Effective Water Confinement and Dual Electrolyte–Electrode Interfaces by Zwitterionic Oligomer for High-Voltage Aqueous Lithium-Ion Batteries

Abstract

Aqueous lithium-ion batteries (ALIBs) have attracted significant interest due to their inherent advantage on safety. However, water itself has a narrow electrochemical stability window (ESW), limiting the energy density of ALIBs. Here, a low-molecular-weight zwitterionic oligomer, oligo(propylsulfonate dimethylammonium propylmethacrylamide) (OPDP), as an effective water binding agent for high-voltage ALIBs is demonstrated. The OPDP can effectively confine water molecules while reducing water activity. The OPDP-based electrolyte, with an ultra-high water weight percentage of 25.4%, possesses an outstanding ESW of up to 3.26 V and an ionic conductivity as high as 3.18 mS cm⁻¹. Furthermore, the aqueous Mo<inf>6</inf>S<inf>8</inf>//LiMn<inf>2</inf>O<inf>4</inf> full cell with OPDP-based electrolyte achieves a 99.7% capacity retention after 200 cycles at 0.5C with a high Coulombic efficiency (CE) of 98.7% and a specific energy of 88–101 Wh kg⁻¹. Also, it achieves an 89% capacity retention after 2000 cycles at 10C with a high CE of 99.9%. These postmortem characterizations suggest that robust organic–inorganic hybrid cathode/anode-electrolyte interfaces have been constructed during the cycling through the heteroatoms of N, S, and O in the zwitterionic oligomer, leading to the inhibited hydrogen/oxygen evolution reactions and high performance of the full cell. This work provides a promising strategy for developing low-cost and high-voltage aqueous batteries.