Lithium-ion batteries are powering a revolutionary transition to electric vehicles. But booming battery use will eventually create a mountain of spent batteries—and very few are currently recycled.
A team led by James M. Tour at Rice University has now developed an appropriately electrifying approach to recycling the batteries’ graphite anodes. The process uses a pulse of electricity to heat impurities in the anode, making them easier to extract so that the remaining graphite can be turned into new anodes. The researchers say their method, dubbed flash recycling, is cheaper and greener than rival methods (Adv. Mater. 2022, DOI: 10.1002/adma.202207303).
Li-ion battery recycling has largely focused on recovering valuable metals such as lithium, cobalt, manganese, and nickel. The graphite anodes are often discarded or burned for energy, even though they represent about 15% of the cost of a battery.
These anodes contain small particles of graphite stuck together with a binder. Over their lifetimes, they accumulate a layer of insoluble organic and inorganic lithium salts and other battery metals. Some experimental recycling methods free graphite from these impurities using strong acids, which can generate polluting waste streams; other methods rely on energy-intensive calcination, heating the anode materials to thousands of degrees for several hours.
In the flash recycling method, the researchers grind the anode into a powder and load it into a quartz tube between two electrodes. A 1 s jolt of electricity, which delivers a current up to 350 A, heats the material to about 2,500 °C. The impurities have a much higher electrical resistance than graphite and take the brunt of this flash of heat.
The burst of heat completely carbonizes the organic impurities in the powder and forms inorganic salts and metal oxide nanoparticles. Washing the material with dilute hydrochloric acid removes all of the inorganic waste, leaving graphite particles behind. The researchers calculate that their approach uses half the energy of calcination recycling, at about 70% of the cost. “The amount of energy we use is much less because the duration is so quick,” Tour says.
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The researchers made new anodes from the flash-recycled graphite and tested them in Li-ion batteries. The anode retained 77% of its energy capacity after 400 recharge cycles. “This is comparable with commercial graphite, which is around 80%,” says Tour’s Rice University colleague Weiyin Chen, who led the experimental work. The team’s life-cycle analyses suggest that using flash recycling to produce graphite for new anodes would require 96% less energy than making fresh synthetic graphite, at roughly 12% of the cost.
“It’s not to be sniffed at,” says Paul Anderson of the University of Birmingham, who leads the Faraday Institution’s Reuse and Recycling of Lithium Ion Batteries (ReLiB) project and was not involved in the work. “They get decent quality graphite that performs reasonably well. But it doesn’t seem to me that it’s good enough yet.”
Anderson says that further improving the quality of the recovered graphite will be crucial. “Anyone who can take low-grade graphite and make it into battery-grade graphite with a lower-temperature, more energy-efficient process, is on to a winner.”
Tour’s team has previously used the technique, known as flash Joule heating, to turn a wide range of carbon-based materials into graphene. He cofounded a company called Universal Matter that is scaling up this method of graphene production and says that anode recycling could use the same technology. The researchers now hope to apply flash recycling to “black mass”—the shredded battery guts that mark the usual starting point for recycling in the battery industry.