Expanding the electrochemical stable window of water through propylene carbonate addition for aqueous-based energy storage devices

Abstract

Aqueous-based electrolytes with inherently low cost and high safety are promising electrolytes for energy storage devices. However, the narrow electrochemical window (∼1.23 V) of water limits the energy density of aqueous-based energy storage devices. Expanding the electrochemical stable window of water and simultaneously maintaining a high ionic conductivity, as well as broad temperature compatibility is highly desirable. Herein, we incorporated propylene carbonate into aqueous LiTFSI electrolyte to regulate the hydrogen bond network of water, thus expanding its electrochemical stable window up to 2.9 V while maintaining decent ionic conductivity (7.96 mS cm⁻¹), wide temperature compatibility (−20 to 50 °C). The electron donating functional group (i.e., CO) in propylene carbonate endows its strong interaction with water molecules and perturbs the pristine hydrogen bonds among water molecules, suppressing the decomposition of water. The prototypes of an EDLCs and Li-ion battery with the developed electrolyte demonstrate excellent electrochemical performance. Particularly, a 2.3 V aqueous lithium-ion battery assembled with LiMn₂O₄ and PTCDI shows high stability, retaining 89.2 % of its capacity after 1500 cycles and delivering an energy density of 116.6 Wh kg⁻¹. In EDLCs, the electrolyte supports operation at up to 2.6 V with 67.3 % capacitance retention after 100, 000 cycles and wide temperature compatibility. Such work paves a new avenue for the advancement of new aqueous electrolytes simultaneously featured with broad electrochemical window, low cost, and wide temperature compatibility.