Se confined in N-doped mesoporous carbon opal as anode for K-Se capacitors with super-long cycle life

Featuring high theoretical capacity of Se and low cost of element K, potassium-selenium (K-Se) batteries are considered as prospective power storage equipment. However, their drawbacks including dramatic volume change of Se, shuttling effect and relatively low operation voltage (< 3 V) can result in short lifespan and low power density. Here, we report a novel type of K-Se capacitors employing Se confined in N-doped mesoporous carbon opal (Se@NMCO) as anode and activated carbon (AC) as cathode based on the K-Se electrochemical reaction mechanism. This prepared K-Se capacitors can achieve large energy and power density (127 Wh kg−1 and 11523 W kg−1) with super-long lifespan (maintaining up to 10, 000 cycles with a capacity retention of 91 % at 2 A g−1). The great performance may arise from the hierarchically porous structure of Se@NMCO, in which the well-ordered macropores can enhance the mass transport effectively and the mesopores can further guide the reactants to the active reaction sites. Additionally, opal nanostructure also plays an importance role in enhancing the K-storage performance. This ingenious design would open an avenue for developing super long-life devices on the basis of K-Se reaction mechanism. [Display omitted] •Se was successfully confined in N-doped mesoporous carbon opal (Se@NMCO).•Se@NMCO electrode shows great electrochemical performance in K-Se batteries.•Se@NMCO//AC K-Se capacitors exhibit high energy/power densities and long lifespan.