Method for preparing battery-grade ammonium dihydrogen phosphate using phosphate fertilizer and application thereof

Abstract

The present invention relates to the field of lithium-ion battery technology, and more specifically, to a method for preparing battery-grade ammonium dihydrogen phosphate using phosphate fertilizer and its application. The method comprises: uniformly mixing the phosphate fertilizer with water, performing a first solid-liquid separation to remove insoluble impurities and obtain a phosphate fertilizer solution; adding an alkali to the phosphate fertilizer solution to remove impurities, and performing a second solid-liquid separation to obtain a cleaned ammonium phosphate solution; adding a nitrogen source to the cleaned ammonium phosphate solution until the molar ratio of N to P in the mixture is ≥3, and performing a third solid-liquid separation after crystallization to obtain solid ammonium phosphate; and thermally decomposing the solid ammonium phosphate to obtain battery-grade ammonium dihydrogen phosphate. This method achieves high-value utilization of phosphate fertilizers while reducing the production cost of lithium-ion batteries.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium ion batteries, and in particular to a method for preparing battery-grade ammonium dihydrogen phosphate by utilizing phosphate fertilizer and an application thereof. Background Art

[0002] Phosphate fertilizers are fertilizers with phosphorus as their primary nutrient. Common chemical phosphate fertilizers include superphosphate, calcium magnesium phosphate, and phosphate rock. In 2007, my country achieved net export of phosphate fertilizers, with production reaching 13.51 million tons, and has maintained a high level of output since then. As phosphate fertilizer production continues to grow, destocking is necessary, and phosphate fertilizer products need to be diversified and repurposed towards higher-value products. Reprocessing phosphate fertilizers for reuse can enhance their added value and is therefore of great significance.

[0003] With the development of the new energy industry, lithium iron phosphate and lithium iron manganese phosphate materials have received more and more attention. At the same time, it has also led to an increase in the prices of upstream raw materials such as lithium and phosphorus, resulting in an increase in the cost of lithium-ion batteries and their positive electrode materials.

[0004] Therefore, it is of great significance to provide a low-cost phosphate fertilizer reprocessing method so that the reprocessed phosphate fertilizer can be used as a raw material for lithium-ion batteries.

[0005] In view of this, the present invention is proposed. Summary of the Invention

[0006] The first objective of the present invention is to provide a method for producing battery-grade ammonium dihydrogen phosphate from phosphate fertilizer. By reprocessing phosphate fertilizer into ammonium dihydrogen phosphate, which is required for lithium-ion battery cathode materials, this method not only achieves high-value utilization of phosphate fertilizer but also effectively reduces the raw material costs of lithium-ion batteries. This method addresses the two supply-demand contradictions: the need to destock excess phosphate fertilizer production capacity and the urgent need for phosphorus sources in the new energy industry.

[0007] The second object of the present invention is to provide an application of battery-grade ammonium dihydrogen phosphate prepared by the method for preparing battery-grade ammonium dihydrogen phosphate using phosphate fertilizer in the preparation of positive electrode materials.

[0008] In order to achieve the above-mentioned purpose of the present invention, the following technical solutions are adopted:

[0009] The present application provides a method for preparing battery-grade ammonium dihydrogen phosphate using phosphate fertilizer, comprising the following steps:

[0010] After the phosphate fertilizer and water are evenly mixed, a first solid-liquid separation is performed to remove insoluble impurities to obtain a phosphate fertilizer solution;

[0011] adding alkali to the phosphate fertilizer solution to remove impurities, and performing a second solid-liquid separation to obtain a cleaned ammonium phosphate solution;

[0012] adding a nitrogen source to the ammonium phosphate solution after impurities removal until the molar ratio of the N element to the P element in the mixture is greater than or equal to 3, and performing a third solid-liquid separation after crystallization to obtain ammonium phosphate solid;

[0013] The ammonium phosphate solid is heated and decomposed to obtain battery-grade ammonium dihydrogen phosphate.

[0014] In some specific embodiments of the present invention, the phosphorus-containing compound in the phosphate fertilizer includes at least one of monocalcium phosphate, calcium phosphate, monoammonium phosphate and diammonium hydrogen phosphate;

[0015] Preferably, the mass fraction of phosphorus in the phosphate fertilizer is ≥15%.

[0016] In some specific embodiments of the present invention, the base includes at least one of sodium hydroxide, potassium hydroxide and ammonia water;

[0017] Preferably, the alkali is added to adjust the pH of the phosphate fertilizer solution to 8-12.

[0018] In some specific embodiments of the present invention, before the step of adding a nitrogen source to the ammonium phosphate solution after impurities are removed, the step further includes: transferring the ammonium phosphate solution after impurities are removed to a system with a temperature of 2 to 10°C.

[0019] In some specific embodiments of the present invention, the nitrogen source includes ammonia water and / or ammonia gas;

[0020] In some specific embodiments of the present invention, the crystallization time is 1 to 60 hours, preferably 12 to 48 hours.

[0021] In some specific embodiments of the present invention, the temperature of the thermal decomposition is 100-150°C;

[0022] Preferably, the heating decomposition time is 6 to 12 hours;

[0023] Preferably, the end point of the thermal decomposition is when the molar ratio of the N element to the P element in the material is 1:1.

[0024] In some specific embodiments of the present invention, the mass ratio of the phosphate fertilizer to the water is 1:0.5-3;

[0025] Preferably, the temperature of the mixture of the phosphate fertilizer and water is 25 to 120°C;

[0026] Preferably, the phosphate fertilizer is mixed with water for 3 to 24 hours.

[0027] In some specific embodiments of the present invention, the content of each impurity element in the battery-grade ammonium dihydrogen phosphate is ≤100 ppm.

[0028] The present application also provides the use of battery-grade ammonium dihydrogen phosphate prepared by the method for preparing battery-grade ammonium dihydrogen phosphate using phosphate fertilizer as described above in the preparation of positive electrode materials.

[0029] Compared with the prior art, the present invention has the following beneficial effects:

[0030] (1) The method provided by the present invention for preparing battery-grade ammonium dihydrogen phosphate using phosphate fertilizer uses cheap and readily available phosphate fertilizer as a raw material, thereby realizing the high-value transformation of phosphate fertilizer. By adopting specific means such as adding alkali to remove impurities, adding nitrogen source to convert ammonium phosphate and crystallize it, and heating and decomposing it, battery-grade ammonium dihydrogen phosphate with high purity that can be used as a positive electrode material for lithium-ion batteries is prepared, thereby effectively reducing the cost of raw materials for producing lithium-ion batteries.

[0031] (2) The method for preparing battery-grade ammonium dihydrogen phosphate using phosphate fertilizer provided by the present invention not only has high impurity removal efficiency and high phosphorus yield, but also has the advantages of simple and easy operation, mild preparation conditions, short process flow, and suitability for mass production. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the specific embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0033] Figure 1 This is a process flow chart of the method for preparing battery-grade ammonium dihydrogen phosphate using phosphate fertilizer provided in Example 1 of the present invention. DETAILED DESCRIPTION

[0034] The technical scheme of the present invention will be clearly and completely described below in conjunction with the accompanying drawings and specific embodiments, but it will be understood by those skilled in the art that the following described embodiments are part of embodiments of the present invention, rather than all embodiments, and are only used to illustrate the present invention, and should not be considered as limiting the scope of the present invention. Based on the embodiments in the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative work are within the scope of protection of the present invention. Those who do not specify specific conditions in the embodiments are carried out according to normal conditions or the conditions recommended by the manufacturer. Those whose reagents or instruments are not specified by the manufacturer are conventional products that can be purchased commercially.

[0035] In a first aspect, the present invention provides a method for preparing battery-grade ammonium dihydrogen phosphate using phosphate fertilizer, comprising the following steps:

[0036] After the phosphate fertilizer and water are evenly mixed, a first solid-liquid separation is performed to remove insoluble impurities in the phosphate fertilizer to obtain a phosphate fertilizer solution.

[0037] Among them, after the phosphate fertilizer is mixed with water, soluble compounds such as ammonium dihydrogen phosphate and diammonium hydrogen phosphate will dissolve in the water, while the solid impurities insoluble in water can be removed by solid-liquid separation.

[0038] In some specific embodiments of the present invention, the phosphate fertilizer includes agricultural phosphate fertilizer, which includes, but is not limited to, superphosphate, triple superphosphate, calcium magnesium phosphate fertilizer, phosphate rock powder, ammonium phosphate fertilizer, and the like.

[0039] Alkali is added to the phosphate fertilizer solution prepared above to perform impurity removal treatment so that the impurity ions in the phosphate fertilizer solution form hydroxide precipitates. After the impurity removal treatment is completed, a second solid-liquid separation is performed to obtain a de-impurified ammonium phosphate solution.

[0040] The phosphate fertilizer solution contains impurity metal ions such as calcium ions and magnesium ions. During the impurity removal process by adding alkali, impurities such as calcium ions and magnesium ions in the phosphate fertilizer solution react with the alkali to form insoluble hydroxide precipitates (including but not limited to calcium hydroxide precipitates and / or magnesium hydroxide precipitates). The hydroxide precipitate impurities can then be removed by solid-liquid separation.

[0041] In some specific embodiments of the present invention, if the phosphate fertilizer contains diammonium hydrogen phosphate and / or ammonium dihydrogen phosphate, when the alkali is added to form the hydroxide precipitate, the diammonium hydrogen phosphate and / or ammonium dihydrogen phosphate in the mixture will be partially or completely converted into ammonium phosphate (or in other words, the diammonium hydrogen phosphate solution and / or ammonium dihydrogen phosphate solution will be partially or completely converted into an ammonium phosphate solution). It can be understood that diammonium hydrogen phosphate, ammonium dihydrogen phosphate, and ammonium phosphate all exist in the solution in the form of ions.

[0042] In some specific embodiments of the present invention, if the added base includes ammonium ions, then while the base is being added to form the hydroxide precipitate, the diammonium hydrogen phosphate and / or ammonium dihydrogen phosphate in the mixture will be partially or completely converted into ammonium phosphate (or in other words, the diammonium hydrogen phosphate solution and / or ammonium dihydrogen phosphate solution will be partially or completely converted into an ammonium phosphate solution). It can be understood that diammonium hydrogen phosphate is formed by the combination of hydrogen phosphate ions and ammonium ions; and ammonium dihydrogen phosphate is formed by the combination of dihydrogen phosphate ions and ammonium ions.

[0043] Then, a nitrogen source is added to the above-prepared ammonium phosphate solution after impurities removal, and the amount of the nitrogen source added is such that the molar ratio of the N element to the P element in the mixed material is ≥3, and then a third solid-liquid separation is performed after crystallization to obtain ammonium phosphate solid.

[0044] The nitrogen source is added to the mixed material in a molar ratio of N to P of ≥ 3, so that diammonium hydrogen phosphate and / or ammonium dihydrogen phosphate are fully converted into ammonium phosphate. The molar ratio includes but is not limited to any one of 3.1, 3.2, 3.3, 3.5, 3.7, 3.9, 4.0, 4.3, 4.5, 4.8, 5.0, 5.3, 5.5, 5.8, 6.0, 7.0, 8.0, 9.0, and 10.0, or a range therebetween.

[0045] During the reaction of the impurity-removed ammonium phosphate solution with the nitrogen source, the ammonium ions in the nitrogen source will react with at least one of the dihydrogen phosphate ions, hydrogen phosphate ions and phosphate ions to generate ammonium phosphate. As the output of ammonium phosphate increases, the ammonium phosphate will crystallize and then be separated into solid-liquid form to obtain ammonium phosphate solid.

[0046] The ammonium phosphate solution after impurity removal contains some soluble impurity ions that do not react with hydroxide ions, such as potassium ions and sodium ions. After the ammonium phosphate crystals are precipitated, the potassium ions and sodium ions remain in the mother liquor, thereby achieving the purpose of further purification and impurity removal.

[0047] The ammonium phosphate solid is heated and decomposed to obtain battery-grade ammonium dihydrogen phosphate.

[0048] When heated, solid ammonium phosphate decomposes into ammonium dihydrogen phosphate, thus obtaining battery-grade ammonium dihydrogen phosphate.

[0049] This invention uses overcapacity, inexpensive, and readily available phosphate fertilizer as a raw material (phosphorus source) to produce battery-grade ammonium dihydrogen phosphate, a cathode material for lithium-ion batteries. This not only achieves a high-value transformation of phosphate fertilizer, but also effectively reduces the raw material cost of lithium-ion battery production. This resolves the supply-demand contradictions between the need to destock excess phosphate fertilizer production and the urgent need for phosphorus sources in the new energy industry, helping to promote the healthier development of both industries.

[0050] Furthermore, the method provided by the present invention has the advantages of simple operation, mild conditions, short process flow, low impurity content and high purity in the prepared ammonium dihydrogen phosphate, and is suitable for mass production.

[0051] In some specific embodiments of the present invention, the phosphorus-containing compound in the phosphate fertilizer includes at least one of monocalcium phosphate, calcium phosphate, monoammonium phosphate and diammonium hydrogen phosphate.

[0052] Wherein, the monocalcium phosphate is also called superphosphate, and its chemical formula is Ca(H2PO4)2.

[0053] Preferably, the mass fraction of phosphorus in the phosphate fertilizer is ≥15%, including but not limited to any one of 17%, 19%, 20%, 22%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, and 95%, or any range therebetween. The above mass fraction is beneficial for increasing the production and yield of battery-grade ammonium dihydrogen phosphate.

[0054] Preferably, stirring is performed during the mixing process to allow the soluble metal ions in the phosphate fertilizer to be fully dissolved in water, and then insoluble solid impurities are removed by solid-liquid separation.

[0055] In some specific embodiments of the present invention, the base includes at least one of sodium hydroxide, potassium hydroxide and ammonia water.

[0056] The use of the above-mentioned types of alkali is conducive to the full precipitation of impurity ions such as calcium and magnesium (if the impurity ions are formed into carbonate compounds, the precipitation is incomplete and there is also the problem of carbon emissions), which improves the impurity removal efficiency and is relatively low in cost.

[0057] In some specific embodiments of the present invention, the base can be added in the form of a solution, for example, sodium hydroxide solution and / or potassium hydroxide solution; its concentration can be any concentration, for example, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80% or 90% by mass, but is not limited thereto.

[0058] Preferably, the alkali is added to adjust the pH of the phosphate fertilizer solution to 8-12, including but not limited to any one of 8.5, 9.0, 9.5, 10.0, 10.5, 11.0, and 11.5, or any range therebetween. This pH range facilitates complete precipitation of impurity metal ions such as calcium and magnesium, thereby improving impurity removal efficiency.

[0059] In some specific embodiments of the present invention, the reaction time of the impurity removal treatment is 1 to 24 hours, including but not limited to any one of 2 hours, 3 hours, 4 hours, 5 hours, 7 hours, 8 hours, 10 hours, 11 hours, 12 hours, 13 hours, 15 hours, 18 hours, 20 hours, and 22 hours, or a range between any two of the points; preferably, it is 3 to 12 hours.

[0060] In some specific embodiments of the present invention, before the step of adding a nitrogen source to the ammonium phosphate solution after impurities are removed, the step further includes: transferring the ammonium phosphate solution after impurities are removed to a system with a temperature of 2 to 10°C, including but not limited to any one of 3°C, 4°C, 5°C, 6°C, 7°C, 8°C, and 9°C or a range of values ​​between any two of them.

[0061] Adopting the above low temperature range is conducive to the crystallization and precipitation of ammonium phosphate, which can increase the yield of phosphorus.

[0062] In some specific embodiments of the present invention, the nitrogen source includes ammonia water and / or ammonia gas.

[0063] Using an excess nitrogen source can promote the crystallization and precipitation of ammonium phosphate, thereby increasing the yield of battery-grade ammonium dihydrogen phosphate. If the nitrogen source addition amount is too low, it cannot be completely converted into ammonium phosphate, resulting in excessive impurities.

[0064] In some specific embodiments of the present invention, the crystallization time is 1 to 60 hours, including but not limited to any one of 3 hours, 5 hours, 8 hours, 10 hours, 12 hours, 15 hours, 18 hours, 20 hours, 24 hours, 30 hours, 36 hours, 42 hours, and 45 hours, or a range between any two of them; preferably, it is 12 to 48 hours.

[0065] In some specific embodiments of the present invention, the temperature of the thermal decomposition is 100-150°C, including but not limited to any one of 105°C, 110°C, 115°C, 120°C, 125°C, 130°C, 135°C, 140°C, and 145°C, or a range between any two of them.

[0066] The above heating temperature is used to facilitate the control of the decomposition of ammonium phosphate, thereby producing ammonium dihydrogen phosphate with higher purity.

[0067] Preferably, the thermal decomposition time is 6 to 12 hours, including but not limited to any one of 7 hours, 8 hours, 9 hours, 10 hours, and 11 hours, or a range between any two of them.

[0068] Preferably, the end point of the thermal decomposition is when the molar ratio of the N element to the P element in the material is 1:1.

[0069] By detecting the molar ratio of N and P elements in the material during thermal decomposition, it can be determined whether the reaction is complete. When the molar ratio of N and P elements is 1:1, heating is stopped to ensure the purity of battery-grade ammonium dihydrogen phosphate.

[0070] In some specific embodiments of the present invention, the heating may be performed by any conventional heating device, such as a drying box, a muffle furnace, etc., but is not limited thereto.

[0071] In some specific embodiments of the present invention, the first solid-liquid separation can be performed by filtration, centrifugation, etc., but is not limited thereto.

[0072] In some specific embodiments of the present invention, the second solid-liquid separation can be performed by filtration, centrifugation, etc., but is not limited thereto.

[0073] In some specific embodiments of the present invention, the third solid-liquid separation can be performed by filtration, centrifugation, etc., but is not limited thereto.

[0074] In some specific embodiments of the present invention, the thermal decomposition process further includes a step of recovering ammonia gas generated by the heating. The recovered ammonia gas can be used as a nitrogen source in the step of generating ammonium phosphate in the process of preparing battery-grade ammonium dihydrogen phosphate. Specifically, the recovered ammonia gas can be directly introduced into the cleaned ammonium phosphate solution, or the recovered ammonia gas can be dissolved in water to produce ammonia water, which is then introduced into the cleaned ammonium phosphate solution.

[0075] In some specific embodiments of the present invention, after the thermal decomposition, the heated material is further crushed and / or packaged. The crushed particle size includes any conventional particle size and can also be specifically set according to the desired particle size.

[0076] In some specific embodiments of the present invention, the mass ratio of the phosphate fertilizer to the water is 1:0.5-3; including but not limited to any one of 1:1, 1:1.5, 1:2, 1:2.5 or a range between any two of them.

[0077] Preferably, the temperature of the mixture of the phosphate fertilizer and water is 25-120°C, including but not limited to any one of 30°C, 40°C, 50°C, 60°C, 70°C, 80°C, 90°C, 100°C, 110°C, 115°C or a range between any two of them.

[0078] Preferably, the mixing time of the phosphate fertilizer and water is 3 to 24 hours, including but not limited to any one of 4 hours, 5 hours, 8 hours, 10 hours, 12 hours, 15 hours, 18 hours, 20 hours, and 22 hours, or a range between any two of the points.

[0079] In some specific embodiments of the present invention, the content of each impurity element in the battery-grade ammonium dihydrogen phosphate is ≤100 ppm, including but not limited to any one of 90 ppm, 80 ppm, 70 ppm, 60 ppm, 50 ppm, and 40 ppm, or a range between any two of the values; preferably ≤81 ppm.

[0080] The ammonium dihydrogen phosphate prepared by the present invention has low content of various impurity elements and can be used as a raw material for preparing positive electrode materials for lithium-ion batteries, thereby realizing the transformation of excess phosphate fertilizer into a high-value product. In addition, the ammonium dihydrogen phosphate has good solubility under acidic conditions and can meet the requirements for preparing lithium iron phosphate batteries using methods such as a liquid phase method.

[0081] In a second aspect, the present invention provides an application of battery-grade ammonium dihydrogen phosphate prepared by a method for preparing battery-grade ammonium dihydrogen phosphate using phosphate fertilizer in the preparation of positive electrode materials for lithium-ion batteries.

[0082] The positive electrode material includes, but is not limited to, lithium iron phosphate positive electrode material and / or lithium iron manganese phosphate positive electrode material.

[0083] The application of the lithium-ion battery positive electrode material uses battery-grade ammonium dihydrogen phosphate obtained from phosphate fertilizer processing as raw material, significantly reduces the production cost of the lithium-ion battery positive electrode material and realizes the high-value utilization of phosphate fertilizer.

[0084] The lithium-ion battery includes a lithium iron phosphate battery and / or a lithium manganese iron phosphate battery, but is not limited thereto.

[0085] The embodiments of the present invention will be described in detail below with reference to the examples, but it will be understood by those skilled in the art that the following examples are merely illustrative of the present invention and should not be construed as limiting the scope of the invention. Where specific conditions are not specified in the examples, the methods were performed according to conventional conditions or the conditions recommended by the manufacturer. Where the manufacturers of the reagents or instruments are not specified, they are all commercially available conventional products.

[0086] Example 1

[0087] The method for preparing battery-grade ammonium dihydrogen phosphate using phosphate fertilizer provided in this embodiment comprises the following steps:

[0088] (1) Preliminary impurity removal: Take 100 g of superphosphate agricultural phosphate fertilizer, add 100 g of tap water thereto, heat to 60 ° C and stir for 5 h to completely dissolve the soluble substances in the agricultural phosphate fertilizer, and then filter to remove insoluble solid impurities to obtain a phosphate fertilizer solution.

[0089] Potassium hydroxide (alkaline substance) is added to the phosphate fertilizer solution prepared above, the pH of the mixture is adjusted to 9, and impurity removal treatment is performed to form hydroxide precipitates (metal impurity precipitates) of impurity metal ions such as calcium and magnesium. After reacting for 6 hours, the mixture is filtered to obtain a preliminarily impurity-removed ammonium phosphate solution.

[0090] (2) Deep purification: The ammonium phosphate solution obtained in step (1) after preliminary impurity removal is transferred to a refrigeration device at a temperature of 3°C, and 400g of ammonia water is added thereto so that the molar ratio of the N element to the P element in the mixture is 3:1, so that ammonium phosphate (triammonium phosphate) is generated by reaction and crystallized at low temperature. After 24 hours, solid-liquid separation is performed to obtain ammonium phosphate solid.

[0091] (3) Thermal decomposition: The ammonium phosphate solid obtained in step (2) is transferred to a drying oven, and the temperature is adjusted to 140°C to thermally decompose the ammonium phosphate to produce ammonium dihydrogen phosphate and ammonia (ammonia is recovered during the heating period and can be used as a nitrogen source for the next low-temperature crystallization). The material is baked until the molar ratio of the N element to the P element in the material is 1:1 (about 8 hours), and then the baked solid material is crushed and sealed to obtain battery-grade ammonium dihydrogen phosphate.

[0092] The process flow chart of the method for preparing battery-grade ammonium dihydrogen phosphate using phosphate fertilizer provided in Example 1 is shown in Figure 1 .

[0093] After testing, the impurity element content in the superphosphate agricultural phosphate fertilizer in this embodiment, the impurity element content in the preliminarily impurity-removed ammonium phosphate solution obtained in step (1), the impurity element content in the ammonium phosphate solid obtained in step (2), and the impurity element content in the battery-grade ammonium dihydrogen phosphate obtained in step (3) are shown in Table 1 below.

[0094] Table 1 Impurity element content

[0095]

[0096] Example 2

[0097] The method for preparing battery-grade ammonium dihydrogen phosphate using phosphate fertilizer provided in this embodiment comprises the following steps:

[0098] (1) Preliminary impurity removal: Take 100 g of agricultural calcium magnesium phosphate fertilizer, add 100 g of tap water thereto, heat to 90 ° C and stir for 5 h to allow the soluble substances in the agricultural calcium magnesium phosphate fertilizer to completely dissolve, and then filter to remove insoluble solid impurities to obtain a phosphate fertilizer solution.

[0099] Potassium hydroxide was added to the phosphate fertilizer solution prepared above, and the pH of the mixture was adjusted to 11. The mixture was subjected to impurity removal treatment to form hydroxide precipitates of impurity metal ions such as calcium and magnesium. After reacting for 6 hours, the mixture was filtered to obtain a preliminarily impurity-removed ammonium phosphate solution.

[0100] (2) Deep purification: The ammonium phosphate solution obtained in step (1) after preliminary impurity removal is transferred to a refrigeration device at a temperature of 3°C, and 400g of ammonia water is added thereto so that the molar ratio of the N element to the P element in the mixture is 3:1, so that ammonium phosphate is generated by reaction and crystallized at low temperature. After 12 hours, solid-liquid separation is performed to obtain ammonium phosphate solid.

[0101] (3) Thermal decomposition: The ammonium phosphate solid obtained in step (2) is transferred to a drying oven, and the temperature is adjusted to 140° C. to decompose the ammonium phosphate into ammonium dihydrogen phosphate and ammonia (ammonia is recovered during heating), and the material is baked until the molar ratio of the N element to the P element in the material is 1:1 (about 8 hours). The baked solid material is then crushed and sealed to obtain battery-grade ammonium dihydrogen phosphate.

[0102] After testing, in this embodiment, the impurity element content in the agricultural calcium magnesium phosphate fertilizer, the impurity element content in the preliminarily removed ammonium phosphate solution obtained in step (1), the impurity element content in the ammonium phosphate solid obtained in step (2), and the impurity element content in the battery-grade ammonium dihydrogen phosphate obtained in step (3) are shown in Table 2 below.

[0103] Table 2 Impurity element content

[0104]

[0105] Example 3

[0106] The method for preparing battery-grade ammonium dihydrogen phosphate using phosphate fertilizer provided in this embodiment comprises the following steps:

[0107] (1) Preliminary impurity removal: 100 g of diammonium phosphate agricultural phosphate fertilizer was taken, 100 g of tap water was added thereto, the temperature was raised to 40°C and stirred for 5 h to completely dissolve the soluble substances in the diammonium phosphate agricultural phosphate fertilizer, and then filtered to remove insoluble solid impurities to obtain a phosphate fertilizer solution.

[0108] Sodium hydroxide was added to the phosphate fertilizer solution prepared above, and the pH of the mixture was adjusted to 8. The mixture was subjected to impurity removal treatment to form hydroxide precipitates of impurity metal ions such as calcium and magnesium. After reacting for 6 hours, the mixture was filtered to obtain a preliminarily impurity-removed ammonium phosphate solution.

[0109] (2) Deep purification: The ammonium phosphate solution obtained in step (1) after preliminary impurity removal was transferred to a refrigeration device at a temperature of 3°C, and 400g of ammonia water was added thereto so that the molar ratio of the N element to the P element in the mixture was 3.5:1, and ammonium phosphate was generated by reaction and crystallized at low temperature. After 36 hours, solid-liquid separation was performed to obtain ammonium phosphate solid.

[0110] (3) Thermal decomposition: The ammonium phosphate solid obtained in step (2) is transferred to a drying oven, and the temperature is adjusted to 120° C. to decompose the ammonium phosphate into ammonium dihydrogen phosphate and ammonia (ammonia is recovered during heating), and the material is baked until the molar ratio of the N element to the P element in the material is 1:1 (about 12 hours). The baked solid material is then crushed and sealed to obtain battery-grade ammonium dihydrogen phosphate.

[0111] After testing, in this embodiment, the impurity element content in the diammonium hydrogen phosphate agricultural phosphate fertilizer, the impurity element content in the preliminarily impurity-removed ammonium phosphate solution obtained in step (1), the impurity element content in the ammonium phosphate solid obtained in step (2), and the impurity element content in the battery-grade diammonium hydrogen phosphate obtained in step (3) are shown in Table 3 below.

[0112] Table 3 Impurity element content

[0113]

[0114] Example 4

[0115] The method for preparing battery-grade ammonium dihydrogen phosphate using phosphate fertilizer provided in this embodiment comprises the following steps:

[0116] (1) Preliminary impurity removal: 100 g of diammonium phosphate agricultural phosphate fertilizer was taken, 80 g of tap water was added thereto, the temperature was raised to 40°C and stirred for 5 h to completely dissolve the soluble substances in the diammonium phosphate agricultural phosphate fertilizer, and then filtered to remove insoluble solid impurities to obtain a phosphate fertilizer solution.

[0117] Ammonia water was added to the phosphate fertilizer solution prepared above, and the pH of the mixture was adjusted to 8. The mixture was treated to remove impurities so that impurity metal ions such as calcium and magnesium formed hydroxide precipitates. After reacting for 6 hours, the mixture was filtered to obtain a preliminarily removed ammonium phosphate solution.

[0118] (2) Deep purification: The ammonium phosphate solution obtained in step (1) after preliminary impurity removal is transferred to a refrigeration device at a temperature of 5°C, and 600g of ammonia water is added thereto so that the molar ratio of the N element to the P element in the mixture is 3.2:1, so that ammonium phosphate is generated by reaction and crystallized at low temperature. After 48 hours, solid-liquid separation is carried out to obtain ammonium phosphate solid.

[0119] (3) Thermal decomposition: The ammonium phosphate solid obtained in step (2) is transferred to a drying oven, and the temperature is adjusted to 140° C. to decompose the ammonium phosphate into ammonium dihydrogen phosphate and ammonia (ammonia is recovered during heating), and the material is baked until the molar ratio of the N element to the P element in the material is 1:1 (about 10 hours), and then the baked solid material is crushed and sealed to obtain battery-grade ammonium dihydrogen phosphate.

[0120] After testing, in this embodiment, the impurity element content in the ammonium dihydrogen phosphate agricultural phosphate fertilizer, the impurity element content in the ammonium phosphate solution obtained after preliminary impurity removal in step (1), the impurity element content in the ammonium phosphate solid obtained in step (2), and the impurity element content in the battery-grade ammonium dihydrogen phosphate obtained in step (3) are shown in Table 4 below.

[0121] Table 4 Impurity element content

[0122]

[0123]

[0124] It can be seen from the experimental data of the above embodiments that the ammonium dihydrogen phosphate prepared by using phosphate fertilizer to prepare battery-grade ammonium dihydrogen phosphate provided by the present invention has a low impurity content and meets the standards of battery-grade ammonium dihydrogen phosphate. Therefore, it can be used to prepare lithium-ion battery positive electrode materials.

[0125] Comparative Example 1

[0126] The method for preparing battery-grade ammonium dihydrogen phosphate using phosphate fertilizer provided in this comparative example refers to patent CN106629644A, which specifically includes the following steps:

[0127] (1) Take 600 g of ammonium dihydrogen phosphate agricultural phosphate fertilizer with the same composition as in Example 4, add 800 g of tap water, stir at 40° C. for 30 min to mix evenly, then filter, and the filtrate is set aside;

[0128] (2) adding ozone as a decolorizing agent to the filtrate obtained in step (1), allowing it to stand for 5 hours for decolorization, then adding ammonia water and sodium carbonate as precipitants, adjusting the pH value to 4, fully mixing and stirring, allowing it to stand for 5 hours, filtering, and the filtrate is set aside;

[0129] (3) Adding precipitants of ammonia and potassium carbonate to the filtrate obtained in step (2), adjusting the pH value to 6, mixing and stirring thoroughly, letting it stand for 5 hours, filtering, and the filtrate is set aside;

[0130] (4) adding potassium sulfide and sodium hydroxide as impurity removers to the filtrate obtained in step (3), mixing and stirring thoroughly, letting it stand for 0.5 h, filtering, and the filtrate is set aside;

[0131] (5) The filtrate obtained in step (4) is heated to 60° C. and concentrated until microcrystals appear, cooled and crystallized, and dried to obtain ammonium dihydrogen phosphate.

[0132] The product quality indicators in Comparative Example 1 are shown in Table 5 below.

[0133] Table 5 Product quality indicators in comparative example 1

[0134]

[0135] Compared with Comparative Example 1, the technical solution of the present application only requires one reagent, ammonia water, and does not require other reagents in the comparative example. In comparison, it saves more reagent costs and does not introduce additional impurities such as potassium and sodium during the impurity removal process.

[0136] Experimental Example 1

[0137] The impurity removal efficiency in step (1) (preliminary impurity removal) and the impurity removal efficiency in step (2) (deep purification) of each of the above embodiments were calculated respectively, and the results are shown in Table 5.

[0138] Table 5 Impurity removal efficiency results

[0139] Group Step (1) impurity removal efficiency Step (2) impurity removal efficiency Example 1 85％ 14.9％ Example 2 92％ 7.8％ Example 3 80％ 19.9％ Example 4 72％ 27.8％

[0140] Among them, impurity removal efficiency = (impurity content in a certain material before treatment - impurity content in a certain material after treatment) ÷ impurity content in a certain material before treatment × 100%.

[0141] Although the present invention has been illustrated and described using specific embodiments, it should be appreciated that the above embodiments are merely intended to illustrate the technical solutions of the present invention rather than to limit them. Those skilled in the art should understand that the technical solutions described in the above embodiments may be modified, or some or all of the technical features thereof may be replaced by equivalents, without departing from the spirit and scope of the present invention. However, these modifications or replacements do not deviate from the essence of the corresponding technical solutions within the scope of the technical solutions of the embodiments of the present invention. Therefore, this means that all such replacements and modifications within the scope of the present invention are included in the appended claims.

Claims

1. A method for preparing battery-grade ammonium dihydrogen phosphate using phosphate fertilizer, characterized in that: The steps include: After the phosphate fertilizer and water are evenly mixed, a first solid-liquid separation is performed to remove insoluble impurities to obtain a phosphate fertilizer solution; adding alkali to the phosphate fertilizer solution to remove impurities, and performing a second solid-liquid separation to obtain a cleaned ammonium phosphate solution; Adding the alkali to adjust the pH of the phosphate fertilizer solution to 8-12; adding a nitrogen source to the ammonium phosphate solution after impurities removal until the molar ratio of the N element to the P element in the mixture is greater than or equal to 3, and performing a third solid-liquid separation after crystallization to obtain ammonium phosphate solid; The ammonium phosphate solid is heated and decomposed to obtain battery-grade ammonium dihydrogen phosphate.

2. The method for preparing battery-grade ammonium dihydrogen phosphate using phosphate fertilizer according to claim 1, wherein: The phosphorus-containing compound in the phosphate fertilizer includes at least one of calcium dihydrogen phosphate, calcium phosphate, ammonium dihydrogen phosphate and diammonium hydrogen phosphate.

3. The method for preparing battery-grade ammonium dihydrogen phosphate using phosphate fertilizer according to claim 1, characterized in that: The mass fraction of phosphorus in the phosphate fertilizer is ≥15%.

4. The method for preparing battery-grade ammonium dihydrogen phosphate using phosphate fertilizer according to claim 1, characterized in that: The alkali includes at least one of sodium hydroxide, potassium hydroxide and ammonia water.

5. The method for preparing battery-grade ammonium dihydrogen phosphate using phosphate fertilizer according to claim 1, characterized in that: Before the step of adding a nitrogen source to the ammonium phosphate solution after impurities are removed, the method further comprises: transferring the ammonium phosphate solution after impurities are removed to a system with a temperature of 2-10°C.

6. The method for preparing battery-grade ammonium dihydrogen phosphate using phosphate fertilizer according to claim 1, characterized in that: The nitrogen source includes ammonia water and / or ammonia gas.

7. The method for preparing battery-grade diammonium phosphate using phosphate fertilizer according to claim 1, characterized in that: The crystallization time is 1 to 60 hours.

8. The method for preparing battery-grade ammonium dihydrogen phosphate using phosphate fertilizer according to claim 1, characterized in that: The crystallization time is 12 to 48 hours.

9. The method for preparing battery-grade diammonium phosphate using phosphate fertilizer according to claim 1, characterized in that: The temperature of the thermal decomposition is 100-150°C.

10. The method for preparing battery-grade diammonium phosphate using phosphate fertilizer according to claim 1, characterized in that: The heating decomposition time is 6 to 12 hours.

11. The method for preparing battery-grade ammonium dihydrogen phosphate using phosphate fertilizer according to claim 1, characterized in that: The end point of the thermal decomposition is when the molar ratio of the N element to the P element in the material is 1:

1.

12. The method for preparing battery-grade diammonium phosphate using phosphate fertilizer according to claim 1, characterized in that: The mass ratio of the phosphate fertilizer to the water is 1:0.5-3.

13. The method for preparing battery-grade diammonium phosphate using phosphate fertilizer according to claim 1, characterized in that: The temperature of the mixture of the phosphate fertilizer and water is 25-120°C.

14. The method for preparing battery-grade ammonium dihydrogen phosphate using phosphate fertilizer according to claim 1, characterized in that: The time for mixing the phosphate fertilizer and water is 3 to 24 hours.

15. The method for preparing battery-grade ammonium dihydrogen phosphate using phosphate fertilizer according to claim 1, characterized in that: The content of each impurity element in the battery-grade ammonium dihydrogen phosphate is ≤100 ppm.

16. Use of the battery-grade ammonium dihydrogen phosphate prepared by the method for preparing battery-grade ammonium dihydrogen phosphate using phosphate fertilizer according to any one of claims 1 to 15 in preparing a cathode material.

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