A dual-protection strategy using CMK-3 coated selenium and modified separators for high-energy Al-Se batteries

The aluminum-selenium (Al-Se) battery is a very promising rechargeable battery system due to its high theoretical specific capacity of 1357 mA h g-1 and high average discharge voltage of ~1.52 V versus Al/Al3+. However, Al-Se batteries suffer poor reversibility, since the intermediate product Se2Cl2 dissolved in the acidic electrolyte causes significant capacity fading. To overcome this critical issue, a dual-protection design with composites of selenium nanoparticles encapsulated in mesoporous carbon (CMK-3) and separators modified by CMK-3 are developed. Because of the great physical blocking of the intermediate product dissolved in the electrolyte, the as-assembled Al-Se batteries can deliver an ultrahigh capacity of ~1295 mA h g-1 (approximate the theoretical specific capacity) in the first two cycles, and retain a capacity of 651 mA h g-1 (retention rate of 50.3%) over 400 cycles at a current density of 1000 mA g-1. The rational design of the Al-Se batteries with dual protection from the CMK-3 coated Se positive electrode and modified separators is effective in promoting the electrochemical performance of the batteries.