Overcharge failure investigation of lithium-ion batteries

• 32 Ah prismatic cell overcharge test was firstly reported.
• The cell temperature difference between inside and outside can reach 100 °C before fire.
• The reaction between cathode and electrolyte is the key for fast heat generation.
• Li-plating was observed after overcharge test.

Safety behaviors of a 32 Ah prismatic lithium-ion battery are investigated under abusive charge conditions by monitoring the internal and external cell temperature variation. Results show that the cell internal temperature can reach 235 °C before firing, which is almost 140 °C higher than the cell external temperature. Although the cell resistance increases abruptly due to electrolyte oxidization when the cell is firstly overcharged to its maximum voltage (5.10 V), the cell internal temperature keeps a low temperature of 50 °C without notable temperature rise. However, the cathode/electrolyte interface becomes highly reactive as the cell is further overcharged. Cell internal temperature goes up to more than 200 °C accompanied with massively gas production when the cell is overcharged to 180% SoC. Post-overcharge analysis on both cathode and anode indicates that lithium plating during overcharge is the major cause responsible for thermal runaway because the observed cell temperature is well above the melting point of lithium metal.