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Batteries in Space: Preventing Catastrophic Failures and Validating Safe Designs

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Ann Nguyen:

Hi everyone. Welcome to this podcast from The Knowledge Foundation for the 5th Annual Battery Safety conference, which runs November 13-14 in Washington, DC. I'm Ann Nguyen, Associate Conference Producer. Today we're chatting with one of the program's speakers, Dr. Judith Jeevarajan, Battery Group Lead in the Power Systems Branch at NASA Johnson Space Center. Judy, thanks so much for joining us.

Judith Jeevarajan:

My pleasure.

Ann Nguyen:

Can you broadly describe the focus of your battery work at NASA, and what the environment and resources are like there for conducting your research?

Judith Jeevarajan:

Sure. My battery work at NASA spans a wide range. I do from research & development or improving batteries for use in a human-rated space environment. The main focus of my work is to confirm battery safety. My research development efforts include testing state-of-the-art cells to categorizing performance and also determine their tolerance to various off-nominal or abusive conditions. When we carry out the tests on the off-nominal conditions or abusive conditions, we can actually determine the worst-case failures that can occur with a particular cell or battery design, and so these research efforts actually help me in understanding the worst-case failure modes, and help the hardware developers also in designing their batteries safely. And finally we also want to test the batteries appropriately to confirm that their battery design is safe. The safety we are concerned about is mainly for these batteries to be safe in a human-rated space environment.

The NASA programs actually recognize the value of this type of independent research, and fully support the effort. They provide the funding to not only carry out the work, but also present it at conferences, so that the others in the battery industry will benefit from it. At Johnson Space Center, we have the required facilities and equipment, and also resources, to carry out the entire range of battery tests from characterizing the performance of these cells and batteries in nominal conditions all the way to determining their tolerance to relevant and credible off-nominal conditions.

Ann Nguyen:

And for your second question, there must be unique challenges when it comes to designing and using safe lithium-ion batteries in the space environment. What are some of them and how do you address them?

Judith Jeevarajan:

Yes. There are a couple of very unique challenges. The first thing is using batteries in space includes a microgravity environment, and the bigger challenge actually is the use of these batteries safely in a confined habitable volume where the crew resides. In this type of environment, we actually have a zero tolerance to a fire, so the confined volume and the [inaudible] tolerance to a fire demands a very stringent evaluation of the safety of the batteries. So the reason we do this is because the crew members cannot really step out of a space vehicle like they would on ground, either like from an automobile or from a portable equipment fire type of event.

The other challenge is that batteries are sometimes located or used in a deep space vacuum environment, and this of course is a bigger problem for us. For instance, with lithium-ion batteries, I would like to talk about that as an example. External shorts and overcharge are two of the many hazards that you would encounter with it, and these can actually lead to fire and thermal runaway. In an ambient pressure environment, most lithium-ion cells in batteries, when shorted, may display some charring, also some minor venting as the heat dissipation and due to convection as well as the conduction between cells is faster. But when you have the same event under vacuum conditions, fire and thermal runaway occur when external shorts occur – when external short conditions are levied on lithium-ion cells and batteries.

When you look at an overcharge condition for instance, under that failure mode, under ambient pressure conditions the events are more catastrophic. You would see instantaneous fire and thermal runaway if there are no protective features or if the battery is not designed correctly. But under deep vacuum conditions, the events are quite benign because the cell-to-cell thermal propagation is minimized due to a lack of convection. So these types of issues are actually addressed by testing under the relevant conditions and environments and also designing the batteries with the right balance to address all the different catastrophic hazards that we can encounter in a space-rated environment.

Ann Nguyen:

And finally, what will be the main theme of your presentation at the conference on November 13th?

Judith Jeevarajan:

On November 13th, I'll be presenting on the topic of meta-propagation of thermal runaway from one cell to the next in a battery design can be prevented. With the recent events in the commercial aerospace, automobile and electronics and batteries, this type of study is very relevant. What we are trying to determine is the factors that cause the propagation in the first place and I'm also trying to use various methods to prevent the heat from spreading from one cell to the next. The preliminary data is what I'll be presenting at the conference on November 13th.

Ann Nguyen:

Excellent. Well, we're really looking forward to hearing more about your research and work which sounds really fascinating to me, so Judy, thanks once again for your time and insights today.

Judith Jeevarajan:

Sure. Thank you.

Ann Nguyen:

That was Dr. Judith Jeevarajan of NASA Johnson Space Center. She'll be speaking at the 2014 Battery Safety Conference taking place November 13-14 in Washington, DC following the Lithium Battery Power conference. If you'd like to hear her in person, visit www.knowledgefoundation.com/battery-safety for registration information and enter the keycode "Podcast". I'm Ann Nguyen. Thanks for listening.

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