Scientists from Cornell University have developed an electrochemical bath that can restore used lithium-ion batteries to 95 percent of their original capacity. Unlike classic recycling, the new procedure does not require the complete destruction of the battery and the complex separation of materials, but instead directly renews the existing electrodes.
The method called Direct Electrode-to-Electrode Regeneration, or DEER, is based on extracting structurally preserved electrodes from an old battery. These are then connected to a current collector and immersed in a solution containing the compound 1,3-dimethyl-2-imidazolidine.
During battery aging, a layer known as the solid electrolyte interface, or SEI, is gradually formed on the electrodes. A thin layer is necessary for the normal operation of the battery, but after hundreds or thousands of charge cycles it becomes thicker and thicker. This increases the electrical resistance, while the available capacity of the battery gradually decreases.
Although this process significantly impairs performance, the electrodes themselves often remain physically preserved. They still contain valuable materials such as lithium, nickel, cobalt, manganese, copper and aluminum.
In conventional recycling, battery packs are first completely discharged and disassembled to the level of individual cells. The cells are then crushed, ground or shredded, after which plastics and metals are separated from the resulting mass. The remaining black powder, known as black mass, is further processed by pyrometallurgical or hydrometallurgical processes, which require a lot of energy, time and additional chemicals.
DEER avoids such a process. The electrochemical solution dissolves the excessively thickened SEI layer, while the electrode structure itself remains preserved. The renewed electrodes can then be directly installed in the new battery.
The process also leaves behind a thin layer of lithium fluoride, which stabilizes the electrode and slows down the re-formation of the intermediate phase. Thanks to this, the regenerated batteries showed better stability during subsequent cycles than the researchers expected.
“We repair them in their existing form, without crushing and turning them into powder, and then put them back into a new battery,” explains Vibha Kalra, project leader and professor of chemistry at Cornell University. According to her, the dissolution of deposits enables the return of 95 percent of capacity and significantly shortens the entire recycling cycle.
Analyzes conducted with the help of software from the American ReCell Center showed that DEER could reduce the cost of producing cells from recycled materials by 56 percent. The procedure simultaneously reduces water consumption, the emission of harmful substances and the amount of energy needed for recycling.
The researchers subjected the refurbished battery to another DEER cycle after a new period of use. Even after the second regeneration, i.e. during its third working life, the battery retained about 90 percent of its original capacity.
The current version of the technology primarily solves the problems caused by the growth of the SEI layer. The next goal of the researchers is to apply the procedure to other forms of degradation, including the loss of lithium. In this way, it would be possible to restore batteries whose state of health has fallen below the usual 70 to 80 percent, when electric vehicle batteries are most often withdrawn from use, reports New Atlas.