Fluorinated Carboxylic Acid Ester and Carbonate Solvent Synergistically Improve Low‐Temperature Performance of LiFePO ₄ Batteries

Lithium iron phosphate (LiFePO₄) batteries are widely used in electric vehicles and energy storage systems due to high safety, long cycle life, and low cost. However, severe low-temperature performance fade limits their deployment in cold climates. To address this challenge, this study focuses on electrolyte design and interface engineering, proposing a novel low-temperature composite electrolyte system. This system simultaneously optimizes the low-temperature ion transport properties and interface stability of the electrolyte through the combination of fluorinated solvents and low-viscosity carbonate solvents with high ionic conductivity, along with rationally selected functional additives. Raman spectroscopy analysis revealed that the modified electrolyte can effectively modulate the electrolyte solvation structure and facilitate the formation of an anion-dominated solvation configuration. This structure not only lowers the energy barrier for lithium ion desolvation but also promotes the formation of a uniform, LiF-rich, and stable composite interface layer on LiFePO₄. As a result of these synergistic effects, the Li||LiFePO₄ battery with this electrolyte exhibits excellent low-temperature performance at -20°C, delivering a discharge specific capacity of about 120 mAh/g. This study offers a potential material design strategy for addressing the low-temperature performance bottleneck of LiFePO₄ batteries through electrolyte structure design and interface chemical regulation.