While electric vehicles have become a cornerstone of the global energy transition, new research led by Princeton University has demonstrated that refining the critical minerals needed for electric vehicle batteries could create pollution hotspots near manufacturing hubs.

Focusing on China and India, the researchers found that national sulfur dioxide (SO2) emissions could increase by up to 20% over current levels if the countries were to fully domesticize their supply chains for electric vehicles. The overwhelming majority of those SO2 emissions would come from refining and manufacturing nickel and cobalt — important minerals for today’s electric vehicle batteries.

“Many discussions about electric vehicles focus on minimizing emissions from the transport and power sectors,” said corresponding author Wei Peng, an assistant professor of public and international affairs and the Andlinger Center for Energy and the Environment. “But we show here that the impacts of electric vehicles don’t end with vehicle tail-pipe emissions or electricity. It’s also about your entire supply chain.”

Publishing their findings in Environmental Science & Technology, the researchers argued that countries must think strategically about building clean supply chains as they develop decarbonization plans.

In the case of battery manufacturing, the team underscored the importance of developing and enforcing strict air pollution standards to avoid unintended consequences of the transition to electric vehicles. They also suggested the development of alternative battery chemistries to avoid the process-based SO2 emissions of manufacturing today’s batteries.

“If you dig deep enough into any clean energy technology, you will find there are challenges or tradeoffs,” said first author Anjali Sharma, who completed the work as a postdoctoral researcher in Peng’s group and is now an assistant professor in the Centre for Climate Studies and Ashank Desai Centre for Policy Studies at the Indian Institute of Technology, Bombay. “The existence of these tradeoffs doesn’t mean that we stop the energy transition, but it does mean that we need to act proactively to mitigate these tradeoffs as much as possible.”

A tale of two countries

Both China and India have good reasons to avoid SO2 emissions: the compound is a precursor to fine particulate matter, contributing to a host of cardiovascular and respiratory problems. The two countries already suffer from high levels of air pollution. In 2019 alone, around 1.4 million premature deaths in China and around 1.7 million premature deaths in India were attributable to fine particulate matter exposure.

However, the two countries are at different stages of development for electric vehicles. Peng said that in China, a domestic supply chain for electric vehicles is the status quo, but that India is still in the early stages of supply chain development. The comparison helped the researchers identify near-term priorities as they continue or begin to build a domestic supply chain for electric vehicles.

“China needs to be thinking about how to clean up a supply chain that already exists, while India has the opportunity to build a better supply chain from the ground up,” said Peng, who is also a core faculty at the Center for Policy Research on Energy and the Environment. “Both situations come with their own challenges and opportunities.”

In India, the lowest-hanging fruit would be to focus first on cleaning up pollution from the power sector. This would require enforcing stringent SO2 pollution control measures for thermal power plants, using mature technologies like flue-gas desulfurization. For China, which already has stringent emissions controls for the power sector, the focus needs to shift to mitigating SO2 emissions from the battery manufacturing process, which the researchers said is less familiar.

However, the researchers underscored that ignoring emissions from battery manufacturing would be a critical misstep. In scenarios where China and India fully onshored their supply chains, prioritizing a cleaner grid did little to nothing to lower SO2 emissions. Instead, only scenarios focused on cleaning up battery manufacturing processes avoided SO2 pollution hotspots.

“People generally assume the transition to a greener technology is always going to be a win-win — there will be climate and air quality benefits,” said Sharma. “But without considering manufacturing, you might lower carbon and nitrogen oxide emissions but end up increasing the air pollution burden for communities near manufacturing centers.”

Human-centered approaches to decarbonization

While the analysis focused on China and India, the researchers argued that if left unaddressed, pollution from battery manufacturing will become an increasingly global challenge as electric vehicle adoption rates rise. Even if countries like China and India were to outsource battery manufacturing, Sharma said that without strategies to mitigate SO2 emissions, they would simply be offloading the problem to another country.

“It’s important to look at electric vehicles from a global supply chain perspective,” Sharma said. “Even if India were to decide against building a domestic supply chain and instead chose to import them from somewhere else, the pollution wouldn’t go away. It would just be outsourced to another country.”

In addition to their policy recommendation for proactive air pollution standards, which would likely happen at the national or subnational level, the researchers also examined how changing the battery chemistry in electric vehicles could avoid unwanted SO2 emissions at a more global scale.

While most electric vehicle batteries today rely on cobalt and nickel, the rise of alternative chemistries that use iron and phosphate (so-called lithium iron phosphate batteries) could circumvent some of the concerns associated with mining and refining cobalt and nickel. By avoiding the two minerals, scenarios with high penetration of lithium phosphate batteries resulted in far fewer SO2 emissions from manufacturing.

In all events, Peng said the findings serve as a reminder to keep people at the top of mind when designing decarbonization plans, as even the most promising technologies could come with unwanted and unintended consequences.

“We know about many of the important technologies for cutting carbon emissions,” said Peng. “But the other part is how people will be affected by those technologies. My approach is to think about the best ways for technologies and people to intersect, because those strategies will have the best outcomes for the greatest number of people.”



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