LiFePO4/activated carbon/graphene composite with capacitive-battery characteristics for superior high-rate lithium-ion storage

LiFePO4 is an attractive cathode material for lithium ion battery due to its high capacity of 170 mAh g−1, long cycle life, good safety and low cost, which suffers from the instinct low electron conductivity and poor rate performance. Herein, a composite material consisting of LiFePO4, activated carbon and graphene is synthesized with a facile solvothermal method, which presents excellent high-rate performance with highly-efficiency capacitive-battery characteristics. The obtained LiFePO4/activated carbon/graphene cathode material has hierarchical porous architecture mainly originated from the activated carbon and interconnected conductive networks constructed by the graphene, ensuring both the abundant pathways for Li+ diffusion and the fast electron transfer. Furthermore, the high surface area (367 m2 g−1) provides a double layer capacitive process during charge/discharge process, and also protects the LiFePO4 against the heavy current attack, especially under high current rate. As a result, the capacitive-battery behavior leads to superior rate capability and long cycle life. The LiFePO4/activated carbon/graphene cathode exhibits a remarkable high capacity of 66 mAh g−1 at an extremely high rate of 100 C, and the brilliant cycle stability is confirmed with the capacity retention of 82% after 3000 cycles, promising the high power applications. Furthermore, this study provides a new insight in simple preparation of the capacitive-battery materials by combing the active components and the capacitive components.