Chemically bonded NaBr@Cyclized-PAN nanocomposite cathode for advanced sodium-ion batteries

A-X (A=Li/Na/K, X=F/Cl/Br/I) rechargeable battery systems show special advantages owing to their high energy and power densities and low costs of halogen elements. Many studies have been focused on A-X systems, including Li-I, Li-Br, and Na-I batteries. However, Na-Br batteries remain unexplored. Herein, we developed a novel chemically bonded NaBr@cyclized-polyacrylonitrile composite, in which nano-sized NaBr was encapsulated within cyclized-polyacrylonitrile, forming a core-shell structure. Then we used it as a cathode and investigated its electrochemical properties in a sodium-ion battery. The cyclized-polyacrylonitrile shell not only promotes the ion and electron transport, but also provides physical and chemical confinement to alleviate the shuttle effect of Br species. This composite cathode exhibits much-improved cycling stability and rate capability with retention capacities of 136.4 and 94 mAh g-1 after 200 cycles at 1C and 5C, respectively. This study achieves stable cycling of Na-Br battery, and promotes the development of high-energy-density Na-Br battery systems.