Bret Trimmer NeoGraf Solutions

1. eGraf® | GraFoil® | GrafGuard® | neograf.com
Fast Charging and Extended Cell Lifetimes through
Advanced Thermal Management
Bret A Trimmer
Applications Engineering Manager
NeoGraf Solutions, LLC
www.neograf.com
May 2nd, 2019
Frankfurt, Germany

2. eGraf® | GraFoil® | GrafGuard® | neograf.com
The main obstacle to consistently fast charging a battery pack
is the inability to remove heat as fast is it is generated…
The main obstacle to obtaining maximum battery pack cycle
lifetimes is overheating and uneven heating of the individual
cells …
Thermal Management of Pouch Cell Battery Packs

3. eGraf® | GraFoil® | GrafGuard® | neograf.com
Because of their high surface area to volume, pouch cells
are the most feasible for effective thermal management.
Thermal Management of Pouch Cell Battery Packs
Cylindrical Prismatic Can Pouch

4. eGraf® | GraFoil® | GrafGuard® | neograf.com
Thermal Management of Pouch Cell Battery Packs
• Battery Pack Goals:
• Maximum Charge / Discharge Rate (2C, 4C, 6C?)
• Cell Lifetime (3,000 cycles, 5,000 cycles, 10,000 cycles?)
• Kilometers / Miles / Operating-Time per Charge
• Safety (Propagation Prevention?)
The common strategy of manufacturers is to provide “just-enough”
thermal management to achieve the basic goals of the battery pack

5. eGraf® | GraFoil® | GrafGuard® | neograf.com
Fast
Charging Rate
• • • •• •
Thermal Management of Pouch Cell Battery Packs
Less Thermal Management More Thermal Management
Propagation
Control
Extended
Cell Lifetime
Average
Cell Lifetime
Short
Cell Lifetime
Moderate
Charging Rate
Slow
Charging Rate
•
Consumer Electronics
Automotive / Grid Storage
Maritime
Propagation
Control
Graphite RangeAluminum Range
Goals

6. eGraf® | GraFoil® | GrafGuard® | neograf.com
Thermal Management of Pouch Cell Battery Packs
Pouch cells already have remarkable cycle lifetime potentials…
But how do you achieve these values in an EV?
The answer is Thermal Management
www.xaltenergy.com www.laclanche.com

7. eGraf® | GraFoil® | GrafGuard® | neograf.com
Thermal Management of Pouch Cell Battery Packs
Fast charging and extended cell lifetimes are determined by the
cell temperature and the cell temperature gradient.
The cell temperature goal is ~25°C (depending on cell chemistry)
The cell gradient goal is ≤ 2 °C
0.25 mm
Graphite
Cooling Fin
0.25 mm
Aluminum
Cooling Fin

8. eGraf® | GraFoil® | GrafGuard® | neograf.com
The most effective way to achieve temperature control in the
individual cells is by Spreading the heat to an external cold plate /
heat sink…
• Thermally conductive materials evenly spread excess heat across the
surface of each cell, maintaining an even cell temperature gradient
• The heat is then spread to an external cold plate or heat sink
• Flexible Graphite Cooling Fins (0.25 – 1.0mm) or Aluminum plates (1.0 -
3.0 mm) are the most common heat spreading materials
• Other materials used in the module -- Dielectric sealing films, thermal
pads, foam pads, Aerogel materials, mica, FR4, FRB®, others…
Thermal Management of Pouch Cell Battery Packs

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Advantages of Spreading heat to a heat sink / cold plate
• Ability to continuously fast charge
• Extended cell cycle lifetimes
• Propagation control
Disadvantages of using Aluminum over graphite for spreading heat
• Low energy density/specific energy due to the thick/heavy aluminum
• Greater pack weight / Greater pack size
If graphite is used instead of aluminum, the pack energy density / specific
energy is significantly improved – resulting in greater driving range…
Thermal Management of Pouch Cell Battery Packs

10. eGraf® | GraFoil® | GrafGuard® | neograf.com
Traditional Thermal Management of Pouch Cell Packs
The problem with using aluminum for fast charging,
extended cell lifetimes, and propagation control is the
added weight and thickness of the aluminum…

11. eGraf® | GraFoil® | GrafGuard® | neograf.com
• Common aluminum alloys
have high densities (2.7g/cm3)
and low thermal conductivities
(~200 W/m·K)
• Graphite has a low density
(1.7g/cm3) and high thermal
conductivity (≥400 W/m·K)
• To spread the same amount of
heat as aluminum, graphite
has ~50% of the thickness
and ~30% of the weight
Finding a Solution to the Aluminum Weight/Thickness Problem
Aluminum WeightGraphite Weight
For the same heat
spreading as aluminum,
graphite has 50% of the
thickness and 30% of the
weight

12. eGraf® | GraFoil® | GrafGuard® | neograf.com
Battery Thermal Management Example
• Flexible graphite cooling fins
replace aluminum to remove
heat from the pouch cells and
spread the heat to an external
heat sink or cold plate
• The graphite constantly presses
against the cell, reducing
thermal gradients within the cell
• In the event of a cell failure, the
non-flammable graphite
spreads the heat to the external
heat sinks, preventing
propagation
• The cold plates can either be
on the bottom or the sides

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Pouch Cell Module Cooling
Typical Configurations
Drawings from NGS patent US 9,774,063 B2

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• If the current design uses 250 mm x
215 mm x 1.5 mm of aluminum per
cell, switching to graphite results in
a weight reduction of 150 g per cell
• For a module with 24 cells,
switching to graphite makes the
module 18 mm shorter and weigh
3.6 kg less
• For a 6 module pack, switching to
graphite results in a pack weight
reduction of 21.5 kg
Graphite Improves Energy Density/Specific Energy over Aluminum

15. eGraf® | GraFoil® | GrafGuard® | neograf.com
What are Flexible Graphite Cooling Fins?
• Flexible graphite is a thin, heat spreading
material, made from thousands of graphene
layers, sealed in thin dielectric plastics
• Over the last 15 years, graphite has become
the standard heat spreader in the electronics
industry to make mobile phones, tablets,
televisions, and laptops thinner and lighter

16. eGraf® | GraFoil® | GrafGuard® | neograf.com
Graphite Cooling Fins use in Battery Thermal Management
• Graphite cooling fins are
used to increase energy
density / specific energy in
most of the pouch cell Li ion
marine battery applications
sold today
• Flexible graphite is well established in Li ion batteries for the marine industry for
enabling long cell life (6 - 10 years) and consistent fast charging (4C – 6C)
• Flexible graphite allows the
batteries to pass mandatory
marine propagation
standards, such as the
NMA and DNV•GL
Images: Corvus.com

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• Graphite is chemically inert to almost
any substance
• Graphite is non-flammable
• UL94V-O flammability rated
• Graphite contain no hazardous materials
• RoHS, REACH, and Lead Free
compliant
• Easy disposal of waste
• Graphite is easy to cut and easy to
laminate with adhesives and plastics
Flexible Graphite Basics

18. eGraf® | GraFoil® | GrafGuard® | neograf.com
1881
Boulton
Carbon
Founded
• •
1917
Union Carbide &
Carbon
Organized
National Carbon Union Carbide
1995
UCAR
International
Organized
•
2001
GrafTech
International
Organized
••
1886
National
Carbon
Organized
2017
NeoGraf
Solutions
Organized
GrafTech
•
UCAR
A 138 Year History of Carbon and Graphite
125 years in the same manufacturing facility…
NeoGraf Solutions| | | | |Boulton

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Our Battery History
1896 1910’s
1940’s 1956
1958 1980’s
2010’s

20. eGraf® | GraFoil® | GrafGuard® | neograf.com
Fast Charging and Extended Cell Lifetimes through
Advanced Thermal Management
Bret A Trimmer
Applications Engineering Manager
NeoGraf Solutions, LLC
btrimmer@neograf.com
www.neograf.com
+1 216.526.3754