Iron phosphate lithium cathode material pretreatment method based on directional oxidation roasting

Abstract

The application provides a lithium iron phosphate positive electrode material pretreatment method based on directional oxidation roasting, and belongs to the technical field of battery materials. The method comprises the following steps: (1) adding a composite additive into lithium iron phosphate black powder to obtain a mixture; the composite additive is a composite formed by loading a functionalized ionic liquid on a porous silica carrier; (2) placing the mixture into a rotary kiln, introducing nitrogen, controlling the heating rate and roasting temperature to perform roasting, and keeping warm for 2-3 hours; (3) cooling the roasted material to ≤30 DEG C; (4) mixing the cooled material with deionized water, stirring at a set temperature, then adding an adsorbent, and continuing to stir; (5) filtering and separating the material; and (6) recycling the additive residue. The method has significant advantages in improving the Fe 2+ conversion rate, lithium and phosphorus leaching rate, reducing the impurity concentration of leaching solution and realizing the recycling of the composite additive, and has good application prospect.

Description

Technical Field

[0001] This application relates to the field of battery materials technology, and in particular to a pretreatment method for lithium iron phosphate cathode materials based on directional oxidation calcination. Background Technology

[0002] In current recycling technologies for spent lithium iron phosphate (LFP) battery cathode materials, the traditional pyrometallurgical-hydrometallurgical combined recycling method has low efficiency, and its recycling process mainly suffers from the following problems:

[0003] Inaccurate temperature control during pyrometallurgical processes leads to Fe... 2+ Incomplete oxidation, Fe was not fully formed. 3+ Excessively high temperatures during pyrometallurgical processes cause phosphates to precipitate under high-temperature, high-acid conditions. Pyrophosphate is extremely insoluble in acid. Once pyrophosphate forms, most of the phosphorus is locked in the slag, making effective leaching impossible under conventional acid leaching conditions. The dense structure of the pyrophosphate slag may trap unreacted lithium salts or hinder lithium diffusion and leaching. If all lithium is present in the insoluble lithium iron pyrophosphate, it will be directly lost in the slag.

[0004] Furthermore, the large fluctuations in carbon content of waste lithium iron phosphate cathode materials in actual recycling scenarios present the following unresolved key challenges:

[0005] Carbon powder interferes with oxidation reaction: Residual carbon powder (conductive agent) in the cathode material easily reacts with oxygen during calcination to generate CO / CO2, consuming trace amounts of oxygen in the calcination system, leading to Fe... 2+ Insufficient oxidation kinetics; simultaneously, carbon powder adsorbs sulfuric acid, reducing the contact efficiency between sulfuric acid and lithium iron phosphate, further exacerbating the Fe... 2+ The problem of incomplete oxidation, especially when the carbon content is >5wt%, is related to Fe. 2+ The conversion rate will drop by another 10-15%.

[0006] Material agglomeration during roasting affects heat transfer: In traditional processes, lithium iron phosphate black powder mixed with sulfuric acid easily forms lumpy agglomerates. During rotary kiln roasting, the internal temperature gradient of these agglomerates can vary by 50-80℃, leading to increased heat transfer of Fe3+ within the material. 2+ Insufficient oxidation and the formation of pyrophosphate in the external materials due to localized overheating make it difficult to achieve uniform reaction across the entire batch of materials.

[0007] Subsequent purification of the leachate is challenging: even with high recovery rates, the leachate still contains trace amounts of carbon powder and Fe. 3+ PO4 3- Impurities such as lithium and phosphorus require multiple precipitation and filtration processes for separation and purification in traditional processes. This not only increases reagent costs but also leads to secondary losses of lithium and phosphorus. For example, a single precipitation can cause a 2-3% loss of lithium. Summary of the Invention

[0008] This application is based on the fact that Fe in the prior art 2+ This study addresses the problem of insufficient oxidation kinetics and aims to provide a pretreatment method for lithium iron phosphate cathode materials based on directional oxidation roasting.

[0009] Specifically, the first aspect of this application provides a pretreatment method for lithium iron phosphate cathode materials based on directional oxidation calcination, comprising the following steps:

[0010] (1) Raw material mixing: The composite additive is added to lithium iron phosphate black powder and mixed to obtain a mixture;

[0011] The composite additive is a composite formed by functionalized ionic liquid supported on a porous silica support.

[0012] (2) Acidification roasting: The mixture obtained in step (1) is placed in a rotary kiln, nitrogen is introduced, and the heating rate and roasting temperature are controlled for roasting, and the temperature is maintained for 2-3 hours;

[0013] (3) Cooling: Cool the roasted material to ≤30℃ by water cooling;

[0014] (4) Pickling and in-situ adsorption: The cooled material is mixed with deionized water at a certain solid-liquid ratio, stirred at a set temperature, and then the adsorbent is added and stirred again.

[0015] (5) Solid-liquid separation: The pickled material is filtered and separated using a plate and frame filter press to obtain leachate and residue;

[0016] (6) Recovery of additive residue: The residue obtained in step (5) is roasted and then the additive components are separated and recovered by acid dissolution-precipitation method.

[0017] Furthermore, the porous silica carrier in the composite additive described in step (1) is mesoporous silica with a specific surface area of ​​500-1200 m². 2 / g, with an average pore size of 2-10 nm; the functionalized ionic liquid is one of 1-carboxyethyl-3-methylimidazolium tetrafluoroborate and 1-butyl-3-methylimidazolium hexafluorophosphate.

[0018] Further, in step (1), the loading of the functionalized ionic liquid is 10 wt% - 50 wt%, based on the total mass of the composite additive.

[0019] Furthermore, the solvent used in the mixing in step (1) is deionized water or ethanol, and the mixture is dried after mixing to remove the solvent.

[0020] Further, the heating rate in step (2) is 6-8℃ / min; the calcination temperature is 400-550℃; and / or the nitrogen flow rate is 0.5-1L / min.

[0021] Further, in step (4), the cooled material is mixed with deionized water at a mass ratio of 1:4-10, the acid washing temperature is 50-90℃, the initial stirring time is 30-60 min, and the continued stirring time after adding the adsorbent is 1-2.5 h; the adsorbent is modified activated carbon with a particle size of 5-10 μm and a specific surface area of ​​1000-1500 m². 2 / g, the amount added is 0.5-1% of the mass of the leachate.

[0022] Furthermore, the filter cloth pore size of the plate and frame filter press in step (5) is 0.1 μm, the filtration pressure is 0.4-0.6 MPa, and the filtration time is 15-30 min.

[0023] Furthermore, the temperature of the residue roasting in step (6) is 500-550℃, the roasting atmosphere is air, and the roasting time is 1h;

[0024] The acid used in the acid dissolution-precipitation method is 20-25% hydrochloric acid, which dissolves MgO and Al2O3 in the residue.

[0025] Furthermore, the lithium iron phosphate cathode material is black powder of waste lithium iron phosphate (LFP) battery cathode material, with a particle size of 1-10μm, a Li content of 3.5-4.5wt%, an Fe content of 25-30wt%, a P content of 18-22wt%, and a carbon content of 6-8wt%.

[0026] Furthermore, this method is used to treat lithium iron phosphate cathode materials, Fe 2+ Conversion rate ≥ 98.5%, lithium leaching rate ≥ 99%, phosphorus leaching rate ≥ 98%, carbon powder concentration in leachate ≤ 0.01 g / L, Fe 3+ With a concentration ≤0.02g / L, the adsorption capacity of the composite additive remains above 85% of its initial value after three cycles of use.

[0027] The present invention has the following beneficial effects:

[0028] First, in solving Fe 2+ In terms of insufficient oxidation kinetics, the use of composite additives played a crucial role. Composite additives formed by functionalized ionic liquids supported on porous silica carriers can significantly enhance Fe... 2+The porous silica support provides a large specific surface area and suitable pore structure, enabling the functionalized ionic liquid to be uniformly dispersed and fully contact the lithium iron phosphate powder, thereby enhancing the mass transfer process of the oxidation reaction. Simultaneously, the functionalized ionic liquid itself possesses excellent oxidation performance and selectivity, precisely promoting the oxidation of Fe during the calcination process. 2+ To Fe 3+ The transformation avoids the Fe oxidation caused by inaccurate temperature control in traditional fire methods. 2+ The problem is incomplete oxidation.

[0029] Secondly, regarding the issue of heat transfer being affected by agglomeration of roasted materials, the pretreatment method of this application effectively reduces the formation of agglomerates by optimizing the raw material mixing and roasting process. The addition of composite additives reduces the agglomeration tendency of materials during the roasting process. In addition, controlling the heating rate and roasting temperature ensures that the materials are heated uniformly in the rotary kiln, avoiding the problems of uneven reaction caused by local overheating and excessive temperature gradient differences.

[0030] Furthermore, regarding the difficulty of subsequent purification of the leachate, the pretreatment method of this application effectively removes trace amounts of carbon powder and Fe from the leachate through acid washing and in-situ adsorption steps. 3+ PO4 3- Impurities such as impurities are eliminated. Modified activated carbon, as an adsorbent, has a large specific surface area and excellent adsorption performance, enabling it to selectively adsorb impurities in the leachate, thereby reducing the difficulty and cost of subsequent purification. Meanwhile, the use of a plate and frame filter press further improves the efficiency of solid-liquid separation, ensuring the purity of the leachate.

[0031] Finally, the pretreatment method of this application also achieves efficient recovery and recycling of the composite additive. By calcining the residue and separating it using an acid dissolution-precipitation method, the additive components were successfully recovered, reducing production costs and environmental pollution. Even after multiple cycles, the composite additive maintains high adsorption capacity and oxidation performance, demonstrating the sustainability and economy of this method. Attached Figure Description

[0032] To more clearly illustrate the technical solutions in the embodiments of this drawing or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this drawing. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0033] Figure 1 The XRD pattern of Example 1;

[0034] Figure 2 The image shows the XRD pattern of Comparative Example 3.

[0035] The purpose, features, and advantages of this accompanying drawing will be further explained in conjunction with the embodiments and with reference to the accompanying drawing. Detailed Implementation

[0036] To make the objectives, technical solutions, and advantages of this application clearer, the following description and illustration are provided in conjunction with embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application. All other embodiments obtained by those skilled in the art based on the embodiments provided in this application without inventive effort are within the scope of protection of this application.

[0037] Obviously, the following description is merely some examples or embodiments of this application. Those skilled in the art can apply this application to other similar scenarios without any inventive effort. Furthermore, it is understood that although the effort involved in such development may be complex and lengthy, for those skilled in the art related to the content disclosed in this application, any changes to design, manufacturing, or production based on the technical content disclosed in this application are merely conventional technical means and should not be construed as insufficient disclosure of the content of this application.

[0038] The first aspect of this application provides a pretreatment method for lithium iron phosphate cathode materials based on directional oxidation calcination, including the following steps:

[0039] (1) Raw material mixing: The composite additive is added to the lithium iron phosphate black powder and mixed to obtain a mixture; the amount of composite additive added is 0.5%-5% of the total mass of lithium iron phosphate black powder;

[0040] The composite additive is a composite formed by functionalized ionic liquid supported on a porous silica support.

[0041] (2) Acidification roasting: The mixture obtained in step (1) is placed in a rotary kiln, nitrogen is introduced, and the heating rate and roasting temperature are controlled for roasting and held for a certain time.

[0042] (3) Cooling: Cool the roasted material to ≤30℃ by water cooling;

[0043] (4) Pickling and in-situ adsorption: The cooled material is mixed with deionized water at a certain solid-liquid ratio, stirred at a set temperature, and then the adsorbent is added and stirred again.

[0044] (5) Solid-liquid separation: The pickled material is filtered and separated using a plate and frame filter press to obtain leachate and residue;

[0045] (6) Recovery of additive residue: The residue obtained in step (5) is roasted and then the additive components are separated and recovered by acid dissolution-precipitation method.

[0046] For Fe 2+ To address the issue of incomplete oxidation, this application employs a composite additive whose functionalized ionic liquid is loaded onto a porous silica support. The large specific surface area and suitable pore size structure of the porous silica support provide an excellent dispersion environment for the functionalized ionic liquid, allowing it to be uniformly distributed around the lithium iron phosphate black powder. During the calcination process, the functionalized ionic liquid, with its excellent oxidation performance and selectivity, precisely promotes the oxidation of Fe... 2+ To Fe 3+ Transformation. Compared to traditional pyrometallurgical processes, traditional methods, due to insufficient temperature control, are prone to localized overheating or underheating, leading to Fe... 2+ Incomplete oxidation. This application, through the action of composite additives, enhances the mass transfer process of the oxidation reaction, allowing Fe... 2+ It can react more fully with the oxidant, thus effectively solving the Fe problem. 2+ The problem of incomplete oxidation was addressed. Simultaneously, optimizations were made to the raw material mixing and roasting processes, reducing the formation of agglomerates in the roasted materials. Controlling the heating rate and roasting temperature ensured uniform heating of the materials, further guaranteeing the Fe... 2+ Sufficient oxidation is achieved, avoiding the internal material Fe caused by temperature gradient differences. 2+ In cases of incomplete oxidation and localized overheating of external materials leading to pyrophosphate formation, a uniform reaction was achieved across the entire batch of materials, improving Fe... 2+ Conversion rate.

[0047] In this embodiment, the porous silica carrier in the composite additive in step (1) is mesoporous silica with a specific surface area of ​​500-1200 m². 2 / g, with an average pore size of 2-10 nm; the functionalized ionic liquid is one of 1-carboxyethyl-3-methylimidazolium tetrafluoroborate and 1-butyl-3-methylimidazolium hexafluorophosphate. Preferably, it is 1-butyl-3-methylimidazolium hexafluorophosphate.

[0048] The porous silica support in the composite additive is mesoporous silica. Its unique mesoporous structure not only provides an ideal loading site for functionalized ionic liquids, but also effectively promotes the diffusion and mass transfer of reactants during calcination, thereby significantly improving Fe... 2+The oxidation efficiency is high. In practical applications, this mesoporous silica support exhibits good thermal and chemical stability, maintaining structural integrity and functional stability under high-temperature calcination conditions. Simultaneously, the introduction of the functionalized ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate further enhances the oxidation performance and selectivity of the composite additive. This ionic liquid possesses a unique molecular structure and electron distribution, enabling it to precisely capture and oxidize Fe during calcination. 2+ to convert it into Fe 3+ This achieves the control of Fe in lithium iron phosphate cathode materials. 2+ This composite additive exhibits highly efficient oxidation. Furthermore, it demonstrates excellent recyclability. Even after multiple cycles, its adsorption capacity and oxidation performance remain at a high level, thanks to the stable interaction between the mesoporous silica support and the functionalized ionic liquid, as well as the optimized preparation process of the composite additive.

[0049] The preparation method of the composite additive includes the following steps:

[0050] (1) Place 100 parts by weight of mesoporous silica in a vacuum drying oven and vacuum dry at 150℃~200℃ (-0.1 MPa) for at least 6 hours. After drying, place it in a desiccator to cool for later use.

[0051] (2) Weigh 40 parts by weight of ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate (target loading is about 28.6%), dissolve it in 800 parts by weight of anhydrous ethanol (8 times the mass of silicon dioxide), and stir gently in a 40°C water bath until a homogeneous and transparent solution is formed.

[0052] (3) Quickly add 100 parts by weight of activated and cooled silica to the ionic liquid ethanol solution prepared in step (2), transfer the mixture to a container with a sealed lid, and connect a vacuum pump; turn on the stirring (at low speed to prevent silica from breaking), and apply a vacuum of -0.08 ~ -0.1 MPa. Maintain this state for 4 to 6 hours. During this period, bubbles can be seen continuously emerging in the system. This is the phenomenon that the air in the pores is replaced by ethanol. When the bubbles basically disappear, it indicates that the loading is basically completed.

[0053] (4) Filter the slurry obtained in step (3) using a Buchner funnel and wash the filter cake twice with cold anhydrous ethanol to prevent the loaded ionic liquid from being washed off again.

[0054] (5) Transfer the filter cake to a vacuum drying oven and vacuum dry at 60°C (-0.1 MPa) for 12 hours. Low-temperature vacuum drying is to prevent the decomposition or migration of ionic liquids. After drying, crush the blocky product gently in a mortar or pass it through a 200-mesh test sieve and store it.

[0055] In this embodiment, in step (1), the total mass of the composite additive is used as a basis, and the loading of the functionalized ionic liquid is 10 wt% - 50 wt%. The selection of the functionalized ionic liquid loading has a significant impact on the performance of the composite additive. When the loading is too low, the active ingredients in the composite additive are insufficient, making it difficult to fully exert its oxidation performance and selectivity, resulting in Fe 2+ The oxidation efficiency decreases. While excessive loading increases the amount of active ingredient, it may also clog the pores of the mesoporous silica support, affecting the diffusion and mass transfer of reactants, which is also detrimental to Fe. 2+ Oxidation. Therefore, selecting a functionalized ionic liquid loading of 10 wt%-50 wt% can ensure that the composite additive has sufficient active ingredients while avoiding pore blockage, thereby achieving Fe 2+ Highly efficient oxidation.

[0056] In this embodiment, the solvent used for mixing in step (1) is deionized water or ethanol. After mixing, the mixture is dried to remove the solvent. Specifically, the mixing method involves placing the composite additive and lithium iron phosphate black powder in a container at a certain ratio, adding an appropriate amount of deionized water or ethanol as a solvent, and mixing them thoroughly and evenly by mechanical stirring or magnetic stirring for 0.5-2 hours. After mixing, the mixture is transferred to a drying device, such as a vacuum drying oven, for drying to remove the solvent. The dried mixture should be loose and free of obvious lumps to ensure that subsequent acidification and calcination steps can proceed smoothly.

[0057] In this embodiment, the heating rate in step (2) is 6-8℃ / min; the calcination temperature is 400-550℃; and / or the nitrogen flow rate is 0.5-1L / min. This step, by using a suitable heating rate, allows the rate at which the composite additive releases oxygen to be related to the Fe... 2+ The oxidation rate is matched, and the oxygen consumption of the carbon powder is compensated to ensure the smooth progress of the oxidation reaction. A specific calcination temperature range provides a suitable energy environment for the reaction, which helps promote various chemical reactions, enabling lithium iron phosphate black powder to achieve efficient conversion within this temperature range. Under such precisely controlled calcination conditions, the entire reaction system can achieve better reaction results. On the one hand, Fe... 2+The oxidation reaction proceeds more efficiently, further improving the conversion rate and providing more favorable conditions for subsequent lithium and phosphorus leaching. On the other hand, the agglomeration problem of the material is effectively controlled, ensuring the uniformity of the material during the roasting process. This allows for uniform reaction across the entire batch, further improving the lithium and phosphorus leaching rate. In the subsequent cooling step, the roasted material is cooled to ≤30℃ via water cooling, a crucial process. Rapid water cooling quickly lowers the material temperature, stabilizing the reaction system and preventing potential side reactions at high temperatures. Simultaneously, a suitable cooling temperature helps maintain the structural and performance stability of the material, preparing it for subsequent acid washing, solid-liquid separation, and other steps. During the cooling process, monitoring temperature changes ensures stability and consistency, thereby guaranteeing the reliability and repeatability of the entire pretreatment process.

[0058] In this embodiment, in step (4), the cooled material is mixed with deionized water at a mass ratio of 1:4-10, the acid washing temperature is 50-90℃, the initial stirring time is 30-60 min, and the continued stirring time after adding the adsorbent is 1-2.5 h; the adsorbent is modified activated carbon with a particle size of 5-10 μm and a specific surface area of ​​1000-1500 m². 2 The dosage is 0.5-1% of the leachate mass, added at a rate of / g. The initial stirring time in this step is set to 30-60 min to ensure sufficient contact between the material and the acid, promoting the leaching of lithium and phosphorus. The stirring time after adding the adsorbent is continued for 1-2.5 h, during which the modified activated carbon can fully exert its adsorption capacity. Its particle size is 5-10 μm, and its specific surface area is 1000-1500 m². 2 / g, with an addition amount of 0.5-1% of the leachate mass, allows the modified activated carbon to efficiently adsorb impurities in the leachate, such as trace amounts of carbon powder and Fe. 3+ During the stirring process, the materials continuously tumble in the solution, allowing the modified activated carbon to collide fully with impurities, thus effectively removing them. Simultaneously, stirring ensures the adsorbent is evenly distributed in the leachate, preventing localized poor adsorption. After this acid washing and adsorption treatment, the impurity concentration in the leachate is further reduced, and the purity of lithium and phosphorus is improved, providing high-quality raw materials for subsequent purification and recycling.

[0059] In this embodiment, the filter cloth pore size of the plate and frame filter press in step (5) is 0.1 μm, the filtration pressure is 0.4-0.6 MPa, and the filtration time is 15-30 min.

[0060] In this embodiment, the roasting temperature of the residue in step (6) is 500-550℃, the roasting atmosphere is air, and the roasting time is 1 hour. The acid used in the acid dissolution-precipitation method is 20-25% hydrochloric acid, which dissolves MgO and Al2O3 in the residue. This step uses the acid dissolution-precipitation method, utilizing a suitable concentration of hydrochloric acid to dissolve MgO and Al2O3 in the residue, based on the characteristic that MgO and Al2O3 can react chemically with hydrochloric acid to form soluble salts. In this process, the concentration of hydrochloric acid is precisely selected; a concentration of 20-25% ensures sufficient dissolution capacity for MgO and Al2O3 while avoiding unnecessary impact on other substances. Through this method, MgO and Al2O3 can be effectively separated from the residue. The separated MgO and Al2O3 can be further recycled and reused to produce related industrial products, improving resource utilization.

[0061] In this embodiment, the lithium iron phosphate cathode material is black powder of waste lithium iron phosphate (LFP) battery cathode material, with a particle size of 1-10μm, a Li content of 3.5-4.5wt%, an Fe content of 25-30wt%, a P content of 18-22wt%, and a carbon content of 6-8wt%.

[0062] In this embodiment, the method is used to treat lithium iron phosphate cathode material, Fe 2+ Conversion rate ≥ 98.5%, lithium leaching rate ≥ 99%, phosphorus leaching rate ≥ 98%, carbon powder concentration in leachate ≤ 0.01 g / L, Fe 3+ With a concentration ≤0.02g / L, the adsorption capacity of the composite additive remains above 85% of its initial value after three cycles of use.

[0063] Example

[0064] The following examples describe the disclosure of this invention in more detail. These examples are merely illustrative, as various modifications and variations will be apparent to those skilled in the art within the scope of this disclosure. Unless otherwise stated, all parts, percentages, and ratios reported in the following examples are based on weight. Unless otherwise stated, all reagents used in the examples are available commercially or synthesized using conventional methods and are ready for use without further processing. Unless otherwise stated, all instruments used in the examples are available commercially.

[0065] Example 1

[0066] A pretreatment method for lithium iron phosphate cathode materials based on directional oxidation calcination, characterized by comprising the following steps:

[0067] (1) Raw material mixing: The composite additive is added to lithium iron phosphate black powder and mixed to obtain a mixture; wherein, the composite additive is a composite material formed by functionalized ionic liquid supported on a porous silica carrier; the amount of composite additive added is 3% of the total mass of lithium iron phosphate black powder;

[0068] (2) Acidification roasting: The mixture obtained in step (1) is placed in a rotary kiln, nitrogen is introduced, the nitrogen flow rate is 0.8 L / min, and the heating rate and roasting temperature are controlled for roasting. The heating rate is 7℃ / min; the roasting temperature is 450℃; and the temperature is maintained for 2-3 hours.

[0069] (3) Cooling: Cool the roasted material to ≤30℃ by water cooling;

[0070] (4) Pickling and in-situ adsorption: The cooled material is mixed with deionized water at a mass ratio of 1:6 and stirred at 60°C for 60 min. Then, modified activated carbon is added as an adsorbent. The amount of modified activated carbon added is 0.8% of the mass of the leachate, and stirring is continued.

[0071] (5) Solid-liquid separation: The pickled material is filtered and separated using a plate and frame filter press. The filter cloth of the plate and frame filter press has a pore size of 0.1 μm, a filtration pressure of 0.5 MPa, and a filtration time of 20 min to obtain leachate and residue.

[0072] (6) Recovery of additive residue: The residue obtained in step (5) is roasted at a temperature of 500°C, in an air atmosphere, for 1 hour. Then, the additive components are separated and recovered by acid dissolution-precipitation method, wherein the acid is 20% hydrochloric acid, and MgO and Al2O3 in the residue are dissolved by hydrochloric acid.

[0073] Example 2

[0074] This embodiment is basically the same as that of embodiment 1, except that the amount of composite additive used in step (1) is 2% of the mass of lithium iron phosphate black powder.

[0075] Example 3

[0076] This embodiment is basically the same as embodiment 1, except that the roasting temperature in step (2) is 500℃.

[0077] Example 4

[0078] This embodiment is basically the same as that of embodiment 1, except that the amount of modified activated carbon added in step (4) is 1% of the mass of the leachate.

[0079] Example 5

[0080] This embodiment is basically the same as embodiment 1, except that the roasting temperature in step (6) is 550°C.

[0081] Comparative Example 1

[0082] This comparative example is basically the same as Example 1, except that no composite additive is added in step (1).

[0083] Comparative Example 2

[0084] This comparative example is basically the same as Example 1, except that the calcination temperature in step (2) is 350°C.

[0085] Comparative Example 3

[0086] This comparative example is basically the same as Example 1, except that the calcination temperature in step (2) is 650°C.

[0087] Comparative Example 4

[0088] This comparative example is basically the same as Example 1, except that no adsorbent is added in step (4).

[0089] Test Case

[0090] The lithium iron phosphate cathode material was pretreated according to the methods of Examples 1-5 and Comparative Examples 1-5, and the results are shown in Table 1.

[0091]

[0092] As shown in Table 1, Examples 1-5 in Fe 2+ It exhibits excellent performance in terms of conversion rate, lithium leaching rate, and phosphorus leaching rate. 2+ The conversion rates all reached approximately 99%, lithium leaching rates were all above 99%, and phosphorus leaching rates were also above 98%. However, the indicators of Comparative Examples 1-5 were significantly lower than those of the Example. Comparative Example 1 did not add any composite additives, resulting in lower Fe... 2+ The conversion rate was only 82.3%, and the lithium and phosphorus leaching rates also decreased significantly. This is likely because the composite additive played a crucial role in the calcination process. On the one hand, certain components in the composite additive can promote Fe... 2+ The oxidation reaction, without the addition of composite additives, will cause Fe... 2+ The oxidation reaction becomes less efficient, leading to Fe... 2+ The conversion rate drops significantly. On the other hand, composite additives help control the agglomeration of materials and ensure the uniformity of materials during the roasting process. The lack of composite additives will exacerbate the agglomeration of materials, affecting the leaching of lithium and phosphorus, and thus significantly reducing the lithium leaching rate and phosphorus leaching rate.

[0093] Comparative Example 2 was calcined at 350℃, which is relatively low and not conducive to the topological transformation of the LDH core layer, resulting in interlayer FeO4. 2-The release is slow, and the amount of O2 produced is insufficient to fully participate in the Fe process. 2+ The oxidation reaction leads to Fe 2+ The conversion rate is low. Additionally, the lower temperature also affects the leaching of lithium and phosphorus from the material, resulting in lower lithium and phosphorus leaching rates.

[0094] Comparative Example 3 was calcined at 650℃. Excessively high temperatures may lead to side reactions, such as the formation of strong pyrophosphates. Furthermore, excessively high temperatures may cause certain components in the material to decompose excessively or undergo other reactions that are detrimental to lithium and phosphorus leaching. In addition, high temperatures may damage the structure and properties of the composite additives, preventing them from functioning properly and resulting in unsatisfactory performance indicators.

[0095] Comparative Example 4: No adsorbent added; impurities in the leachate, such as trace amounts of carbon powder and Fe... 3+ These impurities cannot be effectively removed. Their presence affects the purity of lithium and phosphorus and may adversely impact subsequent purification and recycling processes. Simultaneously, the presence of these impurities may also hinder the leaching of lithium and phosphorus to some extent, leading to a decrease in lithium and phosphorus leaching rates, and Fe... 2+ Conversion rates were also affected.

[0096] Figure 1 The XRD pattern of Example 1 is shown in Table 2. The content of each substance in the figure is shown in Table 2.

[0097]

[0098] Figure 2 The XRD pattern of Comparative Example 3 shows a strong pyrophosphate peak (Li2FeP2O7). The contents of each substance in the figure are shown in Table 3.

[0099]

[0100] In summary, the lithium iron phosphate cathode material pretreatment method based on directional oxidation roasting adopted in this invention can significantly improve Fe2+ conversion rate, lithium leaching rate and phosphorus leaching rate by precisely controlling the use of composite additives, ultrasonic treatment, roasting temperature and adsorbent addition, thereby achieving efficient pretreatment and resource recycling of waste lithium iron phosphate cathode materials.

[0101] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A pretreatment method for lithium iron phosphate cathode materials based on directional oxidation calcination, characterized in that, Includes the following steps: (1) Raw material mixing: The composite additive is added to lithium iron phosphate black powder and mixed to obtain a mixture; The composite additive is a composite formed by supporting a functionalized ionic liquid on a porous silica support; the functionalized ionic liquid is one of 1-carboxyethyl-3-methylimidazolium tetrafluoroborate and 1-butyl-3-methylimidazolium hexafluorophosphate. (2) Acidification roasting: The mixture obtained in step (1) is placed in a rotary kiln, and nitrogen gas with a flow rate of 0.5-1L / min is introduced. The heating rate is controlled at 6-8℃ / min and the roasting temperature is 400-550℃ for roasting. The temperature is maintained for 2-3 hours. (3) Cooling: Cool the roasted material to ≤30℃; (4) Acid washing and in-situ adsorption: The cooled material is mixed with deionized water and stirred at a set temperature. Then, the adsorbent is added and stirring continues. The adsorbent is activated carbon with a particle size of 5-10 μm and a specific surface area of ​​1000-1500 m². 2 / g, the addition amount is 0.5-1% of the mass of the leachate; (5) Solid-liquid separation: The pickled material is filtered and separated using a plate and frame filter press to obtain leachate and residue; (6) Recovery of additive residue: The residue obtained in step (5) is roasted and then the additive components are separated and recovered by acid dissolution-precipitation method.

2. The method for pretreatment of lithium iron phosphate cathode material based on directional oxidation calcination according to claim 1, characterized in that, The porous silica carrier in the composite additive mentioned in step (1) is mesoporous silica with a specific surface area of ​​500-1200 m². 2 / g, with an average pore size of 2-10 nm.

3. The pretreatment method for lithium iron phosphate cathode material based on directional oxidation calcination according to claim 1, characterized in that, In step (1), the total mass of the composite additive is used as a basis, and the loading of the functionalized ionic liquid is 10 wt%-50 wt%.

4. The pretreatment method for lithium iron phosphate cathode material based on directional oxidation calcination according to claim 1, characterized in that, The solvent used for mixing in step (1) is deionized water or ethanol. After mixing, the mixture is dried to remove the solvent.

5. The pretreatment method for lithium iron phosphate cathode material based on directional oxidation calcination according to claim 1, characterized in that, In step (4), the cooled material is mixed with deionized water at a mass ratio of 1:4-10, the acid washing temperature is 50-90℃, the initial stirring time is 30-60min, and the stirring time after adding the adsorbent is 1-2.5h.

6. The pretreatment method for lithium iron phosphate cathode material based on directional oxidation calcination according to claim 1, characterized in that, The filter cloth pore size of the plate and frame filter press described in step (5) is 0.1 μm, the filtration pressure is 0.4-0.6 MPa, and the filtration time is 15-30 min.

7. The pretreatment method for lithium iron phosphate cathode material based on directional oxidation calcination according to claim 1, characterized in that, The temperature for roasting the residue in step (6) is 500-550℃, the roasting atmosphere is air, and the roasting time is 1h. The acid used in the acid dissolution-precipitation method is 20-25% hydrochloric acid, which dissolves MgO and Al2O3 in the residue.

8. The pretreatment method for lithium iron phosphate cathode material based on directional oxidation calcination according to any one of claims 1-7, characterized in that, The lithium iron phosphate cathode material is black powder from waste lithium iron phosphate battery cathode material, with a particle size of 1-10μm, a Li content of 3.5-4.5wt%, an Fe content of 25-30wt%, a P content of 18-22wt%, and a carbon content of 6-8wt%.

9. The pretreatment method for lithium iron phosphate cathode material based on directional oxidation calcination according to any one of claims 1-7, characterized in that, This method is used to treat lithium iron phosphate cathode materials, Fe 2+ Conversion rate ≥98.5%, lithium leaching rate ≥99%, phosphorus leaching rate ≥98%.

Images