Garnet‐Polymer Composite Electrolytes with High Li+ Conductivity and Transference Number via Well‐Fused Grain Boundaries in Microporous Frameworks

Abstract A garnet‐polymer composite electrolyte with high Li + conductivity and transference number is developed using microporous Li 6.4 La 3 Zr 1.4 Ta 0.6 O 12 (LLZTO) framework as the matrix. The LLZTO framework, fabricated by a template‐assisted gel‐casting process, possesses micron‐sized grains and well‐fused grain boundaries, eliminating the low‐conductive bottleneck at the interfaces between the ceramic blocks, and providing conductive and continuous networks for Li + transport. As a result, the garnet‐polymer composite electrolyte displays a high ionic conductivity (2.61×10 −4 S cm −1 at 25 °C), an ultrahigh Li + transference number of 0.71, as well as excellent thermal, structural, and electrochemical stabilities. Benefiting from the desired physical and chemical properties, the presented composite electrolyte enables a Li−Li cell to be cycled for more than 600 h at 25 °C. In addition, the integrated LiFePO 4 /CPCE/Li cells also show excellent cycling stability with a specific capacity of 133.2 mAh g −1 after 100 cycles under 50 °C. This study demonstrates a significant optimization on the microstructure of composite electrolytes that can be utilized for all‐solid‐state lithium batteries.