Low temperature deep eutectic solvents-assisted synthesis of amorphous MnO₂ cathode for zinc ion batteries

Rechargeable aqueous zinc ion batteries (ZIBs) are the promising alternatives to lithium-ion batteries owing to their high safety, high energy density, and low cost. However, the cathode materials of ZIBs commonly face sluggish diffusion kinetics, irreversible phase change, or serious structural collapse, which leads to poor practical energy density and serious capacity fading. Therefore, this work proposed a green, facile, and rapid deep eutectic solvents (DES) assisted synthetic method to produce amorphous MnO₂ and adopted as the cathode material for ZIBs. Different from crystalline structure, the amorphous MnO₂ with short-range order atomic arrangements and numerous structural defects could provide structural plasticity and large active sites for Zn²⁺ storage. Benefiting from these merits, the prepared amorphous MnO₂ display an initial discharge specific capacity up to 328.4 mAh g⁻¹ at the current density of 100 mA g⁻¹. It also maintains a high specific capacity of 278.0 mAh g⁻¹ and an excellent capacity retention rate of 91.6% after 1000 cycles at the high current density of 1000 mAh g⁻¹. Finally, the Zn²⁺ storage mechanism of this MnO₂//Zn battery also has been systematically explored. These findings will provide a green and fast way for designing advanced electrode materials for high-performance ZIBs.