Thermal management is the central engineering challenge of lithium-ion battery pack design. The electrochemical reactions inside lithium-ion cells are strongly temperature-dependent: too cold, and lithium plating on the anode reduces capacity and creates safety risks; too hot, and electrolyte decomposition accelerates, shortening calendar life. At the extremes, thermal runaway — the self-sustaining exothermic decomposition of a lithium-ion cell — can propagate from cell to cell through a module in seconds if adjacent cells are not thermally isolated.
Managing this thermal behaviour requires materials that perform multiple functions within the tightest possible volume envelope. Cell spacers must insulate thermally, comply mechanically with cell swelling, withstand fire without contributing fuel, and add minimal mass. Battery conditioning heaters must distribute heat uniformly across large surfaces at low voltage with minimum added thickness. Both requirements push conventional materials to their limits — and create an application space where specialty nonwovens offer decisive advantages.
Why Battery Spacers Need to Be Thin, Non-Combustible, and Compressible
In a lithium-ion battery module, cell spacers serve three simultaneous functions. Thermally, they limit heat flow between adjacent cells. Mechanically, they accommodate the 2–5% volumetric expansion of lithium-ion cells across their charge-discharge cycle while maintaining contact pressure and preventing cell buckling. In safety terms, they must not contribute to fire propagation in the event of thermal runaway, where cell temperatures can reach 600–900°C locally.
Conventional materials fail at one or more of these requirements. Polymer foams are compressible but flammable. Ceramic papers are non-combustible but brittle, prone to cracking under cyclical compression, and generate dust that can contaminate cell surfaces. Thick glass fiber mats provide adequate insulation only at thicknesses that consume valuable space.
aero365 aerogel nonwoven addresses all three requirements in a single material:
- Thermal conductivity below 25 mW/mK — comparable to aerogel blankets used in cryogenic applications, achieved in a compressible nonwoven format
- UL94 V0 rated — the highest standard flammability classification; the material self-extinguishes and does not drip burning particles
- 1–3 mm thickness range — thin enough to fit between prismatic cells in high-energy-density module designs without sacrificing cell count
- Compressible with shape recovery — accommodates cell swelling across thousands of charge cycles without permanent deformation or cracking
- Thermoformable — can be shaped to conform to three-dimensional cell geometries, module frames, and non-planar interfaces
- Approximately 90% inorganic content — non-combustible above 800°C, providing passive fire containment that polymer alternatives cannot offer
aero365 key figures: Thermal conductivity <25 mW/mK · Thickness 1–3 mm · UL94 V0 · ~90% inorganic · Compressible, shape recovery · Thermoformable · Non-combustible above 800°C
Aerogel vs. Conventional Insulation in Battery Applications
| Property | aero365 Aerogel Nonwoven | Polymer Foam | Ceramic Paper |
|---|---|---|---|
| Thermal conductivity | <25 mW/mK | 30–50 mW/mK | 120–180 mW/mK |
| Flammability (UL94) | V0 | HB to V2 — typically fails V0 | Non-combustible |
| Compression behaviour | Compressible with shape recovery | Compressible; may creep over time | Brittle — cracks under compression cycling |
| Minimum useful thickness | 1 mm | 1–2 mm | 0.5 mm (but brittle) |
| Dust generation | Low — bound fiber structure | Low | High — ceramic fibers shed during handling |
| 3D formability | Yes — thermoformable | Limited | Poor |
The thermal conductivity advantage of aerogel over ceramic paper is particularly significant. To achieve the same thermal resistance as 1 mm of aero365 (<25 mW/mK), a ceramic paper at 150 mW/mK would require approximately 6 mm of thickness — consuming space equivalent to the entire width of a prismatic cell in a high-density module. This makes aero365 not just a safety material but a space-efficiency enabler for battery engineers.
Surface Heating for Battery Conditioning
Cold temperature operation is a primary limitation of lithium-ion chemistry. Below 5°C, lithium plating on graphite anodes during fast charging becomes a significant safety and cycle-life concern. Below –10°C, available discharge power can drop by 30–50%. For electric vehicles operated in northern climates, this directly affects range, charging speed, and long-term battery health.
Battery pre-conditioning — warming cells to 15–35°C before charging or high-power discharge — is increasingly standard in premium EVs and stationary storage systems. thermo365 carbon fiber nonwoven offers a distinctive approach to this heating function:
- Voltage compatibility: operates at 12–220V, with 12V operation enabling direct integration with standard automotive 12V battery systems for pre-heating before high-voltage pack activation
- Power density range: 10–2000 W/m² — tunable via resistivity control in the wet-laid process, allowing heating power to be matched precisely to thermal model requirements
- Homogeneous IR heat distribution: the planar heater format distributes heat evenly across the cell surface, avoiding the hotspot problem common to resistance wire elements
- Minimal added mass and thickness: a planar carbon fiber nonwoven adds far less thickness than PTC ceramic heaters or resistance wire assemblies, preserving module energy density
- Non-flammable substrate: the carbon fiber material is itself non-flammable, an important consideration when locating heaters adjacent to lithium-ion cells
In stationary battery systems for grid storage, thermo365 heaters enable rapid warm-up in unheated outdoor enclosures, reducing the thermal conditioning energy overhead that otherwise degrades round-trip efficiency during winter operation.
Material Certification and Safety
Battery module material qualification demands rigorous certification evidence. For aero365, the UL94 V0 rating is the primary flammability certification, providing a standardised, internationally recognised basis for safety case arguments in automotive and stationary battery approvals. The approximately 90% inorganic content means that even under conditions exceeding the UL94 test (sustained flame contact, temperatures above 800°C), the material does not add fuel to a fire event.
For battery spacer applications subject to UN 38.3 or ECE R100 qualification testing, material data sheets providing thermal conductivity, compression force-displacement curves, and UL94 test reports are available from Phoenix Non Woven on request. Custom thickness and density variants can be developed to meet application-specific module design requirements, including integration with thermal interface materials (TIMs) on cell surfaces.
Evaluate aero365 and thermo365 for Your Battery Module
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Frequently Asked Questions
Battery cell spacers in lithium-ion modules serve a dual function: they must provide thermal isolation between cells to slow propagation in a thermal runaway event, while also maintaining structural compliance under cell swelling forces. For thermal isolation, a spacer thermal conductivity below 30 mW/mK is typically targeted. aero365 aerogel nonwoven achieves less than 25 mW/mK, making it one of the lowest-conductivity compressible materials available in a non-combustible form factor.
aero365 aerogel nonwoven is produced in thicknesses of 1 to 3 mm. This is substantially thinner than conventional ceramic paper or mineral wool insulation achieving equivalent thermal resistance, enabling battery module designers to maximise cell count within a fixed module envelope. At 1 mm, aero365 is thin enough to fit between prismatic cells in high-energy-density EV battery packs.
UL94 V0 is the highest flammability rating in the UL94 standard for plastic materials. A material rated V0 must extinguish within 10 seconds after two applications of a 10-second flame, with no dripping of flaming particles. For battery cell spacers, V0 certification provides evidence that the spacer material will not contribute to fire spread in the event of a thermal runaway event. aero365 meets UL94 V0 due to its approximately 90% inorganic content and high aerogel loading.
Yes. aero365 is thermoformable and can be shaped to conform to three-dimensional battery module geometries, including curved cell surfaces, prismatic cell frames, and pouch cell stacks with non-planar interfaces. The compression and shape recovery characteristics of the material also allow it to accommodate the 3–5% volumetric expansion that lithium-ion cells undergo during charge/discharge cycling, maintaining compressive contact and preventing air gaps that would impair thermal contact.
Lithium-ion batteries experience significantly reduced charge acceptance and available power at low temperatures — a critical limitation for electric vehicles operated in cold climates. Pre-conditioning the battery pack before use (or while plugged in overnight) brings cells to an optimal operating temperature range of 15–35°C. thermo365 carbon fiber nonwoven heaters operate at 12V or higher voltages, generate homogeneous infrared heat across the pack surface, and add negligible mass and thickness compared to conventional resistance wire or PTC element heaters. Their resistivity can be tuned to deliver specific power densities in the 10–2000 W/m² range required for automotive battery conditioning.