If electric vehicles are ever going to outcompete gas-powered ones, batteries must improve. Conventional lithium-ion batteries, the most energy-dense for their weight, can be charged to only about 50 percent of their theoretical capacity. When researchers have tried to pack more lithium into a battery’s electrodes, it hasn’t helped. The electrodes begin to quickly degrade after the first discharge/recharge cycle, and nobody has been able to figure out how to prevent it.

Now there’s a clue. Using a combination of theoretical computer modeling and sophisticated X-ray methods, researchers have for the first time found a relationship between the way atoms rearrange themselves in the electrode when it’s being charged and how electrons are stored in the battery’s atomic and chemical structures. This insight should give battery-makers a blueprint for building lithium-rich electrodes that could dramatically improve battery performance.

At its full potential, a lithium-rich battery could improve the range of today’s electric vehicles by a third or better. A Tesla Model S with the company’s P100D battery pack, for instance, could go from traveling 315 miles (about 500 kilometers) on a single charge to as far as 473 miles. Or the carmaker could keep the range at 315 miles but lower the price to compete with gas-powered vehicles without a rebate.

“The dream is to make an affordable mass-market electric vehicle that is the same upfront cost as a gasoline equivalent. Then the consumer starts saving gas money from day one, and everyone would switch to electric,” said William Gent, a Ph.D. student of chemistry at Stanford University and the first author on the study, which appears today in Nature Communications.

Gent worked with professor William Chueh, an investigator at Stanford University, along with researchers from the Lawrence Berkeley National Laboratory’s Advanced Light Source, on the project.

Conventional lithium-ion batteries are pretty straightforward, technically speaking. They have two electrodes—a positively charged cathode and a negatively charged anode—with a liquid electrolyte between them. The cathodes are made up of layers of lithium and transition metals, namely nickel, manganese, or cobalt.

When the battery is charged, lithium ions move from the positive electrode, through the liquid electrolyte, and then insert themselves into the material that makes up the negative electrode. The transition metal ions stay put. The same happens for electrons, except they travel across the circuit on their way to the negative electrode. Ions and electrons travel in the opposite direction when the battery is discharged.

Lithium-rich batteries replace some of the transition metals in the electrodes with lithium. Although the additional lithium has the potential to increase the cathode’s capacity by 30 to 50 percent, it creates some mysterious voltage behavior. For instance, the average charging voltage is higher than the average discharging voltage, even at low currents. In a perfect battery, said Gent, the voltages would be the same.

Also, the voltage gradually falls after going through cycles of charging and discharging. Electronic devices can’t manage such erratic voltage behavior, said Gent, because the circuits aren’t able to recalibrate on the fly in order to deal with the changes. That’s why lithium-rich electrodes have been so impractical.

In searching for solutions, previous researchers have typically looked at either how the ions rearrange themselves during charge/discharge cycles or how the electrons are stored in the battery’s atomic and chemical structures. Studying both simultaneously has been extremely difficult because it requires advanced analytical techniques to get the best picture, and not many research teams have access to the necessary equipment.

Gent and his colleagues were able to do that. They worked at two facilities that each had very bright, highly sensitive, and finely tuned X-ray sources to develop hypotheses for how the atomic rearrangements might affect the way electrons are stored within the material. They used X-ray diffraction at SLAC’s Stanford Synchrotron Radiation Lightsource to probe changes in the cathode’s atomic and chemical structure as it was being charged and discharged. At Lawrence Berkeley National Laboratory’s Advanced Light Source they used resonant inelastic X-ray scattering to measure the magnetic and electronic properties of the lithium-rich material.

Next, the scientists used computer models to test their hypotheses. They confirmed that when the lithium-rich cathode was charged, the transition metal ions, which normally stay in place in conventional batteries, moved around. They found that this rearrangement drastically impacts the voltage at which the electrons are stored in the cathode. This wouldn’t be so bad if the ions returned to their original location during discharge. But few did. And each time the battery was charged and discharged, the ions moved a little more, which created disorder in the atomic structure and caused the strange voltage behavior.

“We're hoping we can use this understanding to gain better control of these materials and make them more practical,” said Gent.

He and his colleagues have already begun to test different ways to address the problem. One idea is to prevent the transition metal ions from migrating. Another is to design the structure in a way that makes it easier for the migrating ion to return to its original position.

The Conversation (0)
This photograph shows a car with the words “We Drive Solar” on the door, connected to a charging station. A windmill can be seen in the background.

The Dutch city of Utrecht is embracing vehicle-to-grid technology, an example of which is shown here—an EV connected to a bidirectional charger. The historic Rijn en Zon windmill provides a fitting background for this scene.

We Drive Solar

Hundreds of charging stations for electric vehicles dot Utrecht’s urban landscape in the Netherlands like little electric mushrooms. Unlike those you may have grown accustomed to seeing, many of these stations don’t just charge electric cars—they can also send power from vehicle batteries to the local utility grid for use by homes and businesses.

Debates over the feasibility and value of such vehicle-to-grid technology go back decades. Those arguments are not yet settled. But big automakers like Volkswagen, Nissan, and Hyundai have moved to produce the kinds of cars that can use such bidirectional chargers—alongside similar vehicle-to-home technology, whereby your car can power your house, say, during a blackout, as promoted by Ford with its new F-150 Lightning. Given the rapid uptake of electric vehicles, many people are thinking hard about how to make the best use of all that rolling battery power.

The number of charging stations in Utrecht has risen sharply over the past decade.

“People are buying more and more electric cars,” says Eerenberg, the alderman. City officials noticed a surge in such purchases in recent years, only to hear complaints from Utrechters that they then had to go through a long application process to have a charger installed where they could use it. Eerenberg, a computer scientist by training, is still working to unwind these knots. He realizes that the city has to go faster if it is to meet the Dutch government’s mandate for all new cars to be zero-emission in eight years.

The amount of energy being used to charge EVs in Utrecht has skyrocketed in recent years.

Although similar mandates to put more zero-emission vehicles on the road in New York and California failed in the past, the pressure for vehicle electrification is higher now. And Utrecht city officials want to get ahead of demand for greener transportation solutions. This is a city that just built a central underground parking garage for 12,500 bicycles and spent years digging up a freeway that ran through the center of town, replacing it with a canal in the name of clean air and healthy urban living.

A driving force in shaping these changes is Matthijs Kok, the city’s energy-transition manager. He took me on a tour—by bicycle, naturally—of Utrecht’s new green infrastructure, pointing to some recent additions, like a stationary battery designed to store solar energy from the many panels slated for installation at a local public housing development.

This map of Utrecht shows the city’s EV-charging infrastructure. Orange dots are the locations of existing charging stations; red dots denote charging stations under development. Green dots are possible sites for future charging stations.

“This is why we all do it,” Kok says, stepping away from his propped-up bike and pointing to a brick shed that houses a 400-kilowatt transformer. These transformers are the final link in the chain that runs from the power-generating plant to high-tension wires to medium-voltage substations to low-voltage transformers to people’s kitchens.

There are thousands of these transformers in a typical city. But if too many electric cars in one area need charging, transformers like this can easily become overloaded. Bidirectional charging promises to ease such problems.

Kok works with others in city government to compile data and create maps, dividing the city into neighborhoods. Each one is annotated with data on population, types of households, vehicles, and other data. Together with a contracted data-science group, and with input from ordinary citizens, they developed a policy-driven algorithm to help pick the best locations for new charging stations. The city also included incentives for deploying bidirectional chargers in its 10-year contracts with vehicle charge-station operators. So, in these chargers went.

Experts expect bidirectional charging to work particularly well for vehicles that are part of a fleet whose movements are predictable. In such cases, an operator can readily program when to charge and discharge a car’s battery.

We Drive Solar earns credit by sending battery power from its fleet to the local grid during times of peak demand and charges the cars’ batteries back up during off-peak hours. If it does that well, drivers don’t lose any range they might need when they pick up their cars. And these daily energy trades help to keep prices down for subscribers.

Encouraging car-sharing schemes like We Drive Solar appeals to Utrecht officials because of the struggle with parking—a chronic ailment common to most growing cities. A huge construction site near the Utrecht city center will soon add 10,000 new apartments. Additional housing is welcome, but 10,000 additional cars would not be. Planners want the ratio to be more like one car for every 10 households—and the amount of dedicated public parking in the new neighborhoods will reflect that goal.

This photograph shows four parked vehicles, each with the words \u201cWe Drive Solar\u201d prominently displayed, and each plugged into a charge point.Some of the cars available from We Drive Solar, including these Hyundai Ioniq 5s, are capable of bidirectional charging.We Drive Solar

Projections for the large-scale electrification of transportation in Europe are daunting. According to a Eurelectric/Deloitte report, there could be 50 million to 70 million electric vehicles in Europe by 2030, requiring several million new charging points, bidirectional or otherwise. Power-distribution grids will need hundreds of billions of euros in investment to support these new stations.

The morning before Eerenberg sat down with me at city hall to explain Utrecht’s charge-station planning algorithm, war broke out in Ukraine. Energy prices now strain many households to the breaking point. Gasoline has reached $6 a gallon (if not more) in some places in the United States. In Germany in mid-June, the driver of a modest VW Golf had to pay about €100 (more than $100) to fill the tank. In the U.K., utility bills shot up on average by more than 50 percent on the first of April.

The war upended energy policies across the European continent and around the world, focusing people’s attention on energy independence and security, and reinforcing policies already in motion, such as the creation of emission-free zones in city centers and the replacement of conventional cars with electric ones. How best to bring about the needed changes is often unclear, but modeling can help.

Nico Brinkel, who is working on his doctorate in Wilfried van Sark’s photovoltaics-integration lab at Utrecht University, focuses his models at the local level. In his calculations, he figures that, in and around Utrecht, low-voltage grid reinforcements cost about €17,000 per transformer and about €100,000 per kilometer of replacement cable. “If we are moving to a fully electrical system, if we’re adding a lot of wind energy, a lot of solar, a lot of heat pumps, a lot of electric vehicles…,” his voice trails off. “Our grid was not designed for this.”

But the electrical infrastructure will have to keep up. One of Brinkel’s studies suggests that if a good fraction of the EV chargers are bidirectional, such costs could be spread out in a more manageable way. “Ideally, I think it would be best if all of the new chargers were bidirectional,” he says. “The extra costs are not that high.”

Berg doesn’t need convincing. He has been thinking about what bidirectional charging offers the whole of the Netherlands. He figures that 1.5 million EVs with bidirectional capabilities—in a country of 8 million cars—would balance the national grid. “You could do anything with renewable energy then,” he says.

Seeing that his country is starting with just hundreds of cars capable of bidirectional charging, 1.5 million is a big number. But one day, the Dutch might actually get there.

This article appears in the August 2022 print issue as “A Road Test for Vehicle-to-Grid Tech.”

Keep Reading ↓Show less