Tab welding structure, welding method thereof and secondary battery

Abstract

The invention provides a tab welding structure and a welding method thereof and a secondary battery, the tab welding structure comprises a metal tab and at least one composite current collector, the composite current collector comprises a first metal layer, a second metal layer and a polymer layer, the polymer layer is arranged between the first metal layer and the second metal layer, and the first metal layer is arranged between the first metal layer and the second metal layer. The metal tab and the composite current collector are stacked; at least one through hole is formed in the stacking position of the metal tab, and in the stacking position, the first metal layer and the second metal layer are broken and electrically contacted with each other, and the macromolecule layer in the composite current collector is partially molten and permeates into the through hole. According to the tab welding structure provided by the invention, at least one through hole is formed in the stacking position of the metal tab, and the first metal layer and the second metal layer in the stacking position of the composite current collector are in direct contact connection, so that the production efficiency can be improved, the production consistency can be improved, the internal resistance of the battery can be reduced, and the rate capability of the battery can be improved.

Description

Technical Field

[0001] The present invention relates to the technical field of batteries, and in particular to a tab welding structure and a welding method thereof, and a secondary battery. Background Art

[0002] The rapid development of electric vehicles, drones, electric vertical take-off and landing (EVOL) vehicles, and other sectors in recent years has placed higher demands on the energy density and safety performance of power batteries. Traditional aluminum and copper metal current collectors are very hard and have low elongation at break. During battery cell processing or mechanical abuse, burrs on the cross-section edges can easily pierce the separator and cause internal short circuits. Furthermore, the high density of aluminum and copper metals, which contribute significantly to the total weight of the battery cell, hinders the improvement of energy density.

[0003] To reduce the weight of aluminum and copper current collectors, composite current collectors have been developed. Composite current collectors consist of a central polymer layer and metal coatings on both sides. They offer advantages such as high elongation at break, minimal puncture burrs, and low density, significantly improving battery safety and energy density. However, the insulating polymer layer in the composite current collector prevents the metal coatings on both sides from conducting electricity, making it impossible to weld current collectors to each other or to the tabs using traditional laser or ultrasonic welding processes. Currently, ultrasonic transfer welding is the most commonly used method for welding composite current collectors: ultrasonically welding metal foil tabs to one or both sides of the composite current collector, which are then welded to the outer tabs. This transfer welding process is cumbersome and inefficient, and the transfer welding of a single composite current collector to a metal foil tab is prone to cold welds, severely impacting the efficiency and consistency of battery cell welding, increasing battery internal resistance, and reducing battery rate performance. Furthermore, continuous transfer welding requires the development of specialized roll-to-roll welding equipment, increasing equipment investment and battery cell production costs. Summary of the Invention

[0004] In response to the problems that the existing transfer welding process has complicated steps and low efficiency, which affects the efficiency and consistency of battery cell welding, increases the internal resistance of the battery, and reduces the battery rate performance, the present application provides a tab welding structure and its welding method, and a secondary battery.

[0005] In the first aspect, the present invention provides a pole core comprising a metal pole tab and at least one composite current collector, wherein the composite current collector comprises a first metal layer, a second metal layer and a polymer layer, wherein the polymer layer is arranged between the first metal layer and the second metal layer, and the metal pole tab and the composite current collector are stacked; the metal pole tab is provided with at least one through hole at the stacking position, and at the stacking position, the first metal layer and the second metal layer are broken and electrically contacted with each other, and the polymer layer in the composite current collector is partially melted and penetrates into the through hole.

[0006] Preferably, the thickness of the tab is h1, the thickness of the polymer layer is h2, and h1≥0.8h2.

[0007] Preferably, h1 is 0.08~1.0mm.

[0008] Preferably, h1≥h2.

[0009] Preferably, the area of ​​each through hole is 0.01 mm 2 ~100mm 2 .

[0010] Preferably, the area of ​​each through hole is 0.1-10 mm 2 .

[0011] Preferably, at the stacking position, each of the composite current collectors includes a first welding region, the area of ​​the first welding region is S1, the total area of ​​the plurality of through holes is S2, and the ratio of S2:S1 is (0.05-0.95):1.

[0012] In a second aspect, the present application provides a welding method for a tab welding structure, comprising the following steps: obtaining a metal tab provided with at least one through hole; The position where the metal tab is provided with a through hole is stacked with the composite current collector, and welding is performed at the stacking position, so that at the stacking position, the first metal layer and the second metal layer are broken and electrically contacted with each other, and the polymer layer is melted and extruded to fill the through hole.

[0013] Preferably, the position where the metal tab is provided with the through hole is stacked with the composite current collector, and welding is performed at the stacked position, comprising the following steps: At the stacking position of the metal tab and the composite current collector, a welding head is arranged on a side of the composite current collector away from the metal tab, and a plurality of protrusions are provided on the welding head. Ultrasonic welding is performed by applying ultrasonic waves through the welding head, and the protrusions contact and squeeze the composite current collector, so that the first metal layer and the second metal layer at the stacking position are broken, and a portion of the polymer layer is melted and squeezed to flow into the through hole; The ultrasonic welding has a welding amplitude of 1-50 μm, a welding pressure of 1-100 psi, and a welding energy of 10-5000 J.

[0014] In a third aspect, the present application provides a secondary battery, comprising the above-mentioned tab welding structure or a tab welding structure obtained by the above-mentioned method for welding the tab welding structure.

[0015] Preferably, the secondary battery includes a pole piece, the pole piece includes the composite current collector and an active material layer, and the active material layer is arranged at a non-stacked position on the composite current collector.

[0016] Preferably, there are multiple electrode sheets, the multiple electrode sheets include at least one positive electrode sheet and at least one negative electrode sheet, the metal electrode tabs include a positive electrode metal electrode tab and a negative electrode metal electrode tab; the composite current collector of the positive electrode sheet is stacked with the positive electrode metal electrode tab; the composite current collector of the negative electrode sheet is stacked with the negative electrode metal electrode tab.

[0017] Compared with the prior art, the tab welding structure provided by the present application has a composite current collector and a metal tab stacked, and the metal tab is provided with at least one through-hole at the stacking position. During the welding process of the metal tab and the composite current collector at the stacking position, the first metal layer and the second metal layer are broken, and the polymer layer melts under the heat generated by ultrasonic vibration friction. Under the action of welding pressure, the molten polymer material is squeezed out and filled into the through-hole, thereby making the first metal layer and the second metal layer in the stacking position of the composite current collector directly contact and connect, realizing the electrical connection between the metal tab, the first metal layer and the second metal layer. At the same time, after welding at the stacking position, the weld mark is clear and complete, there is no false welding, no leaking welding, the metal tab and the composite current collector are tightly connected at the stacking position, and the welding tensile force is high; at the same time, it can also improve production efficiency and improve production consistency. The battery using the tab welding structure provided by the present application has the effect of reducing battery internal resistance and improving battery rate performance.

[0018] The tab welding structure provided in the present application does not use a transfer welding process when welding the metal tab to the composite current collector. The metal tab and the composite current collector are directly welded at their stacked positions, and a tight connection effect between the composite current collector and the metal tab is achieved through relatively simple process steps. The functional requirements for the equipment are low, the operation is simple, and it is easy to industrialize. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is a schematic diagram of the tab structure after the pore-forming treatment of the tab welding method of the composite current collector provided in this application; Figure 2 This is a front view of the actual picture of the positive electrode welding piece tab produced in Example 1; Figure 3 This is a back view of the actual image of the positive electrode welded composite current collector produced in Example 1; Figure 4 This is a schematic diagram of the secondary battery structure provided by this application.

[0020] Among them, 1. Metal tab; 101. Positive metal tab; 102. Negative metal tab; 2. Tab glue; 3. Welding area; 4. Remaining area after hole making; 5. Through hole; 6. Stacking position. DETAILED DESCRIPTION

[0021] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0022] In order to illustrate the technical solution of the present invention, specific embodiments are provided below.

[0023] In the first aspect, the present application provides a tab welding structure, comprising a metal tab 1 and at least one composite current collector, wherein the composite current collector comprises a first metal layer, a second metal layer and a polymer layer, wherein the polymer layer is arranged between the first metal layer and the second metal layer, and the metal tab 1 and the composite current collector are stacked; the metal tab 1 is provided with at least one through hole 5 at the stacking position 6, and at the stacking position 6, the first metal layer and the second metal layer are broken and electrically contacted with each other, and the polymer layer in the composite current collector is partially melted and penetrates into the through hole 5.

[0024] Specifically, the structure of the existing composite current collector is that a polymer layer is arranged between the first metal layer and the second metal layer. Due to the existence of the intermediate polymer layer, the polymer layer is insulating, and the melting point of the polymer layer is generally much lower than the melting points of the metal tab 1, the first metal layer, and the second metal layer. If the composite current collector is directly welded, the intermediate polymer layer will dissolve due to heat and re-solidify after cooling between the first metal layer and the second metal layer, affecting the welding effect and causing the welding resistance to increase significantly and become very unstable. To address this problem, the inventors have found through extensive research that, taking into account the characteristics of the polymer layer melting due to heat, multiple through holes 5 are provided on the metal tab 1, and the multiple through holes 5 are provided in the welding area 3 of the metal tab 1. It should be noted that the welding area 3 is located in the stacking position 6 of the metal tab 1; the area of ​​the welding area 3 is less than or equal to the area of ​​the stacking position 6 of the metal tab 1.

[0025] The welding area 3 of the metal tab 1 and the stacking position 6 of the composite current collector are welded. During the welding process, there is a protrusion on the welding head. Under the action of welding pressure, the protrusion will destroy the first metal layer and the second metal layer in the composite current collector. At the same time, the ultrasonic frequency vibration causes high-frequency friction between the materials. This high-frequency friction will convert mechanical energy into thermal energy, and the temperature of the welding area rises sharply. When the temperature exceeds the melting point of the polymer material layer, the molten polymer material layer at the stacking position 6 will be squeezed out under the action of welding pressure, and the extruded molten liquid will fill the through hole 5 of the metal tab 1. After the polymer layer at the stacking position 6 is squeezed out, the first metal layer and the second metal layer at the stacking position 6 are in direct contact under the action of welding pressure. When the heat energy generated by the high-frequency friction generated by the ultrasonic frequency vibration is higher than the melting point of the first metal layer and / or the second metal layer, the first metal layer and the second metal layer will be welded together to achieve electrical connection between the first metal layer and the second metal layer. There is no polymer layer between part of the first metal layer and the second metal layer in the stacking position 6, which reduces the welding internal resistance of the battery cell.

[0026] The composite current collector can be one or a single layer, or multiple or multiple layers. The metal tab 1 and the composite current collector are stacked, meaning that the metal tab 1 is located on one side of all the composite current collectors, a portion of the metal tab 1 abuts a portion of the composite current collector, and the projection of a portion of the metal tab 1 falls on the composite current collector. After being stacked, the metal tab 1 and the composite current collector partially overlap. The metal tab 1 is provided with at least one through-hole 5 at the stacking position 6. The metal tab 1 and the composite current collector are welded together, so that the welding region 3 of the metal tab 1 is located within the stacking position 6 of the metal tab 1, and the area of ​​the welding region 3 is less than or equal to the area of ​​the stacking position 6 of the metal tab 1.

[0027] Compared with the prior art, the tab welding structure provided by the present application has a composite current collector and a metal tab 1 stacked, and the metal tab 1 is provided with at least one through-hole 5 at the stacking position 6. During the welding process of the metal tab 1 and the composite current collector at the stacking position 6, the first metal layer and the second metal layer are broken, and the polymer layer melts under the heat generated by ultrasonic vibration friction. Under the action of welding pressure, the molten polymer material is squeezed out and filled into the through-hole 5, thereby making the first metal layer and the second metal layer in the stacking position 6 of the composite current collector directly contact and connect, realizing the electrical connection between the metal tab 1, the first metal layer and the second metal layer. At the same time, after welding at the stacking position 6, the weld mark is clear and complete, there is no false welding, no leaking welding, the metal tab 1 and the composite current collector are tightly connected at the stacking position 6, and the welding tensile force is high; at the same time, it can also improve production efficiency and improve production consistency. The battery using the tab welding structure provided by the present application has the effect of reducing battery internal resistance and improving battery cell rate performance.

[0028] The electrode tab welding structure provided in the present application does not use a transfer welding process when welding the metal electrode tab 1 to the composite current collector. The metal electrode tab 1 and the composite current collector are directly welded at the stacking position 6, and a tight connection effect between the composite current collector and the metal electrode tab 1 is obtained through relatively simple process steps. The functional requirements for the equipment are low, the operation is simple, and it is easy to industrialize.

[0029] In some embodiments, the area of ​​each through hole 5 is 0.01 mm 2 ~100mm 2 .

[0030] Specifically, the area of ​​each through hole 5 is limited to 0.01mm 2 ~100mm 2 , which is convenient for filling the molten polymer layer; if the area of ​​each through hole 5 is greater than 100mm 2 The metal content in the welding area 3 of the metal tab 1 is small, which reduces the connection strength between the metal tab 1 and the composite current collector and reduces the welding tension. Specifically, the area of ​​each through hole 5 can be 0.01mm 2 , 1mm 2 , 5mm 2 , 10mm 2 , 20mm 2 , 30mm 2 , 40mm 2 , 50mm 2 , 60mm 2 , 70mm 2 , 80mm 2 , 90mm 2 , 100mm 2 As long as the area of ​​each through hole 5 is within 0.01mm 2 ~100mm 2 Anything within the range is acceptable.

[0031] In some preferred embodiments, the area of ​​each through hole 5 is 0.1 mm 2 ~10mm 2 .

[0032] Specifically, the area of ​​each through hole 5 is 0.1mm 2 ~10mm 2 Within the range, while ensuring that the extruded molten polymer layer can be completely filled into the inside and outside of the through hole 5, and at the same time, the metal material contained in the welding area 3 of the metal tab 1 accounts for a high proportion, ensuring the connection strength between the metal tab 1 and the composite current collector, and the welding tension meets the process requirements.

[0033] In a further preferred embodiment, the area of ​​each through hole 5 is 0.5 mm 2 ~1mm 2.

[0034] In some embodiments, at the stacking position 6 , each of the composite current collectors includes a first welding region, the area of ​​the first welding region is S1 , the total area of ​​the plurality of through holes 5 is S2 , and S2:S1 is (0.05-0.95):1.

[0035] Specifically, the total area of ​​the plurality of through holes 5 accounts for 0.05-0.95 of the entire area of ​​the first welding zone, which is convenient for filling the extruded molten polymer layer, ensuring the connection strength between the composite current collector and the metal tab 1 in the welding zone, and the welding tensile force meets the process requirements.

[0036] S2:S1 can be 1:0.05, 1:0.1, 1:0.5, 1:0.3, 1:0.6, 1:0.7, 1:0.8, 1:0.9, 1:0.95, etc., as long as S2:S1 is within the range of 1: (0.05~0.95).

[0037] In some preferred embodiments, S2:S1 is (0.4~0.8):1.

[0038] Specifically, the range of S2:S1 is within the above preferred range, which can ensure the connection strength between the composite current collector and the metal tab 1 at the stacking position 6 , and also ensure that most of the extruded molten polymer layer can be filled into the through hole 5 .

[0039] In some embodiments, the thickness of the metal tab 1 is h1, the thickness of the polymer layer is h2, and h1≥0.8h2.

[0040] Specifically, h1≥0.8h2 is defined, that is, the depth of the through hole 5 is defined to be greater than or equal to 0.8 times the thickness of the polymer layer, which is conducive to the extruded molten polymer layer filling into the through hole 5. It should be noted that in the tab welding structure, a composite current collector can also be said to be a layer of composite current collector. If there is only one layer of composite current collector at the stacking position 6, the thickness h2 of the polymer layer at this time is the thickness of the polymer layer in one layer of composite current collector. When there are multiple layers of composite current collectors at the stacking position 6, the thickness h2 of the polymer layer at this time refers to the sum of the thicknesses of the polymer layers of each layer of composite current collector at the stacking position 6.

[0041] In some preferred embodiments, h1 ≥ h2.

[0042] The restriction of h1≥h2 ensures that the extruded molten polymer layer is completely filled into the through hole 5, and avoids the increase of welding resistance caused by subsequent cooling and solidification of part of the extruded molten polymer layer.

[0043] In some embodiments, h1 is 0.08-1.0 mm.

[0044] Specifically, h1 is limited to a range of 0.08-1.0 mm. The thin thickness of the metal tab 1 has a minimal impact on the battery's internal resistance. h1 can be 0.08 mm, 0.09 mm, 0.1 mm, 0.2 mm, 0.4 mm, 0.6 mm, 0.7 mm, 0.8 mm, 0.9 mm, 1.0 mm, etc., as long as h1 is within the range of 0.08-1.0 mm.

[0045] In some embodiments, the composite current collector has a thickness of 4-20 μm.

[0046] Specifically, the thickness of the composite current collector can be 4 um, 6 um, 8 um, 10 um, 12 um, 13 um, 20 um, etc. Composite current collectors of different thicknesses can be selected according to actual needs.

[0047] The composite current collector is a positive electrode composite current collector or a negative electrode composite current collector.

[0048] In some embodiments, the material of the first metal layer and the second metal layer can be one or more of aluminum metal, aluminum alloy, copper metal, and copper alloy.

[0049] For example, when the composite current collector is a positive electrode composite current collector, the first metal layer and the second metal layer are made of aluminum or an aluminum alloy. When the composite current collector is a negative electrode composite current collector, the first metal layer and the second metal layer are made of copper or a copper alloy.

[0050] In some embodiments, the polymer layer is made of a polymer material.

[0051] Specifically, the polymer material is a polymer such as polyethylene terephthalate (PET) or polypropylene (PP).

[0052] Specifically, the melting point of the polymer material of the polymer layer, such as PET, is about 250°C, and the melting point of PP is about 190°C, which is much lower than the melting point of the metal material (such as the melting point of aluminum is about 660°C; the melting point of copper is about 1080°C; the melting point of nickel is about 1450°C). When the metal tab 1 and the composite current collector in the welding area are welded, the polymer material of the polymer layer in the welding area will melt first.

[0053] In some embodiments, the metal tab 1 is made of one or more of aluminum metal, aluminum alloy, copper metal, copper alloy, copper-plated nickel, nickel metal, and nickel alloy.

[0054] The metal electrode tab 1 can be a positive electrode metal electrode tab 101 or a negative electrode metal electrode tab 102. When welded with the positive electrode composite current collector, the metal electrode tab 1 is a positive electrode metal electrode tab 101. When welded with the negative electrode composite current collector, the metal electrode tab 1 is a negative electrode metal electrode tab 102. Different materials are selected according to the polarity of the positive electrode or the negative electrode.

[0055] In some embodiments, the cross-sectional shape of the through hole 5 is circular, elliptical, polygonal, or a combination of arcs and straight lines.

[0056] Specifically, the plurality of through holes 5 may be arranged regularly or irregularly, which is not limited in this application. The cross-sectional shape of the through holes 5 may be circular, elliptical, polygonal, etc. The polygonal shape may be a square, rectangle, rhombus, pentagon, hexagon, etc. The polygonal shape may be regular or irregular. The combination of arcs and straight lines may be a sector shape, etc.

[0057] In a second aspect, the present application provides a welding method for the above-mentioned tab welding structure, comprising the following steps: Obtaining a metal tab 1 provided with at least one through hole 5; The position where the metal tab 1 is provided with the through hole 5 is stacked with the composite current collector, and welding is performed at the stacking position 6, so that at the stacking position 6, the first metal layer and the second metal layer are broken and electrically contacted with each other, and the polymer layer is melted and extruded to fill the through hole 5.

[0058] Compared with the prior art, the welding method of the tab welding structure provided by the present application is to obtain a metal tab 1 containing a plurality of through holes 5. Figure 1 As shown, a plurality of through holes 5 are provided in the welding area 3 of the metal pole ear 1, and then the welding area 3 of the metal pole ear 1 and the composite current collector are stacked and arranged, and welding is performed at the layered position. During the welding process, the polymer layer at the stacking position 6 will melt under the heat conditions generated by the ultrasonic vibration friction, and the molten polymer material will be squeezed out and filled into the through hole 5 under the action of the welding pressure, so that the first metal layer and the second metal layer in the stacking position 6 are directly contacted and connected, realizing the electrical connection between the first metal layer and the second metal layer, and at the same time realizing the electrical connection between the metal pole ear 1 and the first metal layer and the second metal layer, which is beneficial to reducing the internal resistance of the battery and improving the rate performance of the battery cell. After welding, the weld mark is clear and complete, there is no void solder joint, no leak solder joint, and the welding tensile force is high; at the same time, it can also improve production efficiency and production consistency.

[0059] The welding method of the electrode tab welding structure provided in the present application does not use a transfer welding process, but directly welds the metal electrode tab 1 and the composite current collector, thereby achieving a tight connection effect between the composite current collector and the metal electrode tab 1 through relatively simple process steps. It has low functional requirements for the equipment, is simple to operate, and is easy to industrialize.

[0060] In some embodiments, obtaining a metal tab 1 provided with at least one through hole 5 includes the following steps: performing a hole-making process in the welding area 3 of the metal tab 1, wherein the hole-making process includes one of photolithography, mechanical impact, and chemical etching.

[0061] like Figure 1 The figure shows the structure of the metal tab 1 after the hole-making process. As can be seen in the figure, a plurality of regularly arranged through holes 5 are provided in the welding area 3. There is also a residual area 4 after the hole-making process in the welding area 3 of the tab. This area is made of metal and can be welded to the first metal layer and the second metal layer of the composite current collector at the stacking position 6 to improve the welding strength of the weld. The tab glue 2 is provided on the other side of the welding area 3. The tab glue 2 is wrapped around the metal tab 1 to prevent the metal tab 1 from accidentally contacting other conductive components inside the battery or the outer shell and causing a short circuit. The tab glue 2 can also effectively seal the gap between the metal tab 1 and the battery shell or electrode.

[0062] It should be noted that when the welding area 3 of the metal tab 1 is welded to the stacking position 6 of the composite current collector, the welding area 3 of the metal tab 1 and the stacking position 6 have overlapping parts. Preferably, the welding area 3 of the metal tab 1 and the stacking position 6 of the composite current collector have the same area. It can be understood that the area of ​​the welding area 3 of the tab can be smaller than the area of ​​the stacking position 6 of the composite current collector, which can be selected according to actual needs.

[0063] In some embodiments, the position where the through hole 5 of the metal tab 1 is provided is stacked with the composite current collector, and welding is performed at the stacking position 6, comprising the following steps: At the stacking position 6 of the metal electrode tab 1 and the composite current collector, a welding head is set on the side of the composite current collector away from the metal electrode tab 1, and a plurality of protrusions are set on the welding head. Ultrasonic waves are applied by the welding head to perform ultrasonic welding. The protrusions contact and squeeze the composite current collector, so that the first metal layer and the second metal layer at the stacking position 6 are broken, and the polymer layer is partially melted and squeezed to flow into the through hole 5.

[0064] Specifically, when the welding head, the metal pole tab 1, and the composite current collector are welded, the order in which they are placed on the welding table from bottom to top is: first place the metal pole tab 1 on the welding table, and then place the composite current collector on the side of the metal pole tab 1 away from the welding table. The stacking position 6 of the composite current collector is in contact with the welding area 3 of the metal pole tab 1, and the projection of the stacking position 6 of the composite current collector falls on the metal pole tab 1. The welding head is set on the side of the composite current collector away from the metal pole tab 1.

[0065] When the welding head, metal ear 1, and composite current collector are welded, the protrusion on the welding head is in direct contact with the composite current collector. Under the action of welding pressure, the protrusion on the welding head destroys the composite current collector. It can be understood that when there are multiple layers of composite current collectors, the protrusion on the welding head will also damage each layer of the composite current collector. The first metal layer and the second metal layer in each layer of the composite current collector are broken, and the polymer layer in contact with the welding head melts under the heat generated by vibration friction, and the partially melted polymer layer will be squeezed and flow into the through hole 5.

[0066] The specific explanation of the area of ​​the stacking position 6 of the composite current collector is: the area partially overlapping with the metal pole tab 1, including the area in direct contact with the metal pole tab 1, and also including the part of the composite current collector that falls within the projection of the overlapping area. When it is a single layer of composite current collector, the area of ​​the stacking position 6 of the composite current collector includes the area in direct contact with the metal pole tab 1, and also includes the area on the other side that falls within the projection of the overlapping area. When it is two or more layers of composite current collectors, the area of ​​the stacking position 6 of the composite current collector includes the area in direct contact with the metal pole tab 1, and also includes the partial area of ​​each layer of composite current collector that falls within the projection of the overlapping area; such as Figure 4 As shown, if there are 40 layers of composite current collectors, then the stacking position 6 includes 40 layers of composite current collectors and all of them fall within the partial area of ​​the projection of the overlapping area.

[0067] In some embodiments, the ultrasonic welding has a welding amplitude of 1-50 μm, a welding pressure of 1-100 psi, and a welding energy of 10-5000 J.

[0068] Specifically, the equipment used for ultrasonic welding is existing, such as an existing ultrasonic welding machine, which is composed of an ultrasonic generator, a transducer, a pneumatic transmission control system, a welding head and a mechanical transmission device.

[0069] The welding amplitude is limited to 1~50μm, the welding pressure is 1~100psi, and the welding energy is 10~5000J. The extrusion flow effect of the polymer layer at the composite current collector stacking position 6 can be precisely controlled, and the welding effect between the first metal layer, the second metal layer and the metal tab 1 can be controlled, thereby ensuring the consistency of the battery core welding process.

[0070] The welding amplitude may include the following ranges: 1-10 μm, 10-20 μm, 20-30 μm, 30-40 μm, or 40-50 μm. The welding pressure may include the following ranges: 1-10 psi, 10-30 psi, 30-50 psi, 50-70 psi, 70-90 psi, or 90-100 psi. The welding energy may include the following ranges: 10-100 J, 100-500 J, 500-1000 J, 1000-2000 J, 2000-4000 J, or 4000-5000 J.

[0071] In a third aspect, the present application provides a secondary battery comprising the above-mentioned tab welding structure.

[0072] The secondary battery provided in the present application adopts the tab welding structure provided in the present application. The weld marks formed at the welding positions of the metal tab 1 and the composite current collector are clear and complete, the welding strength is high, the internal resistance of the battery is reduced, the battery rate performance is improved, and the production efficiency of the battery is improved.

[0073] In some embodiments, the secondary battery includes a pole piece, the pole piece includes the composite current collector and an active material layer, and the active material layer is disposed at a non-stacked position on the composite current collector.

[0074] Specifically, in a secondary battery, the composite current collector's stacking locations 6 are welded to the metal tab 1, and the active material layer is disposed at the non-stacked locations of the composite current collector. For example, in a battery produced through a lamination process, the composite current collector's stacking locations 6 can be foil tabs, comprising multiple foil tabs welded to the metal tab 1. The non-stacked locations of the composite current collector are all locations other than stacking locations 6, including the coating region, where the active material layer is disposed.

[0075] In some embodiments, the number of the electrode sheets is multiple, and the multiple electrode sheets include at least one positive electrode sheet and at least one negative electrode sheet. The metal electrode tab 1 includes a positive electrode metal electrode tab 101 and a negative electrode metal electrode tab 102; the composite current collector of the positive electrode sheet is stacked with the positive electrode metal electrode tab 101; and the composite current collector of the negative electrode sheet is stacked with the negative electrode metal electrode tab 102.

[0076] For example, a battery is manufactured through a lamination process and includes multiple positive electrode sheets and multiple negative electrode sheets. Each positive electrode sheet is provided with a positive electrode foil tab, and each negative electrode sheet is provided with a negative electrode foil tab. Multiple positive electrode foil tabs are stacked with the positive electrode metal tab 101. A first welding area a is provided at the stacking position 6 of the positive electrode foil tab, and the first welding area a is welded to the welding area 3 of the positive electrode metal tab 101. Similarly, multiple negative electrode foil tabs are stacked with the negative electrode metal tab 102. A first welding area b is provided at the stacking position 6 of the negative electrode foil tab, and the first welding area b is welded to the welding area 3 of the negative electrode metal tab 102. The positive electrode sheet includes a positive electrode active material layer and a positive electrode composite current collector, the non-stacked position of the positive electrode composite current collector includes a coating area, and the positive electrode active material layer is arranged in the coating area of ​​the positive electrode composite current collector. The negative electrode sheet includes a negative electrode active material layer and a negative electrode composite current collector, the non-stacked position of the negative electrode composite current collector includes a coating area, and the negative electrode active material layer is arranged in the coating area of ​​the negative electrode composite current collector.

[0077] The negative electrode active material layer includes a negative electrode active material, a negative electrode conductor, a negative electrode binder, and a negative electrode thickener. The negative electrode active material includes a silicon-based negative electrode, which includes at least one of silicon element, silicon-carbon composite material, and silicon oxide.

[0078] The negative electrode active material, negative electrode conductive agent, negative electrode binder, deionized water and negative electrode thickener are mixed and stirred to obtain negative electrode slurry, and the negative electrode slurry is coated on the coating area surface of the negative electrode composite current collector and dried to obtain a negative electrode active material layer.

[0079] The positive electrode active material layer includes a positive electrode active material, a positive electrode conductor and a positive electrode binder.

[0080] The positive electrode active material, the positive electrode conductive agent, the positive electrode binder and the organic solvent are mixed and stirred to obtain a positive electrode slurry, and the positive electrode slurry is coated on the coating area surface of the positive electrode composite current collector and dried to obtain a positive electrode active material layer.

[0081] The positive electrode active material includes at least one of lithium iron phosphate, lithium manganese oxide, lithium cobalt oxide, and ternary materials.

[0082] The positive electrode conductive agent and the negative electrode conductive agent both include at least one of conductive carbon black, carbon fiber, carbon nanotube, graphene, and conductive graphite.

[0083] The positive electrode binder includes PVDF.

[0084] The negative electrode binder includes SBR.

[0085] The negative electrode thickener includes CMC.

[0086] Organic solvents include NMP.

[0087] In a fourth aspect, the present application provides a method for preparing the aforementioned secondary battery, comprising the following steps: Obtaining a positive electrode sheet and a negative electrode sheet, wherein the positive electrode sheet includes a positive electrode composite current collector, and the negative electrode sheet includes a negative electrode composite current collector; The positive electrode sheet, the separator and the negative electrode sheet are assembled into a pole core by adopting a winding process or a lamination process; Using the above-described welding method for the tab welding structure, weld the positive electrode metal tab 101 to the stacking position 6 of the positive electrode composite current collector, and weld the negative electrode metal tab 102 to the stacking position 6 of the negative electrode composite current collector; After welding is completed, the steps of shell insertion, liquid injection, sealing, formation, secondary sealing, aging and capacity separation are carried out in sequence to obtain the secondary battery.

[0088] By adopting the welding method of the tab welding structure provided in the present application, the positive electrode metal tab 101 and the stacking position 6 of the positive electrode composite current collector are welded, and the negative electrode metal tab 102 and the stacking position 6 of the negative electrode composite current collector are welded. Under the action of welding pressure, the molten polymer material will be squeezed out and filled into the through hole 5, so that the first metal layer and the second metal layer in the welding area of ​​the composite current collector are directly connected, realizing the electrical connection between the metal tab, the first metal layer and the second metal layer, which is beneficial to reducing the internal resistance of the battery and improving the rate performance of the battery cell. After welding, the weld mark is clear and complete, there is no void welding, no leaking welding, and the welding tensile strength is high; at the same time, it can also improve production efficiency and production consistency.

[0089] The present invention is further described below with reference to the following examples.

[0090] Example 1 S1 cathode slurry preparation: A wet pulping process was used to prepare the positive electrode slurry by mixing the binder PVDF-5130, the composite conductive agent Super-P / KS-6 (mass ratio Super-P:KS-6=1:1), and the 811 nickel-cobalt-manganese ternary positive electrode material in a mass ratio of 1.5:2:96.5 with the solvent NMP (N-methyl-2-pyrrolidone). The viscosity of the positive electrode slurry was in the range of 3000~10000Pa·s.

[0091] S2 negative electrode slurry preparation: A wet slurry process was used to prepare the negative electrode slurry by uniformly mixing graphite, conductive agent Super-P, binder SBR, and CMC with solvent H2O in a mass ratio of 95.5:1:1.5:2. The viscosity of the negative electrode slurry was adjusted to be in the range of 5000~15000mPa·s.

[0092] S3 preparation of the core: The designed N / P ratio is 1.1, and the capacity is 3Ah soft-pack battery cell; the positive electrode composite current collector is a composite aluminum foil, and the negative electrode composite current collector is a composite copper foil. The positive electrode slurry is coated on the non-stacked surface of the composite aluminum foil through a coating process, and dried to obtain a positive electrode sheet; the negative electrode slurry is coated on the non-stacked surface of the composite copper foil, and dried to obtain a negative electrode sheet; then, after rolling and die-cutting processes, the positive electrode sheet, negative electrode sheet and separator are laminated to obtain a core.

[0093] The first and second metal layers of the composite aluminum foil are both made of aluminum, with the middle polymer layer made of PET. The first and second metal layers of the composite copper foil are both made of copper, with the middle polymer layer also made of PET. The thickness of each of the two aluminum layers in the composite aluminum foil is 1μm, and the number of composite aluminum foil layers required for welding in the electrode core is 40.

[0094] The thickness of the two copper layers in the composite copper foil is 1 μm respectively, and the number of composite copper foil layers that need to be welded in the pole core is 41.

[0095] S4 metal tab 1 welding: S41: The positive electrode metal tab 101 is 30 mm long and 8 mm wide; the negative electrode metal tab 102 is 30 mm long and 8 mm wide; the thickness of the positive electrode metal tab 101 is 0.2 mm, and the thickness of the negative electrode metal tab 102 is 0.15 mm; the welding area 3 of the positive electrode metal tab 101 and the welding area 3 of the negative electrode metal tab 102 are both 3 mm × 7 mm, and the area of ​​the first welding area on the positive electrode composite current collector and the negative electrode composite current collector is equal to the area of ​​the welding area 3, which is defined as S1 = 21 mm 2 .

[0096] Holes are made in the welding area 3 of the positive metal tab 101 and the welding area 3 of the negative metal tab 102. The hole making process is mechanical impact. The area of ​​each through hole 5 in the welding area 3 of the positive metal tab 101 is 1 mm. 2 The area of ​​each through hole 5 in the welding area of ​​the negative metal tab 102 is 1 mm 2 The total area of ​​all through holes 5 is recorded as S2. The positive electrode metal tab 101 is made of aluminum, and the negative electrode metal tab 102 is made of copper.

[0097] S42: Ultrasonic welding is performed on the positive electrode metal tab 101 and the first welding area of ​​the stacking position 6 of all the composite aluminum foils in the electrode core, with a welding amplitude of 45 μm, a welding pressure of 50 psi, and a welding energy of 200 J. The polymer layer of the composite aluminum foil in the stacking position 6 of the composite aluminum foil will melt and extrude into the through hole 5, and the two layers of aluminum foil in the stacking position 6 of the composite aluminum foil will be directly connected, achieving electrical connection between the two layers of aluminum foil.

[0098] S43: Ultrasonic welding is performed on the negative electrode metal tab 102 and the first welding area of ​​the stacking position 6 of all the composite copper foils in the electrode core. The welding amplitude is 48 μm, the welding pressure is 60 psi, and the welding energy is 300 J. The polymer layer of the composite copper foil in the stacking position 6 of the composite copper foil will melt and extrude into the through hole 5. The two layers of copper foil in the stacking position 6 of the composite copper foil are directly connected, achieving electrical connection between the two layers of copper foil.

[0099] S5: Assembling the battery After welding, the battery is shelled, filled with liquid, sealed, left to soak for 24 hours, formed, sealed twice, aged, and divided into different capacities to obtain a lithium-ion soft-pack battery.

[0100] Example 2-10 Most of the steps of Examples 2-10 are the same as those of Example 1, except that: the area of ​​the through hole 5 in the welding area 3 in the positive electrode metal tab 101 is different, and the area of ​​the through hole 5 in the welding area 3 in the negative electrode tab is different; S2:S1 is different in the positive electrode, and S2:S1 is different in the negative electrode; the ratio of the thickness h1 of the positive electrode metal tab 101 / the thickness h2 of all polymer layers in the composite aluminum foil is different, and the ratio of the thickness h1 of the negative electrode metal tab 102 / the thickness h2 of all polymer layers in the composite copper foil is different, as shown in Table 1 for details.

[0101] The area S1 of the welding zone in Examples 2-10 is the same, which is 3 mm × 7 mm and the area is 21 mm. 2 .

[0102] In Examples 2-3, the thickness of the positive electrode tabs was 0.2 mm, and the thickness of the negative electrode tabs was 0.15 mm. In Example 4, the thickness of the positive electrode tabs was 0.25 mm, and the thickness of the negative electrode tabs was 0.15 mm. In Example 5, the thickness of the positive electrode tabs was 0.15 mm, and the thickness of the negative electrode tabs was 0.15 mm. In Example 6, the thickness of the positive electrode tabs was 0.25 mm, and the thickness of the negative electrode tabs was 0.2 mm. In Example 7, the thickness of the positive electrode tabs and the thickness of the negative electrode tabs were the same as in Example 1. In Examples 8-9, the thickness of the positive electrode tabs and the thickness of the negative electrode tabs were the same as in Example 2. In Example 10, the thickness of the positive electrode tabs and the thickness of the negative electrode tabs were the same as in Example 5.

[0103] Example 11 Most of the steps of this embodiment are the same as those of embodiment 1, except that in step S42, the welding amplitude is 40 μm, the welding pressure is 70 psi, and the welding energy is 250 J; in step S43, the welding amplitude is 45 μm, the welding pressure is 65 psi, and the welding energy is 270 J.

[0104] Example 12 Most of the steps of this embodiment are the same as those of embodiment 1, except that in step S42, the welding amplitude is 70 μm, the welding pressure is 120 psi, and the welding energy is 500 J; in step S43, the welding amplitude is 75 μm, the welding pressure is 120 psi, and the welding energy is 550 J.

[0105] Examples 13-15 Most of the steps in Examples 13-15 are the same as those in Example 1, except that S2 and S1 are different, as shown in Table 1. The thickness h1 of the positive electrode metal tab 101 and the thickness h1 and S1 of the negative electrode metal tab 102 in Examples 13-15 are the same as those in Example 1.

[0106] Comparative Example 1 Most of the steps of this comparative example are the same as those of Example 1, except that in step S41 , the welding area 3 of the positive electrode metal tab 101 and the negative electrode metal tab 102 is not subjected to pore forming treatment.

[0107] Comparative Example 2 Most of the steps of this comparative example are the same as those of Example 6, except that in step S41 , the welding area 3 of the positive electrode metal tab 101 and the negative electrode metal tab 102 is not subjected to pore forming treatment.

[0108] Table 1 Battery performance test: The batteries obtained from the above embodiments and comparative examples were subjected to the following performance tests.

[0109] 1) Test the battery's AC internal resistance: Use an AC internal resistance tester to perform a 1kHz AC internal resistance test on a fully charged battery.

[0110] 2) DC internal resistance of positive electrode welding parts: According to step S42 in Example 1, the welding area 3 of the positive electrode metal tab 101 is welded to the stacking position 6 of the composite aluminum foil to obtain a positive electrode welded part, and the DC internal resistance value at both ends of the positive electrode welded part is tested using a DC internal resistance meter.

[0111] 3) DC internal resistance of negative electrode welding parts: According to step S42 in Example 1, the welding area 3 of the negative electrode metal tab 102 is welded to the stacking position 6 of the composite copper foil to obtain a negative electrode welded part, and the DC internal resistance value at both ends of the negative electrode welded part is tested using a DC internal resistance meter.

[0112] 4) 3C rate discharge capacity retention rate At 25°C, discharge the battery at a rate of 1C to 3.0V, then charge it to 4.2V at a constant current of 1C with a cutoff current of 0.05C. After fully charged, discharge it at a rate of 1C to 3.0V, and record the discharge capacity C1. Then charge it to 4.2V at a constant current of 1C with a cutoff current of 0.05C, and after fully charged, discharge it at a rate of 3C to 3.0V, and record the discharge capacity C2. 3C rate discharge capacity retention rate = C2 / C1×100%.

[0113] The above test results are shown in Table 2.

[0114] Table 2 It can be seen from Tables 1 and 2 that by comparing Example 1 with Comparative Example 1, and by comparing Example 6 with Comparative Example 2, the metal pole ear 1 is subjected to a pore-forming treatment, which can significantly reduce the DC internal resistance at the welding point between the composite current collector and the metal pole ear 1, reduce the internal resistance of the battery, and greatly improve the rate performance of the battery cell. This is because after the metal pole ear 1 is subjected to a pore-forming treatment, the stacking position 6 of the composite current collector and the welding area 3 of the metal pole ear 1 are welded. During the welding process, the first metal layer and the second metal layer at the stacking position 6 of the composite current collector are destroyed, and the polymer layer melts under the heat conditions generated by the ultrasonic vibration friction. Under the action of the welding pressure, the molten polymer material will be squeezed out and filled into the through hole 5, so that the first metal layer and the second metal layer at the stacking position 6 of the composite current collector are directly contacted and connected, thereby realizing electrical connection between the first metal layer and the second metal layer, which is beneficial to reducing the internal resistance of the battery. Figure 2 This is the front side of the actual image of the positive electrode metal tab 101 of the positive electrode welded part produced in Example 1. It can be observed that after ultrasonic welding, the polymer material in the polymer layer, such as polymers such as PET, is filled into the through hole 5 of the positive electrode metal tab 101. Figure 3 On the back of the actual image of the positive electrode composite current collector of the positive electrode welded component produced in Example 1, it can be observed that the weld marks in the welding area 3 and the first welding area of ​​the positive electrode composite current collector stacking position 6 are clear and complete, without obvious cold welding or leaking welding.

[0115] Comparing Examples 1-3, 7-9 and Example 10, the area of ​​each through hole 5 in the metal tab 1 is changed, and the area of ​​the hole 5 is 0.01mm 2 ~100mm 2 When the area of ​​through hole 5 is within the range, the DC internal resistance of the weldment and the AC internal resistance of the battery will first decrease and then increase as the area of ​​hole 5 increases. When the area of ​​each through hole 5 is greater than 100mm 2When the DC internal resistance and AC internal resistance are both large, and the 3C rate discharge capacity retention rate is low, an excessively high pore area may lead to a decrease in the mechanical strength of the metal tab 1. Compared with Examples 1-3, 7-10, and 15 and Examples 13-14, the ratio of the total area S2 of the through-hole 5 to the area S1 of the first welding zone is changed. When S2:S1 is in the range of 0.05-0.95 and the area of ​​the hole 5 is in the range of 0.01-100mm 2 Within the range, the through hole 5 provided in the welding area 3 of the metal tab 1 can effectively improve the welding effect of the composite current collector, the DC internal resistance and the AC internal resistance first decrease and then increase with the increase of the area of ​​the through hole 5, and the rate performance first increases and then decreases with the increase of the area of ​​the through hole 5; when the ratio of S2:S1 is in the range of (0.4~0.8):1, the battery internal resistance is low and the rate performance is high. Comparing Examples 2, 4, and 6 with Example 5, the thickness h1 of the metal tab 1 is more than 0.8 times the total polymer layer thickness of all composite current collectors, and the DC internal resistance and the AC internal resistance show a trend of first decreasing and then increasing with the increase of h / h2. The rate performance first decreases and then increases with the increase of the thickness of the metal tab 1. This is because the polymer layer of the composite current collector dissolved during welding will flow out and fill the through hole 5. The thickness of the metal tab 1 is related to the volume of the through hole 5. The volume of the through hole 5 is large, and the amount of polymer layer filled is large. If the metal tab 1 is too thin, a large amount of polymer layer will overflow between the surface of the metal tab 1 and the composite current collector, affecting the welding effect and increasing the welding internal resistance.

[0116] Comparison between Examples 1 and 11 and Example 12 shows that when the metal tab 1 is ultrasonically welded to the composite current collector, the welding amplitude is 1 to 50 μm, the welding pressure is 1 to 100 psi, and the welding energy is in the range of 10 to 5000 J. The obtained battery cell has low DC internal resistance and AC internal resistance, and the battery has a high 3C rate discharge capacity retention rate.

[0117] The above embodiments are intended only to illustrate the technical solutions of the present invention and are not intended to limit them. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they may still modify the technical solutions described in the aforementioned embodiments or replace some of the technical features therein with equivalents. However, such modifications or replacements do not deviate from the spirit and scope of the technical solutions of the various embodiments of the present invention and are intended to be included within the scope of protection of the present invention.

Claims

1. A tab welding structure, characterized in that: It includes a metal tab and at least one composite current collector, the composite current collector includes a first metal layer, a second metal layer and a polymer layer, the polymer layer is arranged between the first metal layer and the second metal layer, and the metal tab and the composite current collector are stacked; the metal tab is provided with at least one through hole at the stacking position, and at the stacking position, the first metal layer and the second metal layer are broken and electrically contacted with each other, and the polymer layer in the composite current collector partially melts and penetrates into the through hole.

2. The tab welding structure according to claim 1, characterized in that: The thickness of the metal tab is h1, the thickness of the polymer layer is h2, and h1≥0.8h2.

3. The tab welding structure according to claim 2, characterized in that: h1 is 0.08~1.0mm.

4. The tab welding structure according to claim 2, characterized in that: h1≥h2.

5. The tab welding structure according to claim 1, characterized in that: The area of ​​each through hole is 0.01mm 2 ~100mm 2 .

6. The tab welding structure according to claim 5, characterized in that: The area of ​​each through hole is 0.1~10mm 2 .

7. The tab welding structure according to claim 1, characterized in that: At the stacking position, each of the composite current collectors includes a first welding region, the area of ​​the first welding region is S1, the total area of ​​the plurality of through holes is S2, and S2:S1 is (0.05-0.95):

1.

8. A welding method for the tab welding structure according to any one of claims 1 to 7, characterized in that: The following steps are involved: Obtaining a metal tab provided with at least one through hole; The position where the metal tab is provided with a through hole is stacked with the composite current collector, and welding is performed at the stacking position, so that at the stacking position, the first metal layer and the second metal layer are broken and electrically contacted with each other, and the polymer layer is melted and extruded to fill the through hole.

9. The tab welding method of the tab welding structure according to claim 8, characterized in that: The position where the metal tab is provided with the through hole is stacked with the composite current collector, and welding is performed at the stacked position, comprising the following steps: At the stacking position of the metal tab and the composite current collector, a welding head is arranged on a side of the composite current collector away from the metal tab, and a plurality of protrusions are provided on the welding head. Ultrasonic welding is performed by applying ultrasonic waves through the welding head, and the protrusions contact and squeeze the composite current collector, so that the first metal layer and the second metal layer at the stacking position are broken, and a portion of the polymer layer is melted and squeezed to flow into the through hole; The ultrasonic welding has a welding amplitude of 1-50 μm, a welding pressure of 1-100 psi, and a welding energy of 10-5000 J.

10. A secondary battery, characterized in that: A tab welding structure comprising the tab welding structure according to any one of claims 1 to 7 or a tab welding structure obtained by a welding method according to any one of claims 8 to 9.

11. The secondary battery according to claim 10, wherein The secondary battery includes a pole piece, which includes the composite current collector and an active material layer. The active material layer is arranged at a non-stacked position on the composite current collector.

12. The secondary battery according to claim 11, wherein There are multiple electrode sheets, including at least one positive electrode sheet and at least one negative electrode sheet, and the metal electrode tabs include a positive electrode metal electrode tab and a negative electrode metal electrode tab; the composite current collector of the positive electrode sheet is stacked with the positive electrode metal electrode tab; the composite current collector of the negative electrode sheet is stacked with the negative electrode metal electrode tab.

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