1. Introduction
The rapid development of new energy vehicles has led to a significant increase in the application of lithium-ion power batteries. Among them, lithium-iron phosphate (LiFePO4) batteries have attracted extensive attention due to their excellent cycle performance, safety, cost, and environmental protection advantages. According to preliminary research data from GGII, the shipment volume of lithium-iron phosphate in China’s positive electrode materials in 2023 is 1.65 million tons, accounting for 66.53% of the total shipment volume. With the large-scale application of LiFePO4 batteries, the issue of recycling and regenerating used batteries has become crucial. This article reviews the recent research progress on the recycling, repair, and regeneration technology of LiFePO4 cathode materials at home and abroad, providing ideas for their comprehensive resource utilization.
1.1 Lithium-Ion Battery Structure
A lithium-ion battery mainly consists of a cathode material, an anode material, a separator, an electrolyte, a current collector, and an outer package. The cathode material types mainly include layered NCM, spinel-type LiMn2O4, and polyanionic LiFePO4. LiFePO4 belongs to the orthorhombic crystal system and has a stable olivine structure. During the charging and discharging process, it can maintain its structure relatively stable and has relatively good thermodynamic and kinetic stability. The specific capacity of LiFePO4 can reach above 160 mAh/g.
2. Recycling Processes of Spent Lithium-Ion Batteries
2.1 Resource Recovery Process
The resource recovery process of spent lithium-ion batteries is a process of separating and purifying valuable metals inside the battery. It mainly includes pyrometallurgy, hydrometallurgy, and the combination of pyrometallurgy and hydrometallurgy. Some large enterprises such as CATL, GEM, Ganfeng Lithium, and Lvwo are representatives of this process.
| Process Type | Principle | Advantages | Disadvantages |
|---|---|---|---|
| Pyrometallurgy | Using high temperature to melt and separate metals | High metal recovery rate, suitable for large-scale production | High energy consumption, complex equipment, and may produce harmful gases |
| Hydrometallurgy | Using chemical solvents to dissolve and separate metals | Can selectively recover specific metals, relatively low energy consumption | Complex process, long production cycle, and may produce a large amount of waste liquid |
| Pyrometallurgy – Hydrometallurgy Combination | Combining the advantages of the above two methods | Can improve the recovery rate and purity of metals | Complex process control, high cost |
2.2 Direct Repair and Regeneration Process
The direct repair and regeneration process of spent lithium-ion batteries is to directly supplement elements and reshape the structure on the basis of spent lithium-ion batteries. Some small and medium-sized enterprises such as RecycleMe, Sedem, and Qingyan are representatives of this process. Although this process has a relatively short development history and is not as mature as the resource recovery process in terms of technology and industrialization, it has the advantages of fewer process steps, simple operation, and less use of chemical reagents.
| Process Type | Principle | Advantages | Disadvantages |
|---|---|---|---|
| Direct Repair and Regeneration | Directly supplementing missing elements and restoring the structure of cathode materials | Fewer process steps, simple operation, less chemical reagent use, more environmentally friendly and economical | The technology is not mature enough, and the industrialization level is relatively low |
3. Disassembly and Sorting of Unfilled LiFePO4 Battery Cathode Sheets
3.1 Disassembly
The disassembly process is to remove the outer package of the battery and initially separate various materials inside the battery, including manual removal or mechanical automatic removal. In the short-range repair and regeneration process of LiFePO4 cathode waste, the non-destructive separation between the spent LiFePO4 and the current collector is a crucial step. After disassembly, the cathode material sheet mainly consists of the cathode material and the aluminum current collector. The cathode material is tightly bonded to the aluminum current collector through a binder and needs to be further peeled off from the current collector for subsequent repair and regeneration.
3.2 Separation of Cathode and Aluminum Foil
In the lithium battery manufacturing process, a binder such as PVDF is used to fix the cathode material on the current collector, making it difficult to peel off the cathode material from the aluminum foil during the recycling process of spent lithium batteries. There are several common methods for separating the aluminum foil from the cathode material:
| Method | Principle | Advantages | Disadvantages |
|---|---|---|---|
| Mechanical Separation | Using mechanical force to separate the aluminum foil from the cathode material | Simple operation | Low separation degree, residue of cathode active substances in the aluminum foil, dust, noise, and heat pollution, and overflow of volatile substances |
| Heat Treatment | Using the difference in decomposition temperatures of the active substances and binders in the cathode material to separate them at high temperature | Simple process, suitable for industrial-scale production | High energy consumption, generation of harmful gases such as HF, and aluminum doping in the screened products |
| Organic Solvent Separation | Using the similar compatibility characteristics of organic solvents to dissolve the binder and weaken the binding force between the cathode material and the aluminum foil | The organic solvent can be recycled | The toxicity and high price of the organic solvent, and residue of organic substances on the electrode particles after solid-liquid separation |
| Acid – Base Environment Separation | Using acid or base solutions to react with the aluminum foil or the binder to separate the cathode material | Good separation effect | Production of acid – base waste liquid, dissolution of aluminum and cathode material, and difficult treatment of residual binder |
4. Repair and Regeneration of LiFePO4 Materials
4.1 Wet Repair Technology
Wet repair technology involves placing the retired LiFePO4 battery cathode material in a lithium-ion solution with an appropriate amount of a reducing agent and using high temperature or pressure to embed lithium ions into the lithium-deficient LiFePO4 to achieve the repair of LiFePO4.
| Process | Principle | Advantages | Disadvantages |
|---|---|---|---|
| Wet Repair | Using the stability of the LiFePO4 structure and the free lithium ions in the solution to repair the cathode material | No side reactions during the lithium supplementation process, no damage to the structure and surface components of LiFePO4, excellent electrochemical performance | The process may require high temperature or pressure conditions |
4.2 High – Temperature Solid – Phase Method
The high – temperature solid – phase material regeneration technology uses spent cathode materials as raw materials, adds corresponding chemical raw materials according to the types and contents of lost elements, and converts the recovered power lithium battery materials into reactive precursors through high – temperature oxidation treatment. Then, each element recrystallizes through oxidation and carbothermal reduction reactions to achieve the regeneration of materials.
| Process | Principle | Advantages | Disadvantages |
|---|---|---|---|
| High – Temperature Solid – Phase | Using high temperature to recrystallize elements and reshape the structure on the original crystal structure | Similar to the solid – phase method in the synthesis of cathode materials, suitable for large – scale production | High energy consumption, need to accurately analyze the lithium deficiency amount in the waste material |
4.3 Electrochemical Lithium Supplementation Repair Technology
Under the drive of an applied voltage, lithium ions in the electrolyte are directionally embedded into the lithium – deficient LiFePO4 material structure. Using the LiFePO4 waste as the electrolytic cathode, LiFePO4 obtains electrons and reacts with the lithium ions in the electrolyte to achieve the repair and regeneration of the LiFePO4 waste.
| Process | Principle | Advantages | Disadvantages |
|---|---|---|---|
| Electrochemical Lithium Supplementation | Using electrochemical reactions to embed lithium ions into the cathode material | Can directly use the existing battery structure for repair | The process may require special equipment and precise control of voltage and current |
5. Challenges and Future Directions
Although significant progress has been made in the repair and regeneration technology of LiFePO4 cathode materials, there are still some challenges:
5.1 Impurity Removal
The presence of impurities in the waste material can affect the electrochemical performance of the regenerated material. It is necessary to develop efficient impurity removal methods to ensure the quality of the regenerated material.
5.2 Precise Lithium Supplementation
Accurately determining the amount of lithium deficiency in the waste material and precisely supplementing lithium is crucial for obtaining high – quality regenerated materials. Current methods still need to be improved in terms of accuracy.
5.3 Development of Green and Efficient Technologies
The development of green and efficient repair and regeneration technologies that are both environmentally friendly and have high efficiency is the future direction of the industry. This requires continuous exploration and innovation in materials science and electrochemical engineering.
In conclusion, the recycling, repair, and regeneration of LiFePO4 cathode materials are of great significance for the sustainable development of the lithium – ion battery industry. Although there are still some challenges, continuous research and development efforts are expected to bring more breakthroughs and improvements in this field.