SnF2-Induced Highly Current-Tolerant Solid Electrolytes for Solid-State Sodium Batteries

Solid-state sodium batteries have garnered considerable  interest. However, their electrochemical performance is hampered by  severe interfacial resistance between sodium metal and inorganic solid  electrolytes, as well as Na dendrite growth within the electrolytes. To  address these issues, a uniform and compact SnF₂ film is first introduced onto the surface of the inorganic solid electrolyte Na_3.2Zr_1.9Ca_0.1Si₂PO₁₂  (NCZSP) to improve contact through an effective and straightforward  process. Through experiments and computations, the in situ conversion  reaction between SnF₂ and molten Na is adequately confirmed, resulting in a composite conductive layer containing Na_xSn  alloys and NaF at the interface. As a result, the interfacial  resistance of Na/NCZSP is significantly decreased from 813 to 5 Ω cm², and the critical current density is dramatically increased to 1.8 mA cm⁻², as opposed to 0.2 mA cm⁻² with bare NCZSP. The symmetric cell is able to cycle stably at 0.2 mA cm⁻² for 1300 h at 30 °C and exhibits excellent current tolerance of 0.3 and 0.5 mA cm⁻². Moreover, the Na₃V₂(PO₄)₃/SnF₂-NCZSP/Na full cell displays excellent rate performance and cycling stability. The SnF₂-induced  interlayer proves significant in improving interfacial contact and  restraining sodium dendrite propagation, thus promoting the development  of solid-state sodium batteries.