Method for detecting residual alkali in sodium ion layered oxide positive electrode material

Abstract

The invention discloses a method for detecting residual alkali in a sodium ion layered oxide positive electrode material, which comprises the following steps of: 1, adding a dispersing agent into the sodium ion layered oxide positive electrode material, stirring, extracting, carrying out suction filtration, and collecting filtrate; the dispersing agent is formed by combining a polar organic reagent and water; and 2, measuring the pH value of the filtrate by utilizing a potentiometric titration method, and calculating the residual alkali in the sodium ion layered oxide positive electrode material. Compared with the prior art, the invention has the following beneficial effects: on the basis of using water as a dispersant, a proper amount of polar organic reagent is added to inhibit generation of NaOH in the material in the test process and influence on the test, avoid test interference caused by too high organic solvent content, improve the stability of the material during potentiometric titration, and improve the stability of the material in the process of potentiometric titration. The sodium carbonate content detection result is more accurate and stable.

Description

Technical Field

[0001] The present invention relates to the technical field of battery detection, and in particular to a method for detecting residual alkali in a sodium ion layered oxide positive electrode material. Background Art

[0002] At present, lithium-ion batteries have become the mainstream material in the battery industry due to their advantages such as high capacity and long cycle. However, due to the scarcity and uneven distribution of lithium mineral resources, people have turned their attention to sodium, which has similar chemical properties to lithium. Compared with lithium-ion batteries, sodium-ion batteries have lower energy density, but sodium resources are widely distributed, have large reserves, are low in price and have higher safety, and have a wide range of application scenarios (such as energy storage power stations, low-speed power fields, and backup power supplies). Therefore, people regard sodium-ion battery technology as an effective supplement to lithium-ion battery technology, and the research and development and production of sodium-ion battery positive electrode materials have gradually become a hot topic of concern at home and abroad.

[0003] Commonly used positive electrode materials for sodium-ion batteries include transition metal oxides, Prussian blue and Prussian white and their derivatives, polyanionic compounds and organic compounds. Their residual alkali content is one of the key factors affecting battery performance. The residual alkali content can be used to guide the optimization of the preparation process of positive electrode materials for sodium-ion batteries. Among them, the sodium carbonate content is one of the residual alkali indicators and is difficult to test.

[0004] Commonly used positive electrode materials for sodium-ion batteries include transition metal oxides, Prussian blue and Prussian white and their derivatives, polyanionic compounds and organic compounds. Their residual alkali content is one of the key factors affecting battery performance. The residual alkali content can be used to guide the optimization of the preparation process of positive electrode materials for sodium-ion batteries. Among them, the sodium carbonate content is one of the residual alkali indicators and is difficult to test.

[0005] At present, the method for analyzing the residual alkali in the cathode material of sodium-ion batteries is acid-base titration. For example, Chinese Patent No. 202311196598.1 discloses a method for testing the pH of a sodium-ion layered oxide cathode material. In this application's method for testing the pH of a sodium-ion layered oxide cathode material, the pH detected after stirring for 1 minute is relatively close to the pH value after the residual alkali on the material surface is completely dissolved in the solvent, and it can characterize the difference in residual alkali, avoiding the influence of sodium precipitation in the crystal on the accuracy of pH testing, and being closer to the true value than traditional methods. However, as is well known, during the testing of the residual alkali in sodium-ion layered oxide cathode materials, it is found that there will be a replacement of hydrogen ions in water with Na in the material structure, resulting in an increase in the content of NaOH. Since carbonate is insoluble in organic solvents such as ethanol, ethanol is now used as a dispersant for the extraction test of NaOH, and pure water is still used as a dispersant for the extraction test of sodium carbonate. However, excessive NaOH will affect the determination of the end point during potentiometric titration, thus affecting the test stability. Even if new organic solvents such as ethylene glycol are now used as a single dispersant, due to its non-true dissolution property of "like dissolves like", the results obtained are not stable enough. Summary of the Invention

[0006] In view of the above-mentioned disadvantages of the prior art, the purpose of the present invention is to provide a method for detecting residual alkali in sodium-ion layered oxide cathode materials, which is used to solve the problems of easy misjudgment of the titration end point and large error in the detection result during the detection of residual alkali in existing sodium-ion layered oxide cathode materials.

[0007] To achieve the above purpose and other related purposes, the present invention provides a method for detecting residual alkali in sodium-ion layered oxide cathode materials, which is characterized by including the following steps:

[0008] Step 1: Add a dispersant to the sodium-ion layered oxide cathode material, stir, extract, and filter by suction, and collect the filtrate; the dispersant is composed of a polar organic reagent and water.

[0009] Step 2: Measure the pH value of the filtrate by potentiometric titration and calculate the residual alkali in the sodium-ion layered oxide cathode material.

[0010] As a preference of this application, the chemical formula of the sodium-ion layered oxide cathode material is Na x TMO2, 0 < x < 2, and TM is selected from at least one of Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Al, Mg, Zn.

[0011] As a preference of this application, the chemical formula of the sodium-ion layered oxide cathode material is NaNiO2.

[0012] As a preference of the present application, the mass ratio of the sodium ion layered oxide positive electrode material to the dispersant is (1-5):60.

[0013] As a preference of the present application, the mass ratio of the sodium ion layered oxide positive electrode material to the dispersant is 1:20.

[0014] As a preference of the present application, the polar organic reagent is an alcohol having 2 to 3 carbon atoms.

[0015] As a preference of the present application, the polar organic reagent is selected from at least one of ethanol, ethylene glycol and propanol.

[0016] As a preference of the present application, the mass ratio of the polar organic reagent to water is 1:10 to 10:1.

[0017] As a preference of the present application, the mass ratio of the polar organic reagent to water is 7:3, 1:1 or 3:7.

[0018] As a preference of the present application, the mass ratio of the polar organic reagent to water is 7:3.

[0019] As a preferred embodiment of the present application, the extraction temperature in step 1 is 20-26° C., and the extraction time is 5-15 min.

[0020] As a preferred embodiment of the present application, the filtration in step 1 adopts a sand core vacuum filtration device, and the filter membrane is a water filter membrane.

[0021] As a preferred embodiment of the present application, the electrode used in step 2 to measure the pH value of the filtrate by potentiometric titration is an aqueous pH electrode.

[0022] As a preferred embodiment of the present application, in step 2, the pH value of the filtrate is measured by potentiometric titration, and the sodium carbonate test method is selected to calculate the residual alkali in the sodium ion layered oxide positive electrode material.

[0023] The pH value of the filtrate is measured by a potentiometric titrator. The titration endpoint determined by the potentiometric titration curve usually corresponds to the sudden change point of the pH value. The volume difference VmL of the hydrochloric acid standard solution consumed corresponding to the two sudden change points is recorded.

[0024] Calculate the residual alkali content in the sample: The carbonate content A in the sample is:

[0025]

[0026] Wherein, 106 is the molecular weight of carbonate, C is the molar concentration of prepared hydrochloric acid, mol / L; m is the mass of the weighed sample, g; V is the volume difference of the hydrochloric acid standard solution consumed corresponding to the two jump points, mL.

[0027] The present invention has the following beneficial effects: by adding an appropriate amount of polar organic reagent on the basis of using water as a dispersant, the generation of NaOH in the material during the test and the influence on the test are suppressed, the test interference caused by excessive organic solvent is avoided, the sodium carbonate content detection result is made more accurate and stable, and the stability of the material during potentiometric titration is improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is the test potentiometric titration curve of Example 1.

[0029] Figure 2 This is the test potentiometric titration curve diagram of Example 4.

[0030] Figure 3 This is the test potentiometric titration curve diagram of Example 5.

[0031] Figure 4 This is the test potentiometric titration curve diagram of Comparative Example 1.

[0032] Figure 5 This is the test potentiometric titration curve diagram of Comparative Example 2.

[0033] Figure 6 This is the test potentiometric titration curve diagram of Comparative Example 3. DETAILED DESCRIPTION

[0034] The following describes the embodiments of the present invention through specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention.

[0035] It should be noted that the process equipment or devices not specifically specified in the following embodiments are all conventional equipment or devices in the art.

[0036] In addition, it should be understood that one or more method steps mentioned in the present invention do not exclude the existence of other method steps before or after the combination step or the insertion of other method steps between these explicitly mentioned steps, unless otherwise specified; it should also be understood that the combination connection relationship between one or more devices / apparatuses mentioned in the present invention does not exclude the existence of other devices / apparatuses before or after the combination device / apparatus or the insertion of other devices / apparatuses between these explicitly mentioned two devices / apparatuses, unless otherwise specified. Moreover, unless otherwise specified, the numbering of each method step is only a convenient tool for identifying each method step, and is not intended to limit the order of arrangement of each method step or the scope of the present invention. Changes or adjustments in their relative relationships should also be regarded as the scope of the present invention without substantially changing the technical content.

[0037] Example 1

[0038] This embodiment provides a method for preparing a vanadium oxide nanosheet array, comprising the following steps:

[0039] Step 1, weigh 3g of sodium ion layered oxide positive electrode material NaNiO2 and place it in a stoppered conical flask (20°C, the same below), add 42g of ethanol and 18g of pure water in sequence, stir at 20°C, extract for 10min, filter to remove the extracted sodium carbonate, and collect the filtrate;

[0040] Step 2: Determine the pH value of the filtrate using potentiometric titration, and select the sodium carbonate test method to calculate the residual alkali in the sodium ion layered oxide positive electrode material.

[0041] The specific calculation method is as follows:

[0042] The pH value of the filtrate was measured using a 916 potentiometric titrator and a water-based pH electrode. The titration endpoint determined by the potentiometric titration curve usually corresponds to the sudden change point of the pH value. The volume difference VmL of the hydrochloric acid standard solution consumed corresponding to the two sudden change points was recorded.

[0043] Calculate the residual alkali content in the sample: The carbonate content A in the sample is:

[0044]

[0045] Wherein, 106 is the molecular weight of carbonate, C is the molar concentration of prepared hydrochloric acid, mol / L; m is the mass of the weighed sample, g; V is the volume difference of the hydrochloric acid standard solution consumed corresponding to the two jump points, mL.

[0046] The test results are shown in Table 1.

[0047] Example 2

[0048] The difference between this embodiment and embodiment 1 is that the mass ratio of the sodium ion layered oxide positive electrode material to the dispersant is different. In this embodiment, the mass ratio of the sodium ion layered oxide positive electrode material to the dispersant is 1:60, and the rest of the processes are exactly the same.

[0049] Example 3

[0050] The difference between this embodiment and embodiment 1 is that the mass ratio of the sodium ion layered oxide positive electrode material to the dispersant is different. In this embodiment, the mass ratio of the sodium ion layered oxide positive electrode material to the dispersant is 5:60, and the rest of the processes are exactly the same.

[0051] Example 4

[0052] The difference between this embodiment and embodiment 1 is that the mass ratio of the polar organic reagent to pure water in the dispersant is different. In this embodiment, the dispersant is composed of 30g of pure water and 30g of ethanol, and the rest of the processes are exactly the same.

[0053] Example 5

[0054] The difference between this embodiment and embodiment 1 is that the mass ratio of the polar organic reagent to pure water in the dispersant is different. In this embodiment, the dispersant is composed of 18 g of ethanol and 42 g of pure water, and the rest of the processes are exactly the same.

[0055] Example 6

[0056] The difference between this embodiment and embodiment 1 is that the mass ratio of the polar organic reagent and pure water in the dispersant is different. In this embodiment, the dispersant is composed of 5.6 g of ethanol and 54.4 g of pure water, and the rest of the processes are exactly the same.

[0057] Example 7

[0058] The difference between this embodiment and embodiment 1 is that the mass ratio of the polar organic reagent to pure water in the dispersant is different. In this embodiment, the dispersant is composed of 54.5 g of ethanol and 5.5 g of pure water, and the rest of the processes are exactly the same.

[0059] Example 8

[0060] The difference between this embodiment and embodiment 1 is that the type of dispersant is different. In this embodiment, propanol is used instead of ethanol, and the rest of the processes are exactly the same.

[0061] Example 9

[0062] The difference between this embodiment and embodiment 1 is that the type of dispersant is different. In this embodiment, ethylene glycol is used instead of ethanol, and the rest of the processes are exactly the same.

[0063] Example 10

[0064] The difference between this embodiment and embodiment 1 is that the types of dispersants are different. The dispersants in this embodiment are ethanol, propanol and water in a mass ratio of 3.5:3.5:3, and the rest of the processes are exactly the same.

[0065] Embodiment 11

[0066] The difference between this embodiment and embodiment 1 is that the types of dispersants are different. The dispersants in this embodiment are ethylene glycol, ethanol and water in a mass ratio of 3.5:3.5:3, and the rest of the processes are exactly the same.

[0067] Comparative Example 1

[0068] The difference between this comparative example and Example 1 is that pure water is used instead of the dispersant in this comparative example, and the other processes are exactly the same.

[0069] Comparative Example 2

[0070] The difference between this comparative example and Example 1 is that ethylene glycol is used instead of the dispersant in this comparative example, and the rest of the processes are exactly the same.

[0071] Comparative Example 3

[0072] The difference between this comparative example and Example 1 is that ethanol is used instead of the dispersant in this comparative example, and the other processes are exactly the same.

[0073] The methods and results for calculating the residual alkali in the sodium ion layered oxide positive electrode material in Examples 2 to 11 and Comparative Documents 1 to 3 are equivalent to those in Example 1 and will not be described in detail here.

[0074] Table 1 Sodium carbonate test stability results measured by the methods of the embodiments and comparative examples

[0075]

[0076]

[0077] It can be seen from the comparison of Examples 1 to 11 with Comparative Examples 1 to 3 in Table 1 that mixed dispersants generally have better stability than single dispersants. The stability of ethanol + pure water dispersants is generally higher than that of other types of dispersants. Therefore, the dispersant of the present application is based on water as a dispersant, and an appropriate amount of ethanol is added, which can significantly inhibit the production of NaOH in the material during the test and the impact on the test, so that the sodium carbonate content detection result is accurate and stable. Moreover, as the ethanol content increases, the X-axis titrant volume corresponding to EP1 decreases. However, when the mass ratio of ethanol to water is 7:3, the RSD is the smallest, 0.37%, indicating that under this ratio, the test result stability is the best, and it has the function of accurately testing the sodium carbonate content in the residual alkali of the sodium ion layered oxide positive electrode material.

[0078] The above examples are for the purpose of illustrating the embodiments disclosed by the present invention and are not to be construed as limitations of the present invention. In addition, the various modifications listed herein and the variations of methods and compositions in the invention are obvious to those skilled in the art without departing from the scope and spirit of the present invention. Although the present invention has been specifically described in conjunction with various specific preferred embodiments of the present invention, it should be understood that the present invention should not be limited to these specific embodiments. In fact, various modifications obvious to those skilled in the art as described above to obtain the invention should be included within the scope of the present invention.

Claims

1. A method for detecting residual alkali in a sodium ion layered oxide positive electrode material, characterized in that: The following steps are involved: Step 1, adding a dispersant to the sodium ion layered oxide positive electrode material, stirring and extracting, filtering, and collecting the filtrate; the dispersant is composed of a polar organic reagent and pure water; Step 2: Measure the pH value of the filtrate using potentiometric titration to calculate the residual alkali in the sodium ion layered oxide positive electrode material.

2. The method for detecting residual alkali in the sodium ion layered oxide positive electrode material according to claim 1, characterized in that: The chemical formula of the sodium ion layered oxide cathode material is Na x TMO2, where 0 < x < 2, and TM is selected from at least one of Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Al, Mg, Zn.

3. The method for detecting residual alkali in the sodium ion layered oxide positive electrode material according to claim 1, characterized in that: The mass ratio of the sodium ion layered oxide positive electrode material to the dispersant is (1-5):

60.

4. The method for detecting residual alkali in the sodium ion layered oxide positive electrode material according to claim 3, characterized in that: The mass ratio of the sodium ion layered oxide positive electrode material to the dispersant is 3:

60.

5. The method for detecting residual alkali in the sodium ion layered oxide positive electrode material according to claim 1, characterized in that: The organic reagent X is an alcohol having 2 to 3 carbon atoms.

6. The method for detecting residual alkali in the sodium ion layered oxide positive electrode material according to claim 5, characterized in that: The polar organic reagent is selected from at least one of ethanol, ethylene glycol and propanol.

7. The method for detecting residual alkali in the sodium ion layered oxide positive electrode material according to claim 1, characterized in that: The mass ratio of the polar organic reagent to pure water is 1:10 to 10:

1.

8. The method for detecting residual alkali in the sodium ion layered oxide positive electrode material according to claim 7, characterized in that: The mass ratio of the polar organic reagent to water is 7:3, 1:1 or 3:

7.

9. The method for detecting residual alkali in the sodium ion layered oxide positive electrode material according to claim 1, characterized in that: Step 2: The electrode used to measure the pH value of the filtrate by potentiometric titration is an aqueous pH electrode.

10. The method for detecting residual alkali in the sodium ion layered oxide positive electrode material according to claim 1, characterized in that: In step 2, the pH value of the filtrate is measured by potentiometric titration, and the method for calculating the residual alkali in the sodium ion layered oxide positive electrode material is as follows: The pH value of the filtrate is measured by a potentiometric titrator. The titration endpoint determined by the potentiometric titration curve usually corresponds to the sudden change point of the pH value. The volume difference VmL of the hydrochloric acid standard solution consumed corresponding to the two sudden change points is recorded. Calculate the residual alkali content in the sample: The carbonate content A in the sample is: Wherein, 106 is the molecular weight of carbonate, C is the molar concentration of prepared hydrochloric acid, mol / L; m is the mass of the weighed sample, g; V is the volume difference of the hydrochloric acid standard solution consumed corresponding to the two jump points, mL.

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