Enabling Facile Synthesis and High Sodium Ionic Conductivity in NZTO Solid Electrolyte by Substituting Fe³

Solid electrolytes (SEs) have attracted considerable attention in applications such as energy storage systems and electrical devices due to their intrinsic safety and high energy density. Among them, layered oxide-based SEs exhibit high stability, reasonable ionic conductivity, and lower sintering temperatures compared with other oxide-based SEs. Nevertheless, the demand for higher ionic conductivity and lower synthesis temperatures still persists. To address these challenges, this work explores a substitution strategy for Na₂Zn₂TeO₆ (NZTO), which shows the highest ionic conductivity among layered oxide SEs. Iron (Fe³⁺), one of the most earth-abundant elements, is employed to partially substitute Zn²⁺ in NZTO to enhance both stability and performance. This approach successfully improves ionic conductivity and lowers sintering temperature. Specifically, the ionic conductivity increases significantly from 0.469 mS/cm in pristine NZTO to 0.850 mS/cm at 25°C with 0.1 Fe substitution, and a pure P2 NZTO phase is obtained at 750°C, compared with 900°C for pristine NZTO. Furthermore, a 12.9% capacity enhancement and improved stability are achieved when fabricating a solid-state cell with 0.1 Fe³⁺-substituted NZTO compared with pristine NZTO, confirming its potential for applicability in all-solid-state batteries.