Electro-boost in-situ formation of poly(tetrahydrofuran) to enhance interfacial compatibility and charge transfer for solid polymer electrolyte

In-situ polymerization offers a promising approach for next-generation solid polymer electrolytes with excellent interfacial properties. We present a novel method for the in-situ preparation of poly(tetrahydrofuran) (PTHF) electrolyte using streamlined polymerization and accelerated gelation. Structural, compositional, and interfacial properties of the PTHF electrolyte as a function of time were analyzed using NMR, MS, and EIS spectra. This method provides rapid gelation and high purity, addressing common issues such as weak solidification and impurity formation encountered with boron trifluoride diethyl etherate initiators. The amorphous-dominant in-situ derived PTHF exhibited a bulk conductivity of 10^-4 S cm⁻¹ and a wide electrochemical window of up to 5.2 V at RT, owing to rich BF₃ coordination bonds that promote Li-polymer conduction and enhance polymer stability. The in-situ PTHF significantly improves interfacial contact, and the solid electrolyte interface film on the harvested Li was more robust than that of the ex-situ PTHF counterpart. Importantly, in-situ PTHF electrolytes treated with AC voltage were evaluated for their ability to improve interfacial compatibility (e.g., structural stability, uniform Li⁺ deposition, and dendrite suppression) and to facilitate continuous Li⁺ pathways through the alignment of PTHF chains, notably raising t_Li+ from 0.21 to 0.61 compared to before. Validation with a quasi-solid-state Li–O₂ battery using in-situ PTHF demonstrated a 75.7 % round-trip efficiency with 100 % capacity retention over 50 h, and delivered a specific discharge capacity of 3300 mAh g⁻¹, confirming its practical potential. Overall, this work presents a strategically designed PTHF-based electrolyte fabricated via in-situ assembly, offering new insights into advanced electrolyte design.