Flexible high energy density zinc-ion batteries enabled by binder-free MnO2/reduced graphene oxide electrode

We demonstrate a rechargeable zinc-ion battery with high energy density and cyclability using MnO2 and reduced graphene oxide (MnO2/rGO) electrode. The flexible and binder free electrode, with high MnO2 mass ratio (80？wt% of MnO2), is fabricated using vacuum filtration without any additional additives other than rGO. Compared to batteries with conventional MnO2 electrodes, the Zn–MnO2/rGO battery shows a significant enhanced capacity (332.2？mAh？g-1 at 0.3？A？g-1), improved rate capability (172.3？mAh？g-1 at 6？A？g-1) and cyclability. The capacity retention remains 96% after 500 charge/discharge cycles at 6？A？g-1. The high MnO2 mass ratio makes MnO2/rGO electrode advantageous when the capacity is normalized to the whole electrode, particularly at high rates. The calculated gravimetric energy density of Zn–MnO2/rGO battery is 33.17？W？h？kg-1, which is comparable to the existing commercial lead-acid batteries (30–40？W？h kg-1). Furthermore, the discharge profile and capacity of our Zn–MnO2/rGO battery shows no deterioration during bending test, indicating good flexibility. As a result, zinc-ion battery is believed to be a promising technology for powering next generation flexible electronics