Method for testing content of silicon-based material in silicon-based negative electrode of lithium ion battery

Abstract

The invention discloses a method for testing the content of a silicon-based material in a silicon-based negative electrode of a lithium ion battery. The testing method comprises the following steps: 1) preparing battery cells with different silicon doping contents, performing formation and capacity grading on the battery cells, discharging and disassembling to obtain a negative pole piece; 2) separating the powder in the negative pole piece from the negative current collector to obtain first powder; 3) heating the first powder in a muffle furnace; according to the mass of residual substances removed through heat treatment, a series of residual mass percentages are obtained through calculation; according to the known silicon-based material content and the corresponding residual mass percentage, a scatter diagram is drawn and fitted to obtain a relational expression; and (3) carrying out the steps (1)-(3) on the battery cell with the content of the silicon-based material to be measured to obtain the residual mass percent, and calculating the content of the silicon-based material according to the relational expression to obtain the content of the silicon-based material. According to the method, the content of the silicon-based material in the battery can be accurately evaluated, the adopted instrument is low in cost, the test consistency is high, and the accuracy is high.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium-ion batteries, in particular to a method for testing the content of silicon-based materials in a silicon-based negative electrode of a lithium-ion battery. Background Art

[0002] Measuring the silicon content of lithium-ion battery anodes is crucial for several reasons: First, while silicon can increase the battery's energy density, its significant volume changes during charge and discharge can affect battery performance and lifespan. Therefore, accurately measuring silicon content can optimize cycle performance while ensuring high energy density, avoiding battery life and lifespan issues caused by inappropriate content. Second, during production, accurately measuring silicon content helps optimize complex processes, such as properly adjusting binder dosage and controlling coating parameters, thereby improving yield and production efficiency. Third, from a safety perspective, excessive silicon content can lead to hazards such as bulging and short circuits under abnormal operating conditions. Accurately measuring silicon content provides a basis for safety assessments and early warnings, guiding safety design and strategy development. Furthermore, meeting stringent quality standards and customer demands is crucial for companies to maintain their market foothold. Therefore, measuring silicon content is crucial for the stable, efficient, and safe development of the lithium-ion battery industry.

[0003] Currently, methods for determining the silicon-based material content in silicon-based anodes include: preparing multiple silicon-containing anode sheets with varying mass ratios, each made from a mixture of silicon-based and graphite materials; using a thermogravimetric analyzer to determine the residual mass percentage of each silicon-containing anode sheet; plotting a standard curve based on the test data to obtain a quantitative relationship between the residual mass of each silicon-containing anode sheet sample and the mass percentage of silicon-based material in each silicon-containing anode sheet sample; sampling and weighing the silicon-containing anode sheet to be tested, then performing a thermogravimetric test to determine the residual mass percentage of the sample; and calculating the mass percentage of silicon-based material in the sample based on the residual mass percentage and the quantitative relationship. However, this method has the following drawbacks and shortcomings: ① Thermogravimetric analyzers are expensive, resulting in high testing costs; ② Thermogravimetric analyzers cannot test multiple samples simultaneously, resulting in low testing efficiency; and ③ The sample mass for thermogravimetric analysis is typically in the milligram range, making it difficult to ensure consistent test results. Furthermore, existing methods cannot accurately assess the silicon-based material content within batteries. Furthermore, existing methods do not reflect the actual silicon-based material content in batteries.

[0004] Therefore, it is very meaningful to develop a silicon-based material content test with good consistency and enable it to accurately evaluate the silicon-based material content inside the battery. Summary of the Invention

[0005] In view of the above technical problems existing in the prior art, the object of the present invention is to provide a method for testing the content of silicon-based materials in silicon-based negative electrodes of lithium-ion batteries.

[0006] To achieve the above object, the present invention adopts the following technical solutions:

[0007] The present invention provides a method for testing the content of silicon-based material in a silicon-based negative electrode of a lithium-ion battery, characterized in that the testing method comprises the following steps:

[0008] (1) preparing battery cells with different silicon doping contents, forming and dividing the battery cells, discharging and disassembling the battery cells to obtain negative electrode sheets;

[0009] (2) separating the powder in the negative electrode sheet from the negative electrode current collector to obtain a first powder;

[0010] (3) taking 0.5 g to 2 g of the first powder and heating it in a heating device to obtain a second powder;

[0011] According to the mass m0 of the residual material removed by heat treatment, a series of residual mass percentages are calculated, and the calculation formula is:

[0012] Residual mass percentage = m0 / m1×100%, where m1 is the mass of the first powder used in step (3);

[0013] According to the known silicon-based material content and the corresponding residual mass percentage, a scatter plot is drawn and a relationship is obtained by fitting;

[0014] The battery cell to be tested for silicon-based material content is disassembled to obtain the negative electrode sheet, and steps (2)-(3) are performed to obtain the residual mass percentage, and the silicon-based material content is calculated according to the relationship.

[0015] In the method of the present invention, the battery cells with different silicon-doping contents refer to: in the negative electrode of the battery cell, the negative electrode active material includes silicon-based materials and other negative electrode active materials. This negative electrode active material is called silicon-doped negative electrode active material. The silicon doping content of different battery cells is different. The silicon doping content refers to the mass proportion of silicon-based materials in the negative electrode active material.

[0016] The present invention does not specifically limit the type of silicon-based materials, including but not limited to one or more of silicon-carbon materials, silicon-oxygen materials, silicon nitride and pure silicon materials, wherein the silicon-oxygen material can be silicon monoxide.

[0017] The method of the present invention forms and divides the capacity of the battery cell, and then disassembles and tests it after discharge, thereby simulating the silicon-based material content in a real battery. Furthermore, the method of the present invention uses a sampling mass of 0.5g to 2g. If the sampling mass is too small, the sample may not reflect the actual condition of the negative electrode powder; if the sampling mass is too large, it may lead to insufficient material decomposition during the subsequent heating process. Furthermore, the sampling volume of a thermogravimetric analyzer is at the "milligram" level, which tests the instrument's accuracy. The method of the present invention uses a large sampling volume, which results in more consistent and accurate test results.

[0018] Moreover, the method of the present invention produces consistent test results in different electrolyte systems and is suitable for testing the content of silicon-based materials in silicon-based batteries with different electrolyte systems.

[0019] The following are preferred technical solutions of the present invention, but are not intended to limit the technical solutions provided by the present invention. Through the following preferred technical solutions, the technical objectives and beneficial effects of the present invention can be better achieved and realized.

[0020] Preferably, step (2) comprises: placing the negative electrode plate in a solvent and performing ultrasonic treatment, taking out the negative electrode current collector from the powder solution, and drying the powder solution to obtain the first powder.

[0021] After the ultrasound is completed, the negative electrode powder will automatically fall off the negative electrode current collector. After the negative electrode current collector is removed and dried, the first powder can be obtained. This method is more accurate than scraping the negative electrode powder off the negative electrode current collector.

[0022] Preferably, the ultrasonic time is 2 minutes to 20 minutes, for example, 2 minutes, 4 minutes, 5 minutes, 8 minutes, 10 minutes, 12 minutes, 14 minutes, 15 minutes, 17 minutes, or 20 minutes. The ultrasonic power is 95W to 105W, for example, 95W, 96W, 97W, 98W, 99W, 100W, 101W, 102W, 103W, 104W, or 105W. Under certain ultrasonic power conditions, the accuracy of the test can be improved by optimizing the ultrasonic time. This is because: if the ultrasonic time is too short, the negative electrode powder cannot be completely extracted; if the ultrasonic time is too long, the processing efficiency is affected.

[0023] Preferably, the drying method in step (2) is oven drying, and the oven drying temperature is 100°C to 200°C, for example, it can be 100°C, 120°C, 130°C, 140°C, 150°C, 160°C, 170°C, 180°C or 200°C.

[0024] In one embodiment, the dried powder is ground because the dried powder may clump and grinding can obtain a uniformly dispersed powder.

[0025] Preferably, the heating device in step (3) is a muffle furnace. The use of a muffle furnace as a heating device has the following advantages: on the one hand, the price of a muffle furnace is lower than that of a thermogravimetric analyzer, and the instrument cost is reduced; on the other hand, a muffle furnace can test at least 10 samples simultaneously, while a conventional thermogravimetric analyzer can only test one sample. In the same test time, the test efficiency is increased by 10 times.

[0026] Preferably, the heat treatment temperature is 600°C to 1000°C, for example, 600°C, 650°C, 700°C, 750°C, 800°C, 850°C, 900°C, 950°C, or 1000°C. Optimizing the heat treatment temperature can improve test accuracy because, under the premise of the same heating time, high temperature helps accelerate the decomposition efficiency of decomposable components, affecting the residual rate results.

[0027] Preferably, the heating treatment time is 1 h to 5 h, for example, 1 h, 2 h, 2.5 h, 3 h, 3.5 h, 4 h or 5 h.

[0028] Preferably, the atmosphere of the heat treatment is any one of air atmosphere, oxygen atmosphere or nitrogen atmosphere.

[0029] Preferably, the fitting method is linear fitting or curve fitting. The present invention does not specifically limit the fitting method, and those skilled in the art can select it according to their needs.

[0030] Preferably, the method for obtaining m1-m2 is: weighing the mass M1 of the muffle furnace after the first powder is placed therein and the mass M2 of the muffle furnace after the heating treatment, respectively, M1-M2=m1-m2.

[0031] The numerical range described in the present invention includes not only the point values ​​listed above, but also any point values ​​between the above numerical ranges that are not listed. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists the specific point values ​​included in the range.

[0032] Compared with the prior art, the present invention has the following beneficial effects:

[0033] The method of the present invention forms and divides the capacity of the battery cell, and then disassembles and tests it after discharge, thereby simulating the silicon-based material content in a real battery. Furthermore, the method of the present invention uses a sampling mass of 0.5g to 2g. If the sampling mass is too small, the sample may not reflect the actual condition of the negative electrode powder; if the sampling mass is too large, it may lead to insufficient material decomposition during the subsequent heating process. Furthermore, the sampling volume of a thermogravimetric analyzer is at the "milligram" level, which tests the instrument's accuracy. The method of the present invention uses a large sampling volume, which results in more consistent and accurate test results.

[0034] Moreover, the method of the present invention produces consistent test results in different electrolyte systems and is suitable for testing the content of silicon-based materials in silicon-based batteries with different electrolyte systems. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 It is a relationship diagram between silicon-based material content and residual mass percentage. DETAILED DESCRIPTION

[0036] The technical solution of the present invention will be further described below with reference to the accompanying drawings and through specific implementation methods.

[0037] The specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0038] In the embodiments of the present invention, EC represents ethylene carbonate, PC represents propylene carbonate, DEC represents diethyl carbonate, FEC represents fluoroethylene carbonate, PS represents 1,3-propane sultone, EP represents ethyl propionate, SN represents succinonitrile, and ADN represents adiponitrile.

[0039] Example 1

[0040] This embodiment provides a method for testing the content of silicon-based material in a silicon-based negative electrode of a lithium-ion battery, the testing method comprising the following steps:

[0041] (1) preparing battery cells with different silicon-doped contents (the negative electrode active materials are graphite and silicon-based materials, the silicon-based material is silicon carbide, and the mass proportions of the silicon-based materials in the negative electrode active materials are 5.00%, 10.00%, 15.00%, 20.00%, 25.00% and 30.00%, respectively), wherein the electrolyte in the battery cell is composed of a solvent, a lithium salt and an additive, the solvent is a mixed solvent of EC, PC and DEC in a volume ratio of 1:1:1, the lithium salt is 1 mol / L lithium hexafluorophosphate, the additives are FEC and PS, the content of FEC in the electrolyte is 5wt%, and the content of PS in the electrolyte is 2wt%, after the battery cell is formed and volume fractionated, the battery cell is discharged and disassembled to obtain a negative electrode sheet;

[0042] (2) placing the negative electrode sheet in a solvent and performing ultrasonic treatment (power of 100 W, time of 10 min), removing the negative electrode current collector (copper foil) from the powder solution, and drying the powder solution at 150° C. to obtain a first powder;

[0043] (3) The first powder (mass m1 = 1.0 g) was placed in a ceramic crucible, and the mass of the ceramic crucible at this time was weighed as M1. The ceramic crucible was placed in a muffle furnace and heated at a temperature of 800°C for 3 hours to obtain a second powder. The mass of the ceramic crucible after the heating treatment was weighed as M2;

[0044] In this embodiment, multiple ceramic crucibles containing the first powder are heated simultaneously in the muffle furnace, which can improve efficiency.

[0045] According to the mass m0 of the residual material removed by heat treatment, a series of residual mass percentages are calculated, and the calculation formula is:

[0046] Residual mass percentage = (M2-M1) / m1×100%,

[0047] Based on the known silicon-based material content and the corresponding residual mass percentage, a scatter plot is drawn and fitted to obtain a relationship. Figure 1 ;

[0048] Steps (1) to (3) are performed on the battery cell whose silicon-based material content is to be measured to obtain the residual mass percentage. The silicon-based material content is calculated according to the relationship, which is the test value. The test accuracy is calculated based on the test value and the known silicon-based material content: test accuracy = test value / known value. The test accuracy of this embodiment is 100.8%.

[0049] Examples 2 to 6

[0050] The test was carried out in the same manner as in Example 1, except that the ultrasonic time was changed (see Table 1).

[0051] The relationship between ultrasound time and test accuracy is shown in Table 1.

[0052] Table 1

[0053]

[0054] Examples 7 to 11

[0055] The test was carried out in the same manner as in Example 1, except that the temperature of the heating treatment in step (3) was changed (see Table 2).

[0056] The relationship between the heating temperature and the test accuracy is shown in Table 2.

[0057] Table 2

[0058]

[0059] Examples 12 to 14

[0060] The test was carried out in the same manner as in Example 1, except that the composition of the electrolyte was changed.

[0061] The relationship between electrolyte and test accuracy is shown in Table 3.

[0062] Electrolyte 1 consists of a solvent, a lithium salt, and an additive. The solvent is a mixed solvent of EP and DEC in a volume ratio of 1:1, the lithium salt is 1 mol / L lithium hexafluorophosphate, and the additives are FEC and SN. The content of FEC in the electrolyte is 15 wt%, and the content of SN in the electrolyte is 3 wt%.

[0063] Electrolyte 2 is composed of a solvent, a lithium salt, and an additive. The solvent is a mixed solvent of EC, PC, and DEC in a volume ratio of 1:1:3. The lithium salt is 1.5 mol / L lithium hexafluorophosphate. The additives are AND and SN. The content of AND in the electrolyte is 1.5 wt%, and the content of SN in the electrolyte is 0.5 wt%.

[0064] Electrolyte 3 consists of a solvent, a lithium salt, and an additive. The solvent is a mixed solvent of EC, PC, and DEC in a volume ratio of 1:1:3. The lithium salt is 1.5 mol / L lithium hexafluorophosphate. The additives are AND and SN. The content of AND in the electrolyte is 1.5 wt%, and the content of SN in the electrolyte is 0.5 wt%.

[0065] Table 3

[0066] electrolyte Accuracy Example 12 Electrolyte 1 99.6％ Example 13 Electrolyte 2 98.2％ Example 14 Electrolyte 3 101.0％

[0067] The results show that the method of the present invention is suitable for testing the content of silicon-based materials in battery cells with different electrolyte systems.

[0068] In order to verify the reliability of the method of the present invention, the following experiments were performed:

[0069] Battery samples with different known silicon-based contents were disassembled and the silicon-based material content of the negative electrodes of different samples was tested. The test results are shown in Table 4.

[0070] Table 4 Test results of silicon content of different batteries

[0071]

[0072] The results show that the method for testing the content of silicon-based materials in silicon-based negative electrodes of lithium-ion batteries provided by the present invention has the advantages of high test accuracy and reliable test results.

[0073] The applicant states that the present invention is intended to illustrate the detailed methods of the present invention through the above-described embodiments, but the present invention is not limited to the above-described detailed methods, that is, it does not mean that the present invention must rely on the above-described detailed methods in order to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent substitutions for various raw materials in the products of the present invention, addition of auxiliary ingredients, and selection of specific methods, etc., are all within the scope of protection and disclosure of the present invention.

Claims

1. A method for testing the content of silicon-based materials in a silicon-based negative electrode of a lithium-ion battery, characterized in that: The test method comprises the following steps: (1) preparing battery cells with different silicon doping contents, forming and dividing the battery cells, discharging and disassembling the battery cells to obtain negative electrode sheets; (2) separating the powder in the negative electrode sheet from the negative electrode current collector to obtain a first powder; (3) taking 0.5 g to 2 g of the first powder and heating it in a heating furnace to obtain a second powder; According to the mass m0 of the residual material removed by heat treatment, a series of residual mass percentages are calculated, and the calculation formula is: Residual mass percentage = m0 / m1×100%, where m1 is the mass of the first powder used in step (3); According to the known silicon-based material content and the corresponding residual mass percentage, a scatter plot is drawn and a relationship is obtained by fitting; The battery cell to be tested for silicon-based material content is disassembled to obtain the negative electrode sheet, and steps (2)-(3) are performed to obtain the residual mass percentage, and the silicon-based material content is calculated according to the relationship.

2. The method for testing the content of silicon-based material in a silicon-based negative electrode of a lithium-ion battery according to claim 1, wherein step (2) comprises: The negative electrode plate is placed in a solvent and subjected to ultrasonic treatment. After the negative electrode current collector is taken out from the powder solution, the powder solution is dried to obtain a first powder.

3. The method for testing the content of silicon-based material in a silicon-based negative electrode of a lithium-ion battery according to claim 1 or 2, characterized in that: The ultrasonic time is 2 minutes to 20 minutes, and the ultrasonic power is 95W to 105W.

4. The method for testing the content of silicon-based material in a silicon-based negative electrode of a lithium-ion battery according to any one of claims 1 to 3, characterized in that: The drying method in step (2) is oven drying, and the oven drying temperature is 100° C. to 200° C.

5. The method for testing the content of silicon-based material in a silicon-based negative electrode of a lithium-ion battery according to any one of claims 1 to 4, characterized in that: The heating equipment in step (3) is a muffle furnace.

6. The method for testing the content of silicon-based material in a silicon-based negative electrode of a lithium-ion battery according to any one of claims 1 to 5, characterized in that: The temperature of the heating treatment is 600°C to 1000°C.

7. The method for testing the content of silicon-based material in a silicon-based negative electrode of a lithium-ion battery according to any one of claims 1 to 6, characterized in that: The heating treatment time is 1 hour to 5 hours.

8. The method for testing the content of silicon-based material in a silicon-based negative electrode of a lithium-ion battery according to any one of claims 1 to 7, characterized in that: The heat treatment is performed in an atmosphere of air, oxygen or nitrogen.

9. The method for testing the content of silicon-based material in a silicon-based negative electrode of a lithium-ion battery according to any one of claims 1 to 8, characterized in that: The fitting method is linear fitting or curve fitting.

10. The method for testing the content of silicon-based material in a silicon-based negative electrode of a lithium-ion battery according to any one of claims 1 to 7, characterized in that: The mass of the residual material removed by the heat treatment is obtained by weighing the mass M1 of the muffle furnace after the first powder is placed therein and the mass M2 of the muffle furnace after the heat treatment, where M1-M2=m0.

Images