Patent Application
20250233267
The present disclosure relates to a cylindrical secondary battery.
A cylindrical secondary battery is a battery in which an electrode assembly formed by winding a positive electrode and a negative electrode with a separator interposed therebetween is accommodated in a cylindrical outer housing body. Patent Literature 1 and Patent Literature 2 disclose a separator in which irregularities are provided in the surface of the separator for the purpose of easily injecting an electrolytic solution into an outer housing body when a battery is manufactured.
In recent years, for the purpose of increasing the capacity of a cylindrical secondary battery, an increase in size of the cylindrical secondary battery has been studied. As a result of intensive studies by the present inventors, non-uniformity of distribution of an electrolytic solution occurs in a winding-type electrode assembly, and thus a battery capacity may be reduced due to repeated charging and discharging. It has been found that this tendency is remarkable in a large cylindrical secondary battery. The techniques described in Patent Literature 1 and Patent Literature 2 have not studied the increase in the size of the battery, and there is still room for improvement.
An object of the present disclosure is to provide a cylindrical secondary battery having a high capacity and excellent charge-discharge cycle characteristics.
A cylindrical secondary battery according to an aspect of the present disclosure includes: an electrode assembly in which a positive electrode and a negative electrode are wound with a separator interposed therebetween; an electrolytic solution; and a cylindrical outer housing body that accommodates the electrode assembly and the electrolytic solution. A plurality of linear insulators extending in a short direction of the separator are disposed between the separator and at least one of the positive electrode and the negative electrode. The insulators do not overlap each other in a radial direction of the electrode assembly.
The cylindrical secondary battery according to the present disclosure can have an improved battery capacity and charge-discharge cycle characteristics.
In recent years, an increase in the size of a cylindrical secondary battery has been studied for the purpose of improving a battery capacity. However, in a large-sized battery, as compared with a conventional battery, the non-uniformity of the distribution of an electrolytic solution occurs in an electrode assembly, and charge-discharge cycle characteristics are easily deteriorated. In order to solve this problem, the present inventors have extensively conducted studies, and have found that by disposing a plurality of insulators between at least one of a positive electrode and a negative electrode and a separator so as not to overlap each other, charge-discharge cycle characteristics can be improved while a decrease in the battery capacity is suppressed. As a result of further studies by the present inventors, it has been found that the charge-discharge cycle characteristics are further improved by making the interval between the insulators on the outer side of winding wider than the interval between the insulators on the inner side of winding.
Hereinafter, an example embodiment of a cylindrical secondary battery according to the present disclosure will be described in detail with reference to the drawings. In the following description, specific shapes, materials, numerical values, and directions and the like are given as examples for facilitating understanding of the present invention, and can be appropriately changed in accordance with the specifications of the cylindrical secondary battery. When the following description refers to a plurality of embodiments or variants, it is envisioned from the beginning that characteristic features thereof may be appropriately used in combination.
The opening end portion of the outer housing body 15 is closed with the sealing assembly 16, and the inside of the secondary battery 10 is thereby hermetically sealed. Above and below the electrode assembly 14, insulating plates 17 and 18 are provided respectively. A positive electrode lead 19 extends upward through a through hole in the insulating plate 17, and is welded to the lower surface of a filter 22, which is the bottom plate of the sealing assembly 16. In the secondary battery 10, a cap 26, which is the top plate of the sealing assembly 16 electrically connected to the filter 22, serves as a positive electrode terminal. Meanwhile, a negative electrode lead 20 extends toward the bottom portion of the outer housing body 15 through a through hole in the insulating plate 18, and is welded to the inner surface of the bottom portion of the outer housing body 15. In the secondary battery 10, the outer housing body 15 serves as a negative electrode terminal. When the negative electrode lead 20 is provided at an outer winding end portion, the negative electrode lead 20 extends on the outside of the insulating plate 18 and toward the bottom portion of the outer housing body 15, and is welded to the inner surface of the bottom portion of the outer housing body 15.
The outer housing body 15 is, for example, a bottomed cylindrical metal outer can. A gasket 27 is provided between the outer housing body 15 and the sealing assembly 16 to ensure sealability inside the secondary battery 10. The outer housing body 15 has a groove portion 21 which is formed by, for example, pressing a side surface portion from the outside, and which supports the sealing assembly 16. The groove portion 21 is preferably formed in an annular shape along the circumferential direction of the outer housing body 15, and supports the sealing assembly 16 on its upper surface.
The sealing assembly 16 includes the filter 22, a lower vent member 23, an insulating member 24, an upper vent member 25, and the cap 26, which are laminated in this order from the electrode assembly 14 side. Each of the members constituting the sealing assembly 16 has, for example, a disk shape or a ring shape, and the respective members except the insulating member 24 are electrically connected to each other. The lower vent member 23 and the upper vent member 25 are connected to each other at their central portions, and the insulating member 24 is interposed between the circumferential portions of these vent members. When the internal pressure of the battery increases due to abnormal heat generation, for example, the lower vent member 23 ruptures, which causes the upper vent member 25 to swell toward the cap 26 and move away from the lower vent member 23, and the electrical connection between the two vent members is thereby cut off. When the internal pressure further increases, the upper vent member 25 ruptures, and gas is discharged from an opening 26a of the cap 26.
Next, the electrode assembly 14 will be described with reference to
The positive electrode 11 includes a strip-shaped positive electrode current collector and a positive electrode mixture layer formed on the surface of the positive electrode current collector. The positive electrode mixture layer is preferably formed on both surfaces of the positive electrode current collector. As the positive electrode current collector, a foil of a metal, such as aluminum or an aluminum alloy, that is stable in a potential range of the positive electrode 11, or a film in which the metal is disposed on its surface layer, or the like can be used.
The positive electrode mixture layer may contain a positive electrode active material, a conductive agent, and a binder and the like. The positive electrode mixture layer can be produced, for example, by applying a positive electrode mixture slurry containing the positive electrode active material, the conductive agent, the binder, and a solvent such as N-methyl-2-pyrrolidone (NMP) onto both surfaces of the positive electrode current collector, drying the applied slurry, and then rolling the product.
Examples of the positive electrode active material contained in the positive electrode mixture layer include lithium transition metal oxides containing transition metal elements such as Co, Mn, and Ni. Examples of the lithium transition metal oxides include LixCoO2, LixNiO2, LixMnO2, LixCoyNi1-yO2, LixCoyM1-yOz, LixNi1-yMyOz, LixMn2O4, LixMn2-yMyO4, LiMPO4, and Li2MPO4F (M; at least one of Na, Mg, Sc, Y, Mn, Fe, Co, Ni, Cu, Zn, Al, Cr, Pb, Sb, and B, 0<x≤1.2, 0<y≤0.9, 2.0≤z≤2.3). These may be used singly, or a plurality of kinds of them may be mixed and used. From the viewpoint that the high capacity of the secondary battery 10 can be achieved, it is preferable that the positive electrode active material contains a lithium nickel composite oxide such as LixNiO2, LixCoyNi1-yO2, or LixNi1-yMyOz (M; at least one of Na, Mg, Sc, Y, Mn, Fe, Co, Ni, Cu, Zn, Al, Cr, Pb, Sb, and B, 0<x≤1.2, 0≤y≤0.9, 2.0≤z≤2.3).
Examples of the conductive agent contained in the positive electrode mixture layer include carbon-based particles such as carbon black (CB), acetylene black (AB), Ketjenblack, carbon nanotubes (CNTs), graphene, and graphite. These may be used singly or in combination of two or more kinds thereof.
Examples of the binder contained in the positive electrode mixture layer include fluorine-based resins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF), polyimide-based resins, acrylic resins, polyolefin-based resins, and polyacrylonitrile (PAN). These may be used singly or in combination of two or more kinds thereof.
The negative electrode 12 includes a strip-shaped negative electrode current collector and a negative electrode mixture layer formed on the surface of the negative electrode current collector. The negative electrode mixture layer is preferably formed on both surfaces of the negative electrode current collector. As the negative electrode current collector, a foil of a metal, such as copper or a copper alloy, that is stable in a potential range of the negative electrode 12, a film in which the metal is disposed on its surface layer, or the like can be used.
The negative electrode mixture layer may contain a negative active material and a binder and the like. The negative electrode mixture layer can be produced, for example, by applying a negative electrode mixture slurry containing a negative electrode active material, a binder, and a solvent such as water onto both surfaces of the negative electrode current collector, drying the applied slurry, and then rolling the product.
The negative electrode active material contained in the negative electrode mixture layer is not particularly limited as long as it can reversibly occlude and discharge lithium ions, and a carbon material such as graphite is generally used. As the graphite, natural graphites such as scale-like graphite, massive graphite, and earthy graphite, and artificial graphites such as massive artificial graphite and graphitized mesophase carbon microbeads may be used.
The negative electrode active material preferably contains a silicon-containing material. As a result, the battery capacity of the secondary battery 10 can be increased. The negative electrode 12 containing the silicon-containing material has a large volume change due to charging and discharging of the battery, and thus the non-uniformity of the distribution of the electrolytic solution is likely to occur in the electrode assembly 14, but the charge-discharge cycle characteristics can be improved by the effect of the present disclosure. Examples of the silicon-containing material include a silicon-containing compound represented by SiOx (0.5≤x≤1.6), a silicon-containing compound in which Si fine particles are dispersed in a lithium silicate phase represented by Li2ySiO(2+y) (0<y<2), and a silicon-containing compound in which Si fine particles are dispersed in a carbon phase.
Examples of the binder contained in the negative electrode mixture layer include styrene butadiene rubber (SBR), nitrile-butadiene rubber (NBR), carboxymethyl cellulose (CMC) or a salt thereof, polyacrylic acid (PAA) or a salt thereof, and polyvinyl alcohol (PVA). These may be used singly or in combination of two or more kinds thereof.
For example, a porous sheet having an ion permeation property and an insulation property is used for the separator 13. Specific examples of the porous sheet include fine porous thin films, woven fabrics, and nonwoven fabrics. As the material of the separator 13, olefin-based resins such as polyethylene and polypropylene, cellulose, and the like are preferable. The separator 13 may be a laminate including a cellulose fiber layer and a thermoplastic resin fiber layer such as an olefin-based resin, or may be a multilayer separator including a polyethylene layer and a polypropylene layer.
The separator 13 may include a heat resistant layer on at least one surface. In other words, the separator 13 may include a heat resistant layer on at least one of a surface facing the positive electrode 11 and a surface facing the negative electrode 12. The heat resistant layer is preferably provided at least on a surface facing the positive electrode 11. The heat resistant layer is provided on the entire surface of the separator 13, for example.
The heat resistant layer contains, for example, a filler and a binder. Examples of the filler include metal oxide particles made of aluminum oxide and the like, metal nitride particles, metal fluoride particles, metal carbide particles, and sulfide particles. These may be used singly or in combination of two or more kinds thereof. Examples of the binder include fluorine-based resins such as polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE), polyimide-based resins, polyamide-based resins, acrylic resins, polyolefin-based resins, styrene-butadiene rubber (SBR), nitrile-butadiene rubber (NBR), carboxymethyl cellulose (CMC) or a salt thereof, polyacrylic acid (PAA) or a salt thereof, and polyvinyl alcohol (PVA). These may be used singly or in combination of two or more kinds thereof.
In the electrode assembly 14, a plurality of linear insulators 30 extending in the short direction of the separator 13 are disposed between at least one of the positive electrode 11 and the negative electrode 12 and the separator 13. As a result, the electrolytic solution easily permeates the separator 13, so that charge-discharge cycle characteristics are improved.
In the present embodiment shown in
The width of the linear insulator 30 is, for example, less than or equal to 1 mm. The lower limit value of the width of the linear insulator 30 is, for example, 0.01 mm. The height of the linear insulator 30 is, for example, greater than or equal to 0.5 m and less than or equal to 1 mm. The cross-sectional shape of the linear insulator 30 is not particularly limited, and is, for example, a circular shape or a rectangular shape.
The material of the insulator 30 is not particularly limited as long as it has an insulating property, and is, for example, a ceramic or a resin. The material of the insulator 30 is preferably a resin. Examples of the resin used for the insulator 30 include fluorine-based resins such as polyethylene terephthalate (PET), polyimide (PI), polypropylene (PP), polybutylene terephthalate (PBT), and polytetrafluoroethylene (PTFE), and acrylic resins such as polyacrylic acid, polymethacrylic acid, polyacrylate, and polymethacrylate. These may be used singly or in combination of two or more kinds thereof. As the linear insulator 30, for example, PET fibers can be used. The dot-shaped insulator 30 can be formed, for example, on the surface of the positive electrode 11, the negative electrode 12, or the separator 13 by dissolving the resin in a solvent and using an inkjet method or the like.
Hereinafter, the present disclosure will be further described with reference to Examples. However, the present disclosure is not limited to these Examples.
95 parts by mass of LiNi0.8Co0.15Al0.05O2, 2.5 parts by mass of acetylene black (AB), and 2.5 parts by mass of polyvinylidene fluoride (PVDF) having an average molecular weight of 1.1 million were mixed, and an appropriate amount of N-methyl-2-pyrrolidone (NMP) was added thereto to prepare a positive electrode mixture slurry. Next, the positive electrode mixture slurry was applied to both surfaces of a strip-shaped positive electrode current collector made of an aluminum foil, and dried. The product was then rolled and cut into a predetermined electrode plate size to produce a positive electrode including positive electrode mixture layers formed on both surfaces of the positive electrode current collector. At a substantially central part in the longitudinal direction of a positive electrode, there was provided a positive electrode exposed portion where the mixture layer was absent and a surface of the current collector was exposed, and an aluminum positive electrode lead was welded to the positive electrode exposed portion.
94 parts by mass of graphite, 6 parts by mass of SiO, 1 part by mass of carboxymethyl cellulose (CMC), and 1 part by mass of styrene-butadiene rubber (SBR) were mixed, and an appropriate amount of water was added thereto to prepare a negative electrode mixture slurry. Next, the negative electrode mixture slurry was applied to both surfaces of a strip-shaped negative electrode current collector made of a copper foil, and dried. The product was then rolled and cut into a predetermined electrode plate size to produce a negative electrode in which negative electrode mixture layers were formed on both surfaces of the negative electrode current collector. At the inner winding end portion, there was provided a negative electrode exposed portion where the mixture layer was absent and a surface of the current collector was exposed, and a nickel negative electrode lead was welded to the negative electrode exposed portion.
5 parts by mass of vinylene carbonate (VC) was added to 100 parts by mass of a mixed solvent (EC:DMC=1:3 by volume) containing ethylene carbonate (EC) and dimethyl carbonate (DMC). LiPF6 was dissolved in the mixed solvent so as to have a concentration of 1 mol/L to prepare an electrolytic solution.
Eight PET fibers each having a diameter of 0.1 mm were disposed on the surface of the positive electrode. At that time, the PET fibers were arranged at equal intervals from the inner side of winding to the outer side of winding in the longitudinal direction of the separator. The projected area of one PET fiber on the separator was 0.025% with respect to the area of the separator. Thereafter, the positive electrode and the negative electrode were wound with a separator made of polyethylene interposed therebetween to produce an electrode assembly. It was confirmed that insulators do not overlap in the radial direction of the electrode assembly on the upper surface of the electrode assembly. Insulating plates were disposed above and below the electrode assembly, and the electrode assembly was accommodated in a cylindrical outer housing body. Next, a negative electrode lead was welded to the bottom portion of the outer housing body, and a positive electrode lead was welded to a sealing assembly. Thereafter, an electrolytic solution was injected into the outer housing body by a decompression method, and then an opening end portion of the outer housing body was sealed by caulking to the sealing assembly with a gasket interposed therebetween, thereby producing a secondary battery.
A secondary battery was produced in the same manner as in Example 1 except that in the production of the secondary battery, as in example shown in
A secondary battery was produced in the same manner as in Example 1 except that in the production of the secondary battery, no PET fibers were disposed on the surface of a positive electrode, and the positive electrode and the negative electrode were elongated so that the diameter of an electrode assembly was the same as the diameter of the electrode assembly of Example 1.
A secondary battery was produced in the same manner as in Example 1 except that in the production of the secondary battery, as in the example shown in
The secondary batteries of Examples and Comparative Examples were charged to 4.2 V at a constant current of 1 C at an environmental temperature of 25° C., and then charged at a constant voltage of 4.2 V until a current value reached 0.05 C. After the secondary batteries were left for 20 minutes, the secondary batteries were discharged to 2.5 V at a constant current of 1 C. The charge/discharge was defined as one cycle, and 200 cycles were performed. A capacity retention rate during the charge-discharge cycle of the secondary battery of each of Examples and Comparative Examples was calculated using the following formula. The discharge capacity at the first cycle was defined as an initial discharge capacity.
Table 1 shows the evaluation results of the initial discharge capacities and the capacity retention rates of the secondary batteries of Examples and Comparative Examples. The initial discharge capacities of the secondary batteries of Examples 1 and 2 and Comparative Example 2 are relatively expressed with the initial discharge capacity of the secondary battery of Comparative Example 1 as 100. Table 1 also shows the arrangement of the PET fibers as the insulator.
In the secondary batteries of Examples, both the initial discharge capacity and the charge-discharge cycle characteristics can be achieved. Meanwhile, the secondary battery of Comparative Example 1 in which no insulators are disposed has poor charge-discharge cycle characteristics, and the secondary battery of Comparative Example 2 in which the PET fibers are disposed so as to overlap each other in the radial direction of the electrode assembly has a poor initial discharge capacity. Therefore, it is found that the battery capacity and the charge-discharge cycle characteristics are improved by disposing the insulators so as not to overlap each other in the radial direction of the electrode assembly.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2022-058216 | Mar 2022 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2023/008216 | 3/6/2023 | WO |
