Single-Ion-Conducting "Polymer-in-Ceramic" Hybrid Electrolyte with an Intertwined NASICON-Type Nanofiber Skeleton

The fast Li⁺ transportation of "polymer-in-ceramic" electrolytes is highly dependent on the long-range Li⁺ migration pathways, which are determined by the structure and chemistry of the electrolytes. Besides, Li dendrite growth may be promoted in the soft polymer region due to the inhomogeneous electric field caused by the commonly low Li⁺ transference number of the polymer. Herein, a single-ion-conducting polymer electrolyte is infiltrated into intertwined Li_1.3Al_0.3Ti_1.7(PO₄)₃ (LATP) nanofibers to construct free-standing electrolyte membranes. The composite electrolyte possesses a large electrochemical window exceeding 5 V, a high ionic conductivity of 0.31 mS cm^-1 at ambient temperature, and an extraordinary Li⁺ transference number of 0.94. The hybrid electrolyte in the lithium symmetric cell shows stable Li plating/stripping up to 2000 h under 0.1 mA cm^-2 without dendrite formation. The Li|hybrid electrolyte|LiFePO₄ battery exhibits enhanced rate capability up to 1 C and a stable cycling performance with an initial discharge capacity of 131.8 mA h g^-1 and a retention capacity of 122.7 mA h g^-1 after 500 cycles at 0.5 C at ambient temperature. The improved electrochemical performance is attributed to the synergistic effects of the LATP nanofibers and the single-ion-conducting polymer. The fibrous fast ion conductors provide continuous ion transport channels, and the polymer improves the interfacial contact with the electrodes and helps to suppress the Li dendrites.