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.