Single-Ion-Conducting Polymer Electrolytes for Rechargeable Alkaline Ag–Zn Batteries

Recently, we reported on the synthesis and performance of a cross-linked single-anion-conducting solid-state electrolyte (SSE) based on quaternized poly(dimethylaminomethylstyrene) (pDMAMS⁺) via initiated chemical vapor deposition (iCVD). In the homopolymer pDMAMS⁺-based SSE, the cross-linking occurs at the positively charged ammonium cation sites, hindering ion transport and conductivity. To improve ionic conductivity, we now report on a copolymer system, comprising DMAMS and divinylbenzene (DVB). Incorporating DVB moves the cross-links to the polymer backbone leaving the quaternary ammonium cation and its paired anion with maximal dynamic freedom. We evaluate the structure-transport relationships of a series of p[DVB-DMAMS] copolymers with varying DVB content using electrochemical impedance spectroscopy, nuclear magnetic resonance spectroscopy, and small- and wide-angle X-ray scattering. Our best composition containing 2.5 wt % DVB provides 1 mS cm^-1 single-ion OH^- conductivity under hydrated conditions, a significant improvement over the 0.01 mS cm^-1 of the hydrated homopolymer pDMAMS⁺ SSE. All copolymer compositions support Zn-ZnO and Ag-Zn electrochemical reduction-oxidation (redox) chemistry, which demonstrates the feasibility of a Ag-Zn battery using an alkaline single-ion-conducting SSE. Galvanostatic cycling shows some transport of Ag through the polymer electrolyte, however the deleterious effects of Ag migration can be partially mitigated by transitioning from a two-dimensional (2D) planar electrode to a 3D sponge electrode. With these promising results, the foundation is laid for using single-anion-conducting SSEs within alkaline Zn batteries.