Method for detecting porosity of solid electrolyte composite diaphragm

Abstract

The invention discloses a method for detecting porosity of a solid electrolyte composite diaphragm, and relates to the technical field of lithium battery diaphragm detection.The method comprises the following steps that the solid electrolyte composite diaphragm is pretreated in advance, a pretreated diaphragm sample is obtained, and pretreatment at least comprises sample cutting and vacuum freeze drying; establishing a measurement system, performing dynamic adsorption measurement according to the measurement system, obtaining the adsorption quantity and the adsorption rate, obtaining the effective diffusion coefficient De of the diaphragm, and calculating the porosity epsilon. Dynamic adsorption measurement is adopted, the pressure change in the adsorption process is monitored in real time, and rich adsorption capacity and adsorption rate data are obtained. In combination with a linear driving force LDF model, adsorption kinetics factors are fully considered, the effective diffusion coefficient of the diaphragm is obtained by fitting model parameters, and then the porosity is calculated. Compared with a traditional method, the method has the advantages that the influence of a complex pore structure in the diaphragm on the adsorption process can be reflected more accurately, and the accuracy of porosity calculation is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium battery separator detection, and more specifically, to a method for detecting the porosity of a solid electrolyte composite separator. Background Art

[0002] Solid electrolyte composite separators are widely used in many fields, especially in the field of new energy batteries. Their porosity plays a crucial role in the performance of the batteries. An appropriate porosity can ensure good wetting of the electrolyte, promote ion transport, and thus improve the charge and discharge efficiency, cycle life, and safety of the batteries. However, there are many problems in the current detection of the porosity of solid electrolyte composite separators, which are specifically as follows:

[0003] 1) Traditional detection methods have limitations. Existing porosity detection methods, such as mercury intrusion porosimetry, although can measure the porosity of the separator to a certain extent, mercury is toxic, and strict safety protection measures are required during the operation process. This not only poses a potential threat to the health of the operators, but also causes pollution to the environment. In addition, the measurement accuracy of mercury intrusion porosimetry for smaller pore diameters is relatively low, and it is difficult to meet the requirements for precise detection of the microscopic pore structure of solid electrolyte composite separators nowadays. The liquid displacement method is relatively simple to operate, but the selection of the liquid has a great influence on the measurement results. If the selected liquid reacts chemically with the separator material or cannot completely wet the pores of the separator, the measurement results will be inaccurate.

[0004] 2) The accuracy and repeatability of the detection results are poor. Due to the complex structure of solid electrolyte composite separators, there are differences in the pore structures of separators from different batches and different preparation processes. Existing detection technologies are difficult to accurately and stably measure their porosity. In the actual detection process, there are often large differences in the porosity results obtained by different detection methods for the same separator sample. Moreover, even for the same detection method, inconsistent detection results may occur between different laboratories or different operators, which seriously affects the evaluation of the separator quality and the optimization of the production process. At the same time, it cannot meet the needs of real-time and rapid detection on large-scale production lines, restricting the improvement of production efficiency.

[0005] For the problems in the related technologies, no effective solutions have been proposed yet. Summary of the Invention

[0006] In view of the problems in the related technologies, the present invention proposes a method for detecting the porosity of a solid electrolyte composite separator to overcome the above-mentioned technical problems existing in the existing related technologies.

[0007] The technical solution of the present invention is realized as follows:

[0008] A method for detecting the porosity of a solid electrolyte composite separator includes the following steps:

[0009] Step S1, pre-treat the solid electrolyte composite separator in advance to obtain a pre-treated separator sample, where the pre-treatment at least includes: sample cutting and vacuum freeze-drying;

[0010] Step S2, set up the measurement system, place the pre-treated separator sample in the sample cell, install the sample cell at the measurement position of the dynamic sorption analyzer, connect the gas supply system to the dynamic sorption analyzer, set the initial flow value of the gas flow controller, turn on the gas flow controller, so that the adsorption gas is preheated to the set adsorption temperature through the pre-heater and enters the sample cell, connect the pressure sensor to the sample cell, and connect the pressure sensor to the data acquisition system, and record the pressure value measured by the pressure sensor in real time;

[0011] Step S3, according to the measurement system, perform dynamic adsorption measurement to obtain the adsorption amount and adsorption rate, and according to the LDF model equation, obtain the effective diffusion coefficient D of the separator e , calculate the porosity ε, expressed as:

[0012]

[0013] where ρ s is the true density of the separator sample, ρ b is the bulk density of the separator sample, and D0 is the diffusion coefficient of the adsorption gas in free space.

[0014] where the sample cutting includes: using a cutting tool to cut the solid electrolyte composite separator into a circular sample with a diameter of 1-2 cm or a square sample with a side length of 1-2 cm.

[0015] where the vacuum freeze-drying includes: putting the cut separator sample into a vacuum drying oven, performing vacuum drying at a temperature of 50-60 °C for 1-2 hours, then transferring the sample to the sample tray of the freeze-dryer, putting the sample tray into the cold trap of the freeze-dryer, and pre-freezing at a temperature of -40--50 °C for 2-3 hours; after pre-freezing is completed, start the vacuum pump of the freeze-dryer, pump the system vacuum degree to below 10-3 Pa, and maintain freeze-drying at this vacuum degree for 12-24 hours.

[0016] where obtaining the pre-treated separator sample further includes: performing plasma surface cleaning, putting the freeze-dried separator sample into the sample chamber of the plasma processing equipment, setting the plasma processing parameters, and turning on the plasma processing equipment so that the sample surface is bombarded by plasma to remove surface organic pollutants and oxides.

[0017] where obtaining the adsorption amount includes the following steps:

[0018] The state equation of the calibration gas is PV=nRT, and the adsorption amount Δn is calculated and expressed as:

[0019]

[0020] Among them, V is the volume of the sample cell, which is obtained through experimental measurement or the instrument manual. T is the measurement temperature, ΔP is the pressure change, and the gas constant R = 8.314 kPa·cm 3 / (mol·K);

[0021] Among them, to obtain the pressure change ΔP of the gas in the sample cell before and after adsorption, the following steps are included:

[0022] Record the initial pressure P0 of the sample cell. Calibrate at a certain moment t, and read the value of the pressure sensor again, denoted as P1. Then the pressure change ΔP is expressed as: ΔP = P t -P0.

[0023] Among them, to obtain the adsorption rate r, the following steps are included:

[0024] According to the adsorption amount Δn, calibrate the adsorption amount Δ i corresponding to different time points t i , set the time point t j , and its corresponding adsorption amount is Δ j , then the adsorption rate r j at this point is expressed as

[0025]

[0026] Among them, Δt is the time interval between adjacent time points.

[0027] Advantages of the present invention:

[0028] 1) The pretreatment of the solid electrolyte composite separator in the present invention includes sample cutting, vacuum freeze-drying, and plasma surface cleaning. Through precise sample cutting, samples with appropriate sizes are obtained, reducing the interference of edge effects; vacuum freeze-drying can completely remove moisture and volatile impurities, avoiding their influence on the adsorption process; plasma surface cleaning can effectively remove organic pollutants and oxides, making the surface state of the samples consistent, ensuring the stability of the adsorption process during detection, and improving the accuracy of the detection results from the source.

[0029] 2) The present invention uses dynamic adsorption measurement to monitor the pressure change during the adsorption process in real time, obtaining rich adsorption amount and adsorption rate data. Combining with the linear driving force LDF model, fully considering the adsorption kinetic factors, the effective diffusion coefficient of the separator is obtained by fitting the model parameters, and then the porosity is calculated. Compared with traditional methods, this method can more accurately reflect the influence of the complex pore structure inside the separator on the adsorption process and improve the accuracy of porosity calculation.

[0030] Meanwhile, for the dynamic adsorption measurement of the present invention, adsorption data is obtained by continuously monitoring the pressure change without reaching the adsorption equilibrium, and the measurement can be completed in a relatively short time. Usually, a set of measurements can be completed within 10 - 30 minutes in the experiment. Moreover, multiple sets of data can be obtained by changing the gas flow rate, greatly improving the detection efficiency and meeting the requirements of rapid detection in industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0032] Figure 1 is a schematic flow chart of a method for detecting the porosity of a solid electrolyte composite separator according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0033] The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the drawings in the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, rather than all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art belong to the scope of protection of the present invention.

[0034] According to an embodiment of the present invention, a method for detecting the porosity of a solid electrolyte composite separator is provided.

[0035] As Figure 1 shown, the method for detecting the porosity of a solid electrolyte composite separator according to an embodiment of the present invention includes the following steps:

[0036] Step S1, pre-cut the sample. Use a cutting tool to cut the solid electrolyte composite separator into a circular sample with a diameter of about 1 - 2 cm or a square sample with a side length of about 1 - 2 cm.

[0037] Among them, during application, attention should be paid to avoiding damage to the sample during the cutting process and keeping the edges of the sample neat.

[0038] Perform vacuum freeze-drying. Place the cut diaphragm sample into a vacuum drying oven and conduct vacuum drying at a temperature of 50 - 60 °C for 1 - 2 hours to initially remove most of the moisture in the sample. Then transfer the sample to the sample tray of a freeze-dryer, place the sample tray into the cold trap of the freeze-dryer, and pre-freeze at a temperature of -40 - -50 °C for 2 - 3 hours. After pre-freezing is completed, start the vacuum pump of the freeze-dryer, evacuate the system vacuum to below 10-3 Pa, and maintain freeze-drying at this vacuum for 12 - 24 hours to ensure that the moisture and volatile impurities in the sample are thoroughly removed.

[0039] Perform plasma surface cleaning. Place the freeze-dried diaphragm sample into the sample chamber of a plasma processing device, set the plasma processing parameters, and turn on the plasma processing device so that the sample surface is bombarded by plasma to remove organic pollutants and oxides on the surface, improve the hydrophilicity of the sample surface, and enhance the interaction between the adsorbed gas and the sample.

[0040] Among them, when setting the plasma processing parameters, the power can be selected to be 50 - 100 W, the processing time is 5 - 10 minutes, and the gas flow rate is 10 - 20 sccm.

[0041] In step S2, build a measurement system. Place the pretreated diaphragm sample into a sample cell, use a gasket or sealant to ensure the airtightness of the sample cell, and install the sample cell at the measurement position of a dynamic adsorption instrument.

[0042] Connect the gas supply system to the dynamic adsorption instrument to ensure that the gas pipeline is tightly connected without leakage. Turn on the gas purifier to purify the adsorbed gas. Set the initial flow rate value of the gas flow controller, such as 5 sccm, turn on the gas flow controller, preheat the adsorbed gas to the set adsorption temperature (generally room temperature or set between 25 - 50 °C according to experimental requirements) through a preheater, and then let it enter the sample cell.

[0043] Connect the pressure sensor to the sample cell to ensure that the pressure sensor can accurately measure the pressure change in the sample cell. Connect the pressure sensor to the data acquisition system, set the acquisition parameters of the data acquisition system, with an acquisition frequency of 1 Hz, and start recording the pressure values measured by the pressure sensor in real time.

[0044] For the above dynamic adsorption instrument, this technical solution selects a dynamic adsorption instrument with high-precision gas flow control and pressure monitoring functions. The instrument includes a gas flow controller, a sample cell, a pressure sensor, and a data acquisition system. The gas flow controller should be able to accurately control the gas flow, and the accuracy should reach ±0.1 sccm to meet the requirements of different flow experiments. The design of the sample cell should ensure good airtightness and be able to accommodate diaphragm samples of appropriate sizes. The material of the sample cell should be selected as a material with stable chemical properties that does not react with the adsorbed gas and the diaphragm, such as stainless steel or glass. The measurement accuracy of the pressure sensor should reach ±0.01 kPa, and it should be able to accurately measure the minute pressure changes during the adsorption process. The data acquisition system has high-speed data acquisition capabilities and can record in real time the pressure values measured by the pressure sensor and the flow values set by the gas flow controller. The data acquisition frequency should not be lower than 1 Hz.

[0045] Step S3: According to the established measurement system, conduct dynamic adsorption measurements to obtain the adsorption amount and adsorption rate. According to the LDF model equation, obtain the effective diffusion coefficient D of the diaphragm e , and calculate the porosity ε.

[0046] In this technical solution, starting from when the gas begins to flow into the sample cell, closely observe the curve of the pressure recorded by the data acquisition system over time. In the initial stage, due to the rapid inflow of gas into the sample cell, the pressure rises rapidly. As the gas is adsorbed in the pores of the diaphragm, the rate of pressure rise gradually slows down. Continuously record the pressure change data over time until the pressure change curve tends to be relatively stable, and the recording time is 10 - 30 minutes. At the same time, change the gas flow rate, adjust the flow rate to 10 sccm, repeat the above measurement process, and record the pressure change data over time again. In this way, at least select 3 - 5 different gas flow rate values, and the gas flow rate values can be taken as 5 sccm, 10 sccm, 15 sccm, 20 sccm, and 25 sccm for measurement to obtain the adsorption characteristics of the diaphragm at different gas flow velocities.

[0047] Among them, calculating the adsorption amount Δn includes the following steps:

[0048] Calibrate the gas state equation PV = nRT, and calculate the adsorption amount Δn, expressed as:

[0049]

[0050] Among them, V is the volume of the sample cell, obtained through experimental measurement or the instrument manual, T is the measurement temperature, ΔP is the pressure change, and the gas constant R = 8.314 kPa·cm 3 / (mol·K),

[0051] For this technical solution, obtaining the pressure change ΔP of the gas in the sample cell before and after adsorption includes the following steps:

[0052] Record the initial pressure P0 of the sample cell, and the pressure value is measured by a high-precision pressure sensor. As the adsorption process proceeds, the gas is continuously adsorbed by the diaphragm, and the pressure in the sample cell gradually decreases. At a certain moment t, read the value of the pressure sensor again, denoted as P1, then the pressure change ΔP is expressed as: ΔP = P t - P0.

[0053] Among them, calculating the adsorption rate r includes the following steps:

[0054] According to the adsorption amount Δn, calibrate the adsorption amount Δ i corresponding to different time points t i , assuming the time point t j , and its corresponding adsorption amount is Δ j , then the adsorption rate r j at this point is expressed as

[0055]

[0056] Among them, Δt is the time interval between adjacent time points.

[0057] Obtain the porosity ε, which is expressed as:

[0058]

[0059] Among them, ρ s is the true density of the diaphragm (unit: g / cm 3 , obtained from the material manual or through density measurement experiments), ρ b is the bulk density of the diaphragm (unit: g / cm 3 , calculated by using the density formula with the mass m of the diaphragm sample for measuring the sample volume V), D0 is the diffusion coefficient of the adsorbed gas in the free space (standard data of different gases at different temperatures obtained by referring to existing relevant literature), D e is the effective diffusion coefficient of the diaphragm.

[0060] In addition, for the above LDF model (linear driving force model) equation, its basic equation can be expressed as:

[0061]

[0062] Among them, is the adsorption rate, k LDF is the linear driving force rate constant, q is the adsorption amount at time t, and q eq is the adsorption amount at adsorption equilibrium.

[0063] Among them, according to the adsorption amount Δn, adsorption rate r, and the LDF model (linear driving force model) equation, the value of k is adjusted by the non-linear least squares fitting method so that the adsorption amount calculated by the model has the best fitting degree with the experimentally measured adsorption amount during the entire adsorption process. After obtaining k by fitting, the effective diffusion coefficient D of the diaphragm is obtained, which is expressed as: LDF where Z is the characteristic size of the diaphragm, C is a constant, and takes the value of 6 for a flat diaphragm. LDF It should be particularly noted that in the application of this technical solution, on the one hand, it is applicable to a variety of diaphragm materials. Whether it is a solid electrolyte composite diaphragm of any material, as long as it can undergo the adsorption process, this detection method can be applied. Whether it is an organic polymer-based, inorganic ceramic-based or organic-inorganic composite-based diaphragm, the porosity can be accurately measured by this method, providing a unified detection means for the research and quality control of different types of diaphragms. On the other hand, it can be applied under different experimental conditions. Parameters such as adsorption temperature and gas flow rate in its measurement system can be flexibly adjusted according to actual needs. It can meet different research purposes and production requirements. Whether it is the detection under the actual working environment of the simulated battery or the comparative detection of diaphragms prepared under different process conditions, it can be completed by adjusting the experimental parameters, showing strong adaptability. e That is:

[0064]

[0065] where Z is the characteristic size of the diaphragm, C is a constant, and takes the value of 6 for a flat diaphragm.

[0066] To sum up, by means of the above technical solution of the present invention, the following effects can be achieved:

[0067] 1) The pretreatment of the solid electrolyte composite diaphragm in the present invention includes sample cutting, vacuum freeze-drying, and plasma surface cleaning. Through precise sample cutting, samples with appropriate sizes are obtained, reducing the interference of edge effects; vacuum freeze-drying can completely remove moisture and volatile impurities, avoiding their influence on the adsorption process; plasma surface cleaning can effectively remove organic pollutants and oxides, making the surface state of the samples consistent and ensuring a stable adsorption process during detection, improving the accuracy of the detection results from the source.

[0068] 2) The present invention uses dynamic adsorption measurement to monitor the pressure change during the adsorption process in real time, obtaining rich adsorption amount and adsorption rate data. Combining with the linear driving force LDF model, fully considering the adsorption kinetic factors, the effective diffusion coefficient of the diaphragm is obtained by fitting the model parameters, and then the porosity is calculated. Compared with traditional methods, this method can more accurately reflect the influence of the complex pore structure inside the diaphragm on the adsorption process, improving the accuracy of porosity calculation.

[0069] 2) The present invention adopts dynamic adsorption measurement to monitor the pressure change during the adsorption process in real time, obtaining rich adsorption amount and adsorption rate data. Combining with the linear driving force LDF model, fully considering the adsorption kinetic factors, the effective diffusion coefficient of the diaphragm is obtained by fitting the model parameters, and then the porosity is calculated. Compared with traditional methods, this method can more accurately reflect the influence of the complex pore structure inside the diaphragm on the adsorption process, improving the accuracy of porosity calculation.

[0070] Meanwhile, for the dynamic adsorption measurement of the present invention, adsorption data is obtained by continuously monitoring the pressure change without reaching the adsorption equilibrium, and the measurement can be completed in a short time. Usually, a set of measurements can be completed within 10 - 30 minutes in the experiment. Moreover, multiple sets of data can be obtained by changing the gas flow rate, greatly improving the detection efficiency and meeting the requirements of rapid detection in industrial production.

[0071] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. After considering the disclosure in the specification and the embodiments, those skilled in the art will easily think of other implementation schemes of the present disclosure. This application aims to cover any variations, uses, or adaptive changes of the present disclosure, which follow the general principles of the present disclosure and include the common general knowledge or conventional technical means in the technical field not disclosed in the present disclosure. The specification and the embodiments are only regarded as exemplary, and the true scope and spirit of the present disclosure are pointed out by the claims.

[0072] It should be understood that the present disclosure is not limited to the precise structures already described and shown in the drawings, and various modifications and changes can be made without departing from its scope. The scope of the present disclosure is only limited by the appended claims.

Claims

1. A method for detecting the porosity of a solid electrolyte composite separator, characterized in that, It includes the following steps: Pre-treat the solid electrolyte composite separator in advance to obtain a pre-treated separator sample. Among them, the pre-treatment at least includes: sample cutting and vacuum freeze-drying; Build a measurement system. Place the pre-treated separator sample in the sample cell, install the sample cell at the measurement position of the dynamic adsorption instrument, connect the gas supply system to the dynamic adsorption instrument, set the initial flow value of the gas flow controller, turn on the gas flow controller, so that the adsorption gas is preheated to the set adsorption temperature through the preheater and enters the sample cell. Connect the pressure sensor to the sample cell and connect the pressure sensor to the data acquisition system to record the pressure value measured by the pressure sensor in real time; According to the measurement system, dynamic adsorption measurement is carried out to obtain the adsorption amount and adsorption rate. According to the LDF model equation, the effective diffusion coefficient D of the diaphragm is obtained e , and the porosity ε is calculated and expressed as: where ρ s is the true density of the separator sample, ρ b is the bulk density of the separator sample, and D0 is the diffusion coefficient of the adsorbed gas in free space.

2. The porosity detection method of the solid electrolyte composite separator according to claim 1, wherein The sample cutting includes: using a cutting tool to cut the solid electrolyte composite separator into a circular sample with a diameter of 1-2 cm or a square sample with a side length of 1-2 cm.

3. The method for detecting the porosity of the solid electrolyte composite separator according to claim 2, wherein The vacuum freeze-drying includes: putting the cut separator sample into a vacuum drying oven, carrying out vacuum drying at a temperature of 50-60 °C for 1-2 hours, then transferring the sample to the sample tray of the freeze-dryer, putting the sample tray into the cold trap of the freeze-dryer, and pre-freezing at a temperature of -40--50 °C for 2-3 hours; after pre-freezing is completed, start the vacuum pump of the freeze-dryer, pump the system vacuum degree to below 10-3 Pa, and maintain freeze-drying at this vacuum degree for 12-24 hours.

4. The method for detecting the porosity of the solid electrolyte composite separator according to claim 3, characterized in that, The obtaining of the pre-treated separator sample further includes: carrying out plasma surface cleaning, putting the freeze-dried separator sample into the sample chamber of the plasma treatment equipment, setting the plasma treatment parameters, and turning on the plasma treatment equipment so that the sample surface is bombarded by plasma to remove surface organic pollutants and oxides.

5. The method for detecting the porosity of the solid electrolyte composite separator according to claim 1, wherein Obtaining the adsorption amount includes the following steps: Calibrate the gas state equation PV = nRT and calculate the adsorption amount Δn, expressed as: Among them, V is the volume of the sample cell, which is obtained by experimental measurement or the instrument manual, T is the measurement temperature, ΔP is the pressure change, and the gas constant R = 8.314 kPa·cm 3 / (mol·K).

6. The method for detecting the porosity of the solid electrolyte composite separator according to claim 1, wherein Obtaining the pressure change ΔP of the gas pressure in the sample cell before and after adsorption includes the following steps: Record the initial pressure P0 of the sample cell. Calibrate at a certain moment t and read the value of the pressure sensor again, denoted as P1. Then the pressure change ΔP is expressed as: ΔP = P t - P0.

7. The method for detecting the porosity of the solid electrolyte composite separator according to claim 6, characterized in that, Obtaining the adsorption rate r includes the following steps: Calibrate different time points \(t\) according to the adsorption amount \(\Delta n\). i The corresponding adsorption amount \(\Delta\). i Let the time point be \(t\). j The corresponding adsorption amount is \(\Delta\). j Then the adsorption rate \(r\) at this point j is expressed as Among them, Δt is the time interval between adjacent time points.

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