Determination of the operating limits for fast charging

Fast-charging of lithium ion batteries is essential in electromobility as well as in many other areas of application. In the development of fast-charging procedures one has to know the operating limits of the cell. Exceeding the maximum charging rate will result in an excessive aging of the cell, mostly due to lithium-plating at the anode.

In this project a method to acquire the operating limits during fast charging will be developed. This comprises the development of measurement procedures and models to detect and predict lithium plating in the cell.

The experimental detection of lithium will be realized by different measurement procedures:

• analysis of voltage relaxation
• impedance spectroscopy and the distribution of relaxation times (DRT)
• cell thickness measurement
• NFRA - Nonlinear Frequency Response Analysis

which will be combined in a measuring instruction for the acquisition of operating limits in fast charging.

In parallel impedance based models (electrochemical and thermal cell impedance) will be evaluated with respect to predictability of lithium plating.

The application and validation of measurement procedures and models will be carried out for two different cell types (pouch cell, high capacity prismatic cell). After determining the operating limits according to the measuring instruction, the validation will be performed in cycle tests within and beyond the determined operational limits.