{"id":2373,"date":"2026-09-23T13:17:31","date_gmt":"2026-09-23T13:17:31","guid":{"rendered":"https:\/\/haktak.com\/?p=2373"},"modified":"2026-09-23T13:17:32","modified_gmt":"2026-09-23T13:17:32","slug":"gap-filler-for-battery-packs","status":"publish","type":"post","link":"https:\/\/haktak.com\/fr\/gap-filler-for-battery-packs\/","title":{"rendered":"Mat\u00e9riau de calage pour blocs-batteries : consid\u00e9rations thermiques et m\u00e9caniques"},"content":{"rendered":"
\n

On a drawing, a battery module and its cooling plate look like two neat, flat blocks. On the assembly line? Not quite. The tray has a slight bow. Cell heights vary. A fastener pulls one corner down before the others.<\/p>\n\n\n\n

\"battery<\/figure>\n\n\n\n

A thermal gap filler bridges those mismatches. It replaces air with a better path for heat to reach the cold plate. But that is only half its job. The material also sits in a mechanical joint. It must make contact without loading cells, welds, frames or electrical barriers beyond their limits.<\/p>\n\n\n\n

So, how do you choose one? Start with the heat path, then measure the gap and the force needed to close it. A big W\/m\u00b7K figure comes later.<\/p>\n\n\n\n

Start With the Battery Heat Path<\/h2>\n\n\n\n

In many EV designs, heat moves from cells through a module structure and thermal interface into a liquid-cooled plate. In others, the cells sit closer to the plate. The gap filler may contact a cell casing, a module base, a coated tray or another intermediate layer. Those are not interchangeable interfaces.<\/p>\n\n\n\n

A pouch cell, for example, can present a broad surface and a swelling constraint. A prismatic cell has its own casing, support and expansion behavior. Cylindrical-cell packs often use a very different route for heat to leave each cell. Cell-to-pack and module-to-pack layouts change the load path too.<\/p>\n\n\n\n

Before discussing materials, draw a simple stack-up from heat source to coolant. Label every layer. Ask which layer is actually responsible for the temperature rise. If the cold plate has poor flow distribution, changing the filler will not fix the whole system.<\/p>\n\n\n\n

HAKTAK EV battery thermal materials overview<\/a> maps the wider application. Here, the focus is narrower: the gap-filling joint and what it does to the rest of the pack.<\/p>\n\n\n\n

\"battery<\/figure>\n\n\n\n

Gap Filler for Battery Packs Has Two Budgets<\/h2>\n\n\n\n

Think of this as packing a suitcase with a delicate glass item. You want the padding to touch the glass, but you do not want to force the lid shut on it. A battery thermal interface has the same awkward balance, only with much higher stakes.<\/p>\n\n\n\n

The Thermal Budget: Conductivity Is Not the Whole Story<\/h3>\n\n\n\n

Thermal conductivity describes the bulk material. It is not the thermal resistance of the installed joint. For a simple, uniform layer, bulk resistance increases with thickness and falls as conductivity or contact area increases: R = t \/ (k \u00d7 A).<\/p>\n\n\n\n

Real packs add contact resistance at each surface. A dry patch, trapped air, uneven wet-out or a thicker-than-planned bond line can erase the advantage of a more conductive grade. The metal tray, coatings, cell casing and coolant circuit add resistance as well.<\/p>\n\n\n\n

That is why the useful questions are practical ones: What is the temperature of the hottest cell under the relevant duty cycle? How wide is the cell-to-cell temperature spread? What is the filler thickness after<\/em> assembly and aging?<\/p>\n\n\n\n

A bond-line thickness guide<\/a> explains the thickness side in more detail. For this article, the point is simple: compare candidates in the same geometry, at comparable pressure and temperature, not by mixing unmatched datasheet numbers.<\/p>\n\n\n\n

The Mechanical Budget: Closing Force Has to Go Somewhere<\/h3>\n\n\n\n

A liquid filler may spread under low initial force. A preformed pad needs a defined amount of compression. Once a two-part liquid cures, its modulus and adhesion affect how it responds to movement. None of these facts tells you the load on the cell by itself.<\/p>\n\n\n\n

A quick scale check helps. Pressure of 20 kPa across 0.05 m\u00b2 produces 1,000 N of total force. Those numbers are illustrative, non<\/strong> a target for a battery design. The point is that a gentle-looking pressure over a wide module becomes a large load.<\/p>\n\n\n\n

Where does it go? Through fasteners, frames, cell supports, welds and the cold plate. Hard stops and housing stiffness matter as much as material softness. A thermomechanical battery simulation study<\/a> illustrates why pack temperature, deformation and casing stress belong in the same conversation.<\/p>\n\n\n\n

Cell swelling adds another moving piece. Its amount and direction depend on cell format, state of charge, age, temperature and design. Do not assign a generic \u201cswelling allowance\u201d to every pack. Use cell-supplier limits and the actual restraint design. The filler may accommodate motion; it should not be assumed to control cell pressure on its own.<\/p>\n\n\n\n

\"battery<\/figure>\n\n\n\n

Measure the Worst-Case Gap Before Picking a Grade<\/h2>\n\n\n\n

The nominal CAD gap is one number. Production gives you a range.<\/p>\n\n\n\n

Measure the minimum, nominal and maximum gap on production-intent parts. Include cell and module dimensions, tray flatness, plate bow, coatings, adhesive layers, locating features and fastener sequence. Check several positions, not just the easiest corner to reach.<\/p>\n\n\n\n

At the maximum<\/strong> gap, the material must still reach both surfaces. At the minimum<\/strong> gap, it must not create an excessive closing load or squeeze into an electrical keep-out area. After cycling and cell movement, it needs to keep contact.<\/p>\n\n\n\n

A closing sequence deserves its own trial. If one side of a large module touches first, a bead can trap air instead of pushing it toward an exit. Think of laying down a large phone screen protector: the direction you press changes where the bubbles go. Battery joints are less forgiving.<\/p>\n\n\n\n

For a worked approach to min\/max tolerances, see choosing gap filler thickness<\/a>. Here, record the final installed bond line and the force used to get there. Both are specifications, not afterthoughts.<\/p>\n\n\n\n

\"battery<\/figure>\n\n\n\n

Choose Material Behavior, Not Just a Chemistry Name<\/h2>\n\n\n\n

\u201cGap filler\u201d can mean a one-part dispensable gel, a non-curing compound, a two-part cure-in-place elastomer or even a soft pad. Ask how the product arrives, flows, cures and comes apart. The name on the bucket is not enough.<\/p>\n\n\n\n

Format de mat\u00e9riau<\/td>Why a pack designer may consider it<\/td>Question to settle before approval<\/td><\/tr>
One-part, non-curing filler<\/td>No on-line mixing; potential for easier disassembly<\/td>Will it slump, bleed or move at service temperature and orientation?<\/td><\/tr>
Two-part, cure-in-place filler<\/td>Conforms during closure, then develops a stable soft structure<\/td>Are mix ratio, cure, aged modulus and removal acceptable?<\/td><\/tr>
Putty-like material or soft pad<\/td>Useful for localized or more serviceable interfaces<\/td>Can it cover worst-case gaps at an acceptable force?<\/td><\/tr>
Thermally conductive structural adhesive<\/td>Used when bonding is an explicit load-bearing requirement<\/td>Have strength, fracture behavior and end-of-life removal been designed separately?<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n

Silicone and non-silicone polymers are both used. Filled formulations may contain alumina, boron nitride or other thermally conductive particles. More filler can change density, flow, equipment wear and mechanical response along with thermal performance. \u201cSilicone-free\u201d does not automatically mean electrically safer or easier to recycle.<\/p>\n\n\n\n

HAKTAK liquid thermal gap fillers<\/a> are one material route; battery thermal putty considerations<\/a> explain a narrower material form. If the key choice is a preformed sheet versus a dispenser, the separate liquid gap filler versus thermal pad comparison<\/a> goes deeper than we need here.<\/p>\n\n\n\n

One useful market example shows why numbers need labels. Henkel reports 1.7 W\/m\u00b7K<\/strong> conductivity and dispensing above 40 cc\/s<\/strong> for its named Bergquist TGF 2030APS grade, alongside a separate polyurethane-based conductive adhesive. These are that supplier’s product-specific claims<\/a>, not a benchmark for every filler. Neither dispense rate nor conductivity alone decides whether the material suits your pack.<\/p>\n\n\n\n

\"battery<\/figure>\n\n\n\n

When Heat Transfer and Mechanical Limits Disagree<\/h2>\n\n\n\n

A good interface should cool the cells et<\/em> leave the pack structure healthy. If either fails, find the mechanism before swapping to a higher-spec material.<\/p>\n\n\n\n

Ce que vous observez<\/td>Likely mechanism<\/td>First controlled check<\/td>Possible correction to test<\/td><\/tr>
Hot spot despite high W\/m\u00b7K<\/td>Excess bond line, poor wet-out or void<\/td>Map gap and inspect contact\/coverage<\/td>Revise volume, pattern, surface or hardware flatness<\/td><\/tr>
Initial cooling passes, aged unit warms<\/td>Contact loss, separation or material movement<\/td>Compare before\/after impedance and teardown<\/td>Adjust grade, retention or load path<\/td><\/tr>
Cell or module bows on closing<\/td>Excess pressure or poor hard-stop design<\/td>Measure closure force and displacement<\/td>Change stiffness, thickness or stops<\/td><\/tr>
Filler reaches busbars or keep-outs<\/td>Too much material or wrong squeeze direction<\/td>Weigh shot and inspect closure sequence<\/td>Change bead position, volume or escape route<\/td><\/tr>
Good center contact, weak edges<\/td>Tray warp or edge lift<\/td>Measure gap map and contact imprint<\/td>Revisit support, fasteners and bead layout<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n

Change one major variable at a time. If you change the material, shot mass, bolt torque and plate flatness together, a better temperature result tells you very little about why<\/em> it improved.<\/p>\n\n\n\n

\"battery<\/figure>\n\n\n\n

Dispensing Is Part of the Battery Design<\/h2>\n\n\n\n

A sample cartridge can produce a lovely prototype. A full production line has hoses, temperature changes, stop-start cycles and operators on different shifts. The specification has to survive those details.<\/p>\n\n\n\n

Give the Material Somewhere to Go\u2014and Air Somewhere to Leave<\/h3>\n\n\n\n

Define shot mass or volume, bead width, nozzle height, start\/stop positions, acceptable gaps in the pattern and time between dispensing and closure. Keep filler out of vents, seals, electrical terminals and service features.<\/p>\n\n\n\n

Design an air-escape route. A bead that forms a sealed loop may trap a pocket when the module comes down. Slow closure, a revised pattern or a different closing direction might solve the problem. But confirm it by inspection on a representative large interface. Looking at a bead before closure does not prove what happened underneath.<\/p>\n\n\n\n

Vision inspection can check location and approximate width. A mass check catches some missed or excessive shots. Neither guarantees hidden coverage. For process qualification, use representative teardown, imaging or another validated inspection method.<\/p>\n\n\n\n

Two-Part Fillers Add Ratio and Cure Controls<\/h3>\n\n\n\n

With a 2K product, specify A\/B ratio, acceptable pressure, static-mixer life, purge after idle time, working time and cure conditions. Verify cure through the thickest actual bead. A thin laboratory coupon may not behave like the pack interface.<\/p>\n\n\n\n

Also count the real applied cost: material left in pails, purge, machine wear, downtime, inspection, scrap and rework. Price per kilogram does not tell the whole story. Well, not even close.<\/p>\n\n\n\n

Traceability helps when a pack fails later. Record material lot, process recipe, dispense mass, mixer change and relevant cure conditions. That evidence makes a failure investigation much less of a guessing game.<\/p>\n\n\n\n

\"battery<\/figure>\n\n\n\n

Insulation, Aging and End-of-Life Service<\/h2>\n\n\n\n

A ceramic-filled gap filler can be electrically insulating. That does non<\/strong> mean it alone supplies every required electrical barrier. Test dielectric behavior at the production thickness, after aging, and at the edges where material may thin or move. Check compatibility with adjacent coatings, cell surfaces and any plausible coolant exposure.<\/p>\n\n\n\n

Likewise, normal heat transfer and thermal-runaway mitigation are different tasks. A material that conducts operating heat to a cold plate should not be casually described as a fire barrier or a guarantee against propagation. Pack-level safety design must address that separately.<\/p>\n\n\n\n

Aged behavior is where seemingly similar materials part company. Thermal cycling can change adhesion and contact. Vibration can expose poor retention. A non-curing material may slump or bleed; a soft pad can relax under compression; a cured product can stiffen, separate or make disassembly difficult. Those are possible mechanisms<\/em>, not automatic failures for every grade.<\/p>\n\n\n\n

Ask how the pack will be opened. Can the module be lifted without damage? Does filler stay on one surface or tear across both? Can it be removed from a coated cold plate without scraping away the coating? If a structural adhesive is doing double duty, the disassembly plan becomes especially important.<\/p>\n\n\n\n

\"battery<\/figure>\n\n\n\n

Validate the Joint You Will Actually Build<\/h2>\n\n\n\n

Start with material data. Compare thermal transmission under matching pressure, thickness and temperature. ASTM D5470<\/a> provides a method for thermal transmission properties of thermally conductive electrical insulation materials. Check the test conditions before comparing supplier numbers. For insulation, use the applicable dielectric test method and evaluate the whole assembly, not just an ideal coupon.<\/p>\n\n\n\n

Next, build the minimum- and maximum-gap joints on production-intent parts. Record temperature distribution, closing force, cell or module displacement, final bond line and material coverage. Then apply the environmental conditions specified for the vehicle and mounting location.<\/p>\n\n\n\n

ISO 16750-3 and -4 may inform relevant mechanical and climatic tests for road-vehicle electrical\/electronic equipment. The OEM pack program determines applicability and pass\/fail limits. UL 94 is a material flammability classification tied to the tested grade and thickness; it is not evidence that a battery assembly will contain thermal runaway. UL 2580 and UN R100 concern battery-system safety or regulatory evaluation in applicable markets, not a stand-alone approval stamp for gap filler. The TIM testing standards overview<\/a> provides more method context.<\/p>\n\n\n\n

After cycling, vibration and humidity exposure, measure the assembly again. Then take it apart. Look for void growth, edge lift, bleed, cure defects, cell marks, corrosion and evidence of lost contact. Try the intended rework process rather than assuming it will be fine.<\/p>\n\n\n\n

A useful supplier brief includes cell format, interface drawing, min\/nominal\/max gap, contact area, heat load, target temperature spread, allowable assembly load, electrical isolation, orientation, production volume, cure window, environment and service strategy. If you need help comparing candidates against that brief, support pour la s\u00e9lection des mat\u00e9riaux et les essais<\/a> is a logical next step.<\/p>\n\n\n\n

Conclusion<\/h2>\n\n\n\n

The best battery gap filler is not necessarily the one with the largest conductivity number. It is the one that reaches the whole intended interface, does not over-stress the pack, fits the production line and keeps doing its job after aging.<\/p>\n\n\n\n

Measure the gap. Set a thermal and mechanical budget. Then test the assembled joint<\/em>. That is how a material choice becomes a reliable battery design.<\/p>\n\n\n\n

Foire aux questions<\/h2>\n\n\n\n

Where is gap filler placed in an EV battery pack?<\/h3>\n\n\n\n

Often between a cell or module surface and a cooling plate or tray, but the exact location depends on the pack architecture. Map every layer in the heat path before choosing a product.<\/p>\n\n\n\n

Is a thermal gap filler the same as a structural adhesive?<\/h3>\n\n\n\n

No. A soft filler mainly manages the thermal interface. Some formulations adhere or provide limited support, while structural adhesives are chosen and validated for load-bearing bonds. Do not assume one can replace the other.<\/p>\n\n\n\n

Does higher thermal conductivity always lower cell temperature?<\/h3>\n\n\n\n

No. A thick or voided high-conductivity layer can perform worse than a thinner layer with better contact. Compare full-joint thermal resistance and measured cell temperature under similar conditions.<\/p>\n\n\n\n

How do I size filler for minimum and maximum pack gaps?<\/h3>\n\n\n\n

At maximum gap, ensure contact across the target area. At minimum gap, check squeeze-out and closing load. Use measured production tolerances and test both assembled extremes, not only the nominal CAD gap.<\/p>\n\n\n\n

Can gap filler accommodate pouch or prismatic cell swelling?<\/h3>\n\n\n\n

A compliant material may follow some movement, but allowable swelling and cell pressure come from the cell and pack design. Check the actual cell format, restraint, temperature and aging conditions.<\/p>\n\n\n\n

When is liquid gap filler better than a thermal pad?<\/h3>\n\n\n\n

Liquid filler often helps with wide, irregular or multi-height interfaces and low-pressure closure. A pad can simplify placement and service where geometry and compression are predictable. Either choice needs pack-level validation.<\/p>\n\n\n\n

Does battery gap filler need to cure?<\/h3>\n\n\n\n

Not always. Some 1K materials stay soft and non-curing. Many 2K systems cure after mixing. The product data and process guide should state what happens, when, and how cure is confirmed.<\/p>\n\n\n\n

Can gap filler provide electrical isolation on its own?<\/h3>\n\n\n\n

Some grades are electrically insulating, but a bulk dielectric number is not the same as pack-level isolation. Validate thickness, edges, aging, adjacent layers and the applicable electrical safety requirements.<\/p>\n\n\n\n

What happens during thermal cycling and vibration?<\/h3>\n\n\n\n

Depending on the formulation and joint, the material may remain stable or may lose contact, slump, bleed, separate or change stiffness. Measure thermal and mechanical performance before and after the defined test, then inspect the opened joint.<\/p>\n\n\n\n

Can a module be reworked after gap filler cures?<\/h3>\n\n\n\n

Sometimes. Removal depends on adhesion, cured strength, substrates and the approved procedure. Include a real disassembly trial in qualification if repair or end-of-life separation matters.<\/p>\n<\/div><\/div>","protected":false},"excerpt":{"rendered":"

On a drawing, a battery module and its cooling plate look like two neat, flat blocks. On the assembly line? […]<\/p>\n","protected":false},"author":4,"featured_media":2379,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"site-sidebar-layout":"default","site-content-layout":"","ast-site-content-layout":"default","site-content-style":"default","site-sidebar-style":"default","ast-global-header-display":"","ast-banner-title-visibility":"","ast-main-header-display":"","ast-hfb-above-header-display":"","ast-hfb-below-header-display":"","ast-hfb-mobile-header-display":"","site-post-title":"","ast-breadcrumbs-content":"","ast-featured-img":"disabled","footer-sml-layout":"","ast-disable-related-posts":"","theme-transparent-header-meta":"","adv-header-id-meta":"","stick-header-meta":"","header-above-stick-meta":"","header-main-stick-meta":"","header-below-stick-meta":"","astra-migrate-meta-layouts":"default","ast-page-background-enabled":"default","ast-page-background-meta":{"desktop":{"background-color":"var(--ast-global-color-5)","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""},"tablet":{"background-color":"","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""},"mobile":{"background-color":"","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""}},"ast-content-background-meta":{"desktop":{"background-color":"var(--ast-global-color-4)","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""},"tablet":{"background-color":"var(--ast-global-color-4)","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""},"mobile":{"background-color":"var(--ast-global-color-4)","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""}},"footnotes":""},"categories":[799],"tags":[],"class_list":["post-2373","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-liquid-gap-filler"],"_links":{"self":[{"href":"https:\/\/haktak.com\/fr\/wp-json\/wp\/v2\/posts\/2373","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/haktak.com\/fr\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/haktak.com\/fr\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/haktak.com\/fr\/wp-json\/wp\/v2\/users\/4"}],"replies":[{"embeddable":true,"href":"https:\/\/haktak.com\/fr\/wp-json\/wp\/v2\/comments?post=2373"}],"version-history":[{"count":2,"href":"https:\/\/haktak.com\/fr\/wp-json\/wp\/v2\/posts\/2373\/revisions"}],"predecessor-version":[{"id":2385,"href":"https:\/\/haktak.com\/fr\/wp-json\/wp\/v2\/posts\/2373\/revisions\/2385"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/haktak.com\/fr\/wp-json\/wp\/v2\/media\/2379"}],"wp:attachment":[{"href":"https:\/\/haktak.com\/fr\/wp-json\/wp\/v2\/media?parent=2373"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/haktak.com\/fr\/wp-json\/wp\/v2\/categories?post=2373"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/haktak.com\/fr\/wp-json\/wp\/v2\/tags?post=2373"}],"curies":[{"name":"Bien jou\u00e9","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}