Flame-retardant quasi-solid polymer electrolyte enabling sodium metal batteries with highly safe characteristic and superior cycling stability

Con ventio nal liquid electrolytes based sodium metal batteries suffer from severe safety hazards owing to electrolyte leakage,in flammability and dendritic sodium deposit!on.Herein,we report a flame-retardant quasi-solid polymer electrolyte with poly(methyl vinyl ether-alt-maleic an hydride)(P(MVE-alt-MA))as host,bacterial cellulose(BC)as reinforceme nt,and triethyl phosphate/vinyle ne carb on ate/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 I on g-term cycli ng stability(84.4%capacity rete ntion 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°C and 84.8%capacity retention after 50 cycles at-10°C)for Na3V2(PO4)3/Na metal batteries.And this battery also displayed a normal charge/discharge property even at-15°C.These fascinating cycle properties are mainly ascribed to the effective pro怕ctive layers formed on Na3V2(PC>4)3 cathode and sodium metal ano de.More thorough in vestigati on elucidates that such flame-retardant quasi-solid polymer electrolyte plays a multif unctional role in the adva need sodium metal batteries:(1)being in volved in the formatio n of a favorable cathode electrolyte in terface(CEI)to inhibit the dissolutio n of van adium and maintai n the structure integrity of the Na3V2(PO4)3;(2)participati ng in building a stable solid electrolyte in terface(SEI)to suppress the growth of Na dendrites;(3)integrating flame-retardanee into polymer sodium batteries to enhance flame-resistanee,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 withsta nd harsh conditions(be nded or cut off a corn er),confirming the obtai ned polymer electrolyte with superior non-leakage property.In all,these outstanding characteristics would endow this flame-retardant quasi-solid polymer electrolyte a very promising can didate for highly-safe sodium metal batteries.