Engineers at the University of California San Diego and the University of California Los Angeles have developed an energy-efficient approach to regenerate Li-ion battery cathode materials (using LiCoO2 as a model material) by hydrothermal treatment of cycled electrode particles followed by short annealing. Unlike the conventional chemical leaching or solid-state synthesis approach, the approach is much simpler and more environmentally friendly, and can easily process batteries with different capacity degradation conditions.
The regenerated LiCoO2 particles can retain their original morphology and structure, and provide high specific capacity and cycling stability. They also show much better rate capability than particles regenerated through the solid-state synthesis approach. A paper on the work is published in the journal Green Chemistry. The team has filed a provisional patent on this work.
|Illustration of the recycling and regeneration procedure. Shi et al. Click to enlarge.|
This approach can be widely used to recycle and regenerate LiCoO2 cathodes on a large scale, the researchers said, and can be potentially applied to other types of cathode materials in LIBs such as NMC, a popular lithium cathode containing nickel, manganese and cobalt, which is used in most electric vehicles. Currently, less than 5% of used LIBs are recycled today.
The method involves first collecting cathode particles from spent lithium-ion batteries. Researchers then pre-dosed Li into the Li-deficient cathode particles, and pressurized the cathode particles in a hot, alkaline, solution containing lithium salt—this solution can be recycled and reused to process more batches. Afterwards, the particles go through a short annealing process in which they are heated to 800 ˚C 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.
The process is essentially the same one that’s used to make the original cathode particles, said Zheng Chen, corresponding author and a professor of nanoengineering at UC San Diego.
As a lithium ion battery ages, the cathode material loses some of its lithium atoms. The cathode's atomic structure also changes such that it’s less capable of moving ions in and out. The recycling process that Chen’s group developed restores both the cathode’s lithium concentration and atomic structure back to their original states.
Overall, the recycling process uses 5.9 megajoules of energy, equivalent to the energy in about three quarters of a cup of gasoline, to restore one kilogram of cathode material. Several other lithium-ion battery cathode recycling processes that are being developed use at least twice that energy.
The goal is to optimize this process for industrial scales. Chen’s team is planning to work with battery companies in Asia. A particular area of improvement is the cathode harvesting step, Chen said. Right now, the particles have to be manually picked out from the rest of the battery. Researchers are working on simplifying this step so that the entire process is industrially viable.
Chen's team is refining this process so that it can be used to recycle any type of lithium ion battery cathode material, in addition to lithium cobalt oxide and lithium NMC. The team is also working on a process to recycle used anodes.
This work was supported in part by start-up funds from UC San Diego.
Yang Shi, Gen Chen and Zheng Chen (2018) “Effective regeneration of LiCoO2 from spent lithium-ion batteries: a direct approach towards high-performance active particles” Green Chemistry doi: 10.1039/C7GC02831H