Separator with Nitrogen–Phosphorus Flame‐Retardant for LiNi_xCo_yMn_1−x−yO₂ Cathode‐Based Lithium‐Ion Batteries

Abstract With the pursuit of high‐energy‐density for lithium‐ion batteries (LIBs), the hidden safety problems of batteries have gradually emerged. LiNi_xCo_yMn_1−x−yO₂ (NCM) is considered as an ideal cathode material to meet the urgent needs of high‐energy‐density batteries. However, the oxygen precipitation reaction of NCM cathode at high temperature brings serious safety concerns. In order to promote high‐safety lithium‐ion batteries, herein, a new type of flame‐retardant separator is prepared using flame‐retardant (melamine pyrophosphate, MPP) and thermal stable Poly(vinylidene fluoride‐co‐hexafluoropropylene) (PVDF‐HFP). MPP takes the advantage of nitrogen–phosphorus synergistic effect upon the increased internal temperature of LIBs, including the dilution effect of noncombustible gas and the rapidly suppression of undesirable thermal runaway. The developed flame‐retardant separators show negligible shrinkage over 200 °C and it takes only 0.54 s to extinguish the flame in the ignition test, which are much superior to commercial polyolefin separators. Moreover, pouch cells are assembled to demonstrate the application potential of PVDF‐HFP/MPP separators and further verify the safety performance. It is anticipated that the separator with nitrogen–phosphorus flame‐retardant can be extensively applied to various high‐energy‐density devices owing to simplicity and cost‐effectiveness.