Device, system and method for testing local tortuosity of battery pole piece

Abstract

The invention provides a device for testing the local tortuosity of a battery pole piece, and the device comprises a working electrode assembly (1) which comprises a sample carrying vessel (13), a conductive substrate (14), and a porous silver film stack (15); a working electrode binding post (16) is arranged on the conductive substrate; the auxiliary electrode probe (2) is used for contacting a battery pole piece to be measured so as to measure the tortuosity of a contact area of the auxiliary electrode probe in the battery pole piece to be measured; and the position adjusting mechanism is used for driving the auxiliary electrode probe or the sample carrying vessel to move, so that the auxiliary electrode probe covers and is in contact with a test area of the battery pole piece to be tested. According to the invention, the detection of the local tortuosity of the two-dimensional plane of the battery pole piece is realized through the change of the relative position of the auxiliary electrode probe and the battery pole piece, tortuosity calibration is provided for the auxiliary electrode probe, and the result accuracy of the tortuosity detection of the battery pole piece is ensured.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium ion battery measurement, and in particular to a device, system and method for testing the local tortuosity of a battery pole piece. Background Art

[0002] Pore ​​tortuosity refers to the increase in the pore path relative to the straight-line distance. In porous materials, due to the presence of pores, fluids, gases or other substances need to bypass these pores when transported in the material. Pore tortuosity is used to measure the degree of curvature of this path. High pore tortuosity means that the pore path is relatively long or curved relative to the straight-line distance. This may lead to increased resistance to fluid or gas transmission, affecting the permeability, diffusivity and other properties of the porous material.

[0003] The pore tortuosity of lithium batteries refers to the shape and distribution characteristics of pores in the positive and negative electrode materials of lithium batteries. In lithium batteries, electrode materials are usually composite materials composed of active materials, conductive agents and binders. In the preparation process of these materials, the properties of the powder and process parameters may lead to the formation and distribution of pores. Pores can be divided into cross-linked pores, through pores, semi-through pores and closed pores according to their morphology. These types of pores have different functions in the battery reaction process. Cross-linked pores and through pores are the main channels for lithium ions to participate in the reaction and transmission; semi-through pores are not suitable for the complete transmission of lithium ions, but on the premise that lithium ions can enter these pores smoothly, it can serve as a place for electrochemical reactions; closed pores are invalid pores because lithium ions cannot be output, and lithium ion transmission and reaction cannot be carried out.

[0004] Tortuosity is an important parameter that describes the shape and distribution of pores in porous media. A highly tortuous pore structure may affect the performance of lithium batteries, including battery capacity, cycle life, energy density, etc. The tortuosity of the pore structure may affect the electron and ion transport inside the battery, thereby affecting the overall performance of the battery. Therefore, in battery research and development and manufacturing, it is crucial to control the pore tortuosity of the electrode. In order to better understand the characteristics and performance of porous materials, researchers often need to measure and understand the pore tortuosity.

[0005] Commonly used electrode pore tortuosity test methods mainly include gas permeability measurement, resistivity measurement, liquid permeability measurement, imaging technology and mercury intrusion. The above test methods have the following advantages and disadvantages: gas permeability measurement is a non-destructive measurement, and the sample can remain intact. Resistivity measurement can directly evaluate the conductivity of the electrode material, but the test results of the above two test methods may be affected by factors such as test conditions (temperature, pressure), and the measurement accuracy may be limited by the instrument. It is necessary to maintain a constant gas flow to ensure accurate measurement. Liquid permeability measurement can simulate the transmission behavior of battery electrolytes in electrode materials, but the test results may be affected by test conditions such as temperature, pressure, and liquid properties. However, it may be affected by test conditions (temperature, current size, etc.). Imaging technology can provide high-resolution three-dimensional images, which is suitable for non-destructive testing and can obtain detailed information on the pore structure, but it requires special equipment and takes too long to process large samples, resulting in low test efficiency. Mercury intrusion porosimetry is a non-destructive testing method that can measure the pore volume and distribution of materials while keeping the sample intact. However, it requires specialized mercury intrusion porosimetry equipment and may be affected by factors such as sample surface tension and mercury permeability, resulting in low measurement accuracy.

[0006] In summary, the above-mentioned commonly used electrode pore tortuosity test methods are not suitable for the detection of local tortuosity uniformity of battery electrodes, and cannot realize the tortuosity detection of any point within the two-dimensional range of the battery electrode. The operation procedures involved in the detection scheme are relatively complicated, and the test results cannot represent the actual impact of the tortuosity on the electrode.

[0007] The Chinese patent document discloses "a method for measuring the ionic resistance per unit thickness of the liquid phase and the electrode tortuosity", and its announcement number is CN116400240A. The invention accurately quantifies the ionic resistance and electronic resistance of the electrode piece based on the analytical impedance spectrum, decomposes the total impedance of the symmetrical battery to obtain the ionic resistance per unit thickness of the liquid phase in the electrode piece, and solves the problem that the electronic resistance is difficult to measure and obtain in the prior art, making the measurement results of the ionic resistance and the total impedance of the battery more accurate. However, this technology cannot achieve the test characterization of the local tortuosity of the battery electrode piece. Summary of the invention

[0008] In view of the shortcomings of the prior art mentioned above, the purpose of the present invention is to provide a device, system and method for testing the local tortuosity of a battery pole piece, so as to solve the problems that the existing electrode pore tortuosity testing method is complicated to operate, cannot realize tortuosity detection of any point within the two-dimensional range of the battery pole piece, and the detection result cannot characterize the actual impact of the tortuosity on the battery pole piece.

[0009] In order to achieve the above-mentioned and other related purposes, the present invention provides a battery pole piece local tortuosity testing device, comprising: The working electrode assembly comprises a sample loading dish for carrying the battery electrode and electrolyte to be tested, a conductive substrate and a porous silver film stack; the conductive substrate is provided with a working electrode terminal; An auxiliary electrode probe, used for contacting the battery electrode sheet to be tested, so as to measure the tortuosity of the contact area of ​​the auxiliary electrode probe in the battery electrode sheet to be tested; A position adjustment mechanism, used for driving the auxiliary electrode probe or the sample carrier to move so that the auxiliary electrode probe covers and contacts the test area of ​​the battery electrode to be tested; During the test, the battery electrode to be tested is located between the conductive substrate and the porous silver film stack and is immersed in the electrolyte; The porous silver film stack is used to provide a tortuosity calibration area for the auxiliary electrode probe.

[0010] The present application sets a position adjustment mechanism so that the auxiliary electrode probe can flexibly detect the local tortuosity of the two-dimensional plane of the battery pole piece by changing the relative position; the sample dish contains electrolyte, and the battery pole piece to be tested is always immersed in the electrolyte during the test. The electrolyte has the function of providing ion conduction and electrical conductivity, and the tortuosity can be measured based on the actual use environment of the battery pole piece, and the actual impact of the tortuosity on the battery pole piece can be truly characterized. By using a porous silver film stack to provide a tortuosity calibration area for the auxiliary electrode probe, the tortuosity interference of the auxiliary electrode probe itself can be removed, ensuring the accuracy of the results of the battery pole piece tortuosity detection.

[0011] Preferably, the position adjustment mechanism comprises: A first driving mechanism, connected to the auxiliary electrode probe, for driving the auxiliary electrode probe to reciprocate in a direction perpendicular to the electrode piece of the battery to be tested; The second driving mechanism is used to drive the auxiliary electrode probe or the sample carrier to move so that the auxiliary electrode probe covers the test area of ​​the battery electrode to be tested.

[0012] Preferably, the first driving mechanism is a Z-axis slide module, and the Z-axis slide module is provided with a Z-axis control knob; the second driving mechanism includes an X-axis slide module and a Y-axis slide module, and the X-axis slide module and the Y-axis slide module are provided with an X-axis control knob and a Y-axis control knob respectively. The X-axis slide module, the Y-axis slide module and the Z-axis slide module can provide high-precision displacement control for the auxiliary electrode probe. The function of the X-axis slide module and the Y-axis slide module is to realize the tortuosity measurement of any point on the two-dimensional plane of the battery electrode to be tested. The Z-axis slide module is used to realize the downward pressure measurement of the auxiliary electrode probe, and the stress contact with the working electrode assembly forms a local two-electrode test system.

[0013] Preferably, the auxiliary electrode probe is connected to a mechanical pressure gauge for testing the contact stress between the auxiliary electrode probe and the battery electrode to be tested, so as to achieve the repeatability and consistency of the stress measurement, thereby ensuring the consistency of the test results.

[0014] Preferably, the auxiliary electrode probe comprises a mounting seat, a conductive elastic member, an auxiliary electrode terminal and a conductive adapter post, wherein the conductive elastic member and the auxiliary electrode terminal are arranged on the mounting seat, one end of the conductive adapter post is in contact with the conductive elastic member, and the other end is provided with a porous silver film; when power is turned on, the auxiliary electrode terminal is conductively connected to the conductive elastic member, the conductive adapter post and the porous silver film.

[0015] Preferably, the auxiliary electrode probe further includes a connecting sleeve and a fixing ring sleeved on the lower end of the connecting sleeve, the upper end of the connecting sleeve sleeved on the mounting seat, the conductive adapter column is located in the connecting sleeve, and a downward pressing space is provided between the lower end surface of the mounting seat and the connecting sleeve; the porous silver membrane is connected to the conductive adapter column through the fixing ring. The connecting sleeve and the fixing ring improve the assembly stability between the components, realize the integration of the auxiliary electrode probe, and have a more compact structure and strong operability. The downward pressing space ensures that the auxiliary electrode probe can be quickly pressed down, thereby improving the convenience and sensitivity of operation.

[0016] Preferably, a polyimide packaging film is further provided outside the porous silver film, and a test through hole is provided at the center of the polyimide packaging film to improve the detection resolution of the battery pole piece and realize the test of the local tortuosity of the battery pole piece. The polyimide packaging film can effectively fix and protect the four sides of the porous silver film, and the part of the porous silver film exposed to the test through hole is used to test the test area of ​​the battery pole piece to be tested; the area of ​​the test area can be adjusted by adjusting the aperture of the test through hole, and the aperture size of the test through hole is not limited here.

[0017] Preferably, the porous silver film and the porous silver film stack are both composed of 8 to 12 layers of silver thin film, and the thickness of a single layer of silver thin film is 10 to 15 μm; the porous silver film is provided with array through holes, and the aperture of the array through holes is 8 to 12 μm. The array through hole design can increase the reaction specific surface area of ​​the auxiliary electrode probe, making it much larger than the working electrode, reducing impedance, and the electrode with a high specific surface area generates a large amount of current, which can reduce the influence of the probe's own impedance on the test and improve the accuracy of the test results.

[0018] Preferably, the working electrode assembly also includes a lower pressing frame for pressing the battery electrode to be tested during testing, so as to facilitate the clamping of the battery electrode to be tested and avoid displacement of the battery electrode to be tested during the test, thereby improving the overall test stability of the device.

[0019] Preferably, the battery pole piece local tortuosity test device also includes a device housing sheet metal module, the device housing sheet metal module includes a housing, a bottom plate, a damping hinge and an observation door, the observation door is provided with a handle; the housing is provided with a transparent observation window, the four corners of the bottom plate are provided with rubber bases, and the observation door is hinged to the housing through a damping hinge; the housing is provided with a working electrode terminal and an auxiliary electrode terminal; the bottom plate is provided with a limiting groove adapted to the shape of the sample dish. The function of the housing is to connect and fix each functional module, and the manufacturing material is stainless steel 630, which has corrosion resistance and can effectively isolate the corrosion of the electrolyte in the sample dish. The limiting groove effectively limits the position of the sample dish and improves the overall test stability of the device. The transparent observation window is convenient for the test personnel to observe in real time, and the damping hinge can provide the observation door with an opening and closing of any angle, which is convenient for operation, maintenance and experimental observation.

[0020] The present invention provides a battery pole piece local tortuosity testing system, comprising the above-mentioned battery pole piece local tortuosity testing device, an electrochemical workstation and a data processing terminal, wherein the battery pole piece local tortuosity testing device is electrically connected to the electrochemical workstation via a working electrode terminal and an auxiliary electrode probe, and the electrochemical workstation is communicatively connected to the data processing terminal.

[0021] The present invention also provides a method for testing the local tortuosity of a battery pole piece, which is applied to the above-mentioned local tortuosity testing system of a battery pole piece, and comprises the following steps: Step (1): injecting electrolyte into a sample loading dish, stacking a conductive substrate, a battery electrode to be tested, and a porous silver film stack in the sample loading dish in sequence, and allowing the battery electrode to be tested to be immersed in the electrolyte, and electrically connecting the working electrode terminal and the auxiliary electrode probe to the electrochemical workstation respectively; Step (2): Control the position adjustment mechanism to drive the auxiliary electrode probe to move so that the auxiliary electrode probe covers and contacts the porous silver film stack, so that the porous silver film stack and the auxiliary electrode probe form a symmetrical electrode in the electrolyte, and measure the total tortuosity τ of the symmetrical electrode. 总 , calibrate the tortuosity of the auxiliary electrode probe, the tortuosity τ0 of the auxiliary electrode probe is the total tortuosity τ of the symmetrical electrode 总 one-half of; Step (3): Control the second driving mechanism to drive the auxiliary electrode probe to move along the horizontal plane to cover the test area of ​​the battery electrode sheet to be tested; control the first driving mechanism to drive the calibration auxiliary electrode probe to press downward in a direction perpendicular to the battery electrode sheet to be tested, contact the test area of ​​the battery electrode sheet to be tested, and measure the tortuosity measurement value of the auxiliary electrode probe contact area in the battery electrode sheet to be tested, and the actual value τ of the tortuosity of the auxiliary electrode probe contact area in the battery electrode sheet to be tested 实 is the tortuosity measurement value τ 测 The difference between the tortuosity τ0 of the auxiliary electrode probe.

[0022] Preferably, in step (2), the method for obtaining the total tortuosity of the symmetrical electrode comprises the following steps: obtaining the ion diffusion impedance of the symmetrical electrode, which is calculated based on the ion diffusion impedance using a tortuosity calculation formula; In step (3), the method for obtaining the tortuosity measurement value B of the test area of ​​the battery electrode to be tested comprises the following steps: obtaining the ion diffusion impedance of the test area of ​​the battery electrode to be tested, and calculating it based on the ion diffusion impedance by using the tortuosity calculation formula; The tortuosity calculation formula is: Among them, τ is the pole piece tortuosity, ε is the pole piece porosity, k int is the intrinsic ionic conductivity of the electrolyte, k is the effective ionic conductivity of the electrode, R ion is the ion diffusion impedance, A is the test area, and l is the test thickness.

[0023] Among them, the test area refers to the actual contact area between the auxiliary electrode probe and the test object, that is, the actual contact area between the porous silver film and the test object, and can also be equivalent to the cross-sectional area of ​​the test through hole at the center of the polyimide packaging film; specifically: in step (2), the test area is the contact test area between the auxiliary electrode probe and the porous silver film stack; the test thickness is the thickness of the porous silver film stack; in step (3), the test area is the contact test area between the auxiliary electrode probe and the battery electrode to be tested; the test thickness is the thickness of the battery electrode to be tested.

[0024] As described above, the battery pole piece local tortuosity testing device, system and method of the present invention have the following beneficial effects: through the setting of the position adjustment mechanism, the auxiliary electrode probe can realize the flexible detection of the local tortuosity of the two-dimensional plane of the battery pole piece by changing the relative position; the sample dish contains electrolyte, and the battery pole piece to be tested is always immersed in the electrolyte during the test. The electrolyte has the function of providing ion conduction and electrical conductivity, and the tortuosity can be measured based on the actual use environment of the battery pole piece, and the actual impact of the tortuosity on the battery pole piece can be truly characterized. By using a porous silver film stack to provide a tortuosity calibration area for the auxiliary electrode probe, the tortuosity interference of the auxiliary electrode probe itself can be removed, ensuring the accuracy of the results of the battery pole piece tortuosity detection. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 Shown is the general assembly diagram of the battery pole local tortuosity testing device.

[0026] Figure 2 Shown is a schematic diagram of the partial structure of a battery pole piece local tortuosity testing device.

[0027] Figure 3 Display as Figure 1Schematic diagram from another perspective.

[0028] Figure 4 Shown is a schematic diagram of the internal structure of a battery electrode local tortuosity testing device.

[0029] Figure 5 It is a schematic diagram of the structure of the first driving mechanism and the second driving mechanism.

[0030] Figure 6 Shown is a schematic diagram of the structure of the auxiliary electrode probe.

[0031] Figure 7 Shown is an exploded schematic diagram of the auxiliary electrode probe.

[0032] Figure 8 Shown is a cross-sectional view of the auxiliary electrode probe.

[0033] Fig. 9 Display as Figure 8 Enlarged view of point A in the middle.

[0034] Fig.10 Shown is a schematic diagram of the structure of a porous silver membrane.

[0035] Fig.11 Shown is a schematic diagram of the structure of the polyimide encapsulation film.

[0036] Fig.12 Shown is a schematic diagram of the structure of the working electrode assembly.

[0037] Fig.13 Shown is an exploded schematic diagram of the working electrode assembly.

[0038] Fig.14 Shown is a schematic diagram of the assembly structure of the base plate and the sample dish.

[0039] Fig.15 Shown is a schematic diagram of the structure of a battery pole local tortuosity testing system.

[0040] Fig.16 Displayed as electrochemical impedance spectroscopy.

[0041] Description of Figure Numbers: 1. Working electrode assembly; 12. Battery electrode to be tested; 121. Electrode substrate; 122. Electrode active coating; 13. Sample loading dish; 14. Conductive substrate; 15. Porous silver film stack; 16. Working electrode terminal; 17. Pressing frame; 2. Auxiliary electrode probe; 21. Mounting seat; 22. Conductive elastic member; 23. Auxiliary electrode terminal; 24. Conductive adapter post; 25. Porous silver film; 251. Array through hole; 26. Connecting sleeve; 27. Fixing ring; 28. Pressing space; 29. ​​Polyimide packaging film; 291. Test through hole; 3. First driving mechanism 31; 31. Z 1. slide module; 311. Z-axis control knob; 4. second drive mechanism; 41. X-axis slide module; 411. X-axis control knob; 42. Y-axis slide module; 421. Y-axis control knob; 5. device housing sheet metal module; 51. housing; 52. bottom plate; 53. damping hinge; 54. observation door; 541. handle; 55. transparent observation window; 56. rubber base; 57. working electrode terminal; 58. auxiliary electrode terminal; 6. battery pole piece local tortuosity test device; 7. electrochemical workstation; 8. data processing terminal; 9. mechanical pressure gauge, 91. mechanical pressure gauge. DETAILED DESCRIPTION

[0042] The following describes the embodiments of the present invention through specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention.

[0043] It should be noted that the process equipment or devices not specifically specified in the following embodiments are all conventional equipment or devices in the art.

[0044] In addition, it should be understood that one or more method steps mentioned in the present invention do not exclude the existence of other method steps before or after the combination step or the insertion of other method steps between these explicitly mentioned steps, unless otherwise specified; it should also be understood that the combination connection relationship between one or more devices / apparatuses mentioned in the present invention does not exclude the existence of other devices / apparatuses before or after the combination device / apparatus or the insertion of other devices / apparatuses between these explicitly mentioned two devices / apparatuses, unless otherwise specified. Moreover, unless otherwise specified, the numbering of each method step is only a convenient tool for identifying each method step, and is not intended to limit the order of arrangement of each method step or the scope of the present invention. Changes or adjustments in their relative relationships should also be regarded as the scope of the present invention without substantially changing the technical content.

[0045] The electrolyte used in the following examples of this application is a lithium battery electrolyte purchased from the official website of KLD, model KLD-LP20. The role of the electrolyte is to provide ion conduction and conduction, and to indirectly test the tortuosity of the electrode based on the electrochemical workstation.

[0046] Example 1 like Figure 1 , Figure 2 and Figure 3 As shown, this embodiment provides a battery electrode local tortuosity testing device, comprising: like Fig.12 He Ru Fig.13 The working electrode assembly 1 shown comprises a sample dish 13 for carrying a battery electrode sheet 12 to be tested and an electrolyte, a conductive substrate 14, a porous silver film stack 15 and a lower pressing frame 17 for pressing the battery electrode sheet to be tested during testing; a working electrode terminal 16 is provided on the conductive substrate; an auxiliary electrode probe 2 is used to contact the battery electrode sheet to be tested to measure the tortuosity of the auxiliary electrode probe contact area in the battery electrode sheet to be tested; the auxiliary electrode probe is connected to a mechanical pressure gauge 9 for testing the contact stress between the auxiliary electrode probe and the battery electrode sheet to be tested; A first driving mechanism 3, connected to the auxiliary electrode probe, for driving the auxiliary electrode probe to reciprocate in a direction perpendicular to the electrode piece of the battery to be tested; A second driving mechanism 4 is used to drive the auxiliary electrode probe to move so that the auxiliary electrode probe covers the test area of ​​the battery electrode to be tested; The device housing sheet metal module 5 comprises a housing 51, a bottom plate 52, a damping hinge 53 and an observation door 54, wherein the observation door is provided with a handle 541; the housing is provided with a transparent observation window 55, the four corners of the bottom plate are provided with rubber bases 56, and the observation door is hinged to the housing through a damping hinge; the housing is provided with a working electrode terminal 57 and an auxiliary electrode terminal 58; Fig.14 Said bottom plate is provided with a limiting groove 59 adapted to the shape of the sample loading dish; like Fig.13 As shown, the battery electrode 12 to be tested is composed of a electrode substrate 121 and a electrode active coating 122; during the test, the auxiliary electrode probe is in contact with the electrode active coating 122; during the test, the battery electrode to be tested is located between the conductive substrate and the porous silver film stack, and is immersed in the electrolyte; the porous silver film stack is used to provide a tortuosity calibration area for the auxiliary electrode probe.

[0047] like Figure 4 and Figure 5As shown, the first driving mechanism is a Z-axis slide module 31, and the Z-axis slide module is provided with a Z-axis regulating knob 311; the second driving mechanism includes an X-axis slide module 41 and a Y-axis slide module 42, and the X-axis slide module and the Y-axis slide module are respectively provided with an X-axis regulating knob 411 and a Y-axis regulating knob 421.

[0048] like Figure 6 and Figure 7 As shown, the auxiliary electrode probe includes a mounting seat 21, a conductive elastic member 22, an auxiliary electrode terminal 23, a conductive adapter terminal 24, a connecting sleeve 26 and a fixing ring 27 sleeved on the lower end of the connecting sleeve. The conductive elastic member and the auxiliary electrode terminal are arranged on the mounting seat. Figure 8 and Fig. 9 As shown, one end of the conductive transfer post is in contact with the conductive elastic member, and the other end is provided with a porous silver film 25, and the porous silver film is provided with Fig.11 A test through hole 291 with an aperture of 400 μm is provided at the center of the polyimide packaging film 29; the upper end of the connecting sleeve is sleeved on the mounting seat, the conductive adapter post is located in the connecting sleeve, and a downward pressure space 28 is provided between the lower end surface of the mounting seat and the connecting sleeve; the porous silver film is connected to the conductive adapter post through a fixing ring; when power is turned on, the auxiliary electrode terminal is connected to the conductive elastic member, the conductive adapter post and the porous silver film. The porous silver film and the porous silver film stack are both composed of 10 layers of silver film, and the thickness of a single layer of silver film is 12 μm; as shown Fig.10 As shown, the porous silver membrane is provided with array through holes 251, and the aperture of the array through holes is 10 μm.

[0049] like Fig.15 As shown, this embodiment also provides a battery electrode local tortuosity testing system, including the above-mentioned battery electrode local tortuosity testing device 6, an electrochemical workstation 7 and a data processing terminal 8, the battery electrode local tortuosity testing device is electrically connected to the electrochemical workstation through a working electrode terminal and an auxiliary electrode probe, and the electrochemical workstation is communicatively connected to the data processing terminal.

[0050] This embodiment also provides a method for testing the local tortuosity of a battery pole piece, which is applied to the above-mentioned local tortuosity testing system for a battery pole piece, and includes the following steps: Step (1): injecting electrolyte into the sample loading dish, stacking the conductive substrate, the electrode piece of the battery to be tested and the porous silver film stack in the sample loading dish in sequence, and immersing the electrode piece of the battery to be tested in the electrolyte for at least 30 minutes, and electrically connecting the working electrode terminal and the auxiliary electrode probe to the electrochemical workstation respectively; Step (2): Control the second driving mechanism to drive the auxiliary electrode probe to move along the horizontal plane to cover the porous silver film stack; control the second driving mechanism to drive the calibration auxiliary electrode probe to press downward in a direction perpendicular to the battery electrode to be tested to contact the porous silver film stack, so that the porous silver film stack and the auxiliary electrode probe form a symmetrical electrode in the electrolyte, obtain the ion diffusion impedance of the symmetrical electrode, and calculate the total tortuosity τ of the symmetrical electrode based on the ion diffusion impedance using the tortuosity calculation formula 总 , calibrate the tortuosity of the auxiliary electrode probe, the tortuosity τ0 of the auxiliary electrode probe is the total tortuosity τ of the symmetrical electrode 总 one-half of; Step (3): by adjusting the X-direction control knob 411 and the Y-direction control knob 421, the second drive mechanism is controlled to drive the auxiliary electrode probe 2 to move along the horizontal plane to cover the test area of ​​the battery electrode sheet 12 to be tested; by adjusting the Z-direction control knob 311, the first drive mechanism is controlled to drive the calibration auxiliary electrode probe to press downward in a direction perpendicular to the battery electrode sheet to be tested, contacting the test area of ​​the battery electrode sheet to be tested, and obtaining the ion diffusion impedance of the test area of ​​the battery electrode sheet to be tested through the electrochemical workstation, and using the data processing terminal to calculate the tortuosity measurement value B of the contact area of ​​the auxiliary electrode probe in the battery electrode sheet to be tested through the tortuosity calculation formula based on the ion diffusion impedance, and the tortuosity actual value τ of the contact area of ​​the auxiliary electrode probe in the battery electrode sheet to be tested. 实 is the tortuosity measurement value τ 测 The difference between the tortuosity τ0 of the auxiliary electrode probe.

[0051] The tortuosity calculation formula is: Among them, τ is the pole piece tortuosity, ε is the pole piece porosity, k int is the intrinsic ionic conductivity of the electrolyte (S / cm), k is the effective ionic conductivity of the electrode (S / cm), R ion is the ion diffusion impedance (Ω), A is the test area (cm2), and l is the test thickness (cm).

[0052] The main mechanism of measuring and calculating the value of the battery pole tortuosity by the electrochemical workstation in the present invention includes: Using an electrochemical workstation, electrochemical impedance spectroscopy data is obtained by applying a small AC signal at different frequencies and measuring the response of the system. These data are usually expressed in complex form, including the real part of the impedance and the imaginary part of the phase angle; the dimensionless number MacMullin number used in fluid mechanics is as follows: Where τ is the pole piece tortuosity, ε is the pole piece porosity, k int is the intrinsic ionic conductivity of the electrolyte, k is the effective ionic conductivity of the electrode, Rion is the ion diffusion impedance, A is the test area, and l is the test thickness. The calculation formula for the tortuosity of the electrode is: Among them, except R ion Except for , all other parameters are known. Fig.16 As shown, the intersection of the extended line of the Nyquist straight line in the low-frequency region and the real axis is Rs+Rion / 3, where Rs is the intersection of the Nyquist curve in the high-frequency region and the real axis. Then Rion can be obtained, and finally the value of the pole piece tortuosity can be obtained through the tortuosity calculation formula.

[0053] Among them, the test area refers to the actual contact area between the auxiliary electrode probe and the test object, that is, the actual contact area between the porous silver film and the test object, and can also be equivalent to the cross-sectional area of ​​the test through hole at the center of the polyimide packaging film; specifically: in step (2), the test area is the contact test area between the auxiliary electrode probe and the porous silver film stack; the test thickness is the thickness of the porous silver film stack; in step (3), the test area is the contact test area between the auxiliary electrode probe and the battery electrode to be tested; the test thickness is the thickness of the battery electrode to be tested.

[0054] Example 2 The difference between Example 2 and Example 1 is that the function of the second driving mechanism is different, and the rest is exactly the same. The second driving mechanism of this embodiment is used to drive the sample carrier to move so that the auxiliary electrode probe covers the test area of ​​the battery electrode to be tested.

[0055] In this embodiment, the auxiliary electrode probe is kept stationary in the horizontal plane, and the sample carrier and the auxiliary electrode probe are driven to move relative to each other by the second driving mechanism, thereby realizing flexible detection of the local tortuosity of the two-dimensional plane of the battery electrode.

[0056] Example 3 The difference between Example 3 and Example 1 is that the structures of the porous silver film and the porous silver film stack are different, the aperture of the test through hole of the polyimide packaging film is different, and the rest are exactly the same.

[0057] In this embodiment, the porous silver film and the porous silver film stack are both composed of 8 layers of silver film, and the thickness of a single layer of silver film is 15 μm; the porous silver film is provided with an array through hole, and the aperture of the array through hole is 8 μm; the aperture of the test through hole of the polyimide packaging film is 200 μm.

[0058] This embodiment reduces the test area by reducing the aperture of the test through hole to 200 μm compared with Embodiment 1. Therefore, by selecting a silver film with an array through hole having a relatively small aperture, it can ensure that the reaction specific surface area of ​​the auxiliary electrode probe is larger than that of the working electrode, thereby reducing the impedance, generating a large amount of current, reducing the influence of the probe's own impedance on the test, and improving the accuracy of the test results.

[0059] Example 4 The difference between Example 4 and Example 1 is that the structures of the porous silver film and the porous silver film stack are different, the aperture of the test through hole of the polyimide packaging film is different, and the rest are exactly the same.

[0060] In this embodiment, the porous silver film and the porous silver film stack are both composed of 12 layers of silver thin film, and the thickness of a single layer of silver thin film is 10 μm; the porous silver film is provided with array through holes, and the aperture of the array through holes is 12 μm.

[0061] In this embodiment, the aperture of the test through hole is increased to 800 μm, which increases the test area relative to Embodiment 1. By increasing the aperture of the silver film array through hole, the reaction specific surface area of ​​the auxiliary electrode probe is further increased to ensure that it is much larger than the working electrode, thereby reducing the impedance. The high surface area electrode generates a large amount of current, which can reduce the influence of the probe's own impedance on the test and improve the accuracy of the test results.

[0062] In summary, the present invention, through the setting of the position adjustment mechanism, enables the auxiliary electrode probe to realize the flexible detection of the local tortuosity of the two-dimensional plane of the battery pole piece by changing the relative position; the sample dish contains electrolyte, and the battery pole piece to be tested is always immersed in the electrolyte during the test. The electrolyte has the function of providing ion conduction and electrical conductivity, and the tortuosity can be measured based on the actual use environment of the battery pole piece, and the actual impact of the tortuosity on the battery pole piece can be truly characterized. By using a porous silver film stack to provide a tortuosity calibration area for the auxiliary electrode probe, the tortuosity interference of the auxiliary electrode probe itself can be removed, ensuring the accuracy of the results of the battery pole piece tortuosity detection. Therefore, the present invention effectively overcomes the various shortcomings in the prior art and has a high industrial utilization value.

[0063] The above embodiments are merely illustrative of the principles and effects of the present invention, and are not intended to limit the present invention. Anyone familiar with the art may modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by a person of ordinary skill in the art without departing from the spirit and technical concept disclosed by the present invention shall still be covered by the claims of the present invention.

Claims

1. A battery pole piece local tortuosity testing device, characterized in that: include: A working electrode assembly (1) comprises a sample loading dish (13) for carrying a battery electrode (12) to be tested and an electrolyte, a conductive substrate (14) and a porous silver film stack (15); a working electrode terminal (16) is provided on the conductive substrate; An auxiliary electrode probe (2) is used to contact the battery electrode sheet to be tested so as to measure the tortuosity of the area where the auxiliary electrode probe contacts the battery electrode sheet to be tested; A position adjustment mechanism, used for driving the auxiliary electrode probe or the sample carrier to move so that the auxiliary electrode probe covers and contacts the test area of ​​the battery electrode to be tested; During the test, the battery electrode to be tested is located between the conductive substrate and the porous silver film stack and is immersed in the electrolyte; The porous silver film stack is used to provide a tortuosity calibration area for the auxiliary electrode probe.

2. The battery pole piece local tortuosity testing device according to claim 1, characterized in that: The position adjustment mechanism comprises: a first driving mechanism (3) and a second driving mechanism (4), wherein the first driving mechanism is connected to the auxiliary electrode probe and is used to drive the auxiliary electrode probe to reciprocate in a direction perpendicular to the battery electrode sheet to be tested; and the second driving mechanism is used to drive the auxiliary electrode probe or the sample dish to move so that the auxiliary electrode probe covers the test area of ​​the battery electrode sheet to be tested.

3. The local tortuosity testing device for a battery pole piece according to claim 2, characterized in that: The first driving mechanism is a Z-direction slide module (31), and the Z-direction slide module is provided with a Z-direction regulating knob (311); the second driving mechanism comprises an X-direction slide module (41) and a Y-direction slide module (42), and the X-direction slide module and the Y-direction slide module are respectively provided with an X-direction regulating knob (411) and a Y-direction regulating knob (421).

4. The battery pole piece local tortuosity testing device according to claim 1, characterized in that: The auxiliary electrode probe is connected to a mechanical pressure gauge (9) for testing the contact stress between the auxiliary electrode probe and the battery electrode to be tested.

5. The battery pole piece local tortuosity testing device according to claim 1, characterized in that: The auxiliary electrode probe comprises a mounting seat (21), a conductive elastic member (22), an auxiliary electrode terminal (23) and a conductive adapter post (24); the conductive elastic member and the auxiliary electrode terminal are arranged on the mounting seat; one end of the conductive adapter post is in contact with the conductive elastic member, and the other end is provided with a porous silver film (25); when power is turned on, the auxiliary electrode terminal is electrically connected to the conductive elastic member, the conductive adapter post and the porous silver film.

6. The battery pole piece local tortuosity testing device according to claim 5, characterized in that: The auxiliary electrode probe also includes a connecting sleeve (26) and a fixing ring (27) sleeved on the lower end of the connecting sleeve, the upper end of the connecting sleeve is sleeved on the mounting seat, the conductive adapter column is located in the connecting sleeve, and a downward pressure space (28) is provided between the lower end surface of the mounting seat and the connecting sleeve; the porous silver membrane is connected to the conductive adapter column via the fixing ring.

7. The battery pole piece local tortuosity testing device according to claim 5, characterized in that: A polyimide packaging film (29) is also provided outside the porous silver film, and a test through hole (291) is provided at the center of the polyimide packaging film.

8. The battery pole piece local tortuosity testing device according to any one of claims 5 to 7, characterized in that: The porous silver film and the porous silver film stack are both composed of 8 to 12 layers of silver thin films, and the thickness of a single layer of silver thin film is 10 to 15 μm; the porous silver film is provided with array through holes (251), and the aperture of the array through holes is 8 to 12 μm.

9. The battery pole piece local tortuosity testing device according to claim 1, characterized in that: The working electrode assembly also includes a lower pressing frame (17) for pressing the electrode sheet of the battery to be tested during testing.

10. The battery pole piece local tortuosity testing device according to claim 1, characterized in that: The battery electrode local tortuosity testing device also includes a device housing sheet metal module (5), the device housing sheet metal module includes a housing (51), a bottom plate (52), a damping hinge (53) and an observation door (54), the observation door is provided with a handle (541); the housing is provided with a transparent observation window (55), the four corners of the bottom plate are provided with rubber bases (56), and the observation door is hinged to the housing through the damping hinge; the housing is provided with a working electrode terminal (57) and an auxiliary electrode terminal (58); the bottom plate is provided with a limiting groove (59) adapted to the shape of the sample loading dish.

11. A battery pole piece local tortuosity testing system, characterized by: It comprises a battery pole piece local tortuosity testing device (6) as described in any one of claims 1 to 10, an electrochemical workstation (7) and a data processing terminal (8), wherein the battery pole piece local tortuosity testing device is electrically connected to the electrochemical workstation via a working electrode terminal and an auxiliary electrode probe, and the electrochemical workstation is communicatively connected to the data processing terminal.

12. A method for testing the local tortuosity of a battery pole piece, characterized in that: The local tortuosity testing system for a battery pole piece as claimed in claim 11 comprises the following steps: Step (1): injecting electrolyte into a sample loading dish, stacking a conductive substrate, a battery electrode to be tested, and a porous silver film stack in the sample loading dish in sequence, and allowing the battery electrode to be tested to be immersed in the electrolyte, and electrically connecting the working electrode terminal and the auxiliary electrode probe to the electrochemical workstation respectively; Step (2): Control the position adjustment mechanism to drive the auxiliary electrode probe to move so that the auxiliary electrode probe covers and contacts the porous silver film stack, so that the porous silver film stack and the auxiliary electrode probe form a symmetrical electrode in the electrolyte, and measure the total tortuosity τ of the symmetrical electrode. 总 , calibrate the tortuosity of the auxiliary electrode probe, the tortuosity τ0 of the auxiliary electrode probe is the total tortuosity τ of the symmetrical electrode 总 one-half of Step (3): Control the second driving mechanism to drive the auxiliary electrode probe to move along the horizontal plane to cover the test area of ​​the battery electrode sheet to be tested; control the first driving mechanism to drive the calibration auxiliary electrode probe to press downward in a direction perpendicular to the battery electrode sheet to be tested, contact the test area of ​​the battery electrode sheet to be tested, and measure the tortuosity measurement value of the auxiliary electrode probe contact area in the battery electrode sheet to be tested, and the actual value τ of the tortuosity of the auxiliary electrode probe contact area in the battery electrode sheet to be tested 实 is the tortuosity measurement value τ 测 The difference between the tortuosity τ0 of the auxiliary electrode probe.

13. The method for testing local tortuosity of a battery pole piece according to claim 12, characterized in that: In step (2), the method for obtaining the total tortuosity of the symmetrical electrode comprises the following steps: obtaining the ion diffusion impedance of the symmetrical electrode, which is calculated based on the ion diffusion impedance using a tortuosity calculation formula; In step (3), the method for obtaining the tortuosity measurement value B of the test area of ​​the battery electrode to be tested comprises the following steps: obtaining the ion diffusion impedance of the test area of ​​the battery electrode to be tested, and calculating it based on the ion diffusion impedance by using the tortuosity calculation formula; The tortuosity calculation formula is: Among them, τ is the pole piece tortuosity, ε is the pole piece porosity, k int is the intrinsic ionic conductivity of the electrolyte, k is the effective ionic conductivity of the electrode, R ion is the ion diffusion impedance, A is the test area, and l is the test thickness.

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