JP2007128847A - Anode, battery, and their manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an anode and a battery, and with high capacity and improved cycle characteristics, and also to provide their manufacturing methods. <P>SOLUTION: An anode active substance layer 12 contains: an anode active substance containing at least tin, iron, and carbon as constituent elements, with a content of the carbon of 11.9% to 29.7% by mass, and with a ratio of the iron to a total of the tin and the iron of 26.4% to 48.5% by mass; and at least one kind of binder out of a group consisting of copolymers composed of polyvinylidene fluoride and vinylidene fluoride heated and fused at a temperature above the melting point. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a negative electrode including a negative electrode active material containing tin (Sn), iron (Fe), and carbon (C) as constituent elements and a binder, a battery using the negative electrode, and a method for producing the same. .

  In recent years, many portable electronic devices such as a camera-integrated VTR (Videotape Recorder), a mobile phone, and a laptop computer have been introduced, and their size and weight have been reduced. Accordingly, there is a strong demand for an improvement in energy density of batteries used as portable power sources for such electronic devices, particularly secondary batteries.

  Secondary batteries that meet these demands have traditionally been graphite materials that use lithium ion intercalation reactions as the negative electrode active material, or carbon materials that apply lithium ion storage and release into the pores. A so-called lithium ion secondary battery using a battery has been put into practical use.

  However, with the recent improvement in performance of portable devices, the demand for the capacity of the secondary battery has become stronger. As a secondary battery that meets such requirements, it has been proposed to use a light metal such as lithium metal as a negative electrode active material as it is. In this battery, light metal tends to precipitate in a dendrite state on the negative electrode during the charging process, and the current density becomes very high at the end of the dendrite. For this reason, there has been a problem that the cycle life is reduced due to decomposition of the non-aqueous electrolyte, or the dendrite grows excessively and an internal short circuit of the battery occurs.

On the other hand, using various alloy materials etc. as a negative electrode active material is proposed. For example, Patent Documents 1 to 5 describe silicon alloys. Patent Documents 6 to 12 include a tin-nickel alloy, a lithium-aluminum-tin alloy, a tin-zinc alloy, a tin alloy containing phosphorus (P) in a range of 1% by mass to 55% by mass, Cu ₂ NiSn. Mg ₂ Sn, tin-copper alloy, or a tin-containing phase that occludes lithium, and lithium (Li) composed of manganese (Mn), iron, cobalt (Co), nickel (Ni), or copper (Cu) Mixtures with non-occluded phases are described.

However, even when these alloy materials are used, sufficient cycle characteristics cannot be obtained, and the fact is that the features of the high-capacity negative electrode in the alloy materials are not fully utilized.
Japanese Patent Laid-Open No. 7-302588 JP-A-10-199524 JP 7-326342 A Japanese Patent Laid-Open No. 10-255768 JP-A-10-302770 Japanese Examined Patent Publication No. 4-12586 JP-A-10-308207 JP-A-61-66369 Japanese Patent Laid-Open No. Sho 62-145650 JP-A-10-125317 Japanese Patent Laid-Open No. 10-223221 Japanese Patent Application Laid-Open No. 11-86854

  Therefore, as a negative electrode active material capable of sufficiently improving the cycle characteristics, at least tin, iron, and carbon are included as constituent elements, and the carbon content is 11.9 mass% or more and 29.7 mass% or less. And the ratio of iron to the total of tin and iron has been developed from 26.4% by mass to 48.5% by mass. However, this negative electrode active material also has a problem that the cycle characteristics deteriorate due to expansion / contraction associated with charge / discharge, and further improvement has been desired.

  The present invention has been made in view of such problems, and an object of the present invention is to provide a negative electrode capable of improving cycle characteristics with a high capacity, a battery using the negative electrode, and a method for producing the same.

  The negative electrode according to the present invention contains at least tin, iron, and carbon as constituent elements, the carbon content is 11.9 mass% or more and 29.7 mass% or less, and the total of tin and iron is A negative electrode active material having a ratio of iron of 26.4% by mass or more and 48.5% by mass or less, a polyvinylidene fluoride melted by heating at a temperature equal to or higher than a melting point, and a copolymer containing vinylidene fluoride as components. And a binder containing at least one member of the group.

  The battery according to the present invention includes an electrolyte together with a positive electrode and a negative electrode. The negative electrode includes at least tin, iron, and carbon as constituent elements, and the carbon content is 11.9% by mass or more. 0.7% by mass or less, and the ratio of iron to the total of tin and iron was 26.4% by mass or more and 48.5% by mass or less, and the negative electrode active material was heated and melted at a temperature higher than the melting point. And a binder containing at least one member selected from the group consisting of polyvinylidene fluoride and a copolymer containing vinylidene fluoride as a component.

  The negative electrode manufacturing method according to the present invention includes at least tin, iron, and carbon as constituent elements, the carbon content is 11.9 mass% or more and 29.7 mass% or less, and tin and iron At least one member selected from the group consisting of a negative electrode active material having a ratio of iron to 26.4% by mass or more and 48.5% by mass or less, and polyvinylidene fluoride and a copolymer containing vinylidene fluoride as a component. After forming the precursor layer containing the binder, the binder is heated at a temperature equal to or higher than the melting point of the binder.

  A method for producing a battery according to the present invention is a method for producing a battery including an electrolyte together with a positive electrode and a negative electrode. The negative electrode includes at least tin, iron, and carbon as constituent elements, and the carbon content is A negative electrode active material having a ratio of iron of 21.9% to 48.5% by weight, polyvinylidene fluoride, and 11.9% by weight to 29.7% by weight. After forming a precursor layer containing a binder containing at least one member selected from the group consisting of copolymers comprising vinylidene fluoride as a component, it is formed by heating at a temperature equal to or higher than the melting point of the binder. Is.

  According to the negative electrode of the present invention, since the negative electrode active material containing tin is contained as a constituent element, a high capacity can be obtained. In addition, the negative electrode active material contains iron as a constituent element, and the ratio of iron to the total of tin and iron is set to 26.4% by mass or more and 48.5% by mass or less. Cycle characteristics can be improved. Furthermore, since this negative electrode active material contains carbon as a constituent element and the content thereof is set to 11.9 mass% or more and 29.7 mass% or less, cycle characteristics can be further improved. In addition, since the binder contains at least one member selected from the group consisting of polyvinylidene fluoride and a copolymer containing vinylidene fluoride as a component, heated at a temperature equal to or higher than the melting point, A decrease in electronic conductivity due to expansion / contraction of the negative electrode active material accompanying charge / discharge can be suppressed. Therefore, according to the battery of the present invention using this negative electrode, a high capacity can be obtained and excellent cycle characteristics can be obtained.

  According to the negative electrode and battery manufacturing method of the present invention, the constituent elements include at least tin, iron, and carbon, and the carbon content is 11.9 mass% or more and 29.7 mass% or less, and Of the group consisting of a negative electrode active material having a ratio of iron to 26.4% by mass to 48.5% by mass with respect to the total of tin and iron, and polyvinylidene fluoride and a copolymer containing vinylidene fluoride as components Since the precursor layer containing the binder containing at least one kind is formed and then heated at a temperature equal to or higher than the melting point of the binder, the negative electrode and the battery of the present invention can be easily manufactured.

  Further, if the negative electrode active material and the binder are mixed using a dispersion medium having a swelling degree of 10% or less with respect to the binder to form a precursor layer, the negative electrode active material is covered with the binder. The degree can be reduced, and the electrode reactant can be occluded and released in the negative electrode. Therefore, cycle characteristics can be further improved.

  In particular, if the precursor layer is formed using a dispersion medium containing water, the coverage of the negative electrode active material with the binder can be further reduced.

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

  FIG. 1 illustrates a configuration of a negative electrode 10 according to an embodiment of the present invention. The negative electrode 10 includes, for example, a negative electrode current collector 11 having a pair of opposed surfaces, and a negative electrode active material layer 12 provided on one surface of the negative electrode current collector 11. Although not shown, the negative electrode active material layers 12 may be provided on both surfaces of the negative electrode current collector 11.

  The negative electrode current collector 11 preferably has good electrochemical stability, electrical conductivity, and mechanical strength, and is made of a metal material such as copper, nickel, or stainless steel. In particular, copper is preferable because it has high electrical conductivity.

  The negative electrode active material layer 12 can react with, for example, lithium and contains tin and iron as constituent elements. This is because tin has a high reaction amount of lithium per unit mass, and a high capacity can be obtained. Moreover, it is difficult to obtain sufficient cycle characteristics with tin alone, but the cycle characteristics can be improved by including iron.

  The iron content is the ratio of iron to the total of tin and iron, and is in the range of 26.4 mass% to 48.5 mass% and within the range of 29.3 mass% to 45.5 mass%. More preferable. If the ratio is low, the iron content decreases and sufficient cycle characteristics cannot be obtained, and if the ratio is high, the tin content decreases, which has an advantage over the capacity of conventional negative electrode materials such as carbon materials. It is because it cannot be obtained.

  The negative electrode active material also contains carbon as a constituent element in addition to tin and iron. This is because the cycle characteristics can be further improved by including carbon. The carbon content is preferably in the range of 11.9 mass% to 29.7 mass%, preferably in the range of 13.9 mass% to 27.7 mass%, particularly 15.8 mass%. More preferably, it is in the range of 23.8% by mass or less. This is because a high effect can be obtained within this range.

  In some cases, it is preferable that the negative electrode active material further contains silver (Ag) as a constituent element. This is because the reactivity with the electrolyte can be reduced and the cycle characteristics can be improved. The content of silver is preferably in the range of 0.1% by mass to 9.9% by mass, more preferably in the range of 1.0% by mass to 7.4% by mass, particularly , 2.0 mass% or more and 5.0 mass% or less is desirable. When the amount is small, the effect of improving the cycle characteristics is not sufficient, and when the amount is large, the tin content is lowered and a sufficient capacity cannot be obtained.

  In some cases, this negative electrode active material preferably contains silicon (Si) as a constituent element. This is because silicon has a high reaction amount of lithium per unit mass and can further improve the capacity. The silicon content is preferably in the range of 0.5 mass% or more and 7.9 mass% or less. If the amount is small, the effect of increasing the capacity is not sufficient, and if the amount is large, the cycle characteristics deteriorate. Silicon may be included together with silver.

  The negative electrode active material also includes at least one member selected from the group consisting of aluminum (Al), titanium (Ti), vanadium (V), chromium (Cr), niobium (Nb), and tantalum (Ta) as a constituent element. And at least one of the group consisting of cobalt, nickel, copper, zinc (Zn), gallium (Ga) and indium (In) may be preferable. It is because the cycle characteristics can be further improved by including these. The content of aluminum, titanium, vanadium, chromium, niobium and tantalum is preferably 0.1% by mass or more and 9.9% by mass or less, and the content of cobalt, nickel, copper, zinc, gallium and indium is 0.5 mass% or more and 14.9 mass% or less is preferable. If the amount is too small, a sufficient effect cannot be obtained. If the amount is too large, the tin content decreases and a sufficient capacity cannot be obtained. These elements may be contained together with silver or silicon.

  The negative electrode active material has a low crystallinity or amorphous phase. This phase is a reaction phase capable of reacting with lithium or the like, whereby excellent cycle characteristics can be obtained. The half width of the diffraction peak obtained by X-ray diffraction of this phase is 0.5 ° or more at a diffraction angle 2θ when CuKα ray is used as the specific X-ray and the sweep speed is 1 ° / min. preferable. This is because lithium and the like can be occluded and released more smoothly, and the reactivity with the electrolyte can be further reduced.

  Whether the diffraction peak obtained by X-ray diffraction corresponds to the reaction phase capable of reacting with lithium or the like is compared with the X-ray diffraction chart before and after the electrochemical reaction with lithium or the like. Can be easily determined. For example, if the position of the diffraction peak changes before and after an electrochemical reaction with lithium or the like, it corresponds to a reaction phase capable of reacting with lithium or the like. In this negative electrode active material, a diffraction peak of a low crystallinity or amorphous reaction phase is observed, for example, between 2θ = 20 ° and 50 °. This low crystallinity or amorphous reaction phase contains, for example, each of the constituent elements described above, and is considered to be low crystallized or amorphous mainly by carbon.

  In addition to the low crystalline or amorphous phase, the negative electrode active material may have a phase containing a single element or a part of each constituent element.

  As a measuring method for examining the bonding state of elements, for example, X-ray photoelectron spectroscopy (XPS) can be cited. This XPS irradiates a sample surface with soft X-rays (Al-Kα ray or Mg-Kα ray is used in a commercial apparatus), and measures the kinetic energy of photoelectrons jumping out from the sample surface. To elemental composition in the region of several nanometers and the bonding state of the elements.

  The binding energy of the core orbital electrons of the element changes in a first approximation in correlation with the charge density on the element. For example, when the charge density of the carbon element is decreased due to the interaction with an element present in the vicinity, the outer electrons such as 2p electrons are decreased, so that the 1s electron of the carbon element has a strong binding force from the shell. Will receive. That is, the binding energy increases as the charge density of the element decreases. In XPS, when the binding energy increases, the peak shifts to a high energy region.

  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 negative electrode active material appears in a region lower than 284.5 eV, at least a part of the carbon contained in the negative electrode active material is a metal element or a half of other constituent elements. Combined with metal elements.

  In the XPS measurement of the negative electrode active material, when the surface is covered with surface-contaminated carbon, it is preferable to lightly sputter the surface with an argon ion gun attached to the XPS apparatus. Further, when the negative electrode active material to be measured is present in the negative electrode of the battery as described later, the battery is disassembled and the negative electrode is taken out and then washed with a volatile solvent such as dimethyl carbonate. This is for removing the low-volatile solvent and the electrolyte salt present on the surface of the negative electrode. These samplings are desirably performed under an inert atmosphere.

  In XPS measurement, for example, the peak of C1s is used to correct the energy axis of the spectrum. Usually, since surface-contaminated carbon exists on the surface of the substance, the C1s peak of the surface-contaminated carbon is set to 284.8 eV, and this is used as an energy standard. In the XPS measurement, the waveform of the peak of C1s is obtained as a form including the surface contamination carbon peak and the carbon peak in the negative electrode active material. For example, by analyzing using commercially available software, The peak of surface contamination carbon and the peak of carbon in the negative electrode active 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).

  This negative electrode active material is prepared by, for example, mixing raw materials of various constituent elements, melting them in an electric furnace, a high frequency induction furnace, an arc melting furnace, etc., and then solidifying them, various atomizing methods such as gas atomization or water atomization, various rolls, etc. Or a method using a mechanochemical reaction such as a mechanical alloying method or a mechanical milling method. Especially, it is preferable to manufacture by the method using a mechanochemical reaction. This is because the negative electrode active material can have a low crystallinity or an amorphous structure. In this method, for example, a planetary ball mill device can be used.

  The raw material may be a mixture of individual constituent elements, but an alloy is preferably used for some constituent elements other than carbon. By adding carbon to such an alloy and synthesizing it by a method utilizing mechanochemical reaction, it can be made to have a low crystallization or amorphous structure, and the reaction time can be shortened. It is. The raw material may be in the form of a powder or a lump.

  The carbon used as a raw material is any one of carbon materials such as non-graphitizable carbon, graphitizable carbon, graphite, pyrolytic carbons, coke, glassy carbons, organic polymer compound fired bodies, activated carbon, and carbon black. Species or two or more can be used. Among these, cokes include pitch coke, needle coke, and petroleum coke. Organic polymer compound fired bodies are carbonized by firing polymer compounds such as phenol resin and furan resin at an appropriate temperature. What you did. The shape of these carbon materials may be any of fibrous, spherical, granular or scale-like.

  The negative electrode active material layer 12 also contains a binder. This binder is preferably heated and melted at a temperature equal to or higher than the melting point. The negative electrode active material described above expands and contracts with charge and discharge, and the electronic conductivity in the negative electrode 10 decreases. However, since the binder is melted, the decrease in electronic conductivity can be suppressed. Because.

  The binder contains at least one member selected from the group consisting of polyvinylidene fluoride and copolymers having vinylidene fluoride as a component. Specific examples of the copolymer include vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-tetrafluoroethylene copolymer, vinylidene fluoride-chlorotrifluoroethylene copolymer, vinylidene fluoride-hexafluoropropylene. -Tetrafluoroethylene copolymers, or those obtained by further copolymerizing with other ethylenically unsaturated monomers. Examples of copolymerizable ethylenically unsaturated monomers include acrylic acid esters, methacrylic acid esters, vinyl acetate, acrylonitrile, acrylic acid, methacrylic acid, maleic anhydride, butadiene, styrene, N-vinylpyrrolidone, N-vinylpyridine, and glycidyl methacrylate. , Hydroxyethyl methacrylate, methyl vinyl ether, and the like, but are not limited thereto.

  The negative electrode active material layer 12 contains a conductive additive as necessary. This conductive auxiliary agent ensures the electron conductivity inside the negative electrode active material layer 12 and between the negative electrode active material layer 12 and the negative electrode current collector 11 even if the negative electrode active material expands and contracts with charge and discharge. Is for.

  Examples of conductive aids include natural graphite such as scaly graphite, scaly graphite or earthy graphite, petroleum coke, coal coke, mesophase pitch, or polyacrylonitrile (PAN), rayon, polyamide, lignin, polyvinyl alcohol, and the like. Burned at high temperature, artificial graphite such as vapor grown carbon fiber or carbon nanotube, carbon black such as acetylene black, furnace black, ketjen black, channel black, lamp black or thermal black, asphalt pitch, coal tar, Carbon materials such as activated carbon, mesofuse pitch or polyacene, metal powders such as copper, nickel, aluminum and silver or metal fibers, conductive whiskers such as zinc oxide and potassium titanate Or conductive metal oxides such as titanium oxide. Of these, natural graphite, graphites typified by artificial graphite such as vapor-grown carbon fiber and carbon nanotubes, or carbon blacks are preferable. One type of conductive auxiliary may be used alone, or two or more types may be used in combination.

  The negative electrode active material layer 12 may also contain other negative electrode active materials in addition to the negative electrode active materials described above. Examples of the other negative electrode active material include a carbon material that can occlude and release lithium. This carbon material is preferable because it can improve cycle characteristics and also functions as a conductive additive. As a carbon material, the thing similar to what was used when manufacturing a negative electrode active material is mentioned, for example.

  The negative electrode 10 can be manufactured as follows, for example.

  First, a negative electrode active material, a binder, and, if necessary, a conductive additive are dispersed in a dispersion medium to obtain a negative electrode mixture slurry. Examples of the dispersion medium include N-methyl-2-pyrrolidone, water, toluene, xylene, methanol, ethanol, n-propanol, isopropyl alcohol, isobutyl alcohol, acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, ethyl acetate, and butyl acetate. , Tetrahydrofuran or dioxane. Among them, those having a swelling degree with respect to the binder of 10% or less are preferable. This is because the binder does not dissolve in the dispersion medium and exists in the form of particles, so that the coverage of the negative electrode active material by the binder can be reduced. Such a dispersion medium varies depending on the binder used, but water, toluene, xylene, methanol, ethanol, n-propanol, isopropyl alcohol, isobutyl alcohol, acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, ethyl acetate, acetic acid. Among them, butyl, tetrahydrofuran, dioxane, and the like are preferable. Among them, water, ethanol, or methyl isobutyl ketone is preferable, and water having a degree of swelling of approximately 0% with respect to the binder is particularly preferable. One kind of such a dispersion medium may be used alone, or two or more kinds may be mixed and used as long as the degree of swelling with respect to the binder is 10% or less.

  The degree of swelling of the dispersion medium with respect to the binder is determined by the volume change rate of the binder after the binder is immersed in the dispersion medium for 72 hours, that is, the ratio of the volume increased by the immersion. When the solubility of the binder in the dispersion medium is low, the binder is dissolved after being swelled. Therefore, the swelling degree of 10% or less means that the binder is not dissolved in the dispersion medium.

  The average particle size of the binder used for the negative electrode mixture slurry is preferably 30 μm or less, and more preferably 1 μm or less. This is because when the average particle size is increased, uniform dispersion becomes difficult, cycle characteristics are lowered, and molding of the electrode becomes difficult. The average particle diameter here is the median diameter of primary particles, and is measured by a laser diffraction type particle size distribution measuring device.

  In addition, you may add a thickener, a dispersion | distribution adjuvant, etc. to this negative mix slurry as needed. Examples of the thickener include starch, carboxymethyl cellulose, ammonium salt of carboxymethyl cellulose, inorganic salts such as sodium salt or potassium salt of carboxymethyl cellulose, hydroxypropyl cellulose, regenerated cellulose, or diacetyl cellulose. Among these, carboxymethyl cellulose or an inorganic salt of carboxymethyl cellulose is preferable. This is because stable slurry characteristics can be obtained and the electrode reaction is not impaired. One thickener may be used alone, or two or more thickeners may be mixed and used.

  Examples of the dispersion aid include fatty acids such as caproic acid, caprylic acid, lauric acid, myristic acid, palmitic acid, stearic acid, behenic acid, oleic acid, elaidic acid, linoleic acid, linolenic acid or stearic acid, and these fatty acids. Coupling agents such as metal soaps, aliphatic amines, silane coupling agents or titanium coupling agents, and high grades, which are composed of alkenyl and alkali metals (Li, Na, K etc.) or alkaline earth metals (Mg, Ca, Ba etc.) Alcohols, polyalkylene oxide phosphate esters, alkyl phosphate esters, alkyl borate esters, sarcosinates, polyalkylene oxide esters or compounds such as lecithin, nonionic surfactants such as alkylenoxides or glycerols, higher alkyl amines , Quaternary ammonium salts, cationic surfactants such as phosphonium or sulfonium, anionic surfactants such as carboxylic acid, sulfonic acid, phosphoric acid, sulfuric acid ester or phosphoric acid ester, amino acids, aminosulfonic acid, or Amphoteric surfactants such as sulfates or phosphates of amino alcohols, carboxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, polyacrylic acid, polyvinyl alcohol or modified products thereof, polyacrylamide, polyhydroxy (meth) acrylate or styrene Water-soluble polymers such as maleic acid copolymers are mentioned. One type of dispersion aid may be used alone, or two or more types may be used as a mixture.

  The negative electrode mixture slurry may be used as a state in which a negative electrode active material, a binder and, if necessary, a conductive auxiliary agent are simultaneously added and dispersed in a dispersion medium, or the binder may be used alone. Alternatively, it may be used after being dispersed in a dispersion medium together with a dispersion aid, so-called dispersion or emulsion, and then mixed with a negative electrode active material and, if necessary, a conductive aid.

  For mixing, kneading, or dispersing in a dispersion medium, such as a negative electrode active material, a binder, and a conductive auxiliary agent, any mixing stirrer such as a known kneader, mixer, homogenizer, dissolver, planetary mixer, paint shaker, or sand mill May be used.

  Next, the negative electrode mixture slurry is uniformly applied to the negative electrode current collector 11 by a doctor blade method or the like to form a coating layer. Subsequently, after drying the coating layer and removing the dispersion medium, the precursor layer is formed by compression molding using a roll press or the like. Thereafter, the precursor layer is heated at a temperature equal to or higher than the melting point of the binder to melt the binder, thereby forming the negative electrode active material layer 12. Thereby, the negative electrode 10 shown in FIG. 1 is obtained.

  This negative electrode 10 is used for a secondary battery as follows, for example.

(First secondary battery)
FIG. 2 shows a cross-sectional structure of the secondary battery. This secondary battery is called a so-called cylindrical type, and a winding in which a strip-like positive electrode 31 and a strip-like negative electrode 10 are laminated and wound via a separator 32 inside a substantially hollow cylindrical battery can 21. An electrode body 30 is provided. The battery can 21 is made of, for example, iron plated with nickel, and has one end closed and the other end open. Inside the battery can 21, an electrolytic solution that is a liquid electrolyte is injected and impregnated in the separator 32. In addition, a pair of insulating plates 22 and 23 are respectively disposed perpendicular to the winding peripheral surface so as to sandwich the winding electrode body 30.

  At the open end of the battery can 21, a battery lid 24, a safety valve mechanism 25 and a thermal resistance element (PTC element) 26 provided inside the battery lid 24 are interposed via a gasket 27. It is attached by caulking, and the inside of the battery can 21 is sealed. The battery lid 24 is made of the same material as the battery can 21, for example. The safety valve mechanism 25 is electrically connected to the battery lid 24 via the heat sensitive resistance element 26, and the disk plate 25A 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 24 and the wound electrode body 30 is cut off. When the temperature rises, the heat-sensitive resistor element 26 limits the current by increasing the resistance value, and prevents abnormal heat generation due to a large current. The gasket 27 is made of, for example, an insulating material, and asphalt is applied to the surface.

  For example, a center pin 33 is inserted in the center of the wound electrode body 30. A positive electrode lead 34 made of aluminum or the like is connected to the positive electrode 31 of the spirally wound electrode body 30, and a negative electrode lead 35 made of nickel or the like is connected to the negative electrode 10. The positive electrode lead 34 is welded to the safety valve mechanism 25 to be electrically connected to the battery lid 24, and the negative electrode lead 35 is welded to and electrically connected to the battery can 21.

  FIG. 3 shows an enlarged part of the spirally wound electrode body 30 shown in FIG. The negative electrode 10 has the above-described configuration. As a result, the cycle characteristics can be improved while maintaining a high capacity. In FIG. 3, the negative electrode active material layer 12 is represented as being formed on both surfaces of the negative electrode current collector 11.

  The positive electrode 31 has, for example, a structure in which a positive electrode active material layer 31B is provided on both surfaces or one surface of a positive electrode current collector 31A having a pair of opposed surfaces. The positive electrode current collector 31A is made of, for example, a metal foil such as an aluminum foil. The positive electrode active material layer 31B includes, for example, any one or more of positive electrode materials capable of inserting and extracting lithium, which is an electrode reactant, as a positive electrode active material. A conductive additive such as graphite or carbon black and a binder such as polyvinylidene fluoride may be included.

Examples of the positive electrode material capable of inserting and extracting lithium include metal sulfides or oxides not containing lithium, such as TiS ₂ , MoS ₂ , NbSe _2, or V ₂ O ₅ , or lithium oxides, lithium sulfides, Examples include lithium-containing intercalation compounds or lithium-containing compounds such as phosphate compounds, or specific polymers. As the positive electrode material, one kind may be used alone, or two or more kinds may be mixed and used.

Among them, a composite oxide containing lithium and a transition metal element, or a phosphoric acid compound containing lithium and a transition metal element is preferable. In particular, the transition metal element contains at least one of cobalt, nickel, manganese, and iron. Those are preferred. This is because high voltage and high energy density can be obtained. The chemical formulas of these composite oxides or phosphate compounds are represented by, for example, Li _x MIO ₂ or Li _y MIIPO ₄ . In the formula, MI and MII contain 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 LiCoO ₂ , LiNiO ₂ , Li _v Ni _w Co _1-w O ₂ (v and w are different depending on the charge / discharge state of the battery, and generally 0 <v <1, 0.7 <w <1.0.) Or a lithium manganese composite oxide having a spinel structure. Specific examples of the phosphate compound containing lithium and a transition metal element include LiFePO ₄ or LiFe _1-u Mn _u PO ₄ (u <1).

  The separator 32 is made of, for example, a porous film made of synthetic resin such as polytetrafluoroethylene, polypropylene, or polyethylene, or a porous film made of ceramic, and has a structure in which two or more kinds of porous films are laminated. May be.

  The separator 32 is impregnated with an electrolytic solution that is a liquid electrolyte. This electrolytic solution contains, for example, a nonaqueous solvent such as an organic solvent and an electrolyte salt dissolved in the nonaqueous solvent. Examples of the non-aqueous solvent include propylene carbonate, ethylene carbonate, vinylene carbonate, diethyl carbonate, dimethyl carbonate, 1,2-dimethoxyethane, 1,2-diethoxyethane, γ-butyrolactone, tetrahydrofuran, 2-methyltetrahydrofuran, 1 , 3-dioxolane, 4-methyl-1,3-dioxolane, diethyl ether, sulfolane, methyl sulfolane, acetonitrile, propionitrile, anisole, acetic acid ester, butyric acid ester, or propionic acid ester. These may be used alone or in combination of two or more.

For example, LiClO ₄ , LiAsF ₆ , LiPF ₆ , LiBF ₄ , LiB (C ₆ H ₅ ) ₄ , CH ₃ SO ₃ Li, CF ₃ SO ₃ Li, LiCl, or LiBr is used as the electrolyte salt. These may be used individually by 1 type and may be used in mixture of multiple types.

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

  First, for example, the negative electrode 10 is produced as described above. In addition, for example, a positive electrode active material, and optionally a conductive additive and a binder are mixed to prepare a positive electrode mixture, and this positive electrode mixture is dispersed in a dispersion medium such as N-methyl-2-pyrrolidone. Thus, a paste-like positive electrode mixture slurry is obtained. After applying this positive electrode mixture slurry to the positive electrode current collector 31A and drying the dispersion medium, the positive electrode active material layer 31B is formed by compression molding using a roll press or the like, and the positive electrode 31 is manufactured.

  Subsequently, the positive electrode lead 34 is attached to the positive electrode current collector 31A by welding or the like, and the negative electrode lead 35 is attached to the negative electrode current collector 11 by welding or the like. After that, the positive electrode 31 and the negative electrode 10 are laminated and wound via the separator 32, and the tip of the positive electrode lead 34 is welded to the safety valve mechanism 25 and the tip of the negative electrode lead 35 is welded to the battery can 21. The wound positive electrode 31 and negative electrode 10 are sandwiched between a pair of insulating plates 22 and 23 and housed inside the battery can 21. Next, for example, an electrolyte is injected into the battery can 21 and impregnated in the separator 32. After that, the battery lid 24, the safety valve mechanism 25, and the heat sensitive resistance element 26 are fixed to the opening end of the battery can 21 by caulking through a gasket 27. Thereby, the secondary battery shown in FIGS. 2 and 3 is formed.

  In this secondary battery, when charged, lithium ions are released from the positive electrode active material layer 31 </ b> B and inserted in the negative electrode active material layer 12 through the electrolytic solution impregnated in the separator 32. Next, when discharging is performed, lithium ions are released from the negative electrode active material layer 12 and inserted in the positive electrode active material layer 31B through the electrolytic solution impregnated in the separator 32. Here, since the negative electrode 10 contains the negative electrode active material containing tin, iron and carbon in the above-described proportions, the cycle characteristics are improved while maintaining a high capacity. Further, since the binder is heated and melted at a temperature equal to or higher than the melting point, a decrease in electronic conductivity due to expansion / contraction associated with charge / discharge of the negative electrode active material is suppressed.

  Thus, according to the negative electrode 10 according to the present embodiment, since the negative electrode active material containing tin is contained as a constituent element, a high capacity can be obtained. In addition, the negative electrode active material contains iron as a constituent element, and the ratio of iron to the total of tin and iron is set to 26.4% by mass or more and 48.5% by mass or less. Cycle characteristics can be improved. Furthermore, since this negative electrode active material contains carbon as a constituent element and the content thereof is set to 11.9 mass% or more and 29.7 mass% or less, cycle characteristics can be further improved. In addition, since the binder contains at least one member selected from the group consisting of polyvinylidene fluoride and a copolymer containing vinylidene fluoride as a component, heated at a temperature equal to or higher than the melting point, A decrease in electronic conductivity due to expansion / contraction of the negative electrode active material accompanying charge / discharge can be suppressed. Therefore, according to the secondary battery according to the present embodiment using this negative electrode 10, a high capacity can be obtained and an excellent cycle characteristic can be obtained.

  Moreover, according to the manufacturing method of negative electrode 10 and the battery according to the present embodiment, at least tin, iron, and carbon are included as constituent elements, and the carbon content is 11.9% by mass or more and 29.7% by mass. %, And the ratio of iron to the total of tin and iron is 26.4% by mass or more and 48.5% by mass or less, and a copolymer comprising polyvinylidene fluoride and vinylidene fluoride as components. After forming a precursor layer containing a binder containing at least one of the group consisting of the following, it is heated at a temperature equal to or higher than the melting point of the binder. A secondary battery can be manufactured easily.

  Furthermore, if the negative electrode active material and the binder are mixed using a dispersion medium having a swelling degree of 10% or less with respect to the binder to form a precursor layer, the coating of the negative electrode active material with the binder is performed. It is possible to reduce the degree, and it is possible to satisfactorily occlude and release lithium in the negative electrode 10. Therefore, cycle characteristics can be further improved.

  In particular, if the precursor layer is formed using a dispersion medium containing water, the coverage of the negative electrode active material with the binder can be further reduced.

(Secondary secondary battery)
FIG. 4 shows the configuration of the second secondary battery. In this secondary battery, a wound electrode body 40 to which a positive electrode lead 41 and a negative electrode lead 42 are attached is accommodated in a film-like exterior member 50, and can be reduced in size, weight, and thickness. ing.

  The positive electrode lead 41 and the negative electrode lead 42 are led out from the inside of the exterior member 50 to the outside, for example, in the same direction. The positive electrode lead 41 and the negative electrode lead 42 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 50 is made of, for example, a rectangular aluminum laminated film in which a nylon film, an aluminum foil, and a polyethylene film are bonded together in this order. The exterior member 50 is disposed, for example, so that the polyethylene film side and the wound electrode body 40 face each other, and the outer edge portions are in close contact with each other by fusion or an adhesive. An adhesive film 51 for preventing the entry of outside air is inserted between the exterior member 50 and the positive electrode lead 41 and the negative electrode lead 42. The adhesion film 51 is made of a material having adhesion to the positive electrode lead 41 and the negative electrode lead 42, for example, a polyolefin resin such as polyethylene, polypropylene, modified polyethylene, or modified polypropylene.

  The exterior member 50 may be made of a laminated film having another structure, a polymer film such as polypropylene, or a metal film instead of the above-described aluminum laminated film.

  FIG. 5 shows a cross-sectional structure taken along line II of the spirally wound electrode body 40 shown in FIG. The wound electrode body 40 is formed by laminating the positive electrode 43 and the negative electrode 10 via the separator 44 and the electrolyte layer 45 and winding them, and the outermost peripheral portion is protected by a protective tape 46.

  The positive electrode 43 has a structure in which a positive electrode active material layer 43B is provided on one or both surfaces of the positive electrode current collector 43A. The negative electrode 10 has a structure in which a negative electrode active material layer 12 is provided on one side or both sides of a negative electrode current collector 11, and the negative electrode active material layer 12 side is disposed so as to face the positive electrode active material layer 43B. Yes. The configurations of the positive electrode current collector 43A, the positive electrode active material layer 43B, and the separator 44 are the same as those of the positive electrode current collector 31A, the positive electrode active material layer 31B, and the separator 32 described above.

  The electrolyte layer 45 includes an electrolytic solution and a polymer compound serving as a holding body that holds the electrolytic solution, and has a so-called gel shape. The gel electrolyte layer 45 is preferable because high ion conductivity can be obtained and battery leakage can be prevented. The configuration of the electrolytic solution (that is, the solvent and the electrolyte salt) is the same as that of the cylindrical secondary battery shown in FIG. Examples of the polymer compound include a fluorine-based polymer compound such as polyvinylidene fluoride or a copolymer of vinylidene fluoride and hexafluoropropylene, an ether-based polymer compound such as polyethylene oxide or a crosslinked product containing polyethylene oxide, Examples include acrylonitrile. In particular, from the viewpoint of redox stability, a fluorine-based polymer compound is desirable.

  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 43 and the negative electrode 10, and the mixed solvent is volatilized to form the electrolyte layer 45. After that, the positive electrode lead 41 is attached to the end of the positive electrode current collector 43A by welding, and the negative electrode lead 42 is attached to the end of the negative electrode current collector 11 by welding. Next, the positive electrode 43 and the negative electrode 10 on which the electrolyte layer 45 is formed are laminated through a separator 44 to form a laminated body, and then the laminated body is wound in the longitudinal direction, and the protective tape 46 is adhered to the outermost peripheral portion. Thus, the wound electrode body 40 is formed. Finally, for example, the wound electrode body 40 is sandwiched between the exterior members 50, and the outer edges of the exterior members 50 are sealed and sealed by thermal fusion or the like. At that time, the adhesive film 51 is inserted between the positive electrode lead 41 and the negative electrode lead 42 and the exterior member 50. Thereby, the secondary battery shown in FIGS. 4 and 5 is completed.

  Further, this secondary battery may be manufactured as follows. First, the positive electrode 43 and the negative electrode 10 are prepared as described above, and after the positive electrode lead 41 and the negative electrode lead 42 are attached to the positive electrode 43 and the negative electrode 10, the positive electrode 43 and the negative electrode 10 are stacked via the separator 44 and wound. Then, the protective tape 46 is adhered to the outermost peripheral portion to form a wound body that is a precursor of the wound electrode body 40. Next, the wound body is sandwiched between the exterior members 50, and the outer peripheral edge portion excluding one side is heat-sealed to form a bag shape and stored in the interior of the exterior member 50. Subsequently, an electrolyte composition containing an electrolytic solution, a monomer that is a raw material of the polymer compound, and other materials such as a polymerization initiator and a polymerization inhibitor as necessary is prepared, and the interior of the exterior member 50 is prepared. Inject.

  After injecting the electrolyte composition, the opening of the exterior member 50 is heat-sealed in a vacuum atmosphere and sealed. Next, if necessary, heat is applied to polymerize the monomer to form a polymer compound, thereby forming the gel electrolyte layer 45, and assembling the secondary battery shown in FIG.

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

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

(Example 1-1)
First, a negative electrode active material was prepared. Iron powder, tin powder, and graphite powder were prepared as raw materials, and iron powder and tin powder were alloyed to produce an iron / tin alloy powder. Then, graphite powder was added to the alloy powder and dry mixed. At that time, the raw material ratio was mass ratio of iron powder: tin powder: graphite powder = 25.6: 54.4: 20. Subsequently, 20 g of this mixture was set together with about 400 g of steel balls having a diameter of 9 mm in a reaction vessel of a planetary ball mill manufactured by Ito Seisakusho. Next, the inside of the reaction vessel was replaced with an argon atmosphere, and a 10-minute operation at a rotation speed of 250 revolutions per minute and a 10-minute pause were repeated until the total operation time reached 30 hours. Thereafter, the reaction vessel was cooled to room temperature, the synthesized negative electrode active material powder was taken out, and the coarse powder was removed through a 200-mesh sieve.

  The composition of the obtained negative electrode active material was analyzed. The carbon content was measured by a carbon / sulfur analyzer, and the iron and tin contents were measured by ICP (Inductively Coupled Plasma) emission analysis. As a result, the iron content was 25.8 mass%, the tin content was 54.0 mass%, and the carbon content was 19.8 mass%. Further, when XPS was performed on this negative electrode active material, a peak P1 was obtained. When the peak P1 was analyzed, a peak P2 of surface contamination carbon and a peak P3 of C1s in the negative electrode active material on the lower energy side than the peak P2 were obtained. This peak P3 was obtained in a region lower than 284.5 eV. That is, it was confirmed that carbon in the negative electrode active material was bonded to other elements.

  70 parts by mass of this negative electrode active material, 20 parts by mass of artificial graphite, which is another negative electrode active material and also a conductive auxiliary, 2 parts by mass of carbon black as a conductive auxiliary, and an average particle diameter of 1 μm as a binder, 6 parts by mass of polyvinylidene fluoride having a melting point of 170 ° C. and 2 parts by mass of sodium salt of carboxymethyl cellulose as a thickener are weighed and mixed with a planetary mixer using a dispersion medium to prepare a negative electrode mixture slurry. did. The dispersion medium was pure water having a swelling degree of 0% with respect to the binder.

  Subsequently, this negative electrode mixture slurry was applied onto the negative electrode current collector 11 made of a strip-shaped copper foil, dried, and then compression molded with a roll press to form a precursor layer. Next, the precursor layer was heat-treated at 200 ° C. for 2 hours in a vacuum atmosphere to melt the binder to form the negative electrode active material layer 12, thereby preparing the negative electrode 10. After that, a negative electrode lead 35 made of nickel was attached to one end of the negative electrode current collector 11.

Further, lithium carbonate (Li ₂ CO ₃ ) and cobalt carbonate (CoCO ₃ ) are mixed at a molar ratio of 0.5: 1, and calcined in air at 900 ° C. for 5 hours to obtain a lithium / cobalt composite oxide (LiCoO). ₂ ) got. 91 parts by mass of LiCoO _2, 6 parts by mass of graphite as a conductive additive, and 3 parts by mass of polyvinylidene fluoride as a binder are mixed and dispersed in N-methyl-2-pyrrolidone as a dispersion medium to form a positive electrode mixture A slurry was obtained. After that, this positive electrode mixture slurry was uniformly applied to both surfaces of a positive electrode current collector 31A made of a strip-shaped aluminum foil, dried, and compression molded to form a positive electrode active material layer 31B to produce a positive electrode 31. After that, the positive electrode lead 34 made of aluminum was attached to one end of the positive electrode current collector 31A.

  After each of the positive electrode 31 and the negative electrode 10 is prepared, a separator 32 made of a microporous polypropylene film having a thickness of 25 μm is prepared, and the negative electrode 10, the separator 32, the positive electrode 31, and the separator 32 are stacked in this order to form a spiral structure. A wound electrode body 30 was produced by winding a number of times.

After producing the wound electrode body 30, the wound electrode body 30 is sandwiched between the pair of insulating plates 22 and 23, the negative electrode lead 35 is welded to the battery can 21, and the positive electrode lead 34 is welded to the safety valve mechanism 25. The wound electrode body 30 was housed inside a nickel-plated iron battery can 21. After that, the electrolytic solution was injected into the battery can 21 by a reduced pressure method. As the electrolytic solution, a solution obtained by dissolving LiPF ₆ as an electrolyte salt to 1 mol / l in a solvent in which ethylene carbonate and dimethyl carbonate were mixed at a volume ratio of 1: 1 was used.

  After injecting the electrolyte into the battery can 21, the battery lid 24 was caulked to the battery can 21 via a gasket 27 having asphalt coated on the surface, thereby obtaining the cylindrical secondary battery shown in FIG. .

  As Comparative Example 1-1 with respect to Example 1-1, a secondary battery was fabricated in the same manner as in Example 1-1 except that the negative electrode 10 was fabricated without performing the heat treatment of the precursor layer.

  As Comparative Example 1-2, a negative electrode active material was synthesized in the same manner as in Example 1-1 except that no graphite powder was used, and a secondary battery was produced. The raw material ratio of the iron powder and the tin powder was mass ratio, and iron powder: tin powder = 32.0: 68.0. Further, when the composition of the negative electrode active material was analyzed in the same manner as in Example 1-1, the iron content was 32.3 mass% and the tin content was 67.5 mass%. Furthermore, when XPS was performed, a peak P4 was obtained, and when this was analyzed, only a peak P2 of surface contamination carbon was obtained. In addition, as Comparative Example 1-3, a secondary battery was fabricated in the same manner as Comparative Example 1-2, except that the negative electrode 10 was fabricated without performing heat treatment of the precursor layer.

  As Comparative Example 1-4, in place of the negative electrode active material containing iron, tin, and carbon, except that the negative electrode 10 was produced using artificial graphite, that is, the negative electrode was produced with a total of 90 parts by mass of artificial graphite. Except for the above, a secondary battery was fabricated in the same manner as in Example 1-1. Further, as Comparative Example 1-5, a secondary battery was fabricated in the same manner as Comparative Example 1-4 except that the negative electrode 10 was fabricated without performing the heat treatment of the precursor layer.

  The charge / discharge test was done about the obtained secondary battery of Example 1-1 and Comparative Examples 1-1 to 1-5, and capacity | capacitance, charging / discharging efficiency, and cycling characteristics were calculated | required, respectively. At that time, charging was performed at a constant current of 0.5 C at 23 ° C. up to an upper limit of 4.2 V, followed by constant voltage charging at 4.2 V for 4 hours, and discharging was performed at a constant current of 0.5 C. The final voltage was 2.5V. The capacity was obtained as a relative value when the value of Example 1-1 was set to 100 for the discharge capacity at the first cycle. Moreover, the charge / discharge efficiency was calculated | required from the ratio of the discharge amount with respect to the charge amount of the 1st cycle. Furthermore, the cycle characteristics were obtained from the maintenance rate of the discharge capacity at the 100th cycle relative to the discharge capacity at the 1st cycle after 100 cycles of charge / discharge under the conditions described above. The results are shown in Table 1. In addition, the numerical value described before each structural element of a negative electrode active material represents content of each structural element by mass ratio. Further, 0.5 C is a current value at which the theoretical capacity can be discharged in 2 hours.

  As can be seen from Table 1, tin, iron and carbon are contained, the carbon content is 11.9 mass% to 29.7 mass%, and the ratio of iron to the total of tin and iron is 26. According to Example 1-1 using a negative electrode active material that is 4% by mass or more and 48.5% by mass or less, Comparative Example 1-2 using a negative electrode active material not containing carbon, or other negative electrode active material A higher discharge capacity retention rate was obtained than in Comparative Example 1-4 used. Moreover, the improvement effect of the discharge capacity maintenance rate by melting a binder is the comparative example 1-2, 1-3 using the negative electrode active material which does not contain carbon, or the comparative example using another negative electrode active material. In 1-4 and 1-5, it was hardly observed, whereas in Example 1-1 and Comparative Example 1-1, it was remarkably high.

  That is, it contains tin, iron, and carbon, the carbon content is 11.9 mass% or more and 29.7 mass% or less, and the ratio of iron to the total of tin and iron is 26.4 mass%. It was found that the cycle characteristics can be improved by using a negative electrode active material that is not less than 4% and not more than 48.5% by mass and heating the binder at a temperature equal to or higher than the melting point.

(Examples 2-1 and 2-2)
Example 1 except that methyl isobutyl ketone having a swelling degree with respect to the binder of 8.1% or N-methyl-2-pyrrolidone greater than 10% was used as the dispersion medium of the negative electrode mixture slurry. The negative electrode 10 was produced in the same manner as in -1, and a secondary battery was produced. Note that polyvinylidene fluoride as a binder is well dissolved in N-methyl-2-pyrrolidone as a dispersion medium, and the degree of swelling of N-methyl-2-pyrrolidone with respect to polyvinylidene fluoride is almost infinite.

  As Comparative Example 2-1 with respect to Example 2-2, a secondary battery was fabricated in the same manner as in Example 2-2, except that the negative electrode was manufactured without performing heat treatment.

  For the obtained Examples 2-1 and 2-2 and Comparative Example 2-1, the capacity, charge and discharge efficiency, and cycle characteristics were measured in the same manner as in Example 1-1. The results are shown in Table 2. In addition, the discharge capacity was calculated | required by the relative value when the value of Example 1-1 is set to 100.

  As can be seen from Table 2, the same results as in Example 1-1 were obtained. Moreover, in Example 2-1 using the dispersion medium whose swelling degree with respect to the binder is 8.1%, and further in Example 1-1 using pure water being 0%, it is over 10%. Higher values were obtained for the discharge capacity, the charge / discharge efficiency, and the discharge capacity retention rate than in Example 2-2 using N-methyl-2-pyrrolidone.

  That is, it has been found that even when other dispersion medium is used, cycle characteristics and the like can be improved if the binder is melted by heating at a temperature equal to or higher than the melting point. It was also found that cycle characteristics and the like can be further improved if the negative electrode 10 is manufactured using a dispersion medium having a swelling degree with respect to the binder of 10% or less.

(Examples 3-1 to 3-4)
As a binder, instead of polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-tetrafluoroethylene copolymer, vinylidene fluoride-chlorotrifluoroethylene copolymer, or vinylidene fluoride A negative electrode 10 was produced in the same manner as in Example 1-1 except that a hexafluoropropylene-tetrafluoroethylene copolymer was used, and a secondary battery was produced. Note that pure water as a dispersion medium has a swelling degree of 0% with respect to these binders.

  For the obtained secondary batteries of Examples 3-1 to 3-4, the capacity, the charge and discharge efficiency, and the cycle characteristics were determined in the same manner as in Example 1-1. The results are shown in Table 3. In addition, the discharge capacity was calculated | required by the relative value when the value of Example 1-1 is set to 100.

  As can be seen from Table 3, a result equivalent to that of Example 1-1 was obtained. That is, it was found that cycle characteristics and the like can be improved even when a copolymer having vinylidene fluoride as a component is used as a binder.

(Examples 4-1 to 4-3)
A negative electrode 10 was produced in the same manner as in Example 1-1 except that the average particle size of polyvinylidene fluoride as a binder was changed, and a secondary battery was produced. The average particle size of polyvinylidene fluoride was 10 μm in Example 4-1, 20 μm in Example 4-2, and 30 μm in Example 4-3.

  For the obtained secondary batteries of Examples 4-1 to 4-3, the capacity, the charge and discharge efficiency, and the cycle characteristics were determined in the same manner as in Example 1-1. The results are shown in Table 4. In addition, the discharge capacity was calculated | required by the relative value when the value of Example 1-1 is set to 100.

  As can be seen from Table 4, the discharge capacity, the charge / discharge efficiency, and the discharge capacity retention rate tended to increase as the average particle size of the binder decreased. That is, it was found that the average particle diameter of the binder was preferably 30 μm or less, and more preferably 1 μm or less.

(Examples 5-1 to 5-5)
A secondary battery was fabricated in the same manner as in Example 1-1 except that the heat treatment conditions for the precursor layer, that is, the heat treatment conditions for melting the binder were changed. Specifically, the heat treatment is performed in vacuum at 200 ° C. for 10 minutes in Example 5-1, in Example 5-2, at 200 ° C. for 2 hours in an argon atmosphere, and in Example 5-3, the nitrogen atmosphere. It was performed at 200 ° C. for 2 hours, in Example 5-4, it was performed in vacuum at 180 ° C. for 2 hours, and in Example 5-5, it was performed in air at 200 ° C. for 2 hours.

  As Comparative Example 5-1 with respect to Examples 5-1 to 5-5, except that the heat treatment of the precursor layer was performed in a vacuum at 160 ° C. for 2 hours, that is, the binder was not melted, Others were fabricated in the same manner as in Examples 5-1 to 5-5.

  For the obtained secondary batteries of Examples 5-1 to 5-5 and Comparative Example 5-1, the capacity, charge / discharge efficiency, and cycle characteristics were determined in the same manner as in Example 1-1. The results are shown in Table 5. In addition, the discharge capacity was calculated | required by the relative value when the value of Example 1-1 is set to 100.

  As can be seen from Table 5, according to Examples 5-1 to 5-5 in which the heat treatment was performed at a temperature higher than the melting point of polyvinylidene fluoride as the binder, and the binder was melted, the temperature below the melting point A higher value was obtained for the discharge capacity retention rate than in Comparative Example 5-1, in which the binder was not melted by heat treatment. Further, according to Example 5-1 in which the heat treatment time was 10 minutes, a high value was obtained for the discharge capacity retention rate, as in Example 1-1 in which the heat treatment time was 2 hours. Furthermore, according to Examples 1-1, 5-2, and 5-3 in which the heat treatment was performed in a vacuum, an argon atmosphere, or a nitrogen atmosphere, the discharge capacity was maintained as compared with Examples 5-5 that were performed in the air. The rate was high. This is presumably because part of the negative electrode active material was oxidized by oxygen contained in the atmosphere.

  That is, it was found that if the heat treatment is performed at a temperature higher than the melting point of the binder and the binder is melted, the cycle characteristics can be improved regardless of the atmosphere during the heat treatment or the treatment time. .

(Examples 6-1 to 6-9)
A secondary battery was fabricated in the same manner as in Example 1-1 except that the negative electrode active material was synthesized by changing the raw material ratio of iron, tin, and graphite as shown in Table 6. Specifically, the ratio of iron to the total of tin and iron in the raw material ratio (hereinafter referred to as Fe / (Sn + Fe) ratio) is constant at 32% by mass, and the carbon raw material ratio is 12.0% by mass, 14.0 mass%, 16.0 mass%, 18.0 mass%, 22.0 mass%, 24.0 mass%, 26.0 mass%, 28.0 mass%, and 30.0 mass% were set.

  The composition of the obtained negative electrode active materials of Examples 6-1 to 6-9 was analyzed in the same manner as in Example 1-1. The results are shown in Table 6. Moreover, when XPS was performed, the peak P1 was obtained in Examples 6-1 to 6-9. When the peak P1 was analyzed, the surface contamination carbon peak P2 and the C1s peak P3 in the negative electrode active material were obtained in the same manner as in Example 1-1, and the peak P3 was lower than 284.5 eV in both cases. Obtained in the area. That is, it was confirmed that at least a part of carbon contained in the negative electrode active material was bonded to other elements. Furthermore, the capacity and cycle characteristics of the secondary battery were examined in the same manner as in Example 1-1. The results are shown in Table 6. In addition, the discharge capacity was calculated | required by the relative value when the value of Example 1-1 is set to 100.

  As can be seen from Table 6, the same results as in Example 1-1 were obtained. That is, it has been found that when the carbon content in the negative electrode active material is 11.9 mass% or more and 29.7 mass%, the capacity and cycle characteristics can be improved.

(Examples 7-1 to 7-3, 8-1 to 8-3, 9-1 to 9-3)
A secondary battery was fabricated in the same manner as in Example 1-1 except that the negative electrode active material was synthesized by changing the raw material ratio of iron, tin, and graphite as shown in Table 7. Specifically, in Examples 7-1 to 7-3, the carbon raw material ratio is constant at 12.0% by mass, and the Fe / (Sn + Fe) ratio is 26% by mass, 39% by mass, and 48% by mass. It was. In Examples 8-1 to 8-3, the carbon raw material ratio was constant at 20.0 mass%, and the Fe / (Sn + Fe) ratio was 26 mass%, 39 mass%, and 48 mass%. Furthermore, in Examples 9-1 to 9-3, the carbon raw material ratio was constant at 30.0 mass%, and the Fe / (Sn + Fe) ratio was 26 mass%, 39 mass%, and 48 mass%.

  For the obtained negative electrode active materials of Examples 7-1 to 7-3, 8-1 to 8-3, and 9-1 to 9-3, the composition was analyzed in the same manner as in Example 1-1. . The results are shown in Table 7. Moreover, when XPS was performed about these negative electrode active materials, peak P1 was obtained. When the peak P1 was analyzed, the surface contamination carbon peak P2 and the C1s peak P3 in the negative electrode active material were obtained in the same manner as in Example 1-1, and the peak P3 was lower than 284.5 eV in both cases. Obtained in the area. That is, it was confirmed that at least a part of carbon contained in the negative electrode active material was bonded to other elements. Furthermore, the capacity and cycle characteristics of the secondary battery were examined in the same manner as in Example 1-1. The results are shown in Table 7 together with the results of Examples 1-1, 6-1 and 6-9. In addition, the discharge capacity was calculated | required by the relative value when the value of Example 1-1 is set to 100.

  As can be seen from Table 7, Examples 7-1 to 7-3 and 8-1 to 8-3 in which the Fe / (Sn + Fe) ratio in the negative electrode active material was set to 26.4 mass% or more and 48.5 mass%. , 9-1 to 9-3, high values were obtained for the discharge capacity and the discharge capacity retention rate as in Examples 6-1, 1-1, and 6-9.

  That is, it was found that the capacity and cycle characteristics can be improved by setting the Fe / (Sn + Fe) ratio in the negative electrode active material to 26.4 mass% or more and 48.5 mass%.

(Examples 10-1 to 10-22)
In Examples 10-1 to 10-16, the raw materials are iron powder, tin powder, graphite powder, and the first component is aluminum powder, titanium powder, vanadium powder, chromium powder, niobium powder, and tantalum powder. At least one of them, and at least one of cobalt powder, nickel powder, copper powder, zinc powder, gallium powder and indium powder as the second component, tin, iron, carbon, first component and second A negative electrode active material was synthesized in the same manner as in Example 1-1 except that the raw material ratio with respect to the components was as shown in Table 8, and a secondary battery was produced. In Examples 10-17, iron powder, tin powder, graphite powder, and titanium powder as the first component were used as raw materials, and the raw material ratios of tin, iron, carbon, and titanium are shown in Table 8. Except as described above, a negative electrode active material was synthesized in the same manner as in Example 1-1, and a secondary battery was produced. Furthermore, in Example 10-18, iron powder, tin powder, graphite powder, and zinc powder as the second component were used as raw materials, and the raw material ratios of tin, iron, carbon, and zinc are shown in Table 8. Except as described above, a negative electrode active material was synthesized in the same manner as in Example 1-1, and a secondary battery was produced. Furthermore, in Examples 10-19, iron powder, tin powder, graphite powder, and silver powder were used as raw materials, and the raw material ratio of tin, iron, carbon, and silver was as shown in Table 8. Except for the above, a negative electrode active material was synthesized in the same manner as in Example 1-1 to produce a secondary battery. In addition, in Examples 10-20 to 10-22, the raw materials are iron powder, tin powder, graphite powder, silver powder, titanium powder or aluminum powder as the first component, and zinc powder or the second component. The negative electrode active material was the same as in Example 1-1 except that copper powder was used and the raw material ratio of tin, iron, carbon, first component, and second component was as shown in Table 8. To synthesize a secondary battery. The composition of these negative electrode active materials was analyzed in the same manner as in Example 1-1. The results are shown in Table 8. The contents of aluminum, titanium, vanadium, chromium, niobium, tantalum, cobalt, nickel, copper, zinc, gallium and indium were measured by ICP emission analysis. Further, when XPS was performed, a peak P1 was obtained. When the obtained peak was analyzed, a peak P2 of surface-contaminated carbon and a peak P3 of C1s in the negative electrode active material were obtained in the same manner as in Example 1-1, and each peak P3 was higher than 284.5 eV. Obtained in the low area. That is, it was confirmed that at least a part of carbon contained in the negative electrode active material was bonded to other elements. Furthermore, the capacity and cycle characteristics of the secondary battery were examined in the same manner as in Example 1-1. The results are shown in Table 8 together with the results of Example 1-1. In addition, the discharge capacity was calculated | required by the relative value when the value of Example 1-1 is set to 100.

  As can be seen from Table 8, according to Examples 10-1 to 10-16 including the first component and the second component, Example 1-1 not including these, or only the first component or only the second component The discharge capacity retention rate was improved as compared with Examples 10-17 and 10-18.

  Moreover, Examples 10-1 to 10 in which the content of the first component is 0.1% by mass or more and 9.9% by mass or less, and the content of the second component is 0.5% by mass or more and 14.9% by mass or less. According to -14, a high value was also obtained for the discharge capacity.

  Furthermore, according to Example 10-19 containing silver, the discharge capacity retention rate is improved as compared with Example 1-1 not containing silver, and in addition to silver, the first component and the second component are further included. According to Examples 10-20 to 10-22, the discharge capacity retention rate was further improved.

  That is, at least one member selected from the group consisting of aluminum, titanium, vanadium, chromium, niobium and tantalum as the negative electrode active material, and at least one member selected from the group consisting of cobalt, nickel, copper, zinc, gallium and indium. If it is made to contain, cycling characteristics can be improved more and these content shall be 0.1 to 9.9 mass% and 0.5 to 14.9 mass%, respectively. As a result, it was found that a high capacity can be obtained.

  It was also found that cycle characteristics can be improved if silver is included in 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 embodiments and examples, a secondary battery having a winding structure has been specifically described, but the present invention has other shapes such as a coin type, a sheet type, a button type or a square type. The present invention can be similarly applied to a secondary battery having the above structure or a secondary battery having another stacked structure in which a plurality of positive and negative electrodes are stacked.

  In the embodiment and the example, the case where lithium is used as the electrode reactant has been described. However, if it is possible to react with the negative electrode active material, the other in the long-period periodic table such as sodium (Na) or potassium (K) The present invention is also applied to the case of using an element of Group 1 of the above, an element of Group 2 in the long-period periodic table such as magnesium or calcium (Ca), another light metal such as aluminum, lithium, or an alloy thereof. And the same effect can be obtained. At that time, a positive electrode active material or a non-aqueous solvent that can occlude and release the electrode reactant is selected according to the electrode reactant.

  Further, in the above embodiment and examples, the case where an electrolytic solution is used as the electrolyte is described, and in the above 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, ion conductive inorganic compounds such as ion conductive ceramics, ion conductive glass or ionic crystals, or other inorganic compounds, or a mixture of these inorganic compounds and an electrolyte or gel electrolyte. The thing which was done is mentioned.

It is sectional drawing showing the structure of the negative electrode which concerns on one embodiment of this invention. It is sectional drawing showing the structure of the secondary battery using the negative electrode shown in FIG. 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 other secondary battery using the negative electrode shown in FIG. 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 10 ... Negative electrode, 11 ... Negative electrode collector, 12 ... Negative electrode active material layer, 21 ... Battery can, 22, 23 ... Insulation board, 24 ... Battery cover, 25 ... Safety valve mechanism, 25A ... Disc board, 26 ... Heat resistance Element, 27 ... Gasket, 30, 40 ... Winding electrode body, 31, 43 ... Positive electrode, 31A, 43A ... Positive electrode current collector, 31B, 43B ... Positive electrode active material layer, 32, 44 ... Separator, 33 ... Center pin, 34, 41 ... positive electrode lead, 35, 42 ... negative electrode lead, 45 ... electrolyte layer, 46 ... protective tape, 50 ... exterior member, 51 ... adhesion film.

Claims (22)

Constituent elements include at least tin (Sn), iron (Fe), and carbon (C), the carbon content is 11.9 mass% or more and 29.7 mass% or less, and tin and iron A negative electrode active material in which the ratio of iron to the total of 26.4% by mass and 48.5% by mass is;
A negative electrode comprising: a binder containing at least one member selected from the group consisting of polyvinylidene fluoride melted by heating at a temperature equal to or higher than a melting point and a copolymer of vinylidene fluoride as a component.   Furthermore, at least 1 sort (s) of the group which consists of carboxymethylcellulose and its inorganic salt is included, The negative electrode of Claim 1 characterized by the above-mentioned.   The negative electrode according to claim 1, wherein the negative electrode active material further contains silver (Ag) as a constituent element.   The negative electrode active material further includes at least one member selected from the group consisting of aluminum (Al), titanium (Ti), vanadium (V), chromium (Cr), niobium (Nb), and tantalum (Ta) as a constituent element. And a second component composed of at least one selected from the group consisting of cobalt (Co), nickel (Ni), copper (Cu), zinc (Zn), gallium (Ga), and indium (In). The negative electrode according to claim 1, comprising:   5. The negative electrode according to claim 4, wherein the content of the first component in the negative electrode active material is 0.1 mass% or more and 9.9 mass% or less.   5. The negative electrode according to claim 4, wherein the content of the second component in the negative electrode active material is 0.5 mass% or more and 14.9 mass% or less. A battery comprising an electrolyte together with a positive electrode and a negative electrode,
The negative electrode includes at least tin (Sn), iron (Fe), and carbon (C) as constituent elements, and the carbon content is 11.9 mass% or more and 29.7 mass% or less, and An anode active material in which the ratio of iron to the total of tin and iron is 26.4% by mass or more and 48.5% by mass or less, polyvinylidene fluoride and vinylidene fluoride melted by heating at a temperature equal to or higher than the melting point And a binder containing at least one member selected from the group consisting of copolymers.   The battery according to claim 7, wherein the negative electrode further includes at least one selected from the group consisting of carboxymethyl cellulose and an inorganic salt thereof.   The battery according to claim 7, wherein the negative electrode active material further contains silver (Ag) as a constituent element.   The negative electrode active material further includes at least one member selected from the group consisting of aluminum (Al), titanium (Ti), vanadium (V), chromium (Cr), niobium (Nb), and tantalum (Ta) as a constituent element. And a second component composed of at least one selected from the group consisting of cobalt (Co), nickel (Ni), copper (Cu), zinc (Zn), gallium (Ga), and indium (In). The battery according to claim 7, comprising:   The battery according to claim 10, wherein the content of the first component in the negative electrode active material is 0.1 mass% or more and 9.9 mass% or less.   11. The battery according to claim 10, wherein the content of the second component in the negative electrode active material is 0.5% by mass or more and 14.9% by mass or less.   Constituent elements include at least tin (Sn), iron (Fe), and carbon (C), the carbon content is 11.9 mass% or more and 29.7 mass% or less, and tin and iron At least one member selected from the group consisting of a negative electrode active material having a ratio of iron to 26.4% by mass or more and 48.5% by mass or less, and polyvinylidene fluoride and a copolymer containing vinylidene fluoride as a component. A method for producing a negative electrode, comprising: forming a precursor layer containing a binder, and heating at a temperature equal to or higher than a melting point of the binder.   The negative electrode manufacturing method according to claim 13, wherein in addition to the negative electrode active material and the binder, at least one member selected from the group consisting of carboxymethyl cellulose and an inorganic salt thereof is mixed to form a precursor layer. Method.   The negative electrode manufacturing method according to claim 13, wherein the negative electrode active material and the binder are mixed using a dispersion medium having a swelling degree of 10% or less with respect to the binder to form a precursor layer. Method.   The method for producing a negative electrode according to claim 13, wherein the precursor layer is formed using a dispersion medium containing water.   The method for producing a negative electrode according to claim 13, wherein an average particle size of the binder is 30 μm or less.   The method for producing a negative electrode according to claim 13, wherein the negative electrode active material further contains silver (Ag) as a constituent element.   The negative electrode active material further includes at least one member selected from the group consisting of aluminum (Al), titanium (Ti), vanadium (V), chromium (Cr), niobium (Nb), and tantalum (Ta) as a constituent element. And a second component composed of at least one selected from the group consisting of cobalt (Co), nickel (Ni), copper (Cu), zinc (Zn), gallium (Ga), and indium (In). The method for producing a negative electrode according to claim 13, comprising:   The method for producing a negative electrode according to claim 19, wherein the content of the first component in the negative electrode active material is 0.1 mass% or more and 9.9 mass% or less.   The method for producing a battery according to claim 19, wherein the content of the second component in the negative electrode active material is 0.5 mass% or more and 14.9 mass% or less. A method for producing a battery comprising an electrolyte together with a positive electrode and a negative electrode,
The negative electrode contains at least tin (Sn), iron (Fe), and carbon (C) as constituent elements, the carbon content is 11.9 mass% or more and 29.7 mass% or less, and Of the group consisting of a negative electrode active material having a ratio of iron to 26.4% by mass to 48.5% by mass with respect to the total of tin and iron, and polyvinylidene fluoride and a copolymer containing vinylidene fluoride as components A method for manufacturing a battery, comprising: forming a precursor layer containing a binder containing at least one kind, and then heating the precursor layer at a temperature equal to or higher than a melting point of the binder.

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