Method for low-temperature and high-efficiency defluorination of waste lithium battery black powder

Abstract

The application discloses a kind of waste lithium battery black powder low-temperature efficient defluorination method, belong to battery material recycling technical field.The method is to place waste lithium battery black powder in flowing non-reactive gas, heated to 300~600 DEG C temperature and carried out defluorination treatment.This method uses flowing atmosphere in the sintering process and accurately controls temperature, uses airflow to carry out fluorides generated by pyrolysis to promote the rapid, deep decomposition of fluorides in black powder, while the crystal structure of waste lithium battery black powder is not damaged, solves the technical bottleneck of incomplete defluorination of waste lithium battery black powder, serious secondary reaction and high energy consumption in prior art, promotes the large-scale green regeneration of waste lithium battery positive material.

Description

Technical Field

[0001] This invention relates to a method for defluorinating black powder from waste lithium batteries, belonging to the field of battery material recycling technology. Background Technology

[0002] With the rapid development of new energy vehicles and energy storage systems, lithium iron phosphate (LiFePO4, LFP) batteries have gained a significant position in the power and energy storage battery markets due to their advantages such as high safety, long cycle life, good thermal stability, abundant resources, and low cost. In recent years, along with the rapid growth of the electric vehicle industry, the installed capacity of LFP batteries has continued to climb. Simultaneously, a large number of expired LFP batteries have entered the recycling stage. Failure to properly and efficiently treat and reuse them will result in serious resource waste and environmental pollution. On the one hand, waste batteries still contain a large amount of reusable key elements such as lithium, iron, and phosphorus. Direct landfilling as solid waste will not only occupy land resources but may also cause long-term environmental damage through leaching. On the other hand, improper handling of organic electrolyte residues, metal ions, and fluorides contained in waste batteries will exacerbate the environmental burden. Therefore, achieving green, efficient, and low-cost recycling of waste LFP batteries is of great significance for promoting the sustainable development of the lithium battery industry and facilitating resource recycling.

[0003] Currently, the main methods for recycling spent lithium batteries fall into three categories: pyrometallurgy, hydrometallurgy, and direct regeneration. Pyrometallurgy recovers valuable metals through high-temperature smelting. While the technology is mature, it suffers from high energy consumption, large carbon dioxide emissions, and low phosphorus utilization. Hydrometallurgy relies on acid-base leaching to recover metals, but this method is cumbersome, requires large amounts of chemical reagents, is prone to secondary pollution, and has less than ideal resource utilization efficiency. In contrast, direct regeneration technology, through the repair and re-lithiation of spent cathode materials, can retain their original crystal structure and electrochemical properties to the greatest extent. It has advantages such as low energy consumption, controllable cost, and environmental friendliness, and is considered an ideal way to recycle spent lithium iron phosphate cathode materials. However, in the direct regeneration process, the problem of residual fluorine on the surface and inside the material has become a key bottleneck restricting its industrialization.

[0004] In waste LFP electrode materials, the main sources of fluorine include the decomposition products of fluorinated salts (such as LiPF6) in the electrolyte, and the thermal and chemical degradation of the electrode binder, polyvinylidene fluoride (PVDF). With prolonged battery operation and post-retirement processing, fluorides form a coating layer on the surface of the cathode material, and may even enter the crystal lattice through ion exchange or chemical reactions. The presence of fluorine significantly degrades the material's structure and performance. On the one hand, fluoride coatings on particle surfaces hinder lithium-ion diffusion channels, increase interfacial impedance, and reduce the rate performance and cycle life of the electrode material. On the other hand, the interaction between fluoride ions and the active components in the material may induce lattice defects and structural instability, leading to a decline in electrochemical performance. Therefore, efficient removal of fluorides from waste LFP materials is a necessary prerequisite for achieving high-performance regeneration.

[0005] Currently, researchers have proposed various defluorination methods, including water washing, chemical leaching, atmosphere treatment, and high-temperature sintering. Water washing can remove some soluble fluoride salts, but it is almost ineffective against firmly bonded fluorides or fluoride ions embedded in the crystal lattice. Chemical leaching can further dissolve fluorides, but it requires large amounts of acid and alkali solutions, leading to secondary pollution and equipment corrosion. High-temperature treatment removes fluoride through pyrolysis and gasification, but traditional processes are often energy-intensive, and fluorides may re-react at high temperatures to generate difficult-to-remove byproducts, resulting in limited defluorination efficiency. Furthermore, existing methods, while achieving defluorination, easily damage the crystal structure of LFP, making it difficult to restore its electrochemical performance to commercial levels. Chinese patent application (CN 117509743 A) discloses a method of ball milling waste lithium iron phosphate black powder and limestone in a ball mill, mixing them evenly, and then granulating the mixture to obtain granulated material; the granulated material is fed into a rotary kiln at a flow rate of 50~400 Nm³. 3 An oxidative roasting reaction is carried out at 500-800°C for 2 hours using air or oxygen-enriched air per hour, yielding a mixture and kiln tail gas, with a fluorine and chlorine removal rate of 90.0%-99.8%. However, this method requires the additional use of limestone defluorination agents, and the lithium iron phosphate decomposes after defluorination, making it difficult to recycle. Therefore, achieving an efficient, thorough, and environmentally controllable defluorination process while maintaining material structural stability is a crucial scientific problem and engineering challenge that urgently needs to be addressed for the direct regeneration of waste lithium iron phosphate. Summary of the Invention

[0006] To address the technical problems of incomplete fluoride removal, easy damage to crystal structure, and low defluorination efficiency in the regeneration of waste lithium battery black powder (cathode material) in existing technologies, the present invention aims to provide a low-temperature and efficient defluorination method for waste lithium battery black powder. This method utilizes a flowing atmosphere and precise control of the calcination temperature during the sintering process, using airflow to carry away the fluorides generated during pyrolysis, thereby promoting the rapid and deep decomposition and removal of fluorides in the black powder without damaging the crystal structure of the lithium battery cathode material. This method solves the technical bottlenecks of incomplete defluorination, severe secondary reactions, and high energy consumption in existing technologies for waste lithium battery black powder, and promotes the large-scale green regeneration of waste lithium battery cathode materials.

[0007] To achieve the above-mentioned technical objectives, the present invention provides a method for low-temperature and efficient defluorination of waste lithium battery black powder. The method involves placing the waste lithium battery black powder in a flowing non-reactive gas and heating it to a temperature of 300~600℃ for defluorination treatment.

[0008] In existing technologies, during the high-temperature defluorination process of waste lithium-ion battery powder, the pyrolysis products of fluorides are difficult to migrate and remove. Furthermore, their high reactivity makes them prone to secondary reactions with the substrate material under high-temperature conditions. This not only hinders effective defluorination of the lithium-ion battery powder but also further damages its crystal structure. The key to this invention lies in performing high-temperature defluorination of waste lithium-ion battery powder in a flowing, non-reactive gas. On one hand, the calcination temperature is strictly controlled; within an appropriate calcination temperature range, the pyrolysis and volatilization of fluorides can be fully realized while avoiding damage to the crystal structure of the lithium-ion battery powder. On the other hand, a flowing atmosphere is used to promote the migration and removal of fluoride decomposition products, ensuring that the decomposed fluorides are quickly carried away by the flowing atmosphere, preventing their redeposition in localized environments or secondary reactions with the lithium-ion battery cathode material. In summary, this invention can achieve high-temperature defluorination of waste lithium-ion battery powder, significantly reducing its fluoride content while maintaining a relatively intact crystal structure, which is beneficial for subsequent high-performance regeneration.

[0009] As a preferred embodiment, the flow rate of the non-reactive gas is 300~800 mL / min. As a more preferred embodiment, the flow rate of the non-reactive gas is 400~500 mL / min. The flow rate of the non-reactive gas has a significant impact on the defluorination of waste lithium battery black powder. If the gas flow rate is too low, the fluoride decomposition products are not easily carried away in time and are prone to redeposition on the material surface, resulting in incomplete defluorination. If the gas flow rate is too high, it may cause damage to the particle surface structure and powder loss, reducing the yield and electrochemical performance of subsequent recycled materials.

[0010] As a preferred embodiment, the non-reactive gas includes nitrogen and / or an inert gas. The non-reactive gas is a gas commonly found in the art, such as nitrogen, or it may be an inert gas, such as helium or argon.

[0011] The preferred non-reactive gas can prevent the material from being oxidized under high temperature conditions, and at the same time can inhibit the reaction of fluorides with oxygen to form stable byproducts, thereby further improving the defluorination efficiency.

[0012] As a preferred embodiment, the defluorination treatment temperature is 350~400℃, and the time is 2~10 hours. If the calcination temperature is too low, the fluoride is difficult to decompose completely, resulting in insufficient defluorination rate; if the temperature is too high, it is easy to cause particle sintering and agglomeration or lattice distortion, thereby reducing the specific capacity and cycle stability of the material. At the same time, the higher the temperature, the higher the reactivity of the fluoride with the lithium battery black powder, thus increasing the difficulty of defluorination. If the defluorination treatment time is too short, the fluoride decomposition and migration are insufficient, making it difficult to achieve efficient defluorination; if the defluorination treatment time is too long, the defluorination effect will not be significantly increased, and energy consumption will increase. It may also cause abnormal growth of material particles, affecting subsequent slurry preparation and battery performance. The defluorination treatment temperature is further preferably 375~400℃. The defluorination treatment time is further preferably 2~3 hours.

[0013] The waste lithium battery black powder of the present invention is not limited to waste lithium iron phosphate battery black powder, but also includes waste nickel cobalt manganese lithium battery black powder, nickel cobalt aluminum lithium battery black powder, manganese lithium battery black powder, etc. These lithium battery black powders contain fluoride salts (such as LiPF6) and fluorine-containing organic binders (polyvinylidene fluoride PVDF), all of which can be efficiently defluorinated by the method of the present invention.

[0014] The waste lithium battery black powder of the present invention has low fluorine residue and almost no damage to its crystal structure after defluorination treatment. After further solid-phase lithium replenishment or liquid-phase relithiation treatment, the lithium loss during high temperature process is compensated and structural defects are repaired, thereby obtaining a regenerated lithium iron phosphate cathode material with better electrochemical performance.

[0015] The method for low-temperature and efficient defluorination of waste lithium battery black powder provided by this invention includes the following specific steps:

[0016] 1) Disassemble the waste lithium batteries, peel off the waste lithium battery black powder (positive electrode material), and place it in a vacuum oven at 120°C. o C is dried overnight to obtain dried waste lithium battery black powder;

[0017] 2) Place the waste lithium battery black powder obtained in step 1) into a tube furnace and sinter it under a nitrogen or argon protective atmosphere. By adjusting the gas flow rate (300~800mL / min), the decomposition and migration of fluorides are promoted, and the decomposition products of fluorides are removed in time to achieve efficient defluorination. The sintering temperature is controlled at 300~600 ℃ and the sintering time is 2~10h.

[0018] 3) After cooling the defluorinated waste lithium battery black powder from step 2) to room temperature, collect it. If necessary, it can be further mixed with an external lithium source (such as lithium carbonate or lithium hydroxide) in a solid phase, and the lithium-iron ratio can be adjusted to 1.00~1.06. Then, lithium replenishment sintering is carried out again under a nitrogen atmosphere to compensate for the lithium loss during the high-temperature treatment process and repair the lattice defects, so as to obtain high-performance regenerated lithium battery cathode material.

[0019] Compared with the prior art, the technical solution of the present invention brings the following beneficial technical effects:

[0020] This invention addresses the challenges of efficiently removing fluorides from waste lithium-ion battery black powder and the damage to crystal structure caused by traditional high-temperature defluorination methods. It achieves efficient defluorination at low temperatures by employing a flowing, non-reactive atmosphere during heat treatment. This flowing atmosphere ensures that fluoride decomposition products are promptly carried away, preventing secondary deposition on the material surface or inside the furnace tube, thus guaranteeing thorough defluorination. Simultaneously, it maximizes the preservation of the crystal structure of the waste lithium-ion battery cathode material, providing high-quality raw materials for subsequent regeneration. This invention overcomes the challenges of structural damage and fluoride re-deposition caused by high-temperature defluorination in existing technologies.

[0021] The low-temperature, high-efficiency defluorination method provided by this invention is simple to operate and can achieve efficient removal of fluorides under conditions lower than traditional high-temperature defluorination. It has low energy consumption and a short cycle time. The defluorinated waste lithium battery black powder can maintain high electrochemical activity in subsequent solid-phase lithium replenishment or liquid-phase lithiation treatment. The full cells prepared from the regenerated cathode material exhibit excellent cycle performance and capacity recovery rate. The method has good scalability and universality, and can significantly promote the industrial green recycling application of waste lithium iron phosphate electrode materials. Attached Figure Description

[0022] Figure 1 The morphology of waste lithium iron phosphate black powder after defluorination at a gas flow rate of 300 mL / min (Example 1) shows that the lithium iron phosphate particles are in an agglomerated state because PVDF cannot be completely removed.

[0023] Figure 2 The morphology of defluorinated waste lithium iron phosphate black powder at a gas flow rate of 500 mL / min (Example 3). PVDF can be applied at 400... o C is completely removed at low temperatures, and the lithium iron phosphate particles are uniformly dispersed.

[0024] Figure 3 The charging and discharging curves of the defluorinated waste lithium iron phosphate black powder after regeneration under different gas flow rates in Examples 1-3 are shown. When the gas flow rate is low, PVDF cannot be completely removed, and the initial specific capacity of the lithium iron phosphate cathode material is low. When the gas flow rate increases, the initial specific capacity of the lithium iron phosphate cathode material increases significantly. However, if the gas flow rate is too high, the PVDF cracking products in the lithium iron phosphate cathode material will be purged unevenly, resulting in poor consistency of the lithium iron phosphate cathode material and a slight reduction in initial capacity. Detailed Implementation

[0025] The technical solution of the present invention will be further illustrated below with reference to specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the invention and should not be considered as specific limitations thereof. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without innovative effort are within the protection scope of the present invention.

[0026] In the following embodiments, the source of the black powder from waste lithium iron phosphate batteries is as follows: waste lithium iron phosphate batteries are disassembled, and the waste lithium iron phosphate battery black powder (positive electrode material) is separated and placed in a vacuum oven at 120°C. o C is dried overnight to obtain dried waste lithium iron phosphate battery black powder;

[0027] In the following embodiments, the waste lithium iron phosphate battery black powder after defluorination was mixed with lithium carbonate in a solid phase, the lithium iron ratio was adjusted to 1.05, and conventional lithium replenishment sintering was carried out under a nitrogen atmosphere (720 degrees Celsius, 4 hours) to compensate for lithium loss during the high-temperature treatment and repair lattice defects, so as to obtain high-performance recycled lithium iron phosphate cathode material.

[0028] Example 1

[0029] Waste lithium iron phosphate battery black powder was placed in a high-temperature resistant quartz boat and then placed in a tube furnace. A nitrogen protective atmosphere was introduced, with a fixed gas flow rate of 300 mL / min. The temperature was raised to 400℃ and held for 2 hours to complete the defluorination treatment. After cooling to room temperature, the defluorinated waste lithium iron phosphate battery black powder was collected.

[0030] The fluorine content after defluorination was measured to be 0.22 wt%.

[0031] Example 2

[0032] Waste lithium iron phosphate battery black powder was placed in a high-temperature resistant quartz boat and then placed in a tube furnace. A nitrogen protective atmosphere was introduced, with a gas flow rate of 400 mL / min. The temperature was raised to 400℃ and held for 3 hours to complete the defluorination treatment. After cooling to room temperature, the defluorinated waste lithium iron phosphate battery black powder was collected.

[0033] The fluorine content after defluorination was measured to be 0.18 wt%.

[0034] Example 3

[0035] Waste lithium iron phosphate battery black powder was placed in a high-temperature resistant quartz boat and then placed in a tube furnace. A nitrogen protective atmosphere was introduced, with a fixed gas flow rate of 500 mL / min. The temperature was raised to 400 ℃ and held for 3 hours to complete the defluorination treatment. After cooling to room temperature, the defluorinated waste lithium iron phosphate battery black powder was collected.

[0036] The fluorine content after defluorination was measured to be 0.15 wt%.

[0037] Example 4

[0038] Waste lithium iron phosphate battery black powder was placed in a high-temperature resistant quartz boat and then placed in a tube furnace. A nitrogen protective atmosphere was introduced, with a gas flow rate of 800 mL / min. The temperature was raised to 400 ℃ and held for 3 hours to complete the defluorination treatment. After cooling to room temperature, the defluorinated waste lithium iron phosphate battery black powder was collected.

[0039] The fluorine content after defluorination was measured to be 0.14 wt%.

[0040] Example 5

[0041] Waste lithium iron phosphate battery black powder was placed in a high-temperature resistant quartz boat and then placed in a tube furnace. A nitrogen protective atmosphere was introduced, with a fixed gas flow rate of 500 mL / min. The temperature was raised to 350 °C and held for 3 h to complete the defluorination treatment. After cooling to room temperature, the defluorinated waste lithium iron phosphate battery black powder was collected.

[0042] The fluorine content after defluorination was measured to be 0.20 wt%.

[0043] Example 6

[0044] Waste lithium iron phosphate battery black powder was placed in a high-temperature resistant quartz boat and then placed in a tube furnace. A nitrogen protective atmosphere was introduced, with a fixed gas flow rate of 500 mL / min. The temperature was raised to 375 °C and held for 3 h to complete the defluorination treatment. After cooling to room temperature, the defluorinated waste lithium iron phosphate battery black powder was collected.

[0045] The fluorine content after defluorination was measured to be 0.17 wt%.

[0046] Example 7

[0047] Waste lithium iron phosphate battery black powder was placed in a high-temperature resistant quartz boat and then placed in a tube furnace. A nitrogen protective atmosphere was introduced, with a gas flow rate of 500 mL / min. The temperature was raised to 400 ℃ and held for 2 hours to complete the defluorination treatment. After cooling to room temperature, the defluorinated waste lithium iron phosphate battery black powder was collected.

[0048] The fluorine content after defluorination was measured to be 0.18 wt%.

[0049] Example 8

[0050] Waste lithium iron phosphate battery black powder was placed in a high-temperature resistant quartz boat and then placed in a tube furnace. A nitrogen protective atmosphere was introduced, with a fixed gas flow rate of 500 mL / min. The temperature was raised to 400 ℃ and held for 6 h to complete the defluorination treatment. After cooling to room temperature, the defluorinated waste lithium iron phosphate battery black powder was collected.

[0051] The fluorine content after defluorination was measured to be 0.15 wt%.

[0052] Example 9

[0053] Waste lithium iron phosphate battery black powder was placed in a high-temperature resistant quartz boat and then placed in a tube furnace. A nitrogen protective atmosphere was introduced, with a fixed gas flow rate of 500 mL / min. The temperature was raised to 400 ℃ and held for 10 h to complete the defluorination treatment. After cooling to room temperature, the defluorinated waste lithium iron phosphate battery black powder was collected.

[0054] The fluorine content after defluorination was measured to be 0.15 wt%.

[0055] Example 10

[0056] Waste lithium iron phosphate battery black powder was placed in a high-temperature resistant quartz boat and then placed in a tube furnace. Argon gas was introduced into the protective atmosphere at a constant flow rate of 500 mL / min. The temperature was raised to 400℃ and held for 3 hours to complete the defluorination treatment. After cooling to room temperature, the defluorinated waste lithium iron phosphate battery black powder was collected.

[0057] The fluorine content after defluorination was measured to be 0.15 wt%.

[0058]

[0059] The results in Table 1 show that controlling the airflow velocity plays a significant role in the defluorination process. When the airflow velocity is moderate (approximately 500 mL / min), fluorine in waste lithium iron phosphate battery powder can be efficiently removed, and the defluorination effect improves with increasing airflow velocity. However, excessively low airflow velocity leads to insufficient gas replacement and incomplete defluorination; while excessively high airflow velocity may cause powder dispersion or uneven defluorination, affecting the uniformity of the waste lithium iron phosphate material particles. Furthermore, if the defluorination temperature is too low, fluorides are difficult to decompose completely, resulting in insufficient defluorination rate; if the defluorination temperature is too high, particle sintering and agglomeration or lattice distortion are likely to occur, thereby reducing the specific capacity and cycle stability of the material. Additionally, higher defluorination temperatures lead to higher reactivity of fluorides with lithium battery powder, increasing the difficulty of defluorination. If the defluorination treatment time is too short, the decomposition and migration of fluorides will be insufficient, making it difficult to achieve efficient defluorination. If the defluorination treatment time is too long, the defluorination effect will not be significantly increased, and energy consumption will increase. It may also cause abnormal growth of material particles, affecting subsequent slurry preparation and battery performance.

[0060] Example 11

[0061] Waste lithium iron phosphate battery black powder was placed in a high-temperature resistant quartz boat and then placed in a tube furnace. A nitrogen protective atmosphere was introduced, with a fixed gas flow rate of 300 mL / min. The temperature was raised to 300 °C and held for 2 h to complete the defluorination treatment. After cooling to room temperature, the defluorinated waste lithium iron phosphate battery black powder was collected.

[0062] The defluorinated waste lithium iron phosphate battery black powder was regenerated by lithium replenishment. The performance test of the resulting regenerated lithium iron phosphate cathode material showed that the battery initially recovered about 95% of its capacity, and after 100 cycles, the capacity remained at 93%.

[0063] Comparative Example 1

[0064] Waste lithium iron phosphate battery black powder was placed in a high-temperature resistant quartz boat and then placed in a tube furnace. A nitrogen protective atmosphere was introduced, but flowing nitrogen was not used. The temperature was raised to 400°C and held for 2 hours to complete the defluorination treatment. After cooling to room temperature, the defluorinated waste lithium iron phosphate battery black powder was collected.

[0065] The fluorine content after defluorination was measured to be 2.0 wt%.

[0066] This comparative example illustrates that without the use of flowing nitrogen, the residual fluorine in the black powder of waste lithium iron phosphate batteries cannot be thoroughly removed, affecting the battery performance of the cathode material.

Claims

1. A method for low-temperature, high-efficiency defluorination of waste lithium battery black powder, characterized in that: Waste lithium battery black powder is placed in a flowing non-reactive gas and heated to 300~600℃ for defluorination treatment.

2. The method for low-temperature and efficient defluorination of waste lithium battery black powder according to claim 1, characterized in that: The flow rate of the non-reactive gas is 300~800 mL / min.

3. A method for low-temperature, high-efficiency defluorination of waste lithium battery black powder according to claim 1 or 2, characterized in that: The flow rate of the non-reactive gas is 400~500 mL / min.

4. The method for low-temperature and efficient defluorination of waste lithium battery black powder according to claim 3, characterized in that: The non-reactive gas includes nitrogen and / or inert gas.

5. A method for low-temperature, high-efficiency defluorination of waste lithium battery black powder according to claim 1, 2, or 4, characterized in that: The defluorination treatment is performed at a temperature of 350~400℃ for 2~10 hours.

6. The method for low-temperature and efficient defluorination of waste lithium battery black powder according to claim 5, characterized in that: The defluorination treatment is performed at a temperature of 375~400℃ for 2~3 hours.

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