A P2-Type Layered Superionic Conductor Ga-Doped Na₂ Zn₂ TeO₆ for All-Solid-State Sodium-Ion Batteries

Here, a P2-type layered Na₂ Zn₂ TeO₆ (NZTO) is reported with a high Na⁺ ion conductivity ≈0.6×10^-3  S cm^-1 at room temperature (RT), which is comparable to the currently best Na_1+n Zr₂ Si_n P_3-n O₁₂ NASICON structure. As small amounts of Ga³⁺ substitutes for Zn²⁺ , more Na⁺ vacancies are introduced in the interlayer gaps, which greatly reduces strong Na⁺ -Na⁺ coulomb interactions. Ga-substituted NZTO exhibits a superionic conductivity of ≈1.1×10^-3  S cm^-1 at RT, and excellent phase and electrochemical stability. All solid-state batteries have been successfully assembled with a capacity of ≈70 mAh g^-1 over 10 cycles with a rate of 0.2 C at 80 °C. ²³ Na nuclear magnetic resonance (NMR) studies on powder samples show intra-grain (bulk) diffusion coefficients D_NMR on the order of 12.35×10^-12  m²  s^-1 at 65 °C that corresponds to a conductivity σ_NMR of 8.16×10^-3  S cm^-1 , assuming the Nernst-Einstein equation, which thus suggests a new perspective of fast Na⁺ ion conductor for advanced sodium ion batteries.