Phosphorylated cellulose nanofiber as sustainable organic filler and potential flame-retardant for all-solid-state lithium batteries

Phosphorylated cellulose nanofiber (CNF-P) is presented as novel and promising organic filler for the preparation of composite solid polymer electrolytes (SPE). The degree of phosphorylation was evaluated, and the CNF-P was characterized. The results show that the phosphorus incorporation promotes the flame-retardancy property of cellulose nanofiber. Solid polymer electrolytes were prepared using CNF-P and the poly(ethylene oxide) as a matrix and lithium bis(trifluoromethanesulfonyl)imide salt (LiTFSI), with a molar ratio of [EO]/[Li+] ~ 20. The incorporated CNF-P improved significantly the mechanical properties of the resulting SPE, especially its tensile strength reaching a value of 45 MPa. The resulting composite polymer electrolytes showed practical conductivity values exceeding 10−4 S/cm at 70 °C and provide a wide electrochemical stability window above 5 V vs Li/Li+. Cycling performances of these composite SPEs have been evaluated in an all-solid-state battery half-cell configuration using Li metal anode and LiFePO4/C cathode showing the viability of such fillers in solid polymer electrolytes.