Developing lithium-ion batteries that match the lifespan and range of gasoline-powered engines is key to electric-vehicle adoption.
Daniel Abraham is diligently trying to find an antidote to range anxiety.
Abraham, a materials scientist at the Department of Energy's Argonne National Laboratory, and his colleagues are looking for ways to expand the energy-storage capacity of lithium-ion batteries -- which would enable them to last longer on a single charge -- as well as extend their overall lifecycles.
If they're successful, they'll address one of the biggest barriers to adoption of plug-in electric vehicles -- range anxiety, or the fear that such vehicles will run out of "juice" in the middle of nowhere, leaving motorists stranded.
Abraham leads a team of researchers from the Argonne, Lawrence Berkeley, Brookhaven and Oak Ridge national laboratories. Recently, he spoke with IndustryWeek about his research, and the future of advanced-battery technology.
|Daniel Abraham, a leading scientist at Argonne National Laboratory, conducts research in the field of lithium-ion batteries. (Photo courtesy Argonne National Laboratory)|
DA: There are two types of energy density: gravimetric energy density and volumetric energy density. Gravimetric energy density is the energy per unit of weight; volumetric energy density is the energy per unit of volume.
So the higher the gravimetric energy density, the lighter the battery. The higher the volumetric energy density, the smaller the battery.
So obviously we want to work in a technology in which you get the highest gravimetric and the highest volumetric energy density. And that's where the lithium-ion battery is far superior to any of the other [battery] technologies.
For example, if you used a lead-acid battery in your cell phone, it would look like a brick -- because the battery is the main part of the cell phone. Whereas you have such a higher energy density [in lithium-ion batteries], which enables the phones to be smaller and lighter.
IW: What is the ultimate goal of your research?
DA: Well, in an ideal world we would like these batteries to get the range of a gasoline engine -- a single tank of gas.
It is possible to do that, because if you just put more batteries in the pack, you can get the range. But your battery pack will just get bigger, bulkier and heavier.
... Is the range achievable? Is the life achievable? I believe so; I think we can do it. But in order to get the range desired, for example, you might to sacrifice some of the other characteristics [such as the safety of the battery].
It will take some effort, but that's the direction we are moving.
So our research is focused on developing smaller, lighter batteries that are also cheap and safer.
IW: Tell us more about your research.
DA: When you hear the term lithium-ion technology, it's not one chemistry, and I think that's the most important thing to remember.
There are many possible [chemistries] in any battery. You have two electrodes -- the positive electrode and the negative electrode. And you have a separator, which kind of keeps these two apart, and you have an electrolyte.
... So at Argonne, we look at these different types of chemistries and we try to optimize them for particular applications.
For example, for high-power applications, you would use certain combinations. For high-energy applications, you would use other chemistries, other couples -- what I call electrochemical couples. And if you want both high energy and high power, then you would use a third kind of couple.
Essentially we are trying to figure out which electrodes to pair together and which electrolyte to use to get the best performance for a certain condition.
To do that, we work on electrode materials -- what kind of electrode materials exist, and what kind of electrode materials are possible.
... So what we do at Argonne is try to push the boundaries. That is, we are trying to increase the energy density by discovering new materials.
IW: What are the challenges in developing a lithium-ion battery that offers the same range and lifecycle characteristics of a gasoline-powered vehicle?
DA: In an ideal world, you would use lithium metal, because then you would have an infinite amount of lithium ions that you can move back and forth. So you would never have to worry about the capacity or the range, because you have plenty of lithium ions to move back and forth.
But in the mid to late 80s, when batteries were commercialized with lithium metal in them, many of these batteries went up in flames.
So in 1991, Sony introduced a commercial version of the lithium-ion battery, although it had already been in research elsewhere.
A lithium-ion battery has one electrode that is the source of lithium ions -- we call it the positive electrode -- and the negative electrode accepts the lithium ions.
During the charging process, you move lithium ions from the positive electrode to the negative electrode, and for the discharging process it goes in the opposite direction, and when that happens, the battery supplies energy for whatever application it is being used for.
The problem with the lithium-ion battery is the amount of lithium that's present in the cell is limited to the amount that's present in the positive electrode.
In a lithium-metal cell, you have an infinite amount of lithium available that you can move back and forth, because one of your electrodes is lithium metal. In a lithium-ion cell, there is a limited inventory of lithium ions, because it's only there in one of the electrodes.
In an ideal world, if everything works well, this battery should work forever.
But we live in a non-ideal world, and unfortunately there are side reactions that occur that consume lithium ions during [battery] operation.
Because of lithium consumption, we have what we call energy fade, or capacity fade. If you're dealing with a battery-electric vehicle, capacity fade is a problem, because that affects your range.
Sometimes, the side reactions also generate products of films on these electrodes that create additional resistance within these batteries. When there is an increase in resistance, you have a power problem because then you can't move these lithium ions as fast as you could previously. That's what we call power fade.
IW: With all of that said, how close are we to developing lithium-ion batteries that are long-lasting enough, cheap enough and safe enough for mainstream commercial use? Is it a matter of decades or years?
DA: It's certainly not decades. I believe it's a few years.
Because especially now there are a lot more companies working on this, and obviously the companies want to make money on this, so these problems have to be solved.
I believe it's just a matter of years. There are many smart people putting their heads together to solve this.