When a lithium-ion battery cell experiences thermal runaway (due to mechanical intrusion, defects, or electrical abuse), it releases a superheated, highly pressurized gas plume containing vaporized electrolyte and carbon particles. This gas behaves as an electrically conductive fluid. In conventional battery packs, if this gas vents randomly into the pack cavity, the blasting hot airflow can come into direct contact with live electrical components and cell wiring. This exposure melts insulation, bridges electrical gaps, and causes catastrophic high-voltage arcing and secondary short circuits, which then propagates the thermal runaway to adjacent cells.
Creepage and Clearance
High voltage circuits can discharge across a gap, the gap can be through the air or across a surface.
- Creepage: distance between two conductors on the surface.
- Clearance: the distance between two conductors through the air.
To break this cascade of failure, CATL developed thermal-electrical separation technology (also referred to as gas-electric separation) as a core part of its NP 2.0 (No Thermal Propagation) safety framework. The guiding principle of this strategy is that heat and electricity must take entirely decoupled physical pathways. Meaning “vented gases take the heat/gas path, electricity takes the electrical path”.
CATL achieves this physical decoupling primarily through structural redesigns implemented in their CTP (Cell-to-Pack) 3.0 Qilin battery architecture:
- Inverted Cell Arrangement: CATL engineered the pack by turning the prismatic battery cells upside down. This inverted layout positions all of the electrical terminals, high-voltage busbars, and delicate sensor harnesses safely at the top of the battery pack. Conversely, the explosion-proof pressure relief valves are located at the bottom, pointing downward.
- Independent Sealed Exhaust Lanes: Instead of letting ejected gas vent randomly within the battery housing until it finds a global relief valve, CATL designed a dedicated, sealed exhaust channel for every single cell.
- Directional Venting: If a cell becomes damaged and vents, the superheated gases are funneled directly downward and out of the battery pack through its specific exhaust lane.
By physically isolating the live high-voltage components from the pressure relief valves, the escaping conductive gas completely bypasses the electrical circuits.
CATL notes that this approach evolves simple thermal isolation into active “thermal insulation”. It effectively kills thermal runaway at its root by venting gas directionally with zero contact with live electrical parts, preventing a localized thermal event from escalating into a pack-wide electrical failure.
There are two CATL patents that are not definitive, but appear to cover this space:
- Patent CN114497826A: Qilin Cooling and Structural Design Titled “Water Cooling Plate Assembly, Cooling System, Battery, Battery Enclosure, and Electric Device,” this patent specifically outlines the structural innovations of the Qilin battery’s cooling plate, which is central to managing heat and structural stress. Key features include:
- Dual-Layer Cooling Channels: The cooling plate is arranged in a “harmonica tube” configuration with inner and outer channels. One channel is used for liquid cooling to efficiently dissipate heat, while the other acts as a non-liquid cooling path (such as air cooling).
- Deformation Buffer: Because the non-liquid channel is free of coolant, it serves as a deformable pathway. The walls are designed to deform inward to absorb the physical expansion of battery cells during operation, minimizing compression pressure and preventing physical damage.
- Patent US 11,011,797 B2 (and Chinese counterpart CN108493119A): Cell-Level Short Circuit Prevention While the thermal-electric separation strategy works at the pack level to funnel gas away from electronics, CATL also holds foundational patents at the cell level to prevent the internal short circuits that lead to thermal runaway in the first place. Titled “Electrode assembly and battery,” this patent focuses on physical isolation inside the cell:
- Opposite Tab Arrangement: Instead of placing the positive and negative electrode tabs on the same side of the cell (which can lead to misalignment and shorting), this patent places them on entirely opposite sides of the assembly. This physical separation improves heat dissipation and lowers internal resistance by optimizing the current pathways.
- Integrated Separators: To further prevent electrical shorts, a tailored separator film is used to provide electrical insulation. A specific portion of this separator is positioned directly between the electrode tabs to insulate them against unintended contact or abrasion.
This post has been built based on the support of and sponsorship from: illumion, Custom Power, Quarto Technical Services, Eatron Technologies and About:Energy