Challenges of Predicting Temperature Dependent Capacity Loss Using the Example of NMC-LMO Lithium-Ion Battery Cells

In semi-empirical aging modeling of lithium ion-batteries an Arrhenius approach is commonly applied to describe the temperature dependency of a linear capacity loss. However, this dependency can change with degradation modes which was also observed in this cyclic aging study on NMC111-LMO graphite pouch cells in a temperature range of 4 °C to 48 °C. By means of differential voltage analysis and post-mortem analysis we correlated different regimes in capacity loss to degradation modes and aging mechanisms. In the first regime, a power dependency of time was observed. A second accelerated linear regime which followed an increase in loss of active material of the positive electrode was seen for medium (∼19 °C to 25 °C) to high aging temperatures. Transition metal dissolution was suggested to cause accelerated SEI growth. An activation energy could be estimated to 0.83 eV (± 0.17 eV, 95% CI). Finally, at aging temperatures around 45 °C we propose decreased charge transfer kinetics to result in mossy dendrites on the negative electrode which cause a final knee in aging trajectory. The findings highlight the necessity of sufficient aging temperatures and testing time.