Analyzing the effect of electrolyte quantity on the aging of lithium-ion batteries

Lechtenfeld, Christian; Buchmann, Julius; Hagemeister, Jan; Bela, Marlena M.; van Wickeren, Stefan; Daub, Rüdiger; Wiemers-Meyer, Simon; Winter, Martin; Nowak, Sascha

Zusammenfassung

As one of the main components in lithium-ion batteries, the electrolyte has been and continues to be a focal point of extensive research regarding the formulation to improve cell characteristics such as safety, cycle life or rate capabilities. However, the influence of electrolyte quantities is rarely addressed, despite a substantial impact on various economic and cell technology specific factors. In this study, the impact of varying electrolyte quantities (based on the cell pore volume) on electrochemical performance and cell aging processes was investigated using three different electrolytes (1 M LiPF6 in EC:EMC (3:7 w/w) (LP57), LP57 + 2 wt.% VC (LP572), and LP57 with a constant absolute amount of VC (LP57+absVC; 18.351 mg)). For this purpose, comprehensive analytical post mortem investigations were conducted using GC-MS/FID, ICP-OES, SEM, and EDX. The results show that the decreasing performance of cells using LP57 is determined by excessive and continuous electrolyte decomposition, that with increasing electrolyte volume leads to enhanced irreversible lithium-ion loss and thickening of the interphase layers. Impedance rise due to the growth of the interphase at the negative electrode was also identified as the cause of degrading cell performance with increasing amounts of LP572. Instead of electrolyte aging effects, the origin of this degradation was attributed to an increasingly pronounced consumption of VC. By varying the overall electrolyte quantity while keeping the VC amount constant within the cell system, the differences in cell performance were minimized and deteriorating effects by excessive electrolyte degradation or additive consumption were suppressed. This study demonstrates the sensitive interdependence of electrolyte volume and additive concentration, as well as the resulting impact on the aging behavior practically affecting the electrochemical performance. Comprehensively understanding the characteristics of each individual electrolyte component and tailoring the electrolytes to cell-specific cell properties proves to be crucial to optimize cell performance