Hollow MoS₃ Nanospheres as Electrode Material for “Water-in-Salt” Li–Ion Batteries

The use of “water-in-salt” electrolyte (WISE) (i. e., a highly concentrated aqueous solution) in rechargeable batteries has received increasing attention due to the significantly expanded electrochemical window compared to the limited voltage of conventional aqueous electrolytes. It enables the use of more positive/negative electrode material couples in aqueous batteries, resulting in an enhanced output voltage. However, one of the challenges is to identify promising anode materials for the “water-in-salt” Li-ion batteries (WIS-LIBs). Herein we for the first time demonstrate that MoS₃, an amorphous chain-like structured transitional metal trichalcogenide, is promising as anode in the WIS-LIBs. In this work, hollow MoS₃ nanospheres were synthesized via a scalable room-temperature acid precipitation method. When applied in WIS-LIBs, the prepared MoS₃ achieved a high specific capacity of 127 mAh/g at the current density of 0.1 A/g and good stability over 1000 cycles. During operation, MoS₃ underwent irreversible conversion to Li₂MoO₄ (with H₂S and H₂ evolution) during the initial Li ion uptake, and was then converted gradually to a more stable and reversible Li_xMoO_y (2≤y≤4)) phase along cycling. Amorphous Li-deficient Li_x-mMoO_y/MoO_z was formed upon delithiation. Nevertheless, MoS₃ outperformed MoO₃ in WIS-LIBs, which could be accredited to its initial one-dimensional molecular structure and the amorphous nature of the delithiated product facilitating charge transport. These results demonstrated a novel routine for synthesizing metal sulfides with hollow structures using a template-based method and push forward the development of metal sulfides for aqueous energy storage applications.