Understanding the interactions of phosphonate-based flame-retarding additives with graphitic anode for lithium ion batteries

• Diethyl ethylphosphonate (DEEP) and dimethyl methylphosphonate are tested as flame retardants for lithium ion batteries.
• The DMMP shows a destructive reaction with graphitic anode while DEEP shows a self-reduction mechanism.
• DEEP is reported for the first time as flame-retardant additive for lithium ion batteries and demonstrates a much better compatibility with graphitic anode.

The compatibility with graphitic anode has been one key problem in developing flame-retarding additives for lithium ion batteries. To understand the interactions between flame-retarding additives and graphitic anode, two phosphonate esters (dimethyl methylphosphonate DMMP and diethyl ethylphosphonate DEEP) are selected and characterized as flame retardant addtives. DEEP is reported as a flame-retarding additive for the first time. Their interactions with graphite anode are characterized via current-static charge–discharge, ex-situ XRD, FE-SEM and AC impedance. The results reveal that the two phosphonate esters demonstrate different reaction mechanisms with graphitic anode, which result in different anode compatibility. These findings may be useful for designing better flame-retarding additives for lithium ion batteries.