Dipole Moment Dictates the Preferential Immobilization in Gel Electrolytes for Ah-level Aqueous Zinc-Metal Batteries.

Aqueous Zn-metal batteries are of great interest due to their high material abundance, low production cost, and excellent safety. However, they suffer from severe side reactions and notorious dendrite growth closely related to electrolytes. Here, in situ generated zwitterionic polymers are used as gel electrolytes to overcome these problems. It is shown that anions and HO, but not anions and cations, are preferentially immobilized at different sites of zwitterionic polymers, facilitating the free migration of Zn and reducing the side reactions. This immobilization can be associated with the dipole moment of zwitterionic polymers. As a result, poly[3-dimethyl(methacryloyloxy ethyl) ammonium propane sulfonate] (PDMAPS) stands out from a series of zwitterionic polymers and outperforms the other candidates in electrochemical performance. The symmetric cells using PDMAPS smoothly operate ~9000 h at 0.5 mA cm for 0.5 mAh cm, much better than the controls. Moreover, PDMAPS enables an Ah-level pouch cell for continuous cycling. These results not only benefit the rational molecular design of advanced electrolytes, but also demonstrate the promising potential of zwitterionic polymers in aqueous Zn-metal batteries.