Method for detecting free lithium and / or residual base in lithium supplement

Abstract

This invention relates to the field of free lithium detection, specifically to a method for detecting free lithium and / or residual alkali in lithium supplements. The method includes the following steps: dispersing the lithium supplement in a solvent to obtain a first mixed system; filtering the first mixed system after allowing it to stand to obtain a filtrate; detecting the lithium ion content and transition metal element content in the filtrate, and calculating the free lithium and / or residual alkali content in the lithium supplement; the water content of the solvent is ≤500ppm. The method for detecting free lithium and / or residual alkali in the lithium supplement significantly reduces testing errors by controlling ambient humidity, solvent water content, and subtracting lithium hydroxide generated from the reaction with water and lithium contained in the lithium supplement passing through a microporous filter membrane.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of free lithium detection, in particular, to a method for detecting free lithium and / or residual alkali in a lithium supplement. BACKGROUND

[0002] The lithium ion in the free state in the positive electrode material or the positive electrode lithium supplement mainly exists in the form of Li2O, LiOH, LiHCO3, Li2CO3, etc. Excessive lithium source is usually added to participate in the reaction during the preparation of the lithium supplement, and the excess lithium will become free lithium. Too much free lithium will bring many negative effects to the lithium ion battery, such as easy formation of jelly-like slurry in the homogenization stage, affecting the processing performance, etc. Free lithium or residual alkali is usually used as an indicator.

[0003] The prior art discloses a method for detecting residual free lithium in lithium iron phosphate / carbon composite material, which adopts pH control step-by-step titration method to realize accurate determination of residual free lithium element in lithium iron phosphate material and effectively distinguishes whether the free lithium exists in the form of lithium carbonate or lithium bicarbonate.

[0004] The prior art discloses a method for detecting free lithium on the surface of a positive electrode material. First, the positive electrode material product is mixed with deionized water in a certain proportion to prepare a positive electrode material suspension, and then ultrasonic treatment and filtration are performed to prepare a to-be-detected filtrate. A certain amount of to-be-detected filtrate is subjected to constant volume treatment, and finally the lithium content is detected by an atomic absorption instrument.

[0005] The prior art generally uses water as a solvent, and can only detect free lithium (residual alkali) in substances that do not react with water, but the lithium supplement reacts with water to generate lithium hydroxide, which affects the detection result.

[0006] Therefore, the present application is proposed. SUMMARY

[0007] In one aspect of the present application, a method for detecting free lithium and / or residual alkali in a lithium supplement is provided, which comprises the following steps:

[0008] The lithium supplement is dispersed in a solvent to obtain a first mixed system; the first mixed system is left to stand and then filtered to obtain a filtrate; the lithium ion content and the transition metal element content in the filtrate are detected, and the free lithium and / or residual alkali content in the lithium supplement is calculated.

[0009] The water content of the solvent is ≤500ppm.

[0010] The detection method of the free lithium and / or residual alkali in the lithium supplement agent greatly reduces the detection error by controlling the environmental humidity, the water content of the solvent, the selection of the solvent type, deducting the lithium hydroxide generated by the reaction of water and the lithium supplement agent, and deducting the lithium contained in the lithium supplement agent passing through the microporous filter membrane, thereby providing a reliable detection method for the free lithium in the lithium supplement agent.

[0011] Compared with the prior art, the present application has the following beneficial effects:

[0012] The detection method of the free lithium and / or residual alkali in the lithium supplement agent provided by the present application is mainly for the detection of free lithium (residual alkali) of materials prone to reaction with water. Under the condition of strictly controlling the environmental humidity, anhydrous ethanol or propyl alcohol and other organic or inorganic solvents that do not react with the lithium supplement agent but can dissolve a certain amount of lithium oxide, lithium hydroxide, lithium carbonate and lithium bicarbonate are used to prepare a suspension liquid of the lithium supplement agent and the solvent. Then, ultrasonic or stirring is performed to dissolve the free lithium in the lithium supplement agent in the solvent. Then, a microporous filter membrane made of polytetrafluoroethylene (or other alkali-resistant materials) is used for filtration. A certain amount of filtrate is detected (hydrochloric acid titration or dilution to constant volume and then ICP detection) for free lithium and transition metal elements passing through the microporous filter membrane. By controlling the environmental humidity, the water content of the solvent, and deducting the lithium hydroxide generated by the reaction with water and the lithium in the lithium supplement agent passing through the microporous filter membrane, the test error is greatly reduced. BRIEF DESCRIPTION OF DRAWINGS

[0013] In order to more clearly illustrate the specific embodiments of the present application or the technical solutions in the prior art, the drawings needed in the specific embodiments or prior art description will be briefly introduced below. Obviously, the drawings in the following description are some embodiments of the present application, and those skilled in the art can also obtain other drawings according to these drawings without creative labor.

[0014] Figure 1 XRD of the lithium supplement agent lithium ferrite (Li5FeO4) used for detection of the present application;

[0015] Figure 2 XRD of the insoluble substance after the reaction of the lithium supplement agent lithium ferrite with water. DETAILED DESCRIPTION

[0016] The technical solutions of the present application will be described clearly and completely below in combination with the drawings and specific embodiments, but those skilled in the art will understand that the following described embodiments are part of the embodiments of the present application, rather than all the embodiments, and are only used to illustrate the present application, and should not be regarded as limiting the scope of the present application. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without making creative efforts are within the scope of protection of the present application. The specific conditions are not specified in the embodiments, and are carried out according to the conventional conditions or the conditions recommended by the manufacturer. The reagents or instruments used are not specified by the manufacturer, and are conventional products that can be purchased on the market.

[0017] In one aspect of the present application, a method for detecting free lithium and / or residual base in a lithium supplement agent comprises the following steps:

[0018] Dispersing the lithium supplement agent in a solvent to obtain a first mixed system; filtering the first mixed system after standing to obtain a filtrate; detecting the content of lithium ions and the content of transition metal elements in the filtrate, and calculating the content of free lithium and / or residual base in the lithium supplement agent;

[0019] The water content of the solvent is ≤500 ppm.

[0020] In some specific embodiments, the water content of the solvent may, for example, be, but is not limited to, 500 ppm, 400 ppm, 300 ppm, 200 ppm, 100 ppm, 50 ppm, 30 ppm, 10 ppm, 5 ppm or 1 ppm.

[0021] The method for detecting free lithium and / or residual base in the lithium supplement agent is mainly for detecting free lithium (residual base) of materials that are easy to react with water. Under the condition of strictly controlling the environmental humidity, anhydrous ethanol or propyl alcohol and other organic or inorganic solvents that do not react with the lithium supplement agent but can dissolve a certain amount of lithium oxide, lithium hydroxide, lithium carbonate and lithium bicarbonate are used to prepare a suspension of the lithium supplement agent and the solvent, then ultrasonic or stirring is performed to dissolve the free lithium in the lithium supplement agent in the solvent, and then a microporous filter membrane made of polytetrafluoroethylene (or other alkali-resistant materials) is used for filtration, and a certain amount of filtrate is taken for detection (hydrochloric acid titration or ICP detection after dilution and constant volume) of the free lithium therein. By controlling the environmental humidity, the water content of the solvent, deducting the lithium contained in the lithium supplement agent passing through the microporous filter membrane and deducting the lithium hydroxide generated by the reaction with water, the test error is greatly reduced.

[0022] Because lithium supplements react readily with water, the water content of the solvent should be strictly controlled below 500 ppm to reduce the reaction between water in the solvent and the lithium supplement to form lithium hydroxide, thereby reducing detection errors. If the solvent water content is high, 4A (or 5A) molecular sieves that have been calcined at 500℃ for 2 hours and cooled to room temperature can be used. Add the molecular sieve at a ratio of 0.1 g / ml (0.1 g of molecular sieve per milliliter of solvent), let it stand for a period of time to remove the water, and then use a KF moisture meter to detect the water content.

[0023] Preferably, the detection environment humidity for the method of detecting free lithium and / or residual alkali in the lithium replenishing agent is 0%RH to 27%RH (e.g., 1%RH, 5%RH, 10%RH, 15%RH, 20%RH, 23%RH, 24%RH, 25%RH, 26%RH or 27%RH).

[0024] Since lithium supplements react readily with water, the detection humidity should be strictly controlled to reduce the reaction between moisture in the air and the lithium supplement to form lithium hydroxide, thereby reducing detection errors.

[0025] Preferably, the method for detecting the lithium ion content in the filtrate includes at least one of hydrochloric acid titration, inductively coupled plasma atomic absorption spectrometry, or atomic absorption spectrometry.

[0026] Preferably, the formula for calculating the free lithium content in the lithium supplement using the hydrochloric acid titration method is as follows:

[0027]

[0028] Preferably, the formula for calculating the residual alkali content in the lithium supplement using the hydrochloric acid titration method is as follows:

[0029]

[0030] Alternatively, residual alkali (as LiOH) = free lithium content (ppm) * M3 / (10 4 *M1)%.

[0031] Preferably, the formula for calculating the free lithium content in the lithium replenishing agent using inductively coupled plasma atomic emission spectrometry is as follows:

[0032]

[0033] Preferably, the formula for calculating the residual alkali content in the lithium replenishing agent using inductively coupled plasma spectrometry is as follows:

[0034]

[0035] Preferably, the formula for calculating the residual alkali content in the lithium replenishing agent using inductively coupled plasma spectrometry is as follows:

[0036] Residual alkali = Free lithium content (ppm) * M3 / (10 4 *M1)%.

[0037] Wherein, C is the concentration of hydrochloric acid standard solution, in mol / L; V1 is the volume of hydrochloric acid standard solution consumed by the sample, in ml; V0 is the volume of hydrochloric acid standard solution consumed by the blank, in ml; V' is the volume of solvent added, in ml; n is the molar ratio of Li to metal M in the lithium replenishment agent; M1 is the molar mass of lithium, in g / mol; M2 is the molar mass of water, in g / mol; M3 is the molar mass of lithium hydroxide, in g / mol; m is the mass of the sample weighed, in g; M4 is the molar mass of transition metal element M, in g / mol; ω is the water content of the solvent, in %; ρ is the density of the solvent, in g / ml; W1 is the lithium content in the filtrate determined by inductively coupled plasma atomic absorption spectrometry, in μg / ml; W2 is the content of transition metal element M in the filtrate, in μg / ml; and V is the volume of filtrate to be tested transferred, in mL.

[0038] Preferably, the method for detecting the content of transition metal elements in the filtrate is inductively coupled plasma atomic emission spectrometry (ICP-AES).

[0039] Preferably, the lithium supplement is dispersed in the solvent by stirring and / or sonication.

[0040] Preferably, the stirring time for dispersing the lithium supplement in the solvent is 20 to 40 minutes (e.g., 20 minutes, 25 minutes, 30 minutes, 35 minutes, or 40 minutes).

[0041] Preferably, the first mixture is allowed to stand for 15 to 25 minutes (e.g., 15 minutes, 17 minutes, 19 minutes, 21 minutes, 23 minutes, or 25 minutes).

[0042] Preferably, the general chemical formula of the lithium supplement is: Li x MO y ;

[0043] Wherein, M is at least one of the transition metal elements; x takes values ​​of 2 to 6; and y takes values ​​of 2 to 4.

[0044] Preferably, the solvent includes alcohol solvents and / or N-methylpyrrolidone.

[0045] Preferably, the solvent includes at least one of a monohydric alcohol, a dihydric alcohol, or a polyhydric alcohol.

[0046] Preferably, the solvent includes at least one of anhydrous ethanol, isopropanol, methanol, or N-methylpyrrolidone.

[0047] Preferably, the filtration method includes microporous membrane filtration.

[0048] Preferably, the filter material of the microporous filter membrane includes at least one of polytetrafluoroethylene, nylon 6, nylon 66, or polypropylene.

[0049] The test material can be dispersed in the solvent by stirring or sonication, so that the residual free lithium in the test material dissolves in the solvent, and then left to stand for a period of time.

[0050] The embodiments of the present invention will now be described in detail with reference to specific examples and comparative examples.

[0051] Example 1

[0052] The method for detecting free lithium and / or residual alkali in lithium supplements provided in this embodiment includes the following steps:

[0053] (I) Pre-experiment preparation

[0054] 1. All standard titrants, standard solutions, preparations and products used shall be prepared in accordance with the provisions of GB / T 601, GB / T 602 and GB / T 603; the experimental water shall meet the grade III water specifications in GB / T 6682-2008, and all samples shall be measured to an accuracy of 0.1 mL; anhydrous ethanol shall meet the requirements of GB / T 678-2002.

[0055] 2. The water content in anhydrous ethanol shall be determined according to the method specified in GB / T 6283. The water content ω of the anhydrous ethanol used shall not exceed 0.05%. If the water content exceeds the standard, 5A molecular sieve (3-5 mm diameter particles, used as a desiccant, calcined at 500℃ for 2 hours before use and cooled in a desiccator containing molecular sieve) shall be added at a ratio of 0.1 g / ml. The bottle shall be stoppered, left overnight, and the supernatant shall be extracted for use.

[0056] 2. Control the ambient humidity at 25±2%RH and the ambient temperature at 20-25℃ using dehumidifiers or other methods;

[0057] (II) Preparation of lithium iron ferrite (Li5FeO4) sample / solvent test solution as lithium supplement agent

[0058] 3. Weigh 20g of lithium iron ferrite (Li5FeO4) samples prepared by three different processes, accurate to 0.0001g, and add them to a 250ml beaker. Then add 100ml of anhydrous ethanol to each beaker, add a stir bar, seal with plastic wrap, stir with a magnetic stirrer for 30min, let stand for 20min, and filter the supernatant using a 0.45μm polytetrafluoroethylene microporous membrane to obtain a clear filtrate.

[0059] (III) Determination of free lithium (residual alkali) content

[0060] 4. Use a pipette with a large belly to transfer 20 ml of filtrate, add 50 ml of pure water, add 5-6 drops of methyl red bromocresol green indicator, and titrate with hydrochloric acid standard solution, consuming a volume of hydrochloric acid standard solution V1; and transfer anhydrous ethanol for a blank control test, consuming a volume of hydrochloric acid standard solution V0 in the blank.

[0061] 5. The contents of free lithium and residual alkali were calculated, and the results are shown in Table 1.

[0062] Example 2

[0063] Compared with Example 1, the only difference is that the solvent was changed to isopropanol. The water content in the isopropanol was determined according to the method specified in GB / T2366-2008, and the water content in the isopropanol used did not exceed 0.05%. The results are shown in Table 1.

[0064] Example 3

[0065] Compared with Example 1, the only difference was that the ambient humidity was controlled at 35±2%RH. The results are shown in Table 1.

[0066] Example 4

[0067] Compared with Example 1, the only difference was that the ambient humidity was controlled at 15±2%RH. The results are shown in Table 1.

[0068] Example 5

[0069] The sample tested in this embodiment is the same as in Example 1, except that the lithium ion content in the filtrate is detected using ICP detection. The specific steps are as follows:

[0070] 1. Using a large-diameter pipette, transfer 1 ml of the filtrate into an evaporating dish and evaporate it to dryness in a water bath at approximately 75°C. Add 10 ml of hydrochloric acid solution (20% by mass) to dissolve the residue, and then add water to bring the volume to 100 ml. Detect the lithium content using ICP (Inductively Coupled Plasma Emission Spectrometry). Simultaneously, transfer 1 ml of anhydrous ethanol into an evaporating dish and evaporate it to dryness in a water bath at approximately 75°C. Add 10 ml of hydrochloric acid solution (20% by mass) to dissolve the residue, and then add water to bring the volume to 100 ml as a preparative blank.

[0071] 2. Calculate the content of free lithium and residual alkali. The results are shown in Table 2.

[0072] Example 6

[0073] The sample tested in this embodiment is the same as in Example 5, except that the iron ion content in the filtrate is measured. The specific steps are as follows:

[0074] 1. Using a large-diameter pipette, transfer 1 ml of the filtrate into an evaporating dish and evaporate it to dryness in a water bath at approximately 75°C. Add 10 ml of hydrochloric acid solution (20% by mass) to dissolve the residue, and then add water to bring the volume to 100 ml. Use ICP (Inductively Coupled Plasma Emission Spectrometry) to detect the lithium and iron content. Simultaneously, transfer 1 ml of anhydrous ethanol into an evaporating dish and evaporate it to dryness in a water bath at approximately 75°C. Add 10 ml of hydrochloric acid solution (20% by mass) to dissolve the residue, and then add water to bring the volume to 100 ml as a preparative blank.

[0075] 2. Calculate the contents of free lithium and residual alkali. The results are shown in Table 3.

[0076] Comparative Example 1

[0077] Compared to Example 3, the solvent was changed to pure water, and the volume of the test liquid was 1 ml. The lithium hydroxide produced by the reaction of water with the lithium ferrite supplement was not deducted from the calculation. The results are shown in Table 1, and the calculation formula is as follows:

[0078]

[0079]

[0080] Comparative Example 2

[0081] Compared to Example 1, the ambient humidity was controlled at 45±2%RH. The results are shown in Table 1.

[0082] Comparative Example 3

[0083] Compared to Example 1, the ambient humidity was controlled at above 60% RH. The results are shown in Table 1.

[0084] Table 1

[0085]

[0086]

[0087] Table 2

[0088]

[0089]

[0090] Table 3

[0091]

[0092] The data comparison above shows that the free lithium content of the same sample varies under different ambient humidity levels; the lower the ambient humidity, the lower the measured free lithium content. For sample 1, the free lithium content measured at 35% RH is 1.86% higher than that measured at 15% RH. For sample 2, the free lithium content measured at 35% RH is 2.88% higher than that measured at 15% RH. For sample 3, the free lithium content measured at 35% RH is 5.46% higher than that measured at 15% RH. This is due to differences in sample preparation processes, resulting in variations in water absorption. When the ambient humidity reaches 45% RH, the free lithium content of sample 1 is 10.85% higher than that measured at 15% RH, a significantly larger deviation. To ensure the method's universality, the ambient humidity should be controlled at 25% RH or lower.

[0093] When using anhydrous ethanol and isopropanol at an ambient humidity of 25% RH, the relative deviation of the measured results is about 1%.

[0094] When water was used as a solvent, the measured results all deviated from the normal values. The differences between different samples were not significant, which is due to the solubility of lithium hydroxide, formed by the reaction of the lithium supplement with water, in water.

[0095] Examples 1 and 5 used the same test solution, but the free lithium content measured by different methods showed little deviation.

[0096] Example 6 used the lithium content measured in Example 5, and added the iron content to the test. The calculation included a deduction for the corresponding lithium content. Comparison revealed that the lithium supplement that passes through the microporous membrane has a significant impact on the detection results. The magnitude of the impact of the lithium supplement that passes through the microporous membrane on the detection results is related to the size of the lithium supplement particles themselves and the pore size of the microporous membrane. The more small particles in the lithium supplement that can pass through the microporous membrane, the greater the impact of this deduction on the results.

[0097] When the water content of anhydrous ethanol is 0.0342%, the free lithium produced by the reaction of water in the ethanol with the lithium supplement is approximately 520 ppm, which leads to a significant deviation in the results. If this is not subtracted, then to obtain more accurate results, the water content in the anhydrous ethanol used should be controlled to be below 30 ppm.

[0098] from Figure 1 and Figure 2 It can be seen that the composition of the lithium supplement changes significantly after reacting with water.

[0099] Although the present invention has been illustrated and described with specific embodiments, it should be understood that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; those skilled in the art should understand that modifications can be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein, without departing from the spirit and scope of the present invention; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention; therefore, this means that all such substitutions and modifications that fall within the scope of the present invention are included in the appended claims.

Claims

1. A method for detecting free lithium and / or residual alkali in lithium supplements, characterized in that, Includes the following steps: The lithium supplement agent is dispersed in a solvent to obtain a first mixed system; the first mixed system is allowed to stand and then filtered to obtain a filtrate; the lithium ion content and transition metal element content in the filtrate are detected, and the free lithium and / or residual alkali content in the lithium supplement agent is calculated; the lithium hydroxide generated by the reaction of water and lithium supplement agent in the solvent is deducted during the calculation. The solvent has a water content of ≤500ppm; The detection environment humidity for the method of detecting free lithium and / or residual alkali in the lithium replenishing agent is 0%RH~27%RH.

2. The method for detecting free lithium and / or residual alkali in the lithium replenishing agent according to claim 1, characterized in that, The methods for detecting the lithium ion content in the filtrate include at least one of the following: hydrochloric acid titration, inductively coupled plasma atomic absorption spectrometry, or atomic absorption spectrometry.

3. The method for detecting free lithium and / or residual alkali in the lithium replenishing agent according to claim 2, characterized in that, The formula for calculating the free lithium content in the lithium supplement using the hydrochloric acid titration method is as follows: ； And / or, the formula for calculating the residual alkali content in the lithium supplement using the hydrochloric acid titration method is as follows: ； Alternatively, residual alkali = free lithium content * M3 / (10 4 *M1)% And / or, the inductively coupled plasma atomic emission spectrometry (ICP-AES) method is used to calculate the free lithium content in the lithium replenishing agent using the following formula: ； And / or, the formula for calculating the residual alkali content in the lithium replenishing agent using inductively coupled plasma spectrometry is as follows: ； Alternatively, residual alkali = free lithium content * M3 / (10 4 *M1)% Wherein, C is the concentration of hydrochloric acid standard solution, in mol / L; V1 is the volume of hydrochloric acid standard solution consumed by the sample, in ml; V0 is the volume of hydrochloric acid standard solution consumed by the blank, in ml; V' is the volume of solvent added, in ml; n is the molar ratio of Li to metal M in the lithium replenishment agent; M1 is the molar mass of lithium, in g / mol; M2 is the molar mass of water, in g / mol; M3 is the molar mass of lithium hydroxide, in g / mol; m is the mass of the sample weighed, in g; M4 is the molar mass of transition metal element M, in g / mol; ω is the water content of the solvent, in %; ρ is the density of the solvent, in g / ml; W1 is the lithium content in the filtrate determined by inductively coupled plasma atomic absorption spectrometry, in μg / ml; W2 is the content of transition metal element M in the filtrate, in μg / ml; and V is the volume of filtrate to be tested transferred, in mL.

4. The method for detecting free lithium and / or residual alkali in the lithium replenishing agent according to claim 1, characterized in that, The method for detecting the content of transition metal elements in the filtrate is inductively coupled plasma atomic emission spectrometry.

5. The method for detecting free lithium and / or residual alkali in the lithium replenishing agent according to claim 1, characterized in that, The lithium supplement is dispersed in the solvent by stirring and / or sonication.

6. The method for detecting free lithium and / or residual alkali in the lithium replenishing agent according to claim 5, characterized in that, The lithium supplement agent is dispersed in the solvent by stirring for 20-40 minutes.

7. The method for detecting free lithium and / or residual alkali in the lithium replenishing agent according to claim 1, characterized in that, The first mixture is allowed to stand for 15-25 minutes.

8. The method for detecting free lithium and / or residual alkali in the lithium replenishing agent according to claim 1, characterized in that, The general chemical formula of the lithium supplement is: Li x MO y ; Where M is at least one of the transition metal elements; x takes values ​​from 2 to 6; and y takes values ​​from 2 to 4.

9. The method for detecting free lithium and / or residual alkali in the lithium replenishing agent according to claim 1, characterized in that, The solvents include alcohol solvents and / or N-methylpyrrolidone.

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