Facile synthesis of Cu_7.2S₄/RGO composites for an ultrastable and high-rate sodium storage anode

Metal sulfides with high capacity, morphology-controlled, and facile synthesis are considered as potential anodes for Na-ion batteries. However, the conductivity and structural stability of electrode materials are still hampered by its inherent low conductivity and obvious volume changes during cycling. Herein, Cu7.2S4 nanoparticles anchored on reduced graphene oxide (Cu7.2S4/RGO) are successfully prepared by solvothermal and thermal processes. The product, Cu7.2S4/RGO-10, not only features optimized the amount of RGO, but also delivers a large reversible capacity (314.4 mAh g-1 at 2 A g-1), good cycling stability (with a capacity fading of 0.11% per cycle from 2nd to 400th) and excellent rate capability (209 mAh g-1 at a high current density of 20 A g-1), making it the promising anode material for SIBs. Kinetics analysis clarifies that the high ion diffusion coefficient and the pseudo-capacitance contribution are important reasons for the superior performance. As expected, sodium-ion full cells (Cu7.2S4/RGO//Na3V2(PO4)3) also show good cycling stability.