Thinner design of smart phone continuously would need to the high energy density lithium-ion batteries. Lithium-ion batteries are composed of four major component, cathode, anode, electrolyte and separator. Each components’s reaction by pyrolysis and interaction between components are causative of exothermic reaction of lithium ion batteries.

We investigated causes of exothermic reaction of lithium ion batteries having thermal analysis, surface analysis and structure analysis by dismantling two kinds of 3.2Ah lithium-ion batteries composed of most commercialized LiCoO₂ cathode material and Graphite anode material.

In LiCoO₂ cathode material, Li ions are oxidized by charge process, it exists as Li_0.5CoO₂. Near 230^oC, structure of Li_0.5CoO₂ is changed, it causes exothermic reaction. EXAFS, structure analysis, showed change of two kind of Li_0.5CoO₂ structure according to temperature change. By investigating Co-Co and Co-O bond, we can find that structure stability as temperature increasing is different as status of LiCoO₂ such as Mg doping.

Surface analysis showed surface status of cathode material and distribution of anode SEI layer. Especially, in case of anode, Alkyl Carbonate is considered as important factor of thermal stability because it makes exothermic reactions as it decomposed. We identified how thick the alkyl carbonates were deposited and we found difference of exothermic value by DSC thermal analysis between two kinds of graphite of lithium ion batteries.

These analysis data indicate which part is important for thermal stability and investigate exothermic reaction mechanism of Cell components. We made sure structure change of cathode material and distribution of Alkyl carbonate in anode SEI layer is important for thermal runaway of Cell. These results suggest improvement direction for increasing of thermal stability.