Diversifying supply of critical minerals a 'major challenge' in going green, IEA says Hosting a summit on critical minerals in Paris on Thursday, the International Energy Agency said the "major challenge" countries faced was ensuring more diverse supplies and the recycling of metals. Elements like lithium, nickel and cobalt are key for governments hoping to make the green switch as they are needed for producing electric vehicle batteries and wind turbines. Western countries are keen to reduce dependency on China, which accounts for almost 70 percent of rare-earth metal production.