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The latest research published in the journal ACS Sustainable Chemistry and Engineering shows that through the life cycle assessment (LCA) process considering the layout of the environmental footprint, the sustainable and environmentally friendly recycling of graphite is possible.

Research: Based on life cycle assessment of the environmental impact of recycling graphite from waste lithium-ion batteries. Image source: Eaum M/Shutterstock.com

Lithium-ion batteries (LIB) are composed of two electrode materials, in which Li+ ions are reversibly inserted back and forth to provide power for external circuits. Studies have shown that the commercial success of LIB has led to the addition of materials with the lowest added value, such as natural graphite.

The quality of graphite accounts for about 15-20% of the weight of electric vehicle batteries and more than 10% of the economic value of batteries.

A priori recycling seems to provide obvious environmental benefits, such as improved resource efficiency, reduced carbon emissions, and reduced waste. Due to battery recycling operations, waste graphite usually contains unwanted metal impurities (Li, Al, Co, Cu, Ni, Fe, and Mn), organic electrolytes, and polymer binders.

Nine lithium-ion battery negative electrode recycling processes and the most representative impact categories were selected for life cycle assessment analysis. Image source: Rey, I and others, Shutterstock.com

Graphite recovery/regeneration has been achieved through a variety of technologies, such as hydrometallurgical methods based on acid-base leaching processes (for example, using acid HCl or H2SO4) or pyrometallurgical processes that treat graphite at temperatures above 1000 °C. Vaporize residual metals, metal oxides and adhesives to repair the graphite structure.

The Life Cycle Assessment (LCA) method allows the environmental consequences of recycling operations to be quantified. LCA can be used to establish the complete environmental sustainability of batteries by analyzing the contribution of recycling mechanisms to estimable indicators such as global warming, ozone layer depletion potential, ecotoxicity, eutrophication or acidification.

The OpenLCA program and the Ecoinvent 3.7 data set are used to conduct LCA research. The material and energy input for processing 100 kg of graphite are determined, of which 1 kg of recycled graphite is used as a system component. This allows to consider the different graphite recovery rates for each procedure, as a recovery rate of 40% to 95% is achieved according to the strategy.

Global warming potential of waste lithium ion battery graphite recycling process: (a) GWP value in kg·CO2 equivalent. Emissions of 1 kg of recycled graphite from waste LIB. For the process of calcination of graphene, the influence of the upgrading cycle from waste graphite to graphene oxide is also represented by a yellow rectangle, and the GWP produced is 42.49 kg·CO2 equivalent·kg graphene oxide-1. For the processing of graphene microwave, the impact explains the upgrading of waste graphite to graphite oxide (represented by blue rectangles). (b) The relative CO2 contribution of electricity, chemicals, and water used in each graphite recovery process. (c) The relative CO2 contribution of each step in the graphite recovery process. More details of each step are disclosed in the flowchart provided in the supporting information, as shown in Figures S1-S9. Image source: Rey, I and others, Shutterstock.com

In addition to the higher values ​​provided by Fenton + flotation, the GWP ranges from 0.53 to 9.76 kg CO2 equivalent. The realization of kggraphite-1 clearly shows that the graphite recycling program is ecologically feasible in the production of raw graphite.

In order to recover the used graphite, pyrometallurgical methods can be used. Due to the effective use of H2SO4 (only 8.9 kg), H2O2 (0.9 kg) and electricity, the GWP for air heating is very low, only 2.56 kg. CO2 equiv.kggraphite-1 (phenolic resin ethanol solution) is used to regenerate graphite. Surprisingly, the GWP values ​​for pyrolysis + flotation and calcination + leaching operations are as low as 0.53 and 1.08 kg.CO2 equiv.kggraphite-1, respectively.

In pyrometallurgical operations, a large number of inert gases, such as argon, are used, leading to eutrophication, ecotoxicity, ozone depletion, human non-carcinogenic toxicity and human carcinogenic toxicity.

When graphite is upgraded to graphene oxide, electricity is the main contributor (with an average contribution rate of 69%) in five of the seven technologies for recycling waste graphite, while the average contribution rate of chemicals is 94%.

After 50 cycles of charging and discharging at 0.1C, the capacity of the regenerated graphite is 377 mA hg-1 and maintains 98.8% of its initial capacity. When the cycle rate was increased to 0.5C, 1C, and 2C, excellent capacities of 320, 285, and 265 mA hg-1 were obtained. These findings can be explained by the significant specific surface area of ​​11.47 square meters.

Although not used as an energy storage device, it is worth noting to upgrade graphite to graphene-based nanocomposites. In this case, the calcination of the graphene method converts the graphite in the waste lithium battery into graphite oxide, graphene, and finally into graphene oxide copper composite material.

Efforts are being made to prevent the strong acids used in hydrothermal treatment from causing additional damage to the environment. Markey et al. Use 5 weights. Percent boric acid is used as the leaching agent in the frame to recover graphite anodes from the waste LIB.

Based on the sensitivity analysis of the improved H2SO4 curing-leaching method for graphite recovery, the graphite:sulfuric acid ratio is 4:1 instead of the original 1:1. Image source: Rey, I and others, Shutterstock.com

According to research on future environmental plans and regulations, it is estimated that graphite recycling and utilization of hydrometallurgy and pyrometallurgy needs to be modified to further reduce damage to the environment.

At present, the combination of hydrometallurgy and pyrometallurgy seems to be more eco-friendly because it performs better in terms of related impact categories (such as global warming, freshwater toxicity, and human toxicity).

Therefore, the recovery of graphite is an indispensable process. However, environmental constraints must be kept in mind. Although the most ecologically friendly LIB anode technology has been selected and expanded, scientists and industry may be driven by the rational design of biomass-based carbon. By combining the development of the two directions, the sustainable storage of energy can be simplified in the end.

Rey, I., Vallejo, C., Santiago, G., Iturrondobeitia, M. and Lizundia, E. (2021). The environmental impact of graphite recycling of waste lithium-ion batteries based on life cycle assessment. ACS Sustainable Chemistry and Engineering, 14488-14501. https://pubs.acs.org/doi/abs/10.1021/acssuschemeng.1c04938

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Ibtisam graduated from the Islamabad Institute of Space Technology with a bachelor's degree in aerospace engineering. During his academic career, he participated in multiple research projects and successfully managed multiple extracurricular activities such as International World Space Week and International Aerospace Engineering Conference. Ibtisam participated in an English essay competition during his undergraduate course and has always been interested in research, writing and editing. Soon after graduation, he joined AzoNetwork as a freelancer to improve his skills. Ibtisam likes to travel, especially to the countryside. He has always been a sports fan and likes watching tennis, football and cricket. Ibtisam was born in Pakistan and one day hopes to travel the world, build strong bonds of friendship, and spread the message of peace and love.

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