A Multifunctional Na_xBi/NaCl Flexible Interface Layer for Solid‐State Na Metal Batteries

Abstract

Na3Zr2Si2PO12 (NZSP) electrolyte with excellent air stability and acceptable ionic conductivity demonstrates a significant potential for application in solid‐state Na metal batteries. However, the poor interfacial contact between NZSP and Na anode has severely hindered its practical application. Herein, a BiCl3/polytetrafluoroethylene flexible interface layer is constructed between NZSP and Na metal anode. BiCl3 can react with Na metal to form a multifunctional NaxBi/NaCl‐rich flexible interface layer during the cycling process, which can effectively enhance the interfacial contact, avoid the formation of voids and reduce the interfacial resistance. NaxBi with low energy barrier can provide fast Na+ diffusion path, and NaCl with a wide band gap can inhibit electron injection and suppress Na dendrite growth. Owing to the multifunctional NaxBi/NaCl flexible interface layer, the Na/BiCl3@NZSP/Na symmetric cell exhibits a reduced interfacial resistance from 1252.1 to 67.6 Ω and achieves a high critical current density of 2 mA cm⁻2 at 25 °C. At 0.1 mA cm⁻2/0.1 mAh cm⁻2 and 0.3 mA cm⁻2/0.3 mAh cm⁻2, the symmetric cell can stably cycle for 3000 and 1100 h. Additionally, the Na3V2(PO4)3/BiCl3@NZSP/Na full cell can retain 96.7% of initial capacity (≈111 mAh g−1) after 300 cycles at 0.5 C and excellent rate capability.