Invited Presentation: Li-Ion Battery Safety Considerations during Transportation, Storage, and Disposal

The energy of a Li-ion cell is in average about 3,250 kJ/kg. About ¼ of this energy is related to electrochemical energy (chemical energy convertible into electrical energy via normal use or short circuit) and ¾ to thermal energy (chemical energy convertible only in thermal energy released at suitable stimulation; e.g. short circuit).

 The main safety related events are overcharge, external heating, external and internal short circuits, and mechanical deformations of the cell/battery case. These unpredictable events may leads to a temperature increase and at T > 120 °C by internal chemical processes (SEI layer breakup, anode-electrolyte reaction) with gas development and internal pressure increase to cell container rupture at predetermined breaking points. Gas and electrolyte will escape through the rupture holes into the environment and, eventually, inflame by an external ignition source. A further temperature increase till about 200 °C triggers high rate chemical reactions (cathode decomposition with oxygen development, oxygen reaction with the electrolyte, electrolyte decomposition) leading to a very rapid temperature rise (thermal runaway) followed by flames caused by reaching the self-ignition temperature of the electrolyte (~ 450 °C) and possibly explosions.  The specific occurrence of most of the above described safety related events, that may occur during the Li-ion battery life cycle phases of transportation, storage, and disposal, will be discussed in this presentation.

 During transportation and storage, external heating, external and internal short circuits, and mechanical deformations, are the events most likely to happen. Measures which can prevent them (e.g. reliable and low flammable packaging, thermal barriers) and transport related standards (e.g. UN 38.3) are described.

The safety hazard in the disposal phase of the cell/battery are also associated with external heating, external and internal short circuits, and mechanical deformations. After collections it is to proof whether the battery is defective (not all functions properly) or damaged (loss of physical integrity). Defective batteries with capacity ≤ 80 % of the nominal value (end-of-life by definition) could be still used in lower demanding applications, e.g. stationary storage in PV houses. Damaged batteries and defective batteries with << 80 % capacity and other malfunctions have to be recycled. In order to reduce the safety risk before the recycling process (including transport), it is advisable to de-energize the battery by low current discharge and finally short it permanently.