Improving Low-Temperature Tolerance of a Lithium-Ion Battery by a Localized High-Concentration Electrolyte Based on the Weak Solvation Effect

Due to the strong affinity between the solvent and Li⁺, the desolvation process of Li⁺ at the interface as a rate-controlling step slows down, which greatly reduces the low-temperature electrochemical performance of lithium-ion batteries (LIBs) and thus limits its wide application in energy storage. Herein, to improve the low-temperature tolerance, a localized high-concentration electrolyte based on weak solvation (Wb-LHCE) has been designed by adding a diluent hexafluorobenzene (FB) in a weak solvating solvent tetrahydrofuran (THF). Combining theoretical calculations with characterization tests, it is found that with the addition of diluent FB, the dipole–dipole interaction between the diluent and the solvent causes FB to compete with Li⁺ for THF. This competition causes the solvent to move away from Li⁺, weakening the binding energy between Li⁺ and THF, whereas the anions are transported into the solvation shell of Li⁺, forming an anion-rich solvation structure. In addition to accelerating the Li⁺ desolvation process, this unique solvation structure optimizes the composition of the CEI film, making it thin, dense, homogeneous, and rich in inorganic components, and thus improving the interfacial stability of the battery. As a result, the assembled LiFePO₄/Li half-cell shows excellent electrochemical performances at low temperature. That is, it can maintain a high discharge specific capacity of 124.2 mAh g⁻¹ after 100 cycles at a rate of 0.2C at −20°C. This provides an attractive avenue for the design of advanced low-temperature electrolytes and improvement of battery tolerance to harsh conditions.