Aqueous Zn-ion batteries using amorphous Zn-buserite with high activity and stability

Abstract

Amorphous manganese oxides (a-MnO_x) are widely considered promising material systems to fabricate cathodes for aqueous zinc ion batteries (AZIBs). However, the Zn-storage mechanism of a-MnO_x is still not understood, and its electrochemical performance is inadequate. Herein, we report porous reduced graphene oxide boosted a-MnO_x microspheres (denoted as PrGO–MnO_x) as a cathode material for AZIBs. Its electrochemical Zn-storage mechanism was elucidated via a series of ex situ measurements. Particularly, we observe that the a-MnO_x phase in PrGO–MnO_x is transformed into highly active and stable amorphous Zn-buserite during the initial cycles, effectively promoting Zn-storage. The cathode material can deliver a large capacity (296 mA h g⁻¹ after 100 cycles at 0.1 A g⁻¹), high-rate capability (151 mA h g⁻¹ at 2.5 A g⁻¹), and ultra-long lifespan (5000 cycles at 5.0 A g⁻¹). We attribute this performance to several properties, including (i) the amorphous structure of Zn-buserite with high activity and stability, (ii) fast reaction kinetics, (iii) increased electron conductivity, (iv) improved Zn²⁺ diffusion rate, and (v) high pseudocapacitance. We also assembled a PrGO–MnO_x‖AQ (9,10-anthraquinone) full-battery, which possesses a high discharge plateau (0.8 V) and impressive cycling stability (106 mA h g⁻¹ after 500 cycles at 0.3 A g⁻¹), indicating good potential towards practical applications.