The Reactivity of Charged Electrode Materials with Electrolytes Containing the Flame Retardant, Triphenyl Phosphate

The reactivity of lithiated graphite and deintercalated LiNi 1/3 Mn 1/3 Co 1/3 O 2 (called NMC) in electrolytes containing triphenyl phosphate (TPP) was studied by Accelerating Rate Calorimetry (ARC). Lithiated graphite shows similar reactivity in electrolytes containing TPP to those without TPP. By contrast, deintercalated NMC shows an additional exothermic reaction at lower temperature (∼ 200°C) in electrolytes containing TPP compared to electrolytes without TPP. This means charged NMC shows a higher reactivity at a lower temperature when TPP is present. The flame retardance of electrolytes as a function of TPP content was judged using self-extinguishing (SET) measurements. The SET results show that TPP can significantly reduce the self–extinguishing time of the electrolyte, which may lead to a less-flammable electrolyte. However, the SET test results depend heavily on the test method used. Based on these fundamental results, it is not clear if additions of TPP will actually lead to safer Li-ion cells. Abuse testing experiments on large size Li-ion cells are required.