Method for measuring purity of lithium dihydrogen phosphate

Abstract

The invention discloses a method for measuring the purity of lithium dihydrogen phosphate, which comprises the following steps: firstly, weighing a lithium dihydrogen phosphate sample to be measured, and adding water for dissolving to obtain a sample solution; adding a lithium hydroxide solution into the sample solution, and fully reacting to obtain a reaction solution; heating the reaction liquid to a slightly boiling state, carrying out suction filtration on the reaction liquid while the reaction liquid is hot, washing the precipitate with hot water, collecting filtrate and washing liquid, and combining the filtrate and the washing liquid into mixed filtrate; placing the mixed filtrate at room temperature, titrating by taking phenolphthalein as a titration indicator and selecting a hydrochloric acid solution, and finally calculating the purity of lithium dihydrogen phosphate. The buffer system provided by the invention causes great difficulty to a manual titration method; according to the invention, lithium dihydrogen phosphate is completely converted into lithium phosphate by excessive lithium hydroxide, and dissolution of lithium phosphate is reduced under a strong alkaline condition; a manual titration method is adopted, phenolphthalein is used as a titration indicator, the use cost is low, the titration phenomenon is obvious, the color is changed from existence to absence, and the method is an ideal titration model.

Description

Technical Field

[0001] The invention relates to the technical field of lithium salt detection, and in particular to a method for measuring the purity of lithium dihydrogen phosphate. Background Art

[0002] Lithium dihydrogen phosphate (LiH2PO4) is an inorganic compound, mainly used as an analytical reagent and catalyst. It has high solubility, is easily soluble in water, slightly soluble in ethanol, and insoluble in ether. Lithium dihydrogen phosphate has high electrical conductivity, thermal stability and chemical stability, and is an excellent electrolyte material. Lithium dihydrogen phosphate is mainly used in the following fields:

[0003] 1. As a positive electrode material for batteries

[0004] As a positive electrode material for batteries, lithium dihydrogen phosphate has the advantages of high energy density, long cycle life and excellent safety performance. It is an excellent positive electrode material for batteries and is mainly used in secondary batteries such as lithium-ion batteries, nickel-hydrogen batteries and lithium polymer batteries.

[0005] In lithium-ion batteries, lithium dihydrogen phosphate is usually used in combination with negative electrode materials such as graphite. Due to its high energy density and good cycle performance, lithium dihydrogen phosphate can provide longer battery life and higher energy output. In addition, lithium dihydrogen phosphate also has good high-temperature performance and safety, and can work in high-temperature environments.

[0006] 2. Synthetic lithium iron phosphate

[0007] Lithium dihydrogen phosphate can be used to synthesize lithium iron phosphate, which is an important positive electrode material for lithium-ion batteries. Compared with traditional ternary materials, lithium iron phosphate has higher safety performance and longer cycle life, so it has broad application prospects in electric vehicles, energy storage systems and other fields.

[0008] 3. As a food additive

[0009] Lithium dihydrogen phosphate can be used as food acidifier, leavening agent and mineral water treatment agent.

[0010] From the above, we can see that lithium dihydrogen phosphate, as an important lithium salt, has a wide range of practical application value; therefore, the purity of lithium dihydrogen phosphate directly affects the performance and efficacy of derivative products, so detecting the purity of lithium dihydrogen phosphate has great commercial value.

[0011] At present, there are several methods for detecting the purity of lithium dihydrogen phosphate:

[0012] (1) The lithium content is detected by flame atomic absorption spectrometry, thereby calculating the purity of lithium dihydrogen phosphate;

[0013] (2) Automatic potentiometric titration is used to titrate with a sodium hydroxide standard solution. The titration endpoint is indicated by the potential, and the purity of lithium dihydrogen phosphate is calculated by the volume consumption of the sodium hydroxide standard solution.

[0014] However, the above method has the following problems:

[0015] (1) The lithium content is measured by flame atomic absorption spectrometry. Due to the high proportion of lithium content, the product needs to be diluted by a high multiple to meet the injection requirements, which is prone to cause large dilution errors;

[0016] (2) Automatic potentiometric titration is used, but the equipment is expensive and the cost of use is too high. Summary of the invention

[0017] The purpose of the present invention is to circumvent the problems caused by the background method, and provide a method for determining the purity of lithium dihydrogen phosphate, wherein the lithium dihydrogen phosphate in the sample is completely converted into lithium phosphate using a lithium hydroxide standard solution, the generated lithium phosphate is separated from the system, the excess lithium hydroxide standard solution in the solution is titrated with a hydrochloric acid standard solution using phenolphthalein as an indicator until the pink color of the solution just fades and does not return to the original color within 30 seconds, and the volume of the hydrochloric acid standard solution consumed in the titration is recorded. The present invention has low cost, accurate detection, small error, and high commercial value.

[0018] To achieve the above purpose, the technical solution designed by the present invention is as follows:

[0019] The present invention provides a method for determining the purity of lithium dihydrogen phosphate by back titration, comprising the following steps:

[0020] (1) Weighing a lithium dihydrogen phosphate sample with a mass of m (accurate to 0.0001 g) and dissolving it in water to obtain a sample solution;

[0021] (2) adding a lithium hydroxide solution with a volume of V1 and a concentration of c1 to the sample solution under stirring, and obtaining a reaction solution after sufficient reaction; wherein the concentration c1 of the lithium hydroxide solution is 0.2-0.6 mol / L;

[0022] (3) heating the reaction solution to a slightly boiling state, filtering the reaction solution while hot, washing the precipitate with hot water, collecting the filtrate and the washing solution, and combining them into a mixed filtrate;

[0023] (4) After the mixed filtrate is placed at room temperature, phenolphthalein is used as a titration indicator and a hydrochloric acid solution with a concentration of c2 is selected as a titrant for titration. The titration is performed until the reddish color of the solution just fades and does not recover within 30 seconds. The titration is then stopped and the volume of the hydrochloric acid solution consumed at this time, V2, is recorded;

[0024] (5) Calculate the purity of lithium dihydrogen phosphate according to the following formula:

[0025]

[0026] Where: ω is the content of lithium dihydrogen phosphate, %;

[0027] m is the weight of the lithium dihydrogen phosphate sample to be tested, g;

[0028] c1 is the concentration of lithium hydroxide solution, moL / L;

[0029] V1 is the volume of lithium hydroxide solution, mL;

[0030] c2 is the concentration of hydrochloric acid solution, moL / L;

[0031] V2 is the volume of hydrochloric acid solution, mL;

[0032] M is the molar mass of lithium dihydrogen phosphate: 103.928 g / moL.

[0033] Furthermore, in the step (1), the water is ultrapure water, and the dissolution is carried out by stirring or ultrasound.

[0034] Furthermore, in step (2), the mass ratio of the sample to be tested to lithium hydroxide is 1:0.7-1.

[0035] Furthermore, in step (3), the hot water temperature is 80-100°C.

[0036] Furthermore, in step (4), the concentration c2 of the hydrochloric acid solution is 0.2-0.5 mol / L.

[0037] Beneficial effects of the present invention:

[0038] (1) The method of the present invention directly converts all lithium dihydrogen phosphate into lithium phosphate by adding an excess of lithium hydroxide standard solution, without forming a dihydrogen phosphate / monohydrogen phosphate buffer system. The existence of a buffer system causes great difficulties for manual titration;

[0039] (2) The excess lithium hydroxide of the present invention converts all lithium dihydrogen phosphate into lithium phosphate, which can further reduce the dissolution of lithium phosphate under strong alkaline conditions;

[0040] (3) The manual titration method of the present invention uses phenolphthalein as a titration indicator, has low cost, obvious titration phenomenon, and the color changes from presence to absence, which is a relatively ideal titration model. DETAILED DESCRIPTION

[0041] The present invention is further described in detail below in conjunction with specific embodiments so that those skilled in the art can understand.

[0042] Example 1

[0043] (1) Weigh 0.3314 g (accurate to 0.0001 g) of lithium dihydrogen phosphate sample to be tested in a container, add ultrapure water to the container, and stir or ultrasonically dissolve to obtain a sample solution;

[0044] (2) under stirring, adding a lithium hydroxide solution with a volume V1 of 25.00 ml and a concentration c1 of 0.502 mol / L to the sample solution, and obtaining a reaction solution after sufficient reaction;

[0045] (3) heating the reaction solution to a slightly boiling state, filtering the reaction solution while hot, washing the precipitate with hot water, collecting the filtrate and the washing solution, and combining them into a mixed filtrate;

[0046] (4) After the mixed filtrate is placed at room temperature, phenolphthalein is used as a titration indicator and a hydrochloric acid solution with a concentration c2 of 0.256 mol / L is selected as a titrant for titration. The titration is performed until the reddish color of the solution just fades and does not recover within 30 seconds. The titration is stopped and the volume of the hydrochloric acid solution consumed at this time, V2, is recorded as 24.23 ml;

[0047] (5) The formula for calculating the purity of lithium dihydrogen phosphate is as follows:

[0048]

[0049] Where: is the content of lithium dihydrogen phosphate, %;

[0050] m is the weight of the lithium dihydrogen phosphate sample to be tested, g;

[0051] c1 is the concentration of lithium hydroxide solution, moL / L;

[0052] V1 is the volume of lithium hydroxide solution, mL;

[0053] c2 is the concentration of hydrochloric acid solution, moL / L;

[0054] V2 is the volume of hydrochloric acid solution, mL;

[0055] M is the molar mass of lithium dihydrogen phosphate: 103.928 g / moL.

[0056] Example 2

[0057] (1) Weigh 0.3889 g (accurate to 0.0001 g) of lithium dihydrogen phosphate sample to be tested in a container, add ultrapure water to the container, and stir or ultrasonically dissolve to obtain a sample solution;

[0058] (2) under stirring, adding a lithium hydroxide solution with a volume V1 of 25.00 ml and a concentration c1 of 0.510 mol / L to the sample solution, and obtaining a reaction solution after sufficient reaction;

[0059] (3) heating the reaction solution to a slightly boiling state, filtering the reaction solution while hot, washing the precipitate with hot water, collecting the filtrate and the washing solution, and combining them into a mixed filtrate;

[0060] (4) After the mixed filtrate is placed at room temperature, phenolphthalein is used as a titration indicator and a hydrochloric acid solution with a concentration c2 of 0.245 mol / L is selected as a titrant for titration. The titration is performed until the reddish color of the solution just fades and does not recover within 30 seconds. The titration is stopped and the volume of the hydrochloric acid solution consumed at this time, V2, is recorded as 21.63 ml;

[0061] (5) The formula for calculating the purity of lithium dihydrogen phosphate is as follows:

[0062]

[0063] Where: ω is the content of lithium dihydrogen phosphate, %;

[0064] m is the weight of the lithium dihydrogen phosphate sample to be tested, g;

[0065] c1 is the concentration of lithium hydroxide solution, moL / L;

[0066] V1 is the volume of lithium hydroxide solution, mL;

[0067] c2 is the concentration of hydrochloric acid solution, moL / L;

[0068] V2 is the volume of hydrochloric acid solution, mL;

[0069] M is the molar mass of lithium dihydrogen phosphate: 103.928 g / moL.

[0070] Example 3

[0071] (1) Weigh 0.4275 g (accurate to 0.0001 g) of lithium dihydrogen phosphate sample to be tested in a container, add ultrapure water to the container, and stir or ultrasonically dissolve to obtain a sample solution;

[0072] (2) under stirring, adding a lithium hydroxide solution with a volume V1 of 25.00 ml and a concentration c1 of 0.497 mol / L to the sample solution, and obtaining a reaction solution after sufficient reaction;

[0073] (3) heating the reaction solution to a slightly boiling state, filtering the reaction solution while hot, washing the precipitate with hot water, collecting the filtrate and the washing solution, and combining them into a mixed filtrate;

[0074] (4) After the mixed filtrate is placed at room temperature, phenolphthalein is used as a titration indicator and a hydrochloric acid solution with a concentration c2 of 0.260 mol / L is selected as a titrant for titration. The titration is performed until the reddish color of the solution just fades and does not recover within 30 seconds. The titration is stopped and the volume of the hydrochloric acid solution consumed at this time, V2, is recorded as 16.30 ml;

[0075] (5) The formula for calculating the purity of lithium dihydrogen phosphate is as follows:

[0076]

[0077] Where: ω is the content of lithium dihydrogen phosphate, %;

[0078] m is the weight of the lithium dihydrogen phosphate sample to be tested, g;

[0079] c1 is the concentration of lithium hydroxide solution, moL / L;

[0080] V1 is the volume of lithium hydroxide solution, mL;

[0081] c2 is the concentration of hydrochloric acid solution, moL / L;

[0082] V2 is the volume of hydrochloric acid solution, mL;

[0083] M is the molar mass of lithium dihydrogen phosphate: 103.928 g / moL.

[0084] Comparative Example 1

[0085] (1) Weigh 0.4275 g (accurate to 0.0001 g) of lithium dihydrogen phosphate sample to be tested in a container, add ultrapure water to the container, and stir or ultrasonically dissolve to obtain a sample solution;

[0086] (2) under stirring, adding a lithium hydroxide solution with a volume V1 of 25.00 ml and a concentration of 0.497 mol / L to the sample solution, and reacting sufficiently to obtain a reaction solution;

[0087] (3) heating the reaction solution to a slightly boiling state, filtering the reaction solution while hot, washing the precipitate with hot water, collecting the filtrate and the washing solution, and combining them into a mixed filtrate;

[0088] (4) The precipitate obtained in step (3) was transferred to a weighing bottle with a pre-constant weight (mass m1 was 60.1123 g), dried to constant weight, and the total mass was weighed and recorded as m2, which was 60.5863 g. The purity of lithium dihydrogen phosphate was calculated as follows:

[0089]

[0090] Wherein, ω is the content of lithium dihydrogen phosphate, %;

[0091] m is the weight of the lithium dihydrogen phosphate sample to be tested, g;

[0092] m1 is the mass of the weighing bottle, g;

[0093] m2 is the mass of the weighing bottle containing the precipitate, g.

[0094] Comparative Example 2

[0095] (1) Weigh a lithium dihydrogen phosphate sample with a mass m of 0.3377 g (accurate to 0.0001 g) in a container, add ultrapure water to the container, and stir or ultrasonically dissolve to obtain a sample solution;

[0096] (2) Using phenolphthalein as the titration indicator, a lithium hydroxide solution with a concentration of c1 of 0.452 mol / L was selected as the titrant for titration. Titration was performed until the solution turned slightly red and did not recover within 30 s. The titration was stopped and the volume of lithium hydroxide standard solution consumed V1 was recorded as 7.13 ml.

[0097] (3) The formula for calculating the purity of lithium dihydrogen phosphate is as follows:

[0098]

[0099] Where: ω is the content of lithium dihydrogen phosphate, %;

[0100] m is the weight of the lithium dihydrogen phosphate sample to be tested, g;

[0101] c1 is the concentration of lithium hydroxide standard solution, mol / L;

[0102] V1 is the volume of lithium hydroxide standard solution, mL;

[0103] M is the molar mass of lithium dihydrogen phosphate: 103.928 g / moL.

[0104] The lithium dihydrogen phosphate product used in this example is from Shanghai Macklin Biochemical Technology Co., Ltd. (MACKLIN, L812312-100g, with a purity of 99.521%. The purity and deviation comparison between the example and the comparative example are shown in Table 1 below:

[0105] Table 1 Comparison of purity and deviation of lithium dihydrogen phosphate products

[0106]

[0107] As shown in Table 1: Although the purity of lithium dihydrogen phosphate can be accurately calculated by the mass of the precipitate in the method adopted in Comparative Example 1, this method requires overnight standing, which takes a very long time, up to about 10 hours, and requires very high experimental details from the operator.

[0108] The method of Comparative Example 2 uses lithium hydroxide to titrate lithium dihydrogen phosphate, and the theoretical titration endpoint pH value is 9.8. Although phenolphthalein is used as an indicator and the color development pH value is 8.2-10, which just covers the theoretical titration endpoint, the endpoint color is difficult to distinguish due to the formation of a dihydrogen phosphate / monohydrogen phosphate buffer system, and the accurate titration endpoint cannot be obtained, resulting in a large error.

[0109] Compared with Comparative Examples 1 to 2, Examples 1 to 3 all use the same method to conduct experiments, except that the mass of the sample and the mass ratio of the reagents are different. Although the sample mass and the mass ratio of the reagents have a certain influence on the results, the influence is negligible. This method does not require overnight standing, is time-saving, and has low requirements for operators. At the same time, the cost of use is low, the titration phenomenon is obvious, the color changes from presence to absence, the error is small, the detection is accurate, and the overall data reproducibility is good.

[0110] Although the above embodiments have been described in detail, they are only a part of the embodiments of the present invention, not all of them. People can also obtain other embodiments based on this embodiment without creativity, and these embodiments all belong to the protection scope of the present invention.

Claims

1. A method for measuring the purity of lithium dihydrogen phosphate, characterized in that: The following steps are involved: (1) Weighing a lithium dihydrogen phosphate sample with a mass of m and dissolving it in water to obtain a sample solution; (2) adding a lithium hydroxide solution with a volume of V1 and a concentration of c1 to the sample solution under stirring, and obtaining a reaction solution after sufficient reaction; wherein the concentration c1 of the lithium hydroxide solution is 0.2-0.6 mol / L; (3) heating the reaction solution to a slightly boiling state, filtering the reaction solution while hot, washing the precipitate with hot water, collecting the filtrate and the washing solution, and combining them into a mixed filtrate; (4) After the mixed filtrate is placed at room temperature, phenolphthalein is used as a titration indicator and a hydrochloric acid solution with a concentration of c2 is selected as a titrant for titration. The titration is stopped until the reddish color of the solution just fades and does not recover. The volume of the hydrochloric acid solution consumed at this time, V2, is recorded; (5) Calculate the purity of lithium dihydrogen phosphate according to the following formula: Where: ω is the content of lithium dihydrogen phosphate, %; m is the weight of the lithium dihydrogen phosphate sample to be tested, g; c1 is the concentration of lithium hydroxide solution, moL / L; V1 is the volume of lithium hydroxide solution, mL; c2 is the concentration of hydrochloric acid solution, moL / L; V2 is the volume of hydrochloric acid solution, mL; M is the molar mass of lithium dihydrogen phosphate: 103.928 g / moL.

2. The method according to claim 1, characterized in that: In the step (1), the water is ultrapure water, and the dissolution is carried out by stirring or ultrasound.

3. The method according to claim 1, characterized in that: In the step (2), the mass ratio of the sample to be tested to lithium hydroxide is 1:0.7-1.

4. The method according to claim 1, characterized in that: In the step (3), the hot water temperature is 80-100°C.

5. The method according to claim 1, characterized in that: In the step (4), the concentration c2 of the hydrochloric acid solution is 0.2-0.5 mol / L.

Images