Winfried Wilcke is Senior Manager for Nanoscale Science and Technology in the Energy Storage group at IBM Research’s Almaden lab in San Jose, Calif.
I distinctly remember my “eureka moment” about electric cars.
In August 2008, I attended a talk at Stanford by Nobel Physics Laureate Burton Richter. During a coffee break, Richter mentioned to me that the U.S had enough capacity to charge all the nation’s cars at night if they were electric.
Subsequent government studies indicated that more likely, the number is 70%. But what an opportunity! Rather than having to depend on remaking the world by building from the ground up a massive new infrastructure of charging stations, electric cars could fit in more easily to our everyday lives.
That’s what inspired me to start developing new battery technology here at IBM, work that became the Battery 500 Project. The goal? Develop a lightweight, rechargeable car battery that can go 500 miles on a single charge and be as affordable as gas-combustion powered cars. We’ve made big strides in demonstrating basic functionality and are aiming to have a significant laboratory prototype in two years.
Of course, IBM isn’t the only one working away at this goal. Because it’s likely that the ‘intercalation’ lithium ion battery technologies used in today’s electric vehicles can’t improve that much more, by perhaps a factor of two in how much more energy they can store per kilogram or liter of battery mass or volume. This limited “energy density” and the high cost per kW-hour means electric cars won’t go far enough on a charge or be cost effective enough to compete with internal combustion engines.
Practically speaking, most “intercalation” lithium ion batteries get under 200 Watt-hours per kilogram compared to roughly 1,700 usable Watt-hours for a gallon of gasoline. That translates into the cars that we see today, which have ranges of 40 miles to 100 miles per charge — at reasonable battery weights — and are suited mostly for commuting. Of course the exceptions are the Tesla Roadster and S models, which can go much further because they are using a very big, heavy and expensive battery.
So in my opinion, widespread adoption of electric vehicles may depend on advancing battery chemistries beyond traditional ‘intercalation’ Lithium-ion chemistries. Candidates include lithium air, zinc air, and lithium sulfur.
Lithium air is the technology that we in IBM are working on, along with 50 other groups around the world. It has the highest theoretical energy density of these three technologies, but is also the most challenging to master.
Every battery is made up of a anode and a cathode and an electrolyte. In our lithium air battery, the lithium migrates from the anode through the electrolyte to a nano-structured cathode where it reacts with air, creating Lithium-Peroxide Li2O2 during discharge. Applying an external re-charging voltage, the Lithium-Peroxide breaks up into Lithium and oxygen. The latter is returned back to the atmosphere and the lithium migrates back to the anode. We have clearly established that this desired reaction is indeed the dominant process in prototype batteries we built.
Now our main focus is finding the right cathodes and electrolytes to eliminate so-called “side reactions” in these systems. For instance, lithium carbonate can form as a side-reaction, rather than the desired Lithium-peroxide. Even very small amounts of side reactions like these, if you recharge a battery 1,000 times, add up over time to poison a battery.
Zinc air’s energy density of around 400 watt-hours is promising. The technology, which also relies on air in the atmosphere, is already used in products such in hearing aids. The problem, however, is that these batteries are hard to recharge. A metal like zinc with multiple oxidation states just has so many ways that it can misbehave when it’s being recharged that undesired side reactions are a big challenge as well.
However, spurred on by the low cost and availability of zinc, several companies are pushing ahead, and in the process, developing a model where you would replace the spent zinc in your battery after a few weeks or so, the same way you would refill a gas tank.
Lithium sulfur, with a practical energy density of 500 watt-hours, is the furthest along in terms of rechargeable batteries with energy densities beyond intercalation Lithium-ion. The technology has even advanced beyond prototyping cells. Two years ago, it was installed in an aircraft that circled non-stop at about 70,000 feet altitude for two weeks. During the day, solar cells on the wings charged the craft’s batteries and they powered it during the nights.
Lithium sulfur batteries also face the challenge side reactions and therefore limited cycle life. Researchers are still working to figure out what happens during the chemical reactions as lithium ions on the anode react with sulfur at the cathode so that they can ensure that the batteries continue to charge and discharge dependably.
These material science challenges are why, despite their promise, none of these technologies will play a major role in the current decade. For example, I don’t expect a car powered by a lithium air battery to be available until between 2020 and 2030.
But by 2030, I do believe that at least 20% or so of all the cars in the U.S. will be electric. And that will put us on the road to making Prof. Richter’s calculations a reality.
