Potassium ion pre-intercalated MnO2 for aqueous multivalent ion batteries.

Abstract

Manganese dioxide (MnO₂), as a cathode material for multivalent ion (such as Mg²⁺ and Al³⁺) storage, is investigated due to its high initial capacity. However, during multivalent ion insertion/extraction, the crystal structure of MnO₂ partially collapses, leading to fast capacity decay in few charge/discharge cycles. Here, through pre-intercalating potassium-ion (K⁺) into δ-MnO₂, we synthesize a potassium ion pre-intercalated MnO₂, K_0.21MnO₂·0.31H₂O (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 MgSO₄ electrolyte. In addition, we observe that aluminum-ion (Al³⁺) can also insert into a KMO cathode. This work provides a valid method for modification of manganese-based oxides for aqueous multivalent ion batteries.