Enhanced performance of LiFePO4 originating from the synergistic effect of graphene modification and carbon coating

Abstract

LiFePO4@Carbon/reduced graphene oxide (LFP@C/rGO) composites as cathode materials for lithium-ion batteries were prepared by a simple solvothermal method followed with a carbon coating. The characterizations indicated that LiFePO4 particles with pure orthorhombic olivine phase were attached to graphene oxide, which could be reduced in the synthesis of LiFePO4 and constructed a conductive network in the composite. After a post carbon encapsulation, a uniform and thin carbon layer on LiFePO4 was formed and could quickly collect electrons via a shorter pathway around LiFePO4 nanoparticles during the charge/discharge. The results showed LFP@C/rGO composites delivered a discharge specific capacity of 148.3 mAh/g at the rate of 1 C, higher than LiFePO4 only modified with graphene or coated with carbon layers. The discharge capacity of 129 mAh/g can still be maintained when the current density increased to 20 C. Furthermore, LFP@C/rGO manifested a satisfactory lifespan and no capacity fading was observed after 200 cycles at the rate of 10 C. Compared with synthesized LiFePO4@C, LFP@C/rGO composites also exhibited a high capacity of 108 mAh/g at −20 °C at a rate of 1 C. Even after 500 charge/discharge cycles, capacity fading was scarcely seen. Electrochemical tests suggested the unique architecture resulted in a synergistic effect between 3D reduced graphene oxide (rGO) conductive network and carbon coating, which remarkably improved the conductivity of electrode and electrochemical kinetics, contributing to outstanding rate performance and cycle life.