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

Abstract

The present invention provides a negative electrode for a non-aqueous electrolyte energy storage element using a silicon-based active material, wherein expansion of the negative electrode active material layer during charging and discharging is less likely to occur, and the increase in resistance after the charge-discharge cycle is suppressed, and a non-aqueous electrolyte energy storage element using such a negative electrode for a non-aqueous electrolyte energy storage element. [Solution] A negative electrode for a non-aqueous electrolyte energy storage element according to one aspect of the present invention comprises a negative electrode active material layer containing a silicon-based active material and graphite, wherein the total content of the silicon-based active material and graphite in the negative electrode active material layer is 95% by mass or more, and the content of the silicon-based active material is 5% by mass or more, the graphite includes artificial graphite, and the average particle diameter (D) of the silicon-based active material is A ) The average particle size (D) of the above artificial graphite B ) ratio (D B / D A ) is between 2.5 and 3.5.

Description

Technical Field

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

Background Art

[0003] There is known a non-aqueous electrolyte storage element in which a silicon material (silicon-based active material) containing a silicon element such as metallic silicon or silicon oxide is used as a negative electrode active material (see Patent Document 1). The silicon-based material has advantages such as a larger discharge capacity per mass than a carbon material (carbon-based active material) such as graphite.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] Since the silicon-based active material has large changes in expansion and contraction accompanying charge and discharge, the negative electrode for a non-aqueous electrolyte storage element using the silicon-based active material has a disadvantage that the negative electrode active material layer is likely to expand due to charge and discharge. Further, in a non-aqueous electrolyte storage element, it is desirable that the resistance does not increase easily even when charge and discharge are repeated, from the viewpoint of maintaining, for example, regenerative power acceptance and output performance.

[0006] The present invention aims to provide a negative electrode for a non-aqueous electrolyte energy storage element using a silicon-based active material, wherein expansion of the negative electrode active material layer during charging and discharging is less likely to occur, and the increase in resistance after the charge-discharge cycle is suppressed, and a non-aqueous electrolyte energy storage element using such a negative electrode for a non-aqueous electrolyte energy storage element. [Means for solving the problem]

[0007] A negative electrode for a non-aqueous electrolyte energy storage element according to one aspect of the present invention comprises a negative electrode active material layer containing a silicon-based active material and graphite, wherein the total content of the silicon-based active material and graphite in the negative electrode active material layer is 95% by mass or more, and the content of the silicon-based active material is 5% by mass or more, and the graphite includes artificial graphite, and the average particle size of the silicon-based active material is (D A ) The average particle size (D) of the above artificial graphite B ) ratio (D B / D A ) is between 2.5 and 3.5.

[0008] A non-aqueous electrolyte energy storage element according to another aspect of the present invention comprises a negative electrode for a non-aqueous electrolyte energy storage element according to one aspect of the present invention. [Effects of the Invention]

[0009] According to any aspect of the present invention, it is possible to provide a negative electrode for a non-aqueous electrolyte energy storage element using a silicon-based active material, wherein expansion of the negative electrode active material layer during charging and discharging is less likely to occur, and the increase in resistance after the charge-discharge cycle is suppressed, and a non-aqueous electrolyte energy storage element using such a negative electrode for a non-aqueous electrolyte energy storage element is provided. [Brief explanation of the drawing]

[0010] [Figure 1] Figure 1 is a perspective view showing a non-aqueous electrolyte energy storage element according to one embodiment of the present invention. [Figure 2]FIG. 2 is a schematic view showing a power storage device including a non-aqueous electrolyte power storage element according to an embodiment of the present invention.

Mode for Carrying Out the Invention

[0011] First, the outline of the negative electrode for a non-aqueous electrolyte power storage element and the non-aqueous electrolyte power storage element disclosed by this specification will be described.

[0012] [1] The negative electrode for a non-aqueous electrolyte power storage element according to one aspect of the present invention includes a negative electrode active material layer containing a silicon-based active material and graphite, and the total content of the silicon-based active material and the graphite in the negative electrode active material layer is 95% by mass or more and the content of the silicon-based active material is 5% by mass or more. The graphite includes artificial graphite, and the ratio (D A ) of the average particle diameter (D B ) of the artificial graphite to the average particle diameter (D B ) of the silicon-based active material (D A ) is 2.5 or more and 3.5 or less.

[0013] The negative electrode for a non-aqueous electrolyte power storage element described in [1] above (hereinafter, also simply referred to as "negative electrode") is a negative electrode using a silicon-based active material, and it is difficult for the negative electrode active material layer to expand during charge and discharge, and an increase in resistance after charge and discharge cycles is suppressed. The reason for this is not clear, but the following reasons are speculated. Artificial graphite has a small internal porosity and is relatively hard. Therefore, when artificial graphite is contained together with the silicon-based active material in the negative electrode active material layer, relatively hard artificial graphite is arranged around the silicon-based active material, so that the expansion of the silicon-based active material during charging is suppressed, and as a result, the expansion of the negative electrode active material layer accompanying charge and discharge is suppressed. Further, the total content of the silicon-based active material and the graphite in the negative electrode active material layer is 95% by mass or more and the content of the silicon-based active material is 5% by mass or more, and the ratio (D A ) of the average particle diameter (D B ) of the artificial graphite to the average particle diameter (D B ) of the silicon-based active material (D AWhen the ratio is between 2.5 and 3.5, graphite such as artificial graphite is densely and sufficiently arranged around the silicon-based active material. In other words, the voids around the silicon-based active material become smaller, and the expansion and contraction of the silicon-based active material during charging and discharging are further suppressed. In such a case, cracking of the silicon-based active material due to expansion and contraction is suppressed, and the increase in resistance after the charge-discharge cycle is suppressed. For the reasons above, it is presumed that the negative electrode described in [1] above is less prone to expansion of the negative electrode active material layer during charging and discharging, and the increase in resistance after the charge-discharge cycle is suppressed.

[0014] (Regarding graphite and artificial graphite) "Graphite" refers to the average lattice plane spacing (d) of the (002) plane, determined by X-ray diffraction before charging or discharging, or during the discharge state. 002 This refers to carbon materials with a nautical radius of 0.33 nm or more and less than 0.34 nm. "Carbon material" refers to a material whose main constituent element is carbon. "Main constituent element" refers to the element that is present in the largest quantity by mass. For example, the carbon content in a carbon material may be 80% by mass or more, 90% by mass or more, 95% by mass, 99% by mass, or 99.9% by mass or more. "Artificial graphite" refers to graphite that is produced artificially. Artificial graphite may have only two peaks in the diffraction angle 2θ range of 40° to 50° in an X-ray diffraction pattern using CuKα rays. In the case of natural graphite, a total of four peaks are said to appear in the diffraction angle 2θ range of 40° to 50°: two peaks originating from the hexagonal crystal system and two peaks originating from the rhombohedral crystal system. In contrast, in the case of artificial graphite, it is generally said that only two peaks originating from the hexagonal crystal system appear. X-ray diffraction measurements of graphite are performed on graphite before charging and discharging, or, in the case of graphite contained in the negative electrode of a non-aqueous electrolyte energy storage element, on graphite treated according to the following procedure. First, the non-aqueous electrolyte energy storage element is discharged at a constant current of 0.1C to the discharge termination voltage during normal use. It is then disassembled, the negative electrode is removed, and a test battery is assembled using the removed negative electrode as the working electrode and metallic lithium as the counter electrode. Pure metallic lithium is used for the metallic lithium electrode here. For the test battery, with a current of 50mA per gram of negative electrode active material, the closed-circuit potential of the negative electrode is 2.0V (vs.Li / Li + Constant current discharge is performed until the negative electrode active material is fully discharged. The device is disassembled again and the negative electrode is removed. The removed negative electrode is washed with dimethyl carbonate. Then, the negative electrode active material layer containing graphite is peeled off from the negative electrode substrate, and the negative electrode active material layer is washed with a binder-soluble solvent to remove the binder. The washed negative electrode active material layer is immersed in an acid or alkaline solution to remove metals derived from the negative electrode substrate and the SEI (solid electrolyte interface) coating, etc. Then, it is washed with water and dried under reduced pressure at room temperature for 24 hours before being subjected to X-ray diffraction measurement. Disassembly of the non-aqueous electrolyte energy storage element and test battery is performed in an argon atmosphere with a dew point of -60°C or lower. "Normal use" means when the non-aqueous electrolyte energy storage element is used under the charge and discharge conditions recommended or specified for the non-aqueous electrolyte energy storage element, and if equipment for using the non-aqueous electrolyte energy storage element is available, it means when the non-aqueous electrolyte energy storage element is used with that equipment.

[0015] (Regarding average particle size) The "average particle size" of silicon-based active materials and artificial graphite is measured based on the SEM image of the negative electrode active material layer obtained using a scanning electron microscope (SEM). The specific measurement procedure is as follows. First, prepare the sample for measurement using the following procedure. Fix the negative electrode to be measured with a thermosetting resin. Expose the cross-section of the resin-fixed negative electrode using the ion milling method to prepare the sample for measurement. The negative electrode to be measured is prepared using the following procedure. If the negative electrode of the non-aqueous electrolyte energy storage element can be prepared before assembly, use it as is. If preparing from an assembled non-aqueous electrolyte energy storage element, first discharge the non-aqueous electrolyte energy storage element with a constant current of 0.1C to the discharge termination voltage during normal use. Disassemble the element, remove the negative electrode, wash it thoroughly with dimethyl carbonate, and then dry it under reduced pressure at room temperature for 24 hours. The work from disassembling the non-aqueous electrolyte energy storage element to preparing the negative electrode to be measured is performed in a dry air atmosphere with a dew point of -40°C or lower. For the measurement sample (negative electrode) prepared according to the procedure described above, an SEM image of the negative electrode active material layer is obtained. The observation magnification is set so that at least 20 particles of silicon-based active material and artificial graphite appear in one field of view. From the obtained SEM image of the negative electrode active material layer, for the silicon-based active material, 20 particles are extracted, avoiding extremely large and extremely small particles, and the particle diameter of each particle is determined. The average value of these particles is taken as the average particle diameter of the silicon-based active material. Similarly, for artificial graphite, 20 particles are extracted from the obtained SEM image of the negative electrode active material layer, avoiding extremely large and extremely small particles, and the particle diameter of each particle is determined. The average value of these particles is taken as the average particle diameter of the artificial graphite. The particle diameter of each particle is determined as follows: The shortest diameter passing through the center of the smallest circumscribed circle of each particle is defined as the minor axis, and the diameter passing through the center and perpendicular to the minor axis is defined as the major axis. The average value of the major axis and minor axis is taken as the particle diameter of each particle. If there are two or more shortest diameters, the longest of the orthogonal diameters is considered the minor diameter.

[0016] [2] In the negative electrode described in [1] above, the content of the silicon-based active material in the negative electrode active material layer may be 5% by mass or more and 20% by mass or less, and the content of the artificial graphite may be 70% by mass or more and 90% by mass or less.

[0017] According to the negative electrode described in [2] above, a particularly sufficient amount of artificial graphite can be arranged around the silicon-based active material, which further suppresses the expansion of the silicon-based active material during charging, thereby making it less likely for the negative electrode active material layer to expand during charging and discharging, and further suppressing the increase in resistance after the charge-discharge cycle.

[0018] [3] In the negative electrode described in [1] or [2] above, the graphite may further contain flake graphite.

[0019] According to the negative electrode described in [3] above, the presence of flaky graphite in the negative electrode active material layer ensures particularly good electronic conductivity, thereby further suppressing the increase in resistance after charge-discharge cycles.

[0020] [4] In the negative electrode described in any one of [1] to [3] above, the negative electrode active material layer may substantially not contain non-graphitic carbon, or the negative electrode active material layer may further contain non-graphitic carbon, and the non-graphitic carbon content in the negative electrode active material layer may be 5% by mass or less.

[0021] According to the negative electrode described in [4] above, the negative electrode active material layer contains substantially no non-graphitic carbon, or the non-graphitic carbon content in the negative electrode active material layer is low, which makes it less likely for the negative electrode active material layer to expand during charging and discharging, and further suppresses the increase in resistance after the charge-discharge cycle.

[0022] "Non-graphite carbon" refers to the average lattice plane spacing (d) of the (002) plane, which is determined by X-ray diffraction before charging / discharging or during the discharge state. 002 This refers to carbon materials with a nautical radius of 0.34 nm or more and 0.42 nm or less.

[0023] [5] Another embodiment of the present invention provides a non-aqueous electrolyte energy storage element comprising the negative electrode described in any one of [1] to [4] above.

[0024] In the non-aqueous electrolyte energy storage element described in [5] above, expansion of the negative electrode active material layer during charging and discharging is less likely to occur, and the increase in resistance after the charge-discharge cycle is suppressed.

[0025] The following describes in detail an embodiment of a non-aqueous electrolyte energy storage element, a non-aqueous electrolyte energy storage element, a method for manufacturing a non-aqueous electrolyte energy storage element, an energy storage device, and other embodiments related to one embodiment of the present invention.

[0026] Furthermore, the lower and upper limits of each numerical range described in the embodiments of the present invention can be combined in any way.

[0027] <Negative electrode for non-aqueous electrolyte energy storage elements> A negative electrode (negative electrode for a non-aqueous electrolyte energy storage element) according to one embodiment of the present invention comprises a negative electrode substrate and a negative electrode active material layer laminated directly to the negative electrode substrate 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 may be used for a non-aqueous electrolyte secondary battery, a non-aqueous electrolyte energy storage element, or a non-aqueous electrolyte secondary battery.

[0028] The thickness of the negative electrode is set appropriately according to the application of the non-aqueous electrolyte energy storage element. 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 the portion in which the negative electrode active material layer is laminated directly to the negative electrode substrate or via an intermediate layer. If there are portions in which the negative electrode active material layer is laminated on both sides of the negative electrode substrate and portions in which the negative electrode active material layer is laminated on only one side of the negative electrode substrate, then the average thickness of the portion in which the negative electrode active material layer is laminated on both sides of the negative electrode substrate shall be used. Furthermore, in this specification, "average thickness" means the average value of the thickness measured at any five locations.

[0029] The negative electrode substrate is conductive. In this specification, "having conductivity" means that the volume resistivity is 10 -2 This means that it is Ω·cm or less. The volume resistivity shall be the value measured in accordance with JIS-H-0505 (1975). On the other hand, in this specification, "not conductive" or "having (electrical) insulating properties" means that the above volume resistivity is 10 7 This means the resistance is Ω·cm or greater. Examples of materials for the negative electrode substrate include metals such as copper, nickel, iron, and their alloys (stainless steel, etc.), and carbon materials. Among these, copper or copper alloys are preferred.

[0030] The negative electrode substrate has a shape such as a sheet, plate, or strip. Examples of negative electrode substrate forms include foil, vapor-deposited film, mesh, and porous material, with foil being preferred. The negative electrode substrate may also be, for example, copper foil or copper alloy foil.

[0031] 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.

[0032] The intermediate layer is an optional layer placed between the negative electrode substrate and the negative electrode active material layer. The negative electrode does not necessarily have an intermediate layer. The intermediate layer includes, for example, a conductive agent and a binder. When the intermediate layer includes a conductive agent, the contact resistance between the negative electrode substrate and the negative electrode active material layer can be reduced. Examples of conductive agents and binders used in the intermediate layer are the same as those used in the negative electrode active material layer, which will be described later. The conductive agent used in the intermediate layer may be graphite.

[0033] The negative electrode active material layer contains a silicon-based active material and graphite. The silicon-based active material and graphite are usually components that function as the negative electrode active material. The negative electrode active material layer may contain optional components such as other negative electrode active materials, conductive agents, binders, thickeners, fillers, etc. as required. The negative electrode active material layer may be formed from a negative electrode mixture containing a silicon-based active material, graphite, and other optional components. The negative electrode active material layer may be provided only on one side or on both sides of a negative electrode substrate having a shape such as a sheet shape.

[0034] The silicon-based active material is an active material containing silicon element. Examples of the silicon-based active material include a simple substance of silicon element or a compound containing silicon element. Examples of the compound containing silicon element include silicon oxide (SiO x : 0 < x < 2, preferably 0.8 ≤ x ≤ 1.2), silicon nitride, silicon carbide, metal silicon compounds, etc. Examples of the metal silicon compound include compounds containing silicon element and aluminum element, tin element, zinc element, nickel element, copper element, titanium element, vanadium element, magnesium element, etc. In addition, the silicon-based active material may be a composite material such as a SiO / Si / SiO2 composite material. A pre-doped silicon-based active material can also be used. That is, for example, the silicon-based active material may further contain lithium element. One kind or two or more kinds of silicon-based active materials can be mixed and used. Among the silicon-based active materials, silicon oxide is preferred.

[0035] The silicon-based active material may have its surface coated with a conductive material such as a carbon material. By using a silicon-based active material in this form, the electronic conductivity of the negative electrode active material layer can be increased. The silicon-based active material may also form a composite with a conductive material such as a carbon material. Examples of composites formed by silicon-based active material and a conductive material include aggregates of silicon-based active material whose surface is coated with a conductive material such as a carbon material, aggregates of silicon-based active material particles and conductive material particles, silicon-based active material supported in the pores of a porous conductive material, and conductive material supported in the pores of a porous silicon-based active material.

[0036] Average particle size of silicon-based active material (D A The lower limit of the average particle size (D) of the silicon-based active material may be, for example, 5 μm, preferably 6 μm, more preferably 6.3 μm, even more preferably 6.5 μm, and even more preferably 6.7 μm. A If the average particle size (D) is above the lower limit mentioned above, the reaction area becomes smaller, which further suppresses the growth of the surface film of the silicon-based active material associated with repeated charging and discharging cycles, and further suppresses the increase in resistance after the charge-discharge cycle. A The upper limit of the average particle size (D) of the silicon-based active material may be, for example, 15 μm, preferably 12 μm, more preferably 10 μm, even more preferably 8 μm, and even more preferably 7.5 μm. A By keeping the above upper limit below, the electronic conductivity of the negative electrode active material layer is improved. For obtaining silicon-based active material particles with a predetermined particle size, known methods using, for example, a pulverizer or classifier can be employed.

[0037] The lower limit of the silicon-based active material content in the negative electrode active material layer is 5% by mass, preferably 7% by mass, and more preferably 9% by mass. A silicon-based active material content above this lower limit allows for increased discharge capacity. The upper limit of the silicon-based active material content may be, for example, 40% by mass or 30% by mass, but preferably 20% by mass, more preferably 15% by mass, and even more preferably 12% by mass. A silicon-based active material content below this upper limit makes expansion of the negative electrode active material layer during charging and discharging less likely, and further suppresses the increase in resistance after the charge-discharge cycle.

[0038] The graphite contained in the negative electrode active material layer includes artificial graphite. The artificial graphite may be solid particles with virtually no internal voids. Because the artificial graphite is solid, the expansion of the silicon-based active material surrounded by the artificial graphite is further suppressed, making it less likely for the negative electrode active material layer to expand during charging and discharging, and further suppressing the increase in resistance after the charge-discharge cycle. "Solid particles" refers to particles with an internal porosity of 3% or less. On the other hand, "hollow particles" refers to particles with an internal porosity of more than 3%. The porosity of the artificial graphite is preferably 2.5% or less, more preferably 2% or less, and even more preferably 1% or less. The internal porosity of the artificial graphite may be 0%.

[0039] The "internal porosity" of graphite (including artificial graphite) refers to the ratio of the area of ​​voids within a particle to the total area of ​​the particle, as observed in a cross-sectional image obtained using a scanning electron microscope (SEM). The "internal porosity (ratio of the area of ​​voids within a particle to the total area of ​​the particle)" in graphite is determined by the following procedure. (1) Preparation of the sample for measurement The negative electrode to be measured is fixed with a thermosetting resin. The cross-section of the resin-fixed negative electrode is exposed by ion milling to prepare a sample for measurement. The negative electrode to be measured is prepared according to the following procedure. If the negative electrode of the non-aqueous electrolyte energy storage element can be prepared before assembly, it is used as is. If it is prepared from an assembled non-aqueous electrolyte energy storage element, first the non-aqueous electrolyte energy storage element is discharged at a constant current of 0.1C to the discharge termination voltage during normal use. It is then disassembled, the negative electrode is removed, thoroughly washed with dimethyl carbonate, and then dried under reduced pressure at room temperature for 24 hours. The work from disassembling the non-aqueous electrolyte energy storage element to preparing the negative electrode to be measured is performed in a dry air atmosphere with a dew point of -40°C or lower. (2) Acquisition of SEM images For acquiring SEM images, a JSM-7001F (manufactured by JEOL Ltd.) will be used. The SEM images will be secondary electron images. The acceleration voltage will be 5kV. The observation magnification will be set so that 3 to 15 graphite particles appear in one field of view. The obtained SEM images will be saved as image files. Other conditions such as spot diameter, working distance, irradiation current, brightness, and focus will be set appropriately so that the outlines of the graphite particles are clear. (3) Cutting out the outline of graphite particles Using the image cropping function of Adobe Photoshop Elements 11, the outlines of graphite particles are cropped from the acquired SEM image. This cropping is done by selecting the area outside the outline of the graphite particles using the Quick Selection Tool and editing everything except the graphite particles into a black background. If fewer than three graphite particles have had their outlines cropped, the process is repeated until three or more graphite particles have had their outlines cropped. (4) Binarization process For the image of the first graphite particle among the cut-out graphite particles, the image analysis software PopImaging 6.00 is used to perform binarization, setting the threshold to a concentration 20% lower than the concentration where the intensity is maximum. By performing binarization, the area of ​​the side with higher concentration is calculated and defined as the "area of ​​voids within the particle S1". Next, the same first graphite particle image as before is subjected to binarization with a density threshold of 10%. Through binarization, the outer edge of the graphite particle is determined, and the area inside that outer edge is calculated to be the "total area S0 of the particle". Using the S1 and S0 calculated above, the ratio of S1 to S0 (S1 / S0) is calculated to determine the "area ratio R1 of voids within the particle relative to the total area of ​​the particle" in the first graphite particle. For the images of the second and subsequent graphite particles from the cut-out graphite particles, the same binarization process described above is performed to calculate the areas S1 and S0. Based on these calculated areas S1 and S0, the area ratios R2, R3, ... of the voids in each graphite particle are calculated. (5) Determination of the area ratio of voids The average value of the area ratios R1, R2, R3, ... of all voids calculated by the binarization process is used to determine the "area ratio of voids within the particle to the total area of ​​the particle (porosity)". In addition, instead of the scanning electron microscope used for "acquisition of SEM images," the image editing software used for "cutting out the outlines of graphite particles," and the image analysis software used for "binarization processing," devices and software capable of equivalent measurement, image editing, and image analysis may be used.

[0040] Average particle size of silicon-based active material (D A ) The average particle size of artificial graphite (D B ) ratio (D B / D A The lower limit of the above ratio (D) is 2.5, and 2.6 is preferred. B / D A The upper limit of the above ratio (D) is 3.5, preferably 3.2, more preferably 3.0, and even more preferably 2.9. B / D A By keeping the above range, it becomes possible to sufficiently densely arrange artificial graphite around the silicon-based active material, thereby making it less likely for the negative electrode active material layer to expand during charging and discharging, and suppressing the increase in resistance after the charge-discharge cycle.

[0041] Average particle size of artificial graphite (D B The lower limit of the average particle diameter (D) may be, for example, 10 μm, 12 μm, or 15 μm, but 16 μm is preferred, 17 μm is more preferred, 18 μm is even more preferred, and 18.1 μm is even more preferred. B The upper limit of the average particle size of artificial graphite (D) is preferably 30 μm, more preferably 25 μm, even more preferably 22 μm, even more preferably 20 μm, and may also be 19.4 μm. B By keeping the above range, it becomes possible to arrange the artificial graphite more densely around the silicon-based active material, making it less likely for the negative electrode active material layer to expand during charging and discharging, and further suppressing the increase in resistance after the charge-discharge cycle.

[0042] The lower limit of the artificial graphite content in the negative electrode active material layer may be, for example, 50% by mass or 60% by mass, but 70% by mass is preferred, 73% by mass is more preferred, and 76% by mass is even more preferred. The upper limit of the artificial graphite content is preferably 90% by mass, more preferably 85% by mass, and even more preferably 80% by mass. By having the artificial graphite content within the above range, it is possible to arrange the artificial graphite more densely around the silicon-based active material, making it less likely for the negative electrode active material layer to expand during charging and discharging, and further suppressing the increase in resistance after the charge-discharge cycle.

[0043] The lower limit of the mass ratio of artificial graphite content to silicon-based active material content (artificial graphite / silicon-based active material) in the negative electrode active material layer is preferably 4, more preferably 6, still preferably 7, and still more preferably 7.5. The upper limit of the above mass ratio (artificial graphite / silicon-based active material) is preferably 12, more preferably 10, still preferably 9, and still more preferably 8.5. By having the mass ratio (artificial graphite / silicon-based active material) within the above range, it is possible to arrange the artificial graphite more densely around the silicon-based active material, making it less likely for the negative electrode active material layer to expand during charging and discharging, and further suppressing the increase in resistance after the charge-discharge cycle.

[0044] The lower limit of the total content of silicon-based active material and artificial graphite in the negative electrode active material layer is preferably 70% by mass, more preferably 80% by mass, even more preferably 85% by mass, and even more preferably 86% by mass. When the total content of silicon-based active material and artificial graphite in the negative electrode active material layer is above the above lower limit, artificial graphite is more sufficiently arranged around the silicon-based active material, making it less likely for the negative electrode active material layer to expand during charging and discharging, and further suppressing the increase in resistance after the charge-discharge cycle. In addition, when the total content is above the above lower limit, it is also possible to increase the discharge capacity. The upper limit of the total content is preferably 95% by mass, more preferably 93% by mass, and even more preferably 90% by mass.

[0045] The graphite contained in the negative electrode active material layer preferably further contains flake graphite. The flake graphite is natural graphite having a flake (flat plate) shape. The flake graphite may also be a component that functions as a conductive agent. Further inclusion of flake graphite in the negative electrode active material layer can further suppress the increase in resistance after charge-discharge cycles, etc.

[0046] The lower limit of the flake graphite content in the negative electrode active material layer is preferably 3% by mass, more preferably 5% by mass, even more preferably 7% by mass, and still more preferably 8% or 9% by mass. The upper limit of the flake graphite content is preferably 20% by mass, more preferably 15% by mass, and still more preferably 12% by mass.

[0047] The negative electrode active material layer may further contain graphite other than artificial graphite and flake graphite. However, the lower limit of the total content of artificial graphite and flake graphite in the negative electrode active material layer is preferably 90% by mass, more preferably 95% by mass, and even more preferably 98% by mass. By using substantially only artificial graphite and flake graphite as graphite, it is possible to make the expansion of the negative electrode active material layer during charging and discharging less likely, and to further suppress the increase in resistance after the charge-discharge cycle.

[0048] The lower limit of the total content of silicon-based active material, artificial graphite, and flake graphite in the negative electrode active material layer is preferably 80% by mass, more preferably 90% by mass, even more preferably 95% by mass, and even more preferably 96% by mass. When the total content of silicon-based active material, artificial graphite, and flake graphite in the negative electrode active material layer is above the above lower limit, the artificial graphite and the like are more sufficiently arranged around the silicon-based active material, making it less likely for the negative electrode active material layer to expand during charging and discharging, and further suppressing the increase in resistance after the charge-discharge cycle. In addition, when the total content is above the above lower limit, it is also possible to increase the discharge capacity. The upper limit of the total content is preferably 99% by mass, more preferably 98% by mass, and even more preferably 97% by mass.

[0049] The lower limit of the total content of silicon-based active material and graphite in the negative electrode active material layer is 95% by mass, with 96% by mass being preferred. Having a total content of silicon-based active material and graphite in the negative electrode active material layer equal to or greater than the above lower limit ensures that sufficient graphite, such as artificial graphite, is distributed around the silicon-based active material, making it less likely for the negative electrode active material layer to expand during charging and discharging, and suppressing the increase in resistance after the charge-discharge cycle. Furthermore, having a total content equal to or greater than the above lower limit can also increase the discharge capacity. The upper limit of the total content is preferably 99% by mass, more preferably 98% by mass, and even more preferably 97% by mass.

[0050] The negative electrode active material layer is preferably substantially free of non-graphitic carbon, or further contains non-graphitic carbon, with the non-graphitic carbon content in the negative electrode active material layer being 5% by mass or less. "Non-graphite carbon" refers to the average lattice plane spacing (d) of the (002) plane, which is determined by X-ray diffraction before charging / discharging or during the discharge state. 002 ) refers to carbon materials with a nautical index of 0.34 nm to 0.42 nm. Non-graphitic carbons include poorly graphitizable carbons and easily graphitizable carbons. "Potentially graphitizable carbon" refers to the above d 002 This refers to carbon materials with a wavelength of 0.36 nm or more and 0.42 nm or less. "Easily graphitizable carbon" refers to the above d 002This refers to carbon materials with a wavelength of 0.34 nm or more and less than 0.36 nm. Non-graphite carbon may also be a component that functions as a conductive agent. The content of non-graphite carbon in the negative electrode active material layer is more preferably 3% by mass or less, and even more preferably 1% by mass or less. By keeping the content of non-graphite carbon in the negative electrode active material layer below the above upper limit, it is possible to make expansion of the negative electrode active material layer during charging and discharging less likely, and to further suppress the increase in resistance after the charge-discharge cycle. In one embodiment of the present invention, it is preferable that the negative electrode active material layer contains substantially no non-graphite carbon, and it is more preferable that it contains no non-graphite carbon at all.

[0051] The negative electrode active material layer may contain other negative electrode active materials besides silicon-based active materials and graphite. Other negative electrode active materials include metallic lithium; metals such as tin; metal oxides such as titanium oxide and tin oxide; Li4Ti5O 12 LiTiO 2、 Examples include titanium-containing oxides such as TiNb2O7 and polyphosphate compounds. However, in order to further reduce the likelihood of expansion of the negative electrode active material layer during charging and discharging, and to further suppress the increase in resistance after the charge-discharge cycle, the content of other negative electrode active materials in the negative electrode active material layer is preferably 5% by mass or less, more preferably 3% by mass or less, and even more preferably 1% by mass or less. In one embodiment of the present invention, the negative electrode active material layer does not need to contain other negative electrode active materials.

[0052] Conductive agents are typically components made of conductive materials. Even if the volume resistivity of a conductive agent cannot be directly measured, if the volume resistivity is 10 -2Materials known to have a conductivity of Ω·cm or less are classified as conductive agents. Examples of conductive agents include carbon materials, metals, and conductive ceramics. The carbon material is preferably a carbon material other than a non-carbonized polymer compound. Examples of conductive carbon materials include carbon nanofibers, pitch-based carbon fibers, carbon black, graphene, carbon nanotubes (CNTs), and fullerenes. The aforementioned graphite and non-graphite carbon may also function as conductive agents. Conductive agents can take the form of powder or fibers. One or more conductive agents can be used. These materials may also be used in composite form as conductive agents. CNTs are preferred as the conductive agent in the negative electrode active material layer.

[0053] If the negative electrode active material layer contains a conductive agent (excluding graphite and non-graphitic carbon), the content of the conductive agent (excluding graphite and non-graphitic carbon) in the negative electrode active material layer may be 0.01% by mass or more and 10% by mass or less, or 0.03% by mass or more and 5% by mass or less. The upper limit of the content of the conductive agent (excluding graphite and non-graphitic carbon) in the negative electrode active material layer may be 3% by mass, or 1% by mass, 0.5% by mass, or 0.1% by mass. If the negative electrode active material layer contains CNTs, the content of CNTs in the negative electrode active material layer may be 0.01% by mass or more and 10% by mass or less, or 0.03% by mass or more and 5% by mass or less. The upper limit of the content of CNTs in the negative electrode active material layer may be 3% by mass, or 1% by mass, 0.5% by mass, or 0.1% by mass. The technology disclosed herein can also be implemented in a manner in which the negative electrode active material layer does not contain a conductive agent (excluding graphite and non-graphitic carbon).

[0054] Examples of binders include water-based binders and organic solvent-based binders.

[0055] A water-based binder is a binder that dissolves or disperses in water. A water-based binder may be one that dissolves or disperses in 100 parts by mass or more of water at 20°C. When forming a negative electrode active material layer using a negative electrode mixture paste in which the dispersion medium is water or a mixed solvent mainly composed of water, a water-based binder (water-soluble or water-dispersible polymer material) can be used. Examples of water-based binders include polyethylene oxide, polypropylene oxide, polyvinyl alcohol, polyacrylic acid, polymethacrylic acid, polytetrafluoroethylene, styrene-butadiene rubber, polyethylene, polypropylene, nitrile-butadiene rubber, and cellulose.

[0056] An organic solvent-based binder is a binder that dissolves or disperses in an organic solvent (e.g., N-methylpyrrolidone). An 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 in which the dispersion medium is an organic solvent or a mixed solvent mainly composed of an organic solvent, an organic solvent-based binder (a polymer material having solubility or dispersibility 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, and derivatives of chitosan.

[0057] The binder may be a fluororesin (polytetrafluoroethylene, polyvinylidene fluoride, etc.), a polyolefin (polyethylene, polypropylene, etc.), an elastomer (ethylene propylene diene rubber, styrene butadiene rubber, fluororubber, etc.), a polysaccharide polymer (cellulose, chitosan derivatives, etc.), etc. One or more types of binders may be used.

[0058] When the negative electrode active material layer contains a binder, the binder content in the negative electrode active material layer is preferably 0.1% by mass or more and 10% by mass or less, more preferably 0.5% by mass or more and 8% by mass or less, and even more preferably 1% by mass or more and 5% by mass or less. The binder content in the negative electrode active material layer may be 4% by mass or less, or 3% by mass or less. The technology disclosed herein can also be carried out in a form in which the negative electrode active material layer does not contain a binder.

[0059] Examples of thickening agents include polysaccharide polymers such as carboxymethylcellulose and methylcellulose. If the thickening agent has a functional group that reacts with lithium or the like, this functional group may be deactivated beforehand by methylation or the like. The thickening agent may also function as a binder. One or more types of thickening agents can be used.

[0060] When the negative electrode active material layer contains a thickening agent, the content of the thickening agent 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 thickening agent in the negative electrode active material layer may be 5% by mass or less, or 2% by mass or less. The technology disclosed herein can also be carried out in a form in which the negative electrode active material layer does not contain a thickening agent.

[0061] The filler in the negative electrode active material layer is a component other than the negative electrode active material, conductive agent, binder, and thickener, and may be a component that is intentionally included. The filler may be included as a component that fills gaps in the negative electrode active material layer, or it may be included for other purposes. When the negative electrode active material layer contains a filler, the filler content in the negative electrode active material layer can be 0.1% by mass or more and 8% by mass or less, usually preferably 5% by mass or less, and more preferably 2% by mass or less. The technology disclosed herein can also be carried out in a form in which the negative electrode active material layer does not contain a filler.

[0062] The negative electrode active material layer may further contain other components besides the negative electrode active material, conductive agent, binder, thickener, and filler. These other components may include those unintentionally present in the negative electrode active material layer. Furthermore, the negative electrode active material layer may contain impurities unintentionally present as these other components, insofar as they achieve the effects of the present invention. The upper limit of the content of these other components in the negative electrode active material layer may be 10% by mass, 5% by mass, 2% by mass, 1% by mass, 0.1% by mass, or 0.01% by mass. The upper limit of the content of unintentionally present components in the negative electrode active material layer may be 10% by mass, 5% by mass, 2% by mass, 1% by mass, 0.1% by mass, or 0.01% by mass. The upper limit of the content of unintentionally present impurities in the negative electrode active material layer may be 10% by mass, 5% by mass, 2% by mass, 1% by mass, 0.1% by mass, or 0.01% by mass.

[0063] In one embodiment of the present invention, the lower limit of the total content of silicon-based active material, graphite, non-graphitic carbon, conductive agent (excluding graphite and non-graphitic carbon), binder, and thickener in the negative electrode active material layer is preferably 96% by mass, more preferably 97% by mass, even more preferably 98% by mass, and may be 99% by mass, 99.2% by mass, or 99.5% by mass. The upper limit of the above total content may be 100% by mass.

[0064] The thickness of the negative electrode active material layer is set appropriately according to the type of negative electrode active material, the application of the non-aqueous electrolyte energy storage element, etc. 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 may be, for example, 2 mg / cm². 2 More than 50mg / cm 2 The following is also acceptable: The lower limit of the mass per unit area of ​​one negative electrode active material layer is 3 mg / cm². 2 , 4 mg / cm³ 2, 5 mg / cm³ 2 or 6 mg / cm³ 2 It may also be the case that the upper limit of the mass per unit area of ​​one negative electrode active material layer is 30 mg / cm³. 2 , 20 mg / cm³ 2 , 15 mg / cm³ 2 , 12 mg / cm³ 2 or 10 mg / cm³ 2 That's fine.

[0065] The porosity of the negative electrode active material layer may be, for example, 30% to 70%. The lower limit of the porosity of the negative electrode active material layer may be 35%, 40%, or 45%. The upper limit of the porosity of the negative electrode active material layer may be 60%, 50%, or 40%. In cases where the negative electrode active material layer is foil-like, the porosity of the negative electrode active material layer may be 0%. The "porosity (%)" of the negative electrode active material layer and the positive electrode active material layer described later is calculated using the formula (1-V2 / V1)×100, where V1 is the apparent volume (volume including voids) of the negative (positive) electrode active material layer and V2 is the sum of the actual volumes of each material constituting the negative (positive) electrode active material layer. The sum of the actual volumes V2 of each material constituting the negative (positive) electrode active material layer can be calculated from the content of each material in the negative (positive) electrode active material layer and the true density of each material.

[0066] (Method of manufacturing the negative electrode) The negative electrode can be manufactured by known methods. For example, the negative electrode can be manufactured by applying a paste-like negative electrode mixture (negative electrode mixture paste) directly to the negative electrode substrate or via an intermediate layer, and then drying it to form a negative electrode active material layer. After drying, the negative electrode active material layer may be subjected to pressing or other processes.

[0067] <Non-aqueous electrolyte energy storage element> A non-aqueous electrolyte energy storage element according to one embodiment of the present invention comprises a positive electrode, a negative electrode, a non-aqueous electrolyte, and a container housing them. The non-aqueous electrolyte energy storage element may further include a separator interposed between the positive electrode and the negative electrode to electrically insulate them. The positive electrode, the negative electrode, and any separator typically constitute an electrode body. At least a portion of the non-aqueous electrolyte is typically present in a state of permeation into the electrode body. The non-aqueous electrolyte energy storage element according to one embodiment of the present invention may further include other components.

[0068] For example, the non-aqueous electrolyte energy storage element 1 shown in Figure 1, according to one embodiment of the present invention, comprises an electrode body 2, a non-aqueous electrolyte (not shown), and a rectangular parallelepiped container 3 that houses them. The non-aqueous electrolyte energy storage element 1 in Figure 1 further comprises 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 housed together with the electrode body 2, etc., inside the container 3. 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 body 2 is electrically connected to the positive electrode external terminal 5 via the positive electrode lead 4. The negative electrode constituting the electrode body 2 is electrically connected to the negative electrode external terminal 7 via the negative electrode lead 6.

[0069] The non-aqueous electrolyte energy storage element of the present invention may also be a non-aqueous electrolyte secondary battery. Below, the main components constituting the non-aqueous electrolyte energy storage element according to one embodiment of the present invention will be described in detail, focusing on the case where the non-aqueous electrolyte energy storage element is a non-aqueous electrolyte secondary battery (particularly a lithium-ion secondary battery), but this is not intended to limit the scope of application of the present invention.

[0070] (positive electrode) The positive electrode comprises a positive electrode substrate and a positive electrode active material layer laminated directly to the positive electrode substrate or via an intermediate layer. Typically, 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 positive electrode lead described above. The positive electrode may have a shape such as a sheet, plate, or strip.

[0071] The thickness of the positive electrode is set appropriately according to the application of the non-aqueous electrolyte energy storage element. The average thickness of the positive electrode may be, for example, 30 μm or more and 1,000 μm or less. The lower limit of the average thickness of the positive electrode may be 50 μm, 100 μm, or 200 μm. The upper limit of the average thickness of the positive electrode may be 500 μm, 400 μm, 300 μm, 200 μm, or 100 μm. The average thickness of the positive electrode is the average thickness of the portion in which the positive electrode active material layer is laminated directly onto the positive electrode substrate or via an intermediate layer. If both portions exist in which the positive electrode active material layer is laminated on both sides of the positive electrode substrate and portions in which the positive electrode active material layer is laminated on only one side of the positive electrode substrate, then the average thickness of the portion in which the positive electrode active material layer is laminated on both sides of the positive electrode substrate shall be used.

[0072] The positive electrode substrate is electrically conductive. Examples of materials for the positive electrode substrate include metals such as aluminum, titanium, iron, and their alloys (e.g., stainless steel). Among these, aluminum or aluminum alloys are preferred from the viewpoint of high potential resistance, high electronic conductivity, and cost.

[0073] The positive electrode substrate has a shape such as a sheet, plate, or strip. Examples of positive electrode substrate forms include foil, vapor-deposited film, mesh, and porous material, with foil being preferred. The positive electrode substrate may also be, for example, aluminum foil or aluminum alloy foil.

[0074] 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.

[0075] The intermediate layer is any layer placed between the positive electrode substrate and the positive electrode active material layer. The positive electrode does not necessarily have an intermediate layer. The configuration of the intermediate layer of the positive electrode is not particularly limited and can be selected from, for example, the configurations exemplified for the intermediate layer of the negative electrode.

[0076] The positive electrode active material layer contains a positive electrode active material. The positive electrode active material layer optionally contains conductive agents, binders, thickeners, fillers, and other optional components. These optional components can be selected from the materials exemplified above for the negative electrode. The conductive agent used in the positive electrode active material layer may be graphite and non-graphitic carbon. The positive electrode active material layer may be formed from a positive electrode mixture containing the positive electrode active material and other optional components. The positive electrode active material layer may be provided on only one side of a positive electrode substrate having a shape such as a sheet, or it may be provided on both sides.

[0077] For the positive electrode active material, known positive electrode active materials can be used. For lithium-ion secondary batteries, materials capable of intercalating and releasing lithium ions are typically used. Examples of positive electrode active materials 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.

[0078] Examples of transition metal elements included in lithium transition metal composite oxides include nickel, cobalt, and manganese. Lithium transition metal composite oxides may also contain typical metal elements such as aluminum. Examples of lithium transition metal composite oxides include those having an α-NaFeO2 crystal structure and those having a spinel crystal structure.

[0079] Li 1+α Ma 1-α Examples include O2 (where Ma is a metallic element other than lithium, containing one or more transition metal elements, and 0 ≤ α < 1). It is preferable that Ma 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.

[0080] As the lithium transition metal composite oxide having a spinel crystal structure, Li β Mb2O4 (Mb is a metal element other than lithium element, containing one or more transition metal elements. 0 < β ≦ 1.2.) can be mentioned. Mb preferably contains Mn. As the content of Mn with respect to Mb (Mn / Mb), 50 mol% or more is preferable, and 80 mol% or more is more preferable.

[0081] The polyanion compound is a compound composed of a polyanion (that is, 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 LiFePO4, LiMnPO4, LiMn x Fe 1-x PO4 (0 < x < 1), LiNiPO4, LiCoPO4, Li3V2(PO4)3, Li2MnSiO4, Li2CoPO4F, etc. The surface of the particles of the polyanion compound may be coated with other materials (for example, a carbon material described later).

[0082] Examples of the chalcogen compound include titanium disulfide, molybdenum disulfide, molybdenum dioxide, etc.

[0083] Examples of the sulfur-based material include elemental sulfur, metal sulfides such as lithium sulfide, organic disulfide compounds, and organic sulfur compounds such as carbon sulfide compounds [[ID=1)]

[0084] Atoms or polyanions in these materials which are the positive electrode active material may be partially substituted with atoms or anion species composed of other elements. The surfaces of these materials may be coated with other materials.

[0085] The positive electrode active material is usually in particulate form. The average particle size of the positive electrode active material is preferably, for example, 0.1 μm or more and 20 μm or less. Setting the average particle size of the positive electrode active material above the lower limit facilitates the manufacturing and handling of the positive electrode active material. Setting the average particle size of the positive electrode active material below the upper limit improves the electronic conductivity of the positive electrode active material layer. When using a composite material of the positive electrode active material and other materials, the average particle size of the composite material is considered the average particle size of the positive electrode active material.

[0086] The content of the positive electrode active material in the positive electrode active material layer is preferably 50% to 99% by mass, more preferably 70% to 98% by mass, and may also be 80% to 95% by mass. By setting the content of the positive electrode active material within the above range, it is possible to achieve both high energy density and manufacturability in the positive electrode active material layer.

[0087] The conductive agent content 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 conductive agent content may be 5% by mass, 4% by mass, or 3% by mass. By setting the conductive agent content within the above range, it is possible to increase the energy density of the non-aqueous electrolyte energy storage element.

[0088] The binder content 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% by mass, 4% by mass, or 3% by mass. By setting the binder content within the above range, the positive electrode active material can be stably maintained. The technology disclosed herein can also be implemented in a form in which the positive electrode active material layer does not contain a binder.

[0089] When the positive electrode active material layer contains a thickening agent, the content of the thickening agent in the positive electrode active material layer is preferably 0.1% by mass or more and 8% by mass or less, more preferably 5% by mass or less, and even more preferably 2% by mass or less. The technology disclosed herein can also be carried out in a form in which the positive electrode active material layer does not contain a thickening agent.

[0090] When the positive electrode active material layer contains fillers, the filler content in the positive electrode active material layer can be 0.1% by mass or more and 8% by mass or less, usually preferably 5% by mass or less, and more preferably 2% by mass or less. The technology disclosed herein can also be carried out in a form in which the positive electrode active material layer does not contain fillers.

[0091] The positive electrode active material layer may further contain other components besides the positive electrode active material, conductive agent, binder, thickener, and filler. These other components may include those unintentionally present in the positive electrode active material layer. Furthermore, the positive electrode active material layer may contain impurities unintentionally present as these other components, insofar as they achieve the effects of the present invention. The upper limit of the content of these 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 unintentionally present 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 unintentionally present impurities in the positive electrode active material layer may be 10% by mass, 5%, 2%, 1%, 0.1%, or 0.01% by mass.

[0092] The thickness of the positive electrode active material layer is set appropriately according to the type of positive electrode active material, the application of the non-aqueous electrolyte energy storage element, etc. 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 may be, for example, 4 mg / cm². 2 More than 100mg / cm 2 The following is also acceptable: The lower limit of the mass per unit area of ​​one positive electrode active material layer is 6 mg / cm². 2 , 8 mg / cm³ 2 or 10 mg / cm³ 2It may also be the case that the upper limit of the mass per unit area of ​​one positive electrode active material layer is 50 mg / cm². 2 , 20 mg / cm³ 2 , 15 mg / cm³ 2 , 12 mg / cm³ 2 or 10 mg / cm³ 2 That's fine.

[0093] The porosity of the positive electrode active material layer may be, for example, 20% to 50%. 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%.

[0094] (Method of manufacturing the positive electrode) The positive electrode can be manufactured by known methods. The positive electrode can be manufactured, for example, by applying a paste-like positive electrode mixture (positive electrode mixture paste) directly to a positive electrode substrate or via an intermediate layer, and then drying it to form a positive electrode active material layer, similar to the negative electrode manufacturing method described above. The positive electrode mixture paste typically contains positive electrode active material, other optional components, and a dispersion medium. After drying, the positive electrode active material layer may be subjected to pressing or other similar processes.

[0095] (Negative electrode) The negative electrode provided in the non-aqueous electrolyte energy storage element according to one embodiment of the present invention is the negative electrode according to the above-described embodiment of the present invention.

[0096] (Separator) A known separator can be used. Examples of separators include a separator consisting only of a substrate layer, or a separator in which an inorganic layer containing inorganic particles and a binder is formed on one or both sides of the substrate layer.

[0097] Examples of the substrate layer form of the separator 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 liquid retention of non-aqueous electrolytes. The material of the substrate layer of the separator is not particularly limited as long as it has insulating properties, but resins such as polyolefins (polyethylene, polypropylene, etc.), polyimide, and aramid are preferred.

[0098] Examples of inorganic compounds constituting 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; covalent crystals such as silicon; mineral resource-derived materials such as talc, zeolite, kaolin, bentonite, and mica, or their artificial counterparts. 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 inorganic particle content in the inorganic layer is preferably 50% to 99% by mass, and more preferably 80% to 98% by mass.

[0099] Examples of binders used in the inorganic layer include those similar to those exemplified in the positive electrode active material layer.

[0100] The porosity of the separator may be, for example, 20% or more and 80% or less. The lower limit of the separator's porosity may be 30%, 40%, or 50% from the viewpoint of discharge performance, etc. The upper limit of the separator's porosity may be 70%, 60%, or 50% from the viewpoint of strength, etc. In this specification, "porosity" refers to a volume-based value and means a measurement value obtained with a mercury porosimeter.

[0101] The average thickness of the separator may be, for example, 10 μm to 40 μm, or 15 μm to 30 μm.

[0102] A polymer gel composed of a polymer and a non-aqueous electrolyte may be used as a separator. A polymer gel may also be used in combination with a porous resin film, nonwoven fabric, etc., as described above, as a separator.

[0103] (electrode body) As the electrode body, known structures such as wound electrode bodies and laminated electrode bodies can be used.

[0104] A wound electrode has a structure in which the positive electrode and negative electrode are wound together while being insulated. The wound electrode may be cylindrical or flattened. The electrode 2 of the non-aqueous electrolyte energy storage element 1 in Figure 1 is a flattened wound electrode. A wound electrode can be manufactured, for example, by the following procedure. First, a laminate is obtained by stacking a positive electrode, a separator, and a negative electrode, each formed in a strip shape. A wound electrode is obtained by winding this laminate.

[0105] A laminated electrode body 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 body can be obtained by stacking a positive electrode, a separator, and a negative electrode, each formed in a rectangular shape.

[0106] Other electrode structures can also be used, such as those in which at least one of the positive and negative electrodes is folded in a bellows-like manner and stacked.

[0107] (Non-aqueous electrolytes) A known non-aqueous electrolyte can be used as the non-aqueous electrolyte. A non-aqueous electrolyte is a medium that carries charge transport ions (e.g., lithium ions) between the positive and negative electrodes and substantially does not contain water. The water content in the non-aqueous electrolyte may be, for example, 10,000 ppm or less, or 5,000 ppm or less. Examples of non-aqueous electrolytes include non-aqueous electrolyte solutions and solid electrolytes. Non-aqueous electrolyte solutions and solid electrolytes may be used in combination. In one embodiment of the present invention, the non-aqueous electrolyte may be a non-aqueous electrolyte solution. That is, only a non-aqueous electrolyte solution may be used as the non-aqueous electrolyte. Furthermore, the non-aqueous electrolyte energy storage element may be a non-aqueous electrolyte energy storage element or a non-aqueous electrolyte secondary battery.

[0108] (Non-aqueous electrolyte) A non-aqueous electrolyte contains a non-aqueous solvent and an electrolyte salt dissolved in this non-aqueous solvent.

[0109] Any known non-aqueous solvent can be used. Examples of non-aqueous solvents include carbonates, esters, ethers, amides, and nitriles. Examples of carbonates include cyclic carbonates and linear carbonates. Examples of esters include carboxylic acid esters, phosphate esters, and sulfonic acid esters. As non-aqueous solvents, compounds in which some of the hydrogen atoms contained in these compounds are substituted with halogen atoms may also be used. One or more non-aqueous solvents can be used.

[0110] A cyclic carbonate refers to a carbonate having a ring structure containing a carbonate group (-OC(=O)-O-). Examples of cyclic carbonates include ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate, vinylethylene carbonate, chloroethylene carbonate, fluoroethylene carbonate, difluoroethylene carbonate, styrene carbonate, 1-phenylvinylene carbonate, and 1,2-diphenylvinylene carbonate. A cyclic carbonate may be a saturated cyclic carbonate such as ethylene carbonate, or an unsaturated cyclic carbonate such as vinylene carbonate. "Saturated" means not having carbon-carbon unsaturated bonds (carbon-carbon double bonds and carbon-carbon triple bonds). "Unsaturated" means having carbon-carbon unsaturated bonds. As a cyclic carbonate, a saturated cyclic carbonate is preferred, and ethylene carbonate is more preferred.

[0111] A chain-like carbonate refers to a carbonate that does not have a ring structure containing a carbonate group. Examples of chain-like carbonates include diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, diphenyl carbonate, trifluoroethyl methyl carbonate, and bis(trifluoroethyl) carbonate. The chain-like carbonate may be a saturated chain-like carbonate such as dimethyl carbonate, or an unsaturated chain-like carbonate such as diphenyl carbonate. A saturated chain-like carbonate is preferred as the chain-like carbonate, and ethyl methyl carbonate is more preferred.

[0112] The non-aqueous solvent preferably contains carbonate, and more preferably contains both cyclic carbonate and linear carbonate. The carbonate content in the non-aqueous solvent is preferably 80% to 100% by volume, may be 99% to 100% by volume, or 100% by volume. Using cyclic carbonate can promote the dissociation of the electrolyte salt and increase the ionic conductivity of the non-aqueous electrolyte. Using linear carbonate can keep the viscosity of the non-aqueous electrolyte low. When using both cyclic carbonate and linear carbonate, the volume ratio of cyclic carbonate to linear carbonate (cyclic carbonate:linear carbonate) is preferably in the range of 5:95 to 50:50.

[0113] Any known electrolyte salt can be used. Examples of electrolyte salts include lithium salts, sodium salts, potassium salts, magnesium salts, and onium salts. Among these, lithium salts are preferred. One or more electrolyte salts can be used.

[0114] Examples of lithium salts include inorganic lithium salts such as LiPF6, LiPO2F2, LiBF4, and LiClO4; imide salts such as LiN(SO2F)2, LiN(SO2CF3)2, LiN(SO2C2F5)2, and LiN(SO2CF3)(SO2C4F9); and lithium oxalate salts such as LiB(C2O4)2, LiBF2(C2O4), and LiPF2(C2O4)2. LiN(SO2F)2 is also an inorganic lithium salt. Among these, inorganic lithium salts are preferred, and LiPF6 is more preferred. Imide salts are also sometimes preferred.

[0115] The electrolyte salt content in the non-aqueous electrolyte is 0.1 mol / dm³ at 20°C and 1 atm. 3 More than 2.5mol / dm 3 The following is preferred: 0.3 mol / dm 3 More than 2.0mol / dm 3 The following is more preferable: 0.5 mol / dm 3 More than 1.7mol / dm 3The following is even more preferable: 0.7 mol / dm 3 More than 1.5mol / dm 3 The following is particularly preferable. By setting the electrolyte salt content within the above range, the ionic conductivity of the non-aqueous electrolyte can be increased.

[0116] The non-aqueous electrolyte may contain additives in addition to the non-aqueous solvent and electrolyte salt. One or more types of additives may be used. When additives are used in the non-aqueous electrolyte, the additive content in the non-aqueous electrolyte is preferably 0.01% by mass or more and 10% by mass or less, more preferably 0.1% by mass or more and 7% by mass or less, even more preferably 0.2% by mass or more and 5% by mass or less, and particularly preferably 0.3% by mass or more and 3% by mass or less.

[0117] The lower limit of the total content of the non-aqueous solvent and electrolyte salt in the non-aqueous electrolyte may be 90% by mass, 93% by mass, 95% by mass, or 97% by mass. The upper limit of the above total content may be 100% by mass.

[0118] (solid electrolyte) The solid electrolyte can be selected from any material that has ionic conductivity, such as lithium, sodium, or calcium, and is solid at room temperature (e.g., 20°C). Examples of solid electrolytes 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.

[0119] (container) The container houses the electrode body and non-aqueous electrolyte within its internal space. The container material can be a metal material such as aluminum or stainless steel, or a resin material; metal materials are preferred from the viewpoint of strength, etc. Composite materials of metal and resin materials can also be used.

[0120] The shape of the container is not particularly limited, but it can be cylindrical, rectangular (square), disc-shaped, etc. The container may also be in the form of a sheet or other shape formed from a metal-resin composite film.

[0121] (Shape, application, etc. of non-aqueous electrolyte energy storage elements) The shape of the non-aqueous electrolyte energy storage element according to one embodiment of the present invention is not particularly limited. The non-aqueous electrolyte energy storage element may be, for example, a cylindrical battery, a prismatic battery, a flat battery, a coin cell battery, a button cell battery, etc.

[0122] The applications of the non-aqueous electrolyte energy storage element according to one embodiment of the present invention are not particularly limited. The non-aqueous electrolyte energy storage element can be used, for example, as a power source for automobiles such as electric vehicles, hybrid vehicles, and plug-in hybrid vehicles, as a power source for electronic devices such as personal computers and communication terminals, and as a power storage power source.

[0123] The non-aqueous electrolyte energy storage element of the present invention can be used individually or in combination. The non-aqueous electrolyte energy storage element may be used individually when the required output and voltage are small. On the other hand, when at least one of the required output and voltage is large, the non-aqueous electrolyte energy storage element may be used as part of an energy storage device combined with other non-aqueous electrolyte energy storage elements. In an energy storage device composed of multiple non-aqueous electrolyte energy storage elements, at least one of the non-aqueous electrolyte energy storage elements included in the energy storage device may be a non-aqueous electrolyte energy storage element according to one embodiment of the present invention. The energy storage device will be described in detail later.

[0124] In the non-aqueous electrolyte energy storage element according to one embodiment of the present invention, the container may be restrained to maintain a certain thickness, or it may not be restrained in such a way. Alternatively, the container may be restrained to have a certain load applied to it. When the container is restrained, expansion of the container due to charge-discharge cycles, etc., may be suppressed, and a decrease in charge-discharge performance may be suppressed. When the container is restrained, the electrode body inside the container may or may not have a load applied to it. For example, the non-aqueous electrolyte energy storage element or energy storage device may be provided with a restraining member that performs such restraint.

[0125] <Method for manufacturing a non-aqueous electrolyte energy storage element> A non-aqueous electrolyte energy storage element according to one embodiment of the present invention can be manufactured by known methods. The manufacturing method of the non-aqueous electrolyte energy storage element includes, for example, preparing a positive electrode, preparing a negative electrode, preparing a non-aqueous electrolyte, and housing the positive electrode, negative electrode, and non-aqueous electrolyte in a container. The manufacturing method may also include preparing a separator, and manufacturing an electrode body using the positive electrode, negative electrode, and separator. Housing the positive electrode, negative electrode, and non-aqueous electrolyte in a container may be equivalent to housing the electrode body and non-aqueous electrolyte in a container.

[0126] Preparing the positive electrode may also mean manufacturing the positive electrode. The positive electrode can be manufactured by the method described above. Preparing the negative electrode may also mean manufacturing the negative electrode. The negative electrode can be manufactured by the method described above. Preparing the non-aqueous electrolyte may also mean preparing the 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 purchase or other means.

[0127] The electrode body (or positive and negative electrode) and the non-aqueous electrolyte can be housed in a container by known methods. If the non-aqueous electrolyte is a non-aqueous electrolyte solution, for example, the electrode body (or positive and negative electrode) can be housed in the container first, and then the non-aqueous electrolyte solution can be injected through an inlet provided in the container. The inlet is sealed after the non-aqueous electrolyte solution is injected. The method for manufacturing the non-aqueous electrolyte energy storage element may further include initial charging and discharging of the assembled uncharged / discharged energy storage element.

[0128] The non-aqueous electrolyte energy storage element according to one embodiment of the present invention may be manufactured by other methods. For example, if the non-aqueous electrolyte energy storage element according to one embodiment of the present invention is an all-solid-state battery, it may be manufactured by pressing the forming materials of the positive electrode, separator, and negative electrode individually or collectively.

[0129] <Energy storage device> The energy storage device 30 in Figure 2 comprises a plurality of energy storage units 20. Each energy storage unit 20 comprises a plurality of electrically connected non-aqueous electrolyte energy storage elements 1. The energy storage device 30 may also include busbars (not shown) for electrically connecting the plurality of non-aqueous electrolyte energy storage elements 1, busbars (not shown) for electrically connecting the plurality of energy storage units 20, etc. The energy storage unit 20 or the energy storage device 30 may also include a condition monitoring device (not shown) for monitoring the state of one or more non-aqueous electrolyte energy storage elements 1.

[0130] <Other Embodiments> The negative electrode for a non-aqueous electrolyte energy storage element and the non-aqueous electrolyte energy storage element of the present invention are not limited to the embodiments described above, and various modifications may be made without departing from the spirit of the invention. For example, the configuration of one embodiment may be added to the configuration of another embodiment, and a part of the configuration of one embodiment may be replaced with the configuration of another embodiment or with well-known technology. Furthermore, a part of the configuration of one embodiment may be deleted. Also, well-known technology may be added to the configuration of one embodiment.

[0131] In the above embodiment, a case in which a non-aqueous electrolyte energy storage element is used as a rechargeable non-aqueous electrolyte secondary battery was described, but the type, shape, dimensions, capacity, etc. of the non-aqueous electrolyte energy storage element are arbitrary. The present invention can also be applied to various secondary batteries, electric double-layer capacitors, lithium-ion capacitors, and other capacitors.

[0132] In the above embodiment, an electrode body in which a separator is interposed between the positive electrode and the negative electrode was described, but the electrode body does not need to have 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 either the positive electrode or the negative electrode. Thus, the positive electrode and the negative electrode may further have layers other than the base material, intermediate layer, and active material layer. Furthermore, the positive electrode and the negative electrode do not need to have a layered structure. [Examples]

[0133] 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.

[0134] [Example 1] (Fabrication of the negative electrode) A negative electrode mixture paste was prepared containing silicon dioxide (average particle size 6.9 μm), artificial graphite (average particle size 18.1 μm: solid), flake graphite, carbon nanotubes (CNT), styrene-butadiene rubber (SBR), and carboxymethylcellulose (CMC) in a mass ratio of 10:76·95:10:0.05:2.0:1.0 on a solid content basis, with water as the dispersion medium. The negative electrode mixture paste was applied to both sides of a copper foil used as the negative electrode substrate and dried, and then roll-pressed to obtain the negative electrode of Example 1. The average thickness of the negative electrode active material layer was measured and recorded as the average thickness of the negative electrode active material layer before the charge-discharge test.

[0135] [Examples 2 to 3, Comparative Examples 7 to 9] The negative electrodes for Examples 2 to 3 and Comparative Examples 7 to 9 were obtained in the same manner as in Example 1, except that silicon dioxide and artificial graphite having the average particle sizes listed in Table 1 were used.

[0136] [Comparative Examples 1 to 6] The negative electrodes of Comparative Examples 1 to 6 were obtained in the same manner as in Example 1, except that silicon oxide having the average particle size listed in Table 1 was used, and solid or hollow natural graphite having the average particle size listed in Table 1 was used instead of artificial graphite.

[0137] [Rating 1: Expansion Rate] (Preparation of test cells) Test cells were prepared using the negative electrodes of the examples and comparative examples, with pure metallic lithium as the counter electrode. The non-aqueous electrolyte consisted of a solvent prepared by mixing ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate in a volume ratio of 30:35:35, with a concentration of 1.0 mol / dm³. 3 A non-aqueous electrolyte solution containing LiPF6 dissolved at the specified concentration was used. A microporous membrane made of polyolefin was used as the separator.

[0138] (Charge / Discharge Test) Each test cell underwent the following 7-cycle charge-discharge test at 25°C. Constant current charging was performed at a current of 0.1C down to 0.02V, followed by constant voltage charging at 0.02V. The charging termination condition was defined as the current during constant voltage charging decreasing to 0.01C. A 10-minute rest period was then observed. Next, constant current discharge was performed down to 2.0V at the currents listed below, followed by a 10-minute rest period. These charging and discharging processes were performed for 7 cycles. The discharge currents for each cycle were 0.1C for the 1st, 2nd, and 3rd cycles, 0.2C for the 4th cycle, 1.0C for the 5th cycle, 2.0C for the 6th cycle, and 0.2C for the 7th cycle. Note that the reduction reaction in which lithium ions are absorbed into the negative electrode active material is defined as "charging," and the oxidation reaction in which lithium ions are released from the negative electrode active material is defined as "discharging."

[0139] (Measurement of expansion rate) Each test cell was disassembled, and the negative electrodes of the examples and comparative examples were removed. The average thickness of the negative electrode active material layer was measured and recorded as the average thickness of the negative electrode active material layer after the charge-discharge test. The expansion rate was calculated as the percentage of the average thickness of the negative electrode active material layer after the charge-discharge test relative to the average thickness of the negative electrode active material layer before the charge-discharge test. The results are shown in Table 1.

[0140] [Evaluation 2: Resistance Increase Rate] (Fabrication of non-aqueous electrolyte energy storage elements) Non-aqueous electrolyte energy storage elements were fabricated using the negative electrodes from the examples and comparative examples, as well as the following positive electrodes, non-aqueous electrolytes, and separators. The positive electrode used was prepared using the following procedure: LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 A positive electrode mixture paste was prepared containing O2, acetylene black (AB), and polyvinylidene fluoride (PVDF) in a mass ratio of 93:4:3 on a solid content basis, with N-methylpyrrolidone (NMP) as the dispersion medium. The positive electrode mixture paste was applied to both sides of an aluminum foil substrate, dried, and then roll-pressed to obtain the positive electrode. For the non-aqueous electrolyte, 100 parts by mass of a mixed solvent containing ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate in a volume ratio of 30:35:35 was mixed with 2 parts by mass of fluoroethylene carbonate (FEC) to form a non-aqueous solvent containing 1.0 mol / dm³ of electrolyte. 3 A non-aqueous electrolyte was used, in which LiPF6 was dissolved at the specified concentration. A microporous membrane made of polyolefin was used as the separator.

[0141] (Measurement of initial DC resistance) Each obtained non-aqueous electrolyte energy storage element was charged with a constant current of 1.0C at 25°C to bring its State of Charge (SOC) to 50%. After being stored in a -10°C constant temperature bath for 4 hours, it was discharged for 30 seconds at currents of 0.1C, 0.2C, or 0.3C. After each discharge, it was charged with a constant current of 0.05C to bring its SOC to 50%. The relationship between the current during each discharge and the voltage at 10 seconds after the start of discharge was plotted, and the DC resistance (initial DC resistance) was determined from the slope of the straight line obtained from the three plotted points.

[0142] (Charge-discharge cycle test) Next, at 25°C, constant current charging was performed with a current of 1.0C until the voltage reached 4.25V, followed by constant current discharge with a current of 1.0C until the voltage reached 2.75V. A 10-minute rest period was observed after each charging and discharging cycle. This charging and discharging cycle was repeated 700 times.

[0143] (Measurement of resistance increase rate) Subsequently, the DC resistance after the charge-discharge cycle test was determined using the same procedure as that used to determine the initial DC resistance. The increase in DC resistance after the charge-discharge cycle test relative to the initial DC resistance was calculated. The percentage of this increase in DC resistance relative to the initial DC resistance was then calculated as the resistance increase rate. The results are shown in Table 1.

[0144] [Table 1]

[0145] As shown in Table 1, for each of the negative electrodes of Comparative Examples 1 to 6 using natural graphite, the expansion rate exceeded 120%, and significant expansion of the negative electrode active material layer occurred with charge and discharge. Among Comparative Examples 1 to 6, for each of the negative electrodes of Comparative Examples 1 to 4 where the ratio (D A ) of the average particle diameter (D B ) of natural graphite to the average particle diameter (D B ) of the silicon-based active material was less than 2.5, the resistance increase rate exceeded 60%, and a significant increase in resistance occurred after charge and discharge cycles. Also, for those using artificial graphite, for each of the negative electrodes of Comparative Examples 7 to 9 where the ratio (D A ) of the average particle diameter (D B ) of artificial graphite to the average particle diameter (D B ) of the silicon-based active material was more than 3.5, the resistance increase rate was as high as 90% or more, and a significant increase in resistance occurred after charge and discharge cycles. In contrast, for each of the negative electrodes of Examples 1 to 3 using artificial graphite where the ratio (D A ) of the average particle diameter (D B ) of artificial graphite to the average particle diameter (D B ) of the silicon-based active material was 2.5 or more and 3.5 or less, the expansion rate and the resistance increase rate were low. That is, for each of the negative electrodes of Examples 1 to 3, expansion of the negative electrode active material layer with charge and discharge was difficult to occur, and an increase in resistance after charge and discharge cycles was suppressed.

Industrial Applicability

[0146] The present invention can be applied to non-aqueous electrolyte storage elements used as power sources for electronic devices such as personal computers and communication terminals, automobiles, industrial uses, etc.

Explanation of Signs

[0147] ​​​​​​​​​​​​​​​​​​​​​​​30 Energy storage devices

Claims

1. The negative electrode active material layer contains a silicon-based active material and graphite, The total content of the silicon-based active material and the graphite in the above-mentioned negative electrode active material layer is 95% by mass or more, and the content of the silicon-based active material is 5% by mass or more. The above graphite includes artificial graphite. The average particle size (D) of the silicon-based active material mentioned above. Ａ ) The average particle size (D) of the above artificial graphite Ｂ ) ratio (D Ｂ / D Ａ A negative electrode for a non-aqueous electrolyte energy storage element, wherein the ratio is 2.5 or more and 3.5 or less.

2. The negative electrode for a non-aqueous electrolyte energy storage element according to claim 1, wherein the content of the silicon-based active material in the negative electrode active material layer is 5% by mass or more and 20% by mass or less, and the content of the artificial graphite is 70% by mass or more and 90% by mass or less.

3. The negative electrode for a non-aqueous electrolyte energy storage element according to claim 1 or claim 2, further comprising the above-mentioned graphite and flaky graphite.

4. The negative electrode for a non-aqueous electrolyte energy storage element according to claim 1 or claim 2, wherein the negative electrode active material layer substantially does not contain non-graphitic carbon, or the negative electrode active material layer further contains non-graphitic carbon, and the content of non-graphitic carbon in the negative electrode active material layer is 5% by mass or less.

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

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