High-performance sodium-selenium batteries enabled by microporous carbon/selenium cathode and fluoroethylene carbonate electrolyte additive

Sodium-selenium (Na-Se) batteries are promising energy storage systems due to their relatively low cost and high volumetric energy density of Se cathode. However, the practical application of Na-Se batteries has been hindered by the polyselenides dissolution (or shuttle effect phenomena), which could cause low Coulombic efficiency and poor cycling lifetime. Herein, we addressed the polyselenides dissolution by using microporous carbon (MPC) derived from poly (vinylidene fluoride) as the Se host and fluoroethylene carbonate (FEC) as the additive in the electrolyte. The MPC/Se cathode with 3% FEC additive maintained a specific capacity of 382 and 350 mAh g(-1) in the 100th and 200th cycle, respectively, while the MPC/Se cathode without FEC could only deliver 317 and 245 mAh g(-1) after 100 and 200 cycles, respectively. Another important finding was that the use of FEC additive could prevent the corrosion of Na metal anode from soluble polyselenides, and preserve the structural integrity of Na anode, contributing to the enhanced cycling stability and specific capacity of Na-Se batteries. It is expected that this work could draw researchers' attention to the importance of reporting and studying Na metal anode while optimizing Se cathode for Na-Se batteries.