JP2015122306A - Negative electrode material, negative electrode for lithium ion batteries arranged by use thereof, lithium ion battery, and method for manufacturing negative electrode material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a negative electrode material small in irreversible capacity without reducing a battery capacity.SOLUTION: A negative electrode material comprises carbon material, in which a reducible functional group (X) present on the surface of the carbon material is subjected to a reduction treatment with an organic reductant (A). The reducible functional group (X) is preferably a carboxyl group and/or carbonyl group. The organic reductant (A) is preferably at least one compound selected from a group consisting of a reductive organic acid (A1) including no formyl group, a reductive organic acid ester (A2) including no formyl group, a reductive organic acid salt (A3) including no formyl group, and a compound (A4) including a formyl group. The reduction rate of the reducible functional group (X) is preferably 3% or more.

Description

  The present invention relates to a negative electrode material, a negative electrode for a lithium ion battery and a lithium ion battery using the negative electrode material, and a method for producing the negative electrode material.

  Non-aqueous electrolyte secondary batteries such as lithium ion batteries are characterized by high voltage and high energy density, so they are widely used in the field of portable information equipment, and the demand for them is rapidly expanding. A position as a standard battery for mobile information devices such as telephones and notebook computers has been established. Along with higher performance and multi-functionality of portable devices etc., further higher performance (for example, higher capacity and higher energy density) is required for non-aqueous electrolyte secondary batteries as power sources. Yes. In order to meet this demand, various methods, for example, increasing the density by improving the filling rate of electrodes, increasing the depth of use of the current active material, and developing a new high-capacity active material have been performed. In fact, non-aqueous electrolyte secondary batteries are being reliably increased in capacity by these methods.

  As active materials for negative electrodes of lithium ion batteries, carbon-based active materials such as natural graphite and artificial graphite are widely used because of their excellent reliability and safety. However, these have the problem of irreversible capacity that the amount of current that can be discharged is smaller than the amount of current required at the time of initial charge, and this hinders the increase in capacity.

  In order to solve this problem, Patent Document 1 discloses a technique for reducing the irreversible capacity by devising the shape of particles generated during the production of an active material. Patent Document 2 discloses a technique for reducing the irreversible capacity by using a negative electrode material obtained by treating a negative electrode active material with an alkyl lithium compound.

JP 2005-108858 A JP 2002-231247 A

However, even with the method described in Patent Document 1, the irreversible capacity is still large, and it cannot be said that the problem has been solved. In addition, the method described in Patent Document 2 has a problem that the irreversible capacity is reduced, but the battery capacity itself is also reduced and the cycle characteristics are deteriorated, and the alkyl lithium is a compound that is very difficult to handle. .
An object of the present invention is to provide a negative electrode material having a large battery capacity and a small irreversible capacity when a lithium ion battery is used.

  As a result of intensive studies to achieve the above object, the present inventors have reached the present invention. That is, the present invention relates to a negative electrode material obtained by reducing a reducible functional group (X) present on the surface of a carbon material with an organic reducing agent (A); a negative electrode for a lithium ion battery including the negative electrode material; Lithium ion battery including a battery negative electrode; characterized in that a carbon material is heat-treated in the presence of an organic reducing agent (A) to reduce a reducible functional group (X) present on the surface of the carbon material. This is a method for producing a negative electrode material.

  When the negative electrode material of the present invention is a lithium ion battery, the battery capacity is large and the irreversible capacity is also small. The production method of the present invention can safely produce a negative electrode material having a large battery capacity and a small irreversible capacity.

  The negative electrode material of the present invention is characterized in that the reducible functional group (X) present on the surface of the carbon material is reduced with the organic reducing agent (A).

Any carbon material may be used as long as it can occlude lithium ions during the charge reaction and can be released during the discharge reaction. Graphite (natural graphite, artificial graphite, etc.), amorphous carbon, polymer compound fired body (for example, phenol resin) And those obtained by baking and carbonizing furan resin, etc.), cokes (for example, pitch coke, needle coke, and petroleum coke), and carbon fiber. Of these, graphite is preferred from the viewpoint of reactivity with the organic reducing agent (A). There is no restriction | limiting in the shape of a carbon material, Things, such as a scale shape, a lump shape, an amorphous powder form, and a spherical shape, can be used.
In addition, instead of carbon materials, silicon-based materials (such as silicon and lithium-silicon alloys), tin-based materials tin and lithium-tin alloys), conductive polymers (B4) (such as polyacetylene and polypyrrole), and lithium-aluminum alloys (such as A negative electrode material such as a lithium-aluminum alloy and a lithium-aluminum-manganese alloy can also be used.

The reducible functional group (X) present on the surface of the carbon material includes a functional group having a peak appearing at 1400 to 1800 cm ⁻¹ in an infrared spectrophotometer, and examples thereof include a carboxyl group and a carbonyl group.
From the viewpoint of the initial irreversible capacity, the reduction rate of (X) by reduction treatment is preferably 3% or more, more preferably 5% or more, particularly preferably 10% or more, and most preferably 25% or more.
The reduction rate of (X) is 1400 to 1800 cm ⁻¹ of the infrared spectrum of the carbon material before the reduction treatment, using the infrared spectrum measured using an infrared spectrophotometer for each of the carbon materials before and after the reduction treatment. It calculates with the following formula using the total area (Z0) of the peak that appears and the total area (Zk) of the peak that appears at 1400 to 1800 cm ⁻¹ in the infrared spectrum of the carbon material after the reduction treatment in (A). I can do it.
Reduction rate (%) = 100− (Z1) / (Z0) × 100

As the organic reducing agent (A), any organic compound having reducibility can be used without any particular limitation.
As the organic reducing agent (A), a reducing organic acid not containing a formyl group (A1), a reducing organic acid ester not containing a formyl group (A2), a reducing organic acid salt not containing a formyl group (A3), Contains a formyl group-containing compound (A4), a compound containing a group obtained by acetalizing a formyl group (A5), a compound containing a group obtained by hemiacetalizing a formyl group (A6), an aldehyde multimer (A7), and a keto group And monosaccharide (A8).

  Examples of the reducing organic acid (A1) that does not contain a formyl group include oxalic acid, citric acid, and ascorbic acid. Of these, oxalic acid is preferably used from the viewpoint of irreversible capacity.

  As reducible organic acid ester (A2) which does not contain a formyl group, what esterified said (A1) with the C1-C4 linear or branched monohydric alcohol is mentioned. Examples of the linear or branched monohydric alcohol having 1 to 4 carbon atoms include methanol, ethanol, isopropanol, and butanol, and methanol, ethanol, and butanol are particularly preferable.

  Examples of the reducing organic acid salt (A3) that does not contain a formyl group include salts of the above (A1) with an alkali metal. As the alkali metal, lithium, sodium and potassium are preferable.

  The formyl group-containing compound (A4) can be used without particular limitation as long as it has a formyl group in the molecule. Examples of (A4) include formic acid, formic acid and alkali metal salts (sodium formate, potassium formate, lithium formate, etc.), esters of formic acid and linear or branched monohydric alcohols having 1 to 4 carbon atoms (methyl formate, formic acid). Ethyl and butyl formate), aliphatic and aromatic aldehydes having 1 to 9 carbon atoms (formaldehyde, acetaldehyde, propionaldehyde, acrolein, benzaldehyde and cinnamic aldehyde), saccharides containing a formyl group having 3 to 6 carbon atoms (glycel) Among them, formic acid, sodium formate, methyl formate, formaldehyde, acetaldehyde and glyceraldehyde are preferably used from the viewpoint of irreversible capacity.

  Examples of the compound (A5) containing an acetal group include compounds obtained by acetalizing the above (A4), and those obtained by acetalizing formaldehyde or acetaldehyde with methanol or ethanol, respectively. Examples of the compound (A6) containing a hemiacetal group include those obtained by converting (A4) into a hemiacetal, and those obtained by converting formaldehyde or acetaldehyde into hemiacetal with methanol or ethanol.

Examples of the aldehyde multimer (A7) include the above-mentioned multimer (A4), such as 1,3,5-trioxane, which is a multimer of formaldehyde, paraformaldehyde, which is a multimer of acetaldehyde, and metaformaldehyde.
Examples of the monosaccharide (A8) containing a keto group include ketoses having 3 to 7 carbon atoms (such as dihydroxyacetone, erythrulose, xylulose, fructose and sorbose).
These organic reducing agents (A1) to (A8) can be easily obtained as commercially available reagents.

  As the organic reducing agent (A), from the viewpoint of irreversible capacity, a reducing organic acid not containing a formyl group (A1), a reducing organic acid ester not containing a formyl group (A2), a reducing organic acid not containing a formyl group Salt (A3), formyl group-containing compound (A4), compound (A5) containing a group obtained by acetalizing a formyl group, compound (A6) containing a group obtained by hemiacetalizing a formyl group, (A1), (A2), (A3) and (A4) are more preferred, (A1), (A2) and (A4) are particularly preferred, and (A4) is most preferred.

  As a method of reducing the reducible functional group (X) present on the surface of the carbon material with the organic reducing agent (A), for example, a method of heat-treating the carbon material in the presence of the organic reducing agent (A) can be mentioned. It is done.

  As a method for heat-treating the carbon material in the presence of the organic reducing agent (A), a method in which the organic reducing agent (A) and the carbon material are mixed in a liquid and heat-treated (liquid phase method), an organic reducing agent ( A method of heat-treating the carbon material wetted in A) in a powder state (solid phase method), a method of heat-treating the carbon material in the presence of the gasified organic reducing agent (A) (gas phase method), etc. From the viewpoint of irreversible capacity, the liquid phase method and the solid phase method are preferable.

  In the liquid phase method, as a method of mixing the organic reducing agent (A) and the carbon material, a method of mixing the liquid organic reducing agent (A) and the carbon material and the organic reducing agent (A) into the solvent (S1). Examples thereof include a method in which a carbon material is dispersed and mixed in a dissolved solution to form a slurry.

  As the solvent (S1), any solvent that dissolves the organic reducing agent (A) can be used without limitation. Water, lactam compounds (1-methyl-2-pyrrolidone, etc.), ketone compounds (methyl ethyl ketone, etc.), chains And amide compounds (such as dimethylformamide and dimethylacetamide), amine compounds (such as N, N-dimethylaminopropylamine), and cyclic ether compounds (such as tetrahydrofuran).

  In the liquid phase method, a known mixing device such as a vertical wing stirrer, a high-speed shearing disperser (high-speed rotating homomixer, high-pressure homogenizer, dissolver, etc.) is used for mixing the organic reducing agent (A) and the carbon material. Can be used.

In the solid phase method, the organic reducing agent (A) and the carbon material are mixed by a method of wetting the carbon material with the liquid organic reducing agent (A) and the organic reducing agent (A) in the solvent (S1). Examples include a method of wetting the carbon material with a dissolved solution.
As a method of wetting the surface of the carbon material, a method of dropping or spraying the organic reducing agent (A) in a liquid state while stirring the carbon material or a solution of dissolving the organic reducing agent (A) in the solvent (S1) is dropped. Or the method of spraying etc. are mentioned.

  In the gas phase method, as a method of heat-treating the carbon material in the presence of the gasified organic reducing agent (A), the organic reducing agent (A) and the organic reducing agent (A) are mixed in a mixer heated to the boiling point of the organic reducing agent (A) or higher. Examples thereof include a method of coexisting a carbon material.

  In the gas phase method and the solid phase method, the organic reducing agent (A) and the carbon material are mixed by a known mixer {saddle type wing stirrer, high speed shearing disperser (high speed rotating homomixer, high pressure homogenizer). And dissolvers, etc.}, kneaders, triple roll mills, ultrasonic dispersers, planetary mixers, triaxial planetary mixers, wet medium dispersers {bead mills, sand grinders, colloid mills, etc.}, vertical single-shaft powder agitators {Henschel mixer (Mitsui Mining Co., Ltd., “Henschel Mixer” is a registered trademark of Mitsui Mining Co., Ltd.), etc.], horizontal single-shaft stirrer (ribbon mixer, etc.) and vertical single-shaft stirrer (universal mixer Among them, it is preferable to use a ball mill from the viewpoints of the mixing efficiency and irreversible capacity of the organic reducing agent (A) and the carbon material.

  As a method for heat-treating the carbon material in the presence of the organic reducing agent (A), the liquid phase method and the solid phase method are preferable, and the liquid phase method is more preferable from the viewpoint of the uniformity of the reduction treatment.

The temperature of the heat treatment may be any temperature that can reduce the reducible functional group (X) present on the surface of the carbon material, and can be adjusted according to the organic reducing agent (A) used. To 80 to 250 ° C, more preferably 100 to 230 ° C.
As a heating method, a general heating device can be used. The heating device provided in the mixer, a constant temperature dryer (such as DS400 manufactured by Yamato Scientific), a precision thermostat (such as DF411 manufactured by Yamato Scientific) and the like Examples include a method using a constant temperature and temperature chamber (such as DKG610 manufactured by Yamato Kagaku).
In addition, you may perform a reduction process under reduced pressure from a viewpoint of removing the by-product produced by a reductive reaction.

  The weight ratio of the organic reducing agent (A) to the carbon material is preferably 0.001 to 50%, more preferably 0.01 to 20%, and particularly preferably 0.1 to 5% from the viewpoint of irreversible capacity. 1 to 5% is most preferable.

The negative electrode for lithium ion batteries of this invention contains the said negative electrode material.
The negative electrode for a lithium ion battery of the present invention is a method of preparing a negative electrode material slurry in which the negative electrode material is mixed with a binder resin and a solvent (S2), applying the slurry to a current collector, and drying it [negative electrode manufacturing method ( 1)] and a negative electrode active material slurry in which a carbon material is mixed with a binder resin and a solvent (S2), and then an organic reducing agent (A) is mixed with the negative electrode active material slurry, and this is applied to a current collector. And a method of mixing and heating simultaneously with drying [anode manufacturing method (2)]. In addition, you may press the negative electrode for lithium ion batteries with a press if needed.

  Examples of the binder resin include high molecular compounds such as starch, polyvinylidene fluoride, SBR (styrene-butadiene rubber), polyvinyl alcohol, carboxymethyl cellulose, polyvinyl pyrrolidone, tetrafluoroethylene, polyethylene, and polypropylene.

  As the solvent (S2), any solvent that can dissolve the binder resin and the organic reducing agent (A) can be used without limitation, and examples thereof include the same as those exemplified as the solvent (S1).

  For the preparation of the negative electrode material slurry and the negative electrode active material slurry, a commonly used disperser can be used. In addition to a disperser such as a paint shaker, a homomixer, a high-pressure homogenizer, or a disper mill, a medium stirring type dispersion such as a ball mill or a sand mill. A kneading and dispersing machine such as a machine, a roll mill, or a planetary mixer can be used.

  There are no particular limitations on the mixing temperature and mixing time during preparation of the negative electrode material slurry and the negative electrode active material slurry, but the mixing temperature is preferably 10 to 50 ° C, more preferably 20 to 45 ° C, and particularly preferably 25 to 35 ° C. The mixing time is preferably 0.5 hours to 24 hours, more preferably 1 hour to 12 hours. Within this range, the uniformity of the negative electrode slurry becomes even better, and the battery characteristics become better, which is preferable.

  In the negative electrode manufacturing method (1), the weight ratio of the negative electrode material contained in the negative electrode material slurry is preferably 20 to 60% by weight based on the total weight of the solvent (S2) and the negative electrode material.

  In the negative electrode manufacturing method (1), the weight ratio of the negative electrode material is preferably 70 to 98% by weight, more preferably 90 to 90%, from the viewpoint of battery capacity, based on the total weight of the negative electrode material and the binder resin. 98% by weight. The weight ratio of the binder resin is preferably 2 to 30% by weight, more preferably 2 to 10% by weight, based on the total weight of the negative electrode material and the binder resin.

  In said negative electrode manufacturing method (2), it is preferable that the weight ratio of the carbon material contained in a negative electrode active material slurry is 20 to 60 weight% based on the total weight of a solvent (S2) and a carbon material.

  In the negative electrode manufacturing method (2), the weight ratio of the carbon material to the total weight of the carbon material and the binder resin is preferably 70 to 98% by weight, more preferably 90 to 98% by weight, from the viewpoint of battery capacity. It is. The weight ratio of the binder resin is preferably 2 to 30% by weight, more preferably 2 to 10% by weight, based on the total weight of the negative electrode material and the binder resin. The weight ratio of the organic reducing agent (A) to be mixed is preferably 0.001 to 50%, more preferably 0.01 to 20%, and particularly preferably 0.1 to 5% with respect to the carbon material.

  Examples of the current collector to which the negative electrode material slurry and the negative electrode active material slurry are applied include copper, aluminum, titanium, stainless steel, nickel, baked carbon, conductive polymer, and conductive glass.

  As a method of applying the negative electrode material slurry and the negative electrode active material slurry to the current collector, the dip coater method, spray coater method, flow coater method, die coater method, roll coater method, blade coater method, rod coater method, bar coater method Alternatively, a known coating method such as a spin coater method can be used.

  In the negative electrode manufacturing method (1), the temperature at which the current collector coated with the negative electrode material slurry is dried can be adjusted according to the type of the solvent (S2) contained in the negative electrode material slurry. Performed at 200 ° C.

  In the negative electrode production method (2), the temperature at which the mixed heat treatment is performed simultaneously with drying can be adjusted according to the type of the organic reducing agent (A), but is preferably 80 to 250 ° C., more preferably from the reduction efficiency. Is 100-230 degreeC.

The negative electrode for a lithium ion battery of the present invention can further contain a conductive additive (L).
As the conductive auxiliary agent (L), graphite (for example, natural graphite and artificial graphite) [except when graphite is used as the active material (Q)], carbon blacks (for example, carbon black, acetylene black, ketjen black, channel black, Furnace black, lamp black and thermal black), metal powder (for example, aluminum powder and nickel powder), and conductive metal oxide (for example, zinc oxide and titanium oxide). The content of the conductive assistant (L) is preferably 0 to 29% by weight, more preferably 1 to 10% by weight, based on the weight of the negative electrode material, from the viewpoint of battery output.

The lithium ion battery of this invention contains the said negative electrode for lithium ion batteries.
The lithium ion battery of the present invention can be obtained by sealing the battery can after injecting the electrolyte into the battery can containing the positive electrode, the negative electrode for a lithium ion battery, and the separator.

As the positive electrode, such as those used in conventional lithium-ion batteries can be used, a composite oxide of lithium metal, lithium and transition metal _{(LiCoO 2, LiNiO 2, LiMnO} 2 and LiMn ₂ O _4, etc.), transition Metal oxides (MnO ₂ and V ₂ O ₅ ), transition metal sulfides (eg MoS ₂ and TiS ₂ etc.) and conductive polymers (polyaniline, polyvinylidene fluoride, polypyrrole, polythiophene, polyacetylene, poly-p-phenylene and Polycarbazole and the like).

  Examples of separators include microporous films made of polyethylene or polypropylene films, multilayer films of porous polyethylene films and polypropylene, non-woven fabrics made of polyester fibers, aramid fibers, glass fibers, and the like, and silica, alumina, titania, etc. on their surfaces. The thing etc. which apply | coated ceramic fine particles are mentioned.

  As the battery can, metal materials such as stainless steel, iron, aluminum, and nickel-plated steel, and plastic materials can also be used. Further, the battery can can be formed into a cylindrical shape, a coin shape, a square shape, or any other shape depending on the application.

  As the electrolytic solution, those used in ordinary lithium ion batteries can be used, and those obtained by dissolving an electrolyte in a carbonate ester can be used.

  Examples of the carbonate ester include cyclic carbonate esters (propylene carbonate, ethylene carbonate, butylene carbonate, etc.) and chain carbonate esters (dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, methyl n-propyl carbonate, ethyl n-propyl carbonate, di-n- Propyl carbonate, etc.).

As the electrolyte, usually available such as those used in the lithium ion battery, for _{example, LiPF 6, LiBF 4, LiSbF} 6, LiAsF 6 , and lithium salts of inorganic acids LiClO _4, etc., _LiN (CF 3 _SO 2) ₂ , lithium salts of organic acids such as LiN (C ₂ F ₅ SO ₂ ) ₂ and LiC (CF ₃ SO ₂ ) ₃ . Of these, LiPF ₆ is preferable from the viewpoint of battery capacity and the like.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further, this invention is not limited to these. Hereinafter, unless otherwise specified, “%” represents “% by weight” and “parts” represents “parts by weight”.

<Examples 1 to 10: Production of negative electrode material>
In an air atmosphere, the parts of the organic reducing agents (A-1) to (A-10) listed in Table 1, 100 parts of natural graphite and 100 parts of water were placed in a beaker, and a stir bar was added. The mixture was stirred until all of the water had evaporated while heating to 100-110 ° C. Subsequently, heat treatment was performed at 200 ° C. for 2 hours under reduced pressure (0.5 kPa) using a constant temperature dryer (ADP300 manufactured by Yamato Kagaku) that can be reduced by a vacuum pump, and the negative electrode material (B-1) of the present invention. To (B-10) were obtained.

<Example 11: Production of negative electrode material>
In an air atmosphere, 100 parts of natural graphite and 1 part of formic acid were mixed with a ball mill (Asahi Rika Seisakusho, AV-1) for 30 minutes. Thereafter, the mixture was heat-treated in the same manner as in Example 1 to obtain a negative electrode material (B-11) of the present invention.

<Comparative Example 1>
Under an inert gas atmosphere, 100 parts of natural graphite was immersed in 200 parts of a 1.6 mol / L butyl lithium hexane solution (manufactured by Tokyo Kasei Kogyo Co., Ltd.) as a comparative treating agent and left for 50 hours. Thereafter, a butyl lithium solution was removed to obtain a comparative negative electrode material (B′-1).

<Reduction rate of reducible functional group (X)>
Natural graphite and silicon powder before the reduction treatment and the surfaces of the negative electrode materials (B-1) to (B-11) obtained in Examples 1 to 12 were measured with a Fourier transform infrared spectrophotometer (manufactured by Shimadzu Corporation). The peak area appearing at 1400 to 1800 cm ⁻¹ in the infrared spectrum of natural graphite before the reduction treatment is (Z0), and 1400 to 1800 cm ⁻¹ of the infrared spectrum of the negative electrode materials obtained in Examples 1 to 11. The peak area appearing in (1) was defined as (Z1), and the reduction rate was calculated according to the following formula and listed in Table 1.
Reduction rate = 100− (Z1) / (Z0) × 100 (%)

<Preparation of negative electrode for lithium ion battery>
<Examples 12 to 22, Comparative Example 2: Production of negative electrode for lithium ion battery>
90 parts of negative electrode materials (B1) to (B11) or comparative negative electrode material (B′-1), 5 parts of carboxymethylcellulose, 5 parts of styrene-butadiene rubber and 100 parts of water are charged in a mortar and mixed thoroughly in the mortar. A slurry was obtained. The obtained slurry was applied to one side of a copper foil having a thickness of 20 μm to a thickness of 100 μm using an applicator, dried at 100 ° C. for 15 minutes to evaporate water, and then punched to 16.15 mmφ with a press machine. A negative electrode for a lithium ion battery according to the present invention and a negative electrode for a lithium ion battery for comparison were prepared with a thickness of 30 μm.

<Comparative Example 3>
90 parts of natural graphite, 5 parts of carboxymethyl cellulose, 5 parts of styrene-butadiene rubber and 100 parts of water were charged in a mortar and mixed well in the mortar to obtain a slurry. The obtained slurry was applied to one side of a copper foil having a thickness of 20 μm to a thickness of 100 μm using an applicator, dried at 100 ° C. for 15 minutes to evaporate water, and then punched to 16.15 mmφ with a press machine. A negative electrode for a lithium ion battery for comparison was prepared with a thickness of 30 μm.

<Example 23: Manufacturing method of negative electrode for lithium ion battery in which reduction treatment and negative electrode preparation are collectively performed>
90 parts of natural graphite, 5 parts of carboxymethyl cellulose, 5 parts of styrene-butadiene rubber, 100 parts of water and 1 part of sodium formate were charged in a mortar and mixed well in the mortar to obtain a slurry. The obtained slurry was applied to one side of a 20 μm thick copper foil to a thickness of 100 μm using an applicator, dried at 100 ° C. for 2 hours to evaporate water, and then punched to 16.15 mmφ with a press machine. The negative electrode for a lithium ion battery of the present invention was produced with a thickness of 30 μm.

[Production of lithium-ion batteries]
The lithium metal as the positive electrode and the negative electrode for lithium ion battery of the present invention or the negative electrode for comparison lithium ion battery as the negative electrode are respectively arranged at both ends in the 2032 type coin cell, and a separator (polypropylene) is interposed between the positive electrode and the negative electrode. A non-woven fabric) was inserted to produce a lithium ion battery cell. An electrolyte solution obtained by dissolving LiPF ₆ at a ratio of 12 wt% in a mixed solvent of ethylene carbonate (EC) and diethyl carbonate (DEC) (volume ratio 1: 1) was poured into the prepared lithium ion battery cell. The solution was sealed to obtain a lithium ion battery of the present invention and a comparative lithium ion battery. The obtained lithium ion battery was evaluated for initial efficiency and charge / discharge cycle characteristics by the following method, and the results are shown in Table 2. The larger the initial efficiency, the smaller the irreversible capacity and the better the battery characteristics. The larger the charge / discharge cycle characteristics, the better the charge / discharge cycle characteristics and the larger the battery capacity.

<Evaluation of initial efficiency and charge / discharge cycle characteristics>
Using a charge / discharge measuring device “Battery Analyzer 1470” [manufactured by Toyo Technica Co., Ltd.], charge to 0 V with a current of 0.1 C, and after a pause of 10 minutes, adjust the battery voltage to 3 with 0.1 C The battery was discharged to 0.0 V, and this charge / discharge was repeated. At this time, the battery capacity at the first charge and the battery capacity at the 30th cycle charge were measured, and the irreversible capacity and charge / discharge cycle characteristics were calculated from the following equations.
Initial efficiency (%) = (initial discharge capacity / initial charge capacity) × 100
Charging / discharging cycle characteristics (%) = (battery capacity at the 50th cycle charge / battery capacity at the first charge) × 100

  If the negative electrode material of the present invention is used, the initial efficiency can be greatly improved, and the irreversible capacity can be reduced (Examples 12 to 23). In Comparative Example 2 in which the reduction treatment was performed using alkyllithium, the initial efficiency was improved, but the cycle characteristics were deteriorated. This is presumably because an alkyl group is introduced on the surface of the active material and the alkyl group inhibits the charge / discharge reaction. On the other hand, since the negative electrode material of the present invention does not inhibit the charge / discharge reaction, it is considered that the cycle characteristics were not deteriorated. Moreover, it turned out that an irreversible capacity | capacitance can be reduced effectively also by the manufacturing method which performs a reduction process simultaneously with a negative electrode manufacturing process (Example 23).

  The negative electrode material of the present invention can provide a lithium ion battery having a large battery capacity and a small irreversible capacity. The production method of the present invention can safely produce a negative electrode material having a large battery capacity and a small irreversible capacity.

Claims (9)

  A negative electrode material obtained by reducing a reducible functional group (X) present on the surface of a carbon material with an organic reducing agent (A).   The negative electrode material according to claim 1, wherein the reducible functional group (X) is a carboxyl group and / or a carbonyl group.   Reducing organic acid (A1) in which organic reducing agent (A) does not contain formyl group, reducing organic acid ester (A2) not containing formyl group, reducing organic acid salt (A3) and formyl group not containing formyl group The negative electrode material according to claim 1 or 2, which is at least one selected from the group consisting of the containing compound (A4).  The negative electrode material according to claim 1, wherein the reduction ratio of the reducible functional group (X) is 3% or more.  The negative electrode for lithium ion batteries containing the negative electrode material of any one of Claims 1-4.   The lithium ion battery containing the negative electrode for lithium ion batteries of Claim 5.  The carbon material is subjected to a heat treatment in the presence of the organic reducing agent (A), and the reducible functional group (X) present on the surface of the carbon material is subjected to a reduction treatment. The manufacturing method of negative electrode material of description.   The manufacturing method according to claim 7, wherein the weight ratio of the organic reducing agent (A) to the carbon material is 0.001 to 50% by weight. The manufacturing method according to claim 7 or 8, wherein the temperature of the heat treatment is 80 to 250 ° C.