JP4674458B2 - Nonaqueous electrolyte secondary battery - Google Patents

Description

The present invention relates to a non-aqueous electrolyte secondary battery including a wound electrode body wound between a positive electrode and a negative electrode via a separator.

  With the miniaturization of electronic devices, development of batteries having high energy density is required. As a battery that meets this requirement, there is a lithium metal secondary battery that utilizes a precipitation / dissolution reaction of lithium (Li). However, the lithium metal secondary battery has a problem that the cycle life is short because lithium dendrites on the negative electrode during charging and becomes inactive.

  As a battery with improved cycle life, a lithium ion secondary battery has been commercialized. The negative electrode of a lithium ion secondary battery has a negative electrode active material such as a graphite material using lithium intercalation reaction between graphite layers, or a carbonaceous material applying lithium occlusion / release action into pores. It is used. Therefore, in a lithium ion secondary battery, lithium does not deposit dendrites and the cycle life is long. In addition, since the graphite material or the carbonaceous material is stable in the air, there is a great merit in industrial production.

However, the negative electrode capacity due to intercalation has an upper limit as defined by the composition C ₆ Li of the first stage graphite intercalation compound. In addition, it is industrially difficult to control the fine pore structure of the carbonaceous material and causes a decrease in the specific gravity of the carbonaceous material, which is effective in improving the negative electrode capacity per unit volume and thus the battery capacity per unit volume. It cannot be a means.

Therefore, recently, in order to further increase the capacity, materials that apply the electrochemical and reversible generation and decomposition of certain lithium alloys have been widely studied. As such a material, for example, a lithium-aluminum alloy has been widely studied, and a silicon alloy is reported in Patent Document 1.
U.S. Pat. No. 4,950,566

  However, since these materials have larger expansion / contraction during charging / discharging than carbon materials, there is a problem that the separator is easily damaged by repeated charging / discharging and internal short circuit is likely to occur. In particular, the separator is easily damaged at high temperatures, and improvement of the high temperature characteristics has been desired.

This invention is made | formed in view of this problem, The objective is to provide the nonaqueous electrolyte secondary battery which can suppress an internal short circuit.

Non-aqueous electrolyte secondary battery according to the invention comprises a wound electrode body formed by winding via a separator and a positive electrode and the negative electrode, the negative electrode, the negative electrode active material of the electrode reactant Ru can der of occluding and releasing As a constituent element, 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 ratio of cobalt to the total of tin and cobalt is 30 mass% or more and 70 mass%. The separator contains a material having a mass% or less, and the separator has a pin puncture strength of 4.0 N to 9.8 N in terms of thickness converted to 20 μm, and a tensile strength in the winding axis direction of 40 MPa to 150 MPa. It is.

According to the nonaqueous electrolyte secondary battery of the present invention, the negative electrode includes tin, cobalt, and carbon as constituent elements as the negative electrode active material, and the carbon content is 9.9 mass% or more and 29.7 mass% or less. And the ratio of cobalt to the total of tin and cobalt is 30% by mass or more and 70% by mass or less. In this case, the above-described puncture strength of the separator is set to 4.0 N or more and the tensile strength is set to 40 MPa or more. Therefore, even when a negative electrode active material that greatly expands and contracts with charge and discharge is used, damage to the separator is suppressed. It is possible to suppress the occurrence of an internal short circuit. Therefore, high temperature characteristics can be improved. Moreover, since the puncture strength of the separator described above is 9.8 N or less and the tensile strength is 150 MPa or less, thermal shrinkage can be suppressed, and the occurrence of an internal short circuit during heating can also be suppressed. Therefore, reliability can be improved.

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

(First embodiment)
FIG. 1 shows a cross-sectional configuration of the secondary battery according to the first embodiment of the present invention. This secondary battery is a so-called cylindrical type, and a wound electrode body 20 in which a belt-like positive electrode 21 and a negative electrode 22 are wound through a separator 23 inside a substantially hollow cylindrical battery can 11. have. The battery can 11 is made of, for example, iron (Fe) plated with nickel (Ni), and has one end closed and the other end open. Inside the battery can 11, a pair of insulating plates 12, 13 are arranged perpendicular to the winding peripheral surface so as to sandwich the winding electrode body 20.

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

  For example, a center pin 24 is inserted in the center of the wound electrode body 20. A positive electrode lead 25 made of aluminum (Al) or the like is connected to the positive electrode 21 of the spirally wound electrode body 20, and a negative electrode lead 26 made of nickel or the like is connected to the negative electrode 22. The positive electrode lead 25 is electrically connected to the battery lid 14 by being welded to the safety valve mechanism 15, and the negative electrode lead 26 is welded to and electrically connected to the battery can 11.

  FIG. 2 shows an enlarged part of the spirally wound electrode body 20 shown in FIG. The positive electrode 21 has, for example, a structure in which a positive electrode active material layer 21B is provided on both surfaces or one surface of a positive electrode current collector 21A having a pair of opposed surfaces. The positive electrode current collector 21A is made of, for example, a metal foil such as an aluminum foil, a nickel foil, or a stainless steel foil.

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.

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 and manganese (Mn Among these, those containing at least one of them 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)) 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.

  The negative electrode 22 has, for example, a structure in which a negative electrode active material layer 22B is provided on both surfaces or one surface of a negative electrode current collector 22A having a pair of opposed surfaces. The negative electrode current collector 22A is made of, for example, a metal foil such as a copper (Cu) foil, a nickel foil, or a stainless steel foil.

  The negative electrode active material layer 22B can contain and release lithium as an electrode reactant as a negative electrode active material, and contains a negative electrode material containing at least one of a metal element and a metalloid element as a constituent element is doing. This is because a high energy density can be obtained by using such a negative electrode material. 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, gallium (Ga), indium (In), silicon (Si), germanium (Ge), tin (Sn), lead (Pb), bismuth (Bi) ), Cadmium (Cd), silver (Ag), zinc (Zn), hafnium (Hf), zirconium (Zr), yttrium (Y), palladium (Pd) or 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.

  As an alloy of tin, for example, as a second constituent element other than tin, silicon, nickel, copper, iron, cobalt, manganese, zinc, indium, silver, titanium (Ti), germanium, bismuth, antimony (Sb) and The thing containing at least 1 sort (s) of the group which consists of chromium (Cr) is 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 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 or bismuth are preferable, and two or more kinds are included. May be included. 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).

  The negative electrode active material layer 12 may further include other negative electrode active materials, and may include other materials that do not contribute to charging, such as a conductive agent, a binder, or a viscosity modifier. Examples of other negative electrode active materials include carbon materials such as natural graphite, artificial graphite, non-graphitizable carbon, and graphitizable carbon. Examples of the conductive agent include graphite fiber, metal fiber, and metal powder. Examples of the binder include a fluorine-based polymer compound such as polyvinylidene fluoride, or a synthetic rubber such as styrene butadiene rubber or ethylene propylene diene rubber. Examples of the viscosity modifier include carboxymethylcellulose.

  The separator 23 separates the positive electrode 21 and the negative electrode 22 and allows lithium ions to pass through while preventing a short circuit of current due to contact between the two electrodes. Examples of the material constituting the separator 23 include synthetic resins such as polytetrafluoroethylene, polypropylene, and polyethylene. The puncture strength of the separator 23 is preferably in the range of 4.0 N to 9.8 N in terms of the thickness converted to 20 μm, and the tensile strength in the winding axis direction is in the range of 40 MPa to 150 MPa. It is preferable. If the piercing strength and tensile strength are small, the separator 23 is damaged due to expansion / contraction of the negative electrode 22 due to charge / discharge, and an internal short circuit is likely to occur. If the piercing strength and tensile strength are large, the thermal contraction rate of the separator 23 is increased. This is because an internal short circuit is likely to occur during heating. The puncture strength of the separator 23 is converted according to the equation shown in Equation 1.

(Equation 1)
Y (N) = {X (N) / a (μm)} × 20 (μm)
Y: Puncture strength converted to a thickness of 20 μm X: Puncture strength of the separator 23 a: Thickness of the separator 23

  The separator 23 is impregnated with an electrolytic solution that is a liquid electrolyte. The electrolytic solution includes, for example, a solvent and an electrolyte salt dissolved in the solvent.

  Examples of the solvent include ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, 1,2-dimethoxyethane, 1,2-diethoxyethane, γ-butyrolactone, γ-valerolactone, tetrahydrofuran, 2- Methyltetrahydrofuran, 1,3-dioxolane, 4-methyl-1,3-dioxolane, 1,3-dioxol-2-one, 4-vinyl-1,3-dioxolan-2-one, 4-fluoro-1,3 -Dioxolan-2-one, diethyl ether, sulfolane, methyl sulfolane, acetonitrile, propionitrile, anisole, acetate ester, butyrate ester, propionate ester, fluorobenzene, tert-butylbenzene, tert-cyclohexylbenzene, ethylenesulfite, etc. Non-aqueous solvents are mentioned. A solvent may be used individually by 1 type, but 2 or more types may be mixed and used for it.

Examples of the electrolyte salt include LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAsF ₆ , LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ , LiC (CF ₃ SO ₂ ) ₃ , LiB ( Examples thereof include lithium salts such as C ₆ H ₅ ) ₄ , LiB (C ₂ O ₄ ) ₂ , LiCF ₃ SO ₃ , LiCH ₃ SO ₃ , LiCl, or LiBr. One electrolyte salt may be used alone, or two or more electrolyte salts 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 powder, a conductive agent, and a binder to prepare a positive electrode mixture, and then using the positive electrode mixture in a solvent such as N-methyl-2-pyrrolidone. The positive electrode mixture slurry is dispersed to form a positive electrode mixture slurry, and the positive electrode mixture slurry is applied to the positive electrode current collector 21A, dried, and compression molded. Further, for example, in the same manner as the positive electrode 21, the negative electrode active material layer 22 </ b> B is formed on the negative electrode current collector 22 </ b> A to produce the negative electrode 22.

  Next, the positive electrode lead 25 is attached to the positive electrode current collector 21A by welding or the like, and the negative electrode lead 26 is attached to the negative electrode current collector 22A by welding or the like. Subsequently, the positive electrode 21 and the negative electrode 22 are wound through the separator 23, and the tip of the positive electrode lead 25 is welded to the safety valve mechanism 15, and the tip of the negative electrode lead 26 is welded to the battery can 11. The positive electrode 21 and the negative electrode 22 are sandwiched between a pair of insulating plates 12 and 13 and stored in the battery can 11. After the positive electrode 21 and the negative electrode 22 are accommodated in the battery can 11, the electrolytic solution is injected into the battery can 11 and impregnated in the separator 23. After that, the battery lid 14, the safety valve mechanism 15, and the heat sensitive resistance element 16 are fixed to the opening end of the battery can 11 by caulking through a gasket 17. Thereby, the secondary battery shown in FIG. 1 is completed.

  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 electrolytic solution. On the other hand, when discharging is performed, for example, lithium ions are extracted from the negative electrode 22 and inserted in the positive electrode 21 through the electrolytic solution. Along with this charging / discharging, the negative electrode 22 greatly expands and contracts in the laminating direction and the width direction. However, since the puncture strength and tensile strength of the separator 23 are within the predetermined ranges, durability against impact is improved and internal short-circuiting occurs. Is suppressed.

  As described above, according to the present embodiment, the puncture strength of the separator 23 is 4.0 N or more in terms of a thickness of 20 μm, and the tensile strength in the winding axis direction is 40 MPa or more. The electrode reactant can be occluded and released, and even when a material containing at least one of a metal element and a metalloid element as a constituent element is used, damage due to expansion / contraction of the negative electrode 22 can be suppressed. Can do. Therefore, generation | occurrence | production of an internal short circuit can be suppressed and especially the high temperature characteristic which is easy to generate | occur | produce a damage can be improved. Moreover, since the puncture strength of the separator 23 is 9.8 N or less in terms of a thickness of 20 μm and the tensile strength in the winding axis direction is 150 MPa or less, the thermal contraction of the separator 23 can be suppressed, The occurrence of an internal short circuit at the time can also be suppressed. Therefore, reliability can be improved.

(Second Embodiment)
FIG. 3 shows the configuration of the secondary battery according to the second embodiment of the present invention. This secondary battery is a so-called laminate film type, and has a wound electrode body 30 to which a positive electrode lead 31 and a negative electrode lead 32 are attached accommodated in a film-shaped exterior member 40.

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

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

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

  FIG. 4 shows a cross-sectional structure taken along line II of the spirally wound electrode body 30 shown in FIG. The electrode winding body 30 is obtained by laminating a positive electrode 33 and a negative electrode 34 via a separator 35 and an electrolyte layer 36 and winding them, and the outermost periphery is protected by a protective tape 37.

  The positive electrode 33 has a structure in which a positive electrode active material layer 33B is provided on one or both surfaces of a positive electrode current collector 33A. The negative electrode 34 has a structure in which a negative electrode active material layer 34B is provided on one surface or both surfaces of a negative electrode current collector 34A, and the negative electrode active material layer 34B and the positive electrode active material layer 33B are arranged to face each other. Yes. The configurations of the positive electrode current collector 33A, the positive electrode active material layer 33B, the negative electrode current collector 34A, the negative electrode active material layer 34B, and the separator 35 are the same as those of the positive electrode current collector 21A and the positive electrode active material layer 21B in the first embodiment described above. , The same as the anode current collector 22A, the anode active material layer 22B, and the separator 23.

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

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

  First, a precursor solution containing an electrolytic solution, a polymer compound, and a mixed solvent is applied to each of the positive electrode 33 and the negative electrode 34, and the mixed solvent is volatilized to form the electrolyte layer 36. After that, the positive electrode lead 31 is attached to the end of the positive electrode current collector 33A by welding, and the negative electrode lead 32 is attached to the end of the negative electrode current collector 34A by welding. Next, the positive electrode 33 and the negative electrode 34 on which the electrolyte layer 36 is formed are laminated via a separator 35 to form a laminated body, and then the laminated body is wound in the longitudinal direction, and a protective tape 37 is adhered to the outermost peripheral portion. Thus, the wound electrode body 30 is formed. Finally, for example, the wound electrode body 30 is sandwiched between the exterior members 40, and the outer edges of the exterior members 40 are sealed and sealed by heat fusion or the like. At that time, the adhesion film 41 is inserted between the positive electrode lead 31 and the negative electrode lead 32 and the exterior member 40. Thereby, the secondary battery shown in FIGS. 3 and 4 is completed.

  Further, this secondary battery may be manufactured as follows. First, the positive electrode 33 and the negative electrode 34 are prepared as described above, and after the positive electrode lead 31 and the negative electrode lead 32 are attached to the positive electrode 33 and the negative electrode 34, the positive electrode 33 and the negative electrode 34 are stacked via the separator 35 and wound. Rotate and adhere the protective tape 37 to the outermost periphery to form a wound body that is a precursor of the wound electrode body 30. Next, the wound body is sandwiched between the exterior members 40, and the outer peripheral edge portion excluding one side is heat-sealed to form a bag shape, and is stored inside the exterior member 40. Subsequently, an electrolyte composition including an electrolytic solution, a monomer that is a raw material of the polymer compound, a polymerization initiator, and other materials such as a polymerization inhibitor as necessary is prepared, and the interior of the exterior member 40 Inject.

  After injecting the electrolyte composition, the opening of the exterior member 40 is heat-sealed and sealed in a vacuum atmosphere. Next, heat is applied to polymerize the monomer to obtain a polymer compound, thereby forming a gel electrolyte layer 36, and assembling the secondary battery shown in FIGS.

  The operation and effect of the secondary battery are the same as those in the first embodiment described above. That is, since the puncture strength and tensile strength of the separator 35 are set within the predetermined ranges, the occurrence of an internal short circuit can be suppressed.

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

(Examples 1-1 to 1-4)
A cylindrical secondary battery as shown in FIG. 1 was produced.

First, lithium cobalt composite oxide (LiCoO ₂ ) is prepared as a positive electrode active material, 91 parts by mass of this lithium cobalt composite oxide powder, and 6 parts by mass of graphite (KS-15 made by Lonza) as a conductive agent are bound. A positive electrode mixture was prepared by mixing 3 parts by mass of polyvinylidene fluoride as an agent, and then dispersed in N-methyl-2-pyrrolidone as a solvent to prepare a positive electrode mixture slurry. Next, the positive electrode mixture slurry was applied to both surfaces of a positive electrode current collector 21A made of an aluminum foil, dried, and then compression molded to form a positive electrode active material layer 21B, thereby producing a belt-like positive electrode 21.

  On the other hand, 10 parts by mass of cobalt powder and 90 parts by mass of tin powder were mixed, and this mixture was put into a quartz boat, heated to 1000 ° C. in an argon gas atmosphere, and allowed to cool to room temperature. The lump thus obtained was pulverized by a ball mill in an argon gas atmosphere to obtain a cobalt-tin alloy powder (10Co-90Sn). In addition, the number shown before the chemical symbol is a mass ratio. Next, using this cobalt-tin alloy powder as a negative electrode active material, 80 parts by mass of cobalt-tin alloy powder, 11 parts by mass of a conductive agent and negative electrode active material graphite (KS-15 made by Lonza), and 1 part by mass of acetylene black Then, 8 parts by mass of polyvinylidene fluoride as a binder was mixed to prepare a negative electrode mixture, and then dispersed in N-methyl-2-pyrrolidone as a solvent to prepare a negative electrode mixture slurry. Subsequently, the negative electrode mixture slurry was applied to both surfaces of the negative electrode current collector 22A made of copper foil, dried, and then compression-molded to form the negative electrode active material layer 22B. Thus, a strip-shaped negative electrode 22 was produced.

  Next, a separator 23 made of a microporous polyethylene film was prepared and processed to change the puncture strength and tensile strength of the separator 23 as shown in Table 1 in Examples 1-1 to 1-4. It was. Specifically, in Example 1-1, the puncture strength converted to a thickness of 20 μm is 4.0 N, the tensile strength in the winding axis direction is 40 MPa, and in Example 1-2, the puncture strength is 4.0 N. The tensile strength was 70 MPa, in Example 1-3, the piercing strength was 7.0 N, the tensile strength was 88 MPa, and in Example 1-4, the piercing strength was 9.8 N and the tensile strength was 150 MPa.

Subsequently, the produced positive electrode 21 and negative electrode 22 were wound through a separator 23 to produce a wound electrode body 20. After that, the wound electrode body 20 was sandwiched between the insulating plates 12 and 13 and accommodated in the battery can 11 and the electrolyte was injected. The electrolytic solution was prepared by mixing 20% by mass of 4-fluoro-1,3-dioxolan-2-one, 20% by mass of ethylene carbonate, 45% by mass of dimethyl carbonate, and 15% by mass of LiPF _{6 as} an electrolyte salt. Prepared. Next, the battery can 11 was caulked through the gasket 17 to fix the safety valve mechanism 15, the heat sensitive resistance element 16, and the battery lid 14 to obtain a secondary battery.

  Further, as Comparative Examples 1-1 to 1-3 with respect to Examples 1-1 to 1-4, except that the puncture strength and tensile strength of the separator were changed as shown in Table 1, other than Example 1 Secondary batteries were fabricated in the same manner as -1 to 1-4.

  With respect to the fabricated secondary batteries of Examples 1-1 to 1-4 and Comparative Examples 1-1 to 1-3, the high-temperature cycle characteristics, heating safety, and high-temperature storage characteristics were evaluated as follows. These results are shown in Table 1.

<High temperature cycle characteristics>
In an environment of 45 ° C., after performing constant current and constant voltage charging with a current value of 1 C and an upper limit voltage of 4.2 V, 200 cycles of charging and discharging that perform constant current discharging with a current value of 1 C up to a final voltage of 2.5 V, The capacity retention rate (%) of the discharge capacity at the 200th cycle relative to the discharge capacity at the second cycle was determined. Note that 1C is a current value at which the battery capacity can be discharged in one hour.

<Heating safety>
Five batteries were prepared for each example, stored in an oven at 150 ° C. for 1 hour in a charged state, and the number of safety valve mechanisms 15 operated was examined. Table 1 shows the percentage of non-defective products for which the safety valve mechanism 15 did not operate.

<High temperature storage characteristics>
Five batteries were prepared for each example, stored in a 45 ° C. thermostatic bath for one week in an overcharged state of 4.3 V, and the number of safety valve mechanisms 15 operated was examined. Table 1 shows the percentage of non-defective products for which the safety valve mechanism 15 did not operate.

  As shown in Table 1, according to Examples 1-1 to 1-4 in which the puncture strength of the separator 23 is 4.0 N to 9.8 N and the tensile strength is 40 MPa to 150 MPa, high temperature cycle characteristics, heating Excellent results were obtained for both safety and high-temperature storage characteristics. On the other hand, in Comparative Examples 1-1 and 1-2 where the puncture strength or tensile strength of the separator is small, the high-temperature cycle characteristics and high-temperature storage characteristics are low, and in Comparative Example 1-3 where the puncture strength and tensile strength are large, heating is performed. Safety was low.

  That is, if the puncture strength of the separator 23 is 4.0 N to 9.8 N in terms of a thickness of 20 μm and the tensile strength in the winding axis direction is 40 MPa to 150 MPa, the negative electrode containing tin as a constituent element It has been found that even when an active material is used, high temperature characteristics and reliability can be improved.

(Examples 2-1 to 2-4)
A secondary battery was fabricated in the same manner as in Examples 1-1 to 1-4 except that magnesium silicide (Mg ₂ Si) powder was used as the negative electrode active material instead of cobalt-tin alloy powder. did. At that time, in Examples 2-1 to 2-4, as in Examples 1-1 to 1-4, the puncture strength and tensile strength of the separator 23 were changed as shown in Table 2. Further, as Comparative Examples 2-1 to 2-3 with respect to Examples 2-1 to 2-4, except that the puncture strength and tensile strength of the separator were changed as shown in Table 2, the others were Example 2. Secondary batteries were fabricated in the same manner as -1 to 2-4.

  For the fabricated secondary batteries of Examples 2-1 to 2-4 and Comparative Examples 2-1 to 2-3, high-temperature cycle characteristics, heating safety, and high-temperature storage are the same as in Examples 1-1 to 1-4. Characteristics were evaluated. These results are shown in Table 2.

  As shown in Table 2, according to Examples 2-1 to 2-4 in which the puncture strength of the separator 23 is 4.0 N to 9.8 N and the tensile strength is 40 MPa to 150 MPa, high temperature cycle characteristics, heating Whereas excellent results were obtained for both safety and high temperature storage characteristics, Comparative Examples 2-1 and 2-2 with low piercing strength or tensile strength had low high temperature cycle characteristics and high temperature storage characteristics. In Comparative Example 2-3 having high puncture strength and tensile strength, the heating safety was low.

  That is, it has been found that even when a negative electrode active material containing silicon as a constituent element is used, high temperature characteristics and reliability can be improved if the puncture strength and tensile strength of the separator 23 are within the above-described ranges.

(Examples 3-1 to 3-4)
Secondary batteries were fabricated in the same manner as in Examples 1-1 to 1-4 except that a CoSnC-containing material was used as the negative electrode active material instead of the cobalt-tin alloy powder. At that time, in Examples 3-1 to 3-4, as in Examples 1-1 to 1-4, the puncture strength and tensile strength of the separator 23 were changed as shown in Table 3.

  The CoSnC-containing material was produced as follows. 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.

  Further, as Comparative Examples 3-1 to 3-3 with respect to Examples 3-1 to 3-4, except that the puncture strength and tensile strength of the separator were changed as shown in Table 3, the others were Example 3. Secondary batteries were fabricated in the same manner as in -1 to 3-4.

  For the fabricated secondary batteries of Examples 3-1 to 3-4 and Comparative Examples 3-1 to 3-3, high-temperature cycle characteristics, heating safety, and high-temperature storage were the same as in Examples 1-1 to 1-4. Characteristics were evaluated. These results are shown in Table 3. In Table 3, the content of the negative electrode active material was shown in mass% before the constituent elements.

  As shown in Table 3, according to Examples 3-1 to 3-4 in which the puncture strength of the separator 23 is 4.0 N to 9.8 N and the tensile strength is 40 MPa to 150 MPa, high temperature cycle characteristics, heating While excellent results were obtained for both safety and high temperature storage characteristics, Comparative Examples 3-1 and 3-2 having low piercing strength or tensile strength had low high temperature cycle characteristics and high temperature storage characteristics. In Comparative Example 3-3 having high puncture strength and tensile strength, the heating safety was low. That is, it has been found that even when negative electrode active materials having other compositions are used, the high temperature characteristics and reliability can be improved if the puncture strength and tensile strength of the separator 23 are within the above-described ranges.

  Further, as can be seen from a comparison between Table 1 and Table 3, Examples 3-1 to 3- using CoSnC-containing materials as compared with Examples 1-1 to 1-4 using a cobalt-tin alloy. No. 4 was able to obtain excellent cycle characteristics. In other words, it has been found preferable to use a CoSnC-containing material as the negative electrode active material.

  Although the present invention has been described with reference to the embodiments and examples, the present invention is not limited to the embodiments and examples, and various modifications can be made. For example, in the above-described embodiments and examples, the case where an electrolytic solution is used as the electrolyte is described. In the above-described embodiment, the case where a gel electrolyte in which the electrolytic solution is held in a polymer compound is used is also described. Other 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 electrolytic solution, or a mixture of another inorganic compound and an electrolytic solution. Or a mixture of these inorganic compounds and a gel electrolyte.

  In the above embodiment and examples, a battery using lithium as an electrode reactant has been described. However, other alkali metals such as sodium (Na) or potassium (K), or alkalis such as magnesium or calcium (Ca) are used. The present invention can also be applied to the case of using an earth metal or another light metal such as aluminum. At that time, the negative electrode active material described in the above embodiment, for example, a material containing tin or silicon as a constituent element can be used in the same manner for the negative electrode.

  Furthermore, in the above embodiments and examples, a cylindrical or laminated film type secondary battery has been specifically described. However, the present invention also applies to secondary batteries having other shapes such as a square type. 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.

It is sectional drawing showing the structure of the secondary battery which concerns on the 1st Embodiment of this invention. It is sectional drawing which expands and represents a part of winding electrode body in the secondary battery shown in FIG. It is a disassembled perspective view showing the structure of the secondary battery which concerns on the 2nd Embodiment of this invention. It is sectional drawing showing the structure along the II line of the winding electrode body shown in FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 ... Battery can, 12, 13 ... Insulation board, 14 ... Battery cover, 15 ... Safety valve mechanism, 15A ... Disc board, 16 ... Heat sensitive resistance element, 17 ... Gasket, 20, 30 ... Winding electrode body, 21, 33 ... Positive electrode, 21A, 33A ... Positive electrode current collector, 21B, 33B ... Positive electrode active material layer, 22, 34 ... Negative electrode, 22A, 34A ... Negative electrode current collector, 22B, 34B ... Negative electrode active material layer, 23, 35 ... Separator , 24 ... Center pin, 25, 31 ... Positive electrode lead, 26, 32 ... Negative electrode lead, 36 ... Electrolyte layer, 37 ... Protective tape, 40 ... Exterior member, 41 ... Adhesion film.

Claims (3)

A winding electrode body in which a positive electrode and a negative electrode are wound through a separator,
The negative electrode, the electrode reactant as an anode active material Ru can der of occluding and releasing includes as an element tin (Sn) and cobalt (Co) and carbon (C), the content of carbon 9 Containing a material that is not less than 9.9% by mass and not more than 29.7% by mass and the ratio of cobalt to the total of tin and cobalt is not less than 30% by mass and not more than 70% by mass
The separator has a puncture strength of 4.0 N to 9.8 N in terms of thickness converted to 20 μm, and a tensile strength in the winding axis direction of 40 MPa to 150 MPa .
Non-aqueous electrolyte secondary battery. The negative electrode active material includes, as other constituent elements, silicon (Si), iron (Fe), nickel (Ni), chromium (Cr), indium (In), niobium (Nb), germanium (Ge), titanium (Ti ), Molybdenum (Mo), aluminum (Al), phosphorus (P), gallium (Ga), or bismuth (Bi), the nonaqueous electrolyte secondary battery according to claim 1. With respect to the negative electrode active material, the half-value width of the diffraction peak obtained by X-ray diffraction is 1.0 ° or more, and the peak of the synthetic wave of C1s obtained by X-ray photoelectron spectroscopy is in a region lower than 284.5 eV. The nonaqueous electrolyte secondary battery according to claim 1, which appears.

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