Why do Lithium-ion Batteries Need to be Cooled?

Phil Kinnane | June 15, 2012
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Previously, I wrote a blog post about Fiat using modeling to simulate the cooling of their lithium-ion battery packs. This got me wondering how lithium-ion batteries actually get hot in the first place.

The blog site, How Stuff Works, has a couple of interesting posts on how the lithium-ion battery works, and what happens when they get too hot (the worst scenario is that they explode). Unfortunately, they don’t answer the question as to why or how they get hot, just saying that there’s a lot of packed-in energy in a lithium-ion battery, and that means they get hot.

I always assumed that it was due to joule heating — the fact that electrons are moving through the external electrical circuits, as well as the electrolyte and separator — that created this heat. Yet, Dr. Songrui Wang at The Tianjin Institute of Power Sources, in China, simulates the thermal behavior of lithium-ion cells by coupling the physics of heat transfer to the electrochemical. This means that, similarly to normal chemical reactions, these electrochemical reactions can also act exothermically. This fact is also discussed in a White Paper COMSOL and Intertek produced (you can download that lithium-ion battery white paper for free here).

Plot of temperature in a lithium-ion cell
Plot of temperature and temperature rates over time in a lithium-ion cell; the
region and extent of thermal runaway is pretty evident from the sudden and
large increase in temperature.

Dr. Wang analyzes the risk of potential fire hazards associated with lithium-ion batteries, which are fast becoming the most popular sort of battery for vehicles, mobile devices, and many other applications. The models save both the institute and their partners’ money by replacing the costs of running hundreds of dangerous and tedious experiments, while also promoting the awareness of these cells’ safety aspects. I recommend that you read it, by accessing their lithium-ion battery research here.

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