Chapter 10 - Safety Flashcards
What was the matter with the Tesla fires of 2013?
External penetration from below causing a short, leading to thermal runaway.
What was the matter with the Sony 2006 recalls?
Trace metal particle impurities causing short.
What was the matter with the Samsung Galaxy Note 7 recall?
1) Insulation tape missing in some cases
2) Separator penetrated by inhomogenieties (from welding) on positive electrode
3) Anode got got deflected
What was the issue with the Fisker Karma battery fire of 2012?
Lead acid battery catching fire from short caused by corrosion damage from salt water after flooding. Heavy wind spread fire.
What was the issue with the Boeing 787 Dreamliner battery fires?
Internal short in one of the cells. Related to lowered temperatures after having been in air causing dendrite formation to grow rapidly. Void between anode and separator limiting the pathway for Li-ions.
What was the issue with the Houston train explosion?
Train hauling many electric vehicles exploded. Batteries not treated as hazardous materials.
What was the issue with the Ruter battery fire?
Start battery was charging and caught fire (so lead acid). The buses in question were not plug-in hybrids, so the Li-ion batteries were only charged by the engine.
What was the issue in the GM Battery test lab fire?
Gas evolution from battery. The gases themselves caught fire.
How does the thermal energy of a battery compare to the electrochemical energy stored in it?
Can be up to four times as high. Both the cathode (>180C) and anode (>120C) can react with the electrolyte at higher temperatures. Electrolyte combusts at >450C
What are some internal causes for heating up in a battery?
1) Overcharge
2) Overdischarge
3) Overload
4) Internal short
What are some external causes for heating up in a battery?
1) External short
2) Heat exposure
What are some causes of an internal short?
1) Dendrite formation
2) Particles
3) Crash causing deformation
What are some consequences of a battery heating up?
1) Gas evolution
2) Thermal runaway
What are some possible consequences of gas evolution from a battery?
Ignition of gas, casuing fire or explosion.
What are the consequences of a thermal runaway?
1) Fire
2) Explosion
3) Gas evolution
What would be a likely cause of overcharge?
A BMS error - voltage limit set too high.
What is the consequence of overcharge?
The cell chemistry becomes unstable and could cause a violent fire.
What would be a likely cause of overdischarge?
- A BMS error
- Cells in series with different capacities and no cell balancing
- Sensor error
What is the consequence of overdischarge?
- Possible Cu dendrite formation, causing a short
What would be a likely cause of overload?
- A BMS error
- Bad choice of safety devices, e.g. overdimensioned fuse
What is the consequence of overload?
Could cause a heating above the maximum operating temperature. Reduction of life time and possibilities of a fire.
What is the likely cause of an external short?
- Design error
- Accident
What is the consequence of an external short?
External fire outside of the battery - could heat up the battery.
What are likely causes of an internal short?
- Formation of dendrites of Li or Cu (depends on load an temperature of battery)
- Metal particles from production
- Mechanical deformation / vibration
What is the consequence of an internal short?
- Rapid energy release. Up to 70% of the battery’s energy in as little as 60 seconds.
What is the likely cause of external exposure to heat?
- Poor choice of battery placement
- Fire in the vincinity
- Exposure to sun
What is the consequence of external exposure to heat?
- Rapid degradation of battery capacity and shelf life
- Battery fire
In which part of the battery life cycle is it important to consider safety?
All!!
What is the definition of thermal runaway?
Self heating rate above 10 C / min
What are the three steps leading to thermal runaway?
Stage 1: protective layer of anode reacts with electrolyte
Stage 2: at “onset temperature” the separator has melted and local shorts occur. Cathode starts exotherm disintegration.
Stage 3: Thermal runaway. Electrolyte decomposes. Cathode disintegrates (oxygen evolution possible). Gas evolution and possible fire/explosion.
What equipment can be used for conducting heating tests of a battery?
An Accelerating Rate Calorimeter (ARC). Heat, wait and seek. Determines the maximum safe operating temperature and thermal runaway temperature.
What is the option to limit consequences of battery fire?
Cooling, cooling, cooling. Be aware of reignition.
What kind of degradation can happen on the cathode side?
1) Microcracking
2) Structural disordering
3) Re-precipitation of new phases
4) Dissolution
5) Migration of soluble species
6) Surface layer formation
7) Electrolyte decomposition
8) Loss of contact to conductive particles
9) Oxidation of conductive particles
10) Corrosion of current collector
11) Binder decomposition
What kind of degradation can happen on the anode side?
1) Graphite exfoliation, cracking
2) Electrolyte decomposition and SEI formation
3) SEI conversion, stabilisation and growth
4) SEI dissolution, precipitation
5) Lithium plating and subsequent corrosion
