A straightforward, extremely effective, low-cost, and eco-friendly method may offer a promising solution for the sustainable recycling of exhausted lithium-ion batteries (LIBs): The only additive required is citric acid to extract and isolate over 99% of the lithium, nickel, cobalt, and manganese metals present in NCM batteries. The obtained recycled material can be transformed directly into NCM electrodes, according to a research team reported in the journal Angewandte Chemie.
From smartphones to electric vehicles, lithium-ion batteries are a common part of our everyday lives. They play a crucial role in our shift towards renewable energy by storing excess solar and wind energy for later use in the power grid. However, their finite lifespan leads to a significant number of discarded LIBs, which contain hazardous heavy metals and other toxic substances. Furthermore, valuable metal resources are running low.
Many recycling methods are plagued by high energy consumption, significant emissions, and poor-quality material recovery. Some processes necessitate large quantities of chemicals, are complicated and costly, and generate toxic fumes and waste. An alternative is to use biocompatible acids like citric acid for leaching. Traditional methods (such as the chelation-gel process) typically require a large surplus of acid and continuous pH adjustment with ammonia, making them cumbersome and not very eco-friendly.
A group of researchers from the China University of Mining and Technology (Beijing), Fuzhou University, Beijing University of Chemical Technology, and Tsinghua University, Shenzhen (China), spearheaded by Guangmin Zhou and Ruiping Liu, has introduced a new citric acid-based technique for leaching, separating, and recovering metals from NCM cathodes. NCM refers to a mixed oxide structure comprised of nickel, cobalt, and manganese with lithium ions positioned between the layers.
The innovative aspect of their method is the use of a relatively small amount of citric acid instead of the excessive amounts typical of conventional approaches. As a result, only two of the three acidic groups in citric acid dissociate. The released protons disrupt the lithium-oxygen bonds, liberating lithium ions into the solution. Simultaneously, the bonds between the other metal ions and the oxygen are broken, allowing nickel, cobalt, and manganese to enter the solution, where they establish stable complexes with the citric acid anions. The third acidic group of citric acid then interacts with a hydroxyl group on the same molecule. This interaction leads to a ring closure via an intramolecular esterification (Fischer lactonization) reaction, which promotes the formation of solid polyester particles that are easily separable. This process significantly reduces energy consumption and CO2 emissions compared to traditional hydrometallurgical recycling methods.
The resulting gel can be heated to eliminate the organic fragments, yielding a fresh NCM lamellar structure that incorporates lithium ions, making it suitable as a high-quality electrode material.
