This article was reviewed by a Caltech faculty member.
As part of Conversations on Sustainability, a webinar series hosted by the Caltech Science Exchange, Kimberly See, assistant professor of chemistry, discussed her research into batteries that can store more energy and are better for the environment.
See hopes that by developing new battery chemistries, scientists can help reduce the environmental and human costs associated with battery manufacturing, and enable advances in renewable energy, such as wind and solar power, that will create a greener future.
Here, See talks with Caltech science writer Emily Velasco.
The questions and answers below have been edited for clarity and concision.
It seems like everyone's phone and laptop is always running out of charge. Why aren't batteries better?
Batteries are actually really amazing at what they do. They can do a lot more now than they could before the 1990s, and that's because the lithium-ion battery revolutionized portable electronics and portable energy storage.
But batteries do wear out. Their capacity starts to decrease over time, and I think that's what you're talking about when you ask why batteries aren't better. The reason why they hold less and less charge over time is because of changes in the complex mechanisms inside of the battery that allow it to store charge.
So, when a battery wears out, for example, when you have to buy a new battery for your laptop, what is actually happening in there?
There are a lot of things happening in there, and this is actually an active area of research—trying to figure out exactly why batteries fail and why the capacity fades.
But some of the reasons are associated with reactions that happen in the battery that cause the formation of a film on the surface of the electrodes. Another reason is that lithium ions can get stuck in the materials at the two electrodes, and when lithium gets stuck, the battery loses the ability to store as much energy.
Negatives aside, it does seem like batteries have come a long way in our lifetimes. Can you talk a little bit about how batteries have changed in the past few decades?
The very first battery was the voltaic pile, which was invented in the late 1700s by Alessandro Volta. That battery is what's called a primary battery, meaning that you can discharge the cell once and you can't recharge it.
We still use primary batteries all the time. For example, in your TV remote, you likely have a primary battery. When it runs out, you don't plug it into the wall to recharge it. You put a new battery in, and you dispose of the old one.
That was the status quo for a long time, and then rechargeable cells came about. These are called secondary batteries.
The mechanisms inside those two kinds of batteries are very different, and you need different chemistry inside the batteries to do that.
What happened in the 1990s was the invention of the lithium-ion battery. The mechanism by which it stores charge is fundamentally different than the status-quo rechargeable cell before that. It was a huge revolution and won the Nobel Prize a few years ago.
Lithium batteries seem to be the gold standard, at least in consumer technology, but you and other researchers are working on the next generation of batteries. What does that research look like?
Next-generation battery research is all about moving beyond lithium-ion. We're trying to be better than that. Being better can mean a lot of different things: You can think of metrics like capacity, which is the number of electrons I can store in the material and is proportional to the energy density. But you can also think about where materials in the battery come from. Lithium-ion batteries contain resources that are somewhat problematic: things like cobalt, nickel, and lithium. They aren't the most sustainable elements to have in a technology that's going to be widespread across the world, so my group is trying to use materials that are more abundant and more sustainable and less expensive than what's currently used.
To take a step backward: How did you become interested in batteries? What did you find appealing about them?
I was always really interested in energy research, and like a lot of young scientists, I saw the climate crisis and the issues that we have with our energy infrastructure. That's why I ended up going to grad school: I saw chemistry as a way to help solve these problems. And I just got really, really lucky in grad school and worked for an adviser who had a project in battery chemistry.
I was excited to learn about how batteries can fit into the bigger picture of sustainability.
You just alluded to this, but how do batteries fit into plans for renewable energy?
Batteries play a pivotal role in renewable energy resources. Actually, I shouldn't say batteries; I should say energy storage.
We only have wind power when the wind is blowing, and we only have solar power when the sun is shining. That's an issue with the type of energy consumption that we require as a society. In order for intermittent renewable energies to really impact the grid, we need to get rid of the intermittent part. For that, we need storage, so energy can be used when it's needed and not necessarily when it's produced.
Right now, batteries don't play in that area at all. It would be really great, though, if we could come up with a sustainable and inexpensive energy-storage solution that would propel wind and solar into the same regime of something like coal, which is relatively cheap.
Can you talk more about the downsides of materials such as lithium and cobalt? What are the human and environmental costs?
The primary workhorses of lithium-ion batteries are lithium, cobalt, and nickel. We'll start with lithium. Lithium is the ideal charge-storage material. It's small, it's lightweight, and it has a really low reduction potential, which means that you can store a lot of energy. For all of those reasons, lithium is amazing. From a resource perspective, it's not rare, but it's not found everywhere. The downside of lithium is that it is a finite resource, and it's more finite than other alternatives that we work on, like magnesium, calcium, zinc. All of those materials are orders of magnitude more abundant and found all over the world.
When it comes to cobalt, there are significant humanitarian issues. Cobalt is primarily mined in the Democratic Republic of the Congo, and there's not a lot of oversight to those mines. There are issues with child labor. And cobalt is a toxic substance in some forms, so it causes a lot of health issues and environmental issues.
The problem with nickel is that it's expensive, so it makes the cell more expensive.
What developments are you most excited about in battery research right now? Solid-state batteries are a hot topic in the news, for example. What are they, and where is the research focused?
From a fundamental perspective, solid-state batteries are really cool. A normal battery has two electrodes and electrolyte, and that electrolyte is usually a liquid. The job of the electrolyte is to allow the ions to move from one side of the battery to the other. In lithium-ion batteries, that liquid is a flammable organic solvent, and there are safety issues associated with using flammable solvents.
Moving away from flammable solvents means going toward solid-state materials that replace the liquid with a solid. But, from a practical perspective, they're very, very difficult. Making solid-state devices is really, really challenging. Ions intrinsically move easier in a liquid than a solid.
Are there any wild battery theories or technologies that are still a ways off but that people are thinking about right now?
You know, sometimes people will try to marry biology and batteries together, and that always just blows my mind, because I don't understand biology at all. So, there are these virus batteries, which I don't understand, but those are kind of crazy.
What's really exciting is that there are so many options. If you look at the periodic table, there's a lot of elements on there you can think about using. In my group, we limit ourselves to things that are sustainable and inexpensive, but even then, there are a lot of different combinations you can think about.
If you had to put on your fortune teller's hat, what would you say that batteries are going to look like in 10 years? What about 20 years?
In 10 years, I think they'll look a lot like they do now. From a user's perspective, they're not going to be that much different, although the chemistry inside them might change a little bit and there might be improvements here and there.
I think in 20 years the solid-state cells might have a pretty big impact on the market. You might think about new applications for batteries. Eventually what we would love to do is have electric aircraft, and you'd have a battery on that aircraft that would make a huge impact on CO2 emissions from airplanes. I think that there's a lot of fundamental science that needs to happen before we get there.
Here are some of the other questions addressed in the video linked above:
- Can batteries be recycled?
- What needs to happen with our battery technology for us to make better use of these renewables?
- Are commercial energy-storage systems helpful?
- How do scientists prototype new battery chemistry?
- What about batteries that can work on other planets or space-based batteries?