Highly Concentrated Electrolytes Containing a Phosphoric Acid Ester Amide with Self-Extinguishing Properties for Use in Lithium Batteries

Phosphoric acid ester amides were examined as a new self-extinguishing solvent for Li-ion batteries. The phosphoric acid ester amides used in this study contained two fluorinated alkyl groups and one amino group, (CF3CH2O)2(NR1R2)P═O (PNR1R2). The thermal stability of the highly concentrated electrolyte of lithium bis(fluorosulfonyl) amide (LiFSA) and PNR1R2 with a molar ratio of [LiFSA]/[PNR1R2] = 0.5 under overcharge depended on the modification of the amino substituent. Introduction of a phenyl group (R1 = CH3, R2 = C6H5) was effective for improving thermal stability. The release of gases and heat that typically accompanied reaction of the solvent with the charged graphite anode was greatly suppressed. Density functional theory calculations indicated that PNR1R2 decomposed reductively near 0.5 V vs Li+/Li, suggesting poor Li ion insertion into the graphite. However, the highly concentrated electrolyte using LiFSA and PNR1R2 reduced the reductive potential of PNR1R2 and enabled not only the insertion of...