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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
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, [email protected], 773-922-1155 (x244)
Siddique Khateeb, Head of R&D, [email protected]
Greg Albright, VP of Business Development, [email protected], 773-922-1155 (x211)
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