A Monolithic Solid-State Sodium–Sulfur Battery with Al-Doped Na3.4Zr2(Si0.8P0.2O4)3 Electrolyte

The limit of the energy density and increasing security issues on sodium-ion batteries (SIBs) impede their further development. Solid-state sodium metal batteries are potential candidates to replace the present SIBs. However, low ionic conductivity and poor interface contact hinder their progress. In this work, the impact of Al doping on the crystalline structure and ionic transport in Na_3.4Zr₂(Si_0.8P_0.2O₄)₃ was studied by neutron powder diffraction. The ionic conductivity of Na_3.5Zr_1.9Al_0.1Si_2.4P_0.6O₁₂ achieves 4.43 × 10^-3 S cm^-1 at 50 °C. The polarization voltage of the Na||Na symmetric battery is about 40 mV after cycling for more than 1600 h. Moreover, a solid-state sodium-sulfur battery with a monolithic structure was constructed to alleviate the interfacial resistance problems. Its specific discharge capacity can still keep 300 mA h g^-1 after 480 cycles at 300 mA g^-1. The work provides a promising strategy to design solid-state sodium-sulfur batteries with high performances.