Dec 20, 2019 - 07:48 AM
Through our work with battery system designers and manufactures as well as the vehicle manufacturers themselves we have learned that the use of indirect cooling using cold-plates integrated into battery modules of EVs is both very expensive and has been a source of dangerous failures as well.
Attached to this article is a the Technical Paper we published in October 2019 on the efficiency of AmpCool Dielectric Coolants for Battery Thermal Management by Dr. David Sundin and Sebastian Sponholtz.
For those not entirely familiar with the use of cold-plates in battery modules a quick overview helps to provide context. Within the battery module, the battery cells are oriented so that the cold plates ( a liquid cooled heat sinks within which the glycol / water coolant flows) are typically oriented against the positive and negative tabs of the battery cells. The difficulty with this arrangement is that all of the cells must be oriented in such a way that all of the battery tabs are aligned along the same axis, this limits the orientation the dimensioning of the battery module. In addition the cold place, which is typically constructed of aluminum cannot actually be in direct contact with the battery tabs (especially the + tab) as they are electrically charged.th Thus to ensure thermal conductivity from the battery tabs to the cold plates they require a non-conductive thermal interface material between them. This creates a series of "layers" between the heat source, the battery tabs, and the water coolant. These layers all have different levels of heat dispersion so the overall effectiveness of the cooling is far reduced from the capacity of the water based coolant. In addition, the need to insulate the conductive water based coolant from the battery results in a complex system of heat spreaders, piping, custom cold plates, and leak detection systems all of which adds to the weight, cost and manufacturing complexity of the battery module.
In addition this design can result in leakage of the water based coolant within the battery modules which can result in shorting and thermal runaway of the batteries themselves when the water comes into direct contact with the batteries. Eliminating this leakage is nearly impossible during a vehicle crash as the batteries make up a huge mass of the vehicle itself. Once the water based coolant has shorted out a battery cell, its typical that the thermal runaway situation quickly spreads to the other batteries within the module due to the heat generated by the cells resulting in a catastrophic situation.
While thermal runaway situations of standing vehicles has occurred, all of our EV customers have indicated that this represents an insignificant fraction of the failures, while coolant leakage following a vehicle crash or because of a manufacturing defect is a far greater concern and the elimination of these failure conditions is their key focus.
In addition the use of 2 phase (2PIC) coolants, such as fluorinated fluids, like Novec or Galen, has been proved to be less effective and more difficult to use than SLIC coolants. These 2PIC coolants build up high pressure during use, are extremely difficult to trouble shoot for leak detection, and during a catastrophic failure scenario the coolant actually fully evaporates out of the battery leaving the cells completely unprotected from thermal runaway. In addition, these coolants are extremely heavy (typically over 2x the weight of water and 3x the weight of AmpCool) and expensive (10x the cost of AmpCool).
Engineered Fluids' AmpCool Single-phase Liquid Immersion Coolants eliminate all of these issues by enabling the coolant to remain in a liquid state and in direct contact with the battery cells during the entire cooling process. This direct contact with the battery cells results in increased thermal transfer efficiency of the battery and simpler battery management systems. Because the AmpCool coolants have a dielectric strength of >60KV over 2mm they fully avoid all shorting issues by being electrically non-conductive.
The benefits of using AmpCool and SLIC for battery cooling are:
- Elimination of all conductive fluids in the battery
- Increased thermal transfer through direct contact of the coolant with the entire casing and tabs of the battery (as opposed to just tab cooling with cold plates).
- Simplification of the internal battery structure as all the heat sinks, thermal transfer materials, complex support matrices and cold plates are eliminated and replaced with a simple container that surrounds the batteries and is filled with a minimum amount of fluid.
- Reduced cost through the elimination of the complex systems
- Reduced weight through the elimination of the all the excess materials and complex systems.
- Increased reliability through greater thermal transfer and elimination of the failure scenarios.
- Better vehicle range and faster charging due to better thermal management.