A Tetrahydropyran-Based Weakly Solvating Electrolyte for Low-Temperature and High-Voltage Lithium Metal Batteries

Abstract

Ether-based electrolytes show great potential in low-temperature lithium metal batteries (LMBs) for their low viscosity and decent reduction stability. However, conventional ethers with multidentate chelate sites suffer from low oxidation stability and high desolvation energy barrier due to the strong coordination between oxygen and Li⁺. Herein, cyclic tetrahydropyran (THP) with a unidentate site is designed as a solvent, and fluoroethylene carbonate (FEC) and lithium nitrate (LiNO₃) serve as additives for low-temperature LMBs. The cyclic strain and unidentate chelate effect endow THP with a weak affinity to Li⁺ ions, which accelerates Li⁺ desolvation process and induces the anion-derived electrode/electrolyte interface at low temperature. The formed inorganic-rich interface further improves the oxidation stability and expedites the interfacial ion transportation. As a result, the assembled Li-LiNi_0.8Mn_0.1Co_0.1O₂ (NMC811) cell stably cycles with 87% capacity retention after 100 cycles at −40 °C and 4.5 V. The 2.7 Ah Li-NMC811 pouch cell with an energy density of 403 Wh kg⁻¹ delivers 53% of the room-temperature capacity at −50 °C. This work reveals that regulating the chelate site of solvents can well optimize the electrolytes to realize low-temperature LMBs.