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Safe, powerful and reliable lithium batteries are required for an extensive market penetration of electric vehicles and stationary energy storage systems. In operation, lithium batteries are continuously generating and dissipating heat. Therefore, an appropriate thermal management is necessary to provide best electrochemical cycling conditions and avoid battery performance losses and thermal runaway. The rational design of thermal management systems should be based on quantitative information for thermal behavior, heat generation and dissipation of batteries in operation. Both regular and irregular battery use as well as accidents have to be realistically simulated by experiments in the laboratory. Calorimetry and thermography are excellent analysis tools to provide data for batteries applied in different operation modes under various environmental conditions. Simultaneously, (hazardous) reactions of battery materials and correlated pressure changes can be analyzed. The thermal runaway with inflammation and even explosion of a Li-ion cell in a larger battery pack is the worst case scenario which must be avoided in commercial applications under all circumstances. In order to get more insight into the character of exothermic reactions, that trigger the thermal runaway, combined experimental and computer simulation approaches were used. Accelerating Rate Calorimeters (ARC) are perfect tools for in-operando investigations of the cells during electrochemical cycling under isoperibolic and adiabatic conditions and for so-called heat-wait-seek tests. Heating under adiabatic conditions will eventually either stop the cell from cycling or lead to thermal runaway depending on the cycling parameters
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