In-situ formation of quasi-solid polymer electrolyte for improved lithium metal battery performances at low temperatures

Solid-state polymer electrolytes, featuring excellent processability and flexibility, have received considerable attentions. However, the inherent low ionic conductivity, especially at subzero temperatures, limits their widespread application. Herein, quasi-solid polymer electrolyte (QSPE) with high low-temperature ionic conduction ability is prepared by in-situ ring-opening polymerization of 1,3-Dioxlane with fluoroethylene carbonate (FEC) as plasticizer. The in-situ polymerization imparts good interface contact between QSPE and electrode. The addition of FEC improves the chain mobility and facilitates the dissociation of LiTFSI, giving QSPE a remarkable ionic conductivity and Li+ transference number (2.4 × 10−5 S cm−1 at −60 °C and 0.55 at −20 ° C), two orders of magnitude and 2.3 times higher than those of liquid electrolyte, respectively. As a result, the Li/QSPE/Li cell without significant polarization is obtained, which can operate at 0.2 mA cm−2 and 0 °C for 850 h. Moreover, the LiFePO4/Li cell exhibits excellent cycling stability at 0.2 C and 0 °C: its capacity remains 125.2 mAh g−1 at 400th cycle, exceeding most polymer electrolytes. Even at −20 °C, a discharge capacity of 73.3 mAh g−1 is obtained at 100th cycle under 0.2 C.