Alicyclic polyimide-based solid polymer electrolyte for improved thermal stability

Lithium secondary batteries are widely used in applications ranging from small electronic devices, such as mobile phones and laptops, to medium- and large-sized power systems, including electric vehicles and energy storage systems. Accordingly, all-solid-state batteries, which replace liquid electrolytes with solid electrolytes, have been actively investigated as a strategy to achieve high energy density, high capacity, and improved safety. Among solid electrolytes, solid polymer electrolytes have advantages such as high flexibility and processability, allowing them to be applied to various battery designs and manufacturing processes. However, solid polymer electrolytes should exhibit sufficient thermal and electrochemical stability under high-temperature and high-voltage conditions. In this study, polyimide, which has excellent heat resistance, chemical resistance, and mechanical strength, was introduced as a matrix for solid polymer electrolytes. To enable solvent processing, an alicyclic ring was incorporated into the polyimide main chain. In addition, oxyethylene oligomers containing polar groups capable of coordinating lithium ions were introduced to improve ionic conductivity. The resulting alicyclic polyimide-based solid polymer electrolytes exhibited thermal stability above 360 °C and electrochemical stability up to approximately 4.6 V. Among the prepared samples, AliPI021 showed the highest ionic conductivity of 1.48 × 10 −4 S/cm at 25 °C. These results indicate that the incorporation of alicyclic polyimide and oxyethylene oligomer segments is an effective approach for developing thermally stable and processable solid polymer electrolytes for lithium secondary batteries.