Improving the Electrochemical Properties of Advanced Cross-Linked Solid Polymer Composite Electrolytes

Solid-state batteries based on composite polymer electrolytes (CPEs) have shown enormous potential for safe and high-energy-storage systems. The current work is focused on the study of a CPE based on cross-linked poly(ethylene glycol) (PEG) polymer and Li7La3Zr2O12 (LLZO) inorganic solid electrolyte. Nano- and micrometer-sized particles of LLZO were embedded in a cross-linked polymer that was synthesized via a solvent-free ring-opening polymerization technique. CPEs with nanosized LLZO were superior to the pure polymer or CPEs containing microsized particles. Different weight ratios of the nanosized LLZO in the polymer matrix influenced the electrochemical performance of the cells. CPE with 5 wt % LLZO showed significantly improved Li stripping/plating behavior. In contrast to the pure polymer electrolytes, where the voltage polarizations drastically increased after only 27 h of testing, nano-LLZO-5 wt %-CPE maintained stable voltage profiles at 0.05 mA cm2 for over 200 h. Furthermore, the addition of 5 wt % nano-LLZO yielded a wider electrochemical stability window (an increase of ∼1 V), higher transference number (tLi+ increased by 0.1), and about 4 times higher limiting current density than those recorded for the pure polymer. Such enhancements in the performance suggest a favorable role of nanosized LLZO in a composite polymer electrolyte system.