Thermodynamics and Kinetics of LiCoO2/Graphite Commercial Battery

Abstract

With the energy density increase of lithium-ion batteries in electric vehicles, people pay more and more attention to safety issues. The heat generation is the main factor affecting the safety. When the lithium-ion battery is overcharged, the so-called thermal runaway will occur in the battery system. In the process of thermal runaway, the temperature of battery increases due to exothermic reaction. In turn, the increased temperature accelerates these degradation reactions and makes the system unstable.In this paper, we use LiCoO2/graphite commercial battery with assumed uniform heating to study the relationship between the kinetics and thermodynamics of electrode reaction and the function of magnification and temperature by means of electrochemical test. The results are used to estimate the heat production rate, which is related to the ohmic resistance of the LCO electrode, the charge transfer and transfer limitation of SEI film, and the entropy of the electrode reaction. After that, the kinetic and thermodynamic characteristics of the electrode are given. Then, the dependence of different heat sources on magnification and temperature are shown. Finally, the total heating rate of LCO electrode is calculated, and the importance of different individual contributions is discussed.The results show that all the individual heat sources contribute significantly to the total heat in the electrode. The heat source is a function of magnification, temperature and lithium concentration in the active material. Compared with IR drop, the heat generated due to transfer restriction has a greater impact on irreversible heat. When the concentration of lithium ion is small, the irreversible heat accounts for the main part of the total heat. When the concentration of lithium ion is large, the reversible heat accounts for a large proportion of the total heat, but the difference between the reversible heat and the irreversible heat is not significant.