High-purity phase La_0.8Sr_0.2Ga_0.8Mg_0.2O_3-δ electrolyte with superior ionic conductivity for solid oxide electrochemical cells fabricated by solid-state reaction via phase-forming additive

One significant challenge of using Sr and Mg doped LaGaO₃ (LSGM) as an electrolyte for solid oxide electrochemical cells lies in attaining a high-purity phase and exceptional ionic conductivity through a straightforward and cost-effective fabrication process. This study introduces an innovative approach to synthesizing high-purity phase LSGM electrolytes by incorporating Li oxides as a phase formation additive within the conventional solid-state reaction method. The impact of Li oxides addition on the phase structure, sintering characteristics, and conductivity of LSGM electrolytes is thoroughly characterized. Results indicate that addition of 1 mol% Li completely eliminates La₂O₃ impurities, yielding an LSGM electrolyte with a high-purity phase structure. However, increasing Li to 1.5 and 2 mol% introduces common impurities such as LaSrGa₃O₇ and LaSrGaO₄. Notably, the high-purity phase LSGM with 1% Li demonstrates impressive oxygen ionic conductivity. At 800 °C, the conductivity reaches 0.195 S cm⁻¹ and shows remarkable stability across a wide range of oxygen partial pressures. Furthermore, a full cell employing a ∼200 μm high-purity phase LSGM electrolyte achieves an output power density of 1.5 W cm⁻² in solid oxide fuel cell mode and a current density of 3.02 A cm⁻² at 1.5 V in steam electrolysis mode at 800 °C.