Enhanced Solid Polymer Electrolytes for Lithium Metal Batteries: In-situ cured Poly(ethylene oxide) with Lithium Imide and Bis(oxalato)borate salts

To address safety and energy density demands beyond conventional lithium-ion batteries, this study investigates solid polymer electrolytes (SPEs) for solid-state batteries (SSBs) featuring lithium metal anodes. We synthesize SPEs via in-situ polymerization using a poly(ethylene oxide) (PEO) matrix with LiFSI, LiTFSI, or LiBOB salts (5 wt% and 10 wt%). This in-situ method reduces PEO crystallinity, enhancing Li-ion conductivity and interfacial compatibility with electrodes. Results show that SPEs with 10 wt% salt, particularly LiFSI, exhibit the highest ionic conductivity (3.1 × 10⁻⁴ S cm⁻¹ at 25 °C and 6.0 × 10⁻⁴ S cm⁻¹ at 60 °C) and demonstrate superior cycling stability. While LiTFSI and LiBOB electrolytes display comparable initial conductivities, they suffer from limited cycle life. Electrochemical impedance spectroscopy (EIS) indicates this capacity fading stems from the growth of resistive interfacial layers. This work highlights the advantages of in-situ polymerization for SPEs, although mechanical stability requires further optimization to mitigate interfacial failure. These findings suggest LiFSI-based SPEs synthesized in-situ hold significant promise for developing safer, high-energy-density SSBs.