Graphene wrapped LiFePO4/C composites as cathode materials for Li-ion batteries with enhanced rate capability

Abstract

To reduce the reaction time, electrical energy consumption, and cost, LiFePO₄/C/graphene has been synthesized by a rapid, one-pot, microwave-assisted hydrothermal method within 15 min at a temperature of 200 °C, followed by sintering at 600 °C for 2 h under a H₂/Ar (5 : 95, v/v) atmosphere. The microstructure and morphology of the LiFePO₄/C/graphene products were characterized by means of X-ray diffraction, Raman spectroscopy, field emission scanning electron microscopy, and transmission electron microscopy. The carbon coated LiFePO₄/C nanoparticles, around 200 nm in size, are thoroughly wrapped by crumpled micrometer-size graphene sheets. In this kind of structure, the bridging graphene nanosheets can form an effective conducting network and provide interconnected open pores that favor electrolyte absorption and reduce the diffusion path of the lithium ions. The cyclic voltammograms, charge/discharge profiles, and AC impedance measurements indicated that the kinetics of the LiFePO₄/C/graphene was better than that of LiFePO₄/C. The LiFePO₄/C/graphene composite exhibited a discharge capacity of 165 mA h g⁻¹ at 0.1 C and 88 mA h g⁻¹ at 10 C, respectively. Therefore, the LiFePO₄/C/graphene composite is a promising candidate for the development of high-performance, cost-effective lithium batteries for the hybrid vehicle and electric vehicle markets.