Ethylene carbonate (EC) based electrolytes, e.g. Gen2 (1.2 M LiPF₆ in EC/EMC 3/7) are commonly used as a baseline electrolyte for various cathode chemistries. Is EC the best choice for all active materials? Streich [1] investigated several cathodes (NCM111, NCM622 and NCM811) using a 1M LiPF₆in EC/DEM 3/7 electrolyte and reached the conclusion that there is a strong correlation between the Ni content in the active material and the amount of carbon dioxide produced in a first cycle over 4.3V. The study suggests that tailoring electrolyte formulation for the specific electrodes chemistries may be a way of improving performance of the cells. Interestingly, Dahn [2] demonstrated that it is possible to improve the performance of NCM424//graphite pouch cells by completely eliminating EC from the electrolyte formulation. While EC-reach electrolytes proved to be a good choice for some electrode chemistries they may not be the best option in all cases.

We conducted a systematic study of several cathode chemistries in full cells (CR2032) with various electrolyte formulations, with and without EC.

Figure 1 shows the effect of electrolyte formulation on cycle life of NCM523 and NCA based cells. It is clear that for cells with NCA cathode electrolytes containing EC have an adverse effect on performance whereas this effect is not observed with NCM523 cells.

Comprehensive data from cycle life and cell impedance study of several cathode materials (NCM523, NCM622, NCM811, NCA and HE5050) in various electrolyte formulations will be presented and discussed. Our study will help researchers chose electrolyte formulation for the electrode material they investigate.

[1] Daniel Streich et al., Impact of Ni content on interface reactions at NCM electrodes, GRS/GRC Ventura CA, USA, 2016, Poster 160217

[2] J. R. Dahn et al, Electrolyte System for High Voltage Li-Ion Cells, Journal of The Electrochemical Society, 163 (13) A2571-A2578 (2016)