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.