Nanorod-assembled urchin-like molybdenum–manganese oxide heterostructure with enhanced oxygen vacancies as a cathode for quasi solid state zinc-ion batteries

Abstract

The practical utilization of manganese-based cathodes in aqueous zinc-ion batteries (AZIBs) is constrained by their low conductivity and poor cycle stability. The construction of hierarchical structures and modulation of heterogeneous surfaces are significant strategies for improving their performance. Herein, nanorod-assembled urchin-like MoO₃–MnO₂ cathode materials were fabricated using MoO₃ nanobelts as the starting material through a self-assembly strategy. The Mn–O–Mo bond formed between the MoO₃ and MnO₂ heterostructures enhances the oxygen vacancies and improves the reaction kinetics of MoO₃–MnO₂. Moreover, the urchin-like micro-nanostructure provides a large special surface area and an efficient ion transport pathway. The battery assembled with MoO₃–MnO₂ as a cathode possesses a remarkable reversible capacity of 319 mA h g⁻¹ at 0.2 A g⁻¹ and a rate performance of 150 mA h g⁻¹ at 2 A g⁻¹. Even after 1000 cycles at 1 A g⁻¹, it still acquires an appreciable specific capacity of 155 mA h g⁻¹. The excellent electrochemical performance is attributed to the enhancement effect of oxygen vacancies and improved electrical conductivity of the MoO₃–MnO₂ heterostructure, which can be confirmed through electron paramagnetic resonance (EPR) spectra combined with calculation of density of states. Furthermore, ex situ characterization results acknowledge the energy storage mechanism of MoO₃–MnO₂. Additionally, the assembled flexible cells exhibited good mechanical and electrochemical performance.