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September 14, 2011 David Speth, Senior Engineer-Materials Phone: 614.688.5162 Battery Assembly: Joining Dissimilar.

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Presentation on theme: "September 14, 2011 David Speth, Senior Engineer-Materials Phone: 614.688.5162 Battery Assembly: Joining Dissimilar."— Presentation transcript:

1 September 14, 2011 David Speth, Senior Engineer-Materials Phone: Battery Assembly: Joining Dissimilar Materials

2 Outline Developing EV Market Joining Issues for Vehicle Batteries Project with OSU Center for Automotive Research Ultrasonic Metal Welding Laser Welding Resistance Spot Welding Nondestructive Evaluation Summary and Acknowledgements

3 2011 Commercial EV and PHEV Chevrolet Volt Nissan Leaf Tesla Roadster GM Plans 50,000+ Volts Nissan plans 200,000+ EVs Tesla working on Model S

4 EVs ManufacturerVehicle AudieTron EV (2012); PHEV (2014) BMWMiniE EV (2012); City Car (2013) BYDE6 EV (2012); F3DM PHEV (2012) CodaSedan EV (2011) Chrysler/FiatFiat 500 EV (2012) FiskerKarma EV (2011) FordFusion HEV (commercial); Transit Connect EV (commercial); Escape HEV (commercial); Focus EV (2011); CMax PHEV (2013) GMVolt PHEV (commercial); Ampera PHEV (2011); Cadillac SRX HEV (2012) HondaInsight HEV (commercial); Civic HEV (commercial); Fit EV (2012) MazdaMazda 2 EV (2012) MitsubishiiMEV EV (2011) NissanLeaf EV (commercial); other platforms TeslaModel S EV (2012); ToyotaPrius HEV (commercial); Prius PHEV (2012); RAV4 HEV (2012) VolkswagenEup EV (2013); Gold EV (2013); Jetta EV (2013)

5 Vehicle Electrification Challenge Scale factor (size, capacity) Cell phone4 W Laptop80 W HEV1,500 W PHEV10,000 W EV45,000 W Design Life/Life Cycle Cost Cell phone12-24 months Laptop12-18 months HEV, PHEV, EV>120 months New demands require new manufacturing industry Working environment State-of-charge window Rapid charge and discharge

6 Cells to Modules to Packs Can be 100s to 1000s of electrical joints per pack Bus bars Interconnects Collectors Pouch/cell seal Voltage sensor leads Balance of plant Motor connections Thermal management Battery management

7 Joining Issues No single process dominates Ultrasonic Laser Resistance Soldering Adhesives Complex material combinations Copper (native, plated) Aluminum Nickel Steel Dissimilar combinations Need Speed High reliability Durability Low heat input NDE approach

8 Substrate Comparison PropertyCuAlNi Thermal conductivity (W/m-°K) Melting point (°C) Thermal expansion coefficient (ppm/°C) Heat capacity (J/kg-°C) Absorption (at 1064 nm%) Conductivity (10 6 S/m) Resistivity ( cm) Specific heat (J/kg/°K) Latent heat of fusion (J/g) Electrochemical potential (V) Thermal Diffusivity (cm 2 /s) Property mismatch makes direct welding difficult

9 OSU CAR EWI Welding Study 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.) Mechanical and electrical properties Shear strength Peel strength (T peel) Resistance/conductivity/thermal profile Metallography Non-destructive evaluation/process monitoring Electrical cycling (OSU CAR) Mechanical fatigue (Phase 2)

10 Ultrasonic Metal Welding (UMW) Oxides, Contaminants Asperities Advantages Solid-state, low heat input Welds through contaminants Low power No filler or cover gas Fast Excellent for Al, Ni, Cu Disadvantages Unfamiliar process Lap joints, thin sheet only Deforms parts Large weld size Requires open access Noise Substrate-horn adhesion Static Force Sonotrode Vibration Workpieces Anvil Weld Zone

11 USMW Previous Results No Cu-Cu bonding observed Ni-plating broken or thinned in some areas, but never removed Profile of the horn and anvil are important Al Ni-plated Cu 110 Aluminum 1100 Ni-plated Cu 110

12 USMW OSU Preliminary Results 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 Tab to Tab Aluminum and copper join well Aluminum to other substrates less successful Foil to tab USW can easily join multiple thin layers in a single step

13 USMW Tab to Tab Peel Shear

14 Laser Welding Lasers use a focused beam of light to create welds Generic Set-Up for Direct Beam Laser Welding Keyhole Mode Welding Conduction Mode Welding

15 LW Advantages/Disadvantages Advantages Precise location of small welds Low heat input Minimal distortion High speed Non-contact Can weld shapes Disadvantages 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 Nickel Plated Copper on Copper-Shaped Weld

16 LW Test Specimens Laser Welds

17 LW Sample Cross Sections Nickel-Electroplated Copper on Aluminum Copper on Nickel Aluminum on Nickel-Electroplated Copper-Voids Aluminum welded to other metals produced the weakest welds Incomplete mixing of metals

18 Resistance Spot Welding Resistive heating of workpieces or electrodes Common Adaptable Low cycle time and heat input Self-fixturing Self-monitoring equipment Block diagram of AC welding system.

19 RSW Variants Solid state is preferred for battery assembly Advantages Rapid cycle time Low heat input Multiple welds easy Process monitoring possible Disadvantages for batteries Dissimilar metals Low resistance High conductivity Current path can limit geometry Access can be limited Electrodes or Welding Tips Spot Weld

20 RSW Process Development Produce a weld matrix to determine process limits Current Time Force Acceptance requirements Application defined Weld strength Weld size Expulsion Acceptable Nuggets Small Nuggets Minimum Nugget Diameter Weld Current Expulsion Level Time A Smaller Brittle Nuggets Acceptable Nuggets Lobe Curve Nugget Diameter Weld Time Time A

21 RSW Tensile Shear Results 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

22 RSW Peel Test Results Force, current, and time equally important for Al and Cu Weld time becomes more important for Ni and Ni plate

23 Non Destructive Evaluation Can excite welds with external source.

24 NDE X-Ray vs Thermal Signature Good WeldBad Weld X-ray image showing weld nuggets (controlled specimen)

25 Summary Batteries for motive power have numerous joints Material combinations increase complexity Electrical testing is not sufficient to determine if a weld is good Conductivity/resistance good even if weld is weak 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 Nondestructive evaluation approaches can be used for process development and perhaps production

26 Buckeye Bullet 2.5 August 2010 EWI Laser Work Cell Assembled Battery Packs Buckeye Bullet Hood Up Battery New international land-speed record for battery-powered vehicles of mph Over 1500 Batteries

27 Acknowledgements Support of the Department of Energy through the Ohio State University Center for Automotive Research DOE Award DE-EE National Center of Excellence for Energy Storage Team effort Tim Frech Mitch Matheny Jay Eastman Sam Lewis Warren Peterson Barb Christel Nancy Porter Mike Ryan

28 Questions? Dr. David Speth Senior Engineer-Materials Phone:

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