Enhancement of OCV and capacity by activating electrolyte with polyiodide ions towards high-availability self-charging zinc ion batteries

Self-charging zinc ion batteries (ZIBs) without integrated external power generation equipment, featuring simple configuration and strong adaptability, is considered an advanced technology to overcome acute dependence on energy sources and high selectivity on the spatiotemporal environment in the conventional self-charging system. To enable high availability for practical applications, increasing the open-circuit voltage (OCV) and capacity of the self-charging ZIBs is undoubtedly an effective route. In this study, the self-charging mechanism of the VO2/ZnSO4/Zn (VO2/ZS/Zn) battery was revealed as the spontaneous oxidation of discharge product HVO2. Accordingly, polyiodide ions were introduced to activate the ZnSO4 electrolyte to enhance spontaneous oxidation. As a result, the OCV of the self-charging ZIB was increased from 1.15 to over 1.3 V. Further coupling with light stimulation, the self-charging capacity reached 206 mAh g−1 at 0.3 A g−1, while the self-charging process was shortened from more than 20 h to less than 2 h. The assembled pouch ZIBs displayed a stable capacity (retention: 80%) after 50 self-charging cycles. They can be charged at various modes, such as galvanostatic or/and self-charging in dark or light, demonstrating a powerful ability to harvest and store energy in different external environments. This work provides a facile and effective route to optimize performance for the practical applications of self-charging ZIBs in self-powered systems, clean energy harvest/storage, city power supply, etc.