Welding method for Mylar membrane of lithium battery

Abstract

The invention relates to the technical field of battery manufacturing, and discloses a lithium battery Mylar membrane welding method which is applied to a laser welding system and comprises the steps that a battery is rotated to a set angle, positioned and clamped, and the battery is covered with a Mylar membrane; adjusting the distance between a battery holder on the battery and the Mylar film until the distance is smaller than a preset value; controlling a laser welding system to weld and fix the Mylar membrane on the battery; the laser welding system comprises a carbon dioxide laser. And the battery coated with the Mylar film is welded through the carbon dioxide laser, so that the Mylar film can be well welded on the outer side of the battery. According to the characteristics of high precision and low thermal deformation of the carbon dioxide laser, when the gap between the Mylar film and the battery holder is controlled to be smaller than the preset value, the welding quality can be improved, the pseudo soldering phenomenon is avoided, the requirement for the assembly precision between the Mylar film and the battery holder is lowered, and the compatibility of the Mylar film and the battery during welding is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of battery manufacturing, and in particular relates to a welding method for a Mylar film of a lithium battery. Background Art

[0002] In the production process of lithium batteries, the positive and negative electrode materials inside the battery are generally protected by Mylar film. It can isolate the shell, thereby avoiding battery abnormalities caused by contact friction between the battery and the shell. The current coating equipment usually uses hot melt technology to weld the Mylar film, but during the welding process of the hot melt strip and the Mylar film, various problems will occur due to heating and friction, such as: Teflon is frequently damaged, and debris cannot be cleaned up, affecting battery quality; Teflon is frequently replaced, affecting production capacity; hot melt welding often causes wire drawing, affecting the welding quality of the rear cover, etc.

[0003] Therefore, in order to avoid this situation, semiconductor lasers are now used for welding, and laser weld marks are formed at the overlap of the Mylar film and the battery in a non-contact mode, and then the Mylar film is welded to the battery. However, during the welding process, the Mylar film needs to be welded to the base material battery "holder" (hereinafter referred to as the battery holder), and the assembly requirements of the Mylar film and the battery holder are high during welding, and no gap is allowed between the two. If there is a gap between the battery holder and the Mylar film, there will be white smoke after welding, and there will be a phenomenon of cold welding inside the weld. It can be seen that the compatibility of Mylar film and batteries welded by semiconductor lasers is poor. Summary of the invention

[0004] In order to solve the deficiencies of the prior art, the present invention provides a welding method for a Mylar film of a lithium battery.

[0005] A method for welding Mylar film of a lithium battery, the welding method being applied in a laser welding system, the welding method comprising:

[0006] The battery is rotated to a set angle and clamped in position, and the Mylar film is covered on the battery;

[0007] Adjusting the distance between the battery holder on the battery and the Mylar film until the distance is less than a preset value;

[0008] Controlling the laser welding system to weld and fix the Mylar film on the battery;

[0009] Wherein, the laser welding system includes a carbon dioxide laser.

[0010] In some embodiments, the distance between the Mylar film and the battery holder is less than 0.15 mm.

[0011] In some embodiments, the Mylar film is a single layer or a double layer.

[0012] In some embodiments, the Mylar film is a double layer, and the distance between the double layers of the Mylar film is less than 0.15 mm.

[0013] In some embodiments, the laser welding system further includes an optical element disposed in an optical path of the carbon dioxide laser.

[0014] In some embodiments, the laser welding system further includes: a beam expander, which is disposed between the carbon dioxide laser and the optical element to expand the diameter of an output beam of the laser welding system.

[0015] In some embodiments, the optical element is configured as a galvanometer.

[0016] In some embodiments, during welding, the galvanometer moves in a swinging and scribing manner.

[0017] In some embodiments, the overlapping portion of the battery and the Mylar film is configured as a weld bead, a plurality of pre-welding points are configured on the weld bead, and the plurality of pre-welding points are evenly spaced and distributed.

[0018] In some embodiments, the laser welding system further includes a galvanometer, which oscillates and lines so that the laser beam moves along the weld bead in a spiral path.

[0019] In summary, the present invention has at least the following benefits:

[0020] The present invention provides a method for welding Mylar film of lithium battery, which uses a carbon dioxide laser to perform heat-melt welding on the battery coated with Mylar film, so that the Mylar film can be well welded to the outside of the battery. Among them, by using the high precision and low thermal deformation characteristics of the carbon dioxide laser, when the gap between the Mylar film and the battery holder is controlled to be less than a preset value, the welding quality can be improved, the phenomenon of cold welding can be avoided, and the requirements for the assembly accuracy between the Mylar film and the battery holder are reduced, thereby improving the compatibility of the Mylar film and the battery when welding. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 A schematic diagram of a process for welding Mylar film of a lithium battery according to an embodiment of the present invention;

[0022] Figure 2 A schematic diagram of welding a Mylar film and a battery by a laser welding system according to an embodiment of the present invention;

[0023] Figure 3A schematic diagram of the steps of welding a Mylar film and a battery by a laser welding system according to an embodiment of the present invention;

[0024] Figure 4 A schematic diagram of the motion trajectory of a laser beam during welding by a laser welding system according to an embodiment of the present invention;

[0025] Figure 5 A schematic diagram of a carbon dioxide laser welding a Mylar film with a gap of 0.1 mm and a battery holder according to an embodiment of the present invention;

[0026] Figure 6 A schematic diagram of a Mylar film and a battery holder with a gap of 0.05 mm welded by a carbon dioxide laser according to an embodiment of the present invention;

[0027] Figure 7 It is a schematic diagram of a semiconductor laser welding a Mylar film with a gap of 0.1 mm and a battery holder according to an embodiment of the present invention;

[0028] Figure 8 A schematic diagram of a weld between a Mylar film with a gap of 0.1 mm and a battery holder using a semiconductor laser according to an embodiment of the present invention;

[0029] Fig. 9 This is a schematic diagram of welding two layers of Mylar film on a battery holder using a carbon dioxide laser according to an embodiment of the present invention;

[0030] Fig.10 This is a schematic diagram of using a semiconductor laser to weld two layers of Mylar film on a battery holder according to an embodiment of the present invention. DETAILED DESCRIPTION

[0031] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. The described embodiments are only part of the embodiments of the present invention, not all of them.

[0032] Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the invention claimed for protection, but merely represents selected embodiments of the present invention. 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.

[0033] like Figure 1 As shown, a method for welding Mylar film of a lithium battery is provided. The welding method is applied in a laser welding system. The welding method comprises the following steps:

[0034] Step 110, the battery is rotated to a set angle and positioned and clamped, and the Mylar film is covered on the battery.

[0035] Specifically, the battery is placed on a waiting welding station, which may be a waiting station or a welding operation area, and is not specifically limited; the battery is rotated to a set angle and fixed and clamped by a clamp, so that a layer of Mylar film can be covered on the surrounding side of the battery.

[0036] Step 120, adjusting the distance between the battery holder on the battery and the Mylar film until the distance is less than a preset value.

[0037] Specifically, if the battery is in the waiting position, the battery is moved to the welding operation area, and the distance between the battery holder and the Mylar film on the battery is adjusted. By controlling the distance between the Mylar film and the surface of the battery holder, the welding effect during subsequent welding is guaranteed.

[0038] To ensure the welding effect, in some embodiments, the distance between the Mylar film and the battery holder is less than 0.15 mm.

[0039] For example, the distance between the Mylar film and the battery holder is 0.11 mm; for another example, the distance between the Mylar film and the battery holder is 0.09 mm; for another example, the distance between the Mylar film and the battery holder is 0.05 mm.

[0040] To achieve better welding effect, in some embodiments, the distance between the Mylar film and the battery holder is less than or equal to 0.1 mm.

[0041] Specifically, the battery holder is generally made of plastic material. The battery holder includes a bracket (battery holder) provided with the negative electrode of the battery after the film is coated and a battery holder installed on the positive electrode of the battery. The Mylar film is hot-melt welded to the battery by hot-melt welding the Mylar film and the battery holder to achieve welding and fixation of the Mylar film. Based on this, in order to ensure the welding effect, the welding gap between the Mylar film and the battery holder needs to be less than or equal to 0.1 mm. In order to make the welding gap meet the requirements, a gap gasket can be placed between the Mylar film and the battery holder. The gap gasket is 0.1 mm, so that the distance between the Mylar film and the surface of the battery holder is controlled at 0.1 mm. When the carbon dioxide laser performs hot-melt welding on the Mylar film that meets the welding gap requirements, it can hot-melt weld a complete and uniform weld mark on the battery holder, and fully avoid the phenomenon of cold welding and white smoke after welding.

[0042] To facilitate welding, Figure 2As shown, in some embodiments, the overlapped portion of the battery and the Mylar film is set as a weld bead, a plurality of pre-welding points are set on the weld bead, and the plurality of pre-welding points are evenly spaced.

[0043] Specifically, the weld bead is the moving area of ​​the laser beam during laser welding, and by providing a pre-welding point at the overlapping position of the battery holder and the Mylar film, the welding effect of the battery and the Mylar film can be ensured by controlling the position of the pre-welding point.

[0044] Among them, reference Figure 2 and Figure 3 The peripheries of both ends of the battery are respectively arranged as follows: three pre-welding points are arranged on the weld bead at the long side of the battery, and one pre-welding point is arranged on the weld bead at the short side of the battery, and each pre-welding point surrounds and forms a ring surface. In this way, by performing annular positioning on the peripheries of both ends of the battery, the Mylar film can be installed more stably on the periphery of the battery.

[0045] In one embodiment, during welding, the battery is placed horizontally on the workbench with the long side facing upward. At this time, the battery pre-welding points are set. At the periphery of the top of the battery: three pre-welding points are set at the long sides of the upper and lower surfaces, and the three pre-welding points at the long sides of the upper and lower surfaces are aligned or staggered, and one pre-welding point is set at the short sides of the front and rear surfaces; at the periphery of the bottom of the battery: three pre-welding points are set at the long sides of the upper and lower surfaces, and the three pre-welding points at the long sides of the upper and lower surfaces are aligned or staggered, and one pre-welding point is set at the short sides of the front and rear surfaces; the four sides of the outer peripheral side of the battery are welded and fixed with the Mylar film, that is, the Mylar film is hot-melted and fixed on the battery negative pole bracket and the battery holder installed on the positive pole of the battery. It can be understood that the position and number of the pre-welding points can also be set according to actual conditions, and are not limited here, as long as it is conducive to welding and fixing the battery and the Mylar film.

[0046] Step 130, controlling the laser welding system to weld and fix the Mylar film on the battery.

[0047] Specifically, the laser welding system includes a carbon dioxide laser, an optical element and a beam expander arranged on the optical path of the carbon dioxide laser. When welding a battery covered with Mylar film, the pre-set welding control parameters are called up, the battery covered with Mylar film is rotated so that the battery portion to be welded is facing the welding work area, the carbon dioxide laser emits light in response to the welding control parameters, the beam expander adjusts the output light beam, and the optical element cooperates to perform motion welding on the battery covered with Mylar film in a swinging and marking manner, so that the Mylar film can be welded on the battery.

[0048] To facilitate the use of the optical element, in some embodiments, the optical element is configured as a galvanometer.

[0049] Specifically, the galvanometer can be used to control the direction and position of the laser beam, so that the propagation direction of the laser beam can be changed by precise adjustment of the galvanometer.

[0050] In order to produce a better welding effect, in some embodiments, during welding, the galvanometer moves in a swinging and scribing manner.

[0051] Specifically, during welding, the galvanometer uses a swing scribing technology. During the scribing process, the laser beam is first focused on a very small spot, and then the spot is guided to the surface around the battery through the deflection of the galvanometer. As the galvanometer continuously swings, the laser beam scans along a predetermined trajectory, melting the weld to form the desired scribing line.

[0052] Among them, reference Figure 4 The overlap between the battery and the Mylar film is set as a weld bead. The galvanometer uses the swing scribing technology to make the laser beam move along the weld bead in a spiral path. The Mylar film melts due to the laser action, forming a "one"-shaped weld mark. This movement method can avoid the laser beam passing through the same position on the weld bead twice, causing energy concentration at that position, thereby avoiding welding defects caused by energy concentration, which is conducive to improving welding quality.

[0053] In order to facilitate the welding of the battery, the steps of welding and fixing the Mylar film on the battery include:

[0054] In the first placement state of the battery, the periphery of one end of the battery is welded:

[0055] Step 1: The laser welding system welds a first preset number of welding points to a long side of the battery;

[0056] Step 2: Control the battery to rotate by a first preset angle based on the first placement state, and the laser welding system welds a second preset number of welding points to a wide side of the battery;

[0057] Step 3: Control the battery to rotate to a second preset angle based on the first placement state, and the laser welding system welds a third preset number of welding points to the other long side of the battery;

[0058] Step 4: Control the battery to rotate by a third preset angle based on the first placement state, and the laser welding system welds a fourth preset number of welding points to the other wide side of the battery, thereby completing the welding and fixing of the Mylar film on the battery;

[0059] Among them, the welding steps can be adjusted according to actual conditions and are not limited to the welding order of steps one to four; the first preset number of welds and the third preset number of welds can be the same or different; the second preset number of welds and the fourth preset number of welds can be the same or different; the number of welds can be based on actual requirements for welding; when welding the periphery of the battery, welding can also be started from the wide side of the battery, and the welding steps are adjusted based on the above steps one to four, and will not be repeated here.

[0060] The battery position is adjusted so that the battery is in the second placement state, and the welding process of steps 1 to 4 is performed on the periphery of the other end of the battery to obtain a battery with both ends fixed by Mylar film welding.

[0061] In one embodiment, if Figure 2 and Figure 3 As shown, when the Mylar film is welded and fixed on the battery, the battery is placed horizontally on the workbench. First, the top periphery of the battery is welded: the battery is adjusted so that the upper long side of the battery is located within the welding work area, and the laser beam is adjusted by the galvanometer so that the laser acts on the battery covered with the Mylar film to hot-melt weld three welding points; the battery is rotated 90°, and the laser beam hot-melt welds a welding point on the front wide side of the battery; then the battery is rotated 180°, and the laser beam hot-melt welds three welding points on the lower long side of the battery; finally, the battery is rotated 270°, and the laser beam hot-melt welds a welding point on the rear wide side of the battery, thus completing the welding of the top periphery of the battery; then, the battery position is adjusted so that the bottom periphery of the battery is located within the welding work area, and the above welding operations are repeated while coordinating and controlling the rotation of the battery, thereby completing the stable welding of the Mylar film on the battery.

[0062] When the position corresponding to the battery holder can be welded is reached, the welding position for welding the Mylar film to the battery holder is arranged according to the actual production situation, which is not limited here.

[0063] In order to facilitate the control of the welding effect, in some embodiments, the weld mark length of the battery and the Mylar film is set to 1 mm to 2 mm.

[0064] Specifically, by setting the weld mark length to 1 mm to 2 mm, the positioning effect of the Mylar film on the battery can be ensured. For example, the weld mark length of the battery and the Mylar film is set to 1 mm; for another example, the weld mark length of the battery and the Mylar film is set to 1.5 mm; for another example, the weld mark length of the battery and the Mylar film is set to 1.6 mm.

[0065] In some embodiments, the Mylar film can be selected but not limited to two layers. The distance between two adjacent layers of Mylar film is less than 0.15 mm.

[0066] It is understandable that when welding two or more layers of Mylar film on a battery, due to the thin texture of the Mylar film, if a tensile force is applied to keep the Mylar film in a stretched state and then hot-melt welded, it is not only easy to cause the Mylar film to deform, but also not conducive to accurately hot-melt welding it to the preset welding position of the battery frame; if pressure is applied to make the double or multi-layer Mylar film reach a compressed gapless state, it is easy to cause the battery holder welded thereto to be damaged due to the pressure, etc., thereby affecting the battery yield and increasing defective products; based on this, the two or more layers of Mylar film cannot be compressed without gaps. Semiconductor lasers need to be completely compressed to achieve a better welding effect, and the welding requirements are relatively harsh. When the carbon dioxide laser of the present application welds two or more layers of Mylar film, the gap between the two or more layers of Mylar film is controlled within a range of less than 0.15mm, so that the expected welding effect can be achieved while effectively avoiding the deformation of the Mylar film and the production of defective products; it can be seen that compared with the harsh welding requirements of semiconductor lasers, carbon dioxide lasers have good compatibility with welding gaps.

[0067] Specifically, in the process of welding two layers of Mylar film on the battery, the high precision and low thermal deformation characteristics of the carbon dioxide laser can be used to control the gap between the two layers of Mylar film to less than 0.15mm, and obtain a better welding effect, thereby appropriately compatibility with the compression gap between the two layers of Mylar film, and fully improving the compatibility of lithium batteries and Mylar films when welding. For example, the distance between the two layers of Mylar film is 0.11mm; for another example, the distance between the two layers of Mylar film is 0.09mm; for another example, the distance between the two layers of Mylar film is 0.05mm.

[0068] To achieve better welding effect, in some embodiments, the distance between the two layers of Mylar film is less than or equal to 0.1 mm.

[0069] Specifically, a gap of 0.1 mm is created between two layers of Mylar film by padding them with a gap sheet, so that the welding gap is controlled at 0.1 mm, and then a carbon dioxide laser is used for welding, thereby obtaining a good welding effect.

[0070] Among them, Figure 2As shown, the laser welding system includes: a control component, a beam expander, a carbon dioxide laser and an optical element. The control component is electrically connected to the carbon dioxide laser and the optical element respectively to control the carbon dioxide laser and the optical element to work. The beam expander is arranged between the carbon dioxide laser and the optical element, and the optical element is arranged as a galvanometer.

[0071] Specifically, the control component includes a computer and a laser control cabinet, wherein the computer controls the laser control cabinet, which controls the light output of the carbon dioxide laser and the movement trajectory of the optical element. The light output of the carbon dioxide laser reaches the optical element through a beam expander, and the optical element adjusts the direction and position of the light beam so that it acts on the pre-welding position point on the battery and performs hot melt welding.

[0072] In one embodiment, when hot-melting the Mylar film, the welding control parameters pre-set in the computer are read and sent to the laser control cabinet. The laser control cabinet receives the welding control parameters and outputs a light signal control instruction to the carbon dioxide laser according to the welding control parameters, and outputs a laser trajectory control instruction to the optical element. The carbon dioxide laser emits light according to the light signal control instruction. The light beam passes through a beam expander to expand the beam diameter and reaches the optical element. The optical element responds to the laser trajectory control instruction, reflects and adjusts the light beam, so as to control the direction and position of the laser beam to form the required welding trajectory and hot-melt the Mylar film, thereby realizing hot-melt welding of the Mylar film to the battery; wherein the welding control parameters include welding speed, welding time, and a spiral line of the welding trajectory, etc. The spiral line includes a spiral pitch, a spiral radius, etc. The welding control parameters can be set according to actual needs and are not specifically limited here; the beam expander can be selected from but not limited to a lens and a reflector. The beam expander is used to expand the diameter of the output beam of the laser welding system so that it outputs a larger parallel beam; the optical element can be selected from but not limited to a galvanometer, and the direction and position of the laser beam can be reflected and adjusted by the galvanometer; when welding, refer to Figure 4 By controlling the motion trajectory of the galvanometer, the laser beam is controlled to weld two spiral lines, including a positive spiral line and a reverse spiral line, thereby obtaining a "one" weld mark.

[0073] It is worth noting that this method uses a carbon dioxide laser to perform heat-melt welding on the battery coated with Mylar film, so that the Mylar film can be better welded to the outside of the battery. Among them, through the high precision and low thermal deformation characteristics of the carbon dioxide laser, when the gap between the Mylar film and the battery holder is controlled to be less than the preset value, the welding quality can be improved, the phenomenon of cold welding can be avoided, and the requirements for the assembly accuracy between the Mylar film and the battery holder are reduced, thereby improving the compatibility of the Mylar film and the battery when welding.

[0074] Embodiment 1:

[0075] refer to Figure 2 , Figure 3 , Figure 4 , Figure 5 , the wavelength of the carbon dioxide laser is 10.6um; rotate one end of the battery to a set angle and position and clamp it, and cover a layer of Mylar film on the surrounding side of the battery so that the Mylar film and the battery holder are overlapped, wherein the Mylar film covers the battery holder, and a gap sheet is used to pad between the Mylar film and the battery holder, so that the gap between the Mylar film and the battery holder is 0.1mm; the battery covered with the Mylar film is placed horizontally in the welding operation area, and the long side of the battery to be hot-melt welded is facing the galvanometer light output area; the computer reads the preset welding control parameters, which include welding speed, welding time, and the spiral line of the welding trajectory etc.; the computer sends the welding control parameters to the laser control cabinet, the laser control cabinet receives the welding control parameters, and outputs a light signal control instruction to the carbon dioxide laser according to the welding control parameters, and outputs a laser trajectory control instruction to the optical element. The carbon dioxide laser emits light according to the light signal control instruction, and the laser beam passes through the beam expander to expand the beam diameter and reaches the galvanometer. The galvanometer responds to the laser trajectory control instruction and adjusts the direction and position of the laser light speed on the long side of the battery to be hot-melt welded, so that the laser beam moves along a threaded linear path, causing the Mylar film to be hot-melt welded on the battery holder, forming an "I"-shaped weld mark, and obtaining three weld marks with a length of 1 mm. ; Then, based on the horizontal state, the battery is rotated 90°, and the short side of the battery to be hot-melt welded is facing the light emitting area of ​​the galvanometer. The direction and position of the laser light speed are adjusted by the galvanometer so that the laser beam moves along a threaded linear path, causing the Mylar film to be hot-melt welded on the battery holder, forming a "one"-shaped weld mark, and obtaining a weld mark with a length of 1 mm; again, based on the horizontal state, the battery is rotated 180°, and the other long side of the battery to be hot-melt welded is facing the light emitting area of ​​the galvanometer. The direction and position of the laser light speed are adjusted by the galvanometer so that the laser beam moves along a threaded linear path, causing the Mylar film to be hot-melt welded on the battery holder, forming a "one"-shaped weld mark, and obtaining 3 A weld mark with a length of 1 mm; finally, the battery is rotated 270° based on the horizontal state, and the other short side of the battery to be hot-melt welded is facing the light-emitting area of ​​the galvanometer. The direction and position of the laser light speed are adjusted by the galvanometer to make the laser beam move along a spiral linear path, causing the Mylar film to be hot-melt welded on the battery holder to form an "I"-shaped weld mark, and a weld mark with a length of 1 mm is obtained, thereby completing the hot-melt welding between the battery holder and the Mylar film at one end of the battery; repeating the above welding work can complete the hot-melt welding between the battery holder and the Mylar film at the other end of the battery; wherein, the battery weld marks can be weld marks that are aligned with each other or weld marks that are not aligned.

[0076] Embodiment 2:

[0077] refer to Figure 2 , Figure 3 , Figure 4 , Figure 6 , Example 2 is basically the same as Example 1, the only difference is that the gap between the Mylar film and the battery holder is different. Specifically, the distance between the Mylar film and the battery holder is adjusted until the distance is 0.05 mm; the rest of the welding process and welding operation remain unchanged.

[0078] Embodiment 3:

[0079] refer to Figure 2 , Figure 3 , Figure 4 , Fig. 9 Embodiment 3 is basically the same as Embodiment 1, except that two layers of Mylar film are coated on the sides of the battery; the gap between the Mylar film in contact with the battery holder and the battery holder is 0.1 mm, and the gap between the two layers of Mylar film is also 0.1 mm; the rest of the welding process and welding operation remain unchanged.

[0080] Comparative Example 1

[0081] Comparative Example 1 is basically the same as Example 1, except that the wavelength of the semiconductor laser is 910-970nm. In Comparative Example 1, a semiconductor laser with a wavelength of 950nm is used for welding, and when performing the welding operation, the output beam of the semiconductor laser does not pass through a beam expander to expand the beam diameter, but directly reaches the galvanometer. The direction and position of the laser light speed are adjusted by the galvanometer, so that the laser beam moves along a threaded linear path, causing the Mylar film to be hot-melt welded on the battery holder, forming a "I"-shaped weld mark, and obtaining a weld mark with a length of 1mm. The welding effect is referenced Figure 7 , Figure 8 .

[0082] Comparative Example 2

[0083] Comparative Example 2 is basically the same as Example 3, except that the wavelength of the semiconductor laser is 910-970nm. In Comparative Example 2, a semiconductor laser with a wavelength of 950nm is used for welding, and when performing the welding operation, the output beam of the semiconductor laser does not pass through a beam expander to expand the beam diameter, but directly reaches the galvanometer. The direction and position of the laser light speed are adjusted by the galvanometer, so that the laser beam moves along a threaded linear path, causing the Mylar film to be hot-melt welded on the battery holder, forming a "I"-shaped weld mark, and obtaining a weld mark with a length of 1mm. The welding effect is referenced Fig.10 .

[0084] Reference Figure 5, Figure 6 According to Example 1 and Example 2, when the Mylar film is hot-melt welded using a carbon dioxide laser, when the gap between the Mylar film and the battery holder is 0.1 mm and 0.05 mm, the weld mark is uniform and the welding effect is good.

[0085] Reference Figure 5 , Fig. 9 According to Embodiment 1 and Embodiment 3, when a carbon dioxide laser is used to perform heat-melt welding between a single-layer Mylar film or a double-layer Mylar film and a battery holder, the weld mark is uniform and the welding effect is good.

[0086] Reference Figure 5 , Figure 7 and Figure 8 , and according to Example 1 and Comparative Example 1, it can be seen that the carbon dioxide laser is more compatible with the Mylar film welding gap than the semiconductor laser; when the gap between the Mylar film and the battery holder is 0.1mm, there is no white smoke in the welding process of the carbon dioxide laser, and the weld marks formed by its hot melt welding are uniform and there is no cold weld, which is conducive to the Mylar film being firmly welded on the battery holder; while the semiconductor laser has very strict requirements on the welding gap. When the same welding gap is 0.1mm, white smoke will be generated during the welding process, and the weld marks formed by hot melt welding have cold welds, which causes the risk that the Mylar film cannot be firmly welded on the battery holder, thereby affecting the battery yield and the battery production efficiency.

[0087] Reference Fig. 9 , Fig.10 According to Example 3 and Comparative Example 2, when the double-layer Mylar film and the battery holder need to be hot-melt welded, under the same welding gap and welding requirements, the welding effect of the carbon dioxide laser is better than that of the semiconductor laser; the weld marks obtained by hot-melt welding the double-layer Mylar film and the battery holder by the carbon dioxide laser are uniform and have no cold welds; while the weld marks obtained by hot-melt welding the double-layer Mylar film and the battery holder by the semiconductor laser have cold welds, and there is a risk that the Mylar film cannot be stably welded to the battery holder, thereby affecting the battery yield and the battery production efficiency.

[0088] Comparing Examples 1 to 3 with Comparative Examples 1 to 2, the CO2 laser has a higher welding gap compatibility than the semiconductor laser, and the CO2 laser can realize hot melt welding of the double-layer Mylar film and the battery holder; the CO2 laser has a larger welding wavelength than the semiconductor laser, so that the CO2 laser has high energy and high efficiency when performing hot melt welding, so that the Mylar film can be quickly fused with the battery holder, so as to shorten the welding time and reduce the time of high temperature accumulation during the fusion of the Mylar film, thereby obtaining a welding process without white smoke, forming a uniform weld mark without false welding, which is conducive to the stable welding of the Mylar film on the battery holder; and the CO2 laser outputs a laser beam that first passes through a beam expander to expand the beam diameter and then transmits it to the galvanometer. Compared with the semiconductor laser, which does not pass through a beam expander but outputs a laser beam from the semiconductor laser directly to the galvanometer, the semiconductor laser does not have the ability to improve the far-field divergence angle of the laser beam, so that the beam maintains good collimation at a long distance, and thus cannot guarantee hot melt welding during long-distance transmission or precise focusing, and cannot achieve a good welding effect.

[0089] In summary, the Mylar film and the battery holder are hot-melt welded by a carbon dioxide laser, which improves the welding gap between the Mylar film and the battery holder and the compatibility of welding between the two layers of Mylar film and the battery holder.

[0090] In the present invention, unless otherwise clearly specified and limited, the terms "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; 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. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0091] In the description of the present invention, it should be noted that the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inside", "outside", etc. indicate positions or positional relationships based on the positions or positional relationships shown in the accompanying drawings, or the positions or positional relationships in which the product of the invention is usually placed when in use. They 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 position, be constructed and operated in a specific position, and therefore cannot be understood as limiting the present invention. In addition, the terms "first", "second", "third", etc. are only used to distinguish the description, and cannot be understood as indicating or implying relative importance.

[0092] In addition, the terms "horizontal", "vertical", "overhanging" and the like do not mean that the components are required to be absolutely horizontal or overhanging, but can be slightly tilted. For example, "horizontal" only means that its direction is more horizontal than "vertical", and does not mean that the structure must be completely horizontal, but can be slightly tilted.

[0093] In the present invention, unless otherwise clearly specified and limited, a first feature being above or below a second feature may include the first and second features being in direct contact, or may include the first and second features not being in direct contact but being in contact through another feature between them. Moreover, a first feature being above, above, and above a second feature includes the first feature being directly above and obliquely above the second feature, or simply means that the first feature is higher in level than the second feature. A first feature being below, below, and below a second feature includes the first feature being directly below and obliquely below the second feature, or simply means that the first feature is lower in level than the second feature.

[0094] Although the present invention is described in conjunction with the above specific embodiments, it is obvious that those skilled in the art can make many substitutions, modifications and changes according to the above content. Therefore, all such substitutions, improvements and changes are included in the spirit and scope of the appended claims.

Claims

1. A method for welding Mylar film of lithium battery, characterized in that: The welding method is applied to a laser welding system, and the welding method comprises: The battery is rotated to a set angle and clamped in position, and the Mylar film is covered on the battery; Adjusting the distance between the battery holder on the battery and the Mylar film until the distance is less than a preset value; Controlling the laser welding system to weld and fix the Mylar film on the battery; Wherein, the laser welding system includes a carbon dioxide laser.

2. The method for welding Mylar film of lithium battery according to claim 1, characterized in that: The distance between the Mylar film and the battery holder is less than 0.15 mm.

3. The method for welding Mylar film of lithium battery according to claim 1, characterized in that: The Mylar film is a single layer or a double layer.

4. The method for welding Mylar film of lithium battery according to claim 1, characterized in that: The Mylar film is double-layered, and the distance between the double-layered Mylar film is less than 0.15 mm.

5. The method for welding Mylar film of lithium battery according to any one of claims 1 to 4, characterized in that: The laser welding system further comprises an optical element arranged on the optical path of the carbon dioxide laser.

6. The method for welding Mylar film of lithium battery according to claim 5, characterized in that: The laser welding system further includes a beam expander, which is arranged between the carbon dioxide laser and the optical element to expand the diameter of the output beam of the laser welding system.

7. The method for welding Mylar film of lithium battery according to claim 5, characterized in that: The optical element is configured as a galvanometer.

8. The method for welding Mylar film of lithium battery according to claim 7, characterized in that: During welding, the galvanometer moves in a swinging and scribing manner.

9. The method for welding Mylar film of lithium battery according to any one of claims 1 to 4, characterized in that: The overlapping part of the battery and the Mylar film is set as a weld bead, and a plurality of pre-welding points are set on the weld bead, and the plurality of pre-welding points are evenly spaced and distributed.

10. The method for welding Mylar film of lithium battery according to claim 9, characterized in that: The laser welding system further comprises a galvanometer, which is oscillated and scribed to enable the laser beam to move along the weld bead in a spiral path.

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