Interface modification of electrodes through polyethylene glycol in rechargeable zinc-nickel batteries

•An effective additive was demomstrated to suppress spongy zinc growth.•PEG can also enhance the transport of protons in nickel hydroxide.•PEG improves both cycling stability and energy efficiency of ZNBs. Suppressing spongy zinc growth is a critical challenge in the development of alkaline zinc-based batteries. However, most surfactants strongly adsorb on the surface of anodes and depress the kinetic of zinc electrodeposition and dissolution. Here, we demonstrate an effective additive (polyethylene glycol, PEG200) to suppress spongy zinc growth in zinc-nickel flow batteries (ZNFBs) and systematically investigate the effect of PEG200 on zinc morphologies and kinetics of zinc anodes and nickel cathodes. We surprisingly find that 2 × 10−5 mol L−1 PEG200 not only induces a uniform and dense metallic zinc layer without markedly enlarging the overpotential of zinc electrodeposition, but also increases the transfer rate of protons at the interfaces of nickel cathodes. Consequently, the cycle life of ZNFBs is promoted together with the increase of energy efficiency from 75% to 77.5% at 80 mA cm−2.