Detailed explanation of lithium iron phosphate battery dismantling and recycling strategy

Lithium iron phosphate has good cycle performance, low price, good safety, and has the potential for fast charging. Therefore, with the rapid development of the domestic electric vehicle industry, the demand for lithium iron phosphate batteries is also rapidly increasing. At present, electric buses such as Lithium iron phosphate batteries are basically used in cars with higher safety requirements. Therefore, the degradation of lithium iron phosphate batteries during the cycle is generally not caused by the loss of positive and negative active materials. NeelimaPaul and his team of the Technical University of Munich, Germany, used neutron diffraction to analyze long-term cycling lithium iron phosphate batteries (LFP). /MCMB) research believes that the most important factor causing the life decline of lithium iron phosphate batteries is the Li consumption caused by the reconstruction and growth of the SEI film during the cycle. NeelimaPaul used the method of neutron diffraction to decompose 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 lithium insertion, the negative electrode is Lithium state), but a considerable proportion of FePO4 is still observed in the diffraction peak of the positive electrode. The ratio of LFP:FP is 67:33 in the battery cycled 4750 times, and the ratio of LFP:FP is 75: 25, and the diffraction peak of LiC6 is 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 states that both the positive and negative active materials can participate in the charge and discharge reaction during the cycle, and there is no loss of active materials. Therefore, the main 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. Xuelei Li of Tianjin University of Technology and others have designed a green and environmentally friendly process for recycling waste lithium iron phosphate batteries. The detailed 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 solved with low-concentration NaOH. According to the physical characteristics of the different density, solubility and boiling point of the solvent in the electrolyte, the DMC For the separation of, DEC and EC, the solvent salt LiPF6 will be analyzed in the aqueous solution, as shown in the following formula, and then it can be recovered by filtration. In this process, the separated positive electrode LFP material is mixed with a certain amount of Li2CO3, and the regenerated LFP material can be obtained by thermal solution at different temperatures in an Ar/H2 atmosphere. In order to ensure that the recycled and regenerated LFP materials can have good performance, XueleiLi conducted LFP regeneration tests at 600, 650, 700, 750 and 800 degrees Celsius respectively, and conducted performance testing 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 that has not been regenerated is about 143mAh/g, and the capacity of the LFP material that has been solved at 650 degrees Celsius has increased to 147mAh/g, but after other temperatures are solved, 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 clearly lower than that of the unregenerated LFP material. This is mainly caused by the presence of impurities in the regenerated LFP. XueleiLi's research shows that the thermal solution time can be extended by appropriate Improve the first-time efficiency of LFP materials. Disclaimer: Some pictures and content of articles published on this site are from the Internet. If there is any infringement, please contact to delete.