An approach of evaluating the effect of vinylene carbonate additive on graphite anode for lithium ion battery at elevated temperature

• VC effect on graphite anode cycled at 60 °C is evaluated using LC-MS and DART-MS.
• VC suppresses the formation of phosphate esters and carbonate oligomers.
• VC assists the formation of oligomeric phosphate esters on the graphite surface.
• The contribution of VC to the polymerization on the graphite surface is clarified.

An approach is proposed to evaluate the VC effect in a LiFePO4/graphite cell at 60 °C through liquid chromatography mass spectrometry (LC-MS) together with direct analysis in real time mass spectrometry (DART-MS). The LC-MS result shows that VC can effectively suppress the formation of phosphate esters as well as carbonate oligomers during the electrochemical cycling. It is also known from DART-MS analysis that VC assists the formation of thermally resistant oligomeric phosphate ester layer on the graphite surface, storing more solvent EC inside the layer. On the other hand, no compounds are observed on the LiFePO4 cathode surface. The formation of the denser oligomeric phosphate ester layer is found to be the reason for the improved cycle stability of the cell cycled at elevated temperature.

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