Lithium ion battery

Abstract

The lithium ion battery includes a positive electrode, a negative electrode, and an electrolyte. The positive electrode includes a positive electrode active material layer. The positive electrode includes a flat portion and a groove portion. The thickness of the positive electrode active material layer at the groove portion is smaller than the thickness of the positive electrode active material layer at the flat portion. The negative electrode includes a negative electrode active material layer. The negative electrode active material layer includes a first portion and a second portion. The first portion is opposite to the flat portion. The second part is opposite to the groove part. The negative electrode active material layer contains a negative electrode active material. In the first portion, the negative electrode active material contains silicon. In the second part, the negative electrode active material is at least one selected from the group consisting of graphite and lithium titanate.

Description

Technical Field

[0001] The present disclosure relates to a lithium-ion battery. Background Art

[0002] Japanese Unexamined Patent Application Publication No. 2023-101952 discloses a positive electrode active material layer having a groove portion. Summary of the Invention

[0003] In a lithium-ion battery (hereinafter may be abbreviated as "battery" for simplicity), research has been conducted on providing a groove portion in the positive electrode active material layer. The groove portion can form a flow path for the electrolyte. Through the groove portion, it is possible to expect a reduction in the time required for impregnation of the electrolyte (hereinafter also referred to as "impregnation time") during battery manufacturing. For high energy density of the battery, research has been conducted on silicon (Si)-based negative electrode active materials. According to new insights, the cycle characteristics may deteriorate when the positive electrode active material layer having a groove portion is combined with a negative electrode active material layer containing a Si-based negative electrode active material. In addition, with the high energy density of the battery, a design with a high areal mass is required, so there is particularly room for improvement in manufacturing such electrodes.

[0004] An object of the present disclosure is to improve cycle characteristics.

[0005] 1. A lithium-ion battery, comprising a positive electrode, a negative electrode, and an electrolyte. The positive electrode includes a positive electrode active material layer. The positive electrode includes a flat portion and a groove portion. The thickness of the positive electrode active material layer at the groove portion is smaller than the thickness of the positive electrode active material layer at the flat portion. The negative electrode includes a negative electrode active material layer. The negative electrode active material layer includes a first portion and a second portion. The first portion faces the flat portion. The second portion faces the groove portion. The negative electrode active material layer contains a negative electrode active material. In the first portion, the negative electrode active material contains silicon. In the second portion, the negative electrode active material is at least one selected from the group consisting of graphite and lithium titanate.

[0006] The "negative electrode capacity per unit area" below may be abbreviated as "negative electrode capacity" for simplicity. The same applies to the positive electrode capacity per unit area. In the positive electrode active material layer, the positive electrode capacity of the groove portion is lower than that of the flat portion (non-groove portion). Therefore, in the negative electrode active material layer, the portion (second portion) opposite to the groove portion of the positive electrode active material layer has a lower state of charge than the portion (first portion) opposite to the flat portion of the positive electrode active material layer. The discharge curve of the Si-based negative electrode active material tends to have a slopy shape. That is, the potential gradually rises as the discharge proceeds. Therefore, the potential difference between the first portion and the second portion tends to increase easily. Due to the increase in the potential difference, it is possible to promote the diffusion of lithium (Li) ions from the first portion to the second portion. It is considered that a relatively large amount of diffusion of Li ions from the first portion to the second portion is one of the reasons for the degradation of the cycle characteristics.

[0007] In the battery described in 1 above, between the first portion and the second portion, the negative electrode active materials are different. The first portion contains a Si-based negative electrode active material. The second portion contains at least one selected from the group consisting of graphite and lithium titanate (Li 4 Ti 5 O 12 , LTO). The discharge curves of graphite and LTO contain a plateau. That is, the discharge curve contains a flat portion. Therefore, even if Li ions diffuse from the first portion to the second portion, a significant reduction in the diffusion rate of Li ions within the second portion can be expected. As a result, the diffusion of Li ions from the first portion to the second portion may be passivated. Therefore, an improvement in the cycle characteristics can be expected.

[0008] 2. The lithium ion battery described in "1" above may include, for example, the following configuration. The thickness of the positive electrode active material layer at the groove portion is zero.

[0009] The groove portion may also be blank. That is, the positive electrode active material layer may not exist at the groove portion. By making the groove portion blank, a shortening of the impregnation time can be expected.

[0010] 3. The lithium ion battery described in "1" or "2" above may include, for example, the following configuration. The following relationship of formula (1) is satisfied: 0.05 ≤ C2 / C1 (1) In formula (1), C1 represents the negative electrode capacity per unit area at the first portion. C2 represents the negative electrode capacity per unit area at the second portion.

[0011] By satisfying the relationship of the above formula (1), a reduction in short-circuit defects can be expected.

[0012] 4. The lithium ion battery described in any one of the above "1" to "3" may include the following configuration, for example. At least one of the relationships satisfying the following formulas (2) and (3) 30 mg / cm 2 ≤ Ma(2) 100 μm ≤ Ta(3) In formula (2), Ma represents the mass per unit area of the positive electrode active material layer at the flat portion. In formula (3), Ta represents the thickness of the positive electrode active material layer at the flat portion.

[0013] When at least one of the relationships satisfying the above formulas (2) and (3) is satisfied, the impregnation time of the electrolytic solution tends to be particularly long. In other words, it is considered that when at least one of the relationships satisfying the above formulas (2) and (3) is satisfied, the necessity of the groove portion is particularly high.

[0014] 5. The lithium ion battery described in any one of the above "1" to "4" may include the following configuration, for example. The negative electrode active material layer includes a first layer and a second layer. The first part includes the first layer and the second layer. In the first part, the second layer is laminated on the first layer. The second part is composed of the first layer or the second layer. The second layer has a composition different from that of the first layer.

[0015] The negative electrode active material layer may have a multilayer structure. For example, the first part and the second part may be formed by using two layers having different compositions from each other. For example, the first part and the second part may be formed by strip coating either the first layer or the second layer and surface coating the other layer.

[0016] Hereinafter, embodiments of the present disclosure (hereinafter may be abbreviated as "the present embodiment") and examples of the present disclosure (hereinafter may be abbreviated as "the present example") will be described. However, the present embodiment and the present example do not limit the technical scope of the present disclosure. The present embodiment and the present example are illustrative in all respects. The present embodiment and the present example are non-restrictive. The technical scope of the present disclosure includes meanings equivalent to the description in the claims and all changes within the scope. For example, any components may be extracted from the present embodiment from the beginning and combined arbitrarily. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Hereinafter, the features, advantages, and technical and industrial significance of the exemplary embodiments of the present invention will be described with reference to the drawings, in which the same reference numerals denote the same elements. Figure 1It is a schematic cross-sectional view showing an example of a lithium-ion battery in the present embodiment. Figure 2 It is a schematic top view showing an example of a positive electrode. Figure 3 It is a schematic cross-sectional view showing a second example of a negative electrode active material layer. Figure 4 It is a schematic cross-sectional view showing a third example of a negative electrode active material layer. Figure 5 It is a schematic cross-sectional view showing a fourth example of a negative electrode active material layer. Figure 6 It is a table showing experimental conditions. Figure 7 It is a table showing experimental results. Detailed implementation manners Main terms

[0018] "Negative electrode capacity per unit area (unit: mAh / cm 2 )" is the product of the specific capacity of the active material (unit: mAh / g), the blending ratio (mass ratio) of the active material at the target part, and the mass per unit area (mg / cm 2 ). The same applies to the positive electrode capacity. The specific capacity is measured by a single electrode test.

[0019] Geometric terms (such as parallel, perpendicular, orthogonal, etc.) should not be interpreted in a strict sense. For example, "parallel" can deviate slightly from "parallel" in the strict sense. Geometric terms can include tolerances, errors, etc. in design, operation, manufacturing, etc. There are cases where the dimensional relationships in each figure are inconsistent with the actual dimensional relationships. For the convenience of readers' understanding, there are cases where the dimensional relationships in each figure are changed. For example, there are cases where the length, width, thickness, etc. are changed. There are also cases where some components are omitted.

[0020] "Top view" means observing an object with a line of sight parallel to the thickness direction of the object. The shape of the object in the top view is shown in the top view drawing.

[0021] For a numerical range such as "m% to n%", unless otherwise specified, it includes the upper limit value and the lower limit value. That is, "m% to n%" represents a numerical range of "m% or more and n% or less". "m% or more and n% or less" includes "more than m% and less than n%". "Or more" and "or less" are represented by the inequality sign "≤" with an equal sign. "More than" and "less than" are represented by the inequality sign "<" without an equal sign.

[0022] "D50" represents the particle diameter at which the cumulative amount becomes 50% in the volume-based particle size distribution (cumulative distribution). The particle size distribution can be measured by the laser diffraction method.

[0023] The stoichiometric compositional formula represents a representative example of a compound. A compound may have a non-stoichiometric composition. For example, "Li 4 Ti 5 O 12 " is not limited to a compound having a molar ratio (mole ratio) of "Li:Ti:O = 4:5:12". Unless otherwise specified, "Li 4 Ti 5 O 12 " represents a compound containing Li, Ti, and O in an arbitrary molar ratio. For example, trace elements may be doped in this compound. A part of the constituent elements may also be replaced by other elements. Lithium-ion battery

[0024] Figure 1 is a schematic cross-sectional view showing an example of the lithium-ion battery in the present embodiment. The battery 100 includes a power storage element 50 and an electrolytic solution (not shown). The battery 100 may also include an outer package (not shown). The outer package may house the power storage element 50 and the electrolytic solution. The outer package may have any form. The outer package may include, for example, a metal case and a bag made of a metal foil laminate film. Power storage element

[0025] The power storage element 50 may also be referred to as, for example, an "electrode body", an "electrode group", etc. The power storage element 50 may have a single-pole structure, for example. The power storage element 50 may be a wound type, for example. The power storage element 50 may also have a bipolar structure, for example. The power storage element 50 may also be a stacked type, for example.

[0026] As an example, Figure 1 the power storage element 50 in has a bipolar structure. The power storage element 50 includes a positive electrode 10 and a negative electrode 20, for example. The positive electrode 10 includes a positive electrode active material layer 12. The positive electrode 10 may also be composed of the positive electrode active material layer 12. The positive electrode 10 may also include a positive electrode current collector 11. The negative electrode 20 includes a negative electrode active material layer 22. The negative electrode 20 may also be composed of the negative electrode active material layer 22. The negative electrode 20 may also include a negative electrode current collector 21. For example, the positive electrode current collector 11 may be attached to the negative electrode current collector 21 through a conductive adhesive (not shown). The power storage element 50 may also include a plurality of positive electrodes 10 and a plurality of negative electrodes 20. When the power storage element 50 has a bipolar structure, the single cell voltage is adjusted by the number of layers of the positive electrode 10 and the negative electrode 20. In order to obtain a desired single cell voltage (desired number of layers), the mass per unit area and thickness of the positive electrode active material layer 12 tend to increase. It is considered that the necessity of the groove portion (the flow path of the electrolytic solution) increases as at least one of the mass per unit area and thickness of the positive electrode active material layer 12 increases. Positive electrode

[0027] The positive electrode active material layer 12 can be supported on the positive electrode current collector 11, for example. The positive electrode current collector 11 can include, for example, aluminum (Al), a conductive resin, etc. The positive electrode current collector 11 can include, for example, an Al foil, an Al alloy foil. The thickness of the positive electrode current collector 11 can be, for example, 5 μm to 50 μm. A conductive layer can also be interposed between the positive electrode current collector 11 and the positive electrode active material layer 12.

[0028] The positive electrode active material layer 12 includes a flat portion 12a and a groove portion 12b. The groove portion 12b can be formed by any method. For example, the groove portion 12b can be formed by stripe coating. For example, the groove portion 12b can also be formed by laser processing, compression processing, etc. of the positive electrode active material layer 12. The thickness (Tb) of the positive electrode active material layer 12 at the groove portion 12b is smaller than the thickness (Ta) of the positive electrode active material layer 12 at the flat portion 12a. The thickness ratio (Tb / Ta) can be, for example, 0.8 or less, 0.7 or less, 0.6 or less, 0.5 or less, 0.4 or less, 0.3 or less, 0.2 or less, 0.1 or less, or zero. That is, the thickness (Tb) of the positive electrode active material layer 12 at the groove portion 12b can also be zero. For example, the bottom surface of the groove portion 12b can be the surface of the positive electrode current collector 11. In addition, the ratio (Ta min. ) of the minimum thickness (Ta max. ) to the maximum thickness (Ta min. / Ta max. ) within the flat portion 12a can be, for example, more than 0.8, 0.85 or more, 0.9 or more, or 0.95 or more.

[0029] Regarding the thickness (Ta) of the positive electrode active material layer 12 at the flat portion 12a, for example, the relationship of the following formula (3) can be satisfied. 100 μm ≤ Ta (3) The thickness (Ta) can 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, or 500 μm or more. The thickness (Ta) can be, for example, 1000 μm or less, 750 μm or less, 500 μm or less, 300 μm or less, or 200 μm or less.

[0030] Regarding the mass per unit area (Ma) of the positive electrode active material layer 12 at the flat portion 12a, for example, the relationship of the following formula (2) can be satisfied. 30 mg / cm 2 ≤ Ma (2) The mass per unit area (Ma) can be, for example, 10 mg / cm 2 or more, 15 mg / cm 2 or more, 20 mg / cm 2 or more, 25 mg / cm2 30 mg / cm or more 2 or more. In addition, the mass per unit area (Ma) can be, for example, 35 mg / cm 2 or more, 40 mg / cm 2 or more, 45 mg / cm 2 or more, or 50 mg / cm 2 or more. The mass per unit area (Ma) can be, for example, 100 mg / cm 2 or less, 90 mg / cm 2 or less, 80 mg / cm 2 or less, 70 mg / cm 2 or less, 60 mg / cm 2 or less, 50 mg / cm 2 or less, or 40 mg / cm 2 or less.

[0031] Figure 1 The Z direction represents the thickness direction of the positive electrode active material layer 12. The X direction and the Y direction represent directions orthogonal to the thickness direction (an example of in-plane directions). Figure 2 is a schematic plan view showing an example of the positive electrode. For example, the groove portion 12b can also be sandwiched between the flat portions 12a. For example, in a direction orthogonal to the thickness direction of the positive electrode active material layer 12, the flat portions 12a and the groove portion 12b can be alternately arranged. The arrangement of the flat portions 12a and the groove portion 12b can be either regular or random. The planar shape of the groove portion 12b is arbitrary. In plan view, the groove portion 12b can extend linearly, for example. The groove portion 12b can extend in a straight line, for example. The groove portion 12b can also be formed in a stripe shape, for example. The groove portion 12b can also extend in a lattice shape, for example. The groove portion 12b can extend across the positive electrode active material layer 12. The groove portion 12b can also not extend across the positive electrode active material layer 12. The groove portion 12b can be scattered in a dot shape, for example.

[0032] In a top view, the width (Wb) of the groove portion 12b can be smaller than the width (Wa) of the flat portion 12a. The width ratio (Wb / Wa) can be, for example, 0.90 or less, 0.80 or less, 0.70 or less, 0.60 or less, 0.50 or less, 0.40 or less, 0.30 or less, 0.20 or less, 0.10 or less, or 0.05 or less. The width ratio (Wb / Wa) can be, for example, 0.01 or more, 0.02 or more, 0.05 or more, or 0.10 or more. The width (Wa) can be, for example, 5 mm to 100 mm. The width (Wb) can also be, for example, 1 mm to 3 mm. The area (Sb) of the groove portion 12b can be smaller than the area (Sa) of the flat portion 12a. The area ratio (Sb / Sa) can be, for example, 0.90 or less, 0.80 or less, 0.70 or less, 0.60 or less, 0.50 or less, 0.40 or less, 0.30 or less, 0.20 or less, 0.10 or less, or 0.05 or less. The area ratio (Sb / Sa) can be, for example, 0.01 or more, 0.02 or more, 0.05 or more, or 0.10 or more.

[0033] The positive electrode active material layer 12 contains a positive electrode active material. The positive electrode active material can contain, for example, at least one selected from the group consisting of LiCoO 2 , LiNiO 2 , LiMnO 2 , LiMn 2 O 4 , Li(NiCoMn)O 2 , Li(NiCoAl)O 2 , and LiFePO 4 . For example, in "Li(NiCoMn)O 2 ", "(NiCoMn)" indicates that the sum of the composition ratios in the parentheses is 1. As long as the sum is 1, the respective component amounts are arbitrary. Li(NiCoMn)O 2 can contain, for example, LiNi 0.8 Co 0.1 Mn 0.1 O 2 , etc. The D50 of the positive electrode active material can be, for example, 5 μm to 20 μm. The positive electrode active material layer 12 can also further contain a conductive material and an adhesive described later. Negative electrode

[0034] The negative electrode active material layer 22 can be supported on the negative electrode current collector 21, for example. The negative electrode current collector 21 can contain, for example, copper (Cu), nickel (Ni), a conductive resin, etc. The negative electrode current collector 21 can contain, for example, a Cu foil or a Cu alloy foil. The thickness of the negative electrode current collector 21 can be, for example, 5 μm to 50 μm. A conductive layer can also be interposed between the negative electrode current collector 21 and the negative electrode active material layer 22.

[0035] The negative electrode active material layer 22 includes a first portion 22a and a second portion 22b. As Figure 1 shown, the first portion 22a faces the flat portion 12a. As long as the first portion 22a faces the flat portion 12a, a part of it may also face the groove portion 12b. For example, the planar shape of the first portion 22a may correspond to the planar shape of the flat portion 12a. In a plan view, the first portion 22a may be substantially similar to the flat portion 12a. The second portion 22b faces the groove portion 12b. As long as the second portion 22b faces the groove portion 12b, a part of it may also face the flat portion 12a. For example, the planar shape of the second portion 22b may correspond to the planar shape of the groove portion 12b. In a plan view, the second portion 22b may be substantially similar to the groove portion 12b. The negative electrode active material layer 22 contains a negative electrode active material. Between the first portion 22a and the second portion 22b, the negative electrode active material is different.

[0036] In the first portion 22a, the negative electrode active material contains Si. That is, the first portion contains a Si-based negative electrode active material. The Si-based negative electrode active material does not only mean pure Si, but also means a compound containing Si and all materials containing Si. The Si-based negative electrode active material may include, for example, at least one selected from the group consisting of Si, silicon oxide (SiO), and silicon-carbon composite material (Si-C). "Si-C" represents a composite containing Si and C. Si-C may include, for example, composite particles. For example, composite particles can be formed by loading Si with a carbon material. The carbon material may be, for example, crystalline or amorphous. As long as the first portion contains a Si-based negative electrode active material, it may also contain other negative electrode active materials. The first portion may also contain, for example, graphite. The graphite may be artificial graphite or natural graphite. The mixing ratio (mass ratio) of the Si-based negative electrode active material to graphite may be, for example, "Si-based negative electrode active material: graphite = 5:95 to 95:5" or "Si-based negative electrode active material: graphite = 20:80 to 80:20". Or, the mixing ratio (mass ratio) of the Si-based negative electrode active material to graphite may also be, for example, "Si-based negative electrode active material: graphite = 5:95 to 20:80". The D50 of the Si-based negative electrode active material may be smaller than the D50 of graphite. The D50 of the Si-based active material may be, for example, 1 μm to 10 μm. The D50 of graphite may be, for example, 10 μm to 25 μm.

[0037] In the second portion 22b, the negative electrode active material is at least one selected from the group consisting of graphite and LTO. The D50 of LTO may be, for example, 10 μm to 25 μm.

[0038] Between the negative electrode capacity per unit area (C1) of the first portion 22a and the negative electrode capacity per unit area (C2) of the second portion 22b, for example, the following relationship of formula (1) is satisfied. 0.05 ≤ C2 / C1 (1) The negative electrode capacity ratio (C2 / C1) can be, for example, 0.1 or more, 0.15 or more, 0.2 or more, 0.25 or more, 0.3 or more, 0.35 or more, 0.4 or more, 0.45 or more, 0.5 or more, 0.55 or more, or 0.6 or more. The negative electrode capacity ratio (C2 / C1) can be, for example, less than 1, 0.9 or less, 0.8 or less, 0.7 or less, 0.6 or less, 0.5 or less, 0.4 or less, or 0.3 or less.

[0039] As Figure 1 (the first example of the negative electrode active material layer 22) shows, for example, that the thickness of the first part 22a can be equal to the thickness of the second part 22b. In the thickness direction, the first part 22a may not overlap with the second part 22b.

[0040] The negative electrode active material layer 22 can have, for example, a multilayer structure. The first part 22a and the second part 22b can be formed by the multilayer structure. Figure 3 is a schematic cross-sectional view showing a second example of the negative electrode active material layer. The negative electrode active material layer 22 can contain, for example, a first layer 1 and a second layer 2. The second layer 2 has a composition different from that of the first layer 1. For example, the first layer 1 can be formed by applying the first paste in a striped pattern. The second layer 2 can be formed by applying the second paste in a planar manner on top of the first layer 1. In the first part 22a, the second layer 2 is laminated on the first layer 1. The second part 22b is composed of the second layer 2. For example, the first layer 1 can contain Si. For example, the second layer 2 can contain graphite. The thickness of the second part 22b can be smaller than the thickness of the first part 22a.

[0041] Figure 4 is a schematic cross-sectional view showing a third example of the negative electrode active material layer. For example, the first layer 1 can be formed by applying the second paste in a planar manner. The first layer 1 is flat. The second layer 2 can be formed by applying the first paste in a striped pattern on top of the first layer 1. In the first part 22a, the second layer 2 is laminated on the first layer 1. The second part 22b is composed of the first layer 1. For example, the first layer 1 can contain graphite. For example, the second layer 2 can contain Si. The thickness of the second part 22b can be smaller than the thickness of the first part 22a.

[0042] Figure 5 is a schematic cross-sectional view showing a fourth example of the negative electrode active material layer. The overlap between the first layer 1 and the second layer can be partial. For example, the second layer 2 can extend so as to cover the edge portion of the first layer 1. For example, the first layer 1 can contain Si. For example, the second layer 2 can contain graphite. For example, the thickness of the second part 22b can be larger than the thickness of the first part 22a.

[0043] The negative electrode active material layer 22 may also contain a conductive material and a binder in addition to the negative electrode active material. The blending amount of the conductive material may be, for example, 0.1 part by mass to 10 parts by mass with respect to 100 parts by mass of the negative electrode active material. The conductive material may contain, for example, at least one selected from the group consisting of acetylene black (AB), Ketjen black (registered trademark KB), vapor-grown carbon fiber (VGCF), carbon nanotube (CNT), and graphene flake (GF). The blending amount of the binder may be, for example, 0.1 part by mass to 10 parts by mass with respect to 100 parts by mass of the negative electrode active material. The binder may contain, for example, at least one selected from the group consisting of carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), polyacrylic acid (PAA), polyimide, polytetrafluoroethylene (PTFE), and polyvinylidene fluoride (PVdF). Spacer

[0044] The power storage element 50 may also further include a spacer (not shown). The spacer is disposed between the positive electrode active material layer 12 and the negative electrode active material layer 22. The spacer has electrical insulation properties. The spacer may include, for example, a porous film made of polyolefin. The spacer may include, for example, at least one selected from the group consisting of polyethylene (PE) and polypropylene (PP). The thickness of the spacer may be, for example, 5 μm to 50 μm, or 10 μm to 30 μm. The porosity of the spacer may be, for example, 50% to 60%. Electrolyte

[0045] The electrolyte contains a Li salt and a solvent. The concentration of the Li salt may be, for example, 0.5 mol / kg to 2 mol / kg. The Li salt may contain at least one selected from the group consisting of LiPF 6 , LiBF 4 and Li(FSO 2 ) 2 N. The solvent may contain at least one selected from the group consisting of ethylene carbonate (EC), fluoroethylene carbonate (FEC), propylene carbonate (PC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), and diethyl carbonate (DEC). The electrolyte may also further contain an optional additive. No.1

[0046] Mix the positive electrode active material (LiNi 0.8 Co 0.1 Mn 0.1 O 2 , D50: 10 μm), the conductive material (AB), the binder (PVdF), and the dispersion medium (N-methyl-2-pyrrolidone, NMP) to form a positive electrode paste. The blending of the solid components is "LiNi 0.8 Co 0.1 Mn 0.1 O2 : AB: PVdF = 93:4:3 (by mass)”. The solid component concentration is 65% (mass fraction). Using a slot die coater, the positive electrode paste is coated in stripes on one side of the positive electrode current collector (Al foil, thickness: 30 μm), thereby forming a coating film. The coating width (width of the flat part) is 10 mm. The blank width (width of the groove part) is 2 mm. The coating film is dried using a drying furnace, thereby forming the positive electrode active material layer. The drying temperature is 120 °C. The drying time is 10 minutes. After drying, the mass per unit area of the positive electrode active material layer is 35 mg / cm 2 . The positive electrode active material layer is compressed using a roll press, thereby producing a positive electrode roll material. After compression, the density of the positive electrode active material layer is 2.9 g / cm 3 . By cutting the positive electrode roll material, a positive electrode is produced. The planar size of the positive electrode is 24.5 cm × 14.5 cm. Using ultrasonic welding, a current collector tab (Al sheet, width: 5 mm, thickness: 150 μm) is joined to the back surface of the positive electrode current collector.

[0047] SiO (D50: 6 μm), graphite (spheroidized natural graphite, D50: 17 μm), conductive material (KB), binder (PAA), and dispersion medium (water) are mixed using a planetary mixer for 20 minutes, thereby forming a first paste. The formulation of the first paste is “SiO: graphite: KB: PAA: water = 18.6:74.4:5:2:90 (by mass)”. Using a slot die coater, the first paste is coated in stripes on one side of the negative electrode current collector (Cu foil, thickness: 15 μm, width: 25 cm). The coating width (width of the first part) is 10 mm. The blank width (width of the second part) is 2 mm. The first paste is dried, thereby forming the first part. The mass per unit area of the first part is 11.3 mg / cm 2 . The first part is compressed using a roll press. After compression, the density of the first part is 1.3 g / cm 3 .

[0048] Graphite (spheroidized natural graphite, D50: 17 μm), thickening material (CMC), binder (SBR), and dispersion medium (water) are mixed using a planetary mixer for 20 minutes, thereby forming a second paste. The formulation of the second paste is “graphite: CMC: SBR: dispersion medium = 98:1:1:85 (by mass)”. Using a slot die coater, the second paste is coated in stripes on each blank (2 mm) between the first parts. The second paste is dried, thereby forming the second part (width: 2 mm). The mass per unit area of the second part is 6 mg / cm 2Based on the above, a negative electrode coil material is formed. The negative electrode coil material is cut to fabricate the negative electrode. The planar size of the negative electrode is 25 cm × 15 cm. Using resistance welding, a current collector tab (Ni sheet, width: 5 mm, thickness: 50 μm) is joined to the back surface of the negative electrode current collector.

[0049] The positive electrode, spacer, and negative electrode are laminated such that the positive electrode active material layer and the negative electrode active material layer sandwich the spacer (PE porous membrane, porosity: 55%, thickness: 20 μm, planar size: 25.5 cm × 15.5 cm). Thus, an electricity storage element is formed. The electricity storage element has a single-pole structure. 10 g of an electrolytic solution [LiPF 6 (1 mol / kg), EC:FEC:EMC:DMC = 2:1:3:4 (volume ratio)] and the electricity storage element are housed in an outer package (a bag made of an Al laminated film). The outer package is vacuum-sealed to fabricate the laminated type single cell No.1. Hereinafter, the laminated type single cell may be abbreviated as "single cell". No.2 to No.17

[0050] Figure 6 is a table showing the experimental conditions. SiO (D50: 6 μm), a polyamic acid solution, a conductive material (KB), and a dispersion medium (NMP) are mixed for 20 minutes using a planetary mixer to form a first paste. The formulation of the first paste is "SiO: polyamic acid: KB: NMP = 82:12:6:85 (mass ratio)". The first paste is applied in stripes onto one side of a negative electrode current collector (Cu foil, thickness: 15 μm, width: 30 cm) using a slot die coater. The coating width (width of the first part) is 10 mm. The blank width (width of the second part) is 2 mm. The first paste is dried to form the first part. The mass per unit area of the first part is 4.1 mg / cm 2 . The first part is compressed using a roll press. After compression, the density of the first part is 1.3 g / cm 3 . Under an argon atmosphere, heat treatment is performed at 400 °C for 30 minutes to imidize the polyamic acid. Further, as Figure 6 shown, the mass per unit area of the second part, etc. are changed. Other than that, the single cell No.2 is fabricated in the same manner as No.1.

[0051] Si (D50: 2 μm) is used instead of SiO, and further, as Figure 6 shown, the mass per unit area of the second part, etc. are changed. Other than that, the single cell No.3 is fabricated in the same manner as No.1.

[0052] As Figure 6The mass per unit area of the positive electrode active material layer and the negative electrode active material layer was changed as described above, and the monomers of Nos. 4 to 6 were produced in the same manner as No. 1. In addition, in No. 6, the positive electrode paste was coated on the groove portion, and thus a positive electrode active material layer was also formed on the groove portion.

[0053] LTO (D50: 12 μm), a conductive material (KB), a binder (PVdF), and a dispersion medium (NMP) were mixed for 20 minutes using a planetary mixer to form a second paste. The formulation of the second paste was "LTO:KB:PVdF:NMP = 93:5:2:85 (mass ratio)". The second part was formed using the second paste, and the monomer of No. 7 was produced in the same manner as No. 1 except for this.

[0054] The first paste was coated in stripes on one side of a negative electrode current collector (Cu foil, thickness: 15 μm, width: 25 cm) using a slot die coater. The coating width (width of the first part) was 10 mm. The blank width (width of the second part) was 2 mm. The first paste was dried to form a first layer. The mass per unit area of the first layer was 8.4 mg / cm 2 . The first layer was compressed using a roll press. After compression, the density of the first layer was 1.3 g / cm 3 . The second paste was coated over the entire surface from above the first layer using a die coater to form a second layer. The target mass per unit area of the second layer was 6 mg / cm 2 . However, it was difficult to control the mass per unit area in the blank area, so the actual mass per unit area of the second part (groove opposite part) was 9 mg / cm 2 . The monomer of No. 8 was produced in the same manner as No. 1 except for this. It is considered that the negative electrode active material layer of No. 8 has a multilayer structure of the second example ( Figure 3 ).

[0055] The second paste was coated over the entire surface on one side of a negative electrode current collector (Cu foil, thickness: 15 μm, width: 25 cm) using a die coater. The second paste was dried to form a first layer. The mass per unit area of the first layer was 6 mg / cm 2 . The first paste was coated in stripes from above the first layer using a slot die coater. The first paste was dried to form a second layer. The mass per unit area of the second layer was 8.4 mg / cm 2 . The first layer and the second layer were compressed using a roll press. After compression, the average density of the first layer and the second layer was 1.3 g / cm 3 . The monomer of No. 9 was produced in the same manner as No. 1 except for this. It is considered that the negative electrode active material layer of No. 9 has a multilayer structure of the third example ( Figure 4 ).

[0056] The first paste is coated over the entire surface of one side of the negative electrode current collector using a die coater, thereby forming a negative electrode active material layer. In addition, the monomer of No. 10 is produced in the same manner as No. 1.

[0057] The first paste is coated over the entire surface of one side of the negative electrode current collector using a die coater, thereby forming a negative electrode active material layer. In addition, the monomer of No. 11 is produced in the same manner as No. 2.

[0058] The first paste is coated over the entire surface of one side of the negative electrode current collector using a die coater, thereby forming a negative electrode active material layer. In addition, the monomer of No. 12 is produced in the same manner as No. 3.

[0059] No groove portion is formed in the positive electrode active material layer. As Figure 6 shown, the mass per unit area of each part is changed. In addition, the monomers of No. 13 to No. 15 are produced in the same manner as No. 1.

[0060] As Figure 6 shown, the mass per unit area and thickness of the flat portion and the second portion are changed. In addition, the monomer of No. 16 is produced in the same manner as No. 1.

[0061] As Figure 6 shown, the mass per unit area of the second portion is changed. In addition, the monomer of No. 17 is produced in the same manner as No. 1. Evaluate

[0062] The monomer is sandwiched between two Al plates, thereby applying a confinement pressure of 0.3 MPa or more to the monomer. In a state where the confinement pressure is applied to the monomer, the initial discharge capacity is measured using the following CCCV charge and CCCV discharge. CCCV charge: CC current 300 mA, CV voltage 4.2 V, cut-off current 10 mA CCCV discharge: CC current 300 mA, CV voltage 2.5 V, cut-off current 10 mA Figure 7 This is a table showing the experimental results. The impregnation time represents the time from the injection of the electrolytic solution to the start of the first charge. In each sample, the initial discharge capacity is measured with two impregnation times of 30 minutes and 120 minutes.

[0063] In the monomer with an impregnation time of 120 minutes, a cycle test was carried out. One cycle of the following CCCV charge and CCCV discharge was regarded as one cycle, and charge and discharge of 100 cycles were carried out. The discharge capacity of the 100th cycle was divided by the initial discharge capacity, thereby calculating the capacity retention rate. CCCV charging: CC current 1500 mA, CV voltage 4.2 V, cut-off current 100 mA CCCV discharging: CC current 1500 mA, CV voltage 2.5 V, cut-off current 100 mA Results

[0064] From the comparisons of "No.1 vs. No.10", "No.2 vs. No.11", and "No.3 vs. No.12", a tendency of improved cycle characteristics was observed due to the second part (tank relative part) of the negative electrode active material layer containing graphite.

[0065] From the comparison of "No.1, No.4, No.5" with "No.13, No.14, No.15", a tendency was observed that the discharge capacity was significantly lower than the design capacity when there was no tank part in the positive electrode active material layer. The reason is considered to be insufficient impregnation. A tendency was observed that the larger the mass per unit area of the positive electrode active material layer, the more likely insufficient impregnation occurred.

[0066] From the comparison of "No.1, No.4, No.5", a tendency of reduced short-circuit defects was observed because the negative electrode capacity ratio (C2 / C1) was 0.05 or more. This is considered because even if Li diffuses into the second part (tank relative part), the second part has a margin in its bearing capacity. Based on these results, it is considered that the incidence of short-circuit defects may be high when both the positive electrode active material layer and the negative electrode active material layer are striped.

Claims

1. A lithium-ion battery, It includes a positive electrode, a negative electrode, and an electrolyte. The positive electrode comprises a positive electrode active material layer, The positive electrode includes a flat portion and a groove portion, The thickness of the positive electrode active material layer in the groove portion is smaller than the thickness of the positive electrode active material layer in the flat portion. The negative electrode comprises a negative electrode active material layer, The negative electrode active material layer includes a first portion and a second portion, The first portion is opposite to the flat portion, The second portion is opposite to the groove portion, The negative electrode active material layer contains a negative electrode active material. In the first part, the negative electrode active material includes silicon, and In the second part, the negative electrode active material is at least one selected from the group consisting of graphite and lithium titanate.

2. The lithium ion battery according to claim 1, wherein The thickness of the positive electrode active material layer in the groove portion is zero.

3. The lithium ion battery according to claim 1 or 2, wherein: The following equation (1) is satisfied: 0.05≤C2 / C1(1) In the formula (1), C1 represents the negative electrode capacity per unit area of ​​the first portion, and C2 represents the negative electrode capacity per unit area of ​​the second portion.

4. The lithium ion battery according to claim 1 or 2, wherein: Satisfies at least one of the following relationships: 30mg / cm 2 ≤Ma(2) 100μm≤Ta(3) In the formula (2), Ma represents the mass per unit area of ​​the positive electrode active material layer at the flat portion, and In the above formula (3), Ta represents the thickness of the positive electrode active material layer at the flat portion.

5. The lithium ion battery according to claim 1 or 2, wherein: The negative electrode active material layer includes a first layer and a second layer, The first part includes the first layer and the second layer, In the first portion, the second layer is stacked on the first layer, The second portion is composed of the first layer or the second layer, and the second layer has a composition different from that of the first layer.

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