Rational anion selection of the electrolyte additive for highly reversible lithium plating/stripping

Recruiting anions from electrolyte additives into the lithium ion solvation structure is a promising strategy for the construction of long-lifespan Li-metal batteries (LMBs). However, inadequate understanding of the anion-involved Li${}^{+}$ solvation hinders the finding of new anion additives. Herein, using NO${}_3$${}^{-}$ as an example, the effects of the newly-introduced anion on the Li${}^{+}$ solvation structure are investigated. It is demonstrated that the added NO${}_3$${}^{-}$ reduces the electrostatic potential of the Li${}^{+}$ solvation cluster, especially for solvated solvents, which improves electrolyte stability against the Li anode. However, such a conclusion is not universal for all anion additives. It is also confirmed that the anions with higher binding energy and smaller ion size are more apt to improve the Li stability and reversibility. Based on the above understanding, a new selection principle based on anion selection coefficient (the rate of the anion size to the binding energy toward Li${}^{+}$, unit: Å${}^3$ eV${}^{-1}$) is proposed, and with which a new hexafluorosilicate anion is found to be beneficial to LMBs. (© 2023 Wiley‐VCH GmbH)