Three-dimensionally scaffolded Co₃O₄ nanosheet anodes with high rate performance

Advances in secondary batteries are required for realization of many technologies. In particular, there remains a need for stable higher energy batteries. Here we suggest a new anode concept consisting of an ultrathin Co₃O₄ nanosheet-coated Ni inverse opal which provides high charge-discharge rate performance using a material system with potential for high energy densities. Via a hydrothermal process, about 4 nm thick Co₃O₄ nanosheets were grown throughout a three-dimensional Ni scaffold. This architecture provides efficient pathways for both lithium and electron transfer, enabling high charge-discharge rate performance. The scaffold also accommodates volume changes during cycling, which serves to reduce capacity fade. Because the scaffold has a low electrical resistance, and is three-dimensionally porous, it enables most of the electrochemically active nanomaterials to take part in lithiation-delithiation reactions, resulting in a near-theoretical capacity. On a Co₃O₄ basis, the Ni@Co₃O₄ electrode possesses a capacity of about 726 mAh g^-1 at a current density of 500 mA g^-1 after 50 cycles, which is about twice the theoretical capacity of graphite. The capacity is 487 mAh g^-1, even at a current density of 1786 mA g^-1.