Carbon fiber structure electrode interface performance sample preparation and test method

Abstract

The invention discloses a method for preparing and testing a carbon fiber structure electrode interface performance sample, which comprises the following steps of: taking surface modified carbon fiber as a structure electrode, stripping an electrode fiber monofilament from the carbon fiber electrode under a magnifying lens, and respectively fixing two ends of the electrode fiber monofilament on two sides of a concave carrier; enabling the middle part of the electrode fiber monofilament to be suspended in the middle of the carrier and to be in a straightened state, mixing resin, a pore forming agent and a curing agent, and uniformly stirring to prepare a structural electrode resin solution; the method comprises the following steps: dipping a structural electrode resin solution with an injector, dripping the structural electrode resin solution on an electrode fiber monofilament, curing in a low-oxygen pore-forming agent atmosphere, performing ultrasonic post-treatment in a solvent atmosphere, infiltrating electrolyte to obtain a test sample, and testing the interface performance of the carbon fiber structural electrode by adopting a tension testing machine and an ultra-field-depth microscope. The interface strength of the carbon fiber structure electrode can be accurately obtained, and the surface microstructure change rule of the carbon fiber electrode in the interface damage process of the carbon fiber structure electrode can be obtained.

Description

Technical Field

[0001] This invention belongs to the field of structural energy storage composite material testing technology, specifically relating to a method for preparing and testing carbon fiber structure electrode interface performance samples. Background Technology

[0002] For the electrochemical performance of structural batteries, the electrode interface is the site where lithium ions must undergo necessary electrochemical reactions. At the electrode interface, the ionic liquid needs to contact the surface-active material of the carbon fiber, which means that both the solid and liquid phases of the electrolyte need to be in physical contact with the fiber surface. Due to the limited adhesive surface area of ​​the fiber / matrix, the interfacial adhesion performance is expected to be lower than that of traditional fiber / matrix interfaces. For this highly complex interfacial region, further research is needed to understand the interfacial adhesion performance between the structural electrolyte and the carbon fiber electrode.

[0003] The interfacial properties of carbon fiber structure electrodes can be characterized by interfacial bond strength testing, which includes micro-debonding testing, single fiber pull-out, and single fiber fragmentation. These test results can accurately represent the interfacial shear strength (IFSS) of the composite material.

[0004] In preparing single-fiber pull-out specimens, a single fiber is vertically embedded into a resin matrix. The length of the embedded fiber is controlled to prevent breakage during extraction. During the pull-out test, a resin block is fixed, and force is applied to the outer end of the single fiber until it is completely pulled out of the matrix. The force is transmitted from the fiber to the matrix through the interface. Single-fiber pull-out testing has a wide range of applications and can be used in various reinforcing fiber / matrix composite systems. However, the limitation of single-fiber pull-out testing lies in specimen preparation: different single fibers have different critical lengths for embedding in different resins. Excessive fiber length can lead to premature breakage before debonding occurs at the interface, increasing the difficulty of specimen preparation and resulting in poor reproducibility.

[0005] The microdroplet adhesion-detachment test is an improved version of the single-fiber pull-out test, solving the problem of thinner fibers easily breaking during testing in the fiber pull-out test. Microdroplet adhesion-detachment also has advantages such as simple sample preparation, multiple microdroplets on a single fiber, allowing for multiple tests, and high efficiency in interface performance testing. The external load acts directly on the fiber end and is transferred to the matrix through the interface. A symmetrical loading method is used to fix the bottom or top of the matrix, such as... Figure 1 As shown, the single fiber / resin droplet sample is placed in the slit formed by two fixed blades. When the single fiber is subjected to tension, the blades fix the droplets on the fiber and record the force-displacement curve of the fiber filament being pulled out of the droplet. When the shear force reaches the critical value, the interface debonds. At this time, the maximum load F is recorded. Combined with the length L of the fiber covered by the droplet and the fiber diameter d, the interface shear strength is obtained using equation (1).

[0006] This invention proposes a method for preparing and testing samples of the microdroplet debonding interface performance of carbon fiber structured electrodes, providing a basis for evaluating the interface performance of carbon fiber structured electrodes and having significant implications for the performance optimization research of supporting structure energy storage composite materials. Traditional microdroplet debonding test sample preparation often takes place in an air atmosphere. During the curing process, porous resin structures often have a dense resin layer on the surface, which severely affects the accuracy of carbon fiber structured electrode interface performance testing. This invention improves the sample preparation method for microdroplet debonding tests, effectively reducing the dense resin layer on the porous resin surface. Simultaneously, the cured sample is ultrasonically treated in a special solvent to effectively remove the dense resin layer from the porous resin surface, thus improving testing accuracy.

[0007] Since the droplet debonding test requires specific experimental equipment (such as the HM410 interfacial shear strength evaluation device, Toei Co., Ltd., Japan), such equipment is quite expensive due to its high precision. This method is based on a horizontal tensile testing machine, which has been modified to be simpler and cheaper than the above-mentioned equipment, while ensuring the test accuracy.

[0008] Ultra-depth-of-field microscopes can observe characteristic structures such as modified layers on the fiber surface. By using ultra-depth-of-field microscopes to photograph and monitor the debonding process of electrode fiber microdroplets, the changes in surface morphology of electrode fibers during interfacial debonding can be dynamically observed, and the influence of modified layers on the fiber / resin interface can be observed, so as to guide the design of modified layers for carbon fiber structure electrodes. Summary of the Invention

[0009] The purpose of this invention is to provide a method for preparing and testing samples of the interface properties of carbon fiber structure electrodes.

[0010] To achieve the above objectives, the present invention adopts the following technical solution: A method for preparing a carbon fiber structure electrode interface performance sample, the process is as follows: (1) Surface-modified carbon fiber is used as carbon fiber electrode, and the electrode fiber monofilament is peeled off from the carbon fiber electrode under a magnifying glass. (2) Fix the two ends of the electrode fiber monofilament to the two sides of the concave-shaped carrier respectively, so that the middle part of the electrode fiber monofilament is suspended in the middle of the concave-shaped carrier and is in a taut state; (3) Mix the resin, pore-forming agent and curing agent and stir evenly to obtain a structural electrode resin solution; (4) Dip a syringe into the structural electrode resin solution and drip it onto the electrode fiber monofilament. Multiple microdroplets are dripped onto one fiber. The solution is cured in a low-oxygen pore-forming agent vapor atmosphere. After curing, the solution is subjected to ultrasonic post-treatment in a solvent atmosphere and then impregnated with electrolyte to obtain an electrode fiber monofilament test sample containing multiple resin microdroplets.

[0011] Preferably, in step (1), the surface-modified carbon fiber is carbon fiber modified with carbon active material or silicon active material, including carbon nanotubes and silicon particles, etc.

[0012] Preferably, the resin is 1,3-bis(N,N-diglycidylaminomethyl)cyclohexane resin, the pore-forming agent is polyethylene glycol 200, and the curing agent is PACM curing agent. The mass ratio of resin, pore-forming agent, and curing agent is 1:(2~3):(0.2~0.6). The curing process is as follows: first, heat treatment at 120~150℃ for 50min~70min, then heat treatment at 160~200℃ for 20min~40min. The curing atmosphere is an oxygen content of less than 1000 ppm, filled with dry nitrogen, and a pore-forming agent vapor atmosphere at 1 standard atmosphere. (Oxygen content is less than 1000 PPM, filled with dry nitrogen, pressure is 1 standard atmosphere, pore-forming agent is polyethylene glycol 200, and the polyethylene glycol 200 vapor temperature follows the curing temperature).

[0013] Furthermore, the length of all individual microdroplets coated fibers is 50–240 μm.

[0014] Further, the solvent in step (4) is at least one or a mixture of two or more of acetone, ethanol, formic acid and DMF in any proportion; the ultrasonic treatment conditions are: ultrasonic frequency 30~50kHz, power 20~160W, temperature 25±5℃, and treatment time 10~60 seconds.

[0015] Furthermore, the electrolyte is a lithium hexafluorophosphate lithium salt electrolyte (such as LB-002, LB-0010, LB-012, LB-014), and the immersion time in the electrolyte is 20 to 30 hours.

[0016] The carbon fiber structure electrode interface performance sample prepared by the above method.

[0017] The method for testing the interface properties of carbon fiber structure electrodes using the above-mentioned samples is as follows: (1) Fix the concave carrier with the test specimen on the test table of the tensile testing machine, hold the two ends of the fiber in the tensile testing machine fixture, drag the electrode fiber with tensile force at a certain loading rate, so that the microdroplets on the fiber contact the fixed tool, take pictures of the continuous change of the microscopic surface morphology of the electrode fiber using an ultra-depth-of-field microscope, and record the maximum load displayed by the tensile testing machine and the force-displacement curve during the loading process. When the tensile force rapidly decreases by more than 30%, the test is terminated. (2) The shear strength of the carbon fiber structure electrode interface is calculated using formula (1); (3) Using the force-displacement curve of the obtained sample, combined with the super depth-of-field microscopic images corresponding to each point on the curve, the corresponding electrode fiber interface debonding results are obtained, so as to study the microscopic change behavior of the electrode modified layer in the interface debonding process.

[0018] Preferably, the loading rate in step (1) is 0.01~0.1 mm / min.

[0019] Due to the inherent dispersion in the experimental results, this experiment requires multiple tests to obtain a more accurate average interfacial shear strength.

[0020] This invention uses a tensile testing machine and a super depth-of-field microscope to test the interfacial properties of carbon fiber structural electrodes. It can obtain the interfacial strength of carbon fiber structural electrodes relatively accurately and can also obtain the changes in the microstructure of the carbon fiber electrode surface during the interfacial failure process. This is of great significance for guiding the structural design of carbon fiber electrodes.

[0021] Compared with the prior art, the present invention has the following beneficial effects: 1. No dedicated composite material interface evaluation equipment is required; this test can be performed using a tensile testing machine. 2. The interface debonding process of carbon fiber electrode monofilaments during the test can be observed more clearly using an ultra-depth-of-field microscope. Attached Figure Description

[0022] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments: Figure 1 This is a schematic diagram of a microdroplet debonding test in the prior art; Figure 2 Electron microscopy images of the surface of sputtered Si-modified fibers; Figure 3 Electron microscopy images of the surface of CNT-modified fibers; Figure 4 This is a schematic diagram of the sample carrier and testing method for microdroplet debonding. Figure 5 Images of samples under a super depth-of-field microscope; Figure 6 SEM images of CNT-modified fibers after debonding; Figure 7 This is the force-displacement curve for microdroplet testing. Detailed Implementation

[0023] To enable those skilled in the art to better understand the technical solutions of the present invention, the preferred embodiments of the present invention are described below in conjunction with specific examples, but these should not be construed as limiting the present patent.

[0024] Example 1: A method for testing the interface performance of carbon fiber structure electrodes, the process of which is as follows: (1) Carbon nanotube (CNT) surface-modified carbon fiber and Si surface-modified carbon fiber are used as carbon fiber electrodes.

[0025] Preparation of Si-modified carbon fiber microdroplet debonding samples: A silicon layer was prepared by magnetron sputtering onto the surface of carbon fiber fabric, with a thickness of 0.1–1 μm. SEM images of the obtained samples are shown below. Figure 2 As shown, by Figure 2 It can be seen that a relatively uniform Si-modified layer was formed on the surface of the carbon fiber by magnetron sputtering.

[0026] Preparation of CNT-modified carbon fiber microdroplet debonding samples: CNTs were grown on the surface of carbon fiber fabric by CVD, with a CNT layer thickness of 0.5~2.5 μm. SEM images of the CNT-modified carbon fiber microdroplet debonding samples are shown below. Figure 3 As shown, by Figure 3 It can be seen that uniform CNTs are grown on the surface of the carbon fiber.

[0027] (2) Add 1,3-bis(N,N-diglycidylaminomethyl)cyclohexane resin and polyethylene glycol 200 to a beaker in a ratio of 1:3 and stir. After stirring evenly, add 0.6 times the weight of the resin curing agent PACM and stir for 15 min to obtain the structural electrode resin solution.

[0028] (3) Under a magnifying glass, peel the electrode fiber monofilament from the carbon fiber electrode, ensuring that the peeled electrode fiber is a single fiber; fix the two ends of the electrode fiber monofilament to both sides of the U-shaped carrier, such as... Figure 4 As shown, the electrode fiber is suspended in the middle and kept taut.

[0029] (4) The prepared structural electrode resin solution was dripped onto the electrode fiber monofilament using a syringe. Multiple microdroplets were dripped onto one fiber, and the size of the microdroplets was kept as similar as possible to reduce the dispersion of the experimental results. After curing, multiple microdroplets with an embedded fiber length of 50-100 μm were obtained. The curing refers to curing at 130℃ for 1 h and then at 180℃ for 0.5 h. The curing atmosphere was oxygen content below 1000 ppm, filled with dry nitrogen, and polyethylene glycol 200 vapor atmosphere at 1 standard atmosphere. After curing, the sample was cooled to room temperature and placed in ethanol (a solvent that dissolves / swells the dense layer on the surface of the resin but causes less damage to the overall structure) for short-term ultrasonic treatment (ultrasonic frequency 40 kHz, power 100 W, temperature 25 ± 5℃, treatment time 20 seconds) to further destroy the residual dense layer of resin on the surface. Then, the sample was immersed in electrolyte (the electrolyte was selected to match the carbon fiber electrode. In this example, LB-002 electrolyte was used. The sample was immersed in the electrolyte for 24 hours at normal pressure and temperature in a glove box).

[0030] (5) The concave carrier with the test specimen is fixed on the test table of the tensile testing machine. A loading rate of 0.1 mm / min is used to drag the microdroplets on the electrode fiber into contact with the fixed cutter, with the cutter 5 μm away from the fiber surface. Images of the continuous changes in the microscopic surface morphology of the electrode fiber are taken using a super depth-of-field microscope, such as... Figure 5 As shown, the maximum load displayed by the tensile testing machine and the force-displacement curve during the loading process were recorded simultaneously. The test was terminated when the tensile force rapidly decreased by more than 30%. Figure 5 As can be seen, the resin microdroplets completely cover the modified part of the carbon fiber, and the data obtained from the surface test is the interfacial shear strength between the modified fiber and the electrode resin.

[0031] (6) The shear strength of the carbon fiber structure electrode interface is calculated using formula (1); according to Figure 7 The force-displacement curve of the sample was analyzed, along with the corresponding ultra-depth-of-field microscopic images at each point on the curve, to obtain the corresponding electrode fiber interface debonding results. Figure 7 It can be seen that when the force applied to one end of the fiber reaches its maximum value and begins to decay, the surface resin completely detaches from the fiber.

[0032] (7) Through Figure 6 SEM observation revealed that resin residue remained on the debonded surfaces of both modified carbon fibers, indicating that the modified layer did indeed improve the interfacial performance of the carbon fiber electrode.

[0033] Carbon fiber electrode interfacial shear strength test value Example 2: A method for testing the interface performance of carbon fiber structure electrodes, the process of which is as follows: (1) Carbon nanotube (CNT) surface-modified carbon fiber and Si surface-modified carbon fiber of Example 1 were used as carbon fiber electrodes.

[0034] (2) Add 1,3-bis(N,N-diglycidylaminomethyl)cyclohexane resin and polyethylene glycol 200 to a beaker in a ratio of 1:3 and stir. After stirring evenly, add 0.6 times the weight of the resin curing agent PACM and stir for 15 min to obtain the structural electrode resin solution.

[0035] (3) Under a magnifying glass, peel the electrode fiber monofilament from the carbon fiber electrode, ensuring that the peeled electrode fiber is a single fiber; fix the two ends of the electrode fiber monofilament to both sides of the U-shaped carrier, such as... Figure 4 As shown, the electrode fiber is suspended in the middle and kept taut.

[0036] (4) The prepared structural electrode resin solution is dripped onto the electrode fiber monofilament using a syringe. Multiple microdroplets are dripped onto one fiber, ensuring that the size of the microdroplets is as similar as possible. After curing, multiple microdroplets with an embedded fiber length of 100-140 μm are obtained. The curing refers to curing at 130℃ for 1 h and then at 180℃ for 0.5 h. The curing atmosphere is an oxygen content of less than 1000 ppm, filled with dry nitrogen, and a polyethylene glycol 200 vapor atmosphere at 1 standard atmosphere. After curing, the sample is cooled to room temperature and placed in acetone for 20 seconds of ultrasonic treatment (ultrasonic frequency 40 kHz, power 100 W, temperature 25 ± 5℃) to further destroy the dense resin layer remaining on the surface. Then, the sample is immersed in lithium hexafluorophosphate (LB-002) lithium salt electrolyte in a box at normal pressure and temperature for 24 hours.

[0037] (5) Fix the concave carrier with the test specimen onto the test table of the tensile testing machine. With a loading rate of 0.1 mm / min, drag the microdroplets on the electrode fiber to contact the fixed cutter with tensile force. The cutter is 5 μm away from the fiber surface. Use an ultra-depth-of-field microscope to take pictures of the continuous changes in the microscopic surface morphology of the electrode fiber, and record the force-displacement curve during the loading process. When the tensile force rapidly decreases by more than 30%, the test is terminated.

[0038] (6) Record the maximum load during the test and calculate the shear strength of the carbon fiber structure electrode interface using formula (1); obtain the force-displacement curve of the sample, and analyze it in conjunction with the ultra-depth-of-field microscopic images corresponding to each point on the curve to obtain the corresponding electrode fiber interface debonding results.

[0039] (7) SEM observation revealed that resin residue remained on the debonded surfaces of both modified carbon fibers, indicating that the modified layer did indeed improve the interfacial performance of the carbon fiber electrode.

[0040] Carbon fiber electrode interfacial shear strength test value Example 3: A method for testing the interface performance of carbon fiber structure electrodes, the process of which is as follows: (1) Carbon nanotube (CNT) surface-modified carbon fiber and Si surface-modified carbon fiber of Example 1 were used as carbon fiber electrodes.

[0041] (2) Add 1,3-bis(N,N-diglycidylaminomethyl)cyclohexane resin and polyethylene glycol 200 to a beaker in a ratio of 1:3 and stir. After stirring evenly, add 0.6 times the weight of the resin curing agent PACM and stir for 15 min to obtain the structural electrode resin solution.

[0042] (3) Under a magnifying glass, peel the electrode fiber monofilament from the carbon fiber electrode, ensuring that the peeled electrode fiber is a single fiber; fix the two ends of the electrode fiber monofilament to both sides of the U-shaped carrier, such as... Figure 4 As shown, the electrode fiber is suspended in the middle and kept taut.

[0043] (4) The prepared structural electrode resin solution is dripped onto the electrode fiber monofilament using a syringe. Multiple microdroplets are dripped onto one fiber, ensuring that the size of the microdroplets is as similar as possible. After curing, multiple microdroplets with fiber lengths of 160-240 μm are embedded. The curing refers to curing at 130℃ for 1 h and then at 180℃ for 0.5 h. The curing atmosphere is an oxygen content of less than 1000 ppm, filled with dry nitrogen, and a polyethylene glycol 200 vapor atmosphere at 1 standard atmosphere. After curing, the sample is cooled to room temperature and placed in acetone for 20 seconds of ultrasonic treatment (ultrasonic frequency 40 kHz, power 100 W, temperature 25 ± 5℃) to further destroy the dense resin layer remaining on the surface. Then, the sample is immersed in lithium hexafluorophosphate (LB-002) lithium salt electrolyte in a box at normal pressure and temperature for 24 hours.

[0044] (5) Fix the concave carrier with the test specimen onto the test table of the tensile testing machine. With a loading rate of 0.1 mm / min, drag the microdroplets on the electrode fiber to contact the fixed cutter with tensile force. The cutter is 5 μm away from the fiber surface. Use an ultra-depth-of-field microscope to take pictures of the continuous changes in the microscopic surface morphology of the electrode fiber, and record the force-displacement curve during the loading process. When the tensile force rapidly decreases by more than 30%, the test is terminated.

[0045] (6) Record the maximum load during the test and calculate the shear strength of the carbon fiber structure electrode interface using formula (1); obtain the force-displacement curve of the sample, and analyze it in conjunction with the ultra-depth-of-field microscopic images corresponding to each point on the curve to obtain the corresponding electrode fiber interface debonding results.

[0046] (7) SEM observation revealed that resin residue remained on the debonded surfaces of both modified carbon fibers, but the fibers were often broken during the test, indicating that excessively large resin droplets could easily cause fiber breakage during the test, thus increasing the test dispersion.

[0047] Carbon fiber electrode interfacial shear strength test value Example 4: A method for testing the interface performance of carbon fiber structure electrodes, the process of which is as follows: (1) Carbon nanotube (CNT) surface-modified carbon fiber and Si surface-modified carbon fiber of Example 1 were used as carbon fiber electrodes.

[0048] (2) Add 1,3-bis(N,N-diglycidylaminomethyl)cyclohexane resin and polyethylene glycol 200 to a beaker at a ratio of 1:3 and stir. After stirring evenly, add 0.6 times the weight of the resin curing agent PACM and stir for 15 minutes to obtain the structural electrode resin solution. (3) Under a magnifying glass, peel the electrode fiber monofilament from the carbon fiber electrode, ensuring that the peeled electrode fiber is a single fiber; fix the two ends of the electrode fiber monofilament to the two sides of the U-shaped carrier, such as Figure 4 As shown, the electrode fiber is suspended in the middle and kept taut.

[0049] (4) The prepared structural electrode resin solution is dripped onto the electrode fiber monofilament using a syringe. Multiple microdroplets are dripped onto one fiber, ensuring that the size of the microdroplets is as similar as possible. After curing, multiple microdroplets with an embedded fiber length of 100-140 μm are obtained. The curing refers to curing at 130℃ for 1 h and then at 180℃ for 0.5 h. The curing atmosphere is an oxygen content of less than 1000 ppm, filled with dry nitrogen, and a polyethylene glycol 200 vapor atmosphere at 1 standard atmosphere. After curing, the sample is cooled to room temperature and placed in acetone for 20 seconds of ultrasonic treatment (ultrasonic frequency 40 kHz, power 100 W, temperature 25 ± 5℃) to further destroy the dense resin layer remaining on the surface. Then, the sample is immersed in lithium hexafluorophosphate (LB-002) lithium salt electrolyte in a box at normal pressure and temperature for 24 hours.

[0050] (5) Fix the concave carrier with the test specimen onto the test table of the tensile testing machine. With a loading rate of 0.01 mm / min, drag the microdroplets on the electrode fiber to contact the fixed cutter with tensile force. The cutter is 5 μm away from the fiber surface. Use an ultra-depth-of-field microscope to take pictures of the continuous changes in the microscopic surface morphology of the electrode fiber, and record the force-displacement curve during the loading process. When the tensile force rapidly decreases by more than 30%, the test is terminated.

[0051] (6) Record the maximum load during the test and calculate the shear strength of the carbon fiber structure electrode interface using formula (1); obtain the force-displacement curve of the sample, and analyze it in conjunction with the ultra-depth-of-field microscopic images corresponding to each point on the curve to obtain the corresponding electrode fiber interface debonding results.

[0052] Carbon fiber electrode interfacial shear strength test value Example 5: A method for testing the interface performance of carbon fiber structure electrodes, the process of which is as follows: (1) Carbon nanotube (CNT) surface-modified carbon fiber and Si surface-modified carbon fiber of Example 1 were used as carbon fiber electrodes.

[0053] (2) Add 1,3-bis(N,N-diglycidylaminomethyl)cyclohexane resin and polyethylene glycol 200 to a beaker in a ratio of 1:3 and stir. After stirring evenly, add 0.6 times the weight of the resin curing agent PACM and stir for 15 min to obtain the structural electrode resin solution.

[0054] (3) Under a magnifying glass, peel the electrode fiber monofilament from the carbon fiber electrode, ensuring that the peeled electrode fiber is a single fiber; fix the two ends of the electrode fiber monofilament to both sides of the U-shaped carrier, such as... Figure 4 As shown, the electrode fiber is suspended in the middle and kept taut.

[0055] (4) The prepared structural electrode resin solution was dripped onto the electrode fiber monofilament using a syringe. Multiple microdroplets were dripped onto one fiber, ensuring that the size of the microdroplets was as similar as possible. After curing, multiple microdroplets with an embedded fiber length of 100-140 μm were obtained. The curing process involved curing at 130℃ for 1 h, then at 180℃ for 0.5 h, and cooling to room temperature. The curing atmosphere was filled with dry nitrogen gas and polyethylene glycol 200 vapor at 1 standard atmosphere with an oxygen content of less than 1000 ppm. After curing, the sample was cooled to room temperature and placed in acetone for 20 seconds of ultrasonic treatment (ultrasonic frequency 40 kHz, power 100 W, temperature 25 ± 5℃) to further destroy the dense resin layer remaining on the surface. Subsequently, the sample was immersed in lithium hexafluorophosphate (LB-002) lithium salt electrolyte in a box at normal pressure and temperature for 24 hours.

[0056] (5) Fix the concave carrier with the test specimen on the test table of the tensile testing machine. With a loading rate of 0.1 mm / min, drag the microdroplets on the electrode fiber to contact the fixed cutter with tensile force. The cutter is 10 μm away from the fiber surface. Use an ultra-depth-of-field microscope to take pictures of the continuous changes in the microscopic surface morphology of the electrode fiber, and record the force-displacement curve during the loading process until the test is terminated.

[0057] (6) Record the maximum load during the experiment and calculate the shear strength of the carbon fiber structure electrode interface using formula (1); obtain the force-displacement curve of the sample, and analyze it in conjunction with the ultra-depth-of-field microscopic images corresponding to each point on the curve to obtain the corresponding electrode fiber interface debonding results. In this example, some resin microspheres broke in the middle, and a large number of parts were not peeled off, which led to an increase in the experimental dispersion.

[0058] Carbon fiber electrode interfacial shear strength test value The table below shows the measured values ​​of the shear strength at the microdroplet debonding interface for each embodiment. Comparing the above examples, the resin microdroplet-embedded fiber lengths tested in Examples 1-3 were 50-100μm, 100-140μm, and 160-240μm, respectively. Based on the Cv value comparison, the test data obtained when the resin microdroplet length was between 100-140μm was more stable. Examples 2 and 4 compared the loading rates, which were 0.1mm / min and 0.01mm / min, respectively. The Cv values ​​obtained were not significantly different. To improve experimental efficiency and reduce the requirements for instrument loading accuracy, the loading rate can be set to 0.1mm / min. The distance between the cutter and the fiber in Examples 2 and 5 were 5μm and 10μm, respectively. The experimental data showed that a distance of 5μm between the cutter and the fiber was more accurate. Furthermore, in Example 5, a significant portion of the resin microspheres remained intact; therefore, a distance of 5μm between the cutter and the fiber was selected.

[0059] The above description is only a partial embodiment of the present invention. For those skilled in the art, several improvements and substitutions can be made without departing from the principle of the present invention, and these improvements and substitutions should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a carbon fiber structural electrode interface performance test sample, characterized by, The process is as follows: (1) The surface modified carbon fiber is used as the carbon fiber electrode, and the electrode fiber monofilament is stripped from the carbon fiber electrode under a magnifying glass; (2) The two ends of the electrode fiber monofilament are fixed on the two sides of the concave-shaped carrier, and the middle part of the electrode fiber monofilament is suspended in the middle of the concave-shaped carrier and is in a straightened state; (3) The resin, pore-forming agent and curing agent are mixed and stirred uniformly to prepare a structural electrode resin solution; (4) The structural electrode resin solution is taken with a syringe and dropped on the electrode fiber monofilament, a plurality of microdroplets are dropped on one fiber, and curing is carried out in a low-oxygen pore-forming agent vapor atmosphere. After curing, ultrasonic post-treatment is carried out in a solvent atmosphere, and then an electrolyte is infiltrated to obtain an electrode fiber monofilament test sample containing a plurality of resin microdroplets.

2. The method of claim 1, wherein the carbon fiber structure electrode interface performance sample preparation method is characterized by, In step (1), the surface modified carbon fiber is a carbon active substance or a silicon active substance modified carbon fiber.

3. The method of claim 1, wherein the carbon fiber structure electrode interface performance sample preparation method is characterized by, In step (4), the resin is 1,3-bis(N,N-diglycidyl aminomethyl) cyclohexane resin, the pore-forming agent is polyethylene glycol 200, and the curing agent is PACM curing agent. The mass ratio of the resin, pore-forming agent and curing agent is 1:(2-3):(0.2-0.6).

4. The method of claim 1, wherein the carbon fiber structure electrode interface performance sample preparation method is characterized by, The curing process is as follows: first, heat at 120-150°C for 50-70 min, and then heat at 160-200°C for 20-40 min. The curing atmosphere is a pore-forming agent vapor atmosphere with an oxygen content of less than 1000 ppm, filled with dry nitrogen, and 1 atmosphere of pressure.

5. The method of claim 1, wherein the carbon fiber structural electrode interface performance sample preparation method is characterized by, The length of all single microdroplet-coated fibers is 50-240 μm.

6. The method of claim 1, wherein the carbon fiber structural electrode interface performance sample preparation method is characterized by, The solvent in step (4) is at least one of acetone, ethanol, formic acid and DMF, or a mixture of two or more thereof in any ratio. The ultrasonic treatment conditions are as follows: ultrasonic frequency 30-50 kHz, power 20-160 W, temperature 25±5°C, and treatment time 10-60 seconds.

7. The method of claim 1, wherein the carbon fiber structure electrode interface performance sample preparation method is characterized by, The electrolyte is a lithium hexafluorophosphate lithium salt electrolyte, and the electrolyte infiltration time is 20-30 hours.

8. A carbon fiber structural electrode interface performance sample prepared by the preparation method of any one of claims 1 to 7.

9. A method of testing the performance of the interface of a carbon fiber structure electrode using the sample according to claim 8, characterized in that, The process is as follows: (1) The concave-shaped carrier with the test sample is fixed on the test bed of a tensile testing machine, the two ends of the fiber are clamped in the tensile testing machine clamp, and the fiber is pulled at a certain loading rate to make the microdroplets on the fiber contact the fixed knife. An ultra-depth microscope is used to take pictures of the continuous changes in the microstructure of the electrode fiber, and the maximum load and force-displacement curve during the loading process are recorded. When the tensile force rapidly decays by more than 30%, the test is terminated; (2) The carbon fiber structural electrode interface shear strength is calculated by formula (1); F is the maximum load, L is the microdroplet length, d is the fiber diameter, and τ is the interface shear strength; (3) The force-displacement curve of the sample is used to analyze the corresponding ultra-depth microscopic pictures of each point on the curve to obtain the corresponding electrode fiber interface debonding results, so as to study the microstructure changes of the electrode modification layer during the interface debonding process.

10. The test method of claim 9, wherein, The loading rate in step (1) is 0.01-0.1 mm / min.

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