Solvent Co‐Intercalation Enabled Ca Storage in MoS 2 for Ca‐Ion Batteries

ABSTRACT Calcium‐ion batteries (CIBs) have the potential to be the next‐generation large‐scale energy storage system due to the low redox potential of multivalent Ca 2+ /Ca and the abundant Ca reserves in the Earth's crust. The surface passivation of metallic calcium prevents Ca 2 + diffusion, prompting research into intercalation‐type anode materials for CIBs. Herein, it is demonstrated for the first time that solvated Ca 2 + ions with ether molecules can reversibly co‐intercalate into commercial MoS 2 . An investigation is presented to understand the influence of electrolyte solvation level on the CIB performance and cycling stability of MoS 2 . In the highly solvated tetraethylene glycol dimethyl ether (G4) electrolyte, the Ca 2 + ‐G4 complex achieves reversible (de)intercalation in MoS 2 , exhibiting a capacity of 68.5 mAh g − 1 at a 10 mA g − 1 over 100 cycles. The co‐intercalation mechanism is elucidated using a suite of spectroscopic and microscopic characterization techniques as well as first‐principles calculations. Moreover, it is found that the co‐intercalation process is present for nanosized MoS 2 , showing its independence to size effect. This work demonstrates the versatility of the co‐intercalation mechanism for post‐lithium battery technologies and opens possibilities to explore more intercalation‐type electrode materials for CIBs.