Impact of single vs. blended functional electrolyte additives on interphase formation and overall lithium ion battery performance

Two functional high-voltage additives, namely 2-(2,2,3,3,3-pentafluoropropoxy)-1,3,2-dioxaphospholane (PFPOEPi) and 1-methyl-3,5-bis(trifluoromethyl)-1H-pyrazole (MBTFMP) were combined as functional additive mixture in organic carbonate–based electrolyte formulation for high-voltage lithium battery application. Their impact on the overall performance in NMC111 cathode-based cells was compared with the single-additive–containing electrolyte counterpart. The obtained results point to similar cycling performance of the additive mixture containing electrolyte formulation compared with the MBTFMP-containing cells, whereas the single PFPOEPi-containing cells displayed the best cycling performance in NMC111||graphite cells. With regard to the cathode electrolyte interphase (CEI), characterized and analyzed by means of scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS), both the MBTFMP and the PFPOEPi functional additives decompose on the NMC111 surface in single-additive–containing electrolyte formulations. However, the thickness of the CEI formed in the additive mixture–containing electrolyte formulation is determined by the MBTFMP additive, whereas the PFPOEPi additive impacts a change in the composition of the CEI. Furthermore, the MBTFMP additive decomposes prior to the PFPOEPi and, therefore, dominates the cycling performance of NMC111||graphite cells containing functional additive mixture–based electrolyte. This systematic approach allows us to understand the synergistic impact of each functional additive in an electrolyte formulation containing an additive mixture and helps to identify the right additive combination for advanced electrolyte formulation as well as to elucidate whether the single-additive or the additive mixture approach is more effective for the development of advanced functional electrolytes for lithium-based cell chemistries.