Enabling Selenium-Rich Se_xS_y Cathodes to Work in Carbonate-Based Electrolytes

Lithium–sulfur/selenium batteries have attracted broad interest and achieved good performance using ether-based electrolytes. However, when the ether-based electrolytes are employed, Li–S/Se battery systems still have several inevitable drawbacks inhibiting their practical applications, such as intermediate product dissolution issues, and a dependency on a high content of electrolyte. Thus, it is urgent to pay attention to the electrochemical properties of Se_xS_y cathodes in carbonate-based electrolytes, which may avoid the above mentioned problems. In this work, a series of mesoporous carbon/Se_xS_y (CMK-3/Se_xS_y) composites with covalent Se-S bonds and different Se/S molar ratios are prepared and their working mechanism in carbonate-based electrolytes is systematically investigated by combining experimental analysis and theoretical calculations. This work finds that the Se in the CMK-3/Se_xS_y cathode is beneficial for the transportation of Li⁺ ions and forms a thin cathode electrolyte interphase (CEI) during the discharge–charge process. Furthermore, S substitution in Se₈ molecules can enhance the specific capacity and lower the bond breaking and lithiation energies. The optimal CMK-3/Se_xS_y cathode delivers outstanding performance with a high reversible capacity of 609 mA h g⁻¹ at 1 A g⁻¹ over 300 cycles.