Fabrication of (NH4)2V3O8 nanoparticles encapsulated in amorphous carbon for high capacity electrodes in aqueous zinc ion batteries

Aqueous rechargeable Zn-ion batteries (ARZIBs) are being extensively investigated for large scale energy storage applications owing to their high safety, low cost, sustainability and environmental friendliness. Tremendous attention has been paid to developing the high capacity cathode materials, with stable host structures and fast channels for diffusions of Zn2+ giving rise to high performance. Herein, we report (NH4)(2)V3O8 nanoparticles encapsulated into amorphous carbon matrix [denoted as (NH4)(2)V3O8/C] as a high capacity cathode for ARZIBs, for the first time. It is demonstrated to exhibit much enhanced overall electrochemical performance, including high capacities of 356, 327, 299, 261 and 232 mA h g(-1) at 0.1, 0.2, 0.3, 0.4 and 0.5 A g(-1), respectively, high rate capacity as well as excellent cycle lifespan with 212 mA h g(-1) after 50 cycles at 0.1 A g(-1), 201 mA h g(-1) after 100 cycles at 0.2 A g(-1), and 135 mA h g(-1) after 2000 cycles at 1 A g(-1), respectively. The Zn//(NH4)(2)V3O8/C battery thus assembled delivers a high energy density of 334 Wh kg(-1) at 294 W kg(-1), which are superior to some of the state-of-the-art cathode materials for ARZIBs. In parallel with the electrochemical performance demonstrated, we have clarified the key reaction mechanisms involved in the reversible (de)intercalation of Zn2+, studied by multiple analytical methods.