Electrolyte Additive Performance in Lithium Ion Batteries: From Coin Cells to 400-Mah Pouch Cells

Electrolyte additives have been widely reported to improve Lithium-Ion battery performance.  Even small quantities of various additives have been shown to create stable SEIs on both the anode and cathode, improve safety, and stabilize electrolytes.  Our work has focused on SEI forming additives that work on both the anode and cathode electrodes.  Promising bi-functional additives that we have chosen to study in coin cells and larger format pouch cells are lithium bis(oxalate)borate (LiBOB) and lithium difloro(oxalate)borate (LiDFOB).

As part of DOE’s Applied Battery Research for Transportation (ABR) Program, a high voltage and high capacity cathode was paired with a high capacity graphite anode for this study.  This electrode couple has the potential for applications in plug-in hybrid (PHEV) and battery electric vehicles (EV).  The cathode selected was from the LMR-NMC class of materials; Toda HE5050 ( Li_1.2Ni_0.15Mn_0.55Co_0.1O₂) and the anode was A12 graphite from Phillips 66.  Coin cells were assembled with these materials and tested with a number of different electrolyte and additive combinations.  Several compositions have shown an improvement in the coin cell performance, shown in Figure 1.

Based upon promising coin cell results from electrolyte and additive combinations, they were tested in 400-mAh pouch cells.   The improved performance that was present in the coin cells was not observed in the pouch cells.  Figure 2 shows the 400-mAh pouch cell performance of these additive combinations.

This presentation examines the differences in coin cells and pouch cells relative to additive performance.  Examples of these differences are: formation conditions, electrolyte quantity, additive concentrations, etc.  By studying these conditions, we will be able to simulate and vary pouch cell conditions via coin cell analysis.  The coin cell conditions and performance will be verified against 400-mAh pouch cell performance data to ensure that the conditions and performances are scalable.  By following this process less battery materials will be required and will speed up the optimization process in pouch cells.

Lastly, knowing the challenges that electrolyte additives present in scaling up cell size, we will provide some recommendations for coin cell testing that should be considered in the evaluation of research materials.