Customizing compression range tohelp control pressure between cells
and extend EV battery lifespanDavid Gries, 3M Automotive and Aerospace Solutions Division

Abstract
Electric vehicle (EV) battery designs are constantly
evolving, making pressure management a delicate
balancing act. Proper between-cell cushioningis needed to help accommodate volumetric
expansion that can occur over the lifespan ofthe cells. However, cushioning materials take up
precious space that could otherwise be devoted
to increasing battery energy density. This paper
explores how to strike this balance in pouch cellbattery designs by customizing the compression
range of the cushioning material. An advanced
cushioning material from 3M can be tailored
to precise design needs to provide a wide
compression range at relatively low thicknesses.
Consistent pressure can be achieved even withlimited between-cell space, helping EV OEMs
protect cells, ensure reliable performance andextend EV battery lifespan.

Introduction
As the electric vehicle market grows, more attention
is being paid to lithium-ion battery design. To promote
the wide adoption of EVs, OEMs are striving to increase
battery density and extend driving range, all while easing
consumer concerns about battery failure and thermal
runaway.

These are competing priorities because increasing batteryenergy density requires larger cell volumes, leaving little
space for added safety measures. Larger cells needvariable pressure control across the face to account forvolumetric expansion that can occur over the lifespan of
the cells: swelling, breathing, etc. While the right betweencell cushioning can provide the needed compression, any
battery space dedicated to cushioning is dead space that
does not contribute to energy density or driving range.
Achieving effective pressure control while minimizing deadspace and maximizing energy density is thus a fundamental
challenge of modern EV battery design. Effective, spaceefficient cushioning materials are needed to help protect
cells during expansion and help increase battery lifespan.

The importance of compression between cells
All lithium-ion EV battery cell types — cylindrical,
prismatic and pouch — experience volumetric expansion.
As cells charge and discharge, they expand and contract.
Expansion can be observed due to factors including celltype, electrode material, voltages and more. Cells can also
volumetrically change over time due to cycling-relatedchanges to electrodes such as lithium dendrite growth.
A cell’s ability to maintain charging capacity throughout
its lifespan thus depends on whether the between-cellcushioning materials can provide proper compression to
help accommodate volumetric expansion. Without this,lithium-ion batteries will have much shorter lifespans.

Constraining cells so they cannot move is not an option.
Cells must be allowed to expand and contract throughout
their lifespans, a process known as cell breathing [1]. Rigid
constraints that do not account for breathing can create somuch internal force that electrodes within the cells can be
crushed or shattered, leading to battery end of life.
Allowing cells to expand and contract free of constraint is
not optimal either. Cycling between charge and discharge
will eventually create a rippling on the electrodes. This canresult in delamination — loss of contact between the solid
electrolyte interface layer and the electrode — as well as
reduced capacity retention [2].

development of solid-state batteries, which will likely
involve substantially higher between-cell pressures.

Compression force deflection
In sum, to accommodate volumetric cell expansion,
improve uniform cell performance and extend EV battery
lifespan, cushioning materials must provide consistent
restoring force between cells as they expand [3]. Thisability to apply force is called compression force deflection(CFD). CFD is measured in kPa and varies based oncompression percentage, or the percent change incushioning material thickness (Δt) relative to its initial
thickness (tinitial). The larger the compression percentage,
the more CFD is exerted.

Compressive StressForce

Area

CompressiveStrain
Figure 1: Cell breathing causes small cyclic expansion
and contraction; cell swelling causes large, gradual andirreversible expansion.
The optimal solution is to carefully customize between-cellcompression to accommodate cell expansion and meet theneeds of specific cell and battery designs. Compression
requirements vary greatly by cell form factor andpackaging, with each cell type posing unique challenges.
Prismatic cells, for example, are contained within rigid
metal housings. These housings hold the cells in placeand can accommodate small forces without the need forcushioning materials. However, as cells expand over time,cushioning may be needed to accommodate higher forcesand ensure consistent contact of the electrolyte with theelectrodes.
Pouch cells, by contrast, possess no rigid housings at all.
They exhibit a strong cyclic behavior of expansion andcontraction, and a certain minimum pressure is needed
to hold them in place at all times. Based on customer
feedback received by 3M, pouch cells typically require
20 kPa of back pressure at beginning of life. By end of life,
following significant cell expansion, this pressure can be as
high as 300–500 kPa. Pouch cells thus require cushioning
materials with a very wide compression range.
Additionally, the future will likely see the continued

t t
initialFigure 2: CFD is compressive stress, or the force divided by
the area of the foam; compression percentage is a form ofcompressive strain, defined as Δt divided by tinitial.
CFD is thus a form of stress, while compression
percentage is a form of strain. CFD and compression
percentage are used to understand the acceptable
expansion of a cell, with force versus total displacement as
the key parameter. An effective between-cell cushioning
material should provide relatively consistent CFD over abroad range of displacements.

Optimizing between-cell cushioning forconsistent CFD
An advanced between-cell cushioning foam has beendeveloped by 3M to help protect pouch cells as they
expand and contract. 3M™ Cell Expansion Foam
SJCEF Series is a polymeric foam featuring a nonlinear
compressive force response. It can help EV OEMs achieve
consistent pressure control across a wide compressionrange.

words, the foam exerts nearly constant force back on cells
independently of how much the cells expand and deflect
the foam.
A wide compression plateau is one of the most importantfeatures of a space-efficient cushioning material. The wider
the plateau, the larger the design window and smaller thebetween-cell gap. Ordinarily, a thick cushioning material
is needed for a wide compression plateau. However, 3M
Cell Expansion Foam SJCEF Series features a microcellular
structure to help provide a wide compression plateau at
thicknesses of 1.0–2.0 mm. This broad thickness range,
including thin profiles, helps accommodate a varietyof cell designs while reducing the footprint of non-cellcomponents.
Figure 3: 3M™ Cell Expansion Foam SJCEF Series.

3M Cell Expansion Foam SJCEF Series can be customized
to precise design needs to provide a wide compression
plateau. During installation, the foam is compressed
through the linear elastic region until the compression
plateau is reached, which is the operational range of thematerial. Staying within this range helps maintain effective
and consistent cushioning throughout the lifespan of thecells. This is crucial for addressing evolving battery packcompression needs and enabling the next generation of EV
battery designs.

500

Compression Load (kPa)400

3M H2H-0XX-LD
3M SJCEF-0XX-B2300

3M SJCEF-0XX-SR-B1200

1000

Additional product details
0102030

40

50

60

70Compression (%)

Figure 4: The stress–strain curve for various expansion foammaterials from 3M.
Consider the stress–strain curve in Figure 4, which shows
the compression performance of two different samples of3M™ Cell Expansion Foam SJCEF Series and one sampleof 3M™ Cell Expansion Foam H2H.
•For low compression (up to around 20%), the foam
exhibits elastic behavior. There is a roughly linear
relation between compression and CFD.

•For moderate to high compression (around 20% to60%), the cell walls of the foam buckle and the stress–
strain curve reaches a plateau. CFD remains largely
constant relative to compression.

•For very high compression (above 60%) there is analmost exponential increase in CFD. This extreme
region, where the foam cell walls collapse and comeinto contact with one another, is called densification.

The plateau region of the curve is key. In this region, called
the compression plateau, the foam applies relatively
consistent CFD across a wide compression range. In other

3M Cell Expansion Foam SJCEF Series products areflame retardant and can be customized to meet OEM
specifications. A wide range of CFD and customizable
compression plateau can help ensure reliable performance
during repeated charging and discharging cycles over thecell lifespans. Moreover, the foam is highly resilient.
The foam features a self-adhering surface to enableinstallation without requiring additional adhesives.
This helps lower costs and reduce process steps while
facilitating rework and repositioning during assembly. See
Table 1 for more details.
Table 1: Additional details on 3M Cell Expansion Foam
SJCEF Series.
Property

Value

Material

Microcellular polyurethane

ColorBlack

Release liner

Silicone-coated polyester film 0.075 mm

Foam thickness

1.0–2.0 mm

Adhesion

30–80 gf/in

Roll size

550–1,035 mm (width) × 50–100 m (length)

For additional details on foam thicknesses andcustomization options, please contact a 3M applicationengineer.

Innovation born of customer needs
For nearly a century, automotive industry leaders havetapped into the material science expertise of 3M tohelp them overcome key design challenges. Our mostsuccessful innovations are infused with customer insights
throughout the development process, and 3M Cell
Expansion Foam SJCEF is a prime example. By providing
a wide compression plateau at relatively low thicknesses,
this advanced cushioning material can help OEMs
meet pressure control requirements and ensure reliable
performance, all while minimizing the footprint of noncell components and maintaining high battery energy
density. In a world of ever-evolving EV battery designs,
where every inch of space counts, striking this balance isessential.
3M continues to develop relationships with our EV OEM
customers, and our scientists collaborate directly withthem to address their design specifications and help solve
their unique challenges. 3M can respond quickly, tailoringmaterial properties to develop EV battery solutions thatmeet specific application needs. 3M is committed toworking bench-to-bench with customers to ensure
successful implementation.

We'll help you drive the futureof eMobility.
To learn more visit 3M.com/evbattery.

References[1] J. Cannarella and C. B. Arnold, “Stress evolution and capacity fade in constrained
lithium-ion pouch cells,” J. Power Sources, vol. 245, pp. 745–751, Jan. 2014, doi:
10.1016/j.jpowsour.2013.06.165.
[2] V. Müller et al., “Effects of Mechanical Compression on the Aging and theExpansion Behavior of Si/C-Composite|NMC811 in Different Lithium-Ion Battery
Cell Formats,” J. Electrochem. Soc., vol. 166, no. 15, pp. A3796–A3805, Nov.
2019, doi: 10.1149/2.1121915jes.
[3] A. Barai et al., “The effect of external compressive loads on the cycle lifetime oflithium-ion pouch cells,” J. Energy Storage, vol. 13, pp. 211–219, Oct. 2017, doi:
10.1016/j.est.2017.07.021.
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