JP5257569B2 - Secondary battery - Google Patents

Description

The present invention relates to a secondary battery including a wound body having a laminated structure of a positive electrode and a negative electrode and a separator provided therebetween.

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

  In a lithium ion secondary battery, a porous film made of a synthetic resin made of polytetrafluoroethylene, polypropylene, polyethylene or the like or a porous film made of a ceramic is used as a separator that separates a positive electrode and a negative electrode. The separator prevents a short circuit of current due to contact between both electrodes, while holding an electrolyte allows lithium ions to pass therethrough and allows a battery reaction between both electrodes.

Up to now, attempts have been made to improve the electrolyte retention performance in the separator by covering the surface of the porous film constituting the separator with a coating film made of a polymer compound having a high affinity with the electrolyte solvent. (For example, refer to Patent Document 1).
JP-A-8-96788

  On the other hand, as a negative electrode active material used for a lithium ion secondary battery, a non-graphitizable carbon or a carbon material such as graphite having a relatively high capacity and good cycle characteristics is widely used.

  However, when such a carbon material is used, since the negative electrode discharge potential is 0.8 V to 1.0 V with respect to lithium (Li), no significant improvement is expected in terms of battery energy density. Furthermore, there is a drawback that the charge / discharge curve has a large hysteresis and the energy efficiency in each charge / discharge cycle is low.

Therefore, recently, as a negative electrode active material with a capacity higher than that of carbon materials, an alloy material has been developed that applies the fact that a certain metal is electrochemically alloyed with lithium and is reversibly generated and decomposed. Research is also underway. Furthermore, as a method for improving the cycle characteristics, it is studied to alloy tin and silicon (Si) to suppress their expansion. For example, it has been proposed to alloy a transition metal such as iron with tin (see Patent Documents 2 to 4 and Non-Patent Documents 1 to 3). In addition, Mg ₂ Si and the like have been proposed (see Non-Patent Document 4).
Japanese Patent Laid-Open No. 2004-22306 JP 2004-63400 A JP 2005-78999 A “Journal of the Electrochemical Society”, 1999, No. 146, p405 “Journal of the Electrochemical Society”, 1999, No. 146, p414 “Journal of the Electrochemical Society”, 1999, No. 146, p423 “Journal of the Electrochemical Society”, 1999, No. 146, p4401

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

  Specifically, when a wound body is configured using a high-capacity negative electrode made of an alloy material as described above, large friction in the winding direction occurs at the interface between the negative electrode and the separator due to expansion of the negative electrode accompanying charge and discharge, If the separator or the negative electrode current collector is locally subjected to excessive stress, it may be damaged such as cracking or breaking. Such damage can cause a short circuit inside the wound body and deterioration of the cycle characteristics of the battery.

  Recently, a coating film as in Patent Document 1 is formed using polyvinylidene fluoride (PVdF), which has high adhesiveness and excellent chemical stability, and maintains the relative positions of the positive electrode, the negative electrode, and the separator with high accuracy. However, a high molecular compound such as PVdF used as a coating film is generally highly adhesive. Therefore, providing a coating film made of such a polymer compound is likely to cause a friction between the separator and the negative electrode.

  The present invention has been made in view of such problems, and its object is to provide a secondary battery having good battery performance while reducing friction during charging and discharging inside the wound body and ensuring high reliability. There is to do.

Secondary battery of the present invention includes a positive electrode, a negative electrode, a wound body comprising a laminate structure of a separator located between the positive electrode and the negative electrode, a lubricant is provided on at least part of the surface of the separator, the separator The static friction coefficient of the surface is 0.30 or less, and the negative electrode contains, as an active material, at least one selected from the group consisting of silicon simple substance, alloy and compound, and tin simple substance, alloy and compound. It is.

  In the secondary battery of the present invention, since the separator has a lubricant on at least a part of its surface, even when the negative electrode expands during charging and discharging, the separator, the positive electrode and the negative electrode The frictional force generated therebetween is reduced, and the stress applied to the positive electrode, the negative electrode, and the separator is relaxed.

  According to the secondary battery of the present invention, since the lubricant is provided on at least a part of the surface of the separator, the stress received by the positive electrode, the negative electrode, and the separator during charge / discharge can be reduced. As a result, while using a high-capacity negative electrode made of an alloy material to increase the capacity, it is possible to avoid short circuits inside the wound body and deterioration of cycle characteristics, and to ensure high reliability as well as improved battery characteristics. Is possible.

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

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

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

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

  The wound body 20 is obtained by laminating a positive electrode 21 and a negative electrode 22 with a separator 23 having a polymer compound layer 26 provided on the surface therebetween, and wound in a spiral shape. It is formed into a flat shape according to A separator 23 is located on the outermost periphery of the wound body 20, and a positive electrode 21 is located immediately inside the separator 23. In FIG. 2, the laminated structure of the positive electrode 21 and the negative electrode 22 is shown in a simplified manner. Further, the number of windings of the wound body 20 is not limited to that shown in FIGS. 1 and 2 and can be arbitrarily set. A positive electrode lead 24 made of aluminum (Al) or the like is connected to the positive electrode 21 of the wound body 20, and a negative electrode lead 25 made of nickel or the like is connected to the negative electrode 22. The positive electrode lead 24 is electrically connected to the terminal plate 14 by being welded to the lower end of the positive electrode pin 15, and the negative electrode lead 25 is welded and electrically connected to the outer can 11.

  FIG. 3 shows a cross-sectional configuration of the positive electrode 21 shown in FIG. 1 before winding. This positive electrode 21 is obtained by providing a positive electrode active material layer 21B on both surfaces of a strip-shaped positive electrode current collector 21A. Specifically, the positive electrode current collector 21A is located on both sides of the positive electrode active material layer 21B on the both sides of the positive electrode covering region 21C and the winding center side and the winding outer peripheral side so as to sandwich the positive electrode covering region 21C. Both surfaces of the positive electrode current collector 21A have positive electrode exposed regions 21DS and 21DE in which the positive electrode active material layer 21B is exposed without being present. The positive electrode lead 24 is joined to the positive electrode exposed region 21DS on the winding center side.

  The positive electrode current collector 21A has, for example, a thickness of about 5 μm to 50 μm and is made of a metal foil such as an aluminum 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.

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

Specific examples of the composite oxide containing lithium and a transition metal element include lithium cobalt composite oxide (Li _x CoO ₂ ), lithium nickel composite oxide (Li _x NiO ₂ ), and lithium nickel cobalt composite oxide (Li _x Ni _1-z Co _z O ₂ (z <1)) or lithium manganese composite oxide (LiMn ₂ O ₄ ) having a spinel structure. Among these, a composite oxide containing nickel is preferable. This is because a high capacity can be obtained and excellent cycle characteristics can also be obtained. Specific examples of the phosphate compound containing lithium and a transition metal element include, for example, a lithium iron phosphate compound (LiFePO ₄ ) or a lithium iron manganese phosphate compound (LiFe _1-v Mn _v PO ₄ (v <1)). Can be mentioned.

  FIG. 4 shows the configuration of the negative electrode 22. The negative electrode 22 is obtained by providing a negative electrode active material layer 22B on both surfaces of a strip-shaped negative electrode current collector 22A. Specifically, the negative electrode covering region 22C where the negative electrode active material layer 22B exists on both surfaces of the negative electrode current collector 22A, and the winding center side and the winding outer peripheral side so as to sandwich the negative electrode covering region 22C, Both surfaces of the negative electrode current collector 22A have positive electrode exposed regions 22DS and 22DE that are exposed without the negative electrode active material layer 22B. The negative electrode lead 25 is joined to the negative electrode exposed region 22DE on the winding outer periphery side.

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

  The negative electrode active material layer 22B includes, for example, a negative electrode active material, and may include other materials such as a conductive material and a binder as necessary. Examples of the negative electrode active material include a negative electrode material that can occlude and release lithium, which is an electrode reactant, and includes at least one of a metal element and a metalloid element as a constituent element. Use of such a negative electrode material is preferable because a high energy density can be obtained. The negative electrode material may be a single element, alloy or compound of a metal element or metalloid element, or may have at least a part of one or more of these phases. In the present invention, alloys include those containing one or more metal elements and one or more metalloid elements in addition to those composed of two or more metal elements. Moreover, the nonmetallic element may be included. There are structures in which a solid solution, a eutectic (eutectic mixture), an intermetallic compound, or two or more of them coexist.

  Examples of the metal element or metalloid element constituting the anode material include a metal element or metalloid element capable of forming an alloy with lithium. Specifically, magnesium (Mg), boron (B), aluminum (Al), gallium (Ga), indium (In), silicon, germanium (Ge), tin, lead (Pb), bismuth (Bi), cadmium Examples thereof include (Cd), silver (Ag), zinc (Zn), hafnium (Hf), zirconium (Zr), yttrium (Y), palladium (Pd), and platinum (Pt).

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

  Examples of tin alloys include silicon, nickel, copper, iron (Fe), cobalt (Co), manganese (Mn), zinc (Zn), indium (In), and silver as second constituent elements other than tin. (Ag), titanium (Ti), germanium (Ge), bismuth (Bi), antimony (Sb), and the thing containing at least 1 sort (s) of chromium (Cr) are mentioned. As an alloy of silicon, for example, as a second constituent element other than silicon, among the group consisting of tin, nickel, copper, iron, cobalt, manganese, zinc, indium, silver, titanium, germanium, bismuth, antimony and chromium The thing containing at least 1 sort (s) 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 of 30% by mass to 70% by mass is preferable. This is because a high energy density can be obtained in such a composition range, and excellent cycle characteristics can be obtained.

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

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

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

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

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

  Further, the negative electrode active material is made of particles having an average particle diameter of 10 μm or less in laser type particle size distribution measurement, for example. The average particle diameter is preferably 5 μm or less, more preferably 1 μm or less.

  The separator 23 has a base material 26 and a polymer compound layer 27 provided on the surface thereof. The base material 26 is composed of, for example, a porous film made of a polyolefin-based material such as polypropylene or polyethylene, or a porous film made of an inorganic material such as a ceramic nonwoven fabric, and these two or more kinds of porous films are used. A laminated structure may be used. Specifically, the base material 26 may have a single-layer structure made of polyethylene, or a three-layer structure in which a layer made of polyethylene is inserted between a pair of layers made of polypropylene.

  The base material 26 is in contact with the positive electrode 21 and the negative electrode 22 through the polymer compound layer 27. 1 and 2 show the case where the polymer compound layer 27 is provided only on one surface of the base material 26, the polymer compound layer 27 is provided on both surfaces of the base material 26. It is desirable to do.

  The polymer compound layer 27 includes an electrolytic solution in which an electrolyte salt is dissolved in a solvent, and a polymer compound that holds the electrolytic solution. Here, the term “holds” the electrolytic solution by the polymer compound is a concept that includes not only the state in which the polymer compound is swollen in the electrolyte solution but also the state in which the electrolyte solution and the polymer compound are mixed without interaction. It is. That is, the polymer compound layer 27 may be a so-called gel electrolyte in which the polymer compound is swollen in the electrolyte solution, or the electrolyte solution is present in the voids of the rigid polymer compound without causing interaction. It may be an electrolyte. The electrolytic solution may be impregnated in the positive electrode 21, the negative electrode 22, or the base material 26.

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

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

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

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

  The polymer compound constituting the polymer compound layer 27 is required to hold an electrolytic solution and exhibit ionic conductivity. Specifically, the acrylonitrile copolymer is 50% or more ( In particular, acrylonitrile polymers, aromatic polyamides, acrylonitrile / butadiene copolymers, acrylate or methacrylate homopolymers or copolymers, acrylamide polymers, vinylidene fluoride, etc. Examples thereof include celluloses such as fluoropolymer, polysulfone, polyallylsulfone, and carboxymethylcellulose. In particular, a polymer having a copolymerization amount of 50% or more of acrylonitrile has a CN group in its side chain, and thus can form a gel electrolyte having a high dielectric constant and high ion conductivity. Acrylic nitriles and vinyl carboxylic acids such as acrylic acid, methacrylic acid, itaconic acid, acrylamide, methacryl sulfonic acid, hydroxyalkylene glycol (meth) are used to improve the electrolyte support for these polymers and the ionic conductivity of the electrolyte. A copolymer obtained by copolymerizing acrylate, alkoxyalkylene glycol (meth) acrylate, vinyl chloride, vinylidene chloride, vinyl acetate, various (meth) acrylates or the like at a ratio of preferably 50% or less, particularly preferably 20% or less can also be used. . These polymer compounds have a melting point of 200 ° C. or higher and are excellent in heat resistance. In addition, since aromatic polyamide is a high heat resistant polymer, it is suitable when further high heat resistance is required.

As the polymer compound constituting the polymer compound layer 27, in addition to the above, a polymer having a cross-linked structure obtained by copolymerizing butadiene or the like may be used. Furthermore, polymers containing vinylidene fluoride as a constituent component, that is, homopolymers, copolymers, and multi-component copolymers can also be used as the polymer compound. Specifically, polyvinylidene fluoride (PVdF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVdF-HFP), and polyvinylidene fluoride-hexafluoropropylene-chlorotrifluoroethylene copolymer (PVdF-HEP-CTFE). ). In particular, from the viewpoint of redox stability, a fluorine-based polymer compound such as polyvinylidene fluoride or a copolymer of vinylidene fluoride and hexafluoropropylene is desirable. The polymer compound layer 27 further includes aluminum oxide (Al ₂ O ₃ ), titanium oxide (TiO ₂ ), zirconium oxide (ZrO ₂ ), cobalt oxide (CoO) or silicon oxide (SiO ₂ ) for the purpose of improving safety. Insulating particles such as) may be included.

The polymer compound layer 27 further contains a lubricant together with the electrolytic solution and the polymer compound. The lubricant is composed of inorganic solid fine particles such as higher fatty acid salt, talc, boron nitride (BN), or molybdenum disulfide (MoS ₂ ), and is held by a polymer compound in the same manner as the electrolytic solution. . Examples of the higher fatty acid salt used here include lithium stearate, sodium stearate, magnesium stearate, zinc stearate, calcium stearate, barium stearate, aluminum stearate, barium laurate, and zinc laurate. It is done. Talc is a mineral composed of magnesium hydroxide and silicate, and its chemical formula is represented by Mg ₃ Si ₄ O ₁₀ (OH) ₂ . Polymer compound layer 27 is provided on the substrate 26 so that the weight per unit area of the total combination of the polymer compound and the lubricant is in the range of 0.07 mg / cm ² of 1.2 mg / cm ² It is good to have. This is because it is easy to ensure good cycle characteristics together with high initial charge / discharge efficiency.

  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 impregnated in the separator 23. When the discharge is performed, for example, lithium ions are released from the negative electrode 22 and inserted into the positive electrode 21 through the electrolytic solution impregnated in the separator 23.

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

  First, a positive electrode active material, a conductive agent, and a binder are mixed to prepare a positive electrode mixture, and the positive electrode mixture is dispersed in a solvent such as N-methyl-2-pyrrolidone to obtain a paste-like positive electrode mixture. A slurry is obtained. Subsequently, the positive electrode mixture slurry is uniformly applied to the positive electrode current collector 21A using a doctor blade or a bar coater, and the solvent is dried. Then, the positive electrode active material layer 21B is formed by compression molding using a roll press or the like. Then, the positive electrode 21 is produced.

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

  Subsequently, the positive electrode lead 24 is attached to the positive electrode current collector 21A by welding or the like, and the negative electrode lead 25 is attached to the negative electrode current collector 22A by welding or the like. On the other hand, the separator 23 is formed by applying the polymer compound layer 27 on one side or both sides of the substrate 26. Specifically, first, a polymer solution such as polyvinylidene fluoride or carboxymethylcellulose was dissolved in a solvent such as N-methyl-2-pyrrolidone or water, and a lubricant was added to prepare a polymer solution. The polymer solution is applied to one side or both sides of the substrate 26 using a technique such as spin coating, spray coating, roll coating or dipping. Next, the applied polymer solution is dried to remove the solvent, whereby the separator 23 in which the polymer compound layer 27 is provided on the substrate 26 is obtained. After that, the positive electrode 21 and the negative electrode 22 are stacked with the separator 23 interposed therebetween, wound in the winding direction R shown in FIG. 3 and FIG. The body 20 is produced.

  Next, the wound body 20 produced as described above is accommodated in the exterior can 11. At this time, if the polymer compound layer 27 is not provided on the separator 23 (base material 26) which is the outermost peripheral surface of the wound body 20, the wound body 20 is smoothly inserted into the outer can 11. The possibility of damaging the base material 26 and the end of the positive electrode 21 located inside thereof is extremely low. After that, the insulating plate 12 is disposed on the wound body 20, the negative electrode lead 25 is welded to the outer can 11, and the positive electrode lead 24 is welded to the lower end of the positive electrode pin 15. The battery lid 13 is fixed by laser welding. Finally, the electrolytic solution is injected into the outer can 11 from the electrolytic solution injection hole 19 and impregnated in the separator 23, and the electrolytic solution injection hole 19 is closed with the sealing member 19A. Thereby, the secondary battery shown in FIGS. 1 and 2 is completed.

  As described above, in the present embodiment, since the polymer compound layer 27 containing the lubricant is provided between the base material 26 of the separator 23 and the negative electrode 22, the negative electrode 22 expands during charging and discharging. Even in this case, the frictional force generated between the separator 23 and the positive electrode 21 and the negative electrode 22 is reduced, and the stress received by the positive electrode 21, the negative electrode 22, and the substrate 26 is relaxed. As a result, by adopting the negative electrode 22 made of an alloy material, it is possible to avoid a short circuit inside the wound body 20 and deterioration of cycle characteristics while achieving high capacity, and to improve battery characteristics and high reliability. It is possible to ensure the sex.

  The greater the content of the lubricant, the easier it is to relieve stress inside the battery due to the expansion of the negative electrode. However, if it is too much, the conductivity of the separator 23 may be reduced, leading to a decrease in battery capacity and load characteristics. Occurs. Therefore, the content of the lubricant is desirably 0.25 to 9 times by weight with respect to the polymer compound constituting the polymer compound layer 27. Further, it is desirable that the lubricant be uniformly contained in the polymer compound layer 27, but it is sufficient that the lubricant is distributed even if it is non-uniform. However, it is desirable that the lubricant is present to such an extent that the static friction coefficient of the surface of the separator 23 is 0.30 or less. This is because by ensuring such a coefficient of static friction, the stress inside the battery accompanying the expansion of the negative electrode can be further relaxed.

  Moreover, in this Embodiment, since the average particle diameter of the negative electrode active material was 10 micrometers or less, damage to the base material 26 in the manufacturing process of a battery can be avoided. In addition, the uneven distribution of the lubricant contained in the polymer compound layer 27 can be reduced and more uniformly dispersed, and the stress inside the battery can be efficiently relieved even with a small amount of lubricant. .

  Furthermore, since the base material 26 of the separator 23 is in close contact with the positive electrode 21 and the negative electrode 22 via the polymer compound layer 27, it is possible to reduce excess electrolyte solution that is not substantially involved in the battery reaction. The electrolytic solution is efficiently supplied around the positive electrode active material layer 21B and the negative electrode active material layer 22B. Therefore, in the present embodiment, excellent cycle characteristics can be ensured while reducing the total amount of the electrolytic solution, and leakage resistance can be improved.

  Specific examples of the present invention will be described in detail.

(Example 1-1)
The secondary battery described in the above embodiment was manufactured. First, lithium carbonate (Li ₂ CO ₃ ) and cobalt carbonate (CoCO ₃ ) are mixed at a ratio of Li ₂ CO ₃ : CoCO ₃ = 0.5: 1 (molar ratio), and 5 ° C. at 900 ° C. in the air. After firing for a time, lithium-cobalt composite oxide (LiCoO ₂ ) as a positive electrode active material was obtained. Next, 91 parts by mass of this lithium / cobalt composite oxide, 6 parts by mass of graphite as a conductive agent, and 3 parts by mass of polyvinylidene fluoride as a binder were mixed to prepare a positive electrode mixture. Subsequently, this positive electrode mixture is dispersed in N-methyl-2-pyrrolidone as a solvent to form a positive electrode mixture slurry, which is uniformly applied to both surfaces of a positive electrode current collector 21A made of an aluminum foil having a thickness of 20 μm and dried. Then, the positive electrode active material layer 21B was formed by compression molding with a roll press machine, and the positive electrode 21 was produced. Subsequently, a positive electrode lead 24 made of aluminum was attached to one end of the positive electrode current collector 21A.

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

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

  Next, 60 parts by mass of this CoSnC-containing material, 28 parts by mass of artificial graphite as a conductive agent and a negative electrode active material and 2 parts by mass of carbon black, and 10 parts by mass of polyvinylidene fluoride as a binder are mixed. The agent was adjusted. Subsequently, the negative electrode mixture is dispersed in N-methyl-2-pyrrolidone as a solvent to form a negative electrode mixture slurry, which is applied to both surfaces of a negative electrode current collector 22A made of a copper foil having a thickness of 15 μm, and dried. The negative electrode active material layer 22B having a thickness of 9 μm was formed by compression molding with a press. Thereafter, a negative electrode lead 25 made of nickel was attached to one end of the negative electrode current collector 22A.

Subsequently, a base material 26 made of a 20 μm-thick microporous polyethylene film (manufactured by Tonen Chemical) was prepared, and polyvinylidene fluoride was dissolved in N-methyl-2-pyrrolidone and talc as a lubricant was added. The obtained polymer solution was applied to one side of the substrate 26 by roller coating, and then washed with pure water and dried to obtain a separator 23 in which the polymer compound layer 27 was formed on the substrate 26. Here, the polymer compound layer 27 is provided on the substrate 26 so that the weight per unit area of only the polymer compound layer 27 (polymer compound and lubricant) after drying is 0.5 mg / cm ^2. I made it. Regarding this point (that is, the weight per unit area of the polymer compound layer 27 after drying), Examples 1-3, 1-5, 1-7, 1-9 and Comparative Examples 1-1 described below are used. The same applies to 1-3. The mixing ratio of polyvinylidene fluoride and talc was 1: 2. Furthermore, after the positive electrode 21, the separator 23, the negative electrode 22, and the separator 23 were sequentially laminated to form a laminated body, the laminated body was wound in a spiral shape to produce a wound body 20. . When forming the laminate, the surface on which the polymer compound layer 27 was formed was made to face the negative electrode 22. The obtained wound body 20 was formed into a flat shape.

Next, after accommodating the wound body 20 molded in a flat shape inside the outer can 11, the insulating plate 12 is disposed on the wound body 20, and the negative electrode lead 25 is welded to the outer can 11. The positive electrode lead 24 was welded to the lower end of the positive electrode pin 15, and the battery lid 13 was fixed to the open end of the outer can 11 by laser welding. After that, the electrolytic solution was injected into the outer can 11 from the electrolytic solution injection hole 19. As the electrolytic solution, a solution obtained by dissolving LiPF ₆ as an electrolyte salt at a concentration of 1 mol / dm ³ in a solvent in which 30% by volume of ethylene carbonate and 70% by volume of diethyl carbonate were mixed was used. Finally, the electrolytic solution injection hole 19 was closed with a sealing member 19A to obtain a square secondary battery.

(Example 1-2)
A secondary battery was fabricated in the same manner as in Example 1-1 except that the base material 26 of the separator 23 was a three-layer structure. Specifically, a base material 26 having a three-layer structure (total thickness is 20 μm) formed by laminating a microporous polypropylene film on both sides of a microporous polyethylene film is prepared, and the same method as in Example 1-1 is used. Thus, a separator 23 in which the polymer compound layer 27 was formed on one surface of the base material 26 was obtained. Also in this example, the base material 26 having a three-layer structure so that the weight per unit area of only the polymer compound layer 27 (polymer compound and lubricant) after drying is 0.5 mg / cm ^2. The polymer compound layer 27 was provided on the surface. Regarding this point (that is, the weight per unit area of the polymer compound layer 27 after drying), Examples 1-4, 1-6, 1-8, 1-10 and Comparative Examples 1-2 described below are used. The same applies to 1-4.

(Example 1-3)
A secondary battery was fabricated in the same manner as in Example 1-1, except that boron nitride (BN) was used as the lubricant.

(Example 1-4)
A secondary battery was fabricated in the same manner as in Example 1-2, except that boron nitride (BN) was used as the lubricant.

(Example 1-5)
A secondary battery was fabricated in the same manner as in Example 1-1, except that molybdenum disulfide (MoS ₂ ) was used as the lubricant.

(Example 1-6)
A secondary battery was fabricated in the same manner as in Example 1-2, except that molybdenum disulfide (MoS ₂ ) was used as the lubricant.

(Example 1-7)
A secondary battery was fabricated in the same manner as in Example 1-1, except that molybdenum disulfide (MoS ₂ ) and zirconium oxide (ZrO ₂ ) were used as the lubricant. Here, the mixing ratio of molybdenum disulfide (MoS ₂ ) and zirconium oxide (ZrO ₂ ) was 1: 1 by weight.

(Example 1-8)
A secondary battery was fabricated in the same manner as in Example 1-2, except that molybdenum disulfide (MoS ₂ ) and zirconium oxide (ZrO ₂ ) were used as the lubricant. Here, the mixing ratio of molybdenum disulfide (MoS ₂ ) and zirconium oxide (ZrO ₂ ) was 1: 1 by weight.

(Example 1-9)
A secondary battery was fabricated in the same manner as in Example 1-1, except that sodium stearate was used as the lubricant.

(Example 1-10)
A secondary battery was fabricated in the same manner as in Example 1-2 except that sodium stearate was used as the lubricant.

As Comparative Examples 1-1 and 1-2, a secondary battery was prepared in the same manner as in Example 1-1 or Example 1-2 except that the lubricant was not added to the polymer compound layer 27. Produced. Further, as Comparative Examples 1-3 and 1-4, secondary batteries were respectively the same as Example 1-1 or Example 1-2 except that zirconium oxide (ZrO ₂ ) was used as a lubricant. Was made.

  50 secondary batteries of Examples 1-1 to 1-10 and Comparative Examples 1-1 to 1-4 obtained as described above were produced, respectively, and charged and discharged in the following manner in an environment at 25 ° C. went. First, as for charging, constant current charging was performed at a constant current of 500 mA until the battery voltage reached 4.2 V, and then constant voltage charging was performed at a constant voltage of 4.2 V until the current value reached 50 mA. Next, for discharging, constant current discharging was performed at a constant current of 500 mA until the battery voltage reached 2.5V. This combination of charge and discharge is defined as one cycle, and charge / discharge is performed up to 30 cycles. As a discharge capacity retention rate (cycle characteristics), the ratio of the discharge capacity at the 30th cycle to the discharge capacity at the second cycle, that is, (30 cycles) The discharge capacity of the eye / discharge capacity of the second cycle) × 100 (%) was calculated. Further, as the initial charge / discharge efficiency, the ratio of the discharge capacity of the first cycle to the charge capacity of the first cycle, that is, (discharge capacity of the first cycle / charge capacity of the first cycle) × 100 (%) was calculated. The obtained results are shown in Table 1.

  Further, the secondary batteries produced under the same conditions as in Examples 1-1 to 1-10 and Comparative Examples 1-1 to 1-4 were charged and discharged up to 5 cycles under the above conditions, and then disassembled to obtain the separator 23. Was taken out. The separator 23 taken out was thoroughly washed with dimethyl carbonate and dried, and then the coefficient of static friction was measured. Specifically, an inclined driving plate type static friction coefficient measuring device (manufactured by Kumagai Riki Kogyo Co., Ltd.) was used and the inclined plate speed was measured as 8 mm / sec. The obtained results are shown in Table 1 together with the results of the initial charge / discharge efficiency and the discharge capacity retention rate.

  As shown in Table 1, in this example, since the predetermined lubricant was added to the polymer compound layer, the static friction coefficient could be reduced as compared with all the comparative examples. As a result, it was possible to improve the discharge capacity retention rate (cycle characteristics) more than Comparative Examples 1 to 4 while maintaining the same initial charge / discharge efficiency as Comparative Examples 1 to 4. This reduces the frictional force between the negative electrode, the positive electrode and the separator due to the repeated charge / discharge expansion, and damages the positive electrode current collector, the separator and the negative electrode current collector, as well as peeling and dropping off the negative electrode active material. This is thought to be due to the result of the suppression.

  Moreover, when the batteries of the examples and comparative examples that were charged and discharged up to 30 cycles under the above conditions were disassembled and the positive electrodes, the negative electrodes, and the separators were observed, the positive electrode current collectors were compared with the comparative examples. Many wrinkles were observed on the body (aluminum foil) and the base material of the separator, and many cracks were observed particularly on the positive electrode current collector. On the other hand, in each Example, damage to a positive electrode, a negative electrode, and a separator was hardly observed.

(Examples 2-1 to 2-7)
Next, as the polymer compound (resin) constituting the polymer compound layer 27, Example 1-1 was used except that various materials shown in Table 2 (described later) were used instead of polyvinylidene fluoride. A secondary battery was fabricated in the same manner as described above. Specifically, polytetrafluoroethylene (PTFE) is used in Example 2-1, polyimide (PI) is used in Example 2-2, polyamide (PA) is used in Example 2-3, and Example 2 is used. -4 uses polyamideimide (PAI), Example 2-5 uses polyethersulfone (PES), Example 2-6 uses polyaramid (PAR), and Example 2-7 uses carboxymethylcellulose (CMC). ) Was used.

(Examples 2-8 to 2-14)
Further, secondary batteries were fabricated in the same manner as in Examples 2-1 to 2-7, except that boron nitride (BN) was used instead of talc as a lubricant to be added to the polymer compound layer 27. did.

(Examples 2-15 to 2-21)
Further, the secondary battery is similar to each of Examples 2-1 to 2-7 except that molybdenum disulfide (MoS ₂ ) is used instead of talc as a lubricant to be added to the polymer compound layer 27. Was made.

  For the fabricated secondary batteries of Examples 2-1 to 2-21, the initial charge / discharge efficiency and the discharge capacity retention rate were calculated in the same manner as in Examples 1-1 to 1-10. The obtained results are shown in Table 2 together with the results of Examples 1-1, 1-3, and 1-5.

  As shown in Table 2, in Examples 2-1 to 2-7, regardless of which resin was used as the polymer compound constituting the polymer compound layer 27, the same initial level as that of polyvinylidene fluoride was used. Charge / discharge efficiency and discharge capacity retention rate (cycle characteristics) were obtained. Similar results were obtained for Examples 2-8 to 2-14 using boron nitride as a lubricant and Examples 2-15 to 2-21 using molybdenum disulfide.

(Examples 3-1 to 3-7)
Next, a secondary battery was fabricated in the same manner as in Example 1-5 except that the mixing ratio of polyvinylidene fluoride and molybdenum disulfide (MoS ₂ ) in the polymer compound layer 27 was changed.

For the fabricated secondary batteries of Examples 3-1 to 3-7, the initial charge / discharge efficiency and the discharge capacity retention rate were calculated in the same manner as in Examples 1-1 to 1-10. Further, for Examples 3-1, 3-3, 3-4, 3-7 and Comparative Example 1-1, the load characteristics (discharge capacity maintenance rate at the time of load) were also 25 ° C. as follows. We investigated below. First, as for charging, constant current charging was performed at a constant current of 500 mA until the battery voltage reached 4.2 V, and then constant voltage charging was performed at a constant voltage of 4.2 V until the current value reached 50 mA. Next, for discharging, constant current discharging was performed at a constant current of 1500 mA until the battery voltage reached 2.5V. The discharge capacity at this time was the discharge capacity at a current value of 1500 mA. On the other hand, about another sample produced on the same conditions as Example 3-1 to 3-7, after charging on the same conditions as the above, it is constant current with a constant current of 500 mA until the battery voltage becomes 2.5V. Discharge was performed, and the discharge capacity at that time was defined as the discharge capacity at a current value of 500 mA. Here, as load characteristics (discharge capacity maintenance ratio at the time of load), the ratio of the discharge capacity at a current value of 1500 mA to the discharge capacity at a current value of 500 mA, that is, (discharge capacity at 1500 mA / discharge capacity at 500 mA) × 100 (%) Was calculated. The obtained results are shown in Table 3 together with the results of Example 1-5. In Table 3, the cycle characteristics (ratio of the discharge capacity at the 30th cycle to the discharge capacity at the second cycle) are described in the item name “cycle” column, and the load characteristics are described in the item name “load” column. . Further, the weight per unit area of only the polymer compound layer 27 (polymer compound and lubricant) after drying is described in the “area density” column of “whole”, and the weight per unit area of only the polymer compound Was described in the “Area density” column of “Resin (PVdF)”, and the weight per unit area of only the lubricant was described in the “Area density” column of “Lubricant (MoS ₂ )”.

  As shown in Table 3, Examples 3-1 to 3-7 showed higher numerical values in both initial charge / discharge efficiency and cycle characteristics than Comparative Example 1-1 in which no lubricant was added. In particular, higher values were exhibited when the lubricant content was 20 wt% or more and 90 wt% or less. Regarding the cycle characteristics, there is a tendency to increase until the lubricant content reaches 80% by weight (Example 3-5), and to slightly decrease (Examples 3-6 and 3-7). It was. In Example 3-7, it is considered that the content of the polymer compound (PVdF) was small, it was difficult to sufficiently retain the lubricant, and the effect of adding the lubricant was not sufficiently exhibited. Moreover, about load characteristics, in any of Examples 3-1, 3-3, 3-4 and 3-7, it was slightly lower than Comparative Example 1-1. This is considered to be an effect that the impedance is increased by the addition of the lubricant. Therefore, when importance is attached to load characteristics, it is desirable that the amount of lubricant added is as small as possible.

(Examples 4-1 to 4-5)
Next, a secondary battery was fabricated in the same manner as in Example 3-4 except that the weight per unit area of the entire polymer compound layer 27 was changed.

(Example 4-6)
Furthermore, the weight per unit area of the polymer compound layer 27 is changed to 0.4 mg / cm ² while maintaining the weight per unit area of the lubricant, and polyvinylidene fluoride and molybdenum disulfide (MoS ₂ ). A secondary battery was fabricated in the same manner as in Example 3-4 except that the mixing ratio was 8:92.

  As Comparative Examples 4-1 to 4-5, secondary batteries were fabricated in the same manner as in Examples 4-1 to 4-5, except that the lubricant was not added to the polymer compound layer 27. .

  For the fabricated secondary batteries of Examples 4-1 to 4-6 and Comparative Examples 4-1 to 4-5, the initial charge and discharge efficiency and the discharge capacity maintenance were performed in the same manner as in Examples 1-1 to 1-10. The rate was calculated. Further, for Examples 4-2 and 4-4 and Comparative Examples 4-2 and 4-4, the load characteristics were also investigated in the same manner as in Example 3-1. The obtained results are shown in Table 4 together with the results of Example 3-4 and Comparative Example 1-1. In Table 4, the cycle characteristics (ratio of the discharge capacity at the 30th cycle to the discharge capacity at the second cycle) are described in the item name “cycle” column, and the load characteristics are described in the item name “load” column. .

According to the comparison between Examples 3-4, 4-1 to 4-5 and Comparative Examples 1-1, 4-1 to 4-5 shown in Table 4, the weight per unit area of the entire polymer compound layer 27 There in the range of 0.07 mg / cm ² of 1.2 mg / cm ^2, if the weight per same unit area providing a lubricant separator (example 3-4,4-1～4-5) that the It has been found that better cycle characteristics can be ensured than when no lubricant is provided, while ensuring the same initial charge / discharge efficiency as or better than when no lubricant is provided. Moreover, about load characteristics, Examples 4-2 and 4-4 were substantially equivalent to Comparative Examples 4-2 and 4-4, respectively.

(Example 5-1)
A secondary battery was fabricated in the same manner as in Example 1-5, except that tin (Sn) was used instead of CoSnC as the negative electrode active material. Here, by vapor deposition of tin on a 15 μm thick copper foil having a roughened surface by vacuum deposition, and firing at 200 ° C. for 12 hours in a vacuum, the negative electrode active material layer 22B having a thickness of 4 μm Formed.

(Example 5-2)
A secondary battery was fabricated in the same manner as in Example 1-5, except that silicon (Si) was used instead of CoSnC as the negative electrode active material. Here, 80 parts by mass of silicon powder having an average particle diameter of 2 μm and 20 parts by mass of polyvinylidene fluoride were mixed to prepare a negative electrode mixture, and this negative electrode mixture was then added to N-methyl-2-pyrrolidone as a solvent. The mixture was dispersed to form a negative electrode mixture slurry, applied to both surfaces of a negative electrode current collector 22A made of a copper foil having a thickness of 15 μm, dried, and compression molded by a roll press. Furthermore, the negative electrode active material layer 22B having a thickness of 5 μm was formed by baking at 300 ° C. for 12 hours in a vacuum.

(Example 5-3)
A secondary battery was fabricated in the same manner as in Example 1-5, except that silicon copper titanium alloy (SiCuTi) was used as the negative electrode active material instead of CoSnC. Here, first, silicon powder, copper powder, and titanium powder as raw materials are dry-mixed at an atomic ratio of 80:10:10, and then synthesized using a mechanochemical reaction using a planetary ball mill, A SiCuTi-containing material was obtained. When the composition of the obtained SiCuTi-containing material was analyzed, the silicon content was 66.7% by mass, the copper content was 18.4% by mass, and the titanium content was 14.9% by mass. .

  Next, 80 parts by mass of this SiCuTi-containing material and 20 parts by mass of polyvinylidene fluoride were mixed to prepare a negative electrode mixture, and then this negative electrode mixture was dispersed in N-methyl-2-pyrrolidone as a solvent to prepare a negative electrode mixture. The slurry was applied to both surfaces of a negative electrode current collector 22A made of a copper foil having a thickness of 15 μm, dried, and compression molded with a roll press. Furthermore, the negative electrode active material layer 22B having a thickness of 9 μm was formed by baking at 300 ° C. for 12 hours in a vacuum.

(Example 5-4)
A secondary battery was fabricated in the same manner as in Example 1-5, except that silicon was used instead of CoSnC as the negative electrode active material. Here, by vapor deposition of tin on a 15 μm thick copper foil whose surface is roughened by vacuum vapor deposition, the negative electrode active material layer 22B having a thickness of 5 μm is baked at 200 ° C. for 12 hours in a vacuum. Formed.

  As Comparative Examples 5-1 to 5-4, secondary batteries were fabricated in the same manner as in Examples 5-1 to 5-4, except that the lubricant was not added to the polymer compound layer 27.

  For the fabricated secondary batteries of Examples 5-1 to 5-4 and Comparative Examples 5-1 to 5-4, the initial charge and discharge efficiency and the discharge capacity were maintained in the same manner as in Examples 1-1 to 1-10. The rate (cycle characteristics) was calculated. The obtained results are shown in Table 5 together with the results of Example 1-5.

  As shown in Table 5, in Examples 5-1 to 5-4, compared with Comparative Examples 5-1 to 5-4 in which no lubricant was added, substantially the same initial charge / discharge efficiency was maintained. However, a high value was shown in the cycle characteristics. That is, the effect of adding a lubricant was confirmed when not only CoSnC but also tin alone, silicon alone, or a silicon alloy was used as the negative electrode active material.

  As described above, according to this example, the polymer compound layer 27 containing the lubricant is provided between the base material 26 of the separator 23 and the negative electrode 22, so that the negative electrode 22 is not charged during charging and discharging. Even in the case of expansion, the frictional force generated between the separator 23 and the positive electrode 21 and the negative electrode 22 is reduced (the static friction coefficient of the surface of the separator 23 is 0.30 or less), and the positive electrode 21, the negative electrode 22, and the separator As a result of relieving the stress applied to 23, even when the negative electrode 22 made of an alloy material is employed, it is possible to avoid a short circuit inside the wound body 20 or deterioration of cycle characteristics, and to improve battery characteristics. In addition, it was confirmed that high reliability could be secured.

  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, a rectangular secondary battery having a winding structure has been described. However, the present invention is a secondary battery (for example, a cylindrical type) having an outer can together with a winding body having a winding structure. ) Is applicable.

  In the above embodiments and examples, a battery using lithium as an electrode reactant has been described. However, other alkali metals such as sodium or potassium, alkaline earth metals such as magnesium or calcium, or other metals such as aluminum are used. The present invention can also be applied to the case of using a light metal. In that case, as a negative electrode active material, the thing similar to the said embodiment etc. can be used, for example.

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 wound electrode body shown in FIG. FIG. 3 is a development view of a positive electrode 21 shown in FIG. 2. FIG. 3 is a development view of the negative electrode 22 shown in FIG. 2.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 11 ... Exterior can, 12 ... Insulating plate, 13 ... Battery cover, 14 ... Terminal board, 15 ... Positive electrode pin, 16 ... Insulating case, 17 ... Gasket, 18 ... Cleavage valve, 19 ... Electrolyte injection hole, 19A ... Sealing Member, 20 ... Winding body, 21 ... Positive electrode, 21A ... Positive electrode current collector, 21B ... Positive electrode active material layer, 22 ... Negative electrode, 22A ... Negative electrode current collector, 22B ... Negative electrode active material layer, 23 ... Separator, 24 ... Positive electrode lead, 25 ... negative electrode lead, 26 ... base material, 27 ... polymer compound layer.

Claims (8)

A wound body including a laminated structure of a positive electrode, a negative electrode, and a separator located between the positive electrode and the negative electrode,
A lubricant is provided on at least a part of the surface of the separator ,
The coefficient of static friction of the surface of the separator is 0.30 or less,
The negative electrode is a secondary battery including, as an active material, at least one selected from the group consisting of a simple substance, an alloy and a compound of silicon (Si), and a simple substance, an alloy and a compound of tin (Sn) . The secondary battery according to claim 1, wherein the lubricant includes at least one of a higher fatty acid salt, talc, boron nitride (BN), and molybdenum disulfide (MoS ₂ ). The separator has a porous substrate and a polymer compound layer comprising a gel-like or liquid polymer compound provided on the surface of the substrate,
The secondary battery according to claim 1, wherein the lubricant is held in the polymer compound. The polymeric compound and the secondary battery according to claim 3, wherein the weight per unit area of the lubricant is 1.2 mg / cm ² or less 0.07 mg / cm ² or more in total. The secondary battery according to claim 3 , wherein the base material has a single-layer structure made of polyethylene or a three-layer structure in which a layer made of polyethylene is inserted between a pair of layers made of polypropylene. The secondary battery according to claim 3 , wherein the polymer compound has a melting point of 200 ° C. or higher. The secondary battery according to claim 3 , wherein the polymer compound is polyvinylidene fluoride, polytetrafluoroethylene, polyimide, polyamide, polyamideimide, polyethersulfone, polyaramid, or carboxymethylcellulose. The secondary battery according to claim 3 , wherein a content of the lubricant is 0.25 to 9 times by weight with respect to the polymer compound.

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