In-situ carbon coated CoSe microrods as a high-capacity anode for sodium ion batteries

Abstract Sodium ion batteries (SIBs), as one of the most promising alternative to lithium ion batteries (LIBs), have attracted significant attentions during the last decade. Particularly, transition metal selenides have gained widespread interests as potential anodes for SIBs owing to their high capacity, wide availability and low cost. However, the rapid capacity fading and poor rate capability usually limit their development and application, which stem from the structure pulverization and exfoliation of active materials. In this work, CoSe@C microrods have been synthesized via simultaneous selenization and in-situ carbonization of cobalt-nitrilotriacetic acid (Co-NTA) precursors. By adjusting the ratio of water and isopropyl alcohol (IPA), three kinds of samples with high-crystallinity, different diameters and lengths are obtained. The CoSe@C-1 sample, prepared at 3:1 water to IPA, possesses uniform and orderly rod-like morphology with 150 nm diameter and 2 μm length. When employed as an anode for SIBs, the CoSe@C-1 microrod electrode exhibits the best electrochemical performances with high discharge capacity (485 mA h g−1 after 60 cycles at 0.1 A g−1) and excellent rate performance (315 mA h g−1 at 0.5 A g−1). Meanwhile, the reaction mechanism of the CoSe@C microrod is investigated. The CoSe@C-1 microrod also delivers excellent solid state electrochemical properties with a capacity of 230 mA h g−1 after 50 cycles at 0.1 A g−1. Furthermore, the outstanding electrochemical properties can be ascribed to the rational design of carbon-coated and porous structure, which can not only effectively prevents the aggregation of the CoSe@C nanoparticles, but also improve the electrical conductivity of the samples. These results provide a simple approach to fabricate promising anode materials for high-performance SIBs.