Method for detecting purity of battery-grade lithium salt

Abstract

The invention discloses a method for detecting the purity of a battery-grade lithium salt. The method comprises the following steps: weighing the lithium salt, putting into a conical flask, and stirring for dissolving; adding a methyl red-bromocresol green indicator into the first to-be-detected solution, and titrating with a hydrochloric acid standard titration solution until the first to-be-detected solution is wine red; adding a phenolphthalein indicator into the second to-be-detected solution for titration; adding a methyl red-bromocresol green indicator, and titrating to wine red; and finally, calculating the purity percentage of the lithium salt. The detection method can be effectively used for analysis and detection of battery-grade lithium carbonate, lithium hydroxide monohydrate and lithium oxide, and compared with a traditional method, the method has the advantages that the sample dosage is small, the hydrochloric acid consumption is small, and the method is more environmentally friendly; meanwhile, the influence that hydrochloric acid consumption of carbonate ions is not considered in the traditional national standard can be effectively solved, so that the detection accuracy is improved; meanwhile, the method can also be effectively used for analysis and detection of battery-grade lithium oxide.

Description

Technical Field

[0001] The present invention relates to the field of battery material detection, and in particular to a method for detecting the purity of battery-grade lithium salt. Background Art

[0002] In recent years, the market for high-tech, high-value-added products that lead green transformation, represented by lithium batteries, has been booming. According to relevant industry data, the demand for the battery market will exceed 2TWh in two years and will reach more than 6TWh by 2030. By then, the performance, cost and technical requirements for products will only become higher and higher.

[0004] Lithium electrification, energy saving and high speed will be the development trend of lithium batteries in the future. As an important part of the new energy field, the lithium battery industry has developed rapidly and has become a new investment focus in the manufacturing field. Lithium battery companies have stepped up the construction of new factories, hoping to increase production capacity and win with the scale effect. Energy saving and high speed of lithium battery manufacturing have become new industrial trends. Battery-grade anhydrous lithium hydroxide, lithium hydroxide monohydrate and lithium oxide are all lithium compounds. They are in the midstream smelting and processing link of the lithium battery industry chain. They are important sources of lithium for lithium batteries and have a huge market size. Therefore, it is particularly important to control their quality. The purity index of battery-grade anhydrous lithium hydroxide, lithium hydroxide monohydrate and lithium oxide is a key factor in evaluating product quality and a key test item in the product acceptance link. It is of great significance to be able to quickly and accurately detect their purity.

[0005] According to GB / T 1568-2022 "Battery Grade Anhydrous Lithium Hydroxide" and GB / T26008-2020 "Battery Grade Monohydrate Lithium Hydroxide", its main content is lithium hydroxide and lithium carbonate, and other impurities are extremely trace, all at the ppm level; according to YS / T968-2014 "Battery Grade Lithium Oxide", its main content is lithium oxide and lithium carbonate, and there may be some residual lithium hydroxide that has not been converted during the sintering process or lithium hydroxide produced by absorbing water during the production process. The content of other impurities is also extremely trace, all at the ppm level. At present, the purity analysis method of anhydrous lithium hydroxide and monohydrate lithium hydroxide generally adopts GB / T 11064.2-2013 "Chemical Analysis Methods for Lithium Carbonate, Monohydrate Lithium Hydroxide and Lithium Chloride Part 2: Determination of Lithium Hydroxide Content Acid-Base Titration Method"; However, in GB / T 11064.2-2013, because the influence of carbonate ions is not taken into account, the amount of hydrochloric acid consumed during the titration process is too large, which often leads to a high result. There are no relevant industry standards or national standards for battery-grade lithium oxide purity testing. Therefore, the market urgently needs a testing method that can meet the recognition of both supply and demand sides and improve detection accuracy. Summary of the invention

[0006] In view of the above problems, the present invention aims to provide a method for detecting the purity of battery-grade lithium salts which can eliminate the influence of carbonate ions.

[0007] To achieve the technical purpose, the solution of the present invention is: a method for detecting the purity of battery-grade lithium salt, characterized in that the specific steps are as follows:

[0008] S1. Weigh m1 and m2 of lithium salt respectively into a conical flask, and perform parallel samples and blank experiments together; add V0 mL of deionized water, plug with a rubber stopper, and stir to dissolve to obtain a first test solution and a second test solution;

[0009] S2. Add methyl red-bromocresol green indicator to the first test solution, and use a standard hydrochloric acid solution with a molar concentration of c1 to change the color from green to wine red; boil for two minutes, drive off carbon dioxide, cool, and continue titrating until it turns wine red, which is the end point, and record the volume V1 of the standard hydrochloric acid solution consumed; perform a blank experiment at the same time, and record the volume V2 of the standard hydrochloric acid solution consumed by the blank sample;

[0010] S3, add phenolphthalein indicator to the second test solution, and titrate it with hydrochloric acid solution with a molar concentration of c2 until it turns light red under the condition of being isolated from air, and do not record the reading;

[0011] S4, use a standard hydrochloric acid solution with a molar concentration of c2 to titrate until it becomes colorless, and do not record the reading;

[0012] S5, add methyl red-bromocresol green indicator, continue to titrate with standard hydrochloric acid solution with molar concentration of c2 until wine red; boil for another two minutes, cool, and the wine red color is the end point, record the consumed volume V3 of standard hydrochloric acid solution with molar concentration of c2;

[0013] S6. The total alkalinity a of the first solution to be tested, i.e., the total amount of LiOH+LiCO3 in the solution, is calculated based on the consumed volume V1 and the molar concentration of hydrochloric acid c1; the carbonate ion content b in the second solution to be tested, i.e., the Li2CO3 content in the sample, is calculated based on the consumed volume V3 and the molar concentration of hydrochloric acid c2, and finally the purity percentage of the lithium salt is calculated.

[0014] 2. The method for detecting the purity of battery-grade lithium salt according to claim 1, characterized in that: the main components of the lithium salt weighed for testing in step S1 include anhydrous lithium hydroxide and lithium carbonate, or monohydrate lithium hydroxide and lithium carbonate, or lithium oxide and lithium carbonate.

[0015] 3. The method for detecting the purity of battery-grade lithium salt according to claim 2, characterized in that the calculation formula for the content of carbonate ions and lithium carbonate in step S6 is:

[0016]

[0017] Wherein: c2---is the hydrochloric acid standard titration solution in step S5, the unit is mol / L;

[0018] m2---the mass of the sample in the second test solution, in g;

[0019] ω(CO3 2- )---Carbonate ion content in the sample;

[0020] In step S2, the volume V of the standard hydrochloric acid titration solution with concentration c1 consumed by carbonate satisfies the following formula:

[0021]

[0022] The content of hydroxide ions can be calculated using the formula:

[0023]

[0024] 4. The method for detecting the purity of battery-grade lithium salt according to claim 3, characterized in that when the main component is anhydrous lithium hydroxide, the calculation formula is:

[0025]

[0026] 5. The method for detecting the purity of battery-grade lithium salt according to claim 3, characterized in that when the main component is lithium hydroxide monohydrate, the calculation formula is:

[0027]

[0028] 6. The method for detecting the purity of battery-grade lithium salt according to claim 3, characterized in that when the main component is lithium oxide, the calculation formula is:

[0029]

[0030] The beneficial effects of the present invention are that the detection method of the present application can be effectively used for the analysis and detection of battery-grade lithium carbonate, lithium hydroxide monohydrate, and lithium oxide. Compared with traditional methods, less sample usage and less hydrochloric acid consumption are required, which is more environmentally friendly. At the same time, it can effectively solve the problem that the traditional national standard does not take into account the influence of carbonate ions consuming hydrochloric acid, thereby improving the accuracy of the detection. At the same time, the method can also be effectively used for the analysis and detection of battery-grade lithium oxide. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 is a flow chart of an embodiment of the present invention. DETAILED DESCRIPTION

[0032] The following is a combination of specific embodiments and Figure 1The present invention is further described, but the present invention is not limited to the following examples. Unless otherwise defined, all professional terms used hereinafter have the same meaning as those generally understood by those skilled in the art. The professional terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the scope of protection of the present invention. The reagents and materials described in the following examples, unless otherwise specified, can be obtained from commercial sources.

[0033] A method for detecting the purity of battery-grade lithium salt, wherein the main components of the lithium salt are anhydrous lithium hydroxide and lithium carbonate, or monohydrate lithium hydroxide and lithium carbonate, or lithium oxide and lithium carbonate. The specific steps are as follows:

[0034] (1) Place two samples of different weights in 300 mL conical flasks, add 50 mL of deionized water, plug with rubber stopper, and stir to dissolve the samples. When the sample is lithium oxide, the chemical reaction formula when dissolved in water is Li2O+H2O→LiOH.

[0035] (2) Add 10 drops of methyl red-bromocresol green indicator to the first sample to be tested, and use 0.3 mol / L (c1) hydrochloric acid standard titration solution to change from green to wine red; boil for two minutes, drive off carbon dioxide, cool, and continue titrating until it turns wine red, which is the end point. Record the volume V1 of the hydrochloric acid standard titration solution consumed. The titration reaction principle is OH - +H + →H2O, CO3 2- +H + →HCO 3- , HCO 3- +H + →CO2↑+H2O.

[0036] (3) Add 10 drops of phenolphthalein indicator to the second sample and titrate it with 2 mol / L hydrochloric acid solution until it turns light red under air-tight conditions.

[0037] (4) Use 0.05 mol / L (c0) hydrochloric acid standard titration solution to titrate until colorless (do not record the reading). The purpose of steps (3) and (4) is to consume all hydroxide ions and convert carbonate ions into bicarbonate ions. The reaction principle is OH-+H + →H2O, CO3 2- +H+→HCO3 - .

[0038] (5) Perform a blank experiment simultaneously, and record the volume V2 of the standard hydrochloric acid solution consumed by the blank sample; add 10 drops of methyl red-bromocresol green indicator, and continue to titrate with 0.05 mol / L hydrochloric acid (c2) standard solution until the solution turns wine red; boil for another two minutes, cool, and the wine red color is the end point. Record the volume V3 of the standard hydrochloric acid solution consumed. The reaction principle is HCO3 - +H+→CO2↑+H2O, and the content of carbonate ions and lithium carbonate is obtained from this, the calculation formula is:

[0039]

[0040] Where:

[0041] c2---The actual concentration of the hydrochloric acid standard titration solution (0.05mol / L), in moles per liter (mol / L);

[0042] m2---the mass of the sample in step (3), in grams (g);

[0043] ω(CO3 2- )---Carbonate ion content in the sample;

[0044] 30.00 / 36.94---The molar mass with (1 / 2CO3, 1 / 2Li2CO3) as the basic unit, the unit is gram per mole (g / mol).

[0045] (6) When performing parallel sample and blank experiments, when the blank sample consumes the hydrochloric acid standard titration solution, the volume of hydrochloric acid consumed by the blank sample must be subtracted when calculating.

[0046] (7) The total alkalinity is calculated based on the consumption of 0.3 mol / L hydrochloric acid by the first sample to be tested. The volume calculation formula of the standard hydrochloric acid titration solution with a concentration of c1 carbonate ion consumed in step (2) is:

[0047]

[0048] Where:

[0049] c1---The actual concentration of the hydrochloric acid standard titration solution (0.3mol / L), in moles per liter (mol / L);

[0050] m1---the mass of the sample in step (2), in grams (g);

[0051] ω(CO3 2- )---the carbonate content is calculated in step (5);

[0052] 30.00---The molar mass with (1 / 2CO3) as the basic unit, in grams per mole (g / mol).

[0053] From this, the content of hydroxide ions can be calculated using the following formula:

[0054]

[0055] Where:

[0056] c1---The actual concentration of the hydrochloric acid standard titration solution (0.3mol / L), in moles per liter (mol / L);

[0057] m1---the mass of the sample in step (2), in grams (g);

[0058] V1---the total volume of the hydrochloric acid standard titration solution (0.3 mol / L) consumed in the titration of hydroxide and carbonate in step (2), in milliliters (mL);

[0059] V---the volume of the standard hydrochloric acid solution (0.3 mol / L) consumed by carbonate in step (6), in milliliters (mL);

[0060] 17.00---is the molar mass of hydroxide, in grams per mole (g / mol).

[0061] (8) The carbonate ion content was calculated based on the consumption of 0.05 mol / L hydrochloric acid in the second sample to be tested, thereby calculating the contents of anhydrous lithium hydroxide, monohydrate lithium hydroxide and lithium oxide. The calculation formulas are:

[0062]

[0063] Where:

[0064] c1---The actual concentration of the hydrochloric acid standard titration solution (0.3mol / L), in moles per liter (mol / L);

[0065] m1---the mass of the sample in step (2), in grams (g);

[0066] V1---the total volume of the hydrochloric acid standard titration solution (0.3 mol / L) consumed in the titration of hydroxide and carbonate in step (2), in milliliters (mL);

[0067] V---the volume of the standard hydrochloric acid solution (0.3 mol / L) consumed by carbonate in step (6), in milliliters (mL);

[0068] 17.00 / 41.94---are the molar masses of lithium hydroxide / lithium hydroxide monohydrate, respectively, in grams per mole (g / mol).

[0069]

[0070] Where:

[0071] 29.88 / 18.00---are the molar masses of lithium oxide and water, respectively, in grams per mole (g / mol).

[0072] In summary, the detection method provided by the present invention can be used for the purity of battery-grade anhydrous lithium hydroxide, lithium hydroxide monohydrate and lithium oxide. The detection method of the present invention is referred to as the "two-step method", which is based on conventional acid-base titration. Compared with the existing standard method, the method is more effective, more efficient and more accurate; and can fill the gap in the lithium oxide purity detection method.

[0073] Embodiment 1:

[0074] Battery-grade anhydrous lithium hydroxide, battery-grade lithium hydroxide monohydrate and battery-grade lithium oxide were obtained from three different manufacturers (a total of 9 material samples, in which the lithium carbonate content was less than 1%, and the remaining impurities were mostly at the ppm level). This example uses the method of the present invention to study the purity of the above three lithium salts, including the following steps (such as Figure 1 ):

[0075] (1) Step 1: Quickly weigh 0.2 g of lithium hydroxide, 0.3 g of lithium hydroxide monohydrate, and 0.1 g of lithium oxide (accurate to 0.0001 g) and place them in 300 mL conical flasks (a total of 9 portions), add 50 mL of deionized water, plug with a rubber stopper, and stir to dissolve the sample;

[0076] (2) Add 10 drops of methyl red-bromocresol green indicator and titrate the solution with 0.3 mol / L hydrochloric acid standard solution until the color changes from green to wine red. Boil for two minutes, drive off carbon dioxide, cool, and continue titrating until the color turns wine red. This is the end point. Record the volume of hydrochloric acid standard solution consumed.

[0077] (3) Step 2: Quickly weigh 1.0 g of lithium hydroxide, 1.0 g of lithium hydroxide monohydrate, and 1.0 g of lithium oxide (accurate to 0.0001 g) and place them in 300 mL conical flasks (a total of 9 portions), add 50 mL of deionized water, plug with a rubber stopper, and stir to dissolve the sample;

[0078] (4) Add 10 drops of phenolphthalein indicator and titrate with 2 mol / L hydrochloric acid solution to a light red color under air-tight conditions;

[0079] (5) Use 0.05 mol / L hydrochloric acid standard titration solution to titrate until colorless (do not record the reading);

[0080] (6) Add 10 drops of methyl red-bromocresol green indicator and continue to titrate with 0.05 mol / L hydrochloric acid standard titration solution until the color turns wine red;

[0081] (7) Boil for another two minutes, cool, and continue titrating until the color turns orange-red or wine-red, which is the endpoint. Record the volume of 0.05 mol / L hydrochloric acid standard titration solution consumed.

[0082] (8) Conduct parallel sample and blank experiments;

[0083] Comparative Example 1:

[0084] This comparative example adopts the national standard GB / T 11064.2-2013 "Chemical analysis methods for lithium carbonate, lithium hydroxide monohydrate and lithium chloride Part 2: Determination of lithium hydroxide content by acid-base titration method" to detect the purity of battery-grade anhydrous lithium hydroxide, battery-grade lithium hydroxide monohydrate and battery-grade lithium oxide in Example 1, including the following steps:

[0085] (1) Quickly weigh 0.5 g of lithium hydroxide, 0.5 g of lithium hydroxide monohydrate, and 0.5 g of lithium oxide (accurate to 0.0001 g) and place them in a 250 mL conical flask pre-added with 40.00 mL of 0.25 mol / L hydrochloric acid titration solution (a total of 9 portions);

[0086] (2) Add 10 drops of methyl red-bromocresol green indicator and titrate the solution with 0.25 mol / L standard hydrochloric acid until the color changes from green to wine red. Boil for two minutes, drive off carbon dioxide, cool, and continue titrating until the color turns wine red. This is the end point. Record the volume of standard hydrochloric acid solution consumed.

[0087] Comparative Example 1 and Comparative Example 1

[0088]

[0089] As can be seen from the table above, since the national standard GB / T 11064.2-2013 "Chemical analysis methods for lithium carbonate, lithium hydroxide monohydrate, and lithium chloride Part 2: Determination of lithium hydroxide content by acid-base titration" does not take into account the influence of carbonate ion consumption of hydrochloric acid, the overall results are all biased. Moreover, in step (1) of comparative example 1, the sample amount is too large, resulting in a huge amount of hydrochloric acid consumption, which is not conducive to environmental protection. The original national standard GB / T 11064.2-2013 does not involve the detection of lithium oxide, and the lithium oxide purity detection in comparative example 1 is only processed with reference to the steps of the national standard and is a test method derived by the inventor in combination with the method of the present invention.

[0090] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any slight modification, equivalent substitution and improvement made to the above embodiment based on the technical essence of the present invention should be included in the protection scope of the technical solution of the present invention.

Claims

1. A method for detecting the purity of battery-grade lithium salt, characterized in that: The specific steps are as follows: S1. Weigh m1 and m2 of lithium salt respectively into a conical flask, and perform parallel samples and blank experiments together; add V0 mL of deionized water, plug with a rubber stopper, and stir to dissolve to obtain a first test solution and a second test solution; S2. Add methyl red-bromocresol green indicator to the first test solution, and use standard hydrochloric acid with a molar concentration of c1 to titrate the solution from green to wine red; boil for two minutes, drive off carbon dioxide, cool, and continue titrating until it turns wine red, which is the end point, and record the volume V1 consumed by the standard hydrochloric acid solution; S3, add phenolphthalein indicator to the second test solution, isolate it from air, and titrate it with hydrochloric acid solution with a molar concentration of c0 to a light red color, without recording the reading; S4, use a standard hydrochloric acid solution with a molar concentration of c2 to titrate until it becomes colorless, and do not record the reading; S5, add methyl red-bromocresol green indicator, continue to titrate with standard hydrochloric acid solution with molar concentration of c2 until wine red; boil for another two minutes, cool, and the wine red color is the end point, record the consumed volume V3 of standard hydrochloric acid solution with molar concentration of c2; S6. The total alkalinity a of the first solution to be tested, i.e., the total amount of LiOH+LiCO3 in the solution, is calculated based on the consumed volume V1 and the molar concentration of hydrochloric acid c1; the carbonate ion content b in the second solution to be tested, i.e., the Li2CO3 content in the sample, is calculated based on the consumed volume V3 and the molar concentration of hydrochloric acid c2, and finally the purity percentage of the lithium salt is calculated.

2. The method for detecting the purity of battery-grade lithium salt according to claim 1, characterized in that: In step S1, the main components of the lithium salt for testing are weighed, including anhydrous lithium hydroxide and lithium carbonate, or monohydrate lithium hydroxide and lithium carbonate, or lithium oxide and lithium carbonate.

3. The method for detecting the purity of battery-grade lithium salt according to claim 2, characterized in that: The calculation formula for the content of carbonate ions and lithium carbonate in step S6 is: Wherein: c2---is the hydrochloric acid standard titration solution in step S5, the unit is mol / L; m2---the mass of the sample in the second test solution, in g; ω(CO3 2- )---Carbonate ion content in the sample; In step S2, the volume V of the standard hydrochloric acid titration solution with a concentration of c1 consumed by carbonate satisfies the following formula: The content of hydroxide ions can be calculated using the formula:

4. The method for detecting the purity of battery-grade lithium salt according to claim 3, characterized in that: When the main component is anhydrous lithium hydroxide, the calculation formula is:

5. The method for detecting the purity of battery-grade lithium salt according to claim 3, characterized in that: When the main component is lithium hydroxide monohydrate, the calculation formula is:

6. The method for detecting the purity of battery-grade lithium salt according to claim 3, characterized in that: When the main component is lithium oxide, the calculation formula is:

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