A scientific research team at Cornell University in the United States recently announced that they have developed a new electrochemical bath treatment process that can "rejuvenate" scrapped lithium-ion battery electrodes without damaging the battery structure, restoring their capacity to about 95% of the original level, and is expected to reduce battery recycling costs by about 56%. This result has been published in the journal "Energy and Environmental Science" and is regarded as a potential key technology to promote the recycling of lithium batteries and reduce environmental burden.
Traditional lithium battery recycling usually requires physical crushing of the entire battery, and then extracting key metals such as lithium, nickel, cobalt, and manganese through complex, energy-consuming processes such as pyrometallurgy or hydrometallurgy for use in manufacturing new electrodes. In this process, the battery pack needs to be completely discharged first, a large number of auxiliary parts including structural parts and management systems must be dismantled, and then the cells containing electrodes, electrolytes and separators must be mechanically crushed. The mixed particles formed after crushing need to go through multiple rounds of sorting to remove plastic and metal flakes, leaving only a mixture called "black powder", and then enter high-temperature smelting or chemical leaching to purify the metal. This model not only has a long process, high energy consumption and cost, but also produces a certain amount of air pollution and water consumption.
The Cornell University team pointed out that in most electric vehicles and energy storage systems, the main cause of lithium battery retirement is not the physical destruction of the electrode body, but the excessive growth of the solid electrolyte interface (SEI) layer on the electrode surface. SEI is a naturally formed thin film on the surface of the electrode, which is necessary for the normal operation of the battery. However, after hundreds or even thousands of charges and discharges, this layer will continue to thicken, causing the impedance to increase and the capacity to decrease. The electrode skeletons of a large number of retired batteries are still intact and are only covered by a thick SEI layer, which still contains key materials such as lithium, nickel, cobalt, manganese, copper and aluminum.
In response to this phenomenon, the scientific research team proposed a new process called "Direct Electrode-to-Electrode Regeneration" (DEER for short). In this process, the used battery is no longer crushed as a whole, but is opened and the electrodes are completely removed and fixed on the current collector. The electrodes were then immersed in an electrochemical solution containing 1,3-dimethyl-2-imidazolidinone, allowing the solution to selectively dissolve the overly thick SEI layer while preserving the bulk structure of the electrode. After the dissolution is completed, only a thin lithium fluoride film remains on the electrode surface, which helps stabilize the interface and inhibit subsequent excessive growth of SEI. The electrodes after this "bath regeneration" treatment can be directly assembled into new batteries for reuse.
Experimental results show that lithium batteries regenerated by the DEER process can be restored to approximately 95% of their original capacity and show better stability in cycle life. Project leader Vibha Kalra, a professor in the Department of Chemical Engineering at Cornell University, said that this method does not require crushing the electrodes into powder and preparing them again, but "in-situ repair" of the existing electrodes, which greatly shortens the recycling path of battery materials. The team conducted a techno-economic and environmental impact assessment of the process using open source software developed in partnership with the U.S. Department of Energy's Argonne National Laboratory's ReCell Center. Analysis results show that compared with traditional recycling routes, DEER can reduce the manufacturing cost of recycled batteries by approximately 56%, reduce harmful air pollutant emissions and process water consumption, and reduce the manufacturing cost of new electrode production.
The researchers further tested the feasibility of multiple regenerations: on a "second life" battery that was put into service again after being regenerated by DEER and showed capacity fading, the team repeatedly used the same process for regeneration. The results show that the "third life" battery can still maintain about 90% of its original capacity after the second regeneration, indicating that this electrochemical bath method has the potential for multi-cycle repair. The current experiments are mainly focused on the performance degradation caused by the growth of the SEI layer, and the next step of research will be extended to other types of battery aging mechanisms such as lithium loss.
Kalra said that the health status of used batteries currently entering trials is about 70% to 80%, which is equivalent to the status of retired batteries in electric vehicle application scenarios. If more degradation mechanisms can be repaired in the future, this technology is expected to further expand the range of health states of renewable batteries. The team has also expanded its application targets to industrial-grade batteries and other large-scale lithium-ion energy storage systems, hoping to promote this regeneration process in larger-scale energy infrastructure. Cornell University believes that electrochemical bath regeneration technology is expected to become a key link in the lithium battery circular economy, improving resource utilization efficiency while reducing the pressure on the environment from the recycling system.