Malin Li^a,b, Xiaoxue Wang^a, Fei Li^a, Lijun Zheng^a, Jijing Xu^a,b* and Jihong Yu^a,b*. Adv. Mater. DOI: 10.1002/adma.201907098.

^a. State Key Laboratory of Inorganic Synthesis and Preparative Chemistry, College of Chemistry, Jilin University, Changchun 130012, P. R. China
^b. International Center of Future Science, Jilin University, Changchun 130012, P. R. China

Photo-assisted charging is considered an effective approach to reducing the overpotential in lithium-oxygen (Li-O₂) batteries. However, the utilization of photoenergy during the discharge process in a Li-O₂ system has been rarely reported, and the functional mechanism of such a process remains unclear. Herein, a novel bifunctional photo-assisted Li-O₂ system has been established by employing a hierarchical TiO₂-Fe₂O₃ heterojunction, in which the photo-generated electrons and holes played key roles in reducing the overpotential in the discharging and charging processes, respectively. Moreover, the morphology of the discharge product (Li₂O₂) could be modified via the dense surface electrons of the cathode under illumination, resulting in the promoted decomposition kinetics of Li₂O₂ during the charging progress. Accordingly, the output and input energies of the battery could be tuned by illumination, giving an ultralow overpotential of 0.19 V between the charge and discharge plateaus with excellent cyclic stability (retaining a round-trip efficiency of ~86% after 100 cycles). The investigation of the bifunctional photo-assisted process presented in this work provides a significant insight into the mechanism of the photo-assisted Li-O₂ battery and addresses the overpotential bottleneck in this system.