The degraded cathode particles are extracted from the used battery and then boiled and heat treated. New batteries built with the recycled cathodes see the original charge storage capacity, charging time and lifetime, which is a considerable advance. The lithium cobalt oxide cathodes are the most common in consumer batteries, but the process also works on nickel, manganese and cobalt (NMC) cathodes used in most electric vehicles.
Less than five percent of used lithium ion batteries are recycled today, partly as a result of the difficulties and cost of reusing the components. Most have the materials extracted to be re-used from scratch.
"Think about the millions of tons of lithium ion battery waste in the future, especially with the rise of electric vehicles, and the depletion of precious resources like lithium and cobalt--mining more of these resources will contaminate our water and soil. If we can sustainably harvest and reuse materials from old batteries, we can potentially prevent such significant environmental damage and waste," said Zheng Chen, professor of nanoengineering at UC San Diego. "We simply restore the degraded material by putting it through the same processing steps," he said.
This could also address economic issues. "The price of lithium, cobalt and nickel has increased significantly. Recovering these expensive materials could lower battery costs," he said.
The method involves first collecting cathode particles from spent lithium ion batteries. Researchers then pressurize the cathode particles in a hot, alkaline, solution containing lithium salt. This solution can also be recycled and reused to process more batches. Afterwards, the particles go through a short annealing process in which they are heated to 800ºC and then cooled very slowly.
Researchers made new cathodes from the regenerated particles and then tested them in batteries built in the lab. The new cathodes showed the same energy storage capacity, charging time and lifetime as the originals.
More energy efficient process
Overall, the recycling process uses 5.9MJ/kg, equivalent to the energy in about three quarters of a cup of petrol for a kilogram of cathode material. This is half the energy required by other lithium batttery recycling processes.
The next step is to optimise this process for industrial scales and Chen's team is planning to work with battery companies in Asia. A key step is the cathode harvesting, which is currently done by hand, and thi swould be automated.
The team has filed a provisional patent on this work and is aiming to license it through the university's Innovation and Commercialization Office
A further step is to broaden the process to other types of cathodes and anodes. "The goal is to make this a general recycling process for all cathodes," said Chen.