The controversial sourcing of lithium-ion batteries briefly took center stage at the Democratic presidential debate in Las Vegas, Nevada, on Wednesday night in a question directed at Sen. Elizabeth Warren (D-MA).

“The tension here in this state is between people who want renewable energy and people who want conservation on public lands,” said moderator Jon Ralston. He pointed out that Warren had pledged to sign an executive order to stop drilling on public lands on her first day in office. “You’ve got to have lithium, you’ve got to have copper for renewable energy. How do you do that?” he asked Warren.

Switching to electric-powered vehicles and solar energy will be a big piece of the puzzle when it comes to the US weaning itself off planet-heating fossil fuels. That technology requires lithium-ion batteries, and Nevada has a huge reserve of lithium on public land.

Thacker Pass in Humboldt County, Nevada, is one of those potential sources of lithium. A Canadian company, Lithium Americas has been planning to develop the site, which the company estimates is the largest deposit of lithium in the United States.

Lithium Americas’ proposal to mine the Thacker Pass deposit is currently under review by the US Bureau of Land Management. The company hopes to retrieve between 30,000 to 60,000 tons of battery-grade lithium carbonate at the location every year for about 40 years, starting in 2022. It says it could supply “most or all” of the US’s demand for lithium.

Although the company says the operation would bring jobs on top of supplying the transition to more renewable energy, some Nevada residents are concerned about having an open-pit mine essentially in their backyards.

“Well, it takes out a lot of our range, and it has a huge economic impact for us,” Cattle rancher Jhona Bell told the Mountain West News Bureau. “Obviously you can’t run cattle where there’s a mine.” People can submit their comments about the Thacker Pass mine to the Bureau of Land Management through February 27th.

Building batteries without harming people and the environment remains one of the biggest problems to solve when it comes to getting the world on clean energy. Mining for lithium has dried up lagoons and used up groundwater locals depend on in Chile, which is estimated to hold almost half the world’s lithium reserves.

The cobalt that’s also needed to make lithium-ion batteries has led to child labor in the Democratic Republic of the Congo; Apple, Google, and Tesla are facing a lawsuit over child deaths as a result. Finding new places to mine that won’t harm people has ocean advocates concerned about deep-sea mining destroying ecosystems before we even have the chance to understand them.

“Mining, metals, and materials extraction is the hidden foundation of the low-carbon transition. But it is far too dirty, dangerous, and damaging to continue on its current trajectory,” Benjamin Sovacool, a professor of energy policy at the University of Sussex, said in a statement when he published a policy paper in the journal Science last month. Sovacool argued that the success of efforts to take on climate change will depend on how responsibly leaders manage demand for minerals like lithium and cobalt.

Warren responded to the question of how to get the raw materials needed to power a greener energy infrastructure in the US by saying that she might make some exceptions when it comes to protecting public lands from mining. “If we need to make exceptions because there are specific minerals that we’ve got to have access to, then we locate those and we do it not in a way that just is about the profits of giant industries, but in a way that is sustainable for the environment,” Warren said at the debate.

She and other Democratic candidates are vying for environmentally minded voters as climate change becomes a bigger election issue. So how to build a low-carbon energy infrastructure without damaging communities and the environment in the process is a question that’s likely to pop up on the campaign trail again.