Design of anode active materials from hot dip galvanizing waste for lithium ion batteries

Abstract

The galvanizing process, which is especially important in the automotive industry, entails coating steel or iron with zinc to prevent corrosion. In 2023, the global market for galvanized steel is estimated to be approximately $120 billion, with Turkey leading the MENA region and having a production capacity of about 4 million tons. Common waste types in hot dip galvanizing (HDG) plants include flue dust, (which is formed 30-50 thousand tons annually and contains 50-80% Zn), dross (which is formed 600-800 thousand tons annually and contains 92-97% Zn) and zinc ash (which is formed 500-700 thousand contains 50-70% Zn). Recycling these wastes minimizes economic losses and reduces the environmental impacts of the galvanizing process. Therefore, many studies have been conducted in academia and industry to recycle these wastes and/or recover valuable types of zinc rich compounds from these wastes to contribute to environmental sustainability and adding economic value. The hypothesis proposed in this thesis is that by using industrial waste as the starting material, it is possible to fabricate low carbon footprint electrode active materials to be used in LIB. This approach focuses on sustainability and environmental friendliness, seeking to create high value-added applications from waste. Knowing that lithium ion batteries (LIBs) are the most common energy storage solutions today, and their performance heavily depends on the quality of the anode active material, their fabrication is reported to increase exponentially in upcoming years following the high demand of consumers. In the current state-of-the-art graphite is widely used as anode active material (AAM) as it delivers 372 mAh/g theoretical capacity. However, China holds a strong position in the graphite market due to abundant mineral reserves. Also, the extraction of graphite is heavily reliant on mining activities. This dependence on limited resources and the significant CO2 emissions from graphite mining drives the ongoing search for new and more efficient anode materials with higher capacity than graphite. Therefore, for the first time in the literature, by making appropriate material selection and process design, wastes such as HDG flue dust and HDG dross are obtained from the industry and used as starting material to fabricate Fe-doped ZnO/C composite and Zn5(CO3)2(OH)6 powders, respectively. The thesis consists of two parts. In the first part, our hypothesis is to obtain Fe-doped ZnO/C composite from the hot dip galvanizing flue dust to fabricate a low carbon footprint anode active material that delivers higher capacities (than that of the graphite: 372 mAh/g) over 100 cycles. In the design of AAM, Fe doping creates electronic conductive pathways to enhance the electrochemical performance of ZnO, while the addition of C improves the overall conductivity, decreases charge transfer resistance and improves the structural stability of the composite with its stress accommodation ability. Knowing that the flue dust is formulated as Zn(NH3)2Cl2, it contained 0.8% iron (Fe), 52.18% zinc (Zn) and 45.97% chloride (Cl). Therefore, in the experiments firstly the flue dust was processed through a neutral leaching process. The aim was to increase the amount of ammonia and chloride in the leachate while maximizing the amount of zinc and iron in the solid residue.