Negative electrode for non-aqueous electrolyte secondary batteries

Abstract

Reduced swelling. [Solution] The negative electrode for a non-aqueous electrolyte secondary battery includes a current collector, a first active material layer, and a second active material layer in that order. Each of the first and second active material layers contains a negative electrode active material. The negative electrode active material includes artificial graphite and a Si-based active material. The mass fraction of the Si-based active material in the first active material layer is higher than the mass fraction of the Si-based active material in the second active material layer. The orientation angle of the artificial graphite in the first active material layer is larger than the orientation angle of the artificial graphite in the second active material layer. The orientation angle represents the acute angle between the major axis diameter of the artificial graphite and the surface of the current collector.

Description

[Technical Field]

[0001] This disclosure relates to a negative electrode for a non-aqueous electrolyte secondary battery. [Background technology]

[0002] Korean Published Patent No. 10-2021-0155609 (Reference 1) discloses a two-layer negative electrode comprising artificial graphite, natural graphite, and a Si-based active material. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Korean Published Patent Publication No. 10-2021-0155609 [Overview of the Initiative] [Problems that the invention aims to solve]

[0004] Hereinafter, "negative electrode for non-aqueous electrolyte secondary battery" may be abbreviated as "negative electrode." Si-based active materials are being considered. Si-based active materials have a larger specific capacity compared to carbon-based active materials (artificial graphite, natural graphite). On the other hand, Si-based active materials tend to swell significantly during charging. To increase capacity while reducing swelling, it is conceivable to use a mixture of Si-based and carbon-based active materials.

[0005] For example, in reference 1, the application of a mixture of Si-based and carbon-based active materials to a two-layer negative electrode is being considered. However, there is room for improvement in reducing swelling.

[0006] The purpose of this disclosure is to mitigate the expansion. [Means for solving the problem]

[0007] The technical configuration and effects of this disclosure are described below. However, the mechanism of action includes assumptions. The mechanism of action does not limit the technical scope of this disclosure.

[0008] 1. A negative electrode for non-aqueous electrolyte secondary batteries according to one aspect of the present disclosure includes a current collector, a first active material layer, and a second active material layer in this order. Each of the first active material layer and the second active material layer contains a negative electrode active material. The negative electrode active material includes artificial graphite and a Si-based active material. The mass fraction of the Si-based active material in the first active material layer is higher than the mass fraction of the Si-based active material in the second active material layer. The orientation angle of artificial graphite in the first active material layer is larger than the orientation angle of artificial graphite in the second active material layer. The orientation angle refers to the acute angle formed by the major axis diameter of the artificial graphite and the surface of the current collector.

[0009] Figure 1 is a conceptual cross-sectional view showing the first multilayer structure in the present embodiment. In the drawings of the present disclosure, "NG" indicates natural graphite (Natural Graphite). "AG" indicates artificial graphite (Artificial Graphite). "Si" indicates a Si-based active material. The negative electrode 20 includes a current collector 21, a first active material layer 22a (lower layer), and a second active material layer 22b (upper layer) in this order. The first multilayer structure corresponds to the two-layer structure of Document 1. Natural graphite "NG" is unevenly distributed in the lower layer. Artificial graphite "AG" is unevenly distributed in the upper layer. The Si-based active material "Si" is uniformly distributed in both the lower layer and the upper layer. Li is supplied from the upper layer side. Therefore, it is considered that the upper layer swells first. The swelling of the upper layer may reduce the adhesion to the separator. The separator contains a non-aqueous electrolyte. The decrease in adhesion between the negative electrode and the separator may lead to a non-uniform reaction. The non-uniform reaction causes locally severe swelling, which may cause the entire structure to collapse.

[0010] Figure 2 is a conceptual cross-sectional view showing the second multilayer structure in the present embodiment. The second multilayer structure is obtained by unevenly distributing the Si-based active material in the first active material layer 22a (lower layer) in the first multilayer structure. The second multilayer structure is expected to improve the adhesion between the negative electrode and the separator. The swelling of the Si-based active material in the lower layer is expected to be absorbed by the natural graphite in the lower layer and the artificial graphite in the upper layer. However, the absorption of swelling may not be sufficient.

[0011] FIG. 3 is a schematic cross-sectional view showing the third laminated structure in the present embodiment. The third multilayer structure is obtained by replacing natural graphite in the first active material layer 22a (lower layer) in the second multilayer structure with artificial graphite. Similarly to the second multilayer structure, the third multilayer structure may also have insufficient absorption of swelling.

[0012] FIG. 4 is a schematic cross-sectional view showing the fourth laminated structure in the present embodiment. In the drawings of the present disclosure, circular elements represent unoriented active materials, and elliptical elements represent active materials oriented in the thickness direction. The orientation angle is an index of orientation property, and it is considered that the closer the orientation angle is to 90°, the more strongly the particles are oriented in the thickness direction. The fourth laminated structure is obtained by orienting the artificial graphite in the first active material layer 22a (lower layer) in the third laminated structure. According to the new findings of the present disclosure, the swelling of the Si-based active material in the lower layer can be well absorbed by the oriented artificial graphite. Furthermore, the swelling of the entire lower layer can be well absorbed by the unoriented artificial graphite in the upper layer. It is expected that the oriented artificial graphite in the lower layer and the unoriented artificial graphite in the upper layer synergistically absorb the swelling of the Si-based active material, thereby significantly reducing the swelling of the negative electrode 20.

[0013] 2. The negative electrode for a non-aqueous electrolyte secondary battery described in the above item "1" may include, for example, the following configuration. Each of the first active material layer and the second active material layer further contains a binder. The mass fraction of the binder in the first active material layer is higher than the mass fraction of the binder in the second active material layer.

[0014] The relatively high mass fraction of the binder in the first active material layer is expected to inhibit the progress of structural destruction caused by the swelling of the Si-based active material.

[0015] 3. The negative electrode for a non-aqueous electrolyte secondary battery described in the above item "1" or "2" may include, for example, the following configuration. The negative electrode for a non-aqueous electrolyte secondary battery includes a current collector, a first active material layer, a binder layer, and a second active material layer in this order. The mass fraction of the binder in the binder layer is higher than the mass fractions of the binder in the first active material layer and the second active material layer.

[0016] Due to differences in the mass fraction of Si-based active material between the first and second active material layers, a mismatch in expansion and contraction may occur between the two layers. Furthermore, due to differences in the orientation of artificial graphite between the first and second active material layers, a mismatch in expansion and contraction directions may also occur. This mismatch in volume change between layers may lead to delamination between the first and second active material layers. The binder layer is expected to absorb these interlayer mismatches and enhance the adhesion between the first and second active material layers. Therefore, the binder layer is expected to reduce delamination.

[0017] 4. The negative electrode for a non-aqueous electrolyte secondary battery described in any one of the above items "1" to "3" may include, for example, the following configuration: The aspect ratio of the artificial graphite in the first active material layer is greater than the aspect ratio of the artificial graphite in the second active material layer.

[0018] The large aspect ratio of the oriented artificial graphite is expected to promote the absorption of the expansion of the Si-based active material. Furthermore, the large aspect ratio of the oriented artificial graphite may lead to the formation of pores extending in the thickness direction along the surface of the artificial graphite (particles) in the lower layer. These pores can serve as diffusion pathways for the electrolyte. By promoting the diffusion of the electrolyte in the thickness direction (depth direction), improvements in rapid charging characteristics, for example, can be expected.

[0019] 5. A negative electrode for a non-aqueous electrolyte secondary battery in one aspect of the present disclosure comprises, in this order, a current collector, a first active material layer, a binder layer, and a second active material layer. Each of the first and second active material layers comprises a negative electrode active material and a binder. The negative electrode active material comprises artificial graphite and a Si-based active material. The negative electrode active material in the first active material layer consists substantially of artificial graphite and a Si-based active material. The negative electrode active material in the second active material layer consists substantially of artificial graphite. The aspect ratio of the artificial graphite in the first active material layer is greater than that of the artificial graphite in the second active material layer. The orientation angle of the artificial graphite in the first active material layer is greater than that of the artificial graphite in the second active material layer. The orientation angle represents the acute angle between the major axis diameter of the artificial graphite and the surface of the current collector. The mass fraction of the binder in the first active material layer is higher than that of the binder in the second active material layer. The mass fraction of the binder in the binder layer is higher than that of the binder in both the first and second active material layers. The porosity of the first active material layer is higher than that of the second active material layer.

[0020] The relatively high porosity of the first active material layer is expected to reduce swelling. This is thought to be because the voids can absorb the swelling of the Si-based active material.

[0021] One embodiment of the present disclosure (which may be abbreviated as "this embodiment") is described below. However, this embodiment does not limit the technical scope of the present disclosure. This embodiment is illustrative in all respects. This embodiment is non-restrictive. The technical scope of the present disclosure includes all modifications within the meaning and scope equivalent to the claims. For example, it is intended from the outset that any configuration may be extracted from this embodiment and combined in any way. [Brief explanation of the drawing]

[0022] [Figure 1] This is a conceptual cross-sectional view showing the first multilayer structure in this embodiment. [Figure 2] This is a conceptual cross-sectional view showing the second multilayer structure in this embodiment. [Figure 3]This is a cross-sectional conceptual diagram showing the third layered structure in this embodiment. [Figure 4] This is a cross-sectional conceptual diagram showing the fourth layered structure in this embodiment. [Figure 5] This is a conceptual cross-sectional view illustrating the orientation angle in this embodiment. [Figure 6] This is a conceptual diagram showing an example of a non-aqueous electrolyte secondary battery in this embodiment. [Modes for carrying out the invention]

[0023] Terms, phrases "Equipped with," "includes," "possesses," and variations thereof are open-ended expressions. Configurations expressed in an open-ended manner may or may not include additional elements in addition to the essential elements. The statement "consists of" is a closed expression. However, even configurations expressed in a closed manner may include additional elements that are usually incidental impurities or irrelevant to the subject technology. The statement "substantially consists of..." is a semi-closed expression. In configurations expressed in a semi-closed manner, the addition of elements that do not substantially affect the basic and novel characteristics of the subject technology is permitted.

[0024] Geometric terms should not be interpreted strictly. Examples of geometric terms include "parallel," "perpendicular," and "orthogonal." For example, direction, angle, distance, etc., may be relatively distorted within a range where substantially the same or similar function is obtained. Geometric terms may include tolerances, errors, etc., in design, operation, and manufacturing. Dimensional relationships in each figure may not match actual dimensional relationships. Dimensional relationships in each figure may be modified to aid the reader's understanding. For example, length, width, thickness, etc., may be changed. Some components may be omitted.

[0025] Unless otherwise specified, the singular form is not limited to a single element. The singular form can also include multiple elements.

[0026] "Artificial graphite" refers to graphite synthesized by artificial heat treatment. Artificial graphite is also called synthetic graphite (SD). "Natural graphite" refers to graphite produced in nature. Natural graphite includes flake graphite. Flake graphite may be rolled up so that the edges of the particles are folded. "Si-based active material" includes Si (or Si compounds, Si alloys, etc.) that can be alloyed with Li. Si-based active material may include, for example, at least one selected from the group consisting of pure Si, Si-based alloys, SiO, and Si-C. "Si-C" refers to composite particles containing at least one of Si and SiO, and carbon. For example, Si may be supported on a carbon material.

[0027] The "particle size" is determined by microscopy. The particle size represents the arithmetic mean of the long and short sides in the least bounding rectangle (MBR) of the two-dimensional image of the particle. The "average particle size" represents the arithmetic mean of the particle sizes of 100 randomly selected particles. In this embodiment, various image analyses may be performed by software. For example, "ImageJ" may be used.

[0028] The "aspect ratio" indicates the ratio of the longer side to the shorter side of the MBR. The arithmetic mean of the aspect ratios of 100 randomly selected particles is used.

[0029] Figure 5 is a conceptual cross-sectional view illustrating the orientation angle in this embodiment. The "orientation angle" is the acute angle "θ" between the major axis diameter "L" of a particle (e.g., natural graphite) and the surface of the current collector 21 in a cross-sectional SEM (Scanning Electron Microscope) image of the negative electrode 20. The orientation angle can take values ​​from 0° to 90°. The major axis diameter indicates the maximum Ferret diameter of the particle. The arithmetic mean of the orientation angles of 100 randomly selected particles is used.

[0030] "Basis Weight" indicates the mass per unit area.

[0031] The "porosity" is determined by image analysis. Cross-sectional SEM images of each layer are binarized to distinguish between voids and solids. The porosity is calculated by dividing the total area of ​​the voids (total pixels) by the total area of ​​the layer.

[0032] The term "active material layer" is a collective term for the first active material layer and the second active material layer.

[0033] Nonaqueous electrolyte secondary battery Figure 6 is a conceptual diagram showing an example of a non-aqueous electrolyte secondary battery in this embodiment. The non-aqueous electrolyte secondary battery 100 may include, for example, a power generation element 50 and a case 60. The case 60 houses the power generation element 50. The case 60 may be, for example, a metal container, a pouch made of aluminum laminate film, etc. The power generation element 50 may include, for example, a positive electrode 10, a negative electrode 20, a separator 30, and a non-aqueous electrolyte (not shown). The power generation element 50 may be, for example, a wound type or a stacked type. The power generation element 50 may have a monopolar structure or a bipolar structure. The separator 30 can electrically separate the negative electrode 20 from the positive electrode 10. The separator 30 may include, for example, a porous membrane made of resin. The non-aqueous electrolyte is a Li ion conductor. The non-aqueous electrolyte may include, for example, a Li salt and an organic solvent. The non-aqueous electrolyte may, for example, be impregnated into the separator 30. The non-aqueous electrolyte may include, for example, a polymer electrolyte, a gel electrolyte, a solid electrolyte, etc. The solid electrolyte may include, for example, a sulfide solid electrolyte, an oxide solid electrolyte, a halide solid electrolyte, etc. The positive electrode 10 contains a positive electrode active material. The positive electrode active material may include, for example, a lithium transition metal composite oxide (Li[NiCoMn]O2), a lithium phosphate compound (Li[FeMn]PO4), etc. Note that the notation [NiCoMn], [FeMn], etc. indicates that the sum of the composition ratios of the components in [] is "1". As long as the sum is 1, the composition ratio of each component is arbitrary. For example, the composition ratio of some components may be zero.

[0034] negative electrode The negative electrode 20 may be, for example, in the form of a sheet. The negative electrode 20 has a fourth laminated structure (Figure 4). In the thickness direction, the negative electrode 20 includes a current collector 21, a first active material layer 22a, and a second active material layer 22b in this order. The active material layer may be arranged on a part of the surface of the current collector 21 or on the entire surface. The active material layer may be arranged on only one side of the current collector 21 or on both sides of the current collector 21. The current collector 21 may include, for example, a metal foil (Cu foil, Ni foil, etc.), a conductive resin layer, etc. The current collector 21 may have a thickness of, for example, 1 μm to 100 μm.

[0035] The negative electrode 20 may further include any elements as long as it includes the current collector 21, the first active material layer 22a, and the second active material layer 22b in that order. For example, the negative electrode 20 may include the current collector 21, the first active material layer 22a, the binder layer 22c, and the second active material layer 22b in that order. For example, a conductive layer, an adhesion layer (not shown), etc., may be placed between the first active material layer 22a and the current collector 21. For example, a ceramic particle layer (not shown), etc., may be placed on the surface of the second active material layer 22b. The ceramic particle layer may include, for example, a heat-resistant ceramic (alumina, boehmite), etc. The negative electrode 20 may include a third active material layer (not shown).

[0036] Each layer in the negative electrode 20 may be, for example, a coating layer. The coating layer is a layer formed by applying paint. Each paint may be applied substantially simultaneously or sequentially. For example, by applying a magnetic field to the coating layer before the paint dries, the negative electrode active material contained in the coating layer may be oriented in the thickness direction. For example, the orientation angle may be adjusted by the strength of the magnetic field, the concentration of the paint, the press pressure, etc.

[0037] Each layer may have any thickness. For example, the thickness "T1" of the first active material layer 22a and the thickness "T2" of the second active material layer 22b may satisfy a relationship such as "T1 / T2=1 / 9 to 9 / 1", "T1 / T2=2 / 8 to 8 / 2", "T1 / T2=3 / 7 to 7 / 3", or "T1 / T2=4 / 6 to 6 / 4". The thickness "T1" may be, for example, 10 μm or more, 50 μm or more, 100 μm or more, 200 μm or more, or 500 μm or more. The thickness "T1" may be, for example, 1 mm or less, 500 μm or less, or 200 μm or less.

[0038] Each layer may have any basis weight. For example, the basis weight "W1" of the first active material layer 22a and the basis weight "W2" of the second active material layer 22b may satisfy a relationship such as "W1 / W2=1 / 9 to 9 / 1", "W1 / W2=2 / 8 to 8 / 2", "W1 / W2=3 / 7 to 7 / 3", or "W1 / W2=4 / 6 to 6 / 4". The basis weight "W1" is, for example, 1 mg / cm 2 or more, 5 mg / cm 2 or more, 10 mg / cm 2 or more, or 20 mg / cm 2 or more. The basis weight "W1" may be, for example, 50 mg / cm 2 or less, 30 mg / cm 2 or less, 25 mg / cm 2 or less, 15 mg / cm 2 or less, or 10 mg / cm 2 or less.

[0039] The porosity of the active material layer may be substantially constant over the entire region. The porosity of the active material layer may be locally different. For example, the porosity "φ1" of the first active material layer 22a may be lower than the porosity "φ2" of the second active material layer 22b. That is, the relationships "φ1<φ2" and "1<φ2 / φ1" may be satisfied. The ratio "φ2 / φ1" may be, for example, 1.2 or more, 1.5 or more, 2 or more, or 2.5 or more. The ratio "φ2 / φ1" may be, for example, 5 or less, 3 or less, or 2 or less.

[0040] Negative electrode active material Each of the first active material layer 22a and the second active material layer 22b contains a negative electrode active material. Each active material layer may further contain, for example, a conductive material, a binder, etc. Each active material layer may independently contain, for example, 0% to 10% by mass fraction of binder, 0% to 10% of conductive material, and the remainder being the negative electrode active material. The mass fractions of the binder and conductive material in each active material layer may independently be, for example, 0.1% to 3% or 0.5% to 2%.

[0041] The negative electrode active material includes artificial graphite and Si-based active material. In addition to artificial graphite and Si-based active material, the negative electrode active material may further include other active materials. Other active materials may include, for example, natural graphite, lithium titanate, Sn-based alloys, SnO, pure Li, Li-based alloys, etc.

[0042] The negative electrode active material is particulate. The negative electrode active material may have any particle shape. The particle shape may be, for example, spherical, ellipsoidal, flattened, etc. The aspect ratio of the negative electrode active material may be, for example, greater than 1, 1.1 or more, 1.2 or more, 1.5 or more, 2 or more, 4 or more, or 6 or more. The aspect ratio of the negative electrode active material may be, for example, 10 or less, 8 or less, 6 or less, 5 or less, or 4 or less.

[0043] For example, the aspect ratio "R1" of the artificial graphite in the first active material layer 22a may be greater than the aspect ratio "R2" of the artificial graphite in the second active material layer 22b. The ratio "R1 / R2" may be, for example, 1.1 or greater, 1.2 or greater, 1.5 or greater, 2 or greater, 4 or greater, or 6 or greater. The ratio "R1 / R2" may also be, for example, 10 or less, 8 or less, 6 or less, 5 or less, or 4 or less.

[0044] The mass fraction of Si-based active material relative to the total negative electrode active material may be, for example, 1% or more, 3% or more, 5% or more, 10% or more, 15% or more, 20% or more, 25% or more, 30% or more, 40% or more, 50% or more, 60% or more, 70% or more, 80% or more, or 90% or more. The mass fraction of Si-based active material relative to the total negative electrode active material may be, for example, 95% or less, 90% or less, 80% or less, 70% or less, 60% or less, 50% or less, 40% or less, 30% or less, 25% or less, 20% or less, 15% or less, 10% or less, 5% or less, or 3% or less.

[0045] The Si-based active material is unevenly distributed in the first active material layer 22a. The mass fraction of the Si-based active material in the first active material layer 22a is "M 1S " is the mass fraction of the Si-based active material in the second active material layer 22b "M 2S It is higher compared to "M 2S <M 1S "1 <M 1S / M 2S The relationship "M" is satisfied. 1S / M 2S " may be, for example, 1.2 or more, 2 or more, 5 or more, 10 or more, or 100 or more. Ratio "M 1S / M 2S " may be, for example, 1000 or less, 100 or less, 10 or less, or 5 or less. Mass fraction "M 1S " may be, for example, 1% or more, 3% or more, 5% or more, 10% or more, 15% or more, 20% or more, 25% or more, 30% or more, 40% or more, 50% or more, 60% or more, 70% or more, 80% or more, or 90% or more. Mass fraction "M 1S " may be, for example, 95% or less, 90% or less, 80% or less, 70% or less, 60% or less, 50% or less, 40% or less, 30% or less, 25% or less, 20% or less, 15% or less, 10% or less, 5% or less, or 3% or less.

[0046] For example, the negative electrode active material in the first active material layer 22a may consist substantially of artificial graphite and a Si-based active material. For example, the negative electrode active material in the second active material layer 22b may consist substantially of artificial graphite.

[0047] In the first active material layer 22a, the Si-based active material and artificial graphite may satisfy relationships such as, for example, "Si-based active material / artificial graphite = 1 / 99 to 50 / 50" in mass ratio, "Si-based active material / artificial graphite = 1 / 99 to 30 / 70", "Si-based active material / artificial graphite = 1 / 99 to 20 / 80", and "Si-based active material / artificial graphite = 1 / 99 to 10 / 90".

[0048] Artificial graphite is distributed in the first active material layer 22a and the second active material layer 22b. The orientation of the artificial graphite differs between the first active material layer 22a and the second active material layer 22b. That is, the orientation angle "θ1" of the artificial graphite in the first active material layer 22a is larger than the orientation angle "θ2" of the artificial graphite in the second active material layer 22b. That is, the relationship "θ2 < θ1" is satisfied. The orientation angle "θ1" may be, for example, 30° or more, 45° or more, 60° or more, or 75° or more. The orientation angle "θ1" may be, for example, 90° or less, 75° or less, or 60° or less. The orientation angle "θ2" may be, for example, less than 30°, 15° or less, or 5° or less. The orientation angle "θ2" may be, for example, 0° or more.

[0049] The Si-based active material and the artificial graphite can each independently have any average particle size. The average particle size may be, for example, 1 μm or more, 5 μm or more, 10 μm or more, or 15 μm or more. The average particle size may also be, for example, 30 μm or less, 20 μm or less, 15 μm or less, or 10 μm or less.

[0050] For example, the Si-based active material may be small particles and the artificial graphite may be large particles. The average particle size of the Si-based active material is "d S The average particle size of natural graphite "d" A The ratio of "d A / d S " may be, for example, 1 or more, 1.5 or more, 2 or more, 3 or more, 4 or more, or 5 or more. A / d S " may be 10 or less, 8 or less, or 6 or less.

[0051] Binder The binder may include, for example, styrene-butadiene rubber (SBR), carboxymethylcellulose (CMC), polyacrylic acid (PAA), polytetrafluoroethylene (PTFE), etc. The mass fraction of the binder may be approximately constant throughout the active material layer. The mass fraction of the binder may differ locally. For example, the mass fraction of the binder may differ between the first active material layer 22a and the second active material layer 22b. For example, the mass fraction of the binder in the first active material layer 22a is "M 1B " is the mass fraction of the binder in the second active material layer 22b "M 2B It may be higher than "M 2B <M 1B "1 <M 1B / M 2B The relationship "M" may also be satisfied. 1B / M 2B " may be, for example, 1.2 or more, 1.5 or more, 2 or more, 2.5 or more. Ratio "M 1B / M 2B " may be, for example, 3 or less, or 2 or less.

[0052] For example, a binder layer 22c may be formed between the first active material layer 22a and the second active material layer 22b. The mass fraction of the binder in the binder layer 22c is higher than the mass fraction of the binder in the first active material layer 22a and the second active material layer 22b. The binder layer 22c may be a layer that is substantially free of negative electrode active material. The binder layer 22c may contain, for example, 0% to 10% by mass fraction of conductive material and the remainder as binder. The mass fraction of the conductive material in the binder layer 22c may be, for example, 1% to 5%.

[0053] For example, the type of binder may be the same for each layer. For example, the type of binder may be different for each layer. For example, the binder in the binder layer 22c may contain a resin that swells with the electrolyte. For example, the binder in the binder layer 22c may contain an ion-permeable resin, an ion-conductive resin, etc. By allowing the electrolyte and Li ions to permeate the binder layer 22c, an improvement in charge rate characteristics can be expected. For example, the binder in the binder layer 22c may contain a fibrous resin. The fibrous resin may extend so as to crosslink the first active material layer 22a and the second active material layer 22b. By crosslinking the first active material layer 22a and the second active material layer 22b with the fibrous resin, an improvement in peel strength, for example, can be expected. The binder in the binder layer 22c may contain at least one selected from the group consisting of, for example, PAA, polyacrylic acid ester, CMC, alginic acid, polyvinylidene fluoride (PVDF), poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP), and PTFE. For example, PAA, PVDF, PVDF-HFP, etc., may have swelling properties, ion permeability, ion conductivity, etc. For example, PTFE may be fibrous.

[0054] The thickness "T3" of the binder layer 22c may be smaller than, for example, the thickness "T1" of the first active material layer 22a and the thickness "T2" of the second active material layer 22b. The thickness "T3" of the binder layer 22c may be, for example, 10 μm or less, 5 μm or less, or 3 μm or less. The thickness "T3" of the binder layer 22c may be, for example, 0.5 μm or more, 1 μm or more, or 3 μm or more. The basis weight "W3" of the binder layer 22c may be smaller than, for example, the basis weight "W1" of the first active material layer 22a and the basis weight "W2" of the second active material layer 22b. The basis weight "W3" of the binder layer 22c may be, for example, 5 mg / cm 2 Below, 3mg / cm 2 The following, or 1 mg / cm³ 2 The following may also apply: The basis weight "W3" of the binder layer 22c is, for example, 0.1 mg / cm³. 2 Above, or 0.5 mg / cm³ 2That's fine too.

[0055] conductive material The conductive material may include, for example, acetylene black, carbon nanotubes (CNTs), vapor-grown carbon fibers (VGCF), etc. The mass fraction of the conductive material may be substantially constant throughout the active material layer. The mass fraction of the conductive material may differ locally. For example, the mass fraction of the conductive material may differ between each layer. For example, the type of conductive material may differ between each layer. For example, the binder layer 22c may contain a fibrous conductive material. The binder layer 22c may contain, for example, at least one selected from the group consisting of CNTs and VGCF. The fibrous conductive material may extend so as to bridge the first active material layer 22a and the second active material layer 22b. By bridging the first active material layer 22a and the second active material layer 22b with the fibrous conductive material, improvements in charge rate characteristics and reduction of delamination can be expected, for example. [Explanation of Symbols]

[0056] 10 Positive electrode, 20 Negative electrode, 21 Current collector, 22a First active material layer, 22b Second active material layer, 22c Binder layer, 30 Separator, 50 Power generation element, 60 Case, 100 Non-aqueous electrolyte secondary battery.

Claims

1. The current collector, the first active material layer, and the second active material layer are included in this order. Each of the first active material layer and the second active material layer contains a negative electrode active material. The negative electrode active material includes artificial graphite and a Si-based active material. The mass fraction of the Si-based active material in the first active material layer is higher than the mass fraction of the Si-based active material in the second active material layer. The orientation angle of the artificial graphite in the first active material layer is larger than the orientation angle of the artificial graphite in the second active material layer, The orientation angle refers to the acute angle formed by the major axis diameter of the artificial graphite and the surface of the current collector. Negative electrode for non-aqueous electrolyte secondary batteries.

2. Each of the first active material layer and the second active material layer further comprises a binder, The mass fraction of the binder in the first active material layer is higher than the mass fraction of the binder in the second active material layer. The negative electrode for a non-aqueous electrolyte secondary battery according to claim 1.

3. The current collector, the first active material layer, the binder layer, and the second active material layer are included in this order, and The mass fraction of the binder in the binder layer is higher than the mass fraction of the binder in the first active material layer and the second active material layer. The negative electrode for a non-aqueous electrolyte secondary battery according to claim 2.

4. The aspect ratio of the artificial graphite in the first active material layer is larger than the aspect ratio of the artificial graphite in the second active material layer. A negative electrode for a non-aqueous electrolyte secondary battery according to any one of claims 1 to 3.

5. The current collector, the first active material layer, the binder layer, and the second active material layer are included in this order. Each of the first active material layer and the second active material layer comprises a negative electrode active material and a binder. The negative electrode active material includes artificial graphite and a Si-based active material. The negative electrode active material in the first active material layer consists substantially of the artificial graphite and the Si-based active material. The negative electrode active material in the second active material layer is substantially made of the artificial graphite. The aspect ratio of the artificial graphite in the first active material layer is larger than the aspect ratio of the artificial graphite in the second active material layer. The orientation angle of the artificial graphite in the first active material layer is larger than the orientation angle of the artificial graphite in the second active material layer. The orientation angle refers to the acute angle formed by the major axis diameter of the artificial graphite and the surface of the current collector. The mass fraction of the binder in the first active material layer is higher than the mass fraction of the binder in the second active material layer. The mass fraction of the binder in the binder layer is higher than the mass fraction of the binder in the first active material layer and the second active material layer, The porosity of the first active material layer is higher than that of the second active material layer. Negative electrode for non-aqueous electrolyte secondary batteries.

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