Strengthening Aqueous Electrolytes without Strengthening Water
Longteng Tang, Yunkai Xu, Weiyi Zhang, Yiming Sui, Alexis M. Scida, Sean R. Tachibana, Mounesha N. Garaga, Sean K. Sandstrom, Nan‐Chieh Chiu, Kyriakos C. Stylianou, Steve Greenbaum, P. Alex Greaney, Chong Fang, Xiulei Ji
Abstract
Abstract Aqueous electrolytes typically suffer from poor electrochemical stability; however, eutectic aqueous solutions—25 wt.% LiCl and 62 wt.% H 3 PO 4 —cooled to −78 °C exhibit a significantly widened stability window. Integrated experimental and simulation results reveal that, upon cooling, Li + ions become less hydrated and pair up with Cl − , ice‐like water clusters form, and H⋅⋅⋅Cl − bonding strengthens. Surprisingly, this low‐temperature solvation structure does not strengthen water molecules’ O−H bond, bucking the conventional wisdom that increasing water's stability requires stiffening the O−H covalent bond. We propose a more general mechanism for water's low temperature inertness in the electrolyte: less favorable solvation of OH − and H + , the byproducts of hydrogen and oxygen evolution reactions. To showcase this stability, we demonstrate an aqueous Li‐ion battery using LiMn 2 O 4 cathode and CuSe anode with a high energy density of 109 Wh/kg. These results highlight the potential of aqueous batteries for polar and extraterrestrial missions.