High Li<sup>+</sup> Conducting Porous Garnet Enables\nFast Li<sup>+</sup> Conduction in Polymer/Garnet Composite Electrolyte

Li<sup>+</sup> conducting ceramic/polymer composite electrolytes\nare promising candidates for next-generation all-solid-state Li-metal\nbatteries due to their excellent flexibility, relatively high ionic\nconductivity, and fast Li<sup>+</sup> transport at the electrolyte/electrode\ninterface. However, the ionic conductivity of these composite electrolytes\nmainly stems from the Li<sup>+</sup> of dissolved Li salts in the\npolymer electrolytes; the isolated ceramic powders in the composite\nelectrolytes fail to form a continuous transport channel, thus contributing\nminimally to the overall Li<sup>+</sup> conduction. In this study,\nwe designed a high Li<sup>+</sup> conducting garnet electrolyte (1.2\n× 10<sup>–4</sup> S cm<sup>–1</sup>) with unidirectionally\naligned pores using freeze casting. The high open porosity (48.2%)\nof the garnet ceramic provides sufficient space for the incorporation\nof polymer electrolytes. The dense structure of the garnet ceramic\nwall enhances the ionic conductivity of the garnet/polymer composite\nelectrolyte to 1.8 × 10<sup>–4</sup> S cm<sup>–1</sup> at 25 °C and enables stable cycling of symmetric Li/Li and\nall-solid-state Li/Li<sub>1.14</sub>Ni<sub>0.27</sub>Co<sub>0.03</sub>Mn<sub>0.56</sub>O<sub>2</sub> cells at various current densities,\ndemonstrating the excellent capability of the composite electrolytes\nin suppressing dendrite formation. The Li<sup>+</sup> conduction mechanism\nof the composite electrolyte was thoroughly investigated using solid-state <sup>7</sup>Li NMR spectra, which confirmed the ionic contributions of\nthe Li<sup>+</sup> from both the garnet and the polymer.