Battery negative electrode, battery, and method for manufacturing battery negative electrode

Abstract

To provide a negative electrode for a battery, capable of suppressing deterioration of a capacity in a battery.SOLUTION: A negative electrode for a battery includes a negative electrode active material layer containing a silicon-based particle and a carbon-based particle. The negative electrode active material layer includes one silicon-based particle Ps existing so as to be separated from a carbon-based particle Pc while surrounded by the plurality of carbon-based particles Pc when observing a cross-sectional image. In the cross-sectional image, when the silicon-based particle Ps is contained in an inner side in a region where a mean area of the silicon-based particle Ps is A, and the silicon-based particle Ps and the plurality of carbon-based particles Pc are separated, and a mean area of an ellipse or a complete round is B in the case where the ellipse or the complete round of the maximum area that does not overlap with an outline of the plurality of carbon-based particles Pc is drawn, a ratio B / A is 1.05 or more and 3.10 or less, and when a mean particle diameter of the silicon-based particle Ps is C, and a mean particle diameter of each carbon-based particle Pc is D, a ratio D / C is 1.5 or more and 2.8 or less.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a negative electrode for a battery, a battery, and a method for manufacturing a negative electrode for a battery. [Background technology]

[0002] BACKGROUND ART Conventionally, the use of a negative electrode active material layer containing silicon-based particles such as silicon particles in a negative electrode used in a battery has been considered.

[0003] For example, Patent Document 1 discloses a negative electrode for a lithium ion secondary battery having porous silicon particles on at least one surface of a current collector, the porous silicon particles having an average particle size of 0.1 μm to 50 μm, a three-dimensional network structure, an average porosity of 20 to 90%, an average pore size of 5 nm to 2 μm, a ratio of the average particle size to the average pore size of 5 or more, and a composition of the porous silicon particles in which silicon accounts for 80 atomic % or more, excluding oxygen.

[0004] Patent Document 2 also discloses a lithium ion secondary battery having a negative electrode formed by applying a negative electrode mixture to the electrode, wherein the negative electrode mixture contains graphite and a Si-based negative electrode active material as negative electrode active materials, the ratio of the Si-based negative electrode active material to the total of the graphite and the Si-based negative electrode active material being in the range of 2 to 17 wt %, the porosity of the negative electrode mixture being in the range of 30 to 60%, the ratio of the D50 particle size of the negative electrode active material to the film thickness of the mixture layer (film thickness / D50) being 3 to 10, the thickness of the negative electrode mixture layer being 30 μm or less, and the particle size ratio of the graphite to the Si-based negative electrode active material (D50 of Si-based negative electrode active material / D50 of graphite) being in the range of 0.6 to 1.2.

[0005] Furthermore, Patent Document 3 discloses a negative electrode active material for a lithium ion secondary battery, which is obtained by adding a carbonized material to a composite of Si or a Si alloy having an average particle size of 0.01 to 5 μm, and a carbonaceous material or a carbonaceous material and graphite, the composite having an average particle size of 1 to 40 μm.

[0006] Furthermore, Patent Document 4 discloses a negative electrode for a lithium ion secondary battery having a current collector and an active material layer formed on the surface of the current collector, the active material layer containing an active material, a binder, and a buffer material, and the active material is SiO x powder (0.5≦x≦1.5), the buffer material is graphite powder, and SiO x Powder D 50 is the D of graphite powder 50 The blending amount of graphite powder is 1 / 4 to 1 / 2 of the mass of graphite powder and SiO x The negative electrode for a lithium ion secondary battery is disclosed, in which the content of the powders is 36% by mass to 61% by mass when the total mass of the powders is taken as 100% by mass, and the content of the binder is 5% by mass to 25% by mass when the mass of the entire active material layer is taken as 100% by mass. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2012-84522 [Patent Document 2] Japanese Patent Application Laid-Open No. 2017-054660 [Patent Document 3] Japanese Patent Application Laid-Open No. 2015-219989 [Patent Document 4] Japanese Patent Application Laid-Open No. 2013-101921 Summary of the Invention [Problem to be solved by the invention]

[0008] In a negative electrode active material layer containing both silicon-based particles and carbon-based particles, the silicon-based particles may undergo volume expansion during charging and discharging of the battery. This volume expansion can cause the negative electrode active material to pulverize or peel, crack in the negative electrode active material layer, and reduce conductivity between the negative electrode active materials, resulting in a decrease in battery capacity. Therefore, there is a demand for a battery negative electrode that suppresses a decrease in battery capacity even when volume expansion occurs in silicon-based particles during charge and discharge.

[0009] The present disclosure has been made in view of the above circumstances, and aims to provide a battery negative electrode and a battery in which a decrease in capacity in the battery is suppressed, and a method for manufacturing the battery negative electrode. [Means for solving the problem]

[0010] Means for solving the above problems include the following aspects. <1> a negative electrode active material layer containing silicon-based particles and carbon-based particles; When a cross-sectional image is observed, the negative electrode active material layer has one silicon-based particle Ps that is surrounded by a plurality of the carbon-based particles Pc and is spaced apart from the carbon-based particle Pc, In the cross-sectional image, when an average area of ​​the silicon-based particles Ps is defined as A, and an ellipse or a perfect circle of the largest area that contains the silicon-based particle Ps inside and does not overlap with the outlines of the plurality of carbon-based particles Pc is drawn in a region where the silicon-based particle Ps is separated from the plurality of carbon-based particles Pc, the average area of ​​the ellipse or the perfect circle is defined as B, a ratio B / A is 1.05 or more and 3.10 or less, The negative electrode for a battery, wherein when the average particle diameter of the silicon-based particles Ps is C and the average particle diameter of the carbon-based particles Pc is D, the ratio D / C is 1.5 or more and 2.8 or less. <2> The ratio B / A is 1.30 or more and 2.40 or less, <1> The negative electrode for a battery according to claim 1. <3> a water-insoluble cellulose compound is contained in a region where the silicon-based particle Ps and the plurality of carbon-based particles Pc are spaced apart; <1> or <2> The negative electrode for a battery according to claim 1. <4> <1> ~ <3> A battery comprising the negative electrode for a battery according to any one of claims 1 to 4. <5> a step of adhering a water-insoluble cellulose compound to the surface of silicon-based particles; a step of mixing the silicon-based particles having the water-insoluble cellulose compound fixed to the surface thereof with carbon-based particles to form a negative electrode active material layer; A method for manufacturing a negative electrode for a battery, comprising: [Effects of the Invention]

[0011] According to the present disclosure, there are provided a battery anode and a battery in which a decrease in capacity in the battery is suppressed, and a method for manufacturing the battery anode. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 2 is a schematic cross-sectional view showing a part of a cross-sectional image of a negative electrode active material layer of a negative electrode for a battery according to an embodiment of the present disclosure. [Figure 2] FIG. 2 is a schematic cross-sectional view showing a part of a cross-sectional image for explaining one step in a method for producing a negative electrode for a battery according to an embodiment of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0013] Hereinafter, an embodiment of the present disclosure will be described. These descriptions and examples are intended to illustrate the embodiment and are not intended to limit the scope of the invention. In the present specification, the upper or lower limit of one numerical range may be replaced with the upper or lower limit of another numerical range. In addition, in the present specification, the upper or lower limit of a numerical range may be replaced with a value shown in the examples.

[0014] Each component may contain multiple types of corresponding substances. When referring to the amount of each component in a composition, if multiple substances corresponding to each component are present in the composition, the amount refers to the total amount of those multiple substances present in the composition, unless otherwise specified.

[0015] <Battery negative electrodes> A battery negative electrode according to an embodiment of the present disclosure includes a negative electrode active material layer containing silicon-based particles and carbon-based particles, and when a cross-sectional image of the negative electrode active material layer is observed, the negative electrode active material layer includes a single silicon-based particle Ps that is surrounded by a plurality of carbon-based particles Pc and is spaced apart from the carbon-based particle Pc. In the cross-sectional image, when the average area of ​​the silicon-based particles Ps is A and an ellipse or perfect circle of the largest area is drawn in the region where the silicon-based particles Ps and the plurality of carbon-based particles Pc are separated, the ellipse or perfect circle contains the silicon-based particles Ps inside and does not overlap with the outlines of the plurality of carbon-based particles Pc, and the average area of ​​the ellipse or perfect circle is B, the ratio B / A is 1.05 or more and 3.10 or less. Furthermore, when the average particle size of the silicon-based particles Ps is C and the average particle size of the carbon-based particles Pc is D, the ratio D / C is 1.5 or more and 2.8 or less.

[0016] Here, the silicon-based particles and carbon-based particles in the negative electrode active material layer of the negative electrode for a battery according to an embodiment of the present disclosure will be described with reference to the drawings.

[0017] FIG. 1 is a schematic cross-sectional view showing a part of a cross-sectional image of a negative electrode active material layer. 1, the cross-sectional image of the negative electrode active material layer shows a carbon-based particle (Pc) 4 and one silicon-based particle (Ps) 2 that is surrounded by a plurality of carbon-based particles (Pc) 4 and is spaced apart from these carbon-based particles (Pc) 4. Because the silicon-based particle (Ps) 2 and the plurality of carbon-based particles (Pc) 4 surrounding it are spaced apart from each other, a void 8 exists around the silicon-based particle (Ps) 2. In this cross-sectional image, when the average area of ​​the silicon-based particles (Ps) 2 is A and an ellipse or perfect circle 80 of the largest area that contains the silicon-based particle (Ps) 2 inside and does not overlap with the outlines of the plurality of carbon-based particles (Pc) 4 is drawn in the region where the silicon-based particle (Ps) 2 is separated from the plurality of carbon-based particles (Pc) 4 (i.e., the void 8), the average area of ​​the ellipse or perfect circle 80 is B, the ratio B / A is 1.05 or more and 3.10 or less.

[0018] When observing a cross-sectional image of the negative electrode active material layer, there is a possibility that carbon-based particles and silicon-based particles may exist that are not in a state where "one silicon-based particle (Ps) is surrounded by multiple carbon-based particles (Pc) and exists at a distance from the carbon-based particle (Pc)" (hereinafter simply referred to as a "specific state"). For example, carbon-based particles and silicon-based particles that are not in a specific state include a state where a silicon-based particle is adjacent to another silicon-based particle without a carbon-based particle in between. When calculating the average area B of the ellipses or perfect circles 80 described above, carbon-based particles (Pc) and silicon-based particles (Ps) in a specific state are targeted. In this disclosure, carbon-based particles that fall into a specific state are referred to as "carbon-based particles Pc" or "carbon-based particles (Pc)," and silicon-based particles that fall into a specific state are referred to as "silicon-based particles Ps" or "silicon-based particles (Ps)."

[0019] In addition, in the negative electrode active material layer of the battery negative electrode according to the embodiment of the present disclosure, when the average particle diameter of the silicon-based particles 2 is C and the average particle diameter of the carbon-based particles 4 is D, the ratio D / C is 1.5 or more and 2.8 or less.

[0020] It should be noted that particles of water-insoluble cellulose compound 6A are present on the surface of silicon-based particle 2 shown in FIG.

[0021] The negative electrode for a battery according to an embodiment of the present disclosure suppresses a decrease in battery capacity by satisfying the above-described configuration, and the reason for this is presumed to be as follows.

[0022] In a negative electrode active material layer containing both silicon-based particles and carbon-based particles, the volume expansion of the silicon-based particles that occurs during charging and discharging of the battery can cause the negative electrode active material to pulverize or peel off, cracks in the negative electrode active material layer, and a decrease in conductivity between the negative electrode active materials, resulting in a decrease in battery capacity. Furthermore, when voids are provided inside the silicon-based particles (for example, when porous silicon-based particles are used), stress is concentrated inside the silicon-based particles during volume expansion, which tends to accelerate deterioration of the active material and prevents the battery capacity from decreasing sufficiently. Therefore, there is a demand for a battery negative electrode that suppresses a decrease in battery capacity even when volume expansion occurs in silicon-based particles during charge and discharge.

[0023] In contrast, a battery negative electrode according to an embodiment of the present disclosure has a single silicon-based particle (Ps) that is surrounded by a plurality of carbon-based particles (Pc) and spaced apart from the carbon-based particle (Pc) when a cross-sectional image of the negative electrode active material layer is observed. In the cross-sectional image, the average area of ​​the silicon-based particle (Ps) is A, and an ellipse or perfect circle of the largest area that contains the silicon-based particle (Ps) and does not overlap the outlines of the carbon-based particles (Pc) is B. The ratio B / A of 1.05 to 3.10 indicates that the silicon-based particle (Ps) is appropriately spaced apart from the surrounding carbon-based particles (Pc). By creating a gap between the silicon-based particles (Ps) and the surrounding carbon-based particles (Pc), a margin can be created for the volumetric expansion of the silicon-based particles that occurs during battery charging and discharging. Therefore, even if volumetric symptoms occur in the silicon-based particles (Ps), the impact on the surrounding carbon-based particles (Pc) is suppressed, and rearrangement of the carbon-based particles (Pc) is suppressed. As a result, pulverization and peeling of the negative electrode active material, cracks in the negative electrode active material layer, and decreased conductivity between the negative electrode active materials can be suppressed, thereby suppressing a decrease in battery capacity.

[0024] ·Ratio B / A In the battery negative electrode according to the embodiment of the present disclosure, the ratio B / A is 1.05 or more and 3.10 or less. When the ratio B / A is 1.05 or more, the silicon-based particles (Ps) and the multiple carbon-based particles (Pc) surrounding them are appropriately spaced apart, thereby suppressing a decrease in battery capacity. On the other hand, when the ratio B / A is 3.10 or less, contact between the silicon-based particles (Ps) and the carbon-based particles (Pc) can be stabilized. The ratio B / A is more preferably 1.10 or more and 2.80 or less, and even more preferably 1.30 or more and 2.40 or less.

[0025] ·Measuring method for average areas A and B Here, the method for calculating the average area A of the silicon-based particles (Ps) and the average area B of the ellipses or perfect circles will be described. First, a cross-sectional image of the negative electrode active material layer after discharge is obtained. Specifically, if the object is a battery, the battery is discharged to 0% SOC, then disassembled and the negative electrode is extracted. Next, the negative electrode is processed with a cross-section polisher (CP) to prepare a cross-sectional sample, and an SEM (scanning electron microscope) image of this cross-sectional sample is observed. In the SEM image of this negative electrode active material layer, carbon-based particles and silicon-based particles in a specific state (i.e., a state in which one silicon-based particle (Ps) is surrounded by a plurality of carbon-based particles (Pc) and exists at a distance from the carbon-based particle (Pc)) are the objects of measurement.

[0026] First, 10 silicon-based particles (Ps) with their entire cross sections exposed were randomly selected, the area of ​​each cross section was measured, and the arithmetic mean value of each area was calculated as the average area A (μm 2 ) Furthermore, in the region where the silicon-based particle (Ps) and the plurality of carbon-based particles (Pc) are spaced apart, an ellipse or perfect circle of the largest area is drawn, which contains the silicon-based particle (Ps) inside and does not overlap with the outlines of the plurality of carbon-based particles (Pc). For example, in the embodiment shown in FIG. 1, the silicon-based particle (Ps) 2 is surrounded by six carbon-based particles (Pc) 4, and in the region (gap 8) where the silicon-based particle (Ps) 2 and the carbon-based particle (Pc) 4 are spaced apart, an ellipse or perfect circle 80 of the largest area is drawn, which contains the silicon-based particle (Ps) 2 inside and does not overlap with the outlines of any of the six carbon-based particles (Pc) 4. Note that it is sufficient to draw a circle with the largest area, and the shape of the circle may be either an ellipse or a perfect circle. The area of ​​this ellipse or perfect circle is then measured. The measurement of the area of ​​this ellipse or perfect circle is performed on 10 carbon-based particles and silicon-based particles in a specific state, and the arithmetic mean value of each area is calculated as the average area B (μm 2 )

[0027] ·Ratio D / C In the battery negative electrode according to the embodiment of the present disclosure, the ratio D / C is 1.5 or more and 2.8 or less. A ratio D / C of 1.5 or more allows the silicon-based particles (Ps) and the multiple carbon-based particles (Pc) surrounding them to be appropriately spaced apart, thereby suppressing a decrease in battery capacity. On the other hand, a ratio D / C of 2.8 or less ensures that the particle diameters of the silicon-based particles (Ps) and the carbon-based particles (Pc) are balanced within an appropriate range, thereby stabilizing contact between them. The ratio D / C is more preferably 1.6 or more and 2.4 or less, and even more preferably 1.7 or more and 2.0 or less.

[0028] Measurement method for average particle size C and D Here, the method for calculating the average particle diameter C of the silicon-based particles (Ps) and the average particle diameter D of the carbon-based particles (Pc) will be described. First, an SEM (scanning electron microscope) image is observed using the method described above in "Method for measuring average areas A and B." Note that, in the SEM image of the negative electrode active material layer, carbon-based particles and silicon-based particles in a specific state (i.e., a state in which one silicon-based particle (Ps) is surrounded by multiple carbon-based particles (Pc) and exists at a distance from the carbon-based particle (Pc)) are the measurement targets. Then, 10 carbon-based particles (Pc) with their entire cross-sections exposed are randomly selected, and the maximum length of each (the length of the longest straight line in the cross-section of the carbon-based particle (Pc)) is measured. The arithmetic mean value of each maximum length is taken as the average area A (μm) of the carbon-based particle (Pc). Similarly, 10 silicon-based particles (Ps) whose cross sections are completely exposed are randomly selected, the maximum length of each is measured, and the arithmetic mean value of each maximum length is taken as the average area B (μm) of the silicon-based particles (Ps).

[0029] Battery negative electrode components The negative electrode for a battery according to an embodiment of the present disclosure has a negative electrode active material layer containing silicon-based particles and carbon-based particles as negative electrode active materials.

[0030] (Negative electrode active material layer) Silicon-based particles refer to particles containing silicon (Si), and examples thereof include particles of silicon (Si), silicon oxide (SiO), and silicon alloy (SiM (M represents a metal)).

[0031] Carbon-based particles refer to particles containing carbon (C), and examples thereof include natural graphite, artificial graphite, hard carbon (non-graphitizable carbon), and soft carbon (easily graphitizable carbon). Examples of artificial graphite include highly oriented graphite and mesocarbon microbeads. The carbon (C)-containing particles contain graphite in an amount of 50% by mass or more, preferably 80% by mass or more.

[0032] Other negative electrode active materials may be included, such as metallic lithium, metallic indium, metallic aluminum, metallic silicon, metallic tin, or other metals capable of forming alloys with metallic lithium, oxides of these metals, and alloys of these metals with metallic lithium. Examples of oxides include Li4Ti5O 12 Examples of oxide active materials include:

[0033] The negative electrode active material layer may contain a binder in addition to the negative electrode active material. Examples of the binder include rubbers such as styrene butadiene copolymer (SBR) and vinyl halide resins such as polyvinylidene fluoride (PVdF). The negative electrode active material layer may further contain other components, such as a thickener, etc. Examples of the thickener include celluloses such as carboxymethyl cellulose (CMC).

[0034] <Method of manufacturing a negative electrode for a battery> A method for manufacturing a battery negative electrode according to an embodiment of the present disclosure includes a step of adhering a water-insoluble cellulose compound to the surfaces of silicon-based particles, and a step of mixing the silicon-based particles having the water-insoluble cellulose compound adhering to their surfaces with carbon-based particles to form a negative electrode active material layer.

[0035] The battery negative electrode according to the embodiment of the present disclosure described above can be produced by first adhering a water-insoluble cellulose compound to the surface of silicon-based particles, and then mixing the adhering silicon-based particles with carbon-based particles to form a negative electrode active material layer.

[0036] This point will be specifically explained with reference to FIG. FIG. 2 is a schematic cross-sectional view showing a part of a cross-sectional image for explaining one step in the method for producing a negative electrode for a battery according to an embodiment of the present disclosure.

[0037] In a method for manufacturing a battery negative electrode according to an embodiment of the present disclosure, for example, a step of adhering a water-insoluble cellulose compound to the surface of silicon-based particles is performed in advance, and then the adhering silicon-based particles and carbon-based particles are mixed to prepare a slurry. This slurry is then applied and dried to form a negative electrode active material layer. As a result, before drying, the water-insoluble cellulose compound 6B is present on the surface of the silicon-based particles (Ps) 2 in a state where it is adhered thereto, as shown in FIG. 2. Furthermore, the water-insoluble cellulose compound 6B has swelling properties and is in a swollen state due to absorption of water. After drying, the water in the cellulose compound 6B is also released by drying, resulting in a shrinkage similar to that of the cellulose compound 6A shown in FIG. 1. This results in the formation of a specific state (i.e., a state in which a single silicon-based particle (Ps) is surrounded by multiple carbon-based particles (Pc) and exists at a distance from the carbon-based particles (Pc)), and the ratio B / A is controlled within the aforementioned range.

[0038] Examples of the water-insoluble cellulose compound used in the step of fixing the water-insoluble cellulose compound to the surface of the silicon-based particles include water-insoluble cellulose compounds such as carboxymethyl cellulose (CMC).

[0039] <Battery> Next, each component constituting the battery according to the embodiment of the present disclosure will be described.

[0040] (Cathode active material layer) The positive electrode mixture layer contains a positive electrode active material and may further contain, for example, a binder. Examples of the positive electrode active material include, for example, lithium nickel cobalt manganese composite oxide (hereinafter sometimes simply referred to as "LNCM"). The simplest LNCM has the following general formula: LiNi x Co y Mn z O2 (where x, y, and z in the formula satisfy 0 < x < 1, 0 < y < 1, 0 < z < 1, and x + y + z = 1). LNCM may contain, in addition to Li, Ni, Co, and Mn, other additive elements, for example, transition metal elements other than Ni, Co, and Mn, and typical metal elements other than Li. LNCM has a layered crystal structure. LNCM preferably exceeds 50% by mass of the entire positive electrode active material, for example, occupies 80 to 100% by mass. The positive electrode active material may be composed only of LNCM. Examples of other positive electrode active materials include, for example, lithium nickel composite oxide, lithium cobalt composite oxide, lithium nickel manganese composite oxide, and the like.

[0041] Examples of the binder contained in the positive electrode composite material layer include vinyl halide resins such as polyvinylidene fluoride (PVdF). The positive electrode composite material layer may further contain other components, for example, a conductive material. Examples of the conductive material include graphitized carbon such as non-graphitizable carbon and carbon black, and graphite.

[0042] (Negative electrode active layer) The aforementioned negative electrode active material layer is used for the negative electrode active layer. Since the details have already been described, they are omitted here.

[0043] (Positive electrode current collector) The positive electrode active material layer is formed on the positive electrode current collector. As the positive electrode current collector, a conductive member made of a metal with good conductivity (for example, aluminum) is suitable.

[0044] (Negative electrode current collector) The negative electrode active material layer is formed on the negative electrode current collector. As the negative electrode current collector, a conductive member made of a metal with good conductivity (for example, copper) is suitable.

[0045] (separator) The separator is an electrically insulating porous film. The separator electrically isolates the positive electrode and the negative electrode. The separator may have a thickness of, for example, 5 to 30 μm. The separator may be made of, for example, a porous polyethylene (PE) film, a porous polypropylene (PP) film, or the like. The separator may have a multilayer structure. For example, the separator may be made by laminating a porous PP film, a porous PE film, and a porous PP film in this order. The separator may have a heat-resistant layer on its surface. The heat-resistant layer contains a heat-resistant material. Examples of the heat-resistant material include metal oxide particles such as alumina, and high-melting-point resins such as polyimide.

[0046] (electrolyte) The battery according to the embodiment of the present disclosure further includes an electrolyte. Either a solid electrolyte or an electrolytic solution can be used as the electrolyte. Here, the electrolyte will be described using an electrolytic solution as an example. A non-aqueous electrolytic solution is particularly preferred.

[0047] ·solvent The non-aqueous electrolytic solution contains a solvent (non-aqueous solvent) and an electrolyte. Examples of the solvent (non-aqueous solvent) include N,N-diethyl-N-methyl-N-(2-methoxyethyl)ammonium bis(fluorosulfonyl)imide (DEME), 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide (EMI), and 1-ethyl-2,3-dimethylimidazolium bis(fluorosulfonyl)imide (DEMI-FSI).

[0048] ·Electrolytes The electrolyte in the electrolytic solution may be, for example, a Li salt, such as lithium bis(fluorosulfonyl)imide (LiFSI), LiPF6 (lithium hexafluorophosphate), lithium tetrafluoroborate (LiBF4), or Li[N(CF3SO2)2]. The amount of electrolyte may be, for example, 1.0 to 2.0 mol / L, and is preferably 1.0 to 1.5 mol / L.

[0049] In addition to the solvent and electrolyte, the electrolytic solution may contain various additives such as a thickener, a film-forming agent, a gas generating agent, etc. The electrolyte is typically a non-aqueous electrolytic solution that is liquid at room temperature (e.g., 25±10°C). The electrolytic solution typically remains liquid in the environment in which the battery is used (e.g., a temperature environment of -20 to +60°C).

[0050] (Application) Examples of applications of the battery according to the embodiment of the present disclosure include power sources for hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), and electric vehicles (BEVs). [Example]

[0051] The present disclosure will be described below based on examples, but the present disclosure is not limited to these examples in any way.

[0052] (Comparative Example 1) The graphite particles and silicon particles were prepared so that the particle size ratio D / C between the average particle size D of the graphite particles and the average particle size C of the silicon particles was 1.8. These graphite particles and silicon particles were mixed with a conductive additive, carboxymethyl cellulose (CMC), and styrene butadiene rubber (SBR) in the following solid content ratio to obtain a negative electrode-forming slurry. Active material (graphite particles and silicon particles) / conductive additive / CMC / SBR = 97 / 1 / 1 / 1 (solid content ratio)

[0053] Example 1 The silicon particles used in Comparative Example 1 and insoluble carboxymethyl cellulose (insoluble CMC) in an amount of 5% by mass relative to the silicon particles were dispersed in ethanol, dried using an evaporator, and the insoluble CMC was adhered to the surface of the silicon particles to obtain adhered silicon particles 1. A negative electrode-forming slurry was obtained in the same manner as in Comparative Example 1, except that the silicon particles in Comparative Example 1 were replaced with fixed silicon particles 1. The amount of insoluble CMC was calculated as the amount of active material, and a negative electrode-forming slurry was obtained at the above solid content ratio.

[0054] Example 2 A negative electrode-forming slurry was obtained in the same manner as in Example 1, except that the amount of insoluble carboxymethyl cellulose (insoluble CMC) relative to the silicon particles was changed to 7% by mass.

[0055] Example 3 A negative electrode-forming slurry was obtained in the same manner as in Example 1, except that the amount of insoluble carboxymethyl cellulose (insoluble CMC) relative to the silicon particles was 8 mass %.

[0056] Example 4 A negative electrode-forming slurry was obtained in the same manner as in Example 1, except that the amount of insoluble carboxymethyl cellulose (insoluble CMC) relative to the silicon particles was 10 mass %.

[0057] (Comparative Example 2) A negative electrode-forming slurry was obtained in the same manner as in Example 1, except that the amount of insoluble carboxymethyl cellulose (insoluble CMC) relative to the silicon particles was 12 mass %.

[0058] (Comparative Examples 3 and 4, Examples 5 and 6) A slurry for forming a negative electrode was obtained in the same manner as in Example 2, except that the graphite particles and silicon particles used had particle diameter ratios D / C of the average particle diameter D of the graphite particles to the average particle diameter C of the silicon particles, which were values ​​shown in Table 1.

[0059] <Battery construction> -Positive electrode- LiNiCoMnO2 (NCM), acetylene black (AB) as a conductive material, and polyvinylidene fluoride (PVdF) as a binder were mixed in the following ratio to obtain a slurry for forming a positive electrode. NCM / AB / PVdF=92 / 5 / 3(ms%)

[0060] The positive electrode-forming slurry was applied to a positive electrode current collector foil (Al foil, thickness 15 μm) and pressed to a predetermined thickness to form a positive electrode.

[0061] -Negative electrode- The negative electrode-forming slurry obtained in each of the Examples and Comparative Examples was applied to a negative electrode current collector foil (Cu foil, thickness 10 μm), dried, and pressed to a predetermined thickness to form a negative electrode.

[0062] -battery- The positive and negative electrodes were wound with a separator between them to prepare an electrode assembly. The separator had a three-layer structure (thickness: 24 μm) of porous polypropylene (PP) / porous polyethylene (PE) / PP, and the positive electrode surface was coated with ceramic (alumina) (4 μm). Next, current collector plates with lids were welded to both ends of the electrode group, inserted into a case, and the lid plates and case were welded together. A predetermined amount of electrolyte was then poured into the inlet, and a sealing screw was tightened around the inlet. The electrolyte used was a mixture of ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) in a volume ratio of EC:DMC:EMC = 3:3:4, with LiPF61M (mol / L) as the electrolyte salt. After the inlet, the battery was allowed to soak in the electrolyte for a certain period of time, then charged, and aged at 60°C to obtain a battery.

[0063] For the batteries obtained in each of the examples and comparative examples, the ratio (area ratio) B / A and the ratio (particle diameter ratio) D / C were determined by the above-mentioned method. The results are shown in Table 1.

[0064] <Evaluation: Cycle characteristics> The rated capacity of the batteries obtained in each example and comparative example was measured before and after cycling under the following test conditions. The ratio of the rated capacity after cycling to the rated capacity before cycling (capacity retention rate (%)) is shown in Table 1. A higher capacity retention rate was considered to indicate better battery characteristics. Test conditions: 300 cycles of charge and discharge between SOC 0% and 100% at 60°C and 2C rate.

[0065] [Table 1]

[0066] As shown in Table 1, in each Example in which the ratio (area ratio) B / A is 1.05 or more and 3.10 or less and the ratio (particle diameter ratio) D / C is 1.5 or more and 2.8 or less, the cycle characteristics are superior to those of Comparative Examples 1 and 2 in which the ratio (area ratio) B / A is outside the above range, and to Comparative Examples 3 and 4 in which the ratio (particle diameter ratio) D / C is outside the above range. [Explanation of symbols]

[0067] 2 Silicon-based particles (Ps), 4 Carbon-based particles (Pc), 6A, 6B Water-insoluble cellulose compounds, 8 Voids, 80 Ellipse or circle

Claims

1. a negative electrode active material layer containing silicon-based particles and carbon-based particles; When a cross-sectional image of the negative electrode active material layer is observed, the negative electrode active material layer has one silicon-based particle Ps that is surrounded by a plurality of the carbon-based particles Pc and is spaced apart from the carbon-based particle Pc, In the cross-sectional image, when an average area of ​​the silicon-based particles Ps is defined as A, and an ellipse or a perfect circle of the largest area that contains the silicon-based particle Ps inside and does not overlap with the outlines of the plurality of carbon-based particles Pc is drawn in a region where the silicon-based particle Ps is separated from the plurality of carbon-based particles Pc, the average area of ​​the ellipse or the perfect circle is defined as B, a ratio B / A is 1.05 or more and 3.10 or less, In the negative electrode for a battery, when the average particle diameter of the silicon-based particles Ps is C and the average particle diameter of the carbon-based particles Pc is D, the ratio D / C is 1.5 or more and 2.8 or less.

2. 2. The negative electrode for a battery according to claim 1, wherein the ratio B / A is 1.30 or more and 2.40 or less.

3. 2 . The battery negative electrode according to claim 1 , wherein a water-insoluble cellulose compound is contained in a region where the silicon-based particles Ps and the plurality of carbon-based particles Pc are spaced apart from each other.

4. A battery comprising the negative electrode for a battery according to any one of claims 1 to 3.

5. a step of adhering a water-insoluble cellulose compound to the surface of silicon-based particles; a step of mixing the silicon-based particles having the water-insoluble cellulose compound fixed to the surface thereof with carbon-based particles to form a negative electrode active material layer; A method for manufacturing a negative electrode for a battery, comprising:

Images