Negative electrode for non-aqueous electrolyte secondary batteries

Abstract

To improve the adhesion between the separator and the active material layer. [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. The first active material layer contains first natural graphite. The second active material layer contains second natural graphite and artificial graphite. The aspect ratio of the second natural graphite is larger than that of the artificial graphite. The orientation angle of the first natural graphite is larger than that of the second natural graphite. The orientation angle represents the acute angle between the major axis diameter of the particles 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] U.S. Patent Application Publication No. 2021 / 0391570 (Document 1) discloses a negative electrode with a two-layer structure comprising artificial graphite and natural graphite.

RELATED 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 with a two-layer structure has been proposed. In the two-layer structure, each layer has a mutually different composition, so various performance improvements are expected. For example, in Document 1, it is stated that natural graphite is unevenly distributed in the lower layer and artificial graphite is unevenly distributed in the upper layer, which improves the contact force between the active material layer and the current collector. However, there is room for improvement in the adhesion between the separator and the active material layer.

[0005] An object of the present disclosure is to improve the adhesion between the separator and the active material layer.

MEANS FOR SOLVING THE PROBLEMS

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

[0007] 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. The first active material layer contains first natural graphite. The second active material layer contains second natural graphite and artificial graphite. The aspect ratio of the second natural graphite is larger than the aspect ratio of the artificial graphite. The orientation angle of the first natural graphite is larger than the orientation angle of the second natural graphite. The orientation angle indicates the acute angle formed by the major axis diameter of the particle and the surface of the current collector.

[0008] When the adhesion between the separator and the active material layer is low, the reaction becomes non-uniform, which may lead to deterioration of, for example, durability, rapid charging performance, and the like.

[0009] Figure 1 is a schematic cross-sectional view showing the first laminated structure in the present embodiment. In the drawings of the present disclosure, "NG" indicates natural graphite. "AG" indicates artificial graphite. 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. In general, the negative electrode 20 is subjected to roll pressing in the manufacturing process. Graphite has a lubricating effect. Due to the lubricating effect of the artificial graphite in the upper layer, the upper layer may be smoothed during roll pressing. It is considered that the smoothing of the upper layer reduces the adhesion between the upper layer (the negative electrode 20) and the separator.

[0010] Figure 2 is a schematic cross-sectional view showing the second laminated structure in the present embodiment. In the second laminated structure, natural graphite is unevenly distributed in the upper layer. Artificial graphite is unevenly distributed in the lower layer. Also in the second laminated structure, the upper layer may be smoothed during roll pressing due to the lubricating effect of the natural graphite in the upper layer.

[0011] Figure 3 is a conceptual cross-sectional view showing the third layered structure in this embodiment. In the third layered structure, an adhesive layer 22d is formed on the outermost surface of the negative electrode 20. For example, the adhesive layer 22d can be formed by applying a binder coating. The adhesive layer 22d is expected to improve the adhesion between the separator and the negative electrode 20. However, the adhesive layer 22d (polymer binder) can act as a resistive component in Li ion conduction. The formation of the adhesive layer 22d may significantly reduce, for example, the rapid charging performance.

[0012] Figure 4 is a conceptual cross-sectional view showing the fourth layered structure in this embodiment. In the drawings of this disclosure, circular elements represent unoriented active material. Elliptical elements represent active material oriented in the thickness direction. The orientation angle is an indicator of orientation. The closer the orientation angle is to 90°, the more strongly the particles are considered to be oriented in the thickness direction. In the fourth layered structure, the second active material layer 22b (upper layer) contains both natural graphite and artificial graphite. There are differences in hardness and lubrication between natural graphite and artificial graphite. Therefore, it is thought that the upper layer will not be uniformly smoothed during roll pressing. Furthermore, the first active material layer 22a (lower layer) contains oriented natural graphite. Because the natural graphite in the lower layer is oriented, variations may occur in the force applied to the upper layer during roll pressing. Due to the synergistic effect of these effects, the upper layer will not be uniformly smoothed, and moderate irregularities may occur in the upper layer. The moderate unevenness is expected to create an anchoring effect, improving the adhesion between the separator and the negative electrode.

[0013] Furthermore, the recesses in the upper layer can form pathways for Li ions to enter. The oriented natural graphite in the lower layer can form pores that extend in the thickness direction. The synergistic effect of these factors can reduce the degree of bending. This reduction in bending can lead to improvements in performance, such as rapid charging.

[0014] 2. The negative electrode for a non-aqueous electrolyte secondary battery described in item "1" above may include, for example, the following configuration: The first active material layer further comprises a Si-based active material.

[0015] Figure 5 is a conceptual cross-sectional view showing the fifth layered structure in this embodiment. In the drawings of this disclosure, "Si" indicates a Si-based active material. By including the Si-based active material in the negative electrode 20, an improvement in energy density is expected. However, since the Si-based active material expands significantly during charging, measures to counter the expansion are also required. By arranging the Si-based active material in the first active material layer 22a (lower layer), a reduction in expansion is expected. The oriented first natural graphite in the lower layer is expected to absorb the in-plane expansion of the Si-based active material well. The unoriented second natural graphite and artificial graphite in the upper layer are expected to absorb the thickness-direction expansion of the Si-based active material well. Note that "in-plane direction" refers to any direction perpendicular to the thickness direction (Z-axis direction). The X-axis direction and Y-axis direction are examples of in-plane directions.

[0016] 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 average particle size of the second natural graphite is larger than that of the artificial graphite.

[0017] In the upper layer, it is expected that the presence of larger particle sizes in natural graphite compared to artificial graphite will result in the formation of a moderate level of surface irregularities.

[0018] 4. The negative electrode for a non-aqueous electrolyte secondary battery described in any one of items "1" to "3" above may include, for example, the following configuration: The second active material layer is thinner than the first active material layer.

[0019] A reduction in curvature is expected due to the relatively thinness of the first active material layer (upper layer).

[0020] 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, and a second active material layer. The second active material layer is thinner than the first active material layer. The first active material layer contains first natural graphite and a Si-based active material. The second active material layer contains second natural graphite and artificial graphite. The average particle size of the second natural graphite is larger than that of the artificial graphite. The aspect ratio of the second natural graphite is larger than that of the artificial graphite. The orientation angle of the first natural graphite is larger than that of the second natural graphite. The orientation angle represents the acute angle between the major axis diameter of the particle and the surface of the current collector.

[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 cross-sectional conceptual diagram showing the first layered structure in this embodiment. [Figure 2] This is a cross-sectional conceptual diagram showing the second layered 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 cross-sectional conceptual diagram showing the fifth layered structure in this embodiment. [Figure 6] This is a conceptual cross-sectional view illustrating the orientation angle in this embodiment. [Figure 7] 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 6 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] Non-aqueous electrolyte secondary battery Figure 7 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, the negative electrode 20 may include a third active material layer (not shown) between the first active material layer 22a and the second active material layer 22b.

[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 arbitrary thickness. For example, the second active material layer 22b may be thinner than the first active material layer 22a. The ratio "T2 / T1" of the thickness "T2" of the second active material layer 22b to the thickness "T1" of the first active material layer 22a may be, for example, 0.9 or less, 0.8 or less, 0.7 or less, 0.6 or less, 0.5 or less, 0.4 or less, 0.3 or less, 0.2 or less, or 0.1 or less. The thickness ratio "T2 / T1" may be, for example, 0.1 or more, 0.2 or more, 0.3 or more, 0.4 or more, 0.5 or more, 0.6 or more, 0.7 or more, 0.8 or more, or 0.9 or more. The thickness of each layer may be, for example, 10 μm or more, 30 μm or more, 50 μm or more, 100 μm or more, 150 μm or more, 200 μm or more, 250 μm or more, or 300 μm or more. The thickness of each layer may be, for example, 1 mm or less, 500 μm or less, 400 μm or less, 300 μm or less, or 200 μm or less.

[0038] 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", "W1 / W2=4 / 6 to 6 / 4", etc. 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 approximately constant throughout the entire layer. The porosity of the active material layer may differ locally. For example, the porosity "φ1" of the first active material layer 22a may be higher than the porosity "φ2" of the second active material layer 22b. That is, the relationships "φ2 < φ1" and "1 < φ1 / φ2" may be satisfied. The ratio "φ1 / φ2" may be, for example, 1.2 or more, 1.5 or more, 2 or more, or 2.5 or more. The ratio "φ1 / φ2" may be, for example, 5 or less, 3 or less, or 2 or less. The porosity of each layer may be independently, for example, 1% or more, 5% or more, 10% or more, 20% or more, 30% or more, 40% or more, or 50% or more. The porosity of each layer may be independently set to, for example, 80% or less, 60% or less, 50% or less, 40% or less, 30% or less, 20% or less, 10% or less, or 5% or less.

[0040] negative electrode active material The first active material layer 22a is a lower layer. The first active material layer 22a may be formed directly on the surface of the current collector 21. The first active material layer 22a contains negative electrode active material. The first active material layer 22a may further contain conductive material, binder, etc. For example, the first active material layer 22a may contain, by mass fraction, 0% to 10% conductive material, 0% to 10% binder, and the remainder negative electrode active material. For example, the first active material layer 22a may contain, by mass fraction, 0.5% to 1.5% conductive material, 0.5% to 3% binder, and the remainder negative electrode active material.

[0041] In the first active material layer 22a, the negative electrode active material includes first natural graphite. The negative electrode active material in the first active material layer 22a may further include a Si-based active material. For example, the negative electrode active material in the first active material layer 22a may consist of first natural graphite and a Si-based active material. For example, the negative electrode active material in the first active material layer 22a may further include other active materials. Other active materials may include, for example, lithium titanate, Sn-based alloys, SnO, pure Li, Li-based alloys, etc.

[0042] In the first active material layer 22a, the Si-based active material and natural graphite may satisfy relationships such as, for example, in mass ratio, "Si-based active material / first natural graphite = 1 / 99 to 50 / 50", "Si-based active material / first natural graphite = 1 / 99 to 30 / 70", "Si-based active material / first natural graphite = 1 / 99 to 20 / 80", or "Si-based active material / first natural graphite = 1 / 99 to 10 / 90".

[0043] The first natural graphite and the Si-based active material may each independently have any arbitrary 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.

[0044] For example, the primary natural graphite may be large particles. For example, the Si-based active material may be small particles. The average particle size of the Si-based active material is "d S The average particle size of the first natural graphite "d" N1 The ratio of "d N1 / 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. N1 / d S " may be 10 or less, 8 or less, or 6 or less.

[0045] The second active material layer 22b is the upper layer. The second active material layer 22b may be formed directly on the surface of the first active material layer 22a. The second active material layer 22b may be in direct contact with the separator in the non-aqueous electrolyte secondary battery 100. The second active material layer 22b may constitute the outermost surface of the negative electrode 20. The second active material layer 22b also contains negative electrode active material. The second active material layer 22b may further contain conductive material, binder, etc. For example, the second active material layer 22b may contain, by mass fraction, 0% to 10% conductive material, 0% to 10% binder, and the remainder negative electrode active material. For example, the second active material layer 22b may contain, by mass fraction, 0.5% to 1.5% conductive material, 0.5% to 3% binder, and the remainder negative electrode active material.

[0046] In the second active material layer 22b, the negative electrode active material includes second natural graphite and artificial graphite. For example, in the second active material layer 22b, the negative electrode active material may consist of second natural graphite and artificial graphite. For example, in the second active material layer 22b, the negative electrode active material may further include other active materials (mentioned above).

[0047] In the second active material layer 22b, the second natural graphite and the artificial graphite may satisfy relationships such as, for example, in mass ratio: "second natural graphite / artificial graphite = 99 / 1 to 1 / 99", "second natural graphite / artificial graphite = 90 / 10 to 10 / 90", "second natural graphite / artificial graphite = 80 / 20 to 20 / 80", "second natural graphite / artificial graphite = 70 / 30 to 30 / 70", and "second natural graphite / artificial graphite = 60 / 40 to 40 / 60".

[0048] The second natural graphite and the artificial graphite may each independently have any arbitrary 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.

[0049] For example, the secondary natural graphite may have large particles. For example, the artificial graphite may have small particles. The average particle size of the artificial graphite is "d A The average particle size of second-order natural graphite "d" N2 The ratio of "d N2 / d A " may be, for example, 1 or more, 1.5 or more, 2 or more, 3 or more, 4 or more, or 5 or more. N2 / d A " may be 10 or less, 8 or less, or 6 or less.

[0050] The aspect ratio of second-generation natural graphite "R N2 " is the aspect ratio of artificial graphite "R A It is larger in comparison to "R". N2 / R A " may be, for example, 1.1 or higher, 1.2 or higher, 1.5 or higher, 2 or higher, 4 or higher, or 6 or higher. Ratio "R N2 / RA " may be, for example, 10 or less, 8 or less, 6 or less, 5 or less, or 4 or less. Aspect ratio of second natural graphite "R N2 " may be, for example, 1.1 or higher, 1.2 or higher, 1.5 or higher, 2 or higher, 4 or higher, or 6 or higher. Aspect ratio of second natural graphite "R N2 " may be, for example, 10 or less, 8 or less, 6 or less, 5 or less, or 4 or less. Aspect ratio of artificial graphite "R A " may be, for example, 1 or more, 1.1 or more, 1.2 or more, or 1.5 or more. Aspect ratio of artificial graphite "R A " may be, for example, 2 or less, 1.8 or less, 1.5 or less, or 1.2 or less.

[0051] At the negative electrode 20, the first natural graphite and the second natural graphite have different orientations. The orientation angle "θ1" of the first natural graphite is larger than the orientation angle "θ2" of the second natural graphite. 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.

[0052] For example, the first natural graphite may be the same material as the second natural graphite. For example, the first natural graphite and the second natural graphite may differ from each other in terms of size, shape, etc. For example, the average particle size of the second natural graphite "d N2 " is the average particle size of the first natural graphite "d N1 It may be larger than the average particle size of the first natural graphite "d N1 " is the average particle size of secondary natural graphite "d N2 It may be larger than the aspect ratio of "R". For example, the aspect ratio of second natural graphite "R N2 " is the aspect ratio of the first natural graphite "R N1 It may be larger than the aspect ratio of "R". For example, the aspect ratio of first natural graphite "R N1 " is the aspect ratio of second-generation natural graphite "RN2 It can be larger than "[ ]".

[0053] 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.

[0054] As shown in Figure 5, 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, for example, contain 0% to 10% by mass fraction of conductive material and the remainder being binder. The binder layer 22c may, for example, contain 1% to 5% by mass fraction of conductive material and the remainder being binder.

[0055] 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.

[0056] 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.

[0057] 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]

[0058] 10 Positive electrode, 20 Negative electrode, 21 Current collector, 22a First active material layer, 22b Second active material layer, 22c Binder layer, 22d Adhesive 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. The first active material layer contains first natural graphite, The aforementioned second active material layer contains a second natural graphite and artificial graphite, The aspect ratio of the second natural graphite is larger than that of the artificial graphite. The orientation angle of the first natural graphite is larger than that of the second natural graphite, The orientation angle refers to the acute angle formed between the major axis diameter of the particle and the surface of the current collector. Negative electrode for non-aqueous electrolyte secondary batteries.

2. The first active material layer further contains a Si-based active material. The negative electrode for a non-aqueous electrolyte secondary battery according to claim 1.

3. The average particle size of the second natural graphite is larger than that of the artificial graphite. The negative electrode for a non-aqueous electrolyte secondary battery according to claim 1.

4. The second active material layer is thinner than the first 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, and the second active material layer are included in this order. The second active material layer is thinner than the first active material layer. The first active material layer comprises first natural graphite and Si-based active material. The aforementioned second active material layer contains a second natural graphite and artificial graphite, The average particle size of the second natural graphite is larger than that of the artificial graphite. The aspect ratio of the second natural graphite is larger than that of the artificial graphite. The orientation angle of the first natural graphite is larger than that of the second natural graphite, The orientation angle refers to the acute angle formed between the major axis diameter of the particle and the surface of the current collector. Negative electrode for non-aqueous electrolyte secondary batteries.

Images