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The Effect of Thermal Management Material on Thermal Runaway Propagation

Greg Wilk, Siddique Khateeb, Stephen Wilke, Greg Albright, Said Al-Hallaj

R&D Engineer, AllCell Technologies

http://www.allcelltech.com

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Lithium-Ion Battery Fires

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Lithium-Ion Battery Fires

Lithium ion battery fires serious threat

Hoverboards

Galaxy Note 7

Safety concern for aerospace companies

Dreamliner grounded due to battery fire

Jet propulsion laboratory prototype robot destroyed by 98 cell explosion

Must engineer lithium ion packs assuming one cell will short

Boeing with the best BMS and fusing still had a failed cell cause a catastrophic fire

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Thermal Runaway, Cell Level

Thermal runaway: Cell chemistry reacts rapidly generating heat

Accelerating Rate Calorimetry See what temperature

cell enters TR

Depends on cell and state of charge

90°C to 120°C

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0

100

200

300

400

500

600

700

800

0 500 1000 1500

Tem

pera

ture

(°C

)

Total Test Time (min)

Raw Data - Temperature vs Time ( 2.9 Ah)

0146

0153

Threshold: 100°C

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Thermal Runaway Propagation: Heat transfer

Success Criteria: Adjacent cell temperature Tc< 100°C

Q: Cell heat generation from TR Cell energy Parallel welds Combustion

Conduction to adjacent cells Pack material thermal diffusivity Cladding thickness Contact resistance

Convection to surroundings

Thermal diffusivity a function of temperature in phase change materials

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Q

Tc < 100°C

𝑇𝑐 ≈ 𝐷 =𝑘

𝜌𝐶𝑝(𝑇)

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Research Overview

Evaluate what cell packaging materials can prevent the propagation of thermal runaway in a small pack of 18650 style cells. Air

Graphite

Wax

Graphite and Wax (PCC)

Evaluate the importance of battery configuration and weld strength on thermal runaway propagation

Nail penetration test

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Battery Pack Materials Evaluated

Phase Change Composite (PCC)

20 wt.% graphite

80 wt.% wax

Wax micro-encapsulated

Melts at 55°C

½ Latent heat of ice

Graphite only (90% porous)

Wax (100%)

Air

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Li-ion CellsPCC Material

Time

Temperature With No PCC

Temperature with PCC

Melting

Point

Temperature Remains Constant During

Melting

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Different Material Properties

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Air PCCGraphite Only Wax Only

Air Graphite Only Wax Only PCC

Conductivity (W/m-K) 0.024 13.77 (in-plane) 0.15 17.21 (in-plane)

Density (kg/m3) 1.23 200 775 935

Specific Heat (J/kg-K) 1005 725 2384 1837

Latent Heat (J/g) N/A N/A 211 153

Diffusivity (mm2/s) 19.42 94.96 0.08 10.02

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Battery Pack Specifications

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Pack specifications

Specification Value

Configuration 10s4p

Energy (Wh) 413

Voltage, nominal (V) 36.2

Mass (kg) 2.75

Specific Energy (Wh kg-1) 150

Dimensions (cm) 32 x 9 x 13

Casing Aluminum & plastic

Cell specifications

Specification Value

Form Factor 18650

Capacity, nominal (Ah) 2.85

Voltage, nominal (V) 3.62

Specific Energy (Wh kg-1) 224

Energy Density (Wh L-1) 603

Chemistry Graphite anode, NCA

cathode

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Pack Build Procedure

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6 welds on trigger cell (normally 4)

Hole drilled in casing for nail penetration

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Air Pack TRP Video

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https://youtu.be/vmUpbou8VtA

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Air Pack: Thermal Runaway Propagation

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12

4

3

5

Trigger String

Neighbor String0

100

200

300

400

500

600

700

0 100 200 300 400 500 600 700Te

mpe

ratu

re (

C)

Time (s)

T1

T2

T3

T4

T5Threshold

0

1

2

3

4

0 100 200 300 400 500 600 700

Vol

tage

(V

)

Time (s)

Trigger

Neighbor

• TRP occurred slowly due to air low thermal conductivity and low ability to store heat

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Graphite Only: Thermal Runaway Propagation

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0

1

2

3

4

0 50 100 150 200 250 300

Vol

tage

(V

)

Time (s)

Trigger

Neighbor

0

200

400

600

800

1000

1200

0 50 100 150 200 250 300

Tem

pera

ture

(C

)

Time (s)

T/C-1 °C

T/C-3 °C

T/C-4 °C

T/C-5 °C

1 43

5

Trigger String

Neighbor String

Threshold

• TRP occurred quickly due to high thermal conductivity and low ability to store heat

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Wax Only: Thermal Runaway Propagation

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14

5

Trigger StringNeighbor String

2

0

100

200

300

400

500

600

700

0 50 100 150 200 250 300 350 400 450 500

Tem

pera

ture

(C

)

Time (s)

T1

T2

T4

T5

-2

-1

0

1

2

3

4

5

0 50 100 150 200 250 300 350 400 450 500

Vol

tage

(V

)

Time (s)

Trigger

Neighbor

Threshold

• TRP occurred quickly due to liquid wax flow and wax combustion

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0

50

100

150

200

250

0 50 100 150 200 250 300 350 400Te

mpe

ratu

re (

C)

Time (s)

T1T2T3T4T5

Phase Change Composite (PCC): Avoided Thermal Runaway Propagation

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1

2

4

3

5

Trigger StringNeighbor String

0

1

2

3

4

0 50 100 150 200 250 300 350 400

Vol

tage

(V

)

Time (s)

Trigger

Neighbor

Threshold

• TRP was prevented due to phase change absorbing thermal runaway energy

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Comparison Between Packs

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Pack Material

Thermal Runaway Propagation?

Air Fail

Graphite Fail

Wax Fail

PCC Pass

0

100

200

300

400

500

600

700

50 100 150 200 250 300

Tem

pera

ture

(C

)

Time (s)

Trigger Cell

Neighbor Cell

Peak Temperature

Time to neighbor cell peak temp.

100

150

200

250

300

350

0 50 100 150 200 250 300 350 400

Nei

ghbo

r C

ell P

eak

Tem

pera

ture

(C

)

Time to Neighbor Cell Peak Temperature (s)

Air

Graphite

Wax

PCC

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AutopsyThermal Runaway Propagation

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No Thermal Runaway Propagation

*Pack was sprayed with water after second cell propagated in packs that propagated

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Nickel separation during cell venting

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Nickel Cladding can separate from venting cell isolating electrical energy available for thermal runway propagation

Not 100% reliable separation. Cells can vent outside of side casing

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Ongoing Research with PCC

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Cell Energy Pack Configuration Thermal Runaway Propagation

2.9 Ah 10s4p Pass

3.2 Ah 10s4p Pass

3.5 Ah 10s4p Fail

3.5 Ah 10s0p Pass

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Conclusions and Future Work

PCC (graphite and wax) reliably prevented TRP in 2.9 Ah, 10s4p packs

Packs need to be engineered for TRP on a case by case basis Cell energy (2.9, 3.2, 3.5 Ah…)

Material thermal properties

Parallel configuration and cladding separation

Future tests will investigate different cell energies and graphite densities for AllCellBattery Products: http://www.allcelltech.com/

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Contact Information

http://www.allcelltech.com/

Greg Wilk, R&D Engineer, gwilk@allcelltech.com, 773-922-1155 (x244)

Siddique Khateeb, Head of R&D, Skhateeb@allcelltech.com

Greg Albright, VP of Business Development, galbright@allcelltech.com, 773-922-1155 (x211)

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