Method for improving folding marks of lithium battery roll core

Abstract

The invention discloses a method for improving folds of a lithium battery roll core, which comprises the following steps of: setting tension linear attenuation of a winding machine, and winding a negative plate, a diaphragm and a positive plate on the machine to obtain the roll core; after being discharged from the winding needle, the winding core is conveyed to a cold pressing position to be pre-pressed; after code scanning, the roll core enters a hot pressing process; and performing assembly, formation and capacity grading on the hot-pressed roll core. According to the method for improving the folding marks of the lithium battery roll core, by optimizing the winding tension, it is guaranteed that the pole piece and the diaphragm are flat in the winding and hot-pressing processes; according to the invention, a specific pre-hot-pressing mode is selected for diaphragms with different sizes, so that the pole piece is attached to the diaphragms, the pole piece is prevented from collapsing in a roll core shelving process, on the other hand, the paths of the pole piece and the diaphragms are the same when the pole piece and the diaphragms are attached and hot-pressed, and creases of the pole piece are reduced. By optimizing the procedures of winding, preheating, hot pressing and the like, the problem of creases on the outer ring of the large-size roll core is solved, and the problem of wrinkles on the inner ring after full charge is also solved.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium battery winding - hot pressing process, and specifically to a method for improving the creases of a lithium battery core. Background Technique

[0002] With the booming development of the new energy vehicle industry, it has gradually become a common consensus in the automotive industries of various countries to replace traditional fuel vehicles. As the core component, the power battery is more recognized as the key factor affecting the development of new energy vehicles. Therefore, the demand for high - performance and high - safety lithium batteries is becoming increasingly urgent. Currently, the main types of power batteries are square, cylindrical, and soft - pack. The batteries are generally made in two ways: stacking and winding processes. Among them: the stacking process has higher space utilization, lower internal resistance, and better rate performance, but the problem of burrs on the electrode sheets is prominent and the process control is difficult; the winding process is mature, has low cost, and higher yield and production efficiency. Compared with the current stacking production method, the winding process has a high degree of automation and mature supporting equipment. Most cell manufacturers adopt the winding manufacturing process. However, there are also certain difficulties for large - size cores: wrinkles in the inner circle of the core and creases on the outer - circle negative electrode. The wrinkles in the inner circle can be improved by the tension of the electrode sheet, while the creases on the outer - circle negative electrode will only appear after hot pressing and are difficult to identify during the winding process. There are risks of black spots and lithium deposition at the crease of the full - charge interface of the battery, which will affect the overall performance of the battery. Summary of the Invention

[0003] The purpose of the present invention is to provide a method for improving the creases of a lithium battery core to solve the problem of creases on the outer - circle negative electrode after hot pressing of the core, thereby improving the quality of the core, reducing production costs, and ensuring the overall performance of the lithium battery.

[0004] To achieve the above - mentioned purpose, the technical solution adopted by the present invention is as follows:

[0005] A method for improving the creases of a lithium battery core includes the following steps:

[0006] Set the winding machine to linearly decay the tension, wind the negative electrode sheet, separator, and positive electrode sheet on the machine to obtain a core;

[0007] After the core is unloaded from the winding pin, transfer it to the cold - pressing position for pre - pressing, and set the parameters to 2T, 20 - 50s;

[0008] After the core is scanned, enter the hot - pressing process; during this process, control the beat to reduce the shelving time of the core after unloading (≤2h);

[0009] Assemble, form, and grade the core that has completed hot pressing.

[0010] Further solution, the specific process of the linearly decaying tension is as follows: Control the tension applied to the negative electrode sheet and the positive electrode sheet to decay independently for multiple times, and control the tension applied to the separator to be a constant tension or a gradient-decaying tension; where:

[0011] The initial tension applied to the positive electrode sheet is 750 g to 950 g, the tension of the positive electrode sheet decays by 1 to 4 g / turn, and it is reduced to the 17th to 37th turn; the initial tension applied to the negative electrode sheet is 750 g to 950 g, the tension of the negative electrode sheet decays by 1 to 4 g / turn, and it is reduced to the 18th to 38th turn; the initial tension applied to the separator is 150 g to 180 g, and the tension gradient of the separator decays by 1 g / turn. During the winding process, by controlling the decreasing manner of the tension of the positive and negative electrode sheets, the flatness of the surfaces of the positive and negative electrode sheets during the winding process can be ensured; by controlling the variable tension or constant tension of the separator, the flatness and non-crease of the separator inside the electrode sheets of different lengths can be ensured.

[0012] Further solution, during the winding process, the embossing pressure is 0.19 ± 0.03 MPa, and the winding linear speed is 400 ± 10 mm / s. By controlling the embossing pressure, the complete fitting of the electrode sheet and the separator can be ensured, and the quality of the formation interface can be improved;

[0013] Further solution, the hot pressing process includes preheating and hot pressing, where: the temperature of the preheating is 75 to 90 °C; the temperature of the hot pressing is 75 to 90 °C, and the pressure of the hot pressing is 5 to 9.5 T. Through preheating and hot pressing, the fitting between the separator and the positive and negative electrode sheets can be improved, and the occurrence of creases on the negative electrode can be greatly reduced.

[0014] Further solution, the time from when the wound core is taken out of the oven after preheating to hot pressing is controlled within 120 s, the shelving time after preheating is reduced, and the separation of the outer separator and the electrode sheet after the wound core cools down is avoided.

[0015] Further solution, the hot pressing process further includes pre-hot pressing, and the pre-hot pressing is carried out before the preheating process; the pressure of the pre-hot pressing is less than the pressure of the hot pressing. The pre-hot pressing parameters ensure the fitting of the separator and the electrode sheet on half of the thickness of the wound core, and the hot pressing parameters ensure that the area of the glue on the residual separator on the positive electrode sheet > 80%. First, carry out pre-hot pressing for shaping to ensure a certain degree of fitting between the separator and the electrode sheet, and then carry out preheating and hot pressing, and the crease situation of the wound core can be significantly improved.

[0016] The present invention has the following beneficial effects:

[0017] The method for improving the creases of a lithium battery core provided by the present invention ensures the flatness of the electrode sheets and the separator during winding and hot pressing by optimizing the winding tension. For separators of different sizes, the present invention selects a specific pre-hot pressing method to make the electrode sheets adhere to the separator, preventing the electrode sheets from sagging during the storage of the core. On the other hand, when the electrode sheets adhere to the separator, the paths of the electrode sheets and the separator during hot pressing are the same, reducing the creases of the electrode sheets. The present invention reduces the storage time after preheating to avoid the separation of the outer separator and the electrode sheets after the core cools down. By optimizing processes such as winding, preheating, and hot pressing, the present invention improves the problem of outer creases of large-sized cores, and also improves the problem of inner wrinkles after full charge. Description of the Drawings

[0018] Figure 1 Photos of the (9 + 3)μm separator core (left) and the (7 + 2 + 3)μm separator core (right) obtained in the examples;

[0019] Figure 2 Photos of the (9 + 3)μm separator core (left) and the (7 + 2 + 3)μm separator core (right) obtained in the comparative examples. Detailed Embodiments

[0020] The following further illustrates the present invention with reference to embodiments, so that those skilled in the art can better understand the present invention and implement it, but the exemplified embodiments do not limit the present invention.

[0021] In addition, in the preparation processes of the following embodiments, unless otherwise specified, they are all conventional means in the prior art, and therefore will not be described in detail.

[0022] Embodiments

[0023] A method for improving the creases of a lithium battery core includes the following steps:

[0024] Laser cut the positive and negative electrode sheets according to the tab spacing parameters on the process sheet;

[0025] Correctly thread the positive and negative electrode sheets and the separator, and install the winding needle with the required circumference; according to different separator specifications, set different winding parameters on the winding machine, specifically as follows:

[0026] For the (9 + 3)μm separator (PMMA separator), set the parameters on the winding machine as follows: ① Tension of the positive electrode sheet: starting from 950g in the first turn, decreasing by 1g per turn until the 37th turn; ② Tension of the negative electrode sheet: starting from 950g in the first turn, decreasing by 1g per turn until the 38th turn; ③ Tensions of the upper and lower separators: 180g, decreasing by 1g per turn; ④ Other parameters: a. Embossing pressure: 0.19 ± 0.03 MPa; b. Winding line speed: 400 ± 10 mm / s;

[0027] For the (7 + 2 + 3) μm separator, set the parameters on the winding machine as follows: ① Positive electrode sheet tension: starting from 750 g in the first turn, decreasing by 4 g per turn until the 17th turn; ② Negative electrode sheet tension: starting from 750 g in the first turn, decreasing by 4 g per turn until the 18th turn; ③ Upper and lower separator tensions are 150 g, constant tension; ④ Other parameters: a. Embossing pressure: 0.19 ± 0.03 MPa; b. Winding line speed: 400 ± 10 mm / s.

[0028] After the core is unloaded from the winding needle, it is transferred to the cold pressing position for pre-pressing, and the parameter settings are 2 T and 40 s.

[0029] After the core is scanned, it enters the hot pressing process. This process requires controlling the rhythm to reduce the shelving time after the core is unloaded (≤2 h) to prevent the increase in the depression degree of the electrode sheet in the middle position and the collapse of the electrode sheet due to the long shelving time of the core; and for different specifications of separators, the hot pressing parameters are as follows: For the (9 + 3) μm separator: The core is first preheated at 75 °C for 30 min; after preheating, the core is hot pressed at 9 T, 75 °C for 120 s, and the time from when the core is taken out of the oven to hot pressing after preheating is controlled within 120 s to reduce the shelving time after preheating; For the (7 + 2 + 3) μm separator: The core is first preheated and pressed at 7 T, 50 °C for 30 s; the core is preheated at 90 °C for 30 min; after preheating, the core is hot pressed at 7.5 T, 90 °C for 150 s.

[0030] Assemble, form, and grade the cores that have completed hot pressing.

[0031] Comparative example

[0032] For the (9 + 3) μm separator core, compared with the example, the different processes are as follows: The initial tensions of the positive and negative electrode sheets are 850 g, decreasing by 2 g; the separator tension is a constant tension of 150 g.

[0033] For the (7 + 2 + 3) μm separator core, compared with the example, the different processes are as follows: The initial tensions of the positive and negative electrode sheets are 600 g and 650 g respectively, decreasing by 2 g; the separator tension is a constant tension of 150 g; the preheating parameters are 90 °C and 30 min; the hot pressing parameters are: 7.5 T, 90 °C, 120 s; no preheating and pressing are carried out.

[0034] The shelving process involved in the above comparative example is carried out according to the conventional process in the art, and other processes are the same as those in the example.

[0035] Comparison of the effectiveness of the example and the comparative example solutions:

[0036] For the (9 + 3) μm separator core, the method provided by the present invention can reduce the shelving time through artificial control, and the effectiveness from core unloading to hot pressing can be improved by about 2 - 4%.

[0037] For the (7 + 2 + 3) μm diaphragm core, in the embodiment, due to the addition of the pre-heat pressing process but the reduction of the shelving time, the efficiency is basically the same as the original plan, and the production efficiency is not reduced.

[0038] The comparison after hot pressing of the core is as follows:

[0039] After hot pressing the cores of the embodiment and the comparative example, the results are as Figure 1 and Figure 2 shown, where Figure 1 is a photo of the (9 + 3) μm diaphragm core (left) and the (7 + 2 + 3) μm diaphragm core (right) obtained in the embodiment, Figure 2 is a photo of the (9 + 3) μm diaphragm core (left) and the (7 + 2 + 3) μm diaphragm core (right) obtained in the comparative example. It can be seen from the comparison between Figure 1 and Figure 2 that the creases of the core prepared by the method provided by the present invention have been significantly improved.

[0040] The method for improving the creases of the lithium battery core provided by the present invention has been applied in the pilot project. The core crease rate has been reduced from the original 3.85% to ≤0.1%. When disassembling at full charge, the folding situation of the inner ring negative electrode has also been improved, and the degree and quantity of the folds have also decreased. And its solution has been extended to the core projects of similar sizes, and the crease rate after hot pressing has also decreased.

[0041] Obviously, the described embodiments are part of the embodiments of the present invention, rather than all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

Claims

1. A method for improving the creases of a lithium battery core, characterized in that: It includes the following steps: The winding machine is set to linearly decay the tension. The negative electrode sheet, separator, and positive electrode sheet are wound on the machine to obtain a core; After the core is unloaded from the winding needle, it is transferred to the cold pressing position for pre-pressing; After the core is scanned, it enters the hot pressing process; The assembled core after hot pressing is assembled, formed, and capacity-divided.

2. The method for improving the crease of the lithium battery core according to claim 1, wherein: The specific process of the linearly decaying tension is as follows: controlling the tension applied to the negative electrode sheet and the positive electrode sheet to decay independently for multiple times; where: the tension of the positive electrode sheet decays by 1-4 g / turn and is reduced to the 17th to 37th turn; the tension of the negative electrode sheet decays by 1-4 g / turn and is reduced to the 18th to 38th turn; controlling the tension applied to the separator to be a constant tension or the tension decays by 1 g / turn.

3. The method for improving the crease of a lithium battery core according to claim 2, wherein: During the winding process, the initial tension applied to the positive electrode sheet is 750 g to 950 g, the initial tension applied to the negative electrode sheet is 750 g to 950 g, and the initial tension applied to the separator is 150 g to 180 g.

4. The method for improving the crease of the lithium battery core according to claim 2, wherein: During the winding process, the embossing pressure is 0.19 ± 0.03 MPa, and the winding linear speed is 400 ± 10 mm / s.

5. The method for improving the crease of a lithium battery core according to claim 2, wherein: The time of the pre-pressing is 20-50 s.

6. The method for improving the crease of a lithium battery core according to claim 1, characterized in that: The hot pressing process includes preheating and hot pressing, where: the temperature of the preheating is 75-90 °C; the temperature of the hot pressing is 75-90 °C, and the pressure of the hot pressing is 5-9.5 T.

7. The method for improving the crease of the lithium battery core according to claim 6, wherein: The time from when the core is taken out of the oven after preheating to hot pressing is controlled within 120 s.

8. The method for improving the crease of a lithium battery core according to claim 6, wherein: The hot pressing process also includes pre-hot pressing, which is carried out before the preheating process; the pressure of the pre-hot pressing is less than the pressure of the hot pressing.

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