Three-electrode testing device and testing method for secondary battery cells

Abstract

The present application provides a three-electrode testing device for secondary batteries and a testing method thereof, the testing device comprising: an electrolyte structure and a reference electrode, wherein the electrolyte structure comprises a containing space and a first electrolyte, the first electrolyte is located in the containing space, the electrolyte structure is used to place a detection structure and a reference electrode, wherein the detection structure is a conductive structure with the same potential as the positive electrode or negative electrode of the square shell battery cell of the lithium ion to be tested, the detection structure, the first electrolyte and the reference electrode form an external detection circuit to detect the potential difference between the positive electrode and the reference electrode, or to detect the potential difference between the negative electrode and the reference electrode, the first electrolyte and the second electrolyte in the square shell battery cell of the lithium ion to be tested have the same electrolyte system. The potential difference between the positive electrode or negative electrode of the square shell battery cell and the reference electrode is measured by the external detection circuit, which solves the problem in the related art that it is difficult to perform three-electrode testing on square shell batteries due to the complexity of the preparation of the three electrodes.

Description

Technical Field

[0001] The present application relates to the field of three-electrode testing technology, and in particular to a three-electrode testing device for secondary batteries and a testing method thereof. Background Art

[0002] With the rapid development of the energy storage market, energy storage cells are being updated and iterated at an accelerated pace. In the prior art, reference electrodes are introduced inside the cell to detect the actual voltage conditions of the positive and negative electrodes during the charging and discharging process of the cell, and to analyze problems such as lithium deposition and polarization of the cell. At present, due to the complexity of three-electrode production, three-electrode production is mainly carried out in small soft-pack cells, and three-electrode testing is rarely performed on square-shell cells. Therefore, there is currently a lack of effective technical means for testing square-shell cells. Summary of the invention

[0003] The present application provides a three-electrode testing device and a testing method for a secondary battery cell, so as to solve the problem in the related art that it is difficult to perform three-electrode testing on a square shell battery cell due to the complexity of preparing the three electrodes.

[0004] According to one aspect of the present application, a three-electrode testing device for a secondary battery cell is provided, the three-electrode testing device comprising: an electrolyte structure and a reference electrode, wherein the electrolyte structure comprises a containing space and a first electrolyte, the first electrolyte is located in the containing space, and the electrolyte structure is used to place a detection structure and the reference electrode, wherein the detection structure is a conductive structure with the same potential as the positive electrode or negative electrode of the square shell battery cell of the lithium ion to be tested, the detection structure, the first electrolyte and the reference electrode form an external detection circuit to detect the potential difference between the positive electrode and the reference electrode, or to detect the potential difference between the negative electrode and the reference electrode, and the first electrolyte and the second electrolyte in the square shell battery cell of the lithium ion to be tested have the same electrolyte system.

[0005] Optionally, the electrolyte structure includes a sealed top cover, the sealed top cover having a first opening and a second opening, the first opening is used to adapt to the reference electrode, the reference electrode extends into the first electrolyte through the first opening, and the second opening is used to adapt to the detection structure, the detection structure extends into the first electrolyte through the second opening.

[0006] Optionally, the first electrolyte is the same as the second electrolyte.

[0007] Optionally, the detection structure is a connection structure for connecting the positive electrode and the first electrolyte, or the connection structure is used to connect the negative electrode and the first electrolyte, and the connection structure includes a bar sheet.

[0008] Optionally, the reference electrode is not in contact with the bar sheet, and the distance between the reference electrode and the bar sheet is less than a preset distance.

[0009] Optionally, the detection structure is a connection structure consistent with the positive electrode or the negative electrode material.

[0010] Optionally, the detection structure is the outer shell of the square-shell battery cell of the lithium ion to be detected.

[0011] According to another aspect of the present application, a three-electrode testing method for secondary batteries is provided, and the three-electrode testing method is applied to the three-electrode testing device, and the three-electrode testing method includes: connecting the positive electrode or the negative electrode of the square shell battery cell of the lithium ion to be tested to the first electrolyte in the electrolyte structure of the three-electrode testing device, and the electrolyte structure is used to place the detection structure and the reference electrode, wherein the detection structure is a conductive structure with the same potential as the positive electrode or the negative electrode of the square shell battery cell of the lithium ion to be tested, and the detection structure, the first electrolyte and the reference electrode form an external detection circuit; detecting the potential difference between the positive electrode and the reference electrode, or detecting the potential difference between the negative electrode and the reference electrode, the first electrolyte and the second electrolyte in the square shell battery cell of the lithium ion to be tested are the same electrolyte system; and determining the lithium deposition condition of the square shell battery cell of the lithium ion to be tested based at least on the potential difference.

[0012] Optionally, the test method also includes: detecting a second potential difference in the internal circuit, and a third potential difference between the positive electrode and the reference electrode in the external detection circuit, the internal circuit being formed by the positive electrode, the negative electrode and the second electrolyte in the square shell battery cell of the lithium ions to be tested, and obtaining the first potential difference between the negative electrode and the reference electrode based on the second potential difference and the third potential difference; or detecting the first potential difference between the negative electrode and the reference electrode; judging whether the first potential difference is less than a first threshold value, and when the judgment indication indicates that the first potential difference is less than the first threshold value, it is characterized that the square shell battery cell has produced lithium deposition phenomenon.

[0013] Optionally, the testing method further includes: setting the outer shell of the square shell battery cell and the positive electrode to an equipotential state, and connecting the outer shell to the first electrolyte; detecting a third potential difference between the positive electrode and the reference electrode, and a second potential difference in an internal circuit, wherein the internal circuit is formed by the positive electrode, the negative electrode and the second electrolyte of the square shell battery cell of the lithium ion to be tested, and obtaining a first potential difference between the negative electrode and the reference electrode during the charge and discharge process based on the second potential difference and the third potential difference; judging whether the first potential difference is less than a first threshold value, and when the judgment indication indicates that the first potential difference is less than the first threshold value, it is characterized that the square shell battery cell has produced lithium deposition phenomenon.

[0014] Through the technical solution of the present application, a three-electrode testing device for secondary batteries is provided, wherein the device includes an electrolyte structure and a reference electrode, wherein the electrolyte structure contains a first electrolyte, the reference electrode is located in the above electrolyte structure, the square shell battery cell of the lithium ion to be tested is connected to the detection structure, the detection result is located in the above electrolyte structure, the detection structure, the first electrolyte and the reference electrode form an external detection circuit, and the potential difference between the positive or negative electrode of the square shell battery cell of the lithium ion to be tested and the reference electrode is measured through the above external detection circuit, so as to judge the lithium precipitation situation in the square shell battery cell of the lithium ion to be tested, and no structural improvement is required for the square shell battery cell of the lithium ion to be tested, and the scope of application is not limited to soft-pack batteries, but becomes more extensive, and the first electrolyte and the second electrolyte in the square shell battery cell of the lithium ion to be tested are electrolytes of the same system, and the measurement accuracy is higher. The problem that it is difficult to perform three-electrode testing on square shell batteries due to the complexity of the preparation of the three electrodes in the related art is solved. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] The drawings constituting a part of the present application are used to provide a further understanding of the present application. The illustrative embodiments and descriptions of the present application are used to explain the present application and do not constitute an improper limitation on the present application. In the drawings:

[0016] Figure 1 It is a comparative schematic diagram of a three-electrode test principle diagram in the prior art and a three-electrode test principle diagram provided according to an embodiment of the present application;

[0017] Figure 2 is a structural schematic diagram of a three-electrode testing device provided according to an embodiment of the present application;

[0018] Figure 3 is a structural schematic diagram of another three-electrode testing device provided according to an embodiment of the present application;

[0019] Figure 4 is a flow chart of a preparation method of a three-electrode testing method provided in an embodiment of the present application;

[0020] Figure 5 It is a schematic diagram of using the three-electrode testing method provided in the embodiment of the present application to monitor the change in potential voltage of the negative electrode relative to the reference electrode (lithium metal electrode) during the charging process of the same battery cell using different methods.

[0021] The above drawings include the following reference numerals:

[0022] 10. Electrolyte structure; 11. First electrolyte; 12. Sealed top cover; 20. Reference electrode; 30. Detection structure; 40. Square shell battery cell. DETAILED DESCRIPTION

[0023] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application can be combined with each other. The present application will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0024] In order to enable those skilled in the art to better understand the present application, the technical solutions in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of this application.

[0025] It should be noted that the terms "first", "second", etc. in the specification and claims of the present application and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that the data used in this way can be interchanged where appropriate, so as to describe the embodiments of the present application described herein. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions, for example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to those steps or units clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0026] In the related technology, due to the complexity of three-electrode production, three-electrode production is mainly carried out in small soft-pack batteries. The three-electrode preparation method is too complicated, and three-electrode testing is often rarely performed on square shell batteries. Usually, three electrodes are required for testing in the performance evaluation of lithium-ion batteries and the battery research and development stage. The purpose of the test is to be able to comprehensively and in situ analyze the various properties of the battery, such as film formation reaction, cyclic charging and discharging, rate charging and discharging, high and low temperature charging and discharging, and quantitative analysis of lithium precipitation in the battery. The design of the battery can also be optimized according to the test results to improve the yield of the output battery. However, there is currently a lack of effective technical means for testing square shell batteries, which has a certain impact on the output yield and performance optimization of square shell batteries.

[0027] like Figure 1 As shown, the left figure is a schematic diagram of the three-electrode test inside the battery cell in the prior art, RE is the reference electrode, and the right figure is a schematic diagram of the three-electrode test in which an external circuit is set and RE is set in the external circuit in the present application.

[0028] Therefore, in view of the above problems, a three-electrode testing device for a secondary battery cell is provided in an embodiment of the present application. Figure 2 and Figure 3As shown, the three-electrode testing device includes: an electrolyte structure 10 and a reference electrode 20, wherein the electrolyte structure 10 includes a containing space and a first electrolyte 11, the first electrolyte 11 is located in the containing space, and the electrolyte structure 10 is used to place the detection structure 30 and the reference electrode 20, wherein the detection structure 30 is a conductive structure with the same potential as the positive electrode or negative electrode of the square shell battery cell 40 of the lithium ion to be tested, the detection structure 30, the first electrolyte 11 and the reference electrode 20 form an external detection circuit to detect the potential difference between the positive electrode and the reference electrode 20, or to detect the potential difference between the negative electrode and the reference electrode 20, and the first electrolyte 11 and the second electrolyte in the square shell battery cell 40 of the lithium ion to be tested have the same electrolyte system. According to the potential difference between the positive electrode or negative electrode and the reference electrode, the electrochemical state of the positive electrode or negative electrode during the charge and discharge process can be known respectively, and the lithium deposition situation of the square shell battery cell to be tested can be determined.

[0029] The electrolyte structure of the three-electrode testing device contains a first electrolyte, the reference electrode of the three-electrode testing device is located in the electrolyte structure, the square shell battery cell of the lithium ion to be tested is connected to the detection structure, the detection result is located in the electrolyte structure, the detection structure, the first electrolyte and the reference electrode form an external detection circuit, and the potential difference between the positive or negative electrode of the square shell battery cell of the lithium ion to be tested and the reference electrode is measured by the external detection circuit. By adopting the three-electrode testing device, the lithium deposition situation of the square shell battery cell of the lithium ion to be tested during the charging and discharging process can be judged, and no structural improvement is required for the square shell battery cell of the lithium ion to be tested. The scope of application is not limited to soft-pack batteries, but becomes more extensive, and the first electrolyte and the second electrolyte in the square shell battery cell of the lithium ion to be tested are electrolytes of the same system, and the measurement accuracy is higher.

[0030] In some optional embodiments, such as Figure 2 and Figure 3 As shown, the electrolyte structure 10 includes a sealed top cover 12, and the sealed top cover 12 has a first opening and a second opening, the first opening is used to adapt to the reference electrode 20, and the reference electrode 20 extends into the first electrolyte 11 through the first opening, and the second opening is used to adapt to the detection structure 30, and the detection structure 30 extends into the first electrolyte 11 through the second opening.

[0031] In the above optional implementation, if Figure 2 and Figure 3As shown, the electrolyte structure 10 needs to be a sealed structure to simulate the closed environment of the square shell battery cell 40 to be tested for lithium ions, so that the test results are more accurate and the stability of the first electrolyte 11 therein can be ensured. The first opening and the second opening corresponding to the reference electrode 20 and the detection structure 30 are set on the sealed top cover of the electrolyte structure 10, so that after the reference electrode 20 and the detection structure 30 are in contact with the first electrolyte 11 through the holes, the electrolyte structure 10 can also maintain a sealed state to simulate the closed environment of the square shell battery cell 40 to be tested for lithium ions. Figure 2 The middle shell battery cell 40 can be regarded as a detection structure.

[0032] In some optional embodiments, the first electrolyte is the same as the second electrolyte, which can make the test result more accurate.

[0033] In the above optional embodiment, in order to keep the test results in the most accurate state, the solute, solvent and the ratio between the above-mentioned first electrolyte and the above-mentioned second electrolyte are set to be consistent, and in order to simulate the use state of the square shell battery cell of the lithium ion to be tested, the charge and discharge times of the above-mentioned first electrolyte in the preset battery cell are limited to be basically consistent with the charge and discharge times of the square shell battery cell of the lithium ion to be tested, and the above-mentioned first electrolyte can be reused and can be used for three-electrode testing of other battery cells.

[0034] In some optional embodiments, such as Figure 3 As shown, the detection structure 30 is a connection structure for connecting the positive electrode and the first electrolyte 11 (left figure), or the connection structure is used to connect the negative electrode and the first electrolyte 11 (right figure), and the connection structure includes a bar. The connection of the bar can reduce the potential loss of the positive and negative electrodes to the first electrolyte, thereby improving the test accuracy.

[0035] In the above optional implementation, if Figure 3 As shown, the bar sheet package is an aluminum bar sheet, which has good conductivity, low cost, small contact resistance and corrosion resistance. The bar sheet is used to introduce the positive electrode or negative electrode of the square shell battery cell 40 to be tested with lithium ions into the first electrolyte 11, which can reduce the error of the potential difference between the positive electrode and the reference electrode 20, or the potential difference between the negative electrode and the reference electrode 20 obtained by the test, and make the result more accurate.

[0036] In some optional embodiments, such as Figure 3As shown, the reference electrode 20 is not in contact with the bar sheet, and the distance between the reference electrode 20 and the bar sheet is less than the preset distance. In the process of introducing the positive or negative electrode of the square shell battery cell 40 to be tested with the bar sheet into the first electrolyte 11, it should be noted that there needs to be a certain distance between the bar sheet and the reference electrode 20. The range of the above distance can be within 3 cm. If the distance is larger, the resistance of the first electrolyte 11 will be greater during the test, thereby increasing the error of the potential between the positive or negative electrode and the reference electrode 20. The smaller the distance, the smaller the resistance and the more accurate it is. Setting the distance to within 3 cm can eliminate the potential to the maximum extent without short circuit.

[0037] In some optional embodiments, the detection structure is a connection structure consistent with the positive electrode or the negative electrode material. When the connection structure is connected to the positive electrode, aluminum foil can be selected. The aluminum foil is consistent with the current collector of the positive electrode and is a material with the same potential as the positive electrode. When the connection structure is connected to the negative electrode, copper foil can be selected. The copper foil is consistent with the current collector of the negative electrode. When the positive electrode and the negative electrode are introduced into the first electrolyte through materials with the same chemical potential as the positive electrode and the negative electrode, the voltage change caused by the different chemical potentials of the external detection devices of the positive electrode and the negative electrode can be avoided, and the test result is more accurate.

[0038] In some optional embodiments, such as Figure 2 As shown, the detection structure is the shell of the square shell battery cell 40 for lithium ions to be tested. The shell of the square shell battery cell 40 for lithium ions to be tested can be an aluminum shell. To prevent the shell from corroding during the use of the battery cell, the aluminum shell is usually connected to the positive electrode, that is, the shell and the positive electrode are equipotential, and the shell is directly immersed in the electrolyte structure 10 to contact the first electrolyte 11, which is equivalent to connecting the positive electrode to the first electrolyte 11 through the shell.

[0039] In order to make the detection structure more accurate, the three-electrode test device may also include a Luggin capillary, which is connected to a reference electrode and used to connect the reference electrode to the second electrolyte. The connection between the Luggin capillary and the reference electrode can be used to measure the potential difference in the electrochemical reaction. The Luggin capillary can eliminate the resistance in the electrolyte, and the reference electrode can provide a stable reference potential. By connecting the two together, the results can be made more accurate when measuring the three electrodes, so as to understand the lithium precipitation in the square shell battery cell of the lithium ion to be tested.

[0040] The reference electrode may be selected to include at least one of the following: Ag / AgCl electrode or metal Li electrode. In the case where the reference electrode is selected to be an Ag / AgCl reference electrode, the reference electrode has a filling liquid, and the filling liquid may include: potassium chloride (KCl) and dimethyl carbonate (DMC). Such filling liquid and reference electrode materials can facilitate ion transport between the electrode and the electrolyte, improve the stability and reaction speed of the electrode, and improve the performance of the electrode.

[0041] According to another aspect of the present application, a three-electrode testing method for a secondary battery cell is provided. The three-electrode testing method is applied to the three-electrode testing device, such as Figure 4 As shown, the above three-electrode testing method includes:

[0042] Step S101: Connect the positive electrode or negative electrode of the square shell battery cell to be tested with the first electrolyte in the electrolyte structure of the three-electrode testing device, wherein the detection structure is a conductive structure with the same potential as the positive electrode or negative electrode of the square shell battery cell to be tested, and the detection structure, the first electrolyte and the reference electrode form an external detection circuit; wherein the conductive structure with the same potential as the positive electrode or negative electrode of the square shell battery cell to be tested may include aluminum foil, the outer shell and the tab of the square shell battery cell with the same potential as the positive electrode, and copper foil and the tab with the same potential as the negative electrode.

[0043] Step S102: Detecting the potential difference between the positive electrode and the reference electrode during the charge and discharge process, or detecting the potential difference between the negative electrode and the reference electrode during the charge and discharge process, the first electrolyte and the second electrolyte in the square shell battery cell of the lithium ion to be tested are the same electrolyte system; the first electrolyte and the second electrolyte include solutes and solutions of the same material.

[0044] Step S103: Determine the lithium deposition status of the square shell battery cell of the lithium ion to be tested at least according to the potential difference. Set the materials of the first electrolyte and the second electrolyte to be the same, and connect the detection structure to the positive electrode or the negative electrode to make the positive electrode and the negative electrode equal in potential, so that the consumption of the positive and negative electrode potentials during the transmission process is reduced, and the detection accuracy of the three electrodes is improved.

[0045] By adopting the above-mentioned three-electrode testing method and three-electrode testing device to perform three-electrode detection on the square shell battery cell of the lithium ion to be tested, the actual potential change of the negative electrode can be judged by detecting the potential difference between the positive electrode or negative electrode of the square shell battery cell of the lithium ion to be tested and the reference electrode during the charging and discharging process of the battery cell, and the lithium deposition situation of the lithium ion square shell battery cell during the charging and discharging process can be effectively detected, which solves the problem in the related technology that it is difficult to perform three-electrode testing on the square shell battery cell due to the complexity of the preparation of the three electrodes.

[0046] The following is a more detailed description of exemplary embodiments of the three-electrode test method for a secondary battery cell provided in accordance with the present application. However, these exemplary embodiments can be implemented in a variety of different forms and should not be construed as being limited to the embodiments described herein. It should be understood that these embodiments are provided to make the disclosure of this application thorough and complete, and to fully convey the concepts of these exemplary embodiments to those of ordinary skill in the art.

[0047] In some optional embodiments, the above test method further includes:

[0048] Detect the second potential difference of the internal circuit, and the third potential difference between the positive electrode and the reference electrode in the external detection circuit, wherein the internal circuit is formed by the positive electrode, the negative electrode and the second electrolyte in the square shell battery cell of the lithium ions to be tested, and obtain the first potential difference between the negative electrode and the reference electrode according to the second potential difference and the third potential difference; measure the positive and negative electrodes of the square shell battery cell to obtain the second potential difference, introduce the positive electrode into the first electrolyte, measure the third potential difference between the positive electrode and the reference electrode, and obtain the first potential difference between the negative electrode and the reference electrode according to the second potential difference and the third potential difference.

[0049] Or detect the above-mentioned first potential difference between the above-mentioned negative electrode and the above-mentioned reference electrode; judge whether the above-mentioned first potential difference is less than the first threshold value, and when the judgment indication shows that the above-mentioned first potential difference is less than the above-mentioned first threshold value, it indicates that the above-mentioned square shell battery cell has produced lithium deposition. It is also possible to directly introduce the negative electrode into the first electrolyte, measure the first potential difference between the negative electrode and the reference electrode, and finally obtain the lithium deposition situation inside the square shell battery cell according to the preset relationship between the first potential difference and the lithium deposition of the square shell battery cell. It should be noted that the above-mentioned action of detecting the potential difference is performed during the charging and discharging process of the battery cell, which is a dynamic detection process.

[0050] In some optional embodiments, the above test method further includes:

[0051] The shell of the square shell battery cell is connected to the first electrolyte by utilizing the equipotential state between the shell of the square shell battery cell and the positive electrode; the shell of the square shell battery cell is an aluminum shell.

[0052] Detecting a third potential difference between the positive electrode and the reference electrode, and a second potential difference of an internal circuit, wherein the internal circuit is formed by the positive electrode, the negative electrode and the second electrolyte of the square shell battery cell to be tested for lithium ions, and obtaining a first potential difference between the negative electrode and the reference electrode based on the second potential difference and the third potential difference; measuring the positive and negative electrodes of the square shell battery cell to obtain a second potential difference, and introducing the positive electrode into the first electrolyte, measuring the third potential difference between the positive electrode and the reference electrode, and obtaining a first potential difference between the negative electrode and the reference electrode based on the second potential difference and the third potential difference.

[0053] It is determined whether the first potential difference is less than the first threshold value during the charge and discharge process of the battery cell. When the judgment indicates that the first potential difference is less than the first threshold value, it indicates that the square shell battery cell has lithium deposition. When the voltage difference between the negative electrode and the reference electrode (lithium metal electrode) is less than 0 (first threshold value), it indicates that lithium deposition occurs inside the square shell battery cell. In the process of using three electrodes to detect the battery cell, the electrochemical reaction during the positive and negative electrode cycle can be directly seen, and a series of mechanism analyses can be performed, and the state of the positive and negative electrodes during the charge and discharge process can also be understood.

[0054] In the above optional implementation, in order to ensure that the test results are more accurate, the above test method further includes: placing a preset first electrolyte in a preset battery cell, and controlling the above preset battery cell to be charged and discharged a certain number of times to obtain the above first electrolyte, and the above cycle number is the number of charge and discharge times of the above battery cell. The charge and discharge times of the first electrolyte are set to be consistent with the charge and discharge times of the square shell battery cell to be tested, which can simulate the second electrolyte of the square shell battery cell to be tested to the greatest extent. The internal and external circuits of the square shell battery cell use basically the same electrolyte, which can reduce the potential difference between the internal circuit and the external circuit and reduce the measurement error.

[0055] The three-electrode testing device for secondary battery cells of the present application will be described in detail below in conjunction with specific embodiments.

[0056] Example 1

[0057] This embodiment provides a three-electrode testing device for a secondary battery cell, including:

[0058] Electrolyte structure and reference electrode, wherein the electrolyte structure includes a containing space and a first electrolyte, the first electrolyte is located in the containing space, the electrolyte structure is a sealed structure for placing the bar sheet and the reference electrode, the bar sheet, the first electrolyte and the reference electrode form an external detection circuit, the first electrolyte is the same as the second electrolyte in the square shell battery cell of the lithium ion to be tested, and the distance between the reference electrode and the bar sheet is 1 cm.

[0059] Example 2

[0060] This embodiment provides a three-electrode testing device for a secondary battery cell, including:

[0061] An electrolyte structure and a reference electrode, wherein the electrolyte structure comprises a containing space and a first electrolyte, the first electrolyte is located in the containing space, the electrolyte structure is a sealed structure for placing an aluminum foil and the reference electrode, the aluminum foil, the first electrolyte and the reference electrode form an external detection circuit, the first electrolyte is the same as the second electrolyte in the square shell battery cell of the lithium ion to be tested, and the distance between the reference electrode and the aluminum foil is 1 cm.

[0062] Example 3

[0063] This embodiment provides a three-electrode testing device for a secondary battery cell, including:

[0064] An electrolyte structure and a reference electrode, wherein the electrolyte structure comprises a containing space and a first electrolyte, the first electrolyte is located in the containing space, the electrolyte structure is a sealed structure for placing the copper foil and the reference electrode, the copper foil, the first electrolyte and the reference electrode form an external detection circuit, the first electrolyte is the same as the second electrolyte in the square shell battery cell of the lithium ion to be tested, and the distance between the reference electrode and the copper foil is 1 cm.

[0065] Example 4

[0066] This embodiment provides a three-electrode testing device for a secondary battery cell, including:

[0067] An electrolyte structure and a reference electrode, wherein the electrolyte structure comprises a containing space and a first electrolyte, the first electrolyte is located in the containing space, the electrolyte structure is a sealed structure, and is used to place the outer shell of the square shell battery cell for lithium ions to be tested and the reference electrode, the shell, the first electrolyte and the reference electrode form an external detection circuit, the first electrolyte is the same as the second electrolyte in the square shell battery cell for lithium ions to be tested, and the distance between the square shell battery cell shell and the reference electrode is 1 cm.

[0068] Comparative Example 1

[0069] A three-electrode testing device is provided, comprising:

[0070] The modified square shell battery cell for lithium ions to be tested comprises: a reference electrode, a positive electrode, a negative electrode and a preset electrode. The preset electrode is an electrode added to the modified battery cell and is used to lead out the reference electrode from the inside of the battery cell so that the reference electrode contacts the second electrolyte of the square shell battery cell for lithium ions to be tested. The modified square shell battery cell for lithium ions to be tested has sealing properties.

[0071] The square shell battery cell was tested using the three-electrode test device for secondary battery cells in the above-mentioned Examples 1 to 4 and Comparative Example 1. The test results are as follows: Figure 5 As shown in Table 1:

[0072] Table 1

[0073]

[0074] Figure 5 The schematic diagram of the change of the potential voltage of the negative electrode relative to the reference electrode (lithium metal electrode) during the charging process of the battery cell is used to monitor the change of the potential voltage of the negative electrode relative to the reference electrode (lithium metal electrode) during the charging and discharging process of the battery cell by using the methods of Example 1 and Comparative Example 1. It can be seen from the voltage change curve of the negative electrode relative to the reference electrode during the charging and discharging process of the battery cell that the voltage change curve of Example 1 is close to the voltage change curve of Comparative Example 1. Table 1 is the monitoring data of the potential and capacity of the negative electrode relative to the reference electrode (lithium metal electrode) during the charging process of the battery cell by using the methods of different embodiments (Examples 1-4 and Comparative Example 1) for the same battery cell. Among them, the voltage change curves in Example 2 (the charging end voltage is about: 0.00496V) and Example 3 (the charging end voltage is about: 0.00496V) are closest to the voltage change curve in Comparative Example 1 (the charging end voltage is about: 0.00496V), indicating that the test methods of Examples 2 and 3 have the highest accuracy.

[0075] And in Comparative Example 1, by setting a reference electrode, a positive electrode, a negative electrode and a preset electrode inside the battery cell, the internal structure of the battery cell is modified, and then the reference electrode is drawn out from the inside of the battery cell to perform a three-electrode test on the battery cell. The process itself has a certain degree of complexity and is not easy to implement for square shell batteries (hard shell batteries). The charging end voltage of the negative electrode relative to the reference electrode measured in the above embodiments is greater than the lithium deposition potential (0V), and is relatively close to the test results of Comparative Example 1, indicating that lithium deposition does not occur during the charging process. It can be seen that the three-electrode detection scheme of the square shell battery cell through an external circuit in the present application is feasible, and on the basis of feasibility, the present application is more concise than the prior art that the comparative example 1 needs to modify the inside of the battery cell, and the technical scheme of adding one more electrode is more concise. In the present application, the use of an external circuit for three-electrode detection of square shell batteries becomes simpler and more practical.

[0076] From the above description, it can be seen that the above embodiments of the present application achieve the following technical effects:

[0077] 1) The present application adopts the above-mentioned three-electrode testing device to determine the lithium plating situation in the square shell battery cell of the lithium ion to be tested, introduces an external detection circuit, and does not require any structural improvement to the square shell battery cell of the lithium ion to be tested. The scope of application is not limited to soft-pack batteries, but becomes more extensive. The first electrolyte and the second electrolyte in the square shell battery cell of the lithium ion to be tested are electrolytes of the same system, and the measurement accuracy is higher.

[0078] 2) The present application further reduces the error of the potential difference between the internal circuit and the external detection circuit by simulating the second electrolyte as the first electrolyte that has been cyclically charged and discharged, thereby improving the accuracy of the potential difference detection of the square shell battery cell.

[0079] It should also be noted that the terms "include", "comprises" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method, commodity or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, commodity or device. In the absence of more restrictions, the elements defined by the sentence "comprises a ..." do not exclude the existence of other identical elements in the process, method, commodity or device including the elements.

[0080] The above are only embodiments of the present application and are not intended to limit the present application. For those skilled in the art, the present application may have various changes and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application should be included within the scope of the claims of the present application.

Claims

1. A three-electrode testing device for a secondary battery cell, characterized in that: The three-electrode testing device comprises: An electrolyte structure and a reference electrode, wherein the electrolyte structure includes a containing space and a first electrolyte, the first electrolyte is located in the containing space, and the electrolyte structure is used to place a detection structure and the reference electrode, wherein the detection structure is a conductive structure with the same potential as the positive electrode or negative electrode of the square shell battery cell to be detected, and the structure of the square shell battery cell has not been modified. The detection structure, the first electrolyte and the reference electrode form an external detection circuit of the square shell battery cell to detect the potential difference between the positive electrode and the reference electrode, or to detect the potential difference between the negative electrode and the reference electrode. The first electrolyte and the second electrolyte in the square shell battery cell to be detected have the same electrolyte system. The detection structure is a connecting structure or the outer shell of the square shell battery cell to be detected. The detection structure is used to connect the positive electrode and the first electrolyte, or the detection structure is used to connect the negative electrode and the first electrolyte.

2. The three-electrode testing device according to claim 1, characterized in that: The electrolyte structure includes a sealed top cover, which has a first opening and a second opening. The first opening is used to adapt to the reference electrode, and the reference electrode extends into the first electrolyte through the first opening. The second opening is used to adapt to the detection structure, and the detection structure extends into the first electrolyte through the second opening.

3. The testing device according to claim 1, characterized in that: The first electrolyte is the same as the second electrolyte.

4. The three-electrode testing device according to claim 1, characterized in that: The connecting structure includes a bar.

5. The three-electrode testing device according to claim 4, characterized in that: The reference electrode is not in contact with the bar sheet, and a distance between the reference electrode and the bar sheet is less than a preset distance.

6. The three-electrode testing device according to claim 4, characterized in that: The detection structure is a connection structure having the same material as that of the positive electrode or the negative electrode.

7. A three-electrode test method for a secondary battery cell, characterized in that: The three-electrode testing method is applied to the three-electrode testing device according to any one of claims 1 to 6, and the three-electrode testing method comprises: Connecting the positive electrode or negative electrode of the square shell battery cell of the lithium ion to be tested to the first electrolyte in the electrolyte structure of the three-electrode testing device, the electrolyte structure is used to place the detection structure and the reference electrode, wherein the detection structure is a conductive structure with the same potential as the positive electrode or negative electrode of the square shell battery cell of the lithium ion to be tested, the structure of the square shell battery cell is not modified, the detection structure, the first electrolyte and the reference electrode form an external detection circuit of the square shell battery cell, the detection structure is a connecting structure or a shell of the square shell battery cell of the lithium ion to be tested, the detection structure is used to connect the positive electrode and the first electrolyte, or the detection structure is used to connect the negative electrode and the first electrolyte; Detecting the potential difference between the positive electrode and the reference electrode, or detecting the potential difference between the negative electrode and the reference electrode, wherein the first electrolyte and the second electrolyte in the square shell battery cell of the lithium ion to be detected are the same electrolyte system; The lithium deposition condition of the square-shell battery cell of the lithium ion to be tested is determined at least according to the potential difference.

8. The testing method according to claim 7, characterized in that: The test method also includes: Detecting a second potential difference in an internal circuit, and a third potential difference between the positive electrode and the reference electrode in the external detection circuit, wherein the internal circuit is formed by the positive electrode, the negative electrode, and the second electrolyte in the square shell battery cell of the lithium ion to be detected, and obtaining a first potential difference between the negative electrode and the reference electrode according to the second potential difference and the third potential difference; or detecting the first potential difference between the negative electrode and the reference electrode; It is determined whether the first potential difference is less than a first threshold value. If the determination indicates that the first potential difference is less than the first threshold value, it indicates that lithium deposition occurs in the square shell battery cell.

9. The testing method according to claim 7, characterized in that: The test method also includes: Setting the outer shell of the square shell battery cell and the positive electrode to an equipotential state, and connecting the outer shell to the first electrolyte; Detecting a third potential difference between the positive electrode and the reference electrode, and a second potential difference of an internal circuit, wherein the internal circuit is formed by the positive electrode, the negative electrode, and the second electrolyte of the square shell battery cell of the lithium ion to be tested, and obtaining a first potential difference between the negative electrode and the reference electrode according to the second potential difference and the third potential difference; It is determined whether the first potential difference is less than a first threshold value. If the determination indicates that the first potential difference is less than the first threshold value, it indicates that lithium deposition occurs in the square shell battery cell.

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