Abstract: This study investigates a commercial 185 Ah sodium-ion battery using 0.5C rate overcharge to trigger thermal runaway while employing multi-dimensional real-time monitoring of temperature, voltage, and expansion force. The research reveals that the thermal runaway process occurs in three distinct phases: initial response period （0~50 min）, acceleration period （50~90 min）, and complete thermal runaway period （90~110 min）. The thermal runaway evolution sequentially involves sodium-ion concentration saturation and migration at the negative electrode, sodiation reactions at the positive electrode, ultimately leading to cascade reactions of oxide decomposition and electrolyte oxidation. This study employs multi-parameter monitoring methodology, obtaining expansion force evolution data during the thermal runaway of large-capacity sodium-ion batteries, with results showing exponential growth characteristics reaching a peak value of 2 474 kPa.

Key words: sodium-ion battery, overcharge, thermal runaway, temperature characteristic, pressure characteristics, voltage characteristic