Recycled lithium batteries may perform better than new ones

A new recycling method for lithium batteries would help meet the ever-increasing demand.

Lithium-ion batteries are the basis of almost all electric vehicles, laptops and smartphones, and are essential for storing renewable energy in the face of the climate emergency. But all the world's current mining operations are unable to extract sufficient lithium and other key minerals to meet the soaring demand for these batteries. Creating new mines is an expensive and years-long effort. In addition, mining creates a number of environmental problems-such as depletion of local water resources and pollution of the surrounding region with runoff debris-that have led to protests against new mines.

All this means that the ability to recycle existing batteries is critical to sustainably changing the global energy system. But lithium-ion battery recycling has only recently entered the market. Battery manufacturers have been hesitant because of concerns that recycled products might be of lower quality than those made from newly mined minerals, potentially causing shorter battery life or damage to battery internals. The consequences could be severe, especially in an application such as electric vehicles.

Methods recycling lithium from spent batteries

But new research published in Joule has developed what experts describe as a more elegant recycling method that refurbishes the cathode, the carefully machined crystal that is the most expensive component of the lithium-ion battery and the key to providing the correct voltage. The researchers found that batteries made with the new cathode recycling technique work just as well as those with a cathode made from scratch. In fact, batteries with the recycled cathode last longer and charge faster. The team's approach and demonstration of success are "truly unique and impressive," says Kang Xu, an electrochemist at the U.S. Army Research Laboratory, who was not involved in the study.

Yan Wang, professor of materials science at Worcester Polytechnic Institute and co-author of the new study, began researching battery recycling 11 years ago. At the time, he recounts, "some people joked with me, 'There are not enough batteries to recycle.'" That joke is not aging well. The Department of Energy estimates that the battery market could grow 10 times over the next decade. To alleviate the market's growing pains, "recycling lithium-ion batteries-that is, getting the material back into the supply chain-is critical," says Dave Howell, director of DOE's Vehicle Technologies Office. DOE funded the new research as part of its massive effort to spur large-scale innovations in battery recycling in the United States.

How the lithium battery works

When a lithium-ion battery provides energy, a group of lithium ions moves from one crystalline "cage" (the anode) to another (the cathode). The most common methods currently used to recycle these batteries involve disassembling and crushing the entire battery, then melting or dissolving it in acid. The result is a black mass-with a consistency that can vary from dust to mush-from which chemical elements or simple compounds can be recovered. These recovered products can then undergo the same commercial production process that is applied to newly extracted elements to obtain cathodes.

Wang and his colleagues use a very similar process, but instead of completely breaking down the battery into its constituent chemical elements, their technique keeps some of the crucial composition of the old cathode intact. After tearing the battery apart, they physically remove the less expensive parts (such as the electronic circuits and the battery's steel casing) and recycle them separately. What remains is mainly the cathode material, which is dissolved in acid and then removed of impurities. Next, they carefully add just a pinch of fresh cathode elements, such as nickel and cobalt, to ensure that the ratio of ingredients is right-another distinction from common recycling methods. After a few more steps, the result is an effectively refreshed cathode powder composed of tiny crystalline particles that can be pasted onto a strip of metal and inserted into a "new" battery.

Because the cathode is made from a precise mixture of valuable minerals to achieve the battery's specific voltage, slight changes to its structure or composition can compromise its performance. Therefore, much of the value of the cathode powder lies "in the way the [powder] particles were designed in the first place," says Emma Kendrick, a professor of energy materials at England's University of Birmingham, who was not involved in the new study. This value is lost if the entire battery is simply melted or dissolved in one go, as is the case with current recycling methods.

Wang's research to recycle lithium

Wang and his colleagues compared the particles of their recycled cathode powder with those of commercially produced cathode powder (largely derived from newly mined ores). They found that the particles of the recycled powder were more porous, with particularly large voids in the center of each. These characteristics allow the cathode crystal to swell slightly when lithium ions seep into it, and this leeway prevents the crystal from cracking as easily as cathodes built from scratch. Such cracks are a major cause of battery degradation over time.

More pores also mean more exposed surface area, where the chemical reactions needed to charge the battery can take place - which is why Wang's recycled batteries charge faster than their commercially produced counterparts. A future ambition might be to design all cathodes with this superior structure, rather than just those made from recycled material, Wang says.

The latest findings show that "the cathode they can produce is as good as, or even better than, the commercial material we have imported," says Linda Gaines, a transportation analyst at Argonne National Laboratory and chief scientist at the ReCell Center, an organization that studies and promotes battery recycling. (Such imports come largely from China, which is a world leader in battery recycling. But this situation means that materials must be moved from one part of the world to another to be recycled, increasing the carbon footprint of recycled batteries and decreasing their appeal as a more sustainable pathway. The approach developed by Wang's team eliminates a significant portion of international trade and transportation requirements, creating a potential pathway for other countries to strengthen battery recycling domestically. The process is currently being expanded by Ascend Elements, formerly Battery Resourcers, a recycling company that Wang co-founded.