Phosphoryl-Rich Flame-Retardant Ions (FRIONs): Towards Safer Lithium-Ion Batteries

The functionalized catecholate, tetraethyl (2,3‐dihydroxy‐1,4‐phenylene)bis(phosphonate) (H2‐DPC), has been used to prepare a series of lithium salts Li[B(DPC)(oxalato)], Li[B(DPC)2], Li[B(DPC)F2], and Li[P(DPC)3]. The phosphoryl‐rich character of these anions was designed to impart flame‐retardant properties for their use as potential flame‐retardant ions (FRIONs), additives, or replacements for other lithium salts for safer lithium‐ion batteries. The new materials were fully characterized, and the single‐crystal structures of Li[B(DPC)(oxalato)] and Li[P(DPC)3] have been determined. Thermogravimetric analysis of the four lithium salts show that they are thermally stable up to around 200 °C. Pyrolysis combustion flow calorimetry reveals that these salts produce high char yields upon combustion. Playing with fire: A series of borate and phosphate anions (flame‐retardant ions; FRIONs) have been produced in high yields and purity using a readily accessible diphosphinatocatechol. The phosphoryl‐rich character of the anions imparts flame‐retardant qualities and offers potential utility as lithium salts for safer lithium‐ion batteries.