Superior electrochemical performance of alkali metal anodes enabled by milder Lewis acidity

In the development of electrolytes for high-performance alkali metal batteries, significantly different electrochemical performances were often reported among lithium (Li), sodium (Na), and potassium (K) metals tested in the electrolytes with similar compositions but the underlying mechanism behind these observed discrepancies remains unclear. Here, by adopting a suite of complementary analytical techniques aided with theoretical calculations, we show a close correlation between the Lewis acidity of alkali metal ions and the electrochemical performance of corresponding alkali metals. The lower Lewis acidity of K compared with that of Li and Na endows K with distinctive advantages to easily strip off the reduction-vulnerable solvent and greatly reduces the dissociation degree of K salts to form an anion-rich solvation sheath, resulting in a robust solid electrolyte interphase. These features lead K metal to outperform Li and Na metals in terms of both electrochemical cycling reversibility and calendar aging stability in the present study. Weak Lewis acidity of potassium-ions promotes enhanced anion incorporation into the solvation shell, facilitating the formation of a more stable and dissolution-resistant solid electrolyte interphase for K metal compared with that for Li and Na metals.