Highly-Conductive Mixed PEO/PAN-Based Membranes for Solid State Li-Ion Batteries via Electro-Spinning and Hot-Press Synthesis Routes

Polyethylene oxide (PEO)-based solid polymer electrolytes (SPEs) have been extensively studied for all solid-state batteries (ASSBs) but still suffer from low thermal stability and ionic conductivity. Here, we report on PEO-based solid electrolytes containing a second polymer, polyacrylonitrile (PAN) and succinonitrile (SN). Two different synthesis routes have been followed, synthesis via hot-pressing and synthesis via electrospinning. Whereas the hot-pressing route offers a well-established and robust approach without the need of using solvents, electrospinning provide samples with a distinctively superior performance as compared to those prepared via solution casting. Both routes resulted in materials exhibiting an ionic conductivity around 10⁻⁴ S cm⁻¹ at room temperature. Using solid-state NMR approaches, we could show that SN increases the chain segment mobility of PEO and hence supports Li mobility, whereas PAN remains virtually immobile. Using a deuterated sample d₄-SN dipolar NMR experiments (⁷Li-¹H-REDOR) at 190 K revealed that the coordination of the Li cations within the mixed polymer electrolytes in solely accomplished by the polyether functionalities without the help of SN. The addition of PAN seems to increase the relative amount of amorphous PEO, hence supporting the overall Li mobility, and it increased the mechanical stability of the membranes.