Method for testing content of silicon element in silicon-based material

Abstract

The invention belongs to the field of electrochemistry, and particularly discloses a method for testing the content of a silicon element in a silicon-based material. According to the testing method disclosed by the invention, after the silicon-based material is burnt, high-temperature alkali fusion and water dissolution treatment are sequentially carried out, and finally, the content of the silicon element is tested by adopting ICP, so that the condition that the silicon content is obtained by adopting a constant-weight weighing mode in a traditional burning gravimetric method is not needed, the repeated weighing process is reduced, the process is simplified, and the time is shortened; meanwhile, silicon is converted into water-soluble silicate in an alkali fusion mode, the content of silicon oxide and the content of silicon elementary substance can be measured at the same time, universality is high, only water is used as a solvent, corrosive solvents such as strong acid do not need to be adopted, and the method is more environmentally friendly and safer; in addition, the silicon content in the solution is measured through ICP, so that the result is more accurate, and the precision is higher.

Description

Technical Field

[0001] This application belongs to the field of electrochemistry, and particularly relates to a method for testing the silicon element content in a silicon-based material. Background Art

[0002] For lithium-ion silicon-based anode materials such as typical silicon-carbon composite materials, their silicon content has a strong correlation with the specific capacity of the battery and is one of the indicators concerned in battery production. Accurately measuring the silicon content in the silicon-based anode material has important guiding significance for predicting the specific capacity of the battery and capacity design. Currently, the silicon content is mostly measured by the ignition gravimetric method. The ignition gravimetric method is to ignite and dehydrate the silicon-based material at high temperature to generate silicon dioxide and then weigh it, and calculate the silicon content therein. However, in some silicon-based materials, such as those containing elemental silicon, especially nano-silicon, when elemental silicon reacts with oxygen at high temperature, it is easy to form a dense silicon dioxide protective film on the surface, thus preventing further reaction. Therefore, under normal conditions, this method cannot completely convert elemental silicon into silicon dioxide, resulting in a low result. In addition, the product after ignition needs to be weighed to a constant weight, which takes a long time, and silicon dioxide is easy to absorb moisture, and the weighing requires strict control of humidity, which is easy to introduce a positive error; the weighing accuracy depends on the experience of the weigher and the reproducibility is poor. Therefore, the universality of the ignition gravimetric method is not high and the measurement is inaccurate. Summary of the Invention

[0003] Aiming at the above problems existing in the prior art, this application provides a method for testing the silicon element content in a silicon-based material to improve the accuracy of measuring the silicon-based material and expand the universality of the measurement method.

[0004] To achieve the above object, a method for testing the silicon element content in a silicon-based material is provided, including the following steps:

[0005] (1) Ignite the silicon-based material sample to obtain a first product;

[0006] (2) Mix the first product with an alkali flux and then carry out an alkali fusion reaction to obtain a second product;

[0007] (3) Dissolve the second product in water to obtain a test solution;

[0008] (4) Use ICP to test the mass percentage content of silicon element in the test solution;

[0009] (5) Obtain the mass percentage content of silicon element in the silicon-based material sample according to the following calculation formula;

[0010] w Si = c×V / m×0.0001;

[0011] wherein, w Siis the mass percentage of silicon in the silicon-based material sample, in %,

[0012] c is the concentration of silicon in the solution to be tested, in μg / mL;

[0013] V is the volume of the solution to be tested, in mL;

[0014] m is the mass of the silicon-based material sample in g.

[0015] In the test method of the present application, the silicon-based material is first subjected to high-temperature calcination, which can convert part or all of the silicon element into silicon oxide, and when carbon exists in the silicon-based material, the carbon can be removed by high-temperature calcination to avoid carbon coating silicon and causing inaccurate measurement; then after alkali fusion, the silicon element is converted into silicate, which is then dissolved in water, and finally the silicon content in the aqueous solution is accurately tested by ICP. The test method of the present application does not need to use constant weight weighing to obtain its silicon content after calcination as in the traditional calcination weight method, which reduces the process of repeated weighing, simplifies the process, and shortens the time; at the same time, alkali fusion is used to convert silicon into water-soluble silicate, which can simultaneously measure the silicon content in silicon oxide and silicon element, and has high universality; and the solvent only needs water, and there is no need to use corrosive solvents such as strong acids, which is more environmentally friendly and safe; in addition, the silicon content in the solution is measured by ICP, which makes the result more accurate and more precise.

[0016] In some embodiments, in step (1), the calcination temperature is 800° C. to 1000° C., and the calcination time is 2 h to 5 h.

[0017] In some embodiments, in step (1), the heating rate to the burning temperature is 10°C / min to 20°C / min, and the burning atmosphere is air or a mixed atmosphere of oxygen and an inert gas.

[0018] In some embodiments, in step (1), the silicon-based material sample contains carbon.

[0019] In some embodiments, in step (2), the mass of the alkali flux is 12-20 g based on the mass of the silicon-based material sample per gram.

[0020] In some embodiments, in step (2), the alkali flux includes at least one of KOH and NaOH.

[0021] In some embodiments, in step (2), the temperature of the alkali fusion reaction is 400° C. to 450° C., and the time of the alkali fusion reaction is 30 min to 60 min.

[0022] In some embodiments, in step (2), the heating rate to the temperature of the alkali fusion reaction is 10°C / min to 20°C / min, and the atmosphere of the alkali fusion reaction is air or a mixed atmosphere of oxygen and an inert gas.

[0023] In some embodiments, in step (3), the mass of the water is 1500 g to 2000 g based on the mass of the silicon-based material sample per gram.

[0024] In some embodiments, in step (3), the dissolution temperature is 80 to 100° C., and the dissolution time is 60 to 90 min.

[0025] Compared with the prior art, the present application has the following beneficial effects: in the testing method of the present application, after the silicon-based material is calcined, high-temperature alkali fusion and water dissolution treatment are carried out in sequence, and finally the silicon content is tested by ICP. There is no need to obtain the silicon content by constant weight weighing as in the traditional calcination weight method, which reduces the process of repeated weighing, simplifies the process, and shortens the time; at the same time, the silicon is converted into water-soluble silicates by alkali fusion, and the silicon content of silicon oxide and silicon element can be measured at the same time, and the only solvent involved is water, and there is no need to use corrosive solvents such as strong acids, which is more environmentally friendly and safe; in addition, the silicon content in the solution is measured by ICP, so that the result is more accurate and has higher precision. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is a physical picture of the original powder of silicon-based material sample 1.

[0027] Figure 2 This is a physical picture of the first product after the silicon-based material sample 1 is burned.

[0028] Figure 3 This is a physical picture of the first product after the silicon-based material sample 2 is calcined.

[0029] Figure 4 This is a physical picture of the first product after the silicon-based material sample 3 is calcined.

[0030] Figure 5 This is a picture of the filter paper after filtering the test solution in Example 1.

[0031] Figure 6 This is a picture of the filter paper after filtering the test solution of Comparative Example 2. DETAILED DESCRIPTION

[0032] To better illustrate the purpose, technical solution and advantages of the present application, the technical solution of the present application will be clearly and completely described below in conjunction with embodiments. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. The embodiments described herein are illustrative in nature and are used to provide a basic understanding of the present application. And the embodiments of the present application should not be construed as a limitation of the present application.

[0033] For the sake of brevity, only some numerical ranges are specifically disclosed herein. However, any lower limit can be combined with any upper limit to form a range not explicitly recited; and any lower limit can be combined with other lower limits to form a range not explicitly recited, and similarly any upper limit can be combined with any other upper limit to form a range not explicitly recited. In addition, each individually disclosed point or single numerical value itself can be used as a lower limit or an upper limit and combined with any other point or single numerical value or combined with other lower limits or upper limits to form a range not explicitly recited.

[0034] In the description herein, unless otherwise specified, "above" and "below" include the number itself. Unless otherwise specified, the terms used in the present application have the well-known meanings commonly understood by those skilled in the art. Unless otherwise specified, the numerical values of the various parameters mentioned in the present application can be measured by various common measurement methods in the art. In the description herein, a list of items connected by the terms "at least one of", "at least one of", "at least one of" or other similar terms may mean any combination of the listed items.

[0035] To improve the accuracy of measuring silicon-based materials and expand the universality of measurement methods, a test method for the content of silicon elements in silicon-based materials is provided, including the following steps:

[0036] (1) Burn the silicon-based material sample to obtain a first product;

[0037] (2) Mix the first product with an alkali flux and then carry out an alkali fusion reaction to obtain a second product;

[0038] (3) Dissolve the second product in water to obtain a test solution;

[0039] (4) Use ICP to test the mass percentage of silicon elements in the test solution;

[0040] (5) Obtain the mass percentage of silicon elements in the silicon-based material sample according to the following calculation formula;

[0041] w Si = c×V / m×0.0001;

[0042] where, w Si is the mass percentage of silicon elements in the silicon-based material sample, with the unit of %,

[0043] c is the concentration of silicon in the solution to be tested, in μg / mL;

[0044] V is the volume of the solution to be tested, in mL;

[0045] m is the mass of the silicon-based material sample, in g;

[0046] 0.0001 is the unit conversion factor.

[0047] In the test method of the present application, the silicon-based material is first subjected to high-temperature calcination, which can convert part or all of the silicon element into silicon oxide, and when carbon exists in the silicon-based material, the carbon can be removed by high-temperature calcination to avoid carbon coating silicon and causing inaccurate measurement; then after alkali fusion, the silicon element is converted into silicate, which is then dissolved in water, and finally the silicon content in the aqueous solution is accurately tested by ICP. The test method of the present application does not need to use constant weight weighing to obtain its silicon content after calcination as in the traditional calcination weight method, which reduces the process of repeated weighing, simplifies the process, and shortens the time; at the same time, alkali fusion is used to convert silicon into water-soluble silicate, which can simultaneously measure the silicon content in silicon dioxide and silicon element, and the solvent only needs water, without the need to use corrosive solvents such as strong acid, which is more environmentally friendly and safer; in addition, the silicon content in the solution is measured by ICP, so that the result is more accurate and the precision is higher.

[0048] In some embodiments, in step (1), the calcination temperature is 800°C to 1000°C, specifically, it can be 800°C, 825°C, 850°C, 875°C, 900°C, 925°C, 950°C, 975°C, 1000°C, or a range consisting of any two of these values.

[0049] In some embodiments, in step (1), the burning time is 2 h to 5 h, specifically, it can be 2 h, 2.25 h, 2.5 h, 2.75 h, 3 h, 3.25 h, 3.5, 3.75 h, 4 h, 4.25 h, 4.5 h, 4.75 h, 5 h, or a range consisting of any two of these values.

[0050] Among the chemical reactions that may be involved in the burning process:

[0051] (1) C+O 2 →CO 2 ↑;

[0052] (2)2Si+O 2 →2SiO;

[0053] (3)Si+O 2 →SiO 2 .

[0054] When the burning temperature is relatively high and the burning time is appropriate, the carbon in the silicon-based material can be completely removed, and the formation of SiC compounds that cannot be alkali-fused by silicon and carbon elements can be avoided, which is beneficial to the more complete reaction of the product after burning during the alkali-fusion process and improves the detection accuracy.

[0055] In some embodiments, in step (1), the heating rate for heating to the burning temperature is 10 °C / min to 20 °C / min. Specifically, it can be 10 °C / min, 11 °C / min, 12 °C / min, 13 °C / min, 14 °C / min, 15 °C / min, 16 °C / min, 17 °C / min, 18 °C / min, 19 °C / min, 20 °C / min, or the range composed of any two of these values.

[0056] In some embodiments, in step (1), the burning atmosphere is air or a mixed atmosphere of oxygen and an inert gas.

[0057] In the mixed atmosphere of oxygen and an inert gas, the volume ratio of oxygen is 10% to 80%. Specifically, it can be 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, or the range composed of any two of these values.

[0058] When burning in an oxygen-containing atmosphere, the carbon in the silicon-based material reacts with oxygen to generate carbon dioxide gas, which volatilizes and is removed, releasing silicon coated with carbon and improving the detection accuracy of silicon elements.

[0059] In some embodiments, in step (1), the specific process of burning includes: placing the silicon-based material in a nickel crucible, transferring it to a muffle furnace, burning in an air atmosphere, naturally cooling to below 100 °C, then taking out the product and the nickel crucible from the muffle furnace together, and naturally cooling to room temperature to obtain a first product in the nickel crucible.

[0060] In some embodiments, in step (1), the silicon-based material sample includes at least one of a carbon-containing silicon-based material, a silicon-based material containing elemental silicon, a silicon-based material containing silicon oxide, or a silicon-based material containing an additive.

[0061] In some embodiments, in step (1), the silicon-based material sample contains carbon elements.

[0062] When used as a negative electrode material, the silicon-based material often contains carbon materials to improve the electrochemical activity of the negative electrode material.

[0063] In some embodiments, in step (1), the additive includes at least one of lithium element, aluminum element, magnesium element, or titanium element.

[0064] The method of the present application is not only applicable to common carbon-containing silicon-based materials, silicon-based materials containing elemental silicon or nanosilicon, overcoming the defect that the traditional ignition gravimetric method for testing silicon-based materials containing elemental silicon, especially nanosilicon, is inaccurate in measuring the silicon content because silicon forms a dense oxide layer with oxygen at high temperature, resulting in the inability to continue the reaction; but also for silicon-based materials whose products after ignition are not silicon dioxide, such as silicon-based materials added with metal element additives including lithium element, aluminum element, magnesium element or titanium element, etc. When they are ignited at high temperature, silicon forms a solid solution with these metals, resulting in the inability to be converted into silicon dioxide. If the traditional ignition gravimetric method is used, the silicon element in this part cannot be accurately measured, resulting in low accuracy of the test results. The method of the present application requires an alkali fusion process after ignition. In the alkali fusion process, the silicon form solid-solved during the ignition process can be converted into water-soluble silicate, releasing silicon elements more thoroughly and improving the accuracy of the test results.

[0065] In some embodiments, in step (2), based on the mass of each gram of the silicon-based material sample, the mass of the alkali flux is 12 - 20 g. Specifically, it can be 12 g, 13 g, 14 g, 15 g, 16 g, 17 g, 18 g, 19 g, 20 g, or the range composed of any two of these values. Using an appropriate amount of alkali solvent can increase the degree of the alkali fusion reaction, enabling various forms of silicon such as elemental silicon, silicon monoxide, and silicon dioxide to be completely converted into the form of silicate. And because the alkali flux is appropriate, after the product of the alkali fusion reaction dissolves in water, the salt concentration in the test solution is appropriate and will not significantly interfere with the baseline of the ICP test result, improving the accuracy of measuring the silicon content in the silicon-based material.

[0066] In some embodiments, in step (2), the alkali flux includes at least one of KOH or NaOH. Using strong alkali-based alkali fluxes can increase the rate of the alkali fusion reaction, shorten the reaction time, and also make the conversion of various forms of silicon into water-soluble silicate more complete, improving the accuracy of measuring the silicon content in the silicon-based material. At the same time, in order to avoid the splashing of the melt during the alkali fusion process, an alkali fusion aid is added to the alkali fusion reaction to avoid the splashing of the melt during the alkali fusion process and improve the degree of the alkali fusion reaction. For example, the alkali fusion aid includes KNO 3 or NaNO 3 at least one of them.

[0067] For example, when using KOH alkali flux to melt with SiO x (x is from 0 to 2) at high temperature to generate potassium silicate, the following reactions may occur:

[0068] (1) 2Si + 4KOH + O 2 →2K 2 SiO 3 + 2H 2 ↑;

[0069] (2) SiO + 2KOH → K 2 SiO 3 + H 2 ↑;

[0070] (3) SiO 2 + 2KOH → K 2 SiO 3 + H 2 O。

[0071] In some embodiments, in step (2), the temperature of the alkali fusion reaction is 400 °C to 450 °C. Specifically, it can be 400 °C, 405 °C, 410 °C, 415 °C, 420 °C, 425 °C, 430 °C, 435 °C, 440 °C, 445 °C, 450 °C, or a range composed of any two of these values. By using the above suitable alkali fusion temperature, the alkali fusion reaction can be completed, and it can also avoid the melt splashing and sample loss caused by the too violent alkali fusion reaction, improve the repeat stability of the detection results, and can save energy consumption.

[0072] In some embodiments, in step (2), the time of the alkali fusion reaction is 30 min to 60 min. Specifically, it can be 30 min, 35 min, 40 min, 45 min, 50 min, 55 min, 60 min, or a range composed of any two of these values. By using the above suitable alkali fusion reaction time, on the basis of making the alkali fusion reaction proceed sufficiently, more energy can be saved.

[0073] In some embodiments, in step (2), the heating rate of rising to the temperature of the alkali fusion reaction is 10 °C / min to 20 °C / min. Specifically, it can be 10 °C / min, 11 °C / min, 12 °C / min, 13 °C / min, 14 °C / min, 15 °C / min, 16 °C / min, 17 °C / min, 18 °C / min, 19 °C / min, 20 °C / min, or a range composed of any two of these values.

[0074] In some embodiments, in step (2), the atmosphere of the alkali fusion reaction is air or a mixed atmosphere of oxygen and inert gas.

[0075] In some embodiments, in the mixed atmosphere of oxygen and inert gas, the volume ratio of oxygen is 10% to 80%. Specifically, it can be 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, or a range composed of any two of these values.

[0076] In some embodiments, in step (2), the process of the alkali fusion reaction specifically includes the following steps: adding an alkali fusion agent to the first product in a nickel crucible, mixing evenly, then transferring it to a muffle furnace, carrying out the alkali fusion reaction in an air atmosphere, naturally cooling to below 100 °C, then taking out the product and the nickel crucible from the muffle furnace together, and naturally cooling to room temperature to obtain a second product in the nickel crucible.

[0077] In some embodiments, in step (3), based on the mass of each gram of the silicon-based material sample, the mass of the water is 1500 g to 2000 g. Specifically, it can be 1500 g, 1550 g, 1600 g, 1650 g, 1700 g, 1750 g, 1800 g, 1850 g, 1900 g, 2000 g, or the range composed of any two of these values.

[0078] In some embodiments, in step (3), the temperature of the dissolution is 80 to 100 °C. Specifically, it can be 80 °C, 82 °C, 84 °C, 85 °C, 88 °C, 90 °C, 92 °C, 94 °C, 96 °C, 98 °C, 100 °C, or the range composed of any two of these values. Heating and dissolving the product after alkali fusion can increase the dissolution rate of the product after the alkali fusion reaction, accelerate its dissolution in water, increase the dissolution degree of the product, and improve the accuracy of measuring the silicon content in the silicon-based material.

[0079] In some embodiments, in step (3), the time of the dissolution is 60 min to 90 min. Specifically, it can be 60 min, 65 min, 70 min, 75 min, 80 min, 85 min, 90 min, or the range composed of any two of these values.

[0080] In some embodiments, in step (3), the specific process of the dissolution includes the following: placing the second product and the nickel crucible in a plastic beaker, adding deionized water so that the deionized water completely immerses the nickel crucible. After the second product is completely dissolved and cooled to room temperature, then transferring the solution to a plastic volumetric flask, using deionized water to wash the plastic beaker and the nickel crucible, and transferring the washed solution to the volumetric flask together, adding deionized water to make up the volume to obtain a test solution with a volume of V.

[0081] In some embodiments, in step (4), the specific process of using ICP to test the mass percentage of silicon element in the solution to be tested includes the following steps: Take V1 volume of the solution to be tested from the V volume of the solution to be tested, and dilute it a times with deionized water to obtain a diluted solution with a volume of V2. Use ICP-OES to test the silicon element concentration c2 in the diluted solution, and calculate the concentration c of the solution to be tested through c = c2 × a, where the units of V, V1, and V2 are mL, the units of c2 and c are μg / mL, and a has no unit.

[0082] To better illustrate the purpose, technical solution, and advantages of the present invention, the present invention will be further described below through specific comparative examples and examples.

[0083] Silicon-based material samples 1, 2, and 3 are all commercially available carbon-containing silicon-based materials.

[0084] The relevant parameters and conditions of the inductively coupled plasma optical emission spectrometry (ICP-OES) equipment used in the following examples and comparative examples are shown in Table 1.

[0085] Table 1

[0086]

[0087] Example 1

[0088] A method for testing the silicon element content in a silicon-based material includes the following steps:

[0089] (1) Place silicon-based material sample 1 with an accurately weighed mass of m = 0.1 g in a nickel crucible, cover it, leave a gap for oxygen to enter, transfer it to the muffle furnace body, heat it from room temperature to the burning temperature in an air atmosphere, burn it, naturally cool it to below 100 °C, take out the product and the nickel crucible together, and cool it to room temperature to obtain the first product;

[0090] (2) Add a flux to the first product in the nickel crucible and mix it evenly, cover it and leave a gap for oxygen to enter, then transfer it to the muffle furnace body, heat it from room temperature to the alkali fusion reaction temperature in an air atmosphere, carry out the alkali fusion reaction, naturally cool it to below 100 °C, take it out, and cool it to room temperature to obtain the second product;

[0091] (3) Place the second product and the nickel crucible together in a clean plastic beaker (avoid contacting glassware), add a certain mass of hot deionized water to completely immerse the nickel crucible and the lid, completely dissolve the second product in water, cool it to room temperature, transfer the solution to a plastic volumetric flask, use a small amount of deionized water to wash the plastic beaker, nickel crucible, and its lid, and then add deionized water to make up the volume to obtain a V volume of the solution to be tested;

[0092] (4) Take a volume V1 of the solution to be tested, dilute it by a factor of a with deionized water, and make up the volume to obtain a diluted sample with a volume of V2. Use an inductively coupled plasma optical emission spectrometry (ICP-OES) device to measure the concentration c2 (μg / mL) of silicon in the diluted sample. Calculate the concentration c of the solution to be tested through c = c2 × a. The dilution factor a can be selected according to the actual situation of the corresponding sample.

[0093] (5) Obtain the mass percentage w of silicon in the silicon-based material sample according to the following calculation formula Si ;

[0094] w Si = c × V / m × 0.0001;

[0095] where, w Si is the mass percentage of silicon in the silicon-based material sample, in %,

[0096] c is the concentration of silicon in the solution to be tested, in μg / mL;

[0097] V is the volume of the solution to be tested, in mL;

[0098] m is the mass of the silicon-based material sample, in g.

[0099] (6) According to the above method, each sample is measured in parallel three times. Take the average value of w Si results, and calculate the repeatability COV% of the three test results in the way of COV% = standard deviation / average value * 100.

[0100] The mass of the silicon-based material, ignition conditions, alkali fusion reaction conditions, type and dosage of alkali fusion agent, deionized water dosage, c, a, V, silicon content w obtained from each test Si 、w Si average value and other parameters are shown in Table 1-2.

[0101] Example 2

[0102] This example is different from Example 1 in that: this example uses silicon-based material sample 2 for testing, and the rest are the same. See Tables 1 and 2 for details.

[0103] Example 3

[0104] This example is different from Example 1 in that: this example uses silicon-based material sample 3 for testing, and the rest are the same. See Tables 2 and 3 for details.

[0105] Table 2

[0106]

[0107] Table 3

[0108]

[0109]

[0110] Examples 4 - 23

[0111] Compared with Example 1, Example 4 - 23 is different in parameters such as the type of silicon-based material sample, the conditions of burning, the conditions of alkali fusion reaction, the type and dosage of alkali fusion agent, the dosage of deionized water, etc., and w obtained by testing with the corresponding examples. Si , as shown in Table 4 in detail, and the rest are the same.

[0112] Table 4

[0113]

[0114]

[0115] Comparative Example 1

[0116] Compared with Example 1, this comparative example uses the traditional ignition gravimetric method for testing. For the specific method, refer to GB / T38823 - 2020 Silicon Carbon - Ignition Gravimetric Method. Among them, the ignition temperature is 1200 °C and the ignition time is 8 h.

[0117] Comparative Example 2

[0118] Compared with Example 1, this comparative example does not perform ignition. The specific process is as follows:

[0119] (1) Place a silicon-based material sample 1 with an accurately weighed mass of m = 0.1 g in a nickel crucible, add the alkali fusion agent and mix evenly. Cover it with a lid and leave a gap for oxygen to enter. Then transfer it to the furnace body of the muffle furnace, heat it from room temperature to the ignition temperature in a programmed manner, and carry out the alkali fusion reaction in an air atmosphere. Naturally cool it to below 100 °C, take out the product and the nickel crucible together, and cool it to room temperature to obtain the first product;

[0120] (2) Place the second product and the nickel crucible together in a clean plastic beaker (to avoid contact with glassware), add a certain mass of hot deionized water to completely immerse the nickel crucible and the lid, dissolve the second product completely in water, cool it to room temperature, transfer the solution to a plastic volumetric flask, use a small amount of deionized water to wash the plastic beaker, the nickel crucible and its lid, and then add deionized water to make up the volume to obtain a measured solution with a volume of V;

[0121] (3) Take a volume V1 of the solution to be tested, dilute it by a factor of a with deionized water, and make up the volume to obtain a diluted sample with a volume of V2. Use an inductively coupled plasma optical emission spectrometry (ICP-OES) device to measure the concentration c2 (μg / mL) of silicon in the diluted sample; calculate the concentration c of the solution to be tested through c = c2 × a;

[0122] (4) Obtain the mass percentage w of silicon in the silicon-based material sample according to the following calculation formula Si ;

[0123] w Si = c × V / m × 0.0001;

[0124] where, w Si is the mass percentage of silicon in the silicon-based material sample, with the unit of %,

[0125] c is the concentration of silicon in the solution to be tested, with the unit of μg / mL;

[0126] V is the volume of the solution to be tested, with the unit of mL;

[0127] m is the mass of the silicon-based material sample, with the unit of g.

[0128] (6) According to the above method, each sample is measured in parallel three times, and the w Si results are averaged, and the repeatability COV% of the three test results is calculated in the way of COV% = standard deviation / average * 100.

[0129] The mass of the silicon-based material involved in this comparative example, the burning conditions, the conditions of the alkali fusion reaction, the type and dosage of the alkali fusion agent, the dosage of deionized water, c, a, V, the w Si , w Si average value, etc. of each test are shown in Table 5.

[0130] Table 5

[0131]

[0132] Sample 1 is a composite material of nano-silicon and carbon, which is a black powder sample. As Figure 1 shown, the product after burning is SiO 2 white powder, as Figure 2 shown. Sample 2 is a composite material of silicon oxide and carbon, which is a black powder sample. The product after burning shows a reddish-brown color, as Figure 3 shown. According to the literature, SiO shows a reddish-brown color, which can confirm that the product after its burning contains SiO. The product after burning of Sample 2 is not SiO 2White powder, not suitable for testing by the traditional ignition gravimetric method. When testing sample 2 by the traditional ignition gravimetric method in Comparative Example 1, the measured silicon content was on the low side. Sample 3 is a silicon-oxygen and carbon composite material after pre-lithiation treatment, which is a black powder sample. The Li and Al element contents of the original powders of the 3 parallel samples corresponding to sample 3 used in the examples were tested by ICP. The test results of the Li and Al element contents are shown in Table 6. The burned sample 3 is gray, as Figure 3 shown. Due to the high Li and Al element contents, silicon forms solid solution with these metals, resulting in its inability to be converted into silicon dioxide. Therefore, the burned product cannot be completely converted into SiO 2 , and it is also not suitable for testing by the traditional ignition gravimetric method. It can be seen from Examples 1-3 that the method of the present application is universal for silicon-based materials containing nano-silicon, silicon-oxygen, and metal element additives such as Li and Al, and accurate silicon content information can be obtained by testing.

[0133] Table 6

[0134] Sample 3 Al / wt% Li / wt% Parallel Sample 1 0.153 8.99 Parallel Sample 2 0.154 8.92 Parallel Sample 3 0.137 8.55

[0135] Meanwhile, based on Examples 1 and 4-23, it can be known that the ignition conditions, alkali fusion reaction conditions, and reaction conditions during the water dissolution process have a certain impact on the test results. Under the test conditions selected in the present application, it is more conducive to obtaining accurate silicon content information.

[0136] In Comparative Example 2, the carbon-containing silicon-based material sample 1 was not subjected to ignition treatment and was directly subjected to alkali fusion. The product after alkali fusion was dissolved in water to obtain a test solution, which was filtered using filter paper. The effect was as Figure 5 shown. Obvious black solid particles were observed on the filter paper, and the alkali fusion product could not be completely dissolved in water, resulting in a low measured silicon content and inaccurate measurement results. The product after alkali fusion in Example 1 was dissolved in water and then filtered using filter paper. The effect was as Figure 4 shown. No solid particles were observed on the filter paper, and the alkali fusion product was completely dissolved. For carbon-containing silicon-based materials, by first performing ignition treatment and then alkali fusion treatment according to the present application, the influence of carbon on the measurement of silicon content can be avoided, and the product can be completely dissolved in water, with high accuracy in measuring the silicon element content.

[0137] Accuracy verification

[0138] The accuracy of the test method of the present application was verified by a standard addition experiment, which specifically included the following steps: Graphite samples without silicon, graphite samples without silicon and SiO 2The mixed samples of the standard samples (Si content 46.75 wt%, particle size 1 - 3 μm, purity 99%), the graphite samples without silicon, the mixed samples of the SiO standard samples (Si content 63.71 wt%, particle size 1 - 3 μm, purity 99%) and the high-purity Si powder standard samples (particle size 1 - 3 μm, purity 99%) were used as the standard test samples respectively. The method of Example 1 was used to test each standard test sample. The detailed sample information and test results are shown in Tables 7 and 8.

[0139] Table 7

[0140]

[0141]

[0142] Table 8

[0143]

[0144] In Tables 7 - 8, the spike recovery rate (%) = (c × V × a - m1 × m0 × 10000) / (m3 × 10 6 ) × 100; m3 = m2 × w1 × w2, where the unit of m1 is g, the unit of m3 is g, the unit of w1 is %, and the unit of w2 is %.

[0145] It can be seen that for testing the carbon-containing silicon-based materials by the test method of the present application, the spike recovery rate is very close to 100%. It can be confirmed that the test method of the present application has high accuracy, good repeatability and stability, and is applicable to the materials containing elemental silicon, SiO 2 and Si-based materials, with high universality and high accuracy.

Claims

1. A method for testing the silicon content in a silicon-based material, characterized in that: The steps include: (1) burning a silicon-based material sample to obtain a first product; (2) mixing the first product with an alkali flux, and then subjecting the mixture to an alkali fusion reaction to obtain a second product; (3) dissolving the second product in water to obtain a test solution; (4) using ICP to test the mass percentage of silicon in the solution to be tested; (5) Obtain the mass percentage of silicon in the silicon-based material sample according to the following calculation formula; In Si =c×V / m×0.0001; Among them, w Si is the mass percentage of silicon in the silicon-based material sample, in %, c is the concentration of silicon in the solution to be tested, in μg / mL; V is the volume of the solution to be tested, in mL; m is the mass of the silicon-based material sample in g.

2. The method for testing the silicon content in silicon-based materials according to claim 1, characterized in that: In step (1), the calcination temperature is 800° C. to 1000° C., and the calcination time is 2 h to 5 h.

3. The method for testing the silicon content in silicon-based materials according to claim 2, characterized in that: In step (1), the heating rate to the burning temperature is 10°C / min to 20°C / min, and the burning atmosphere is air or a mixed atmosphere of oxygen and an inert gas.

4. The method for testing the silicon content in silicon-based materials according to claim 1, characterized in that: In step (1), the silicon-based material sample contains carbon element.

5. The method for testing the silicon content in silicon-based materials according to claim 1, characterized in that: In step (2), based on the mass of the silicon-based material sample per gram, the mass of the alkali flux is 12-20 g.

6. The method for testing the silicon content in silicon-based materials according to claim 1, characterized in that: In step (2), the alkali flux includes at least one of KOH or NaOH.

7. The method for testing the silicon content in silicon-based materials according to claim 1, characterized in that: In step (2), the temperature of the alkali fusion reaction is 400° C. to 450° C., and the time of the alkali fusion reaction is 30 min to 60 min.

8. The method for testing the silicon content in silicon-based materials according to claim 7, characterized in that: In step (2), the heating rate to the temperature of the alkali fusion reaction is 10°C / min to 20°C / min, and the atmosphere of the alkali fusion reaction is air or a mixed atmosphere of oxygen and an inert gas.

9. The method for testing the silicon content in silicon-based materials according to claim 1, characterized in that: In step (3), based on the mass of the silicon-based material sample per gram, the mass of the water is 1500 g to 2000 g.

10. The method for testing the silicon content in silicon-based materials according to claim 1, characterized in that: In step (3), the dissolution temperature is 80 to 100° C., and the dissolution time is 60 to 90 minutes.

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