JP2010027415A - Secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a secondary battery with high reliability in which a stress in a wound body is alleviated as well as securing a sufficient capacity. <P>SOLUTION: The wound body 20 of a secondary battery includes a positive electrode 21 and a negative electrode 22 laminated and wound with a separator 23 in-between and is housed inside a battery can 11 of a hollow parallelepiped shape. Further, it is wound along the winding direction R from the winding center side toward the winding outer circumference side and includes a flat shape being conformed to the shape of the battery can 11 so as to include a pair of flat portions 20S and a pair of curved portions 20R facing each other. The positive electrode current collector 21A is an aluminum alloy having a tensile strength of 90 N/mm<SP>2</SP>or more. When the surface density of a positive electrode active material layer 21B located on a wound inner circumferential face side of the positive electrode current collector 21A is denoted by A and the surface density of the positive electrode active material layer 21B located on the wound outer circumferential face side of the positive electrode current collector 21A is denoted by B, the following formula (1): 0.35≤äA/(A+B)}≤0.45 is satisfied at the curved portions 20R. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a secondary battery having a wound body in which a positive electrode and a negative electrode are laminated via a separator.

  In recent years, many portable electronic devices such as a camera-integrated VTR (video tape recorder), a mobile phone, or a notebook computer have appeared, and their size and weight have been reduced. Batteries used as portable power sources for these electronic devices, particularly secondary batteries, are actively used as key devices for research and development aimed at improving energy density. Among them, non-aqueous electrolyte secondary batteries (for example, lithium ion secondary batteries) can provide a larger energy density than conventional lead batteries and nickel cadmium batteries, which are conventional aqueous electrolyte secondary batteries. Considerations are being made in various directions.

  As a negative electrode active material used for a lithium ion secondary battery, a carbon material such as non-graphitizable carbon or graphite having a relatively high capacity and good cycle characteristics is widely used. However, considering the recent demand for higher capacity, further increase in capacity of carbon-based materials has become an issue.

  Against this background, a technique for achieving a high capacity with a carbon material by selecting a carbonization raw material and production conditions has been developed (see, for example, Patent Document 1). However, when such a carbon material is used, since the negative electrode discharge potential is 0.8 V to 1.0 V with respect to lithium (Li), the battery discharge voltage when the battery is configured becomes low. No significant improvement is expected in terms of battery energy density. Furthermore, there is a drawback that the charge / discharge curve has a large hysteresis and the energy efficiency in each charge / discharge cycle is low.

On the other hand, as a high-capacity negative electrode that surpasses carbon materials, research is being conducted on alloy materials that apply the fact that a certain metal is electrochemically alloyed with lithium and is reversibly generated and decomposed. Furthermore, as a method for improving the cycle characteristics, it is studied to alloy tin and silicon (Si) to suppress their expansion. For example, it has been proposed to alloy a transition metal such as iron with tin (see Patent Documents 2 to 4 and Non-Patent Documents 1 to 3). In addition, Mg ₂ Si and the like have been proposed (see Non-Patent Document 4).
JP-A-8-315825 Japanese Patent Laid-Open No. 2004-22306 JP 2004-63400 A JP 2005-78999 A “Journal of the Electrochemical Society”, 1999, No. 146, p405 “Journal of the Electrochemical Society”, 1999, No. 146, p414 “Journal of the Electrochemical Society”, 1999, No. 146, p423 “Journal of the Electrochemical Society”, 1999, No. 146, p4401

  However, even when these methods are used, it is difficult to sufficiently suppress the expansion and contraction of the negative electrode during charging and discharging. If an attempt is made to fill a large number of current collectors and active material layers into a battery can of a predetermined size for the purpose of increasing the capacity of the battery, the current collector and the separator may be damaged. The reality is that the features of the high-capacity negative electrode adopted are not fully utilized.

  Specifically, for example, a wound body that is accommodated in a rectangular battery can having a substantially rectangular parallelepiped shape and has a flat cross section including a pair of flat portions and a pair of curved portions is made of the above alloy material. When the negative electrode is used, the pressure distribution inside the wound body becomes non-uniform due to expansion associated with charge and discharge. As a result, in an extreme case, for example, the positive electrode current collector may break at the curved portion of the wound body. In particular, although there was no abnormality in the positive electrode current collector in the initial stage in the charge / discharge cycle test, there was a case where the metal fatigue due to repeated charge / discharge eventually led to fracture. In order to increase the capacity of the battery, it is necessary to increase the thickness of the positive electrode active material layer so as to correspond to the negative electrode capacity. However, as the thickness is increased, the load applied to the positive electrode current collector is increased when the wound body is pressure-molded so that the cross section becomes flat. This is likely to occur and hinders the increase in battery capacity.

  The present invention has been made in view of such problems, and an object of the present invention is to provide a secondary battery having high reliability by relaxing stress inside the wound body while securing a sufficient capacity. .

In the secondary battery of the present invention, a positive electrode in which a positive electrode active material layer is provided on a belt-like positive electrode current collector and a negative electrode having a negative electrode active material layer on the belt-like negative electrode current collector are laminated via a separator, The positive electrode current collector is an aluminum alloy having a tensile strength of 90 N / mm or more, wherein the positive electrode current collector is provided with a wound body having a flat cross section including a pair of opposed curved portions, and the positive electrode active material layer has a thickness of the positive electrode The thickness is 10 times or more and 15 times or less of the thickness of the current collector, and at least a pair of curved portions satisfy the following conditional expression (1). However, in conditional expression (1), A is the surface density of the positive electrode active material layer located on the winding inner peripheral surface side of the positive electrode current collector, and B is located on the winding outer peripheral surface side of the positive electrode current collector. It is the surface density of the positive electrode active material layer. The surface density of the positive electrode active material layer is the weight of the positive electrode active material layer per unit area on the surface of the positive electrode current collector.
0.35 ≦ {A / (A + B)} ≦ 0.45 (1)

  In the secondary battery of the present invention, the surface density of the positive electrode active material layer on the inner peripheral surface side of the positive electrode current collector is smaller than the surface density of the positive electrode active material layer on the outer peripheral surface side of the positive electrode current collector, The stress applied to the positive electrode current collector at the time of charge / discharge or pressure molding is relieved in the curved portion of the wound body. Moreover, since the positive electrode current collector is an aluminum alloy having a tensile strength of 90 N / mm or more, the positive electrode current collector has sufficient resistance against a mechanical load during charging / discharging or work molding. On the other hand, the thickness of the positive electrode active material layer is as large as 10 to 15 times the thickness of the positive electrode current collector, and the surface density of the positive electrode active material layer on the inner peripheral surface side of the positive electrode current collector is more than a certain level. Since it is maintained, sufficient capacity is secured.

  According to the secondary battery of the present invention, a predetermined aluminum alloy is used as the positive electrode current collector, and the surface density of the positive electrode active material layers located on both surfaces of the positive electrode current collector satisfies the conditional expression (1). Therefore, even when the thickness of the positive electrode active material layer is increased to 10 times or more and 15 times or less than the thickness of the positive electrode current collector, the positive electrode current collector is formed during pressure molding or charge / discharge of the wound body. The stress applied to the electric body can be relaxed. For this reason, damage to the positive electrode current collector can be prevented, and high capacity can be achieved while ensuring high reliability.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the figure, each component schematically shows the shape, size, and arrangement relationship to the extent that the present invention can be understood, and is different from the actual size.

[First Embodiment]
1 and 2 show a cross-sectional structure of the secondary battery according to the first embodiment of the present invention. The cross section shown in FIG. 1 and the cross section shown in FIG. 2 are in a positional relationship orthogonal to each other. That is, FIG. 2 is a cross-sectional view in the arrow direction along the line II-II shown in FIG. This secondary battery is a so-called rectangular shape, and has a flat wound body 20 accommodated inside a battery can 11 having a substantially hollow rectangular parallelepiped shape.

  The battery can 11 is made of, for example, iron (Fe) plated with nickel (Ni), and also has a function as a negative electrode terminal. The battery can 11 has one end closed and the other end open, and the inside of the battery can 11 is sealed by attaching an insulating plate 12 and a battery lid 13 to the open end. The insulating plate 12 is made of polypropylene or the like, and is disposed on the wound body 20 perpendicular to the winding peripheral surface. The battery lid 13 is made of, for example, the same material as the battery can 11 and has a function as a negative electrode terminal together with the battery can 11. A terminal plate 14 serving as a positive electrode terminal is disposed outside the battery lid 13. A through hole is provided near the center of the battery lid 13, and a positive electrode pin 15 electrically connected to the terminal plate 14 is inserted into the through hole. The terminal plate 14 and the battery lid 13 are electrically insulated by an insulating case 16, and the positive electrode pin 15 and the battery lid 13 are electrically insulated by a gasket 17. The insulating case 16 is made of, for example, polybutylene terephthalate. The gasket 17 is made of, for example, an insulating material.

  A cleavage valve 18 and an electrolyte injection hole 19 are provided near the periphery of the battery lid 13. The cleaving valve 18 is electrically connected to the battery lid 13 and is cleaved when the internal pressure of the battery exceeds a certain level due to an internal short circuit or external heating, thereby suppressing an increase in the internal pressure. . The electrolyte injection hole 19 is closed by a sealing member 19A made of, for example, a stainless steel ball.

  The wound body 20 is formed by winding a positive electrode 21 and a negative electrode 22 with a separator 23 interposed therebetween. The wound body 20 is wound along a winding direction R indicated by an arrow in FIG. 2 from the winding center side toward the winding outer peripheral side, and a pair of flat portions 20S and a pair of curved portions 20R facing each other are wound. In order to include, it is formed into a flat shape according to the shape of the battery can 11. In addition, about the frequency | count of winding of the wound body 20, FIG.1 and FIG.2 is only an illustration and can be set arbitrarily. The negative electrode 22 is positioned on the outermost periphery of the wound body 20, and the outer peripheral side end of the negative electrode 22 is fixed by a protective tape 26 that covers the outermost peripheral surface of the wound body 20. Both end portions of the protective tape 26 are overlapped by the flat portion 20S. That is, both end surfaces 26TS and 26TE of the protective tape 26 are located in the flat portion 20S. The protective tape 26 is made of, for example, a polyester film coated with an adhesive on one side, and has a thickness of 22 μm.

  A positive electrode lead 24 made of aluminum (Al) or the like is connected to the positive electrode 21 of the wound body 20, and a negative electrode lead 25 made of nickel or the like is connected to the negative electrode 22. The positive electrode lead 24 is welded to the lower end of the positive electrode pin 15 to be electrically connected to the terminal plate 14, and the negative electrode lead 25 is welded to and electrically connected to the battery can 11.

  FIG. 3 shows a cross-sectional configuration in a state where the positive electrode 21 shown in FIGS. 1 and 2 is disassembled and linearly extended. This positive electrode 21 is obtained by selectively providing a positive electrode active material layer 21B on both surfaces of a strip-shaped positive electrode current collector 21A. Specifically, the positive electrode current collector 21A is located on both sides of the positive electrode active material layer 21B on the both sides of the positive electrode covering region 21C and the winding center side and the winding outer peripheral side so as to sandwich the positive electrode covering region 21C. Both surfaces of the positive electrode current collector 21A have positive electrode exposed regions 21DS and 21DE in which the positive electrode active material layer 21B is exposed without being present. The positive electrode lead 24 is joined to the positive electrode exposed region 21DS on the winding center side. Note that the positive electrode covering region 21C and the positive electrode exposed regions 21DS, DE do not need to coincide on both surfaces of the positive electrode current collector 21A, and even if a region where the positive electrode active material layer 21B is provided on only one surface exists. Good.

The positive electrode current collector 21A has, for example, a thickness of about 5 μm to 50 μm and is made of a metal foil such as an aluminum alloy foil, a nickel foil, or a stainless steel foil. The positive electrode current collector 21A is particularly an aluminum alloy having a tensile strength of 90 N / mm ² or more, more specifically, aluminum alloys A8021H, A8021H-O, A1085H, A1085H-O defined by Japanese Industrial Standards (JIS). , A1N30H, A3003H, or A3003H-O.

The positive electrode active material layer 21B is, for example, not less than 10 times and not more than 15 times the thickness of the positive electrode current collector 21A, and is configured to satisfy the following conditional expression (1) in at least a pair of curved portions 20R. However, in conditional expression (1), A is the surface density of the positive electrode active material layer 21B located on the winding inner peripheral surface side of the positive electrode current collector 21A, and B is the winding outer peripheral surface side of the positive electrode current collector 21A. Is the surface density of the positive electrode active material layer 21 </ b> B located in
0.35 ≦ {A / (A + B)} ≦ 0.45 (1)
If the lower limit of conditional expression (1) is not more than the lower limit, the positive electrode active material layer 21B on the winding outer peripheral surface side is too thick with respect to the positive electrode active material layer 21B on the winding inner peripheral surface side. Battery reaction is unlikely to occur, and cycle characteristics may be degraded. Therefore, by exceeding the lower limit, the battery reaction occurs without waste even in the positive electrode active material layer 21B on the winding outer peripheral surface side, and as a result, good cycle characteristics are ensured. On the other hand, by falling below the upper limit in conditional expression (1), the stress applied to the positive electrode current collector 21A is relaxed, and cracks and breaks in the positive electrode current collector 21A can be avoided.

The positive electrode active material layer 21B includes, 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 such as polyvinylidene fluoride may be included. 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 sulfides, metal selenides, metal oxides, etc., or lithium-containing compounds containing lithium.

Some lithium-containing compounds can obtain high voltage and 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 and manganese (Mn ) Including at least one of them is preferable because a higher voltage 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 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. Among these, a composite oxide containing nickel is preferable. This is because a high capacity can be obtained and excellent cycle characteristics can also be obtained. 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.

  FIG. 4 shows the configuration of the negative electrode 22. The negative electrode 22 is obtained by selectively providing a negative electrode active material layer 22B on both surfaces of a strip-shaped negative electrode current collector 22A. Specifically, the negative electrode covering region 22C where the negative electrode active material layer 22B exists on both surfaces of the negative electrode current collector 22A, and the winding center side and the winding outer peripheral side so as to sandwich the negative electrode covering region 22C, Both surfaces of the negative electrode current collector 22A have negative electrode exposed regions 22DS and 22DE that are exposed without the negative electrode active material layer 22B. The negative electrode lead 25 is joined to the negative electrode exposed region 22DE on the winding outer periphery side. Note that the negative electrode covering region 22D and the negative electrode exposed regions 22DS and 22DE do not need to coincide on both surfaces of the negative electrode current collector 22A, and there may be a region where the negative electrode active material layer 22B is provided only on one surface. Good.

  The negative electrode current collector 22A is made of, for example, a metal foil such as a copper foil, a nickel foil, or a stainless steel foil. The thickness of the negative electrode current collector 22A is, for example, 5 μm to 50 μm.

  The negative electrode active material layer 22B includes, for example, a negative electrode active material, and may include other materials such as a conductive material and a binder as necessary. Examples of the negative electrode active material include a negative electrode material that can occlude and release lithium, which is an electrode reactant, and includes at least one of a metal element and a metalloid element as a constituent element. Use of such a negative electrode material is preferable because a high energy density can be obtained. 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 the metal element or metalloid element constituting the negative electrode material include a metal element or metalloid element capable of forming an alloy with lithium. Specifically, magnesium (Mg), boron (B), aluminum (Al), gallium (Ga), indium (In), silicon, germanium (Ge), tin, lead (Pb), bismuth (Bi), cadmium Examples thereof include (Cd), silver (Ag), zinc (Zn), hafnium (Hf), zirconium (Zr), yttrium (Y), palladium (Pd), and platinum (Pt).

  Among these, the negative electrode material preferably includes a group 14 metal element or metalloid element in the long-period periodic table as a constituent element, and particularly preferably includes at least one of silicon and tin as a constituent element. This is because silicon and tin have a large ability to occlude and release lithium, and a high energy density can be obtained. Specifically, for example, a simple substance, an alloy, or a compound of silicon, a simple substance, an alloy, or a compound of tin, or a material having one or two or more phases thereof at least in part.

  Examples of tin alloys include silicon, nickel, copper, iron (Fe), cobalt (Co), manganese (Mn), zinc (Zn), indium (In), and silver as second constituent elements other than tin. (Ag), titanium (Ti), germanium (Ge), bismuth (Bi), antimony (Sb), and the thing containing at least 1 sort (s) of chromium (Cr) are mentioned. As an alloy of silicon, for example, as a second constituent element other than silicon, among the group consisting of tin, nickel, copper, iron, cobalt, manganese, zinc, indium, silver, titanium, germanium, bismuth, antimony and chromium The thing containing at least 1 sort (s) is mentioned.

  Examples of the tin compound or silicon compound include those containing oxygen (O) or carbon (C), and may contain the second constituent element described above in addition to tin or silicon.

  Among these, as this negative electrode material, tin, cobalt, and carbon are included as constituent elements, the carbon content is 9.9 mass% or more and 29.7 mass% or less, and the total of tin and cobalt is A CoSnC-containing material having a cobalt ratio of 30% by mass to 70% by mass is preferable. This is because a high energy density can be obtained in such a composition range, and excellent cycle characteristics can be obtained.

  This CoSnC-containing material may further contain any one or more of the other constituent elements listed below as required. Examples of other constituent elements here include silicon, iron, nickel, chromium, indium, niobium (Nb), germanium, titanium, molybdenum (Mo), aluminum (Al), phosphorus (P), and gallium (Ga). And bismuth. It is because the capacity or cycle characteristics can be further improved by including these.

  This CoSnC-containing material has a phase containing tin, cobalt, and carbon, and this phase preferably has a low crystallinity or an amorphous structure. In this CoSnC-containing material, it is preferable that at least a part of carbon as a constituent element is bonded to a metal element or a semimetal element as 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. .

  As a measuring method for examining the bonding state of elements, for example, X-ray photoelectron spectroscopy (XPS) can be cited. In XPS, the peak of the carbon 1s orbital (C1s) appears at 284.5 eV in an energy calibrated apparatus so that the peak of the gold atom 4f orbital (Au4f) is obtained at 84.0 eV if it is graphite. . Moreover, if it is surface contamination carbon, it will appear at 284.8 eV. On the other hand, when the charge density of the carbon element increases, for example, when carbon is bonded to a metal element or a metalloid element, the C1s peak appears in a region lower than 284.5 eV. That is, when the peak of the synthetic wave of C1s obtained for the CoSnC-containing material appears in a region lower than 284.5 eV, at least a part of the carbon contained in the CoSnC-containing material is a metal element or a half of other constituent elements. Combined with metal elements.

  In XPS measurement, for example, the C1s peak is used to correct the energy axis of the spectrum. Usually, since surface-contaminated carbon exists on the surface, the C1s peak of the surface-contaminated carbon is set to 284.8 eV, which is used as an energy standard. In the XPS measurement, the waveform of the C1s peak is obtained as a shape including the surface contamination carbon peak and the carbon peak in the CoSnC-containing material. For example, by analyzing using a commercially available software, the surface contamination The carbon peak and the carbon peak in the CoSnC-containing material are separated. In the waveform analysis, the position of the main peak existing on the lowest bound energy side is used as the energy reference (284.8 eV).

  As the negative electrode active material, a carbon material such as natural graphite, artificial graphite, non-graphitizable carbon, or graphitizable carbon may be used. Use of a carbon material is preferable because excellent cycle characteristics can be obtained. Moreover, lithium metal is also mentioned as a negative electrode active material. The negative electrode active material may be used alone or in combination of two or more.

  Further, in the secondary battery, it is desirable that at least the pair of curved portions 20R is configured to satisfy both of the following conditional expressions (2) and (3). However, C1 is the capacity | capacitance of the positive electrode active material layer 21B located in the winding inner peripheral surface side of 21 A of positive electrode collectors, and C2 is the negative electrode active material layer 22B located in the winding outer peripheral surface side of 22 A of negative electrode collectors. D1 is the capacity of the positive electrode active material layer 21B located on the winding outer peripheral surface side of the positive electrode current collector 21A, and D2 is the negative electrode active material located on the winding inner peripheral surface side of the negative electrode current collector 22A. This is the capacity of the material layer 22B.

85% ≦ (C1 / C2) ≦ 99% (2)
85% ≦ (D1 / D2) ≦ 99% (3)
In conditional expressions (2) and (3), if the lower limit of 85% is not reached, the positive electrode potential during charging becomes too high, and the progress of oxidative decomposition of the electrolytic solution at the positive electrode 21 and the crystal structure of the positive electrode active material are poor. There is a risk that the cycle characteristics may deteriorate due to stabilization or the like. On the other hand, by lowering the upper limit of 99% in conditional expressions (2) and (3), it is possible to avoid a decrease in cycle characteristics due to lithium precipitation. Therefore, by satisfying conditional expressions (2) and (3), sufficient capacity and good cycle characteristics can be ensured.

  The separator 23 is made of, for example, a porous film made of a polyolefin-based material such as polypropylene or polyethylene, or a porous film made of an inorganic material such as a ceramic nonwoven fabric, and these two or more kinds of porous films are laminated. It may be made the structure. A polymer compound layer (not shown) is provided on the surface of the separator 23, and the separator 23 is bonded to the positive electrode 21 and the negative electrode 22 through this layer.

  The polymer compound layer includes an electrolytic solution in which an electrolyte salt is dissolved in a solvent and a polymer compound that holds the electrolytic solution. Here, the term “holds” the electrolytic solution by the polymer compound is a concept that includes not only the state in which the polymer compound is swollen in the electrolyte solution but also the state in which the electrolyte solution and the polymer compound are mixed without interaction. It is. That is, the polymer compound layer may be a so-called gel electrolyte in which the polymer compound is swollen in the electrolyte solution, or the electrolyte solution exists in the void of the rigid polymer compound without causing interaction. It may be an electrolyte. The electrolytic solution may be impregnated in the positive electrode 21, the negative electrode 22, or the separator 23.

  As the solvent contained in the electrolytic solution, various high dielectric constant solvents and low viscosity solvents can be used. For example, as a high dielectric constant solvent, in addition to ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate, 4-fluoro-1,3-dioxolan-2-one (fluoroethylene carbonate), 4-chloro-1,3-dioxolane Cyclic carbonates such as 2-one (chloroethylene carbonate) and trifluoromethylethylene carbonate are preferably used. As the high dielectric constant solvent, a lactone such as γ-butyrolactone, γ-valerolactone, δ-valerolactone or ε-caprolactone, N-methylpyrrolidone, etc., instead of or in combination with the above cyclic carbonate Lactam, cyclic carbamates such as N-methyloxazolidinone, and sulfone compounds such as tetramethylene sulfone can also be used. On the other hand, as low-viscosity solvents, in addition to diethyl carbonate, chain carbonates such as dimethyl carbonate, ethyl methyl carbonate and methyl propyl carbonate, methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, methyl butyrate, methyl isobutyrate, Chain carboxylic acid esters such as methyl trimethylacetate and ethyl trimethylacetate, chain amides such as N, N-dimethylacetamide, chain carbamic acid such as methyl N, N-diethylcarbamate and ethyl N, N-diethylcarbamate Esters and ethers such as 1,2-dimethoxyethane, tetrahydrofuran, tetrahydropyran and 1,3-dioxolane can be used.

  In addition, as a solvent, 1 type in the above-mentioned high-dielectric-constant solvent and low-viscosity solvent can be used individually, or 2 or more types can be arbitrarily mixed, but 20-50 mass% cyclic carbonate can be used. And a low-viscosity solvent of 50 to 80% by mass are preferable, and a low-viscosity solvent including a chain carbonate having a boiling point of 130 ° C. or less is particularly preferable. By using such a solvent, the polymer compound can be swelled satisfactorily with a small amount of electrolytic solution, and it is possible to achieve both suppression of battery swelling and prevention of leakage and high ion conductivity. Here, if the content of the low-viscosity solvent occupying the electrolytic solution is too high, the dielectric constant will be lowered, and if the content of the low-viscosity solvent is too low, the viscosity will be lowered. Ionic conductivity may not be obtained, and good battery characteristics may not be obtained.

Any electrolyte salt may be used as long as it dissolves in a solvent to generate ions, and one kind may be used alone, or two or more kinds may be mixed and used. For example, if the lithium salt, lithium hexafluorophosphate (LiPF _6), lithium tetrafluoroborate (LiBF _4), lithium hexafluoroarsenate (LiAsF _6), lithium hexafluoro antimonate (LiSbF ₆₎ Inorganic lithium salts such as lithium perchlorate (LiClO ₄ ) and lithium tetrachloride aluminum oxide (LiAlCl ₄ ), lithium trifluoromethanesulfonate (LiCF ₃ SO ₃ ), lithium bis (trifluoromethanesulfone) imide (LiN (CF ₃ SO _2
2 ), perfluoroalkanes such as lithium bis (pentafluoromethanesulfone) imide (LiN (C ₂ F ₅ SO ₂ ) ₂ ) and lithium tris (trifluoromethanesulfone) methide (LiC (CF ₃ SO ₂ ) ₃ ) Lithium salts of sulfonic acid derivatives can be used. Of these, lithium hexafluorophosphate and lithium tetrafluoroborate are preferable from the viewpoint of oxidation stability.

Incidentally, the concentration of such electrolyte salt is preferably at 0.1mol or more 3.0mol or less with respect to solvent 1 dm ^3, in particular, 0.5 mol or more 2.0mol or less with respect to solvent 1 dm ³ Is preferred. This is because higher ion conductivity can be obtained in such a range.

  The polymer compound constituting the polymer compound layer is not particularly limited as long as it retains the electrolytic solution and exhibits ionic conductivity, but the acrylonitrile copolymer is 50% or more (particularly 80% or more). Acrylonitrile polymers, aromatic polyamides, acrylonitrile / butadiene copolymers, acrylic polymers made of acrylate or methacrylate homopolymers or copolymers, acrylamide polymers, fluorine-containing polymers such as vinylidene fluoride, polysulfone, Examples thereof include celluloses such as polyallylsulfone and carboxymethylcellulose. In particular, a polymer having a copolymerization amount of 50% or more of acrylonitrile has a CN group in its side chain, and thus can form a gel electrolyte having a high dielectric constant and high ion conductivity. Acrylic nitriles and vinyl carboxylic acids such as acrylic acid, methacrylic acid, itaconic acid, acrylamide, methacryl sulfonic acid, hydroxyalkylene glycol (meth) are used to improve the electrolyte support for these polymers and the ionic conductivity of the electrolyte. A copolymer obtained by copolymerizing acrylate, alkoxyalkylene glycol (meth) acrylate, vinyl chloride, vinylidene chloride, vinyl acetate, various (meth) acrylates or the like at a ratio of preferably 50% or less, particularly preferably 20% or less can also be used. . Moreover, since aromatic polyamide is a high heat resistant polymer, it is suitable when high heat resistance is required.

Examples of the polymer compound constituting the polymer compound layer include a polymer having a crosslinked structure obtained by copolymerizing butadiene or the like in addition to the above. Furthermore, polymers containing vinylidene fluoride as a constituent component, that is, homopolymers, copolymers, and multi-component copolymers can also be used as the polymer compound. Specifically, polyvinylidene fluoride (PVdF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVdF-HFP), and polyvinylidene fluoride-hexafluoropropylene-chlorotrifluoroethylene copolymer (PVdF-HEP-CTFE). ). In particular, from the viewpoint of redox stability, a fluorine-based polymer compound such as polyvinylidene fluoride or a copolymer of vinylidene fluoride and hexafluoropropylene is desirable. The polymer compound layer 26 may further contain insulating particles such as aluminum oxide (Al ₂ O ₃ ), titanium oxide (TiO ₂ ) or silicon oxide (SiO ₂ ) for the purpose of improving safety. Good.

  By attaching the separator 23 to the positive electrode 21 and the negative electrode 22 through the polymer compound layer, it is possible to reduce excess electrolyte solution that is not substantially involved in the battery reaction, and the electrolyte solution is used as the cathode active material layer 21B. And efficiently supplied around the negative electrode active material layer 22B. Therefore, the secondary battery of the present embodiment exhibits excellent cycle characteristics while reducing the total amount of the electrolytic solution, and also has excellent leakage resistance. Here, the peel strength between each of the positive electrode exposed regions 21DS and 21DE of the positive electrode current collector 21A and the negative electrode exposed regions 22DS and 22E of the negative electrode current collector 22A and the separator 23 is preferably 1 mN / mm or more. / Mm or more is particularly desirable. The peel strength is determined by fixing the separator 23 on a support base and pulling the positive electrode current collector 21A or the negative electrode current collector 22A in a 180 ° direction at a speed of 10 cm / min so as to peel from the separator 23. In the meantime, it means the average value of the force required to peel them between 6 and 25 seconds after starting to pull.

  Further, in this secondary battery, the positive electrode active material layer 21B and the negative electrode active material layer 22B are arranged so as to face each other, but they are arranged at the ends of the winding center 20 and the winding outer peripheral side. In this part, the negative electrode active material layer 22B is formed to be longer along the winding direction R than the positive electrode active material layer 21B (see FIG. 2). That is, a region where the negative electrode active material layer 22B and the positive electrode current collector 21A face each other is provided. This is to prevent the current from concentrating on the end portion of the negative electrode active material layer 22B to deposit lithium metal and cause an internal short circuit.

  Here, among the positive electrode exposed regions 21DS and 21DE, insulating tapes 27 and 28 are provided at least in regions facing the negative electrode active material layer 22B, respectively. If the insulating tapes 27 and 28 are not provided, when the battery is charged, lithium is inserted into the negative electrode active material layer 22B in the opposite region between the positive electrode active material layer 21B and the negative electrode active material layer 22B, so that the negative electrode active material layer Although the electric potential of 22B becomes low, since the lithium is not inserted into the negative electrode active material layer 22B in the opposite region between the one positive electrode current collector 21A and the negative electrode active material layer 22B, the electric potential of the negative electrode active material layer 22B is maintained. As a result, the potential of the positive electrode active material layer 21B is higher in the opposing region between the positive electrode current collector 21A and the negative electrode active material layer 22B than in the opposing region between the positive electrode active material layer 21B and the negative electrode active material layer 22B. Therefore, by providing the insulating tapes 27 and 28, such an increase in the potential of the positive electrode 21 is suppressed.

The insulating tapes 27 and 28 are preferably those capable of inhibiting or blocking the movement of ions. For example, those having an air permeability measurement of 5,000 s / 100 cm ³ or more as defined in JIS P8117 are preferable. Specific examples of the constituent material include synthetic resins such as polyethylene, polypropylene, polyimide, and polyethylene terephthalate. The thickness in that case is good to set it as 8 micrometers-50 micrometers, for example. The insulating tapes 27 and 28 may be attached by, for example, an adhesive, or may be attached by heat fusion or the like.

  In the secondary battery, when charged, for example, lithium ions are released from the positive electrode 21 and inserted in the negative electrode 22 through the electrolytic solution held in the polymer compound layer on the separator 23. When discharging is performed, for example, lithium ions are released from the negative electrode 22 and inserted in the positive electrode 21 through the electrolytic solution.

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

  First, a positive electrode active material, a conductive agent, and a binder are mixed to prepare a positive electrode mixture, and the positive electrode mixture is dispersed in a solvent such as N-methyl-2-pyrrolidone to obtain a paste-like positive electrode mixture. A slurry is obtained. Subsequently, the positive electrode mixture slurry is uniformly applied to the positive electrode current collector 21A using a doctor blade or a bar coater, and the solvent is dried. Then, the positive electrode active material layer 21B is formed by compression molding using a roll press or the like. Then, the positive electrode 21 is produced. Furthermore, insulating tapes 27 and 28 are provided at least in regions that will face the negative electrode active material layer 22B in the positive electrode exposed regions 21DS and 21DE, respectively.

  Next, a negative electrode active material and a binder are mixed to prepare a negative electrode mixture, and the negative electrode mixture is dispersed in a solvent such as N-methyl-2-pyrrolidone to obtain a paste-like negative electrode mixture slurry. . Subsequently, the negative electrode mixture slurry is uniformly applied to the negative electrode current collector 22A using a doctor blade or a bar coater, and the solvent is dried. Then, the negative electrode mixture layer 22B is formed by compression molding using a roll press. Then, the negative electrode 22 is produced. The roll press machine may be used by heating. Moreover, you may compression-mold several times until it becomes the target physical-property value. Furthermore, you may use press machines other than a roll press machine.

  Subsequently, the positive electrode lead 24 is attached to the positive electrode current collector 21A by welding or the like, and the negative electrode lead 25 is attached to the negative electrode current collector 22A by welding or the like. On the other hand, a polymer compound layer is selectively formed on one side or both sides of the separator 23. Specifically, first, a polymer solution in which a polymer compound such as polyvinylidene fluoride or carboxymethylcellulose is dissolved in a solvent such as N-methyl-2-pyrrolidone or water is applied to one or both surfaces of the separator 23. Subsequently, the separator 23 on which the polymer compound layer is formed is prepared, and the positive electrode 21, the separator 23, the negative electrode 22, and the separator 23 are laminated in this order to form a laminate. Further, the laminated body is wound many times to form a flat wound body 20 by pressure forming, and then the outermost peripheral surface is covered with a protective tape 26 over the entire surface to form the negative electrode 22 (negative electrode). The end of the current collector 22A) is fixed.

  Next, after the wound body 20 produced as described above is accommodated in the battery can 11, the insulating plate 12 is disposed on the wound body 20, the negative electrode lead 25 is welded to the battery can 11, and the positive electrode The lead 24 is welded to the lower end of the positive electrode pin 15, and the battery lid 13 is fixed to the open end of the battery can 11 by laser welding. Finally, the electrolytic solution is injected into the battery can 11 from the electrolytic solution injection hole 19, impregnated in the separator 23, and the electrolytic solution injection hole 19 is closed with the sealing member 19A. Thereby, the secondary battery shown in FIGS. 1 and 2 is completed.

  Thus, in the present embodiment, the surface density of the positive electrode active material layer 21B on the inner peripheral surface side of the positive electrode current collector 21 is higher than the surface density of the positive electrode active material layer 21B on the outer peripheral surface side of the positive electrode current collector 21A. Since it is small, the stress applied to the positive electrode current collector 21A at the time of charging / discharging or processing / molding in the curved portion 20R of the wound body 20 is relaxed. Moreover, sufficient tolerance with respect to the mechanical load at the time of charging / discharging or process shaping | molding is securable by using 21 A of positive electrode collectors for the aluminum alloy which has a tensile strength of 90 N / mm or more. On the other hand, the surface of the positive electrode active material layer 21B on the inner peripheral surface side of the positive electrode current collector 21A is larger than the thickness of the positive electrode current collector 21A by 10 to 15 times the thickness of the positive electrode current collector 21A. Since the density is kept above a certain level, a sufficient capacity is secured. That is, since the positive electrode current collector 21A having a predetermined mechanical strength is used and the surface density of the positive electrode active material layer 21B located on both surfaces of the positive electrode current collector 21A satisfies the conditional expression (1), Even when the thickness of the positive electrode active material layer 21B is increased to 10 times or more and 15 times or less than the thickness of the positive electrode current collector 21A, the positive electrode current collector is subjected to pressure molding or charging / discharging of the wound body 20. The stress applied to the body 21A can be relaxed. For this reason, damage to the positive electrode current collector 21A can be prevented, and high capacity can be achieved while ensuring high reliability.

  Moreover, by satisfying the conditional expressions (2) and (3), lithium deposition on the surface of the negative electrode 22 can be suppressed, and more excellent cycle characteristics can be secured.

  Moreover, in this Embodiment, since the end surfaces 26TS and 26TE of the protective tape 26 which fixes the outer peripheral side edge part of the wound body 20 were located in the flat part 20S, they are located in the curved part 20R. In comparison, even if the negative electrode active material layer 22B expands during charging and discharging, the local increase in internal pressure in the wound body 20 is alleviated. When the end surfaces 26TS and 26TE of the protective tape 26 are positioned on the curved portion 20R, stress concentration tends to occur in the vicinity thereof, so that the end surfaces in the stacking direction of the wound bodies 20 (the normal direction of the peripheral surface of the wound body 20). Local stress is applied to the positive electrode current collector 21A, the negative electrode current collector 22A, the separator 23, and the like located at positions corresponding to 26TS and 26TE, which may cause cracks or breakage of these. However, in the secondary battery of the present embodiment, the pressure distribution inside the wound body 20 is less likely to be biased, so that damage to the negative electrode current collector 22A and the separator 23 is avoided, and the function as a secondary battery is stabilized. Can be maintained.

  Next, specific examples of the present invention will be described in detail.

Example 1
A secondary battery corresponding to FIGS. 1 and 2 described in the above embodiment was manufactured. First, lithium carbonate (Li ₂ CO ₃ ) and cobalt carbonate (CoCO ₃ ) are mixed at a ratio of Li ₂ CO ₃ : CoCO ₃ = 0.5: 1 (molar ratio), and 5 ° C. at 900 ° C. in the air. After firing for a time, lithium-cobalt composite oxide (LiCoO ₂ ) as a positive electrode active material was obtained. Next, 91 parts by mass of this lithium / cobalt composite oxide, 6 parts by mass of graphite as a conductive agent, and 3 parts by mass of polyvinylidene fluoride as a binder were mixed to prepare a positive electrode mixture. Subsequently, this positive electrode mixture was dispersed in N-methyl-2-pyrrolidone as a solvent to form a positive electrode mixture slurry, and an aluminum alloy foil having a thickness of 20 μm (Japanese Industrial Standard JIS aluminum alloy having a tensile strength of 90 N / mm ² ) A positive electrode current collector 21A made of A8021H) was uniformly applied to both surfaces, dried, and compression-molded with a roll press to form a positive electrode active material layer 21B having a thickness of 200 μm. Here, the surface density of the positive electrode active material layer 21B on the winding outer peripheral surface side of the positive electrode current collector 21A is 35.7 mg / cm ² , and the positive electrode active material layer on the winding inner peripheral surface side of the positive electrode current collector 21A The coating amount of the positive electrode mixture slurry was adjusted so that the surface density of 21B was 29.3 mg / cm ² . Subsequently, a positive electrode lead 24 made of aluminum was attached to one end of the positive electrode current collector 21A. Furthermore, insulating tapes 27 and 28 were disposed in at least regions of the positive electrode exposed regions 21DS and 21DE that would face the negative electrode active material layer 22B, respectively. The insulating tapes 27 and 28 were made of a polyester film coated with an adhesive material on one side and had a thickness of 22 μm.

  In addition, a CoSnC-containing material was produced as a negative electrode active material. First, cobalt powder, tin powder, and carbon powder were prepared as raw materials, and cobalt powder and tin powder were alloyed to produce a cobalt-tin alloy powder. Then, carbon powder was added to the alloy powder and dry mixed. Subsequently, this mixture was synthesized using a mechanochemical reaction using a planetary ball mill to obtain a CoSnC-containing material.

  When the composition of the obtained 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 obtained CoSnC-containing material, a diffraction peak having a wide half-width with a diffraction angle 2θ of 1.0 ° or more was observed between diffraction angles 2θ = 20 ° to 50 °. It was. Further, when XPS 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. That is, it was confirmed that carbon in the CoSnC-containing material was bonded to other elements.

Next, 60 parts by mass of this CoSnC-containing material, 28 parts by mass of artificial graphite as a conductive agent and a negative electrode active material and 2 parts by mass of carbon black, and 10 parts by mass of polyvinylidene fluoride as a binder are mixed together. The agent was adjusted. Subsequently, the negative electrode mixture was dispersed in N-methyl-2-pyrrolidone as a solvent to form a negative electrode mixture slurry, which was applied to both surfaces of a negative electrode current collector 22A made of a copper foil having a thickness of 15 μm and dried. A negative electrode 22 was obtained by compression molding with a roll press to form a negative electrode active material layer 22B having a thickness of 80 μm. Here, the negative electrode active material layer surface density of the anode active material layer 22B made of a spirally wound outer peripheral surface of the anode current collector 22A is 8.2 mg / cm ^2, winding the peripheral surface of the anode current collector 22A The coating amount of the negative electrode mixture slurry was adjusted so that the surface density of 22B was 9.7 mg / cm ² . Thereafter, a negative electrode lead 25 made of nickel was attached to one end of the negative electrode current collector 22A. As the negative electrode lead 25, one having a thickness of 50 μm and a negative electrode current collector 22A having a width in the longitudinal direction of 4.0 mm was used.

  Subsequently, a separator 23 made of a microporous polypropylene film having a thickness of 20 μm was prepared, and the positive electrode 21, the separator 23, the negative electrode 22, and the separator 23 were laminated in this order to form a laminate. Further, the laminated body is wound many times to form a flat wound body 20 by pressure forming, and then the outermost peripheral surface is covered with a protective tape 26 over the entire surface to form the negative electrode 22 (negative electrode). The end of the current collector 22A) was fixed. As the protective tape 26, one having a thickness of 22 μm made of a polyester film coated with an adhesive on one side was used. The cross-sectional dimension of the wound body 20 was 9.1 mm × 28.5 mm, and the height was 37.0 mm.

After the wound body 20 thus obtained is accommodated in the battery can 11, the insulating plate 12 is disposed on the wound body 20, the negative electrode lead 25 is welded to the battery can 11, and the positive electrode lead 24. Was welded to the lower end of the positive electrode pin 15. Furthermore, after the battery lid 13 having an opening corresponding to the positive electrode pin 15 was disposed at the open end of the battery can 11 via the gasket 17, the battery lid 13 was fixed by laser welding. After that, an electrolytic solution was injected into the battery can 11 from the electrolytic solution injection hole 19. 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 in which 30% by volume of ethylene carbonate and 70% by volume of dimethyl carbonate were mixed was used. Finally, the electrolyte injection hole 19 was closed with a sealing member 19A to obtain a rectangular secondary battery having outer dimensions of a thickness of 10.5 mm, a width of 29.7 mm, and a height of 41.0 mm.

  Table 1 shows the structural conditions of the secondary battery thus manufactured.

(Examples 2 to 8)
At least one of the surface density of the positive electrode active material layer 21B and the negative electrode active material layer 22B, the tensile strength and thickness of the positive electrode current collector 21A, the thickness of the positive electrode active material layer 21B, and the thickness of the negative electrode active material layer 22B A secondary battery was produced in the same manner as in Example 1 except that the value was changed to the value shown in Table 1. Here, Examples 2 to 8 all satisfy the conditional expressions (1) to (3).

(Comparative Examples 1-9)
At least one of the surface density of the positive electrode active material layer 21B and the negative electrode active material layer 22B, the tensile strength and thickness of the positive electrode current collector 21A, the thickness of the positive electrode active material layer 21B, and the thickness of the negative electrode active material layer 22B A secondary battery was produced in the same manner as in Example 1 except that the value was changed to the value shown in Table 1.

  About the secondary battery of each Example and each comparative example produced as mentioned above, the fracture occurrence rate of the positive electrode current collector 21A after pressure forming of the wound body, and the negative electrode surface after charging at 4.3V The lithium deposition state, initial discharge capacity (mAh) and charge / discharge efficiency were examined. The results are shown in Table 2.

  The rate of occurrence of breakage of the positive electrode current collector 21A is such that when the wound body 20 is produced by winding a laminate in which the positive electrode 21, the separator 23, the negative electrode 22, and the separator 23 are laminated in order and then press-molding the laminate, The current collector 21A was completely broken and was determined as NG and divided by the total number of samples. The total number of samples (n number) was 20.

  The lithium deposition state was investigated as follows. Specifically, in an environment of 23 ° C., first, each secondary battery is charged at a constant current of 1 C until the battery voltage reaches 4.3 V, and then the constant current charging is started. Constant voltage charging was performed at a constant voltage of 4.3 V until the total time after that reached 3 hours. Thereafter, each secondary battery was disassembled, the negative electrode was taken out, and the presence or absence of metallic lithium deposition on the surface of the negative electrode active material layer was examined.

  The discharge capacity (mAh / g) was determined as follows. Specifically, in an environment of 23 ° C., first, constant current charging is performed until the battery voltage reaches 4.2 V at a constant current of 1 C, and then the total time after starting the constant current charging is 2 The battery was charged at a constant voltage of 4.2 V until reaching 5 hours. Subsequently, constant current discharge was performed at a constant current of 0.2 C until the battery voltage reached 2.5 V, and the discharge capacity at that time was measured. Note that 0.2 C is a current value at which the theoretical capacity can be discharged in 5 hours.

  Furthermore, about charging / discharging efficiency, it charged / discharged about each secondary battery and investigated the capacity | capacitance maintenance factor. Specifically, in an environment of 23 ° C., charging is performed until the battery voltage reaches 4.2 V at a constant current of 1 C, and then the total charging time is 2.5 hours at a constant voltage of 4.2 V. Then, discharging was performed at a constant current of 1 C until the battery voltage reached 2.5V. This was regarded as one cycle and repeated up to 300 cycles for charging / discharging. Here, as the capacity maintenance rate, the ratio of the discharge capacity at the 300th cycle to the discharge capacity at the first cycle, that is, the capacity maintenance rate (%) = (discharge capacity at the 300th cycle / discharge capacity at the first cycle) × 100. Asked.

  As shown in Table 2, in Examples 1 to 8, no breakage of the positive electrode current collector 21A occurred, and no lithium deposition on the negative electrode was observed. On the other hand, in Comparative Examples 1 to 9, at least one of breakage of the positive electrode current collector 21A or deposition of lithium on the negative electrode occurred. Furthermore, in Examples 1-8, compared with Comparative Examples 1-9, it turned out that the outstanding capacity | capacitance maintenance factor is expressed, ensuring an equivalent discharge capacity. Therefore, according to the secondary battery of the present invention, even if the thickness of the positive electrode active material layer is increased to 10 to 15 times the thickness of the positive electrode current collector, the pressure forming of the wound body It was confirmed that the stress applied to the positive electrode current collector at the time of charging and discharging can be relieved, and it is possible to achieve both high reliability, high capacity, and improved cycle characteristics.

  The present invention has been described with reference to some embodiments and examples. However, the present invention is not limited to the above embodiments and examples, and various modifications can be made. For example, in the above-described embodiments and examples, the case where a gel electrolyte in which an electrolytic solution is held in a polymer compound is used as a battery electrolyte has been described. However, a liquid electrolytic solution can be used as an electrolyte as it is. . Alternatively, other types of electrolytes may be used. Other electrolytes include, for example, a mixture of an ion conductive inorganic compound such as ion conductive ceramics, ion conductive glass or ionic crystal and an electrolyte, or a mixture of another inorganic compound and an electrolyte. Or a mixture of these inorganic compounds and a gel electrolyte.

  In the above embodiments and examples, the appropriate ranges derived from the results of the examples have been described with respect to parameters such as the ratio of the surface density of the positive electrode active material layer and the negative electrode active material layer. This does not completely deny the possibility that the parameter will be outside the above range. That is, the appropriate range described above is a particularly preferable range for obtaining the effects of the present invention, and each parameter may be slightly deviated from the above ranges as long as the effects of the present invention are obtained.

  Further, in the above embodiments and examples, the case where lithium is used as the electrode reactant has been described, but other group 1 elements in the long-period periodic table such as sodium (Na) or potassium (K), or magnesium Alternatively, the present invention can be applied to the case where a Group 2 element in a long-period periodic table such as calcium (Ca), another light metal such as aluminum, lithium, or an alloy thereof is used, and similar effects are obtained. Can be obtained. At that time, a negative electrode active material, a positive electrode active material, a solvent, or the like that can occlude and release the electrode reactant is selected according to the electrode reactant.

It is sectional drawing showing the structure of the secondary battery as one embodiment in this invention. It is sectional drawing showing the structure along the II-II line of the secondary battery shown in FIG. It is sectional drawing showing the structure before winding of the positive electrode shown in FIG. It is sectional drawing showing the structure before winding of the negative electrode shown in FIG.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 11 ... Battery can, 12, 13 ... Insulating plate, 14 ... Battery cover, 15 ... Safety valve mechanism, 16 ... Heat sensitive resistance element, 17 ... Gasket, 20 ... Winding body, 20S ... Flat part, 20R ... Curve part, 21 ... positive electrode, 21A ... positive electrode current collector, 21AE ... end face, 21B ... positive electrode active material layer, 22 ... negative electrode, 22A ... negative electrode current collector, 22AE ... end face, 22B ... negative electrode active material layer, 23 ... separator, 23E ... end face , 24 ... positive lead, 25 ... negative lead, 25TS, 25TE ... end face, 26 ... protective tape, 26TS, 26TE ... end face, 27 ... insulating tape, 28 ... protective tape.

Claims (4)

A pair of curved portions in which a positive electrode in which a positive electrode active material layer is provided on a belt-like positive electrode current collector and a negative electrode having a negative electrode active material layer on the belt-like negative electrode current collector are stacked with a separator interposed therebetween. Comprising a wound body having a flat cross section including
The positive electrode current collector is an aluminum alloy having a tensile strength of 90 N / mm ² or more;
The thickness of the positive electrode active material layer is not less than 10 times and not more than 15 times the thickness of the positive electrode current collector;
A secondary battery in which the following conditional expression (1) is satisfied at least in the pair of curved portions.
0.35 ≦ {A / (A + B)} ≦ 0.45 (1)
(However, A is the surface density of the positive electrode active material layer located on the winding inner peripheral surface side of the positive electrode current collector, and B is the positive electrode active material layer located on the winding outer peripheral surface side of the positive electrode current collector. Is the surface density.) 2. The secondary battery according to claim 1, wherein at least the pair of curved portions satisfy the following conditional expressions (2) and (3).
85% ≦ (C1 / C2) ≦ 99% (2)
85% ≦ (D1 / D2) ≦ 99% (3)
(However, C1 is the capacity of the positive electrode active material layer located on the winding inner peripheral surface side of the positive electrode current collector, and C2 is the capacity of the negative electrode active material layer located on the winding outer peripheral surface side of the negative electrode current collector. D1 is the capacity of the positive electrode active material layer located on the winding outer peripheral surface side of the positive electrode current collector, and D2 is the capacity of the negative electrode active material layer located on the winding inner peripheral surface side of the negative electrode current collector .) The positive electrode active material layer includes a compound containing lithium (Li) and cobalt (Co) as a positive electrode active material,
The secondary battery according to claim 1, wherein the negative electrode active material layer includes at least one of tin (Sn) and silicon (Si). The said positive electrode electrical power collector is comprised by the aluminum alloys A8021H, A8021H-O, A1085H, A1085H-O, A1N30H, A3003H, or A3003H-O defined by Japanese Industrial Standard (JIS). Secondary battery.

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