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

Abstract

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 Na3V2(PO4)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.