Phase‐Change Organic Small Molecules Enable Operation at Room Temperature in All‐Solid‐State Lithium‐Metal Pouch Cells

Abstract Poly(ethylene oxide) (PEO)‐based electrolytes exhibit huge potential for application in all‐solid‐state lithium batteries (ASSLBs). However, effective strategies to address the temperature‐dependent limitation of the solvent‐free polymer electrolytes remain elusive. Herein, this study pioneers the application of organic small‐molecule with phase‐change properties within all‐solid‐state batteries. The hydrogen bond‐induced crystallization suppression and localized thermal environmental influences during phase transition are proposed. The effect is based on a mechanism of crystallization space occupation, implemented through a secondary cooling crystallization following the conventional evaporation crystallization. The defect‐rich PEO crystal structure is induced within the confined spaces between preferentially crystallized phase‐change material myristic acid. Moreover, the constructed spatial gradient of myristic acid content within the whole electrolyte can create a high amorphous region and stable electrolyte/electrode interfaces, enabling rapid lithium‐ion transport. Consequently, the temperature‐responsive electrolyte after the secondary cooling crystallization exhibits enhanced ionic conductivity (from 7.20 × 10 −5 to 1.23 × 10 −4 S cm −1 at 30 °C) and lithium‐ion transference number. The assembled all‐solid‐state pouch cells demonstrate stable cycling with a discharge specific capacity of 152.1 mAh g −1 at 35 °C and 106.5 mAh g −1 at room temperature with average Coulomb efficiency over 96%. This work advances the development of solvent‐free ASSLBs for ambient‐temperature operation.