Recycling of Precious Metals from Spent Lithium-Ion Batteries

Introduction

With developing technology and increasing consumption, electrical and electronic equipment usage is rising. This leads to a general increase in battery consumption. Batteries vary according to the device and sector in which they are used, and are classified into two types based on their working principle: primary (non-rechargeable) batteries and secondary (rechargeable) batteries. While reactions in primary batteries are irreversible, reactions in secondary batteries can be reversed by supplying electrical energy from an external source. As disposable battery use increases, the problem of battery waste arises, and the volume of waste is growing due to the widespread use of lithium-ion batteries, a type of rechargeable battery. The most common types of lithium-ion batteries are lithium cobalt oxide (LiCoO2), lithium manganese oxide (LiMnO₂), lithium nickel cobalt manganese (LiNiCoMnO₂), lithium iron phosphate (LiFePO₄), lithium nickel cobalt aluminum (LiNiCoAlO₂), and lithium titanate (Li₄Ti₅O₁₂). In addition to graphite, cobalt, and lithium, lithium-ion batteries contain aluminum, nickel, manganese, copper, titanium, certain rare earth elements, and plastics. Recovery of these elements, known as critical and strategic raw materials, is of great importance. Recovery of precious metals from lithium-ion batteries has become viable from economic, technological, and rising demand perspectives for certain critical raw materials. Lithium-ion batteries generally consist of three parts: anode, cathode, and electrolyte. The cathode contains metal oxides, with LiCoO₂ being the most widely used commercial type. The anode consists of a porous carbon structure, with graphite being the primary material used for this purpose. The electrolyte consists of organic solvents such as LiPF₆, which generally contain lithium ions (Vıcıl, 2011). Figure 1 shows the battery components and their material contents (Ellingsen and Hung, 2018). Lithium-ion battery technology is advancing continuously. With these developments, applications are expanding, and usage volume is increasing proportionally. Lithium-ion batteries, which became widespread with mobile phones and laptops, are now used in solar energy storage systems in much larger capacities, in electric vehicles, and in buses. Their use in almost all technological devices has greatly expanded the lithium-ion battery market volume (Pillot, 2019). Lithium-ion batteries can cause dangerous situations such as ignition and flashing when exposed to high heat. For this reason, many studies and technologies have been developed on the safe use of lithium-ion batteries from past to present. Especially in technological devices that contain large battery quantities, such as electric vehicles, cooling systems are installed. Devices without cooling systems, such as mobile phones, should not be exposed to direct sunlight. New technology in lithium-ion batteries provides much safer use than previous types. Thus, lithium-ion batteries can be easily used in electric vehicles. They are also preferred due to their low cost and simple maintenance. Lithium-ion batteries offer a variety of advantages due to their long lifespan and long-term storage capability (Prabhakar, 2008). Lithium cobalt oxide (LCO) type lithium-ion batteries have high specific energy. High specific energy means that the ratio of stored energy to battery volume is quite high. Therefore, LCO type batteries are mostly used in portable technological devices such as mobile phones and laptops (Akkuş, 2011). Lithium-ion batteries mainly consist of graphite on the copper anode and lithium cobalt oxide on the aluminum cathode. During operation, lithium ions move from the anode to the cathode; this electrochemical reaction occurs in the opposite direction of charging (Şahan and Patat, 2014). Despite their high specific energy, LCO type batteries have a low cycle count. Therefore, they need to be replaced frequently. Although the type of lithium-ion battery varies according to the area of use, they are used as small hand tools, electric vehicles, and high energy storage sources. The structure and components of lithium-ion batteries used in mobile phones are shown in Figure 2, and the anode and cathode reactions in LCO batteries are shown in reactions 1 and 2 (Gülbeyaz, 2019). Significant chemical changes occur in the active cathode material. These changes, which create different types of lithium-ion batteries, directly affect usage requirements. Thanks to different raw materials used, increases in capacity, power, and lifetime can be achieved in lithium-ion batteries (Miao et al., 2019). The anode and cathode can be referred to generally as electrodes, and these electrodes have a layered structure, which can also be spinel structures. Because of its layered structure, the cathode enables cell charging and discharging. During charging and discharging, lithium ions are exchanged between the positive and negative electrodes, and the displacement reactions of lithium ions are called topotactic (Bolat et al., 2012). The anode and cathode are active materials in the chemical reaction in the battery. As shown in Figure 3, lithium moves between active materials (Şahan and Patat, 2014; Gülbeyaz, 2019). According to reports, the lithium-ion battery market volume reached USD 1 billion in 2017, is predicted to reach USD 36 billion in 2020, and USD 75 billion in 2030 (Pillot, 2019). Lithium-ion batteries, which were used only in devices such as laptops and mobile phones in the early 2000s, have reached very high gigawatt values in the 2020s due to their use in advanced technology areas such as electric vehicles. The change in the total amount of spent lithium-ion batteries over the past ten years is shown in Figure 4 (Melin, 2020). The volume, which was 1,000 gigawatt-hours in 2020, is expected to increase approximately three times by 2025. According to analytical reports, this figure is expected to increase elevenfold in 2030 with the rapid increase in the number of electric vehicles (Melin, 2020).

Research Assistant Zeynep Üçerler Istanbul Technical University Faculty of Mines, Department of Mineral Processing Engineering

Research Assistant Nazlım İlkyaz Dinç Istanbul Technical University Faculty of Mines, Department of Mineral Processing Engineering

Associate Professor Dr. Fırat Burat Istanbul Technical University Faculty of Mines, Department of Mineral Processing Engineering