Lithium ion battery

Abstract

A lithium ion battery includes a positive active material layer, a negative active material layer, and an electrolyte. The negative electrode active material layer includes a first region and a second region. The first regions and the second regions are alternately arranged in a direction orthogonal to the thickness direction of the negative electrode active material layer. The negative electrode active material layer includes a first active material and a second active material. The second active material has a larger specific capacity than the first active material. And the relation of 'T2lt, T1' and 'R1lt, R2' is satisfied. T1 represents the thickness of the first region during discharge. T2 represents the thickness of the second region during discharge. And R1 represents the ratio of the mass of the second active material in the first region to the total mass of the first active material and the second active material. And R2 represents the ratio of the mass of the second active material in the second region to the total mass of the first active material and the second active material.

Description

Technical Field

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

[0002] Japanese Unexamined Patent Application Publication No. 2019-192338 discloses an all-solid-state battery in which at least one of a positive electrode surface and a negative electrode surface has a slit-shaped groove. Summary of the Invention

[0003] When manufacturing a lithium-ion battery (hereinafter may be simply referred to as "battery"), an electrolytic solution is infiltrated into a power storage element. When the infiltration of the electrolytic solution is insufficient and the electrolytic solution does not cover the whole, the discharge capacity may be lower than the designed capacity.

[0004] Generally, as a means for increasing the capacity, a means of increasing the weight per unit area of the active material layer (hereinafter also referred to as "first means") or a means of increasing the area of the active material layer (hereinafter also referred to as "second means") is considered. In the first means, there is a tendency for many drawbacks such as difficulty in infiltrating the electrolytic solution and an increase in resistance. Therefore, in the past, the second means was often selected. However, in the case where the power storage element has a bipolar structure, in most cases, the first means has to be selected. Because in the case of a bipolar structure, the battery voltage depends on the number of electrode layers. In the second means, the number of layers also increases. In order to obtain a predetermined battery voltage, in most cases, the second means cannot be selected.

[0005] In the first means, the active material layer becomes thicker. There is a tendency that the longer the active material layer is, the longer the time required for infiltrating the electrolytic solution (hereinafter also referred to as "infiltration time") becomes. In order to shorten the infiltration time, forming a groove in the active material layer is considered. By forming a groove to form a flow path for the electrolytic solution, shortening of the infiltration time can be expected. Generally, it is considered appropriate to form the groove in the positive electrode active material layer. When a groove is formed in the negative electrode active material layer, during charging, lithium (Li) ions concentrate on the edge of the groove, and thus Li may precipitate. However, generally, the positive electrode active material layer is the source of capacity. Before the first charge, the positive electrode active material layer contains Li. Since a groove is formed in the positive electrode active material layer, the volume of the positive electrode active material layer is reduced. As a result, the designed capacity decreases.

[0006] An object of the present disclosure is to shorten the infiltration time. 1.

[0008] In one aspect of the present disclosure, the lithium-ion battery includes the following solutions.

[0009] A lithium-ion battery,

[0010] including a positive electrode active material layer, a negative electrode active material layer, and an electrolytic solution.

[0011] The negative electrode active material layer includes a first region and a second region.

[0012] In a direction orthogonal to the thickness direction of the negative electrode active material layer, the first region and the second region are alternately arranged.

[0013] The negative electrode active material layer includes a first active material and a second active material.

[0014] The specific capacity of the second active material is greater than that of the first active material.

[0015] The lithium ion battery satisfies the relationships of the following formulas (1) and (2).

[0016] T2 < T1 (1)

[0017] R1 < R2 (2)

[0018] In formula (1),

[0019] T1 represents the thickness of the first region during discharge.

[0020] T2 represents the thickness of the second region during discharge.

[0021] In formula (2),

[0022] R1 represents the ratio of the mass of the second active material in the first region to the total mass of the first active material and the second active material.

[0023] R2 represents the ratio of the mass of the second active material in the second region to the total mass of the first active material and the second active material.

[0024] The negative electrode active material layer includes a first region and a second region. The second region is thinner than the first region. There is a step difference between the surface of the second region and the surface of the first region. That is, the second region is the bottom wall of the groove. The negative electrode active material layer includes a first active material and a second active material. The second active material is a high-capacity active material. Compared with the first region, in the second region (the bottom wall of the groove), the ratio of the high-capacity active material becomes higher. Therefore, compared with the surroundings, the Li acceptance in the groove can be locally improved. That is, the precipitation of Li can be reduced. Moreover, by forming the groove, a shortening of the infiltration time can be expected. By providing a groove in the negative electrode active material layer, the reduction of the positive electrode active material layer can be avoided. 2.

[0026] The lithium ion battery described in the above 1 may also include, for example, the following solutions. It also satisfies at least one of the relationships of the following formulas (3) and (4).

[0027] T2 / T1 ≤ 0.4 (3)

[0028] T 02 / T 0 1 ≤ 0.3 (4)

[0029] In formula (4),

[0030] T 0 1 represents the thickness of the first region before the first charge.

[0031] T 0 2 represents the thickness of the second region before the first charge.

[0032] By satisfying at least one of the relationships in the above formulas (3) and (4), it is possible to expect a reduction in the infiltration time. Furthermore, the thickness of the negative electrode active material layer increases during charging and decreases during discharging. However, after the first charge, the thickness during discharging does not return to the thickness before the first charge. That is, generally, the relationships of "T 0 1 < T1" and "T 0 2 < T2" are satisfied. 3.

[0034] The lithium-ion battery described in the above 2 may also include the following solutions, for example. At least one of the relationships of the following formulas (5) and (6) is also satisfied.

[0035] 130μm ≤ T1 (5)

[0036] 100μm ≤ T 0 1 (6)

[0037] In the past, when at least one of the relationships in the above formulas (5) and (6) was satisfied, the infiltration time increased significantly. In the battery described in the above "1", even when at least one of the relationships in the above formulas (5) and (6) is satisfied, a reduction in the infiltration time can be expected. 4.

[0039] The lithium-ion battery described in any one of the above 1 to 3 may also include the following solutions, for example.

[0040] The first active material contains graphite.

[0041] The second active material contains at least one selected from silicon, silicon oxide, and silicon-carbon composite materials.

[0042] Compared with graphite, silicon (Si), silicon oxide (SiO), and silicon-carbon composite material (Si-C) can have a larger specific capacity. 5.

[0044] In one aspect of the present disclosure, the lithium-ion battery may also include the following solutions.

[0045] A lithium-ion battery,

[0046] It contains a positive electrode active material layer, a negative electrode active material layer and an electrolyte.

[0047] The negative electrode active material layer includes a first region and a second region.

[0048] In the direction perpendicular to the thickness direction of the negative electrode active material layer, the first region and the second region are alternately arranged.

[0049] The negative electrode active material layer includes a first active material and a second active material.

[0050] The specific capacity of the second active material is greater than that of the first active material.

[0051] The first active material includes graphite.

[0052] The second active material includes at least one selected from silicon, silicon oxide, and a silicon-carbon composite material.

[0053] The lithium-ion battery satisfies the relationship between the above equations (1) and (2).

[0054] The lithium-ion battery satisfies at least one of the relationships of the above-mentioned formula (3) and formula (4).

[0055] The lithium-ion battery also satisfies at least one of the relationships of the above-mentioned formula (5) and formula (6).

[0056] The following describes an embodiment of the present disclosure (hereinafter referred to as "the present embodiment") and an example of the present disclosure (hereinafter referred to as "the present example"). 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 aspects. The present embodiment and the present example are non-restrictive. The technical scope of the present disclosure includes all changes within the same meaning and scope as the claims. For example, it is intended from the outset to include the case where any scheme is extracted from the present embodiment and they are arbitrarily combined. Brief Description of the Figures

[0057] Hereinafter, features, advantages, and technical and industrial significance of exemplary embodiments of the present invention are described with reference to the accompanying drawings, wherein like reference numerals represent like elements.

[0058] Figure 1 This is a schematic diagram showing an example of a lithium ion battery in this embodiment.

[0059] Figure 2 This is a schematic plan view showing an example of a negative electrode active material layer in this embodiment.

[0060] Figure 3 is a table showing the experimental conditions.

[0061] Figure 4This is a table showing the experimental results. Detailed implementation

[0062] Main terms

[0063] "Specific capacity (unit: mAh / g)" represents the discharge capacity per unit mass. The specific capacity is measured by a single-pole test.

[0064] Geometric terms (such as parallel, perpendicular, orthogonal, etc.) should not be understood in a strict sense. For example, "parallel" can also deviate slightly from the strict sense of "parallel". For example, geometric terms can include tolerances, errors, etc. in terms of design, operation, manufacturing, etc. The dimensional relationships in each figure are sometimes inconsistent with the actual dimensional relationships. To help readers understand, the dimensional relationships in each figure are sometimes changed. For example, sometimes the length, width, thickness, etc. are changed. Sometimes part of the structure is also omitted.

[0065] "During discharge" represents the state where the SOC (state of charge) is 0%. "SOC" represents the ratio obtained by removing the discharged charge amount from the fully charged state of the battery. SOC can also be referred to as "charge level".

[0066] "Silicon-carbon composite material (Si-C)" represents a composite containing Si and C. For example, Si-C can also include composite particles. For example, composite particles can be formed by supporting Si with a carbon material. The carbon material can be crystalline or amorphous, for example.

[0067] "Looking from above" means observing an object with a line of sight parallel to the thickness direction of the object. The shape of the object when looking from above is shown in the top view.

[0068] For numerical ranges such as "m to n%", unless otherwise specified, the upper limit and the lower limit are included. "m to n%" represents the numerical range of "m% or more and n% or less". "m% or more and n% or less" includes "greater than m% and less than n%". "Or more" and "or less" are represented by the inequality sign "≤" with an equal sign. "Greater than" and "less than" are represented by the inequality sign "<" without an equal sign.

[0069] "D50" represents the particle size at which the cumulative distribution reaches 50% in the volume-based particle size distribution (cumulative distribution). The particle size distribution can be measured by the laser diffraction method.

[0070] Lithium-ion battery

[0071] Figure 1It is a conceptual diagram showing an example of a lithium-ion battery in this embodiment. The battery 100 includes a power storage element 50 and an electrolytic solution (not shown). The battery 100 may also include an exterior body (not shown). The exterior body may also house the power storage element 50 and the electrolytic solution. The exterior body can have any form. For example, the exterior body may also include a metal case and a pouch made of a metal foil laminate film, etc.

[0072] Power storage element

[0073] The power storage element 50 may also be referred to as an "electrode body", "electrode group", etc. For example, the power storage element 50 may have a monopolar structure. For example, the power storage element 50 may be of a wound type. For example, the power storage element 50 may have a bipolar structure. For example, the power storage element 50 may be of a laminated type.

[0074] Figure 1 The power storage element 50 in [embodiment] has a bipolar structure as an example. The power storage element 50 may also include a positive electrode current collector 14, a positive electrode active material layer 10, a negative electrode active material layer 20, and a negative electrode current collector 24. For example, the positive electrode current collector 14 may be adhered to the negative electrode current collector 24 through a conductive adhesive (not shown). The power storage element 50 may also include a plurality of positive electrode active material layers 10 and a plurality of negative electrode active material layers 20.

[0075] Negative electrode active material layer

[0076] The negative electrode active material layer 20 may be supported by the negative electrode current collector 24, for example. The negative electrode current collector 24 may contain copper (Cu), nickel (Ni), a conductive resin, etc., for example. The negative electrode current collector 24 may include a Cu foil, a Cu alloy foil, etc., for example. The thickness of the negative electrode current collector 24 may be 5 to 50 μm, for example. A conductive layer may exist between the negative electrode current collector 24 and the negative electrode active material layer 20. The conductive layer may include metal particles, carbon particles, etc., for example.

[0077] The negative electrode active material layer 20 includes a first region 21 and a second region 22. The thickness and composition are different between the first region 21 and the second region 22. In the direction (in-plane direction) orthogonal to the thickness direction of the negative electrode active material layer 20, the first region 21 and the second region 22 are alternately arranged. In Figure 1 [embodiment], the Z direction is the thickness direction. The X direction and the Y direction are an example of the in-plane direction. The in-plane direction can be any direction as long as it is orthogonal to the thickness direction.

[0078] Figure 2This is a schematic plan view showing an example of the negative electrode active material layer in the present embodiment. The arrangement of the first region 21 and the second region 22 can be regular or random. The plan view shape of the second region 22 is arbitrary. When viewed from above, the second region 22 can also extend linearly, for example. The second region 22 can also extend linearly, for example. The second region 22 can also be strip-shaped, for example. The second region 22 can also extend in a lattice shape, for example. The second region 22 can also extend across the negative electrode active material layer 20. The second region 22 can also not extend across the negative electrode active material layer 20. The second region 22 can also be scattered in dots, for example.

[0079] When viewed from above, the width (W2) of the second region 22 can also be smaller than the width (W1) of the first region 21. The width ratio (W2 / W1) can also be 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, for example. The width ratio (W2 / W1) can also be 0.01 or more, 0.02 or more, 0.05 or more, or 0.10 or more, for example. The width (W1) can also be 5 to 100 mm, for example. The width (W2) can also be 1 to 3 mm, for example. The area (S2) of the second region 22 can also be smaller than the area (S1) of the first region 21. The area ratio (S2 / S1) can also be 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, for example. The area ratio (S2 / S1) can also be 0.01 or more, 0.02 or more, 0.05 or more, or 0.10 or more, for example.

[0080] As Figure 1 shown, the second region 22 forms a groove. The relationship satisfying the following formula (1) holds.

[0081] T2 < T1 (1)

[0082] T1: Thickness of the first region 21 during discharge

[0083] T2: Thickness of the second region 22 during discharge

[0084] Regarding the thickness of each region, for example, the relationship satisfying the following formula (3) can also hold.

[0085] T2 / T1 ≤ 0.4 (3)

[0086] The thickness ratio (T2 / T1) can also be, for example, 0.55 or less, 0.50 or less, 0.45 or less, 0.35 or less, 0.30 or less, 0.25 or less, or 0.20 or less. The thickness ratio (T2 / T1) can also be, for example, 0.10 or more, 0.15 or more, 0.20 or more, 0.25 or more, 0.30 or more, 0.35 or more, or 0.40 or more.

[0087] Regarding the thickness of each region, for example, the relationship of the following formula (4) can also be satisfied.

[0088] T 0 2 / T 0 1 ≤ 0.3 (4)

[0089] T 0 1: Thickness of the first region 21 before the first charge

[0090] T 0 2: Thickness of the second region 22 before the first charge

[0091] The thickness ratio (T 0 2 / T 0 1) can also be, for example, 0.35 or less, 0.3 or less, 0.25 or less, 0.2 or less, 0.15 or less, 0.10 or less, or 0.05 or less. The thickness ratio (T 0 2 / T 0 1) can also be, for example, 0.01 or more, 0.05 or more, 0.10 or more, 0.15 or more, or 0.20 or more.

[0092] The thickness (T1) can also be, for example, 10 μm or more, 50 μm or more, 100 μm or more, 150 μm or more, 200 μm or more, 250 μm or more, or 300 μm or more. For example, the relationship of the following formula (5) can also be satisfied.

[0093] 130 μm ≤ T1 (5)

[0094] The thickness (T1) can also be, for example, 1000 μm or less, 500 μm or less, 300 μm or less, 250 μm or less, 200 μm or less, or 150 μm or less.

[0095] For example, the relationship of "T 0 1<T1" can also be satisfied. The thickness (T 0 1) can also be, for example, 10 μm or more, 50 μm or more, 150 μm or more, 200 μm or more, 250 μm or more, or 300 μm or more. For example, the relationship of the following formula (6) can also be satisfied.

[0096] 100 μm ≤ T 0 1 (6)

[0097] Thickness (T 0 1) For example, it can also be 1000 μm or less, 500 μm or less, 300 μm or less, 250 μm or less, 200 μm or less, or 150 μm or less.

[0098] Thickness (T2) can also be, for example, 10 μm or more, 30 μm or more, 50 μm or more, 75 μm or more, or 100 μm or more. Thickness (T2) can also be, for example, 150 μm or less, 100 μm or less, or 75 μm or less. Thickness (T 0 2) For example, it can also be 5 μm or more, 10 μm or more, 20 μm or more, 30 μm or more, 40 μm or more, 50 μm or more, or 60 μm or more. Thickness (T 0 2) For example, it can also be 100 μm or less, 75 μm or less, or 50 μm or less.

[0099] The negative electrode active material layer 20 contains a first active material and a second active material. The first active material can also contain, for example, at least one selected from the group consisting of graphite, soft carbon, hard carbon, and lithium titanate. The graphite can be natural graphite or artificial graphite. The D50 of the first active material can also be greater than that of the second active material. The D50 of the first active material can also be 10 to 25 μm. The specific capacity of the second active material is greater than that of the first active material. The second active material can also contain, for example, at least one selected from the group consisting of Si, SiO, and Si-C. The D50 of the second active material can also be 1 to 10 μm. In the entire negative electrode active material layer 20, the mass ratio of the second active material to the total mass of the first active material and the second active material can also be 0.01 to 0.20, 0.01 to 0.10, 0.01 to 0.05, or 0.01 to 0.03. Furthermore, the negative electrode active material layer 20 only needs to contain two or more active materials with different specific capacities, and can also contain three or more, four or more active materials.

[0100] The negative electrode active material layer 20 may also contain a conductive material and a binder. The compounding 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 negative electrode active material. For example, the conductive material may include at least one selected from acetylene black (AB), Ketjen black (registered trademark, KB), vapor grown carbon fiber (VGCF), carbon nanotube (CNT), and graphene sheet (GF). The compounding amount of the binder may be, for example, 0.1 to 10 parts by mass with respect to 100 parts by mass of the negative electrode active material. The binder may include, for example, at least one selected from carboxymethyl cellulose (CMC), styrene butadiene rubber (SBR), polyacrylic acid (PAA), polyimide, polytetrafluoroethylene (PTFE), and polyvinylidene fluoride (PVdF). Regarding the types and compounding amounts of the conductive material and the binder, the same applies to the positive electrode active material layer 10 described later.

[0101] The composition of the second region 22 is different from that of the first region 21. The following relationship of formula (2) is satisfied.

[0102] R1 < R2 (2)

[0103] R1: The ratio of the mass of the second active material in the first region 21 to the total mass of the first active material and the second active material

[0104] R2: The ratio of the mass of the second active material in the second region 22 to the total mass of the first active material and the second active material

[0105] The mass ratio (R1) may be, for example, 0 or more, 0.01 or more, 0.03 or more, or 0.05 or more. The mass ratio (R1) may be, for example, 0.10 or less, 0.075 or less, or 0.05 or less. The mass ratio (R2) may be, for example, greater than 0, 0.05 or more, 0.10 or more, 0.15 or more, 0.20 or more, 0.25 or more, 0.30 or more, 0.35 or more, 0.40 or more, 0.45 or more, 0.50 or more, 0.55 or more, 0.6 or more, 0.7 or more, 0.8 or more, or 0.9 or more. The mass ratio (R2) may be, for example, 1 or less, 0.95 or less, 0.90 or less, 0.80 or less, 0.70 or less, or 0.60 or less.

[0106] The acceptance capacity per unit area (unit: mAh / cm 2 ) is obtained based on the unit area weight (unit: mg / cm 2 ), the compounding ratio (mass ratio) of the active material, and the specific capacity (unit: mAh / g) of the active material. Between the first region 21 and the second region 22, the acceptance capacity per unit area may be approximate. For example, the following relationship of formula (7) may be satisfied.

[0107] 0.8 ≤ C2 / C1 ≤ 1.2 (7)

[0108] C1: The acceptance capacity per unit area in the first region 21

[0109] C2: The acceptance capacity per unit area in the second region 22

[0110] The closer the capacity ratio (C2 / C1) is to 1, the smaller the non-uniformity of the electrode reaction in the in-plane direction can be expected. The capacity ratio (C2 / C1) can also be, for example, 0.85 or more, 0.90 or more, 0.95 or more, 0.99 or more. The capacity ratio (C2 / C1) can also be, for example, 1.15 or less, 1.10 or less, 1.05 or less, or 1.01 or less.

[0111] Positive electrode active material layer

[0112] In a plan view, the area of the positive electrode active material layer 10 can also be smaller than that of the negative electrode active material layer 20. The ratio (Sn / Sp) of the area (Sn) of the negative electrode active material layer 20 to the area (Sp) of the positive electrode active material layer 10 can also be, for example, 1.01 to 1.1. The positive electrode active material layer 10 can also be completely flat. The positive electrode active material layer 10 does not have grooves, and thus an increase in the design capacity can be expected. Furthermore, "flat" means that the ratio of the minimum thickness (Tmin) of the layer to the maximum thickness (Tmax) of the layer is 0.8 to 1 (or 0.9 to 1).

[0113] For example, the positive electrode active material layer 10 can also be supported by the positive electrode current collector 14. The positive electrode current collector 14 can also contain, for example, aluminum (Al), a conductive resin, etc. For example, the positive electrode current collector can also contain an Al foil, an Al alloy foil. The thickness of the positive electrode current collector 14 can also be, for example, 5 to 50 μm. A conductive layer can also exist between the positive electrode current collector 14 and the positive electrode active material layer 10. The thickness of the positive electrode active material layer 10 can also be, for example, 10 to 1000 μm, 50 to 500 μm, or 100 to 300 μm.

[0114] The positive electrode active material layer 10 contains a positive electrode active material. The positive electrode active material can also contain, for example, at least one selected from LiCoO 2 , LiNiO 2 , LiMnO 2 , LiMn 2 O 4 , Li(NiCoMn)O 2 , Li(NiCoAl)O 2 , and LiFePO 4 . For example, "Li(NiCoMn)O 2"(NiCoMn)" in "" means that the sum of the composition ratios within the parentheses is 1. As long as the sum is 1, the amount of each component can be arbitrary. Li(NiCoMn)O 2 For example, it may also contain LiNi 0.8 Co 0.1 Mn 0.1 O 2 etc. The D50 of the positive electrode active material may also be, for example, 5 to 20 μm. The positive electrode active material layer 10 may further contain the above-mentioned conductive material and binder.

[0115] Separator

[0116] The power storage element 50 may further include a separator (not shown). The separator is disposed between the positive electrode active material layer 10 and the negative electrode active material layer 20. The separator has electrical insulation properties. The separator may also include, for example, a porous film made of polyolefin. The separator may also include at least one selected from polyethylene (PE) and polypropylene (PP). The thickness of the separator may also be, for example, 5 to 50 μm or 10 to 30 μm. The porosity of the separator may also be, for example, 50 to 60%.

[0117] Electrolyte

[0118] The electrolyte contains a Li salt and a solvent. The concentration of the Li salt may also be, for example, 0.5 to 2 mol / kg. The Li salt may also include at least one selected from LiPF 6 , LiBF 4 and Li(FSO 2 ) 2 N. The solvent may also include at least one selected from ethylene carbonate (EC), fluoroethylene carbonate (FEC), propylene carbonate (PC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), and diethyl carbonate (DEC). The electrolyte may further contain optional additives.

[0119] No.1

[0120] By mixing 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), a positive electrode paste is formed. The ratio of the solid components is "LiNi 0.8 Co 0.1 Mn 0.1 O 2: AB: PVdF = 93:4:3 (by mass). The concentration of the solid component is 65% (mass fraction). The positive electrode paste is coated on one side of the positive electrode current collector (Al foil, thickness: 30 μm) by a comma coater to form a coating film. The coating film is dried in a drying furnace to form a positive electrode active material layer. The drying temperature is 120 °C. The drying time is 10 minutes. After drying, the weight per unit area of the positive electrode active material layer is 35 mg / cm 2 . The positive electrode active material layer is compressed by a roll press to produce a positive electrode green sheet. After compression, the density of the positive electrode active material layer is 2.9 g / cm 3 . The positive electrode is produced by cutting the positive electrode green sheet. The planar size of the positive electrode is 24.5 cm × 14.5 cm. The electrode tab (Al sheet, width: 5 mm, thickness: 150 μm) is joined to the back of the positive electrode current collector by ultrasonic welding.

[0121] The first active material (spheroidized natural graphite, D50: 17 μm), thickener (CMC), binder (SBR), and dispersion medium (water) are mixed by a planetary mixer for 20 minutes to form the first paste. The ratio of the first paste is "graphite: CMC: SBR: water = 98:1:1:85 (by mass)". The first paste is coated in a strip shape on one side of the negative electrode current collector (Cu foil, thickness: 15 μm, width: 25 cm) by a slot die coater. The coating width (width of the first region) is 10 mm. The blank width (width of the second region) is 2 mm. The first region (width: 10 mm) is formed by drying the first paste. The weight per unit area of the first region is 21.6 mg / cm 2 . The first region is compressed by a roll press. After compression, the density of the first region is 1.5 g / cm 3 .

[0122] The second active material (SiO, D50: 6 μm), conductive material (KB), binder (PAA), and dispersion medium (water) are mixed by a planetary mixer for 20 minutes to form the second paste. The ratio of the second paste is "SiO: KB: PAA: water = 93:5:2:90 (by mass)". The second paste is coated in a strip shape on each blank part (2 mm) between the first regions by a slot die coater. The second region (width: 2 mm) is formed by drying the second paste. The weight per unit area of the second region is 3.6 mg / cm 2 . Through the above treatment, a negative electrode green sheet is formed. The negative electrode is produced by cutting the negative electrode green sheet. The planar size of the negative electrode is 25 cm × 15 cm. The electrode tab (Ni sheet, width: 5 mm, thickness: 50 μm) is joined to the back of the negative electrode current collector by resistance welding.

[0123] The positive electrode and the negative electrode are stacked with a separator (PE porous membrane, porosity: 55%, thickness: 20 μm, planar size: 25.5 cm × 15.5 cm) in between, so that a power storage element is formed. The power storage element has a unipolar structure. 10 g of electrolyte [LiPF 6 (1 mol / kg), EC:FEC:EMC:DMC = 2:1:3:4 (volume ratio)] and the power storage element are housed in an outer package (a pouch made of an Al laminated film). The outer package is vacuum-sealed, and thus the laminated type cell No.1 is fabricated. Hereinafter, the laminated type cell may be simply referred to as "cell".

[0124] No.2 to No.11

[0125] Figure 3 is a table showing the experimental conditions. Instead of SiO, Si (D50: 2 μm) is used as the second active material, and the weight per unit area and thickness of each region are changed. Except for this, the cell No.2 is fabricated in the same manner as No.1.

[0126] The mass ratio, weight per unit area and thickness of the first active material and the second active material in the second region are changed. Except for this, the cells No.3, No.4 and No.9 are fabricated in the same manner as No.1.

[0127] The weight per unit area of the positive electrode active material layer is changed to 43 mg / cm 2 , and the mass ratio, weight per unit area and thickness of the first active material and the second active material in the second region are changed. Except for this, the cells No.5 and No.10 are fabricated in the same manner as No.1.

[0128] By coating the positive electrode paste in a strip shape, grooves are given to the positive electrode active material layer. The coating width of the positive electrode active material layer is 10 mm, and the blank width is 2 mm. The negative electrode active material layer is formed by coating the first paste on the entire surface of the negative electrode current collector. The negative electrode active material layer does not have grooves. Except for this, the cell No.7 is fabricated in the same manner as No.1.

[0129] Grooves are not provided on both the positive electrode active material layer and the negative electrode active material layer to form the power storage element. Except for this, the cell No.8 is fabricated in the same manner as No.1.

[0130] The second paste is not coated in the second region, and the second region remains blank to form the power storage element. In the first region, the weight per unit area of the first region is increased compared with No.1 so as to completely receive Li from the positive electrode. Except for this, the cell No.11 is fabricated in the same manner as No.1.

[0131] Evaluation

[0132] The unit is clamped between two Al plates, and a constraint pressure of 0.3 MPa or more is applied to the unit. The first charge and discharge are performed under the following conditions while the constraint pressure is applied to the unit.

[0133] CCCV charging: CC current: 300 mA, CV voltage: 4.2 V, cut-off current: 10 mA CCCV discharging: CC current: 300 mA, CV voltage: 2.5 V, cut-off current: 10 mA

[0134] Figure 4 This is a table showing the experimental results. The impregnation time represents the time from the injection of the electrolyte to the start of the first charge. For each sample, the first discharge capacity was measured under two conditions: an impregnation time of 30 minutes and an impregnation time of 120 minutes.

[0135] Results

[0136] In No. 8, the actual discharge capacity decreased significantly compared to the designed capacity. In No. 8, neither the positive electrode active material layer nor the negative electrode active material layer has a groove. It is considered that the impregnation of the electrolyte is insufficient.

[0137] No. 7 shows a higher discharge capacity compared to No. 8. It is considered that the impregnation of the electrolyte is promoted by forming a groove in the positive electrode active material layer. However, as the groove is formed, the positive electrode active material layer is reduced, so the designed capacity decreases.

[0138] In No. 1 to No. 6, No. 9, and No. 10, a groove (second region) is provided in the negative electrode active material layer. In these samples, a discharge capacity close to the designed capacity was obtained. It is considered that this is because the groove promotes the impregnation of the electrolyte.

[0139] From the comparison within No. 1 to No. 6, No. 9, and No. 10, it can be seen that the smaller the thickness ratio (T 0 2 / T 0 1, T2 / T1), the greater the tendency to promote impregnation.

[0140] It is considered that compared with other samples, the positive electrode active material layer of No. 5 and No. 8 is of high density, so the difficulty of impregnation increases. It is considered that in No. 5, a groove is provided in the negative electrode active material layer, thereby completing the impregnation of the electrolyte in a short time.

[0141] The first region of No. 6 contains both the first active material (graphite) and the second active material (SiO). It is considered that even if the second active material is contained in the first region, as long as there is a thickness difference between the first region and the second region, the impregnation of the electrolyte can be promoted.

[0142] In No. 11, the voltage dropped during charging, so the test was aborted. After the test was aborted, the cell was disassembled. Lithium precipitation was visible at the boundary between the negative electrode active material layer and the groove (blank). It is considered that the voltage drop occurred due to lithium precipitation.

Claims

1. A lithium-ion battery, comprising a positive electrode active material layer, a negative electrode active material layer and an electrolyte, The negative electrode active material layer includes a first region and a second region, The first regions and the second regions are alternately arranged in a direction perpendicular to the thickness direction of the negative electrode active material layer. The negative electrode active material layer includes a first active material and a second active material. The second active material has a larger specific capacity than the first active material, The lithium-ion battery satisfies the following relationship between equations (1) and (2): T2 < T1 (1) R1 < R2 (2) In the formula (1), T1 represents the thickness of the first region during discharge, T2 represents the thickness of the second region during discharge, In the formula (2), R1 represents the ratio of the mass of the second active material in the first region to the total mass of the first active material and the second active material, and R2 represents the ratio of the mass of the second active material in the second region to the total mass of the first active material and the second active material.

2. The lithium ion battery according to claim 1, Also satisfies at least one of the following relationships of formula (3) and formula (4), T2 / T1 ≤ 0.4 (3) T02 / T01 ≤ 0.3 (4) In the formula (4), T01 represents the thickness of the first region before initial charging, and T02 represents the thickness of the second region before initial charging.

3. The lithium ion battery according to claim 2, Also satisfies at least one of the following relationships of formula (5) and formula (6), 130μm ≤ T1 (5) 100μm ≤ T01 (6).

4. The lithium ion battery according to any one of claims 1 to 3, The first active material includes graphite, and The second active material includes at least one selected from the group consisting of silicon, silicon oxide, and a silicon-carbon composite material.

5. A lithium ion battery, comprising a positive electrode active material layer, a negative electrode active material layer and an electrolyte, The negative electrode active material layer includes a first region and a second region, The first regions and the second regions are alternately arranged in a direction perpendicular to the thickness direction of the negative electrode active material layer. The negative electrode active material layer includes a first active material and a second active material. The second active material has a larger specific capacity than the first active material, The first active material includes graphite, The second active material comprises at least one selected from silicon, silicon oxide and a silicon-carbon composite material. The lithium-ion battery satisfies the following relationship between equations (1) and (2): T2 < T1 (1) R1 < R2 (2) In the formula (1), T1 represents the thickness of the first region during discharge, T2 represents the thickness of the second region during discharge, In the formula (2), R1 represents the ratio of the mass of the second active material in the first region to the total mass of the first active material and the second active material, R2 represents the ratio of the mass of the second active material in the second region to the total mass of the first active material and the second active material, The lithium ion battery satisfies at least one of the following relationships: And satisfying at least one of the following relationships of formula (5) and formula (6), T2 / T1 ≤ 0.4 (3) T02 / T01 ≤ 0.3 (4) 130μm ≤ T1 (5) 100μm ≤ T01 (6) In the formula (4) and the formula (6), T01 represents the thickness of the first region before initial charge, and T02 represents the thickness of the second region before initial charge.

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