Transcript Document

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Pipeline and Hazardous Material Administration
(PHMSA)
Department of Transportation
AN OVERVIEW OF INTERNAL SHORT CIRCUIT
SCREENING TEST METHODS FOR
LITHIUM BATTERIES and a Proposal for
Test T.6 Modification
Presented at 1st Workshop on Lithium Batteries, Brussels, Belgium
March 17-18, 2015
Steve Hwang, Ph.D.
[email protected]
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UN Test Guidelines
Tests
Test Name
T1
T2
T3
T4
Altitude
Thermal
Vibration
Shock
T5
T6
T7
T8
Purpose
Requirement
Vacuum @ 11.6 kPa 1
-40 – 72 oC
1
7 Hz – 200 Hz
1
Small 150 g 6 ms
1
Large 50 g 11 ms
External Short
External short
2
Impact/Crush
Internal short by
2
applying external impact
Overcharge
<18 V
3
> 18 V x 1.2
Forced Discharge Maximum discharge 3
current
1. No leakage, no venting, no disassembly, no rupture, no fire, <90% of V
2. Not exceeding 170 oC, no disassembly, no rupture, no fire
3. disassembly, no fire
Primary
Cell Battery
yes yes
yes yes
yes yes
yes yes
Secondary
Cell Battery
yes
yes
yes
yes
yes
yes
yes
yes
yes yes
yes no
yes
yes
yes
no
no
no
no
yes
yes
no
yes
no
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Causes of Internal Short-Circuiting
Causes
Why can this
happen?
1. Shock or Dropping
2. Formation of Dendrite
3. Existence of Impurities
due to Poor Quality Control
during Manufacturing
4. Imbalance of Voltage
among Cells
5. High Charging Voltage
applied to a cell
6. Propagation of Thermal
Runaway
Physical Abuse
Lithium Plating
Manufacturing
defects
7.
Separator Failure
Can it be managed?
Strong casing by design
New Techniques needed
New Techniques needed
Voltage
BMS
Imbalance
High Charging
BMS
Voltage
Damaged Cell
Proper venting, insulation
can raise temp.
of surrounding
cells
Temp, Defects, wearT control, quality
out, puncture, degrad. control, struct.
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Cases of Thermal Runaway as it relates to Internal Shorts
• Nail Penetration - Did not cause thermal runaway
• Manufacturing Defects – Possible thermal runaway
(Metal particle in cathode slurry)
• Cell Crushing - Can cause massive internal shorts and
thermal runaway
• Metal Plating (Dendrite) - Can reach 200 oC with
thermal runaway
• Elevated Temp - Can cause thermal runaway @ >170 oC
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Comparison of Internal Shorts Screening Tests
How Applied
• NREL
During Manufacturing
ISC Device
Process
• UL Indentation Rounded Tip
Induced ISC
Nail
• IEC (62133)
Nickel Powder
Forced ISC Tech
• Nail
Nail
Penetration
• Impact/Crash Small: Steel Bar
(UN 38.3)
Large: Flat Surface
• Propagation
Insulated
Test
Thermal Chamber
1. No Fire
2. No fire, No disassembly , not exceeding 170 oC
3. No external fire, No battery case rupture
Method for
Inducing ISC
As a Test
Requirement
for Prevention
Heat to ~55 oC Can reduce IS with
1
to Melt Wax
Shut-down Separator
Pressure
Safety Level req’d
1
in the Market
Pressure
Safe Cell Design
1
Piecing
Drop weight
Force applied
Heating of a
Cell
Safety Level req’d
in the Market
Survival of
Deformation
Proper Venting
1
2
3
6
7
8
Cell Separator Deformation from Indentation Test
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Data Search
Test Type (Li Ion cells)
Indentation ISC
% of Explosion
or Fire
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Forced Nickel Powder
None
NREL ISC Device
Depending on existence
of shut-down separator
Techniques
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-10 oC
DENDRITE
GROWTH
PATTERN
5 oC
20 oC
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separator
cross-section
Separator vs. Dendrite
Mechanical Interaction: Mixed Penetration
Polymer Property: Elastic, Softened
Failure Mode*: Conductive Matrix of Li0 Particles
Desire Property: High Puncture Strength
Ideal Material: Small Pore Size
Mechanical Interaction: Puncture Stress
Polymer Property: Ductile-to-Brittle Transition
Failure Mode*: Hard Short Pierces Separator
Desire Property: Puncture Strength & Elastic Modulus
Ideal Material: Biaxial Orientation
Mechanical Interaction: Compressive Stress
Polymer Property: Brittle
Failure Mode*: Crack Propagation & Growth
Desire Property: High Bulk Modulus; Low Compressibility
Ideal Material: Large Pore Size OK; High Ductility
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SUMMARY
•
•
•
•
•
Many companies are testing cells and batteries to
determine their integrity as it relates to ISC using the
test methods of their choosing.
None of the ISC screening methods can address the
basic concern on IS prevention.
It is not clear why these tests are conducted by he
manufacturers.
No recommendable test methods for preventing
occurrence of ISC can be identified from literature
search.
Though many field failures are reported to be caused
by IS resulting from manufacturing defects or
impurities inadvertently incorporated during
manufacturing, no tools presently exist to detect or
mitigate these defects.
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SUMMARY (cont’d)
• Recent research information indicates that
dendrite formed at the anode migrates to the
cathode through the separator membrane to
cause an internal short circuiting.
• A corollary to the finding is that the integrity of
separator membranes plays a significant role in
retarding or preventing the dendrite penetration
through the membrane.
• It is important to test for the desired mechanical
properties of the separator membranes to
mitigate the occurrence of internal shortcircuiting and thermal runaway.