Abstract:

The thermal-runaway characteristics and mechanisms of large-capacity sodium-ion batteries (SIBs) are systematically investigated under different abuse conditions. Using commercial prismatic SIBs with a nominal capacity of 185 Ah as research objects, thermal runaway was induced by two methods: heating plate and continuous charging, while monitoring the temperature distribution, voltage changes, and expansion-force evolution. The experimental results reveal significant differences in the thermal-runaway processes and characteristics under different abuse conditions: (1) Heating-induced thermal runaway is characterized by localized overheating as the trigger, with heat diffusing from the outside to the inside, resulting in a non-uniform temperature distribution. The battery safety valve opens prematurely at 268.61 ℃, with a maximum expansion force of 1213 kPa. This process is relatively gradual, lasting approximately 820 s; (2) Overcharge-induced thermal runaway exhibits accumulative electrochemical instability, with the voltage increasing from 3.85 V to a peak of 4.89 V before plummeting. The expansion force gradually increases to 2402 kPa before the safety valve opens, resulting in more intense thermal runaway, accompanied by open flames, with the entire process lasting approximately 6996 s, which is 8.5 times longer than the duration of heating-induced thermal runaway; (3) Regarding the temperature characteristics, heating-induced thermal runaway can exceed 600 ℃ with uneven distribution, while overcharge-induced thermal runaway reaches peak temperatures exceeding 500 ℃, accompanied by more abrupt changes; (4) regarding the post-runaway physical states of the SIBs, the battery safety valve remains relatively intact under heating conditions, although with cracks appearing on the heated surface. However, the safety-valve area is severely damaged under overcharging conditions; (5) A comparison of the thermal-runaway initiation times reveals that the batteries subjected to heating begin to enter the thermal-runaway phase in just 597 s, whereas those subjected to overcharging require 3400 s of accumulation to trigger thermal runaway, indicating fundamental differences in the initiation mechanisms under different abuse conditions. These findings elucidate the triggering mechanisms and evolution processes of thermal runaway in SIBs and provide significant insights into understanding the safety characteristics of large-capacity SIBs, optimizing battery-management systems, and formulating early warning strategies for thermal runaway.

Key words: sodium-ion batteries, thermal runaway, thermal abuse, electrical abuse