The cobalt, manganese and nickel found in battery cathodes are expensive to mine; scientists have for years sought a way to create new batteries from spent ones. When a car battery reaches the end of its service life, it is collected, dismantled and shredded. The shredded material is processed to produce “black mass” which contains the valuable metals that then need to be extracted.
Separating out the useful chemicals is not easy. Researchers at the US Department of Energy’s (DOE) Argonne National Laboratory have turned to a process called capacitive deionization that uses the electric charges of nickel, manganese and cobalt to select them out from the waste stream.
Capacitive deionization (CDI)—first proposed in the 1960s—operates by applying a low voltage to mobilize charged species from water or a solution to electrodes. Although looked to primarily as a desalinization technology, CDI is being developed for a number of other applications, including removal of lithium from brines. (One emerging approach of interest is the use of battery materials themselves as the CDI electrodes in desalinization processes.)
“There are different separation technologies used for different purposes, based on physical principles, chemical principles and electrochemical principles. There’s only so much you can do with mechanical processes in the first step, so we turn to things like membrane, adsorbent and capacitive deionization technologies, which can all be used to recapture chemicals of interest.”, says Argonne engineer Lauren Valentino
According to Valentino, battery recycling is complicated because not all car batteries are the same:”It’s hard to control what you get when it comes time to recycle a car battery. When the battery is shredded, you have all sorts of things mixed together—cathode, anode, electrolyte and separator.Building a battery is like building a tower out of Legos. You use small blocks with different shapes to build a tower, but if you want to re-build, you have to take apart and sort all of the bricks to get what you need.”
Recycling a battery thus requires breaking down and separating large chemical components into basic elements.
One major advantage of capacitive deionization is that it is flexible. According to Valentino, it can be used to accommodate different materials and various operating strategies by controlling flow rates and operating time.
The capacitive deionization process that Valentino and her colleagues use for battery recycling also has uses in other areas, including bioenergy production. Valentino leads the Bioprocessing Separations Consortium, a group of researchers from six national laboratories that together research and develop separations processes and technology needed for the conversion of biomass to biofuel. (The group was established in 2016 by DOE’s Bioenergy Technologies Office within the Office of Energy Efficiency and Renewable Energy.) “At some point there is a conversion step followed by a separations process. What comes out of these reactors is a complex mixture with many different components, and we have to be able to isolate and concentrate the products of interest in the system to catalytically upgrade them to produce the biofuels we’re after.” says Valentino
Unlike the battery recycling technology, which targets positively charged ions, bioenergy production requires Valentino and her colleagues to search for negatively charged molecules. The capacitive deionization essentially acts like a claw that picks out the molecules of interest, Valentino said.
Once separated, these compounds are versatile and can be converted into hydrocarbon biofuels, such as renewable diesel or sustainable aviation fuel.