Aqueous zinc-metal batteries are promising next-generation energy storage systems due to their low cost, high abundance, non-toxicity and environmental friendliness. The usage of aqueous electrolytes ensures high safety and easy handling, making them particularly attractive for stationary energy storage applications. Various cathode materials such as vanadium-based, manganese-based and Prussian blue analogues have been investigated. Among them, layered MnO2 stands out due to its high theoretical specific capacity, low cost and wide availability, making it one of the most promising cathode materials not only for primary but also for secondary zinc-metal and zinc-ion batteries. However, the large-scale commercialization of Zn-MnO2 rechargeable batteries is still hindered by several challenges. The zinc anode faces hydrogen evolution and dendrite formation, while the cathode materials suffer from sluggish Zn2+ kinetics and structural degradation caused by strong electrostatic interactions between the Zn2+ ions and the host lattice as well as Mn dissolution. Pre-intercalation of alkali metal ions is an effective strategy to expand the interlayer spacing where the cations act as structural pillars. This approach can facilitate reversible Zn2+ intercalation and thereby enhance the structural stability of the active material. In this work, a series of K- and Na- pre-intercalated δ-MnO₂ cathode materials were synthesized and investigated with regards of the type and concentration of the intercalated cations on the interlayer spacing. The electrochemical performance was evaluated using cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and galvanostatic charge discharge measurements. As the electrochemical performance is strongly influenced by the (micro)structural properties, these were additional analyzed on the one hand by X-ray diffraction (XRD) and scanning electron microscopy (SEM) and on the other hand by Raman spectroscopy as it is very sensitive to oxygen-cation vibrations and serves as an exceptional probe for local disorder and ordering effects. The findings are discussed in light of the above analysis and in relation to previous findings.Acknowledgements: Elias Bodin is Ph.D. student at the International Graduate School for Battery Chemistry, Characterization, Analysis, Recycling and Application BACCARA which is funded by the Ministry of Culture and Science of the State North-Rhine Westphalia.Literature1 B. Zhang et al., Chem & Bio Engineering, 2024, 1 (2), 113-132.2 J. Ruppert et al. Adv. Energy Mater., 2025, 15, (38): e02866.
Bodin et al. (Thu,) studied this question.