Organophosphorus flame retardants (OPFRs) in lithium-ion batteries: Classification, physicochemical properties, environmental behavior, human exposure and toxicity.

Lithium-ion batteries (LIBs) stand as a pivotal technology to achieve decarbonization goals amidst the challenges of climate change, and their applications and market size are expanding rapidly. Organophosphorus flame retardants (OPFRs) are crucial components for ensuring the safety performance of LIBs. These chemicals mainly include organophosphates, organophosphites, organophosphonates, and organophosphazenes, with a growing number of new OPFRs continually being synthesized and introduced into the market. OPFRs in LIBs (LIB-OPFRs) can be released into environmental media during battery production, dismantling, and recycling processes, subsequently leading to their occupational and environmental exposure in humans. This review presents the classification, physicochemical properties, environmental behavior, human exposure, and toxicity of LIB-OPFRs. Our analysis reveals that current research predominantly centers on organophosphate flame retardants, while studies on other categories of LIB-OPFRs exhibit a significant research gap. For emerging LIB-OPFRs with a dearth of relevant data, their physicochemical properties and potential toxicity are predicted in this study. Notably, all four categories of LIB-OPFRs show limited but consistent signals of toxicity, and some newly emerging LIB-OPFRs may exhibit higher toxicity compared to traditional ones. Aryl- and halogenated-OPFRs generally exhibit greater bioaccumulative potential and pose higher health risks in comparison to alkyl-OPFRs. Currently, it is imperative to enhance environmental monitoring, toxicological testing, and health risk assessment of new LIB-OPFRs, which are crucial for bridging data gaps and providing guidance for health protective measures as well as policy formulation.