Method for determining average valence state of transition metal in NCM lithium battery material

Abstract

The invention discloses a method for determining the average valence state of transition metal in an NCM lithium battery material, and relates to the technical field of chemical analysis. Determining the total amount of transition metal in unit mass of the NCM lithium battery material through an EDTA complexometric titration method; the method comprises the following steps: reducing more than bivalent transition metal in the NCM lithium battery material by using an acidic potassium iodide solution, oxidizing the transition metal into elemental iodine, and titrating the elemental iodine by using a sodium thiosulfate standard solution, so as to obtain the total amount of the actually reduced transition metal in the NCM lithium battery material per unit mass; and finally, calculating the average valence state of the transition metal in the NCM lithium battery material by combining the total amount of the transition metal in the unit mass of the NCM lithium battery material and the total amount of the actually reduced transition metal in the unit mass of the NCM lithium battery material. The detection method provided by the invention is simple and quick to operate, high in test speed and stable and accurate in result, and completely meets the requirement of timely monitoring of large-scale and continuous industrial production and the requirement of research and development on accurate determination.

Description

Technical Field

[0001] The invention relates to the technical field of chemical analysis, and in particular to a method for determining the average valence state of transition metals in NCM lithium battery materials. Background Art

[0002] With the rapid development of new energy technologies, the application of lithium batteries is becoming more and more extensive. The positive electrode material of ternary lithium-ion batteries has the advantages of high specific capacity, wide discharge voltage range, stable electrochemical performance, and good safety performance, and occupies a very important proportion in lithium battery materials. Nickel-cobalt-manganese ternary positive electrode materials were developed the earliest, and people have also studied this material very thoroughly; people have found that in theory, the molecular formula of a certain type of nickel-cobalt-manganese ternary precursor is: Ni 1 / 3 Mn 1 / 3 Co 1 / 3 (OH)2, the average valence state of transition metals is +2; however, in fact, NCM ternary precursors are easily oxidized when exposed to air, especially at high temperatures, and are first converted to Ni 1 / 3 Mn 1 / 3 Co 1 / 3 (OOH); the commercial product (NCM ternary precursor) may be a mixture of hydroxide and oxyhydroxide, as reported by Yabuuchi et al.

[0003] As for whether the NCM ternary precursor is a hydroxide, an oxyhydroxide, or a mixture thereof, we can actually test the average valence state of the transition metal in the precursor product, and thus deduce the specific phase state of the ternary precursor. There are many instruments that can analyze the valence state of elements, but the accuracy is not high, too many can only be qualitative analysis, and the instrument price is very expensive.

[0004] There is an authorized patent "Authorization Announcement No. CN 100533131C", which uses conventional chemical methods to determine the average valence of cobalt in cobalt compounds; the specific scheme is: an acidic solution containing ferrous ions is brought into contact with the cobalt compound, and the divalent iron reduces the cobalt with a valence of more than 2 to divalent cobalt, thereby completely dissolving the cobalt compound, and the divalent iron is oxidized to trivalent iron; the pH value is adjusted to completely precipitate the trivalent ferrous ions, and the ferrous ions are kept dissolved, and the trivalent iron is filtered to separate; an ICP instrument is used to determine the molar number of cobalt and iron elements in the filtrate; and the average valence of cobalt in the cobalt compound is calculated based on the content of divalent iron and divalent cobalt (actually total cobalt) in the filtrate, as well as the amount of divalent iron added. In this method, since ferric iron needs to be separated by precipitation and ferrous iron is easily oxidized, errors will be introduced in the precipitation and filtration separation process; in addition, the remaining ferrous iron content and total cobalt content are both determined by ICP method, and the error of ICP measurement of constant elements is large; in the 8 parallel samples in the two embodiments of the authorized patent, the average valence test relative standard deviations are 0.26% and 0.27% respectively, and there is still room for improvement.

[0005] Therefore, there is an urgent need to provide a simple, fast and stable average valence state detection method that can accurately detect the average valence state of transition metals in the nickel-cobalt-manganese ternary precursor.

[0006] In view of this, the present invention is proposed. Summary of the invention

[0007] The purpose of the present invention is to provide a method for determining the average valence state of transition metals in NCM lithium battery materials, aiming to provide a simple, fast and stable average valence state detection method to accurately detect the average valence state of transition metals in nickel-cobalt-manganese ternary precursors.

[0008] The present invention is achieved in that:

[0009] The present invention provides a method for determining the average valence state of transition metals in NCM lithium battery materials, comprising: dissolving the NCM lithium battery materials to obtain a nickel-cobalt-manganese solution, and determining the total amount of transition metals in the NCM lithium battery materials per unit mass;

[0010] The divalent or higher transition metals in the NCM lithium battery material are reduced by an acidic potassium iodide solution, and the iodine content oxidized to elemental iodine is titrated by a sodium thiosulfate standard solution, thereby obtaining the total amount of transition metals actually reduced per unit mass in the NCM lithium battery material;

[0011] The average valence state of the transition metal in the NCM lithium battery material is calculated by combining the total amount of transition metal in the NCM lithium battery material per unit mass and the total amount of transition metal actually reduced in the NCM lithium battery material per unit mass.

[0012] In an optional embodiment, the NCM lithium battery material is dissolved in a hydrochloric acid solution to obtain the nickel-cobalt-manganese solution, and the solution is titrated using an EDTA standard solution. An ammonia-ammonium chloride buffer solution and a murexide indicator are added, and the EDTA standard solution is continuously titrated until it turns purple-red, and the volume of the EDTA standard solution consumed by the titration sample is recorded;

[0013] The calculation formula for the total amount of transition metals in the NCM lithium battery material is as follows:

[0014]

[0015] Where:

[0016] n 过渡金属总量 ——Indicates the total amount of transition metal per unit mass, in millimole per gram (mmol / g);

[0017] c——represents the concentration of the EDTA standard solution, in moles per liter (mol / L);

[0018] V2——indicates the volume of EDTA standard solution consumed by the titration sample, in milliliters (mL);

[0019] V0——indicates the volume of EDTA standard solution consumed in titrating the blank sample, in milliliters (mL);

[0020] V3——indicates the volume of the sample taken, in milliliters (mL);

[0021] V4——indicates the constant volume of the sample, in milliliters (mL);

[0022] m——represents the mass of the sample when the total amount of transition metal is measured, in grams (g).

[0023] In an optional embodiment, the NCM lithium battery material and the hydrochloric acid solution are mixed, then heated and fixed to volume to obtain the nickel-cobalt-manganese solution; a portion of the nickel-cobalt-manganese solution is diluted and titrated with the EDTA standard solution to 1 mL-3 mL before the endpoint, and then an ammonia-ammonium chloride buffer solution with a pH value of 9-10 and the murexide indicator are added, and the EDTA standard solution is continued to be titrated until it turns purple.

[0024] In an optional embodiment, the sample weight of the NCM lithium battery material is 0.2000g-0.2100g;

[0025] And / or, the fixed volume of the NCM lithium battery material is 200.0 mL;

[0026] And / or, the aliquot volume is 25.00 mL.

[0027] In an optional embodiment, the process of obtaining the total amount of transition metals actually reduced in a unit mass of the NCM lithium battery material includes: mixing the NCM lithium battery material with water, potassium iodide solution and sulfuric acid solution, and then promoting the oxidation-reduction reaction by heating in a water bath and magnetic stirring in a sealed, light-proof container to completely dissolve the NCM lithium battery material; wherein potassium iodide is oxidized into elemental iodine, and transition metals with a valence of two or more are reduced to divalent metals, and the total amount of transition metals actually reduced in a unit mass of the NCM lithium battery material can be calculated by titrating the elemental iodine content.

[0028] In an optional embodiment, the iodine content oxidized to elemental iodine is subjected to redox titration using a sodium thiosulfate standard solution, and the titration is suspended when the wine red color of the solution becomes lighter and is about to disappear. After adding a starch indicator, the solution turns blue, and then titrated until the blue disappears, and the volume of the sodium thiosulfate standard solution consumed is recorded; the calculation formula for the total amount of transition metal actually reduced in the NCM lithium battery material per unit mass is as follows:

[0029]

[0030] Where:

[0031] n 被还原过渡金属总量 ——Indicates the total amount of reduced transition metal per unit mass, in millimole per gram mmol / g;

[0032] c0——indicates the concentration of sodium thiosulfate standard solution, in moles per liter (mol / L);

[0033] V 01 ——Indicates the volume of sodium thiosulfate standard solution consumed by the titration sample, in milliliters (mL);

[0034] V 00 ——Indicates the volume of sodium thiosulfate standard solution consumed in titrating the blank sample, in milliliters (mL);

[0035] m0——represents the mass of the sample during the potassium iodide reduction reaction, in grams (g).

[0036] In an optional embodiment, during the mixed reaction with potassium iodide solution and sulfuric acid solution, the reaction conditions are controlled to be closed and light-proof.

[0037] In an optional embodiment, during the mixed reaction with the potassium iodide solution and the sulfuric acid solution, the water bath reaction temperature is controlled to be 40° C.-80° C., and the reaction time is more than 10 min;

[0038] And / or, magnetic stirring is used during the mixing reaction with the potassium iodide solution and the sulfuric acid solution.

[0039] In an optional embodiment, the amount of potassium iodide in the lithium battery material and the potassium iodide solution is controlled so that the consumption volume of sodium thiosulfate is 10-15 mL during the indirect iodometric titration process.

[0040] In an optional embodiment, the average valence state of the transition metal in the NCM lithium battery material is calculated as follows:

[0041]

[0042] Where:

[0043] n 被还原过渡金属总量 ——Indicates the total amount of reduced transition metal per unit mass, in millimole per gram (mmol / g);

[0044] n 过渡金属总量 ——Indicates the total amount of transition metal per unit mass, in millimole per gram (mmol / g).

[0045] The present invention has the following beneficial effects: the total amount of transition metals in a unit mass of NCM lithium battery materials is determined by EDTA complexometric titration; the divalent or higher transition metals in the NCM lithium battery materials are reduced by an acidic potassium iodide solution, and the iodine content oxidized to elemental iodine is titrated by a sodium thiosulfate standard solution, thereby obtaining the total amount of transition metals actually reduced in the unit mass of the NCM lithium battery materials; finally, the total amount of transition metals in the unit mass of the NCM lithium battery materials and the total amount of transition metals actually reduced in the unit mass of the NCM lithium battery materials are combined to calculate the average valence state of the transition metals in the NCM lithium battery materials. The detection method provided by the present invention is simple and fast to operate, has a fast test speed, and has stable and accurate results, which fully meets the needs of timely monitoring of large-scale and continuous industrial production, as well as the needs of research and development for accurate determination. DETAILED DESCRIPTION

[0046] In order to make the purpose, technical scheme and advantages of the embodiments of the present invention clearer, the technical scheme in the embodiments of the present invention will be described clearly and completely below. If the specific conditions are not specified in the embodiments, they are carried out according to conventional conditions or conditions recommended by the manufacturer. If the manufacturer of the reagents or instruments used is not specified, they are all conventional products that can be purchased commercially.

[0047] The embodiment of the present invention provides a method for determining the average valence state of transition metals in NCM lithium battery materials, comprising the following steps:

[0048] S1. Determination of the total amount of transition metals per unit mass of NCM lithium battery materials

[0049] Dissolve the NCM lithium battery material to obtain a nickel-cobalt-manganese solution, and use the EDTA complexometric titration method to determine the total amount of transition metals in the unit mass of NCM lithium battery material. The total amount of transition metals in the material is determined by the EDTA complexometric titration method. The classic EDTA complexometric titration method for determining constants can reduce errors and ensure the accuracy and stability of the measurement results. Compared with the ICP method, the constant complexometric titration method is used to determine the total amount of nickel, cobalt and manganese in the material, which can improve the accuracy and stability of the test results.

[0050] In some embodiments, the total amount of nickel, cobalt and manganese in the material can be determined by EDTA complexometric titration in accordance with the industry standard "YS / T 1006.1-2014 Chemical Analysis Method for Lithium Nickel, Cobalt and Manganese Oxide Part 1 Determination of the Total Amount of Nickel, Cobalt and Manganese EDTA Titration Method"; in the calculation stage, the average molar mass of nickel, cobalt and manganese is not required, and only the amount of nickel, cobalt and manganese per unit mass of the material is calculated; thereby obtaining an accurate and stable total amount of nickel, cobalt and manganese determination value.

[0051] Further, the specific steps are as follows: use hydrochloric acid solution to dissolve NCM lithium battery material to obtain nickel-cobalt-manganese solution, use EDTA standard solution for titration, add ammonia-ammonium chloride buffer solution and murexide indicator 1mL-3mL before the end point, continue to titrate with EDTA standard solution until purple-red, and record the volume of EDTA standard solution consumed by the titrated sample; at the same time, perform a blank test and record the volume of EDTA standard solution consumed by the blank sample. In the blank test, except for not adding NCM lithium battery material, other raw materials are added and the titration steps are the same. The total amount of transition metals in NCM lithium battery material is calculated as shown in formula (1):

[0052]

[0053] In the formula,

[0054] n 过渡金属总量 ——Indicates the total amount of transition metal per unit mass, in millimole per gram (mmol / g);

[0055] c——indicates the concentration of EDTA standard solution, in moles per liter (mol / L);

[0056] V2——indicates the volume of EDTA standard solution consumed by the titration sample, in milliliters (mL);

[0057] V0——indicates the volume of EDTA standard solution consumed in titrating the blank sample, in milliliters (mL);

[0058] V3——indicates the volume of the sample taken, in milliliters (mL);

[0059] V4——indicates the fixed volume of the sample, in milliliters (mL);

[0060] m——represents the mass of the sample when the total amount of transition metal is measured, that is, the mass of the sample NCM lithium battery material, in grams (g).

[0061] In some embodiments, NCM lithium battery material and hydrochloric acid solution are mixed, then heated to promote dissolution, and fixed volume to obtain nickel-cobalt-manganese solution; the sample weight is 0.2000-0.2100 g, such as 0.2077 g or 0.2013 g; the fixed volume is 200.0 mL, and the fraction volume is 25.00 mL.

[0062] Further, 25.00 mL of the nickel-cobalt-manganese solution is diluted and pre-titrated with the EDTA standard solution to 1 mL to 3 mL (such as 1 mL, 2 mL, 3 mL, etc.) before the end point, and then an ammonia-ammonium chloride buffer solution with a pH value of 9 to 10 and a murexide indicator are added, and the EDTA standard solution is continued to be titrated to purple-red. Before adding the ammonia-ammonium chloride buffer solution, the pre-added amount of the EDTA standard solution is calculated according to the total amount of the EDTA standard solution required. If the total amount required is approximately 25 mL, about 23 mL is added here.

[0063] S2. Determine the total amount of transition metals actually reduced per unit mass of NCM lithium battery materials

[0064] An acidic potassium iodide solution is used to reduce the divalent or higher transition metals in the NCM lithium battery material, and the iodine content oxidized to elemental iodine is titrated with a sodium thiosulfate standard solution. The total amount of transition metals actually reduced per unit mass of the NCM lithium battery material is calculated based on the amount of iodine oxidized to elemental iodine. The embodiment of the present invention uses potassium iodide as a reducing agent, and the elemental iodine generated by oxidation can react chemically with sodium thiosulfate, while potassium iodide (reducing agent) does not react chemically with sodium thiosulfate. Therefore, there is no need for a precipitation filtration separation process, the simplified operation steps, and the error source are reduced.

[0065] It should be added that some NCM ternary precursor manufacturers produce unqualified ternary precursors and need to be reworked; these waste materials must be re-dissolved with acid, but hydrochloric acid cannot be added to dissolve, because hydrochloric acid is volatile and easily corrodes equipment, and sulfuric acid must be used for re-dissolution. However, sulfuric acid is not a reducing acid, and waste materials cannot be dissolved with sulfuric acid alone, so a reducing agent must be added, and the reducing agent is generally hydrogen peroxide. There are many methods for detecting and analyzing hydrogen peroxide, and there are two constant titration analysis methods, one is potassium permanganate titration, and the other is iodine titration; the iodine titration method can be used to determine the content of hydrogen peroxide, which means that the reducing ability of potassium iodide is significantly stronger than that of hydrogen peroxide. Through the above analysis, it can be seen that hydrogen peroxide can reduce the ternary precursor, so potassium iodide is more likely to reduce the ternary precursor, which demonstrates the feasibility of the reduction method provided by the embodiment of the present invention.

[0066] In some embodiments, the process of obtaining the total amount of transition metal actually reduced in a unit mass of NCM lithium battery material comprises: (1) mixing the NCM lithium battery material with water, and then reacting the mixture with potassium iodide solution and sulfuric acid solution to reduce the divalent or higher transition metal in the material to divalent metal under acidic conditions, wherein the acidic potassium iodide can completely dissolve the NCM lithium battery material (such as the NCM ternary precursor), and the dissolved solution is transparent and clear without any insoluble matter; (2) titrating the solution after the reaction with a sodium thiosulfate standard solution, and pausing the titration when the wine red color of the solution becomes lighter and is about to disappear, adding a starch indicator solution to turn blue, and then titrating until the blue color disappears, and recording the volume of the sodium thiosulfate standard solution consumed; (3) simultaneously performing a blank test, and recording the volume of the sodium thiosulfate standard solution consumed in the blank test. In the blank test, except that the NCM lithium battery material is not added, the other raw materials and steps refer to (1) and (2).

[0067] The calculation formula for the total amount of transition metal actually reduced in unit mass of NCM lithium battery material is as follows:

[0068]

[0069] Where:

[0070] n 被还原过渡金属总量 ——Indicates the total amount of reduced transition metal per unit mass, in millimole per gram (mmol / g);

[0071] c0——indicates the concentration of sodium thiosulfate standard solution, in moles per liter (mol / L);

[0072] V 01 ——Indicates the volume of sodium thiosulfate standard solution consumed by the titration sample, in milliliters (mL);

[0073] V 00 ——Indicates the volume of sodium thiosulfate standard solution consumed in titrating the blank sample, in milliliters (mL);

[0074] m0——represents the mass of the sample during the potassium iodide reduction reaction, in grams (g).

[0075] It should be noted that in the redox reaction, the amount of nickel, cobalt and manganese transition metals reduced is equal to the amount of elemental iodine generated; the number of electrons lost by potassium iodide is equal to the number of electrons gained by the transition metal. Therefore, by measuring the content of elemental iodine, the content of the reduced transition metal can be obtained. The method of using sodium thiosulfate to determine elemental iodine is a classic redox method (also known as iodometric method), and the accuracy and stability of the method are beyond doubt.

[0076] In some embodiments, during the reaction of the NCM sample with the potassium iodide solution and the sulfuric acid solution, the reaction conditions are controlled to be closed and light-proof. The closed environment isolates the air, reducing the interference of air oxidation; the light-proof dissolution avoids the interference of light. The reaction process can be carried out in a water bath, and the reaction process is combined with magnetic stirring, magnetic stirring, and water bath heating to accelerate the redox reaction rate. In the redox process, interference is avoided as much as possible and the reaction speed is accelerated, so as to ensure that the reaction is complete and not disturbed; through the above measures, complex operations are avoided, the reaction is ensured to be complete, and interference is avoided as much as possible, thereby improving the accuracy and stability of the test results.

[0077] Specifically, a 25 mL volumetric flask can be used as a closed reaction container. With the stopper tightly closed, a sealed environment can be created to complete the redox dissolution reaction, which can prevent the potassium iodide reducing agent from being oxidized by air and the NCM ternary precursor from being oxidized by air. A constant temperature magnetic stirrer can be used to stir the solution with a magnetic stirrer to speed up the reaction, and to speed up the reaction by heating in a water bath. Using water bath heating can better control the reaction temperature and avoid volatilization of elemental iodine vapor caused by excessive temperature.

[0078] Furthermore, during the mixed reaction with potassium iodide solution and sulfuric acid solution, the water bath reaction temperature is controlled to be 40°C-80°C, such as 40°C, 50°C, 60°C, 70°C, 80°C, etc.; the reaction time can be 10min, 15min, 20min, etc., and magnetic stirring is used during the reaction to accelerate the reaction speed and avoid interference. For easily soluble samples, such as NCM ternary precursors, the reaction temperature is controlled in the range of 40°C to 60°C, and the reaction time is controlled to be more than 10min, such as 10min to 20min; for difficultly soluble samples, such as NCM ternary cathode materials, the reaction temperature is controlled in the range of 60°C to 80°C, and the reaction time is controlled to be more than 10min, such as 10min to 20min.

[0079] Furthermore, the sample weight of the NCM lithium battery material and the amount of potassium iodide solution added are controlled to ensure that after the sample is completely dissolved and clear, the consumption of the sodium thiosulfate standard solution is preferably 10mL to 15mL (such as 10mL, 13mL, 15mL) during the indirect iodine titration process; in this way, the redox reaction is ensured to be thorough and the precision of the titration result can be improved. For example: when the sample weight of the NCM sample is not less than 0.2g, 10mL (200g / L) of potassium iodide solution is fixedly added, and the titration volume of the sodium thiosulfate standard solution is preferably 10mL to 15mL by increasing or decreasing the sample weight; when the sample weight of the NCM sample is not less than 0.2g, the sample weight of the NCM sample is fixed, and the titration volume of the sodium thiosulfate standard solution is preferably 10mL to 15mL by increasing or decreasing the amount of potassium iodide solution added.

[0080] S3. Calculate the average valence of transition metals in NCM lithium battery materials

[0081] The average valence of transition metals in NCM lithium battery materials is calculated by combining the total amount of transition metals in NCM lithium battery materials per unit mass and the total amount of transition metals actually reduced in NCM lithium battery materials per unit mass. The average valence is determined by two accurate and stable constant chemical titrations to ensure that the calculated average valence is accurate and stable.

[0082] In some embodiments, the average valence state of transition metals in NCM lithium battery materials is calculated as shown in formula (3):

[0083]

[0084] Where:

[0085] n 被还原过渡金属总量 ——Indicates the total amount of reduced transition metal per unit mass, in millimole per gram (mmol / g);

[0086] n 过渡金属总量 ——Indicates the total amount of transition metal per unit mass, in millimole per gram (mmol / g).

[0087] It should be noted that, through stability experiments, the relative standard deviation of our average valence test results is 0.012% to 0.038%, and the stability of the test results is significantly better (the relative standard deviations of the patent application number "CN 100533131C" are 0.26% and 0.27% respectively).

[0088] The features and performance of the present invention are further described in detail below in conjunction with the embodiments.

[0089] Example 1

[0090] In this example, the average valence state of sample 1# (close to a +2-valent NCM ternary hydroxide precursor, with a molar percentage of nickel, cobalt and manganese of 88%:6%:6%) was determined.

[0091] In this example, 7 parallel samples were measured to verify the stability of the method.

[0092] The specific steps are as follows:

[0093] (1) Determination of total amount of transition metals:

[0094] ① Calibrate the EDTA standard solution according to the industry standard “YS / T 1006.1-2014 Chemical analysis method of lithium nickel cobalt manganese oxide Part 1 Determination of total nickel, cobalt and manganese EDTA titration method”.

[0095] ②Sample determination:

[0096] EDTA standard solution (0.01 mol / L): weigh 3.72 g of disodium ethylenediaminetetraacetate in a 400 mL beaker, add water and heat until completely dissolved, cool to room temperature, transfer to a 1000 mL volumetric flask, dilute to scale with water, and mix well. Calibrate according to the industry standard method.

[0097] (1+1) Hydrochloric acid: obtained by mixing hydrochloric acid (ρ1.17 g / mL) with an equal volume of water.

[0098] Ammonia-ammonium chloride buffer solution pH 9-10: Weigh 54.5g of ammonium chloride and dissolve it in water, add 200mL of concentrated ammonia, dilute to 1000mL with water, and mix well.

[0099] Weigh 0.20g (0.2000g~0.2100g) of sample into a 150mL quartz beaker, add about 10mL of water to wet the sample, add 25mL (1+1) hydrochloric acid, heat on a low-temperature electric heating plate until completely dissolved, transfer to a 200.0mL volumetric flask after cooling, dilute to scale with water, and mix well. Take 25.00mL into a 250mL conical flask, add about 20mL of water, first titrate to 24mL with EDTA standard solution, then add 10mL of ammonia-ammonium chloride buffer solution and about 0.1g of murexide indicator, and continue to titrate with EDTA standard solution until purple-red.

[0100] At the same time, a blank experiment was performed; 25.00 mL of the blank solution was taken into a 250 mL conical flask, and about 20 mL of water was added. Then, 10 mL of ammonia-ammonium chloride buffer solution and about 0.1 g of murexide indicator were added, and EDTA standard solution was added dropwise until it turned purple-red.

[0101] ③Calculation of titration results:

[0102] The molar amount of nickel, cobalt and manganese in unit mass of material was calculated according to formula (1). The calculation results are shown in Table 1.

[0103] Table 1 Determination of the total amount of transition metals in sample 1#

[0104]

[0105] (2) Determination of the total amount of reduced transition metals:

[0106] ① Preparation and calibration of sodium thiosulfate standard solution:

[0107] According to the national standard "GB / T 601-2016 Preparation of standard titration solutions for chemical reagents", prepare and calibrate 0.1M sodium thiosulfate standard solution.

[0108] ②Dissolution of sample:

[0109] Add appropriate amount of water to a 500mL beaker, then wrap the beaker with a cardboard box to protect it from light, place it on a constant temperature magnetic stirrer, heat it at a fixed temperature of 50℃, and wait until the heating light goes out, indicating that the water temperature in the beaker has reached 50℃, and it is used as a reaction water bath.

[0110] Weigh 0.35g of the sample into a clean and dry 25mL volumetric flask, rinse the flask mouth with 2mL of water; add a stirring bar into the flask, rinse the flask mouth with 1mL of water again; transfer 10mL of potassium iodide solution (200g / L) into the flask, rinse the flask mouth with 2mL of water; transfer 5mL (1+1) of sulfuric acid into the flask, cover the bottle stopper, and then seal the bottle mouth with transparent tape.

[0111] Place the volumetric flask in a water bath to heat it and start stirring. Cover it with cardboard to avoid light. Start the timer. After 20 minutes, take out the volumetric flask, rinse it with water and cool it to room temperature.

[0112] ③Titration of samples:

[0113] Cut the tape with scissors, rinse the bottle cap with a washing bottle, connect the washing liquid to a 250mL conical flask, transfer all the liquid in the volumetric flask to the conical flask, and rinse the volumetric flask at least 3 times, and collect them in the conical flask. Note that the test solution in the conical flask should be no less than 200mL. At this time, the solution is wine red and transparent, and no insoluble matter can be observed. (If insoluble matter is found, it means that the dissolution is incomplete: the reaction time is not enough, the reaction temperature is not enough, the sample amount is too much, and the reducing agent potassium iodide is not added enough; find the reason and dissolve the sample again).

[0114] Use sodium thiosulfate standard solution to titrate. When the wine red color in the sample becomes lighter and is about to disappear, stop titration and rinse the bottle mouth with water. Then add 2mL starch indicator (10g / L). At this time, the solution is blue. Titrate carefully to the end point. At this time, the end point color is the complete disappearance of starch blue.

[0115] ④Determination of blank samples:

[0116] The blank value is determined along with the sample, except that no sample is added. The addition of other reagents is the same as the sample test, and the reaction temperature and reaction time are also exactly the same. During titration, starch indicator is added first, and then sodium thiosulfate standard solution is used for titration. The endpoint changes from blue to colorless.

[0117] ⑤Calculation of titration results:

[0118] The molar amount of reduced nickel, cobalt and manganese per unit mass of material was calculated according to formula (2). The calculation results are shown in Table 2.

[0119] Table 2 Determination of the total amount of reduced transition metals in sample 1#

[0120]

[0121] It can be seen from Table 2 that, since the average valence is close to 2, weighing 0.35 grams of sample consumes only about 5.40 mL of sodium thiosulfate standard solution, and the titration volume is a bit too low; more sample should be weighed so that the titration volume is above 10 mL, but not more than 15 mL.

[0122] (3) Calculation of average valence:

[0123] Combining the test results of the total amount of transition metals and the determination results of the total amount of reduced transition metals, we can calculate the average valence state of nickel, cobalt and manganese in sample 1# according to calculation formula (3); the calculation results are shown in Table 3.

[0124] Table 3 Average valence of samples tested 7 times

[0125]

[0126] It can be seen from the test results in Table 3 that the test method provided by the present invention has good data repeatability, and the relative standard deviation of 7 groups of test data is only 0.023%, which indicates that the potassium iodide reduction and dissolution of the ternary precursor material adopted in the present invention can avoid various interferences during the reaction process and ensure that the material is completely dissolved, thereby ensuring the stability of the test results.

[0127] Example 2

[0128] The average valence state of the 2# sample (close to the +2-valent NCM ternary hydroxide precursor, with the molar percentage of nickel, cobalt and manganese being 88%:6%:6%) tested in this example is:

[0129] In this example, 7 parallel samples were measured to verify the stability of the method. The specific operation steps are as follows:

[0130] (1) Determination of total amount of transition metals:

[0131] The titration results are consistent with those in Example 1. The specific test results are shown in Table 4.

[0132] Table 4 Determination of the total amount of transition metals in sample 2#

[0133]

[0134] (2) Determination of the total amount of reduced transition metals:

[0135] The titration situation is consistent with that of Example 1, except that the amount of sample weighed is increased. The specific test results are shown in Table 5.

[0136] Table 5 Determination of the total amount of reduced transition metals in sample 2#

[0137]

[0138] It can be seen from Table 5 that when we increase the sample weight to more than 0.70 g, the titration volume is more than 10 mL; the consumption volume of 0.90 g sample sodium thiosulfate is 13.20 mL, which is consistent with our imagined titration volume.

[0139] (3) Calculation of average valence:

[0140] Combining the test results of the total amount of transition metals and the determination results of the total amount of reduced transition metals, we can calculate the average valence state of nickel, cobalt and manganese in sample 2# according to calculation formula (3); the calculation results are shown in Table 6.

[0141] Table 6 Average valence of samples after 7 tests

[0142]

[0143] It can be seen from the test results in Table 6 that the test method provided by the present invention has good data repeatability, and the relative standard deviation of 7 groups of test data is only 0.027%, which indicates that the potassium iodide reduction and dissolution of the ternary precursor material adopted in the present invention can avoid various interferences during the reaction process and ensure that the material is completely dissolved, thereby ensuring the stability of the test results.

[0144] Example 3

[0145] This example re-measures the average valence state of sample 1# (close to the +2-valence NCM ternary precursor):

[0146] Since the titration volume of the sodium thiosulfate standard solution in the previous redox titration process of sample 1# was only about 5.4mL, the titration volume was too small; this time, the retest increased the sample weight to see whether the relative standard deviation of the average valence state could be reduced. This example verifies the stability of the method by measuring 7 parallel samples. The specific operating steps are as follows:

[0147] (1) Determination of total amount of transition metals:

[0148] Same as Example 1, no repeated measurements were performed.

[0149] (2) Determination of the total amount of reduced transition metals:

[0150] The titration was consistent with that in Example 1, except that the water bath time was changed to 15 minutes and the amount of sample weighed was increased. The specific test results are shown in Table 7.

[0151] Table 7 Re-determination of the total amount of reduced transition metals in sample 1#

[0152]

[0153] It can be seen from Table 7 that when we increase the sample weight to above 0.74 g, the titration volume is above 10 mL; the consumption volume of 0.8121 g sample sodium thiosulfate is 11.88 mL, both of which are in line with our imagined titration volume.

[0154] (3) Calculation of average valence:

[0155] Combining the test results of the total amount of transition metals and the determination results of the total amount of reduced transition metals, we can recalculate the average valence state of nickel, cobalt and manganese in sample 1# according to calculation formula (3); the calculation results are shown in Table 8.

[0156] Table 8 Average valence of samples after 7 tests

[0157]

[0158] It can be seen from the test results in Table 8 that the test method provided by the embodiment of the present invention has good data repeatability, and the relative standard deviation of the 7 groups of test data is only 0.012%; this indicates that the potassium iodide used in the present invention to reduce and dissolve the ternary precursor material can avoid various interferences during the reaction while ensuring that the material is completely dissolved, thereby ensuring the stability of the test results; at the same time, compared with Example 1, the relative standard deviation is smaller, indicating that in the redox titration process, the titration volume of sodium thiosulfate is kept as high as possible and not less than 10 mL, which is beneficial to improving the precision of the test results.

[0159] Example 4

[0160] This example measures the average valence of sample #3 (normal ternary precursor):

[0161] Examples 1-3 are repeatability tests on samples with an average valence state of transition metals close to +2; this example is an average valence analysis of a normal ternary precursor, and the stability of the method is also verified by measuring 7 parallel samples.

[0162] The specific steps are as follows:

[0163] (1) Determination of total amount of transition metals:

[0164] The titration results are consistent with those in Example 1. The specific test results are shown in Table 9.

[0165] Table 9 Determination of the total amount of transition metals in sample 3#

[0166]

[0167] (2) Determination of the total amount of reduced transition metals:

[0168] The titration was consistent with that in Example 1, except that the water bath time was changed to 15 minutes. The specific test results are shown in Table 10.

[0169] Table 10 Determination of the total amount of reduced transition metals in sample 3#

[0170]

[0171] As can be seen from Table 10, for this ternary precursor with a high average valence, when we only weigh 0.20g of sample, the titration volume of sodium thiosulfate is also above 10mL; so the sample weight is determined by the consumption of sodium thiosulfate. In general, the consumption volume of sodium thiosulfate cannot exceed 20mL, otherwise there is a concern that the amount of potassium iodide added is insufficient, the sample is not dissolved, and the precision of the titration result becomes poor.

[0172] (3) Calculation of average valence

[0173] Combining the test results of the total amount of transition metals and the determination results of the total amount of reduced transition metals, we can calculate the average valence state of nickel, cobalt and manganese in sample 3# according to calculation formula (3); the calculation results are shown in Table 11.

[0174] Table 11 Average valence of samples after 7 tests

[0175]

[0176] It can be seen from the test results in Table 11 that the test method provided by the embodiment of the present invention has good data repeatability, and the relative standard deviation of 7 groups of test data is only 0.038%; it shows that the potassium iodide reduction and dissolution of the ternary precursor material adopted by the present invention can avoid various interferences during the reaction process and ensure that the material is completely dissolved, thereby ensuring the stability of the test results. For this ternary precursor with a high average valence state, if an average valence state analysis is performed, the sample weight can be less to ensure that the titration volume of sodium thiosulfate is within 20mL, and the existing amount of potassium iodide added can also ensure that the redox reaction is complete.

[0177] The average valence of this batch of samples is 2.551, which is an ordinary ternary precursor product with a normal black color, that is, a normal commercial ternary precursor.

[0178] In summary, the above embodiments illustrate that the average valence test method of the present invention is simple to operate and can avoid various interferences as much as possible; the use of the classic chemical titration method can ensure both the accuracy and precision of the test results.

[0179] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for determining the average valence state of transition metals in NCM lithium battery materials, characterized in that: include: Dissolving the NCM lithium battery material to obtain a nickel-cobalt-manganese solution, and determining the total amount of transition metals in the NCM lithium battery material per unit mass; The divalent or higher transition metals in the NCM lithium battery material are reduced by an acidic potassium iodide solution, and the iodine content oxidized to elemental iodine is titrated by a sodium thiosulfate standard solution, thereby obtaining the total amount of transition metals actually reduced per unit mass in the NCM lithium battery material; The average valence state of the transition metal in the NCM lithium battery material is calculated by combining the total amount of transition metal in the NCM lithium battery material per unit mass and the total amount of transition metal actually reduced in the NCM lithium battery material per unit mass.

2. The method according to claim 1, characterized in that The NCM lithium battery material is dissolved in hydrochloric acid solution to obtain the nickel-cobalt-manganese solution, and the EDTA standard solution is used for titration. Ammonia-ammonium chloride buffer solution and murexide indicator are added, and the EDTA standard solution is continuously used for titration until purple-red, and the volume of the EDTA standard solution consumed by the titration sample is recorded; The calculation formula for the total amount of transition metals in the NCM lithium battery material is as follows: Where: n 过渡金属总量 ——Indicates the total amount of transition metal per unit mass, in millimole per gram (mmol / g); c——represents the concentration of the EDTA standard solution, in moles per liter (mol / L); V2——indicates the volume of EDTA standard solution consumed by the titration sample, in milliliters (mL); V0——indicates the volume of EDTA standard solution consumed in titrating the blank sample, in milliliters (mL); V3——indicates the volume of the sample taken, in milliliters (mL); V4——indicates the constant volume of the sample, in milliliters (mL); m——represents the mass of the sample when the total amount of transition metal is measured, in grams (g).

3. The method according to claim 2, characterized in that The NCM lithium battery material and the hydrochloric acid solution are mixed, then heated, and the volume is fixed to obtain the nickel-cobalt-manganese solution; a portion of the nickel-cobalt-manganese solution is diluted and titrated with the EDTA standard solution to 1 mL-3 mL before the endpoint, and then the ammonia-ammonium chloride buffer solution with a pH value of 9-10 and the murexide indicator are added, and the EDTA standard solution is continued to be titrated until purple-red.

4. The method according to claim 3, characterized in that The sample weight of the NCM lithium battery material is 0.2000g-0.2100g; And / or, the fixed volume of the NCM lithium battery material is 200.0 mL; And / or, the aliquot volume is 25.00 mL.

5. The method according to claim 1, characterized in that The process of obtaining the total amount of transition metal actually reduced in the unit mass of the NCM lithium battery material includes: mixing the NCM lithium battery material with water, potassium iodide solution and sulfuric acid solution, and then promoting the oxidation-reduction reaction in a sealed container by water bath heating and magnetic stirring to completely dissolve the NCM lithium battery material; wherein potassium iodide is oxidized into elemental iodine, and transition metals with a valence of two or more are reduced to divalent metals, and the total amount of transition metal actually reduced in the unit mass of the NCM lithium battery material can be calculated by titrating the elemental iodine content.

6. The method according to claim 5, characterized in that The iodine content oxidized to elemental iodine is subjected to redox titration using a sodium thiosulfate standard solution. The titration is suspended when the wine red color of the solution becomes lighter and is about to disappear. After adding a starch indicator, the solution turns blue and is titrated again until the blue disappears. The volume of the sodium thiosulfate standard solution consumed is recorded. The total amount of transition metals actually reduced per unit mass in the NCM lithium battery material is calculated as follows: Where: n 被还原过渡金属总量 ——Indicates the total amount of reduced transition metal per unit mass, in millimole per gram mmol / g; c0——indicates the concentration of sodium thiosulfate standard solution, in moles per liter (mol / L); V 01 ——Indicates the volume of sodium thiosulfate standard solution consumed by the titration sample, in milliliters (mL); V 00 ——Indicates the volume of sodium thiosulfate standard solution consumed in titrating the blank sample, in milliliters (mL); m0——represents the mass of the sample during the potassium iodide reduction reaction, in grams (g).

7. The method according to claim 6, characterized in that During the mixed reaction with the potassium iodide solution and the sulfuric acid solution, the reaction conditions are controlled to be closed and protected from light.

8. The method according to claim 7, characterized in that During the reaction with potassium iodide solution and sulfuric acid solution, the water bath reaction temperature is controlled to be 40°C-80°C, and the reaction time is more than 10 minutes; And / or, magnetic stirring is used during the mixing reaction with the potassium iodide solution and the sulfuric acid solution.

9. The method according to claim 8, characterized in that The amount of potassium iodide in the lithium battery material and the potassium iodide solution is controlled so that the consumption volume of sodium thiosulfate is 10-15 mL during the indirect iodometric titration process.

10. The method according to claim 1, characterized in that The calculation formula for the average valence state of transition metals in the NCM lithium battery material is as follows: Where: n 被还原过渡金属总量 ——Indicates the total amount of reduced transition metal per unit mass, in millimole per gram (mmol / g); n 过渡金属总量 ——Indicates the total amount of transition metal per unit mass, in millimole per gram (mmol / g).

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