Tailored PEO/PEG-PPG Polymer Electrolyte for Solid-State Lithium-Ion Battery

Abstract Solid polymer electrolytes (SPEs) offer a promising avenue for advancing the performance and safety of all-solid-state batteries. In this study, we investigated the effects of blending poly(ethylene oxide) (PEO) with amorphous poly(propylene glycol) (PPG) or poly(ethylene glycol-ran-propylene glycol) (PEG-PPG) to engineer SPEs with enhanced electrochemical properties. By blending PEO with PEG-PPG or PPG, we effectively lowered the crystallinity of PEO, facilitating the diffusion of lithium ions through the SPE and broadening its operational temperature range. This optimization strategy enhanced ionic conductivity and significantly reduced the interfacial resistance between the electrolyte and electrode, thus improving electrochemical stability. The solid-state lithium/lithium iron phosphate (LiFePO4 or LFP) with PEO blended with 7% PEG-PPG showed excellent charge/discharge cycling stability, with maximal discharge capacities of 165 mAh g-1 and 162 mAh g-1 at a current rate of 0.2 C at 60 and 125°C, respectively. The PEG-PPG-based SPE outperformed the PPG polymer-based SPE in terms of better electrochemical performance and a wider temperature range due to its longer polymer chain. This combination offered improved ionic conductivity, interface stability, and electrolyte compatibility with electrodes, making it highly suitable for high-demand applications of lithium-ion batteries.