Current innovations in liquid cooling systems:

Liquid coolants are typically mixtures of water and petroleum-based products (such as propylene glycol), which have higher heat capacity, low freezing points, and better thermal conductivity. Notably, extensive research on the direction of cooling with liquid coolant showed that tab cooling is more efficient and can extend the battery life by three times that of surface cooling. However, the engineering of tab cooling is complex.

The liquid cooling system can be direct or indirect. Indirect liquid cooling typically involves circulating a water-glycol mixture through tubing around the battery pack. Several current models (such as Tesla, Chevy Volt, BMW i-3 and i-8, Jaguar I-pace) use this system. The Tesla Model 3 uses a machine assembled tubing (also called “bandolero”), which has significant improvements over the previous models. Audi e-tron has a more sophisticated cooling system for maintaining an optimum battery temperature and cooling the motor parts. It uses 5.8 gallons of coolant circulating through a 40 meter tube in combination with a typical heat pump. The Chevy volt cooling system comprises rectangular aluminum cooling plates (containing coolant paths), which are stacked between the battery packs as shown in the animation below.

In the direct cooling system, the battery is in direct contact with the liquid coolant. Therefore, the coolant must be nonconducting to prevent any electrical hazard from the cell current flow. Although there are no EVs on the market that use the direct cooling system, innovative approaches are emerging rapidly with practical testing. XING Mobility has launched an immersion cooling technology by sinking the battery pack into a nonconducting liquid that has a high boiling point (3M Novec 7200 engineered fluid). Additionally, their research team is developing modular battery systems for different manufacturers.