There were 10 million electric cars on the world’s roads at the end of 2020, following a decade of rapid growth. Electric car registrations increased by 41% in 2020, despite the pandemic-related worldwide downturn in car sales in which global car sales dropped 16%. Around 3 million electric cars were sold globally (a 4.6% sales share), and Europe overtook the People’s Republic of China (“China”) as the world’s largest electric vehicle (EV) market for the first time. Electric bus and truck registrations also expanded in major markets, reaching global stocks of 600 000 and 31 000 respectively.[1]
Lithium-ion batteries are energy-dense devices in which large currents flow between an anode and a cathode immersed in a liquid electrolyte. These store all the energy necessary for the vehicle to travel hundreds of kilometers and are exposed to considerable mechanical, electrical and environmental stresses. To ensure that no failures occur under these working conditions, batteries must undergo extensive testing before they can be marketed.
In fact, in severe operating conditions, undesirable events such as formation of dendrites, breakdown of the separator, generation of heat, exothermic chemical reactions can occur inside the battery. These often lead to low-severity consequences that pose no risk to the car's passengers. However, in some cases, serious consequences such as fire, rupture or explosion can occur. Fire is typically associated with the phenomenon of "thermal leak", a series of self-sustaining exothermic electrochemical reactions that lead to an uncontrolled rise in temperature. In turn, rupture can be caused by the formation of unwanted gases inside the battery, increasing the pressure over what can be tolerated or discharged.
Failures are normal events during the development phase and as such the safety of the technicians involved in the tests must be guaranteed at all levels.
[1] Read the overview on IEA (2021), Global EV Outlook 2021, IEA, Paris