Regeneration method of lithium iron phosphate positive electrode material in waste lithium battery

Abstract

The regeneration method of the lithium iron phosphate positive electrode material in the waste lithium battery comprises the following steps: pretreating the waste lithium iron phosphate battery to obtain the lithium iron phosphate positive electrode material; sequentially carrying out acidolysis, lithium supplementation and evaporation concentration on the lithium iron phosphate positive electrode material to obtain precursor gel; carrying out spontaneous combustion reaction on the precursor gel in the presence of a combustion improver to obtain a combustion product; and carrying out carbon coating treatment on the combustion product by adopting a carbon source in an inert atmosphere to obtain the regenerated lithium iron phosphate positive electrode material. According to the regeneration method provided by the invention, different components in the system do not need to be separated in the whole process, and all-component recovery of the waste lithium iron phosphate positive electrode material can be realized. According to the regeneration method, a large amount of heat can be released in a short time, and gas is produced, so that the particle size of the reaction product particles is small, the morphology requirement of the lithium iron phosphate morphology is met, and the gram volume of the lithium iron phosphate can be improved. In addition, the regeneration method provided by the invention does not need a high-pressure reaction condition.

Description

Technical Field

[0001] The present invention relates to the field of waste battery recycling, and more particularly, to a method for recycling lithium iron phosphate cathode materials in waste lithium batteries. Background Art

[0002] The global sales volume of new energy vehicles has reached record highs, and the resulting increase in retired batteries has made the research on retired battery recycling technologies extremely urgent. The commonly used retired battery recycling routes include two technical routes: pyrometallurgy and hydrometallurgy. The pyrometallurgical route is limited by its high energy consumption and has a narrow application range. Most domestic related manufacturers use the hydrometallurgical process, specifically including: dissolving the black powder obtained from the preliminary pretreatment, separating different components, and recovering different metal salt products. For lithium iron phosphate (LFP) cathode materials, except for lithium, other components do not have economic value for recycling, and it is necessary to develop an integrated value-added recycling technology to promote the recycling of lithium iron phosphate batteries.

[0003] There are problems with the structure damage of retired lithium iron phosphate cathode materials. Some divalent iron ions will be oxidized to trivalent iron ions, occupying the positions of lithium ions, resulting in an increase in the lithium ion diffusion impedance. At the same time, there is also a loss of lithium ions during long-term cycling, which will also cause the degradation of material performance. In traditional methods for repairing lithium iron phosphate cathode materials, after mixing iron sources (such as iron phosphate), lithium sources (such as lithium carbonate), and carbon sources (such as glucose), it is necessary to perform long-term high-temperature sintering under an inert atmosphere to complete the repair of lithium iron phosphate. Existing literature provides a hydrothermal repair method for lithium iron phosphate cathode materials, including: mixing the failed LFP powder, lithium source solution, and reducing agent and placing them in a hydrothermal autoclave, reacting at 120 - 300 °C and 0.1 - 10 MPa for 2 - 48 h. The disadvantages of this method are that the liquid-phase reaction temperature is high and high-pressure reaction equipment is required. Another piece of existing literature provides a method for repairing by combining low-temperature liquid-phase lithium supplementation and high-temperature calcination. The temperature of the liquid-phase lithium supplementation reaction is 50 - 95 °C and the reaction time is 4 - 10 h. The liquid-phase reaction temperature in the above repair methods is relatively low, no high pressure is generated, and no high-pressure reaction equipment is required, but the liquid-phase reaction time is long, and there are deficiencies in terms of cost and performance.

[0004] To overcome the deficiencies of the above existing technologies, it is necessary to provide a method for recycling lithium iron phosphate cathode materials in waste lithium batteries that simultaneously satisfies the advantages of short process time, low cost, and short process flow. Summary of the Invention

[0005] The present invention aims to provide a method for recycling lithium iron phosphate cathode materials in waste lithium batteries to solve the problem that the existing methods for recycling lithium iron phosphate cathode materials cannot simultaneously meet the requirements of low reaction temperature, short process flow, and low cost.

[0006] The present application provides a method for regenerating lithium iron phosphate cathode material in waste lithium batteries. The method for regenerating lithium iron phosphate cathode material in waste lithium batteries includes: pretreating waste lithium iron phosphate cathode sheets to obtain lithium iron phosphate cathode material; subjecting the lithium iron phosphate cathode material to acidolysis, lithium supplementation, and evaporation and concentration in sequence to obtain a precursor gel; allowing the precursor gel to undergo a self-combustion reaction in the presence of a combustion aid containing an amino group to obtain a combustion product; and performing carbon coating treatment on the combustion product with a carbon source under an inert atmosphere to obtain the regenerated lithium iron phosphate cathode material.

[0007] In some embodiments of the present application, the combustion aid containing an amino group includes urea and / or dimethylformohydrazine.

[0008] In some embodiments of the present application, the molar ratio of the combustion aid containing an amino group to the lithium element in the reaction system after lithium supplementation is 1:(2 - 6).

[0009] In some embodiments of the present application, the timing of adding the combustion aid containing an amino group is after lithium supplementation and before evaporation and concentration.

[0010] In some embodiments of the present application, the acid used in acidolysis includes at least one of nitric acid, hydrochloric acid, and sulfuric acid.

[0011] In some embodiments of the present application, in acidolysis, the dosage of the acid required per gram of lithium iron phosphate cathode material is 3 mL - 4 mL, and the concentration of the acid is 1.5 mol / L - 2 mol / L.

[0012] In some embodiments of the present application, the temperature of evaporation and concentration is 80°C - 95°C; and / or the temperature of the self-combustion reaction is 240°C - 350°C.

[0013] In some embodiments of the present application, the pretreatment includes soaking waste lithium iron phosphate cathode sheets with an N-methylpyrrolidone solvent to obtain lithium iron phosphate cathode material.

[0014] In some embodiments of the present application, the temperature of the carbon coating treatment is 700°C - 800°C.

[0015] In some embodiments of the present application, the carbon source used in the carbon coating treatment is selected from one or more of glucose, sucrose, citric acid, and hydroxyethyl cellulose; and / or the coating amount of the carbon source accounts for 0.8% - 1.4% of the weight of the combustion product.

[0016] Compared with the traditional method, the beneficial effects of the present application are:

[0017] By pretreating waste lithium iron phosphate cathode sheets, lithium iron phosphate cathode materials are obtained. The waste lithium iron phosphate materials are dissolved with an acid to generate a metal nitrate solution. After filtration and lithium supplementation, it is mixed with a specific amino-containing combustion aid and subjected to evaporation and concentration. During the evaporation and concentration process, this type of amino-containing combustion aid reacts and releases ammonia, which intensifies the combustion reaction, accelerates the completion of the reaction, and has obvious advantages in terms of energy consumption and carbon emissions. Compared with traditional wet recycling, which generally only extracts lithium element and does not recycle elements Fe and P, the entire process of the regeneration method provided in this application does not require the separation of different components in the system and can achieve the full-component recycling of waste lithium iron phosphate cathode materials. The above regeneration method can release a large amount of heat in a short time, accelerating the reduction of ferric ions and the re-embedding of lithium ions. At the same time, the particle size of the reaction product is smaller, making it not only meet the morphological requirements of lithium iron phosphate but also further improve the specific capacity of the regenerated lithium iron phosphate. In addition, the regeneration method provided in this application does not require high-pressure reaction conditions. In particular, the reactants of the above combustion reaction are gels formed by a mixed solution containing various components, so it has a high fit with the recycling process. Description of the Drawings

[0018] Figure 1 Schematic process flow diagram of the regeneration method for lithium iron phosphate cathode materials in waste lithium batteries provided in Example 1. Detailed Embodiments

[0019] For the sake of brevity, only some numerical ranges are specifically disclosed herein. However, any lower limit can be combined with any upper limit to form a range not explicitly recorded; and any lower limit can be combined with other lower limits to form a range not explicitly recorded. Similarly, any upper limit can be combined with any other upper limit to form a range not explicitly recorded. In addition, each individually disclosed point or single numerical value itself can be used as a lower limit or upper limit and combined with any other point or single numerical value or combined with other lower limits or upper limits to form a range not explicitly recorded.

[0020] In the description herein, unless otherwise specified, "above" and "below" include the number itself.

[0021] Unless otherwise specified, the terms used in this application have the well-known meanings commonly understood by those skilled in the art. Unless otherwise specified, the numerical values of the various parameters mentioned in this application can be measured by various commonly used measurement methods in the art (for example, they can be tested according to the methods given in the embodiments of this application). It should be noted that, without conflict, the embodiments in this application and the features in the embodiments can be combined with each other.

[0022] The present invention aims to provide a method for regenerating lithium iron phosphate cathode materials in waste lithium batteries, so as to solve the problem that the existing methods for regenerating lithium iron phosphate cathode materials cannot simultaneously meet the requirements of low reaction temperature, short process flow and low cost. Specifically, a method for regenerating lithium iron phosphate cathode materials in waste lithium batteries provided by a typical embodiment of the present application includes: pretreating waste lithium iron phosphate cathode sheets to obtain lithium iron phosphate cathode materials; successively subjecting the lithium iron phosphate cathode materials to acidolysis, lithium supplementation and evaporation concentration to obtain a precursor gel; allowing the precursor gel to undergo a spontaneous combustion reaction in the presence of a combustion aid containing amino groups to obtain a combustion product; and performing carbon coating treatment on the combustion product with a carbon source under an inert atmosphere to obtain the regenerated lithium iron phosphate cathode materials.

[0023] In the above regeneration method, lithium iron phosphate cathode materials are obtained by pretreating waste lithium iron phosphate cathode sheets; through the acidolysis process, the lithium iron phosphate cathode materials are dissolved in an acid to obtain an acidolysis solution; lithium elements are supplemented into the acidolysis solution according to the content of lithium elements in the target cathode materials, and then a precursor gel is formed through evaporation concentration; due to the relatively low ignition point, in the presence of a combustion aid containing amino groups, the above precursor sol can undergo a spontaneous combustion reaction at a relatively low temperature to obtain a combustion product; finally, a carbon coating layer is formed on the surface of the combustion product through the carbon coating process, thereby obtaining the regenerated lithium iron phosphate cathode materials.

[0024] Compared with the traditional method, the regeneration method provided by the present application initiates a self-excitation reaction in the system through a low-temperature heating process, which releases a large amount of heat violently, enabling the material synthesis to be completed in a short time. The whole process does not require the separation of different components in the system, nor high-temperature and high-pressure reaction conditions, so it can effectively shorten the process flow of the regeneration process and reduce costs. In particular, the reactants of the above combustion reaction are a gel formed by a mixed solution containing various components, so it is more compatible with the recovery process; at the same time, the above regeneration process also has obvious advantages in terms of energy consumption and carbon emissions, and can realize the full-component recovery of waste lithium iron phosphate cathode materials. In addition, compared with conventional combustion aids, under the action of a specific combustion aid, the above reaction can release more heat in a short time, making the whole reaction process more violent, accelerating the reduction of ferric ions and the re-embedding of lithium ions, and at the same time, the particle size of the reaction product is smaller, making it not only meet the morphological requirements of lithium iron phosphate, but also further improve the specific capacity of the regenerated lithium iron phosphate.

[0025] The cathode material in the waste lithium iron phosphate battery used in the present application is LiFePO 4 。

[0026] In some embodiments of the present application, the combustion aid containing amino groups includes urea and / or dimethylformyl hydrazine.

[0027] In a preferred embodiment of the present application, the ratio of the amount of the combustion aid containing amino groups to the amount of lithium in the reaction system after lithium supplementation is 1:(2-6). Optionally, in the reaction system, the ratio of the amount of the combustion aid to the amount of lithium in the reaction system after lithium supplementation is 1:2, 1:3, 1:4, 1:5, 1:6, or a range formed by any two of the above values.

[0028] Preferably, the amino-containing combustion improver is added after lithium supplementation and before evaporation and concentration.

[0029] The acid is used to release the valuable elements in the phosphoric acid positive electrode material into the solution, so as to facilitate recovery. Therefore, the acid that can achieve this function can be applied to the present application. The above-mentioned acid includes at least one of nitric acid, hydrochloric acid and sulfuric acid. In a preferred embodiment of the present application, the acid used in the acidolysis includes nitric acid. After acidolysis, nitric acid is converted into nitrates. During the evaporation and concentration process, the nitrates will decompose to produce nitrogen oxides, and ammonia reacts with nitrogen oxides and releases heat, which further intensifies the intensity of the reaction. This can not only reduce process energy consumption and cost, but also further reduce the particle size of lithium iron phosphate and increase its gram capacity. In order to dissolve as much lithium element as possible in the lithium iron phosphate positive electrode material, the amount of acid in the acidolysis and the acidolysis temperature can be optimized. In a preferred embodiment, the amount of acid required for each gram of lithium iron phosphate positive electrode material is 3mL~4mL, the concentration of the acid is 1.5mol / L~2mol / L, and the acidolysis temperature is 80℃~95℃.

[0030] In a preferred embodiment of the present application, the temperature of evaporation concentration is 80°C to 95°C, and the temperature of the spontaneous combustion reaction is 240°C to 350°C. The temperatures of the evaporation concentration process and the spontaneous combustion reaction process include but are not limited to the above ranges, and limiting them within the above ranges is beneficial to further improve the yield of the combustion products. Optionally, the temperature of the above-mentioned spontaneous combustion reaction process is 240°C, 250°C, 260°C, 270°C, 280°C, 290°C, 300°C, 310°C, 320°C, 330°C, 340°C, 350°C, or a range formed by any two of the above values.

[0031] Preferably, the above-mentioned autoignition process is carried out in a muffle furnace.

[0032] The lithium source compound used in the lithium replenishment process is preferably a lithium soluble salt. The lithium soluble salt can be a lithium source type commonly used to form a positive electrode material. For solubility and cost considerations, LiNO 3 , Li 2 SO 4 and Li 2 C 2 O 4 One or more of the groups.

[0033] The carbon coating process is achieved through high-temperature sintering under an inert atmosphere. Through the carbon coating process, on the one hand, the conductivity of the regenerated lithium iron phosphate cathode material can be improved, and on the other hand, the structural stability and performance stability of the electrode material can be enhanced. In a preferred embodiment of the present application, the temperature of the carbon coating treatment is 700 °C to 800 °C. During the carbon coating process, the temperature of the carbon coating treatment includes but is not limited to the above range, and limiting it within the above range is beneficial to improving the coating uniformity and coating amount of carbon elements, and further improving the structural stability and conductivity of the cathode material. Optionally, the temperature of the above carbon coating treatment is 700 °C, 710 °C, 720 °C, 730 °C, 740 °C, 750 °C, 760 °C, 770 °C, 780 °C, 790 °C, 800 °C, or the range formed by any two of the above values.

[0034] In the above carbon coating process, the carbon source can be selected from the types commonly used in the art. In a preferred embodiment of the present application, the carbon source used in the carbon coating treatment is one or more of glucose, sucrose, citric acid, and hydroxyethyl cellulose.

[0035] The coating amount of the carbon source will affect the electrochemical performance of the regenerated lithium iron phosphate cathode material. Preferably, based on the weight percentage of the combustion product, the coating amount of the carbon source is 0.8% to 1.4%.

[0036] The following further describes the present application in detail with specific embodiments, and these embodiments should not be construed as limiting the scope claimed by the present application.

[0037] Example 1

[0038] A method for regenerating lithium iron phosphate cathode material in waste lithium batteries, the process flow is as Figure 1 shown, including the following steps:

[0039] 1) Disassemble the waste lithium battery, and after pre-treating the electrode sheet, 500 g of lithium iron phosphate cathode powder is obtained.

[0040] 2) Mix the above lithium iron phosphate cathode powder with 3.5 L of nitric acid aqueous solution with a concentration of 1.5 mol / L, heat and stir at 80 °C to 95 °C for 3 h to 5 h, then perform solid-liquid separation to obtain a solid residue mainly composed of a mixed solution containing lithium ions, phosphoric acid, and iron ions and carbon powder. According to the synthesis requirements of lithium iron phosphate and the ICP results, lithium salts are added to adjust the metal ratio. At the same time, according to the concentration of nitrate ions in the solution, urea is added as a combustion aid, and the molar ratio of urea to nitric acid is 2:1.

[0041] 3) Evaporate and concentrate the mixed solution containing lithium ions, phosphoric acid and iron ions obtained in step 2 at a temperature set at 90 °C until a gel is formed; then raise the temperature to 350 °C and keep it warm for 30 min. The reaction inside the gel is excited and self-ignites to form a combustion product.

[0042] 4) The combustion product obtained in step 3 is ball-milled and mixed with glucose at a mass ratio of 10%, and then calcined under an inert atmosphere to complete carbon coating. The carbon coating amount is 1.0 wt%, the calcination time is set at 6 h, and the calcination temperature is set at 700 °C.

[0043] 5) The positive electrode powder obtained in step 4 is mixed with a conductive agent (carbon black) and a binder (PVDF) to make a positive electrode sheet, and the mass ratio of the three is 9:0.5:0.5. This positive electrode and a lithium metal sheet negative electrode form a button cell. It is measured that the discharge specific capacity of the repaired lithium iron phosphate positive electrode material reaches 157.5 mA·h at a 0.1C rate, which is equivalent to the specific capacity of 158.1 mA·h of the fresh material.

[0044] Example 2

[0045] The waste lithium battery lithium iron phosphate positive electrode material selected in this example and the recycling process are the same as those in Example 1. The difference is that the ratio of the combustion aid urea to nitric acid is 4:1, and the specific capacity of the finally obtained lithium iron phosphate positive electrode material at a 0.1C rate is 148.2 mA·h.

[0046] Example 3

[0047] The waste lithium battery lithium iron phosphate positive electrode material selected in this example and the recycling process are the same as those in Example 1. The difference is that the calcination temperature with glucose is 800 °C, and the specific capacity of the finally obtained lithium iron phosphate positive electrode material at a 0.1C rate is 140.4 mA·h.

[0048] Example 4

[0049] The waste lithium battery lithium iron phosphate positive electrode material selected in this example and the recycling process are the same as those in Example 1. The difference is that the ratio of the combustion aid urea to nitric acid during the regeneration process is 6:1. The specific capacity of the finally obtained lithium iron phosphate positive electrode material at a 0.1C rate is 146.9 mA·h.

[0050] Example 5

[0051] The waste lithium battery lithium iron phosphate positive electrode material selected in this example and the recycling process are the same as those in Example 1. The difference is that the ratio of the combustion aid urea to nitric acid during the regeneration process is 8:1. The specific capacity of the finally obtained lithium iron phosphate positive electrode material at a 0.1C rate is 144.8 mA·h.

[0052] Example 6

[0053] The lithium iron phosphate cathode material of waste lithium batteries selected in this example and the recycling process are the same as those in Example 1. The difference is that the combustion aid is dimethylformyl hydrazine. The specific capacity of the finally obtained lithium iron phosphate cathode material at a 0.1C rate is 154.6 mA·h.

[0054] Example 7

[0055] The lithium iron phosphate cathode material of waste lithium batteries selected in this example and the recycling process are the same as those in Example 4. The difference is that the combustion aid is glucose. The specific capacity of the finally obtained lithium iron phosphate cathode material at a 0.1C rate is 140.0 mA·h.

[0056] Example 8

[0057] The lithium iron phosphate cathode material of waste lithium batteries selected in this example and the recycling process are the same as those in Example 4. The difference is that the temperature of carbon coating is 900 °C. The specific capacity of the finally obtained lithium iron phosphate cathode material at a 0.1C rate is 146.1 mA·h.

[0058] Comparative Example 1

[0059] It is known from testing a commercially available lithium iron phosphate cathode material of the same model as that in Example 1 that the specific capacity of the cathode material at a 0.1C rate is 158.1 mA·h.

[0060] Comparative Example 2

[0061] The lithium iron phosphate cathode material of waste lithium batteries selected in this example and the recycling process are the same as those in Example 4. The difference is that the combustion aid is glycine. The specific capacity of the finally obtained lithium iron phosphate cathode material at a 0.1C rate is 139.1 mA·h.

[0062] Comparative Example 3

[0063] The lithium iron phosphate cathode material of waste lithium batteries selected in this example and the recycling process are the same as those in Example 4. The difference is that the combustion aid is citric acid. The specific capacity of the finally obtained lithium iron phosphate cathode material at a 0.1C rate is 138.8 mA·h.

[0064] By comparing Examples 1 to 8 with Comparative Examples 1 to 3, it can be seen that the specific capacity of the lithium iron phosphate cathode material obtained by using the regeneration method provided in this application is comparable to that of commercially available products, which sufficiently shows that the regeneration method provided in this application has good effects; and by carefully studying its regeneration process, it can be found that the entire process has a short process flow and relatively low cost. At the same time, compared with other combustion aids, the specific capacity of the regenerated lithium iron phosphate cathode material obtained by using the combustion aid used in this application is higher. The reason for this result may be that the particle size of lithium iron phosphate becomes smaller, thereby improving the specific capacity of the regenerated lithium iron phosphate material.

[0065] Comparing Examples 1, 2, 4 and 5, it can be seen that limiting the ratio of the combustion improver to nitric acid within the preferred range of the present application is beneficial to increasing the specific capacity per gram of the regenerated lithium iron phosphate cathode material.

[0066] It should be noted that the terms "first", "second", etc. in the description and claims of the present application are used to distinguish similar objects and do not necessarily have to be used to describe a specific order or sequence. It should be understood that such terms can be interchanged under appropriate circumstances so that the embodiments of the present application described herein can be implemented in an order different from those described herein, for example.

[0067] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention can have various modifications and changes. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for regenerating lithium iron phosphate cathode material from waste lithium batteries, characterized in that, the regeneration method includes: pre-treating waste lithium iron phosphate cathode sheets to obtain lithium iron phosphate cathode material; subjecting the lithium iron phosphate cathode material to acidolysis, lithium supplementation and evaporation concentration in sequence to obtain a precursor gel; in the presence of a combustion aid containing amino groups, causing the precursor gel to undergo a self-combustion reaction to obtain a combustion product; under an inert atmosphere, performing carbon coating treatment on the combustion product with a carbon source to obtain the regenerated lithium iron phosphate cathode material.

2. The method for regenerating lithium iron phosphate cathode material from waste lithium batteries according to claim 1, characterized in that, the combustion aid containing amino groups includes at least one of urea and dimethylformylhydrazine.

3. The method for regenerating lithium iron phosphate cathode material from waste lithium batteries according to claim 1, characterized in that, the molar ratio of the combustion aid containing amino groups to the lithium element in the reaction system after lithium supplementation is 1:(2 - 6).

4. The method for regenerating lithium iron phosphate cathode material from waste lithium batteries according to claim 1, characterized in that, the timing of adding the combustion aid containing amino groups is after lithium supplementation and before evaporation concentration.

5. The method for regenerating lithium iron phosphate cathode material from waste lithium batteries according to claim 1, characterized in that, the acid used in the acidolysis includes at least one of nitric acid, hydrochloric acid and sulfuric acid.

6. The method for regenerating lithium iron phosphate cathode material from waste lithium batteries according to claim 5, characterized in that, in the acidolysis, the dosage of the acid required per gram of the lithium iron phosphate cathode material is 3 mL - 4 mL, and the concentration of the acid is 1.5 mol / L - 2 mol / L.

7. The method for regenerating lithium iron phosphate cathode material from waste lithium batteries according to claim 1, characterized in that, the temperature of the evaporation concentration is 80°C - 95°C; and / or the temperature of the self-combustion reaction is 240°C - 350°C.

8. The method for regenerating lithium iron phosphate cathode material from waste lithium batteries according to claim 1, characterized in that, the pre-treatment includes soaking the waste lithium iron phosphate cathode sheets with an N-methylpyrrolidone solvent to obtain the lithium iron phosphate cathode material.

9. The method for regenerating lithium iron phosphate cathode material from waste lithium batteries according to claim 1, characterized in that, the temperature of the carbon coating treatment is 700°C - 800°C.

10. The method for regenerating lithium iron phosphate cathode material from waste lithium batteries according to claim 1, characterized in that, the carbon source used in the carbon coating treatment includes at least one of glucose, sucrose, citric acid and hydroxyethyl cellulose; and / or the coating amount of the carbon source accounts for 0.8% - 1.4% of the weight of the combustion product.

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