A “Polymer‐in‐Salt” Solid Electrolyte Enabled by Fast Phase Transition Route for Stable Zn Batteries

Abstract Solid polymer electrolyte‐based batteries show great promise because of their safe operating properties, wide voltage window and suitable flexibility. However, low ionic conductivity, low cation transfer number, weak oxidation/reduction resistance and low mechanical strength limit their implementation in Zn ion batteries. Here, w e developed a “polymer‐in‐salt” Zn 2+ ‐conductive solid electrolyte (denoted as 70% salt‐SPE) constructed by a simple and fast phase transition method. The room‐temperature ionic conductivity and the transfer number of the 70% salt‐SPE reaches 1.6 mS cm −1 and 0.78, respectively. Meanwhile, the ZnF2‐rich inorganic/organic hybrid solid electrolyte interface is formed, and the stable voltage window reaches 9.35 V. In consequence, the Zn||Zn symmetric cell continuously cycles over 700 hours at current density of 2 mA cm −2 and the Zn||Cu symmetric battery runs with Coulombic efficiency of >99%. The Zn||MnPBA full battery delivers a discharge specific capacity of 109 mAh g −1 at room temperature and 190 mAh g −1 at 60 °C. Meanwhile, impressive cyclic stability of 6000 cycles with capacity retention of 80% is achieved, which originates from the effectively optimized ion transport action and dendrite‐free Zn plating/stripping.