An electrode sheet electrochemical impedance test structure and a test method thereof

Abstract

This invention discloses an electrode electrochemical impedance spectroscopy (EIS) testing structure, which is equivalent to a simple battery. Its assembly is simple and convenient, and the electrode undergoes no physical or chemical changes during assembly, thus having no impact on the EIS test and ensuring accurate results. This invention also provides a method for testing electrode EIS using this EIS testing structure. The method involves fixing the test component within a fixing component to form the test structure. The assembled test structure is then immersed in an electrolyte, with the fixing component holding it in place. The component structure remains unchanged, and sufficient lithium ions remain on the electrode surface. The lithium ions embed and extract on the electrode surface, making the test component a simple battery. This method reduces the difficulty and time required for EIS testing.

Description

Technical Field

[0001] This invention belongs to the field of battery component performance testing technology, and specifically relates to an electrode electrochemical impedance testing structure and its testing method. Background Technology

[0002] Lithium-ion rechargeable batteries mainly consist of a positive electrode, a negative electrode, a separator, and an electrolyte. The main components of the electrode are active materials, binders, conductive agents, solvents, and foil, which are coated to form the electrode. The primary function of the electrode is to facilitate the extraction and insertion of lithium ions during battery operation, forming a closed circuit to generate current. However, the extraction and insertion process of lithium ions inevitably encounters resistance from the electrode; this is known as electrochemical impedance spectroscopy (EIS). EIS is a widely used electrochemical analysis technique, and as lithium-ion battery technology matures, it plays an increasingly important role in lithium-ion battery and materials research.

[0003] This review summarizes the progress of electrochemical impedance spectroscopy (EIS) in lithium-ion battery and materials research, including the electrochemical lithium storage performance and mechanisms of positive and negative electrode materials, electrolyte conductivity and its mechanisms, interfacial reactions between electrolyte and electrode materials, lithium-ion interfacial conduction, battery material deactivation mechanisms, and the causes and predictions of full-cell performance degradation. EIS testing is essential in the lithium-ion battery production process. The electrochemical impedance of the electrode itself limits ion conductivity, thus directly affecting the overall performance of the lithium-ion rechargeable battery.

[0004] The electrochemical impedance of an electrode mainly consists of ohmic resistance, SEI film resistance, mass transfer resistance, and diffusion resistance. Ions move between the positive and negative electrodes through numerous tortuous resistances, forming conductive pathways for the ions. Simultaneously, electrons are transported through the active materials, conductive agents, and current collectors at the positive and negative electrodes, forming conductive pathways for the electrons. The migration of ions and electrons between the positive and negative electrodes generates current. Therefore, the number of ions that can be inserted and extracted per unit time becomes one of the important indicators for evaluating electrode performance.

[0005] The traditional method for testing the electrode impedance of lithium-ion secondary batteries involves assembling the positive and negative electrodes into a button cell and then measuring the electrochemical impedance of the electrodes using an EIS electrochemical workstation. Assembling a button cell requires cutting the positive and negative electrodes to fit the casing size, and the entire assembly process is carried out inside a glove box. Adding electrolyte in a glove box is extremely inconvenient, and the amount of electrolyte is difficult to control. Furthermore, the electrolyte is prone to decomposition in the glove box, causing excessive humidity, which affects the testing process and causes significant equipment wear. On the one hand, due to the difficulty in controlling the electrolyte amount and the inconvenience of operation in a glove box, the yield rate of the assembled button cell samples is low. On the other hand, the assembly process can cause the coating on the electrodes to peel off, affecting the electrochemical impedance measurement and leading to large errors in the test results. On the other hand, the manufactured button batteries need to be stored at room temperature for 24 hours before testing, which increases the testing time. Furthermore, assembling the button batteries requires testing the impedance of either the positive or negative electrode in conjunction with a lithium sheet. Therefore, assembling the button batteries before testing the electrochemical impedance of the electrodes results in significant wear and tear on the glove box, a time-consuming sample assembly process, cumbersome operations, low sample yield, and delays in normal production. Summary of the Invention

[0006] To address the shortcomings of the prior art, this invention provides an electrode electrochemical impedance spectroscopy (EIS) testing structure. This structure is equivalent to a simple battery, which is easy and convenient to assemble. During assembly, the coating area is not squeezed, and the electrode coating does not fall off. Therefore, the electrode does not undergo any physical or chemical changes, and it does not affect the EIS testing, thus ensuring accurate EIS test results.

[0007] This invention also provides a method for testing the electrochemical impedance of electrodes using an electrode electrochemical test structure. This method involves immersing a test structure, consisting of a test component and a fixed component, in an electrolyte, ensuring sufficient lithium ions remain on the electrode surface. The lithium ions embed and extract on the electrode surface, creating a potential difference within the test component, thus transforming the test component into a simple battery. This method, by immersing the test structure in the electrolyte, quickly ensures sufficient lithium ions remain on the electrode surface, reducing testing time.

[0008] The technical effects to be achieved by this invention are accomplished through the following solutions:

[0009] An electrode electrochemical impedance spectroscopy (EIS) test structure includes a test component and a fixing component.

[0010] The test assembly includes a first electrode, a second electrode, and a diaphragm material separating the first electrode and the second electrode; both the first electrode and the second electrode have an empty foil area and a coating area, the coating areas of the two electrodes overlap, and the empty foil areas of the two electrodes are located on opposite sides.

[0011] The fixing component clamps the test component in the middle.

[0012] The fixing components clamp the test components in the middle, which not only secures the test components but also protects the coated areas of the two electrodes from paint peeling off. The empty foil areas are not clamped between the fixing components; that is, the empty foil areas are exposed outside the fixing components, allowing the empty foil areas to be used as test electrodes for testing.

[0013] Furthermore, the fixing component is a flat insulating material.

[0014] To avoid interfering with the lithium ion residue on the electrode surface, the fixing component is preferably made of a flat insulating material. The flat design is intended to cover the coating area and better fix the test component.

[0015] Furthermore, the fixing component is in contact with the coating areas of the first electrode and the second electrode, respectively.

[0016] The fixing components are in contact with the coating areas of the first and second electrodes respectively, in order to further protect the coating areas from peeling off.

[0017] Furthermore, the fixing component is a combination of a glass slide and a clamping device.

[0018] Furthermore, the area of ​​the glass slide is not less than the area of ​​the coating area.

[0019] The area of ​​the glass slide is not less than the area of ​​the coating area, so that the glass slide can cover all the coating areas of the electrode. The purpose of this design is, on the one hand, to protect the coating area from falling off during the immersion process, and on the other hand, to prevent the clamping device from touching the coating area and damaging the coating layer.

[0020] A method for testing the electrochemical impedance of an electrode using the above-mentioned electrode electrochemical impedance testing structure includes the following steps:

[0021] S01: The test component is clamped and fixed in the fixed component to form a test structure;

[0022] S02: Immerse the assembled test structure in the electrolyte to complete the pretreatment and obtain the pretreated test structure;

[0023] S03: Take out the test structure that has been pretreated in step S02 and use the empty foil area of ​​the first electrode and the empty foil area of ​​the second electrode as the two test electrodes to perform electrochemical impedance testing.

[0024] Furthermore, step S02 is performed in a vacuum environment.

[0025] Furthermore, the method for forming the vacuum environment is as follows: a vacuum device is provided, the vacuum device including a vacuum chamber, an electrolyte cup and a vacuum pump, the vacuum chamber is connected to the vacuum pump through a suction pipe, the electrolyte cup is disposed in the vacuum chamber and contains the electrolyte.

[0026] Furthermore, the test component is immersed in the electrolyte for 15-30 minutes.

[0027] When the test components are immersed in the electrolyte for a time within the above range, sufficient lithium ions remain on the surface of the electrode. The insertion and extraction of lithium ions cause changes in the potential between the electrodes, thereby disrupting the original equilibrium state and causing an electrochemical reaction.

[0028] Furthermore, the electrochemical impedance of the electrodes was tested using an EIS electrochemical workstation in S03.

[0029] The present invention has the following advantages:

[0030] 1. The electrode electrochemical impedance testing structure of the present invention is equivalent to a simple battery. It is simple and convenient to assemble, and the coating area is not squeezed during the assembly process. The electrode coating does not fall off, so the electrode does not undergo any physical or chemical changes, which makes the test results of the electrode electrochemical impedance accurate.

[0031] 2. The present invention provides an electrode electrochemical impedance spectroscopy method. This method involves immersing a test structure, consisting of a test component and a fixed component, in an electrolyte solution, ensuring sufficient lithium ions remain on the electrode surface. The lithium ions embed and extract on the electrode surface, creating a potential difference within the test component, thus transforming the test component into a simple battery. This method, by immersing the test structure in the electrolyte solution, quickly ensures sufficient lithium ions remain on the electrode surface, reducing testing time. Attached Figure Description

[0032] Figure 1 This is a three-dimensional assembly diagram of the test structure in this invention;

[0033] Figure 2 This is a three-dimensional assembly diagram of the test components in this invention;

[0034] Figure 3 This is a schematic diagram of the structure of the first or second electrode in this invention;

[0035] Figure 4 This is a schematic diagram of the preprocessing of the test structure according to the present invention;

[0036] Explanation of symbols in the attached drawings: 1. Test assembly; 1C, first electrode; 1D, second electrode; 11C and 11D, coating area; 12C and 12D, empty foil area; 2. Fixing assembly; 3. Diaphragm material; 01, vacuum chamber; 02, electrolyte cup; 03, vacuum pump; 04, suction pipe. Detailed Implementation

[0037] To better explain the present invention and to highlight its steps and advantages, the following description is provided in conjunction with the appendix. Figure 1-4 The present invention will be described in detail with reference to the embodiments.

[0038] As shown in the attached figure in this embodiment Figure 1 As shown, the electrode electrochemical impedance spectroscopy test structure includes a test component 1 and a fixing component 2.

[0039] As attached Figure 2 As shown, test assembly 1 includes a first electrode 1C, a second electrode 1D stacked together, and a separator material 3 separating the first electrode and the second electrode 1D. (See attached diagram.) Figure 3 As shown, both the first electrode 1C and the second electrode 1D are provided with empty foil areas 12C and 12D and coating areas 11C and 11D. The coating areas 11C and 11D of the two electrodes are in the same position, while the empty foil areas 12C and 12D of the two electrodes are located on opposite sides.

[0040] Fixing component 2 clamps test component 1 in the middle.

[0041] In this embodiment, the first electrode 1C and the second electrode 1D have the same shape and area, preferably square. The length and width of the two electrodes are preferably 15-45 mm, which facilitates handling and allows for the electrodes to be rolled. The length of the empty foil area is preferably 15-45 mm, and the width is preferably 8-12 mm. The empty foil areas 12C and 12D of the two electrodes are located on opposite sides, corresponding to the positive and negative electrodes of the battery. The empty foil areas are not stacked together to facilitate subsequent electrochemical impedance spectroscopy testing. In this embodiment, the separator material 3 covers the coating areas 11C and 11D, ensuring that the two electrodes do not contact each other.

[0042] The fixing component 2 clamps the test component 1 in the middle, which can fix the test component on the one hand and protect the coating area of ​​the two electrodes from peeling off on the other. The empty foil area is not clamped between the fixing components, that is, the empty foil area is exposed outside the fixing components, which can be used as the test electrodes for testing.

[0043] It should be noted here that the electrode has two different surfaces, surface A and surface B. During the assembly of the test assembly, in order to better form a potential difference between the first electrode 1C and the second electrode 1D within the test assembly, the opposite surfaces of the first electrode 1C and the second electrode 1D are preferably the same, that is, the opposite surfaces of the first electrode 1C and the second electrode 1D are both surface A or both are surface B.

[0044] In this embodiment, in order not to interfere with the lithium ions remaining on the electrode surface, the fixing component 2 is preferably a flat insulating material. The flat design is to cover the coating areas 11C and 11D and to better fix the test component.

[0045] In this embodiment, preferably, the fixing component contacts the coating areas of the first electrode 1C and the second electrode 1D respectively, in order to further protect the coating areas from peeling off.

[0046] In this embodiment, in order to independently test the electrochemical impedance of an electrode with a specific attribute of the battery, the materials of the first electrode 1C and the second electrode 1D are electrode materials with the same attribute as the battery, that is, both the first electrode 1C and the second electrode 1D are cut from the positive electrode material or the negative electrode material of the battery. Two electrodes made of the same attribute material can be used to independently test the electrochemical impedance of an electrode with a specific attribute, which facilitates understanding and control of the electrochemical impedance of an electrode with a specific attribute.

[0047] In this embodiment, the materials of the first electrode 1C and the second electrode 1D can also be electrode materials with different properties from those of the battery. Specifically, the first electrode 1C and the second electrode 1D are cut from the positive electrode material and the negative electrode material of the battery, respectively. The two electrodes with different properties allow the test assembly to simulate a battery, enabling the testing of the electrochemical impedance between electrodes with different properties, thus facilitating the understanding and control of the battery's electrochemical impedance. The specific electrode material properties of the first electrode 1C and the second electrode 1D can be determined according to production needs.

[0048] In this embodiment, to better fix the test component and prevent relative movement when the test component is immersed in the electrolyte, the fixing component is preferably a combination of a glass slide (not shown in the figure) and a clamping device (not shown in the figure). In this embodiment, the clamping device is a dovetail clip, but the present invention is not limited to a clamping device; any clamping device that achieves the technical objective is acceptable. The clamping position of the dovetail clip is offset from the position of the empty foil area, and the number of dovetail clips used should be sufficient to firmly clamp the test structure. Preferably, the number of dovetail clips is two, and the clamping positions of the dovetail clips are on the other two sides of the test structure offset from the empty foil area. This design avoids the dovetail clips from interfering with subsequent electrochemical impedance spectroscopy. In this embodiment, two dovetail clips are used to clamp the test structure on opposite sides offset from the empty foil area. In this embodiment, the fixing component 2 has two glass slides, preferably square in shape, which clamp the test component. The length of the glass slide is preferably 15-75 mm, and the width is preferably 15-45 mm.

[0049] The area of ​​the glass slide is not less than the area of ​​the coating area, so that the glass slide can cover all the coating areas of the electrode. The purpose of this design is, on the one hand, to protect the coating area from falling off during the immersion process, and on the other hand, to prevent the clamping device from touching the coating area and damaging the coating layer.

[0050] A method for testing the electrochemical impedance of an electrode using the above-mentioned electrode electrochemical impedance testing structure includes the following steps:

[0051] S01: The test component is clamped and fixed in the fixed component to form a test structure;

[0052] S02: Immerse the assembled test structure in the electrolyte to complete the pretreatment and obtain the pretreated test structure;

[0053] S03: Take out the test structure that has been pretreated in step S02, and use the empty foil region 12C of the first electrode 1C and the empty foil region 12D of the second electrode 1D as the two test electrodes to perform electrochemical impedance spectroscopy.

[0054] In the above steps, after the fixing component fixes the test component, the assembled test structure is immersed in the electrolyte to ensure that enough lithium ions remain on the surface of the two electrodes. The insertion and extraction of lithium ions causes the potential between the electrodes to change, thereby disrupting the original equilibrium state and causing an electrochemical reaction.

[0055] In this embodiment, step 2 is preferably performed in a vacuum environment with a vacuum level of 45-75 kPa. This design aims to prevent air from entering between the two electrodes, thus preventing lithium ions from intercalating or deintercalating and affecting the test results. This design further ensures the accuracy of the test results.

[0056] As attached Figure 4 As shown, to ensure that step S02 can be completed in a vacuum environment, the method for forming the vacuum environment is as follows: A vacuum device is provided, comprising a vacuum chamber 01, an electrolyte cup 02, and a vacuum pump 03. The vacuum chamber 01 is connected to the vacuum pump 03 via a suction pipe 04. The electrolyte cup 02 is disposed inside the vacuum chamber 01 and contains electrolyte. In this embodiment, the electrolyte cup 02 is a beaker. The vacuum chamber 01 is in a vacuum state under the suction action of the vacuum pump 03. To facilitate the entry and exit of the electrolyte cup 02 from the vacuum chamber 01, the vacuum chamber 01 consists of a vacuum chamber body (not shown in the figure) and a vacuum cover (not shown in the figure). The vacuum chamber body and the vacuum cover are preferably connected by a snap-fit, which facilitates the connection of the vacuum cover to the vacuum chamber body to form a sealed state; and facilitates the separation of the vacuum cover from the vacuum chamber body, thereby facilitating the entry and exit of the electrolyte cup 02 into the vacuum chamber 01.

[0057] In this invention, the immersion time of the test component in the electrolyte is preferably 15-30 minutes. Immersion time within this range allows sufficient lithium ions to remain on the electrode surface. The insertion and extraction of lithium ions causes a change in the potential between the electrodes, thereby disrupting the original equilibrium state and initiating an electrochemical reaction.

[0058] In this embodiment, in step S03, it is preferable to use an EIS electrochemical workstation to test the electrochemical impedance of the electrode. In this invention, there are many devices for testing electrochemical impedance, but the EIS electrochemical workstation provides relatively accurate results and is simple to operate. Based on testing the electrochemical impedance of the electrode using an EIS electrochemical workstation, the impedance of the electrode assembly is tested using a dual-electrode method. Since the electrode assembly of this invention is designed with two empty foil regions serving as positive and negative electrodes, the dual-electrode method is most suitable for testing the impedance of the electrode assembly.

[0059] In the description of this invention, it should be understood that the terms "length", "width", "upper", "lower", "first", "second", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this invention.

[0060] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the embodiments of the present invention and not to limit them. Although the embodiments of the present invention have been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the embodiments of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for testing the electrochemical impedance of electrodes, characterized in that, The steps include: S01: The test component is clamped and fixed in the fixed component to form a test structure; S02: Immerse the assembled test structure in the electrolyte to complete the pretreatment and obtain the pretreated test structure; S03: Take out the test structure that has been pretreated in step S02, and use the empty foil area of ​​the first electrode and the empty foil area of ​​the second electrode as the two test electrodes to perform electrochemical impedance testing. Step S02 is completed in a vacuum environment; The method for forming the vacuum environment is as follows: a vacuum device is provided, the vacuum device includes a vacuum chamber, an electrolyte cup and a vacuum pump, the vacuum chamber is connected to the vacuum pump through a suction pipe, the electrolyte cup is disposed in the vacuum chamber and contains the electrolyte; The test assembly includes a first electrode, a second electrode, and a diaphragm material separating the first electrode and the second electrode; both the first electrode and the second electrode have an empty foil area and a coating area, the coating areas of the two electrodes overlap, and the empty foil areas of the two electrodes are located on opposite sides. The fixing component clamps the test component in the middle; The test components are immersed in the electrolyte for 15-30 minutes; In step S03, an EIS electrochemical workstation is used to test the electrochemical impedance of the electrode. The fixing component is a flat insulating material; The fixing component is in contact with the coating area of ​​the first electrode and the second electrode, respectively; The fixing component is a combination of a glass slide and a clamping device; The area of ​​the glass slide is not less than the area of ​​the coating area.

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