KR20210034963A - Method for manufacturing cylindrical secondary battery - Google Patents

Abstract

The present invention provides a method of manufacturing a cylindrical secondary battery, comprising a welding step of welding a plurality of negative electrode tabs located on a surface inside a battery case and a battery case by irradiating laser to a surface outside the battery case, wherein the negative electrode tabs include a first negative electrode tab located on the surface inside the battery case and a second negative electrode tab located on the first negative electrode tab and having the thickness thicker than that of the first negative electrode tab. According to the method of manufacturing a cylindrical secondary battery, it is possible to expand a weldable output range that can show sufficient peeling strength (bonding strength) during laser welding, thereby improving manufacturing processability of cylindrical secondary batteries. Also, it is possible to reduce back bead defects in a welding area and to improve bonding strength (peeling strength) of the negative electrode tab, thereby solving the defect problem that may occur due to laser welding.

Description

Manufacturing method of cylindrical secondary battery {METHOD FOR MANUFACTURING CYLINDRICAL SECONDARY BATTERY}

The present invention relates to a method of manufacturing a cylindrical secondary battery.

As technology development and demand for mobile devices increase, rechargeable batteries are widely used as energy sources for various mobile devices. In addition, secondary batteries are attracting attention as energy sources such as electric vehicles and hybrid electric vehicles, which are proposed as a solution to air pollution such as existing gasoline vehicles and diesel vehicles using fossil fuels.

In general, secondary batteries are cylindrical batteries and prismatic batteries in which an electrode assembly is embedded in a cylindrical or rectangular metal can, and a pouch-type battery in which the electrode assembly is embedded in a pouch-shaped case of an aluminum laminate sheet, depending on the shape of the battery case. Classified as.

The electrode assembly built into the battery case is a charge/discharge power generator consisting of a positive electrode, a negative electrode, and a separator structure interposed between the positive electrode and the negative electrode, and a separator is interposed between the positive electrode and the negative electrode in a long sheet shape coated with an active material. Thus, it is classified into a jelly-roll type wound and a stack type in which a separator is interposed between a plurality of positive and negative electrodes of a predetermined size. Among them, the jelly-roll type electrode assembly is widely used in fields requiring application of a high-capacity secondary battery because it is easy to manufacture and has a high energy density per weight.

The cylindrical secondary battery is manufactured in such a way that the jelly-roll type electrode assembly is accommodated in a cylindrical battery case together with an electrolyte. In general, the jelly-roll type electrode assembly has a positive electrode tab protruding upwardly coupled to the cap assembly so that the top cap is The positive terminal serves as a positive electrode, and the negative electrode tab protruding downward is coupled to the battery case, so that the battery case serves as a negative terminal. In addition, in the case of a cylindrical battery housing such a jelly-roll type electrode assembly, as the demand for high output increases, the number of positive and negative tabs that have been used only one by one to manufacture low-resistance batteries is increasing. to be.

Conventionally, resistance welding has been used to couple the negative electrode tab to the lower surface of the battery case. However, such resistance welding is performed in a state in which a welding rod is inserted into an empty space in the center of the jelly-roll type electrode assembly, and the welding rod must be applied in consideration of the size and shape of the center of the jelly-roll type electrode assembly, The versatility of the welding rod is low, fairness is inferior, and when a copper tab is used as a negative electrode tab, resistance heat is difficult to generate due to low resistance of copper, resulting in poor welding. Therefore, as the welding method, a welding method using a laser is being studied.

However, even in laser welding, when a green laser (515 nm) is used, the weldable power range is relatively high, but there is a problem that it is difficult to reduce the beam size, and when such a beam size is large, corrosion is prevented. There is a problem in that the effect is increased and the welding bead-depth ratio (Aspect Ratio) decreases, so that the welding efficiency may be deteriorated, and thus, laser welding using an IR laser (1070 nm) is being studied.

However, welding using an IR laser also has a problem in that the weldable output range is narrow when two copper cathode tabs are applied. Specifically, when the output is small, the welding strength decreases, and when the output is too large, there is a problem that a back bead occurs. Here, the back bead is a phenomenon that may occur due to over-welding, and refers to a phenomenon in which a welding bead is generated on the opposite surface of the surface on which laser welding is performed.

Accordingly, in the relevant technical field, a method of manufacturing a cylindrical secondary battery having high processability while solving the above-described problem is required.

Korean Patent Publication No. 10-0502315

In the method of welding a plurality of negative electrode tabs to a battery case, a cylindrical secondary that solves the problem of damage to the welding object and the decrease in welding strength of the conventional laser welding and resistance welding, and thereby improves the fairness of welding. To provide a method of manufacturing a battery.

In order to achieve the above object, the present invention includes a welding step of irradiating a laser on an outer surface of a battery case to weld a plurality of negative electrode tabs and a battery case positioned on the inner surface of the battery case, and the plurality of The negative electrode tab comprises a first negative electrode tab disposed on an inner surface of the battery case, and a second negative electrode tab disposed on the first negative electrode tab and having a thickness greater than that of the first negative electrode tab. It provides a method of manufacturing a cylindrical secondary battery.

In addition, the present invention provides a method of manufacturing a cylindrical secondary battery, wherein the first negative electrode tab has a thickness of 40 μm to 120 μm, and the second negative electrode tab has a thickness of 80 μm to 260 μm.

In addition, the present invention provides a method of manufacturing a cylindrical secondary battery in which the ratio of the thickness of the first negative electrode tab and the second negative electrode tab is 1:1.2 to 1:4.

In addition, the present invention provides a method of manufacturing a cylindrical secondary battery having a beam size of 10 to 50 μm of the laser.

In addition, the present invention provides a method of manufacturing a cylindrical secondary battery in which the processing speed of the laser is 100 to 1000 mm/s in the welding step.

In addition, the present invention provides a method of manufacturing a cylindrical secondary battery having a wavelength of 400 to 600 nm or 1000 to 1100 nm of the laser.

In addition, the present invention provides a method of manufacturing a cylindrical secondary battery in which the line energy of the laser is 1350 to 2250 W·s/m in the welding step.

In addition, the present invention provides a method of manufacturing a cylindrical secondary battery, wherein the negative electrode tab is copper, nickel, nickel-plated copper or nickel-clad copper.

In addition, the present invention provides a method of manufacturing a cylindrical secondary battery in which the welding portion of the battery case is made of iron, nickel-plated iron or stainless steel (SUS).

In addition, in the present invention, the cylindrical secondary battery is a method of manufacturing a cylindrical secondary battery, wherein an electrode assembly including a positive electrode, a negative electrode, and a separator is enclosed in a cylindrical battery case.

In addition, the present invention is a cylindrical secondary battery in which an electrode assembly including a positive electrode, a negative electrode, and a separator is enclosed in a cylindrical battery case, comprising a plurality of negative electrode tabs, and a first negative electrode positioned on the inner surface of the battery case It provides a cylindrical secondary battery comprising a tab and a second negative electrode tab disposed on the first negative electrode tab and having a thickness thicker than that of the first negative electrode tab.

In addition, the present invention provides a cylindrical secondary battery in which the thickness of the first negative electrode tab is 40㎛ to 120㎛, and the thickness of the second negative electrode tab is 80㎛ to 260㎛.

In addition, the present invention provides a cylindrical secondary battery having a thickness ratio of 1:1.2 to 1:4 between the first negative electrode tab and the second negative electrode tab.

In addition, the present invention provides a cylindrical secondary battery in which the negative electrode tab is copper, nickel, nickel-plated copper or nickel-clad copper.

In addition, the present invention provides a cylindrical secondary battery in which the battery case is made of iron, nickel-plated iron or stainless steel (SUS).

In addition, in the present invention, the cylindrical secondary battery is manufactured by the method for manufacturing the cylindrical secondary battery described above.

In the method of manufacturing a cylindrical secondary battery according to the present invention, by attaching a plurality of negative electrode tabs to the lower surface of the battery case, it is possible to meet the demand for a high-output and low-resistance battery in the relevant technical field.

In laser welding the plurality of negative electrode tabs to the surface of the battery case, by adjusting the thickness of the second negative electrode tab to be thicker than the thickness of the first negative electrode tab positioned between the battery case and the second negative electrode tab, when laser welding Since the weldable output range can be expanded, manufacturing processability of the cylindrical secondary battery can be improved.

In addition, by the above manufacturing method, defects of a back bead at a welding site may be reduced, and bonding strength (peel strength) of the negative electrode tab may be improved, thereby solving a defect problem that may occur due to laser welding.

1 is a schematic diagram showing a conventional method of welding a plurality of negative electrode tabs to a battery case.
2 is a schematic diagram showing a step of welding a plurality of negative electrode tabs to a battery case according to an embodiment of the present invention.
3 is a detailed view showing a step of welding a plurality of negative electrode tabs to a battery case according to an embodiment of the present invention.
4 is a schematic diagram showing a step of welding a plurality of negative electrode tabs to a battery case according to Example 1 of the present invention.
5 is a schematic diagram showing a step of welding a plurality of negative electrode tabs to a battery case according to Comparative Example 1 of the present invention.
6 is an image showing a surface, a rear surface, and a cross section of a battery case after welding a plurality of negative electrode tabs according to Example 1 of the present invention to a battery case.
7 is an image showing the surface and cross section of a battery case after welding a plurality of negative electrode tabs according to Comparative Example 1 of the present invention to a battery case.

Hereinafter, preferred embodiments of the present invention will be described in detail in order to enable those of ordinary skill in the art to easily implement the present invention.

Method of manufacturing cylindrical secondary battery

The present invention relates to a method of manufacturing a cylindrical secondary battery in which an electrode assembly including a positive electrode, a negative electrode, and a separator is enclosed in a cylindrical battery case. In general, a cylindrical secondary battery uses a jelly-roll type electrode assembly wound with a separator interposed between a long sheet-shaped positive electrode and a negative electrode, and the jelly-roll type electrode assembly has a positive electrode tab and a negative electrode tab attached thereto. . The positive electrode tab extends upward and is coupled to the cap assembly, and the negative electrode tab extends downward and is attached to the lower surface of the battery case. In addition, with respect to the negative electrode tab, since resistance increases when the amount of current increases, a plurality of negative electrode tabs may be used to achieve low resistance. The method for manufacturing a cylindrical secondary battery according to the present invention may use a method known in the art except for attaching the plurality of negative electrode tabs to the lower surface of the battery case.

The method of manufacturing a cylindrical secondary battery of the present invention may include a welding step of irradiating a laser on an outer surface of a battery case to weld a plurality of negative electrode tabs positioned on the inner surface of the battery case to the battery case. The plurality of negative electrode tabs may include a first negative electrode tab disposed on an inner surface of the battery case, and a second negative electrode tab disposed on the first negative electrode tab and having a thickness greater than that of the first negative electrode tab. have.

1 is a schematic diagram showing a conventional method of welding a plurality of negative electrode tabs to a battery case. Specifically, in the prior art, as shown in FIG. 1, the first negative electrode tab and the second negative electrode tab are positioned between the jelly-roll type electrode assembly and the battery case, and finally, a laser is irradiated from the outer surface of the battery case to form a plurality of negative electrode tabs and a plurality of negative electrode tabs. Weld the battery case. In particular, in the prior art, as shown in FIG. 1, a plurality of negative electrode tabs welded to the battery case have the same thickness. However, in this case, there is a problem in that a defect in a back bead due to over-welding occurs or a defect in which the bonding strength is deteriorated due to insufficient welding occurs.

In contrast, in the method of manufacturing a cylindrical secondary battery of the present invention, as shown in FIGS. 2 and 3, when laser welding a plurality of negative electrode tabs to the outer surface of the battery case, the thickness of the second negative electrode tab is determined, as shown in FIGS. By controlling the thickness to be thicker than the thickness of the first negative electrode tab located between the and the second negative electrode tab, welding is properly performed to reduce back bead defects, and the bonding strength between the plurality of negative electrode tabs and the negative electrode tab and the battery case It is possible to improve the bonding strength between. In addition, by using the method for manufacturing a cylindrical secondary battery of the present invention, in laser welding, it is possible to expand the range of the weldable output, thereby improving the manufacturing processability of the cylindrical secondary battery.

The thickness of the first negative electrode tab may be 40 μm to 120 μm, preferably 50 μm to 100 μm, and the thickness of the second negative electrode tab may be 80 μm to 260 μm, respectively, preferably It may be 125㎛ to 200㎛. When the thickness of the first and second negative electrode tabs is less than the above range, there is a risk of damage to the negative electrode tab and occurrence of a back bead when performing laser welding, and the strength is easily There is a problem of deterioration. In addition, when the thickness of the first and second negative electrode tabs exceeds the above range, the material cost may increase, and as the thickness of the negative electrode tab increases, it is difficult to fold and process the tab during the process, resulting in a decrease in workability. In addition, there is a problem in that the capacity of the battery may decrease due to a decrease in the space inside the battery case. Therefore, it is preferable that the thicknesses of the first and second negative electrode tabs satisfy the above range.

In addition, the ratio of the thickness of the first negative electrode tab and the second negative electrode tab may be 1:1.2 to 1:4, preferably 1:1.4 to 1:3, more preferably 1:1.6 to May be 1:2. When the ratio of the thickness of the first negative electrode tab and the second negative electrode tab is out of the above range, a back bead may occur due to a narrow weldable output range, or a problem in that the bonding strength may decrease. Accordingly, it is preferable that the ratio of the thickness of the first negative electrode tab and the second negative electrode tab satisfies the above range.

In addition, it may be desirable to adjust the beam size of the laser in order to reduce the influence on corrosion of the laser used in the welding step. The beam size of the laser of the present invention may be 10 to 50 μm, preferably 15 to 30 μm, more preferably 15 to 25 μm. When the beam size of the laser is greater than 50 μm, there is a disadvantage in that the influence on corrosion increases and the aspect ratio of the weld bead to the depth decreases, resulting in a decrease in welding efficiency. In addition, when the beam size of the laser is less than 10 μm, the area to be welded is small, so that sufficient welding strength cannot be secured with a single welding. Therefore, it is preferable that the beam size of the laser satisfies the above range.

In addition, the wavelength of the laser is not particularly limited as long as efficient welding is possible, but in consideration of the material of the negative electrode tab and the battery case to be welded, according to a specific example of the present invention, 1000 to 1500 nm, preferably 900 To 1350nm, more preferably 1060 to 1080nm. When the wavelength of the laser is less than the above range, the weldable output range may be widened, but there is a problem in that it is difficult to reduce the beam size of the laser. In addition, when the wavelength of the laser exceeds the above range, the possible welding power range is narrow, and thus there is a high possibility that welding failure may occur. Therefore, it is preferable that the wavelength of the laser satisfies the above range. In addition, in addition, a laser having a wavelength of 400 nm to 600 nm may be used.

In addition, in manufacturing a cylindrical secondary battery, when irradiating a laser on the outer surface of the battery case, since the shape of the battery case surface may vary depending on the processing speed of the laser, the processing speed of the laser may be important. In the welding step of the present invention, the processing speed of the laser may be 100 to 1000 mm/s, preferably 200 to 500 mm/s, and more preferably 200 to 300 mm/s. If the processing speed of the laser is less than the above range, there is a possibility that a back bead may occur, and if the processing speed of the laser exceeds the above range, a problem of lowering the bonding strength occurs, so that the processing speed of the laser satisfies the above range. It is desirable to do it.

In addition, in the welding step, the line energy of the laser may be 1350 to 2250 W·s/m, preferably 1500 to 2200 W·s/m, and more preferably 1800 to 2100 W·s/m. I can. The line energy (W·s/m) represents the laser output value (laser output (W)/laser processing speed (mm/s)×1000) with respect to the laser processing speed. If the line energy of the laser is less than the above range, there may be a problem that the bonding strength is lowered, and if it exceeds the above range, there is a possibility that a back bead may occur, so the output of the laser satisfies the above range. It is desirable to do it.

In addition, the type of the negative electrode tab of the present invention is not particularly limited as long as it is a material generally used in the relevant technical field. According to the present invention, the negative electrode tab may be copper, nickel, nickel-plated copper or nickel-clad copper, and the welding method according to the present invention may be more preferably applied to the material. The plurality of negative electrode tabs to be welded in the welding step may be two or more, preferably 2 to 5, more preferably 2 to 3 negative electrode tabs.

In addition, the type of the battery case of the present invention is not particularly limited as long as it is a material generally used in the relevant technical field. According to a specific embodiment of the present invention, the battery case may be made of iron, nickel-plated iron or stainless steel (SUS) as a welding part, and the welding method according to the present invention is more preferably applied when targeting the material. I can.

Please consider whether there are any additional restrictions such as patterns when welding.

In addition, the welding pattern in the welding step of the present invention is not particularly limited as long as it can maintain the bonding strength of the negative electrode tab. As a specific example, various patterns such as linear, circular, polygonal, and the like may be represented, and in particular, among the patterns, a circular shape is preferable because the force can be uniformly distributed even when a force is applied in various directions. In addition, the circular and polygonal patterns may not coincide with the start and end points of laser irradiation. That is, in the case of a circle and a polygon, when the starting point and the end point coincide, there is a risk of penetrating the battery case, and thus an incomplete circle or polygon shape may be obtained.

And, this maintains the bonding strength of the cathode tab.

Cylindrical secondary battery

The present invention relates to a cylindrical secondary battery in which an electrode assembly including a positive electrode, a negative electrode, and a separator is enclosed in a cylindrical battery case. The cylindrical secondary battery of the present invention may be a cylindrical secondary battery manufactured by the method for manufacturing a cylindrical secondary battery described above. As described above, a cylindrical secondary battery generally uses a jelly-roll type electrode assembly wound with a separator interposed between a long sheet-shaped positive electrode and a negative electrode, and the jelly-roll type electrode assembly includes a positive electrode tab and a negative electrode. The tab is attached. The positive electrode tab extends upward and is coupled to the cap assembly, and the negative electrode tab extends downward and is attached to the lower surface of the battery case. In addition, with respect to the negative electrode tab, since resistance increases when the amount of current increases, a plurality of negative electrode tabs may be used to achieve low resistance.

The cylindrical secondary battery of the present invention includes a plurality of negative electrode tabs, a first negative electrode tab positioned on an inner surface of a battery case, and a thickness greater than that of the first negative electrode tab, positioned on the first negative electrode tab. It may include a second negative electrode tab.

In the cylindrical secondary battery, by making the thickness of the second negative electrode tab thicker than the thickness of the first negative electrode tab positioned between the second negative electrode tab and the battery case, the battery case, the first negative electrode tab, and the second negative electrode tab are laser In performing welding, welding is properly performed to reduce back bead defects, improve bonding strength, and also, in laser welding, to expand the weldable output range, Manufacturing processability can be improved.

In addition, the thickness of the first negative electrode tab may be 40㎛ to 120㎛, preferably 50㎛ to 100㎛, the thickness of the second negative electrode tab may be 80㎛ to 260㎛, preferably May range from 125 μm to 200 μm. When the thickness of the first and second negative electrode tabs is less than the above range, there is a risk of damage to the negative electrode tab and occurrence of a back bead when performing laser welding, and the strength is easily There is a problem of deterioration. In addition, when the thickness of the first and second negative electrode tabs exceeds the above range, the material cost may increase, and as the thickness of the negative electrode tab increases, it is difficult to fold and process the tab during the process, resulting in a decrease in workability. In addition, there is a problem in that the capacity of the battery may decrease due to a decrease in the space inside the battery case. Therefore, it is preferable that the thicknesses of the first and second negative electrode tabs satisfy the above range.

In addition, the ratio of the thickness of the first negative electrode tab and the second negative electrode tab may be 1:1.2 to 1:4, preferably 1:1.4 to 1:3, more preferably 1:1.6 to May be 1:2. When the ratio of the thickness of the first negative electrode tab and the second negative electrode tab is out of the above range, a back bead may occur due to a narrow weldable output range, or a problem in that the bonding strength may decrease. Accordingly, it is preferable that the ratio of the thickness of the first negative electrode tab and the second negative electrode tab satisfies the above range.

In addition, the type of the negative electrode tab of the present invention is not particularly limited as long as it is a material generally used in the relevant technical field. According to the present invention, the negative electrode tab may be copper, nickel, nickel-plated copper or nickel-clad copper, and the welding method according to the present invention may be more preferably applied to the material. The plurality of negative electrode tabs to be welded in the welding step may be two or more, preferably 2 to 5, more preferably 2 to 3 negative electrode tabs.

In addition, the type of the battery case of the present invention is not particularly limited as long as it is a material generally used in the relevant technical field. According to a specific embodiment of the present invention, the battery case may be made of iron, nickel-plated iron or stainless steel (SUS) as a welding part, and the welding method according to the present invention is more preferably applied when targeting the material. I can.

Hereinafter, preferred embodiments are presented to aid in the understanding of the present invention, but the following examples are provided for easier understanding of the present invention, and the present invention is not limited thereto.

Example

After overlapping the first negative electrode tab and the second negative electrode tab on the inner surface of the battery case, IR laser was irradiated to perform welding. Hereinafter, in the examples, iron (Fe) was used as the battery case, copper (Cu) was used as the first negative electrode tab and the second negative electrode tab, and the thickness was as described in the following Examples, and used during welding. The laser specifications are as follows.

<Laser specification>

Wavelength: 1070nm

Laser: IPG Fiber Laser

Type: Scan Type

Max power: 500W

Beam size: 23.3㎛

Welding area: Ф 1.5

Example 1

As shown in FIG. 4, after superimposing a first negative electrode tab having a thickness of 100 μm and a second negative electrode tab having a thickness of 200 μm on the inner surface of the battery case having a thickness of 300 μm, 200 mm/s in the outer direction of the battery case. IR laser (maximum output: 500W) was irradiated at a processing speed, and welding was performed.

Example 2

After superimposing a first negative electrode tab having a thickness of 75 μm and a second negative electrode tab having a thickness of 125 μm on the inner surface of a battery case having a thickness of 300 μm, an IR laser (maximum Output: 500W) was irradiated and welding was carried out.

Example 3

After superimposing the first negative electrode tab of 50 μm and the second negative electrode tab of 150 μm on the inner surface of the battery case having a thickness of 300 μm, the IR laser (maximum Output: 500W) was irradiated and welding was carried out.

Comparative Example 1

As shown in FIG. 5, after overlapping the same first negative electrode tab and second negative electrode tab with a thickness of 100 μm on the inner surface of a battery case having a thickness of 300 μm, a processing speed of 200 mm/s in the outer direction of the battery case A furnace IR laser (maximum output: 500W) was irradiated and welding was carried out.

Comparative Example 2

After superimposing a first negative electrode tab having a thickness of 25 μm and a second negative electrode tab having a thickness of 175 μm on the inner surface of the battery case having a thickness of 300 μm, the IR laser (maximum Output: 500W) was irradiated and welding was carried out.

Experimental Example 1: Weldable output range when welding the first cathode tab and the second cathode tab

In Examples 1 to 3 and Comparative Examples 1 to 2 of the present invention, welding was performed while controlling the output of the IR laser at a processing speed of 200 mm/s by overlapping only the first cathode tab and the second cathode tab. The welding and peeling strength of the 1 negative electrode tab and the second negative electrode tab were measured.

Detailed results are shown in Table 1 below.

Print
(% based on the maximum output) Comparative Example 1 Comparative Example 2 Example 1 Example 2 Example 3 welding
Whether Exfoliation
burglar
(kgf) Whether to weld Exfoliation
burglar
(kgf) Whether to weld Exfoliation
burglar
(kgf) Whether to weld Exfoliation
burglar
(kgf) Whether to weld Exfoliation
burglar
(kgf) 56 × - × - × - × - × - 58 × - ○ 0.19 × - × - × - 60 ○ 0.54 ○ 0.32 × - ○ 0.98 ○ 0.47 62 ○ 2.17 ○ 0.30 ○ 0.22 ○ 1.31 ○ 1.24 66 ○ 2.31 ○ 0.18 ○ 1.43 ○ 1.25 ○ 1.79 68 B - ○ 0.28 ○ 1.45 ○ 1.62 ○ 1.52 70 B - ○ 0.25 ○ 1.77 ○ 1.58 ○ 1.42 74 B - ○ 0.33 ○ 1.47 B 1.95 ○ 1.31 78 B - ○ 0.11 ○ 1.32 B - B 1.52 80 B - ○ 0.31 ○ 1.73 B - B - 82 B - B 0.29 ○ 1.73 B - B - 84 B - B - B - B - B -

*'B' in Table 1 indicates that a back bead is formed by over-welding.

According to Table 1, a weldable output range capable of exhibiting sufficient peel strength (bonding strength) when laser welding the first and second cathode tabs of 100 μm and 200 μm in thickness according to Example 1, respectively, is 16. % (66-82%), significantly compared to the weldable power range (4%, 62-66%) when laser welding the first and second cathode tabs having a thickness of 100 μm according to Comparative Example 1 You can see that it is wide. If the peel strength is 1.2kgf or more, when using a conventional cylindrical secondary battery, the performance of the secondary battery is not affected, and the negative electrode tab is not detached from the battery case due to vibration or pressure of equipment generated during the process. In addition, in the case of Comparative Example 2, when laser welding the first cathode tab and the second cathode tab having a thickness of 25 μm and 175 μm, the weldable output range was widened to 22% (58-80%), It can be seen that it is very degraded and cannot be used.

On the other hand, when laser welding the first cathode tab and the second cathode tab having a thickness of 75 μm and 125 μm, 50 μm and 150 μm according to Examples 2 and 3, respectively, the weldable output range was 8% (62 to 70%). ) And 12% (62-74%), it can be seen that it is significantly wider than that of Comparative Example 1. In addition, in Comparative Example 2, the range of the weldable power during laser welding was as wide as 22%, but it can be seen that the peel strength was greatly reduced and there was no satisfactory range.

Experimental Example 2: Welding of the battery case, the first negative electrode tab, and the second negative electrode tab, the weldable output range

On the inner surfaces of the battery cases of Examples 1 to 3 and Comparative Examples 1 to 2 of the present invention, the first negative electrode tab and the second negative electrode tab were overlapped, and in the outer direction of the battery case, at a processing speed of 200 mm/s. Welding was performed while controlling the output of the IR laser, and whether the first negative electrode tab and the second negative electrode tab were welded, whether the first negative electrode tab and the battery case were welded, and the peel strength of each negative electrode tab were measured.

Detailed results are shown in Table 2 below.

Print
(% based on the maximum output) Comparative Example 1 Comparative Example 2 Example 1 Example 2 Example 3 welding
Whether Exfoliation
burglar
(kgf) Whether to weld Exfoliation
burglar
(kgf) Whether to weld Exfoliation
burglar
(kgf) Whether to weld Exfoliation
burglar
(kgf) Whether to weld Exfoliation
burglar
(kgf) 62 1 Tab - × - - - × - × - 64 2 Tab 0.3
/1.66 × - - - × - × - 66 2 Tab 0.42
/2.11 1 Tab - - - × - 1 Tab - 68 2 Tab 0.87
/1.9 2 Tab 0.18
/1.97 - - 1 Tab - 2 Tab 0.42
/1.84 70 2 Tab 1.17
/2.18 2 Tab 0.67
/2.12 - - 2 Tab 1.10
/2.32 2 Tab 1.24
/2.21 72 2 Tab 1.37
/2.22 2 Tab 0.74
/2.39 - - 2 Tab 1.87
/3.11 2 Tab 1.33
/1.83 74 2 Tab 2.04
/2.31 2 Tab 0.83
/2.68 - - 2 Tab 2.11
/2.28 2 Tab 1.64
/2.54 76 B - 2 Tab 1.10
/3.12 - - 2 Tab 1.77
/1.99 2 Tab 1.88
/2.68 78 B - 2 Tab 0.82
/2.17 2 Tab 0.24
/2.2 2 Tab 2.20
/1.93 2 Tab 1.56
/2.77 80 B - 2 Tab 0.74
/2.84 2 Tab 2.56
/2.22 B - B - 82 - - 2 Tab 0.34
/1.78 2 Tab 3.45
/1.85 B - B - 84 - - 2 Tab 0.84
/2.17 2 Tab 2.93
/2.24 B - B - 88 - - B - 2 Tab 3.15
/1.9 B - B - 90 - - B - B - B - B -

* The '1 Tab' indicates that only the first negative electrode tab is welded. * '2 Tab' indicates that both the first negative electrode tab and the second negative electrode tab are welded.

* The'B' indicates that a back bead is formed by over-welding.

* The'peel strength' indicates the peel strength of the second negative electrode tab/the peel strength of the first negative electrode tab.

According to Table 2, when laser welding the first negative electrode tab and the second negative electrode tab of 100 μm and 200 μm in thickness according to Example 1 to a battery case, a weldable output capable of exhibiting sufficient peel strength (bonding strength) The range is 8% (80-88%), and a weldable output range that shows sufficient peel strength (bonding strength) when laser welding the first cathode tab and the second cathode tab having a thickness of 100 μm according to Comparative Example 1 ( 4%, 70~74%). In addition, it can be seen that the first negative electrode tab and the second negative electrode tab having a thickness of 25 μm and 175 μm, respectively, according to Comparative Example 2, were wider than the weldable output range (0%, low peel strength) when laser welding the battery case. have. If the peel strength is 1.2kgf or more, when using a conventional cylindrical secondary battery, the performance of the secondary battery is not affected, and the negative electrode tab is not detached from the battery case due to vibration or pressure of equipment generated during the process.

On the other hand, when laser welding the first negative electrode tab and the second negative electrode tab having the thicknesses of 75 μm and 125 μm, 50 μm and 150 μm, respectively, according to Examples 2 and 3, the welding power range was 6% (72 to 78%) and 8% (70-78%), it can be seen that compared to Comparative Examples 1 and 2 significantly wider.

In addition, the surface and cross section after laser welding of Example 1 and Comparative Example 1 are as shown in FIGS. 6 and 7. Referring to FIG. 6, a bead of about 180 μm is formed on the outer surface of the battery case at the welding portion of the cylindrical secondary battery according to Example 1, and in the cross section, the battery case, the first negative electrode tab, and the second negative electrode tab are solid. It can be confirmed that it is welded properly and has not penetrated. On the other hand, looking at FIG. 7 of the cylindrical secondary battery according to Comparative Example 1, the plated nickel layer is peeled off and the molten metal is recrystallized to confirm the remaining shape.

On the other hand, the outer surface of the battery case in FIGS. 6 and 7 shows the shape of the bead generated after laser welding, and the cross section shows the area and shape of the welding generated after laser welding. Specifically, it can be seen that reddish copper (cathode tab) is melted by heat to give black light, and iron (battery case) and copper (cathode tab) are melt-mixed to form a metal compound.

Therefore, by adjusting the thickness and the ratio of the first and second negative electrode tabs of the present invention within the above range, not only the weldable output range capable of exhibiting sufficient peel strength (bonding strength) during laser welding is expanded, but also It is possible to reduce defects in the back bead of the welding area and improve the bonding strength (peel strength), and thus process stability can be further improved.

All simple modifications to changes of the present invention belong to the scope of the present invention, and the specific scope of protection of the present invention will be made clear by the appended claims.

Claims (16)

A welding step of irradiating a laser on an outer surface of the battery case to weld a plurality of negative electrode tabs located on the inner surface of the battery case and the battery case,
The plurality of negative electrode tabs,
A first negative electrode tab positioned on the inner surface of the battery case,
And a second negative electrode tab disposed on the first negative electrode tab and having a thickness thicker than that of the first negative electrode tab. The method according to claim 1,
The method of manufacturing a cylindrical secondary battery, wherein the first negative electrode tab has a thickness of 40 μm to 120 μm, and the second negative electrode tab has a thickness of 80 μm to 260 μm. The method according to claim 1,
The method of manufacturing a cylindrical secondary battery, characterized in that the ratio of the thickness of the first negative electrode tab and the second negative electrode tab is 1:1.2 to 1:4. The method according to claim 1,
The method of manufacturing a cylindrical secondary battery, characterized in that the beam size of the laser is 10 to 50㎛. The method according to claim 1,
The method of manufacturing a cylindrical secondary battery, characterized in that the processing speed of the laser in the welding step is 100 to 1000mm/s. The method according to claim 1,
The method of manufacturing a cylindrical secondary battery, characterized in that the wavelength of the laser is 1000 to 1100nm or 400 to 600nm. The method according to claim 1,
The method of manufacturing a cylindrical secondary battery, characterized in that the line energy of the laser in the welding step is 1350 to 2250 W·s/m. The method according to claim 1,
The negative electrode tab is a method of manufacturing a cylindrical secondary battery, characterized in that copper, nickel, nickel-plated copper or nickel-clad copper. The method according to claim 1,
The battery case is a method of manufacturing a cylindrical secondary battery, characterized in that the welding portion is made of iron, nickel-plated iron or stainless steel (SUS). The method according to claim 1,
The cylindrical secondary battery is a method of manufacturing a cylindrical secondary battery, characterized in that the electrode assembly including a positive electrode, a negative electrode, and a separator are enclosed in a cylindrical battery case. As a cylindrical secondary battery in which an electrode assembly including a positive electrode, a negative electrode, and a separator is enclosed in a cylindrical battery case,
Including a plurality of negative electrode tabs,
A first negative electrode tab positioned on the inner surface of the battery case,
And a second negative electrode tab disposed on the first negative electrode tab and having a thickness greater than that of the first negative electrode tab. The method of claim 11,
Cylindrical secondary battery, characterized in that the thickness of the first negative electrode tab is 40㎛ to 120㎛, and the thickness of the second negative electrode tab is 80㎛ to 260㎛. The method of claim 11,
Cylindrical secondary battery, characterized in that the ratio of the thickness of the first negative electrode tab and the second negative electrode tab is 1:1.2 ~ 1:4. The method of claim 11,
The negative electrode tab is a cylindrical secondary battery, characterized in that the copper, nickel, nickel-plated copper or nickel-clad copper. The method of claim 11,
The battery case is a cylindrical secondary battery, characterized in that made of iron, nickel-plated iron or stainless steel (SUS). The method of claim 11,
The cylindrical secondary battery is manufactured by the method of manufacturing a cylindrical secondary battery according to claim 1.

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