Patent ID: 7144659

Claim:
A negative electrode for a lithium ion secondary battery comprising a material mixture layer, said material mixture layer comprising a carbonaceous material, said carbonaceous material comprising a spherical graphite (A) and a graphitized carbon tibet (B), wherein said materiat mixture layer has a carbon density of not less than 1.6 g/cm 3 , which is determined by dividing the weight of said carbonaceous material by the volume of said material mixture layer; said spherical natural graphite (A) has: (1) an interplanar spacing d002 between the (002) planes determined by an X-ray diffraction pattern of not less than 0.3354 nm and not more than 0.3357 nm, (2) a mean particle circularity of not less than 0.86, and (3) a mean particle size of not less than 5 μm and not more than 20 μm; said graphitized carbon fiber (B) has: (1) a mean fiber length of not less than 20 μm, and not more than 200 μm, and (2) a mean aspect ratio of not less than 2 and not more than 10; and the amount of said graphitized carbon fiber (B) is not less than 60% by weight and not more than 80% by weight of whole of said carbonaceous material.