The adoption of electric cars has risen quickly in the US, with a doubling of sales between 2012 and 2013, and a further 30% increase projected for last year. According to a 2013 report by the US National Research Council, by 2050, electric cars will account for 80% of new car sales. That's seen as good news for the environment, because recharging an electric-car battery generates less emissions than burning fuel in a combustion engine, particularly as centralized electricity generation is likely to be made less carbon-intensive over time.

But electric-car batteries themselves are not necessarily environmentally friendly. Most are based on lithium-ion technology – a relatively affordable and energy-dense option – and need to be recycled. A study published last year by US researchers at Argonne National Laboratory and Michigan State University showed that if all of the cars in California turned electric, that would create solid waste totalling more than 600,000 tonnes a year. But lithium-ion technology is evolving, which forces recycling methods to evolve too. Worse, some manufacturers have shifted away from using precious metals in lithium-ion batteries to reduce upfront costs, which lowers the incentive to recycle.

Nonetheless, many see recycling as a necessity to keep electric cars as a green option. The European Union has already set targets for lithium-ion battery collection and recycling, for instance, and it's expected that, with its other goals for zero waste, California will soon follow suit.

That's why Corinne Scown, Thomas Hendrickson and colleagues at Lawrence Berkeley National Laboratory in California analysed the state's lithium-ion recycling options, and how they affect the use of energy and water, and the production of greenhouse gases and air pollution. The team created a geographic model to understand the infrastructure needed for lithium-ion recycling, and then explored various battery lifecycles.

The researchers found that there would probably be less return on investment if more than two dismantling facilities were constructed in California. They also calculated that rail, in addition to road transport, could reduce greenhouse-gas transportation emissions by between 23 and 45%, whether recycling were done in-state or out-of-state. Meanwhile, environmental damage from battery production could be significantly offset if battery materials were recovered with pyrometallurgy, a smelting process that can accept a range of lithium-ion and other battery types.

"While our study has results tailored to California, the real value of the analysis lies in the methodology," said Hendrickson. "These models can be recreated and applied in regions, both nationally and globally, that face increasing electric-vehicle lithium-ion-battery waste-streams. Based on industry feedback, the recycling technologies and supply chains will be similar everywhere."

According to Hendrickson, the team's work assesses an often-overlooked aspect of increasing electric-vehicle use, namely "scaling up the infrastructure required to manage batteries at their end-of-life, and the environmental trade-offs of competing recycling processes".

The study is published in Environmental Research Letters (ERL).

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