A Safe Flexible Self-Powered Wristband System by Integrating Defective MnO2–x Nanosheet-Based Zinc-Ion Batteries with Perovskite Solar Cells

The booming market of portable and wearable electronics has aroused the requests for advanced flexible self-powered energy systems featuring both excellent performance and high safety. Herein, we report a safe, flexible, self-powered wristband system by integrating high-performance zinc-ion batteries (ZIBs) with perovskite solar cells (PSCs). ZIBs were first fabricated on the basis of a defective MnO_2-x nanosheet-grown carbon cloth (MnO_2-x@CC), which was obtained via the simple lithium treatment of the MnO₂ nanosheets to slightly expand the interlayer spacing and generate rich oxygen vacancies. When used as a ZIB cathode, the MnO_2-x@CC with a ultrahigh mass loading (up to 25.5 mg cm^-2) exhibits a much enhanced specific capacity (3.63 mAh cm^-2 at current density of 3.93 mA cm^-2), rate performance, and long cycle stability (no obvious degradation after 5000 cycles) than those of the MnO₂@CC. Importantly, the MnO_2-x@CC-based quasi-solid-state ZIB not only achieves excellent flexibility and an ultrahigh energy density of 5.11 mWh cm^-2 (59.42 mWh cm^-3) but also presents a high safety under a wide temperature range and various severe conditions. More importantly, the flexible ZIBs can be integrated with flexible PSCs to construct a safe, self-powered wristband, which is able to harvest light energy and power a commercial smart bracelet. This work sheds light on the development of high-performance ZIB cathodes and thus offers a good strategy to construct wearable self-powered energy systems for wearable electronics.