A high energy efficiency and long life aqueous Zn–I2 battery†
Herein, a high energy efficiency and long life aqueous Zn–I2 battery based on an activated carbon encapsulated I2 (I2@C-50) cathode is reported. It is found that an optimized electrolyte of Zn(CF3SO3)2 can significantly boost the initial coulombic efficiency from 61.1% to 91.3% due to the coordination effect, which accounts for the high energy efficiency of the battery. Moreover, the in situ formed solid electrolyte interphase (SEI) film on the Zn surface can effectively stabilize Zn stripping/plating and ensure the long-term cycling stability of the aqueous Zn–I2 battery. Besides, an activated carbon host with a large surface area, strong adsorption and spatial confinement suppresses the loss of active materials. As a result, the I2@C-50 cathode realizes a capacity of 210 mA h g−1 and a high energy efficiency of 96.7% at 0.1 A g−1, and exhibits a capacity retention of 66% after 10 000 cycles at 5 A g−1. In addition, pouch batteries with different sizes also demonstrate feasibility in practical applications. The results presented in this work provide insights on electrode, electrolyte and interface engineering to design high performance aqueous batteries.