Failure Mode and Degradation Analysis of a Commercial Sodium‐Ion Battery With Severe Gassing Issue

Abstract 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.