Synergistic Molecular Engineering Strategies for Enhancing Diffusion Kinetics and Interfacial Stability of the δ-MnO2 Cathode in Aqueous Zinc-Ion Batteries

Abstract

Layered manganese dioxide (δ-MnO<inf>2</inf>) is a promising cathode material for aqueous zinc-ion batteries (AZIBs) due to its high theoretical capacity, high operating voltage, and low cost. However, its practical application faces challenges, such as low electronic conductivity, sluggish diffusion kinetics, and severe dissolution of Mn²⁺. In this study, we developed a δ-MnO<inf>2</inf> coated with a 2-methylimidazole (δ-MnO<inf>2</inf>@2-ML) hybrid cathode. Density functional theory (DFT) calculations indicate that 2-ML can be integrated into δ-MnO<inf>2</inf> through both pre-intercalation and surface coating, with thermodynamically favorable outcomes. This modification expands the interlayer spacing of δ-MnO<inf>2</inf> and generates Mn–N bonds on the surface, enhancing Zn²⁺ accommodation and diffusion kinetics as well as stabilizing surface Mn sites. The experimentally prepared δ-MnO<inf>2</inf>@2-ML cathode, as predicted by DFT, features both 2-ML pre-intercalation and surface coating, providing more zinc-ion insertion sites and improved structural stability. Furthermore, X-ray diffraction shows the expanded interlayer spacing, which effectively buffers local electrostatic interactions, leading to an enhanced Zn²⁺ diffusion rate. Consequently, the optimized cathode (δ-MnO<inf>2</inf>@2-ML) presents improved electrochemical performance and stability, and the fabricated AZIBs exhibit a high specific capacity (309.5 mAh/g at 0.1 A/g), superior multiplicative performance (137.6 mAh/g at 1 A/g), and impressive capacity retention (80% after 1350 cycles at 1 A/g). These results surpass the performance of most manganese-based and vanadium-based cathode materials reported to date. This dual-modulation strategy, combining interlayer engineering and interface optimization, offers a straightforward and scalable approach, potentially advancing the commercial viability of low-cost, high-performance AZIBs.