Aims:

• Presenting the current state of science and technology at the beginning of the project
• Providing available knowledge with regard to the hazards of lithium-ion batteries

Results:

• Determination of the current state of research regarding potential hazards
• Overview of necessary technical solutions
• Determination of the initial situation with regard to extinguishing agents

Insights into the Results:

Structure of lithium-ion batteries

Secondary lithium-ion batteries (LIB) belong to the category of electrochemical energy storage systems. LIBs consist of individual cells that are usually combined in modules, which are assembled together with other modules in a battery housing to form a pack. Schematic illustration:

An LIB cell contains two electrodes (cathode and anode), with graphite being the most commonly used anode material. Relevant cathode materials (so-called cell chemistries) are:

• NCA (lithium nickel cobalt aluminium oxide)
• NMC (lithium nickel manganese cobalt oxide)
• LMO (lithium manganese oxide)
• LCO (lithium cobalt oxide)
• LFP (lithium iron phosphate)

The two electrodes are separated by a polymer separator. The cell is filled with a liquid electrolyte (usually lithium hexafluorophosphate in a solvent mixture of organic carbonates).

There are LIB cells of different geometries – prismatic, pouch and cylindrical cells. Both the cell chemistry and the cell geometry have an influence on the fire behaviour of the cell.

Fire behaviour of lithium-ion batteries

A battery fire is caused by the phenomenon of thermal runaway. Self-accelerating exothermic chain reactions and internal short circuits in the cell lead to an uncontrolled rise in temperature, followed by the cell bursting and the release of flammable gases.

Without external intervention, thermal runaway quickly propagates to other cells.

There are detailed reviews in the literature on the progression of thermal runaway, e.g. by Feng et al.