Researchers Seeking Next Generation Electric Vehicle Battery

July 24, 1998

By Eli Kintisch

Berkeley Lab scientists are working on the preliminary stages of a project, which when completed, will allow you to purchase a sporty, sleek sedan with the worst gasoline mileage you have ever imagined: zero miles per gallon.

The battery of GM's EV-1 electric car must be recharged every 90 miles. By developing powerful lithium fuel cells, Berkeley Lab scientists hope to triple the battery life of future models and make electric cars competitive.

And consumers will love it.

This future car won't need gas at all, but instead will rely on clean, inexpensive electric power, a much more efficient source of energy. Researchers in the Environmental Energy Technologies Division (EETD) are devising rechargeable batteries to power the next generation of electric vehicles.

Led by Elton Cairns, head of the Electrochemical Technologies Group, scientists are developing high performance batteries that utilize lithium electrodes and synthetic plastic materials. These batteries may one day make electric cars a viable, competitive alternative to current automobiles.

"Making a high performance battery is easy," said Cairns, noting that lithium batteries are very successful in cell phones and notebook computers, applications in which the current expensive cells are affordable. "But making a high performance battery that costs less is hard. The way it stands now, currently available lithium batteries are too expensive to use to power cars."

A battery consists of a positive and negative electrode separated by an electrolyte, a material through which flow charged atoms, known as ions. To produce electricity, ions from the negative electrode flow towards the positive electrode, leaving a buildup of electrons on the negative electrode, which generates a current. If designed properly, a battery may be recharged by applying a current in the reverse direction, which forces the metal ions to return to the negative electrode.

Depending on the materials used for the electrodes, batteries can have different capabilities for storing energy. Standard rechargeable batteries use lead and lead oxide for the electrodes, usually with a liquid electrolyte. As a light metal which gives its electrons up easily, lithium offers a high electrochemical capacity and an environmentally-benign alternative to harmful lead. Researchers are looking at both manganese oxide and sulfur as possible positive electrode materials.

In order to make a rechargeable lithium battery, Cairns says, scientists must tackle "a mile-long list of requirements that almost no materials will satisfy." Because lithium is so reactive, a specially designed organic solid electrolyte must be used instead of an aqueous liquid, which would react with the metal. But the electrolyte must be very thin to allow ion and electron flow.

In addition, making a battery that can be repeatedly recharged requires that the molecular structure of the electrodes allow repeated ion movement. And the battery should be light, cheap to produce, environmentally benign, and -- in order to be feasible for cars -- contain materials that pack an electrochemical bang-for-the buck.

Undertaking this challenge is a range of scientists from EETD, the Material Science Division (MSD), and UC Berkeley departments. Collaborators on the project include EETD's Jim Evans, John Kerr, Kim Kinoshita, Frank McLarnon, John Newman, Tom Devine, and Kathryn Striebel, along with MSD's Lutgard DeJonghe, Marca Doeff, Phil Ross, and Steve Visco.

Because electric vehicles are a priority for the Department of Energy, the project receives funding for its two-million-dollar budget through DOE's Offices of Transportation Technologies and Basic Energy Sciences.

The environmental advantages offered by electric cars are dazzling. Their engines are far more efficient than combustion competitors, and unlike gasoline cars, they don't waste fuel idling. Most importantly, electric cars generate no fumes. Instead, the energy to recharge batteries is produced at power plants, whose smokestacks can be treated to cut pollution.

"It's much easier to control emissions at the power plant than on many individual automobiles," says Cairns.

Although still in their infancy, electric cars can perform remarkably well alongside their smoky competitors. GM's currently available two-door EV-1, which can be leased for as low as $340 a month, can attain a 0-to-60 in a sporty eight seconds flat. The car uses advanced lead/acid batteries, which are relatively inexpensive to produce, but must be recharged after driving about 80 miles.

Scientists calculate that lithium batteries could store three times more energy per kilogram than lead cells, allowing drivers to travel more than two hundred miles before a recharge -- roughly the same range afforded between gasoline fill-ups.

"According to the market projections, for some time the electric vehicle will be 30 percent more expensive than its gasoline counterpart," said Cairns. "But operating costs will be much lower and fuel costs extremely lower."

Cairns estimates that fuel costs for future battery-powered cars will vary from one to two cents per mile, depending on the electric company, as opposed to five to 10 cents per mile, the cost of gasoline for most cars. This could translate into yearly savings of thousands of dollars on gasoline alone -- not to mention maintenance: electric vehicles do not require transmissions, motor oil or tune-ups.

In order to investigate different combinations of materials for the batteries, Cairns' team builds dime-sized test cells. Computer-controlled cyclers are used to discharge and recharge the cells to test their performance.

The final product will be a paper-thin cell with a shiny side of lithium, a side covered in black carbon, and a thin polymer electrolyte in between. The multi-layered sheets may be rolled into a cylindrical shaped cell or stacked on top one another to resemble standard car batteries.

Building a better battery has been a lifelong objective for Cairns, who has served as an international leader in chemical engineering for over 30 years. In addition to a long span of fruitful research with the Department of Energy, he has served as president of the Electrochemical Society and will soon head the International Society of Electrochemistry.