Unveiling the mysteries of operating voltages of lithium-carbon dioxide batteries

Lithium-carbon dioxide (Li-CO₂) batteries are regarded as a promising electrochemical system owing to their energy storage capability and CO₂ utilization. However, the reported operating voltage of ~2.6 V is increasingly questioned as seemingly beyond the capability of the electrochemical carbon dioxide reduction reaction to carbon. Herein, the real operating voltage of a Li-CO₂ battery is reacquainted, and the operating voltage and the equilibrium potential are clarified to be ~1.1 V and ~2.82 V, respectively. The products formed at low voltage are identified to be crystalline Li₂CO₃, amorphous C, and explicitly amorphous Li₂CO₃. Moreover, by decoupling small currents, 1% O₂, and 500 ppm H₂O, the operating voltage plateaus are stimulated to ~2.0 V. An ever-increasing plateau can be achieved up to the reported level of ~2.6 V activated by a minor air leak or residue in test environments. Conclusively, the operating voltages of Li-CO₂ batteries are proposed to be deceptive and extremely sensitive to the surrounding environments. This work unveils the real operating voltage and provides the voltage regulation rules to advance next-generation Li-CO₂ batteries.