N plasma treatment on graphene oxide-MoS2 composites for improved performance in lithium ion batteries

Abstract

Petal-like graphene oxide-MoS2 (GO-MoS2) composites are prepared by the hydrothermal method. The structural characterizations confirm the metallic phase (1T) of MoS2 sheets with a few layers, and the uniform distribution of graphene oxide (GO) and MoS2. However, the functional groups on the surface of GO and the intrinsic low conductivity of MoS2 lead to the poor electrochemical performance of GO-MoS2 in lithium ion batteries. N-doped GO-MoS2 (N-GO-MoS2) composites are prepared by N plasma treatment on GO-MoS2 composites at room temperature. N is clearly confirmed to be doped into both graphene oxide and MoS2 uniformly, and MoS2 changes to semiconducting phase (2H). In lithium ion batteries, it is found that the initial capacity increases from 561.4 mAh g−1 for GO-MoS2 to 726.9 mAh g−1 for N-GO-MoS2 at 1 C. After 100 cycles, N-GO-MoS2 still exhibits capacity of 592.7 mAh g−1 (1.34 mAh g−1 loss per cycles and 81.5% capacity retention rate), which is much better than that of GO-MoS2 (only 31.6 mAh g−1 after 100 cycles). The significantly improved high-rate cycling electrochemical performance for N-GO-MoS2 can be attributed to the improved stability of MoS2 by the phase transition from 1T to 2H, the enhanced electron transportation by the reduction of graphene oxide to graphene and the simultaneous N doping in MoS2 and graphene oxide.