Dampening Lithium Charge Density by Clustering Solvents and Anions to Tame Lithium De-Coordination Energy for Low-Temperature Lithium-Metal Batteries

Sluggish lithium (Li) de-coordination kinetics on the interface hinder the development of high-energy and low-temperature Li-metal batteries (LMBs). In principle, weakly coordinated solvents and anions contribute to improved low-temperature battery performances due to low Li de-solvation and de-anion energy barrier on the anode interface. However, extensive works employ strategies that go against the above-mentioned principle, commonly using strong coordination strength solvents and anions to facilitate rate and cyclic performances. The in-depth understanding of this refined Li coordination structure that accelerates Li redox kinetics remains rather elusive. To bridge such gap between theoretical implication and realistic practice of solvent and salt selection, this work examines a model electrolyte involving the strong coordination strength salt (lithium nitrate, LiNO₃) and solvent (triethyl phosphate, TEP) to decipher how electron transfer occurred in the cluster solvation impacts Li charge density and dictates Li transport kinetics. One of the critical interpretations is that the electron-donating nature of LiNO₃ reduces the positive charge of Li⁺, which dampens the interaction between Li⁺ and TEP ligands. Another key finding is that clustering [LiNO₃–Li⁺–TEP] intensifies the interfacial charge exchange to hasten Li transport kinetics, since anion-participated cluster solvates exhibit high effective charges than that of anion-lean Li solvates. This work updates the understanding of why the cluster solvates benefits Li de-coordination kinetics and hopes to finger out new principles to select Li salts and solvents for better low-temperature Li metal batteries.