Battery

Abstract

A battery according to the present disclosure comprises: an electrode group that includes a first electrode, a second electrode, and a separator, and that is wound in a cylindrical shape; and a tab that is connected to the first electrode. The tab has: a thin section that is formed at the winding-direction end of the electrode group; and a main section that is thicker than the thin section.

Description

battery

[0001] The present disclosure relates to batteries.

[0002]

[0003] A known non-aqueous electrolyte secondary battery, such as a lithium-ion secondary battery, includes an electrode assembly in which a positive electrode plate and a negative electrode plate are wound with a separator interposed therebetween, and an outer can containing the electrode assembly and an electrolyte. Each of the positive electrode and the negative electrode has a tab attached thereto for extracting power. For example, Patent Document 1 discloses a cylindrical battery in which an electrode winding having a circular cross section is housed in a cylindrical battery can.

[0003] Japanese Patent Application Laid-Open No. 2009-245650

[0004] In conventional non-aqueous electrolyte secondary batteries, the ends of the tabs are difficult to bend during winding, which can result in gaps around the tabs in the wound electrode assembly. If such gaps are large, this is undesirable from the viewpoint of improving the battery characteristics and safety.

[0005] The present disclosure provides techniques for reducing gaps near the ends of tabs in wound electrode groups.

[0006] The present disclosure provides a battery comprising: an electrode group including a first electrode, a second electrode, and a separator and wound into a cylindrical shape; and a tab connected to the first electrode, wherein the tab has a thin portion formed at an end in the winding direction of the electrode group, and a main portion that is thicker than the thin portion.

[0007] According to the present disclosure, it is possible to reduce gaps near the ends of the tabs in a wound electrode group.

[0008] FIG. 1 is a cross-sectional view of a battery according to an embodiment of the present disclosure. FIG. 2 is a partial plan view of a positive electrode in a state in which the electrode group is unwrapped. FIG. 3 is a partial cross-sectional view of the positive electrode taken along line III-III shown in FIG. 2. FIG. 4 is a partial cross-sectional view of a positive electrode showing another example of a positive electrode tab. FIG. 5 is a partial cross-sectional view of a positive electrode showing another example of a protective tape. FIG. 6 is a partial cross-sectional view of a positive electrode showing yet another example of a protective tape.

[0009] (Findings underlying the present disclosure) In an electrode assembly having a wound structure, a tab attached to an electrode is difficult to bend when the electrode is wound, and therefore, a gap occurs around the tab, particularly near both ends of the tab in the winding direction. This gap is, for example, a gap between the electrode plate to which the tab is attached and the separator stacked on the electrode plate. If the tab bends together with the electrode plate during winding, the gap is less likely to occur. For example, reducing the thickness of the tab makes it easier for the tab to bend, which can reduce the gap that occurs in the wound structure. However, reducing the thickness of the tab reduces the cross-sectional area of ​​the tab, which affects the resistance value of the battery.

[0010] The present disclosure provides a technology for reducing gaps near the ends of tabs in a wound electrode group by devising a tab structure to make the ends of the tabs easier to bend without making the thickness of the tabs extremely small.

[0011] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. The present disclosure is not limited to the following embodiments.

[0012] (Embodiment) FIG. 1 is a cross-sectional view of a battery according to an embodiment of the present disclosure.

[0013] The battery 100 includes a bottomed cylindrical container 1 and an electrode group 4. The electrode group 4 is housed in the container 1. The electrode group 4 has a wound structure. The electrode group 4 includes a positive electrode 5, a negative electrode 6, and a pair of separators 7. That is, the electrode group 4 is formed by stacking the positive electrode 5 and the negative electrode 6 with the separator 7 disposed between the positive electrode 5 and the negative electrode 6, and then spirally winding the stack. The electrode group 4 is impregnated with an electrolytic solution, which is a non-aqueous electrolyte. The opening of the container 1 is closed by a sealing plate 2. The positive electrode 5 includes a positive electrode current collector 5a and a positive electrode active material layer 5b. One end of a positive electrode tab 15 is connected to the positive electrode 5. The other end of the positive electrode tab 15 is connected to the back surface of the sealing plate 2. An insulating gasket 3 is disposed around the sealing plate 2. The negative electrode 6 includes a negative electrode current collector 6a and a negative electrode active material layer 6b. One end of a negative electrode tab 16 is connected to the negative electrode 6. The other end of the negative electrode tab 16 is connected to the bottom surface of the container 1. An insulating ring 8 is disposed on each of the upper and lower surfaces of the electrode group 4.

[0014] In the battery 100, the positive electrode 5 and the negative electrode 6 are the first electrode and the second electrode, respectively, that face each other. However, the position of the positive electrode 5 and the position of the negative electrode 6 may be interchanged. In this case, the positive electrode 5 and the negative electrode 6 are the second electrode and the first electrode, respectively. The technology of the present disclosure is applicable to both the positive electrode 5 and the negative electrode 6, specifically, the positive electrode tab 15 and the negative electrode tab 16.

[0015] When the electrode group 4 is unfolded and viewed in a plan view, the positive electrode 5 and the negative electrode 6 have a strip-like shape. The width of the negative electrode 6 may be wider than the width of the positive electrode 5. The outer edge of the positive electrode 5 in the width direction may overlap the negative electrode 6, or the positive electrode 5 may be contained within the negative electrode 6 in the width direction. The width of the separator 7 may be wider than the width of the positive electrode 5 and the width of the negative electrode 6. With this configuration, the safety of the battery 100 is improved.

[0016] The positive electrode current collector 5a can be a sheet or film made of a metal material such as aluminum, stainless steel, titanium, or an alloy thereof. Aluminum and its alloys are suitable materials for the positive electrode current collector 5a because they are inexpensive and easy to form into thin films. The sheet or film may be porous or non-porous. Metal foil, metal mesh, or the like may be used as the sheet or film. A carbon material such as carbon may be applied to the surface of the positive electrode current collector 5a as a conductive auxiliary material.

[0017] The positive electrode active material layer 5b contains a positive electrode active material. The positive electrode active material is not particularly limited as long as it is a material that can reversibly absorb and release lithium ions. Typically, a lithium-containing transition metal compound can be used as the positive electrode active material. Examples of the lithium-containing transition metal compound include composite oxides containing lithium and at least one element selected from the group consisting of cobalt, manganese, nickel, chromium, iron, and vanadium. Specific examples include LiCoO2, LiMnO2, LiNiO2, and LiNiO3. x M (1-x) O2 (wherein M is at least one selected from the group consisting of Co, Mn, Fe, Mg, Ti, and Al, and x satisfies 0.3≦x≦0.95), LiCrO2, αLiFeO2, LiVO2, and the like.

[0018] The positive electrode active material layer 5b may contain other materials such as a conductive additive, an ion conductor, and a binder.

[0019] The conductive additive and the ion conductor are used to reduce the resistance of the positive electrode 5. Examples of the conductive additive include carbon materials and conductive polymer compounds. Examples of the carbon materials include carbon black, graphite, acetylene black, carbon nanotubes, carbon nanofibers, graphene, fullerene, and graphite oxide. Examples of the conductive polymer compounds include polyaniline, polypyrrole, and polythiophene. Examples of the ion conductor include gel electrolytes, organic solid electrolytes, and inorganic solid electrolytes. Examples of the gel electrolyte include polymethyl methacrylate and polymethyl methacrylate. Examples of the organic solid electrolyte include polyethylene oxide. Examples of the inorganic solid electrolyte include Li7La3Zr2O 12 Examples include:

[0020] The binder is used to improve the binding property of the material constituting the positive electrode 5. As the binder, polymer materials such as polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-tetrafluoroethylene copolymer, polytetrafluoroethylene, carboxymethyl cellulose, polyacrylic acid, styrene-butadiene copolymer rubber, polypropylene, polyethylene, and polyimide can be used.

[0021] The negative electrode current collector 6a may be a sheet or film made of a metal material such as stainless steel, nickel, copper, or an alloy thereof. The sheet or film may be porous or non-porous. Examples of the sheet or film include metal foil and metal mesh. A carbon material such as carbon may be applied to the surface of the negative electrode current collector 6a as a conductive auxiliary material.

[0022] The negative electrode active material layer 6b includes a negative electrode active material. The negative electrode active material is not particularly limited as long as it is a material that can reversibly absorb and release lithium ions. Typically, a carbon material containing graphite having a graphite crystal structure can be used as the negative electrode active material. Examples of such carbon materials include natural graphite, spherical or fibrous artificial graphite, non-graphitizable carbon (hard carbon), and easily graphitizable carbon (soft carbon). Examples of materials other than carbon materials include lithium titanate. In addition, from the viewpoint of increasing the energy density of the battery 100, high-capacity materials such as silicon, tin, silicon alloys, tin alloys, silicon oxide, silicon nitride, tin oxide, and composites of silicon and carbon can also be suitably used as the negative electrode active material.

[0023] The negative electrode active material layer 6b may contain at least one selected from the group consisting of graphite and silicon as the negative electrode active material. Graphite may be the only negative electrode active material contained in the negative electrode active material layer 6b. Graphite is recommended because it is less likely to deteriorate even when repeatedly charged and discharged at a deep depth. Carbon materials other than graphite may also be used as the negative electrode active material. Silicon exhibits a larger capacity than graphite and is therefore advantageous for increasing the capacity of the battery 100.

[0024] The negative electrode active material layer 6b may contain other materials such as a conductive additive, an ion conductor, a binder, etc. Materials that can be used as the conductive additive, the ion conductor, and the binder for the positive electrode active material layer 5b can also be used for the negative electrode active material layer 6b.

[0025] The separator 7 is permeable to lithium ions. The material of the separator 7 is not particularly limited as long as it allows the passage of lithium ions. The material of the separator 7 can be at least one selected from the group consisting of a gel electrolyte, an ion exchange resin membrane, a semipermeable membrane, and a porous membrane. Making the separator 7 from these materials can adequately ensure the safety of the battery 100. Examples of gel electrolytes include gel electrolytes containing fluororesins such as PVdF. Examples of ion exchange resin membranes include cation exchange membranes and anion exchange membranes. Examples of porous membranes include porous membranes made of polyolefin resins and porous membranes containing glass paper obtained by weaving glass fibers into nonwoven fabric.

[0026] The electrolyte is a non-aqueous electrolyte impregnated into the positive electrode 5, the negative electrode 6, and the separator 7. The electrolyte may fill the internal space of the container 1. The electrolyte allows lithium ions to move between the positive electrode 5 and the negative electrode 6.

[0027] The electrolyte solution contains, for example, a non-aqueous solvent and a lithium salt.

[0028] Examples of non-aqueous solvents are cyclic carbonate ester solvents, chain carbonate ester solvents, cyclic ether solvents, chain ether solvents, cyclic ester solvents, chain ester solvents, or fluorine-containing solvents. Examples of cyclic carbonate ester solvents are ethylene carbonate, propylene carbonate, or butylene carbonate. Examples of chain carbonate ester solvents are dimethyl carbonate, ethyl methyl carbonate, or diethyl carbonate. Examples of cyclic ether solvents are tetrahydrofuran, 1,4-dioxane, or 1,3-dioxolane. Examples of chain ether solvents are 1,2-dimethoxyethane or 1,2-diethoxyethane. An example of a cyclic ester solvent is γ-butyrolactone. An example of a chain ester solvent is methyl acetate. Examples of fluorine-containing solvents are fluoroethylene carbonate, methyl fluoropropionate, fluorobenzene, fluoroethyl methyl carbonate, or fluorodimethylene carbonate. One non-aqueous solvent selected from these may be used alone, or a mixture of two or more non-aqueous solvents selected from these may be used.

[0029] Examples of lithium salts include lithium hexafluorophosphate (LiPF), lithium tetrafluoroborate (LiBF), lithium perchlorate (LiClO), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium bisperfluoroethylsulfonylimide (LiN(SO2C2F5)2), LiAsF6, LiCF3SO3, and lithium difluoro(oxalato)borate. One selected from these lithium salts may be used, or two or more may be used in combination.

[0030] The container 1 is a cylindrical container made of metal such as aluminum or stainless steel.

[0031] The electrode group 4 is wound into a cylindrical shape.

[0032] The positive electrode tab 15 and the negative electrode tab 16 are strip-shaped members. The positive electrode tab 15 is made of a metal material such as aluminum, stainless steel, titanium, or an alloy thereof. The negative electrode tab 16 is made of a metal material such as nickel, a nickel alloy, titanium, a titanium alloy, copper, or a copper alloy.

[0033] Hereinafter, an example will be described in which the first electrode in the battery of the present disclosure is a positive electrode.

[0034] Fig. 2 is a partial plan view of the positive electrode 5 in a state where the electrode group 4 is removed. Fig. 3 is a partial cross-sectional view of the positive electrode 5 taken along line III-III shown in Fig. 2.

[0035] As shown in FIG. 2 , the positive electrode tab 15 is joined to an exposed portion E of the positive electrode current collector 5a formed on at least a portion of the positive electrode 5 in the longitudinal direction. Specifically, the positive electrode tab 15 is welded to the exposed portion E and connected to the positive electrode 5 so as to protrude from the positive electrode 5. The exposed portion E is a portion of the surface of the positive electrode current collector 5a that is not covered with the positive electrode active material layer 5b, i.e., a portion where the surface of the metal constituting the positive electrode current collector 5a is exposed. The exposed portion E has a rectangular shape in a plan view. The exposed portion E is formed on at least a portion of the positive electrode 5 in the longitudinal direction, for example, in an approximately central portion. In FIG. 2 , the exposed portion E is formed over the entire length of the positive electrode 5 in the lateral direction. The positive electrode tab 15 has a first main surface S1 that is a bonding surface with the exposed portion E, and a second main surface S2 that faces the first main surface S1.

[0036] The longitudinal direction of the positive electrode 5 coincides with the winding direction of the electrode group 4. In this specification, the winding direction may be referred to as direction LD. In FIG. 2 , direction LD is the width direction of the paper. Direction LD coincides with the width direction of the positive electrode tab 15.

[0037] The exposed portion E may be formed in a portion other than the longitudinal center of the positive electrode 5, for example, near an end portion in the longitudinal direction. The exposed portion E is provided, for example, by intermittent application of a positive electrode mixture containing a positive electrode active material to a portion of the positive electrode current collector 5a.

[0038] The electrode group 4 further includes a protective tape 10 that covers the exposed portion E of the positive electrode current collector 5a and at least a portion of the positive electrode tab 15. In FIG. 2 , the protective tape 10 has a rectangular shape in a plan view and covers the exposed portion E and a portion of the positive electrode tab 15 that overlaps the exposed portion E. FIG. 2 shows a configuration example in which the protective tape 10 is attached to the positive electrode 5 so as to cover portions of the surface of the positive electrode active material layer 5b that are arranged on both sides of the exposed portion E in the longitudinal direction of the positive electrode 5, the entire portion of the positive electrode tab 15 that overlaps the exposed portion E, and the entire exposed portion E. In the electrode group 4, the main surface of the positive electrode 5 on the side where the protective tape 10 is arranged faces the main surface of the negative electrode 6 with the separator 7 interposed therebetween.

[0039] The protective tape 10 has insulating properties. A material with excellent chemical resistance, insulating properties, and processability is used for the protective tape 10. The protective tape 10 is preferably thin to avoid increasing the volume occupied by the electrode group 4. The protective tape 10 includes, for example, a substrate. The protective tape 10 may include a resin film as the substrate. Examples of resin films include those with excellent insulating properties, such as polyimide film. The protective tape 10 may be formed solely from the substrate. In this case, the protective tape 10 can be attached to the positive electrode 5 by applying heat and pressure or by heating. As another example, the protective tape 10 may further include an adhesive layer provided on at least one surface of the substrate. This configuration simplifies attachment of the protective tape. The adhesive layer may be provided on one surface or both surfaces of the substrate. Examples of adhesives that can be used in the adhesive layer include acrylic adhesives, rubber adhesives, and silicone adhesives.

[0040] Fig. 3 is a partial cross-sectional view of the positive electrode 5 taken along line III-III in Fig. 2. Fig. 3 shows the vicinity of the positive electrode tab 15. The positive electrode tab 15 has a thin portion 15b formed at the end in the direction LD, i.e., the end in the width direction of the positive electrode tab 15, and a main portion 15a that is thicker than the thin portion 15b. The main portion 15a is formed in the central region of the positive electrode tab 15 in the direction LD.

[0041] The positive electrode tab 15 further has a step portion 15c at the boundary between the main portion 15a and the thin portion 15b. Figure 3 shows an example of a configuration in which the positive electrode tab 15 has thin portions 15b1 and 15b2 at both ends in the direction LD, a step portion 15c1 at the boundary between the main portion 15a and the thin portion 15b1, and a step portion 15c2 at the boundary between the main portion 15a and the thin portion 15b2. In this specification, a step portion refers to a structure formed by a difference in height from its surroundings.

[0042] In the positive electrode tab 15, the thin portion 15b may be formed on only one of the ends in the direction LD. However, if the positive electrode tab 15 has thin portions 15b1 and 15b2 at both ends in the direction LD, the positive electrode tab 15 is more likely to bend along the positive electrode 5 during winding, which may further reduce the gap around the positive electrode tab 15 in the wound electrode group 4. In an electrode group 4 having a wound structure, the thin portion 15b may be curved along the positive electrode 5, or may be bent at a bending point located at the boundary between the step portion 15c and the thin portion 15b, for example. When the electrode group 4 is unwound, the thin portion 15b may be flat.

[0043] The thin portion 15b is formed at the end of the positive electrode tab 15 in the direction LD, over the entire longitudinal length of the positive electrode tab 15. The main portion 15a is formed in the central region of the positive electrode tab 15 in the direction LD, over the entire longitudinal length of the positive electrode tab 15. The longitudinal direction of the positive electrode tab 15 coincides with the winding axis direction.

[0044] The ratio of the length of the thin portion 15b in the direction LD to the length of the positive electrode tab 15 in the direction LD may be 10% or more and 50% or less. Here, the length of the positive electrode tab 15 in the direction LD is the width W2 of the positive electrode tab, and the length of the thin portion 15b in the direction LD is the width W1 of the thin portion 15b. The ratio may be 15% or more and 45% or less, or 20% or more and 40% or less. In other words, the thin portion 15b may be formed only in a range of 10% or more and 50% or less, 15% or more and 45% or less, or even 20% or more and 40% or less of the width W2 of the positive electrode tab 15 from the end of the positive electrode tab.

[0045] The thin portion 15b may be a rolled portion. The thin portion 15b is formed, for example, by rolling the widthwise end of the positive electrode tab. The main portion 15a may be a region of the positive electrode tab that has not been rolled. Alternatively, the main portion 15a may be a region that has been rolled to a lesser extent than the thin portion 15b. For example, the main portion 15a and the thin portion 15b may be formed simultaneously by rolling the entire positive electrode tab under conditions that form the thin portion 15b, or the main portion 15a may be formed first by rolling, and then the thin portion 15b may be formed by further rolling. Note that the method for forming the thin portion 15b is not limited to rolling. For example, the thin portion 15b may be formed by notching the positive electrode tab so that the widthwise end of the positive electrode tab is thinner.

[0046] The ratio of the thickness T1 of the thin-walled portion 15b to the thickness T2 of the main portion 15a may be 50% or less, 40% or less, 30% or less, 20% or less, or even 10% or less. The ratio may be 1% or more. In this specification, the thickness refers to the length in the stacking direction in which the respective members are stacked on top of each other.

[0047] The thin portion 15b is formed at the LD end of the positive electrode tab 15 and has a thickness of, for example, 150 μm or less. The thickness T1 of the thin portion 15b may be 10 μm or more and 140 μm or less, or 20 μm or more and 130 μm or less. The thickness T2 of the main portion 15a may be 100 μm or more and 300 μm or less, or 150 μm or more and 250 μm or less.

[0048] A step portion 15c may be provided on the second main surface S2 of the positive electrode tab 15. FIG. 3 shows a configuration example in which the step portion 15c is provided on the second main surface S2 of the positive electrode tab 15 and the step portion 15c is not present on the first main surface S1. In other words, the thin portion 15b is thinned from the second main surface S2 side of the positive electrode tab 15, and the first main surface S1 of the positive electrode tab 15 has a flat plate shape when the electrode group 4 is unwound. In this way, when the step portion 15c is provided only on the second main surface S2 of the positive electrode tab 15, a gap near the end of the tab in the wound electrode group 4, for example, a gap between the positive electrode 5 and the separator 7, can be reduced without creating a gap between the positive electrode current collector 5a and the positive electrode tab 15. The step portion 15c may have a tapered shape in which the thickness of the positive electrode tab 15 decreases from the main portion 15a side toward the thin portion 15b side. Alternatively, the step portion 15c may have a portion extending in a direction perpendicular to the main surface of the main portion 15a.

[0049] FIG. 4 is a partial cross-sectional view of a positive electrode 5 showing another example of a positive electrode tab. The positive electrode tab 25 shown in FIG. 4 has a step 25c1 at the boundary between the main portion 25a and the thin portion 25b1 and a step 25c2 at the boundary between the main portion 25a and the thin portion 25b2 on the second main surface S2 of the positive electrode tab 25, and a step 25c3 at the boundary between the main portion 25a and the thin portion 25b1 and a step 25c4 at the boundary between the main portion 25a and the thin portion 25b2 on the first main surface S1. That is, in the positive electrode tab 25, the thin portion 25b is thinned from both the first main surface S1 and the second main surface S2 of the positive electrode tab 25. This configuration also makes the end of the positive electrode tab 25 more easily bent during winding, thereby reducing gaps near the ends of the tab in the wound electrode group 4.

[0050] FIG. 5 is a partial cross-sectional view of a positive electrode 5 showing another example of a protective tape. The protective tape 20 includes a substrate 20a and an adhesive layer 20b provided on the surface of the substrate 20a. In the protective tape 20, the adhesive layer 20b is not present in a position overlapping the main portion 15a in a plan view. With the above configuration, the thickness of the protective tape 20 in a position overlapping the main portion 15a is reduced by the absence of the adhesive layer. This reduces the thickness of the positive electrode 5 while protecting the exposed portion E and the positive electrode tab 15, and can further reduce the gap near the end of the positive electrode tab 15 in the wound electrode group 4.

[0051] FIG. 6 is a partial cross-sectional view of a positive electrode 5 showing yet another example of a protective tape. The protective tape 30 includes a substrate 30a and an adhesive layer 30b provided on the surface of the substrate 30a. In the protective tape 30, the adhesive layer 30b is not present in a position overlapping the positive electrode tab 15 in a plan view. With the above configuration, the thickness of the protective tape 30 at the position overlapping the positive electrode tab 15 is reduced by the absence of the adhesive layer. This reduces the thickness of the positive electrode 5 while protecting the exposed portion E and the positive electrode tab 15, and can further reduce the gap near the end of the positive electrode tab 15 in the wound electrode group 4.

[0052] Next, an example of a method for manufacturing the battery 100 will be described.

[0053] First, the positive electrode tab 15 is prepared. The positive electrode tab 15 having the thin-walled portion 15b formed thereon is manufactured by rolling both ends of the width direction of the power output tab.

[0054] Next, the electrode group 4 is produced. Specifically, a positive electrode 5 having a positive electrode tab 15, a negative electrode 6, a separator 7, and a protective tape 10 are prepared. The protective tape 10 is attached to a predetermined position on the positive electrode 5. The positive electrode 5, the negative electrode 6, and a pair of separators 7 are stacked and wound so as to form a spirally wound electrode group 4, thereby obtaining the electrode group 4.

[0055] The positive electrode 5 is fabricated, for example, as follows: A positive electrode mixture is applied to one or both surfaces of a positive electrode current collector 5a, followed by drying and rolling. The positive electrode mixture is obtained by kneading and uniformly dispersing materials such as a positive electrode active material, a binder, and a conductive material using a dispersion medium. The positive electrode mixture is applied intermittently, for example, so as to form an exposed portion E on the surface of the positive electrode current collector 5a. The applied positive electrode mixture may be dried naturally or using a drying device. After drying, the positive electrode 5 is rolled so that the positive electrode active material layer 5b has a predetermined thickness. The rolling may be performed multiple times using a roll press, or may be performed multiple times while changing the pressing pressure of the roll press.

[0056] After rolling, a positive electrode tab 15 for taking out power is welded to the exposed portion E of the positive electrode current collector 5a.

[0057] The protective tape 10 is attached to the positive electrode 5 so as to cover the exposed portion E and the portion of the positive electrode tab 15 that overlaps the exposed portion E.

[0058] The negative electrode 6 can be produced, for example, by applying a negative electrode mixture to one or both surfaces of a negative electrode current collector 6 a, followed by drying and rolling. The negative electrode mixture is obtained by kneading and uniformly dispersing materials such as a negative electrode active material, a binder, and a conductive material using a dispersion medium.

[0059] A dry method may be used instead of the above-described wet method to form the negative electrode 6. Examples of dry film formation methods include vapor deposition, sputtering, and CVD (chemical vapor deposition).

[0060] Next, the electrode group 4 is placed in the container 1, and then an electrolyte solution is poured into the container 1. Finally, the container 1 is sealed.

[0061] Through the above steps, the battery 100 shown in FIG. 1 is obtained.

[0062] While the above description has been given using an example in which the first electrode is a positive electrode, in the battery of the present disclosure, the first electrode may be a negative electrode and the second electrode may be a positive electrode. That is, the technology of the present disclosure can also be applied to a negative electrode tab. Negative electrode tabs generally tend to be made of a hard, less flexible material, which makes the technology of the present disclosure useful. Alternatively, the curvature of the electrode assembly near the start of winding or near the center of winding is greater than that of the end of winding, so the technology of the present disclosure is particularly useful for tabs connected to the electrode assembly near the start of winding or near the center of winding.

[0063] The battery of the present disclosure is not limited to a lithium secondary battery, but may be other batteries such as a sodium secondary battery or a magnesium secondary battery.

[0064] (Other Embodiments) (Additional Notes) The above description of the embodiments discloses the following techniques.

[0065] (Technology 1) A battery comprising: an electrode group including a first electrode, a second electrode, and a separator, and wound into a cylindrical shape; and a tab connected to the first electrode, wherein the tab has a thin portion formed at an end of the tab in the winding direction of the electrode group, and a main portion that is thicker than the thin portion.

[0066] According to the above configuration, the end of the tab is easily bent during winding, and therefore, the gap near the end of the tab in the wound electrode group can be reduced while suppressing the effect on the resistance value.

[0067] (Technology 2) The battery according to Technology 1, wherein the tab further has a step portion formed at the boundary between the main portion and the thin-walled portion. This configuration makes it easier for the end of the tab to bend during winding. Therefore, it is possible to reduce the gap near the end of the tab in the wound electrode group while minimizing the effect on the resistance value.

[0068] (Technology 3) The battery according to Technology 2, wherein the first electrode includes a current collector and an active material layer, the current collector includes an exposed portion on which the active material layer is not provided, the tab is joined to the exposed portion, the tab has a first main surface having a joining surface with the exposed portion and a second main surface opposite to the first main surface, and the step portion is provided on the second main surface.

[0069] (Technology 4) The battery according to any one of Technologies 1 to 3, wherein the ratio of the thickness of the thin-walled portion to the thickness of the main portion is 50% or less. With this configuration, the end of the tab is more easily bent during winding, and the gap near the end of the tab in the wound electrode group can be made smaller.

[0070] (Technology 5) The battery according to any one of Technologies 1 to 4, wherein a ratio of the length of the thin-walled portion in the winding direction to the length of the tab in the winding direction is 10% or more and 50% or less. With this configuration, it is possible to reduce gaps near the ends of the tab in the wound electrode group while suppressing the effect on the resistance value.

[0071] (Technology 6) The battery according to any one of Technologies 1 to 5, wherein the thin-walled portion is a rolled portion. This makes it possible to easily obtain a tab for the battery of the technology of the present disclosure.

[0072] (Technology 7) The battery according to any one of Technologies 1 to 6, wherein the first electrode includes a current collector and an active material layer, the current collector includes an exposed portion where the active material layer is not provided, the tab is joined to the exposed portion, and the battery further includes a protective tape covering the exposed portion and at least a portion of the tab. The protective tape can protect the exposed portion of the current collector.

[0073] (Technology 8) The battery according to Technology 7, wherein the protective tape includes a substrate and an adhesive layer provided on the substrate, and the adhesive layer is not present in a position that overlaps the main portion of the first electrode in a plan view. With this configuration, the thickness of the protective tape at the position that overlaps the main portion of the tab is reduced, allowing the thickness of the first electrode to be reduced. This can further reduce the gap near the end of the tab in the wound electrode group.

[0074] (Technology 9) The battery according to Technology 8, wherein the pressure-sensitive adhesive layer is not present in a position of the first electrode that overlaps the tab in a plan view. This configuration can further reduce the thickness of the first electrode, thereby further reducing the gap near the end of the tab in the wound electrode group.

[0075] The technology of the present disclosure is useful for non-aqueous electrolyte secondary batteries such as lithium secondary batteries.

Claims

1. A battery comprising: an electrode group including a first electrode, a second electrode, and a separator, wound into a cylindrical shape; and a tab connected to the first electrode, wherein the tab has a thin portion formed at an end in the winding direction of the electrode group, and a main portion that is thicker than the thin portion.

2. The battery according to claim 1, wherein the tab further has a step portion formed at the boundary between the main portion and the thin portion.

3. The battery according to claim 2, wherein the first electrode includes a current collector and an active material layer, the current collector includes an exposed portion where the active material layer is not provided, the tab is joined to the exposed portion, the tab has a first main surface having a joining surface with the exposed portion and a second main surface opposite to the first main surface, and the step portion is provided on the second main surface.

4. The battery according to claim 1, wherein the ratio of the thickness of the thin-walled portion to the thickness of the main portion is 50% or less.

5. The battery according to claim 1, wherein the ratio of the length of the thin portion in the winding direction to the length of the tab in the winding direction is 10% or more and 50% or less.

6. The battery according to claim 1, wherein the thin-walled portion is a rolled portion.

7. The battery according to claim 1, wherein the first electrode includes a current collector and an active material layer, the current collector includes an exposed portion where the active material layer is not provided, the tab is joined to the exposed portion, and the battery further includes a protective tape covering the exposed portion and at least a portion of the tab.

8. The battery according to claim 7, wherein the protective tape includes a substrate and an adhesive layer provided on the substrate, and the adhesive layer is not present in a position that overlaps the main portion of the first electrode in a plan view.

9. The battery according to claim 8, wherein the adhesive layer is not present in a position of the first electrode that overlaps the tab in a plan view.

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