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Rice develops efficient lithium recovery method from battery waste

Lithium, often referred to as the "white gold" of clean energy, is an essential component in batteries of all sizes, from mobile devices to large-scale energy storage systems. Despite its abundance, the demand for lithium is growing rapidly due to the surge in electric vehicle (EV) usage, ambitious net-zero targets, and complex geopolitical issues. The global lithium-ion battery (LIB) market, valued at over $65 billion in 2023, is projected to expand by over 23% in the next eight years, exacerbating the challenges in lithium supply.

Traditionally, extracting lithium from used batteries is both environmentally damaging and highly inefficient. A team of researchers at Rice University, led by Pulickel Ajayan, is working to address this issue. Their recent study in Advanced Functional Materials outlines a rapid, efficient, and eco-friendly method for selectively recovering lithium using microwave radiation and a biodegradable solvent. The process can recover up to 50% of lithium from spent LIB cathodes in just 30 seconds, significantly improving upon current recycling technologies.

"We've seen a colossal growth in LIB use in recent years, which inevitably raises concerns as to the availability of critical metals like lithium, cobalt, and nickel that are used in the cathodes," explained Sohini Bhattacharyya, a lead author of the study and a Rice Academy Postdoctoral Fellow in Ajayan's Nanomaterials Laboratory. "It's therefore really important to recycle spent LIBs to recover these metals."

Current recycling methods often employ harsh acids, while alternative eco-friendly solvents, such as deep eutectic solvents (DESs), have struggled with efficiency and cost-effectiveness. Additionally, existing methods recover less than 5% of lithium, primarily due to contamination, losses during the process, and the energy-intensive nature of the recovery.

"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, another lead author of the study and a Rice doctoral alumna. "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."

To leach metals like cobalt or nickel, both choline chloride and ethylene glycol are necessary. Knowing that only choline chloride effectively absorbs microwaves, the researchers submerged the battery waste in the solvent and exposed it to microwave radiation.

"This allowed us to leach lithium selectively over other metals," Bhattacharyya noted. "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."

Compared to traditional heating methods like an oil bath, microwave-assisted heating can achieve similar efficiencies nearly 100 times faster. For instance, the microwave-based process took 15 minutes to leach 87% of the lithium, whereas the oil bath method required 12 hours to achieve the same recovery rate.

"This also shows that selectivity towards specific elements can be achieved simply by tuning the DES composition," Alhashim added. "Another advantage is solvent stability: Because the oil bath method takes so much longer, the solvent begins to decompose, whereas this does not happen with the short heating cycles of a microwave."

This innovative method could significantly enhance the economics and environmental impact of LIB recycling, offering a sustainable solution to a growing global problem.

"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 Ajayan, the corresponding author of the study and Rice's Benjamin M. and Mary Greenwood Anderson Professor of Engineering and professor and department chair of materials science and nanoengineering.

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