NASICON-structured Na₃Zr₂Si₂PO₁₂ (NZSP) has been considered as one of the ideal electrolytes for all-solid-state sodium metal batteries (ASSSB). However, the practical application of NZSP-based ASSSB is hindered by the low ionic conductivity and large interfacial resistance caused by the poor contact between NZSP and Na metal. Herein, the introduction of Fe₂O₃ not only improves ionic conductivity and reduces activation energy by the doping of Fe³⁺ in the crystal structure of NZSP, but also reduces the interfacial resistance and enhances interface stability between NZSP and Na metal anode. The synergistic effects significantly enhance the cycling stability, rate capability, and critical current density of the symmetrical solid-state cells. The interfacial reaction mechanism indicates that Fe³⁺ in the interface is reduced Fe²⁺ by Na anode, which effectively even the electric-filed distribution and suppresses the dendrite growth. Consequently, the symmetric solid-state cells exhibit stable cycling performance for 1,500 h at 0.1 mA·cm⁻¹/0.1 mA·h·cm⁻¹ and over 900 h at 0.2 mA·cm⁻¹/0.2 mA·h·cm⁻¹. The Na|NZSP-0.075%Fe₂O₃|Na₂FePO₄F solid-state full cells display high capacity retention of 94.2% after 100 cycles at 0.5 C. The stable interface of NZSP/Na and improved ionic conductivity contribute to excellent electrochemical performance, which accelerates the practical application of ASSSB.

Fe_xMo_1–xS₂ with an expanded interlayer spacing of 0.75 nm was prepared via a simple solvothermal method. The larger interlayer spacing enhances the rate of Na⁺ diffusion during initial cycle. Fe_xMo_1–xS₂ as an anode for sodium ion batteries exhibits a high capacity of 285 m A·h/g at 0.1 A/g after 100 cycles and an excellent rate capability of 178 m A·h/g at 5 A/g. The fresh and cycled electrodes were characterized by in-situ X-ray photoelectric spectroscopy and transmission electronic microscopy to investigate electrochemical reaction mechanism of Fe_xMo_1–xS₂ during cycling. The results indicate that the irreversible conversion reaction of Fe_xMo_1–xS₂ with Na⁺ results in the formation of main products of Fe–Mo alloy and S.