You know how rejuvenating a bath feels after a long day of work? Almost like you’re renewed. Turns out that’s not exclusive to humans. Scientists at Cornell University have developed an electrochemical bath that restores spent lithium batteries to nearly 100% capacity.
Unlike conventional battery recycling methods that involve the complete physical destruction of batteries, followed by complex, energy-intensive recovery processes to extract critical battery-making materials, the scientists’ method recycles lithium-ion battery electrodes directly. Rather than breaking down structurally intact electrodes to extract materials that will make other electrodes, their approach regenerates the existing electrodes using an electrochemical solution.
The researchers say this method restored batteries to 95% of their original capacity, and even helped recycled batteries last longer. According to them, the method could also slash recycling costs by 56% while being more environmentally friendly.
As lithium-ion batteries age, a layer called the solid electrolyte interphase (SEI) gradually grows on the electrodes. A thin SEI layer is actually necessary for battery operation. However, over hundreds or thousands of charge cycles, it becomes thicker and thicker, increasing resistance and reducing battery capacity. This phenomenon is one of the foremost drivers of battery wearout, leading to EV batteries and stationary electricity storage systems being retired with much of their structure still intact. This structure includes the now-coated electrodes, which contain critical minerals such as lithium, nickel, cobalt, manganese, copper, and aluminum.
To recover these materials, the decommissioned batteries are sent for recycling. Hurray for circularity. Alas, however, the conventional battery recycling processes themselves are far from ideal. First, the batteries are inspected and completely discharged. Next, because the batteries come as complete battery packs and not bare cells, they are carefully stripped of all supporting components and systems, down to the cells. The cell, comprising the electrodes, electrolyte, and separator, is then mechanically shredded, crushed, or pulverized.
The resulting particles are sorted via various techniques to remove plastic and metal pieces, such as aluminum, copper, and steel, leaving a black, powdery substance known as black mass. What comes next is the final extraction of the critical minerals, typically involving one of two complex, energy-intensive processes: pyrometallurgy and hydrometallurgy.
Now, while there are other battery issues that physically damage the electrodes, SEI layer growth, considered the primary cause of standard battery capacity fade and decommissioning under normal operating conditions, does not … it just coats them. Therefore, conventional recycling processes take structurally intact electrodes, pulverize them, and undergo several complex recovery steps to extract the materials, which may then be used to make … wait for it … electrodes!
Of course, the whole thing is more nuanced than that, but on the surface, the irony of that process is obvious. This is what the Cornell University solution, detailed in the journal Energy and Environmental Science, aims to address. The process is called Direct Electrode-to-Electrode Regeneration (DEER). In this process, instead of shredding the spent battery, the scientists open it and remove the electrodes intact. The electrodes are then attached to a current collector and placed in a bath containing 1,3-dimethyl-2-imidazolidinone.
The solution dissolves the offending thick SEI layer, leaving behind renewed electrodes ready to be placed in a new battery. The process also leaves a thin lithium fluoride layer that helps stabilize the electrode and suppress further interphase growth. Thanks to this residual layer, the regenerated batteries showed even better cycle stability than expected.
“We repair them, as is, without shredding or powdering them, and then put them back into a new battery,” says Vibha Kalra, project leader and Cornell Professor of Chemical Engineering. “The dissolution is basically what helps the battery recover its capacity. It shows 95% recovery. So we are shortening the circularity loop immensely.”
Using open-source software developed by their research collaborators at Argonne National Laboratory’s ReCell Center, the researchers conducted techno-economic and environmental impact analyses to assess the potential of DEER. The results revealed that the process would cut the cost of recycled cell manufacturing by 56% while reducing harmful air pollutants and water use compared with conventional recycling methods. In addition to the cost, effort, time, and energy saved by eliminating the extraction processes in conventional recycling, DEER also reduces the manufacturing costs of new electrodes.
Restoring a spent battery to 95% capacity is impressive enough, but apparently not for the researchers. In case you are wondering what happens when the renewed battery loses capacity again, due to SEI deposit, after another long life of service, the researchers regenerated the battery again using DEER, with the third-life battery still retaining about 90% of its original capacity after a second regeneration cycle!
While the current technology focuses on SEI damage, the researchers aim to demonstrate its usefulness on other forms of battery degradation, such as lithium loss.
“Right now, the spent batteries we are treating have 70-80% state of health, which is typical in electric vehicle applications,” Kalra says. “So we can expand that window if we can address some of these other degradation mechanisms.”
They also have their eyes set on industrial batteries and other large lithium-ion battery systems.
Source: Cornell University
