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Thursday, April 18, 2024

The Surprising Climate Cost of the Humblest Battery Material

An ode, for a moment, to the anode, for it is so frequently overlooked. When a battery is powered up, lithium ions rush toward this positively-charged end and ensconce themselves there until the energy is needed. Originally, anodes were made from lithium metal. But lithium metal is unstable, and liable to explode in contact with air or water, so scientists tried out carbon instead. Over the years, they refined it into a material composed of hexagonal atomic rings—a lattice that could hold an abundance of ions, without the explodey-ness. That material is graphite, the same stuff found in the tip of a No. 2 pencil. It is often said that the cathode—that’s the other end of the battery—is where the magic happens. It’s home to an arrangement of metals like cobalt, nickel, and manganese. But each of those metals is negotiable, depending on the specific battery design. Humble graphite isn’t. It helps define how much energy a battery can hold, and how fast it charges up.

And if the anode itself is overlooked, so is its carbon footprint. As with other battery materials, automakers rely on estimates to determine the environmental cost of graphite’s globe-spanning journey before it ends up inside a car. But a pair of recent studies suggest that those estimates are woefully out-of-date and undercounted, failing to include the energy-intensive processes required to produce modern, anode-ready graphite. Those bad estimates are undermining efforts to clean up the supply chain for electric vehicles. “The same thing kept coming up again and again,” says Robert Pell, CEO of Minviro, a consultancy that works with electric car companies on environmental assessments. “Everybody cares about the cathode, but the reality is we knew the impact of the anode was significantly underestimated.”

Electric vehicles are, by and large, greener than their gas-combusting counterparts. Plugging them in creates emissions because it taps into a dirty electricity grid, but on the whole, the grid is getting greener, and going electric is already a lot better than exploding gallon after gallon of gasoline. It’s the raw materials for the battery that are harder to decarbonize. The cathode indeed has the biggest environmental consequences—including both carbon emissions and the ecological and human rights harms of mining minerals like lithium, nickel, and cobalt. In some cases, car companies have tried to kick their dependence on cobalt and nickel by swapping them out for other metals.

But graphite shouldn’t get a pass, says Pell, an author of one of the two studies. The results illuminate the problems with how corporations measure their carbon emissions, especially the critical component of “Scope 3.” That’s usually the biggest chunk, including all the energy a company doesn’t consume directly. For an automaker, that includes the carbon emitted by the vast supply chains that produce components, including batteries, and the carbon involved in getting energy into the charging cable. But it’s tricky to take stock of. Go back deep enough into the supply chain, all the way back to the processing of raw materials, and the specifics get fuzzy, the true energy demands opaque.

This is particularly true for graphite. The second study, published earlier this year by researchers at the Technical University of Braunschweig and Volkswagen, included a litany of assumptions and caveats found in previous estimates for graphite carbon emissions. Some of the most popular references used to calculate climate impact inferred details from old manufacturing manuals and borrowed corollaries from processing other materials, like aluminum. Others simply took estimates for other carbon-based materials, and did not factor in the uniquely intensive refining steps needed to rearrange the atoms into graphite.

Pell’s research started with jotting down some back-of-the-envelope calculations. It helped to know that more than 90 percent of graphite for anodes comes from China, and the bulk of that from the northern Inner Mongolia region, where energy is cheap but depends largely on coal-fired power plants. Knowing the approximate carbon intensity of the power supply, he began mapping out the laborious steps for turning that graphite into anodes.

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Graphite comes in two forms: natural and synthetic. For natural graphite, that process begins with a mined ore that is crushed and milled into flakes, then separated in liquid and dried using coal furnaces. Next comes spheronization, in which the flakes are transported to another facility and run through dozens of mills to produce a spherical shape. At that point, the graphite is good enough for a pencil. To get anode-ready, the particles are treated with chemicals to remove impurities, and then they go through a coating step that makes them more conductive and better able to hold lithium ions. This requires blasting the particles in a furnace for about 15 hours at 1,300 degrees Celsius, or nearly 2,400 degrees Fahrenheit.

Synthetic graphite involves even more blazing temperatures. It typically requires taking a carbon product, like petroleum coke left over from producing oil, and heating it up for multiple weeks at 1,000 degrees Celsius to create a more homogenous material. The next step is graphitization, which involves cranking the temperature up to 3,000 degrees Celsius (that’s 5,400 degrees Fahrenheit, by the way) for days, a process that forces randomly ordered carbon atoms to straighten themselves out into a neat hexagonal lattice. Typically, these heating steps are done in open pit furnaces that take tremendous amounts of electricity to stay hot.

The two teams arrived at different numbers for the overall climate effect of graphite, which in part reflects differing data sources. (The German team relied on direct data from graphite suppliers and factored in the overall mix of energy sources in China, while the Minviro team used published estimates for graphite processing and the Inner Mongolian energy supply, which is dirtier than the average.) But the takeaway is effectively the same: Both show that the figures companies commonly use to assess their climate impact are often vast underestimates. Minviro estimates the emissions for synthetic graphite are up to 10 times higher than standard published estimates, or eight times for natural graphite. The German team arrived at four times higher for natural graphite, compared with a popular reference. Both teams advocate for more research and data to improve the estimates.

One of the primary ways to reduce those emissions would be to invest in graphite recycling, says Felipe Cerdas, one of the TU Braunschweig researchers—taking the anode out of a dead battery and retrieving the fine graphite powder for use in new batteries. That’s often less carbon-intensive than trying to make the material from scratch. But because graphite is so abundant and cheap, the economics of recycling don’t currently make sense. Most recyclers target higher-value metals like cobalt and nickel, using recycling methods that burn the graphite away.

That’s one reason having an accurate measure of graphite’s climate effects is important, Pell says. European officials are debating new regulations that would reduce the carbon emissions of battery production and require manufacturers to include specific ratios of recycled materials in new cells. Better awareness could help inform those rules, he says, and encourage a switch toward cleaner sources.

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One option would be to locate graphite processing in places where the electricity supply is greener. Vianode, a subsidiary of the Norwegian metals processing company Elkem, is building a facility to produce synthetic graphite that would use closed, energy-efficient furnaces that run on electricity from the country’s abundant hydropower. The company has seen interest from others interested in bolstering their green reputations, says Stian Madshus, Vianode’s general manager for Europe. “It doesn’t make much sense to produce the world’s cleanest battery if the graphite inside it involves 20 kilograms of CO2 equivalent,” he says. “That’s a bad story.”

But there’s catching up to do. Chinese firms have decades of experience producing anode-quality graphite, making it difficult for Western companies to compete. But the country has the power to make a difference, Pell says, noting that the Chinese government has recently pushed to distribute energy-intensive industries across the country and increase the use of clean energy. “The ability to enact change is stronger there than anywhere else,” he says.


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