JP4910281B2 - Negative electrode for lithium ion secondary battery and lithium ion secondary battery - Google Patents

Description

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

  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 (Li) composed of manganese (Mn), iron (Fe), cobalt, 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 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. However, this negative electrode active material also has a problem that the charge / discharge 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 thereof is to provide a negative electrode for a lithium ion secondary battery having high capacity and excellent cycle characteristics, and a lithium ion secondary battery using the same. .

The negative electrode for a lithium ion secondary battery 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 tin A negative electrode active material in which the ratio of cobalt to the total of cobalt and cobalt is 30% by mass or more and 70% by mass or less, a true specific gravity is 2.23 g / cm ³ or more, and a tap density is 0.8 g / cm ³ or less. The half-value width of the diffraction peak obtained by X-ray diffraction of the negative electrode active material is 1.0 ° or more in the range of diffraction angle 2θ = 20 ° to 50 ° .

The lithium ion secondary battery according to the present invention includes an electrolyte together with a positive electrode and a negative electrode, and the negative electrode includes at least tin, cobalt, and carbon as constituent elements, and the carbon content is 9.9% by mass or more and 29.29%. A negative electrode active material having a ratio of cobalt of 30% by mass to 70% by mass with respect to the total of tin and cobalt, a true specific gravity of 2.23 g / cm ³ or more, and a tap density of 7% by mass or less There contains a carbon material is 0.8 g / cm ³ or less, 1.0 ° in half-width is the diffraction angle 2 [Theta] = 20 ° to 50 ° range of a diffraction peak obtained by X-ray diffraction of the anode active material That's all.

According to the negative electrode for a lithium ion secondary battery of the present invention , the negative electrode active material contains at least tin, cobalt, and carbon as constituent elements, and the half width of the diffraction peak obtained by X-ray diffraction of the negative electrode active material is a diffraction angle. 2θ = 1.0 ° or more in a range of 20 ° or more and 50 ° or less. In this case, since the scan's and the negative electrode active material is a constituent element were free Muyo Unishi, a high capacity can be obtained. In addition, since this negative electrode active material contains cobalt as a constituent element and the ratio of cobalt to the total of tin and cobalt is 30% by mass or more and 70% by mass or less, the charge / discharge cycle characteristics are maintained while maintaining a high capacity. Can be improved. 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, the charge / discharge cycle characteristics can be further improved. In addition, since a carbon material having a true specific gravity of 2.23 g / cm ³ or more and a tap density of 0.8 g / cm ³ or less is included, it is caused by expansion / contraction of the negative electrode active material accompanying charge / discharge. A decrease in electron conductivity can be suppressed. Therefore, according to the lithium ion secondary battery of the present invention using this negative electrode, a high capacity can be obtained and an excellent charge / discharge cycle characteristic can be obtained.

In addition, if the content of the carbon material in the negative electrode for a lithium ion secondary battery is 15% by mass or more and 50% by mass or less with respect to the negative electrode active material, a high effect can be obtained.

Furthermore, it is possible to be to contain at least one binder of a copolymer containing polyvinylidene fluoride and vinylidene fluoride in a negative electrode for a lithium ion secondary battery as a component, to obtain a high effect, It is particularly preferable that the content of the binder in the negative electrode active material layer is 1% by mass or more and 10% by mass or less.

  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 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. Further, it is difficult to obtain sufficient charge / discharge cycle characteristics with tin alone, but the charge / discharge 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 charge / discharge cycle characteristics can be further improved by containing 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 degraded.

  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 also preferably contains a carbon material capable of inserting and extracting lithium and the like. This is because the negative electrode active material described above expands and contracts with charge and discharge and reduces the electronic conductivity of the negative electrode 10, but the inclusion of this carbon material can suppress a decrease in electronic conductivity. .

  Specific examples of such carbon materials 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, etc. fired at high temperature, and artificial graphites such as vapor-grown carbon fiber or carbon nanotube.

The true specific gravity of the carbon material is preferably 2.23 g / cm ³ or more. This is because the conductivity can be increased. Further, the tap density is preferably 0.8 g / cm ³ or less, and more preferably 0.1 g / cm ³ or more. This is because, within this range, even when the negative electrode active material expands / contracts with charge / discharge, the contact can be maintained. Therefore, the effect which suppresses the electronic conductivity fall in the negative electrode 10 improves more in these ranges. The upper limit of the true specific gravity, for example in the case of graphite is ^{2.26g / cm 3 ~2.28g / cm 3} . The tap density can be measured by, for example, putting a 100 cm ³ carbon material into a 150 mL measuring cylinder and using a powder reduction degree measuring device.

  Further, the content of the carbon material is preferably in the range of 15% by mass or more and 50% by mass or less, particularly in the range of 20% by mass or more and 40% by mass or less with respect to the negative electrode active material described above. If the amount is small, the effect of suppressing a decrease in electronic conductivity due to expansion / contraction due to charging / discharging of the negative electrode active material is reduced. It is.

  The negative electrode active material layer 12 may contain a binder as necessary. As the binder, polyvinylidene fluoride or a copolymer containing vinylidene fluoride as a component is preferable. The binding property of the material constituting the negative electrode active material layer 12 such as the above-described negative electrode active material or carbon material can be improved, and the decrease in electronic conductivity accompanying expansion and contraction of the negative electrode active material can be further suppressed. Because it can. 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 content of the binder is preferably in the range of 1% by mass to 10% by mass, particularly in the range of 2% by mass to 5% by mass with respect to the entire material constituting the negative electrode active material layer 12. This is because if the amount is small, the effect of suppressing the decrease in electron conductivity associated with the expansion / contraction of the negative electrode active material is lowered, and if the amount is large, the content of the negative electrode active material is lowered, so that the capacity is lowered.

  The negative electrode active material layer 12 may also contain other negative electrode active materials in addition to the above-described negative electrode active material or carbon material.

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

  First, the negative electrode active material, the carbon material, and a binder as necessary are mixed to prepare a negative electrode mixture, and the negative electrode mixture is dispersed in a dispersion medium to form a negative electrode mixture slurry. Examples of the dispersion medium include pure water, N-methyl-2-pyrrolidone, toluene, xylene, methanol, ethanol, n-propanol, isopropyl alcohol, isobutyl alcohol, acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, ethyl acetate, acetic acid. Examples include butyl, tetrahydrofuran or dioxane. Of these, pure water or N-methyl-2-pyrrolidone is preferred.

  In addition, you may add a thickener etc. to this negative mix slurry as needed. Examples of the thickening agent include starch, carboxymethyl cellulose, ammonium salt, sodium salt or potassium salt of carboxymethyl cellulose, hydroxypropyl cellulose, regenerated cellulose, or diacetyl cellulose. Of these, carboxymethylcellulose, ammonium salt or sodium salt of carboxymethylcellulose are 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.

  To mix, knead, or disperse the negative electrode active material, carbon material and binder, etc. in a dispersion medium, any mixing agitator such as a known kneader, mixer, homogenizer, dissolver, planetary mixer, paint shaker, or sand mill can be used. It 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 inside a substantially hollow cylindrical battery can 21 via a separator 32. 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 charge / discharge 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 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 <1,0.7 <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 material and, if necessary, 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. To make a paste-like positive electrode mixture slurry. 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 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 charge / discharge cycle characteristics are improved while maintaining a high capacity. Moreover, since the carbon material having the true specific gravity and the tap density described above is contained, a decrease in electronic conductivity due to expansion / contraction associated with charging / discharging 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, since this negative electrode active material contains cobalt as a constituent element and the ratio of cobalt to the total of tin and cobalt is 30% by mass or more and 70% by mass or less, the charge / discharge cycle characteristics are maintained while maintaining a high capacity. Can be improved. 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, the charge / discharge cycle characteristics can be further improved. In addition, since a carbon material having a true specific gravity of 2.23 g / cm ³ or more and a tap density of 0.8 g / cm ³ or less is included, it is caused by expansion / contraction of the negative electrode active material accompanying charge / discharge. A decrease in electron conductivity can be suppressed. Therefore, according to the battery of the present invention using this negative electrode 10, a high capacity can be obtained and excellent charge / discharge cycle characteristics can be obtained.

  Further, if the content of the carbon material in the negative electrode 10 is set to 15% by mass or more and 50% by mass or less with respect to the negative electrode active material, a high effect can be obtained.

  Further, if the negative electrode 10 contains at least one binder selected from the group consisting of polyvinylidene fluoride and a copolymer containing vinylidene fluoride as a component, a high effect can be obtained, and the negative electrode active It is particularly preferable that the content of the binder in the material layer 12 is 1% by mass or more and 10% by mass or less.

(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 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. 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 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 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.

(Example 1-1)
First, a negative electrode active material was prepared. Cobalt powder, tin powder, and graphite powder were prepared as raw materials, and cobalt powder and tin powder were alloyed to produce a cobalt-tin alloy powder. 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 = 29.6: 50.4: 20 by mass ratio. The ratio of cobalt to the total of tin and cobalt (hereinafter referred to as Co / (Sn + Co) ratio) was 37% by mass. 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 cobalt and tin contents were measured by ICP (Inductively Coupled Plasma) emission analysis. As a result, the cobalt content was 29.3 mass%, the tin content was 49.9 mass%, and the carbon content was 19.8 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.

After preparing the negative electrode mixture by mixing the obtained negative electrode active material, the carbon material, polyvinylidene fluoride as the binder, and carboxymethyl cellulose as the thickener, this negative electrode mixture was used as a dispersion medium. A pure water was mixed by a planetary mixer to prepare a negative electrode mixture slurry. Carbon material, a true specific gravity of 2.24 g / cm ^3, a tap density using artificial graphite of 0.6 g / cm ^3. The true specific gravity was measured with MAT-7000 manufactured by Seishin Enterprise Co., Ltd. using butanol as a dispersion medium. Furthermore, the tap density was obtained by gently charging 100 cm ³ of carbon material into a 150 mL measuring cylinder using a powder reduction measuring instrument (TPM) manufactured by Tsutsui Rika Instruments Co., Ltd., and reading the density after 20 operations. In addition, the mixing amount of the carbon material was 20% by mass with respect to the negative electrode active material. The mixing amount of the binder was 4.0% by mass with respect to the whole negative electrode mixture. The mixing amount of the thickener was 1% by mass with respect to the whole negative electrode mixture.

  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 by performing this, 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, 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 negative electrode active material was synthesized in the same manner as in Example 1-1 except that graphite powder was not used, and a secondary battery was manufactured. The raw material ratio of the cobalt powder and the tin powder was a mass ratio of cobalt powder: tin powder = 37.0: 63.0. The composition of the negative electrode active material was analyzed in the same manner as in Example 1-1. As a result, the cobalt content was 36.6% by mass and the tin content was 62.4% by mass. Further, when XPS was performed, a peak P4 was obtained as shown in FIG. 8. When this was analyzed, only a peak P2 of surface contamination carbon was obtained.

  Further, as Comparative Example 1-2, except that the negative electrode 10 was produced without using a negative electrode active material containing cobalt, tin, and carbon, that is, the mixing amount of the carbon material was 95 mass with respect to the whole negative electrode mixture. A secondary battery was fabricated in the same manner as in Example 1-1 except that the content was%.

  The obtained secondary batteries of Example 1-1 and Comparative Examples 1-1 and 1-2 were subjected to a charge / discharge test, and the discharge capacity and the charge / discharge cycle characteristics were determined, 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. In addition, discharge capacity was calculated | required by the relative value when the value of Example 1-1 was set to 100 about the discharge capacity of the 1st cycle. The charge / discharge cycle characteristics were determined 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. 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, cobalt and carbon are contained, the carbon content is 9.9 mass% or more and 29.7 mass% or less, and the ratio of cobalt to the total of tin and cobalt is 30 mass. According to Example 1-1 using a negative electrode active material of not less than 70% and not more than 70% by mass, Comparative Example 1-1 using a negative electrode active material not containing carbon, or a negative electrode containing tin, cobalt and carbon The discharge capacity and capacity retention rate were dramatically improved over Comparative Example 1-2 in which no active material was used.

That is, it contains tin, cobalt, and carbon, the carbon content is 9.9 mass% or more and 29.7 mass% or less, and the ratio of cobalt to the total of tin and cobalt is 30 mass% or more and 70 mass%. a negative electrode active material is less, the true specific gravity of 2.24 g / cm ^3, when the tap density was used and the carbon material is 0.6 g / cm ^3, to obtain an excellent charge-discharge cycle characteristics at high capacity I found out that

(Examples 2-1 and 2-2)
As the carbon material, a true specific gravity of 2.26 g / cm ^3, artificial graphite tap density of 0.5 g / cm ³ or true specific gravity, is 2.23 g / cm ^3, a tap density of 0.8 g / A secondary battery was fabricated in the same manner as in Example 1-1 except that the negative electrode 10 was fabricated using artificial graphite of cm ³ .

  As Comparative Examples 2-1 to 2-6 with respect to Examples 2-1 and 2-2, except that the true specific gravity and tap density of the carbon material were changed as shown in Table 2, and the negative electrode 10 was produced. Produced secondary batteries in the same manner as in Examples 2-1 and 2-2.

For the obtained Examples 2-1 and 2-2 and Comparative Examples 2-1 to 2-6, the discharge capacity and the charge / discharge cycle characteristics were examined 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. 9 and 10 show the relationship between true specific gravity or tap density and charge / discharge cycle characteristics. In FIGS. 9 and 10, the region where the true specific gravity is 2.23 g / cm ³ or more and the region where the tap density is 0.8 g / cm ³ or less are represented by nashiji.

As can be seen from Table 2 and FIGS. 9 and 10, Examples 2-1 and 2 using a carbon material having a true specific gravity of 2.23 g / cm ³ or more and a tap density of 0.8 g / cm ³ or less. According to -2, higher values were obtained for the discharge capacity and capacity retention rate than Comparative Examples 2-1 to 2-6 using carbon materials outside these ranges.

That is, it has been found that if the true specific gravity of the carbon material is 2.23 g / cm ³ or more and the tap density is 0.8 g / cm ³ or less, a high capacity and excellent cycle characteristics can be obtained.

(Examples 3-1 and 4-1)
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 powder, tin powder, and graphite powder. In Example 3-1, the raw material ratio (material ratio) of the cobalt powder, tin powder, and graphite powder was set to cobalt powder: tin powder: graphite powder = 33.3: 56.7: 10, and Example 4-1 Then, it was set as cobalt powder: tin powder: graphite powder = 25.9: 44.1: 30. The Co / (Sn + Co) ratio) was 37% by mass. The true specific gravity of the carbon material was 2.23 g / cm ³ , the tap density was 0.8 g / cm ³ , and the same one as used in Example 2-2 was used.

  About the obtained negative electrode active material of Examples 3-1 and 4-1, composition was analyzed like Example 1-1. As a result, in Example 3-1, the cobalt content was 33.0% by mass, the tin content was 56.1% by mass, and the carbon content was 9.9% by mass. In Example 4-1, the cobalt content was 25.6% by mass, the tin content was 43.7% by mass, and the carbon content was 29.7% by mass. Furthermore, when X-ray diffraction was performed on these negative electrode active materials, diffraction peaks having a wide half-value width between 2θ = 20 ° and 50 ° were 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 3-1, 4-1 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.

  As Comparative Examples 3-1 to 3-6 and 4-1 to 4-6 with respect to Examples 3-1 and 4-1, the true specific gravity and tap density of the carbon material were changed as shown in Tables 3 and 4. A secondary battery was fabricated in the same manner as in Examples 3-1 and 4-1, except that the negative electrode 10 was fabricated.

  For the obtained secondary batteries of Examples 3-1 and 4-1 and Comparative examples 3-1 to 3-6 and 4-1 to 4-6, in the same manner as in Example 1-1, the discharge capacity and The charge / discharge cycle characteristics were investigated. The results are shown in Tables 3 and 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 Tables 3 and 4, the same results as in Examples 1-1, 2-1, and 2-2 were obtained. That is, if the carbon content in the negative electrode active material is 9.9 mass% or more and 29.7 mass%, the capacity and charge / discharge cycle characteristics can be improved, and the true specific gravity is 2. It was found that if a carbon material having a tap density of 23 g / cm ³ or more and a tap density of 0.8 g / cm ³ or less is used, a high capacity and excellent charge / discharge cycle characteristics can be obtained.

(Examples 5-1 and 6-1)
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 powder, tin powder, and graphite powder. In Example 5-1, the raw material ratio (material ratio) of the cobalt powder, tin powder, and graphite powder was cobalt powder: tin powder: graphite powder = 27.0: 63.0: 10, and Example 4-1 Then, it was set as cobalt powder: tin powder: graphite powder = 63.0: 27.0: 10. The Co / (Sn + Co) ratio was 30% by mass or 70% by mass. The true specific gravity of the carbon material was 2.23 g / cm ³ , the tap density was 0.8 g / cm ³ , and the same one as used in Example 2-2 was used.

  About the obtained negative electrode active material of Example 5-1, 6-1, the composition was analyzed like Example 1-1. As a result, in Example 5-1, the cobalt content was 26.7% by mass, the tin content was 62.4% by mass, and the carbon content was 9.9% by mass. In Example 5-1, the cobalt content was 62.4% by mass, the tin content was 26.7% by mass, and the carbon content was 9.9% by mass. Furthermore, when X-ray diffraction was performed on these negative electrode active materials, diffraction peaks having a wide half-value width between 2θ = 20 ° and 50 ° were 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, 6-1, 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.

  As Comparative Examples 5-1 to 5-6 and 6-1 to 6-6 for Examples 5-1 and 6-1, the true specific gravity and tap density of the carbon material were changed as shown in Tables 5 and 6. A secondary battery was fabricated in the same manner as in Examples 5-1 and 6-1 except that the negative electrode 10 was fabricated.

  For the obtained secondary batteries of Examples 5-1 and 6-1 and Comparative Examples 5-1 to 5-6 and 6-1 to 6-6, in the same manner as in Example 1-1, the discharge capacity and The charge / discharge cycle characteristics were investigated. The results are shown in Tables 5 and 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 Tables 5 and 6, the same results as in Examples 1-1, 2-1, and 2-2 were obtained. That is, when the Co / (Sn + Co) ratio in the negative electrode active material is 30% by mass or more and 70% by mass or less, the capacity and charge / discharge cycle characteristics can be improved. .23g / cm ³ or more, and a tap density of the joint use of such a carbon material is 0.8 g / cm ³ or less, a high capacity, it was found that it is possible to obtain an excellent charge-discharge cycle characteristics .

(Examples 7-1 to 7-6)
Except that the mixing amount of the carbon material with respect to the negative electrode active material was changed within the range of 10% by mass or more and 60% by mass or less as shown in Table 7, the same as in Example 1-1. A battery was produced. At that time, the carbon material, in the same manner as in Example 1-1, the true specific gravity of 2.24 g / cm ^3, a tap density was assumed to be 0.6 g / cm ^3.

  For the obtained secondary batteries of Examples 7-1 to 7-6, the discharge capacity and the charge / discharge cycle characteristics were examined in the same manner as in Example 1-1. The results are shown in Table 7. 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, the discharge capacity increased as the mixing amount of the carbon material with respect to the negative electrode active material increased, and decreased after showing the maximum value. In addition, the capacity retention rate increased as the amount of carbon material added increased, and showed a substantially constant value.

  That is, it was found that the content of the carbon material in the negative electrode 10 is preferably in the range of 15% by mass to 50% by mass, particularly in the range of 20% by mass to 40% by mass with respect to the negative electrode active material.

(Examples 8-1 to 8-6)
Except that the amount of the carbon material added to the negative electrode active material was changed within the range of 10% by mass or more and 60% by mass or less as shown in Table 8, the other secondary conditions were performed in the same manner as in Example 1-1. A battery was produced. At that time, the carbon material, in the same manner as in Example 2-1, the true specific gravity of 2.26 g / cm ^3, a tap density was assumed to be 0.5 g / cm ^3.

  For the obtained secondary batteries of Examples 8-1 to 8-6, the discharge capacity and the charge / discharge cycle characteristics were examined in the same manner as in Example 1-1. The results are shown in Table 8. 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, the same results as in Examples 7-1 to 7-6 were obtained. That is, even when another carbon material satisfying the requirement that the true specific gravity is 2.23 g / cm ³ or more and the tap density is 0.8 g / cm ³ or less is used, the content of the carbon material is It was found that the range of 15% by mass or more and 50% by mass or less, particularly 20% by mass or more and 40% by mass or less of the active material is preferable.

(Examples 9-1 to 9-3)
Other than using vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-tetrafluoroethylene copolymer, or vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer as the binder, A secondary battery was fabricated in the same manner as Example 1-1.

  For the obtained secondary batteries of Examples 9-1 to 9-3, the discharge capacity and the charge / discharge cycle characteristics were examined in the same manner as in Example 1-1. The results are shown in Table 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 9, the same results as in Example 1-1 were obtained. That is, it has been found preferable to use polyvinylidene fluoride or a copolymer containing vinylidene fluoride as a component for the binder.

(Examples 10-1 to 10-7)
Except that the mixing amount of the binder in the negative electrode mixture was changed within the range of 0.5% by mass or more and 12.0% by mass or less as shown in Table 10, the others were the same as Example 1-1. Similarly, a secondary battery was produced.

  For the obtained secondary batteries of Examples 10-1 to 10-7, the discharge capacity and the charge / discharge cycle characteristics were examined in the same manner as in Example 1-1. The results are shown in Table 10. 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 10, the discharge capacity increased as the mixing amount of the binder in the negative electrode mixture increased, and decreased after showing the maximum value. Further, the capacity retention rate increased as the amount of the binder mixed increased, and showed a substantially constant value.

  That is, it was found that the content of the binder is preferably in the range of 1% by mass to 10% by mass, particularly in the range of 2% by mass to 5% by mass.

  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 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.

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. It is a characteristic view showing the relationship between the true specific gravity of a carbon material and a capacity | capacitance maintenance factor. It is a characteristic view showing the relationship between the tap density of a carbon material and a capacity | capacitance maintenance factor.

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 (8)

Constituent elements include at least tin (Sn), cobalt (Co), and carbon (C), the carbon content is 9.9 mass% to 29.7 mass%, and tin and cobalt A negative electrode active material in which a ratio of cobalt to the total of 30% by mass to 70% by mass;
A carbon material having a true specific gravity of 2.23 g / cm ³ or more and a tap density of 0.8 g / cm ³ or less ,
The half width of the diffraction peak obtained by X-ray diffraction of the negative electrode active material is 1.0 ° or more in the range of diffraction angle 2θ = 20 ° to 50 °,
Negative electrode for lithium ion secondary battery . The content of the carbon material, the negative active is 50 wt% or less than 15 wt% with respect to material, according to claim 1 for a lithium ion secondary battery negative electrode according. A negative electrode active material layer including the negative electrode active material, the carbon material, and a binder; and a negative electrode current collector provided with the negative electrode active material layer,
The binder contains at least one of polyvinylidene fluoride and a copolymer containing vinylidene fluoride as a component,
The content of the binder in the negative electrode active material layer is not more than 10 mass% to 1 mass%, claim 1 for a lithium ion secondary battery negative electrode according. The negative electrode for a lithium ion secondary battery according to claim 1, wherein the peak of the synthetic wave of C1s obtained by X-ray photoelectron spectroscopy of the negative electrode active material appears in a region lower than 284.5 eV. An electrolyte is provided with a positive electrode and a negative electrode ,
The negative electrode includes at least tin (Sn), cobalt (Co), and carbon (C) as constituent elements, the carbon content is 9.9 mass% or more and 29.7 mass% or less, and The 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, the true specific gravity is 2.23 g / cm ³ or more, and the tap density is 0.8 g / cm ³ or less. It contains a carbon material is,
The half width of the diffraction peak obtained by X-ray diffraction of the negative electrode active material is 1.0 ° or more in the range of diffraction angle 2θ = 20 ° to 50 °,
Lithium ion secondary battery. The content of the carbon material in the negative electrode, the negative active is 50 wt% or less than 15 wt% with respect to materials, the lithium ion secondary battery according to claim 5, wherein. The negative electrode includes a negative electrode active material layer including the negative electrode active material, the carbon material, and a binder , and a negative electrode current collector provided with the negative electrode active material layer,
The binder contains at least one of polyvinylidene fluoride and a copolymer containing vinylidene fluoride as a component,
The lithium ion secondary battery according to claim 5 , wherein the content of the binder in the negative electrode active material layer is 1% by mass or more and 10% by mass or less. The lithium ion secondary battery according to claim 5, wherein a peak of a synthetic wave of C1s obtained by X-ray photoelectron spectroscopy of the negative electrode active material appears in a region lower than 284.5 eV.

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