A battery pole piece rebound test method and test device

Abstract

The present invention relates to a battery electrode rebound test method and test device. The test method comprises the following steps: obtaining the initial thickness of the battery electrode; heating the battery electrode from the initial temperature to a set temperature, and keeping the temperature until the battery electrode thickness change rate is less than a%; obtaining the thickness of the battery electrode after rebound; and calculating the electrode rebound thickness based on the measured relevant parameters. The present invention also provides a battery electrode rebound test device, comprising: an electrode support plate for placing the battery electrode; a temperature sensor, arranged on the electrode support plate, for measuring the temperature of the battery electrode; a displacement sensor, for measuring the thickness of the battery electrode; a fixed beam, on which the displacement sensor is fixed; a heating and heat-insulating box, for rapidly heating and heat-insulating the battery electrode; the battery electrode, the electrode support plate, the temperature sensor, the displacement sensor and the fixed beam are all located in the heating and heat-insulating box. The present invention can achieve rapid and accurate measurement of the rebound amount of lithium-ion battery electrodes.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium batteries, and in particular to a battery pole piece rebound testing method and testing device. Background Art

[0002] Since their commercialization, lithium-ion batteries have expanded beyond the consumer electronics sector into power batteries and large-scale energy storage due to their significant advantages, such as high energy density, high output voltage, low self-discharge, and lack of memory effect. The production process for lithium-ion batteries primarily involves homogenization, coating, roller pressing, sheeting, stacking assembly, and pre-charging and formation. Each step requires extremely stringent manufacturing process requirements and environmental control.

[0003] Among them, pole piece rolling is a key step in the lithium-ion battery manufacturing process. Rolling not only effectively reduces the internal porosity of the active material, lowers the internal resistance of the lithium-ion battery, and improves the battery's cycling performance, but more importantly, it also increases the energy density of the lithium-ion battery. The battery energy density is generally controlled by the rolling process through the compaction density. If the compaction density is too low, the internal resistance of the pole piece will be high, which will affect the battery's energy density and lead to poor battery cycling performance. If the compaction density is too high, the active material particles are at risk of being crushed, which may hinder the lithium ion deintercalation process.

[0004] Pole piece rebound is the phenomenon in which the pole piece naturally rebounds in the opposite direction of rolling after being rolled. The rebound of the pole piece directly affects the pole piece compaction density, liquid retention and pole core shell assembly. If the pole piece rebounds too much, it will directly affect the normal progress of the subsequent battery process. Generally speaking, the pole piece begins to rebound 1 to 2 hours after rolling, and the entire rebound process will last for 24 to 48 hours. This is especially true for negative pole pieces, which require a longer time to fully rebound and remain stable thereafter. Only when the pole piece fully rebounds can the test results be guaranteed to be valid. However, the pole piece rebound amount is an important parameter for testing and evaluating intermediate products in the lithium-ion battery production process. Therefore, the natural rebound test method has the disadvantages of being time-consuming and inefficient. How to quickly and accurately measure the pole piece rebound amount is an issue that needs to be solved urgently. Summary of the Invention

[0005] The purpose of the present invention is to provide a battery pole piece rebound test method and test device to achieve rapid and accurate measurement of the rebound amount of lithium-ion battery pole pieces, provide a reference basis for the formulation of subsequent lithium-ion battery production process standards, and thus improve battery performance.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is as follows:

[0007] A battery electrode rebound test method includes the following steps:

[0008] Obtaining the initial thickness of the battery electrode after rolling;

[0009] The battery electrode is heated from the initial temperature to the set temperature, and kept warm until the thickness change rate of the battery electrode is less than a%, and the thickness of the battery electrode after rebound is obtained;

[0010] The rebound thickness of the battery electrode is obtained by calculating the initial thickness, initial temperature, set temperature and thickness of the battery electrode after rebound.

[0011] According to the above technical means, temperature is used as an acceleration factor to accelerate the rebound of the electrode by increasing the temperature. At the same time, the temperature increase brings about the thermal expansion of the material. Therefore, the temperature change is combined to calculate the rebound thickness of the battery electrode, thereby quickly and accurately realizing the measurement of the rebound amount of the lithium-ion battery electrode, providing a reliable reference basis for the subsequent formulation of lithium-ion battery production process standards, thereby effectively improving battery performance.

[0012] Preferably, the method comprises the following steps:

[0013] Obtain the initial thickness L0 of the battery electrode after rolling;

[0014] Heat the battery electrode from the initial temperature T0 to the set temperature T, and keep it warm until the thickness change rate of the battery electrode is less than a%, and obtain the thickness L of the battery electrode after rebound;

[0015] The calculation formula I of the battery electrode rebound thickness B is derived based on the linear expansion coefficient formula;

[0016] B=L-L0-a*L0(T-T0) (Ⅰ)

[0017] In formula I, L0 represents the initial thickness of the battery electrode, in μm; L represents the thickness of the battery electrode after rebound, in μm; a represents the linear expansion coefficient of the solid, T0 represents the initial temperature, in ℃; T represents the set temperature, in ℃; B represents the rebound thickness of the battery electrode, in μm.

[0018] Among them, the linear expansion coefficient a of the solid is not affected by the test temperature, so a is considered to be a constant.

[0019] Since the thickness of the battery electrode after heating is the sum of the battery electrode rebound thickness and the material expansion thickness, the formula between the battery electrode thickness and the battery electrode rebound thickness is derived according to the linear expansion coefficient formula, which effectively ensures the accuracy of the test results of the battery electrode rebound thickness.

[0020] Among them, because heating is used to accelerate the rebound of the battery electrode, the material of the battery electrode itself will expand due to heat. The thickness of the battery electrode after heating should be the sum of the rebound thickness and the material expansion thickness. Therefore, it is necessary to derive the calculation formula of the battery electrode rebound thickness based on the linear expansion coefficient formula.

[0021] Preferably, when the number of battery electrode samples N=2, the following steps are included:

[0022] Obtaining the initial thickness X1 of the battery electrode sample 1 and the initial thickness X2 of the battery electrode sample 2 after rolling;

[0023] Heat the battery electrode sample 1 from the initial temperature T0°C to the set temperature T1°C and keep it warm until the thickness change rate of the battery electrode sample 1 is less than a%, and obtain the thickness X of the battery electrode sample 1 after rebounding measured for the nth time. 1n ;

[0024] Heat the battery electrode sample 2 from the initial temperature T0°C to the set temperature T2°C and keep it warm until the thickness change rate of the battery electrode sample 2 is less than a%, and obtain the thickness X of the battery electrode sample 2 after rebounding measured for the nth time. 2n ; Wherein, n represents the number of times the battery electrode thickness is tested, and n is an integer ≥ 2;

[0025] According to the initial thickness X1, X2, T0℃, T1℃, T2℃, X 1n and X 2n Solve jointly to obtain the pole piece rebound thickness B0.

[0026] Since errors are inevitable during actual testing, in order to balance the speed and accuracy of data testing, the number of identical battery electrode samples, N, was set to 2, resulting in more accurate test results. If the number of samples, N, were greater than 2, while the accuracy of the test results would be further improved, the calculation process would become more complex. Taking all factors into consideration, the number of samples was set to 2, thus balancing the speed and accuracy of data testing. Furthermore, because battery electrode material expands differently under different temperature conditions, different heating temperatures were selected when heating the two battery electrode samples to improve the accuracy of the test results.

[0027] Preferably, the calculation formula II of the rebound thickness B0 of the battery electrode is derived according to the linear expansion coefficient formula;

[0028]

[0029] In formula II, X1 represents the initial thickness of the battery electrode sample 1, in μm; X2 represents the initial thickness of the battery electrode sample 2, in μm; X 1nIt represents the thickness of the battery electrode sample 1 after rebound measured for the nth time, in μm; X 2n It represents the thickness of the battery electrode sample 2 after rebound measured for the nth time, in μm; T1 represents the initial temperature, in °C; T2 represents the set temperature, in °C; B0 represents the rebound thickness of the battery electrode, in μm.

[0030] Since the thickness of the battery electrode after heating is the sum of the battery electrode rebound thickness and the material expansion thickness, the formula between the battery electrode thickness and the battery electrode rebound thickness is derived according to the linear expansion coefficient formula, which effectively ensures the accuracy of the test results of the battery electrode rebound thickness.

[0031] Preferably, when X1=X2, the rebound thickness B0 of the battery electrode is calculated using Formula III:

[0032]

[0033] In formula III, X1 represents the initial thickness of the battery electrode sample 1, in μm; X2 represents the initial thickness of the battery electrode sample 2, in μm; X 1n It represents the thickness of the battery electrode sample 1 after rebound measured for the nth time, in μm; X 2n It represents the thickness of the battery electrode sample 2 after rebound measured for the nth time, in μm; T1 represents the initial temperature, in °C; T2 represents the set temperature, in °C; B0 represents the rebound thickness of the battery electrode, in μm.

[0034] Since under actual test conditions, the thickness of the same battery electrode after rolling is generally the thickness required by the process, X1=X2, which further simplifies the calculation formula and greatly reduces the calculation amount and the complexity of the corresponding device design.

[0035] Preferably, the set temperature T is between 45°C and 150°C.

[0036] By controlling the set temperature between 45°C and 150°C, the rebound speed of the battery electrode is kept within a certain range, avoiding excessive expansion of the material caused by too high a temperature, which would affect the test accuracy of the rebound thickness of the battery electrode.

[0037] Preferably, the battery electrode thickness change rate a is calculated using formula IV;

[0038]

[0039] In Formula IV, X n and X n-1 It represents the thickness of the battery electrode sheet measured twice adjacently, both in μm; n represents the number of times the battery electrode sheet thickness is tested, and n is an integer ≥ 2;

[0040] Among them, when the battery electrode thickness change rate is less than 1%, that is, a=1, it is the end point of the battery electrode thickness test.

[0041] After many tests, we know that when the battery electrode thickness change rate is less than 1%, the battery electrode rebound end point can be used as the rebound thickness of the battery electrode to accurately obtain.

[0042] The present invention also provides a testing device based on the battery electrode rebound testing method of the present invention, comprising:

[0043] Pole plate, used to place battery poles;

[0044] A temperature sensor is provided on the electrode support plate and is used to measure the temperature of the battery electrode;

[0045] Displacement sensor, used to measure the thickness of battery pole pieces;

[0046] a fixed crossbeam, the displacement sensor being fixed on the fixed crossbeam;

[0047] Heating and insulation box, used for rapid heating and insulation of battery pole pieces;

[0048] The battery pole piece, pole piece support plate, temperature sensor, displacement sensor and fixed crossbeam are all located in the heating and heat preservation box.

[0049] According to the above technical means, by setting a pole piece support plate for placing battery pole pieces, setting a temperature sensor and a displacement sensor for real-time measurement of the temperature and thickness of the battery pole pieces, setting a fixed beam for fixing the displacement sensor, and setting a heating and insulation box, the pole piece support plate, temperature sensor, displacement sensor and fixed beam are all located therein, effectively ensuring the accuracy of the test results.

[0050] Preferably, the electrode plate supports include at least two to simultaneously measure multiple battery electrode plates;

[0051] A through hole is provided on the electrode support plate at a position for placing the battery electrode, and the displacement sensor is provided on the fixed beam at a position corresponding to the through hole to measure the thickness of the battery electrode.

[0052] By setting up multiple electrode support plates in the heating and insulation box, the measurement of multiple battery electrodes can be achieved simultaneously, thereby effectively improving the test efficiency; at the same time, by setting through holes on the electrode support plates for placing battery electrodes, and setting displacement sensors at positions corresponding to the through holes on the fixed beams, the accuracy of the battery electrode thickness test is effectively guaranteed.

[0053] Preferably, it also includes a control device electrically connected to the heating and insulation box, the temperature sensor and the displacement sensor.

[0054] By setting up a control device electrically connected to the heating and insulation box, the temperature sensor and the displacement sensor, the control device can realize the input of the set temperature, the temperature increase, and the display and recording of the real-time test data of the temperature sensor and the displacement sensor, which facilitates observation and operation.

[0055] Beneficial effects of the present invention:

[0056] 1) The battery electrode rebound test method of the present invention uses temperature as an acceleration factor to shorten the electrode rebound time by increasing the temperature, thereby improving the test efficiency. At the same time, due to the increase in temperature, the material expands due to heat. The thickness of the battery electrode after heating is the sum of the rebound thickness and the collision thickness. Therefore, when calculating the rebound amount of the battery electrode, the temperature change is combined to calculate the rebound thickness of the battery electrode, effectively ensuring the accuracy of the test results, providing a reliable reference basis for the subsequent formulation of lithium-ion battery production process standards, and thus effectively improving battery performance.

[0057] 2) The battery pole piece rebound test device of the present invention is provided with a temperature sensor and a displacement sensor to achieve real-time and accurate measurement of the temperature and thickness of the battery pole piece, and a fixed beam for fixing the displacement sensor is provided to ensure the stability of the displacement sensor, and a heating and insulation box is provided so that the pole piece support plate, temperature sensor, displacement sensor and fixed beam are all located therein, effectively avoiding the influence of the external environment on the test results, thereby ensuring the accuracy of the test results, and providing a reliable guarantee for the accurate testing of the battery pole piece rebound amount. In the field of lithium-ion battery technology, it has promotion and application value. BRIEF DESCRIPTION OF THE DRAWINGS

[0058] Figure 1 Schematic diagram of the structure of the battery electrode rebound testing device of the present invention;

[0059] Figure 2 This is a flow chart of the battery electrode rebound testing method of the present invention;

[0060] Among them, 1-battery electrode; 2-electrode plate, 21-through hole; 3-temperature sensor; 4-displacement sensor; 5-fixed beam; 6-heating and insulation box; 7-control device. DETAILED DESCRIPTION

[0061] The following describes the embodiments of the present invention with reference to the accompanying drawings and preferred embodiments. Those skilled in the art will readily appreciate the other advantages and benefits of the present invention from the disclosure herein. The present invention may also be implemented or applied through various other specific embodiments, and the various details in this specification may be modified or altered based on different viewpoints and applications without departing from the spirit of the present invention. It should be understood that the preferred embodiments are intended only to illustrate the present invention and are not intended to limit the scope of protection of the present invention.

[0062] It should be noted that the illustrations provided in the following embodiments are merely schematic illustrations of the basic concept of the present invention. Therefore, the illustrations only show components related to the present invention and are not drawn according to the number, shape, and size of components in actual implementation. In actual implementation, the type, quantity, and proportion of each component may be changed arbitrarily, and the component layout may also be more complex.

[0063] In the following description, numerous details are discussed to provide a more thorough explanation of the embodiments of the present application. However, it is obvious to those skilled in the art that the embodiments of the present application can be implemented without these specific details.

[0064] Example 1

[0065] like Figure 1 As shown, a battery electrode rebound testing device includes:

[0066] The electrode plate 2 is used to place the battery electrode 1, and a through hole 21 is provided at the position for placing the battery electrode 1;

[0067] The temperature sensor 3 is provided on the electrode support plate 2 and is used to measure the temperature of the battery electrode 1;

[0068] The displacement sensor 4 is used to measure the thickness of the battery electrode 1. The displacement sensor 4 is a laser displacement sensor. In this embodiment, two laser displacement sensors are used to align the through hole 21 with one electrode support plate 2 for laser beaming. The battery electrode 1 is placed at the through hole 21. The distance between the upper and lower surfaces of the battery electrode 1 is measured to calculate the thickness of the electrode. Alternatively, a fixed battery electrode placement table can be used to perform positioning and distance measurement using a single laser displacement sensor to calculate the thickness of the battery electrode.

[0069] A fixed beam 5, on which the displacement sensor 4 is fixed, is provided to improve the test accuracy and reliability;

[0070] The heating and heat preservation box 6 is used to quickly heat and control the temperature of the battery electrode 1;

[0071] The battery electrode 1, electrode support plate 2, temperature sensor 3, displacement sensor 4 and fixed beam 5 are all located in the heating and heat preservation box 6;

[0072] The heating and insulation box 6 is also provided with a control device 7 electrically connected to the temperature sensor 3 and the displacement sensor 4; wherein the control device 7 includes a temperature display and setting component, a test process and result display interface, a test program and parameter setting input, etc., which are used to realize the setting of test method related parameters and human-computer interaction of the interface display; the temperature sensor 3 is used to monitor the temperature in the heating and insulation box 6 in real time, and feed back to the heating module of the heating and insulation box for precise temperature control.

[0073] Example 2

[0074] like Figure 2 As shown, a method for testing the rebound of a battery electrode using the testing device in Example 1 includes the following steps:

[0075] S1. Select a coated negative electrode sheet and roll it through a double-roller press to a compaction density of 1.6 g / cc. After rolling, cut two battery electrode sheets of the same size and place them into the through holes 21 of the electrode support plates 2 in two heating and insulation boxes 6. Start the control device 7 to initialize and measure the initial thickness of the battery electrode sheets after rolling. The measurement shows that the thickness of both battery electrode sheets is X1 = 136 μm.

[0076] S2, using the temperature sensor in the heating and insulation box 6 to identify that the initial temperature of the two battery electrodes is T0 = 20 ° C, then heat the first battery electrode to the set temperature T1 = 80 ° C, and heat the second battery electrode to the set temperature T2 = 100 ° C. After heating, keep the temperature constant, and use a laser displacement sensor to measure the thickness of the first battery electrode and the second battery electrode every 30 minutes. The measurement results are shown in Table 1. The thickness of the first battery electrode after rebound is X 1n The thickness of the second battery electrode after rebound is X 2n , until (X 1n -X 1n-1 ) / X 1n-1 ≤1%, (X 2n -X 2n-1 ) / X 2n-1 When ≤1% (n is an integer ≥2), retain the last battery electrode thickness test result, that is, X 1n and X 2n ;

[0077] According to the calculation formula of battery electrode rebound thickness B0: The calculated average value of the rebound thickness of the first battery electrode sheet and the rebound thickness of the second battery electrode sheet is 11 μm.

[0078] Table 1 Test results of battery electrode thickness for each 30min

[0079] <![CDATA[X 1n ]]> <![CDATA[X 2n ]]> <![CDATA[(X 1n -X 1n-1 ) / X 1n-1 ]]> <![CDATA[(X 2n -X 2n-1 ) / X 2n-1 ]]> 0min 143 142 30min 146 144 2.10％ 1.41％ 60min 147 146 0.68％ 1.39％ 90 minutes 147 0.68％ Pole rebound (μm) 11 11

[0080] Comparative Example 1

[0081] The coated negative electrode sheet selected from S1 of Example 2 was rolled on a double-roller press to a compaction density of 1.6 g / cc. After rolling, 5 battery sheets of the same size were cut. After natural rebound for 72 hours, the thickness of the 5 battery sheets after rebound was tested. The results are shown in Table 2.

[0082] Table 2 Test results of battery electrode thickness at each 30-minute natural rebound

[0083]

[0084] From the comparative analysis of Table 1 and Table 2, it can be seen that the difference between the rebound thickness of the battery electrode obtained by the test calculation after the temperature-accelerated rebound and the rebound thickness of the battery electrode measured after 72 hours of natural rebound is ≤ 2μm, which proves that the temperature-accelerated method is used to accelerate the rebound of the battery electrode. At the same time, combined with the formula derived from the linear expansion coefficient formula, the rebound thickness of the battery electrode can be accurately and effectively tested and calculated, thereby providing a reliable reference basis for the formulation of subsequent lithium-ion battery production process standards, thereby improving battery performance. It has promotion and application value in the field of lithium-ion battery technology.

[0085] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit this application. Anyone skilled in the art may modify or alter the above embodiments without departing from the spirit and scope of this application. Therefore, any equivalent modifications or alterations made by a person of ordinary skill in the art without departing from the spirit and technical concepts disclosed in this application shall be encompassed by the claims of this application.

Claims

1. A battery pole piece rebound test method, characterized in that: The following steps are involved: Obtaining the initial thickness of the battery electrode after rolling; Heat the battery electrode from the initial temperature to the set temperature and keep it warm until the thickness change rate of the battery electrode is less than a, and obtain the thickness of the battery electrode after rebound; According to the initial thickness, initial temperature, set temperature and thickness of the battery electrode after rebound, the rebound thickness of the electrode after eliminating the influence of thermal expansion is calculated in combination with the thermal expansion coefficient of the material; Calculation formula; （Ⅰ）， In formula I, L0 represents the initial thickness of the battery electrode, in μm; L represents the thickness of the battery electrode after rebound, in μm; a represents the linear expansion coefficient of the solid, T0 represents the initial temperature, in °C; T represents the set temperature, in °C; B represents the rebound thickness of the battery electrode, in μm; When the number of battery electrode samples N=2, the following steps are included: Obtaining the initial thickness X1 of the battery electrode sample 1 and the initial thickness X2 of the battery electrode sample 2 after rolling; Heat the battery electrode sample 1 from the initial temperature T0°C to the set temperature T1°C and keep it warm until the thickness change rate of the battery electrode sample 1 is less than a. Obtain the thickness X of the battery electrode sample 1 after rebounding measured for the nth time. 1n ; Heat the battery electrode sample 2 from the initial temperature T0°C to the set temperature T2°C and keep it warm until the thickness change rate of the battery electrode sample 2 is less than a. Obtain the thickness X of the battery electrode sample 2 after rebounding measured for the nth time. 2n ; Wherein, n represents the number of times the battery electrode thickness is tested, and n is an integer ≥ 2; According to the initial thickness X1, X2, T0℃, T1℃, T2℃, X 1n and X 2n The combined solution is used to obtain the electrode rebound thickness B0; the calculation formula II for the battery electrode rebound thickness B0 is as follows: （Ⅱ）， In formula II, X 1n It represents the thickness of the battery electrode sample 1 after rebound measured for the nth time, in μm; X 2n It represents the thickness of the battery electrode sample 2 after rebound measured for the nth time, in μm.

2. The battery pole piece rebound test method according to claim 1, characterized in that: When X1= X2, use Formula III to calculate the battery electrode rebound thickness B0: （Ⅲ）。 3. The battery pole piece rebound test method according to claim 1, characterized in that: The set temperature T is between 45°C and 150°C.

4. The battery pole piece rebound test method according to claim 1, characterized in that: Formula IV is used to calculate the battery electrode thickness change rate a; （Ⅳ） In Formula IV, X n and X n-1 Indicates the thickness of the battery electrode measured twice adjacently, both in μm; Among them, when the battery electrode thickness change rate is less than 1%, that is, a=1%, it is the test end point of the battery electrode thickness.

5. A testing device based on the battery pole piece rebound testing method according to any one of claims 1 to 4, characterized in that: include: A pole piece support plate (2) for placing the battery pole piece (1); A temperature sensor (3), which is arranged on the electrode support plate (2) and is used to measure the temperature of the battery electrode (1); A displacement sensor (4) for measuring the thickness of the battery electrode (1); A fixed crossbeam (5), the displacement sensor (4) being fixed on the fixed crossbeam (5); A heating and heat-insulating box (6) is used to quickly heat and keep the battery pole piece (1) warm; The battery pole piece (1), pole piece support plate (2), temperature sensor (3), displacement sensor (4) and fixed crossbeam (5) are all located in the heating and heat preservation box (6).

6. The testing device according to claim 5, characterized in that: The electrode support plates (2) include at least two to enable the measurement of multiple battery electrodes at the same time; A through hole (21) is provided on the electrode support plate (2) at a position for placing the battery electrode (1), and the displacement sensor (4) is provided on the fixed crossbeam (5) at a position corresponding to the through hole (21) to measure the thickness of the battery electrode (1).

7. The testing device according to claim 5, characterized in that: It also includes a control device (7) electrically connected to the heating and heat-insulating box (6), the temperature sensor (3) and the displacement sensor (4).

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