Practicality assessment: Temperature-governed performance of CO₂-containing Li–O₂ batteries

Practical lithium–oxygen batteries require a shift from pure O₂ to air. CO₂ traces, however, fundamentally alter the O₂ electrochemistry towards Li₂CO₃ formation via peroxocarbonate intermediates in highly-solvating electrolytes e.g., tetraethylene glycol dimethyl ether (G4). Here, we reveal that operating temperatures (0∼70 °C) critically dictate Li₂CO₃-associated cell overcharges (4.60∼3.77 V), by determining temperature-dependent reaction kinetics and evolving species mobility, as analogously witnessed under pure O₂-conditions. Against what is observed for Li₂O₂ formation in the Li–O₂ cell, however, cell temperatures do not govern the crystallinity of the Li₂CO₃ discharge product. In agreement with experimental observations, comprehensive density functional theory calculations also uncover the effect of the temperature on the Li₂CO₃ precipitation mechanism and shed light on the dwindling stabilization of metastable peroxocarbonate intermediates during discharge at increasing cycling temperatures. On the other hand, during extended operation, the temperature-dependent reactants mobility in the viscous G4 electrolyte and remnant Li-deficient carbonate surfaces from precedent recharge steps play equally prominent roles on the Li₂CO₃ precipitation mechanism and the resulting cell capacity. Our study highlights the complexity of practical Li–O₂ cells with temperature-dependent performances.