Cost effective all‐solid‐state sodium‐ion batteries that operate at room temperature are appealing candidates for use in large‐scale energy storage systems. Although low voltage sulfur was primarily used as cathode for fabrication of all solid-state Na ion battery, limited research was done for cost effective high voltage layered oxide cathode. Here we developed a bulk-type Na-ion all-solid-state battery, fabricated using a high voltage layered oxide cathode Na_0.8[Li_0.12Ni_0.22Mn_0.66]O₂(NLNMO, 4.2V vs. Na/Na⁺) and Na₃PS₄(NPS) glass-ceramic as the solid electrolyte, is expected to have high energy density and improved safety over batteries containing liquid electrolytes. However, the observed interfacial chemical reactions between the oxide cathode and sulfide solid electrolyte as well as electrochemical decomposition of NPS limits the high voltage electrochemical performance. Such reactions were probed using Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and X-ray diffraction (XRD). To improve the performance, the surface of NLNMO was modified by applying a cost-effective, solution-processed and computationally guided resistive coating of additional oxide layer. STEM revealed that coating layer is amorphous about 5nm thick. After optimizing the coating process, the electrochemical performance of the cell dramatically improved, achieving a specific capacity comparable to that of the liquid cell while exhibiting 80% capacity retention after 300 cycles. This coating method can be an effective strategy for achieving higher electrochemical performance in room temperature all-solid-state Na-ion batteries.