Governing Role of Solvent on Discharge Activity in Lithium-CO2 Batteries.

Non-aqueous Li-CO2 batteries reported in  literature have almost exclusively relied upon glyme-based electrolytes, leading to a hypothesis that they are uniquely active for CO2 discharge. Here, we study the effect of electrolyte composition on CO2 activity to examine whether this is the case. The results indicate that TEGDME-based electrolytes containing moderate concentrations of Li+ salts (roughly within the range of 0.7-2 M examined herein) are most conducive to CO2 activation, especially compared to dimethyl sulfoxide and propylene carbonate-based electrolytes. Through electrochemical, spectroscopic, and computational methods, we determine that glymes have lower desolvation energies for Li+  compared to other solvent candidates, whereas high salt concentrations increase the local density of Li+ surrounding CO2 and reduction intermediates. These attributes collectively increase the availability of Li+, crossing a threshold necessary to support CO2  activation. Discharge voltage and reaction rates are also sensitive to the alkali cation identity, further invoking its key role in enabling or suppressing reactivity.