Phosphorus FRs for battery electrolytes

Review summarises 150 studies of different phosphorus-based flame retardants in lithium-ion battery electrolytes: testing safety and electrical performance. Batteries use liquid organic electrolytes to enable ion transport between electrodes, and so electrical current. Lithium hexafluorophosphate (LiPF₆) is generally added to facilitate ion transport and protect electrodes. The organic electrolytes are however flammable, and can also react with lithium under heat generating flammable gases. Studies of phosphate, phosphonate, phosphinate, phosphine oxide, cyclotriphosphazene and phosphite compounds, as well as fluorine – phosphorus compounds are summarised. A challenge noted is the absence of standardised test methods for flammability of liquid electrolytes, making different study results non comparable. Nonetheless, studies show that a range of phosphorus FRs not only reduce fire risks in batteries, but also improve electrolyte stability and even enhance electrical performance.

“Phosphorus-Based Flame-Retardant Electrolytes for Lithium Batteries’, J-H. Kim et al., Adv. Energy Mater. 2025, 2500587, https://doi.org/10.1002/aenm.202500587