Safety and Thermal Management for Li-ion Batteries in Transportation
Applications
Said Al-Hallaj
Presented at:
EV Li-ion Battery Forum 2012
AllCell Technologies LLC 2321 W. 41st Street
Presentation Outline
• Overview of lithium-ion batteries
• Importance of thermal management
– Safety
– Performance
• Passive thermal management with phase change material (PCM)
• Concluding remarks
Lithium-ion chemistry has large power/energy range
HEV
EV PHEV
Cycle life and cost per kWh generally
Automotive applications require full range of lithium-ion batteries
LEV
0.5-10 kWh
Hybrid
0.5-1.5 kWh
Plug-in Hybrid
4 -16 kWh
Full EVs
20-70 kWh
Priority Not
Power Energy Density Shallow/Cycle life
Priority Not
Cost Power
Deep cycle life
Priority Not
Energy Density Power Cost
Deep/ cycle life
Priority Not
Energy Density Cost
Divas of the EV world
• Li-ion batteries have high performance, but very temperamental
• Key problem: dealing with heat generated by cells during charge, discharge and ambient conditions
• If cells get too hot, three problems:
– Decreased battery life
– Decreased performance
– Risk of fire or explosion
Thermal degradation is a hot button issue
“Thermal management of lithium-ion battery systems is critical to the success of all-electric vehicles because extreme temperatures can affect performance, reliability, safety and
durability.” – V. Anand Sankaran, Executive technical leader, Ford Energy Storage
& High Voltage Electrical Systems
“The different chemistries have different thermal
characteristics and so we‟ve been able to incorporate how to make sure from a thermal perspective that we‟ve got it...” - Denise Gray, Advanced Battery Director of GM
“As a result, the LEAF pack will have temperatures „all over the place,‟
causing it to suffer „huge degradation‟ in cold environments and basically „shut off‟ in hot environments.” – Elon Musk, CEO Tesla
“Thermal management of the system...all of those little details go into effect to take it to the next level” – Jay Iyengar, Global Director & Chief Engineer for Electrified Powertrains, Chrysler
Chemical reactions inside cell add complexity to the heat problem
Heat
accumulation in Cell
Net Heat Entering/Leaving
=
Cell+
Generation HeatInsufficient heat transfer causes heat accumulation in cell
heat accumulation in cell creates burden
on cooling
Heat from Chemical reaction
accumulates in cell heat accumulation in cell creates additional
chemical reactions
AllCell’s PCM Solution
• Phase change material (PCM) and conductive matrix used to absorb and conduct heat to and from lithium-ion batteries
• PCM improves battery cost, efficiency, and weight when compared to active systems
• Phase change materials have a long track record in other applications:
– Vehicle HVAC – Delphi, Behr – Building thermal systems – Spacecraft thermal systems – Medical supply shipping
– Chemical reaction exotherm smoothing Cell PCM
Cell
Why not apply PCM to batteries?
PCM
Cell
Safety issues still exist
Safety reputation bad for industry, but...
Auto safety chief denies sitting on Chevy Volt warnings in heated hearing – Fox News
Chevy Volt Fire Prompts Federal Investigation Into Lithium-Ion Batteries – NY Times
Fisker Karma recall is official, 239 cars will need their battery packs swapped - engadget Fisker Recalling 239 Karma Plug-In
Hybrids for Fire Hazard – NY Times
Fire deals new setback to Navy's heralded mini-sub – navyseals.com
PC Notebook Computer Batteries Recalled Due to Fire and Burn Hazard -
...it’s really about lives
Lithium Ion Batteries Faulted for Jet Crash - Gigaom
2 Die as Asiana Cargo Plane Crashes Off South Korea – NY
Times
Safety improvements are being made on multiple fronts
Cell Level Pack Level
Cell Design Cell Chemistry
Active Cooling Passive Cooling
Liquid Cooling (refrigerant)
Air Cooling Phase Change
Material
Safety Circuits Safety Vents
Shutdown Separators
Positive Thermal Coefficient Devices
Electrode Coatings
Conductive Ceramic
Electrolytes Additives
Anode/
Cathode
AllCell PCM prevents thermal
runaway propagation
Operational performance must evolve to achieve mass adoption
Gen 1 – Product Introduction
Gen 2 – Mass market/cost sensitive
Safety Must Must
Low Cost Good to have Must
Performance Good to have Must
Gen 1 Chevy Volt uses 16 kWh battery to achieve 25-50 mi AER
11 kWh go to vehicle propulsion
+ 3.5 kWh oversize to limit SOC window and heat generation + 1.5 kWh oversize for thermal management power requirements 16 kWh
Gen 2 must meet more difficult technical goals at a lower cost
11 kWh still required for propulsion
+ 2.5 kWh oversize to limit SOC window and heat generation + 0.2 kWh thermal management (cabin air/PCM system) 13.7 kWh – (2.3 kWhr or 14% battery size reduction)
Optimal solution balances multiple methods
• Oversize battery
• Curtail performance
• Effective thermal management
• Must consider cost, efficiency, life and
customer satisfaction when evaluating options
When is liquid cooling used?
HEV PHEV EV
Low High
Air cooling Air cooling Liquid cooling
Without
PCM With
PCM
C-rate
Energy Density Heat Removal Intensity
Hybrid air/PCM cooling for hybrid and EV normal operation
PCM eliminates the need for active cooling and heating during the majority of operating time – combined with cabin air system for remainder of
situations
Ambient EV HEV
Cold Delays cool down. Adds minimal heating time/energy.
Delays cool down. Heat with engine heat.
Moderate No active management required Peak shaving of heat removal requirement
Hot Keeps battery below ambient during hot days
Peak shaving of heat removal requirement
AllCell system simplifies design
Al air channel
PCM-graphite
Copper mesh
Copper mesh enhances heat transfer to air
500 Wh LFP battery
Battery can be used more aggressively without needing liquid cooling
10 m/s air flow – 0.4 m3/s
45 40 35 30 25 20
Air only
PCM+Air
2 m/s air
