JP2007018926A - Battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a battery capable of suppressing swelling thereof. <P>SOLUTION: A positive electrode 21 and a negative electrode 22 are laminated through an electrolyte layer 24. The gelatinous electrolyte layer 24 contains an electrolytic solution and a polymer compound. The electrolytic solution contains LiPF<SB>6</SB>and a lithium salt expressed by LiB (C<SB>p</SB>H<SB>2(p-2)</SB>O<SB>4</SB>) (C<SB>q</SB>H<SB>2(q-2)</SB>O<SB>4</SB>)(p and q are respectively integers of 2 or more). It is preferable that 1,3-dioxol-2-on or 4-vinyl-1,3-dioxolane-2-on are contained in the electrolytic solution. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a battery in which a positive electrode, a negative electrode, and an electrolyte are housed in a film-shaped exterior member.

  In recent years, portable electronic devices such as a camera-integrated VTR (Videotape Recorder), a mobile phone, or a laptop computer have appeared one after another, and their size and weight have been reduced. Along with this, as portable power sources for these electronic devices, batteries, particularly secondary batteries, have been spotlighted, and active research has been carried out and put into practical use to obtain higher energy density. Among these, lithium ion secondary batteries are expected because they can provide a higher energy density than aqueous electrolyte secondary batteries such as lead batteries or nickel cadmium batteries.

  In such a lithium ion secondary battery, conventionally, an electrolytic solution that is a liquid electrolyte in which a lithium salt is dissolved in a nonaqueous solvent has been used. Therefore, a metal container has been used as an exterior member in order to prevent liquid leakage. However, if a metal container is used for the exterior member, it is extremely difficult to produce a thin and large area sheet type battery, a thin and small area card type battery or a flexible and flexible battery. there were.

Therefore, a battery in which a sealed structure is formed by hot sealing or the like using a moisture-proof laminated film made of a polymer film capable of heat fusion and metal foil as an exterior member has been proposed (see, for example, Patent Document 1). .) This laminate film is inexpensive, has strong film strength and excellent airtightness, can be further reduced in size, weight and thickness, and has a high degree of freedom in shape. Is possible.
JP 2001-283910 A

  In recent years, many notebook computers equipped with a high-performance CPU (Central Processing Unit) have appeared. Since the heat generation temperature of the CPU becomes high, the batteries used are often placed in a high temperature environment. However, a battery using a laminate film has a problem that the battery pack is deformed by swelling due to generation of gas due to decomposition of the electrolytic solution or the like.

  This invention is made | formed in view of this problem, The objective is to provide the battery which can suppress a swelling.

The battery according to the present invention is provided with an electrolyte together with a positive electrode and a negative electrode inside a film-shaped exterior member, and the electrolyte contains an electrolytic solution containing LiPF ₆ and the lithium salt shown in Chemical formula 1. Is.
(Chemical formula 1)
_{LiB (C p H 2 (p} -2) O 4) (C q H 2 (q-2) O 4)
(In the formula, p and q are each an integer of 2 or more.)

According to the battery of the present invention, since the electrolyte contains an electrolyte solution containing LiPF ₆ and the lithium salt shown in Chemical Formula 1, even in a high temperature environment while maintaining high ionic conductivity, Swelling can be suppressed.

  In particular, if the concentration of the lithium salt shown in Chemical Formula 1 in the electrolytic solution is in the range of 0.005 mol / l or more and 0.2 mol / l or less, a higher effect can be obtained.

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

(First embodiment)
FIG. 1 shows an exploded configuration example of the secondary battery according to the first embodiment. This secondary battery has a configuration in which a wound electrode body 20 to which a positive electrode lead 11 and a negative electrode lead 12 are attached is housed in a film-shaped exterior member 31.

  Each of the positive electrode lead 11 and the negative electrode lead 12 has, for example, a strip shape, and is led out from the inside of the exterior member 31 to the outside, for example, in the same direction. The positive electrode lead 11 is made of a metal material such as aluminum (Al), and the negative electrode lead 12 is made of a metal material such as nickel (Ni).

  The exterior member 31 is made of, for example, a rectangular laminate film in which a nylon film, an aluminum foil, and a polypropylene film are bonded together in this order. The exterior member 31 is disposed, for example, so that the polypropylene film side and the wound electrode body 20 face each other, and the outer edge portions are in close contact with each other by fusion or an adhesive.

  An adhesion film 32 between the exterior member 31 and the positive electrode lead 11 and the negative electrode lead 12 for improving the adhesion between the positive electrode lead 11 and the negative electrode lead 12 and the inside of the exterior member 31 and preventing the intrusion of outside air. Has been inserted. The adhesion film 32 is made of a material having adhesion to the positive electrode lead 11 and the negative electrode lead 12. For example, when the positive electrode lead 11 and the negative electrode lead 12 are made of the metal materials described above, polyethylene, polypropylene, It is preferably composed of a polyolefin resin such as modified polyethylene or modified polypropylene.

  FIG. 2 shows a cross-sectional structure taken along line II-II of the spirally wound electrode body 20 shown in FIG. The wound electrode body 20 is obtained by stacking and winding a positive electrode 21 and a negative electrode 22 with a separator 23 and an electrolyte layer 24 interposed therebetween, and the outermost peripheral portion is protected by a protective tape 25.

  The positive electrode 21 includes, for example, a positive electrode current collector 21A and a positive electrode active material layer 21B provided on both surfaces or one surface of the positive electrode current collector 21A. In the positive electrode current collector 21A, for example, there is an exposed portion without providing the positive electrode active material layer 21B at one end portion in the longitudinal direction, and the positive electrode lead 11 is attached to this exposed portion. The positive electrode current collector 21A is made of, for example, a metal material such as aluminum.

The positive electrode active material layer 21B includes, for example, one or more of positive electrode materials capable of inserting and extracting lithium (Li) as an electrode reactant as a positive electrode active material, and carbon as necessary. A conductive material such as a 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 include chalcogenides and 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 ), Iron (Fe), aluminum, vanadium (V), titanium (Ti) and zirconium (Zr) are preferred. This is 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)), lithium nickel cobalt manganese composite oxide (Li _x Ni _(1-vw) Co _v Mn _w O ₂ (v + w <1)), or a spinel structure Examples thereof include lithium manganese composite oxide (LiMn ₂ O 4). 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-u Mn _u PO ₄ (u <1)). Can be mentioned.

  The positive electrode active material layer 21B may contain, for example, a compound by-produced when the positive electrode active material is industrially produced, for example, lithium carbonate. Lithium carbonate is decomposed and gasified in a high temperature environment and causes swelling, so the lithium carbonate content in the positive electrode active material layer 21B is preferably 0.5% by mass or less.

  The negative electrode 22 includes, for example, a negative electrode current collector 22A and a negative electrode active material layer 22B provided on both surfaces or one surface of the negative electrode current collector 22A, as with the positive electrode 21. The negative electrode current collector 22A has, for example, an exposed portion where the negative electrode active material layer 22B is not provided at one end in the longitudinal direction, and the negative electrode lead 12 is attached to the exposed portion. The anode current collector 22A is made of a metal material such as copper (Cu), for example.

  The negative electrode active material layer 22B includes one or more negative electrode materials capable of occluding and releasing lithium as an electrode reactant as a negative electrode active material. The binder similar to the positive electrode active material layer 21B may be included.

  As a negative electrode material capable of occluding and releasing lithium, a material capable of occluding and releasing lithium at a potential of 2.0 V or less with respect to lithium metal is preferably exemplified. Specific examples include carbon materials such as non-graphitizable carbon, artificial graphite, natural graphite, pyrolytic carbons, cokes, glassy carbons, organic polymer compound fired bodies, carbon fibers, activated carbon or carbon black. It is done. Among these, examples of coke include pitch coke, needle coke, and petroleum coke. An organic polymer compound fired body is a carbonized material obtained by firing a polymer material such as a phenol resin or a furan resin at an appropriate temperature, and part of it is non-graphitizable carbon or graphitizable carbon. Some are classified as: These carbon materials are preferable because the change in crystal structure that occurs during charge and discharge is very small, a high charge and discharge capacity can be obtained, and good cycle characteristics can be obtained. In particular, graphite is preferable because it has a high electrochemical equivalent and can provide a high energy density. Further, non-graphitizable carbon is preferable because excellent cycle characteristics can be obtained.

  Such a carbon material preferably includes a first carbon material having a small specific surface area and a second carbon material having a specific surface area larger than that of the first carbon material. It is because the gas generated in a high temperature environment can be adsorbed by including the second carbon material, and swelling can be suppressed. The content of the second carbon material in the negative electrode active material layer 22B is preferably in the range of 2 mass% to 40 mass% or less, and more preferably in the range of 3 mass% to 30 mass%. This is because if the amount is small, the effect of suppressing swelling is not sufficient, and if the amount is large, the capacity decreases.

The specific surface area of the second carbon material is preferably in the range of ² m ² / g or more and 8 m ² / g or less, more preferably 3 m ² / g or more, and still more preferably 6 m ² / g or less. Is within. This is because if it is small, the effect of suppressing swelling is not sufficient, and if it is large, the capacity decreases.

  Examples of the negative electrode material capable of inserting and extracting lithium also include materials containing tin (Sn) or silicon (Si) as a constituent element. This is because tin and silicon have a large ability to occlude and release lithium, and a high energy density can be obtained.

  As such a negative electrode material, specifically, a simple substance, an alloy, or a compound of tin, a simple substance, an alloy, or a compound of silicon, or a material having one or more phases thereof at least in part. Is mentioned. 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 tin alloys include silicon, nickel, copper (Cu), iron, 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) of these 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 Co / (Sn + Co) 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 other constituent elements as necessary. As other constituent elements, for example, silicon, iron, nickel, chromium, indium, niobium (Nb), germanium, titanium, molybdenum (Mo), aluminum, phosphorus (P), gallium (Ga) or bismuth is preferable. It may contain more than seeds. This is because the capacity or cycle characteristics can be further improved.

  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 a negative electrode material capable of inserting and extracting lithium, for example, a material containing another metal element or other metalloid element capable of forming an alloy with lithium as a constituent element can also be used. Such metal elements or metalloid elements include magnesium (Mg), boron (B), aluminum, gallium, indium, germanium, lead (Pb), bismuth, cadmium (Cd), silver, zinc, hafnium (Hf). , Zirconium (Zr), yttrium (Y), palladium (Pd), or platinum (Pt).

  The separator 23 is made of, for example, a porous film made of synthetic resin such as polytetrafluoroethylene, polypropylene, or polyethylene, or a porous film made of ceramic, and has a structure in which two or more kinds of porous films are laminated. May be. Among these, a porous film made of polyolefin is preferable because it is excellent in short-circuit preventing effect and can improve the safety of the battery due to the shutdown effect. In particular, polyethylene is preferable as a material constituting the separator 23 because a shutdown effect can be obtained within a range of 100 ° C. or higher and 160 ° C. or lower and the electrochemical stability is excellent. Polypropylene is also preferable, and any other resin having chemical stability can be used by copolymerizing or blending with polyethylene or polypropylene.

  The electrolyte layer 24 includes, for example, an electrolytic solution and a polymer compound that holds the electrolytic solution, and has a so-called gel shape. The electrolytic solution contains, for example, a solvent such as a nonaqueous solvent and an electrolyte salt dissolved in the solvent.

The electrolyte salt contains LiPF ₆ and the lithium salt shown in Chemical formula 1. This is because high ionic conductivity can be obtained by including LiPF ₆ . Moreover, it is because the decomposition reaction of the electrolyte solution in a high temperature environment can be suppressed by including the lithium salt shown in Chemical formula 1.
(Chemical formula 1)
_{LiB (C p H 2 (p} -2) O 4) (C q H 2 (q-2) O 4)
(In the formula, p and q are each an integer of 2 or more.)

Specific examples of the lithium salt shown in Chemical Formula 1 include LiB (C ₂ O ₄ ) ₂ represented by the structural formula shown in Chemical Formula ₂ , LiB (C ₂ C expressed in the structural formula shown in Chemical Formula 3 (C ₂ O ₄ ) (C ₄ H ₄ O ₄ ), LiB (C ₃ H ₂ O ₄ ) (C ₄ H ₄ O ₄ ) represented by the structural formula shown in Chemical formula ₄ , and the structural formula shown in Chemical formula 5 LiB (C ₄ H ₄ O ₄ ) ₂ represented, LiB (C ₆ H ₈ O ₄ ) (C ₇ H ₁₀ O ₄ ) represented by the structural formula shown in Chemical formula 6, or the structure shown in Chemical formula 7 LiB (C ₇ H ₁₀ O ₄ ) (C ₈ H ₁₂ O ₄ ) represented by the formula can be used. Any one of the lithium salts shown in Chemical Formula 1 may be used alone, or a plurality of them may be used in combination.

  The concentration of the lithium salt shown in Chemical Formula 1 in the electrolytic solution is preferably in the range of 0.005 mol / l to 0.2 mol / l. This is because if the concentration is low, the effect of suppressing swelling is not sufficient, and if the concentration is high, the charge / discharge efficiency decreases.

As the electrolyte salt, in addition to these, other electrolyte salts may be mixed. Examples of other electrolyte salts include LiClO ₄ , LiAsF ₆ , LiBF ₄ , LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ , LiB (C ₆ H ₅ ) ₄ , LiCH ₃ SO. ₃ , lithium salts such as LiCF ₃ SO ₃ , LiCl, or LiBr. You may use any 1 type (s) or 2 or more types for other electrolyte salt in mixture.

  Examples of the solvent include propylene carbonate, ethylene carbonate, 4-fluoro-1,3-dioxolan-2-one, 1,3-dioxol-2-one (vinylene carbonate), 4-vinyl-1 shown in Chemical Formula 8. , 3-dioxolan-2-one, γ-butyrolactone, diethyl carbonate, dimethyl carbonate, 1,2-dimethoxyethane, 1,2-diethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane, 4-methyl Examples include -1,3-dioxolane, diethyl ether, sulfolane, methylsulfolane, acetonitrile, propionitrile, acetate ester, butyrate ester, and propionate ester. Among these, 1,3-dioxol-2-one or 4-vinyl-1,3-dioxolan-2-one is preferable because capacity and charge / discharge efficiency can be improved. 4-Fluoro-1,3-dioxolan-2-one is preferable because it can suppress the decomposition reaction of the electrolytic solution. As the solvent, one kind may be used alone, or a plurality of kinds may be mixed and used.

  The polymer compound may be any one that gels upon absorption of a solvent. For example, a fluorine polymer compound such as polyvinylidene fluoride or a copolymer of vinylidene fluoride and hexafluoropropylene, polyethylene oxide or polyethylene oxide. And ether-based polymer compounds such as a crosslinked product containing polyacrylonitrile, polyacrylonitrile, polymethacrylate or polyacrylate. In particular, a fluorine-based polymer compound is desirable from the viewpoint of redox stability. Any one of these polymer compounds may be used alone, or two or more thereof may be mixed and used.

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

  First, for example, the positive electrode active material layer 21B is formed on the positive electrode current collector 21A to produce the positive electrode 21. The positive electrode active material layer 21B is prepared, for example, by mixing a positive electrode active material, a binder, and a conductive agent to prepare a positive electrode mixture, and dispersing it in a solvent such as N-methyl-2-pyrrolidone to thereby produce a positive electrode mixture slurry. After that, the positive electrode mixture slurry is applied to both surfaces or one surface of the positive electrode current collector 21A, dried, and compression molded. At that time, pressure molding may be performed while applying heat. This is preferable because the strength of the positive electrode 21 can be improved. Further, without applying the positive electrode mixture slurry, the positive electrode active material, the binder, and a conductive agent as necessary are mixed and heated to be applied to the positive electrode current collector 21A. Alternatively, the positive electrode active material, the binder, and, if necessary, a conductive agent may be mixed and molded or the like. Subsequently, for example, the positive electrode lead 11 is joined to the positive electrode current collector 21A by, for example, ultrasonic welding or spot welding. After that, a precursor solution containing an electrolytic solution, a polymer compound, and a mixed solvent is prepared and applied on the positive electrode active material layer 21B, that is, on both sides or one side of the positive electrode 21, and the mixed solvent is volatilized to obtain an electrolyte. Layer 24 is formed.

  Also, for example, a negative electrode mixture slurry is prepared by mixing a negative electrode active material and a binder to prepare a negative electrode mixture and dispersing it in a solvent such as N-methyl-2-pyrrolidone. Next, the negative electrode mixture slurry is applied to both surfaces or one surface of the negative electrode current collector 22A, dried, and compression molded to form the negative electrode active material layer 22B, whereby the negative electrode 22 is fabricated. Subsequently, the negative electrode lead 12 is joined to the negative electrode current collector 22A by, for example, ultrasonic welding or spot welding, and the electrolyte is formed on the negative electrode active material layer 22B, that is, on both sides or one side of the negative electrode 22 in the same manner as the positive electrode 21. Layer 24 is formed.

  After that, the positive electrode 21 and the negative electrode 22 on which the electrolyte layer 24 is formed are laminated and wound via the separator 23, and the protective tape 25 is adhered to the outermost peripheral portion to form the wound electrode body 20. Finally, for example, the wound electrode body 20 is sandwiched between the exterior members 31, and the outer edges of the exterior members 31 are in close contact with each other by thermal fusion or the like and sealed. At that time, an adhesion film 32 is inserted between the positive electrode lead 11 and the negative electrode lead 12 and the exterior member 31. Thereby, the secondary battery shown in FIGS. 1 and 2 is completed.

  Further, this secondary battery may be manufactured as follows. First, the positive electrode 21 and the negative electrode 22 are prepared as described above, and the positive electrode lead 11 and the negative electrode lead 12 are attached to the positive electrode 21 and the negative electrode 22, and then the positive electrode 21 and the negative electrode 22 are stacked via the separator 23 and wound. Rotate and adhere the protective tape 25 to the outermost periphery to form a wound body that is a precursor of the wound electrode body 20. Next, the wound body is sandwiched between the exterior members 31, and the outer peripheral edge portion excluding one side is heat-sealed to form a bag shape, and is stored inside the exterior member 31. Subsequently, an electrolyte composition containing an electrolytic solution, a monomer that is a raw material of the polymer compound, and, if necessary, other materials such as a polymerization initiator and a polymerization inhibitor is prepared. Then, the opening of the exterior member 30 is heat-sealed and sealed. After that, if necessary, heat is applied to polymerize the monomer to form a polymer compound, thereby forming the gel electrolyte layer 24 and assembling the secondary battery shown in FIGS.

  Instead of injecting the electrolyte composition after producing the wound body, for example, the electrolyte composition is applied on the positive electrode 21 and the negative electrode 22 and then wound and enclosed in the exterior member 31. Further, the electrolyte layer 24 may be formed by heating as necessary. Alternatively, the electrolyte composition may be applied onto the positive electrode 21 and the negative electrode 22, heated as necessary to form the electrolyte layer 24, wound, and sealed in the exterior member 31. However, it is preferable to form the electrolyte layer 24 after enclosing it in the exterior member 31. This is because interfacial bonding between the electrolyte layer 24 and the separator 23 can be sufficiently improved, and an increase in internal resistance can be suppressed.

In the secondary battery, when charged, for example, lithium ions are extracted from the positive electrode 21 and inserted in the negative electrode 22 through the electrolyte layer 24. On the other hand, when discharging is performed, for example, lithium ions are released from the negative electrode 22 and inserted into the positive electrode 21 through the electrolyte layer 24. At that time, since the electrolyte layer 24 contains an electrolyte solution containing LiPF ₆ and the lithium salt shown in Chemical Formula 1, the electrolyte layer 24 exhibits high ionic conductivity and decomposes the electrolyte solution even in a high temperature environment. The reaction is suppressed.

As described above, according to the secondary battery according to the present embodiment, since the electrolyte layer 24 contains the electrolytic solution containing LiPF ₆ and the lithium salt shown in Chemical Formula 1, high ionic conductivity is maintained. However, swelling can be suppressed even in a high temperature environment.

  In particular, if the concentration of the lithium salt shown in Chemical Formula 1 in the electrolytic solution is in the range of 0.005 mol / l or more and 0.2 mol / l or less, a higher effect can be obtained.

Further, the electrolytic solution contains at least one of 1,3-dioxol-2-one and 4-vinyl-1,3-dioxolan-2-one, or the content of lithium carbonate in the positive electrode active material layer 21B Of 0.5% by mass or less, or the content of the second carbon material in the negative electrode active material layer 22B is in the range of 2% by mass to 40% by mass, or the second carbon material. If the specific surface area is within the range of ² m ² / g or more and 8 m ² / g or less, a higher effect can be obtained and the capacity can be improved.

(Second Embodiment)
The secondary battery according to the second embodiment has the same configuration and operation as the secondary battery according to the first embodiment except that the configuration of the negative electrode is different. Can be manufactured. Therefore, with reference to FIG. 1 and FIG. 2, the same code | symbol is attached | subjected to a corresponding component and description of the same part is abbreviate | omitted.

  The negative electrode 22 has a structure in which a negative electrode active material layer 22B is provided on both surfaces of a negative electrode current collector 22A, similarly to the secondary battery according to the first embodiment. The negative electrode active material layer 22B contains, for example, a negative electrode active material containing tin or silicon as a constituent element. Specifically, for example, it contains a simple substance, an alloy, or a compound of tin, or a simple substance, an alloy, or a compound of silicon, and may contain two or more of them.

  The negative electrode active material layer 22B is formed by using, for example, a vapor phase method, a liquid phase method, a thermal spraying method, a firing method, or two or more of these methods. The electrical conductor 22A is preferably alloyed at least at a part of the interface. Specifically, it is preferable that the constituent element of the negative electrode current collector 22A is diffused in the negative electrode active material layer 22B, the constituent element of the negative electrode active material is diffused in the negative electrode current collector 22A, or they are mutually diffused at the interface. This is because breakage due to expansion / contraction of the negative electrode active material layer 22B due to charging / discharging can be suppressed, and electronic conductivity between the negative electrode active material layer 22B and the negative electrode current collector 22A can be improved. . The firing method is, for example, a method in which a particulate negative electrode active material is mixed with a binder or the like, dispersed in a solvent, applied, and then heat-treated at a temperature higher than the melting point of the binder or the like. .

(Third embodiment)
In the secondary battery according to the third embodiment of the present invention, a polymer compound having a structure obtained by polymerizing at least one member selected from the group consisting of polyvinyl acetal and derivatives thereof is used as the polymer compound that holds the electrolytic solution. Except for the use, the rest has the same configuration, operation, and effects as the first or second embodiment.

  Polyvinyl acetal includes a structural unit containing an acetal group shown in Chemical formula 9 (1), a structural unit containing a hydroxyl group shown in Chemical formula 9 (2), and a structural unit containing an acetyl group shown in Chemical formula 9 (3) In a repeating unit. Specifically, for example, as shown in Chemical Formula 9 (1), R is hydrogen polyvinyl formal, or R is propyl group polyvinyl butyral.

（式中、Ｒは水素原子もしくは炭素数１〜３のアルキル基を表す。）

(In the formula, R represents a hydrogen atom or an alkyl group having 1 to 3 carbon atoms.)

  The ratio of the acetal group in the polyvinyl acetal is preferably in the range of 60 mol% to 80 mol%. This is because the solubility with the solvent can be improved within this range, and the stability of the electrolyte can be further increased. Moreover, it is preferable that the weight average molecular weight of polyvinyl acetal exists in the range of 10,000 or more and 500,000 or less. This is because if the molecular weight is too low, the polymerization reaction does not proceed easily, and if it is too high, the viscosity of the electrolytic solution increases.

  The polymer compound may be a polymer obtained by polymerizing only polyvinyl acetal or one of its derivatives, or a polymer obtained by polymerizing two or more of them, and a copolymer with monomers other than polyvinyl acetal and its derivatives. But you can. Further, it may be polymerized with a crosslinking agent or a crosslinking accelerator.

  In the electrolyte layer 24, a polymer compound having a structure obtained by polymerizing at least one member selected from the group consisting of polyvinyl acetal and derivatives thereof is used as the polymer compound that holds the electrolyte solution. Thus, the ionic conductivity can be improved.

(Fourth embodiment)
The secondary battery according to the fourth embodiment of the present invention is a liquid electrolyte in which the electrolyte structure does not include a polymer compound. Except that the separator 23 is impregnated with this electrolyte, It has the same configuration, operation, and effect as the first or second embodiment. The configuration of the electrolytic solution is the same as that in the first or second embodiment.

  The secondary battery can be manufactured in the same manner as in the first or second embodiment except that, for example, only an electrolytic solution is injected instead of the electrolyte composition.

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

(Examples 1-1 to 1-4)
The secondary battery shown in FIGS.

A positive electrode active material was prepared. First, a mixture of lithium carbonate (Li ₂ CO ₃₎ and cobalt carbonate (CoCO _3), and calcined 5 hours at 900 ° C. in air to obtain a calcined article. When the obtained fired product was subjected to X-ray diffraction measurement, it was in good agreement with the LiCoO ₂ peak described in the JCPDS file. Further, lithium carbonate remained in the fired product. Subsequently, the fired product was pulverized to obtain a powder having an average particle size of 10 μm, which was used as a positive electrode active material.

Then, the positive electrode 21 was produced using this positive electrode active material. First, 95 parts by mass of the positive electrode active material described above, 2 parts by mass of Ketjen Black (manufactured by Lion Corporation) having a specific surface area of 800 m ² / g as a conductive agent, and 3 parts by mass of polyvinylidene fluoride as a binder are mixed. After preparing a positive electrode mixture, the mixture was dispersed in N-methyl-2-pyrrolidone as a solvent to prepare a positive electrode mixture slurry. Next, the positive electrode mixture slurry was uniformly applied to both surfaces of a positive electrode current collector 21A made of an aluminum foil having a thickness of 20 μm, dried, and then compression molded to form the positive electrode active material layer 21B, whereby the positive electrode 21 was produced. The content of lithium carbonate in the positive electrode active material layer 21B was 0.05% by mass.

Moreover, the negative electrode active material was produced. First, 100 parts by mass of coal-based coke as a filler and 30 parts by mass of coal tar-based pitch as a binder were mixed at about 100 ° C., and then compression molded by a press to obtain a precursor of a carbon molded body. This precursor was heat-treated at 1000 ° C. or lower, and the resulting carbon molded body was impregnated with a binder pitch melted at 200 ° C. or lower and fired at 1000 ° C. or lower. This impregnation and firing were repeated several times, and the resulting carbon molded body was fired at 2800 ° C. in an inert atmosphere to produce a graphitized molded body. This graphitized molded body was pulverized and classified to obtain graphite powder, which was used as a negative electrode active material. At this time, the pulverization conditions are appropriately changed, and a first carbon material made of graphite powder having a specific surface area of 1 m ² / g and a ^second carbon material made of graphite powder having a specific surface area of 4 m ² / g are obtained. Produced.

Then, the negative electrode 22 was produced using this negative electrode active material. First, 85 parts by mass of the first carbon material (graphite powder having a specific surface area of 1 m ² / g), 5 parts by mass of the second carbon material (graphite powder having a specific surface area of 4 m ² / g), and a conductive agent As a negative electrode mixture was prepared by mixing 2 parts by mass of fibrous carbon (VGCF manufactured by Showa Denko) and 8 parts by mass of polyvinylidene fluoride as a binder, and then dispersed in N-methyl-2-pyrrolidone as a solvent Thus, a negative electrode mixture slurry was produced. Next, the negative electrode mixture slurry was uniformly applied to both surfaces of the negative electrode current collector 22A made of a copper foil having a thickness of 10 μm, dried, and then compression molded to form the negative electrode active material layer 22B, whereby the negative electrode 22 was produced.

Next, among the copolymers of vinylidene fluoride and hexafluoropropylene as a polymer compound, those having a molecular weight of 700,000 in terms of weight average molecular weight (A) and those having a molecular weight of 310,000 (B) (A) : (B) = 9: 1 mixed at a mass ratio was prepared. The ratio of hexafluoropropylene in the copolymer was 7% by mass. Subsequently, the polymer compound, the electrolytic solution, and dimethyl carbonate, which is a mixed solvent, are mixed at a mass ratio of polymer compound: electrolyte solution: dimethyl carbonate = 1: 8: 13 and dissolved by stirring at 70 ° C. A sol precursor solution was prepared. In the electrolytic solution, ethylene carbonate, propylene carbonate, and 1,3-dioxol-2-one (VC) and 4-vinyl-1,3-dioxolan-2-one (VEC) as necessary are used as a solvent. the mixed solvent, as an electrolyte salt, LiB (C ₂ O ₄₎ represented by the structural formula shown in LiPF ₆ and of 2 was prepared by dissolving _2. Ethylene carbonate: propylene carbonate: 1,3-dioxol-2-one: 4-vinyl-1,3-dioxolan-2-one (mass ratio) is 50: 50: 0: 0 in Example 1-1, In Example 1-2, 49.5: 49.5: 1: 0, 49.5: 49.5: 0: 1 in Example 1-3, and 49: 49: 1: in Example 1-4. It was set to 1. The concentration of LiPF _{6 in} the electrolytic solution was 0.65 mol / l, and the concentration of LiB (C ₂ O ₄ ) ₂ was 0.05 mol / l.

  The obtained precursor solution was applied to each of the positive electrode 21 and the negative electrode 22 using a bar coater, and then the mixed solvent was evaporated in a constant temperature bath at 70 ° C. to form a gel electrolyte 24.

  After that, the positive electrode 21 and the negative electrode 22 each having the electrolyte layer 24 formed thereon were bonded together via a separator 23 and flatly wound to form a wound electrode body 20.

  The obtained wound electrode body 20 was sealed in an exterior member 31 made of a laminate film under reduced pressure to produce the secondary battery shown in FIGS.

As Comparative Examples 1-1 to 1-4 with respect to Examples 1-1 to 1-4, except that LiB (C ₂ O ₄ ) ₂ shown in Chemical Formula ₂ was not used, the others were Examples 1-1 to 1-4. A secondary battery was fabricated in the same manner as in 1-4. At that time, the concentration of LiPF _{6 in} the electrolytic solution was 0.7 mol / l.

  Regarding the fabricated secondary batteries of Examples 1-1 to 1-4 and Comparative Examples 1-1 to 1-4, the capacity, the cycle characteristics in a high temperature environment, and the swelling amount were examined. The results are shown in Table 1.

  The capacity was obtained as follows. First, in a 25 ° C. environment, 400 mA constant current constant voltage charging was performed up to an upper limit voltage of 4.2 V for a total charging time of 3 hours, and then 160 mA constant current discharging was performed up to a final voltage of 3 V to obtain the discharge capacity. . The capacity was determined using the discharge capacity at this time as the initial capacity.

  The cycle characteristics were determined as follows. First, in an environment of 45 ° C., charge / discharge of 800 mA constant current constant voltage charge up to an upper limit voltage of 4.2 V for a total charge time of 3 hours, and then 800 mA constant current discharge up to a final voltage of 3 V is performed. The cycle was repeated. The cycle characteristics were obtained from the maintenance rate of the discharge capacity at the 500th cycle relative to the discharge capacity at the first cycle, that is, (discharge capacity at the 500th cycle / discharge capacity at the first cycle) × 100 (%).

  Furthermore, the amount of swelling was examined as follows. First, charge / discharge was performed in the same manner as when the cycle characteristics were obtained, and the thickness of the battery in the charged state at the first cycle and the charged state at the 500th cycle was measured with a dial gauge. The swollen amount was obtained from (battery thickness in the 500th cycle charge state−battery thickness in the 500th cycle charge state).

As can be seen from Table 1, according to Examples 1-1 to 1-4 using LiB (C ₂ O ₄ ) ₂ represented by the structural formula shown in Chemical Formula ₂ , Comparative Example 1 in which this was not used The amount of swelling in a high temperature environment was smaller than each of -1 to 1-4. In addition, according to Examples 1-2 to 1-4 using 1,3-dioxol-2-one or 4-vinyl-1,3-dioxolan-2-one, Example 1 without using these examples The discharge capacity retention rate was improved from 1. Further, in Comparative Examples 1-1 to 1-4 in which LiB (C ₂ O ₄ ) ₂ represented by the structural formula shown in Chemical Formula ₂ is not used, 1,3-dioxol-2-one or 4-vinyl- By adding 1,3-dioxolan-2-one, the amount of swelling increased, but LiB (C ₂ O ₄ ) ₂ represented by the structural formula shown in Chemical Formula ₂ and 1,3-dioxole-2- In Examples 1-2 to 1-4 together with ON or 4-vinyl-1,3-dioxolan-2-one, 1,3-dioxol-2-one or 4-vinyl-1,3-dioxolane- The amount of swelling was smaller than in Example 1-1 in which 2-one was not used.

  That is, if the electrolyte layer 24 contains an electrolytic solution containing the lithium salt shown in Chemical Formula 1, swelling can be suppressed even in a high temperature environment, and 1,3-dioxole-2 When at least one of -one and 4-vinyl-1,3-dioxolan-2-one is mixed, cycle characteristics can be improved and swelling can be further suppressed.

(Examples 2-1 to 2-5)
In place of LiB (C ₂ O ₄ ) ₂ represented by the structural formula shown in Chemical Formula _2, LiB (C ₂ O ₄ ) (C ₄ H ₄ O ₄ ) represented by the structural formula shown in Chemical Formula 3, LiB (C ₃ H ₂ O ₄ ) (C ₄ H ₄ O ₄ ) represented by the structural formula shown in Chemical formula _4, LiB (C ₄ H ₄ O ₄ ) ₂ represented by the structural formula shown in Chemical formula 5 , of 6 LiB represented by the structural formula shown in _{(C 6 H 8 O 4)} (C 7 H 10 O 4), or of 7 LiB represented by the structural formula shown in (C ₇ H ₁₀ O ₄ ) A secondary battery was fabricated in the same manner as in Example 1-2 except that (C ₈ H ₁₂ O ₄ ) was used.

  For the fabricated secondary batteries of Examples 2-1 to 2-5, the capacity, the cycle characteristics under a high temperature environment, and the swelling amount were examined in the same manner as in Examples 1-1 to 1-4. The results are shown in Table 2 together with the results of Example 1-2 and Comparative Example 1-2.

  As can be seen from Table 2, the swelling amount was small in Examples 2-1 to 2-5 using the lithium salts shown in other chemical formulas 1 as in Example 1-2.

  That is, it was found that even when the lithium salt shown in the other chemical formula 1 is used, swelling in a high temperature environment can be suppressed.

(Examples 3-1 to 3-8)
The concentration of LiB (C ₂ O ₄ ) ₂ represented by the structural formula shown in Chemical Formula 2 in the electrolytic solution was changed in the range of 0.001 mol / l to 0.3 mol / l as shown in Table 3. Other than that, a secondary battery was fabricated in the same manner as in Example 1-2. At that time, the concentration of LiPF ₆ was changed so that the total concentration of LiB (C ₂ O ₄ ) ₂ and LiPF ₆ was 0.7 mol / l.

  For the fabricated secondary batteries of Examples 3-1 to 3-8, the capacity, the cycle characteristics under a high temperature environment, and the swelling amount were examined in the same manner as in Examples 1-1 to 1-4. The results are shown in Table 3 together with the results of Example 1-2.

As can be seen from Table 3, as the concentration of LiB (C ₂ O ₄ ) ₂ decreased, the amount of swelling increased. On the other hand, the discharge capacity retention rate increased as the concentration of LiB (C ₂ O ₄ ) ₂ decreased, and thereafter a tendency to become constant was observed.

  That is, it has been found that it is preferable that the concentration of the lithium salt shown in Chemical Formula 1 in the electrolytic solution be in the range of 0.005 mol / l to 0.2 mol / l.

(Examples 4-1 to 4-6)
A secondary battery was fabricated in the same manner as in Example 1-2 except that the concentration of LiPF _{6 in} the electrolytic solution was changed in the range of 0.05 mol / l to 3 mol / l as shown in Table 4. .

  For the fabricated secondary batteries of Examples 4-1 to 4-8, the capacity, the cycle characteristics under a high temperature environment, and the swelling amount were examined in the same manner as in Examples 1-1 to 1-4. The results are shown in Table 4 together with the results of Example 1-2.

As can be seen from Table 4, the initial capacity and the discharge capacity retention ratio increased as the concentration of LiPF _{6 in} the electrolytic solution increased, and a tendency to decrease after showing the maximum value was observed. That is, it was found that the capacity and cycle characteristics can be improved even if the concentration of LiPF _{6 in} the electrolytic solution is changed.

(Examples 5-1 to 5-6)
Except that the lithium carbonate content in the positive electrode active material layer 21B was changed within the range of 0% by mass to 0.5% by mass as shown in Table 5, the others were the same as in Example 1-2. A secondary battery was produced. At that time, the lithium carbonate content was adjusted by changing the mixing ratio of lithium carbonate (Li ₂ CO ₃ ) and cobalt carbonate (CoCO ₃ ).

  For the fabricated secondary batteries of Examples 5-1 to 5-6, the capacity, the cycle characteristics under a high temperature environment, and the swelling amount were examined in the same manner as in Examples 1-1 to 1-4. The results are shown in Table 5 together with the results of Example 1-2.

  As can be seen from Table 5, there was a tendency for the swollen amount to increase as the lithium carbonate content increased. That is, it was found that it was preferable to adjust the lithium carbonate content in the positive electrode active material layer 22B to 0.5% by mass or less.

(Examples 6-1 to 6-8)
As shown in Table 6, the mixing amount of the first carbon material (graphite powder having a specific surface area of 1 m ² / g) and the mixing amount of the second carbon material (graphite powder having a specific surface area of 4 m ² / g) are changed. A secondary battery was fabricated in the same manner as in Example 1-2 except that the anode 22 was fabricated.

  For the fabricated secondary batteries of Examples 6-1 to 6-8, the capacity, the cycle characteristics under a high temperature environment, and the swelling amount were examined in the same manner as in Examples 1-1 to 1-4. The results are shown in Table 6 together with the results of Example 1-2.

  As can be seen from Table 6, as the mixing amount of the second carbon material increased, the amount of swelling decreased and the initial capacity and the discharge capacity retention rate tended to decrease. That is, it has been found that the content of the second carbon material in the negative electrode active material layer 22B is preferably 2% by mass or more and 40% by mass or less.

(Examples 7-1 to 7-6)
The specific surface area of the second carbon material except that varied from 1.5m ² / g~12m ² / g as shown in Table 7, the secondary in the same manner as other embodiments 1-2 A battery was produced. At that time, the specific surface area of the second carbon material was adjusted by appropriately changing the grinding condition of the graphite powder.

  For the fabricated secondary batteries of Examples 7-1 to 7-6, the capacity, the cycle characteristics under a high temperature environment, and the swelling amount were examined in the same manner as in Examples 1-1 to 1-4. The results are shown in Table 7 together with the results of Example 1-2.

As can be seen from Table 7, as the specific surface area of the second carbon material increased, the amount of swelling decreased and the discharge capacity retention rate tended to decrease. That is, it has been found that it is preferable to set the specific surface area of the second carbon material to 2 m ² / g or more and 8 m ² / g or less.

(Examples 8-1 and 8-2)
As Example 8-1, a secondary battery was fabricated in the same manner as Example 1-1 except that a liquid electrolyte solution was used instead of the gel electrolyte layer 24. Specifically, it was produced as follows.

First, in the same manner as in Example 1-1, the positive electrode 21 and the negative electrode 22 were prepared, and the positive electrode lead 11 and the negative electrode lead 12 were attached, laminated through the separator 23, wound in the longitudinal direction, and A wound body, which is a precursor of the wound electrode body 20, was produced by attaching the protective tape 25 to the outer periphery. Next, the wound body thus prepared is loaded between the exterior members 31, and the three sides of the exterior member 31 are heat-sealed, and then an electrolyte is injected into the exterior member 31, and the remaining one side of the exterior member 31 is placed. Was heat-sealed under reduced pressure to produce a secondary battery. At that time, the electrolytic solution contains ethylene carbonate, propylene carbonate, ethylene carbonate, and dimethyl carbonate as a solvent in a mass ratio of ethylene carbonate: propylene carbonate: ethylene carbonate: dimethyl carbonate = 2: 2: 3: 3. A solution obtained by dissolving LiPF ₆ and LiB (C ₂ O ₄ ) ₂ represented by the structural formula shown in Chemical Formula 2 as an electrolyte salt was used in the mixed solvent. The concentration of LiPF _{6 in} the electrolytic solution was 0.65 mol / l, and the concentration of LiB (C ₂ O ₄ ) ₂ was 0.05 mol / l.

  Further, as Example 8-2, a secondary battery was fabricated in the same manner as Example 1-1 except that the polymer compound holding the electrolytic solution was a polyvinyl formal polymer. Specifically, it was produced as follows.

  First, in the same manner as in Example 1-1, the positive electrode 21 and the negative electrode 22 were prepared, and the positive electrode lead 11 and the negative electrode lead 12 were attached, laminated through the separator 23, wound in the longitudinal direction, and A wound body, which is a precursor of the wound electrode body 20, was produced by attaching the protective tape 25 to the outer periphery. Subsequently, the wound body thus prepared is loaded between the exterior members 31, and the three sides of the exterior member 31 are heat-sealed, and then the electrolyte composition is injected into the exterior member 31, and the open side of the exterior member 31 is After heat bonding, the gel electrolyte layer 24 was formed by being sandwiched between glass plates to keep the battery shape constant, and a secondary battery was manufactured.

The electrolyte composition used was a mixture of 2 parts by mass of polyvinyl formal and 1 part by mass of tris (trimethylsilyl) phosphate as a crosslinking accelerator with respect to 100 parts by mass of the electrolytic solution. In the electrolytic solution, a solvent obtained by mixing ethylene carbonate, propylene carbonate, ethylene carbonate, and dimethyl carbonate as a solvent in a mass ratio of ethylene carbonate: propylene carbonate: ethylene carbonate: dimethyl carbonate = 2: 2: 3: 3. As the electrolyte salt, LiPF ₆ and LiB (C ₂ O ₄ ) ₂ represented by the structural formula shown in Chemical Formula ₂ were used. The concentration of LiPF _{6 in} the electrolytic solution was 0.65 mol / l, and the concentration of LiB (C ₂ O ₄ ) ₂ was 0.05 mol / l.

  Further, a part of the electrolyte composition and the formed gel electrolyte layer 24 are extracted, each of which is diluted 300-fold with N-methyl-2-pyrrolidone, and then GPC (Gel Permeation Chromatography; gel permeation chromatography). Graph) Analysis was performed using a dedicated system (Showa DPC, Shodex GPC-101). As a result, the weight average molecular weight of the gel electrolyte layer 24 was larger than the weight average molecular weight of the electrolyte composition, and it was confirmed that polyvinyl formal was polymerized.

As Comparative Examples 8-1 and 8-2 with respect to Examples 8-1 and 8-2, except that LiB (C ₂ O ₄ ) ₂ was not used, the others were the same as Examples 8-1 and 8-2. Thus, a secondary battery was produced. At that time, the concentration of LiPF _{6 in} the electrolytic solution was 0.7 mol / l.

  Regarding the fabricated secondary batteries of Examples 8-1 and 8-2 and Comparative Examples 8-1 and 8-2, the capacity, the cycle characteristics under the high temperature environment, and the swelling as in Examples 1-1 to 1-4 The amount was examined. The results are shown in Table 8 together with the results of Example 1-1 and Comparative example 1-1.

  As can be seen from Table 8, the same results as in Example 1-1 were obtained. That is, even when a liquid electrolyte or another electrolyte is used, it has been found that if the lithium salt shown in Chemical Formula 1 is included in the electrolyte, swelling in a high temperature environment can be suppressed.

(Example 9-1)
A secondary battery was fabricated in the same manner as in Example 1-2, except that the first carbon material was replaced with a CoSnC-containing material and the negative electrode 22 was fabricated. At that time, the CoSnC-containing material, the second carbon material, the conductive agent, and the binder are CoSnC-containing material: second carbon material: conductive agent: binder = 80: 10: 2: 8 Mixed by mass ratio. In addition, in the electrolytic solution, 4-fluoro-1,3-dioxolan-2-one, ethylene carbonate, propylene carbonate, and 1,3-dioxol-2-one as a solvent, 4-fluoro-1, LiPF ₆ as an electrolyte salt in a solvent mixed in a mass ratio of 3-dioxolan-2-one: ethylene carbonate: propylene carbonate: 1,3-dioxol-2-one = 25: 24.5: 49.5: 1 And what dissolved LiB (C ₂ O ₄ ) ₂ represented by the structural formula shown in Chemical Formula ₂ was used. The concentration of LiPF _{6 in} the electrolytic solution was 0.65 mol / l, and the concentration of LiB (C ₂ O ₄ ) ₂ was 0.05 mol / l.

  Further, the CoSnC-containing material powder was synthesized by mixing a cobalt-tin alloy powder and a carbon powder and utilizing a mechanochemical reaction. When the composition of the obtained CoSnC-containing material was analyzed, the content of cobalt was 29.4% by mass, the content of tin was 50% by mass, the content of carbon was 19.6% by mass, tin and cobalt The ratio of cobalt to the total of Co / (Sn + Co) was 37% by 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, a peak P1 was obtained as shown in FIG. When the peak P1 was analyzed, a peak P2 of surface contamination carbon and a peak P3 of C1s in the CoSnC-containing material on the lower energy side than the peak P2 were obtained. This peak P3 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.

As Comparative Example 9-1 with respect to Example 9-1, a secondary battery was fabricated in the same manner as Example 9-1 except that LiB (C ₂ O ₄ ) ₂ was not used. At that time, the concentration of LiPF _{6 in} the electrolytic solution was 0.7 mol / l.

  For the fabricated secondary batteries of Example 9-1 and Comparative Example 9-1, the capacity, the cycle characteristics under a high temperature environment, and the swelling amount were examined in the same manner as in Examples 1-1 to 1-4. The results are shown in Table 9 together with the results of Example 1-2 and Comparative example 1-2.

  As can be seen from Table 9, the same results as in Example 1-2 were obtained. That is, even when other negative electrode active materials were used, it was found that if the lithium salt shown in Chemical Formula 1 was included in the electrolyte, swelling in a high temperature environment could be suppressed.

  Although the present invention has been described with reference to the embodiments and examples, 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 secondary battery having a winding structure has been specifically described, but the present invention also applies to a secondary battery having another stacked structure in which a positive electrode and a negative electrode are stacked. The same can be applied. Further, the present invention is not limited to the secondary battery, and can be similarly applied to other batteries such as a primary battery.

  Furthermore, in the above-described embodiment and examples, the case where lithium is used as the electrode reactant has been described. However, 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 positive electrode active material or a solvent that can occlude and release the electrode reactant is selected according to the electrode reactant.

  Furthermore, in the above-described embodiments and examples, the description has been given of the case of using an electrolyte solution that is a liquid electrolyte or a gel electrolyte in which an electrolyte solution is held in a polymer compound. The electrolyte may be used. Examples of other electrolytes include a mixture of a solid electrolyte having ionic conductivity and an electrolyte solution, or a mixture of a solid electrolyte and a gel electrolyte.

  As the solid electrolyte, for example, a polymer solid electrolyte in which an electrolyte salt is dispersed in a polymer compound having ion conductivity, or an inorganic solid electrolyte made of ion conductive glass or ionic crystals can be used. In this case, as the polymer compound, 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 polyacrylate, or a mixture thereof, or in the molecule It can be used after being copolymerized. As the inorganic solid electrolyte, lithium nitride, lithium iodide, or the like can be used.

It is a disassembled perspective view showing the structure of the secondary battery which concerns on one embodiment of this invention. It is sectional drawing showing the structure along the II-II line of the winding electrode body shown in FIG. 1 shows an example of a peak obtained by X-ray photoelectron spectroscopy relating to a CoSnC-containing material produced in an example.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 11 ... Positive electrode lead, 12 ... Negative electrode lead, 20 ... Winding electrode body, 21 ... Positive electrode, 21A ... Positive electrode collector, 21B ... Positive electrode active material layer, 22 ... Negative electrode, 22A ... Negative electrode collector, 22B ... Negative electrode active Material layer 23 ... Separator 24 ... Electrolyte layer 25 ... Protective tape 31 ... Exterior member 32 ... Adhesion film

Claims (6)

A battery having an electrolyte together with a positive electrode and a negative electrode inside a film-shaped exterior member,
The battery contains an electrolytic solution containing LiPF ₆ and the lithium salt shown in Chemical formula 1.
(Chemical formula 1)
_{LiB (C p H 2 (p} -2) O 4) (C q H 2 (q-2) O 4)
(In the formula, p and q are each an integer of 2 or more.)   2. The battery according to claim 1, wherein the concentration of the lithium salt shown in Chemical Formula 1 in the electrolytic solution is in the range of 0.005 mol / l to 0.2 mol / l.   The battery according to claim 1, wherein the electrolytic solution contains at least one of 1,3-dioxol-2-one and 4-vinyl-1,3-dioxolan-2-one. The positive electrode has a positive electrode current collector and a positive electrode active material layer provided on the positive electrode current collector,
The battery according to claim 1, wherein the content of lithium carbonate in the positive electrode active material layer is 0.5 mass% or less. The negative electrode has a negative electrode current collector and a negative electrode active material layer provided on the negative electrode current collector,
The negative electrode active material layer includes a first carbon material and a second carbon material having a specific surface area larger than that of the carbon material,
2. The battery according to claim 1, wherein the content of the second carbon material in the negative electrode active material layer is in the range of 2% by mass to 40% by mass. The specific surface area of the second carbon material, a battery according to claim 5, characterized in that within the scope of the following 2m ² / g or more 8m ² / g.

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