Graphical Abstract
![](https://wqketang.oss-cn-beijing.aliyuncs.com/zip-unzip/zip-ef768e05-f30c-464c-a043-6b869a50ef9b/nr-12-9-2230/files/nr-12-9-2230-FE1.jpg?Expires=1739869934&OSSAccessKeyId=STS.NT28qGGsyFYd3ME3qtkU9D2ZS&Signature=urklW2KIDCuskTnNOrITjTMoNQw%3D&security-token=CAISywJ1q6Ft5B2yfSjIr5eHc8vzqqxY8ZuPMWv013EhZ9oVq%2FfxsTz2IHtKenhsBOsbtfk1mG5W5%2FgZlqJ9SptIAEfJa9d99MzBVvgc2tCT1fau5Jko1beHewHKeTOZsebWZ%2BLmNqC%2FHt6md1HDkAJq3LL%2Bbk%2FMdle5MJqP%2B%2FUFB5ZtKWveVzddA8pMLQZPsdITMWCrVcygKRn3mGHdfiEK00he8TouufTinpHMskGA1Aell7Mvyt6vcsT%2BXa5FJ4xiVtq55utye5fa3TRYgxowr%2Fwo0v0YpGya5YzHXwcPskvdKZbo78UqLQlla6w%2BGqFJqvPxr%2Fp8t%2Fx5fWJKAezhVgs8cVM8JOjIqKOscIsipkmoxV8YFV55c8Fdm%2BgUooJVgIMhTnduUfAPJAGOxzJitP%2BUVGGphr60TEnBL4rB5MUctfzRp5axMwTUTzDnGoABmf5JZxNQ%2Fp6hVt7Xbd%2FKctsP8KiJsJguGmWXG6ubZj2u3KMbL6fDomDDJ6%2B%2BzGSQ041gcjiT4OMo94H1sHIzrijufa2PjfEJ1zB%2FdAqLgHor398Tv8JY5qGw4jANoNpGRKGUSVMaWNx2WGC8i2e%2FcHOKoVPmi1x2z1feyofpRfcgAA%3D%3D)
Conventional liquid electrolytes based sodium metal batteries suffer from severe safety hazards owing to electrolyte leakage, inflammability and dendritic sodium deposition. Herein, we report a flame-retardant quasi-solid polymer electrolyte with poly(methyl vinyl ether-alt-maleic anhydride) (P(MVE-alt-MA)) as host, bacterial cellulose (BC) as reinforcement, and triethyl phosphate/vinylene carbonate/sodium perchlorate (TEP/VC/NaClO4) as plasticizer for highly safe sodium metal batteries. The as-obtained quasi-solid polymer electrolyte exhibits superior flame retardancy (self-extinguish within 1 s), complete non-leakage property and wide electrochemical windows (4.4 V). More importantly, Na3V2(PO4)3/Na metal batteries using such polymer electrolyte delivers superior long-term cycling stability (84.4% capacity retention after 1000 cycles) which is significantly better than that (only 2% after 240 cycles) of liquid electrolyte. In addition, this flame-retardant quasi-solid polymer electrolyte provides favorable cycle performance (80.2% capacity retention after 70 cycles at 50 ℃ and 84.8% capacity retention after 50 cycles at -10 ℃) for Na3V2(PO4)3/Na metal batteries. And this battery also displayed a normal charge/discharge property even at -15 ℃. These fascinating cycle properties are mainly ascribed to the effective protective layers formed on Na3V2(PO4)3 cathode and sodium metal anode. More thorough investigation elucidates that such flame-retardant quasi-solid polymer electrolyte plays a multifunctional role in the advanced sodium metal batteries: (1) Being involved in the formation of a favorable cathode electrolyte interface (CEI) to inhibit the dissolution of vanadium and maintain the structure integrity of the Na3V2(PO4)3; (2) Participating in building a stable solid electrolyte interface (SEI) to suppress the growth of Na dendrites; (3) Integrating flame-retardance into polymer sodium batteries to enhance flame-resistance, eliminate electrolyte leakage, and thus improve safety of sodium batteries. Based on these results, we further assembled Na3V2(PO4)3/MoS2 pouch cell which can withstand harsh conditions (bended or cut off a corner), confirming the obtained polymer electrolyte with superior non-leakage property. In all, these outstanding characteristics would endow this flame-retardant quasi-solid polymer electrolyte a very promising candidate for highly-safe sodium metal batteries.
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