Negative electrode material for lithium battery, and lithium battery
The present invention relates to a negative electrode material for a lithium battery comprising a carbonaceous negative electrode active substance having a specific surface area of 1 m 2 /g or more, a binder formed of styrene-butadiene rubber and a carbon fiber having a fiber diameter of 1 to 1,000 nm; and to a lithium battery using the negative electrode material, which has excellent characteristics, i.e., low electrode resistance, high electrode strength, excellent electrolytic solution permeability, high energy density, and good high-speed charging/discharging performance. The negative electrode material contains carbon fiber in the amount of 0.05 to 20 mass % and the binder formed of styrene-butadiene rubber in 0.1 to 6.0 mass %, and may further contain a thickener such as carboxymethyl cellulose in the amount of 0.3 to 3 mass %.
1. A method for producing a composition for forming a negative electrode material for a lithium battery, comprising adding an aqueous styrene-butadiene rubber dispersion to a carbon fiber/active substance dispersion prepared by dispersing, in an aqueous thickener solution, a carbon fiber having a fiber diameter of 1 to 1,000 nm, a carbonaceous negative electrode active substance having a specific surface area of 1 m 2 /g or more; and stifling the resultant mixture,
wherein the carbon fiber/active substance dispersion is prepared by
(1) dispersing a carbon fiber having a fiber diameter of 1 to 1,000 nm in an aqueous thickener solution under stifling; and by adding thereto a carbonaceous negative electrode active substance having a specific surface area of 1 m 2 /g or more followed by mixing with stirring, or
(2) adding, to an aqueous thickener solution, a carbonaceous negative electrode active substance having a specific surface area of 1 m 2 /g or more followed by mixing with stirring; and by dispersing a carbon fiber having a fiber diameter of 1 to 1,000 nm in the resultant mixture under stirring.
2. The method for producing a composition for forming a negative electrode material for a lithium battery as claimed in claim 1 , wherein the carbon fiber/active substance dispersion is prepared by step (1) and further by being regulated using an aqueous thickener solution.
3. The method for producing a composition for forming a negative electrode material for a lithium battery as claimed in claim 1 , wherein the content of the thickener in the aqueous thickener solution is 0.3 to 5 mass %, and the content of the styrene-butadiene rubber in the aqueous styrene-butadiene rubber dispersion is 10 to 60 mass %.
4. The method for producing a composition for forming a negative electrode material for a lithium battery as claimed in claim 1 , wherein the thickener is carboxymethyl cellulose.