Negative electrode for nonaqueous electrolyte secondary battery

Abstract

The negative electrode for a non-aqueous electrolyte secondary battery comprises a negative electrode current collector and a negative electrode active material layer. The negative electrode active material layer is disposed on the surface of the negative electrode current collector. The negative electrode active material layer comprises a first layer and a second layer. The first layer is disposed between the negative electrode current collector and the second layer. The negative electrode active material layer comprises artificial graphite, natural graphite, and Si-based active materials as negative electrode active materials. The mass fraction of artificial graphite in the first layer is higher than that in the second layer. The mass fraction of natural graphite in the first layer is lower than that in the second layer. The mass fraction of Si-based active materials in the first layer is higher than that in the second layer.

Description

Technical Field

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

[0002] Japanese Patent Application Publication No. 2009-064574 discloses a multilayer structure in which a first negative electrode layer near the negative electrode current collector is made of artificial graphite, and a second negative electrode layer away from the negative electrode current collector is made of natural graphite. Summary of the Invention

[0003] Hereinafter, "negative electrode for non-aqueous electrolyte secondary batteries" can be abbreviated as "negative electrode". Multilayer negative electrode structures have been proposed. For example, one proposal involves placing artificial graphite in the lower layer near the negative electrode current collector and natural graphite in the upper layer away from the negative electrode current collector. By placing natural graphite, which has relatively good charging rate characteristics, near the positive electrode, improvements in charging rate characteristics can be expected. However, there is room for improvement in energy density and expansion.

[0004] The purpose of this invention is to improve the energy density and charging rate characteristics of the negative electrode, and to reduce the expansion of the negative electrode.

[0005] The technical structure and effects of the present invention will be described below. The mechanism of action includes inference. The mechanism of action does not limit the technical scope of the present invention.

[0006] 1. In the negative electrode of a non-aqueous electrolyte secondary battery according to one embodiment of the present invention,

[0007] It includes a negative electrode current collector and a negative electrode active material layer.

[0008] The negative electrode active material layer is disposed on the surface of the negative electrode current collector.

[0009] The negative electrode active material layer consists of a first layer and a second layer.

[0010] The first layer is positioned between the negative current collector and the second layer.

[0011] The negative electrode active material layer contains artificial graphite, natural graphite, and Si-based active materials as negative electrode active materials.

[0012] The mass fraction of artificial graphite in the first layer is higher than that in the second layer.

[0013] The mass fraction of natural graphite in the first layer is lower than that in the second layer.

[0014] The mass fraction of Si-based active material in the first layer is higher than that in the second layer.

[0015] To improve energy density, silicon-based active materials can be considered. However, silicon-based active materials may expand significantly during charging. The negative electrode active material layer may not be able to withstand the expansion of the silicon-based active material and may disintegrate. With the introduction of silicon-based active materials, measures to address the expansion are required. For example, to mitigate expansion while improving energy density, it is possible to consider mixing carbon-based active materials (artificial graphite, natural graphite) with silicon-based active materials.

[0016] Figure 1 This is a conceptual cross-sectional view representing the first multilayer structure. In the accompanying drawings of this invention, "NG" represents natural graphite. "AG" represents artificial graphite. "Si" represents Si-based active material. "Li" represents Li ions. The negative electrode includes a negative electrode current collector 21 and a negative electrode active material layer 22. The negative electrode active material layer 22 has a multilayer structure. In a multilayer structure intended to improve charging rate characteristics, artificial graphite can be disposed in the first layer 1 (lower layer), and natural graphite can be disposed in the second layer 2 (upper layer).

[0017] Figure 2 This is a conceptual cross-sectional view representing the second multi-layer structure. This is to maintain the first layer structure ( Figure 1 While improving the charging rate characteristics in the second-layer stacked structure, the energy density is also improved. Figure 2 In this process, Si-based active materials are evenly mixed in the first layer 1 and the second layer 2. However, in the second multilayer structure, the network structure between the natural graphite layers may be disrupted due to the expansion of the Si-based active materials in the second layer 2. As a result, the desired charging rate characteristics may not be obtained.

[0018] Figure 3 This is a conceptual cross-sectional view representing the third multi-layer structure. This is to maintain the first layer structure ( Figure 1 While improving the charging rate characteristics in the third-layer stacked structure, the energy density is also improved. Figure 3 In this multilayer structure, natural graphite is placed in the second layer (upper layer), and Si-based active material is placed in the first layer (lower layer). In this third multilayer structure, the expansion of the Si-based active material in the thickness direction is mitigated. This is believed to be because natural graphite absorbs the expansion of the Si-based active material. However, due to the intense expansion of the Si-based active material in the in-plane direction, the laminated structure may not be able to be maintained. Furthermore, "in-plane direction" refers to any direction orthogonal to the thickness direction (Z-axis direction). The X-axis and Y-axis directions are examples of in-plane directions.

[0019] Figure 4 This is a conceptual cross-sectional view representing the fourth layer of the structure. Regarding the fourth layer structure ( Figure 4 ), in the third layer of the stacked structure ( Figure 3 In the second layer (upper layer), artificial graphite is replaced. In the fourth layer stack ( Figure 4 In this structure, charging rate characteristics cannot be expected, but it may be possible to mitigate the expansion of Si-based active materials. However, according to the novel insights of the present invention, artificial graphite tends to poorly absorb the expansion of Si-based active materials in the thickness direction. The fourth layer structure ( Figure 4 In this structure, the expansion amount may be greater than that of the third-layer stacked structure. Figure 3 )big.

[0020] Figure 5 This is a conceptual cross-sectional view representing the fifth layer of the structure. Regarding the fifth layer structure ( Figure 5 ), in the second layer of the stacked structure ( Figure 2 In the first layer 1 (lower layer), Si-based active material is biased. In the fifth layer structure, natural graphite is biased into the second layer 2 (upper layer), thereby expecting the desired charging rate characteristics. Moreover, according to the novel insights of the present invention, natural graphite has a tendency to readily absorb the expansion of Si-based active material in the thickness direction, and artificial graphite has a tendency to readily absorb the expansion of Si-based active material in the in-plane direction. Therefore, the expansion of Si-based active material in the first layer 1 (lower layer) in both the thickness direction and the in-plane direction can be synergistically absorbed. Therefore, it is expected that a negative electrode with high energy density and charging rate characteristics and reduced expansion can be provided in the fifth layer structure.

[0021] 2. The negative electrode for the non-aqueous electrolyte secondary battery described in item “1” above may, for example, include the following structure.

[0022] The negative electrode active material layer also contains a binder.

[0023] The mass fraction of the adhesive in the first layer is higher than that in the second layer.

[0024] In the first layer (lower layer), the relatively high mass fraction of the binder helps to prevent structural damage caused by the expansion of the Si-based active material. In the second layer (upper layer), the relatively low mass fraction of the binder allows for the expectation of improved charging rate characteristics.

[0025] 3. The negative electrode for a non-aqueous electrolyte secondary battery described in item “1” or “2” above may, for example, include the following structure.

[0026] The negative electrode active material layer also includes a binder layer.

[0027] An adhesive layer is disposed between the first layer and the second layer.

[0028] The mass fraction of adhesive in the adhesive layer is higher than that in the first and second layers.

[0029] Because the Si-based active material is biased towards the first (lower) layer, a difference in expansion may occur between the first and second layers. This mismatch in expansion can also lead to interlayer delamination. It is desirable that the adhesive layer between the first and second layers absorb this expansion mismatch and prevent interlayer delamination.

[0030] 4. The negative electrode for a non-aqueous electrolyte secondary battery, as described in any one of items “1” to “3” above, may, for example, include the following structure.

[0031] The porosity of the first layer is higher than that of the second layer.

[0032] Since the first layer has relatively high porosity, it is expected to mitigate expansion. This is believed to be because the pores can absorb the expansion of the Si-based active material. Since the second layer has relatively low porosity, it is expected to improve the charging rate characteristics.

[0033] 5. In the negative electrode of a non-aqueous electrolyte secondary battery according to one aspect of the present invention,

[0034] It includes a negative electrode current collector and a negative electrode active material layer.

[0035] The negative electrode active material layer is disposed on the surface of the negative electrode current collector.

[0036] The negative electrode active material layer includes a first layer, a second layer, and a binder layer.

[0037] The first layer is positioned between the negative current collector and the second layer.

[0038] The negative electrode active material layer contains negative electrode active material and binder.

[0039] The negative electrode active material in the first layer is actually composed of artificial graphite and Si-based active materials.

[0040] The negative electrode active material in the second layer is actually composed of natural graphite.

[0041] Natural graphite has a larger aspect ratio than synthetic graphite.

[0042] The porosity of the first layer is higher than that of the second layer.

[0043] The mass fraction of the adhesive in the first layer is higher than that in the second layer.

[0044] An adhesive layer is disposed between the first layer and the second layer.

[0045] The mass fraction of adhesive in the adhesive layer is higher than that in the first and second layers.

[0046] Hereinafter, one embodiment of the present invention (hereinafter referred to as "this embodiment") will be described. However, this embodiment and this example do not limit the technical scope of the present invention. This embodiment and this example are illustrative in all respects. This embodiment and this example are non-limiting. The technical scope of the present invention includes all modifications within the meaning and scope equivalent to the claims. For example, it is contemplated from the outset that any structure can be extracted from this embodiment and combined arbitrarily. Attached Figure Description

[0047] Hereinafter, with reference to the accompanying drawings, the features, advantages, and technical and industrial significance of exemplary embodiments of the present invention will be described, in which the same reference numerals denote the same elements, and wherein:

[0048] Figure 1 This is a conceptual cross-sectional view representing the first multi-layer structure.

[0049] Figure 2 This is a conceptual cross-sectional view representing the second multi-layer structure.

[0050] Figure 3 This is a conceptual cross-sectional view representing the third layer of the structure.

[0051] Figure 4 This is a conceptual cross-sectional view representing the fourth layer of the structure.

[0052] Figure 5 This is a conceptual cross-sectional view representing the fifth layer of the structure.

[0053] Figure 6 This is a conceptual diagram illustrating an example of a non-aqueous electrolyte secondary battery in this embodiment.

[0054] Figure 7 This is a cross-sectional view illustrating the concept of orientation angle. Detailed Implementation

[0055] Terms and statements

[0056] The terms "possessing," "comprises," "have," and their variations are open-ended expressions. Structures using open-ended expressions may include additional requirements in addition to essential ones, or they may not include additional requirements. The statement "consisting of ~" is a closed-ended expression. However, even structures using closed-ended expressions may include commonly implied impurities or additional requirements unrelated to the target technology. The statement "substantially constituted of ~" is a semi-closed-ended expression. In structures using semi-closed-ended expressions, it is permissible to add requirements that do not substantially affect the fundamental and novel characteristics of the target technology.

[0057] Geometric terms should not be interpreted in a strict sense. As geometric terms, they may represent, for example, "parallel," "perpendicular," and "orthogonal." For instance, directions, angles, and distances can be relative displacements within a range that achieves substantially the same or similar function. Geometric terms may also encompass tolerances and errors in design, operation, and manufacturing. Dimensional relationships in drawings may sometimes differ from actual dimensional relationships. To aid understanding, dimensional relationships in drawings may be altered. For example, length, width, and thickness may be changed. Sometimes, parts of the structure may be omitted.

[0058] "Artificial graphite" refers to graphite synthesized through artificial heat treatment. Artificial graphite is also called synthetic graphite (SD). "Natural graphite" refers to graphite that occurs naturally. Natural graphite includes flake graphite. Flake graphite can be curled by bending the ends of the particles. Natural graphite can be coated, for example, with amorphous carbon. "Si-based active materials" include Si (or Si compounds, Si alloys, etc.) capable of forming alloys with Li. Si-based active materials 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 Si (or SiO) and carbon. For example, Si can be loaded into carbon materials.

[0059] The "particle size" is determined by microscopy. The particle size is represented by the arithmetic mean of the long and short sides of the smallest bounding rectangle (MBR) of the particle's two-dimensional image. The "average particle size" is the arithmetic mean of 100 particle sizes. Furthermore, various image analyses in this embodiment can be performed using software. For example, software such as "ImageJ" can be used.

[0060] "Aspect Ratio" refers to the ratio of the long side to the short side of the MBR. It is calculated using the arithmetic mean of 100 aspect ratios.

[0061] "Basis Weight" refers to the mass per unit area.

[0062] Porosity is determined using image analysis. The cross-sectional scanning electron microscope (SEM) images of each layer are binarized to distinguish between pores and solids. The porosity is calculated by dividing the total area of ​​the pores (total pixels) by the total area of ​​the layer.

[0063] Non-aqueous electrolyte secondary battery

[0064] Figure 6This is a conceptual diagram illustrating an example of a non-aqueous electrolyte secondary battery according to this embodiment. The non-aqueous electrolyte secondary battery 100 may include, for example, a power generation element 50 and a casing 60. The casing 60 houses the power generation element 50. The casing 60 may be, for example, a metal container, an aluminum laminated bag, 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 unipolar structure or a bipolar structure. The separator 30 can electrically separate the positive electrode 10 and the negative electrode 20. The separator 30 may, for example, be a porous membrane made of resin. The non-aqueous electrolyte is a Li ion conductor. The non-aqueous electrolyte may, for example, contain Li salts and organic solvents. The non-aqueous electrolyte may, for example, be impregnated in the separator 30. The non-aqueous electrolyte may, for example, contain a gel electrolyte, a solid electrolyte (oxide solid electrolyte, sulfide solid electrolyte), etc. The positive electrode 10 contains a positive electrode active material. Positive electrode active materials may include, for example, lithium transition metal composite oxides (Li[NiCoMn]O2), lithium phosphate compounds (Li[FeMn]PO4), etc. Furthermore, the description of [NiCoMn], [FeMn], etc., indicates that the total composition ratio of the components within [ ] is "1". As long as the total is 1, the composition ratio of each component is arbitrary. For example, the composition ratio of some components can be zero.

[0065] negative electrode

[0066] The negative electrode 20 can be, for example, in sheet form. Figure 5 As shown, the negative electrode 20 includes a negative electrode current collector 21 and a negative electrode active material layer 22. The negative electrode active material layer 22 is disposed on the surface of the negative electrode current collector 21. The negative electrode active material layer 22 may be disposed on a portion of the surface of the negative electrode current collector 21, or it may be disposed on the entire surface. The negative electrode active material layer 22 may be disposed on only one side of the negative electrode current collector 21, or it may be disposed on both sides of the negative electrode current collector 21. The negative electrode current collector 21 may, for example, include a metal foil (Cu foil, Ni foil, etc.), a conductive resin layer, etc. The negative electrode current collector 21 may, for example, have a thickness of 1 μm to 100 μm.

[0067] Negative electrode active material layer

[0068] The negative electrode active material layer 22 has a multilayer structure. The negative electrode active material layer 22 includes a first layer 1 and a second layer 2. As long as it includes a first layer 1 and a second layer 2, the negative electrode active material layer 22 may also include any other layer. For example, an adhesive layer 3 (described later) may be disposed between the first layer 1 and the second layer 2. For example, a conductive layer or a sealing layer (neither shown) may be disposed between the first layer 1 and the negative electrode current collector 21. For example, a ceramic particle layer (not shown) may be disposed on the surface of the second layer 2. The ceramic particle layer may, for example, include heat-resistant ceramics (alumina, boehmite), etc.

[0069] The layers contained in the negative electrode active material layer 22 may be, for example, coating layers. A coating layer refers to a layer formed by applying a coating material. The coating materials may be applied substantially simultaneously or sequentially.

[0070] The first layer 1 is disposed between the negative current collector 21 and the second layer 2. The first layer 1 can be formed directly on the surface of the negative current collector 21, for example. The second layer 2 can be formed on the surface of the negative active material layer 22, for example. The second layer 2 can be formed directly on the surface of the first layer 1.

[0071] Each layer can have any thickness. For example, let the thickness of layer 1 be "T1" and the thickness of layer 2 be "T2". In this case, "T1" and "T2" can 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" can be, for example, 10μm or more, 50μm or more, 100μm or more, 200μm or more, or 500μm or more. The thickness "T1" can also be less than 1mm, less than 500μm, or less than 200μm.

[0072] Each layer can have any weight per unit area. For example, let the weight per unit area of ​​layer 1 be "W1" and the weight per unit area of ​​layer 2 be "W2". In this case, "W1" and "W2" can 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 weight per unit area "W1" can be, for example, 1 mg / cm³. 2 Above, 5mg / cm 2 Above, 10mg / cm 2 Above or 20 mg / cm 2 The above. The weight per unit area "W1" can be, for example, 50 mg / cm³. 2 Below, 30mg / cm 2 Below, 25mg / cm 2 Below, 15mg / cm 2 Below or 10 mg / cm 2 the following.

[0073] The porosity of the negative electrode active material layer 22 can be approximately constant throughout the entire region. However, the porosity can vary locally. For example, the porosity "φ1" of the first layer 1 can be higher than the porosity "φ2" of the second layer 2. That is, the relationship "φ2 < φ1" and "1 < φ1 / φ2" can be satisfied. The ratio "φ1 / φ2" can be, for example, 1.2 or higher, 1.5 or higher, 2 or higher, or 2.5 or higher. Conversely, the ratio "φ1 / φ2" can be, for example, less than 5, less than 3, or less than 2.

[0074] Negative electrode active material

[0075] The negative electrode active material layer 22 contains a negative electrode active material. The negative electrode active material layer 22 may further contain, for example, conductive materials, adhesives, etc. The negative electrode active material layer 22 may, for example, contain 0 to 10% adhesive, 0 to 10% conductive material, and the remainder of negative electrode active material by mass fraction. The negative electrode active material layer 22 may, for example, contain 0.1 to 3% adhesive, 0 to 3% conductive material, and the remainder of negative electrode active material by mass fraction. The negative electrode active material layer 22 may, for example, contain 0.5% to 2% adhesive, 0.5% to 2% conductive material, and the remainder of negative electrode active material by mass fraction.

[0076] The negative electrode active material includes artificial graphite, natural graphite, and Si-based active materials. In addition to artificial graphite, natural graphite, and Si-based active materials, the negative electrode active material may further include other active materials. These other active materials may include lithium titanate, Sn-based alloys, SnO, pure Li, and Li-based alloys.

[0077] Artificial graphite is biased into layer 1. The mass fraction of artificial graphite in layer 1 is "M". 1A "The mass fraction of artificial graphite higher than that in layer 2" M 2A That is, satisfying "M" 2A <M 1A “1 < M” 1A / M 2A The relationship is "". It is more related to "M". 1A / M 2A "For example, it can be 1.5 or higher, 2 or higher, 3 or higher, 5 or higher, 10 or higher, 50 or higher, or 100 or higher. Compared to 'M'..." 1A / M 2A "For example, it can be below 1000 or below 100. Mass fraction" M 1A "For example, it can be 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. Quality fraction "M" 1A "For example, it can be below 100%, below 99%, below 98%, or below 95%."

[0078] Natural graphite is biased into layer 2. The mass fraction of natural graphite in layer 1 is "M". 1N "The mass fraction of natural graphite in layer 2" M 2N "Low. That is, satisfying "M" 1N <M 2N “M” 1N / M 2N The relationship is <1. Compared to "M" 1N / M 2N "For example, it can be below 0.9, below 0.5, below 0.3, below 0.1, or below 0.01. Compared to 'M'..." 1N / M 2N "For example, it can be above 0, above 0.001, above 0.01, or above 0.1. Mass fraction "M" 2N "For example, it can be 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. Quality fraction "M" 2N "For example, it can be below 100%, below 99%, below 98%, or below 95%."

[0079] The Si-based active material is biased into the first layer 1. The mass fraction of the Si-based active material in the first layer 1 is "M". 1S "The mass fraction of Si-based active material in the second layer 2" M 2S "High. That is, satisfying "M" 2S <M 1S “1 < M” 1S / M 2S The relationship is "". It is more related to "M". 1S / M 2S "For example, it can be 1.5 or higher, 2 or higher, 3 or higher, 5 or higher, 10 or higher, 50 or higher, or 100 or higher. Compared to 'M'..." 1S / M 2S "For example, it can be below 1000 or below 100. Mass fraction" M 1S "For example, it can be 3% or higher, 5% or higher, 10% or higher, 20% or higher, 30% or higher, 40% or higher, 50% or higher, 60% or higher, 70% or higher, 80% or higher, 90% or higher, 95% or higher, 98% or higher, or 99% or higher. Quality fraction "M" 1S "For example, it can be below 100%, below 99%, below 98%, below 95%, below 90%, below 80%, below 70%, below 60%, below 50%, below 40%, below 30%, below 20%, below 10%, or below 5%."

[0080] As mentioned above, as long as "M" is satisfied 2A <M1A “M” 1N <M 2N "and M" 2S <M 1S Given the relationship between the first layer (1) and the second layer (2), each layer can independently contain artificial graphite, natural graphite, and Si-based active materials. For example, the negative electrode active material in the first layer (1) can be substantially composed of artificial graphite and Si-based active materials. Similarly, the negative electrode active material in the second layer (2) can be substantially composed of natural graphite.

[0081] For example, in layer 1, let the mass fraction of artificial graphite be "M". 1A "and the mass fraction of Si-based active materials" M 1S At this time, "M" 1A “M” 1S "Can satisfy "M" 1A / M 1S =1 / 9 to 9 / 1", M 1A / M 1S =2 / 8 to 8 / 2", M 1A / M 1S =3 / 7 to 7 / 3", M 1A / M 1S =4 / 6 to 6 / 4” and other relationships.

[0082] The average particle size of artificial graphite is "d A The average particle size of natural graphite is d. N "and the average particle size of Si-based active materials" S "Each can independently take any value. For example, it can satisfy "d" S <d A The relationship is "". It is more related to "d". S / d A "For example, it can be below 0.8, below 0.6, below 0.4, or below 0.2. Compared to 'd'..." S / d A "For example, it can be above 0.1. Compared to 'd'..." A / d N "For example, it can be 0.5 or higher, 1 or higher, or 2 or higher. Compared to 'd'..." A / d N "For example, it can be less than 2, less than 1, or less than 0.5. Average particle size d" A "For example, it can be 1μm or larger, 5μm or larger, 10μm or larger, 15μm or larger, or 20μm or larger. Average particle size 'd'" A "For example, it can be below 30μm, below 25μm, below 20μm, or below 15μm."

[0083] Artificial graphite, natural graphite, and Si-based active materials can each independently possess arbitrary particle shapes. Particle shapes can be, for example, spherical, ellipsoidal, or flattened. For instance, the aspect ratio of natural graphite is "R". N "It can be compared to the aspect ratio of artificial graphite"R A "Large. For example, it can satisfy "1 < R" N / R A Relationships such as ≤5. The aspect ratio of natural graphite is "R". N "For example, it can be 1.5 or higher, 2 or higher, or 3 or higher. The aspect ratio of natural graphite is 'R'." N "For example, it can be below 5. The aspect ratio of artificial graphite is "R". A "For example, it can be less than 1.5, 1.4 or less, 1.3 or less, 1.2 or less, or 1.1 or less. The aspect ratio of artificial graphite is 'R'." A "For example, it can be 1 or more."

[0084] When the natural graphite has an aspect ratio greater than 1, the natural graphite in the second layer 2 can be oriented in the in-plane direction (lateral direction). With the natural graphite in the second layer 2 oriented in the in-plane direction, it is expected that the expansion of the Si-based active material contained in the first layer 1 will be easily absorbed. The degree of orientation can be evaluated by the orientation angle "θ". Figure 7 This is a cross-sectional view illustrating the concept of orientation angle. The orientation angle "θ" is the acute angle (angle) formed by the major axis "L" of the natural graphite (particle) and the surface of the negative electrode current collector 21 in the cross-sectional SEM image of the negative electrode 20. The major axis is the extension of the particle's maximum Feret diameter. It can be evaluated that the smaller the orientation angle "θ", the more laterally oriented the particles. The orientation angle "θ" can be, for example, less than 45°, less than 30°, less than 15°, or less than 5°. The orientation angle "θ" can also be, for example, greater than 0°, greater than 1°, or greater than 3°.

[0085] adhesives

[0086] The adhesive may include, for example, styrene-butadiene rubber (SBR), carboxymethyl cellulose (CMC), polyacrylic acid (PAA), polytetrafluoroethylene (PTFE), etc. The mass fraction of the adhesive can be approximately constant throughout the entire region of the negative electrode active material layer 22. The mass fraction of the adhesive may vary locally. For example, the mass fraction of the adhesive may differ between layer 1 and layer 2. For example, the mass fraction of the adhesive in layer 1 may be "M". 1B "The mass fraction of the adhesive in the second layer 2 can be compared to "M" 2B "High. That is, it can satisfy "M" 2B <M 1B “1 < M” 1B / M 2B The relationship is "". It is more related to "M". 1B / M2B "For example, it can be 1.2 or higher, 1.5 or higher, 2 or higher, 2.5 or higher. Compared to 'M'..." 1B / M 2B "For example, it can be 3 or less or 2 or less."

[0087] For example, an adhesive layer 3 may be formed between the first layer 1 and the second layer 2. The mass fraction of the adhesive in the adhesive layer 3 is higher than that of the adhesives in the first layer 1 and the second layer 2. The adhesive layer 3 may be a layer that substantially does not contain any negative electrode active material. The adhesive layer 3 may, for example, contain 0 to 10% conductive material and the remainder adhesive by mass fraction. The adhesive layer 3 may, for example, contain 1% to 5% conductive material and the remainder adhesive by mass fraction. For example, the type of adhesive between each layer may be the same. For example, the type of adhesive between each layer may be different. For example, the adhesive in the adhesive layer 3 may contain a resin that swells due to the electrolyte. For example, the adhesive in the adhesive layer 3 may contain an ion-permeable resin, an ion-conducting resin, etc. By allowing the electrolyte and Li ions to permeate the adhesive layer 3, an improvement in charging rate characteristics can be expected. For example, the adhesive in the adhesive layer 3 may contain a fibrous resin. The fibrous resin may be extended in a manner that crosslinks the first layer 1 and the second layer 2. By crosslinking the first layer 1 and the second layer 2 with a fibrous resin, improvements in peel strength, for example, can be expected. The adhesive in the adhesive layer 3 may, for example, contain at least one selected from the group consisting of PAA, polyacrylate, CMC, alginate, polyvinylidene fluoride (PVDF), poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP), and PTFE. For example, PAA, PVDF, PVDF-HFP, etc., can possess swelling properties, ion permeability, ion conductivity, etc. For example, PTFE may be fibrous.

[0088] The thickness "T3" of adhesive layer 3 can, for example, be smaller than the thickness "T1" of layer 1 and the thickness "T2" of layer 2. The thickness "T3" of adhesive layer 3 can, for example, be less than 10 μm, less than 5 μm, or less than 3 μm. The thickness "T3" of adhesive layer 3 can, for example, be more than 0.5 μm, more than 1 μm, or more than 3 μm. The area weight "W3" of adhesive layer 3 can, for example, be smaller than the area weight "W1" of layer 1 and the area weight "W2" of layer 2. The area weight "W3" of adhesive layer 3 can, for example, be 5 mg / cm³. 2 Below, 3mg / cm 2 Below or 1 mg / cm 2 The following is an example of the adhesive layer 3's unit area weight "W3", which can be 0.1 mg / cm³. 2 Above or 0.5 mg / cm 2 above.

[0089] conductive materials

[0090] The conductive material may include, for example, acetylene black, carbon nanotubes (CNTs), and vapor-grown carbon fibers (VGCF). The mass fraction of the conductive material can be approximately constant throughout the entire region of the negative electrode active material layer 22. The mass fraction of the conductive material may vary locally. For example, the mass fraction of the conductive material may differ between layers. For example, the types of conductive materials may differ between layers. For example, the adhesive layer 3 may contain a fibrous conductive material. The adhesive layer 3 may, for example, contain at least one material selected from the group consisting of CNTs and VGCF. The fibrous conductive material may be extended in a manner that crosslinks the first layer 1 and the second layer 2. By crosslinking the first layer 1 and the second layer 2 with the fibrous conductive material, for example, improvements in charge rate characteristics and peel strength can be expected.

Claims

1. A negative electrode for a non-aqueous electrolyte secondary battery, characterized in that, It includes a negative electrode current collector and a negative electrode active material layer. The negative electrode active material layer is disposed on the surface of the negative electrode current collector. The negative electrode active material layer comprises a first layer and a second layer. The first layer is disposed between the negative current collector and the second layer. The negative electrode active material layer comprises artificial graphite, natural graphite, and Si-based active materials as negative electrode active materials. The mass fraction of the artificial graphite in the first layer is higher than the mass fraction of the artificial graphite in the second layer. The mass fraction of natural graphite in the first layer is lower than that in the second layer, and The mass fraction of the Si-based active material in the first layer is higher than that in the second layer.

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

3. The negative electrode for a non-aqueous electrolyte secondary battery according to claim 2, characterized in that, The negative electrode active material layer also includes an adhesive layer. The adhesive layer is disposed between the first layer and the second layer. The mass fraction of the adhesive in the adhesive layer is higher than the mass fraction of the adhesive in the first layer and the second layer.

4. The negative electrode for a non-aqueous electrolyte secondary battery according to any one of claims 1 to 3, characterized in that, The porosity of the first layer is higher than that of the second layer.

5. A negative electrode for a non-aqueous electrolyte secondary battery, characterized in that, It includes a negative electrode current collector and a negative electrode active material layer. The negative electrode active material layer is disposed on the surface of the negative electrode current collector. The negative electrode active material layer comprises a first layer, a second layer, and a binder layer. The first layer is disposed between the negative current collector and the second layer. The negative electrode active material layer comprises a negative electrode active material and a binder. The negative electrode active material in the first layer is essentially composed of artificial graphite and Si-based active materials. The negative electrode active material in the second layer is essentially composed of natural graphite. The natural graphite has a larger aspect ratio than the artificial graphite. The porosity of the first layer is higher than that of the second layer. The mass fraction of the adhesive in the first layer is higher than the mass fraction of the adhesive in the second layer. The adhesive layer is disposed between the first layer and the second layer, and The mass fraction of the adhesive in the adhesive layer is higher than the mass fraction of the adhesive in the first layer and the second layer.

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