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 Ca2+/Ca and the abundant Ca reserves in the Earth's crust. The surface passivation of metallic calcium prevents Ca2 + diffusion, prompting research into intercalation-type anode materials for CIBs. Herein, it is demonstrated for the first time that solvated Ca2 + ions with ether molecules can reversibly co-intercalate into commercial MoS2. An investigation is presented to understand the influence of electrolyte solvation level on the CIB performance and cycling stability of MoS2. In the highly solvated tetraethylene glycol dimethyl ether (G4) electrolyte, the Ca2 +-G4 complex achieves reversible (de)intercalation in MoS2, 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 MoS2, 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.