Diaphragm testing device

Abstract

The utility model relates to the technical field of battery detection, in particular to a diaphragm testing device. The device comprises a container at least provided with a side wall, at least two electrodes and an electrochemical workstation electrically connected with the electrodes, the side edge of at least one electrode is hermetically connected with the side wall of the container, so that an accommodating cavity for accommodating a diaphragm and electrolyte is formed between the electrode and the side wall of the container; the diaphragm testing device further comprises an electrolyte storage tank communicated with the containing cavity and a first control piece used for controlling electrolyte to flow into the electrolyte storage tank from the interior of the containing cavity. By arranging the electrolyte storage tank communicated with the accommodating cavity, when the diaphragm is used, a dry diaphragm can be directly placed in the accommodating cavity, then the electrolyte is introduced for soaking, the electrolyte can be directly discharged after soaking, and any operation such as transfer on the wet diaphragm is not needed; and the problems of inconvenient operation, increased pollution, easy wrinkling and the like in the wet diaphragm transfer process are avoided.

Description

Technical Field

[0001] This utility model relates to the field of battery testing technology, and in particular to a diaphragm testing device. Background Technology

[0002] Lithium-ion batteries generally consist of a positive electrode material, a negative electrode material, an electrolyte, and a separator. The separator has a porous structure, with the electrolyte wetting the pores. During electrochemical reactions, lithium ions can be transferred through the pores. Higher porosity and lower pore tortuosity can improve the conductivity of lithium ions; therefore, porosity and pore tortuosity are important indicators for evaluating separator characteristics. Currently, separator performance evaluation mostly uses methods such as ASTM D4284-92 to determine porosity. This measurement process is complex, and separator performance is only characterized by porosity, failing to reflect the actual structural characteristics of the separator within the battery. KR102041329B1 uses a pouch-type symmetrical battery to measure the diffusion coefficient of lithium ions in the separator, and then calculates the separator tortuosity. This requires the fabrication of a pouch-type symmetrical battery, which involves a complex and time-consuming sample preparation and testing process with low testing efficiency. Furthermore, the diffusion of lithium ions in the porous electrode interferes with the measurement of the separator's diffusion impedance. CN115932393A uses one of copper foil, aluminum foil, and lithium foil as the test electrode and working electrode, and employs a coin cell to evaluate the ion resistance of the separator. However, the separator is small, resulting in a large error in the test results.

[0003] Patent document CN106370930A discloses a lithium-ion battery separator electrical performance testing device and method, including a transparent sample container, a movable electrode, a fixed electrode, and electrode leads; the sample container is equipped with a scale; the movable electrode and the fixed electrode are disposed inside the sample container and cooperate with the sample container, and the movable electrode and the fixed electrode are placed parallel to each other; the sample container, the movable electrode, and the fixed electrode form a sample chamber; the electrode leads are respectively connected to the movable electrode and the fixed electrode.

[0004] The existing testing device requires the membrane to be soaked in electrolyte in another container before being transferred to the testing device for testing. This process of transferring the wet membrane presents several problems: First, it is inconvenient to operate, as the wet membrane becomes more viscous and easily adheres to the transfer tools or equipment. Second, the wet membrane easily attracts dust or impurities during transfer, potentially increasing the risk of contamination. Third, the wet membrane becomes more flexible and less strong, making it prone to wrinkling during transfer and difficult to lay flat between the electrodes, thus affecting the test results. Fourth, the transferred wet membrane may not make a tight contact with the electrodes, resulting in air bubbles or gaps that hinder ion transport and also affect the test results. Utility Model Content

[0005] This invention aims to solve the above-mentioned problems by providing a diaphragm testing device that is easy to operate, less prone to contamination, and provides more accurate test results, especially a device for testing the tortuosity of diaphragms.

[0006] The technical solution to the problem of this utility model is to provide a diaphragm testing device, including a container with at least a sidewall, at least two electrodes, and an electrochemical workstation electrically connected to the electrodes; the side edge of at least one of the electrodes is sealed to the sidewall of the container, so that a accommodating cavity for accommodating the diaphragm and electrolyte is formed between the electrode and the sidewall of the container; the diaphragm testing device further includes an electrolyte storage tank communicating with the accommodating cavity, and a first control component for controlling the flow of electrolyte from the accommodating cavity to the electrolyte storage tank.

[0007] As a preferred embodiment of this invention, the accommodating cavity is in cyclic communication with the electrolyte storage tank, and further includes a second control component for controlling the flow of electrolyte from the electrolyte storage tank to the accommodating cavity.

[0008] As a preferred embodiment of the present invention, a first sealing ring is provided between the electrode used to form the accommodating cavity and the side wall of the container with an interference fit.

[0009] As a preferred embodiment of this utility model, the side wall of the container is provided with an outlet for the electrolyte to flow out of the accommodating cavity, the electrolyte storage tank is provided with an inlet for the electrolyte to flow in, the outlet and the inlet are connected by a discharge pipe, and the horizontal plane of the outlet is not lower than the horizontal plane of the inlet; the first control component includes a discharge valve disposed on the discharge pipe.

[0010] As a preferred embodiment of the present invention, at least one of the electrodes is movably disposed within the accommodating cavity along the thickness direction of the diaphragm.

[0011] As a preferred embodiment of the present invention, a second sealing ring is provided between the movable electrode and the side wall of the container with an interference fit.

[0012] As a preferred embodiment of the present invention, the first control element includes the movable electrode.

[0013] As a preferred embodiment of this invention, the first control component includes an electrolyte pump.

[0014] As a preferred embodiment of this invention, a valve for controlling the flow of electrolyte is provided between the accommodating cavity and the electrolyte storage tank.

[0015] As a preferred embodiment of this invention, the container has an opening at one end and a receiving plate at the other end, with the electrode for forming the accommodating cavity disposed on the receiving plate.

[0016] As a preferred embodiment of the present invention, it further includes an incubator for containing the container.

[0017] The beneficial effects of this utility model are:

[0018] 1. In this application, by setting up an electrolyte storage tank connected to the accommodating cavity, the dry diaphragm can be directly placed in the accommodating cavity and then soaked in electrolyte during use. After soaking, the electrolyte can be directly discharged, and then another electrode can be stacked for electrical performance testing. There is no need to transfer the wet diaphragm, thus avoiding the inconvenience, increased contamination, and easy wrinkling problems during the transfer of wet diaphragms. This ensures the flatness of the diaphragm between the electrodes, thereby improving the accuracy of the test results.

[0019] 2. In some embodiments, a sealing ring is provided between both electrodes and the side wall of the container to ensure the sealing of the accommodating cavity and further prevent diaphragm contamination.

[0020] 3. In some embodiments, the electrolyte storage tank is in continuous communication with the containment cavity, and the discharged electrolyte can be recycled to avoid waste and is environmentally friendly.

[0021] 4. In some embodiments, the container may be placed in an incubator to evaluate the high and low temperature characteristics of diaphragms of different materials and types, thereby improving the versatility of the device. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of a diaphragm testing device;

[0023] In the figure: container 1, accommodating cavity 11, electrode 2, lower electrode 2a, upper electrode 2b, first sealing ring 21, second sealing ring 22, electrolyte storage tank 3, electrolyte pump 4, outlet valve 51, inlet valve 52. Detailed Implementation

[0024] The following are specific embodiments of the present invention, and the technical solution of the present invention will be further described in conjunction with the accompanying drawings. However, the present invention is not limited to these embodiments.

[0025] A diaphragm testing device, firstly as follows Figure 1 As shown, it includes at least two electrodes 2. In some embodiments, only two electrodes 2 are required. The material of the two electrodes 2 can be stainless steel. The two electrodes 2 can be configured according to... Figure 1 The electrodes can be arranged vertically or horizontally, as long as the two electrodes 2 are parallel. Each electrode 2 has an electrode lead wire, which is electrically connected to the electrochemical workstation. Figure 1 The electrode 2 is not shown in the diagram and can be any existing device capable of detecting the impedance between the two electrodes 2, such as a resistivity meter. In use, the diaphragm that has absorbed the electrolyte is placed between the two electrodes 2, and both sides of the diaphragm are controlled to be in contact with the electrodes 2 respectively. The electrical properties of the two electrodes and the diaphragm can be obtained through an electrochemical workstation, and the electrical properties of the diaphragm can be further obtained.

[0026] Secondly, based on this, in this application, to avoid operational inconvenience, contamination, wrinkles, and other problems that occur when transferring the wet diaphragm that has absorbed the electrolyte between the two electrodes 2, the diaphragm testing device is further modified as follows:

[0027] First, such as Figure 1 As shown, a container 1 is provided. The shape of the container 1 is not limited and can be cylindrical, prismatic, etc. In some embodiments, the container 1 is cylindrical in order to fit the shape of the electrode 2. The material of the container 1 is preferably polytetrafluoroethylene.

[0028] The container 1 has at least a sidewall, which forms a cavity 11 between the sidewall and an electrode 2. Since the purpose of the cavity 11 is to house the diaphragm and electrolyte, and the diaphragm should be laid flat on the electrode 2, in some embodiments, the container 1 is preferably vertically designed, and the two electrodes 2 are preferably arranged vertically, with the sidewall of the container 1 serving as the sidewall of the cavity 11, and the electrode 2 serving as the bottom of the cavity 11. For ease of explanation, the electrode 2 serving as the bottom of the cavity 11 is referred to as the lower electrode 2a.

[0029] The accommodating cavity 11 should not leak, therefore the side edge of the lower electrode 2a is sealed to the side wall of the container 1. The method of sealing is not limited. In some embodiments, a first sealing ring 21 is provided between the side edge of the lower electrode 2a and the side wall of the container 1 to achieve a seal. The first sealing ring 21 is preferably made of fluororubber.

[0030] The container 1 has an open end located above the lower electrode 2a to facilitate the filling of the diaphragm. The end of the container 1 located below the lower electrode 2a can also be open, or in some embodiments, such as... Figure 1 As shown, the lower end of container 1 is provided with a receiving plate, and the lower electrode 2a is disposed on the receiving plate to assist the lower electrode 2a in receiving the diaphragm and electrolyte. In addition, the receiving plate is also provided with small holes for the electrode leads of the lower electrode 2a to extend out.

[0031] Once a non-leaking accommodating cavity 11 is formed at the bottom, electrolyte can be directly introduced into the accommodating cavity 11 through the opening at the top of container 1. This allows the diaphragm to be immersed in the electrolyte on the lower electrode 2a, improving the adhesion between the wet diaphragm and the lower electrode 2a. Furthermore, during operation, the dry diaphragm can be transferred onto the lower electrode 2a first, and then the electrolyte can be introduced. The transfer of the dry diaphragm is more convenient and less prone to contamination and wrinkles, avoiding a series of problems in the wet diaphragm transfer process in the prior art.

[0032] Second, after the diaphragm is soaked in electrolyte within the accommodating cavity 11 and on the lower electrode 2a, excess electrolyte needs to be drained. Therefore, as Figure 1 As shown, the diaphragm testing device also includes an electrolyte storage tank 3 connected to the accommodating cavity 11, and a first control component for controlling the flow of electrolyte from the accommodating cavity 11 to the electrolyte storage tank 3. To control the communication between the electrolyte storage tank 3 and the accommodating cavity 11, the portion of the side wall of the container 1 located within the accommodating cavity 11 has an outlet for electrolyte to flow out of the accommodating cavity 11. The electrolyte storage tank 3 has an inlet for electrolyte to flow in. The outlet and inlet are connected via a discharge pipe, and a sealing structure is also provided between the inner wall of the outlet and the discharge pipe to prevent leakage. The horizontal plane of the outlet of the accommodating cavity 11 should be no lower than, and preferably higher than, the horizontal plane of the inlet of the electrolyte storage tank 3, so that electrolyte in the accommodating cavity 11 can flow into the electrolyte storage tank 3 under the liquid level difference. To ensure sufficient discharge of electrolyte, the horizontal plane of the outlet of the container 1 should be higher than, but as close as possible to, the horizontal plane of the lower electrode 2a. At this time, the first control component includes an outlet valve 51 installed on the outlet pipe to control whether the electrolyte flows. By opening the outlet valve 51, the electrolyte can flow from the containment cavity 11 to the electrolyte storage tank 3 under the liquid level difference.

[0033] Based on this, a wet diaphragm that has absorbed the electrolyte can be obtained and laid flat on the lower electrode 2a. In order to further conduct electrical performance tests, another electrode 2 needs to be superimposed on the wet diaphragm. For ease of explanation, this electrode 2 will be referred to as the upper electrode 2b.

[0034] The stacking method of the upper electrode 2b is not limited. In some embodiments, to ensure the accuracy of the test results and to make the testing device applicable to diaphragms of different thicknesses, it is necessary to control the upper electrode 2b to be movably disposed in the receiving cavity 11 along the thickness direction of the diaphragm, so that the upper electrode 2b can be parallel to the lower electrode 2a and attached to both sides of the wet diaphragm. The specific design method is not limited. In some embodiments, such as Figure 1 As shown, a second sealing ring 22 is provided between the upper electrode 2b and the side wall of the container 1 with an interference fit. The second sealing ring 22 is preferably made of fluororubber. The side wall of the container 1 can be used to restrict the movement direction of the upper electrode 2b to ensure the accuracy of its movement direction. The design of the movable second sealing ring 22 is not limited and can refer to the piston structure in the syringe in the prior art. At the same time, the setting of the second sealing ring 22 can also form a sealed space between the accommodating cavity 11 and the upper electrode 2b, further preventing diaphragm contamination; and when the upper electrode 2b moves towards the diaphragm, it compresses the volume of the sealed space, which can promote the discharge of electrolyte and air in the sealed space into the electrolyte storage tank 3, effectively discharging electrolyte and air from the accommodating cavity 11, ensuring tight contact between the wet diaphragm and the electrode, and further improving the accuracy of the detection results. Therefore, the upper electrode 2b can also be understood as part of the first control component. When in use, firstly, the outlet valve 51 is opened to discharge the electrolyte by utilizing the liquid level difference; secondly, the upper electrode 2b is moved downwards, and the upper electrode 2b will come into close contact with the lower electrode 2a to further squeeze out excess electrolyte.

[0035] To further ensure the accuracy of the movement direction of the upper electrode 2b, in some embodiments, at least two guide strips are provided on the side wall of the container 1 in the vertical direction, and the two guide strips are symmetrically arranged with the central axis of the container 1 as the center; the second sealing ring 22 of the upper electrode 2b is provided with a groove that cooperates with the two guide strips respectively, and the accuracy of the movement of the upper electrode 2b is controlled by the cooperation of the guide strips and the grooves. In some embodiments, a detachable cover can be added to the container 1, with a through hole in the center of the cover, and the upper electrode 2b is provided with a connecting post that can pass through the through hole. At the same time, a knob is provided on the cover through a rotating bearing, and the connecting post is threadedly connected to the knob. In use, rotating the knob causes the connecting post and the upper electrode 2b to move axially under the action of the threaded connection and the limiting action of the guide strips.

[0036] In some implementations, such as Figure 1As shown, the accommodating cavity 11 is circulated with the electrolyte storage tank 3. In addition to the outlet and outlet pipe mentioned above, an inlet is also provided on the side wall of the container 1. The horizontal plane of the inlet is higher than that of the outlet. The inlet is connected to the electrolyte storage tank 3 through an inlet pipe, which is equipped with an inlet valve 52 to control the flow of electrolyte. A second control component is also included to control the flow of electrolyte from the electrolyte storage tank 3 to the accommodating cavity 11. The structure of the second control component is not limited; for example, an electrolyte pump 4 can be installed on the inlet pipe. In use, after closing the outlet valve 51 on the outlet pipe and opening the inlet valve 52 on the inlet pipe, the electrolyte is pumped from the electrolyte storage tank 3 to the accommodating cavity 11 by the electrolyte pump 4. This allows for the recycling of electrolyte, avoiding waste and being environmentally friendly.

[0037] In some embodiments, the diaphragm testing apparatus further includes a temperature chamber for housing the container 1. Figure 1 Not shown, its structure is not limited and can be any existing device capable of accommodating container 1 and having temperature regulation function. Container 1 can be placed in a temperature chamber to evaluate the high and low temperature characteristics of diaphragms of different materials and types, thereby improving the versatility of the device.

[0038] The method for testing the tortuosity of a diaphragm using this diaphragm testing device includes the following steps:

[0039] (1) Cut a multilayer membrane sample that is slightly smaller than the inner diameter of container 1;

[0040] (2) Remove the upper electrode 2b and place the dry diaphragm on the lower electrode 2a, ensuring that the diaphragm sample is wrinkle-free;

[0041] (3) Place the upper electrode 2b inside the container 1, parallel to the lower electrode 2a;

[0042] (4) Close the outlet valve 51 on the outlet tube, open the inlet valve 52 on the inlet tube, and draw the electrolyte into the accommodating cavity 11. The electrolyte level must be higher than the diaphragm to ensure that the diaphragm is immersed in it. Then close the inlet valve 52 on the inlet tube.

[0043] (5) After the diaphragm is soaked in the electrolyte for 10 minutes, open the outlet valve 51 on the outlet tube to let the excess electrolyte flow into the electrolyte storage tank 3;

[0044] (6) Connect the electrode leads to the electrochemical workstation;

[0045] (7) Press down the upper electrode 2b to contact the diaphragm and test the EIS impedance spectrum of the diaphragm;

[0046] (8) The EIS impedance spectra of membranes with different numbers of layers were tested multiple times to obtain the resistance values ​​of membranes with different numbers of layers. The test results were linearly fitted, and the slope was the lithium-ion diffusion impedance R of the membrane.ion .

[0047] (9) According to the formula τ=(R ion The tortuosity τ of the diaphragm is calculated using the formula *S*ε*κ) / L. Here, L is the diaphragm thickness, S is the electrode area, κ is the intrinsic conductivity of the electrolyte, and ε is the diaphragm porosity.

[0048] Using the testing apparatus of this application, the ionic impedance of the separator is obtained through electrochemical impedance spectroscopy and fitting, and then the separator tortuosity is calculated. This allows for a more accurate evaluation of the separator's characteristics and quantitative analysis of the impact of materials, adhesive coating amount, ceramic coating amount, and manufacturing process on separator performance. This contributes to a deeper understanding of the factors influencing separator performance, thereby enabling further selection of separators and improving the performance of lithium-ion batteries.

[0049] The specific embodiments described herein are merely illustrative examples illustrating the spirit of this utility model. Those skilled in the art to which this utility model pertains may make various modifications or additions to the described specific embodiments or use similar methods to substitute them, without departing from the spirit of this utility model or exceeding the scope defined by the appended claims.

Claims

1. A diaphragm testing device, comprising a container (1) having at least sidewalls, at least two electrodes (2), and an electrochemical workstation electrically connected to the electrodes (2); characterized in that: At least one of the electrodes (2) has its side edge sealed to the side wall of the container (1) so that a accommodating cavity (11) for accommodating the diaphragm and electrolyte is formed between the electrode (2) and the side wall of the container (1). The diaphragm testing device also includes an electrolyte storage tank (3) connected to the accommodating cavity (11) and a first control element for controlling the flow of electrolyte from the accommodating cavity (11) to the electrolyte storage tank (3).

2. The diaphragm testing device according to claim 1, characterized in that: The accommodating cavity (11) is in cyclic communication with the electrolyte storage tank (3), and also includes a second control component for controlling the electrolyte to flow from the electrolyte storage tank (3) to the accommodating cavity (11).

3. The diaphragm testing device according to claim 1, characterized in that: A first sealing ring (21) is provided between the electrode (2) used to form the accommodating cavity (11) and the side wall of the container (1) with interference fit.

4. The diaphragm testing device according to claim 1, characterized in that: The side wall of the container (1) is provided with an outlet for the electrolyte to flow out of the accommodating cavity (11), and the electrolyte storage tank (3) is provided with an inlet for the electrolyte to flow in. The outlet and the inlet are connected by a discharge pipe, and the horizontal plane of the outlet is not lower than the horizontal plane of the inlet. The first control component includes a discharge valve (51) provided on the discharge pipe.

5. A diaphragm testing device according to claim 1 or 4, characterized in that: At least one of the electrodes (2) is movably disposed in the accommodating cavity (11) along the thickness direction of the diaphragm.

6. The diaphragm testing device according to claim 5, characterized in that: A second sealing ring (22) is provided between the movable electrode (2) and the side wall of the container (1) with an interference fit.

7. A diaphragm testing device according to claim 6, characterized in that: The first control element includes the movable electrode (2).

8. A diaphragm testing device according to claim 2, characterized in that: The second control component includes an electrolyte pump (4).

9. A diaphragm testing device according to claim 1, characterized in that: The container (1) has an opening at one end and a receiving plate at the other end, and the electrode (2) for forming the accommodating cavity (11) is disposed on the receiving plate.

10. A diaphragm testing device according to claim 1, characterized in that: It also includes a temperature chamber for containing the container (1).

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