Crystalline and amorphous MnO 2 cathodes with open framework enable high-performance aqueous zinc-ion batteries

Currently, δ-MnO 2 is one of the popularly studied cathode materials for aqueous zinc-ion batteries (ZIBs) but impeded by the sluggish kinetics of Zn 2+ and the Mn cathode dissolution. Here, we report our discovery in the study of crystalline/amorphous MnO 2 (disordered MnO 2 ), prepared by a simple redox reaction in the order/disorder engineering. This disordered MnO 2 cathode material, having open framework with more active sites and more stable structure, shows improved electrochemical performance in 2 mol·L −1 ZnSO 4 /0.1 mol·L −1 MnSO 4 aqueous electrolyte. It delivers an ultrahigh discharge specific capacity of 636 mA·h·g −1 at 0.1 A·g −1 and remains a large discharge capacity of 216 mA·h·g −1 even at a high current density of 1 A·g −1 after 400 cycles. Hence disordered MnO 2 could be a promising cathode material for aqueous ZIBs. The storage mechanism of the disordered MnO 2 electrode is also systematically investigated by structural and morphological examinations of ex situ , ultimately proving that the mechanism is the same as that of the δ-MnO 2 electrode. This work may pave the way for the possibility of using the order/disorder engineering to introduce novel properties in electrode materials for high-performance aqueous ZIBs.