Microwave technique recovers 87% of batteries' lithium in 15 minutes

Lithium is a finite resource, and the more we lock inside rechargeable batteries, the less we have to use. A new speedy method to free the element from such sources could be a game changer in terms of the material's availability.

Thanks to our modern day way of purchasing rechargeable everything – including cars – the demand for the lithium-ion batteries that power much of our consumer technology has been skyrocketing. Currently valued at approximately $65 billion, the market for lithium-ion batteries is expected to grow by 23% in the next eight years.

As a relatively lightweight material with the ability to store a lot of energy, the value of lithium is clear. But mining the element can be environmentally destructive, and geopolitical concerns in several of the areas where it is plentiful can threaten supply chains. Plus we've previously reported that there are predictions that current lithium mines will only be able to produce half of what's needed to satisfy demand by 2030.

Taking those factors into account, it's important to either find ways to produce lithium-free battery technologies, look to new methods and sources for extracting it, or find ways to recycle the lithium stored in used up batteries. Yet recycling lithium can be time consuming, use harsh chemicals, and lead to the recovery of less than 5% of the total amount of the element originally used.

Nuking it

So researchers at Rice University came up with a better solution. They started by using chemicals known as deep eutectic solvents (DES), which are eco-friendly liquids that can precipitate lithium and other metals out of a solution.

“The recovery rate is so low because lithium is usually precipitated last after all other metals, so our goal was to figure out how we can target lithium specifically,” said Salma Alhashim, a Rice doctoral alumna who is one of the study’s lead authors. “Here we used a DES that is a mixture of choline chloride and ethylene glycol, knowing from our previous work that during leaching in this DES, lithium gets surrounded by chloride ions from the choline chloride and is leached out into solution.”

Normally a compound needs to be heated in order to force metals to precipitate out and in the case of lithium-containing compounds, an oil bath usually provides that heat source. But the process takes a fair bit of time during which the lithium itself can begin to degrade.

To speed things up, the Rice team decided to give microwaves a try, knowing that the choline chloride that leads to the isolation of the lithium is very good at absorbing microwave radiation.

15-minute milestone

The speed boost was impressive. The researchers were able to precipitate out the lithium almost 100 times faster than an oil bath. In fact, it took them just 15 minutes to get back 87% of the lithium – a process that would take 12 hours using an oil bath.

“This allowed us to leach lithium selectively over other metals,” said Sohini Bhattacharyya, one of the other lead authors and a postdoctoral fellow in the Nanomaterials Laboratory. “Using microwave radiation for this process is akin to how a kitchen microwave heats food quickly. The energy is transferred directly to the molecules, making the reaction occur much faster than conventional heating methods.”

The researchers say the method can also be tailored to target other elements by tuning the DES composition, so it could have the ability to recover other metals like cobalt or nickel from batteries. The team also highlights the eco-friendly benefits of its approach.

“This method not only enhances the recovery rate but also minimizes environmental impact, which makes it a promising step toward deploying DES-based recycling systems at scale for selective metal recovery,” said Pulickel Ajayan, the corresponding author on the study and department chair of materials science and nanoengineering.

The work has been published in the journal Advanced Functional Materials.