Negative electrode for nonaqueous electrolyte power storage element, and nonaqueous electrolyte power storage element

Abstract

A negative electrode for a nonaqueous electrolyte power storage element according to one aspect of the present invention comprises a negative electrode active material layer containing coated graphite particles in which at least a part of the surface of the graphite is coated with non-graphitic carbon. The density of the negative electrode active material layer is 1.09 g / cm3 or more. The ratio (D10 / D90) of the D10 particle diameter to the D90 particle diameter of the coated graphite particles is 0.36 or more. The non-graphitic carbon content of the coated graphite particles is 10 mass% or more, and the BET specific surface area of the negative electrode active material layer is 4.0 m2 / g or less.

Description

Negative electrode for non-aqueous electrolyte storage element and non-aqueous electrolyte storage element

[0001] The present invention relates to a negative electrode for a nonaqueous electrolyte storage element and a nonaqueous electrolyte storage element.

[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. In addition to non-aqueous electrolyte secondary batteries, capacitors such as lithium ion capacitors and electric double layer capacitors are also widely used as non-aqueous electrolyte energy storage elements.

[0003] A typical nonaqueous electrolyte storage element includes an electrode assembly in which a positive electrode containing a positive electrode active material and a negative electrode containing a negative electrode active material are stacked with a separator interposed therebetween. This electrode assembly is housed in a container together with a nonaqueous electrolyte to form a nonaqueous electrolyte storage element. Carbon materials such as graphite are widely used as the negative electrode active material (see Patent Documents 1 and 2).

[0004] Japanese Patent Application Publication No. 2005-222933 Japanese Patent Application Publication No. 2017-069039

[0005] Graphite used as a negative electrode active material may be surface-coated with non-graphitic carbon or the like to improve charge / discharge performance (e.g., discharge capacity). Conventionally, in the manufacture of negative electrodes, a negative electrode active material layer is laminated on a negative electrode substrate, and then pressed to improve adhesion between the negative electrode substrate and the negative electrode active material layer, increase the volumetric energy density, or the like. However, a negative electrode in which the density of the negative electrode active material layer is increased by pressing or the like may have insufficient discharge capacity.

[0006] An object of the present invention is to provide a negative electrode for a nonaqueous electrolyte storage element having a negative electrode active material layer with a sufficiently high density and a large discharge capacity, and a nonaqueous electrolyte storage element including such a negative electrode for a nonaqueous electrolyte storage element.

[0007] A negative electrode for a non-aqueous electrolyte storage element according to one aspect of the present invention comprises a negative electrode active material layer containing coated graphite particles in which at least a portion of the surface of graphite is coated with non-graphitic carbon, and the density of the negative electrode active material layer is 1.09 g / cm ３ the ratio of the D10 particle size to the D90 particle size (D10 / D90) of the coated graphite particles is 0.36 or more, the content of the non-graphitic carbon in the coated graphite particles is 10% by mass or more, and the BET specific surface area of ​​the negative electrode active material layer is 4.0 m ２ / g or less.

[0008] A nonaqueous electrolyte storage element according to another aspect of the present invention includes the negative electrode for a nonaqueous electrolyte storage element according to the aspect of the present invention.

[0009] According to any one aspect of the present invention, it is possible to provide a negative electrode for a nonaqueous electrolyte storage element having a negative electrode active material layer with a sufficiently high density and a large discharge capacity, and a nonaqueous electrolyte storage element including such a negative electrode for a nonaqueous electrolyte storage element.

[0010] Fig. 1 is a perspective view showing a nonaqueous electrolyte energy storage element according to one embodiment of the present invention. Fig. 2 is a schematic diagram showing an energy storage device including a plurality of nonaqueous electrolyte energy storage elements according to one embodiment of the present invention. Fig. 3 is a graph showing the relationship between the density of the negative electrode active material layer and the discharge capacity in Examples.

[0011] First, an outline of the negative electrode for a nonaqueous electrolyte electricity storage element and the nonaqueous electrolyte electricity storage element disclosed in this specification will be described.

[0012] [1] A negative electrode for a nonaqueous electrolyte storage element (hereinafter also simply referred to as "negative electrode") according to one aspect of the present invention comprises a negative electrode active material layer containing coated graphite particles in which at least a portion of the surface of graphite is coated with non-graphitic carbon, and the density of the negative electrode active material layer is 1.09 g / cm ３ the ratio of the D10 particle size to the D90 particle size (D10 / D90) of the coated graphite particles is 0.36 or more, the content of the non-graphitic carbon in the coated graphite particles is 10% by mass or more, and the BET specific surface area of ​​the negative electrode active material layer is 4.0 m ２ / g or less.

[0013] The negative electrode described in [1] above has a sufficiently high density of the negative electrode active material layer and a large discharge capacity. The reason for this is unclear, but the following reason is presumed. First, the negative electrode described in [1] above has a density of the negative electrode active material layer of 1.09 g / cm ３As a result, the density of the negative electrode active material layer is sufficiently high. Furthermore, as described above, in the conventional manufacturing of negative electrodes using coated graphite particles, it is common to laminate a negative electrode active material layer on a negative electrode substrate and then press the laminate for purposes such as increasing the volumetric energy density. However, during pressing, cracks may occur in the coated graphite particles in the negative electrode active material layer, increasing the BET specific surface area of ​​the negative electrode active material layer and exposing the graphite matrix that is not coated with non-graphitic carbon, resulting in an insufficient discharge capacity of the resulting negative electrode. That is, when an attempt is made to form a high-density negative electrode active material layer by pressing the negative electrode active material layer for purposes such as increasing the volumetric energy density, the tradeoff is that cracks may easily occur in the coated graphite particles in the negative electrode active material layer, increasing the BET specific surface area of ​​the negative electrode active material layer and exposing the graphite matrix that is not coated with non-graphitic carbon, resulting in an insufficient discharge capacity of the resulting negative electrode. One possible reason why the coated graphite particles are more likely to crack during pressing is that when the packing ratio of the negative electrode active material layer is high before pressing, the negative electrode active material layer has fewer voids, making it difficult for the voids to be crushed by pressing, and as a result, the coated graphite particles are more likely to crack due to the pressure of the press. In contrast, in the negative electrode described in [1] above, the ratio of the D10 particle size to the D90 particle size of the coated graphite particles (D10 / D90) is 0.36 or more, which means that the particle size variation of the coated graphite particles is relatively small. In such cases, the packing ratio of the negative electrode active material layer before pressing is low, resulting in many voids, making it easier for the voids to be crushed by pressing, and therefore less likely to crack the coated graphite particles. Furthermore, in the negative electrode described in [1] above, the content of non-graphitic carbon coating the graphite in the coated graphite particles is 10% by mass or more, and the graphite is sufficiently coated with non-graphitic carbon, making it less likely to crack the coated graphite particles due to the pressure of the press. Therefore, coupled with the fact that the variation in particle size of the coated graphite particles is relatively small (and thus the voids in the negative electrode active material layer are easily crushed by pressing) (due to interaction), cracking of the coated graphite particles is less likely to occur than in the past, an increase in the BET specific surface area of ​​the negative electrode active material layer is suppressed, and the graphite base material is sufficiently coated with non-graphitic carbon, which is thought to result in a large discharge capacity.Therefore, the negative electrode described in the above [1] can realize a high-performance nonaqueous electrolyte storage element that achieves both high density of the negative electrode active material layer and large discharge capacity.

[0014] "Graphite" refers to a graphite material that has an average lattice spacing (d ００２ "Non-graphitic carbon" refers to a carbon material having an average lattice spacing (d ) of the (002) plane determined by X-ray diffraction before charge / discharge or in a discharged state. ００２ The term "discharged state" refers to a carbon material having a particle size of 0.34 nm or more and 0.42 nm or less. Here, the term "discharged state" of a carbon material refers to a state in which the carbon material, which is a negative electrode active material, is discharged so that charge transport ions that can be absorbed and released during charging and discharging are sufficiently released. For example, this refers to a state in which the open circuit voltage is 0.6 V or more in a half cell using a negative electrode containing a carbon material as a negative electrode active material as a working electrode and metallic lithium as a counter electrode.

[0015] When preparing a carbon material (coated graphite particles) for X-ray diffraction measurement from an assembled nonaqueous electrolyte storage element, the carbon material is brought to the above-mentioned discharged state by the following method. First, the nonaqueous electrolyte storage element is discharged at a constant current of 0.1 C to the discharge end voltage during normal use. Then, the nonaqueous electrolyte storage element is disassembled, and the negative electrode is removed. A half-cell is assembled using the removed negative electrode as the working electrode and metallic lithium as the counter electrode. If the open circuit voltage of this half-cell is less than 0.6 V, the half-cell is discharged at a current of 0.1 C so that the open circuit voltage becomes 0.6 V or higher. Note that discharging in the half-cell refers to an oxidation reaction in which charge-transporting ions are released from the carbon material, which is the negative electrode active material. The half-cell is disassembled, and the negative electrode is removed and thoroughly washed with dimethyl carbonate, followed by drying under reduced pressure at room temperature. Thereafter, the negative electrode active material layer containing the carbon material is peeled from the negative electrode substrate, and the negative electrode active material layer is washed with a solvent that dissolves components such as the binder to remove the binder and other components. The washed negative electrode active material layer is immersed in an acid or alkaline solution to remove metals derived from the negative electrode substrate, an SEI (solid electrolyte interface) coating, and the like, and then washed with water and dried under reduced pressure to obtain a carbon material. The operations from disassembly of the nonaqueous electrolyte storage element to preparation of the carbon material to be measured are carried out in a dry air atmosphere with a dew point of −40°C or less. Here, normal use refers to the use of the nonaqueous electrolyte storage element under charge and discharge conditions recommended or specified for the nonaqueous electrolyte storage element.

[0016] The "content of non-graphitic carbon in the coated graphite particles" is measured by the following procedure. Using a thermogravimetric / differential thermal (TG / DTA) analyzer, the coated graphite particles are heated from room temperature to 1,200°C at a heating rate of 5°C / min in a water vapor atmosphere at a humidity of 65% RH, and the thermogravimetric curve (horizontal axis: temperature, vertical axis: mass of coated graphite particles) of the coated graphite particles is measured. In the thermogravimetric curve, the mass decreases with increasing temperature; first, a mass corresponding to the moisture adsorbed on the coated graphite particles decreases around 100°C, then the non-graphitic carbon coating the graphite decomposes, resulting in a decrease in the mass corresponding to the non-graphitic carbon, and then the graphite matrix decomposes, resulting in a decrease in the mass corresponding to the graphite. Therefore, in the obtained thermogravimetric curve, the mass of the coated graphite particle after the mass corresponding to the water adsorbed on the graphite at around 100°C is taken as the reference (100%), and the proportion of the mass loss from this reference until the graphite decomposition onset temperature is reached (= [mass loss from the reference until the graphite decomposition onset temperature is reached / mass of the coated graphite particle at the reference] × 100) is taken as the content of non-graphitic carbon. The thermogravimetric curve is typically divided into the following regions after the mass corresponding to the water adsorbed on the graphite decreases at around 100°C with increasing temperature: (1) a first region in which there is almost no mass change, (2) a second region in which the mass of the non-graphitic carbon in the coated graphite particle decreases rapidly after the first region, (3) a third region in which the mass decreases more slowly than in the second region or there is almost no mass loss after the second region, and (4) a fourth region in which the mass of the graphite decreases more rapidly than in the third region after the third region. The temperature at which an inflection point (a measurement point at which the slope of the curve changes) occurring during the transition from the third region of (3) above to the fourth region of (4) above is observed is a typical example of the graphite decomposition initiation temperature referred to here. The graphite decomposition initiation temperature is determined from the intersection of the approximate line of the curve for the process (3) above with the approximate line of the curve showing the rapid mass loss for the process (4) above. The graphite decomposition initiation temperature can be generally 950°C or higher (e.g., 950°C or higher and 1,000°C or lower for natural graphite, and 980°C or higher and 1,100°C or lower for artificial graphite).

[0017] "D90 particle size" means the value at which the cumulative volume from the smaller particle size side in the volume-based cumulative distribution calculated in accordance with JIS-Z-8819-2 (2001) is 90% based on the particle size distribution measured in accordance with JIS-Z-8825 (2013) using a laser diffraction / scattering method for a diluted solution of particles diluted with a solvent. Similarly, "D10 particle size" means the value at which the cumulative volume is 10%, and "D50 particle size" means the value at which the cumulative volume is 50%.

[0018] Measurement of the "content of non-graphitic carbon in the coated graphite particles" and the "D90 particle size," "D10 particle size," and "D50 particle size" of the coated graphite particles are performed on the coated graphite particles before assembly of the negative electrode, if such particles can be prepared. When the coated graphite particles to be measured are prepared from the negative electrode provided in the assembled non-aqueous electrolyte electricity storage element, measurements are performed on the coated graphite particles prepared according to the procedure for preparing the carbon material (coated graphite particles) to be subjected to the X-ray diffraction method from the assembled non-aqueous electrolyte electricity storage element.

[0019] The "density of the negative electrode active material layer" is the value obtained by dividing the mass of the negative electrode active material layer by the apparent volume (volume including voids) of the negative electrode active material layer. In other words, the density of the negative electrode active material layer is a density that takes into account the volume of voids in the negative electrode active material layer. The density of the negative electrode active material layer is calculated from the area, average thickness, and mass of the negative electrode active material layer. The average thickness is the average value of thicknesses measured at any five points. The same applies to the average thickness of layers other than the negative electrode active material layer.

[0020] When a negative electrode before assembling a nonaqueous electrolyte storage element can be prepared, the "density of the negative electrode active material layer" and the "BET specific surface area of ​​the negative electrode active material layer" described later are measured on the negative electrode active material layer of that negative electrode. When the negative electrode to be measured is prepared from an assembled nonaqueous electrolyte storage element, the measurements are performed on the negative electrode active material layer of a negative electrode that has been subjected to the above-described steps of disassembling the nonaqueous electrolyte storage element and drying the negative electrode under reduced pressure, in accordance with the procedure for preparing the carbon material (coated graphite particles) to be subjected to the X-ray diffraction method from the assembled nonaqueous electrolyte storage element.

[0021] [2] In the negative electrode for a nonaqueous electrolyte storage element according to [1] above, the BET specific surface area of ​​the negative electrode active material layer is 2.0 m２ / g or more 3.8m ２ / g or less.

[0022] The negative electrode for a nonaqueous electrolyte storage element according to the above [2] has a BET specific surface area of ​​the negative electrode active material layer of 2.0 m ２ / g or more 3.8m ２ / g or less, and the discharge capacity is larger.

[0023] The "BET specific surface area of ​​the negative electrode active material layer" is determined by measuring the pore size distribution using a nitrogen adsorption method. This measurement is performed using an "autosorb iQ" manufactured by Quantachrome. Five points are extracted from the region of the resulting adsorption isotherm where P / P0 = 0.06 to 0.3, and a BET plot is performed. The BET specific surface area is calculated from the y-intercept and slope of the line.

[0024] [3] In the negative electrode for a nonaqueous electrolyte storage element according to the above [1] or [2], the ratio of the D10 particle size to the D90 particle size (D10 / D90) of the coated graphite particles may be 0.36 or more and 0.50 or less.

[0025] In the negative electrode for a nonaqueous electrolyte storage element described in [3] above, the ratio of the D10 particle size to the D90 particle size (D10 / D90) of the coated graphite particles is 0.36 or more and 0.50 or less, and the above-mentioned effects are more effectively exhibited.

[0026] [4] The negative electrode for a nonaqueous electrolyte storage element according to any one of [1] to [3] above, wherein the density of the negative electrode active material layer is 1.20 g / cm ３ Super 1.40g / cm ３ The following is also acceptable.

[0027] The negative electrode for a nonaqueous electrolyte storage element according to [4] above has a density of the negative electrode active material layer of 1.20 g / cm ３ Super 1.40g / cm ３ The above-mentioned effects are more effectively achieved as follows.

[0028] [5] A nonaqueous electrolyte storage element according to another aspect of the present invention includes the negative electrode for a nonaqueous electrolyte storage element according to any one of [1] to [4] above.

[0029] The nonaqueous electrolyte storage element described in [5] above has a large discharge capacity because it includes the negative electrode for a nonaqueous electrolyte storage element described in any one of [1] to [4] above.

[0030] A negative electrode for a nonaqueous electrolyte electricity storage element, a nonaqueous electrolyte electricity storage element, a method for manufacturing a nonaqueous electrolyte electricity storage element, an electricity storage device, and other embodiments according to one embodiment of the present invention will be described in detail below.

[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] <Negative electrode> A negative electrode (negative electrode for a non-aqueous electrolyte storage element) according to one embodiment of the present invention has a negative electrode substrate and a negative electrode active material layer laminated on the negative electrode substrate directly or via an intermediate layer. Typically, the negative electrode has a portion where the negative electrode substrate is exposed. This exposed portion of the negative electrode substrate is typically connected to a negative electrode lead, which will be described later. The negative electrode may have a shape such as a sheet, plate, or strip. The negative electrode is a negative electrode used in a non-aqueous electrolyte storage element such as a non-aqueous electrolyte secondary battery. The negative electrode may be a negative electrode used in a non-aqueous electrolyte storage element such as a non-aqueous electrolyte secondary battery.

[0033] 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 there are both a portion where the negative electrode active material layer is laminated on both sides of the negative electrode substrate and a portion where the negative electrode active material layer is laminated on only one side of the negative electrode substrate, 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.

[0034] The negative electrode substrate has electrical conductivity. In this specification, "having electrical conductivity" means that the volume resistivity is 10 －２The 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 It means that the resistance is Ω·cm or more.

[0035] Examples of materials for the negative electrode substrate include metals such as copper, nickel, iron, and alloys thereof (such as stainless steel), carbon materials, etc. Among these, copper and copper alloys are preferred.

[0036] 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.

[0037] 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.

[0038] The intermediate layer is a layer disposed between the negative electrode substrate and the negative 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 negative electrode substrate and the negative 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 negative electrode active material layer described below.

[0039] The negative electrode active material layer contains coated graphite particles. The negative electrode active material layer contains optional components such as a negative electrode active material other than the coated graphite particles, a conductive agent, a binder, a thickener, and a filler, as necessary. The negative electrode active material layer may be formed from a negative electrode mixture containing the 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.

[0040] The coated graphite particles are a component that functions as a negative electrode active material. The coated graphite particles include graphite as a base material and non-graphitic carbon that coats at least a portion of the surface of the graphite. The non-graphitic carbon may coat the entire surface of the graphite. Alternatively, the non-graphitic carbon may be contained within the graphite. Coating the graphite base material with non-graphitic carbon can be achieved, for example, by coating the surface of graphite particles with pitch and firing the resulting mixture.

[0041] The coated graphite particles may be particles substantially composed of graphite and non-graphitic carbon. The total content of graphite and non-graphitic carbon in the coated graphite particles is preferably 90% by mass or less and 100% by mass or less, and may be 99% by mass or more and 100% by mass or less. Note that the content of each component in the coated graphite particles does not include moisture. In other words, the mass of the coated graphite particles excluding moisture (the mass of the coated graphite particles in a dry state) is taken as the reference (100% by mass).

[0042] The graphite that is the base material of the coated graphite particles may be either artificial graphite or natural graphite, but is preferably natural graphite. Examples of natural graphite include flake graphite, lump graphite (flake graphite), and amorphous graphite. The graphite may be obtained by spheroidizing flake graphite and subjecting it to a compaction treatment.

[0043] "Artificial graphite" refers to graphite that has been artificially produced. The artificial graphite may be one in which only two peaks appear in the diffraction angle 2θ range of 40° to 50° in an X-ray diffraction pattern using CuKα radiation. In the case of artificial graphite, it is generally believed that only two peaks resulting from a hexagonal crystal structure appear.

[0044] "Natural graphite" refers to graphite extracted from natural resources. Natural graphite may have four peaks in an X-ray diffraction pattern using CuKα radiation within a diffraction angle 2θ range of 40° to 50°. In the case of natural graphite, it is believed that a total of four peaks appear within a diffraction angle 2θ range of 40° to 50°: two peaks derived from a hexagonal crystal structure and two peaks derived from a rhombohedral crystal structure. 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 is derived from a hexagonal crystal structure, and the (012) plane is derived from a rhombohedral crystal structure.

[0045] The lower limit of the non-graphitic carbon content in the coated graphite particles is 10% by mass, preferably 11% by mass, and more preferably 12% by mass. When the non-graphitic carbon content in the coated graphite particles is equal to or greater than the above lower limit, the surface of the particulate graphite is sufficiently coated with non-graphitic carbon (for example, the non-graphitic carbon fills micropores present on the surface of the graphite particles, thereby reducing the BET specific surface area of ​​the negative electrode active material layer), thereby increasing the discharge capacity. The upper limit of the non-graphitic carbon content in the coated graphite particles is, for example, preferably 20% by mass, more preferably 16% by mass, and even more preferably 14% by mass. When the non-graphitic carbon content in the coated graphite particles is equal to or less than the above upper limit, the advantages of graphite as a negative electrode active material can be particularly fully exhibited.

[0046] The graphite content in the coated graphite particles is preferably 80% by mass or more and 90% by mass or less, more preferably 84% by mass or more and 89% by mass or less, and even more preferably 86% by mass or more and 88% by mass or less.

[0047] The D50 particle size of the coated graphite particles is, for example, preferably 3 μm or more and 20 μm or less, more preferably 5 μm or more and 15 μm or less, even more preferably 7 μm or more and 10 μm or less, and particularly preferably 8.0 μm or more and 9.0 μm or less. When the D50 particle size of the coated graphite particles is in the above range, the discharge capacity can be further increased, etc.

[0048] The lower limit of the ratio of the D10 particle size to the D90 particle size (D10 / D90) of the coated graphite particles is 0.36, and preferably 0.37. When the ratio (D10 / D90) is equal to or greater than the lower limit, the particle size variation of the coated graphite particles is small, and the negative electrode active material layer before pressing has many voids. In such a case, cracking of the coated graphite particles due to pressing is less likely to occur, and the discharge capacity can be increased. The upper limit of the ratio (D10 / D90) is 1, and may be 0.50, 0.45, or 0.40. The ratio (D10 / D90) may be equal to or greater than any of the above lower limits and equal to or less than any of the above upper limits.

[0049] The lower limit of the D10 particle size of the coated graphite particles is, for example, 2 μm, preferably 4.0 μm, more preferably 4.5 μm, and even more preferably 4.8 μm. The upper limit of the D10 particle size is, for example, 10 μm, preferably 8 μm, more preferably 7 μm, and even more preferably 6 μm. The D10 particle size may be equal to or greater than any of the above lower limits and equal to or less than any of the above upper limits.

[0050] The lower limit of the ratio of the D10 particle size to the D50 particle size (D10 / D50) of the coated graphite particles may be, for example, 0.55, but is preferably 0.60. When the ratio (D10 / D50) is equal to or greater than the lower limit, the coated graphite particles contain fewer particles with relatively small particle sizes, resulting in a greater number of voids in the negative electrode active material layer before pressing. In such cases, cracking of the coated graphite particles due to pressing (and thus an increase in the BET specific surface area of ​​the negative electrode active material layer) is less likely to occur, thereby enabling a greater discharge capacity. The upper limit of the ratio (D10 / D50) is 1, and may be 0.80, 0.70, or 0.65. The ratio (D10 / D50) may be equal to or greater than any of the above-mentioned lower limits and equal to or less than any of the above-mentioned upper limits.

[0051] The lower limit of the D90 particle size of the coated graphite particles is, for example, 8 μm, preferably 10 μm, more preferably 12 μm, and even more preferably 13 μm. The upper limit of the D90 particle size is, for example, 30 μm, preferably 20 μm, more preferably 16 μm, and even more preferably 14 μm. The D90 particle size may be equal to or greater than any of the above lower limits and equal to or less than any of the above upper limits.

[0052] In order to obtain particles (powders) such as coated graphite particles with a predetermined particle size and particle size distribution, a pulverizer, a classifier, or the like is used. Examples of pulverization methods include methods using a mortar, a ball mill, a sand mill, a vibration ball mill, a planetary ball mill, a jet mill, a counter jet mill, a swirling airflow jet mill, or a sieve. Wet pulverization in the presence of water or an organic solvent such as hexane can also be used. As a classification method, a sieve, an air classifier, or the like is used as needed for both dry and wet methods.

[0053] The content of the coated graphite particles in the negative electrode active material layer is preferably 60% by mass or more and 99.5% by mass or less, and more preferably 90% by mass or more and 99% by mass or less. The lower limit of the content of the coated graphite particles in the negative electrode active material layer may be 95% by mass or may be 97% by mass. By setting the content of the coated graphite particles in the above range, it is possible to achieve both high energy density and manufacturability of the negative electrode active material layer, and to further increase the discharge capacity.

[0054] The negative electrode active material layer may contain other negative electrode active materials in addition to the coated graphite particles. Examples of other negative electrode active materials include non-graphitic carbon (easily graphitizable carbon or non-graphitizable carbon), metallic lithium, metals or semimetals such as Si and Sn, metal oxides or semimetal oxides such as Si oxide, Ti oxide, and Sn oxide, and Li ４ Ti ５ O １２ , LiTiO ２、 TiNb ２ O ７Examples of the coated graphite particles include titanium-containing oxides such as titanium dioxide, polyphosphate compounds, and silicon carbide. However, the content of the coated graphite particles relative to the total negative electrode active material is preferably 80% by mass or more, more preferably 90% by mass or more, even more preferably 99% by mass or more, even more preferably 99.9% by mass or more, and particularly preferably 100% by mass. In this way, when the negative electrode active material is essentially composed of coated graphite particles, the effect of increasing the discharge capacity is particularly remarkable.

[0055] The conductive agent is usually a component made of a material having electrical conductivity. Even when the volume resistivity of the 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 －２ Conductive 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 main constituent element is carbon. The main constituent element refers to the element with the highest content by mass. For example, the carbon content in the 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 nanofibers, pitch-based carbon fibers, and carbon black. Examples of carbon black include furnace black, acetylene black, and ketjen black. Examples of graphene-based carbon include graphene, carbon nanotubes (CNTs), and fullerenes. However, the conductive agent in the negative electrode active material layer does not include the coated graphite particles contained in the negative electrode active material layer and other carbon materials in conventionally known negative electrode active materials. The conductive agent may be in the form of powder, fiber, or the like. One or more conductive agents may be used. A composite of these materials may also be used as the conductive agent. For example, a composite material of carbon black and CNT may also be used.

[0056] When the negative electrode active material layer contains a conductive agent, the content of the conductive agent in the negative electrode active material layer is preferably 1% by mass or more and 10% by mass or less, and more preferably 3% by mass or more and 9% by mass or less. The content of the conductive agent in the negative electrode active material layer may be 5% by mass or less, or may be 2% by mass or less, 1% by mass or less, 0.5% by mass or less, or 0.1% 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 conductive agent.

[0057] Examples of the binder include a water-based binder and an organic solvent-based binder.

[0058] The aqueous binder is a binder that dissolves or disperses in water. The aqueous binder may be a binder that dissolves or disperses 1 part by mass or more in 100 parts by mass of water at 20°C. When forming a negative electrode active material layer using a negative 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.

[0059] 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 per 100 parts by mass of an organic solvent (e.g., N-methylpyrrolidone) at 20°C. When forming a negative electrode active material layer using a negative electrode mixture paste whose dispersion medium is an organic solvent or a mixed solvent mainly composed of 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.

[0060] 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 can be used.

[0061] 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 mass% to 10 mass%, more preferably 0.5 mass% to 8 mass%. The content of the binder in the negative electrode active material layer may be 5 mass% or less, or may be 2 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.

[0062] 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.

[0063] 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 0.5% 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.

[0064] The filler is not particularly limited. 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 another purpose. When the negative electrode active material layer contains a filler, the content of the filler in the negative electrode active material layer may be 0.1% by mass or more and 8% by mass or less, and typically 5% by mass or less is preferred, and may be 2% by mass or less, 1% by mass or less, 0.5% by mass or less, or 0.1% 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 filler.

[0065] The negative electrode active material layer may further contain other components in addition to the coated graphite particles, other negative electrode active materials other than the coated graphite particles, conductive agents, binders, thickeners, and fillers. These other components include those unintentionally present in the negative electrode active material layer. The negative 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 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 contained 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 contained impurities in the negative electrode active material layer may be 10% by mass, 5%, 2%, 1%, 0.1%, or 0.01% by mass.

[0066] The lower limit of the density of the negative electrode active material layer is 1.09 g / cm ３ and 1.10 g / cm ３ , 1.13 g / cm ３ , 1.15 g / cm ３ , 1.17 g / cm ３ , 1.18 g / cm ３ , 1.19 g / cm ３ or 1.20 g / cm ３ The density of the negative electrode active material layer may be 1.20 g / cm ３ According to this configuration, even when a high-density negative electrode active material layer is formed, which is equal to or higher than the lower limit, cracking of the coated graphite particles is unlikely to occur. Therefore, it is possible to increase the volume-based energy density while maintaining a large discharge capacity. The upper limit of the density of the negative electrode active material layer is, for example, 1.40 g / cm ３ and 1.30 g / cm ３ , 1.25 g / cm ３ , 1.23 g / cm ３ or 1.20 g / cm ３ The density of the negative electrode active material layer may be equal to or greater than any of the above-mentioned lower limits and equal to or less than any of the above-mentioned upper limits. The density of the negative electrode active material layer can be adjusted by the particle size of the coated graphite particles, whether or not pressing is performed during production, the pressure of pressing, etc.

[0067] The upper limit of the BET specific surface area of ​​the negative electrode active material layer is 4.0 m ２ / g, and 3.9m ２ / g is preferred, and 3.8m ２ When the BET specific surface area of ​​the negative electrode active material layer is equal to or less than the upper limit, cracking of the coated graphite particles is sufficiently suppressed, and the graphite base material is particularly sufficiently coated, which makes it possible to increase the discharge capacity, etc. The lower limit of the BET specific surface area of ​​the negative electrode active material layer is 2.0 m ２ / g, and 2.5m ２ / g, 2.8m ２ / g or 3.0m ２ / g. The BET specific surface area of ​​the negative electrode active material layer may be equal to or greater than any of the above-mentioned lower limits and equal to or less than any of the above-mentioned upper limits. The BET specific surface area of ​​the negative electrode active material layer can be adjusted by the content of non-graphitic carbon in the coated graphite particles, the particle size of the coated graphite particles, whether or not pressing is performed during production, the pressure of pressing, etc.

[0068] The lower limit of the value ((D10 / D90) / BET specific surface area) obtained by dividing the ratio of the D10 particle size to the D90 particle size of the coated graphite particles (D10 / D90) by the BET specific surface area of ​​the negative electrode active material layer is 0.10 g / m ２ This value ((D10 / D90) / BET specific surface area) is preferably 0.10 g / m ２ or more (for example, 0.10 g / m ２ 0.20g / m or more ２ hereinafter) means that the specific surface area of ​​the negative electrode active material layer is relatively small and the variation in particle size of the coated graphite particles is relatively small, and in such a case, the discharge capacity can be made larger.

[0069] 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%, 55%, or 50%. The porosity of the negative electrode active material layer may be equal to or more than any of the lower limits and equal to or less than any of the upper limits. The "porosity (%)" of the negative electrode active material layer and the positive electrode active material layer described later is calculated by dividing the apparent volume (volume including voids) of the negative (positive) electrode active material layer by V １ The sum of the actual volumes of the materials constituting the negative (positive) electrode active material layer is V ２ In this case, (1-V ２ / V １ ) × 100. The sum of the actual volumes of the materials constituting the negative (positive) electrode active material layer, V ２ can be calculated from the content of each material in the negative (positive) electrode active material layer and the true density of each material.

[0070] 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 50mg / cm or more 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.

[0071] (Method for manufacturing a negative electrode) A negative electrode according to one embodiment of the present invention can be manufactured, for example, by applying a paste-like negative electrode mixture (negative electrode mixture paste) to a negative electrode substrate directly or via an intermediate layer, and then drying the mixture to form a negative electrode active material layer. After drying, the negative electrode active material layer may be pressed, for example. The negative electrode mixture paste contains the components that constitute the negative electrode active material layer, such as coated graphite particles and an optional binder. The negative electrode mixture paste usually further contains a dispersion medium. Water is preferred as the dispersion medium used in the negative electrode mixture paste.

[0072] <Non-aqueous electrolyte storage element> A non-aqueous electrolyte storage element according to one embodiment of the present invention includes a positive electrode, a negative electrode, a non-aqueous electrolyte, and a container that accommodates these. The non-aqueous electrolyte storage element may further include a separator that is 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 non-aqueous electrolyte typically exists in a state of being impregnated into the electrode assembly. The non-aqueous electrolyte storage element according to one embodiment of the present invention may further include other components.

[0073] 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.

[0074] 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, focusing on 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 scope of application of the present invention.

[0075] (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.

[0076] The thickness of the positive electrode is appropriately set depending on the application of the nonaqueous electrolyte storage element, etc. 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 a portion where a positive electrode active material layer is laminated on a positive electrode substrate directly or via an intermediate layer. When there are both a portion where a positive electrode active material layer is laminated on both sides of the positive electrode substrate and a portion where a positive electrode active material layer is laminated on only one side of the positive electrode substrate, the average thickness of the portion where a positive electrode active material layer is laminated on both sides of the positive electrode substrate is used.

[0077] The positive electrode substrate is electrically conductive. Examples of the material for the positive electrode substrate include metals such as aluminum, titanium, iron, and alloys thereof (e.g., stainless steel). Among these, aluminum or an aluminum alloy is preferred from the viewpoints of potential resistance, high electronic conductivity, and cost.

[0078] The positive electrode substrate has a shape such as a sheet, plate, or strip. Examples 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.

[0079] 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.

[0080] The structure of the intermediate layer of the positive electrode is not particularly limited, and can be selected from the structures exemplified for the intermediate layer of the negative electrode, for example.

[0081] The positive electrode active material layer contains a 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 optional components such as the conductive agent, the binder, the thickener, and the filler can be selected from the materials exemplified for the negative electrode above. The positive electrode active material layer may be formed from a positive electrode mixture containing a 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.

[0082] As the positive electrode active material, a known positive electrode active material can be used. A material capable of absorbing and releasing lithium ions is typically used as the positive electrode active material for a lithium ion secondary battery. Examples of the positive electrode active material include lithium transition metal composite oxides, polyanion compounds, chalcogen compounds, sulfur-based materials, and lithium oxide. One or more positive electrode active materials can be used.

[0083] Examples of the transition metal element contained in the lithium transition metal composite oxide include nickel, cobalt, and manganese. The lithium transition metal composite oxide may also contain a typical metal element such as aluminum. Examples of the lithium transition metal composite oxide include α-NaFeO ２ Examples of the lithium transition metal composite oxide include a lithium transition metal composite oxide having a crystalline structure and a lithium transition metal composite oxide having a spinel crystalline structure.

[0084] α-NaFeO ２ As the lithium transition metal composite oxide having a crystalline structure, Li １＋α Ma １－α O ２ (Ma is a metal element other than lithium containing one or more transition metal elements, where 0≦α<1.) Ma preferably contains one or more of Ni, Co, and Mn. The total content of Ni, Co, and Mn relative to Ma ((Ni+Co+Mn) / Ma) is preferably 90 mol% or more, and more preferably 98 mol% or more.

[0085] Examples of lithium transition metal composite oxides having a spinel crystal structure include Li βMb ２ O ４ (Mb is a metal element other than lithium containing one or more transition metal elements, and β is 0<β≦1.2). Mb preferably contains Mn. The content of Mn relative to Mb (Mn / Mb) is preferably 50 mol % or more, and more preferably 80 mol % or more.

[0086] The polyanion compound is a compound composed of a polyanion (i.e., a polyvalent oxoacid anion) and a cation. The polyanion compound preferably contains a lithium cation and a transition metal cation as the cation. Examples of the polyanion compound include LiFePO ４ , LiMnPO ４ , LiMn ｘ Fe １－ｘ P.O. ４ (0<x<1), LiNiPO ４ , LiCoPO ４ , Li ３ V ２ (P.O. ４ ) ３ , Li ２ MnSiO ４ , Li ２ CoPO ４ The surface of the particles of the polyanionic compound may be coated with another material (for example, a carbon material).

[0087] Examples of the chalcogen compound include titanium disulfide, molybdenum disulfide, and molybdenum dioxide.

[0088] Examples of sulfur-based materials include elemental sulfur, metal sulfides such as lithium sulfide, organic disulfide compounds, and organic sulfur compounds such as carbon sulfide compounds.

[0089] The atoms or polyanions in these materials serving as the positive electrode active material may be partially substituted with atoms or anion species of other elements, and the surfaces of these materials may be coated with other materials.

[0090] The positive electrode active material is usually particulate. The D50 particle size of the positive electrode active material is preferably, for example, 0.1 μm or more and 20 μm or less. By setting the D50 particle size of the positive electrode active material to the above lower limit or more, the positive electrode active material becomes easy to manufacture or handle. By setting the D50 particle size of the positive electrode active material to the above upper limit or less, the electronic conductivity of the positive electrode active material layer is improved. Note that when a composite of the positive electrode active material and another material is used, the D50 particle size of the composite is taken as the D50 particle size of the positive electrode active material.

[0091] The content of the positive electrode active material in the positive electrode active material layer is preferably 50% by mass or more and 99% by mass or less, more preferably 70% by mass or more and 98% by mass or less, and may be 80% by mass or more and 95% by mass or less. By setting the content of the positive electrode active material within the above range, both high energy density and manufacturability of the positive electrode active material layer can be achieved.

[0092] 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 5%, 4%, or 3% 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.

[0093] The content of the binder in the positive electrode active material layer is preferably 0.1% by mass or more and 10% by mass or less, more preferably 1% by mass or more and 9% by mass or less, and even more preferably 3% by mass or more and 8% by mass or less. 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, etc. The technology disclosed herein can also be implemented in an embodiment in which the positive electrode active material layer does not contain a binder.

[0094] 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 mass% or more and 8 mass% or less, more preferably 5 mass% or less, and even more preferably 2 mass% or less. The technology disclosed herein can also be implemented in an embodiment in which the positive electrode active material layer does not contain a thickener.

[0095] 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 as a component 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 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 positive electrode active material layer does not contain a filler.

[0096] 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. These other components include those unintentionally generated 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 generated 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.

[0097] 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, 4 mg / cm. ２ 100mg / cm or more ２ The lower limit of the mass per unit area of ​​one positive electrode active material layer may be 6 mg / cm or less. ２ , 8 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.

[0098] 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%.

[0099] (Method for manufacturing positive electrode) 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 drying the paste to form a positive electrode active material layer. The positive electrode mixture paste usually contains a positive electrode active material, other optional components, and a dispersion medium. After drying, the positive electrode active material layer may be pressed, etc.

[0100] (Negative Electrode) The negative electrode provided in the nonaqueous electrolyte electricity storage element according to one embodiment of the present invention is the above-described negative electrode for a nonaqueous electrolyte electricity storage element according to one embodiment of the present invention.

[0101] (Separator) A known separator can be used as the separator, for example, a separator consisting of only a base layer, or a separator in which an inorganic layer containing inorganic particles and a binder is formed on one or both surfaces of a base layer.

[0102] Examples of the form of the separator substrate layer include woven fabric, nonwoven fabric, and porous resin film. Among these forms, porous resin film is preferred from the viewpoint of strength, and nonwoven fabric is preferred from the viewpoint of nonaqueous electrolyte retention. The material of the separator substrate layer is not particularly limited as long as it has insulating properties, but resins such as polyolefin (polyethylene, polypropylene, etc.), polyimide, and aramid are preferred.

[0103] 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 resource-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, 0.5 μm to 10 μm. The content of the inorganic particles in the inorganic layer is preferably 50% by mass to 99% by mass, more preferably 80% by mass to 98% by mass.

[0104] Examples of binders used in the inorganic layer include the same binders as those exemplified for the negative electrode active material layer.

[0105] 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.

[0106] 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.

[0107] 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.

[0108] (Electrode Body) As the electrode body, for example, a wound type electrode body, a laminated type electrode body, or the like having a known structure can be used.

[0109] 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.

[0110] 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 into a rectangular shape, in this order.

[0111] 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.

[0112] (Non-aqueous electrolyte) A known non-aqueous electrolyte can be used as the non-aqueous electrolyte. The non-aqueous electrolyte is a medium responsible for transporting charge-transporting ions (e.g., lithium ions) between the positive electrode and the 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, 5,000 ppm or less, 1,000 ppm or less, 500 ppm or less, or 100 ppm or less, preferably 50 ppm or less, and more preferably 20 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.

[0113] (Non-aqueous Electrolyte) The non-aqueous electrolyte contains a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent.

[0114] 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.

[0115] The term "cyclic carbonate" refers to a carbonate having a ring structure containing a carbonate group (-O-C(=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, saturated cyclic carbonates are preferred, and ethylene carbonate is more preferred.

[0116] 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.

[0117] 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 in the range of, for example, 5:95 to 50:50.

[0118] 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.

[0119] The lithium salt is LiPF ６ , LiPO ２ F ２ , LiBF ４ , LiClO ４ Inorganic lithium salts such as LiN(SO ２ F) ２ , LiN(SO ２ CF ３ ) ２ , LiN(SO ２ C ２ F ５ ) ２ , LiN(SO ２ CF ３ ) (SO ２ C ４ F ９ ), imide salts such as LiB(C ２ O ４ ) ２ , LiBF ２ (C ２ O ４ ), LiPF ２ (C ２ O ４ ) ２Lithium oxalate salts such as LiN(SO ２ F) ２ Among these, inorganic lithium salts are preferred, and LiPF ６ In some cases, an imide salt is also preferred.

[0120] The content of the electrolyte salt in the non-aqueous electrolyte solution is 0.1 mol / dm at 20°C and 1 atmosphere. ３ 2.5mol / dm or more ３ Preferably, 0.3 mol / dm or less ３ 2.0mol / dm or more ３ More preferably, 0.5 mol / dm or less ３ More than 1.7mol / dm ３ More preferably, 0.7 mol / dm or less ３ 1.5mol / dm or more 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.

[0121] 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.

[0122] (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.

[0123] (Container) The container accommodates the electrode assembly and the non-aqueous electrolyte in its internal space. Materials for the container include metal materials such as aluminum and stainless steel, and resin materials, with metal materials being preferred from the standpoint of strength, etc. Composite materials of metal and resin materials can also be used.

[0124] 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.

[0125] (Shape, Use, etc. of Nonaqueous Electrolyte Storage Element) The shape of the nonaqueous electrolyte storage element according to one embodiment of the present invention is not particularly limited. The nonaqueous electrolyte storage element may be, for example, a cylindrical battery, a prismatic battery, a flat battery, a coin battery, a button battery, etc.

[0126] The use of the nonaqueous electrolyte electricity storage element according to one embodiment of the present invention is not particularly limited, and the nonaqueous electrolyte electricity 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, a power source for power storage, etc.

[0127] 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.

[0128] 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.

[0129] <Method for manufacturing nonaqueous electrolyte storage element> A nonaqueous electrolyte storage element according to one embodiment of the present invention can be manufactured by a known method. The method for manufacturing 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.

[0130] 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.

[0131] 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.

[0132] 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.

[0133] 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.

[0134] <Other Embodiments> The negative electrode for a nonaqueous electrolyte storage element and the nonaqueous electrolyte storage element of the present invention are 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 can be added to the configuration of another embodiment, or part of the configuration of one embodiment can be replaced with the configuration of another embodiment or well-known technology. Furthermore, part of the configuration of one embodiment can be deleted. Also, well-known technology can be added to the configuration of one embodiment.

[0135] 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.

[0136] 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.

[0137] 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.

[0138] [Example 1] (Preparation of Negative Electrode) Natural graphite (coated graphite particles: particles A) at least a portion of whose surface was coated with non-graphitic carbon was prepared as a negative electrode active material. The coated graphite particles (particles A) had a D10 particle size of 5.0 μm, a D50 particle size of 8.2 μm, a D90 particle size of 13.3 μm, a ratio (D10 / D90) of 0.376, and a non-graphitic carbon content of 12.5 mass%. A negative electrode mixture paste was prepared using the coated 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 coated graphite particles, binder, and thickener was 98.5:1.0:0.5 in terms of solid content. The negative electrode mixture paste was applied to both sides of copper foil as a negative electrode substrate so that the mass per unit area (mass of solid content) was 4 mg / cm. ２ The coating was then applied and dried. Thereafter, roll pressing was performed to obtain a negative electrode in which negative electrode active material layers were laminated on both sides of the negative electrode substrate. The BET specific surface area of ​​the negative electrode active material layer in the obtained negative electrode was 3.50 m ２ / g, density is 1.19 g / cm ３ The porosity was 45%.

[0139] (Preparation of Positive Electrode) LiNi as a positive electrode active material１／３ Mn １／３ Co １／３ O ２ A positive electrode mixture paste was prepared using 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 positive electrode active material, conductive agent, and binder was 93:5:2 in terms of solid content. The positive electrode mixture paste was applied to both sides of an aluminum foil serving as a positive electrode substrate so that the mass per unit area (mass of solid content) was 6 mg / cm. ２ The coating was then dried, followed by roll pressing to obtain a positive electrode in which positive electrode active material layers were laminated on both sides of the positive electrode substrate.

[0140] (Preparation of non-aqueous electrolyte) LiPF 6 was dissolved in a solvent prepared by mixing ethylene carbonate and ethyl methyl carbonate in a volume ratio of 30:70. ６ to 1.2 mol / dm ３ The non-aqueous electrolyte was obtained by dissolving the non-aqueous electrolyte at a concentration of 100 ppm.

[0141] (Preparation of Separator) A microporous polyolefin film was used as the separator.

[0142] (Assembly of non-aqueous electrolyte storage element) The negative electrode, positive electrode, and separator were used to obtain a wound electrode body. The electrode body was placed in a container, and a non-aqueous electrolyte was poured into the container and sealed to obtain the non-aqueous electrolyte storage element of Example 1.

[0143] [Examples 2 to 4, Comparative Examples 1 to 11] Non-aqueous electrolyte storage elements of Examples 2 to 4 and Comparative Examples 1 to 11 were obtained in the same manner as in Example 1, except that the types of particles shown in Table 1 were used as the coated graphite particles, and the BET specific surface area, density, and porosity of the negative electrode active material layer were set to the values ​​shown in Table 1. Table 1 also shows the particle size (D10 particle size, D50 particle size, D90 particle size, and ratio (D10 / D90)) and non-graphitic carbon content of each coated graphite particle. Natural graphite was used as the graphite base material for each coated graphite particle. The BET specific surface area, density, and porosity of negative electrode active material layers using the same type of coated graphite particles were adjusted by changing the pressure during roll pressing.

[0144] (Measurement of Initial Charge / Discharge and Discharge Capacity) The obtained nonaqueous electrolyte storage elements of Examples 1 to 4 and Comparative Examples 1 to 11 were 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 charge cut-off voltage of 4.10 V, followed by constant-voltage charging at 4.10 V. The charge was terminated until the total charge time reached 3 hours. A 10-minute rest period was then provided. Constant-current discharging was performed with a discharging current of 1.0 C and a discharge cut-off voltage of 3.0 V. These charge and discharge steps constitute one cycle, and two cycles were performed. The discharged quantity of electricity (Ah) in the second cycle was taken as the discharge capacity. The discharge capacity (relative value) of each nonaqueous electrolyte storage element, with the discharge capacity of the nonaqueous electrolyte storage element of Example 1 as the reference (100.0%), is shown in Table 1 and FIG. 3 .

[0145]

[0146] As shown in Table 1, the nonaqueous electrolyte storage elements of Examples 1 to 4, which used coated graphite particles having a ratio of D10 particle size to D90 particle size (D10 / D90) of 0.36 or more and a non-graphitic carbon content of 10 mass % or more, had a discharge capacity (relative value) of 99.7% or more, and thus had a large discharge capacity. Furthermore, in each of the nonaqueous electrolyte storage elements of Examples 1 to 4, the density of the negative electrode active material layer was 1.09 g / cm ３3 , when particles A having a D10 particle size ratio to D90 particle size (D10 / D90) of 0.36 or more and a non-graphitic carbon content of 10% by mass or more were used as coated graphite particles, the discharge capacity (relative value) was less than 99.7%, and the discharge capacity was small. Furthermore, as shown in FIG. 3 , when particles A having a D10 particle size ratio to D90 particle size (D10 / D90) of 0.36 or more and a non-graphitic carbon content of 10% by mass or more were used as coated graphite particles, the discharge capacity was less likely to decrease even when the negative electrode active material layer was sufficiently pressed to increase the density of the negative electrode active material layer. In contrast, when particles B or the like having a ratio of D10 particle size to D90 particle size (D10 / D90) of less than 0.36 and / or a non-graphitic carbon content of less than 10 mass% were used as the coated graphite particles, increasing the pressure applied to the negative electrode active material layer and increasing the density of the negative electrode active material layer tended to significantly decrease the discharge capacity. From these results, it was confirmed that by applying a combination of the above ratio (D10 / D90) of 0.36 or more and a non-graphitic carbon content of 10 mass% or more to the coated graphite particles, a non-aqueous electrolyte storage element with a large discharge capacity can be realized, due to the synergistic effect of this combination, even when the density of the negative electrode active material layer is increased.

[0147] 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.

[0148] REFERENCE SIGNS LIST 1 nonaqueous electrolyte energy storage element 2 electrode body 3 container 4 positive electrode lead 5 positive electrode external terminal 6 negative electrode lead 7 negative electrode external terminal 20 energy storage unit 30 energy storage device

Claims

1. A negative electrode active material layer including coated graphite particles in which at least a portion of the surface of graphite is coated with non-graphitic carbon, and the density of the negative electrode active material layer is 1.09 g / cm ３ the ratio of the D10 particle size to the D90 particle size (D10 / D90) of the coated graphite particles is 0.36 or more, the content of the non-graphitic carbon in the coated graphite particles is 10 mass % or more, and the BET specific surface area of ​​the negative electrode active material layer is 4.0 m ２ / g or less.

2. The BET specific surface area of ​​the negative electrode active material layer is 2.0 m ２ / g or more 3.8m ２ The negative electrode for a nonaqueous electrolyte storage element according to claim 1 , wherein the surface area of ​​the negative electrode is 0.1 μm or less.

3. The negative electrode for a non-aqueous electrolyte storage element according to claim 1 or 2, wherein the ratio of the D10 particle size to the D90 particle size (D10 / D90) of the coated graphite particles is 0.36 or more and 0.50 or less.

4. The density of the negative electrode active material layer is 1.20 g / cm ３ Super 1.40g / cm ３ The negative electrode for a nonaqueous electrolyte storage element according to claim 1 or 2, wherein:

5. A non-aqueous electrolyte storage element comprising the negative electrode for a non-aqueous electrolyte storage element according to claim 1 or 2.

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