Overcharge cycling effect on the thermal behavior, structure, and material of lithium-ion batteries

The present study investigates the overcharge cycling effect on thermal behavior, structure, and electrode material of lithium-ion batteries (LIB) with a Li_x(Ni_0.3Co_0.3Mn_0.2)O₂ cathode. The thermal behavior of LIBs with different overcharged degrees was studied using vent sizing package 2 and differential scanning calorimetry. Changes in the internal composition of the batteries during overcharge were observed using a scanning electron microscope and an inductively coupled plasma optical emission spectrometer. The results indicate that the overcharge process can be divided into four stages. A battery was more likely to trigger thermal runaway during overcharge under adiabatic conditions than in an ambient environment. During overcharge, the surface temperature of a 150% state-of-charge (SOC) battery was approximately 3.0 °C higher than that of a 100% SOC battery. Because of generated gas and lithium deposition during overcharge cycling, the battery thickness increases and coulombic efficiency decreases. The apparent exothermic onset temperature (T₀) of a battery with 150% SOC was 87 °C below that of a 100% SOC battery. Cathode material becomes highly reactive when the battery was overcharged to 150% SOC. Here, the released heat was 1026.4 J/g. These results provide feasible support for understanding the overcharge mechanism and battery management system.