Lithium self-supply regenerated positive electrode material in retired lithium battery and preparation method of lithium self-supply regenerated positive electrode material

Abstract

The invention relates to the technical field of lithium batteries, in particular to a lithium self-supply regenerated positive electrode material in a decommissioned lithium battery and a preparation method thereof.The positive electrode material is formed through nitrogen doping modification and repair regeneration, and the preparation method comprises the following steps that the decommissioned lithium battery is disassembled, a separated graphite pole piece is treated, and a lithium recovery solution is obtained; adding dopamine hydrochloride into the lithium recovery liquid, dispersing the decommissioned positive electrode material, and coating the positive electrode material with dopamine to obtain an endogenous lithium supplement and dopamine polymerization coated positive electrode material; the preparation method comprises the following steps: dispersing an endogenous lithium supplement and dopamine polymerization coated positive electrode material through spray drying, carrying out multi-stage rapid annealing treatment, reconstructing a crystal structure of the waste positive electrode material and decomposing polydopamine to obtain a regenerated positive electrode material, and the preparation method can be directly used for direct modification regeneration of the waste positive electrode material. The treatment process is simple, the safety is high, and full recycling of lithium resources can be achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium batteries, and in particular to a positive electrode material for lithium self-supply regeneration in retired lithium batteries and a preparation method thereof. Background Art

[0002] Lithium-ion batteries are widely used in electric vehicles, energy storage and other fields, but their service life is short, which leads to a large number of batteries entering the retirement stage quickly. If the used batteries can be recycled efficiently, in terms of environmental protection, it can prevent the heavy metals and organic matter in the retired batteries from polluting the ecological environment; in terms of resource security, it can effectively alleviate the supply pressure of key metal resources such as lithium; in terms of economic benefits, it can improve the recycling value of resources.

[0003] At present, the recycling of retired lithium-ion batteries mainly includes pyrometallurgical process and hydrometallurgical process. The pyrometallurgical process is mature, but it still has prominent problems such as high energy consumption, low resource utilization and serious emission of harmful gases; hydrometallurgical technology extracts lithium resources from waste batteries from black powder materials through acid / alkali, and finally recovers them in the form of inorganic lithium salts such as lithium carbonate or lithium hydroxide. Although this technology has a high recovery rate, its process route is complicated, involving multiple steps of leaching and separation processes, and requires a large amount of inorganic acid or organic reagents. Therefore, wastewater discharge and secondary pollution are serious problems.

[0004] In addition, the conventional method for repairing waste materials is to mix lithium salts and waste materials and regenerate them through a high-temperature solid-phase sintering process. However, for severely degraded retired materials, this process usually requires sintering at a high temperature of more than 800°C for more than 10 hours to achieve complete regeneration of the materials. High-temperature solid-phase sintering is a solid-solid contact reaction process. The mass transfer process is limited during sintering, resulting in the electrochemical performance of the recycled materials not being excellent enough.

[0005] The above regeneration methods all require additional lithium sources to compensate for the lithium loss in the waste positive electrode, and the dead lithium remaining in the waste graphite is wasted. Therefore, how to efficiently recycle lithium resources while reducing environmental pollution is a technical problem that needs to be solved in the field of waste battery recycling. Summary of the invention

[0006] The present invention aims to solve at least one of the technical problems existing in the related art. To this end, the first object of the present invention is to provide a method for preparing a positive electrode material for lithium self-supply regeneration in retired lithium batteries; the second object of the present invention is to provide a positive electrode material for lithium self-supply regeneration in retired lithium batteries.

[0007] In order to achieve the first purpose, the technical solution adopted by the present invention is: A method for preparing a positive electrode material for lithium self-supply regeneration in retired lithium batteries comprises the following steps: S100, dismantling retired lithium batteries, separating waste graphite pole pieces, immersing them in water to peel off current collectors, obtaining a solution containing waste graphite powder, subjecting the solution to ultrasonic heating treatment, allowing it to settle, filtering and separating, and obtaining lithium recovery liquid and graphite residue; Among them, the waste graphite negative electrode sheet is immersed in an aqueous solution. Since the negative electrode generally uses an aqueous binder, the graphite powder and the current collector will be directly separated; The cavitation effect during the ultrasonic process will destroy the solid electrolyte interface (SEI) on the graphite surface and the layered structure of graphite, exposing inactive lithium (including dead lithium and lithium in the solid electrolyte interface) to dissolve in the aqueous solution. Heating can increase the reaction kinetics between the solution and the surface of graphite powder, improve the leaching rate and recovery rate of lithium, and thus achieve full recycling of lithium resources in retired lithium batteries. The lithium content in the lithium recovery solution obtained above can be determined by inductively coupled atomic emission spectroscopy test (ICP), and the waste positive electrode material is preferably a lithium-deficient Li 1-x FePO 4 , where 0.2 <x<1。

[0008] S200, adding dopamine hydrochloride to the lithium recovery liquid, and obtaining a lithium recovery liquid containing dopamine hydrochloride after sufficient dissolution, dispersing the retired positive electrode material in the lithium recovery liquid of dopamine hydrochloride, heating with microwaves to cause dopamine to undergo a self-polymerization reaction on the surface of the positive electrode material to form a coating modification, washing and separating, and obtaining an endogenous lithium supplement and dopamine polymerized coated positive electrode material; The main failure mechanism of lithium iron phosphate materials comes from the loss of active lithium. 4 The corrosion and destruction of impurities and conductive carbon layer. Since dopamine hydrochloride has a certain reducing property when dissolved in water, this property can reduce the Fe in the waste lithium iron phosphate positive electrode material. 3+ , thereby eliminating FePO 4 During the reaction, the lithium ions in the solution will spontaneously embed into the lattice sites of lithium iron phosphate, thereby achieving lithium compensation and elimination of impurities in the waste lithium iron phosphate positive electrode material. 3+ As an oxidant, dopamine hydrochloride can be catalyzed to undergo a self-polymerization reaction, so that a polydopamine coating layer is uniformly formed on the surface of the waste lithium iron phosphate particles. After the reaction, lithium supplementation and coated lithium iron phosphate materials are obtained by washing and separation with water; In this step, the reaction is stirred fully under the condition of microwave heating assistance. Microwave heating interacts with polar water molecules and dopamine molecules in the material through electromagnetic waves, causing these molecules to rotate and vibrate under the action of the alternating electric field to generate friction heat, thereby heating the solution or material. It can directly heat the material at the molecular scale, rather than heating layer by layer through heat conduction as in traditional heating methods. This heating method can utilize energy more efficiently, and the heat generated during the heating process usually acts directly on the reactants, especially dopamine and water with higher polarity, thereby improving the reaction efficiency. In the reaction process of dopamine-lithium complex and waste positive electrode material, microwave energy accelerates the oxidation reaction of dopamine catalyzed by transition metal ions, and can increase the solubility of oxygen in the solution, thereby increasing the rate of dopamine oxidative polymerization reaction, so that the chemical lithiation and self-polymerization process can be completed in a shorter time, and it helps to form a stable polydopamine structure on the particle surface, reducing reaction time and energy consumption; S300, dispersing the endogenous lithium supplement and dopamine polymer-coated positive electrode material obtained in step S200 by spray drying, and then undergoing multi-stage rapid annealing treatment under an inert atmosphere to reconstruct the crystal structure of the waste positive electrode material and decompose the polydopamine, thereby obtaining a positive electrode material for lithium self-supply regeneration in retired lithium batteries, wherein the positive electrode material is modified by nitrogen doping and repaired and regenerated.

[0009] In this step, the particle size and distribution of the powder are controlled by spray drying, thereby improving the uniformity of the material. The precursor powder prepared by spray drying has a large surface area, which helps to enhance its reactivity. The powder after spray drying often has better fluidity and smaller particle aggregation, and can be more evenly distributed during the sintering process. The powder obtained by spray drying is subjected to multi-stage rapid sintering to obtain a modified and regenerated positive electrode material.

[0010] Furthermore, in step S100, the mass ratio of the waste graphite electrode to water is 1:1 to 1:5.

[0011] Furthermore, in step S100, during the ultrasonic heating treatment, the ultrasonic power is 500W to 1000W, the temperature is 20°C to 50°C, and the time is 0.5h to 3h.

[0012] Furthermore, in step S200, the mass ratio of the added dopamine hydrochloride to the mass ratio of the retired positive electrode material is 1:1 to 1:3.

[0013] Further, in step S200, the molar ratio of lithium loss in the retired positive electrode material to lithium in the lithium recovery solution is 1:(1-1.05); The lithium in the lithium recovery liquid has a slight excess, which can ensure that the lithium lost in the waste lithium iron phosphate positive electrode material can be fully replenished.

[0014] Further, in step S200, during the microwave heating process, the temperature is 30°C to 70°C, the speed is 500rpm to 1500rpm, and the time is 0.5h to 3h; During the microwave heating process, when the temperature is lower than 30°C, the excitation effect of microwave heating on molecular motion is weak and the reaction rate will be significantly reduced; when the temperature is higher than 70°C, dopamine may be over-oxidized or decomposed, thereby generating impurity by-products. In addition, dopamine polymers may also be affected by thermal decomposition, resulting in molecular chain breakage or incomplete cross-linking, thereby reducing the mechanical properties, chemical stability, and adhesion of the polymer.

[0015] Furthermore, in step S300, the size of dispersed particles is controlled to be nanoparticles during the spray drying dispersion process.

[0016] Furthermore, the multi-stage rapid annealing process in step S300 includes at least two stages of rapid annealing processes, namely, the first stage and the second stage; The sintering temperature of the first stage is 300°C to 500°C, and the sintering time is 0.5h to 1h. This stage can initially realize the initial transformation of the structure of the positive electrode material and help control the growth of the grains, thus avoiding the degradation of the electrochemical performance of the material caused by excessively large grains. The sintering temperature of the second stage is 600℃~700℃, and the sintering time is 2h~4h. This stage can reconstruct and improve the crystal structure of the waste positive electrode material, and improve the crystallinity of the material, thereby improving the structural stability and chemical stability of the material. In addition, it also helps to reduce defects and impurities in the crystal and improve the purity of the material. During the sintering process, the lithium supplemented by chemical lithiation will thermally migrate into the lithium iron phosphate olivine structure, thereby achieving crystal reconstruction and repair. During the pyrolysis process, the surface self-polymerized polydopamine will also undergo pyrolysis and transform into a nitrogen-doped carbon layer that is evenly coated on the surface of the lithium iron phosphate particles. The nitrogen-doped carbon layer coated on the surface can increase the conductivity of the lithium iron phosphate particles, significantly improve the electronic conductivity and lithium ion migration rate, and thus significantly improve the electrochemical performance of the lithium iron phosphate positive electrode material.

[0017] By modifying and regenerating the waste positive electrode materials through a two-stage rapid annealing treatment method, the crystal phase transformation and repair can be achieved at a lower temperature and in a shorter time, significantly reducing energy consumption and saving time costs.

[0018] Furthermore, the inert atmosphere in step S300 is an argon atmosphere or a nitrogen atmosphere.

[0019] In order to achieve the second purpose, the technical solution adopted by the present invention is: A positive electrode material for lithium self-supply and regeneration in retired lithium batteries is prepared by nitrogen doping modification and repair regeneration, and is prepared by any of the above-mentioned methods for preparing a positive electrode material for lithium self-supply and regeneration in retired lithium batteries.

[0020] The above one or more technical solutions in the embodiments of the present invention have at least one of the following technical effects: The present invention provides a positive electrode material for lithium self-supply regeneration in retired lithium batteries and a preparation method thereof, which can efficiently and conveniently separate lithium from other substances. The whole process avoids the use of high energy consumption and corrosive chemical reagents. The treatment process is simple to operate, highly safe, and has good compatibility with existing battery processes. It has low equipment requirements and is suitable for large-scale promotion and use. At the same time, the lithium recovery liquid obtained by the present invention is derived from the negative electrode of retired lithium batteries, can be directly used for direct modification and regeneration of waste positive electrode materials, can be reassembled into new batteries, has high economic benefits, and provides a new way to prepare batteries.

[0021] Additional aspects and advantages of the present invention will be given in part in the following description and in part will be obvious from the following description, or will be learned through practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is the XRD spectrum of the positive electrode material for lithium self-supply regeneration in retired lithium batteries provided in Example 1 of the present invention.

[0023] Figure 2 This is a SEM spectrum of the positive electrode material for lithium self-supply regeneration in the retired lithium battery provided in Example 1 of the present invention.

[0024] Figure 3 This is a graph showing the electrochemical test results of a lithium-ion battery assembled with positive electrode materials for lithium self-supply regeneration in retired lithium batteries provided in Example 1 of the present invention.

[0025] Figure 4 This is a graph showing the electrochemical test results of a lithium-ion battery assembled with positive electrode materials for lithium self-supply regeneration in retired lithium batteries provided in Example 2 of the present invention. DETAILED DESCRIPTION

[0026] In order to make the purpose, technical scheme and advantages of the present invention clearer, the technical scheme in the present invention will be clearly and completely described below in conjunction with specific embodiments. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in the field without creative work are within the scope of protection of the present invention. The following embodiments are used to illustrate the present invention, but cannot be used to limit the scope of the present invention.

[0027] In the following examples, the experimental methods used are conventional methods unless otherwise specified, and are carried out according to the techniques or conditions described in the literature in the field or according to the product instructions. The materials, reagents, etc. used are all commercially available unless otherwise specified.

[0028] Example 1 1. Pretreatment of retired batteries: The pretreatment of retired batteries mainly uses a small current constant current discharge method to discharge retired lithium iron phosphate batteries (capacity decays to less than 80% of the initial capacity) to 2.0V, so that the active lithium in the graphite negative electrode is completely released, and charging is stopped after the voltage remains stable.

[0029] Disassemble retired lithium-ion batteries in a humidity-controlled room temperature environment (relative humidity <10%), separate the battery components, remove the waste positive and negative electrode materials, and mechanically crush them for later use.

[0030] 2. Regeneration of waste positive electrode materials: The crushed lithium-containing negative electrode sheet is placed in a certain amount of aqueous solution with a solid-liquid mass ratio of 1:3. The leaching reaction is carried out for 1 hour under the conditions of ultrasonic power of 800W and temperature of 40°C. After the leaching is completed, the solution is allowed to stand and settle and filtered for separation. The standing process can preferentially settle the heavier large graphite particles, and then filtering and separating the upper layer of liquid can significantly improve the separation efficiency, and the recovered lithium solution and graphite solid powder are separated.

[0031] A certain amount of dopamine hydrochloride is added to the above-mentioned recovered lithium solution, the ratio of the mass of dopamine hydrochloride added to the mass of the above-mentioned waste positive electrode material is 1:2, and it is fully stirred and dissolved to obtain a lithium recovery solution containing dopamine hydrochloride. The waste positive electrode material (Li 1-x FePO 4 ) powder, Li 1-x FePO 4 The molar ratio of lithium loss (x value) to lithium content in the recovered liquid is 1:1.05, and a slightly excess of lithium can make up for the lithium volatilization loss during sintering. The reaction was stirred for 2 hours at a microwave heating temperature of 50°C and a stirring rate of 1000 rpm, and the chemical reduction and lithiation of the waste material were fully reacted, and the self-polymerization coating of dopamine on the surface of the waste positive electrode material particles was achieved.

[0032] The mixed solution is directly separated by static sedimentation and filtration, and then washed with water to remove impurities remaining on the surface, to obtain a chemically lithium-supplemented and coated lithium iron phosphate positive electrode material and a lithium-free separation solution, and the lithium content in the separation solution is detected by inductively coupled plasma optical emission spectrometer (ICP-OES), and it is determined that the lithium utilization rate can reach 98%. Then the lithium-supplemented and coated lithium iron phosphate material is dispersed in water and spray-dried, and then in argon gas, it undergoes a first stage and a second stage of rapid annealing treatment to obtain a lithium self-supply regeneration positive electrode material in a retired lithium battery, which is a nitrogen-doped modified and regenerated lithium iron phosphate positive electrode material; In the first stage, the temperature is 400°C and the sintering time is 1h; in the second stage, the temperature is 700°C and the sintering time is 3h.

[0033] The XRD spectrum of the lithium iron phosphate positive electrode material provided in this embodiment is as follows: Figure 1 As shown, the results show that the diffraction peak of the lithium iron phosphate positive electrode material is completely consistent with the standard card; The SEM spectrum of the lithium iron phosphate positive electrode material provided in this embodiment is as follows: Figure 2 As shown, and from Figure 2 It can be seen that the lithium iron phosphate particles are nanometer-sized and the particle surface is complete and smooth, indicating that a lithium iron phosphate positive electrode material with perfect crystal phase and morphology has been successfully prepared.

[0034] The lithium-ion battery assembled with the lithium iron phosphate positive electrode material provided in this embodiment was subjected to electrochemical testing, such as Figure 3 The results show that the performance of the nitrogen-doped modified regenerated lithium iron phosphate cathode material is significantly improved compared with the waste cathode material, and the first cycle discharge capacity can reach 165 mAh g −1 , the coulombic efficiency is 98%; in addition, the modified and regenerated positive electrode material provided by the preparation method provided by the present invention exhibits very excellent rate performance and still has a high specific capacity at a large rate of 4 to 10C.

[0035] Example 2 The difference between this embodiment and embodiment 1 is that in the second stage rapid annealing process, the sintering time is 4 hours, and the rest of the process is the same as embodiment 1.

[0036] The lithium ion battery assembled with the lithium iron phosphate positive electrode material provided in this embodiment was tested for cycle performance. Figure 4 As shown, after 200 cycles at a rate of 0.5C, the capacity retention rate is 97% of the initial specific capacity. This result shows that the nitrogen-doped modified and repaired regenerated lithium iron phosphate positive electrode material provided by the present invention has excellent electrochemical properties.

[0037] Example 3 The difference between this embodiment and embodiment 1 is that in the second stage rapid annealing process, the sintering time is 2 hours, and the rest of the process is the same as embodiment 1.

[0038] Example 4 The difference between this embodiment and embodiment 1 is that in the second stage rapid annealing process, the sintering temperature is 600° C. and the time is 1 hour. The rest of the process is the same as embodiment 1.

[0039] Example 5 The difference between this embodiment and embodiment 1 is that in the second stage rapid annealing process, the sintering temperature is 600° C. and the time is 3 hours, and the rest of the process is the same as embodiment 1.

[0040] Example 6 The difference between this embodiment and embodiment 1 is that in the second stage rapid annealing process, the sintering temperature is 600° C. and the time is 4 hours. The rest of the process is the same as embodiment 1.

[0041] Comparative Example 1 The difference between this comparative example and Example 1 is that commercial LiOH is dissolved in an aqueous solution to prepare a lithium-containing solution, replacing the lithium solution recovered from retired batteries, and the rest of the process is the same as Example 1.

[0042] Comparative Example 2 A certain amount of waste cathode material and LiOH are directly mixed, Li 1-x FePO 4 The molar ratio of lithium loss (x value) to LiOH content is 1:1.05. A slightly excess amount of lithium can make up for the lithium volatilization loss during the sintering process. The mixed powder is sintered at 700°C in argon for 4 hours to obtain a solid-phase sintered regenerated lithium iron phosphate positive electrode material.

[0043] The parameters of sintering temperature and time and the results of electrochemical performance testing of Examples 1 to 6 are shown in Table 1; The electrochemical properties of the positive electrode materials provided in different embodiments and comparative examples were tested by a button half-cell test method. Table 1 Electrochemical performance test results of sintering parameters of different embodiments and comparative examples

[0044] Example 1 is a positive electrode material regenerated by utilizing the lithium self-supply in retired lithium batteries, and Comparative Example 1 is a lithium iron phosphate positive electrode material regenerated by additionally adding LiOH. From the data provided in Table 1, it can be seen that the electrochemical properties of Example 1 and Comparative Example 1 are basically the same. This result shows that the preparation method provided by the present invention can achieve closed-loop recycling and utilization of retired lithium batteries, and is expected to achieve efficient recycling and utilization of waste battery resources.

[0045] Example 1 is a nitrogen-doped, modified and regenerated positive electrode material obtained by the preparation method provided by the present invention, and Comparative Example 2 is an unmodified lithium iron phosphate positive electrode material prepared by traditional solid phase sintering. From the data provided in Table 1, it can be seen that the preparation method provided by the present invention can obtain a lithium battery positive electrode material with better electrochemical properties.

[0046] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a positive electrode material for lithium self-supply regeneration in retired lithium batteries, characterized in that: The steps include: S100, dismantling retired lithium batteries, separating waste graphite pole pieces, immersing them in water to peel off current collectors, obtaining a solution containing waste graphite powder, subjecting the solution to ultrasonic heating treatment, allowing it to settle, filtering and separating, and obtaining a lithium recovery solution; S200, adding dopamine hydrochloride to the lithium recovery liquid, and obtaining a lithium recovery liquid of dopamine hydrochloride after sufficient dissolution, dispersing the retired positive electrode material powder in the lithium recovery liquid of dopamine hydrochloride, heating with microwaves to cause dopamine to undergo a self-polymerization reaction on the surface of the positive electrode material to form a coating modification, and washing and separating to obtain an endogenous lithium supplement and dopamine polymerized coated positive electrode material; S300, dispersing the endogenous lithium supplement and dopamine polymer-coated positive electrode material obtained in step S200 by spray drying, and then undergoing multi-stage rapid annealing treatment under an inert atmosphere to reconstruct the crystal structure of the waste positive electrode material and decompose the polydopamine, thereby obtaining a positive electrode material for lithium self-supply regeneration in retired lithium batteries.

2. The method for preparing a positive electrode material for lithium self-supply regeneration in retired lithium batteries according to claim 1, characterized in that: In step S100, the mass ratio of the waste graphite electrode to water is 1:1 to 1:

5.

3. The method for preparing a positive electrode material for lithium self-supply regeneration in retired lithium batteries according to claim 1, characterized in that: In step S100, during the ultrasonic heating treatment, the ultrasonic power is 500W to 1000W, the temperature is 20°C to 50°C, and the time is 0.5h to 3h.

4. The method for preparing a positive electrode material for lithium self-supply regeneration in retired lithium batteries according to claim 1, characterized in that: In step S200, the mass ratio of the added dopamine hydrochloride to the mass ratio of the retired positive electrode material is 1:1 to 1:

3.

5. The method for preparing a positive electrode material for lithium self-supply regeneration in retired lithium batteries according to claim 1, characterized in that: In step S200, the molar ratio of lithium loss in the retired positive electrode material to lithium in the lithium recovery solution is 1:(1-1.05).

6. The method for preparing a positive electrode material for lithium self-supply regeneration in retired lithium batteries according to claim 1, characterized in that: In step S200, during the microwave heating process, the temperature is 30°C to 70°C, the speed is 500rpm to 1500rpm, and the time is 0.5h to 3h.

7. The method for preparing a positive electrode material for lithium self-supply regeneration in retired lithium batteries according to claim 1, characterized in that: In step S300, the size of dispersed particles is controlled to be nanoparticles during the spray drying dispersion process.

8. The method for preparing a positive electrode material for lithium self-supply regeneration in retired lithium batteries according to claim 1, characterized in that: The multi-stage rapid annealing process in step S300 includes at least two stages of rapid annealing processes, namely, the first stage and the second stage; The sintering temperature of the first stage is 300°C to 500°C, and the sintering time is 0.5h to 1h; The sintering temperature of the second stage is 600°C to 700°C, and the sintering time is 2h to 4h.

9. The method for preparing a positive electrode material for lithium self-supply regeneration in retired lithium batteries according to claim 1, characterized in that: The inert atmosphere in step S300 is an argon atmosphere or a nitrogen atmosphere.

10. A positive electrode material for lithium self-supply regeneration in retired lithium batteries, characterized in that: The cathode material is prepared by nitrogen doping modification and repair regeneration, and is prepared by the method for preparing a cathode material for lithium self-supply regeneration in a retired lithium battery as described in any one of claims 1 to 9.

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