Enhancing H+ intercalation kinetics and stability in Cu2+ pre-intercalated δ-MnO2 for aqueous aluminum batteries

Aqueous aluminum ion batteries (AAIBs) have garnered extensive attention due to their environmental friendliness, high theoretical capacity, and low cost. However, the sluggish reaction kinetics and severe structural collapse of the cathode material, especially manganese oxide, during the cycling process have hindered its further application. Herein, Cu²⁺ pre-intercalated layered δ-MnO₂ was synthesized via a hydrothermal method. The pre-intercalated Cu²⁺ ions not only improve the conductivity of MnO₂ cathode but also stabilize the structure to enhance stability. X-ray absorption fine structure (XAFS) combined with density functional theory (DFT) calculations confirm the formation of the covalent bond between Cu and O, increasing the electronegativity of O atoms and enhancing the H⁺ adsorption energy. Moreover, ex-situ measurements not only elucidate the Al³⁺/H⁺ co-insertion energy storage mechanism but also demonstrate the high reversibility of the Cu-MnO₂ cathode during cycling. This work provides a promising modification approach for the application of manganese oxides in AAIBs.