Single-Crystal Copper Sulfide Anode with Fast Ion Diffusion for High-Rate Sodium-Ion Batteries

Copper sulfide has been considered the promising alternative anode material due to the high theoretical capacity and weak Cu–S bonds for sodium-ion batteries (SIBs). However, conversion-type copper sulfide anode materials undergo huge volume expansion, sluggish sodium-ion diffusion kinetics, and low conductivity. Herein, the single-crystal Cu9S5 nanorods fabricated via an efficient microwave-assisted synthesis method are demonstrated with fast ion diffusion, favorable long-term stability, and exceptional rate performance in SIBs. The optimized single-crystalline Cu9S5 nanorods can realize high rate capability, including a specific discharge capacity of 670.2 mAh g–1 at 100 mA g–1 and 519.1 mAh g–1 at 3000 mA g–1, which is equivalent to 77.5% of the capacity at 100 mA g–1. More importantly, the single-crystalline microrods greatly alleviate the structure degradation during repeated sodiation–desodiation reactions, offering 95% capacity retention at 1 A g–1 current density and a slight decay of 0.0099% per cycle. The microwave-induced crystallographic and morphologic transformations of copper sulfide are confirmed for the first time under prolonged irradiation time. This work provides a insight to develop high-rate anode materials for sodium-ion batteries.