Negative Electrode Material for Lithium Battery, and Lithium Battery

Abstract

The present invention relates to a negative electrode material for a lithium battery characterized by comprising a carbonaceous negative electrode active substance having a specific surface area of 1 m2 / 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 thickner such as carboxymethyl cellulose in the amount of 0.3 to 3 mass %.

Description

CROSS REFERENCE TO THE RELATED APPLICATIONS [0001] This is an application filed pursuant to 35 U.S.C. Section 111(a) with claiming the benefit of U.S. Provisional application Ser. No. 60 / 534,989 filed Jan. 9, 2004 under the provision of 35 U.S.C. Section 111(b), pursuant to 35 U.S.C. Section 119(e)(1).TECHNICAL FIELD [0002] The present invention relates to a carbonaceous negative electrode material for producing a lithium battery having high volumetric charge / discharge capacity, and exhibiting excellent characteristics in terms of the charge / discharge cycle and large-current load; to a composition for forming the negative electrode material (hereinafter may be referred to as a “negative electrode material composition”); to a method for producing the composition; to a lithium battery and a lithium secondary battery employing the carbonaceous negative electrode material. BACKGROUND ART [0003] With the progress of small-size, lightweight and high-performance portable apparatuses, incre...

AI Technical Summary

Benefits of technology

The present invention provides a carbonaceous negative electrode material for a lithium battery that exhibits high energy density, low electrode resistance, high electrolytic solution permeability, high charging / discharging performance, and good high-speed charging / discharging performance. The material comprises a carbonaceous negative electrode active substance, a binder, and a carbon fiber. The carbon fiber is dispersed uniformly in the material and acts as an electrically conductive additive. The binder is formed of styrene-butadiene rubber and the carbon fiber has a fiber diameter of 1 to 1,000 nm. The amount of carbon fiber is 0.1 to 20 mass% and the amount of binder is 0.1 to 6.0 mass%. The material also contains a thickener in an amount of 0.1 to 4 mass% on the basis of the total amount of carbonaceous negative electrode active substance, carbon fiber, and binder. The negative electrode material has a specific resistance of 0.5 Ωcm or less at 25°C. The carbon fiber can be a graphite carbon fiber that has undergone thermal treatment at 2,000°C or higher. The material can be used in a lithium battery to achieve high energy density, low electrode resistance, and good high-speed charging / discharging performance.

Problems solved by technology

However, such an electrode material employed in the battery exhibits a gravimetric charge / discharge capacity nearly equal to the theoretical value, and thus the gravimetric energy density of the battery is approaching its limit.

However, when the density of a negative electrode is increased, the amount of pores contained in the negative electrode is reduced, leading to problems such as deficiency of an electrolytic solution, which is generally present in the pores and plays an important role for electrode reaction, and lowering of the rate of permeation of the electrolytic solution into the negative electrode.

When the amount of the electrolytic solution in the negative electrode is insufficient, the electrode reaction proceeds at a lower rate, resulting in lowering of energy density and high-speed charging / discharging performance.

Meanwhile, when the electrolytic solution permeability is impaired, longer time is required for producing a battery, leading to an increase in production cost.

Such problems become more pronounced in the case of a lithium polymer battery, which employs a polymer electrolytic solution of high viscosity.