Lithium-ion polymer batteries have slightly higher energy density than regular lithium-ion versions—a prototype Audi vehicle went 372 miles on a single charge—but they can’t be charged and depleted as many times, so they have lesser endurance.
It’s worth remembering that despite these limitations, batteries designed to power automobiles have come a long way in a relatively short period of time—just 40 years ago, a battery with less than half the energy density of those found in today’s hybrids and electric vehicles was considered an exotic dream—and they are bound to improve further. “We see a clear pathway to doubling battery capability,” says Ford’s Miller. “That's without changing the technology dramatically, but improving the process so we have high-quality automotive batteries with the same energy content as we find on portable devices today.”
Such a battery for all-electric vehicles would transform transportation, making it much more climate-friendly. Transportation accounts for about 27 percent of U.S. greenhouse gas emissions, and about 14 percent of worldwide emissions. Ninety-five percent of U.S. passenger vehicles run on petroleum. If those cars and trucks could be replaced with electric vehicles, if would significantly reduce pollution even if the electricity continues to come mainly from coal, the Department of Energy has found. That’s because internal combustion engines are so inefficient, losing as much as 80 percent of the energy in their fuel to heat, while electric motors put almost all their energy into propelling the vehicle.
Batteries can play a role in changing the source of our electricity, as well, by storing energy produced from renewable sources like wind and solar. As utilities have increased the percentage of electricity they produce from these sources, the guiding principle has been that natural gas-fired power plants would be necessary to meet demand when wind turbines and photovoltaic cells aren’t producing. If excess renewable energy produced when demand is low could be transferred to a battery, stored without significant loss and drained out quickly when demand rises—and if the system were cheap enough—it would obviate the need for both the coal-fired plants renewables would replace, and the natural-gas plants considered essential to accompany wind and solar.
“Large-volume batteries that can time-shift energy would be the game changer,” says Peter Rothstein, president of the New England Clean Energy Council.
Batteries that store energy for the grid have different requirements than those that go into cars, because vehicles require relatively compact batteries that can transfer their energy almost instantaneously. So technologies that don’t work well for powering electric vehicles can be great at storing power for the grid.
Lithium-air batteries, a relatively new technology that has generated a lot of excitement, can have greater energy density than existing lithium batteries, but they provide much less of the power that would be needed to accelerate a vehicle, says Ford’s Miller. “If you need 120 kilowatts of power capability, with lithium-air you might need 80-to-100 kilowatt-hours of battery energy to meet that requirement,” Miller explains. “That’s a very cumbersome, very large battery.” It wouldn’t work well in a car--the Ford Focus EV, by comparison, uses a little over 100 kilowatts of power with a 23 kilowatt-hour battery--but it might when sitting next to a wind farm.
Vanadium flow batteries, another promising development, also have high energy density, and they have a fast discharge time, which make them ideal for storage. That’s the application for which Ron MacDonald, CEO of American Vanadium, is pitching them. “There are lots of good storage options, but every one has an issue,” MacDonald acknowledges. “Our issue has always been upfront cost, because we're more expensive.” A vanadium-flow battery can last 20 years, though, “so we’re below most others if you look at cost over the life of the battery,” he says.
But the development of the so-called “smart” grid--which will use advanced algorithms and communications technology to respond quickly as power supply and consumer demand ebb and flow--and distributed storage has perhaps made more energy-dense batteries less necessary than experts have thought in the past. With tens of thousands of small batteries in cars, traffic lights and elsewhere throughout a city, an electric utility could theoretically draw down power from these batteries during times of high demand, and return the energy to customers several hours later.
Utilities may also attempt to change when and how people use energy by charging exorbitant rates for electricity purchases over a certain level during periods of high demand. Customers will be discouraged from placing high loads on the system, such as by operating large appliances or charging their electric car, during those times. Like batteries, such practices would flatten the curve of electricity production needs imposed on the utility.