Hendrik Laufen

Sodium‐ion batteries offer a promising alternative to lithium‐ion batteries by addressing ecological and economic challenges. However, to assess the applicability of these cells for different sectors, understanding aging behavior, including degradation modes, is crucial. This work presents a comprehensive aging analysis of 67 commercial sodium‐ion batteries under various temperatures, C‐rates, and depths of discharge. We analyzed the initial cell‐to‐cell variance and the aging trajectories regarding capacity fade and resistance increase. We demonstrated that the cycling rate does not significantly influence the aging trajectories, whereas smaller depths of discharge significantly reduce degradation. The degradation gradients for 25 °C and 40 °C were similar; for −10 °C, we observed rapid capacity fading that can be attributed to irreversible sodium plating. Furthermore, we identified the degradation modes for four different aging categories. Since some aging tests stopped due to gas‐induced current interrupt device triggering at low current rates and states of charge, we proposed two hypotheses for the gassing under specific conditions, suggesting inadequate gas consumption in cathode‐electrolyte side reactions or solid electrolyte interphase instability as potential causes. Overall, this work provides a valuable in‐depth analysis of the aging behavior of a commercial sodium‐ion battery as a function of temperature, C‐rate, and depth of discharge, with data made available for further research.

Fulfilling the service life of a Lithium‐Ion battery in each intended application requires further understanding of the cells' lifetime and reliability. Derived from literature, controlling the external pressure constant on Lithium‐Ion battery cells is an inevitable factor to extend the cycle lifetime. Thus, active knowledge of the cells' strain and understanding the impact of an external pressure on the impedance is mandatory to evaluate an optimum pressure to improve the cell performance. This work presents correlations between voltage, strain, and impedance as a function of the applied constant external pressure on a nickel‐rich nickel‐mangan‐cobalt (NMC) lithium‐ion pouch cell. Utilizing a high precision universal testing machine reveals a negligible change of the cells' maximum stroke within the pressure range from 0 to 1000 kPa. Additionally, an optimum pressure between 100 and 300 kPa is revealed by analyzing a series of electrochemical impedance spectroscopy data measured at different constant external pressures. Within this pressure range the charge transfer resistance as well as the diffusive processes exhibit its optimum.