Abstract: Whether the lithium-ion battery can enter the EV, HEV and PHEV markets depends on its safety, and the
thermal runaway control is the most critical challenges. This paper discusses the field failure abuse thermal runaway
of large format lithium ion batteries in vehicular applications, focusing on the evolution of the insight process of thermal
runaway. In terms of the positive electrode, negative electrode, electrolyte, separator and current collector, the impacts on
safety of the key materials are reviewed, with the battery safety control strategy proposed. The LiNi1/3Co1/3Mn1/3O2 based
battery with nominal capacity of 12 Ah was developed with modified key materials with energy density of 160 Wh/kg and
power density of 1.25 kW/kg. Tests were carried out for 0.5 C rate / 20 V overcharge and fully charged state (4.2 V) hot-box
at 150 °C for 4 h. The results show that the batteries are safe, the effectiveness of the proposed safety control strategy is
verified, and the self-discharge and chemical stability of the safe batteries arebetter than those of traditional batteries.

Key words: lithium-ion battery, safety, thermal runaway process, control strategy, LiNi1/3Co1/3Mn1/3O2 based power battery