The rapid development of electronic devices and electric transportation increases the demand for safe and high energy density batteries. All solid-state batteries comprising of solid-state electrolytes such as ceramic electrolytes and polymer electrolytes can meet these requirements. The electrochemical stability of solid-state electrolytes enables the use of lithium-metal anodes and high voltage cathodes to increase the energy density in lithium-based batteries.

Garnet Li₇La₃Zr₂O₁₂ (LLZO) ceramic electrolyte constitutes one of the most promising solid-state electrolytes for all-solid-state batteries. This is due to its good ionic conductivity, stability against lithium metal anode, and a wide electrochemical window of operation [1]. However, the use of LLZO ceramic electrolytes in all-solid-state batteries remains a challenge. This is because the hard, brittle and rigid nature of LLZO ceramic electrolytes result in high interfacial resistance and poor physical contact with both electrodes. To address these challenges, in this presentation, a poly(ε-caprolactone-co-trimethylene carbonate (PCL-PTMC) co-polymer is incorporated in the garnet Al-doped LLZO ceramic electrolyte with the ambition of utilizing the advantages of the PCL-PTMC co-polymer electrolyte to fabricate a ceramic-polymer composite electrolytes with improved performance. The PCL-PTMC co-polymer electrolyte exhibits higher cation transference numbers and better ambient-temperature ionic conductivities compared to the traditional poly(ethylene oxide) polymer electrolyte [2]. The polymer-in-ceramic composite electrolyte with 80 wt.% Al-LLZO and 20 wt.% polymer (PCL-PTMC and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) at 72:28 wt.%) exhibited a Li-ion conductivity of 1.31×10^-4 S/cm and a transference number (t_Li⁺) of 0.84 at 60 °C. The garnet-PCL-PTMC composite electrolyte was benchmarked in all-solid-state batteries using LiFePO₄ (LFP) and Li-metal as cathode and anode, respectively. The results of this work suggest that this type of amorphous polyester-based polymer can be suitable for the realization of advanced composite electrolytes for all-solid-state lithium-ion batteries.