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Effective Thermal Management Solutions for EV Lithium-Ion Battery Packs
The performance, longevity, and safety of lithium-ion batteries are intrinsically linked to their operating temperature. An effective thermal management system (TMS) is essential to ensure the performance, safety and lifetime of these battery packs. Its importance is multifaceted:
Safety Assurance: Elevated temperatures (typically >60°C) can cause the battery's internal separator to melt, leading to a short circuit. This can trigger thermal runaway, a catastrophic event resulting in fire or explosion.
Performance Maintenance: Batteries operate at peak charge/discharge efficiency only within an optimal temperature range (usually 20°C-40°C). Low temperatures increase internal resistance, causing a sharp drop in power and capacity. High temperatures accelerate irreversible chemical reactions, leading to permanent capacity loss.
Extended Service Life: Research indicates that for every 10°C increase in operating temperature, the battery's degradation rate approximately doubles. Precise thermal management maintains the battery within its ideal window, significantly extending the pack's usable life.
Temperature Uniformity: A large temperature gradient between individual cells within a pack creates a "bucket-brigade effect," where some cells overcharge or over-discharge, accelerating the performance decay and aging of the entire pack. Superior thermal management must minimize inter-cell temperature differences (ideally <5°C).
Targeted Strategies for Different Areas of the Battery System
A typical battery pack can be broken down into three critical levels of thermal management, each requiring a distinct strategy:
Level 1: Cell Level - The core focus is "Heat Absorption & Conduction"
Goal: Rapidly absorb the heat generated during charge/discharge cycles and conduct it away efficiently. This ensures uniform temperature across the cell itself and prevents localized hot spots.
Challenge: Gaps exist between cells and within cell assemblies. Since air is a poor thermal conductor, these spaces must be filled with materials that create efficient thermal pathways.
Strategy:
Thermal Silicone Pads:
Location: Filling larger gaps between cells (typically 0.5mm - 3mm); between cells and side/end plates.
Advantages: Offer an excellent balance of high thermal conductivity (selectable, e.g., 1.5W/mK, 2.0W/mK, 3.0W/mK), high compressibility (accommodates tolerances and absorbs vibration), and superior electrical insulation. The premier choice for filling larger gaps and providing structural support.
Value: Directly conducts heat away from cells and promotes temperature uniformity, preventing hot spots.
Phase Change Materials (PCMs):
Location: Wrapped around cylindrical cells or filled between prismatic/pouch cells.
Advantages: A revolutionary solution. During normal operation, PCMs conduct heat in their solid state. When the cell temperature reaches the PCM's melting point (e.g., 45°C), it absorbs a significant amount of latent heat as it melts, effectively suppressing a rapid temperature rise and providing a critical safety buffer.
Value: Enables "intelligent" thermal management, ideal for handling peak heat generation from transient high-power events (e.g., rapid acceleration), and is a key material for preventing thermal runaway.
Thermally Conductive Double-Sided Tapes:
Location: Securely attaching temperature sensors, FPC/PCB sampling boards, and other small components directly to cell surfaces or busbars.
Advantages: Provide both strong adhesion and thermal conduction, ensuring sensors accurately measure the true cell temperature, avoiding inaccuracies caused by air gaps.
Level 2: Module & Pack Level - The core focus is "Heat Transfer & Temperature Homogenization"
Goal: Effectively transfer the heat collected from multiple cells within a module to the pack's cooling system (e.g., liquid cold plates, air channels), while ensuring temperature equilibrium across modules and throughout the pack.
Strategy:
Thermal Silicone Tapes:
Location: Wrapped around individual cells or small modules.
Advantages: Provide basic electrical insulation and thermal protection. They are thin, flexible, and easy to apply, making them ideal for the initial bundling, insulation, and mild temperature homogenization of cell groups.
Thermal Silicone Pads (Revisited):
Location: Between the module base and the liquid cold plate; between the battery module and the pack's lower casing.
Advantages: This is one of the most critical applications. Even with precision-machined surfaces, microscopic gaps remain. Thermal pads fill these micron-sized voids, minimizing interfacial thermal resistance and maximizing cooling efficiency. Selecting pads with low hardness and high compressibility is key for large-area conformity.
Thermal Gap Filler Gel or High-Conductivity Silicone Pads:
Location: Dispensed or screen-printed between cells/modules and the cooling plate in highly automated production lines.
Advantages: Liquid application allows for perfect filling of any irregular surface gap, achieving near-zero thermal contact resistance. Once cured, it forms a resilient, shock-absorbing elastomer. This is ideally suited for high-end vehicles where maximum thermal efficiency is paramount.
Level 3: Pack to External Environment - The core focus is "Ultimate Heat Dissipation & Isolation"
Goal: Dissipate the accumulated heat into the external environment via the cooling system. Concurrently, the battery pack casing requires thermal insulation properties to protect the internal cells from extreme ambient conditions (e.g., summer sun, winter cold).
Strategy: Utilize thermal insulation materials inside the battery pack to mitigate the impact of external environmental temperatures on the internal core temperature.
Expanded Application of Our Materials (Potential Development):
Aerogel Blankets:
Location: Laminated to the inner surface of the battery pack upper cover or used as a barrier between modules.
Advantages: Represent the state-of-the-art in insulation. Their nanoporous structure effectively blocks heat transfer. In the event of a thermal runaway in a single cell, aerogel can significantly delay the propagation of heat to adjacent modules and the pack cover, buying crucial time for occupant safety.
Recommendation: Integrating aerogel solutions with our existing conductive material portfolio would allow us to offer a complete suite from "Operational Thermal Management" to "Thermal Runaway Protection."
Conclusion
By systematically and strategically applying our portfolio of Thermal Silicone Pads, Phase Change Materials, Thermal Silicone Tapes, and Thermally Conductive Tapes, we can construct a comprehensive, efficient, and safe thermal management system for electric vehicle battery packs.
At the Cell Level: PCMs and Thermal Pads enable efficient heat absorption and conduction at the source.
At the Module Level: Thermal Pads and Gap Fillers optimize interface contact with the cooling system, maximizing heat dissipation.
At the System Level: Thermal Tapes and Conductive Tapes secure and insulate auxiliary components.
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