JP2008198568A - Manufacturing method of negative electrode material for lithium secondary battery, negative electrode material for lithium secondary battery manufactured by manufacturing method, and lithium secondary battery using negative electrode material - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing method of a lithium secondary battery of a long cycle life which can be mass produced at low cost, easily, and safely, and in which decreasing tendency of cycle characteristics is alleviated while retaining high discharge capacity, and the lithium secondary battery manufactured by this manufacturing method. <P>SOLUTION: This is the manufacturing method of a negative electrode material which, by preparing an acidic solution containing metal ion of either Sn ion or Sb ion, or both the Sb ion and the Sn ion, by mixing while putting carbon material into the acidic solution, and by carrying out heat treatment in a prescribed atmosphere containing at least one kind of gas selected from a group consisting of nitrogen, argon, helium, carbon dioxide, and nitrogen dioxide to a dried object obtained while carrying out drying treatment, the manufacturing method of the negative electrode material which is surface-modified by metal or metal compound formed by the metal ion in a carbon material, the negative electrode material for the lithium secondary battery manufactured by the manufacturing method, and the lithium secondary battery using the negative electrode material are provided. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

    The present invention relates to a method for producing a negative electrode material for a lithium secondary battery, a negative electrode material for a lithium secondary battery produced by the production method, and a lithium secondary battery using the negative electrode material, and in particular, low cost and easy to control. The present invention relates to a method for producing a negative electrode material for a lithium secondary battery, a negative electrode material for a lithium secondary battery produced by the production method, and a lithium secondary battery using the negative electrode material.

    Although lithium secondary batteries are small, they have high charge / discharge capacity characteristics, and therefore are increasingly used in fields where importance is placed on miniaturization of electrical equipment such as electronics, communication, and biotechnology.

    Conventionally, various carbon materials such as graphite and carbon having low crystallinity have been widely used as negative electrodes for lithium secondary batteries. However, a negative electrode made of a carbon material has a low usable current density and an insufficient theoretical capacity. For example, when only graphite, which is one of the carbon materials, is used for the negative electrode, the theoretical capacity is as low as 372 mAh / g, and therefore, further increase in capacity is desired.

    On the other hand, development of a negative electrode material for a lithium secondary battery, which is a substance having a discharge capacity larger than that of a general-purpose carbon material and made of a material other than lithium metal, is desired. For example, elements such as tin and silicon, nitrides and oxides thereof can form an alloy with lithium and occlude lithium, and the amount of occlusion is much larger than that of carbon materials. It has been proposed to develop an alloy negative electrode.

For example, according to Non-Patent Document 1, glycerin is used as a solvent, and SbCl ₃ and SbCl ₂ · H ₂ O with a ratio of 5: 4 are put into a glycerin solvent to prepare a solution having an ionic concentration of 0.5M. To do. Then, MCMB (mesophase microsphere carbon) powder is put into the solution and stirred while cooling at a temperature of 0 to 1 ° C., and at the same time, zinc powder as a reducing agent is added, washed with an alcohol solution, filtered and placed in an oven. If it heat-drys at the temperature of 55 degreeC, the negative electrode material by which the surface modification of Sb and Sn metal with a particle size of 100 nm or less with MCMB carbon material can be obtained.

According to the measurement, the negative electrode material produced by this method has a discharge capacity of 420 mAh / g. However, in this method, since zinc powder is used as a reducing agent, it is costly to remove the zinc powder by filtration. In addition, since SbCl ₂ · H ₂ O is used in the method, antimony hydroxide or tin hydroxide that easily absorbs moisture may be generated in the course of the reaction. May be affected by moisture and performance may be degraded. Furthermore, the particle size of the Sb and Sn metals that modify the surface of the negative electrode material is already at the nm level, and may react with oxygen in the atmosphere to oxidize, thereby reducing the performance. The possibility of such performance degradation can be avoided by isolating the negative electrode material from moisture and air, but this further increases the cost.

    Non-Patent Document 2 discloses a negative electrode material that modifies the surface by spraying nickel particles having a particle size of about 300 nm on the surface of a graphite material using a hydroterm hydrogen reduction method. However, since this production method uses high-pressure hydrogen at a high temperature, its danger cannot be ignored.

    Further, even when a carbon material whose surface is modified with these metals is used as a negative electrode material, the electrode expands and contracts with the insertion and extraction of lithium during repeated charge and discharge cycles, and the electrode itself There is a risk of demolition.

To deal with this problem, Non-Patent Document 3 mixes a 0.06M SnCl ₂ aqueous solution and a 0.02M SbCl ₃ aqueous solution, and puts a nanocarbon tube into the mixed aqueous solution, and then KBH as a metal reducing agent. A method is disclosed in which ₄ is added little by little, and a negative electrode material is obtained by filtration and drying. The negative electrode materials thus produced are two types of nanocarbon tubes that are surface-modified with appropriate amounts of Sb and SnSb _0.5 , respectively, and have discharge capacities of 462 mAh / g and 518 mAh / g, respectively. And, even after lithium secondary batteries using these negative electrode materials have undergone 30 cycles of charge / discharge, they have a cycle life superior to those made of nanocarbon tubes that are not surface-modified or alloys of Sn and Sb. ing.

However, the lithium secondary battery using the negative electrode material disclosed in Non-Patent Document 3 still shows a clearly decreasing tendency in the cycle characteristics under normal use (see FIG. 1).
Lihong Shi, Hong Li, Zhaoxiang Wang, Xuejie Huang and Liquan Chen, J. Mater. Chem, 11 (2001) 1502 Lihong Shi, Qing Wang, Zhaoxiang Wang, Xuejie Huang and Liquan Chen, Journal of Power Sources, 102 (2001) 60-67 Wei Xiang Chen, Jim Yang Lee and Zhaolin Liu, Carbon, 41 (2003) 959

    As described above, although the lithium secondary battery has already been put into practical use, there are still many points to be improved, and the present invention can be mass-produced easily and safely at a low cost and has a high discharge capacity. The present invention provides a method for manufacturing a lithium secondary battery having a long cycle life, and a lithium secondary battery manufactured by this manufacturing method.

  As described above, the technology for surface modification of carbon materials with metal is to prepare an environment in which reduction reaction to return all metal compounds to metal is easy to occur, and to be suitable for lithium secondary batteries. This is a method for manufacturing a material, and although improvements have been seen in some places, it has not been possible to obtain a revolutionary and totally advanced method. On the other hand, the inventors of the present invention can reverse the idea and obtain a negative electrode material more suitable for a lithium secondary battery if the environment of the reduction reaction for returning the metal compound to the metal is unfavorable for the reaction. I experimented to see if I could do it, and I was able to obtain excellent results.

That is, according to the inventors, the present invention prepares an acidic solution containing Sb ions, Sn ions, or metal ions of both Sb ions and Sn ions, mixes the carbon material in the acidic solution, and performs a drying treatment. by performing a heat treatment in a predetermined atmosphere containing a done by can drying product _{N 2, Ar 2, He 2} , CO 2, at least one et gas selected from the group consisting of NO _2, by the metal ions in the carbon material Provided is a method for producing a negative electrode material for a lithium secondary battery, which produces a negative electrode material for a lithium secondary battery that is surface-modified with the formed metal or metal compound.

In the method for producing a negative electrode material for a lithium secondary battery of the present invention, the concentration of metal ions in the acidic solution is preferably 0.01 M or more and less than or equal to a saturation concentration, and more preferably 2 M.

  In the method for producing a negative electrode material for a lithium secondary battery of the present invention, the amount of metal ions in the acidic solution is preferably 0.185 mol or less per gram of the carbon material added, and is 0.001 to 0.185 mol. Is more preferable, and 0.005 to 0.185 mol is particularly preferable.

  In the method for producing a negative electrode material for a lithium secondary battery according to the present invention, the acidic solution preferably includes an acid as a solute, a solvent, and a precursor capable of forming the metal ion when dissolved in the acid. .

  The acid is preferably composed of at least one acid selected from the group consisting of formic acid, benzoic acid, sulfuric acid, hydrochloric acid, fluoroboric acid, acetic acid, and nitric acid, and among them, hydrochloric acid is more preferable.

  The solvent is preferably composed of at least one solvent selected from the group consisting of water, alkanes, ketones, aldehydes, alcohols, ethers, benzene, toluene, xylene, and kerosene. Ethane, propane, pentane, acetone, butanone, n -Methyl-2--2-pyrrolidone, methyl alcohol, ethyl alcohol, propyl alcohol, butyl alcohol, pentyl alcohol, isopropanol, butanal, more preferably consisting of at least one solvent selected from the group consisting of 2-ethyl ether, Isopropanol is particularly preferred.

  The precursor is preferably made of at least one substance selected from the group consisting of Sb compounds, Sb metals, Sn compounds, and Sn metals.

  The Sb compound is preferably composed of at least one substance selected from the group consisting of antimony chloride, antimony sulfate, and antimony borofluoride, and among them, it is more preferable to use antimony chloride.

  The Sn compound is preferably made of at least one substance selected from the group consisting of divalent tin chloride, tetravalent tin chloride, tin sulfate and tin borofluoride, and among them, divalent tin Tin chloride or tetravalent tin chloride is more preferred.

  In the method for producing a negative electrode material for a lithium secondary battery of the present invention, the carbon material is a group consisting of mesophase graphite powder (MGP), mesophase microsphere carbon powder, spherical carbon material, artificial graphite material, natural graphite material, and nanocarbon tube. It is preferable to use at least one carbon material selected from the above, and it is more preferable to use mesophase graphite powder or natural graphite material.

  In the method for producing a negative electrode material for a lithium secondary battery of the present invention, the predetermined atmosphere is preferably nitrogen, and more preferably hydrogen is further contained in the atmosphere.

When hydrogen is contained in the atmosphere, the hydrogen concentration is preferably 3 VOL% or less.
The atmospheric pressure is preferably 10 ⁻² Torr or less.

  In the method for producing a negative electrode material for a lithium secondary battery of the present invention, the heat treatment is preferably performed at a temperature within a range of 200 to 800 ° C, and more preferably within a range of 350 to 700 ° C.

  The heat treatment is preferably performed for 10 to 300 minutes, more preferably 10 to 120 minutes, and particularly preferably 120 minutes.

  Moreover, this invention also provides the lithium secondary battery using the negative electrode material for lithium secondary batteries manufactured by the said manufacturing method, and this negative electrode material for lithium secondary batteries.

    According to the above method for producing a negative electrode material for a lithium secondary battery, the present invention does not use special equipment or raw materials and does not require a purification procedure. A method for producing a negative electrode material for a lithium secondary battery having a high level of discharge capacity and cycle characteristics in a lithium secondary battery produced using the negative electrode material, and the production method A negative electrode material for a lithium secondary battery and a lithium secondary battery using the negative electrode material can be provided.

  The present invention provides a dried product obtained by preparing an acidic solution containing Sn ions, Sb ions, or both Sb ions and Sn ions, mixing a carbon material in the acidic solution, and performing a drying treatment. By a heat treatment in a predetermined atmosphere containing at least one gas selected from the group consisting of nitrogen, argon, helium, carbon dioxide, and nitrogen dioxide, by the metal or metal compound formed on the carbon material by the metal ions This is a method for producing a surface-modified negative electrode material.

  The acidic solution is preferably composed of an acid as a solute, a solvent, and a precursor that forms the metal ion (either Sn ion, Sb ion, or both) when dissolved in the acid.

Therefore, the acidic solution can be obtained by purchase or simple preparation.
Further, there are no particular restrictions on the types and amounts of metal ions, acids, and solvents used in the acidic solution, and the selection and setting of the atmosphere in production. It can be set appropriately according to the cost, convenience of material procurement, convenience in the manufacturing process, and planned performance of the lithium secondary battery to be manufactured at the end. Selection and usage of materials introduced below It should be noted in advance that the concentration, temperature setting, etc. are merely examples, and are not necessary limitations for the present invention.

  The acid used in the acidic solution is preferably composed of at least one acid selected from the group consisting of formic acid, benzoic acid, sulfuric acid, hydrochloric acid, fluoroboric acid, acetic acid, and nitric acid. Specific examples of the present invention introduced below In each example, hydrochloric acid is used.

  The precursor used in the acidic solution is preferably composed of at least one substance selected from the group consisting of Sb compounds, Sb metals, Sn compounds, and Sn metals. When the Sb compound is selected, it is preferably made of at least one substance selected from the group consisting of antimony chloride, antimony sulfate, and antimony fluoride. When the Sn compound is selected, it is preferably made of at least one substance selected from the group consisting of divalent tin chloride, tetravalent tin chloride, tin sulfate, and tin borofluoride. In the specific examples of the present invention introduced below, divalent tin chloride, tetravalent tin chloride, antimony chloride, and a mixture of tetravalent tin chloride and antimony chloride. Select.

The solvent used for the acidic solution is preferably composed of at least one solvent selected from the group consisting of water, alkanes, ketones, aldehydes, alcohols, ethers, benzene, toluene, xylene, kerosene, ethane, propane, pentane, Consists of at least one solvent selected from the group consisting of acetone, butanone, n-methyl-2--2-pyrrolidone, methyl alcohol, ethyl alcohol, propyl alcohol, butyl alcohol, pentyl alcohol, isopropanol, butanal, and 2-ethyl ether. It is more preferred that isopropanol be used in each of the specific embodiments of the present invention introduced below.

  The concentration of metal ions in the acidic solution should not exceed the saturation concentration, but is preferably 0.01 M or more and less than or equal to the saturation concentration. In each of the specific embodiments of the present invention introduced below, 2M is set.

  In the method for producing a negative electrode material for a lithium secondary battery of the present invention, the carbon material is a group consisting of mesophase graphite powder (MGP), mesophase microsphere carbon powder, spherical carbon material, artificial graphite material, natural graphite material, and nanocarbon tube. It is preferable that the material is made of at least one carbon material selected from the above. In each specific example of the present invention introduced below, mesophase graphite powder and natural graphite material are selected.

  The amount of acid used in the acidic solution may be an amount sufficient to dissolve the precursor as described above. In the acidic solution, the absolute amount of the precursor other than the concentration of the precursor, in particular, the amount of the precursor used relative to the amount of the carbon material added is the last in each example of the present invention introduced below. According to the test results of the test cell fabricated in the above, the performance of the lithium ion battery is greatly affected, and the amount of the precursor used relative to the surface area of the carbon material added may also affect the battery performance. There are no particular restrictions on the amount of precursor used in the acidic solution and the amount of precursor used relative to the amount of carbon material used, but as a reference, in the specific examples of the present invention introduced below, According to the test results of the prepared test cell, the amount of metal ions in the acidic solution is preferably 0.185 mol or less per gram of the carbon material introduced. Properly, more preferably 0.001 to 0.185 mol, the result that particularly preferably from 0.005 to 0.185 mol is obtained.

Further, in the method for producing a negative electrode material for a lithium secondary battery of the present invention, the atmosphere during the heat treatment is limited to include at least one gas selected from the group consisting of nitrogen, argon, helium, carbon dioxide, and nitrogen dioxide. However, this is to prevent oxidation of the dried product, and it should be avoided as much as possible that the atmosphere contains moisture and oxygen. Moreover, the atmospheric pressure of the atmosphere can be suppressed to 10 ⁻² Torr or less to prevent oxidation of the dried product. In each of the specific examples of the present invention introduced below, nitrogen is used.

  In addition, if hydrogen is contained in the atmosphere, there is a risk of explosion when heat treatment is performed. Therefore, it is preferable to suppress the hydrogen concentration to 3 VOL% or less. The atmosphere can also contain other reducing agents.

  Further, in the method for producing a negative electrode material for a lithium secondary battery of the present invention, the heat treatment time and temperature are not particularly limited, but the time is preferably 10 to 300 minutes, preferably 10 to 120 minutes. More preferably, it is set to 120 minutes in each of the specific embodiments of the present invention introduced below. About the temperature, it is preferable to carry out at the temperature within the range of 200-800 degreeC, and in each concrete Example of this invention introduced below, for comparison, 350 degreeC, 450 degreeC, and 550 degreeC , Heat treatment at 650 ° C. is selectively performed. According to the inventor's estimation, the reaction rate of the heat treatment is increased at a high temperature. Therefore, the treatment time can be shortened by increasing the treatment temperature. Since the acid group of the acid in the acidic solution is vaporized by the heat treatment, the inventors have speculated that the start of a decrease in the amount of gas to be vaporized can be regarded as a go-ahead that stops the heat treatment.

The following describes a method for producing a negative electrode and a lithium secondary battery using the negative electrode material produced by the above method. In addition, the following description is an illustration and this invention is not restrict | limited by the following description.

  First, FIG. 2 is a schematic diagram showing a configuration of a general coin-shaped lithium secondary battery. As shown in the drawing, the lithium secondary battery 1 includes an upper case portion 11 and a lower case portion 12. A spring unit 13 housed in a sealed space defined between them, a stainless steel plate 14 pressed against the lower case portion 12 from the spring unit 13, a negative electrode 15, a separator 16, and a positive electrode 17 And an electrolytic solution that evenly fills the sealed space. In the present invention, the spring unit 13, the stainless steel plate 14, the separator 16, and the positive electrode 17 can adopt conventional techniques, and the following detailed description is given as an example. There are no particular restrictions on use.

<Manufacture of negative electrode>
The negative electrode material produced according to the present invention is mixed with a conductive agent and a binder, mixed and stirred to form a slurry, and this slurry is applied to a foil-like current collector to form a negative electrode. After this electrode is dried, the discharge capacity of the battery to be produced can be improved by pressing as necessary.

  As a conductive agent, a binder, a solvent, and a current collector, they can be suitably employed according to conventional techniques. For example, carbon black and nanofibers are generally used as the conductive agent, and 0 to 10% by weight can be added to the entire slurry. Further, the coating thickness of the slurry is preferably 20 to 350 μm.

  As the binder, those having high chemical stability and high voltage stability in the electrochemical field with respect to the electrolytic solution are preferably used. For example, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (polytetrafluoroethylene) ), Fluorinated polymers such as polyethylene, polyvinyl alcohol, polyolefins such as styrene / butadiene rubber, and fibrous materials such as carboxymethylcellulose, or combinations thereof. Moreover, as the usage-amount, it can add 1 to 10% by weight ratio with respect to a negative electrode material.

  As the solvent, water, n-methylpyrrolidone, dimethylformamide, and alcohols such as alcohol and isopropanol, or combinations thereof can be used. In particular, n-methylpyrrolidone is most widely used. Moreover, as the usage-amount, it can use according to the conventional technique as needed.

  As the current collector, metals such as copper and nickel can be used. There is no restriction | limiting in particular about the shape, Generally, what was formed in foil shape and net shape is used. The size (for example, length, width, thickness, weight, etc.) can be formed as necessary, but the thickness is preferably 5 to 20 μm.

<Production of positive electrode>
The manufacturing method of the positive electrode is almost the same as that of the negative electrode. Instead of the negative electrode material, a positive electrode material made of a lithium transition metal composite oxide material such as Ti, V, Cr, Mn, Fe, Co, Ni, Zn, Al, Sn is used. use. If necessary, the positive electrode material may further contain other components such as lithium carbonate, or foil-like metallic lithium may be used without using a lithium transition metal composite oxide material.

<Manufacture of separator>
The main function of the separator 16 is insulation, which prevents the short circuit in the battery and improves safety, yet allows lithium ions to pass between the positive and negative electrodes. The separator suitable for the present invention is not particularly limited, and for example, a porous sheet or a non-woven fabric made of a polyolefin such as polyethylene or polypropylene that is generally employed can be used.

  The material and shape of the separator are not particularly limited. The separator is separated so that the positive electrode and the negative electrode do not come into physical contact with each other, and preferably has high ion permeability and low electrical resistance. The separator is preferably selected from materials that are stable with respect to the electrolyte and excellent in liquid retention. As a specific example, the said electrolyte solution can be impregnated using the porous sheet or nonwoven fabric which uses polyolefin, such as polyethylene and a polypropylene, as a raw material.

<About production of electrolyte>
As the electrolytic solution, a solution obtained by dissolving an electrolyte as a solute in a non-aqueous solvent is used. As the solute, it is preferable to use one or more compounds selected from the group consisting of LiPF ₆ , LiBF ₄ , LiCF ₃ SO ₃ , and LiN (CF ₃ SO ₂ ) ₂ . Among them, the LiPF ₆ and LiBF _4, and it is more preferable to use a mixture of LiPF ₆ and LiBF _4. And about the density | concentration of electrolyte, 0.1-1.5M is preferable, and it is still more preferable that it is 0.5-1.2M.

  As the nonaqueous solvent, a liquid one can be used. Examples of the liquid nonaqueous solvent include carbonates such as ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate, tetrahydrofuran, diethyl ether, methyl sulfolane, Acetonitrile, propanenitrile, etc. can be used. One type of solute and solvent may be selected and used, or two or more types may be mixed and used.

  The nonaqueous electrolytic solution may contain an organic polymer compound in the electrolytic solution, and may use a solid solvent in the form of a gel, rubber, or solid sheet. Specific examples of organic polymer compounds include polyether polymer compounds such as polyethylene oxide and polypropylene oxide; crosslinked polymers of polyether polymer compounds; vinyl alcohol polymer compounds such as polyvinyl alcohol and polyvinyl butyral; vinyl Insoluble matter of alcohol polymer compound; polyepichlorohydrin; polyphosphazene; polysiloxane; vinyl polymer compound such as polyvinylpyrrolidone, polyvinylidene carbonate, polyacrylonitrile; poly (ω-methoxyoligooxyethylene methacrylate), poly (ω -Methoxyoligooxyethylene methacrylate-co-methyl methacrylate) and the like.

  As a specific method for preparing the electrolytic solution, for example, it can be obtained by dissolving an electrolyte in a liquid non-aqueous solvent. In the case of a solid solvent, first dissolve the electrolyte and the solid solvent in an organic solvent such as alkane, ketone, aldehyde, alcohol, ether, benzene, toluene, xylene, kerosene, and mix well, then heat to evaporate the organic solvent and use the electrolyte solution. You can

Then, each Example of this invention and the comparative example for performing a charge / discharge test are demonstrated. The material used for preparation of the negative electrode material of each Example and a comparative example is as follows.
Acid: hydrochloric acid, manufactured by Merck, Germany, purity 37%
Solvent: Isopropanol, manufactured by Merck, Germany, purity 99.8%
Carbon material: Mesophase graphite powder or natural graphite, Taiwan Central Steel Carbon Chemical Co., Ltd. Precursor: SbCl ₃ , SHOWA, purity 99.5%
Precursor: SnCl ₄ , manufactured by Showa, purity 98%
_Precursor: SnCl 2, SHOWA Co., Ltd., purity of 98%
Conductive agent: Carbon black, manufactured by TIMACAL, product number Super-S
[Example 1]
(A) Hydrochloric acid and isopropanol are mixed at a volume ratio of 1: 1, and the precursor SbCl ₃ is added to prepare a 2.0 M concentration SbCl ₃ acidic solution.
(B) 60 g of MGP carbon material that had been dehydrated at 110 ° C. for 2 hours in advance was mixed with 465 ml of the acidic solution (the amount of metal ions in the acidic solution per 1 g of MGP carbon material was 0.0155 mol). After stirring for 8 hours, transfer to an oven set at a temperature of 100 ° C. and dry until a solid dry product is obtained.
(C) After putting the obtained dried product into a crucible, the crucible is transferred to a high-temperature furnace with a nitrogen atmosphere set at 450 ° C., heat treated for 120 minutes, and taken out after natural cooling to be used as a negative electrode material. .

  When the negative electrode material obtained in Example 1 was subjected to SEM analysis with a scanning microscope (manufactured by JEOL Japan, product number JSM-6340F) and the surface was observed at a magnification of 5000 times, an image as shown in FIG. 3 could be observed. .

[Examples 2 to 17]
In Examples 2-17, the usage-amount of each material is changed and a negative electrode material is manufactured using the manufacturing method substantially the same as Example 1. FIG.

[Example 2]
The precursor used in the procedure (A) is changed to SnCl ₄ , natural graphite is used instead of the MGP carbon material in the procedure (B), and the amount of the acidic solution used is 233 ml (metal ions in the acidic solution per 1 g of natural graphite). In the amount of 0.0078 mol).

[Example 3]
Prepare 233 ml of two kinds of acidic solutions with the precursors SbCl ₃ and SnCl ₄ respectively by the method of the procedure (A) and mix them to prepare an acidic solution with a volume of 466 ml and a concentration of 1M each of SbCl ₃ and SnCl ₄ To do. In step (B), natural graphite is used instead of the MGP carbon material (that is, the amount of metal ions in an acidic solution is 0.0155 mol per 1 g of natural graphite).

[Example 4]
Changing procedure precursor used in (A) to SnCl _2, using natural graphite instead of MGP carbon material in step (B), and, the metal in the natural graphite per acidic solution of the amount 233 ml (1 g of an acidic solution ionic In the amount of 0.0078 mol).

[Example 5]
In step (B), the usage amount of the acidic solution is changed to 930 ml (the amount of metal ions in the acidic solution per 1 g of MGP carbon material is 0.0031 mol).

[Example 6]
In step (B), the usage amount of the acidic solution is changed to 1395 ml (the amount of metal ions in the acidic solution per 1 g of MGP carbon material is 0.00465 mol).

[Example 7]
In step (B), the usage amount of the acidic solution is changed to 2790 ml (the amount of metal ions in the acidic solution per 1 g of MGP carbon material is 0.0093 mol).

[Example 8]
In step (B), the usage amount of the acidic solution is changed to 4185 ml (the amount of metal ions in the acidic solution per 1 g of MGP carbon material is 0.01395 mol).

[Example 9]
In step (B), the amount of acidic solution used is changed to 5580 ml (the amount of metal ions in the acidic solution per 1 g of MGP carbon material is 0.0186 mol).

[Example 10]
The precursor used in the procedure (A) is changed to SnCl ₄ , natural graphite is used instead of the MGP carbon material in the procedure (B), and the amount of the acidic solution used is 466 ml (metal ions in the acidic solution per 1 g of natural graphite). In the amount of 0.0155 mol).

[Example 11]
The precursor used in the procedure (A) is changed to SnCl ₄ , natural graphite is used instead of the MGP carbon material in the procedure (B), and the amount of the acidic solution used is 700 ml (metal ions in the acidic solution per 1 g of natural graphite). To 0.023 mol).

[Example 12]
The precursor used in the procedure (A) is changed to SnCl ₄ , natural graphite is used in place of the MGP carbon material in the procedure (B), and the amount of the acidic solution used is 933 ml (metal ions in the acidic solution per 1 g of natural graphite). In the amount of 0.0311 mol).

[Example 13]
The precursor used in procedure (A) is changed to SnCl ₄ , natural graphite is used in place of MGP carbon material in procedure (B), and the amount of acidic solution used is 1866 ml (metal ions in acidic solution per 1 g of natural graphite). In the amount of 0.0622 mol).

[Example 14]
In step (C), the heat treatment temperature is set to 350 ° C.

[Example 15]
In step (C), the temperature of the heat treatment is set to 550 ° C.

[Example 16]
In step (C), the temperature of the heat treatment is set to 650 ° C.

[Example 17]
In the procedure (B), natural graphite is used instead of the MGP carbon material.

[Comparative Examples 1 and 2]
In Comparative Examples 1 and 2, a negative electrode material is manufactured using substantially the same manufacturing method as in Example 1. In Step (A), no precursor is added, and MGP carbon material and natural graphite are used as carbon materials, respectively. use.

  When the negative electrode material obtained in Comparative Example 1 is subjected to SEM analysis with a scanning microscope and the surface is observed at a magnification of 5000 times, an image as shown in FIG. 4 can be observed.

Comparing FIG. 3 and FIG. 4, a clear difference can be found on the surface of these negative electrode materials. The inventors have speculated that this difference is related to the presence or absence of metal ions in the acidic solution used. That is, the deposits scattered on the surface of the MGP carbon material in FIG. 3 are the metal formed by the metal ions or the compound thereof. And the negative electrode material obtained by the other Example should also have shown the surface state like FIG.

  Then, using the negative electrode material produced by each Example, the negative electrode for lithium secondary batteries using the following material, and the coin battery (lithium secondary battery) for charge / discharge test evaluation using this negative electrode Make it.

<Negative electrode>
Solvent: n-methyl-2--2-pyrrolidone (NMP, C ₅ H ₉ NO) manufactured by Aldrich, purity 99.5
Binder: PVDF, manufactured by Solef, product number 6020, molecular weight of about 304,000
Oxalic acid: manufactured by Showa, purity 99.0%
Current collector: Copper foil, manufactured by Nippon foil, thickness 15 μm
<Electrolyte>
Electrolyte: LiPF ₆ , manufactured by Ferro, purity 99.0%
Solvent: Ethylene carbonate and dimethyl carbonate, manufactured by Merck, Germany, 99% purity
<Other battery components>
Upper and lower case parts: Taiwan Koju Industrial Co., Ltd., product number 2032
Spring unit: Stainless steel plate manufactured by Taiwan Hoju Industry Co., Ltd. Plate: Taiwan Hoju Industry Co., Ltd. separator: Celgard, product number Celgard2300
Positive electrode: Lithium foil, manufactured by FMC, purity 99.9%, circular, diameter 1.65 cm
[Production of lithium secondary battery]
A lithium secondary battery is manufactured by the following manufacturing method using the negative electrode material obtained by each Example and each comparative example of the present invention, and their discharge capacity, discharge efficiency, and the like are compared.

First, a negative electrode material to be used, carbon black as a conductive agent, PVDF as a binder, and oxalic acid that prevents precipitation of fluorine ions in PVDF and improves the stability of PVDF are 90: 3: 6. 9: A solid mixture mixed at a weight ratio of 0.1 was mixed and stirred with n-methyl-2--2-pyrrolidone (NMP, C ₅ H ₉ NO) at a weight ratio of 51% based on the mixture. The slurry is coated on the copper foil to a thickness of 250 μm including the copper foil, and dried by an oven set at 110 ° C. (manufactured by Gaikichi Dryer Denki Co., Ltd.) for 2 hours to remain. NMP is removed to form an electrode. Thereafter, pressing is performed so that the electrode thickness becomes 75% of the original. Also, a 16 mmφ electrode is punched from the pressed electrode to complete the negative electrode.

Each negative electrode produced by the above electrode production method was vacuum-dried at 110 ° C. and then transferred to a glove box, and in an atmosphere containing water and oxygen of 10 ppm or less, ethylene carbonate (EC) / diethyl carbonate ( The coin cell for evaluation (lithium) was prepared so as to have the configuration shown in FIG. 2 using a 1M-LiPF ₆ electrolytic solution using a mixed solution of (DEC) = 1/1, a separator, and a lithium metal counter electrode as a counter electrode. Secondary battery) was produced.

<Charge / discharge test>
About the produced coin battery for each evaluation, the following discharge tests were performed, and the discharge capacity, initial charge / discharge efficiency, and cycle characteristics were calculated. The charge / discharge characteristics (discharge capacity, initial charge / discharge efficiency, and cycle characteristics) are shown in Table 2.

[Initial discharge capacity / Charge / discharge efficiency]
Constant current charging was performed until the circuit voltage reached 0.01 V at a current value of 0.326 mAcm ⁻² , and the charging capacity was determined from the amount of electricity applied during that time. Then, it rested for 10 minutes. Next, 0.326
A constant current discharge was performed until the circuit voltage reached 2.0 V at a current value of mA cm ⁻² , and the discharge capacity was obtained from the energization amount during this period. The initial charge / discharge efficiency was calculated from the following equation.

Initial charge / discharge efficiency (%) = (first cycle discharge capacity / first cycle charge capacity) × 100
In this test, the process of occluding lithium into the graphite particles was charged and the process of detaching was defined as discharge.

Moreover, the charge / discharge capacity per 1 g of carbon material was calculated from the following formula.
Charge / discharge capacity per 1 g of carbon material (mAh / g) = (discharge capacity at the first cycle / amount of carbon material used)
(Cycle characteristics)
The same procedure as the initial discharge capacity / charge / discharge efficiency is repeated 20 cycles, and the discharge capacity and charge / discharge efficiency are measured and recorded each time the charge / discharge cycle is performed, and the first and 20th cycles are recorded. Using the discharge capacity at, the cycle characteristics were calculated from the following equation.

Cycle characteristics at 20th cycle (%) = (discharge capacity at 20th cycle / discharge capacity at 1st cycle) × 100
In each example and comparative example, the type and amount of carbon material used, the temperature of heat treatment, the precursor used, the amount of acidic solution used, the initial (first cycle) release / charge capacity, the 20th cycle Refer to Table 1 below for data such as discharge capacity and cycle characteristics at the 20th cycle.

  Further, the graph of FIG. 5 shows changes in cycle characteristics of Comparative Example 1, Example 1, Example 6, Example 7, Example 8, and Example 9. The y-axis in the figure represents the discharge capacity, and the x-axis represents the number of cycles. FIG. 5 shows the effect of the change in the amount of the acidic solution used, that is, the change in the amount of Sb ion used when the MGP carbon material is used. As shown in FIG. Each of the examples shows better cycle characteristics than the comparative example. Among them, Example 1 (the amount of metal ions in an acidic solution per 1 g of MGP carbon material is 0.0155 mol) shows that it has a high discharge capacity and the most stable cycle characteristics. Example 6 of the next point (the amount of metal ions in an acidic solution per 1 g of MGP carbon material is 0.00465 mol) also has high cycle characteristics that are stable.

The graph of FIG. 6 shows changes in the cycle characteristics of Comparative Example 1 and Comparative Example 2, and Examples 1 and 17. The y-axis in the figure represents the discharge capacity, and the x-axis represents the number of cycles. This FIG. 6 shows the influence caused by the difference in using the MGP carbon material and natural graphite. As shown in the figure, Example 1 and Example 17 have differences in using the MGP carbon material and natural graphite, Both show stable cycle characteristics superior to those of Comparative Example 1 and Comparative Example 2. In the case of the present invention, a discharge capacity higher than that of natural graphite can be obtained by using an MGP carbon material.

  The graph of FIG. 7 shows changes in cycle characteristics of Comparative Example 2, Example 10, Example 11, Example 12, and Example 13. The y-axis in the figure represents the discharge capacity, and the x-axis represents the number of cycles. FIG. 7 shows the effect of the change in the amount of acidic solution used, that is, the change in the amount of Sb ion used when natural graphite is used. As shown in the figure, each example of the present invention is compared with the comparative example. It has excellent discharge capacity and cycle characteristics that greatly exceed.

  Example 9 is the only example that does not show stable cycle characteristics in the examples of the present invention, and the amount of the acidic solution used in Example 9 is conspicuous compared with other examples. . Moreover, although the usage-amount of the acidic solution of Example 8 is less than Example 9, although the acidic solution is used more than other Examples and the cycling characteristics are superior to Example 9, other examples and It is still lacking in stability. Therefore, the inventors have speculated that there is a specific value for obtaining the most excellent cycle characteristics in the usage amount of the acidic solution (or the usage amount of metal ions), and the metal in the acidic solution per 1 g of MGP carbon material. It is judged that more desirable cycle characteristics can be obtained when the amount of ions is within the range of 0.005 to 0.185 mol.

Further, referring to data of each example in Table 1, in the present invention, any of SnCl ₂ , SnCl ₄ , SbCl ₃ , or a mixture thereof can be used as a precursor. Then, referring to the data of Example 1, Example 14, Example 15, and Example 16, the temperature at which the heat treatment is performed also affects the cycle characteristics of the present invention, and the temperature at which the heat treatment is performed per 550 ° C. By setting, more ideal cycle characteristics can be obtained.

  In Tables 2 and 3 below, the amount of acidic solution used and the initial discharge capacity, the discharge capacity at the 20th cycle, the initial charge / discharge efficiency, the cycle characteristics at the 20th cycle, and the like are compared in each example. The numerical values subtracted from the example data are listed, and the data of each example is compared with the comparative example. The numerical value represented as “+” indicates a numerical value that is still positive even when subtracted by the data of the comparative example (that is, a numerical value higher than the data of the comparative example), and the numerical value represented as “-” is the data of the comparative example. It shows a numerical value that is negative when subtracted by (that is, a numerical value lower than the data of the comparative example).

    As described above, according to the method for manufacturing a negative electrode material for a lithium secondary battery, the present invention does not use special equipment or raw materials and does not require a purification procedure. A method for producing a negative electrode material for a lithium secondary battery having a high level discharge capacity and cycle characteristics in a lithium secondary battery produced using the negative electrode material, and a method for producing the same A negative electrode material for a lithium secondary battery manufactured by the above and a lithium secondary battery using the negative electrode material can be provided.

It is a graph which shows the cycling characteristics of the conventional lithium secondary battery. 1 is a schematic diagram illustrating a configuration of a general coin-shaped lithium secondary battery. It is a negative electrode material SEM photograph by Example 1 in this invention. It is a negative electrode material SEM photograph by the comparative example 1 in this invention. The graph which shows the change of the cycle characteristic of the comparative example 1, Example 1, Example 6, Example 7, Example 8, and Example 9. FIG. The graph which shows the change of the cycle characteristic of the comparative example 1 and the comparative example 2, Example 1 and Example 17. FIG. The graph which shows the change of the cycle characteristic of the comparative example 2, Example 10, Example 11, Example 12, and Example 13. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Lithium secondary battery 11 Upper case part 12 Lower case part 13 Spring unit 14 Stainless steel plate 15 Negative electrode 16 Separator 17 Positive electrode

Claims (30)

An acidic solution containing Sb ions, Sn ions, or metal ions of both Sb ions and Sn ions is prepared, a carbon material is put into the acidic solution, mixed, and dried to obtain a dried product obtained by N ₂ , Ar _2. By performing a heat treatment in a predetermined atmosphere containing at least one gas selected from the group consisting of He ₂ , CO ₂ , and NO ₂ ,
The manufacturing method of the negative electrode material for lithium secondary batteries which manufactures the negative electrode material for lithium secondary batteries by which the carbon material is surface-modified with the metal or metal compound formed with the said metal ion.   2. The method for producing a negative electrode material for a lithium secondary battery according to claim 1, wherein the concentration of metal ions in the acidic solution is 0.01 M or more and a saturation concentration or less.   The method for producing a negative electrode material for a lithium secondary battery according to claim 2, wherein the concentration of metal ions in the acidic solution is 2M.   2. The method for producing a negative electrode material for a lithium secondary battery according to claim 1, wherein the amount of metal ions in the acidic solution is 0.185 mol or less per gram of the charged carbon material.   5. The method for producing a negative electrode material for a lithium secondary battery according to claim 4, wherein the amount of metal ions in the acidic solution is 0.001 to 0.185 mol per gram of the charged carbon material.   6. The method for producing a negative electrode material for a lithium secondary battery according to claim 5, wherein the amount of metal ions in the acidic solution is 0.005 to 0.185 mol per gram of the charged carbon material.   The method for producing a negative electrode material for a lithium secondary battery according to claim 1, wherein the acidic solution comprises an acid as a solute, a solvent, and a precursor that forms the metal ion when dissolved in the acid. .   8. The negative electrode material for a lithium secondary battery according to claim 7, wherein the acid comprises at least one acid selected from the group consisting of formic acid, benzoic acid, sulfuric acid, hydrochloric acid, fluoroboric acid, acetic acid, and nitric acid. Production method.   The method for producing a negative electrode material for a lithium secondary battery according to claim 8, wherein the acid is hydrochloric acid.   The lithium secondary battery according to claim 7, wherein the solvent comprises at least one solvent selected from the group consisting of water, alkane, ketone, aldehyde, alcohol, ether, benzene, toluene, xylene, and kerosene. Manufacturing method for negative electrode material.   The solvent is selected from the group consisting of ethane, propane, pentane, acetone, butanone, n-methyl-2--2-pyrrolidone, methyl alcohol, ethanol, propanol, butyl alcohol, pentyl alcohol, isopropanol, butanal, 2-ethyl ether. The method for producing a negative electrode material for a lithium secondary battery according to claim 10, comprising at least one kind of solvent.   The method for producing a negative electrode material for a lithium secondary battery according to claim 11, wherein the solvent is isopropanol.   The method for producing a negative electrode material for a lithium secondary battery according to claim 7, wherein the precursor is made of at least one substance selected from the group consisting of Sb compounds, Sb metals, Sn compounds, and Sn metals.   The method for producing a negative electrode material for a lithium secondary battery according to claim 13, wherein the Sb compound is made of at least one substance selected from the group consisting of antimony chloride, antimony sulfate, and antimony borofluoride.   The method for producing a negative electrode material for a lithium secondary battery according to claim 14, wherein the Sb compound is antimony chloride.   The Sn compound is made of at least one substance selected from the group consisting of divalent tin chloride, tetravalent tin chloride, tin sulfate, and tin borofluoride. Manufacturing method of negative electrode material for lithium secondary battery.   The method for producing a negative electrode material for a lithium secondary battery according to claim 16, wherein the Sn compound is divalent tin chloride or tetravalent tin chloride.   The carbon material is composed of at least one carbon material selected from the group consisting of mesophase graphite powder (MGP), mesophase microsphere carbon powder, spherical carbon material, artificial graphite material, natural graphite material, and nanocarbon tube. The manufacturing method of the negative electrode material for lithium secondary batteries of Claim 1.   The method for producing a negative electrode material for a lithium secondary battery according to claim 18, wherein the carbon material is mesophase graphite powder or natural graphite material.   The method for producing a negative electrode material for a lithium secondary battery according to claim 1, wherein the predetermined atmosphere is nitrogen.   The method for producing a negative electrode material for a lithium secondary battery according to claim 20, wherein the predetermined atmosphere further contains hydrogen.   The method for producing a negative electrode material for a lithium secondary battery according to claim 21, wherein the hydrogen concentration in the atmosphere is 3 VOL% or less. The method for producing a negative electrode material for a lithium secondary battery according to claim 1, wherein the atmospheric pressure is 10 ⁻² Torr or less.   The method for producing a negative electrode material for a lithium secondary battery according to claim 1, wherein the heat treatment is performed at a temperature within a range of 200 to 800 ° C.   The method for producing a negative electrode material for a lithium secondary battery according to claim 24, wherein the heat treatment is performed at a temperature within a range of 350 to 700 ° C.   The method for producing a negative electrode material for a lithium secondary battery according to claim 1, wherein the heat treatment is performed for 10 to 300 minutes.   27. The method for producing a negative electrode material for a lithium secondary battery according to claim 26, wherein the heat treatment is performed for 10 to 120 minutes.   The method of manufacturing a negative electrode material for a lithium secondary battery according to claim 27, wherein the heat treatment is performed for 120 minutes.   The negative electrode material for lithium secondary batteries manufactured by any one of Claims 1-28.   A lithium secondary battery using the negative electrode material for a lithium secondary battery according to claim 29.