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The electrolyte plays a critical role in lithium-ion batteries, as it impacts almost every facet of a battery’s performance. However, our understanding of the electrolyte, especially solvation of Li+, lags behind its significance. In this work, we introduce a potentiometric technique to probe the relative solvation energy of Li+ in battery electrolytes. By measuring open circuit potential in a cell with symmetric electrodes and asymmetric electrolytes, we quantitatively characterize the effects of concentration, anions, and solvents on solvation energy across varied electrolytes. Using the technique, we establish a correlation between cell potential (Ecell) and cyclability of high-performance electrolytes for lithium metal anodes, where we find that solvents with more negative cell potentials and positive solvation energies—those weakly binding to Li+—lead to improved cycling stability. Cryogenic electron microscopy reveals that weaker solvation leads to an anion-derived solid-electrolyte interphase that stabilizes cycling. Using the potentiometric measurement for characterizing electrolytes, we establish a correlation that can guide the engineering of effective electrolytes for the lithium metal anode.
Kim et al. (Tue,) studied this question.