Lithium Ion Thermal Runaway
Less than 2 Wh Lithium Ion Batteries
Presented to:International Aircraft Systems Fire
Protection Working Group

By:

Matthew Karp

Date:

November 1, 2017

Scope of Test
•RTCA SC-225 committee working on developing document DO-311A•Document contains Minimum Operational Performance Standards (MOPS)
for rechargeable lithium battery systems•Proposed to exempt battery cells that are < 2Wh from testing standards•provided they are certified to existing UL and IEC standards•Comments were received that the exemption level should be raised to as highas 5 Wh
•Tests were conducted to determine if the exemption level should be raised2

Scope of Test
•Tests were conducted with lithium ion rechargeable 3.7V 500mAh (1.85Wh)
polymer pouch cells and button cells at 100% SOC•The cells were forced into thermal runaway using the overheat method at20°C/min• Tests were conducted in a 21.7L pressure vessel where a pressure transducer
and thermocouple were used to quantify the gas release from each lithium
battery cell
• The gases were collected and analyzed for percent hydrogen, carbon
monoxide, carbon dioxide, oxygen, and total hydrocarbon content (THC)•The maximum temperature rise and peak pressure rise were annotated3

Test Equipment•Experiments were conducted in a 21.7 liter stainlesssteel pressure vessel•Gas chromatography (GC) with thermal conductivity
detector (TCD) to measure H2•Paramagnetic sensor (pO2) to measure CO/O2•Non-dispersive infrared radiation to measure CO2•Flame ionization detector (FID) to measure totalhydrocarbon content (THC)
Test Apparatus
4

Test Procedure•The pressure vessel is vacuumed to less than 0.1 psia
•The pressure vessel is filled to 14.7 psia with nitrogen gas•Nitrogen gas is used because of its inert properties and to prevent
interference with the gas analyzers•The battery is forced into thermal runaway by overheating and the vent gases
are released•More nitrogen is added to the pressure vessel until the pressure reaches
18 psia, this creates a positive pressure to feed into gas analyzers•The samples are analyzed for gas composition
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Test Procedure•The battery cells were placed on top of a flexible
heater•Heated at 20°C/min until thermal runaway isinduced•The temperature heating rate was controlled bya Proportional-Integral-Derivative (PID)
controller•Temperature was measured at the side of the pouchcell and on top of the button cell

6

Pouch Thermocouple Location•Thermocouples were placed at two
separate locations•The locations•On top•On the side7

Pouch Maximum Temperature•Vent gas vents out of the sides•The average maximum temperature are:•Side 621±25°C•Top 412±24°C•The average thermal runaway onset
temperature is 135±13°C

800
Max Case Temp, °C•The maximum temperature at the side ofthe pouch cell is hotter than on top of thepouch cell

Max Case Temperature
672591600

454400371

601
411

2000
Battery Side, C

Battery Top, C8

Pouch Vent Gas Volume
1.0Vent Gas Volume, L•The average vent gas volume is
0.76±0.03L

Total Vent Gas Volume
0.73

0.78

0.78

0.5

0.09

•Note: The measured pressure isinversely proportional to thepressure vessels volume.
•The average maximum pressure is•17.1±0.1psia•The average percent pressure rise is•15.1±0.6%

17.5

20.0%
17.1

17.0

17.2

16.9
15.0%

16.5

16.0

14.4%

14.7%

Peak Pressure, PSIa

16.2%

10.0%

% Pressure Rise
10Percent Pressure Rise

•The pressure is measured inside of a
21.7L pressure vessel.

Maximum Pressure, psia

Pouch Pressure Rise

Pouch Cell Gas Constituents•The gas concentrations used for thecalculation of the lower flammability
limit (LFL) were measured andaveraged. The results are tabulated•The LFL can be calculated using Le
Chatelier’s Mixing Rule
•The calculated LFL is 8.5%volbattery gas in airGas Specie
carbon dioxidecarbon monoxide
ethaneethylenehydrogenmethane
propanepropyleneoxygen
THC

Averaged Gas
Concentration, %volLFL, %vol25.3±0.7
20.0±6.2
0.6±0.1
7.3±0.824.0±2.5
3.1±0.3
0.2±0.02
1.6±0.4
6.0±2.7
18.7±1.00
12.5
3.00
3.10
4.95
5.30
2.10
2.40
NANA

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Button Thermocouple Location•The thermocouple was places on top of thebutton cell and wrapped with fiberglass tapeto insure good contact

12Button Maximum Temperature•Variations in thermal runaway reactions
has also been observed in 18650 cells•This is often observed with a delay inthermal runaway reaction as represented
by the black vertical lines•The delayed reaction allows time for theelectrolyte to evaporate away from thecell

Cell Temperature, °C•The two tested button cells had
drastically different maximum temperature

Temperature Rise
750
500

250
00

250500Time, s750

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20.0%

17.5
17.3

17.5%

17.3

17.0

18.2% 15.8%630500
387

250

15.0%

Peak Pressure, PSIa% Pressure Rise

00.82
Vent Gas Volume, L

17.6

1.0750Max Temp, °C

17.8

Percent Pressure Rise

Maximum Pressure, psia

Button Cell Significant Values
0.76

0.50.014

Button Cell Gas Constituents•The gas concentrations used for thecalculation of the lower flammability
limit (LFL) were measured andaveraged. The results are tabulated•The LFL can be calculated using Le
Chatelier’s Mixing Rule
•The calculated LFL is 8.2%volbattery gas in airGas Specie
carbon dioxidecarbon monoxide
ethaneethylenehydrogenmethanepropanepropylene
oxygenTHC

Averaged Gas
Concentration, %vol

LFL, %vol23.4±0.8
25.0±3.7
0.5±0.04
8.4±0.423.8±1.9
2.7±0.20.1±0.01
2.0±0.2
5.1±3.017.9±1.70
12.5
3.00
3.10
4.95
5.30
2.10
2.40
NANA15Summary <2Wh Lithium Ion
Carbon Dioxide
Carbon Monoxide
Hydrogen
Percent Pressure Rise
Maximum Pressure
Off Gas Volume
Maximum Temperature
Calculated LFL

Pouch Cell

Button Cell

Total Average

25.3±0.7%
20.0±6.2%
24±2.5%15.1±1.13%17.1±0.1%
0.76±0.03L
621±50°C
8.5%

23.4±0.8%
25.0±3.7%23.8±1.9%17.0±2.3%
17.4±0.3psia
0.79±0.06L
508±238°C
8.2%

24.5±1.0%
22.0±4.3%
23.9±1.5%15.9±1.3%
17.2±0.2psia
0.77±0.04L
576±97°C
NA

9.25 Wh Pouch
Cell 30% SOC
41.2%
3.82%
16.98%
20.4%
NA0.92L
404°C
9.1%

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Conclusion•While there may be examples of safer cells of higher capacity, there are also
cells at or near the 2 Wh level that could pose a threat to aircraft safety•Based on the testing, the committee decided to maintain the 2Whr limit and notto extend the exemption level.

17References[1] Coward, Hubert Frank, and George William Jones. Limits of flammability ofgases and vapors. No. BM-BULL-503. Bureau of Mines Washington DC, 1952.

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Contact Information
Matthew Karp
Matthew.Karp@FAA.gov

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