Nitrogen and sulfur co-doped three-dimensional graphene@NiO composite as cathode catalyst for the Li-O2 and Li-CO2 batteries

The problem of Li-O-2 batteries lies in the lack of high performance and low-cost catalyst that can promote the decomposition of discharge products. The trouble is even more serious when it cycles in CO2. Herein, we synthesize a nitrogen (N) and sulfur (S) co-doped 3D graphene@NiO (N, S-3DG@NiO) composite as a bi-functional electrode catalyst, which can concurrently support the stable cycling of Li-O-2 and Li-CO2 batteries. In this design, the N, S-3DG@NiO has three-dimensional porous structure, which can provide extra storage space for discharge products, and N and S co-doping provides more reaction active sites. The bi-functional electrode catalyst delivers a high discharge capacity of 17 300 mAh g(-1) and excellent cyclability (more than 50 cycles, limited capacity 500 mA g(-1)) when it is applied for Li-O-2 batteries. In addition, the N, S-3DG@NiO catalyst also exhibits a large discharge capacity of 13 400 mAh g(-1) when it is used as cathode for Li-CO2 batteries (more than 50 cycles, limited capacity 500 mA g(-1)). This study not only provides a high efficiency bi-functional cathode catalyst for Li-O-2 and Li-CO2 batteries, but also promotes the development of high specific energy batteries.