Phase change thermal management for batteries

[edatoakrun]

First mention I'd read of this technology applied to a BEV, so I thought it worthy of a new thread.

The LEAF battery, as I understand, is inherently stable, so the "thermal runaway" argument does not apply for us, but the more rapid capacity loss of LEAF battery packs in hotter climates certainly has upset a lot of LEAF drivers.

The potential for much simpler and cheaper heat regulation for all BEV batteries may be quite significant, IMO.

AllCell Technologies’ new material

If you have spent time at any of the EV industry trade shows, you’ve probably heard the term thermal runaway. It refers to a chain reaction in which an increase in temperature causes further increases in temperature and uncontrollable release of energy. It’s the technical way that engineers like to say “explode.”

Lithium batteries are particularly susceptible to these thermal runaway events for a few different reasons, including their high energy content and their propensity to self-heat once the electrolyte reaches a certain temperature (anywhere from 70° to 130° C, depending on the chemistry).

This makes the thermal management of an EV battery pack extremely important. Engineers who set out to design energy-dense packs have to employ robust cooling systems, often using liquid cooling loops with hundreds of channels. The complexity of these systems adds cost - somewhere around 10-20 percent of the overall cost of the battery pack.


The Chicago-based firm AllCell Technologies thinks it may have a better solution: phase-change material (PCM).

A PCM is a substance that is good at absorbing large amounts of heat energy while melting from solid to liquid, and then releasing the energy while freezing back into a solid.

There are a lot of other industries that use PCM for thermal management. You will find it in everything from aeronautical to building applications. As of October 2012, AllCell holds the applications patent for PCM use in thermal management of lithium-ion batteries, ultracapacitors, and fuel cells.

How it works

The company’s PCM of choice is a graphite composite material - basically a combination of wax and the same stuff that’s inside pencils. A battery cell is surrounded by the PCM, and as it heats up, the waxy material softens, absorbing the heat. When the cell cools off, the PCM hardens, releasing the heat into the atmosphere.

The key to using it in packs with a large number of individual cells is the material’s thermal conductivity. If you have an individual cell that has a problem, such as an internal short circuit or nail penetration, that cell will create more heat than others.

When you have a big thermal runaway, the problem starts with a single cell, and then spreads quickly through the entire pack. This material can quickly move the heat away from the problematic cell and absorb it to prevent a chain reaction.

Massively passive

AllCell is now producing battery packs with its PCM technology for light EVs like bikes and scooters.

“Currently, in bikes and scooters there are no active cooling systems, so this is the only thermal management system that we believe is currently in that market,” says Jake Edie, AllCell’s VP of Business Development.

Thermal management systems that use fans and pumps add cost and weight, and take up precious physical space that light EVs can’t spare. AllCell’s PCM has a big advantage here, because it mainly occupies the space between the cells, previously filled with air...

http://www.chargedevs.com/content/features-inside/allcell-technologies%E2%80%99-new-phase-change-thermal-management-material" onclick="window.open(this.href);return false;

BTW, I have a "massively passive" Solar home, and it works quite well.

I am already thinking of how many more South facing windows I could have put in (I already need to open a few windows to cool down on occasional balmy 50+ F January afternoons) if I had a reservoir of some phase change material in my home.

 

[linkim]

Further information on AllCell can be found at:

http://www.altenergymag.com/news/2012/10/11/allcell-granted-us-patent-to-prevent-thermal-runaway-propagation-in-li-ion-batteries/26660" onclick="window.open(this.href);return false;