Biofuels, Batteries, And Solar Cells: The Future Of Driving

Pumping versus plugging in. In the next decade, people may have to start making that decision when purchasing a new car. Plug-in hybrid-electric vehicles, or PHEVs, are set to hit car showrooms in the next couple of years. If they click with consumers as expected, the way we refuel our cars could start to change drastically.

Looking into the future of driving, a panel of automotive industry executives and experts met in February at a forum held in Washington, D.C., to discuss the potential of PHEVs and the lithium-ion batteries that will power them. The event was sponsored by the Center for American Progress, a Washington, D.C., think tank.

"When we in the auto industry look at the energy and environmental picture, one fact stands out among all others: The automobile industry can no longer rely exclusively on oil as the basis for the fuel for our vehicles," commented panel member Jonathan J. Lauckner, a mechanical engineer and vice president of global program management at General Motors. "As GM prepares for the rest of this century, our strategy is really simple: We want to displace petroleum and reduce greenhouse gases by establishing technologies that allow us to take advantage of energy diversity."

Most people in the U.S. currently fill up with petroleum-derived gasoline that in many places is blended with ethanol. Diesel is also popular, but it's not as widely used for passenger cars in the U.S. as it is in Europe.

Alternative fuels such as bioethanol and biodiesel are exciting developments that could go a long way in stretching out dwindling fossil fuel supplies. But biofuels can't be produced in a large enough volume to completely replace traditional gasoline and diesel fuel. Hydrogen-powered fuel cells for cars have received a lot of attention as well, but for now fuel-cell technology is still stymied by the inability to conveniently store and use hydrogen. In fact, fuel cells may never be as practical and convenient as current transportation fuels or as simple as sticking a plug into a power outlet.

That makes vehicles that run on a combination of biofuels and rechargeable batteries a logical technological progression for automakers. The most common type, with several hundred thousand cars already sold during the past five years, is the hybrid-electric vehicle (HEV), with Toyota's Prius serving as the genre's poster child.

HEVs are propelled by an electric motor energized by a relatively heavy nickel-metal hydride battery that is charged when the brakes are applied—so-called regenerative braking. When the battery runs low, a conventional gas- or diesel-powered engine kicks in to run a small generator that charges the battery.

A major shortcoming in the technology is the limited driving range on battery power, which typically is less than 20 miles. Other limiting factors include the hefty size and weight of the battery and the still relatively high cost of the battery system. Unlike a small single cell for portable electronics, automotive batteries consist of dozens of cells grouped into modules with sensors and other electronics controlled by a battery management system. Researchers are counting on lithium-ion batteries to work around these limitations.

Lithium, in the periodic table's top left corner, is the most electropositive and lightest metal, making it an optimum choice for fabricating high-energy-density batteries—it can store a lot of energy in a small, lightweight unit. The original commercial lithium-ion battery, introduced in 1991 by Sony in a camcorder, combined a lithium cobalt dioxide (LiCoO₂) cathode and a graphite-based anode (LiC₆). Most of today's lithium-ion batteries still use this combination.

The world already has an insatiable appetite for these rechargeable batteries. People everywhere walk around with at least one small lithium-ion battery inside a cell phone or other device tucked in their pocket. Lithium-ion batteries have also powered their way beyond cell phones and laptops into beefier appliances such as nail guns and cordless drills (C&EN, July 9, 2007, page 24).

Battery researchers have been tweaking everything possible to squeeze a little more performance out of lithium-ion batteries. One approach is to dope the cathode with different transition metals that help stabilize the material and increase the mobility of lithium ions. Another way is to replace the graphite anode with lithium/transition-metal alloys that can host more ions in the same volume. Nanotechnology also is playing a role in the form of nanoparticles, nanowires, and other types of nanostructured materials that provide greater surface area for the cathodes and anodes.

The result is a host of lithium-ion chemistries, including LiMnO₂ and LiFePO₄ cathodes and Li₄Ti₅O₁₂ and lithium-metal nitride anodes. These advanced designs are also helping battery manufacturers improve battery safety and move beyond the high-profile computer battery failures that occurred during the past two years, which led to the recall of millions of batteries (C&EN, Dec. 17, 2007, page 26). No doubt additional technologies will emerge to decrease battery size and weight, reduce recharging time, and improve battery energy capacity and lifetime.

The next step for lithium-ion batteries and electric vehicles is to put them together in the plug-in hybrid—the PHEV—which runs on a battery charged by plugging into a power outlet. When the battery nears exhaustion, the car switches over to HEV mode.

In GM's strategy to develop several hybrid vehicle models, the enabling technology, which is also the greatest cost challenge, is the lithium-ion battery, Lauckner said. "Automotive batteries operate in a rugged and hostile environment relative to consumer electronics," he pointed out. "Yet customers are going to expect the battery pack to last the lifetime of the vehicle. For the car company, this means a design standard of 10 years or 150,000 miles.

"Our research also shows that most drivers cover less than 40 miles in their daily commute, so that makes 40 miles per battery charge an important target," Lauckner continued. If automakers meet that specification, "78% of all drivers would not need to use a single drop of gas in their daily driving," he said.

One of GM's key efforts to meet those magic numbers is the Chevy Volt, which the company expects to be the first commercial PHEV. Powered by a lithium-ion battery, likely using a LiFePO₄ cathode and LiC₆ anode when production starts, the Volt can go 40 miles per charge, Lauckner said. Overall it gets about 50 mpg when operating in HEV mode and has a driving range of more than 300 miles before refueling.

He expects the Volt to go on sale in late 2010 with a price tag of around $40,000—still a little expensive, but affordable to many people. It will have the same warranties as Chevy's gasoline-powered cars. Lauckner anticipates sales to reach tens of thousands of cars per year. "This is not a prototype," he emphasized.

Chevy's Volt will have some stiff competition. The current best-selling HEV is the Toyota Prius, which goes for about $21,000 and gets 48 mpg in city driving. A close second is the Honda Civic HEV, which sells for $22,600 and gets an estimated 40 mpg. Toyota is working on a PHEV Prius model that could also release by 2010, and Honda is working on a PHEV Civic.

Beyond optimizing the battery technology, automakers and their battery company partners need the manufacturing capability to produce batteries in large quantities. Although the sudden production of millions more lithium batteries could impact lithium supplies, the panelists at the forum indicated that the global supply of lithium, which is obtained from lithium carbonate (Li₂CO₃) derived from brine pools in desert regions, particularly in South America, is more than adequate. In fact, it was noted at the forum that one battery producer concerned about electric vehicles being held hostage by lithium supplies had checked with the U.S. Geological Survey before adopting new lithium-ion chemistry. USGS gave the company a thumbs-up, so they are moving full-speed ahead.

Global production of Li₂CO₃ is estimated to be about 207 million lb per year and growing, according to industry sources. Approximately 30% of that amount is used to make rechargeable and nonrechargeable batteries.

And beyond what PHEVs might mean to consumers, automakers, and battery producers, researchers are producing a steady flow of studies to sort out the effects of electric cars on the environment. In two studies, researchers found that PHEVs operating on a lithium-ion battery have significantly lower greenhouse gas emissions compared with gasoline-powered cars and also offer additional benefits over HEVs when electricity sources with low carbon emissions are factored in (Environ. Sci. Technol. 2008, 42, 1185 and 3170).

Another study shows that a large-scale shift to PHEVs also will impact water use because more power plants will be needed to generate electricity to charge car batteries (Environ. Sci. Technol. 2008, 42, 4305). Power plants require a lot of water to run steam turbines. Thus, driving a car on electricity requires about three times as much water as driving on gasoline, according to the study. Implementing PHEVs on a large scale could be a factor in managing water resources in arid regions such as the southwestern U.S. if electricity is produced locally. Such details should be factored into policy decisions on electric vehicles, the researchers suggest.

Indeed, policy decisions in the next decade on how additional electricity will be generated from coal, natural gas, and renewable sources will be important in determining the costs to operate PHEVs and in gauging the environmental impact of their greenhouse gas emissions.

A rapid increase in electric vehicles should reduce CO₂ and other emissions, because the cars are more efficient. But simply shifting the emissions upstream from cars that burn less fuel to power plants that generate more electricity will not make the kind of substantial reduction in global CO₂ emissions needed to help fight back the threat of global warming, especially if the electricity is generated at coal-fired power plants. This is why clean coal technology and developing chemistry to produce renewable sources of electricity such as hydrogen fuels cells and solar cells are imperative. It's also why biofuels will remain important: They will help provide a fuel with net low carbon emissions to power HEVs and PHEVs when the battery runs down, because the CO₂ they emit is approximately balanced by the CO₂ incorporated into the biomass used to make biofuels.

"Electric vehicles are very attractive because they have the potential to help solve climate change and sustainability problems at the same time," noted panel member John German, manager of environmental and energy analysis at American Honda Motor Co. Before joining Honda, German, a physicist by training, worked in the field of fuel economy at Chrysler and for the Environmental Protection Agency.

During the discussion, German addressed what he says are some common misperceptions about transportation. First is the impact of fuel price and fuel economy. With several graphs he showed that it currently costs about 13 cents per mile to drive in the U.S., which is still slightly less than in 1973 just before the first "oil crisis." That was back in February, when the U.S. average gasoline price was about $3.15 per gal—still "relatively cheap," German said. Now that gasoline is about $4 per gal on average, the cost per mile is on par with or perhaps a bit more than in 1973.

"But that still is not the real story, because our standard of living has gone up," German said. "The cost of driving 10,000 miles as a percentage of per capita disposable income is currently about 4%, while in the early 1970s it was more than 6%—the cost of driving is 40% lower now than in the good old days."

Crunching the numbers shows that an HEV pays for itself in about 6.4 years. In other words, that's how long it takes to cover the cost above that of a conventional gasoline-powered car, German said. The current payback time for a PHEV is about 13 years, longer than the average vehicle's useful life.

German also ran through a few "technology of the day" comparisons during the forum. "Twenty-five years ago, methanol was the hot solution to energy problems; 15 years ago, it was electric vehicles; 10 years ago, hybrid-electric; five years ago, fuel cells; two years ago, ethanol; and today, it's the plug-in hybrid," German pointed out. Throughout this period, gasoline has remained the primary transportation fuel in the U.S., he added.

"My point here is that quickly accepting a new technology and just as quickly abandoning it when it's not immediately adopted is very disruptive—wasteful—for the development process," German said. For example, fuel-cell vehicles are more than meeting the targets set for them, he noted. Most car companies have demonstrated road-worthy fuel-cell cars, but none of them are in commercial production today, he noted. They have virtually been abandoned because of hydrogen storage issues.

That doesn't mean fuel cells won't have a place in the future. Large stationary fuel cells running on hydrogen, methanol, or other fuels may still be vital for generating electricity to run factories or might come to be used by utility companies to help supply the power grid. They could replace traditional gas-powered emergency generators. And they still could end up powering cars if the technological hurdles can be overcome.

The hype has been detrimental to the auto industry and federal programs that support hydrogen technologies, German said. The same technology-busting hype could happen to HEVs and PHEVs, he added. "It's not a good idea to force-feed electric cars to consumers," he said. Clearly the panel's pessimist, German was suggesting that PHEVs could face an uphill battle to wide adoption because of their higher cost.

The transportation energy problem "is so immense that we are going to need to do everything we can in all areas," German said. "We need to avoid the trap of looking at a single solution." PHEVs will likely be important down the road, he added, but efforts to push their use in the short term should not be made at the risk of leapfrogging biofuels and HEVs and wasting the resources already used to develop them.

Besides making cars and batteries and producing the electricity to run them, an infrastructure for recharging cars is needed. This will require an efficient mechanism that takes advantage of recharging in off-peak energy-demand periods, which is generally late at night. One of the aforementioned environmental studies on PHEVs suggested that a significant fraction of cars could currently be reenergized with spare nighttime electricity capacity without additional electricity generation. Automated controls also might be needed to shut down recharging car batteries during peak demand periods, whether at home, in a parking garage, or at a parking meter on the street.

All of the engineering, development, testing, and capital investment to create this infrastructure drives up costs, GM's Lauckner noted. It will be difficult for the auto industry to bear this burden alone, he says, given the large initial cost barriers.

"The government ought to step up and give us a hand by funding a major effort to strengthen domestic advanced battery development," Lauckner said. "It should be targeted at basic R&D, but also, more important, at manufacturing process technology so that production can be scaled up. Finally, we need to take a look at tax incentives so these technologies get adopted by a lot of people.

"We in the industry are ready to do our part," Lauckner said. "In fact, we are already doing it. What we are looking for is the government to step up and do its part so that we can really transform automotive transportation, do something meaningful about greenhouse gases, and get our nation and the world past oil dependence."

The Department of Energy already is providing some $30 million in funding to help PHEV development, but the panelists suggested much more needs to be done. The DOE plan is to make PHEVs cost-competitive with gasoline-powered cars by 2014 and ready for broad commercialization by 2016. Those target dates leave car companies with little time to choose which technology to focus on. While GM is charging ahead with the Chevy Volt and Toyota is preparing to launch the PHEV Prius, other major automakers appear to be betting that waiting a few more years to see how HEVs continue to do will be a better business approach before launching a PHEV model. The risk for them is that GM and Toyota might have gotten it right, leaving them in a lurch and having to play catch-up.

"There is a time element to this discussion," Lauckner said. "We are talking about the future of the automobile industry. There is somewhere in the neighborhood of 850 million cars globally on the road today. If we start today to replace some of those vehicles, it is going to take a decade or more before we can turn over that entire fleet into hybrid vehicles or some other advanced technology."

The total number of hybrid-electric vehicles is expected to reach 4.5 million by 2013, according to market research firm Freedonia Group. AllianceBernstein, an asset-management firm, further projects that by 2030 some 72% of cars on the road worldwide will be hybrids and 85% of new cars will be hybrids.

The panelists pointed out that it's difficult for policymakers to pursue technologies that operate on a decade or longer time horizon. But if the U.S. and other countries really want a sustainable transportation system, it's going to take some long-term planning, they said. There needs to be a technology portfolio and an awareness that some technologies will be ready sooner than others, they noted, and it will be important to weigh the tradeoffs in implementing them.

Perhaps one day a rechargeable lithium-ion or other type of battery the size of a shoe box will power a PHEV or fully electric car for 200 miles or more, and the car could be recharged in about 15 minutes by plugging into an outlet in a driveway or parking garage, with the electricity coming from yet another battery that's charged by a dedicated solar panel on the roof of a house, apartment building, or office building.

Gasoline served as a matchmaker to fuel America's love affair with the automobile that began more than a century ago. And as biofuels, batteries, and solar cells step in to replace gasoline, that relationship conceivably can continue in a sustainable fashion and perhaps will never have to end.