JP5093054B2 - Secondary battery - Google Patents

Description

  The present invention relates to a secondary battery including a wound body in which a positive electrode and a negative electrode are stacked with a separator interposed therebetween and wound.

  In recent years, many portable electronic devices such as a camera-integrated VTR (Videotape Recorder), a mobile phone, and a laptop computer have appeared, and as a power source, a small, lightweight battery having a high energy density, particularly a secondary battery. Development is strongly requested. As a secondary battery that meets such requirements, for example, a lithium secondary battery using lithium as an electrode reactant has been put to practical use. Is required.

One method for increasing the capacity is, for example, increasing the amount of active material filled in the battery. For example, in a lithium secondary battery having a structure in which a positive electrode and a negative electrode each provided with an active material layer on both sides of a current collector are stacked via a separator and wound, if the thickness of the active material layer is increased, The ratio of the current collector and the separator is reduced, the active material filling amount is increased, and the capacity can be improved. However, when the thickness of the active material layer is increased, there is a problem that the active material layer is easily cracked or broken during winding. Thus, for example, it has been proposed to reduce the stress by making the thickness of the active material layer on the wound inner surface side thinner than the thickness of the active material layer on the wound outer surface side (see, for example, Patent Document 1). ).
JP-A-8-130035

  However, even if the thickness of the active material layer on the inner surface side of the winding is reduced in this way, the stress is sufficiently relieved at the winding center side where the diameter is small for the cylindrical type, and at the crease part for the rectangular type. There is a problem that cracks and fractures occur. In particular, this problem is likely to occur in the positive electrode. In particular, when a high-capacity material such as tin or silicon is used for the negative electrode, the thickness of the positive electrode active material layer is increased, which is remarkable.

  The present invention has been made in view of such problems, and an object of the present invention is to provide a secondary battery capable of suppressing the occurrence of cracks and breaks even when the thickness of the positive electrode is increased.

A first secondary battery according to the present invention includes a wound body in which a positive electrode and a negative electrode are stacked and wound with a separator interposed therebetween, and the wound body has at least one lead attached to the winding center side. A positive electrode current collector having a pair of opposing surfaces, an outer surface positive electrode active material layer provided on the winding outer surface side of the positive electrode current collector, and an inner surface positive electrode active material provided on the winding inner surface side The inner surface positive electrode active material layer is thinner than the outer surface positive electrode active material layer, and only the outer surface positive electrode active material layer is provided on the positive electrode winding center side at a position overlapping the lead. A negative electrode current collector having a pair of opposed surfaces, an outer surface negative electrode active material layer provided on the winding outer surface side of the negative electrode current collector, and a winding inner surface An inner surface negative electrode active material layer provided on the side, and the thickness of the outer surface negative electrode active material layer is Same as body or thinner than the thickness of the inner face anode active material layer, the negative electrode, as an anode active material, it comprises a CoSnC containing material comprising as constituent elements tin, cobalt and carbon, in CoSnC containing material, containing carbon The amount is 16.8% by mass or more and 24.8% by mass or less, and the half width of the diffraction peak obtained by X-ray diffraction is 1.0 ° or more.

A second secondary battery according to the present invention includes a wound body in which a positive electrode and a negative electrode are stacked and wound with a separator in between, and the wound body includes a pair of opposed bent portions and the pair of bent portions. A positive electrode current collector having a pair of opposing surfaces, and an outer surface positive electrode active material layer provided on the wound outer surface side of the positive electrode current collector, The inner surface positive electrode active material layer provided on the inner surface side of the winding, and the thickness of the inner surface positive electrode active material layer is thinner than the thickness of the outer surface positive electrode active material layer. In addition, an outer surface active material region in which only the outer surface positive electrode active material layer is provided is formed, and the negative electrode is provided on the outer surface side of the negative electrode current collector having a pair of opposing surfaces and the negative electrode current collector. The outer surface negative electrode active material layer and the inner surface negative electrode active material layer provided on the wound inner surface side, the thickness of the outer surface negative electrode active material layer is the inner surface negative electrode Same as the thickness of the material layer, or smaller than the thickness of the inner face anode active material layer, the negative electrode, as an anode active material, comprises a CoSnC containing material comprising as constituent elements tin, cobalt and carbon, in CoSnC containing material, The carbon content is 16.8% by mass or more and 24.8% by mass or less, and the half width of the diffraction peak obtained by X-ray diffraction is 1.0 ° or more.

  According to the first secondary battery of the present invention, the outer surface active material region in which only the outer surface positive electrode active material layer is provided is provided at a position overlapping the lead on the winding center side of the positive electrode. According to the second secondary battery of the present invention, since the outer surface active material region is provided in the bent portion on the winding center side of the positive electrode, the step due to the lead or the bending in the bent portion is not caused by the outer surface positive electrode active material layer. Therefore, the influence on the inner surface positive electrode active material layer can be reduced. Moreover, according to the first and second secondary batteries of the present invention, the negative electrode includes a CoSnC-containing material as a negative electrode active material, and the content of carbon in the CoSnC-containing material is 16.8% by mass or more and 24.8% by mass. %, And the half-value width of the diffraction peak obtained by X-ray diffraction is 1.0 ° or more, so that high energy density can be obtained and excellent cycle characteristics can be obtained. Therefore, even if the thickness of the positive electrode is increased, the capacity and cycle characteristics can be improved while suppressing the occurrence of cracks and breaks on the winding center side.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

(First embodiment)
FIG. 1 shows the configuration of the secondary battery according to the first embodiment of the present invention. This secondary battery is a so-called cylindrical type, and has a wound body 20 inside a substantially hollow cylindrical battery can 11. The battery can 11 is made of, for example, iron (Fe) plated with nickel (Ni), and has one end closed and the other end open. Inside the battery can 11, a pair of insulating plates 12 and 13 are arranged perpendicular to the winding peripheral surface so as to sandwich the wound body 20.

  At the open end of the battery can 11, a battery lid 14, a safety valve mechanism 15 provided inside the battery lid 14 and a heat sensitive resistance element (Positive Temperature Coefficient; PTC element) 16 are interposed via a gasket 17. It is attached by caulking, and the inside of the battery can 11 is sealed. The battery lid 14 is made of, for example, the same material as the battery can 11. The safety valve mechanism 15 is electrically connected to the battery lid 14 via the heat sensitive resistance element 16, and the disk plate 15A is reversed when the internal pressure of the battery exceeds a certain level due to an internal short circuit or external heating. Thus, the electrical connection between the battery lid 14 and the wound body 20 is cut off. When the temperature rises, the heat sensitive resistance element 16 limits the current by increasing the resistance value and prevents abnormal heat generation due to a large current. The gasket 17 is made of, for example, an insulating material, and asphalt is applied to the surface.

  FIG. 2 shows a cross-sectional structure taken along line II-II of the wound body 20 shown in FIG. The wound body 20 is formed by laminating a belt-like positive electrode 21 and a belt-like negative electrode 22 with a separator 23 therebetween and winding them into a cylindrical shape, and a center pin 24 is inserted in the center. In FIG. 2, the separator 23 is omitted. A lead 25 made of aluminum (Al) or the like is connected to the positive electrode 21, and a lead 26 made of nickel or the like is connected to the negative electrode 22. The lead 25 is electrically connected to the battery lid 14 by being attached to the safety valve mechanism 15, and the lead 26 is attached to and electrically connected to the battery can 11.

  The positive electrode 21 includes, for example, a positive electrode current collector 21A having a pair of opposed surfaces, an outer surface positive electrode active material layer 21B provided on the outer surface of the positive electrode current collector 21A, and a wound inner surface of the positive electrode current collector 21A. And an inner surface positive electrode active material layer 21 </ b> C provided on the side. The positive electrode 21 is formed with a double-sided active material region 21D in which an outer-side positive-electrode active material layer 21B and an inner-side positive-electrode active material layer 21C are provided on both sides, and the inner-side positive-electrode active material layer is larger than the thickness of the outer-side positive-electrode active material layer 21B. The thickness of 21C is thinner. This is because the inner surface positive electrode active material layer 21 </ b> C is more susceptible to stress and is more likely to crack or break. The outer surface positive electrode active material layer 21B has a thickness T21B, the inner surface positive electrode active material layer 21C has a thickness T21C, and the outer surface positive electrode active material layer 21B and the inner surface positive electrode active material layer 21C have a total thickness T21 = T21B + T21C. The thickness T21B of the layer 21B is preferably in the range of 0.5 × T21 <T21B <0.6 × T21, for example, and the thickness T21C of the inner surface positive electrode active material layer 21C is, for example, 0.4 × T21 <T21C <0. Within the range of 5 × T21 is preferable. This is because in such a range, the capacity can be improved while suppressing cracks and breakage.

  The porosity of the outer surface positive electrode active material layer 21B and the inner surface positive electrode active material layer 21C is preferably in the range of 20% to 27%. In such a range, it is possible to maintain a high capacity even when cracks and fractures are suppressed and the capacity is improved, and even when a higher load current is output.

  The porosity (%) is a value obtained by subtracting the filling rate (%) from 100. This filling rate is the ratio of the volume of the material (positive electrode active material, etc.) constituting them in the volume of the outer surface positive electrode active material layer 21B and the inner surface positive electrode active material layer 21C. For example, the filling rate is obtained from the volume of the outer surface positive electrode active material layer 21B and the inner surface positive electrode active material layer 21C per unit weight and the volume of material per unit weight (total volume of the positive electrode active material and the like). The former volume is expressed by the reciprocal (unit weight) of the volume density. The latter volume is calculated from the ratio and true density of each material. For example, when each material is a positive electrode active material, a conductive material, and a binder, when the ratio of the positive electrode active material + the ratio of the conductive material + the ratio of the binder = 1 (the ratio of the positive electrode active material / The true density of the positive electrode active material) + (the ratio of the conductive material / the true density of the conductive material) + (the ratio of the binder / the true density of the binder).

  On the winding center side of the positive electrode 21, for example, a double-sided exposed region 21E where both surfaces of the positive electrode current collector 21A are exposed without the outer surface positive electrode active material layer 21B and the inner surface positive electrode active material layer 21C being formed. The lead 25 is attached. Further, on the winding center side of the positive electrode 21, an outer surface active material region 21F in which only the outer surface positive electrode active material layer 21B is provided is formed between the double-sided exposed region 21E and the double-sided active material region 21D. The outer surface active material region 21F is formed at least at a position overlapping the lead 25, and the step generated by the lead 25 is relaxed by the outer surface positive electrode active material layer 21B so as to reduce the influence on the inner surface positive electrode active material layer 21C. It has become.

  That is, as shown in FIG. 3, the double-sided active material region 21 </ b> D is bent at a position where it overlaps the lead 25, and a step 21 </ b> G is generated. At this time, by providing the outer surface active material region 21F, the diameter from the winding center of the wound body 20 to the double-sided active material region 21D increases as the thickness of the outer surface positive electrode active material layer 21B of the outer surface active material region 21F increases. growing. As a result, the bending angle θ of the step 21G increases, and the stress is relieved.

  Note that a double-sided exposed region 21H where both sides of the positive electrode current collector 21A are exposed may be formed on the winding outer peripheral side of the positive electrode 21 as necessary, and although not shown, the inner surface positive electrode active material layer 21C The inner surface active material region provided only with the first electrode may be formed.

The positive electrode current collector 21A is made of, for example, a metal foil such as aluminum, nickel, or stainless steel. The outer surface positive electrode active material layer 21B and the inner surface positive electrode active material layer 21C include, for example, any one or more of positive electrode materials capable of occluding and releasing lithium, which is an electrode reactant, as a positive electrode active material, A conductive material and a binder may be included as necessary. The positive electrode material capable of inserting and extracting lithium does not contain lithium such as titanium sulfide (TiS ₂ ), molybdenum sulfide (MoS ₂ ), niobium selenide (NbSe ₂ ), or vanadium oxide (V ₂ O ₅ ). Examples thereof include metal chalcogenides or lithium-containing compounds containing lithium.

Among these, lithium-containing compounds are preferable because some compounds can obtain a high voltage and a high energy density. Examples of such a lithium-containing compound include a composite oxide containing lithium and a transition metal element, or a phosphate compound containing lithium and a transition metal element. In particular, cobalt (Co), nickel, manganese (Mn And those containing at least one of iron. This is because a higher capacity can be obtained. The chemical formula is represented by, for example, Li _x MIO ₂ or Li _y MIIPO ₄ . In the formula, MI and MII represent one or more transition metal elements. The values of x and y vary depending on the charge / discharge state of the secondary battery, and are generally 0.05 ≦ x ≦ 1.10 and 0.05 ≦ y ≦ 1.10.

Specific examples of the composite oxide containing lithium and a transition metal element include lithium cobalt composite oxide (Li _x CoO ₂ ), lithium nickel composite oxide (Li _x NiO ₂ ), and lithium nickel cobalt composite oxide (Li _x Ni _1-z Co _z O ₂ (z <1)) or lithium manganese composite oxide (LiMn ₂ O ₄ ) having a spinel structure. Specific examples of the phosphate compound containing lithium and a transition metal element include, for example, a lithium iron phosphate compound (LiFePO ₄ ) or a lithium iron manganese phosphate compound (LiFe _1-v Mn _v PO ₄ (v <1)). Can be mentioned.

  The negative electrode 22 includes, for example, a negative electrode current collector 22A having a pair of opposing surfaces, an outer negative electrode active material layer 22B provided on the outer surface of the negative electrode current collector 22A, and a wound inner surface of the negative electrode current collector 22A. And an inner surface negative electrode active material layer 22C provided on the side. Similarly to the positive electrode 21, the negative electrode 22 has a double-sided active material region 22 </ b> D in which an outer surface negative electrode active material layer 22 </ b> B and an inner surface negative electrode active material layer 22 </ b> C are provided on both sides. The layer 22B is disposed to face the inner surface positive electrode active material layer 21C, and the inner surface negative electrode active material layer 22C is disposed to face the outer surface cathode active material layer 21B. The outer surface negative electrode active material layer 22B may have the same thickness as the inner surface negative electrode active material layer 22C, but is preferably thinner than the inner surface negative electrode active material layer 22C. Since the outer surface negative electrode active material layer 22B faces the inner surface positive electrode active material layer 21C, the capacity per unit area may be smaller than that of the inner surface negative electrode active material layer 22C. This is because the capacity can be improved.

  On the winding center side of the negative electrode 22, a double-sided exposed region 22 </ b> E in which both surfaces of the negative electrode current collector 22 </ b> A are exposed without the outer negative electrode active material layer 22 </ b> B and the inner negative electrode active material layer 22 </ b> C is formed as necessary. May be. Further, on the winding center side of the negative electrode 22, a single-sided region 22F in which only the outer-surface negative electrode active material layer 22B or the inner-surface negative electrode active material layer 22C is provided between the double-sided exposed region 22E and the double-sided active material region 22D is formed. May be.

  On the winding outer peripheral side of the negative electrode 22, for example, a double-sided exposed region 22G where both surfaces of the negative electrode current collector 22A are exposed is formed, and a lead 26 is attached. Further, although not shown, an inner surface active material region in which only the inner surface negative electrode active material layer 22C is provided may be formed on the winding outer peripheral side of the negative electrode 22.

  The anode current collector 22A is made of, for example, a metal foil such as copper (Cu), nickel, or stainless steel. The outer surface negative electrode active material layer 22B and the inner surface negative electrode active material layer 22C include, for example, any one or more of negative electrode materials capable of occluding and releasing lithium as an electrode reactant as a negative electrode active material, A conductive material and a binder may be included as necessary. Examples of the anode material capable of inserting and extracting lithium include carbon materials such as natural graphite, artificial graphite, non-graphitizable carbon, and graphitizable carbon, or metal elements and metalloid elements capable of forming an alloy with lithium. The thing containing at least 1 sort (s) of them as a structural element is also mentioned.

  Among these, it is preferable to use a negative electrode material containing such a metal element or metalloid element as a constituent element because the capacity can be improved. The negative electrode material may be a single element, alloy or compound of a metal element or metalloid element, or may have at least a part of one or more of these phases. In the present invention, alloys include those containing one or more metal elements and one or more metalloid elements in addition to those composed of two or more metal elements. Moreover, the nonmetallic element may be included. There are structures in which a solid solution, a eutectic (eutectic mixture), an intermetallic compound, or two or more of them coexist.

  Examples of metal elements or metalloid elements constituting the negative electrode material include magnesium (Mg), boron (B), aluminum, gallium (Ga), indium (In), silicon (Si), germanium (Ge), and tin (Sn). ), Lead (Pb), bismuth (Bi), cadmium (Cd), silver (Ag), zinc (Zn), hafnium (Hf), zirconium (Zr), yttrium (Y), palladium (Pd) or platinum (Pt) Among them, silicon or tin is preferable.

  In particular, the negative electrode material is preferably a CoSnC-containing material containing tin, cobalt, and carbon (C) as constituent elements, or a FeSnC-containing material containing tin, iron, and carbon as constituent elements. This is because a high energy density can be obtained and excellent cycle characteristics can be obtained. The content of carbon in the CoSnC-containing material is preferably 16.8% by mass or more and 24.8% by mass or less, and the ratio of cobalt to the total of tin and cobalt is preferably 30% by mass or more and 45% by mass or less. The carbon content in the FeSnC-containing material is 11.9 mass% or more and 29.7 mass% or less, and the ratio of iron to the total of tin and iron is 26.4 mass% or more and 48.5 mass% or less. Is preferred. This is because higher characteristics can be obtained within this range.

  Further, these CoSnC-containing material and FeSnC-containing material may further contain other constituent elements as necessary. If it is a CoSnC-containing material, for example, silicon, iron, nickel, chromium (Cr), indium, niobium (Nb), germanium, titanium (Ti), molybdenum (Mo), aluminum, phosphorus (P), gallium or bismuth may be used. Preferably, 2 or more types may be included. In the case of a FeSnC-containing material, for example, at least one member selected from the group consisting of aluminum, titanium, vanadium (V), chromium, niobium, and tantalum (Ta), and cobalt, nickel, copper, zinc, gallium, and indium. At least one member of the group is preferred, and silver is also preferred.

  This CoSnC-containing material has a phase containing tin, cobalt, and carbon, and this phase preferably has a low crystallinity or an amorphous structure. Similarly, the FeSnC-containing material has a phase containing tin, iron, and carbon, and this phase preferably has a low crystallinity or an amorphous structure. In the CoSnC-containing material and the FeSnC-containing material, it is preferable that at least a part of carbon that is a constituent element is bonded to a metal element or a metalloid element that is another constituent element. The decrease in cycle characteristics is thought to be due to the aggregation or crystallization of tin or the like, but this is because such aggregation or crystallization can be suppressed by combining carbon with other elements. .

  The separator 23 separates the positive electrode 21 and the negative electrode 22 and allows lithium ions to pass through while preventing a short circuit of current due to contact between the two electrodes. The separator 23 is made of, for example, a porous film made of synthetic resin made of polytetrafluoroethylene, polypropylene, polyethylene, or the like, or a porous film made of ceramic, and these two or more kinds of porous films are laminated. It may be a structure.

For example, the separator 23 is impregnated with an electrolytic solution. The electrolytic solution includes, for example, a solvent and an electrolyte salt. Examples of the solvent include ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, 1,2-dimethoxyethane, 1,2-diethoxyethane, γ-butyrolactone, γ-valerolactone, tetrahydrofuran, 2- Methyltetrahydrofuran, 1,3-dioxolane, 4-methyl-1,3-dioxolane, 1,3-dioxol-2-one, 4-vinyl-1,3-dioxolan-2-one, 4-fluoro-1,3 -Non-aqueous solvents such as dioxolan-2-one, diethyl ether, sulfolane, methyl sulfolane, acetonitrile, propionitrile, anisole, acetate, butyrate, propionate, fluorobenzene, or ethylene sulfite. Examples of the electrolyte salt include LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAsF ₆ , LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ , LiC (CF ₃ SO ₂ ) ₃ , LiB ( Examples thereof include lithium salts such as C ₆ H ₅ ) ₄ , LiB (C ₂ O ₄ ) ₂ , LiCF ₃ SO ₃ , LiCH ₃ SO ₃ , LiCl, or LiBr. As the solvent and the electrolyte salt, one kind may be used alone, or two or more kinds may be mixed and used.

  For example, the secondary battery can be manufactured as follows.

  First, the positive electrode 21 is manufactured by forming the outer surface positive electrode active material layer 21B and the inner surface positive electrode active material layer 21C on the positive electrode current collector 21A. The outer surface positive electrode active material layer 21B and the inner surface positive electrode active material layer 21C were, for example, mixed with a positive electrode active material, a conductive material, and a binder, dispersed in a dispersion medium, applied to the positive electrode current collector 21A, and dried. After that, it is formed by compression molding. Similarly to the positive electrode 21, the negative electrode current collector 22 </ b> A is formed with the outer-surface negative electrode active material layer 22 </ b> B and the inner-surface negative electrode active material layer 22 </ b> C to produce the negative electrode 22. At that time, the thickness and positional relationship of the outer surface positive electrode active material layer 21B, the inner surface positive electrode active material layer 21C, the outer surface positive electrode active material layer 21B, and the inner surface positive electrode active material layer 21C are adjusted as described above. Next, the lead 25 is attached to the positive electrode current collector 21A by welding or the like, and the lead 26 is attached to the negative electrode current collector 22A by welding or the like.

  Subsequently, the positive electrode 21 and the negative electrode 22 are wound with the separator 23 therebetween, and the center pin 24 is inserted in the center. At this time, according to the present embodiment, the inner surface positive electrode active material layer 21C is made thinner than the outer surface positive electrode active material layer 21B, and only the outer surface positive electrode active material layer 21B is provided. Since it arrange | positions so that it may overlap with the lead | read | reed 25 and the level | step difference of the lead | read | reed 25 is eased, it is suppressed that a crack and a fracture | rupture generate | occur | produce in the inner surface positive electrode active material layer 21C. Thereafter, the tip of the lead 25 is welded to the safety valve mechanism 15, and the tip of the lead 26 is welded to the battery can 11, and the wound positive electrode 21 and negative electrode 22 are sandwiched between the pair of insulating plates 12 and 13. The can 11 is stored inside. Next, an electrolytic solution is injected into the battery can 11 and impregnated in the separator 23. After that, the battery lid 14, the safety valve mechanism 15, and the heat sensitive resistance element 16 are fixed to the opening end of the battery can 11 by caulking through a gasket 17. Thereby, the secondary battery shown in FIGS. 1 and 2 is completed.

  Thus, according to the present embodiment, the thickness of the inner surface positive electrode active material layer 21C is made thinner than that of the outer surface positive electrode active material layer 21B, and the outer surface positive electrode active material layer 21B is located at the position overlapping the lead 25 on the winding center side. Since the outer surface active material region 21F provided only with the lead 25 is provided and the step due to the lead 25 is relaxed, the occurrence of cracks and breakage can be suppressed even if the thickness of the positive electrode 21 is increased. Thus, the capacity can be improved.

(Second Embodiment)
FIG. 4 shows the configuration of the secondary battery according to the second embodiment of the present invention. This secondary battery is a so-called laminate film type, in which a wound body 30 to which leads 31 and 32 are attached is accommodated in a film-like exterior member 40.

  The leads 31 and 32 are led out from the inside of the exterior member 40 to the outside, for example, in the same direction. The leads 31 and 32 are made of a metal material such as aluminum, copper, nickel, or stainless steel, respectively, and have a thin plate shape or a mesh shape, respectively.

  The exterior member 40 is made of, for example, a rectangular aluminum laminated film in which a nylon film, an aluminum foil, and a polyethylene film are bonded together in this order. The exterior member 40 is disposed, for example, so that the polyethylene film side and the winding 30 are opposed to each other, and the outer edge portions are in close contact with each other by fusion or an adhesive. An adhesion film 41 for preventing the entry of outside air is inserted between the exterior member 40 and the leads 31 and 32. The adhesion film 41 is made of a material having adhesion to the leads 31 and 32, for example, a polyolefin resin such as polyethylene, polypropylene, modified polyethylene, or modified polypropylene.

  The exterior member 40 may be made of a laminated film having another structure, a polymer film such as polypropylene, or a metal film instead of the above-described aluminum laminated film.

  FIG. 5 shows a cross-sectional structure taken along line VV of the wound body 30 shown in FIG. The wound body 30 is formed by laminating a positive electrode 33 and a negative electrode 34 with a separator 35 and an electrolyte layer 36 interposed therebetween, and is wound. The outermost peripheral portion is protected by a protective tape 37. Further, the wound body 30 has a flat shape including a pair of opposed bent portions 30A and a flat portion 30B between the pair of bent portions 30A.

  The positive electrode 33 has a structure in which an outer surface positive electrode active material layer 33B is provided on the winding outer surface side of the positive electrode current collector 33A, and an inner surface positive electrode active material layer 33C is provided on the winding inner surface side. The configurations of the positive electrode current collector 33A, the outer surface positive electrode active material layer 33B, and the inner surface positive electrode active material layer 33C are the same as the positive electrode current collector 21A, the outer surface positive electrode active material layer 21B, and the inner surface positive electrode active material layer 21C in the first embodiment. It is the same.

  That is, the positive electrode 33 is formed with a double-sided active material region 33D in which an outer surface positive electrode active material layer 33B and an inner surface positive electrode active material layer 33C are provided on both surfaces, and the inner surface positive electrode active material is larger than the thickness of the outer surface positive electrode active material layer 33B. The thickness of the material layer 33C is thinner. The thickness of the outer surface positive electrode active material layer 33B and the thickness of the inner surface positive electrode active material layer 33C are the same as the thickness of the outer surface positive electrode active material layer 21B and the thickness of the inner surface positive electrode active material layer 21C in the first embodiment. The porosity of the outer surface positive electrode active material layer 33B and the inner surface positive electrode active material layer 33C is also the same as that of the outer surface positive electrode active material layer 21B and inner surface positive electrode active material layer 21C in the first embodiment.

  On the winding center side of the positive electrode 33, a double-sided exposed region 33E where both surfaces of the positive electrode current collector 33A are exposed without the outer surface positive electrode active material layer 33B and the inner surface positive electrode active material layer 33C being formed is formed. 31 is attached. On the winding center side of the positive electrode 33, an outer surface active material region 33F in which only the outer surface positive electrode active material layer 33B is provided is formed between the double-sided exposed region 33E and the double-sided active material region 33D.

  The outer surface active material region 33F is formed at least in the bent portion 30A, and the bending generated by the bent portion 30A is relaxed by the outer surface positive electrode active material layer 33B, and the influence on the inner surface positive electrode active material layer 33C is reduced. ing.

  That is, as shown in FIG. 6, the double-sided active material region 33D is bent at the bent portion 30A. At this time, by providing the outer surface active material region 33F, the diameter from the winding center of the bent portion 30A to the double-sided active material region 33D increases as the thickness of the outer surface positive electrode active material layer 33B of the outer surface active material region 33F increases. Become. As a result, the bending angle θ of the bent portion 30A increases, and the stress is relieved.

  The negative electrode 34 has a structure in which an outer surface negative electrode active material layer 34B is provided on the winding outer surface side of the negative electrode current collector 34A, and an inner surface negative electrode active material layer 34C is provided on the winding inner surface side. Similarly to the positive electrode 33, the negative electrode 34 has a double-sided active material region 34 </ b> D in which an outer-surface negative electrode active material layer 34 </ b> B and an inner-surface negative electrode active material layer 34 </ b> C are provided on both surfaces. The negative electrode current collector 34A, the outer surface negative electrode active material layer 34B, and the inner surface negative electrode active material layer 34C are the same as the negative electrode current collector 22A, outer surface negative electrode active material layer 22B, and inner surface negative electrode active material layer 22C in the first embodiment. It is configured.

  A double-sided exposed region 34E where both surfaces of the negative electrode current collector 34A are exposed may be provided on the winding outer peripheral side of the negative electrode 34 as necessary. Further, an inner surface active material region 34 </ b> F in which only the inner surface negative electrode active material layer 34 </ b> C is provided is provided on the winding outer peripheral side of the negative electrode 34.

  On the winding center side of the negative electrode 34, for example, a double-sided exposed region 34G where both surfaces of the negative electrode current collector 34A are exposed without the outer negative electrode active material layer 34B and the inner negative electrode active material layer 34C being formed. The lead 32 is attached. Further, on the winding center side of the negative electrode 34, although not shown, only one side of the outer surface negative electrode active material layer 34B or the inner surface negative electrode active material layer 34C provided between the double-sided exposed region 34G and the double-sided active material region 34D. A region may be formed.

  The separator 35 is configured in the same manner as the separator 23 in the first embodiment.

  The electrolyte layer 36 includes an electrolytic solution and a polymer compound serving as a holding body that holds the electrolytic solution, and has a so-called gel shape. The gel electrolyte is preferable because it can obtain high ionic conductivity and prevent leakage of the secondary battery. The configuration of the electrolytic solution is the same as that of the first embodiment. Examples of the polymer compound include, for example, an ether polymer compound such as polyethylene oxide or a crosslinked product containing polyethylene oxide, an ester polymer compound such as polymethacrylate, or an acrylate polymer compound, or polyvinylidene fluoride or vinylidene fluoride. Examples thereof include polymers of vinylidene fluoride such as a copolymer with hexafluoropropylene, and any one of these or a mixture of two or more thereof is used. In particular, from the viewpoint of redox stability, it is desirable to use a fluorine-based polymer compound such as a vinylidene fluoride polymer.

  For example, the secondary battery can be manufactured as follows.

  First, the positive electrode 33 and the negative electrode 34 are produced in the same manner as in the first embodiment described above, and a precursor solution containing an electrolytic solution, a polymer compound, and a mixed solvent is applied to each of the positive electrode 33 and the negative electrode 34. Then, the mixed solvent is volatilized to form the electrolyte layer 36. Next, the lead 31 is attached to the positive electrode current collector 33A, and the lead 32 is attached to the negative electrode current collector 34A. Subsequently, the positive electrode 33 and the negative electrode 34 on which the electrolyte layer 36 is formed are laminated via a separator 35 to form a laminated body, and then the laminated body is wound in the longitudinal direction, and the protective tape 37 is attached to the outermost peripheral portion. The wound body 30 is formed by bonding. After that, for example, the wound body 30 is sandwiched between the exterior members 40, and the outer edge portions of the exterior members 40 are sealed and sealed by thermal fusion or the like. At that time, an adhesive film 41 is inserted between the leads 31 and 32 and the exterior member 40. Thereby, the secondary battery shown in FIGS. 4 and 5 is completed.

  Further, this secondary battery may be manufactured as follows. First, the positive electrode 33 and the negative electrode 34 are prepared in the same manner as in the first embodiment described above, and the leads 31 and 32 are respectively attached to the positive electrode 33 and the negative electrode 34, and then the positive electrode 33 and the negative electrode 34 are connected via the separator 35. Then, the protective tape 37 is bonded to the outermost peripheral portion to form a precursor of the wound body 30. Next, the precursor is sandwiched between the exterior members 40, and the outer peripheral edge except for one side is heat-sealed into a bag shape, and stored in the interior of the exterior member 40. Subsequently, an electrolyte composition including an electrolytic solution, a monomer that is a raw material of the polymer compound, and other materials such as a polymerization initiator or a polymerization inhibitor as necessary is prepared, and the interior of the exterior member 40 is prepared. After the injection, the opening of the exterior member 40 is heat-sealed and sealed. Thereafter, heat is applied to polymerize the monomer to form a polymer compound, thereby forming a gel electrolyte layer 36, and assembling the secondary battery shown in FIGS.

  This secondary battery operates in the same manner as in the first embodiment, and can obtain the same effect.

  Further, specific embodiments of the present invention will be described in detail.

As Experimental Examples 1 to 5, cylindrical secondary batteries as shown in FIGS. First, lithium cobalt oxide (LiCoO ₂ ) is used as a positive electrode active material, and the lithium cobalt oxide, graphite as a conductive material, and polyvinylidene fluoride as a binder are mixed and dispersed in a dispersion medium, and aluminum having a thickness of 15 μm. After applying and drying on both surfaces of the positive electrode current collector 21A made of foil, compression molding was performed to form the outer surface positive electrode active material layer 21B and the inner surface positive electrode active material layer 21C, and the positive electrode 21 was produced. At that time, the thickness of the outer surface positive electrode active material layer 21B and the inner surface positive electrode active material layer 21C was changed as shown in Table 1 in Experimental Examples 1 to 5, and the porosity was 22%. Further, an outer surface active material region 21F provided with only the outer surface positive electrode active material layer 21B was formed on the winding center side. Next, an aluminum lead 25 was attached to the winding center side of the positive electrode current collector 21A. The position of the outer surface active material region 21F and the lead 25 was adjusted so as to overlap as shown in FIG.

  In addition, a CoSnC-containing material is used as the negative electrode active material, and this CoSnC-containing material, the conductive material and the artificial graphite and carbon black as the negative electrode active material, and the polyvinylidene fluoride as the binder are mixed and dispersed in the dispersion medium. The negative electrode current collector 22A made of copper foil was applied to both surfaces and dried, and then compression molded to form the outer negative electrode active material layer 22B and the inner negative electrode active material layer 22C, thereby preparing the negative electrode 22. At that time, the thicknesses of the outer surface negative electrode active material layer 22B and the inner surface negative electrode active material layer 22C were changed as shown in Table 1 in Experimental Examples 1 to 5. Next, a nickel lead 26 was attached to the winding outer peripheral side of the negative electrode current collector 22A.

  The CoSnC-containing material was synthesized by mixing a tin cobalt alloy powder and a carbon powder and utilizing a mechanochemical reaction. When the composition of the synthesized CoSnC-containing material was analyzed, the cobalt content was 29.3 mass%, the tin content was 49.9 mass%, and the carbon content was 19.8 mass%. The carbon content was measured by a carbon / sulfur analyzer, and the cobalt and tin contents were measured by ICP (Inductively Coupled Plasma) emission analysis. Further, when X-ray diffraction was performed on the CoSnC-containing material, a diffraction peak having a wide half-width with a diffraction angle 2θ of 1.0 ° or more was observed between the diffraction angle 2θ = 20 ° and 50 °. Further, when XPS (X-ray Photoelectron Spectroscopy) was performed on the CoSnC-containing material, the C1s peak in the CoSnC-containing material was obtained in a region lower than 284.5 eV, and the CoSnC-containing material It was confirmed that the carbon of this was bonded to other elements.

Subsequently, a separator 23 made of a microporous polypropylene film was prepared, and the positive electrode 21, the separator 23, the negative electrode 22, and the separator 23 were laminated in this order, and then wound many times in a spiral shape, and the center pin 24 was inserted in the center. After that, the lead 25 was joined to the safety valve mechanism 15 and the lead 26 was joined to the battery can 11, and the wound positive electrode 21 and negative electrode 22 were sandwiched between the insulating plates 12 and 13 and stored inside the battery can 11. Next, an electrolytic solution was injected into the battery can 11. As the electrolytic solution, a solution obtained by dissolving LiPF ₆ as an electrolyte salt at a content of 1 mol / dm ³ in a solvent obtained by mixing 50% by volume of ethylene carbonate and 50% by volume of diethyl carbonate was used. Subsequently, the safety valve mechanism 15, the heat sensitive resistance element 16, and the battery lid 14 were fixed to the open portion of the battery can 11 by caulking through the gasket 17. Thus, secondary batteries of Experimental Examples 1 to 5 were obtained.

  In addition, when three secondary batteries were produced for each of Experimental Examples 1 to 5 and it was observed whether cracks or fractures occurred in the positive electrode 21 in the winding process, no cracks or fractures were observed in all of them. The size of the step due to the lead 25 in Experimental Examples 1 to 5 is about 100 μm.

  As Comparative Examples 1 and 2, the thicknesses of the outer surface positive electrode active material layer, the inner surface positive electrode active material layer, the outer surface negative electrode active material layer, and the inner surface negative electrode active material layer were changed as shown in Table 1, A secondary battery was fabricated in the same manner as in Experimental Examples 1 to 5, except that the thickness of the inner surface positive electrode active material layer was the same, and the thickness of the outer surface negative electrode active material layer and the inner surface negative electrode active material layer were the same. . As Comparative Example 3, as shown in FIG. 7, the outer surface active material region 121B and the inner surface positive electrode active material layer 121C are aligned with the end portions on the winding center side to form the outer surface active material region. Except that the thicknesses of the positive electrode active material layer 121B, the inner surface positive electrode active material layer 121C, the outer surface negative electrode active material layer 122B, and the inner surface negative electrode active material layer 122C are the same as those in Experimental Example 2 as shown in Table 1, Secondary batteries were fabricated in the same manner as in Experimental Examples 1-5. Further, as Comparative Example 4, a secondary battery was fabricated in the same manner as Comparative Example 2 except that the thickness of the positive electrode current collector was changed to 20 μm.

  For Comparative Examples 1 to 4, three secondary batteries were prepared, and it was observed whether cracks or fractures occurred in the positive electrode in the winding process. As a result, in Comparative Examples 1 and 4, no cracks or breaks were observed in all, whereas in Comparative Example 2, cracks or breaks occurred in all. In Comparative Example 3, two cracks or breaks occurred.

  Further, for the fabricated secondary batteries of Experimental Examples 1 to 5 and Comparative Examples 1, 3, and 4, the discharge capacity at the first cycle and the discharge capacity at the 100th cycle were measured according to the following procedure, and then the discharge capacity maintenance ratio was determined. Asked. First, constant current / constant voltage charging was performed until the total charging time from the start of charging reached 3 hours under the conditions of an upper limit voltage of 4.2 V and a current of 0.7 C, and then a condition of a current of 0.2 C and a final voltage of 2.5 V. A constant current discharge was performed, and the discharge capacity at the first cycle was measured. Subsequently, charging / discharging was performed until the total number of cycles reached 100 under the same charging / discharging conditions, and the discharge capacity at the 100th cycle was measured. Finally, discharge capacity retention ratio (%) = (discharge capacity at the 100th cycle / discharge capacity at the first cycle) × 100 was calculated. 0.7 C is a current value at which the battery capacity can be discharged in (1 / 0.7) hours, and 0.2 C is a current value at which the battery capacity can be discharged in 5 hours. The obtained results are shown in Table 1. The discharge capacity at the first cycle, the discharge capacity at the 100th cycle, and the discharge capacity retention rate shown in Table 1 are all average values for three secondary batteries. The determination of the average value in this way is the same in the following unless otherwise specified. In Comparative Example 2, since the crack and fracture occurred in the positive electrode, the discharge capacity retention rate was not obtained. Moreover, in Comparative Example 3, the discharge capacity retention rate was determined for one piece in which no cracks or breakage occurred.

  As shown in Table 1, according to Experimental Examples 1 to 5, cracks and breakage did not occur even when the thickness of the positive electrode 21 was increased, and the discharge capacity at the first cycle could be improved. Further, in Experimental Examples 1 to 5, the discharge capacity at the 100th cycle could be improved substantially, and a discharge capacity retention rate equivalent to that of Comparative Examples 1, 3, and 4 (85% or more) was obtained. In contrast, in Comparative Example 1 in which the thickness of the positive electrode was reduced, cracks and fractures did not occur, but the discharge capacity at the first cycle was low. Further, the outer surface positive electrode active material layer and the inner surface positive electrode active material layer are made thicker with the same thickness, and the thickness of the outer surface active material region 122C and the inner surface negative electrode active material layer 122C are made thinner. In Comparative Example 3 in which the outer surface active material region was not provided, cracks and fractures occurred.

  That is, the outer surface active material region in which only the outer surface positive electrode active material layer 21B is provided at a position overlapping the lead 25 on the winding center side while making the thickness of the inner surface positive electrode active material layer 21C thinner than the outer surface positive electrode active material layer 21B. If 21F is provided, when the negative electrode active material contains at least one of tin and silicon as a constituent element, the occurrence of cracks and breaks can be suppressed even if the thickness of the positive electrode 21 is increased. It was found that can be improved.

  Further, as can be seen from a comparison between Experimental Example 2 and Experimental Example 4, the discharge capacity at the first cycle in Experimental Example 2 was increased. That is, it has been found that the capacity can be further improved by making the thickness of the outer negative electrode active material layer 22B thinner than the thickness of the inner negative electrode active material layer 22C.

  As Experimental Examples 6 to 10, the porosity of the outer surface positive electrode active material layer 21B and the inner surface positive electrode active material layer 21C, the thickness of the outer surface negative electrode active material layer 22B, and the thickness of the inner surface negative electrode active material layer 22C are as shown in Table 2. A secondary battery was fabricated in the same manner as in Experimental Example 1 except for the change. At this time, the porosity was changed within a range of 18% to 29%.

  For the fabricated secondary batteries of Experimental Examples 6 to 10, in order to investigate the capacity under high load conditions (high load discharge capacity), the total charge time from the start of charging under the conditions of an upper limit voltage of 4.2 V and a current of 0.7 C After performing constant current and constant voltage charging until 3 hours, constant current discharge was performed under the conditions of a current of 2 C and a final voltage of 2.5 V, and the high load discharge capacity in the first cycle was measured. 2C is a current value at which the battery capacity can be discharged in 0.5 hours. The obtained results are shown in Table 2 and FIG. 8 together with the results of Experimental Example 1.

  As shown in Table 2 and FIG. 8, according to Experimental Examples 1 and 6 to 10, the high load discharge capacity tends to increase and become almost constant after increasing as the porosity increases. Indicated. In this case, when the porosity was smaller than 20% or larger than 27%, the high-load discharge capacity was greatly reduced. That is, by making the porosity of the outer surface positive electrode active material layer 21B and the inner surface positive electrode active material layer 21C in the range of 20% or more and 27% or less, the occurrence of cracks and breakage is suppressed and the capacity is improved. It was found that a high capacity was maintained even when output with a load current.

  As Experimental Example 11, artificial graphite was used as the negative electrode active material and conductive material, and the thicknesses of the outer surface positive electrode active material layer 21B, the inner surface positive electrode active material layer 21C, the outer surface negative electrode active material layer 22B, and the inner surface negative electrode active material layer 22C are shown in Table 3. A secondary battery was fabricated in the same manner as in Experimental Examples 1 to 5 except for the above. For Experimental Example 11, three secondary batteries were prepared, and it was observed whether cracks or fractures occurred in the positive electrode 21 in the winding process, and no cracks or fractures were observed in all of them. The size of the step due to the lead 25 in Experimental Example 11 is the same as in Experimental Example 1.

  As Comparative Examples 5 and 6, the outer surface positive electrode active material layer, the inner surface positive electrode active material layer, the outer surface negative electrode active material layer, and the inner surface negative electrode active material layer were changed in thickness as shown in Table 3, A secondary battery was fabricated in the same manner as in Experimental Example 11, except that the thickness of the inner surface positive electrode active material layer was the same, and the outer surface negative electrode active material layer and the inner surface negative electrode active material layer were the same thickness. Further, as Comparative Example 7, except that the porosity of the outer surface positive electrode active material layer and the inner surface positive electrode active material layer was changed to 25%, and the thickness of the outer surface negative electrode active material layer and the inner surface negative electrode active material layer was changed to 80 μm. A secondary battery was fabricated in the same manner as in Example 6.

  For Comparative Examples 5 to 7, three secondary batteries were prepared, and it was observed whether cracks or breaks occurred in the positive electrode in the winding process. As a result, in Comparative Examples 5 and 7, no cracks or fractures were observed in all, whereas in Comparative Example 6, one crack or fracture occurred.

  About the produced secondary battery of Experimental example 11 and Comparative Examples 5-7, the discharge capacity of 1st cycle and 100th cycle was measured similarly to Experimental example 1-5, and the discharge capacity maintenance factor was calculated | required. The obtained results are shown in Table 3. For Comparative Example 6, the discharge capacity maintenance rate was determined for two positive electrodes that did not crack or break.

  As shown in Table 3, according to Experimental Example 11, cracks and fractures do not occur even when the thickness of the positive electrode 21 is increased, and the discharge capacity at the first cycle and the 100th cycle can be substantially improved. It was. Furthermore, in Experimental Example 11, a discharge capacity retention rate equal to or higher than that of Comparative Examples 5 to 7 was obtained. In contrast, in Comparative Example 5 in which the thickness of the positive electrode was reduced, cracks and fractures did not occur, but the discharge capacity at the first cycle was low. Further, in Comparative Example 6 in which the outer surface positive electrode active material layer and the inner surface positive electrode active material layer were thickened to the same thickness, cracks and breaks occurred. Furthermore, in Comparative Example 7 in which the porosity was increased, cracks and fractures did not occur, but the discharge capacity at the first cycle was low.

  That is, the outer surface active material region in which only the outer surface positive electrode active material layer 21B is provided at a position overlapping the lead 25 on the winding center side while making the thickness of the inner surface positive electrode active material layer 21C thinner than the outer surface positive electrode active material layer 21B. It was found that if 21F is provided, when the negative electrode active material contains a carbon material, cracks and breakage can be suppressed even when the thickness of the positive electrode 21 is increased, and the capacity can be improved. .

  As apparent from the results of Tables 1 to 3, the inner surface positive electrode active material layer 21C is made thinner than the outer surface positive electrode active material layer 21B regardless of the material of the negative electrode active material, and at the winding center side. If the outer surface active material region 21F in which only the outer surface positive electrode active material layer 21B is provided is provided at a position overlapping the lead 25, the occurrence of cracks and breakage can be suppressed even if the thickness of the positive electrode 21 is increased. It was found that the capacity can be improved. In particular, it has been found that a higher effect can be obtained when the negative electrode active material contains at least one of tin and silicon, which are advantageous for increasing the capacity, as a constituent element. 4 and FIG. 5, even when the flat wound body 30 is provided, the inner surface positive electrode active material layer 33C is made thinner than the outer surface positive electrode active material layer 33B and the winding center. Needless to say, if the outer surface active material region 33F is formed in the bent portion 30A on the side, the same effect as that of the cylindrical wound body 20 described above can be obtained.

  Although the present invention has been described with reference to the embodiments and examples, the present invention is not limited to the embodiments and examples, and various modifications can be made. For example, in the second embodiment, the flat wound body 30 including a pair of opposed bent portions 30A and a flat portion 30B between the pair of bent portions 30A is replaced with an exterior member 40 made of an aluminum laminate film. However, the present invention is also applicable to a so-called square type in which the wound body 30 is housed in a can made of iron (Fe) plated with nickel (Ni). Applicable. In that case, the gel electrolyte layer 36 is not provided, and the electrolyte is injected into the inside of the can and impregnated in the separator as in the first embodiment.

  Further, for example, in the above-described embodiment and examples, the materials such as the positive electrode 21 and the electrolytic solution are specifically described. However, the present invention uses other materials as long as it has the above-described winding structure. Also good.

It is sectional drawing showing the structure of the secondary battery which concerns on the 1st Embodiment of this invention. It is sectional drawing showing the structure along the II-II line | wire of the wound body shown in FIG. It is sectional drawing which expands and expresses a part of winding body shown in FIG. It is a disassembled perspective view showing the structure of the secondary battery which concerns on the 2nd Embodiment of this invention. It is sectional drawing showing the structure along the VV line of the wound body shown in FIG. It is sectional drawing which expands and represents a part of winding body shown in FIG. 10 is a cross-sectional view showing a winding structure of Comparative Example 3. FIG. It is a characteristic view showing the correlation between porosity and high load discharge capacity.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 11 ... Battery can, 12, 13 ... Insulation board, 14 ... Battery cover, 15 ... Safety valve mechanism, 15A ... Disc board, 16 ... Heat sensitive resistance element, 17 ... Gasket, 20, 30 ... Winding body, 21, 33 ... Positive electrode, 21A, 33A ... Positive electrode current collector, 21B, 33B ... Outer surface positive electrode active material layer, 21C, 33C ... Inner surface positive electrode active material layer, 21F, 33F ... Outer surface active material region, 22, 34 ... Negative electrode, 22A, 34A ... Negative electrode current collector, 22B, 34B ... outer surface negative electrode active material layer, 22C, 34C ... inner surface negative electrode active material layer, 23, 35 ... separator, 24 ... center pin, 25, 26, 31, 32 ... lead, 36 ... electrolyte layer 37 ... protective tape, 40 ... exterior member, 41 ... adhesive film.

Claims (6)

A winding body in which a positive electrode and a negative electrode are laminated and wound with a separator in between,
The wound body has at least one lead attached to the winding center side;
The positive electrode includes a positive electrode current collector having a pair of opposed surfaces, an outer surface positive electrode active material layer provided on the winding outer surface side of the positive electrode current collector, and an inner surface positive electrode active material layer provided on the winding inner surface side. And
The thickness of the inner surface positive electrode active material layer is thinner than the thickness of the outer surface positive electrode active material layer,
On the winding center side of the positive electrode, an outer surface active material region provided with only the outer surface positive electrode active material layer is formed at a position overlapping the lead,
The negative electrode includes a negative electrode current collector having a pair of opposing surfaces, an outer surface negative electrode active material layer provided on the winding outer surface side of the negative electrode current collector, and an inner surface negative electrode active material layer provided on the winding inner surface side. And
The outer surface negative electrode active material layer has the same thickness as the inner surface negative electrode active material layer or thinner than the inner surface negative electrode active material layer,
The negative electrode includes, as a negative electrode active material, a CoSnC-containing material containing tin (Sn), cobalt (Co), and carbon (C) as constituent elements,
In the CoSnC-containing material, the carbon content is 16.8% by mass or more and 24.8% by mass or less, and the half width of a diffraction peak obtained by X-ray diffraction is 1.0 ° or more. The secondary battery according to claim 1, wherein in the CoSnC-containing material, a ratio of cobalt to a total of tin and cobalt (Co / (Sn + Co)) is 30% by mass or more and 45% by mass or less. The secondary battery according to claim 1, wherein a porosity of the outer surface positive electrode active material layer and the inner surface positive electrode active material layer is in a range of 20% to 27%. A winding body in which a positive electrode and a negative electrode are laminated and wound with a separator in between,
The wound body has a flat shape including a pair of opposed bent portions and a flat portion between the pair of bent portions,
The positive electrode includes a positive electrode current collector having a pair of opposed surfaces, an outer surface positive electrode active material layer provided on the winding outer surface side of the positive electrode current collector, and an inner surface positive electrode active material layer provided on the winding inner surface side. And
The thickness of the inner surface positive electrode active material layer is thinner than the thickness of the outer surface positive electrode active material layer,
On the winding center side of the positive electrode, an outer surface active material region in which only the outer surface positive electrode active material layer is provided in the bent portion is formed,
The negative electrode includes a negative electrode current collector having a pair of opposing surfaces, an outer surface negative electrode active material layer provided on the winding outer surface side of the negative electrode current collector, and an inner surface negative electrode active material layer provided on the winding inner surface side. And
The outer surface negative electrode active material layer has the same thickness as the inner surface negative electrode active material layer or thinner than the inner surface negative electrode active material layer,
The negative electrode includes a CoSnC-containing material containing tin, cobalt, and carbon as constituent elements as a negative electrode active material,
In the CoSnC-containing material, the carbon content is 16.8% by mass or more and 24.8% by mass or less, and the half width of the diffraction peak obtained by X-ray diffraction is 1.0 ° or more.
Secondary battery. The secondary battery according to claim 4 , wherein in the CoSnC-containing material, a ratio of cobalt to the total of tin and cobalt (Co / (Sn + Co)) is 30% by mass or more and 45% by mass or less. The secondary battery according to claim 4, wherein a porosity of the outer surface positive electrode active material layer and the inner surface positive electrode active material layer is in a range of 20% to 27%.

Images