Effects of Sodium Sources on Nonaqueous Precipitation Synthesis of β″-Al₂O₃ and Formation Mechanism of Uniform Ionic Channels

Abstract

High-temperature and long-term sintering of β″-Al₂O₃ solid electrolyte (Beta″ Alumina Solid Electrolyte, BASE) can easily cause Na₂O volatilization. It reduces the solid electrolyte (SE) quality, resulting in low ion conductivity of the electrolyte. It is also difficult to form uniform ionic channels. This work designs a simple nonaqueous precipitation through de-etherification heterogeneous polymerization reaction between optimal sodium source sodium ethoxide and aluminum isopropoxide to synthesize highly active precursor powders with Na-O-Al as the skeleton, effectively reducing the synthesis and sintering temperatures of β″-Al₂O₃ solid electrolyte and minimizing the Na₂O volatilization. Importantly, residual organic groups and a low synthesis temperature of 1150 °C promote the formation of in situ carbon uniformly. In-situ carbon with a mass fraction of about 3.98% will form uniformly distributed ion transport channels with a diameter of 1-3 μm when sintering at 1580 °C. These channels ensure a migration rate of sodium ions and ion conductivity of β″-Al₂O₃ solid electrolyte of 0.028 S/cm at 300 °C.