Stable sodium anodes for sodium metal batteries (SMBs) enabled by in-situ formed quasi solid-state polymer electrolyte

A poly(DOL)-based quasi-solid electrolyte for sodium metal batteries is prepared by in-situ polymerization, and the crucial roles of FEC on forming stable SEI and preventing interfacial side reactions are demonstrated. • A poly(DOL)-based quasi-solid electrolyte for SMBs is in-situ prepared. • Ionic conductivity of 3.3×10 −3 S cm −1 and oxidation potential of 4.4 V are gained. • The crucial role of FEC on forming stable SEI is demonstrated. • The Na//Na 3 V 2 (PO 4 ) 3 full cell shows good cycling and rate performances. A high-performance quasi-solid polymer electrolyte for sodium metal batteries (SMBs) based on in-situ polymerized poly(1,3-dioxolane) (DOL) with 20% volume ratio of fluoroethylene carbonate (FEC), termed “PDFE-20”, is proposed in this work. It is demonstrated PDFE-20 possesses a room-temperature ionic conductivity of 3.31×10 −3 S cm −1 , an ionic diffusion activation energy of 0.10 eV, and an oxidation potential of 4.4 V. SMBs based on PDFE-20 and Na 3 V 2 (PO 4 ) 3 (NVP) cathodes were evaluated with an active material mass loading of 6.8 mg cm −2 . The cell displayed an initial discharge specific capacity of 104 mA h g −1 , and 97.1% capacity retention after 100 cycles at 0.5 C. In-situ polymerization conformally coats the anode/cathode interfaces, avoiding geometrical gaps and high charge transfer resistance with ex-situ polymerization of the same chemistry. FEC acts as a plasticizer during polymerization to suppress crystallization and significantly improves ionic transport. During battery cycling FEC promotes mechanical congruence of electrolyte-electrode interfaces while forming a stable NaF-rich solid electrolyte interphase (SEI) at the anode. Density functional theory (DFT) calculations were also performed to further understand the role FEC in the poly(DOL)-FEC electrolytes. This work broadens the application of in-situ prepared poly(DOL) electrolytes to sodium storage and demonstrates the crucial role of FEC in improving the electrochemical performance.