Method for separating positive and negative electrode materials in lithium iron phosphate mixed black powder
By extruding the surface of lithium iron phosphate and using magnetic separation technology, the separation of positive and negative electrode materials in lithium-ion battery recycling has been successfully achieved, solving the problem of inseparable materials in the prior art, and improving the recycling efficiency of lithium, iron and phosphorus elements and the utilization rate of graphite materials.
Patent Information
- Application Number
- CN202510371999.9
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-03-27
- Publication Date
- 2025-05-13
AI Technical Summary
In the existing lithium-ion battery recycling process, the positive and negative electrode materials of waste lithium iron phosphate batteries cannot be effectively separated, resulting in low extraction efficiency of lithium, complex processing technology, high energy consumption and cost, and the negative electrode materials eventually mixed with the leaching slag, resulting in waste of resources.
By extruding the surface of lithium iron phosphate, separation of positive and negative electrode materials is achieved by magnetic separation. The specific steps include dynamic sintering under the protection of an inert gas, adding alkali metal hydroxide powder for solid phase sintering, and then adding water to disperse and performing liquid phase magnetic separation to obtain a magnetic imparting mixture and an unmagnetized negative electrode material.
It realizes efficient leaching and recycling of lithium, iron and phosphorus elements in lithium iron phosphate positive electrode materials. At the same time, graphite materials are sold as by-products, solving the problem of inseparable positive and negative electrode materials and improving resource utilization.
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Figure CN119976784A_ABST
Abstract
Description
Technical Field
[0001] The invention belongs to the technical field of recycling waste lithium-ion batteries, and in particular relates to a method for separating positive and negative electrode materials in lithium iron phosphate mixed black powder. Background Art
[0002] In recent years, with the development of new energy industries such as electric vehicles, the demand for lithium-ion batteries has continued to increase, resulting in an increase in the amount of scrapped lithium-ion batteries year by year. With the current lithium battery recycling process, after mechanical crushing and screening of waste lithium iron phosphate batteries, only positive and negative electrode mixed powders can be obtained. The content of lithium iron phosphate positive electrode materials in the material is about 66%, and the rest is mainly graphite negative electrode materials. The presence of the negative electrode makes it more difficult to leach lithium iron phosphate, the lithium extraction efficiency is low, the processing process is complicated, the energy consumption and cost are high, and the negative electrode materials are finally mixed with the leached residue and can only be treated as solid waste, resulting in a waste of resources.
[0003] Most of the existing technologies currently separate the positive and negative electrodes semi-automatically, which requires a lot of manual participation and is very harmful to the human body. Summary of the invention
[0004] In view of the deficiencies of the prior art, the present invention provides a method for separating positive and negative electrode materials in lithium iron phosphate mixed black powder. The present invention performs magnetic treatment on the surface of lithium iron phosphate, and separates the surface-magnetized lithium iron phosphate from the non-magnetized negative electrode graphite by magnetic separation, while not causing excessive side reactions, which is beneficial to the leaching and recovery of lithium, iron, and phosphorus elements in the lithium iron phosphate positive electrode material. At the same time, the graphite material can also be sold as a by-product, which can solve the problem that the positive and negative electrode materials in the battery black powder cannot be separated.
[0005] The technical solution of the present invention is as follows:
[0006] The present invention first provides a method for separating positive and negative electrode materials in lithium iron phosphate mixed black powder, the method comprising the following steps:
[0007] S1: Under the protection of inert gas, the mixed black powder is subjected to the first stage of dynamic sintering, and after sintering, alkali metal hydroxide powder is added, and after the temperature is further raised, the second stage of dynamic solid phase sintering is performed again to obtain a sintered product;
[0008] S2: Add water to the sintered product to disperse it to obtain a slurry, and perform liquid phase magnetic separation to obtain a magnetic mixture and a non-magnetic negative electrode material.
[0009] Preferably, in step S1, the mixed black powder is a positive and negative electrode mixed black powder.
[0010] Preferably, in step S1, the mixed black powder is the positive and negative electrode black powder obtained by discharging, physically crushing and sorting waste lithium iron phosphate batteries.
[0011] Preferably, in step S1, the alkaline metal hydroxide includes at least one of sodium hydroxide and potassium hydroxide.
[0012] Preferably, in step S1, the mass ratio of the mixed black powder to the alkaline metal hydroxide powder is 100:10-15.
[0013] Preferably, in step S1, the inert gas includes nitrogen; the temperature of the first stage of dynamic sintering is 400-420°C, and the time is 3-5 hours; the temperature of the second stage of dynamic solid phase sintering is 500-650°C, and the time is 1-3 hours. The dynamic sintering equipment can be a high temperature VC mixer, etc.
[0014] Preferably, in step S1, the atmosphere of the solid phase sintering is nitrogen.
[0015] Preferably, in step S2, the liquid phase magnetic separation is carried out in a liquid phase magnetic separator.
[0016] Preferably, in step S2, the magnetic separation intensity of the liquid phase magnetic separation is 6000 to 10000 Gs.
[0017] Preferably, in step S2, the magnetic mixture is lithium iron phosphate with ferroferric oxide loaded on the surface, wherein the mass fraction of the magnetic substance loaded on the surface of the lithium iron phosphate is 5-10%.
[0018] The beneficial technical effects of the present invention are:
[0019] The present invention magnetizes the surface of lithium iron phosphate, and the magnetization amount accounts for about 5-10% of the lithium iron phosphate material. It will not cause excessive side reactions while magnetizing, which is beneficial to the leaching and recovery of lithium, iron and phosphorus elements in the lithium iron phosphate positive electrode material. At the same time, the graphite material can also be sold as a by-product, which can solve a major problem that has plagued the industry. BRIEF DESCRIPTION OF THE DRAWINGS
[0020] Figure 1 This is a photo of the magnetic adsorption of positive and negative electrode materials after sintering. DETAILED DESCRIPTION
[0021] The present invention is described in detail below in conjunction with the accompanying drawings and embodiments.
[0022] The present invention first provides a method for separating positive and negative electrode materials in lithium iron phosphate mixed black powder, the method comprising the following steps:
[0023] S1: Under the protection of inert gas, the lithium iron phosphate mixed with black powder is subjected to the first stage of dynamic sintering, and after sintering, alkali metal hydroxide powder is added, and the temperature is continued to be raised before the second stage of dynamic solid phase sintering is performed again to obtain a sintered product;
[0024] S2: Add water to the sintered product to disperse it to obtain a slurry, and perform liquid phase magnetic separation to obtain a magnetic mixture and a non-magnetic negative electrode material.
[0025] It can be understood that the present invention magnetizes the surface of lithium iron phosphate, and the magnetization amount accounts for about 5-10% of the lithium iron phosphate material. It will not cause excessive side reactions while magnetizing, which is beneficial to the leaching and recovery of lithium, iron and phosphorus elements in the lithium iron phosphate positive electrode material. At the same time, the graphite material can also be sold as a by-product, which can solve a major problem that has plagued the industry.
[0026] It is understandable that since the recycled lithium iron phosphate material is in a lithium-depleted state, there is LiFePO4 (Fe 2 + ) and FePO4(Fe 3+ ) phases, during the sintering process under alkaline conditions, Fe 2+ and Fe 3+ First, it transforms into Fe(OH)2 and Fe(OH)3, and then dehydrates at high temperature to form magnetic Fe3O4 on the surface of the positive electrode material. The chemical reactions occurring on the surface of lithium iron phosphate during the process are as follows:
[0027] 3[(xLiFePO4+(1-x)FePO4]+6NaOH→Fe3O4+Li3PO4+2Na3PO4 (1);
[0028] Where: 0 <x<1。
[0029] In some embodiments, in step S1, the mixed black powder is a positive and negative electrode mixed black powder.
[0030] In some embodiments, in step S1, the mixed black powder is positive and negative electrode black powder obtained by discharging, physically crushing and sorting waste lithium iron phosphate batteries.
[0031] In some embodiments, in step S1, the alkaline metal hydroxide includes at least one of sodium hydroxide and potassium hydroxide.
[0032] In some embodiments, in step S1, the mass ratio of the mixed black powder to the alkaline metal hydroxide powder is 100:10-15, including but not limited to 100:10, 100:11, 100:12, 100:13, 100:14, 100:15.
[0033] It is understandable that under the conditions of dynamic sintering, the amount of magnetization on the surface of the positive electrode material can be controlled by controlling the amount of alkali metal hydroxide added. When the magnetization amount is too large, it will not only lead to an increase in side reactions, but also affect the recovery quality and subsequent processing of the material. If the magnetization amount is too small, the positive and negative electrodes cannot be completely separated during magnetic screening, the content of lithium iron phosphate in the graphite is relatively high, and the graphite cannot be recycled.
[0034] In some embodiments, in step S1, the inert gas includes nitrogen; the temperature of the first stage dynamic sintering is 400-420°C, and the time is 3-5 hours; the temperature of the second stage dynamic solid phase sintering is 500-650°C, and the time is 1-3 hours.
[0035] It is understandable that during the first sintering process, CMC (sodium carboxymethyl cellulose) and styrene-butadiene rubber binders in the negative electrode are first cracked at a temperature of 400-420°C. Within this temperature, the amount of cracking of the negative electrode binder is about 80%, and the binder PVDF in the positive electrode will not be cracked, so there is no adhesion between the materials, which is conducive to the subsequent magnetic separation. After adding alkali metal hydroxide, the second stage of dynamic sintering is carried out at a sintering temperature of 500-650°C. PVDF decomposes under alkaline conditions and its residual amount is reduced. Therefore, while magnetizing the positive electrode material, it will not cause the binder to crack and adhere. At the same time, sintering under dynamic conditions makes it less likely for the materials to adhere, which is conducive to the subsequent separation of mixed materials.
[0036] It is understandable that the first stage sintering temperature is 400-420℃. If the temperature is too low, the binder in the negative electrode will not decompose, and more alkali metal hydroxide will be consumed later. If the temperature is too high, it is easy to cause PVDF to crack, causing adhesion between materials, affecting the sorting efficiency. The second stage sintering temperature is 500-650℃. If the sintering temperature is too low, magnetic ferroferric oxide will not be formed. If the temperature is too high, the alkali metal hydroxide will react with graphite, and the lithium iron phosphate positive electrode will also self-decompose. At the same time, the sintering time is controlled at 1-3h.
[0037] In some embodiments, in step S1, the solid phase sintering atmosphere is nitrogen.
[0038] In the present invention, water is added to the sintered product to obtain a slurry, and the solid content of the slurry is controlled at 10-15%, preferably 15%.
[0039] In some embodiments, in step S2, the liquid phase magnetic separation is performed in a liquid phase magnetic separator.
[0040] In some embodiments, in step S2, the magnetic separation intensity of the liquid phase magnetic separation is 6000-10000 Gs, including but not limited to 6000 Gs, 7000 Gs, 8000 Gs, 9000 Gs, and 100000 Gs.
[0041] The intensity of the magnetic separation of the present invention is 6000-10000 Gs. If the intensity is too high, a small amount of negative electrode powder may be adsorbed, and if the intensity is too low, the separation efficiency may decrease.
[0042] In some embodiments, in step S2, the magnetic mixture is lithium iron phosphate with ferroferric oxide loaded on the surface, wherein the mass fraction of the magnetic substance loaded on the surface of the lithium iron phosphate is 5-10%.
[0043] It can be understood that the present invention obtains magnetic lithium iron phosphate powder and negative electrode material containing a small amount of lithium by magnetic separation, and the lithium element can be further recovered after washing the negative electrode material.
[0044] In some embodiments, after the magnetic separation, the slurry containing the lithium iron phosphate positive electrode and the graphite negative electrode is washed and separated by filter pressing to obtain positive electrode materials and negative electrode materials that do not contain slurry after separation.
[0045] The present invention will be further described below by way of examples and the like.
[0046] Embodiment 1:
[0047] The method for separating positive and negative electrode materials in lithium iron phosphate mixed black powder comprises the following steps:
[0048] (1) Under nitrogen conditions, the lithium iron phosphate mixed black powder was heated to 400°C in a VC mixer and kept warm for 5 hours. After cooling, 15% sodium hydroxide powder was mixed (i.e., the mass of the added sodium hydroxide powder was 15% of the lithium iron phosphate mixed black powder). The mixture was reacted at 650°C for 1 hour under nitrogen protection to obtain a sintered material.
[0049] (2) The sintered material is dispersed in water, the solid content is controlled at 15%, and liquid phase magnetic separation is performed with a magnetic roller strength of 8000 Gs. After two magnetic separations, lithium iron phosphate positive electrode and graphite negative electrode slurry are obtained. The slurry is washed and filtered to separate the positive and negative electrode materials.
[0050] Embodiment 2:
[0051] The method for separating positive and negative electrode materials in lithium iron phosphate mixed black powder comprises the following steps:
[0052] (1) The lithium iron phosphate mixed black powder was heated to 420° C. in a VC mixer, kept warm for 3 h, and then mixed with 10% potassium hydroxide powder after cooling, and sintered at 600° C. for 1.5 h under nitrogen protection to obtain a sintered material.
[0053] (2) The sintered material is dispersed in water, the solid content is controlled at 15%, and liquid phase magnetic separation is performed with a magnetic roller strength of 10000 Gs. After two magnetic separations, lithium iron phosphate positive electrode and graphite negative electrode slurry are obtained. The slurry is filtered and separated to obtain the separated positive and negative electrode materials.
[0054] Embodiment 3:
[0055] The method for separating positive and negative electrode materials in lithium iron phosphate mixed black powder comprises the following steps:
[0056] (1) The lithium iron phosphate mixed black powder was heated to 410° C. in a VC mixer, kept warm for 3 h, and then mixed with 12% sodium hydroxide powder after cooling, and sintered at 550° C. for 1.0 h under nitrogen protection to obtain a sintered material.
[0057] (2) The sintered material is dispersed in water, the solid content is controlled at 15%, and liquid phase magnetic separation is performed with a magnetic roller strength of 6000 Gs. After two magnetic separations, lithium iron phosphate positive electrode and graphite negative electrode slurry are obtained. The slurry is filtered and separated to obtain separated positive and negative electrode materials.
[0058] Comparative Example 1:
[0059] The method for separating positive and negative electrode materials in lithium iron phosphate mixed black powder is basically the same as that in Example 1, except that 40% of sodium hydroxide solid is added in step (1) and then a second heating is performed. Under nitrogen protection, the material is sintered at 550° C. for 2 h in a nitrogen atmosphere to obtain a sintered material.
[0060] Comparative Example 2:
[0061] The method for separating positive and negative electrode materials in lithium iron phosphate mixed black powder is basically the same as that in Example 1, except that the temperature during the second heating in step (1) is 700° C. and the time is 2 hours.
[0062] Comparative Example 3:
[0063] The method for separating positive and negative electrode materials in lithium iron phosphate mixed black powder is basically the same as that in Example 1, except that 5% of sodium hydroxide solid is added during the second heating in step (1), and the material is sintered at 550° C. for 2 h in a nitrogen atmosphere under nitrogen protection to obtain a sintered material.
[0064] Comparative Example 4:
[0065] The method for separating positive and negative electrode materials in lithium iron phosphate mixed black powder is basically the same as that in Example 1, except that there is no first stage heating condition in step (1), and the mixed sodium hydroxide powder is directly heated to 650° C. and kept warm for 1 hour.
[0066] Test example:
[0067] The purity of the separated magnetized mixture and the non-magnetized negative electrode material in the embodiment and the comparative example is shown in Table 1. The content of each element is tested according to the method in the test standard YS / T 1028.1-2015.
[0068] Table 1 Products and purity after treatment in Examples and Comparative Examples
[0069]
[0070] As can be seen from Table 1, the amount of alkali metal hydroxide added needs to be appropriate. Too high will cause an increase in side reactions; too low will lead to uneven reactions and poor magnetic separation effects. And two stages of sintering are required to achieve better separation effects. If the sintering temperature is too low, magnetic ferroferric oxide will not be formed. If the temperature is too high, the alkali metal hydroxide will react with graphite, and the lithium iron phosphate positive electrode will also self-decompose.
[0071] The present invention solves the problem that the positive and negative electrode materials in the black powder cannot be separated during lithium battery recycling, and the subsequent processing process is difficult. While magnetizing the lithium iron phosphate mixed powder, the side reaction of the material is avoided, and the subsequent utilization rate of phosphorus, iron and graphite elements is improved.
[0072] The above is only a preferred embodiment of the present invention, and the present invention is not limited to the above embodiments. It is understood that other improvements and changes directly derived or associated by those skilled in the art without departing from the spirit and concept of the present invention should be considered to be included in the protection scope of the present invention.
Claims
1. A method for separating positive and negative electrode materials in lithium iron phosphate mixed black powder, characterized in that: The method comprises the following steps: S1: Under the protection of inert gas, the mixed black powder is subjected to the first stage of dynamic sintering, and after sintering, alkali metal hydroxide powder is added, and after continuing to increase the temperature, the second stage of dynamic solid phase sintering is carried out to obtain a sintered product; S2: Add water to the sintered product to disperse it to obtain a slurry, and perform liquid phase magnetic separation to obtain a magnetic mixture and a non-magnetic negative electrode material.
2. The method according to claim 1, characterized in that In step S1, the mixed black powder is a positive and negative electrode mixed black powder.
3. The method according to claim 1, characterized in that In step S1, the mixed black powder is the positive and negative electrode black powder obtained by discharging, physically crushing and sorting the waste lithium iron phosphate batteries.
4. The method according to claim 1, characterized in that: In step S1, the alkaline metal hydroxide includes at least one of sodium hydroxide and potassium hydroxide.
5. The method according to claim 1, characterized in that In step S1, the mass ratio of the mixed black powder to the alkaline metal hydroxide powder is 100:10-15.
6. The method according to claim 1, characterized in that In step S1, the inert gas includes nitrogen; the temperature of the first stage dynamic sintering is 400-420°C, and the time is 3-5 hours; the temperature of the second stage dynamic solid phase sintering is 500-650°C, and the time is 1-3 hours.
7. The method according to claim 1, characterized in that In step S1, the atmosphere of the solid phase sintering is nitrogen.
8. The method according to claim 1, characterized in that In step S2, the liquid phase magnetic separation is carried out in a liquid phase magnetic separator.
9. The method according to claim 1, characterized in that: In step S2, the magnetic separation intensity of the liquid phase magnetic separation is 6000-10000 Gs.
10. The method according to claim 1, characterized in that In step S2, the magnetic mixture is lithium iron phosphate with ferroferric oxide loaded on the surface, wherein the mass fraction of the magnetic substance loaded on the surface of the lithium iron phosphate is 5-10%.