Method for measuring content of silicon element in material

Abstract

The invention provides a method for measuring the content of a silicon element in a material. The determination method comprises the following steps: carrying out ashing treatment on a carbon-based material to obtain an ashed substance containing a silicon element; dissolving a silicon element in the ashing substance by adopting an alkali solution to obtain a silicon-containing solution; performing ICP-OES test on the silicon-containing solution to obtain the content of the silicon element in the silicon-containing solution; and calculating the content of the silicon element in the carbon-based material according to the content of the silicon element in the silicon-containing solution.

Description

Technical Field

[0001] This application relates to the field of chemical analysis, and particularly to a method for determining the silicon element content in a material. Background Art

[0002] Silicon-based anode materials have become a research hotspot due to their high theoretical capacity. However, the silicon anode will cause damage to the electrode structure due to its huge volume effect, which will affect the formation of the SEI film, consume a large amount of lithium ions, and lead to rapid capacity decay. Silicon nanonization, compounding, and alloying can solve the above problems. Among them, doping silicon into carbon-based materials can effectively improve the specific capacity of the anode active material and can effectively alleviate the problems caused by silicon volume expansion.

[0003] The amount of silicon in carbon-based materials has a great influence on the performance of the materials. Therefore, it is particularly important to accurately determine the silicon element content in carbon-based materials. Summary of the Invention

[0004] This application provides a method for determining the silicon element content in a material to solve the problem of inaccurate determination of the silicon element content in current carbon-based materials.

[0005] This application provides a method for determining the silicon element content in a material, including: subjecting the material to ashing treatment to obtain an ashed product containing silicon elements; dissolving the silicon elements in the ashed product with an alkali solution to obtain a silicon-containing solution; performing ICP-OES testing on the silicon-containing solution to obtain the content of silicon elements in the silicon-containing solution; and calculating the silicon element content in the material based on the content of silicon elements in the silicon-containing solution.

[0006] The determination method of this application first subjects the material to ashing treatment. During the ashing process, carbon is removed in the form of gases such as carbon dioxide, and the silicon material wrapped by carbon is exposed, thus providing a good material basis for subsequent dissolution with an alkali solution. Moreover, during this process, part of the silicon will be converted into silicon oxides; then, the silicon elements in the ashed product are dissolved with an alkali solution, so that the silicon elements enter the solution to form a silicon-containing solution; performing ICP-OES (Inductively Coupled Plasma Atomic Emission Spectrometry) testing on the silicon-containing solution can obtain the content of silicon elements in the silicon-containing solution, and further calculate the silicon element content in the material.

[0007] In any embodiment of this application, the alkali solution includes any one or more of an aqueous sodium hydroxide solution and an aqueous potassium hydroxide solution; optionally, the concentration of OH - in the alkali solution is 4 mol / L - 10 mol / L; optionally, the concentration of the alkali in the alkali solution is 4 mol / L - 10 mol / L. Optionally, the mass ratio of the ashed product to the alkali solution is 1:40 - 1:60. The dissolution efficiency of silicon elements is improved.

[0008] In any embodiment of the present application, the process of dissolving silicon in the ashed product with an alkali solution includes: mixing the ashed product with the alkali solution to form a mixture; heating the mixture to a temperature T1 and holding for a first predetermined time to obtain a silicon-containing solution. Optionally, the temperature T1 is 160°C - 200°C, and optionally the first predetermined time is 10 min - 40 min. Heating during the dissolution process improves the reaction efficiency between the silicon and the alkali solution and shortens the dissolution time.

[0009] In any embodiment of the present application, before performing ICP-OES testing on the silicon-containing solution, the determination method further includes the process of diluting the silicon-containing solution with water; optionally, the alkalinity of the diluted silicon-containing solution is ≤10%, and the silicon content is 0.2 mg / L - 10 mg / L.

[0010] In any embodiment of the present application, after dissolution with an alkali solution, there is residue in the ashed product. The determination method further includes: dissolving the remaining ashed product with a hydrofluoric acid solution to obtain a hexafluorosilicic acid solution; performing ICP-OES testing on the hexafluorosilicic acid solution to obtain the silicon element content in the hexafluorosilicic acid; calculating the silicon element content in the carbon-based material based on the silicon element content in the hexafluorosilicic acid and the silicon element content in the silicon-containing solution. A small amount of residue can be dissolved with an excessive amount of hydrofluoric acid solution without generating a large amount of SiF 4 so there will be no problem of low silicon element content test caused by the volatilization of SiF 4 Instead, the silicon element content in the carbon-based material can be measured more accurately.

[0011] In any embodiment of the present application, before dissolving the remaining ashed product with hydrofluoric acid, the remaining ashed product is acidified, optionally with concentrated nitric acid.

[0012] In any embodiment of the present application, the process of dissolving the remaining ashed product with a hydrofluoric acid solution includes: after mixing the remaining ashed product with the hydrofluoric acid solution, heating to a temperature T2 and holding for a second predetermined time to obtain a hexafluorosilicic acid solution. Optionally, the temperature T2 is 160°C - 200°C, and optionally the second predetermined time is 10 min - 40 min.

[0013] In any embodiment of the present application, before performing ICP-OES testing on the hexafluorosilicic acid solution, the determination method further includes the process of diluting the hexafluorosilicic acid solution; optionally, the silicon content in the diluted hexafluorosilicic acid solution is 0.2 mg / L - 10 mg / L.

[0014] In any embodiment of the present application, the inner wall of the nebulizer used for ICP testing is an inner wall resistant to acid and alkali corrosion.

[0015] In any embodiment of the present application, the carbon-based material includes any one or more of the anode materials for sodium batteries and anode materials for lithium batteries. Optionally, the carbon-based material includes hard carbon materials and silicon-containing graphite materials. Description of the Drawings

[0016] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required for use in the embodiments of the present application will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on the drawings.

[0017] Figure 1 Shows the filtration photo of the substance after digestion of the anode material of the sodium battery in Comparative Example 1.

[0018] Figure 2 Shows the filtration photo of the dissolved substance after alkali fusion of the ashed sample in Comparative Example 4.

[0019] Figure 3 This is the standard curve graph established with a standard solution containing an alkali matrix during the ICP-OES test of the embodiment of the present application. Detailed Embodiments

[0020] The embodiments of the present application will be further described in detail below in conjunction with the drawings and embodiments. The following detailed description of the embodiments and the drawings are used to exemplarily illustrate the principles of the present application, but cannot be used to limit the scope of the present application, that is, the present application is not limited to the described embodiments.

[0021] Hereinafter, embodiments of a method for determining the silicon element content in the carbon-based material of the present application specifically disclosed will be described in detail with appropriate reference to the drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there are cases where detailed descriptions of well-known matters and repeated descriptions of actually identical structures are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the drawings and the following description are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter recited in the claims.

[0022] The "ranges" disclosed in this application are defined in the form of a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundaries of a particular range. The ranges defined in this way can include the end values or not include the end values, and can be combined arbitrarily, that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, ranges of 60-110 and 80-120 are also contemplated. In addition, if the minimum range values 1 and 2 are listed, and if the maximum range values 3, 4, and 5 are listed, then the following ranges are all contemplated: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise specified, the numerical range "a-b" represents an abbreviated representation of any real number combination between a and b, where both a and b are real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" have been fully listed herein, and "0-5" is only an abbreviated representation of these numerical combinations. Additionally, when stating that a certain parameter is an integer ≥2, it is equivalent to disclosing that the parameter is, for example, the integers 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0023] If there is no special instruction, all embodiments and optional embodiments of this application can be combined with each other to form new technical solutions.

[0024] If there is no special instruction, all technical features and optional technical features of this application can be combined with each other to form new technical solutions.

[0025] If there is no special instruction, all steps of this application can be carried out in sequence or randomly, and preferably in sequence. For example, the method includes steps (a) and (b), which means that the method can include steps (a) and (b) carried out in sequence, or can also include steps (b) and (a) carried out in sequence. For example, it is mentioned that the method may further include step (c), which means that step (c) can be added to the method in any order. For example, the method can include steps (a), (b), and (c), or can also include steps (a), (c), and (b), or can also include steps (c), (a), and (b), etc.

[0026] If there is no special instruction, the "including" and "comprising" mentioned in this application mean open-ended. For example, the "including" and "comprising" can mean that other components not listed can also be included or comprised.

[0027] Unless otherwise specified, the term "or" is inclusive in this application. For example, any of the following conditions satisfies the condition "A or B": A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0028] As described above, the amount of silicon in the carbon-based material has a great influence on the performance of the material. Therefore, it is particularly important to accurately determine the silicon content in the carbon-based material. However, in the currently commonly used test method of directly dissolving the carbon-based material with concentrated nitric acid + hydrofluoric acid, since hydrofluoric acid reacts with silicon and silicon dioxide therein to form silicon tetrafluoride, the silicon tetrafluoride is easily volatilized and lost, resulting in a low silicon element content.

[0029] To solve this problem, this application provides a method for determining the silicon element content in a material. The determination method includes: subjecting the material to ashing treatment to obtain an ash containing silicon elements; dissolving the silicon elements in the ash with an alkali solution to obtain a silicon-containing solution; performing ICP-OES testing on the silicon-containing solution to obtain the silicon element content in the silicon-containing solution; and calculating the silicon element content in the material based on the silicon element content in the silicon-containing solution.

[0030] The determination method of this application first subjects the material to ashing treatment. During the ashing process, carbon is removed in the form of gases such as carbon dioxide, exposing the silicon material wrapped by carbon, thus providing a good material basis for subsequent dissolution with an alkali solution. Moreover, during this process, part of the silicon will be converted into silicon oxides; then, the silicon elements in the ash are dissolved with an alkali solution, so that the silicon elements enter the solution to form a silicon-containing solution; performing ICP-OES (Inductively Coupled Plasma Atomic Emission Spectrometry) testing on the silicon-containing solution can obtain the silicon element content in the silicon-containing solution, and further calculate the silicon element content in the material.

[0031] The specific process of the above ICP-OES testing can refer to the prior art, and the calibration method can adopt the external standard method.

[0032] In some embodiments, the above material includes a carbon-based material containing silicon elements.

[0033] The above ashing treatment can refer to the conventional ashing treatment method of carbon-based materials. For example, the carbon-based material is burned in air. Optionally, the combustion temperature is controlled at 650°C - 850°C and kept warm for 2h - 6h.

[0034] After ashing, in some embodiments, the silicon elements in the material exist in the ash in the form of silicon or silicon oxides. For example, the negative electrode material of a metal ion battery is mainly hard carbon, but also contains a small amount of silicon and its silicides (introduced by raw materials). The surface of the silicon and its silicides is coated with carbon, and the carbon cannot be dissolved in acid or alkali, resulting in a low test result. According to C+O2 = CO 2 ↑, Si + O 2 = SiO 2 Principle: By ashing, the hard carbon in the material and the carbon coated on the surface of silicon and its silicides are removed, exposing silicon and its silicides, and even converting silicon and its silicides into silicon dioxide, which is beneficial to the dissolution by the alkali solution.

[0035] In some embodiments, a strong alkali solution is used as the above-mentioned alkali solution, and the above-mentioned alkali solution includes any one or more of an aqueous sodium hydroxide solution and an aqueous potassium hydroxide solution. In the process of dissolving with the alkali solution, taking silicon and silicon dioxide as examples to illustrate the reaction process of this process: Si + 2NaOH + H 2 O = Na 2 SiO 3 + 2H 2 ↑ and SiO 2 + 2NaOH = Na 2 SiO 3 + H 2 O. It can be seen that silicon or silicon dioxide can react with the alkali solution to form a water-soluble silicate.

[0036] In order to improve the dissolution efficiency of silicon element, in some embodiments, optionally, the concentration of OH - in the alkali solution is 4 mol / L - 10 mol / L; optionally, the concentration of the alkali in the alkali solution is 4 mol / L - 10 mol / L, and optionally, the mass ratio of the ashed product to the alkali solution is 1:40 - 1:60.

[0037] In some embodiments, the process of dissolving the silicon element in the ashed product with the alkali solution includes: mixing the ashed product with the alkali solution to form a mixture; heating the mixture to a temperature T1 and holding for a first predetermined time to obtain a silicon-containing solution. Optionally, the temperature T1 is 160°C - 200°C, and optionally, the first predetermined time is 10 min - 40 min. Heating during the dissolution process improves the reaction efficiency of the silicon element with the alkali solution and shortens the dissolution time.

[0038] Since the alkali concentration in the silicon-containing solution obtained after dissolution with an alkali solution is also relatively high, if ICP-OES testing is directly carried out, the alkali therein will adhere to the equipment pipeline, resulting in pipeline blockage after long-term repeated testing and affecting the service life of the equipment. In some embodiments of the present application, in order to reduce the impact of the testing process on the ICP-OES tester, before performing ICP-OES testing on the silicon-containing solution, the above-mentioned determination method further includes a process of diluting the silicon-containing solution with water; optionally, the alkalinity of the diluted silicon-containing solution ≤ 10%, and the silicon content is 0.2 mg / L - 10 mg / L. The above-mentioned silicon content can only be known after ICP-OES testing. In actual operation, the silicon-containing solution can be diluted in parallel gradients, and after ICP-OES determination, it can be determined which dilution concentrations can meet the above-mentioned silicon content requirements, and the dilution concentration at this time can be referred to for dilution when testing the same carbon-based material to be measured subsequently.

[0039] In some embodiments, there may be some silicon dioxide in the carbon-based material or the ash that cannot be dissolved in the alkali solution due to certain reasons (such as crystal phase structure), and there is residue after dissolving the ash with the alkali solution, that is, there is precipitation. In order to fully dissolve this part of the residual ash to determine the silicon element content therein, in some embodiments, the above-mentioned determination method further includes: dissolving the residual ash with a hydrofluoric acid solution to obtain a hexafluorosilicic acid solution; performing ICP-OES testing on the hexafluorosilicic acid solution to obtain the silicon element content in the hexafluorosilicic acid; calculating the silicon element content in the carbon-based material based on the silicon element content in the hexafluorosilicic acid and the silicon element content in the silicon-containing solution.

[0040] The main reaction formula involved in the process of dissolving the residual ash with a hydrofluoric acid solution is: SiO 2 + 4HF = SiF 4 + 2H 2 O, SiF 4 + 2HF = H 2 SiF 6 .

[0041] Since the mass of the above-mentioned residual ash is very small, even if it is dissolved with a hydrofluoric acid solution, a large amount of SiF 4 will not be generated. Therefore, there will be no problem of low silicon element content test caused by the volatilization of SiF 4 , but instead, the silicon element content in the carbon-based material can be measured more accurately.

[0042] The above-mentioned hydrofluoric acid can use hydrofluoric acid with a relatively high concentration, such as hydrofluoric acid with a concentration of 40%. Moreover, since the mass of the residual ash is very small, the addition of hydrofluoric acid is usually in an excessive amount when adding hydrofluoric acid. Therefore, the generated SiF 4 quickly reacts to generate H 2SiF 6 。

[0043] In some embodiments, since the surface of the residual ash obtained after dissolution in an alkaline solution is alkaline due to the residual alkali, in order to reduce the amount of hydrofluoric acid used, before dissolving the residual ash with hydrofluoric acid, the residual ash is acidified. Optionally, concentrated nitric acid is used to acidify the residual ash. Since the presence of concentrated nitric acid will not have a negative impact on the subsequent reaction between hydrofluoric acid and silicon oxide, and even promotes the above reaction, the addition amount of concentrated nitric acid can be not particularly controlled. In some embodiments, taking 8 mol / L concentrated nitric acid as an example, its volume addition amount can be 1-3 times the volume addition amount of 40% hydrofluoric acid.

[0044] In some embodiments of the present application, the process of dissolving the residual ash with a hydrofluoric acid solution includes: after mixing the residual ash with the hydrofluoric acid solution, heating to temperature T2 and holding for a second predetermined time to obtain a hexafluorosilicic acid solution. Optionally, temperature T2 is 160-200 °C, and optionally the second predetermined time is 10-40 min. Heating increases the reaction rate between the residual ash and hydrofluoric acid and shortens the reaction time.

[0045] In order to further alleviate the corrosion of the ICP-OES test instrument by hydrofluoric acid, especially the corrosion of the nebulizer chamber, in some embodiments, before performing the ICP-OES test on the hexafluorosilicic acid solution, the above measurement method further includes a process of diluting the hexafluorosilicic acid solution; optionally, the silicon content in the diluted hexafluorosilicic acid solution is 0.2 mg / L - 10 mg / L. The silicon content of the above diluted hexafluorosilicic acid solution needs to be known after the ICP test. In actual operation, the silicon-containing solution can be diluted in parallel gradients, and after the ICP determination, it is determined which dilution concentrations can meet the above silicon content requirements. When testing the same carbon-based material to be measured subsequently, the dilution concentration at this time can be referred to for dilution.

[0046] In some embodiments, in order to extend the service life of the ICP-OES test instrument, optionally, the inner wall of the nebulizer used in the ICP-OES test is an inner wall resistant to acid and alkali corrosion.

[0047] In some embodiments, the carbon-based material includes any one or more of a sodium battery anode material and a lithium battery anode material. Optionally, the carbon-based material includes a hard carbon material and a silicon-containing graphite material.

[0048] [Examples]

[0049] Hereinafter, embodiments of the present application will be described. The embodiments described below are exemplary and are only used to explain the present application, and should not be construed as a limitation of the present application. For those without specific technical or conditions noted in the embodiments, the techniques or conditions described in the literature in this field or according to the product specifications are followed. For reagents or instruments without the manufacturer noted, they are all conventional products that can be obtained through commercial purchases.

[0050] Comparative Example 1

[0051] Weigh 0.1 g of the sodium battery anode material (mainly hard carbon, containing a relatively large amount of silicon, hereinafter referred to as the sodium battery anode material) into a microwave digestion tank; add 3 mL of hydrofluoric acid (concentration 40%) to the above microwave digestion tank; seal the digestion tank, set the power of the microwave digester to 1800 W, and let it rise to 180 °C in 25 minutes.

[0052] Observe the phenomenon after digestion: incomplete digestion, with precipitation in the solution, as Figure 1 shown.

[0053] Comparative Example 2

[0054] Except that the addition amount of hydrofluoric acid is changed to 6 mL, other steps of Comparative Example 2 are the same as those of Comparative Example 1.

[0055] Observe the phenomenon after digestion: incomplete digestion, with precipitation in the solution.

[0056] Comparative Example 3

[0057] Except that adding 3 mL of hydrofluoric acid is changed to adding 10 mL of nitric acid (8 mol / L) and 5 mL of hydrofluoric acid, other steps are the same as those of Comparative Example 1.

[0058] Observe the phenomenon after digestion: incomplete digestion, with precipitation in the solution.

[0059] Example 1

[0060]

Ashing of the sodium ion battery anode material

[0061] Mix the sodium battery anode material evenly, accurately weigh 10 ± 0.01 g of the material, and record the actual mass as m 1 , thinly spread it flat in an alumina crucible of 30 cm × 30 cm, place the crucible in the middle position of the muffle furnace, close the furnace body, slowly adjust the air flow rate to 1 L / min, set the temperature program, and let it heat up to 750 °C at a temperature rise rate of 5 °C / min, keep it warm for 4 h. After that, wait until it cools down to room temperature, open the muffle furnace, take out the crucible, collect the ashed sample and weigh it, and record the actual mass as m 2 .

[0062]

Preparation of the alkali solution

[0063] Take a clean plastic beaker, accurately weigh 20 g of sodium hydroxide (AR grade) pellets, add 50 mL of ultrapure water, stir until completely dissolved, transfer the solution to a 100 mL plastic volumetric flask, rinse the beaker 3 times with ultrapure water, add the rinsing liquid into the volumetric flask, then add ultrapure water to make up the volume to 100 mL, tighten the stopper of the volumetric flask, invert it up and down to mix evenly, and obtain a sodium hydroxide solution with a concentration of 5 mol / L.

[0064]

Dissolution of the ashed sample in alkaline solution

[0065] Mix the ashed sample evenly, accurately weigh the ashed sample into a clean 50 mL polytetrafluoroethylene beaker, and record the actual mass m. 3 , slowly drop 4 mL of 5 mol / L sodium hydroxide solution, react at 180 °C for 12 min until there is a small amount of precipitate in the solution that cannot be dissolved anymore. Filter it while it is hot into a 100 mL plastic volumetric flask, rinse the precipitate 4 times with ultrapure water, add the rinsing liquid into the volumetric flask, add ultrapure water to make up the volume, mix evenly, take 1 mL and dilute it to 100 mL, mix evenly, and obtain the silicon-containing solution to be measured.

[0066]

Dissolution of the precipitate

[0067] Put the precipitate and the filter paper together into a clean polytetrafluoroethylene beaker, acidify it with 4 mL of 8 mol / L nitric acid, then add 2 mL of 40% HF solution, dissolve it at 180 °C for 25 min until the solution is clear, transfer the solution to a 100 mL plastic volumetric flask, add ultrapure water to make up the volume, mix evenly, take 1 mL and dilute it to 100 mL, mix evenly, and obtain the hexafluorosilicic acid solution to be measured.

[0068] Example 2

[0069] Except that when dissolving the ashed sample in alkaline solution, change it to slowly drop 6 mL of 5 mol / L sodium hydroxide solution and react at 180 °C for 20 min, the other steps are the same as those in Example 1.

[0070] Example 3

[0071] Except that when dissolving the ashed sample in alkaline solution, adjust the reaction time to 40 min at 180 °C, the other steps are the same as those in Example 1.

[0072] Example 4

[0073] Except that when dissolving the ashed sample in alkaline solution, adjust the reaction time to 120 min at 180 °C, the other steps are the same as those in Example 1.

[0074] Example 5

[0075] Except that when dissolving the ashed sample in alkaline solution, adjust the reaction temperature to 160 °C and the reaction time to 20 min, the other steps are the same as those in Example 1.

[0076] Example 6

[0077] When dissolving the sample after ashing in an alkaline solution, adjust the reaction temperature to 200 °C for 20 min. Other steps are the same as in Example 1.

[0078] Example 7

[0079] When dissolving the sample after ashing in an alkaline solution, adjust the reaction temperature to 150 °C for 20 min. Other steps are the same as in Example 1.

[0080] Example 8

[0081] When dissolving the sample after ashing in an alkaline solution, adjust the reaction temperature to 220 °C for 20 min. Other steps are the same as in Example 1.

[0082] Example 9

[0083] When preparing the alkaline solution, prepare a sodium hydroxide solution with a concentration of 4 mol / L. During the dissolution of the sample after ashing in the alkaline solution, use this 4 mol / L sodium hydroxide solution to replace the 5 mol / L sodium hydroxide solution in Example 1. The remaining steps are the same as in Example 1.

[0084] Example 10

[0085] When preparing the alkaline solution, prepare a sodium hydroxide solution with a concentration of 10 mol / L. During the dissolution of the sample after ashing in the alkaline solution, use this 10 mol / L sodium hydroxide solution to replace the 5 mol / L sodium hydroxide solution in Example 1. The remaining steps are the same as in Example 1.

[0086] Example 11

[0087] When preparing the alkaline solution, prepare a potassium hydroxide solution with a concentration of 5 mol / L. During the dissolution of the sample after ashing in the alkaline solution, use this 5 mol / L potassium hydroxide solution to replace the 5 mol / L sodium hydroxide solution in Example 1. The remaining steps are the same as in Example 1.

[0088] Example 12

[0089] In the precipitation dissolution step, adjust the dissolution temperature to 160 °C. The remaining steps are the same as in Example 1.

[0090] Example 13

[0091] In the precipitation dissolution step, adjust the dissolution temperature to 200 °C. The remaining steps are the same as in Example 1.

[0092] Example 14

[0093] In the precipitation dissolution step, adjust the dissolution temperature to 150 °C. The remaining steps are the same as in Example 1.

[0094] Embodiment 15

[0095] In the precipitation dissolution step, the dissolution temperature was adjusted to 220° C. The remaining steps were the same as in Example 1.

[0096] Example 16

[0097] In the precipitation dissolution step, the dissolution time was adjusted to 10 min. The remaining steps were the same as in Example 1.

[0098] Embodiment 17

[0099] In the precipitation dissolution step, the dissolution time was adjusted to 40 min. The remaining steps were the same as in Example 1.

[0100] Embodiment 18

[0101] In the precipitation dissolution step, the dissolution time was adjusted to 60 min. The remaining steps were the same as in Example 1.

[0102] Embodiment 19

[0103] The sodium negative electrode material of Example 1 was replaced with silicon dioxide powder, and the silicon dioxide powder was not ashed. The silicon dioxide powder sample was accurately weighed in a clean 50 mL polytetrafluoroethylene beaker, and the actual mass m was recorded. 3 , slowly drop 4mL of 5mol / L sodium hydroxide solution, react at 180℃ for 12min, and all the solution will dissolve without precipitation.

[0104] Comparative Example 4

[0105] [Alkali fusion of sample after ashing]

[0106] Weigh 0.1 g of the ashed material in Example 1 into a nickel crucible, add 2 g of sodium hydroxide (AR grade) particles, cover the crucible with a small gap, place it in the middle of a muffle furnace, close the furnace, heat it to 600 ° C at a temperature rise rate of 5 ° C / min, keep it warm for 20 min, cool it to room temperature, open the muffle furnace, and take out the crucible.

[0107]

Eutectic Dissolution

[0108] Add 30 mL of boiling water to the crucible containing the eutectic and dissolve it.

[0109]

Phenomenon after dissolution

[0110] Failed to dissolve completely, with more precipitation, such as Figure 2 shown.

[0111] Since Comparative Examples 1 to 4 all had precipitation, the ICP test was not performed.

[0112] Comparative Example 5

[0113]

Ashing of the anode material of the sodium-ion battery

[0114]

Dissolution of the ashed sample

[0115] Mix the ashed samples evenly, accurately weigh 0.1 ± 0.05 g of the ashed sample into a clean 50 mL polytetrafluoroethylene beaker, and record the actual mass m 3 , add 10 mL of hydrofluoric acid solution with a concentration of 40% and 5 mL of HNO 3 solution, cover with a polyethylene watch glass, decompose completely in a 60 °C constant temperature water bath, remove and cool, then filter, collect the filtrate in a 200 mL polytetrafluoroethylene volumetric flask after thorough washing, make up the volume, shake well to obtain the test solution.

[0116] ICP-OES test

[0117] The following method is used to test the silicon-containing solution to be tested, hexafluorosilicic acid solution to be tested, and test solution of each example respectively.

[0118] Separate Si single standards with alkali solution as the matrix (C NaOH = 0.05 mol / L) and Si single standards with acid solution as the matrix (1% HF, trace HNO 3 ) are used to prepare gradient Si concentration standard solutions (0.2, 1.0, 2.0, 5.0, 10.0 mg / L) by adding ultrapure water.

[0119] Use an ICP-OES tester with a corrosion-resistant (HF-resistant) nebulizer chamber, select the Si spectral line 252.611 nm, and the working parameters meet: ① The cooling gas, auxiliary gas, and carrier gas are all argon with a volume concentration of 99.999%; ② The RF power is 1395 - 1405 W; ③ The nebulizer flow rate is 0.6 - 0.8 L / min; ④ The observation angle is radial, customize the Si standard curve, and an exemplary standard curve calibrated with alkali solution as the matrix is shown as Figure 3 shown, and the linear correlation coefficient R 2 > 0.999. After testing, the silicon content (unit: mg / L) in the silicon-containing solution to be tested is quantified by the standard curve of the Si standard solution prepared with the above alkali solution as the matrix, and the mass percentage content w 1 is obtained after correction by the correction factor (i.e., multiplying by the dilution volume and dividing by the mass of the burned sample), and the Si content (unit: mg / L) in the hexafluorosilicic acid solution to be tested is quantified by the standard curve of the Si standard solution prepared with acid solution as the matrix, and the mass percentage content w 2 .

[0120] The mass percentage of silicon element in the sodium - ion battery anode material in each example is calculated using the following formula.

[0121] The mass percentage ω of Si element in the material:

[0122] W = m Si / m 1 =(w 1 ×m 3 +w 2 ×m 3 ) / (m 3 ÷w 收率 )=(w 1 +w 2 ) ×m 3 / [m 3 / (m 2 / m 1 )]=(w 1 +w 2 )×(m 2 / m 1 )

[0123] w 1 —— The content (mass percentage) of Si element in the silicon - containing material to be measured in the ashed material for testing, which is calibrated using a standard solution with an alkali solution as the matrix;

[0124] w 2 —— The content (mass percentage) of Si element in the hexafluorosilicic acid solution to be measured in the ashed material for testing, which is calibrated using a standard solution with an acid solution as the matrix;

[0125] w 收率 —— The mass percentage of the ashed material to the pre - ashed material;

[0126] m 1 —— The mass of the pre - ashed material;

[0127] m 2 —— The mass of the ashed material;

[0128] m 3 —— The mass of the ashed material for testing.

[0129] The content of silicon element in the sodium - ion battery anode material in Comparative Example 5 is calculated using the following formula.

[0130]

[0131] The above calculation results are recorded in Table 1. m1 (g) m2 (g) m3 (g) W1(％) W2(％) W(％) Example 1 10.0883 0.9995 0.1045 20.54 12.3025 3.25 Example 2 10.0883 1.0005 0.1015 26.805 13.45 3.99 Example 3 10.0017 1.0021 0.0964 21.76 12.7 3.45 Example 4 10.0028 1.0011 0.1002 24.74 13.36 3.81 Example 5 10.0006 1.0010 0.0982 20.01 12.29 3.23 Example 6 10.0042 1.0023 0.0974 24.56 13.54 3.82 Example 7 10.0029 1.0009 0.1018 6.43 22.99 2.94 Example 8 10.0012 1.0001 0.1011 27.99 12.04 4.00 Example 9 10.0032 1.0013 0.0989 20.86 15.9 3.68 Example 10 10.0028 1.0004 0.101 28.45 11.53 4.00 Example 11 10.0037 1.0012 0.1045 26.17 13.29 3.95 Example 12 10.0019 1.0007 0.1096 26.07 9.25 3.53 Example 13 10.0016 1.0002 0.1057 25.97 13.5 3.95 Example 14 9.9987 0.999 0.0966 26.01 6.69 3.27 Example 15 10.0049 1.0013 0.1106 26.12 12.9 3.91 Example 16 10.0024 1.0031 0.0987 25.98 7.249 3.33 Example 17 9.9987 0.9993 0.0987 26.02 13.81 3.98 Example 18 10.0021 1.0001 0.1026 26.1 13.62 3.97 Comparative Example 5 10.0865 1.0002 0.1043 - 27.43 2.72

[0132] According to the comparison of Example 1, Example 3 and Example 4 in Table 1, it can be seen that as the reaction time of the alkaline solution increases, more silicon elements are dissolved, making w 1 The increase in w2 may be due to the fact that the alkaline solution makes the silicon element and soluble silicon oxide dissolve fully, which is beneficial to the exposure of insoluble silicon oxide and promotes its dissolution in the subsequent hydrofluoric acid. According to the comparison between Example 1, Example 5 and Example 6, it can be seen that as the reaction temperature of the alkaline solution increases, more silicon elements are dissolved, making w 1 Increase; According to the comparison of Examples 2 and 3, it can be seen that the amount of alkaline solution has a key influence on the dissolution efficiency of silicon, and this influence is more significant than the influence of dissolution time and dissolution temperature.

[0133] According to the comparison of Example 2 and Examples 12 to 18 in Table 1, it can be seen that the extension of the hydrofluoric acid dissolution time and the increase of the temperature are both conducive to the dissolution of the silicon element. However, when the temperature is higher than 200°C or the time is extended to more than 40 minutes, there is no further effect on the dissolution of the silicon element. In particular, when the temperature is higher than 200°C, the measured results decrease instead. This may be due to the problem that silicon tetrafluoride is formed too quickly due to the high temperature, resulting in loss.

[0134] Example 19 uses silicon dioxide to conduct experiments. After dissolution with sodium hydroxide solution, no precipitate remains, indicating that all of it has been dissolved. That is to say, when the object being tested does not contain alkali-insoluble silicon oxide compounds after ashing, the silicon element therein can be completely recovered using sodium hydroxide solution without the need for further dissolution using acid.

[0135] The results of Comparative Example 5 are obviously lower than those of the examples because the generated silicon tetrafluoride is seriously lost due to volatilization, resulting in a low result.

[0136] Although the present application has been described with reference to preferred embodiments, various modifications may be made thereto and parts thereof may be replaced with equivalents without departing from the scope of the present application. In particular, the various technical features mentioned in the various embodiments may be combined in any manner as long as there are no structural conflicts. The present application is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A method for determining the silicon element content in a material, comprising: ashing the material to obtain an ashed product containing silicon element; dissolving the silicon element in the ashed product with an alkali solution to obtain a silicon-containing solution; performing ICP-OES testing on the silicon-containing solution to obtain the content of silicon element in the silicon-containing solution; calculating the silicon element content in the material based on the silicon element content in the silicon-containing solution.

2. The determination method according to claim 1, wherein, The alkali solution includes any one or more of an aqueous sodium hydroxide solution and an aqueous potassium hydroxide solution; optionally, the concentration of OH - in the alkali solution is 4 mol / L - 10 mol / L; optionally, the concentration of the alkali in the alkali solution is 4 mol / L - 10 mol / L, and optionally, the mass ratio of the ashed product to the alkali solution is 1:40 - 1:

60.

3. The determination method according to claim 1 or 2, wherein, the process of dissolving the silicon element in the ashed product with an alkali solution includes: mixing the ashed product with the alkali solution to form a mixture; heating the mixture to a temperature T1 and holding for a first predetermined time to obtain the silicon-containing solution, optionally the temperature T1 is 160°C - 200°C, and optionally the first predetermined time is 10 min - 40 min.

4. The determination method according to any one of claims 1 to 3, wherein, before performing ICP-OES testing on the silicon-containing solution, the determination method further includes a process of diluting the silicon-containing solution with water; optionally, the alkalinity of the diluted silicon-containing solution ≤ 10%, and the silicon content is 0.2 mg / L - 10 mg / L.

5. The determination method according to any one of claims 1 to 4, wherein, after dissolving with the alkali solution, there is residue in the ashed product, and the determination method further includes: dissolving the remaining ashed product with a hydrofluoric acid solution to obtain a hexafluorosilicic acid solution; performing ICP-OES testing on the hexafluorosilicic acid solution to obtain the content of silicon element in the hexafluorosilicic acid; calculating the silicon element content in the carbon-based material based on the silicon element content in the hexafluorosilicic acid and the silicon element content in the silicon-containing solution.

6. The determination method according to claim 5, wherein, before dissolving the remaining ashed product with hydrofluoric acid, acidifying the remaining ashed product, optionally acidifying the remaining ashed product with concentrated nitric acid.

7. The determination method according to claim 5 or 6, wherein, the process of dissolving the remaining ashed product with a hydrofluoric acid solution includes: after mixing the remaining ashed product with the hydrofluoric acid solution, heating to a temperature T2 and holding for a second predetermined time to obtain the hexafluorosilicic acid solution, optionally the temperature T2 is 160°C - 200°C, and optionally the second predetermined time is 10 min - 40 min.

8. The determination method according to any one of claims 5 to 7, wherein, before performing ICP-OES testing on the hexafluorosilicic acid solution, the determination method further includes a process of diluting the hexafluorosilicic acid solution; optionally, the silicon content in the diluted hexafluorosilicic acid solution is 0.2 mg / L - 10 mg / L.

9. The determination method according to any one of claims 1 to 8, wherein, the inner wall of the atomization chamber used for the ICP test is an inner wall resistant to acid and alkali corrosion.

10. The determination method according to any one of claims 1 to 9, wherein, The carbon-based material includes any one or more of sodium battery anode materials and lithium battery anode materials. Optionally, the carbon-based material includes hard carbon materials and silicon-containing graphite materials.

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