Thermal Runaway: Battery and battery protection
There are major challenges in the manufacture of batteries and rechargeable batteries for electromobility. A big topic in protecting batteries and rechargeable batteries from thermal runaway.
Thermal runaway describes the overheating of an exothermic chemical reaction or a technical apparatus due to a self-reinforcing heat-producing process. A runaway often leads to fire or explosion and, as a result, causes the equipment to be destroyed by overpressure (bursting).
What is thermal runaway in batteries?
Thermal runaway is a dynamic phenomenon. An EV battery that experiences thermal runaway can react in a number of ways, such as: B. with a jet of flame erupting from the battery. In combination with the flame, the battery emits particles that can erode the protective housing. These burning gases build up pressure inside the housing. Therefore, it is important to test the case to assess how the material will respond to the combination of high temperature, pressure and ejected battery particles.
If a local short-circuit occurs in the internal electrodes of a lithium-ion battery with liquid, solid or bound electrolyte (lithium-polymer battery), for example due to contamination of the separator by an enclosed foreign particle or mechanical damage, the short-circuit current can flow through the internal resistance heat up the vicinity of the damaged area to such an extent that the surrounding areas are also affected. This process expands and quickly releases the energy stored in the accumulator. Lithium-cobalt dioxide accumulators are particularly at risk. Such thermal runaways were held responsible for the fires in laptop batteries that have occurred more frequently in the past. The triggers were probably manufacturing errors in connection with fluctuations in the operating temperature.
How does thermal runaway in a lithium-ion battery occur?
Several factors can cause thermal runaway in a lithium-ion battery:
- internal short circuit: due to an accident or a similar mechanical effect, e.g. B. if a tool falls from a great height, the battery is deformed, material enters the battery cell and causes an internal short circuit.
- External short circuit: The deformation of the battery cell causes an external short circuit.
- Overcharging the battery beyond the maximum voltage specified in the data sheet, e.g. B. to increase the range of an electric car. Depending on the degree of overcharging, the battery can be permanently damaged and the battery life will decrease.
- Excessive currents when charging or discharging the battery, e.g. B. when fast charging.
What can be done about thermal runaway?
Cooling
Liquid cooling systems, fans, thermal plates, and thermal foils must be deployed to cool the battery or remove heat from a hotspot.
In order to dissipate the heat effectively, a thermally conductive foil is recommended. Thin (1950 µm to 10 µm) graphite foils offer particularly high thermal conductivity (up to 500W/mK).
barrier formation
Rigid mica sheets and mica laminates can be used to create barriers between battery cells in batteries and accumulators, isolating the system from the rest of the vehicle. Should a thermal runaway occur, the barriers can help slow the process, giving users more time to get to safety.
A barrier can also be formed with 3M™ Flame Barrier FRB. 3M™ Flame Barrier FRB processes well into stamped parts and has various approvals.
A thermal runaway cannot be completely prevented or stopped once the process has started, but implementing the right insulation solution can help buy occupants more time, which can potentially save lives.
Use membranes
The use of membranes to reduce pressure in batteries and accumulators has also proven itself.