Improving Ionic Conductivity in NASICON-Type Solid Electrolytes through Suppression of Lithium Volatilization

Abstract LiZr2(PO4)3 (LZP) materials have suffered from low lithium ion conductivity and an inherently poor sintering activity of precursor powder. The issue of lithium volatilization caused by prolonged sintering is a persistent challenge for researchers. Herein, a series of Li0.88Ga0.04Zr2(PO4)3 (LGZP) ceramic electrolytes were prepared by spark plasma sintering (SPS) with different sintering temperatures. The combined effects of externally applied high pressure and rapid sintering effectively suppressed the volatilization loss of lithium during the sintering process and addressed the insufficient densification drive. The SPS process exhibited a lithium loss rate of merely 3.5%, substantially lower than the 37.6% loss rate associated with the conventional sintering (CS) method. Notably, the LGZP sintered by SPS at 1125 °C exhibited the highest room temperature Li+ conductivity of 2.10 × 10−4 S cm−1, which is 2.5 times that of the CS-sintered pellet, coupled with a high relative density of approximately 97%. The SPS-sintered sample demonstrated better stability in moist air and a higher critical current density compared to that sintered by CS. All LGZP pellets demonstrated a high Li+ ion transference number, approaching 1. Furthermore, the lithium symmetric cell based on SPS-derived LGZP exhibited a cycle stability for 550 h at currents of 0.1 and 0.2 mA. The maximum specific capacity of Li|LGZP-1125|LFP is 151.4 mAh g−1, and the capacity retention rate remains at 97.9% after 100 cycles.