Cobalt selenide decorated carbon spheres for excellent cycling performance of sodium ion batteries

Abstract

Development of electrode materials with high capacity, superior rate performance, long cycle life and low cost is critical to commercialize sodium ion batteries (SIBs). Herein, a unique composite consisted of cobalt selenide (Co0.89Se) nanoparticles (3–10nm) embedded in carbon spheres (CoSe@CSs) is presented as anode for SIBs. The exclusive structure of CoSe@CSs enables the pseudocapacitive charge storage, improves the electronic properties and provides buffer for volumetric changes during the repeated charge-discharge processes. The composite with an average diameter of ~100nm, denoted as CoSe@100CSs, presented the best electrochemical performance (with a reversible charge storage capacity of 554mAh g-1 after 50 cycles at a rate of 100mAg-1) when compared with composites of 300nm and 500nm diameters and also pure CoSe. Additional to high storage capacity, the CoSe@100CSs also showed excellent rate capability and ultra-long cycling life when examined at higher discharge rates. Storage capacities are as high as 350mAh g-1 at the rate of 1000mAg-1 and 260mAh g-1 at the rate of 4000mAg-1 after 4000 and even 10,000 cycles, respectively. Hence, due to this synergetic effect of uniformly distributed cobalt selenide nanoparticles and carbon matrix, the CoSe@CSs composite exhibits exceptional electrochemical performance for SIBs. This strategy is expected to open up new methodologies for the development of advanced electrode materials of high performance SIBs.