In-situ formation of inorganic-rich solid electrolyte interphase by using antimony and fluorine-modified Cu foam for dendrite-free sodium metal anodes

The practical application of sodium metal batteries (SMB) is hindered by severe dendrite formation. In-situ growth of an artificial inorganic-rich solid electrolyte interphase (SEI) to mitigate dendrite formation has garnered significant attention. This study reports the design and fabrication of an antimony and fluorine-modified 3D Cu foam current collector (Sb-CuF₂@Cu), which induces the in-situ forming of inorganic-rich SEI layer during Na metal deposition. As investigated by X-ray depth profiles and ex-situ transmission electron microscopy, the SEI consists of a Sb^{3 +} (Na₂Sb₄O₇)-containing external layer and a NaF-rich internal layer. Theoretical calculations and in-situ optical microscopy have demonstrated that the inorganic-rich SEI facilitates rapid Na⁺ transfer across the entire 3D framework, resulting in densely packed and dendrite-free Na metal anodes. The external layer facilitates Na⁺ conduction, stabilizes Na⁺ flux, and acts as a buffer layer; whereas the inner layer inhibits ongoing reduction reactions and equalizes the electric field, further suppressing dendrite growth. Consequently, the symmetrical cells exhibit an extended cycle life of 1000 hours at 2 mA cm⁻² and 1 mAh cm⁻². Moreover, the Sb-CuF₂@Cu/Na anode combined with the Na₃V₂(PO₄)₃ cathode results in a full battery with a long service life of 1000 cycles at 5 C.