Probing the Thermal Stability of the In Situ Ring-Opening Polymerized Solid Polymer Electrolytes

Area of Science:

• Materials Science
• Electrochemistry
• Polymer Chemistry

Background:

• Ring-opening polymerization (ROP) is a common method for in situ synthesis of solid polymer electrolytes (SPEs) in batteries.
• The thermal stability of these ROP-prepared SPEs, particularly under operational conditions with Li-salts and catalysts, remains under-investigated.

Purpose of the Study:

• To systematically evaluate the thermal stability of popular ether-based (poly(1,3-dioxolane) and poly(1,3,5-trioxane)) and ester-based (poly(valerolactone) and poly(trimethylene carbonate)) SPEs prepared via in situ ROP.
• To assess the impact of Li-salts and residual catalysts on the thermal degradation of these SPEs.

Main Methods:

• Investigated thermal stability using techniques such as thermogravimetric analysis (TGA) under relevant conditions.
• Analyzed the degradation mechanisms of ether-based and ester-based SPEs in the presence of Li-salts and Li-metal.

Main Results:

• Ether-based SPEs (PDOL, PTXE) showed rapid gaseous degradation starting at 100 °C, linked to a ROP-pyrolysis equilibrium.
• Ester-based SPEs (PVL, PTMC) decomposed around 180 °C, but this decreased to 110 °C in the presence of Li-metal.

Conclusions:

• ROP-prepared SPEs, especially ether-based ones, exhibit significant thermal stability challenges for practical battery applications.
• The findings underscore the need for developing intrinsically more thermally stable SPEs for safer solid-state batteries.