Homogeneous Microphase Structure and Polymer‐Dominated Ion Transport Network Enable Durable Quasi‐Solid‐State Sodium Metal Batteries

Abstract Uncontrollable dendrite growth, unstable solid electrolyte interphase (SEI) and excessive consumption of electrolytes significantly limit the practical applications of sodium metal batteries (SMBs). Here, a 3D co‐continuous quasi‐solid‐state electrolyte (QSSE) is constructed by introducing the star‐shaped crosslinker octavinyl polyhedral oligomeric silsesquioxane (OV‐POSS) into the in situ polymerization of butyl acrylate (BA) monomers. The enhanced homogeneity of the QSSE generates abundant interfacial transport pathways, facilitating uniform ion flux and mitigating concentration polarization, thereby enabling uniform Na metal deposition. In addition, polymer‐involved hybrid solvation structures with a reduced desolvation energy barrier promote fast charge transfer kinetics and the formation of a stable polymer‐driven inorganic–organic hybrid electrode/electrolyte interphase. Owing to the outstanding ion transport properties and interfacial compatibility of the QSSE, the Na|P‐QSSE|Na 3 V 2 (PO 4 ) 3 cell demonstrates high capacity retention (81%@2000 cycles, 64.7%@4000 cycles). This study provides valuable insights into the rational design of high‐performance quasi‐solid‐state SMBs.