Method for analyzing and testing chlorine content in ternary precursor battery material

Abstract

The invention relates to a method for analyzing and testing chlorine content in a ternary precursor battery material, and belongs to the technical field of chemical analysis of ternary materials. The method comprises the following steps: distilling a sample, separating a part of solution, adding nitric acid, acetone and a silver nitrate solution, diluting with water to prepare a test solution, drawing a standard working curve, determining the content of the chlorine element and the like. The analysis and test method adopts silver chloride turbidimetric spectrophotometry for testing, has the advantages of high sensitivity, strong anti-interference capability, good selectivity, high accuracy, wide applicable concentration range, low analysis cost and simplicity, convenience and rapidness in operation, and can be used as a conventional method for analyzing and testing the chlorine content in the ternary precursor battery material. The samples suitable for the method comprise ternary precursor battery material products of NCM series, NCA series, NCM90, NCMA series and the like.

Description

Technical Field

[0001] The present invention relates to an analytical test method for the chlorine content in ternary precursor battery materials, and particularly to an analytical test method for determining the chlorine content in ternary precursor battery materials by using silver chloride turbidimetric spectrophotometry. The present invention belongs to the technical field of ternary material chemical analysis. Background Art

[0002] Ternary precursor materials are an important part of the cathode materials for lithium-ion batteries, and their performance directly affects key indicators such as the energy density, cycle life, and safety of the batteries. With the continuous growth of the demand for new energy vehicles and renewable energy storage, the demand for high-performance lithium-ion batteries is also rapidly increasing, thus promoting the research and development of ternary precursor materials.

[0003] Ternary precursor materials (such as NCM and NCA materials) are widely used in lithium-ion batteries, and their performance directly affects the energy density, cycle life, and safety of the batteries. During the preparation process of these materials, chloride ions, as a common impurity element, may have a negative impact on the electrochemical performance of the materials. Therefore, accurately determining the chlorine content in ternary precursor materials has important technical background and practical significance.

[0004] The presence of chloride ions in ternary precursor materials may cause the following problems: Chloride ions may react with lithium ions to form undesirable compounds, reducing the conductivity and ion migration ability of the materials. The presence of chloride ions may cause the crystal structure of the materials to be unstable, affecting their cycle performance during charge and discharge. Under high temperature or overcharge conditions of the battery, chloride ions may trigger unsafe reactions, increasing the risk of the battery.

[0005] With the wide application of ternary precursor materials, the relevant test standards and specifications are also constantly being improved. For example, the requirements for determining the chloride ion content are gradually increasing in national standards and industry standards to ensure the quality and safety of the materials. Summary of the Invention

[0006] In order to solve the technical problem of determining the chlorine content in ternary precursor battery materials, the present invention, in order to accurately determine the chlorine content in ternary precursor materials, adopts the silver chloride turbidimetric method. This method generates a silver chloride suspension by reacting the sample with silver nitrate after dissolution, and uses a spectrophotometer to measure the absorbance of the suspension, thereby calculating the concentration of chloride ions. This method has the advantages of simple operation, low cost, and high sensitivity.

[0007] The present invention uses the method of silver chloride turbidimetric spectrophotometry for determination, which has the characteristics of short process, accurate results, and easy operation.

[0008] The present invention adopts the following technical solutions to solve the above technical problems:

[0009] An analytical test method for the chlorine content in a ternary precursor battery material, which is determined by the silver chloride turbidimetric spectrophotometry, includes the following steps:

[0010] (1) Sample distillation: When the temperature of the pre-distilled sulfuric acid drops to 25°C - 70°C, weigh a sample of the ternary precursor battery material (with a mass of m0) and add it to the distillation flask. Connect the distillation device to conduct distillation; heat to raise the temperature of the solution in the distillation flask, adjust the steam flow rate and heating power, control the temperature at 100°C - 200°C. After receiving the liquid, remove the receiving flask, transfer the solution in the receiving flask to a volumetric flask, dilute it to the mark with water (the total volume of the test solution is V0), shake well, and set aside; conduct a blank sample test simultaneously.

[0011] (2) Pipette a part of the solution (V1) into a glass volumetric flask.

[0012] (3) Add water to a certain volume, add nitric acid, mix well, then add acetone, mix well, and finally add silver nitrate solution. Dilute it to the mark with water and mix well; place the volumetric flask in a water bath for heating, take it out, cool it to room temperature with running water, transfer it to a dark room for placement, and mix well.

[0013] (4) Transfer a part of the solution into a colorimetric cell. Using the blank solution of the test sample as a reference, measure its absorbance at a wavelength of 410 - 460 nm on a spectrophotometer, and calculate the mass of chlorine (m1) from the corresponding working curve.

[0014] In step (1), the time for receiving the liquid is 10 min - 40 min. The mass of the sample of the ternary precursor battery material weighed is 0.05 - 1.00 g. The mass - volume ratio of the mass of the sample of the ternary precursor battery material weighed to the total volume of the test solution diluted to the mark with water is (0.05 - 1.00) g: 100 ml.

[0015] The sample of the ternary precursor battery material includes ternary precursor battery material products such as NCM (lithium nickel cobalt manganese oxide) series, NCA (lithium nickel cobalt aluminate) series, NCM90 (lithium nickel cobalt manganese oxide with high nickel content), and / or NCMA (lithium nickel cobalt manganese aluminate) series, etc.

[0016] A method for pre-distillation and purification of sulfuric acid, comprising the following steps: Place 150 - 300 parts by volume of water in a distillation flask of a steam distillation apparatus, heat it to boiling, and set aside; Take 5 - 20 parts by volume of water and place it in a receiving flask of 50 - 200 parts by volume as an absorption liquid, and set aside; Add 20 - 100 parts by volume of sulfuric acid to the distillation flask, wash the bottle mouth with water, add zeolite, and connect the distillation apparatus; Heat the solution in the distillation flask, adjust the steam flow rate and heating power to maintain the temperature at 100°C to 200°C, stop heating after distillation for 10 min - 40 min, and discard the receiving liquid. The sulfuric acid is concentrated sulfuric acid with a mass fraction of 95% - 98%.

[0017] In step (3), after diluting to the mark with water, the addition amount of nitric acid is 1 vol.% - 5 vol.%, the addition amount of acetone is 1 vol.% - 5 vol.%, and the addition amount of silver nitrate solution is 1 vol.% - 5 vol.%; The nitric acid is concentrated nitric acid with a mass fraction of 65% - 70%, and the mass concentration of the silver nitrate solution is 5 g / L - 15 g / L. The heating temperature in the water bath is 70°C ± 1°C, and the time is 5 min - 15 min. The room temperature is 25°C ± 3°C, and it is transferred to a dark room and left for 5 min - 15 min.

[0018] In step (4), the diameter of the colorimetric cell is 1 - 3 cm, and the volume of the transferred partial solution is 1 mL - 3 mL.

[0019] The method for drawing the working curve comprises the following steps:

[0020] (I) Applicable to a Cl content of 0.005% - 0.010% (mass%, including 0.010%)

[0021] (1) Pipette 0, 0.50, 1.00, 2.00, 3.00, 4.00 mL of chlorine standard solution into a group of 100 mL volumetric flasks, add 1:1 nitric acid, dilute to a certain volume with water, and mix well; Then add acetone and mix well, and finally add silver nitrate solution, dilute to the mark with water, and mix well; Place the volumetric flask in a water bath for heating, take it out, cool it to room temperature with running water, transfer it to a dark room and leave it, and mix well; The concentration of the chlorine standard solution is 10 μg / ml;

[0022] (2) Transfer a part of the colored solution into a colorimetric cell, and measure its absorbance at a wavelength of 430 nm on a spectrophotometer; Use the chlorine content as the abscissa and the absorbance as the ordinate to draw the working curve.

[0023] (II) Applicable to a Cl content of 0.010% - 0.20% (mass%, excluding 0.010%)

[0024] (1) Pipette 0 mL, 0.20 mL, 0.60 mL, 0.80 mL, 1.00 mL, 1.20 mL, 1.60 mL of chlorine standard solution into a group of 100-mL volumetric flasks. Add 1:1 nitric acid, dilute to a certain volume with water, and mix well; then add acetone and mix well. Finally, add silver nitrate solution and dilute to the mark with water, and mix well. Place the volumetric flasks in a water bath, heat, take out, cool to room temperature with running water, transfer to a dark room, place, and mix well. The concentration of the chlorine standard solution is 50 μg / ml;

[0025] (2) Transfer a part of the colored solution into a cuvette, and measure its absorbance at a wavelength of 410 - 460 nm on a spectrophotometer. Plot a working curve with the chlorine amount as the abscissa and the absorbance as the ordinate.

[0026] Among them, after diluting to the mark with water, the addition amount of 1:1 nitric acid is 1 vol.% - 5 vol.%, the addition amount of acetone is 1 vol.% - 5 vol.%, and the addition amount of silver nitrate solution is 1 vol.% - 5 vol.%; 1:1 nitric acid is a mixture of nitric acid (mass fraction 65% - 70%) and water in a volume ratio of 1:1, and the mass concentration of the silver nitrate solution is 5 g / L - 15 g / L. The heating temperature in the water bath is 70°C ± 1°C, and the time is 5 min - 15 min. The room temperature is 25°C ± 3°C, and transfer to a dark room and place for 5 min - 15 min.

[0027] Among them, the diameter of the cuvette is 1 - 3 cm, and the volume of the transferred part of the solution is 1 mL - 3 mL.

[0028] Calculation of the analysis result:

[0029] The chlorine amount is calculated as the mass fraction w, and the value is expressed in %, according to formula (1):

[0030]

[0031] In the formula:

[0032] m1——The mass of chlorine calculated from the working curve, in micrograms (μg);

[0033] V0——The total volume of the test solution, in milliliters (mL);

[0034] m0——The mass of the test sample, in grams (g);

[0035] V1——The volume of the aliquot taken from the test solution, in milliliters (mL).

[0036] The analysis result is expressed to four decimal places.

[0037] The water mentioned above is secondary distilled water and above in purity.

[0038] The analytical test method of the present invention uses turbidimetric spectrophotometry with silver chloride for testing, which has the advantages of high sensitivity, strong anti-interference ability, good selectivity, high accuracy, wide applicable concentration range, low analysis cost, and simple and rapid operation. It can be used as a conventional method for analyzing and testing the chlorine content in ternary precursor battery materials.

[0039] The samples applicable to this method include ternary precursor battery material products such as NCM series, NCA series, NCM90, and NCMA series. Description of the Drawings

[0040] Figure 1 It is the chlorine working curve diagram of Example 1 of the present invention;

[0041] Figure 2 It is the chlorine working curve diagram of Example 2 of the present invention. Detailed Embodiments

[0042] The following will describe the present invention in detail with reference to the embodiments.

[0043] The analytical test method for the chlorine content in the ternary precursor battery material of the present invention is determined by turbidimetric spectrophotometry with silver chloride, and includes steps such as sample distillation, aliquoting part of the solution, adding nitric acid, acetone, silver nitrate solution and diluting with water to prepare a test solution, drawing a standard working curve, and determining the content of chlorine element.

[0044] Sample determination:

[0045] 1.1 Pre-distillation and purification with sulfuric acid: Place 150 mL - 300 mL of water in the distillation flask of the steam distillation device, heat it until the water boils, and set aside. Take 5 mL - 20 mL of water and place it in a 50 mL - 200 mL receiving flask as the absorption liquid, and set aside. Add 20 mL - 100 mL of sulfuric acid to the distillation flask, wash the bottle mouth with water, add zeolite, and connect the distillation device. Heat the solution in the distillation flask, adjust the steam flow rate and heating power to maintain the temperature at 100°C - 200°C, stop heating after distilling for 10 min - 40 min, and discard the receiving liquid.

[0046] 1.2 Sample distillation: When the temperature of the sulfuric acid after pre-distillation in the distillation flask drops to 25°C - 70°C, add the test sample to the distillation flask, connect the distillation device for distillation. Heat the solution in the distillation flask, adjust the steam flow rate and heating power to maintain the temperature at 100°C - 200°C, after distilling for 10 min - 40 min, remove the receiving flask, transfer the solution in the receiving flask to a 100 mL volumetric flask, dilute it to the mark with water, shake well, and set aside.

[0047] 2.1 Aliquot part of the solution into a 100 ml glass volumetric flask.

[0048] 3.1 Add water to a volume of approximately 30 mL, add 3 mL of nitric acid, mix well, add 2 mL of acetone, mix well, add 2 mL of silver nitrate solution, dilute to the mark with water, and mix well. Place the volumetric flask in a water bath at 70 °C (±1 °C) and heat for 8 min, take it out, cool it to room temperature with running water, transfer it to a dark room and let it stand for 10 min, and mix well.

[0049] 4.1 Transfer part of the solution into a 1 - 3 cm cuvette, use the blank solution of the test sample as the reference, measure its absorbance at a wavelength of 410 - 460 nm on a spectrophotometer, and calculate the mass of chlorine from the corresponding working curve.

[0050] Drawing of the working curve:

[0051] Applicable to Cl content of 0.005% - 0.010%

[0052] Pipette 0, 0.50, 1.00, 2.00, 3.00, 4.00 mL of chlorine standard solution (10 μg / ml) into a group of 100 mL volumetric flasks, add 3 mL of 1:1 nitric acid, dilute to 30 mL with water, and mix well. Proceed as in step 3.1 below.

[0053] Transfer part of the colored solution into a 3 cm cuvette, measure its absorbance at a wavelength of 430 nm on a spectrophotometer. Plot the working curve with the chlorine amount as the abscissa and the absorbance as the ordinate.

[0054] Applicable to Cl content of 0.010% - 0.20%

[0055] 1. Pipette 0 mL, 0.20 mL, 0.60 mL, 0.80 mL, 1.00 mL, 1.20 mL, 1.60 mL of chlorine standard solution (50 μg / ml) into a group of 100 mL volumetric flasks, add 3 mL of 1:1 nitric acid, dilute to 30 mL with water, and mix well. Proceed as in step 3.1 below.

[0056] 2. Transfer part of the colored solution into a 1 - 3 cm cuvette, measure its absorbance at a wavelength of 410 - 460 nm on a spectrophotometer. Plot the working curve with the chlorine amount as the abscissa and the absorbance as the ordinate.

[0057] Calculation of the analysis result:

[0058] The chlorine content, expressed as the mass fraction w and in %, is calculated according to formula (1):

[0059]

[0060] In the formula:

[0061] m1——The mass of chlorine calculated from the working curve, in micrograms (μg);

[0062] V0—the total volume of the test solution, in milliliters (mL);

[0063] m0—the mass of the test sample, in grams (g);

[0064] V1—the volume of the aliquot taken from the test solution, in milliliters (mL).

[0065] The analysis results are expressed to four decimal places.

[0066] The water mentioned above is secondary distilled water or of higher purity.

[0067] Example 1:

[0068] In Example 1 of the present invention, a method for analyzing and testing the chlorine content in ternary precursor battery materials by turbidimetric spectrophotometry with silver chloride is adopted, and the reagents used are as follows:

[0069] Nitric acid (ρ = 1.42 g / mL);

[0070] 1:1 nitric acid is a mixture of nitric acid (ρ = 1.42 g / mL) and water with a volume ratio of 1:1;

[0071] Sulfuric acid (ρ = 1.84 g / mL);

[0072] Acetone;

[0073] Silver nitrate solution (10 g / L);

[0074] Chlorine standard solution (10 μg / ml);

[0075] The water is secondary distilled water or of higher purity. At least secondary distilled water is used, and the water is chlorine-free water: Take 50 mL of deionized water, add 2 drops of HNO3 and 1 mL of silver nitrate solution, and observe in the dark. There should be no chlorine ion reaction; wherever this method involves reagent preparation, dilution water, etc., this kind of water is referred to.

[0076] In this example, the NCM series is used as the sample for the determination of chlorine content, which specifically includes the following steps:

[0077] (1) Drawing of the working curve: Applicable to Cl content of 0.0050% - 0.010%

[0078] 1. Pipette 0, 0.50, 1.00, 2.00, 3.00, 4.00 mL of chlorine standard solution (10 μg / ml) into a group of 100 mL volumetric flasks, add 3 mL of 1:1 nitric acid, dilute to 30 mL with water, and mix well. Add 2 mL of acetone, mix well, add 2 mL of silver nitrate solution, dilute to the mark with water, and mix well. Place the volumetric flask in a water bath at 70 °C and heat for 8 min, take it out, cool it to room temperature with running water, transfer it to a dark room and place it for 10 min, and mix well.

[0079] 2. Transfer a portion of the color-developing solution (3 mL) into a 3-cm cuvette, and measure its absorbance at a wavelength of 440 nm on a spectrophotometer. Using the chlorine content as the abscissa and the absorbance as the ordinate, plot the working curve as shown in Figure 1 the following figure.

[0080] (II) Distillation and testing of samples

[0081] 3. Sample distillation: After the temperature of the pre-distilled sulfuric acid in the distillation flask drops to 50 °C, weigh 1.00 g of the ternary precursor battery material sample and add it to the distillation flask. Connect the distillation device and perform distillation. Heat to raise the temperature of the solution in the distillation flask, adjust the steam flow rate and heating power, control the temperature at 100 °C, after receiving the liquid for 40 min, remove the receiving flask, transfer the solution in the receiving flask to a 100-mL volumetric flask, dilute to the mark with water, shake well, and reserve. Conduct a blank sample in the same way.

[0082] Purification of sulfuric acid by pre-distillation: Place 150 mL of water in the distillation flask of the steam distillation device, heat until the water boils, and reserve. Take 15 mL of water and place it in a 200-mL receiving flask as the absorption liquid, and reserve. Add 100 mL of sulfuric acid to the distillation flask, wash the bottle mouth with water, add zeolite, and connect the distillation device. Heat the solution in the distillation flask, adjust the steam flow rate and heating power to maintain the temperature at 180 °C, stop heating after distilling for 30 min, and discard the receiving liquid.

[0083] 4. Pipette a portion of the solution into a 100-ml glass volumetric flask.

[0084] 5. Add water until the volume is approximately 30 mL, add 3 mL of nitric acid, mix well, add 2 mL of acetone, mix well, add 2 mL of silver nitrate solution, dilute to the mark with water, and mix well. Place the volumetric flask in a water bath at 70 °C (±1 °C) and heat for 8 min, take it out, cool it to room temperature with running water, transfer it to a dark room and let it stand for 10 min, and mix well.

[0085] 6. Transfer a portion of the solution (3 mL) into a 3-cm cuvette, use the blank solution of the test sample as the reference, measure its absorbance at a wavelength of 440 nm on a spectrophotometer, and calculate the mass of chlorine from the corresponding working curve.

[0086] Repeat the test 11 times according to the same process, calculate according to formula (1), and the results are shown in Table 1. After determination, the chlorine content in the measured sample is 0.0064 wt.%.

[0087] Example 2:

[0088] This example is basically the same as Example 1, the difference is:

[0089] In this example, the NCA series is used as the sample for the determination of chlorine content

[0090] The reagents used are as follows:

[0091] Nitric acid (ρ = 1.42 g / mL);

[0092] 1:1 nitric acid is a mixture of nitric acid (ρ = 1.42 g / mL) and water with a volume ratio of 1:1;

[0093] Sulfuric acid (ρ = 1.84 g / mL);

[0094] Acetone;

[0095] Silver nitrate solution (10 g / L);

[0096] Chlorine standard solution (50 μg / ml);

[0097] The water is secondary distilled water or above in purity, at least secondary distilled water, and the water is chlorine - free water: Take 50 mL of deionized water, add 2 drops of HNO3 and 1 mL of silver nitrate solution, observe in the dark place, there should be no chlorine ion reaction; wherever reagent preparation, dilution water, etc. are involved in this method, this kind of water is referred to.

[0098] Specifically, it includes the following steps:

[0099] (1) Drawing of the working curve: Applicable to Cl content of >0.010% - 0.20%

[0100] 1. Pipette 0 mL, 0.20 mL, 0.60 mL, 0.80 mL, 1.00 mL, 1.20 mL, 1.60 mL of chlorine standard solution (50 μg / ml) into a group of 100 - mL volumetric flasks, add 3 mL of 1:1 nitric acid, dilute to 30 mL with water, and mix well. Add 2 mL of acetone, mix well, add 2 mL of silver nitrate solution, dilute to the mark with water, and mix well. Place the volumetric flask in a water bath at 70 °C and heat for 8 min, take it out, cool it to room temperature with running water, transfer it to a dark room and place it for 10 min, and mix well.

[0101] 2. Transfer a part of the colored solution (2 mL) into a 1 - cm cuvette, and measure its absorbance at a wavelength of 440 nm on a spectrophotometer. With the chlorine content as the abscissa and the absorbance as the ordinate, draw the working curve as shown Figure 2 in the figure.

[0102] (2) Distillation and testing of the sample

[0103] 3. Sample distillation: After the temperature of the pre-distilled sulfuric acid in the distillation flask drops to 25 °C, weigh 0.50 g of the ternary precursor battery material sample and add it to the distillation flask. Connect the distillation device and conduct distillation. Heat to raise the temperature of the solution in the distillation flask, adjust the steam flow rate and heating power, and control the temperature at 200 °C. After receiving the liquid for 10 min, remove the receiving flask, transfer the solution in the receiving flask to a 100 mL volumetric flask, dilute it to the mark with water, shake well, and set aside. Conduct a blank sample test in the same way.

[0104] Pre-distillation and purification of sulfuric acid: Place 150 mL of water in the distillation flask of the steam distillation device, heat it to boiling, and set aside. Take 15 mL of water and place it in a 200 mL receiving flask as the absorption liquid, set aside. Add 100 mL of sulfuric acid to the distillation flask, wash the bottle mouth with water, and add zeolite. Connect the distillation device. Heat the solution in the distillation flask, adjust the steam flow rate and heating power to maintain the temperature at 180 °C, stop heating after distilling for 30 min, and discard the receiving liquid.

[0105] 4. Pipette a portion of the solution into a 100 ml glass volumetric flask.

[0106] 5. Add water to a volume of approximately 30 mL, add 3 mL of nitric acid, mix well, add 2 mL of acetone, mix well, add 2 mL of silver nitrate solution, dilute to the mark with water, and mix well. Place the volumetric flask in a water bath at 70 °C (±1 °C) and heat for 8 min, take it out, cool it to room temperature with running water, transfer it to a dark room and let it stand for 10 min, and mix well.

[0107] 6. Transfer a portion of the solution (2 mL) into a 1 cm cuvette. Use the blank solution of the test sample as the reference, measure its absorbance at a wavelength of 440 nm on a spectrophotometer, and calculate the mass of chlorine from the corresponding working curve.

[0108] Repeat the test 11 times according to the same process, calculate according to formula (1), and the results are shown in Table 1. It is determined that the chlorine content in the measured sample is 0.0160 wt.%.

[0109] The above chemical reaction mainly decomposes the test sample with sulfuric acid. The chlorine in it escapes with the steam and is separated from the sample, absorbed by water, and determined by spectrophotometry. Add silver nitrate to form a suspension, measure the absorbance at 440 nm, deduct the reagent blank, and obtain the mass concentration of chloride ions from the working curve. Its absorbance is proportional to the chlorine content within a certain concentration range.

[0110] Table 1 Results of precision test

[0111]

[0112] From the results in Table 1, it can be seen that the RSD of the chlorine element content is 2.93% - 3.70%, indicating that the precision of this method is good and it can meet the analysis requirements.

[0113] Table 2 Spike recovery test

[0114]

[0115] It can be seen from the results in Table 2 that the spike recovery rate of the chlorine content in the ternary precursor battery material measured according to this experimental method is 95.4% - 101.2%, with high accuracy and meeting the analysis requirements.

Claims

1. A method for analyzing and testing the chlorine content in a ternary precursor battery material, which is determined by the silver chloride turbidimetric spectrophotometry, and includes the following steps: (1) Sample distillation: When the temperature of the pre-distilled sulfuric acid drops to 25°C - 70°C, weigh a sample of the ternary precursor battery material and add it to the distillation flask. Connect the distillation device for distillation; heat to raise the temperature of the solution in the distillation flask, adjust the steam flow rate and heating power, control the temperature at 100°C - 200°C. After receiving the liquid, remove the receiving flask, transfer the solution in the receiving flask to a volumetric flask, dilute it to the mark with water, shake well, and set aside; perform a blank sample simultaneously. (2) Pipette a part of the solution into a glass volumetric flask. (3) Add water to a certain volume, add nitric acid, mix well, then add acetone, mix well, and finally add silver nitrate solution, dilute to the mark with water, and mix well; place the volumetric flask in a water bath for heating, take it out, cool it to room temperature with running water, transfer it to a dark room for placement, and mix well. (4) Transfer a part of the solution into a colorimetric cell, use the blank solution of the test sample as a reference, measure its absorbance at a wavelength of 410 - 460 nm on a spectrophotometer, and calculate the mass of chlorine from the corresponding working curve.

2. The analytical test method for the chlorine content in the ternary precursor battery material according to claim 1, wherein: The mass-volume ratio of the mass of the ternary precursor battery material sample weighed to the total volume of the test solution diluted to the mark with water is 0.05 g:100 ml to 1.00 g:100 ml.

3. The analytical test method for the chlorine content in the ternary precursor battery material according to claim 1, wherein: The time for receiving the liquid is 10 min - 40 min.

4. The analytical test method for the chlorine content in the ternary precursor battery material according to claim 1, wherein: A method for pre-distilling and purifying sulfuric acid includes the following steps: Place 150 - 300 volume parts of water in the distillation flask of the steam distillation device, heat it to boiling, and set aside; place 5 - 20 volume parts of water in a receiving flask of 50 - 200 volume parts as an absorption liquid, and set aside; add 20 - 100 volume parts of sulfuric acid to the distillation flask, wash the bottle mouth with water, add zeolite, and connect the distillation device; heat the solution in the distillation flask, adjust the steam flow rate and heating power to maintain the temperature at 100°C - 200°C, stop heating after distilling for 10 min - 40 min, and discard the receiving liquid.

5. The analytical test method for the chlorine content in the ternary precursor battery material according to claim 1, characterized in that: After diluting to the mark with water, the addition amount of nitric acid is 1 vol.% - 5 vol.%, the addition amount of acetone is 1 vol.% - 5 vol.%, and the addition amount of silver nitrate solution is 1 vol.% - 5 vol.%; the heating temperature in the water bath is 70°C ± 1°C, and the time is 5 min - 15 min; transfer it to a dark room for placement for 5 min - 15 min.

6. The analytical test method for the chlorine content in the ternary precursor battery material according to claim 5, characterized in that: The nitric acid is concentrated nitric acid with a mass fraction of 65% - 70%, and the mass concentration of the silver nitrate solution is 5 g / L - 15 g / L.

7. The analytical test method for the chlorine content in the ternary precursor battery material according to claim 1, characterized in that: The diameter of the colorimetric cell is 1 - 3 cm, and the volume of the transferred part of the solution is 1 mL - 3 mL.

8. The analytical test method for the chlorine content in the ternary precursor battery material according to claim 1, wherein: The method for drawing the working curve includes the following steps: (I) Applicable to a Cl content of 0.005 wt.% - 0.010 wt.% (1) Pipette 0, 0.50, 1.00, 2.00, 3.00, 4.00 mL of chlorine standard solution into a group of 100 mL volumetric flasks, add 1:1 nitric acid, dilute to a certain volume with water, and mix well; then add acetone and mix well. Finally, add silver nitrate solution and dilute to the mark with water, and mix well. Place the volumetric flasks in a water bath and heat, take out, cool to room temperature with running water, transfer to a dark room and place, and mix well. The concentration of the chlorine standard solution is 10 μg / ml; (2) Transfer part of the colored solution into a colorimetric cell, and measure its absorbance at a wavelength of 430 nm on a spectrophotometer. Plot a working curve with the chlorine content as the abscissa and the absorbance as the ordinate; (2) Applicable to Cl content greater than 0.010 wt.% and less than or equal to 0.20 wt.% (1) Pipette 0 mL, 0.20 mL, 0.60 mL, 0.80 mL, 1.00 mL, 1.20 mL, 1.60 mL of chlorine standard solution into a group of 100 mL volumetric flasks, add 1:1 nitric acid, dilute to a certain volume with water, and mix well; then add acetone and mix well. Finally, add silver nitrate solution and dilute to the mark with water, and mix well. Place the volumetric flasks in a water bath and heat, take out, cool to room temperature with running water, transfer to a dark room and place, and mix well. The concentration of the chlorine standard solution is 50 μg / ml; (2) Transfer part of the colored solution into a colorimetric cell, and measure its absorbance at a wavelength of 410 - 460 nm on a spectrophotometer. Plot a working curve with the chlorine content as the abscissa and the absorbance as the ordinate.

9. The analytical test method for the chlorine content in the ternary precursor battery material according to claim 8, characterized in that: After diluting to the mark with water, the addition amount of nitric acid is 1 vol.% - 5 vol.%, the addition amount of acetone is 1 vol.% - 5 vol.%, and the addition amount of silver nitrate solution is 1 vol.% - 5 vol.%; the mass concentration of the silver nitrate solution is 5 g / L - 15 g / L; the heating temperature in the water bath is 70°C ± 1°C, and the time is 5 min - 15 min; transfer to a dark room and place for 5 min - 15 min.

10. The analytical test method for the chlorine content in the ternary precursor battery material according to claim 1, wherein: For the calculation of the analysis result, the chlorine content is calculated as the mass fraction w, and the value is expressed in %, and is calculated according to formula (1): In the formula: m1——The mass of chlorine calculated from the working curve, in micrograms; V0——The total volume of the test solution, in milliliters; m0——The mass of the test sample, in grams; V1——The volume of the aliquot of the test solution, in milliliters.

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