JP3452943B2 - Intercalate material / soluble conductive polymer material composite and electrode for secondary battery using the same - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an intercalating material / soluble conductive polymer material composite, a method for producing the composite, and a secondary battery characterized by using the composite as a positive electrode active material. .

[0002]

2. Description of the Related Art In recent years, lithium secondary batteries using lithium as a negative electrode active material have attracted attention as secondary batteries having high energy density. However, in order to make a lithium battery into a secondary battery, the cycle characteristics, formability, and high energy density of the positive electrode material are important issues as well as the improvement of the cycle characteristics by the negative electrode material, but it has been found that all requirements are sufficiently satisfied. It is not. The positive electrode active material used in this lithium secondary battery has hitherto been titanium (Ti), molybdenum (Mo), niobium (Nb), chromium (Cr), manganese (Mn), vanadium (V), cobalt (Co), Also, metal oxides such as nickel (Ni), chalcogen compounds or conductive polymer substances such as polyaniline and polypyrrole have been studied. However, when an inorganic active material such as the above inorganic chalcogen compound or an inorganic oxide is used for the positive electrode, the diffusion rate of cations in the electrode in the electrode reaction accompanying charging and discharging is slow, and the inorganic active material Since the electric conductivity is low, the electrode using it has a high internal impedance, which makes rapid charging and discharging difficult, and has the problem of poor reversibility with respect to overdischarge. In addition, as a possible electrode active material, there is a conductive polymer that can perform an electrode reaction by reversibly inserting and releasing anions. Since the conductive polymer is a plastic in terms of molding and processability, it can take advantage of the characteristics that have not existed in the past.
High cycle characteristics are exhibited even at a discharge depth of 00%.
However, the problem with this type of secondary battery is that the volume energy density is low due to the low density of the active material, and
When anion is taken in and out of the conductive polymer, the reaction of the negative electrode is a reaction of cation in and out, so an electrolyte sufficient in the electrolytic solution for the electrode reaction is necessary, and electrolysis with charge and discharge reaction Since the change in the liquid concentration is large, the change in the liquid resistance and the like is large, and an excessive amount of electrolytic solution is required for smooth charge and discharge reaction. This is also disadvantageous in improving the volumetric energy density. In order to solve these problems, there is a technique of kneading a positive electrode with a cationic intercalating type substance and a conductive polymer, and molding an electrode having advantages of each other, but it has not been made into a composite, When discharging at a high current, the cycle characteristics were not always good. Further, the conductive polymer has a problem that it repeats swelling and contraction by repeating charging and discharging, and finally cracks. Therefore, sufficient lithium secondary batteries with high energy density and high reliability have not yet been realized.

[0003]

[Object] To solve the above problems, the present invention provides a positive electrode active material having a low internal impedance, an excellent current collecting effect, a good cycle characteristic, and a high energy density that is durable even at a deep discharge depth. It is intended to provide a used secondary battery.

[0004]

[Structure] The inventors of the present invention have conducted extensive studies to solve the above-mentioned problems, and as a result, mixed a material for intercalating an electrolyte cation and a conductive polymer material and formed a composite active material with excellent workability. As a result of further studies, it was found that intercalating material / soluble conductive polymer composite particles in which particles of a material that intercalates electrolyte cations are coated with a soluble polymer are electrically conductive. High degree, low internal impedance, excellent workability,
Moreover, they have found that they have a performance as a high energy density electrode. That is, the present invention provides an intercalating material / soluble conductive polymer composite particle characterized by coating a material particle for intercalating an electrolyte cation with a soluble conductive polymer, and the composite particle. It is a secondary battery characterized by using the positive electrode formed by using the positive electrode, and further using the positive electrode.

The conductive polymer material according to the present invention has a capability as an active material, does not dissolve in an electrolytic solution, and has a binding property between conductive polymers. At this time, the intercalating material is completely covered with the conductive polymer material, so that the entire circumference of the intercalating material becomes conductive. The soluble conductive polymer in the present invention is a solvent-soluble polymer material, for example, the following formula (I)

[Chemical 1] (In the formula, at least one of R1 and R2 is an alkyl group or an alkoxyl group)

[Chemical 2]

[Chemical 3] [In the above formulas (II) and (III), R3 to R6 represent hydrogen, an alkyl group or an aryl group. Examples of the polymer of the polythiophene derivative represented by the above formula, polyaniline-based polymer, and the like can be given, but when considering the use of the composite as a battery electrode, a polyaniline-based polymer, particularly polyaniline, is preferable. All of these soluble conductive polymer materials have high electrical conductivity due to doping,
It is desirable to have an electrical conductivity of 0-3 S / cm or more. These soluble conductive materials have high electric conductivity, current collecting ability, binding ability, and further function as an active material.

Materials for intercalating the electrolyte cations in the present invention include transition metal oxides such as chromium (Cr), manganese (Mn), vanadium (V), and cobalt (Co), chalcogenite or transition metals. A phthalocyanine, which is a composite oxide with an alkali metal or an alkaline earth metal, is used. It is preferable to use those whose electrode potentials associated with the insertion and release of electrolyte cations of these substances are relatively close to the electrode potentials associated with the insertion and release of anions of the soluble conductive polymer. The intercalating material used in the present invention is preferably used in the form of powder or gel. In the case of powder, the particle size of the powder is 500 μm or less, preferably 1 to 200 μm. When it is 500 μm or more, the moldability and energy density of the electrode are lowered.

The composite particles may contain a conductive additive as a constituent of the positive electrode, if necessary. Conductive aids include acetylene black, aniline black,
Activated carbon, conductive carbon powder such as graphite powder, carbon body starting from polyacrylonitrile, pitch, cellulose, phenol, etc., carbon fiber, Ti, Sn, I
Examples thereof include metal oxide powders such as n, metal powders such as stainless steel and nickel, and fibers. As the properties required for these conductive aids, in addition to high electrical conductivity, an effect with a small addition amount is required.

Next, a method for producing composite particles of the intercalating material / soluble conductive polymer material of the present invention will be described. (1) Disperse intercalating material particles in a solution in which a soluble conductive polymer material is dissolved in a suitable solvent (A), and the dispersion liquid is compatible with the solvent (A) of the soluble conductive polymer. A method in which a solvent (B) is added and the soluble conductive polymer is coprecipitated with particles of the intercalating material, (2) a solution of the soluble conductive polymer material dissolved in a suitable solvent (A) The method of obtaining by dispersing the intercalating material particles and evaporating the solvent (A) can be exemplified. However, due to the problem of the wettability between the soluble conductive polymer solution and the intercalating material particles, a uniform soluble conductive material can be obtained. The method (1) is preferable for coating the particles of the intercalating material with the hydrophilic polymer material.

Examples of the solvent (A) for the polyalkylthiophene derivative capable of dissolving the soluble conductive polymer material include toluene, tetrahydrofuran and dimethoxyethane, and the solvent (B) includes water, propylene carbonate,
Examples include γ-butyl lactone, methanol, ethanol, and mixtures thereof. Examples of the solvent (A) for the polyaniline-based compound include n-methylpyridone, dimethylformamide, tetrahydrofuran, formic acid, pyridine, and the like, and examples of the solvent (B) include water, methanol, ethanol, acetonitrile, or a mixture thereof. it can. Among them, the soluble conductive polymer material is a polyaniline compound, the solvent (A) is formic acid,
The method of using water as the solvent (B) has the highest effect of the present invention and is most preferable from the economical viewpoint.

Since the composite particles of the present invention cover the particles of the intercalating material with the soluble conductive polymer material, the electric conductivity and workability are superior to those obtained by simply mechanically mixing the materials. , With energy density. The amount of the soluble conductive polymer material used in the composite particles of the present invention is 1 to 99%, preferably 2 to 70%. The intercalating material / soluble conductive polymer material composite particles of the present invention can be applied to various electrochemical devices such as batteries, sensors, capacitors, etc., but is most effective when applied to the positive electrode of batteries. high.

The electrolyte solvent for the battery of the present invention includes carbonates such as propylene carbonate, ethylene carbonate and butylene carbonate, tetrahydrofuran and 2-
Ethers such as methyltetrahydrofuran, 1,2-dimethoxyethane, ethoxymethoxyethane, methyldiglyme, and methyltriglyme, 1,3-dioxolane, 4-methyldioxolane, gammabutyllactone,
Sulfolane, 3-methylsulfolane and the like can be used alone or in a mixture, and a mixed system of carbonates as a main component and ethers and lactones shows a particularly excellent high energy capacity. Particularly, the lactone type is excellent in terms of stability of the electrolytic solution.

Further, the electrolyte salt in the present invention comprises an anion containing a halogen and a cation, and the following can be exemplified. (1) Halogen anions such as anions Cl ⁻ , Br ⁻ , I ⁻ , PF ₆ ⁻ ,
A halide anion of a Va group element such as SbF ₆ ⁻ , AsF ₆ ⁻ , SbCl ₆ ⁻ ; a group IIIa element halide anion such as BF ₄ ⁻ ; a perchlorate anion such as ClO ₄ ⁻ . (2) Cations Li (+), Na (+), alkali metal ions such as K (+), (R ₄ N) (+) [R: hydrocarbon group having 1 to 20 carbon atoms] and the like. Specific examples of the compound that gives the above-mentioned electrolyte ion include:
_{LiPF 6, LiSbF 6, LiAsF 6} , LiClO 4,
NaClO ₄ , KPF ₆ , KSbF ₆ , KAsF ₆ , KCl
_{O 4, [(n-Bu} ) 4 N] (+) BF 4 -, [(n-B
_{u) 4 N] (+)} · ClO 4 -, LiAlCl 4, LiBF
₄ , LiCF ₃ SO _{3 and the} like are exemplified.

As the negative electrode active material, alkali metals such as Li, K and Na, Li and Al, Pb, Cd, Si, Ga,
Polymer materials such as alloys with In, Zn and Mg, polyacetylene, polythiophene, polyparaphenylene, polypyridine, polyparaphenylene vinylene, polyparaxylylene and reduction polymers of halogen-substituted butadiene, graphite, carbonaceous materials, etc. Can be mentioned.

As the separator, one having a low resistance to the movement of ions of the electrolyte solution and having an excellent solution holding property is used. For example, a glass fiber filter; a polymer pore filter such as polyester, Teflon, polyflon, or polypropylene; a non-woven fabric; or a non-woven fabric composed of glass fiber and these polymers can be used.
Further, a solid electrolyte can be used as a component that replaces the electrolytic solution and the separator. For example, in the case of inorganic materials, metal halides such as AgCl, AgBr, AgI and LiI, and RbAg ₄ I ₅ and RbAg ₄ I ₄ CN ion conductive glass can be used. In organic systems, polyethylene oxide, polypropylene oxide, polyvinylidene fluoride, polyacrylonitrile, polyvinyl alcohol, etc. as a polymer matrix, the above-mentioned electrolyte salt is dissolved in the polymer matrix to form a complex, or a cross-linked product thereof, Examples thereof include a polymer electrolyte in which an ionic dissociative group such as a molecular weight polyethylene oxide, polyethyleneimine, or a crown ether is grafted on a polymer main chain, and a gel polymer solid electrolyte in which the electrolyte solution is contained in a high molecular weight polymer. Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples.

[0015]

Example 1 100 ml of formic acid was mixed with 10 g of polyaniline, electrolytic manganese dioxide and lithium carbonate at a ratio of 7: 3, and 40
14 g of the Mn-Li composite oxide obtained by firing at 0 ° C. was mixed and stirred to dissolve polyaniline in formic acid and disperse it in electrolytic manganese dioxide. When this solution was poured into 5 liters of water, a green precipitate was obtained. The precipitate was filtered, washed thoroughly with water, and then dried to give Mn-
Mn-L prepared by coating Li composite oxide particles with polyaniline
i composite oxide / polyaniline composite particles were obtained. 150 mg of the composite particles were mixed with 20 mg of graphite in an inert gas atmosphere and molded into a disk having a diameter of 16 mm to prepare a positive electrode for secondary battery having a density of 1.3 g / cm ³ . Li in the negative electrode and 1.5M LiClO ₄ / PC- as the electrolytic solution.
Using DME (volume ratio 1: 1), constant current is 2 to 3.7V
Charge and discharge were performed in the range.

Example 2 M was prepared in the same manner as in Example 1 except that 10 g of polyaniline and 10 g of Mn-Li composite oxide were used in Example 1.
A secondary battery using the n-Li composite oxide / polyaniline composite particles was prepared and the battery characteristics were measured.

Comparative Example 1 Polyaniline 60 mg, Mn-Li composite oxide 90 m
g and 20 mg of graphite were kneaded to prepare a secondary battery positive electrode similar to that of Example 1, and a secondary battery was prepared using this to measure battery characteristics. The results of the above implementation are shown in Table 1 below.

[Table 1]

[0018]

[Effect] Since the composite of the present invention coats the intercalating material, in particular the one in the form of particles, with the conductive polymer material from the solution state, it is superior to the case where the respective materials are simply mechanically mixed. There is provided an excellent electrode having electric conductivity, binding ability and energy density, and an electrode for a secondary battery using the electrode as a positive electrode.

─────────────────────────────────────────────────── --- Continuation of the front page (72) Inventor Kouri Kimura 1-3-6 Nakamagome, Ota-ku, Tokyo Inside Ricoh Co., Ltd. (56) Reference JP-A-63-314760 (JP, A) JP 63-224147 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) H01B 5/00 H01B 1/12 H01M 4/02 H01M 4/04

Claims (4)

(57) [Claims] 1. Intercalating material / soluble conductive polymer material composite particles , wherein the material particles for intercalating electrolyte cations are coated with a soluble conductive polymer material . 2. A solvent in which material particles for intercalating an electrolyte cation are dispersed in a solution in which a soluble conductive polymer material is dissolved, and then the soluble conductive polymer material is dissolved.
Compared with the above, the solubility of the soluble conductive polymer is lower than that of the solvent.
The method for producing intercalating material / soluble conductive polymer material composite particles according to claim 1 , wherein the soluble conductive polymer and the intercalating material particles are coprecipitated. 3. The intercalating material according to claim 1.
A secondary battery positive electrode, wherein soluble conductive polymer material composite particles are used as a positive electrode active material. 4. A secondary battery using the secondary battery positive electrode according to claim 3.