This blog post examines why spent lithium-ion batteries are emerging as pivotal to future resource dominance. It explores the strategic significance of recycling technology amid surging battery demand and competition for rare metals.
The device most emblematic of the ubiquitous era that has fully arrived in our society since the 21st century is undoubtedly portable electronics. The explosive proliferation of these portable devices has played a decisive role in dramatically increasing demand for lithium-ion secondary batteries (LIB), the core devices for producing and storing electricity. Despite starting related technology development later than advanced nations, South Korea has positioned itself as a global market leader based on over two decades of active R&D and industrial investment. Particularly since the 2020s, Korean battery manufacturers have steadily maintained top-tier global market share alongside the growth of the global electric vehicle market, while their battery manufacturing unit costs are also ranked second globally.
However, despite these industrial achievements, Korea’s battery industry still relies entirely on overseas sources for key rare metals like lithium, cobalt, and nickel. Considering the reality of modern society where portable electronics have become essential items, this dependency structure suggests that rare metals, much like oil, could be weaponized as a resource at any time. In other words, if raw material supply is restricted due to international political situations or supply chain disruptions, the entire Korean battery industry could suffer severe damage. Given this environment, it is essential for South Korea to establish a certain level of self-production capacity or a strategic approach to securing these raw materials.
However, considering South Korea’s geological characteristics, which feature an absolute scarcity of basic mineral resources, the most realistic and strategic method available to ensure stable access to rare metals like lithium and cobalt is to actively promote the recycling of spent lithium-ion batteries. Waste batteries are already globally recognized as the most important urban mines, and their value is rising even more rapidly, especially since the late 2020s when electric vehicle adoption became widespread. Therefore, this article will first examine the basic structure and operating principles of lithium-ion secondary batteries. It will then explain the recycling processes currently in use, along with the concept and necessity of bio-leaching—a next-generation technology gaining attention as a complement to existing chemical processes.
Secondary batteries are devices that store electrical energy in the form of chemical energy and convert it back into electrical energy for supply when power is demanded externally. Among these, the most widely used lithium-ion secondary battery consists of four key components: the cathode, anode, electrolyte, and separator. Lithium-ion batteries are composed of a mixture of heavy metals, organic materials, and plastics derived from packaging materials. While the ratios vary slightly depending on the manufacturer or battery type, they generally consist of approximately 5-20% cobalt, 5-7% lithium, 5-10% nickel, 15% organic chemicals, and about 7% plastic. While various compositions like NCM (nickel-cobalt-manganese), NCA (nickel-cobalt-aluminum), and LFP (lithium iron phosphate) are now used in electric vehicle batteries, cobalt-based series remain widely used in portable devices, making cobalt supply critically important.
The cathode (cathode active material) of a lithium-ion secondary battery consists of a lithium oxide with a structure that can readily lose and accept lithium ions during charging and discharging. A representative material is lithium cobalt oxide (LiCoO₂). LiCoO₂ is a compound where lithium is inserted between a layered structure composed of one cobalt atom and two oxygen atoms. In contrast, graphite is typically used for the cathode. Due to its layered structure, lithium ions insert between the graphite layers during charging, forming a lithium-graphite intercalation compound (Li-GIC). In other words, during charging, lithium ions are released from the cathode and migrate into the graphite layers of the anode, forming Li-GIC in the form of LiC₆. During discharging, this process reverses: lithium ions leave the graphite layers and return to the cathode, reforming LiCoO₂. This creates a cyclic structure.
Of course, this charging and discharging process is not permanent. Typically, after 300 to 500 or more charge-discharge cycles, the capacity is known to decrease to about 80% of its initial value, which is one of the main reasons for battery replacement. Lithium-ion batteries are generally designed with a voltage upper limit in the range of 4.1 to 4.2V, and organic solvents are used as the electrolyte to ensure stable operation even at high DC voltages. This electrolyte contains dissolved substances like LiClO₄, LiBF₄, and LiPF₆, which are highly toxic and flammable, requiring extreme caution during handling. Finally, a separator is installed to prevent direct contact between the anode and cathode. The thermal stability and mechanical strength of this separator are critical factors, leading to the recent development of increasingly advanced materials.
Generally, lithium is highly flammable and poses significant safety risks during handling. Therefore, except for limited exceptional situations, manual individual collection is not performed. Instead, an automated process is used to treat waste batteries, followed by the recovery and reuse of valuable metals like lithium and cobalt. The recycling process for spent lithium-ion batteries is fundamentally divided into physical and chemical processes. The chemical process is further subdivided into wet and dry methods. Among these, we will first examine the physical and chemical steps of the wet processing method, which is currently being actively researched in several countries, including South Korea. The physical process primarily involves disassembly and sorting, while the chemical process includes acid leaching to dissolve metals using acids, followed by the separation and purification of each metal from the resulting aqueous solution.
In the physical process, after disassembling the waste batteries, steps such as sorting, crushing, and magnetic separation are performed to recover the electrode active material LiCoO₂, which is the target for recycling. The physical process is crucial because the sorting quality achieved here directly and decisively impacts the metal recovery rate obtained through subsequent chemical processes. In South Korea, extensive research on optimizing physical processes has been conducted by multiple institutions, including the Korea Institute of Geoscience and Mineral Resources (KIGAM), and these technologies are already being applied in some commercial plants. However, due to the structurally complex intertwining of metals, organics, and inorganics within spent lithium-ion batteries, it is difficult to completely separate all components using physical processes alone. Therefore, the subsequent chemical processes play a crucial role in the recycling of spent lithium-ion batteries.
Acid leaching and electrochemical methods for recycling cobalt and lithium from waste lithium-ion batteries have been steadily researched since the 1990s. In chemical processes, acid leaching—using strong acids to dissolve the cathode active material from spent batteries—is considered the most critical step. Consequently, various approaches to optimize the acid leaching process have been proposed, leading to the development of multiple processes. Diverse inorganic acids, such as hydrochloric acid, sulfuric acid, and nitric acid, have been utilized as leaching agents to dissolve the cathode active material from spent lithium-ion batteries. Initially, a method using hydrochloric acid, which offers the fastest leaching rate, was proposed. However, environmental concerns arose due to the massive generation of chlorine gas, leading to its replacement with methods using sulfuric acid or nitric acid.
In the acid leaching process using pure sulfuric acid, metals dissolve in the order aluminum > cobalt > lithium >> copper. Particularly, cobalt’s leaching rate was excessively slow, posing a problem in securing economic viability. To overcome this limitation, a method combining sulfuric acid solution with hydrogen peroxide as a reducing agent was devised. When applying sulfuric acid leaching using hydrogen peroxide, the leaching reaction equation for LiCoO₂ is as follows.
- 2LiCoO₂ + 6H⁺ + H₂O₂ ⇄ 2Co²⁺ + O₂ + 2Li⁺ + 4H₂O
Using hydrogen peroxide as a reducing agent was found to increase the leaching rates of cobalt and lithium by approximately 45% and 10% or more, respectively. This was attributed to a reduction in insoluble Co³⁺ ions and an increase in soluble Co²⁺ ions. These results are considered a significant advancement in terms of improving leaching rates and enhancing economic viability.
Furthermore, moving beyond the traditional method of separately extracting lithium and cobalt, a new process is gaining attention as an alternative: directly reusing the high-purity LiCoO₂ cathode active material itself as electrode active material for new lithium-ion batteries. This approach holds high future potential due to its ability to reduce process steps and significantly cut energy consumption. However, to recycle lithium and cobalt obtained in urban mining form for other applications, proper separation and extraction of each metal must be achieved at the final process stage.
The chemical process using the wet method is currently the most widely used process worldwide, including in South Korea, for recovering valuable metals from waste lithium-ion batteries. This wet process inherently relies on the leaching of electrode active materials using strong inorganic acids like nitric acid and sulfuric acid. Consequently, plant operation requires high costs and high energy inputs, accompanied by increased risks to equipment safety and the potential for environmental pollution due to the release of hazardous substances. Particularly considering the current situation, marked by the continuous growth of portable electronic devices and the full-fledged arrival of the electric vehicle era, the volume of waste batteries requiring processing will far exceed current levels. Consequently, projections indicate a significant increase in environmental impact assessment burdens and related processing costs, a factor assessed as an increasingly serious concern for future society. The alternative chemical process proposed to address these issues is bioleaching.
Bioleaching refers to a technology that utilizes the fact that specific bacteria act as catalysts oxidizing iron and sulfur to dissolve sulfide minerals containing heavy metals. This process has primarily been used to extract metals such as iron, copper, nickel, and zinc from low-to-medium grade ores in stockpiles or abandoned mines. It is known to have achieved a high level of technical maturity through extensive commercialization experience over many years. The bacteria used in bioleaching exist as mixed communities of several species and are primarily classified based on their operating temperature. Bacterial groups active within the 30–40°C range suitable for plant operation are classified as mesophilic organisms. Representative examples include iron-oxidizing bacteria such as Acidithiobacillus ferrooxidans and Leptospirillum ferrooxidans, and sulfur-oxidizing bacteria such as A. thiooxidans. These bacterial species have also been frequently used in prior research conducted for the leaching of cathode active materials from spent lithium-ion batteries.
However, applying bioleaching to the recycling process of spent lithium-ion batteries has not yet reached the commercialization stage. Research to determine optimal leaching conditions continues at the laboratory level, primarily at universities and research institutions worldwide. In South Korea, several research teams, including the Korea Institute of Geoscience and Mineral Resources (KIGAM), have accumulated excellent results in related technologies. In a study by D. Mishra et al., bioleaching was successfully performed on waste lithium-ion battery powder with particle sizes below 150 μm at an initial pH of 2.5, utilizing iron-oxidizing bacteria primarily used in mine bioleaching. This research holds significant importance as it first demonstrated the feasibility of bioleaching for actually leaching and recovering cobalt and lithium from waste lithium-ion battery powder. However, this process presents challenges: the leaching time is extremely long, exceeding approximately 20 days, and the metal leaching rate remains low, insufficient to ensure economic viability, leaving the need for process improvement.
G. Zeng et al. succeeded in dramatically shortening the leaching time for cobalt from LiCoO₂ and significantly increasing the leaching yield by using the same iron-oxidizing bacteria but employing copper ions as a catalyst. The researchers hypothesized that in the presence of copper ions, LiCoO₂ undergoes a cation exchange reaction to form CuCo₂O₄, and this CuCo₂O₄ is then dissolved by Fe³⁺, accelerating cobalt leaching. Zeng et al.’s research is considered highly significant as it can elevate the long processing time and low leaching rate—long considered the greatest weaknesses of bioleaching—to levels economically viable. Nevertheless, even with the copper catalyst, lithium leaching remains slow and recovery rates are still low, necessitating further research to improve these aspects.
If bioleaching can be applied to lithium-ion battery recycling, it offers the advantage of significantly reducing costs compared to existing chemical processes. Compared to chemical acid leaching using strong acids, bioleaching is superior in environmental friendliness and resource recycling efficiency. It also consumes less energy, enabling low-cost facility construction, and can be performed under relatively mild conditions. Given these characteristics, if bioleaching can be effectively applied to the recycling process of waste lithium-ion batteries through continued research, it has great potential to become a future-oriented next-generation process that can overcome all the shortcomings of existing chemical acid leaching methods.
Considering the explosive potential demand, shortening replacement cycles, and the necessity to secure domestic production capacity for strategic resources, waste lithium-ion batteries are projected to remain the most critical urban mineral not only currently but also in the near future. This paper examined the structure and operating principles of lithium-ion batteries, investigated regeneration and recycling processes for waste lithium-ion batteries, and introduced bio-leaching as a novel method that could complement existing chemical recycling processes. Lithium-ion batteries are certain to become the core energy source for future portable devices and personal transportation like electric vehicles. Consequently, the prices of raw materials, including lithium, are currently following an exponential upward trajectory. From the perspective of South Korea, which relies entirely on imports for these resources, it is necessary to respond to increasing demand, secure resources domestically through the recycling of waste lithium-ion batteries that will rapidly increase in the future, and simultaneously implement strategies for the safe recovery and reuse of abandoned batteries. In particular, developing energy-efficient and environmentally friendly recycling process technologies for waste lithium-ion batteries appears to be an urgent task. Furthermore, if South Korea successfully advances bio-leaching methods—which require relatively less energy—in the field of spent lithium-ion battery recycling, it could leap forward as an industrial powerhouse and resource-rich nation, rivaling rare metal-producing countries.
