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

Abstract

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 <i>in situ</i>/<i>ex situ</i> 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.