Method for determining content of silicon in material

Abstract

The present disclosure provides a method for determining the content of silicon in a material. The determination method comprises: ashing a carbon-based material, so as to obtain an ashed product containing silicon; dissolving silicon in the ashed product by using an alkali solution, so as to obtain a silicon-containing solution; subjecting the silicon-containing solution to an ICP-OES test, so as to obtain the content of silicon in the silicon-containing solution; and calculating the content of silicon in the carbon-based material on the basis of the content of silicon in the silicon-containing solution.

Description

A method for determining silicon content in a material

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] The present disclosure claims priority to Chinese patent application No. 202311643921.5 filed on December 01, 2023, entitled “A method for determining the silicon content in a material,” the entire contents of which are incorporated herein by reference. Technical Field

[0003] The present disclosure relates to the field of chemical analysis, and in particular to a method for determining the silicon content in a material. Background Art

[0004] Silicon-based anode materials have become a research hotspot due to their high theoretical capacity. However, the significant volume effect of silicon anodes can lead to structural damage, which in turn affects the formation of the SEI film, consumes a large amount of lithium ions, and causes rapid capacity decay. Silicon nano-scaling, composite formation, and alloying can address these issues. In particular, doping carbon-based materials with silicon can effectively increase the specific capacity of the anode active material and effectively alleviate the problem of silicon volume expansion.

[0005] The silicon content in carbon-based materials has a great influence on the performance of the materials, so it is particularly important to accurately measure the silicon content in carbon-based materials.

[0006] Summary of the Invention

[0007] The present disclosure provides a method for determining the silicon content in a material to solve the problem of inaccurate determination of the silicon content in the current carbon-based materials.

[0008] The present disclosure provides a method for determining the silicon content in a material, comprising: ashing the material to obtain an ash containing silicon; dissolving the silicon in the ash using an alkaline solution to obtain a silicon-containing solution; performing an ICP-OES test on the silicon-containing solution to obtain the silicon content in the silicon-containing solution; and calculating the silicon content in the material based on the silicon content in the silicon-containing solution.

[0009] The determination method disclosed herein first ashes the material, during which carbon is removed in the form of gases such as carbon dioxide, exposing the silicon material wrapped by the carbon, thereby providing a good material basis for subsequent dissolution in an alkaline solution. In addition, part of the silicon will be converted into silicon oxide during this process. An alkaline solution is then used to dissolve the silicon element in the ashed material, allowing the silicon element to enter the solution to form a silicon-containing solution. The silicon-containing solution is then tested by ICP-OES (inductively coupled plasma atomic emission spectrometry) to obtain the silicon content in the silicon-containing solution, and then the silicon content in the material is calculated.

[0010] In any embodiment of the present disclosure, the alkaline solution includes any one or more of a sodium hydroxide aqueous solution and a potassium hydroxide aqueous solution; - The concentration of the alkali in the alkaline solution is 4mol / L-10mol / L; optionally, the concentration of the alkali in the alkaline solution is 4mol / L-10mol / L, and optionally, the mass ratio of the ash to the alkaline solution is 1:40-1:60. This improves the dissolution efficiency of the silicon element.

[0011] In any embodiment of the present disclosure, the process of dissolving silicon in ash using an alkaline solution includes: mixing the ash with the alkaline solution to form a mixture; heating the mixture to a temperature T1 and maintaining the temperature for a first predetermined time to obtain a silicon-containing solution, wherein the temperature T1 is optionally 160° C. to 200° C., and the first predetermined time is optionally 10 minutes to 40 minutes. Heating during the dissolution process improves the reaction efficiency of the silicon and the alkaline solution and shortens the dissolution time.

[0012] In any embodiment of the present disclosure, 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 is ≤10%, and the silicon content is 0.2 mg / L-10 mg / L.

[0013] In any embodiment of the present disclosure, after dissolving with an alkaline solution, there is a residual ash, and the determination method further includes: using a hydrofluoric acid solution to dissolve the residual ash to obtain a hexafluorosilicic acid solution; performing an ICP-OES test on the hexafluorosilicic acid solution to obtain the content of silicon in the hexafluorosilicic acid; and calculating the silicon content in the carbon-based material based on the content of silicon in the hexafluorosilicic acid and the content of silicon in the silicon-containing solution. A small amount of residue will not produce a large amount of SiF4 when dissolved with an excess of hydrofluoric acid solution, so there will be no problem of low silicon content test due to volatilization of SiF4, but instead the silicon content in the carbon-based material can be more accurately determined.

[0014] In any embodiment of the present disclosure, before using hydrofluoric acid to dissolve the residual ash, the residual ash is acidified, and optionally concentrated nitric acid is used to acidify the residual ash.

[0015] In any embodiment of the present disclosure, the process of dissolving the residual ash using a hydrofluoric acid solution includes: mixing the residual ash with the hydrofluoric acid solution, heating to a temperature T2 and keeping it warm 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 10min-40min.

[0016] In any embodiment of the present disclosure, 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.

[0017] In any embodiment of the present disclosure, the inner wall of the atomization chamber used for ICP testing is an inner wall resistant to acid and alkali corrosion.

[0018] In any embodiment of the present disclosure, the carbon-based material includes any one or more of a sodium battery negative electrode material and a lithium battery negative electrode material. Optionally, the carbon-based material includes a hard carbon material and a silicon-containing graphite material. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the technical solutions of the embodiments of the present disclosure, the following briefly introduces the drawings required for use in the embodiments of the present disclosure. Obviously, the drawings described below are only some embodiments of the present disclosure. For ordinary technicians in this field, other drawings can be obtained based on the drawings without any creative work.

[0020] FIG1 shows a filtered photograph of the substance after digestion of the sodium battery negative electrode material of Comparative Example 1.

[0021] FIG2 shows a filtration photograph of the dissolved product after alkali melting of the ashing sample of Comparative Example 4.

[0022] FIG3 is a graph showing a standard curve established using a standard solution containing a base matrix during ICP-OES testing in an embodiment of the present disclosure. DETAILED DESCRIPTION

[0023] The following detailed description of the embodiments of the present disclosure is provided in conjunction with the accompanying drawings and examples. The detailed description of the following embodiments and the accompanying drawings are used to illustrate the principles of the present disclosure, but are not intended to limit the scope of the present disclosure, that is, the present disclosure is not limited to the described embodiments.

[0024] Below, the embodiment of the method for determining the silicon content in the carbon-based material disclosed in the present invention is described in detail with appropriate reference to the accompanying drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there may be cases where detailed descriptions of well-known matters and repeated descriptions of actually the same structures are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate understanding by 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 disclosure and are not intended to limit the subject matter described in the claims.

[0025] " scope " disclosed in the present disclosure is limited in the form of lower limit and upper limit, and given range is limited by selecting a lower limit and an upper limit, and selected lower limit and upper limit define the boundary of special scope.The scope that this mode limits can be to include end value or not include end value, and can be combined arbitrarily, and promptly any lower limit can form a scope with any upper limit combination.For example, if the scope of 60-120 and 80-110 is listed for specific parameter, it is understood that the scope of 60-110 and 80-120 is also expected.In addition, if the minimum range value 1 and 2 listed, and if the maximum range value 3,4 and 5 listed, then the following scope can all be expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5.In the present disclosure, unless otherwise specified, numerical range " ab " represents the abbreviation of any real number combination between a and b, and wherein a and b are all real numbers. For example, a numerical range of "0-5" indicates that all real numbers between "0-5" are listed herein, and "0-5" is simply an abbreviation for these numerical combinations. Furthermore, when a parameter is expressed as an integer ≥ 2, this is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0026] Unless otherwise specified, all embodiments and optional embodiments of the present disclosure can be combined with each other to form new technical solutions.

[0027] Unless otherwise specified, all technical features and optional technical features disclosed herein can be combined with each other to form a new technical solution.

[0028] Unless otherwise specified, all steps of the present disclosure may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), which means that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), which means that step (c) may be added to the method in any order, for example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0029] If not otherwise specified, the “include” and “comprising” mentioned in the present disclosure are open-ended. For example, the “include” and “comprising” may indicate that other components not listed may also be included or comprised.

[0030] Unless otherwise specified, the term "or" is inclusive in this disclosure. For example, the condition "A or B" is satisfied by any of the following conditions: 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).

[0031] As mentioned above, the silicon content in carbon-based materials significantly impacts their performance, making accurate determination of silicon content in carbon-based materials crucial. However, the commonly used testing method for directly dissolving carbon-based materials using concentrated nitric acid and hydrofluoric acid results in a low silicon content due to the reaction of hydrofluoric acid with silicon and silicon dioxide to form silicon tetrafluoride, which is easily lost due to volatilization.

[0032] In order to solve this problem, the present disclosure provides a method for determining the silicon content in a material, which comprises: ashing the material to obtain an ash containing silicon; dissolving the silicon in the ash with an alkaline solution to obtain a silicon-containing solution; performing an ICP-OES test on the silicon-containing solution to obtain the silicon content in the silicon-containing solution; and calculating the silicon content in the material based on the silicon content in the silicon-containing solution.

[0033] The determination method disclosed herein first ashes the material, during which carbon is removed in the form of gases such as carbon dioxide, exposing the silicon material wrapped by the carbon, thereby providing a good material basis for subsequent dissolution in an alkaline solution. In addition, part of the silicon will be converted into silicon oxide during this process. An alkaline solution is then used to dissolve the silicon element in the ashed material, allowing the silicon element to enter the solution to form a silicon-containing solution. The silicon-containing solution is then tested by ICP-OES (inductively coupled plasma atomic emission spectrometry) to obtain the silicon content in the silicon-containing solution, and then the silicon content in the material is calculated.

[0034] The specific process of the above-mentioned ICP-OES test can refer to the existing technology, wherein the calibration method can adopt the external standard method.

[0035] In some embodiments, the material includes a carbon-based material containing silicon.

[0036] The above-mentioned ashing treatment can refer to the conventional ashing treatment method of carbon-based materials, such as burning the carbon-based material in air, optionally controlling the combustion temperature to 650° C.-850° C., and keeping the temperature for 2 h-6 h.

[0037] After ashing, in some embodiments, the silicon element in the material exists in the ash in the form of silicon or silicon oxide. 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 silicide (introduced from the raw materials). The surface of silicon and its silicide is coated with carbon, which cannot be dissolved in acid or alkali, resulting in low test results. According to the principle of C+O2=CO2↑, Si+O2=SiO2, ashing is used to remove the hard carbon and the carbon coated on the surface of silicon and its silicide in the material, exposing the silicon and its silicide, and even converting the silicon and its silicide into silicon dioxide, which is conducive to dissolution in alkaline solution.

[0038] In some embodiments, a strong alkaline solution is used as the alkaline solution. The alkaline solution includes any one or more of an aqueous sodium hydroxide solution and an aqueous potassium hydroxide solution. The reaction process of silicon and silicon dioxide is illustrated using the following examples: Si + 2NaOH + H2O = Na2SiO3 + 2H2↑ and SiO2 + 2NaOH = Na2SiO3 + H2O. It can be seen that silicon or silicon dioxide can react with the alkaline solution to form a water-soluble silicate.

[0039] In order to improve the dissolution efficiency of silicon, in some embodiments, OH in the alkaline solution may be optionally - The concentration of the alkali is 4mol / L-10mol / L; optionally, the concentration of the alkali in the alkali solution is 4mol / L-10mol / L, optionally, the mass ratio of the ash to the alkali solution is 1:40-1:60.

[0040] In some embodiments, the process of dissolving silicon in ash using an alkaline solution includes: mixing the ash with the alkaline solution to form a mixture; heating the mixture to a temperature T1 and maintaining the temperature for a first predetermined time to obtain a silicon-containing solution. Optionally, the temperature T1 is 160° C. to 200° C., and the first predetermined time is 10 minutes to 40 minutes. Heating during the dissolution process improves the reaction efficiency of the silicon and the alkaline solution and shortens the dissolution time.

[0041] Because the alkali concentration in the silicon-containing solution obtained after dissolution with an alkaline solution is also high, if the ICP-OES test is performed directly, the alkali therein will adhere to the equipment pipeline, and after repeated testing for a long time, the pipeline will be blocked, affecting the service life of the equipment. In order to reduce the impact of the testing process on the ICP-OES tester, in some embodiments of the present disclosure, before the silicon-containing solution is subjected to the ICP-OES test, the above-mentioned determination method also includes a 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 0.2mg / L-10mg / L. The above-mentioned silicon content needs to be known after the ICP-OES test. In actual operation, a parallel gradient dilution of the silicon-containing solution can be used. After the ICP-OES test, it is determined which dilution concentrations can meet the above-mentioned silicon content requirements. When the subsequent test of the same carbon-based material to be tested is carried out, the dilution concentration at this time can be referred to for dilution.

[0042] In some embodiments, there may be some silicon dioxide in the carbon-based material or ash that cannot be dissolved in the alkaline solution due to certain reasons (such as crystal phase structure), and there is a residue after the ash is dissolved in the alkaline solution, that is, there is a precipitate. In order to fully dissolve the residual ash to determine the silicon 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 an ICP-OES test on the hexafluorosilicic acid solution to obtain the silicon content in the hexafluorosilicic acid; and calculating the silicon content in the carbon-based material based on the silicon content in the hexafluorosilicic acid and the silicon content in the silicon-containing solution.

[0043] The main reaction formulas involved in the process of dissolving the residual ash using hydrofluoric acid solution are: SiO2+4HF=SiF4+2H2O, SiF4+2HF=H2SiF6.

[0044] Since the mass of the residual ash is very small, even if it is dissolved with hydrofluoric acid solution, a large amount of SiF4 will not be produced. Therefore, there will be no problem of low silicon content test due to SiF4 volatilization. Instead, the silicon content in the carbon-based material can be determined more accurately.

[0045] The hydrofluoric acid can be a higher concentration of hydrofluoric acid, such as 40% hydrofluoric acid. Since the residual ash mass is very small, the hydrofluoric acid is usually added in excess. Therefore, the generated SiF4 reacts rapidly to generate H2SiF6 due to the excess hydrofluoric acid.

[0046] In some embodiments, since the surface of the residual ash obtained after dissolving with an alkaline solution is alkaline due to the residue of the alkali, in order to reduce the consumption of hydrofluoric acid, before using hydrofluoric acid to dissolve the residual ash, the residual ash is acidified, and concentrated nitric acid is optionally used to acidify the residual ash. Since the presence of concentrated nitric acid will not have a negative impact on the reaction of subsequent hydrofluoric acid and silicon oxide, and may even promote the above reaction, the addition of concentrated nitric acid may not be particularly controlled. In some embodiments, taking 8mol / L concentrated nitric acid as an example, its volume addition amount may be 1-3 times that of the volume addition amount of 40% hydrofluoric acid.

[0047] In some embodiments of the present disclosure, the process of dissolving the residual ash with a hydrofluoric acid solution includes: mixing the residual ash with the hydrofluoric acid solution, heating to a temperature T2, and maintaining the temperature for a second predetermined time to obtain a hexafluorosilicic acid solution. Optionally, the temperature T2 is 160-200° C., and the second predetermined time is 10-40 minutes. Heating increases the reaction rate of the residual ash with the hydrofluoric acid, thereby shortening the reaction time.

[0048] To further alleviate the corrosion of hydrofluoric acid on the ICP-OES testing instrument, especially the corrosion of the atomization chamber, in some embodiments, the above-mentioned measurement method also includes a process of diluting the hexafluorosilicic acid solution before performing ICP-OES testing on 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 diluted hexafluorosilicic acid solution needs to be known after the ICP test. In actual operation, a parallel gradient dilution of the silicon-containing solution can be used. After the ICP test, it is determined which dilution concentration can meet the above-mentioned silicon content requirements. When subsequently testing the same carbon-based material to be tested, the dilution concentration at this time can be used as a reference for dilution.

[0049] In some embodiments, in order to extend the service life of the ICP-OES testing instrument, the inner wall of the atomization chamber used in the ICP-OES test is optionally an inner wall resistant to acid and alkali corrosion.

[0050] In some embodiments, the carbon-based material includes any one or more of a sodium battery negative electrode material and a lithium battery negative electrode material. Optionally, the carbon-based material includes a hard carbon material and a silicon-containing graphite material.

[0051] [Example]

[0052] The following examples are provided. The examples described below are illustrative and are intended only to explain the present disclosure and are not to be construed as limiting the present disclosure. Where specific techniques or conditions are not specified in the examples, the methods were performed according to those described in the literature in the art or according to the product specifications. Reagents or instruments used without manufacturer's indication are all commercially available conventional products.

[0053] Comparative Example 1

[0054] Weigh 0.1 g of sodium battery negative electrode material (mainly hard carbon, containing a relatively large amount of silicon, hereinafter referred to as sodium battery negative electrode material) into a microwave digestion vessel; add 3 mL of hydrofluoric acid (concentration of 40%) to the microwave digestion vessel; seal the digestion vessel, set the power of the microwave digester to 1800 W, and ramp up to 180° C. for 25 minutes.

[0055] Observe the phenomenon after digestion: the digestion was not complete and there was precipitation in the solution, as shown in Figure 1.

[0056] Comparative Example 2

[0057] Except that the amount of hydrofluoric acid added was changed to 6 mL, the other steps of Comparative Example 2 were the same as those of Comparative Example 1.

[0058] Observe the phenomenon after digestion: not completely digested, there is precipitation in the solution.

[0059] Comparative Example 3

[0060] Except that 10 mL of nitric acid (8 mol / L) and 5 mL of hydrofluoric acid were added instead of 3 mL of hydrofluoric acid, other steps were the same as those in Comparative Example 1.

[0061] Observe the phenomenon after digestion: not completely digested, there is precipitation in the solution.

[0062] Example 1

[0063] Ashing of negative electrode materials for sodium ion batteries

[0064] Mix the sodium negative electrode materials evenly, accurately weigh 10±0.01g of materials, and record the actual mass as m1. Spread them thinly in a 30cm×30cm alumina crucible, place the crucible in the middle of the muffle furnace, close the furnace body, slowly adjust the air flow to 1L / min, set the temperature program, and heat it to 750℃ at a temperature rise rate of 5℃ / min, keep warm for 4h, and after cooling to room temperature, open the muffle furnace, take out the crucible, collect the ashed sample and weigh it, and record the actual mass as m2.

[0065] Preparation of alkaline solution

[0066] Take a clean plastic beaker, accurately weigh 20g of sodium hydroxide (AR grade) particles, add 50mL of ultrapure water, stir until completely dissolved, transfer the solution to a 100mL plastic volumetric flask, rinse the beaker with ultrapure water three times, add the rinse liquid into the volumetric flask, add ultrapure water to make the volume up to 100mL, cover the volumetric flask tightly, and mix evenly by inverting to obtain a sodium hydroxide solution with a concentration of 5mol / L.

[0067] [Dissolution of the sample in alkaline solution after ashing]

[0068] Mix the ashed sample evenly. Accurately weigh the ashed sample into a clean 50mL polytetrafluoroethylene beaker, record the actual mass (m³), and slowly dropwise add 4mL of 5mol / L sodium hydroxide solution. React at 180°C for 12 minutes until a small amount of precipitate remains in the solution and can no longer be dissolved. Filter the sample while hot into a 100mL plastic volumetric flask. Rinse the precipitate four times with ultrapure water. Combine the washings with the volumetric flask, add ultrapure water to the volume, mix thoroughly, pipette 1mL and dilute to 100mL. Mix thoroughly to obtain the silicon-containing solution to be tested.

[0069]

Precipitation and dissolution

[0070] Place the precipitate and filter paper in a clean polytetrafluoroethylene beaker, add 4 mL of 8 mol / L nitric acid to acidify, then add 2 mL of 40% HF solution and dissolve at 180°C for 25 min. When the solution is clear, transfer the solution to a 100 mL plastic volumetric flask, add ultrapure water to the volume, mix well, transfer 1 mL to dilute to 100 mL, mix well, and obtain the hexafluorosilicic acid solution to be tested.

[0071] Example 2

[0072] The other steps were the same as those in Example 1, except that 6 mL of 5 mol / L sodium hydroxide solution was slowly added dropwise during the dissolution of the ashing sample in the alkaline solution and the reaction was carried out at 180° C. for 20 min.

[0073] Example 3

[0074] When dissolving the deashed sample in an alkaline solution, the temperature was adjusted to 180° C. and the reaction was carried out for 40 minutes. Other steps were the same as those in Example 1.

[0075] Example 4

[0076] When dissolving the deashed sample in an alkaline solution, the temperature was adjusted to 180° C. and the reaction was carried out for 120 min. Other steps were the same as those in Example 1.

[0077] Example 5

[0078] When dissolving the deashed sample in an alkaline solution, the temperature was adjusted to 160° C. and the reaction was carried out for 20 minutes. Other steps were the same as those in Example 1.

[0079] Example 6

[0080] When dissolving the deashed sample in an alkaline solution, the temperature was adjusted to 200° C. and the reaction temperature was 20 min. Other steps were the same as those in Example 1.

[0081] Example 7

[0082] When dissolving the deashed sample in an alkaline solution, the temperature was adjusted to 150° C. and the reaction was carried out for 20 minutes. Other steps were the same as those in Example 1.

[0083] Example 8

[0084] When dissolving the deashed sample in an alkaline solution, the temperature was adjusted to 220° C. and the reaction time was 20 min. Other steps were the same as those in Example 1.

[0085] Example 9

[0086] When preparing the alkaline solution, a 4 mol / L sodium hydroxide solution was prepared. This 4 mol / L sodium hydroxide solution was used to replace the 5 mol / L sodium hydroxide solution in Example 1 during the dissolution of the alkaline solution of the sample after ashing. The remaining steps were the same as in Example 1.

[0087] Example 10

[0088] When preparing the alkaline solution, a 10 mol / L sodium hydroxide solution was prepared. This 10 mol / L sodium hydroxide solution was used to replace the 5 mol / L sodium hydroxide solution in Example 1 during the dissolution of the alkaline solution of the sample after ashing. The remaining steps were the same as in Example 1.

[0089] Example 11

[0090] When preparing the alkaline solution, a 5 mol / L potassium hydroxide solution was prepared. This 5 mol / L potassium hydroxide solution was used to replace the 5 mol / L sodium hydroxide solution in Example 1 during the dissolution of the alkaline solution of the sample after ashing. The remaining steps were the same as in Example 1.

[0091] Example 12

[0092] In the precipitation dissolution step, the dissolution temperature was adjusted to 160° C. The remaining steps were the same as in Example 1.

[0093] Example 13

[0094] In the precipitation dissolution step, the dissolution temperature was adjusted to 200° C. The remaining steps were the same as in Example 1.

[0095] Example 14

[0096] In the precipitation dissolution step, the dissolution temperature was adjusted to 150° C. The remaining steps were the same as in Example 1.

[0097] Example 15

[0098] In the precipitation dissolution step, the dissolution temperature was adjusted to 220° C. The remaining steps were the same as in Example 1.

[0099] Example 16

[0100] In the precipitation dissolution step, the dissolution time was adjusted to 10 min. The remaining steps were the same as in Example 1.

[0101] Example 17

[0102] In the precipitation dissolution step, the dissolution time was adjusted to 40 min. The remaining steps were the same as in Example 1.

[0103] Example 18

[0104] In the precipitation dissolution step, the dissolution time was adjusted to 60 min. The remaining steps were the same as in Example 1.

[0105] Example 19

[0106] Silica powder was used to replace the sodium negative electrode material of Example 1, and the silica powder was not ashed. A sample of silica powder was accurately weighed in a clean 50 mL polytetrafluoroethylene beaker, and the actual mass m3 was recorded. 4 mL of 5 mol / L sodium hydroxide solution was slowly added dropwise, and the mixture was reacted at 180 ° C for 12 min until it was completely dissolved without precipitation.

[0107] Comparative Example 4

[0108] [Alkali fusion of sample after ashing]

[0109] 0.1 g of the ashed material in Example 1 was weighed into a nickel crucible, 2 g of sodium hydroxide (AR grade) particles were added, the crucible was covered with a small gap, and placed in the middle of a muffle furnace. The furnace was closed and heated to 600 ° C at a temperature rise rate of 5 ° C / min, kept warm for 20 min, and cooled to room temperature. The muffle furnace was opened and the crucible was taken out.

[0110]

Eutectic Dissolution

[0111] Add 30 mL of boiling water to the crucible containing the eutectic and dissolve it.

[0112]

Phenomenon after dissolution

[0113] It failed to dissolve completely and there was a lot of precipitation, as shown in Figure 2.

[0114] Since Comparative Examples 1 to 4 all had precipitates, ICP testing was not performed.

[0115] Comparative Example 5

[0116] [Ashing of sodium ion battery negative electrode materials] Same as Example 1

[0117]

Dissolution of sample after ashing

[0118] Mix the ashed sample evenly, accurately weigh 0.1±0.05g of the ashed sample into a clean 50mL polytetrafluoroethylene beaker, record the actual mass m3, add 10mL of 40% hydrofluoric acid solution and 5mL of 8mol / L HNO3 solution, cover with a polyethylene watch glass, decompose completely in a 60℃ constant temperature water bath, remove and cool, then filter, collect the filtrate into a 200mL polytetrafluoroethylene volumetric flask after thorough washing, make up to volume, shake well to obtain the solution to be tested.

[0119] ICP-OES testing

[0120] The following methods were used to test the silicon-containing solution to be tested, the hexafluorosilicic acid solution to be tested, and the solution to be tested in each embodiment.

[0121] Using alkali solution as the matrix (C NaOH =0.05mol / L) and a Si standard in an acid solution (1% HF, trace HNO3) were added to ultrapure water to prepare gradient Si concentration standard solutions (0.2, 1.0, 2.0, 5.0, 10.0 mg / L).

[0122] An ICP-OES tester with a corrosion-resistant (HF-resistant) spray chamber was used, and the Si spectral line 252.611 nm was selected. The operating parameters were as follows: ① the cooling gas, auxiliary gas, and carrier gas were all argon with a volume concentration of 99.999%; ② the RF power was 1395-1405 W; ③ the nebulizer flow rate was 0.6-0.8 L / min; ④ the observation angle was radial. A Si standard curve was customized, in which an example of the customized standard curve when calibrated with alkali solution as the matrix is ​​shown in Figure 3. The linear correlation coefficient R 2 >0.999. After the test, the silicon content (in mg / L) in the silicon-containing solution to be tested is quantified using the standard curve of the Si standard solution prepared using the above-mentioned alkali solution as the matrix, and the mass percentage w1 is obtained after correction by the correction factor (i.e., multiplying by the dilution volume and dividing by the mass of the calcined material). The Si content (in mg / L) in the hexafluorosilicic acid solution to be tested is quantified using the standard curve of the Si standard solution prepared using the acid solution as the matrix, and the mass percentage w2 is obtained after correction by the correction factor (i.e., multiplying by the dilution volume and dividing by the mass of the calcined material).

[0123] The following formula is used to calculate the mass percentage of silicon element in the sodium battery negative electrode material in each embodiment.

[0124] The mass percentage of Si element in the material ω:

[0125] W=m Si / m1=(w1×m3+w2×m3) / (m3÷w 收率)=(w1+w2)×m3 / [m3 / (m2 / m1)]=(w1+w2)×(m2 / m1)

[0126] w1——The Si content (mass percentage) in the silicon-containing material to be tested in the ashing material used for testing, which is calibrated using a standard solution based on alkali liquor;

[0127] w2——The Si content (mass percentage) in the hexafluorosilicic acid solution to be tested in the ashed material, which is calibrated using a standard solution based on acid;

[0128] w 收率 ——Mass percentage of material after ashing to material before ashing;

[0129] m1 - the mass of the material before ashing;

[0130] m2——mass of material after ashing;

[0131] m3 - the mass of the ashing material used for testing.

[0132] The silicon content in the sodium negative electrode material in Comparative Example 5 was calculated using the following formula.

[0133] The above calculation results are recorded in Table 1.

[0134] According to the comparison between Example 1, Example 3 and Example 4 in Table 1, it can be seen that as the reaction time of the alkaline solution is prolonged, more silicon element is dissolved, which increases w1 and even w2. This may be because the alkaline solution fully dissolves silicon element and soluble silicon oxide, which is beneficial to the exposure of insoluble silicon oxide and promotes its dissolution in 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 element is dissolved, which increases w1; according to the comparison between Examples 2 and 3, it can be seen that the amount of alkaline solution used has a key influence on the dissolution efficiency of silicon element, and this influence is more significant than the influence of dissolution time and dissolution temperature.

[0135] 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 beneficial 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. This may be due to the problem of excessively high temperature causing the rapid formation of silicon tetrafluoride, resulting in loss.

[0136] Example 19 used silicon dioxide for the experiment. After dissolution with sodium hydroxide solution, no precipitate remained, indicating that all of it was dissolved. That is to say, when the tested object 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.

[0137] The results of Comparative Example 5 are obviously lower than those of the examples. This is because the generated silicon tetrafluoride is seriously lost due to volatilization, resulting in a low result.

[0138] While the present disclosure has been described with reference to preferred embodiments, various modifications may be made thereto and equivalent components may be substituted without departing from the scope of the present disclosure. In particular, the various technical features described in the various embodiments may be combined in any manner, provided no structural conflicts exist. The present disclosure is not limited to the specific embodiments disclosed herein, but encompasses all technical solutions within the scope of the claims.

Claims

1. A method for determining the silicon content in a material, comprising: The material is subjected to an ashing treatment to obtain an ashed product containing silicon element; dissolving silicon in the ash by using an alkaline solution to obtain a silicon-containing solution; Performing ICP-OES test on the silicon-containing solution to obtain the content of silicon element in the silicon-containing solution; The silicon content in the material is calculated based on the silicon content in the silicon-containing solution.

2. The assay method according to claim 1, wherein The alkaline solution includes any one or more of a sodium hydroxide aqueous solution and a potassium hydroxide aqueous solution.

3. The assay method according to claim 1 or 2, wherein The OH in the alkaline solution - The concentration is 4mol / L-10mol / L.

4. The assay method according to any one of claims 1 to 3, wherein The concentration of the alkali in the alkali solution is 4 mol / L-10 mol / L.

5. The assay method according to any one of claims 1 to 4, wherein The mass ratio of the ash to the alkaline solution is 1:40-1:

60.

6. The assay method according to any one of claims 1 to 5, wherein The process of using an alkaline solution to dissolve silicon in the ash comprises: mixing the ash and the alkaline solution to form a mixture; The mixture is heated to a temperature T1 and kept at that temperature for a first predetermined time to obtain the silicon-containing solution.

7. The assay method according to claim 6, wherein The temperature T1 is 160°C-200°C.

8. The assay method according to claim 6 or 7, wherein The first predetermined time is 10 minutes to 40 minutes.

9. The assay method according to any one of claims 1 to 8, 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.

10. The measuring method according to claim 9, wherein The alkalinity of the diluted silicon-containing solution is ≤10%, and the silicon content is 0.2 mg / L-10 mg / L.

11. The assay method according to any one of claims 1 to 10, wherein After the ash is dissolved by the alkaline solution, there is a residue, and the determination method further comprises: dissolving the remaining incinerated material with a hydrofluoric acid solution to obtain a hexafluorosilicic acid solution; Performing ICP-OES test on the hexafluorosilicic acid solution to obtain the content of silicon in the hexafluorosilicic acid; The silicon content in the carbon-based material is calculated based on the silicon content in the hexafluorosilicic acid and the silicon content in the silicon-containing solution.

12. The assay method according to claim 11, wherein Before using hydrofluoric acid to dissolve the residual ash, the residual ash is acidified.

13. The assay method according to claim 12, wherein The residual ash is acidified with concentrated nitric acid.

14. The assay method according to any one of claims 11 to 13, wherein The process of dissolving the residual ash by using a hydrofluoric acid solution comprises: The residual ash is mixed with the hydrofluoric acid solution, and then heated to a temperature T2 and kept warm for a second predetermined time to obtain the hexafluorosilicic acid solution.

15. The assay method according to claim 14, wherein The temperature T2 is 160°C-200°C.

16. The assay method according to claim 14 or 15, wherein The second predetermined time is 10 minutes to 40 minutes.

17. The assay method according to any one of claims 11 to 16, wherein Before performing ICP-OES test on the hexafluorosilicic acid solution, the determination method further includes a process of diluting the hexafluorosilicic acid solution.

18. The assay method according to claim 17, wherein The silicon content in the diluted hexafluorosilicic acid solution is 0.2 mg / L-10 mg / L.

19. The assay method according to any one of claims 1 to 18, wherein The inner wall of the atomization chamber used in the ICP test is an inner wall resistant to acid and alkali corrosion.

20. The assay method according to any one of claims 1 to 19, wherein The carbon-based material includes any one or more of a sodium battery negative electrode material and a lithium battery negative electrode material.

21. The assay method according to claim 20, wherein The carbon-based material includes a hard carbon material and a silicon-containing graphite material.

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