EV Battery Pack EMI Shielding: Best Practices for 2026 and Beyond

Every electric vehicle puts passengers on top of a battery pack that continuously emits electromagnetic radiation across a broad frequency spectrum. As the industry shifts to 800V architectures and wideband-gap semiconductors from Wolfspeed, Infineon, and onsemi, the EMI profile of battery systems is changing faster than many shielding designs can accommodate. Engineers and procurement managers specifying shielding for 2026 and beyond need to evaluate materials, gasket designs, and compliance strategies against this new reality.

What Makes EV Battery Packs Such Potent EMI Sources?

EV battery packs generate EMI across a frequency range spanning several orders of magnitude, driven by the density of high-power switching electronics packed into compact enclosures.

The primary EMI contributors within a battery pack assembly include DC-DC converters, traction inverters, onboard chargers, and battery management system (BMS) communication buses. Low-frequency emissions from battery charging and discharging cycles range from tens to several thousand hertz. High-frequency components from switching power supplies and communication systems extend from a few kilohertz to hundreds of megahertz.

The adoption of wideband-gap semiconductors is accelerating this shift. SiC MOSFETs now standard in traction inverters switch at up to 1 MHz with slew rates of 5-50 V/ns, generating harmonics that extend to 200 MHz and beyond. GaN HEMTs used in onboard chargers and DC-DC converters switch at up to 4 MHz, pushing EMI energy above 500 MHz—directly into the 2.4 and 5 GHz bands used by Wi-Fi, Bluetooth, and vehicle-to-everything (V2X) communication systems.

Compact battery packaging compounds the problem. High-voltage busbars, signal harnesses, and sensitive BMS circuits share tight quarters inside the enclosure, creating short coupling paths that allow radiated and conducted emissions to interfere with adjacent systems. The result is an EMI environment significantly more demanding than the IGBT-based platforms it replaces.

Which Shielding Materials Work Best for High-Voltage Battery Enclosures?

The choice of shielding material depends on the target attenuation, operating temperature range, flame resistance requirements, and cost constraints of the specific battery platform.

High-Performance: Fluorosilicone Conductive Gaskets

Fluorosilicone gaskets filled with silver-plated copper particles (conforming to MIL-DTL-83528 Type C) represent the current performance benchmark. These materials achieve approximately 110 dB attenuation at 10 GHz, operate from -55°C to +125°C, and resist automotive fluids including coolants and battery electrolytes. Flame-retardant versions meet UL 94 V-0, a baseline requirement for battery enclosure applications.

Mid-Range: Nickel-Graphite Silicones

For applications where moderate shielding effectiveness is sufficient—typically secondary enclosures or lower-power subsystems—nickel-graphite-filled silicones provide adequate conductivity at significantly lower cost. These materials are suitable when the primary enclosure provides the bulk of attenuation and the gasket needs to maintain continuity at seams and interfaces.

Enclosure-Level: Aluminum EMI Shields

Embossed aluminum electromagnetic shields (EMS) placed on top of battery lids provide a cost-effective baseline. With shielding effectiveness exceeding 70 dB, aluminum EMS outperform alternatives like conductive fillers or sprayed metal coatings while remaining straightforward to manufacture. Autoneum and similar suppliers offer production-ready aluminum EMS solutions for major OEM battery platforms.

Emerging: CFRC Sandwich Composites and MXene Films

Carbon fiber-reinforced composites (CFRC) with copper-plated polyester non-woven fabric in sandwich structures combine mechanical strength, EMI shielding, and thermal management in a single lightweight material. These composites can reduce enclosure weight by 30-50% compared to aluminum while maintaining comparable shielding performance.

At the research frontier, MXene films—titanium carbide materials with conductivity around 10,000 S/cm²—self-assemble into films as thin as 55 nm that provide 99% shielding efficiency. While not yet production-ready for automotive battery applications, MXene represents the direction of next-generation ultra-thin shielding materials.

How Should Engineers Design Gaskets and Enclosures for Dual-Function Performance?

Effective battery enclosure design must address both EMI shielding and environmental sealing simultaneously, since battery housings require IP67 or higher ingress protection ratings.

Conductive Extrusions vs. Form-in-Place

Conductive extrusions are the preferred manufacturing method for EMI gaskets in high-volume EV production. Extrusion produces material at 3-5 feet per minute with consistent cross-section geometry, offering better scalability than form-in-place (FIP) gaskets for the large perimeters typical of battery enclosures. For long runs, gaskets are spliced or vulcanized into closed loops—the splice joint must be electrically bonded and mechanically secure using conductive adhesives to prevent it from becoming a leakage point.

Dual-Durometer Gaskets

Where a single component must provide both environmental sealing and EMI shielding, dual-durometer gaskets combine a soft foam layer for water and dust exclusion with a conductive elastomer layer for electromagnetic attenuation. This approach eliminates the need for separate sealing and shielding gaskets, reducing assembly steps and ensuring consistent contact pressure across both functions.

Mechanical Design: Flanges, Fasteners, and Compression

Engineers should specify flange widths and fastener spacing that deliver consistent gasket compression across the entire enclosure perimeter. Contact pressure must be sufficient for the conductive elastomer to make intimate metal-to-metal contact through oxide films on mating surfaces. Compression limiters prevent over-compression that degrades gasket life, while maintaining the minimum compression needed for both sealing and shielding.

Thermal Integration

Battery enclosures must manage heat from cells and power electronics without creating EMI leakage paths. Advanced gaskets incorporate graphite sheets or thermally conductive fillers that spread heat laterally while maintaining electromagnetic continuity. Vapor chamber and EMI shielding laminates as thin as 0.25 mm can increase thermal conductivity by 5x compared to standard shielding materials, addressing both requirements in a single layer.

Environmental stress—continuous vibration, thermal cycling from -40°C to +125°C, and potential exposure to high-voltage arcing—accelerates material fatigue. Gasket materials must maintain both sealing and shielding performance across the vehicle's 10-15 year service life under these conditions.

What Does CISPR 25 Class 5 Compliance Require for Battery Systems?

CISPR 25 is the de facto standard for automotive component EMI emissions, and understanding its current requirements and limitations is essential for battery shielding design.

Edition 5.0: EV-Specific Additions

CISPR 25:2021 (Edition 5.0) introduced significant changes relevant to EV battery systems: test methods for charging mode operation of EVs and PHEVs, chamber validation procedures, and—critically—shielded power supply test methods specifically for high-voltage electric and hybrid electric vehicle systems. These additions reflect the recognition that HV battery components require dedicated test approaches.

CISPR 25 classifies emissions limits from Class 1 (most lenient) to Class 5 (most stringent). Major OEMs universally specify Class 5 for battery pack components. While CISPR 25 is technically not a regulatory test—compliance judgment rests with the manufacturer—failing to meet Class 5 effectively disqualifies a component from most OEM qualification processes.

The 1 kV Scope Limitation

The current CISPR 25 scope covers voltages up to 1 kV. With battery architectures moving to 800V nominal (and transient voltages during switching events exceeding 1 kV), this scope limitation requires careful interpretation. Components operating at the edge of this boundary may need supplementary testing beyond the standard's defined methods.

Pre-Compliance Scanning

Pre-compliance EMI scanning at the prototype stage—before investing in full CISPR 25 chamber testing—significantly reduces certification costs and design iteration cycles. Using EMI receivers from Rohde & Schwarz or Keysight, engineers can identify shielding weaknesses early and validate gasket effectiveness at frequencies relevant to SiC switching profiles. A multi-layered approach using 6-sided metal enclosures with grounded conductive gaskets at every interface, as demonstrated by Bosch in their OBC reference designs, provides a proven foundation for Class 5 compliance.

Frequently Asked Questions

What makes EV battery packs such strong EMI emitters?

EV battery packs contain DC-DC converters, inverters, and battery management systems that collectively generate EMI from tens of hertz through hundreds of megahertz. The adoption of SiC MOSFETs switching at up to 1 MHz and GaN HEMTs at up to 4 MHz pushes EMI harmonics into the 2.4 and 5 GHz bands, while compact packaging creates short coupling paths between high-power and sensitive low-voltage circuits.

Which gasket materials provide the best EMI shielding for EV battery enclosures?

Fluorosilicone gaskets filled with silver-plated copper particles (MIL-DTL-83528 Type C) deliver approximately 110 dB attenuation at 10 GHz and operate from -55°C to +125°C. For moderate shielding requirements, nickel-graphite-filled silicones offer a lower-cost alternative with adequate conductivity. Both types should meet UL 94 V-0 flame ratings for battery applications.

Can one gasket handle both IP67 sealing and EMI shielding?

Yes. Dual-durometer gaskets combine a soft foam layer for water and dust sealing with a conductive elastomer layer for EMI shielding in a single component. This approach meets IP67 ingress protection requirements while maintaining electromagnetic shielding, reducing assembly complexity and ensuring consistent performance at the battery enclosure interface.

What does CISPR 25 Class 5 require for EV battery systems?

CISPR 25 Class 5 is the most stringent emissions classification, covering 150 kHz to 5.9 GHz. Edition 5.0 (2021) added EV-specific provisions including charging mode test methods and shielded power supply test procedures for high-voltage systems. While not legally mandatory, Class 5 compliance is a de facto requirement from major OEMs for all HV battery components.

How do emerging materials like carbon fiber composites compare to aluminum for battery EMI shielding?

Carbon fiber-reinforced composites (CFRC) with conductive layers such as copper-plated polyester fabric can approach aluminum's shielding effectiveness while reducing weight by 30-50%. Sandwich structures combining CFRC with melamine foam also provide thermal insulation. However, aluminum remains the benchmark at 70+ dB shielding effectiveness with lower manufacturing complexity for most battery enclosure geometries.

What Comes Next for Battery Pack Shielding?

EMI shielding for EV battery packs is evolving from a passive, bolt-on component to an integrated system-level design discipline. Smart monitoring with embedded sensing for real-time shielding health, functional materials that combine EMI attenuation with thermal management and structural support, and advanced simulation tools that enable virtual CISPR 25 testing before physical prototyping are all moving from research into production engineering workflows.

Engineers specifying shielding for next-generation battery platforms should engage material suppliers and shielding integrators during the architecture phase—not after the first failed pre-compliance scan. The cost of redesigning an enclosure after tooling is committed is an order of magnitude higher than designing shielding in from the start.

---

Designing EMI shielding for your EV battery pack? Contact POCONS USA to discuss material selection, gasket design, and CISPR 25 compliance strategy with our engineering team.