Method for relieving black spot wrinkles of PMMA (Polymethyl Methacrylate) gluing diaphragm lithium battery pole piece

Abstract

The invention discloses a method for retarding black spot wrinkles of a PMMA (Polymethyl Methacrylate) gluing diaphragm lithium battery pole piece, which comprises the following steps: S1, adjusting parameters of a winding machine, adjusting the distance between pole pieces and tabs according to different parameters, and winding a battery cell; s2, performing hot pressing on the wound roll core by using different hot pressing parameters; s3, the hot-pressed roll core is assembled, put into a shell and fully charged in a capacity grading mode; wherein the parameter of the winding machine is embossing pressure; the hot pressing parameters comprise temperature, pressure and time. Therefore, by selecting the most appropriate embossing pressure and hot pressing parameter, black spots and wrinkles on the lithium battery interface of the PMMA glued diaphragm can be relieved, so that the electrochemical performance and the safety performance of the battery are improved.

Description

Technical Field

[0001] The invention belongs to the technical field of lithium-ion battery manufacturing, and in particular relates to a method for alleviating black spot wrinkles on a PMMA-coated diaphragm lithium battery pole piece. Background Art

[0002] With the continuous advancement of science and technology, lithium-ion batteries have become one of the new generation of green, environmentally friendly, and recyclable new energy sources. They are widely used in various fields, with rapid development in the electric vehicle sector. Lithium batteries are batteries containing lithium (including metallic lithium, lithium alloys, lithium ions, and lithium polymers) in their electrochemical systems. During the lithium battery manufacturing process, the positive and negative electrode sheets and separators are typically assembled into a cell using winding or lamination equipment. PMMA separators have been widely used in lithium-ion batteries due to their cost and adhesion advantages.

[0003] At present, due to inconsistent battery performance or imperfect battery management systems, the proportion of batteries with reduced cycle life, reduced safety performance, and substandard capacity is becoming increasingly prominent. In particular, safety performance is related to whether lithium-ion batteries can be actually used. Therefore, improving the safety performance and quality consistency of battery cells has become a key breakthrough and also a difficulty. For batteries manufactured using the winding method, the probability of interface wrinkles and black spots appearing at the disassembly interface is relatively high (the rebound rate of the negative electrode is greater than the rebound rate of the positive electrode. Due to the different rebound rates of the positive and negative electrodes, when the rebound rate of the negative electrode is too large, the positive electrode sheet will exert a binding force on the negative electrode. Under the action of the binding force, the negative electrode will curl up, i.e., negative electrode wrinkles), which seriously affects the safety and electrochemical performance of the battery. Wrinkles will also cause lithium deposition. In the subsequent use of the lithium deposition area, lithium dendrites will further form, piercing the diaphragm and causing the battery to short-circuit. Therefore, how to slow down the interface wrinkles and black spots after battery capacity separation has become an important problem to be overcome. Summary of the Invention

[0004] In view of the defects of the prior art, the present invention proposes a method for alleviating black spot wrinkles on PMMA-coated diaphragm lithium battery pole pieces.

[0005] The present invention provides a method for alleviating black spot wrinkles on a PMMA-coated diaphragm lithium battery electrode, comprising the following steps:

[0006] S1, adjusting the embossing pressure parameters of the winding machine, adjusting the distance between the tabs of the electrode sheet according to different embossing pressure parameters, and winding the battery cell; the battery cell is wound in a layered structure of positive electrode-PMMA coated separator-negative electrode-PMMA coated separator; the positive electrode sheet and the negative electrode sheet are both provided with tabs, the tabs are top tabs, and one tab is provided every two folds;

[0007] S2, adjusting the hot pressing parameters of the hot pressing machine, and hot pressing the wound core using different hot pressing parameters; the hot pressing parameters include temperature, pressure, and time;

[0008] S3, assemble the hot-pressed core, put it into the shell, divide the capacity and fully charge it.

[0009] By selecting the most appropriate embossing pressure and hot pressing parameters according to the above method of the present invention, the black spot wrinkles on the lithium battery interface of the PMMA coated separator can be alleviated, thereby improving the electrochemical performance and safety performance of the battery.

[0010] Furthermore, in step (S1), adjusting the winding machine parameters includes:

[0011] (S11) selecting an appropriate embossing pressure to wind the lithium battery electrode;

[0012] (S12) Selecting the most appropriate embossing pressure based on the experiment in (S11).

[0013] In the step (S11), the appropriate value of the embossing pressure should be determined based on the equipment capacity and the conditions during the winding process. If poor coating or tab misalignment occurs, it should be adjusted promptly, and the maximum value of the embossing pressure should be found. Increasing the embossing pressure will cause overpressure on the electrode and the winding core to be unable to enter the shell. At the same time, black spots caused by overpressure at the R corner of the electrode will be caused.

[0014] In the step (S12), the embossing pressure is increased from 0 MPa. If the core wound under a certain pressure is stable in the equipment, there is no tab misalignment, and after hot pressing, there is no obvious deformation caused by the rebound of the negative electrode for a period of time, and the core can be easily put into the shell, the embossing pressure should be further increased to explore the maximum pressure.

[0015] Taking into account the equipment capabilities, preferably, in the step (S11), the embossing pressure of the winding machine is selected to be between 0-0.18 MPa for verification.

[0016] Furthermore, in step (S2), adjusting the hot pressing parameters includes:

[0017] S21, selecting a hot pressing temperature for the core obtained by using the optimal embossing pressure parameters in step S1;

[0018] S22, selecting the optimal hot pressing temperature and hot pressing pressure;

[0019] S23, selecting the optimal hot pressing pressure and hot pressing time;

[0020] S24, performing an orthogonal experiment based on the above parameters of embossing pressure, hot pressing temperature, and pressing time.

[0021] Preferably, in the step (S21), the temperature of the hot press is selected to be between 70-85°C for verification.

[0022] Preferably, in the step (S22), the pressure of the hot press is selected to be between 0.3-0.5 MPa for verification.

[0023] Preferably, in the step (S23), the time of the hot press is selected to be between 30-60s for verification.

[0024] Furthermore, the method for performing the orthogonal experiment in step (S24) is as follows:

[0025] (S241) According to the orthogonal experimental method, the hot pressing temperature is first fixed at 70°C, and the hot pressing pressure is randomly matched to 0.3 MPa and 0.5 MPa; the hot pressing time is 30 s, 45 s, and 60 s; and the black spot and wrinkle data of the fully charged interface are recorded.

[0026] (S242) According to the orthogonal experimental method, the hot pressing temperature is first fixed at 75°C, and the hot pressing pressure is randomly matched to 0.3 MPa and 0.5 MPa; the hot pressing time is 30 s, 45 s, and 60 s; and the black spot and wrinkle data of the fully charged interface are recorded.

[0027] (S243) According to the orthogonal experimental method, the hot pressing temperature is first fixed at 80°C, and the hot pressing pressure is randomly matched to 0.3 MPa and 0.5 MPa; the hot pressing time is 30 s, 45 s, and 60 s; and the black spot and wrinkle data of the fully charged interface are recorded.

[0028] (S244) According to the orthogonal experimental method, the hot pressing temperature is first fixed at 85°C, and the hot pressing pressures are randomly set to 0.3 MPa and 0.5 MPa; the hot pressing time is 30 s, 45 s, and 60 s; and the black spot and wrinkle data of the fully charged interface are recorded.

[0029] In summary, the present invention has the following beneficial effects:

[0030] The present invention can reduce interface wrinkles and black spots by adjusting the winding parameters and hot pressing parameters and selecting appropriate embossing pressure, hot pressing temperature, pressure and time. By adjusting the embossing pressure of the winding, a concave-convex texture is formed on the surface of the electrode, which can effectively improve the compaction density of the battery electrode and alleviate the problem of excessive expansion of the battery electrode during charging and discharging, avoiding wrinkles and black spots caused by repeated contraction and expansion of the negative electrode, thereby limiting the capacity; appropriate hot pressing temperature, pressure and time can keep the core in the optimal state, avoiding the core being too loose to be easily inserted into the shell or overpressure causing poor electrolyte infiltration and causing black spots. At the same time, the difference between PMMA membranes and other membranes is that they are not suitable for high temperature hot pressing, and the looser the core is under the condition that it can be inserted into the shell, the better the interface.

[0031] Additional aspects and advantages of the present invention will be set forth in part in the description which follows and, in part, will be obvious from the description which follows, or may be learned by practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 Flowchart of a method for alleviating wrinkles on a lithium battery electrode according to an embodiment of the present invention. DETAILED DESCRIPTION

[0033] The present invention will be further described in detail below in conjunction with specific embodiments. The examples provided are only for illustrating the present invention and are not intended to limit the scope of the present invention. The examples provided below can serve as a guide for further improvements by those skilled in the art and are not intended to limit the present invention in any way.

[0034] Unless otherwise specified, the experimental methods in the following examples are conventional methods and were performed according to the techniques or conditions described in the literature in the field or according to the product instructions. The materials and reagents used in the following examples, unless otherwise specified, were all commercially available.

[0035] like Figure 1 As shown, the present embodiment provides a method for alleviating wrinkles in a lithium battery electrode, comprising the following steps:

[0036] S1: Adjust the embossing pressure of the winding machine, adjust the spacing between the electrode tabs according to the pressure parameter, and wind the battery cell. The battery cell is wound in a layered structure of positive electrode sheet - PMMA-coated separator - negative electrode sheet - PMMA-coated separator. Both the positive and negative electrode sheets are provided with tabs. The tabs are top tabs, and one tab is provided every two folds.

[0037] It should be noted that by adjusting the embossing pressure, a concave-convex texture can be formed on the surface of the electrode, which can better improve the compaction density of the battery electrode, and can alleviate the problem of excessive expansion of the battery electrode during charging and discharging, and avoid wrinkles caused by repeated contraction and expansion of the negative electrode.

[0038] S2, adjusting the hot pressing parameters, and hot pressing the wound core using different hot pressing parameters.

[0039] Specifically, the cell hot pressing temperature is 70-85°C, the pressure is 0.3-0.5 MPa, and the time is 30-60 seconds. In particular, by adjusting the cell hot pressing parameters, the appropriate winding tension can be selected to avoid difficulty in inserting the cell into the shell or poor infiltration due to excessive looseness or overpressure.

[0040] S3, assemble the hot-pressed core, put it into the shell, and divide the capacity and fully charge it.

[0041] The standing time is 8-12 minutes, and the constant temperature is 23-27°C.

[0042] In this way, by adjusting the winding parameters and hot pressing parameters, and selecting the appropriate embossing pressure, hot pressing temperature, pressure and time, the interface wrinkles and black spots can be alleviated. By adjusting the embossing pressure of the winding, a concave-convex texture is formed on the surface of the electrode, which can better improve the compaction density of the battery electrode and alleviate the problem of excessive expansion of the battery electrode during charging and discharging, avoiding the repeated contraction and expansion of the negative electrode to cause wrinkles and black spots, thereby limiting the capacity; the appropriate hot pressing temperature, pressure and time can keep the core in the optimal state, avoiding the core being too loose to enter the shell or overpressure causing poor electrolyte infiltration and causing black spots. At the same time, the difference between PMMA coated diaphragms and other diaphragms is that they are not suitable for high temperature hot pressing, and the looser the core is under the condition that it can enter the shell, the better the interface.

[0043] Furthermore, in step S1, adjusting the embossing pressure parameters of the winding machine includes:

[0044] S11, selecting an appropriate embossing pressure to wind the lithium battery electrode;

[0045] The appropriate value of embossing pressure should be determined based on the equipment capacity and the conditions during winding. If poor coating or tab misalignment occurs, adjustments should be made promptly, and the maximum embossing pressure should be determined. Increasing the embossing pressure will result in overpressure on the electrode and the core being unable to fit into the shell. It will also cause black spots at the R corner of the electrode due to overpressure.

[0046] S12, select the most appropriate embossing pressure based on the experiment in S11:

[0047] The embossing pressure is increased starting from 0 MPa. If the winding core at a certain pressure is stable in the equipment, with no tab misalignment, and if, after hot pressing, there is no noticeable deformation due to negative electrode rebound for a period of time, and the core can be easily inserted into the shell, the embossing pressure should be further increased to explore the maximum pressure. Considering the equipment capabilities, the embossing pressure in this experiment was tentatively set between 0 and 0.18 MPa.

[0048] Furthermore, adjusting the hot pressing parameters in step S2 includes:

[0049] S21, selecting the hot pressing temperature according to the parameters of the optimal embossing pressure.

[0050] Specifically, the hot pressing temperatures are selected to be 70°C, 75°C, 80°C and 85°C.

[0051] S22, selecting the hot pressing pressure according to the optimal hot pressing temperature.

[0052] Specifically, the hot pressing pressures are selected to be 0.3 MPa and 0.5 MPa.

[0053] S23, selecting the hot pressing time according to the optimal hot pressing pressure.

[0054] Specifically, the hot pressing times are selected to be 30s, 45s and 60s.

[0055] S24, conducting an orthogonal experiment based on the above embossing pressure, hot pressing temperature, and pressing time parameters.

[0056] According to the above verification scheme, the method of slowing down the black spots and wrinkles on the pole pieces of PMMA diaphragm lithium batteries in this embodiment can significantly slow down the black spots and wrinkles on the pole pieces of lithium-ion batteries after they are fully charged, thereby preventing the occurrence of black spots and wrinkles in the battery, capacity attenuation, and reduced safety.

[0057] Furthermore, in step S24, the factors in step S21, step S22 and step S23 are combined according to an orthogonal experiment.

[0058] Specifically, the orthogonal experiment of step S24 includes the following steps:

[0059] S241, according to the orthogonal experimental method, first fix the hot pressing temperature at 70℃, and randomly match the hot pressing pressure to 0.3MPa and 0.5MPa; the hot pressing time is 30s, 45s, and 60s; and record the black spot and wrinkle data of the fully charged interface.

[0060] S242, according to the orthogonal experimental method, first fix the hot pressing temperature at 75°C, and randomly match the hot pressing pressure to 0.3MPa, 0.5MPa; the hot pressing time is 30s, 45s, and 60s; and record the black spot and wrinkle data of the fully charged interface.

[0061] S243, according to the orthogonal experimental method, first fix the hot pressing temperature at 80°C, and randomly match the hot pressing pressure to 0.3MPa, 0.5MPa; the hot pressing time is 30s, 45s, and 60s; and record the black spot and wrinkle data of the fully charged interface.

[0062] S244, according to the orthogonal experimental method, first fix the hot pressing temperature at 85°C, and randomly match the hot pressing pressure to 0.3MPa and 0.5MPa; the hot pressing time is 30s, 45s, and 60s; and record the black spot and wrinkle data of the fully charged interface.

[0063] S245, based on the data recorded in the above steps, select hot pressing parameters that can alleviate the black spot wrinkles of the electrode.

[0064] plan wrinkles dark spots 70℃, 0.3MPa, 30s 20% off A few dark spots 70℃, 0.3MPa, 45s 75% off Large facial wrinkles and dark spots 70℃, 0.3MPa, 60s 77% off Large facial wrinkles and dark spots 70℃, 0.5MPa, 45s 78% off Large facial wrinkles and dark spots 75℃, 0.5MPa, 45s 78% off Large facial wrinkles and dark spots 80℃, 0.5MPa, 45s 20% off Large surface material loss, wrinkles and black spots 85℃, 0.5MPa, 45s 19% off Large surface material loss, wrinkles and black spots

[0065] In summary, by adjusting the winding parameters and hot pressing parameters, and selecting appropriate embossing pressure, hot pressing temperature, pressure, and time, the interface wrinkles and black spots can be alleviated. By adjusting the embossing pressure of the winding, a concave-convex texture is formed on the surface of the electrode, which can better improve the compaction density of the battery electrode and alleviate the problem of excessive expansion of the battery electrode during charging and discharging, avoiding the repeated contraction and expansion of the negative electrode to cause wrinkles and black spots, thereby limiting the capacity; while excessive embossing pressure will cause the electrode to be over-pressurized, resulting in R-corner printed black spots. Appropriate hot pressing temperature, pressure, and time can keep the core in the optimal state, avoiding the core being too loose to enter the shell or over-pressurized to cause poor electrolyte infiltration and cause black spots. At the same time, the difference between PMMA diaphragms and other diaphragms is that they are not suitable for high-temperature hot pressing, and the looser the core is under the condition that it can enter the shell, the better the interface.

[0066] The present invention has been described in detail above. It will be apparent to those skilled in the art that the present invention may be practiced over a wide range of parameters, concentrations, and conditions without departing from the spirit and scope of the present invention and without unnecessary experimentation. Although specific embodiments have been given herein, it should be understood that further modifications may be made to the present invention. In summary, this application is intended to encompass any variations, uses, or improvements to the present invention, including those made by conventional techniques known in the art that depart from the scope of the present invention. Applications of the essential features may be made within the scope of the following claims.

Claims

1. A method for alleviating black spot wrinkles on PMMA-coated diaphragm lithium battery pole pieces, characterized by: The method comprises the following steps: S1, adjusting the embossing pressure parameters of the winding machine, adjusting the distance between the tabs of the electrode sheet according to different embossing pressure parameters, and winding the battery cell; the battery cell is wound in a layered structure of positive electrode sheet-PMMA coated separator-negative electrode sheet-PMMA coated separator; the positive electrode sheet and the negative electrode sheet are both provided with tabs, the tabs are top tabs, and one tab is provided every two folds; S2, adjusting the hot pressing parameters of the hot pressing machine, and hot pressing the wound core using different hot pressing parameters; the hot pressing parameters include temperature, pressure, and time; S3, assemble the hot-pressed core, put it into the shell, divide the capacity and fully charge it.

2. The method for alleviating black spot wrinkles on PMMA-coated diaphragm lithium battery pole pieces according to claim 1, characterized in that: The winding machine parameters adjusted in step S1 include: S11, selecting an appropriate embossing pressure to wind the lithium battery electrode; S12, selecting the most appropriate embossing pressure according to the experiment in S11.

3. The method for alleviating black spot wrinkles on PMMA-coated diaphragm lithium battery pole pieces according to claim 2, characterized in that: In the step (S11), the appropriate value of the embossing pressure should refer to the equipment capacity and the situation during the winding operation. If poor coating or tab misalignment occurs, it should be adjusted in time, and the maximum value of the embossing pressure should be explored at the same time.

4. The method for alleviating black spot wrinkles on PMMA-coated diaphragm lithium battery pole pieces according to claim 2 or 3, characterized in that: In the step S11, the embossing pressure is selected to be 0-0.18 MPa for verification.

5. The method for alleviating black spot wrinkles on PMMA-coated diaphragm lithium battery pole pieces according to claim 2, characterized in that: Adjusting the hot pressing parameters in step S2 includes: S21, selecting a hot pressing temperature for the core obtained by using the optimal embossing pressure parameters in step S1; S22, selecting the optimal hot pressing temperature and hot pressing pressure; S23, selecting the optimal hot pressing pressure and hot pressing time; S24, conducting an orthogonal experiment based on the above embossing pressure, hot pressing temperature, and pressing time parameters.

6. The method for alleviating black spot wrinkles on PMMA-coated diaphragm lithium battery pole pieces according to claim 5, characterized in that: In step S21, the hot pressing temperature is selected to be 70-85°C.

7. The method for alleviating black spot wrinkles on PMMA-coated diaphragm lithium battery pole pieces according to claim 5, characterized in that: In step S22, the hot pressing pressure is selected to be 0.3 MPa-0.5 MPa.

8. The method for alleviating black spot wrinkles on PMMA-coated diaphragm lithium battery pole pieces according to claim 5, characterized in that: In step S23, the hot pressing time is selected to be 30-60s.

9. The method for alleviating black spot wrinkles on PMMA-coated diaphragm lithium battery pole pieces according to any one of claims 5 to 8, characterized in that: In step S24, the parameters in steps S21, S22 and S23 are combined according to an orthogonal experiment.

10. The method for alleviating black spot wrinkles on PMMA-coated diaphragm lithium battery pole pieces according to claim 9, characterized in that: The orthogonal experiment in step S24 includes the following experiments: S241, according to the orthogonal experimental method, first fix the hot pressing temperature at 70℃, and randomly match the hot pressing pressure to 0.3MPa and 0.5MPa; the hot pressing time is 30s, 45s, and 60s; and record the black spot and wrinkle data of the fully charged interface. S242, according to the orthogonal experimental method, first fix the hot pressing temperature at 75°C, and randomly match the hot pressing pressure to 0.3MPa, 0.5MPa; the hot pressing time is 30s, 45s, and 60s; and record the black spot and wrinkle data of the fully charged interface. S243, according to the orthogonal experimental method, first fix the hot pressing temperature at 80°C, and randomly match the hot pressing pressure to 0.3MPa, 0.5MPa; the hot pressing time is 30s, 45s, and 60s; and record the black spot and wrinkle data of the fully charged interface. S244, according to the orthogonal experimental method, first fix the hot pressing temperature at 85°C, and randomly match the hot pressing pressure to 0.3MPa and 0.5MPa; the hot pressing time is 30s, 45s, and 60s; and record the black spot and wrinkle data of the fully charged interface. According to the data analysis recorded in the above steps, the winding parameters and hot pressing parameters that can slow down the black spot wrinkles of PMMA coated diaphragm lithium battery pole pieces are selected.

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