EXCELLENT THERMAL CONTROL: IMMERSION-COOLING TECHNOLOGY

The Technology Behind IMMERSIO™ Modular Battery System : Immersion-Cooling

 With immersion cooling technology, the battery cells are directly immersed in a non-conductive, non-flammable, and non-toxic coolant. This coolant is pumped through the system with a dynamic flow rate. In the scenario of a cell failure, the coolant will absorb the heat more effectively with its direct contact with the cell and cut off the thermal stresses onto surrounding cells, preventing thermal runaway and propagation. Because of the fact that the coolant is non-flammable, it also acts as a fire suppressant.

Superior Thermal Control

The Challenge For Thermal Control 

Thermal control is one of the most critical features and considerations when designing battery systems for electric vehicles. The battery cells only have a narrow window of operating temperature for optimal performance. Fast charge under low temperature could lead to lithium plating, and operating at high temperature could lead to the rapid build-up of solid-electrolyte interphase, all of which have a negative impact on battery life and potentially have safety implications. The conventional method of hybrid battery system cooling is air cooling via fans and air ducts, whereas electric vehicle battery systems are typically liquid-cooled, with extensive coolant channels, cold plates, and coolant pipes in the interior of the battery system, supported by pumps, fans, coolant tanks, and radiators outside of the battery system. At low volume production, designing a manufacturable and safe liquid-cooled is challenging and costly. Moreover, the contact between coolant and the battery cells is still secondary, separated by a coolant jacket, electrical insulators, cold plates, or both.

All battery cells' performance and cycle life decrease due to heat, therefore thermal management is one of the most crucial part of battery system design.

Enhanced Safety Design for Advanced Applications

While a lithium-ion battery cell is powerful to deliver optimal performance to suit versatile needs, it is very sensitive and prone to failure. Thermal stresses (e.g. overheating), electrical stresses (e.g. overcharge, over discharge, and short-circuit), and mechanical stresses (e.g. penetration, and crush) can all lead to severe cell failures. When a single cell fails, the material within starts an exothermic (energy-releasing) decomposition reaction, and the rate of decomposition is positively correlated with temperature. In short, as temperature increases, decomposition occurs, further increasing the temperature, which causes further decomposition. This forms a feedback loop until the temperature reaches a point to rupture the cell and the remaining energy within the cell is released in the form of heat and pressure.  

Many can lead to severe battery cell failure: overheating, overcharge, over discharge, short-circuit, foreign object penetration, and crush.

Most battery systems consist of battery cells densely and tightly packed with each other. With such a release of heat and pressure, surrounding cells are now also exposed to the mechanical, electrical, and thermal stresses, causing them to fail. This sets off an uncontrollable, powerful, and extremely dangerous chain reaction, commonly referred to as the thermal runaway event or thermal propagation event. In addition, when cells fail and rupture, gases are generated and vented from them. These released gases consist mainly of water, carbon dioxide, carbon monoxide, hydrogen fluoride (HF), and some light hydrocarbons (methane and ethane). Some of these gases are toxic (e.g. carbon monoxide and hydrogen fluoride), whereas the light hydrocarbons are extremely flammable. Under high temperature and an oxygen-rich environment, the gases will easily reach their flash points and set off further explosions and fires, which are different from conventional fires and more difficult to put out. 

As a result, one of the most critical safety concerns with existing battery system design is how to prevent these thermal runaway events and deal with their aftermaths. With immersion cooling technology, the battery cells are directly immersed in a non-conductive, non-flammable, and non-toxic coolant. This coolant is pumped through the system with a dynamic flow rate. In the scenario of a cell failure, the coolant will absorb the heat more effectively with its direct contact with the cell and cut off the thermal stresses onto surrounding cells, preventing thermal runaway and propagation. The coolant with its direct contact with the cell is also more capable of managing the pressure from the release of gases. With immersion cooling, the lower overall temperature in the case of a single cell failure will prevent the gases released from reaching their flash points, eliminating the possibility of further explosions and fire. Because of the fact that the coolant is non-flammable, it also acts as a fire suppressant. 

Lithium-Ion Battery Cells

Cooling Fluid

Isolation Shield

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With immersion cooling technology, the battery cells are directly immersed in a non-conductive, non-flammable, and non-toxic coolant.

To design and build such an immersion-cooled battery system, one has to take into consideration the flow channels within the battery modules for optimal coolant flow. To reduce the number of coolant piping, modules should be stacked together tightly, leaving a continuous flow channel for the coolant. The entire system should also be designed to be leak-tight and leak-tested. Furthermore, coolant selection is also a critical consideration. Because of the fact that the coolant is expected to directly contact the battery cells, this coolant has to be non-conductive, eliminating water and ethylene glycol from the choices for consideration. Hydrofluoroether has gained popularity in recent years as a substitute for ozone-depleting refrigerants such as CFCs and HFCS, and can be used as a non-conductive coolant in immersion cooled battery systems.

Immersion-cooling achieves effective distribution of heat and homogeneity between the battery cell temperatures.

The proper design considerations for immersion-cooled battery systems are completely different yet much simpler than conventional liquid-cooled battery systems. Essentially, an immersion-cooled battery system integrates the cooling system into the battery housing itself, without extensive coolant channels, cold plates, and coolant pipes. Pressure relief features are now part of the battery housing, rather than only a feature of the cooling system. However, it does mean that the battery housing needs to be leak-tight, as any moisture or air would compromise the coolant’s ability to conduct heat away or to the battery cells and to flow through the system. This offers the added benefit of environmental sealing to ingress protection (IP67) as part of the basic design.

An Innovative Method for Battery System Thermal Control

With an ever increasing global demand for electric vehicles, demand for safer and longer lasting electric vehicles and EV batteries are on the rise. Immersion cooling is an innovative method for battery system thermal control, opening up new frontiers for thermal runaway prevention and battery cycle life, increasing the battery system’s environmental adaptability. In addition to enhancing the optimal performance and safety of passenger electric vehicles, immersion cooling also presents a new pathway towards the electrification of off-highway vehicles, especially for low-volume high-mix applications. 

Want to Learn More?

XING Mobility is The Immersion-Cooling Technology Market Leader 

WHITE PAPER

HOW TO ENGINEER A BETTER SYSTEM FOR OFF-HIGHWAY VEHICLES

Certain challenges emerge with the electrification of off-highway vehicles, also includes most non-road mobile machinery, there are also opportunities for battery makers to tap into the off-highway vehicle market and secure a significant market share. This white paper aims to address two critical areas for battery design for off-highway vehicles, cycle life and thermal management.

SAFETY
BROCHURE

IMMERSIO™ MODULAR BATTERY SYSTEM SAFETY BROCHURE

Within IMMERSIO™, there are three major components that make this battery system the safest choice on the market: the Cooling System, the Battery Management System (“BMS”), and the Battery Active Safety System (“BASS”). The philosophy that threads these three parts together is XING Mobility’s Advanced Safety engineering design.

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