Approaches for recycling cathode active materials from used lithium-ion batteries generally face a tradeoff wherein recovering materials with the widest range of possibilities for re-use, such as pyrometallurgical methods, generally require high energy and long process times, while direct-recycling approaches may reduce time and energy, but also restrict the options for reuse. Now, a process developed by scientists at Sandia National Laboratories (Albuquerque, N.M.; www.sandia.gov) avoids this tradeoff: it can upcycle spent cathodes into a wide range of possible formulations with substantially less energy and time required than pyrometallurgical or hydrometallurgical recycling.
The Sandia process, known as BatterUP, uses microwave irradiation and ion-exchange of spent cathode material, such as lithium cobalt oxide, to make new cathode material with the possibility of multiple cathode formulations, while also recovering valuable materials, such as cobalt.
Source: Sandia National Laboratories
In the Sandia upcycling process, spent batteries first must be pre-treated to remove organic binders, leaving powdered cathode material. Then, a microwave reactor with power similar to that of a household microwave oven is used to stimulate polarizable bonds in the cathode material, separating the layers to form nanosheets. “The layered structure of the cathode allows us the opportunity to use microwaves, along with a sterically large cation compound, to physically separate the layers into 5- to 10-nm-thick nanosheets that are stable for long periods,” explains Clare Davis-Wheeler Chin, the Sandia nanomaterials chemist who invented the method along with Kirsten D. Jones, a graduate intern from the University of New Orleans.
A key benefit of separating nanosheets with microwaves and bulky cations is that impurities can be easily removed, allowing better-quality cathodes when the material is re-used in new batteries. “Because these impurity phases do not have a layered structure, the microwave-and-cation separation doesn’t affect them, and the impurities fall out of solution and can be separated,” explains Davis-Wheeler Chin.
Once the spent cathode is exfoliated into nanosheets, the negatively charged sheet surfaces can undergo ion-exchange to substitute surface-bound cations, such as swapping nickel for cobalt. “We can change cathode makeup using differences in redox potentials to get a cathode with higher nickel content, for example,” says Aliya Lapp, a Sandia electrochemist. “This is really useful, because it allows us to adopt new cathode formulations as the industry evolves, and recover a critical material like cobalt at the same time,” she says.
The Sandia team has demonstrated the process in the laboratory and is currently scaling up the process to kilogram scale. The team is also seeking industry development partners and investigating ways to retrofit microwave dryers in battery manufacturing for use in recycling.