hazard evaluation labs (hel)
TRANSCRIPT
Thermal Runaway Risk of Li-ion batteries
HEL Inc New Jersey, USA
HEL Italia Italy
HEL India Mumbai
HEL AG Germany
HEL Ltd London, UK
HEL China Beijing
Graham Hibbert (MSc) ([email protected]) Hazard Evaluation Labs (HEL) www.Hazards.co
Dreamliner Incident Boeing Plane operated by Japanese airline
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The fire involving a Li-ion battery resulted in the grounding of the entire fleet operated by Japan Airlines
BASIC CAUSE OF PROBLEM …. Balance of heat
Heat Generation
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Heat loss (cooling)
If generation is higher than loss … battery temperature rises
Batteries in use … generate Heat …
Cells stacked together, little or no air circulation, possibly hot at times …… difficult to cool. This is like “Adiabatic” environment …. no heat loss.
Cooling problem …
Single cell … easy to cool on all sides
Results from single cell will be false …cannot be used in practical situations.
better chemistry - faster
Role of Calorimetry in Battery Hazards
Understanding Nature of Problem - How serious could a thermal runaway be? - What conditions could trigger it? Duty of thermal management system to prevent this? - How much heat must it cope with - How to improve battery design
Principle of “ARC”- Battery Testing Calorimeter (BTC )
C Y C L E R
Battery
Temp
Battery heater
Radiant heat
Protective outer shield
Heated inner Chamber (guard heater)
Thermal Testing of larger prototype Battery
better chemistry - faster
Stepwise heating
Before After
Thermal explosion starts – Maximum Safe temperature
Li-ion Polymer Battery Pack (3-cell 2.2Ah) Test
Battery Temp Guard Temp
Time (minutes)300250200150100500
Tem
pera
ture
(°C
)
250
200
150
100
Max safe temperature
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Conclusions – Thermal Explosion Testing
Adiabatic Testing in “ARC®” type BTC - Safe for operator: even when battery explodes - Instrument safe to re-use: robust design - Results are widely accepted and required under many regulations (such as SAE or Sandia Labs). - Provides safe limits of Temperature, discharge current and overcharge voltage. - Video evidence of explosion
Important safety data that CANNOT be produced in other ways.
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‘
Data for thermal Management ?
Instrument that is needed should: - Enable the battery to be tested under all operating temperatures
- Enable Charging/discharging at different rates (battery held at constant temperature)
- Measure heat generated while cycling. This requires an ISOTHERMAL (ie constant temperature) calorimeter. iso-BTC (Battery Testing calorimeter) is such a device
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iso- BTC for thermal duty measurement
Isothermal control chamber
Range of chamber sizes and shapes
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Thermal Management data from iso-BTC
Constant Temp
Thermal management duty Cycler controls
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Heat Profile at Different discharge Rates (3-cell Li-ion polymer battery (2.2Ah capacity))
This is at a single temperature: need to test a range of temperatures
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Heat Generated while discharging at different temperatures (3-cell Li-ion polymer battery (2.2Ah capacity))
Fixed discharge rate but Range of Temperatures
Complex heat generation profile
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Temperature dependence of Overlander battery calorimetry
-5
0
5
10
0 20 40 60
Temperature (oC)
Pow
er (W
)
-5
0
5
10
Ener
gy (k
J)
Peak discharge power
Discharge energy
Max Heat Generated during discharge at different temperatures (3-cell Li-ion polymer battery (2.2Ah capacity))
50% increase in heat generation with temperature
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Fast discharge conceals details
Heat Generated during discharge at different temperatures (NMC –graphite Li-ion battery (8Ah capacity))
Much more complex heat profile than last battery type
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Charge (@5A) and discharge (@7A) peak power release for NMC and Graphite chemistry Pouch-type battery (8AH capacity) at different
temperatures
0
1
2
3
4
5
6
0 10 20 30 40 50 60 70
Temperature (oC)
Pow
er re
leas
e (W
)
Discharge peak power release
Charging peak power release
Max Heat Generated during cycling at different temperatures (NMC-graphite Li-ion battery (8Ah capacity))
3-fold increase in heat release with temperature
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Complexity of thermal profile revealed at low discharge rate (3-cell Li-ion polymer battery (2.2Ah capacity))
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Explanation of Capacity change at different temperatures (Li-ion NMC battery (8Ah capacity)
Profile of charging/discharging confirms drop in capacity
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Charge passed during charge and discharge of NMC and Graphite chemistry Pouch-type battery (8AH capacity)
0
5000
10000
15000
20000
25000
30000
35000
0 10 20 30 40 50 60 70
Temperaure (oC)
Cha
rge
(C)
Discharge capacity
Charge capacity
Nominal capacity (8AH)
Capacity change at different temperatures ( Li-ion NMC cell (8Ah capacity))
3-fold drop in discharge capacity with temperature
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Temperature dependence of charge (@5A)/ discharge (@8A) cycling of Overlander battery.
0
0.5
1
1.5
2
2.5
0 10 20 30 40 50 60 70
Temperature (oC)
Cap
acity
(Ah)
Charge capacity
Discharge capacity
Battery Capacity change at different temperatures (3-cell Li-ion polymer battery (2.2Ah capacity))
Around 20% drop in discharge capacity with temperature
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Temperature dependence of charge (@5A)/ discharge (@8A) cycling of Overlander battery.
0
0.5
1
1.5
2
2.5
0 10 20 30 40 50 60 70
Temperature (oC)
Cap
acity
(Ah)
Charge capacity
Discharge capacity
Battery Capacity change at different temperatures (3-cell Li-ion polymer battery (2.2Ah capacity))
Around 20% drop in discharge capacity with temperature
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CONCLUSIONS
Understanding Thermal Runaway Problem - How serious could a thermal runaway be? - What conditions (T, V and I) could trigger it? Duty of thermal management system to prevent this? - How much heat must it cope with? - Test the battery under all operating temperatures. What else can we learn from heat data? - Heat release profiles are available and change at different conditions – could this be useful to battery developers?
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