Method for testing silicon content in lithium supplement

Abstract

The application provides a test method for the content of silicon in a lithium supplement, and belongs to the technical field of lithium ion batteries. The test method is a test method for completely dissolving the lithium supplement and obtaining an accurate test result, and actually solves the problems of incomplete dissolution of the lithium supplement before element analysis, incomplete element precipitation and the like.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery technology, specifically relating to a method for testing the silicon content in lithium replenishing agents. Background Technology

[0002] A lithium-ion battery is a rechargeable battery that uses a lithium-containing compound as the positive electrode. During charging and discharging, lithium ions are repeatedly extracted and inserted between the positive and negative electrodes. During charging, lithium ions are extracted from the positive electrode, pass through the electrolyte, and insert into the negative electrode, which is then in a lithium-rich state. The battery is fully charged when all the lithium ions have returned to the negative electrode. During discharging, lithium ions return from the negative electrode to the positive electrode, and the battery is fully discharged when all the lithium ions have returned to the positive electrode. Therefore, the capacity of a lithium-ion battery is determined by the amount of lithium that can be extracted and inserted into the negative electrode material and the active lithium ion content of the positive electrode material.

[0003] Therefore, adding a small amount of lithium source to the battery material before the lithium-ion battery operates to compensate for the lithium source consumed during charging and discharging is an effective way to improve battery capacity and energy density. Currently, lithium silicate materials such as lithium orthosilicate (Li4SiO4) or lithium metasilicate (Li2SiO3) are generally used as a framework to construct lithium replenishing agents. Moreover, in order to improve the effect of lithium replenishing agents, various structures and elements are used in the design. For example, some related technologies use non-metallic elements as dopants to be embedded in the framework to replace part of the silicon element to form doped lithium replenishing agents, while other related technologies coat the surface of lithium silicate materials with a carbon coating layer or organic polymer to form a core-shell structure lithium replenishing agent. This increases the difficulty of determining the silicon content in the lithium replenishing agent.

[0004] The commonly used method for testing silicon content in lithium replenishers is ICP-OES. According to the national standard GB / T 33822-2017, after the lithium replenisher sample is dissolved in hydrochloric acid, the silicon content is tested using an inductively coupled plasma atomic emission spectrometer (ICP-OES) with a standard curve method. However, in practice, because silicon cannot react with hydrochloric acid at high temperatures, the silicon in the lithium replenisher sample cannot be completely dissolved in the reagent, resulting in only the detection of silicon suspended in the solution, leading to highly inaccurate results. Furthermore, the ICP-OES method is even less suitable for lithium replenishers with complex structures and compositions, such as doped lithium replenishers and core-shell lithium replenishers. Therefore, there is an urgent need to design a method for testing the silicon content in lithium replenishers. Summary of the Invention

[0005] This invention aims to at least partially solve one of the technical problems in related technologies. To this end, embodiments of this invention propose a method for testing the silicon content in lithium supplements.

[0006] The method for testing the silicon content in the lithium supplement of this invention includes the following steps:

[0007] (1) The lithium supplement is mixed with sodium carbonate and sodium peroxide in a crucible and then sintered to obtain a molten alkaline fusible mixture.

[0008] (2) The alkaline fusion reagent is mixed with concentrated nitric acid solution and water in a glass container and then heated and concentrated. When the solution is reduced to 30-60%, concentrated hydrochloric acid solution is added for the first heating acidolysis treatment. The solution is evaporated to near dryness to obtain the first precipitate. Then the first precipitate is mixed with concentrated perchloric acid solution and heated to boiling. After filtration, the second precipitate is obtained. The second precipitate is then washed with hot concentrated sulfuric acid solution to obtain the third precipitate.

[0009] (3) The third precipitate is placed in the crucible, and first ashing treatment is performed, followed by a first calcination treatment until constant weight is obtained to obtain the fourth precipitate;

[0010] (4) Add concentrated sulfuric acid solution and water to the fourth precipitate in the crucible, then add concentrated hydrofluoric acid solution, and perform a second heating acidolysis treatment. Evaporate the solution to near dryness to obtain the first residue, and then perform a second calcination treatment on the first residue until constant weight to obtain the second residue.

[0011] (5) Repeat steps (1)-(4) for a blank experiment without the lithium supplementation agent;

[0012] (6) Calculate the mass fraction ω of silicon in the lithium replenisher according to the following formula. Si :

[0013]

[0014] Wherein, m1 is the total mass of the fourth precipitate and the crucible, m2 is the total mass of the second residue and the crucible, m3 is the total mass of the fourth precipitate and the crucible in the blank experiment, m4 is the total mass of the second residue and the crucible in the blank experiment, 0.4675 is the mass conversion factor for silicon dioxide to silicon, and m is the mass of the lithium replenishing agent.

[0015] The advantages and technical effects of the testing method in this embodiment of the invention are as follows:

[0016] 1. Step (1) has the following three functions: firstly, it is to convert the silicates formed by impurity elemental silicon, silicon dioxide and some impurity metals in the lithium replenishing agent into sodium silicate (Na2SiO3); secondly, it is to remove some carbon, sulfur and phosphorus that will not be acidified in the subsequent melting process; and thirdly, it is to destroy the spatial structure of the lithium replenishing agent and make the dense structure loose.

[0017] 2. Step (2) involves the first heating acidolysis treatment to digest sodium silicate into silicic acid (H2SiO3) precipitate. The order of adding various acids must be in accordance with the above-described manner; otherwise, it will affect the accuracy of the test results or be corrosive to the crucible.

[0018] 3. Step (3) can convert the third precipitate (silicic acid precipitate) into silicon dioxide; Step (4) then uses concentrated hydrofluoric acid solution to digest the silicon dioxide, and the resulting gaseous silicon fluoride (SiF4) will evaporate. The addition of concentrated sulfuric acid solution is to accelerate the digestion rate; Finally, Step (5) can be used to calculate the silicon content in the lithium replenishing agent.

[0019] 4. The testing method in this embodiment of the invention has high accuracy. Detailed Implementation

[0020] Embodiments of the present invention are described in detail below. These embodiments are exemplary and intended to explain the present invention, and should not be construed as limiting the invention.

[0021] This invention provides a method for testing the silicon content in a lithium supplement, comprising the following steps:

[0022] (1) The lithium supplement is mixed with sodium carbonate and sodium peroxide in a crucible and then sintered to obtain a molten alkaline fusible mixture.

[0023] (2) The alkaline fusion reagent is mixed with concentrated nitric acid solution and water in a glass container and then heated and concentrated. When the solution is reduced to 30-60%, concentrated hydrochloric acid solution is added for the first heating acidolysis treatment. The solution is evaporated to near dryness to obtain the first precipitate. Then the first precipitate is mixed with concentrated perchloric acid solution and heated to boiling. After filtration, the second precipitate is obtained. The second precipitate is then washed with hot concentrated sulfuric acid solution to obtain the third precipitate.

[0024] (3) The third precipitate is placed in the crucible, and first ashing treatment is performed, followed by a first calcination treatment until constant weight is obtained to obtain the fourth precipitate;

[0025] (4) Add concentrated sulfuric acid solution and water to the fourth precipitate in the crucible, then add concentrated hydrofluoric acid solution, and perform a second heating acidolysis treatment. After the solution is evaporated to dryness, place it in a muffle furnace to completely dry the moisture and achieve constant weight.

[0026] (5) Repeat steps (1)-(4) for a blank experiment without the lithium supplementation agent;

[0027] (6) Calculate the mass fraction ω of silicon in the lithium replenisher according to the following formula. Si :

[0028]

[0029] Wherein, m1 is the total mass of the fourth precipitate and the crucible, m2 is the total mass of the second residue and the crucible, m3 is the total mass of the fourth precipitate and the crucible in the blank experiment, m4 is the total mass of the second residue and the crucible in the blank experiment, 0.4675 is the mass conversion factor for silicon dioxide to silicon, and m is the mass of the lithium replenishing agent.

[0030] Working principle: The purpose of step (1) is threefold. First, it is to convert the silicates formed by impurity elemental silicon, silicon dioxide and some impurity metals in the lithium replenishing agent into sodium silicate (Na2SiO3). Second, it is to remove some carbon, sulfur and phosphorus that will not be acidified in the subsequent melting process. Third, it is to destroy the spatial structure of the lithium replenishing agent and make the dense structure loose.

[0031] Step (2) involves a first heating acidolysis treatment to digest sodium silicate into silicic acid (H2SiO3) precipitate. The order of adding various acids should follow the steps described above. When transferring the alkali-fusible mixture from the crucible to the glass container, there may still be residue on the crucible. Therefore, the residue on the crucible should first be rinsed into the beaker with a mixture of concentrated nitric acid and water. After heating and concentration, it can be mixed with the added concentrated hydrochloric acid to form aqua regia. Aqua regia has good solubility for most metals and can digest sodium silicate into silicic acid (H2SiO3) precipitate. The reason for using this method instead of directly rinsing the residue on the crucible with aqua regia is that aqua regia can also dissolve the crucible. The reason for not rinsing the residue on the crucible into the beaker with concentrated hydrochloric acid and water and then heating and concentrating it is that the boiling points of hydrochloric acid and water are relatively close. If hydrochloric acid is used instead, it is difficult to control the temperature during concentration, and the hydrochloric acid is easy to volatilize.

[0032] To prevent aqua regia from corroding the crucible in step (3), in step (2), a perchloric acid solution (203°C) with a boiling point higher than nitric acid (122°C) and hydrochloric acid (110°C) is added to the first precipitate and heated at high temperature to completely evaporate the aqua regia, resulting in a second precipitate without aqua regia residue. Since the hot concentrated sulfuric acid solution is more corrosive than nitric acid and hydrochloric acid and can better wash off the residue, the second precipitate in the glass container is then transferred to filter paper, and the remaining second precipitate in the glass container is also washed off with concentrated sulfuric acid solution. The second precipitate is washed repeatedly to obtain a third precipitate, namely silica precipitate.

[0033] Step (3) is to convert the third precipitate (silicic acid precipitate) into silicon dioxide. The third precipitate can be transferred separately from the filter paper to the crucible, or it can be transferred together with the filter paper. Considering the need to improve the accuracy of the test results, the latter is preferred, and the carbonization and blackening of the filter paper will not affect the accuracy of subsequent test results. The third precipitate should be ashed before the first ignition treatment. If ignition is performed directly, the heating rate will be too fast, causing the moisture on the third precipitate and filter paper to evaporate rapidly, which can easily lead to sample splashing and affect the test accuracy.

[0034] Step (4) mainly uses concentrated hydrofluoric acid solution to digest silicon dioxide, resulting in the volatilization of gaseous silicon fluoride (SiF4). The addition of concentrated sulfuric acid solution is to accelerate the digestion rate. After a second calcination treatment in step (4) until constant weight is achieved, all silicon-containing substances are digested and volatilized. Finally, step (5) is used to calculate the silicon content in the lithium replenisher.

[0035] In some embodiments, in step (1), the lithium replenishing agent includes at least one of lithium silicate, non-metallic element-doped lithium silicate, carbon-coated lithium silicate, and organic polymer-coated lithium silicate. The test method of this embodiment is applicable to all of the above types of lithium replenishing agents.

[0036] In some embodiments, in step (1), the mass ratio of the lithium replenishing agent to the alkaline reagent is (1-10):(15-25), and the mass ratio of the sodium carbonate to the sodium peroxide is 1:(1-2). The above material ratios help to decompose the lithium replenishing agent and its impurities into sodium silicate.

[0037] In some embodiments, in step (1), the sintering treatment temperature is 300-900℃ and the time is 10-15 min. When the sintering treatment temperature is too low or the time is too short, it is not conducive to the complete decomposition of the lithium supplement and its impurities into sodium silicate. When the sintering treatment temperature is too high or the time is too long, it is not conducive to cost reduction and efficiency improvement.

[0038] In step (1), to prevent the lithium replenishing agent from sticking to the crucible after melting and affecting the accuracy of subsequent test results, a layer of sodium carbonate and sodium peroxide mixture can be first laid at the bottom of the crucible. Then, a specified amount of lithium replenishing agent is mixed with sodium carbonate and sodium peroxide in the crucible, and another layer of sodium carbonate and sodium peroxide mixture is laid on top. Then, the mixture is melted to obtain a molten alkaline fusion reagent. Additionally, it is understandable that to prevent the lithium replenishing agent from splashing out of the crucible during the melting process and affecting the accuracy of subsequent test results, the crucible lid can be partially covered, leaving space for ventilation and observation.

[0039] In some embodiments, in step (2), the volume ratio of concentrated nitric acid to water is 1:(4-5). In some embodiments, in step (2), the temperature of the heating concentration treatment is 100-120°C.

[0040] Since the boiling point of nitric acid solution is 122°C, low-temperature concentration at a temperature below the boiling point of nitric acid solution helps to reduce the volatilization of nitric acid.

[0041] In some embodiments, in step (2), the volume ratio of the concentrated nitric acid solution to the concentrated hydrochloric acid solution is (16.6-40):(15-20). Under this material ratio, aqua regia is formed in step (2) and used for the digestion of sodium silicate. Concentrated nitric acid has strong oxidizing properties; adding an excess of concentrated nitric acid when preparing aqua regia ensures that the metal ions are completely oxidized during the reaction, preventing the formation of residual metal ions. Furthermore, concentrated nitric acid can also act as a strong acid to neutralize impurities in concentrated hydrochloric acid, ensuring the purity and accuracy of the reaction. Therefore, adding an excess of nitric acid when preparing aqua regia can improve the efficiency and accuracy of the reaction.

[0042] In some embodiments, in step (2), the temperature of the first heating acid hydrolysis treatment is 90-110℃, and the time is 15-30 min. The reaction that occurs here is Na2SiO3 + 2HCl = 2NaCl + H2SiO3↓. The concentrated nitric acid solution is then mixed with the added concentrated hydrochloric acid solution to prepare aqua regia, which can accelerate the digestion reaction. When the temperature of the first heating acid hydrolysis treatment is too low or the time is too short, it is not conducive to increasing the digestion rate of sodium silicate. On the other hand, when the temperature of the first heating acid hydrolysis treatment is too high or the time is too long, the digestion effect will not be significantly enhanced, which is not conducive to cost reduction and efficiency improvement.

[0043] In some embodiments, in step (2), the volume ratio of the concentrated hydrochloric acid solution to the concentrated perchloric acid solution is 1:(0.8-1.2). When this ratio is too low, it is not conducive to the complete digestion of sodium silicate. When this ratio is too high, the amount of concentrated perchloric acid solution used is too small, which is not conducive to the evaporation of aqua regia and will corrode the crucible in subsequent step (3).

[0044] In some embodiments, in step (2), the temperature of the hot concentrated sulfuric acid solution is 70-90°C. The hot concentrated sulfuric acid solution is more corrosive than the concentrated nitric acid solution and the concentrated hydrochloric acid solution, which can better clean the residue on the glass container wall, and can also better dissolve the impurities in the second precipitate and improve the purity of the third precipitate (silicic acid).

[0045] In some embodiments, in step (3), the ashing temperature is 500-600°C, and ashing is performed until the filter paper is completely carbonized and turns black, typically for 3-6 hours. If the ashing temperature is too low or the time is too short, the subsequent first calcination treatment will heat up too quickly, and the moisture on the third precipitate and filter paper will evaporate rapidly, easily causing sample splashing and affecting the test accuracy.

[0046] In some embodiments, in step (3), the temperature of the first calcination treatment is 1085-1200℃, and / or the time for a single first calcination treatment is 20-30 minutes, and constant weight is achieved after repeated first calcination treatments. The third precipitate (silicic acid) becomes the fourth precipitate, namely silicon dioxide, after the first calcination treatment. When the temperature of the first calcination treatment is too low or the time is too short, it is not conducive to the complete conversion of sodium silicate into silicon dioxide. When the temperature of the first calcination treatment is too high or the time is too long, it is not conducive to cost reduction and efficiency improvement.

[0047] In some embodiments, in step (4), the volume ratio of concentrated sulfuric acid to water is (0.8-1.2):(0.8-1.2); and / or, the volume ratio of concentrated sulfuric acid to concentrated hydrofluoric acid is (2.5-5):(10-20). The reaction that occurs in step (4) is Si + 4HF = SiF4↑ + 2H2↑, wherein the proportions of the materials are within the above range, which helps to improve the digestion effect of the fourth precipitate (silicon dioxide).

[0048] In some embodiments, in step (4), concentrated sulfuric acid solution and water are added to the fourth precipitate in the crucible, followed by a portion of the concentrated hydrofluoric acid solution. The mixture is heated until fumes are emitted, and after slightly cooling, the remaining hydrofluoric acid solution is added. The mixture is heated until the sulfuric acid is completely decomposed and no longer fumes are emitted. The mixture is then evaporated to near dryness to obtain the first residue. The first residue is then subjected to a second calcination treatment until constant weight is achieved to obtain the second residue. The concentrated hydrofluoric acid solution is added in steps to reduce the intensity of the reaction and avoid reagent splashing, which could affect the accuracy of the test results.

[0049] In some embodiments, in step (4), the temperature of the second calcination treatment is 1000-1100°C; and / or, the time for a single first calcination treatment is 20-30 minutes, and constant weight is achieved after repeated first calcination treatments. The second calcination treatment is to remove excess moisture and make the results more accurate.

[0050] The present invention will now be described in detail with reference to the embodiments.

[0051] The lithium supplement selected for testing was a boron-doped lithium silicate powder that had been purchased. 1.0000±0.0010g of the powder was weighed, and 6 parallel samples were tested for each of the following examples or comparative examples.

[0052] Example 1

[0053] A method for testing the silicon content in a lithium supplement includes the following steps:

[0054] (1) Using sodium carbonate and sodium peroxide in a mass ratio of 1:1 as a mixed reagent, first spread a layer of mixed reagent at the bottom of the nickel crucible, add 1.0000±0.0010g of lithium replenishing agent powder, then add 20g of mixed reagent, mix the lithium replenishing agent powder and mixed reagent thoroughly, then cover it with another layer of mixed reagent, loosely cover the crucible lid, leaving room for ventilation and observation, place the nickel crucible on a hot plate and bake until the reagent turns yellow, remove it, place it in a heating device and heat it from room temperature to 600℃ and maintain this temperature for 12 minutes until the sample becomes molten, remove it and cool it.

[0055] (2) Using a 1:4 volume ratio of concentrated nitric acid solution (volume fraction: 67-68%) and ultrapure water as a mixed solution, wash the residue on the crucible and crucible lid into a beaker with the mixed solution and stir until no precipitate forms. Add the mixed solution to 150 mL in the beaker and heat it on a hot plate at 115 °C to concentrate the solution. When half of the reagent remains, cover it with a watch glass and add 18 mL of concentrated hydrochloric acid solution (volume fraction: 34-37%). Perform the first acidolysis treatment at 110 °C for 15-30 min, allowing the hydrochloric acid to reflux and react fully. The sample was stirred until nearly dry, then cooled to room temperature to obtain the first precipitate. 18 mL of concentrated perchloric acid solution (70-72% by volume) was added to the first precipitate and stirred until homogeneous. The mixture was then heated to boiling, cooled, and filtered using ash-free medium-speed quantitative filter paper to obtain the second precipitate. The inner walls of the watch glass and beaker were wiped with a glass rod with a rubber tip. The watch glass, beaker, and glass rod were rinsed with a hot concentrated sulfuric acid solution (greater than 98% by volume) at 70-90°C to completely transfer the precipitate onto the filter paper. The precipitate was washed 7-9 times to obtain the third precipitate.

[0056] (3) Carefully fold the filter paper containing the third precipitate and place it in a platinum crucible. Heat and dry it on a hot plate. Ash it at 550°C for 4 hours. Then heat it in a high-temperature furnace to 1150°C for the first calcination treatment for 25 minutes. Take it out and put it in a desiccator to cool to room temperature. Calcinate it multiple times until constant weight to obtain the fourth precipitate. Weigh the total mass m1 of the fourth precipitate and the crucible.

[0057] (4) Use a 1:1 volume ratio of concentrated sulfuric acid solution (volume fraction greater than 98%) and ultrapure water as a mixed solution. Add 8 mL of the mixed solution to the crucible and wash the substances on the wall of the crucible to the bottom. Then add 8 mL of concentrated hydrofluoric acid solution (volume fraction of 53%) and place it on a hot plate for a second heating acidolysis treatment. The second heating acidolysis treatment is to first heat until the sulfuric acid smokes. After it cools slightly, add 8 mL of concentrated hydrofluoric acid solution (volume fraction of 53%) and continue heating until the sulfuric acid is completely decomposed and no longer smokes. Evaporate to near dryness and place it in a 1050℃ high-temperature furnace for a second calcination treatment until constant weight to obtain the second residue. Weigh the total mass m2 of the second residue and the crucible.

[0058] (5) Repeat steps (1)-(4) for a blank experiment without the lithium supplementation agent;

[0059] (6) Calculate the mass fraction ω of silicon in the lithium replenisher according to the following formula. Si :

[0060]

[0061] Where m1 is the total mass of the fourth precipitate and the crucible, in grams (g);

[0062] m2 is the total mass of the second residue and the crucible, in grams (g);

[0063] m3 is the total mass of the fourth precipitate and the crucible in the blank experiment, in grams (g).

[0064] m4 is the total mass of the second residue and the crucible in the blank experiment, in grams (g).

[0065] 0.4675 is the mass conversion factor for silicon dioxide to silicon.

[0066] m represents the mass of the lithium supplement powder, expressed in grams (g).

[0067] The above experimental procedure was performed in 6 parallel sets.

[0068] Verification Test 1

[0069] The test method for verification test 1 is the same as that for example 1, the only difference is that 0.1g of quartz sand (purity of 99.95%) was added along with 1.0000±0.0010g of lithium supplement powder.

[0070] Verification Test 2

[0071] The verification test 2 and the test method of Example 1 are the same, the only difference is that 0.2g of quartz sand (purity of 99.95%) is added at the same time as 1.0000±0.0010g of lithium supplement powder.

[0072] Verification Test 3

[0073] The verification test 3 and the test method of Example 1 are the same, the only difference is that 0.5g of quartz sand (purity of 99.95%) is added at the same time as 1.0000±0.0010g of lithium supplement powder.

[0074] Verification Test 4

[0075] The test method for verification test 1 is the same as that for example 1, the only difference is that 1.0g of quartz sand (silica purity reaches 99.95%) was added along with 1.0000±0.0010g of lithium supplement powder.

[0076] Comparative Example 1

[0077] A method for testing the silicon content in a lithium supplement includes the following steps:

[0078] (1) Using a 100mL beaker, weigh 1.2500g of lithium supplement powder and place it in the beaker to make 6 parallel samples (referred to as group 1-6).

[0079] (2) Add 30 mL of concentrated hydrochloric acid (GR grade) to a beaker and rinse the powder off the beaker wall. Place the beaker on a graphite heating plate and heat at 180°C until 3-5 mL remains. Filter the solution and then transfer it to a 500 mL A-grade volumetric flask using ultrapure water to obtain the test solution. Perform a process blank at the same time.

[0080] (3) Turn on the inductively coupled plasma atomic emission spectrometer, set the plasma flow rate to 15 L / min, the nebulizer gas flow rate to 0.6-0.8 L / min, the pump speed to 1.5 mL / min, the delay time to 40-60 s, the number of tests to 2, and the nebulizer pressure to approximately 300. Take silicon element standard solutions of different concentrations and prepare standard solutions of 0.2, 0.5, 1.0, and 2.0 μg / mL to obtain multi-element standard curves, and fit the standard curve equations, with a linearity ≥ 0.999. Then test the blank and the test solution to obtain the silicon element content.

[0081] (4) Calculation of results:

[0082] Silicon content = (Sample silicon content - Process blank silicon content) / Solid content c

[0083] Verification Test 1

[0084] The testing methods for verification test 1 and comparative example 1 are the same, the only difference being that 0.1g of silica sand (with a silica purity of 99.95%) was added along with 1.2500g of lithium supplement powder.

[0085] Verification Test 2

[0086] The verification test 2 and the comparative example 1 were tested using the same method. The only difference was that 0.2g of silica sand (with a silica purity of 99.95%) was added along with 1.2500g of lithium supplement powder.

[0087] Verification Test 3

[0088] The verification test 3 and the comparative example 1 were tested using the same method. The only difference was that 0.5g of silica sand (with a silica purity of 99.95%) was added along with 1.2500g of lithium supplement powder.

[0089] Verification Test 1

[0090] The testing methods for verification test 1 and comparative example 1 are the same, the only difference being that 1.0g of silica sand (with a silica purity of 99.95%) was added along with 1.2500g of lithium supplement powder.

[0091] The test method for this comparative example is the same as that for Example 1, except that step (1) is omitted. In step (2), the lithium supplement powder is directly mixed with concentrated nitric acid solution and water in a glass container and then heated and concentrated before proceeding to the next step.

[0092] Comparative Example 2

[0093] The test method for this comparative example is the same as that for Example 1, except that the step of washing the second precipitate with hot concentrated sulfuric acid solution is omitted in step (2), and the second precipitate is directly placed in the crucible in step (3), first ashing treatment is performed, and then the first calcination treatment is performed until constant weight is obtained to obtain the fourth precipitate.

[0094] Comparative Example 3

[0095] The test method for this comparative example is the same as that for Example 1, except that step (3) omits the ashing treatment and directly performs the first burning treatment.

[0096] Comparative Example 4

[0097] A method for testing the silicon content in a lithium supplement includes the following steps: According to the method summary of national standard GB / T 33822-2017, weigh 5g of boron-doped lithium silicate material sample (same as in Example 1), mix with 20mL of concentrated hydrochloric acid (volume fraction: 34-37%), heat at 105℃ for 30min to obtain the test solution, and use an inductively coupled plasma atomic emission spectrometer (ICP-AES) to test the silicon content in the test solution using the standard curve method, thereby calculating the mass fraction ω of silicon in the boron-doped lithium silicate material. Si .

[0098] Table 1. Verification experiment on the consistency of silicon content test results in the lithium supplement of Example 1

[0099]

[0100] The verification test used a gradient addition method of standard silica sand (i.e., high-purity silica) to verify the test results of Example 1, which is equivalent to using a spiking method to verify the accuracy of the experimental results. Table 1 shows that the RSD of silicon content in the lithium supplement detected was less than 5%, and the silicon content showed the same proportion as the content of the additionally added silica sand, indicating that the test method of this invention has high accuracy.

[0101] Table 2. Verification experiment on the consistency of silicon content test results in the lithium supplement of Comparative Example 1

[0102]

[0103] As can be seen from Table 2, although the RSD of silicon content in the lithium replenishing agent obtained by the detection method of Comparative Example 1 was less than 5%, the addition of quartz sand did not cause a change in silicon content. Therefore, it was determined that this method could not detect samples with excessively high silicon content.

[0104] As can be seen from the comparison between Example 1 and Comparative Example 1 above, the test method of Example 1 actually solves the problems in the industry such as incomplete dissolution of lithium supplements before elemental analysis and incomplete precipitation of elements due to incomplete dissolution. It is a completely dissolved and accurate test method.

[0105] In this invention, the terms "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to a specific feature, structure, material, or characteristic described in connection with that embodiment or example, which is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0106] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A method for testing the silicon content in a lithium supplement, characterized in that, Includes the following steps: (1) The lithium supplement is mixed with sodium carbonate and sodium peroxide in a crucible and then subjected to calcination treatment to obtain a molten alkaline fusion mixture; (2) The alkaline fusion mixed reagent is mixed with concentrated nitric acid solution and water in a glass container and then heated and concentrated. When the solution is 30-60% remaining, concentrated hydrochloric acid solution is added for the first heating acidolysis treatment. The solution is evaporated to near dryness to obtain the first precipitate. The first precipitate was then mixed with concentrated perchloric acid solution and heated to boiling. After filtration, a second precipitate was obtained. The second precipitate was then washed with hot concentrated sulfuric acid solution to obtain a third precipitate. (3) The third precipitate is placed in the crucible, and first ashing is performed, followed by a first calcination until constant weight is obtained to obtain the fourth precipitate; (4) Add concentrated sulfuric acid solution and water to the fourth precipitate in the crucible, then add concentrated hydrofluoric acid solution, and perform a second heating acidolysis treatment. Evaporate the solution to near dryness to obtain the first residue, and then perform a second calcination treatment on the first residue until constant weight to obtain the second residue. (5) Repeat steps (1)-(4) for a blank experiment without the lithium supplementation agent; (6) Calculate the mass fraction ω of silicon in the lithium replenishing agent according to the following formula. Si : Wherein, m1 is the total mass of the fourth precipitate and the crucible, m2 is the total mass of the second residue and the crucible, m3 is the total mass of the fourth precipitate and the crucible in the blank experiment, m4 is the total mass of the second residue and the crucible in the blank experiment, 0.4675 is the mass conversion factor for silicon dioxide to silicon, and m is the mass of the lithium replenishing agent.

2. The method for testing the silicon content in the lithium supplement according to claim 1, characterized in that, In step (1), the lithium replenishing agent includes at least one of lithium silicate, non-metallic element-doped lithium silicate, carbon-coated lithium silicate, and organic polymer-coated lithium silicate.

3. The method for testing the silicon content in the lithium supplement according to claim 1, characterized in that, In step (1), the mass ratio of the lithium replenishing agent to the mixed reagent is (1-10):(15-25), the mixed reagent is a mixture of sodium carbonate and sodium peroxide, and the mass ratio of the sodium carbonate to the sodium peroxide is 1:(1-2); and / or, the melting treatment temperature is 300-900℃ and the time is 10-15min.

4. The method for testing the silicon content in the lithium supplement according to claim 1, characterized in that, In step (2), the volume ratio of the concentrated nitric acid to the water is 1:(4-5); and / or, the temperature of the heating concentration treatment is 100-120℃.

5. The method for testing the silicon content in the lithium supplement according to claim 1 or 4, characterized in that, In step (2), the volume ratio of the concentrated nitric acid solution to the concentrated hydrochloric acid solution is (16.6-40):(15-20), and / or the temperature of the first heating acidolysis treatment is 110°C and the time is 15-30 min.

6. The method for testing the silicon content in the lithium supplement according to claim 1 or 4, characterized in that, In step (2), the volume ratio of the concentrated hydrochloric acid solution to the concentrated perchloric acid solution is 1:(0.8-1.2), and / or the temperature of the hot concentrated sulfuric acid solution is 70-90℃.

7. The method for testing the silicon content in the lithium supplement according to claim 1, characterized in that, In step (3), the ashing treatment temperature is 500-600℃ and the time is 3-6h; and / or, the first calcination treatment temperature is 1085-1200℃, and / or, the time of a single first calcination treatment is 20-30min, and constant weight is achieved after repeated first calcination treatments.

8. The method for testing the silicon content in the lithium supplement according to claim 1, characterized in that, In step (4), the volume ratio of the concentrated sulfuric acid to the water is (0.8-1.2):(0.8-1.2); and / or, the volume ratio of the concentrated sulfuric acid to the concentrated hydrofluoric acid is (2.5-5):(10-20).

9. The method for testing the silicon content in the lithium supplement according to claim 8, characterized in that, In step (4), concentrated sulfuric acid solution and water are added to the fourth precipitate in the crucible, and then a portion of the concentrated hydrofluoric acid solution is added. The mixture is heated until it smokes, and after it cools slightly, the remaining hydrofluoric acid solution is added. The mixture is heated until the sulfuric acid is completely decomposed and no longer smokes. The mixture is evaporated to near dryness to obtain the first residue. The first residue is then subjected to a second calcination treatment until constant weight is achieved to obtain the second residue.

10. The method for testing the silicon content in the lithium supplement according to claim 1, characterized in that, In step (4), the temperature of the second calcination treatment is 1000-1100℃; and / or, the time of a single first calcination treatment is 20-30 min, and constant weight is achieved after repeated first calcination treatments.

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