JP2006310265A - Anode material for non-aqueous electrolyte secondary battery and non-aqueous electrolyte secondary battery using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To realize a high performance non-aqueous electrolytic liquid secondary battery by improving electrochemical characteristics of a negative electrode material. <P>SOLUTION: The negative electrode material for non-aqueous electrolytic liquid secondary battery contains a negative electrode active material capable of storage and release of lithium, halides of alkali metal and/or halides of alkali earth metal. The non-aqueous electrolytic liquid secondary battery comprises a positive electrode and a negative electrode capable of storage and release of lithium ion, and a non-aqueous electrolytic liquid, and the negative electrode contains this negative electrode material for non-aqueous electrolytic secondary battery. <P>COPYRIGHT: (C)2007,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 a negative electrode configured using the negative electrode material.

  In recent years, with the miniaturization of electronic devices, it is desired to increase the capacity of secondary batteries. Therefore, a non-aqueous electrolyte secondary battery typified by a lithium secondary battery having higher energy density is attracting attention as compared with an aqueous electrolyte secondary battery such as a nickel / cadmium battery or a nickel / hydrogen battery.

  In the past, it was attempted to use lithium metal as the negative electrode active material of the non-aqueous electrolyte secondary battery. However, when lithium metal was used, dendritic lithium precipitated during repeated charging and discharging. It has been found that there is a possibility of causing a fire accident by penetrating the separator, reaching the positive electrode, and short-circuiting. Therefore, at present, it is common to use, as a negative electrode active material, a carbon material that allows lithium ions to enter and exit between layers and prevent lithium metal precipitation during the charge / discharge process.

  As this carbon material, for example, Patent Document 1 describes that graphite is used. However, when graphite having a high graphitization degree is used, it is close to 372 mAh / g, which is the theoretical capacity of lithium storage of graphite. It is known that capacity is obtained and preferred.

When graphite is used as the negative electrode active material of a lithium secondary battery, its ideal charge / discharge reaction formula is
Charging (Li ion insertion into graphite)
C (graphite) + xLi ⁺ + xe ⁻ → C · Li _x (Formula 1)
Discharge (desorption of Li ions from graphite)
C · Lix → C (graphite) + xLi ⁺ + xe ⁻ (Formula 2)
It is a reversible reaction represented by.

  However, in a lithium secondary battery, the negative electrode approaches a base potential close to that of lithium metal, so that a reductive decomposition reaction (irreversible reaction) of the electrolyte solvent occurs on the surface of the negative electrode active material during charging, and the original secondary battery is charged. The reaction, Formula 1, may not occur sufficiently. In this case, the ratio (efficiency) of the discharge capacity to the charge capacity of the battery is reduced.

  In addition, there may be a “cointercalation phenomenon” in which the solvent is inserted into the active material while being coordinated to lithium ions during charging. In this case, the active material is inserted by inserting a large solvated ion. It is destroyed and becomes an irreversible reaction, not only the charge / discharge efficiency is lowered, but also the deterioration during the cycle is increased.

  The magnitude of such an irreversible reaction greatly depends on the properties of the negative electrode active material used in the secondary battery, the type of the electrolytic solution, and the like.

  For example, in the case where graphite is used as the negative electrode active material, if the propylene carbonate used as the electrolyte solution of the lithium primary battery is used as the electrolyte solution, the charge reaction of Formula 1 hardly occurs and the discharge reaction also occurs. I can hardly do it. On the other hand, when ethylene carbonate is used as the solvent of the electrolytic solution, the insertion of lithium ions, that is, the charging reaction of (Formula 1) occurs, and therefore the discharge reaction of (Formula 2) also occurs.

  The reason for this is that when propylene carbonate is used, lithium ions and the solvent co-intercalate simultaneously with the decomposition of the solvent on the graphite surface during charging, so the graphite layer is destroyed and the decomposition of the solvent continues from there. In the case of using ethylene carbonate, the decomposition reaction occurs on the graphite surface at the initial stage of charging, but at this time, an ion-conductive film is formed. However, it is considered that it takes precedence over the co-intercalation reaction, and after that, insertion and desorption of lithium ions can occur through the film.

  However, even when ethylene carbonate is used, the magnitude of the initial solvent decomposition reaction (film formation reaction) depends on the properties of graphite. In general, graphite having a high specific surface area has a large surface that is involved in the decomposition of the solvent, so that the initial decomposition reaction becomes large, and the initial charge / discharge efficiency decreases.

  In addition, when the battery is subjected to a cycle test or storage at a high temperature, the coating is destroyed by dissolution or the like, and a re-decomposition reaction of the electrolytic solution occurs, so that deterioration may occur.

  As a means for solving such a problem, there is a method of reducing the specific surface area of the negative electrode active material, but in this case, there is a problem that the charge / discharge reactivity of the active material is lowered and the output of the battery is lowered. . In addition, a method of adding an additive that forms a highly heat-stable film such as vinylene carbonate has been developed in the electrolytic solution. However, the addition of the additive usually increases the manufacturing cost of the electrolytic solution. There is a problem that the resistance increases due to the formation of a thick film and the output of the battery decreases.

On the other hand, as the positive electrode active material of the positive electrode used for the nonaqueous electrolyte secondary battery, a lithium transition metal composite oxide is usually used. Examples of the lithium transition metal composite oxide include LiMeO ₂ having a layered structure such as LiCoO ₂ , LiNiO _2, and LiMnO ₂ (Me is one or more elements selected from transition metals), and spinel such as LiMn ₂ O _4. Examples thereof include compounds having a structure as a basic skeleton. Among these, lithium manganese complex oxides containing manganese as the main component are cheaper because manganese has a larger reserve than cobalt and nickel, and is safer when overcharged due to battery malfunction. Since it has the merit of being high, it attracts attention as a candidate for a positive electrode active material for a large non-aqueous electrolyte secondary battery such as a battery for an automobile in the future.

However, a battery using a lithium manganese composite oxide, particularly a spinel type LiMn ₂ O ₄ , as the positive electrode has a problem that the deterioration is large in a high temperature environment.

  This is thought to be because the lithium manganese composite oxide dissolves in a high temperature environment and the dissolved manganese ions have various adverse effects. In particular, it is considered that the manganese compound deposited on the negative electrode increases irreversible lithium, reduces reversible lithium originally required for the secondary battery, and increases cycle deterioration (for example, Non-Patent Document 1).

  As a method for solving such a problem, in order to increase the stability of the positive electrode, addition of a small amount of an element other than Mn or coating with an ion conductive solid electrolyte has been studied. In some cases, the dissolution of manganese cannot be completely suppressed when used in a battery.

For this reason, studies have been made to suppress the reaction of manganese ions on the negative electrode side. For example, Patent Document 2 discloses a nonaqueous electrolyte secondary battery using a lithium manganese composite oxide as a positive electrode material. It has been proposed to prevent the formation of a manganese compound that promotes deterioration on the negative electrode by containing strontium or the like, but it has not been fully satisfactory.
JP-A-57-208079 Japanese Patent Laid-Open No. 2001-6661 Electrochemistry, 69,784 (2001)

  Development of non-aqueous electrolyte secondary batteries for automobiles has become important due to environmental problems in recent years, but for practical use, it is important to reduce the cost of the battery and increase its output. For that purpose, it is important to make an active material which is inexpensive and has a high specific surface area function effectively. In particular, it is necessary to make a battery with good performance using an inexpensive carbon material such as graphite having a high specific surface area for the negative electrode and a lithium manganese based composite oxide for the positive electrode. For this purpose, control of the negative electrode film is important, but as described above, the conventional technique is insufficient to solve these problems.

  The present invention has been made in view of the above-described conventional situation, and an object thereof is to provide a technique for realizing a high-performance nonaqueous electrolyte secondary battery by improving the electrochemical characteristics of the negative electrode material. And

In order to solve such a problem, the present inventors have used an alkali metal halide and / or an alkaline earth metal halide (hereinafter referred to as “alkali (earth)) as a negative electrode material for a non-aqueous electrolyte secondary battery. It has been found that the electrochemical performance of the negative electrode material can be improved by adding the “metal halide” in some cases, and consequently the performance of the battery using the same can be improved.
The present invention has been achieved based on such knowledge, and the gist thereof is as follows.

(1) A negative electrode material for a non-aqueous electrolyte secondary battery, comprising a negative electrode active material capable of occluding and releasing lithium and an alkali metal halide and / or an alkaline earth metal halide .

(2) The negative electrode material for a non-aqueous electrolyte secondary battery according to (1), wherein the negative electrode active material is mainly composed of graphite and / or a carbon material that is less crystalline than graphite.

(3) The non-aqueous electrolysis according to (1) or (2), wherein the specific surface area of graphite and / or a carbon material having lower crystallinity than graphite is 2 m ² / g or more and 20 m ² / g or less. Negative electrode material for liquid secondary batteries.

(4) The negative electrode material for a non-aqueous electrolyte secondary battery according to any one of (1) to (3), wherein the alkali metal halide is sodium halide.

(5) It is obtained by mixing an aqueous solution containing an alkali metal halide and / or an alkaline earth metal halide with an active material capable of occluding and releasing lithium, and then removing moisture and drying. The negative electrode material for a non-aqueous electrolyte secondary battery according to any one of (1) to (4).

(6) The content of alkali metal halide and / or alkaline earth metal halide is 100 ppm or more and 10,000 ppm or less in terms of alkali metal and / or alkaline earth metal equivalent (1) The negative electrode material for a nonaqueous electrolyte secondary battery according to any one of) to (5).

(7) A non-aqueous electrolyte secondary battery comprising a positive electrode and a negative electrode capable of inserting and extracting lithium ions, and a non-aqueous electrolyte, wherein the negative electrode is the non-aqueous electrolyte described in (1) to (6) A nonaqueous electrolyte secondary battery comprising a negative electrode material for a secondary battery.

(8) The nonaqueous electrolyte secondary battery according to (7), wherein the positive electrode active material contained in the positive electrode is a lithium transition metal composite oxide.

(9) The nonaqueous electrolyte secondary battery according to (8), wherein the lithium transition metal composite oxide contains manganese.

  The negative electrode material for a non-aqueous electrolyte secondary battery of the present invention improves the electrochemical characteristics of the negative electrode active material by blending an alkali (earth) metal halide. As a result, such a negative electrode material is used. The non-aqueous electrolyte secondary battery of the present invention is excellent in battery performance.

  As described above, the effect of the present invention by containing the alkali (earth) metal halide in the negative electrode material is that the negative electrode active material is charged during charging of the battery by containing the alkali (earth) metal halide in the negative electrode material. This is presumably due to the fact that the electrolytic solution is decomposed more than necessary on the surface of the material, or solvated lithium ions are taken in from the surface of the active material to destroy the active material itself. Moreover, in order to make a film effective for stabilization, it is considered that extra resistance does not stand in and out of lithium ions, leading to an improvement in output.

Although the details of the principle are not yet clear, for example, when sodium ions are added to the electrolyte, there is a report that the film on the surface of the graphite negative electrode formed during charging is modified and the electrochemical properties are improved. (Electrochem. Commun., 5 , 962 (2003)).
Moreover, in the said patent document 2, deterioration is accelerated | stimulated on a negative electrode by making a negative electrode contain sodium, potassium, calcium, strontium, etc. in the nonaqueous electrolyte secondary battery which uses lithium manganese complex oxide for a positive electrode material. It is trying to improve by not producing manganese compounds.

As described above, it is considered that ions of alkali metal or alkaline earth metal play some role in stabilizing the film formed on the surface of the negative electrode active material when the battery is charged. It has been found that when an alkali (earth) metal halide is used as a source and an alkaline earth metal source, the effect can be exerted strongly. It was also found that sodium halide is more effective and sodium chloride is particularly preferred.
This is presumably due to a synergistic effect that halide ions further enhance the film stabilizing effect of sodium ions and the like that have been known so far.

  DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments of the present invention will be described in detail. However, the description of the constituent elements described below is an example (representative example) of an embodiment of the present invention, and the present invention is not limited to the gist thereof. The content of is not specified.

[Negative electrode material for non-aqueous electrolyte secondary battery]
The negative electrode material for a non-aqueous electrolyte secondary battery of the present invention is characterized by containing a negative electrode active material capable of occluding and releasing lithium and an alkali (earth) metal halide.

<Negative electrode active material>
The negative electrode active material capable of occluding and releasing lithium used in the present invention includes carbon materials of various degrees of graphitization ranging from graphite to amorphous carbon materials, and metal particles that can be alloyed with Li However, as will be described later, graphite or a carbon material having a lower crystallinity than carbon (a carbon material having a low graphitization degree) is preferable, and a case of using graphite is more preferable. preferable. This is because the alkali (earth) metal halide 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 (d ₀₀₂ ) 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; and thermoplastic polymers such as polyvinyl alcohol.

  The firing temperature of these carbon materials having a low degree of graphitization is usually 600 ° C. or higher, preferably 900 ° C. or higher, more preferably 950 ° C. or higher, and the upper limit varies depending on the degree of graphitization desired for the carbon material. It is 2500 degrees C or less. Generally, it is often fired at 2000 ° C. or lower, particularly 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 with a high degree of graphitization 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 graphite to the total of the core graphite and the surrounding carbon material with a low crystallinity is 80% by weight or more, particularly 85% by weight or more in order to increase the negative electrode capacity. Preferably there is. However, if this ratio is too large, the coating effect is lost, so this ratio is preferably 99% by weight or less. The most preferred ratio of core graphite to surrounding coated carbon material is 85:15 to 99: 1 (weight ratio).

  These carbon materials including graphite have an average particle size of usually 35 μm or less, preferably 25 μm or less, most preferably 18 μm or less, usually 3 μm or more, and preferably 5 μm 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-mentioned range, and the average particle size of the primary particles is usually 15 μm or less. If the particle size is too small, the specific surface area becomes too large, the reaction with the electrolyte increases, and the irreversible capacity tends to increase. Also, when preparing the negative electrode of a nonaqueous electrolyte secondary battery, the negative electrode active material is slurried with a solvent together with a binder, applied to a current collector and dried, but if the particle size is too large, it is applied to form an electrode. In doing so, so-called streaks due to large lumps occur, making it difficult to form an active material layer having a uniform thickness.

The specific surface area (BET specific surface area) by the measurement of the BET adsorption method of carbon materials including graphite, the lower limit is preferably not less than ^2m 2 / g, more preferably at least more ^4m 2 / g, the upper limit is 20m ² / g or less is preferable, and 15 m ² / g or less is more preferable. This is because if the specific surface area of the carbon material is too small, the effectiveness of the alkali (earth) metal halide used in the present invention is reduced, and if it is too high, the reactivity with the electrolyte is increased. This is because it is necessary to contain a large amount of alkali (earth) metal halide in order to suppress it, resulting in inefficiency due to a decrease in capacity.

  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.

<Alkali (earth) metal halide>
Alkali (earth) metal halides used in the present invention are alkali metal (Li, Na, K, Rb, Cs), alkaline earth metal (Be, Mg, Ca, Sr, Ba) fluoride, chloride. , Bromide, and iodide, but from the viewpoint of cost and ease of handling of the compound, sodium halides such as LiF, LiCl, NaF, and NaCl, KF, KCl, MgF ₂ , MgCl ₂ , CaF ₂ , CaCl _2, etc. Is preferable, and sodium halide is particularly preferable. These alkali (earth) metal halides 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 halide 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. Is preferably an aqueous solution having a high solubility in water so that it can be uniformly mixed with the negative electrode active material.

  In the present invention, any method may be used as a method for containing the alkali (earth) metal halide in the negative electrode material, but the alkali (earth) metal halide is uniformly contained especially by adding a small amount. First, an alkali (earth) metal halide 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, followed by drying. The method is effective. When such a treatment is performed, it is presumed that the alkali metal or alkaline earth metal halide exists relatively uniformly in a form covering the surface of the negative electrode material. When the amount of the coating is very small, it may be difficult to confirm the presence of a clear halide by SEM observation or the like. In that case, the presence of alkali metal or alkaline earth metal can be confirmed by surface analysis using TOF-SIMS or the like.

  In the present invention, even if the amount of alkali (earth) metal halide in the negative electrode material is too small, the effect of the present invention cannot be obtained sufficiently. Therefore, there is an optimum value for the alkali (earth) metal halide content in the negative electrode material.

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

  The content of the alkali (earth) metal halide in the negative electrode material of the present invention containing the alkali (earth) metal halide is, for example, coated or attached with an alkali (earth) metal halide. Although not particularly limited, the lower limit of the content in terms of alkali (earth) metal is preferably 100 ppm (0.01 wt%) or more, more preferably 200 ppm (0.02 wt%) or more, and 500 ppm (0.05 wt%). The above is particularly preferable. Moreover, as the upper limit, 10,000 ppm (1.0 weight%) or less is preferable, 9000 ppm (0.9 weight%) or less is more preferable, 5000 ppm (0.5 weight%) or less is especially preferable.

  The content of the alkali (earth) metal halide in the negative electrode material is extracted, for example, by dispersing the sample in a sufficient amount of water and extracting the alkali (earth) metal halide contained in the negative electrode material. The obtained alkali (earth) metal halide can be determined by quantifying the amount of alkali (earth) metal by ICP-AES (Inductively Coupled Plasma Atomic Emission Spectroscopy) or the like.

[Nonaqueous electrolyte secondary battery]
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.

  The following is a nonaqueous electrolyte secondary battery comprising a positive electrode and a negative electrode capable of occluding and releasing lithium ions and a nonaqueous electrolyte, wherein the negative electrode is a negative electrode material for a nonaqueous electrolyte secondary battery of the present invention. The contained nonaqueous electrolyte secondary battery of the present invention will be described.

<Non-aqueous electrolyte>
(Organic solvent)
The organic solvent for the non-aqueous electrolyte is not particularly limited, but for example, carbonates, ethers, ketones, sulfolane compounds, lactones, nitriles, chlorinated hydrocarbons, ethers, amines , Esters, amides, phosphate ester compounds and the like can be used.

  A typical list of these is dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, propylene carbonate, ethylene carbonate, vinylene carbonate, tetrahydrofuran, 2-methyltetrahydrofuran, 1,4-dioxane, 4-methyl-2-pentanone, 1,2-dimethoxyethane, 1,2-diethoxyethane, γ-butyrolactone, 1,3-dioxolane, 4-methyl-1,3-dioxolane, diethyl ether, sulfolane, methylsulfolane, acetonitrile, propionitrile, benzo Nitrile, butyronitrile, valeronitrile, 1,2-dichloroethane, dimethylformamide, dimethyl sulfoxide, trimethyl phosphate, triethyl phosphate, or a mixture of two or more types And the like.

  The organic solvent preferably 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 the high dielectric constant solvents, ethylene carbonate, propylene carbonate, and compounds in which hydrogen atoms thereof are substituted with other elements such as halogen or alkyl groups are preferable.

  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 most preferably 40% by weight or more. If the content of the high dielectric constant solvent in the electrolytic solution is small, desired battery characteristics may not be obtained.

(Lithium salt)
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 lower limit of the concentration of these lithium salts in the non-aqueous electrolyte is usually 0.5 mol / L or more, especially 0.75 mol / L or more, and the upper limit is usually 2 mol / L or less, especially 1.5 mol / L. L or less. When the concentration of the lithium salt exceeds this upper limit, the viscosity of the non-aqueous electrolyte increases and the electrical conductivity also decreases. Moreover, since electrical conductivity will become low if less than this lower limit, it is preferable to prepare a non-aqueous electrolyte within the said concentration range.

<Positive electrode>
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 may be any material as long as it can reversibly occlude and release Li, and among these, a lithium transition metal composite oxide is more preferable. Examples of the lithium transition metal 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. it can. Specific compositional formula, for example, the general formula _{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, Examples thereof include compounds represented by Li ₂ CuO ₂ and LiCuO ₂ . 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 alone or in a combination of two or more.

  Examples of the binder used for the positive electrode include polyvinylidene fluoride, polytetrafluoroethylene, fluorinated polyvinylidene fluoride, EPDM (ethylene-propylene-diene terpolymer), SBR (styrene-butadiene rubber), NBR ( Acrylonitrile-butadiene rubber), fluoro rubber, polyvinyl acetate, polymethyl methacrylate, polyethylene, nitrocellulose and the like. The ratio of the binder in the positive electrode mixture layer is usually 0.1% by weight or more, preferably 1% by weight or more, more preferably 5% by weight or more, and usually 80% by weight or less, preferably 60% by weight or less, Preferably it is 40 weight% or less, Most preferably, it is 10 weight% or less. If the ratio of the binder in the positive electrode mixture layer is too low, the active material cannot be sufficiently retained, the positive electrode mechanical strength may be insufficient, and the battery performance such as cycle characteristics may be deteriorated. May reduce capacity and conductivity.

  Examples of the conductive agent for the positive electrode mixture layer include 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 usually 0.01% by weight or more, preferably 0.1% by weight or more, more preferably 1% by weight or more, and usually 50% by weight or less, preferably 30% by weight. Hereinafter, it is more preferably 15% by weight or less. If the proportion of the conductive agent in the positive electrode mixture layer is too low, the conductivity may be insufficient. Conversely, if it is too high, the battery capacity may be reduced.

  As the material of the current collector used for the positive electrode, aluminum, stainless steel, nickel-plated steel or the like is used, and preferably aluminum. The thickness of the current collector is usually about 1 to 1000 μm, preferably about 5 to 500 μm. If the current collector is too thick, the capacity of the non-aqueous electrolyte secondary battery as a whole decreases, and if it is too thin, the mechanical strength may be insufficient.

  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 individually by 1 type, or may use multiple types together. 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 usually about 1 to 1000 μm, preferably about 10 to 200 μm. If the positive electrode mixture layer is too thick, the conductivity tends to decrease, and if it is too thin, the capacity tends to decrease.

  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.

<Negative electrode>
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. In this case, as the binder to be used and the conductive agent to be used as necessary, the same ones as used for the positive electrode can be used.
In the present invention, the negative electrode material of the present invention is used as the negative electrode active material. In addition, the negative electrode material of the present invention may be used in combination of two or more types such as those using different negative electrode active materials and those using different alkali (earth) metal halides. Further, the negative electrode material of the present invention and a normal negative electrode active material not containing an alkali (earth) metal halide may be mixed and used.

  The ratio of the binder to the negative electrode material is usually 0.1% by weight or more, preferably 0.5% by weight or more, more preferably 1% by weight or more, usually 20% by weight or less, preferably 10% by weight or less, more preferably 5% by weight or less. If the binder ratio is too low, the negative electrode material cannot be sufficiently retained and the negative electrode mechanical strength may be insufficient, which may deteriorate battery performance such as cycle characteristics. On the other hand, if the binder ratio is too high, the battery capacity and conductivity may be reduced. Sometimes.

  As the current collector for the negative electrode, copper, nickel, stainless steel, nickel-plated steel or the like is used, and copper is preferably used. The thickness of the current collector is usually about 1 to 1000 μm, preferably about 5 to 500 μm. If the current collector is too thick, the capacity of the non-aqueous electrolyte secondary battery as a whole decreases, and if it is too thin, the mechanical strength may be insufficient.

  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 that are added as necessary, to a current collector and drying it. can do. As the solvent used for slurrying, the same solvent as used for preparing the positive electrode can be used.

  The thickness of the negative electrode mixture layer thus formed is usually about 1 to 1000 μm, preferably about 10 to 200 μm. If the negative electrode mixture layer is too thick, the conductivity tends to decrease, and if it is too thin, the capacity tends to decrease.

  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.

<separator>
In the non-aqueous electrolyte secondary battery of the present invention, a separator is preferably interposed between the positive electrode and the negative electrode. As this separator, a microporous polymer film is used, and a separator made of a polyolefin polymer such as nylon, cellulose acetate, nitrocellulose, polysulfone, polyacrylonitrile, polyvinylidene fluoride, polypropylene, polyethylene, polybutene or the like is used. The chemical and electrochemical stability of the separator is an important factor. In this respect, a polyolefin-based polymer is preferable, and it is desirable that the polymer is made of polyethylene in view of the self-occluding temperature which is one of the purposes of the battery separator.

  In the case of a polyethylene separator, ultrahigh molecular weight polyethylene is preferable from the viewpoint of high temperature shape maintenance, and the lower limit of the molecular weight is preferably 500,000, more preferably 1,000,000, and most preferably 1,500,000. On the other hand, the upper limit of the molecular weight is preferably 5 million, more preferably 4 million, and most preferably 3 million. This is because if the molecular weight is too large, the pores of the separator may not close when heated because the fluidity is too low.

<Battery configuration>
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 spiral sheet electrode and separator, a cylinder type with an inside-out structure combining a pellet electrode and a separator, a coin type with stacked pellet electrodes and a separator, and a sheet Examples include a laminate type in which electrodes and separators are laminated. 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 Next, although an Example demonstrates this invention further more concretely, this invention is not limited to description of a following example, unless the summary is exceeded.

Example 1
Natural graphite having a BET specific surface area of 11.8 m ² / g (surface distance (d ₀₀₂ ) of 3.356 mm by X-ray wide angle diffraction method (d ₀₀₂ ) 3.356 mm) 0.3 g of 0.1% by weight sodium chloride (NaCl) aqueous solution After dispersing in 100 ml and 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 chloride.
This negative electrode material was mixed in a N-methyl-2-pyrrolidone (NMP) solvent at a ratio of 9: 1 (weight ratio) with polyvinylidene fluoride (PVdF) as a binder to form a slurry. After applying to a foil and drying, it was pressed to obtain a negative electrode.

The negative electrode was evaluated for electrochemical characteristics by the following method, and the results are shown in Table 1.
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 obtained by dissolving 1 mol / L of LiClO ₄ in a 1: 1 (weight ratio) mixed solvent of ethylene carbonate and diethyl carbonate was used.
The test was performed at a constant current of C / 2 (175 mA / g) at a current density in the range of 0.0 V 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.

Example 2
A negative electrode material was prepared in the same manner as in Example 1 except that the concentration of the NaCl aqueous solution in which natural graphite as a raw material for the negative electrode active material was dispersed was 0.5% by weight. The characteristics were evaluated and the results are shown in Table 1.

Comparative Example 1
Using natural graphite as the negative electrode material as it was, preparation of the negative electrode and evaluation of electrochemical characteristics were performed in the same manner as in Example 1, and the results are shown in Table 1.

Comparative Example 2
A negative electrode material was prepared in the same manner as in Example 1 except that a 0.1 wt% sodium carbonate (Na ₂ CO ₃ ) aqueous solution was used as the aqueous solution in which natural graphite was dispersed. The characteristics were evaluated and the results are shown in Table 1.

Comparative Example 3
A negative electrode material was prepared in the same manner as in Example 1 except that a 0.5 wt% Na ₂ CO ₃ aqueous solution was used as the aqueous solution in which natural graphite was dispersed. Similarly, preparation of the negative electrode and evaluation of electrochemical characteristics were performed. The results are shown in Table 1.

Comparative Example 4
A negative electrode material was prepared in the same manner as in Example 1 except that a 5 wt% NaCl aqueous solution was used as the aqueous solution in which natural graphite was dispersed. Similarly, the negative electrode was prepared and the electrochemical characteristics were evaluated. It is shown in Table 1.

Table 1 also shows the results of analysis and quantification of Na content derived from NaCl or Na ₂ CO ₃ contained in the negative electrode materials in Examples and Comparative Examples by ICP-AES.

From the results of Table 1, the active material treated with the NaCl aqueous solution as in Examples 1 and 2 was not treated at all as in Comparative Example 1, or Patent Document 2 as in Comparative Examples 2 and 3. It can be seen that the discharge capacity or initial efficiency of a battery using the negative electrode material is higher than that of the Na ₂ CO ₃ aqueous solution treatment as shown in FIG.
Further, as in Comparative Example 4, it is understood that if the NaCl content in the negative electrode material is too large, the capacity is decreased, which is not preferable.
FIG. 1 shows initial charge / discharge test curves of the battery of Example 2 and the battery of Comparative Example 1. FIG. 1 shows that the battery of Example 2 is less polarized than the battery of Comparative Example 1 and thus has a larger charge capacity and therefore a larger discharge capacity.
From these facts, a nonaqueous electrolyte secondary battery using a negative electrode using a negative electrode material containing NaCl is expected to have a high reversible capacity and a large output.

  The non-aqueous electrolyte secondary battery of the present invention comprising the negative electrode material for a non-aqueous electrolyte secondary battery of the present invention having excellent electrochemical characteristics is excellent in battery performance and can be used for various known applications. is there. 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 fixtures, toys, gaming devices, small devices such as watches, strobes, cameras, and large devices such as electric vehicles and hybrid vehicles However, the present invention is not limited to these examples.

It is a graph which shows the initial stage charge / discharge test curve of the battery of Example 2, and the battery of Comparative Example 1.

Claims (9)

  A negative electrode material for a non-aqueous electrolyte secondary battery, comprising: a negative electrode active material capable of inserting and extracting lithium; and an alkali metal halide and / or an alkaline earth metal halide.   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 that is less crystalline than graphite. 3. The nonaqueous electrolyte secondary battery according to claim 1 or 2, wherein the specific surface area of graphite and / or a carbon material that is less crystalline than graphite is 2 m ² / g or more and 20 m ² / g or less. Negative electrode material.   4. The negative electrode material for a non-aqueous electrolyte secondary battery according to claim 1, wherein the alkali metal halide is sodium halide. 5.   It is obtained by mixing an aqueous solution containing an alkali metal halide and / or an alkaline earth metal halide and an active material capable of occluding and releasing lithium, and then removing and drying the moisture. The negative electrode material for a nonaqueous electrolyte secondary battery according to any one of claims 1 to 4.   6. The content of alkali metal halide and / or alkaline earth metal halide is 100 ppm or more and 10,000 ppm or less in terms of alkali metal and / or alkaline earth metal equivalent. The negative electrode material for nonaqueous electrolyte secondary batteries of any one of these.   A nonaqueous electrolyte secondary battery comprising a positive electrode and a negative electrode capable of inserting and extracting lithium ions, and a nonaqueous electrolyte, wherein the negative electrode is the nonaqueous electrolyte according to any one of claims 1 to 6. A nonaqueous electrolyte secondary battery comprising a negative electrode material for a secondary battery.   The nonaqueous electrolyte secondary battery according to claim 7, wherein the positive electrode active material contained in the positive electrode is a lithium transition metal composite oxide.   The nonaqueous electrolyte secondary battery according to claim 8, wherein the lithium transition metal composite oxide contains manganese.

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