Tuning the Thermodynamic Equilibrium of Electrolyte Solvation Structures via Formation Entropy for Wide-Temperature Lithium-Ion Batteries

An anion-enriched solvation structure is crucial for electrolytes in establishing stable electrode-electrolyte interfaces and facilitating rapid Li⁺ transport kinetics. However, even a well-designed solvation structure can be sensitive to temperature variations, compromising the long-term cycling stability of batteries over wide temperature ranges. Herein, we design an electrolyte with temperature-independent anion-enriched solvation structures, by leveraging the ionic solvation/association equilibrium of Li⁺ in solvation structures based on the formation entropy (∂ΔG/∂T = -ΔS) counterbalancing of the mixed salts. This strategy effectively stabilizes the anion-enriched solvation structure and ensures the formation of robust inorganic interphases over a wide temperature range. Specifically, the electrolyte enables stable operation of Li||LiNi0.8Mn0.1Co0.1O₂ cells from -70 to 80 °C at a high charging voltage of 4.6 V, maintaining long-term cycling stability with no observable capacity decay over 1000 cycles at -20 °C. Further toward practical application, 4.5 V Ah-level Si/C||LiNi0.9Mn0.05Co0.05O₂ pouch cells achieve 92% capacity retention after 500 cycles over 250 days of operation at -20 °C. This work underscores the critical importance of understanding solvation structures from a thermodynamic perspective for the rational design of electrolytes, enabling their efficient implementation in batteries and other electrochemical systems.