阅读说明：本技术 锂二次电池 (Lithium secondary battery ) 是由 蚊野聪 宫前亮平 石井圣启 名仓健祐 于 2019-05-23 设计创作，主要内容包括：本公开提供一种循环特性优异的锂二次电池。该锂二次电池具备电极群和具有锂离子传导性的非水电解质,所述电极群是正极、负极(134)和介于正极与负极(134)之间的隔板卷绕而成的,正极包含含锂的正极活性物质,负极(134)包含负极集电体(132)和配置于负极集电体(132)上的多个凸部。负极(134)在充电时析出锂金属,锂金属在放电时溶解于非水电解质中。多个凸部具备多个外周侧凸部(133A)和多个内周侧凸部(133B)。在第1表面和第2表面中的至少一个表面,多个外周侧凸部(133A)向第1区域(OW)投影的面积合计在第1区域的面积中所占的第1面积比例,大于多个内周侧凸部(133B)向第2区域投影的面积合计在第2区域的面积中所占的第2面积比例。(disclosed is a lithium secondary battery having excellent cycle characteristics. The lithium secondary battery comprises an electrode group and a lithium ion conductive non-aqueous electrolyte, wherein the electrode group is formed by winding a positive electrode, a negative electrode (134) and a separator between the positive electrode and the negative electrode (134), the positive electrode comprises a positive electrode active material containing lithium, and the negative electrode (134) comprises a negative electrode current collector (132) and a plurality of convex parts arranged on the negative electrode current collector (132). The negative electrode (134) deposits lithium metal during charging, and the lithium metal dissolves in the nonaqueous electrolyte during discharging. The plurality of protrusions include a plurality of outer circumferential protrusions (133A) and a plurality of inner circumferential protrusions (133B). On at least one of the 1 st surface and the 2 nd surface, the ratio of the 1 st area occupied by the total area of the 1 st area projected by the plurality of outer peripheral protrusions (133A) to the 1 st area (OW) is greater than the ratio of the 2 nd area occupied by the total area of the 2 nd area projected by the plurality of inner peripheral protrusions (133B) to the 2 nd area.)

1. A lithium secondary battery comprising an electrode group and a lithium ion conductive nonaqueous electrolyte, wherein the electrode group is formed by winding a positive electrode, a negative electrode and a separator interposed between the positive electrode and the negative electrode,

The positive electrode includes a positive electrode active material containing lithium, the negative electrode includes a negative electrode current collector and a plurality of projections arranged on the negative electrode current collector,

The negative electrode precipitates lithium metal during charging, the lithium metal is dissolved in the nonaqueous electrolyte during discharging,

The negative electrode current collector includes a 1 st surface facing a winding outer direction of the electrode group and a 2 nd surface facing a winding inner direction of the electrode group,

at least one of the 1 st surface and the 2 nd surface includes a 1 st region and a 2 nd region, the 2 nd region being closer to a winding innermost circumference of the electrode group than the 1 st region,

The plurality of convex parts comprise a plurality of outer periphery convex parts arranged on the 1 st area and a plurality of inner periphery convex parts arranged on the 2 nd area,

On at least one of the 1 st surface and the 2 nd surface, a ratio of a 1 st area occupied by a total of areas of the plurality of outer peripheral protrusions projected onto the 1 st region to an area of the 1 st region is larger than a ratio of a 2 nd area occupied by a total of areas of the plurality of inner peripheral protrusions projected onto the 2 nd region to an area of the 2 nd region.

2. The lithium secondary battery according to claim 1,

At least one of the 1 st surface and the 2 nd surface, the 1 st region being farther from the innermost circumference than a center line in a longitudinal direction,

The 2 nd region is proximate to the innermost periphery compared to the centerline at least one of the 1 st surface and the 2 nd surface.

3. The lithium secondary battery according to claim 1 or 2,

The difference between the 1 st area ratio and the 2 nd area ratio is 3% or more and 50% or less.

4. The lithium secondary battery according to any one of claims 1 to 3,

The 1 st area ratio is 0.2% or more and 70% or less.

5. The lithium secondary battery according to any one of claims 1 to 4,

The difference between the 1 st average height of the plurality of outer peripheral protrusions and the 2 nd average height of the plurality of inner peripheral protrusions is less than 3% of the 2 nd average height.

6. The lithium secondary battery according to any one of claims 1 to 5,

The 1 st average height of the plurality of outer peripheral side protrusions is 15 μm or more and 120 μm or less,

The 2 nd average height of the plurality of inner periphery-side protrusions is 15 μm or more and 120 μm or less.

7. The lithium secondary battery according to any one of claims 1 to 6,

the projection shapes of the plurality of outer periphery-side protrusions to the 1 st region are linear on at least one of the 1 st surface and the 2 nd surface,

the shapes of the projections of the plurality of inner periphery-side protrusions to the 2 nd region are linear on at least one of the 1 st surface and the 2 nd surface,

a minimum value of a distance between adjacent 2 outer-peripheral-side convex portions among the plurality of outer-peripheral-side convex portions is larger than a maximum width of the adjacent 2 outer-peripheral-side convex portions on at least one of the 1 st surface and the 2 nd surface,

At least one of the 1 st surface and the 2 nd surface, a minimum value of a separation distance between adjacent 2 inner circumference-side protrusions among the plurality of inner circumference-side protrusions is larger than a maximum width of the adjacent 2 inner circumference-side protrusions.

8. The lithium secondary battery according to any one of claims 1 to 7,

The negative electrode current collector is provided with a copper foil or a copper alloy foil.

9. The lithium secondary battery according to any one of claims 1 to 8,

The plurality of protrusions are respectively in contact with the separator,

During the charging, the lithium metal is precipitated in a space between the negative electrode current collector and the separator.

10. The lithium secondary battery according to any one of claims 1 to 9,

the material of the plurality of projections is different from the material of the negative electrode current collector.

11. the lithium secondary battery according to any one of claims 1 to 10,

The plurality of projections are made of a resin material.

12. The lithium secondary battery according to any one of claims 1 to 9,

the negative electrode current collector and the plurality of projections are integrally formed of the same material.

13. The lithium secondary battery according to any one of claims 1 to 12,

The 1 st and 2 nd surfaces comprise the 1 st and 2 nd regions respectively,

The plurality of outer circumference-side protrusions include a plurality of 1 st protrusions disposed on the 1 st surface and a plurality of 2 nd protrusions disposed on the 2 nd surface,

The plurality of inner peripheral-side protrusions include a plurality of 1 st protrusions disposed on the 1 st surface and a plurality of 2 nd protrusions disposed on the 2 nd surface.

14. The lithium secondary battery according to claim 13,

The difference between the average height of the 1 st protrusions and the average height of the 2 nd protrusions is less than 3% of the average height of the 2 nd protrusions.

15. The lithium secondary battery according to any one of claims 1 to 14,

The non-aqueous electrolyte contains lithium ions and anions,

The anion comprises at least one selected from the group consisting of PF ₆ ^- , imide-based anions, and oxalate-based anions.

16. A lithium secondary battery comprising an electrode group and a lithium ion conductive nonaqueous electrolyte, wherein the electrode group is formed by winding a positive electrode, a negative electrode and a separator interposed between the positive electrode and the negative electrode,

The positive electrode includes a positive electrode active material containing lithium, the negative electrode includes a negative electrode current collector and a plurality of projections arranged on the negative electrode current collector,

The negative electrode precipitates lithium metal during charging, the lithium metal is dissolved in the nonaqueous electrolyte during discharging,

The negative electrode current collector includes a 1 st surface facing a winding outer direction of the electrode group and a 2 nd surface facing a winding inner direction of the electrode group,

the 1 st surface and the 2 nd surface each include a 1 st region and a 2 nd region, the 2 nd region being closer to a winding innermost circumference of the electrode group than the 1 st region,

the plurality of convex parts comprise a plurality of outer periphery convex parts arranged on the 1 st area and a plurality of inner periphery convex parts arranged on the 2 nd area,

A ratio of a total area of the plurality of outer peripheral side convex portions projected onto the 1 st region on the 1 st region to the area of the 1 st region on the 1 st surface is set as a 3 rd area ratio,

On the 2 nd surface, the ratio of the total area of the projections of the plurality of outer peripheral side projections on the 1 st region onto the 1 st region to the area of the 1 st region is set as the 4 th area ratio,

Setting an arithmetic average of the 3 rd area ratio and the 4 th area ratio as a 1 st area ratio,

A ratio of a total area of the plurality of inner peripheral-side protrusions on the 2 nd region projected onto the 2 nd region to the area of the 2 nd region on the 1 st surface is set to a 5 th area ratio,

A ratio of a total area of the plurality of inner peripheral-side protrusions on the 2 nd region projected onto the 2 nd region to the area of the 2 nd region on the 2 nd surface is set to a 6 th area ratio,

Setting an arithmetic average of the 5 th area ratio and the 6 th area ratio as a 2 nd area ratio,

In the above-mentioned case, the first step,

The 1 st area fraction is greater than the 2 nd area fraction.

Technical Field

the present disclosure relates to a lithium secondary battery including a lithium ion conductive nonaqueous electrolyte.

Background

Nonaqueous electrolyte secondary batteries are used for ICT applications such as personal computers and smart phones, for vehicles, for power storage, and the like. In such applications, nonaqueous electrolyte secondary batteries are required to have further high capacity. As a high-capacity nonaqueous electrolyte secondary battery, a lithium ion battery is known. The capacity of the lithium ion battery can be increased by using an alloy active material such as graphite and a silicon compound as a negative electrode active material. However, the capacity of lithium ion batteries is increasing to a limit.

Lithium secondary batteries are expected to be a promising candidate for high-capacity nonaqueous electrolyte secondary batteries exceeding lithium ion batteries. In a lithium secondary battery, lithium metal is precipitated on a negative electrode during charging, and the lithium metal is dissolved in a nonaqueous electrolyte during discharging.

In order to suppress the deterioration of battery characteristics due to the dendritic precipitation of lithium metal, studies have been made on the lithium secondary battery in which the shape of the negative electrode current collector is improved. For example, patent document 1 proposes that the ten-point average roughness Rz of the lithium metal deposition surface of the negative electrode current collector be 10 μm or less. Patent document 2 proposes that a negative electrode including a porous metal current collector and lithium metal inserted into pores of the current collector be used in a lithium secondary battery. Patent document 3 proposes a lithium metal polymer secondary battery using a negative electrode current collector having a surface formed with a plurality of concave grooves recessed in a predetermined shape.

Prior art documents

Patent document 1: japanese patent laid-open No. 2001 and 243957

patent document 2: japanese laid-open patent publication No. 2016-527680

patent document 3: japanese patent laid-open publication No. 2006 and 156351

Disclosure of Invention

Embodiments of the present disclosure provide a lithium secondary battery including a wound electrode group in which negative electrode swelling during charging is suppressed.

A lithium secondary battery according to an aspect of the present disclosure includes an electrode group formed by winding a positive electrode including a positive electrode active material containing lithium, a negative electrode including a negative electrode current collector and a plurality of projections arranged on the negative electrode current collector, and a separator interposed between the positive electrode and the negative electrode, and a nonaqueous electrolyte having lithium ion conductivity. The negative electrode precipitates lithium metal during charging, and the lithium metal dissolves in the nonaqueous electrolyte during discharging. The negative electrode current collector includes a 1 st surface and a 2 nd surface, the 1 st surface faces a winding outer side direction of the electrode group, and the 2 nd surface faces a winding inner side direction of the electrode group. At least one of the 1 st surface and the 2 nd surface includes a 1 st region and a 2 nd region, and the 2 nd region is closer to the winding innermost circumference of the electrode group than the 1 st region. The plurality of convex portions include a plurality of outer circumferential convex portions disposed on the 1 st region and a plurality of inner circumferential convex portions disposed on the 2 nd region. On at least one of the 1 st surface and the 2 nd surface, a ratio of a 1 st area occupied by a total of areas of the plurality of outer peripheral-side protrusions projected onto the 1 st region in an area of the 1 st region is larger than a ratio of a 2 nd area occupied by a total of areas of the plurality of inner peripheral-side protrusions projected onto the 2 nd region in an area of the 2 nd region.

According to the embodiments of the present disclosure, it is possible to suppress negative electrode swelling associated with charging in a lithium secondary battery using a coiled electrode group.

Drawings

Fig. 1 is a plan view schematically showing a negative electrode for a lithium secondary battery according to an embodiment of the present disclosure.

Fig. 2A is a sectional view of a cut surface along line IIA-IIA in fig. 1, as viewed in the direction of the arrow.

Fig. 2B is a sectional view of a cut surface along line IIB-IIB of fig. 1 as viewed in the direction of the arrows.

Fig. 3 is a plan view schematically showing another negative electrode for a lithium secondary battery according to an embodiment of the present disclosure.

Fig. 4A is a sectional view of a cut surface of line IVA-IVA of fig. 3 as viewed in the direction of the arrow.

fig. 4B is a sectional view of a cut surface of the IVB-IVB line of fig. 3 as viewed in the direction of the arrow.

Fig. 5 is a longitudinal sectional view schematically showing a lithium secondary battery according to another embodiment of the present disclosure.

Fig. 6 is an enlarged sectional view schematically showing a VI region of fig. 5.

Fig. 7 is an enlarged sectional view schematically showing a VII region of fig. 5.

Description of the reference numerals

10 lithium secondary battery

11 positive electrode

12 negative electrode

13 baffle

14 electrode group

15 casing body

16 sealing body

17. 18 insulating board

19 positive electrode lead

20 cathode lead

21 step part

22 filter

23 lower valve body

24 insulating member

25 upper valve body

26 cap

27 sealing gasket

30 positive electrode current collector

31 positive electrode mixture layer

32. 132 negative electrode collector

132a, 132c 1 st strip region

132b 2 nd band region

33a 1 st projection

33b 2 nd projection

133A outer peripheral side projection

133B inner peripheral side projection

134 negative electrode

35 space

S1 surface No. 1

s2 surface 2

1 st length direction of LD1

LD2 length 2

LD3 length No. 3

LD4 length 4

WD1 Width 1 st direction

CL center line

IW inner peripheral side winding part

OW outer circumference side winding part

Detailed Description

(insight underlying the present disclosure)

embodiments of the present disclosure relate to a lithium secondary battery including a wound electrode group and a lithium metal as a negative electrode active material. More specifically, embodiments of the present disclosure relate to improvements in negative electrode collectors in wound electrode groups. Further, the lithium secondary battery is sometimes referred to as a lithium metal secondary battery. In a lithium secondary battery, lithium metal is precipitated in a dendritic form in a negative electrode during charging. Further, the specific surface area of the negative electrode increases with the formation of dendrites, and side reactions increase. Therefore, the discharge capacity and cycle characteristics are degraded. On the other hand, patent document 1 teaches that the ten-point average roughness Rz of the lithium metal deposition surface of the negative electrode is 10 μm or less to suppress the generation of dendrites and to obtain high charge/discharge efficiency.

in addition, since lithium metal is deposited on the negative electrode during charging, the lithium secondary battery is particularly likely to have a large amount of swelling of the negative electrode. Here, "expansion of the negative electrode" means that the total volume of the negative electrode volume and the deposited lithium metal volume increases. In particular, when lithium metal is precipitated in a dendritic form, the amount of expansion further increases. In the case of a cylindrical lithium battery including a wound electrode group, stress is generated due to excessive expansion of the negative electrode. In order to absorb the volume change of the negative electrode during charge and discharge, patent document 2 proposes to use a porous negative electrode current collector of copper or nickel having a porosity of 50 to 99% and a pore size of 5 to 500 μm, for example. In the negative electrode current collector of patent document 3, a groove is provided to secure a space for forming the dendritic lithium metal.

The stress associated with the deposition of lithium metal is released from the main surface, side surface, and the like of the negative electrode in the coin-type electrode group, and is released from the end portion, and the like of the negative electrode in the laminated electrode group. On the other hand, in the coiled electrode group, as lithium metal is deposited, stress due to tensile strain is generated in the circumferential direction of the cross section perpendicular to the coiling axis of the electrode group. In the wound electrode group, stress caused by deposition of lithium metal is hard to be released from the inner peripheral side and the negative electrode end portion of the electrode group, and therefore, the stress is directed toward the outer peripheral side of the electrode group. In addition, in the case where the wound end of the wound electrode group is fixed with a tape and surrounded by the battery case, stress is applied from the outside. In this way, the wound electrode group is less likely to disperse stress than other electrode groups such as coin-type or laminated-type ones, and therefore, the negative electrode is likely to be excessively or unevenly expanded.

The negative electrode collector of the wound electrode group has a 1 st surface facing the outside of the electrode group in the wound state and a 2 nd surface facing the inside of the electrode group in the wound state. That is, the 1 st surface faces a direction away from the winding axis of the electrode group with respect to the negative electrode collector, and the 2 nd surface faces a direction close to the winding axis of the electrode group with respect to the negative electrode collector. Hereinafter, in the negative electrode collector, the side of the electrode group facing the outside in the winding direction may be referred to as the outside, and the side of the electrode group facing the inside in the winding direction may be referred to as the inside. In addition, at least one of the outer and inner surfaces of the negative electrode current collector includes a 1 st region and a 2 nd region, and the 2 nd region is closer to the innermost wound periphery of the electrode group than the 1 st region, and in this case, in the electrode group, a portion including the 1 st region is referred to as an outer peripheral wound portion, and a portion including the 2 nd region is referred to as an inner peripheral wound portion.

Due to the stress toward the outer circumferential side and the stress from the outside of the electrode group as described above, the pressure applied to the surface of the negative electrode collector is larger in the outer circumferential wound part than in the inner circumferential wound part of the electrode group. Hereinafter, the pressure applied to the surface of the negative electrode current collector may be referred to as a surface pressure. As described above, in the wound electrode group, a large stress and a large surface pressure are applied to the wound portion on the outer peripheral side of the electrode group. Therefore, the lithium metal deposited on the negative electrode surface of the outer peripheral winding portion is pressed more strongly than the lithium metal deposited on the negative electrode surface of the inner peripheral winding portion. By this large pressure, the lithium metal deposited on the surface of the negative electrode is compressed in the wound portion on the outer peripheral side of the electrode group. On the other hand, in the inner circumferential wound portion of the electrode group, lithium metal deposited on the surface of the negative electrode is less likely to be compressed, and the thickness of the lithium metal is greater than that in the outer circumferential wound portion.

due to the difference in stress and surface pressure between the inner and outer wound portions of the electrode group, lithium metal deposition on the surface of the negative electrode tends to become uneven, and the negative electrode may partially swell excessively. In addition, charge and discharge efficiency may be reduced.

in the negative electrode current collector of patent document 2 or patent document 3, lithium metal is deposited in the pores or in the spaces in the grooves by charging. Patent documents 2 and 3 basically assume a laminated or coin-type electrode group. Therefore, the lithium metal in the pores or in the grooves is less likely to be subjected to the pressure generated in the electrode group. Even if the negative electrode collector of patent document 2 or patent document 3 is used for a wound electrode group, uneven deformation is likely to occur due to winding. As a result, stress applied to the precipitated lithium metal becomes uneven, and therefore expansion of the negative electrode at the time of charging easily becomes uneven. Therefore, it is difficult to sufficiently suppress the expansion of the negative electrode during charging. In addition, lithium metal in the pores or in the grooves is less likely to be stressed and is therefore likely to peel off from the wall surfaces of the current collector. The peeled lithium metal is not dissolved at the time of discharge, and thus the charge and discharge efficiency is lowered.

the inventors have intensively studied to solve the above problems, and as a result, have conceived a lithium secondary battery according to the present disclosure. A lithium secondary battery according to an aspect of the present disclosure includes an electrode group in which a positive electrode including a positive electrode active material containing lithium, a negative electrode including a negative electrode current collector and a plurality of projections arranged on the negative electrode current collector, and a separator interposed between the positive electrode and the negative electrode are wound, and a nonaqueous electrolyte having lithium ion conductivity. The negative electrode precipitates lithium metal during charging, and the lithium metal dissolves in the nonaqueous electrolyte during discharging. The plurality of projections include a plurality of outer circumferential projections located at the outer circumferential winding portion of the electrode group and a plurality of inner circumferential projections located at the inner circumferential winding portion of the electrode group. The ratio of the 1 st area occupied by the plurality of outer peripheral side protrusions in the outer peripheral side winding portion is larger than the ratio of the 2 nd area occupied by the plurality of inner peripheral side protrusions in the inner peripheral side winding portion.

In the present disclosure, the "1 st area ratio of the plurality of outer circumferential protrusions to the outer circumferential wound portion" refers to a ratio of the total area of the plurality of outer circumferential protrusions projected onto the 1 st region on the 1 st surface or the 2 nd surface of the negative electrode current collector to the 1 st region. The "2 nd area ratio of the plurality of inner peripheral protrusions to the inner peripheral wound portion" means a ratio of the total area of the plurality of inner peripheral protrusions projected onto the 2 nd region on the 1 st surface or the 2 nd surface of the negative electrode current collector to the area of the 2 nd region.

According to the aspect of the present disclosure, a negative electrode including a negative electrode current collector and a plurality of protrusions arranged on the negative electrode current collector is used in the wound electrode group. Since the plurality of projections can secure a space for lithium metal to precipitate in the negative electrode, the change in the apparent volume of the negative electrode due to lithium metal precipitation can be reduced. Here, the apparent volume of the negative electrode means the total volume of the negative electrode volume, the volume of the deposited lithium metal, and the volume of the space secured by the plurality of projections.

In addition, the ratio of the 1 st area occupied by the plurality of outer-peripheral-side protrusions in the outer-peripheral-side wound portion is larger than the ratio of the 2 nd area occupied by the plurality of inner-peripheral-side protrusions in the inner-peripheral-side wound portion. In other words, by making the ratio of the 2 nd area occupied by the plurality of inner peripheral side protrusions in the inner peripheral side wound portion smaller than the ratio of the 1 st area occupied by the plurality of outer peripheral side protrusions in the outer peripheral side wound portion, even if the thickness of lithium metal deposited in the inner peripheral side wound portion due to charging becomes large, this increase in volume can be effectively absorbed in the space between the inner peripheral side protrusions. Therefore, an increase in the apparent volume of the anode can be further suppressed. In this way, in each of the outer-peripheral wound portion and the inner-peripheral wound portion of the electrode group, a volume space suitable for the thickness of lithium metal deposited by charging can be secured in advance by the plurality of convex portions. Therefore, it is not necessary to estimate the expansion of the negative electrode, and thus it is not necessary to reduce the volume of the negative electrode and/or the positive electrode at an early stage. As a result, a high discharge capacity is easily ensured. Even if lithium metal is produced in a dendrite form, it can be accommodated in a space formed in the negative electrode through the plurality of projections.

Since the electrode group is of a wound type, a certain degree of pressure is applied to the lithium metal deposited in the space of the negative electrode. Therefore, unlike the cases of patent documents 2 and 3, the lithium metal deposited in the space is difficult to be peeled off. Therefore, the charge-discharge efficiency can be suppressed from decreasing. Further, since a suitable pressure is applied to the deposited lithium metal, the lithium metal can be prevented from being deposited in a dendritic form without smoothing the negative electrode as in patent document 1.

For example, on each of the outer surface and the inner surface (i.e., the 1 st surface and the 2 nd surface) of the negative electrode current collector, a region facing the positive electrode active material is divided into 2 parts by a center line in the longitudinal direction of the region. For example, a portion farther from the center line toward the innermost wound portion of the electrode group than the center line is defined as a 1 st region located in the outer-peripheral wound portion of the electrode group, and a portion closer to the innermost wound portion of the electrode group than the center line is defined as a 2 nd region located in the inner-peripheral wound portion of the electrode group.

The negative electrode current collector generally has a 1 st surface and a 2 nd surface opposite to the 1 st surface. The 1 st surface and the 2 nd surface mean 2 main surfaces of the sheet-like negative electrode collector. The outer peripheral side projection and the inner peripheral side projection are disposed on at least one of the 1 st surface side and the 2 nd surface side. The 1 st surface may be an outer side surface of the anode current collector. In addition, the 2 nd surface may be an inner side surface of the negative electrode collector. The outer circumferential protrusion and the inner circumferential protrusion may include a plurality of 1 st protrusions disposed on the 1 st surface side and a plurality of 2 nd protrusions disposed on the 2 nd surface side, respectively, on the 1 st surface and the 2 nd surface of the negative electrode current collector and in the vicinity thereof, from the viewpoint of ensuring a space for deposition of lithium metal during charging. The 1 st projection projects from the 1 st surface side of the negative electrode current collector toward the separator surface opposite to the 1 st surface. The 2 nd projection projects from the 2 nd surface side of the negative electrode current collector toward the separator surface opposite to the 2 nd surface.

In this case, the plurality of outer circumferential protrusions are a plurality of protrusions disposed on the outer circumferential 1 st surface and the outer circumferential 2 nd surface (i.e., the 1 st region of the 1 st surface and the 1 st region of the 2 nd surface) of the outer circumferential wound portion. As the 1 st area ratio, an average value of a ratio of an area occupied by a total of areas of the plurality of convex portions arranged on the outer circumferential side 1 st surface projected onto the outer circumferential side 1 st surface (an example of the 3 rd area ratio) to an area occupied by the outer circumferential side 1 st surface and a ratio of an area occupied by a total of areas of the plurality of convex portions arranged on the outer circumferential side 2 nd surface projected onto the outer circumferential side 2 nd surface (an example of the 4 th area ratio) to an area occupied by the outer circumferential side 2 nd surface can be used. The inner circumferential protrusions are a plurality of protrusions arranged on the inner circumferential 1 st surface and the inner circumferential 2 nd surface (i.e., the 2 nd region of the 1 st surface and the 2 nd region of the 2 nd surface) of the inner circumferential winding part. As the 2 nd area ratio, an average value of the area ratio (an example of the 5 th area ratio) of the total area of the plurality of convex portions arranged on the inner peripheral side 1 st surface projected onto the inner peripheral side 1 st surface and the area ratio (an example of the 6 th area ratio) of the total area of the plurality of convex portions arranged on the inner peripheral side 2 nd surface projected onto the inner peripheral side 2 nd surface, which are the total area of the inner peripheral side 2 nd surface, can be used.

Hereinafter, the total of the areas of the projected shapes (i.e., projected areas) obtained by projecting the plurality of convex portions on the surface of the negative electrode current collector on which the plurality of convex portions are arranged may be referred to as the areas of the plurality of convex portions. The projection shape of the plurality of projections on the surface of the negative electrode current collector is a shape formed by projecting the plurality of projections on the surface of the negative electrode current collector on the side where the plurality of projections are formed, in the thickness direction of the negative electrode current collector. Some layers may be formed between the negative electrode current collector and the plurality of projections, but the projection shape or the projection area may be determined by projecting the plurality of projections on the surface of the negative electrode current collector. The areas of the 1 st region and the 2 nd region and the areas of the plurality of projections can be determined from the negative electrode in which the 1 st surface and the 2 nd surface are spread in a planar state. The areas of the negative electrode before the wound electrode group is produced can be determined. As described later, when the convex portions are linear in shape and the plurality of convex portions are arranged substantially in parallel, the area ratio of the plurality of convex portions can be estimated from the distance between 2 adjacent convex portions and the width of the convex portions.

however, in the calculation of the 1 st area ratio and the 2 nd area ratio, the surface region of the negative electrode current collector that does not face the positive electrode active material may not be considered. That is, the 1 st region and the 2 nd region do not include a surface region of the negative electrode current collector that does not oppose the positive electrode active material. Therefore, the areas of the 1 st region and the 2 nd region do not include the area of the surface region of the negative electrode current collector that does not face the positive electrode active material. In the wound electrode group, for example, at the outermost winding periphery, the outer region of the negative electrode current collector may not face the positive electrode active material. In this case, since it is difficult to deposit lithium metal in the outer region not facing the positive electrode active material, it is not considered in calculating the 1 st area ratio. In addition, the inner region of the negative electrode current collector may not face the positive electrode active material at the innermost wound periphery. In this case, since it is difficult to deposit lithium metal in the region inside the positive electrode active material, it is not considered in calculating the 2 nd area ratio.

In addition, when the width of the negative electrode current collector in the direction parallel to the winding axis is larger than that of the positive electrode current collector, the band-shaped negative electrode current collector region extending in the longitudinal direction perpendicular to the winding axis does not face the positive electrode active material at the upper end portion and/or the lower end portion of the electrode group (i.e., at one end portion and/or the other end portion in the direction parallel to the winding axis). In this case, the band-shaped regions are not considered when calculating the area ratios. The longitudinal direction of the region of the negative electrode current collector facing the positive electrode active material is parallel to the longitudinal direction of the negative electrode current collector. In each of the 1 st surface and the 2 nd surface of the negative electrode current collector, a direction perpendicular to a winding axis of the electrode group is defined as a longitudinal direction of the negative electrode current collector, and a direction parallel to the winding axis is defined as a width direction of the negative electrode current collector. Hereinafter, the longitudinal direction of the negative electrode current collector is referred to as the 1 st longitudinal direction, and the width direction is referred to as the 1 st width direction. More specifically, at 2 ends of the negative electrode current collector in the longitudinal direction, a line connecting the respective midpoints in the width direction is defined as a 1 st center line, and the direction of the 1 st center line is defined as a 1 st longitudinal direction. The direction perpendicular to the 1 st longitudinal direction is defined as the 1 st width direction.

The 1 st area proportion is larger than the 2 nd area proportion, and the difference between the 1 st area proportion and the 2 nd area proportion can be adjusted according to the energy density, the size and the like of the battery. The difference between the 1 st area ratio and the 2 nd area ratio may be 3% or more, or may be 5% or more. When the difference is within such a range, even if the thickness of lithium metal deposited on the inner peripheral side of the electrode group is increased, the volume change of the negative electrode due to the deposition is easily absorbed. The difference between the 1 st area ratio and the 2 nd area ratio is, for example, 50% or less, and may be 20% or less. When the difference is within such a range, it is easy to secure a volume space suitable for the amount of lithium deposited, and therefore it is easy to secure a higher discharge capacity while maintaining the negative electrode expansion suppressing effect. These lower and upper limits may be arbitrarily combined. The difference between the 1 st area ratio and the 2 nd area ratio is a value obtained by subtracting the 2 nd area ratio from the 1 st area ratio.

The 1 st area ratio and the 2 nd area ratio may be 0.2% or more, 1% or more, or 3% or more. When the ratio is within such a range, the separator is easily supported by the protrusions, and the distance between the negative electrode current collector and the separator is easily made constant. Therefore, the effect of suppressing the expansion of the negative electrode can be further improved. The effect of uniformly performing charge and discharge reactions can be improved. The 1 st area ratio and the 2 nd area ratio may be 70% or less, or may be 50% or less. When the above ratio is in such a range, a space is easily secured between the surface of the negative electrode current collector and the separator, and therefore, expansion of the negative electrode due to deposition of lithium metal can be suppressed while securing a high capacity. These lower limit values and upper limit values may be arbitrarily combined.

Hereinafter, the structure of the lithium secondary battery of the above-described embodiment will be described in more detail with reference to the drawings as appropriate. First, the structure of the negative electrode will be described.

(cathode)

The negative electrode includes a negative electrode current collector and a plurality of projections arranged on the negative electrode current collector. The negative electrode current collector generally has a 1 st surface and a 2 nd surface opposite to the 1 st surface. The 1 st surface and the 2 nd surface are respectively the outer surface and the inner surface of the negative electrode collector in the coiled electrode group. In the negative electrode of the lithium secondary battery, lithium metal is deposited by charging. More specifically, lithium ions contained in the nonaqueous electrolyte receive electrons in the negative electrode by charging to form lithium metal, and are deposited on the surface of the negative electrode. The precipitated lithium metal is dissolved as lithium ions in the nonaqueous electrolyte by discharge. The lithium ions contained in the nonaqueous electrolyte may be derived from a lithium salt added to the nonaqueous electrolyte, may be supplied from the positive electrode active material by charging, or may be both of them.

The negative electrode has a plurality of projections, and thus a space for accommodating lithium metal deposited on the surface of the negative electrode can be ensured. Therefore, the expansion of the negative electrode due to the deposition of lithium metal can be reduced by this space. In addition, the ratio of the 2 nd area occupied by the plurality of inner peripheral side protrusions in the inner peripheral side wound portion is smaller than the ratio of the 1 st area occupied by the plurality of outer peripheral side protrusions in the outer peripheral side wound portion. This allows the volume increase to be effectively absorbed even if the thickness of the lithium metal deposited in the inner peripheral winding portion due to charging becomes large, as described above. Therefore, the increase in the apparent volume of the anode can be more suppressed.

The height of the outer circumferential projection or the inner circumferential projection (hereinafter, may be simply referred to as a projection) may be determined according to the position where the projection is formed and the amount of lithium metal deposited. The average height of the plurality of outer circumferential protrusions may be 15 μm or more, 20 μm or more, or 30 μm or more. The average height of the plurality of outer circumferential protrusions may be 40 μm or more, or 50 μm or more. The average height of the plurality of inner peripheral protrusions may be 15 μm or more, 20 μm or more, or 30 μm or more. The average height of the plurality of inner peripheral protrusions may be 40 μm or more, or 50 μm or more. When the average height is within these ranges, the effect of absorbing a large stress applied to the outer peripheral wound portion and the effect of absorbing a change in the volume of the negative electrode due to deposition of lithium metal can be further improved. The effect of suppressing damage to the electrode can be improved.

The average height of the plurality of outer peripheral protrusions may be 120 μm or less, or may be 110 μm or less. The average height of the plurality of outer circumferential protrusions may be 100 μm or less, or 90 μm or less. The average height of the plurality of inner peripheral protrusions may be 120 μm or less, or may be 110 μm or less. The average height of the plurality of inner peripheral protrusions may be 100 μm or less, or 90 μm or less. When the average height is within these ranges, the lithium metal deposited on the surface of the negative electrode is moderately pressed by the separator, and the conductivity between the lithium metal and the negative electrode current collector is improved, so that the charge/discharge efficiency can be improved. In addition, excessive pressing of the separator against the convex portion can be suppressed, and the electrode can be protected. These lower limit values and upper limit values may be arbitrarily combined.

In terms of becoming easy to manufacture, the difference between the 1 st average height of the outer periphery-side protrusions and the 2 nd average height of the inner periphery-side protrusions may be less than 3% of the 2 nd average height. That is, the average heights of the outer periphery-side protrusions and the inner periphery-side protrusions may be substantially equal. From the same viewpoint, the difference between the average height of the plurality of 1 st projections and the average height of the plurality of 2 nd projections may be less than 3% of the average height of the 2 nd projections. That is, the average heights of the 1 st and 2 nd convex portions may be substantially equal.

The average height of the plurality of projections can be obtained by, for example, arbitrarily selecting 3 projections from a cross-sectional photograph of the negative electrode in the thickness direction, calculating the distance from the end portion of each of the selected projections on the negative electrode current collector side to the end portion on the side opposite to the negative electrode current collector as the height of the projection, and averaging the heights of the projections, the average height 1 can be obtained by cutting a certain area (for example, 5cm ² or the like) or a plurality of arbitrary areas in the 1 st area of the negative electrode current collector, and averaging the heights of a plurality of arbitrary projections existing in the certain area or the plurality of areas.

When the end portion of each convex portion on the negative electrode current collector side and/or the end portion on the opposite side are/is not flat in the measurement of the average height of the plurality of convex portions, the maximum value of the length in the direction parallel to the thickness direction of the negative electrode between the both end portions of each convex portion is defined as the height of each convex portion. In the measurement of the average height of the plurality of projections, when the plurality of projections are formed on both the 1 st surface and the 2 nd surface of the negative electrode current collector, the 3 projections are arbitrarily selected from the plurality of projections formed on the 1 st surface and the 2 nd surface. Each average height can be determined based on a cross-sectional photograph of the electrode group in which the cross section in the thickness direction of the negative electrode can be observed.

In the case where the 1 st surface and/or the 2 nd surface are rough, the surface roughness Rz of the 1 st surface and/or the 2 nd surface may be 1 μm or less. In addition, the height of each of the plurality of projections on the 1 st surface and/or the 2 nd surface may exceed 1 μm. When the 1 st surface and/or the 2 nd surface are rough and the plurality of projections and the negative electrode current collector are integrally formed of the same material, the height of each of the plurality of projections on the 1 st surface and/or the 2 nd surface is measured with reference to the bottom of the roughness. In this case, the winding of the electrode group was unwound, and the 1 st surface and the 2 nd surface were measured in a state of being extended in a planar shape.

At least a portion of the plurality of protrusions may contact the separator. For example, the plurality of 1 st protrusions may contact a surface of the separator opposite to the 1 st surface. In addition, the plurality of 2 nd protrusions may contact a surface of the separator opposite to the 2 nd surface. By the presence of the plurality of projections, a space is ensured between the negative electrode and the separator. In this case, lithium metal is deposited by charging in the space formed between the negative electrode current collector and the separator. The convex portion is in contact with the separator, whereby the influence of the relationship between the 1 st area ratio and the 2 nd area ratio is remarkably exhibited, and the effect of suppressing the expansion of the negative electrode can be improved. In addition, since precipitation of lithium metal is suppressed at a portion where each convex portion contacts the separator, such as the tip of the convex portion, local expansion of the negative electrode can be suppressed.

From the viewpoint of further improving the effect of suppressing swelling of the negative electrode, 80% or more of the total area of the projections projected onto the surface of the negative electrode current collector may be in contact with the separator, for each of the 1 st surface and the 2 nd surface of the negative electrode current collector. From the same viewpoint, all of the plurality of projections formed on the 1 st surface and the 2 nd surface may be in contact with the separator. The shape of projection of each projection onto the surface of the negative electrode current collector is not particularly limited. The shape of projection of each convex portion on the surface of the negative electrode current collector may be linear or the like, from the viewpoint of easy support of the separator and easy supply of the nonaqueous electrolyte to the vicinity of the electrode. Linear also includes bar-shaped. The stripe shape is a shape having a relatively short length among linear shapes.

From the viewpoint of ensuring a suitable volume space for accommodating the precipitated lithium metal, 2 adjacent projections among the plurality of projections may be spaced apart from each other to some extent in a direction parallel to the surface of the negative electrode. For example, the minimum value of the separation distance between the adjacent 2 projections may be larger than the maximum width of the adjacent 2 projections. The minimum value of the distance between the adjacent 2 projections means the minimum value of the distances between the outer edges of the projected shapes of the adjacent 2 projections when the adjacent 2 projections are arbitrarily selected from the plurality of projections and the surface of the negative electrode current collector on which the projections are formed is projected in the thickness direction of the negative electrode current collector. The maximum width of the adjacent 2 convex portions is the maximum width (length in a direction perpendicular to the longitudinal direction of the convex portions) of the shape of the projection of the adjacent 2 convex portions onto the surface of the negative electrode current collector on the side where the convex portions are formed. When the projected shape is a circle, the maximum width is the largest of the diameters of the projected shapes of the 2 projections.

The shape of the projection of the plurality of projections on the surface of the negative electrode current collector may be linear, and the longitudinal directions of the plurality of projections may be arranged substantially in parallel, for each of the 1 st surface and the 2 nd surface of the negative electrode current collector. In this case, the minimum value of the distance between the adjacent 2 projections may be larger than the maximum width of the adjacent 2 projections. In this case, the partition plate is easily supported by the plurality of projections, and an appropriate volume space is easily secured between the adjacent 2 projections. Hereinafter, the longitudinal direction of each projection having a linear projection shape is referred to as the 2 nd longitudinal direction. More specifically, at 2 ends in the longitudinal direction of the projection having the linear shape, a line connecting the centers in the width direction is defined as a 2 nd center line, and the direction of the 2 nd center line is defined as a 2 nd longitudinal direction.

the state where the 2 nd longitudinal directions of the plurality of projections are arranged substantially in parallel means a case where the 2 nd longitudinal directions of the projections are parallel to each other or an angle on an acute angle side formed by the 2 nd longitudinal directions of the projections is 30 ° or less. The projections are projected in the thickness direction of the negative electrode current collector with respect to the surface of the negative electrode current collector on which the projections are formed, and the longitudinal direction of the projected shape formed at this time is the 2 nd longitudinal direction of each projection.

The minimum value of the distance is not particularly limited as long as it is larger than the minimum width of the convex portion, and may be 150% or more, 400% or more, or 500% or more. The minimum value of the separation distance may be 3000% or less of the minimum width of the convex portion.

When a plurality of linear projections are arranged substantially in parallel, the distance between the projections can be determined from the distance between the centers of 2 adjacent projections and the width of each projection. The center of the convex portion in this case refers to the 2 nd center line of the convex portion. The distance between the 2 nd center lines of the adjacent 2 convex portions may be defined as an inter-center distance.

The frame-like continuous projections surrounding the entire surface or a partial region of the surface may not be formed on the 1 st surface and/or the 2 nd surface so that the nonaqueous electrolyte can easily penetrate into the electrode group. A frame-like continuous projection may not be formed on the peripheral edge of the No. 1 surface and/or No. 2 surface so as to surround most of the surfaces. In the case where the frame-like continuous projection is not formed, the nonaqueous electrolyte easily penetrates into the inside of the separator at the portion where the projection is not formed, and the separator easily contacts the precipitated lithium metal. Therefore, the effect of suppressing the uneven precipitation of lithium metal is improved, and therefore, the generation of dendrites can be suppressed, and the decrease in charge-discharge efficiency can be suppressed.

A stripe-shaped region, in which no convex portion is formed in at least one of the 1 st length direction and the 1 st width direction, may be provided on the 1 st surface and/or the 2 nd surface. Each surface may have at least 1 band-shaped region, or may have 2 or more. In this case, the nonaqueous electrolyte easily penetrates into the electrode group through the band-shaped region. Since the nonaqueous electrolyte can be easily held between the positive electrode and the negative electrode, precipitation and dissolution of lithium metal proceed smoothly, and a decrease in capacity and a decrease in charge-discharge efficiency can be suppressed. In addition, the separator easily contacts the precipitated lithium metal in the band-shaped region. This improves the effect of suppressing the uneven precipitation of lithium metal, and therefore, the generation of dendrites can be suppressed.

The stripe region may be formed along the 1 st length direction or the 1 st width direction. The negative electrode current collector may have both a belt-shaped region (1 st belt-shaped region) along one of the 1 st longitudinal direction and the 1 st width direction and a belt-shaped region (2 nd belt-shaped region) along the other direction on the 1 st surface and/or the 2 nd surface. The 1 st strip-shaped region may be provided along the 1 st longitudinal direction from the viewpoint of easily penetrating the nonaqueous electrolyte to the more inner peripheral side of the wound electrode group and easily ensuring high capacity and high charge/discharge efficiency. The 1 st band-shaped region is easily formed if a plurality of linear projections projected on each surface of the negative electrode current collector are provided. In particular, if the convex portions are provided such that the 2 nd longitudinal direction of the plurality of convex portions is substantially parallel to the 1 st longitudinal direction, the 1 st band-shaped region is easily formed between the 2 convex portions adjacent in the 1 st width direction.

The 1 st band-shaped region provided along the 1 st longitudinal direction means that a band-shaped region in which no convex portion is formed in a direction substantially parallel to the 1 st longitudinal direction exists on the negative electrode current collector. The 2 nd band-shaped region provided along the 1 st width direction means that a band-shaped region in which no convex portion is formed in a direction substantially parallel to the 1 st width direction exists on the negative electrode current collector.

Hereinafter, the longitudinal direction of the 1 st band-like region is referred to as the 3 rd longitudinal direction. More specifically, at 2 ends in the longitudinal direction of the 1 st band-like region, a line connecting the respective widthwise midpoints is defined as a 3 rd center line, and the direction of the 3 rd center line is defined as a 3 rd longitudinal direction. The width-directional midpoint of each end portion may be determined, for example, for a maximum rectangular band-shaped region virtually formed between the end portions of the adjacent convex portions. In this case, the direction substantially parallel to the 1 st longitudinal direction means a case where the 3 rd longitudinal direction is parallel to the 1 st longitudinal direction and a case where the angle on the acute angle side formed by the 3 rd longitudinal direction and the 1 st longitudinal direction is 30 ° or less.

The longitudinal direction of the 2 nd band-like region is referred to as the 4 th longitudinal direction. More specifically, at 2 ends in the longitudinal direction of the 2 nd band-like region, a line connecting the respective widthwise midpoints is defined as a 4 th centerline, and the direction of the 4 th centerline is defined as a 4 th longitudinal direction. The above-mentioned direction substantially parallel to the 1 st width direction means a case where the 4 th longitudinal direction is parallel to the 1 st width direction and a case where the angle on the acute angle side formed by the 4 th longitudinal direction and the 1 st width direction is 30 ° or less.

on each of the 1 st surface and the 2 nd surface of the negative electrode current collector, for example, the innermost peripheral wound part and/or the outermost peripheral wound part may be provided with another region where no convex part is disposed, as necessary. That is, the negative electrode current collector may be provided with a region in which the 1 st projection and/or the 2 nd projection are not formed in a portion closest to the winding axis of the electrode group and/or a portion farthest from the winding axis of the electrode group. The negative electrode lead for electrical connection to the negative electrode may be connected to the 1 st surface or the 2 nd surface of the negative electrode current collector by, for example, welding in the region where the projection is not formed.

Fig. 1 is a plan view schematically showing a negative electrode for a lithium secondary battery according to an embodiment. In fig. 1, one surface of the negative electrode is shown. Fig. 2A is a sectional view of a cut surface along line IIA-IIA in fig. 1, as viewed in the direction of the arrow. Fig. 2B is a sectional view of a cut surface along the line IIB-IIB in fig. 1 as viewed in the direction of the arrows.

Negative electrode 134 includes: a negative electrode current collector 132 made of metal foil or the like, and a plurality of outer circumferential protrusions 133A and inner circumferential protrusions 133B protruding from the surface of the negative electrode current collector 132. The projection shape of each projection on the surface of the negative electrode current collector 132 in the thickness direction of the negative electrode current collector 132 is the same as the planar shape of the projection shown in fig. 1, and is linear. When the surface of the negative electrode current collector 132 shown in fig. 1 is the 1 st surface, the convex portion is the 1 st convex portion, and when the surface is the 2 nd surface, the convex portion is the 2 nd convex portion.

When the surface is viewed from the normal direction, the negative electrode current collector 132 has a rectangular shape in which the length in the direction perpendicular to the winding axis when the electrode group is formed by winding is longer than the length in the direction parallel to the winding axis. In fig. 1, the 1 st longitudinal direction LD1 indicates a direction perpendicular to the winding axis, and the 1 st width direction WD1 indicates a direction parallel to the winding axis, on the surface of the negative electrode current collector 132.

In fig. 1, the plurality of projections are provided on the surface of the negative electrode current collector 132 such that the 2 nd longitudinal direction LD2 of each projection is parallel to the 1 st longitudinal direction LD 1. The negative electrode current collector 132 is divided into a region located at the inner circumferential side wound part IW and a region located at the outer circumferential side wound part OW of the electrode group, with a center line CL that divides the length of the region facing the positive electrode active material of the negative electrode current collector 132 into two in the 1 st longitudinal direction LD 1.

As shown in fig. 2A and 2B, the inner peripheral side wound portion IW is provided with a plurality of projections having a width narrower than that of the outer peripheral side wound portion OW. Therefore, the area ratio of the plurality of inner circumferential protrusions 133B of the inner circumferential wound portion IW becomes smaller than the area ratio of the plurality of outer circumferential protrusions 133A of the outer circumferential wound portion OW. Thus, even if the thickness of the lithium metal deposited on the inner circumferential side of the electrode group at the wound portion IW becomes large, the volume change caused by the increase in the thickness can be absorbed. Thus, an increase in the apparent volume of the anode can be suppressed.

The 1 st band-shaped region 132a is provided on the surface of the outer peripheral side winding portion OW, and the outer peripheral side convex portion 133A is not formed in the 1 st band-shaped region 132a along the 1 st longitudinal direction LD 1. The 3 rd longitudinal direction LD3 of the 1 st stripe region 132a is parallel to the 1 st longitudinal direction LD 1. In addition, a 2 nd band-shaped region 132b in which no convex portion is formed is provided on each of the 1 st surface and the 2 nd surface of the negative electrode current collector 132 at the center line CL and the vicinity thereof. The 4 th longitudinal direction LD4 of the 2 nd band-shaped region 132b is parallel to the 1 st widthwise direction WD 1. On the surface of the inner peripheral side wound portion IW, the other 1 st strip-shaped region 132c is provided in which the inner peripheral side protrusions 133B are not formed along the 3 rd longitudinal direction LD3 of the 1 st strip-shaped region 132 a.

The minimum value of the distance between the adjacent 2 outer circumferential protrusions 133A is greater than the maximum width of the adjacent 2 outer circumferential protrusions 133A, and the minimum value of the distance between the adjacent 2 inner circumferential protrusions 133B is greater than the maximum width of the adjacent 2 inner circumferential protrusions 133B.

When the negative electrode 134 is wound together with the positive electrode and the separator from the end on the inner peripheral winding part IW side to form a wound electrode group for use in a lithium secondary battery, a space is formed between the negative electrode current collector 132 and the separator between the adjacent 2 projections. Lithium metal precipitated by charging is contained in the space, and therefore expansion of negative electrode 134 is suppressed.

Fig. 3 is a plan view schematically showing another negative electrode for a lithium secondary battery according to an embodiment. One surface of the negative electrode is shown in fig. 3. Fig. 4A is a sectional view of a cut surface of line IVA-IVA of fig. 3 as viewed in the direction of the arrow. Fig. 4B is a sectional view of a cut surface of the IVB-IVB line of fig. 3 as viewed in the direction of the arrow.

As shown in fig. 4A and 4B, the widths (i.e., the lengths in the direction perpendicular to the 2 nd longitudinal direction LD 2) of the outer circumferential side protrusions 133A provided in the outer circumferential side wound portion OW and the inner circumferential side protrusions 133B provided in the inner circumferential side wound portion IW are the same. On the other hand, the number of inner peripheral side projections 133B is smaller than the number of outer peripheral side projections 133A. Therefore, the area ratio of the plurality of convex portions of the inner peripheral wound portion IW becomes smaller than the area ratio of the plurality of convex portions of the outer peripheral wound portion OW. Except for the above, the negative electrode of fig. 3 has the same configuration as the negative electrode of fig. 1.

For example, the projection shape, height, number, direction, width of the convex portions, and the distance between adjacent 2 convex portions may be changed in whole or in part without being limited to the case of fig. 1 and 3. These features may be the same or different in the inner peripheral side wound portion IW and the outer peripheral side wound portion OW. In addition, in the case where the projections are formed on both the 1 st surface and the 2 nd surface of the negative electrode collector 132, these features may be the same or different between the 1 st surface side and the 2 nd surface side of the negative electrode collector 132. In this case, the convex portions arranged on the 1 st surface side (i.e., the 1 st convex portions) and the convex portions arranged on the 2 nd surface side (i.e., the 2 nd convex portions) may be arranged in a staggered manner when viewed from the normal direction of the 1 st surface. That is, the convex portions may be arranged such that 1 of the 2 nd convex portions are arranged between 2 of the adjacent 1 st convex portions.

The negative electrode 134 includes a negative electrode current collector 132 that is a conductive sheet such as a metal foil, and a plurality of protrusions formed on each surface of the conductive sheet. In the wound electrode group, the outer surface and the inner surface of the negative electrode collector 132 are the 1 st surface and the 2 nd surface of the negative electrode collector 132, respectively.

The conductive sheet is a conductive material other than lithium metal and lithium alloy, for example. The conductive material may be a metal material such as a metal or an alloy, or may be a carbon material. The conductive material may be a material that does not react with lithium. Such a material includes a material that does not react with lithium metal and/or lithium ions, and more specifically, may be a material that does not form any of an alloy and an intermetallic compound with lithium. As the carbon material, graphite or the like in which the base surface is preferentially exposed can be used. The metal material is, for example, copper (Cu), nickel (Ni), iron (Fe), an alloy containing these metal elements, or the like. As the alloy, a copper alloy, stainless steel, or the like can be used. From the viewpoint of easily obtaining high strength, at least one selected from copper, copper alloys, and stainless steel can be used as the conductive material. The conductive material may be copper and/or a copper alloy from the viewpoint of easily ensuring high capacity and high charge-discharge efficiency by having high conductivity. The conductive sheet may contain one of these conductive materials, or may contain two or more of these conductive materials.

As the conductive sheet, a foil, a film, or the like can be used, and a sheet made of the above-described carbon material can also be used. The conductive sheet may be porous within a range not to impair the winding property. The conductive sheet may be a metal foil or a metal foil containing copper, from the viewpoint of easily ensuring high conductivity. Such metal foil may be a copper foil or a copper alloy foil. The copper content in the metal foil may be 50 mass% or more, or may be 80 mass% or more. The metal foil may be particularly a copper foil containing substantially only copper as a metal element.

In order to provide a plurality of projections on the negative electrode 134, each of the 1 st and 2 nd surfaces of the negative electrode collector 132 may be smooth. Thus, lithium metal is likely to be uniformly deposited on the 1 st surface and the 2 nd surface of the negative electrode current collector 132 during charging. The term "smooth" means that the maximum height roughness Rz of each of the 1 st surface and the 2 nd surface of the negative electrode current collector 132 is 20 μm or less. The maximum height roughness Rz of each of the 1 st surface and the 2 nd surface of the negative electrode current collector 132 may be 10 μm or less. The maximum height roughness Rz is based on JIS B0601: 2013.

In addition, from the viewpoint of easily ensuring a high volumetric energy density, negative electrode 134 may include only negative electrode current collector 132 and a plurality of projections in a fully discharged state of the lithium secondary battery. In addition, from the viewpoint of easily ensuring high charge and discharge efficiency, the negative electrode may include a negative electrode active material layer disposed on the surface of the negative electrode current collector in addition to the negative electrode current collector and the plurality of protrusions in the fully discharged state.

In the present disclosure, the fully discharged State of the lithium secondary battery is a State of Charge (SOC: State of Charge) in which the battery is discharged to 0.05C or less, assuming that the rated capacity of the battery is C. For example, a state of being discharged to a lower limit voltage at a constant current of 0.05C. The lower limit voltage is, for example, 2.5V.

Examples of the negative electrode active material contained in the negative electrode active material layer include metallic lithium, a lithium alloy, and a material capable of reversibly occluding and releasing lithium ions. As the negative electrode active material, a negative electrode active material used in a lithium ion battery can be used. Examples of the lithium alloy include a lithium-aluminum alloy and the like. Examples of the material that reversibly stores and releases lithium ions include carbon materials and alloy materials. Examples of the carbon material include at least one selected from a graphite material, soft carbon, hard carbon, and amorphous carbon. Examples of the alloy-based material include materials containing silicon and/or tin. Examples of the alloy-based material include at least one selected from the group consisting of a simple substance of silicon, a silicon alloy, a silicon compound, a simple substance of tin, a tin alloy, and a tin compound. Examples of the silicon compound and the tin compound include an oxide and/or a nitride, respectively.

The negative electrode active material layer can be formed by depositing a negative electrode active material on the surface of a negative electrode current collector by a vapor phase method such as electrodeposition or vapor deposition. The negative electrode mixture may be formed by applying a negative electrode mixture containing a negative electrode active material, a binder, and other components added as needed to the surface of a negative electrode current collector. The other component includes at least one selected from the group consisting of a conductive agent, a tackifier, and an additive. The thickness of the negative electrode active material layer is not particularly limited, and each surface of the negative electrode current collector is, for example, 1 μm or more and 150 μm or less in a fully discharged state of the lithium secondary battery.

The order of forming the anode active material layer and the plurality of projections is not particularly limited, and the plurality of projections may be formed after forming the anode active material layer. In addition, the negative electrode active material layer may be formed after the plurality of projections are formed. More specifically, a plurality of protrusions may protrude from the 1 st surface and/or the 2 nd surface of the anode current collector 132 in a state of being in direct contact with each surface. In addition, the negative electrode active material layer may protrude from the 1 st surface and/or the 2 nd surface of the negative electrode current collector 132 in a state where the negative electrode active material layer is present between each surface and the plurality of projections.

The thickness of the negative electrode current collector or the conductive sheet is not particularly limited, and is, for example, 5 μm or more and 20 μm or less.

The material constituting the plurality of projections is not particularly limited. The material of the plurality of projections may be different from the material of the negative electrode current collector 132. Alternatively, the plurality of projections and the negative electrode collector 132 may be integrally formed of the same material. The plurality of projections may be made of a conductive material and/or an insulating material. The conductive material can be appropriately selected from the materials exemplified for the conductive sheet. Such a negative electrode current collector 132 having a convex portion can be obtained by forming a convex portion on the surface of a conductive sheet by press working or the like, for example. The negative electrode current collector 132 may be formed by applying a coating material of a conductive material to the surface of the conductive sheet or by attaching a belt of a conductive material.

the plurality of projections may be made of a resin material. The resin material may be insulating. If the convex portions are made of an insulating material such as a resin material, deposition of lithium metal at the tips of the convex portions 133 due to charging can be suppressed. The deposited lithium metal is contained in the negative electrode 134, more specifically, in a space formed in the vicinity of the surface of the negative electrode current collector 132 which is a conductive sheet such as a metal foil. Therefore, the effect of suppressing the expansion of the negative electrode can be improved.

Examples of the resin material include at least one selected from olefin resins, acrylic resins, polyamide resins, polyimide resins, and silicone resins. As the resin material, a cured product of a curable resin such as an epoxy resin can be used. The convex portion is formed by, for example, attaching a resin adhesive tape to the surface of the negative electrode current collector 132 or the surface of the negative electrode current collector 132 via the negative electrode active material layer. The convex portion may be formed by applying a solution or dispersion containing a resin material to the surface of the negative electrode current collector 132 or the negative electrode active material layer and drying the solution or dispersion. The convex portion may be formed by applying a curable resin to the surface of the negative electrode current collector 132 in a desired shape and curing the curable resin.

further, the negative electrode 134 may further include a protective layer. The protective layer may be formed on the surface of the anode current collector 132, or may be formed on the surface of the anode active material layer in the case where the anode 134 has the anode active material layer. The protective layer has an effect of making the surface reaction of the electrode more uniform, and lithium metal is more likely to be more uniformly deposited in the negative electrode. The protective layer may be made of, for example, an organic substance and/or an inorganic substance. As these materials, materials that do not inhibit lithium ion conductivity are used. Examples of the organic material include polymers having lithium ion conductivity. Examples of the inorganic substance include ceramics and solid electrolytes.

(lithium secondary battery)

Hereinafter, the structure of the lithium secondary battery will be described in more detail. A lithium secondary battery includes a group of wound electrodes and a nonaqueous electrolyte. The wound electrode group is formed by winding a positive electrode, a negative electrode, and a separator interposed between these electrodes.

Fig. 5 is a longitudinal sectional view schematically showing a lithium secondary battery according to an embodiment of the present disclosure. Fig. 6 is an enlarged sectional view schematically showing a VI region of fig. 5. Fig. 7 is an enlarged sectional view schematically showing a VII region of fig. 5. Fig. 7 is a cross section in a fully discharged state.

The lithium secondary battery 10 is a cylindrical battery including a cylindrical battery case, a wound electrode group 14 housed in the battery case, and a non-aqueous electrolyte not shown. The battery case is composed of a case main body 15 and a sealing member 16, the case main body 15 is a bottomed cylindrical metal container, and the sealing member 16 seals an opening of the case main body 15. A gasket 27 is disposed between the case main body 15 and the sealing body 16, thereby ensuring the sealing property of the battery case. In the case body 15, insulating plates 17 and 18 are disposed at both ends of the electrode group 14 in the winding axis direction, respectively.

The case body 15 has, for example, a step portion 21, and the step portion 21 is formed by partially pressing a side wall of the case body 15 from an outer side. The step portion 21 may be formed in a ring shape along the circumferential direction of the case main body 15 at the side wall of the case main body 15. In this case, the sealing body 16 is supported by the surface of the stepped portion 21 on the opening side.

sealing body 16 includes filter 22, lower valve element 23, insulating member 24, upper valve element 25, and cap 26. In sealing body 16, these members are laminated in the above-described order. Sealing body 16 is attached to the opening of case body 15 such that cap 26 is positioned outside case body 15 and filter 22 is positioned inside case body 15. The members constituting the sealing body 16 are, for example, circular plate-shaped or ring-shaped. The members other than the insulating member 24 are electrically connected to each other.

the electrode group 14 includes a positive electrode 11, a negative electrode 12, and a separator 13. The positive electrode 11, the negative electrode 12, and the separator 13 are all in the form of a belt. The positive electrode 11 and the negative electrode 12 are wound in a spiral shape with the separator 13 interposed therebetween so that the width direction of the strip-shaped positive electrode 11 and the negative electrode 12 is parallel to the winding axis. In a cross section perpendicular to the winding axis of the electrode group 14, the positive electrodes 11 and the negative electrodes 12 are alternately stacked in the radial direction of the electrode group 14 with the separators 13 interposed therebetween.

the positive electrode 11 is electrically connected to a cap 26 also serving as a positive electrode terminal via a positive electrode lead 19. One end of the positive electrode lead 19 is connected to, for example, the vicinity of the center in the longitudinal direction of the positive electrode 11. A positive electrode lead 19 extending from the positive electrode 11 extends to the filter 22 through a through hole, not shown, formed in the insulating plate 17. The other end of the positive electrode lead 19 is welded to the surface of the filter 22 on the electrode group 14 side.

The negative electrode 12 is electrically connected to the case main body 15 also serving as a negative electrode terminal via a negative electrode lead 20. One end of the negative electrode lead 20 is connected to, for example, the end of the negative electrode 12 in the longitudinal direction, and the other end is welded to the inner bottom surface of the case main body 15.

Fig. 6 shows the positive electrode 11 opposite the separator 13. Fig. 7 shows the negative electrode 12 opposite to the separator 13. The positive electrode 11 includes a positive electrode current collector 30 and a positive electrode mixture layer 31 disposed on both the 1 st surface and the 2 nd surface of the positive electrode current collector 30. The negative electrode 12 includes a negative electrode current collector 32, a plurality of 1 st protrusions 33a disposed on a 1 st surface S1 that is an outer side of the negative electrode current collector 32, and a plurality of 2 nd protrusions 33b disposed on a 2 nd surface S2 that is an inner side of the negative electrode current collector 32. The 1 st surface S1 and the 2 nd surface S2 of the negative electrode current collector 32 are the 1 st surface and the 2 nd surface, respectively, of a conductive sheet such as a metal foil constituting the negative electrode current collector 32. The plurality of 1 st convex portions 33a protrude from the 1 st surface S1 toward a surface of the partition plate 13 opposite to the 1 st surface S1. The plurality of 2 nd convex portions 33b protrude from the 2 nd surface S2 toward the surface of the partition plate 13 opposite to the 2 nd surface S2.

A plurality of 1 st protrusions 33a and a plurality of 2 nd protrusions 33b are formed on the 1 st surface S1 and the 2 nd surface S2, respectively. Between the adjacent 21 st projections 33a, a space 35 is formed between the 1 st surface S1 and the partition plate 13. Further, between the 2 nd convex portions 33b adjacent to each other, a space 35 is formed between the 2 nd surface S2 and the partition plate 13. In the lithium secondary battery 10, lithium metal is deposited in the space 35 by charging, and the deposited lithium metal is dissolved in the nonaqueous electrolyte by discharging. Since lithium metal deposited in the space 35 can be stored, the change in apparent volume of the negative electrode 12 due to deposition of lithium metal can be reduced. Further, by making the area ratio of the convex portions of the inner peripheral side wound portion IW, in which the thickness of the deposited lithium metal is increased, smaller than the area ratio of the convex portions of the outer peripheral side wound portion OW in advance, it is possible to absorb the volume change accompanying the deposition of lithium metal. Therefore, the expansion of the negative electrode can be suppressed. In addition, since the pressure is also applied to the lithium metal accommodated in the space 35 in the electrode group 14, the peeling of the lithium metal can be suppressed. Therefore, the charge/discharge efficiency of the lithium secondary battery 10 can be suppressed from decreasing.

As the negative electrode 12 including the plurality of projections and the negative electrode current collector 32, the negative electrode 134 including the plurality of projections and the negative electrode current collector 132 described above can be used. Therefore, for the negative electrode 12, the plurality of projections, and the negative electrode current collector 32, the description of the negative electrode 134, the plurality of projections, and the negative electrode current collector 132 described above can be referred to. The following describes the structure of the lithium secondary battery other than the negative electrode 12 in more detail.

(Positive electrode 11)

The positive electrode 11 includes, for example, a positive electrode current collector 30 and a positive electrode mixture layer 31 formed on the positive electrode current collector 30. The positive electrode mixture layer 31 may be formed on both the 1 st surface and the 2 nd surface of the positive electrode collector 30. The positive electrode mixture layer 31 may be formed on one surface of the positive electrode current collector 30. For example, the positive electrode mixture layer 31 may be formed only on one surface of the positive electrode current collector 30 in a region where the positive electrode lead 19 is connected and/or a region not facing the negative electrode 12. For example, since there may be a region not facing the negative electrode 12 in a region located at and near the innermost winding periphery and/or a region located at and near the outermost winding periphery, the positive electrode mixture layer 31 may be formed only on one surface of the positive electrode current collector 30 in such a region, and the positive electrode mixture layer 31 may not be formed on both the 1 st surface and the 2 nd surface.

the positive electrode mixture layer 31 may contain a positive electrode active material, and contain a conductive material and/or a binder as optional components. The positive electrode mixture layer 31 may contain an additive as needed. Between the positive electrode current collector 30 and the positive electrode mixture layer 31, a conductive carbon material may be disposed as necessary.

The positive electrode 11 is obtained by, for example, applying a slurry containing the constituent components of the positive electrode mixture layer and the dispersion medium to the surface of the positive electrode current collector 30, drying the coating film, and then rolling. If necessary, a conductive carbon material may be applied to the surface of the positive electrode current collector 30. Examples of the dispersion medium include water and/or an organic medium.

Examples of the positive electrode active material include materials that occlude and emit lithium ions. As the positive electrode active material, at least one selected from the group consisting of lithium-containing transition metal oxides, transition metal fluorides, polyanions, fluorinated polyanions, and transition metal sulfides can be exemplified. The positive electrode active material may be a lithium-containing transition metal oxide from the viewpoint of high average discharge voltage and advantageous cost.

examples of the transition metal element contained in the lithium-containing transition metal oxide include Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Y, Zr, W, and the like. The lithium-containing transition metal oxide may contain one transition metal element, or may contain two or more transition metal elements. The transition metal element may be at least one selected from Co, Ni, and Mn. The lithium-containing transition metal oxide may contain one or two or more typical metal elements, as needed. Typical examples of the metal elements include Mg, Al, Ca, Zn, Ga, Ge, Sn, Sb, Pb, and Bi. Typical metal elements may be Al and the like.

The conductive material is, for example, a carbon material. Examples of the carbon material include carbon black, carbon nanotubes, and graphite. Examples of the carbon black include acetylene black and ketjen black. The positive electrode mixture layer 31 may contain one or two or more kinds of conductive materials. At least one selected from these carbon materials can be used as the conductive carbon material present between the positive electrode current collector 30 and the positive electrode mixture layer 31.

Examples of the binder include fluororesins, polyacrylonitrile, polyimide resins, acrylic resins, polyolefin resins, and rubbery polymers. Examples of the fluororesin include polytetrafluoroethylene and polyvinylidene fluoride. The positive electrode mixture layer 31 may contain one kind of binder, or may contain two or more kinds of binders.

Examples of the material of the positive electrode current collector 30 include metal materials containing Al, Ti, Fe, and the like. The metal material may be Al, Al alloy, Ti alloy, Fe alloy, and the like. The Fe alloy may be stainless steel. Examples of the positive electrode current collector 30 include a foil and a film. The positive electrode collector 30 may be porous. For example, a metal mesh or the like can be used as the positive electrode collector 30.

(partition plate 13)

The separator 13 is a porous sheet having ion permeability and insulation properties. Examples of the porous sheet include a microporous film, woven fabric, and nonwoven fabric. The material of the separator is not particularly limited, and may be a polymer material. Examples of the polymer material include olefin resins, polyamide resins, and cellulose. Examples of the olefin resin include polyethylene, polypropylene, and a copolymer of ethylene and propylene. The separator 13 may contain an additive as needed. Examples of the additive include inorganic fillers.

Separator 13 may comprise multiple layers of differing morphology and/or composition. Such a separator 13 may be, for example, a laminate of a polyethylene microporous membrane and a polypropylene microporous membrane, or a laminate of a nonwoven fabric including cellulose fibers and a nonwoven fabric including thermoplastic resin fibers. A material having a polyamide resin coating film formed on the surface of a microporous membrane, woven fabric, nonwoven fabric, or the like can be used as the separator 13. Such a separator 13 has high durability even when pressure is applied in a state of being in contact with the plurality of convex portions. In addition, the separator 13 may be provided with a layer containing an inorganic filler on the side facing the positive electrode 11 and/or the side facing the negative electrode 12, from the viewpoint of ensuring heat resistance and/or strength.

(non-aqueous electrolyte)

As the nonaqueous electrolyte, a material having lithium ion conductivity is used. Such a nonaqueous electrolyte contains a nonaqueous solvent and lithium ions and anions dissolved in the nonaqueous solvent. The nonaqueous electrolyte may be in a liquid state or a gel state. In addition, the nonaqueous electrolyte may be a solid electrolyte.

The liquid nonaqueous electrolyte is prepared by dissolving a lithium salt in a nonaqueous solvent. The non-aqueous electrolyte may contain a non-dissociative lithium salt by dissolving the lithium salt in the non-aqueous solvent to generate lithium ions and anions. As the lithium salt, a salt of a lithium ion and an anion is used.

The gel-like nonaqueous electrolyte includes a liquid nonaqueous electrolyte and a matrix polymer. As the matrix polymer, for example, a polymer material that absorbs a nonaqueous solvent to be gelled is used. Examples of such a polymer material include at least one selected from a fluororesin, an acrylic resin, a polyether resin, and the like.

₄ ^- ₄ ^- ₆ ^- _{3 3} ^- _{3 2} ^- _{2 m 2m+1 2 n 2n+1} ^- _{2 3 2} ^- _{2 2 5 2} ^- _{2 2} ^- _{2 2 4} ^- _{4 2 4} ^- _{2 2 4 2} ^-The lithium salt or the anion may be a known substance used for a nonaqueous electrolyte of a lithium secondary battery, and examples of the anion include BF, ClO, PF, CF SO, CF CO, imide anions, and oxalic acid anions, and examples of the imide anions include N (SO C F) (SO C F) (m and N are each independently an integer of 0 or more) and m and N may be 0 to 3, and may be 0, 1, or 2, and examples of the imide anions include N (SO CF), N (SO C F), and N (SO F), and the oxalic acid anions may contain boron and/or phosphorus.

₆ ^- ₆ ^-in particular, if a nonaqueous electrolyte containing an oxalate anion is used, lithium metal is likely to be uniformly precipitated in a fine particle form due to the interaction of the oxalate anion with lithium.

examples of the nonaqueous solvent include esters, ethers, nitriles, amides, and halogen substitutes thereof. The nonaqueous electrolyte may contain one of these nonaqueous solvents, or may contain two or more of these nonaqueous solvents. Examples of the halogen substituent include fluoride.

Examples of the ester include a carbonate ester and a carboxylic acid ester. Examples of the cyclic carbonate include ethylene carbonate, propylene carbonate, fluoroethylene carbonate, and the like. Examples of the chain carbonate include dimethyl carbonate, ethyl methyl carbonate, and diethyl carbonate. Examples of the cyclic carboxylic acid ester include γ -butyrolactone and γ -valerolactone. Examples of the chain carboxylic acid ester include ethyl acetate, methyl propionate, and methyl fluoropropionate.

Examples of the ether include cyclic ethers and chain ethers. Examples of the cyclic ether include 1, 3-dioxolane, 4-methyl-1, 3-dioxolane, tetrahydrofuran, and 2-methyltetrahydrofuran. Examples of the chain ether include 1, 2-dimethoxyethane, diethyl ether, ethyl vinyl ether, methylphenyl ether, benzylethyl ether, diphenyl ether, dibenzyl ether, 1, 2-diethoxyethane, and diethylene glycol dimethyl ether.

Examples of the nitrile include acetonitrile, propionitrile, and benzonitrile. Examples of the amide include dimethylformamide and dimethylacetamide.

The concentration of the lithium salt in the nonaqueous electrolyte is, for example, 0.5mol/L to 3.5 mol/L. Here, the lithium salt concentration is the total of the dissociated lithium salt concentration and the undissociated lithium salt concentration. The concentration of anions in the nonaqueous electrolyte can be set to 0.5mol/L to 3.5 mol/L.

The nonaqueous electrolyte may contain an additive. The additive may form a coating on the negative electrode. By forming a coating film derived from the additive on the negative electrode, the formation of dendrites is easily suppressed. Examples of such additives include vinylene carbonate, fluoroethylene carbonate, and vinylethylene carbonate. One additive may be used alone, or two or more additives may be used in combination.

(others)

In the illustrated example, the cylindrical lithium secondary battery is described, but the present embodiment is not limited to this case, and the present embodiment can also be applied to a lithium secondary battery including a rolled electrode group in which the end surface shape in the rolling axis direction of the rolled electrode group is elliptical or oval. In addition, as for the structure other than the electrode group and the nonaqueous electrolyte of the lithium secondary battery, a known structure may be used without particular limitation.