Designing In2S3@Bi2S3 type II heterostructure for bifunctional photo-enhanced Li-O2 batteries

Li-O2 batteries (LOBs) are expected to be one of the next-generation energy storage devices, but the problems of large overpotential and short lifespan are still obstacles. Utilizing light energy is an efficient way to overcome sluggish electrode reactions of LOBs. Here, we designed type II In2S3@Bi2S3 photoelectrode with enhanced visible light harvesting capability and spatial separation of photogenerated electron-hole pairs. Under illumination, photo-generated electrons are transferred from In2S3 to Bi2S3, then participate in Oxygen Reduction Reaction (ORR) during discharging, while photo-induced holes in valence band of In2S3 are conducive to the oxidation reaction of discharge products during charge process. Excitingly, the In2S3@Bi2S3 photoelectrode exhibited super high round-trip efficiency of 97.7 % under illumination, far exceeding that of 73 % in the dark. Besides, long cycle life of 1000 h at 200 mA g−1 with a limited capacity of 1000 mAh g−1 were achieved. Further tests on the photoelectrode surface show that the application of light energy promotes the depth of the electrode reaction, which are confirmed by theoretical calculations. This work provides a strategy to energy shortage and reveals the mechanism of photo-generated charge carriers in LOBs.