The reduced graphene oxide conductive additives with a certain defect concentration enabling rate-capability of lithium-ion batteries

Abstract

Graphene as conductive additives for enhancing the electrochemical performance of commercial cathode materials (e.g., LiFePO4, LiCoO2, and LiMn2O4) in advanced Li-ion batteries (LIBs) has attracted great attention in recent years. However, the LiFePO4 and LiCoO2 electrodes usually show a poor rate capability when using graphene as the conductive additive, since its planar structure hinders ion transmission. Herein, a variety of reduced graphene oxides (rGO-x) have been successfully prepared using the modified Hummer's method followed by calcination. The results show that due to a large specific area and moderate defect density, rGO-5 can ensure good enough interfacial contact between active material particles and collector, thus maintaining fast electron/ion transportation. It has been found that LiFePO4 and LiCoO2 electrodes exhibit good lithium storage properties of 160.95 and 139.41 mA h g-1 at a rate of 0.1 C when rGO-5 is utilized as a conductivity additive. Meanwhile, combined with the electrochemical impedance and kinetic exploration, it can be seen that the LiFePO4 and LiCoO2 electrodes demonstrate a high Li+ diffusion coefficient (DLi+) of 6.7 × 10-14 cm2 s-1 and 4.3 × 10-13 cm2 s-1, respectively. Therefore, this research sheds new light on the practical utilization of rGO additives in high-performance lithium-ion batteries.