General Synthesis of MxS (M = Co, Cu) Hollow Spheres with Enhanced Sodium-Ion Storage Property in Ether-Based Electrolyte

As one of the promising anode candidates of sodium-ion batteries, the development of transition metal sulfides (TMSs) was severely limited by the large volume variation and sluggish kinetics during sodiation/desodiation processes. Integrated optimizations including preparation method, structure design, electrolyte, etc. are highly in demand. Herein, a general synthesis method of MxS (M = Co, Cu) hollow spheres is developed. After a combined modification of the cut-off voltages and electrolytes, the as-prepared MxS samples exhibit improved sodium-ion storage properties. A high capacity of 470 mAh g(-1) with 88% capacity retention at 100 mA g(-1) after 100 cycles is delivered by CoS. As to Cu1.765S, a reversible capacity of 317.6 mAh g(-1) with no obvious capacity decay could be found at 100 mA g(-1) after 100 cycles. The selected NaCF3SO3/diethylene glycol dimethyl ether electrolyte plays a crucial role in promoting the electrochemical property of the MxS samples. This general synthesis method and electrolyte optimization strategy is expected to be applicable to other TMS anodes.