Tuning Intermolecular Interactions of Molecular Crowding Electrolyte for High-Performance Aqueous Batteries

Using cost-effective and environmentally friendly molecular crowding agents to replace highly concentrated salts is a promising strategy to suppress water decomposition in electrochemical energy storage devices. However, the lack of comprehensive understanding on how a crowding agent structure affects the key properties of electrolyte prevents rational design of molecular crowding electrolyte for high-power and high-voltage aqueous batteries. Here, we investigated how the terminal group and the chain length of the crowding agent affect the conductivity and the voltage window. On the basis of the design principles revealed, we developed a new crowding agent, polyethylene glycol dimethyl ether (PEGDME) 450, demonstrating 3 times higher conductivity (2.4 mS cm–1 vs 0.8 mS cm–1) than state-of-the-art polyethylene glycol (PEG) 400 without sacrificing the voltage window (3.2 V). A high-power and high-voltage aqueous Li4Ti5O12/LiMn2O4 cells with this new electrolyte operated (5 C, 72 Wh kg–1 vs 10 Wh kg–1 PEG400) for 800 cycles. This work demonstrates a universal strategy for advanced aqueous electrolyte design and high-performance batteries.