■ Weight Reduction Is Also Important in EVs
Adding thermal management components can sometimes improve cooling and safety.
In vehicles, however, weight is also important.
As weight increases, it affects
● Driving range
● Energy efficiency
● Driving performance
That is why there are limits to countermeasures such as
adding thick metal plates
or putting in large amounts of thermal insulation.
In other words, in EV thermal management, it is necessary to consider
thermal performance
safety
weight reduction
at the same time.
■ Thinner Films Are Advantageous for Weight Reduction
Insulating films.
Metal foils.
Adhesives.
If these can be made thinner, weight can be reduced.
Because battery packs have large areas,
even a difference of a few grams per sheet may become a large weight difference overall.
However, the thinner they become, the greater the effects of
● Tearing
● Burrs
● Foreign matter
● Application misalignment
In other words, thinner films and processing accuracy must be considered as a set.
■ Large-Area Processing Is Not Easy
Some components for EV batteries are large in size.
At large areas,
● Wrinkles
● Air bubbles
● Warping
● Dimensional changes
● Application misalignment
occur more easily.
A 0.2 mm shift in a small component
and a shift of several mm at the edge of a 1 m-class material mean different things.
At large areas, uniformity across the entire surface is important.
■ With Long Materials, Material Stretching Is Also a Problem
When processing insulating films or adhesives in reel form,
tension is applied to the material.
Thin films stretch under tension.
If processed while stretched, the dimensions may change after the tension is released.
In other words, for large EV components, dimensions on the processing machine alone are not enough.
Dimensional stability after completion must be checked.
■ Compatibility with Automation Is Extremely Important
EV batteries are mass-produced.
A single vehicle uses many cells and many functional components.
That is why there are limits to processes such as
applying insulating films by hand one at a time
or people aligning thermally conductive materials.
That is where automated application becomes important.
■ Reel Supply Makes Automation Easier
For small and medium components,
they are arranged at a constant pitch on a carrier
and supplied as reels.
This can be connected to processes in which automated machines
peel,
pick up,
correct position,
and apply.
In other words, for EV components,
not only the product shape, but also a supply format that is easy to automate is important.
■ Processing Design Is Also Important for Battery Insulating Covers
When placing insulating films or insulating covers around cells and modules,
they are not just simple rectangles.
● Holes
● Notches
● Folds
● Terminal clearances
● Partial adhesion
may be needed.
Furthermore,
not shifting during assembly,
not wrinkling,
and being handleable by automated machines
are also needed.
In other words, insulating covers must be designed not so much as insulating materials, but as functional parts that include the assembly process.
■ From "Applying Sheets" to "Supplying Components"
For example, suppose a customer performs the processes of
cutting insulating film,
peeling the release paper,
applying it to the cell,
and checking the position.
If the processing manufacturer goes as far as
● Processing to the required outer shape
● Making only the necessary parts adhesive
● A structure that is easy to peel
● Arranging on reels
customer processes can be reduced.
In other words, value expands from processing materials
to reducing customer processes.
■ Integrating Thermally Conductive, Insulating and Cushioning Materials
Around batteries,
thermally conductive materials,
insulating materials,
and cushioning materials
are sometimes placed separately.
Depending on the application,
it is also conceivable to laminate these in advance and supply them as
a single composite component.
For example, a configuration such as
Thermally conductive layer
＋
Insulating layer
＋
Adhesive layer
The customer only needs to apply it once.
The positional relationships are also determined in advance.
This is a good match for automated volume production.
■ However, Caution Is Needed with Combining
Thermally conductive materials.
Insulating materials.
Foams.
Adhesives.
These differ in
● Thermal expansion
● Hardness
● Thickness
● Compression characteristics
When laminated,
● Warping
● Interlayer delamination
● Thickness variation
may occur.
In other words, it is not the case that reducing the number of parts is always good.
The optimal range of integration must be decided while looking at the customer process and performance.
■ Thermosetting Materials Are Also Important in Batteries
In battery assembly, thermosetting materials are sometimes used for
● Bonding
● Fixing
● Insulation
● Sealing
Because they cure when heat is applied,
● Heating temperature
● Heating time
● Pressure
● Material storage
affect quality.
In other words, with batteries, not only thermal management after completion, but also how heat is used in the manufacturing process is important.
■ Combinations of UV Curing and Thermal Curing Are Also Conceivable
To increase productivity,
processes such as
temporarily fixing with UV
and then fully curing with heat
are also conceivable.
With such materials, it is necessary to consider
● Application position
● Curing conditions
● Thickness
● The range light can reach
The boundary between thermal management materials and bonding technologies may also come even closer in the future.
■ Will Heat Problems Disappear with Solid-State Batteries?
As a next-generation battery,
all-solid-state batteries
are attracting attention.
However, making the electrolyte solid does not mean all heat problems disappear.
Current flows.
There is internal resistance.
It charges and discharges.
As long as this is so, heat is generated.
Furthermore, if materials and structures change, the problems of
● Thermal conduction
● Contact pressure
● Thermal expansion
● Interfacial resistance
also change.
In other words, even with next-generation batteries, thermal management is necessary.
■ In All-Solid-State Batteries, the Relationship with Pressure Control Is Also Important
In all-solid-state batteries, structures are conceivable in which a certain pressure is important to maintain contact between materials.
Applying pressure may also change
● Contact state
● Electrical characteristics
● Thermal conduction
In other words,
electrical contact
thermal contact
mechanical pressure
must be considered together.
■ Thermal Management Is Also Needed for Sodium-Ion Batteries and Others
There are multiple candidates for next-generation batteries, such as
● All-solid-state batteries
● Sodium-ion batteries
● Other new types of storage batteries
Even if materials change,
heat is generated by charging and discharging.
Many cells are combined.
They are used safely.
These basic conditions do not change.
That is why the challenges of heat, insulation, fixing and sealing are likely to remain even if the battery type changes.
■ ESS Has Heat Problems Different from EVs
ESS also use many battery cells.
Unlike EVs, however, they have the characteristics that
● Vehicle weight constraints are relatively small
● They are stationary
● They are easy to scale up
● They operate over long periods
That is why
large-scale cooling,
fire protection,
thermal runaway propagation countermeasures,
and maintenance
are important.
■ In ESS, a Single Abnormality Easily Becomes Large-Scale
In large-scale ESS, a very large number of cells are placed close together.
That is why, if the abnormality of one cell spreads to its surroundings, it may lead to a major accident.
In other words, achieving both efficient heat dissipation in normal times and prevention of heat propagation in abnormal times is extremely important.
■ EVs and ESS Share Many Component Challenges
Even though their applications differ,
● Thermally conductive materials
● Insulating materials
● Flame-retardant materials
● Thermal insulation materials
● Seal materials
● Adhesives
● Metal foils
are needed.
In other words, from the perspective of a processing company like OTIS,
it is possible to target not finished-product markets, but common functional component challenges.
■ The Researcher's Perspective: The Heat Problem of Batteries Is Not Just "Maximum Temperature"
In battery thermal management,
it is not enough just to lower the maximum temperature.
What matters is
● Average temperature
● Temperature differences between cells
● Rate of temperature change
● Peak temperature during charging/discharging
● Heat propagation in abnormal situations
In other words, it is necessary to look not only at the temperature value, but at temperature distribution and change over time.
■ The Shop-Floor Perspective: Cells Can Be Hot Even When the Cooling Plate Is Cold
The coolant is normal.
The cooling plate is also cold.
Even so, cell temperatures are high.
In this case, possibly
● The thermally conductive material is lifting
● Contact pressure is insufficient
● The material thickness does not match
● There are air bubbles
● Only some cells are misaligned
In other words, the cooling equipment running and heat leaving the cells are not the same thing.
It is necessary to look at the entire heat path from the heat source to the coolant.
■ Things to Check at the Design Stage
In thermal management for EVs and next-generation batteries, at least the following need to be checked.
Cells
● How much heat is generated?
● How does it change during fast charging?
● How do characteristics change at high and low temperatures?
● Is there swelling due to charging/discharging?
● How does heat generation change after degradation?
Temperature uniformity
● How large are the temperature differences between cells?
● Is there a difference between the center and periphery of the pack?
● Is there a difference between the coolant inlet and outlet?
● Where are the hot spots?
Thermally conductive components
● How much thickness is required?
● Can it conform to gaps?
● Is the compression ratio appropriate?
● Can conformability be maintained over long periods?
● Is thermal resistance sufficiently low?
Insulation
● Where is insulation needed?
● Are there effects from metal burrs?
● Is the insulating material thickness appropriate?
● Can it be maintained after temperature cycling and vibration?
● Is there damage from foreign matter?
Safety
● Can heat propagation during abnormal heating be suppressed?
● Are thermal insulation and flame-retardant materials needed?
● Do they hinder heat dissipation in normal times?
● How will smoke and gas be handled?
Liquid cooling and sealing
● Where does the coolant flow?
● Are the gaskets appropriate?
● Is the compression ratio appropriate?
● Is there material compatibility with the coolant?
● Will it not leak after vibration?
Adhesion and fixing
● Will it shift at high temperatures?
● Will it peel at low temperatures?
● Is long-term creep a problem?
● Does the adhesive layer become thermal resistance?
Volume production
● Can it be applied automatically?
● Can it be supplied on reels?
● Can it be processed without wrinkles even at large areas?
● Can positional accuracy be reproduced in volume production?
● Can it be inspected by images?
In EV batteries, it is necessary to design heat, insulation, flame retardancy, sealing, adhesion and volume production at the same time.
■ OTIS's Perspective: View EV Batteries Not as a "Thermal Materials Market," but as a "Composite Functional Components Market"
OTIS is
not a cell manufacturer.
Not a battery pack manufacturer.
Not a cooling plate manufacturer.
Not a BMS manufacturer.
However, large amounts of thin-film, sheet, adhesive and metal components are used around batteries.
For example,
● Thermally conductive sheets
● Insulating films
● Insulating covers
● Flame-retardant materials
● Thermal insulation materials
● Foams
● Seal materials
● Adhesives
● Copper foil
● Aluminum foil
● Sensor fixing materials
And in batteries, rather than single functions alone, combinations such as
heat + insulation
heat + cushioning
insulation + adhesion
sealing + flame retardancy
thermal insulation + fixing are common.
This is where OTIS’s point of contact lies.
■ Where OTIS Should Aim
There is no need to target the finished vehicle itself.
There is no need to develop cells themselves either.
What to target is the common challenges that arise repeatedly inside batteries.
For example,
● Thermally conductive materials between cells and cooling plates
● Insulating materials around cooling plates
● Insulating films around busbars
● Insulating covers around cells
● Flame-retardant and thermal insulation components between cells
● Cushioning and swelling-absorption materials
● Perimeter seal materials for packs
● Sensor fixing components
● Copper foil and aluminum foil components
● Reel components for automated application
■ "Reducing One Process" Rather Than "Selling One Sheet of Material"
For example, a customer has the processes of
applying insulating material,
then applying cushioning material,
then applying adhesive.
If these can be supplied as an integrated component, customer processes may be reduced.
In other words, the value lies not only in the processing unit price, but also in reducing customer processes.
In a mass-production market like EVs, this is highly significant.
■ A Good Match for Reel Components
Small insulating and adhesive components
are supplied on reels at a constant pitch.
On the customer’s equipment,
automated peeling,
automated pick-up,
and automated application are performed.
This can lead to
● Less manual labor
● Improved positional accuracy
● Shorter takt time
● Less foreign matter
In other words, for OTIS, EV batteries are also a market where material processing and
automated supply are easy to combine.
■ Large-Area Components Are Also an Important Theme for OTIS
On the other hand, with
● Large insulating covers
● Large-area heat dissipation sheets
● Large gaskets
there are difficulties different from microfabrication:
● Wrinkles
● Warping
● Tension
● Dimensional stability
● Lamination accuracy
In other words, in EVs, processing technology is needed for both small, high-precision components and large-area, uniform components.
■ What OTIS Can Do
At OTIS, through
● Thermally conductive sheet processing
● TIM and gap filler processing
● Insulating film processing
● Insulating cover processing
● Thermal insulation material processing
● Flame-retardant material processing
● Foam and cushioning material processing
● Gasket and seal material processing
● Adhesive processing
● Copper foil processing
● Aluminum foil processing
● Sensor fixing component processing
● High-precision die-cutting
● Large-area die-cutting
● High-precision lamination
● Lamination of dissimilar materials
● Partial lamination
● Half-cut processing
● Reel-to-reel processing
● Supply formats for automated application
● Integration of multiple functional materials
● Image inspection
● Volume production control including traceability
we may be able to contribute to
turning functional materials for EVs and next-generation batteries into parts that can be used in volume production processes.
■ Outside OTIS's Expertise
OTIS is not a company that specializes in
● Development of battery cells themselves
● Chemical design of battery materials
● BMS design
● Cooling plate flow path design
● Thermal design of entire battery packs
● Thermal runaway analysis itself
● Dedicated CFD analysis
● Thermal management design of entire vehicles
However, by working with
● Cell manufacturers
● Material manufacturers
● Battery pack manufacturers
● Cooling equipment manufacturers
● Automation equipment manufacturers
we may be able to contribute in the area of
making the functional components responsible for heat, insulation, flame retardancy, sealing and adhesion work in volume production.
■ Markets Where This Technology Will Be Important
★★★★★ EVs
★★★★★ Next-generation lithium-ion batteries
★★★★★ All-solid-state batteries
★★★★★ ESS
★★★★★ Fast-charging systems
★★★★☆ Hybrid vehicles
★★★★☆ Industrial storage batteries
★★★★☆ Electric construction machinery and logistics equipment
★★★★☆ Batteries for robots
■ Summary
Battery thermal management is not “cooling,” but a technology for “creating safety while managing temperature”
In EVs and next-generation batteries,
high output,
large capacity,
fast charging,
long life,
and weight reduction
are required at the same time.
As a result, heat problems become even more important.
However, with batteries, it is not enough to simply cool them.
Not getting too hot.
Not getting too cold.
Reducing temperature differences between cells.
Cooling even during fast charging.
Releasing heat to the cooling plate in normal times.
Not transferring heat to neighboring cells in abnormal times.
Insulating electricity.
Not leaking coolant.
Maintaining performance even under vibration and temperature cycling.
These must be achieved at the same time.
In other words, in EV batteries,
thermally conductive materials,
insulating materials,
thermal insulation materials,
flame-retardant materials,
seal materials,
adhesives,
cushioning materials,
and metal foils,
components with functions that at first glance seem contradictory, coexist.
That is why battery thermal design is not choosing the material with the highest thermal conductivity.
It is designing
where to let heat flow,
where to stop heat,
where to stop electricity,
where to stop liquid,
and where to absorb cell movement.
And to bring this complex functionality into volume production,
materials alone are not enough.
Shape.
Thickness.
Lamination.
Position.
Compression ratio.
Supply format.
Automation. These must all be considered.
What OTIS should target is not the battery itself.
Nor the cooling plate itself.
It is the common challenges needed in between: heat, insulation, flame retardancy, sealing, adhesion, thin films and automation.
Even if next-generation batteries change, even if cell materials change, these challenges remain.
That is why the EV and next-generation battery market is an area in which OTIS can evolve from “a company that processes materials”
into “a functional component company that makes battery volume production processes work”.
Column Supervisor: Koji Kakumoto (President, OTIS Co., Ltd.)
After studying abroad and working in planning and development at a trading company, he joined OTIS Co., Ltd. in 2011. While primarily working in the Corporate Planning Department, he has also served concurrently in manufacturing and technical divisions, and since 2018 has served as President, working to drive business growth and strengthen the organization.
This article is a general technical explanation intended for educational purposes and does not refer to any specific company, product, or technology.
