Causes and mechanism of thermal runaway in lithium-ion batteries, contradictions in the generally accepted mechanism

In this paper, experimental results are analyzed that contradict the generally accepted scheme of thermal runaway reactions. Also, it was experimentally proved that three main exothermic reactions determine the thermal runaway process of lithium-ion batteries. The first main exothermic reaction of the thermal runaway is the reaction releasing the electrochemical energy accumulated in the lithium-ion batteries during their charging. The second main exothermic reaction of the thermal runaway is the reaction of lithiation of surface layers of a cathode active material; this reaction is performed by the lithium atoms coming from both the anode and the inner layers of the cathode active material. The third main exothermic reaction of the thermal runaway is the reaction of the cathode metal-oxides decomposition and the electrolyte oxidation by the released oxygen. Besides, it is shown here that the open circuit voltage drop in batteries during the thermal runaway is mainly due to the lithiation of the cathode active material and – to a much lesser extent – to short circuits occurrence of the electrodes. The established mechanism of thermal runaway of lithium-ion batteries makes it possible to quantitatively describe all currently known experimental results. •New mechanism of thermal runaway (TR) in lithium-ion batteries has been proven.•This TR mechanism quantitatively explains all known experimental results.•Three main exothermic reactions determine TR in lithium-ion batteries.•Reactions: release of stored energy, lithiation of cathode, oxidation of electrolyte•Cathode lithiation is the main cause of battery voltage drop at TR.