Enabling Reversible MnO2/Mn2+ Transformation by Al3+ Addition for Aqueous Zn-MnO2 Hybrid Batteries

Aqueous rechargeable Zn-manganese dioxide (Zn-MnO2) hybrid batteries based on dissolution-deposition mechanisms exhibit ultrahigh capacities and energy densities due to the two-electron transformation between MnO2/Mn2+. However, the reported Zn-MnO2 hybrid batteries usually use strongly acidic and/or alkaline electrolytes, which may lead to environmental hazards and corrosion issues of the Zn anodes. Herein, we propose a new Zn-MnO2 hybrid battery by adding Al3+ into the sulfate-based electrolyte. The hybrid battery undergoes reversible MnO2/Mn2+ transformation and exhibits good electrochemical performances, such as a high discharge capacity of 564.7 mAh g(-1) with a discharge plateau of 1.65 V, an energy density of 520.8 Wh kg(-1), and good cycle life without capacity decay upon 2000 cycles. Experimental results and theoretical calculation suggest that the aquo Al3+ with Bronsted weak acid nature can act as the proton-donor reservoir to maintain the electrolyte acidity near the electrode surface and prevent the formation of Zn-4(OH)(6)(SO4)center dot 0.5H(2)O during discharging. In addition, Al3+ doping during charging introduces oxygen vacancies in the oxide structure and weakens the Mn-O bond, which facilitates the dissolution reaction during discharge. The mechanistic investigation discloses the important role of Al3+ in the electrolyte, providing a new fundamental understanding of the promising aqueous Zn-MnO2 batteries.

Automated summary

A new Zn-MnO2 hybrid battery using Al3+ in the sulfate-based electrolyte is proposed, which exhibits excellent electrochemical performance and cycle life while avoiding environmental hazards and corrosion of the Zn anodes.