Electrolyte Chemistry Design via Mediumly Solvating Structure for High‐Voltage and Low‐Temperature Aqueous Batteries

High‐voltage aqueous batteries (>2 V) are highly anticipated as the next generation of low‐cost, intrinsically safe battery technology for renewable energy harvesting. However, parasitic water‐related reactions and the restricted operating temperature range of electrolytes pose obstacles for their broader applicability. An ideal high‐voltage and low‐temperature electrolyte must balance seemingly contradictory properties of low water activity but high ionic conductivity, facile de‐solvation but anion‐derived interphase. Achieving this multifaceted balance has remained a longstanding challenge. Here, leveraging both conceptual modeling and experimental design approaches, mediumly solvating electrolytes (MSEs) are proposed that enable precise modulation of ionic solvation behavior. As a representative model, MSE employing succinonitrile as a co‐solvent can mediumly coordinate with Li + , reshaping the solvation shell into Li + ‐anion‐water incorporated structures. This tailored solvation environment reduces Li⁺ desolvation energy and promotes a robust and stable electrode/electrolyte interphase. 2.5 V LiMn 2 O 4 ||Li 4 Ti 5 O 12 full cells achieve an average 99.3% Coulombic efficiency for 1000 cycles with 98% capacity retention at 1 C. At −20 °C, the full cell exhibits outstanding rate performance and maintains stable cycling over 200 cycles at 0.5C. This work offers guidance for designing high‐stability and temperature‐adaptability batteries toward practical application.