ZnO@MnO ₂ Heterojunction Photocathode for High‐Capacity Photo‐Assisted Zinc‐Ion Battery

ABSTRACT Photo‐assisted zinc ion batteries (PAZIB) integrating solar energy harvesting, conversion, and storage attract increasing attention, but it remains challenging to design high‐capacity PAZIB. In this study, the ZnO@MnO ₂ heterojunction is proposed to function as the photocathode of PAZIB and has demonstrated high energy storage performance. The specific capacity of ZnO@MnO ₂ PAZIB is about 545 mAh g ⁻¹ at the current density of 0.2 A g ⁻¹ under illumination, which is 92.58% higher than that in the dark and exceeds most reported PAZIB. Moreover, the capacity retention rate of heterojunction PAZIB is 80.28% after 200 illumination cycles at the high current density of 1 A g ⁻¹ , which is better than that of pure MnO ₂ (61.5%). The improved performance is due to the construction of ZnO@MnO ₂ heterojunction, which improves the photogenerated electron–hole separation efficiency, enhances the conductivity, and accelerates electrochemical reaction kinetics. In addition, a series of ex situ characterization tests have been conducted to explore the mechanism of PAZIB energy storage, demonstrating that Zn ²⁺ embedding/deembedding behavior leads to reversible material conversion between MnO ₂ and ZnMn ₂ O ₄ . Our work provides more strategies for designing high‐performance PAZIB.