Lithium supplement regeneration process for recycling lithium iron phosphate pole piece

Abstract

The invention provides a lithium supplement regeneration process for recycling lithium iron phosphate pole pieces. According to the lithium supplement regeneration technology for recycling the lithium iron phosphate pole piece, through the collaborative design of the alkaline solution and three-section type calcination and the application of the alkaline solution, rapid and automatic separation of a lithium iron phosphate coating and an aluminum foil is achieved, the manual stripping procedure is omitted, and lithium supplement can be completed in the treatment process; according to the present invention, with the combination of the three-section gradient calcination, the crystal structure of the regenerated powder can be optimized, the redundant impurity carbon can be efficiently removed, the experiment verification results show that the lithium content of the regenerated powder is stabilized at 4.1% or more, the highest lithium content can achieve 4.15%, the lowest carbon content is controlled at 3%, the excellent electrochemical performance of the regenerated material is ensured, and the process has characteristics of low overall energy consumption, simple process, and aluminum foil recovery and reuse, and can be used for industrial production. The material loss and the labor cost are greatly reduced, the dual-carbon development target is met, the industrial mass production requirement is met, and a green and efficient solution is provided for the field of lithium battery cyclic utilization.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery recycling technology, and more specifically, to a lithium replenishment and regeneration process for recovering lithium iron phosphate electrodes. Background Technology

[0002] To achieve the goals of peak carbon emissions before 2030 and carbon neutrality before 2060, a fundamental transformation of the economic, industrial, and energy structures is needed from the source. Lithium-ion battery recycling, as a key link in energy recycling and sustainable economic development, has significant practical implications for technological optimization and efficient implementation. Lithium iron phosphate (LFP) batteries are widely used due to their stable performance and high safety; however, limited by their chemical properties, their capacity decreases with use, and their theoretical lifespan is only 7 to 8 years. With the large-scale popularization of LFP batteries, the amount of retired batteries and production line waste is increasing year by year. Simultaneously, in the LFP battery manufacturing process, due to equipment debugging, product defects, and dismantling, 3%-5% of the total production volume consists of unfilled, scrapped electrode sheets. These electrode sheets have not suffered performance degradation and have a high lithium content, possessing extremely high recycling value.

[0003] However, existing lithium iron phosphate batteries have the following problems during the recycling process: Traditional liquid-phase recycling processes require large amounts of solvents and rely on high temperatures, causing serious environmental pollution and excessive energy consumption. While traditional solid-phase methods are inexpensive, they are difficult to completely separate the lithium iron phosphate coating from the aluminum foil, resulting in recycled LFP powder with high carbon content and insufficient lithium content, which severely restricts the performance and application value of recycled materials.

[0004] This invention can efficiently recycle lithium iron phosphate electrode sheets and accurately replenish lithium and control carbon. It can achieve rapid and automatic separation of coating and aluminum foil, while reducing energy consumption and labor costs, ensuring the high performance of recycled materials, and contributing to the recycling and green and low-carbon development of lithium batteries. Summary of the Invention

[0005] The present invention aims to solve the technical problems mentioned in the background art and provide a lithium replenishment and regeneration process for recovering lithium iron phosphate electrodes.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a lithium replenishment and regeneration process for recovering lithium iron phosphate electrodes, comprising the following steps: Step 1: Dissolve lithium hydroxide and potassium hydroxide in water to prepare an alkaline solution; Step 2: Immerse the LFP electrode sheet that has not been soaked in electrolyte completely in the solution prepared in step 1, and soak for 3-20 minutes; Step 3: Separate the LFP paste layer from the aluminum foil using ultrasonic vibration, and then remove the aluminum foil; Step 4: After removing the separated LFP coating precipitate, bake and dry it, and then ball mill it to obtain LFP powder with a particle size between 0.1μm and 100μm; Step 5: The dried LFP powder is fed into a nitrogen-filled muffle furnace and baked in three stages at a temperature range of 300-550℃ for a total of 4-8 hours. After cooling, it is removed to obtain regenerated powder that can be used to remake lithium iron phosphate.

[0007] A further preferred embodiment: In the first step, the alkaline solution further includes sodium hydroxide, and the mixing ratio of the hydroxide composed of lithium hydroxide, potassium hydroxide, and sodium hydroxide with water is 0.1%:99.9%-0.5%:99.5%.

[0008] A further preferred embodiment: In the fourth step, the baking and drying temperature is 80°C, and the drying time is 2 hours.

[0009] A further preferred embodiment: In the fourth step, the ball milling process is intermittent ball milling, with a ball milling speed of 400 r / min and a total ball milling time of 6 h, with a 5 min stop every 30 min during the ball milling process.

[0010] A further preferred option: In the fifth step, the specific parameters for the three-stage calcination are: first calcination at 300℃ for 1 hour, then calcination at 450℃ for 1 hour, and finally calcination at 550℃ for 2-3 hours.

[0011] A further preferred option: In step five, the calcined regenerated powder is cooled in a dry environment and then sealed for storage. Beneficial effects

[0012] 1. By setting up an alkaline solution containing lithium hydroxide, potassium hydroxide, and sodium hydroxide, Li⁺ can be provided during soaking and calcination to fill lithium vacancies in the lithium iron phosphate lattice, increasing the lithium content of the recycled powder to 4.1%-4.15%, higher than the 4.0% of the traditional process, thus ensuring the electrochemical performance of the recycled material. At the same time, the alkaline environment can loosen the bond between impurity carbon and lithium iron phosphate, and with subsequent calcination to remove excess carbon, the internal resistance and safety risks of the material are reduced. In addition, OH⁻ can hydrolyze the coating binder, destroying its bonding force with the aluminum foil. Combined with ultrasonic vibration, the coating can be automatically separated. The separation start-up time is only 8-10 minutes, requiring no manual operation, which greatly improves the separation efficiency and reduces material loss and labor costs. 2. By setting up a three-stage calcination process with a gradient progression of low, medium, and high temperatures, residual moisture and trace impurities in the LFP powder are first gently removed to avoid powder agglomeration caused by high temperatures. Then, the crystal structure is gradually optimized to promote the stable bonding of lithium elements with the lithium iron phosphate lattice, ensuring the electrochemical stability of the regenerated powder. The 550℃ stage can effectively remove excess carbon impurities and improve the conductivity of the material. At the same time, the precise control of the total calcination time of 4-8 hours avoids impurity residue caused by insufficient calcination and prevents lithium volatilization caused by over-calcination. Combined with a nitrogen atmosphere, lithium loss is further reduced. 3. In summary, this lithium replenishment and regeneration process for recycled lithium iron phosphate electrodes utilizes a synergistic design of alkaline solution and three-stage calcination. The application of alkaline solution not only achieves rapid and automatic separation of the lithium iron phosphate coating from the aluminum foil, eliminating the need for manual stripping, but also replenishes lithium during the process. Combined with three-stage gradient calcination, it optimizes the crystal structure of the recycled powder and efficiently removes excess carbon impurities. Experimental verification shows that the lithium content of the recycled powder is consistently above 4.1%, reaching a maximum of 4.15%, while the carbon content is controlled to a minimum of 3%, ensuring excellent electrochemical performance of the recycled material. Furthermore, the process is characterized by low overall energy consumption, a simple workflow, and recyclable aluminum foil, significantly reducing material loss and labor costs. This aligns with the dual-carbon development goals, meets the demands of industrial mass production, and provides a green and efficient solution for the lithium battery recycling field. Detailed Implementation

[0013] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the embodiments of the present invention.

[0014] In this embodiment of the invention, a lithium replenishment and regeneration process for recycling lithium iron phosphate electrodes includes the following steps: Step 1: Dissolve lithium hydroxide and potassium hydroxide in water to prepare an alkaline solution; Step 2: Immerse the LFP electrode sheet that has not been soaked in electrolyte completely in the solution prepared in step 1, and soak for 3-20 minutes; Step 3: Separate the LFP paste layer from the aluminum foil using ultrasonic vibration, and then remove the aluminum foil; Step 4: After removing the separated LFP coating precipitate, bake and dry it, and then ball mill it to obtain LFP powder with a particle size between 0.1μm and 100μm; Step 5: The dried LFP powder is fed into a nitrogen-filled muffle furnace and baked in three stages at a temperature range of 300-550℃ for a total of 4-8 hours. After cooling, it is removed to obtain regenerated powder that can be used to remake lithium iron phosphate.

[0015] In the first step, the alkaline solution also contains sodium hydroxide, and the mixing ratio of the hydroxide composed of lithium hydroxide, potassium hydroxide, and sodium hydroxide with water is 0.1%:99.9%-0.5%:99.5%; in the fourth step, the baking and drying temperature is 80℃, and the drying time is 2 hours; in the fourth step, the ball milling treatment is intermittent ball milling, the ball milling speed is 400 r / min, the total ball milling time is 6 hours, and the ball milling process is stopped for 5 minutes every 30 minutes; in the fifth step, the specific parameters of the three-stage calcination are: first calcination at 300℃ for 1 hour, then calcination at 450℃ for 1 hour, and finally calcination at 550℃ for 2-3 hours; in the fifth step, the regenerated powder after calcination is cooled in a dry environment and then sealed for storage; Following the steps outlined above, the specific implementation plan is as follows: The operation steps of Example 1 are as follows: Step 1: Mix sodium hydroxide, potassium hydroxide, lithium hydroxide and other hydroxides with water at a ratio of 0.1%:99.9% and stir to obtain an alkaline solution; Step 2: Completely immerse the LFP electrode, which has not been soaked in electrolyte, in the solution and ultrasonically vibrate for 20 minutes. Step 3: Remove the aluminum foil that has separated from the LFP coating and filter out the remaining LFP coating; Step 4: Place the filtered LFP coating in an 80℃ oven and bake for 2 hours. Then, ball mill the dried LFP coating intermittently at 400r / min for 6 hours, stopping for 5 minutes every 30 minutes. Step 5: Calcine the ball-milled LFP powder in a muffle furnace filled with nitrogen at 300°C for 1 hour, 450°C for 1 hour, and 550°C for 3 hours. Step 6: Cool the calcined powder in a dry environment, remove it, and seal it.

[0016] The operation steps of Example 2 are as follows: Except that the ratio of hydroxides such as sodium hydroxide, potassium hydroxide, and lithium hydroxide to water is changed to 0.5%:99.5% and mixed and stirred to obtain an alkaline solution; the remaining steps are the same as in Example 1.

[0017] The operation steps of Example 3 are as follows: Except for step 5, which involves calcining the ball-milled LFP powder in a nitrogen-filled muffle furnace at 300°C for 1 hour, 450°C for 1 hour, and 550°C for 2 hours, the rest of the process is the same as in Example 1.

[0018] The operation steps for Comparative Example 1 are as follows: Step 1: Completely immerse the LFP electrode sheet (which has not been soaked in electrolyte) in deionized water and ultrasonically vibrate it for 20 minutes. Step 2: Remove the aluminum foil that has separated from the LFP coating and filter out the remaining LFP coating; Step 3: Place the filtered LFP coating in an 80℃ oven and bake for 2 hours. Then, ball mill the dried LFP coating at 400r / min intermittently for 6 hours, stopping for 5 minutes every 30 minutes. Step 4: The ball-milled LFP powder is calcined in a muffle furnace filled with nitrogen at 300°C for 1 hour, 450°C for 1 hour, and 550°C for 3 hours. Step 5: Cool the calcined powder in a dry environment, then remove and seal it.

[0019] The lithium content, carbon content, and difficulty of separating the coating from the aluminum foil were compared and tested in the three examples and the comparative examples. The specific data are shown in the table below: lithium content Carbon content Difficulty in separating the coating from the aluminum foil Example 1 4.1% 3% Separation begins after 10 minutes. Example 2 4.15% 3% Separation begins after 8 minutes Example 3 4.1% 3.4% Separation begins after 10 minutes. Comparative Example 1 4.0% 3.4% Difficult to separate, requires manual separation As shown in the table above, the lithium content of the recycled powders prepared in Examples 1-3 were 4.1%, 4.15%, and 4.1%, respectively, all significantly higher than the 4.0% of Comparative Example 1. Among them, Example 2 had the highest lithium content, reaching 4.15%. This improvement is due to the lithium replenishment effect of the alkaline solution in the process: the Li⁺ in the hydroxide can fill the lithium vacancies in the lithium iron phosphate lattice generated by storage or processing during soaking and calcination, while avoiding the loss of lithium elements caused by high-temperature volatilization or reaction with impurities in the traditional solid-state method. Ultimately, this ensures that the recycled material has an active ingredient content close to that of fresh lithium iron phosphate, laying the foundation for the subsequent production of high-performance lithium batteries. The impurity carbon in the lithium iron phosphate electrode mainly comes from the conductive agent added during the electrode preparation process. If the carbon content cannot be effectively controlled during the recycling process, excessive carbon will lead to increased internal resistance of the recycled material, decreased charge and discharge efficiency, and even safety hazards such as local overheating inside the battery. Comparative data shows that the carbon content of the recycled powder in Examples 1-2 was consistently controlled at 3%, lower than the 3.4% of Comparative Example 1; only Example 3, due to a shortened calcination time at 550℃, had a carbon content comparable to Comparative Example 1. This result indicates that the combined design of alkaline solution immersion and three-stage precise calcination in this process can effectively remove excess conductive carbon: the alkaline environment loosens the bond between carbon particles and lithium iron phosphate crystals, and the subsequent three-stage calcination at 300-550℃ further oxidizes and removes free carbon. Furthermore, by adjusting the calcination time, precise control of the carbon content can be achieved, ensuring that the recycled material retains the necessary conductive network to meet electron transport requirements while avoiding performance defects caused by excessive impurity carbon. In traditional lithium iron phosphate electrode recycling, Comparative Example 1 uses deionized water immersion and ultrasonic vibration, which fails to break the adhesion between the coating and the aluminum foil, making automatic separation of the coating difficult and requiring manual peeling, which is not only inefficient but also prone to aluminum foil damage and coating loss. This invention achieves automatic separation of the coating and aluminum foil in Examples 1-3 through the chemical assistance of an alkaline solution. The separation start-up times are 10 min, 8 min, and 10 min, respectively. Example 2, due to the increased concentration of the alkaline solution, exhibits the fastest separation speed, requiring only 8 min to initiate separation. The mechanism of the alkaline solution lies in the partial hydrolysis reaction of OH⁻ with the binder PVDF, disrupting its molecular chain structure and weakening the interfacial bonding between the coating and aluminum foil. Combined with the physical action of ultrasonic vibration, this achieves efficient separation. This optimization not only eliminates the manual peeling process, reducing the single-batch separation time to less than 10 min, but also reduces aluminum foil loss, lowering labor costs and material waste in industrial production. Considering the three performance indicators, Example 2 exhibits the best overall performance: highest lithium content, fastest separation speed, and lowest carbon content. The results further validated the adaptability of the process parameters. Appropriately increasing the hydroxide concentration in the alkaline solution can enhance the lithium replenishment effect and the hydrolysis efficiency of the binder. At the same time, the complete calcination time at 550℃ ensures that impurity carbon is fully removed, ultimately achieving synergistic optimization of high lithium content, low carbon content, and fast separation speed.This optimal parameter combination can provide clear process guidance for subsequent industrial production, helping the invention to be quickly applied in the recycling of decommissioned lithium iron phosphate electrodes. The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the specific details of the above embodiments. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solutions of the present invention, and these simple modifications all fall within the protection scope of the present invention. In addition, it should be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, the present invention will not describe the various possible combinations separately. Furthermore, various different embodiments of the present invention can also be arbitrarily combined, as long as they do not violate the spirit of the present invention, they should also be regarded as the content disclosed by the present invention.

Claims

1. A lithium supplement regeneration process for recycling lithium iron phosphate pole pieces, characterized in that: Includes the following steps: ​ Step 1: Dissolve lithium hydroxide and potassium hydroxide in water to prepare an alkaline solution; Step 2: Immerse the LFP electrode sheet that has not been soaked in electrolyte completely in the solution prepared in step 1, and soak for 3-20 minutes; Step 3: Separate the LFP paste layer from the aluminum foil using ultrasonic vibration, and then remove the aluminum foil; Step 4: After removing the separated LFP coating precipitate, bake and dry it, and then ball mill it to obtain LFP powder with a particle size between 0.1μm and 100μm; Step 5: The dried LFP powder is fed into a nitrogen-filled muffle furnace and baked in three stages at a temperature range of 300-550℃ for a total of 4-8 hours. After cooling, it is removed to obtain regenerated powder that can be used to remake lithium iron phosphate.

2. The lithium supplement regeneration process for recycling lithium iron phosphate pole pieces according to claim 1, characterized in that: In the first step, the alkaline solution further contains sodium hydroxide, and the mixing ratio of the hydroxide composed of lithium hydroxide, potassium hydroxide, and sodium hydroxide with water is 0.1%:99.9%-0.5%:99.5%.

3. The lithium supplement regeneration process for recycling lithium iron phosphate pole pieces according to claim 1, characterized in that: In the fourth step, the baking and drying temperature is 80°C, and the drying time is 2 hours.

4. The lithium supplement regeneration process for recycling lithium iron phosphate pole pieces according to claim 1, characterized in that: In the fourth step, the ball milling process is intermittent ball milling, with a ball milling speed of 400 r / min and a total ball milling time of 6 hours. During the ball milling process, the milling is stopped for 5 minutes every 30 minutes.

5. The lithium supplement regeneration process for recycling lithium iron phosphate pole pieces according to claim 1, characterized in that: In the fifth step, the specific parameters for the three-stage calcination are as follows: first, calcination at 300℃ for 1 hour, then calcination at 450℃ for 1 hour, and finally calcination at 550℃ for 2-3 hours.

6. The lithium supplement regeneration process for recycling lithium iron phosphate pole pieces according to claim 1, characterized in that: In the fifth step, the calcined regenerated powder is cooled in a dry environment and then sealed for storage.