DFT Study On Effects of CO₂ Contamination in Non-Aqueous Li-Air Batteries

Density Functional Theory (DFT) studies on the effects of carbon dioxide (CO₂) contamination at the cathode of rechargeable non-aqueous Li-O₂ batteries, where the insulating material Lithium peroxide (Li₂O₂) is the main discharge product. The Li₂O₂ growth mechanism and overpotentials are investigated with and without CO₂ at different nucleation sites such as steps, kinks and terraces of valley and ridge of the stable (1-100) Li₂O₂ surface. Though their corresponding binding energies show that CO₂ binds weakly at the surface, it binds preferentially at steps and kinks of the vally (1-100) Li₂O₂ surfaces, forming a type of Lithium coordinated carbonate species (Li_nCO₃), which reduces the effective equilibrium potential by 0.2 V. Small amounts of CO₂ can also affects the morphological growth directions of Li₂O₂ due to blocking of nucleation centers; why may enhance the electronic conduction and result in an increased battery capacity. However, CO₂ contamination on the Li₂O₂ surface confirms an asymmetric increase in the overpotentials; particularly the charging overvoltage exhibits sustantial increase, which would reduce the efficiency of the Li-air battery.