Growing electrification and skyrocketing demand for batteries is creating a new problem: what to do with battery waste. While efforts to recycle batteries and extract valuable elements intensify, a group of researchers from Australia now suggest that a mixed-metal compound left after end-of-life batteries have been stripped of their major components could be used directly as second-life anodes. They report their findings in Green Chemistry.

Neeraj Sharma, a materials chemist at the University of New South Wales in Sydney, first became concerned with the problem of battery recycling when he met Andrew Mackenzie of Envirostream Australia at a conference in 2018. Envirostream, a battery recycling company, receives a mix of used batteries such as alkaline, nickel hydride, lead acid, and lithium-ion ones and recovers some 95% of battery material. The aluminum, copper, and steel are stripped off, leaving behind a mixed-metal compound.

Most battery recycling processes will generate such mixed-metal compounds, says Yan Wang, a battery scientist at Worcester Polytechnic Institute. These compounds typically go for further refining to extract individual elements, he says. Envirostream’s mixed-metal compound, for example, is sent to Japan, South Korea, or China and its elements extracted and purified with acid-leaching processes, says Sharma.

To figure out a direct use for this mixed-metal compound, Mackenzie sent Sharma some samples. Sharma and colleagues analyzed and sintered the material, to see what happens.

The material as-received—a black, fluffy powder—contained about 27.4% cobalt, 3.8% lithium, 2.9% nickel, and 1.44% manganese, among several other elements. After sintering for 30 minutes at 900°C, the material lost up to 51.63% of its mass and its metallic content generally increased across the board. But instead of trying to separate the individual elements, the researchers decided and attempted to make electrodes from the material as-received, and its sintered versions.

The researchers prepared electrodes by mixing the material with carbon black and polyvinylidene fluoride (PVDF) in an 8:1:1 ratio. Then, they placed the mixture onto copper foil, dried it overnight in a vacuum oven, and pressed it with 100 kN force in a flat-plate press. They tested the electrodes as cathodes and anodes in CR2032 coin cells against lithium, potassium, and sodium ions in half-cell configurations.

While the materials did not perform well as cathodes, they put up reasonable performance as anodes. In fact, the material as-received performed better than the sintered versions, generating stable reversible capacities over 310 mAh/g even after 100 cycles against lithium ion.  

“If you just simply get the material and basically make another electrode, it’s actually pretty good,” Sharma says. “It was …. a fortuitous finding.”

“The innovation here is to try to use [the compound] directly, because if you add processing, you increase the costs,” Wang says. Additional processing also generates more solvent and chemical waste.

But while the idea is nice, Wang is skeptical of its impact on industry. No battery maker is currently using mixed-metal compounds for anodes, he says, and it is unlikely they will displace the current standard, graphite. Another major challenge is the feedstock’s variability, which could present problems as battery products need to adhere to strict quality control guidelines. While direct uses for the mixed-metal compounds might be found, Wang believes it is unlikely to be in batteries.

For Sharma however, the question is more of “’what do you need for your application?’ rather than a standard battery for everything.” While the anodes perhaps should not be used in a high-performance setting such as in grid storage, Sharma thinks they could find uses in smaller consumer applications, particularly if they can be made cheaply enough.

He and his colleagues are now working to fully characterize the material in detail, including figuring out its various multiple phases and how they evolve as the battery charges and discharges. They also hope to determine the tolerance limits in material quality so as to cope with feedstock variability.

Read the abstract in Green Chemistry.