Improved Mechanical Strength without Sacrificing Li-Ion Transport in Polymer Electrolytes

Abstract

Next-generation batteries demand solid polymer electrolytes (SPEs) with rapid ion transport and robust mechanical properties. However, many SPEs with liquid-like Li⁺ transport mechanisms suffer a fundamental trade-off between conductivity and strength. Dynamic polymer networks can improve bulk mechanics with minimal impact to segmental relaxation or ionic conductivity. This study demonstrates a system where a single polymer-bound ligand simultaneously dissociates Li⁺ and forms long-lived Ni²⁺ networks. The polymer comprises an ethylene oxide backbone and imidazole (Im) ligands, blended with Li⁺ and Ni²⁺ salts. Ni²⁺–Im dynamic cross-links result in the formation of a rubbery plateau resulting in, consequently, storage modulus improvement by a factor of 133× with the introduction of Ni²⁺ at r_Ni = 0.08, from 0.014 to 1.907 MPa. Even with Ni²⁺ loading, the high Li⁺ conductivity of 3.7 × 10^–6 S/cm is retained at 90 °C. This work demonstrates that decoupling of ion transport and bulk mechanics can be readily achieved by the addition of multivalent metal cations to polymers with chelating ligands.