Transcript EWI Winter 2009 Industry Advisory Board Meeting

Battery Assembly:
Joining Dissimilar Materials
September 14, 2011
David Speth, Senior Engineer-Materials
Email: [email protected]
Phone: 614.688.5162
Outline
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Developing EV Market
Joining Issues for Vehicle Batteries
─ Project with OSU Center for Automotive Research
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Ultrasonic Metal Welding
Laser Welding
Resistance Spot Welding
Nondestructive Evaluation
Summary and Acknowledgements
2011 Commercial EV and PHEV
Chevrolet Volt
Nissan Leaf
GM Plans 50,000+ Volts
Nissan plans 200,000+ EVs
Tesla working on Model S
Tesla Roadster
EVs 2011-2014
Manufacturer
Vehicle
Audi
eTron EV (2012); PHEV (2014)
BMW
MiniE EV (2012); City Car (2013)
BYD
E6 EV (2012); F3DM PHEV (2012)
Coda
Sedan EV (2011)
Chrysler/Fiat
Fiat 500 EV (2012)
Fisker
Karma EV (2011)
Ford
Fusion HEV (commercial); Transit Connect EV (commercial); Escape HEV
(commercial); Focus EV (2011); CMax PHEV (2013)
GM
Volt PHEV (commercial); Ampera PHEV (2011); Cadillac SRX HEV (2012)
Honda
Insight HEV (commercial); Civic HEV (commercial); Fit EV (2012)
Mazda
Mazda 2 EV (2012)
Mitsubishi
iMEV EV (2011)
Nissan
Leaf EV (commercial); other platforms
Tesla
Model S EV (2012);
Toyota
Prius HEV (commercial); Prius PHEV (2012); RAV4 HEV (2012)
Volkswagen
Eup EV (2013); Gold EV (2013); Jetta EV (2013)
Vehicle Electrification
Challenge
Scale factor (size, capacity)
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Cell phone
Laptop
HEV
PHEV
EV
Relative Power
100000
Design Life/Life Cycle Cost
─ Cell phone
─ Laptop
─ HEV, PHEV, EV
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4W
80 W
1,500 W
10,000 W
45,000 W
12-24 months
12-18 months
>120 months
New demands require new
manufacturing industry
─ Working environment
─ State-of-charge window
─ Rapid charge and discharge
10000
Power (W)
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1000
100
10
1
Cell phone
Laptop
HEV
Application
PHEV
EV
Cells to Modules to Packs
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Can be 100s to 1000s of
electrical joints per pack
─ Bus bars
─ Interconnects
─ Collectors
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Pouch/cell seal
Voltage sensor leads
Balance of plant
─ Motor connections
─ Thermal management
─ Battery management
Joining Issues
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No single process dominates
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Complex material combinations
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Ultrasonic
Laser
Resistance
Soldering
Adhesives
Copper (native, plated)
Aluminum
Nickel
Steel
Dissimilar combinations
Need
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Speed
High reliability
Durability
Low heat input
NDE approach
Substrate Comparison
Property
Cu
Al
Ni
Thermal conductivity (W/m-°K)
390
229
70
Melting point (°C)
1080
652
1430
Thermal expansion coefficient (ppm/°C)
17.3
24.1
12
Heat capacity (J/kg-°C)
386
900
456
Absorption (at 1064 nm%)
2-5
8
32
Conductivity (106 S/m)
57
34
18
Resistivity (10-6 -cm)
2.11
2.87
9.5
Specific heat (J/kg/°K)
386
238
455
Latent heat of fusion (J/g)
205
388
298
Electrochemical potential (V)
0.34
-1.66
-0.257
Thermal Diffusivity (cm2/s)
1.14
0.91
0.11
Property mismatch makes direct welding difficult
OSU CAR EWI Welding Study
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Process screening study for module/pack assembly
─ Laser, resistance and ultrasonic metal welding
─ Copper, aluminum, nickel, nickel-plated copper (electro- and
electroless-)
─ Foil (0.001 in.); tab (0.005 in.); bus (0.032 in.)
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Mechanical and electrical properties
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Shear strength
Peel strength (T peel)
Resistance/conductivity/thermal profile
Metallography
Non-destructive evaluation/process monitoring
Electrical cycling (OSU CAR)
Mechanical fatigue (Phase 2)
Ultrasonic Metal Welding (UMW)
Static Force
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Advantages
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Solid-state, low heat input
Welds through contaminants
Low power
No filler or cover gas
Fast
Excellent for Al, Ni, Cu
Sonotrode
Vibration
Anvil
Disadvantages
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Unfamiliar process
Lap joints, thin sheet only
Deforms parts
Large weld size
Requires open access
Noise
Substrate-horn adhesion
Weld Zone
Workpieces
Asperities
Oxides,
Contaminants
USMW Previous Results
Ni-plated Cu 110
Aluminum 1100
Ni-plated Cu 110
Ni-plated Cu 110
Ni-plated Cu 110
Ni-plated Cu 110
Ni-plated Cu 110
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Ni-plated Cu 110
Al 1100-0
No Cu-Cu bonding observed
Ni-plating broken or thinned in
some areas, but never removed
Profile of the horn and anvil are
important
Ni-plated Cu 110
USMW OSU Preliminary Results
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Tab to Bus
─ Aluminum tabs to all bus materials (Al, Cu, and Ni-plated Cu) result
in weld joints with similar mechanical strength
─ Ni-plated copper tabs to all bus materials-lower than expected peel
strength
─ Copper tab to aluminum bus shows low peel but high tensile
strength
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Tab to Tab
─ Aluminum and copper join well
─ Aluminum to other substrates less successful
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Foil to tab
─ USW can easily join multiple thin layers in a single step
USMW Tab to Tab
Peel
Shear
Laser Welding
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Lasers use a focused beam of light to create welds
Keyhole Mode Welding
Generic Set-Up for Direct Beam Laser Welding
Conduction Mode Welding
LW Advantages/Disadvantages
Advantages
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Precise location of
small welds
Low heat input
Minimal distortion
High speed
Non-contact
Can weld “shapes”
Disadvantages
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Nickel Plated Copper on Copper-Shaped Weld
Laser cost $$
Need line-of-sight access
Requires good fit-up, tooling
Heating starts on the surface
Limited weld penetration
especially on copper
Makes fusion welds
Welds very narrow
Eye safety hazard
LW Test Specimens
Laser Welds
LW Sample Cross Sections
Aluminum on Nickel-Electroplated
Copper-Voids
Nickel-Electroplated Copper on
Aluminum
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Copper on Nickel
Aluminum welded to other
metals produced the weakest
welds
Incomplete mixing of metals
Resistance Spot Welding
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Resistive heating of
workpieces or electrodes
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Common
Adaptable
Low cycle time and heat input
Self-fixturing
Self-monitoring equipment
Block diagram of AC welding system.
RSW Variants
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Solid state is preferred for
battery assembly
Advantages
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Rapid cycle time
Low heat input
Multiple welds easy
Process monitoring possible
Disadvantages for
batteries
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Dissimilar metals
Low resistance
High conductivity
Current path can limit geometry
Access can be limited
Electrodes or
Welding Tips
Spot Weld
Produce a weld matrix to
determine process limits
─ Current
─ Time
─ Force
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Acceptance requirements
Acceptable
Nuggets
─ Application defined
─ Weld strength
─ Weld size
Expulsion
Minimum Nugget Diameter
Time A
Small Nuggets
Weld Current
Weld Time
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Nugget Diameter
RSW Process Development
Lobe
Curve
Time
A
Smaller
“Brittle”
Nuggets
Acceptable
Nuggets
Weld Current
Expulsion
Level
RSW Tensile Shear Results
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Weld force and current
important for Al and Cu
Force and current
become less important
for Ni and Ni-plate
Weld time less important
for al and cu becomes
important for Ni plate
RSW Peel Test Results
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Force, current, and time
equally important for Al
and Cu
Weld time becomes
more important for Ni
and Ni plate
Non Destructive Evaluation
Activation
Energy
Activation
Energy
Source
Activation
Energy
Activation
Energy
Source
Good Fusion
Can excite welds with external source.
Poor Fusion
NDE X-Ray vs Thermal Signature
Bad Weld
Good Weld
X-ray image showing weld nuggets
(controlled specimen)
Summary
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Batteries for motive power have numerous joints
─ Material combinations increase complexity
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Electrical testing is not sufficient to determine if a weld is good
─ Conductivity/resistance good even if weld is weak
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Several processes are used
─ Ultrasonic metal welding
─ Excellent for Al, Cu, Ni
─ Good for multiple layers
─ Need to complete metallurgy and data analysis
─ Laser welding
─ Flexible
─ May be limited to like-to-like welds
─ Need to look for intermetallic compound formation
─ Resistance Welding
─ Most combinations can be welded
─ Parameter selection can be based on like-to-like results
─ Need to finish metallurgical analysis
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Nondestructive evaluation approaches can be used for process
development and perhaps production
Buckeye Bullet 2.5 August 2010
New international land-speed record for
battery-powered vehicles of 307.66 mph
Buckeye Bullet “Hood Up”
Over 1500
Batteries
http://blog.buckeyebullet.com/
EWI Laser Work Cell
Battery
Assembled Battery Packs
Acknowledgements
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Support of the Department of Energy through the
Ohio State University Center for Automotive
Research
─ DOE Award DE-EE0004188
─ National Center of Excellence for Energy Storage 168.10
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Team effort
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Tim Frech
Mitch Matheny
Jay Eastman
Sam Lewis
Warren Peterson
Barb Christel
Nancy Porter
Mike Ryan
Questions?
Dr. David Speth
Senior Engineer-Materials
Email: [email protected]
Phone: 614.688.5162