Scientists building a better battery typically strive for lower cost, lower weight or higher energy density, but Steven Chu, the Nobel Prize-winning former Energy Secretary, just emphasized another metric:
Charging rate.
"If you can put 120 miles in five minutes onto a car, then the game is over," Chu says in a video released yesterday by Stanford University, where he serves as a professor of physics. "This is what we need for electric vehicles really to go viral."
Chu has mentioned before that he and Yi Cui of Stanford's Materials Science Department are working on a next-generation battery that could improve energy density five times and charging rate up to ten times over conventional lithium-ion batteries. The new battery would be made from lithium and sulfur.
Argonne National Laboratory's Joint Center for Energy Storage Research has also identified lithium-sulfur as the most promising successor to lithium-ion in the transportation sector.
George Crabtree, the director of that program, told me JCESR's research is currently focused on greater cycle life.
"The Li-S battery is not expected to be inherently fast charging," he said via email. "Its advantages are inexpensive, abundant sulfur and potentially high energy density. The major focus of research at present is greater cycle life. Cycle life trades off against energy density, so the highest energy density Li-S batteries may last only a few cycles, not acceptable for most applications. The approach to reducing charging time may depend on the approach to lengthening cycle life, so charging time has taken a back seat to cycle life up to now."
But Crabtree agrees that charging rate is of concern:
"True, the charging rate for Li-ion batteries is much slower than filling a gasoline tank. The fastest time to charge a Li-ion battery from 0% to 100% is about an hour, with the highest power charger available. Charging from home on 110 volts typically takes 4-6 hours. The first and last 20% are the slowest, so one often hears proposals to partially charge in 15-30 minutes. Everyone has their own estimate of where the tipping point is, and Steve's is as good as any."
Just Tuesday, the Energy Information Administration noted that electric vehicles "have been slow to gain market share in the United States" and cited the usual suspects of cost and lack of charging stations. Slow Charging was not among the EIA's suspected hindrances.
Chu suggests charging rate can electrify transportation, and within this century.
"By the end of the century I would say most transportation could be electrified," he says in the video, which you can watch below. "Wherever possible trains should be electrified. Personal transportation should be electrified. I'll be optimistic and likely by the end of the century we will have liquid hydrocarbon fuels for airplanes that can be made in a clean way, not from traditional oil sources."
Yesterday I asked the CEO of Proterra, leading maker of electric buses, if he too was looking beyond lithium ion.
Proterra's job would be easier, CEO Ryan Popple said, if batteries had improved safety, higher energy density and lower cost.
"I will admit, though, we are paying less for lithium-ion batteries than I ever thought we would," he said during a Q&A session at Co-Invest Cleantech in Chicago.
Proterra is paying less than $250 per kilowatt hour for lithium-ion batteries and can efficiently bundle them in modules and packs, he said, so the company is comfortable right now with lithium-ion.
"We're not arrogant about it, though. Next week there could be a black-swan announcement. I lose track of the all of the VC investments in early-stage batteries, and I don't know what it'll be. I could see us being on lithium-ion chemistries, though, for another five years."
On charging, Popple said he doesn't think a technological breakthrough needs to occur in bus charging.
"With our biggest charger going into our smallest battery configuration, you can recharge a bus in 15 minutes. We do that with some circulator fleets that run basically 24-7. If you take our smallest charger into our biggest battery it's eight hours, so it's an overnight charge."
Watch Steven Chu's video on the future of energy:
