JP2011023343A - Negative electrode material for nonaqueous electrolyte secondary battery and nonaqueous electrolyte secondary battery equipped with it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve discharge capacity in a negative electrode material in order to further improve electric performance of a nonaqueous electrolyte secondary battery. <P>SOLUTION: This is a negative electrode material for nonaqueous electrolyte secondary battery which contains a negative electrode active material capable of doping and dedoping of lithium ion and borate of alkali metal and/or borate of alkaline earth metal, and a nonaqueous electrolyte secondary battery equipped with this is provided. It is preferable that the negative electrode active material has graphite and/or a carbon material inferior in crystallinity than graphite as a main component, and that the borate of alkali metal is sodium borate. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a negative electrode material for a non-aqueous electrolyte secondary battery and a non-aqueous electrolyte secondary battery including the same.

  In a non-aqueous electrolyte secondary battery, a negative electrode material containing an alkali metal halide and / or an alkaline earth metal halide is known.

JP 2006-310265 A

  In order to further improve the electrical performance of the nonaqueous electrolyte secondary battery, further improvement in the discharge capacity of the negative electrode material has been demanded.

  Under such circumstances, the present inventor has intensively studied the negative electrode material in order to improve the electrical performance of the nonaqueous electrolyte secondary battery, and as a result, has reached the present invention.

That is, the present invention
<1> a non-aqueous electrolyte secondary battery comprising a negative electrode active material capable of being doped and dedoped with lithium ions, and an alkali metal borate and / or an alkaline earth metal borate Negative electrode materials;
<2> The negative electrode active material for a non-aqueous electrolyte secondary battery according to item 1 above, wherein the negative electrode active material is mainly composed of graphite and / or a carbon material having lower crystallinity than graphite;
<3> The negative electrode material for a non-aqueous electrolyte secondary battery according to the preceding item 1 or 2, wherein the specific surface area of graphite and / or a carbon material having lower crystallinity than graphite is 1 to 600 m ² / g;
<4> The negative electrode material for a non-aqueous electrolyte secondary battery according to any one of items 1 to 3, wherein the alkali metal borate is sodium borate;
<5> An aqueous solution containing an alkali metal borate and / or an alkaline earth metal borate and a negative electrode active material capable of being doped and dedoped with lithium ions are mixed, and then water is removed and dried. The negative electrode material for a nonaqueous electrolyte secondary battery according to any one of items 1 to 4 obtained by
<6> The content of the alkali metal borate and / or alkaline earth metal borate is 50 to 10,000 ppm in terms of alkali metal and / or alkaline earth metal equivalent, Or a negative electrode material for a non-aqueous electrolyte secondary battery according to claim 1;
<7> Further, the negative electrode material for a non-aqueous electrolyte secondary battery described in any one of 1 to 6 above, which further comprises a binder and a solvent;
<8> The binder is polyvinylidene fluoride, polytetrafluoroethylene, fluorinated polyvinylidene fluoride, ethylene-propylene-diene terpolymer, styrene-butadiene rubber, acrylonitrile-butadiene rubber, fluorine rubber, polyvinyl acetate, poly The negative electrode material for a non-aqueous electrolyte secondary battery as described in 7 above, which is at least one selected from the group consisting of methyl methacrylate, polyethylene and nitrocellulose;
<9> The solvent is selected from the group consisting of N-methylpyrrolidone, dimethylformamide, dimethylacetamide, methyl ethyl ketone, cyclohexanone, methyl acetate, methyl acrylate, diethyltriamine, N, N-dimethylaminopropylamine, ethylene oxide, tetrahydrofuran and water. The negative electrode material for a non-aqueous electrolyte secondary battery according to the preceding item 7, which is at least one kind of
<10> A nonaqueous electrolyte secondary battery comprising a positive electrode and a negative electrode that can be doped and dedoped with lithium ions, and a nonaqueous electrolyte solution, wherein the negative electrode is described in any one of items 1 to 9 above A nonaqueous electrolyte secondary battery comprising: a negative electrode material for a nonaqueous electrolyte secondary battery;
<11> The non-aqueous electrolyte secondary battery according to item 10 above, wherein the positive electrode active material contained in the positive electrode is a lithium transition metal composite oxide;
<12> The non-aqueous electrolyte secondary battery as described in 11 above, wherein the lithium transition metal composite oxide contains manganese;
Etc. are provided.

  According to the present invention, the discharge capacity of the negative electrode material for a non-aqueous electrolyte secondary battery is improved, and as a result, the non-aqueous electrolyte secondary battery equipped with this has better electrical performance.

  Hereinafter, the present invention will be described in detail.

  The negative electrode material for a non-aqueous electrolyte secondary battery of the present invention includes a negative electrode active material that can be doped and dedoped with lithium ions, an alkali metal borate and / or an alkaline earth metal borate (hereinafter, “ It may be referred to as “alkaline (earth) metal borate”.

  The negative electrode active material that can be doped and dedoped with lithium ions used in the present invention is composed of carbon materials having various degrees of graphitization ranging from graphite to amorphous carbon materials, and metal particles that can be alloyed with lithium. A material selected from the group can be used, but as will be described later, graphite or a carbon material having a lower crystallinity than graphite (a carbon material having a low graphitization degree) is preferable, and a case of using graphite is more preferable. This is because the alkali (earth) metal borate used in the present invention works more effectively because they are inexpensive and highly reactive with the electrolyte.

  As graphite, both natural graphite and artificial graphite can be used. It is preferable that graphite has few impurities, and it is used after being subjected to various purification treatments as necessary. As the graphite, it is preferable to use a graphite having a large degree of graphitization of (002) plane spacing (d002) of less than 3.37 mm by X-ray wide angle diffraction method.

  Specific examples of artificial graphite include coal tar pitch, coal heavy oil, atmospheric residue, petroleum heavy oil, aromatic hydrocarbon, nitrogen-containing cyclic compound, sulfur-containing cyclic compound, polyphenylene, polyvinyl chloride, Polyvinyl alcohol, polyacrylonitrile, polyvinyl butyral, natural polymer, polyphenylene sulfide, polyphenylene oxide, furfuryl alcohol resin, phenol-formaldehyde resin, imide resin, etc. Is mentioned.

  In addition, as the carbon material having a low graphitization degree, a material obtained by firing an organic substance at a temperature of usually 2500 ° C. or lower is used. Specific examples of organic substances include coal-based heavy oils such as coal tar pitch and dry-distilled liquefied oil; straight-run heavy oils such as atmospheric residual oil and vacuum residual oil; by-product during thermal decomposition of crude oil, naphtha, etc. Petroleum heavy oils such as cracked heavy oils such as ethylene tar; Aromatic hydrocarbons such as acenaphthylene, decacyclene and anthracene; Nitrogen-containing cyclic compounds such as phenazine and acridine; Sulfur-containing cyclic compounds such as thiophene; Aliphatic cyclic compounds; polyphenylenes such as biphenyl and terphenyl; polyvinyl esters such as polyvinyl chloride, polyvinyl acetate, and polyvinyl butyral; thermoplastic polymers such as polyvinyl alcohol; thermosetting polymers such as phenol resins and epoxy resins And biomass raw materials such as cellulose and sawdust.

  The firing temperature of these carbon materials having a low degree of graphitization is preferably 600 ° C. or higher, more preferably 900 ° C. or higher, and further preferably 950 ° C. or higher. The upper limit varies depending on the degree of graphitization desired for the carbon material, but is preferably 2500 ° C. or lower, more preferably 2000 ° C. or lower, and further preferably 1400 ° C. or lower.

  Further, one preferable as the negative electrode active material used in the present invention is one in which the surface of the above-mentioned graphite having a high graphitization degree is coated with a carbon material having a lower graphitization degree than that described above. This can be obtained by coating the surface of graphite having a high graphitization degree with the above-mentioned coal tar pitch, various heavy oils, etc., and then firing to carbonize the organic matter used for the coating. In such a two-layer carbon material, the ratio of the graphite to the total of the core graphite and the surrounding carbon material with low crystallinity is preferably 80% by weight or more in order to increase the negative electrode capacity. More preferably, it is at least wt%. However, if this ratio is too large, the coating effect is reduced, so this ratio is preferably 99% by weight or less. A particularly preferred ratio of core graphite to surrounding coated carbon material is 85:15 to 99: 1 (weight ratio).

  The average particle diameter of these carbon materials including graphite is preferably 35 μm or less, more preferably 25 μm or less, and further preferably 18 μm or less. Moreover, Preferably it is 3 micrometers or more, More preferably, it is 5 micrometers or more. Note that the carbon material that is less crystalline than graphite may be secondary particles in which a plurality of particles are aggregated. In this case, the average particle size of the secondary particles is preferably in the above range, and the average particle size of the primary particles is preferably 15 μm or less.

The specific surface area by the measurement of the BET adsorption method of carbon materials including graphite (BET specific surface area) is preferably 1~600m ² / g, more to be 1~15m ² / g preferable.

  As the negative electrode active material, a mixture of two or more of the above-described graphite and carbon materials having different graphitization degrees may be used.

  The alkali (earth) metal borate used in the present invention is a borate of alkali metal (Li, Na, K, Rb, Cs) or alkaline earth metal (Be, Mg, Ca, Sr, Ba). is there. As a metal which comprises an alkali (earth) metal borate, an alkali metal is preferable and sodium is more preferable. Alkali (earth) metal borates include orthoborate, diborate, metaborate, tetraborate, pentaborate, octaborate, etc. However, tetraborate is preferred. As the alkali (earth) metal borate, sodium tetraborate is particularly preferable. These alkali (earth) metal borates may be used alone or in combination of two or more.

  In addition, when used in a battery, it is more preferable that the alkali (earth) metal borate is difficult to dissolve in the electrolytic solution in order to exhibit the effects of the present invention, and when it is contained in the negative electrode material. The aqueous solution preferably has a high solubility in water so that the aqueous solution can be uniformly mixed with the negative electrode active material.

  In the present invention, any method may be used as a method for incorporating the alkali (earth) metal borate into the negative electrode material. However, the alkali (earth) metal borate is uniformly added particularly in a small amount. To contain, first, an alkali (earth) metal borate is dissolved in water to form an aqueous solution, then the negative electrode active material and this aqueous solution are mixed, and then the mixed solution is filtered to remove moisture. The method of drying is effective. When such a treatment is performed, it is presumed that the alkali (earth) metal borate is present relatively uniformly in a form covering the negative electrode material surface. When the amount of the coating is very small, it may be difficult to confirm the presence of a clear borate by observation with an electron microscope (SEM). In that case, the presence of alkali metal or alkaline earth metal can be usually confirmed by surface analysis using a time-of-flight secondary ion mass spectrometer (TOF-SIMS) or the like.

  The content of the alkali (earth) metal borate in the negative electrode material is, for example, the alkali (earth) metal borate used in the method for containing the alkali (earth) metal borate in the negative electrode material described above. It can be adjusted by adjusting the concentration of the alkali (earth) metal borate in the aqueous solution.

  Inclusion of alkali (earth) metal borate in the negative electrode material of the present invention containing alkali (earth) metal borate by coating or attaching alkali (earth) metal borate. The amount is not particularly limited, but is preferably 50 to 10000 ppm, more preferably 200 to 9000 ppm, and further preferably 500 to 5000 ppm.

  The content of the alkali (earth) metal borate in the negative electrode material is extracted, for example, by dispersing the sample in a sufficient amount of water to extract the alkali (earth) metal borate contained in the negative electrode material. The extracted alkali (earth) metal borate can be obtained by quantifying the amount of alkali (earth) metal by inductively coupled plasma emission spectroscopy (ICP-AES) or the like.

  The negative electrode material for a non-aqueous electrolyte secondary battery of the present invention may further contain a binder and a solvent. Such a negative electrode material is preferably obtained by mixing a negative electrode material containing an alkali (earth) metal borate, a binder, and a solvent by the method described above.

  Examples of the binder include polyvinylidene fluoride, polytetrafluoroethylene, fluorinated polyvinylidene fluoride, ethylene-propylene-diene terpolymer (EPDM), styrene-butadiene rubber (SBR), and acrylonitrile-butadiene rubber (NBR). Fluorine rubber, polyvinyl acetate, polymethyl methacrylate, polyethylene or nitrocellulose are preferably used. The ratio of the binder to the negative electrode active material in the negative electrode material is preferably 0.1 to 20% by weight, more preferably 0.5 to 10% by weight, and further preferably 1 to 5% by weight. preferable.

  As the solvent, an organic solvent capable of dissolving the binder is usually used. For example, N-methylpyrrolidone, dimethylformamide, dimethylacetamide, methylethylketone, cyclohexanone, methyl acetate, methyl acrylate, diethyltriamine, N, N- Dimethylaminopropylamine, ethylene oxide, tetrahydrofuran or water is preferably used. These may be used alone or in combination of two or more. Moreover, when using water as a solvent, a negative electrode active material can also be slurried with latex, such as SBR, by adding a dispersing agent, a thickener, etc. further. The amount of the solvent used is preferably 0.8 to 2.0 times the weight of the negative electrode active material in the negative electrode material.

  The negative electrode material for a non-aqueous electrolyte secondary battery according to the present invention as described above is used as a material for forming a negative electrode active material layer of a non-aqueous electrolyte secondary battery.

  A non-aqueous electrolyte secondary battery comprising a positive and negative electrodes capable of doping and dedoping lithium ions and a non-aqueous electrolyte, wherein the negative electrode is a negative electrode material for a non-aqueous electrolyte secondary battery of the present invention The non-aqueous electrolyte secondary battery of the present invention containing the above will be described.

  The organic solvent for the non-aqueous electrolyte is not particularly limited, but for example, carbonate solvents such as dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, propylene carbonate, ethylene carbonate, vinylene carbonate; tetrahydrofuran, 2-methyltetrahydrofuran Ether solvents such as 1,4-dioxane, 1,2-dimethoxyethane, 1,2-diethoxyethane, 1,3-dioxolane, 4-methyl-1,3-dioxolane, diethyl ether; -Ketone solvents such as pentanone; lactone solvents such as γ-butyrolactone; sulfone solvents such as sulfolane and methyl sulfolane; nitrile solvents such as acetonitrile, propionitrile, benzonitrile, butyronitrile, valeronitrile; Chlorinated hydrocarbon solvents dichloroethane and the like; dimethylformamide, amide solvents such as dimethyl sulfoxide; trimethyl phosphate, phosphoric acid ester solvents such as triethyl phosphate; and the like can be used. These organic solvents may be used alone or in combination of two or more.

  The organic solvent preferably further contains a high dielectric constant solvent in order to dissociate the electrolyte. Here, the high dielectric constant solvent means a compound having a relative dielectric constant of 20 or more at 25 ° C. Among such high dielectric constant solvents, ethylene carbonate, propylene carbonate, and compounds in which their hydrogen atoms are substituted with other elements such as halogen or alkyl groups are preferred.

  The proportion of such a high dielectric constant solvent in the electrolytic solution is preferably 20% by weight or more, more preferably 30% by weight or more, and further preferably 40% by weight or more.

The lithium salt dissolved in the organic solvent is not particularly limited, and any conventionally known salt can be used. For example, LiClO ₄ , LiAsF ₆ , LiPF ₆ , LiBF ₄ , LiB (C ₆ H ₅ ) ₄ , LiCl, LiBr, CH ₃ SO ₃ Li, CF ₃ SO ₃ Li, LiN (SO ₂ CF ₃ ) ₂ , LiN (SO ₂ C ₂ F ₅ ) ₂ , LiC (SO ₂ CF ₃ ) ₃ , LiN (SO ₃ CF ₃ ) ₂ or the like can be used. These lithium salts may be used alone or in combination of two or more.

  The concentration of these lithium salts in the non-aqueous electrolyte is preferably 0.5 to 2 mol / L, and more preferably 0.75 to 1.5 mol / L.

  The positive electrode has a positive electrode active material, a binder, and a conductive agent. Preferably, the positive electrode includes a positive electrode current collector, a positive electrode active material, a binder, and a positive electrode mixture layer containing a conductive agent.

The positive electrode active material is not particularly limited as long as it can reversibly dope and dedope lithium ions, and among them, a lithium transition metal composite oxide is preferable. Examples of lithium transition metal composite oxides include lithium manganese oxide, lithium nickel oxide, lithium cobalt oxide, lithium iron oxide, lithium chromium oxide, lithium vanadium oxide, lithium titanium oxide, and lithium copper oxide. Can be mentioned. Specifically, for example, _{LiMn 2 O 4, LiMnO 2,} LiNiO 2, LiCoO 2, LiFeO 2, LiCrO 2, Li 1 + x V 3 O 8, LiV 2 O 4, LiTi 2 O 4, Li 2 CuO 2, A compound represented by LiCuO ₂ can be given. In order to further stabilize the charge / discharge, a part of the main transition metal element may be replaced with another metal element.

However, the positive electrode active material preferably contains manganese in that the effect of the present invention is remarkable. Examples of manganese-containing compounds include lithium-manganese composite oxides, particularly lithium-manganese composite oxides having a spinel structure as represented by the general formula LiMn ₂ O ₄ , and LiNi ₁ having a layered structure that has been actively studied recently. _{/ 3} Mn _1/3 Co _1/3 O ₂ and LiNi _1/2 Mn _1/2 O ₂ are preferred.

  These positive electrode active materials may be used individually by 1 type, and may use 2 or more types together.

  Examples of the binder used for the positive electrode include polyvinylidene fluoride, polytetrafluoroethylene, fluorinated polyvinylidene fluoride, ethylene-propylene-diene terpolymer (EPDM), styrene-butadiene rubber (SBR), and acrylonitrile. Examples include butadiene rubber (NBR), fluoro rubber, polyvinyl acetate, polymethyl methacrylate, polyethylene, and nitrocellulose. The ratio of the binder in the positive electrode mixture layer is preferably 0.1% by weight or more, more preferably 1% by weight or more, further preferably 5% by weight or more, preferably 80% by weight or less, more preferably 60% by weight. % Or less, more preferably 40% by weight or less, and particularly preferably 10% by weight or less.

  In addition, examples of the conductive agent for the positive electrode mixture layer include carbon materials such as graphite such as natural graphite and artificial graphite, carbon black such as acetylene black, and amorphous carbon such as needle coke. The proportion of the conductive agent in the positive electrode mixture layer is preferably 0.01 to 50% by weight, more preferably 0.1 to 30% by weight, and further preferably 1 to 15% by weight or more. preferable.

  As the material of the current collector used for the positive electrode, aluminum, stainless steel, nickel-plated steel or the like is preferably used, and aluminum is more preferable. The thickness of the current collector is preferably 1 to 1000 μm, and more preferably 5 to 500 μm.

  The positive electrode can be prepared by applying a slurry obtained by slurrying the above-described positive electrode active material, a binder, a conductive agent, and other additives added as necessary with a solvent to a current collector, and drying the positive electrode active material. .

  As the solvent used for slurrying, an organic solvent that dissolves the binder is usually used. For example, N-methylpyrrolidone, dimethylformamide, dimethylacetamide, methyl ethyl ketone, cyclohexanone, methyl acetate, methyl acrylate, diethyltriamine, N, N-dimethylaminopropylamine, ethylene oxide, tetrahydrofuran and the like are used, but not limited thereto. These may be used alone or in combination of two or more. Moreover, a dispersing agent, a thickener, etc. can be added to water, and an active material can also be slurried with latex, such as SBR.

  The thickness of the positive electrode mixture layer thus formed is preferably 1 to 1000 μm, and more preferably 10 to 200 μm.

  The positive electrode mixture layer obtained by coating and drying is preferably consolidated by a roller press or the like in order to increase the packing density of the active material.

  As in the case of the positive electrode, the negative electrode is usually formed by forming a negative electrode active material, a binder, and, if necessary, a negative electrode mixture layer containing a conductive agent on the current collector. At this time, the negative electrode material of the present invention is used. The negative electrode material of the present invention may be used in combination of two or more, such as those using different negative electrode active materials and those using different alkali (earth) metal borates. Further, the negative electrode material of the present invention and a normal negative electrode active material not containing an alkali (earth) metal borate may be mixed and used. As the conductive agent used as necessary, the same conductive agent as that used in the positive electrode can be used.

  The ratio of the binder to the negative electrode active material in the negative electrode material is preferably 0.1 to 20% by weight, more preferably 0.5 to 10% by weight, and further preferably 1 to 5% by weight. preferable.

  As the negative electrode current collector, copper, nickel, stainless steel, nickel-plated steel or the like is preferably used, and copper is more preferably used. The thickness of the current collector is preferably 1 to 1000 μm, and more preferably 5 to 500 μm.

  Similarly to the positive electrode, the negative electrode is prepared by applying a slurry of the above-described negative electrode material, a binder, and a conductive agent and other additives, which are added as necessary, to a current collector and drying it. can do. Here, when a negative electrode material containing a binder and a solvent is used as the negative electrode material, the negative electrode material is mixed with a conductive agent and other additives that are added as necessary without using a binder or a solvent. The slurry obtained in this manner may be applied to a current collector and dried. As a solvent used for slurrying, the same solvent as that which may be contained in the above-described negative electrode material can be used.

  The thickness of the negative electrode mixture layer formed in this manner is preferably 1 to 1000 μm, and more preferably 10 to 200 μm.

  The negative electrode mixture layer obtained by coating and drying is preferably consolidated by a roller press or the like in order to increase the packing density of the active material.

  In the nonaqueous electrolyte secondary battery of the present invention, it is preferable to interpose a separator between the positive electrode and the negative electrode. As this separator, a microporous polymer film is usually used, and one made of a polyolefin polymer such as nylon, cellulose acetate, nitrocellulose, polysulfone, polyacrylonitrile, polyvinylidene fluoride, polypropylene, polyethylene, polybutene or the like. Preferably used. A polyolefin polymer is more preferable from the viewpoint of chemical and electrochemical stability of the separator, and it is preferable that the polymer is made of polyethylene from the viewpoint of the self-occluding temperature, which is one of the purposes of the battery separator.

  In the case of a polyethylene separator, it is preferably ultrahigh molecular weight polyethylene from the viewpoint of maintaining high-temperature shape, and the molecular weight is preferably 500,000 to 5,000,000, more preferably 1,000,000 to 4,000,000, 150 More preferably, it is 10,000 to 3,000,000.

  The non-aqueous electrolyte secondary battery of the present invention is manufactured by assembling the above-described positive electrode, negative electrode, non-aqueous electrolyte, and separator used as necessary into an appropriate shape. Furthermore, other components such as an outer case can be used as necessary.

  The battery shape is not particularly limited, and can be appropriately selected from various commonly used shapes according to the application. Examples of commonly used shapes include a cylinder type with a sheet electrode and separator spiral, an inside-out cylinder type with a combination of pellet electrode and separator, a coin type with a stack of pellet electrode and separator, and a sheet Examples include a laminate type in which electrodes and separators are laminated. Also, the method for assembling the battery is not particularly limited, and can be appropriately selected from various commonly used methods according to the shape of the target battery.

  The general embodiment of the non-aqueous electrolyte secondary battery of the present invention has been described above, but the non-aqueous electrolyte secondary battery of the present invention is not limited to the above-described embodiment and does not exceed the gist thereof. As long as it is possible, various modifications can be made.

  EXAMPLES Hereinafter, although an Example, a test example, a manufacture example, etc. are given and this invention is demonstrated concretely, this invention is not limited to these.

Example 1
Natural graphite having a BET specific surface area of 6.0 m ² / g (surface distance (d ₀₀₂ ) 3.354 mm) according to X-ray wide angle diffraction method in 0.3 ml of 0.1 wt% aqueous sodium tetraborate solution After stirring for 30 minutes, suction filtration was performed, followed by vacuum drying at 100 ° C. for 6 hours to obtain natural graphite (negative electrode material) coated with sodium tetraborate.
This negative electrode material was mixed with N-methyl-2-pyrrolidone solvent in a ratio of 9: 1 (weight ratio) with polyvinylidene fluoride as a binder to form a slurry, which was applied to the copper foil of the current collector and dried. Then, it was pressed to obtain a negative electrode.

Example 2
In Example 1, a negative electrode was prepared in the same manner as in Example 1 except that instead of the 0.1 wt% sodium tetraborate aqueous solution, a 0.5 wt% sodium tetraborate aqueous solution was used.

Comparative Example 1
In Example 1, a negative electrode was prepared in the same manner as in Example 1 except that a 0.1% by weight sodium tetraborate aqueous solution was used instead of the 0.1% by weight sodium tetraborate aqueous solution.

Comparative Example 2
In Example 1, a negative electrode was prepared in the same manner as in Example 1 except that instead of the 0.1 wt% sodium tetraborate aqueous solution, a 0.5 wt% sodium chloride aqueous solution was used.

Example 3
In Example 1, instead of natural graphite having a BET specific surface area of 6.0 m ² / g (surface spacing (d ₀₀₂ ) of 3.002 mm by X-ray wide angle diffraction method), the BET specific surface area is 4.0 m ^2. A negative electrode was prepared in the same manner as in Example 1, except that / g of artificial graphite (the (002) plane spacing (d ₀₀₂ ) of 3.358 mm by X-ray wide angle diffraction method) was used.

Example 4
In Example 3, a negative electrode was prepared in the same manner as in Example 3 except that a 0.5 wt% sodium tetraborate aqueous solution was used instead of the 0.1 wt% sodium tetraborate aqueous solution.

Comparative Example 3
In Example 3, a negative electrode was prepared in the same manner as in Example 3 except that a 0.1 wt% sodium tetraborate aqueous solution was used instead of the 0.1 wt% sodium tetraborate aqueous solution.

Comparative Example 4
In Example 3, a negative electrode was prepared in the same manner as in Example 3 except that instead of the 0.1 wt% sodium tetraborate aqueous solution, a 0.5 wt% sodium chloride aqueous solution was used.

Example 5
In Example 1, instead of natural graphite having a BET specific surface area of 6.0 m ² / g (surface spacing (d ₀₀₂ ) of 3.002 mm by X-ray wide angle diffraction method), the BET specific surface area is 4.0 m ^2. A negative electrode was prepared in the same manner as in Example 1 except that / g hard carbon ((002) plane spacing (d ₀₀₂ ) 3.786 mm by X-ray wide angle diffraction method) was used.

Example 6
In Example 5, a negative electrode was prepared in the same manner as in Example 5 except that a 0.5 wt% sodium tetraborate aqueous solution was used instead of the 0.1 wt% sodium tetraborate aqueous solution.

Comparative Example 5
In Example 5, a negative electrode was prepared in the same manner as in Example 5 except that a 0.1 wt% sodium tetraborate aqueous solution was used instead of the 0.1 wt% sodium tetraborate aqueous solution.

Comparative Example 6
In Example 5, a negative electrode was prepared in the same manner as in Example 5 except that a 0.5 wt% sodium chloride aqueous solution was used instead of the 0.1 wt% sodium tetraborate aqueous solution.

Test example 1
The negative electrodes obtained in Examples 1 to 4 and Comparative Examples 1 to 4 were evaluated for electrochemical characteristics by the following method. The results are shown in Tables 1 and 2.
A 2032 type coin cell was used, and the negative electrode was used for the working electrode and lithium metal was used for the counter electrode. As the electrolytic solution, a solution in which 1 mol / L LiPF ₆ was dissolved in a 1: 1 (weight ratio) mixed solvent of ethylene carbonate and diethyl carbonate was used.
The test was conducted at a constant current of C / 2 (175 mA / g) at a current density in the range of 0.0 to 2.0 V on the basis of the counter electrode Li / Li ⁺ and charged (insertion of Li ions) and discharged (of Li ions). Desorption) and measuring the capacity and efficiency. The initial efficiency was calculated from the capacity ratio of the charge capacity and discharge capacity in the first cycle. In Table 1, the sodium content derived from sodium tetraborate or sodium chloride contained in the negative electrode material in each example and comparative example is analyzed and determined by a high frequency inductively coupled plasma emission spectrometer (ICP-AES). The results are also shown.

Test example 2
In Test Example 1, the negative electrode obtained in each of Examples 5 and 6 and Comparative Examples 5 and 6 was used as the negative electrode, and the electrolyte was changed to a 1: 1 (weight ratio) mixed solvent of ethylene carbonate and diethyl carbonate as the electrolyte. Evaluation was performed in the same manner as in Test Example 1 except that propylene carbonate was used. The results are shown in Table 3.

  From the results of Tables 1 to 3, the active material subjected to the sodium tetraborate aqueous solution treatment as in Examples 1 to 6 was more effective than the case where the sodium chloride treatment was applied as in Comparative Examples 1 to 6. It can be seen that the discharge capacity of the battery using NO as a negative electrode material is large and exhibits excellent performance. From this, it is expected that the electrical performance of the non-aqueous electrolyte secondary battery using a negative electrode using a negative electrode material containing an alkali (earth) metal borate will be further improved.

  The nonaqueous electrolyte secondary battery of the present invention comprising the negative electrode material for a nonaqueous electrolyte secondary battery of the present invention with improved discharge capacity is excellent in battery performance and can be used for various known applications. . Specific examples include notebook computers, pen input computers, mobile computers, electronic book players, mobile phones, mobile faxes, mobile copy, mobile printers, headphone stereos, video movies, LCD TVs, handy cleaners, portable CDs, minidiscs, and transceivers. , Electronic notebooks, calculators, memory cards, portable tape recorders, radios, backup power supplies, motors, lighting equipment, toys, game machines, small devices such as watches, strobes, cameras, and large devices such as electric cars and hybrid cars, Etc.

Claims (12)

A negative electrode material for a non-aqueous electrolyte secondary battery, comprising a negative electrode active material capable of being doped and dedoped with lithium ions, and an alkali metal borate and / or an alkaline earth metal borate . 2. The negative electrode material for a non-aqueous electrolyte secondary battery according to claim 1, wherein the negative electrode active material is mainly composed of graphite and / or a carbon material having lower crystallinity than graphite. 3. The negative electrode material for a non-aqueous electrolyte secondary battery according to claim 1, wherein the specific surface area of graphite and / or a carbon material having lower crystallinity than graphite is 1 to 600 m ² / g. The negative electrode material for a nonaqueous electrolyte secondary battery according to any one of claims 1 to 3, wherein the alkali metal borate is sodium borate. Obtained by mixing an aqueous solution containing an alkali metal borate and / or an alkaline earth metal borate and a negative electrode active material capable of doping and dedoping with lithium ions, and then removing moisture and drying. The negative electrode material for nonaqueous electrolyte secondary batteries described in any one of claims 1 to 4. The content of alkali metal borate and / or alkaline earth metal borate is 50 to 10,000 ppm in terms of alkali metal and / or alkaline earth metal equivalent. The negative electrode material for nonaqueous electrolyte secondary batteries described in the paragraph. Furthermore, the negative electrode material for nonaqueous electrolyte secondary batteries as described in any one of Claims 1-6 containing a binder and a solvent. The binder is polyvinylidene fluoride, polytetrafluoroethylene, fluorinated polyvinylidene fluoride, ethylene-propylene-diene terpolymer, styrene-butadiene rubber, acrylonitrile-butadiene rubber, fluorine rubber, polyvinyl acetate, polymethyl methacrylate, The negative electrode material for a nonaqueous electrolyte secondary battery according to claim 7, which is at least one selected from the group consisting of polyethylene and nitrocellulose. The solvent is at least one selected from the group consisting of N-methylpyrrolidone, dimethylformamide, dimethylacetamide, methyl ethyl ketone, cyclohexanone, methyl acetate, methyl acrylate, diethyltriamine, N, N-dimethylaminopropylamine, ethylene oxide, tetrahydrofuran and water. The negative electrode material for a nonaqueous electrolyte secondary battery according to claim 7, which is a seed. A non-aqueous electrolyte secondary battery comprising a positive and negative electrode capable of being doped and dedoped with lithium ions, and a non-aqueous electrolyte, wherein the negative electrode is a non-aqueous electrolyte according to any one of claims 1 to 9. A non-aqueous electrolyte secondary battery comprising a negative electrode material for an aqueous electrolyte secondary battery. The non-aqueous electrolyte secondary battery according to claim 10, wherein the positive electrode active material contained in the positive electrode is a lithium transition metal composite oxide. The non-aqueous electrolyte secondary battery according to claim 11, wherein the lithium transition metal composite oxide contains manganese.