Hierarchically porous delta–manganese dioxide films prepared by an electrochemically assistant method for Mg ion battery cathodes with high rate performance

One of the challenges hindering the development of magnesium ion batteries is the slow diffusion kinetics of Mg²⁺ in host materials due to the strong electrostatic interactions. Delta–manganese dioxide (δ–MnO₂) have been investigated as highly capable Mg²⁺ host material owing to its structural water, which effectively screening the interaction of Mg²⁺ with host lattices and therefore facilitates the Mg²⁺ intercalation/deintercalation. Herein, hierarchically porous δ–MnO₂ films are synthesized on Ti foils by an electrochemically assistant method. Electron microscope results demonstrate that the films are array structures of δ–MnO₂ nanoflakes, which are constructed by mesopores and δ–MnO₂ nanograins. In aqueous electrolyte, the accelerated kinetics of Mg²⁺ in host lattice enables the high rate performance (250 mAh g⁻¹ at 100 mA g⁻¹) and excellent cycle performance (84% retains after 1500 cycles at 3 A g⁻¹) of the cathode material.