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) (hibbert@hel-inc.com) Hazard Evaluation Labs (HEL) www.Hazards.co

Thermal hazard of Batteries ..

www.Hazards.co

A common battery in PC

Fire in electric car

Dreamliner Incident Boeing Plane operated by Japanese airline

www.Hazards.co

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

www.Hazards.co

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 runaway videos

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

www.Hazards.co 17/47

Nail Penetration

Force ~ 400N ~40kg-force =85lb-force

Thermal runaway videos

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.

www.Hazards.co

‘

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

www.Hazards.co

Principle of iso-BTC

C Y C L E R

Battery

Temp

Thermal controller

coolant

Thermal chamber

iso- BTC for thermal duty measurement

Isothermal control chamber

Range of chamber sizes and shapes

www.Hazards.co

Thermal Management data from iso-BTC

Constant Temp

Thermal management duty Cycler controls

www.Hazards.co

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

www.Hazards.co

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

www.Hazards.co

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

www.Hazards.co

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

www.Hazards.co

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

www.Hazards.co

Complexity of thermal profile revealed at low discharge rate (3-cell Li-ion polymer battery (2.2Ah capacity))

www.Hazards.co

Explanation of Capacity change at different temperatures (Li-ion NMC battery (8Ah capacity)

Profile of charging/discharging confirms drop in capacity

www.Hazards.co

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

www.Hazards.co

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

www.Hazards.co

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

www.Hazards.co

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?

www.Hazards.co