Chemical reactivity of lithium difluorophosphate as electrolyte additive in LiNi0.6Co0.2Mn0.2O2/graphite cells

From the literature overview, lithium difluorophosphate salt, LiPO2F2, is considered a powerful electrolyte additive capable of enhancing lithium-ion batteries’ capacity retention. Lower cell impedance associated with SEI and/or CEI layers composition and texture modifications had been widely demonstrated, but without providing clear mechanisms. This paper sheds light on the reactivity of LiPO2F2 by combining electrochemical measurements and analyzes of electrolyte degradation products at the interphases and in the electrolytes by means of infrared and mass spectrometry techniques. Fluorine substitution reaction by electrochemically formed anions leads to a mitigation of electrolyte solvents degradation and to the enrichment of the SEI layer with LiF and lithium organofluorophosphates. Furthermore, a discussion on the composition of the CEI layer that enables the prevention of the transition metals dissolution from positive electrode layered oxides materials is also presented.