Flame-Retardant Solid Polymer Electrolyte Based on Phosphorus-Containing Polyurethane Acrylate/Succinonitrile for Lithium-Ion Batteries

A flame-retardant solid polymer electrolyte (FR-SPE) membrane was successfully designed through UV-curing flame-retardant polyurethane acrylate (PUA) oligomers, succinonitrile, aluminum oxide (Al2O3), and lithium salt. The flame retardant PUA is formed by grafting reactive flame-retardant 9,10-dihydro-9-oxa-10-phenanthrene-10-oxide (DOPO) on the main chain of the oligomer. The cross-linked PUA ensures excellent mechanical properties and high flame retardancy of FR-SPE. Moreover, the flame retardancy of the FR-SPE can reach the V-0 level of the UL-94 test when the grafting rate of DOPO on PUA reached 39%, and the obtained FR-SPE achieves a high ionic conductivity of 2.66 × 10–4 S cm–1 at room temperature, a wide electrochemical stability window of 5 V, and a high lithium-ion transfer number of 0.55. Moreover, FR-SPE shows a stable lithium plating/stripping response for over 600 h under a constant current density of 0.1 mA cm–2. Meanwhile, the cell of LiFePO4/FR-SPE/Li4Ti5O12 has excellent cycling stability (144.6 mA h g–1 at 0.2 C after 100 cycles) and rate capability (107.4 mA h g–1 at 5 C). In addition, the electrolyte has no adverse effect on the cycle performance of batteries with graphite electrodes. Thus, such cross-linked flame-retardant SPEs are argued to provide an effective method for more broadly enhancing lithium battery safety and performance.