Accelerated Aging Tests and Lifetime Predictions (BALd)

Focus:

• Development of apparatus for expansion measurement of cylindrical cells and for pressing of pouch cells
• Investigation of mechanical stress as a factor for the inhomogenization of the lithium distribution in lithium-ion batteries
• Development of strategies for rehomogenization of the lithium distribution

Summary:

The project BALd is a research consortium consisting of THI-ELS, RWTH-ISEA, KIT-TVT, TUM-FTM, RWTH-ISW, TUM-EES and ZSW-ECA with the aim to accelerate ageing tests in order to obtain the best possible lifetime predictions for models in the shortest possible test duration.
 

The goal of the subproject is to accelerate common cyclic aging tests of Li-ion cells and at the same time to ensure a reliable state diagnosis and lifetime prognosis. Thereby a feedback between cell aging and production parameters should be achieved within 2 weeks, 6 weeks and after 3 months during cell production. This requires very precise aging tests which, despite acceleration, lead to representative aging, analogous to real long-term application.

For this reason, this subproject will first investigate in practice under which conditions (C-rate, tension, temperature, cycle window) inhomogeneities in the lithium distribution arise and how these can be rehomogenized as efficiently as possible. The aim is to understand how cycling strategies cause inhomogeneities in the lithium distribution and how the inhomogeneities can be rehomogenized as efficiently as possible. The degree of inhomogeneity will be quantified by differential voltage analysis (DVA) and will be correlated with the measured reversible capacity effect.
 

The findings will then be incorporated into the modelling of the project partners. The aim is to determine the influence of the pressure on the irreversible capacity losses for the respective test condition and thus to increase the precision of lifetime prediction for long-term applications within short test duration. On the one hand, the quality of the cells can be quickly determined and reported back to the FFB, and on the other hand, the cells can be better designed for real applications on the basis of more accurate lifetime predictions.
 

Relevant literature: