Cross-Linked Ethylene Carbonate-based Copolymer Composite Electrolytes Filled with TiO2 for Lithium Metal Batteries

To avoid the safety concerns of lithium–metal batteries (LMBs), which stem from the leaking of liquid electrolytes, solid polymer electrolytes (SPEs) are increasingly considered as alternative electrolytes. Carbon dioxide-derived poly(ethylene carbonate)-based SPE has drawn increasing attention due to its unique salt dissolution behavior, where the glass transition temperature (Tg) is reduced with increasing salt concentration. The limitations of the carbonate-based SPE are low mechanical strength and thermal decomposition induced by backbiting reaction at high temperatures, leading to unstable charge/discharge of LMBs. Accordingly, we prepared a cross-linked ethylene carbonated-based copolymer SPE filled with TiO2 (CP-CPE) to achieve good thermal resistance and ionic conductivity simultaneously. The morphology observation, mechanical strength, thermal properties, and electrochemical performance of the CP-CPEs were investigated using scanning electron microscopy, tensile test, thermogravimetric analysis, differential scanning calorimetry, electrochemical impedance spectroscopy, linear sweep voltammetry, and galvanostatic charge/discharge tests. The surface morphology showed that the 5.0 wt % of TiO2 is an appropriate amount that provided good filler dispersion for CP-CPE and gave the Young's modulus three-times higher than the ceramic-free CP-SPE. A CP-CPE incorporated with 5.0 wt % TiO2 exhibits the highest ionic conductivity of 3.4 × 10–5 S cm–1 at 60 °C, which was almost 10 times higher than that of the original cross-linked SPE without a filler (CP-SPE). The results also revealed that the 5.0 wt % CP-CPE promises to achieve a discharge capacity as high as 156 mA h g–1, and the Coulombic efficiency remained more than 97% after 20 cycles. All results share the evidence that this research achieved the appropriate amount of TiO2, which significantly enhanced the electrolyte properties of CP-SPE.