A positive electrode material for lithium self-supply regeneration in retired lithium batteries and a preparation method thereof

Abstract

The present invention relates to the technical field of lithium batteries, and in particular to a positive electrode material capable of self-supplying and regenerating lithium in retired lithium batteries and a preparation method thereof. The positive electrode material is formed by nitrogen doping modification and repair regeneration. The preparation method comprises the following steps: disassembling retired lithium batteries, treating separated graphite pole pieces, and obtaining a lithium recovery liquid; adding dopamine hydrochloride to the lithium recovery liquid to disperse the retired positive electrode material, so that the dopamine coats the positive electrode material, thereby obtaining an endogenous lithium-supplemented and dopamine-polymer-coated positive electrode material; and dispersing the endogenous lithium-supplemented and dopamine-polymer-coated positive electrode material by spray drying, and subjecting the endogenous lithium-supplemented and dopamine-polymer-coated positive electrode material to a multi-stage rapid annealing treatment to reconstruct the crystal structure of the waste positive electrode material and decompose polydopamine, thereby obtaining a regenerated positive electrode material. The preparation method can be directly used for direct modification and regeneration of waste positive electrode materials, has a simple treatment process, is highly safe, and can achieve full recycling of lithium resources.

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 short lifespans result in a large number of batteries rapidly entering retirement. Efficiently recycling used batteries can protect the environment by preventing heavy metals and organic matter from polluting the environment; effectively alleviate supply pressures on key metal resources like lithium; and enhance the economic value of resource recycling.

[0003] Currently, the recycling of retired lithium-ion batteries primarily involves pyrometallurgical and hydrometallurgical processes. While pyrometallurgical processes are mature, they still suffer from significant issues such as high energy consumption, low resource utilization, and the emission of hazardous gases. Hydrometallurgical processes extract lithium from spent batteries through acid / alkali extraction of black powder, ultimately recovering it as inorganic lithium salts such as lithium carbonate or lithium hydroxide. While this technology offers high recovery rates, it is complex, involving multiple leaching and separation steps and requiring large amounts of inorganic acid or organic reagents. Consequently, this leads to significant wastewater discharge and secondary pollution.

[0004] Furthermore, the conventional method for remediating waste materials is to regenerate them by mixing lithium salts with the waste materials through a high-temperature solid-phase sintering process. However, for severely degraded retired materials, this process typically requires sintering at temperatures exceeding 800°C for more than 10 hours to achieve complete regeneration. High-temperature solid-phase sintering involves a solid-solid contact reaction, which limits mass transfer during sintering, resulting in suboptimal electrochemical performance of the recycled materials.

[0005] All of the aforementioned regeneration methods require the addition of a lithium source to compensate for lithium loss in the spent cathode, while any dead lithium remaining in the spent graphite is wasted. Therefore, efficiently recovering lithium resources while minimizing environmental pollution remains a pressing technical challenge in the waste battery recycling field. 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 cathode material capable of self-supplying lithium in retired lithium batteries; the second object of the present invention is to provide a cathode material capable of self-supplying lithium in retired lithium batteries.

[0007] In order to achieve the first purpose, the technical solution adopted by the present invention is:

[0008] A method for preparing a positive electrode material for lithium self-supply regeneration in retired lithium batteries comprises the following steps:

[0009] S100, dismantling retired lithium batteries, separating waste graphite pole pieces, immersing the pole pieces in water to peel off the current collector, obtaining a solution containing waste graphite powder, subjecting the solution to ultrasonic heating treatment, allowing it to settle, and filtering and separating to obtain a lithium recovery solution and graphite residue;

[0010] Among them, the waste graphite negative electrode 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;

[0011] The cavitation effect during the ultrasonic process destroys 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) and dissolving it in the aqueous solution. Heating can increase the reaction kinetics between the solution and the graphite powder surface, improving the lithium leaching rate and recovery rate, thereby achieving the full recycling of lithium resources in retired lithium batteries.

[0012] The lithium content in the lithium recovery solution obtained above can be determined by inductively coupled atomic emission spectroscopy test (ICP). The waste positive electrode material is preferably a lithium-deficient Li 1-x FePO4, of which 0.2 <x<1。

[0013] S200, adding dopamine hydrochloride to the lithium recovery solution, and after fully dissolving, obtaining a lithium recovery solution containing dopamine hydrochloride, dispersing the retired positive electrode material in the lithium recovery solution containing 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-supplemented and dopamine-polymerized positive electrode material;

[0014] The main failure mechanism of lithium iron phosphate materials comes from the loss of active lithium, FePO4 impurities and corrosion and destruction of the 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 the FePO4 impurity phase. At the same time, during the reaction process, the lithium ions in the solution will spontaneously embed into the lattice sites of lithium iron phosphate, thereby achieving lithium compensation and impurity phase elimination 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-supplemented and coated lithium iron phosphate materials are obtained by washing with water and separation.

[0015] 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 frictional 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. 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. During the reaction 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 helps to form a stable polydopamine structure on the surface of the particles, reducing reaction time and energy consumption;

[0016] S300, the endogenous lithium supplement and dopamine polymer-coated positive electrode material obtained in step S200 is dispersed by spray drying, and then subjected to 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.

[0017] In this step, spray drying controls the particle size and distribution of the powder, thereby improving the uniformity of the material. The larger surface area of ​​the precursor powder prepared by spray drying helps enhance its reactivity. The spray-dried powder often has better flowability and smaller particle aggregation, allowing for more uniform distribution during the sintering process. The spray-dried powder is then subjected to multiple rapid sintering stages to produce the modified and regenerated cathode material.

[0018] Furthermore, in step S100, the mass ratio of the waste graphite electrode to water is 1:1 to 1:5.

[0019] 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.

[0020] Furthermore, in step S200, the mass ratio of the added dopamine hydrochloride to the retired positive electrode material is 1:1 to 1:3.

[0021] Furthermore, 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);

[0022] The lithium in the lithium recovery liquid is slightly excessive, which can ensure that the lithium lost in the waste lithium iron phosphate positive electrode material can be fully replenished.

[0023] Furthermore, 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;

[0024] During microwave heating, when the temperature is below 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 above 70°C, it may cause excessive oxidation or decomposition of dopamine, 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.

[0025] Furthermore, in step S300, the size of dispersed particles is controlled to be nanoparticles during the spray drying dispersion process.

[0026] 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;

[0027] The sintering temperature in the first stage is 300°C to 500°C, and the sintering time is 0.5h to 1h. This stage can initially achieve the initial transformation of the cathode material structure and help control the growth of grains, thus avoiding the degradation of the electrochemical performance of the material caused by excessively large grains.

[0028] The second stage of sintering is carried out at a temperature of 600°C to 700°C for 2 to 4 hours. This stage can reconstruct and improve the crystal structure of the waste cathode material and increase the crystallinity of the material, thereby improving the structural and chemical stability of the material. It also helps to reduce defects and impurities in the crystal and improve the purity of the material.

[0029] During the sintering process, lithium added by chemical lithiation thermally migrates into the lithium iron phosphate olivine structure, thereby reconstructing and repairing the crystals. During the pyrolysis process, the surface-self-polymerized polydopamine also undergoes pyrolysis, transforming into a nitrogen-doped carbon layer that uniformly coats the surface of the lithium iron phosphate particles. This surface-coating nitrogen-doped carbon layer increases the conductivity of the lithium iron phosphate particles, significantly improving electronic conductivity and lithium ion migration rate, thereby significantly enhancing the electrochemical performance of the lithium iron phosphate cathode material.

[0030] By modifying and regenerating 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.

[0031] Furthermore, the inert atmosphere in step S300 is an argon atmosphere or a nitrogen atmosphere.

[0032] In order to achieve the second purpose, the technical solution adopted by the present invention is:

[0033] 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 using any of the above-mentioned methods for preparing a positive electrode material for lithium self-supply and regeneration in retired lithium batteries.

[0034] The above one or more technical solutions in the embodiments of the present invention have at least one of the following technical effects:

[0035] The present invention provides a positive electrode material for lithium self-supply regeneration in retired lithium batteries and a preparation method thereof. The material can efficiently and conveniently separate lithium from other substances, avoiding the use of high energy consumption and corrosive chemical reagents. The treatment process is simple to operate, highly safe, and compatible with existing battery processes. The material requires minimal equipment and is suitable for large-scale deployment. Furthermore, the lithium recovery liquid obtained by the present invention is derived from the negative electrode of retired lithium batteries and can be directly used to modify and regenerate waste positive electrode materials, allowing for reassembly into new batteries. This method offers high economic benefits and provides a new approach to battery preparation.

[0036] Additional aspects and advantages of the present invention will be set forth in part in the description which follows and, in part, will be obvious from the description which follows, or may be learned by practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] 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.

[0038] Figure 2 This is an SEM image of the positive electrode material for lithium self-supply regeneration in retired lithium batteries provided in Example 1 of the present invention.

[0039] Figure 3 This is a graph showing the electrochemical test results of a lithium-ion battery assembled with a positive electrode material for lithium self-supply regeneration in retired lithium batteries provided in Example 1 of the present invention.

[0040] Figure 4 This is a graph showing the electrochemical test results of a lithium-ion battery assembled with a positive electrode material for lithium self-supply regeneration in retired lithium batteries provided in Example 2 of the present invention. DETAILED DESCRIPTION

[0041] To make the purpose, technical solutions and advantages of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below in conjunction with specific embodiments. Obviously, the embodiments described 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 this field without making creative work are within the scope of protection of the present invention. The following embodiments are used to illustrate the present invention, but are not used to limit the scope of the present invention.

[0042] 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 this field or according to the product instructions. The materials, reagents, etc. used are all commercially available unless otherwise specified.

[0043] Example 1

[0044] 1. Pretreatment of retired batteries:

[0045] The pretreatment of retired batteries mainly adopts the method of small current constant current discharge to discharge retired lithium iron phosphate batteries (capacity decayed 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.

[0046] Dismantle 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.

[0047] 2. Regeneration of waste cathode materials:

[0048] 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. The standing process can preferentially settle the heavier large graphite particles. Then, filtering and separating the upper liquid can significantly improve the separation efficiency, and the recovered lithium solution and graphite solid powder are separated.

[0049] A certain amount of dopamine hydrochloride is added to the above-mentioned recovered lithium solution, and the ratio of the mass of dopamine hydrochloride added to the mass of the above-mentioned waste positive electrode material is 1:2. Stir and dissolve thoroughly to obtain a lithium recovery solution containing dopamine hydrochloride. Add the waste positive electrode material (Li 1-x FePO4) powder, Li 1-xThe molar ratio of lithium loss (x value) in FePO4 to lithium content in the recovered solution was 1:1.05. A slight excess of lithium compensated for lithium volatilization losses during sintering. The reaction was stirred for 2 hours at a microwave heating temperature of 50°C and a stirring rate of 1000 rpm, achieving sufficient chemical reduction and lithiation of the waste material and self-polymerization of dopamine on the surface of the waste cathode material particles.

[0050] The mixed solution is directly separated by static sedimentation and filtration, and then washed with water to remove residual impurities on the surface, resulting in a chemically lithium-supplemented and coated lithium iron phosphate cathode material and a lithium-free separated solution. The lithium content in the separated solution is measured by inductively coupled plasma optical emission spectrometry (ICP-OES), confirming a lithium utilization rate of up to 98%. The lithium-supplemented and coated lithium iron phosphate material is then dispersed in water and spray-dried. It then undergoes a first and second stage rapid annealing treatment in argon to obtain a cathode material for lithium self-supply regeneration in retired lithium batteries. This cathode material is a nitrogen-doped, modified, and regenerated lithium iron phosphate cathode material.

[0051] In the first stage, the temperature is 400°C and the sintering time is 1 hour; in the second stage, the temperature is 700°C and the sintering time is 3 hours.

[0052] The XRD pattern of the lithium iron phosphate cathode material provided in this embodiment is as follows: Figure 1 As shown, the results show that the diffraction peak of the lithium iron phosphate cathode material is completely consistent with the standard card;

[0053] 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.

[0054] The lithium ion battery assembled with the lithium iron phosphate cathode 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 165mAh·g −1 , and 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.

[0055] Example 2

[0056] 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.

[0057] The lithium ion battery assembled with the lithium iron phosphate positive electrode material provided in this embodiment was subjected to a cycle performance test. Figure 4 As shown in the figure, the capacity retention rate after 200 cycles at a rate of 0.5C is 97% of the initial specific capacity. This result shows that the nitrogen-doped, modified and repaired lithium iron phosphate positive electrode material provided by the present invention has excellent electrochemical properties.

[0058] Example 3

[0059] 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.

[0060] Example 4

[0061] 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.

[0062] Example 5

[0063] 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. The rest of the process is the same as embodiment 1.

[0064] Example 6

[0065] 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.

[0066] Comparative Example 1

[0067] 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. The rest of the process is the same as Example 1.

[0068] Comparative Example 2

[0069] A certain amount of waste cathode material and LiOH are directly mixed, Li 1-x The molar ratio of the lithium loss (x value) in FePO4 to the LiOH content is 1:1.05. A slightly excess of lithium can make up for the lithium volatilization loss during the sintering process. The above 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.

[0070] The parameters of sintering temperature and time and the results of electrochemical performance testing of Examples 1 to 6 are shown in Table 1;

[0071] The electrochemical properties of the positive electrode materials provided in different embodiments and comparative examples were tested by a button half-cell test method.

[0072] Table 1 Electrochemical performance test results of sintering parameters of different examples and comparative examples

[0073]

[0074] Example 1 is a positive electrode material regenerated by utilizing the self-supply of lithium 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.

[0075] Example 1 is a nitrogen-doped, modified and regenerated positive electrode material obtained by the preparation method provided by the present invention. 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.

[0076] 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 various 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 the pole pieces in water to peel off the current collector, obtaining a solution containing waste graphite powder, subjecting the solution to ultrasonic heating treatment, allowing it to settle, and filtering and separating to obtain a lithium recovery solution; In the ultrasonic heating process, the ultrasonic power is 500W to 1000W, the temperature is 20°C to 50°C, and the time is 0.5h to 3h; S200, adding dopamine hydrochloride to the lithium recovery solution, and after fully dissolving, obtaining a lithium recovery solution of dopamine hydrochloride, dispersing retired positive electrode material powder in the lithium recovery solution 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-supplemented and dopamine-polymerized positive electrode material; The microwave heating process is performed at a temperature of 30°C to 70°C, a speed of 500 rpm to 1500 rpm, and a time of 0.5 h to 3 h. S300, dispersing the endogenous lithium-supplemented and dopamine-polymerized positive electrode material obtained in step S200 by spray drying, and then subjecting it to a 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; The multi-stage rapid annealing process includes at least two stages of rapid annealing: the first stage and the second stage. The sintering temperature of the first stage is 300℃~500℃, and the sintering time is 0.5h~1h; The sintering temperature of the second stage is 600°C to 700°C, and the sintering time is 2h to 4h.

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 S200 , the mass ratio of the added dopamine hydrochloride to the retired positive electrode material is 1:1 to 1:

3.

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 molar ratio of lithium loss in the retired positive electrode material to lithium in the lithium recovery solution is 1:(1-1.05).

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 S300, the size of dispersed particles is controlled to be nanoparticles during the spray drying dispersion process.

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: The inert atmosphere in step S300 is an argon atmosphere or a nitrogen atmosphere.

7. 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 using the method for preparing a cathode material for lithium self-supply regeneration in retired lithium batteries as described in any one of claims 1 to 6.

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