Method for detecting content of residual sodium in sodium ion battery positive electrode material

Abstract

The invention discloses a method for detecting the content of residual sodium in a sodium-ion battery positive electrode material, which comprises the following steps: (1) mixing the sodium-ion battery positive electrode material to be detected in a solvent, and carrying out solid-liquid separation on the obtained solution to obtain filtrate; (2) titrating the filtrate in a dynamic potential jump mode by adopting a potentiometric titrator and taking an acid solution as a titration solution, and recording the titration solution consumption corresponding to two potential jump end points when two potential jump points appear; and (3) respectively calculating the mass percentage contents of sodium carbonate omegaNa2CO3 and sodium hydroxide omegaNaOH in the filtrate according to a formula, and further calculating the mass percentage content omegaNa + of residual sodium according to the formula. According to the method, the content of all free sodium in the sodium ion positive electrode material can be accurately measured, influences of environmental factors and other impurity factors are eliminated, it is guaranteed that the consistency of detection results is good, operation is easy and rapid, and accuracy is high.

Description

Technical Field

[0001] The invention relates to an impurity detection method, and in particular to a method for detecting residual sodium content in a positive electrode material of a sodium ion battery. Background Art

[0002] The free sodium on the surface of the positive electrode material of sodium ion batteries will bring many negative effects to the sodium ion batteries. When the free sodium content is high, on the one hand, it will react with carbon dioxide and water in the air to generate sodium hydroxide and sodium carbonate, causing the pH of the material to increase, which in turn causes the positive electrode material to absorb water and expand. On the other hand, it is easy to form a jelly-like slurry during the homogenization stage, thus affecting the reversible capacity, cycle performance, high temperature performance and safety of the battery. Therefore, in actual production, it is necessary to accurately determine the residual sodium content in the positive electrode material of sodium ion batteries to predict the performance of the positive electrode material.

[0003] At present, the test methods for residual sodium in the positive electrode materials of sodium ion batteries are mainly through the indicator method and the potentiometric titration method. The color change range of the indicator method is not sensitive enough, the color distribution range is large, and it is not easy to distinguish. The principle of the potentiometric titration method regards the process of measuring the residual alkali on the surface of the positive electrode material of the sodium ion battery as an acid-base reaction. The solution to be tested is taken as an alkaline solution, and a standard hydrochloric acid solution is used as a titrant. When the hydrochloric acid in the titrant is added dropwise to the solution to be tested, the concentration of hydrogen ions gradually decreases, the acidity of the solution gradually decreases, and the content of residual alkali on the surface of the positive electrode material also decreases accordingly. When the sodium hydroxide in the titrant is added dropwise to the surface of the positive electrode material, the residual alkali is almost completely neutralized, and the acidity of the solution is neutralized, and the electrode potential at this time is the equivalent point potential. The existing testing technologies all calculate the residual alkali content through the consumed hydrochloric acid standard solution, and directly convert the residual alkali into the residual sodium content, ignoring the possible influence of other metal elements, and cannot accurately test the true content of residual sodium in the positive electrode material of the sodium ion battery.

[0004] In addition, the positive electrode materials of sodium ion batteries and the residual alkali solution prepared therefrom are easily exposed to the air and absorb CO 2 , which causes sodium and other metal elements in the bulk phase of the material to continuously dissolve, resulting in a high residual alkali test result, and the storage conditions need to be controlled. The amount of test samples and the concentration of the standard solution will both affect the test results. The current technology is relatively broad and no requirements are made. The existing indicator method and potentiometric titration method both have difficulties in process control and cannot directly observe and accurately analyze the residual sodium content in the positive electrode material. Summary of the invention

[0005] Purpose of the invention: The purpose of the present invention is to provide a method for detecting the residual sodium content in a positive electrode material of a sodium ion battery with high detection precision and accuracy.

[0006] Technical solution: The present invention provides a method for detecting the residual sodium content in a positive electrode material of a sodium ion battery, comprising the following steps:

[0007] (1) mixing a sodium ion battery positive electrode material to be tested in a solvent, and subjecting the obtained solution to solid-liquid separation to obtain a filtrate;

[0008] (2) using a potentiometric titrator and an acid solution as a titration solution to titrate the filtrate in a dynamic potential jump mode, until two potential jump points appear, and recording the titration solution consumption corresponding to the two potential jump points;

[0009] (3) Calculate the mass percentage of sodium carbonate in the filtrate according to formula (I): Na2CO3 According to formula (II), sodium hydroxide ω NaOH The mass percentage of residual sodium ω is calculated according to formula (III) Na+ ,

[0010] Formula (Ⅰ):

[0011]

[0012] Formula (II):

[0013]

[0014] Formula (III):

[0015]

[0016] Where: V1 represents the consumption of the titration solution in the first section corresponding to the first potential jump point and the reaction with sodium carbonate, in mL; V2 represents the consumption of the titration solution in the second section corresponding to the second potential jump point and the reaction with sodium hydroxide, in mL; C represents the molar concentration of the titration solution, in mol / L; m represents the mass of the positive electrode material of the sodium ion battery, in g; M Na2CO3 Indicates Na 2 CO 3 The molar mass of NaOH Indicates the molar mass of NaOH in g / mol; M Na+ Indicates Na + The molar mass of a substance is expressed in g / mol.

[0017] Furthermore, in step (1), the sodium ion battery positive electrode material is sodium iron pyrophosphate positive electrode material; the solvent is water or a water-alcohol mixture; in the water-alcohol mixture, the volume ratio of water to ethanol is less than 1:3.

[0018] Furthermore, in step (1), the solvent also includes an inhibitor triethanolamine borate, and the mass ratio of the sodium ion battery positive electrode material to the inhibitor triethanolamine borate is 1:0.5-2.

[0019] Furthermore, in step (1), the mass ratio of the sodium ion battery positive electrode material to the solvent is 1-10:100.

[0020] Furthermore, in step (1), the mixing is carried out in a sealed environment, and a drying tube is provided in the dry environment. The desiccant used in the drying tube can absorb moisture and carbon dioxide in the air, thereby shielding the influence of air components in the environment by adjusting the storage method of the sodium ion battery positive electrode material.

[0021] Furthermore, in step (1), the mixing conditions are: magnetic stirring, a stirring speed of 400 rpm-1000 rpm, and a stirring time of 10 min-40 min.

[0022] Furthermore, in step (1), the solid-liquid separation method is: centrifugal filtration; the filtration is performed using a 0.2um-0.45um water filter membrane.

[0023] Furthermore, in step (2), the acid solution is a hydrochloric acid solution, and the concentration of the hydrochloric acid solution is 0.2 mol / L.

[0024] Invention principle: Sodium iron pyrophosphate is one of the positive electrode materials for sodium ion batteries. The usual synthesis method is to use sodium salt, iron salt, and pyrophosphate as raw materials, fully mix them according to the stoichiometric ratio, and then calcine them at high temperature and grind them into powder. However, the sodium salt used to synthesize sodium iron pyrophosphate will volatilize a small amount during high-temperature calcination, causing an imbalance in the chemical ratio of each element. Therefore, excessive sodium salt is generally added to participate in the high-temperature reaction, and the excess sodium salt will become free sodium. During the synthesis process, the excess sodium salt reacts at high temperature to generate Na 2 O, during the cooling stage, NaO 2 CO in the air 2 , H 2 O reacts to form NaOH and Na 2 CO 3 The substance mainly composed of sodium is the main source of residual alkali. In actual situations, the form of residual alkali may be more complicated, and free sodium is the sodium in the residual alkali.

[0025] The residual sodium test method is developed for the situation in the prior art that sodium iron pyrophosphate positive electrode materials are unstable with water and sodium ions are replaced by iron ions and hydronium ions, resulting in a high hydroxide test result. The present invention is applicable to sodium iron pyrophosphate, and uses hydrochloric acid titration, uses a mixed solvent of water and ethanol to inhibit excessive replacement of sodium ions with water and hydrogen ions, and uses inhibitors to inhibit the precipitation of iron ions. The chemical equation generated during the titration process is:

[0026] Step 1: NaOH + HCl = NaCl + H 2 O,Na 2CO 3 + HCl = NaCl + NaHCO 2

[0027] Step 2: NaHCO 2 + HCl = NaCl + H 2 O+CO 2 ↑.

[0028] At the same time, the present invention adopts ultrapure water and anhydrous ethanol mixed in a certain ratio as a solvent to dissolve the positive electrode material of the sodium ion battery, and adds a triethanolamine borate inhibitor to inhibit the dissolution of iron interfering elements.

[0029] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages: (1) it can accurately measure all free sodium contents in the sodium ion positive electrode material, eliminating the influence of environmental factors and other impurity factors to ensure good consistency of the test results; (2) it is simple and fast to operate with high accuracy. DETAILED DESCRIPTION

[0030] The present invention is further described below in conjunction with specific embodiments.

[0031] Embodiment 1: The method for detecting the residual sodium content in the positive electrode material of a sodium ion battery provided in this embodiment comprises the following steps:

[0032] (1) Weigh 1 g, 2 g, 5 g, and 10 g of sodium iron pyrophosphate samples, respectively, and place them in four 250 ml beakers, add 100 ml of ultrapure water and a magnetic stirrer to each beaker, place them on a magnetic stirrer for stirring, set the speed of the magnetic stirring device to 400 rpm, and set the stirring time to 10 min. Filter the filtrate with a 0.45 μm water filter membrane to obtain four portions of clear filtrate;

[0033] (2) The four portions of filtrate were transferred to four 250 ml titration cups respectively, and titrated using a potentiometric titrator in the dynamic potential jump mode. The titration solution was a 0.02 mol / L standard hydrochloric acid solution. After the potential jump endpoint was generated, the volume of the titration solution consumed corresponding to the potential jump endpoint was recorded;

[0034] (3) Calculate the mass content of sodium carbonate in the filtrate according to formula (I): Na2CO3 According to formula (II), sodium hydroxide ω NaOH The content of residual sodium is calculated according to formula (III) Na+ ,

[0035] Formula (Ⅰ):

[0036]

[0037] Formula (II):

[0038]

[0039] Formula (III):

[0040]

[0041] Where: V1 represents the consumption of the titration solution corresponding to the first potential jump point, in mL; V2 represents the consumption of the titration solution corresponding to the second potential jump point, in mL; C represents the molar concentration of the titration solution, in mol / L; m represents the mass of the positive electrode material of the sodium ion battery, in g; M Na2CO3 Indicates Na 2 CO 3 The molar mass of NaOH Indicates the molar mass of NaOH in g / mol; M Na+ Indicates Na + The molar mass of a substance is expressed in g / mol.

[0042] The mass percentage of the residual free sodium element in the measured sodium ion positive electrode material sample is shown in Table 1. It can be seen from Table 1 that the percentage of the residual free sodium element in the sodium ion positive electrode material sample detected in 2g sample of this embodiment remains consistent at 0.1413%.

[0043] Table 1 Residual free sodium element percentage content measured in Example 1

[0044]

[0045] Embodiment 2: The method for detecting the residual sodium content in the positive electrode material of a sodium ion battery provided in this embodiment comprises the following steps:

[0046] (1) Weigh 3 portions of 2 g sodium ion cathode material sample and place them in 3 250 ml beakers respectively, add 1 g, 2.5 g, and 4 g triethanolamine borate to the three 250 ml beakers respectively, then add 100 ml ultrapure water and a magnetic stirrer to each beaker, place on a magnetic stirrer for stirring, set the speed of the magnetic stirring device to 400 rpm, and set the stirring time to 30 min; filter the suspension using a 0.45 μm water filter membrane to obtain 3 portions of filtrate;

[0047] (2) The three portions of filtrate were transferred to three 250 ml titration cups respectively, and the three portions of filtrate were titrated using a potentiometric titrator in the dynamic potential jump mode. The titration solution was a 0.02 mol / L standard hydrochloric acid solution. After the potential jump endpoint was generated, the volume of the titration solution consumed corresponding to the potential jump endpoint was recorded;

[0048] (3) Calculate the mass content of sodium carbonate in the filtrate according to formula (I) in Example 1: Na2CO3 According to the formula (II) in Example 1, sodium hydroxide ω NaOH The content of residual sodium is calculated according to the formula (III) in Example 1: Na+ .

[0049] The mass percentage of the residual free sodium element in the measured sodium ion positive electrode material sample is shown in Table 2. It can be seen from Table 2 that in this embodiment, 2g of sample material was added with 2.5g of triethanolamine borate to detect the average percentage of the residual free sodium element in the sodium ion positive electrode material sample of 0.1342%. The residual sodium value remained unchanged when the amount of triethanolamine borate was further increased.

[0050] Table 2 Residual free sodium element percentage content measured in Example 2

[0051]

[0052] Embodiment 3: The method for detecting the residual sodium content in the positive electrode material of a sodium ion battery provided in this embodiment comprises the following steps:

[0053] (1) Weigh 4 portions of 2 g of sodium ion positive electrode material sample and place them in 4 250 ml beakers respectively, add 2.5 g of triethanolamine borate to each of the 4 250 ml beakers, and then add 100 g of a mixed solution with a water-to-alcohol ratio of 3:1, 1:1, 1:3, and 0:1 and a magnetic stirrer, place the mixture on a magnetic stirrer for stirring, set the speed of the magnetic stirring device to 400 rpm, and set the stirring time to 30 min; filter the suspension using a 0.45 μm water filter membrane to obtain 4 portions of filtrate;

[0054] (2) Transfer the four portions of filtrate to four 250 ml titration cups respectively, and titrate the four portions of filtrate using a potentiometric titrator in the dynamic potential jump mode. The titration solution is a 0.02 mol / L standard hydrochloric acid solution. After the potential jump endpoint is generated, record the volume of the titration solution consumed corresponding to the potential jump endpoint;

[0055] (3) Calculate the mass content of sodium carbonate in the filtrate according to formula (I) in Example 1: Na2CO3 According to the formula (II) in Example 1, sodium hydroxide ω NaOH The content of residual sodium is calculated according to the formula (III) in Example 1: Na+ .

[0056] The mass percentage of the residual free sodium element in the measured sodium ion positive electrode material samples is shown in Table 3. It can be seen from Table 3 that the average mass percentage of the residual free sodium element in the sodium ion positive electrode material samples detected in this embodiment is 0.1309%, indicating that the measurement results of the free sodium element content when the water-to-alcohol ratio is lower than 1:3 are consistent with excellent results.

[0057] Table 3 Residual free sodium element percentage content measured in Example 3

[0058]

[0059]

[0060] Embodiment 4: The method for detecting the residual sodium content in the positive electrode material of a sodium ion battery provided in this embodiment comprises the following steps:

[0061] (1) Weigh 3 portions of 2 g sodium ion positive electrode material sample and place them in 2 250 ml beakers respectively, add 2.5 g of triethanolamine borate to each of the 250 ml beakers, and then add 100 g of a mixed solution with a water-alcohol ratio of 1:3 and a magnetic stirrer to each beaker, add a drying tube into one of the beakers and put calcium oxide desiccant in it, seal the other beaker with a sealing film, and then place them on a magnetic stirrer for stirring, the speed of the magnetic stirring equipment is set to 400 rpm, and the stirring time is set to 30 min respectively; filter the suspension using a 0.45 μm water filter membrane to obtain 2 portions of filtrate;

[0062] (2) The two portions of filtrate were transferred to two 250 ml titration cups respectively, and the two portions of filtrate were titrated using a potentiometric titrator in a dynamic potential jump mode, with the titration solution being a 0.02 mol / L standard hydrochloric acid solution; after the potential jump endpoint was generated, the volume of the titration solution consumed corresponding to the potential jump endpoint was recorded;

[0063] (3) Calculate the mass content of sodium carbonate in the filtrate according to formula (I) in Example 1: Na2CO3 According to the formula (II) in Example 1, sodium hydroxide ω NaOH The content of residual sodium is calculated according to the formula (III) in Example 1: Na+ .

[0064] The mass percentage of the residual free sodium element in the measured sodium ion positive electrode material samples is shown in Table 4. It can be seen from Table 4 that the average percentage of the residual free sodium element in the sodium ion positive electrode material samples detected in this embodiment is 0.1302%, indicating that calcium oxide is beneficial in blocking the influence of carbon dioxide and moisture in the environment.

[0065] Table 4 Residual free sodium element percentage content measured in Example 4

[0066]

Claims

1. A method for detecting residual sodium content in a positive electrode material of a sodium ion battery, characterized in that: The following steps are involved: (1) mixing a sodium ion battery positive electrode material to be tested in a solvent, and subjecting the obtained solution to solid-liquid separation to obtain a filtrate; (2) using a potentiometric titrator and an acid solution as a titration solution to titrate the filtrate in a dynamic potential jump mode, until two potential jump points appear, and recording the titration solution consumption corresponding to the two potential jump points; (3) Calculate the mass percentage of sodium carbonate in the filtrate according to formula (I): Na2CO3 According to formula (II), sodium hydroxide ω NaOH The mass percentage of residual sodium ω is calculated according to formula (III) Na+ , Formula (I): Formula (II): Formula (III): Where: V1 represents the consumption of the titration solution in the first section corresponding to the first potential jump point and the reaction with sodium carbonate, in mL; V2 represents the consumption of the titration solution in the second section corresponding to the second potential jump point and the reaction with sodium hydroxide, in mL; C represents the molar concentration of the titration solution, in mol / L; m represents the mass of the positive electrode material of the sodium ion battery, in g; M Na2CO3 Indicates the molar mass of Na2CO3 in g / mol; M NaOH Indicates the molar mass of NaOH in g / mol; M Na+ Indicates Na + The molar mass of a substance is expressed in g / mol.

2. The detection method according to claim 1, characterized in that: In step (1), the positive electrode material of the sodium ion battery is a sodium iron pyrophosphate positive electrode material.

3. The detection method according to claim 1, characterized in that: In step (1), the solvent is water or a water-alcohol mixture.

4. The detection method according to claim 3, characterized in that: In the water-alcohol mixture, the volume ratio of water to ethanol is less than 1:

3.

5. The detection method according to claim 1, characterized in that: In step (1), the solvent also includes an inhibitor triethanolamine borate, and the mass ratio of the sodium ion battery positive electrode material to the inhibitor triethanolamine borate is 1:0.5-2.

6. The detection method according to claim 1, characterized in that: In step (1), the mass ratio of the sodium ion battery positive electrode material to the solvent is 1-10:

100.

7. The detection method according to claim 1, characterized in that: In step (1), the mixing is carried out in a sealed environment, and a drying tube is provided in the dry environment, and the desiccant used in the drying tube is a calcium oxide desiccant.

8. The detection method according to claim 1, characterized in that: In step (1), the mixing conditions are: magnetic stirring, stirring speed is 400rpm-1000rpm, and stirring time is 10min-40min.

9. The detection method according to claim 1, characterized in that: In step (1), the solid-liquid separation method is: centrifugal filtration; the filtration is performed using a 0.2um-0.45um water filter membrane.

10. The detection method according to claim 1, characterized in that: In step (2), the acid solution is a hydrochloric acid solution.

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