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.