An optimized MnO2 photocathode by doping engineering for high capacity and stability photo-assisted zinc-ion batteries

Abstract

Photo-assisted zinc-ion batteries (PAZIB) are expected to solve the problem of intermittent solar energy supply for sustainable development due to their ability to integrate light absorption and energy storage. However, the low conductivity, low photoelectric conversion efficiency, and poor cycling stability of photocathodes have impeded their practical applications. Herein, an Al-doped MnO₂ (Al-MnO₂) photocathode is designed for a high-performance PAZIB with high capacity and stability. The specific capacity of the Al-MnO₂-based PAZIB increases from 320 mA h g⁻¹ in the dark to 526 mA h g⁻¹ under illumination (64.4% increase) at 0.2 A g⁻¹. Furthermore, the capacity retention of the Al-MnO₂-based PAZIB is 96% after 1000 cycles at 1 A g⁻¹ under irradiation, demonstrating excellent cycling stability. Theoretical simulation and systematic experiments demonstrate that Al-doping engineering reduces the bandgap with a downward conduction band, accelerates carrier transport between MnO₂ and the collector, and improves photogenerated carrier separation efficiency, synergistically boosting the photo-assisted charging capacity of PAZIB. Meanwhile, the enlarged layer spacing of Al-MnO₂ and robust Al–O bonds alleviate the structural collapse, thereby realizing excellent multicycle stability under illumination. This work provides a new approach for designing efficient and stable photocathodes.