Investigation of Pr3+ and Nd3+ Doping Effects on Sodium Gadolinium Silicate Ceramics as Fast Na+ Conductors

Sodium metal batteries (SMBs) with ceramic solid electrolytes offer a promising route to improve the energy density of conventional Na-ion batteries (SIBs). Silicate-based ceramics have recently gained attention for their favourable properties, including better ionic conduction and wider stability windows. In this study, 10% Pr3+ and Nd3+ were doped into sodium gadolinium silicate ceramics to examine the effects on phase purity, ionic conductivity, and interfacial compatibility with sodium metal anodes. The materials were synthesized via solid-state methods and sintered at 950–1075 °C to study the impact of sintering temperature on densification and microstructure. Na5Gd0.9Pr0.1Si4O12 (NGPS) and Na5Gd0.9Nd0.1Si4O12 (NGNS) sintered at 1075 °C showed the highest room temperature total ionic conductivities of 1.64 and 1.74 mS cm−1, respectively. The highest critical current density of 0.5 mA cm−2 is achieved with a low interfacial area-specific resistance of 29.47 Ω cm2 for NGPS and 22.88 Ω cm2 for NGNS after Na plating/stripping experiments. These results highlight how doping enhances phase purity, ionic conductivity, and interfacial stability of silicates with Na metal anodes.