Chuo Denki Kogyo Co., Ltd.

Nippon Steel Sumitomo Metal Corporation

Tooru Fujiwara

Hiroshi Yamamoto

Tatsuo Nagata

A negative electrode material provided by the present invention capable of suppressing a decrease in charge acceptance and high temperature storage properties in an electrode with a high capacity and a high density is a mixed carbon material comprising carbon material A having cores of graphite powder with amorphous carbon and/or turbostratic carbon adhered to or coated on the surface of the cores and carbon material B which is graphite powder, the compressibility which is the density (g/cm) of the material when 1.00 grams of the material are packed into a cylindrical mold with an inner diameter of 15 mm and compressed by applying a pressing force of 8.7 kN and reducing the pressing force to 0.15 kN is 1.60-1.78 g/cmfor carbon material A and 1.75-1.85 g/cmfor carbon material B, the compressibility of carbon material A is less than the compressibility of carbon material B, and the mixing ratio (carbon material A/carbon material B) is 1-9 as a mass ratio.

Mixed carbon material and negative electrode for a nonaqueous secondary battery

The present invention provides a mixed carbon material which comprises carbon material A and carbon material B and which is a carbon material suitable for a negative electrode material which can provide a nonaqueous secondary battery having a low irreversible capacity and having a negative electrode with a high capacity and high charge acceptance. Carbon material A and carbon material B both have cores made of graphite powder and a surface carbon material in the form of at least one of amorphous carbon and turbostratic carbon adhered to or coated on at least a portion of the surface of the graphite powder. The compressed density is 1.80-1.90 g/cmfor carbon material A alone, 1.45-1.65 g/cmfor carbon material B alone, and 1.75-1.84 g/cmfor the mixed carbon material.

Mixed carbon material including graphite powder cores and surface carbon material on a surface thereof and negative electrode for nonaqueous secondary battery

A carbon material suitable as a negative electrode material for a lithium ion battery which can suppress decomposition of a nonaqueous electrolytic solution, which has excellent compressibility capable of highly dense packing, and which can form an electrode of high capacity without worsening charge and discharge efficiency or cycling performance. Graphite powder A having an average particle diameter of 10-30 &#x3bc;m and a specific surface area S1 of at most 12.5 m/g and pitch powder B having a softening point of 80-180&#xb0; C. and an average particle diameter of 15-150 &#x3bc;m are mixed in proportions such that the mass ratio A/B is 98/2-95.5/4.5, and the resulting mixed powder is subjected to heat treatment in a stationary condition in an inert atmosphere at 900-1100&#xb0; C. to carbonize the pitch and thereby manufacture a carbon material having carbon adhered to the surface of the above-described graphite powder. Carbon preferentially adheres to the edge planes of the graphite particles. The carbon material has a specific surface area S2 of 1.0-5.0 m/g, and it satisfies 0.4&#x2266;S2/S1&#x2266;0.8.

Carbon material and a process for its manufacture

Carbon powder having low temperature calcined carbon derived from pitch adhered to a portion of the surface of natural graphite powder is obtained by solids mixing of natural graphite powder and pitch powder as a carbon precursor followed by heat treatment at 900-1500&#xb0; C. to carbonize the pitch. The amount of pitch powder is such that the ratio V/Vof the pore volume Vof pores having a diameter of 50-200 nm to the pore volume Vof pores having a diameter of 2-50 nm in a pore size distribution curve obtained by analysis of the nitrogen desorption isotherm of the resulting carbon powder by the BJH method is at least 1. This carbon powder can be used as a negative electrode material for a nonaqueous secondary battery able to operate at low temperatures.

Growing community of inventors

Nishinomiya, Japan

Tooru Fujiwara