Carbon fiber, electrode material for lithium secondary battery, and lithium secondary battery

A carbon fiber has a coaxial stacking morphology of truncated conical tubular graphene layers, wherein each of the truncated conical tubular graphene layers includes a hexagonal carbon layer and has a large ring end at one end and a small ring end at the other end in an axial direction. The hexagonal carbon layers are exposed on at least a part of the large ring ends. Part of carbon atoms of the hexagonal carbon layers are replaced with boron atoms, whereby projections with the boron atoms at the top are formed. An electrode material for a secondary battery using the carbon fiber excels in lifetime performance, has a large electric energy density, enables an increase in capacity, and excels in conductivity and electrode reinforcement.