Energy Dependencies in Li-Ion Cells and Their Influence on the Safety of Electric Motor Vehicles and Other Large Battery Packs

Abstract

For this work, the specific heat value of a Li-ion cell was determined experimentally as if it were a homogeneous body. The heat absorbed in the cell was compared with the amount of energy contained in the charged cell. It was found that a fully charged cell poses a risk of spontaneous combustion in the event of the release of electrical energy. On the basis of literature research, the combustion process of a lithium cell has been described. The formula was derived for the value of the state of charge that does not pose a risk of self-ignition. In view of the existing threats, the currently used protection against cell damage and tests to demonstrate the safety of cells were analyzed. It has been indicated that currently used battery management systems do not guarantee the safety in a state of developing thermal runaway process. A new active way of protecting cells in a battery has been proposed, consisting in sectoral discharge of cells. The use of this solution would be important for the improvement of fire safety in the automotive industry as well as in mining and in the construction of energy storage.