Guided-formation of favourable interface for stabilizing Na metal solid-state batteries

The sodium (Na) anode suffers severe interfacial resistance and dendrite issues in classic NASICON-type Na3Zr2Si2PO12 (NZSP) electrolyte, resulting in poor electrochemical performance for solid-state Na metal batteries. There has been little success in reduction of interfacial resistance in recent years. The exact mechanism of this resistance has not been fully understood because of little information at the interface. In this work, we effectively address the large interfacial resistance issue and the metal dendrite problem between Na anode and NZSP by introducing TiO2 film as an active interphase. We employ the quasi-in-situ X-ray photoelectron spectroscopy (XPS) to uncover the interphase formation mechanism at the Na/TiO2-NZSP electrolyte interface. Our quasi-in-situ XPS results confirm a formation of sodiated-TiO2 interphase upon the stepwise Na evaporation on the surface of NZSP electrolyte. Further investigation by molten Na contact angle measurement, impedance spectroscopy and DFT calculations demonstrates that the sodiated-TiO2 interphase promotes Na ion transport between Na anode and NZSP electrolyte. Moreover, the electrostatic potential formed at NZSP/NaxTiO2 interface can effectively reduce electronic conductivity at the interface and hence prevent the growth of sodium dendrites. A representative paradigm for interphase design is provided to address the interface contact for developing stable solid-state batteries with high performance.