Dynamic performance characterization method of gas-phase silicon porous negative electrode material

Abstract

The invention discloses a dynamic performance characterization method of gas-phase silicon porous negative electrode materials, which comprises the following steps: providing a plurality of to-be-tested pole pieces provided with the gas-phase silicon porous negative electrode materials, enabling the gas-phase silicon porous negative electrode materials on the plurality of to-be-tested pole pieces to be different, and respectively assembling the plurality of to-be-tested pole pieces into a plurality of to-be-evaluated batteries; obtaining the porosity K of the gas-phase silicon porous negative electrode material on the to-be-tested pole piece, the lithium ion diffusion path length D in the to-be-evaluated battery and the lithium ion diffusion time t; calculating the lithium ion motion rate according to a formula v = (D * K) / t; and evaluating the dynamic performance of the corresponding gas-phase silicon porous negative electrode material according to the calculated lithium ion motion rate v. According to the method, the kinetic performance of the speed of the lithium ions in the pole piece is represented by the motion rate, the method is very intuitive, the v value calculation of a single sample can be completed within 5 minutes, and the efficiency is improved by hundreds of times compared with the traditional full battery test needing several days.

Description

Technical Field

[0001] This invention relates to the field of batteries, and more particularly to a method for characterizing the kinetic properties of a porous fumed silicon anode material. Background Technology

[0002] With the increasing market demand for lithium-ion batteries, the development of high-performance anode materials has become a research hotspot. Traditional anodes suffer from structural pulverization and interfacial side reactions caused by volume expansion during charging and discharging, severely limiting their practical applications. To overcome this bottleneck, porous fumed silicon anode materials have been proposed. Their core strategy involves constructing buffer spaces through a porous framework (such as a carbon matrix) to alleviate the volume effect of silicon, while simultaneously utilizing the pore network to provide ion / electron transport channels.

[0003] Vaporized silicon porous anode materials are currently a hot research topic in lithium-ion batteries. Their core focus is on mitigating electrode pulverization and capacity decay caused by silicon's volume expansion (approximately 300%) during charge and discharge through porous structures. The design and optimization of different porous materials as vapor-phase frameworks are crucial for improving the cycle stability and rate performance of the anode.

[0004] Current methods mostly rely on indirect characterization of kinetic performance. Therefore, there is an urgent need for more intuitive methods and parameters for characterization. To address the characterization requirements of lithium-ion kinetic performance in porous fumed silicon anode materials, it is necessary to combine various experimental methods and theoretical analysis tools to conduct a comprehensive evaluation from multiple dimensions, including material structure, electrochemical behavior, and ion transport mechanisms. This will provide theoretical support for the rational design of high-performance fumed silicon-based anode materials. The mobility of lithium ions in the gaps of the electrode material can indirectly reflect the kinetic performance of the corresponding anode material. Summary of the Invention

[0005] The purpose of this invention is to provide a method for characterizing the kinetic properties of porous fumed silicon anode materials, so as to solve the problem that the existing methods for characterizing the kinetic properties of porous fumed silicon anode materials are not intuitive.

[0006] To achieve the above objectives, the present invention provides a method for characterizing the kinetic performance of a vapor-phase silicon porous anode material, characterized by the following steps: providing a plurality of test electrode sheets on which a vapor-phase silicon porous anode material is disposed, wherein the vapor-phase silicon porous anode materials on the plurality of test electrode sheets are different; assembling the plurality of test electrode sheets into a plurality of test batteries; obtaining the porosity K of the vapor-phase silicon porous anode material on the test electrode sheet, the lithium-ion diffusion path length D in the test battery, and the lithium-ion diffusion time t; calculating the lithium-ion mobility rate according to the formula v=(D×K) / t; and evaluating the kinetic performance of the corresponding vapor-phase silicon porous anode material based on the calculated lithium-ion mobility rate v.

[0007] Preferably, the step of obtaining the porosity K of the fumed silicon porous anode material on the electrode to be tested includes: obtaining the apparent density ρ and the true density ρ0 of the fumed silicon porous anode material on the electrode to be tested; and calculating the porosity K of the fumed silicon porous anode material according to the formula K=(1-ρ / ρ0)×100%.

[0008] Preferably, the true density ρ0 of the fumed silicon porous anode material is obtained by testing with a true density meter.

[0009] Preferably, the apparent density ρ of the vapor-phase silicon porous anode material is obtained by the ratio of the mass of the vapor-phase silicon porous anode material on the electrode to the volume of the vapor-phase silicon porous anode material.

[0010] Preferably, the lithium-ion diffusion path length D is calculated according to the formula D=R×S×σ, where R is the ion resistance, S is the electrode area, and σ is the conductivity of the electrolyte in the battery to be tested.

[0011] Preferably, the ionic resistance R is obtained by AC impedance spectroscopy.

[0012] Preferably, the conductivity σ of the electrolyte is obtained by a conductivity meter.

[0013] Preferably, the lithium-ion diffusion time t is obtained by a relaxation time distribution method.

[0014] Preferably, evaluating the kinetic performance of the corresponding porous silicon anode material based on the calculated lithium-ion mobility v includes: determining the maximum value among several lithium-ion mobility v values; and determining that the porous silicon anode material corresponding to the maximum value has the best kinetic performance.

[0015] Compared with existing technologies, this invention uses the motion rate to characterize the kinetic performance of lithium ions in the electrode, which is very intuitive. The v value of a single sample can be calculated within 5 minutes. Compared with the traditional full-cell test that requires several days, the efficiency is improved by a hundred times, effectively solving the problem that the kinetic performance of porous fumed silicon anode materials cannot be intuitively expressed. Attached Figure Description

[0016] Figure 1 This is a top view of the electrode under test in an embodiment of the present invention.

[0017] Figure 2 This is a side view of the electrode under test in an embodiment of the present invention.

[0018] Figure 3 This is a fitted diagram of the EIS spectra of three types of porous silicon anode materials in the embodiments of the present invention. Detailed Implementation

[0019] To illustrate the technical content, structural features, and effects of the present invention in detail, the following description is provided in conjunction with the embodiments and accompanying drawings.

[0020] This invention provides a method for characterizing the kinetic properties of a vapor-phase silicon porous anode material, comprising the following steps: S1, several test electrode sheets 10 with fumed silicon porous anode material 2 are provided. The fumed silicon porous anode material 2 on the several test electrode sheets 10 are different. The several test electrode sheets 10 are assembled into several batteries to be evaluated.

[0021] In this embodiment of the invention, the electrode to be tested 10 can be manufactured using conventional methods. For example, the manufacturing method of the electrode to be tested 10 includes the following steps: S11. Fabrication of fumed silicon porous anode material 2: Specifically, place the mixing jar on a balance, add an appropriate amount of deionized water, for example, 33g, weigh 0.253g of carboxymethyl cellulose (CMC) using the balance, add it to the mixing jar, cover it, set the stirring time to 15min, slowly increase the speed to 3000r / min, weigh 0.458g of conductive carbon powder (SP), add it to the mixing jar and stir well, then add tripropylene glycol (SD-3), stir at a low initial speed for 10min, for example, 1000r / min, then use a spoon to stir the mixing jar. The conductive carbon powder (SP) on the tank wall is scraped off, and then the rotation speed is slowly increased to a second speed, for example, 3000 r / min, and stirred for 10 min. 25.0 g of active material (fumed silicon porous carbon material) is added to the stirred tank, and after stirring and scraping the tank wall, it is placed in a mixer. The rotation speed is slowly increased to 3500 r / min and stirred for 10 min. 1.513 g of binder tripropylene glycol (SD-3) is weighed out, and the rotation speed is slowly adjusted to 3000 r / min, and stirred for 10 min to form a fumed silicon porous carbon slurry. The fumed silicon porous carbon slurry is then sealed and stored promptly. It should be noted that the amount of active material added can be different to form different fumed silicon porous anode materials.

[0022] S12. The fumed silicon porous carbon slurry prepared in step S11 is sieved. Specifically, after stirring, it is sieved through a 200-mesh sieve to obtain the final fumed silicon porous anode material 2. Then, the work surface of the coating machine is wiped clean with lint-free paper soaked in alcohol. The cut copper foil is laid flat on the work surface, and the adsorption is turned on so that the fumed silicon porous anode material 2 is adsorbed onto the copper foil. The adsorbed copper foil is gently transferred to a glass plate and placed in a constant temperature forced-air drying oven at 100°C. At the same time, the four corners of the copper foil are pressed with a crucible to prevent the copper foil from being blown up and folded during the drying process. The drying time is 4 hours.

[0023] S13. Roll forming the porous silicon anode material 2 on the copper foil. Specifically, first, cut off the last 3cm of the copper foil and discard it. Then, cut off the middle part for rolling. Turn on the roller press and rotate the roller shaft in the reverse direction. Clean the roller shaft with lint-free paper sprayed with alcohol. Then, adjust the roller spacing to be consistent on both sides. Next, place the cut copper foil on the roller press table, align it left and right (do not roll at an angle), and slowly push it into the roller shaft for rolling. Roll it once in the front and once in the back, i.e., once. Repeat the rolling process on the porous silicon anode material 2. After rolling, measure the thickness of the porous silicon anode material 2 with a micrometer. Measure it three times consecutively, record the three measurements, and take the average value to obtain the thickness d of the porous silicon anode material 2 after rolling.

[0024] S14. The rolled fumed silicon porous anode material 2 and copper foil are stamped. Specifically, the 14mm diameter circular stamping mold is cleaned with alcohol and lint-free paper. The rolled electrode is then stamped into a circular electrode with a diameter L of 14mm using the mold. Six parallel samples are required, and four blank copper foils 1 at both ends of the electrode are required. Impurities on the surface of the circular electrode and copper foil 1 are blown away using a rubber bulb. The balance port on the left side of the vacuum drying oven is then opened. When the pressure gauge reaches zero, the door of the vacuum drying oven is opened, and the stamped circular electrode is placed into the vacuum drying oven. The electrode is then pressed tightly with a crucible to prevent it from being blown away by the wind. The vacuum valve is opened, and the vacuum pump button is pressed. After the vacuum is evacuated to -33MPa, the vacuum valve is closed first, followed by the vacuum pump. The drying temperature is set to 105℃, and the drying time is at least 4 hours. Six circular electrode sheets were weighed using a 1 / 100,000 electronic balance. Four sheets with similar masses (range difference less than 0.2 mg) were placed in a paper bag. The average mass of these four circular electrode sheets was recorded as the electrode mass M1. The selected circular electrode sheet is the electrode sheet 10 to be tested in this embodiment. Four copper foil sheets 1 were then weighed, and the average mass was recorded as the blank copper foil 1 mass M2. The area of ​​the circular electrode sheet can be calculated from its diameter L. This area is the area S of the porous silicon anode material 2 on the circular electrode sheet. The compaction density of the porous silicon anode material 2 on the circular electrode sheet was calculated using the formula ρ1=(M1-M2) / (S×d). The calculated compaction density is the apparent density ρ of the porous silicon anode material 2 in step S21. To ensure battery quality, the compaction density is typically controlled to be greater than or equal to 0.8 g / cm³. 3 And less than or equal to 1.5 g / cm 3 Then, the data are recorded in a conspicuous place on the paper bag. It should be noted that the compaction density can also be calculated before the stamping step, as long as the mass and volume of the fumed silicon porous anode material 2 on the electrode sheet 10 to be tested can be obtained.

[0025] In this embodiment of the invention, the battery to be tested can be a button cell, and the assembly method adopts a conventional assembly method, including, for example, the following steps: S15. In the glove box, place the negative electrode shell, electrode sheet, separator, electrode sheet, and positive electrode shell into the fixture in that order. Add electrolyte and assemble and seal the assembly. Record the parameters of each battery in the original record sheet, including the electrode sheet mass, the thickness d of the fumed silicon porous negative electrode material 2, and the mass of the copper foil 1. Select a test channel for each battery to confirm the content of active material corresponding to the formula. In addition, the electrolyte of the present invention can be a commercially available lithium-ion electrolyte or can be made from existing conventional materials. For example, an electrolyte including solvent, lithium salt, and additives can be used. The lithium salt is lithium hexafluorophosphate (LiPF6) with a molar concentration of 1.0 mol / L. The solvent is a 1:1 volume mixture of ethylene carbonate (EC) and diethyl carbonate (DEC). The additive is 5% by volume of fluoroethylene carbonate (FEC). The separator can be a PP separator.

[0026] In this embodiment of the invention, step S1 is followed by: S2. Obtain the porosity K of the fumed silicon porous anode material 2 on the electrode to be tested 10, the lithium-ion diffusion path length D in the battery to be tested, and the lithium-ion diffusion time t.

[0027] S3. Calculate the lithium-ion mobility rate using the formula v=(D×K) / t. Specifically, calculate the lithium-ion mobility rate v corresponding to the kinetic index of the fumed silicon porous anode material 2. Through the synergistic mechanism of diffusion-reaction-time three parameters, compare the kinetic performance of active materials in different fumed silicon porous carbon materials. This provides a comprehensive, efficient, and visualized performance evaluation method for the application of lithium-ion transfer kinetics in silicon-based anode materials. Measure the lithium-ion diffusion path length D, porosity K, and lithium-ion diffusion time t of the fumed silicon porous anode material under test, and calculate the lithium-ion mobility rate v using the formula v=(D×K) / t. Compare the kinetic performance of different materials based on the v value. A larger v value indicates better kinetic performance of the active material. As the core indicator of lithium-ion mobility rate, it integrates the dual parameters of diffusion and reaction kinetics, breaking through the limitations of traditional single parameters, such as using only D or K for evaluation. It establishes a new performance evaluation dimension by demonstrating the coupling effect of porosity K, diffusion path length D, and lithium-ion diffusion time t on lithium-ion movement.

[0028] S4. Evaluate the kinetic performance of the corresponding porous silicon anode material 2 based on the calculated lithium-ion mobility v. Specifically, a larger v value indicates better kinetic performance of the active material.

[0029] In this embodiment of the invention, step S2, which involves obtaining the porosity K of the porous silicon anode material 2 on the electrode to be tested 10, includes: S21. Obtain the apparent density ρ and true density ρ0 of the fumed silicon porous anode material 2 on the electrode sheet 10 to be tested; specifically, the true density ρ0 of the fumed silicon porous anode material 2 is obtained by testing with a true density meter; the apparent density ρ of the fumed silicon porous anode material 2 is obtained by the ratio of the mass of the fumed silicon porous anode material 2 on the electrode sheet to the volume of the fumed silicon porous anode material 2, that is, it can be obtained by the compaction density calculated in step S14.

[0030] S22. Calculate the porosity K of the fumed silicon porous anode material 2 according to the formula K=(1-ρ / ρ0)×100%.

[0031] In this embodiment of the invention, the lithium-ion diffusion path length D in step S2 is calculated according to the formula D=R×S×σ, where R is the ion resistance, S is the electrode area, and σ is the conductivity of the electrolyte in the battery under test. Specifically, the ion resistance R is obtained by electrochemical impedance spectroscopy (EIS) testing. The battery is placed in the testing equipment, and parameters such as the force, resting time, and EIS testing are set. Then, the experiment is started, and the EIS spectrum is obtained. For different fumed silicon porous anode materials 2, the EIS spectrum can be fitted to obtain... Figure 3 The diagram shown, Figure 3 The horizontal axis represents the real part of the impedance, and the vertical axis represents the imaginary part. In the EIS spectrum, the lower first frequency corresponds to the first impedance value on the X-axis. The first frequency can be, for example, greater than or equal to 0.1 Hz and less than or equal to 1 Hz. The higher second frequency corresponds to the second impedance value on the X-axis. The second frequency can be, for example, greater than or equal to 1 kHz and less than or equal to 10 kHz. The first and second frequencies can be selected according to actual needs and are not restricted here. The difference between the second impedance value and the first impedance value is the ion resistance R of the vapor-phase silicon porous anode material 2. See [reference needed] for details. Figure 3 As shown. The electrode area S can be obtained in step S14, and the conductivity σ of the electrolyte can be directly obtained through a conductivity meter. It should be noted that the method for obtaining the lithium-ion diffusion path length D is not limited and can be selected according to actual needs.

[0032] In this embodiment of the invention, the lithium-ion diffusion time t is obtained by the relaxation time distribution (DRT) method. Specifically, the relaxation time distribution (DRT) method is a method for analyzing electrochemical impedance spectroscopy (EIS), which is a conventional method in the industry and can be used directly.

[0033] In this embodiment of the invention, step S4, evaluating the kinetic performance of the corresponding porous fumed silicon anode material 2 based on the calculated lithium-ion mobility v, includes: S41. Determine the maximum value among several lithium-ion mobility rates v based on the calculated lithium-ion mobility rates v. Specifically, the porosity K, diffusion path length D, and lithium-ion diffusion time t of different formulations of vapor-phase silicon porous anode materials 2 will differ. For example, three vapor-phase silicon porous anode materials 2 prepared by vapor deposition method are provided, namely SiPC-1, SiPC-2, and SiPC-3. The three vapor-phase silicon porous anode materials 2 are assembled into batteries to be tested. Based on the data recorded during the preparation of vapor-phase silicon porous anode materials 2 and the test data of the batteries to be tested, the data shown in Table 1 are formed. Table 1 shows the porosity K, diffusion path length D, lithium-ion diffusion time t, and lithium-ion mobility rate v corresponding to the three vapor-phase silicon porous anode materials 2. Table 2 shows the rate data obtained after rate testing of the full batteries assembled from the three vapor-phase silicon porous anode materials 2.

[0034]

[0035] Table 1

[0036] Table 2 S42, determine the kinetic performance of the vapor-phase silicon porous anode material 2 corresponding to the maximum value. Specifically, as shown in Table 1, SiPC-2 has the highest v value and the best kinetic performance. This is consistent with the rate test results of the full cells assembled from the three vapor-phase silicon porous anode materials 2 in Table 2. That is, as shown by the three sets of data in Table 2 (SiPC-1, SiPC-2, and SiPC-3), SiPC-2 has the best performance. This also shows that the kinetic performance of the lithium-ion mobility in the electrode is characterized by the mobility rate in this embodiment, which is very intuitive and accurate. In some other specific embodiments, the judgment can also be graded. For example, a certain lithium-ion mobility rate v value can be used as the standard value. The kinetic performance of the vapor-phase silicon porous anode material 2 that is greater than the standard value is judged as good, and the kinetic performance of the vapor-phase silicon porous anode material 2 that is less than the standard value is judged as poor.

[0037] This invention uses the motion rate to characterize the kinetic performance of lithium ions in the electrode, which is very intuitive. The v value of a single sample can be calculated within 5 minutes. Compared with the traditional full-cell test that requires several days, the efficiency is improved by a hundred times. It effectively solves the problem that the kinetic performance of porous fumed silicon anode materials cannot be intuitively expressed.

[0038] The above-disclosed examples are merely preferred embodiments of the present invention and should not be construed as limiting the scope of the present invention. Therefore, any equivalent variations made in accordance with the claims of the present invention shall still fall within the scope of the present invention.

Claims

1. A method for characterizing the kinetic properties of a vapor-phase silicon porous anode material, characterized in that, Includes the following steps: A plurality of test electrode sheets with fumed silicon porous anode material are provided, wherein the fumed silicon porous anode materials on the plurality of test electrode sheets are different, and the plurality of test electrode sheets are assembled into a plurality of test batteries. The porosity K of the porous silicon anode material on the electrode under test, the lithium-ion diffusion path length D in the battery under test, and the lithium-ion diffusion time t are obtained. The lithium-ion mobility rate is calculated using the formula v=(D×K) / t. The kinetic performance of the corresponding porous silicon anode material is evaluated based on the calculated lithium-ion mobility v.

2. The method for characterizing the kinetic properties of the porous silicon anode material according to claim 1, characterized in that, The steps for obtaining the porosity K of the fumed silicon porous anode material on the electrode to be tested include: Obtain the apparent density ρ and the true density ρ0 of the vapor-phase silicon porous anode material on the electrode sheet to be tested; The porosity K of the fumed silicon porous anode material is calculated using the formula K=(1-ρ / ρ0)×100%.

3. The method for characterizing the kinetic properties of the porous silicon anode material according to claim 2, characterized in that, The true density ρ0 of the fumed silicon porous anode material was obtained by testing with a true density meter.

4. The method for characterizing the kinetic properties of the porous silicon anode material according to claim 2, characterized in that, The apparent density ρ of the vapor-phase silicon porous anode material is obtained by the ratio of the mass of the vapor-phase silicon porous anode material on the electrode to the volume of the vapor-phase silicon porous anode material.

5. The method for characterizing the kinetic properties of the porous silicon anode material according to claim 1, characterized in that, The lithium-ion diffusion path length D is calculated using the formula D=R×S×σ, where R is the ion resistance, S is the electrode area, and σ is the conductivity of the electrolyte in the battery under test.

6. The method for characterizing the kinetic properties of the porous silicon anode material according to claim 5, characterized in that, The ionic resistance R was obtained by AC impedance spectroscopy.

7. The method for characterizing the kinetic properties of the porous silicon anode material according to claim 5, characterized in that, The conductivity σ of the electrolyte was obtained using a conductivity meter.

8. The method for characterizing the kinetic properties of the porous silicon anode material according to claim 5, characterized in that, The lithium-ion diffusion time t was obtained using the relaxation time distribution method.

9. The method for characterizing the kinetic properties of the porous silicon anode material according to claim 1, characterized in that, The kinetic performance of the corresponding porous silicon anode material is evaluated based on the calculated lithium-ion mobility v, including: The maximum value among several lithium ion mobility rates v is determined based on the calculated lithium ion mobility rates v. The kinetic performance of the vapor-phase silicon porous anode material corresponding to the maximum value is determined to be the best.

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