Sandwich-like cobalt sulfide-graphene composite - an anode material with excellent electrochemical performance for sodium ion batteries

Recently, sodium-ion batteries have been considered alternatives to lithium-ion batteries. However, the poor cycling performance and unsatisfactory rate capability of existing anodes hinder the development of sodium-ion batteries. Here we fabricate a sandwich-like cobalt sulfide-reduced graphene oxide (CoS/rGO) composite using a hydrothermal method as the anode material for sodium ion batteries. According to the SEM analysis, CoS nanoparticles anchor on both sides of the reduced graphene oxide nanosheets in such a way that the nanoporous structure with a large amount of void spaces can be prepared. And the cycling performance of the sandwich-like CoS/rGO composite is drastically enhanced compared with that of the bare CoS nanoparticles. After 100 cycles, the discharge capacity of CoS/rGO still remains at 230 mA h g(-1), while the specific capacity of the bare CoS nanoparticles at the first cycle is 601 mA h g(-1), dropping rapidly to 68 mA h g(-1) after only 40 cycles. Furthermore, CoS/rGO gives an excellent rate capability even up to a large current of 2 A g(-1). It is noted that the synergistic effect between CoS and graphene can contribute to the improved electrochemical performance.