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- 1. Electric Vehicle BatteryThermal Issues and Thermal Management Techniques John P. Rugh, NREL Ahmad Pesaran, NREL Kandler Smith, NREL NREL/PR-5400-52818 Presented at the SAE 2011 Alternative Refrigerant and System Efficiency Symposium September 27-29, 2011 Scottsdale, Arizona USA
- 2. 2 Outline • Introduction • Importanceof battery temperature • Review of electric drive vehicle (EDV) battery thermal management options • Techniques to improve battery life – Standby thermal management – Preconditioning • Tradeoff with thermal comfort • Summary
- 3. 3 Battery is TheCritical Technology for EDVs Enables hybridization and electrification Provides power to motor for acceleration Provides energy for electric range and other auxiliaries Helps downsizing or eliminating the engine Enables regenerative braking × Adds cost, weight, and volume × Could decrease reliability and durability × Decreased performance with aging × Raises safety concerns 3 Lithium-ion battery cells, module, and battery pack for the Mitsubishi iMiEV (Courtesy of Mitsubishi)
- 4. 4 As The Sizeof The Engine Is Reduced, The Battery Size Increases Size of Electric Motor (and associated energy storage system) Size of Fueled Engine Conventional internal combustion engine (ICE) vehicles Electric vehicles (EVs) (battery or fuel cell) Micro hybrids (start/stop) Mild hybrids (start/stop + kinetic energy recovery) Full hybrids (medium hybrid capabilities + electric launch) Plug-in hybrids (full hybrid capabilities + electric range) Medium hybrids (mild hybrid + engine assist ) Axes not to scale
- 5. 5 Battery Requirements forDifferent EDVs Vehicle Power (kW) Energy (kW/h) Cycles Micro and Mild Hybrid Electric Vehicles (HEVs) Very high power Low energy Many (400K) shallow charge/discharge cycles (±5% change) Medium and Full HEVs High power Moderate energy Many (300K) shallow charge/discharge cycles (±10% change) Plug-in HEVs (PHEVs) High power High energy Many (200K) shallow charge/discharge cycles (±5% change) Many (3-5K)deep discharge cycles (50% change) Battery EVs Moderate power Very high energy Many (3-5K) deep discharges (70% change) Calendar life of 10+ years Safety: the same as ICE vehicles
- 6. 6 Lithium ion technologycomes close to meeting most of the required technical and cost targets in the next 10 years. Energy and Power by Battery Type www1.eere.energy.gov/vehiclesandfuels/facts/2010_fotw609.html
- 7. 7 Battery Cycle LifeDepends on State-of-Charge Swing 4,000 50% 70% • PHEV battery likely to deep-cycle each day driven: 15 yrs equates to 4,000–5,000 deep cycles Source: Christian Rosenkranz (Johnson Controls) at EVS 20, Long Beach, CA, November 15-19, 2003 Potential Potential Potential Potential
- 8. 8 Outline • Introduction • Importanceof battery temperature • Review of EDV battery thermal management options • Techniques to improve battery life – Standby thermal management – Preconditioning • Tradeoff with thermal comfort • Summary
- 9. 9 Phoenix 44oC max, 24oCavg 0oC Houston 39oC max, 20oC avg Minneapolis 37oC max, 8oC avg 10oC 20oC 30oC Impact of Geography and Temperature on Battery Life Li-ion technology must be sized with significant excess power to last 15 years in hot climates
- 10. 10 Li-Ion Battery ResistanceIncreases with Decreasing Temperature • Power decreases with decrease in temperature • Impacts power capability of motor and vehicle acceleration
- 11. 11 • Useful energyfrom the battery decreases with decrease in temperature • Impacts driving range and performance of vehicle Li-Ion Battery Capacity Decreases with Decreasing Temperature
- 12. 12 Battery Temperature isImportant Temperature affects battery: Operation of the electrochemical system Round trip efficiency Charge acceptance Power and energy availability Safety and reliability Life and life-cycle cost Battery temperature affects vehicle performance, reliability, safety, and life-cycle cost http://autogreenmag.com/tag/chevroletvolt/page/2/
- 13. 13 Temperature Impacts BatterySizing & Life and Thus Cost Power Limits 15°C 35°C discharge charge Rated Power T Degradation Sluggish Electrochemistry Power Limits 15°C 35°C discharge charge Rated Power T Degradation Sluggish Electrochemistry Dictates power capability Also limits the electric driving range Power and energy fade rates determine the original battery size Power limited to minimize T increase and degradation Kandler Smith, NREL Milestone Report, 2008 Desired Operating Temperature
- 14. 14 Battery High-Temperature Summary •Primary considerations – Life – Safety – Non-uniform aging due to thermal gradients • Cooling typically required – In hot environments (could be 24 hr) – During moderate to large current demands during drive – During fast charging Photo Credit: John Rugh, NREL
- 15. 15 Battery Low-Temperature Summary •Primary considerations – Performance – Damage due to charging too fast • Heating typically required – In cold environments during charging and discharging Photo Credit: Mike Simpson, NREL
- 16. 16 Outline • Introduction • Importanceof battery temperature • Review of EDV battery thermal management options • Techniques to improve battery life – Standby thermal management – Preconditioning • Tradeoff with thermal comfort • Summary
- 17. 17 • Regulate packto operate in the desired temperature range for optimum performance/life 15o C – 35o C • Reduce uneven temperature distribution Less than 3o C – 4o C • Eliminate potential hazards related to uncontrolled temperatures – thermal runaway Battery Pack Thermal Management Is Needed
- 18. 18 Battery Thermal ManagementSystem Requirements • Compact • Lightweight • Easily packaged • Reliable • Serviceable • Low-cost • Low parasitic power • Optimum temperature range • Small temperature variation http://www.toyota.com/esq/articles/2010/Lithium_Ion_Battery.html
- 19. 19 Battery Pack Outside Air Exhaust Fan BatteryPack Cabin Air Exhaust Fan Outside Air Return Vehicle heater and evaporator cores Battery Pack Exhaust Fan Outside Air Return Auxiliary or vehicle heater and evaporator cores Outside Air Ventilation Cabin Air Ventilation Heating/cooling of Air to Battery – Outside or Cabin Air Prius & Insight Thermal Control Using Air i-MiEV (fast charge)
- 20. 20 Battery Heating andCooling Using Air Pro Con All waste heat eventually has to go to air Low heat transport capacity Separate cooling loop not required More temperature variation in pack Low mass of air and distribution system Connected to cabin temperature control No leakage concern Potential of venting battery gas into cabin No electrical short due to fluid concern High blower power Simple design Blower noise Lower cost Easier maintenance
- 21. 21 Thermal Control UsingLiquid Liquid Pump Liquid/air heat exchanger Fan Outside Air Exhaust Battery Pack Pump Liquid/air heat exchanger Fan Outside air Exhaust Battery Pack Liquid direct -contact or jacketed Refrigerant Liquid Pump Liquid/liquid heat exchanger or electric heater Pump Vehicle engine coolant Return Battery Pack A/C heat exchanger Liquid direct-contact or jacketed Ambient cooling Active dedicated cooling/heating Volt, Tesla
- 22. 22 Battery Heating andCooling Using Liquid Pro Con Pack temperature is more uniform - thermally stable Additional components Good heat transport capacity Weight Better thermal control Liquid conductivity – electrical isolation Lower pumping power Leakage potential Lower volume, compact design Higher maintenance Higher viscosity at cold temperatures Higher cost
- 23. 23 Outline • Introduction • Importanceof battery temperature • Review of EDV battery thermal management options • Techniques to improve battery life – Standby thermal management – Preconditioning • Tradeoff with thermal comfort • Summary
- 24. 24 Standby Thermal Coolingin Hot Climates • Battery life can greatly benefit from cooling the battery during standby, i.e., while vehicle is plugged in to the grid • Slower battery degradation rate enables smaller, lower cost battery • NREL study investigated – Insulation – Insulation and air cooling – Insulation and small vapor compression system (VC) – Insulation, small VC system, and phase change material (PCM)
- 25. 25 Phoenix Houston MinneapolisPhoenix Houston Minneapolis Saft HP-12LC Cell (Belt/INL, ECS Mtg. 2008) • low fade rate, high cost DOE/TLVT Cell (Christopersen/INL, Battaglia/LBL, 2007 Merit Review) • moderate fade rate, lower cost 5%-10% less power fade with Ins. + VC 9%-22% less power fade with Ins. + VC Lower cost cell preferred, provided it can meet life. Next slide compares Δcosts of DOE/TLVT battery sized for 15 years in Phoenix, w/ and w/o insulation + VC system. Battery Life for Various Standby Systems can differ widely depending on cell chemistry, materials, and manufacturer
- 26. 26 Savings from DownsizedBattery Expected to Significantly Outweigh Cost of Added Components DOE/TLVT cell sized for 15 years; in Phoenix, AZ, charged nightly ($360) ($320) ($250) PHEV10 ΔkWh ΔkW VC Fan Insulation ΔkWh ΔkW VC Fan Insulation ΔkWh ΔkW VC Fan Insulation PHEV20 PHEV40 Total Savings ($) Total savings assuming components represent additional cost PHEV10 PHEV20 PHEV40
- 27. 27 Standby Thermal Management– Passive Techniques to Reduce Battery Temperatures • Installed metalized solar reflective film on the glazings of a Toyota Prius in Phoenix • Cabin air temperature reduced ~6o C • Before: Battery daily max temp 1.5o C above ambient • After: Battery daily max temp 2o C below ambient Photo Credit: John Rugh, NREL
- 28. 28 Thermal Preconditioning Issues: • Forconventional vehicle and HEV platforms, A/C use leads to increased fuel consumption • For PHEV and EV platforms, climate control energy is supplied by the traction battery Charge depletion (CD) range reduction • Batteries degrade rapidly at high temperatures and benefit from active cooling • Batteries suffer from reduced power and energy at cold temperatures; their performance can be improved by preheating Battery wear and life impacts Potential Solution: • Use grid power to thermally precondition cabin and battery • Save valuable onboard stored energy for propulsion
- 29. 29 Preconditioning, Driving &Charging Patterns Affect Battery Temperature and Duty-Cycle 24-hour profiles created to estimate impact of preconditioning on battery life 6 am 10 am 3 pm 8 pm 1 am 6 am Rest 20 minute preconditioning 8:00 am: 26.6 km trip Rest 20 minute preconditioning 5:00 pm: 26.6 km trip 10:00 pm: Charge at 6.6 kW Rest 6 am 10 am 3 pm 8 pm 1 am 6 am PHEV40s, hwy cycle, 95°F (35°C) ambient. Battery heat generation rates and SOC extracted from PSAT vehicle simulations of charge-depleting and charge-sustaining operation.
- 30. 30 Thermal Preconditioning canRegain CD Range as well as Improve Thermal Comfort *Compared to no thermal preconditioning EDV Platform (Climate Control) Fuel Consumption Impact* CD Range Impact* PHEV15 (heat) -1.4% +19.2% PHEV15 (AC) -0.6% +5.2% PHEV40 (heat) -2.7% +5.7% PHEV40 (AC) -1.5% +4.3% EV (heat) NA +3.9% EV (AC) NA +1.7%
- 31. 31 Thermal Preconditioning CanAlso Improve Battery Life • Battery capacity loss over time is driven by ambient temperature • Thermal preconditioning has a small benefit in reducing battery capacity loss (2%–7%), primarily by reducing pack temperature (2%–6%) in the high ambient temperature (35o C/95o F) scenario EDV Platform (Climate Control) Capacity Loss Reduction* PHEV15(A/C) +2.1% PHEV40 (A/C) +4.1% EV (A/C) +7.1% *Compared to no thermal preconditioning
- 32. 32 Thermal Preconditioning Considerations •Timing – avoid cooling or heating too early – does the heating/cooling coincide with peak demand on the grid? • Can the charge circuit provide power for simultaneous heating/cooling and charging? • When not plugged in, is it worth using onboard stored energy for preconditioning? – Trade stored energy (range) for battery life
- 33. 33 Systems Approach -Options for Improving Electric Range with Climate Control • Incorporate thermal preconditioning strategies • Reduced heat transfer into/out of the cabin • Use efficient HVAC equipment • Reduce cooling capacity or heat load – Zonal climate control – Focus on occupant comfort • HVAC controls – Eco mode (temporarily minimize energy use) – Eliminate inefficient HVAC control practices
- 34. 34 Outline • Introduction • Importanceof battery temperature • Review of EDV battery thermal management options • Techniques to improve battery life – Standby thermal management – Preconditioning • Tradeoff with thermal comfort • Summary
- 35. 35 Tradeoff of BatteryCooling with Thermal Comfort • NREL Integrated Vehicle Thermal Management task • KULI thermal model – A/C and cabin – Battery cooling loop – Motor and power electronics cooling loop • Nissan Leaf size EV • Environment – 35 o C – 40% RH • 0% recirc • US06 drive cycle • Cooldown simulation from a hot soak Source: David Howell, DOE Vehicle Technologies Annual Merit Review
- 36. 36 After 10 Minutes,the Battery Cools to Control Setpoint While the Cabin is Still Warm Cabin Air Battery Cells
- 37. 37 Initially Less Than50% of the A/C System Capacity is Going to the Cabin Evaporator Chiller
- 38. 38 Outline • Introduction • Importanceof battery temperature • Review of EDV battery thermal management options • Techniques to improve battery life – Standby thermal management – Preconditioning • Tradeoff with thermal comfort • Summary
- 39. 39 Summary • Temperature impactsthe life, performance, and cost of batteries in HEVs, PHEVs, and EVs • Battery life and performance are extremely sensitive to temperature exposure • Thermal management is a must for batteries • Thermal control of PHEVs and EVs (when parked or driving) could be a cost-effective method to reduce over-sizing of battery for the beginning of life • Future trends – Some variation of today’s Li-ion chemistries – Same sized packs – larger range – Improved cell designs to solve life issues
- 40. 40 Special thanks to: DavidAnderson David Howell Susan Rogers Lee Slezak U.S. Department of Energy Vehicle Technologies Program For more information: John P. Rugh National Renewable Energy Laboratory [email protected] 303-275-4413 Acknowledgments, Contacts, and Team Members NREL: Robb Barnitt Laurie Ramroth