Key Considerations for Crash Safety Design in Lithium-ion Battery Packs

Ensuring the crash safety of lithium-ion battery packs is critical for protecting occupants, preventing catastrophic failures, and maintaining the integrity of electric vehicle systems. Below are systematic approaches to enhance crash safety through structural design, material selection, and system-level protections.

Structural Protection and Energy Absorption

High-Strength Enclosure Materials

Battery pack enclosures are typically constructed from aluminum alloys, carbon fiber composites, or high-strength steel to balance lightweight design with impact resistance. For example, bottom-mounted steel plates or "sandwich" structures with composite layers can absorb and distribute collision forces. Enclosures must meet IP67 or IP69K standards for water and dust ingress protection, using sealing gaskets and pressure-relief valves to prevent electrolyte leakage.

Crash-Optimized Layout and Mounting

Battery packs should be positioned in non-deformable zones of the vehicle, such as between the frame rails or ahead of the rear axle. This minimizes exposure to frontal, rear, or side impacts. For instance, the Nissan Leaf positions its battery pack centrally, protected by reinforced chassis structures. Mounting brackets must use high-strength bolts (e.g., 10.9-grade M14) and include multiple attachment points (10+ per pack) to prevent detachment during collisions.

Internal Component Isolation

Modules within the battery pack should be separated by ceramic fiber barriers or aerogel insulation pads to delay thermal runaway propagation. Additionally, mechanical buffers or crumple zones can absorb impact energy, reducing the risk of internal short circuits. For example, Tesla’s Model S uses a reinforced battery frame to act as a structural member while protecting cells from deformation.

Thermal Management and Fire Suppression

Active Cooling and Heating Systems

Liquid cooling systems or phase-change materials (PCMs) help maintain optimal operating temperatures, reducing the risk of thermal runaway during collisions. BMS-controlled cooling loops can adjust flow rates based on real-time temperature data, while heating elements ensure performance in cold climates. For instance, BMW’s i3 uses a glycol-based cooling system to dissipate heat efficiently.

Thermal Runaway Mitigation

In the event of a collision, pressure-relief valves can vent hot gases away from occupants, while fire suppressants like perfluorohexane can extinguish flames. Battery packs may also include fire-resistant coatings or intumescent materials that expand when exposed to heat, sealing off compromised areas. For example, some designs use ceramic coatings on cell casings to delay thermal propagation.

Post-Crash Thermal Monitoring

After a collision, the BMS should continuously monitor cell temperatures and voltages. If abnormal heating is detected, the system can isolate faulty modules or initiate cooling to prevent cascading failures. This requires redundant temperature sensors and fast-acting relays to disconnect affected sections within milliseconds.

Electrical Protection and Fault Isolation

High-Voltage Disconnection Mechanisms

Inertial switches or accelerometers can trigger the immediate disconnection of high-voltage contactors upon collision detection. For example, a 100g+ acceleration threshold might cut power to the battery pack, ensuring no electrical hazards for occupants or first responders. This system must operate independently of the vehicle’s main power supply to remain functional during severe impacts.

Insulation and Short-Circuit Prevention

High-voltage components should be encapsulated in insulative materials, with clearances and creepage distances meeting automotive safety standards (e.g., IEC 60664-1). Additionally, fuse links or polymer positive temperature coefficient (PPTC) devices can interrupt current flow during short circuits, preventing overheating. For instance, FPC (flexible printed circuit) fuses are used to protect sampling lines from short-circuit risks.

Post-Crash Electrical Integrity Checks

After a collision, the BMS should verify the integrity of electrical connections, including high-voltage plugs and busbars. Diagnostics can include resistance measurements, continuity tests, and insulation resistance checks (e.g., >100 MΩ at max operating voltage). If damage is detected, the system can isolate affected sections to prevent further degradation.

By integrating these structural, thermal, and electrical safeguards, lithium-ion battery packs can achieve robust crash safety performance. Continuous testing against standards like GB/T 31467.3, UN38.3, and ISO 26262 ensures compliance and drives innovation in safety design.