Approaching Practically Accessible and Environmentally Adaptive Sodium Metal Batteries with High Loading Cathodes through In Situ Interlock Interface

Abstract Fast‐charging and high‐energy‐density solid‐state sodium metal batteries (SMBs) working under harsh temperatures are in urgent demand for the state‐of‐the‐art secondary batteries. However, the unmatched interfacial contact and temperature‐limited ionic conductivity still impede SMBs from authentic commercialization. Constructing a 3D ion diffusion channel through in situ interlock interfaces can effectively address these bottlenecks. Herein, an in situ cured gel polymer electrolyte (GPE) is developed by introducing trihydroxymethylpropyl triacrylate (TMPTA) into conventional electrolytes. The as‐prepared GPE can generate superior 3D ionic conductive networks in the cathodes with high ionic conductivity at universal temperatures (0–60 °C) and a wide working potential, which successfully pairs with the high‐voltage cathodes with ultrahigh loads of 13.01 mg cm⁻¹ to develop a practical solid‐state battery. Furthermore, as deciphered by in‐depth X‐ray photoelectron spectroscopy, the flexible solid electrolyte interphase layer is stable enough to prevent sodium metal from the corrosion of the electrolyte and the formation of sodium dendrites. Benefitting from this “two‐in‐one” effect, solid‐state SMBs with the in situ GPE exhibit an excellent long‐term cycling stability at 60 °C with a capacity retention of 80% after 1000 cycles at 1 C, and superior temperature adaptability even at 0 °C with a rate capacity retention of 90% at 1 C compared with that at 0.1 C.