Small‐Molecule Selenium Cathode Constructed by Tailoring‐Immobilization Strategy enables High‐Power Lithium‐Selenium Batteries

ABSTRACT Lithium‐selenium batteries (LSeBs) are regarded as the next‐generation energy‐storage device due to the high energy density (2528 Wh L −1 ) and favorable electric conductivity (10 −3 S cm −1 ) of Se. The introduction of carbonate‐based electrolytes could suppress the polyselenide shuttle effect in LSeBs via the solid‐phase conversion, while the accompanying sluggish kinetics and uncontrollable volume expansion would hamper its commercialization. Herein, a tailoring‐immobilization strategy is proposed to prepare small‐molecule selenium aiming to enhance the reaction kinetics and restrain the volume expansion. In this strategy, long‐chain Se is firstly cut into small Se 2 and Se 3 molecules using single‐atom Co as molecular scissors and immediately encapsulated into a tailored carbon host (CoPC) with abundant ultra‐micropores (∼0.5 nm). The small‐molecule Se could possess higher reactivity and accelerate the reaction kinetics, while the CoPC ensures the long‐term immobilization for small‐molecule Se and guarantees ∼100% Se‐utilization. As a result, the as‐obtained small‐molecule Se in CoPC (CoPC@TI‐Se) could deliver 99.25% of theoretical specific capacity at 0.2 C (675 mAh g −1 ) and almost 100% retention after 500 cycles at 10 C, which ranks the best cyclic performances among recently reported. This tailored‐immobilization strategy provides a novel optimization and development direction for the practical LSeBs.