A new method could dramatically improve the economics of lithium-ion battery recycling, according to the researchers involved.
Lithium is a key ingredient in batteries - from the modest one in your phone through to bigger home energy storage or even giant grid-scale systems. While relatively abundant, lithium supplies are likely to come under pressure as demand from electric vehicle manufacturers and others increases, but recovering lithium from spent batteries is currently difficult and inefficient.
Now a team at Rice University have set out a method for recovering lithium using microwave radiation and a biodegradable solvent which they said is rapid, efficient - and environmentally friendly.
They said the process can retrieve as much as 50% of the lithium in spent lithium-ion battery cathodes in 30 seconds, overcoming a “significant bottleneck” in battery recycling.
Sohini Bhattacharyya (above right) one of the two lead authors on the study published in Advanced Functional Materials said there has been “colossal” growth in lithium-ion battery use in recent years, leading to concerns about the availability of metals including lithium, cobalt and nickel which are used in the cathodes.
Current recycling methods recover less than 5% of lithium, largely due to contamination and loss during the process.
“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 (above left) the study’s other lead author.
The team used a deep eutectic solvent (DES) that is a mixture of choline chloride and ethylene glycol, because they know from previous work that during leaching in this DES, lithium gets surrounded by chloride ions from the choline chloride and is leached out into solution. In order to leach other metals like cobalt or nickel, both the choline chloride and the ethylene glycol have to be involved in the process.
Choline chloride is good at absorbing microwaves, so the researchers submerged the battery waste material in the solvent and used microwave radiation which allowed them to leach lithium selectively over other metals. Using microwave radiation transferred energy directly to the molecules, making the reaction occur much faster than conventional heating method, the researchers said. They found it took 15 minutes to leach 87% of the lithium as opposed to the 12 hours needed to obtain the same recovery rate via oil bath heating. This also meant the solvent didn’t have time to decompose.
A separate team of researchers also at Rice have also published details of a different approach to recycling lithium-ion batteries.
Their technique used a method known as solvent-free flash Joule heating (FJH). This technique, devised by James Tour, the T.T. and W.F. Chao Professor of Chemistry and professor of materials science and nanoengineering, involved passing a current through a moderately resistive material to rapidly heat and transform it into other substances.
Using FJH, the researchers heated battery waste to 2,500 Kelvin within seconds, creating unique features with magnetic shells and stable core structures. During the process, the cobalt-based battery cathodes — typically used in EVs — unexpectedly showed magnetism in the outer spinel cobalt oxide layers, allowing for easy separation. Taking this approach resulted in a high battery metal recovery yield of 98%.
“Notably, the metal impurities were significantly reduced after separation while preserving the structure and functionality of the materials,” said Tour who noted the bulk structure of battery materials remains stable and is ready to be reconstituted into new cathodes.
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