Battery-grade iron phosphate and preparation method thereof, positive electrode material, positive electrode sheet and secondary battery

Abstract

The present application provides a battery-grade iron phosphate and its preparation method, positive electrode material, positive electrode sheet and battery, which belongs to the technical field of battery positive electrode materials. The preparation method of the above-mentioned battery-grade iron phosphate includes: mixing iron phosphate waste with water, and then filtering to obtain an iron phosphate filter cake; mixing the iron phosphate filter cake, ammonium phosphate salt and acid solution to obtain a first slurry; heating and stirring the first slurry to obtain a second slurry; filtering and rinsing the second slurry to obtain a basic ammonium ferric phosphate filter cake; drying and calcining the basic ammonium ferric phosphate filter cake to obtain battery-grade iron phosphate. The iron phosphate obtained by calcining basic ammonium ferric phosphate in the present application has a uniform morphology, high tapping and specific surface area, and is also beneficial for recovering iron phosphate in iron phosphate waste and reducing the production cost of lithium iron phosphate positive electrode materials.

Description

Technical Field

[0001] The present invention relates to the technical field of battery positive electrode materials, and in particular to battery-grade iron phosphate and a preparation method thereof, a positive electrode material, a positive electrode sheet and a secondary battery. Background Art

[0002] With the rapid development of new energy vehicles, lithium iron phosphate (LIFP), a newly developed lithium-ion battery electrode material, has gradually become the preferred rechargeable battery material for new energy vehicles due to its advantages such as good safety, long cycle life, and low price. Research shows that the main raw material for the production of LFP is iron phosphate, and the micromorphological characteristics of the iron phosphate material significantly affect the performance of LFP batteries.

[0003] In the industrial production of iron phosphate, defective products are often produced due to objective factors such as process changes, poor quality control, and equipment adjustments. These defective products are typically scrapped as solid waste. With the annual increase in iron phosphate industry output, the disposal of iron phosphate waste has become a concern. However, existing iron phosphate waste recycling processes are complex and costly, and the resulting iron phosphate particles are uneven in size and have a small specific surface area, significantly impacting the performance of lithium iron phosphate batteries.

[0004] Therefore, there is an urgent need for a battery-grade iron phosphate and a preparation method thereof, a positive electrode material, a positive electrode sheet and a secondary battery to solve the above problems. Summary of the Invention

[0005] In view of the technical problems existing in the background technology, the present application provides a battery-grade iron phosphate and its preparation method, positive electrode material, positive electrode sheet and battery, aiming to solve the technical problems of high recycling cost, uneven particle size and small specific surface area of the iron phosphate products synthesized by the existing iron phosphate waste recycling process.

[0006] In a first aspect, the present invention provides a method for preparing battery-grade iron phosphate, comprising the following steps:

[0007] The iron phosphate waste is mixed with water, and then filtered to obtain an iron phosphate filter cake;

[0008] Mixing the ferric phosphate filter cake, ammonium phosphate and acid solution to obtain a first slurry;

[0009] heating and stirring the first slurry to obtain a second slurry;

[0010] The second slurry is filtered and rinsed to obtain a basic ammonium ferric phosphate filter cake;

[0011] The basic ammonium ferric phosphate filter cake is dried and calcined to obtain battery-grade ferric phosphate.

[0012] In the technical solution of the embodiment of the present application, the present application first obtains the basic ammonium ferric phosphate filter cake by dissolving the iron phosphate filter cake and then aging and recrystallizing it. The ammonia molecules formed by deamination of the basic ammonium ferric phosphate during calcination effectively prevent the agglomeration of particles, and the micro-positive pressure formed can also improve the ability to control the particle morphology. The iron phosphate obtained in this way has a uniform morphology and has a high specific surface area and high tap density. In addition, the present application is also conducive to recovering iron phosphate in iron phosphate waste and reducing the production cost of lithium iron phosphate positive electrode materials.

[0013] In some embodiments, in the step of mixing the waste ferric phosphate with water and then filtering to obtain a ferric phosphate filter cake, the mass ratio of the waste ferric phosphate to water is 1:(5-10).

[0014] In this embodiment, the soluble impurities in the ferric phosphate waste can be effectively removed by filtering the ferric phosphate waste after mixing the ferric phosphate waste with water.

[0015] In some embodiments, in the step of mixing the ferric phosphate filter cake, ammonium phosphate salt and acid solution to obtain the first slurry, the molar ratio of the iron element in the ferric phosphate filter cake to the ammonium ion in the ammonium phosphate salt is 1:(0.55~0.7); and / or, the molar ratio of the iron element in the ferric phosphate filter cake to the acid ion in the acid solution is 1:(0.3~0.6).

[0016] In this embodiment, the ratios of iron, ammonium ions, and acid ions are different, and the specific surface area and tap density of the resulting battery-grade iron phosphate fluctuate. In the case of excess iron or excess acid, it is difficult to simultaneously obtain iron phosphate with a higher specific surface area and a higher tap density.

[0017] In some embodiments, the ammonium phosphate salt is one or more of ammonium dihydrogen phosphate and diammonium phosphate; and / or the acid solution is one or more of phosphoric acid, nitric acid, and hydrochloric acid.

[0018] In this embodiment, the ammonium phosphate salt is selected from ammonium dihydrogen phosphate or diammonium phosphate, and the acid solution is selected from phosphoric acid to avoid the introduction of new impurities.

[0019] In some embodiments, in the step of heating and stirring the first slurry to obtain the second slurry, the heating temperature is 80-95° C. and the stirring time is 2-3 h.

[0020] In this embodiment, if the temperature of the aging reaction is too low, basic ammonium ferric phosphate cannot be generated; if the temperature of the aging reaction is too high, energy will be wasted; within this temperature and time range, the ferric phosphate filter cake can undergo crystal transformation to obtain basic ammonium ferric phosphate, and energy waste can be avoided.

[0021] In some embodiments, in the step of filtering and rinsing the second slurry to obtain a basic ammonium ferric phosphate filter cake, the second slurry is filtered and then rinsed until the conductivity of the rinsing liquid is less than or equal to 300 ms / cm to obtain a basic ammonium ferric phosphate filter cake.

[0022] In this embodiment, rinsing is performed until the conductivity of the rinsing liquid is less than or equal to 300 ms / cm, so that the impurity ions in the second slurry can be better removed.

[0023] In a second aspect, the embodiments of the present application further provide a battery-grade iron phosphate, which is prepared using the above-mentioned preparation method of battery-grade iron phosphate;

[0024] Preferably, the specific surface area of battery-grade iron phosphate is ≥8.34m 2 / g;

[0025] Preferably, the tap density of battery-grade iron phosphate is ≥1.27 g / cm 3 ;

[0026] Preferably, the particle size of the battery-grade iron phosphate satisfies: D50 particle size ≥ 1.943 um, D100 particle size ≥ 6.289 um.

[0027] In this embodiment, battery-grade iron phosphate is prepared by the above method, and thus has the advantages of large specific surface area and high tap density. On the one hand, it is conducive to the smooth growth of lithium iron phosphate through solid-phase reaction of iron phosphate and lithium source. On the other hand, the finally obtained lithium iron phosphate product has a higher energy density, which can well meet market needs.

[0028] In a third aspect, an embodiment of the present application further provides a lithium iron phosphate positive electrode material, which includes the above-mentioned battery-grade iron phosphate.

[0029] In this embodiment, the lithium iron phosphate positive electrode material is prepared from the above-mentioned battery-grade iron phosphate, which is conducive to solid-phase reaction synthesis and has the advantage of high energy density.

[0030] In a fourth aspect, an embodiment of the present application further provides a positive electrode plate, which includes the above-mentioned lithium iron phosphate positive electrode material.

[0031] In this embodiment, the positive electrode plate is made of the above-mentioned lithium iron phosphate positive electrode material, and thus has the advantage of high energy density.

[0032] In a fifth aspect, an embodiment of the present application further provides a secondary battery, which includes the above-mentioned positive electrode plate.

[0033] In this embodiment, the secondary battery is prepared from the above-mentioned positive electrode sheet, and thus has the advantage of high energy density.

[0034] Compared with the prior art, the advantages of this application include:

[0035] The present application first obtains a basic ammonium ferric phosphate filter cake by dissolving the iron phosphate filter cake and then aging and recrystallizing it. The ammonia molecules formed by deamination of the basic ammonium ferric phosphate during calcination effectively prevent the particles from agglomerating, and the micro-positive pressure formed can also improve the ability to control the particle morphology. The iron phosphate obtained in this way has a uniform morphology and has a high specific surface area and high tap density. In addition, the present application is also conducive to recovering iron phosphate from iron phosphate waste and reducing the production cost of lithium iron phosphate positive electrode materials.

[0036] The above description is only an overview of the technical solution of the present application. In order to more clearly understand the technical means of the present application, it can be implemented in accordance with the contents of the specification. In order to make the above and other purposes, features and advantages of the present application more obvious and easy to understand, the specific implementation methods of the present application are listed below. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] To more clearly illustrate the technical solution of this application, the following is a brief introduction to the drawings used in this application. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be derived from these drawings without inventive effort.

[0038] Figure 1 A schematic diagram of the process flow of the method for preparing battery-grade iron phosphate provided in an embodiment of the present application;

[0039] Figure 2 A schematic diagram of the specific process of the preparation method of battery-grade iron phosphate provided in Example 1 of the present application;

[0040] Figure 3 This is the XRD diffraction pattern of the basic ammonium ferric phosphate filter cake obtained in the preparation method of battery-grade ferric phosphate provided in Example 1 of the present application after drying;

[0041] Figure 4 This is a SEM image of the basic ammonium ferric phosphate filter cake obtained in the preparation method of battery-grade ferric phosphate provided in Example 1 of the present application after drying;

[0042] Figure 5 The XRD diffraction pattern of the battery-grade iron phosphate sample obtained in the preparation method of the battery-grade iron phosphate provided in Example 1 of the present application;

[0043] Figure 6 This is an SEM image of the battery-grade iron phosphate sample obtained in the preparation method of battery-grade iron phosphate provided in Example 1 of the present application. DETAILED DESCRIPTION

[0044] The following embodiments of the technical solution of the present application will be described in detail with reference to the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present application and are therefore only examples and are not intended to limit the scope of protection of the present application.

[0045] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which this application belongs; the terms used herein are only for the purpose of describing specific embodiments and are not intended to limit this application; the terms "including" and "having" and any variations thereof in the specification and claims of this application and the above-mentioned figure descriptions are intended to cover non-exclusive inclusions.

[0046] References herein to "embodiments" mean that a particular feature, structure, or characteristic described in connection with the embodiments may be included in at least one embodiment of the present application. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor does it constitute an independent or alternative embodiment that is mutually exclusive of other embodiments. It is understood, both explicitly and implicitly, by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0047] In the description of the embodiments of this application, the term "and / or" is simply a description of the association relationship between associated objects, indicating that three relationships can exist. For example, A and / or B can represent the following three situations: A exists alone, A and B exist simultaneously, and B exists alone. In addition, the character " / " in this document generally indicates that the associated objects are in an "or" relationship.

[0048] At present, the method for recovering iron phosphate waste used in the prior art is usually to dissolve the iron phosphate waste by acid leaching to obtain an iron-phosphorus solution, use alkaline solution to adjust the pH to precipitate amorphous iron phosphate, then add phosphoric acid to carry out aging reaction under high temperature conditions to obtain dihydrated iron phosphate or basic ammonium ferric phosphate, and finally obtain iron phosphate by calcination. In the actual production process, the existing iron phosphate waste recovery process is complicated and costly, and the synthesized iron phosphate particles have uneven particle size and small specific surface area. When the above-mentioned iron phosphate is used as a battery positive electrode material, there is a disadvantage of low energy density, which greatly affects the product performance of lithium iron phosphate batteries.

[0049] In order to solve the technical problem that the energy density of the iron phosphate prepared by the existing iron phosphate preparation method is too low when used as the positive electrode material of lithium iron phosphate batteries, the present application provides a battery-grade iron phosphate and its preparation method, positive electrode material, positive electrode sheet and battery, wherein, through the above-mentioned battery-grade iron phosphate preparation method, battery-grade iron phosphate with uniform morphology, high tap compaction and specific surface area can be obtained; in addition, the present application also has the advantage of simple process.

[0050] The batteries provided in the embodiments of the present application can provide power and electrical supply for, but are not limited to, mobile phones, tablets, laptop computers, electric toys, electric tools, battery-powered vehicles, electric cars, ships, spacecraft, etc. Among them, electric toys can include fixed or mobile electric toys, such as game consoles, electric car toys, electric ship toys, and electric airplane toys, and spacecraft can include airplanes, rockets, space shuttles, and spacecraft, etc.

[0051] Please refer to Figure 1 , Figure 1 A process flow diagram of a method for preparing battery-grade iron phosphate provided in an embodiment of the present application; in a first aspect, an embodiment of the present application provides a method for preparing battery-grade iron phosphate, comprising the following steps:

[0052] S10, mixing the ferric phosphate waste with water and filtering the mixture, taking a filter residue to obtain an ferric phosphate filter cake.

[0053] Specifically, step S10 is: slurrying the ferric phosphate waste material and water according to a certain solid-liquid ratio, filtering, removing soluble impurities in the ferric phosphate waste material, and obtaining an ferric phosphate filter cake.

[0054] In some embodiments, in the step of filtering the mixed ferric phosphate waste with water, the mass ratio of the ferric phosphate waste to water is 1:(5-10), preferably 1:5; wherein, a suitable solid-liquid ratio can better dissolve the soluble impurities in the ferric phosphate waste without wasting resources.

[0055] S20, mixing the iron phosphate filter cake, ammonium phosphate and acid solution to obtain a first slurry.

[0056] Specifically, in step S20, the molar ratio of the iron element in the ferric phosphate filter cake to the ammonium ion in the ammonium phosphate salt is 1:(0.55~0.7), and / or the molar ratio of the iron element in the ferric phosphate filter cake to the acid ion in the acid solution is 1:(0.3~0.6).

[0057] In some embodiments, in the step of mixing the ferric phosphate filter cake, ammonium phosphate salt and acid solution, the ammonium phosphate salt is one or more of ammonium dihydrogen phosphate and diammonium phosphate, and / or the acid solution is any one or more of phosphoric acid, nitric acid and hydrochloric acid.

[0058] In this embodiment, the ammonium phosphate salt is selected from ammonium dihydrogen phosphate or diammonium phosphate, and the acid solution is selected from phosphoric acid to avoid the introduction of new impurities. The use of the ammonium phosphate salt is to provide ammonium ions and phosphate ions, and to reduce the amount of acid used for subsequent pH adjustment compared to other salts. When the ammonium phosphate salt is used, other acids such as hydrochloric acid and nitric acid can be used for subsequent pH adjustment.

[0059] In one embodiment, a 10% by mass fraction ammonium dihydrogen phosphate solution is prepared, and the iron phosphate filter cake is added to the ammonium dihydrogen phosphate solution to re-slurry according to a molar ratio of iron in the filter cake to ammonium ions in the ammonium dihydrogen phosphate solution of 1:(0.55-0.7), and 85% phosphoric acid is added to the solution to obtain a yellow first slurry; wherein the amount of phosphoric acid added is according to a molar ratio of iron in the solution to phosphate in phosphoric acid of 1:(0.3-0.6).

[0060] S30, heating and stirring the first slurry to obtain a second slurry.

[0061] Specifically, step S30 is: heating the first slurry to 80-95° C., stirring at 100-500 r / min for 2 h for recrystallization to obtain a yellow-green second slurry.

[0062] In some embodiments, the stirring rate includes but is not limited to 100 r / min, 200 r / min, 300 r / min, 400 r / min, 500 r / min, etc.

[0063] In steps S20 and S30, the ferric phosphate filter cake and ammonium phosphate salt are first dissolved under acidic conditions to form a first slurry; then, under heating conditions, the ammonium phosphate salt is used as an aging agent to recrystallize the iron ions, ammonium ions and phosphate ions into basic ammonium ferric phosphate through an aging reaction. The chemical formula of basic ammonium ferric phosphate is NH4Fe2(OH)(PO4)2·nH2O, where n is 0 to 2.

[0064] In this embodiment, the ratios of iron, ammonium ions, and acid ions are different, and the specific surface area and tap density of the resulting battery-grade iron phosphate fluctuate. In the case of excess iron or excess acid, it is impossible to obtain an iron phosphate with a higher specific surface area and a higher tap density.

[0065] In this embodiment, if the aging reaction temperature is too low, basic ammonium ferric phosphate cannot be produced; if the aging reaction temperature is too high, energy will be wasted. Within this temperature and time range, the ferric phosphate filter cake can undergo crystal transformation to obtain basic ammonium ferric phosphate without wasting energy.

[0066] S40, filtering and rinsing the second slurry to obtain a basic ammonium ferric phosphate filter cake.

[0067] Specifically, step S40 further includes:

[0068] After filtering, the second slurry is rinsed until the conductivity of the rinse water is less than or equal to 300 ms / cm to obtain a basic ammonium ferric phosphate filter cake.

[0069] In this embodiment, rinsing until the conductivity of the washing liquid is less than or equal to 300 ms / cm can better remove impurity ions such as ammonium radicals in the second slurry that affect subsequent reactions.

[0070] S50, drying and calcining the basic ammonium ferric phosphate filter cake to obtain battery-grade ferric phosphate.

[0071] Specifically, step S50 further includes:

[0072] First, the basic ammonium ferric phosphate filter cake is dried in a blast oven at a drying temperature of 85-115°C for 8-15 hours, and then calcined to obtain battery-grade iron phosphate (anhydrous iron phosphate).

[0073] In this embodiment, the calcination temperature is 500-800° C., including but not limited to 500° C., 550° C., 600° C., 800° C., etc.; the calcination time is 3-5 h, including but not limited to 3 h, 4 h, etc.

[0074] In this embodiment, ammonia molecules formed by deamination of basic ammonium ferric phosphate during calcination effectively prevent particle agglomeration, and the resulting micro-positive pressure can also enhance the ability to control particle morphology. The iron phosphate obtained in this way has a higher specific surface area and high tap density.

[0075] Specifically, the specific surface area refers to the total area per unit mass of a substance. In this application, the nitrogen adsorption BET test method is used, with reference to the standard GB / T19587-2017.

[0076] Specifically, high tap density refers to the filling density of the powder in the tapped state. In this application, a tap density meter is used for testing, with reference to the standard GB / T5162-2021.

[0077] The invention uses ferric phosphate waste as raw material and ammonium phosphate solution as aging agent, and adopts a recrystallization method to obtain basic ammonium ferric phosphate to obtain ferric phosphate with uniform morphology, small and uniform particle size distribution and high tap compactness.

[0078] In a second aspect, the present invention also provides a battery-grade iron phosphate, which is prepared by the above-mentioned preparation method of battery-grade iron phosphate; the specific surface area of battery-grade iron phosphate is ≥8.34m 2 / g; the tap density of battery-grade iron phosphate is ≥1.27g / cm 3 ; The particle size of battery-grade iron phosphate meets the following requirements: D0 particle size ≥ 0.147um, D10 particle size ≥ 0.94um, D50 particle size ≥ 1.943um, D90 particle size ≥ 3.684um, D99 particle size ≥ 5.208um, and D100 particle size ≥ 6.289um.

[0079] In this embodiment, battery-grade iron phosphate is prepared by the above method, and thus has the advantages of large specific surface area and high tap density. On the one hand, it is conducive to the smooth generation of lithium iron phosphate through subsequent solid-phase reaction with a lithium source. On the other hand, the final lithium iron phosphate product has a higher energy density, which can well meet market needs.

[0080] In a third aspect, an embodiment of the present application further provides a lithium iron phosphate positive electrode material, which includes the above-mentioned battery-grade iron phosphate, and the above-mentioned battery-grade iron phosphate is prepared by a solid-phase reaction with a lithium source to form the lithium iron phosphate positive electrode material.

[0081] In this embodiment, the lithium iron phosphate positive electrode material is prepared from the above-mentioned battery-grade iron phosphate, which is conducive to solid-phase reaction synthesis and has the advantage of high energy density.

[0082] In a fourth aspect, an embodiment of the present application further provides a positive electrode plate, which includes the lithium iron phosphate positive electrode material as described above.

[0083] In this embodiment, the positive electrode plate is made of the above-mentioned lithium iron phosphate positive electrode material, and thus has the advantage of high energy density.

[0084] In a fifth aspect, an embodiment of the present application further provides a battery, comprising the positive electrode plate as described above.

[0085] In this embodiment, the battery is prepared from the above-mentioned positive electrode sheet, and thus has the advantage of high energy density.

[0086] Some specific examples are listed below. It should be noted that the examples described below are exemplary and are only used to explain the present application, and should not be construed as limiting the present application. Where specific techniques or conditions are not specified in the examples, the techniques or conditions described in the literature in this area or the product specifications are used. Reagents or instruments used without manufacturer's indication are all commercially available conventional products.

[0087] 1. Preparation method

[0088] Example 1:

[0089] See also Figure 2 , Figure 2 This is a schematic diagram of a specific process for preparing the battery-grade iron phosphate provided in Example 1 of the present application. Specifically, the steps of the preparation method of the battery-grade iron phosphate provided in Example 1 of the present application are as follows:

[0090] Step 1: slurrying the iron phosphate waste with water in a solid-liquid ratio of 1:5, filtering to remove soluble impurities in the waste, and obtaining an iron phosphate filter cake.

[0091] Step 2: prepare a 10% by mass fraction ammonium dihydrogen phosphate solution, add the iron phosphate filter cake obtained in step 1 into the ammonium dihydrogen phosphate solution according to a molar ratio of iron in the filter cake to ammonium ions in the ammonium dihydrogen phosphate solution of 1:0.55 to re-slurry, and at the same time, add 85% phosphoric acid to the solution, and the amount of phosphoric acid added is according to a molar ratio of iron in the solution to phosphate in the phosphoric acid of 1:0.3.

[0092] Step 3: The yellow slurry obtained in step 2 was heated to 90° C. and stirred at 400 rpm for 2 h for recrystallization to obtain a yellow-green slurry.

[0093] Step 4: Filter and rinse the yellow slurry obtained in step 3 until the conductivity of the rinse water is lower than 300 ms / cm to obtain a basic ammonium ferric phosphate filter cake.

[0094] Step 5: Dry the basic ammonium ferric phosphate filter cake in a blast oven at a drying temperature of 105° C. for 10 hours, and then calcine to obtain anhydrous ferric phosphate, wherein the calcination temperature is 600° C. and the calcination time is 3 hours.

[0095] Example 2:

[0096] Step 1: slurrying the iron phosphate waste with water in a solid-liquid ratio of 1:5, filtering to remove soluble impurities in the waste, and obtaining an iron phosphate filter cake.

[0097] Step 2: prepare a 10% by mass fraction ammonium dihydrogen phosphate solution, add the iron phosphate filter cake obtained in step 1 into the ammonium dihydrogen phosphate solution according to a molar ratio of iron in the filter cake to ammonium ions in the ammonium dihydrogen phosphate solution of 1:0.6 to re-slurry, and at the same time, add 85% phosphoric acid to the solution, and the amount of phosphoric acid added is according to a molar ratio of iron in the solution to phosphate in the phosphoric acid of 1:0.4.

[0098] Step 3: The yellow slurry obtained in step 2 was heated to 85° C. and stirred at 400 rpm for 2.5 h for recrystallization to obtain a yellow-green slurry.

[0099] Step 4: Filter and rinse the yellow slurry obtained in step 3 until the conductivity of the rinse water is lower than 300 ms / cm to obtain a basic ammonium ferric phosphate filter cake.

[0100] Step 5: Dry the basic ammonium ferric phosphate filter cake in a blast oven at a drying temperature of 105° C. for 10 hours, and then calcine to obtain anhydrous ferric phosphate, wherein the calcination temperature is 600° C. and the calcination time is 3 hours.

[0101] Example 3:

[0102] Step 1: slurrying the iron phosphate waste with water in a solid-liquid ratio of 1:5, filtering to remove soluble impurities in the waste, and obtaining an iron phosphate filter cake.

[0103] Step 2: prepare a 10% by mass ammonium dihydrogen phosphate solution, add the iron phosphate filter cake obtained in step 1 into the ammonium dihydrogen phosphate solution according to a molar ratio of iron in the filter cake to ammonium ions in the ammonium dihydrogen phosphate solution of 1:0.7 to re-slurry, and at the same time, add 85% phosphoric acid to the solution, and the amount of phosphoric acid added is according to a molar ratio of iron in the solution to phosphate in the phosphoric acid of 1:0.6.

[0104] Step 3: The yellow slurry obtained in step 2 was heated to 95° C. and stirred at 400 rpm for 2 h for recrystallization to obtain a yellow-green slurry.

[0105] Step 4: Filter and rinse the yellow slurry obtained in step 3 until the conductivity of the rinse water is lower than 300 ms / cm to obtain a basic ammonium ferric phosphate filter cake.

[0106] Step 5: Dry the basic ammonium ferric phosphate filter cake in a blast oven at a drying temperature of 105° C. for 10 hours, and then calcine to obtain anhydrous ferric phosphate, wherein the calcination temperature is 600° C. and the calcination time is 3 hours.

[0107] Comparative Example 1:

[0108] Step 1: slurrying the iron phosphate waste with water in a solid-liquid ratio of 1:5, filtering to remove soluble impurities in the waste, and obtaining an iron phosphate filter cake.

[0109] Step 2: prepare a 10% by mass ammonium dihydrogen phosphate solution, and add the iron phosphate filter cake obtained in step 1 into the ammonium dihydrogen phosphate solution according to a molar ratio of iron element in the filter cake to ammonium ions in the ammonium dihydrogen phosphate solution of 1:0.55 to re-slurry.

[0110] Step 3: The yellow slurry obtained in step 2 was heated to 90° C. and stirred at 400 rpm for 2 h for recrystallization to obtain a yellow-green slurry.

[0111] Step 4: Filter and rinse the yellow slurry obtained in step 3 until the conductivity of the rinse water is lower than 300 ms / cm to obtain a basic ammonium ferric phosphate filter cake.

[0112] Step 5: Dry the basic ammonium ferric phosphate filter cake in a blast oven at a drying temperature of 105° C. for 10 hours, and then calcine to obtain anhydrous ferric phosphate, wherein the calcination temperature is 600° C. and the calcination time is 3 hours.

[0113] Comparative Example 2:

[0114] Step 1: slurrying the iron phosphate waste with water in a solid-liquid ratio of 1:5, filtering to remove soluble impurities in the waste, and obtaining an iron phosphate filter cake.

[0115] Step 2: The iron phosphate filter cake obtained in step 1 is mixed with water at a solid-liquid ratio of 1:5 and then re-pulped. At the same time, 85% phosphoric acid is added to the solution, and the amount of phosphoric acid added is based on a molar ratio of 1:0.3 between the iron element in the solution and the phosphate in the phosphoric acid.

[0116] Step 3: The yellow slurry obtained in step 2 was heated to 90° C. and stirred at 400 rpm for 2 h for recrystallization to obtain a yellow-green slurry.

[0117] Step 4: Filter and rinse the yellow slurry obtained in step 3 until the conductivity of the rinse water is lower than 300 ms / cm to obtain a basic ammonium ferric phosphate filter cake.

[0118] Step 5: Dry the basic ammonium ferric phosphate filter cake in a blast oven at a drying temperature of 105° C. for 10 hours, and then calcine to obtain anhydrous ferric phosphate, wherein the calcination temperature is 600° C. and the calcination time is 3 hours.

[0119] 2. Test Method

[0120] The basic ammonium ferric phosphate filter cake obtained in the preparation method of battery-grade ferric phosphate provided in Example 1 of the present application was dried and then subjected to XRD diffraction analysis and SEM surface morphology analysis.

[0121] The battery-grade iron phosphate product obtained in the preparation method of the battery-grade iron phosphate provided in Example 1 of the present application was subjected to XRD diffraction analysis and SEM surface morphology analysis.

[0122] The anhydrous ferric phosphate obtained in Examples 1-3 and Comparative Examples 1-2 of the present application was subjected to performance tests; the specific surface area was measured using the nitrogen adsorption BET test method, with reference to standard GB / T19587-2017; the tap density was measured using a tap density meter, with reference to standard GB / T5162-2021.

[0123] III. Performance Test Results Analysis of Various Examples and Comparative Examples

[0124] See also Figure 3 , Figure 3 The XRD diffraction pattern of the basic ammonium ferric phosphate filter cake obtained in the preparation method of battery-grade ferric phosphate provided in Example 1 of the present application after drying; Figure 3 It can be seen that the obtained basic ammonium ferric phosphate has a high degree of crystallinity.

[0125] See also Figure 4 , Figure 4 This is an SEM (electron microscope) image of the basic ammonium ferric phosphate filter cake obtained in the preparation method of battery-grade ferric phosphate provided in Example 1 of the present application after drying; Figure 4 It can be seen that the obtained basic ammonium ferric phosphate has a small primary particle size and is granular.

[0126] See also Figure 5 , Figure 5 The XRD diffraction pattern of the battery-grade iron phosphate sample obtained in the preparation method of the battery-grade iron phosphate provided in Example 1 of the present application; Figure 5 It can be seen that the obtained iron phosphate has a high crystallinity.

[0127] See also Figure 6 , Figure 6 This is a SEM image of the battery-grade iron phosphate sample obtained in the preparation method of battery-grade iron phosphate provided in Example 1 of this application. Figure 6 It can be seen that the obtained iron phosphate has a larger specific surface area.

[0128] The results of the performance tests on the anhydrous ferric phosphate obtained in Examples 1-3 and Comparative Examples 1-2 of the present application are shown in Table 1 below:

[0129] Table 1 Performance test results of battery-grade iron phosphate prepared in each group

[0130]

[0131] In the embodiments of the present invention, the battery-grade iron phosphate obtained in Example 1 is compared with the battery-grade iron phosphate obtained in Comparative Example 1. It can be seen that when no phosphoric acid is added, the specific surface area and tap density of the battery-grade iron phosphate obtained in Example 1 are greater than the specific surface area and tap density of the battery-grade iron phosphate obtained in Comparative Example 1, and the D10 particle size, D50 particle size, D90 particle size, D99 particle size and D100 particle size of the battery-grade iron phosphate obtained in Example 1 are all smaller than the corresponding particle size of the battery-grade iron phosphate obtained in Comparative Example 1; this may be because part of the iron phosphate filter cake is not completely dissolved and aged into basic ammonium ferric phosphate.

[0132] In the embodiments of the present invention, the battery-grade iron phosphate obtained in Example 1 is compared with the battery-grade iron phosphate obtained in Comparative Example 2. It can be seen that when no ammonium phosphate solution is added, the specific surface area and tap density of the battery-grade iron phosphate obtained in Example 1 are greater than the specific surface area and tap density of the battery-grade iron phosphate obtained in Comparative Example 1, and the D10 particle size, D50 particle size, D90 particle size, D99 particle size and D100 particle size of the battery-grade iron phosphate obtained in Example 1 are all smaller than the corresponding particle size of the battery-grade iron phosphate obtained in Comparative Example 1; this is mainly because the ammonia molecules formed by deamination of basic ammonium ferric phosphate during calcination effectively prevent particle agglomeration, and the micro-positive pressure formed can also enhance the particle morphology control ability. The iron phosphate obtained in this way has a uniform morphology, a high specific surface area and a high tap density, and a relatively small particle size from D10 to D100.

[0133] The present invention addresses the problems of complex and high cost in the existing waste iron phosphate recycling process, uneven particle size of synthesized iron phosphate particles, and small specific surface area. The waste iron phosphate is re-pulped and added to a phosphoric acid and ammonium sulfate solution, and then aged and filtered again under high temperature conditions to obtain basic ammonium ferric phosphate, which is then calcined to obtain anhydrous iron phosphate.

[0134] Compared with the prior art, the present invention has the following advantages:

[0135] First, the present invention uses waste ferric phosphate as raw material, obtains basic ammonium ferric phosphate through recrystallization, and then obtains battery-grade ferric phosphate through calcination. This process is simple, low-cost, and achieves the recycling of waste resources.

[0136] Second, basic ammonium ferric phosphate is prepared by recrystallizing ferric phosphate and then calcining it. This avoids the problems of uneven particle size, irregular morphology, and small specific surface area encountered in conventional ferric phosphate regeneration solutions, which use iron-phosphorus solutions to synthesize ferric phosphate. The ferric phosphate obtained by calcining basic ammonium ferric phosphate has a uniform morphology and high tap compactness and specific surface area.

[0137] In summary, different from the prior art, the present invention provides a battery-grade iron phosphate and a preparation method thereof, a positive electrode material, a positive electrode sheet and a battery. The preparation method of battery-grade iron phosphate comprises the following steps: first, mixing iron phosphate waste with water and filtering the mixture, taking the filter residue to obtain an iron phosphate filter cake, secondly, mixing the iron phosphate filter cake, ammonium phosphate salt and acid solution to obtain a first slurry, thirdly, heating and stirring the first slurry and then performing recrystallization treatment to obtain a second slurry, thirdly, filtering and rinsing the second slurry in sequence, taking the filter residue to obtain a basic ammonium ferric phosphate filter cake, and finally The basic ammonium ferric phosphate filter cake is dried and calcined in sequence to obtain battery-grade iron phosphate; the present application first obtains the basic ammonium ferric phosphate filter cake by dissolving the iron phosphate filter cake and then aging and recrystallizing it. The ammonia molecules formed by deamination of the basic ammonium ferric phosphate during calcination effectively prevent the particles from agglomerating, and the micro-positive pressure formed can also improve the ability to control the particle morphology. The iron phosphate obtained in this way has a uniform morphology and has a high specific surface area and high tap density; in addition, the present application is also conducive to recovering iron phosphate from iron phosphate waste and reducing the production cost of lithium iron phosphate positive electrode materials.

[0138] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are merely examples, and any embodiments having substantially the same structure and effect as the technical concept within the scope of the present application are all included in the technical scope of the present application. In addition, without departing from the scope of the present application, any other embodiments that can be conceived by those skilled in the art and that combine some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims

1. A method for preparing battery-grade iron phosphate, characterized in that: The steps include: The iron phosphate waste is mixed with water, and then filtered to obtain an iron phosphate filter cake; Mixing the ferric phosphate filter cake, ammonium phosphate and acid solution to obtain a first slurry; heating and stirring the first slurry to obtain a second slurry; The second slurry is filtered and rinsed to obtain a basic ammonium ferric phosphate filter cake; The basic ammonium ferric phosphate filter cake is dried and calcined to obtain battery-grade ferric phosphate; Wherein, in the step of mixing the ferric phosphate filter cake, ammonium phosphate salt and acid solution to obtain the first slurry, the molar ratio of the iron element in the ferric phosphate filter cake to the ammonium ion in the ammonium phosphate salt is 1:(0.55-0.7); and / or the molar ratio of the iron element in the ferric phosphate filter cake to the acid ion in the acid solution is 1:(0.3-0.6); In the step of heating and stirring the first slurry to obtain the second slurry, the heating temperature is 80-95° C. and the stirring time is 2-3 hours.

2. The method for preparing battery-grade iron phosphate according to claim 1, wherein In the step of mixing the waste ferric phosphate with water and then filtering to obtain a ferric phosphate filter cake, the mass ratio of the waste ferric phosphate to water is 1:(5-10).

3. The method for preparing battery-grade iron phosphate according to claim 1, wherein: The ammonium phosphate salt is one or more of ammonium dihydrogen phosphate and diammonium phosphate; and / or the acid solution is one or more of phosphoric acid, nitric acid and hydrochloric acid.

4. The method for preparing battery-grade iron phosphate according to claim 1, wherein: In the step of filtering and rinsing the second slurry to obtain a basic ammonium ferric phosphate filter cake, the second slurry is filtered and then rinsed until the conductivity of the rinsing liquid is less than or equal to 300 ms / cm to obtain the basic ammonium ferric phosphate filter cake.

5. A battery-grade iron phosphate, characterized in that: The battery-grade iron phosphate is prepared by the preparation method of the battery-grade iron phosphate according to any one of claims 1 to 4; The specific surface area of the battery-grade iron phosphate is ≥8.34m 2 / g; The tap density of the battery-grade iron phosphate is ≥1.27 g / cm 3 ; The particle size distribution of the battery-grade iron phosphate satisfies: D50≥1.943um, D100≥6.289um.

6. A lithium iron phosphate positive electrode material, characterized in that: The raw material of the lithium iron phosphate positive electrode material includes the battery-grade iron phosphate according to claim 5.

7. A positive electrode plate, characterized in that: The positive electrode plate includes the lithium iron phosphate positive electrode material as claimed in claim 6.

8. A secondary battery, characterized in that: The secondary battery includes the positive electrode sheet according to claim 7.

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