China Imposes Low Conductive Water Glycol-Based Coolants for BEVs

24 October 2023 / e-Mobility

The Chinese national Ministry of Transport has the intention issuing a new standard for water glycol-based coolants, which will require the use of a safety coolant in battery cooling loops. Tests conducted by its affiliated "Research Institute On Highway" ("RIOH") point to the added value of coolants with much reduced, yet non-zero, electrical conductivity. Drawing lessons from recent thermal events in its ever-expanding electric car fleet, it aims to enhance the safety of battery-powered electric cars. This initiative can be seen as a larger-scale effort to enhance safety, not only for passengers and the surrounding environment but also for firefighting and rescue services. China is ahead in many ways in the adoption of BEVs, and for other regions, this can be viewed as an 'early warning' of what is yet to come on a larger, global scale. As a country, China is the first to put forwards such measures. On an OEM level, Korean manufacturers have already been pursuing lower electric conductivity coolants for the same reason: the safe discharge of energy through the coolant in case of an incident.

With an increasing number of electric cars on the roads, the frequency of a coolant-induced or facilitated thermal event may rise. The occurrence of such a thermal event, even with the best containment measures in the battery housing, will still have a significant impact. An event like this may not only damage the car itself but also harm the OEM’s (Original Equipment Manufacturer) reputation. So, while the occurrence may be rare, the impact of such an occurrence is very high. Because a thermal event should be avoided, one should not forget how a coolant fits into this picture. It can be either your friend or your foe.

The idea behind the safety coolant is following: it's better to prevent propagation than to deal with it through containment. In the event of inadvertent or accidental (partial) battery flooding, a non-zero but significantly reduced electrical conductivity coolant should enable a system to safely discharge the contained energy of a cell or group of cells through this coolant without further adverse effects.

RIOH's findings, in cooperation with CATL as a leading battery manufacturer, indicate that there is a sweet spot or range in electrical conductivity in terms of safety. These findings suggest a maximum starting value of 100µS/cm for such a coolant on factory fill and a cut-off value to replace the coolant of approximately 300-500µS/cm, depending the architecture. Compared to a non- or very low conductive coolant, the energy can be dissipated in a controlled way, neither too fast nor too slow. The idea is that the energy load gets channeled away and dissipated in such a way that the chain of events leading up to a thermal event is interrupted.

When a 100µS/cm coolant short-circuits the battery module or pack, the flowing current cannot generate excessive heat inside the cell, and the discharge is harmless. The generation of combustible hydrogen by electrolysis is also minimal, about 96% less than compared to a classic coolant. This discharge process may last for several hours, even days, depending on the state of charge. A fully discharged cell can also avoid thermal runaway.

A well-designed system can also easily detect such a current loss or faulty cell – potentially even through the coolant - well before anything happens; it can disconnect the module or cell cluster to prevent it from being charged when connected to a charger. When 800V is applied in such a situation, a classic coolant will virtually immediately lead to a thermal event as it will facilitate high currents through the fluid and cells. A coolant of about 100µS/cm will only heat up slightly.

Maintaining the electrical conductivity of the coolant throughout the lifetime of the vehicle and detecting whether it has risen above a critical level then become necessary concerns. Measurement of the electrical conductivity can be relatively easily solved by using conductivity sensors. Maintaining the coolant's electrical conductivity, though, depends on how robustly it has been designed and how little contamination is present in the cooling system prior to its filling. To understand how critical this is, consider the following: Electric cars use more and more aluminium, which is being brazed using a so-called brazing 'flux' powder. This compound, if dissolved in the coolant, is very detrimental to electrical conductivity and catalyses coolant degradation quite rapidly. It is very difficult to clean this out prior filling, especially under large number series production.

This is why Freecor® EV Milli may be the right answer to these concerns. As a coolant with a starting conductivity below 100µS/cm in its ready-to-use version, its distinctive composition incorporates a flux compensation package. This feature enhances the likelihood to sustaining long-term reduced electrical conductivity. Thereby reducing the need for premature coolant replacement and the associated frequent and costly servicing.

Get to know more about Freecor®  EV Milli 10.