JP2007095641A - Battery constructing material - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrode active material coating agent capable of improving charge and discharge characteristics of a lithium ion secondary battery and increasing its capacity, by preventing decomposition of an electrolyte caused by charge and discharge for a long time. <P>SOLUTION: When manufacturing an electrode acting as the constituent material of the lithium ion battery, a high polymer solution having a kind of carboxymethylcellose sodium salt obtained by making graphite based carbon acting as an electrode active material dissolved and dispersed in water is used for electrode active material carbon as a coating agent to constitute a nonaqueous electrolyte lithium ion secondary battery. Thereby, since decomposition of the nonaqueous electrolyte can be prevented for a long time, a more excellent lithium ion secondary battery capable of keeping stable and good charge and discharge characteristics for a long time can be manufactured, in comparison with a nonaqueous electrolyte lithium ion secondary battery in which a carbon electrode is not coated with this coating agent, or a nonaqueous electrolyte lithium ion secondary battery using a coating agent containing no coating agent pertinent to this invention as the electrode active material. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention has a lithium ion secondary battery, a lithium battery, and other battery structures, where a coating material is used, where the electrolyte is composed of an electrolyte and a solvent, or It consists of electrolyte and polymer, or electrolyte, polymer and solvent. The electrode material includes a material containing an active material coated with a coating agent, a conductive agent, and a binder.

2. Description of the Related Art In recent years, electronic devices have become rapidly portable and cordless, and there is a strong demand for secondary batteries that are compact and lightweight and require high energy density as power sources for driving these devices. In this respect, non-aqueous secondary batteries, particularly lithium ion secondary batteries, are particularly expected as batteries having high voltage and high energy density.

  In particular, a battery system using a lithium composite oxide such as LiCoO 2 or LiNiO 2 as a positive electrode active material and a carbon material as a negative electrode material has recently attracted attention as a high energy density lithium ion secondary battery. The characteristics of this battery system are that the battery voltage is high and that both positive and negative electrodes use an intercalation reaction. Batteries using LiCoO 2 as a positive electrode and a carbon material as a negative electrode have already been commercialized. In the case of such a lithium ion secondary battery, since it is an important factor to perform the charge / discharge reaction uniformly, in most cases, a mixture in which both the positive electrode and the negative electrode include an active material in the current collector of the metal foil A sheet-like electrode plate coated with a layer is used. In addition, the current collector material is made of aluminum for the current collector metal foil for the current collector of the positive electrode and copper for the metal foil of the negative electrode because it is electrochemically stable at each operating potential when used in a battery. in use.

In the past, technical ingenuity has been made in order to prevent decomposition due to charging and discharging of nonaqueous aprotic solvents used in lithium ion secondary batteries.
A method of preventing the reductive decomposition of propylene carbonate (PC) and ethylene carbonate (EC) at the negative electrode interface by adding a certain organic substance to the electrolytic solution, and the graphite surface which is the negative electrode active material with toluene or ethylene by the CVD method. Conventionally, a method of preventing decomposition of PC or the like by contacting with graphite by making a certain carbon structure by pyrolysis, PC or the like by oxidizing a part of the graphite surface as the negative electrode active material or oxidizing etching There is a method for preventing decomposition of the aprotic solvent, or a method for preventing decomposition of the aprotic solvent by a method such as radiation polymerization of acrylic resin or application of ethylene oxide polymer to the surface of graphite, which is a negative electrode active material. Proposed and electrolyte-containing electrolytes have been implemented in graphite and electrolyte manufacturing companies that are negative electrode active materials

However, when producing a negative electrode for a lithium ion battery using a coating agent, the content is that the improved lithium ion battery that has been studied and improved environmentally has been maintained and has a higher capacity. There are few patents.
Moreover, it is preferable if the coating agent used is a very ordinary chemical. Therefore, it is possible to prevent the long-term decomposition of the aprotic solvent, which is a non-aqueous electrolyte used in the lithium-ion battery, by charging and discharging, and the long-term charging and discharging characteristics of the lithium-ion battery are improved. It is preferable if the lithium ion battery has high performance and high capacity.
Furthermore, if a normal electrolyte solution can be used or graphite, which is a normal negative electrode active material, can be used, it is possible to reduce manufacturing costs related to lithium battery manufacturing.

A lithium ion secondary battery is composed of a positive electrode and a negative electrode, an electrolyte solution, and a separation membrane. The positive electrode is composed of a positive electrode active material, a conductive agent, a binder, and a current collector metal foil film, and the negative electrode is a negative electrode active material. The material is composed of carbon such as graphite, binder, conductive agent and current collector metal foil film, and the electrolyte is composed of non-aqueous aprotic solvent and electrolyte. It is desirable if it is possible to prevent the aprotic solvent from being decomposed in the long term due to charging / discharging of the battery comprising the above, and thus to stabilize the increase in capacity. As a result of earnest research, the inventors have previously coated a carbon negative electrode active material with the carboxymethylcellulose alkali salt of the present invention, and applied the coated carbon negative electrode active material to a current collector metal thin film to form a lithium ion It was discovered that secondary batteries can prevent long-term degradation associated with charge and discharge of aprotic solvents such as propylene carbonate (PC) used, and electrolytes and batteries derived from the decomposition of aprotic solvents Generation of degradable organisms that adversely affect the characteristics can be prevented for a long period of time, and the charge-discharge characteristics of the lithium ion secondary battery using the coating agent of the present invention have been dramatically improved. Furthermore, the carboxymethylcellulose alkali salt coating agents and the polyaniline sulfonic acid mixture coating agents of the present invention are also water-soluble polymer binders that are excellent in terms of the environment, and therefore the metal thin film directly serving as the negative electrode current collector. It is also easy to apply to.

Here, production of a lithium ion battery positive electrode using polyaniline sulfonic acids has been successively presented at the American Electrochemical Society. As a result, a conventional manufacturing method in which polyvinylidene fluoride (PVDF) has been used as a binder resin, and a highly toxic solvent such as N-methylpyrrolidone (NMP) has been used as the solvent. It was found that polyaniline sulfonic acids can be used as the resin for the agent and water can be used as the solvent. When these polyaniline sulfonic acids are used, in the charge / discharge cycle test, there is no inferiority to lithium ions produced using polyvinylidene fluoride, and the amount of binder added is polyvinylidene fluoride (PVDF). The amount of positive electrode active material added per unit volume is reduced due to the large amount of addition required, so that the capacity per unit volume is limited, whereas polyaniline sulfonic acids are used. In this case, since the addition amount is small, the addition amount of the positive electrode active material per unit volume is increased, so that the capacity per unit volume is relatively increased.
As a result of diligent research by applying such conventional research and the invention described in the published patent publication (Japanese Patent Application Laid-Open No. 2003-142104) to a coating material for a negative electrode active material such as graphite, the performance of the battery is improved and the battery is manufactured. The electrode coating agent in consideration of the environmental aspect was found.

Next, preferred embodiments will be listed to describe the present invention in more detail. The electrolyte for non-aqueous electrolyte secondary batteries of the present invention is characterized by a method for forming a negative electrode material on a current collecting material and a negative electrode material selected by the method.

Examples of the current collector used in the present invention include metal foils such as aluminum and copper. The thickness of the metal foil is about 10 to 30 microns.

The dry thickness of the negative electrode layer applied to the metal foil current collector of the present invention is preferably in the range of 0.001 to 5 microns.

Examples of the positive electrode active material used in the present invention include lithium oxides such as LiCoO2, LiNiO2, and LiMn2O4, and one or more kinds of chalcogen compounds such as TiO2, MnO2, MoO3, and V2O5. On the other hand, as the negative electrode active material, natural graphite, synthetic graphite, and other carbon materials such as multilayer aromatic carbon are used. In particular, a lithium secondary battery having a high discharge voltage of about 4 V can be obtained by using LiCoO 2 as a positive electrode active material and a graphite-based active material as a negative electrode material.

In particular, in the present invention, when a metal foil such as a copper foil is used as the current collector and carbon is used as the negative electrode active material, the carbon active material is coated with a polymer so that the non-aqueous electrolyte is used during charge and discharge. It is possible to provide an electrode plate for a non-aqueous electrolyte secondary battery having stable battery characteristics over a long period of time.

These active materials are preferably dispersed uniformly in the coating layer to be formed. As the coating agent used for the preparation of the coating liquid containing the active material, a carboxymethyl cellulose alkali salt selected by the method of the present invention or a mixture of the polymer and other polymers can be used.

A specific method for adjusting the coating solution containing the active material used in the present invention will be described. First, a coating solution appropriately selected from the materials listed above and a powdered negative electrode active material are placed in a dispersion medium composed of a solvent such as water or a light solvent, and a conductive agent is mixed as necessary. The above composition is prepared by mixing and dispersing using a conventional dispersing machine such as a homogenizer, a ball mill, a sand mill, or a roll mill.

This active material coating solution is applied on the surface of the metal foil current collector by various coating methods in a dry thickness range of 10-200 microns, preferably 50-180 microns, and then dried by heating. .

Further, in order to further improve the homogeneity of the coating layer formed by coating and drying as described above, the coating layer is subjected to a press treatment using a metal roll, a heating roll, a sheet press machine, etc. It is preferable to form the electrode plate of the invention. Furthermore, before the battery assembly process using the above electrode plate, in order to remove moisture in the active material layer of the electrode plate, it is preferable to further perform heat treatment, decompression treatment, or the like.

When, for example, a lithium-based secondary battery is produced using the negative electrode nonaqueous electrolyte secondary battery electrode plate of the present invention produced as described above, a solute lithium salt is used as the electrolyte. A nonaqueous electrolytic solution dissolved in a solvent is used. Examples of the solute lithium salt that forms the non-aqueous electrolyte include inorganic lithium salts such as LiCLO4, LiBF4, LiPF6, LiAsF6, LiCl, LiBr, and LiB (C6H5) 4, LiN (SO2CF3) 2, LiC (SO2CF3). Organolithium salts such as 3, LiOSO2CF3, LiOSO2C2F5, LiOSO2C3F7, LiOSO2C4F9, LiOSO2C5F11, LiOSO2C6F13, LiOSO2C7F15 are used.

Examples of the organic solvent used in this case include cyclic esters, chain esters, cyclic ethers, chain ethers and the like. Examples of the cyclic esters include propylene carbonate, butylene carbonate, gamma butyrolactone, vinylene carbonate, 2-methyl-gamma butyrolactone, acetyl-gamma butyrolactone, and gamma valerolactone.

Examples of chain esters include dimethyl carbonate, diethyl carbonate, dibutyl carbonate, dipropyl carbonate, methyl ethyl carbonate, propionic acid alkyl ester, malonic acid dialkyl ester, and acetic acid alkyl ester.

Examples of cyclic ethers include tetrahydroquinone, alkyltetrahydrofuran, dialkylalkyltetrahydrofuran, alkoxytetrahydrofuran, dialkoxytetrahydrofuran, 1,3-dioxolane, alkyl-1,3-dioxolane, 1,4-dioxolane. Etc. Examples of chain ethers include 1,2-dimethoxyethane, 1,2-diethoxyethane, diethyl ether, ethylene glycol dialkyl ether, diethylene glycol dialkyl ether, triethylene glycol dialkyl ether, tetraethylene glycol dialkyl ether, and the like. Is mentioned.

The embodiment will be described.

The first embodiment will be described.
Example 1) The constituent materials of the battery structure were first determined as follows, and a battery was configured with these constituent materials and a charge / discharge test was performed.
Working electrode: Active material MCMB6-28 (Osaka Gas), Conductive agent: Acetylene black,
Coating agent and binder: Carboxymethylcellulose sodium salt Counter electrode: Lithium metal Separator: Glass wool Electrolyte: PC (propylene carbonate) / DMC (dimethyl carbonate)
: 1L (volume ratio: 1/3), electrolyte LiPF6 (phosphorus hexafluoride)
A solution containing 1 mol of lithium oxide Current collector: Working electrode: Copper foil, Counter electrode: SUS mesh

The second embodiment will be described.
Example 2 A battery was composed of the same constituent materials as in Example 1) except for the working electrode coating agent, and a charge / discharge test was conducted.
Working electrode: Active material MCMB6-28 (manufactured by Osaka Gas), conductive agent: acetylene black,
Coating agent and binder: carboxymethylcellulose sodium salt and polyaniline
Sulfonic acid counter electrode: Lithium metal separator: Glass wool Electrolyte: PC (propylene carbonate) / DMC (dimethyl carbonate)
1 L (volume ratio: 1/3) of electrolyte LiPF6 (1 mol of lithium hexafluorophosphate) current collector: working electrode: copper foil Counter electrode: SUS mesh

Comparative Example 1

The comparative example 1 will be described.
A battery was constructed with the same constituent materials as in Example 1) except for the working electrode coating material in Example 1), and a charge / discharge test was conducted.
Working electrode: active material: MCMB6-28, conductive agent: acetylene black,
Coating agent and binder: SBR water dispersion emulsion Counter electrode: Lithium metal Separator: Glass wool Electrolytic solution: PC (propylene carbonate) / DMC (dimethyl carbonate)
1 L (volume ratio: 1/3) and electrolyte solution LiPF6 (1 mol of lithium hexafluorophosphate mixed) Current collector: Working electrode: Copper foil, Counter electrode: SUS mesh

First, the electrode active material MCMB6-28 was coated using carboxymethyl cellulose sodium salt (CMCNa) or a mixture of carboxymethyl cellulose sodium salt (CMCNa) and polyaniline sulfonic acid (PAS) or styrene butadiene rubber aqueous dispersion emulsion (SBR) as a coating agent. . When the coating agent was CMCNa, 0.0371 gram of the coating agent CMCNa and 0.021 gram of the conductive agent were blended with 2.175 grams of the active material MCMB5-28.

When the coating agent was a CMCNa and PAS mixture, the active material MCMB6-28 was mixed with 4.403 grams of the coating agent CMCNa and PAS mixture 0.0828 grams and the conductive agent 0.0406 grams.

When the coating agent is SBR, a lithium ion secondary battery is manufactured in accordance with the case where the coating agent is CMCNa, except that 0.031 gram of SBR and 0.031 gram of conductive agent are used for 2.814 grams of MCMB6-28. Used for battery characteristics test.

The charge / discharge capacities in Example 1, Example 2 and Comparative Example 1 are shown in Table 1.

The invention's effect

As described above, according to the present invention, by covering the electrode active material with the carboxymethyl cellulose of the present invention as a coating agent, it is possible to prevent decomposition associated with charging and discharging of the non-aqueous electrolyte solution over a long period of time, The charge capacity is high and the charge / discharge characteristics can be stabilized for a long time.
On the other hand, in a lithium ion battery using carbon MCMB6-28 as the electrode active material and using a propylene carbonate (PC) electrolyte as the non-aqueous electrolyte, the charge / discharge voltage is about 0.8 volts, and propylene carbonate ( Since PC) is decomposed, the battery characteristics are naturally deteriorated.

Claims (9)

Lithium battery electrode active material coating agent comprising carboxymethylcelluloses whose coating agent is carboxymethylcellulose or carboxymethylcellulose alkali salt, other polymer and conductive agent Lithium battery electrode active material coating material comprising a cation exchangeable cellulose, a cation exchangeable cellulose derivative, a cation exchangeable ion exchange resin or an alkali salt thereof, another polymer, and a conductive agent. The other polymer is composed of polyaniline which is polyaniline or polyaniline sulfonic acid and other polymer. The other polymer is composed of polyaniline which is polyaniline or polyaniline sulfonic acid and other polymer. A lithium battery electrode comprising an electrode active material, an electrode active material coating agent according to claim 1, a binder, a conductive agent, and a current collector. A lithium battery comprising a negative electrode, a positive electrode, a separation membrane, an electrolyte, a battery case enclosing them, and a charge / discharge control device according to claim 5 A lithium battery comprising a positive electrode, a negative electrode, a separation membrane, an electrolyte, a battery case enclosing them, and a charge / discharge control device according to claim 5 A lithium battery comprising a negative electrode according to claim 5, a positive electrode according to claim 5, a separation membrane, an electrolytic solution, and a battery case enclosing them. A method for producing a lithium battery, wherein the method comprises producing a lithium battery comprising claim 6 or claim 7 or claim 8.