Concentration Effects on the Entropy of Electrochemical Lithium Deposition: Implications for Li+ Solvation

The solvation behavior of Li+ in ethylene carbonate and dimethylcarbonate upon dilution has been investigated by electrochemical microcalorimetry. We measured the heat effects at a Li electrode upon electrochemical Li deposition and dissolution from Li+ solutions of varying concentration. The exchanged heat is correlated to the entropy of lithium deposition and therefore reveals information about the solvation of Li+. Lithium deposition from electrolytes with lower concentrations showed less entropy gain than deposition from electrolytes with higher concentrations. This can be fully explained by the entropy of dilution of the Li+ ions. From our data we further concluded that the inner coordination shell of the Li+ ions does not significantly change between 0.01 and 1 M Li+ concentration. The results also suggest that contact ion pairs, which are probably present in the electrolyte, show a similar solvation behavior as regular lithium ions.