Vascular cooling
Battery packing for electric vehicles must protect the enclosed battery cells while removing heat to keep the cells operating at maximum efficiency. The electrification of transport vehicles presents a key technical challenge for packaging the hundreds of individual battery cells present within the vehicle. We are investigating the use of microvascular composites that contain internal cooling networks to provide both self-cooling functionality coupled with mechanical protection and crashworthiness.
Our approach to battery packaging is to surround prismatic battery cells with carbon fiber composites containing internal cooling networks. To design the cooling networks, we perform computational fluid dynamics (CFD) simulations that model the cooling of a composite fin subjected to a battery-generated heat flux. Using these simulations as a guide, we then manufacture microvascular carbon fiber fins using vacuum assisted resin transfer molding (VARTM) and vaporization of sacrificial components (VaSC) to yield fully integrated microvascular composites . During thermal testing the fins are cooled by pumping coolant through the material at prescribed flow rates while imaging with an IR camera.
A second approach to battery packaging we are exploring is the creation of a composite flow battery. With this approach, energy storing fluids are pumped through channels within a structural composite. Flow battery systems that can be used include aqueous redox flow batteries, such as vanadium and zinc-bromide batteries, and semi-solid flow batteries such as lithium-ion semi-solid batteries. Two major challenges for this design are how to form a current collector within the composite and how to form an ion-conducting separator film between the channels. Our approach is to use carbon fiber as a current collector material while using a porous polyimide film as a separator.
Microvascular structural composites for battery packaging. Woven carbon fiber textile fabrics (left image) are laminated and infused with resin through VARTM processing to yield a solid composite cooling panel (middle image). VaSC processing removes the sacrificial fibers that are embedded to yield cooling channels (right image) through which a coolant is pumped during thermal testing.
Thermal testing experiment and results. The image on the left shows the experimental set-up which includes a surface heat flux source below the composite specimen together with external pumps to circulate the coolant through the specimen during the experiment. An IR camera provides surface temperature mapping of the composite through the experiment. The image on the right is the steady state surface temperature of a composite fin with six embedded cooling channels at a flow rate of 28 ml/min while exposed to a heat flux of 500 W/m2 from the bottom surface (typical of the heat load from prismatic battery cells).