High‐Content Carbon Layer Confined Small‐Molecule/Covalent Sulfur Cathode Enables Long‐Life Calcium–Sulfur Batteries in Hybrid‐Ion Electrolyte

Abstract Calcium‐sulfur (Ca‐S) battery is a promising candidate for large‐scale energy storage system. However, the development of long‐life room‐temperature Ca–S batteries is hindered by the lack of effective sulfur cathode and the incompatibility between electrodes and electrolytes, leading to irreversible sulfur conversion, inefficient calcium plating/stripping and improper cathode/anode‐electrolyte interfaces (CEI/SEI). Herein, a turbo carbon layer confined small‐molecule/covalent sulfur cathode (S@C NS) with a record‐high content of 65.7% and enlarged carbon layer space is prepared via a C/S co‐deposition process. By using such a cathode and optimizing interfacial electrochemistry in LiPF 6 /Ca(BF 4 ) 2 ‐based hybrid electrolyte, a record‐breaking long‐life room‐temperature Ca‐S battery is reported. The capacity reaches 824.6 mAh g −1 at 100 mA g −1 with a retention of 47.9% after 145 cycles, and 462.1 mAh g −1 at even 500 mA g −1 . Mechanism studies demonstrated that a Li/Ca‐based hybrid CEI with porous microstructure is found to facilitate the transfer kinetics of Ca 2+ across the CEI; Turbo carbon layers with large inter‐layer space and their strong confinement on small‐molecule sulfur enabled reversible solid‐state sulfur conversion in situ inside the cathode; An effective Li/Ca‐based hybrid SEI formed on anode, allowing reversible Ca plating/stripping with low deposition potential and small overpotential.