Tailoring LiPF6-based electrolyte solvation structures via solvent regulation strategies for low-temperature lithium metal batteries

Abstract

Lithium metal batteries (LMBs) offer exceptional energy density, yet their practical application is limited by unstable solid electrolyte interphase (SEI) formation and sluggish Li⁺ transport, particularly under low-temperature conditions. Here, a carbonate electrolyte employing a cosolvent and dual-salt strategy is proposed to simultaneously tailor the Li⁺ solvation and interfacial chemistry of LiPF₆-based electrolytes. The introduction of ethyl methyl carbonate weakens the strong Li⁺–ethylene carbonate coordination, while difluoro(oxalato)borate anions preferentially undergo interfacial reduction to construct a robust, inorganic-rich SEI. This tailored solvation environment affords a low Li⁺ diffusion energy barrier and effectively suppresses lithium dendrite formation. As a result, the electrolyte delivers exceptional low-temperature performance, achieving an ionic conductivity of 1.013 mS cm⁻¹ at −30 °C and a reduced desolvation energy of 66.84 kJ mol⁻¹. High-loading LFP∥Li full cells exhibit a specific capacity of 163.06 mAh g⁻¹ at 0.2C and retain over 80% capacity after 200 cycles at 25 °C. Even at −30 °C, the cells maintain 58% capacity retention after 100 cycles. This work highlights the interplay between solvation chemistry, SEI composition, and interfacial ion transport, offering a viable design paradigm for high-performance carbonate electrolytes in low-temperature LMBs.