Secondary battery

Abstract

The purpose of the present disclosure is to provide a secondary battery capable of maintaining a favorable conduction state between a case main body and an exposed section of a negative electrode current collector. A secondary battery according to one embodiment of the present disclosure is characterized by comprising a metal case main body that has an opening, a sealing body that seals the opening of the case main body, and an electrode body that is accommodated in the case main body and formed by winding a positive electrode and negative electrode with a separator interposed therebetween, wherein: the negative electrode includes a negative electrode current collector, a negative electrode active material layer formed on the negative electrode current collector, and a negative electrode current collector exposed section where the negative electrode active material layer is not formed and the negative electrode current collector is exposed; the negative electrode current collector exposed section is disposed on a winding ending section of the electrode body and makes more than one lap circling in the winding starting direction L from the winding ending section of the electrode body, thereby forming a laminated part comprising the negative electrode exposed section, the laminated part and the case main body being welded together.

Description

Technical Field

[0001] The present disclosure relates to secondary batteries.

Background Art

[0002] A secondary battery represented by a lithium-ion secondary battery is configured, for example, by accommodating an electrode body wound between a positive electrode and a negative electrode via a separator in a case body of a battery case.

[0003] For example, Patent Document 1 discloses a non-aqueous electrolyte secondary battery in which an electrode body having an exposed portion where a negative electrode current collector is exposed on the outermost peripheral surface of the electrode body is accommodated in a case body, and the exposed portion is brought into direct contact with the inner surface of the case body.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] By the way, depending on the charging state of the electrode body, the deterioration state due to use and aging, etc., the contact state between the exposed portion of the negative electrode current collector and the case body fluctuates, and it may be difficult to maintain a good conduction state between the exposed portion of the negative electrode current collector and the case body.

[0006] Therefore, an object of the present disclosure is to provide a secondary battery capable of maintaining a good conduction state between the exposed portion of the negative electrode current collector and the case body.

Means for Solving the Problems

[0007] A secondary battery according to one aspect of the present disclosure includes a metal case body having an opening, a sealing body that seals the opening of the case body, and an electrode body housed in the case body, in which a positive electrode and a negative electrode are wound with a separator interposed therebetween. The negative electrode has a negative electrode current collector, a negative electrode active material layer formed on the negative electrode current collector, and an exposed portion where the negative electrode active material layer is not formed and the negative electrode current collector is exposed. The exposed portion is disposed at the end of the winding of the negative electrode. The electrode body has a laminated portion in which a metal foil including the exposed portion is laminated, and the laminated portion is welded to the case body.

Effect of the Invention

[0008] According to one aspect of the present disclosure, it is possible to provide a secondary battery capable of maintaining a good conduction state between the exposed portion of the negative electrode current collector and the case body.

Brief Description of the Drawings

[0009]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Embodiments for Carrying Out the Invention

[0010] In the present disclosure, a secondary battery is a rechargeable power storage device, and examples thereof include non-aqueous electrolyte secondary batteries such as lithium-ion secondary batteries, and aqueous secondary batteries such as alkaline secondary batteries. Hereinafter, as an example of a secondary battery which is one aspect of the present disclosure, a non-aqueous electrolyte secondary battery will be described as an example. Note that the drawings referred to in the following description of the embodiments are schematically drawn, and the dimensional ratios of the components drawn in the drawings may be different from the actual ones.

[0011] FIG. 1 is a perspective view showing the appearance of a non-aqueous electrolyte secondary battery according to an embodiment. FIG. 2 is a cross-sectional view of the non-aqueous electrolyte secondary battery taken along line L1-L1 in FIG. 1.

[0012] The non-aqueous electrolyte secondary battery 1 according to the present embodiment includes an electrode body 2, a non-aqueous electrolyte (not shown), and a battery case 3.

[0013] The battery case 3 includes a metal case body 5 having an opening, and a sealing body 6 that seals the opening of the case body 5. The electrode body 2, the non-aqueous electrolyte, and the like are accommodated in the case body 5. The case body 5 is, for example, a bottomed cylindrical metal exterior can, and a groove portion 5c that protrudes inward along the circumferential direction is formed in the upper portion of the case body 5. The sealing body 6 is supported by the groove portion 5c and seals the opening of the case body 5. In order to ensure the airtightness inside the battery, it is desirable to provide a gasket between the case body 5 and the sealing body 6.

[0014] The electrode body 2 shown in FIG. 2 is a wound type electrode body in which a positive electrode 11 and a negative electrode 12 are wound with a separator interposed therebetween. However, in FIG. 2, the separator disposed between the positive electrode 11 and the negative electrode 12 is not shown. The electrode body 2 shown in FIG. 2 is cylindrical, but the shape of the electrode body 2 is not limited thereto, and a flat type or the like may be used.

[0015] The negative electrode 12 includes a negative electrode current collector 14 and a negative electrode active material layer 16 formed on the negative electrode current collector 14. Note that it is desirable for the negative electrode active material layer 16 to be formed on both surfaces of the negative electrode current collector 14.

[0016] Further, the negative electrode 12 has negative electrode current collector exposed portions 14a and 14b where the negative electrode active material layer 16 is not disposed on the negative electrode current collector 14 and the negative electrode current collector 14 is exposed. The negative electrode current collector exposed portion 14a is located at the starting end of the winding of the negative electrode 12, and the negative electrode current collector exposed portion 14b is located at the ending end of the winding of the negative electrode 12. The negative electrode current collector exposed portion 14b forms the outermost peripheral surface of the electrode body 2, and by circulating more than one turn in the winding start direction (arrow L direction) from the ending end 2a of the winding of the electrode body 2, a laminated portion 17 composed of the negative electrode current collector exposed portion 14b is formed. At this time, a part of the negative electrode current collector exposed portion 14b forming the laminated portion 17 may be folded back in a direction opposite to the winding direction from the ending end of the winding of the electrode body 2. The laminated portion 17 has a structure in which the negative electrode current collector exposed portion 14b is laminated in the radial direction from the outermost peripheral surface of the electrode body 2. And the laminated portion 17 composed of the negative electrode current collector exposed portion 14b and the case body 5 are welded. The welding of the laminated portion 17 and the case body 5 is performed, for example, by irradiating a laser from the outside of the case body 5 in a state where the laminated portion 17 is in contact with the inner surface of the case body 5 after the electrode body 2 is housed in the case body 5. The type of welding is not particularly limited as long as the laminated portion 17 and the case body 5 can be welded, and examples include laser welding and electron beam welding. In terms of workability, welding strength, etc., laser welding is preferable, and it is preferable to use a semiconductor laser or a fiber laser for laser welding. A tape for fixing the ending end 2a can be adhered to the outermost peripheral surface of the electrode body 2 within a range that does not inhibit the welding of the laminated portion 17 and the case body 5.

[0017] In this way, since the laminated portion 17 composed of the exposed portion 14b of the negative electrode current collector and the case body 5 are welded, a good electrical conduction state between the exposed portion 14b of the negative electrode current collector and the case body 5 can be maintained as compared with the case where the exposed portion 14b of the negative electrode current collector simply contacts the case body 5. For example, it is possible to suppress fluctuations in the contact state between the exposed portion 14b of the negative electrode current collector and the case body 5 due to the charge state of the electrode body 2, deterioration due to use and aging, etc., and maintain a good electrical conduction state between the exposed portion 14b of the negative electrode current collector and the case body 5.

[0018] Also, since the laminated portion 17 composed of the exposed portion 14b of the negative electrode current collector and the case body 5 are welded, the following effects may be achieved. (1) For example, it is possible to ensure a good electrical conduction state without using a negative electrode tab attached to the negative electrode. Further, this enables a uniform layout of the electrode body, and it becomes difficult for local stress, performance degradation, electrode buckling, etc. to occur in the electrode. (2) For example, since the electrode body is fixed to the case body, the insulators disposed above and below the electrode body become unnecessary, and the displacement applied to the connection portion of the electrode tab becomes small, improving the vibration resistance.

[0019] The exposed portion 14b of the negative electrode current collector forms the outermost peripheral surface of the electrode body 2, and preferably orbits two or more times in the winding start direction (arrow L direction) from the winding end portion 2a of the electrode body 2, more preferably orbits five or more times, and even more preferably orbits ten or more times. Thereby, for example, the laminated portion 17 composed of the exposed portion 14b of the negative electrode current collector can be formed over the entire circumference of the side surface of the electrode body 2, and the thickness of the laminated portion 17 can be increased. And by forming the laminated portion 17 over the entire circumference of the side surface of the electrode body 2, the weldable range expands, making the welding operation easier. Further, by increasing the thickness of the laminated portion 17, the occurrence of damage to the laminated portion 17 (that is, damage to the negative electrode current collector 14) during welding is suppressed. The thickness of the laminated portion 17 is preferably, for example, 20 μm or more and 200 μm or less, and more preferably 40 μm or more and 200 μm or less, in terms of suppressing the occurrence of damage to the laminated portion 17 during welding.

[0020] Figs. 3 to 8 are schematic perspective views of a secondary battery showing a welded portion between a laminated portion formed of an exposed portion of a negative electrode current collector and a case body. When welding the laminated portion 17 and the case body 5, for example, a laser is continuously irradiated over the entire outer side surface of the case body 5, and it is preferable that the welded portion 22 between the laminated portion 17 and the case body 5 is continuously formed over the entire side surface of the case body 5. As the shape of the welded portion 22 continuously formed over the entire side surface of the case body 5, for example, an annular shape as shown in Fig. 3 or Fig. 6 (in Fig. 6, a plurality of annular welded portions 22 are formed at predetermined intervals), a spiral shape as shown in Fig. 4, etc. are exemplified. By forming the welded portion 22 between the laminated portion 17 and the case body 5 continuously over the entire side surface of the case body 5 in this way, for example, when gas is generated inside the battery case 3, gas is more likely to be discharged from the winding core portion of the electrode body 2 than from between the electrode body 2 and the case body 5, so the risk of damage to the case body 5 due to gas generation can be suppressed.

[0021] Also, for example, a laser may be irradiated at predetermined intervals over the entire outer side surface of the case body 5, and the welded portion 22 between the laminated portion 17 and the case body 5 may be formed at predetermined intervals over the entire side surface of the case body 5. As the shape of such a welded portion 22, for example, a linear shape as shown in Fig. 5, a wavy shape as shown in Fig. 7, a sawtooth shape as shown in Fig. 8, etc. are exemplified.

[0022] In the present embodiment, as described above, the negative electrode tab can be made unnecessary, but a negative electrode tab may also be used. When using a negative electrode tab, for example, it is desirable to connect one end of the negative electrode tab to the exposed portion 14a of the negative electrode current collector and connect the other end of the negative electrode tab to the bottom of the case body 5.

[0023] The negative electrode current collector 14 is made of, for example, a foil of a metal that is stable within the potential range of the negative electrode 12 such as copper. The thickness of the negative electrode current collector 14 is preferably, for example, 4 μm or more and 40 μm or less, and more preferably 8 μm or more and 40 μm or less, in terms of suppressing the occurrence of damage to the laminated portion 17 during welding.

[0024] In the non-aqueous electrolyte secondary battery 1 according to the present embodiment, the laminated portion 17 composed of the exposed portion 14b of the negative electrode current collector has been described. However, the laminated portion 17 can also be formed by attaching another metal foil to the exposed portion 14b of the negative electrode current collector. That is, the metal foil constituting the laminated portion 17 is not limited to the negative electrode current collector 14. It is preferable that the exposed portion 14b of the negative electrode current collector and the other metal foil are welded to each other. Further, it is preferable that the laminated portion 17 is disposed on the entire outer periphery of the electrode body 2.

[0025] The negative electrode active material layer 16 contains, for example, a negative electrode active material, a binder, and the like.

[0026] The negative electrode active material is not particularly limited as long as it is a material capable of occluding and releasing lithium ions. For example, carbon materials such as graphite, graphitizable carbon, easily graphitizable carbon, fibrous carbon, coke, and carbon black, metals alloyed with Li such as Si and Sn, metal compounds containing Si, Sn, etc., lithium titanium composite oxides, etc. may be used. In terms of increasing the battery capacity, the negative electrode active material preferably contains, for example, a carbon material and an Si material, and the ratio of the Si material to the total mass of the negative electrode active material is preferably 5.5% by mass or more. The Si material is, for example, SiO x (0.5 ≦ x ≦ 1.6), etc. may be mentioned.

[0027] Examples of the binder include fluororesins, PAN, polyimide resins, acrylic resins, polyolefin resins, styrene-butadiene rubber (SBR), nitrile-butadiene rubber (NBR), carboxymethyl cellulose (CMC) or its salts, polyacrylic acid (PAA) or its salts (PAA-Na, PAA-K, etc., and partially neutralized salts may also be used), polyvinyl alcohol (PVA), etc. These may be used alone or in combination of two or more.

[0028] The negative electrode 12 can be produced, for example, by preparing a negative electrode composite material slurry containing a negative electrode active material, a binder, etc., applying this negative electrode composite material slurry onto the negative electrode current collector 14 except for the region that becomes the negative electrode current collector exposed portion, drying it to form the negative electrode active material layer 16, and rolling this negative electrode active material layer.

[0029] The positive electrode 11 includes a positive electrode current collector 18 and a positive electrode active material layer 20 disposed on the positive electrode current collector 18. As shown in FIG. 2, it is desirable that the positive electrode active material layer 20 be disposed on both surfaces of the positive electrode current collector 18. Although the description in the figure is omitted, the positive electrode 11 has, for example, a positive electrode current collector exposed portion where the positive electrode active material layer 20 is not disposed on the positive electrode current collector 18 and the positive electrode current collector is exposed. Then, one end of the positive electrode tab is connected to the positive electrode current collector exposed portion, and the other end is connected to the inner wall of the sealing body 6. Thereby, the sealing body 6 becomes the positive electrode 11 terminal.

[0030] For the positive electrode current collector 18, a foil of a metal stable within the potential range of the positive electrode 11 such as aluminum, a film having the metal disposed on the surface layer, etc. can be used.

[0031] The positive electrode active material layer 20 contains, for example, a positive electrode active material, a binder, a conductive material, etc.

[0032] Examples of the positive electrode active material include lithium transition metal oxides containing transition metal elements such as Co, Mn, and Ni. The lithium transition metal oxide is, for example, Li x CoO2, Li x NiO2, Li x MnO2, Li x Co y Ni 1-y O2, Li x Co y M 1-y O z 、Li x Ni 1-y M y O z 、Li x Mn2O4, Li x Mn 2-y M yO4, LiMPO4, Li2MPO4F (M is at least one of Na, Mg, Sc, Y, Mn, Fe, Co, Ni, Cu, Zn, Al, Cr, Pb, Sb, B; 0 < x ≤ 1.2, 0 < y ≤ 0.9, 2.0 ≤ z ≤ 2.3). These may be used alone or in combination of multiple types. In terms of achieving high capacity of the battery, the cathode active material is Li x NiO2, Li x Co y Ni 1-y O2, Li x Ni 1-y M y O z (M is at least one of Na, Mg, Sc, Y, Mn, Fe, Co, Ni, Cu, Zn, Al, Cr, Pb, Sb, B; 0 < x ≤ 1.2, 0 < y ≤ 0.9, 2.0 ≤ z ≤ 2.3), etc., and preferably contains lithium nickel composite oxides.

[0033] Examples of the conductive material include carbon-based particles such as carbon black (CB), acetylene black (AB), ketjen black, and graphite. These may be used alone or in combination of two or more types.

[0034] Examples of the binder include fluorine-based resins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVdF), polyacrylonitrile (PAN), polyimide-based resins, acrylic resins, and polyolefin-based resins. These may be used alone or in combination of two or more types.

[0035] The positive electrode 11 can be manufactured, for example, by applying a positive electrode composite material slurry containing a positive electrode active material, a binder, a conductive material, etc. onto the positive electrode current collector 18, drying to form the positive electrode active material layer 20, and then rolling the positive electrode active material layer 20.

[0036] For the separator, for example, a porous sheet having ion permeability and insulation properties is used. Specific examples of the porous sheet include microporous thin films, woven fabrics, non-woven fabrics, etc. As the material of the separator, olefin resins such as polyethylene and polypropylene, cellulose, etc. are suitable. The separator may be a laminate having a cellulose fiber layer and a thermoplastic resin fiber layer such as an olefin resin. Also, a multilayer separator including a polyethylene layer and a polypropylene layer may be used, or a separator with a material such as an aramid resin or ceramic coated on the surface of the separator may be used.

[0037] The non-aqueous electrolyte includes, for example, an electrolyte salt and a non-aqueous solvent for dissolving the electrolyte salt. The electrolyte salt is preferably a lithium salt. Examples of the lithium salt include LiBF4, LiClO4, LiPF6, LiAsF6, LiSbF6, LiAlCl4, LiSCN, LiCF3SO3, LiCF3CO2, Li(P(C2O4)F4), LiPF 6-x (C n F 2n+1 ) x (1 < x < 6, n is 1 or 2), LiB 10 Cl 10 , LiCl, LiBr, LiI, lithium chloroborane, lithium lower aliphatic carboxylate, borate salts such as Li2B4O7, Li(B(C2O4)F2), imide salts such as LiN(SO2CF3)2, LiN(C1F 2l+1 SO2)(C m F 2m+1 SO2){l, m are integers of 0 or more}, etc. The lithium salt may be used alone or in combination of multiple kinds. Among these, from the viewpoints of ion conductivity, electrochemical stability, etc., it is preferable to use LiPF6. The concentration of the lithium salt is preferably 0.8 to 1.8 mol per 1 L of the non-aqueous solvent.

[0038] As the non-aqueous solvent, for example, esters, ethers, nitriles such as acetonitrile, amides such as dimethylformamide, and a mixed solvent of two or more of these can be used. The non-aqueous solvent may contain a halogen-substituted product in which at least a part of the hydrogen of these solvents is substituted with a halogen atom such as fluorine.

[0039] Examples of the above esters include cyclic carbonates such as ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate; chain carbonates such as dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), methyl propyl carbonate, ethyl propyl carbonate, methyl isopropyl carbonate; cyclic carboxylic acid esters such as γ-butyrolactone, γ-valerolactone; and chain carboxylic acid esters such as methyl acetate, ethyl acetate, propyl acetate, methyl propionate (MP), ethyl propionate, etc.

[0040] Examples of the above ethers include cyclic ethers such as 1,3-dioxolane, 4-methyl-1,3-dioxolane, tetrahydrofuran, 2-methyltetrahydrofuran, propylene oxide, 1,2-butylene oxide, 1,3-dioxane, 1,4-dioxane, 1,3,5-trioxane, furan, 2-methylfuran, 1,8-cineole, crown ether; and chain ethers such as 1,2-dimethoxyethane, diethyl ether, dipropyl ether, diisopropyl ether, dibutyl ether, dihexyl ether, ethyl vinyl ether, butyl vinyl ether, methyl phenyl ether, ethyl phenyl ether, butyl phenyl ether, pentyl phenyl ether, methoxytoluene, benzyl ethyl ether, diphenyl ether, dibenzyl ether, o-dimethoxybenzene, 1,2-diethoxyethane, 1,2-dibutoxyethane, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol dibutyl ether, 1,1-dimethoxymethane, 1,1-diethoxyethane, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, etc.

[0041] As the above-mentioned halogenated compound, it is preferable to use fluorinated cyclic carbonates such as fluoroethylene carbonate (FEC), fluorinated chain carbonates, fluorinated chain carboxylic acid esters such as methyl fluoropropionate (FMP), and the like.

Explanation of symbols

[0042] 1 Non-aqueous electrolyte secondary battery, 2 Electrode body, 2a End portion of winding end, 3 Battery case, 5 Case body, 5c Groove portion, 6 Sealing body, 11 Positive electrode, 12 Negative electrode, 14 Negative electrode current collector, 14a, 14b Exposed portions of negative electrode current collector, 16 Negative electrode active material layer, 17 Laminated portion, 18 Positive electrode current collector, 20 Positive electrode active material layer, 22 Welded portion.

Claims

1. A metal case body having an opening, A sealing body that seals the opening of the case body, A secondary battery having an electrode body housed in the case body, in which a positive electrode and a negative electrode are wound with a separator therebetween, The negative electrode has a negative electrode current collector, a negative electrode active material layer formed on the negative electrode current collector, and an exposed portion where the negative electrode active material layer is not formed and the negative electrode current collector is exposed, The exposed portion is disposed at the end of the winding of the negative electrode, The electrode body has a laminated portion in which metal foils including the exposed portion are laminated, A secondary battery in which the laminated portion and the case body are welded.

2. The secondary battery according to claim 1, wherein the laminated portion is disposed over the entire outer circumference of the outermost circumference of the electrode body.

3. The secondary battery according to claim 1, wherein the laminated portion is composed of the exposed portion that has wound more than one turn in the winding start direction from the end of the winding of the electrode body.

4. The secondary battery according to claim 3, wherein the exposed portion has wound two or more turns in the winding start direction from the end of the winding of the electrode body.

5. The secondary battery according to claim 2 or 4, wherein the laminated portion and the case body are continuously welded over the entire circumference of the side surface of the case body.

6. The secondary battery according to any one of claims 1 to 5, wherein the thickness of the laminated portion is 20 μm or more and 200 μm or less.

Images