Flexible high energy density zinc-ion batteries enabled by binder-free MnO 2 /reduced graphene oxide electrode

We demonstrate a rechargeable zinc-ion battery with high energy density and cyclability using MnO 2 and reduced graphene oxide (MnO 2 /rGO) electrode. The flexible and binder free electrode, with high MnO 2 mass ratio (80 wt% of MnO 2 ), is fabricated using vacuum filtration without any additional additives other than rGO. Compared to batteries with conventional MnO 2 electrodes, the Zn–MnO 2 /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 MnO 2 mass ratio makes MnO 2 /rGO electrode advantageous when the capacity is normalized to the whole electrode, particularly at high rates. The calculated gravimetric energy density of Zn–MnO 2 /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–MnO 2 /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.