Why do batteries matter? Look at all your electronic devices: from laptops to smartphones to Kindles or iPads, even your watch. Those electronics are getting better at reducing the amount of energy they need, but as they do, you get greedy and want their capability to increase. The battery, and how much energy you can store in a given volume and weight, is the defining factor in this whole field.
Then there are electric cars. If we can make batteries with double the energy density of today’s and drive the price below $200 a kilowatt-hour (versus $300 to $800 today, depending on type and weight), we could have a car with a 300-mile range, even with the air conditioner or heater turned up, that sells for $25,000 to $30,000. The Department of Energy’s goal is to get batteries to $150 a kilowatt-hour by 2020.
Finally, there are the utility-scale batteries, which are very important for renewable energy. Wind and solar power are going to keep increasing. Wind is already the second-cheapest form of new energy, after shale gas, and it will become the cheapest within a decade. Right now utility companies get about 4 percent of their power from renewable sources other than hydro—and that 4 percent is roughly all from wind. You want to see a day when renewables are 50, 60, 70 percent. Utility companies will need batteries to stabilize the flow of renewable energy into the grid, plus a better electrical control system to do the switching. People may have these batteries at their houses instead of generators.
All of this would be a huge market. But the effects are more profound. There are mountainous places even in the U.S., like western Alaska, that will never be connected to the electric grid. There aren’t enough people, and the distances are too great. There are many parts of South Asia like this, too.
But they will have solar and wind power—which, in 10 or 15 years, are going to be as cheap as any other form of energy, or cheaper. Once you have storage systems, you can put a little solar installation on your roof or a plot of land, and now you have your electric supply! It will be like cellphones’ leapfrogging the land-line era. It will transform the prosperity of the world.
There is a slow march toward improving today’s systems, by 5 or 10 percent a year. Meanwhile, many innovative companies, scientists, and engineers are exploring novel approaches. Many of them may not work. But there is a reasonable chance that a couple may work—and really work, to double or triple energy density and lower cost. If you are a battery company and your cost per unit of storage doesn’t drop by a factor of two in the next five years, you are going to be out of business.
— Steven Chu, as told to James Fallows
The Cutting Edge of Battery Technology
At Stanford, Chu and Cui are experimenting with new battery technologies. Here, they discuss three materials on the verge of transforming battery storage.
Silicon Electrodes, through which current flows, are the working heart of a battery. In most batteries, lithium ions carry electrons from the anode to the cathode in order to create an electric current. According to Cui, silicon can store 10 times more lithium than can carbon, which is used in existing technology. “But silicon has an expansion problem,” Cui says. “It gets physically larger as it absorbs ions, and it can break.” Cui’s research group has been addressing this problem via nanotechnology, using very thin, resilient strands of silicon “wire” that can swell and absorb ions without breaking.
Lithium metal Cui calls this metal the “holy grail” for anodes. In the past, researchers have had trouble with dendrite formation, whereby fingers of material grow off lithium-metal anodes, creating short circuits and safety concerns. But Cui is optimistic that, thanks to “lots of great minds coming together,” these problems will be “solvable in the next few years.”
Metal-air In what Chu calls a “whole other class of batteries,” oxygen acts as a cathode, interacting with a metal anode to create electricity. In Chu’s estimate, these batteries have “the very highest energy density, maybe eight times higher than current lithium-ion batteries.” They’re primarily used in hearing aids but are not yet rechargeable—a deficit that, according to Chu, researchers may be close to fixing.