Performance Optimization of Electrospun Lithium-Ion Conducting PAN/PEO Solid Polymer Electrolyte

Storing energy in rechargeable lithium-ion batteries is essential for a renewable energy supply. Replacing liquid with solid electrolytes in all-solid-state batteries minimizes safety concerns while increasing energy density. This study introduces a solid polymer electrolyte membrane that can be produced in a scalable, one-step process. The polymer blend consisting of the matrix-giving polyacrylonitrile (PAN) and the ion-conducting poly(ethylene oxide) (PEO) with lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) as the conducting salt is electrospun, ensuring mechanical flexibility and low crystallinity. Flexible, free-standing membranes exhibit fiber retention up to 100 °C, enabling a wide thermal application window above PEO's melting point. Adjusting the plasticizer ratio, humidity, and drying conditions allows fine-tuning of the membrane's morphology, porosity, and ionic conductivity, reaching 0.1 mS cm^-1 at 328 K. A slight increase in cell pressure from 0.6 to 2.1 MPa decreases porosity and further increases ionic conductivity without affecting the fiber structure, enabling low-pressure utilization. Moreover, variable-temperature ⁷Li solid-state nuclear magnetic resonance spectroscopy studies of the dry membrane further demonstrated rapid local Li-ion exchange processes with very low activation energies. An electrochemical window between 0 and 4.5 V, and reversible lithium-ion transport, confirmed by galvanostatic cycling, imply the promising application of high-performance electrospun solid polymer electrolytes.