Boosting Na-O Affinity in Na₃Zr₂Si₂PO₁₂ Electrolyte Promises Highly Rechargeable Solid-State Sodium Batteries

All-solid-state batteries have drawn a lot of concern owing to their distinct advantages in energy density and safety. However, the interfacial issues between the solid electrolyte and electrodes are still roadblocks to large scale application of rechargeable solid-state batteries. In this work, it reveals that promoting the Na-O affinity in Na₃Zr₂Si₂PO₁₂ electrolyte can effectively boost its air stability. Specifically, a two-step sintering approach is employed to actively regulate the microstructure evolution of Na₃Zr₂Si₂PO₁₂ electrolyte. Apart from the enhanced strength of the Na-O bond, the mechanical performance and ionic conductivity are also apparently improved in comparison with the traditional one-step sintering. Moreover, a low resistance of 68 Ω cm² is achieved with the Na/Na₃Zr₂Si₂PO₁₂ interface, demonstrating long cycling stability of 1000 cycles at 0.1 mA cm⁻². The designed Na₃Zr₂Si₂PO₁₂ ceramic electrolyte paired with Na_3.5V_0.5Mn_0.5Fe_0.5Ti_0.5(PO₄)₃ cathode and metallic Na anode manifests outstanding cycling stability with a high reversible discharge capacity of 136 mAh g⁻¹ after nearly 400 cycles at 1 C, and 25 °C. Therefore, it is believed that the delicate modulation of solid electrolyte microstructure is of great importance for accelerating the application of solid-state batteries.