As consumers, we are all-too-familiar with the daily chore of charging our smartphones or tablet. With increasing emphasis on greener technologies such as electric vehicles and renewable energy generation, battery technology becomes more important. Words byDr Robert Camilleri.
As consumers, we are all-too-familiar with the daily chore of charging our smartphones or tablet. With increasing emphasis on greener technologies such as electric vehicles and renewable energy generation, battery technology becomes more important.
Classic lithium-ion (Li-ion) batteries are currently the most common, storing energy in chemical form. The problem with these is their temperature sensitivity. During repeated cycles of charging and discharging, the chemical reaction that drives the battery creates heat which affects its storage capacity and lifetime. Not only that, but these high temperatures present a real health and safety concern. Thermal runaway, where a battery creates a vicious cycle of heat generation, can lead to catastrophic failure. Remember the Galaxy Note 7 explosions? So how can we cool batteries down?
Keeping things chill
While a number of studies have attempted to apply traditional cooling (such as the air cooling in the laptop I’m using to write this article) to batteries, this was found to be inefficient for high-performance battery packs. As air passes over the battery cells, it gradually warms up and its effectiveness cooling subsequent batteries deteriorates, leaving battery cells in the same pack operating at different temperatures. The battery cell with the highest temperature becomes the weakest link.
The need to have a fast charging mechanism, especially when it comes to consumer products, is real.
High temperatures limit dis/charging rates and energy storage capacity, causing batteries to degrade faster, dictating the life of the pack. While attempts to use liquid cooling proved to be more efficient than air cooling, they still did not solve the issue. To counter this problem, the industry has developed complex and expensive electronic battery management systems that monitor the temperature of each cell and adjust the charging rate. But again, while this protects the cells, it limits the current flow during discharging, causing long waiting times in between battery use. The need to have a fast charging mechanism, especially when it comes to consumer products, is real. Battery-powered electric vehicles, for example, are much more likely to be accepted if a fast charging mechanism is introduced. This would make them comparable with regular cars that need to be taken to traditional petrol stations for fuel.
A different approach
Our project NEVAC (short for Novel EVAporative Cooled battery technology) solves this problem with a novel cooling strategy. With NEVAC, we want to keep the entire battery pack at a uniform temperature. We’re using a liquid coolant with a low boiling point which absorbs latent heat as battery cells warm up. When the coolant reaches its boiling point, it evaporates and turns into gas. The gas travels to a cooler part of the battery pack, lets off the heat it has absorbed into the ambient environment, and condenses back to liquid, closing the loop of this self-sustained cooling cycle. As the coolant within the entire battery pack boils at a single temperature, all the battery cells within the pack are kept at one uniform temperature.
NEVAC is currently developing an experimental proof of concept of this technology with Abertax, our industrial partner. Following a proof of concept, the project will be scaled up with the prospect of developing the technology for the market. It will show how an improved battery cooling technology will lead to higher battery storage capacity, longer battery life, and better dis/charging rates. That daily chore of charging your smartphone for more than a few minutes could soon be forgotten.
The research is led by Dr Robert Camilleri (University of Malta), in collaboration with industrial partner Abertax Kemtroniks. Project NEVAC is funded by the Malta Council for Science and Technology Fusion: The R&I Technology Development Programme 2017.
Selyukh, A., As Batteries Keep Catching Fire, U.S. Safety Agency Prepares For Change, retrieved on 30th March 2017