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It's one of the biggest unanswered questions as electric vehicles (EVs) rapidly proliferate: What will happen to all of the degraded lithium-ion batteries once the vehicles reach the end of their lives? "Recycling" is the optimistic solution offered by EV advocates and supporters of green technology, but will battery recycling actually make economic and environmental sense?

According to the International Energy Agency, a predicted 23 million EVs sold worldwide in 2030 could lead to 5,750,000 tonnes of retired batteries by 2040, and this waste will keep piling up as EVs replace internal combustion engine vehicles. The prospect is of pressing interest to a team of scientists and engineers in the UK, which recently published a paper on the "financial viability of electric vehicle lithium-ion battery recycling" in the journal iScience.

"If recycling remains unprofitable, battery waste mountains could build up, which, if uncontrolled, bear a significant environmental and safety risk, as toxic chemicals could leak into the environment and landfill fires might occur," the researchers warned.

Luckily, the researchers aren't the only ones to notice this looming calamity. According to Circular Energy Storage, about a hundred companies worldwide recycle lithium-ion batteries or plan to do so soon. These include battery-making giants like China's Gangfeng Lithium, Elon Musk's Tesla, and numerous startups flush with fresh investor funding.

Though they all utilize differing methods to break down the batteries and secure the precious elements inside –– predominantly cobalt, nickel, and manganese, and to a lesser extent, the lithium itself –– these methods invariably fall into three categories: pyrometallurgy, in which the battery is shredded and burned, hydrometallurgy, in which the battery is dunked into a pool of acid to dissolve the target metals, and the experimental direct method, in which the battery is meticulously disassembled and its prized cathode recovered intact.

Hydrometallurgy and pyrometallurgy are presently the easiest and most common strategies, but they have the unfortunate side effects of producing toxic waste and emitting greenhouse gases. Scientists are presently working to lessen their impact and increase their efficiency.

Good news, reported recently, is that lithium-ion batteries made of recycled materials perform just as well and may even outlast batteries built from novel materials. And they could be economically-produced as well.

The UK researchers behind the iScience report found that, while EV battery recycling is generally unprofitable at present time, it should grow to be financially viable if a few key actions are achieved. One, recycling should be performed domestically and as locally as possible to reduce transportation costs, as used batteries weigh hundreds of kilograms. Two, facilities must take advantage of economies of scale, handling at minimum a few thousands tonnes of material each year and preferably tens of thousands of tonnes. Three, researchers and companies need to refine the direct method of battery recycling, as it can be two to four times as economical as hydrometallurgy or pyrometallurgy, and much less environmentally intense. Four, battery manufacturers need to make their products easier to disassemble, as this is often the most labor-intensive part of the recycling process. EV battery packs are often tightly packed and bound with chemically intricate glues. Policy interventions in the form of subsidies or regulations can help with any of these areas, the researchers say.

"This becomes especially essential in the first operating years of a recycling plant until economies of scale are reached or when high value materials such as cobalt are not included anymore in future battery chemistries."

Perhaps the two biggest risks to the profitability of EV battery recycling are if cobalt, easily the most prized metal in batteries, is replaced, or if its price and the price of other elements falls precipitously. In this case, there is an alternative to conventional recycling which may prove to be the most popular option anyway: plugging old EV batteries into utility-scale grid storage. A team from Nanjing University in China actually estimates that this will be the most attractive proposition long-term, as this route wouldn't require as many costly inputs.

Luckily, experts generally acknowledge that spent EV batteries won't start to disconcertingly pile up for another decade or so, so there's still time to figure out a workable recycling solution.

This article originally ran on realclearscience.com.

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