Taming the Ion-Dipole Interaction via Rational Diluent Selection for Low-Temperature Li-Metal Batteries

Developing advanced electrolytes with high Li affinity is crucial for achieving long-cycling lithium metal batteries (LMBs). However, the strong Li⁺-solvent interactions in conventional electrolytes often induce difficult Li⁺ desolvation especially under low-temperature conditions, resulting in the formation of fragile electrode interfaces involving solvents, and thus dissatisfactory cycling stability of LMBs. Herein, by introducing various diluents into the lithium hexafluorophosphate in 1, 2-dimethoxyethane electrolyte, we reveal that Li⁺ desolvation is influenced by not only the diluent-solvent interaction but also the diluent-anion interaction. Based on these findings, a diluent selection parameter (DSP), which is calculated based on the product of interaction energies of diluent-solvent/diluent-Li⁺ and diluent-anion/diluent-Li⁺, is proposed for diluent selection. A diluent with a larger DSP is more favorable for promoting Li⁺ desolvation and improving the low-temperature performance of LMBs. With the rationally selected 1, 2-dichloroethane diluent (DSP=3.95), the Li $$ Cu cell enables high Li reversibility (98.5 % after 300 cycles). Li $$ LiFePO₄ cell barely loses capacity at -20 °C for 300 cycles. The Li $$ LiNi_0.8Co_0.1Mn_0.1O₂ cell with the anode-to-cathode capacity ratio of 2.7 retains 87 % capacity retention after 100 cycles. This work provides new insights into taming strong Li-solvent interactions and offers a new paradigm for advanced electrolyte design.