Control method for improving middle opening of naked battery cell after hot pressing

Abstract

The invention discloses a control method for improving a middle opening after hot pressing of a naked battery cell. The control method comprises the following steps: 1) carrying out first hot pressing; 2) carrying out secondary hot pressing; and (3) the product subjected to hot pressing is subjected to a pressure resistance test, the function of regulating and controlling hot pressing parameters in sections can be achieved, the problems existing in one-time hot pressing can be effectively avoided after stepped hot pressing is conducted, the production pressure of the shell entering process section of lithium battery production is relieved, and the production efficiency is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of new energy batteries, and in particular relates to a control method for improving the middle opening of a bare battery cell after hot pressing. Background Art

[0002] In the process of implementing the present invention, the inventors found that the prior art has at least the following problems:

[0003] At present, in the production process of lithium-ion batteries, there are problems with poor hot pressing of bare cells after winding, such as large openings of the bare cells after hot pressing and powder loss of the inner electrode, which affects the shelling and winding of the bare cells.

[0004] CN217361687U - Battery cell hot pressing device, battery cell hot pressing workstation and battery production system, discloses a battery cell hot pressing device, a battery cell hot pressing workstation and a battery production system, wherein the battery cell hot pressing device includes a fixture module, which can support multiple stacked battery cells and can generate a pressing force on each battery cell respectively; a box body, which has a accommodating space inside, and the side wall of the box body is provided with an opening for the fixture module to enter and exit the box body and a door assembly for controlling the opening and closing state of the opening; a pressing mechanism, because it cannot solve the above-mentioned technical problems. Summary of the invention

[0005] The technical problem to be solved by the present invention is to provide a control method for improving the middle opening of a bare cell after hot pressing.

[0006] In order to solve the above technical problems, the technical solution adopted by the present invention is: a control method for improving the middle opening of a bare cell after hot pressing, comprising the following steps:

[0007] 1) First hot pressing;

[0008] 2) Second hot pressing;

[0009] 3) The products after hot pressing are subjected to pressure resistance test.

[0010] In the above step 1), the bare battery cell after cold pressing is placed in a hot pressing station, and the upper pressing plate presses down to apply pressure to a set value and then maintains the pressure for a set time.

[0011] In the above step 1), the first hot pressing parameters are: pressure 4.5T, temperature 85°C, and holding time 60s.

[0012] In the above step 2), in the second hot pressing, the upper pressing plate presses down to apply pressure to a set value and then maintains the pressure for a set time. The second hot pressing pressure is greater than the first hot pressing pressure.

[0013] The second hot pressing parameters are: pressure 6T, temperature 85°C, and holding time 60s.

[0014] In the above step 3), a pressure test is performed after the hot pressing is completed, and the next process is entered after the test is passed.

[0015] In the above step 3), if the withstand voltage test fails, a manual retest is performed. If the retest passes, the next process is entered; if the manual retest fails, the unqualified battery cell is disassembled.

[0016] In the above step 1), the bare battery cell after winding and cold pressing is placed in the hot pressing station by a robot.

[0017] The hot pressing station can be controlled in sections, and there is a real-time pressure monitor to feedback the pressure; when the first section pressure reaches the set value, the timing starts. After the first section set time ends, it increases to the second section pressure setting value and starts timing. When the two sections of pressure are completed, the hot pressing of the bare cell ends.

[0018] The production process of lithium-ion square aluminum shell batteries is mainly divided into two processes: winding and lamination. The winding process is widely used in actual production. The winding process uses the winding needle of the winding machine to wind the positive electrode sheet, the negative electrode sheet, and the separator into a bare cell in sequence, and then the bare cell is shaped by hot pressing at the hot pressing station to facilitate the subsequent process. At present, the hot pressing of bare cells generally has the problem of large opening in the middle of the bare cell after hot pressing, which affects the entry of the bare cell into the shell. The time, temperature, and pressure of a hot pressing have a great influence on the bare cell. Small pressure and long-term pressing affect the production capacity; while high pressure can easily cause the inner ring of the bare cell to fall off or even break, affecting the safety of the cell; high temperature can easily cause the diaphragm to wrinkle, affecting the cell interface and Hi-pot. In order to avoid the problem of large opening of the bare cell, the cell pre-baking process is introduced, and the cell is hot pressed after pre-baking. This solution can effectively improve the size of the cell opening, and can optimize the hot pressing process parameters, without the need for high pressure and long-term hot pressing. However, during the actual verification process, it was found that the thickness of the negative electrode plate of the battery cell rebounded severely after pre-baking, posing a risk of being too thick.

[0019] One of the above technical solutions has the following advantages or beneficial effects: it can regulate the hot pressing parameters in sections, and the problems existing in the single hot pressing can be effectively avoided by performing step hot pressing, thereby alleviating the production pressure of the shelling process section in the lithium battery production and improving the production efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 A schematic diagram of a control method for improving the middle opening of a bare cell after hot pressing provided in an embodiment of the present invention;

[0021] Figure 2 It is a box plot of the cell opening size after hot pressing with different parameters;

[0022] Figure 3 It is a box plot of the size of the opening of the bare cell during step hot pressing;

[0023] Figure 4 is the rebound rate of the thickness of the negative electrode sheet under different hot pressing parameters; DETAILED DESCRIPTION

[0024] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0025] See also Figures 1 to 4 A method for improving the control of the middle opening of a bare cell after hot pressing, comprising the following steps: 1) first hot pressing; 2) second hot pressing; 3) performing a withstand voltage test on the product after hot pressing.

[0026] In the above step 1), the bare battery cell after cold pressing is placed in the hot pressing station, and the upper pressing plate is pressed down to apply pressure to reach the set value and then maintain the pressure for the set time. The parameters for the first hot pressing are: pressure 4.5T, temperature 85°C, and holding time 60s. This parameter shapes the bare battery cell once with a small pressure, and its parameters can be adjusted according to different types of battery cells. The main purpose is to reduce the phenomenon of the inner ring of the bare battery cell breaking and powdering due to excessive pressure at one time. Through low-pressure shaping, the opening of the bare battery cell is smaller than that before hot pressing during the experiment, and the phenomenon of inner ring breaking and powdering is significantly improved.

[0027] In the above step 2), in the second hot pressing, the upper pressing plate presses down to apply pressure to the set value and then maintains the pressure for the set time. The second hot pressing pressure is greater than the first hot pressing pressure. The second hot pressing parameters are: pressure 6T, temperature 85°C, and holding time 60s. This parameter suppresses the opening of the bare cell to the thickness set in this process by applying a certain large pressure, which has a significant improvement effect on the size of the bare cell opening, and significantly reduces the defective rate of Mylar packaging and shell entry.

[0028] In the above step 3), a pressure test is performed after the hot pressing is completed, and the next process is entered after the test is passed.

[0029] In the above step 3), if the withstand voltage test fails, a manual retest is performed. If the retest passes, the next process is entered; if the manual retest fails, the unqualified battery cell is disassembled.

[0030] In the above step 1), the bare battery cell after winding and cold pressing is placed in the hot pressing station by a robot.

[0031] The hot pressing station can be controlled in sections, and there is a real-time pressure monitor to feedback the pressure; when the first section pressure reaches the set value, the timing starts. After the first section set time ends, it increases to the second section pressure setting value and starts timing. When the two sections of pressure are completed, the hot pressing of the bare cell ends.

[0032] The production process of lithium-ion square aluminum shell batteries is mainly divided into two processes: winding and lamination. The winding process is widely used in actual production. The winding process uses the winding needle of the winding machine to wind the positive electrode sheet, the negative electrode sheet, and the separator into a bare cell in sequence, and then the bare cell is shaped by hot pressing at the hot pressing station to facilitate the subsequent process. At present, the hot pressing of bare cells generally has the problem of large opening in the middle of the bare cell after hot pressing, which affects the entry of the bare cell into the shell. The time, temperature, and pressure of a hot pressing have a great influence on the bare cell. Small pressure and long-term pressing affect the production capacity; while high pressure can easily cause the inner ring of the bare cell to fall off or even break, affecting the safety of the cell; high temperature can easily cause the diaphragm to wrinkle, affecting the cell interface and Hi-pot. In order to avoid the problem of large opening of the bare cell, the cell pre-baking process is introduced, and the cell is hot pressed after pre-baking. This solution can effectively improve the size of the cell opening, and can optimize the hot pressing process parameters, without the need for high pressure and long-term hot pressing. However, during the actual verification process, it was found that the thickness of the negative electrode plate of the battery cell rebounded severely after pre-baking, posing a risk of being too thick.

[0033] Hardware modification:

[0034] The hot pressing station is renovated to achieve controllable and adjustable pressure and improve the process window.

[0035] Software transformation:

[0036] Compatible pressure, temperature and parameters are adjustable.

[0037] The original hot pressing station is remodeled, the cylinder pressure is increased (greater than 6T), the pressure can be adjusted in stages, and the pressure is fed back by a real-time pressure monitor. When the first stage pressure reaches the set value, the timing starts, and the first stage set time ends. It increases to the second stage pressure setting value and starts timing, and the bare cell hot pressing ends when the two stages of pressure end.

[0038] Specific process flow: In the first step, the bare battery cell after cold pressing is placed in the hot pressing station by a robot. The upper pressing plate presses down to apply pressure to the set value of 4.5T and maintains the pressure until the end of the hot pressing time (60s) at a temperature of 85°C. The hot pressing parameters of the first step of step hot pressing are 4.5T, 85°C, and 60s. The bare battery cell is shaped by a small pressure to avoid the inner ring of the pole piece from breaking and powdering, and at the same time, the defective rate of Hi-pot test can be reduced. It is also a prerequisite for improving the opening size in the second step of step hot pressing.

[0039] Then, in the second step, after the first step, a second hot pressing is performed (at the same station). The upper pressing plate continues to apply pressure at 4.5T to reach the set value of 6T and maintains this pressure for hot pressing until the hot pressing time ends (60s), and the temperature remains unchanged. The parameters of the second step hot pressing are 6T, 85℃, and 60s. The main purpose is to suppress the size of the bare cell opening by applying greater pressure and reduce the overall thickness to within the specified specifications.

[0040] The third step is to conduct a Hi-pot test after the hot pressing. If the result is OK, the battery can be pulled down normally. If it is judged as NG, it will be retested manually (if there is a fold or damage at the tab, it will be retested). If the second result is OK, the battery can be pulled down normally. If it is judged as NG, the engineer will dismantle and investigate the unqualified battery and scrap it. The use of this step hot pressing method can effectively control the opening size of the battery cell and avoid problems such as difficulty in inserting the bare battery cell into the shell.

[0041] Compared with the existing hot pressing process, this invention has the function of regulating the hot pressing parameters in sections. The problems existing in the single hot pressing can be effectively avoided by performing step-by-step hot pressing, thereby alleviating the production pressure in the shelling process of lithium battery production and improving production efficiency.

[0042] In the initial stage of the experiment, DOE was used for verification, and four experimental groups were selected: Group A was normal hot pressing parameters 4.5T / 85℃ / 70s, Group B was an experimental group with step hot pressing parameters 4.5T / 85℃ / 60s-6T / 85℃ / 60s, Group C was an experimental group with increased temperature and step hot pressing parameters 4.5T / 100℃ / 60s-6T / 100℃ / 60s, and Group D was an experimental group with increased pressure and step hot pressing parameters 4.5T / 85℃ / 60s-9T / 85℃ / 60s (the following description of groups does not indicate that the parameters have been replaced by A, B, C, and D). The above experiments were carried out separately to measure the thickness and opening size, and the experimental data are shown in the figure. Figures 2 to 4 shown.

[0043] Through data comparison: the experimental results of group A show that the opening of the bare cell is the largest, and the opening size of group B is not much different from that of group C. Step hot pressing has obvious improvement on the opening size of the bare cell; increasing the temperature is effective in improving the opening size of the bare cell, but the increase in hot pressing temperature causes the negative electrode to have the highest rebound rate, and there is a risk of over-thickness; increasing step hot pressing is effective in improving the opening size of the bare cell, but increasing the pressure will cause serious powder loss of the positive electrode in the inner circle of the bare cell. Based on the experimental data, the step hot pressing parameters are selected as 4.5T / 85℃ / 60s-6T / 85℃ / 60s. The opening of the bare cell is small, and the inner positive electrode does not lose powder. This solution can effectively avoid problems such as the bare cell entering the shell due to the large opening.

[0044] After adopting the above scheme, the function of hot pressing parameters can be adjusted in sections, and the problems existing in the primary hot pressing can be effectively avoided by performing step-by-step hot pressing, thereby alleviating the production pressure of the shelling process section of lithium battery production and improving production efficiency.

[0045] In the description of the present invention, it is necessary to understand that the terms "coaxial", "bottom", "one end", "top", "middle", "the other end", "upper", "one side", "top", "inside", "front", "center", "both ends" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present invention.

[0046] In the present invention, unless otherwise clearly stipulated and limited, the terms such as "installation", "setting", "connection", "fixation" and "screw-on" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral one; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium; it can be the internal connection of two elements or the interaction relationship between two elements. Unless otherwise clearly defined, ordinary technicians in this field can understand the specific meanings of the above terms in the present invention according to the specific circumstances.

[0047] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for improving the control of the middle opening of a bare cell after hot pressing, characterized in that: The steps include: 1) First hot pressing; 2) Second hot pressing; 3) The products after hot pressing are subjected to pressure resistance test.

2. The method for improving the control of the middle opening of a bare cell after hot pressing as claimed in claim 1, characterized in that: In the above step 1), the bare battery cell after cold pressing is placed in a hot pressing station, and the upper pressing plate presses down to apply pressure to a set value and then maintains the pressure for a set time.

3. The control method for improving the middle opening of a bare cell after hot pressing as claimed in claim 2, characterized in that: In the above step 1), the first hot pressing parameters are: pressure 4.5T, temperature 85°C, and holding time 60s.

4. The method for improving the control of the middle opening of a bare cell after hot pressing as claimed in claim 3, characterized in that: In the above step 2), in the second hot pressing, the upper pressing plate presses down to apply pressure to a set value and then maintains the pressure for a set time. The second hot pressing pressure is greater than the first hot pressing pressure.

5. The method for improving the control of the middle opening of a bare cell after hot pressing as claimed in claim 4, characterized in that: The second hot pressing parameters are: pressure 6T, temperature 85°C, and holding time 60s.

6. The method for improving the control of the middle opening of a bare cell after hot pressing as claimed in claim 5, characterized in that: In the above step 3), a pressure test is performed after the hot pressing is completed, and the next process is entered after the test is passed.

7. The method for improving the control of the middle opening of a bare cell after hot pressing as claimed in claim 6, characterized in that: In the above step 3), if the withstand voltage test fails, a manual retest is performed. If the retest passes, the next process is entered; if the manual retest fails, the unqualified battery cell is disassembled.

8. The control method for improving the middle opening of a bare cell after hot pressing as claimed in claim 7, characterized in that: In the above step 1), the bare battery cell after winding and cold pressing is placed in the hot pressing station by a robot.

9. The method for improving the control of the middle opening of a bare cell after hot pressing as claimed in claim 8, characterized in that: The hot pressing station can be controlled in sections, and there is a real-time pressure monitor to feedback the pressure; when the first section pressure reaches the set value, the timing starts. After the first section set time ends, it increases to the second section pressure setting value and starts timing. When the two sections of pressure are completed, the hot pressing of the bare cell ends.

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