Unveiling the Formation and Electrochemical Properties of Nano-Clusters in Lithium Battery Electrolyte Induced by Nitrate Ion

LiNO₃ is known to significantly enhance the reversibility of lithium metal batteries; however, the modification of solvation structures in various solvents and its further impact on the interface have not been fully revealed. Herein, we systematically studied the evolution of solvation structures with increasing LiNO₃ concentration in both carbonate and ether electrolytes. The results from molecular dynamics simulations unveil that the Li⁺ solvation structure is less affected in carbonate electrolytes, while in ether electrolytes, there is a significant decrease of solvent molecules in Li⁺ coordination, and a larger average size of Li⁺ solvation structure emerges as LiNO₃ concentration increases. Notably, the formation of large ion aggregates with size of several nanometers (nano-clusters), is observed in ether-based electrolytes at conventional Li⁺ concentration (1 $\mathrm{M}$) with higher NO₃⁻ ratio, which is further proved by infrared spectroscopy and small-angle X-ray scattering experiments. The nano-clusters with abundant anions are endowed with a narrow energy gap of molecular orbitals, contributing to the formation of an inorganic rich electrode/electrolyte interphase that enhances the reversibility of lithium stripping/plating with Coulombic efficiency up to 99.71%. The discovery of nano-clusters elucidates the underlying mechanism linking ions/solvent aggregation states of electrolytes to interfacial stability in advanced battery systems.