With the advancement of global energy transition and emission reduction goals, lithium-ion batteries (LIBs) are increasingly used in electric vehicles and energy storage. Lithium iron phosphate (LiFePO4, LFP) batteries have become one of the most popular types of LIBs due to their structural stability, cost-effectiveness, and non-toxicity. However, with the increase in the use of LIBs, the recycling of used batteries has become increasingly prominent. At present, the recycling methods of waste LIBs mainly include direct regeneration, hot metal method and wet metal method. Although hot and wet metal processes are theoretically feasible, they are not economically suitable for the recycling of waste LIBs, as these methods are not only energy-intensive, time-consuming, but also have a potentially negative impact on the environment. Therefore, direct regeneration methods, especially solid-phase methods, have become a hot topic of research due to their simplicity, high efficiency and ease of large-scale production. However, the existing direct regeneration methods still have the problems of long heating time and high energy consumption, and there is an urgent need to develop a faster and more efficient regeneration technology to achieve both economic and environmental benefits of used LFP batteries.
In December 2023, Professor Wu Xinglong of Northeast Normal University, Professor Zeng Ronghua of South China Normal University and others published a paper entitled "Direct and rapid regeneration of spent LiFePO4 cathodes via a high-temperature shock strategy" in the journal Journal of Power Sources. In this study, we propose an efficient, low-cost, and ultra-fast regeneration strategy that can rapidly regenerate waste lithium iron phosphate (LiFePO4) cathode materials in just 20 seconds. Compared to traditional methods, this ultra-fast method not only consumes less energy and shortens the processing time, but also enables complete lithium replenishment and structural repair of LiFePO4. The regenerated LiFePO4 exhibited an excellent initial capacity of 152 mAh/g at 0.1C, and the RLFP-800 sample exhibited good rate performance and long-cycling stability (400 cycles at 2C without volume decay). It is expected that this rapid recycling strategy can realize the practical recycling application of waste LiFePO4 at a low cost, and provide a new solution for the recycling of waste LIBs.
In this study, in order to achieve low-energy consumption and high-efficiency regeneration of spent lithium iron phosphate (LiFePO4) cathode materials, the researchers proposed an ultra-fast heating method that is able to complete the regeneration process in a few seconds. Compared to conventional calcination methods, this ultra-fast high-temperature impact method has an extremely fast heating rate (approx. 105 °C/min) and cooling rate (approx. 103 °C/min), which not only significantly reduces energy and time costs, but also minimizes the loss of lithium. After rapid high-temperature calcination, the structure of the material is restored and the performance is significantly improved.
Figure 1 shows a schematic diagram of the regeneration process of used LiFePO4 cathode materials, detailing the ultra-fast calcination steps from the pretreatment of used batteries to the final calcination.
In the experimental part, used bagged LFP batteries were first pre-treated, including discharge, transfer, separation, and baking, in order to facilitate scraping of waste LFP powder (SLFP) from aluminum foil. Subsequently, a certain proportion of lithium acetic acid and sucrose is mixed with SLFP through steps such as ball milling, rotary evaporation and drying, and finally an ultra-fast high-temperature calcination at 800°C for 20 seconds in an argon atmosphere.
In the material characterization part, the elemental content of Li, Fe and P was confirmed by inductively coupled plasma atomic emission spectroscopy (ICP-AES), and the crystal structure and surface chemistry of the materials were analyzed in detail by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). Figure 2(a) shows the XRD patterns of SLFP and LFP regenerated at different temperatures (RLFP-700, RLFP-800, RLFP-900), Figures 2(b) to 2(e) show SEM images of these materials, respectively, and Figures 2(f) and 2(g) show TEM images of SLFP and RLFP-800.
X-ray photoelectron spectroscopy (XPS) analysis was used to determine the surface chemistry of SLFP and RLFP-800.
Figure 3 shows the XPS spectra of Fe 2p, C 1s and O 1s, indicating that the lithium element in RLFP-800 has been re-replenished and the crystal structure has been well restored.
In the electrochemical performance test part, the electrochemical properties of all materials are measured in the CR2032 button battery. Figure 4 shows the charge-discharge capacitance of the SLFP and RLFP samples at 0.1C, and Figures 4(a) to 4(e) show the rate performance, cycling performance, and charge-discharge curves of these samples, respectively.
Figure 5 further shows the charge-discharge curves and cyclic voltammetry (CV) curves of the SLFP and RLFP samples at 0.2C, Figure 5(a) shows the discharge specific capacity of the different samples, and Figure 5(b) shows the CV curve and electrochemical reversibility.
Figure 6 shows the CV curves of the RLFP-800 at different scan rates, as well as the electrochemical impedance spectroscopy (EIS) results of SLFP and RLFP. Figures 6(a) to 6(d) show the CV curve, the peak current vs. scan rate, the EIS curve, and the Z' vs. ω^-1/2 in the low-frequency region, respectively.
Finally, Figure 7 shows the in-situ X-ray diffraction (in situ XRD) spectrum of RLFP-800 during the first charge-discharge cycle, which monitors the insertion and ejection of Li+ in FP/LFP, and demonstrates the excellent reversibility of the Li+ intercalation/deintercalation process.
In this study, we successfully developed a rapid, green, and low-cost regeneration process for the recovery of spent lithium iron phosphate (LFP) cathode materials. Unlike traditional regeneration strategies, this method achieves efficient regeneration of waste LFP through an ultra-fast calcination process of only 20 seconds at 800°C. The results of structure and morphology characterization showed that the crystal structure of the spent LFP was completely restored to its original olivine structure, and the electrochemical performance of the regenerated LFP was significantly improved. The optimized regenerative LFP (RLFP-800) has an initial discharge specific capacity of up to 152 mAh/g at 0.1C and exhibits significant cycling stability over a long period of more than 400 cycles. In addition, cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and in-situ X-ray diffraction test results show that the regenerated RLFP-800 has improved lithium-ion diffusion coefficient, excellent stability, and reversibility during charge-discharge cycles. This time-saving and energy-efficient method is ideal for the actual restoration of used LFP materials.
This study not only provides a new strategy for the remediation of waste LFP materials, but also opens up a new way for the rapid and efficient repair of cathode materials for waste lithium-ion batteries (LIBs). With the rapid development of electric vehicles and new energy storage technology, the recycling and reuse of waste LIBs has become increasingly prominent. The ultra-fast regeneration method proposed in this study can not only significantly reduce the energy consumption and time cost in the regeneration process, but also minimize the loss of lithium, which is of great significance for the sustainable use of resources and environmental protection.
In the future, researchers can further optimize the recycling process, explore the recycling strategies of different types of waste battery materials, and promote the development of lithium battery recycling and reuse technology. At the same time, the popularization and application of this method will also provide a cost-effective solution for battery manufacturers and recycling companies to promote the green transformation of the battery recycling industry. In addition, considering the efficiency and simplicity of this method, it has great potential for application in large-scale industrial production, and is expected to realize the efficient recycling and reuse of used battery materials, contributing to the realization of a circular economy and sustainable development goals.
Shuo-Hang Zheng, Xiao-Tong Wang, Zhen-Yi Gu, Hong-Yan Lü, Xin-Yi Zhang, Jun-Ming Cao, Jin-Zhi Guo, Xiao-Tong Deng, Ze-Tao Wu, Rong-Hua Zeng, Xing-Long Wu. Direct and rapid regeneration of spent LiFePO4 cathodes via a high-temperature shock strategy. Journal of Power Sources, 2023.
https://doi.org/10.1016/j.jpowsour.2023.233697.
Article source: Research Zhichengli
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