Method and system for measuring chlorine content in ternary precursor

Abstract

The invention relates to the technical field of element content determination, and provides a method and a system for determining chlorine content in a ternary precursor. The method for measuring the chlorine content in the ternary precursor comprises the steps that the ternary precursor, an HNO3 solution and an H2O2 solution are mixed in a closed container, a mixed solution is obtained, and the substance amount ratio of HNO3 to H2O2 is (2-3): 1; heating and reacting the mixed solution to obtain a solution; the chlorine content in the solution is measured, and then the chlorine content in the ternary precursor is obtained; the ternary precursor comprises a spinel type oxide. The method can accurately measure the chlorine content in the ternary precursor.

Description

Technical Field

[0001] The present invention relates to the technical field of element content determination, and particularly relates to a method and a system for determining the chlorine content in a ternary precursor. Background Art

[0002] Ternary cathode materials refer to lithium-ion battery cathode materials composed of three elements, nickel (Ni), cobalt (Co), and manganese (Mn), which are usually abbreviated as NCM. Lithium-ion batteries containing ternary cathode materials have the characteristics of high energy density, high power output, good low-temperature performance, low internal resistance, and excellent cycle stability, and occupy an important position in the new energy market, being widely used in the fields of unmanned aerial vehicles and new energy vehicles.

[0003] Ternary precursors are the key raw materials for preparing ternary cathode materials, with a cost accounting for more than 50% of the entire cost of ternary cathode materials, and are the key link for reducing the cost of ternary cathode materials. The existing ternary precursors mainly use the sulfate co-precipitation precursor process, which has a complex process, a long time consumption, generates a large amount of ammonia-nitrogen wastewater, and has a high treatment cost; developing an efficient, environmentally friendly, and low-cost preparation process is an inevitable trend in the industry development. The materials prepared from chlorides as raw materials meet these requirements, and thus have received more and more attention and research.

[0004] However, during the preparation process of ternary precursor materials, chloride ions will enter the final product along with the reaction system, affecting the product quality; and during the synthesis process of ternary precursors and ternary cathode materials, chlorine-containing gases are volatilized, corroding the equipment. Therefore, it is necessary to accurately control and detect the chloride ion content in ternary precursors.

[0005] For the existing methods for detecting the chlorine content in ternary precursors, such as the ultra-pure water leaching method, only the chlorine element on the surface of the ternary precursor can be detected, and the chlorine element inside the material cannot be detected, resulting in inaccurate detection data; or after the sample is digested with nitric acid or sulfuric acid and then tested, some ternary precursors (such as spinel-type oxides) have a stable structure, are not only difficult to hydrolyze, but also not easily dissolved in nitric acid, and chlorine is easily volatilized during the testing process, resulting in a low chlorine content result. In summary, for the existing methods for determining the chlorine content in ternary precursors, the test results are inaccurate. Summary of the Invention

[0006] The present invention aims to at least solve one of the technical problems in the related technologies to some extent. To this end, an object of the present invention is to provide a method for determining the chlorine content in a ternary precursor, which can accurately determine the chlorine content in the ternary precursor.

[0007] To this end, a first aspect of the present invention provides a method for determining the chlorine content in a ternary precursor, comprising: mixing the ternary precursor, an HNO3 solution, and an H2O2 solution in a closed container to obtain a mixed solution, wherein the molar ratio of HNO3 to H2O2 is (2 to 3):1; heating and reacting the mixed solution to obtain a solution; determining the chlorine content in the solution, and thus obtaining the chlorine content in the ternary precursor; the ternary precursor includes a spinel-type oxide.

[0008] According to the method for determining the chlorine content in a ternary precursor of an embodiment of the present invention, the ternary precursor, an HNO3 solution, and an H2O2 solution are mixed and heated, and the molar ratio of HNO3 to H2O2 is controlled. The addition amount of H2O2 is relatively high. Hydrogen peroxide (H2O2) can decompose to generate active oxygen (·OH and O2) in an acidic environment, which can reduce the high-valent metals (such as Ni 3+ 、Mn 4+ ) in the ternary precursor to a low valence state, reducing the binding energy of the above metal elements with oxygen, and the low-valent metal elements are more easily dissolved by HNO3. At the same time, the oxygen bubbles generated by the decomposition of H2O2 can physically peel off the passivation layer (such as the stable oxide shell formed by sintering) on the surface of the dense ternary precursor particles, exposing their internal active sites, accelerating the penetration of the HNO3 solution into the interior of the ternary precursor, and dissolving it. Through the above effects, the ternary precursor is more easily dissolved to form a solution, facilitating the transfer of the chlorine element therein into the solution. In addition, the reaction is set in a closed container, which can avoid the volatilization of the chlorine element and ensure the accuracy of the chlorine element measurement. In summary, the method for determining the chlorine content in a ternary precursor proposed by the present invention can accurately measure the chlorine element content in the ternary precursor.

[0009] In some embodiments of the present invention, the molar ratio of the sum of the amounts of metal elements in the ternary precursor to the amount of HNO3 is 1:(40 to 80), and may be optionally 1:(50 to 70).

[0010] In some embodiments of the present invention, the temperature of the heating reaction is 150°C to 200°C, and may be optionally 160°C to 180°C.

[0011] In some embodiments of the present invention, after the step of heating and reacting the mixed solution to obtain a solution and before the step of using the silver chloride turbidimetry to determine the chlorine content in the solution, the method further includes: cooling the solution in ice water and shaking it.

[0012] In some embodiments of the present invention, the cooling time is greater than or equal to 10 min, and may be optionally 10 min to 30 min.

[0013] In some embodiments of the present invention, the shaking time is 1 min to 3 min.

[0014] In some embodiments of the present invention, the temperature of the ice water is 0°C to 5°C.

[0015] In some embodiments of the present invention, the step of measuring the chlorine content in the solution and then obtaining the chlorine content in the ternary precursor includes: diluting the solution to a fixed volume, measuring a certain volume of the diluted liquid, adding a nitric acid solution and a silver nitrate solution to react, diluting again to a fixed volume, measuring the absorbance using a spectrophotometer to obtain the absorbance to be measured; taking standard solutions with different amounts of chloride ions, adding a nitric acid solution and a silver nitrate solution to react, measuring the absorbance using a spectrophotometer, and establishing a curve of absorbance - chloride ion mass; based on the curve of absorbance - chloride ion mass and the absorbance to be measured, obtaining the chlorine content in the solution, and then obtaining the chlorine content in the ternary precursor.

[0016] In some embodiments of the present invention, the measurement wavelengths of the absorbance to be measured and the absorbance of the standard solution are 360 nm to 450 nm, and can be optionally 380 nm to 420 nm.

[0017] In some embodiments of the present invention, the closed container includes any one of a perfluoroalkoxy polymer bottle and a high-pressure microwave digestion tank.

[0018] In some embodiments of the present invention, based on the total mass of the ternary precursor, the mass percentage of chlorine element is 0.01% to 1%.

[0019] In some embodiments of the present invention, the chemical formula of the ternary precursor includes [Ni x1 Co y1 Mn z1 (OH)2, [Ni x2 Co y2 Mn z2 a O b One or more of them, where x1 + y1 + z1 = 1, 0.5 ≤ x1 ≤ 0.98, 0 < y1 ≤ 0.35, 0.03 ≤ z1 ≤ 0.40, x2 + y2 + z2 = 1, 0.5 ≤ x2 ≤ 0.98, 0 < y2 ≤ 0.35, 0.03 ≤ z2 ≤ 0.40, 0.7 ≤ a / b ≤ 1.

[0020] In some embodiments of the present invention, the ternary precursor includes a spinel-type oxide.

[0021] In some embodiments of the present invention, the chlorine content measured by the method has a coefficient of variation < 5% and a standard addition recovery range of 95% to 105%.

[0022] ​In a second aspect of the present invention, the present invention provides a system for determining the chlorine content in a ternary precursor, and the system for determining the chlorine content in the ternary precursor is used to perform the method described in the first aspect of the present invention.

[0023] Additional aspects and advantages of the present invention will be given in part in the following description, become apparent in part from the following description, or be learned through the practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The above and / or additional aspects and advantages of the present invention will become apparent and be readily understood from the description of the embodiments in conjunction with the following drawings, in which:

[0025] Figure 1 A schematic flowchart of a method for determining the chlorine content in a ternary precursor according to an embodiment of the present invention is shown. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0026] Embodiments of the present invention will be described in detail below. The following described embodiments are exemplary and are only used to explain the present invention, and should not be construed as a limitation of the present invention.

[0027] It should be noted that the terms "first" and "second" are only used for descriptive purposes and should not be construed as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, features defined with "first" and "second" may explicitly or implicitly include one or more of such features. Further, in the description of the present invention, unless otherwise specified, the meaning of "plurality" is two or more.

[0028] In a first aspect of the present invention, the present invention provides a method for determining the chlorine content in a ternary precursor. Refer to Figure 1 , the method includes:

[0029] S1. Mix the ternary precursor, HNO3 solution, and H2O2 solution in a closed container to obtain a mixed solution, wherein the molar ratio of HNO3 to H2O2 is (2 - 3):1.

[0030] Specifically, in this step, the ternary precursor, HNO3 solution, and H2O2 solution are mixed in a closed container, and the closed container can prevent the volatilization of chlorine elements. As an example, the molar ratio of HNO3 to H2O2 can be 2:1, 2.2:1, 2.6:1, 2.8:1, 3:1, etc. In some embodiments of the present invention, during specific operation, a concentrated nitric acid solution with a mass concentration of 68% and a hydrogen peroxide solution with a mass concentration of 30% can be selected and mixed in an appropriate volume ratio so that the molar ratio of HNO3 to H2O2 is (2 - 3):1.

[0031] In the embodiments of the present invention, by accurately controlling the molar ratio of HNO3 and H2O2, if the proportion of H2O2 is too small, the ternary precursor cannot be dissolved. By precisely controlling the proportion of hydrogen peroxide, the digestion effect of the ternary precursor is ensured while accelerating the reaction rate, further improving the accuracy of the test and the experimental efficiency.

[0032] It can be understood that the molar ratio of HNO3 and H2O2 refers to the molar ratio of HNO3 molecules in the HNO3 solution to H2O2 molecules in the H2O2 solution. The chlorine content can refer to any content, such as mass fraction, molar fraction, etc. In the embodiments of the present invention, the chlorine content refers to the mass fraction.

[0033] In some embodiments of the present invention, the ternary precursor includes a spinel-type oxide. The spinel-type oxide can be obtained by spray pyrolysis, that is, by atomizing the ternary mixed chloride solution into micron-sized small droplets, and then introducing them into a spray pyrolysis device. With the characteristics of high temperature and extremely short residence time, a ternary precursor with few impurities and uniform particle size can be prepared in one step, and the equipment is simple, time-consuming is short, there are no liquid-phase by-products, the cost is low, and it is easy to scale up for industrial production. Due to the high-temperature spray pyrolysis in the process, the sample has a high crystallinity and a dense structure; at the same time, the high nickel content on the surface will lead to the formation of a stable oxide layer, hindering the entry of nitric acid. By using the molar ratio system of HNO3 and H2O2 in this application, the ternary precursor of the spinel-type oxide can be completely digested, further improving the accuracy of the chlorine content determination in the ternary precursor.

[0034] In some embodiments of the present invention, the molar ratio of the sum of the amounts of metal elements in the ternary precursor to HNO3 is 1:(40 - 80). For example, the molar ratio of the sum of the amounts of metal elements in the ternary precursor to HNO3 can be 1:40, 1:50, 1:60, 1:70, 1:80, etc. In some other embodiments of the present invention, the molar ratio of the sum of the amounts of metal elements in the ternary precursor to HNO3 is 1:(50 - 70). Controlling the molar ratio of the sum of the amounts of metal elements in the ternary precursor to HNO3 within the above range is sufficient to cause the ternary precursor to react and dissolve with nitric acid, and will not cause excessive addition of HNO3 resulting in waste.

[0035] In some embodiments of the present invention, the chemical formula of the ternary precursor includes [Ni x1 Co y1 Mn z1 (OH)2, [Ni x2 Co y2 Mn z2 a O b ​One or more of them, where x1 + y1 + z1 = 1, 0.5 ≤ x1 ≤ 0.98, 0 < y1 ≤ 0.35, 0.03 ≤ z1 ≤ 0.40, x2 + y2 + z2 = 1, 0.5 ≤ x2 ≤ 0.98, 0 < y2 ≤ 0.35, 0.03 ≤ z2 ≤ 0.40, 0.7 ≤ a / b ≤ 1. In some other embodiments of the present invention, the ternary precursor may also contain doping elements, such as one or more of Al, Ti, Zr, Mo, Cr, W, B, Mg, Ba, Nb, and Sr, etc.

[0036] As an example, x1 can be 0.5, 0.6, 0.7, 0.8, 0.9, 0.98, etc., y1 can be 0.01, 0.1, 0.2, 0.3, 0.35, etc., z1 can be 0.03, 0.1, 0.2, 0.3, 0.4, etc.; x2 can be 0.5, 0.6, 0.7, 0.8, 0.9, 0.98, etc., y2 can be 0.01, 0.1, 0.2, 0.3, 0.35, etc., z2 can be 0.03, 0.1, 0.2, 0.3, 0.4, etc.

[0037] In some embodiments of the present invention, based on the total mass of the ternary precursor, the mass proportion of chlorine element is 0.01% - 1%. For example, it can be 0.01%, 0.1%, 0.3%, 0.5%, 0.9%, 1%, etc. Experiments show that when the mass proportion of chlorine element in the ternary precursor is within the above range, using the method for measuring the chlorine content in the ternary precursor of the present invention can more accurately measure the chlorine content therein.

[0038] In some embodiments of the present invention, the closed container includes any one of perfluoroalkoxy polymer bottles (PFA bottles, for example, screw - mouth PFA bottles) and high - pressure microwave digestion tanks. In some other embodiments of the present invention, the closed container includes a perfluoroalkoxy polymer bottle, which has better sealing performance compared with a conventional beaker and has strong universality compared with a high - pressure microwave digestion tank and can be used with a heating plate. Different specifications can be selected according to the amount of sample and reagent.

[0039] S2. Heat the mixed solution to react to obtain a solution.

[0040] In this step, the mixed solution formed by the ternary precursor, HNO3 solution, and H2O2 solution is heated and reacted to dissolve the ternary precursor to form a solution and transfer the chlorine element therein into the solution.

[0041] In some embodiments of the present invention, the temperature of the heating reaction is 150 °C to 200 °C. For example, the temperature of the heating reaction can be 150 °C, 160 °C, 170 °C, 180 °C, 190 °C, 200 °C, etc. In other embodiments of the present invention, the temperature of the heating reaction is 160 °C to 180 °C. Controlling the temperature of the heating reaction within the above range further facilitates the decomposition of hydrogen peroxide (H2O2) in an acidic environment to generate reactive oxygen species (·OH and O2), which can reduce the high-valent metals (such as Ni 3+ , Mn 4+ ) in the ternary precursor to a low valence state, reducing the binding energy of the above metal elements with oxygen, and the low-valent metal elements are more easily dissolved by nitric acid. At the same time, the oxygen bubbles generated by the decomposition of H2O2 can physically strip the passivation layer (such as the stable oxide shell formed by sintering) on the surface of the dense ternary precursor oxide particles, exposing the internal active sites, accelerating the penetration of the HNO3 solution. In addition, the temperature of the heating reaction is not too high to cause the decomposition of nitric acid and affect the reaction between the ternary precursor and HNO3, further improving the accuracy of the measured chlorine content.

[0042] In some embodiments of the present invention, after step S2 and before step S3, the method further includes:

[0043] S21. Cooling the solution in ice water and shaking it.

[0044] Since the chlorine element in the solution is easily volatilized in the heating state, such as volatilizing in the form of HCl, before measuring the chlorine content in the solution in step S3, the closed container containing the solution is first cooled in ice water and shaken. The purpose is to make the hydrogen chloride completely enter the liquid-phase solution as much as possible to reduce the loss of gaseous hydrogen chloride after opening the lid, improve the recovery rate of chlorine, and further improve the accuracy of the measured chlorine content.

[0045] In the embodiments of the present invention, after the heating digestion of the ternary precursor sample is completed, it is cooled using an ice-water bath and shaken well before opening the lid for transfer, dilution, and volume fixation, which can make the hydrogen chloride completely enter the liquid phase, reduce the loss of gaseous hydrogen chloride after opening the lid, improve the recovery rate of chlorine, and further improve the accuracy of the measured chlorine content.

[0046] In some embodiments of the present invention, the cooling time is greater than or equal to 10 min. For example, the cooling time can be 10 min, 20 min, 30 min, 50 min, 100 min, 200 min, etc. In other embodiments of the present invention, the cooling time is 10 min to 30 min. Cooling can increase the solubility of chlorine in the gaseous form in the solution, make the gaseous hydrogen chloride completely enter the liquid-phase solution, reduce the loss of gaseous hydrogen chloride after opening the lid, improve the recovery rate of chlorine, and further improve the accuracy of the measured chlorine content.

[0047] In some embodiments of the present invention, the shaking time is 1 min to 3 min. For example, it can be 1 min, 2 min, 3 min, etc. Shaking can further enable gaseous hydrogen chloride to completely enter the liquid-phase solution, reduce the loss of gaseous hydrogen chloride after opening the lid, improve the recovery rate of chlorine, and further improve the accuracy of the measured chlorine content.

[0048] In some embodiments of the present invention, the temperature of the ice water is 0°C to 5°C. For example, the temperature of the ice water can be 0°C, 1°C, 2°C, 5°C, etc. Controlling the temperature of the ice water within the above range can further enable gaseous hydrogen chloride to completely enter the liquid-phase solution, reduce the loss of gaseous hydrogen chloride after opening the lid, improve the recovery rate of chlorine, and further improve the accuracy of the measured chlorine content.

[0049] S3. Measure the chlorine content in the solution, and then obtain the chlorine content in the ternary precursor.

[0050] In this step, measure the chlorine content in the solution, and then calculate the chlorine content in the ternary precursor according to the mass of the ternary precursor added in step S1.

[0051] In some embodiments of the present invention, step S3 includes:

[0052] S31. Make the solution reach a constant volume, measure the liquid after reaching a constant volume, add it to react with a nitric acid solution and a silver nitrate solution, reach a constant volume again, and use a spectrophotometer to measure the absorbance to obtain the absorbance to be measured;

[0053] S32. Take standard solutions with different amounts of chloride ions, add them to react with a nitric acid solution and a silver nitrate solution, use a spectrophotometer to measure the absorbance, and establish a curve of absorbance - chloride ion mass;

[0054] S33. According to the curve of absorbance - chloride ion mass and the absorbance to be measured, obtain the chlorine content in the solution, and then obtain the chlorine content in the ternary precursor.

[0055] The above method is the silver chloride turbidimetry method, which uses a spectrophotometer to measure the chlorine content in the solution. The silver chloride turbidimetry method is based on the reaction of chloride ions with silver ions to form insoluble silver chloride precipitate. When chloride ions react with silver ions in the silver nitrate solution, white silver chloride precipitate will be formed, making the solution turbid. The turbidity of the solution is linearly related to the chloride ion concentration. By measuring the turbidity of the solution, the content of chloride ions can be quantitatively analyzed, with high accuracy, which can further facilitate improving the accuracy of the method for measuring the chlorine content in the ternary precursor.

[0056] In some embodiments of the present invention, the measurement wavelengths of the absorbance to be measured and the absorbance of the standard solution are 360 nm to 450 nm. As an example, the measurement wavelengths of the absorbance can be 360 nm, 390 nm, 400 nm, 420 nm, 430 nm, 440 nm, 450 nm, etc. Experiments show that the above wavelengths are the most suitable bands for chlorine elements in the ternary precursor of the present application. This is because the principle of the silver chloride turbidimetry method is that Ag + and Cl - react to form AgCl white precipitate, and the absorbance of the suspension is used to reflect the chloride ion concentration. This reaction has neither other chromogenic groups nor characteristic absorption peaks. The measurement of the absorbance depends on the scattering and absorption characteristics of light with a specific wavelength on AgCl particles. The wavelength range of 360 nm to 450 nm is the transition region between ultraviolet light and visible light. In this band, the scattering and absorption characteristics of AgCl particles are relatively stable and are not easily interfered by external factors such as temperature and solution pH value. As a result, the absorbance measurement results are more reliable, can more accurately reflect the content of chlorine elements, and thus have good stability and repeatability, and can effectively avoid possible interferences in other bands. In some other embodiments of the present invention, the measurement wavelengths of the absorbance to be measured and the absorbance of the standard solution are 380 nm to 420 nm.

[0057] In the embodiments of the present invention, the chlorine content is measured by the silver chloride turbidimetry method in the 360 nm to 450 nm band using a spectrophotometer. This method can accurately measure the chlorine content and provides a reliable basis for product quality control.

[0058] In summary, for the method for measuring the chlorine content in the ternary precursor proposed in the present application, the ternary precursor, HNO3 solution and H2O2 solution are mixed and heated, and the molar ratio of HNO3 and H2O2 is controlled. The addition amount of H2O2 is relatively high. Hydrogen peroxide (H2O2) can decompose to generate active oxygen (·OH and O2) in an acidic environment, and can convert the high-valent metals in the ternary precursor (such as Ni 3+ 、Mn 4+)Reduced to a low valence state, the binding energy between the above metal elements and oxygen is decreased, and the metal elements in the low valence state are more easily dissolved by HNO3. Meanwhile, the oxygen bubbles generated by the decomposition of H2O2 can physically strip the passivation layer (such as the stable oxide shell formed by sintering) on the surface of the dense ternary precursor particles, expose the internal active sites, accelerate the penetration of the HNO3 solution into the interior of the ternary precursor, dissolve it, and overcome the limitations of the traditional method. Through the above effects, the ternary precursor is more easily dissolved to form a solution, facilitating the transfer of chlorine elements therein into the solution. In addition, the reaction is set in a closed container, which can avoid the volatilization of chlorine elements and ensure the accuracy of chlorine element measurement. In summary, the method for measuring the chlorine content in the ternary precursor proposed by the present invention can accurately measure the chlorine element content in the ternary precursor.

[0059] The present invention can quickly and accurately test the chlorine content in the ternary precursor, which helps to improve production efficiency and product quality. In addition, the test device and method of the present invention are relatively simple, easy to operate, can reduce the test cost, take into account both efficiency and safety, and improve economic benefits.

[0060] The coefficient of variation of the chlorine content in the ternary precursor measured by the method of the present invention is <5%, and the spiked recovery range is 95% - 105%. It shows that the chlorine content obtained by the method of the present invention is highly accurate.

[0061] In the second aspect of the present invention, the present invention proposes a system for measuring the chlorine content in the ternary precursor, and the system for measuring the chlorine content in the ternary precursor is used to execute the method described in the first aspect of the present invention. Thus, the system for measuring the chlorine content in the ternary precursor proposed by the present invention has all the beneficial effects of the above method, which will not be elaborated here one by one.

[0062] Hereinafter, the solutions of the present disclosure will be explained with reference to the embodiments. Those skilled in the art will understand that the following embodiments are only used to illustrate the present disclosure and should not be regarded as limiting the scope of the present disclosure. For those not specified in the embodiments regarding specific technologies or conditions, they shall be carried out according to the technologies or conditions described in the literature in the art or according to the product specifications. For the reagents or instruments not specified regarding the manufacturers, they are all conventional products that can be obtained through commercial purchase.

[0063] Example 1

[0064] (1) Weigh 0.2 g of the ternary precursor sample (chemical formula (Ni 0.623 Co 0.073 Mn 0.304) In a 30 mL screw-cap PFA bottle, 10 mL of concentrated nitric acid with a mass concentration of 68% and 6 mL of hydrogen peroxide with a mass concentration of 30% were added in sequence. The bottle cap was quickly tightened to prevent liquid volatilization loss. The molar ratio of HNO3 to H2O2 was 2.6:1, and the molar ratio of the sum of the metal elements in the ternary precursor to the amount of substance of HNO3 was 1:60.

[0065] (2) Place the screw-cap PFA bottle on a heating plate, set the heating temperature to 170 °C, and heat until the solution boils. After the reaction in the bottle becomes relatively quiet and no obvious large bubbles are generated, continue heating for 30 min to ensure complete reaction. The color of the solution in the bottle turns slightly green and no longer changes. Then, carefully use pliers to pick up the screw-cap PFA bottle and quickly place it in an ice-water bath (temperature 0 °C) to cool for 30 min to quickly terminate the reaction and reduce the solution temperature.

[0066] (3) Carefully shake the screw-cap PFA bottle for 2 min to allow the acid to fully react with the sample and enter the liquid phase as much as possible to ensure full and uniform reaction. Slowly open the bottle cap of the screw-cap PFA bottle, avoiding splashing of the solution, transfer and make up the volume to a 50 mL volumetric flask, and shake well.

[0067] (4) Use a pipette to accurately transfer two 10.0 mL portions of the above-made-up solution and place them in two 25.0 mL dry and clean colorimetric tubes respectively. One serves as a blank control and the other as a sample solution. Accurately add 2 mL of nitric acid solution (1+1, that is, the volume ratio of nitric acid to water is 1:1) to both liquids. Then, accurately add 2 mL of silver nitrate solution to the sample solution to ensure accurate reagent addition volume and order. Place the two colorimetric tubes in the dark for a 10-min reaction to ensure consistent and full reaction conditions for subsequent accurate detection.

[0068] (5) Determination: Transfer the solution into a 1 cm cuvette, use the reagent blank as a reference, and measure its absorbance at a wavelength of 380 nm on a spectrophotometer.

[0069] (6) Standard curve drawing: Accurately transfer 0 mL, 5.00 mL, 10.00 mL, 20.00 mL, and 40.00 mL of chloride ion standard solution (chloride ion mass fraction is 1000 ppm) and place them in 5 100 mL volumetric flasks respectively, and make up the volume to 100 mL. Take 10.0 mL of each and place it in a 25.0 mL colorimetric tube, add 2 mL of nitric acid (1+1) and 2 mL of silver nitrate solution, dilute to the mark with water and mix well. After standing in the dark for 10 min, transfer some of the solution into a 1 cm cuvette and measure its absorbance at a wavelength of 380 nm on a spectrophotometer. Use the chloride ion mass as the abscissa (μg) and the absorbance as the ordinate to draw a working curve, and the correlation coefficient should be not less than 0.999.

[0070] (7) Calculation: Subtract the absorbance of the blank solution corresponding to the sample, and find the mass percentage of chlorine element corresponding to it from the working curve.

[0071] Comparative Example 1

[0072] The chlorine content was measured by the combination of an on-line combustion system and the coulometric method. The principle is that the accurately weighed sample is quickly heated to 1000 °C to vaporize and then enters the chlorine collection cell. By measuring the amount of electricity consumed by Ag + during the electrolytic titration process, according to Faraday's law, the total chlorine content of the sample can be obtained. The specific steps are as follows:

[0073] Combustion process: A 0.1 g ternary precursor sample undergoes an oxidation-reduction reaction by combustion in a cracking tube at 1000 °C, converting the chlorine element in it into hydrogen chloride (HCl) gas.

[0074] Absorption process: The hydrogen chloride gas generated by combustion is carried by the carrier gas into the titration cell to be converted into titratable ions and absorbed by the absorption liquid, converting them into detectable ions.

[0075] Coulometric detection: Through an electrolytic reaction, the chloride ions in the absorption liquid react with silver ions to form silver chloride precipitate, and the chlorine content is calculated based on the amount of electricity consumed during the electrolysis process.

[0076] The steps of Examples 2-11 and Comparative Examples 2-3 are the same as those of Example 1, except for the specific parameters. See Table 1. The mass percentages of chlorine element (based on the ternary precursor) measured in Examples 1-11 and Comparative Examples 1-3 are shown in Table 2.

[0077] Table 1

[0078]

[0079] The following measurements were carried out on Examples 1-11 and Comparative Examples 1-3:

[0080] 1. Determination of the coefficient of variation of the measured chlorine content: To ensure the accuracy of the measurement, the absorbance of the same solution needs to be measured multiple times, generally 3-5 parallel determinations are carried out, and then the average value, standard deviation, and coefficient of variation are calculated. Coefficient of variation (CV) = (standard deviation (SD) / average value (Mean)) × 100%.

[0081] 2. Spike recovery determination of the measured chlorine content: Taking Example 1 as an example, 200 μg and 400 μg of standard chloride ions (pipetting 0.2 mL and 0.4 mL of 1000 mg / L chloride ion standard solution) were added to 0.2 g of the ternary precursor sample respectively to form Sample 1 and Sample 2. According to the steps in Example 1, the chlorine content of Sample 1 and Sample 2 was determined by the same measurement method, and the measured values (the measured values after spiking) of Sample 1 and Sample 2 were recorded. Then the spike recovery of the two samples = (the measured value after spiking - the measured value before spiking) / the spiked amount × 100%. Taking Sample 1 as an example, the measured value before spiking is the result measured in Example 1, and the spiked amount is 200 μg. The average value of the spike recoveries of the two samples is the spike recovery, and the measurement results are shown in Table 2.

[0082] Table 2

[0083] Mass percentage of chlorine element based on the total mass of ternary precursor Coefficient of variation Spiked recovery rate Example 1 0.2050％ 3.48％ 101.0％ Example 2 0.2052％ 4.52％ 100.5％ Example 3 0.2045％ 4.80％ 97.8％ Example 4 0.2005％ 3.88％ 96.5％ Example 5 0.2008％ 5.01％ 99.5％ Example 6 0.1865％ 3.28％ 91.0％ Example 7 0.2029％ 5.90％ 93.2％ Example 8 0.1957％ 9.3％ 91.0％ Example 9 0.1964％ 4.99％ 96.7％ Example 10 0.1850％ 4.78％ 91.1％ Example 11 0.1914％ 4.75％ 90.3％ Comparative Example 1 0.1084％ 2.4％ 120.0％ Comparative Example 2 0.1148％ 3.9％ 82.1％ Comparative Example 3 0.1526％ 5.1％ 88.8％

[0084] It can be understood that the smaller the coefficient of variation, the stronger the stability of the test method, and the closer the spike recovery is to 100%, the higher the accuracy of the measurement result. As can be seen from Table 2, in Examples 1-11 of the present application, the ternary precursor, HNO3 solution and H2O2 solution were mixed and heated, and the molar ratio of HNO3 and H2O2 was controlled at (2-3):1. The measured chlorine content was relatively high and the coefficient of variation was small, indicating good stability of the test results. The spike recovery was close to 100%, indicating that the test results were relatively accurate. Compared with Examples 1-11, the measured chlorine content results in Comparative Examples 1-3 were significantly lower, and the gap between the spike recovery and 100% was large. Among them, in Comparative Example 2, the molar ratio of HNO3 and H2O2 was too low, that is, the proportion and content of H2O2 increased, and H2O2 generated excessive gas, which further carried out the chlorine element in the solution, making a large amount of chlorine element exist in the form of HCl gas, which was not conducive to the determination of the chlorine element content and affected its accuracy. Therefore, the measured chlorine content was low and the gap between the spike recovery and 100% was large; in Comparative Example 3, the molar ratio of HNO3 and H2O2 was too high, that is, the proportion and content of H2O2 decreased, and the ternary precursor was not completely digested, and the chlorine element was not completely released and recovered. Therefore, the chlorine content was low and the gap between the spike recovery and 100% was large.

[0085] Compared with Example 1, in Example 6, the temperature of the heating reaction was decreased, and the ternary precursor was not completely dissolved. Therefore, the measured chlorine content was decreased, and the recovery rate of standard addition deviated greatly from 100%. Compared with Example 1, in Example 7, the temperature of the heating reaction was increased, and the amount of the generated gas was increased, so that a large amount of chlorine element in the solution existed in the form of HCl gas, which was not conducive to the determination of the chlorine element content and affected its accuracy. Therefore, the measured chlorine content was decreased, and the recovery rate of standard addition deviated more from 100%. Compared with Example 1, in Example 8, no ice bath and shaking were carried out, and the gaseous hydrogen chloride in the PFA bottle was not completely dissolved in the solution and was lost after opening the lid, resulting in a lower measured chlorine content, a larger coefficient of variation, a lower stability of the measurement method, and a greater deviation of the recovery rate of standard addition from 100%. Compared with Example 1, in Examples 10 and 11, the absorbance measurement wavelength was not within the preferred range of 380 nm to 420 nm, and the stability of the scattering and absorption characteristics of AgCl particles to light became poor and was easily interfered by external factors such as temperature and solution pH value. Therefore, the measured chlorine content was lower, the coefficient of variation was larger, and the recovery rate of standard addition deviated greatly from 100%.

[0086] In the description of the present specification, the descriptions referring to the terms "one embodiment", "some embodiments", "example", "specific example", "some implementation manners" or "some examples", etc. mean that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present invention. In the present specification, the schematic expressions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, without contradiction, those skilled in the art may combine and combine the different embodiments or examples described in the present specification and the features of the different embodiments or examples.

[0087] Although the embodiments of the present invention have been shown and described above, it can be understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those of ordinary skill in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A method for determining the chlorine content in a ternary precursor, characterized in that: include: The ternary precursor, HNO3 solution and H2O2 solution are mixed in a sealed container to obtain a mixed solution, wherein the molar ratio of HNO3 to H2O2 is (2-3):1; heating the mixed solution to react and obtain a solution; Determining the chlorine content in the solution, thereby obtaining the chlorine content in the ternary precursor; The ternary precursor includes a spinel oxide.

2. The method according to claim 1, characterized in that The ratio of the sum of the amounts of the metal elements in the ternary precursor to the amount of HNO3 is 1:(40-80), and can be optionally 1:(50-70).

3. The method according to claim 1 or 2, characterized in that: The temperature of the heating reaction is 150°C to 200°C, and can be optionally 160°C to 180°C.

4. The method according to claim 1 or 2, characterized in that: After the step of heating the mixed solution to react and obtaining a solution, and before the step of using silver chloride turbidimetry to determine the chlorine content in the solution, the method further comprises: The solution was cooled in ice water and shaken.

5. The method according to claim 4, characterized in that The cooling time is greater than or equal to 10 minutes, and can be 10 minutes to 30 minutes; and / or, The shaking time is 1 min to 3 min; and / or, The temperature of the ice water is 0°C to 5°C.

6. The method according to claim 1 or 2, characterized in that: The step of determining the chlorine content in the solution to obtain the chlorine content in the ternary precursor comprises: The solution is diluted to volume, a nitric acid solution and a silver nitrate solution are added to the diluted solution for reaction, the solution is diluted to volume again, and the absorbance is measured using a spectrophotometer to obtain an absorbance to be measured; Take different amounts of standard chloride ion solutions, add nitric acid solution and silver nitrate solution to react, use a spectrophotometer to measure the absorbance, and establish a curve of absorbance-chloride ion mass; The chlorine content in the solution is obtained according to the absorbance-chloride ion mass curve and the absorbance to be measured, and then the chlorine content in the ternary precursor is obtained.

7. The method according to claim 6, characterized in that The measuring wavelengths of the absorbance to be measured and the absorbance of the standard solution are 360nm to 450nm, and can be optionally 380nm to 420nm.

8. The method according to claim 1 or 2, characterized in that: The sealed container includes any one of a perfluoroalkoxy polymer bottle and a high-pressure microwave digestion tank; and / or, Based on the total mass of the ternary precursor, the mass proportion of chlorine element is 0.01% to 1%; and / or, The chemical formula of the ternary precursor includes [Ni x1 Co y1 Mn z1 ](OH)2,[Ni x2 Co y2 Mn z2 ] a O b One or more of, wherein x1+y1+z1=1, 0.5≤x1≤0.98, 0 <y1≤0.35,0.03≤z1≤0.40,x2+y2+z2=1,0.5≤x2≤0.98,0<y2≤0.35,0.03≤z2≤0.40,0.7≤a / b≤1。 9. The method according to claim 1 or 2, characterized in that: The chlorine content determined by the method has a coefficient of variation of less than 5% and a spike recovery range of 95% to 105%.

10. A system for determining the chlorine content in a ternary precursor, characterized in that: The system for determining the chlorine content in a ternary precursor is used to perform the method according to any one of claims 1 to 9.

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