The solution seems to be liquid vs. air cooling. The article states that air is less dense at higher altitudes and is less efficient in cooling anything even though it's at a lower temperature. Volt has gone to liquid cooling that works. What is Boeing waiting for? Call the GM engineers and find out what they did. A Volt did go on fire a little while ago.
Yes, Gorksi, it's a matter of liquid versus air cooling. It's also a matter of passive versus active cooling. As far as we can tell, Boeing is using passive air cooling. There reportedly are no fans to draw the hot air away. Toyota uses air cooling on its Prius PHV, but it is active air cooling -- they use three fans to draw the heat away from the battery's cells.
I don't know how much it would cost to add liquid cooling, Cabe. In today's electric cars and plug-in hybrids, packaging is said to be about 50% of the cost of the entire battery package. How much that differs between passive and active cooling situations, I don't know. Whatever the cost, though, the production volumes for a 787 are ridiculously small compared to those of a production car, so the cost wouldn't be multiplied by hundreds of thousands of units.
Liquid cooling is not my favorite solution. The thermal energy developed during lithium ion battery charge discharge cycles should be just moved away from the source. To obtain an efficient thermal energy transport the use of heat pipes will bring much more benefit. In case of battery thermal runaway the water system will be a big, big problem.
Thermal runaway occurs at 120 -200 deg. Celsius, is a strong exoterm reaction which can not stop until all active material is consumed. Actually is the liquid electrolyte which starts decompose. The only commercial available technology able to transfer more than100 watt/ cm2 is the heat pipe. Boeing should have experience with this technology. It was extensive in the spacecraft technology to cool the sunside of a spaceship (transfer the heat from the hot to the cool side). More than that the heat can be transferred to a heat exchanger outside the battery walls (trough the firewalls). Another system should be also included to cool down the cells at bellow 20 degrees Celsius where the liquid electrolyte ions stop to move (available for the military technology). This approach is possible to be implemented with special designed hot pipes at reduced volumes. The space for the cooling pipes (integrated into cooling plates between the cells) is the same as with the current (empty space between the cells) Boeing solution. Yes, Walter can be dangerous, if water comes in contact with battery electrodes the battery will explode.
You've been all over this story, Chuck, and it seems like it will continue for awhile. Great coverage. I agree that it seems to be a liquid vs. air debate. Perhaps some of the latest research I've covered about lithium-ion battery design could be helpful in terms of what best way to design the battery so this doesn't happen again. I guess it's a little too late to start from scratch, though, so Boeing will have to fix the problem based on what it's already done.
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