The composites of CoCO3 submicrocubes and graphene nanosheets (GNSs) were prepared through a solvothermal route and were tested as anode materials for lithium ion batteries. Profiting from the advantages of GNSs, CoCO3/GNS composites delivered high capacities of over 1000mAhg−1, much higher than theoretical values based on available lithium storage mechanisms. Instead, we propose an electrochemical catalytic conversion mechanism for lithium storage, in which not only cations (Co2+) but also anions (CO3 2−) are involved in the electron transfer. C4+ in CO3 2− is reduced to C0 or other low-valence C under the electrochemical catalysis of newly-generated Co nanoparticles. This new mechanism may provide more clues for exploiting advanced materials for Li ion batteries and other energy storage devices.