Chapter 10 - Safety

Question 1

What was the matter with the Tesla fires of 2013?

Answer 1

External penetration from below causing a short, leading to thermal runaway.

Question 2

What was the matter with the Sony 2006 recalls?

Answer 2

Trace metal particle impurities causing short.

Question 3

What was the matter with the Samsung Galaxy Note 7 recall?

Answer 3

1) Insulation tape missing in some cases
2) Separator penetrated by inhomogenieties (from welding) on positive electrode
3) Anode got got deflected

Question 4

What was the issue with the Fisker Karma battery fire of 2012?

Answer 4

Lead acid battery catching fire from short caused by corrosion damage from salt water after flooding. Heavy wind spread fire.

Question 5

What was the issue with the Boeing 787 Dreamliner battery fires?

Answer 5

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.

Question 6

What was the issue with the Houston train explosion?

Answer 6

Train hauling many electric vehicles exploded. Batteries not treated as hazardous materials.

Question 7

What was the issue with the Ruter battery fire?

Answer 7

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.

Question 8

What was the issue in the GM Battery test lab fire?

Answer 8

Gas evolution from battery. The gases themselves caught fire.

Question 9

How does the thermal energy of a battery compare to the electrochemical energy stored in it?

Answer 9

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

Question 10

What are some internal causes for heating up in a battery?

Answer 10

1) Overcharge
2) Overdischarge
3) Overload
4) Internal short

Question 11

What are some external causes for heating up in a battery?

Answer 11

1) External short

2) Heat exposure

Question 12

What are some causes of an internal short?

Answer 12

1) Dendrite formation
2) Particles
3) Crash causing deformation

Question 13

What are some consequences of a battery heating up?

Answer 13

1) Gas evolution

2) Thermal runaway

Question 14

What are some possible consequences of gas evolution from a battery?

Answer 14

Ignition of gas, casuing fire or explosion.

Question 15

What are the consequences of a thermal runaway?

Answer 15

1) Fire
2) Explosion
3) Gas evolution

Question 16

What would be a likely cause of overcharge?

Answer 16

A BMS error - voltage limit set too high.

Question 17

What is the consequence of overcharge?

Answer 17

The cell chemistry becomes unstable and could cause a violent fire.

Question 18

What would be a likely cause of overdischarge?

Answer 18

• A BMS error
• Cells in series with different capacities and no cell balancing
• Sensor error

Question 19

What is the consequence of overdischarge?

Answer 19

• Possible Cu dendrite formation, causing a short

Question 20

What would be a likely cause of overload?

Answer 20

• A BMS error

- Bad choice of safety devices, e.g. overdimensioned fuse

Question 21

What is the consequence of overload?

Answer 21

Could cause a heating above the maximum operating temperature. Reduction of life time and possibilities of a fire.

Question 22

What is the likely cause of an external short?

Answer 22

• Design error

- Accident

Question 23

What is the consequence of an external short?

Answer 23

External fire outside of the battery - could heat up the battery.

Question 24

What are likely causes of an internal short?

Answer 24

• Formation of dendrites of Li or Cu (depends on load an temperature of battery)
• Metal particles from production
• Mechanical deformation / vibration

Question 25

What is the consequence of an internal short?

Answer 25

• Rapid energy release. Up to 70% of the battery’s energy in as little as 60 seconds.

Question 26

What is the likely cause of external exposure to heat?

Answer 26

• Poor choice of battery placement
• Fire in the vincinity
• Exposure to sun

Question 27

What is the consequence of external exposure to heat?

Answer 27

• Rapid degradation of battery capacity and shelf life

- Battery fire

Question 28

In which part of the battery life cycle is it important to consider safety?

Answer 28

All!!

Question 29

What is the definition of thermal runaway?

Answer 29

Self heating rate above 10 C / min

Question 30

What are the three steps leading to thermal runaway?

Answer 30

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.

Question 31

What equipment can be used for conducting heating tests of a battery?

Answer 31

An Accelerating Rate Calorimeter (ARC). Heat, wait and seek. Determines the maximum safe operating temperature and thermal runaway temperature.

Question 32

What is the option to limit consequences of battery fire?

Answer 32

Cooling, cooling, cooling. Be aware of reignition.

Question 33

What kind of degradation can happen on the cathode side?

Answer 33

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

Question 34

What kind of degradation can happen on the anode side?

Answer 34

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