Battery-grade yttrium metaphosphate and preparation method thereof

Abstract

In order to solve the technical problem that the yttrium metaphosphate with higher purity cannot be prepared due to non-uniform and incomplete reaction in the existing preparation method of the yttrium metaphosphate, the invention provides the preparation method of the battery-grade yttrium metaphosphate, and the battery-grade yttrium metaphosphate with the purity of 99.99% or above can be produced. The preparation method comprises the following steps: firstly preparing yttrium chloride, then stirring and heating phosphoric acid and yttrium chloride to obtain a phosphoric acid and yttrium chloride mixed suspension, then slowly adding diluted reagent-grade ammonia water into the phosphoric acid and yttrium chloride mixed suspension for heating and stirring reaction, centrifuging, filtering and washing to obtain a hydrated high-activity yttrium phosphate filter cake; adding the hydrated high-activity yttrium phosphate filter cake into the diluted food-grade phosphoric acid premium-grade product, and carrying out a concentration reaction to obtain pasty yttrium metaphosphate; and finally, drying the pasty yttrium metaphosphate to obtain the yttrium metaphosphate with the purity of 99.99%.

Description

Technical Field

[0001] The invention relates to yttrium metaphosphate and a preparation method thereof. Background Art

[0002] The application of yttrium metaphosphate (Y(PO3)3) in batteries is mainly reflected in the coating technology of positive electrode materials for lithium-ion batteries. As a coating material, yttrium metaphosphate reacts in situ with residual alkali (such as LiOH, Li2CO3) on the surface of the parent material to generate a composite multifunctional phosphate coating layer. This process not only greatly reduces the residual lithium salt on the surface of the parent material, improves processing performance, reduces environmental requirements for use, and increases the ionic conductivity of the positive electrode material, but also effectively inhibits phase change and interface side reactions, thereby improving the safety and cycle life of the battery.

[0003] A method for preparing optical grade yttrium metaphosphate is disclosed in a patent document with publication number CN 111547696A, which comprises the following steps: preparing an aqueous solution of ammonium dihydrogen phosphate and removing water insolubles; removing nonferrous metals and impurity ions from the aqueous solution of ammonium dihydrogen phosphate through an ion exchange device; evaporating, concentrating, crystallizing and centrifuging the aqueous solution of ammonium dihydrogen phosphate after impurities removal to obtain optical grade ammonium dihydrogen phosphate; using optical grade ammonium dihydrogen phosphate to polymerize with yttrium oxide to generate an yttrium metaphosphate intermediate; crushing the yttrium metaphosphate intermediate cleanly and calcining it to obtain yttrium metaphosphate powder; crushing and mixing the yttrium metaphosphate powder cleanly to obtain an optical grade yttrium metaphosphate powder product. This method has strong adaptability to raw materials, and the main technical indicators of the prepared yttrium metaphosphate meet the requirements of optical grade raw materials. However, this method is a dry production method, and the acidity of ammonium dihydrogen phosphate is insufficient, and it cannot completely react with yttrium oxide, and has the disadvantages of uneven and incomplete reaction. Therefore, this method cannot prepare yttrium metaphosphate with high purity. Summary of the invention

[0004] In order to solve the technical problem that the existing method for preparing yttrium metaphosphate has uneven and incomplete reaction and cannot prepare yttrium metaphosphate with high purity, the present invention provides a method for preparing battery-grade yttrium metaphosphate, which can produce battery-grade yttrium metaphosphate with a purity of more than 99.99%. The present invention also provides a battery-grade yttrium metaphosphate and a lithium-ion battery.

[0005] The technical solution of the present invention is:

[0006] A method for preparing battery-grade yttrium metaphosphate, which is special in that it comprises the following steps:

[0007] Step 1: purification of yttrium salt;

[0008] High-purity hydrochloric acid diluted with pure water reacts with 4N high-purity yttrium oxide to obtain yttrium chloride solution;

[0009] After diluting the yttrium chloride solution with pure water, fine filtration is performed to obtain a pure yttrium chloride solution;

[0010] Here, yttrium chloride is prepared first because only by dissolving yttrium oxide into a solution can there be no unreacted yttrium oxide, and mechanical impurities and heavy insolubles in yttrium oxide can be removed;

[0011] Step 2: preparing highly active yttrium phosphate;

[0012] Step 2.1 Dilute the food-grade phosphoric acid with less than 0.3 ppm of iron, cobalt, nickel, copper, cadmium and vanadium to a mass fraction of 20-25% with pure water, add the solution to the pure yttrium chloride solution obtained in step 1, stir and heat to 70-80°C to obtain a mixed suspension of phosphoric acid and yttrium chloride; the molar ratio of phosphoric acid to yttrium chloride is 1:1; in this step, the phosphoric acid is diluted to a mass fraction of 20-25% because if the mass fraction is too high, it is not conducive to stirring, and if the mass fraction is too low, the concentration of the formed yttrium phosphate slurry is too low, resulting in too low production capacity of yttrium metaphosphate; stirring and heating to 70-80°C helps to reduce intermolecular bound water;

[0013] Step 2.2: After adding reagent-grade ammonia water containing less than 0.5 ppm of iron, cobalt, nickel, copper, cadmium and vanadium to a mass fraction of 20-25%, the solution is slowly added to the mixed suspension of phosphoric acid and yttrium chloride, and the solution is stirred and reacted at 70-100° C. to adjust the pH value to 2-3 to control the amount of ammonia water added and prevent the hydrolysis of yttrium ions, and then stirred and reacted at 70-100° C. for 2-3 hours to fully form particles, thereby obtaining a synthetic yttrium phosphate solution; stirring the reaction at 70-100° C. in this step can avoid the combination of excessive bound water, which is more conducive to production;

[0014] Step 2.3: centrifuge, filter, and wash the yttrium phosphate synthesis solution, control the chloride ion to be less than 50 ppm, and control the iron, cobalt, nickel, copper, cadmium, and vanadium to be less than 0.5 ppm, to obtain a hydrated high-activity yttrium phosphate filter cake;

[0015] The purpose of preparing yttrium phosphate here is to carry out phosphorylation in steps later, reduce the intensity of the reaction and corrosion to the equipment. In the process of phosphate precipitation formed by yttrium chloride and phosphoric acid, only yttrium phosphate can be formed, and it can be ensured that there is no unreacted yttrium oxide.

[0016] Step 3: Synthesizing yttrium metaphosphate;

[0017] Add an equal amount of water to dilute a high-quality food-grade phosphoric acid, then add the hydrated high-activity yttrium phosphate filter cake, wherein the molar ratio of phosphoric acid to yttrium phosphate is 2:1, heat to 110-120°C for concentration reaction, concentrate to a paste state for discharge, cool to 30-40°C, and obtain a paste of yttrium metaphosphate; since yttrium metaphosphate has better fluidity at a higher temperature, when the temperature is reduced to 30-40°C by cooling, the yttrium metaphosphate becomes a non-flowing paste, which is convenient for operation.

[0018] Step 4: drying the yttrium metaphosphate;

[0019] The paste yttrium metaphosphate is evaporated at 200-250° C. for 3-5 hours, evaporated to a hardened state, and then heated to 500-700° C. and dried for 3-5 hours to obtain a finished yttrium metaphosphate. XRD detection shows that the yttrium metaphosphate is yttrium metaphosphate, with a moisture content of less than 0.05%, an iron content of less than 1 ppm, and cobalt, nickel, copper, cadmium, cadmium, and vanadium all less than 0.5 ppm, and a purity of 99.99%.

[0020] Furthermore, step 1 is specifically as follows:

[0021] Step 1.1 Take high-purity hydrochloric acid and add pure water to dilute it, then add 4N high-purity yttrium oxide with less than 0.5 ppm of iron, cobalt, nickel, copper, cadmium and vanadium, and dissolve it until transparent to obtain yttrium chloride solution; the molar ratio of hydrochloric acid to yttrium oxide is 6:1; the metal impurity elements include;

[0022] Step 1.2: After diluting the yttrium chloride solution with pure water, it is finely filtered to remove insoluble matter and mechanical impurities to obtain a pure yttrium chloride solution.

[0023] Furthermore, in order to facilitate operation while ensuring production efficiency, when diluting high-purity hydrochloric acid in step 1.1, the mass ratio of high-purity hydrochloric acid to water is 1:1-1.5, and when diluting yttrium chloride solution in step 1.2, the mass ratio of yttrium chloride solution to pure water is 1:2-2.3; in step 1.2, insoluble matter and mechanical impurities are removed through a precision filter with a filtration accuracy of 0.5 microns.

[0024] Furthermore, in the step 2.3: the centrifugal speed is 1000-1200 rpm, and filtration is performed using a 1500 mesh filter cloth.

[0025] Furthermore, considering that adding too much pure water will increase the concentration time, while adding too little pure water will result in insufficient concentration time to reach a paste state, resulting in incomplete reaction, the step 3 is to dilute the food-grade phosphoric acid with an equal mass of pure water.

[0026] Furthermore, step 4 is specifically as follows:

[0027] Step 4.1: placing the paste of yttrium metaphosphate in a PTFE plate, flattening it to 3-5 cm, and evaporating it at 200-250° C. for 3-5 hours until it is hardened (the stickiness of the yttrium metaphosphate is removed at this time), thereby obtaining a primary dried yttrium metaphosphate;

[0028] Step 4.2: Add the dried yttrium metaphosphate once into a high-purity quartz crucible, heat it to 500-700° C., and dry it for 3-5 hours to obtain a finished yttrium metaphosphate product.

[0029] The present invention also provides a battery-grade yttrium metaphosphate, which is special in that it is prepared by the above method.

[0030] The present invention also provides a lithium-ion battery, which is special in that the coating layer of the positive electrode material of the lithium-ion battery is generated by in-situ reaction of the above-mentioned battery-grade yttrium metaphosphate and residual alkali on the surface of the matrix material.

[0031] The advantages of the present invention are:

[0032] 1. The present invention can produce battery-grade yttrium metaphosphate with a purity of more than 99.99%.

[0033] 2. In the method of the present invention, the material reaction is uniform and complete, and there is no yttrium oxide inclusion, which meets the hard indicator of the battery industry for yttrium metaphosphate that the yttrium salt must be completely phosphorylated.

[0034] 3. The method of the present invention is a wet synthesis, which is convenient to operate and easy to mass produce. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 This is the XRD diagram of yttrium metaphosphate prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0036] The present invention is conceived as follows:

[0037] When adding yttrium metaphosphate to battery materials, the battery industry mainly proposed the following hard indicators:

[0038] First, the yttrium salt must be completely phosphorylated. If the phosphorylation is incomplete, other battery materials wrapped by yttrium metaphosphate will have abnormal discharge. For this hard indicator, the present invention has formulated a step-by-step phosphorylation process to eliminate the presence of yttrium oxide as much as possible, so as to achieve complete phosphorylation of the yttrium salt.

[0039] Second, the purity of yttrium metaphosphate must reach battery-grade use conditions. For this hard indicator, the present invention uses yttrium oxide raw materials with higher purity and purifies them to avoid the influence of raw material purity on product purity.

[0040] The reaction equation involved in the present invention is:

[0041] Y2O3+6HCl====2YCl3+3H2O

[0042] YCl3+H3PO4+3NH4OH====YPO4+3NH4Cl+3H2O

[0043] YPO4+2H3PO4====Y(PO3)3+3H2O

[0044] The present invention is further described in detail below by way of examples.

[0045] Example 1

[0046] In this embodiment, yttrium metaphosphate is prepared by the following steps:

[0047] Step 1: purification of yttrium salt;

[0048] Step 1.1 Take high-purity hydrochloric acid and add pure water to dilute it. The mass ratio of hydrochloric acid to water is 1:1. Add 4N high-purity yttrium oxide in which iron, cobalt, nickel, copper, cadmium and vanadium are all less than 0.5 ppm to the diluted hydrochloric acid. The molar ratio of hydrochloric acid to yttrium oxide is 6:1. Dissolve until transparent to obtain yttrium chloride solution;

[0049] Step 1.2: Add pure water to the yttrium chloride solution obtained in step 1.1 for dilution, the mass ratio of yttrium chloride solution to pure water being 1:2, and remove insoluble matter and mechanical impurities through a precision filter with a filtration accuracy of 0.5 microns to obtain a pure yttrium chloride solution.

[0050] Step 2: preparing highly active yttrium phosphate;

[0051] Step 2.1: Dilute a high-quality food-grade phosphoric acid containing less than 0.3 ppm of iron, cobalt, nickel, copper, cadmium and vanadium to a mass fraction of 20% with pure water, and then add the mixture to the pure yttrium chloride solution obtained in step 1.2, wherein the molar ratio of phosphoric acid to yttrium chloride is 1:1, and stir and heat the mixture to 70°C to obtain a mixed suspension of phosphoric acid and yttrium chloride;

[0052] Step 2.2: dilute reagent-grade ammonia water containing less than 0.5 ppm of iron, cobalt, nickel, copper, cadmium and vanadium to a mass fraction of 20% with pure water, and then slowly add the solution to the mixed suspension of phosphoric acid and yttrium chloride in step 2.1, keep the mixture at 80°C and stir for about 30 minutes, adjust the pH value to 2.3, keep the mixture at 80°C and stir for 2 hours to allow the particles to be fully formed, and obtain a yttrium phosphate synthesis solution;

[0053] Step 2.3: Centrifuge the yttrium phosphate synthesis liquid obtained in step 2.2 at a centrifugal speed of 1000 rpm, filter with a 1500-mesh filter cloth, and wash with pure water. The chloride ion is controlled to be less than 50 ppm, and the iron, cobalt, nickel, copper, cadmium, and vanadium are all less than 0.5 ppm to obtain a hydrated high-activity yttrium phosphate filter cake.

[0054] Step 3: Synthesizing yttrium metaphosphate;

[0055] Step 3.1 Take a high-grade food-grade phosphoric acid, add it to an enameled reactor, add pure water for dilution, the mass ratio of phosphoric acid to pure water is 1:1, and then add the hydrated high-activity yttrium phosphate filter cake obtained in step 2.3 to the diluted phosphoric acid, the molar ratio of phosphoric acid to yttrium phosphate is 2:1, heat to 110°C for concentration reaction, concentrate to a paste state, discharge, cool, and cool to 30°C to obtain paste yttrium metaphosphate.

[0056] Step 4: drying the yttrium metaphosphate;

[0057] Step 4.1: Place the paste yttrium metaphosphate obtained in step 3.1 in a PTFE plate, flatten it to 3-5 cm, and evaporate it at 200°C for 5 hours until it is hardened to obtain a primary dried yttrium metaphosphate;

[0058] Step 4.2: Add the dried yttrium metaphosphate obtained in step 4.1 into a high-purity quartz crucible, heat to 580°C and dry for 5 hours to obtain a finished yttrium metaphosphate. The product is identified as yttrium metaphosphate by XRD test. The corresponding XRD diagram is as follows: Figure 1 As shown; after ICP-OES testing, the moisture content in the product is less than 0.05%, iron is less than 1ppm, cobalt, nickel, copper, cadmium, vanadium and other elements are all less than 0.5ppm, and the purity is 99.99%.

[0059] Example 2

[0060] In this embodiment, yttrium metaphosphate is prepared by the following steps:

[0061] Step 1: purification of yttrium salt;

[0062] Step 1.1 Take high-purity hydrochloric acid and add pure water to dilute it. The mass ratio of hydrochloric acid to water is 1:1.2. Add 4N high-purity yttrium oxide in which iron, cobalt, nickel, copper, cadmium and vanadium are all less than 0.5 ppm to the diluted hydrochloric acid. The molar ratio of hydrochloric acid to yttrium oxide is 6:1. Dissolve until transparent to obtain yttrium chloride solution.

[0063] Step 1.2: Add pure water to the yttrium chloride solution obtained in step 1.1 for dilution, the mass ratio of yttrium chloride solution to pure water is 1:2.1, and remove insoluble matter and mechanical impurities through a precision filter with a filtration accuracy of 0.5 microns to obtain a pure yttrium chloride solution.

[0064] Step 2: preparing highly active yttrium phosphate;

[0065] Step 2.1: Dilute a high-quality food-grade phosphoric acid containing less than 0.3 ppm of iron, cobalt, nickel, copper, cadmium and vanadium to a mass fraction of 23% with pure water, and then add the mixture to the pure yttrium chloride solution obtained in step 1.2, wherein the molar ratio of phosphoric acid to yttrium chloride is 1:1, and stir and heat the mixture to 80° C. to obtain a mixed suspension of phosphoric acid and yttrium chloride;

[0066] Step 2.2: dilute reagent-grade ammonia water containing less than 0.5 ppm of iron, cobalt, nickel, copper, cadmium and vanadium to a mass fraction of 22% with pure water, and then slowly add the solution to the mixed suspension of phosphoric acid and yttrium chloride in step 2.1, keep the mixture at 70°C and stir for about 30 minutes, adjust the pH to 2, keep the mixture at 70°C and stir for 2.5 hours to allow the particles to be fully formed, and obtain a yttrium phosphate synthesis solution;

[0067] Step 2.3: Centrifuge the yttrium phosphate synthesis liquid obtained in step 2.2 at a centrifugal speed of 1100 rpm, filter with a 1500-mesh filter cloth, and wash with pure water. The chloride ion is controlled to be less than 50 ppm, and the iron, cobalt, nickel, copper, cadmium, and vanadium are all less than 0.5 ppm to obtain a hydrated high-activity yttrium phosphate filter cake.

[0068] Step 3: Synthesizing yttrium metaphosphate;

[0069] Step 3.1 Take a high-grade food-grade phosphoric acid, add it to an enameled reactor, add pure water for dilution, the mass ratio of phosphoric acid to pure water is 1:1.1, and then add the hydrated high-activity yttrium phosphate filter cake obtained in step 2.3 to the diluted phosphoric acid, the molar ratio of phosphoric acid to yttrium phosphate is 2:1, heat to 110°C for concentration reaction, concentrate to a paste state, discharge, cool, and cool to 35°C to obtain paste yttrium metaphosphate.

[0070] Step 4: drying the yttrium metaphosphate;

[0071] Step 4.1: Place the yttrium metaphosphate paste obtained in step 3.1 into a PTFE plate, flatten it to 3-5 cm, and evaporate it at 230°C for 4 hours until it is hardened to obtain a primary dried yttrium metaphosphate;

[0072] Step 4.2: Add the dried yttrium metaphosphate obtained in step 4.1 into a high-purity quartz crucible, heat to 600°C and dry for 4 hours to obtain a finished yttrium metaphosphate. The product is characterized as yttrium metaphosphate by XRD; and the product has a moisture content of less than 0.05%, an iron content of less than 1ppm, and cobalt, nickel, copper, cadmium, and vanadium content of less than 0.5ppm by ICP-OES, and a purity of 99.99%.

[0073] Example 3

[0074] In this example, yttrium metaphosphate was prepared by the following steps:

[0075] Step 1: purification of yttrium salt;

[0076] Step 1.1 Take high-purity hydrochloric acid and add pure water to dilute it. The mass ratio of hydrochloric acid to water is 1:1.3. Add 4N high-purity yttrium oxide in which iron, cobalt, nickel, copper, cadmium and vanadium are all less than 0.5 ppm to the diluted hydrochloric acid. The molar ratio of hydrochloric acid to yttrium oxide is 6:1. Dissolve until transparent to obtain yttrium chloride solution.

[0077] Step 1.2: Add pure water to the yttrium chloride solution obtained in step 1.1 for dilution, the mass ratio of yttrium chloride solution to pure water is 1:2.2, and remove insoluble matter and mechanical impurities through a precision filter with a filtration accuracy of 0.5 microns to obtain a pure yttrium chloride solution.

[0078] Step 2: preparing highly active yttrium phosphate;

[0079] Step 2.1: Dilute a high-quality food-grade phosphoric acid containing less than 0.3 ppm of iron, cobalt, nickel, copper, cadmium and vanadium to a mass fraction of 25% with pure water, and then add the mixture to the pure yttrium chloride solution obtained in step 1.2, wherein the molar ratio of phosphoric acid to yttrium chloride is 1:1, and stir and heat the mixture to 75°C to obtain a mixed suspension of phosphoric acid and yttrium chloride;

[0080] Step 2.2: dilute the reagent-grade ammonia water containing less than 0.5 ppm of iron, cobalt, nickel, copper, cadmium and vanadium to a mass fraction of 25%, and then slowly add the solution to the mixed suspension of phosphoric acid and yttrium chloride in step 2.1, keep the mixture at 90°C and stir for about 30 minutes, adjust the pH to 3, keep the mixture at 90°C and stir for 3 hours, so that the particles are fully formed, and obtain the yttrium phosphate synthesis solution;

[0081] Step 2.3: Centrifuge the yttrium phosphate synthesis liquid obtained in step 2.2 at a centrifugal speed of 1200 rpm, filter with a 1500-mesh filter cloth, and wash with pure water. The chloride ion is controlled to be less than 50 ppm, and the iron, cobalt, nickel, copper, cadmium, and vanadium are all less than 0.5 ppm to obtain a hydrated high-activity yttrium phosphate filter cake.

[0082] Step 3: Synthesizing yttrium metaphosphate;

[0083] Step 3.1 Take a high-grade food-grade phosphoric acid, add it to an enameled reactor, add pure water for dilution, the mass ratio of phosphoric acid to pure water is 1:1.2, and then add the hydrated high-activity yttrium phosphate filter cake obtained in step 2.3 to the diluted phosphoric acid, the molar ratio of phosphoric acid to yttrium phosphate is 2:1, heat to 115°C for concentration reaction, concentrate to a paste state, discharge, cool, and cool to 36°C to obtain paste yttrium metaphosphate.

[0084] Step 4: drying the yttrium metaphosphate;

[0085] Step 4.1 Place the paste yttrium metaphosphate obtained in step 3.1 into a PTFE plate, flatten it to 3-5 cm, and evaporate it at 250°C for 3 hours until it is hardened to obtain a primary dried yttrium metaphosphate;

[0086] Step 4.2: Add the dried yttrium metaphosphate obtained in step 4.1 into a high-purity quartz crucible, heat to 700°C and dry for 3 hours to obtain a finished yttrium metaphosphate product. The product is identified as yttrium metaphosphate by XRD; the product has a moisture content of less than 0.05%, an iron content of less than 1ppm, and cobalt, nickel, copper, cadmium, and vanadium content of less than 0.5ppm by ICP-OES, and a purity of 99.99%.

[0087] Example 4

[0088] In this embodiment, yttrium metaphosphate is prepared by the following steps:

[0089] Step 1: purification of yttrium salt;

[0090] Step 1.1 Take high-purity hydrochloric acid and add pure water to dilute it. The mass ratio of hydrochloric acid to water is 1:1.5. Add 4N high-purity yttrium oxide in which iron, cobalt, nickel, copper, cadmium and vanadium are all less than 0.5 ppm to the diluted hydrochloric acid. The molar ratio of hydrochloric acid to yttrium oxide is 6:1. Dissolve until transparent to obtain yttrium chloride solution;

[0091] Step 1.2: Add pure water to the yttrium chloride solution obtained in step 1.1 for dilution, the mass ratio of yttrium chloride solution to pure water is 1:2.3, and remove insoluble matter and mechanical impurities through a precision filter with a filtration accuracy of 0.5 microns to obtain a pure yttrium chloride solution.

[0092] Step 2: preparing highly active yttrium phosphate;

[0093] Step 2.1: Dilute a high-quality food-grade phosphoric acid containing less than 0.3 ppm of iron, cobalt, nickel, copper, cadmium and vanadium to a mass fraction of 21% with pure water, and then add the mixture to the pure yttrium chloride solution obtained in step 1.2, wherein the molar ratio of phosphoric acid to yttrium chloride is 1:1, and stir and heat the mixture to 72° C. to obtain a mixed suspension of phosphoric acid and yttrium chloride;

[0094] Step 2.2: dilute the reagent-grade ammonia water with less than 0.5 ppm of iron, cobalt, nickel, copper, cadmium and vanadium to a mass fraction of 25%, and then slowly add it to the mixed suspension of phosphoric acid and yttrium chloride in step 2.1, keep it at 100°C and stir it for 30 minutes, adjust the acidity to 2.5, keep it at 100°C and stir it for 3 hours, so that the particles are fully formed, and obtain the yttrium phosphate synthesis solution;

[0095] Step 2.3: Centrifuge the yttrium phosphate synthesis liquid obtained in step 2.2 at a centrifugal speed of 1200 rpm, filter with a 1500-mesh filter cloth, and wash with pure water. The chloride ion is controlled to be less than 50 ppm, and the iron, cobalt, nickel, copper, cadmium, and vanadium are all less than 0.5 ppm to obtain a hydrated high-activity yttrium phosphate filter cake.

[0096] Step 3: Synthesizing yttrium metaphosphate;

[0097] Step 3.1 Take a high-grade food-grade phosphoric acid, add it to an enameled reactor, add pure water for dilution, the mass ratio of phosphoric acid to pure water is 1:1.3, and then add the hydrated high-activity yttrium phosphate filter cake obtained in step 2.3 to the diluted phosphoric acid, the molar ratio of phosphoric acid to yttrium phosphate is 2:1, heat to 120°C for concentration reaction, concentrate to a paste state, discharge, cool, and cool to 40°C to obtain paste yttrium metaphosphate.

[0098] Step 4: drying the yttrium metaphosphate;

[0099] Step 4.1 Place the paste yttrium metaphosphate obtained in step 3.1 into a PTFE plate, flatten it to 3-5 cm, and evaporate it at 250°C for 3 hours until it is hardened to obtain a primary dried yttrium metaphosphate;

[0100] Step 4.2: Add the dried yttrium metaphosphate obtained in step 4.1 into a high-purity quartz crucible, heat to 500°C and dry for 5 hours to obtain a finished yttrium metaphosphate. The product is identified as yttrium metaphosphate by XRD; the product contains less than 0.05% water, less than 1ppm iron, less than 0.5ppm cobalt, nickel, copper, cadmium, vanadium and other elements, and has a purity of 99.99%.

Claims

1. A method for preparing battery-grade yttrium metaphosphate, characterized in that: The following steps are involved: Step 1: purification of yttrium salt; High-purity hydrochloric acid diluted with pure water reacts with 4N high-purity yttrium oxide to obtain yttrium chloride solution; After diluting the yttrium chloride solution with pure water, fine filtration is performed to obtain a pure yttrium chloride solution; Step 2: preparing highly active yttrium phosphate; Step 2.1: Dilute a high-quality food-grade phosphoric acid containing less than 0.3 ppm of iron, cobalt, nickel, copper, cadmium and vanadium to a mass fraction of 20-25% with pure water, and then add the diluted product to the pure yttrium chloride solution obtained in step 1, stir and heat to 70-80° C. to obtain a mixed suspension of phosphoric acid and yttrium chloride; the molar ratio of phosphoric acid to yttrium chloride is 1:1; Step 2.2: dilute reagent-grade ammonia containing less than 0.5 ppm of iron, cobalt, nickel, copper, cadmium and vanadium to a mass fraction of 20-25% with pure water, and then slowly add the mixture to the mixed suspension of phosphoric acid and yttrium chloride, keep the mixture at 70-100° C. and stir to adjust the pH value to 2-3, and then continue to keep the mixture at 70-100° C. and stir for 2-3 hours to fully form particles, thereby obtaining a yttrium phosphate synthesis solution; Step 2.3: centrifuge, filter, and wash the yttrium phosphate synthesis solution, control the chloride ion to be less than 50 ppm, and control the iron, cobalt, nickel, copper, cadmium, and vanadium to be less than 0.5 ppm, to obtain a hydrated high-activity yttrium phosphate filter cake; Step 3: Synthesizing yttrium metaphosphate; Dilute the superior food-grade phosphoric acid with pure water, add the hydrated high-activity yttrium phosphate filter cake thereto, the molar ratio of phosphoric acid to yttrium phosphate being 2:1, heat to 110-120° C. for concentration reaction, discharge after concentrating to a paste, cool to 30-40° C., and obtain a paste of yttrium metaphosphate; Step 4: drying the yttrium metaphosphate; The paste of yttrium metaphosphate is evaporated at 200-250° C. for 3-5 hours, evaporated to a hardened state, heated to 500-700° C., and dried for 3-5 hours to obtain a finished yttrium metaphosphate product.

2. The method for preparing battery-grade yttrium metaphosphate according to claim 1, characterized in that: Step 1 is as follows: Step 1.1 Take high-purity hydrochloric acid and add pure water to dilute it, then add 4N high-purity yttrium oxide with iron, cobalt, nickel, copper, cadmium and vanadium less than 0.5 ppm, dissolve it until transparent, and obtain yttrium chloride solution; The molar ratio of hydrochloric acid to yttrium oxide is 6:1; the metal impurity elements include: Step 1.2: After diluting the yttrium chloride solution with pure water, it is finely filtered to remove insoluble matter and mechanical impurities to obtain a pure yttrium chloride solution.

3. The method for preparing battery-grade yttrium metaphosphate according to claim 2, characterized in that: When diluting high-purity hydrochloric acid in step 1.1, the mass ratio of high-purity hydrochloric acid to water is 1:1-1.5; when diluting yttrium chloride solution in step 1.2, the mass ratio of yttrium chloride solution to pure water is 1:2-2.3; in step 1.2, insoluble matter and mechanical impurities are removed through a precision filter with a filtration accuracy of 0.5 microns.

4. The method for preparing battery-grade yttrium metaphosphate according to any one of claims 1 to 3, characterized in that: In the step 2.3: the centrifugal speed is 1000-1200 rpm, and filtration is performed using a 1500 mesh filter cloth.

5. The method for preparing battery-grade yttrium metaphosphate according to claim 4, characterized in that: In step 3, the high-quality food-grade phosphoric acid is diluted with pure water of equal mass.

6. The method for preparing battery-grade yttrium metaphosphate according to claim 5, characterized in that: Step 4 is as follows: Step 4.1: Place the paste of yttrium metaphosphate in a PTFE plate, flatten it to 3-5 cm, and evaporate it at 200-250° C. for 3-5 hours until it is hardened to obtain a primary dried yttrium metaphosphate; Step 4.2: Add the dried yttrium metaphosphate once into a high-purity quartz crucible, heat it to 500-700° C., and dry it for 3-5 hours to obtain a finished yttrium metaphosphate product.

7. A battery-grade yttrium metaphosphate, characterized in that: The method is prepared by any one of claims 1 to 6.

8. A lithium ion battery, characterized in that: The coating layer of the positive electrode material of the lithium-ion battery is generated by the in-situ reaction of the battery-grade yttrium metaphosphate described in claim 7 with the residual alkali on the surface of the parent material.

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