Molecular Engineering to Construct MoS2 with Expanded Interlayer Spacing and Enriched 1T Phase for “Rocking-Chair” Aqueous Calcium-Ion Pouch Cells

The moderate working voltage and high capacity of transition metal dichalcogenides (TMDs) make them promising anode materials for aqueous calcium-ion batteries (ACIBs). However, the large radius and two charges of Ca2+ cause TMDs to exhibit poor performance in ACIBs. Therefore, effective regulation strategies are crucial for enabling the application of TMDs in ACIBs. Herein, MoS2 with expanded interlayer spacing and an enriched 1T phase (ES-1T-MoS2) is constructed by molecular engineering and reported as an anode material for ACIBs. Molecular engineering increases the capacity of MoS2 from 29.4 to 91.2 mAh g-1 and improves its rate performance from 20 to 76.1 mAh g-1 at 2.0 A g-1. ES-1T-MoS2 also shows a -20 to 50 °C wide temperature working capability. Furthermore, the capacity improvement reasons and the calcium storage mechanism of ES-1T-MoS2 are revealed through density functional theory calculations and in situ/ex situ characterizations. Finally, a "rocking-chair" aqueous calcium-ion pouch cell with a Prussian blue analogue cathode and ES-1T-MoS2 anode is assembled. The pouch cell exhibits a life of 150 cycles with over 90.8% capacity retention at 0 and 25 °C. This work demonstrates that molecular engineering is an effective strategy to improve the calcium storage performance of TMDs and promotes the advancement of ACIBs.