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, a second active material layer, and a third active material layer in this order. Each of the first and third active material layers independently contains at least one of natural graphite and artificial graphite. The second active material layer contains natural graphite and a Si-based active material. The natural graphite in the second active material layer is oriented in the thickness direction of the second active material layer.

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. 10-2022-0012577 (Reference 1) discloses a three-layer negative electrode comprising a graphite-based active material and a Si-based active material. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Korean Published Patent Publication No. 10-2022-0012577 [Overview of the Initiative] [Problems that the invention aims to solve]

[0004] Si-based active materials have a larger specific capacity compared to carbon-based active materials (natural graphite, artificial graphite). On the other hand, Si-based active materials have the property of expanding significantly during charging. Due to the expansion of the active material layer, there is a possibility that a part of the active material layer may collapse. To mitigate the expansion of the active material layer caused by Si-based active materials, for example, it is conceivable to use a mixture of Si-based and carbon-based active materials.

[0005] For example, in reference 1, the reduction of swelling is being considered by unevenly distributing the Si-based active material in the middle and lower layers of a three-layer structure consisting of an upper, middle, and lower layer. However, there is still room for improvement.

[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 a non-aqueous electrolyte secondary battery according to one aspect of the present disclosure includes a current collector, a first active material layer, a second active material layer, and a third active material layer in this order. Each of the first active material layer and the third active material layer independently contains at least one of natural graphite and artificial graphite. The second active material layer contains natural graphite and a Si-based active material. The natural graphite in the second active material layer is oriented in the thickness direction of the second active material layer.

[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, "G" indicates any graphite material. "Si" indicates a Si-based active material. The negative electrode 20 includes a current collector 21, a first active material layer 22a (lower layer), a second active material layer 22b (intermediate layer), and a third active material layer 22c (upper layer) in this order. Each layer contains any graphite material. The Si-based active material is unevenly distributed in the intermediate layer and the lower layer. In the first laminated structure, since the Si-based active material is separated from the surface of the negative electrode 20, reduction of swelling in the thickness direction is expected. However, the swelling in the thickness direction may not be sufficiently reduced. Swelling also occurs in the in-plane direction. In the first laminated structure, the swelling in the in-plane direction may not be reduced. Due to the in-plane swelling, structural destruction of the negative electrode 20 may progress.

[0010] Figure 2 is a schematic cross-sectional view showing the second laminated structure in the present embodiment. In the second laminated structure, the Si-based active material is unevenly distributed in the second active material layer 22b (intermediate layer). It is expected that the lower layer and the upper layer absorb the swelling of the intermediate layer. However, even in the second laminated structure, the in-plane swelling of the intermediate layer may not be reduced.

[0011] Figure 3 is a schematic cross-sectional view showing the third laminated structure in the present embodiment. In the drawings of the present disclosure, "AG" indicates artificial graphite. Also in the third laminated structure, the Si-based active material is unevenly distributed in the second active material layer 22b (intermediate layer). The intermediate layer further contains artificial graphite. However, even in the third laminated structure, the in-plane swelling of the intermediate layer may not be reduced.

[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. In the fourth laminated structure, the artificial graphite in the intermediate layer is oriented in the thickness direction. However, even in the fourth laminated structure, there is a possibility that the swelling of the intermediate layer in the in-plane direction cannot be mitigated.

[0013] FIG. 5 is a schematic cross-sectional view showing the fifth laminated structure in the present embodiment. In the drawings of the present disclosure, "NG" denotes natural graphite. In the fifth laminated structure, the intermediate layer further contains natural graphite. However, even in the fifth laminated structure, there is a possibility that the swelling of the intermediate layer in the in-plane direction cannot be mitigated.

[0014] FIG. 6 is a schematic cross-sectional view showing the sixth laminated structure in the present embodiment. In the sixth laminated structure, the natural graphite in the intermediate layer is oriented in the thickness direction. According to the new findings of the present disclosure, the orientation of the natural graphite in the intermediate layer in the thickness direction is expected to reduce the swelling of the intermediate layer in the in-plane direction. Furthermore, it is expected that the swelling absorption effect in the thickness direction by the upper layer and the lower layer is also improved. Therefore, in the sixth laminated structure, the swelling in the thickness direction and the in-plane direction is synergistically reduced, so that the swelling of the entire negative electrode 20 is expected to be significantly reduced.

[0015] 2. The negative electrode for non-aqueous electrolyte secondary batteries described in the above item "1" may include, for example, the following configuration. The natural graphite in the second active material layer has an orientation angle of 30° or more. The orientation angle refers to the acute angle formed by the major axis diameter of the particle and the surface of the current collector.

[0016] The orientation angle is an index of orientation. It is considered that the closer the orientation angle is to 90°, the more strongly the particles are oriented in the thickness direction. When the orientation angle of the natural graphite in the intermediate layer is 30° or more, reduction of swelling of the negative electrode is expected.

[0017] 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 first active material layer contains natural graphite. The third active material layer contains artificial graphite and natural graphite. The relationship "θ1 < θ3 < θ2" is satisfied. "θ1" represents the orientation angle of the natural graphite in the first active material layer. "θ2" represents the orientation angle of the natural graphite in the second active material layer. "θ3" represents the orientation angle of the natural graphite in the third active material layer.

[0018] Figure 7 is a conceptual cross-sectional view showing the seventh layered structure in this embodiment. The first active material layer 22a (lower layer) contains natural graphite. The third active material layer 22c (upper layer) contains artificial graphite and oriented natural graphite. As the orientation of the natural graphite increases in the order of lower, upper, and middle layers, a reduction in swelling and a reduction in resistance are expected. The oriented natural graphite can form a diffusion path for Li ions from the upper layer to the lower layer of the negative electrode 20. In the lower layer, the unoriented natural graphite can form a diffusion path for Li ions that extends in the in-plane direction. It is believed that the resistance is reduced by connecting the diffusion paths in the upper, middle, and lower layers.

[0019] 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 first active material layer, the second active material layer, and the third active material layer each independently further include a binder. B3 <M B1 <M B2 The relationship "M" is satisfied. B1 " indicates the mass fraction of the binder in the first active material layer. B2 " indicates the mass fraction of the binder in the second active material layer. B3 This indicates the mass fraction of the binder in the third active material layer.

[0020] The mass fraction of the binder in the middle layer containing the Si-based active material "M B2 The relatively high "M" is expected to inhibit structural breakdown associated with the expansion and contraction of the Si-based active material. B3」is relatively low, it is expected that the penetration and diffusion of Li ions from the negative electrode surface are promoted. In the lower layer in contact with the current collector, the mass fraction of the binder "M B1 " is relatively high, improvement in peel strength is expected.

[0021] 5. A negative electrode for a non-aqueous electrolyte secondary battery in one aspect of the present disclosure includes a current collector, a first active material layer, a second active material layer, and a third active material layer in this order. The first active material layer includes natural graphite and a binder. The second active material layer includes natural graphite, a Si-based active material, and a binder. The third active material layer includes artificial graphite, natural graphite, and a binder. The natural graphite in the second active material layer has an orientation angle of 30° or more. The orientation angle indicates the acute angle formed by the major axis diameter of the particle and the surface of the current collector. The relationship "θ1<θ3<θ2" is satisfied. "θ1" indicates the orientation angle of natural graphite in the first active material layer. "θ2" indicates the orientation angle of natural graphite in the second active material layer. "θ3" indicates the orientation angle of natural graphite in the third active material layer. "M B3 <M B1 <M B2 " is satisfied. "M B1 " indicates the mass fraction of the binder in the first active material layer. "M B2 " indicates the mass fraction of the binder in the second active material layer. "M B3 " indicates the mass fraction of the binder in the third active material layer. The relationship "φ1<φ3<φ2" is satisfied. "φ1" indicates the porosity of the first active material layer. "φ2" indicates the porosity of the second active material layer. "φ3" indicates the porosity of the third active material layer.

[0022] Since the porosity "φ2" in the middle layer containing the Si-based active material is relatively high, it is expected that the voids absorb the expansion of the Si-based active material. Since the porosity "φ3" in the upper layer is relatively high, it is expected that the penetration and diffusion of Li ions from the negative electrode surface are promoted. Since the porosity "φ1" in the lower layer is relatively low, improvement in peel strength is expected.

[0023] 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]

[0024] [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 cross-sectional conceptual diagram showing the sixth layered structure in this embodiment. [Figure 7] This is a cross-sectional conceptual diagram showing the seventh layered structure in this embodiment. [Figure 8] This is a conceptual cross-sectional view illustrating the orientation angle in this embodiment. [Figure 9] This is a conceptual diagram showing an example of a non-aqueous electrolyte secondary battery in this embodiment. [Figure 10] This is a cross-sectional conceptual diagram showing the eighth layered structure in this embodiment. [Modes for carrying out the invention]

[0025] 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.

[0026] 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.

[0027] Unless otherwise specified, the singular form is not limited to a single element. The singular form can also include multiple elements.

[0028] "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.

[0029] 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.

[0030] 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.

[0031] Figure 8 is a conceptual cross-sectional view illustrating the orientation angle in this disclosure. 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 represents the maximum Ferret diameter of the particle. The arithmetic mean of the orientation angles of 100 randomly selected particles is used.

[0032] "Basis Weight" indicates the mass per unit area.

[0033] 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.

[0034] The term "active material layer" is a collective term for the first active material layer, the second active material layer, and the third active material layer.

[0035] Non-aqueous electrolyte secondary battery Figure 9 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.

[0036] negative electrode Figure 10 is a conceptual cross-sectional view showing the eighth layered structure in this embodiment. The negative electrode 20 may be, for example, in the form of a sheet. The negative electrode 20 has a multilayer structure. In the thickness direction, the negative electrode 20 includes a current collector 21, a first active material layer 22a, a second active material layer 22b, and a third active material layer 22c in this order. The first active material layer 22a may be arranged on a part of the surface of the current collector 21 or on the entire surface. The first active material layer 22a 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.

[0037] The negative electrode 20 may further include any elements as long as it includes the first active material layer 22a, the second active material layer 22b, and the third active material layer 22c. For example, it may further include fourth and fifth active material layers (not shown) at any position in the thickness direction. For example, a conductive layer, an adhesion layer (neither 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 third active material layer 22c. For example, a binder layer 22d may be placed between one or more of the layers.

[0038] Each layer may be, for example, a coating layer. A coating layer is a layer formed by the application of 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 graphite 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 pressing pressure, etc.

[0039] Each layer may independently have any arbitrary thickness. The thickness of each layer may be substantially the same or different. For example, the thickness "T1" of the first active material layer 22a, the thickness "T2" of the second active material layer 22b, and the thickness "T3" of the third active material layer 22c may satisfy relationships such as "T1≦T3<T2", "T2<T1≦T3", and the like. The ratio of the minimum thickness to the maximum thickness among the three layers 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 ratio of the minimum thickness to the maximum thickness among the three layers 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 independently 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 independently be, for example, 1 mm or less, 500 μm or less, 400 μm or less, 300 μm or less, or 200 μm or less.

[0040] Each layer may independently have any arbitrary basis weight. The basis weight of each layer may be substantially the same or different. For example, the basis weight "W1" of the first active material layer 22a, the basis weight "W2" of the second active material layer 22b, and the basis weight "W3" of the third active material layer 22c may satisfy relationships such as "W1≦W3<W2", "W2<W1≦W3", and the like. The ratio of the minimum basis weight to the maximum basis weight among the three layers 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 ratio of the minimum basis weight to the maximum basis weight among the three layers 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 basis weight of each layer may independently be, for example, 1 mg / cm 2 or more, 5 mg / cm 2 or more, 10 mg / cm 2 or more, or 20 mg / cm 2The above is also acceptable. The basis weight of each layer can be determined independently, for example, 50 mg / cm³. 2 Below 30mg / cm 2 Below, 25mg / cm 2 Below, 15mg / cm 2 The following, or 10 mg / cm³ 2 The following is also acceptable.

[0041] Each layer may independently have any porosity. The porosities of each layer may be substantially the same or different. For example, the porosity "φ1" of the first active material layer 22a, the porosity "φ2" of the second active material layer 22b, and the porosity "φ3" of the third active material layer 22c may satisfy a relationship such as "φ1 < φ3 < φ2". The ratio of the maximum porosity to the minimum porosity among the three layers may be, for example, 1.2 or more, 1.5 or more, 2 or more, or 2.5 or more. The ratio of the maximum porosity to the minimum porosity among the three layers may be, for example, 5 or less, 3 or less, or 2 or less. The porosity of each layer may independently be, 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, 70% or less, 60% or less, 50% or less, 40% or less, 30% or less, 20% or less, 10% or less, or 5% or less.

[0042] 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 the first negative electrode active material. The first active material layer 22a may further contain a conductive material, a binder, etc. For example, the first active material layer 22a may contain, by mass fraction, 0% to 10% of a conductive material, 0% to 10% of a binder, and the remainder being the first negative electrode active material. For example, the first active material layer 22a may contain, by mass fraction, 0.5% to 1.5% of a conductive material, 0.5% to 3% of a binder, and the remainder being the first negative electrode active material. The first negative electrode active material contains at least one of natural graphite and artificial graphite. The first negative electrode active material may consist of, for example, natural graphite.

[0043] The second active material layer 22b is an intermediate 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 contains a second negative electrode active material. The second active material layer 22b may further contain a conductive material, a binder, etc. For example, the second active material layer 22b may contain, by mass fraction, 0% to 10% of a conductive material, 0% to 10% of a binder, and the remainder being the second negative electrode active material. For example, the second active material layer 22b may contain, by mass fraction, 0.5% to 1.5% of a conductive material, 0.5% to 3% of a binder, and the remainder being the second negative electrode active material. The second negative electrode active material includes natural graphite and a Si-based active material. The negative electrode active material may consist of natural graphite and a Si-based active material. For example, relationships such as "Si-based active material / natural graphite = 1 / 99 to 50 / 50" in terms of mass ratio, "Si-based active material / natural graphite = 1 / 99 to 30 / 70", "Si-based active material / natural graphite = 1 / 99 to 20 / 80", and "Si-based active material / natural graphite = 1 / 99 to 10 / 90" may be satisfied.

[0044] The third active material layer 22c is the upper layer. The third active material layer 22c may form the outermost surface of the negative electrode 20. The third active material layer 22c may be formed directly on the surface of the second active material layer 22b. The third active material layer 22c contains the third negative electrode active material. The third active material layer 22c may further contain a conductive material, a binder, etc. For example, the third active material layer 22c may contain, by mass fraction, 0% to 10% of a conductive material, 0% to 10% of a binder, and the remainder being the third negative electrode active material. For example, the third active material layer 22c may contain, by mass fraction, 0.5% to 1.5% of a conductive material, 0.5% to 3% of a binder, and the remainder being the third negative electrode active material. The third negative electrode active material contains at least one of natural graphite and artificial graphite. The third negative electrode active material may consist of, for example, artificial graphite and natural graphite. For example, the following relationships may be satisfied in terms of mass ratio: "artificial graphite / natural graphite = 1 / 99 to 50 / 50", "artificial graphite / natural graphite = 1 / 99 to 30 / 70", "artificial graphite / natural graphite = 1 / 99 to 20 / 80", and "artificial graphite / natural graphite = 1 / 99 to 10 / 90".

[0045] The first negative electrode active material, the second negative electrode active material, and the third negative electrode active material may each independently further contain lithium titanate, Sn-based alloy, SnO, pure Li, Li-based alloy, etc.

[0046] The first negative electrode active material, the second negative electrode active material, and the third negative electrode active material may 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 be, for example, 30 μm or less, 20 μm or less, 15 μm or less, or 10 μm or less. For example, between natural graphite and Si-based active material, the natural graphite may be large particles and the Si-based active material may be small particles. For example, between natural graphite and artificial graphite, the natural graphite may be large particles and the artificial graphite may be small particles. The ratio of the average particle size of the large particles to the average particle size of the small particles may be, for example, 1 or more, 1.5 or more, 2 or more, 3 or more, 4 or more, or 5 or more. The ratio of the average particle size of the large particles to the average particle size of the small particles may be, for example, 10 or less, 8 or less, or 6 or less.

[0047] Natural graphite, artificial graphite, and Si-based active materials can each independently have any particle shape. The particle shape may be, for example, spherical, ellipsoidal, flake-shaped, or flaky. For example, the aspect ratio of natural graphite may be greater than that of artificial graphite and Si-based active materials. The aspect ratio of natural graphite may be, for example, 1.2 or more, 1.5 or more, 1.8 or more, 2.1 or more, 2.4 or more, 3 or more, 4 or more, 5 or more, or 6 or more. The aspect ratio of natural graphite may be, for example, 8 or less, 6 or less, 4 or less, or 3 or less. The aspect ratios of artificial graphite and Si-based active materials may each independently be, for example, 2 or less, 1.5 or less, or 1.2 or less. The aspect ratios of artificial graphite and Si-based active materials may each independently be, for example, 1 or more, or 1.1 or more.

[0048] The natural graphite in the second active material layer 22b is oriented in the thickness direction. The natural graphite in the second active material layer 22b may have an orientation angle "θ2" of 30° or more. The orientation angle "θ2" may be, for example, 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.

[0049] In the first active material layer 22a and the third active material layer 22c, the natural graphite may have any orientation angle. For example, the orientation angle "θ1" in the first active material layer 22a, the orientation angle "θ2" in the second active material layer 22b, and the orientation angle "θ3" in the third active material layer 22c may satisfy the relationship "θ1 < θ3 < θ2". The orientation angle "θ1" may be, for example, 0° or more, 5° or more, 10° or more, or 15° or more. The orientation angle "θ1" may be, for example, 20° or less, or 15° or less. The orientation angle "θ3" may be, for example, 15° or more, 20° or more, 25° or more, or 30° or more. The orientation angle "θ3" may be, for example, 45° or less, 30° or less, or 25° or less.

[0050] Binder The binder may include, for example, styrene-butadiene rubber (SBR), carboxymethylcellulose (CMC), polyacrylic acid (PAA), polytetrafluoroethylene (PTFE), etc. The mass fractions of the binder may be substantially the same between each layer, or they may be different from one another. For example, the mass fraction of the binder in the first active material layer 22a is "M B1 ", the mass fraction of the binder in the second active material layer 22b "M B2 ", and the mass fraction of the binder in the third active material layer 22c "M B3 " is "M B3 <M B1 <M B2 The relationship "M" may also be satisfied. B2 / M B1 " and ratio "M B1 / M B3 Each of these can be independent, for example, 1.2 or more, 1.5 or more, 2 or more, and 2.5 or more.B2 / M B1 " and ratio "M B1 / M B3 Each of these can be independent, for example, 3 or less, or 2 or less.

[0051] For example, a binder layer 22d may be formed in at least one of the following locations: between the first active material layer 22a and the second active material layer 22b, and between the second active material layer 22b and the third active material layer 22c. The mass fraction of the binder in the binder layer 22d is higher than the mass fraction of the binder in the active material layer. The binder layer 22d may be a layer that is substantially free of negative electrode active material. The binder layer 22d may, for example, contain 0% to 10% by mass fraction of conductive material and the remainder being binder. The binder layer 22d may, for example, contain 1% to 5% by mass fraction of conductive material and the remainder being binder.

[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 22d may contain a resin that swells with the electrolyte. For example, the binder in the binder layer 22d may contain an ion-permeable resin, an ion-conductive resin, etc. By allowing the electrolyte and Li ions to permeate the binder layer 22d, an improvement in charge rate characteristics can be expected. For example, the binder in the binder layer 22d may contain a fibrous resin. The fibrous resin may extend to crosslink each active material layer. By the fibrous resin crosslinking each active material layer, an improvement in peel strength, etc., can be expected. The binder in the binder layer 22d may contain at least one selected from the group consisting of 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 "T4" of the binder layer 22d may be smaller than, for example, the thickness "T1, T2, T3" of the active material layer. The thickness "T4" of the binder layer 22d may be, for example, 10 μm or less, 5 μm or less, or 3 μm or less. The thickness "T4" of the binder layer 22d may be, for example, 0.5 μm or more, 1 μm or more, or 3 μm or more. The basis weight "W4" of the binder layer 22d may be smaller than, for example, the basis weight "W1, W2, W3" of the active material layer. The basis weight "W4" of the binder layer 22d 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 "W4" of the binder layer 22d is, for example, 0.1 mg / cm³. 2 Above, or 0.5 mg / cm³ 2 That'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 22d may contain a fibrous conductive material. The binder layer 22d may contain, for example, at least one selected from the group consisting of CNTs and VGCF. The fibrous conductive material may extend to crosslink each active material layer. By crosslinking each active material layer with the fibrous conductive material, improvements in charge rate characteristics and reduction of delamination can be expected. [Explanation of symbols]

[0055] 10 Positive electrode, 20 Negative electrode, 21 Current collector, 22a First active material layer, 22b Second active material layer, 22c Third active material layer, 22d Binder layer, 30 Separator, 50 Power generation element, 60 Case, 100 Non-aqueous electrolyte secondary battery.

Claims

1. It includes a current collector, a first active material layer, a second active material layer, and a third active material layer in this order. Each of the first active material layer and the third active material layer independently comprises at least one of natural graphite and artificial graphite. The second active material layer comprises natural graphite and a Si-based active material, The natural graphite in the second active material layer is oriented in the thickness direction of the second active material layer. Negative electrode for non-aqueous electrolyte secondary batteries.

2. The natural graphite in the second active material layer has an orientation angle of 30° or more, The orientation angle indicates the acute angle formed between the major axis diameter of the particle and the surface of the current collector. The negative electrode for a non-aqueous electrolyte secondary battery according to claim 1.

3. The first active material layer contains natural graphite, The third active material layer contains artificial graphite and natural graphite. i 1 <θ 3 <θ 2 The relationship is satisfied, Said θ 1 This indicates the orientation angle of natural graphite in the first active material layer. Said θ 2 This indicates the orientation angle of natural graphite in the second active material layer, and, Said θ 3 This indicates the orientation angle of natural graphite in the third active material layer. The negative electrode for a non-aqueous electrolyte secondary battery according to claim 2.

4. The first active material layer, the second active material layer, and the third active material layer each independently further include a binder. M B3 <M B1 <M B2 The relationship is satisfied, Said M B1 This indicates the mass fraction of the binder in the first active material layer. Said M B2 This indicates the mass fraction of the binder in the second active material layer, and, Said M B3 This indicates the mass fraction of the binder in the third active material layer. A negative electrode for a non-aqueous electrolyte secondary battery according to any one of claims 1 to 3.

5. It includes a current collector, a first active material layer, a second active material layer, and a third active material layer in this order. The first active material layer comprises natural graphite and a binder. The second active material layer comprises natural graphite, a Si-based active material, and a binder. The third active material layer comprises artificial graphite, natural graphite, and a binder. The natural graphite in the second active material layer has an orientation angle of 30° or more. The orientation angle refers to the acute angle formed between the major axis diameter of the particle and the surface of the current collector. i 1 <θ 3 <θ 2 The relationship is satisfied, Said θ 1 This indicates the orientation angle of natural graphite in the first active material layer. Said θ 2 This indicates the orientation angle of natural graphite in the second active material layer. Said θ 3 This indicates the orientation angle of natural graphite in the third active material layer. M B3 <M B1 <M B2 The relationship is satisfied, Said M B1 This indicates the mass fraction of the binder in the first active material layer. Said M B2 This indicates the mass fraction of the binder in the second active material layer. Said M B3 This indicates the mass fraction of the binder in the third active material layer. f 1 <φ 3 <φ 2 The relationship is satisfied, Said φ 1 This indicates the porosity of the first active material layer. Said φ 2 This indicates the porosity of the second active material layer, and Said φ 3 This indicates the porosity of the third active material layer. Negative electrode for non-aqueous electrolyte secondary batteries.

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