Decoupling the Modulus and Toughness Effects of Solid Polymer Electrolytes in All-Solid-State Lithium Batteries

Solid polymer electrolytes (SPEs) have attracted increasing attention for all solid-state lithium battery (ASSLB) applications. Previous SPE design has been focusing on improving the polymer shear modulus without sacrificing ionic conductivity, whereas recent development suggests that other mechanical properties such as elasticity and toughness are also important. Unfortunately, the toughness and modulus are often intertwined in SPEs, and the exact role of toughness in SPE performance remains elusive. In this work, we introduce ultrahigh-molecular-weight poly(ethylene oxide) to a PEO-based network SPE to form semi-interpenetrating network (s-IPN) SPEs. This design allows for the s-IPN SPEs to achieve a significant toughness change while retaining similar ionic conductivities and moduli, which effectively decouples the toughness and modulus effects. Our results show that increasing toughness can significantly improve lithium symmetric cell cycling life. Excellent Coulombic efficiency and full battery performance have also been achieved. This work therefore demonstrates that toughness should be an important criterion for future SPE design.