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Lithium-ion batteries are important commercial equipment that can provide low-carbon energy storage solutions for many industries. At the end of their useful life, recycling their materials can improve resource sustainability. A paper published in the journal Journal of Materials explores the recovery of graphite from lithium-ion batteries.

Research: Evaluation of separation of graphite and metal by flotation in the recycling of lithium-ion batteries. Image Credit: petrmalinak/Shutterstock.com

The global shift to carbon neutrality and to get rid of dependence on fossil fuels is accelerating. Recent international agreements, such as COP26, have clarified the need for processes and technologies that significantly reduce carbon dioxide emissions, and implement technologies that can fill the gap in energy harvesting and storage.

Lithium-ion batteries have become a pioneer in technological development, and the industry is expected to grow due to the transportation industry’s demand for low-emission and zero-emission vehicles. The market is expected to grow at a compound annual growth rate of 15% between 2020 and 2026.

The global electric vehicle market is expected to grow by 47% during the same period. According to a report from the IMARC Group, global shipments of the electric vehicle industry in 2020 will be 2.45 million units.

However, with the development of the electric vehicle and lithium-ion battery industries, an old problem has emerged: waste. In 2013-2014, the recycling rate of used lithium-ion batteries was 1,900 tons, compared with 65,000 tons in Europe.

Particle size distribution. Image source: Yang, X et al., material conference proceedings

Batteries contain many important commercial materials. At present, the main targets for recycling through pyrometallurgical processes are cobalt, nickel and manganese. Lithium is recovered as part of the cathode active material. Copper, iron and aluminum are recovered through physical and mechanical processes (such as magnetic separation).

At present, graphite is not considered in many recycling strategies, and it is mainly lost during the recycling process. However, from the perspective of circular economy, graphite recycling is very important to the battery industry because it is an important economic material that can improve the efficiency of subsequent metal recycling.

Recently, more and more researches have focused on the recovery of graphite from lithium-ion batteries. One method that has been studied to recover graphite from broken battery materials is selective flotation, which involves thermal or chemical pretreatment of the material. Due to the presence of organic binders such as polyvinylidene fluoride used as coatings, both graphite and lithium-containing metal oxides show good floatability.

Comparison of the recovery rate and mass yield of Cu, Ni, Co, Al, Mn and C. Image source: Yang, X et al., material conference proceedings

However, the direct flotation of black matter (BM) materials does not selectively separate graphite, nickel, manganese, and copper. In order to remove the organic coating before flotation, heat treatment such as roasting or pyrolysis has been applied, which is very effective.

The study in "Journal of Materials Science and Technology" investigated the efficiency of using flotation to separate graphite from positive electrode active materials containing elements such as nickel, cobalt, manganese, and aluminum. This study explored the effect of roasting at 350-450 oC on the separation efficiency of flotation methods.

The black substance of used lithium-ion batteries is purchased from a recycling facility. Divide 50 kg BM shredded material samples into 500 g samples for analysis and testing. These samples are then sieved into different parts, and their chemical composition is analyzed by XRF. The carbon content is determined by a separate process. Bake the sample for 30 minutes.

The chemical analysis results show that the main elements with significant content in the sample are aluminum, copper, cobalt, nickel, manganese and carbon. The thicker part contains more copper and aluminum, while the thinner part contains more nickel, manganese, and cobalt. All fractions show a fairly uniform carbon distribution.

Mineralogy analysis shows that the composition is complex, but graphite and four lithium-containing metal oxides account for 92-94% of the total.

Use different apertures to screen the contents of the sample to classify them. The results of the roasting technique showed excellent separation efficiency between carbon and metal elements in BM. The roasting temperature also affects the flotation and separation efficiency, and the higher temperature hinders the flotation. The best baking temperature was found to be 400 oC.

Fine part-0.25 mm backscattered electron image. Image source: Yang, X et al., material conference proceedings

By examining the flotation and separation process of graphite recovery, the team behind the research published in the Journal of Materials proved that as a treatment method, roasting can significantly increase the recovery rate of waste black materials from lithium-ion batteries.

The information provided by this research can provide information for improving the efficiency of recycling commercially important materials from waste batteries in the future, improving the sustainability of the battery industry and reducing the resources needed to meet the growing global demand for lithium-ion batteries in the automotive industry, etc. field.

Yang, X, Torpa, A & Kärenlampi, K (2021) Evaluation of graphite and metal separation by flotation in the recycling of lithium-ion batteries [Online] Collection of Materials Papers 5:1 | mdpi.com. Available at: https://www.mdpi.com/2673-4605/5/1/30/htm

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Reg Davey is a freelance writer and editor based in Nottingham, UK. Writing for news medicine represents a fusion of various interests and fields in which he has been interested and involved for many years, including microbiology, biomedical sciences, and environmental sciences.

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