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

Amorphous manganese oxides (a-MnOx) are widely considered promising material systems to fabricate cathodes for aqueous zinc ion batteries (AZIBs). However, the Zn-storage mechanism of a-MnOx is still not understood, and its electrochemical performance is inadequate. Herein, we report porous reduced graphene oxide boosted a-MnOx microspheres (denoted as PrGO–MnOx) 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-MnOx phase in PrGO–MnOx 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–MnOx‖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.