Monitoring and safety tests of batteries: From state of charge (SOC) and health (SOH) to misuse, abuse and crash

The paper describes, especially for EV applications, the requirements for the battery. In the focus are especially the car parameters (total car weight, driving behavior, temperature) and the battery parameters (discharge current, temperature, age), which are to be considered in order to estimate the available range. From the battery point of view important parameters are the state-of-charge (SOC) and the state-of-health (SOH). Advantages and disadvantages of SOC and SOH determination methods are discussed. But the priority of the requirements belongs to the safety of the car and the battery. The main risks, electrical, kinetic, chemical, and thermal, are addressed. Mainly the chemical and thermal risks and their safety relevant consequences are discussed. The thermal problems, which are leading to a thermal runaway with catastrophic consequences as fire or/and explosions, are highlighted. Furthermore, the energy of the cell is considered, which consists of the electrochemical energy (active masses) and the chemical energy (mainly combustion energy of the electrolyte). In case of a short circuit of the cell the electrochemical energy generates so much heat, that the chemical energy, i.e. the electrolyte, is autoignated at about 450°C. Thus, the electrochemical energy plays the role of a “lighter” and the chemical energy of combustibles.