Fast-charging is a key requirement for customer acceptance of battery electric vehicles. In this work, various methods for lithium-plating detection are applied to prismatic hard-case lithium-ion cells to demonstrate their applicability for large-format automotive cells despite possible thermal and electrochemical inhomogeneities. Different fast-charging profiles with a charging time of less than 30 min from 10% to 80% state-of-charge are examined with methods based on coulombic efficiency, cell voltage analysis and swelling force. To validate these results, a lifetime cycling test with a subsequent cell opening is performed, followed by a discussion on lithium-plating detectability and the restrictions of each method. In order to further illustrate the applicability of the lithium-plating detection methods, the fast-charging ability of two cells with the same format but different cathode active materials, namely NMC622 and NMC811, are compared. Furthermore, a coupled electrochemical-thermal simulation is performed to study the effect of the cell design on the fast-charging ability and to elucidate why a higher cell energy density does not necessarily lead to a worse fast-charging ability.

Electrolyte motion induced salt inhomogeneity (EMSI): during cycling, electrolyte moves into and out of the jelly roll, which leads to a lasting in-plane LiPF₆ concentration gradient, possibly causing secondary effects like localized lithium plating.

Besides the performance of a lithium-ion battery cell, the manufacturing costs are crucial for the success of battery electric vehicles. To enable cost efficient yet well performing battery cells, an optimization of the manufacturing steps with respect to the cell properties is necessary. The slurry mixing process, being the initial step of the lithium-ion battery cell manufacturing process, is well known to affect the structure of the electrode coating (e.g. porosity, tortuosity or the distribution of the binder and conductive additive), which is further connected to its electrical and ionic resistances. Therefore, a variation of the formulation strategy or mixing device can affect the performance of the lithium-ion battery cell. In this study, several variations of the slurry mixing process are investigated with respect to its effect on the fast-charge capability of the lithium-ion battery cell. Properties of the slurry, the electrode and the resulting lithium-ion battery cell are characterized for each variation to detect interdependencies and derive process-structure-property relations.

The trend for increased nickel content in layered transition metal oxide cathode active materials and increasing charging cut-off voltages aggravates aging of lithium-ion battery cells at high state of charge (SOC). We investigate the calendaric aging behavior of large-format automotive prototype cells and laboratory single-layer pouch cells at high but realistic cell voltages/SOCs and demonstrate that electrolyte oxidation in combination with follow-up reactions can cause a significant loss of the LiPF₆ salt in the electrolyte. For this, we analyze the LiPF₆ concentration in aged cells, the generation of H₂ upon storage, and the cell resistance for different aging conditions. We show that the LiPF₆ loss is a critical aging phenomenon, as it cannot readily be detected by capacity fading measurements at low/medium C-rates or by cell resistance measurements, while it severely reduces rate and fast-charging capability. Under certain circumstances, LiPF₆ loss can even lead to a temporary capacity increase due to conversion of the conducting salt in the electrolyte to cyclable lithium in the active material. Finally, we suggest a possible reaction mechanism and a simple accounting model to keep track of how different side reactions involved in LiPF₆ loss change the cyclable lithium inventory of a lithium-ion cell.