Fast-charging capability of lithium-ion cells: Influence of electrode aging and electrolyte consumption

Fast charging of electric vehicles is becoming more and more important for achieving customer acceptance of electromobility. During fast charging, the maximum charging rate of the lithium-ion cells used in the traction batteries of electric vehicles has to be controlled properly to avoid the deposition of metallic lithium on the surface of the negative electrode, known as lithium plating. However, cycle life tests have shown that after a few hundred cycles at a moderate aging rate, the fast-charging capability of lithium-ion cells decreases and a sudden, rapid loss of capacity is observable. Therefore, to achieve a long service life and, concurrently, short charging times, it is crucial to analyze the non-plating critical charging rate depending on the mode of battery degradation. In this paper, we separately investigate the influence of the main aging factors, such as electrode aging and electrolyte consumption, on the fast-charging capability of large-format automotive lithium-ion pouch cells. The pouch cells are cycled to different states of health and a post-mortem local degradation analysis is performed. Using three-electrode test cells, the non-plating critical charging curves are determined for the aged electrode material and for test cells assembled with different amounts of electrolyte. Our findings reveal that for the investigated lithium-ion pouch cells the fast-charging capability is reduced over cycling not by the aging of the electrodes but by the consumption of electrolyte.