Analisi micro-Raman della qualità della grafite riciclata da batterie agli ioni di litio esauste

In recent years, we have become more aware of the effects of the fossil fuel combustion on human health and their negative impact on the environment. Furthermore, due to the anticipated scarcity of these fuels, the cost of maintaining private vehicles is expected to rise. Society is gradually switching towards more ecological and sustainable resource consumption, and one significant consequence of this shift is the raise of the electric automation market. However, the increasing demand for electric vehicles, as well as energy storage solutions to power them and portable devices, is impacting the global battery demand. In particular, we are witnessing a considerable growth in the production of lithium-ion batteries, which are used across various industrial sectors. This continuously growing trend of production and consumption will lead to large amounts of spent batteries that are potentially toxic and environmentally polluting. Additionally, it will result in a shortage of the raw materials necessary for their production. Recycling all the components of a lithium-ion battery would enable the establishment of a circular economy. This approach aims to extend the life of products within the consumption chain and to minimize the produced waste and the harm to the environment. The techniques currently used at an industrial level are not capable of handling the incoming large volumes of spent batteries and also require high energy consumption. It is worth noting that these industrial techniques focus primarily on recycling the battery cathode, which is composed of the most valuable materials, such as cobalt, lithium and nickel. However, the European Commission has declared that graphite, which comprises 10-28% of the total battery weight, is also a critical raw material. This recognition, along with other factors, has driven scientists and industries to seek the most effective methods of recycling graphite. The graphite inside a spent battery anode is expected to have lost its crystallinity and to be contaminated with various metal oxides and other compounds found in other parts of the battery. This work is developed in the frame of the EU project RENOVATE led by Prof. Eliana Quartarone of the Department of Chemistry of the University of Pavia. Raman spectroscopy can be considered probably as the gold standard technique to monitor crystallinity, disorder and phase impurities in carbon allotropes. The aim of this work is to validate a Raman spectroscopy-based protocol and a data analysis routine to monitor the quality of graphite and its reusability at the end of the recycling process, which is designed to restore the spent graphite's purity and morphology. After identifying the most effective experimental conditions, we performed the Raman spectroscopy analysis of the graphite samples obtained from each step of the restoration process, in order to evaluate the changes of their physical structure and the reduction in impurity levels. By coupling the sensitivity of the Raman effect to C-C bond motion with the possibility of macro- and microscopic sampling, the mapping of Raman signals from different regions of each sample allowed for the collection of a large amount of data useful for extracting statistically weighted Raman band parameters (peak position, bandwidth and intensity). The results indicate the potential of using portable Raman instruments to efficiently evaluate the quality of a large amount of spent graphite in an industrial restoration process.