Designing a photo-assisted Co-C3N4 cathode for high performance Li-O2 batteries

Li-O2 batteries with extremely high specific energy density have been regarded as a kind of promising successor to current Li-ion batteries. However, the high charge overpotential for the decomposition of Li2O2 discharge product reduces the energy efficiency and triggers a series of side reactions that cause the Li-O2 batteries to have a limited lifetime. Herein, Co-doped C3N4 (Co-C3N4) photocatalysts were designed by an in situ thermal evaporation method to take advantage of the photo-assisted charging technology to conquer the shortcomings of Li-O2 batteries encountered in the charge process. Different from the commonly used photocatalysts, the Co-C3N4 photocatalysts perform well no matter with and without illumination, owing to the Co doping induced conductivity and electrocatalytic ability enhancement. This makes the Co-C3N4 reduce the charge and discharge overpotentials and improve the cycling performance of Li-O2 batteries (from 20 to 106 cycles) without illumination. While introducing illumination, the performance can be further improved: Charge voltage reduces to 3.3 V, and the energy efficiency increases to 84.84%, indicating that the Co-C3N4 could behave as a suitable photocathode for Li-O2 batteries. Besides, the low charge voltage and the continuous illumination together weaken the corrosion of the Li anode, making the long-term high-efficiency operation of Li-O2 batteries no longer just extravagant hope.