Electrochemical Study of Polymorphic MnO2 in Rechargeable Aqueous Zinc Batteries

Manganese dioxide is regarded as a promising energy functional material due to its open tunnel structure with enormous applications in energy storage and catalysis. In this paper, α-MnO2with a 2 × 2 tunnel structure and β-MnO2with a 1 × 1 tunnel structure were hydrothermally synthesized, which possess characteristic tunnel structures formed by the interconnected unit structure of [MnO6] octahedrons. With regards to their different tunnel dimensions, the specific mechanism of ion intercalation in these two phases and the effect on their performance as aqueous Zn-MnO2battery cathodes are explored and compared. Comprehensive analyses illustrate that both α-MnO2and β-MnO2provide decent capacity in the aqueous battery system, but their intrinsic stability is poor due to the structural instability upon cycling. At the same time, experiments show that α-MnO2has a better rate performance than β-MnO2under larger currents, thus implying that the former has a broader application in this aqueous battery system.Keywords:α-MnO2and β-MnO2nanostructures;aqueous zinc batteries;electrochemical characterization