KOH-activated hollow carbon spheres with surface functionalization for high-capacity and long-cycle-life...

Lithium-selenium (Li-Se) batteries are considered promising alternatives to lithium-ion batteries due to their higher volumetric capacity and energy density. However, they still face limitations in efficiently utilizing the active selenium. Here, we develop surface-functionalized mesoporous hollow carbon nanospheres as the selenium host. By using KOH activation, the surface of the carbon nanospheres is functionalized with hydroxyl groups, which greatly improve the utilization of selenium and facilitate the conversion of lithium selenides, leading to much higher capacities compared to ZnCl₂ activation and untreated carbon nanospheres. Theory and experimental evidence suggest that surface hydroxyl groups can enhance the reduction conversion of polyselenides to selenides and facilitate the oxidation reaction of selenides to elemental selenium. In-situ and ex-situ characterization techniques provided additional confirmation of the hydroxyl groups electrochemical durability in catalyzing selenium conversion. The meticulously engineered Se cathode demonstrates a high specific capacity of 594 mA h g^-1 at 0.5C, excellent rate capability of 464 mA h g^-1 at 2C, and a stable cycling performance of 500 cycles at 2C with a capacity retention of 84.8 %, corresponding to an ultra-low-capacity decay rate of 0.0144 % per cycle, surpassing many reported lithium-selenium battery technologies.