High Li⁺ Conducting Porous Garnet Enables Fast Li⁺ Conduction in Polymer/Garnet Composite Electrolyte

Li+ conducting ceramic/polymer composite electrolytes are promising candidates for next-generation all-solid-state Li-metal batteries due to their excellent flexibility, relatively high ionic conductivity, and fast Li+ transport at the electrolyte/electrode interface. However, the ionic conductivity of these composite electrolytes mainly stems from the Li+ of dissolved Li salts in the polymer electrolytes; the isolated ceramic powders in the composite electrolytes fail to form a continuous transport channel, thus contributing minimally to the overall Li+ conduction. In this study, we designed a high Li+ conducting garnet electrolyte (1.2 × 10–4 S cm–1) with unidirectionally aligned pores using freeze casting. The high open porosity (48.2%) of the garnet ceramic provides sufficient space for the incorporation of polymer electrolytes. The dense structure of the garnet ceramic wall enhances the ionic conductivity of the garnet/polymer composite electrolyte to 1.8 × 10–4 S cm–1 at 25 °C and enables stable cycling of symmetric Li/Li and all-solid-state Li/Li1.14Ni0.27Co0.03Mn0.56O2 cells at various current densities, demonstrating the excellent capability of the composite electrolytes in suppressing dendrite formation. The Li+ conduction mechanism of the composite electrolyte was thoroughly investigated using solid-state 7Li NMR spectra, which confirmed the ionic contributions of the Li+ from both the garnet and the polymer.