Potassium ion pre-intercalated MnO(2) for aqueous multivalent ion batteries

Manganese dioxide (MnO(2)), as a cathode material for multivalent ion (such as Mg(2+) and Al(3+)) storage, is investigated due to its high initial capacity. However, during multivalent ion insertion/extraction, the crystal structure of MnO(2) partially collapses, leading to fast capacity decay in few charge/discharge cycles. Here, through pre-intercalating potassium-ion (K(+)) into δ-MnO(2), we synthesize a potassium ion pre-intercalated MnO(2), K(0.21)MnO(2)·0.31H(2)O (KMO), as a reliable cathode material for multivalent ion batteries. The as-prepared KMO exhibits a high reversible capacity of 185 mAh/g at 1 A/g, with considerable rate performance and improved cycling stability in 1 mol/L MgSO(4) electrolyte. In addition, we observe that aluminum-ion (Al(3+)) can also insert into a KMO cathode. This work provides a valid method for modification of manganese-based oxides for aqueous multivalent ion batteries. GRAPHICAL ABSTRACT: [Image: see text] SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s12200-023-00093-0.