Secondary battery
Patent Information
- Authority / Receiving Office
- WO · WO
- Patent Type
- Applications
- Current Assignee / Owner
- PANASONIC INTELLECTUAL PROPERTY MANAGEMENT CO LTD
- Filing Date
- 2026-01-26
- Publication Date
- 2026-08-06
Smart Images
Figure JP2026002511_06082026_PF_FP_ABST
Abstract
Description
secondary battery
[0001] This invention relates to a secondary battery.
[0002] Secondary batteries, such as lithium-ion batteries, are used in a variety of applications due to their characteristics, including high capacity. A secondary battery, for example, comprises an electrode group consisting of a positive electrode, a negative electrode, and a separator wound between the positive and negative electrodes, and an outer casing that houses the electrode group.
[0003] Patent Document 1 discloses a cylindrical non-aqueous electrolyte battery in which a group of electrodes, wound so that the negative electrode ends on the outside of the positive electrode, is filled into a battery container together with an electrolyte, with a separator interposed between a long positive electrode plate and a negative electrode plate made of a metallic lithium plate, and the negative electrode plate ends on the outside of the positive electrode plate, a thin metal plate as a current collector is pressed against the end of the negative electrode plate by a convex portion, covering the outermost periphery of the electrode group via the separator on the outside of the negative electrode plate, and further, a highly convex portion is provided adjacent to the end of the negative electrode plate for press-fit conductive connection to the inner wall of the battery container.
[0004] Furthermore, Patent Document 1 discloses that the electrode group configured as described above has a winding end region at the end of the winding direction, and by placing the metal sheet configured as described above in this winding end region, the metal sheet can be sufficiently brought into contact with the inner wall of the battery container via the high-convex portion and connected. It also discloses that by connecting the metal sheet and the inner wall of the battery container via the high-convex portion, a conductive path can be formed between the electrode group and the battery container with reduced influence from the inherent resistance of the metal sheet.
[0005] Japanese Unexamined Patent Publication No. 63-45758
[0006] Incidentally, in the winding end region of the electrode group, for example, a metal thin plate or the like as described above is disposed, or an exposed portion of the positive electrode current collector provided in the positive electrode, an exposed portion of the negative electrode current collector provided in the negative electrode, or a separator is disposed. When manufacturing the electrode group, after winding a laminate of a positive electrode, a separator, and a negative electrode (hereinafter also referred to as an electrode laminate) until reaching the winding end region, while pressing with a touch roller or the like, the winding end region is brought into contact with the outer surface of the electrode laminate located further inside (on the winding axis side) (hereinafter also referred to as the inner electrode laminate).
[0007] However, as described above, after bringing the winding end region into contact with the outer surface of the inner electrode laminate while pressing with a touch roller or the like, linear winding wrinkles may be formed in the winding end region along the winding axis direction. When large winding wrinkles are formed, when the electrode group expands and contracts during charge and discharge, stress is likely to concentrate on a part of the inner electrode laminate (specifically, the part of the inner electrode laminate that contacts the winding wrinkles) starting from these winding wrinkles. In this case, due to stress concentration, a part of the inner electrode laminate may be locally deformed and the battery performance may deteriorate. Also, when fixing the winding end region to the outer surface of the inner electrode laminate using a tape, the tape may not be uniformly attached to the winding end region due to the winding wrinkles.
[0008] Therefore, an object of the present disclosure is to provide a secondary battery capable of suppressing the formation of winding wrinkles in the winding end region of the electrode group.
[0009] One aspect of the present invention relates to a secondary battery comprising an electrode group in which a strip-shaped positive electrode and a strip-shaped negative electrode are wound around a strip-shaped separator, and an outer casing for housing the electrode group. The strip-shaped positive electrode has a strip-shaped positive electrode current collector and a positive electrode mixture layer disposed on at least one surface of the strip-shaped positive electrode current collector, and the strip-shaped negative electrode has a strip-shaped negative electrode current collector and a negative electrode mixture layer disposed on at least one surface of the strip-shaped negative electrode current collector. The electrode group has a winding end region at the end of the winding direction, and the winding end region has an exposed portion of the strip-shaped positive electrode current collector, an exposed portion of the strip-shaped negative electrode current collector, or the strip-shaped separator. The winding end region has an uneven region in which at least a portion of it has a concave shape that is recessed from the outer circumferential surface of the winding end region toward the winding axis side of the electrode group, and a convex shape that is projected from the outer circumferential surface of the winding end region toward the opposite side of the winding axis side of the electrode group.
[0010] According to this disclosure, it is possible to provide a secondary battery that can suppress the formation of winding wrinkles in the winding end region of the electrode group.
[0011] This is a schematic cross-sectional view showing a part of an electrode group according to one embodiment of the present disclosure. This is a cross-sectional view showing a concave shape formed in the winding end region. This is a cross-sectional view showing a convex shape formed in the winding end region. This is a schematic cross-sectional view showing a secondary battery according to one embodiment of the present disclosure. This is a cross-sectional view showing the state before the winding end region is brought into contact with the outer surface of the inner electrode stack in a method for manufacturing a secondary battery according to one embodiment of the present disclosure. This is a cross-sectional view showing the state in which conventional method for manufacturing a secondary battery.
[0012] Hereinafter, embodiments of the present disclosure will be described with examples, but the present disclosure is not limited to the examples described below. In the following description, specific numerical values and materials may be exemplified, but other numerical values, materials, etc. may be applied as long as the effects of the present disclosure can be obtained. Note that known components may be applied to the components characteristic of the present disclosure. In this specification, when it is said "range of numerical value A to numerical value B", this range includes numerical value A and numerical value B.
[0013] In the following description, when the lower limit and the upper limit of a numerical value regarding a specific physical property or condition are exemplified, any combination of any of the exemplified lower limits and any of the exemplified upper limits can be made as long as the lower limit is not greater than the upper limit. When a plurality of materials are exemplified, unless otherwise specified, one kind may be selected and used alone, or two or more kinds may be combined and used.
[0014] The present disclosure includes combinations of matters described in two or more claims arbitrarily selected from a plurality of claims described in the appended claims. That is, as long as no technical contradiction occurs, matters described in two or more claims arbitrarily selected from a plurality of claims described in the appended claims can be combined.
[0015] [Secondary battery] The secondary battery according to an embodiment of the present disclosure includes an electrode group in which a strip-shaped positive electrode and a strip-shaped negative electrode are wound via a strip-shaped separator, and an exterior can that houses the electrode group. In the secondary battery according to an embodiment of the present disclosure, the strip-shaped positive electrode has a strip-shaped positive electrode current collector and a positive electrode mixture layer disposed on at least one surface of the strip-shaped positive electrode current collector, and the strip-shaped negative electrode has a strip-shaped negative electrode current collector and a negative electrode mixture layer disposed on at least one surface of the strip-shaped negative electrode current collector.
[0016] In the secondary battery according to the embodiment of the present disclosure, the electrode group has a winding end region at the end of the winding direction, and in the winding end region, either an exposed portion of a strip-shaped positive electrode current collector, an exposed portion of a strip-shaped negative electrode current collector, or a strip-shaped separator is arranged. In the secondary battery according to the embodiment of the present disclosure, the winding end region has an uneven region in which at least a part of it has at least one of a concave shape that is recessed toward the winding axis side of the electrode group from the outer circumferential surface of the winding end region, and a convex shape that protrudes toward the opposite side of the winding axis side of the electrode group from the outer circumferential surface of the winding end region.
[0017] In the secondary battery according to the embodiment of this disclosure, (i) the electrode group has a winding end region at the end of the winding direction, and the winding end region is provided with either an exposed portion of a strip-shaped positive electrode current collector, an exposed portion of a strip-shaped negative electrode current collector, or a strip-shaped separator; and (ii) the winding end region has an uneven region in which at least a part of it has a concave shape that is recessed from the outer circumferential surface of the winding end region toward the winding axis side of the electrode group, and a convex shape that is projected from the outer circumferential surface of the winding end region toward the opposite side of the winding axis side of the electrode group. The reasons for this will be explained below.
[0018] As a secondary battery, there is a known type that comprises an electrode group in which a strip-shaped positive electrode and a strip-shaped negative electrode are wound around a strip-shaped separator. Such an electrode group has a winding end region at the end of the winding direction, and in the winding end region, the exposed portion of the positive electrode current collector of the positive electrode, the exposed portion of the negative electrode current collector of the negative electrode, or the separator may be located. More specifically, in a laminate of a strip-shaped positive electrode, a strip-shaped negative electrode, and a strip-shaped separator (hereinafter also referred to as an electrode laminate), the components arranged in the outermost layer are configured to have larger dimensions than the components arranged inward in the winding direction. Then, at the outermost periphery of the electrode group, the winding end region is formed by the components arranged in this outermost layer. For example, when a strip-shaped negative electrode is arranged in the outermost layer of the electrode laminate, the strip-shaped negative electrode is configured to have larger dimensions than the strip-shaped positive electrode and the strip-shaped separator in the winding direction, and at the outermost periphery of the electrode group, the winding end region is formed by the exposed portion of the strip-shaped negative electrode current collector of the strip-shaped negative electrode.
[0019] When fabricating the electrode array described above, first, the electrode stack is wound up to the end of the winding region. Next, while pressing with a touch roller or the like, the end of the winding region is brought into contact with the outer surface of the electrode stack located further inside (towards the winding axis) (hereinafter also referred to as the inner electrode stack). Then, a portion of the contact area between the end of the winding region and the inner electrode stack is fixed using tape or the like. The pressing with the touch roller is performed by rolling the touch roller from the electrode stack located at the boundary with the end of the winding region toward the end of the winding region.
[0020] Because there is a large difference in thickness between the electrode stack located at the outermost periphery of the electrode group and the end-of-winding region, a large step is formed between the electrode stack at the outermost periphery and the end-of-winding region. Therefore, when pressing with a touch roller, this large step causes a large impact force toward the winding axis to be applied to the end-of-winding region at the boundary with the electrode stack at the outermost periphery when transitioning from the outermost electrode stack to the end-of-winding region. Furthermore, as mentioned above, the end-of-winding region is thinner than the electrode stack, so the pressing force per unit thickness applied to the end-of-winding region by the touch roller is much larger than the pressing force per unit thickness applied to the electrode stack. Consequently, when the touch roller transitions from the outermost electrode stack to the end-of-winding region, the pressing force per unit thickness applied in the thickness direction fluctuates rapidly. As a result, large linear winding wrinkles along the winding axis may be formed at the contact point with the inner electrode stack in the end-of-winding region. When large winding creases like those described above form in the winding end region, stress tends to concentrate in a part of the inner electrode stack (specifically, the part of the inner electrode stack that contacts the winding crease) when the electrode group expands and contracts during charging and discharging. In this case, stress concentration can cause localized deformation of a part of the inner electrode stack, potentially degrading battery performance. Furthermore, when using tape to secure the winding end region to the outer surface of the inner electrode stack, the winding creases can prevent uniform application of the tape to the winding end region.
[0021] Here, the secondary battery according to the embodiment of the present disclosure has the configurations of (i) and (ii) above. Specifically, the winding end region, formed by the exposed portion of the strip-shaped positive electrode current collector, the exposed portion of the strip-shaped negative electrode current collector, or the strip-shaped separator, has an uneven region in which at least a part of it has at least one of a concave shape that is recessed from the outer circumferential surface of the winding end region toward the winding axis side of the electrode group, and a convex shape that is projected from the outer circumferential surface of the winding end region toward the opposite side of the winding axis side of the electrode group. In this way, because the winding end region has an uneven region in at least a part of it, when a touch roller or the like is moved from the electrode stack arranged on the outermost periphery to the winding end region, even if a large impact force toward the winding axis side is applied to the winding end region, or if the pressing force per unit thickness fluctuates rapidly in the winding end region, it is thought that such a large impact force and rapid fluctuations in the pressing force per unit thickness can be dispersed or absorbed by the uneven region. This is thought to suppress the formation of large linear winding wrinkles along the winding axis at the contact point with the inner electrode laminate in the winding end region.
[0022] The configuration of the secondary battery according to the embodiment of this disclosure will be described in detail below.
[0023] (Positive Electrode) In the secondary battery according to the embodiment of this disclosure, the positive electrode is strip-shaped. The strip-shaped positive electrode comprises a strip-shaped positive electrode current collector and a positive electrode mixture layer disposed on at least one surface of the strip-shaped positive electrode current collector. The positive electrode mixture layer may be formed in the form of a film. Preferably, the strip-shaped positive electrode has an exposed portion of the strip-shaped positive electrode current collector on at least one end in the longitudinal direction.
[0024] The positive electrode mixture layer is composed of a positive electrode mixture. The positive electrode mixture contains a positive electrode active material as an essential component. The positive electrode mixture may also contain conductive materials, binders, and thickeners as optional components. As the positive electrode mixture contains a positive electrode active material as an essential component, as described above, the positive electrode mixture layer may also be called the positive electrode active material layer. The positive electrode mixture layer is arranged on at least one surface of the strip-shaped positive electrode current collector. The positive electrode mixture layer may be arranged on only one surface of the strip-shaped positive electrode current collector, or on both surfaces of the strip-shaped positive electrode current collector.
[0025] The positive electrode mixture layer can be formed by applying a positive electrode mixture slurry in which a positive electrode mixture containing particles of a positive electrode active material (essential component), a conductive material, and a binder (optional components) is dispersed in a dispersion medium onto at least one surface of a strip-shaped positive electrode current collector to obtain a coating film, and then drying this coating film. The dried coating film may be rolled if necessary. The positive electrode mixture layer may be formed on only one surface of the strip-shaped positive electrode current collector, or may be formed on both surfaces of the strip-shaped positive electrode current collector. As the dispersion medium used for preparing the positive electrode mixture slurry, for example, N-methyl-2-pyrrolidone (NMP), cyclohexanone, alcohols, ethers, etc. can be used.
[0026] The positive electrode active material is, for example, a material that can reversibly occlude and release lithium ions. The positive electrode active material may be, for example, a lithium-containing transition metal oxide. Examples of the lithium-containing transition metal oxide include lithium cobalt oxide and lithium nickel oxide, which have a layered crystal structure and are of the rock salt type.
[0027] As the positive electrode active material, for example, a composite oxide containing lithium and transition metals such as Ni, Co, and Mn can be used. Examples of such composite oxides include ａ CoO ２ Li ａ NiO ２ Li ａ MnO ２ Li ａ Co ｂ Ni １－ｂ O ２ Li ａ Co ｂ M １－ｂ O ｃ Li ａ Ni １－ｂ M ｂ O ｃ Li ａ Mn ２ O ４ Li ａ Mn ２－ｂ M ｂ O ４ LiMPO ４ Li ２MPO ４ Examples include F. However, M is at least one selected from the group consisting of Na, Mg, K, Ca, Rb, Sr, Sc, Y, Ti, Zr, V, Nb, Mn, Fe, Co, Ni, Cu, Zn, Al, Cr, Pb, Sb, and B. Also, 0 < a ≤ 1.2, 0 < b ≤ 0.9, and 2.0 ≤ c ≤ 2.3. Note that the value of a, which represents the molar ratio of lithium, increases or decreases with charging and discharging.
[0028] Among the various composite oxides mentioned above, Li ａ Ni １－ｂ M ｂ O ２ It is preferable to use a lithium nickel composite oxide represented by . However, M is at least one selected from the group consisting of Mn, Co, and Al, and 0 < a ≤ 1.2 and 0 < b < 0.7. From the viewpoint of increasing capacity, it is preferable that 0 < b < 0.2 is satisfied. Also, from the viewpoint of crystal structure stability, as M, Li containing Co and Al ａ Ni １－ｂ Co ｄ Al ｅ O ｃ , or as M, Li including Co and Mn ａ Ni １－ｂ Co ｄ Mn ｅ O ｃ This is even more preferable, where 0 < a ≤ 1.2, 0 < b < 0.2, 0 < d < 0.15, 0 < e ≤ 0.1, and b = d + e.
[0029] Examples of conductive materials include carbon black, graphite, carbon fiber, and graphene. Examples of carbon black include furnace black and acetylene black. The carbon fiber may be carbon nanotubes (CNTs) or other types of carbon fibers. The conductive material may be used alone or in combination of two or more types.
[0030] The binder may include, for example, a fluorinated polymer. Fluorinated polymers can exhibit high binding strength. A fluorinated polymer is a general term for polymers that have fluorine atoms bonded to carbon atoms that make up the main chain. Because fluorine atoms have a small atomic radius and polarizability, the carbon-fluorine bond contained in fluorinated polymers exhibits high stability. Therefore, fluorinated polymers have excellent crystallinity. As a result, fluorinated polymers also have excellent heat resistance, weather resistance, and chemical resistance.
[0031] Examples of fluorinated polymers include polyvinylidene fluoride polymers and polytetrafluoroethylene polymers, but the fluorinated polymer is not limited to these. It is preferable that the fluorinated polymer includes a polyvinylidene fluoride polymer. The polyvinylidene fluoride polymer may account for 50% or more by mass of the fluorinated polymer, or 80% or more by mass. Furthermore, all of the fluorinated polymer may be a polyvinylidene fluoride polymer; that is, 100% of the fluorinated polymer may be a polyvinylidene fluoride polymer.
[0032] Polyvinylidene fluoride polymers are fluorinated polymers containing vinylidene fluoride units. Polyvinylidene fluoride polymers can exhibit high binding strength. Because polyvinylidene fluoride polymers maintain polarity through the vinylidene fluoride units, they have a higher affinity for polar solvents such as N-methyl-2-pyrrolidone (NMP) than other fluorinated polymers.
[0033] The polyvinylidene fluoride polymer may be polyvinylidene fluoride (PVDF) or a copolymer of vinylidene fluoride and other monomers. Examples of other monomers include ethylene, propylene, tetrafluoroethylene (TFE), and hexafluoropropylene (HFP). The molar ratio of vinylidene fluoride units to total monomer units is preferably in the range of 50 to 100 mol%, and more preferably in the range of 75 to 100 mol%.
[0034] The polyvinylidene fluoride polymer may be polyvinylidene fluoride (PVDF), its modified form, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-tetrafluoroethylene copolymer, vinylidene fluoride-chlorotrifluoroethylene copolymer, or vinylidene fluoride-pentafluoropropylene copolymer. The polyvinylidene fluoride polymer may be used alone or in combination of two or more types.
[0035] Polytetrafluoroethylene polymers are fluorine-based polymers containing tetrafluoroethylene units. Polytetrafluoroethylene polymers may be polytetrafluoroethylene (PTFE) or copolymers of tetrafluoroethylene with other monomers. Examples of other monomers include ethylene, propylene, and hexafluoropropylene (HFP). The molar ratio of tetrafluoroethylene units to total monomer units is preferably in the range of 50 to 100 mol%, and more preferably in the range of 75 to 100 mol%.
[0036] The weight-average molecular weight Mw of the polyvinylidene fluoride polymer and the polytetrafluoroethylene polymer is, for example, 300,000 to 2,000,000, and may also be 500,000 to 1,500,000, or 1,000,000 to 1,500,000. This increases the strength of the positive electrode mixture layer, thereby suppressing the peeling of the positive electrode mixture layer from the positive electrode current collector. The weight-average molecular weight Mw is a polystyrene equivalent value determined by gel permeation chromatography (GPC).
[0037] The positive electrode mixture layer may contain binders other than fluorine-based polymers. Examples of other binders include styrene-butadiene copolymers and their hydrides, acrylonitrile-butadiene copolymers and their hydrides, acrylonitrile-butadiene-styrene copolymers and their hydrides, and N-vinylacetamide. The mass ratio of fluorine-based polymers in the binder is preferably 80% by mass or more, and more preferably 90% by mass or more.
[0038] Examples of thickening agents that can be used include carboxymethylcellulose (CMC) and its modified forms (including salts such as Na salts), cellulose derivatives such as methylcellulose (e.g., cellulose ethers), and saponified polymers having vinyl acetate units such as polyvinyl alcohol. The thickening agent may be used alone or in combination of two or more types.
[0039] The positive electrode mixture layer may contain a dispersant as an optional component. That is, the positive electrode mixture slurry for forming the positive electrode mixture layer may contain a dispersant. By including a dispersant in the positive electrode mixture slurry, the dispersibility of the conductive material within the slurry can be improved. Examples of dispersants include nitrile group-containing rubber, polyvinylpyrrolidone resin, and cellulose resin. Cellulose resin is also called a cellulose-based polymer. The dispersant may be used alone or in combination of two or more types.
[0040] As the positive electrode current collector, a non-porous conductive substrate (e.g., metal foil) or a porous conductive substrate (e.g., mesh, net, and perforated sheet) can be used. Examples of materials constituting the positive electrode current collector include stainless steel, aluminum, aluminum alloy, and titanium. The thickness of the positive electrode current collector is not particularly limited, but is preferably 1 to 50 μm, and more preferably 5 to 20 μm.
[0041] (Negative electrode) In the secondary battery according to the embodiment of this disclosure, the negative electrode is strip-shaped. The strip-shaped negative electrode comprises a strip-shaped negative electrode current collector and a negative electrode mixture layer disposed on at least one surface of the strip-shaped negative electrode current collector. The negative electrode mixture layer may be formed in the form of a film. Preferably, the strip-shaped negative electrode has an exposed portion of the strip-shaped negative electrode current collector on at least one end in the longitudinal direction.
[0042] The negative electrode mixture layer is composed of a negative electrode mixture. The negative electrode mixture contains a negative electrode active material as an essential component. The negative electrode mixture may also contain conductive materials, binders, and thickeners as optional components. As described above, the negative electrode mixture contains a negative electrode active material as an essential component, so the negative electrode mixture layer may also be called the negative electrode active material layer. The negative electrode mixture layer is disposed on at least one surface of the strip-shaped negative electrode current collector. The negative electrode mixture layer may be disposed on only one surface of the strip-shaped negative electrode current collector, or on both surfaces of the strip-shaped negative electrode current collector.
[0043] The negative electrode mixture layer can be formed, for example, by dispersing a negative electrode mixture slurry containing particles of negative electrode active material (essential component), a conductive material, and a binder (optional component) in a dispersion medium onto at least one surface of a strip-shaped negative electrode current collector to obtain a coating, and then drying this coating. The dried coating may be rolled if necessary. The negative electrode mixture layer may be formed on only one surface of the strip-shaped negative electrode current collector, or on both surfaces of the strip-shaped negative electrode current collector. Examples of dispersion media that can be used to prepare the negative electrode mixture slurry include N-methyl-2-pyrrolidone (NMP), cyclohexanone, alcohols, and ethers.
[0044] The negative electrode active material is, for example, a material that reversibly intercepts and releases lithium ions. The negative electrode mixture layer may contain, for example, an alloying material as the negative electrode active material. The alloying material contains a phase that reversibly forms an alloy with lithium. The phase that reversibly forms an alloy with lithium may be, for example, silicon (silicon phase).
[0045] Examples of alloying materials include Si-containing materials, Sn-containing materials, Si-Sn-Si alloys, and Sn alloys. Among these, Si-containing materials are preferred from the viewpoint of stably obtaining high capacity. Si-containing materials contain a silicon phase. Silicon can reversibly form alloys with lithium. Therefore, Si-containing materials are materials that can reversibly intercept and release lithium ions.
[0046] The Si-containing material may be a composite particle comprising a silicon phase and a matrix phase in which the silicon phase is dispersed. The matrix phase may be composed of a material having lithium-ion conductivity. For example, the matrix phase may include at least one selected from the group consisting of a silicon oxide phase and a carbon phase.
[0047] The silicon oxide phase contains Si and O. The silicon oxide phase may also contain other elements besides Si and O. The silicon oxide phase is SiO ２ It may be composed of, or it may be composed of lithium silicate, or SiO ２ It may consist of both and lithium silicate.
[0048] The composite particles, which are made of Si-containing material, specifically the composite particles comprising a silicon phase and a matrix phase in which the silicon phase is dispersed, may take any of the following forms (a) to (c).
[0049] (a) A silicon phase and silicon dioxide (SiO₂) in which the silicon phase is dispersed. ２ (b) A first composite particle containing a silicon phase and a lithium silicate phase in which the silicon phase is dispersed (c) A third composite particle containing a silicon phase and a carbon phase in which the silicon phase is dispersed
[0050] The negative electrode mixture layer may contain negative electrode active materials other than Si-containing materials. Examples of other negative electrode active materials include carbon materials, spinel-type lithium titanium oxide, and spinel-type lithium manganese oxide. Among these, it is preferable to use a carbon material as the other negative electrode active material. The carbon material may be graphite, easily graphitizable carbon (soft carbon), and difficult-to-graphitize carbon (hard carbon). Among these, it is preferable to use graphite as the carbon material because it provides stable charge-discharge characteristics and has low irreversible capacity.
[0051] Graphite refers to a carbon material in which the interplanar spacing d002 of (002) planes, as measured by X-ray diffraction, is, for example, 0.340 nm or less. Furthermore, the crystallite size L of graphite as measured by X-ray diffraction is also defined. Ｃ(002) may be, for example, 5 nm or more, 5 nm to 300 nm, or 10 nm to 200 nm. The average particle size of the graphite is, for example, 1 μm to 30 μm.
[0052] When graphite and a Si-containing material are used together as the negative electrode active material, the mass ratio of the Si-containing material to the total negative electrode active material (graphite and Si-containing material) is, for example, 1% by mass or more and 20% by mass or less. The above mass ratio may also be 3% by mass or more and 15% by mass or 3% by mass or more and 10% by mass or less. By keeping the above mass ratio within the numerical range described above, it becomes easier to achieve a good balance between improved cycle characteristics and increased capacity.
[0053] Resin materials can be used as binders. Examples of resin materials include fluororesins, polyolefin resins, polyamide resins, polyimide resins, acrylic resins, vinyl resins, and rubber-like materials. Examples of fluororesins include polytetrafluoroethylene and polyvinylidene fluoride (PVDF), examples of polyolefin resins include polyethylene and polypropylene, examples of polyamide resins include aramid resin, examples of acrylic resins include polyacrylic acid, methyl polyacrylate, and ethylene-acrylic acid copolymers, examples of vinyl resins include polyacrylonitrile and polyvinyl acetate, and examples of rubber-like materials include styrene-butadiene copolymer rubber (SBR). Polyvinylpyrrolidone and polyethersulfone may also be used as resin materials. The binder may be one of the above resin materials used alone, or two or more may be used in combination.
[0054] Examples of conductive materials that can be used include carbon compounds such as acetylene black, carbon fibers (e.g., carbon nanotubes (CNTs) and carbon fibers other than CNTs), graphene, metal fibers, and metal powders such as aluminum. Conductive materials may be used individually or in combination of two or more types.
[0055] Examples of thickening agents that can be used include carboxymethylcellulose (CMC) and its modified forms (including salts such as Na salts), cellulose derivatives such as methylcellulose (e.g., cellulose ethers), and saponified polymers having vinyl acetate units such as polyvinyl alcohol. The thickening agent may be used alone or in combination of two or more types.
[0056] As the negative electrode current collector, a non-porous conductive substrate (e.g., metal foil) or a porous conductive substrate (e.g., mesh, net, and perforated sheet) can be used. Examples of materials constituting the negative electrode current collector include stainless steel, nickel, nickel alloy, copper, and copper alloy. The thickness of the negative electrode current collector is not particularly limited, but is preferably 1 to 50 μm, and more preferably 5 to 20 μm.
[0057] (Separator) In the secondary battery according to the embodiment of this disclosure, the separator is strip-shaped. The strip-shaped separator is interposed between a strip-shaped positive electrode and a strip-shaped negative electrode. In the secondary battery according to the embodiment of this disclosure, as described above, the strip-shaped positive electrode and the strip-shaped negative electrode are wound around the strip-shaped separator to form an electrode group.
[0058] As the separator, a porous sheet having ion permeability and insulating properties can be used. As the porous sheet, for example, a thin film, woven fabric, and nonwoven fabric having microporous properties can be used. The material constituting the separator is not particularly limited, and for example, polymer materials can be used. Examples of polymer materials include polyolefin resins, polyamide resins, and cellulose. Examples of polyolefin resins include polyethylene resins, polypropylene resins, and copolymers of ethylene and propylene. The separator may contain additives (such as inorganic fillers) as needed. The thickness of the separator is not particularly limited and may be 10 μm or more, or 15 μm or more. The thickness of the separator may be 30 μm or less, or 20 μm or less.
[0059] (Electrode Group) The electrode group of the secondary battery according to the embodiment of this disclosure will be described in detail with reference to the drawings. In the secondary battery according to the embodiment of this disclosure, as shown in Figure 1, the electrode group 14 is formed by winding a strip-shaped positive electrode 11 and a strip-shaped negative electrode 12 via a separator 13. Hereinafter, the stack of the positive electrode 11, separator 13 and negative electrode 12 will also be referred to as the electrode stack. For convenience, Figure 1 shows only the electrode stack located on the outermost periphery of the electrode group 14 and the electrode stack located one turn inward (towards the winding axis). Furthermore, Figure 1 shows only half of the electrode group 14 as viewed from the winding axis direction WD.
[0060] As shown in Figure 1, the electrode group 14 has a winding end region WE at the end of the winding direction RD. In the electrode group 14, the strip-shaped positive electrode 11 has, as described above, a strip-shaped positive electrode current collector and a positive electrode mixture layer disposed on at least one surface of the strip-shaped positive electrode current collector, and the strip-shaped negative electrode 12 has, as described above, a strip-shaped negative electrode current collector and a negative electrode mixture layer disposed on at least one surface of the strip-shaped negative electrode current collector. The winding end region WE contains either an exposed portion of the strip-shaped positive electrode current collector, an exposed portion of the strip-shaped negative electrode current collector, or a strip-shaped separator. Figure 1 shows an example in which the strip-shaped negative electrode 12 is disposed in the winding end region WE. That is, in the example of Figure 1, the exposed portion of the strip-shaped negative electrode current collector is disposed in the winding end region WE.
[0061] The winding end region WE has an uneven region in which at least one of the following is formed: a concave shape CC (see Figure 2A) that is recessed from the outer circumferential surface of the winding end region WE toward the winding axis WA side of the electrode group 14, and a convex shape CV (see Figure 2B) that is projected from the outer circumferential surface of the winding end region WE toward the opposite side of the winding axis WA side of the electrode group 14. It is preferable that the winding end region WE has an uneven region in a location where winding wrinkles are likely to form. For example, in the winding end region WE, as explained above, a large impact force toward the winding axis side is likely to be applied to the boundary portion with the electrode stack arranged at the outermost periphery of the electrode group 14. It is preferable that the winding end region WE has an uneven region in a location that includes the boundary portion with the electrode stack arranged at the outermost periphery of the electrode group 14. In the winding end region WE, the location that includes the boundary portion with the electrode stack arranged at the outermost periphery of the electrode group 14 means the area from the boundary portion to 1 / 5 to 1 / 3 of the total length of the winding end region WE. On the other hand, from the viewpoint of suppressing the formation of winding wrinkles in the winding end region WE due to fluctuations (more specifically, increases) in the pressing force per unit thickness by touch rollers, etc., it is preferable that the winding end region WE has an uneven surface area throughout its entirety. Note that the uneven surface area is not shown in Figure 1.
[0062] In the winding end region WE, it is preferable that an exposed portion of a strip-shaped positive electrode current collector or an exposed portion of a strip-shaped negative electrode current collector is located, and that the uneven region is formed on the exposed portion of the strip-shaped positive electrode current collector or the exposed portion of the strip-shaped negative electrode current collector. When the outer casing also serves as the positive or negative electrode terminal, if the exposed portion of the strip-shaped positive electrode current collector or the exposed portion of the strip-shaped negative electrode current collector located in the winding end region WE is configured as described above, a sufficient conductive path can be formed between the exposed portion of the strip-shaped positive electrode current collector or the exposed portion of the strip-shaped negative electrode current collector and the inner wall surface (side inner wall surface) of the outer casing via the uneven region. It is more preferable that an exposed portion of a strip-shaped negative electrode current collector is located in the winding end region WE. Since the outer casing often also serves as the negative electrode terminal, if the exposed portion of the strip-shaped negative electrode current collector located in the winding end region WE is configured as described above, a sufficient conductive path can be formed between the exposed portion of the strip-shaped negative electrode current collector and the inner wall surface (side inner wall surface) of the outer casing via the uneven region. It is preferable to place a strip-shaped separator in the winding end region WE. In this case, the strip-shaped separator blocks electrical contact between the electrode group and the inner wall surface (side inner wall surface) of the outer casing, while allowing electrical contact between the positive and negative electrodes via the upper and lower ends of the outer casing. In other words, the secondary battery can have an end-face current collection structure.
[0063] When the exposed portion of the strip-shaped negative electrode current collector is positioned in the winding end region WE, it is preferable that at least one of the depth of the concave shape and the height of the convex shape be 10% to 90% of the thickness of the strip-shaped negative electrode current collector, and more preferably 20% to 80% of the thickness of the strip-shaped negative electrode current collector. In this case, the formation of winding wrinkles in the winding end region WE can be effectively suppressed.
[0064] When a strip-shaped separator is placed in the winding end region WE, it is preferable that at least one of the depth of the concave shape and the height of the convex shape be 10% to 90% of the thickness of the strip-shaped separator, and more preferably 20% to 80% of the thickness of the strip-shaped separator. In this case as well, the formation of winding wrinkles in the winding end region WE can be effectively suppressed.
[0065] The electrode group 14 has a laminate (i.e., electrode laminate) of a strip-shaped positive electrode 11, a strip-shaped separator 13, and a strip-shaped negative electrode 12 on the starting end side in the winding direction RD, rather than the winding end region WE. Preferably, the ratio of the thickness of the winding end region WE to the thickness of the laminate (electrode laminate) is 3% or more and 10% or less. In recent years, in order to increase the capacity of secondary batteries, the thickness of the positive electrode composite layer of the positive electrode 11 and the thickness of the negative electrode composite layer of the negative electrode 12 have been increasing. However, by keeping the ratio of the thickness of the winding end region WE to the thickness of the electrode laminate within the above range, the formation of winding wrinkles in the winding end region WE can be suitably suppressed. In other words, it is possible to achieve high capacity secondary batteries while suitably suppressing the formation of winding wrinkles in the winding end region WE.
[0066] The electrode group 14 has a laminate of a strip-shaped positive electrode 11, a strip-shaped separator 13, and a strip-shaped negative electrode 12 (i.e., an electrode laminate) located on the starting end side in the winding direction RD, rather than the winding end region WE. The winding end region WE is continuously connected to the outermost layer of the laminate, and it is preferable that the surface roughness of the uneven region in the winding end region WE is greater than the surface roughness of the outermost layer of the laminate. In this case, an uneven region that can suitably suppress the formation of winding wrinkles can be formed in the winding end region WE.
[0067] When the exposed portion of the strip-shaped negative electrode current collector is positioned in the winding end region WE, it is preferable that the winding end region WE is in contact with the inner wall surface of the outer casing. This allows for the formation of a sufficient conductive path between the exposed portion of the strip-shaped negative electrode current collector positioned in the winding end region WE and the inner wall surface (side inner wall surface) of the outer casing. In this case, the outer casing functions as a negative electrode terminal.
[0068] (Electrolyte) The secondary battery according to the embodiment of this disclosure may contain an electrolyte. The electrolyte may be a liquid electrolyte, a gel electrolyte, or a solid electrolyte. A liquid electrolyte is, for example, an electrolyte solution containing a non-aqueous solvent and a salt dissolved in the non-aqueous solvent. Such a liquid electrolyte is also called a non-aqueous electrolyte (non-aqueous electrolyte solution). The concentration of the salt in the electrolyte solution is, for example, 0.5 mol / L or more and 2.0 mol / L or less. The electrolyte solution may contain various known additives.
[0069] The gel-like electrolyte comprises a salt and a matrix polymer, or a salt, a non-aqueous solvent, and a matrix polymer. As the matrix polymer, for example, a polymer material that absorbs a non-aqueous solvent and gels is used. Examples of polymer materials include fluororesins, acrylic resins, polyether resins, and polyethylene oxide.
[0070] As the solid electrolyte, for example, known materials from all-solid-state lithium-ion secondary batteries can be used. Examples of such known materials include oxide-based solid electrolytes, sulfide-based solid electrolytes, and halide-based solid electrolytes.
[0071] Liquid non-aqueous electrolytes can be prepared, for example, by dissolving a salt in a non-aqueous solvent. The salt is an electrolyte salt that undergoes ion dissociation in the electrolyte, and may include, for example, lithium salts. Various additives may be included in the electrolyte. Electrolytes are usually used in liquid form, but their fluidity may be restricted by gelling agents or other means.
[0072] Examples of non-aqueous solvents include cyclic carbonate esters, linear carbonate esters, cyclic carboxylic acid esters, and linear carboxylic acid esters. Examples of cyclic carbonate esters include propylene carbonate (PC) and ethylene carbonate (EC). As cyclic carbonate esters, cyclic carbonate esters having unsaturated bonds, such as vinylene carbonate (VC), may be used, or cyclic carbonate esters having fluorine atoms, such as fluoroethylene carbonate (FEC), may be used. Examples of linear carbonate esters include diethyl carbonate (DEC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC). Examples of cyclic carboxylic acid esters include γ-butyrolactone (GBL) and γ-valerolactone (GVL). Examples of linear carboxylic acid esters include methyl formate, ethyl formate, propyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, and propyl propionate. Non-aqueous solvents may be used individually or in combination of two or more.
[0073] Examples of lithium salts include LiClO ４ LiBF ４ LiPF ６ LiAlCl ４ LiSbF ６ , LiSCN, LiCF ３ SO ３ LiCF ３ CO ２ LiAsF ６ LiB １０ Cl １０Examples of these include lithium lower aliphatic carboxylates, LiCl, LiBr, LiI, borates, and imide salts. Examples of borates include lithium bis(1,2-benzenediolate(2-)-O,O')borate, lithium bis(2,3-naphthalenediolate(2-)-O,O')borate, lithium bis(2,2-biphenyldiolate(2-)-O,O')borate, and lithium bis(5-fluoro-2-oleate-1-benzenesulfonic acid-O,O')borate. Examples of imide salts include lithium bisfluorosulfonylimide (LIN(FSO ２ ) ２ ), bisfluoromethanesulfonate lithium (LIN(CF ２ SO ２ ) ２ ), trifluoromethanesulfonic acid nonafluorobutanesulfonic acid lithium (LiN(CF ３ SO ２ ) (C ４ F ９ SO ２ )), and bispentafluoroethanesulfonate lithium (LiN(C) ２ F ５ SO ２ ) ２ Examples include the following. The lithium salt may be used alone or in combination of two or more types. The concentration of the lithium salt in the non-aqueous electrolyte is, for example, 0.5 mol / L or more and 2.0 mol / L or less.
[0074] The non-aqueous electrolyte may contain various known additives. Examples of additives include 1,3-propanesalton, methylbenzenesulfonate, cyclohexylbenzene, biphenyl, diphenyl ether, and fluorobenzene. Cyclic carbonate esters such as vinylene carbonate (VC) and fluoroethylene carbonate (FEC), which were exemplified as solvents, may also be used as additives.
[0075] (Outer casing) Various known outer casings (battery cases) can be used. The outer casing may include an outer can and a sealing body that seals the opening of the outer can. In this case, the outer can functions as the negative terminal, and the sealing body functions as the positive terminal. The sealing body may include a sealing plate and a gasket.
[0076] The outer casing (battery case) houses the electrode group and the electrolyte. In the secondary battery according to the embodiment of this disclosure, the electrode group consists of a positive electrode, a negative electrode, and a separator interposed between the positive and negative electrodes. The electrode group is formed by winding a laminate of the positive electrode, the negative electrode, and the separator interposed between the positive and negative electrodes. When a secondary battery has an electrode group formed by winding a laminate of the positive electrode, the separator, and the negative electrode as described above, the shape of the secondary battery is usually cylindrical.
[0077] Hereinafter, an example of a secondary battery according to one embodiment of the present disclosure will be described with reference to the drawings. The components of the example described below can be the components described above. Furthermore, the components of the example described below can be modified based on the above description. In addition, the matters described below may be applied to the above embodiment. Furthermore, in the example described below, components that are not essential to the non-aqueous electrolyte secondary battery according to the present disclosure may be omitted.
[0078] Figure 3 is a schematic longitudinal cross-sectional view showing a secondary battery according to one embodiment of the present disclosure. The secondary battery 10 shown in Figure 3 has a cylindrical shape. The secondary battery 10 includes a cylindrical battery case and an electrode group 14 and a non-aqueous electrolyte (not shown) housed in the battery case. The electrode group 14 is a wound electrode group and includes a positive electrode 11, a negative electrode 12, and a separator 13 interposed between the positive electrode 11 and the negative electrode 12. The electrode group 14 is formed by winding a laminate of the positive electrode 11, the negative electrode 12, and the separator 13. The electrode group 14 is configured as described above. Specifically, the end region of the electrode group 14 has an uneven region in which at least a part of it has a concave shape that is recessed from the outer circumferential surface of the end region toward the winding axis side of the electrode group 14, and a convex shape that protrudes from the outer circumferential surface of the end region toward the opposite side of the winding axis side of the electrode group 14.
[0079] The battery case includes a case body 15, which is a bottomed cylindrical metal container, and a sealing body 16 that seals the opening of the case body 15. A gasket 27 is placed between the case body 15 and the sealing body 16. The placement of the gasket 27 ensures that the battery case is airtight. Inside the case body 15, insulating plates 17 and 18 are placed at both ends of the electrode group 14 in the direction of the winding axis, respectively. The case body 15 has a stepped portion 21.
[0080] The sealing body 16 includes a filter 22, a lower valve body 23, an insulating member 24, an upper valve body 25, and a cap 26. The lower valve body 23 and the upper valve body 25 are connected at their respective centers. The insulating member 24 is positioned between the peripheral edge of the lower valve body 23 and the peripheral edge of the upper valve body 25. The filter 22 and the lower valve body 23 are connected at their respective peripheral edges. The upper valve body 25 and the cap 26 are connected at their respective peripheral edges. Of the components of the sealing body 16, all components except the insulating member 24 are electrically connected.
[0081] The lower valve body 23 has a ventilation hole. Therefore, if the internal pressure of the battery case rises due to abnormal heat generation or other reasons, the upper valve body 25 bulges towards the cap 26 and separates from the lower valve body 23. This disconnects the electrical connection between the lower valve body 23 and the upper valve body 25. If the internal pressure rises further, the upper valve body 25 ruptures, and gas is released through the opening formed in the cap 26.
[0082] The positive electrode 11 is electrically connected to the cap 26, which functions as a positive terminal, via the positive lead 19. The negative electrode 12 is electrically connected to the case body 15, which functions as a negative terminal, via the negative lead 20.
[0083] [Method for Manufacturing a Secondary Battery] The method for manufacturing a secondary battery according to one embodiment of this disclosure will be described below.
[0084] (First step) The first step includes a first substep of producing a strip-shaped negative electrode, a second substep of producing a strip-shaped positive electrode, and a third substep of producing an electrode group by interposing a strip-shaped separator between the strip-shaped positive electrode and the strip-shaped negative electrode.
[0085] In the first substep, a negative electrode mixture containing a negative electrode active material and a binder component is mixed with a dispersion medium to prepare a negative electrode mixture slurry. As the dispersion medium, for example, water, alcohol (e.g., ethanol), ether (e.g., tetrahydrafuran), N-methyl-2-pyrrolidone (NMP), or a mixture thereof can be used. The negative electrode active material preferably contains at least one of artificial graphite and a silicon-containing material. The negative electrode mixture may optionally contain other substances besides the negative electrode active material and binder component.
[0086] Next, a negative electrode mixture slurry is applied to at least one surface of a strip-shaped negative electrode current collector to obtain a coating film, and this coating film is dried to obtain a laminate comprising a strip-shaped negative electrode current collector and a negative electrode mixture layer disposed on at least one surface of the strip-shaped negative electrode current collector. Next, the negative electrode is manufactured by rolling this laminate. The thickness of the negative electrode mixture layer may be 3 μm or more, or 5 μm or more. The thickness of the negative electrode mixture layer may be 200 μm or less, or 150 μm or less. The strip-shaped negative electrode may be cut to a predetermined size as needed. The negative electrode mixture layer may be formed on only one side of the strip-shaped negative electrode current collector, or on both sides. The strip-shaped negative electrode has an exposed portion of the strip-shaped negative electrode current collector at at least one end in the longitudinal direction.
[0087] The second substep can be carried out in the same manner as the first substep, except that a positive electrode mixture slurry is used instead of a negative electrode mixture slurry, and a strip-shaped positive electrode current collector is used instead of a strip-shaped negative electrode current collector. The positive electrode mixture slurry contains a positive electrode active material, a binder compound (binding agent), and a conductive material as the positive electrode mixture, and further contains a dispersion medium. As the dispersion medium, those exemplified in the first substep can be used. The strip-shaped positive electrode also has an exposed portion of the strip-shaped positive electrode current collector on at least one end in the longitudinal direction.
[0088] In the third substep, as described above, an electrode group is fabricated by interposing a strip-shaped separator between a strip-shaped positive electrode and a strip-shaped negative electrode. In a method for manufacturing a secondary battery according to one embodiment of the present disclosure, the electrode group is of the wound type. The wound type electrode group is fabricated by winding a positive electrode, a negative electrode, and a separator. In other words, the electrode group is fabricated by winding a laminate of a positive electrode, a separator, and a negative electrode (electrode laminate). The electrode laminate is formed such that, at the end of the winding direction, the outermost component extends outward beyond the inner components. For example, if the outermost component is the negative electrode, the electrode laminate is formed such that, at the end of the winding direction, the negative electrode (specifically, the exposed portion of the negative electrode current collector) extends outward beyond the positive electrode and the separator. Therefore, in the third substep, the electrode group is fabricated such that it has a winding end region at the end of the winding direction. The winding end region is formed by a part of the outermost component.
[0089] The winding end region has an uneven region in which at least a portion of it has at least one of the following: a concave shape that is recessed from the outer circumferential surface of the winding end region toward the winding axis of the electrode group (see Figure 2A), and a convex shape that is projected from the outer circumferential surface of the winding end region toward the opposite side of the winding axis of the electrode group (see Figure 2B). Such an uneven region may be formed in the winding end region before the third substep, or it may be formed in the winding end region during the third substep. Before the third substep, at least a portion of the outermost layer component of the electrode stack (e.g., the negative electrode) may be subjected to at least one of embossing and debossing to form the uneven region. In the third substep, for example, after winding the electrode stack, at least a portion of the winding end region located on the end side in the winding direction may be subjected to at least one of embossing and debossing to form the uneven region. Furthermore, by applying embossing, a convex shape is formed in the winding end region that protrudes from the outer surface of the winding end region toward the opposite side of the winding axis of the electrode group, and by applying debossing, a concave shape is formed in the winding end region that is recessed from the outer surface of the winding end region toward the winding axis of the electrode group.
[0090] Furthermore, in the third substep, as shown in Figures 4A and 4B, the winding end region WE is brought into contact with the outer surface of the electrode stack (inner electrode stack) located further inward (towards the winding axis) while being pressed with a touch roller TR. Figures 4A and 4B show an example in which a strip-shaped negative electrode 12 is placed in the winding end region WE. That is, in the example of Figures 4A and 4B, the exposed portion of the strip-shaped negative electrode current collector is placed in the winding end region WE. The pressing with the touch roller TR is performed by rolling the touch roller TR towards the winding end region WE, starting from the electrode stack located at the boundary with the winding end region WE (see Figure 4A). Then, as shown in Figure 4B, after bringing the winding end region WE into contact with the outer surface of the inner electrode stack, a portion of the contact area between the winding end region WE and the inner electrode stack is fixed using tape.
[0091] In a secondary battery manufacturing method according to one embodiment of the present disclosure, since the winding end region has an uneven region as described above in at least a part of it, when the touch roller is moved from the electrode stack arranged on the outermost periphery to the winding end region WE, even if a large impact force toward the winding axis side is applied to the winding end region WE, or if the pressing force per unit thickness fluctuates rapidly in the winding end region WE, it is thought that such a large impact force and rapid fluctuations in pressing force per unit thickness can be dispersed or absorbed by the uneven region. As a result, it is thought that it is possible to suppress the formation of large linear winding wrinkles along the winding axis direction in the portion of the winding end region WE that comes into contact with the inner electrode stack.
[0092] Figure 4C shows a state in which the winding end region WE is in contact with the outer surface of the inner electrode stack in a conventional secondary battery manufacturing method. In this example, since the winding end region WE does not have an uneven surface area in at least a part of it, there is a concern that large winding wrinkles will be formed in the winding end region WE, as shown in Figure 4C.
[0093] (Second Step) In the second step, the electrode group and the non-aqueous electrolyte are housed inside the outer casing. The method for housing the electrode group and the non-aqueous electrolyte inside the outer casing is not particularly limited, and various known methods can be employed. The non-aqueous electrolyte can be prepared, for example, by dissolving predetermined components (salts, additives, etc.) in a non-aqueous solvent. The outer casing is not particularly limited, and various known outer casings can be used.
[0094] (Note) The following technologies are disclosed as described above. (Technical 1) A secondary battery comprising: an electrode group in which a strip-shaped positive electrode and a strip-shaped negative electrode are wound around a strip-shaped separator; and an outer can for housing the electrode group, wherein the strip-shaped positive electrode has a strip-shaped positive electrode current collector and a positive electrode mixture layer disposed on at least one surface of the strip-shaped positive electrode current collector; the strip-shaped negative electrode has a strip-shaped negative electrode current collector and a negative electrode mixture layer disposed on at least one surface of the strip-shaped negative electrode current collector; the electrode group has a winding end region at the end of the winding direction; the winding end region has an exposed portion of the strip-shaped positive electrode current collector, an exposed portion of the strip-shaped negative electrode current collector, or the strip-shaped separator; and the winding end region has an uneven region in which at least a part of it has a concave shape that is recessed from the outer circumferential surface of the winding end region toward the winding axis side of the electrode group, and a convex shape that is projected from the outer circumferential surface of the winding end region toward the opposite side of the winding axis side of the electrode group. (Technology 2) The winding end region is provided with an exposed portion of the strip-shaped positive electrode current collector or an exposed portion of the strip-shaped negative electrode current collector, and at least a part of the exposed portion of the strip-shaped positive electrode current collector or the exposed portion of the strip-shaped negative electrode current collector has the uneven region, as described in Technology 1. (Technology 3) The winding end region is provided with an exposed portion of the strip-shaped negative electrode current collector, as described in Technology 2. (Technology 4) The winding end region is provided with a strip-shaped separator, as described in Technology 1. (Technology 5) The depth of the concave shape and the height of the convex shape are at least 10% to 90% of the thickness of the strip-shaped negative electrode current collector, as described in Technology 3. (Technology 6) The depth of the concave shape and the height of the convex shape are at least 10% to 90% of the thickness of the strip-shaped separator, as described in Technology 4. (Technical 7) The electrode group has a laminate of the strip-shaped positive electrode, the strip-shaped separator, and the strip-shaped negative electrode on the starting end side in the winding direction of the winding end region, and the ratio of the thickness of the winding end region to the thickness of the laminate is 3% or more and 10% or less, as described in any one of Technical 1 to 6.(Technical 8) The electrode group has a laminate of the strip-shaped positive electrode, the strip-shaped separator, and the strip-shaped negative electrode on the starting end side in the winding direction from the winding end region, the winding end region is continuously connected to the outermost layer of the laminate, and the surface roughness of the uneven region of the winding end region is greater than the surface roughness of the outermost layer of the laminate, the secondary battery according to any one of Technical 1 to 7. (Technical 9) The winding end region is in contact with the inner wall surface of the outer casing, the secondary battery according to Technical 3.
[0095] Although the present invention has been described in relation to preferred embodiments at present, such disclosure should not be interpreted restrictively. Various modifications and alterations will undoubtedly become apparent to those skilled in the art in the field to which the invention pertains by reading the above disclosure. Accordingly, the appended claims should be interpreted as encompassing all modifications and alterations without departing from the true spirit and scope of the invention.
[0096] The secondary battery described herein can be used in applications where it is required to suppress the formation of winding wrinkles at the end of the winding of the electrode group.
[0097] 10: Secondary battery, 11: Positive electrode, 12: Negative electrode, 13: Separator, 14: Electrode group
Claims
1. A secondary battery comprising: an electrode group in which a strip-shaped positive electrode and a strip-shaped negative electrode are wound around a strip-shaped separator; and an outer casing for housing the electrode group, wherein the strip-shaped positive electrode has a strip-shaped positive electrode current collector and a positive electrode mixture layer disposed on at least one surface of the strip-shaped positive electrode current collector; the strip-shaped negative electrode has a strip-shaped negative electrode current collector and a negative electrode mixture layer disposed on at least one surface of the strip-shaped negative electrode current collector; the electrode group has a winding end region at the end of the winding direction; the winding end region has an exposed portion of the strip-shaped positive electrode current collector, an exposed portion of the strip-shaped negative electrode current collector, or the strip-shaped separator; and the winding end region has an uneven region in which at least a portion of it has a concave shape that is recessed from the outer circumferential surface of the winding end region toward the winding axis side of the electrode group, and a convex shape that is projected from the outer circumferential surface of the winding end region toward the opposite side of the winding axis side of the electrode group.
2. The winding end region is provided with an exposed portion of the strip-shaped positive electrode current collector or an exposed portion of the strip-shaped negative electrode current collector, wherein at least a portion of the exposed portion of the strip-shaped positive electrode current collector or the exposed portion of the strip-shaped negative electrode current collector has the uneven region, as described in claim 1.
3. The exposed portion of the strip-shaped negative electrode current collector is located in the winding end region, as described in claim 2.
4. The secondary battery according to claim 1, wherein the strip-shaped separator is arranged in the winding end region.
5. The secondary battery according to claim 3, wherein at least one of the depth of the concave shape and the height of the convex shape is 10% or more and 90% or less of the thickness of the strip-shaped negative electrode current collector.
6. The secondary battery according to claim 4, wherein at least one of the depth of the concave shape and the height of the convex shape is 10% or more and 90% or less of the thickness of the strip-shaped separator.
7. The electrode group has a laminate of the strip-shaped positive electrode, the strip-shaped separator, and the strip-shaped negative electrode on the starting end side in the winding direction of the winding end region, and the ratio of the thickness of the winding end region to the thickness of the laminate is 3% or more and 10% or less, as described in claim 1 or 2.
8. The electrode group has a laminate of the strip-shaped positive electrode, the strip-shaped separator, and the strip-shaped negative electrode on the starting end side in the winding direction from the winding end region, the winding end region is continuously connected to the outermost layer of the laminate, and the surface roughness of the uneven region of the winding end region is greater than the surface roughness of the outermost layer of the laminate, the secondary battery according to claim 1 or 2.
9. The secondary battery according to claim 3, wherein the winding end region is in contact with the inner wall surface of the outer casing.