α-Methyl Group Reinforced Amphiphilic Poly(Ionic Liquid) Additive for High-Performance Zinc-Iodine Batteries

Aqueous zinc-iodine (Zn-I2) batteries are prospective on energy storage, yet the practical application is severely hindered by side reactions of Zn metal and the shuttle effects for polyiodide. Herein, a polymer additive was copolymerized by 1-vinyl-3-ethylimidazolium trifluoromethanesulfonate (VEImOTf) and methacrylamide (MAAm) (PVEMA) to alleviate the above issues. The polymer chain of PVEMA endows amphipathic properties for Zn2+ diffusion and solvation structure regulation, and the alpha-methyl of MAAm enhances the hydrophobic properties to avoid side reactions on Zn metal. In addition, the imidazole groups adsorb onto Zn metal with electrostatic shielding effect for further side reaction alleviation and mitigate shuttle effects by electrostatic interactions with polyiodides. Consequently, the PVEMA confers the symmetrical Zn battery with great cycling stability for over 400 h at 20 mA cm-2 and high depth of discharge (DOD) of 77.7%. The Zn-I2 batteries with PVEMA also demonstrate stable cycling performance under various current densities and temperatures.