Engineering Inorganic-Rich and Composition-Gradient Solid-Electrolyte Interphases for Enhanced Ion Transport and Dendrite Suppression toward Durable Quasi-Solid Sodium-Metal Batteries

Quasi-solid polymer electrolytes (QSPEs) are being explored as a promising alternative to liquid electrolytes to enhance the safety of sodium-metal batteries (SMBs). However, their practical application is hindered by a low Na + transference number, Na dendrite growth, and interfacial deterioration. Herein, a highly conductive and flame-retardant poly(1,3-dioxolane) (PDOL) electrolyte is developed through in situ polymerization at room temperature using GaCl 3 as both the initiator and interfacial modifier. The incorporation of 0.6 mM GaCl 3 achieves a high conversion rate of 90.2% for DOL, along with a Na + transference number of 0.477. An in situ construction of a Ga 0 /NaCl-rich solid electrolyte interphase (SEI) film with composition-gradient distribution is achieved. The NaCl-rich outer layer of the SEI reduces the Na + migration energy barrier and inhibits electron transfer to mitigate interfacial side reactions. The Ga metal in the inner layer of the SEI, characterized by a strong affinity for sodium and high homogeneous diffusion capability due to its low melting point, promotes uniform Na deposition and suppresses dendrite formation. As a result, the Na||Na 3 V 2 (PO 4 ) 3 full cell with GaCl 3 -initiated PDOL electrolyte exhibits superior cycling stability, retaining 91.0% discharge capacity after 3000 cycles at 1C. This work broadens the prospects for developing safe and high-performance solid-state SMBs by integrating electrolyte design with interfacial engineering.