A method for preparing battery-grade lithium dihydrogen phosphate

Abstract

The application provides a preparation method of battery-grade lithium dihydrogen phosphate, comprising the following steps: adding a phosphate into a lithium hydroxide circulating mother liquor to obtain lithium phosphate precipitation; separating and washing the lithium phosphate precipitation, and reacting with phosphoric acid to obtain a crude lithium dihydrogen phosphate solution; adding a precipitant into the crude lithium dihydrogen phosphate solution, and performing solid-liquid separation to obtain a primary refined lithium dihydrogen phosphate solution; using ion exchange resin to remove impurities from the primary refined lithium dihydrogen phosphate solution to obtain a secondary refined lithium dihydrogen phosphate solution; adding phosphoric acid into the secondary refined lithium dihydrogen phosphate solution to obtain a tertiary refined lithium dihydrogen phosphate solution; sequentially performing evaporation concentration, cooling crystallization and centrifugal separation on the tertiary refined lithium dihydrogen phosphate solution to obtain a lithium dihydrogen phosphate crude product; and using a saturated lithium dihydrogen phosphate solution to leach the lithium dihydrogen phosphate crude product, and drying to obtain a battery-grade lithium dihydrogen phosphate product.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lithium dihydrogen phosphate preparation, in particular to a preparation method of battery-grade lithium dihydrogen phosphate. BACKGROUND

[0002] Lithium iron phosphate has the advantages of safety, environmental protection, low cost, long cycle life and good high-temperature performance, and is one of the most potential anode materials of lithium ion batteries, and lithium dihydrogen phosphate is a key raw material for preparing lithium iron phosphate.

[0003] On the one hand, the traditional production of battery-grade lithium dihydrogen phosphate in China generally adopts a preparation method of dissolving lithium carbonate or lithium hydroxide in a phosphoric acid solution and then evaporating and crystallizing, since the lithium hydroxide and lithium carbonate used are battery-grade materials with high purity, the traditional preparation method of battery-grade lithium dihydrogen phosphate has high cost, which limits its application in the synthesis of lithium iron phosphate.

[0004] On the other hand, a large amount of lithium hydroxide circulating mother liquor is generated in the process route of producing battery-grade lithium hydroxide by lithium carbonate causticization, the lithium hydroxide circulating mother liquor is rich in lithium and other impurities, and currently the lithium extraction from the lithium hydroxide circulating mother liquor is mainly through the ways of carbon dioxide lithium precipitation and sodium carbonate lithium precipitation, the lithium-containing product obtained by the ways can be returned to the causticization process for reuse. However, the lithium content in the lithium hydroxide circulating mother liquor after lithium precipitation still reaches 2-4 g / L, so the lithium extraction rate of the ways is low.

[0005] Therefore, it is urgent to study a preparation method for extracting lithium from lithium hydroxide circulating mother liquor with a high extraction rate and preparing battery-grade lithium dihydrogen phosphate from the extracted lithium, so as to improve the utilization rate of resources. SUMMARY

[0006] Based on this, the purpose of the present application is to provide a preparation method of battery-grade lithium dihydrogen phosphate, which can extract lithium in lithium hydroxide circulating mother liquor with a high extraction rate and prepare battery-grade lithium dihydrogen phosphate.

[0007] The present application provides a preparation method of battery-grade lithium dihydrogen phosphate, comprising the following steps:

[0008] Step one: gradually adding a phosphate to the lithium hydroxide circulating mother liquor and stirring to obtain a lithium phosphate precipitate by reaction;

[0009] Step two: separating and washing the lithium phosphate precipitate in step one, and then mixing and stirring with a phosphoric acid with a preset concentration to obtain a crude lithium dihydrogen phosphate solution;

[0010] Step three: adding a precipitant to the crude lithium dihydrogen phosphate solution in step two and stirring to preliminarily remove metal ions in the solution, and then solid-liquid separation to obtain a primary refined lithium dihydrogen phosphate solution;

[0011] Step four: flowing the once-refined lithium dihydrogen phosphate solution in step three through ion exchange resin at a set rate to further remove metal ions in the solution to obtain a twice-refined lithium dihydrogen phosphate solution;

[0012] Step five: adding phosphoric acid to the twice-refined lithium dihydrogen phosphate solution in step four to obtain a thrice-refined lithium dihydrogen phosphate solution with a set pH value;

[0013] Step six: evaporating and concentrating the thrice-refined lithium dihydrogen phosphate solution in step five, and then quenching to a set temperature after the solution is saturated, and centrifuging to obtain a lithium dihydrogen phosphate crude product when no crystals continue to precipitate;

[0014] Step seven: leaching the lithium dihydrogen phosphate crude product in step six with a saturated lithium dihydrogen phosphate solution, and then drying to obtain a battery-grade lithium dihydrogen phosphate product.

[0015] In addition, the battery-grade lithium dihydrogen phosphate preparation method according to the above-mentioned application can also have the following additional technical features:

[0016] Further, the precipitant in step three includes oxalic acid or oxalate, the stirring rate is 300-500 r / min, and the stirring time is 1-3 h.

[0017] Further, the ion exchange resin in step four includes 724 resin or D401 resin, and the once-refined lithium dihydrogen phosphate solution flows through the ion exchange resin at a rate of 1-5 L / min.

[0018] Further, the pH value of the thrice-refined lithium dihydrogen phosphate solution in step five is 1.5-2.2.

[0019] Further, the concentration of the phosphoric acid in step two is greater than or equal to 85%.

[0020] Further, the molar ratio of the lithium phosphate precipitate to the phosphoric acid in step two is 1:2.1-2.4, and the stirring rate is 300-500 r / min.

[0021] Further, the stirring rate in step one is 300-600 r / min, and the reaction temperature is 60-100℃.

[0022] Further, the evaporation temperature in step six is 110-130℃, and the quenching temperature is 30-50℃.

[0023] Further, the leaching frequency in step seven is 2-3 times, the drying temperature is 100-120℃, and the drying time is 3-4 h.

[0024] The present application has the following beneficial effects: lithium in the lithium hydroxide circulating mother liquor reacts with phosphate ions to generate lithium phosphate precipitation, at this time most of the lithium elements in the lithium hydroxide circulating mother liquor are fixed into the lithium phosphate precipitation, and then the lithium phosphate precipitation is converted into lithium dihydrogen phosphate solution by reacting with phosphoric acid, and then through two-stage metal ion impurity removal, evaporation concentration, cooling crystallization, washing and drying, the battery-grade lithium dihydrogen phosphate product with high purity can be obtained; compared with the traditional preparation method of lithium dihydrogen phosphate, the lithium hydroxide circulating mother liquor obtained from the process route of producing battery-grade lithium hydroxide from lithium carbonate causticization is used as a lithium source in the present application, so the purity of the lithium source is not required to be high, and therefore the raw material cost is low, and the lithium phosphate precipitation has a high lithium extraction rate, so the lithium elements in the lithium hydroxide circulating mother liquor can be maximizedly recovered, and has a broad market prospect. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 A flowchart of the preparation method of the battery-grade lithium dihydrogen phosphate provided by the embodiments of the present application. DETAILED DESCRIPTION

[0026] In order to facilitate the understanding of the present application, the present application will be described more fully below with reference to the related drawings. The drawings show several embodiments of the present application. However, the present application can be realized in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the disclosure of the present application more thorough and comprehensive.

[0027] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the present application belongs. The terms used in the specification of the present application are only for the purpose of describing specific embodiments and are not intended to limit the present application. The term "and / or" used herein includes any and all combinations of one or more related listed items.

[0028] In order to be able to extract lithium in the lithium hydroxide circulating mother liquor with a high extraction rate and prepare battery-grade lithium dihydrogen phosphate, the present application proposes a preparation method of battery-grade lithium dihydrogen phosphate, please refer to Figure 1 , specifically including the following steps S100-S700:

[0029] S100, gradually adding sodium phosphate into the lithium hydroxide circulating mother liquor and stirring to obtain lithium phosphate precipitation;

[0030] Specifically, gradually add the phosphate, for example, the phosphate can be selected as sodium phosphate, to the reaction kettle containing the lithium hydroxide circulating mother liquor, and generate lithium phosphate precipitate through the reaction of lithium ions in the lithium hydroxide circulating mother liquor with phosphate ions. In order to ensure sufficient reaction, the stirring rate is preferably controlled at 300-600 r / min, and the reaction temperature is controlled at 60-100°C. The lithium hydroxide circulating mother liquor in this step can be obtained in large quantities from the process route of producing battery-grade lithium hydroxide by lithium carbonate causticization.

[0031] S200, separate the lithium phosphate precipitate in step S100 and wash, and then mix and stir with phosphoric acid of a preset concentration to obtain a crude lithium dihydrogen phosphate solution;

[0032] Specifically, after the lithium phosphate precipitate obtained by reaction in step S100 is separated and washed with deionized water, a certain proportion of the lithium phosphate precipitate is mixed and stirred with phosphoric acid to generate a crude lithium dihydrogen phosphate solution. Preferably, the molar ratio of lithium phosphate precipitate to phosphoric acid is 1:2.1-2.4, the stirring rate is controlled at 300-500 r / min, and the concentration of phosphoric acid is greater than or equal to 85%. It should be noted that the concentration of phosphoric acid will affect the reaction speed and the quality of the product. Generally speaking, the higher the concentration of phosphoric acid, the faster the reaction speed and the higher the quality of the product. However, the higher the concentration of phosphoric acid, the higher the cost.

[0033] S300, add a precipitant to the crude lithium dihydrogen phosphate solution in step S200 and stir to preliminarily remove metal ions such as calcium, magnesium and the like in the solution, and then obtain a primary refined lithium dihydrogen phosphate solution after solid-liquid separation; preferably, the precipitant in this step includes oxalic acid and oxalate, for example, the oxalate can be selected as sodium oxalate. In addition, in order to ensure sufficient reaction, the stirring rate is controlled at 300-500 r / min, and the stirring time is controlled at 1-3 h.

[0034] S400, flow the primary refined lithium dihydrogen phosphate solution in step S300 through ion exchange resin at a set rate to further remove metal ions such as calcium, magnesium and the like in the solution, and finally obtain a secondary refined lithium dihydrogen phosphate solution; preferably, the ion exchange resin in this step can be selected from one or more of 724 resin and D401 resin, and the primary refined lithium dihydrogen phosphate solution is flowed through the ion exchange resin at a rate of 1-5 L / min.

[0035] S500, adding a certain amount of phosphoric acid into the secondary refined lithium dihydrogen phosphate solution obtained in step S400 to adjust the pH value of the solution to 1.5-2.2, and thereby obtaining a tertiary refined lithium dihydrogen phosphate solution; in this step, the phosphoric acid is mainly added to adjust the pH value of the secondary refined lithium dihydrogen phosphate solution, so that it is kept in the optimal acid-base balance state, because lithium dihydrogen phosphate is a weak acid substance, and its solubility and stability are both affected by the pH value, when the pH value of the solution is too high or too low, the solubility of lithium dihydrogen phosphate can be reduced, thereby affecting the quality and yield of the product. Preferably, the pH value is 1.7.

[0036] S600, evaporating and concentrating the tertiary refined lithium dihydrogen phosphate solution in step S500, and then quenching to a set temperature after the solution is saturated, and centrifuging to obtain a lithium dihydrogen phosphate crude product when no crystal continues to precipitate;

[0037] Specifically, in this step, the tertiary refined lithium dihydrogen phosphate solution is evaporated and concentrated, the evaporation temperature is 110-130℃, after a large amount of crystals precipitate from the saturated solution, it is quenched to 30-50℃, and when no crystal precipitates, centrifugation is performed, and finally a lithium dihydrogen phosphate crude product is obtained.

[0038] S700, washing the lithium dihydrogen phosphate crude product in step S600 with a saturated lithium dihydrogen phosphate solution, and then drying to obtain a battery-grade lithium dihydrogen phosphate product.

[0039] Specifically, in this step, the obtained lithium dihydrogen phosphate crude product is washed with a saturated lithium dihydrogen phosphate solution for 2-3 times to remove impurities and incompletely reacted substances, improve the purity of the product, and after the washing is completed, drying is performed to remove free water in the product, wherein the drying temperature is set to 100-120℃, and the drying time is set to 3-4h, and finally a battery-grade lithium dihydrogen phosphate product can be obtained.

[0040] In the present application, there is no requirement for the purity of lithium compounds, that is, it is not necessary to purify the lithium compound by first deeply removing impurities from the lithium hydroxide circulating mother liquor, but to directly react lithium in the lithium hydroxide circulating mother liquor with phosphate ions to generate lithium phosphate precipitate, at this time, a variety of impurity elements have been removed from the lithium phosphate precipitate, so that the types of impurities are less when the lithium dihydrogen phosphate solution is converted to lithium dihydrogen phosphate solution for subsequent impurity removal, and finally a battery-grade lithium dihydrogen phosphate product with high purity can be obtained through two-stage metal ion removal, evaporation and concentration, cooling crystallization, washing and drying.

[0041] In addition, the present application also provides a battery-grade lithium dihydrogen phosphate, which is prepared by the above-mentioned method for preparing a battery-grade lithium dihydrogen phosphate.

[0042] The present application will be further described in the following specific examples:

[0043] Comparative Example 1:

[0044] The present comparative example proposes a preparation method of battery-grade lithium dihydrogen phosphate

[0045] Step one: gradually add sodium phosphate into the reactor containing 500 mL of lithium hydroxide circulating mother liquor (Li content = 28 g / L), and fully react to obtain about 245 g of lithium phosphate precipitate, wherein the stirring rate is controlled at 300-600 r / min, and the reaction temperature is controlled at 60-100℃;

[0046] Step two: after washing the lithium phosphate precipitate obtained in step one, stir and react with phosphoric acid at a molar ratio of 1:2.1-2.4 to generate a preliminary lithium dihydrogen phosphate solution, wherein the stirring rate is controlled at 300-500 r / min, and the concentration of phosphoric acid is 85%;

[0047] Step three: add an appropriate amount of phosphoric acid to the preliminary lithium dihydrogen phosphate solution obtained in step two to adjust the pH value of the solution to 1.5-2.2;

[0048] Step four: evaporate and concentrate the lithium dihydrogen phosphate solution in step three at an evaporation temperature of 110-130℃, and when the solution is saturated and a large amount of crystals precipitate, quickly cool it to 30-50℃, and when no more crystals precipitate, centrifuge to obtain a crude lithium dihydrogen phosphate product;

[0049] Step five: rinse the obtained crude lithium dihydrogen phosphate product with saturated lithium dihydrogen phosphate solution for 2-3 times, and then dry, wherein the drying temperature is set to 100-120℃, and the drying time is set to 3-4 h, to obtain a battery-grade lithium dihydrogen phosphate product A0.

[0050] Example 1:

[0051] The present example proposes a preparation method of battery-grade lithium dihydrogen phosphate, which specifically comprises the following steps:

[0052] Step one: gradually add sodium phosphate into the reactor containing 500 mL of lithium hydroxide circulating mother liquor (Li content = 28 g / L), and fully react to obtain about 245 g of lithium phosphate precipitate, wherein the stirring rate is controlled at 300-600 r / min, and the reaction temperature is controlled at 60-100℃;

[0053] Step two: after washing the lithium phosphate precipitate obtained in step one, stir and react with phosphoric acid at a molar ratio of 1:2.1 to generate a crude lithium dihydrogen phosphate solution, wherein the stirring rate is controlled at 300-500 r / min, and the concentration of phosphoric acid is 85%;

[0054] Step three: add a suitable amount of precipitant to the crude lithium dihydrogen phosphate solution obtained in step two, stir at a speed of 500 r / min, continue stirring for 2 h, and then separate the solid and liquid to obtain a first refined lithium dihydrogen phosphate solution;

[0055] Step four: flow the first refined lithium dihydrogen phosphate solution in step three through a 724 resin at a flow rate of 5 L / min to obtain a second refined lithium dihydrogen phosphate solution;

[0056] Step five: add a suitable amount of phosphoric acid to the second refined lithium dihydrogen phosphate solution obtained in step four to adjust the pH value of the solution to 1.7;

[0057] Step six: evaporate and concentrate the second refined lithium dihydrogen phosphate solution in step five at an evaporation temperature of 130℃, and then quench to 50℃ when a large amount of crystals precipitate, and then centrifuge to obtain a crude lithium dihydrogen phosphate product;

[0058] Step seven: rinse the crude lithium dihydrogen phosphate product obtained in step six with saturated lithium dihydrogen phosphate solution for 3 times, and then dry, wherein the drying temperature is set to 120℃ and the drying time is set to 3 h, to obtain a battery-grade lithium dihydrogen phosphate product A1.

[0059] Example 2:

[0060] The present embodiment provides a method for preparing a battery-grade lithium dihydrogen phosphate, which specifically comprises the following steps:

[0061] Step one: gradually add sodium phosphate to a reaction kettle containing 500 mL of lithium hydroxide circulating mother liquor (Li content = 28 g / L) to obtain about 245 g of lithium phosphate precipitate, wherein the stirring speed is controlled at 500 r / min and the reaction temperature is controlled at 85℃;

[0062] Step two: wash the lithium phosphate precipitate obtained in step one, and then stir and react with phosphoric acid at a molar ratio of 1:2.2 to generate a crude lithium dihydrogen phosphate solution, wherein the stirring speed is controlled at 500 r / min and the concentration of phosphoric acid is 85%;

[0063] Step three: add a suitable amount of precipitant to the crude lithium dihydrogen phosphate solution obtained in step two, stir at a speed of 300 r / min, continue stirring for 3 h, and then separate the solid and liquid to obtain a first refined lithium dihydrogen phosphate solution;

[0064] Step four: flow the first refined lithium dihydrogen phosphate solution in step three through a D401 resin at a flow rate of 3 L / min to obtain a second refined lithium dihydrogen phosphate solution;

[0065] Step five: add appropriate amount of phosphoric acid to the secondary refined lithium dihydrogen phosphate solution obtained in step four to adjust the pH value of the solution to 1.8;

[0066] Step six: evaporate and concentrate the secondary refined lithium dihydrogen phosphate solution in step five, the evaporation temperature is 130℃, and when the solution is saturated, a large amount of crystals are precipitated, and it is suddenly cooled to 50℃, and when no more crystals are precipitated, centrifugal separation is carried out to obtain the crude lithium dihydrogen phosphate product;

[0067] Step seven: the crude lithium dihydrogen phosphate product obtained in step six is washed with saturated lithium dihydrogen phosphate solution for 3 times, and then dried, wherein the drying temperature is set to 110℃ and the drying time is set to 4h, to obtain the battery grade lithium dihydrogen phosphate product A2.

[0068] Example 3:

[0069] The embodiment provides a preparation method of battery grade lithium dihydrogen phosphate, which specifically comprises the following steps:

[0070] Step one: gradually add sodium phosphate into a reaction kettle containing 500 mL lithium hydroxide circulating mother liquor (Li content = 28 g / L), and fully react to obtain about 245 g lithium phosphate precipitate, wherein the stirring rate is controlled at 500 r / min and the reaction temperature is controlled at 75℃;

[0071] Step two: after washing the lithium phosphate precipitate obtained in step one, the lithium phosphate precipitate is reacted with phosphoric acid at a molar ratio of 1:2.3 to generate a crude lithium dihydrogen phosphate solution, wherein the stirring rate is controlled at 500 r / min and the concentration of phosphoric acid is 85%;

[0072] Step three: add an appropriate amount of precipitant to the crude lithium dihydrogen phosphate solution obtained in step two, and stir at a stirring rate of 500 r / min for 3h, and then perform solid-liquid separation to obtain a primary refined lithium dihydrogen phosphate solution;

[0073] Step four: pass the primary refined lithium dihydrogen phosphate solution in step three through the 724 resin at a flow rate of 3 L / min to obtain a secondary refined lithium dihydrogen phosphate solution;

[0074] Step five: add appropriate amount of phosphoric acid to the secondary refined lithium dihydrogen phosphate solution obtained in step four to adjust the pH value of the solution to 2;

[0075] Step six: evaporate and concentrate the secondary refined lithium dihydrogen phosphate solution in step five, the evaporation temperature is 130℃, and when the solution is saturated, a large amount of crystals are precipitated, and it is suddenly cooled to 40℃, and when no more crystals are precipitated, centrifugal separation is carried out to obtain the crude lithium dihydrogen phosphate product;

[0076] Step seven: the obtained lithium phosphate crude product is rinsed with saturated lithium phosphate solution for 3 times, and then dried, wherein the drying temperature is set to 120℃, and the drying time is set to 3h, to obtain the battery-grade lithium phosphate product A3.

[0077] In the specific implementation, the battery-grade lithium phosphate is prepared according to the process flow and process parameters defined in the above comparative example 1 and examples 1-3 respectively, and then the battery-grade lithium phosphate prepared in the above examples is detected for the content of components, and the results are shown in Table 1 below, and it should be noted that the detection components are according to the standard YS / T 967-2014 Battery-grade lithium phosphate:

[0078] Table 1

[0079]

[0080] As can be clearly seen from the data A1-A3 in Table 1, by the present application, lithium in the lithium hydroxide circulating mother liquor reacts with phosphate ions to generate lithium phosphate precipitate, the lithium phosphate precipitate is converted into lithium phosphate solution by reacting with phosphoric acid, and then the battery-grade lithium phosphate product prepared by two-stage metal ion impurity removal, evaporation concentration, cooling crystallization, washing and drying has high purity, which meets the requirements of preparing lithium ion positive electrode material.

[0081] In addition, as can be clearly seen from the data A0, if two-stage metal ion impurity removal is not performed in the preparation process of the present application, the battery-grade lithium phosphate product prepared will have the problem of excessive content of most impurities, and the content far exceeds the maximum value specified in the standard. At the same time, compared with examples 1-3, after two-stage metal ion impurity removal, the main content and impurity content of the battery-grade lithium phosphate product obtained are within the standard range.

[0082] In summary, the lithium in the lithium hydroxide circulating mother liquor is extracted with high efficiency, and the battery-grade lithium dihydrogen phosphate product prepared therefrom is stable in quality and high in purity. Compared with the traditional technology, the method in the application can fully utilize the lithium element in the lithium hydroxide circulating mother liquor obtained from the process route of producing battery-grade lithium hydroxide from lithium carbonate causticization, thereby improving the utilization rate of resources and having a broad market prospect. At the same time, in order to obtain lithium dihydrogen phosphate with high purity, most of the prior art is to first remove impurities from the reactants to obtain corresponding high-purity reactants, and then react to generate lithium dihydrogen phosphate. The purity of the lithium compound as the lithium source reactant in the present application is not required, that is, before reacting with phosphoric acid, there is no need to deeply remove and purify the pure lithium compound, but directly use the crude lithium compound to react with the phosphate to obtain crude lithium phosphate precipitate. At this time, the crude lithium phosphate precipitate obtained has removed various impurity elements, and when it is converted into lithium dihydrogen phosphate solution and then removed in the subsequent step, the types of impurities to be removed will be reduced, the impurity removal process step is reduced, and the production cost is reduced.

[0083] In the description of the present specification, the description referring to the terms "one embodiment", "some embodiments", "an example", "a specific example", or "some examples" and the like means that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present application. In the present specification, the illustrative description of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0084] The above-described embodiments only express several implementation manners of the present application, and the description is more specific and detailed, but it should not be understood as a limitation on the scope of the patent of the present application. It should be noted that, for those skilled in the art, without departing from the concept of the present application, a number of modifications and improvements can be made, which are all within the protection scope of the present application. Therefore, the protection scope of the patent of the present application should be subject to the appended claims.

Claims

1. A process for the preparation of battery grade lithium dihydrogen phosphate, characterized in that, The method comprises the following steps: Step one: gradually add phosphate to lithium hydroxide circulating mother liquor and stir, and obtain lithium phosphate precipitate by reaction; Step two: separate and wash the lithium phosphate precipitate in step one, and then mix and react with phosphoric acid of a preset concentration to obtain crude lithium dihydrogen phosphate solution; Step three: add a precipitant to the crude lithium dihydrogen phosphate solution in step two and stir to preliminarily remove metal ions in the solution, and then separate the solid and the liquid to obtain primary refined lithium dihydrogen phosphate solution; Step four: flow the primary refined lithium dihydrogen phosphate solution in step three through ion exchange resin at a set rate to further remove metal ions in the solution, and obtain secondary refined lithium dihydrogen phosphate solution; Step five: add phosphoric acid to the secondary refined lithium dihydrogen phosphate solution in step four to obtain tertiary refined lithium dihydrogen phosphate solution with a set pH value; Step six: evaporate and concentrate the tertiary refined lithium dihydrogen phosphate solution in step five, and then quench to a set temperature after the solution is saturated, and centrifugal separation is performed when no crystal continues to precipitate to obtain crude lithium dihydrogen phosphate; Step seven: perform elution of the crude lithium dihydrogen phosphate in step six with saturated lithium dihydrogen phosphate solution, and then perform drying to obtain battery-grade lithium dihydrogen phosphate product.

2. The method for preparing battery-grade lithium dihydrogen phosphate according to claim 1, characterized in that, The precipitant in step three comprises oxalic acid and oxalate, the stirring rate is 300-500 r / min, and the stirring time is 1-3 h.

3. The method for preparing battery-grade lithium dihydrogen phosphate according to claim 1, characterized in that, The ion exchange resin in step four comprises 724 resin and D401 resin, and the primary refined lithium dihydrogen phosphate solution flows through the ion exchange resin at a rate of 1-5 L / min.

4. The method for preparing battery-grade lithium dihydrogen phosphate according to claim 1, characterized in that, The pH value of the tertiary refined lithium dihydrogen phosphate solution in step five is 1.5-2.

2.

5. The method for preparing battery-grade lithium dihydrogen phosphate according to claim 1, characterized in that, The concentration of the phosphoric acid in step two is greater than or equal to 85%.

6. The method of claim 1 or 5, wherein the lithium dihydrogen phosphate is prepared by the process comprising: The molar ratio of the lithium phosphate precipitate to the phosphoric acid in step two is 1:2.1-2.4, and the stirring rate is 300-500 r / min. ​ 7. The method for preparing battery-grade lithium dihydrogen phosphate according to claim 1, characterized in that, The stirring rate in step one is 300-600 r / min, and the reaction temperature is 60-100°C.

8. The method for preparing battery-grade lithium dihydrogen phosphate according to claim 1, characterized in that, The evaporation temperature in step six is 110-130°C, and the quenching temperature is 30-50°C.

9. The method for preparing battery-grade lithium dihydrogen phosphate according to claim 1, characterized in that, The elution frequency in step seven is 2-3 times, the drying temperature is 100-120°C, and the drying time is 3-4 h.

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