Solvent-Free Solid-State Ionic Conductive Elastomer with Li+–O Coordination for Flexible Strain Sensors

Solvent-free solid-state ionic conducting elastomers (SICEs) are emerging as ideal ionic conductors for flexible wearable electronics due to their superior environmental stability and mechanical compliance. However, it remains a great challenge to simultaneously achieve high ionic conductivity, robust mechanical properties, and low hysteresis in SICEs. Herein, we report a one-pot ultraviolet-initiated copolymerization strategy to fabricate high-performance poly(4-hydroxybutyl acrylate- co -poly(ethylene glycol) methyl ether methacrylate)/lithium bis(trifluoromethanesulphonyl)imide (denoted as P(HBA- co -PEGMA)/LiTFSI) SICEs, where 4-hydroxybutyl acrylate (HBA) serves as the elastic backbone, poly(ethylene glycol) methyl ether methacrylate (PEGMA) provides ether-rich segments to facilitate ion migration, and Li + –O coordination bonds are proposed to provide physical cross-linking sites and contribute to the balance between mechanical robustness and ionic conductivity. The incorporation of PEGMA results in a 2921.74% enhancement in ionic conductivity compared with the neat PHBA/LiTFSI SICE (1.84 × 10 –5 S m –1 ), suggesting that the introduction of ether-rich PEGMA segments effectively facilitates ion transport in the solvent-free system. By systematically optimizing the HBA:PEGMA mass ratio and LiTFSI content, the optimal SICE (HBA:PEGMA mass ratio of 7:3, 30 wt % LiTFSI) exhibits a high ionic conductivity of 3.16 × 10 –4 S m –1 , a tensile strength of 277.25 kPa, an elongation at break of 315.73%, and excellent environmental stability (weight change rate <4% after 7 days of ambient storage). Furthermore, the as-assembled SICE-based strain sensor displays a wide sensing range (0–300% strain), a linear gauge factor of 1.605 ± 0.015, an ultralow electrical hysteresis (∼0.52%), outstanding cyclic stability, and reliable static sensing performance. This work provides a facile and effective design paradigm for developing high-performance solvent-free ionic conductors toward advanced flexible sensing applications.