Electrode for battery, and battery

Abstract

To improve the rate performance.SOLUTION: An electrode for a battery includes a base material and a negative electrode active material layer. The negative electrode active material layer is disposed on a surface of the base material. A cross section parallel to a thickness direction of the negative electrode active material layer includes a first region and a second region. In the thickness direction, the first region is disposed between the second region and the base material. The first region includes a first active material and a first binder. The second region includes a second active material and a second binder. Relations of A2<A1 and B2<B1 are satisfied or relations of A2>A1 and B2>B1 are satisfied. A1 represents an aspect ratio of the first active material. A2 represents an aspect ratio of the second active material. B1 indicates an area fraction of the first binder in the first region. B2 indicates an area fraction of the second binder in the second region.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to a battery electrode and a battery. [Background technology]

[0002] Japanese Patent Application Laid-Open No. 10-284059 discloses an electrode in which a larger amount of binder is distributed at the interface between a negative electrode material layer and a current collector than at the outer surface of the negative electrode material layer. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 10-284059 Summary of the Invention [Problem to be solved by the invention]

[0004] It has been considered to orient the active material in the negative electrode active material layer. For example, the active material may be oriented in the negative electrode active material layer by using an active material with a large aspect ratio. The orientation of the active material is expected to improve the rate performance. However, in general, the negative electrode active material layer is subjected to a press process during the electrode manufacturing process. During the press process, the active material is crushed, which may cause the orientation state of the active material to be lost.

[0005] An objective of the present disclosure is to improve rate performance. [Means for solving the problem]

[0006] The technical configuration and the effects of the present disclosure will be described below. However, the mechanism of action includes assumptions. The mechanism of action does not limit the technical scope of the present disclosure.

[0007] 1. A battery electrode includes a substrate and a negative electrode active material layer. The negative electrode active material layer is disposed on a surface of the substrate. A cross section parallel to the thickness direction of the negative electrode active material layer includes a first region and a second region. In the thickness direction, the first region is disposed between the second region and the substrate. The first region includes a first active material and a first binder. The second region includes a second active material and a second binder. The relationship of the following formulas (1) and (2) is satisfied, or the relationship of the following formulas (3) and (4) is satisfied. A2 <A1 (1) B2<B1 (2) A2> A1 (3) B2>B1 (4) In formulas (1) to (4), A1 represents the aspect ratio of the first active material, A2 represents the aspect ratio of the second active material, B1 represents the area fraction of the first binder in the first region, and B2 represents the area fraction of the second binder in the second region.

[0008] The first region is closer to the substrate than the second region. The aspect ratio of the active material is different between the first region and the second region. The area fraction of the binder in the cross section of the negative electrode active material layer indicates the amount of the binder present. The amount of the binder present is different between the first region and the second region. As shown in the relationship of the above formula (1) and formula (2), or the relationship of the above formula (3) and formula (4), the amount of the binder present is relatively large in the region in which the aspect ratio of the active material is relatively large between the first region and the second region. In the region containing the active material with a large aspect ratio, the active material may be strongly oriented. It is expected that the orientation state of the active material is strongly fixed by the amount of the binder present in the region. Furthermore, since the aspect ratio of the active material is relatively small and the amount of the binder present in the other region is relatively small, the other region may function as a cushion during press processing. This can reduce the load on the oriented active material. That is, it is expected that the orientation of the active material will not easily be lost during press working. By maintaining the orientation of the active material, it is expected that ion conduction will be promoted.

[0009] The binder can inhibit ion conduction. If the amount of binder present in the entire negative electrode active material layer becomes excessive, the rate performance may decrease. By having a small amount of binder present in one of the first and second regions, it is expected that the desired ion conduction will occur in the entire negative electrode active material layer. The synergistic effect of the above actions is expected to improve the rate performance.

[0010] 2. The battery electrode described in the above item "1" may include, for example, the following configuration. The negative electrode active material layer has a tortuosity of 1.8 or less.

[0011] The smaller the degree of bending, the more improved the rate performance is expected. In the negative electrode active material layer, a degree of bending of 1.8 or less can be achieved by the active material being well oriented.

[0012] 3. The battery electrode according to the above item "1" or "2" may include, for example, the following configuration. The relationship of the following formula (5) is further satisfied. 0.05≦I 110 / I 002 (5) In formula (5), I 110 indicates the diffraction intensity of the (110) plane in the X-ray diffraction profile of the negative electrode active material layer. 002 indicates the diffraction intensity of the (002) plane in the X-ray diffraction profile of the negative electrode active material layer.

[0013] "I 110 / I 002 " is an index of the orientation state. 110 / I 002 " is also called "degree of orientation." The higher the value of the degree of orientation, the more improved the rate performance is expected. In the negative electrode active material layer, when the active material is well oriented, an orientation degree of 0.05 or more can be realized.

[0014] 4. The battery electrode according to any one of the above items "1" to "3" may include, for example, the following configuration. Of the relationship of formula (1) and formula (2) above, or the relationship of formula (3) and formula (4) above, only the relationship of formula (1) and formula (2) is satisfied.

[0015] By disposing an active material with a large aspect ratio in the first region, the active material can be strongly oriented in the first region. During press processing, the first region (lower layer) does not come into direct contact with the rolling roll. Therefore, it is expected that the orientation state of the first region is less likely to be lost during press processing.

[0016] 5. The battery electrode according to any one of the above items "1" to "4" may include, for example, the following configuration. The first active material and the second active material each independently include artificial graphite.

[0017] 6. The battery electrode according to any one of the above items "1" to "5" may include, for example, the following configuration. The negative electrode active material layer is 20 mg / cm 2 The negative electrode active material layer has a weight per unit area of ​​1.1 to 1.6 g / cm 3 has a density of

[0018] High density electrodes are 20mg / cm 2 With a basis weight of 1.1 to 1.6 g / cm 3 In high-density electrodes, a large load is applied to the active material during press processing, and the orientation of the active material tends to be easily lost. With the above configuration of "1," a good orientation is expected even in high-density electrodes.

[0019] 7. The battery electrode according to any one of the above items "1" to "6" may include, for example, the following configuration. The relationship of the following equation (6) is further satisfied. 0.5≦Tx / (T1+T2)≦0.7 (6) In formula (6), T1 represents the thickness of the first region. T2 represents the thickness of the second region. When the relationship of formula (1) is satisfied, Tx represents the thickness of the first region. When the relationship of formula (3) is satisfied, Tx represents the thickness of the second region.

[0020] In regions containing active material with a large aspect ratio, the active material can be strongly oriented. By making the thickness ratio of the region where the active material is strongly oriented 50% or more of the total, it is expected that the rate performance will be improved. In the region where the active material is strongly oriented, the amount of binder is also large. By making the ratio of such regions 70% or less, it is expected that the amount of binder will be within an appropriate range.

[0021] 8. The battery electrode according to any one of the above items "1" to "7" may include, for example, the following configuration. The relationship of the following equation (7) is further satisfied. 1.8%≦|B1-B2| (7)

[0022] When the absolute value of the difference between the area fraction of the binder in the first region and the area fraction of the binder in the second region is 1.8% or more, a desired alignment state tends to be easily formed.

[0023] 9. The battery electrode according to any one of the above items "1" to "8" may include, for example, the following configuration. The relationship of the following equation (8) is further satisfied. 1.8≦Ax (8) In formula (8), when the relationship of formula (1) is satisfied, Ax represents the aspect ratio of the first active material, and when the relationship of formula (3) is satisfied, Ax represents the aspect ratio of the second active material.

[0024] When the active material has an aspect ratio of 1.8 or more, a desired alignment state tends to be easily formed.

[0025] 10. A battery comprising the battery electrode according to any one of the above items "1" to "9".

[0026] 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 embodiment") will be described. However, the present embodiment and the present embodiment do not limit the technical scope of the present disclosure. The present embodiment and the present embodiment are illustrative in all respects. The present embodiment and the present embodiment are non-restrictive. The technical scope of the present disclosure encompasses all modifications within the meaning and scope equivalent to the description of the claims. For example, it is also intended from the beginning that any configuration may be extracted from the present embodiment and arbitrarily combined. [Brief description of the drawings]

[0027] [Figure 1] 1 is a schematic cross-sectional view showing an example of a battery electrode according to an embodiment of the present invention. [Diagram 2] 1 is an example of a mapping analysis of a cross section of a negative electrode active material layer. [Diagram 3] 2 is a schematic flowchart of a method for producing a battery electrode in the present embodiment. [Figure 4] FIG. 2 is a conceptual diagram showing an example of a battery according to the present embodiment. [Diagram 5] 1 is a table showing a first battery configuration. [Figure 6] 11 is a table showing a second battery configuration. [Figure 7] 3 is a table showing a third battery configuration. [Figure 8] 13 is a table showing experimental results. [Figure 9] 1 shows cross-sectional SEM images of the first and second regions in No. 1-1. [Figure 10] This is the discharge curve when discharging at 1C. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0028] <Key terms> "Comprise," "include," "have," and variations thereof are open-ended terms. Open-ended terms may or may not include additional elements in addition to the required elements. "Consisting of" is a closed term. However, even a configuration expressed in closed terminology may include additional elements that are normally associated with the technology or that are unrelated to the technology in question. "Consisting essentially of..." is a semi-closed term. Semi-closed terminology allows for the addition of elements that do not substantially affect the basic and novel characteristics of the technology in question.

[0029] Expressions such as "may" and "may" are used in the permissive sense, meaning "to have the possibility," rather than in the obligatory sense, meaning "to have to."

[0030] Unless otherwise specified, the order of execution of the steps, operations, and the like included in various methods is not limited to the order described. For example, the steps may proceed simultaneously. For example, the steps may be performed in sequence.

[0031] Geometric terms should not be interpreted in a strict sense. Examples of geometric terms include "parallel," "perpendicular," and the like. For example, "parallel" may deviate slightly from the strict meaning of "parallel." Geometric terms may include, for example, tolerances, errors, and the like in design, work, and manufacturing. The dimensional relationships in each figure may not match the actual dimensional relationships. The dimensional relationships in each figure may be changed to help the reader understand. For example, the length, width, thickness, and the like may be changed. Some configurations may be omitted.

[0032] Numerical ranges such as "m to n%" include upper and lower limits unless otherwise specified. That is, "m to n%" indicates a numerical range of "m% or more and n% or less". Also, "m% or more and n% or less" includes "more than m% and less than n%". "More than" and "less than" are represented by an inequality sign with an equal sign "≦". "More than" and "less than" are represented by an inequality sign without an equal sign "<". A numerical value arbitrarily selected from within the numerical range may be set as a new upper or lower limit. For example, a new numerical range may be set by arbitrarily combining a numerical value within the numerical range with a numerical value described in another part, table, figure, etc. of this specification.

[0033] All numerical values ​​are modified by the term "about". The term "about" may mean, for example, ±5%, ±3%, ±1%, etc. All numerical values ​​may be approximations that may vary depending on the application of the disclosed technology. All numerical values ​​may be expressed in significant figures. Measurements may be average values ​​of multiple measurements unless otherwise specified. The number of measurements may be three or more, five or more, or ten or more. In general, the more measurements are made, the more reliable the average value is expected to be. Measurements may be rounded off based on the number of significant figures. Measurements may include errors associated with, for example, the detection limit of the measurement device.

[0034] The "aspect ratio" is measured by the following method. A cross-sectional sample is prepared by cutting the negative electrode active material layer. The cross-sectional sample includes a cross section parallel to the thickness direction of the negative electrode active material layer. For example, the observation target portion may be cleaned by a cross-section polisher (registered trademark) or the like. A cross-sectional SEM image is obtained by observing the cross-sectional sample with a SEM (Scanning Electron Microscope). Five or more cross-sectional SEM images may be prepared. In each cross-sectional SEM image, 10 or more active materials (particles) are randomly extracted. The major axis diameter and minor axis diameter of the extracted particles are measured. The major axis diameter (φ1) indicates the diameter connecting the two most distant points on the contour line of the particle. The minor axis diameter (φ2) indicates the largest diameter among the diameters perpendicular to the major axis diameter. The aspect ratio is the ratio of the major axis diameter to the minor axis diameter (φ1 / φ2). The arithmetic average of 50 or more aspect ratios is adopted.

[0035] The "area fraction" is measured by the following method. For example, a dyeing process of the binder may be performed on a cross-sectional sample of the negative electrode active material layer. For example, styrene butadiene rubber (SBR) may be dyed with osmium oxide. A mapping analysis of the binder is performed on the cross-sectional sample by SEM-EDX (Scanning Electron Microscope-Energy Dispersive X-ray spectrometry). FIG. 2 is an example of a mapping analysis on a cross-section of the negative electrode active material layer. In the negative electrode active material layer 220, pixels with a white tinge correspond to the binder. In the example of FIG. 2, there is a tendency that the binder is more abundant in the region (first region 221) close to the substrate 210 than in the region (second region 222) far from the substrate 210. For example, the pixels corresponding to the binder are counted in the first region 221. The number of pixels corresponding to the binder is divided by the number of pixels in the entire first region 221 to obtain the area fraction of the binder in the first region 221. The area fraction is expressed as a percentage (%). The same is true for the area fraction of the binder in the second region 222.

[0036] The "degree of bending" is a value calculated by the following formula. τ = (R ion ·A·K·ε) / 2d τ: degree of curvature R ion : Ion resistance A: Area of ​​the negative electrode active material layer K: Conductivity of the electrolyte ε: porosity of negative electrode active material layer d: thickness of negative electrode active material layer The "ionic resistance" is measured by the following procedure: An impedance measurement is carried out on a symmetrical cell. A symmetrical cell refers to a cell in which two equivalent electrodes are arranged symmetrically within the cell. The real component of the impedance at the lowest frequency is measured. Three times the real component is considered to be the ionic resistance. The conductivity is measured at 25°C. An electrolyte is sealed in a cell containing lithium (Li). In the cell, the resistance at 10 kHz is measured by the AC method. The conductivity is calculated from the resistance.

[0037] The "degree of orientation" is measured by the following method. The XRD profile of the negative electrode active material layer is measured by XRD (X-ray diffraction). The X-ray source is CuKα radiation. The measurement range is "10°≦2θ≦90°". In the XRD profile, the diffraction peak of the (002) plane can be detected in the range of "25°≦2θ≦30°". The diffraction peak of the (110) plane can be detected in the range of "75°≦2θ≦80°". The diffraction intensity (I 002 , I 110 ) are measured. As shown in the above equation (5), I 110 I 002 By dividing by 110 / I 002 ) is obtained.

[0038] The stoichiometric composition formula shows 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 amount ratio (molar ratio) of "Al / O=2 / 3". "Al2O3" indicates a compound containing Al and O in any molar ratio unless otherwise specified. For example, the compound may be doped with a trace element. A part of Al and O may be replaced with another element.

[0039] 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 introduction of a substituent, substitution of an atom, 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, an alkyl group, an alkenyl group, an alkynyl group, a cycloalkyl group, an unsaturated cycloalkyl group, an aromatic group, a heterocyclic group, a halogen atom (F, Cl, Br, I, etc.), an OH group, an SH group, a CN group, an SCN group, an OCN group, a nitro group, an alkoxy group, an unsaturated alkoxy group, an amino group, an alkylamino group, a dialkylamino group, an aryloxy group, an acyl group, an alkoxycarbonyl group, an acyloxy group, an aryloxycarbonyl group, an acylamino group, an alkoxycarbonylamino group, an aryloxycarbonylamino group, a sulfonylamino group, a sulfamoyl group, a carbamoyl group, an alkylthio group, an arylthio group, a sulfonyl group, a sulfinyl group, a ureido group, a phosphoric acid amide group, a sulfo group, a carboxy group, a hydroxamic acid group, a sulfino group, a hydrazino group, an imino group, and a silyl group. These substituents may be further substituted. When there are two or more substituents, the substituents may be the same or different. A plurality of substituents may be bonded to each other to form a ring. The derivative of the polymer compound (resin material) may also be called a "modified product."

[0040] The "copolymer" includes at least one type selected from the group consisting of an unspecified type, a statistical type, a random type, an alternating type, a periodic type, a block type, and a graft type.

[0041] "D50" refers to the particle size at which the cumulative distribution becomes 50% in the volume-based particle size distribution (cumulative distribution). The particle size distribution can be measured by a laser diffraction method.

[0042] "BET specific surface area" refers to the specific surface area measured by gas adsorption method (BET single point method). Nitrogen is used as the adsorption gas.

[0043] <Battery electrode> Hereinafter, the battery electrode may be abbreviated as "electrode". The electrode is in a sheet form. The electrode may be applied to any purpose as long as it is for a battery. The electrode may be, for example, for a monopolar battery (unipolar battery), a bipolar battery, a non-aqueous battery, a lithium ion battery, etc.

[0044] 1 is a schematic cross-sectional view showing an example of a battery electrode in this embodiment. The electrode 200 may be, for example, a negative electrode of a monopolar lithium ion battery. The cross section of FIG. 1 is parallel to the thickness direction (Z direction) of the electrode 200. The electrode 200 includes a substrate 210 and a negative electrode active material layer 220.

[0045] The substrate 210 supports the negative electrode active material layer 220. The substrate 210 may be, for example, sheet-shaped. The thickness of the substrate 210 may be, for example, 1 to 50 μm, 3 to 30 μm, or 5 to 15 μm. The substrate 210 is conductive. The substrate 210 may include, for example, a metal foil or the like. The substrate 210 may include, for example, at least one selected from the group consisting of Cu, Ni, Zn, Pb, Al, Ti, Fe, Ag, Au, and a conductive resin. The substrate 210 may include, for example, a Cu foil, a Cu alloy foil, or the like. The substrate 210 may have, for example, a multilayer structure. For example, the substrate 210 may be formed by bonding a Cu foil and an Al foil together.

[0046] The negative electrode active material layer 220 is disposed on the surface of the substrate 210. The negative electrode active material layer 220 may be disposed on only one surface of the substrate 210. The negative electrode active material layer 220 may be disposed on both surfaces of the substrate 210. When the electrode 200 is for a bipolar battery, the negative electrode active material layer 220 may be disposed on one surface (front surface) of the substrate 210, and a positive electrode active material layer (not shown) may be disposed on the other surface (rear surface).

[0047] The thickness of the negative electrode active material layer 220 may be, for example, 10 μm or more, 50 μm or more, 100 μm or more, 150 μm or more, 200 μm or more, 300 μm or more, 400 μm or more, or 500 μm or more. The thickness of the negative electrode active material layer 220 may be, for example, 1000 μm or less, 500 μm or less, 400 μm or less, 300 μm or less, or 200 μm or less. The thickness of the negative electrode active material layer 220 may be, for example, 100 to 400 μm.

[0048] The weight of the negative electrode active material layer 220 is, for example, 5 mg / cm 2 More than 10mg / cm 2 More than 15mg / cm 2 More than 20mg / cm 2 More than 25mg / cm 2 More than 30mg / cm 2 More than 40mg / cm 2 or more than 50 mg / cm 2 The weight per unit area of ​​the negative electrode active material layer 220 may be, for example, 100 mg / cm 2 Below, 75mg / cm 2 Below, 50mg / cm 2 Below 40mg / cm 2 or less than 30 mg / cm 2 It may be the following.

[0049] The density (apparent density) of the negative electrode active material layer 220 is, for example, 0.8 g / cm 3 More than 1.0g / cm 3 More than 1.2g / cm 3 More than 1.4g / cm 3 More than 1.6g / cm 3 or more, or 1.8g / cm3 The density of the negative electrode active material layer 220 may be, for example, 2.0 g / cm 3 Below 1.8g / cm 3 Below 1.6g / cm 3 Below 1.4g / cm 3 Below, 1.2g / cm 3 Less than or equal to 1.0g / cm 3 It may be the following.

[0050] <1st area, 2nd area> A cross section of the negative electrode active material layer 220 includes a first region 221 and a second region 222. The first region 221 may be referred to as a "lower layer". In the thickness direction (Z direction), the first region 221 is disposed between the second region 222 and the base material 210. The first region 221 may be in direct contact with the base material 210, for example. The first region 221 may include an interface between the base material 210 and the negative electrode active material layer 220, for example. The second region 222 may be referred to as an "upper layer". The second region 222 may include a surface of the negative electrode active material layer 220, for example.

[0051] The negative electrode active material layer 220 may further include additional regions (a third region, a fourth region, etc.) so long as it includes the first region 221 and the second region 222. The additional region may be distinguished from the first region 221 and the second region 222, for example, by at least one of the composition and the structure. For example, the additional region may be disposed between the substrate 210 and the first region 221. For example, the additional region may be disposed between the first region 221 and the second region 222. For example, the additional region may be disposed between the surface of the negative electrode active material layer 220 and the second region 222.

[0052] The first region 221 includes a first active material 12 and a first binder 14. The second region 222 includes a second active material 22 and a second binder 24. The first active material 12 and the second active material 22 are negative electrode active materials. The chemical composition of the first active material 12 may be the same as or different from the chemical composition of the second active material 22. The first active material 12 and the second active material 22 may each independently include at least one selected from the group consisting of natural graphite and artificial graphite. The negative electrode active material layer 220 may further include other negative electrode active materials as long as it includes the first active material 12 and the second active material 22. The negative electrode active material layer 220 may include at least one selected from the group consisting of silicon (Si), silicon oxide (SiO), silicon-carbon composite material (Si-C), silicon-based alloy, tin, tin oxide, and lithium titanate. For example, Si-C may be formed by dispersing Si fine particles in carbon particles. The mass fraction of the other negative electrode active materials relative to the total negative electrode active materials may be, for example, 50% or less, 40% or less, 30% or less, 20% or less, 10% or less, 5% or less, or 1% or less.

[0053] The first active material 12 and the second active material 22 may each independently have a D50 of, for example, 1 to 50 μm, 5 to 30 μm, or 10 to 25 μm. 2 / g, 1 to 4m 2 / g or 1.5 to 3m 2 / g.

[0054] The chemical composition of the first binder 14 may be the same as or different from that of the second binder 24. The first binder 14 and the second binder 24 may each independently contain at least one selected from the group consisting of SBR, acrylate butadiene rubber (ABR), polyacrylonitrile (PAN), polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE), acrylic resin (acrylic acid ester copolymer), methacrylic resin (methacrylic acid ester copolymer), polyvinyl alcohol (PVA), and derivatives thereof. The amount of the binder may be, for example, 0.1 to 10 parts by mass, 1 to 6.5 parts by mass, 2 to 6.5 parts by mass, 3 to 6.5 parts by mass, 4 to 6.5 parts by mass, or 5 to 6.5 parts by mass relative to 100 parts by mass of the active material.

[0055] A specific relationship is satisfied between the aspect ratio of the active material and the area fraction of the binder between the first region 221 and the second region 222. In one embodiment, the relationship of the following formula (1) and formula (2) is satisfied. A2 <A1 (1) B2 <B1 (2) A1: Aspect ratio of the first active material 12 A2: Aspect ratio of the second active material 22 B1: Area fraction of the first binder 14 in the first region 221 B2: Area fraction of the second binder 24 in the second region 222

[0056] 1, as an example, the present embodiment, which satisfies the relationship of the above formula (1) and formula (2), is shown typically. In the first region 221, the aspect ratio of the first active material 12 is large, and the area fraction of the first binder 14 is large. By disposing the active material with the larger aspect ratio in the first region 221 (lower layer), it is expected that the orientation state will be more easily maintained.

[0057] In another embodiment of the present invention, the following relationship of formulas (3) and (4) is satisfied instead of the relationship of formulas (1) and (2) above. By disposing the active material having the larger aspect ratio in the second region 222 (upper layer), it is expected that ion diffusion will be promoted in the thickness direction of the negative electrode active material layer 220. A2>A1 (3) B2>B1 (4)

[0058] As long as the above relationship is satisfied, the first active material 12 and the second active material 22 may have any particle shape. The first active material 12 and the second active material 22 may each independently contain at least one type selected from the group consisting of spherical particles, scaly particles, needle particles, and clumped particles.

[0059] Regarding the thickness of each region, for example, the relationship of the following formula (6) may further be satisfied. 0.5≦Tx / (T1+T2)≦0.7 (6) T1: Thickness of the first region 221 T2: Thickness of the second region 222 Tx: the thickness of the region having the larger aspect ratio of the active material out of the first region 221 and the second region 222 The thickness ratio {Tx / (T1+T2)} may be, for example, greater than or equal to 0.6 or less than or equal to 0.6.

[0060] Regarding the area fractions (B1, B2) of the binder, for example, the relationship of the following formula (7) may be satisfied. 1.8%≦|B1-B2| (7) B1: Area fraction of the first binder 14 in the first region 221 B2: Area fraction of the second binder 24 in the second region 222 The absolute value of the difference between B1 and B2 (|B1-B2|) may be, for example, 2% or more, 2.5% or more, or 3% or more. |B1-B2| may be, for example, 4% or less, 3% or less, or 2.5% or less.

[0061] The larger of B1 and B2 may be, for example, 3.5% or more, 4% or more, or 5% or more. The larger of B1 and B2 may be, for example, 10% or less, 8% or less, or 6% or less. The smaller of B1 and B2 may be, for example, less than 3.5%, 3% or less, 2.5% or less, 2% or less, 1.5% or less, or 1% or less. The smaller of B1 and B2 may be, for example, 0.5% or more, 1% or more, 1.5% or more, 2% or more, or 3% or more.

[0062] The aspect ratios (A1, A2) of the active materials may satisfy, for example, the relationship of the following formula (8). 1.8≦Ax (8) Ax: The greater of A1 and A2 Ax may be, for example, 2 or more, 2.5 or more, 3 or more, 3.5 or more, 4 or more, 4.5 or more, 5 or more, 5.5 or more, 6 or more, 6.5 or more, or 7 or more. Ax may be, for example, 8 or less, 7.5 or less, 7 or less, 6.5 or less, 6 or less, 5.5 or less, 5 or less, 4.5 or less, 4 or less, 3.5 or less, or 3 or less.

[0063] The smaller of A1 and A2 (Ay) may be, for example, less than 1.8, 1.7 or less, 1.6 or less, 1.5 or less, 1.4 or less, 1.3 or less, 1.2 or less, or 1.1 or less. Ay may be, for example, 1 or more, 1.1 or more, 1.2 or more, 1.3 or more, 1.4 or more, 1.5 or more, or 1.6 or more.

[0064] <Optional ingredients> The negative electrode active material layer 220 may contain, for example, a thickener. The thickener can impart viscosity to the slurry. The thickener may contain, for example, at least one selected from the group consisting of sodium alginate, carboxymethylcellulose (CMC), polyacrylic acid (PAA), and polyvinylpyrrolidone (PVP). CMC and PAA may be in the form of, for example, Na salt, Li salt, NH4 salt, etc. The blending amount of the thickener may be, for example, 0.1 to 2 parts by mass, 0.1 to 1 part by mass, or 0.1 to 0.5 parts by mass with respect to 100 parts by mass of the active material.

[0065] The negative electrode active material layer 220 may contain, for example, a conductive material. The conductive material can form an electron conduction path. The conductive material may contain, for example, at least one selected from the group consisting of acetylene black (AB), Ketjen Black (registered trademark), vapor grown carbon fiber (VGCF), carbon nanotube (CNT), and graphene flake (GF). The CNT may contain at least one selected from the group consisting of single-walled CNT (SWCNT) and multi-walled CNT (MWCNT). 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 active material.

[0066] The negative electrode active material layer 220 may 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 220 may contain, for example, a layered silicate (smectite, montmorillonite, bentonite, hectorite, etc.), an inorganic filler (solid alumina, hollow silica, boehmite, etc.), a polysiloxane compound, etc.

[0067] <Orientation degree> Degree of orientation (I 110 / I 002 The greater the degree of orientation (I 110 / I 002) may be, for example, 0.03 or more, 0.05 or more, 0.08 or more, 0.10 or more, or 0.12 or more. That is, the relationship of the following formula (5) may be satisfied. 0.05≦I 110 / I 002 (5) I 110 : Diffraction intensity of (110) plane in XRD profile I 002 : Diffraction intensity of (002) plane in XRD profile The degree of orientation may be, for example, 0.30 or less, 0.25 or less, 0.20 or less, 0.15 or less, 0.12 or less, 0.10 or less, 0.08 or less, or 0.05 or less.

[0068] <Bending degree> The smaller the degree of bending, the more the ion conduction is expected to be promoted. In this embodiment, a small degree of bending can be realized. The degree of bending of the negative electrode active material layer 220 may be, for example, less than 2.8, 2.5 or less, 2.0 or less, or 1.8 or less. The degree of bending may be, for example, 0.1 or more, 0.5 or more, 1.0 or more, or 1.5 or more.

[0069] <Method of manufacturing battery electrodes> 3 is a schematic flow chart of the method for producing a battery electrode in this embodiment. Hereinafter, the "method for producing a battery electrode in this embodiment" may be abbreviated as "this production method." This production method includes "(a) lower layer coating," "(b) upper layer coating," "(c) application of a magnetic field," "(d) drying," and "(e) pressing."

[0070] <(a) Undercoat> The manufacturing method includes forming a first region 221 by applying a first slurry to a surface of a substrate 210. The first slurry includes a first active material 12, a first binder 14, and a dispersion medium. For example, the first active material 12, the first binder 14, a thickener, and a dispersion medium may be mixed to form the first slurry. The amount of the first binder 14 may be determined depending on the magnitude relationship between the aspect ratios of the first active material 12 and the second active material 22. Any mixing device may be used. For example, a planetary mixer or the like may be used. The viscosity of the first slurry may be, for example, 10,000 to 30,000 mPa·s.

[0071] The first region 221 (lower layer) can be formed by applying the first slurry to the surface of the substrate 210. Any coating device can be used. For example, a die coater, a roll coater, or the like may be used.

[0072] <(b) Top Coating> The present manufacturing method includes forming a second region 222 by applying a second slurry onto the first region 221. The second slurry includes a second active material 22, a second binder 24, and a dispersion medium. For example, the second active material 22, the second binder 24, a thickener, and a dispersion medium may be mixed to form the second slurry. The amount of the second binder 24 may be determined depending on the magnitude relationship between the aspect ratios of the first active material 12 and the second active material 22. The viscosity of the second slurry may be, for example, 10,000 to 30,000 mPa·s.

[0073] The second region 222 (upper layer) can be formed by coating the second slurry on the first region 221. At this stage, the first region 221 and the second region 222 (coating film) are in a wet state. That is, the first region 221 and the second region 222 contain a dispersion medium.

[0074] <(c) Magnetic field orientation> The present manufacturing method includes applying a magnetic field to the first region 221 and the second region 222. For example, the magnetic field may be applied before the first region 221 is completely dried. It is expected that a desired orientation state is formed by applying a magnetic field before the first region 221 is completely dried.

[0075] The magnetic field may be applied, for example, along the thickness direction of the first region 221 and the second region 222. The active material contained in the first region 221 and the second region 222 may be oriented in response to the magnetic field. The active material may be oriented so that its major axis is along the thickness direction (Z direction). The larger the aspect ratio of an active material, the easier it tends to be oriented. The magnetic flux density and application time of the magnetic field may be adjusted to obtain a desired oriented state. The magnetic flux density may be, for example, 100 to 1000 mT. The application time may be, for example, 1 to 60 minutes.

[0076] <(d) Drying> The manufacturing method includes forming the negative electrode active material layer 220 by drying the first region 221 and the second region 222. The dispersion medium can be removed by drying. Any drying device can be used. For example, a hot air drying device or the like can be used. The drying temperature can be, for example, 40 to 80° C., or 40 to 60° C. By removing the dispersion medium, the electrode 200 can be completed.

[0077] <(e)Press> This manufacturing method may include, for example, compressing the negative electrode active material layer 220. For example, the negative electrode active material layer 220 may be compressed by a rolling machine or the like. During the press processing, it is expected that the orientation state of the active material will be maintained by the function of a cushion in which the aspect ratio of the active material is relatively small and the amount of binder is relatively small.

[0078] <Battery> 4 is a conceptual diagram showing an example of a battery in this embodiment. The battery 1000 may be, for example, a monopolar lithium ion battery. The battery 1000 includes an exterior body 900. The exterior body 900 houses a power generating element 500 and an electrolyte (not shown).

[0079] <Exterior body> The exterior body 900 may have any shape. The exterior body 900 may be, for example, a metal case, a pouch made of a laminate film, or the like. The case may have any shape. The case may be, for example, cylindrical, rectangular, flat, coin-shaped, or the like. The exterior body 900 may contain, for example, Al, or the like. The exterior body 900 may house, for example, one or more power generating elements 500. The multiple power generating elements 500 may form, for example, a series circuit or a parallel circuit. In the exterior body 900, the multiple power generating elements 500 may be stacked in the thickness direction of the battery 1000.

[0080] <Power generation elements> The power generating element 500 may also be referred to as an "electrode group", an "electrode body", or the like. The power generating element 500 includes an electrode 200 and a counter electrode 100. In this embodiment, the electrode 200 is a negative electrode. The counter electrode 100 is a positive electrode. The power generating element 500 may further include a separator 300. The separator 300 is disposed between a positive electrode and a negative electrode. The power generating element 500 may have any shape. The power generating element 500 may be, for example, a laminated type. For example, the power generating element 500 may be formed by alternately laminating a positive electrode and a negative electrode while sandwiching the separator 300 between the positive electrode and the negative electrode. The power generating element 500 may be, for example, a wound type. For example, a strip-shaped positive electrode, a strip-shaped separator 300, and a strip-shaped negative electrode may be laminated to form a laminate. The power generating element 500 may be formed by spirally winding the laminate. The wound type power generating element 500 may be formed into a flat shape after winding.

[0081] <Positive electrode> The positive electrode is in a sheet form. The positive electrode may include a substrate and a positive electrode active material layer. The substrate has electrical conductivity. The substrate supports the positive electrode active material layer. The substrate may be, for example, in a sheet form. The substrate may have a thickness of, for example, 5 to 50 μm. The substrate may include, for example, a metal foil. The substrate may include, for example, at least one selected from the group consisting of Al, Mn, Ti, Fe, and Cr. The substrate may include, for example, an Al foil, an Al alloy foil, a Ti foil, a stainless steel (SUS) foil, or the like.

[0082] An intermediate layer may be formed between the substrate and the positive electrode active material layer. The intermediate layer does not include a positive electrode active material. The intermediate layer may have a thickness of, for example, 0.1 to 5 μm. The intermediate layer may include, for example, a conductive material, an insulating material, a binder, etc. The conductive material may include, for example, carbon black, etc. The insulating material may include, for example, alumina, boehmite, aluminum hydroxide, etc. The binder may include, for example, PVdF, etc.

[0083] The positive electrode active material layer is disposed on the surface of the substrate. The positive electrode active material layer may be disposed on only one side of the substrate. The positive electrode active material layer may be disposed on both sides of the substrate. The thickness of the positive electrode active material layer may be, for example, 10 to 1000 μm, 50 to 500 μm, or 100 to 300 μm. The positive electrode active material layer includes a positive electrode active material. The positive electrode active material layer may further include, for example, a conductive material and a binder.

[0084] 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 may include 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.

[0085] The amount of the binder 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 binder may contain any component. The binder may contain, for example, at least one selected from the group consisting of PVdF, vinylidene fluoride-hexafluoropropylene copolymer (PVdF-HFP), PTFE, CMC, PAA, PVA, PVP, polyoxyethylene alkyl ether, and derivatives thereof.

[0086] The positive electrode active material layer 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 positive electrode active material layer may further contain, for example, polyoxyethylene allyl phenyl ether phosphate, zeolite, a silane coupling agent, MoS2, WO3, etc.

[0087] The positive electrode active material may be, for example, in the form of particles. The D50 of the positive electrode active material may be, for example, 1 to 30 μm, 10 to 20 μm, or 1 to 10 μm. 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 may be uniform or non-uniform within one particle (positive electrode active material). For example, the composition may be graded from the surface to the center of the particle. The change in composition may be continuous or discontinuous (stepwise).

[0088] <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 represented by, for example, the following general formula: Li 1-a Ni x M 1-x O2 In the formula, the relationships of -0.5 ≦ a ≦ 0.5 and 0 ≦ x ≦ 1 are satisfied. M may contain at least one selected from the group consisting of, for example, Co, Mn, and Al. For example, the relationships 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 may be satisfied. For example, the relationships of -0.4 ≦ a ≦ 0.4, -0.3 ≦ a ≦ 0.3, -0.2 ≦ a ≦ 0.2, or -0.1 ≦ a ≦ 0.1 may be satisfied.

[0089] The transition metal oxide may 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.

[0090] <ncm> The transition metal oxide may be represented, for example, by the following general formula. The compound represented by the following general formula may also be referred to as "NCM". Li 1-a Ni x Co y Mn z O2 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. 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 may be satisfied. 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 may be satisfied. 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 may be satisfied.

[0091] 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 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 0.7 Co 0.2 Mn 0.1 O2, LiNi 0.8 Co 0.1 Mn 0.1 O2 and LiNi 0.9 Co 0.05 Mn 0.05 O2.

[0092] <nca> The transition metal oxide may be represented, for example, by the following general formula. The compound represented by the following general formula may also be referred to as "NCA". Li 1-a Ni x Co y Al z O2 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. 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 may be satisfied. 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 may be satisfied. 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 may be satisfied.

[0093] NCA may be, for example, LiNi 0.7 Co 0.1 Al 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 at least one selected from the group consisting of LiNi 0.9 Co 0.05 Al 0.05 O2 may be included.

[0094] <Multi-component system> The positive electrode active material may contain, for example, two or more kinds of NCMs. 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 represented by the general formula "Li 1-a Ni x Co y Mn z In the term "NuO2", x (Ni ratio) is 0.6 or more. NCM (0.6≦x) may also be called "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)" is a compound with the general formula "Li 1-a Ni x Co y Mn z In "NuO2", x (Ni ratio) is less than 0.6. 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."

[0095] The positive electrode active material may include, 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.

[0096] <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 general formula: Li2MO3 In the formula, M may include at least one selected from the group consisting of Ni, Co, Mn, and Fe. The positive electrode active material may include, for example, a mixture of LiMO2 (space group R-3m) and Li2MO3 (space group C2 / m). The positive electrode active material may include, for example, a solid solution of LiMO2 and Li2MO3 (Li2MO3-LiMO2), etc.

[0097] <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 general formula: LiMn 2-x M x O4 In the formula, the relationship 0≦x≦2 is satisfied. M may include, for example, at least one selected from the group consisting of Ni, Fe, and Zn.

[0098] 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 mixture 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".

[0099] <Polyanion compounds> The polyanionic compounds may include, for example, phosphates (e.g., LiFePO4, etc.), silicates, borates, etc. The polyanionic compounds may be represented, for example, by the following general formulae: LiMPO4 Li 2-x MPO4F Li2MSiO4 LiMBO3 In the above general formula group, M may include, for example, at least one selected from the group consisting of Fe, Mn, and Co. 2-x In "MPO4F", for example, the relationship 0≦x≦2 may be satisfied.

[0100] The positive electrode active material may contain, for example, a mixture of LiMO2 (space group R-3m) and a polyanion compound. The mixture ratio (mass ratio) of LiMO2 (space group R-3m) and the polyanion compound may be, for example, "LiMO2 / polyanion compound=9 / 1 to 9 / 1", "LiMO2 / polyanion compound=9 / 1 to 5 / 5", or "LiMO2 / polyanion compound=9 / 1 to 7 / 3".

[0101] <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 or more dopants may be added. Two or more dopants may form a complex.

[0102] The dopant may include at least one selected from the group consisting of, for example, B, C, N, halogens, 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.

[0103] For example, the set of "Zr, Mg, W, Sm", the set of "Ti, Mn, Nb, Si, Mo", or the set of "Er, Mg" may be added to the NCA. For example, Ti may be added to the NCM. For example, the set of "Zr, W", the set of "Si, W", or the set of "Zr, W, Al, Ti, Co" may be added to the NCM.

[0104] <Surface coating> The positive electrode active material may form a composite particle. The composite particle may include, for example, a core particle and a coating layer. The core particle includes a positive electrode active material. The coating layer covers at least a part of the surface of the core particle. The thickness of the coating layer may be, for example, 1 to 3000 nm, 5 to 2000 nm, 10 to 1000 nm, 10 to 100 nm, or 10 to 50 nm. The thickness of the coating layer may be measured, for example, in an SEM image of a particle cross section. That is, a sample is prepared by embedding the composite particle in a resin material. The sample is subjected to a cross-section processing by an ion milling device. The cross section of the sample is observed by SEM. The thickness of the coating layer is measured in 20 fields of view for each of 10 composite particles. The arithmetic average of the thicknesses of 200 points in total is adopted.

[0105] The proportion of the surface of the core particle that is covered by 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.

[0106] The coverage can be measured, for example, by XPS (X-ray Photoelectron Spectroscopy). A powder sample consisting of composite particles is set in the XPS. Narrow scan analysis is performed. The measurement data is processed by analysis software. By analyzing the measurement data, multiple elements are detected. The ratio of each detected element is calculated from the area of ​​each peak. The coverage can be calculated by the following formula. γ = {I1 / (I0+I1)} × 100 γ: Coverage rate [%] I0: Ratio of elements originating from the core particle I1: Ratio of elements originating 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".

[0107] 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, a lithium compound (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.).

[0108] <Hollow particles / solid particles> Both hollow particles and solid particles are secondary particles. In a cross-sectional image of a "hollow particle", the area ratio of the cavity in the center is 30% or more of the cross-sectional area of ​​the entire particle. The ratio of the cavity in a hollow particle may be, for example, 40% or more, 50% or more, or 60% or more. In a cross-sectional image of a "solid particle", the area ratio of the cavity in the center is less than 30% of the cross-sectional area of ​​the entire particle. The ratio 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 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."

[0109] <Large particles / Small particles> The active material may have, for example, a unimodal particle size distribution (based on number). The active material may have, for example, a multimodal particle size distribution. The active material may have, for example, a bimodal particle size distribution. That is, the active material may contain large particles and small particles. When the particle size distribution is bimodal, the particle size corresponding to the peak top of the larger particle size is the particle size of the large particles (d L The particle size corresponding to the peak top with 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.

[0110] For example, a peak separation process may be performed on the particle size distribution 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 to 9 / 1", "S L / S S =5 / 5 to 9 / 1" or "S L / S S =7 / 3 to 9 / 1".

[0111] The particle size distribution based on the number is measured by a microscopy method. A plurality of cross-sectional samples are taken from the active material layer. The cross-sectional samples may include, for example, a cross-section perpendicular to the surface of the active material layer. For example, the surface to be observed is cleaned by ion milling or the like. The cross-sectional samples are observed by SEM. The observation magnification is adjusted so that 10 to 100 particles are included in the observation field of view. 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 contour line of a particle. By observing a plurality of cross-sectional samples, a total of 1000 or more Feret diameters are obtained. A particle size distribution based on the number is created from the 1000 or more Feret diameters.

[0112] The bimodal particle size distribution can be formed by mixing two kinds of particles. The two kinds of particles have different particle size distributions. For example, the two kinds of particles may have different D50s. The measurement sample is a powder. For example, the D50 of the large particles may be 8 to 20 μm, or 8 to 15 μm. For example, the D50 of the small particles may be 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 the large particles and the 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".

[0113] 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).

[0114] <Electrolyte> The electrolyte is a liquid electrolyte. The electrolyte includes a solute and a solvent. The concentration of the solute may be, for example, 0.5 to 1 mol / L, 1 to 1.5 mol / L, 1.5 to 2 mol / L, 2 to 2.5 mol / L, or 2.5 to 3 mol / L. "mol / L" may be written as "M". The solute includes a supporting salt (Li salt). The solute may include, for example, an inorganic acid salt, an imide salt, an oxalate complex, a halide, etc. The solute may include, for example, at least one selected from the group consisting of LiPF6, LiBF4, LiClO4, LiAsF6, LiSbF6, LiN(SO2F)2 "LiFSI", LiN(SO2CF3)2 "LiTFSI", LiB(C2O4)2 "LiBOB", LiBF2(C2O4) "LiDFOB", LiPF2(C2O4)2 "LiDFOP", LiPO2F2, FSO3Li, LiI, LiBr, and derivatives thereof.

[0115] 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.

[0116] 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".

[0117] 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 and 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".

[0118] The solvent may include, 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. V EC +V FEC +V EMC +V DMC +V DEC =10 In the above formula, V EC , V FEC , V EMC , V DMC , V DEC indicates the volume ratio of EC, FEC, EMC, DMC, and DEC, respectively. 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. For example, 1≦V EC ≦2, or 2≦V EC The relationship ≦3 may be satisfied. 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. 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.

[0119] The solvent may have a composition, for example, by volume, 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", "EC / FEC / DMC / EMC=1 / 2 / 3 / 4", or the like.

[0120] The electrolyte may contain an ether-based solvent, such as tetrahydrofuran (THF), 1,4-dioxane (DOX), 1,3-dioxolane (DOL), 1,2-dimethoxyethane (DME), 1,2-diethoxyethane (DEE), hydrofluoroether (HFE), ethylglyme, triglyme, tetraglyme, and at least one selected from the group consisting of derivatives thereof.

[0121] The electrolyte may contain any additive. The amount of additive (mass fraction relative to the entire 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 promoter, an SEI formation inhibitor, a gas generating agent, an overcharge inhibitor, a flame retardant, an antioxidant, an electrode protector, a surfactant, and the like.

[0122] 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-methylbenzyl The solvent may contain at least one selected from the group consisting of anhydrides (e.g., benzothiazole, tetrathiafulvane, etc.), nitrile compounds (e.g., adiponitrile, succinonitrile, etc.), phosphates (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.

[0123] The components described above as solutes and solvents may be used as minor components (additives). The additives may include at least one selected from the group consisting of LiBF4, LiFSI, LiTFSI, LiBOB, LiDFOB, LiDFOP, LiPO2F2, FSO3Li, LiI, LiBr, HFE, DOX, PC, FEC, and derivatives thereof.

[0124] The electrolyte may include an ionic liquid, which may include 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.

[0125] <Gel electrolyte> The battery 1000 may include a gel electrolyte. The gel electrolyte may include an electrolytic solution and a polymer material. The polymer material may form a polymer matrix. The polymer material may include at least one selected from the group consisting of, for example, PVdF, PVdF-HFP, PAN, PVdF-PAN, polyethylene oxide (PEO), polyethylene glycol (PEG), and derivatives thereof.

[0126] <separator> The separator 300 can separate the positive electrode from the negative electrode. The separator 300 has electrical insulation properties. The separator 300 may include at least one selected from the group consisting of a resin film, an inorganic particle layer, and an organic particle layer. The separator 300 may include, for example, a resin film and an inorganic particle layer.

[0127] 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 of the resin skeleton. The resin film can allow electrolytes to pass through. The resin film may have an average pore size of, for example, 1 μm or less. The average pore size of the resin film may be, for example, 0.01 to 1 μm, or 0.1 to 0.5 μm. The "average pore size" can be measured by mercury intrusion porosimetry. The Gurley value of the resin film is, for example, 50 to 250 s / 100 cm. 3 The "Gurley value" may be measured by the Gurley test method.

[0128] 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 thickness of the resin film may be, for example, 5 to 50 μm, or 10 to 25 μm.

[0129] 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.

[0130] 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 sides. The inorganic particle layer may be formed on the surface facing the positive electrode, or on the surface facing the negative electrode. The inorganic particle layer may be formed on the surface of the positive electrode, or on the surface of the negative electrode.

[0131] The inorganic particle layer is porous. The inorganic particle layer includes inorganic particles. The inorganic particles may also be referred to as "inorganic filler". Pores are formed in the gaps between the inorganic particles. The thickness of the inorganic particle layer may be, for example, 0.5 to 10 μm, or 1 to 5 μm. The inorganic particles may include, for example, a heat-resistant material. The inorganic particle layer including the heat-resistant material is also referred to as "HRL (Heat Resistance Layer)". The inorganic particles may include at least one 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, and the like. The D50 of the inorganic particles may be, for example, 0.1 to 10 μm, or 0.5 to 3 μm. The inorganic particle layer may further include a binder. The binder may contain at least one selected from the group consisting of, for example, acrylic resins, polyamide resins, fluorine resins, aromatic polyether resins, and liquid crystal polyester resins.

[0132] The separator 300 may include, for example, an organic particle layer. The separator 300 may include, for example, an organic particle layer instead of a resin film. The separator 300 may include, for example, an organic particle layer instead of an inorganic particle layer. The separator 300 may include both a resin film and an organic particle layer. The separator 300 may include both an inorganic particle layer and an organic particle layer. The separator 300 may include a resin film, an inorganic particle layer, and an organic particle layer.

[0133] The thickness of the organic particle layer may be, 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 includes organic particles. The organic particles may also be referred to as "organic fillers". The organic particles may include a heat-resistant material. The organic particles may include 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 D50 of the organic particles may be, for example, 0.1 to 10 μm, or 0.5 to 3 μm.

[0134] Separator 300 may, for example, include a mixed layer, which includes both inorganic and organic particles.

[0135] <Battery configuration> FIG. 5 is a table showing the first battery configuration. FIG. 6 is a table showing the second battery configuration. FIG. 7 is a table showing the third battery configuration. In each table, when multiple types of materials are described in a cell, the description includes each material alone and their combinations. For example, when materials "α, β, γ" are described in a cell, the description indicates "at least one selected from the group consisting of α, β, and γ." Any element may be extracted from each of the first battery configuration, the second battery configuration, and the third battery configuration, and may be arbitrarily combined. EXAMPLES

[0136] <Preparation of electrodes for evaluation> The experimental results are shown in a table in Figure 8. Various evaluation electrodes (negative electrodes) were manufactured according to the following procedure.

[0137] <No.1-1> Anode manufacturing The following materials were prepared: Active material: Graphite A (flake particles, artificial graphite), Graphite B (spherical particles, artificial graphite) Binder: SBR Thickener: CMC Dispersion medium: water Substrate: Cu foil (thickness: 15 μm)

[0138] (a) Undercoat A first slurry was prepared by mixing graphite A, SBR, CMC and water. The solid content ratio was graphite A / CMC / SBR=95.8 / 0.6 / 3.6 (mass ratio). The first slurry was applied to a substrate to form a first region (lower layer). The first region had a basis weight of 13 mg / cm2 after drying. 2 It was formed to be.

[0139] (b) Top Coating The second slurry was prepared by mixing graphite B, SBR, CMC and a dispersion medium. The solid content ratio was graphite B / CMC / SBR=98.2 / 0.6 / 1.2 (mass ratio). The second slurry was applied on top of the first slurry to form a second region (upper layer). The second region had a basis weight of 13 mg / cm2 after drying. 2 It was formed to be.

[0140] (c) Magnetic field orientation A magnetic field was applied to the coating (first and second regions).

[0141] (d)Drying The coating was dried to form a negative electrode active material layer.

[0142] (e) Press The negative electrode active material layer was compressed. After compression, the density of the negative electrode active material layer was 1.2 g / cm 3 In the above manner, a negative electrode was produced. In each region of the cross-sectional sample of the negative electrode active material layer, the aspect ratio of the active material and the area fraction of the binder were measured. Furthermore, the degree of orientation and the degree of bending of the negative electrode active material layer were measured.

[0143] <No.1-2> The negative electrode No. 1-2 is the product before pressing in No. 1-1.

[0144] <No.1-3> No. 1-3 is the product before the application of the magnetic field to No. 1-1.

[0145] <No.2> Graphite A, SBR, CMC, and water were mixed to prepare a slurry. The solid content ratio was graphite A / CMC / SBR=97 / 0.6 / 2.4 (mass ratio). The slurry was applied to the substrate to form a coating film (single layer). The negative electrode active material layer had a basis weight of 26 mg / cm2 after drying. 2 A magnetic field was applied to the coating film. The coating film was dried to form a negative electrode active material layer. The negative electrode active material layer was compressed. After compression, the density of the negative electrode active material layer was 1.2 g / cm 3 In this way, the negative electrode was produced.

[0146] <No.3> A negative electrode was manufactured in the same manner as No. 2, except that the solid content was changed to "graphite A / CMC / SBR = 95.8 / 0.6 / 3.6 (mass ratio)".

[0147] <No.4> A negative electrode was manufactured in the same manner as No. 2, except that the solid content was changed to "graphite B / CMC / SBR = 98.2 / 0.6 / 1.2 (mass ratio)".

[0148] <No.5> A negative electrode was prepared in the same manner as No. 2, except that no magnetic field was applied to the coating.

[0149] <Preparation of evaluation cell> An evaluation cell (laminate type cell) was manufactured containing the negative electrode obtained above. The rated capacity of the evaluation cell was 155 mAh.

[0150] Preparation of the positive electrode The following materials were prepared: Cathode active material: LiNi 0.8 Co 0.1 Mn 0.1 O2(NCM) Conductive material: AB Binder: PVdF Dispersion medium: N-methyl-pyrrolidone (NMP) Base material: Aluminum foil (thickness: 30 μm)

[0151] NCM, AB, PVdF, and NMP were mixed to prepare a slurry. The solid content was NCM / AB / PVdF=97.8 / 0.8 / 1.4 (mass ratio). The slurry was applied to a substrate to form a positive electrode active material layer. The positive electrode active material layer was dried. The positive electrode active material layer was compressed to produce a positive electrode.

[0152] assembly The following materials were prepared: Separator: PE porous sheet Electrolyte: 1.0mol / L LiPF6, EC+DMC+EMC Exterior: Pouch made of aluminum laminated film

[0153] A power generating element was formed by stacking the positive electrode, the separator, and the negative electrode in this order, and the power generating element and the electrolyte were enclosed in an exterior body to produce an evaluation cell.

[0154] <Evaluation> The discharge capacity of the evaluation cell was measured at 0.1C and 1C. The ambient temperature during discharge was 25°C. The ratio of the capacity during 1C discharge (1C discharge capacity) to the capacity during 0.1C discharge (0.1C discharge capacity) (1C discharge capacity / 0.1C discharge capacity) was calculated. It is considered that the larger the 1C discharge capacity / 0.1C discharge capacity, the better the rate performance.

[0155] <Result> From the orientation degrees of No.1-1, No.1-2, and No.1-3, it can be seen that the orientation degree tends to increase with the application of a magnetic field. From the orientation degrees of No.1-1 and No.1-2, it is considered that the oriented state is maintained in No.1-1 even after pressing. In No.1-1, the relationships of "A2 < A1" and "B2 < B1" are satisfied. It is considered that the second region where the aspect ratio of the active material is relatively small and the abundance of the binder is relatively low functions as a cushion, making it difficult for the oriented state to collapse.

[0156] Figure 9 is a cross-sectional SEM image of the first region and the second region in No.1-1. In the first region (lower layer), it seems that the flaky particles with a relatively large aspect ratio are oriented in the thickness direction. In the second region (upper layer), the spherical particles with a relatively small aspect ratio are distributed.

[0157] Figure 10 is a discharge curve during 1C discharge. No.1-1 and No.2 tend to have better rate performance compared to No.5. No.1-1 and No.2 have a larger orientation degree compared to No.5. No.1-1 tends to have better rate performance compared to No.2. No.1-1 has a smaller degree of bending compared to No.2. The negative electrode active material layer of No.1-1 includes the first region and the second region. The negative electrode active material layer of No.2 consists of a single region.

Explanation of symbols

[0158] 12 First active material, 14 First binder, 22 Second active material, 24 Second binder, 100 Counter electrode, 200 Electrode (electrode for battery), 210 Substrate, 220 Negative electrode active material layer, 221 First region, 222 Second region, 300 Separator, 500 Power generation element, 900 Outer package, 1000 Battery.< / nca> < / ncm>

Claims

1. A substrate and a negative electrode active material layer, the negative electrode active material layer is disposed on a surface of the substrate, a cross section parallel to a thickness direction of the negative electrode active material layer includes a first region and a second region, In the thickness direction, the first region is disposed between the second region and the base material, the first region includes a first active material and a first binder; the second region includes a second active material and a second binder; The relationship of the following formula (1) and formula (2) is satisfied, or the relationship of the following formula (3) and formula (4) is satisfied, A2<A1 (1) B2 < B1 (2) A2>A1 (3) B2>B1 (4) In the formulas (1) to (4), A1 represents the aspect ratio of the first active material; A2 represents the aspect ratio of the second active material; B1 represents an area fraction of the first binder in the first region, and B2 indicates an area fraction of the second binder in the second region; Electrodes for batteries.

2. The negative electrode active material layer has a tortuosity of 1.8 or less. The battery electrode according to claim 1 .

3. The relationship of the following formula (5) is further satisfied: 0.05≦I 110 / I 002 (5) In the formula (5), I 110 indicates a diffraction intensity of the (110) plane in the X-ray diffraction profile of the negative electrode active material layer, and I 002 indicates the diffraction intensity of the (002) plane in the X-ray diffraction profile of the negative electrode active material layer, The battery electrode according to claim 1 .

4. Of the relationship of the formula (1) and the formula (2) or the relationship of the formula (3) and the formula (4), only the relationship of the formula (1) and the formula (2) is satisfied. The battery electrode according to any one of claims 1 to 3.

5. The first active material and the second active material each independently contain artificial graphite; The battery electrode according to any one of claims 1 to 3.

6. The negative electrode active material layer has a thickness of 20 mg / cm 2 or more and 1.1 to 1.6 g / cm 3 having a density of The battery electrode according to any one of claims 1 to 3.

7. The relationship of the following formula (6) is further satisfied: 0.5≦Tx / (T1+T2)≦0.7 (6) In the formula (6), T1 represents the thickness of the first region, T2 represents the thickness of the second region, When the relationship of the formula (1) is satisfied, Tx represents the thickness of the first region, and When the relationship of the formula (3) is satisfied, Tx represents the thickness of the second region. The battery electrode according to any one of claims 1 to 3.

8. The relationship of the following formula (7) is further satisfied: 1.8%≦|B1-B2| (7) The battery electrode according to any one of claims 1 to 3.

9. The relationship of the following formula (8) is further satisfied: 1.8≦Ax (8) In the formula (8), When the relationship of the formula (1) is satisfied, Ax represents the aspect ratio of the first active material, and When the relationship of the formula (3) is satisfied, Ax represents the aspect ratio of the second active material, The battery electrode according to any one of claims 1 to 3.

10. The battery electrode according to any one of claims 1 to 3, battery.

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