LAUSR

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 (Co 0.89 Se) nanoparticles (3–10 nm) 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 ~100 nm, denoted as CoSe@100CSs, presented the best electrochemical performance (with a reversible charge storage capacity of 554 mA h g -1 after 50 cycles at a rate of 100 mA g -1 ) when compared with composites of 300 nm and 500 nm 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 350 mA h g -1 at the rate of 1000 mA g -1 and 260 mA h g -1 at the rate of 4000 mA g -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.