LAUSR

Selenium‐carbon materials present an interesting opportunity for rechargeable battery systems. They are usually obtained through infusing elemental Se into various carbon sources. Herein, a self‐thermal‐reduction method is successfully applied to prepare covalent Se carbon material (CPSe, Se: 10.8 wt%) utilizing polyselenophene (PSe) as a dual source of selenium and carbon matrix, in which selenium is mainly present with the form of CSe bond. Interestingly, most of them are found to break away from the carbon skeleton as the discharge voltage is gradually scanned down to a lower stage, and then selenide is progressively oxidized to elemental Se in the charge process. Furthermore, employing a space‐confined strategy, a high Se mass loading composite (Se‐CPSe, 56.8 wt%) is effectively produced with the simultaneous introduction of covalent Se and physical‐trapped Se. In this electrode, the physical‐restricted Se part exhibits a reversible capacity of 420 mA h g−1 at 100 mA g−1 for the Na‐Se battery. More significantly, after being activated at 0.01–3.0 V in the initial cycles, the electrochemical cleaved covalent Se and physical‐confined Se can jointly contribute specific capacity of ≈590 mA h g−1. Such strategies and understanding are important for the future design and optimization of electrode materials for Na‐Se batteries.