Unveiling the crucial morphological effect of non-conducting polymer binders on inorganic-rich hybrid electrolytes

Comparison of the non-conducting polymer binders for hybrids based on Li 3 InCl 6 . Ordered nanostructured SEBS block copolymer provides more tortuous pathways for Li ions in the inorganic electrolyte (Li 3 InCl 6 ) than disordered PIB homopolymer. The limited fundamental knowledge about polymer binder selection in inorganic-rich hybrid electrolytes (HSEs) hinders their optimization and translation to an industrial scale. Herein, we investigate, for the first time, the crucial morphological effect of non-conducting polymer binders in HSEs based on a halide electrolyte (Li 3 InCl 6 ). We compared the effect of the ordered nanostructured styrene–ethylene–butylene–styrene (SEBS) block copolymer and disordered polyisobutylene (PIB) homopolymer binders. This work was aimed at understanding ionic conduction transport across halide-based inorganic-rich HSEs with different polymer morphologies to optimize their design. We investigated ionic conductivity via EIS and Li + diffusion using 7 Li PFG-NMR, and the obtained results were supported by 3D reconstruction from cryo-plasma FIB-SEM images, which were further correlated with rheology measurements. PIB HSE presented higher transport properties than SEBS HSE with higher ionic conductivity (0.39 × 10 −4 and 0.23 × 10 −4 S cm −1 at 30 °C, respectively) and 7 Li diffusion (6.3 × 10 −13 and 4.3 × 10 −13 m 2 s −1 at 30 °C, respectively) owing to a less tortuous percolated inorganic network observed via the 3D reconstruction of cryo-plasma FIB-SEM images. Moreover, rheology measurements indicated that HSEs composed of ordered block copolymers should be processed in the disordered state ( T > T ODT ) (in which the ordered microdomains disappear), reaching the terminal flow zone as disordered homopolymers to improve the percolated inorganic network and thereby achieving high transport properties in HSEs. Finally, Li plating/stripping demonstrated a more stable electrochemical performance of PIB HSE and higher critical current density (400 μA cm −2 ) compared with SEBS HSE (25 μA cm −2 ), which was in good agreement with the obtained transport and morphological properties.