Detailed explanation of the recycling and utilization of lithium iron phosphate batteries

The recycling of lithium iron phosphate batteries has its own characteristics. Compared with other layered structural materials, lithium iron phosphate materials have a more stable olivine structure, so they are very stable. Even when all Li+ is charged from lithium iron phosphate, When the material is released from the inside, the lithium iron phosphate material can still maintain the FePO4 structure without structural collapse and transformation. Therefore, the decline of the lithium iron phosphate battery during the cycle is generally not caused by the loss of the positive and negative active materials. Germany NeelimaPaul of the Technical University of Munich and his team used neutron diffraction methods to study long-term cycling lithium iron phosphate batteries (LFP/MCMB) that the important factor that causes the life decline of lithium iron phosphate batteries is in the process of cycling. Li consumption due to SEI film reconstruction and growth [1]. NeelimaPaul used the method of neutron diffraction to analyze the battery after 4750 cycles of 1C cycle and 2 years (20%SoC) stored at 23℃ and found that even after the battery is fully discharged (the positive electrode is in the state of intercalating lithium ions, the negative electrode is in the state of lithium ion insertion). Lithium-free state), but a considerable proportion of FePO4 is still observed in the diffraction peaks of the positive electrode. The ratio of LFP:FP is 67:33 in the battery cycled 4750 times, and the ratio of LFP:FP in the battery stored for 2 years is 75:25, while the diffraction peak of LiC6 was not observed in the diffraction peak of the negative electrode. This result shows that a considerable proportion of Li+ disappears in the lithium iron phosphate battery during cycling and storage. It also shows that the positive and negative active materials can participate in the charge and discharge reaction during the cycling process, and no active material loss occurs. Therefore, an important reason for the degradation of lithium iron phosphate batteries is the loss of Li during the cycle. Since the LFP material can maintain the stability of the crystal structure during the battery cycle, regarding the recycling of discarded LFP batteries, we can regain good performance LFP materials as long as we supplement the appropriate Li, which can greatly reduce LFP The processing cost of materials reduces environmental pollution. XueleiLi et al. [2] of Tianjin University of Technology designed a green and environmentally friendly process for recycling waste lithium iron phosphate batteries. The specific process steps are shown in the figure below. The biggest feature of this step is that it realizes low-cost, high-efficiency and environmentally friendly recycling based on the characteristics of lithium iron phosphate materials. From the flow chart, we can see that the process not only realizes the recovery and regeneration of the positive electrode LFP material and the negative electrode graphite material, but also recovers the electrolyte and other materials that are difficult to recover. XueleiLi and others first discharged and dismantled the discarded lithium iron phosphate battery. The remaining electrolyte was treated with low-concentration NaOH. According to the physical characteristics of the different density, solubility and boiling point of the solvent in the electrolyte, it was For the separation of DMC, DEC, EC, etc., the solvent salt LiPF6 will decompose in the aqueous solution, as shown in the following formula, and then it can be recovered by filtration. After the positive electrode LFP material separated in this process is mixed with a certain amount of Li2CO3, the regenerated LFP material can be obtained by heat treatment at different temperatures in an Ar/H2 atmosphere. In order to ensure that the recycled and recycled LFP materials can have good performance, XueleiLi conducted LFP regeneration experiments at 600, 650, 700, 750 and 800 degrees Celsius respectively, and performed performance tests using button half-cells. The results are shown in the following table. From the table, we can see that the capacity of the LFP material without regeneration treatment is about 143mAh/g, and the capacity of the LFP material after 650 degrees Celsius treatment has increased to 147mAh/g, but after other temperature treatments, LFP On the contrary, the capacity of materials has decreased to varying degrees. At the same time, we have also noticed that the first time efficiency of the regenerated material is significantly lower than that of the unregenerated LFP material. This is mainly due to the presence of impurity phases in the regenerated LFP. XueleiLi’s research shows that the heat treatment time can be appropriately extended to improve The first efficiency of LFP material. Disclaimer: Some pictures and content of articles published on this site are from the Internet. If there is any infringement, please contact to delete. Previous post: Analysis on the storage and use of lithium-ion batteries