Once the cells are stacked, the pack still has to survive 15 years of vibration, humidity, salt fog, and thermal cycling. SEMITECH supplies silanol-terminated PDMS for module potting and zinc-phosphate-grade anti-corrosive pigment for outdoor ESS housing coatings.
Sealing the pack — why it gets harder every generation
Cell-to-pack and cell-to-chassis architectures eliminate the module case as a separate barrier. The full burden of waterproofing, vibration damping, and thermal isolation now falls on the pack-level encapsulation layer.
Three sealing functions converge in modern pack design. RTV silicone potting fixes cells to the pack base and damps vibration. Module sealing creates the IP67/IP68 barrier between coolant channels and electrical busbars. External anti-corrosion coatings protect the steel or aluminum housing — especially critical for stationary ESS containers exposed to coastal salt fog.
RTV silicone chemistry for pack potting
One-component RTV (room-temperature-vulcanizing) silicones are the workhorse for module potting. The base is silanol-terminated PDMS — exactly what SEMITECH MESIL OH polymer provides. Combined with a moisture-curing crosslinker (alkoxy or oxime), the polymer cures by exposure to atmospheric humidity, forming a high-elongation elastomer that absorbs vibration and accommodates cell breathing over thousands of charge cycles.
Why MESIL OH polymer for battery RTVs: SEMITECH’s silanol PDMS has tightly controlled molecular weight distribution (low-end tail removed), which keeps cured elastomer modulus consistent batch-to-batch. For battery applications where modulus drift translates directly to vibration response variability, this matters more than headline TS or elongation numbers.
ESS container anti-corrosion coatings
Stationary energy storage systems sit outside in conditions that EV packs never see — coastal salt fog, desert thermal cycling, industrial SO₂ exposure, and 20-year service expectations. The container coating system has to deliver more than aesthetics: it’s the first failure point if mechanical integrity goes.
SEMITECH’s anti-corrosive pigment line (zinc phosphate, modified) provides the active corrosion-inhibiting layer in epoxy primer coats applied to ESS container steel. Unlike chromate-based legacy chemistry, zinc phosphate meets RoHS / REACH and gives 1000+ hour salt fog performance when properly formulated.
SEMITECH product portfolio
MESIL OH Polymer
Silanol-terminated PDMS, viscosities 750–80,000 cSt. Base for one-component RTV potting compounds, module sealants, and gap-fill silicones. Tightly controlled MW distribution.
Anti-Corrosive Pigment
Zinc phosphate-grade and modified zinc phosphate. Designed for epoxy and polyurethane primer coats on ESS containers, charging station enclosures, and bus bars.
Fumed Silica (rheology)
SEMISIL 200 hydrophobic-treated grade for sag control in thixotropic RTV pastes. 1–3 wt% loading prevents drip on vertical surfaces during pack assembly.
Hydrogen / Vinyl Silicone
For two-component addition-cure pottants where cure-by-heat is preferred over moisture cure (e.g., closed-housing modules where atmospheric humidity is unavailable).
Selection guide
| Application | Function | SEMITECH Product | Reference Grade |
|---|---|---|---|
| Module potting (RTV) | One-component cure | MESIL OH Polymer | MESIL-OH 5000 |
| Module gap-fill | Two-component cure | Vinyl + H Silicone | MESIL VTM |
| Sag control | Thixotropy | Fumed Silica (hydrophobic) | SEMISIL 200H |
| ESS container primer | Anti-corrosion | Zinc Phosphate Pigment | SEMICOR ZP |
| ESS topcoat | UV resistance | Silicone-modified resin | By formulator |
FAQ
+Why use silicone RTV for pack potting and not polyurethane?
Polyurethane gives higher tensile strength and adhesion at lower cost — but it stiffens dramatically below −20 °C and softens above 100 °C. Silicone RTV maintains elastomer behavior from −60 to 200 °C, which matches the actual EV operating envelope. For ESS in milder climates, polyurethane is sometimes acceptable. For automotive and northern climates, silicone wins.
+What’s the difference between alkoxy and oxime cure RTV?
Alkoxy releases methanol or ethanol during cure — non-corrosive to copper bus bars, preferred for battery applications. Oxime releases methyl ethyl ketoxime, faster cure but slightly corrosive. Use alkoxy systems for any contact with electronics.
+Is zinc phosphate RoHS / REACH compliant?
Yes. Standard zinc phosphate (Zn₃(PO₄)₂·4H₂O) is non-toxic and meets all current heavy metal restrictions. Modified versions (zinc aluminum molybdate orthophosphate) extend salt fog performance while staying compliant.
+Can your RTV silicones contact lithium-ion electrolyte?
Cured silicone elastomers tolerate occasional contact with carbonate electrolytes at < 60 °C. For prolonged or high-temperature contact, request our chemical compatibility datasheet — we’ll recommend specific grades and cure systems.
+Do you offer anti-corrosion pigment for marine ESS?
Yes. Modified zinc aluminum molybdate orthophosphate grades deliver >1500 h salt fog when formulated into a 2-coat epoxy/polyurethane system. Suitable for offshore wind ESS and coastal substations.
Part of the Lithium Battery Materials hub. Pack-level formulation support and ESS coating system advice available.