Impact of Aluminum Trifluoride AlF 3 Impurities in Electrolyte on NMC 811 /Graphite Lithium-Ion Battery Performance

The impact of aluminum fluoride (AlF 3 ) as electrolyte impurity in lithium-ion battery cells has been studied. Deteriorated capacity retention of NMC 811 /Graphite full cells is observed especially when they are operated at high temperature. We found an acceleration of electrolyte degradation during battery cell operation in presence of AlF 3 impurities. The NMC 811 cathode and Graphite anode electrodes were characterized by cross-section scanning electron microscopy, focused-ion beam, Raman spectroscopy, and X-ray photoelectron spectroscopy methods. Cells with AlF 3 , especially when cycled at elevated temperatures, form polymers on the cathode and anode surfaces, likely due to electrolyte degradation. Corresponding pathways for the reaction forming the SEI and CEI layers are postulated. In particular, we proposed a formation path for polyethylene and polyethylene glycol polymers on the anode and cathode surfaces due to the presence of aluminum alkoxide as a catalyst activated by the AlF 3 impurities.