To increase the conductivity and electric capacity of an electrode which includes active material particles and the like and is used in a battery, a graphene net including 1 to 100 graphene sheets is used instead of a conventionally used conduction auxiliary agent and binder. The graphene net which has a two-dimensional expansion and a three-dimensional structure is more likely to touch active material particles or another conduction auxiliary agent, thereby increasing the conductivity and the bonding strength between active material particles. This graphene net is obtained by mixing graphene oxide and active material particles and then heating the mixture in a vacuum or a reducing atmosphere.