Lithium-Air Batteries Could Give Electric Vehicles a 1,000 Mile Range
Range anxiety is the #1 consumer concern for electric vehicles, but a new breed of ultra-high energy density batteries may change everything. We’re joined by Dr. K.M. Abraham, an award-winning pioneer in lithium-ion battery research and the inventor of the lithium-air battery, who explains how a 40-year-old breakthrough in battery technology may lead to electric vehicles with a 1,000 mile range, smartphones that last for a week & drones that fly for hours.
K.M., welcome! Let me start out by citing a bit of your work on lithium-ion batteries. Now in your career, you’ve written more than 200 journal articles and have some 15 patents on lithium-ion batteries. I’m wondering what some of your key innovations have been and how they’ve contributed to advancing this technology.
I’ve been developing rechargeable lithium batteries for more than 40 years. I started my career in 1976 at a small startup company in the Boston area called EIC Laboratories, and one of the programs that we were involved in was to develop a rechargeable lithium battery. This was just after the invention of titanium disulfide as a positive electrode by Professor Stanley Whittingham, who was employed back then at Exxon in New Jersey.
So Whittingham was developing a solid cathode intercalation electrode using titanium disulfide, and our efforts concentrated on developing the lithium metal anode. As you know, a battery has two electrodes, and they both have to work with equal efficiency to get a long cycle life for the battery.
We combined his cathode with our anode, and in 1978 we published one of the first papers on a practical, rechargeable lithium titanium disulfide battery with more than 100 charge-discharge cycles. It was a big thing at that time, to come up with a rechargeable lithium battery that goes for more than 100 cycles.
So, that was one of the early key contributions of mine, and I published that paper in an Electrochemical Society meeting in 1978 in Los Angeles and subsequently published in the Electrochemical Society Proceedings Volume. We published more papers later, early in 1981, ’82 timeframe with different cathode materials, on lithium metal anode rechargeable batteries with capacities as high as 5 ampere hours and hundreds of charge-discharge cycles.
At that time, we were poised to go into business developing these batteries, but the safety became an issue, so they never became a practical system. However, that research helped lead to the development of the lithium-ion battery by Sony, and in 1991, they came out with the first lithium-ion battery.
Now you mentioned the charge-discharge cycles a moment ago. How have you seen the efficiency of these increase over your career?
Well, I mean there are a couple of key things that you look for in a rechargeable battery. The first is cycle life, which is the number of charge/discharge cycles before its capacity falls under 80% of it’s original capacity.
The other is energy density, which is measured as energy per kilogram of the battery for the specific energy, or energy per liter for the volumetric energy density. Those give us the energy density measurements for weight & volume.
In 1991, when Sony came out with their first lithium-ion battery, the 18650 cell, it had slightly less than one ampere-hour capacity. Now, that same size battery has 3.6 ampere-hour capacity. So in the last 29 years, the capacity of 18650 lithium-ion batteries increased by four times.
During that time we’ve also seen the cycle life increase — from maybe around a hundred cycles originally to over 1,000 cycles now. So in terms of lithium-ion cells we’ve seen a large increase in both energy storage and longevity.
From what I’ve read, lithium-ion technology is reaching the fundamental limits for energy storage. Is that becoming an issue?
Right, and here’s why that is happening: the energy density of a lithium-ion battery is a substantially dependent upon the capacity that you can get from the positive electrode, or the cathode.
The material used today’s lithium-ion batteries is a Lithium-containing transition metal oxide, and that material is reaching the maximum number of electrons that it can accommodate reversibly in that material — it is reaching a one electron limit. In order to increase that capacity further, we need to have materials that can accommodate more than one electron, or what’s called multi-electron transfer.
In other words, we need to find new metal oxides or other materials that can accommodate more than one electron per equivalent of a reaction. That’s where sulfur, oxygen and all these new materials come in.
This brings us to your invention: the lithium-air battery. I’ve read that that you discovered it by accident when you noticed that a lithium-ion cells you were testing had an air leak in the electrolyte that produced a higher voltage output. Is that how the discovery happened?
Yes. In fact, I have a paper on that called “A Brief History of Non-Aqueous Metal-Air Batteries”, which is published in one of the electrochemical society proceeding volumes — you can find it in my Google Scholar citations.
Back in the early ’90s we had a fairly large program to develop lithium-ion polymer batteries for electric vehicles — it was part of the effort by the DOE and Big Three automakers. At the time, they were using a key material that we’d developed at EIC Laboratories, a polymer electrolyte, and I was doing research on its chemistry.
During the course of our research, we made a lithium graphite anode half-cell to examine the behavior of the graphite electrode in combination with this polymer electrolyte — and while we were testing this, a colleague came over to me and said, “it looks like I made a mistake because the voltage that we’re getting for the test cell is much higher than it should be.”
We had been expecting to see a small voltage for this half cell, but it was producing a voltage of nearly three volts. So he said, “Oh, I must have made some mistake. Let’s throw it away and I’m going to start over again.” I was intrigued, though, and decided to try to discharge the cell to see if we could any capacity from it. Surprisingly, not only were we able to get capacity, but we were able to get a few charge/discharge cycles from the cell also.
After a bit of thought, I realized that we had a leak in the cell, which meant that the voltage was coming from the electrochemistry of oxygen. Our graphite anode was simply acting as a catalytic electrode for reducing and oxidizing the oxygen. That inspired us to build some experimental lithium oxygen cells, and we were able to demonstrate that they worked, which we later published and patented.
From what I’ve read, lithium-air cells have much, much higher energy densities than lithium-ion cells, with a the theoretical specific energy of non-aqueous lithium-air batteries is around 40.1 MJ per kilogram, which is about 85% of the energy density of gasoline. Is that accurate?
Yes, that’s right. I usually quote that number as about 11,400 Watt-hours per kilogram, which is only accurate for the lithium metal reactant in the cell because you’re bringing in oxygen from the outside atmosphere.
After the first cycle, the weight of the cell increases due to the accumulation of reduced oxygen, so I use the 11.4 kW⋅h/kg along with another number using both lithium & oxygen in the theoretical energy-density calculation, which comes out to about 5,000 Watt-hours per kilogram. In any case, the amount of energy that you can get from a lithium-air battery is significantly higher.
OK, so that’s the theoretical limit — but in practical terms, I understand that current lithium-air prototypes can store about five times more energy a commercial lithium-ion battery. Does that sound right?
Yes, in practice you can usually achieve 20% to 50% of the theoretical total energy density in a experimental prototype due to factors like the electrolyte & cell packaging.
However, even if we take the worst case scenario of 20% efficiency, we would still end up with more than 1,000 Watt-hours per kilogram for a lithium-air battery, which is about five times more than a lithium-ion battery. In terms of future commercial designs, we believe lithium-air batteries can achieve much greater efficiency than even that.
Now in terms of packaging, for many years Tesla used the 18650 cells you mentioned earlier, which are nearly AA sized batteries — but I’ve seen mockups for lithium-air cells that are much larger, perhaps the size of lead-acid cells. Can we expect to see a wide array of sizes for lithium-air batteries?
Well yeah, you can package and shape these cells in many different ways. In terms of weight, it should be significantly lighter than a lithium-ion battery, but you can design the packaging as needed to fit your application.
You know, these cells won’t just be bigger: you’ll see much smaller designs as well, for smartphones and medical applications. There are all kinds of medical devices could use this technology, and they’ll need very small cells. Also, the military has some strategic applications for it in remote areas where they don’t have ready access to chargers.
Consumer need is driving demand for better smartphone batteries, and I’ve read that range anxiety is the only thing holding back electric vehicles. Given the potential of lithium-air batteries, I’m wondering if you’re seeing a lot more pressure these days for advances?
Yes, the public wants more energy from their devices, which puts manufacturers under pressure. So yes, there is significantly more interest, and what you might call passive pressure, from a variety of sources.
In terms of electric vehicles, the standard battery in a Tesla right now is a 60 kilowatt hour battery, and that’ll give you at best about a 200 mile range. If you upgrade to a larger 80 kilowatt hour battery, you’ll get about 300 miles — but that’s only at the beginning of the life of the battery.
You have to remember that with each charge/discharge cycle, the battery capacity goes down, and in a year or so you will get much less. That creates a lot of pressure for batteries that can give you a 400 or 500 mile range without any difficulty in the near term.
In the future, I’d speculate that electric vehicles may reach even a thousand miles range, but you have to remember that vehicle range depends on a lot of factors. It’s not only the battery energy that matters, but also motor efficiency, the weight of the vehicle, and many other things. Overall, though, you could get a that range up to a thousand miles in some vehicles.
Now, I understand that the electrodes in lithium-air cells are where most of the development challenges been. Do you think these will be resolved soon, or will another type of battery such as lithium sulfur come to market first?
Well the major problem of lithium-air is that in order to access oxygen, you need to expose the cell to the air. That leads to the possibility of bringing other materials into the cell like moisture, and lithium doesn’t like moisture. So you need to be able to filter the air to access only oxygen without having other contaminants. We believe putting a semi-permeable membrane on the cell that can do that, but its area we were still have to make progress.
You’ve also mentioned exploring the concept of lithium-oxygen in a polymer electrolyte, right? Does that solve the issue of contamination?
Right, that’s another possibility that may work, and we actually published results 10 years ago on a solid-state lithium-air battery in which we replaced the liquid electrolyte with an inorganic solid-state electrolyte. That’s yet another technology that could find practical use. There are several options available to allow solid state cells to overcome some of the issues associated with water ingression into the cell, and we’re examining all of them.
Flammability is a concern with smartphone batteries — this is another area worth exploring. Is it a concern with lithium-air cells as well?
Well, safety issue in lithium-ion cells comes from the flammability of liquid electrolytes used in the battery, combined with internal short circuits that can happen due to a manufacturing defect or abuse of the cell. Once the short circuit happens, it generates a lot of heat, which vents the electrolyte out into the atmosphere where it can catch fire.
Lithium-air batteries can’t have internal short circuits like lithium-ion cells because the oxygen is always in the air, and you don’t have enough material inside the cells for that type of reaction. So it’s safer, from my point of view.
Now in terms of lithium-ion cells, we need to be looking at how to replace today’s flammable liquid electrolytes with some sort of a semi-solid or solid electrolyte to make all batteries safer.
Batteries are going to be with us forever — we cannot live without this technology now, so we need to have batteries that are so safe that we don’t have to worry about charging them when we’re sleeping at night or when we’re not at home.
Now that we’ve talked electric vehicles potentially having a thousand mile range — what about drones? They need longer battery life as well.
Yes. The military will be using them in drones for sure because lithium-air cells will be very light, which provides advantages for drones & aircraft. In fact, there was a recent article in C&E News from the American Chemical Society about the applications of lithium-air batteries for airplanes, and some companies are seriously looking into this because of the lighter weight.
For aircraft, it may be necessary to use these batteries with another power source for the takeoff of the plane, but for cruising purposes its possible to use a lithium-air battery to allow the plane to go very long distances.
How do you think lithium-air will affect smartphone life? This has been a long-time consumer complaint about smartphones. Do you think we’ll see smartphones that last three or four days on a charge?
Oh, yeah. Easily three or four days, probably even a week depending on the habits of the person using it. Yes.
Electric vehicles, drones, smartphones, medical implants, and more — there are a lot of big changes coming. Let me close by asking what comes next for lithium-air batteries, and what should we be looking for in future news headlines?
Well, as you mentioned earlier, we are reaching a limit in the capacity of materials to pack more and more energy. If I look at the periodic table of elements, and look at the possibilities of making new batteries, we are already reaching a limit in the availability low equivalent weight materials for new battery systems capable significantly higher energy densities. Really what that means is that people will be investigating variations on today’s battery technology for years to come, and I have no doubts that we’ll find a solution to the challenges of the lithium-air battery.
About Our Guest
Dr. Kuzhikalail M. Abraham is the inventor of the lithium-air battery and a recognized expert on lithium-ion & lithium-sulfur batteries, with over 200 journal articles and fifteen patents on lithium and lithium-ion battery materials and performance, along with media contributions to news organizations such as Wired Magazine & the Wall Street Journal.
His 45-year career and pioneering work in battery technology has been recognized through numerous awards & honors, including the Electrochemical Society’s Battery Research Award, the International Battery Association’s Yeager Award, and fellowships at the Electrochemical Society and the Royal Society of Chemistry, and many others.
Dr. Abraham is the principal of E-KEM Sciences in Needham, Massachusetts and a Professor at the Northeastern University Center for Renewable Energy Technologies. Learn more at his NEU faculty page and Google Scholar.