Enhanced electrochemical performance of a LTO/N-doped graphene composite as an anode material for Li-ion batteries

Abstract

A Li4Ti5O12/N-doped graphene composite has been successfully prepared by a solid-state method. For comparison, pure Li4Ti5O12 and Li4Ti5O12/graphene composite were also synthesized. The results reveal that nitrogen-doped graphene sheets can provide additional free electrons and enhance the electronic conductivity between adjacent Li4Ti5O12 particles. Comparing the electrochemical performances of the three materials, the Li4Ti5O12/N-doped graphene composite exhibits excellent performance with specific capacities of 164, 161.5, 157.9, 144.6, 127.8, 104.4, and 80.5mAhg−1 at rates of 0.2, 0.5, 1, 3, 5, 10 and 20C (1C=160mAhg−1), respectively. Moreover, Li4Ti5O12/N-doped graphene composite showed a charge capacity retention of 92% after 200cycles at a rate of 5C, which is higher than that of Li4Ti5O12/graphene composite (89.0%) and pure Li4Ti5O12 (87.0%). Electrochemical impedance (EIS) and cyclic voltammetry (CV) were used to characterize the electrochemical kinetics. The charge transfer resistance of the Li4Ti5O12/N-doped graphene composite (70.9Ω) is lower than that of Li4Ti5O12/graphene composite (94.4Ω) and pure Li4Ti5O12 (120.7Ω). The Li+ diffusion coefficient of the Li4Ti5O12/N-doped graphene composite is 5.76×10−10cm2s−1, which is larger than that of Li4Ti5O12/graphene composite (3.61×10−10cm2s−1) and pure Li4Ti5O12 (2.31×10−10cm2s−1). The improved electrochemical performance of the Li4Ti5O12/N-doped graphene composite may be ascribed to that the N-doped graphene distributed around Li4Ti5O12 particles, providing high electronic conductivity and fast lithium ion diffusion.