Method for obtaining tortuosity of porous electrode

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By opening the fixed -pole -type symmetrical battery structure on the surface of the limited pad, the conventional buckle battery cannot be used for the pedoric electrode tortuous test, and the accuracy and consistency of the test data are achieved. Test process.

CN119354819APending Publication Date: 2025-01-24JIANGXI GANFENG BATTERY TECH

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Patent Information

Application Number: CN202411529520.1
Authority / Receiving Office: CN · China
Patent Type: Applications(China)
Current Assignee / Owner
Filing Date: 2024-10-30
Publication Date: 2025-01-24

AI Technical Summary

Technical Problem

In the prior art, conventional buckle batteries cannot be used for porous electrode tortuosity testing, and other test methods are complex to operate, resulting in poor consistency of test results.

Method used

Adopt a new buckle symmetrical battery structure. By opening the groove on the surface of the limited pad to fix the pole, ensure the fixing of the active area and the exclusion of the non -active area, and then calculate the tortuous porous electrode through the electrochemical impedance spectrum testing Spend.

Benefits of technology

This method simplifies the test process, ensures the accuracy and consistency of the test data, and can quickly and accurately evaluate the pedorrheal degree of polar chip.

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Abstract

The invention provides a method for obtaining tortuosity of a porous electrode, which comprises the following steps of: preparing a pole piece, keeping active substances on one surface of the pole piece, wiping the active substances on the other surface of the pole piece, and drying the pole piece in a drying oven; punching the pole piece to form two small wafers with different diameters, naming the small wafers as a to-be-measured pole piece I and a to-be-measured pole piece II, and punching a required diaphragm; preparing two gaskets, forming grooves matched with the outer diameters of the to-be-tested pole piece I and the to-be-tested pole piece II in the centers of the surfaces of the gaskets, and naming the grooves as a limiting gasket I and a limiting gasket II; symmetrical buckle electricity is assembled in the glove box according to the sequence; packaging and standing the assembled battery; testing the electrochemical impedance of the symmetric button cell; calculating tortuosity through a formula; the button type symmetrical battery is simple in structure and convenient to manufacture, and the cycle and consumables are saved; the active area of the reaction is fixed; the influence of an inactive area is eliminated, and the accuracy and consistency of test data are ensured.

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Description

Technical Field

[0001] The invention relates to the field of lithium ion batteries, and in particular to a method for obtaining the tortuosity of a porous electrode. Background Art

[0002] Since its commercialization, lithium-ion batteries have been widely used in different fields due to their advantages such as high energy density, long cycle life, high voltage and low self-discharge rate.

[0003] In recent years, the rapid development and application of large-scale energy storage and electric vehicles have put forward higher requirements for energy density. At present, the most direct way to improve the energy density of batteries is to increase the coating thickness, that is, to increase the content of active substances per unit volume of the battery without changing the battery chemical system. This method has the advantages of being compatible with various electrode materials. However, as the thickness increases, the porosity of the electrode decreases, the migration path of lithium ions increases, and the diffusion resistance increases. The tortuosity of the porous electrode is the ratio of the actual path length of lithium ions to the thickness of the electrode, which is one of the important parameters for evaluating the electrode.

[0004] Button cells are a common way to evaluate electrode parameters. Conventional button cells have a large inner diameter and a small electrode radius. During the assembly process, the electrode is easily misaligned, the active reaction area is difficult to align, and the size is uncontrolled, resulting in changes in the active area, affecting the accuracy and consistency of the test results.

[0005] To this end, we propose a method to obtain the tortuosity of porous electrodes to solve the problem that conventional buckling cannot be used for tortuosity testing and other test methods have poor consistency due to their complex operations. Summary of the invention

[0006] The purpose of the present invention is to solve the shortcomings existing in the prior art. In order to achieve the above purpose, the present invention adopts the following technical solutions:

[0007] A method for obtaining the tortuosity of a porous electrode, comprising the following steps:

[0008] S1: Prepare the electrode, keep the active material on one side of the electrode and wipe off the active material on the other side, and then place it in an oven to dry;

[0009] S2: Punch out two small discs of different diameters from the electrode, named as the electrode piece to be tested 1 and the electrode piece to be tested 2, and punch out the required diaphragm;

[0010] S3: prepare two gaskets, and open grooves matching the outer diameters of the first and second pole pieces to be tested at the center of the gasket surfaces, and name them as limit gasket one and limit gasket two;

[0011] S4: In the glove box, a symmetrical buckle battery is assembled in the order of a negative electrode shell, a spring, a second limiting gasket, a second electrode piece to be tested, an electrolyte, a diaphragm, an electrolyte, a first electrode piece to be tested, an electrolyte, a first limiting gasket, and a positive electrode shell, wherein the active materials on the second electrode piece to be tested and the first electrode piece to be tested are both facing the diaphragm;

[0012] S5: Encapsulate the assembled battery and let it stand;

[0013] S6: Test the electrochemical impedance of symmetrical buckling;

[0014] S7: The tortuosity is calculated by the formula τ = (Rion*A*ε*σ) / d, where τ is the tortuosity of the electrode, Rion is the ionic impedance, A is the cross-sectional area of the minimum diameter electrode to be tested, ε is the porosity of the electrode, σ is the conductivity of the electrolyte, and d is the thickness of the electrode.

[0015] The button-type symmetrical battery in the present invention has a simple structure, is easy to manufacture, saves cycles and consumables, fixes the active area of the reaction, eliminates the influence of the inactive area, and ensures the accuracy and consistency of the test data.

[0016] Further preferably, the first electrode piece to be tested and the second electrode piece to be tested are both positive electrode pieces or both negative electrode pieces.

[0017] Further preferably, the diameter of the diaphragm is larger than the diameter of the first electrode piece to be tested and the second electrode piece to be tested.

[0018] Further preferably, the depth of the groove is less than the thickness of the pole piece.

[0019] Further preferably, when the electrode is a positive electrode, the active material of the electrode is wiped off by NMP.

[0020] Further preferably, when the electrode is a negative electrode, the active material of the electrode is wiped off by deionized water.

[0021] Further preferably, in S1, the oven temperature is 80-120° C., and the drying time is 15-45 min.

[0022] More preferably, in S5, the standing time is 5-30 min.

[0023] Further preferably, in S6, the disturbance voltage tested is 5 mV and the frequency is 0.1-10 kHz.

[0024] Further preferably, the limiting gasket is cylindrical, the limiting gasket is coaxially arranged with the groove on the surface thereof, and the outer diameters of the limiting gasket 1 and the limiting gasket 2 are respectively adapted to the inner cavities of the positive electrode shell and the negative electrode shell.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] The present invention utilizes a button-type electrical structure system and fixes the electrode piece by opening a groove on the surface of a limiting gasket, thereby fixing the active area of the reaction and eliminating the influence of the inactive coating area. It can ensure that there is no misalignment during the assembly process and that the active area does not change, thereby ensuring the accuracy and consistency of the results when testing the AC impedance of a button-type symmetrical battery, and is simple and easy to operate.

[0027] The present invention manufactures a novel button-type symmetrical battery, performs an electrochemical impedance spectrum test and calculates the tortuosity of a porous electrode piece through a formula; the method is simple and easy to operate, and can quickly and accurately evaluate the tortuosity of a porous electrode piece. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 It is a schematic diagram of the structure of symmetrical buckle power supply;

[0029] Figure 2 It is a cross-sectional view of the limit gasket and the pole piece to be tested;

[0030] Figure 3 The impedance diagram of the positive electrode NCM button-type symmetrical battery;

[0031] Figure 4 The impedance diagram of the positive LFP button-type symmetrical battery;

[0032] Figure 5 The impedance diagram of the negative electrode graphite button symmetrical battery;

[0033] Figure 6 This is the impedance diagram of the negative electrode graphite soft-pack symmetrical battery.

[0034] In the figure: positive electrode shell 1, limiting gasket 1 2, electrode piece 1 to be tested 3, diaphragm 4, electrode piece 2 to be tested 5, limiting gasket 2 6, spring 7, negative electrode shell 8, foil 51, active material 52. DETAILED DESCRIPTION

[0035] The technical solutions in the embodiments of the present invention will be described clearly and completely below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments.

[0036] Reference Figure 1-Figure 2 , a method for obtaining the tortuosity of a porous electrode, the steps are as follows:

[0037] S1: Prepare the electrode, keep the active material on one side of the electrode and wipe off the active material on the other side, and then place it in an oven to dry; the electrode to be tested one and the electrode to be tested two are both positive electrodes or both negative electrodes; when the electrode is a positive electrode, the active material of the electrode is wiped off by NMP; when the electrode is a negative electrode, the active material of the electrode is wiped off by deionized water; the oven temperature is 80-120°C, and the drying time is 15-45min.

[0038] In the embodiment: the electrode piece is composed of a foil 51 and an active material 52, the positive electrode foil is an aluminum foil, and the negative electrode foil is a copper foil. Prepare a fresh electrode piece to be tested after rolling: a positive electrode or a negative electrode, wherein NMP is used for the positive electrode and deionized water is used for the negative electrode (NMP can dissolve binders such as PVDF very well, can better remove the coating on the aluminum foil, and can avoid damage to the positive electrode material. Deionized water for the negative electrode can dissolve aqueous binders and does not react adversely with the negative electrode material). Slowly wipe one side of the electrode piece to be tested in the same direction until the foil is clean, and keep the other side. At the same time, place the treated electrode piece to be tested in a vacuum drying oven at 105°C and bake for 30 minutes.

[0039] S2: Punching out two small discs of different diameters from the electrode, named as the electrode piece to be tested one and the electrode piece to be tested two, and punching out the required diaphragm; the diameter of the diaphragm is larger than the diameter of the electrode piece to be tested one and the electrode piece to be tested two.

[0040] In the embodiment: a punching device is used to punch a certain number of small discs at different positions of the electrode to be tested, wherein the diameter of the electrode 1 3 to be tested is 18 mm, the diameter of the electrode 2 5 to be tested is 14 mm, and the diameter of the diaphragm 4 used is 20 mm.

[0041] S3: Prepare two gaskets, and open grooves in the center of the gasket surface that are compatible with the outer diameters of the electrode piece 3 to be tested and the electrode piece 5 to be tested, and name them as limit gasket 1 2 and limit gasket 2 6; the limit gasket is cylindrical, and the limit gasket is coaxially arranged with the groove on its surface, and the outer diameters of the limit gasket 1 2 and the limit gasket 2 6 are respectively compatible with the inner cavity of the positive electrode shell 1 and the negative electrode shell 8; the depth of the groove is less than the thickness of the electrode piece.

[0042] In the embodiment: a limiting gasket 2 with a groove diameter of 19 mm and a limiting gasket 6 with a groove diameter of 15 mm are used; the pole piece 3 to be tested is limitedly installed in the groove of the limiting gasket 2, and the pole piece 2 5 to be tested is limitedly installed in the groove of the limiting gasket 6.

[0043] S4: In the glove box, symmetrical buckle batteries are assembled in the order of negative electrode shell 8, spring piece 7, stopper gasket 2 6, electrode piece 2 to be tested 5, electrolyte, diaphragm 4, electrolyte, electrode piece 1 to be tested 3, electrolyte, stopper gasket 1 2, and positive electrode shell 1, wherein the active materials 52 on the electrode piece 2 to be tested and the electrode piece 1 to be tested are both facing the diaphragm 4;

[0044] In the embodiment: the outer diameter of the limiting gasket is adapted to the inner cavity of the positive electrode shell 1 and the negative electrode shell 8, so that the limiting gasket is fixed in the inner cavity of the symmetrical button battery. The groove on the limiting gasket fixes the electrode to be tested, thereby fixing the reactive area on the electrode to be tested, eliminating the influence of the inactive coating area, ensuring that there is no misalignment during the assembly process, and the active area does not change, ensuring the accuracy and consistency of the results when testing the AC impedance of the button-type symmetrical battery, and being simple and easy to operate.

[0045] S5: Encapsulate the assembled battery and let it stand for 5-30 minutes.

[0046] In the embodiment: the assembled battery is packaged using a packaging machine and allowed to stand for 10 minutes.

[0047] S6: Test the electrochemical impedance of symmetrical buckling;

[0048] In the embodiment: an electrochemical workstation is used to test the electrochemical impedance of a symmetrical buckle, the disturbance voltage is 5 mV, and the frequency is 0.1 Hz to 10 kHz.

[0049] S7: The tortuosity is calculated by the formula τ = (Rion*A*ε*σ) / d, where τ is the tortuosity of the electrode, Rion is the ionic impedance, A is the cross-sectional area of the minimum diameter electrode to be tested, ε is the porosity of the electrode, σ is the conductivity of the electrolyte, and d is the thickness of the electrode.

[0050] Example 1

[0051] Using freshly rolled NCM cathode sheets, 3 parallel samples were assembled and tested according to the above steps. Figure 3 The impedance diagram of the positive electrode NCM button-type symmetrical cell is shown, and the ionic impedance is calculated;

[0052] Example 2

[0053] Using fresh rolled cathode sheets made of LFP as the main material, 3 parallel samples were assembled and tested according to the above steps. Figure 4 The impedance diagram of the positive LFP button-type symmetrical cell is shown, and the ionic impedance is calculated;

[0054] Example 3

[0055] Using fresh graphite electrode sheets after rolling, three parallel samples were assembled and tested according to the above steps. Figure 5 The impedance diagram of the negative electrode graphite button-type symmetrical battery is shown, and the ionic impedance is calculated.

[0056] Comparative Example

[0057] Using fresh graphite negative electrode sheets after rolling, three parallel samples of soft-pack symmetrical batteries were assembled. The soft-pack symmetrical battery consisted of an aluminum-plastic film, a foil with tabs, a confined diaphragm and the negative electrode sheet to be tested. Figure 6 Impedance diagram of negative electrode soft-pack lithium-ion symmetric battery, and calculated ionic impedance.

[0058] The test data is as follows:

[0059] Table 1 shows the ionic impedance data of button-type symmetrical batteries and soft-pack symmetrical batteries:

[0060]

[0061]

[0062] Table 1 shows the calculated ionic impedance data of button-type symmetrical batteries and soft-pack symmetrical batteries. Figure 3-6 It can be seen that the coefficient of variation COV of the button-type symmetrical battery is smaller than that of the soft-pack symmetrical battery. The button-type symmetrical battery has good consistency and high accuracy.

[0063] Table 2 Tortuosity data of button-type symmetrical battery:

[0064]

[0065] The button-type symmetrical battery in the present invention has a simple structure, is easy to manufacture, saves cycles and consumables, fixes the active area of the reaction, eliminates the influence of the inactive area, and ensures the accuracy and consistency of the test data.

[0066] The present invention manufactures a novel button-type symmetrical battery, performs an electrochemical impedance spectrum test and calculates the tortuosity of a porous electrode piece through a formula; the method is simple and easy to operate, and can quickly and accurately evaluate the tortuosity of a porous electrode piece.

Claims

1. A method for obtaining the tortuosity of a porous electrode, characterized in that: Here are the steps: S1: Prepare the electrode, keep the active material on one side of the electrode and wipe off the active material on the other side, and then place it in an oven to dry; S2: Punch out two small discs of different diameters from the electrode, named as the electrode piece to be tested 1 and the electrode piece to be tested 2, and punch out the required diaphragm; S3: prepare two gaskets, and open grooves matching the outer diameters of the first and second pole pieces to be tested at the center of the gasket surfaces, and name them as limit gasket one and limit gasket two; S4: In the glove box, a symmetrical buckle battery is assembled in the order of a negative electrode shell, a spring, a second limiting gasket, a second electrode piece to be tested, an electrolyte, a diaphragm, an electrolyte, a first electrode piece to be tested, an electrolyte, a first limiting gasket, and a positive electrode shell, wherein the active materials on the second electrode piece to be tested and the first electrode piece to be tested are both facing the diaphragm; S5: Encapsulate the assembled battery and let it stand; S6: Test the electrochemical impedance of symmetrical buckling; S7: The tortuosity is calculated by the formula τ = (Rion*A*ε*σ) / d, where τ is the tortuosity of the electrode, Rion is the ionic impedance, A is the cross-sectional area of the minimum diameter electrode to be tested, ε is the porosity of the electrode, σ is the conductivity of the electrolyte, and d is the thickness of the electrode.

2. The method for obtaining the tortuosity of a porous electrode according to claim 1, characterized in that: The first electrode piece to be tested and the second electrode piece to be tested are both positive electrode pieces or both negative electrode pieces.

3. The method for obtaining the tortuosity of a porous electrode according to claim 1, characterized in that: The diameter of the diaphragm is larger than the diameter of the first electrode piece to be tested and the second electrode piece to be tested.

4. The method for obtaining the tortuosity of a porous electrode according to claim 1, characterized in that: The depth of the groove is less than the thickness of the pole piece.

5. The method for obtaining the tortuosity of a porous electrode according to claim 1, characterized in that: When the electrode is a positive electrode, the active material of the electrode is wiped off by NMP.

6. The method for obtaining the tortuosity of a porous electrode according to claim 1, characterized in that: When the electrode is a negative electrode, the active material of the electrode is wiped off by deionized water.

7. The method for obtaining the tortuosity of a porous electrode according to claim 1, characterized in that: In S1, the oven temperature is 80-120°C and the drying time is 15-45 minutes.

8. The method for obtaining the tortuosity of a porous electrode according to claim 1, characterized in that: In S5, the standing time is 5-30 minutes.

9. The method for obtaining the tortuosity of a porous electrode according to claim 1, characterized in that: In S6, the tested disturbance voltage is 5mV and the frequency is 0.1-10kHz.

10. The method for obtaining the tortuosity of a porous electrode according to claim 1, characterized in that: The limiting gasket is cylindrical and is coaxially arranged with the groove on its surface. The outer diameters of the limiting gasket 1 and the limiting gasket 2 are respectively adapted to the inner cavities of the positive electrode shell and the negative electrode shell.