Nonaqueous electrolyte energy storage device

Abstract

To provide a nonaqueous electrolyte power storage element having a large output and a high capacity retention rate after a charge / discharge cycle.SOLUTION: A nonaqueous electrolyte energy storage device according to one aspect of the present invention includes a positive electrode containing lithium transition metal composite oxide particles and a negative electrode containing graphite particles, wherein the lithium transition metal composite oxide particles contain a nickel element, a cobalt element, and a manganese element, a content of the nickel element is 40 mol% or more and a content of the cobalt element is 30 mol% or more with respect to all metal elements other than the lithium element in the lithium transition metal composite oxide particles, a porosity due to closed pores of the lithium transition metal composite oxide particles is 15% or more, and a porosity due to closed pores of the graphite particles is 2% or less.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a non-aqueous electrolyte electricity storage element. [Background technology]

[0002] Due to their high energy density, non-aqueous electrolyte secondary batteries, typified by lithium ion secondary batteries, are widely used in electronic devices such as personal computers and communication terminals, automobiles, etc. As non-aqueous electrolyte energy storage elements other than non-aqueous electrolyte secondary batteries, capacitors such as lithium ion capacitors and electric double layer capacitors are also widely used.

[0003] The positive electrode active material for non-aqueous electrolyte storage elements is LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 Lithium transition metal composite oxides such as O2 have been developed and put to practical use (see Patent Document 1). On the other hand, carbon materials such as graphite are widely used as negative electrode active materials (see Patent Document 2). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-18678 [Patent Document 2] Japanese Patent Application Laid-Open No. 2005-222933 Summary of the Invention [Problem to be solved by the invention]

[0005] One of the performance requirements for a non-aqueous electrolyte storage element is output performance, but non-aqueous electrolyte storage elements with improved output performance tend to have poor life performance, and achieving both is not easy.

[0006] An object of the present invention is to provide a nonaqueous electrolyte electricity storage element that has a high output and a high capacity retention rate after charge / discharge cycles. [Means for solving the problem]

[0007] A nonaqueous electrolyte storage element according to one aspect of the present invention comprises a positive electrode containing lithium transition metal composite oxide particles and a negative electrode containing graphite particles, wherein the lithium transition metal composite oxide particles contain nickel, cobalt, and manganese, and the content of nickel and cobalt in the lithium transition metal composite oxide particles relative to all metal elements other than lithium is 40 mol % or more and 30 mol % or more, respectively, and the internal porosity of the lithium transition metal composite oxide particles is 15% or more, and the internal porosity of the graphite particles is 2% or less. [Effects of the Invention]

[0008] According to one aspect of the present invention, a nonaqueous electrolyte electricity storage element having a high output and a high capacity retention rate after charge / discharge cycles can be provided. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a perspective view showing a nonaqueous electrolyte electricity storage element according to one embodiment of the present invention. [Figure 2] FIG. 2 is a schematic diagram showing an electricity storage device including a plurality of nonaqueous electrolyte electricity storage elements according to one embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0010] First, an outline of the nonaqueous electrolyte electricity storage element disclosed in this specification will be described.

[0011] [1] A nonaqueous electrolyte storage element according to one embodiment of the present invention comprises a positive electrode containing lithium transition metal composite oxide particles and a negative electrode containing graphite particles, wherein the lithium transition metal composite oxide particles contain nickel, cobalt, and manganese, and the content of nickel and cobalt in the lithium transition metal composite oxide particles is 40 mol % or more and 30 mol % or more of all metal elements other than lithium, respectively, and the lithium transition metal composite oxide particles have an internal porosity of 15% or more, and the graphite particles have an internal porosity of 2% or less.

[0012] The nonaqueous electrolyte storage element described in [1] above has a high output and a high capacity retention rate after charge-discharge cycles. The reason for this effect is not clear, but the following reasons are presumed. Lithium transition metal composite oxides with a high nickel content have a large theoretical capacity per unit mass when used as a positive electrode active material for nonaqueous electrolyte energy storage devices. Therefore, using such lithium transition metal composite oxides as positive electrode active materials enables nonaqueous electrolyte energy storage devices to have a large capacity and be smaller and lighter. However, lithium transition metal composite oxides with a high nickel content are prone to cation disorder (specifically, site exchange between lithium ions and nickel ions). This cation disorder inhibits lithium ion diffusibility, which is thought to be one of the reasons why nonaqueous electrolyte energy storage devices using lithium transition metal composite oxides with a high nickel content cannot sufficiently increase their output. One cause of this cation disorder is the close ionic radius of nickel ions in the divalent cation state to that of lithium ions. Here, in lithium transition metal composite oxides containing nickel, cobalt, and manganese and with a high nickel content, cation disorder can be suppressed by increasing the cobalt content (i.e., decreasing the manganese content). This is thought to be because, since the cobalt element in the lithium transition metal composite oxide exists mainly in the state of trivalent cations and the manganese element exists mainly in the state of tetravalent cations, a decrease in the content of manganese, which has a relatively high valence, makes it easier for the nickel element to exist in the state of trivalent cations, which has a high valence. By using lithium transition metal composite oxide particles having such a transition metal element composition and further increasing the internal porosity of 15% or more, the surface area can be increased, thereby increasing the output of the nonaqueous electrolyte energy storage element. On the other hand, lithium transition metal composite oxide particles having the above-described transition metal element composition and high internal porosity are prone to cracking due to repeated charge / discharge cycles, and the particle cracking causes the transition metal elements to ionize and dissolve into the non-aqueous electrolyte. The transition metal elements dissolved into the non-aqueous electrolyte are precipitated on the surface of graphite particles, which serve as the negative electrode active material. When graphite particles repeatedly change volume due to expansion and contraction, the coating formed on the surface of the graphite particles repeatedly collapses and reforms, which also causes repeated precipitation of the transition metal elements and tends to reduce the discharge capacity. In contrast, when graphite particles with an internal porosity of 2% or less are used as the negative electrode active material, the graphite particles with a low internal porosity experience minimal volume change due to expansion and contraction, thereby suppressing the collapse and reformation of the coating and reducing the decrease in the discharge capacity of the non-aqueous electrolyte storage element. For the reasons described above, it is presumed that the nonaqueous electrolyte electricity storage element described in [1] above has a high output and a high capacity retention rate after charge-discharge cycles.

[0013] The elemental composition ratio of the lithium transition metal composite oxide particles is the value of the lithium transition metal composite oxide particles before charge / discharge, or, in the case of lithium transition metal composite oxide particles contained in the positive electrode of a nonaqueous electrolyte storage element, the value after processing by the following procedure. First, the nonaqueous electrolyte storage element is charged at a constant current of 0.05 C until the charge end voltage in normal use is reached, and the element is fully charged. After a 30-minute rest, the element is discharged at a constant current of 0.05 C until the discharge end voltage in normal use is reached. The element is disassembled, the positive electrode is removed, and a test battery is assembled using the removed positive electrode as the working electrode and a metallic lithium electrode as the counter electrode. Pure metallic lithium is used for the metallic lithium electrode here. For the test battery, the positive electrode potential is 2.75 V (vs. Li / Li) at a current of 7 mA per 1 g of positive electrode active material. +) to adjust the positive electrode to a fully discharged state. The device is disassembled again, and the positive electrode is removed. The removed positive electrode is washed with dimethyl carbonate. The positive electrode active material layer containing the lithium transition metal composite oxide particles is then peeled from the positive electrode substrate, and the positive electrode active material layer is washed with a solvent capable of dissolving the binder to remove the binder. The device is then washed with water and dried under reduced pressure at room temperature for 24 hours to obtain lithium transition metal composite oxide particles. The obtained lithium transition metal composite oxide particles are then subjected to measurement. The operations from disassembling the nonaqueous electrolyte storage element to obtaining the lithium transition metal composite oxide particles are carried out in an argon atmosphere with a dew point of -60°C or below.

[0014] Here, "normal use" refers to the case where the nonaqueous electrolyte storage element is used under the charge / discharge conditions recommended or specified for the nonaqueous electrolyte storage element, and, if equipment for using the nonaqueous electrolyte storage element is available, the nonaqueous electrolyte storage element is used using that equipment.

[0015] "Graphite" refers to the graphite that has an average lattice spacing (d 002 ) is 0.33 nm or more and less than 0.34 nm.

[0016] The X-ray diffraction pattern, BET specific surface area, and average particle size of the graphite particles are the values ​​of the graphite particles before charge / discharge, or, for the graphite particles contained in the negative electrode of the nonaqueous electrolyte storage element, the values ​​are the values ​​after processing according to the following procedure. First, the nonaqueous electrolyte storage element is discharged at a constant current of 0.1 C to the discharge end voltage during normal use. The element is disassembled, the negative electrode is removed, and a test battery is assembled using the removed negative electrode as the working electrode and metallic lithium as the counter electrode. Pure metallic lithium is used for the metallic lithium electrode here. For the test battery, a current of 10 mA per 1 g of negative electrode active material is applied, and the closed circuit potential of the negative electrode is 2.0 V (vs. Li / Li +), and adjust the graphite particles to a fully discharged state. The battery is disassembled again, and the negative electrode is removed. The removed negative electrode is washed with dimethyl carbonate. The negative electrode active material layer containing the graphite particles is then peeled from the negative electrode substrate, and the negative electrode active material layer is washed with a binder-soluble solvent to remove the binder. The washed negative electrode active material layer is immersed in an acid or alkaline solution to remove metals and the SEI (solid electrolyte interface) coating from the negative electrode substrate. The battery is then washed with water and dried under reduced pressure at room temperature for 24 hours to obtain graphite particles. Disassembly of the nonaqueous electrolyte storage element and test battery is carried out in an argon atmosphere with a dew point of -60°C or below.

[0017] X-ray diffraction measurements of carbon materials (graphite particles) were performed using a powder X-ray diffraction instrument (Rigaku "MiniFlex II") with a CuKα source, a tube voltage of 30 kV, and a tube current of 15 mA. The diffracted X-rays passed through a 30 μm-thick Kβ filter and were detected by a high-speed one-dimensional detector (D / teX Ultra 2). The sampling width was 0.02°, the scan speed was 5° / min, the divergence slit width was 0.625°, the receiving slit width was 13 mm (open), and the scattering slit width was 8 mm. The Kα2 ray was removed from the CuKα ray, and an X-ray diffraction pattern based on the Kα1 ray was obtained.

[0018] The "internal porosity" of lithium transition metal composite oxide particles and graphite particles refers to the area ratio of voids within a particle to the total area of ​​the particle in a cross section of the particle observed in an SEM image obtained using a scanning electron microscope (SEM). The "internal porosity (area ratio of voids within a particle to the total area of ​​the particle)" of lithium transition metal composite oxide particles and graphite particles is determined by the following procedure. (1) Preparation of measurement samples The positive and negative electrodes to be measured are fixed with a thermosetting resin, and the cross sections of the fixed positive and negative electrodes are exposed by ion milling to prepare measurement samples. The positive and negative electrodes to be measured are prepared using the following procedure. If the positive and negative electrodes can be prepared before assembling the nonaqueous electrolyte storage element, they are used as is. When preparing from an assembled nonaqueous electrolyte storage element, the nonaqueous electrolyte storage element is first discharged at a constant current of 0.1 C to the discharge end voltage during normal use. The element is then disassembled, and the positive and negative electrodes are removed and thoroughly washed with dimethyl carbonate, followed by drying under reduced pressure at room temperature for 24 hours. The entire process from disassembling the nonaqueous electrolyte storage element to preparing the positive and negative electrodes to be measured is carried out in a dry air atmosphere with a dew point of -40°C or below. (2) Obtaining SEM images To obtain SEM images, a JSM-7001F SEM (manufactured by JEOL Ltd.) is used. SEM images are obtained by observing secondary electron images. The acceleration voltage is 5 kV. The observation magnification is set so that 3 to 15 lithium transition metal composite oxide particles or graphite particles appear in one field of view. The obtained SEM image is saved as an image file. Other conditions such as spot diameter, working distance, irradiation current, brightness, and focus are set appropriately so that the outlines of the lithium transition metal composite oxide particles or graphite particles are clearly visible. (3) Cutting out the outline of lithium transition metal composite oxide particles or graphite particles The image cropping function of the image editing software Adobe Photoshop Elements 11 is used to crop the outlines of the lithium transition metal composite oxide particles or graphite particles from the acquired SEM image. This cropping is performed by using the quick selection tool to select the area outside the outlines of the lithium transition metal composite oxide particles or graphite particles, and then editing everything except the lithium transition metal composite oxide particles or graphite particles to a black background. If the number of lithium transition metal composite oxide particles or graphite particles that have been successfully cropped is less than three, another SEM image is acquired and this process is repeated until three or more lithium transition metal composite oxide particles or graphite particles have been successfully cropped. (4) Binarization The image of the first of the cut-out lithium transition metal composite oxide particles or graphite particles is binarized using the image analysis software PopImaging 6.00, with a threshold set to a concentration 20% lower than the concentration at which the intensity is at its maximum. The area of ​​the higher concentration side is calculated through the binarization process, and this is taken as the "area S1 of the voids within the particle." Next, the same image of the first lithium transition metal composite oxide particle or graphite particle as before is subjected to binarization processing using a concentration threshold of 10%. Through the binarization processing, the outer periphery of the lithium transition metal composite oxide particle or graphite particle is determined, and the area inside the outer periphery is calculated to obtain the "area S0 of the entire particle." Using the calculated S1 and S0, the ratio of S1 to S0 (S1 / S0) is calculated to calculate the "area ratio R1 of voids within the particle to the area of ​​the entire particle" for the first lithium transition metal composite oxide particle or graphite particle. The above-described binarization process is also performed on the images of the second and subsequent lithium transition metal composite oxide particles or graphite particles among the cut-out lithium transition metal composite oxide particles or graphite particles, and the areas S1 and S0 are calculated. Based on the calculated areas S1 and S0, the void area ratios R2, R3, ... of each lithium transition metal composite oxide particle or graphite particle are calculated. (5) Determination of void area ratio For lithium transition metal composite oxide particles or graphite particles, the "internal porosity (area ratio of voids within a particle to the total area of ​​the particle)" is determined by calculating the average value of all void area ratios R1, R2, R3, ... calculated by binarization processing. In addition, instead of the scanning electron microscope used in the "obtaining SEM images," the image editing software used in the "cutting out the contours of the lithium transition metal composite oxide particles or graphite particles," and the image analysis software used in the "binarization processing," devices and software capable of equivalent measurements, image editing, and image analysis may be used.

[0019] [2] In the nonaqueous electrolyte storage element according to [1] above, the BET specific surface area of ​​the graphite particles is 3 m2 / g or less.

[0020] The nonaqueous electrolyte storage element described in [2] above can further increase the capacity retention rate after charge-discharge cycles.

[0021] The "BET specific surface area" of graphite particles is a value obtained by measuring using the following procedure. 1.00 g of graphite particles is placed in a measurement sample tube and dried under reduced pressure at 120°C for 12 hours. Next, an adsorption isotherm is measured using nitrogen gas adsorption with liquid nitrogen within a relative pressure P / P0 (P0 = approximately 770 mmHg) range of 0 to 1. The measurement device used is a Quantachrome "autosorb iQ." Five points are extracted from the region of P / P0 = 0.05 to 0.3 of the obtained adsorption isotherm, and a BET plot is performed. The BET specific surface area is calculated from the y-intercept and slope of the line.

[0022] [3] In the nonaqueous electrolyte storage element according to [1] or [2] above, the graphite particles may have an average particle size of 5 μm or more and 10 μm or less.

[0023] The nonaqueous electrolyte storage element described in the above item [3] can achieve a larger output and a higher capacity retention rate after charge-discharge cycles.

[0024] "Average particle size" refers to the value (D50) at which the volume-based cumulative distribution is 50% as calculated in accordance with JIS-Z-8819-2 (2001), based on the particle size distribution measured by laser diffraction / scattering in accordance with JIS-Z-8825 (2013) for a diluted solution of particles diluted with a solvent.

[0025] [4] In the nonaqueous electrolyte storage element according to any one of [1] to [3] above, the molar ratio of the cobalt content to the manganese content in the lithium transition metal composite oxide particles may be 1.2 or more.

[0026] The nonaqueous electrolyte energy storage element described in [4] above can achieve higher output, etc. The following reasons are presumed to be the reasons for this. As described above, the cobalt element in the lithium transition metal composite oxide exists primarily in the state of trivalent cations, the manganese element exists primarily in the state of tetravalent cations, and the presence of nickel element in the state of divalent cations is a factor in causing cation disorder. Therefore, by increasing the molar ratio of the content of cobalt element, which exists primarily in the state of trivalent cations, to the content of manganese element, which exists primarily in the state of tetravalent cations, nickel element is more likely to exist in the state of trivalent cations than in the state of divalent cations. As a result, the amount of nickel element in the state of divalent cations is further reduced, making cation disorder less likely to occur, and it is presumed that the output of the nonaqueous electrolyte energy storage element is increased.

[0027] A nonaqueous electrolyte electricity storage element according to one embodiment of the present invention, a method for manufacturing a nonaqueous electrolyte electricity storage element, an electricity storage device, and other embodiments will be described in detail below.

[0028] <Non-aqueous electrolyte energy storage element> A nonaqueous electrolyte storage element according to one embodiment of the present invention comprises a positive electrode, a negative electrode, a nonaqueous electrolyte, and a container for accommodating these. The nonaqueous electrolyte storage element may further comprise a separator interposed between the positive electrode and the negative electrode to electrically insulate the positive electrode from the negative electrode. The positive electrode, the negative electrode, and any separator typically constitute an electrode assembly. At least a portion of the nonaqueous electrolyte typically exists in a state of being impregnated into the electrode assembly. The nonaqueous electrolyte storage element according to one embodiment of the present invention may further comprise other components.

[0029] For example, a nonaqueous electrolyte storage element 1 according to one embodiment of the present invention shown in FIG. 1 includes an electrode assembly 2, a nonaqueous electrolyte (not shown), and a rectangular parallelepiped container 3 that accommodates these. The nonaqueous electrolyte storage element 1 of FIG. 1 further includes a positive electrode lead 4, a positive electrode external terminal 5, a negative electrode lead 6, and a negative electrode external terminal 7. The positive electrode lead 4 and the negative electrode lead 6 are accommodated in the container 3 together with the electrode assembly 2 and the like. The positive electrode external terminal 5 and the negative electrode external terminal 7 are provided outside the container 3. The positive electrode constituting the electrode assembly 2 is electrically connected to the positive electrode external terminal 5 via the positive electrode lead 4. The negative electrode constituting the electrode assembly 2 is electrically connected to the negative electrode external terminal 7 via the negative electrode lead 6.

[0030] The nonaqueous electrolyte storage element of the present invention may be a nonaqueous electrolyte secondary battery. Below, the main components constituting the nonaqueous electrolyte storage element according to one embodiment of the present invention will be described in detail, mainly in the case where the nonaqueous electrolyte storage element is a nonaqueous electrolyte secondary battery (particularly a lithium ion secondary battery), but this is not intended to limit the application of the present invention.

[0031] The lower and upper limits of each numerical range described in the embodiments of the present invention can be combined in any manner.

[0032] (positive electrode) The positive electrode has a positive electrode substrate and a positive electrode active material layer laminated on the positive electrode substrate directly or via an intermediate layer. Usually, the positive electrode has a portion where the positive electrode substrate is exposed. This exposed portion of the positive electrode substrate is usually connected to the above-mentioned positive electrode lead. The positive electrode may have a shape such as a sheet, plate, or strip.

[0033] The thickness of the positive electrode is appropriately set depending on the application of the nonaqueous electrolyte storage element. The average thickness of the positive electrode may be, for example, 30 μm or more and 1,000 μm or less. The lower limit of the average thickness of the positive electrode may be 50 μm, 100 μm, or 200 μm. The upper limit of the average thickness of the positive electrode may be 500 μm, 400 μm, 300 μm, 200 μm, or 100 μm. The average thickness of the positive electrode is the average thickness of the portion where the positive electrode active material layer is laminated on the positive electrode substrate directly or via an intermediate layer. When the positive electrode substrate has both a portion where the positive electrode active material layer is laminated on both sides and a portion where the positive electrode active material layer is laminated on only one side, the average thickness of the portion where the positive electrode active material layer is laminated on both sides of the positive electrode substrate is referred to. In addition, in this specification, "average thickness" means the average thickness of thicknesses measured at any five positions.

[0034] The positive electrode substrate has electrical conductivity. In this specification, "having electrical conductivity" means that the volume resistivity is 10 -2 The volume resistivity is a value measured in accordance with JIS-H-0505 (1975). On the other hand, in this specification, "not having electrical conductivity" or "having (electrical) insulation" means that the volume resistivity is 10 7 This means that the resistance is Ω·cm or more.

[0035] Examples of materials for the positive electrode substrate include metals such as aluminum, titanium, iron, and alloys thereof (stainless steel, etc.). Among these, aluminum or an aluminum alloy is preferred from the viewpoints of potential resistance, high electronic conductivity, and cost.

[0036] The positive electrode substrate has a shape such as a sheet, plate, or strip. Examples of the form of the positive electrode substrate include foil, vapor-deposited film, mesh, and porous material, and foil is preferred. The positive electrode substrate may be, for example, aluminum foil or aluminum alloy foil.

[0037] The average thickness of the positive electrode substrate may be, for example, 3 μm or more and 50 μm or less. The lower limit of the average thickness of the positive electrode substrate may be 5 μm, 8 μm, 10 μm, or 15 μm. The upper limit of the average thickness of the positive electrode substrate may be 40 μm, 30 μm, 20 μm, or 15 μm.

[0038] The intermediate layer is a layer disposed between the positive electrode substrate and the positive electrode active material layer. The intermediate layer contains, for example, a conductive agent and a binder. When the intermediate layer contains a conductive agent, the contact resistance between the positive electrode substrate and the positive electrode active material layer can be reduced. Examples of the conductive agent and binder used in the intermediate layer include the same conductive agent and binder used in the positive electrode active material layer described below.

[0039] The positive electrode active material layer contains lithium transition metal composite oxide particles as the positive electrode active material. The positive electrode active material layer contains optional components such as a conductive agent, a binder, a thickener, and a filler as needed. The positive electrode active material layer may be formed from a positive electrode mixture containing the positive electrode active material and other optional components. The positive electrode active material layer may be provided on only one side or on both sides of a positive electrode substrate having a shape such as a sheet.

[0040] The lithium transition metal composite oxide particles contain nickel, cobalt, and manganese, and typically have an α-NaFeO 2 crystal structure.

[0041] The lower limit of the content of nickel element relative to all metal elements other than lithium element in the lithium transition metal composite oxide particles is 40 mol%, preferably 42 mol%, and more preferably 44 mol%. Having a nickel element content equal to or greater than the above lower limit allows for the nonaqueous electrolyte storage element to have a large capacity and be small and lightweight. On the other hand, the upper limit of the nickel element content is preferably 60 mol%, more preferably 55 mol%, even more preferably 50 mol%, and even more preferably 48 mol%. Having a nickel element content equal to or less than the above upper limit allows for the nonaqueous electrolyte storage element to have high thermal stability and a higher capacity retention rate after charge / discharge cycling.

[0042] The lower limit of the cobalt content relative to all metal elements other than lithium in the lithium transition metal composite oxide particles is 30 mol%, preferably 32 mol%, and more preferably 34 mol%. By ensuring that the cobalt content is equal to or greater than the lower limit, it is possible to increase the output of the nonaqueous electrolyte storage element. On the other hand, the upper limit of the cobalt content is preferably 50 mol%, more preferably 45 mol%, even more preferably 40 mol%, and even more preferably 38 mol%.

[0043] The lower limit of the manganese content relative to all metal elements other than lithium in the lithium transition metal composite oxide particles is preferably 5 mol%, more preferably 10 mol%, and even more preferably 15 mol%, while the upper limit of the manganese content is preferably 30 mol%, more preferably 28 mol%, even more preferably 25 mol%, and even more preferably 23 mol%.

[0044] The lower limit of the molar ratio (Co / Mn) of the cobalt content to the manganese content in the lithium transition metal composite oxide particles is, for example, preferably 1.2, more preferably 1.5, even more preferably 1.6, and even more preferably 1.7. By ensuring that the molar ratio (Co / Mn) is equal to or greater than the above lower limit, it is possible to increase the output of the nonaqueous electrolyte energy storage element. The upper limit of the molar ratio (Co / Mn) may be, for example, 3.0, or may be 2.5, 2.0, 1.9, or 1.8.

[0045] The lithium transition metal composite oxide particles may further contain transition metal elements other than nickel, cobalt, and manganese, and typical metal elements other than lithium, such as aluminum. However, the lower limit of the total content of nickel, cobalt, and manganese relative to all metal elements other than lithium in the lithium transition metal composite oxide particles is preferably 90 mol%, more preferably 95 mol%, and even more preferably 99 mol%. The metal elements other than lithium in the lithium transition metal composite oxide particles may be substantially composed of only the three elements of nickel, cobalt, and manganese. When the metal elements other than lithium in the lithium transition metal composite oxide particles are substantially composed of only the three elements of nickel, cobalt, and manganese, the effects of a nonaqueous electrolyte storage element having a high output and a high capacity retention rate after charge-discharge cycling are particularly sufficiently achieved.

[0046] The lower limit of the molar ratio of the lithium element content to all metal elements other than lithium in the lithium transition metal composite oxide particles may be 1.0, and the upper limit of the molar ratio of the lithium element content to all metal elements other than lithium in the lithium transition metal composite oxide particles may be 1.5, 1.4, 1.3, 1.2, 1.1, 1.05, or 1.0.

[0047] The lithium transition metal composite oxide particles may be formed from a compound represented by the following formula (1). Li 1+α Me 1-α O2···(1) In formula (1), Me is a metal element other than Li, including Ni, Co, and Mn. However, the content of Ni in Me is 40 mol% or more, and the content of Co in Me is 30 mol% or more. 0≦α<1.

[0048] The preferred contents of each element in the compound represented by the formula (1) are the same as those described above in the description of the lithium transition metal composite oxide particles.

[0049] Lithium transition metal composite oxide particles are particles having internal voids. Lithium transition metal composite oxide particles are usually secondary particles formed by agglomeration of multiple primary particles. The lower limit of the internal porosity of the lithium transition metal composite oxide particles is 15%, preferably 16%, more preferably 17%, and even more preferably 18%. When the internal porosity of the lithium transition metal composite oxide particles is equal to or greater than the above lower limit, the output of the non-aqueous electrolyte energy storage element can be increased. The upper limit of the internal porosity of the lithium transition metal composite oxide particles is preferably 30%, more preferably 25%, and even more preferably 22%. When the internal porosity of the lithium transition metal composite oxide particles is equal to or less than the above upper limit, the capacity retention rate of the non-aqueous electrolyte energy storage element after charge-discharge cycling can be further increased. Lithium transition metal composite oxide particles having an internal porosity of 15% or more can be produced by a known method.

[0050] The average particle size of the lithium transition metal composite oxide particles is, for example, preferably 0.1 μm to 20 μm, more preferably 0.5 μm to 10 μm, even more preferably 1 μm to 8 μm, even more preferably 2 μm to 6 μm, and may be 3 μm to 5 μm. By setting the average particle size of the lithium transition metal composite oxide particles to the above lower limit or above, the lithium transition metal composite oxide particles are easy to manufacture or handle. By setting the average particle size of the lithium transition metal composite oxide particles to the above upper limit or below, the electronic conductivity of the positive electrode active material layer is improved. Particles such as lithium transition metal composite oxide particles having a predetermined particle size can be obtained by known methods using, for example, a pulverizer, a classifier, or the like.

[0051] The content of the lithium transition metal composite oxide particles in the positive electrode active material layer is preferably 70% by mass to 99% by mass, more preferably 80% by mass to 98% by mass, and may be 90% by mass to 95% by mass. By setting the content of the lithium transition metal composite oxide particles within this range, it is possible to achieve both high energy density and manufacturability in the positive electrode active material layer, and to further increase the output of the nonaqueous electrolyte storage element.

[0052] The positive electrode active material layer may contain a positive electrode active material other than the lithium transition metal composite oxide particles. The other positive electrode active material may be any of various conventionally known positive electrode active materials. However, the content of the lithium transition metal composite oxide particles relative to the total positive electrode active material in the positive electrode active material is preferably 90% by mass or more, more preferably 95% by mass or more, even more preferably 99% by mass or more, and may even be substantially 100% by mass. By primarily using the lithium transition metal composite oxide particles as the positive electrode active material, the nonaqueous electrolyte storage element can be particularly effectively provided with high output and a high capacity retention rate after charge / discharge cycling.

[0053] The content of all the positive electrode active materials in the positive electrode active material layer is preferably 70% by mass or more and 99% by mass or less, more preferably 80% by mass or more and 98% by mass or less, and may be 90% by mass or more and 95% by mass or less. By setting the content of all the positive electrode active materials within the above range, it is possible to achieve both a high energy density and manufacturability of the positive electrode active material layer, and to further increase the output of the nonaqueous electrolyte storage element.

[0054] Conductive agents are usually components made of materials that have electrical conductivity. Even if the volume resistivity of a conductive agent cannot be measured directly, it is possible to measure the volume resistivity by measuring the volume resistivity of the conductive agent when the volume resistivity is 10 -2Conductive agents are materials known to have a resistivity of Ω·cm or less. Examples of conductive agents include carbon materials, metals, and conductive ceramics. Carbon materials are materials whose primary constituent element is carbon. The primary constituent element refers to the element with the highest content by mass. For example, the carbon content in a carbon material may be 80% by mass or more, 90% by mass or more, 95% by mass, 99% by mass, or 99.9% by mass or more. The carbon material is preferably a carbon material other than an uncarbonized polymer compound. Examples of carbon materials include graphite, non-graphitic carbon, and graphene-based carbon. Examples of non-graphitic carbon include carbon nanofiber, pitch-based carbon fiber, and carbon black. Examples of carbon black include furnace black, acetylene black, and ketjen black. Examples of graphene-based carbon include graphene, carbon nanotubes (CNT), and fullerene. Conductive agents may be in the form of powder, fiber, or the like. The conductive agent may be one or more kinds. The conductive agent may be a composite of these materials. For example, a composite material of carbon black and CNT may be used.

[0055] The content of the conductive agent in the positive electrode active material layer is preferably 0.1% by mass to 10% by mass, more preferably 1% by mass to 9% by mass, and even more preferably 3% by mass to 8% by mass. The upper limit of the content of the conductive agent may be 6% by mass or 5% by mass. By setting the content of the conductive agent within the above range, it is possible to increase the energy density of the nonaqueous electrolyte storage element.

[0056] Examples of the binder include a water-based binder and an organic solvent-based binder.

[0057] The aqueous binder is a binder that dissolves or disperses in water. The aqueous binder may be a binder that dissolves or disperses at 1 part by mass or more in 100 parts by mass of water at 20°C. When a positive electrode active material layer is formed using a positive electrode mixture paste whose dispersion medium is water or a mixed solvent mainly composed of water, an aqueous binder (a water-soluble or water-dispersible polymer material) can be used. Examples of aqueous binders include polyethylene oxide, polypropylene oxide, polyvinyl alcohol, polyacrylic acid, polymethacrylic acid, polytetrafluoroethylene, styrene-butadiene rubber, polyethylene, polypropylene, nitrile-butadiene rubber, and cellulose.

[0058] The organic solvent-based binder is a binder that dissolves or disperses in an organic solvent (e.g., N-methylpyrrolidone). The organic solvent-based binder may be a binder that dissolves or disperses at 1 part by mass or more in 100 parts by mass of an organic solvent (e.g., N-methylpyrrolidone) at 20°C. When a positive electrode active material layer is formed using a positive electrode mixture paste whose dispersion medium is an organic solvent or a mixed solvent mainly containing an organic solvent, an organic solvent-based binder (a polymer material that is soluble or dispersible in an organic solvent) can be used. Examples of organic solvent-based binders include polyvinylidene fluoride, copolymers of vinylidene fluoride and hexafluoropropylene, copolymers of ethylene and vinyl alcohol, polyacrylonitrile, polyphosphazene, polysiloxane, polyvinyl acetate, polymethyl methacrylate, polystyrene, polycarbonate, polyamide, polyimide, polyamideimide, crosslinked polymers of cellulose and chitosan pyrrolidone carboxylate, chitosan derivatives, and the like.

[0059] The binder may be a fluororesin (polytetrafluoroethylene, polyvinylidene fluoride, etc.), a polyolefin (polyethylene, polypropylene, etc.), an elastomer (ethylene propylene diene rubber, styrene butadiene rubber, fluororubber, etc.), a polysaccharide polymer (cellulose, chitosan derivatives, etc.), etc. One or more types of binders may be used.

[0060] The content of the binder in the positive electrode active material layer is preferably 0.1% by mass to 10% by mass, more preferably 1% by mass to 9% by mass, and even more preferably 2% by mass to 8% by mass. The upper limit of the binder content may be 5%, 4%, or 3% by mass. By setting the binder content within the above range, it is possible to stably hold the positive electrode active material. The technology disclosed herein can also be implemented in an embodiment in which the positive electrode active material layer does not contain a binder.

[0061] Examples of thickeners include polysaccharide polymers such as carboxymethyl cellulose and methyl cellulose. When the thickener has a functional group that reacts with lithium or the like, the functional group may be deactivated in advance by methylation or the like. The thickener may also function as a binder. One or more types of thickeners may be used. When the positive electrode active material layer contains a thickener, the content of the thickener in the positive electrode active material layer is preferably 0.1% by mass or more and 8% by mass or less, more preferably 5% by mass or less, and even more preferably 2% by mass or less. The technology disclosed herein may also be implemented in an embodiment in which the positive electrode active material layer does not contain a thickener.

[0062] The filler is not particularly limited. The filler may be a component other than the positive electrode active material, conductive agent, binder, and thickener, and may be intentionally added. The filler may be added to fill gaps in the positive electrode active material layer, or may be added for other purposes. The filler may be an organic substance such as polyolefin, or an inorganic substance such as an inorganic oxide, hydroxide, or carbonate. One or more fillers may be used. When the positive electrode active material layer contains a filler, the content of the filler in the positive electrode active material layer may be 0.1% by mass or more and 8% by mass or less, typically preferably 5% by mass or less, and more preferably 2% by mass or less. The technology disclosed herein may also be implemented in an embodiment in which the positive electrode active material layer does not contain a filler.

[0063] The positive electrode active material layer may further contain other components in addition to the positive electrode active material, conductive agent, binder, thickener, and filler. The other components include those unintentionally present in the positive electrode active material layer. The positive electrode active material layer may also contain unintentionally contained impurities as the other components, as long as the effects of the present invention are achieved. The upper limit of the content of the other components in the positive electrode active material layer may be 10% by mass, 5%, 2%, 1%, 0.1%, or 0.01% by mass. The upper limit of the content of the unintentionally contained components in the positive electrode active material layer may be 10% by mass, 5%, 2%, 1%, 0.1%, or 0.01% by mass. The upper limit of the content of the unintentionally contained impurities in the positive electrode active material layer may be 10% by mass, 5%, 2%, 1%, 0.1%, or 0.01% by mass.

[0064] The thickness of the positive electrode active material layer is appropriately set depending on the type of positive electrode active material, the application of the nonaqueous electrolyte storage element, and the like. The average thickness of one positive electrode active material layer may be, for example, 5 μm or more and 1,000 μm or less. The lower limit of the average thickness of one positive electrode active material layer may be 10 μm, 20 μm, 30 μm, 40 μm, 50 μm, 60 μm, or 100 μm. The upper limit of the average thickness of one positive electrode active material layer may be 800 μm, 500 μm, 200 μm, 100 μm, 80 μm, 60 μm, or 40 μm. The mass per unit area of ​​one positive electrode active material layer is, for example, 3 mg / cm. 2 More than 100mg / cm 2 The lower limit of the mass per unit area of ​​one positive electrode active material layer is 5 mg / cm. 2 , 7 mg / cm 2 or 10 mg / cm 2 The upper limit of the mass per unit area of ​​one positive electrode active material layer is 50 mg / cm. 2 , 20 mg / cm 2 , 15 mg / cm 2 , 12 mg / cm 2 or 10 mg / cm 2 may be.

[0065] The porosity of the positive electrode active material layer may be, for example, 20% or more and 50% or less. The lower limit of the porosity of the positive electrode active material layer may be 25%, 30%, or 35%. The upper limit of the porosity of the positive electrode active material layer may be 45%, 40%, or 35%. The "porosity (%)" of the positive electrode active material layer and the negative electrode active material layer described below is calculated by the formula (1-V2 / V1) × 100, where V1 is the apparent volume (volume including voids) of the positive (negative) electrode active material layer and V2 is the sum of the actual volumes of the materials constituting the positive (negative) electrode active material layer. The sum V2 of the actual volumes of the materials constituting the positive (negative) electrode active material layer can be calculated from the content of each material in the positive (negative) electrode active material layer and the true density of each material.

[0066] (Positive electrode manufacturing method) The positive electrode can be manufactured by a known method. The positive electrode can be manufactured, for example, by applying a paste-like positive electrode mixture (positive electrode mixture paste) to a positive electrode substrate directly or via an intermediate layer, and then drying the paste to form a positive electrode active material layer. The positive electrode mixture paste usually contains lithium transition metal composite oxide particles, which are the positive electrode active material, other optional components, and a dispersion medium. After drying, the positive electrode active material layer may be pressed, etc.

[0067] (Negative electrode) The negative electrode has a negative electrode substrate and a negative electrode active material layer laminated on the negative electrode substrate directly or via an intermediate layer. Usually, the negative electrode has a portion where the negative electrode substrate is exposed. This exposed portion of the negative electrode substrate is usually connected to the above-mentioned negative electrode lead. The negative electrode may have a shape such as a sheet, plate, or strip.

[0068] The thickness of the negative electrode is appropriately set depending on the application of the nonaqueous electrolyte storage element, etc. The average thickness of the negative electrode may be, for example, 30 μm or more and 1,000 μm or less. The lower limit of the average thickness of the negative electrode may be 50 μm, 100 μm, or 200 μm. The upper limit of the average thickness of the negative electrode may be 500 μm, 400 μm, 300 μm, 200 μm, or 100 μm. The average thickness of the negative electrode is the average thickness of a portion where the negative electrode active material layer is laminated on the negative electrode substrate directly or via an intermediate layer. When the negative electrode substrate has both a portion where the negative electrode active material layer is laminated on both sides and a portion where the negative electrode active material layer is laminated on only one side, the average thickness of the portion where the negative electrode active material layer is laminated on both sides of the negative electrode substrate is taken as the average thickness.

[0069] The negative electrode substrate is conductive. Examples of materials for the negative electrode substrate include metals such as copper, nickel, iron, and alloys thereof (such as stainless steel), and carbon materials. Among these, copper or copper alloys are preferred.

[0070] The negative electrode substrate has a shape such as a sheet, plate, or strip. Examples of the form of the negative electrode substrate include foil, vapor-deposited film, mesh, and porous material, and foil is preferred. The negative electrode substrate may be, for example, copper foil or copper alloy foil.

[0071] The average thickness of the negative electrode substrate may be, for example, 2 μm or more and 35 μm or less. The lower limit of the average thickness of the negative electrode substrate may be 3 μm, 4 μm, 5 μm, or 10 μm. The upper limit of the average thickness of the negative electrode substrate may be 30 μm, 20 μm, 15 μm, or 10 μm.

[0072] The structure of the intermediate layer of the negative electrode is not particularly limited, and can be selected from the structures exemplified for the intermediate layer of the positive electrode, for example.

[0073] The negative electrode active material layer contains graphite particles as the negative electrode active material. The negative electrode active material layer contains optional components such as a conductive agent, a binder, a thickener, and a filler as needed. The optional components such as the conductive agent, the binder, the thickener, and the filler can be selected from the materials exemplified for the positive electrode above. The negative electrode active material layer may be formed from a negative electrode mixture containing a negative electrode active material and other optional components. The negative electrode active material layer may be provided on only one side or on both sides of a negative electrode substrate having a shape such as a sheet.

[0074] Graphite particles are a component that functions as a negative electrode active material. The upper limit of the internal porosity of the graphite particles contained in the negative electrode active material layer is 2%, preferably 1%, and more preferably 0.7%. When the internal porosity of the graphite particles is equal to or less than the upper limit, expansion and contraction of the graphite particles during charge and discharge is suppressed, and the capacity retention rate of the nonaqueous electrolyte storage element after charge and discharge cycles can be increased. The lower limit of the internal porosity of the graphite particles may be 0%, 0.1%, 0.2%, or 0.3%. Graphite particles with an internal porosity of 2% or less can be obtained by compressing conventional graphite, for example.

[0075] The graphite particles may be natural graphite or artificial graphite, but are preferably natural graphite, which can reduce the resistance of the nonaqueous electrolyte electricity storage element and increase its output.

[0076] Natural graphite is a general term for graphite extracted from natural resources. Graphite particles made of natural graphite may be spherical natural graphite particles obtained by spheroidizing flake natural graphite or the like. Natural graphite may exhibit four peaks at a diffraction angle 2θ ranging from 40° to 50° in an X-ray diffraction pattern using CuKα radiation measured before charge / discharge or in a discharged state. These four peaks are believed to be two peaks derived from a hexagonal crystal structure and two peaks derived from a rhombohedral crystal structure. In the case of artificial graphite, it is generally believed that only two peaks derived from a hexagonal crystal structure are exhibited. In the X-ray diffraction pattern, the ratio of the peak intensity derived from the (012) plane to the peak intensity derived from the (100) plane ((012) / (100)) is preferably 0.3 or more, more preferably 0.4 or more. The peak intensity ratio ((012) / (100)) is preferably 0.6 or less. Here, the (100) plane originates from the hexagonal crystal structure, and the (012) plane originates from the rhombohedral crystal structure.

[0077] The upper limit of the BET specific surface area of ​​graphite particles is, for example, 5 m 2 / g or 4m 2 / g, but 3m 2 / g, and 2.9m 2 / g. When the BET specific surface area of ​​the graphite particles is equal to or less than the upper limit, the capacity retention rate after charge / discharge cycles of the nonaqueous electrolyte energy storage element can be further increased. The lower limit of the BET specific surface area of ​​the graphite particles is 1 m 2 / g is preferred, and 2m 2 / g is more preferred, 2.5m 2 When the BET specific surface area of ​​the graphite particles is equal to or greater than the above lower limit, the output of the nonaqueous electrolyte electricity storage element can be increased.

[0078] The average particle size of the graphite particles may be, for example, from 1 μm to 20 μm, preferably from 5 μm to 10 μm, and more preferably from 6 μm to 8 μm. When the average particle size of the graphite particles is in the above range, it is possible to increase the output of the nonaqueous electrolyte energy storage element and further improve the capacity retention rate after charge-discharge cycling.

[0079] The content of graphite particles in the negative electrode active material layer is preferably 60% by mass or more and 99.5% by mass or less. The lower limit of the content of graphite particles in the negative electrode active material layer is more preferably 80%, 90%, 95%, 97%, or 98% by mass. By setting the content of graphite particles within the above range, it is possible to achieve both high energy density and manufacturability of the negative electrode active material layer, and also to increase the output of the nonaqueous electrolyte storage element and further improve the capacity retention rate after charge-discharge cycling.

[0080] The negative electrode active material layer may contain a negative electrode active material other than graphite particles. The other negative electrode active material may be any of various conventionally known negative electrode active materials. However, the content of graphite particles in the total negative electrode active material contained in the negative electrode active material layer is preferably 90% by mass or more, more preferably 95% by mass or more, and even more preferably 99% by mass or more, and may be substantially 100% by mass. By primarily using graphite particles as the negative electrode active material, the nonaqueous electrolyte storage element can be particularly effectively provided with high output and a high capacity retention rate after charge / discharge cycling.

[0081] The content of all negative electrode active materials in the negative electrode active material layer is preferably 60% by mass or more and 99.5% by mass or less. The lower limit of the content of all negative electrode active materials in the negative electrode active material layer is more preferably 80% by mass, 90% by mass, 95% by mass, 97% by mass, or 98% by mass. By setting the content of all negative electrode active materials within the above range, it is possible to achieve both a high energy density and manufacturability of the negative electrode active material layer, and to increase the output of the nonaqueous electrolyte storage element and further improve the capacity retention rate after charge-discharge cycling.

[0082] When the negative electrode active material layer contains a conductive agent, the content of the conductive agent in the negative electrode active material layer may be, for example, 1% by mass or more and 10% by mass or less. The content of the conductive agent in the negative electrode active material layer is preferably 5% by mass or less, and may more preferably be 2% by mass or less, 1% by mass or less, 0.1% by mass or less, or 0% by mass or less. When the content of the conductive agent in the negative electrode active material layer is low or no conductive agent is contained, the content of the negative electrode active material such as graphite particles can be increased, thereby increasing the energy density, etc. Note that the graphite particles in the negative electrode active material layer do not fall under the category of the conductive agent in the negative electrode active material layer.

[0083] When the negative electrode active material layer contains a binder, the content of the binder in the negative electrode active material layer is preferably 0.1% by mass to 10% by mass, more preferably 0.5% by mass to 8% by mass. The content of the binder in the negative electrode active material layer may be 5% by mass or less, 2% by mass or less, or 1% by mass or less. The technology disclosed herein may also be implemented in an embodiment in which the negative electrode active material layer does not contain a binder.

[0084] When the negative electrode active material layer contains a thickener, the content of the thickener in the negative electrode active material layer is preferably 0.1% by mass or more and 10% by mass or less, and more preferably 0.3% by mass or more and 8% by mass or less. The content of the thickener in the negative electrode active material layer may be 5% by mass or less, 2% by mass or less, or 1% by mass or less. The technology disclosed herein may also be implemented in an embodiment in which the negative electrode active material layer does not contain a thickener.

[0085] The filler in the negative electrode active material layer may be a component other than the negative electrode active material, conductive agent, binder, and thickener, and may be an intentionally contained component. The filler may be contained as a component to fill gaps in the negative electrode active material layer, or may be contained for other purposes. When the negative electrode active material layer contains a filler, the content of the filler in the negative electrode active material layer can be 0.1% by mass or more and 8% by mass or less, and typically 5% by mass or less is preferred, and 2% by mass or less is more preferred. The technology disclosed herein may also be implemented in an embodiment in which the negative electrode active material layer does not contain a filler.

[0086] The negative electrode active material layer may further contain components other than the negative electrode active material, conductive agent, binder, thickener, and filler. These other components include those unintentionally present in the negative electrode active material layer. The negative electrode active material layer may also contain unintentionally present impurities as the other components, as long as the effects of the present invention are achieved. The upper limit of the content of the other components in the negative electrode active material layer may be 10% by mass, 5%, 2%, 1%, 0.1%, or 0.01% by mass. The upper limit of the content of the unintentionally present components in the negative electrode active material layer may be 10% by mass, 5%, 2%, 1%, 0.1%, or 0.01% by mass. The upper limit of the content of the unintentionally present impurities in the negative electrode active material layer may be 10% by mass, 5%, 2%, 1%, 0.1%, or 0.01% by mass.

[0087] The thickness of the negative electrode active material layer is appropriately set depending on the type of negative electrode active material, the application of the non-aqueous electrolyte storage element, and the like. The average thickness of one negative electrode active material layer may be, for example, 5 μm or more and 1,000 μm or less. The lower limit of the average thickness of one negative electrode active material layer may be 10 μm, 20 μm, 30 μm, 40 μm, 50 μm, 60 μm, or 100 μm. The upper limit of the average thickness of one negative electrode active material layer may be 800 μm, 500 μm, 200 μm, 100 μm, 80 μm, 60 μm, or 40 μm. The mass per unit area of ​​one negative electrode active material layer is, for example, 2 mg / cm. 2 More than 50mg / cm 2 The lower limit of the mass per unit area of ​​one negative electrode active material layer may be 3 mg / cm or less. 2 , 4 mg / cm 2 , 5 mg / cm 2 or 6 mg / cm 2 The upper limit of the mass per unit area of ​​one negative electrode active material layer is 30 mg / cm. 2 , 20 mg / cm 2 , 15 mg / cm 2 , 12 mg / cm 2 or 10 mg / cm 2 may be.

[0088] The porosity of the negative electrode active material layer may be, for example, 30% or more and 70% or less. The lower limit of the porosity of the negative electrode active material layer may be 35%, 40%, or 45%. The upper limit of the porosity of the negative electrode active material layer may be 60%, 50%, or 40%.

[0089] (Method of manufacturing negative electrode) The negative electrode can be manufactured by a known method. The negative electrode can be manufactured, for example, in the same manner as the above-described positive electrode manufacturing method, by applying a paste-like negative electrode mixture (negative electrode mixture paste) to a negative electrode substrate directly or via an intermediate layer, and drying the mixture to form a negative electrode active material layer. After drying, the negative electrode active material layer may be pressed, etc.

[0090] (separator) The separator may be a known separator, such as a separator consisting of only a base layer, or a separator having an inorganic layer containing inorganic particles and a binder formed on one or both surfaces of a base layer.

[0091] Examples of the form of the substrate layer of the separator include woven fabric, nonwoven fabric, porous resin film, etc. Among these forms, porous resin film is preferred from the viewpoint of strength, etc., and nonwoven fabric is preferred from the viewpoint of non-aqueous electrolyte retention, etc. The material of the substrate layer of the separator is not particularly limited as long as it has insulating properties, but resins such as polyolefin (polyethylene, polypropylene, etc.), polyimide, aramid, etc. are preferred.

[0092] Examples of inorganic compounds constituting the inorganic particles include oxides such as iron oxide, silicon oxide, aluminum oxide, titanium oxide, zirconium oxide, calcium oxide, and magnesium oxide; nitrides such as aluminum nitride and silicon nitride; carbonates such as calcium carbonate; sulfates such as barium sulfate; sparingly soluble ionic crystals such as calcium fluoride, barium fluoride, and barium titanate; covalently bonded crystals such as silicon; mineral-derived substances such as talc, zeolite, kaolin, bentonite, and mica, or artificial products thereof. One or more types of inorganic particles can be used. The average particle size of the inorganic particles is preferably, for example, from 0.5 μm to 10 μm. The content of the inorganic particles in the inorganic layer is preferably from 50% to 99% by mass, and more preferably from 80% to 98% by mass.

[0093] Examples of binders used in the inorganic layer include the same binders as those exemplified for the positive electrode active material layer.

[0094] The porosity of the separator may be, for example, 20% or more and 80% or less. The lower limit of the porosity of the separator may be 30%, 40%, or 50% from the viewpoint of discharge performance, etc. The upper limit of the porosity of the separator may be 70%, 60%, or 50% from the viewpoint of strength, etc. In this specification, "porosity" refers to a volume-based value measured with a mercury porosimeter.

[0095] The average thickness of the separator may be, for example, 10 μm or more and 40 μm or less, or 15 μm or more and 30 μm or less.

[0096] The separator may be a polymer gel composed of a polymer and a non-aqueous electrolyte, or may be a combination of the porous resin film, nonwoven fabric, or the like described above and a polymer gel.

[0097] (electrode body) As the electrode body, for example, a wound type electrode body, a laminated type electrode body, or other electrode body having a known structure can be used.

[0098] A wound electrode body has a structure in which a positive electrode and a negative electrode are wound in an insulated state. The wound electrode body may be cylindrical (columnar) or flat. The electrode body 2 provided in the nonaqueous electrolyte storage element 1 of FIG. 1 is a flat wound electrode body. The wound electrode body can be produced, for example, by the following procedure. First, a positive electrode, a separator, and a negative electrode, each formed in a strip shape, are stacked in this order to obtain a laminate. The wound electrode body is obtained by rolling this laminate.

[0099] A laminated electrode assembly has a structure in which one or more positive electrodes and one or more negative electrodes are stacked in an insulated state. For example, a laminated electrode assembly can be obtained by stacking a positive electrode, a separator, and a negative electrode, each of which is formed in a rectangular shape, in this order.

[0100] As the electrode body, for example, one having a structure in which at least one of the positive electrode and the negative electrode is folded in an accordion-like manner and stacked can also be used.

[0101] (non-aqueous electrolyte) As the non-aqueous electrolyte, a known non-aqueous electrolyte can be used. The non-aqueous electrolyte is a medium responsible for transporting charge-transporting ions (e.g., lithium ions) between a positive electrode and a negative electrode, and is substantially free of water. The water content in the non-aqueous electrolyte may be, for example, 10,000 ppm or less, or 5,000 ppm or less. Examples of the non-aqueous electrolyte include non-aqueous electrolyte solutions and solid electrolytes. A non-aqueous electrolyte solution and a solid electrolyte may be used in combination. As the non-aqueous electrolyte, it is preferable to use a non-aqueous electrolyte solution, and it is more preferable to use only a non-aqueous electrolyte solution.

[0102] (Non-aqueous electrolyte) The non-aqueous electrolyte contains a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent.

[0103] As the non-aqueous solvent, known non-aqueous solvents can be used. Examples of non-aqueous solvents include carbonates, esters, ethers, amides, and nitriles. Examples of carbonates include cyclic carbonates and chain carbonates. Examples of esters include carboxylic acid esters, phosphate esters, and sulfonic acid esters. Non-aqueous solvents in which some of the hydrogen atoms contained in these compounds have been substituted with halogen atoms may also be used. One or more non-aqueous solvents can be used.

[0104] The term "cyclic carbonate" refers to a carbonate having a ring structure containing a carbonate group (-OC(=O)-O-). Examples of cyclic carbonates include ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate, vinylethylene carbonate, chloroethylene carbonate, fluoroethylene carbonate, difluoroethylene carbonate, styrene carbonate, 1-phenylvinylene carbonate, and 1,2-diphenylvinylene carbonate. The cyclic carbonate may be a saturated cyclic carbonate such as ethylene carbonate, or an unsaturated cyclic carbonate such as vinylene carbonate. "Saturated" refers to the absence of a carbon-carbon unsaturated bond (a carbon-carbon double bond or a carbon-carbon triple bond). "Unsaturated" refers to the presence of a carbon-carbon unsaturated bond. As the cyclic carbonate, a saturated cyclic carbonate is preferred, and ethylene carbonate is more preferred.

[0105] The chain carbonate means a carbonate that does not have a ring structure containing a carbonate group. Examples of the chain carbonate include diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, diphenyl carbonate, trifluoroethyl methyl carbonate, and bis(trifluoroethyl) carbonate. The chain carbonate may be a saturated chain carbonate such as dimethyl carbonate, or an unsaturated chain carbonate such as diphenyl carbonate. The chain carbonate is preferably a saturated chain carbonate, and more preferably ethyl methyl carbonate.

[0106] The non-aqueous solvent preferably contains a carbonate, and more preferably contains a cyclic carbonate and a chain carbonate. The content of the carbonate in the non-aqueous solvent is preferably 80% by volume or more and 100% by volume or less, and may be 99% by volume or more and 100% by volume or less, or even 100% by volume. The use of a cyclic carbonate can promote dissociation of the electrolyte salt and increase the ionic conductivity of the non-aqueous electrolyte. The use of a chain carbonate can reduce the viscosity of the non-aqueous electrolyte. When a cyclic carbonate and a chain carbonate are used in combination, the volume ratio of the cyclic carbonate to the chain carbonate (cyclic carbonate:chain carbonate) is preferably, for example, in the range of 5:95 to 50:50.

[0107] The electrolyte salt may be a known electrolyte salt. Examples of the electrolyte salt include lithium salt, sodium salt, potassium salt, magnesium salt, and onium salt. Among these, lithium salt is preferred. One or more types of electrolyte salt may be used.

[0108] Examples of lithium salts include inorganic lithium salts such as LiPF6, LiPO2F2, LiBF4, and LiClO4; imide salts such as LiN(SO2F)2, LiN(SO2CF3)2, LiN(SO2C2F5)2, and LiN(SO2CF3)(SO2C4F9); and lithium oxalates such as LiB(C2O4)2, LiBF2(C2O4), and LiPF2(C2O4)2. LiN(SO2F)2 also falls under the category of inorganic lithium salts. Among these, inorganic lithium salts are preferred, with LiPF6 being more preferred. In some cases, imide salts are also preferred.

[0109] The content of electrolyte salt in the non-aqueous electrolyte is 0.1 mol / dm at 20°C and 1 atmosphere. 3 More than 2.5mol / dm 3 Preferably less than 0.3 mol / dm 3 More than 2.0mol / dm 3 Less than 0.5 mol / dm is more preferable. 3More than 1.7mol / dm 3 More preferably, 0.7 mol / dm 3 More than 1.5mol / dm 3 The following is particularly preferred: By setting the content of the electrolyte salt within the above range, the ionic conductivity of the non-aqueous electrolyte can be increased.

[0110] The non-aqueous electrolyte may contain an additive in addition to the non-aqueous solvent and the electrolyte salt. One or more additives may be used. When an additive is used in the non-aqueous electrolyte, the content of the additive in the non-aqueous electrolyte is preferably 0.01% by mass to 10% by mass, more preferably 0.1% by mass to 7% by mass, even more preferably 0.2% by mass to 5% by mass, and particularly preferably 0.3% by mass to 3% by mass.

[0111] (solid electrolyte) The solid electrolyte can be selected from any material that has ionic conductivity of lithium, sodium, calcium, etc. and is solid at room temperature (e.g., 20°C). Examples of the solid electrolyte include sulfide solid electrolytes, oxide solid electrolytes, nitride solid electrolytes, halide solid electrolytes, and polymer solid electrolytes. One or more types of solid electrolytes can be used.

[0112] (container) The container accommodates the electrode assembly and the non-aqueous electrolyte in its internal space. The container may be made of a metal material such as aluminum or stainless steel, or a resin material. Metal materials are preferred from the viewpoint of strength, etc. Composite materials of metal and resin may also be used.

[0113] The shape of the container is not particularly limited, and may be cylindrical, rectangular (square), disk-like, etc. The container may also be in the shape of a sheet formed from a metal resin composite film.

[0114] (shape, use, etc. of non-aqueous electrolyte storage element) The shape of the nonaqueous electrolyte storage element according to one embodiment of the present invention is not particularly limited, and may be, for example, a cylindrical battery, a prismatic battery, a flat battery, a coin battery, a button battery, or the like.

[0115] The use of the nonaqueous electrolyte energy storage element according to one embodiment of the present invention is not particularly limited. The nonaqueous electrolyte energy storage element can be used, for example, as a power source for automobiles such as electric vehicles, hybrid vehicles, and plug-in hybrid vehicles; a power source for electronic devices such as personal computers and communication terminals; and a power source for power storage. The nonaqueous electrolyte energy storage element according to one embodiment of the present invention has the advantages of high output and a high capacity retention rate after charge / discharge cycles. Taking full advantage of these advantages, the element can be suitably used as a power source for automobiles, and particularly suitably used as a power source for hybrid automobiles.

[0116] The nonaqueous electrolyte electricity storage element of the present invention may be used singly or in plural. When the required output and required voltage are small, the nonaqueous electrolyte electricity storage element may be used singly. On the other hand, when at least one of the required output and required voltage is large, the nonaqueous electrolyte electricity storage element may be used as an electricity storage device in combination with other nonaqueous electrolyte electricity storage elements. In an electricity storage device in which a plurality of nonaqueous electrolyte electricity storage elements are combined, at least one nonaqueous electrolyte electricity storage element included in the electricity storage device may be the nonaqueous electrolyte electricity storage element according to one embodiment of the present invention. The electricity storage device will be described in detail later.

[0117] In a nonaqueous electrolyte energy storage element according to one embodiment of the present invention, for example, the container may be constrained so as to maintain a constant thickness, or may not be constrained in this manner. Alternatively, the container may be constrained so as to apply a constant load to it. When the container is constrained, expansion of the container due to charge / discharge cycles, etc., may be suppressed, and deterioration of charge / discharge performance may be suppressed. When the container is constrained, a load may or may not be applied to the electrode assembly within the container. For example, a constraining member that performs such constraining may be provided in the nonaqueous electrolyte energy storage element or the energy storage device.

[0118] <Method of manufacturing nonaqueous electrolyte energy storage element> A nonaqueous electrolyte storage element according to one embodiment of the present invention can be manufactured by a known method. The manufacturing method of the nonaqueous electrolyte storage element includes, for example, preparing a positive electrode, preparing a negative electrode, preparing a nonaqueous electrolyte, and housing the positive electrode, negative electrode, and nonaqueous electrolyte in a container. The manufacturing method may also include preparing a separator, and manufacturing an electrode assembly using the positive electrode, negative electrode, and separator. Housing the positive electrode, negative electrode, and nonaqueous electrolyte in a container may include housing the electrode assembly and nonaqueous electrolyte in the container.

[0119] Preparing a positive electrode may mean manufacturing a positive electrode. Manufacturing a positive electrode can be performed by the method described above. Preparing a negative electrode may mean manufacturing a negative electrode. Manufacturing a negative electrode can be performed by the method described above. Preparing a non-aqueous electrolyte may mean preparing a non-aqueous electrolyte. The non-aqueous electrolyte can be prepared, for example, by dissolving an electrolyte salt in a non-aqueous solvent. The positive electrode, negative electrode, separator, non-aqueous electrolyte, etc. may be prepared by purchasing, etc.

[0120] The electrode assembly (or the positive electrode and negative electrode) and the nonaqueous electrolyte can be housed in a container by a known method. When the nonaqueous electrolyte is a nonaqueous electrolyte solution, for example, the electrode assembly (or the positive electrode and negative electrode) is first housed in a container, and then the nonaqueous electrolyte solution is poured into the container through an inlet provided in the container. The inlet is sealed after the nonaqueous electrolyte solution is poured into the container. The method for producing the nonaqueous electrolyte storage element may further include initially charging and discharging the assembled, uncharged storage element.

[0121] The nonaqueous electrolyte storage element according to one embodiment of the present invention may be manufactured by other methods. For example, when the nonaqueous electrolyte storage element according to one embodiment of the present invention is an all-solid-state battery, it may be manufactured by pressing the materials for forming the positive electrode, separator, and negative electrode individually or collectively.

[0122] <Electricity storage device> 2 includes a plurality of energy storage units 20. Each energy storage unit 20 includes a plurality of electrically connected nonaqueous electrolyte energy storage elements 1. The energy storage device 30 may include a bus bar (not shown) that electrically connects the plurality of nonaqueous electrolyte energy storage elements 1, a bus bar (not shown) that electrically connects the plurality of energy storage units 20, and the like. The energy storage unit 20 or the energy storage device 30 may include a state monitoring device (not shown) that monitors the state of one or more nonaqueous electrolyte energy storage elements 1.

[0123] <Other embodiments> The nonaqueous electrolyte storage element of the present invention is not limited to the above-described embodiments, and various modifications may be made without departing from the spirit of the present invention. For example, the configuration of one embodiment may be added to the configuration of another embodiment, or part of the configuration of one embodiment may be replaced with the configuration of another embodiment or well-known technology. Furthermore, part of the configuration of one embodiment may be deleted. Also, well-known technology may be added to the configuration of one embodiment.

[0124] In the above embodiment, the nonaqueous electrolyte storage element is used as a chargeable and dischargeable nonaqueous electrolyte secondary battery, but the nonaqueous electrolyte storage element may be of any type, shape, size, capacity, etc. The present invention can also be applied to various secondary batteries, electric double layer capacitors, lithium ion capacitors, and other capacitors.

[0125] In the above embodiment, the electrode assembly is described in which a separator is interposed between the positive electrode and the negative electrode. However, the electrode assembly may not include a separator. For example, the positive electrode and the negative electrode may be in direct contact with each other, with a non-conductive layer formed on the active material layer of the positive electrode or the negative electrode. In this way, the positive electrode and the negative electrode may further include layers other than the substrate, the intermediate layer, and the active material layer. Furthermore, the positive electrode and the negative electrode may not have a layer structure. [Example]

[0126] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples.

[0127] [Example 1] (Preparation of positive electrode) The lithium transition metal composite oxide particles are secondary particles with an internal porosity of 19% and an average particle size of 4 μm, LiNi 0.45 Co 0.35 Mn 0.20 O2 was prepared. A positive electrode mixture paste was prepared using the lithium transition metal composite oxide particles, acetylene black (AB) as a conductive agent, polyvinylidene fluoride (PVDF) as a binder, and N-methylpyrrolidone (NMP) as a dispersion medium. The mass ratio of the lithium transition metal composite oxide particles, AB, and PVDF was 93.0:4.5:2.5 (solid content equivalent). The positive electrode mixture paste was applied to both sides of aluminum foil as a positive electrode substrate and dried. Then, a roll press was performed to obtain a positive electrode.

[0128] (Preparation of negative electrode) As graphite particles, the internal porosity is 0.5% and the BET specific surface area is 2.8m 2Graphite particles having a particle size of 7 μm and a carbon black content of 1000 kJ / g were prepared. A negative electrode mixture paste was prepared using the graphite particles, styrene-butadiene rubber (SBR) as a binder, carboxymethyl cellulose (CMC) as a thickener, and water as a dispersion medium. The mass ratio of the graphite particles, SBR, and CMC was 98.6:0.8:0.6 (solid content equivalent). The negative electrode mixture paste was applied to both sides of copper foil as a negative electrode substrate and dried. Then, a roll press was performed to obtain a negative electrode.

[0129] (non-aqueous electrolyte) A 1.2 mol / dm 3 LiPF6 was dissolved in the solution at a concentration of 1000 to obtain a non-aqueous electrolyte.

[0130] (separator) The separator was a microporous polyolefin film.

[0131] (Assembly of non-aqueous electrolyte energy storage element) The positive electrode, the negative electrode, and the separator were used to obtain a flat, wound electrode assembly, which was then placed in a rectangular container, and the nonaqueous electrolyte was poured into the container, which was then sealed to obtain the nonaqueous electrolyte storage element of Example 1.

[0132] [Comparative Examples 1 to 5] Non-aqueous electrolyte storage elements of Comparative Examples 1 to 5 were obtained in the same manner as in Example 1, except that the lithium transition metal composite oxide particles and graphite particles shown in Table 1 were used.

[0133] [evaluation] (1)Initial charge / discharge Each of the obtained nonaqueous electrolyte storage elements was initially charged and discharged under the following conditions. In a thermostatic chamber at 25°C, constant current charging was performed with a charging current of 1.0 C and a cut-off voltage of 4.1 V, followed by constant voltage charging at 4.1 V. The charge was terminated until the total charge time reached 3 hours. A 10-minute rest period was then provided. Constant current discharge was performed with a discharging current of 1.0 C and a cut-off voltage of 3.0 V. The discharge capacity in the above discharge was taken as the initial discharge capacity.

[0134] (2) Output measurement Each nonaqueous electrolyte storage element was subjected to constant-current charging at 25°C at a current of 1.0 C, with an amount of electricity equal to 50% of the initial discharge capacity (the discharge capacity in the initial charge / discharge cycle described above), to bring the SOC (state of charge) to 50%. After storing the element in a thermostatic chamber at -10°C for 4 hours, it was discharged for 10 seconds at a current of 20 C, 30 C, or 35 C. After each discharge, the element was subjected to constant-current charging at a current of 1.0 C to bring the SOC to 50%. The relationship between the current and the voltage 10 seconds after the start of discharge was plotted, and the DC resistance was calculated from the slope of the approximate line of the three plots. Furthermore, the current value obtained by extrapolating the approximate line to a voltage of 2.5 V was calculated, and the output was calculated by multiplying the current value by 2.5 V. The results are shown in Table 1 as relative values, with the output of the nonaqueous electrolyte storage element of Comparative Example 1 taken as 100%.

[0135] (3) Charge / discharge cycle test Next, each nonaqueous electrolyte storage element was subjected to constant current discharge at a current of 1.0 C at 25°C to bring the SOC to 0%, and then constant current charging at a current of 0.5 C to an SOC of 50%. Subsequently, the element was stored in a thermostatic chamber at 60°C for 4 hours. Subsequently, constant current charging at a current of 10 C to a voltage corresponding to an SOC of 80%, and then constant current discharging at a current of 10 C to a voltage corresponding to an SOC of 20%. The above charge and discharge cycle was repeated for 1,000 hours without rest periods between the charge and discharge.

[0136] (4) Capacity retention measurement After the charge-discharge cycle test, the discharge capacity of each nonaqueous electrolyte storage element was measured under the same conditions as the initial charge-discharge cycle test. The percentage of the discharge capacity after the charge-discharge cycle test relative to the initial discharge capacity was calculated as the capacity retention rate. The results are shown in Table 1.

[0137] [Table 1]

[0138] The results shown in Table 1 reveal the following: Compared to the nonaqueous electrolyte storage element of Comparative Example 1, the nonaqueous electrolyte storage element of Comparative Example 3, which used lithium transition metal composite oxide particles in its positive electrode, in which the nickel content, among all metal elements other than lithium, was 40 mol % or more and the cobalt content was 30 mol % or more and the internal porosity was 15% or more, showed a significant improvement in output but a significant decrease in capacity retention. Compared to the nonaqueous electrolyte storage element of Comparative Example 3, the nonaqueous electrolyte storage element of Example 1, which used graphite particles in its negative electrode, in which the internal porosity was 2% or less, showed an improved capacity retention while maintaining a sufficiently high output. On the other hand, in the nonaqueous electrolyte storage element of Comparative Example 2, which used graphite particles with an internal porosity of 2% or less in the negative electrode, the output was significantly reduced and the capacity retention rate was hardly improved compared to the nonaqueous electrolyte storage element of Comparative Example 1. Furthermore, the output of the nonaqueous electrolyte storage element of Comparative Example 4, which used lithium transition metal composite oxide particles in the positive electrode in which the nickel content among all metal elements other than lithium was 40 mol % or more and the internal porosity was 15% or more, but the cobalt content among all metal elements other than lithium was less than 30 mol %, was reduced compared to the nonaqueous electrolyte storage element of Comparative Example 1. Furthermore, the capacity retention rate of the nonaqueous electrolyte storage element of Comparative Example 5, which used graphite particles in the negative electrode in which the internal porosity was 2% or less, was hardly improved compared to the nonaqueous electrolyte storage element of Comparative Example 4. The effect of improving the capacity retention of nonaqueous electrolyte energy storage elements when graphite particles with an internal porosity of 2% or less are used in the negative electrode is particularly pronounced when lithium transition metal composite oxide particles with a nickel content of 40 mol% or more and a cobalt content of 30 mol% or more, and an internal porosity of 15% or more, are used in the positive electrode. Furthermore, by using lithium transition metal composite oxide particles with a nickel content of 40 mol% or more and a cobalt content of 30 mol% or more, and an internal porosity of 15% or more, and graphite particles with an internal porosity of 2% or less, a nonaqueous electrolyte energy storage element with high output and high capacity retention after charge-discharge cycling was obtained. A power output (relative value) of 120% or more and a capacity retention of 85% or more was determined to be high and a capacity retention after charge-discharge cycling high. [Industrial Applicability]

[0139] The present invention can be applied to nonaqueous electrolyte storage elements used as power sources for electronic devices such as personal computers and communication terminals, automobiles, industrial equipment, and the like. [Explanation of symbols]

[0140] 1. Non-aqueous electrolyte energy storage element 2 Electrode body 3 containers 4 Positive lead 5 Positive external terminal 6 Negative lead 7 Negative external terminal 20 Energy storage unit 30 Electricity storage device

Claims

1. a positive electrode containing lithium transition metal composite oxide particles; a negative electrode containing graphite particles; Equipped with the lithium transition metal composite oxide particles contain nickel, cobalt, and manganese; the content of the nickel element in the lithium transition metal composite oxide particles is 40 mol % or more and the content of the cobalt element is 30 mol % or more relative to all metal elements other than lithium element, the lithium transition metal composite oxide particles have an internal porosity of 15% or more; The graphite particles have an internal porosity of 2% or less.

2. The BET specific surface area of ​​the graphite particles is 3 m ２ 2. The nonaqueous electrolyte electricity storage element according to claim 1, wherein the nonaqueous electrolyte has a molecular weight of 1 / g or less.

3. 3. The nonaqueous electrolyte storage element according to claim 1, wherein the graphite particles have an average particle size of 5 μm or more and 10 μm or less.

4. 3. The nonaqueous electrolyte storage element according to claim 1, wherein the molar ratio of the content of said cobalt element to the content of said manganese element in said lithium transition metal composite oxide particles is 1.2 or more.

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