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

Abstract

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 (T g ) 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 TiO 2 (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 TiO 2 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 % TiO 2 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 TiO 2 , which significantly enhanced the electrolyte properties of CP-SPE.

A highly salt concentrated ethylene carbonate-based self-standing copolymer electrolyte for solid-state lithium metal batteries

“…16 Therefore, the shift of the ν CO peak of CP 29 is probably because the presence of the AGE unit somehow facilitates the carbonate conformation changes from gauche to trans by restricting the former. 27 To distinguish the peak positions of free CO and CO interacting with the Li cation (CO⋯Li + ), the SPEs with 10 mol% of LiFSI were utilized. It was clear that the CO⋯Li + peak appeared at approximately 1720 cm −1 50 in these polymer systems.…”

“…26 Moreover, the CP electrolytes filled with TiO 2 were proved to enhance mechanical and ion-conductive properties, although long-cycle-life SSLMBs are yet to be obtained. 27 Crosslinking has also been commonly studied as a strategy to enhance the mechanical stability of the polyether-based SPE system, although the crosslinked polyether structures have been found to limit the salt dissolving power, particularly at high salt concentrations. 23,28–32 Therefore, the mechanically stable crosslinked copolymer-based SPE with high salt concentration should be an interesting novel concept to be explored.…”