Core–Shell Fe1–xS@Na2.9PS3.95Se0.05 Nanorods for Room Temperature All-Solid-State Sodium Batteries with High Energy Density

High ionic conductivity electrolyte and intimate interfacial contact are crucial factors to realize high-performance all-solid-state sodium batteries. Na2.9PS3.95Se0.05 electrolyte with reduced particle size of 500 nm is first synthesized by a simple liquid-phase method and exhibits a high ionic conductivity of 1.21 × 10–4 S cm–1, which is comparable with that synthesized with a solid-state reaction. Meanwhile, a general interfacial architecture, that is, Na2.9PS3.95Se0.05 electrolyte uniformly anchored on Fe1–xS nanorods, is designed and successfully prepared by an in situ liquid-phase coating approach, forming core–shell structured Fe1–xS@Na2.9PS3.95Se0.05 nanorods and thus realizing an intimate contact interface. The Fe1–xS@Na2.9PS3.95Se0.05/Na2.9PS3.95Se0.05/Na all-solid-state sodium battery demonstrates high specific capacity and excellent rate capability at room temperature, showing reversible discharge capacities of 899.2, 795.5, 655.1, 437.9, and 300.4 mAh g–1 at current densities of 20, 50, 100, 150, and 200 mA g–1, respectively. The obtained all-solid-state sodium batteries show very high energy and power densities up to 910.6 Wh kg–1 and 201.6 W kg–1 based on the mass of Fe1–xS at current densities of 20 and 200 mA g–1, respectively. Moreover, the reaction mechanism of Fe1–xS is confirmed by means of ex situ X-ray diffraction techniques, showing that partially reversible reaction occurs in the Fe1–xS electrode after the second cycle, which gives the obtained all-solid-state sodium battery an exceptional cycling stability, exhibiting a high capacity of 494.3 mAh g–1 after cycling at 100 mA g–1 for 100 cycles. This contribution provides a strategy for designing high-performance room temperature all-solid-state sodium battery.