JP2006134684A - Negative electrode and battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a negative electrode and a battery capable of improving cycle property and further improving safety while keeping high capacity. <P>SOLUTION: A negative electrode active material layer 12 contains a negative electrode active material at least containing tin, cobalt, carbon as constituent elements, with a content of carbon of 9.9% by mass or more and 29.7% by mass or less, and a content of cobalt to a total of tin and cobalt of 30% by mass or more and 70% by mass or less, and at least a kind of additive out of a group consisting of organic acid and organic acid salt such as lithium acetate, sodium acetate, lithium phosphate, or lithium oxalate. With this, the cycle characteristics are improved, while a high capacity is maintained, and further, stability is improved. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a negative electrode including a negative electrode active material containing tin (Sn), cobalt (Co), and carbon (C) as constituent elements, and a battery using the negative electrode.

  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 14 include a tin-nickel alloy, a lithium-aluminum-tin alloy, a tin-zinc alloy, a tin alloy containing phosphorus (P) in the 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 (Mn), iron (Fe), cobalt (Co), nickel (Ni) or copper (Cu) Mixtures with phases that do not occlude Li) 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 Japanese Patent Laid-Open No. 10-16823 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 JP-A-10-308207 Japanese Patent Application Laid-Open No. 11-86854

  Therefore, as a negative electrode active material capable of sufficiently improving cycle characteristics, at least tin, cobalt, and carbon are contained as constituent elements, and the carbon content is 9.9 mass% or more and 29.7 mass% or less. In addition, the inventors have developed a material in which the ratio of cobalt to the total of tin and cobalt is 30% by mass or more and 70% by mass or less, but it is necessary to further improve safety.

  The present invention has been made in view of such problems, and an object thereof is to provide a negative electrode having a high capacity, excellent cycle characteristics and safety, and a battery using the same.

  The negative electrode according to the present invention contains at least tin, cobalt, and carbon 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. The negative electrode active material whose ratio of cobalt to 30 mass% or more and 70 mass% or less is included, and at least one kind of additive selected from the group consisting of organic acids and organic acid salts.

  The battery according to the present invention includes an electrolyte together with a positive electrode and a negative electrode, and the negative electrode contains at least tin, cobalt, and carbon as constituent elements, and the carbon content is 9.9% by mass or more. At least one member selected from the group consisting of a negative electrode active material that is 29.7% by mass or less and the ratio of cobalt to the total of tin and cobalt is 30% by mass to 70% by mass, and an organic acid and an organic acid salt Seed additives.

  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 cobalt as a constituent element, and the ratio of cobalt to the total of tin and cobalt is set to 30% by mass or more and 70% by mass or less, thereby improving cycle characteristics while maintaining a high capacity. Can be made. Furthermore, since this negative electrode active material contains carbon as a constituent element and its content is set to 9.9 mass% or more and 29.7 mass% or less, cycle characteristics can be further improved. In addition, since at least one additive from the group consisting of organic acids and organic acid salts is included, safety can be improved. Therefore, according to the battery of the present invention using this negative electrode, a high capacity can be obtained, and excellent cycle characteristics and safety can be obtained.

  In particular, when the content of at least one additive selected from the group consisting of an organic acid and an organic acid salt in the negative electrode active material layer is 5% by mass or less, a high effect can be obtained. Moreover, even if it includes at least one member selected from the group consisting of lithium acetate, sodium acetate, lithium phosphate and lithium oxalate as an additive, a high effect can be obtained.

  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, for example, 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 a negative electrode active material containing tin and cobalt 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 cobalt.

  The cobalt content in the negative electrode active material is the ratio of cobalt to the total of tin and cobalt, and is preferably in the range of 30% by mass to 70% by mass, and in the range of 30% by mass to 60% by mass. If it is in, it is more preferable. If the ratio is low, the cobalt content decreases and sufficient cycle characteristics cannot be obtained, and if the ratio is high, the tin content decreases and a capacity exceeding conventional negative electrode materials such as carbon materials cannot be obtained. It is.

  The negative electrode active material also contains carbon as a constituent element in addition to tin and cobalt. This is because the cycle characteristics can be further improved by including carbon. The carbon content is preferably in the range of 9.9% by mass to 29.7% by mass, more preferably in the range of 14.9% by mass to 29.7% by mass, particularly 16.8% by mass or more. It is more preferable if it is in the range of 24.8% by mass or less. This is because a high effect can be obtained within this range.

  In some cases, the negative electrode active material preferably contains silicon 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 too small, the effect of increasing the capacity is not sufficient, and if the amount is large, the charge / discharge is pulverized and the charge / discharge cycle characteristics are deteriorated.

  In some cases, the negative electrode active material preferably contains at least one member selected from the group consisting of iron, nickel, and chromium (Cr) as a constituent element. This is because the cycle characteristics can be further improved. The iron content is preferably in the range of 0.3 mass% or more and 5.9 mass% or less. Moreover, it is preferable that content of nickel and chromium exists in the range of 0.1 to 3.0 mass%. When the amount is small, the effect of improving the charge / discharge cycle characteristics is not sufficient, and when the amount is large, the tin content is lowered and a sufficient capacity cannot be obtained. These elements may be contained together with silicon.

  In some cases, the negative electrode active material preferably contains at least one member selected from the group consisting of indium, niobium, germanium, titanium, molybdenum, aluminum, phosphorus, gallium, and bismuth as a constituent element. This is because the cycle characteristics can be further improved. These contents are preferably in the range of 14.9% by mass or less, preferably in the range of 2.4% by mass or more and 14.9% by mass or less, particularly 4.0% by mass or more and 12.9% by mass or less. If it is in the range, it is more preferable. If the amount is too small, a sufficient effect cannot be obtained. If the amount is large, the tin content decreases, a sufficient capacity cannot be obtained, and charge / discharge cycle characteristics also deteriorate. These elements may be contained together with silicon, iron, nickel or chromium.

  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 1.0 ° or more at a diffraction angle 2θ when CuKα ray is used as the specific X-ray and the drawing speed is 1 ° / min. Is preferred. 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 constituent element 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.

  Further, in this negative electrode active material, it is preferable that at least a part of carbon as a constituent element is bonded to a metal element or a metalloid 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. 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. This is because by adding carbon to such an alloy and synthesizing it by a mechanical alloying method, the alloy can have a low crystallinity or an amorphous structure, and the reaction time can be shortened. 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 may contain other materials such as a binder or a conductive aid as necessary. Examples of the binder include polyacrylic acid, carboxymethyl cellulose, polytetrafluoroethylene, polyvinylidene fluoride, vinylidene fluoride copolymer, polyvinyl alcohol, starch, diacetyl cellulose, hydroxypropyl cellulose, polyvinyl chloride, polyvinyl pyrrolidone, and polyethylene. , Polypropylene, styrene butadiene rubber (SBR), ethylene propylene diene terpolymer (EPDM), sulfonated ethylene propylene diene terpolymer, fluorine rubber, polybutadiene or polyethylene oxide. Among these, polyvinylidene fluoride, a copolymer of vinylidene fluoride, styrene butadiene rubber or carboxymethyl cellulose is preferable. It is because it is excellent in binding property and battery performance can be improved. One type of binder may be used alone, or two or more types may be mixed and used.

  The conductive auxiliary agent ensures 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 when the negative electrode active material expands and contracts due to charge and discharge. belongs to.

  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. Fired 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, silver (Ag) or metal fibers, conductive wires such as zinc oxide or potassium titanate Car acids, 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 assistant may be used alone, or two or more types may be used in combination.

The negative electrode active material layer 12 also contains an organic acid or an organic acid salt as an additive capable of improving the thermal stability. Examples of the organic acid include a carboxylic acid group (—COOH), a phosphoric acid group (—PO ₃ H), a sulfonic acid group (—SO ₃ H), a sulfinic acid group (—SO ₂ H), and sulfenic acid in one molecule. Examples thereof include those having a group (—SOH), a boric acid group (—BO ₃ H ₃ ), and a phenol group. Among them, an organic compound having one or two carboxylic acid groups, or an organic compound having a phosphoric acid group is used. preferable. Examples of the organic acid salt include lithium salts, sodium salts, potassium salts, cesium salts, magnesium salts, calcium salts, and barium salts of the organic acids described above, and among them, lithium salts, sodium salts, and potassium salts are preferable. Specifically, lithium acetate, sodium acetate, lithium phosphate or lithium oxalate is preferable. This is because a high effect can be obtained.

  For example, the content of the organic acid and the organic acid salt is preferably 5% by mass or less with respect to the entire material constituting the negative electrode active material layer 12. This is because if the amount is large, the capacity decreases.

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

  First, the negative electrode active material described above, an organic acid or an organic acid salt, and, if necessary, a binder and a conductive auxiliary agent in a dispersion medium such as water, N-methyl-2-pyrrolidone, or methyl isobutyl ketone. Disperse to obtain a negative electrode mixture slurry.

  In addition, you may add a thickener etc. to a negative mix slurry as needed. Examples of the thickener include starch, carboxymethyl cellulose, carboxymethyl cellulose ammonium salt, sodium salt or potassium salt, hydroxypropyl cellulose, regenerated cellulose, or diacetyl cellulose. One thickener may be used alone, or two or more thickeners may be mixed and used.

  For mixing, kneading, or dispersing in a dispersion medium such as a negative electrode active material, an organic acid or an organic acid salt, a binder and a conductive aid, a known kneader, mixer, homogenizer, dissolver, planetary mixer, paint shaker, or Any mixing stirrer such as a 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 to remove the dispersion medium, the negative electrode active material layer 12 is formed by compression molding using a roll press or the like. 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 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.

  The wound electrode body 30 is wound around a center pin 33, for example. 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, and the thermal stability can be further improved. 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 occluding and releasing lithium as a positive electrode active material, and artificial graphite or carbon black as necessary. And a binder such as polyvinylidene fluoride.

Examples of the positive electrode material capable of inserting and extracting lithium include metal sulfides or oxides that do not contain lithium, such as TiS ₂ , MoS ₂ , NbSe _{2, and} V ₂ O _5, and a chemical formula of Li _x M1O ₂ ( M1 represents one or more transition metals, x is different depending on the charge / discharge state of the battery, and is generally 0.05 ≦ x ≦ 1.10. Specific polymers are exemplified. As the positive electrode material, one kind may be used alone, or two or more kinds may be mixed and used.

Among these, in the chemical formula Li _x M1O ₂ , a lithium composite oxide containing at least one member selected from the group consisting of cobalt, nickel, and manganese as the transition metal M1 is preferable. _{Specifically, LiCoO 2, LiNiO 2, Li} y Ni z Co 1-z O 2 (y and z vary according to charge and discharge state of the battery, generally 0 <y <1,0.2 <z < 1.0 Or a lithium manganese composite oxide having a spinel structure. This is because these lithium composite oxides can obtain a high voltage and a high energy density.

  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. Nonaqueous solvents include, for example, 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, acetate, butyrate, or propionate. 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 alone or in combination of two or more.

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

  First, for example, the negative electrode 10 is produced as described above. Next, for example, a positive electrode active material is mixed with a conductive additive and a binder as necessary to prepare a positive electrode mixture, and the 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. The positive electrode mixture slurry is applied to the positive electrode current collector 31A and the solvent is dried. Then, 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 electrolyte 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 31 </ b> B through the electrolyte impregnated in the separator 32. Here, since the negative electrode 10 contains the negative electrode active material containing tin, cobalt, and carbon in the above-described proportions, the cycle characteristics are improved while maintaining a high capacity. Further, since it contains an organic acid or an organic acid salt, the thermal stability is improved.

  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 cobalt as a constituent element, and the ratio of cobalt to the total of tin and cobalt is set to 30% by mass or more and 70% by mass or less, thereby improving cycle characteristics while maintaining a high capacity. Can be made. Furthermore, since this negative electrode active material contains carbon as a constituent element and its content is set to 9.9 mass% or more and 29.7 mass% or less, cycle characteristics can be further improved. In addition, since at least one additive from the group consisting of organic acids and organic acid salts is included, safety can be improved. Therefore, according to the battery according to the present embodiment using this negative electrode 10, a high capacity can be obtained, and excellent cycle characteristics and safety can be obtained.

  In particular, if the content of at least one additive selected from the group consisting of an organic acid and an organic acid salt in the negative electrode active material layer 12 is 5% by mass or less, a high effect can be obtained. Moreover, even if it includes at least one member selected from the group consisting of lithium acetate, sodium acetate, lithium phosphate and lithium oxalate as an additive, a high effect can be obtained.

(Second 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 obtained by laminating the positive electrode 43 and the negative electrode 10 via the separator 44 and the electrolyte 45 and winding them, and the outermost periphery 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. The polymer compound is, for example, a fluorine polymer compound such as polyvinylidene fluoride or a copolymer of vinylidene fluoride and hexafluoropropylene, an ether polymer compound such as polyethylene oxide or a crosslinked product containing polyethylene oxide, or polyacrylonitrile. Etc. 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 a solvent, an electrolyte salt, 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 adhesion 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 including a solvent, an electrolyte salt, a monomer that is a raw material of the polymer compound, a polymerization initiator, and other materials such as a polymerization inhibitor as necessary is prepared, and the exterior Inject into the member 50.

  After injecting the electrolyte composition, the opening of the exterior member 50 is heat-sealed in a vacuum atmosphere and sealed. Next, heat is applied to polymerize the monomer to obtain 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.

(Third battery)
FIG. 6 illustrates a cross-sectional configuration of the third secondary battery. In this secondary battery, a flat electrode body 60 in which a positive electrode 62 to which a positive electrode lead 61 is attached and a negative electrode 10 to which a negative electrode lead 63 is attached is arranged to face each other with an electrolyte layer 64 interposed therebetween is formed into a film-like exterior. It is accommodated in the member 65. The configuration of the exterior member 65 is the same as that of the exterior member 50 described above.

  The positive electrode 62 has a structure in which a positive electrode active material layer 62B is provided on a positive electrode current collector 62A. The negative electrode 10 is disposed so that the negative electrode active material layer 12 side faces the positive electrode active material layer 62B. The configurations of the positive electrode current collector 62A and the positive electrode active material layer 62B are the same as those of the positive electrode current collector 31A and the positive electrode active material layer 31B described above, respectively.

  The electrolyte layer 64 is made of, for example, a solid electrolyte. As the solid electrolyte, for example, an inorganic solid electrolyte or a polymer solid electrolyte can be used as long as the material has lithium ion conductivity. Examples of the inorganic solid electrolyte include those containing lithium nitride or lithium iodide. The polymer solid electrolyte is mainly composed of an electrolyte salt and a polymer compound that dissolves the electrolyte salt. Examples of the polymer compound of the solid polymer electrolyte include, for example, an ether polymer compound such as polyethylene oxide or a crosslinked product containing polyethylene oxide, an ester polymer compound such as polymethacrylate, and an acrylate polymer compound. Or can be copolymerized.

  The polymer solid electrolyte can be formed, for example, by mixing a polymer compound, an electrolyte salt, and a mixed solvent, and then volatilizing the mixed solvent. Moreover, after dissolving electrolyte salt, the monomer which is a raw material of a polymer compound, a polymerization initiator, and other materials such as a polymerization inhibitor as necessary in a mixed solvent, the mixed solvent is volatilized, It can also be formed by polymerizing the monomer by applying heat to form a polymer compound.

  The inorganic solid electrolyte may be formed on the surface of the positive electrode 62 or the negative electrode 10 by a sputtering method, a vacuum deposition method, a laser ablation method, an ion plating method, a vapor phase method such as a CVD (Chemical Vapor Deposition) method, or a sol-gel method. It can be formed by a liquid phase method.

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

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

(Examples 1-1 to 1-4)
First, a negative electrode active material was prepared. Cobalt powder, tin powder, and graphite powder were prepared as raw materials. Cobalt powder and tin powder were alloyed to produce a cobalt-tin alloy powder, and then graphite powder was added to the alloy powder and dry mixed. At that time, the raw material ratio was cobalt powder: tin powder: graphite powder = 32.6: 55.4: 12 by mass ratio. 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 synthesized negative electrode active material powder was taken out by cooling the reaction vessel to room temperature, and coarse powder was removed through a 280 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 cobalt and tin contents were measured by ICP (Inductively Coupled Plasma) emission analysis. As a result, the cobalt content was 32.4 mass%, the tin content was 55.2 mass%, and the carbon content was 11.8 mass%. Moreover, when X-ray diffraction was performed about the obtained negative electrode active material, the diffraction peak which has a wide half value width between 2 (theta) = 20 degrees-50 degrees was observed. When the half width of this diffraction peak was measured, it was 1.0 ° or more. Further, when XPS was performed on this negative electrode active material, a peak P1 was obtained as shown in FIG. When the peak P1 was analyzed, a peak P2 of surface contamination carbon and a peak P3 of C1s in the 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.

  72 parts by mass of this negative electrode active material powder, 20 parts by mass of artificial graphite as a conductive additive, 5 parts by mass of polyvinylidene fluoride as a binder, 2 parts by mass of carboxymethyl cellulose as a thickener, and 1 part by mass of an organic acid salt Were weighed and mixed with a planetary mixer using pure water as a dispersion medium to prepare a negative electrode mixture slurry. At that time, the organic acid salt was lithium acetate in Example 1-1, sodium acetate in Example 1-2, lithium phosphate in Example 1-3, and lithium oxalate in Example 1-4. .

  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, and further heat treated at 200 ° C. for 2 hours in a vacuum atmosphere. The negative electrode active material layer 12 was formed and the negative electrode 10 was produced. 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 mix the positive electrode. An agent 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. 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 in an equal volume 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 Examples 1-1 to 1-4, secondary batteries were fabricated in the same manner as in Examples 1-1 to 1-4 except that the organic acid salt was not used.

  The obtained secondary batteries of Examples 1-1 to 1-4 and Comparative Example 1-1 were subjected to a charge / discharge test, and the initial discharge capacity, cycle characteristics, and thermal stability were examined. The results are shown in Table 1. In this case, charging is 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 is performed at a constant current of 0.5 C at 23 ° C. Current discharge was performed to a final voltage of 2.5V. The initial discharge capacity was determined as a relative value when the value of Example 1-1 was set to 100. The cycle characteristics were obtained from the ratio of the discharge capacity at the 100th cycle when 100 cycles of charge / discharge were performed under the conditions described above and the discharge capacity at the first cycle was taken as 100. Furthermore, thermal stability performed 5 cycles charge / discharge on the conditions mentioned above, measured the highest temperature of the battery at the time of discharge of each cycle, and calculated | required these average values. 0.5 C is a current value that can discharge the battery capacity in 2 hours.

  As can be seen from Table 1, according to Examples 1-1 to 1-4 using the negative electrode 10 containing an organic acid or an organic acid salt, the discharge time was higher than that of Comparative Example 1-1 using a negative electrode not containing these. The maximum temperature of was low.

  That is, it has been found that if the negative electrode 10 contains an organic acid or an organic acid salt, the safety can be improved.

(Examples 2-1 to 2-3)
A secondary battery was fabricated in the same manner as in Example 1-1 except that the negative electrode 10 was fabricated by changing the mixing ratio of lithium acetate, which is an organic acid salt. At that time, in Example 2-1, the negative electrode 10 was 70 parts by mass of the negative electrode active material powder, 20 parts by mass of artificial graphite, 5 parts by mass of polyvinylidene fluoride, 2 parts by mass of carboxymethyl cellulose, and 3 parts by mass of lithium acetate. In Example 2-2, 70 parts by mass of the negative electrode active material powder, 18 parts by mass of artificial graphite, 5 parts by mass of polyvinylidene fluoride, 2 parts by mass of carboxymethyl cellulose, and 5 parts by mass of lithium acetate In Example 2-3, 69 parts by mass of the negative electrode active material powder, 16 parts by mass of artificial graphite, 5 parts by mass of polyvinylidene fluoride, 2 parts by mass of carboxymethylcellulose, and 8 parts by mass of lithium acetate were prepared. It was produced using.

  For the obtained secondary batteries of Examples 2-1 to 2-3, the initial discharge capacity, the cycle characteristics, and the thermal stability were examined in the same manner as in Example 1-1. The results are shown in Table 2 together with the results of Example 1-1. The initial discharge capacity was determined as a relative value when the value of Example 1-1 was set to 100.

  As can be seen from Table 2, the maximum temperature of the battery decreased as the proportion of lithium acetate increased and became constant when it exceeded 5 mass%. On the other hand, the initial discharge capacity and capacity retention rate decreased as the proportion of lithium acetate increased.

  That is, if the content of the organic acid or the organic acid salt with respect to the material constituting the negative electrode active material layer 12 is 5% by mass or less, the safety can be improved while maintaining high cycle characteristics with a high capacity, It turned out to be preferable.

(Examples 3-1 to 3-4)
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 cobalt, tin, and graphite as shown in Table 3. Specifically, the ratio of cobalt to the total of tin and cobalt (hereinafter referred to as Co / (Sn + Co) ratio) is constant at 37% by mass, and the carbon raw material ratio is 10% by mass to 30% by mass. Varyed within range.

  As Comparative Example 3-1, compared with Examples 3-1 to 3-4, a negative electrode active material was synthesized in the same manner as in Examples 3-1 to 3-4 except that graphite powder was not used as a raw material. A secondary battery was produced. Further, as Comparative Example 3-2, a negative electrode active material was synthesized in the same manner as in Examples 3-1 to 3-4 except that the raw material ratio of graphite was 8 mass%, and a secondary battery was produced. did.

  For the obtained negative electrode active materials of Examples 3-1 to 3-4 and Comparative examples 3-1 and 3-2, the composition was analyzed in the same manner as in Examples 1-1 to 1-4. The results are shown in Table 3. Moreover, when the X-ray diffraction was performed about the negative electrode active material of Examples 1-1 to 1-4, the diffraction peak which has a wide half value width between 2 (theta) = 20 degrees-50 degrees was observed. When the half-value widths of these diffraction peaks were measured, all were 1.0 ° or more. Furthermore, when XPS was performed, in Examples 3-1 to 3-4 and Comparative Example 3-2, a peak P1 was obtained as shown in FIG. 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. On the other hand, in Comparative Example 3-1, a peak P4 was obtained as shown in FIG. 8, and when this was analyzed, only a peak P2 of surface contamination carbon was obtained. Further, the secondary batteries were also examined for initial discharge capacity, cycle characteristics, and thermal stability in the same manner as in Examples 1-1 to 1-4. The results are shown in Table 3. The initial discharge capacity was determined as a relative value when the value of Example 1-1 was set to 100.

  As can be seen from Table 3, according to Examples 3-1 to 3-4 in which carbon is included in the range of 9.9 mass% to 29.7 mass%, the carbon content is outside this range. As compared with Comparative Examples 3-1 and 3-2, higher values were obtained for the initial discharge capacity and the capacity retention rate. Even when these negative electrode active materials were used, the maximum temperature during discharge could be kept low.

  That is, when the carbon content in the negative electrode active material is 9.9 mass% or more and 29.7 mass%, the capacity and cycle characteristics can be improved, and further, an organic acid or an organic acid salt is included. It turned out that safety can be improved if it is made.

(Examples 4-1 and 4-2)
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 cobalt, tin, and graphite as shown in Table 4. Specifically, the carbon raw material ratio was constant at 10% by mass, and the Co / (Sn + Co) ratio was 30% by mass and 70% by mass.

  For the obtained negative electrode active materials of Examples 4-1 and 4-2, the composition was analyzed in the same manner as in Examples 1-1 to 1-4. The results are shown in Table 4. Moreover, when X-ray diffraction was performed about the obtained negative electrode active material, the diffraction peak which has a wide half value width between 2 (theta) = 20 degrees-50 degrees was observed. When the half-value widths of these diffraction peaks were measured, all were 1.0 ° or more. Furthermore, when XPS was performed, in Example 4-1, 4-2, peak P1 was obtained as shown in FIG. 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. Further, the secondary batteries were also examined for initial discharge capacity, cycle characteristics, and thermal stability in the same manner as in Examples 1-1 to 1-4. The results are shown in Table 4. The initial discharge capacity was determined as a relative value when the value of Example 1-1 was set to 100.

  As can be seen from Table 4, according to Examples 4-1 and 4-2 in which the Co / (Sn + Co) ratio was 30% by mass or more and 70% by mass, high values were obtained for the initial discharge capacity and the capacity retention rate. It was. Even when these negative electrode active materials were used, the maximum temperature during discharge could be kept low.

  That is, when the Co / (Sn + Co) ratio in the negative electrode active material is 30% by mass or more and 70% by mass, the capacity and cycle characteristics can be improved, and further, an organic acid or an organic acid salt can be included. It has been found that safety can be improved.

(Examples 5-1 and 5-2)
In Example 5-1, cobalt powder, tin powder, graphite powder, and germanium powder were prepared as raw materials. After cobalt powder and tin powder were alloyed to produce cobalt-tin alloy powder, graphite powder was added to the alloy powder. A secondary battery was fabricated in the same manner as in Example 1-1 except that the negative electrode active material was synthesized by mixing powder and germanium powder. In Example 5-2, cobalt powder, tin powder, graphite powder, and titanium powder were prepared as raw materials, and cobalt powder, tin powder, and titanium powder were alloyed to produce a cobalt-tin-titanium alloy powder. A secondary battery was fabricated in the same manner as in Example 1-1 except that graphite powder was mixed with this alloy powder to synthesize a negative electrode active material. Each raw material ratio was as shown in Table 5.

  For the obtained negative electrode active materials of Examples 5-1 and 5-2, the composition was analyzed in the same manner as in Examples 1-1 to 1-4. The results are shown in Table 5. The contents of germanium and titanium were measured by ICP emission analysis. Moreover, when X-ray diffraction was performed about the obtained negative electrode active material, the diffraction peak which has a wide half value width between 2 (theta) = 20 degrees-50 degrees was observed. When the half-value widths of these diffraction peaks were measured, all were 1.0 ° or more. Furthermore, when XPS was performed, in Example 5-1 and 5-2, peak P1 was obtained as shown in FIG. 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. Further, the secondary batteries were also examined for initial discharge capacity, cycle characteristics, and thermal stability in the same manner as in Examples 1-1 to 1-4. The results are shown in Tables 5 and 6. The initial discharge capacity was determined as a relative value when the value of Example 1-1 was set to 100.

  As can be seen from Table 6, according to Examples 5-1 and 5-2 using the negative electrode active material containing germanium or titanium, the capacity retention ratio was higher than that of Example 3-3 not containing germanium and titanium. Improved. Even when these negative electrode active materials were used, the maximum temperature during discharge could be kept low.

  That is, if the negative electrode active material contains at least one member selected from the group consisting of indium, niobium, germanium, titanium, molybdenum, aluminum, phosphorus, gallium and bismuth, cycle characteristics can be further improved. Furthermore, it has been found that the safety can be improved by including an organic acid or an organic acid salt.

  Although the present invention has been described with reference to the embodiments and examples, the present invention is not limited to the embodiments and examples, and various modifications can be made. For example, in the above-described embodiments and examples, the secondary battery having a sheet type and a winding structure has been specifically described. However, the present invention provides an exterior member such as a coin type, a button type, or a square type. The present invention can be similarly applied to a secondary battery having another shape used or a secondary battery having a stacked structure in which a plurality of positive and negative electrodes are stacked.

  In the embodiments and examples, 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, other elements in the long-period periodic table such as sodium (Na) or potassium (K) are used. 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. 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.

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 which concerns on one embodiment of this invention. It is sectional drawing showing the structure along the II line of the winding electrode body shown in FIG. It is sectional drawing showing the structure of the other secondary battery which concerns on one embodiment of this invention. An example of the peak obtained by the X-ray photoelectron spectroscopy which concerns on the negative electrode active material produced in the Example is represented. It represents an example of a peak obtained by X-ray photoelectron spectroscopy relating to a negative electrode active material produced in a comparative example.

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, 62 ... Positive electrode, 31A, 43A, 62A ... Positive electrode current collector, 31B, 43B, 62B ... Positive electrode active material layer, 32, 44 ... Separator 33, center pin, 34, 41, 61 ... positive electrode lead, 35, 42, 63 ... negative electrode lead 45, 64 ... electrolyte layer, 46 ... protective tape, 50, 65 ... exterior member, 51 ... adhesion film, 60 ... electrode body.

Claims (6)

Constituent elements include at least tin (Sn), cobalt (Co), and carbon (C), the carbon content is 9.9 mass% or more and 29.7 mass% or less, and tin and cobalt A negative electrode active material in which the ratio of cobalt to the total of
An anode comprising: at least one additive selected from the group consisting of an organic acid and an organic acid salt. A negative electrode active material layer containing the negative electrode active material and the additive, and a negative electrode current collector provided with the negative electrode active material layer,
The negative electrode according to claim 1, wherein the content of the additive in the negative electrode active material layer is 5% by mass or less.   The negative electrode according to claim 1, wherein the additive includes at least one member selected from the group consisting of lithium acetate, sodium acetate, lithium phosphate, and lithium oxalate. A battery comprising an electrolyte together with a positive electrode and a negative electrode,
The negative electrode contains at least tin (Sn), cobalt (Co), and carbon (C) as constituent elements, and the carbon content is 9.9 mass% or more and 29.7 mass% or less, And a negative electrode active material in which the ratio of cobalt to the total of tin and cobalt is 30% by mass or more and 70% by mass or less, and at least one additive selected from the group consisting of organic acids and organic acid salts. Battery characterized. The negative electrode includes a negative electrode active material layer containing the negative electrode active material and the additive, and a negative electrode current collector provided with the negative electrode active material layer,
The battery according to claim 4, wherein the content of the additive in the negative electrode active material layer is 5% by mass or less. The battery according to claim 4, wherein the additive includes at least one member selected from the group consisting of lithium acetate, sodium acetate, lithium phosphate, and lithium oxalate.

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