D. Rajagopalan Kannan, J. Yap, V. Premnath, J.A. Jeevarajan
UL Research Institutes,
United States
Keywords: safety, sodium-ion, thermal runaway, cell, module
Summary:
Assessing the safety characteristics of secondary batteries is critical for designing robust battery management systems and implementing effective hazard mitigation strategies. Sodium-ion batteries are emerging as a sustainable and cost-effective alternative to lithium-ion batteries, driven by the abundance and low cost of sodium resources. While significant progress has been made in improving their electrochemical performance, research on their safety under various abuse conditions remains limited. While sodium-ion and lithium-ion batteries function on similar principles, their safety profiles may differ due to the differences in active materials and energy density. There are different formats of sodium-ion batteries existing in the market. In this study, commercial sodium-ion cells of 18650 and 40140 formats from different manufacturers were investigated. The 18650 cells had rated capacities of 1.2 Ah and 1.5 Ah, while the 40140 cells have a rated capacity of 15 Ah. A series of off-nominal safety tests were conducted in triplicate at both, cell and module levels. The tests included overcharge, overdischarge, external short, and external heating tests. Modules were built by connecting three cells in series. Cell-level results showed electrolyte venting during an overcharge test on one of the 18650 cells, and during overdischarge tests on the 40140 cells. All cells resulted in thermal runaway during external heating tests. At the module level, during external heating tests, thermal runaway of the trigger cell (the cell on which the heater was installed) was observed, but propagation of thermal runaway to other cells was not observed. Destructive physical analysis of the cells that were subjected to safety tests was conducted to gain additional insights. In general, results from these tests suggest that there may not be significant differences in safety between sodium-ion and lithium-ion cells. Results from this study can be leveraged to develop safer sodium-ion-based energy storage systems and understand the limitations of this battery chemistry.