Negative electrode active material having nanosize tin oxide particle disperded on surface of nanosize conductive carbon powder, method for producing the same, and lithium ion secondary battery using the same

摘要

Disclosed is a negative electrode active material which is capable of occluding and releasing lithium, and has high reversible capacity and reduced initial irreversible capacity. This negative electrode active material includes a granulated substance, in which a composite containing nanosize conductive carbon powder and tin oxide powder contacting the surface of the conductive carbon powder in a highly dispersed state and an aggregate selected from the group consisting of graphite and nongraphitizable carbon are aggregated. The electrochemical decomposition of electrolytic solution is suppressed due to a reduction in the area where the carbon material in the granulated substance and the electrolytic solution are in contact, resulting in a significant reduction in the initial irreversible capacity of the negative electrode active material.

主权项

1. A negative electrode active material capable of reversibly occluding and releasing lithium according to a conversion reaction of an equation (I) and an alloying reaction of an equation (II),
SnO2+4Li++4e−2Li2O+Sn  (I) Sn+4.4Li++4.4e−Li4.4Sn  (II) in which nanosize conductive carbon powder and a nanosize tin oxide spherical particle contacting a surface of the conductive carbon powder are comprised in a highly dispersed state such that 30% by mass or more of primary particles of the conductive carbon powder are not aggregated and 30% by mass or more of primary particles of the tin oxide spherical particles are not aggregated, and a low-conductive amorphous carbon film with 1/100 or less of an electric conductivity of the conductive carbon powder covering an area which is included in a surface of the tin oxide spherical particle and which does not contact the surface of the conductive carbon powder is further comprised, the nanosize conductive carbon powder has an inner vacancy and the surface composed of an outer surface and an inner surface, and the tin oxide spherical particle has an average particle diameter of 1 to 2 nm and exists in the inner vacancy and on the outer surface of the conductive carbon powder.