Mechanical and Interfacial Regulation of NASICON Electrolytes Through NiO Additives Toward Stable Sodium Metal Anodes

Solid‐state sodium metal batteries (SMBs) are regarded as one of the most promising next‐generation energy storage technologies because of their intrinsic safety and high energy density. However, their practical development is severely hindered by sodium dendrite formation and sluggish charge transport across solid–solid interfaces. Herein, a Na 3 Zr 2 Si 2 PO 12 solid electrolyte incorporating a NiO additive is proposed to systematically improve mechanical properties and interfacial wettability, thereby enhancing dendrite resistance and interfacial contact. The results show that introducing an appropriate amount of NiO into Na 3 Zr 2 Si 2 PO 12 reduces the anode interfacial resistance to 217 Ω, which is more than a twofold decrease compared with pristine Na 3 Zr 2 Si 2 PO 12 . The assembled symmetric sodium cells exhibit stable Na plating/stripping for 2000 h at a current density of 0.3 mA cm −2 . In addition, quasi‐solid‐state sodium metal batteries assembled with a Na 3 V 2 (PO 4 ) 3 cathode also deliver stable cycling performance, retaining 89% of the initial discharge capacity after 1300 cycles. This work provides a valuable reference for the development of high‐performance, dendrite‐free quasi‐solid‐state sodium metal batteries.