Negative electrode and non-aqueous electrolyte secondary battery

Abstract

To suppress reduction of input-output characteristics.SOLUTION: A negative electrode includes a negative electrode collector, and a negative electrode active material layer including a negative electrode active material. The negative electrode active material layer includes a first region and a second region. The second region is less dense than the first region by at least 7%. The value of the second region occupies more than 7% and 50% at most of the volume of the negative electrode active material layer.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a negative electrode and a non-aqueous electrolyte secondary battery. [Background technology]

[0002] Patent Document 1 (Japanese Patent Laid-Open Publication No. 2022-27413) discloses a secondary battery in which the basis weight of the negative electrode active material layer is increased in order to increase the capacity. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2022-27413 Summary of the Invention [Problem to be solved by the invention]

[0004] There is a demand for further increases in the capacity of non-aqueous electrolyte secondary batteries. To achieve this, the basis weight of the electrodes has been increased. However, when the basis weight of the electrodes is increased, the diffusion path of ions such as lithium ions contained in the electrolyte becomes longer, which causes a problem of deterioration in input / output characteristics.

[0005] An object of the present disclosure is to suppress degradation of input / output characteristics. [Means for solving the problem]

[0006] [1] A negative electrode having a negative electrode current collector and a negative electrode active material layer containing a negative electrode active material, the negative electrode active material layer includes a first region and a second region, the density of the second region is at least 7% lower than the density of the first region; a volume ratio of the second region in the negative electrode active material layer that is greater than 7% and not greater than 50%;

[0007] If the negative electrode active material layer is composed only of high-density regions, it is possible to achieve high capacity, but the ion diffusion path becomes longer, resulting in poor input / output characteristics.On the other hand, if the negative electrode active material layer is composed only of low-density regions, it is difficult to achieve high capacity, although the input / output characteristics are improved.

[0008] The inventors have found that in a negative electrode active material layer having two regions with a density difference of 7% or more, each region having a predetermined volume ratio, the ion diffusion path is shortened, thereby suppressing deterioration in input / output characteristics.

[0009] [2] The negative electrode according to [1], wherein the second region is in a lattice pattern. [3] The negative electrode active material layer includes a plurality of the second regions, the second region is columnar, The negative electrode according to [1], wherein the closest distance between the plurality of second regions is 50 μm or less.

[0010] [4] The coating weight of the negative electrode active material layer is 20 mg / cm 2 The negative electrode according to any one of [1] to [3] above.

[0011] [5] A non-aqueous electrolyte secondary battery comprising the negative electrode according to any one of [1] to [4]. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a conceptual diagram showing an example of the negative electrode in this embodiment. [Figure 2] FIG. 2 is a schematic plan view showing the negative electrode of FIG. [Figure 3] FIG. 3 is a conceptual diagram showing another example of the negative electrode in this embodiment. [Figure 4] FIG. 4 is a schematic plan view showing the negative electrode of FIG. [Figure 5] FIG. 5 is a conceptual diagram showing an example of a nonaqueous electrolyte secondary battery according to this embodiment. [Figure 6] FIG. 6 is a table showing the first battery configuration. [Figure 7]FIG. 7 is a table showing the second battery configuration. [Figure 8] FIG. 8 is a table showing the third battery configuration. [Figure 9] FIG. 9 is a table showing the sample configurations and evaluation results of test batteries Nos. 1 to 17. [Figure 10] FIG. 10 is a graph showing the relationship between the density of the negative electrode active material layer and the CC charge rate for test batteries Nos. 1 to 17. [Figure 11] FIG. 11 is a graph showing the relationship between the volume fraction of the second region in the negative electrode active material layer and the CC charge rate for test batteries Nos. 8 and 11 to 14. [Figure 12] FIG. 12 is a graph showing the relationship between the closest distance between the second regions and the CC storage rate in the test batteries Nos. 15 to 17. DETAILED DESCRIPTION OF THE INVENTION

[0013] Hereinafter, an embodiment of the present disclosure (hereinafter may be abbreviated as "the present embodiment") and an example of the present disclosure (hereinafter may be abbreviated as "the present example") will be described. However, the present embodiment and the example do not limit the technical scope of the present disclosure.

[0014] The stoichiometric composition formula indicates a representative example of a compound. The compound may have a non-stoichiometric composition. For example, "Al2O3" is not limited to a compound having a substance ratio (molar ratio) of "Al / O = 2 / 3." Unless otherwise specified, "Al2O3" indicates a compound containing Al and O in any composition ratio. Furthermore, for example, the compound may be doped with a trace element, or a portion of Al and O may be substituted with another element.

[0015] The term "derivative" refers to a compound in which a part of a parent compound has been modified by at least one method selected from the group consisting of the introduction of a functional group, atomic substitution, oxidation, reduction, and other chemical reactions. The modification may be at one or more locations. The "substituent" may include at least one selected from the group consisting of, for example, alkyl groups, alkenyl groups, alkynyl groups, cycloalkyl groups, unsaturated cycloalkyl groups, aromatic groups, heterocyclic groups, halogen atoms (such as F, Cl, Br, and I), OH groups, SH groups, CN groups, SCN groups, OCN groups, nitro groups, alkoxy groups, unsaturated alkoxy groups, amino groups, alkylamino groups, dialkylamino groups, aryloxy groups, acyl groups, alkoxycarbonyl groups, acyloxy groups, aryloxycarbonyl groups, acylamino groups, alkoxycarbonylamino groups, aryloxycarbonylamino groups, sulfonylamino groups, sulfamoyl groups, carbamoyl groups, alkylthio groups, arylthio groups, sulfonyl groups, sulfinyl groups, ureido groups, phosphoric acid amide groups, sulfo groups, carboxy groups, hydroxamic acid groups, sulfino groups, hydrazino groups, imino groups, and silyl groups. These substituents may be further substituted. When there are two or more substituents, the substituents may be the same or different, and multiple substituents may be bonded to each other to form a ring.

[0016] The "copolymer" includes at least one selected from the group consisting of unspecified type, statistical type, random type, alternating type, periodic type, block type, and graft type.

[0017] <<Negative electrode>> 1 to 4 are conceptual diagrams and schematic plan views showing an example of a negative electrode in this embodiment. As shown in Figures 1 to 4, a negative electrode 10 includes a negative electrode current collector 11 and a negative electrode active material layer 12. The negative electrode active material layer 12 includes a first region 13 and a second region 14.

[0018] 《Negative electrode current collector》 The negative electrode current collector 11 is conductive. The negative electrode current collector 11 may have a thickness of, for example, 5 to 50 μm. The negative electrode current collector 11 may include, for example, a metal foil. The negative electrode current collector 11 may include, for example, at least one selected from the group consisting of Cu, Ni, Fe, Zn, Pb, Ag, and Au. The negative electrode current collector 11 may include, for example, a Cu foil, a Cu alloy foil, or the like.

[0019] 《Negative electrode active material layer》 The negative electrode active material layer 12 may have a thickness of, for example, 10 to 1000 μm, 50 to 500 μm, or 100 to 300 μm. The negative electrode active material layer 12 contains a negative electrode active material. The negative electrode active material layer 12 may further contain, for example, a conductive material and a binder. Note that the first region 13 and the second region 14 described below also contain the negative electrode active material and may further contain a conductive material, a binder, a thickener, etc.

[0020] <Conductive material> The conductive material can form an electron conduction path within the negative electrode active material layer 12. The content of the conductive material may be, for example, 0.1 to 10 parts by mass relative to 100 parts by mass of the negative electrode active material. The conductive material may contain any component. The conductive material may include, for example, at least one selected from the group consisting of graphite, AB, Ketjen Black, VGCF, CNT, and GF. The CNT may include at least one selected from the group consisting of single-walled CNT (SWCNT) and multi-walled CNT (MWCNT).

[0021] <Binder> The content of the binder may be, for example, 0.1 to 10 parts by mass per 100 parts by mass of the negative electrode active material. The binder may contain any component. For example, the binder may contain at least one selected from the group consisting of styrene butadiene rubber (SBR), acrylate butadiene rubber (ABR), sodium alginate, carboxymethyl cellulose (CMC-H, CMC-Na, CMC-Li, CMC-NH4, etc.), polyacrylic acid (PAA-H, PAA-Na, PAA-Li, etc.), polyacrylonitrile (PAN), polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE), acrylic resin (acrylic acid ester copolymer), methacrylic resin (methacrylic acid ester copolymer), polyvinylpyrrolidone (PVP), polyvinyl alcohol (PVA), and derivatives thereof. For example, "CMC-Na" refers to the Na salt of CMC. For example, "CMC-H" refers to acid-type CMC. The same is true for "PAA-Na" etc.

[0022] <Thickener> The content of the thickener may be, for example, 0.1 to 10 parts by mass relative to 100 parts by mass of the negative electrode active material. The thickener may contain any component. For example, the thickener may contain carboxymethyl cellulose (CMC), methyl cellulose (MC), etc.

[0023] <Other ingredients> The negative electrode active material layer 12 may further contain, for example, an inorganic filler, an organic filler, a solid electrolyte, a surface modifier, a dispersant, a lubricant, a flame retardant, a protective agent, a flux, a coupling agent, an adsorbent, etc. The negative electrode active material layer may also contain, for example, a layered silicate (smectite, montmorillonite, bentonite, hectorite, etc.), an inorganic filler (solid alumina, hollow silica, boehmite, etc.), a polysiloxane compound, etc.

[0024] <Negative electrode active material> The negative electrode active material may contain, for example, at least one selected from the group consisting of natural graphite, artificial graphite, soft carbon, hard carbon, silicon (Si), SiO, Li silicate, Si-based alloy, tin (Sn), SnO, Sn-based alloy, and Li4Ti5O 12 and the like.

[0025] 〈Carbon-based active material〉 "Graphite" is a general term for natural graphite and artificial graphite. Graphite may be a mixture of natural graphite and artificial graphite. The mixing ratio (mass ratio) may be, for example, "natural graphite / artificial graphite = 1 / 9 to 9 / 1", "natural graphite / artificial graphite = 2 / 8 to 8 / 2", or "natural graphite / artificial graphite = 3 / 7 to 7 / 3".

[0026] Graphite may contain a dopant. The dopant may contain, for example, at least one selected from the group consisting of B, N, P, Li, and Ca. The addition amount may be, in molar fraction, for example, 0.01 to 5%, 0.1 to 3%, or 0.1 to 1%.

[0027] The surface of the graphite may be coated with, for example, amorphous carbon. The surface of the graphite may be coated with, for example, a different material from the graphite. The different material may contain, for example, at least one selected from the group consisting of P, W, Al, and O. The different material may contain, for example, at least one selected from the group consisting of Al(OH)3, AlOOH, Al2O3, WO3, Li2CO3, LiHCO[[ID=​​​​​​​​​​​​​​​​​​​

[0031] The Li silicate may include at least one selected from the group consisting of Li4SiO4, Li2SiO3, Li2Si2O5, and Li8SiO6. The second negative electrode active material may include a mixture of Si and Li silicate. The mixing ratio (mass ratio) may be, for example, "Si / Li silicate = 1 / 9 to 9 / 1," "Si / Li silicate = 2 / 8 to 8 / 2," "Si / Li silicate = 3 / 7 to 7 / 3," or "Si / Li silicate = 4 / 6 to 6 / 4."

[0032] The alloy-based active material (e.g., Si, SiO) may contain an additive. The additive may be, for example, a substitutional solute atom or an interstitial solute atom. The additive may be a deposit attached to the surface of the alloy-based active material. The deposit may be, for example, an element, an oxide, a carbide, a nitride, a halide, or the like. The amount added may be, for example, 0.01 to 5%, 0.1 to 3%, or 0.1 to 1% by mole fraction. The additive may contain, for example, at least one selected from the group consisting of Li, Na, K, Rb, Be, Mg, Ca, Sr, Fe, Ba, B, Al, Ga, In, C, Ge, Sn, Pb, N, P, As, Y, Sb, and S. That is, SiO may be doped with Mg or Na. For example, Mg silicate or Na silicate may be formed. For example, boron oxide (for example, B2O3), yttrium oxide (for example, Y2O3, etc.), etc. may be added to SiO.

[0033] <Si-C composite material> The negative electrode active material may include, for example, a composite material of a carbon-based active material (such as graphite) and an alloy-based active material (such as Si). A composite material containing Si and carbon may also be called a "Si-C composite material." For example, Si fine particles may be dispersed in carbon particles. For example, Si fine particles may be dispersed in graphite particles. For example, Li silicate particles may be coated with a carbon material (such as amorphous carbon). A Si-C composite material and graphite may be mixed and used.

[0034] <Multi-component system> The negative electrode active material may contain two or more components. The negative electrode active material may contain a carbon-based active material (such as graphite) and an alloy-based active material (such as Si or SiO). The mixing ratio (mass ratio) of the carbon-based active material to the alloy-based active material may be, for example, "carbon-based active material / alloy-based active material=1 / 9 to 9 / 1," "carbon-based active material / alloy-based active material=2 / 8 to 8 / 2," "carbon-based active material / alloy-based active material=3 / 7 to 7 / 3," or "carbon-based active material / alloy-based active material=4 / 6 to 6 / 4."

[0035] <Structure of negative electrode active material layer> The negative electrode active material layer 12 includes a first region 13 and a second region 14 having different densities. The first region 13 and the second region 14 are each connected from the surface of the negative electrode current collector 11 to the surface opposite the negative electrode current collector 11.

[0036] In the negative electrode active material layer 12, the first regions 13 and the second regions 14 are in contact with each other. There are no particular limitations on the positional relationship between the first regions 13 and the second regions 14. As shown in FIGS. 1 and 2 , in the negative electrode active material layer 12, the second regions 14 may have, for example, a lattice shape in a planar view. That is, the first regions 13 are separated by the second regions 14. For example, in a planar view, the second regions 14 may have a regular lattice shape, a short lattice shape, a triangular lattice shape, a diagonal lattice shape, or the like.

[0037] When the second region 14 has a lattice pattern, the mesh size (μm) ("p1" in FIG. 2) and wire diameter (μm) ("p2" in FIG. 2) of the second region 14 in a plan view are not particularly limited, and may be adjusted so that the volume ratio of the first region 13 to the second region 14 described below falls within the range. The mesh size may be, for example, 20 μm or more, 30 μm or more, 50 μm or less, or 40 μm or less. The wire diameter may be, for example, 5 μm or more, 15 μm or more, 25 μm or less, or 20 μm or less. The mesh size and wire diameter may be measured, for example, using an SEM image.

[0038] 3 and 4, in the negative electrode active material layer 12, the second regions 14 may be, for example, columnar. That is, the second regions 14 are separated by the first regions 13. The second regions 14 may be, for example, cylindrical or prismatic. The second regions 14 may be, for example, rectangular or oblique. The second regions 14 may be, for example, randomly dispersed or regularly arranged.

[0039] When the second regions 14 are columnar, the closest distance between the multiple second regions 14 ("q" in FIG. 4) is 50 μm or less. Here, the "closest distance" refers to the distance between the closest second regions 14 among the multiple second regions 14 in the negative electrode active material layer 12. If the closest distance between the multiple second regions 14 exceeds 50 μm, ion migration between the second regions 14 is suppressed, which may result in a deterioration in input / output characteristics. The closest distance between the multiple second regions 14 is preferably 40 μm or less. Note that there is no particular restriction on the lower limit of the closest distance between the multiple second regions 14 as long as it exceeds 0 μm, and it may be, for example, 5 μm or more, or 10 μm or more.

[0040] Density of the second region 14 (g / cm 3 ) is the density (g / cm 3 ) of the first region 13 3 ) is 7% or more lower than the density of the first region 13. If the density of the second region 14 is 7% or more lower than the density of the first region 13, ions are more likely to diffuse into the second region 14, which is a low-density region. This shortens the ion diffusion path in the negative electrode active material layer 12, and as a result, it is expected that the deterioration of input / output characteristics will be suppressed. The density of the second region 14 may be 10% or more lower, 15% or more lower, or 20% or more lower than the density of the first region 13. Furthermore, from the viewpoint of ensuring input / output performance, the density of the second region 14 may be 50% or less lower, or 30% or less lower than the density of the first region 13.

[0041] The volume ratio of the second region 14 in the negative electrode active material layer 12 is more than 7% and not more than 50%. That is, the volume ratio of the first region 13 in the negative electrode active material layer 12 is not less than 50% and less than 93%. If the volume ratio of the second region 14 in the negative electrode active material layer 12 is not more than 7%, ions cannot easily diffuse, which may result in a deterioration in input / output characteristics. If the volume ratio of the second region 14 in the negative electrode active material layer 12 exceeds 50%, an increase in the amount of negative electrode active material unused during high-load charging may result in a deterioration in input / output characteristics. Preferably, the volume ratio of the second region 14 in the negative electrode active material layer 12 is not less than 10% and not more than 40%.

[0042] Negative electrode active material layer 12 may contain two or more negative electrode active materials. That is, first region 13 and second region 14 may contain two or more negative electrode active materials. When first region 13 and second region 14 each contain two or more negative electrode active materials, it is preferable that the types of negative electrode active materials contained in each region are the same, and that the content ratios (weight ratios) of the same type of negative electrode active materials contained in each region are also the same in each region.

[0043] <Basis Weight> The weight of the negative electrode active material layer 12 is 20 mg / cm 2 The weight of the negative electrode active material layer 12 is preferably 25 mg / cm or more. This is because the effect of suppressing the deterioration of the input / output characteristics in this embodiment is more effectively exhibited when the capacity is increased. 2 It is more preferable that the basis weight in this embodiment is the sum of values ​​obtained by multiplying the basis weight in each of the first region 13 and the second region 14 by the volume ratio occupied by each region.

[0044] <<Negative electrode manufacturing method>> The method for producing a negative electrode in this embodiment includes, for example, a step of preparing a slurry containing a negative electrode active material and a solvent (preparation step), a step of applying the slurry to a negative electrode current collector to form a coating film (coating step), a step of drying the coating film (drying step), and a step of compressing the coating film to form a negative electrode active material layer (compression step). Examples of the method for producing a negative electrode in this embodiment are shown below, but the present invention is not limited to these.

[0045] <Production Example 1> <Preparation process> In this step, a slurry containing a negative electrode active material and a solvent is prepared. In this step, a conductive material, a binder, and the like may be further added. For example, the negative electrode active material, the conductive material, the binder, and the solvent are mixed to prepare the slurry.

[0046] Examples of the solvent include an aqueous solvent and an organic solvent. The aqueous solvent refers to water or a mixed solvent containing water and a polar organic solvent. For example, an appropriate dispersion medium can be selected depending on the types of the negative electrode active material, binder, etc.

[0047] As the aqueous solvent, water is preferably used because of its ease of handling. Examples of polar organic solvents that can be used in the mixed solvent include alcohols such as methanol, ethanol, and isopropyl alcohol, ketones such as acetone, and ethers such as tetrahydrofuran. Examples of organic solvents include N-methyl-2-pyrrolidone (NMP).

[0048] The slurry may have a solids concentration of, for example, 40% to 80%. Mixing can be carried out using any suitable stirring, mixing, or dispersing device.

[0049] <Coating process> In this step, the slurry is applied to the negative electrode current collector to form a coating film. In this manufacturing example, the slurry is applied to the negative electrode current collector by screen coating. Any screen printing machine can be used for the coating.

[0050] A negative electrode current collector and a mesh are prepared. The mesh has a mesh-like structure and is appropriately set depending on the desired volume ratio of the first and second regions and the desired basis weight. The mesh is placed on the negative electrode current collector. After placement, slurry is supplied to the mesh, and the slurry filling the openings of the mesh is transferred to the surface of the negative electrode current collector. After transfer, the mesh is removed, and the slurry flows into the mesh, forming a coating film on the negative electrode current collector.

[0051] <Drying process> In this step, the coating film is dried to evaporate the solvent in the coating film. Any drying device can be used for drying. For example, a hot air drying device, a hot plate, an infrared drying device, etc. may be used.

[0052] <Compression process> In this step, the coating film is compressed to form the negative electrode active material layer. Any compression device can be used for compression. The pressure can be adjusted depending on, for example, the desired densities of the first and second regions.

[0053] In the negative electrode active material layer of the negative electrode produced by the above method, the second region can be formed in a lattice pattern.

[0054] <Production Example 2> This manufacturing example differs from Manufacturing Example 1 in that the slurry is applied to the negative electrode current collector by gravure coating. The coating step in this manufacturing example will be described below. Note that the preparation step, drying step, and compression step are the same as those in Manufacturing Example 1, so their description will be omitted.

[0055] Any gravure printing machine can be used for coating. The gravure printing machine has a pressure roller, a gravure plate, and a doctor blade. The surface of the gravure plate has projections and recesses, and is appropriately set depending on the desired volume ratio between the first and second regions, the desired closest distance between the multiple second regions, and the desired basis weight. As the gravure plate rotates, the surface is filled with slurry. The slurry on the projections on the surface is removed by the doctor blade, leaving only the recesses on the surface. The transported negative electrode current collector is sandwiched between the pressure roller and the gravure plate, and is pressed by the pressure roller, transferring the slurry to the surface of the negative electrode current collector. After transfer, the slurry flows into the areas of the negative electrode current collector where the slurry has not been transferred, forming a coating film.

[0056] Thereafter, a negative electrode is produced through a drying step and a compression step in the same manner as in Production Example 1. In the negative electrode active material layer of the negative electrode produced by the above method, the second region can be formed in a columnar shape.

[0057] <<Nonaqueous electrolyte secondary battery>> 5 is a conceptual diagram showing an example of a non-aqueous electrolyte secondary battery according to this embodiment. A battery 100 includes a power generating element 50 and an electrolyte (not shown).

[0058] <Exterior body> The battery 100 may include an exterior body (not shown). The exterior body may house the power generating element 50 and the electrolyte. The exterior body may have any shape. For example, the exterior body may be a metal case or a pouch made of a metal foil laminated film. The case may have any shape. For example, the case may be cylindrical, rectangular, flat, coin-shaped, or the like. The exterior body may contain, for example, Al. The exterior body may house, for example, one power generating element 50, or may house multiple power generating elements 50. The multiple power generating elements 50 may form, for example, a series circuit or a parallel circuit. Within the exterior body, the multiple power generating elements 50 may be stacked in the thickness direction of the battery 100.

[0059] <Power generation elements> The power generating element 50 may also be referred to as an "electrode group," an "electrode body," or the like. The power generating element 50 includes a positive electrode 20 and a negative electrode 10. The power generating element 50 may further include a separator 30. The separator 30 is disposed between the positive electrode 20 and the negative electrode 10. The power generating element 50 may have any configuration. The power generating element 50 may be, for example, a laminated type. For example, the power generating element 50 may be formed by alternately stacking the positive electrodes 20 and the negative electrodes 10 with the separator 30 sandwiched between them. The power generating element 50 may be, for example, a wound type. For example, a laminate may be formed by stacking a strip-shaped positive electrode 20, a strip-shaped separator 30, and a strip-shaped negative electrode 10. The power generating element 50 may be formed by spirally winding the laminate. The wound type power generating element 50 may be formed into a flat shape after winding.

[0060] <Positive electrode> The positive electrode 20 may be, for example, in the form of a sheet. The positive electrode 20 includes a positive electrode current collector 21 and a positive electrode active material layer 22. The positive electrode current collector 21 is electrically conductive. The positive electrode current collector 21 supports the positive electrode active material layer 22. The positive electrode current collector 21 may be, for example, in the form of a sheet. The positive electrode current collector 21 may have a thickness of, for example, 5 to 50 μm. The positive electrode current collector 21 may include, for example, a metal foil. The positive electrode current collector 21 may include, for example, at least one selected from the group consisting of Al, Mn, Ti, Fe, and Cr. The positive electrode current collector 21 may include, for example, an Al foil, an Al alloy foil, a Ti foil, a stainless steel (SUS) foil, or the like.

[0061] An intermediate layer (not shown) may be formed between the positive electrode current collector 21 and the positive electrode active material layer 22. The intermediate layer does not contain a positive electrode active material. The intermediate layer may have a thickness of, for example, 0.1 to 5 μm. The intermediate layer may contain, for example, a conductive material, an insulating material, a binder, etc. The conductive material and the binder will be described later. The insulating material may contain, for example, alumina, boehmite, aluminum hydroxide, etc.

[0062] The positive electrode active material layer 22 is disposed on the surface of the positive electrode current collector 21. The positive electrode active material layer 22 may be disposed on only one surface of the positive electrode current collector 21. The positive electrode active material layer 22 may be disposed on both the front and back surfaces of the positive electrode current collector 21. The positive electrode active material layer 22 may have a thickness of, for example, 10 μm or more, 50 μm or more, 80 μm or more, or 100 μm or more. When the thickness of the positive electrode active material layer 22 is large, specifically, when the thickness is 80 μm or more, it is believed that the durability maintenance rate is further improved. Furthermore, the positive electrode active material layer 22 may have a thickness of 1000 μm or less, 500 μm or less, or 300 μm or less. The positive electrode active material layer 22 includes a positive electrode active material. The positive electrode active material layer 22 may further include, for example, a conductive material and a binder.

[0063] Conductive materials The conductive material can form an electron conduction path within the positive electrode active material layer 22. The amount of the conductive material may be, for example, 0.1 to 10 parts by mass with respect to 100 parts by mass of the positive electrode active material. The conductive material can contain any component. For example, the conductive material may contain at least one material selected from the group consisting of graphite, acetylene black (AB), Ketjen Black (registered trademark), vapor grown carbon fiber (VGCF), carbon nanotubes (CNT), and graphene flakes (GF).

[0064] Binder The binder can fix the positive electrode active material layer 22 to the positive electrode current collector 21. The amount of binder may be, for example, 0.1 to 10 parts by mass per 100 parts by mass of the positive electrode active material. The binder may contain any component. For example, the binder may contain at least one selected from the group consisting of polyvinylidene fluoride (PVdF), vinylidene fluoride-hexafluoropropylene copolymer (PVdF-HFP), tetrafluoroethylene (PTFE), CMC, PAA, polyvinyl alcohol (PVA), polyvinylpyrrolidone (PVP), polyoxyethylene alkyl ether, and derivatives thereof.

[0065] Other ingredients The positive electrode active material layer 22 may further contain, for example, an inorganic filler, an organic filler, a solid electrolyte, a surface modifier, a lubricant, a flame retardant, a protective agent, a flux, a coupling agent, an adsorbent, etc. The positive electrode active material layer 22 may also contain, for example, polyoxyethylene allyl phenyl ether phosphate, zeolite, a silane coupling agent, MoS2, WO3, etc.

[0066] <Cathode active material> The positive electrode active material may be, for example, in a particulate form. The positive electrode active material may have a D50 of, for example, 1 to 30 μm, 10 to 20 μm, or 1 to 10 μm. "D50" refers to the particle size at which the cumulative frequency from the smallest particle size reaches 50% in a volume-based particle size distribution. D50 can be measured by a laser diffraction method. The measurement sample is a powder.

[0067] The positive electrode active material may contain any component. The positive electrode active material may contain, for example, a transition metal oxide, a polyanion compound, etc. The composition within one particle (positive electrode active material) may be uniform or non-uniform. For example, the composition may be graded from the surface to the center of the particle. The composition may change continuously or discontinuously (in steps).

[0068] <Transition metal oxides: space group R-3m> The transition metal oxide may have any crystal structure. The transition metal oxide may include, for example, a crystal structure belonging to the space group R-3m. For example, a compound represented by the general formula "LiMO2" may have a crystal structure belonging to the space group R-3m. The transition metal oxide may be, for example, a compound represented by the following formula ( B -1).

[0069] Li 1-a Ni x M 1-x O2…(B-1) In the formula, the relationships of -0.5≦a≦0.5 and 0≦x≦1 are satisfied.

[0070] M may optionally contain at least one selected from the group consisting of, for example, Co, Mn, and Al.

[0071] In the above formula (B-1), x may satisfy, for example, the relationship of 0 < x ≦ 0.1, 0.1 ≦ x ≦ 0.2, 0.2 ≦ x ≦ 0.3, 0.3 ≦ x ≦ 0.4, 0.4 ≦ x ≦ 0.5, 0.5 ≦ x ≦ 0.6, 0.6 ≦ x ≦ 0.7, 0.7 ≦ x ≦ 0.8, 0.8 ≦ x ≦ 0.9, or 0.9 ≦ x ≦ 1. a may satisfy, for example, the relationship of -0.4 ≦ a ≦ 0.4, -0.3 ≦ a ≦ 0.3, -0.2 ≦ a ≦ 0.2, or -0.1 ≦ a ≦ 0.1.

[0072] The transition metal oxide may optionally contain at least one selected from the group consisting of, for example, LiCoO2, LiMnO2, LiNi 0.9 Co 0.1 O2, LiNi 0.9 Mn 0.1 O2, and LiNiO2.

[0073] The transition metal oxide may be represented, for example, by the following formula (B-2). The compound represented by the following formula ( B -2) may also be referred to as "NCM".

[0074] Li 1-a Ni x Co y Mn z O2…(B-2) In the formula, the relationships of -0.5 ≦ a ≦ 0.5, 0 < x < 1, 0 < y < 1, 0 < z < 1, and x + y + z = 1 are satisfied.

[0075] In the above formula (B-2), x may satisfy, for example, the relationship of 0 < x ≦ 0.1, 0.1 ≦ x ≦ 0.2, 0.2 ≦ x ≦ 0.3, 0.3 ≦ x ≦ 0.4, 0.4 ≦ x ≦ 0.5, 0.5 ≦ x ≦ 0.6, 0.6 ≦ x ≦ 0.7, 0.7 ≦ x ≦ 0.8, 0.8 ≦ x ≦ 0.9, or 0.9 ≦ x < 1.

[0076] <00In the above formula (B-2), y may satisfy, for example, the relationship of 0 < y ≤ 0.1, 0.1 ≤ y ≤ 0.2, 0.2 ≤ y ≤ 0.3, 0.3 ≤ y ≤ 0.4, 0.4 ≤ y ≤ 0.5, 0.5 ≤ y ≤ 0.6, 0.6 ≤ y ≤ 0.7, 0.7 ≤ y ≤ 0.8, 0.8 ≤ y ≤ 0.9, or 0.9 ≤ y < 1.

[0077] In the above formula (B-2), z may satisfy, for example, the relationship of 0 < z ≤ 0.1, 0.1 ≤ z ≤ 0.2, 0.2 ≤ z ≤ 0.3, 0.3 ≤ z ≤ 0.4, 0.4 ≤ z ≤ 0.5, 0.5 ≤ z ≤ 0.6, 0.6 ≤ z ≤ 0.7, 0.7 ≤ z ≤ 0.8, 0.8 ≤ z ≤ 0.9, or 0.9 ≤ z < 1.

[0078] NCM is, for example, LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2, LiNi 0.4 Co 0.3 Mn 0.3 O2, LiNi 0.3 Co 0.4 Mn 0.3 O2, LiNi 0.3 Co 0.3 Mn 0.4 O2, LiNi 0.5 Co 0.2 Mn 0.3 O2, LiNi 0.5 Co 0.3 Mn 0.2 O2, LiNi 0.5 Co 0.4 Mn 0.1 O2, LiNi 0.5 Co 0.1 Mn 0.4 O2, LiNi 0.6 Co 0.2 [[ID=...]] Mn 0.2 O2, LiNi 0.6 Co 0.3 Mn 0.1 O2, LiNi 0.6 Co 0.1 Mn 0.3 O2, LiNi 0.7 Co 0.1 Mn 0.2 O2, LiNi [[ID=...]] 0.7 Co 0.2 Mn 0.1 O2, LiNi0.8 Co 0.1 Mn 0.1 O2, and, LiNi 0.9 Co 0.05 Mn 0.05 It may contain at least one selected from the group consisting of O2.

[0079] 〈NCA〉 The transition metal oxide may be represented, for example, by the following formula (B-3). The compound represented by the following formula (B-3) may also be referred to as "NCA".

[0080] Li 1-a [[ID=2)]Ni x Co y Al z O2…(B-3)<0)000474>In the formula, the relationships of -0.5 ≦ a ≦ 0.5, 0 < x < 1, 0 < y < 1, 0 < z < 1, and x + y + z = 1 are satisfied.

[0081] In the above formula (B-3), x may satisfy, for example, the relationship of 0 < x ≦ 0.1, 0.1 ≦ x ≦ 0.2, 0.2 ≦ x ≦ 0.3, 0.3 ≦ x ≦ 0.4, 0.4 ≦ x ≦ 0.5, 0.5 ≦ x ≦ 0.6, 0.6 ≦ x ≦ 0.7, 0.7 ≦ x ≦ 0.8, 0.8 ≦ x ≦ 0.9, or 0.9 ≦ x < 1.

[0082] In the above formula (B-3), y may satisfy, for example, the relationship of 0 < y ≦ 0.1, 0.1 ≦ y ≦ 0.2, 0.2 ≦ y ≦ 0.3, 0.3 ≦ y ≦ 0.4, 0.4 ≦ y ≦ 0.5, 0.5 ≦ y ≦ 0.6, 0.6 ≦ y ≦ 0.7, 0.7 ≦ y ≦ 0.8, 0.8 ≦ y ≦ 0.9, or 0.9 ≦ y < 1.

[0083] In the above formula (B-3), z may satisfy, for example, the relationship of 0 < z ≦ 0.1, 0. ≦ z ≦ 0.2, 0.2 ≦ z ≦ 0.3, 0.3 ≦ z ≦ 0.4, 0.4 ≦ z ≦ 0.5, 0.5 ≦ z ≦ 0.6, 0.6 ≦ z ≦ 0.7, 0.7 ≦ z ≦ 0.8, 0.8 ≦ z ≦ 0.9, or 0.9 ≦ z < 1.

[0084] NCA is, for example, LiNi 0.7 Co 0.1Al 0.2 O2, LiNi 0.7 Co 0.2 Al 0.1 O2, LiNi 0.8 Co 0.1 Al 0.1 O2, LiNi 0.8 Co 0.17 Al 0.03 O2, LiNi 0.8 Co 0.15 Al 0.05 O2 and LiNi 0.9 Co 0.05 Al 0.05 O2.

[0085] <Multi-component system> The positive electrode active material may contain, for example, two or more types of NCM. The positive electrode active material may contain, for example, NCM (0.6≦x) and NCM (x<0.6). "NCM (0.6≦x)" refers to a compound in which x (Ni ratio) in the above formula (B-2) is 0.6 or more. NCM (0.6≦x) may also be referred to as, for example, a "high nickel material." NCM (0.6≦x) is, for example, LiNi 0.8 Co 0.1 Mn 0.1 O2, etc. "NCM (x<0.6)" refers to a compound in which x (Ni ratio) is less than 0.6 in the above formula (B-2). NCM (x<0.6) is, for example, LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2, etc. The mixing ratio (mass ratio) of NCM(0.6≦x) and NCM(x<0.6) may be, for example, "NCM(0.6≦x) / NCM(x<0.6)=9 / 1 to 1 / 9," "NCM(0.6≦x) / NCM(x<0.6)=9 / 1 to 4 / 6," or "NCM(0.6≦x) / NCM(x<0.6)=9 / 1 to 3 / 7."

[0086] The positive electrode active material may contain, for example, NCA and NCM. The mixing ratio (mass ratio) of NCA and NCM may be, for example, "NCA / NCM = 9 / 1 to 1 / 9," "NCA / NCM = 9 / 1 to 4 / 6," or "NCA / NCM = 9 / 1 to 3 / 7." The Ni ratios of NCA and NCM may be the same or different. The Ni ratio of NCA may be higher than the Ni ratio of NCM. The Ni ratio of NCA may be lower than the Ni ratio of NCM.

[0087] <Transition metal oxides: space group C2 / m> The transition metal oxide may have, for example, a crystal structure belonging to the space group C2 / m. The transition metal oxide may be represented by, for example, the following formula (B-4).

[0088] Li2MO3…(B-4) In the formula, M may include, for example, at least one selected from the group consisting of Ni, Co, Mn, and Fe.

[0089] The positive electrode active material may include, for example, a mixture of LiMO2 (space group R-3m) and Li2MO3 (space group C2 / m), or a solid solution of LiMO2 and Li2MO3 (Li2MO3-LiMO2).

[0090] <Transition metal oxides: space group Fd-3m> The transition metal oxide may have, for example, a crystal structure belonging to the space group Fd-3m. The transition metal oxide may be represented by, for example, the following formula (B-5).

[0091] LiMn 2-x M x O4…(B-5) In the formula, the relationship 0≦x≦2 is satisfied.

[0092] M may include, for example, at least one selected from the group consisting of Ni, Fe, and Zn.

[0093] LiM2O4 (space group Fd-3m) is, for example, LiMn2O4 and LiMn 1.5 Ni 0.5 The positive electrode active material may contain at least one selected from the group consisting of LiMO2 (space group R-3m) and LiM2O4 (space group Fd-3m). The positive electrode active material may contain, for example, a mixture of LiMO2 (space group R-3m) and LiM2O4 (space group Fd-3m). The mixing ratio (mass ratio) of LiMO2 (space group R-3m) and LiM2O4 (space group Fd-3m) may be, for example, "LiMO2 / LiM2O4 = 9 / 1 to 9 / 1," "LiMO2 / LiM2O4 = 9 / 1 to 5 / 5," or "LiMO2 / LiM2O4 = 9 / 1 to 7 / 3."

[0094] <Polyanion Compounds> The polyanion compound may include, for example, a phosphate (such as LiFePO4), a silicate, a borate, etc. The polyanion compound may be represented by, for example, the following formulas (B-6) to (B-9).

[0095] LiMPO4…(B-6) Li 2-x MPO4F...(B-7) Li2MSiO4…(B-8) LiMBO3…(B-9) In the above formulas (B-6) to (B-9), M may include, for example, at least one selected from the group consisting of Fe, Mn, and Co. In the above formula (B-7), for example, the relationship 0≦x≦2 may be satisfied.

[0096] The positive electrode active material may contain, for example, a mixture of LiMO2 (space group R-3m) and a polyanionic compound. The mixing ratio (mass ratio) of LiMO2 (space group R-3m) and the polyanionic compound may be, for example, "LiMO2 / polyanionic compound = 9 / 1 to 9 / 1," "LiMO2 / polyanionic compound = 9 / 1 to 5 / 5," or "LiMO2 / polyanionic compound = 9 / 1 to 7 / 3."

[0097] Dopant A dopant may be added to the positive electrode active material. The dopant may be diffused throughout the particle or distributed locally. For example, the dopant may be unevenly distributed on the particle surface. The dopant may be a substitutional solid solution atom or an interstitial solid solution atom. The amount of dopant added (molar fraction relative to the entire positive electrode active material) may be, for example, 0.01 to 5%, 0.1 to 3%, or 0.1 to 1%. One type of dopant may be added, or two or more types of dopants may be added. Two or more types of dopants may form a composite.

[0098] The dopant may include at least one selected from the group consisting of, for example, B, C, N, halogen, Si, Na, Mg, Al, Mn, Co, Cr, Sc, Ti, V, Cu, Zn, Ga, Ge, Se, Sr, Y, Zr, Nb, Mo, In, Pb, Bi, Sb, Sn, W, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, and actinides.

[0099] For example, the set "Zr, Mg, W, Sm", the set "Ti, Mn, Nb, Si, Mo", or the set "Er, Mg" may be added to the NCA.

[0100] For example, Ti may be added to the NCM. For example, a combination of "Zr, W", a combination of "Si, W", or a combination of "Zr, W, Al, Ti, Co" may be added to the NCM.

[0101] <Surface coating> The positive electrode 20 may include composite particles. The composite particles include a core particle and a coating layer. The core particle includes a positive electrode active material. The coating layer covers at least a portion of the surface of the core particle. The coating layer may have a thickness of, for example, 1 to 3,000 nm, 5 to 2,000 nm, 10 to 1,000 nm, 10 to 100 nm, or 10 to 50 nm. The thickness of the coating layer can be measured, for example, from an SEM image of the particle cross section. That is, a sample is prepared by embedding the composite particles in a resin material. The sample is cross-sectioned using an ion milling device. For example, an ion milling device manufactured by Hitachi High-Technologies Corporation, product name: ArBlade (registered trademark) 5000 (or equivalent), may be used. The cross section of the sample is observed using an SEM. For example, an SEM device manufactured by Hitachi High-Technologies Corporation, product name: SU8030 (or equivalent), may be used. The thickness of the coating layer is measured in 20 fields for each of 10 composite particles, and the arithmetic mean of the thicknesses of 200 points in total is used.

[0102] The proportion of the surface of the core particle that is covered with the coating layer is also referred to as the "coverage." The coverage may be, for example, 1% or more, 10% or more, 30% or more, 50% or more, or 70% or more. The coverage may be, for example, 100% or less, 90% or less, or 80% or less.

[0103] The coverage can be measured, for example, by XPS (X-ray Photoelectron Spectroscopy). For example, an XPS device manufactured by ULVAC-PHI, Inc., product name: PHI X-tool (or equivalent) may be used. A sample powder consisting of composite particles is placed in the XPS. Narrow scan analysis is performed. The measurement data is processed by analysis software. For example, analysis software manufactured by ULVAC-PHI, Inc., product name: MulTiPak (or equivalent) may be used. Multiple elements are detected by analyzing the measurement data. The ratio of each detected element is calculated from the area of ​​each peak. The coverage can be calculated using the following formula (F-2).

[0104] θ={I1 / (I0+I1)}×100 …(F-2) θ: Coverage rate [%] I0: Ratio of elements originating from the core particle I1: Ratio of elements derived from the coating layer For example, if the core particle contains NCM, I0 indicates the total element ratio of "Ni, Co, Mn." For example, if the core particle contains NCA, I0 indicates the total element ratio of "Ni, Co, Al." For example, if the coating layer contains P and B, I1 indicates the total element ratio of "P, B."

[0105] The coating layer may contain any component. The coating layer may contain, for example, an element, an organic substance, an inorganic acid salt, an organic acid salt, a hydroxide, an oxide, a carbide, a nitride, a sulfide, a halide, or the like. The coating layer may contain, for example, B, Al, W, Zr, Ti, Co, F, lithium compounds (e.g., Li2CO3, LiHCO3, LiOH, Li2O, etc.), tungsten oxide (e.g., WO3, etc.), titanium oxide (e.g., TiO2, etc.), zirconium oxide (e.g., ZrO2), boron oxide, boron phosphate (e.g., BPO4, etc.), aluminum oxide (e.g., Al2O3, etc.), boehmite, aluminum hydroxide, phosphate (e.g., Li3PO 4、 (NH4)3PO4, AlPO4), borates (e.g., Li2B4O7, LiBO3, etc.), polyacrylates (Li salts, Na salts, NH4 salts, etc.), acetates (e.g., Li salts, etc.), CMC (CMC-Na, CMC-Li, CMC-NH4, etc.), LiNbO 3、 It may contain at least one selected from the group consisting of Li2TiO3 and Li-containing halides (for example, LiAlCl4, LiTiAlF6, LiYBr6, LiYCl6, etc.).

[0106] <Hollow particles / solid particles> "Hollow particles" refer to secondary particles in which, in a cross-sectional image, the area of ​​the cavity in the center is 30% or more of the cross-sectional area of ​​the entire particle. The proportion of the cavity in a hollow particle may be, for example, 40% or more, 50% or more, or 60% or more. "Solid particles" refer to secondary particles in which, in a cross-sectional image of the particle, the area of ​​the cavity in the center is less than 30% of the cross-sectional area of ​​the entire particle. The proportion of the cavity in a solid particle may be, for example, 20% or less, 10% or less, or 5% or less. The positive electrode active material may be either hollow particles or solid particles. A mixture of hollow particles and solid particles may be used. The mixing ratio (mass ratio) of hollow particles to solid particles may be, for example, "hollow particles / solid particles = 1 / 9 to 9 / 1," "hollow particles / solid particles = 2 / 8 to 8 / 2," "hollow particles / solid particles = 3 / 7 to 7 / 3," or "hollow particles / solid particles = 4 / 6 to 6 / 4."

[0107] <Large particles / Small particles> "Electrode active material" is a general term for positive electrode active material and negative electrode active material. The electrode active material may have, for example, a unimodal particle size distribution (number basis). The electrode active material may have, for example, a multimodal particle size distribution. The electrode active material may have, for example, a bimodal particle size distribution. That is, the electrode active material may contain large particles and small particles. When the particle size distribution is bimodal, the particle diameter corresponding to the peak top of the larger particle diameter is the particle diameter of the large particles (d L The particle size corresponding to the peak top of the smaller particle size is considered to be the particle size of the small particles (d S ) is considered as the particle size ratio (d L / d S ) may be, for example, 2 to 10, 2 to 5, or 2 to 4. L may be, for example, 8 to 20 μm or 8 to 15 μm. S may be, for example, 1 to 10 μm, or 1 to 5 μm.

[0108] For example, the particle size distribution may be subjected to peak separation processing using waveform analysis software. L ) and the peak area due to small particles (S S) is expressed as, for example, "S L / S S =1 / 9~9 / 1", "S L / S S =5 / 5~9 / 1" or "S L / S S =7 / 3~9 / 1" is also acceptable.

[0109] The number-based particle size distribution is measured by microscopy. Multiple cross-sectional samples are taken from the electrode active material layer. The cross-sectional samples may include, for example, cross sections perpendicular to the surface of the electrode active material layer. For example, the surface to be observed is cleaned by ion milling or the like. The cross-sectional samples are observed using an SEM. The observation magnification is adjusted so that 10 to 100 particles fit within the observation field. The Feret diameters of all particles in the image are measured. The "Feret diameter" refers to the distance between the two most distant points on the particle's contour. By observing multiple cross-sectional samples, a total of 1,000 or more Feret diameters are obtained. A number-based particle size distribution is created from the 1,000 or more Feret diameters.

[0110] A bimodal particle size distribution can be formed by mixing two types of particles. The two types of particles have different particle size distributions. For example, the two types of particles may have different D50s. "D50" refers to the particle size at which the cumulative frequency from the smaller particle size reaches 50% in a volume-based particle size distribution. D50 can be measured by laser diffraction. The measurement sample is a powder. For example, the large particles may have a D50 of 8 to 20 μm or 8 to 15 μm. For example, the small particles may have a D50 of 1 to 10 μm or 1 to 5 μm. The ratio of the D50 of the large particles to the D50 of the small particles may be, for example, 2 to 10, 2 to 5, or 2 to 4. The mixing ratio (mass ratio) of large particles to small particles may be, for example, "large particles / small particles=1 / 9 to 9 / 1," "large particles / small particles=5 / 5 to 9 / 1," or "large particles / small particles=7 / 3 to 9 / 1."

[0111] The large particles and the small particles may have the same composition or different compositions. For example, the large particles may be NCA and the small particles may be NCM. For example, the large particles may be NCM (0.6≦x) and the small particles may be NCM (x<0.6).

[0112] <Separator> The separator 30 can separate the positive electrode 20 from the negative electrode 10. The separator 30 has electrical insulation properties. The separator 30 may include, for example, at least one selected from the group consisting of a resin film, an inorganic particle layer, and an organic particle layer. The separator 30 may include, for example, a resin film and an inorganic particle layer.

[0113] Resin film The resin film is porous. The resin film may include, for example, a microporous film, a nonwoven fabric, etc. The resin film includes a resin skeleton. The resin skeleton may be continuous, for example, in a network form. Pores are formed in the gaps in the resin skeleton. The resin film can allow electrolytes to pass through. The resin film may have, for example, an average pore size of 1 μm or less. The resin film may have, for example, an average pore size of 0.01 to 1 μm, or 0.1 to 0.5 μm. The "average pore size" can be measured by mercury intrusion porosimetry. The resin film may have, for example, a pore size of 50 to 250 s / 100 cm. 3 The "Gurley value" can be measured by the Gurley test method.

[0114] The resin film may contain at least one selected from the group consisting of, for example, olefin-based resins, polyurethane-based resins, polyamide-based resins, cellulose-based resins, polyether-based resins, acrylic-based resins, and polyester-based resins. The resin film may contain at least one selected from the group consisting of, for example, polyethylene (PE), polypropylene (PP), polyamide (PA), polyamideimide (PAI), polyimide (PI), aromatic polyamide (aramid), polyphenylene ether (PPE), and derivatives thereof. The resin film may be formed by, for example, a stretching method, a phase separation method, or the like. The resin film may have a thickness of, for example, 5 to 50 μm or 10 to 25 μm.

[0115] The resin film may have, for example, a single-layer structure. The resin film may be made of, for example, a PE layer. The skeleton of the PE layer is formed of PE. The PE layer may have a shutdown function. The resin film may have, for example, a multi-layer structure. The resin film may include, for example, a PP layer and a PE layer. The skeleton of the PP layer is formed of PP. The resin film may have, for example, a three-layer structure. The resin film may be formed by laminating, for example, a PP layer, a PE layer, and a PP layer in this order. The thickness of the PE layer may be, for example, 5 to 20 μm. The thickness of the PP layer may be, for example, 3 to 10 μm.

[0116] 《Inorganic particle layer》 The inorganic particle layer may be formed on the surface of the resin film. The inorganic particle layer may be formed on only one side of the resin film, or on both the front and back sides. The inorganic particle layer may be formed on the surface facing the positive electrode 20, or on the surface facing the negative electrode 10. The inorganic particle layer may be formed on the surface of the positive electrode 20, or on the surface of the negative electrode 10.

[0117] The inorganic particle layer is porous. The inorganic particle layer contains inorganic particles. The inorganic particles may also be referred to as "inorganic filler." Pores are formed in the gaps between the inorganic particles. The inorganic particle layer may have a thickness of, for example, 0.5 to 10 μm, or 1 to 5 μm. The inorganic particles may contain, for example, a heat-resistant material. An inorganic particle layer containing a heat-resistant material is also referred to as an "HRL (Heat Resistance Layer)." The inorganic particles may contain at least one type selected from the group consisting of boehmite, alumina, zirconia, titania, magnesia, silica, and the like. The inorganic particles may have any shape. The inorganic particles may be, for example, spherical, rod-like, plate-like, fibrous, or the like. The inorganic particles may have a D50 of, for example, 0.1 to 10 μm, or 0.5 to 3 μm. The inorganic particle layer may further contain a binder. The binder may contain, for example, at least one selected from the group consisting of acrylic resins, polyamide resins, fluorine resins, aromatic polyether resins, and liquid crystal polyester resins.

[0118] 《Organic particle layer》 The separator 30 may include, for example, an organic particle layer. The separator 30 may include, for example, an organic particle layer instead of a resin film. The separator 30 may include, for example, an organic particle layer instead of an inorganic particle layer. The separator 30 may include both a resin film and an organic particle layer. The separator 30 may include both an inorganic particle layer and an organic particle layer. The separator 30 may include a resin film, an inorganic particle layer, and an organic particle layer.

[0119] The organic particle layer may have a thickness of, for example, 0.1 to 50 μm, 0.5 to 20 μm, 0.5 to 10 μm, or 1 to 5 μm. The organic particle layer contains organic particles. The organic particles may also be referred to as "organic filler." The organic particles may contain a heat-resistant material. The organic particles may contain at least one selected from the group consisting of, for example, PE, PP, PTFE, PI, PAI, PA, and aramid. The organic particles may be, for example, spherical, rod-like, plate-like, fibrous, or the like. The organic particles may have a D50 of, for example, 0.1 to 10 μm or 0.5 to 3 μm.

[0120] Separator 30 may include, for example, a mixed layer, which includes both inorganic and organic particles.

[0121] <Electrolyte> The electrolyte dissolves Li ions. The electrolyte may be a liquid electrolyte or a gel electrolyte. The liquid electrolyte may include, for example, an electrolytic solution. The electrolytic solution includes a solvent and a solute.

[0122] "solvent" <Ether solvents> The electrolytic solution may contain, for example, an ether-based solvent. The solvent may contain, for example, a hydrofluoroether (HFE). The HFE may contain, for example, at least one selected from the group consisting of a difluoromethyl group, a 2,2-difluoroethyl group, a 2,2,2-trifluoroethyl group, a 1,1,2,2-tetrafluoroethyl group, a 2,2,3,3,3-pentafluoropropyl group, a 2,2,3,3-tetrafluoropropyl group, a 1,1,1,3,3,3-hexafluoroisopropyl group, a 1,1,2,3,3,3-hexafluoropropyl group, a 2,2,3,3,4,4,4-heptafluorobutyl group, a 2,2,3,3,4,4-hexafluorobutyl group, and a 2,2,3,3,4,4,5,5-octafluoropentyl group.

[0123] The solvent may also contain an ether other than HFE (hereinafter also referred to as "second ether"). The second ether may contain, for example, at least one selected from the group consisting of tetrahydrofuran (THF), 1,4-dioxane (DOX), 1,3-dioxolane (DOL), 1,2-dimethoxyethane (DME), 1,2-diethoxyethane (DEE), ethylglyme, triglyme, tetraglyme, and derivatives thereof. The solvent may contain, for example, 1 to 50% by volume of the second ether (DME, etc.), with the balance being HFE. The solvent may contain, for example, 10 to 40% by volume of the second ether, with the balance being HFE.

[0124] <Carbonate solvent> The electrolytic solution may contain, for example, a carbonate-based solvent (carbonate ester-based solvent). The solvent may contain, for example, a cyclic carbonate, a chain carbonate, a fluorinated carbonate, or the like. The solvent may contain, for example, at least one selected from the group consisting of ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), monofluoroethylene carbonate (FEC), difluoroethylene carbonate, 4,4-difluoroethylene carbonate, trifluoroethylene carbonate, perfluoroethylene carbonate, fluoropropylene carbonate, difluoropropylene carbonate, and derivatives thereof.

[0125] The solvent may contain a cyclic carbonate (EC, PC, FEC, etc.) and a chain carbonate (EMC, DMC, DEC, etc.). The mixing ratio (volume ratio) of the cyclic carbonate to the chain carbonate may be, for example, "cyclic carbonate / chain carbonate = 1 / 9 to 4 / 6," "cyclic carbonate / chain carbonate = 2 / 8 to 3 / 7," or "cyclic carbonate / chain carbonate = 3 / 7 to 4 / 6."

[0126] The solvent may contain a cyclic carbonate (EC, PC, etc.) and a fluorinated cyclic carbonate (FEC, etc.). The mixing ratio (volume ratio) of the cyclic carbonate to the fluorinated cyclic carbonate may be, for example, "cyclic carbonate / fluorinated cyclic carbonate = 99 / 1 to 90 / 10", "cyclic carbonate / fluorinated cyclic carbonate = 9 / 1 to 1 / 9", "cyclic carbonate / fluorinated cyclic carbonate = 9 / 1 to 7 / 3", or "cyclic carbonate / fluorinated cyclic carbonate = 3 / 7 to 1 / 9".

[0127] The solvent may contain, for example, EC, FEC, EMC, DMC, and DEC. The volume ratio of each component may satisfy, for example, the relationship represented by the following formula (C-1).

[0128] V EC +V FEC +V EMC +V DMC +V DEC =10 …(C-1) In the formula, V EC , V FEC , V EMC , V DMC , V DEC indicates the volume ratio of EC, FEC, EMC, DMC, and DEC, respectively.

[0129] 1≦V EC ≦4, 0≦V FEC ≦3, V EC +V FEC ≦4, 0≦V EMC ≦9, 0≦V DMC ≦9, 0≦V DEC ≦9, 6≦V EMC +V DMC +V DEC ≦9 The relationship is satisfied.

[0130] In the above formula (C-1), For example, 1 ≤ V EC ≦2, or 2≦V EC The relationship ≦3 may be satisfied.

[0131] For example, 1 ≤ V FEC ≦2, or 2≦V FEC The relationship ≦4 may be satisfied. For example, 3≦V EMC ≦4, or 6≦V EMC The relationship ≦8 may be satisfied.

[0132] For example, 3≦V DMC ≦4, or 6≦V DMC The relationship ≦8 may be satisfied. For example, 3≦V DEC ≦4, or 6≦V DEC The relationship ≦8 may be satisfied.

[0133] The solvent may have a composition, for example, in volume ratios of "EC / EMC=3 / 7," "EC / DMC=3 / 7," "EC / FEC / DEC=1 / 2 / 7," "EC / DMC / EMC=3 / 4 / 3," "EC / DMC / EMC=3 / 3 / 4," "EC / FEC / DMC / EMC=2 / 1 / 4 / 3," "EC / FEC / DMC / EMC=1 / 2 / 4 / 3," "EC / FEC / DMC / EMC=2 / 1 / 3 / 4," or "EC / FEC / DMC / EMC=1 / 2 / 3 / 4."

[0134] <Additives> The electrolyte may contain any additive. The amount of additive (mass fraction relative to the total amount of the electrolyte) may be, for example, 0.01 to 5%, 0.05 to 3%, or 0.1 to 1%. The additive may include, for example, an SEI (Solid Electrolyte Interphase) formation accelerator, an SEI formation inhibitor, a gas generator, an overcharge inhibitor, a flame retardant, an antioxidant, an electrode protectant, a surfactant, etc.

[0135] Examples of the additives include vinylene carbonate (VC), vinyl ethylene carbonate (VEC), 1,3-propane sultone (PS), tert-amylbenzene, 1,4-di-tert-butylbenzene, biphenyl (BP), cyclohexylbenzene (CHB), ethylene sulfite (ES), propane sultone (PS), ethylene sulfate (DTD), γ-butyrolactone, phosphazene compounds, carboxylic acid esters (e.g., methyl formate (MF), methyl acetate (MA), methyl propionate (MP), diethyl malonate (DEM), etc.), fluorobenzenes (e.g., monofluorobenzene (FB), 1,2-difluorobenzene, 1,3-difluorobenzene, 1,4-difluorobenzene, 1,2,3-trifluorobenzene, 1,2,4-trifluorobenzene, 1,3,5-trifluorobenzene, 1,2,3,4-tetrafluorobenzene, 1,2,3,5-tetrafluorobenzene, 1,2,4,5-tetrafluorobenzene, pentafluorobenzene, hexafluorobenzene, etc.), fluorotoluenes (e.g., 2-fluorotoluene, 3-fluorotoluene, 4-fluorotoluene, 2,3-difluorotoluene, 2,4-difluorotoluene, 2,5-difluorotoluene, 2,6-difluorotoluene, 3,4-difluorotoluene, octafluorotoluene, etc.), benzotrifluorides (e.g., benzotrifluoride, 2-fluorobenzotrifluoride, 3-fluorobenzotrifluoride, 4-fluorobenzotrifluoride, 2-methylbenzotrifluoride, 3-methylbenzotrifluoride, 4-methylbenzotrifluoride, etc.), fluoroxylenes (e.g., 3-fluoro-o-xylene, 4-fluoro-o-xylene, 2-fluoro-m-xylene, 5-fluoro-m-xylene, etc.), sulfur-containing heterocyclic compounds (e.g., benzothiazole, 2-methylbenzotrifluoride, The solvent may contain at least one selected from the group consisting of solvents such as benzothiazole, tetrathiafulvane, etc., nitrile compounds (e.g., adiponitrile, succinonitrile, etc.), phosphate esters (e.g., trimethyl phosphate, triethyl phosphate, etc.), carboxylic acid anhydrides (e.g., acetic anhydride, propionic anhydride, oxalic anhydride, succinic anhydride, maleic anhydride, phthalic anhydride, benzoic anhydride, etc.), alcohols (e.g., methanol, ethanol, n-propyl alcohol, ethylene glycol, diethylene glycol monomethyl ether, etc.), and derivatives thereof.

[0136] The components described above as solutes and solvents may be used as minor components (additives). The additives may include, for example, at least one selected from the group consisting of LiBF, LiFSI, LiTFSI, LiBOB, LiDFOB, LiDFOP, LiPOF, FSOLi, LiI, LiBr, HFE, DOX, PC, FEC, and derivatives thereof.

[0137] Ionic liquids The liquid electrolyte may contain an ionic liquid. The liquid electrolyte may contain, for example, at least one selected from the group consisting of sulfonium salts, ammonium salts, pyridinium salts, piperidinium salts, pyrrolidinium salts, morpholinium salts, phosphonium salts, imidazolium salts, and derivatives thereof.

[0138] Gel electrolyte The gel electrolyte may include a liquid electrolyte and a polymer material. The polymer material may form a polymer matrix. The polymer material may include, for example, at least one selected from the group consisting of PVdF, PVdF-HFP, PAN, PVdF-PAN, polyethylene oxide (PEO), polyethylene glycol (PEG), and derivatives thereof.

[0139] <Battery configuration> FIG. 6 is a table showing the first battery configuration. FIG. 7 is a table showing the second battery configuration. FIG. 8 is a table showing the third battery configuration. In each table, when multiple materials are listed in a box, the listing includes each material alone and combinations thereof. For example, when materials "α, β, γ" are listed in a box, the listing indicates "at least one selected from the group consisting of α, β, and γ." Any element may be extracted from the first to third battery configurations and combined in any desired manner.

[0140] This embodiment may be incorporated into, for example, the first to third battery configurations. This embodiment may be combined with, for example, the first to third battery configurations. This embodiment may replace, for example, a portion of the first to third battery configurations. For example, the negative electrode in the first battery configuration may be replaced with the negative electrode in this embodiment. For example, the negative electrode in the first battery configuration may be used in combination with the negative electrode in this embodiment. Battery performance may be improved by combining the first to third battery configurations with this embodiment, etc. [Example]

[0141] The present embodiment will be described below using examples, but the present embodiment is not limited to these.

[0142] <No.1> (Negative electrode) A Cu foil (thickness: 10 μm) was prepared as the negative electrode current collector, graphite as the negative electrode active material, CNT as the conductive material, SBR as the binder, CMC as the thickener, and pure water as the dispersion medium. The negative electrode active material, conductive material, binder, thickener, and dispersion medium were mixed to prepare a negative electrode slurry. The mixing ratio (mass ratio) of the negative electrode active material, conductive material, binder, and thickener was 97.9:0.1:1.5:0.5. The negative electrode slurry was applied to the surface of the negative electrode current collector using a die coater and dried to form a negative electrode active material layer (basis weight: 25 mg / cm). 2 ) was formed. The negative electrode active material layer was linearly compressed at a pressure of 0.3 kN / cm to produce a negative electrode. In Nos. 2 to 17 described below, the negative electrodes were also produced using the same materials and prepared to have the same basis weight.

[0143] (positive electrode) The positive electrode current collector was made of Al foil (thickness: 15 μm), and the positive electrode active material was Li(Ni 1 / 3 Co 1 / 3 Mn 1 / 3 )O2, CNT as a conductive material, PVdF as a binder, and NMP as a dispersion medium were prepared. The positive electrode active material, the conductive material, the binder, and the dispersion medium were mixed to prepare a positive electrode slurry. The mixing ratio (mass ratio) of the positive electrode active material, the conductive material, and the binder was 98.9:0.1:1.0. The positive electrode slurry was applied to the surface of a positive electrode current collector and dried to form a positive electrode active material layer. The positive electrode active material layer was compressed to produce a positive electrode.

[0144] (separator) A resin film (thickness: 15 μm) was prepared as a separator. The resin film had a three-layer structure (PP layer / PE layer / PP layer).

[0145] (electrolyte) A mixed solvent was prepared by mixing EC, DMC, and EMC. The mixing ratio (volume ratio) of EC, DMC, and EMC was 3:3:4. The solvent contained LiPF6 (1.1 mol / L) was dissolved in the electrolyte to prepare the electrolyte.

[0146] (Nonaqueous electrolyte secondary battery) A power generating element was formed by laminating a positive electrode, a separator, and a negative electrode in this order. An external terminal was attached to the power generating element. A pouch made of laminated film was prepared as a case. The power generating element was housed in the case. An electrolyte solution was poured into the case. After the electrolyte solution was poured, the case was sealed. In this manner, a nonaqueous electrolyte secondary battery (test battery) No. 1 was produced. Note that test batteries No. 2 to No. 17, which will be described later, were also produced with the same capacity using the same positive electrode, separator, and electrolyte solution.

[0147] <No.2> (Negative electrode) In No. 2, the negative electrode slurry was applied to the negative electrode current collector by screen coating. A mesh was placed on the negative electrode current collector, and the negative electrode slurry was supplied to the mesh, transferring the negative electrode slurry to the surface of the negative electrode current collector. After transfer, the mesh was removed. After the drying process, the negative electrode and test battery were manufactured in the same manner as in No. 1.

[0148] <No.3、5、7、9> The negative electrodes and test batteries were fabricated in the same manner as No. 1, except that the linear pressure applied when compressing the negative electrode active material layer was changed: 0.6 kN / cm for No. 3, 1.0 kN / cm for No. 5, 1.5 kN / cm for No. 7, and 2.0 kN / cm for No. 9.

[0149] <No.4、6、8、10> The negative electrodes and test batteries were fabricated in the same manner as No. 2, except that the linear pressure applied when compressing the negative electrode active material layer was changed: 0.6 kN / cm for No. 4, 1.0 kN / cm for No. 6, 1.5 kN / cm for No. 8, and 2.0 kN / cm for No. 10.

[0150] <No.11~14> The negative electrode and test battery were fabricated in the same manner as No. 8, except that the mesh used to coat the negative electrode slurry on the negative electrode current collector was changed.

[0151] <No.15> In No. 15, the negative electrode slurry was applied to the negative electrode current collector by gravure coating. A gravure plate was used that provided a closest distance between multiple second regions of 35 μm. The gravure plate was rotated, and the negative electrode current collector was sandwiched between a pressure roller and the gravure plate and pressed, transferring the negative electrode slurry to the surface of the negative electrode current collector. After the drying process, the negative electrode and test battery were manufactured in the same manner as No. 1.

[0152] <No.16~17> Except for the fact that the gravure plate was changed, the negative electrode and test battery were each manufactured in the same manner as in No. 15. Regarding the gravure plate, one in which the nearest distance between the multiple second regions was 50 μm was used in No. 16, and one in which the nearest distance between the multiple second regions was 80 μm was used in No. 17.

[0153] (evaluation) CC charging (upper voltage: 4.0 V) was performed at 25°C. The design capacity of the test battery was 3000 mAh. The CC charging time rate was 1 C. At a time rate of 1 C, the design capacity is discharged in 1 hour.

[0154] The CC charge capacity (mAh) and CC charge rate (%) after charging were calculated. The results are shown in Figures 9 to 12. In this example, comparisons are made between test batteries with similar ranges of negative electrode active material layer density. Note that the CC charge rate in this example is a value when a CC charge capacity of 2400 mAh is set to 100%.

[0155] (result) 9 and 10, when comparing No. 1 and 2, No. 3 and 4, No. 5 and 6, No. 7 and 8, and No. 9 and 10, No. 2, 4, 6, 8, and 10 had higher CC charge rates than No. 1, 3, 5, 7, and 9. This is thought to be because the presence of the second region in part of the negative electrode lengthened the ion diffusion path.

[0156] 9 to 11, when comparing Nos. 8 and 11 to 14, which were produced under the same conditions except for varying the volume fraction of the second region in the negative electrode active material layer, the CC charge rate was higher when the volume fraction of the second region was 10 to 40%. This is thought to be because ions cannot easily diffuse when the volume fraction of the second region is less than 10%, and because an increase in the amount of negative electrode active material unused during high-load charging occurs when the volume fraction of the second region is more than 40%.

[0157] 9, 10, and 12, when comparing test batteries No. 15 to 17 manufactured under the same conditions except for varying the closest distance between the multiple second regions, the CC charging rate was high when the closest distance between the multiple second regions was 50 μm or less. This is thought to be due to the fact that when the closest distance between the multiple second regions exceeds 50 μm, the movement of ions between the second regions is suppressed.

[0158] The embodiments and examples disclosed herein should be considered to be illustrative in all respects and not restrictive. The scope of the present disclosure is defined by the claims, not by the above description, and is intended to include all modifications within the meaning and scope of the claims. [Explanation of symbols]

[0159] 10 negative electrode, 11 negative electrode current collector, 12 negative electrode active material layer, 13 first region, 14 second region, 20 positive electrode, 21 positive electrode current collector, 22 positive electrode active material layer, 30 separator, 50 power generating element, 100 non-aqueous electrolyte secondary battery.

Claims

1. A negative electrode having a negative electrode current collector and a negative electrode active material layer containing a negative electrode active material, the negative electrode active material layer includes a first region and a second region, the second region is in a lattice shape, the density of the second region is 7% or more lower than the density of the first region; a volume ratio of the second region in the negative electrode active material layer is 10% or more and 40% or less; The negative electrode, wherein the negative electrode active material layer has a basis weight of 20 mg / cm 2 or more.

2. A non-aqueous electrolyte secondary battery comprising the negative electrode according to claim 1.

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