In Situ Forming Na─Sn Alloy/Na2S Interface Layer for Ultrastable Solid State Sodium Batteries

Abstract The poor interfacial compatibility between sodium superionic conductor (NASICON) electrolyte and metallic sodium anode will lead to severe dendrite penetration, impeding the application of NASICON electrolytes for solid state sodium batteries. Herein, a homogeneous SnS 2 coating layer is sputtered on the surface of Na 3.4 Zn 0.1 Zr 1.9 Si 2.2 P 0.8 O 12 electrolyte to in situ construct a kinetically stable Na─Sn alloy/Na 2 S interlayer, possessing superior Na affinity, low diffusion barrier, and electronic insulating character to suppress dendrite growth, which is confirmed by experiments and density‐functional theory calculations. Benefiting from the Na─Sn alloy/Na 2 S interphase, the critical current density of Na 3.4 Zn 0.1 Zr 1.9 Si 2.2 P 0.8 O 12 increases from 2.4 to 9.4 mA cm −2 . In addition, the obtained Na 3 V 2 (PO 4 ) 3 /Na 3.4 Zn 0.1 Zr 1.9 Si 2.2 P 0.8 O 12 @SnS 2 /Na solid state batteries exhibit a high initial reversible discharge capacity of 115.1 mAh g −1 at 0.1 °C with an initial Coulombic efficiency of 93.6%, and a capacity retention rate of 88.1% after 1000 cycles at 1 C.