Infiltration rate testing method and device

Abstract

The invention provides an infiltration rate testing method and testing device, and belongs to the technical field of secondary batteries. The test method can accurately measure the infiltration rate of the to-be-tested structure.

Description

Technical Field

[0001] The present invention belongs to the technical field of secondary batteries, and particularly relates to a method and a device for testing the infiltration rate. Background Art

[0002] The infiltration of the electrolyte plays an important role in the performance of lithium batteries. Insufficient infiltration will lead to an increase or blockage of the lithium ion diffusion path, seriously affecting the capacity and interface quality of lithium ion batteries. The existing technologies mainly focus on the research of the infiltration rate of the negative electrode sheet or the separator, such as the wetting angle and the hanging climbing method. Most of the existing invention patents on the infiltration rate research are based on the above infiltration research methods.

[0003] The above methods have the following problems in practical applications: The compaction of the negative electrode sheet, the porosity of the separator, and the viscosity and surface tension of the electrolyte are the main influencing mechanisms of the infiltration rate. However, there are many production processes for lithium batteries. Considering only the properties of the negative electrode sheet, the separator, and the electrolyte is difficult to get rid of the influence of the process. In addition, the existing professional testing equipment is relatively complex and expensive, such as high-frame rate cameras, which is not conducive to research and promotion. Based on this, in the existing testing methods, visual inspection or manual shooting methods are mostly used. Different samples and different methods are difficult to ensure the accuracy of the test. Therefore, it is necessary to design a high-precision method for testing the infiltration rate and a testing device for implementing the testing method. Summary of the Invention

[0004] The present invention aims to solve at least one of the technical problems in the related technologies to some extent. For this purpose, an embodiment of the present invention provides a method and a device for testing the infiltration rate.

[0005] An embodiment of the present invention provides a method for testing the infiltration rate, including the following steps:

[0006] S1. Suspend the structure to be tested on the inner top surface of the cover of the electronic analytical balance, wherein the structure to be tested includes a core package, an electrode sheet or a separator, and the distance between the bottom of the structure to be tested and the inner top surface of the cover is h1;

[0007] S2. Place the measuring tool containing the electrolyte on the weighing pan of the electronic analytical balance, and zero the electronic analytical balance, wherein the distance between the liquid surface of the electrolyte and the inner top surface of the cover is h2, and the distance between the bottom of the measuring tool and the inner top surface of the cover is h3;

[0008] S3. Place the structure to be tested in the electrolyte, and keep h3>h1>h2; at the same time, record the infiltration time t of the structure to be tested and the reading -m of the electronic analytical balance corresponding to the infiltration time t;

[0009] S4. Take the opposite of the reading -m of the electronic analytical balance to obtain the curve of the liquid absorption mass m varying with the wetting time t; then perform a linear fit with m 2 = μt to obtain the wetting rate μ of the structure to be measured.

[0010] The advantages and technical effects brought by the test method of the embodiment of the present invention are as follows:

[0011] (1) When the structure to be measured is a pole piece or a separator, the test method of the embodiment of the present invention can consider the wetting rate of a single factor, such as the wetting rate of the positive electrode, negative electrode or separator; when the structure to be measured is a core package, it can comprehensively consider the wetting rates between the positive and negative pole pieces, the separator and the electrolyte. It has a wide range of applicable objects and flexible test methods.

[0012] (2) During the test process of step S3, it is always necessary to ensure that h3>h1>h2, so that the bottom of the structure to be measured is always suspended in the electrolyte and does not contact the bottom of the measuring tool, thereby ensuring the natural wetting of the structure to be measured, ensuring the accuracy of the liquid absorption mass m, and ultimately ensuring the accuracy of the wetting rate μ.

[0013] (3) In step S3, it is necessary to record both the wetting time t of the structure to be measured and the reading -m of the electronic analytical balance corresponding to the wetting time t, that is, t and -m have a one-to-one correspondence, so as to ensure the accuracy of the wetting rate μ.

[0014] (4) In step S2, the electronic analytical balance is zeroed. Therefore, after the structure to be measured wets the electrolyte in step S3, the mass of the electrolyte in the measuring tool gradually decreases, and the reading of the electronic analytical balance is negative and gradually decreases. Therefore, in step S4, taking the opposite of the reading -m of the electronic analytical balance, the obtained liquid absorption mass m is the mass of the electrolyte adsorbed by the structure to be measured. Since the corresponding wetting time is also recorded while measuring the liquid absorption mass, the curve of the liquid absorption mass m varying with the wetting time t can be obtained, and then by performing a linear fit with m 2 = μt, the wetting rate μ of the structure to be measured can be obtained. The above test process for the liquid absorption mass m is relatively simple, making the test process of the wetting rate μ simple and convenient.

[0015] (5) The main structures of the test equipment required for the test method of the embodiment of the present invention are an electronic analytical balance and a timer, and no expensive components are needed. Therefore, the overall cost of the test equipment is not high, making the test method of the embodiment of the present invention suitable for industrial promotion.

[0016] In some embodiments, the accuracy of the electronic analytical balance is above one-thousandth.

[0017] In some embodiments, the distance between the bottom of the structure to be measured and the liquid level of the electrolyte is 4 - 6 mm.

[0018] An embodiment of the present invention also provides a wetting rate testing device, including:

[0019] An electronic analytical balance, a measuring tool, a hanging tool, and a timer;

[0020] The measuring tool can be placed on the weighing pan of the electronic analytical balance, and the measuring tool can hold electrolyte;

[0021] The upper end of the hanging tool is connected to the inner top surface of the cover of the electronic analytical balance, and the lower end of the hanging tool is connected to the structure to be tested, where the structure to be tested includes a core package, a pole piece, or a separator;

[0022] The timer is used to record the wetting time of the structure to be tested.

[0023] The advantages and technical effects brought by the testing device of the embodiment of the present invention are:

[0024] (1) The testing device of the embodiment of the present invention is used to test the wetting rate, and the test result is highly accurate.

[0025] (2) The testing device of the embodiment of the present invention has a simple structure, is convenient to operate, and is not expensive.

[0026] In some embodiments, the cover and the measuring tool are transparent.

[0027] In some embodiments, the testing device further includes a controller, and the controller is electrically connected to the electronic analytical balance and the timer. Description of the Drawings

[0028] Figure 1 is a schematic structural diagram of the testing device of the embodiment of the present invention;

[0029] Figure 2 is a curve of the liquid absorption mass m changing with the wetting time t obtained by the wetting rate testing method of Embodiment 1;

[0030] Figure 3 is the m obtained by the wetting rate testing method of Embodiment 1 2 = μt linear fitting diagram.

[0031] Description of the Reference Numerals:

[0032] 1 - Electronic analytical balance, 11 - Weighing pan, 12 - Cover, 2 - Measuring tool, 3 - Hanging tool, 4 - Timer, 5 - Electrolyte, 6 - Structure to be tested. Detailed Embodiments

[0033] Embodiments of the present invention will be described in detail below, and examples of the embodiments are shown in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to explain the present invention and should not be construed as limiting the present invention.

[0034] An embodiment of the present invention provides a method for testing the infiltration rate, including the following steps:

[0035] S1. Suspend the structure to be tested on the inner top surface of the cover of the electronic analytical balance, where the structure to be tested includes a core package, a pole piece or a separator, and the distance between the bottom of the structure to be tested and the inner top surface of the cover is h1;

[0036] S2. Place a measuring tool containing the electrolyte on the weighing pan of the electronic analytical balance, and zero the electronic analytical balance. Wherein, the distance between the liquid level of the electrolyte and the inner top surface of the cover is h2, and the distance between the bottom of the measuring tool and the inner top surface of the cover is h3;

[0037] S3. Place the structure to be tested in the electrolyte, and keep h3>h1>h2; at the same time, record the infiltration time t of the structure to be tested and the reading -m of the electronic analytical balance corresponding to the infiltration time t;

[0038] S4. Take the opposite number of the reading -m of the electronic analytical balance to obtain a curve of the liquid absorption mass m changing with the infiltration time t; then perform a linear fit with m 2 =μt to obtain the infiltration rate μ of the structure to be tested.

[0039] When the structure to be tested is a pole piece or a separator, the test method of the embodiment of the present invention can consider the infiltration rate of a single factor, such as the infiltration rate of the positive electrode, the negative electrode or the separator; when the structure to be tested is a core package, it can also comprehensively consider the infiltration rates between the positive and negative pole pieces, the separator and the electrolyte. The applicable objects are numerous and the test methods are flexible and variable.

[0040] During the test process of step S3, it is always necessary to keep h3>h1>h2, so that the bottom of the structure to be tested is always suspended in the electrolyte and does not touch the bottom of the measuring tool, thereby ensuring the natural infiltration of the structure to be tested, ensuring the accuracy of the liquid absorption mass m, and ultimately ensuring the accuracy of the infiltration rate μ.

[0041] In step S3, it is necessary to record the infiltration time t of the structure to be tested and the reading -m of the electronic analytical balance corresponding to the infiltration time t at the same time, that is, t and -m are in a one-to-one correspondence relationship, so as to ensure the accuracy of the infiltration rate μ.

[0042] In step S2, the electronic analytical balance is zeroed. Therefore, after the structure to be tested is immersed in the electrolyte in step S3, the mass of the electrolyte in the measuring tool gradually decreases, and the reading of the electronic analytical balance is negative and gradually decreases. Thus, in step S4, the opposite of the reading -m of the electronic analytical balance is taken, and the liquid absorption mass m obtained is the mass of the electrolyte adsorbed by the structure to be tested. Since the corresponding immersion time is recorded while measuring the liquid absorption mass, a curve of the liquid absorption mass m varying with the immersion time t can be obtained, and then with m 2 = μt for linear fitting, the immersion rate μ of the structure to be tested can be obtained. The above process of measuring the liquid absorption mass m is relatively simple, making the process of measuring the immersion rate μ simple and convenient.

[0043] The main structures of the testing equipment required for the testing method of the embodiment of the present invention are an electronic analytical balance and a timer, without expensive components. Therefore, the overall cost of the testing equipment is not high, making the testing method of the embodiment of the present invention suitable for industrial promotion.

[0044] In some embodiments, the precision of the electronic analytical balance is above one-thousandth. This can improve the accuracy of the measured liquid absorption mass m, thereby improving the accuracy of the immersion rate μ.

[0045] In some embodiments, the distance between the bottom of the structure to be tested and the liquid level of the electrolyte is 4 - 6 mm, such as 4 mm, 4.5 mm, 5 mm, 5.5 mm, 6 mm, etc. This can ensure that during the testing process of step S3, h3 > h1 > h2 can always be maintained. It can prevent the bottom of the structure to be tested from exposing above the liquid level of the electrolyte before the structure to be tested is saturated with immersion as the immersion time extends.

[0046] The embodiment of the present invention also provides an immersion rate testing device, as Figure 1 shown, including:

[0047] An electronic analytical balance 1, a measuring tool 2, a hanging tool 3, and a timer 4;

[0048] The measuring tool 2 can be placed on the weighing pan 11 of the electronic analytical balance 1, and the electrolyte 5 can be placed in the measuring tool 2;

[0049] The upper end of the hanging tool 3 is connected to the inner top surface of the cover body 12 of the electronic analytical balance 1, and the lower end of the hanging tool 3 is connected to the structure to be tested 6, where the structure to be tested 6 includes a core package, a pole piece, or a separator;

[0050] The timer 4 is used to record the immersion time of the structure to be tested 6.

[0051] The testing device of the embodiment of the present invention is used to test the immersion rate, and the test result has high accuracy. In addition, the testing device of the embodiment of the present invention has a simple structure, convenient operation, and is not expensive.

[0052] In some embodiments, the cover 12 and the measuring tool 2 are transparent. The height of the electrolyte liquid level in the measuring tool and the immersion of the bottom of the structure to be measured in the electrolyte can be observed manually, so as to ensure that h3 > h1 > h2 in step S3.

[0053] In some embodiments, the testing device may further include a controller (not shown in the figure), which is electrically connected to the electronic analytical balance 1 and the timer 4. The controller can automatically collect the time recorded by the timer and the corresponding reading -m of the electronic analytical balance at this time, and can take the opposite of the reading -m of the electronic analytical balance to obtain the liquid absorption mass m, and further obtain the curve of the liquid absorption mass m changing with the wetting time t. It can also automatically perform a linear fit with m 2 = μt to obtain the wetting rate μ of the structure to be measured, which is beneficial to improving the automation degree of the testing method and facilitating industrial promotion. Moreover, the controller collects information in a timely manner, which can ensure the one - to - one correspondence between the wetting time t and the reading -m of the electronic analytical balance, and ultimately is beneficial to improving the accuracy of the wetting rate μ test result.

[0054] The present invention will be described in detail below with reference to the embodiments and the drawings.

[0055] Embodiment 1

[0056] A wetting rate testing device includes:

[0057] An electronic analytical balance 1 with a precision of one - thousandth, a measuring tool 2, a hanging tool 3, a timer 4, and a controller;

[0058] The cover 12 of the electronic analytical balance 1 is made of transparent acrylic material.

[0059] The measuring tool 2 is a transparent glass beaker. The measuring tool 2 can be placed on the weighing pan 11 of the electronic analytical balance 1, and the electrolyte 5 can be placed in the measuring tool 2.

[0060] The upper end of the hanging tool 3 is connected to the inner top surface of the cover 12 of the electronic analytical balance 1, and the lower end of the hanging tool 3 is connected to the structure to be measured 6, where the structure to be measured 6 is a core package, a pole piece, or a separator.

[0061] The timer 4 is used to record the wetting time of the structure to be measured 6.

[0062] The controller is electrically connected to the electronic analytical balance 1 and the timer 4.

[0063] Embodiment 2

[0064] The testing device of Embodiment 1 is used to explore the influence of different hot - pressing pressures on the wetting rate of the core package. During the implementation process, three pressure gradients are considered, namely pressures of 7 tons, 8 tons, and 9 tons.

[0065] The specific steps are as follows:

[0066] (1) Provide the structure 6 to be tested. The structure 6 to be tested is one of the following three core packages: a lithium battery core package made under a hot pressing pressure of 7 tons (denoted as 7T), a lithium battery core package made under a hot pressing pressure of 8 tons (denoted as 8T), and a lithium battery core package made under a hot pressing pressure of 9 tons (denoted as 9T).

[0067] (2) Hang the structure 6 (7T) to be tested on the inner top surface of the cover 12 of the electronic analytical balance 1. Among them, the distance between the bottom of the structure 6 (7T) to be tested and the inner top surface of the cover 12 is h1.

[0068] (3) Place the measuring tool 2 containing the electrolyte 5 on the weighing pan 11 of the electronic analytical balance 1, and zero the electronic analytical balance 1. Among them, the distance between the liquid surface of the electrolyte 5 and the inner top surface of the cover 12 is h2, and the distance between the bottom of the measuring tool 2 and the inner top surface of the cover 12 is h3.

[0069] (4) Place the structure 6 (7T) to be tested in the electrolyte 5, and keep h3>h1>h2; at the same time, record the infiltration time t of the structure 6 (7T) to be tested and the reading -m of the electronic analytical balance 1 corresponding to the infiltration time t.

[0070] (5) Take the opposite of the reading -m of the electronic analytical balance 1 to obtain the curve of the liquid absorption mass m changing with the infiltration time t; then perform a linear fit with m 2 =μt to obtain the infiltration rate μ of the structure 6 (7T) to be tested.

[0071] (6) Take out the structure 6 (7T) from the cover 12, and hang the structure 6 (8T) to be tested on the inner top surface of the cover 12 of the electronic analytical balance 1. Among them, the distance between the bottom of the structure 6 (8T) to be tested and the inner top surface of the cover 12 is h1.

[0072] (7) Replace the electrolyte 5 in the measuring tool 2 again, and keep the composition, content, added volume, and temperature of the electrolyte the same as those of the electrolyte 5 used in step (3). Place the measuring tool 2 after replacing the electrolyte 5 on the weighing pan 11 of the electronic analytical balance 1, and zero the electronic analytical balance 1. Among them, the distance between the liquid surface of the electrolyte 5 and the inner top surface of the cover 12 is h2, and the distance between the bottom of the measuring tool 2 and the inner top surface of the cover 12 is h3.

[0073] (8) Place the structure 6 (8T) to be tested in the electrolyte 5, and keep h3>h1>h2; at the same time, record the infiltration time t of the structure 6 (8T) to be tested and the reading -m of the electronic analytical balance 1 corresponding to the infiltration time t.

[0074] (9) Take the opposite of the reading -m of the electronic analytical balance 1 to obtain the curve of the liquid absorption mass m changing with the infiltration time t; then perform a linear fit with m 2Perform a linear fit with m = μt to obtain the infiltration rate μ of the structure 6(8T) to be measured.

[0075] (10) Take out the structure 6(8T) to be measured from the cover 12, and suspend the structure 6(9T) to be measured on the inner top surface inside the cover 12 of the electronic analytical balance 1. Here, the distance from the bottom of the structure 6(9T) to the inner top surface of the cover 12 is h1.

[0076] (11) Replace the electrolyte 5 in the measuring tool 2 again, and keep the composition, content, added volume, and temperature of the electrolyte the same as those of the electrolyte 5 used in step (3). Place the measuring tool 2 after replacing the electrolyte 5 on the weighing pan 11 of the electronic analytical balance 1, and zero the electronic analytical balance 1. Here, the distance from the liquid surface of the electrolyte 5 to the inner top surface of the cover 12 is h2, and the distance from the bottom of the measuring tool 2 to the inner top surface of the cover 12 is h3.

[0077] (12) Place the structure 6(9T) to be measured in the electrolyte 5, and keep h3 > h1 > h2; at the same time, record the infiltration time t of the structure 6(9T) to be measured and the reading -m of the electronic analytical balance 1 corresponding to the infiltration time t.

[0078] (13) Take the opposite of the reading -m of the electronic analytical balance 1 to obtain the curve of the liquid absorption mass m varying with the infiltration time t; then use m 2 = μt to perform a linear fit to obtain the infiltration rate μ of the structure 6(9T) to be measured.

[0079] The curves of the liquid absorption mass m of the structure 6(7T) to be measured, the structure 6(8T) to be measured, and the structure 6(9T) to be measured varying with time t are as Figure 2 shown. The m 2 = μt linear fit curves of the structure 6(7T) to be measured, the structure 6(8T) to be measured, and the structure 6(9T) to be measured are as Figure 3 shown, and their respective infiltration rates μ are shown in Table 1.

[0080] Table 1. Infiltration rates μ of the structure 6(7T) to be measured, the structure 6(8T) to be measured, and the structure 6(9T) to be measured

[0081] Infiltration rate μ Structure to be measured 6(7T) 0.419 Structure to be measured 6(7T) 0.376 Structure to be measured 6(7T) 0.298

[0082] As can be seen from Table 1, the infiltration rate μ of the structure 6(7T) to be measured is greater than the infiltration rate μ of the structure 6(8T) to be measured, and the infiltration rate μ of the structure 6(8T) to be measured is greater than the infiltration rate μ of the structure 6(9T) to be measured, indicating that in the range of 7T to 9T, the greater the hot pressing pressure, the smaller the infiltration rate of the obtained core package.

[0083] It can be understood that the test method of Embodiment 2 can not only evaluate the influence of the hot pressing pressure of the core roll on the liquid absorption rate of the core package, but also be used to evaluate the influence of other different manufacturing processes such as the compaction of the negative electrode on the liquid absorption rate of the core package. In addition, the test method of Embodiment 2 can not only test the wetting rate of the core package under different process parameters, but also consider the wetting rate of a single factor, such as the wetting rates of the positive and negative electrodes and the separator. For all the above situations, only the structure to be measured 6 needs to be changed. Preferably, like in Embodiment 2, a single-factor comparison is maintained among multiple samples of the structure to be measured 6, which can improve the effectiveness of the evaluation results.

[0084] In the present invention, the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples", etc. mean that the specific features, structures, materials, or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described can be combined in a suitable manner in any one or more embodiments or examples. In addition, without contradiction, those skilled in the art can combine and combine the different embodiments or examples described in this specification and the features of different embodiments or examples.

[0085] Although the embodiments of the present invention have been shown and described above, it can be understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those of ordinary skill in the art can make changes, modifications, substitutions, and variations to the above embodiments within the scope of the present invention.

Claims

1. A method for testing the infiltration rate, characterized in that: The following steps are involved: S1. Suspending the structure to be measured on the top surface of the cover of the electronic analytical balance, wherein the structure to be measured includes a core package, a pole piece or a diaphragm, and the distance between the bottom of the structure to be measured and the top surface of the cover is h1; S2. Place the measuring tool containing the electrolyte on the weighing pan of the electronic analytical balance and return the electronic analytical balance to zero, wherein the distance between the liquid surface of the electrolyte and the top surface of the cover is h2, and the distance between the bottom of the measuring tool and the top surface of the cover is h3; S3. placing the structure to be tested in the electrolyte, maintaining h3>h1>h2; while recording the infiltration time t of the structure to be tested and the reading -m of the electronic analytical balance corresponding to the infiltration time t; S4. Take the opposite number of the reading -m of the electronic analytical balance to obtain a curve of the liquid absorption mass m versus the infiltration time t; then m 2 =μt for linear fitting to obtain the wetting rate μ of the structure to be tested.

2. The testing method according to claim 1, characterized in that: The accuracy of the electronic analytical balance is above one thousandth.

3. The testing method according to claim 1, characterized in that: The distance between the bottom of the structure to be tested and the surface of the electrolyte is 4 to 6 mm.

4. A wetting rate testing device, characterized in that: include: Electronic analytical balance, measuring tools, hangers, timers; The measuring tool can be placed on the weighing pan of the electronic analytical balance, and the measuring tool can contain electrolyte; The upper end of the hanger is connected to the inner top surface of the cover of the electronic analytical balance, and the lower end of the hanger is connected to the structure to be measured, wherein the structure to be measured includes a core package, a pole piece or a diaphragm; The timer is used to record the infiltration time of the structure to be tested.

5. The testing device according to claim 4, characterized in that: The cover body is transparent.

6. The testing device according to claim 4, characterized in that: The gauge is transparent.

7. The testing device according to claim 4, characterized in that: The device also includes a controller which is electrically connected to the electronic analytical balance and the timer.

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