Titanium oxide engineered ceramic electrolytes and layered metal oxide cathodes for high-performance solid-state sodium-ion batteries

Sodium superionic conductor Na 3 Zr 2 Si 2 PO 12 (NZSP) is a leading oxide electrolyte for next-generation solid-state sodium batteries, yet its performance remains constrained by grain-boundary impedance and unstable Na//electrolyte interfaces. Here, we introduce a combined interfacial engineering strategy that integrates bulk stabilization with precise interfacial engineering using TiO 2 atomic layer deposition (ALD). Unlike physical TiO 2 mixing, which yields only modest improvements, ALD forms an ultrathin amorphous TiO 2 interphase that uniformly passivates grain boundaries, suppresses Na-induced surface degradation, and establishes continuous Na + transport pathways. The 40-cycle TiO 2 ALD coated sample delivered a room-temperature ionic conductivity of ∼1.1 mS·cm −1 , the lowest activation energy among all NZSP variants investigated in this study, and the most stable Na interfacial chemistry, enabling a critical current density of 1.4 mA·cm −2 in symmetric cells. Complementary TiO 2 ALD modification of the Na 0.7 MnO 2 cathode mitigated Jahn-Teller-driven lattice distortion and suppressed Mn dissolution, preserving structural integrity and enabling highly reversible Na + redox behavior. Together, the integrated ALD-engineered cathode and electrolyte (10Ti-NMO//40Ti-NZSP) cell exhibited reduced polarization and stable capacities of ∼160 mAh g −1 . These results establish ALD as a high-precision approach for simultaneously optimizing electrolyte and cathode interfaces, offering a unified pathway toward high-performance solid-state sodium batteries.