Electric vehicles are poised to have a dramatic impact on quality of life in our cities, reducing both air and noise pollution. As the world looks to more sustainable solutions, there is political will behind this evolution in transport, and we are already seeing healthy growth in EV use.

However, the adoption of EVs is still impeded due to concerns around a specific safety issue: thermal propagation.

How is the issue of thermal propagation being addressed?

Thermal propagation, or thermal runaway propagation, occurs when thermal runaway in an individual battery cell spreads to the surrounding cells. This is exceedingly difficult to suppress once this chain reaction initiates.

Up to now, regulations and system design approaches have been more focused on managing around these events vs complete prevention, such as focusing on slowing thermal propagation to provide occupants more time to retreat to safety. Guidance from the UNECE in 2018 [ii] and China in 2020 [iii] suggested that occupants of EV vehicles should be warned of an issue at least five minutes in advance of a hazardous condition due to thermal runaway or propagation.

However, it is preferable to completely prevent thermal propagation in EV battery systems, by detecting the causes of thermal events even earlier. Within the industry, OEMs have begun to insist on zero thermal propagation in EV systems. Chinese EV battery manufacturer CATL reports that 86 percent of their customers in 2021 insisted on zero thermal propagation in their battery systems, up from 6 percent only two years earlier [iv].

This is leading to a shift in focus for preventing thermal propagation altogether.

Thermal propagation legislative requirements

How can thermal propagation be prevented?

Preventing thermal propagation is a challenge that can be approached in multiple ways. Initial solutions include implementing thermal barriers between the cells to minimise heat transfer. Identifying runaway in advance of a fire could be as simple as monitoring temperature and alerting the driver when it gets too hot, or using gas sensors to identify key bi-products of battery cell over-heating.

However, it would be more effective to address the cause of thermal propagation by preventing thermal runaway in the first place. To achieve this, defects in the cells that could serve as a runaway source must be located before that process begins. That requires the employment of a battery management system (BMS) that includes real-time, effective mapping of each battery cell and the associated circuitry. Such a BMS can identify shorts or other current anomalies within a cell, identifying defects before hotspots are formed. Once those locations are identified, controls within the battery system can be implemented to prevent thermal runaway.

How can Paragraf help?

Paragraf’s current sensors enable cell-level monitoring, opening the door to new solutions for preventing thermal propagation. The 2D geometry of our graphene-based sensors allows for high immunity to stray magnetic fields in the plane of the sensor, which is critical in electrically noisy environments. Combined with the low power requirement of these sensors and ability to place externally to the cell circuit, this enables complete cell-level mapping of the battery by employing more sensors throughout the system.

Paragraf is aware that the industry is now demanding zero thermal propagation in next-generation EV and we are becoming part of system solutions to achieve that goal. Please contact us to discuss how we and our partners are redefining BMS in next generation EV.


[i]Facts and Factors – Electric Vehicle Market Size, Share Global Analysis Report, 2022–2028

[ii] 1714758 (unece.org)

[iii] Electric vehicles traction battery safety requirements – Standards of China

[iv] EV battery technology innovation promotes comprehensive electrification (catl.com)

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