Negative electrode for non-aqueous electrolyte secondary batteries

Abstract

Improved charging rate characteristics. [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 natural graphite. The mass fraction of artificial graphite in the first active material layer is higher than that of artificial graphite in the second active material layer. The mass fraction of natural graphite in the first active material layer is lower than that of natural graphite in the second active material layer. The orientation angle of the negative electrode active material in the second active material layer is larger than that of the negative electrode active material in the first active material layer. The orientation angle represents the acute angle between the major axis diameter of the negative electrode active material and the surface of the current collector.

Description

Technical Field

[0001] The present disclosure relates to a negative electrode for non-aqueous electrolyte secondary batteries.

Background Art

[0002] JP 2009-064574 A discloses a multilayer structure in which a first negative electrode layer on the side close to the negative electrode current collector comprises artificial graphite, and a second negative electrode layer on the side far from the negative electrode current collector comprises natural graphite.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] Hereinafter, the "negative electrode for non-aqueous electrolyte secondary batteries" may be abbreviated as "negative electrode". A negative electrode having a multilayer structure has been proposed. For example, it has been proposed to dispose artificial graphite in the lower layer on the side close to the negative electrode current collector, and dispose natural graphite in the upper layer on the side far from the negative electrode current collector. By arranging natural graphite, which has relatively good charge rate characteristics, on the side close to the positive electrode, improvement in charge rate characteristics is expected. However, there is still room for further improvement in the charge rate characteristics.

[0005] An object of the present disclosure is to improve the charge rate characteristics.

Means for Solving the Problems

[0006] Hereinafter, the technical configuration and operational effects of the present disclosure will be described. However, the operational mechanism includes estimations. The operational mechanism does not limit the technical scope of the present disclosure.

[0007] 1. A negative electrode for a non-aqueous electrolyte secondary battery in one aspect of this disclosure comprises, in this order, a current collector, a first active material layer, and a second active material layer. Each of the first and second active material layers contains a negative electrode active material. The negative electrode active material includes artificial graphite and natural graphite. The mass fraction of artificial graphite in the first active material layer is higher than that of artificial graphite in the second active material layer. The mass fraction of natural graphite in the first active material layer is lower than that of natural graphite in the second active material layer. The orientation angle of the negative electrode active material in the second active material layer is larger than that of the negative electrode active material in the first active material layer. The orientation angle represents the acute angle between the major axis diameter of the negative electrode active material and the surface of the current collector.

[0008] According to the new findings in this disclosure, improvements in charge rate characteristics can be expected by balancing Li ion acceptance, electronic conductivity, and curvature in the thickness direction of the active material layer. In this disclosure, "curvature" refers to the curvature of the pores in the thickness direction of the active material layer. The smaller the curvature, the more linearly the pores are considered to extend in the thickness direction. It is thought that a small curvature can promote the diffusion of the electrolyte in the thickness direction of the active material layer.

[0009] Figure 1 is a conceptual cross-sectional view showing the first multilayer structure in this embodiment. In the drawings of this disclosure, "NG" indicates natural graphite, and "AG" indicates artificial graphite. Circular elements indicate unoriented active material, while elliptical elements indicate active material oriented in the thickness direction. The degree of orientation is evaluated by the orientation angle. A larger orientation angle indicates that the particles are more strongly oriented in the thickness direction. 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. For example, it is conceivable to place artificial graphite "AG" in the first active material layer 22a and natural graphite "NG" in the second active material layer 22b. Natural graphite tends to have better Li-ion acceptance than artificial graphite. By placing natural graphite in the upper layer, an improvement in charge rate characteristics can be expected. However, in the first multilayer structure, the balance between Li-ion acceptance, electronic conductivity, and flexibility may not be maintained, potentially preventing the acquisition of the desired charge rate characteristics.

[0010] Figure 2 is a conceptual cross-sectional view showing the second multilayer structure in this embodiment. One way to reduce the degree of curvature is to orient the negative electrode active material in the thickness direction of the negative electrode. In the second multilayer structure, the negative electrode active material is oriented in the thickness direction in both the upper and lower layers. In the second multilayer structure, the degree of curvature may be excessively small throughout the thickness direction. In addition, electron conduction between the current collector 21 and the lower layer, and electron conduction within the lower layer may be insufficient. In the second multilayer structure as well, the desired charge rate characteristics may not be obtained because the balance between Li ion acceptance, electron conductivity, and degree of curvature cannot be achieved.

[0011] Figure 3 is a conceptual cross-sectional view showing the third multilayer structure in this embodiment. In the third multilayer structure, the lower negative electrode active material (artificial graphite) is oriented in the thickness direction. The electrolyte penetrates from the surface of the negative electrode 20 toward the interior. Due to the high curvature of the upper layer, it may be difficult for the electrolyte to pass through the upper layer. Insufficient supply of electrolyte to the lower layer may result in inactive acceptance of Li ions in the lower layer. Even in the third multilayer structure, the balance between Li ion acceptance, electronic conductivity, and curvature may not be maintained, which may prevent the acquisition of the desired charge rate characteristics.

[0012] Figure 4 is a conceptual cross-sectional view showing the fourth multilayer structure in this embodiment. In the fourth multilayer structure, the upper negative electrode active material (natural graphite) is oriented in the thickness direction. The relatively strongly oriented natural graphite is expected to further promote the acceptance of Li ions in the upper layer and to promote the supply of electrolyte to the lower layer. The relatively weakly oriented artificial graphite is expected to promote electron conduction and ion conduction in the in-plane direction in the lower layer. As a result, the balance of Li ion acceptance, electron conductivity, and flexibility is improved throughout the negative electrode 20, which is expected to further improve the charge rate characteristics.

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

[0014] During the manufacturing process of the negative electrode, it may be subjected to roll pressing. Roll pressing can cause the negative electrode active material on the surface of the negative electrode to bend sideways, potentially reducing its orientation angle. It is expected that the relatively high mass fraction of the binder in the second active material layer will make it less likely for the negative electrode active material to be bent over.

[0015] 3. The negative electrode for a non-aqueous electrolyte secondary battery described in item "1" or "2" above 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 fraction of the binder in the first active material layer and the second active material layer.

[0016] The negative electrode active material expands during charging and contracts during discharge. Due to differences in the orientation of the negative electrode active material between the upper and lower layers, a mismatch in the expansion and contraction directions of the negative electrode active material may occur at the interface between the upper and lower layers. This volume change mismatch can lead to delamination. The binder layer is expected to absorb this volume change mismatch and improve adhesion between the upper and lower 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 negative electrode active material in the first active material layer has a bimodal particle size distribution. The negative electrode active material in the second active material layer has a monomodal particle size distribution.

[0018] Because the lower negative electrode active material is bimodal, the particles can be densely packed, which is expected to improve adhesion strength with the current collector, for example. Because the upper negative electrode active material is monomodal, when the negative electrode active material is oriented in the thickness direction, it is expected that pores along the thickness direction will be more easily formed.

[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 contains a negative electrode active material and a binder. The negative electrode active material in the first active material layer has a bimodal particle size distribution. The negative electrode active material in the second active material layer has a monomodal particle size distribution. The mass fraction of the binder in the first active material layer is lower than that of the binder in the second active material layer. The negative electrode active material includes artificial graphite and natural graphite. The natural graphite has a larger aspect ratio than the artificial graphite. The negative electrode active material in the first active material layer consists substantially of artificial graphite. The negative electrode active material in the second active material layer consists substantially of natural graphite. The orientation angle of the negative electrode active material in the second active material layer is larger than that of the negative electrode active material in the first active material layer. The orientation angle represents the acute angle between the major axis diameter of the negative electrode active material and the surface of the current collector. The mass fraction of the binder in the binder layer is higher than that of the binder in the first and second active material layers.

[0020] 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]

[0021] [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 conceptual cross-sectional view showing the third multilayer structure in this embodiment. [Figure 4] This is a conceptual cross-sectional view showing the fourth multilayer 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. [Figure 7] This graph shows an example of the first particle size distribution in this embodiment. [Figure 8] This graph shows an example of the second particle size distribution in this embodiment. [Modes for carrying out the invention]

[0022] 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.

[0023] 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.

[0024] "Artificial graphite" refers to graphite synthesized through artificial heat treatment. Artificial graphite is also called synthetic graphite (SD). "Natural graphite" refers to graphite produced in nature. Natural graphite includes flaky graphite. Flaky graphite may be rounded by folding the edges of the particles.

[0025] 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.

[0026] 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.

[0027] 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 the particle 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.

[0028] "Basis Weight" indicates the mass per unit area.

[0029] 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.

[0030] The term "active material layer" is a collective term for the first active material layer and the second active material layer.

[0031] Non-aqueous 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.

[0032] 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.

[0033] 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.

[0034] Each layer in the negative electrode active material layer 22 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.

[0035] Each layer may have any arbitrary 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 relationships such as "T1 / T2=1 / 9 to 9 / 1", "T1 / T2=2 / 8 to 8 / 2", "T1 / T2=3 / 7 to 7 / 3", and "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.

[0036] Each layer may have any arbitrary 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 relationships such as "W1 / W2=1 / 9 to 9 / 1", "W1 / W2=2 / 8 to 8 / 2", "W1 / W2=3 / 7 to 7 / 3", and "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.

[0037] The porosity of the active material layer may be substantially constant over the entire region. The porosity of the active material layer may vary locally. 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.

[0038] 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 0.1% to 3% or 0.5% to 2%.

[0039] The negative electrode active material includes artificial graphite and natural graphite. In addition to artificial graphite and natural graphite, the negative electrode active material may further include other active materials. Other active materials may include, for example, Si, SiO, lithium titanate, Sn-based alloys, SnO, pure Li, Li-based alloys, etc.

[0040] Artificial graphite is unevenly distributed in the first active material layer 22a. The mass fraction of artificial graphite in the first active material layer 22a is "M 1A " is the mass fraction of artificial graphite in the second active material layer 22b "M 2A It is higher compared to "M 2A <M 1A "1 <M 1A / M 2A The relationship "M" is satisfied. 1A / M 2A " may be, for example, 1.5 or more, 2 or more, 3 or more, 5 or more, 10 or more, 50 or more, or 100 or more. 1A / M 2A " may be, for example, 1000 or less, or 100 or less. Mass fraction "M 1A " may be, for example, 40% or more, 50% or more, 60% or more, 70% or more, 80% or more, 90% or more, 95% or more, 98% or more, or 99% or more. Mass fraction "M 1A " may be, for example, 100% or less, 99% or less, 98% or less, or 95% or less.

[0041] Natural graphite is unevenly distributed in the second active material layer 22b. The mass fraction of natural graphite in the first active material layer 22a is "M 1N" is the mass fraction of natural graphite in the second active material layer 22b "M 2N It is lower compared to "M 1N <M 2N "M 1N / M 2N The relationship "<1" is satisfied. Ratio "M 1N / M 2N " may be, for example, 0.9 or less, 0.5 or less, 0.3 or less, 0.1 or less, or 0.01 or less. 1N / M 2N " may be, for example, 0 or more, 0.001 or more, 0.01 or more, or 0.1 or more. Mass fraction "M 2N " may be, for example, 40% or more, 50% or more, 60% or more, 70% or more, 80% or more, 90% or more, 95% or more, 98% or more, or 99% or more. Mass fraction "M 2N " may be, for example, 100% or less, 99% or less, 98% or less, or 95% or less.

[0042] As mentioned above, "M 2A <M 1A " and "M 1N <M 2N As long as the relationship '' is satisfied, the first active material layer 22a and the second active material layer 22b may each independently contain artificial graphite, natural graphite, and other active materials. For example, the negative electrode active material in the first active material layer 22a may consist substantially of artificial graphite and Si-based active material. The negative electrode active material in the second active material layer 22b may consist substantially of natural graphite.

[0043] Artificial graphite and natural graphite can each independently have any particle shape. The particle shape may be, for example, spherical, ellipsoidal, or flattened. For example, the aspect ratio of natural graphite is "R N " is the aspect ratio of artificial graphite "R A It may be larger than "1 <R N / R A Relationships such as "≤5" may also be satisfied. Aspect ratio of natural graphite "R N" may be, for example, 1.5 or more, 2 or more, or 3 or more. Aspect ratio of natural graphite "R N " may be, for example, 5 or less. Aspect ratio of artificial graphite "R A " may be, for example, less than 1.5, 1.4 or less, 1.3 or less, 1.2 or less, or 1.1 or less. Aspect ratio of artificial graphite "R A " may be, for example, 1 or more.

[0044] The orientation of the negative electrode active material differs between the first active material layer 22a and the second active material layer 22b. The orientation angle "θ2" of the negative electrode active material in the second active material layer 22b is larger than the orientation angle "θ1" of the negative electrode active material in the first active material layer 22a. That is, the relationship "θ1 < θ2" is satisfied. The orientation angle "θ2" may be, for example, 30° or more, 45° or more, 60° or more, or 75° or more. The orientation angle "θ2" may be, for example, 90° or less, 75° or less, or 60° or less. The orientation angle "θ1" may be, for example, less than 30°, 15° or less, or 5° or less. The orientation angle "θ1" may be, for example, 0° or more.

[0045] Artificial graphite and natural 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.

[0046] The particle size distribution may differ between the first active material layer 22a and the second active material layer 22b. The particle size distribution may be volume-based or number-based. In this embodiment, in the histogram, a convex region having a height of 0.1 times or more the height of the maximum peak is considered a peak. The number of peaks may be, for example, one or more, two or more, or three or more. A "monomodal type (also called a unimodal type)" shows a distribution with substantially one peak. A "bimodal type" shows a distribution with substantially two peaks. A "multimodal type" shows a distribution with three or more peaks.

[0047] Figure 7 is a graph showing an example of the first particle size distribution in this embodiment. The negative electrode active material in the first active material layer 22a may have the first particle size distribution. The first particle size distribution is bimodal. The peak on the side with larger particle size is the mode diameter "d 1L It has "mode diameter (mode)". The "mode diameter (mode value)" indicates the particle size corresponding to the peak top. Mode diameter "d 1L This can be considered as the average particle size of the large particle group. The peak on the smaller particle size side is the mode diameter "d 1S It has a mode diameter "d 1S The particle size ratio "d" may be considered the average particle size of the small particle group. 1L / d 1S " may be, for example, 2 or more, 3 or more, 4 or more, or 5 or more. The particle size ratio "d 1L / d 1S " may be, for example, 10 or less, 8 or less, or 6 or less.

[0048] Figure 8 is a graph showing an example of the second particle size distribution in this embodiment. The negative electrode active material in the second active material layer 22b may have a second particle size distribution. The second particle size distribution is monomodal. The peak has a mode diameter "d2". The mode diameter "d2" may be considered as the average particle size of the negative electrode active material in the second active material layer 22b.

[0049] Between the first particle size distribution (Figure 7) and the second particle size distribution (Figure 8), for example, "d 1S <d2<d 1L "d 1S <d 1L <d2」、「d2<d 1S <d 1L Relationships such as the above may also be satisfied. When these relationships are satisfied, improvements in the balance of Li ion acceptance, electronic conductivity, and flexibility can be expected, for example.

[0050] 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 can be lower than "M 1B <M 2B "1 <M 2B / M 1B The relationship "M" may also be satisfied. 2B / M 1B " may be, for example, 1.2 or more, 1.5 or more, 2 or more, 2.5 or more. Ratio "M 2B / M 1B " may be, for example, 3 or less, or 2 or less.

[0051] 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%.

[0052] 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.

[0053] 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.

[0054] 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]

[0055] 10 Positive electrode, 20 Negative electrode, 21 Current collector, 22 Negative electrode active material layer, 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 natural graphite. The mass fraction of the artificial graphite in the first active material layer is higher than the mass fraction of the artificial graphite in the second active material layer. The mass fraction of natural graphite in the first active material layer is lower than the mass fraction of natural graphite in the second active material layer. The orientation angle of the negative electrode active material in the second active material layer is larger than the orientation angle of the negative electrode active material in the first active material layer, The orientation angle refers to the acute angle formed by the major axis diameter of the negative electrode active material 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 lower 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 negative electrode active material in the first active material layer has a bimodal particle size distribution, and The negative electrode active material in the second active material layer has a monomodal particle size distribution. The negative electrode for a non-aqueous electrolyte secondary battery according to claim 1.

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 in the first active material layer has a bimodal particle size distribution. The negative electrode active material in the second active material layer has a monomodal particle size distribution. The mass fraction of the binder in the first active material layer is lower than the mass fraction of the binder in the second active material layer. The negative electrode active material includes artificial graphite and natural graphite. The aforementioned natural graphite has a larger aspect ratio than the aforementioned artificial graphite. The negative electrode active material in the first active material layer is substantially made of the artificial graphite. The negative electrode active material in the second active material layer is substantially made of the natural graphite, The orientation angle of the negative electrode active material in the second active material layer is larger than the orientation angle of the negative electrode active material in the first active material layer. The orientation angle indicates the acute angle formed by the major axis diameter of the negative electrode active material and the surface of the current collector, 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. Negative electrode for non-aqueous electrolyte secondary batteries.

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