Method for directly preparing secondary battery from waste lithium iron phosphate by ultrasonic repair

Abstract

The application introduces a method for directly preparing secondary batteries from waste lithium iron phosphate by ultrasonic repair, comprising the following steps: step S1, mixing a reducing agent, a lithium salt and a solvent to configure a repair solution; step S2, adding waste lithium iron phosphate powder into the repair solution and stirring to obtain a mixed solution; step S3, putting the mixed solution into an ultrasonic cell crusher for two-stage ultrasonic treatment; step S4, centrifuging and washing the solution after ultrasonic treatment; step S5, drying the solution after centrifugation in an oven to obtain repaired lithium iron phosphate particles; step S6, using the repaired lithium iron phosphate particles to prepare a positive electrode sheet; step S7, using a lithium sheet as a counter electrode, assembling a secondary battery together with the positive electrode sheet, an electrolyte and a separator. Through the above design, N2H4·H2O is used as a reducing agent, and Li + vacancies and Li / Fe anti-site defects in waste LiFePO4 are repaired in a short time by high-power ultrasonic technology, realizing rapid and low-energy consumption recovery of waste lithium iron phosphate.

Description

Technical Field

[0001] This invention belongs to the field of battery manufacturing, specifically relating to a method for directly preparing secondary batteries from waste lithium iron phosphate through ultrasonic repair. Background Technology

[0002] Lithium iron phosphate (LFP) batteries are widely used in new energy vehicles and energy storage power stations due to their advantages such as good thermal stability, high safety, long cycle life, and low cost. However, with the booming LFP battery market, the potential battery recycling problem is becoming increasingly serious. If retired batteries are not disposed of in a timely manner, they will cause serious resource waste and environmental pollution. Currently, the main methods for recycling waste LFP batteries are selective lithium leaching and direct regeneration.

[0003] Selective lithium leaching refers to the recovery of Li from waste lithium iron phosphate materials without completely destroying the crystal structure of lithium iron phosphate, while Fe and P are recovered in the form of FePO4. This method consumes less chemical reagents and has a lower recycling cost; however, it requires a large amount of acid and alkali reagents during the recycling process and easily generates a large amount of waste gas and wastewater that is harmful to human health.

[0004] The direct regeneration method mainly involves replenishing the missing active Li. + By repairing structural defects and restoring the electrochemical activity of the cathode material, the regenerated cathode material can be directly used to manufacture lithium-ion batteries. Direct regeneration eliminates the need for cumbersome metal element separation and purification processes, significantly reducing chemical reagent and energy consumption and maximizing economic efficiency. However, existing methods for preparing lithium iron phosphate are solid-phase methods, which require harsh reaction conditions, including prolonged nitrogen atmosphere even at atmospheric pressure. This significantly hinders commercial production. Therefore, developing a low-cost, high-efficiency, and easy-to-operate liquid-phase regeneration method is imperative.

[0005] Existing methods for recycling waste lithium iron phosphate (LFP) mainly include electrochemical methods and selective lithium leaching. For example, Chinese patent CN116315229A discloses a method for recovering lithium from waste lithium-ion batteries and co-repairing LFP materials. Its main steps include: pretreating the waste positive electrode sheet, then electrochemically performing constant current electrolysis between the pretreated positive electrode and the waste LFP positive electrode to repair the LFP material; the repaired material undergoes drying, ball milling, and calcination to finally obtain regenerated LFP positive electrode material. This method can regenerate waste LFP material through lithium replenishment and repair, thereby preparing new LFP electrode materials; and obtain useful materials such as iron phosphate as a byproduct after delithiation. However, its operation is complex, the yield is low, and it neglects the impact of antisite defects formed during cycling.

[0006] Selective leaching of lithium, such as the method for recycling waste lithium iron phosphate cathode materials disclosed in Chinese patent CN112429752A, mainly includes the following steps: Step S1, dissolving aluminum in the waste lithium iron phosphate cathode material with alkali and collecting the solid; Step S2, dissolving the solid from Step S1 with sulfuric acid, performing a first evaporation and concentration on the solution obtained from solid-liquid separation, cooling and crystallizing to obtain liquid and crystals; Step S3, performing a second evaporation and concentration on the liquid obtained from Step S2, performing solid-liquid separation to obtain liquid and solid, and removing impurities and carbonizing the solid; Step S4, performing a third evaporation and concentration on the liquid obtained from Step S3. Although this method can separate lithium, iron, and phosphorus from waste lithium iron phosphate materials, the process is complex and uses reagents such as sodium hydroxide and concentrated sulfuric acid, which can easily cause environmental pollution.

[0007] Currently, the main methods for remediating waste lithium iron phosphate are electrochemical methods and selective lithium leaching. However, both methods are complex to operate, energy-intensive, time-consuming, and cause significant environmental pollution. To address these issues, there is an urgent need to design a new method for remediating waste lithium iron phosphate. Summary of the Invention

[0008] The main methods for remediating waste lithium iron phosphate currently include electrochemical methods and selective lithium leaching. However, these two methods are complex to operate, energy-intensive, time-consuming, and cause significant environmental pollution. To address these issues, this application proposes a method for directly preparing secondary batteries from waste lithium iron phosphate through ultrasonic remediation, aiming to achieve rapid and low-energy recycling of waste lithium iron phosphate.

[0009] A method for directly preparing secondary batteries from waste lithium iron phosphate through ultrasonic repair includes the following steps:

[0010] Step S1: Mix the reducing agent, lithium salt, and solvent to prepare a repair solution;

[0011] Step S2: Add the waste lithium iron phosphate powder to the repair solution and stir to mix, thus obtaining a mixture;

[0012] Step S3: Place the well-mixed liquid into an ultrasonic device for two-stage ultrasonic treatment.

[0013] Step S4: Centrifuge and wash the sonicated solution with water.

[0014] Step S5: Place the centrifuged solution into an oven to dry, and obtain the repaired lithium iron phosphate particles;

[0015] Step S6: Prepare the positive electrode sheet using the repaired lithium iron phosphate particles;

[0016] Step S7: Use a lithium sheet as the counter electrode, and assemble it with the positive electrode, electrolyte, and separator to form a secondary battery.

[0017] Preferably, the reducing agent in step S1 is hydrazine hydrate, the lithium salt is lithium chloride, and the solvent is ethylene glycol.

[0018] Preferably, in the preliminary solution prepared from lithium chloride and ethylene glycol, Li + The concentration is 0.5–2.0 M.

[0019] Preferably, the amount of hydrazine hydrate added to the repair solution is 0.5 to 2.0 mL.

[0020] Preferably, in step S2, the mixing method is to stir at 500 rpm / min for 10 min at room temperature.

[0021] Preferably, the specific method of step S3 includes:

[0022] Step S301: Transfer the mixture to the chamber of the ultrasonic cell disruptor, insert the amplitude transformer into the mixture below 1 cm, and set the ultrasonic power to 500W.

[0023] Step S302: Place the 50mL beaker containing the mixture into the 500mL beaker containing tap water, and set the sonication process to two stages with a sonication time of 25min; then let it stand for 10min, and then sonicate for another 25min.

[0024] Preferably, the specific method of step S4 is as follows:

[0025] S401. After the second ultrasonic treatment, the mixture is centrifuged to separate the lithium iron phosphate particles.

[0026] S402. Next, wash repeatedly with deionized water and ethanol to remove residual lithium chloride and hydrazine hydrate on the surface of lithium iron phosphate particles.

[0027] Preferably, the specific method of step S5 is as follows: the lithium iron phosphate particles obtained in step S4 are placed in a vacuum drying oven at 60°C for 12 hours to dry, thereby obtaining the repaired dried lithium iron phosphate particles.

[0028] Preferably, the specific method of step S6 includes:

[0029] Step S601: Weigh lithium iron phosphate particles, conductive agent and binder in a mass ratio of 8:1:1 and add them to the ball mill jar;

[0030] Step S602: Add an appropriate amount of N-methylpyrrolidone and mix evenly to form an electrode slurry;

[0031] Step S603: Use a 120μm scraper to evenly spread the electrode slurry on the surface of the aluminum foil, and then put it into an 80℃ forced-air drying oven to dry for 8 hours. After it is completely dried, the positive electrode sheet is obtained.

[0032] Preferably, the specific method of step S7 includes:

[0033] Step S701: Compact the positive electrode sheet using a roller press, and cut the positive electrode sheet into positive electrode round sheets with a diameter of 14mm using a punching machine. Place the cut positive electrode round sheets into a 60℃ vacuum drying oven and dry for 12 hours for later use.

[0034] Step S702: At room temperature, ethylene carbonate and diethyl carbonate are mixed at a mass ratio of 1:1, and LiPF6 with a concentration of 1 mol / L is added. After thorough mixing, the mixture is allowed to stand for 24 hours to obtain the electrolyte.

[0035] Step S703: The ceramic-coated polyethylene material is punched into a disc with a diameter of 16 mm and transferred to a vacuum drying oven at 55°C for 24 h to obtain a diaphragm.

[0036] Step S704: Use the lithium sheet as the counter electrode, and assemble it with the electrolyte obtained in step S702, the positive electrode obtained in step S6, and the separator obtained in step S703 to form a secondary battery.

[0037] The advantages and effects of this application are as follows:

[0038] 1. This application discloses a method for directly preparing secondary batteries from waste lithium iron phosphate through ultrasonic regeneration. The method utilizes a direct regeneration process, employing N2H4·H2O as a reducing agent, and employs high-power ultrasonic technology to repair the Li in waste lithium iron phosphate in a relatively short time. + Compared to conventional hydrothermal and selective lithium leaching methods, ultrasonic methods for vacancy defects and Li / Fe antisite defects require less time, consume less energy, can be carried out at room temperature, greatly improve recycling efficiency, and result in superior performance of the repaired cathode material.

[0039] 2. This application presents a method for directly preparing secondary batteries from waste lithium iron phosphate through ultrasonic repair. It utilizes the local high temperature, high pressure and strong shock wave jet generated by the collapse of ultrasonic cavitation bubbles to provide a very special physicochemical environment for repairing waste lithium iron phosphate, thereby achieving the effect of rapid and efficient repair of waste lithium iron phosphate. It also has the advantages of simple operation, short reaction time and low energy consumption.

[0040] 3. This application presents a method for directly preparing secondary batteries from waste lithium iron phosphate through ultrasonic repair, which repairs Li in waste lithium iron phosphate through ultrasonic reaction. +Vacancies and Li / Fe antisite defects can be eliminated without short-time annealing or cumbersome metal element separation and purification processes. This significantly reduces chemical reagent and energy consumption, thereby greatly reducing energy consumption, simplifying the recycling process, and maximizing economic benefits.

[0041] The above description is only an overview of the technical solution of this application. In order to better understand the technical means of this application and implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of this application more obvious and understandable, the preferred embodiments of this application are described in detail below with reference to the accompanying drawings.

[0042] The above and other objects, advantages and features of this application will become more apparent to those skilled in the art from the following detailed description of specific embodiments in conjunction with the accompanying drawings. Attached Figure Description

[0043] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. In all drawings, similar elements or parts are generally identified by similar reference numerals. In the drawings, the elements or parts are not necessarily drawn to scale.

[0044] Figure 1 A flowchart of a method for directly preparing secondary batteries from waste lithium iron phosphate through ultrasonic repair provided in this application;

[0045] Figure 2 XRD patterns of lithium iron phosphate before and after remediation provided for this application;

[0046] Figure 3 HRTEM image of waste lithium iron phosphate provided in this application;

[0047] Figure 4 HRTEM images of lithium iron phosphate after ultrasonic repair provided in this application. Detailed Implementation

[0048] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. In the following description, specific details such as specific configurations and components are provided merely to help fully understand the embodiments of this application. Therefore, those skilled in the art should understand that various changes and modifications can be made to the embodiments described herein without departing from the scope and spirit of this application. In addition, for clarity and brevity, descriptions of known functions and structures are omitted in the embodiments.

[0049] It should be understood that the phrase "an embodiment" or "this embodiment" throughout the specification means that a specific feature, structure, or characteristic related to the embodiment is included in at least one embodiment of this application. Therefore, "an embodiment" or "this embodiment" appearing throughout the specification does not necessarily refer to the same embodiment. Furthermore, these specific features, structures, or characteristics can be combined in any suitable manner in one or more embodiments.

[0050] Furthermore, reference numerals and / or letters may be repeated in different examples within this application. Such repetition is for the purpose of simplification and clarity and does not in itself indicate a relationship between the various embodiments and / or settings discussed.

[0051] In this article, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can mean: A exists alone, B exists alone, and A and B exist simultaneously. The term " / and" in this article describes another type of relationship between related objects, indicating that two relationships can exist. For example, A / and B can mean: A exists alone, and A and B exist alone. In addition, the character " / " in this article generally indicates that the related objects before and after it are in an "or" relationship.

[0052] In this article, the term "at least one" is merely a description of the relationship between related objects, indicating that there can be three relationships. For example, "at least one of A and B" can mean: A exists alone, A and B exist simultaneously, or B exists alone.

[0053] It should also be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion.

[0054] Example 1

[0055] This embodiment mainly introduces the first method for directly preparing secondary batteries from waste lithium iron phosphate through ultrasonic repair. Please refer to [link / reference]. Figure 1 Specifically, it includes:

[0056] Step S1: Mix the reducing agent, lithium salt, and solvent to prepare a repair solution;

[0057] Step S2: Add the waste lithium iron phosphate powder to the repair solution and stir to mix, thus obtaining a mixture;

[0058] Step S3: Place the well-mixed liquid into an ultrasonic device for two-stage ultrasonic treatment.

[0059] Step S4: Centrifuge and wash the sonicated solution with water.

[0060] Step S5: Place the centrifuged solution into an oven to dry, and obtain the repaired lithium iron phosphate particles;

[0061] Step S6: Prepare the positive electrode sheet using the repaired lithium iron phosphate particles;

[0062] Step S7: Use a lithium sheet as the counter electrode, and assemble it with the positive electrode, electrolyte, and separator to form a secondary battery.

[0063] Furthermore, in step S1, the method for preparing the repair solution is as follows: first, 1.2717 LiCl and 30 mL of 50 vol% ethylene glycol solution are mixed to prepare a LiCl solution. + A 1M solution is initially prepared, and then 1.5 mL of N2H4·H2O is gradually added. The N2H4·H2O is added in step S2.

[0064] Furthermore, the specific method of step S2 is as follows: weigh 1g of waste lithium iron phosphate powder and place it in the prepared preliminary solution. Under the action of ultrasound, the powder is completely dispersed. Then, while stirring, 1.5mL of N2H4·H2O is added dropwise to the solution. Then, the mixture is stirred at 500rpm / min for 10min at room temperature to obtain a mixed solution.

[0065] Furthermore, the specific method for step S3 is as follows:

[0066] Step S301: Transfer the mixture to the chamber of the ultrasonic cell disruptor, insert the amplitude transformer into the mixture below 1 cm, and set the ultrasonic power to 500W.

[0067] Step S302: In order to prevent the temperature from rising sharply during the ultrasound process, place the 50mL beaker containing the mixture into the 500mL beaker containing tap water, and set the ultrasound process to two stages with an ultrasound time of 25min; then let it stand for 10min, and then ultrasound for another 25min.

[0068] Furthermore, the specific method for step S4 is as follows:

[0069] S401. After the second ultrasonic treatment, the mixture is centrifuged to separate the lithium iron phosphate particles.

[0070] S402. Next, wash repeatedly with deionized water and ethanol to remove residual lithium chloride and hydrazine hydrate on the surface of lithium iron phosphate particles.

[0071] Furthermore, the specific method of step S5 is as follows: the lithium iron phosphate particles obtained in step S4 are placed in a vacuum drying oven at 60°C for 12 hours to dry, thereby obtaining the repaired dried lithium iron phosphate particles. Please refer to the XRD pattern of the lithium iron phosphate before repair. Figure 2 Please refer to the HRTEM image of waste lithium iron phosphate. Figure 3 Please refer to the HRTEM images of lithium iron phosphate after ultrasound repair. Figure 4 .

[0072] Furthermore, the specific method of step S6 includes:

[0073] Step S601: Weigh lithium iron phosphate particles, conductive agent (conductive carbon black, SP) and binder (polyvinylidene fluoride, PVDF) in a mass ratio of 8:1:1 and add them to the ball mill jar.

[0074] Step S602: Add an appropriate amount of solvent (N-methylpyrrolidone, NMP) to ensure the viscosity of the electrode paste. All substances are uniformly mixed to form a fluid paste.

[0075] Step S603: Use a 120μm scraper to evenly spread the electrode slurry on the surface of the aluminum foil, and then put it into an 80℃ forced-air drying oven to dry for 8 hours. After it is completely dried, the positive electrode sheet is obtained.

[0076] Furthermore, the specific method of step S7 includes:

[0077] Step S701: Compact the positive electrode sheet using a roller press, and cut the positive electrode sheet into positive electrode round sheets with a diameter of 14mm using a punching machine. Place the cut positive electrode round sheets into a 60℃ vacuum drying oven and dry for 12 hours for later use.

[0078] Step S702: At room temperature, ethylene carbonate and diethyl carbonate are mixed at a mass ratio of 1:1, and LiPF6 with a concentration of 1 mol / L is added. After thorough mixing, the mixture is allowed to stand for 24 hours to obtain the electrolyte.

[0079] Step S703: The ceramic-coated polyethylene material is punched into a disc with a diameter of 16 mm and transferred to a vacuum drying oven at 55°C for 24 h to obtain a diaphragm.

[0080] Step S704: In a glove box where the water and oxygen content are both less than 0.1 ppm, a lithium sheet is used as the counter electrode, and it is assembled with the electrolyte obtained in step S702, the positive electrode obtained in step S6, and the separator obtained in step S703 to form a secondary battery.

[0081] The method for repairing waste lithium iron phosphate is a direct regeneration method. This method does not require a cumbersome metal element separation and purification process, which can significantly reduce the consumption of chemical reagents and energy, and maximize economic benefits.

[0082] Example 2

[0083] Based on Example 1, this example mainly introduces a second method for directly preparing secondary batteries from waste lithium iron phosphate through ultrasonic repair, specifically including:

[0084] Step S1: Mix the reducing agent, lithium salt, and solvent to prepare a repair solution;

[0085] Step S2: Add the waste lithium iron phosphate powder to the repair solution and stir to mix, thus obtaining a mixture;

[0086] Step S3: Place the well-mixed liquid into an ultrasonic device for two-stage ultrasonic treatment.

[0087] Step S4: Centrifuge and wash the sonicated solution with water.

[0088] Step S5: Place the centrifuged solution into an oven to dry, and obtain the repaired lithium iron phosphate particles;

[0089] Step S6: Prepare the positive electrode sheet using the repaired lithium iron phosphate particles;

[0090] Step S7: Use a lithium sheet as the counter electrode, and assemble it with the positive electrode, electrolyte, and separator to form a secondary battery.

[0091] Furthermore, in step S1, the method for preparing the repair solution is as follows: first, 0.763g of LiCl and 30mL of 50vol% ethylene glycol solution are mixed to prepare LiCl solution. + A 0.6M solution is initially prepared, and then 1 mL of N2H4·H2O is gradually added. The N2H4·H2O is added in step S2.

[0092] Furthermore, the specific method of step S2 is as follows: weigh 1g of waste lithium iron phosphate powder and place it in the prepared preliminary solution. Under the action of ultrasound, the powder is completely dispersed. Then, while stirring, 1mL of N2H4·H2O is added dropwise to the solution. Then, the mixture is stirred at 500rpm / min for 10min at room temperature to obtain a mixed solution.

[0093] Furthermore, the specific method for step S3 is as follows:

[0094] Step S301: Transfer the mixture to the chamber of the ultrasonic cell disruptor, insert the amplitude transformer into the mixture below 1 cm, and set the ultrasonic power to 500W.

[0095] Step S302: In order to prevent the temperature from rising sharply during the ultrasound process, place the 50mL beaker containing the mixture into the 500mL beaker containing tap water, and set the ultrasound process to two stages with an ultrasound time of 25min; then let it stand for 10min, and then ultrasound for another 25min.

[0096] Furthermore, the specific method for step S4 is as follows:

[0097] S401. After the second ultrasonic treatment, the mixture is centrifuged to separate the lithium iron phosphate particles.

[0098] S402. Next, wash repeatedly with deionized water and ethanol to remove residual lithium chloride and hydrazine hydrate on the surface of lithium iron phosphate particles.

[0099] Furthermore, the specific method of step S5 is as follows: the lithium iron phosphate particles obtained in step S4 are placed in a vacuum drying oven at 60°C for 12 hours to dry, thereby obtaining the repaired dried lithium iron phosphate particles.

[0100] Furthermore, the specific method of step S6 includes:

[0101] Step S601: Weigh lithium iron phosphate particles, conductive agent (conductive carbon black, SP) and binder (polyvinylidene fluoride, PVDF) in a mass ratio of 8:1:1 and add them to the ball mill jar.

[0102] Step S602: Add an appropriate amount of solvent (N-methylpyrrolidone, NMP) to ensure the viscosity of the electrode paste. All substances are uniformly mixed to form a fluid paste.

[0103] Step S603: Use a 120μm scraper to evenly spread the electrode slurry on the surface of the aluminum foil, and then put it into an 80℃ forced-air drying oven to dry for 8 hours. After it is completely dried, the positive electrode sheet is obtained.

[0104] Furthermore, the specific method of step S7 includes:

[0105] Step S701: Compact the positive electrode sheet using a roller press, and cut the positive electrode sheet into positive electrode round sheets with a diameter of 14mm using a punching machine. Place the cut positive electrode round sheets into a 60℃ vacuum drying oven and dry for 12 hours for later use.

[0106] Step S702: At room temperature, ethylene carbonate and diethyl carbonate are mixed at a mass ratio of 1:1, and LiPF6 with a concentration of 1 mol / L is added. After thorough mixing, the mixture is allowed to stand for 24 hours to obtain the electrolyte.

[0107] Step S703: The ceramic-coated polyethylene material is punched into a disc with a diameter of 16 mm and transferred to a vacuum drying oven at 55°C for 24 h to obtain a diaphragm.

[0108] Step S704: In a glove box where the water and oxygen content are both less than 0.1 ppm, a lithium sheet is used as the counter electrode, and it is assembled with the electrolyte obtained in step S702, the positive electrode obtained in step S6, and the separator obtained in step S703 to form a secondary battery.

[0109] This application presents a method for directly preparing secondary batteries from waste lithium iron phosphate through ultrasonic regeneration. Using N2H4·H2O as a reducing agent, a high-power ultrasonic process is employed to regenerate the Li in waste lithium iron phosphate in a relatively short time. + Compared to conventional hydrothermal and selective lithium leaching methods, the two-stage ultrasonic method of this application requires less time to address vacancy defects and Li / Fe antisite defects, significantly improving recovery efficiency and resulting in superior performance of the repaired cathode material.

[0110] Example 3

[0111] Based on Example 1, this example mainly introduces a third method for directly preparing secondary batteries from waste lithium iron phosphate through ultrasonic repair, specifically including:

[0112] Step S1: Mix the reducing agent, lithium salt, and solvent to prepare a repair solution;

[0113] Step S2: Add the waste lithium iron phosphate powder to the repair solution and stir to mix, thus obtaining a mixture;

[0114] Step S3: Place the well-mixed liquid into an ultrasonic device for two-stage ultrasonic treatment.

[0115] Step S4: Centrifuge and wash the sonicated solution with water.

[0116] Step S5: Place the centrifuged solution into an oven to dry, and obtain the repaired lithium iron phosphate particles;

[0117] Step S6: Prepare the positive electrode sheet using the repaired lithium iron phosphate particles;

[0118] Step S7: Use a lithium sheet as the counter electrode, and assemble it with the positive electrode, electrolyte, and separator to form a secondary battery.

[0119] Furthermore, in step S1, the preparation method of the repair solution is as follows: first, 1.2717 g of LiCl and 30 mL of 50 vol% ethylene glycol solution are prepared to form LiCl solution. + A 1M solution is initially prepared, and then 1 mL of N2H4·H2O is gradually added. The N2H4·H2O is added in step S2.

[0120] Furthermore, the specific method of step S2 is as follows: weigh 1g of waste lithium iron phosphate powder and place it in the prepared preliminary solution. Under the action of ultrasound, the powder is completely dispersed. Then, while stirring, 1.mL of N2H4·H2O is added dropwise to the solution. Then, the mixture is stirred at 500rpm / min for 10min at room temperature to obtain a mixed solution.

[0121] Furthermore, the specific method for step S3 is as follows:

[0122] Step S301: Transfer the mixture to the chamber of the ultrasonic cell disruptor, insert the amplitude transformer into the mixture below 1 cm, and set the ultrasonic power to 500W.

[0123] Step S302: In order to prevent the temperature from rising sharply during the ultrasound process, place the 50mL beaker containing the mixture into the 500mL beaker containing tap water, and set the ultrasound process to two stages with an ultrasound time of 25min; then let it stand for 10min, and then ultrasound for another 25min.

[0124] Furthermore, the specific method for step S4 is as follows:

[0125] S401. After the second ultrasonic treatment, the mixture is centrifuged to separate the lithium iron phosphate particles.

[0126] S402. Next, wash repeatedly with deionized water and ethanol to remove residual lithium chloride and hydrazine hydrate on the surface of lithium iron phosphate particles.

[0127] Furthermore, the specific method of step S5 is as follows: place the lithium iron phosphate particles obtained in step S4 into a vacuum drying oven and dry them at 60°C for 12 hours to obtain the repaired dried lithium iron phosphate particles.

[0128] Furthermore, the specific method of step S6 includes:

[0129] Step S601: Weigh lithium iron phosphate particles, conductive agent (conductive carbon black, SP) and binder (polyvinylidene fluoride, PVDF) in a mass ratio of 8:1:1 and add them to the ball mill jar.

[0130] Step S602: Add an appropriate amount of solvent (N-methylpyrrolidone, NMP) to ensure the viscosity of the electrode paste. All substances are uniformly mixed to form a fluid paste.

[0131] Step S603: Use a 120μm scraper to evenly spread the electrode slurry on the surface of the aluminum foil, and then put it into an 80℃ forced-air drying oven to dry for 8 hours. After it is completely dried, the positive electrode sheet is obtained.

[0132] Furthermore, the specific method of step S7 includes:

[0133] Step S701: Compact the positive electrode sheet using a roller press, and cut the positive electrode sheet into positive electrode round sheets with a diameter of 14mm using a punching machine. Place the cut positive electrode round sheets into a 60℃ vacuum drying oven and dry for 12 hours for later use.

[0134] Step S702: At room temperature, ethylene carbonate and diethyl carbonate are mixed at a mass ratio of 1:1, and LiPF6 with a concentration of 1 mol / L is added. After thorough mixing, the mixture is allowed to stand for 24 hours to obtain the electrolyte.

[0135] Step S703: The ceramic-coated polyethylene material is punched into a disc with a diameter of 16 mm and transferred to a vacuum drying oven at 55°C for 24 h to obtain a diaphragm.

[0136] Step S704: In a glove box where the water and oxygen content are both less than 0.1 ppm, a lithium sheet is used as the counter electrode, and it is assembled with the electrolyte obtained in step S702, the positive electrode obtained in step S6, and the separator obtained in step S703 to form a secondary battery.

[0137] This application presents a method for directly preparing secondary batteries from waste lithium iron phosphate through ultrasonic repair. It utilizes the localized high temperature, high pressure, and strong shock wave jet generated by the collapse of ultrasonic cavitation bubbles to provide a very special physicochemical environment for repairing waste lithium iron phosphate, thereby achieving rapid and efficient repair of waste lithium iron phosphate. Furthermore, it has the advantages of simple operation and short reaction time.

[0138] Example 4

[0139] Based on Example 1, this example mainly introduces the fourth method for directly preparing secondary batteries from waste lithium iron phosphate through ultrasonic repair, specifically including:

[0140] Step S1: Mix the reducing agent, lithium salt, and solvent to prepare a repair solution;

[0141] Step S2: Add the waste lithium iron phosphate powder to the repair solution and stir to mix, thus obtaining a mixture;

[0142] Step S3: Place the well-mixed liquid into an ultrasonic device for two-stage ultrasonic treatment.

[0143] Step S4: Centrifuge and wash the sonicated solution with water.

[0144] Step S5: Place the centrifuged solution into an oven to dry, and obtain the repaired lithium iron phosphate particles;

[0145] Step S6: Prepare the positive electrode sheet using the repaired lithium iron phosphate particles;

[0146] Step S7: Use a lithium sheet as the counter electrode, and assemble it with the positive electrode, electrolyte, and separator to form a secondary battery.

[0147] Furthermore, in step S1, the preparation method of the repair solution is as follows: first, 1.9076g of LiCl and 30mL of 50vol% ethylene glycol solution are prepared to form LiCl solution. + A 1.5M solution is initially prepared, and then 1.5 mL of N2H4·H2O is gradually added. The N2H4·H2O needs to be added in step S2.

[0148] Furthermore, the specific method of step S2 is as follows: weigh 1g of waste lithium iron phosphate powder and place it in the prepared preliminary solution. Under the action of ultrasound, the powder is completely dispersed. Then, while stirring, 1.5mL of N2H4·H2O is added dropwise to the solution. Then, the mixture is stirred at 500rpm / min for 10min at room temperature to obtain a mixed solution.

[0149] Furthermore, the specific method for step S3 is as follows:

[0150] Step S301: Transfer the mixture to the chamber of the ultrasonic cell disruptor, insert the amplitude transformer into the mixture below 1 cm, and set the ultrasonic power to 500W.

[0151] Step S302: In order to prevent the temperature from rising sharply during the ultrasound process, place the 50mL beaker containing the mixture into the 500mL beaker containing tap water, and set the ultrasound process to two stages with an ultrasound time of 25min; then let it stand for 10min, and then ultrasound for another 25min.

[0152] Furthermore, the specific method for step S4 is as follows:

[0153] S401. After the second ultrasonic treatment, the mixture is centrifuged to separate the lithium iron phosphate particles.

[0154] S402. Next, wash repeatedly with deionized water and ethanol to remove residual lithium chloride and hydrazine hydrate on the surface of lithium iron phosphate particles.

[0155] Furthermore, the specific method of step S5 is as follows: the lithium iron phosphate particles obtained in step S4 are placed in a vacuum drying oven at 60°C for 12 hours to dry, thereby obtaining the repaired dried lithium iron phosphate particles.

[0156] Furthermore, the specific method of step S6 includes:

[0157] Step S601: Weigh lithium iron phosphate particles, conductive agent (conductive carbon black, SP) and binder (polyvinylidene fluoride, PVDF) in a mass ratio of 8:1:1 and add them to the ball mill jar.

[0158] Step S602: Add an appropriate amount of solvent (N-methylpyrrolidone, NMP) to ensure the viscosity of the electrode paste. All substances are uniformly mixed to form a fluid paste.

[0159] Step S603: Use a 120μm scraper to evenly spread the electrode slurry on the surface of the aluminum foil, and then put it into an 80℃ forced-air drying oven to dry for 8 hours. After it is completely dried, the positive electrode sheet is obtained.

[0160] Furthermore, the specific method of step S7 includes:

[0161] Step S701: Compact the positive electrode sheet using a roller press, and cut the positive electrode sheet into positive electrode round sheets with a diameter of 14mm using a punching machine. Place the cut positive electrode round sheets into a 60℃ vacuum drying oven and dry for 12 hours for later use.

[0162] Step S702: At room temperature, ethylene carbonate and diethyl carbonate are mixed at a mass ratio of 1:1, and LiPF6 with a concentration of 1 mol / L is added. After thorough mixing, the mixture is allowed to stand for 24 hours to obtain the electrolyte.

[0163] Step S703: The ceramic-coated polyethylene material is punched into a disc with a diameter of 16 mm and transferred to a vacuum drying oven at 55°C for 24 h to obtain a diaphragm.

[0164] Step S704: In a glove box where the water and oxygen content are both less than 0.1 ppm, a lithium sheet is used as the counter electrode, and it is assembled with the electrolyte obtained in step S702, the positive electrode obtained in step S6, and the separator obtained in step S703 to form a secondary battery.

[0165] This application presents a method for directly preparing secondary batteries from waste lithium iron phosphate through ultrasonic remediation, which uses ultrasonic reaction to repair Li in waste lithium iron phosphate. + Vacancies and Li / Fe antisite defects can be eliminated without short-time annealing or cumbersome metal element separation and purification processes. This significantly reduces chemical reagent and energy consumption, greatly lowers energy consumption, simplifies the recycling process, and maximizes economic benefits.

[0166] Example 5

[0167] Based on Example 1, this example mainly introduces a method for directly preparing secondary batteries from waste lithium iron phosphate, specifically including:

[0168] Step S1: Prepare positive electrode sheets using waste lithium iron phosphate particles;

[0169] Step S2: Using a lithium sheet as the counter electrode, assemble it with the positive electrode, electrolyte, and separator to form a secondary battery.

[0170] Furthermore, the specific method of step S1 includes:

[0171] Step S601: Weigh waste lithium iron phosphate particles, conductive agent (conductive carbon black, SP) and binder (polyvinylidene fluoride, PVDF) in a mass ratio of 8:1:1 and add them to the ball mill jar.

[0172] Step S602: Add an appropriate amount of solvent (N-methylpyrrolidone, NMP) to ensure the viscosity of the electrode paste. All substances are uniformly mixed to form a fluid paste.

[0173] Step S603: Use a 120μm scraper to evenly spread the electrode slurry on the surface of the aluminum foil, and then put it into an 80℃ forced-air drying oven to dry for 8 hours. After it is completely dried, the positive electrode sheet is obtained.

[0174] Furthermore, the specific method of step S2 includes:

[0175] Step S701: Compact the positive electrode sheet using a roller press, and cut the positive electrode sheet into positive electrode round sheets with a diameter of 14mm using a punching machine. Place the cut positive electrode round sheets into a 60℃ vacuum drying oven and dry for 12 hours for later use.

[0176] Step S702: At room temperature, ethylene carbonate and diethyl carbonate are mixed at a mass ratio of 1:1, and LiPF6 with a concentration of 1 mol / L is added. After thorough mixing, the mixture is allowed to stand for 24 hours to obtain the electrolyte.

[0177] Step S703: The ceramic-coated polyethylene material is punched into a disc with a diameter of 16 mm and transferred to a vacuum drying oven at 55°C for 24 h to obtain a diaphragm.

[0178] Step S704: In a glove box where the water and oxygen content are both less than 0.1 ppm, a lithium sheet is used as the counter electrode, and it is assembled with the electrolyte obtained in step S702, the positive electrode obtained in step S6, and the separator obtained in step S703 to form a secondary battery.

[0179] This application presents a method for directly preparing secondary batteries from waste lithium iron phosphate through ultrasonic remediation, which uses ultrasonic reaction to repair Li in waste lithium iron phosphate. + Vacancies and Li / Fe antisite defects can be eliminated without short-time annealing or cumbersome metal element separation and purification processes. This significantly reduces chemical reagent and energy consumption, greatly lowers energy consumption, simplifies the recycling process, and maximizes economic benefits.

[0180] Example 6

[0181] Based on Examples 1-5, this example mainly introduces the test results of a method for directly preparing secondary batteries from waste lithium iron phosphate using ultrasonic repair designed in this application.

[0182] The secondary batteries in Examples 1-4 were tested using an Arbin BT2000 testing system. The charge / discharge voltage range was 2.5–4.2V, and the batteries were cycled 100 times at 1C (25°C) to obtain the initial coulombic efficiency and cycle performance.

[0183] In addition, the high-rate performance of the secondary batteries in Examples 1-4 was tested using an Arbin BT2000 testing system, with a voltage range of 2.5–4.2V and a current density of 0.2C–5C. The test results are shown in Table 1.

[0184] Table 1. Test results of secondary batteries tested by the Arbin BT2000 test system.

[0185]

[0186]

[0187] It can be seen that S-LFP (waste lithium iron phosphate) retains only 87% of its capacity after 100 cycles at 1C, while LiFePO4 regenerated by ultrasonication generally retains over 90% of its capacity after 100 cycles at 1C. RLFP (restored lithium iron phosphate) - 1.0M / 1.5mL still retains 135.1 mAh·g after 100 cycles at this current. -1 The discharge specific capacity retention rate is as high as 97%. This demonstrates that LiFePO4 regenerated via high-power ultrasound exhibits superior cycling performance compared to conventional liquid-phase methods. This result is primarily attributed to the high activation energy provided by the localized high temperature and pressure generated by the collapse of ultrasonic cavitation bubbles, which, combined with the action of the reducing agent, promotes the regeneration of LiFePO4 in the solution. + Embedding into the FePO4 lattice reduces Li / Fe antisite defects (2.52%). The reduction in antisite defects significantly enhances lithium-ion migration kinetics, thereby improving electrochemical performance.

[0188] The above description is merely a preferred embodiment of the present invention and does not limit the scope of protection of the present invention. For those skilled in the art, the present invention can have various modifications and variations. Any changes, modifications, substitutions, integrations, and parameter alterations to these embodiments within the spirit and principles of the present invention, achieved through conventional substitutions or by achieving the same function without departing from the principles and spirit of the present invention, fall within the scope of protection of the present invention.

Claims

1. A method for directly preparing secondary batteries from waste lithium iron phosphate through ultrasonic repair, characterized in that, Includes the following steps: Step S1: Mix the reducing agent, lithium salt, and solvent to prepare a repair solution. The reducing agent is hydrazine hydrate, the lithium salt is lithium chloride, and the solvent is ethylene glycol. In the preliminary solution prepared by lithium chloride and ethylene glycol, the Li+ concentration is 0.5-2.0M, and the amount of hydrazine hydrate added to the repair solution is 0.5-2.0mL. Step S2: Add the waste lithium iron phosphate powder to the repair solution and stir to mix, thus obtaining a mixture; Step S3: Place the well-mixed liquid into an ultrasonic device for two-stage ultrasonic treatment. The specific method includes: Step S301: Transfer the mixture to the chamber of the ultrasonic cell disruptor, insert the amplitude transformer into the mixture below 1 cm, and set the ultrasonic power to 500W. Step S302: Place the 50mL beaker containing the mixture into the 500mL beaker containing tap water, and set the sonication process to two stages with a sonication time of 25min; then let it stand for 10min, and then sonicate for another 25min. Step S4: After sonication, the solution is centrifuged and washed with water. The specific method is as follows: S401. After the second ultrasonic treatment, the mixture is centrifuged to separate the lithium iron phosphate particles. S402. Next, wash repeatedly with deionized water and ethanol to remove residual lithium chloride and hydrazine hydrate on the surface of lithium iron phosphate particles. Step S5: Place the centrifuged solution into an oven to dry, and obtain the repaired lithium iron phosphate particles; Step S6: Prepare the positive electrode sheet using the repaired lithium iron phosphate particles; Step S7: Use a lithium sheet as the counter electrode, and assemble it with the positive electrode, electrolyte, and separator to form a secondary battery.

2. The method for directly preparing secondary batteries from waste lithium iron phosphate via ultrasonic repair according to claim 1, characterized in that, In step S2, the mixing method is to stir at 500 rpm for 10 minutes at room temperature.

3. The method for directly preparing secondary batteries from waste lithium iron phosphate via ultrasonic repair according to claim 1, characterized in that, The specific method of step S5 is as follows: place the lithium iron phosphate particles obtained in step S4 into a vacuum drying oven at 60°C for 12 hours to dry them, and obtain the repaired dried lithium iron phosphate particles.

4. The method for directly preparing secondary batteries from waste lithium iron phosphate through ultrasonic repair according to any one of claims 1, 2, or 3, characterized in that, The specific method of step S6 includes: Step S601: Weigh lithium iron phosphate particles, conductive agent and binder in a mass ratio of 8:1:1 and add them to the ball mill jar; Step S602: Add an appropriate amount of N Methylpyrrolidone is uniformly mixed to form an electrode paste; Step S603: Use a 120μm scraper to evenly spread the electrode slurry on the surface of the aluminum foil, and then put it into an 80℃ forced-air drying oven to dry for 8 hours. After it is completely dried, the positive electrode sheet is obtained.

5. The method for directly preparing secondary batteries from waste lithium iron phosphate via ultrasonic repair according to any one of claims 1, 2, or 3, characterized in that, The specific method of step S7 includes: Step S701: Compact the positive electrode sheet using a roller press, and cut the positive electrode sheet into positive electrode round sheets with a diameter of 14mm using a punching machine. Place the cut positive electrode round sheets into a 60℃ vacuum drying oven and dry for 12 hours for later use. Step S702: At room temperature, ethylene carbonate and diethyl carbonate are mixed at a mass ratio of 1:1, and LiPF6 with a concentration of 1 mol / L is added. After thorough mixing, the mixture is allowed to stand for 24 hours to obtain the electrolyte. Step S703: The ceramic-coated polyethylene material is punched into a disc with a diameter of 16 mm and transferred to a vacuum drying oven at 55°C for 24 h to obtain a diaphragm. Step S704: Use the lithium sheet as the counter electrode, and assemble it with the electrolyte obtained in step S702, the positive electrode obtained in step S6, and the separator obtained in step S703 to form a secondary battery.

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