Building a better battery

[MUSIC: "Lithium” by Nirvana.]

KEITH HAUTALA: And that was Nirvana, coming in at No. 3 on your periodic table, with “Lithium.” A little trivia for you folks: Way back in 1991, they called that kind of music “grunge.” We’re not talking about heavy metal here. It’s really more of a light metal. In fact, lithium is the lightest metal there is. Well, whatever, nevermind. We’ll be back with more lithium in just a moment, here on the Engineering Out Loud show!

[MUSIC: “The Ether Bunny” by Eyes Closed Audio, used with permission of Creative Commons Attribution License.]

NARRATOR: From the College of Engineering at Oregon State University, this is Engineering Out Loud.

HAUTALA: Welcome back. I’m Keith Hautala. This season on Engineering Out Loud, we’re highlighting research by some of our talented students here at Oregon State. Now, if you’re listening to this podcast on a mobile phone, or a laptop, or perhaps on the stereo system of your hybrid or electric vehicle, chances are you’re using the technology we’re featuring today. We’re talking, of course, about lithium-ion batteries.

LYNZA SPROWL: Exactly! Batteries are what we’re talking about.

HAUTALA: We should probably get some introductions out of the way.

[MUSIC: “Sleep,” by Ryley Martin used with permission of the artist.]

SPROWL: My name is Lynza Sprowl. I am a fifth-year Ph.D. student in chemical engineering and I study lithium-ion batteries. I do computer modeling of atomic-scale reactions. So, we look at electrons and nuclei in atoms and see how different atoms interact with each other and we can get energies of atomic systems. And so we can look at reactions that are happening, products that are formed, and compare different energies and see what reactions are most favorable, the amount of charge that’s transferred between different atoms. Things like that.

HAUTALA: I was curious: Of all the things you could study as a chemical engineer, what would make somebody choose to dedicate their life to building a better battery? I’ll let Lynza explain.  

SPROWL: I went to a talk, and a guy was talking about solar energy. And one plot he showed was a plot of when the sun shines – and when solar energy can be generated – versus when people use energy, and they’re the exact opposite. So, the sun shines during the day, people use electricity to power lights in the morning and at night. And just looking at this difference between the two plots, I was like: “Wow, you need some kind of storage!”

[MUSIC: “Sleep,” by Ryley Martin used with permission of the artist.]

SPROWL:  I like being immersed in batteries and renewable energy. I like learning about it. I like contributing to the field. I like the idea of other people who actually make batteries commercially maybe looking at my work and using it to actually make a better lithium-ion battery.

HAUTALA: Lynza’s passion is for the future of energy. She says the limitations of our current energy storage present a major challenge. Especially as we move to adopt more sustainable, renewable sources of energy, such as wind and solar power.

SPROWL: Energy storage is a bottleneck for the future of energy. Solar is moving along, wind is moving along, but if you don’t have batteries to store that energy, renewable energy isn’t going to go as far.

HAUTALA: That sounded to me like what we need is just a whole BUNCH of batteries. And we already have a whole bunch of batteries. So, problem solved, right? But as Lynza explains, it’s not quite that simple.

SPROWL: We do have batteries, but they’re not really big enough or powerful enough for what we really need. We have batteries in cell phones, laptops … there are getting to be more cars and electric vehicles. But there’s more that we can do to make them better.

HAUTALA: All batteries store energy in chemical bonds. Lithium-ion batteries use lithium, which as one of the Group 1 alkali metals, is highly reactive. This is due to its electron configuration, with its single valence electron, which is readily given up to create bonds and form compounds. I asked Lynza to give us a crash course in how lithium-ion batteries work.

SPROWL: At the anode side of the battery, the lithium binds with a higher energy, and then when the battery is discharged, lithium ions move across to the cathode.

HAUTALA: Anodes and cathodes and electrolytes? Oh my. Let’s back things up a bit for those of us who might not have studied all that chemistry in a while.

SPROWL: The anode and cathode are two electrodes in the battery. The anode is the negative electrode, which holds lithium with more energy, whereas the cathode is the positive electrode and binds lithium with a lower energy. And so you charge a battery, you’re putting high-energy electrons into the anode to meet up with the positive lithium ions to store that lithium atom in a high-energy state in the anode. Whereas when you discharge a battery, the electrons power your device, lose some energy, and meet back up with the lithium plus ion to store the lithium atom in a lower-energy state in the cathode.

[MUSIC: “Sleep,” by Ryley Martin used with permission of the artist.]

HAUTALA: A key measure for improving battery technology is energy density, or the amount of energy a battery can store relative to its size or weight. Here’s where the chemical engineering comes in.

SPROWL: One way to make batteries have a larger energy density is to be able to store more lithium, and move more lithium back and forth between the cathode and the anode. So, the first way is more lithium. The second way is to have the bonds be higher-energy bonds in the anode and lower-energy bonds in the cathode. And you can do that by changing the material. Different materials bind to lithium with different strengths. So if you can find an anode that’s stronger, you can store more energy. Typically, lithium-ion batteries have a graphite anode. But silicon can store 10 times more lithium. So, if you can increase the amount of lithium that’s stored, you can increase the energy density of your battery.

[MUSIC: “Sleep,” by Ryley Martin used with permission of the artist.]

HAUTALA: As you might guess, the chemical reactions that occur inside a lithium-ion battery are pretty complex, and when you start changing things around, it fundamentally alters the way the battery performs.

SPROWL: A problem with silicon anodes is that the electrolyte breaks down on the anode surface, and this breakdown of the electrolyte forms a solid barrier. So this barrier inhibits lithium ions from reaching the anode. And if the lithium ions can’t reach the anode, then you can’t charge the battery fully, which is a problem.

HAUTALA: But that’s not the only problem.

SPROWL: As the electrolyte breaks down on the anode surface, it also consumes some lithium. So you have fewer lithium ions that can reach the anode. And so I’m looking at the breakdown of electrolyte on the silicon surface.

HAUTALA: So, if the problem is caused by the electrolyte breaking down, it seems like the obvious question would be “How do you stop the electrolyte from breaking down?” As it turns out, that question is just a little bit too obvious, and the answer is way more complicated.

SPROWL: You can’t stop it from breaking down, but you can add different organic solvents that break down differently, so you can kind of control what products go into this barrier.

HAUTALA: So, basically, you want to engineer an electrolyte that will break down to form a barrier that lithium ions can still get through.

SPROWL: You want a barrier which is ionically conductive, so the lithium ions can diffuse through and reach the anode. If the electrolyte solvent breaks down differently, you make a more ionically insulative barrier which doesn’t allow lithium ions, or it can be more conductive to allow lithium ions.

HAUTALA: When it comes to improving battery technology, chances are we’ll be looking at an incremental, slow but steady, increase in battery life and energy density over the coming years, rather than some revolutionary new technology that will change how we think of batteries overnight.

SPROWL: So far the history kind of shows that batteries improve about 7 percent every year – whether that’s getting a little bit more inexpensive or whether you can store a little bit more energy – it’s about 7 percent.

HAUTALA: That means the batteries we’ll be using  10 years from now should be about twice as good as the ones we have today. But can we do better?

SPROWL: If you fundamentally change the technology – by putting in a different anode, a different cathode, that kind of stuff – you could make a bigger jump. If you changed to silicon anodes for instance, it would jump a little bit more than that – 10 to 15 percent.

HAUTALA:  We don’t have lithium-ion batteries with silicon anodes just yet. But we might start to see that and other promising new technologies in the near- to intermediate future.

SPROWL: Right now, it’s lithium ions with a graphite anode. In the future, the near future, it’s lithium-ion with a silicon anode. Beyond that, there’s lithium-sulfur batteries which have have a sulfur cathode which is way cheaper than a transition-metal oxide.

HAUTALA: Lynza recently spent a full year working with scientists at the Department of Energy’s Argonne National Laboratory, just outside Chicago. I asked her to talk a little bit about what she got out of her experience there.

SPROWL: Being at Argonne was really cool. There’s lots of leaders in the battery field and there’s also lots of battery researchers. So there’s always someone that I could bounce ideas off of, or learn from and ask questions. I worked mainly under a computational scientist there who helped guide me, but I also talked a lot with an experimentalist, who talked with me about what are actually problems in batteries from the experimental side. So, I could learn a lot from other people there. Grad school can be rough after a little while, but I guess going to Argonne for a year in the middle of it, for me, was a nice change of scenery.

HAUTALA: Before we go, I wanted to share with you something I learned from Lynza’s research that has practical implications for all of us, today, in our everyday lives.

[MUSIC: “Harps Uplifting,” by Mortal Thing used with permission of the artist]

SPROWL: Something that my research found was that in a higher charge state, the electrolyte breaks down more readily. And with the electrolyte breakdown, the lithium ions can’t reach the anode as easily, so you can’t charge your battery as much. And so, if you leave your cell phone – or your laptop, whatever – in a high charge state, for a long time more electrolyte will break down and you will decrease the lifetime of your battery much quicker than if you have your phone in a lower charge state. So if you plug your phone in overnight to charge it and it gets to 100 percent in a couple hours, the rest of the time you’re sleeping, you’re just decreasing the lifetime of your battery. Whereas, if you charge it a little bit until it reaches 100 percent, take it off the charger and let it start going down, and keep doing that, you’ll increase the lifetime of your battery.

HAUTALA: So, you got that? Unplug your charger when your device gets to 100 percent! The planet will thank you.

[MUSIC: “The Ether Bunny” by Eyes Closed Audio, used with permission of Creative Commons Attribution License.]

This episode was produced by me, Keith Hautala, with additional audio help from Brian Blythe and Rachel Robertson. Our intro music is “The Ether Bunny” by Eyes Closed Audio on Soundcloud, used with permission under a Creative Commons Attribution license. Other music and sound effects were also used with appropriate licenses. You can find the details in our show notes, which are online, along with other episodes, at engineeringoutloud.oregonstate.edu. Subscribe on our website, or by searching for “Engineering Out Loud” on your favorite podcast app.