All-solid-state lithium-ion batteries based on electrolytes in the solid-state have a high energy density and are safe compared to conventional lithium-ion batteries based on liquid electrolytes. Ceramic-polymer composite electrolytes combine the advantages of both polymer and ceramic electrolytes, leveraging on additional synergies between these electrolytic materials to improve the properties of the solid-state electrolytes. Composite electrolytes with high ceramic loadings also known as ‘polymer-in-ceramic’ composites are interesting as they promise high lithium cation transference numbers, electrochemical stability, and thermal stability necessary for highly performing all-solid-state batteries. However, the ionic conductivities of these electrolytes tend to decrease with an increase in the ceramic filler typically above 50 wt.%. To address this challenge, an amorphous polyester-based poly(ε-caprolactone-co-trimethylene carbonate) (PCL-PTMC) co-polymer is employed as a polymer matrix in these composites with the ambition of utilizing the advantages of the PCL-PTMC co-polymer. PCL-PTMC co-polymer electrolytes are superior to traditional poly(ethylene oxide) (PEO) electrolytes since they have higher lithium cation transference numbers, weaker Li–O coordination, and better ambient-temperature ionic conductivities. Therefore, a composite electrolyte based on a PCL-PTMC: LiTFSI salt and a garnet-type electrolyte was studied in this work. Garnet Li7La3Zr2O12 (LLZO) ceramic was used because of its chemical stability against lithium metal anodes, wide potential window for electrochemical operation, and high ionic conductivity. The composite electrolyte with 80 wt.% LLZO ceramic component exhibited an ionic conductivity of 1.31 x10-4 S/cm at 60 °C, and a high transference number of 0.82 at 60 °C. The prepared composite electrolyte also exhibited electrochemical stability up to 5.4 V vs. Li+/Li and improved electrode-electrolyte interfacial stability. These attributes allowed good cycling performance of the composite electrolyte at 55 °C in Li/composite electrolyte/LFP all-solid-state cells. This study clearly suggests that this type of amorphous polyester-based polymers can find application in ‘polymer-in-ceramic’ composite electrolytes for the realization of advanced all-solid-state lithium-ion batteries.

Garnet-poly(ε-caprolactone-co-trimethylene carbonate) polymer-in-ceramic composite electrolyte for all-solid-state lithium-ion batteries

ACS Fall 2021

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