Nonaqueous-electrolyte secondary battery negative electrode and nonaqueous-electrolyte secondary battery

Abstract

The present invention is characterized by having a negative electrode core body (40) and a negative electrode mixture layer (41) disposed on the negative electrode core body (40), the negative electrode mixture layer (41) including a first negative electrode mixture layer (43) disposed on the surface of the negative electrode core body (40) and a second negative electrode mixture layer (44) disposed on the surface of a negative electrode (12), the porosity of the second negative electrode mixture layer (44) being greater than the porosity of the first negative electrode mixture layer (43), and a recess (50) recessed in the thickness direction of a negative electrode mixture layer 42 being provided on the surface of the negative electrode mixture layer (42).

Description

Negative electrode for non-aqueous electrolyte secondary battery and non-aqueous electrolyte secondary battery

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

[0002] Non-aqueous electrolyte secondary batteries are widely used as high-energy-density secondary batteries. A non-aqueous electrolyte secondary battery comprises, for example, an electrode body in which a positive electrode and a negative electrode are wound with a separator in between, a non-aqueous electrolyte, and an outer casing that houses the electrode body and the non-aqueous electrolyte. The positive electrode and the negative electrode also have a core body and a composite layer disposed on the surface of the core body. Patent Document 1 discloses a technique for providing a plurality of circular holes in plan view on the surface of the composite layer in order to reduce internal resistance.

[0003] Japanese Patent Publication No. 2021-190288

[0004] In recent years, with the increasing adoption of non-aqueous electrolyte secondary batteries in automotive and energy storage applications, there has been a growing demand for non-aqueous electrolyte secondary batteries with high energy density and excellent charge-discharge cycle characteristics. In non-aqueous electrolyte secondary batteries equipped with wound electrode bodies, repeated rapid charge-discharge cycles tend to push the non-aqueous electrolyte outwards at both axial ends of the electrode body due to volume changes in the electrode plates. This can lead to a decrease in the concentration of electrolyte salts at both axial ends of the electrode body, causing lithium deposition at the negative electrode at both axial ends and potentially degrading the charge-discharge cycle characteristics.

[0005] A negative electrode for a non-aqueous electrolyte secondary battery according to one aspect of the present disclosure is a negative electrode for a non-aqueous electrolyte secondary battery having a negative electrode core and a negative electrode mixture layer disposed on the negative electrode core, wherein the negative electrode mixture layer includes a first negative electrode mixture layer disposed on the surface of the negative electrode core and a second negative electrode mixture layer disposed on the surface of the negative electrode, wherein the porosity of the second negative electrode mixture layer is greater than that of the first negative electrode mixture layer, and the surface of the negative electrode mixture layer is provided with recesses that are indented in the thickness direction of the negative electrode mixture layer.

[0006] According to one aspect of this disclosure, a negative electrode for a non-aqueous electrolyte secondary battery can provide a non-aqueous electrolyte secondary battery with high energy density and excellent charge-discharge cycle characteristics.

[0007] This is an axial cross-sectional view of a non-aqueous electrolyte secondary battery, which is one example of an embodiment. This is a perspective view of the electrode body of a non-aqueous electrolyte secondary battery, which is one example of an embodiment. This is a cross-sectional view of the negative electrode of a non-aqueous electrolyte secondary battery, which is one example of an embodiment. This is a diagram showing the negative electrode of a non-aqueous electrolyte secondary battery, which is one example of an embodiment, in an unfolded state. This is a diagram showing the negative electrode of a non-aqueous electrolyte secondary battery, which is another example of an embodiment, in an unfolded state. This is a diagram showing the negative electrode of a non-aqueous electrolyte secondary battery, which is yet another example of an embodiment, in an unfolded state.

[0008] Hereinafter, an example of an embodiment of a non-aqueous electrolyte secondary battery according to this disclosure will be described in detail with reference to the drawings. Note that configurations obtained by selectively combining the components of the multiple embodiments and modified examples described below are included within the scope of this disclosure.

[0009] In the following, a cylindrical battery in which a wound electrode body 14 is housed in a bottomed cylindrical outer casing 15 is given as an example of a non-aqueous electrolyte secondary battery, but the battery's outer casing is not limited to a cylindrical shape. The non-aqueous electrolyte secondary battery according to this disclosure may be, for example, a rectangular battery with a rectangular outer casing. The electrode body may also be a wound electrode body formed into a flat shape.

[0010] Referring to Figures 1 and 2, the configuration of a non-aqueous electrolyte secondary battery 10, which is an example of an embodiment, will be described. Figure 1 is a schematic diagram showing a cross-section of the non-aqueous electrolyte secondary battery 10, and Figure 2 is a perspective view of the electrode body 14 that constitutes the non-aqueous electrolyte secondary battery 10.

[0011] As shown in Figures 1 and 2, the non-aqueous electrolyte secondary battery 10 comprises an electrode body 14 in which a positive electrode 11 and a negative electrode 12 are wound around a separator 13, a non-aqueous electrolyte (not shown), an outer casing 15 that houses the electrode body 14 and the non-aqueous electrolyte, and a sealing body 16 that closes the opening of the outer casing 15. In this specification, the side of the non-aqueous electrolyte secondary battery 10 with the sealing body 16 is referred to as "upper," and the bottom side of the outer casing 15 is referred to as "lower."

[0012] The electrode body 14 has a positive electrode 11, a negative electrode 12, and a separator 13, and the positive electrode 11 and the negative electrode 12 are wound in a spiral shape via the separator 13. The positive electrode 11, the negative electrode 12, and the separator 13 that make up the electrode body 14 are all elongated strips, and are alternately stacked in the radial direction of the electrode body 14 by being wound in a spiral shape. The positive electrode 11 protrudes above the negative electrode 12 and the separator 13, and the negative electrode 12 protrudes below the positive electrode 11 and the separator 13. For example, two separators 13 are arranged so as to sandwich the positive electrode 11.

[0013] The positive electrode 11 comprises a positive electrode core 30 and a positive electrode mixture layer 31 formed on the positive electrode core 30. The positive electrode core 30 can be made of a metal foil that is stable within the potential range of the positive electrode 11, such as aluminum or an aluminum alloy, or a film with the metal arranged on its surface. The positive electrode mixture layer 31 contains a positive electrode active material, a conductive agent, and a binder, and is formed on both sides of the positive electrode core 30, excluding the non-mixture layer portion 32, which will be described later. The positive electrode 11 can be manufactured, for example, by applying a positive electrode mixture slurry containing a positive electrode active material, a conductive agent, and a binder onto the positive electrode core 30, drying the coating, and then compressing it to form the positive electrode mixture layer 31 on both sides of the positive electrode core 30.

[0014] The positive electrode composite layer 31 contains particulate lithium metal composite oxide as the positive electrode active material. The lithium metal composite oxide is a composite oxide containing metal elements such as Co, Mn, Ni, and Al in addition to Li. The metal elements constituting the lithium metal composite oxide are, for example, at least one selected from Mg, Al, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, Y, Zr, Sn, Sb, W, Pb, and Bi. Among these, it is preferable to contain at least one selected from Co, Ni, and Mn. Examples of suitable composite oxides include lithium metal composite oxides containing Ni, Co, and Mn, or lithium metal composite oxides containing Ni, Co, and Al.

[0015] Examples of conductive agents included in the positive electrode mixture layer 31 include carbon black such as acetylene black and Ketjenblack, graphite, carbon nanotubes (CNTs), carbon nanofibers, and graphene. Examples of binders included in the positive electrode mixture layer 31 include fluororesins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF), polyacrylonitrile (PAN), polyimide, acrylic resins, and polyolefins. In addition, these resins may be used in combination with carboxymethylcellulose (CMC) or its salts, polyethylene oxide (PEO), etc.

[0016] As shown in Figures 1 and 2, the positive electrode 11 has a non-compound layer portion 32 at the upper axial end of the electrode body 14, where the positive electrode compound layer 31 is not provided on the positive electrode core body 30. The non-compound layer portion 32 is provided over the range from the beginning end to the end end of the winding in the longitudinal direction of the elongated positive electrode 11. The non-compound layer portion 32 is bent radially inward and welded to the lower surface of the positive electrode current collector plate 17. By joining the non-compound layer portion 32 to the positive electrode current collector plate 17, the contact area between the non-compound layer portion 32 and the positive electrode current collector plate 17 is increased, so the internal resistance of the positive electrode 11 can be reduced compared to when the positive electrode 11 and the positive electrode current collector plate 17 are connected by a positive electrode tab or the like.

[0017] As will be described in more detail later, the negative electrode 12 has a negative electrode core 40 and a negative electrode mixture layer 41 formed on the negative electrode core 40. The negative electrode 12 can be manufactured by applying a negative electrode mixture slurry containing a negative electrode active material and a binder to the surface of the negative electrode core 40, drying the coating film, and then compressing it to form the negative electrode mixture layer 41 on both sides of the negative electrode core 40.

[0018] As shown in Figures 1 and 2, the negative electrode 12 has a non-compound layer portion 42 at the lower axial end of the electrode body 14 where the negative electrode compound layer 41 is not provided on the negative electrode core body 40. The non-compound layer portion 42 is provided over the range from the beginning end to the end end of the winding in the longitudinal direction of the elongated negative electrode 12, similar to the case of the positive electrode 11. The non-compound layer portion 42 is bent radially inward at its lower end and welded to the negative electrode current collector plate 18. In addition, the non-aqueous electrolyte secondary battery 10 may not have a negative electrode current collector plate 18, and the non-compound layer portion 42 may be directly joined to the inner surface of the bottom plate of the outer casing 15.

[0019] A porous sheet having ion permeability and insulating properties is used for the separator 13. Specific examples of porous sheets include microporous thin films, woven fabrics, and nonwoven fabrics. Suitable materials for the separator 13 include polyethylene, polyolefins such as polypropylene, and cellulose. The separator 13 may have a single-layer structure or a multi-layer structure. A heat-resistant resin layer, such as aramid resin, may be formed on the surface of the separator 13. A filler layer containing an inorganic filler may be formed at the interface between the separator 13 and at least one of the positive electrode 11 and the negative electrode 12.

[0020] Non-aqueous electrolytes (electrolytes) are lithium ion conductive. Non-aqueous electrolytes consist of a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent. Examples of non-aqueous solvents include esters, ethers, nitriles, amides, and mixtures of two or more of these. Examples of non-aqueous solvents include ethylene carbonate (EC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and mixtures thereof. Non-aqueous solvents may also contain halogen-substituted solvents (e.g., fluoroethylene carbonate) in which at least some of the hydrogen atoms of these solvents are replaced with halogen atoms such as fluorine.

[0021] For example, lithium salts are used as electrolyte salts. LiClO ４ LiBF ４ LiPF ６ LiAlCl４ , LiSbF ６ , LiSCN, LiCF ３ SO ３ , LiCF ３ CO ２ , LiAsF ６ , LiB １０ Cl １０ , lower aliphatic carboxylic acid lithium, LiCl, LiBr, LiI, phosphates, borates, and imide salts. Examples of the phosphate include lithium difluorophosphate (LiPO ２ F ２ ), lithium difluorobis(oxalato) phosphate (LiDFBOP), lithium tetrafluoro(oxalato) phosphate, and the like. Examples of the borate include lithium bis(oxalato) borate (LiBOB), lithium difluoro(oxalato) borate (LiDFOB), and the like. Examples of the imide salt include lithium bis(fluorosulfonyl)imide (LiN(FSO ２ ) ２ ), lithium bis(trifluoromethanesulfonyl)imide (LiN(CF ３ SO ２ ) ２ ), lithium trifluoromethanesulfonyl nonafluorobutanesulfonyl imide (LiN(CF ３ SO ２ )(C ４ F ９ SO ２ )), lithium bis(pentafluoroethanesulfonyl)imide (LiN(C ２ F ５ SO ２ ) ２ ) and the like are used. Among these, from the viewpoints of ion conductivity, electrochemical stability, etc., LiPF ６ is preferably used. The concentration of the lithium salt may be, for example, 4 mol or less per 1 L of the non-aqueous solvent, may be 3 mol or less, preferably 2 mol or less, more preferably 0.8 mol or more and 1.8 mol or less.

[0022] Furthermore, the non-aqueous electrolyte may contain additives. Examples of additives include unsaturated carbonate esters, acid anhydrides, phenol compounds, benzene compounds, nitrile compounds, isocyanate compounds, sultone compounds, sulfuric acid compounds, boric acid ester compounds, phosphate ester compounds, and phosphite ester compounds.

[0023] The outer container 15 is a bottomed cylindrical metal container with one end open in the axial direction, and the opening of the outer container 15 is sealed by a sealing body 16.

[0024] A gasket 27 is provided between the outer casing 15 and the sealing body 16 to ensure airtightness inside the battery. The outer casing 15 has a grooved portion 21 formed on its side surface, which protrudes inward to support the sealing body 16. The grooved portion 21 is preferably formed in an annular shape along the circumferential direction of the outer casing 15, and its upper surface supports the sealing body 16. The sealing body 16 is fixed to the upper part of the outer casing 15 by the grooved portion 21 and the open end of the outer casing 15 which is crimped to the sealing body 16.

[0025] The sealing body 16 has a structure in which a filter 22, a lower valve body 23, an insulating member 24, an upper valve body 25, and a cap 26 are stacked in order from the electrode body 14 side. Each component constituting the sealing body 16 has, for example, a disc shape or a ring shape, and each component except the insulating member 24 is electrically connected to one another. The filter 22 has at least one through hole. The lower valve body 23 and the upper valve body 25 are connected at their respective centers, and the insulating member 24 is interposed between their respective peripheral edges.

[0026] When the non-aqueous electrolyte secondary battery 10 overheats abnormally and its internal pressure rises, the lower valve body 23 deforms and ruptures, pushing the upper valve body 25 towards the cap 26, thereby interrupting the current path between the lower valve body 23 and the upper valve body 25. If the internal pressure rises further, the upper valve body 25 ruptures, and gas is released from the through-hole 26a of the cap 26. This release of gas prevents the non-aqueous electrolyte secondary battery 10 from rupturing due to an excessive rise in internal pressure, thus improving the safety of the non-aqueous electrolyte secondary battery 10. The configuration of the sealing body 16 is not limited to this, as long as it can seal the opening of the outer casing 15.

[0027] The non-aqueous electrolyte secondary battery 10 includes a metal positive electrode current collector plate 17 on the upper side of an electrode assembly 14. The positive electrode current collector plate 17 is made of, for example, aluminum, an aluminum alloy, or the like. A mixture layer non-formed portion 32 of the positive electrode 11 is connected to the lower surface of the positive electrode current collector plate 17 by welding or the like. The shape of the positive electrode current collector plate 17 is not particularly limited. For example, it may have a disk shape, an annular shape, or a substantially cross shape. A positive electrode lead 20 is connected to the upper surface of the positive electrode current collector plate 17. The positive electrode lead 20 extends through a through hole of an insulating plate 19 toward the sealing body 16 side, and the upper end portion of the positive electrode lead 20 is connected to the lower surface of a filter 22 of the sealing body 16 by welding or the like. Accordingly, a cap 26 constituting the top plate of the sealing body 16 is electrically connected to the filter 22, and the cap 26 serves as the positive electrode terminal.

[0028] In addition, the non-aqueous electrolyte secondary battery 10 includes a metal negative electrode current collector plate 18 on the lower side of the electrode assembly 14. A mixture layer non-formed portion 42 of the negative electrode 12 is connected to the upper surface of the negative electrode current collector plate 18. Further, the negative electrode current collector plate 18 is joined to the inner surface of the bottom plate of an outer can 15. Accordingly, the outer can 15 electrically connected to the negative electrode 12 via the negative electrode current collector plate 18 serves as the negative electrode terminal.

[0029] Next, the negative electrode 12 will be described in detail with further reference to FIG. 3 and FIG. 4. FIG. 3 is a cross-sectional view of the negative electrode 12, and FIG. 4 is a diagram showing the negative electrode 12 in an unfolded state.

[0030] As shown in FIG. 3, the negative electrode 12 includes a negative electrode core 40 and a negative electrode mixture layer 41 disposed on the negative electrode core 40. The negative electrode mixture layer 41 includes a first negative electrode mixture layer 43 disposed on the surface of the negative electrode core 40, and a second negative electrode mixture layer 44 disposed on the surface of the negative electrode 12 and having a larger porosity than the first negative electrode mixture layer 43. That is, the negative electrode mixture layer 41 has a two-layer structure in which the first negative electrode mixture layer 43 and the second negative electrode mixture layer 44 are stacked in order from the negative electrode core 40 side. Hereinafter, the first negative electrode mixture layer 43 and the second negative electrode mixture layer 44 may be collectively referred to as the negative electrode mixture layer 41.

[0031] The negative electrode core 40 can be made of a metal foil that is stable within the potential range of the negative electrode 12, such as copper, or a film with such metal arranged on its surface. The thickness of the negative electrode core 40 is not particularly limited, but from the viewpoint of balancing the strength and weight reduction of the negative electrode 12, it is, for example, 5 μm or more and 30 μm or less. The negative electrode mixture layer 41 is preferably formed on both sides of the negative electrode core 40, excluding the non-mixture layer portion 42 (see Figure 4) provided at the lower end of the negative electrode 12.

[0032] The negative electrode mixture layer 41 contains a negative electrode active material, a binder, and optionally a conductive agent. Preferably, the negative electrode mixture layer 41 contains a carbon material and a silicon-containing material as the negative electrode active material. Including a silicon-containing material as the negative electrode active material makes it easier to achieve high capacity. In addition, the negative electrode active material may also contain, for example, an element that alloys with Li such as Sn, and at least one of a material containing said element.

[0033] From the viewpoint of increasing capacity, the silicon-containing material content is preferably 5% by mass or more, and more preferably 10% by mass or more, of the total mass of the negative electrode active material. Generally, silicon-containing materials undergo a larger volume change during charging and discharging compared to carbon materials. Therefore, when a silicon-containing material is included as the negative electrode active material, the negative electrode mixture layer 41 tends to expand when charging and discharging is repeated. This makes it easier for the non-aqueous electrolyte to be pushed out from both the upper and lower sides of the electrode body 14. Thus, when a silicon-containing material is included as the negative electrode active material, the effects of the disclosure described later are exhibited more significantly.

[0034] The carbon material that functions as the negative electrode active material is, for example, at least one selected from the group consisting of natural graphite, artificial graphite, soft carbon, and hard carbon. In particular, it is preferable to use artificial graphite such as massive artificial graphite (MAG) or graphitized mesophase carbon microbeads (MCMB), natural graphite such as flake graphite, massive graphite, or earthy graphite, or a mixture thereof as the carbon material. The volume-based D50 of the carbon material is, for example, 1 μm or more and 30 μm or less, preferably 5 μm or more and 25 μm or less.

[0035] Silicon-containing materials can be any material containing Si, and examples include silicon alloys, silicon compounds, and Si-containing composite materials. Among these, Si-containing composite materials are preferred. The D50 of composite materials is generally smaller than that of graphite. The volume-based D50 of composite materials is, for example, 1 μm or more and 15 μm or less. One type of silicon-containing material may be used alone, or two or more types may be used in combination.

[0036] A suitable silicon-containing material (composite material) is a composite particle comprising an ionic conductive phase and a Si phase dispersed within the ionic conductive phase. The ionic conductive phase is, for example, at least one selected from the group consisting of a silicate phase, an amorphous carbon phase, a silicide phase, and a silicon oxide phase. The Si phase is formed by dispersing Si in the form of fine particles. The ionic conductive phase is a continuous phase composed of an aggregate of particles finer than those of the Si phase. Furthermore, a conductive layer composed of a material with higher conductivity than the ionic conductive phase may be formed on the surface of the ionic conductive phase.

[0037] An example of a suitable composite material containing Si is one having a sea-island structure in which fine Si particles are dispersed substantially uniformly in an amorphous silicon oxide phase, and the overall general formula is SiO ｘ These are composite particles represented by (0 < x ≤ 2). The main component of silicon oxide may be silicon dioxide. The oxygen content ratio (x) to Si is, for example, 0.5 ≤ x < 2.0, and preferably 0.8 ≤ x ≤ 1.5.

[0038] The binder contained in the negative electrode mixture layer 41 may include fluororesin, PAN, polyimide, acrylic resin, polyolefin, etc., but styrene-butadiene rubber (SBR) is preferred. Furthermore, the negative electrode mixture layer 41 preferably contains CMC or a salt thereof, polyacrylic acid (PAA) or a salt thereof, polyvinyl alcohol (PVA), etc. In particular, it is preferable to use SBR in combination with CMC or a salt thereof, PAA or a salt thereof. The negative electrode mixture layer 41 may also contain a conductive agent such as CNT.

[0039] As described above, the negative electrode mixture layer 41 includes a first negative electrode mixture layer 43 and a second negative electrode mixture layer 44 having a larger porosity than the first negative electrode mixture layer 43. By making the porosity of the second negative electrode mixture layer 44, which is positioned on the surface of the negative electrode 12, larger than that of the first negative electrode mixture layer 43, which is positioned on the negative electrode core 40 side, the non-aqueous electrolyte can diffuse more easily to the negative electrode core 40 side, and the concentration variation of the non-aqueous electrolyte within the negative electrode mixture layer 41 is reduced. As a result, for example, the internal resistance is reduced, and a high-energy-density non-aqueous electrolyte secondary battery 10 can be realized. Furthermore, by making the porosity of the second negative electrode mixture layer 44 larger than that of the first negative electrode mixture layer 43, the diffusivity of the non-aqueous electrolyte on the surface of the negative electrode 12 is improved, and the effect of improving the diffusivity of the non-aqueous electrolyte by providing the recess 50, which will be described later, is more pronounced.

[0040] Furthermore, if the negative electrode mixture layer 41 is composed only of the second negative electrode mixture layer 44, which has a large porosity, the amount of negative electrode active material contained in the negative electrode mixture layer 41 decreases, and the energy density tends to decrease. Therefore, by including both the first negative electrode mixture layer 43 and the second negative electrode mixture layer 44 in the negative electrode mixture layer 41, it is possible to maintain energy density while reducing the concentration variation of the non-aqueous electrolyte within the negative electrode mixture layer 41.

[0041] When the porosity of the first negative electrode mixture layer 43 is S1 and the porosity of the second negative electrode mixture layer 44 is S2, the ratio of S2 to S1 (S2 / S1) may be greater than 1 and 5 or less, preferably 1.2 or more and 4 or less, and more preferably 1.4 or more and 3 or less. When the ratio (S2 / S1) is 1.2 or more and 4 or less, the amount of negative electrode active material contained in the negative electrode mixture layer 41 is ensured, while the non-aqueous electrolyte diffuses more easily to the negative electrode core 40 side, and the concentration variation of the non-aqueous electrolyte within the negative electrode mixture layer 41 becomes smaller.

[0042] The porosity S1 of the first negative electrode mixture layer 43 is, for example, 5% or more and 30% or less, and may be 10% or more and 30% or less. The porosity S2 of the second negative electrode mixture layer 44 is preferably 20% or more and 50% or less, and more preferably 25% or more and 45% or less. The porosity of the negative electrode mixture layer 41 is a two-dimensional value obtained from the ratio of the area of ​​voids to the cross-sectional area of ​​the negative electrode mixture layer 41. More specifically, it is calculated by the following procedure.

[0043] (1) A portion of the negative electrode 12 is cut off and processed using an ion milling device (e.g., Hitachi High-Tech Corporation, IM4000) to expose the cross-section of the negative electrode mixture layer 41. (2) A backscattered electron image of the cross-section of the first negative electrode mixture layer 43 of the exposed negative electrode mixture layer 41 is taken using a scanning electron microscope. (3) The cross-sectional image obtained above is imported into a computer and binarized using image analysis software (e.g., ImageJ, National Institutes of Health, USA) to obtain a binarized image in which the particle cross-sections in the cross-sectional image are made black and the interparticle voids are made white. (4) To determine the porosity of the first negative electrode mixture layer 43, the area of ​​the interparticle voids in the measurement range (e.g., 50 μm × 50 μm) is calculated from the binarized image. Then, the measurement range is set to the cross-sectional area of ​​the first negative electrode mixture layer 43 (2500 μm). ２ The area of ​​the interparticle voids is set to 50 μm x 50 μm, and the porosity of the first negative electrode mixture layer 43 (area of ​​interparticle voids x 100 / cross-sectional area of ​​the first negative electrode mixture layer 43) is calculated from the calculated area of ​​the interparticle voids. The porosity of the second negative electrode mixture layer 44 is measured in the same manner.

[0044] One method for adjusting the porosity of the first anode mixture layer 43 and the second anode mixture layer 44 is to adjust the compressive strength of the anode active material contained in each layer. For example, the compressive strength of the graphite particles (carbon material) contained in the second anode mixture layer 44 is made greater than that of the graphite particles contained in the first anode mixture layer 43. This makes it less likely for the graphite particles in the second anode mixture layer 44 to be crushed when rolled during the production of the anode 12, and thus increases the porosity of the second anode mixture layer 44. Alternatively, the porosity of the first anode mixture layer 43 and the second anode mixture layer 44 may be adjusted by changing the mixing ratio of the carbon material and the silicon-containing material in each layer.

[0045] Another method for adjusting the porosity of the first negative electrode mixture layer 43 and the second negative electrode mixture layer 44 is to adjust the rolling force applied to the first coating film constituting the first negative electrode mixture layer 43 and the second coating film constituting the second negative electrode mixture layer 44 during the formation of the negative electrode mixture layer 41. By reducing the rolling force, the particles of the negative electrode active material become less likely to be crushed, and the porosity can be increased. In addition, the porosity can be adjusted by changing the compression characteristics by changing the particle size distribution of the negative electrode active material.

[0046] The thickness of the first negative electrode mixture layer 43 may be 20% or more and 80% or less of the thickness of the negative electrode mixture layer 41, and is preferably 30% or more and 70% or less. For example, the thickness of the first negative electrode mixture layer 43 is 20 μm or more and 200 μm or less. Note that the thickness of the negative electrode mixture layer 41 (and the same applies to the first negative electrode mixture layer 43 and the second negative electrode mixture layer 44) refers to the thickness on one side of the negative electrode core body 40.

[0047] The thickness of the second negative electrode mixture layer 44 may be 10% or more and 70% or less of the thickness of the negative electrode mixture layer 41, and preferably 20% or more and 60% or less. When the thickness of the second negative electrode mixture layer 44 is 20% or more and 60% or less of the thickness of the negative electrode mixture layer 41, it becomes easier to improve the diffusivity of the non-aqueous electrolyte while ensuring energy density. The thickness of the second negative electrode mixture layer 44 may be approximately the same as the thickness of the first negative electrode mixture layer 43, or it may be less than the thickness of the first negative electrode mixture layer 43. For example, the thickness of the second negative electrode mixture layer 44 is 10 μm or more and 150 μm or less.

[0048] As shown in Figures 3 and 4, the surface of the negative electrode mixture layer 41 (second negative electrode mixture layer 44) is provided with a plurality of recesses 50 that are indented in the thickness direction of the negative electrode mixture layer 41. The recesses 50 are formed, for example, by laser processing.

[0049] In a non-aqueous electrolyte secondary battery 10 equipped with a wound electrode body 14, when rapid charge-discharge cycles are repeated, the volume change of the positive electrode 11 and the negative electrode 12 tends to push the non-aqueous electrolyte to both ends in the vertical direction of the electrode body 14. As a result, the concentration of electrolyte salt at both ends in the vertical direction of the electrode body 14 decreases compared to the concentration of electrolyte salt at the center of the electrode body 14. Consequently, lithium deposition occurs at both ends of the negative electrode 12 where the electrolyte salt concentration is low, leading to a decrease in charge-discharge cycle characteristics.

[0050] As in this embodiment, by forming recesses 50 on the surface of the negative electrode mixture layer 41, the non-aqueous electrolyte that has been pushed out to both ends of the electrode body 14 in the vertical direction can easily diffuse towards the center of the electrode body 14 in the vertical direction through the recesses 50. In other words, the gaps formed by the recesses 50 function as diffusion pathways for the non-aqueous electrolyte. This suppresses the decrease in electrolyte salt concentration at both ends of the electrode body 14 in the vertical direction. As a result, lithium deposition at the negative electrode 12 is suppressed, and the charge-discharge cycle characteristics are improved.

[0051] Furthermore, by forming recesses 50 on the surface of the negative electrode mixture layer 41, the non-aqueous electrolyte can more easily diffuse to the negative electrode core 40 side through the recesses 50. As a result, the concentration variation of the non-aqueous electrolyte within the negative electrode mixture layer 41 is reduced, making it possible to realize a non-aqueous electrolyte secondary battery 10 with high energy density and excellent charge-discharge cycle characteristics.

[0052] The depth of the recess 50 is preferably less than or equal to the thickness of the second negative electrode mixture layer 44, and preferably does not reach the first negative electrode mixture layer 43. By not reaching the first negative electrode mixture layer 43, the non-aqueous electrolyte that has been pushed out to both ends of the electrode body 14 in the vertical direction can easily diffuse towards the vertical center of the electrode body 14 through the recess 50. In other words, if the recess 50 reaches the first negative electrode mixture layer 43, the non-aqueous electrolyte may diffuse excessively in the thickness direction of the negative electrode mixture layer 41, making it difficult to diffuse towards the vertical center of the electrode body 14. The depth of the recess 50 refers to the length along the thickness direction of the negative electrode mixture layer 41 from the outermost surface of the negative electrode mixture layer 41 (second negative electrode mixture layer 44) to the deepest part of the recess 50. The depth of the recess 50 also refers to the average value of the depths of 50 recesses 50 obtained by cross-sectional observation of the negative electrode 12.

[0053] The depth of the recess 50 can be appropriately set according to the thickness of the first negative electrode mixture layer 43 and the second negative electrode mixture layer 44, but is preferably 10 μm or more and 50 μm or less, and preferably 15 μm or more and 50 μm or less. Note that unintended irregularities may be formed on the surface of the negative electrode mixture layer 41. In this specification, the recess 50 refers to a depression with a depth of 10 μm or more, and does not include depressions with a depth of less than 10 μm. In other words, depressions unintentionally formed on the surface of the negative electrode mixture layer 41 are not included in the recess 50.

[0054] As shown in Figure 3, the region of the negative electrode mixture layer 41 directly below the recess 50 is defined as the direct region 45, and the region from the periphery of the direct region 45 to 50 μm in the in-plane direction of the negative electrode mixture layer 41 (excluding the region overlapping with the direct region 45) is defined as the peripheral region 46. In this case, it is preferable that the porosity of the negative electrode mixture layer 41 in the direct region 45 is approximately the same as the porosity of the negative electrode mixture layer 41 in the peripheral region 46. In this case, the non-aqueous electrolyte can easily diffuse to the negative electrode core 40 side, and the concentration variation of the non-aqueous electrolyte within the negative electrode mixture layer 41 is reduced. Note that approximately the same porosity means that the difference in porosity between each region is 3% or less.

[0055] By forming the recess 50 by laser processing, the porosity of the region directly beneath 45 and the porosity of the peripheral region 46 can be made approximately the same. In other words, when the negative electrode mixture layer 41 is locally compressed from the surface side by embossing such as roll pressing to form the recess 50, the porosity in the region directly beneath 45 becomes smaller than the porosity in the peripheral region 46. As a result, the non-aqueous electrolyte becomes less likely to diffuse to the negative electrode core 40 side, and lithium deposition is more likely to occur near the region directly beneath 45, for example.

[0056] As shown in Figure 4, the recess 50 is positioned to extend along the width direction of the negative electrode 12 over substantially the entire negative electrode mixture layer 41. By positioning the recess 50 in this way, the non-aqueous electrolyte that has been pushed out to both ends in the vertical direction of the electrode body 14 can easily diffuse towards the center of the electrode body 14 in the vertical direction through the recess 50.

[0057] In this embodiment, a plurality of recesses 50, which are substantially circular in plan view, are arranged along the width direction with small gaps between them in the width direction. That is, the gaps between adjacent recesses 50 in the width direction are smaller than the gaps between adjacent recesses 50 in the longitudinal direction. Note that adjacent recesses 50 in the width direction may be connected. In other words, the recesses 50 are elongated holes that extend along the width direction, and the spaces formed by the recesses 50 may be continuously formed along the width direction of the negative electrode 12.

[0058] The spacing between adjacent recesses 50 in the width direction is, for example, 50 μm or less, and may be between 0.05 μm and 45 μm. The spacing between adjacent recesses 50 in the longitudinal direction is, for example, between 50 μm and 500 μm, and may be between 100 μm and 1000 μm. When the spacing between adjacent recesses 50 in the longitudinal direction is between 50 μm and 300 μm, an appropriate amount of recesses 50 can be formed on the surface of the negative electrode mixture layer 41 while ensuring the area of ​​the negative electrode mixture layer 41. As a result, a non-aqueous electrolyte secondary battery 10 with high energy density and excellent charge-discharge cycle characteristics can be realized.

[0059] The diameter of the circumscribed circle of each recess 50 is, for example, 5 μm or more and 200 μm or less, and may be 10 μm or more and 150 μm or less. The shape of the recess 50 is not limited to a roughly circular shape in plan view, and may, for example, have a roughly rectangular shape in plan view.

[0060] In this embodiment, in a cross-sectional view of the negative electrode 12, the recess 50 has a substantially constant width along the thickness direction of the negative electrode 12. That is, the side walls of the recess 50 extend along the thickness direction of the negative electrode 12. The shape of the recess 50 is not limited to this, and for example, the width of the recess 50 may decrease towards the negative electrode core 40 side.

[0061] Next, an example of a method for manufacturing the negative electrode 12 having the negative electrode mixture layer 41 of this embodiment will be described. However, the method for manufacturing the negative electrode 12 is not limited to the method described below.

[0062] A method for manufacturing the negative electrode 12 includes, for example, a preparation step of preparing a negative electrode mixture slurry, a coating step of applying the negative electrode mixture slurry to the surface of the negative electrode core 40, and a recess formation step of forming a recess 50 on the surface of the negative electrode mixture layer 41.

[0063] In the preparation process, the negative electrode active material, a binder, and a dispersion medium such as water are mixed to prepare a negative electrode mixture slurry. At this time, a first negative electrode mixture slurry constituting the first negative electrode mixture layer 43 and a second negative electrode mixture slurry constituting the second negative electrode mixture layer 44 may also be prepared.

[0064] In the coating process, the first negative electrode slurry and the second negative electrode slurry are applied to both sides of the negative electrode core 40 in that order. The method of applying the first negative electrode slurry and the second negative electrode slurry to the surface of the negative electrode core 40 is not particularly limited and can be done, for example, by die coating. The negative electrode 12 can be manufactured by drying and rolling the coating film produced in the coating process. Note that drying and rolling may be performed together after applying the first negative electrode slurry and the second negative electrode slurry, or they may be performed after applying the first negative electrode slurry and after applying the second negative electrode slurry, respectively.

[0065] In the recess formation step, recesses 50 are formed on the surface of the negative electrode mixture layer 41. The recesses 50 may be formed by electrolytic treatment, chemical etching, etc., but it is preferable that they be formed by laser processing. Known methods can be used for laser processing, and the size and depth of the recesses 50 can be adjusted by adjusting the wavelength, output, frequency, etc., of the laser light.

[0066] Next, a modified example of the arrangement of the recess 50 in the negative electrode 12 will be described with reference to Figures 5 and 6. Figures 5 and 6 show the modified negative electrode 12 in an unfolded state and correspond to Figure 4.

[0067] In the example shown in Figure 5, the recesses 50 are arranged to extend along the longitudinal direction of the negative electrode 12 over substantially the entire negative electrode mixture layer 41. In this embodiment, a plurality of recesses 50, which are substantially circular in plan view, are arranged along the width direction with small gaps in the longitudinal direction. That is, the gaps between adjacent recesses 50 in the longitudinal direction are smaller than the gaps between adjacent recesses 50 in the width direction. Note that adjacent recesses 50 in the longitudinal direction may be connected. In other words, the recesses 50 are elongated holes extending along the longitudinal direction, and the spaces formed by the recesses 50 may be continuously formed along the longitudinal direction of the negative electrode 12.

[0068] The spacing between adjacent recesses 50 in the longitudinal direction is, for example, 50 μm or less, and may be between 0.05 μm and 45 μm. The spacing between adjacent recesses 50 in the width direction is, for example, between 50 μm and 500 μm, and may be between 100 μm and 1000 μm.

[0069] The example shown in Figure 6 differs from the examples shown in Figures 4 and 5 in that the recesses 50 are formed only in a portion of the area on both ends in the width direction of the negative electrode mixture layer 41. As described above, the recesses 50 function as diffusion pathways for the non-aqueous electrolyte, which has been pushed out to both ends in the vertical direction of the electrode body 14, to diffuse towards the vertical center of the electrode body 14. Therefore, by forming the recesses 50 on both ends in the width direction of the negative electrode mixture layer 41, the non-aqueous electrolyte can be diffused towards the vertical center of the electrode body 14. On the other hand, if the area in which the recesses 50 are formed is too large, the volume of the negative electrode mixture layer 41 decreases, and the energy density tends to decrease.

[0070] As shown in Figure 6, by forming recesses 50 only in a portion of the widthwise ends of the negative electrode mixture layer 41, the volume of the negative electrode mixture layer 41 can be secured while diffusing the non-aqueous electrolyte towards the vertical center of the electrode body 14. As a result, a non-aqueous electrolyte secondary battery 10 with higher energy density and superior charge-discharge cycle characteristics can be realized.

[0071] The recess 50 may be formed only in a region extending 30% of the widthwise length of the negative electrode mixture layer 41 from both ends in the widthwise direction, or only in a region extending 20% ​​of the widthwise length of the negative electrode mixture layer 41 from both ends in the widthwise direction. In the example shown in Figure 6, the recess 50 is formed only on the lower end side of the negative electrode mixture layer 41 and not on the upper end side of the negative electrode mixture layer 41. The recess 50 may also be formed on the upper end side of the negative electrode mixture layer 41 in addition to, or instead of, the lower end side of the negative electrode mixture layer 41.

[0072] The above embodiments can be modified as appropriate within the scope of the purpose of this disclosure. For example, in the above embodiments, the negative electrode 12 has a non-compound layer forming portion 42, and the non-compound layer forming portion 42 is electrically connected to the outer casing 15 by being joined to the negative electrode current collector plate 18, but the current collection method of the negative electrode 12 is not limited to this. For example, the negative electrode 12 may be electrically connected to the outer casing 15 via a negative electrode tab or the like connected to the negative electrode core 40. In this case, there may be one negative electrode tab or multiple negative electrode tabs. In addition, when a non-compound layer forming portion 42 is provided as in the above embodiments, the non-compound layer forming portion 42 obstructs the flow path of the non-aqueous electrolyte, and the non-aqueous electrolyte pushed out to both ends in the vertical direction of the electrode body 14 tends not to return to the center in the vertical direction of the electrode body 14. Therefore, the effects of this disclosure are more pronounced when a non-compound layer forming portion 42 is provided.

[0073] Furthermore, in the above embodiment, the negative electrode mixture layer 41 has a two-layer structure in which a first negative electrode mixture layer 43 and a second negative electrode mixture layer 44 are stacked, but the negative electrode mixture layer 41 may have other layers between the first negative electrode mixture layer 43 and the second negative electrode mixture layer 44. That is, the negative electrode mixture layer 41 may have a multilayer structure in which three or more layers are stacked. In this case, it is preferable that the recess 50 does not reach the first negative electrode mixture layer 43, but it may reach the layer between the first negative electrode mixture layer 43 and the second negative electrode mixture layer 44. That is, it is preferable that the depth of the recess 50 is less than or equal to the thickness of the portion of the negative electrode mixture layer 41 other than the first negative electrode mixture layer 43.

[0074] The present disclosure will be further illustrated below with reference to examples, but the present disclosure is not limited to these examples.

[0075] [Fabrication of the positive electrode] As the positive electrode active material, particulate LiNi ０．９０ Co ０．０５ Mn ０．０５ O ２A lithium transition metal oxide represented by [formula] was used. The above positive electrode active material, acetylene black (AB) as a conductive agent, and polyvinylidene fluoride powder as a binder were mixed in a mass ratio of 95:2.5:2.5, and an appropriate amount of N-methyl-2-pyrrolidone (NMP) was added to prepare a positive electrode mixture slurry. The positive electrode mixture slurry was then applied to both sides of a positive electrode core made of long aluminum foil, and after the coating film was dried, the coating film was rolled with a rolling roller to produce a positive electrode in which a positive electrode mixture layer was formed on both sides of the positive electrode core. At this time, a 6 mm wide non-composite portion was provided at one end in the width direction of the positive electrode, where the positive electrode mixture layer was not formed.

[0076] [Preparation of the negative electrode] As the first negative electrode active material, a mixture of first graphite particles and Si oxide (SiO) in a mass ratio of 90:10 was used. As the second negative electrode active material, a mixture of second graphite particles, which have a higher compressive strength than the first graphite particles, and Si oxide (SiO) in a mass ratio of 90:10 was used. The first negative electrode active material, styrene-butadiene rubber dispersion, and carboxymethylcellulose sodium were mixed in a solid content mass ratio of 98:1:1, and the first negative electrode mixture slurry was prepared using water as the dispersion medium. Similarly, the second negative electrode active material, styrene-butadiene rubber dispersion, and carboxymethylcellulose sodium were mixed in a solid content mass ratio of 98:1:1, and the second negative electrode mixture slurry was prepared using water as the dispersion medium.

[0077] Then, a first negative electrode mixture slurry and a second negative electrode mixture slurry were applied in that order to the surface of a long copper foil negative electrode core body with a thickness of 8 μm. The coating film was dried and compressed to obtain a negative electrode in which a negative electrode mixture layer was formed on the negative electrode core body. At this time, a 6 mm wide non-composite portion was provided at one end in the width direction of the negative electrode where the negative electrode mixture layer was not formed.

[0078] Subsequently, as shown in Figure 4, recesses were formed by laser processing, extending in the width direction of the negative electrode across almost the entire negative electrode mixture layer. Each recess had a roughly circular shape in plan view, and the average diameter of the recesses was 90 μm. The distance between adjacent recesses in the width direction was 200 μm, and the distance between adjacent recesses in the longitudinal direction was 40 μm. The depth of the recesses was 30 μm.

[0079] Cross-sectional analysis of the fabricated negative electrode revealed that the thickness of the first negative electrode mixture layer was 50 μm, and the thickness of the second negative electrode mixture layer was 40 μm. Furthermore, the porosity of the first and second negative electrode mixture layers 44 was calculated using the method described above and was 19% and 36%, respectively. In addition, the porosity of the region directly below the recess and the porosity of the peripheral region around the periphery of the region directly below were the same.

[0080] [Preparation of non-aqueous electrolyte] A mixed solvent is prepared by mixing ethylene carbonate (EC) and dimethyl carbonate (DMC) in a volume ratio of 3:7, to which LiPF is added. ６ A non-aqueous electrolyte was prepared by dissolving 1.5 mol / liter of [the substance].

[0081] [Preparation of Test Cell] The positive electrode, the negative electrode, and a polyethylene separator described above were wound in a spiral shape using a cylindrical winding core to obtain an electrode body. A positive electrode current collector plate and a negative electrode current collector plate were then placed on the upper and lower ends of the prepared electrode body. The portion of the positive electrode at the upper end of the electrode body where the composite layer was not formed, and the portion of the negative electrode at the lower end of the electrode body where the composite layer was not formed, were bent radially inward and welded to the positive electrode current collector plate and the negative electrode current collector plate, respectively.

[0082] Subsequently, the electrode assembly was housed in a bottomed cylindrical outer casing, the negative electrode current collector plate was welded to the bottom of the bottomed cylindrical outer casing, and the positive electrode current collector plate and the sealing body were connected with a positive electrode lead. After pouring in the non-aqueous electrolyte, the opening of the outer casing was sealed with the sealing body via a gasket to fabricate a test cell (non-aqueous electrolyte secondary battery).

[0083] [Evaluation of Initial Discharge Capacity and Capacity Retention Rate] Under an ambient temperature of 25°C, the battery was charged at 1C with a constant current to 4.2V, and then charged at 4.2V with a constant voltage to 0.02C. Afterward, it was discharged at 0.5C with a constant current to 2.5V, and the initial discharge capacity was measured. This charge-discharge cycle was considered one cycle, and 100 cycles were performed. The capacity retention rate in the charge-discharge cycle was then calculated using the following formula: Capacity Retention Rate [%] = (Discharge Capacity at Cycle 100 / Discharge Capacity at Cycle 1)

[0084] <Example 2> In the preparation of the negative electrode, a test cell was prepared and evaluated in the same manner as in Example 1, except that a recess was formed extending in the longitudinal direction of the negative electrode over substantially the entire negative electrode mixture layer, as shown in Figure 5. Each recess had a substantially circular shape in plan view, and the average diameter of the recesses was 90 μm. The distance between adjacent recesses in the width direction was 200 μm, and the distance between adjacent recesses in the longitudinal direction was 40 μm. The depth of the recesses was 30 μm.

[0085] <Example 3> In the preparation of the negative electrode, a test cell was prepared and evaluated in the same manner as in Example 1, except that a recess was formed only in a portion of the lower end region of the negative electrode mixture layer, as shown in Figure 6, so as to extend in the longitudinal direction of the negative electrode. Each recess had a roughly circular shape in plan view, and the average diameter of the recesses was 90 μm. The distance between adjacent recesses in the width direction was 200 μm, and the distance between adjacent recesses in the longitudinal direction was 40 μm. The depth of the recesses was 30 μm. Furthermore, the recesses were formed only in a region extending from the lower end in the width direction of the negative electrode mixture layer to 20% of the width direction length of the negative electrode mixture layer.

[0086] <Example 4> In Example 4, a test cell was prepared and evaluated in the same manner as in Example 1, except that during the rolling process for the production of the negative electrode, an embossing treatment was performed using a rolling roller with irregularities on its surface to form recesses over substantially the entire negative electrode mixture layer. Each recess had a substantially circular shape in plan view, and the average diameter of the recesses was 90 μm. The distance between adjacent recesses in the width direction was 40 μm, and the distance between adjacent recesses in the longitudinal direction was 200 μm. The average depth of the recesses was 30 μm. In Example 4, the void ratio of the region directly below the recess was smaller than the void ratio of the peripheral region around the periphery of the region directly below the recess.

[0087] <Comparative Example 1> A test cell was prepared and evaluated in the same manner as in Example 1, except that no recesses were formed on the surface of the negative electrode mixture layer during the preparation of the negative electrode.

[0088] <Comparative Example 2> In the preparation of the negative electrode, the test cell was prepared and evaluated in the same manner as in Comparative Example 1, except that the rolling conditions of the coating film were changed. Cross-sectional analysis of the prepared negative electrode showed that the thickness of the first negative electrode mixture layer was 55 μm and the thickness of the second negative electrode mixture layer was 45 μm. Furthermore, the porosity of the first negative electrode mixture layer and the second negative electrode mixture layer 44 was calculated using the method described above and was found to be 27% and 43%, respectively.

[0089] Table 1 shows the initial discharge capacity and capacity retention rate results for each test cell. The initial discharge capacity and capacity retention rate values ​​shown in Table 1 are relative to the initial discharge capacity and capacity retention rate values ​​of the test cell in Comparative Example 1, which are set to 100. A larger initial discharge capacity value indicates higher energy density, and a larger capacity retention rate indicates superior charge-discharge cycle characteristics.

[0090]

[0091] As shown in Table 1, the test cell of the example maintains the initial discharge capacity while improving the capacity retention rate compared to the test cell of Comparative Example 1. This is presumed to be because the formation of recesses made it easier for the non-aqueous electrolyte, which was pushed out to both ends in the vertical direction of the electrode body during repeated charging and discharging, to diffuse towards the center in the vertical direction of the electrode body. As a result, the decrease in the concentration of electrolyte salts at both ends in the vertical direction of the electrode body is suppressed, and lithium deposition is less likely to occur on the negative electrode at both ends in the vertical direction. In fact, when the test cell was disassembled after the cycle test and the surface of the negative electrode was observed, the amount of lithium deposition on the negative electrode surface of the test cell of the example was significantly reduced compared to the test cell of Comparative Example 1.

[0092] Furthermore, the test cell of Comparative Example 2, which did not have recesses and increased the porosity of the negative electrode mixture layer, showed improved capacity retention compared to the test cell of Comparative Example 1, but a significant decrease in initial discharge capacity. This is presumed to be because the increased porosity of the negative electrode mixture layer reduced the volume of positive and negative electrodes that could be filled into the cell. Therefore, it can be said that by increasing only the porosity on the surface side of the negative electrode and forming recesses on the surface of the negative electrode, as in the test cell of the example, it is possible to improve charge-discharge cycle characteristics while ensuring high energy density.

[0093] This disclosure is further illustrated by the following embodiments. Configuration 1: A negative electrode for a non-aqueous electrolyte secondary battery, comprising a negative electrode core and a negative electrode mixture layer disposed on the negative electrode core, wherein the negative electrode mixture layer includes a first negative electrode mixture layer disposed on the surface of the negative electrode core and a second negative electrode mixture layer disposed on the surface of the negative electrode, the porosity of the second negative electrode mixture layer being greater than that of the first negative electrode mixture layer, and the surface of the negative electrode mixture layer is provided with a recess that is indented in the thickness direction of the negative electrode mixture layer. Configuration 2: The negative electrode for a non-aqueous electrolyte secondary battery according to Configuration 1, wherein the depth of the recess is less than or equal to the thickness of the portion of the negative electrode mixture layer other than the first negative electrode mixture layer. Configuration 3: The negative electrode for a non-aqueous electrolyte secondary battery according to Configuration 1 or 2, wherein the porosity of the negative electrode mixture layer in the region directly below the recess is substantially the same as the porosity of the negative electrode mixture layer in the peripheral region, which is the region from the periphery of the region directly below to 50 μm in the in-plane direction of the negative electrode mixture layer. Configuration 4: The negative electrode for a non-aqueous electrolyte secondary battery according to any one of Configurations 1 to 3, wherein when the porosity of the first negative electrode mixture layer is S1 and the porosity of the second negative electrode mixture layer is S2, the ratio of S2 to S1 (S2 / S1) is 1.2 or more and 4 or less. Configuration 5: The negative electrode for a non-aqueous electrolyte secondary battery according to any one of Configurations 1 to 4, wherein the porosity S1 of the first negative electrode mixture layer is 5% or more and 30% or less. Configuration 6: A negative electrode for a non-aqueous electrolyte secondary battery according to any one of Configurations 1 to 5, wherein the porosity S2 of the second negative electrode mixture layer is 20% or more and 50% or less. Configuration 7: A negative electrode for a non-aqueous electrolyte secondary battery according to any one of Configurations 1 to 6, wherein the thickness of the second negative electrode mixture layer is 20% or more and 60% or less of the thickness of the negative electrode mixture layer. Configuration 8: A negative electrode for a non-aqueous electrolyte secondary battery according to any one of Configurations 1 to 7, wherein the recess is arranged to extend along the longitudinal or widthwise direction of the negative electrode. Configuration 9: A negative electrode for a non-aqueous electrolyte secondary battery according to any one of Configurations 1 to 8, wherein the recess is formed by laser processing. Configuration 10: A non-aqueous electrolyte secondary battery comprising an electrode body in which the negative electrode and positive electrode according to any one of Configurations 1 to 9 are wound via a separator, and a non-aqueous electrolyte.

[0094] 10 Non-aqueous electrolyte secondary battery, 11 Positive electrode, 12 Negative electrode, 13 Separator, 14 Electrode body, 15 Outer casing, 16 Sealing body, 17 Positive electrode current collector plate, 18 Negative electrode current collector plate, 19 Insulating plate, 20 Positive electrode lead, 21 Grooved section, 22 Filter, 23 Lower valve body, 24 Insulating member, 25 Upper valve body, 26 Cap, 26a Through hole, 27 Gasket, 30 Positive electrode core body, 31 Positive electrode mixture layer, 32 Non-mixing layer section, 40 Negative electrode core body, 41 Negative electrode mixture layer, 42 Non-mixing layer section, 43 First negative electrode mixture layer, 44 Second negative electrode mixture layer, 45 Directly below region, 46 Peripheral region, 50 Recess

Claims

1. A negative electrode for a non-aqueous electrolyte secondary battery, comprising a negative electrode core and a negative electrode mixture layer disposed on the negative electrode core, wherein the negative electrode mixture layer includes a first negative electrode mixture layer disposed on the surface of the negative electrode core and a second negative electrode mixture layer disposed on the surface of the negative electrode, the porosity of the second negative electrode mixture layer being greater than that of the first negative electrode mixture layer, and the surface of the negative electrode mixture layer is provided with recesses that are indented in the thickness direction of the negative electrode mixture layer.

2. The depth of the recess is less than or equal to the thickness of the portion of the negative electrode mixture layer other than the first negative electrode mixture layer, according to claim 1, for a negative electrode for a non-aqueous electrolyte secondary battery.

3. The negative electrode for a non-aqueous electrolyte secondary battery according to claim 1, wherein the porosity of the negative electrode mixture layer in the region directly below the recess is substantially the same as the porosity of the negative electrode mixture layer in the peripheral region, which is the region from the periphery of the region directly below to 50 μm in the in-plane direction of the negative electrode mixture layer.

4. The negative electrode for a non-aqueous electrolyte secondary battery according to claim 1, wherein when the porosity of the first negative electrode mixture layer is S1 and the porosity of the second negative electrode mixture layer is S2, the ratio of S2 to S1 (S2 / S1) is 1.2 or more and 4 or less.

5. The negative electrode for a non-aqueous electrolyte secondary battery according to claim 1, wherein the porosity S1 of the first negative electrode mixture layer is 5% or more and 30% or less.

6. The negative electrode for a non-aqueous electrolyte secondary battery according to claim 1, wherein the porosity S2 of the second negative electrode mixture layer is 20% or more and 50% or less.

7. The anode for a non-aqueous electrolyte secondary battery according to claim 1, wherein the thickness of the second anode mixture layer is 20% or more and 60% or less of the thickness of the anode mixture layer.

8. The negative electrode for a non-aqueous electrolyte secondary battery according to claim 1, wherein the recess is arranged to extend along the longitudinal or widthwise direction of the negative electrode.

9. The non-aqueous electrolyte secondary battery according to claim 1, wherein the recess is formed by laser processing.

10. A non-aqueous electrolyte secondary battery comprising an electrode body in which a negative electrode and a positive electrode are wound via a separator, and a non-aqueous electrolyte, as described in any one of claims 1 to 9.

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