Negative electrode and battery

Abstract

A negative electrode 10 according to the present disclosure comprises: copper foil 11; and a negative electrode mixture layer 12 that contains a negative electrode active material and is disposed on the copper foil 11. The average crystallite size in a cross section of the copper foil 11 is no greater than 0.55 μm or at least 0.85 μm. The negative electrode active material includes at least one selected from the group consisting of, for example, a carbon material and a material capable of forming an alloy with lithium. A battery according to the present disclosure comprises: a negative electrode 10; a positive electrode; and an electrolyte.

Description

Anode and battery

[0001] The present disclosure relates to anodes and batteries.

[0002] A battery electrode has a configuration in which, for example, an electrode mixture layer containing an electrode active material is provided on a current collector. Such an electrode is produced, for example, by applying a slurry containing an electrode mixture containing an electrode active material to a metal foil current collector, drying the coating, and then cutting it into a predetermined shape.

[0003] The secondary battery disclosed in Patent Document 1 has a power generating element in which a long electrode having an electrode mixture layer provided on the surface of a metal foil is wound. Such a long electrode can be manufactured, for example, by slitting a sheet-like electrode having an electrode mixture layer provided on the surface of a metal foil to a predetermined width and cutting the obtained electrode of the predetermined width to a predetermined length.

[0004] JP 2016-184482 A

[0005] In order to accurately cut the electrode into a predetermined shape, it is necessary to keep the blades, such as slit blades, used to cut the electrode sharp. Therefore, the blades used to cut the electrode must be replaced when they wear out and lose their sharpness. If the blades need to be replaced frequently, the electrode manufacturing efficiency will decrease and the manufacturing costs will increase.

[0006] Therefore, the present disclosure provides a negative electrode that can reduce the frequency of replacing the blade used to cut the electrode.

[0007] The negative electrode of the present disclosure includes: a copper foil; and a negative electrode mixture layer containing a negative electrode active material disposed on the copper foil, wherein the average crystallite size in a cross section of the copper foil is 0.55 μm or less, or 0.85 μm or more.

[0008] The negative electrode of the present disclosure can reduce the frequency of replacing the blade used to cut the electrode.

[0009] Fig. 1 is a cross-sectional view showing a schematic configuration of a negative electrode according to embodiment 1. Fig. 2 is a longitudinal cross-sectional view showing a schematic example of a battery according to embodiment 2.

[0010] [Findings that Form the Basis of the Present Disclosure] The present inventors conducted extensive research into the relationship between electrode configuration and blade wear for cutting electrodes, particularly negative electrodes. As a result, they discovered that when copper foil is used as the electrode current collector, the crystallite size of the copper foil is related to blade wear. Specifically, the present inventors investigated the relationship between the average crystallite size in the cross section of the copper foil and the sharpness of the cut surface. When the average crystallite size was small or large, the cut surface of the electrode was sharp and had few burrs, while when the average crystallite size was larger than small and within a certain range, the cut surface of the electrode was burred and poorly sharp. After further extensive research, the present inventors discovered a new fact: the reduced burrs on the cut surface are related to a longer cumulative cut length, which is the length of the electrode that the blade can accurately cut into a predetermined shape, i.e., a reduced frequency of blade replacement. The cumulative cut length is the cumulative value of the length of the electrode cut by the blade.

[0011] Therefore, the present inventors conducted a detailed study on the average crystallite size in the cross section of the copper foil and came up with the negative electrode of the present disclosure, which is described below and can reduce the frequency of replacing the blade used to cut the electrode.

[0012] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. The present disclosure is not limited to the following embodiments.

[0013] [Embodiments of the Present Disclosure] (Embodiment 1) Fig. 1 is a cross-sectional view showing a schematic configuration of a negative electrode according to embodiment 1. The negative electrode 10 according to embodiment 1 includes a copper foil 11 as a negative electrode current collector and a negative electrode mixture layer 12 disposed on the copper foil 11. The average crystallite size in the cross section of the copper foil 11 is 0.55 µm or less, or 0.85 µm or more. Note that while the negative electrode 10 shown in Fig. 1 has a configuration in which the negative electrode mixture layer 12 is provided on one side of the copper foil 11, the negative electrode mixture layer 12 may be provided on both sides of the copper foil 11.

[0014] By having the average crystallite size in the cross section of the copper foil 11 be 0.55 μm or less or 0.85 μm or more, the frequency of blade replacement used to cut the negative electrode 10 can be reduced. When the average crystallite size in the cross section of the copper foil 11 is 0.55 μm or less, the crystal grains of the copper foil 11 are small and there are many crystal grain boundaries, so the copper foil 11 is easily cut into the desired shape with a sharp cross section. Also, when the average crystallite size in the cross section of the copper foil 11 is 0.85 μm or more, the crystal grains of the copper foil 11 are large and there are very few crystal grain boundaries, so the copper foil 11 is easily cut into the desired shape with a sharp cross section by cutting the crystal grains. Therefore, the negative electrode 10 according to embodiment 1 can be cut while suppressing blade wear, thereby reducing the frequency of blade replacement. On the other hand, when the average crystallite size in the cross section of the copper foil 11 is more than 0.55 μm and less than 0.85 μm, the crystal grains of the copper foil 11 have a moderate size, so there are few crystal grain boundaries, and the crystal grains are not large enough to be easily cut, so it is difficult to cut into a desired shape with a sharp cross section. Therefore, the blade is easily worn during cutting, making it difficult to reduce the frequency of blade replacement.

[0015] The average crystallite size in the cross section of the copper foil 11 may be 0.55 μm or less, or 0.85 μm or more and 3.0 μm or less, thereby further reducing the frequency of replacing the blade used to cut the negative electrode 10. The average crystallite size may be, for example, 0.1 μm or more.

[0016] The average crystallite size on the surface of the copper foil 11 may be 0.55 μm or less, or 0.85 μm or more and 3.0 μm or less, thereby further reducing the frequency of replacing the blade used to cut the negative electrode 10. The average crystallite size may be, for example, 0.1 μm or more.

[0017] Here, in this specification, the average crystallite size in the cross section of the copper foil 11 is determined by the following method. The diffraction pattern of the cross section of the copper foil 11 obtained by EBSD (Electron Back-Scattered Diffraction pattern) analysis of the cross section of the copper foil 11 is analyzed, and the bands are detected by the Hough transform method to determine the crystal orientation, thereby identifying the individual crystallite sizes. The crystallite sizes (crystallite diameters) of crystallites within a 100 μm wide region (i.e., within a region of copper foil thickness × 100 μm wide) in an arbitrarily selected copper foil cross section are determined, and the sum is divided by the number of crystallites in the same region to obtain the average crystallite size. The average crystallite size on the surface of the copper foil 11 can also be determined by the same method.

[0018] The thickness of the copper foil 11 is, for example, not less than 5 μm and not more than 50 μm.

[0019] The negative electrode mixture layer 12 is supported on the copper foil 11. The negative electrode mixture layer 12 includes a negative electrode active material. The negative electrode active material may be a material capable of absorbing and releasing lithium ions. The negative electrode active material includes, for example, at least one selected from the group consisting of materials capable of forming an alloy with lithium and carbon materials. Examples of carbon materials include graphite. Examples of materials capable of forming an alloy with lithium include silicon-containing materials, tin, zinc alloys, bismuth, and germanium. One type selected from these negative electrode active materials may be used, or two or more types may be used in combination.

[0020] The negative electrode active material may contain a silicon-containing material. A silicon-containing negative electrode active material is effective in increasing the capacity of a battery. Therefore, by including a silicon-containing material in the negative electrode active material, the battery capacity can be increased. Here, examples of the silicon-containing material include silicon, silicon alloys, silicon compounds, and silicon-containing composite materials. The silicon-containing composite material is, for example, a composite material containing an ion-conducting phase and a silicon phase dispersed in the ion-conducting phase. The ion-conducting phase includes, for example, at least one selected from the group consisting of an aluminate phase, a silicate phase, a carbon phase, a silicide phase, and a silicon oxide phase. The ion-conducting phase may be composed of a single phase or multiple phases. The silicon phase is, for example, silicon formed into fine particles and dispersed in the ion-conducting phase. Although silicon is a relatively hard material, the negative electrode 10 of embodiment 1 can reduce the frequency of replacing the blade used to cut the negative electrode 10, even when the negative electrode mixture layer 12 contains a relatively hard silicon-containing material.

[0021] When the negative electrode mixture layer 12 contains a silicon-containing material, the mass proportion of the silicon-containing material in the negative electrode mixture layer 12 may be 2% or more. This makes it possible to achieve a high battery capacity while further reducing the frequency of replacing the blade used to cut the negative electrode 10. In order to further reduce the frequency of replacing the blade used to cut the negative electrode 10, the mass proportion of the silicon-containing material in the negative electrode mixture layer 12 may be, for example, 75% or less.

[0022] The negative electrode mixture layer 12 may contain other materials such as a conductive additive and a binder.

[0023] The conductive additive is used to reduce the resistance of the negative electrode 10. Examples of the conductive additive include a carbon material and a conductive polymer compound. Examples of the carbon material include carbon black, graphite, acetylene black, carbon nanotubes, carbon nanofibers, graphene, fullerene, and graphite oxide. Examples of the conductive polymer compound include polyaniline, polypyrrole, and polythiophene.

[0024] The binder is used to improve the binding properties of the materials that make up the negative electrode 10. Examples of the binder that can be used include polymeric materials such as polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-tetrafluoroethylene copolymer, polytetrafluoroethylene, carboxymethyl cellulose (CMC), polyacrylic acid, styrene-butadiene copolymer rubber (SBR), polypropylene, polyethylene, and polyimide.

[0025] The shape of the negative electrode 10 is not particularly limited, but for example, when the negative electrode 10 constitutes an electrode group having a wound structure in a battery, the negative electrode 10 has a strip shape.

[0026] The negative electrode 10 can be manufactured, for example, by the following method. For example, a slurry containing a negative electrode mixture including a negative electrode active material is applied to one or both sides of a copper foil, the coating is dried, and compressed to produce a sheet-like negative electrode in which a negative electrode mixture layer is provided on the surface of the copper foil. The sheet-like negative electrode is then cut into a predetermined shape to produce the negative electrode 10. When the negative electrode 10 has a strip-like shape, it can be manufactured, for example, by cutting the sheet-like negative electrode to a predetermined width (i.e., slitting), and then further cutting the obtained negative electrode of the predetermined width to a predetermined length. Note that the sheet-like negative electrode may be first cut to a predetermined length, and then cut to the predetermined width.

[0027] (Embodiment 2) A battery according to embodiment 2 includes a positive electrode, a negative electrode, and an electrolyte. The negative electrode is the negative electrode according to embodiment 1. Therefore, with this configuration, the battery according to embodiment 2 can reduce the frequency of replacing the blade used to cut the electrode.

[0028] 2 is a longitudinal cross-sectional view schematically illustrating an example of a battery according to embodiment 2. The battery 100 is a cylindrical battery including a cylindrical battery case, an electrode group 24 having a wound structure, and an electrolyte (not shown). The electrode group 24 is housed in the battery case and is in contact with the electrolyte.

[0029] The battery case is composed of a case body 25, which is a cylindrical metal container with a bottom, and a sealing body 26 that seals the opening of the case body 25. A gasket 37 is disposed between the case body 25 and the sealing body 26. The gasket 37 ensures the airtightness of the battery case. Within the case body 25, insulating plates 27 and 28 are disposed on both ends of the electrode group 24 in the direction of the winding axis of the electrode group 24, respectively.

[0030] Case body 25 has, for example, a step portion 31. Step portion 31 can be formed by partially pressing the side wall of case body 25 from the outside. Step portion 31 may be formed in an annular shape on the side wall of case body 25 along the circumferential direction of an imaginary circle defined by case body 25. In this case, sealing body 26 is supported by, for example, the surface of step portion 31 on the opening side.

[0031] The sealing body 26 includes a filter 32, a lower valve body 33, an insulating member 34, an upper valve body 35, and a cap 36. These members are stacked in this order in the sealing body 26. The sealing body 26 is attached to the opening of the case body 25 so that the cap 36 is located outside the case body 25 and the filter 32 is located inside the case body 25.

[0032] Each of the above-mentioned members constituting the sealing body 26 has, for example, a disk or ring shape. The above-mentioned members, except for the insulating member 34, are electrically connected to one another.

[0033] The electrode group 24 has a positive electrode 21, a separator 22, and a negative electrode 23. The positive electrode 21, the separator 22, and the negative electrode 23 are all strip-shaped. The width direction of the strip-shaped positive electrode 21 and the negative electrode 23 is, for example, parallel to the winding axis of the electrode group 24. The separator 22 is disposed between the positive electrode 21 and the negative electrode 23. The positive electrode 21 and the negative electrode 23 are spirally wound with the separator 22 interposed between these electrodes.

[0034] When observing the cross section of the battery 100 in a direction perpendicular to the winding axis of the electrode group 24, the positive electrodes 21 and negative electrodes 23 are stacked alternately in the radial direction of an imaginary circle defined by the case body 25, with a separator 22 interposed between these electrodes.

[0035] The positive electrode 21 is electrically connected to a cap 36, which also serves as a positive electrode terminal, via a positive electrode lead 29. One end of the positive electrode lead 29 is connected, for example, to near the center of the positive electrode 21 in the longitudinal direction of the positive electrode 21. The positive electrode lead 29 passes through a through-hole formed in the insulating plate 27 and extends from the positive electrode 21 to the filter 32. The other end of the positive electrode lead 29 is welded, for example, to the surface of the filter 32 on the electrode group 24 side.

[0036] The negative electrode 23 is electrically connected to the case body 25, which also serves as a negative electrode terminal, via a negative electrode lead 30. One end of the negative electrode lead 30 is connected to, for example, an end of the negative electrode 23 in the longitudinal direction of the negative electrode 23. The other end of the negative electrode lead 30 is welded to, for example, the inner bottom surface of the case body 25.

[0037] Each component of the battery 100 will be specifically described below.

[0038] The positive electrode 21 includes a material having the property of absorbing and releasing metal ions (e.g., lithium ions). The positive electrode 21 includes, for example, a positive electrode active material. The positive electrode 21 includes, for example, a positive electrode current collector and a positive electrode mixture layer supported on the surface of the positive electrode current collector.

[0039] The positive electrode current collector may be, for example, a sheet or film made of a metal material such as aluminum, stainless steel, titanium, or an alloy thereof. Aluminum and its alloys are suitable as materials for the positive electrode current collector because they are inexpensive and easy to form into a thin film. The sheet or film may be porous or non-porous. Metal foil, metal mesh, or the like may be used as the sheet or film. A carbon material such as carbon may be applied to the surface of the positive electrode current collector as a conductive auxiliary material.

[0040] The positive electrode mixture layer includes a positive electrode active material. The positive electrode active material may be a material capable of absorbing and releasing metal ions (e.g., lithium ions). Examples of the positive electrode active material include lithium-containing transition metal oxides, lithium-containing transition metal phosphates, transition metal fluorides, polyanionic materials, fluorinated polyanionic materials, transition metal sulfides, transition metal oxysulfides, and transition metal oxynitrides. In particular, using a lithium-containing transition metal oxide or a lithium-containing transition metal phosphate as the positive electrode active material can reduce the manufacturing cost of the battery and increase the average discharge voltage. Examples of lithium-containing transition metal oxides include lithium cobalt oxide, lithium nickel cobalt aluminum oxide, lithium nickel cobalt manganese oxide, and lithium nickel manganese oxide. Examples of lithium-containing transition metal phosphates include lithium iron phosphate, lithium vanadium phosphate, lithium cobalt phosphate, and lithium nickel phosphate.

[0041] The positive electrode mixture layer may further contain a binder. As the binder, the materials described in the first embodiment as binders usable in the negative electrode mixture layer can also be used in the positive electrode mixture layer.

[0042] The positive electrode mixture layer may further contain a conductive agent. As the conductive agent, the materials described in the first embodiment as conductive agents usable in the negative electrode mixture layer can also be used in the positive electrode mixture layer.

[0043] The negative electrode 23 is the negative electrode 10 according to the first embodiment.

[0044] The electrolyte solution used as the electrolyte may contain a non-aqueous solvent and a lithium salt dissolved in the non-aqueous solvent. The concentration of the lithium salt in the electrolyte solution may be, for example, 0.5 mol / L or more and 2 mol / L or less. By controlling the lithium salt concentration within the above range, an electrolyte solution having excellent ionic conductivity and appropriate viscosity can be obtained. However, the lithium salt concentration is not limited to the above.

[0045] The non-aqueous solvent may be a cyclic carbonate, a chain carbonate, a cyclic ether, a chain ether, a nitrile, an amide, etc. One selected from these solvents may be used, or two or more may be used in combination.

[0046] Examples of lithium salts that can be used include lithium hexafluorophosphate (LiPF), lithium tetrafluoroborate (LiBF), lithium perchlorate (LiClO), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium bisperfluoroethylsulfonylimide (LiN(SO2C2F5)2), LiAsF6, LiCF3SO3, and lithium difluoro(oxalato)borate. One selected from these electrolyte salts may be used, or two or more may be used in combination.

[0047] It is usually desirable to interpose a separator between the positive electrode and the negative electrode. The separator 22 has high ion permeability and adequate mechanical strength and insulating properties. The separator 22 may be made of a microporous thin film, a woven fabric, a nonwoven fabric, or the like. The separator 22 may be made of a polymer, for example. The polymer may be a polyolefin such as polypropylene or polyethylene.

[0048] In the battery according to the second embodiment, the electrolyte may be impregnated into a polymer provided as a separator, for example, i.e., the battery according to the second embodiment may have a structure in which the electrolyte and the polymer are used in combination.

[0049] The battery according to the second embodiment may further include a solid electrolyte as the electrolyte. That is, the battery according to the present disclosure may have a hybrid structure in which an electrolytic solution and a solid electrolyte are used in combination. Examples of solid electrolyte materials include halide solid electrolytes, sulfide solid electrolytes, oxide solid electrolytes, and organic polymer solid electrolytes. In the present disclosure, the term "halide solid electrolyte" refers to a solid electrolyte containing a halogen element as the main anion component. The term "sulfide solid electrolyte" refers to a solid electrolyte containing sulfur as the main anion component. The term "oxide solid electrolyte" refers to a solid electrolyte containing oxygen as the main anion component. The term "main anion component" refers to the anion with the largest mass among all anions constituting the solid electrolyte.

[0050] As an example of the structure of the battery according to the second embodiment, the configuration example shown in FIG. 2 is described, i.e., a cylindrical nonaqueous electrolyte secondary battery in which an electrode group having a wound structure in which a positive electrode and a negative electrode are wound with a separator interposed therebetween, and an electrolyte solution are housed in an outer casing. However, the battery according to the present disclosure is not limited to this configuration example. The battery according to the second embodiment may have any shape, such as a prismatic shape, a coin shape, a button shape, or a laminate shape. Furthermore, as the electrode group in the battery according to the second embodiment, instead of the electrode group having a wound structure, an electrode group of another shape, such as an electrode group in which a positive electrode and a negative electrode are stacked with a separator interposed therebetween, may be used.

[0051] (Other Embodiments) (Additional Notes) The above description of the embodiments discloses the following techniques.

[0052] (Technology 1) A negative electrode comprising: a copper foil; and a negative electrode mixture layer containing a negative electrode active material disposed on the copper foil, wherein the average crystallite size in a cross section of the copper foil is 0.55 μm or less, or 0.85 μm or more.

[0053] With this configuration, the negative electrode of Technology 1 can reduce the frequency of replacing the blade used to cut the electrode.

[0054] (Technology 2) The negative electrode according to Technology 1, wherein the negative electrode active material includes at least one selected from the group consisting of a material capable of forming an alloy with lithium and a carbon material.

[0055] With this configuration, the negative electrode of Technology 2 can reduce the frequency of replacing the blade used to cut the electrode.

[0056] (Technology 3) The anode according to Technology 2, wherein the anode active material includes a silicon-containing material as the material capable of forming an alloy with lithium.

[0057] With this configuration, the negative electrode of Technology 3 can achieve a high capacity battery while reducing the frequency of replacing the blade used to cut the electrode.

[0058] (Technology 4) The negative electrode according to Technology 3, wherein the mass ratio of the silicon-containing material in the negative electrode mixture layer is 2% or more.

[0059] With this configuration, the negative electrode of Technology 4 can achieve a high capacity battery while further reducing the frequency of replacing the blade used to cut the electrode.

[0060] (Technology 5) The negative electrode according to any one of Technologies 1 to 4, wherein the average crystallite size in the cross section of the copper foil is 0.55 μm or less, or 0.85 μm or more and 3.0 μm or less.

[0061] With this configuration, the negative electrode of Technology 5 can further reduce the frequency of replacing the blade used to cut the electrode.

[0062] (Technology 6) The negative electrode according to any one of Technologies 1 to 5, wherein the average crystallite size on the surface of the copper foil is 0.55 μm or less, or 0.85 μm or more and 3.0 μm or less.

[0063] With this configuration, the negative electrode of Technology 6 can further reduce the frequency of replacing the blade used to cut the electrode.

[0064] (Technology 7) A battery comprising: the negative electrode according to any one of technologies 1 to 6; a positive electrode; and an electrolyte.

[0065] This configuration allows the battery of Technique 7 to reduce the frequency of replacing the blade used to cut the electrodes.

[0066] The present disclosure will be described in more detail below using examples. The following examples are merely examples of embodiments, and are not intended to limit the scope of the present disclosure.

[0067] [Examples 1A to 1D] <Preparation of copper foil> A copper foil having a thickness of 15 μm was prepared and subjected to heat treatment. The average crystallite size in the cross section of the copper foil after the heat treatment was measured by the method described below, and the average crystallite size was 0.17 μm.

[0068] <Preparation of Negative Electrode Mixture Slurries (a) to (d)> Negative Electrode Mixture Slurry (a) Graphite was used as the negative electrode active material. The negative electrode active material was mixed with a mixture of SBR and CMC as a binder in a mass ratio of negative electrode active material:binder = 97:3, and an appropriate amount of water was added thereto to prepare negative electrode mixture slurry (a).

[0069] Negative electrode mixture slurry (b) Silicon and graphite were mixed in a mass ratio of silicon:graphite = 1:99, and the resulting mixture was used as the negative electrode active material. The negative electrode active material was mixed with a mixture of SBR and CMC as a binder in a mass ratio of negative electrode active material:binder = 97:3, and an appropriate amount of water was added to prepare negative electrode mixture slurry (b). In the negative electrode mixture slurry (b), the mass proportion of silicon in the solid content was 1%.

[0070] Negative electrode mixture slurry (c) Silicon and graphite were mixed in a mass ratio of silicon:graphite = 2:98, and the resulting mixture was used as the negative electrode active material. The negative electrode active material was mixed with a mixture of SBR and CMC as a binder in a mass ratio of negative electrode active material:binder = 97:3, and an appropriate amount of water was added to prepare negative electrode mixture slurry (c). In the negative electrode mixture slurry (c), the mass proportion of silicon in the solid content was 2%.

[0071] Negative electrode mixture slurry (d) Silicon and graphite were mixed in a mass ratio of silicon:graphite = 51:49, and the resulting mixture was used as the negative electrode active material. The negative electrode active material and a mixture of SBR and CMC as a binder were mixed in a mass ratio of negative electrode active material:binder = 97:3, and an appropriate amount of water was added to prepare negative electrode mixture slurry (d). In the negative electrode mixture slurry (d), the mass proportion of silicon in the solid content was 50%.

[0072] <Preparation of negative electrode> The negative electrode mixture slurry (a) was applied to both sides of the copper foil prepared by the above method, having an average crystallite size in cross section of 0.17 μm, and the coating was dried and compressed to prepare a sheet-like negative electrode having a negative electrode mixture layer (a) on the surface of the copper foil. The size of the copper foil used to prepare the sheet-like negative electrode was 600 mm wide and 15 μm thick. The total thickness of the negative electrode mixture layer formed on both sides of the copper foil was 170 μm. The obtained sheet-like negative electrode was the negative electrode of Example 1A.

[0073] A sheet-shaped negative electrode was prepared by using the negative electrode mixture slurry (b) instead of the negative electrode mixture slurry (a) in the same manner as for the negative electrode mixture layer (a). The total thickness of the negative electrode mixture layer (b) formed on both sides of the copper foil was 170 μm. The obtained sheet-shaped negative electrode was designated as the negative electrode of Example 1B.

[0074] A sheet-shaped negative electrode was prepared by using the negative electrode mixture slurry (c) instead of the negative electrode mixture slurry (a) in the same manner as for the negative electrode mixture layer (a). The total thickness of the negative electrode mixture layer (c) formed on both sides of the copper foil was 170 μm. The obtained sheet-shaped negative electrode was designated as the negative electrode of Example 1C.

[0075] A sheet-shaped negative electrode having a negative electrode mixture layer (d) formed on both sides of a copper foil was produced in the same manner as for the negative electrode mixture layer (a) using the negative electrode mixture slurry (d) instead of the negative electrode mixture slurry (a). The total thickness of the negative electrode mixture layer (d) formed on both sides of the copper foil was 170 μm. The obtained sheet-shaped negative electrode was designated as the negative electrode of Example 1D.

[0076] [Examples 2A to 2D] <Preparation of copper foil> A copper foil having a thickness of 15 μm was prepared and subjected to heat treatment. The average crystallite size in the cross section of the copper foil after the heat treatment was measured by the method described below, and the average crystallite size was 0.44 μm.

[0077] <Preparation of Negative Electrode Mixture Slurries (a) to (d)> Negative electrode mixture slurries (a) to (d) identical to those prepared in Examples 1A to 1D were prepared.

[0078] <Preparation of negative electrode> The negative electrode mixture slurry (a) was applied to both sides of the copper foil prepared by the above method, having an average crystallite size in cross section of 0.44 μm, and the coating was dried and compressed to prepare a sheet-like negative electrode having a negative electrode mixture layer (a) on the surface of the copper foil. The size of the copper foil used to prepare the sheet-like negative electrode was 600 mm wide and 15 μm thick. The total thickness of the negative electrode mixture layer formed on both sides of the copper foil was 170 μm. The obtained sheet-like negative electrode was the negative electrode of Example 2A.

[0079] A sheet-shaped negative electrode was prepared by using the negative electrode mixture slurry (b) instead of the negative electrode mixture slurry (a) in the same manner as the negative electrode mixture layer (a). The total thickness of the negative electrode mixture layer (b) formed on both sides of the copper foil was 170 μm. The obtained sheet-shaped negative electrode was designated as the negative electrode of Example 2B.

[0080] A sheet-shaped negative electrode was prepared by using the negative electrode mixture slurry (c) instead of the negative electrode mixture slurry (a) in the same manner as for the negative electrode mixture layer (a). The total thickness of the negative electrode mixture layer (c) formed on both sides of the copper foil was 170 μm. The obtained sheet-shaped negative electrode was designated as the negative electrode of Example 2C.

[0081] A sheet-shaped negative electrode having a negative electrode mixture layer (d) formed on both sides of a copper foil was produced in the same manner as in the case of the negative electrode mixture layer (a) using the negative electrode mixture slurry (d) instead of the negative electrode mixture slurry (a). The total thickness of the negative electrode mixture layer (d) formed on both sides of the copper foil was 170 μm. The obtained sheet-shaped negative electrode was designated as the negative electrode of Example 2D.

[0082] [Examples 3A to 3D] <Preparation of copper foil> A copper foil having a thickness of 15 μm was prepared and subjected to heat treatment. The average crystallite size in the cross section of the copper foil after the heat treatment was measured by the method described below, and the average crystallite size was 0.53 μm.

[0083] <Preparation of Negative Electrode Mixture Slurries (a) to (d)> Negative electrode mixture slurries (a) to (d) identical to those prepared in Examples 1A to 1D were prepared.

[0084] <Preparation of negative electrode> The negative electrode mixture slurry (a) was applied to both sides of the copper foil prepared by the above method, having an average crystallite size in cross section of 0.53 μm, and the coating was dried and compressed to prepare a sheet-like negative electrode having a negative electrode mixture layer (a) on the surface of the copper foil. The size of the copper foil used to prepare the sheet-like negative electrode was 600 mm wide and 15 μm thick. The total thickness of the negative electrode mixture layer formed on both sides of the copper foil was 170 μm. The obtained sheet-like negative electrode was the negative electrode of Example 3A.

[0085] A sheet-shaped negative electrode was prepared by using the negative electrode mixture slurry (b) instead of the negative electrode mixture slurry (a) in the same manner as the negative electrode mixture layer (a). The total thickness of the negative electrode mixture layer (b) formed on both sides of the copper foil was 170 μm. The obtained sheet-shaped negative electrode was designated as the negative electrode of Example 3B.

[0086] A sheet-shaped negative electrode was prepared by using the negative electrode mixture slurry (c) instead of the negative electrode mixture slurry (a) in the same manner as the negative electrode mixture layer (a). The total thickness of the negative electrode mixture layer (c) formed on both sides of the copper foil was 170 μm. The obtained sheet-shaped negative electrode was designated as the negative electrode of Example 3C.

[0087] A sheet-shaped negative electrode having a negative electrode mixture layer (d) formed on both sides of a copper foil was produced in the same manner as in the case of the negative electrode mixture layer (a) using the negative electrode mixture slurry (d) instead of the negative electrode mixture slurry (a). The total thickness of the negative electrode mixture layer (d) formed on both sides of the copper foil was 170 μm. The obtained sheet-shaped negative electrode was designated as the negative electrode of Example 3D.

[0088] [Examples 4A to 4D] <Preparation of copper foil> A copper foil having a thickness of 15 μm was prepared and subjected to heat treatment. The average crystallite size in the cross section of the copper foil after the heat treatment was measured by the method described below, and the average crystallite size was 0.88 μm.

[0089] <Preparation of Negative Electrode Mixture Slurries (a) to (d)> Negative electrode mixture slurries (a) to (d) identical to those prepared in Examples 1A to 1D were prepared.

[0090] <Preparation of negative electrode> The negative electrode mixture slurry (a) was applied to both sides of the copper foil prepared by the above method, having an average crystallite size in cross section of 0.88 μm, and the coating was dried and compressed to prepare a sheet-like negative electrode having a negative electrode mixture layer (a) on the surface of the copper foil. The size of the copper foil used to prepare the sheet-like negative electrode was 600 mm wide and 15 μm thick. The total thickness of the negative electrode mixture layer formed on both sides of the copper foil was 170 μm. The obtained sheet-like negative electrode was the negative electrode of Example 4A.

[0091] A sheet-shaped negative electrode was prepared by using the negative electrode mixture slurry (b) instead of the negative electrode mixture slurry (a) in the same manner as the negative electrode mixture layer (a). The total thickness of the negative electrode mixture layer (b) formed on both sides of the copper foil was 170 μm. The obtained sheet-shaped negative electrode was designated as the negative electrode of Example 4B.

[0092] A sheet-shaped negative electrode having a negative electrode mixture layer (c) formed on both sides of a copper foil was produced in the same manner as for the negative electrode mixture layer (a) using the negative electrode mixture slurry (c) instead of the negative electrode mixture slurry (a). The total thickness of the negative electrode mixture layer (c) formed on both sides of the copper foil was 170 μm. The resulting sheet-shaped negative electrode was designated as the negative electrode of Example 4C.

[0093] A sheet-shaped negative electrode having a negative electrode mixture layer (d) formed on both sides of a copper foil was produced in the same manner as for the negative electrode mixture layer (a) using the negative electrode mixture slurry (d) instead of the negative electrode mixture slurry (a). The total thickness of the negative electrode mixture layer (d) formed on both sides of the copper foil was 170 μm. The obtained sheet-shaped negative electrode was designated as the negative electrode of Example 4D.

[0094] [Examples 5A to 5D] <Preparation of copper foil> A copper foil having a thickness of 15 μm was prepared and subjected to heat treatment. The average crystallite size in the cross section of the copper foil after the heat treatment was measured by the method described below, and the average crystallite size was 0.99 μm.

[0095] <Preparation of Negative Electrode Mixture Slurries (a) to (d)> Negative electrode mixture slurries (a) to (d) identical to those prepared in Examples 1A to 1D were prepared.

[0096] <Preparation of negative electrode> The negative electrode mixture slurry (a) was applied to both sides of the copper foil prepared by the above method, having an average crystallite size in cross section of 0.99 μm, and the coating was dried and compressed to prepare a sheet-like negative electrode having a negative electrode mixture layer (a) on the surface of the copper foil. The size of the copper foil used to prepare the sheet-like negative electrode was 600 mm wide and 15 μm thick. The total thickness of the negative electrode mixture layer formed on both sides of the copper foil was 170 μm. The obtained sheet-like negative electrode was the negative electrode of Example 5A.

[0097] A sheet-shaped negative electrode was prepared by using the negative electrode mixture slurry (b) instead of the negative electrode mixture slurry (a) in the same manner as the negative electrode mixture layer (a). The total thickness of the negative electrode mixture layer (b) formed on both sides of the copper foil was 170 μm. The obtained sheet-shaped negative electrode was designated as the negative electrode of Example 5B.

[0098] A sheet-shaped negative electrode was prepared by using the negative electrode mixture slurry (c) instead of the negative electrode mixture slurry (a) in the same manner as the negative electrode mixture layer (a). The total thickness of the negative electrode mixture layer (c) formed on both sides of the copper foil was 170 μm. The obtained sheet-shaped negative electrode was designated as the negative electrode of Example 5C.

[0099] A sheet-shaped negative electrode having a negative electrode mixture layer (d) formed on both sides of a copper foil was produced in the same manner as in the case of the negative electrode mixture layer (a) using the negative electrode mixture slurry (d) instead of the negative electrode mixture slurry (a). The total thickness of the negative electrode mixture layer (d) formed on both sides of the copper foil was 170 μm. The obtained sheet-shaped negative electrode was designated as the negative electrode of Example 5D.

[0100] [Examples 6A to 6D] <Preparation of copper foil> A copper foil having a thickness of 15 μm was prepared and subjected to heat treatment. The average crystallite size in the cross section of the copper foil after the heat treatment was measured by the method described below, and the average crystallite size was 1.24 μm.

[0101] <Preparation of Negative Electrode Mixture Slurries (a) to (d)> Negative electrode mixture slurries (a) to (d) identical to those prepared in Examples 1A to 1D were prepared.

[0102] <Preparation of negative electrode> The negative electrode mixture slurry (a) was applied to both sides of the copper foil prepared by the above method, having an average crystallite size in cross section of 1.2 μm, and the coating was dried and compressed to prepare a sheet-like negative electrode having a negative electrode mixture layer (a) on the surface of the copper foil. The size of the copper foil used to prepare the sheet-like negative electrode was 600 mm wide and 15 μm thick. The total thickness of the negative electrode mixture layer formed on both sides of the copper foil was 170 μm. The obtained sheet-like negative electrode was the negative electrode of Example 6A.

[0103] A sheet-shaped negative electrode was prepared by using the negative electrode mixture slurry (b) instead of the negative electrode mixture slurry (a) in the same manner as the negative electrode mixture layer (a). The total thickness of the negative electrode mixture layer (b) formed on both sides of the copper foil was 170 μm. The obtained sheet-shaped negative electrode was designated as the negative electrode of Example 6B.

[0104] A sheet-shaped negative electrode was prepared by using the negative electrode mixture slurry (c) instead of the negative electrode mixture slurry (a) in the same manner as the negative electrode mixture layer (a). The total thickness of the negative electrode mixture layer (c) formed on both sides of the copper foil was 170 μm. The obtained sheet-shaped negative electrode was designated as the negative electrode of Example 6C.

[0105] A sheet-shaped negative electrode having a negative electrode mixture layer (d) formed on both sides of a copper foil was produced in the same manner as in the case of the negative electrode mixture layer (a) using the negative electrode mixture slurry (d) instead of the negative electrode mixture slurry (a). The total thickness of the negative electrode mixture layer (d) formed on both sides of the copper foil was 170 μm. The obtained sheet-shaped negative electrode was designated as the negative electrode of Example 6D.

[0106] [Examples 7A to 7D] <Preparation of copper foil> A copper foil having a thickness of 15 μm was prepared and subjected to heat treatment. The average crystallite size in the cross section of the copper foil after the heat treatment was measured by the method described below, and the average crystallite size was 3.05 μm.

[0107] <Preparation of Negative Electrode Mixture Slurries (a) to (d)> Negative electrode mixture slurries (a) to (d) identical to those prepared in Examples 1A to 1D were prepared.

[0108] <Preparation of negative electrode> The negative electrode mixture slurry (a) was applied to both sides of the copper foil prepared by the above method, having an average crystallite size in cross section of 3.05 μm, and the coating was dried and compressed to prepare a sheet-like negative electrode having a negative electrode mixture layer (a) on the surface of the copper foil. The size of the copper foil used to prepare the sheet-like negative electrode was 600 mm wide and 15 μm thick. The total thickness of the negative electrode mixture layer formed on both sides of the copper foil was 170 μm. The obtained sheet-like negative electrode was the negative electrode of Example 7A.

[0109] A sheet-shaped negative electrode was prepared by using the negative electrode mixture slurry (b) instead of the negative electrode mixture slurry (a) in the same manner as the negative electrode mixture layer (a). The total thickness of the negative electrode mixture layer (b) formed on both sides of the copper foil was 170 μm. The obtained sheet-shaped negative electrode was designated as the negative electrode of Example 7B.

[0110] A sheet-shaped negative electrode having a negative electrode mixture layer (c) formed on both sides of a copper foil was produced in the same manner as for the negative electrode mixture layer (a) using the negative electrode mixture slurry (c) instead of the negative electrode mixture slurry (a). The total thickness of the negative electrode mixture layer (c) formed on both sides of the copper foil was 170 μm. The obtained sheet-shaped negative electrode was designated as the negative electrode of Example 7C.

[0111] A sheet-shaped negative electrode having a negative electrode mixture layer (d) formed on both sides of a copper foil was prepared in the same manner as in the negative electrode mixture layer (a) using the negative electrode mixture slurry (d) instead of the negative electrode mixture slurry (a). The total thickness of the negative electrode mixture layer (d) formed on both sides of the copper foil was 170 μm. The obtained sheet-shaped negative electrode was designated as the negative electrode of Example 7D.

[0112] [Comparative Examples 1A to 1D] <Preparation of Copper Foil> A copper foil having a thickness of 15 μm was prepared. The average crystallite size in the cross section of the copper foil was measured by the method described below, and was found to be 0.71 μm.

[0113] <Preparation of Negative Electrode Mixture Slurries (a) to (d)> Negative electrode mixture slurries (a) to (d) identical to those prepared in Examples 1A to 1D were prepared.

[0114] <Preparation of negative electrode> The negative electrode mixture slurry (a) was applied to both sides of the copper foil prepared by the above method, having an average crystallite size in cross section of 0.71 μm, and the coating was dried and compressed to prepare a sheet-like negative electrode having a negative electrode mixture layer (a) on the surface of the copper foil. The size of the copper foil used to prepare the sheet-like negative electrode was 600 mm wide and 15 μm thick. The total thickness of the negative electrode mixture layer formed on both sides of the copper foil was 170 μm. The obtained sheet-like negative electrode was designated as the negative electrode of Comparative Example 1A.

[0115] A sheet-shaped negative electrode was prepared by using the negative electrode mixture slurry (b) instead of the negative electrode mixture slurry (a) in the same manner as for the negative electrode mixture layer (a). The total thickness of the negative electrode mixture layer (b) formed on both sides of the copper foil was 170 μm. The obtained sheet-shaped negative electrode was designated as the negative electrode of Comparative Example 1B.

[0116] A sheet-shaped negative electrode was prepared by using the negative electrode mixture slurry (c) instead of the negative electrode mixture slurry (a) in the same manner as for the negative electrode mixture layer (a). The total thickness of the negative electrode mixture layer (c) formed on both sides of the copper foil was 170 μm. The obtained sheet-shaped negative electrode was designated as the negative electrode of Comparative Example 1C.

[0117] A sheet-shaped negative electrode having a negative electrode mixture layer (d) formed on both sides of a copper foil was produced in the same manner as for the negative electrode mixture layer (a) using the negative electrode mixture slurry (d) instead of the negative electrode mixture slurry (a). The total thickness of the negative electrode mixture layer (d) formed on both sides of the copper foil was 170 μm. The obtained sheet-shaped negative electrode was designated as the negative electrode of Comparative Example 1D.

[0118] [Comparative Examples 2A to 2D] <Preparation of Copper Foil> A copper foil having a thickness of 15 μm was prepared. The average crystallite size in the cross section of the copper foil was measured by the method described below, and was found to be 0.62 μm.

[0119] <Preparation of Negative Electrode Mixture Slurries (a) to (d)> Negative electrode mixture slurries (a) to (d) identical to those prepared in Examples 1A to 1D were prepared.

[0120] <Preparation of negative electrode> The negative electrode mixture slurry (a) was applied to both sides of the copper foil prepared by the above method, having an average crystallite size in cross section of 0.62 μm, and the coating was dried and compressed to prepare a sheet-like negative electrode having a negative electrode mixture layer (a) on the surface of the copper foil. The size of the copper foil used to prepare the sheet-like negative electrode was 600 mm wide and 15 μm thick. The total thickness of the negative electrode mixture layer formed on both sides of the copper foil was 170 μm. The obtained sheet-like negative electrode was designated as the negative electrode of Comparative Example 2A.

[0121] A sheet-shaped negative electrode was prepared by using the negative electrode mixture slurry (b) instead of the negative electrode mixture slurry (a) in the same manner as for the negative electrode mixture layer (a). The total thickness of the negative electrode mixture layer (b) formed on both sides of the copper foil was 170 μm. The obtained sheet-shaped negative electrode was designated as the negative electrode of Comparative Example 2B.

[0122] A sheet-shaped negative electrode was prepared by using the negative electrode mixture slurry (c) instead of the negative electrode mixture slurry (a) in the same manner as for the negative electrode mixture layer (a). The total thickness of the negative electrode mixture layer (c) formed on both sides of the copper foil was 170 μm. The obtained sheet-shaped negative electrode was designated as the negative electrode of Comparative Example 2C.

[0123] A sheet-shaped negative electrode having a negative electrode mixture layer (d) formed on both sides of a copper foil was produced in the same manner as in the case of the negative electrode mixture layer (a) using the negative electrode mixture slurry (d) instead of the negative electrode mixture slurry (a). The total thickness of the negative electrode mixture layer (d) formed on both sides of the copper foil was 170 μm. The obtained sheet-shaped negative electrode was designated as the negative electrode of Comparative Example 2D.

[0124] [Measurement of average crystallite size] A portion of the copper foil was cut out and processed with an ion milling device to expose the cross section of the copper foil. EBSD analysis was performed on this cross section using a scanning electron microscope, and the obtained diffraction pattern was analyzed by detecting bands using the Hough transformation method to determine the crystal orientation, thereby identifying the individual crystallite sizes. The crystallite size (crystallite diameter) of crystallites within a 100 μm wide region (i.e., within a region of copper foil thickness × 100 μm wide) in an arbitrarily selected copper foil cross section was determined, and the sum was divided by the number of crystallites in the same region to determine the average crystallite size.

[0125] [Evaluation of Blade Replacement Frequency] The sheet-shaped negative electrodes of the Examples and Comparative Examples were cut using a slitting device. The cut surface of the negative electrode was visually inspected, and if the cut surface became jagged rather than sharp, it was determined that the slit blade needed replacing. The negative electrode was cut until the cumulative cut length reached 100,000 m, and the slit blade replacement frequency (i.e., the number of replacements) during that time was measured. The results are shown in Table 1. Table 1 shows the evaluation results for Examples 1A to 7A and Comparative Examples 1A and 2A, in which the same negative electrode mixture layer (a) was formed, based on the replacement frequency of Comparative Example 1A. Table 1 shows the evaluation results for Examples 1B to 7B and Comparative Examples 1B and 2B, in which the same negative electrode mixture layer (b) was formed, based on the replacement frequency of Comparative Example 1B. Similarly, negative electrodes in which the same negative electrode mixture layers (c) and (d) were formed were also compared.

[0126] The meanings of the notations for the evaluation results in Table 1 are as follows: A: Replacement frequency is 1 / 10 or less of the standard (Comparative Example 1); B: Replacement frequency is more than 1 / 10 and 1 / 2 or less of the standard (Comparative Example 1); C: Replacement frequency is more than 1 / 2 of the standard (Comparative Example 1).

[0127]

[0128] As shown in Table 1, the negative electrodes in which the average crystallite size in the cross section of the copper foil was 0.55 μm or less or 0.85 μm or more were able to reduce the frequency of blade replacement compared to the negative electrodes of Comparative Examples 1 and 2.

[0129] The technology of the present disclosure is useful for batteries such as lithium ion secondary batteries.

Claims

1. A negative electrode comprising: a copper foil; and a negative electrode mixture layer containing a negative electrode active material disposed on the copper foil, wherein the average crystallite size in a cross section of the copper foil is 0.55 μm or less, or 0.85 μm or more.

2. The negative electrode according to claim 1, wherein the negative electrode active material comprises at least one selected from the group consisting of a material capable of forming an alloy with lithium and a carbon material.

3. The negative electrode according to claim 2, wherein the negative electrode active material includes a silicon-containing material as the material capable of forming an alloy with lithium.

4. The negative electrode according to claim 3, wherein the mass ratio of the silicon-containing material in the negative electrode mixture layer is 2% or more.

5. The negative electrode according to claim 1, wherein the average crystallite size in the cross section of the copper foil is 0.55 μm or less, or 0.85 μm or more and 3.0 μm or less.

6. The negative electrode according to claim 1, wherein the average crystallite size on the surface of the copper foil is 0.55 μm or less, or 0.85 μm or more and 3.0 μm or less.

7. A battery comprising: a negative electrode according to any one of claims 1 to 6; a positive electrode; and an electrolyte.

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