mass, more preferably 2 parts by mass to 50 parts by mass, and even more preferably 5 parts by mass to 30 parts by mass, based on the total mass of the negative electrode active material layer. When the second negative electrode active material is in the form of a composite material of an alloy-based material and carbon or a carbonaceous material, the proportion of the second negative electrode active material is calculated based on the mass excluding the carbon or carbonaceous material.

[0185] It is preferable that the first negative electrode active material be contained in the above proportion (e.g., 50 parts by mass or more and 95 parts by mass or less) and the second negative electrode active material be contained in the above proportion (e.g., 1 part by mass or more and 30 parts by mass or less) based on the total mass of the negative electrode active material layer. If the second negative electrode active material is 1% or more, it is easy to make the negative electrode thin, which makes it easy to increase the energy density of the non-aqueous lithium storage battery element. In addition, it is easy to suppress a sudden voltage drop at the end of discharge of the non-aqueous lithium storage battery element. If the second negative electrode active material is 30% or less, it is possible to reduce the irreversible capacity of the negative electrode during the initial charge / discharge, and therefore it is possible to reduce the amount of lithium compound contained in the positive electrode precursor. Therefore, it is easy to increase the energy density of the non-aqueous lithium storage battery element.

[0186] In this embodiment, the total content of the first and second negative electrode active materials in the negative electrode active material layer of the negative electrode is preferably 70 parts by mass or more, more preferably 80 parts by mass or more, based on the total mass of the negative electrode active layer.

[0187] Average particle size of the negative electrode active material The average particle diameter of the negative electrode active material is preferably 1 μm or more and 20 μm or less, with the lower limit being more preferably 2 μm or more, even more preferably 3 μm or more, and the upper limit being more preferably 18 μm or less, even more preferably 15 μm or less. If the average particle diameter is 1 μm or more, the contact area with the nonaqueous electrolyte increases, making it easier to reduce the resistance of the nonaqueous lithium storage element. If the average particle diameter of the negative electrode active material is 20 μm or less, it is easier to make the negative electrode active material layer thinner, making it easier to improve the energy density of the nonaqueous lithium storage element. The average particle diameter of the negative electrode active material can be measured in the same manner as the average particle diameter of the positive electrode active material.

[0188] The average particle size of the negative electrode active material can be adjusted by pulverizing it using a wet or dry jet mill with a built-in classifier, an agitator ball mill, etc. The pulverizer is equipped with a centrifugal classifier, and the fine particles pulverized in an inert gas environment such as nitrogen or argon can be collected with a cyclone or a dust collector.

[0189] Other components of the negative electrode active material layer The negative electrode active material layer may contain optional components such as a binder, a conductive filler, and a dispersion stabilizer, in addition to the negative electrode active material, as required.

[0190] Examples of the conductive filler include acetylene black, ketjen black, vapor-grown carbon fiber, etc. The amount of the conductive filler is preferably more than 0 parts by mass and not more than 30 parts by mass, more preferably more than 0 parts by mass and not more than 20 parts by mass, and even more preferably more than 0 parts by mass and not more than 15 parts by mass, relative to 100 parts by mass of the negative electrode active material.

[0191] Examples of binders that can be used include polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE), fluororubber, styrene-butadiene rubber, acrylic latex, and acrylic polymer. The amount of binder used in the negative electrode active material layer is preferably 0 to 10 parts by mass, more preferably 1 to 7 parts by mass, per 100 parts by mass of the negative electrode active material. If the amount of binder exceeds 10 parts by mass, the binder will excessively cover the surface of the active material of the negative electrode (precursor), increasing the ion diffusion resistance within the active material pores. If the amount of binder is 10 parts by mass or less, it is easy to prevent the binder from excessively covering the surface of the active material of the negative electrode (precursor), and therefore it is easy to suppress an increase in the ion diffusion resistance within the active material pores.

[0192] Examples of binders that can be used include those exemplified above, such as PVdF (polyvinylidene fluoride), PTFE (polytetrafluoroethylene), polyimide, latex, styrene-butadiene copolymer, fluororubber, acrylic copolymer, polyacrylic acid, and polyglutamic acid. The amount of binder is preferably 1 part by mass or more and 20 parts by mass or less, more preferably 2 parts by mass or more and 15 parts by mass or less, and even more preferably 3 parts by mass or more and 10 parts by mass or less, relative to 100 parts by mass of the negative electrode active material. When the amount of binder is 1 part by mass or more, sufficient electrode strength is easily achieved. When the amount of binder is 20 parts by mass or less, the movement of lithium ions, such as lithium ions, into and out of the negative electrode active material is less likely to be hindered, and therefore high input / output characteristics are easily achieved.

[0193] Examples of the dispersion stabilizer that can be used include PVP (polyvinylpyrrolidone), PVA (polyvinyl alcohol), and cellulose derivatives. The amount of the binder is preferably 0 to 10 parts by mass relative to 100 parts by mass of the negative electrode active material. When the amount of the dispersion stabilizer is 10 parts by mass or less, the movement of lithium ions, such as lithium ions, into and out of the negative electrode active material is less likely to be hindered, and high input / output characteristics are likely to be exhibited.

[0194] The conductive filler is preferably made of a conductive carbonaceous material having higher conductivity than the negative electrode active material, such as carbon black, vapor-grown carbon fiber, graphite, carbon nanotubes, or a mixture thereof.

[0195] The amount of conductive filler mixed in the negative electrode active material layer is preferably 20 parts by mass or less, more preferably 1 to 15 parts by mass, per 100 parts by mass of the negative electrode active material. From the viewpoint of high input power, it is preferable to mix the conductive filler in the negative electrode active material layer, but if the mixed amount exceeds 20 mass%, the content of the negative electrode active material in the negative electrode active material layer tends to decrease. Conversely, if the mixed amount is 20 parts by mass or less, the content of the negative electrode active material in the negative electrode active material layer increases, which is preferable because it improves the energy density per volume.

[0196] The amount of conductive filler mixed in the negative electrode active material layer is preferably 1 to 20 mass %, more preferably 5 to 16 mass %, based on the entire negative electrode active material layer. From the viewpoint of high input power, it is preferable to mix the conductive filler in the negative electrode active material layer. If the mixed amount is 20 parts by mass or less, the content of the negative electrode active material in the negative electrode active material layer increases, making it easier to suppress a decrease in energy density per volume. The amount of voids in the negative electrode can be increased in accordance with the amount of conductive filler added.

[0197] The dispersant is not particularly limited, but may be at least one selected from the group consisting of carboxymethyl cellulose, methyl cellulose, ethyl cellulose, cellulose acetate phthalate, hydroxymethyl cellulose, hydroxypropyl methyl cellulose, hydroxyethyl methyl cellulose, hydroxypropyl methyl cellulose phthalate, polyvinyl pyrrolidone, polyvinyl alcohol, and polyvinyl acetal, and is particularly preferably carboxymethyl cellulose.

[0198] Thickness of the negative electrode active material layer The average thickness of the material constituting the negative electrode active material layer is preferably 0.2 μm or more and 1.0 μm or less (e.g., 0.20 μm or more and 1.00 μm or less), and more preferably 0.3 μm or more and 0.8 μm or less (e.g., 0.30 μm or more and 0.80 μm or less). When the average thickness of the material constituting the negative electrode active material layer is 0.2 μm or more, the number of negative electrode material particles per weight is small, and the diffusion path of the electrolyte is not complicated. Therefore, even when doping is performed at room temperature and a high rate, doping into the negative electrode proceeds uniformly, and therefore, micro-short circuits due to precipitates and the like are unlikely to occur. This reduces the load on production facilities. In addition, the diffusion resistance component of the internal resistance is reduced, thereby reducing the internal resistance. Furthermore, even when repeated charge-discharge cycles are performed at low temperatures, precipitation and the like are unlikely to occur, and therefore capacity degradation can be suppressed. Furthermore, when the average thickness of the material constituting the negative electrode active material layer is 0.2 μm or more, the surface area of ​​the negative electrode material particles per weight is reduced, thereby reducing the contact area with the electrolyte solvent. This reduces the reduction in cyclable lithium due to the decomposition reaction of the electrolyte solvent and the formation of a coating at high temperatures. This reduces capacity degradation even when repeated charge-discharge cycles are performed at high temperatures.

[0199] When the average thickness of the material constituting the negative electrode active material layer is 1.0 μm or less, the particle surface area per weight of the negative electrode material is sufficient, ensuring a sufficient reaction area for Li-ion insertion and desorption. Therefore, even when doping is performed at room temperature and a high rate, doping into the negative electrode proceeds uniformly, thus reducing the likelihood of micro-short circuits due to deposits, etc. This reduces the load on production equipment. Furthermore, the reaction resistance component of the internal resistance is reduced, thereby reducing internal resistance. On the other hand, even when repeated charge-discharge cycles are performed at low temperatures, deposits, etc., are less likely to occur, thereby suppressing capacity degradation. Furthermore, when the average thickness of the material constituting the negative electrode active material layer is 1.0 μm or less, the small particle size of the negative electrode material reduces reaction unevenness during charge-discharge cycles. In this case, localized current concentration, which can lead to decomposition reactions of the electrolyte solvent and film formation, suppressing the loss of cyclable lithium. Therefore, capacity degradation is reduced even when repeated charge-discharge cycles are performed at high temperatures.

[0200] The average thickness of the material constituting the negative electrode active material layer can be controlled by, for example, the particle size of graphite that functions as the negative electrode active material or the composition of the negative electrode active material layer. The average thickness of the material constituting the negative electrode active material layer can also be obtained by local thickness analysis using a cross-sectional SEM, as described below.

[0201] Pore ​​diameter of the negative electrode active material layer The pore diameter of the negative electrode is preferably 0.15 μm or more and 0.7 μm or less (e.g., 0.15 μm or more and 0.70 μm or less), and more preferably 0.15 μm or more and 0.68 μm or less, or 0.2 μm or more and 0.6 μm or less (e.g., 0.20 μm or more and 0.60 μm or less). When the pore diameter of the negative electrode is 0.15 μm or more, pores of a size sufficient for the diffusion of the electrolyte are ensured. Therefore, even when doping is performed at room temperature and a high rate, doping into the negative electrode proceeds uniformly, and in this case, micro-short circuits due to precipitates or the like are unlikely to occur. This reduces the load on production facilities. In addition, the diffusion resistance component of the internal resistance is reduced, thereby reducing the internal resistance. On the other hand, even when repeated charge-discharge cycles are performed at low temperatures, precipitation or the like is unlikely to occur, and therefore capacity degradation can be suppressed. Furthermore, when the pore diameter of the negative electrode is 0.15 μm or more, the electrolyte solution easily diffuses within the negative electrode active material layer, reducing the occurrence of reaction irregularities during charge-discharge cycling. In this case, the reduction in cyclable lithium due to the decomposition reaction of the electrolyte solution solvent and the formation of a coating caused by local current concentration can be suppressed. Therefore, capacity degradation can be reduced even when repeated charge-discharge cycles are performed at high temperatures.

[0202] When the pore diameter of the negative electrode is 0.7 μm or less, the electrolyte is not retained in the pores of the negative electrode active material layer more than necessary. Therefore, gas generation due to solvent decomposition is less likely. In this case, even when doping is performed at room temperature and a high rate, doping into the negative electrode proceeds uniformly, and therefore, micro-short circuits due to deposits caused by localized current concentration are less likely to occur. This reduces the load on production equipment. Furthermore, when the pore diameter of the negative electrode is 0.7 μm or less, sufficient contact points between the active materials are secured, and sufficient conductive paths are formed. This reduces the bulk resistance component of the internal resistance, thereby reducing internal resistance. Furthermore, when the pore diameter of the negative electrode is 0.7 μm or less, the electrolyte is not retained in the pores of the negative electrode active material layer more than necessary. This prevents the loss of cyclable lithium due to the decomposition reaction of the electrolyte solvent and the formation of a coating. Therefore, capacity degradation is reduced even when repeated charge / discharge cycles are performed over a wide temperature range from low to high. The pore size of the negative electrode can be controlled, for example, by adjusting the solid content of the negative electrode coating solution, and can be obtained by mode diameter analysis of mercury porosimeter measurement of the negative electrode, as described below.

[0203] Porosity of the negative electrode active material layer The void volume of the negative electrode is based on the weight of the negative electrode active material layer and is 0.5 cm 3 / g or more 1.2cm 3 / g or less (e.g., 0.50 cm 3 / g or more 1.20cm 3 / g or less), and 3 / g or more 1.1cm 3 / g or less (e.g., 0.60 cm 3 / g or more 1.10cm 3 / g or less). 3 / g or more is acceptable, but 0.5cm 3When the porosity of the negative electrode is 1.2 / g or more, the electrolyte is sufficiently retained in the pores of the negative electrode active material layer. Therefore, the diffusion resistance component of the internal resistance can be reduced, which is preferable. When the porosity of the negative electrode is 1.2 / g or less, a conductive path between the negative electrode active materials is sufficiently formed. Therefore, the bulk resistance component of the internal resistance can be reduced, which is preferable. The porosity of the negative electrode can be controlled, for example, by adjusting the amount of conductive filler when producing the negative electrode coating solution. The porosity of the negative electrode can also be obtained by total pore volume analysis using mercury porosimetry measurement of the negative electrode, as described below.

[0204] Relationship between the thickness of the negative electrode active material layer and the mode diameter of the voids in the negative electrode active material layer The negative electrode preferably satisfies the relationship 1.0≦(1.35−p) / t≦2.8, where t (μm) is the average local thickness of the material in a cross-sectional SEM image of the negative electrode, and p (μm) is the mode diameter (pore diameter of the negative electrode active material layer) of a mercury porosimeter. The lower limit of "1.0" is, for example, "1.00," and the upper limit of "2.8" is, for example, "2.80." If the negative electrode material thickness is small, the density increases, making it easier for stacking, and therefore, it may be difficult to fully utilize the material surface. Therefore, from the perspective of electrolyte diffusion, it is preferable to ensure a larger pore size as the material thickness decreases. If (1.35−p) / t is 2.8 or less, an appropriate electrode pore size is ensured depending on the material thickness, and electrolyte diffusion is less likely to be hindered. Therefore, Li precipitation is less likely to occur even with repeated charge and discharge. This makes it possible to suppress deactivation of Li, which in turn makes it easier to suppress capacity degradation during charge-discharge cycles, particularly at high temperatures.

[0205] If the thickness of the negative electrode material is small, it becomes difficult to fully utilize the surface of the material, as described above. Therefore, even if the voids are large and the amount of electrolyte retention is large, the decomposition reaction of the electrolyte solution in the negative electrode can be suppressed. If (1.35-p) / t is 1.0 or greater, the electrode void size is not larger than necessary relative to the material thickness, and therefore, the electrolyte solution tends not to be retained in the negative electrode more than necessary. This makes it easier to suppress capacity degradation due to the decomposition reaction of the electrolyte solution solvent and the loss of cyclable lithium due to film formation, especially during charge-discharge cycles at high temperatures. This makes it easier to reduce capacity degradation. The (1.35-p) / t value in the present disclosure can be obtained by local thickness analysis of the material on a cross-sectional SEM of the negative electrode and mercury porosimeter analysis.

[0206] Specific surface area of ​​the negative electrode active material layer The specific surface area of ​​the negative electrode active material layer is 8m2 based on the weight of the negative electrode active material layer. 2 / g or more 40m 2 / g or less (e.g., 8.0m 2 / g or more 40.0m 2 / g or less), and 12m 2 / g or more 30m 2 / g or less (e.g., 12.0m 2 / g or more 30.0m 2 / g or less). 2 / g or more, a sufficient reaction area for Li ion insertion and desorption can be secured. Therefore, even when doping is performed at room temperature and a high rate, doping into the negative electrode proceeds uniformly, and therefore, micro-short circuits due to deposits and the like are unlikely to occur. This reduces the load on production equipment. Furthermore, the reaction resistance component of the internal resistance is reduced, thereby reducing the internal resistance. On the other hand, even when charge-discharge cycles are repeated at low temperatures, deposits and the like are unlikely to occur. Therefore, capacity degradation can be suppressed. Furthermore, a sufficient reaction area for Li ion insertion and desorption can be secured. This makes it difficult for uneven reactions to occur during charge-discharge cycles, and in this case, it is possible to suppress the loss of cyclable lithium due to the decomposition reaction of the electrolyte solvent and the formation of a coating caused by local current concentration. Therefore, capacity degradation can be reduced even when charge-discharge cycles are repeated at high temperatures.

[0207] The specific surface area of ​​the negative electrode active material layer is 40m 2 / g or less, the contact area between the electrolyte solvent and the negative electrode active material can be reduced. This makes it possible to suppress gas generation due to the decomposition reaction of the electrolyte solvent. In this case, doping into the negative electrode proceeds uniformly, and therefore, micro-short circuits due to deposits and the like are unlikely to occur. This makes it possible to perform doping at room temperature and at a high rate. In this case, the load on the production equipment can be reduced. In addition, when the specific surface area of ​​the negative electrode active material layer is 40 m 2 When the specific surface area of ​​the negative electrode active material layer is 40 m / g or less, the contact area between the electrolyte solvent and the negative electrode active material can be reduced. Therefore, the amount of film formed by decomposition of the electrolyte can be suppressed. Therefore, the internal resistance can be reduced. 2 When the ionic strength is 0.05g / g or less, the contact area between the electrolyte solvent and the negative electrode active material can be reduced, which can suppress the reduction of cyclable lithium due to the decomposition reaction of the electrolyte solvent and the formation of a coating film. In this case, capacity degradation can be reduced even when charge-discharge cycles are repeated over a wide temperature range from low to high temperatures.

[0208] The specific surface area of ​​the negative electrode active material layer can be controlled, for example, by adjusting the specific surface area of ​​the material used or by adjusting the method of preparing the negative electrode coating liquid. The specific surface area of ​​the negative electrode active material layer can also be measured by a nitrogen gas adsorption method for the negative electrode active material layer, which will be described later.

[0209] Thickness of the negative electrode active material layer The thickness of the negative electrode active material layer is preferably 5 μm or more and 100 μm or less per side of the negative electrode current collector. The lower limit of the thickness of the negative electrode active material layer is more preferably 7 μm or more, and even more preferably 10 μm or more. The upper limit of the thickness of the negative electrode active material layer is more preferably 80 μm or less, and even more preferably 60 μm or less. When the thickness of the negative electrode active material layer is 5 μm or more, streaks are less likely to occur when the negative electrode active material layer is applied, and therefore, excellent coatability is likely to be achieved. When the thickness of the negative electrode active material layer is 100 μm or less, a high energy density is likely to be achieved by reducing the cell volume. Note that, when the negative electrode current collector has through holes and / or irregularities, the thickness of the negative electrode active material layer refers to the average thickness of the negative electrode active material layer per side in the portion of the negative electrode current collector that does not have through holes and / or irregularities.

[0210] ·Bulk density of the negative electrode active material layer The bulk density of the negative electrode active material layer is preferably 0.50 g / cm 3 More than 3.00g / cm 3 or less, more preferably 0.60 g / cm 3 More than 2.50g / cm 3 More preferably, 0.70 g / cm or less 3 More than 2.00g / cm 3 The bulk density of the negative electrode active material layer is 0.50 g / cm or less. 3 If the bulk density of the negative electrode active material layer is 3.00 g / cm or more, sufficient strength can be easily maintained and electrical conductivity between the negative electrode active materials can be easily exhibited. 3 If the thickness is equal to or less than this, pores through which ions can be sufficiently diffused can be easily secured in the negative electrode active material layer.

[0211] (Negative electrode current collector) The material constituting the negative electrode current collector is preferably a metal foil that has high electronic conductivity and is not susceptible to degradation due to leaching into the electrolyte or reaction with the electrolyte or ions. Such metal foils are not particularly limited, and examples include aluminum foil, copper foil, nickel foil, and stainless steel foil. Copper foil is preferred as the negative electrode current collector. The metal foil may be a normal metal foil without irregularities or through holes, or a metal foil with irregularities obtained by embossing, chemical etching, electrolytic deposition, blasting, or the like, or a metal foil with through holes such as expanded metal, punched metal, or etched foil. The negative electrode current collector is preferably a non-porous copper foil. It is more preferred that the positive electrode current collector be a non-porous aluminum foil and the negative electrode current collector be a non-porous copper foil.

[0212] The thickness of the negative electrode current collector is not particularly limited as long as it can sufficiently maintain the shape and strength of the negative electrode, and is, for example, 1 to 100 μm.

[0213] The thickness of the negative electrode active material layer is preferably 10 μm or more and 100 μm or less per side, preferably 10 μm or more and 70 μm or less per side, and more preferably 20 μm or more and 60 μm or less. If the thickness is 10 μm or more, the charge / discharge capacity is improved. On the other hand, if the thickness is 70 μm or less, the cell volume can be reduced, thereby increasing the energy density. When the current collector has holes, the thickness of the negative electrode active material layer refers to the average thickness per side of the non-hole portion of the current collector.

[0214] (Relationship between lithium fluoride in the negative electrode active material layer and the interface resistance of the positive electrode) The non-aqueous lithium storage element has an interface resistance between the positive electrode active material layer and the positive electrode current collector of A [Ωcm 2 [A / B] is preferably in the range of 0.02 to 250, more preferably 0.04 to 250, and even more preferably 0.07 to 5.5. If A / B is 0.02 to 250, the internal resistance of the completed cell can be reduced, and gas generation in high-temperature environments can be suppressed. The mechanism behind this effect is unclear, but is presumed to be as follows.

[0215] When A / B is between 0.02 and 250, the balance between the interface resistance of the positive electrode and the resistance due to lithium fluoride in the negative electrode is achieved, reducing the internal resistance of the completed cell. When A / B is 0.02 or higher, there is a large amount of lithium fluoride on the negative electrode, which suppresses the reductive decomposition of the electrolyte on the negative electrode under high-temperature conditions and reduces gas generation. When A / B is 250 or lower, there is little lithium fluoride on the negative electrode, which allows the negative electrode to trap by-products produced by the oxidative decomposition of the electrolyte on the activated carbon surface exposed by micro-peeling between the positive electrode current collector and the positive electrode active material layer due to aluminum expansion under high-temperature conditions, thereby suppressing the generation or amount of gas generation.

[0216] Examples of methods for incorporating lithium fluoride into the negative electrode active material layer include a method of mixing the lithium fluoride source or the fluorine-containing compound described below into the negative electrode active material layer; a method of adsorbing the lithium fluoride source or the fluorine-containing compound described below onto the negative electrode active material layer; and a method of electrochemically depositing the lithium fluoride into the negative electrode active material layer. Among these, a method is preferred in which a material that can be decomposed to produce lithium fluoride is contained in a nonaqueous electrolyte solution, and in the process of producing an energy storage element, the compound is deposited in the negative electrode active material layer by utilizing the decomposition reaction of a lithium compound in a positive electrode precursor due to the application of a voltage, and the amount of lithium fluoride can be adjusted by the applied voltage, etc.

[0217] Examples of materials that form lithium fluoride include fluorine-containing compounds. Among them, from the viewpoint of being able to efficiently decompose to generate lithium fluoride without causing deterioration in characteristics, it is preferable to use fluorine-containing electrolyte salts such as (LiN(SO2F)2), LiN(SO2CF3)2, LiN(SO2C2F5)2, LiN(SO2CF3)(SO2C2F5), LiN(SO2CF3)(SO2C2F4H), LiC(SO2F)3, LiC(SO2CF3)3, LiC(SO2C2F5)3, LiCF3SO3, LiC4F9SO3, LiPF6, and LiBF4, among which LiPF6 and LiBF4 are more preferable, and LiPF6 is most preferable.

[0218] (Interfacial resistance of negative electrodes for electric double layer capacitors) When the electric storage element according to the present disclosure is an electric double layer capacitor, the negative electrode active material layer contains the activated carbon described above, and the interface resistance between the negative electrode active material layer of the negative electrode and the negative electrode current collector is 0.05 Ω cm 2 More than 5.00Ωcm 2 Preferably, it is 0.06 to 4.94 Ωcm or less. 2It is preferable that the interfacial resistance is within the range. After the cell is completed, the electric double layer capacitor may be disassembled and the negative electrode taken out may be subjected to the above-mentioned interfacial resistance measurement. When the interfacial resistance of the negative electrode is within the above-mentioned numerical range, the electric double layer capacitor tends to have all of low resistance performance, vibration resistance, and high-temperature durability.

[0219] (Frequency of aggregates on the negative electrode surface) 20,000 μm of the negative electrode surface 2 The frequency of aggregates above 1 / cm 2 Less than (e.g., 1.00 pieces / cm 2 It is preferable that the number of particles is 0.2 or less per cm. 2 Below (0.20 pieces / cm 2 It is more preferable that the thickness is 20,000 μm or less. 2 The frequency of aggregates above 0 particles / cm 2 or more (e.g., 0.00 pieces / cm 2 (The above is sufficient.)

[0220] 20,000 μm of the negative electrode surface 2 Aggregate frequency of 1 particle / cm or more 2 If the thickness is less than 20,000 μm, the surface irregularities of the negative electrode are sufficiently small. Therefore, when doping is performed at room temperature and at a high rate, localized concentration of current in the aggregates does not occur, and therefore doping of the negative electrode proceeds uniformly. In this case, micro-short circuits due to precipitates, etc., are unlikely to occur. This reduces the load on the production equipment. In addition, current is unlikely to concentrate in the aggregates. Therefore, the entire negative electrode can be used uniformly, reducing internal resistance. 2 Aggregate frequency of 1 particle / cm or more 2 If the surface roughness of the negative electrode is less than 20,000 μm, the surface roughness of the negative electrode is sufficiently small. Therefore, even if charge / discharge cycles are repeated at low temperatures, precipitation on the aggregates is unlikely to occur. Therefore, capacity degradation can be suppressed. 2 Aggregate frequency of 1 particle / cm or more 2If the surface roughness of the negative electrode is less than 1 / 2 mm, the surface roughness of the negative electrode is sufficiently small. Therefore, uneven reactions during charge-discharge cycling are less likely to occur. In this case, the reduction in cyclable lithium due to the decomposition reaction of the electrolyte solvent and the formation of a coating caused by local current concentration can be suppressed. Therefore, capacity degradation can be reduced even when charge-discharge cycling is repeated at high temperatures.

[0221] The average thickness of the negative electrode material is 0.2 μm or more and 1.0 μm or less, and the specific surface area of ​​the negative electrode active material layer is 8 m 2 / g or more 40m 2 In order to prepare a negative electrode having a small material thickness and a large specific surface area, the average particle diameter is preferably 9 μm or less, and the specific surface area is preferably 10 m 2 It is preferable to use graphite with a particle size of 20,000 μm or more. However, if graphite with a small particle size and a large specific surface area is used, re-aggregation of the graphite occurs during storage in the negative electrode coating solution, making it difficult to maintain a stable dispersion state, and it is thought that aggregates may occur on the surface of the negative electrode after coating. 2 The inventors have found that the above-mentioned frequency of agglomerates can be controlled by adjusting the storage temperature of the negative electrode coating solution from the time of preparation to coating. As a result, even if graphite with a small particle size and a high specific surface area is used, the agglomerates on the negative electrode surface of 20,000 μm 2 Aggregate frequency of 1 particle / cm or more 2 The following negative electrodes can be produced. 2 The above-mentioned agglomerate frequency can be measured by the method described later in the measurement of agglomerate frequency on the negative electrode surface.

[0222] The negative electrode has the following (1) to (4): (1) the average thickness of the negative electrode material is 0.2 μm or more and 1.0 μm or less, (2) the pore diameter (mode diameter of the pores) of the negative electrode active material layer is 0.15 μm or more and 0.7 μm or less, and (3) the specific surface area of ​​the negative electrode active material layer is 8 m 2 / g or more 40m 2 / g or less, and (4) 20,000 μm 2 The frequency of aggregates above 0 particles / cm 2 More than 1 piece / cm 2It is particularly preferable to satisfy all of the following conditions: When these conditions are satisfied, it is possible to provide a negative electrode that can reduce the micro-short circuit rate during pre-doping at room temperature and a high rate, further reduce the internal resistance, and further improve the cycle durability over a wide temperature range from high to low temperatures.

[0223] According to the above embodiment, firstly, it is possible to reduce the production equipment costs of the charge / discharge device and the thermostatic bath, and also to minimize micro-short circuits in the pre-doping process at room temperature and high rate to increase the production takt time, thereby realizing pre-doping with a high yield; secondly, it is possible to realize a non-aqueous lithium storage element with low internal resistance; and thirdly, it is possible to ship non-aqueous lithium storage elements with the same electrode and cell specifications from tropical regions to cold regions, thereby improving productivity and improving cycle durability over a wide temperature range from high to low temperatures.

[0224] <Separator> The positive electrode precursor and the negative electrode are stacked or wound with a separator interposed therebetween to form an electrode laminate having the positive electrode precursor, the negative electrode, and the separator. The separator may be a polyethylene microporous film or a polypropylene microporous film used in nonaqueous lithium storage elements, or a cellulose nonwoven paper used in electric double layer capacitors. A film made of organic or inorganic fine particles may be laminated on one or both sides of the separator. The separator may also contain organic or inorganic fine particles.

[0225] The thickness of the separator is preferably 5 μm or more and 35 μm or less. A separator thickness of 5 μm or more is preferred because it tends to reduce self-discharge due to internal micro-short circuits. On the other hand, a separator thickness of 35 μm or less is preferred because it tends to improve the output characteristics of the energy storage element.

[0226] The thickness of the film made of organic or inorganic fine particles is preferably 1 μm or more and 10 μm or less. A thickness of 1 μm or more is preferred because it tends to reduce self-discharge due to internal micro-short circuits. On the other hand, a thickness of 10 μm or less is preferred because it tends to improve the output characteristics of the energy storage element.

[0227] The separator may contain an organic polymer that swells upon penetration of the non-aqueous electrolyte solution. Alternatively, an organic polymer may be used alone as a separator. The organic polymer preferably has good affinity with the non-aqueous electrolyte solution and gels upon penetration and swelling of the electrolyte solution. Suitable organic polymers include polyethylene oxide, polyacrylonitrile, polyvinylidene fluoride, polymethyl methacrylate, and mixtures thereof, which tend to exhibit high lithium ion conductivity upon gelation.

[0228] The organic polymer can contain the electrolyte solution within the organic polymer, which is preferable from the standpoint of safety because it has the effect of preventing the electrolyte solution from leaking out of the nonaqueous lithium-ion storage element when the exterior is damaged.

[0229] <Exterior body> Examples of the exterior body include metal cans and laminated films. Aluminum metal cans are preferred. Metal cans may be rectangular, round, or cylindrical. Laminated films are preferably films made of a metal foil and a resin film, such as a three-layer structure consisting of an outer resin film, a metal foil, and an interior resin film. The outer resin film is intended to prevent damage to the metal foil due to contact, and resins such as nylon or polyester are suitable. The metal foil is intended to prevent moisture and gas permeation, and foils such as copper, aluminum, and stainless steel are suitable. The interior resin film protects the metal foil from the electrolyte solution stored inside and melts and seals the opening during heat sealing of the exterior body. Polyolefins, acid-modified polyolefins, and the like are suitable.

[0230] <Electrolyte> The electrolyte solution for the non-aqueous lithium storage element can be an electrolyte solution generally used in lithium ion secondary batteries or lithium ion capacitors. The non-aqueous electrolyte solution preferably contains 0.5 mol / L or more of a lithium salt as an electrolyte, based on the total amount of the non-aqueous electrolyte solution. The lithium salt of the electrolyte can be an electrolyte generally used in non-aqueous lithium storage elements. Examples of lithium salts containing fluorine base paper include LiBF4, LiPF6, LiPO2F2, LiFSI (=LiN(SO2F)2, LiTFSI (=LiN(SO2CF3)2), LiN(SO2C2F5)2, LiN(SO2CF3)(SO2C2F5), LiN(SO2CF3)(SO2C2F4H), LiC(SO2F)3, LiC(SO2CF3)3, LiC(SO2C2F5)3, LiCF3SO3, LiC4F9SO3, etc. Examples of lithium salts that do not contain fluorine atoms include LiCiO4, etc. The electrolyte is These may be used alone or in combination of two or more. The nonaqueous electrolyte solution of this embodiment may contain alkali metal ions such as sodium ions and potassium ions in addition to lithium ions. Examples of organic solvents include cyclic carbonates such as ethylene carbonate and propylene carbonate, and chain carbonates such as dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate. The solvent may be used alone or in combination of two or more in any ratio.

[0231] The lithium salt concentration of the electrolyte in the electrolytic solution is preferably in the range of 0.5 to 2.0 mol / L. At an electrolyte salt concentration of 0.5 mol / L or more, sufficient anions are present, maintaining the capacity of the nonaqueous lithium storage element. On the other hand, at an electrolyte salt concentration of 2.0 mol / L or less, the salt is sufficiently dissolved in the electrolytic solution, maintaining the appropriate viscosity and conductivity of the electrolytic solution.

[0232] The non-aqueous electrolyte solution in this embodiment preferably contains a cyclic carbonate and / or a chain carbonate as a non-aqueous solvent (organic solvent). The solvent may be used alone or in a mixture of two or more solvents in any ratio. The non-aqueous electrolyte solution may contain a cyclic carbonate and a chain carbonate in order to dissolve a lithium salt at a desired concentration and to exhibit high ionic conductivity. Examples of cyclic carbonates include alkylene carbonate compounds such as ethylene carbonate, propylene carbonate, and butylene carbonate. The alkylene carbonate compound is typically unsubstituted. Examples of chain carbonates include dialkyl carbonate compounds such as dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, dipropyl carbonate, and dibutyl carbonate. The dialkyl carbonate compound is typically unsubstituted and is preferably one or more selected from dimethyl carbonate, ethyl methyl carbonate, and diethyl carbonate.

[0233] The total content of the cyclic carbonate and the chain carbonate is preferably 50 parts by mass or more, more preferably 65 parts by mass or more, even more preferably 95 parts by mass or less, and even more preferably 90 parts by mass or less, based on the total mass of the non-aqueous electrolyte solution. When the total content of the cyclic carbonate and the chain carbonate is 50 parts by mass or more, it is easy to dissolve the alkali metal salt at a desired concentration, and therefore high ionic conductivity is easily achieved. When the total concentration of the cyclic carbonate and the chain carbonate is 95 parts by mass or less, it is easy to further add additives described below to the electrolyte solution. The ratio of the cyclic carbonate and the chain carbonate, expressed as the mass ratio of the cyclic carbonate to the total mass of the two, is preferably 15 to 50 parts by mass, more preferably 20 to 45 parts by mass, and particularly preferably 25 to 40 parts by mass.

[0234] Examples of electrolyte salts containing alkali metal ions that dissolve in nonaqueous solvents include MFSI, MBF4, and MPF6, where M is Li, Na, K, Rb, or Cs. The nonaqueous electrolyte solution of this embodiment may contain at least one alkali metal ion. It may contain two or more alkali metal salts, or it may contain an alkali metal salt and an alkaline earth metal salt selected from beryllium salts, magnesium salts, calcium salts, strontium salts, and barium salts. When the nonaqueous electrolyte solution contains two or more alkali metal salts, the presence of cations with different Stokes radii in the nonaqueous electrolyte can suppress viscosity increases at low temperatures, thereby improving the low-temperature characteristics of nonaqueous lithium energy storage elements. When the nonaqueous electrolyte solution contains alkaline earth metal ions other than the alkali metal ions, the beryllium ions, magnesium ions, calcium ions, strontium ions, and barium ions are divalent cations, thereby increasing the capacity of nonaqueous lithium energy storage elements.

[0235] The method of adding two or more alkali metal salts to a non-aqueous electrolyte solution, or the method of adding an alkali metal salt and an alkaline earth metal salt to a non-aqueous electrolyte solution is not particularly limited, but an alkali metal salt consisting of two or more alkali metal ions can be dissolved in advance in a non-aqueous electrolyte solution, or an alkali metal salt and an alkaline earth metal salt can be dissolved. In addition, in the positive electrode precursor, M in the following formula is one or more selected from Na, K, Rb, and Cs, and carbonates such as M2CO3, oxides such as MO, hydroxides such as MOH, halides such as MF and MCl, carboxylates such as RCOOM (wherein R is H, an alkyl group, or an aryl group), alkaline earth metal carbonates selected from BeCO3, MgCO3, CaCO3, SrCO3, or BaCO3, and alkaline earth metal oxides, alkaline earth metal hydroxides, alkaline earth metal halides, and alkaline earth metal carboxylates are added, and the resulting mixture is decomposed in a pre-doping step described below.

[0236] The lithium salt concentration of the electrolyte in the electrolytic solution is preferably in the range of 0.5 to 2.0 mol / L. At an electrolyte salt concentration of 0.5 mol / L or more, sufficient anions are present, maintaining the capacity of the nonaqueous lithium storage element. On the other hand, at an electrolyte salt concentration of 2.0 mol / L or less, the salt is sufficiently dissolved in the electrolytic solution, maintaining the appropriate viscosity and conductivity of the electrolytic solution.

[0237] When the non-aqueous electrolytic solution contains two or more alkali metal salts, or when it contains an alkali metal salt and an alkaline earth metal salt, the total concentration of these salts is preferably 0.5 mol / L or more, and more preferably in the range of 0.5 to 2.0 mol / L.

[0238] (Electrolyte for electric double layer capacitors) The electrolyte solution for the electric double layer capacitor can be an electrolyte solution generally used in electric double layer capacitors. For example, an electrolyte dissolved in an organic solvent can be used. As the electrolyte, for example, an ammonium salt such as a quaternary ammonium salt such as tetraethylammonium tetrafluoroborate or triethylmonomethylammonium tetrafluoroborate, an amine salt, or an amidine salt can be preferably used. One type of electrolyte can be used alone, or two or more types can be used in combination. Furthermore, known solvents can be used as the organic solvent, such as propylene carbonate, ethylene carbonate, dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, γ-butyrolactone, acetonitrile, propionitrile, and methoxyacetonitrile. Among these, propylene carbonate is particularly preferred. The solvent can be used alone, or two or more types can be mixed in any ratio.

[0239] <Characteristics of non-aqueous lithium storage elements> (current rest resistance) In the nonaqueous lithium-ion storage element, the ratio (R1 / R2) of the 5°C 10-second current-rest resistance R1 (Ω) to the 25°C 10-second current-rest resistance R2 (Ω) (hereinafter referred to as the "current-rest resistance ratio") is preferably 1.05 or greater and 1.90 or less. Here, the 5°C 10-second current-rest resistance R1 (Ω) is calculated by discharging at a constant current of 18 A from 4.0 V to 2.8 V at 5°C, pausing the discharge, and dividing the voltage change (ΔV) 10 seconds after the discharge pause by 18 A. The 25°C 10-second current-rest resistance R2 (Ω) is calculated by repeating the same procedure at 25°C. A current-rest resistance ratio within this range allows both the lithium iron phosphate and activated carbon to contribute to low-temperature charge / discharge, thereby suppressing lithium deposition on the negative electrode due to uneven loads. This reduces the micro-short circuit rate after low-temperature constant-power cycling, which is preferable.

[0240] In systems where the mass ratio of lithium iron phosphate in the positive electrode active material layer is high, Fe generated from lithium iron phosphate placed in an alkaline environment with lithium carbonate in the manufactured positive electrode coating solution. 3+ This crosslinks the binder and thickener, causing the lithium iron phosphate to aggregate. As a result, the current-rest resistance ratio tends to increase. There are no particular limitations on the method for controlling the current-rest resistance ratio; however, a preferred method is to suppress the aggregation of lithium iron phosphate in the positive electrode in an alkaline environment by adjusting the temperature during storage of the positive electrode coating solution. This suppresses aggregation even when the proportion of lithium iron phosphate is high, and can reduce the ratio of the 10-second resistance at 5°C with current rest to the 10-second resistance at 25°C with current rest. The method for measuring the current-rest resistance ratio will be described later.

[0241] (Ratio of discharge capacity of positive electrode to charge capacity of negative electrode) The discharge capacity per unit area of ​​the positive electrode is A1 (mAh / cm 2 ) and the charge capacity per unit area of ​​the negative electrode is B1 (mAh / cm 2), it is preferable to satisfy 0.71≦A1 / B1≦0.96. This allows the voltage change at the end of discharge of a lithium ion secondary battery using LFP and / or LMFP to be gradual. "0.71≦A1 / B1≦0.96" can be, for example, "0.710≦A1 / B1≦0.960."

[0242] This state indicates that the amount of lithium ions absorbed in the negative electrode is greater than the amount of lithium ions that the positive electrode can absorb. At the end of discharge of a lithium ion secondary battery, the potential of the positive electrode using LFP and / or LMFP drops sharply, while the potential of the negative electrode rises sharply. In a lithium ion secondary battery without pre-doping, there are no excess lithium ions that do not contribute to charging and discharging, so the values ​​of A1 and B1 are almost equal. At the end of discharge of such a lithium ion secondary battery, the sharp potential fluctuations of the positive and negative electrodes overlap, resulting in a sharp fluctuation in cell voltage. In this embodiment, by satisfying A1 / B1≦0.96, lithium ions are not completely released from the negative electrode even at the end of discharge of the lithium ion secondary battery, thereby suppressing the potential fluctuation of the negative electrode. As a result, the fluctuation in cell voltage can be alleviated. Furthermore, by configuring the battery so that 0.71≦A1 / B1 is satisfied, it is possible to reduce excess lithium ions that do not contribute to charging and discharging, thereby increasing the energy density of the lithium ion secondary battery.

[0243] From the same viewpoint as above, it is more preferable that A1 / B1 satisfy the following relationship: 0.730≦A1 / B1≦0.950.

[0244] A1 / B1 can be controlled by adjusting A1 and / or B1. The above A1 and / or B1 can be used to, for example, adjust the charge capacity per unit area of ​​the positive electrode precursor to A2 (mAh / cm 2 ), and the discharge capacity per unit area of ​​the positive electrode precursor is A3 (mAh / cm 2 ), and the charge capacity per unit area of ​​the negative electrode precursor is B2 (mAh / cm 2), it can be controlled by adjusting A2, A3, and / or B2. For example, the above-mentioned A1 and / or B1 can be adjusted by performing the above-mentioned pre-doping on a lithium ion secondary battery precursor that satisfies 0.65≦A3 / A2≦0.93 and 1.03≦B2 / A3≦1.26. Details will be described in the section on manufacturing method.

[0245] <<Method for manufacturing a non-aqueous lithium storage element>> The method for producing a nonaqueous lithium storage battery element of the present disclosure includes the steps of preparing a positive electrode coating liquid, obtaining a positive electrode precursor, producing a negative electrode, fabricating an electrode laminate or an electrode wound body from the positive electrode precursor and the negative electrode, housing the electrode laminate or the electrode wound body in an outer casing and injecting a nonaqueous electrolyte solution, and applying a voltage between the positive electrode precursor and the negative electrode to pre-dope lithium ions into the negative electrode active material layer. To obtain the nonaqueous lithium storage battery element of the present disclosure, preferably, the dispersion or dissolution operation in the step of preparing the positive electrode coating liquid is performed at a temperature of 15°C or less, and the positive electrode coating liquid obtained in the step of preparing the positive electrode coating liquid is stored at a temperature of 15°C or less until the step of obtaining the positive electrode precursor is performed.

[0246] <Production of positive electrode coating liquid> In the present disclosure, a coating liquid used to produce a positive electrode precursor or a positive electrode is referred to as a "positive electrode coating liquid." The positive electrode coating liquid may take the form of a known coating liquid, as well as a known suspension, dispersion, emulsion, composition, or mixture. The positive electrode coating liquid may also be simply referred to as a slurry, coating liquid, or the like. The positive electrode coating liquid contains solid components for forming a positive electrode precursor, such as a carbon material, a lithium transition metal oxide, and an alkali metal compound, in a dispersion solvent. In addition to these, the positive electrode coating liquid may contain optional components such as a conductive material, a binder, a dispersant, a dispersion stabilizer, and a pH adjuster, as necessary.

[0247] (Dispersion or dissolution of positive electrode coating liquid) The positive electrode coating liquid for the nonaqueous lithium storage element can be produced by known production techniques for coating liquids used in lithium ion secondary batteries, electric double layer capacitors, etc. For example, a slurry-like coating liquid can be prepared by dispersing or dissolving the positive electrode active material, alkali metal compound, and other optional components used as needed in water or an organic solvent in any order.

[0248] The dispersion method for preparing the positive electrode coating solution is not particularly limited, but dispersers such as a bead mill, ball mill, jet mill, homogenizer, emulsifying disperser, rotation-revolution mixer, homodisper, multi-axis disperser, planetary mixer, and thin film swirl high-speed mixer can be used. It is also possible to combine multiple dispersers for dispersion. To obtain a well-dispersed coating solution, for example, when using a thin film swirl high-speed mixer, dispersion is preferably performed at a peripheral speed of 1 m / s or more and 50 m / s or less. A peripheral speed of 1 m / s or more is preferred because various materials are well dissolved or dispersed. A peripheral speed of 50 m / s or less is also preferred because the various materials are not destroyed by heat or shear force generated by dispersion, and re-agglomeration does not occur. A method in which the coating solution is dispersed while being cooled is preferred to prevent destruction of various materials due to heat generated during dispersion.

[0249] Dispersion or dissolution when using lithium transition metal oxides For example, a method for producing a positive electrode coating solution includes dry-mixing solids containing a carbon material, a lithium transition metal oxide, and an alkali metal compound, and then mixing the dry-mixed solids with a dispersion solvent to disperse the solids. More specifically, for example, the positive electrode coating solution may be prepared by dry-mixing (also referred to as "dry blending") some or all of the solids containing a carbon material, a lithium transition metal oxide, and an alkali metal compound, and then adding a dispersion solvent and / or a liquid or slurry-like substance in which a binder, a dispersant, and a pH adjuster are dissolved or dispersed in the dispersion solvent. Alternatively, the positive electrode coating solution may be prepared by adding a solid containing a carbon material, a lithium transition metal oxide, and an alkali metal compound that has been dry-mixed in advance to a liquid or slurry-like substance in which a binder, a dispersant, and a pH adjuster are dissolved or dispersed in the dispersion solvent. The dry-mixing method is not limited, and can be performed using, for example, a ball mill.

[0250] In another embodiment, a carbon material and an alkali metal compound may be dry-mixed, and then other solids and a dispersion solvent may be mixed and dispersed by any procedure. This procedure is preferable because the carbon material and the alkali metal compound are more intimately mixed, thereby increasing the electronic conductivity of the alkali metal compound and facilitating decomposition of the alkali metal compound during the pre-doping process. More specifically, for example, a portion or all of the carbon material and the alkali metal compound may be dry-mixed, followed by adding a lithium transition metal oxide and dry-mixing. The positive electrode coating solution may then be prepared by adding a dispersion solvent and / or a liquid or slurry-like substance in which a binder, a dispersant, and a pH adjuster are dissolved or dispersed in the dispersion solvent. Alternatively, the positive electrode coating solution may be prepared by adding a pre-dry-mixed carbon material, an alkali metal compound, a lithium transition metal oxide, and the like, by any procedure, to a liquid or slurry-like substance in which a binder, a dispersant, and a pH adjuster are dissolved or dispersed in the dispersion solvent. The dry-mixing method is not limited, but may be performed using, for example, a ball mill.

[0251] In yet another embodiment, the conductive material and the alkali metal compound may be dry-mixed, and then other solids and the dispersion solvent may be mixed and dispersed by any procedure. This procedure is preferable because coating the low-conductivity alkali metal compound with the conductive material can increase the electronic conductivity of the alkali metal compound and facilitate decomposition of the alkali metal compound during the pre-doping process. More specifically, for example, the conductive material and some or all of the alkali metal compound may be dry-mixed, followed by adding a carbon material and a lithium transition metal oxide and dry-mixing the mixture. The positive electrode coating solution may then be prepared by adding a dispersion solvent and / or a liquid or slurry-like substance in which a binder, dispersant, and / or pH adjuster are dissolved or dispersed in the dispersion solvent. Alternatively, the conductive material and alkali metal compound, as well as the carbon material and lithium transition metal oxide, which have been dry-mixed in advance, may be added by any procedure to a liquid or slurry-like substance in which a binder, dispersant, and / or pH adjuster are dissolved or dispersed in the dispersion solvent. The dry-mixing method is not limited, but may be performed using, for example, a ball mill.

[0252] Temperature of the positive electrode coating solution when using lithium iron phosphate In systems where the mass ratio of lithium iron phosphate in the positive electrode active material layer is high, Fe generated from lithium iron phosphate placed in an alkaline environment with lithium compounds such as lithium carbonate during the production of the positive electrode coating solution. 3+ This crosslinks the binder and thickener, which tends to cause the activated carbon and conductive material to form minute aggregates. As a result, the decomposition reaction of lithium carbonate in the pre-dope becomes difficult to proceed. In the conventional method of increasing the shear during dispersion, 2 It is possible to remove aggregates exceeding this limit, but increasing the shear will cause the slurry to heat up, which will actually increase the Fe 3+This cross-linking of the binder and thickener occurs, resulting in minute aggregation of the activated carbon and conductive material. Therefore, it is preferable to suppress aggregation of the activated carbon and conductive material in the positive electrode in an alkaline environment by adjusting the temperature during dispersion of the positive electrode coating liquid. This allows the decomposition reaction of lithium carbonate to proceed sufficiently, even when the ratio of lithium iron phosphate is high, and the total pore volume and pore diameter can be adjusted. Note that the temperature during dispersion of the positive electrode coating liquid is preferably 15°C or lower.

[0253] Furthermore, in systems in which the mass proportion of lithium iron phosphate in the positive electrode active material layer is high, the formation of fine aggregates of lithium iron phosphate as described above leads to an increase in the positive electrode surface aggregates and an increase in the volume resistivity of the positive electrode active material layer. Therefore, it is preferable to suppress the aggregation of lithium iron phosphate in the positive electrode in an alkaline environment by adjusting the temperature during storage of the positive electrode coating solution. This can suppress the increase in the positive electrode surface aggregates, the increase in the volume resistivity of the positive electrode active material layer, and the increase in the current-rest resistance ratio. The storage temperature of the positive electrode coating solution is preferably 15°C or lower.

[0254] Dispersion or dissolution when using lithium compound complexes When the positive electrode coating liquid contains a lithium compound composite, some of the lithium compound and / or some of the MO2 may separate from the lithium compound composite during the dispersion process of the positive electrode coating liquid. Therefore, the positive electrode active material layer may contain particles of lithium compound and / or MO2 that are not present as a lithium compound composite and exist alone. Even in such a state, MO2 acts as a decomposition catalyst for the lithium compound. To enhance this effect, it is preferable to adjust the load during dispersion so as to reduce the amount of lithium compound and / or MO2 separated.

[0255] - Microgas suppression In the production of a positive electrode coating solution containing activated carbon, the acidic and basic functional groups present on the surface of the activated carbon react with the binder and dispersant, which easily generates minute submicron gases. These minute gases cause aggregation of the active material during storage of the positive electrode coating solution before coating the positive electrode, and when observing the surface of the positive electrode, agglomeration of 1000 μm particles is observed on the surface of the positive electrode.2 More than 10000μm 2 The conventional method of increasing the shear strength during dispersion caused the following problem: 2 Although it is possible to remove aggregates exceeding 1000 μm, increasing the shear generates heat in the slurry, which in turn accelerates the reaction of the acidic and basic functional groups present on the surface of the activated carbon, generating minute gases. This causes the minute gases to form particles of 1000 μm or more during storage of the positive electrode coating solution. 2 More than 10000μm 2 Furthermore, when removing fine gases by conventional methods such as degassing under reduced pressure, the gases contained in the activated carbon pores escape, generating fine gases, causing the same problem.

[0256] On the other hand, the inventors have found that by lowering the temperature of the slurry during dispersion, the reaction caused by the acidic and basic functional groups present on the surface of the activated carbon is suppressed, and the generation of agglomerates during storage of the positive electrode coating solution is suppressed, resulting in a 1000 μm 2 More than 10000μm 2 It was found that the generation of the following fine aggregates can be suppressed. From the viewpoint of suppressing aggregates by reducing fine gases, the temperature of the slurry is preferably 15°C or less, with 10°C being most preferable, and it is also preferable to store the slurry at 15°C or less during the storage period from the completion of the coating liquid until coating.

[0257] It is preferable to add the dispersing agent in aqueous solution form rather than in powder form during dispersion. Adding it as an aqueous solution maintains a good dispersion state of the activated carbon and suppresses the formation of agglomerates during storage of the coating liquid. Furthermore, when lithium iron phosphate is included as an active material, it is preferable to disperse it before the activated carbon in order to suppress agglomerates. This is because if the activated carbon is dispersed first, the dispersing agent will adsorb to the surface of the activated carbon, which is rich in functional groups, and shear will be required when dispersing the lithium iron phosphate, generating heat and making it easier for microgases to be generated by reactions with the acidic and basic functional groups present on the surface of the activated carbon.

[0258] (Solid content of positive electrode coating liquid) The solid content of the positive electrode coating fluid is preferably 15% or more and 50% or less. If the solid content is 15% or more, drying can be performed under gentle conditions during coating. If the solid content is 50% or less, the occurrence of coating streaks and cracks during coating can be suppressed. The solid content is the ratio of the total weight of solids such as carbon materials, lithium transition metal oxides, alkali metal compounds, and other binders and conductive materials to the total weight of the coating fluid.

[0259] (defoaming) After dispersion of the coating liquid, it is preferable to degas the coating liquid. The degassing method is not particularly limited, but examples include stirring the coating liquid at low speed under reduced pressure, leaving the coating liquid to stand, and stirring the coating liquid at low speed using a planetary mixer. It is also preferable to remove aggregates from the dispersed coating liquid using a filter. Removing aggregates with large particle sizes can prevent streaks and other problems from occurring in the coating film.

[0260] (Dispersion degree of positive electrode coating liquid) The degree of dispersion of the positive electrode coating liquid is preferably a particle size of 0.1 μm or more and 100 μm or less, as measured with a particle gauge. The upper limit of the degree of dispersion is more preferably a particle size of 80 μm or less, and even more preferably a particle size of 50 μm or less. A particle size of 0.1 μm or less is less than the particle size of the powders of various materials, including the positive electrode active material, which is undesirable because the materials are crushed during preparation of the coating liquid. Furthermore, a particle size of 100 μm or less allows stable coating without clogging during discharge of the coating liquid or streaks in the coating film.

[0261] The degree of dispersion is determined by a dispersion evaluation test using a particle gauge as specified in JIS K5600. Specifically, a sufficient amount of sample is poured into the deep end of a particle gauge with a groove of the desired depth corresponding to the particle size, allowing it to slightly overflow the groove. Next, the long side of the scraper is placed parallel to the width of the gauge, with the cutting edge in contact with the deep end of the groove of the particle gauge. While holding the scraper so that it is on the surface of the gauge, the scraper is pulled perpendicular to the long side of the groove at a uniform speed over 1 to 2 seconds to a depth of 0 (zero). Within 3 seconds after the scraper is finished, the scraper is observed by shining light at an angle of 20° to 30°, and the depth at which the particles appear in the groove of the particle gauge is read.

[0262] (Viscosity of positive electrode coating liquid) In one embodiment, the viscosity (ηb) of the coating solution of the positive electrode precursor is preferably 100 mPa·s or more and 5,000 mPa·s or less. More preferably, it is 200 mPa·s or more and 3,000 mPa·s or less. If the viscosity (ηb) is 100 mPa·s or more, dripping during coating film formation is suppressed, and the width and thickness of the coating film can be well controlled. Furthermore, if the viscosity is 5,000 mPa·s or less, stable coating can be achieved with little pressure loss in the flow path of the coating solution when using a coating machine, and the coating film thickness can be controlled to a desired value or less.

[0263] In another embodiment, the viscosity (ηb) of the positive electrode coating fluid is preferably 1,000 mPa·s or more and 20,000 mPa·s or less, more preferably 1,500 mPa·s or more and 10,000 mPa·s or less, and even more preferably 1,700 mPa·s or more and 5,000 mPa·s or less. A viscosity (ηb) of 1,000 mPa·s or more suppresses dripping during coating film formation, allowing for good control of the coating film width and thickness. Furthermore, a viscosity (ηb) of 20,000 mPa·s or less minimizes pressure loss in the coating fluid flow path when using a coating machine, enabling stable coating and controlling the coating film thickness to a desired level or less.

[0264] When the viscosity of the positive electrode coating solution is ηb1 and the viscosity after 24 hours of standing after measuring ηb1 is ηb2, ηb2 / ηb1 is preferably 0.40 or more and 1.30 or less. When ηb2 / ηb1 is 0.40 or more, uneven distribution of the binder in the coating solution is suppressed, thereby increasing the peel strength of the positive electrode precursor and suppressing the loss of the positive electrode active material layer during pre-doping. When ηb2 / ηb1 is 1.30 or less, denaturation of the binder in the coating solution by the alkaline compound is suppressed, thereby increasing the peel strength of the positive electrode precursor and suppressing the loss of the positive electrode active material layer during pre-doping. Generally, the time required for coating the positive electrode precursor is often within 24 hours per reel of electrode. Therefore, by evaluating ηb1 and ηb2, which is the viscosity 24 hours after measuring ηb1, uniformity of the electrode condition, such as basis weight and film thickness, from the start point of coating to the end point of coating can be ensured. From the above viewpoint, it is more preferable that ηb2 / ηb1 is within the range of 0.40 to 1.30.

[0265] (TI value of positive electrode coating fluid) The TI value (thixotropy index value) of the positive electrode coating fluid is preferably 1.1 or more, more preferably 1.2 or more, and even more preferably 1.5 or more. The upper limit of the TI value is preferably 6.0 or less, more preferably 5.0 or less. If the TI value is 1.1 or more, the width and thickness of the coating film can be well controlled. If the TI value is 6.0 or less, the occurrence of streaks and defects after coating film formation can be easily suppressed.

[0266] When TI1 is the thixotropy index value of the positive electrode coating solution and TI2 is the thixotropy index value after measuring TI1 and leaving the solution standing for 24 hours, TI2 / TI1 is preferably 0.50 or more and 1.20 or less. When TI2 / TI1 is 0.50 or more, dripping during electrode coating can be suppressed, and the positive electrode active material layer can be made uniform in thickness, resulting in high capacity. When TI2 / TI1 is 1.20 or less, localized thickening of the edge of the positive electrode active material layer can be suppressed, and chipping of the positive electrode active material layer during pre-doping can be suppressed. By evaluating TI1 and TI2, which is the TI value 24 hours after measuring TI1, uniformity of the coating weight and thickness at the edge of the coating film from the start point to the end point of coating can be ensured.

[0267] The viscosity (ηb) and TI value are values ​​that can be determined by the following methods. First, an E-type viscometer is used at a temperature of 25°C and a shear rate of 2 s -1 After measuring for 2 minutes or more under the above conditions, obtain a stable viscosity (ηa). Then, reduce the shear rate to 20 s -1 The viscosity (ηb) was measured under the same conditions as above except that the shear rate was changed to . The TI value was calculated using the viscosity value obtained above using the formula TI value = ηa / ηb. -1 From the 20s -1 When increasing the shear rate to 100°C, the increase may be made in one step, or the shear rate may be increased in multiple steps within the above range, while appropriately measuring the viscosity at each shear rate. TI1 and ηb1 are measured using the above method after dispersing the coating solution at 600 rpm for 1 minute using a planetary / revolutionary mixer. The coating solution is then left to stand in a sealed state for 24 hours at 25°C. The values ​​measured again using the above method are TI2 and ηb2. There are no particular restrictions on the weight of the positive electrode coating solution used for measurement, but a weight of 10 g or more and 100 g or less is preferred to reduce measurement variability. A weight of 10 g or more ensures measurement reproducibility. A weight of 100 g or less provides excellent sample handling.

[0268] <Production of Positive Electrode Precursor> The positive electrode precursor serving as the positive electrode of the nonaqueous lithium storage element can be produced by known electrode production techniques for lithium-ion secondary batteries, electric double layer capacitors, etc. For example, a coating liquid is prepared as described above, and the coating liquid is applied to one or both sides of a positive electrode current collector to form a coating film, which is then dried to obtain a positive electrode precursor. The resulting positive electrode precursor may then be pressed to adjust the film thickness or bulk density of the positive electrode active material layer. Alternatively, a method is also possible in which the positive electrode active material, alkali metal compound, and other optional components used as needed are dry-mixed without using a solvent, the resulting mixture is press-molded, and then attached to the positive electrode current collector using a conductive adhesive, or the resulting mixture is hot-pressed onto the positive electrode current collector to form a positive electrode active material layer.

[0269] (Formation of coating film) The coating film of the positive electrode precursor can be formed using any suitable coating machine, including, but not limited to, a die coater, comma coater, knife coater, or gravure coater. The coating film may be formed by single-layer coating or multi-layer coating. In the case of multi-layer coating, the coating liquid composition may be adjusted so that the content of the alkali metal compound in each layer of the coating film varies. When applying the coating film to the positive electrode current collector, multi-line coating, intermittent coating, or multi-line intermittent coating may be used. Sequential coating may be performed by coating one side of the positive electrode current collector and drying, followed by coating the other side and drying. Simultaneous double-sided coating may also be performed by simultaneously coating both sides of the positive electrode current collector with the coating liquid and drying. When applying the coating liquid to both sides of the positive electrode current collector, the respective ratios of the carbon material, lithium transition metal oxide, and alkali metal compound on the front and back surfaces are preferably 10% or less. For example, the ratio A1(front) / A1(back) of the mass ratio of activated carbon on the front surface of the positive electrode current collector to A1(back) on the back surface is 0.9 or more and 1.1 or less. Furthermore, the thickness ratio of the positive electrode active material layer on the front surface and back surface of the positive electrode current collector is preferably 10% or less. The closer the mass ratio and film thickness ratio of the front surface to the back surface are to 1.0, the less the charge / discharge load is concentrated on one surface, resulting in improved high-load charge / discharge cycle characteristics.

[0270] Furthermore, in the TD (direction perpendicular to the machine direction MD) of the positive electrode active material layer, it is preferable to make the edge portions thinner than the center portion. When forming an electrode assembly (described later), stress is applied to the portion near the terminal portion, which makes the positive electrode active material layer more likely to chip. Therefore, by thinning the edge portion of the positive electrode active material layer, stress can be alleviated and chipping of the positive electrode active material layer can be suppressed. Regarding the range of thinning the edge portion, it is more preferable that the thickness of the positive electrode active material layer within a range of 10% from the edge of the longest line segment of the positive electrode active material layer along the TD of the positive electrode active material layer toward the center is 90% to less than 100% of the thickness of the positive electrode active material layer at the midpoint of the longest line segment of the positive electrode active material layer. The coating speed is preferably 0.1 m / min to 100 m / min, more preferably 0.5 m / min to 70 m / min, and even more preferably 1 m / min to 50 m / min. A coating speed of 0.1 m / min or more ensures stable coating. On the other hand, if the coating speed is 100 m / min or less, coating accuracy can be sufficiently ensured.

[0271] (Drying of the coating) The coating film of the positive electrode precursor is preferably dried using a drying method such as hot air drying or infrared (IR) drying, more preferably far infrared radiation, near infrared radiation, or hot air at 80°C or higher. The coating film may be dried at a single temperature or at multiple stages with varying temperatures. Alternatively, a combination of multiple drying methods may be used. The drying temperature is preferably 25°C or higher and 200°C or lower, more preferably 40°C or higher and 180°C or lower, and even more preferably 50°C or higher and 160°C or lower. A drying temperature of 25°C or higher allows the solvent in the coating film to be sufficiently evaporated. On the other hand, a drying temperature of 200°C or lower can prevent cracking of the coating film due to rapid solvent evaporation, uneven distribution of the binder due to migration, and oxidation of the positive electrode current collector or positive electrode active material layer.

[0272] The moisture content of the dried positive electrode precursor is preferably 0.1% to 10% based on the mass of the positive electrode active material layer (100%). A moisture content of 0.1% by mass or more can prevent binder degradation due to excessive drying, resulting in low resistance. A moisture content of 10% by mass or less can prevent deactivation of alkali metal ions in nonaqueous lithium storage elements, resulting in high capacity.

[0273] When N-methyl-2-pyrrolidone (NMP) is used to prepare the coating liquid, the NMP content in the dried positive electrode precursor is preferably 0.1% to 10% based on the mass of the positive electrode active material layer (100%). When the NMP content is 0.1% by mass or more, deterioration of the binder due to excessive drying can be suppressed, resulting in low resistance. When the NMP content is 10% by mass or less, the self-discharge characteristics of the nonaqueous lithium storage element can be improved.

[0274] The water content of the positive electrode precursor can be measured by, for example, Karl Fischer titration (JIS 0068 (2001) "Method for measuring water content in chemical products"). Furthermore, the NMP content of the positive electrode precursor can be determined by immersing the positive electrode precursor 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 the NMP, then measuring the NMP with GC / MS and quantifying the NMP based on a previously prepared calibration curve.

[0275] (Pressing of cathode precursor) A hydraulic press, vacuum press, or other press can be suitably used to press the positive electrode precursor. The thickness, bulk density, and electrode strength of the positive electrode active material layer can be adjusted by the press pressure, the gap between the press rolls, and the surface temperature of the press unit, as described below. The press pressure is preferably 0.5 kN / cm or more and 20 kN / cm or less, more preferably 1 kN / cm or more and 10 kN / cm or less, and even more preferably 2 kN / cm or more and 7 kN / cm or less. A press pressure of 0.5 kN / cm or more can sufficiently increase the electrode strength. On the other hand, a press pressure of 20 kN / cm or less can be adjusted to the desired thickness or bulk density of the positive electrode active material layer without causing warping or wrinkling in the positive electrode precursor. The gap between the press rolls can be set to any value depending on the thickness of the positive electrode precursor after drying to achieve the desired thickness or bulk density of the positive electrode active material layer. Furthermore, the press speed can be set to any speed that does not cause warping or wrinkling in the positive electrode precursor. The surface temperature of the press unit can be room temperature, or it can be heated as necessary. The lower limit of the surface temperature of the press part when heated is preferably at least 60°C below the melting point of the binder used, more preferably at least 45°C below the melting point of the binder, and even more preferably at least 30°C below the melting point of the binder. On the other hand, the upper limit of the surface temperature of the press part when heated is preferably at most 50°C above the melting point of the binder used, more preferably at most 30°C above the melting point of the binder, and even more preferably at most 20°C above the melting point of the binder. For example, when PVdF (polyvinylidene fluoride: melting point 150°C) is used as the binder, heating is preferably from 90°C to 200°C, more preferably from 105°C to 180°C, and even more preferably from 120°C to 170°C. Furthermore, when a styrene-butadiene copolymer (melting point 100°C) is used as the binder, it is preferable to heat the mixture to a temperature of 40°C or higher and 150°C or lower, more preferably 55°C or higher and 130°C or lower, and even more preferably 70°C or higher and 120°C or lower.

[0276] The melting point of the binder can be determined from the endothermic peak position in DSC (Differential Scanning Calorimetry). For example, using a PerkinElmer DSC7 differential scanning calorimeter, 10 mg of sample resin is placed in the measurement cell, and the temperature is raised from 30°C to 250°C at a rate of 10°C / min in a nitrogen gas atmosphere. The endothermic peak temperature during the temperature rise is the melting point.

[0277] Pressing may be performed multiple times while changing the conditions of the press pressure, gap, speed, and surface temperature of the press part. When the positive electrode precursor is multi-line coated, it is preferable to slit it before pressing. By slitting and pressing the multi-line coated positive electrode precursor, stress is applied to the current collector portion not coated with the positive electrode active material layer, which can prevent wrinkles from forming. The positive electrode precursor can also be slit again after pressing.

[0278] (Thickness of the positive electrode active material layer) The thickness of the positive electrode active material layer is preferably 10 μm or more and 200 μm or less per side of the positive electrode current collector. The thickness of the positive electrode active material layer is more preferably 20 μm or more and 100 μm or less per side, and even more preferably 30 μm or more and 80 μm or less. If this thickness is 10 μm or more, sufficient charge / discharge capacity can be achieved. On the other hand, if this thickness is 200 μm or less, ion diffusion resistance within the electrode can be maintained low. Therefore, sufficient output characteristics can be obtained, and the cell volume can be reduced, thereby increasing the energy density. Note that when the current collector has through-holes or irregularities, the thickness of the positive electrode active material layer refers to the average thickness per side of the portion of the current collector that does not have through-holes or irregularities.

[0279] (Peeling strength of positive electrode active material layer) The peel strength of the positive electrode active material layer of the positive electrode precursor is preferably 0.02 N / cm or more and 3.00 N / cm or less. If the peel strength is 0.02 N / cm or more, it is possible to prevent the positive electrode active material layer from being chipped due to gas generation in the pre-doping step, and to prevent micro-short circuits. If the peel strength is 3.00 N / cm or less, this means that there is no excess binder or the like in the positive electrode active material layer, improving the diffusibility of the electrolyte and reducing resistance. The peel strength of the positive electrode active material layer is preferably 0.03 to 2.76 N / cm, more preferably 0.05 to 1.64 N / cm.

[0280] The peel strength of the positive electrode active material layer of the positive electrode precursor is a value measured after the above-mentioned pressing. If pressing is performed multiple times, it is a value measured after the final pressing. If an electrode body described below is produced without pressing, it is a value measured in an unpressed state.

[0281] The peel strength of the positive electrode active material layer can be measured by a known method, for example, a peel test in accordance with JIS Z0237 (2009) "Test method for adhesive tapes and adhesive sheets" or the test method used in the examples described below may be used.

[0282] The peel strength of the positive electrode active material layer of the positive electrode can be measured as follows. A nonaqueous lithium storage element with a voltage adjusted to 2.9 V is disassembled to remove the electrode laminate, and the positive electrode is cut out from the electrode laminate and washed with an organic solvent. The organic solvent is not particularly limited as long as it can remove the electrolyte decomposition products deposited on the positive electrode surface. However, using an organic solvent with a solubility of lithium compounds of 2% or less suppresses the elution of lithium compounds. Suitable examples of such organic solvents include polar solvents such as methanol, ethanol, acetone, and methyl acetate. The resulting positive electrode is vacuum-dried, and the peel strength can be measured using the method described above.

[0283] <Production of negative electrodes> The negative electrode can be produced by forming 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. The negative electrode can be produced by known electrode production techniques for lithium ion secondary batteries, electric double layer capacitors, etc. For example, various materials including the negative electrode active material are dispersed or dissolved in water or an organic solvent to prepare a slurry-like coating liquid, and this coating liquid is applied to one or both sides of the negative electrode current collector to form a coating film, which is then dried to obtain a negative electrode. The resulting negative electrode may then be pressed to adjust the film thickness or bulk density of the negative electrode active material layer.

[0284] (Production of negative electrode coating solution) The method for preparing the negative electrode coating liquid is not particularly limited, but it can be suitably carried out using a dispersing machine such as a homodisper, a multi-axis dispersing machine, a planetary mixer, a thin film rotating high-speed mixer, or a planetary mixer.

[0285] It is preferable to adjust the solid content of the negative electrode coating solution to 16% or more and 21% or less (e.g., 16.0% or more and 21.0% or less) from the viewpoint of controlling the mode diameter of the voids in the negative electrode active material layer within an appropriate range. By decreasing the solid content, the mode diameter tends to be controlled to be large, and by increasing the solid content, the mode diameter tends to be controlled to be small.

[0286] The above graphite is preferably used as the negative electrode material. The inventors have noticed that when graphite with a small particle size and a high specific surface area is used, aggregates are generated on the negative electrode surface after coating. As a result of extensive research by the inventors, it has been found that during storage at room temperature before coating, dispersants and binders, etc., separate from the dispersed graphite in the negative electrode coating solution, and re-aggregation of the graphite occurs. In this case, it may be difficult to maintain a stable dispersion state. In the present disclosure, the inventors have found that it is preferable to set the storage temperature of the negative electrode coating solution from the preparation of the negative electrode coating solution until coating to 15°C or less, more preferably 10°C or less, which makes it easier to suppress the generation of aggregates. As a result, even when graphite with a small particle size and a high specific surface area is used, the generation of aggregates on the negative electrode surface is prevented. 2 Aggregate frequency of 1 particle / cm or more2 The following negative electrode can be easily produced. The storage temperature is preferably maintained at 15°C or below from immediately after dispersing the negative electrode coating liquid until immediately before coating. There are no particular restrictions on the method for controlling the storage temperature. The storage temperature can be controlled by the temperature of the storage environment, water cooling of the coating liquid tank, etc. Controlling by water cooling of the coating liquid tank, etc., is more preferable because it allows the temperature to be controlled until immediately before coating.

[0287] (Formation of coating film) The coating film of the negative electrode active material layer is not particularly limited, but a coating machine such as a die coater, comma coater, knife coater, or gravure coater can be preferably used. The coating film may be formed by single-layer coating or multi-layer coating. In the case of multi-layer coating, the coating liquid composition may be adjusted so that the content of components in each coating layer is different. When applying the coating film to the negative electrode current collector, it may be multi-line coating, intermittent coating, or multi-line intermittent coating. When forming the negative electrode active material layer on both sides of the negative electrode current collector, sequential coating may be performed by coating one side of the negative electrode current collector and drying, and then coating the other side and drying. Alternatively, simultaneous double-sided coating may be performed by simultaneously coating and drying the coating liquid on both sides of the negative electrode current collector. In this case, the difference in thickness between the negative electrode active material layers on the front and back surfaces of the negative electrode current collector is preferably 10% or less of the average thickness of both surfaces. The closer the mass ratio and film thickness ratio of the negative electrode active material layers on the front and back surfaces is to 1.0, the less the charge / discharge load is concentrated on one surface, and the more likely it is that the high-load charge / discharge cycle characteristics will improve.

[0288] (Drying of the coating) After forming a coating film of the negative electrode active material layer on the negative electrode current collector, the coating film is dried. The coating film of the negative electrode precursor is preferably dried by an appropriate drying method such as hot air drying or infrared (IR) drying, preferably using far infrared rays, near infrared rays, or hot air. The coating film may be dried at a single temperature or by changing the temperature in multiple stages. A combination of drying methods may also be used. The drying temperature is preferably 25°C or higher and 200°C or lower, more preferably 40°C or higher and 180°C or lower, and even more preferably 50°C or higher and 160°C or lower. A drying temperature of 25°C or higher facilitates sufficient volatilization of the solvent in the coating film. On the other hand, a drying temperature of 200°C or lower facilitates suppressing cracking of the coating film due to rapid solvent evaporation, uneven distribution of the binder due to migration, and oxidation of the negative electrode current collector or negative electrode active material layer.

[0289] The moisture content of the negative electrode active material layer after drying is preferably 0.1% by mass or more and 10% by mass or less, when the total mass of the negative electrode active material layer is taken as 100% by mass. A moisture content of 0.1% by mass or more suppresses deterioration of the binder due to excessive drying, facilitating low resistance. A moisture content of 10% by mass or less suppresses deactivation of alkali metal ions, facilitating high capacity. When N-methyl-2-pyrrolidone (NMP) is used to prepare the coating liquid, the NMP content in the negative electrode active material layer after drying is preferably 0.1% by mass or more and 10% by mass or less, when the total mass of the negative electrode active material layer is taken as 100%. The moisture content of the negative electrode active material layer can be measured, for example, by Karl Fischer titration (JIS 0068 (2001) "Method for measuring moisture content in chemical products"). The amount of NMP contained in the negative electrode active material layer can be determined by immersing the negative electrode active material layer in ethanol with a mass that is 50 to 100 times the mass of the negative electrode active material layer for 24 hours in a 25°C environment to extract the NMP, and then measuring the result with GC / MS, and quantifying the amount based on a calibration curve that has been prepared in advance.

[0290] (pressing negative electrode) In order to maintain the mode diameter of the voids in the negative electrode adjusted by the solid content of the negative electrode coating liquid at an appropriate size, it is preferable not to perform pressing. The negative electrode active material layer can be pressed as long as the mode diameter of the voids in the negative electrode can be maintained. Suitable pressing machines such as hydraulic presses, vacuum presses, and roll presses can be used. 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 press rolls, and the surface temperature of the press unit, as described below. When a roll press is used for pressing, the gap between the press rolls can be set to an appropriate value so that the negative electrode active material layer has the desired thickness and bulk density. The pressing speed can be set to an appropriate speed that does not cause bending or wrinkling in the negative electrode.

[0291] The surface temperature of the press part may be room temperature, or may be heated as necessary. When heated, the lower limit of the surface temperature of the press part is preferably at least 60°C below the melting point of the binder used, more preferably at least 45°C below the melting point of the binder, and even more preferably at least 30°C below the melting point of the binder. On the other hand, when heated, the upper limit of the surface temperature of the press part is preferably at most 50°C above the melting point of the binder used, more preferably at most 30°C above the melting point of the binder, and even more preferably at most 20°C above the melting point of the binder. For example, when polyvinylidene fluoride (melting point 150°C) is used as the binder, the press part is preferably heated to a temperature of 90°C to 200°C, more preferably at most 105°C to 180°C, and even more preferably at most 120°C to 170°C. Furthermore, when a styrene-butadiene copolymer (melting point 100°C) is used as the binder, the press section 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. The melting point of the binder can be determined from the endothermic peak position in DSC (Differential Scanning Calorimetry). For example, using a PerkinElmer DSC7 differential scanning calorimeter, 10 mg of sample resin is placed in the measurement cell and heated from 30°C to 250°C at a heating rate of 10°C / min in a nitrogen gas atmosphere. The endothermic peak temperature during the heating process is the melting point.

[0292] Pressing may be performed multiple times while changing the conditions of the press pressure, gap, speed, and surface temperature of the press part. When the negative electrode active material layer is multi-line coated, it is preferable to slit it before pressing. If the negative electrode is pressed without slitting the multi-line coated negative electrode active material layer, excessive stress may be applied to the portion of the negative electrode current collector not coated with the negative electrode active material layer, which may cause wrinkles. After pressing, the negative electrode active material layer may be slit again.

[0293] (Thickness of negative electrode active material layer) The thickness of the negative electrode active material layer is preferably 10 μm or more and 70 μm or less per side, more preferably 20 μm or more and 60 μm or less. If this thickness is 10 μm or more, good charge / discharge capacity can be achieved. On the other hand, if this thickness is 70 μm or less, the cell volume can be reduced, thereby increasing the energy density. When the current collector has holes, the thickness of the negative electrode active material layer refers to the average thickness per side of the non-hole portion of the current collector.

[0294] <Assembly process: Electrode body fabrication> In the assembly process, for example, a positive electrode terminal and a negative electrode terminal can be connected to a laminate formed by stacking a positive electrode precursor and a negative electrode cut into a sheet shape with a separator interposed therebetween to produce an electrode laminate. Alternatively, a positive electrode terminal and a negative electrode terminal can be connected to a wound body formed by stacking and winding a positive electrode precursor and a negative electrode with a separator interposed therebetween to produce an electrode wound body. The shape of the electrode wound body may be cylindrical or flat.

[0295] The method for connecting the positive electrode terminal and the negative electrode terminal is not particularly limited, but methods such as resistance welding and ultrasonic welding can be used. It is preferable to remove the remaining solvent by drying the electrode assembly (electrode stack or electrode wound assembly) to which the terminals are connected. The drying method is not limited, but drying by vacuum drying or the like is possible. The remaining solvent is preferably 1.5 mass % or less based on the total mass of the positive electrode active material layer or the negative electrode active material layer. If the remaining solvent is 1.5 mass % or less, the self-discharge characteristics are improved, which is preferable.

[0296] (Suppression of interfacial peeling) When using activated carbon as the positive electrode active material and non-porous or smooth aluminum foil as the positive electrode current collector, the heat and vibration generated during welding can easily cause peeling at the interface between the positive electrode active material layer and the positive electrode current collector. By suppressing interfacial peeling, we have been able to reduce the positive electrode interface resistance to 5.00 Ωcm at the time of cell completion or after cell completion. 2 In order to control the following, when welding the external terminal, the wound body or laminated body is fixed with a jig such as a stainless steel (SUS) plate, and the entire surface is fixed with a spring, and the pressure is 0.1 kgf / cm 2 It is desirable to fix the positive electrode current collector and the activated carbon of the positive electrode active material layer under the above load. This can prevent the smooth-surface aluminum foil serving as the positive electrode current collector from peeling off at the interface with the activated carbon of the positive electrode active material layer due to vibrations and heat during welding.

[0297] (Secondary drying of electrode body) The residual solvent in the positive electrode precursor or negative electrode can be further reduced by secondary drying. In secondary drying, the positive electrode precursor or negative electrode can be heated under reduced pressure (vacuum heating and drying) or by infrared heating. In secondary drying, the positive electrode precursor or negative electrode can be dried at a single temperature or at multiple temperatures. In the case of reduced pressure heating, the reduced pressure can efficiently reduce the residual solvent in the positive electrode precursor or negative electrode active material layer. Secondary drying of the electrode can be performed any time between after the primary drying of the electrode and before the injection of the liquid. The timing is preferably selected taking into consideration the efficiency of reducing the residual solvent and productivity. The residual solvent is preferably 1.5% by mass or less based on the total mass of the positive electrode active material layer or negative electrode active material layer. Residual solvent exceeding 1.5% by mass is undesirable because residual solvent remains in the system, deteriorating self-discharge characteristics.

[0298] The dried electrode assembly is preferably housed in an outer package, such as a metal can or a laminate film, in a dry environment with a dew point of -40°C or lower, and sealed except for one opening for injecting a nonaqueous electrolyte solution. A dew point of -40°C or lower is preferred because it prevents moisture from adhering to the electrode assembly and remaining in the system, improving self-discharge characteristics. The method for sealing the outer package is not particularly limited, but methods such as heat sealing and impulse sealing can be used.

[0299] <Injection, impregnation, and sealing processes> After the assembly process, a nonaqueous electrolyte solution is injected into the electrode body housed in the outer casing. After the injection, it is desirable to further impregnate the electrode body so that the positive electrode, negative electrode, and separator are thoroughly soaked with the nonaqueous electrolyte solution. If the electrolyte solution is not immersed in at least a portion of the positive electrode, negative electrode, and separator, lithium doping will proceed unevenly in the lithium doping process described below, resulting in increased resistance and reduced durability of the resulting nonaqueous lithium storage element. The impregnation method is not particularly limited, but for example, the electrode body after the injection can be placed in a decompression chamber with the outer casing open, and the chamber can be decompressed using a vacuum pump and then returned to atmospheric pressure. After the impregnation, the electrode body with the outer casing open can be sealed while decompressing.

[0300] (Control of positive electrode interfacial resistance) When using activated carbon as the positive electrode active material and nonporous or smooth-surfaced aluminum foil as the positive electrode current collector, it is preferable to suppress swelling of the positive electrode active material layer during impregnation and to suppress peeling at the interface between the positive electrode active material layer and the positive electrode current collector due to air being expelled from the pores of the activated carbon as the electrolyte penetrates into the pores. To achieve this, it is preferable to reduce the decompression rate in a high vacuum state during impregnation. This slows the rate of penetration of the electrolyte into the positive electrode active material layer and the activated carbon pores of the positive electrode active material, thereby suppressing interfacial peeling. Specifically, it is desirable to perform a multi-stage decompression process, reducing the pressure to -50 kPa (based on atmospheric pressure) at a rate of approximately 1.0 kPa / s, and then reducing the rate to approximately 0.1 kPa / s below -50 kPa. This reduces the interfacial resistance between the positive electrode active material layer and the positive electrode current collector to 0.05 Ωcm when the cell is completed. 2 More than 5.00Ωcm 2 It can be controlled as follows:

[0301] (Secondary electrode drying) The residual solvent in the positive electrode precursor or negative electrode can be further reduced by secondary drying. In secondary drying, the positive electrode precursor or negative electrode can be heated under reduced pressure (vacuum heating and drying) or by infrared heating. In secondary drying, the positive electrode precursor or negative electrode can be dried at a single temperature or at multiple temperatures. In the case of reduced pressure heating, the reduced pressure can efficiently reduce the residual solvent in the positive electrode precursor or negative electrode active material layer. Secondary drying of the electrode can be performed any time between after the primary drying of the electrode and before the injection of the liquid. The timing is preferably selected taking into consideration the efficiency of reducing the residual solvent and productivity. The residual solvent is preferably 1.5% by mass or less based on the total mass of the positive electrode active material layer or negative electrode active material layer. Residual solvent exceeding 1.5% by mass is undesirable because residual solvent remains in the system, deteriorating self-discharge characteristics.

[0302] <Lithium doping process> In the lithium doping step, a voltage is applied between the positive electrode precursor and the negative electrode to decompose the lithium compound in the positive electrode precursor, releasing lithium ions, and then reducing the lithium ions at the negative electrode, thereby pre-doping the lithium ions into the negative electrode active material layer. In the lithium doping step, gases such as CO2 are generated as a result of the oxidative decomposition of the lithium compound in the positive electrode precursor. Therefore, when applying a voltage, it is preferable to provide a means for releasing the generated gas to the outside of the exterior body. Examples of such a means include applying a voltage with a portion of the exterior body open; or applying a voltage with a suitable gas release means, such as a gas vent valve or a gas-permeable film, already installed in a portion of the exterior body. When an alkali metal is used, the term "lithium doping" is used interchangeably with "alkali doping" (the same applies hereinafter).

[0303] The voltage applied in the doping step is preferably 4.3 V or more and 4.6 V or less. This range allows the oxidative decomposition of the lithium compound to proceed and prevents excessive film formation on the positive electrode active material. Furthermore, the amount of lithium fluoride in the negative electrode active material layer can be increased by increasing the doping voltage.

[0304] The temperature in the doping step is preferably 40°C or higher and 70°C or lower. Within this range, the oxidative decomposition of the lithium compound proceeds and excessive film formation on the positive electrode active material can be suppressed. The amount of lithium fluoride in the negative electrode active material layer can be increased by increasing the doping voltage. Increasing the doping temperature also promotes the decomposition of the lithium compound, making it easier to form voids in the positive electrode active material layer.

[0305] (Lithium doping when using lithium compound complex) When the positive electrode active material layer contains a lithium compound composite, a pre-doping (lithium doping) step is preferably performed at a temperature of 20° C. or higher and 60° C. or lower. In this embodiment, the positive electrode active material containing lithium ions and the lithium compound in the lithium compound composite function as a dopant source for lithium ions to the negative electrode active material. In the lithium doping step, a voltage is preferably applied between the positive electrode precursor and the negative electrode precursor to decompose the lithium compound in the positive electrode precursor to release lithium ions, and then the lithium ions are reduced by the negative electrode precursor, thereby pre-doping the lithium ions into the negative electrode active material layer.

[0306] When the positive electrode active material layer contains a lithium compound composite, the voltage applied between the positive electrode precursor and the negative electrode precursor during pre-doping is preferably 4.2 V or higher. This voltage is preferably 4.2 to 5.0 V, more preferably 4.3 to 4.9 V. Examples of voltage application methods include applying a constant voltage of 4.2 V or higher using a charge / discharge device, a power source, or the like; superimposing a pulse voltage while applying a constant voltage of 4.2 V or higher; and using a charge / discharge device to perform charge / discharge cycles within a voltage range including 4.2 V or higher. When pre-doping is performed by constant-current, constant-voltage charging, the completion of pre-doping can be determined when the current value during constant-voltage charging becomes 0.3 times or less that during constant-current charging. Current flows due to the decomposition of the lithium compound in the positive electrode precursor, and the current value attenuates as the amount of this lithium compound decreases. Applying a voltage of 4.2 V or higher will cause the decomposition of the lithium compound and the decomposition reaction of the electrolyte to proceed, but by ending pre-doping when the current value becomes 0.3 times or less that during constant current charging, it is easier to decompose a sufficient amount of lithium compound and to suppress the decomposition of the electrolyte, which is a side reaction.

[0307] When the positive electrode active material layer contains a lithium compound composite, the temperature of the lithium ion secondary battery during pre-doping is preferably adjusted to 20°C or higher and 60°C or lower. If the temperature is 20°C or higher, decomposition of the lithium compound is promoted, making it easier to perform pre-doping in a short time. If the temperature is 60°C or lower, it is easier to suppress side reactions accompanying the decomposition of the lithium compound.

[0308] (Gas release) During the pre-doping operation, gases such as CO2 are generated due to the oxidative decomposition of the lithium compound in the positive electrode precursor. Therefore, when applying a voltage, it is preferable to take measures to release the generated gas to the outside of the exterior body. Examples of such measures include a method of applying a voltage with a part of the exterior body open; and a method of applying a voltage with a suitable gas release means, such as a gas vent valve or a gas permeable film, previously installed in a part of the exterior body.

[0309] <Aging process> After the lithium doping step, it is preferable to perform aging on the electrode body. In the aging step, the solvent in the electrolyte solution is decomposed at the negative electrode, and a lithium ion-permeable solid polymer coating is formed on the surface of the negative electrode. The aging method is not particularly limited, but for example, a method of reacting the solvent in the electrolyte solution in a high-temperature environment can be used.

[0310] <Gas removal process> After the aging step, it is preferable to further degas the electrode stack to completely remove any remaining gas from the electrolyte, the positive electrode, and the negative electrode. Gas remaining in at least a portion of the electrolyte, the positive electrode, and the negative electrode inhibits ionic conduction, preventing an increase in the resistance of the resulting nonaqueous lithium storage element. The degassing method is not particularly limited, and examples include placing the electrode stack in a vacuum chamber with the outer casing open and using a vacuum pump to reduce the pressure inside the chamber. After degassing, the outer casing is sealed to produce a nonaqueous lithium storage element.

[0311] A nonaqueous lithium storage battery element can be manufactured by the above method. When the positive electrode precursor contains a lithium compound composite, the nonaqueous lithium storage battery element may include a positive electrode having MO2 remaining after the lithium compound in the lithium compound composite contained in the positive electrode precursor is decomposed, and a negative electrode having a negative electrode active material layer doped with lithium ions using the lithium compound as a dopant source. The positive electrode may further contain a lithium compound that was not decomposed during pre-doping.

[0312] <Cell design for non-aqueous lithium storage element precursor> The charge capacity per unit area of ​​the positive electrode precursor is A2 (mAh / cm 2 ), and the discharge capacity per unit area of ​​the positive electrode precursor is A3 (mAh / cm 2 ), and the charge capacity per unit area of ​​the negative electrode precursor is B2 (mAh / cm 2 ), it is preferable to configure the battery so that 0.65≦A3 / A2≦0.93 and 1.03≦B2 / A3≦1.26 are satisfied. This allows the voltage change at the end of discharge of a lithium-ion secondary battery using LFP and / or LMFP to be gradual. "0.65≦A3 / A2≦0.93" can be, for example, "0.650≦A3 / A2≦0.930," and "1.03≦B2 / A3≦1.26" can be, for example, "1.030≦B2 / A3≦1.260."

[0313] In the relationship between A2 and A3, A3 / A2≦0.93 indicates that the amount of lithium ions that can be absorbed into the positive electrode precursor is small compared to the amount of lithium ions released from the positive electrode precursor. In other words, this indicates that a certain amount of lithium ion source (lithium ions derived from lithium compounds) other than the positive electrode active material is present in the positive electrode precursor. Furthermore, B2 / A3 1.03≦B2 / A3 indicates that the amount of lithium ions that can be absorbed into the negative electrode precursor is greater than that of the positive electrode precursor. Lithium ion secondary battery precursors that satisfy these relationships satisfy the above-mentioned lithium ion secondary battery cell design requirement of A1 / B1≦0.96.

[0314] On the other hand, a condition of 0.65≦A3 / A2 indicates that there is no excess lithium ion source in the positive electrode precursor. Furthermore, a condition of B2 / A3≦1.26 allows for the reduction of excess negative electrode active material. A lithium ion secondary battery precursor satisfying these relationships satisfies the aforementioned lithium ion secondary battery cell design requirement of 0.71≦A1 / B1. A3 / A2 and / or B2 / A3 can be controlled by adjusting A2, A3, and / or B2. For example, A2, A3, and / or B2 can be adjusted by adjusting the amount of positive electrode active material and lithium compound mixed in the positive electrode precursor production. Subsequently, when producing the positive electrode precursor, the values ​​of A2 and / or A3 can be adjusted by adjusting the thickness of the coating film so that the active material layer has a desired basis weight. Furthermore, the value of B1 can be adjusted by adjusting the amount of active material mixed in the negative electrode precursor production to achieve a desired composition, and then adjusting the thickness of the coating film so that the active material layer has a desired basis weight.

[0315] Energy storage module The nonaqueous lithium-ion storage element of the present disclosure can be used to fabricate an energy storage module. For example, a desired energy storage system can be fabricated by connecting multiple nonaqueous lithium-ion storage elements in series or in parallel.

[0316] The energy storage module of the present disclosure can achieve both high input / output characteristics and safety at high temperatures, and can therefore be used as a power regeneration assist system, a power load leveling system, an uninterruptible power supply system, a contactless power supply system, an energy harvesting system, an energy storage system, a solar power generation energy storage system, an electric power steering system, an emergency power supply system, an in-wheel motor system, an idling stop system, an electric vehicle, a plug-in hybrid vehicle, a hybrid vehicle, an electric motorcycle, a quick charging system, a smart grid system, and the like.

[0317] Energy storage systems are suitable for use in natural power generation such as solar power generation or wind power generation, power load leveling systems are suitable for use in microgrids, and uninterruptible power supply systems are suitable for use in factory production facilities, etc. In contactless power supply systems, non-aqueous lithium energy storage elements are suitable for use in leveling voltage fluctuations such as those caused by microwave power transmission or electric field resonance and for storing energy, and in energy harvesting systems, non-aqueous lithium energy storage elements are suitable for use in using power generated by vibration power generation or the like.

[0318] In the energy storage system, a plurality of nonaqueous lithium-ion storage elements are connected in series or parallel to form a cell stack, or a nonaqueous lithium-ion storage element is connected in series or parallel to a lead battery, a nickel-metal hydride battery, a lithium-ion secondary battery, a sodium-ion secondary battery, a zinc-ion secondary battery, a fluoride-ion secondary battery, or a fuel cell. Furthermore, the nonaqueous lithium-ion storage element of the present disclosure can achieve both high input / output characteristics and safety at high temperatures, and therefore can be installed in vehicles such as electric vehicles, plug-in hybrid vehicles, hybrid vehicles, and electric motorcycles. The above-described power regeneration assist system, electric power steering system, emergency power supply system, in-wheel motor system, idling stop system, or a combination thereof can be suitably installed in the vehicle. [Example]

[0319] Examples and comparative examples of the present disclosure will be specifically described below, but the present disclosure is not limited in any way by the following examples and comparative examples.

[0320] <<Measurement and Evaluation Methods>> <1000μm of the positive electrode surface 2 More than 10000μm 2 Aggregate frequency of: 1000 μm of the positive electrode surface 2 More than 10000μm 2The following aggregate frequency was determined by the following method. First, in the case of a nonaqueous lithium storage element, the voltage was adjusted by constant current discharge to 2.0 V at a 1C rate current in a 25°C environment, followed by constant voltage discharge at 2.0 V for 1 hour. Then, the nonaqueous lithium storage element was disassembled in an argon atmosphere with a dew point of -60°C or lower, and the positive electrode was removed. The obtained positive electrode was washed three times with methyl ethyl carbonate and vacuum dried at 25°C for 12 hours to obtain a positive electrode sample.

[0321] In the case of the electric double layer capacitor, the voltage was adjusted by constant current discharge to 0 V at a rate of 1 C in a 25°C environment, followed by constant voltage discharge at 0 V for 1 hour. The nonaqueous lithium storage element was then disassembled in an argon atmosphere with a dew point of -60°C or lower, and the positive electrode was removed. The obtained positive electrode was washed three times with methyl ethyl carbonate and vacuum dried at 25°C for 12 hours to obtain a positive electrode sample.

[0322] A positive electrode sample measuring at least 8cm x 6cm was measured using a scanner (RICOH MP C5503). The measurement settings were grayscale, 600 dpi, medium density, JPEG / TIFF file format, and a size large enough to fit the entire positive electrode sample. All other settings were default. The scanned image, excluding 1cm from each end, was imported into ImageJ (ver. 1.53t). The imported image was converted to 8-bit type in ImageJ, and the mean (average brightness) was obtained using the getStatics function. The threshold was set to min = mean + 15 and max = 255 for binarization. The scale distance was set to 600, known = 25400, and unit = μm (i.e., a width of 600 pixels corresponds to 1 inch (25.4 mm)). The area distribution was then obtained using Analyze Particles. From this area distribution, a 1000 μm area was determined to represent an aggregate. 2 More than 10000μm 2 Count the number of areas n below. The area S (cm) of the area analyzed by ImageJ 2) and 1000 μm 2 More than 10000μm 2 The following aggregate frequency Dn was calculated by Dn=n / S.

[0323] <Total pore volume of positive electrode> The total pore volume of the positive electrode in the present disclosure based on the weight of the positive electrode active material layer can be obtained by mercury porosimeter measurement. The nonaqueous lithium storage element was subjected to constant current discharge to 2.0 V at a rate of 1 C in an environment of 25°C, and then subjected to constant voltage discharge at 2.0 V for 1 hour to adjust the voltage. The nonaqueous lithium storage element was then disassembled in an argon atmosphere with a dew point of -60°C or lower, and the positive electrode was removed. The obtained positive electrode was washed three times with methyl ethyl carbonate and vacuum dried at 25°C for 12 hours to obtain a positive electrode sample. The positive electrode weight was M1 (g / sheet), the positive electrode area was S1, and the basis weight of the current collector was m1 (g / m 2 ), the weight of the active material layer per positive electrode sample was calculated as M = M1 - S1 × m1 (g). The pore size distribution was measured using a MICRO Meritics AutoPore 9500. The sample was placed in a sample container, degassed, and then mercury was introduced into the container. The pressure was gradually increased to force the mercury into the pores of the sample (maximum pressure: 0.33 MPa). The pore size distribution of the sample was measured using the following equation, based on the relationship between the pressure and the amount of mercury injected. To calculate the pore size, when mercury is injected into a cylindrical pore with a diameter of D at a pressure P, the contact angle of the mercury is θ, and the surface tension of the mercury is γ, the following equation holds true based on the balance between the surface tension and the pressure acting on the pore cross section. D=-(1 / P)4γcosθ In this disclosure, the contact angle θ of mercury is set to 130° and the surface tension γ is set to 485° / cm. tot (cc) when the differential pore volume dV tot This was integrated over the range of the membrane pores (0.0055 to 5 μm) to obtain the total intrusion volume V tot (cc) was obtained. Total pore volume I tot (cc / g) was obtained from the weight of the active material layer of the sample, M (g), using the following formula: I tot =V tot / M

[0324] <Pore diameter of positive electrode active material layer> The pore diameters D25, D75, and D75-D25 of the positive electrode active material layer in this disclosure are obtained by mercury porosimeter measurement. From the results obtained by the mercury porosimeter measurement described above in "Total Pore Volume of Positive Electrode," the differential pore volume V (mL / g) for each pore diameter D (μm) is calculated. The differential pore volume is integrated over the following pore range, and the following V tot and V i Ask for. The total pore volume within the membrane pore range of 0.0055 to 5 μm is V tot (mL / g), Membrane pore diameter D i The cumulative pore volume of ~5 μm is V i (mL / g) Next, the pore volume ratio V pi (%) was calculated using the following formula: V pi (%)=V i ×100 / V tot The V obtained at this time pi -Pore diameter D i From the graph, the pore diameter D (μm) at Vpi = 25, 75 (%) was read from the graph, and the cumulative pore diameters D25 and D75 (μm) were calculated. Of the pore diameters obtained with the mercury porosimeter, those of 5.0 μm or less were considered to be pores in the positive electrode active material layer. This is because pores of a larger size include cracks and chips in the active material layer, and voids between electrodes when the electrodes are stacked when the sample is placed in the sample container.

[0325] <C Rate> The current discharge rate (also called "C rate") is the relative ratio of the current during discharge to the discharge capacity. Generally, 1C is the current value at which discharge is completed in one hour when constant current discharge is performed from the upper limit voltage to the lower limit voltage. In this disclosure, for a nonaqueous lithium storage element, 1C is the current value at which discharge is completed in one hour when constant current discharge is performed from 4.0 V to 2.0 V. For an electric double layer capacitor, 1C is the current value at which discharge is completed in one hour when constant current discharge is performed from 2.5 V to 0 V.

[0326] <Capacitance measurement> The capacity Q (mAh) of the nonaqueous lithium storage element from 4.0 to 2.0 V is determined as follows: The nonaqueous lithium storage element is charged at a constant current of 1 C in a thermostatic chamber set at 25°C until the voltage reaches 4.0 V, and then a constant voltage charge of 4.0 V is applied for 30 minutes. After that, the element is discharged at a constant current of 1 C until the voltage reaches 2.0 V, and the capacity Q (mAh) is determined.

[0327] <Quantitative determination of lithium carbonate, lithium iron phosphate, and carbon material in the positive electrode, and calculation of the mass proportion of lithium iron phosphate> The lithium carbonate content X3, lithium iron phosphate content X2, and carbon material content X1, such as activated carbon, contained in the positive electrode active material layer of the positive electrode of a nonaqueous lithium storage element are quantified by the following method. First, the nonaqueous lithium storage element is subjected to constant current discharge to 2.0 V at a 1C rate current in a 25°C environment, followed by constant voltage discharge at 2.0 V for 1 hour to adjust the voltage. The nonaqueous lithium storage element is then disassembled in an argon atmosphere ...

Claims

1. A non-aqueous lithium storage element comprising: a positive electrode including a positive electrode active material layer disposed on a positive electrode current collector; a negative electrode including a negative electrode active material layer disposed on a negative electrode current collector; a separator; and a non-aqueous electrolyte solution containing lithium ions, the positive electrode active material layer contains a carbon material including activated carbon as a positive electrode active material, and lithium iron phosphate; The content of the carbon material in the positive electrode active material layer is X １ (mass%), the content of lithium iron phosphate is X ２ (mass%), the mass ratio of lithium iron phosphate (X ２ / (X １ +X ２ ) is 0.40 or more and 0.85 or less, a total pore volume of the positive electrode active material layer based on the weight of the positive electrode active material layer is 0.29 cc / g or more and 0.70 cc / g or less, the positive electrode active material layer has a pore diameter D25 of 0.34 μm or more and 0.64 μm or less, as measured by a mercury porosimeter; The pore diameter D75 of the positive electrode active material layer, measured by mercury porosimeter, is 0.10 μm or more and 0.20 μm or less, and A non-aqueous lithium storage element in which the difference between void diameters D25 and D75 (D25-D75) is 0.20 μm or more and 0.45 μm or less.

2. 2. The nonaqueous lithium storage element according to claim 1, wherein the positive electrode active material layer contains 0.01 mass % to 5.0 mass % of lithium carbonate based on the total mass of the positive electrode active material layer.

3. 3. The nonaqueous lithium storage element according to claim 2, wherein the positive electrode active material layer has a volume resistivity of 1.5 Ωcm or more and 8.0 Ωcm or less.

4. 1000 μm of the surface of the positive electrode active material layer ２ 10000 μm or more ２ The aggregate frequency is 0.5 particles / cm or less. ２ The nonaqueous lithium storage element according to claim 2, wherein:

5. 2. A positive electrode precursor for use in the energy storage device according to claim 1, the positive electrode precursor comprising a positive electrode current collector and a positive electrode active material layer disposed on the positive electrode current collector, the positive electrode active material layer comprising a carbon material containing at least activated carbon, a lithium transition metal oxide, and an alkali metal compound, and a mass ratio A of the carbon material in the positive electrode active material layer is 1 is 38% by mass or more and 60% by mass or less, and the mass ratio A of the lithium transition metal oxide in the positive electrode active material layer is ２ is 15% by mass or more and 45% by mass or less, and A １ +A ２ is 74% by mass or more and 93% by mass or less, and A ２ / A １ is 0.30 or more and 1.20 or less, and the specific surface area B of the lithium transition metal oxide measured by the BET method is 7.5 m ２ / g or more 11.0m ２ / g or less, and the D of the lithium transition metal oxide １０ C １ , D of the lithium transition metal oxide ９０ C ２ When this is done, C ２ / C １ The positive electrode precursor used in the energy storage device according to claim 1 , wherein the value of the positive electrode precursor is 10 or more and 25 or less.

6. 6. The positive electrode precursor of claim 5, wherein the alkali metal compound is lithium carbonate and the lithium transition metal oxide is lithium iron phosphate.

7. A non-aqueous lithium storage element including a positive electrode having a positive electrode current collector and a positive electrode active material layer disposed on the positive electrode current collector, a negative electrode, a separator, and a non-aqueous electrolyte solution containing lithium ions, The positive electrode active material layer contains a carbon material containing at least activated carbon, a lithium transition metal oxide, and an alkali metal compound, and the mass ratio X of the carbon material in the positive electrode active material layer is １ is 43 mass % or more and 74 mass % or less, and the mass ratio X of the lithium transition metal oxide in the positive electrode active material layer is ２ is 23% by mass or more and 55% by mass or less, and X ２ / X １ is 0.30 or more and 1.20 or less, and X １ +X ２ is 92.5 mass % or more and 99.3 mass % or less, and the specific surface area Y of the lithium transition metal oxide measured by the BET method is 7.5 m ２ / g or more 11.0m ２ / g or less, and the D of the lithium transition metal oxide １０ Z １ , D of the lithium transition metal oxide ９０ Z ２ When Z ２ / Z １ 2. The nonaqueous lithium storage element according to claim 1, wherein the value of σ is 10 or more and 25 or less.

8. 8. The nonaqueous lithium storage element according to claim 7, wherein the alkali metal compound is lithium carbonate and the lithium transition metal oxide is lithium iron phosphate.

9. An electric storage element including: a positive electrode including a positive electrode active material layer disposed on a positive electrode current collector; a negative electrode including a negative electrode active material layer disposed on a negative electrode current collector; a separator; and an electrolytic solution, the positive electrode current collector is a non-porous aluminum foil, there is no undercoat layer on the positive electrode current collector, and the positive electrode active material layer is formed directly on the positive electrode current collector; the positive electrode active material layer contains activated carbon as a positive electrode active material, The electric storage element is disassembled and removed, and the interface resistance between the positive electrode active material layer and the positive electrode current collector of the positive electrode is 0.05 Ω cm ２ 5.00Ωcm or more ２ is less than or equal to, and The electric storage element was disassembled and removed, and the positive electrode surface was measured to obtain a 1000 μm ２ 10000 μm or more ２ The frequency of aggregates is 0.5 / cm ２ 2. The nonaqueous lithium storage element according to claim 1, wherein:

10. The positive electrode active material layer contains a lithium transition metal oxide as a positive electrode active material, and the lithium transition metal oxide has the following formula: Li ｘ Ni ａ Co ｂ Al （１－ａ－ｂ） O ２ {wherein x satisfies 0≦x≦1, and a and b satisfy 0.2<a<0.97 and 0.2<b<0.97.} Li ｘ Ni ｃ Co ｄ Mn （１－ｃ－ｄ） O ２ {wherein x satisfies 0≦x≦1, and c and d satisfy 0.2<c<0.97 and 0.2<d<0.97.} Li ｘ CoO ２ {wherein x satisfies 0≦x≦1.} Li ｘ Mn ２ O ４ {wherein x satisfies 0≦x≦1.} Li ｘ FePO ４ {wherein x satisfies 0≦x≦1.} Li ｘ MnPO ４ {wherein x satisfies 0≦x≦1.}, or Li ｚ V ２ (P.O. ４ ) ３ The nonaqueous lithium storage element according to claim 9 , wherein z satisfies the formula: {wherein z satisfies 0≦z≦3.}

11. 11. The nonaqueous lithium storage element according to claim 9, wherein the positive electrode active material layer contains a lithium transition metal oxide as a positive electrode active material, and the lithium transition metal oxide is lithium iron phosphate.

12. 12. The non-aqueous lithium storage element according to claim 11, wherein the lithium transition metal oxide is lithium iron phosphate, and the ratio of the 3.4-3.0 V capacity (mAh) to the 4.0-2.0 V capacity (mAh) of the non-aqueous lithium storage element is 25 to 82%.

13. The interface resistance between the positive electrode active material layer of the positive electrode and the positive electrode current collector is A [Ωcm ２ ] and a concentration of lithium fluoride contained in the negative electrode relative to the weight of the negative electrode active material layer is B [mmol / g], A / B is 0.02 to 250.

14. 2. A negative electrode for use in the nonaqueous lithium storage element of claim 1, the negative electrode comprising: a negative electrode current collector; and a negative electrode active material layer formed on one or both surfaces of the negative electrode current collector, the negative electrode active material layer including a negative electrode active material made of graphite capable of absorbing and desorbing lithium ions; The following (1) to (4): (1) The average thickness of the material constituting the negative electrode active material layer is 0.2 μm or more and 1.0 μm or less. (2) The pore diameter of the negative electrode active material layer is 0.15 μm or more and 0.70 μm or less. (3) The negative electrode active material layer has a specific surface area of ​​8 m2 calculated based on the mass of the negative electrode active material layer. ２ / g or more 40m ２ / g or less, and (4) The frequency of aggregates on the surface of the negative electrode is 0 pieces / cm ２ 1.0 pieces / cm or more ２ 2. The negative electrode for use in the nonaqueous lithium storage element of claim 1, which satisfies all of the following conditions:

15. 15. The negative electrode according to claim 14, wherein 1.0≦(1.35−p) / t≦2.8 is satisfied, where t (μm) is an average thickness of a material constituting the negative electrode active material layer and p (μm) is a pore diameter of the negative electrode active material layer.

16. The void volume of the negative electrode active material layer is 0.5 cm ３ / g or more 1.2cm ３ The negative electrode according to claim 14 or 15, wherein the SiO2 content is 1 / g or less.

17. The negative electrode active material layer has a specific surface area of ​​12 m2 calculated based on the mass of the negative electrode active material layer. ２ / g or more 30m ２ The negative electrode according to claim 14 or 15, wherein the SiO2 content is 1 / g or less.

18. 2. The nonaqueous lithium storage element according to claim 1, comprising a positive electrode, a negative electrode, and a nonaqueous electrolyte solution containing lithium ions, the positive electrode includes a positive electrode current collector and a positive electrode active material layer provided on one or both surfaces of the positive electrode current collector; The positive electrode active material layer comprises a positive electrode active material and MO ２ {wherein M is one or more selected from the group consisting of Co, Ni, and Mn}, The positive electrode active material is Li ｘ Mn （１－ｙ） Fe ｙ P.O. ４ {wherein x satisfies 0≦x≦1, and y satisfies 0<y≦1.}, the negative electrode includes a negative electrode current collector and a negative electrode active material layer provided on one or both surfaces of the negative electrode current collector, The discharge capacity per unit area of ​​the positive electrode is A1 (mAh / cm ２ ), and the charge capacity per unit area of ​​the negative electrode is B1 (mAh / cm ２ ) , 0.71≦A1 / B1≦0.96 is satisfied; The non-aqueous lithium storage element according to claim 1 .

19. 19. The nonaqueous lithium storage element according to claim 18, wherein the positive electrode active material layer further contains activated carbon.

20. The negative electrode active material layer has, based on the total mass of the negative electrode active material layer, 20. The nonaqueous lithium storage element according to claim 18 or 19, comprising, as a negative electrode active material, one or more selected from the group consisting of silicon, silicon compounds, tin, and tin compounds in an amount of 5 parts by mass or more and 30 parts by mass or less.

21. The negative electrode active material layer has, based on the total mass of the negative electrode active material layer, The first negative electrode active material contains a carbon material in a ratio of 50 parts by mass or more and 95 parts by mass or less, 20. The nonaqueous lithium storage element according to claim 18, wherein the second negative electrode active material contains at least one of silicon and a silicon compound in an amount of 5 parts by mass or more and 30 parts by mass or less.

22. A non-aqueous lithium storage element precursor for use in the non-aqueous lithium storage element according to claim 1, the non-aqueous lithium storage element precursor comprising a positive electrode precursor, a negative electrode precursor, and a non-aqueous electrolyte solution containing lithium ions, the positive electrode precursor includes a positive electrode current collector and a positive electrode active material layer provided on one or both surfaces of the positive electrode current collector, the positive electrode active material layer contains a positive electrode active material and a lithium compound composite, The positive electrode active material is Li ｘ Mn （１－ｙ） Fe ｙ P.O. ４ {wherein x satisfies 0≦x≦1, and y satisfies 0<y≦1.}, The lithium compound composite comprises a lithium compound and MO ２ {wherein M is one selected from the group consisting of Co, Ni, and Mn.} the negative electrode precursor includes a negative electrode current collector and a negative electrode active material layer provided on one or both surfaces of the negative electrode current collector, The charge capacity per unit area of ​​the positive electrode precursor is defined as A2 (mAh / cm ２ ), and the discharge capacity per unit area of ​​the positive electrode precursor is A3 (mAh / cm ２ ), and the charge capacity per unit area of ​​the negative electrode precursor is B2 (mAh / cm ２ ) the relationship 0.65≦A3 / A2≦0.93 is satisfied and the relationship 1.03≦B2 / A3≦1.26 is satisfied. Non-aqueous lithium storage element precursor.

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