Composite current collector full-tab structure, battery and preparation method

Abstract

The invention discloses a composite current collector full-tab structure, a battery and a preparation method of the composite current collector full-tab structure, and the composite current collector full-tab structure comprises a composite current collector which comprises a middle base film, and a first metal layer and a second metal layer which are formed on the two sides of the middle base film; the first metal belt is fixed on the first metal layer through welding; the second metal belt is fixed on the second metal layer through welding; wherein the first metal belt and the second metal belt are mutually welded at the edge of the composite current collector so as to form a metal edge wrapping structure wrapping the edge of the composite current collector, and the metal edge wrapping structure forms a continuous metal interface used for being welded with the current collector plate; a plurality of tab units are formed on the edge of the composite current collector, and any tab unit is provided with a metal edge covering structure. According to the invention, the metal edge wrapping structure wrapping the edge of the composite current collector is formed at the edge of the composite current collector, so that an integral conductive bridging structure is formed, and connection failure caused by melting of a polymer layer during laser welding is eliminated.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of battery manufacturing, in particular to a composite current collector full-tab structure, a battery and a preparation method. BACKGROUND

[0002] Currently, lithium ion batteries mainly use single metal foil (such as copper foil, aluminum foil) as a current collector. In order to overcome the limitations of traditional current collectors in energy density, safety and cost, the industry has developed composite current collector technology. The structure takes a polymer polymer film (such as PET, PP, PI) as the core, and deposits a thin layer of metal (copper or aluminum) on both sides to form a "sandwich" configuration. Its main advantages are: significantly reducing weight and improving energy density; using the high polymer layer melting mechanism to block thermal runaway and short circuit, enhancing safety; reducing metal usage and reducing cost. Currently, this technology is still in the process of research and development.

[0003] However, when the composite current collector is applied to the full-tab battery structure with high power and low internal resistance, it faces two fatal defects:

[0004] 1. Welding failure: full-tab welding needs to connect the end face (Z direction) of the current collector. The melting point of the polymer layer in the middle of the composite current collector is much lower than that of the metal, and it is easy to melt, shrink or decompose during laser welding, resulting in that the upper and lower metal layers cannot form reliable connection with the current collector disc, and the welding strength and consistency are poor.

[0005] 2. Current blocking: the middle polymer insulating layer completely blocks the conduction path of the current at the end face (Z direction) of the current collector. Even if the local spot welding is successful, the current cannot effectively utilize the entire end face current collection, resulting in that the advantage of reducing internal resistance of the full-tab structure is lost.

[0006] The current full-tab battery is prone to low yield due to the above problems and its complex manufacturing process, which increases the overall cost of the battery. SUMMARY

[0007] The technical problem solved by the present application is to solve the technical problem of insufficient welding strength and poor reliability of the composite current collector and the current collector disc in the composite current collector full-tab structure.

[0008] According to a first aspect, in one embodiment, a composite current collector full-tab structure is provided, comprising:

[0009] a composite current collector, comprising an intermediate base film and a first metal layer and a second metal layer formed on both sides of the intermediate base film;

[0010] a first metal strip, the first metal strip being fixed to the first metal layer by welding; and

[0011] a second metal strip, the second metal strip being fixed to the second metal layer by welding;

[0012] wherein the first metal strip and the second metal strip are welded to each other at the edge of the composite current collector to form a metal edge wrapping structure wrapping the edge of the composite current collector, the metal edge wrapping structure constituting a continuous metal interface for welding with the current collecting plate;

[0013] The edge of the composite current collector is formed with a plurality of tab units, and any of the tab units has the metal edge wrapping structure.

[0014] Preferably, the surfaces of the first metal strip and the second metal strip are provided with a composite coating for enhancing the welding performance.

[0015] Preferably, the welding regions of the first metal strip and the second metal strip are distributed with a plurality of pre-pressing lines.

[0016] Preferably, the welding regions of the first metal layer and the second metal layer are distributed with a plurality of marking points for positioning marks.

[0017] Preferably, the first metal strip and the second metal strip are made of the same material as the first metal layer and the second metal layer, respectively.

[0018] According to a second aspect, an embodiment provides a battery, comprising:

[0019] a housing;

[0020] an electric core arranged in the housing, the electric core comprising a tab sheet having the composite current collector full-tab structure as described above;

[0021] a current collecting plate;

[0022] wherein the metal edge wrapping structure of the tab sheet is electrically connected to the current collecting plate by welding.

[0023] According to a third aspect, an embodiment provides a method for manufacturing a battery with a composite current collector full-tab structure, comprising the following steps:

[0024] providing a composite current collector, comprising an intermediate base film and a first metal layer and a second metal layer formed on both sides of the intermediate base film;

[0025] providing a first metal strip and a second metal strip;

[0026] preprocessing the composite current collector;

[0027] pre-pressing the first metal strip and the second metal strip to form pre-pressing lines for improving the welding strength;

[0028] metal banding structure is formed by welding the first metal band and the second metal band to each other at the edge of the composite current collector, thereby forming a metal banding structure wrapping the edge of the composite current collector and bridging the first metal layer and the second metal layer;

[0029] the tab is slit, die-cut, wound and welded.

[0030] Preferably, the pre-treatment of the composite current collector comprises:

[0031] the composite current collector is debunched;

[0032] the composite current collector is cleaned to remove the oxides on the first metal layer and the second metal layer;

[0033] a micro-pit array is precisely marked on the first metal layer and the second metal layer at the predetermined welding position by laser, as a mark point for subsequent welding positioning.

[0034] Preferably, after the welding of the metal banding structure is completed, the composite current collector with the welded metal banding structure is coated to obtain a composite current collector tab with the metal banding structure.

[0035] Preferably, in the step of slitting, die-cutting, winding and welding the tab, the area of the edge of the composite current collector where the first metal band and the second metal band have been welded is die-cut to form a plurality of individual tab units, and any individual tab unit has the metal banding structure.

[0036] According to the full-tab structure of the composite current collector of the above embodiment, by introducing and welding the specially designed metal band at the edges of the metal layers on both sides of the composite current collector, an integrated full-metal banding structure wrapping the edge of the composite current collector is formed, which constitutes a whole conductive bridging structure, and then the high-strength metal banding structure is welded and connected with the current collector plate. The original "metal-polymer-metal" composite cross section is completely replaced, and the connection failure caused by the melting of the polymer layer during laser welding is completely eliminated, thereby providing a thick, flat and uniform standardized interface for the subsequent connection with the current collector plate, and realizing high-strength and high-reliability welding with the current collector plate. BRIEF DESCRIPTION OF DRAWINGS

[0037] Figure 1 is a sectional view of the full-tab structure of the composite current collector in an embodiment;

[0038] Figure 2 is a schematic view of the welding area of the composite current collector in an embodiment;

[0039] Figure 3 FIG. 8 is a schematic view of a welding area of the first metal strip and the second metal strip in one embodiment;

[0040] Figure 4 FIG. 9 is a process diagram of a method of manufacturing a battery having a full tab structure of a composite current collector in Example 3;

[0041] Figure 5 FIG. 10 is a comparison graph of the cycle performance of the composite current collector and the common current collector under the same test conditions in one embodiment;

[0042] Figure 6 FIG. 11 is a comparison graph of the effect of omitting a key process step of the composite current collector tab on the welding performance in one embodiment.

[0043] Reference numerals:

[0044] 1. composite current collector; 11. first metal layer; 12. intermediate base film; 13. second metal layer; 14. marker point;

[0045] 2. first metal strip;

[0046] 3. second metal strip;

[0047] 4. pre-pressing groove. DETAILED DESCRIPTION

[0048] The application will be further described in detail by specific embodiments with reference to the accompanying drawings. In different embodiments, similar elements are denoted by associated similar element reference numerals. In the following embodiments, many details are described in order to make the application better understood. However, those skilled in the art can easily recognize that some features can be omitted in different cases, or can be replaced by other elements, materials, methods. In some cases, some operations related to the application are not shown or described in the specification in order to avoid the core part of the application being overwhelmed by too much description, and it is not necessary to describe these related operations in detail for those skilled in the art according to the description in the specification and general technical knowledge in the art.

[0049] In addition, the features, operations or characteristics described in the specification can be combined in any appropriate manner to form various embodiments. At the same time, the steps or actions in the method description can also be sequentially adjusted or adjusted in a manner that is obvious to those skilled in the art. Therefore, the order in the specification and the drawings is only for the purpose of clearly describing one embodiment, and does not mean that it is the necessary order, unless otherwise stated that a certain order must be followed.

[0050] The serial numbers of components in this document, such as "first", "second", etc., are only used to distinguish the described objects, and have no technical meaning. Unless otherwise specified, "connection" and "coupling" in this application include direct and indirect connections (couplings).

[0051] The composite current collector 1 applied to the full tab battery structure faces the following key obstacles: 1. Welding failure: when laser welding the current collector end face and the current collector disc, the intermediate layer of high polymer material has a low melting point, and is melted, shrunk or decomposed under heat, resulting in that the metal layers cannot form a reliable connection. 2. Current interruption: the high polymer insulating layer blocks the longitudinal (Z-direction) current conduction between the metal layers on both sides of the current collector. Even if the local welding is successful, the entire end face cannot achieve effective current collection, resulting in the failure of the full tab structure. 3. Cost disadvantage: the above problems result in a high assembly process failure rate, and the complex manufacturing process itself makes the comprehensive cost significantly higher than that of the traditional metal current collector, hindering commercialization.

[0052] The prior art attempts to solve the above problems, such as using conductive glue connection (increasing contact but poor reliability), punching and filling glue in the tab area (complex process, which may affect the mechanical strength), or using additional metal foil for clamping or switching (increasing thickness and cost, and not fundamentally solving the reliability problem of the welding interface). Therefore, there is an urgent need for an innovative solution that can fundamentally solve the problem of reliable welding and efficient Z-direction conduction of the composite current collector 1 full tab.

[0053] In this application, by introducing a specially designed metal strip (aluminum strip for the positive electrode and copper strip for the negative electrode) in the tab area of the composite current collector 1 through a precise welding process, a "full metal edge covering" tab structure is formed. The metal strip is welded with the metal layers on both sides of the composite current collector 1 and the edge of the metal strip itself, forming a whole conductive bridging structure. Finally, the metal strip is welded with the corresponding current collector disc (positive current collector disc / negative current collector disc).

[0054] Embodiment one: composite current collector full tab structure.

[0055] Please refer to Figure 1 In this embodiment, a composite current collector full tab structure is provided, which comprises: a composite current collector 1, comprising an intermediate base film 12 and first and second metal layers 11 and 13 formed on both sides of the intermediate base film 12; a first metal strip 2 fixed to the first metal layer 11 by welding; and a second metal strip 3 fixed to the second metal layer 13 by welding; wherein the first and second metal strips 2 and 3 are welded with each other at the edge of the composite current collector 1 to form a metal edge covering structure covering the edge of the composite current collector 1, and the metal edge covering structure forms a continuous metal interface for welding with the current collector disc; the edge of the composite current collector 1 forms a plurality of tab units, and any tab unit has the metal edge covering structure.

[0056] In this embodiment, the plurality of tab units are formed by die cutting the full tab structure that has formed a metal edge wrap structure.

[0057] In this embodiment, the first metal strip 2 and the second metal strip 3 are used to provide sufficient weldable metal area. Compared to the nano / micro level thin metal layer on the composite current collector 1, the thickness of the strip provides sufficient molten metal to form a deep fusion weld with the current collector disc, solving the problem of “thin layer difficult to weld”.

[0058] In this embodiment, the first metal strip 2 is the same material as the first metal layer 11, and the second metal strip 3 is the same material as the second metal layer 13. In this embodiment, the composite current collector 1 of the positive electrode uses an aluminum strip, and the composite current collector 1 of the negative electrode uses a copper strip.

[0059] Please refer to Figure 1 , the composite current collector 1 as the basic substrate, the intermediate base film 12 generally uses a polymer base film (such as a PET film, PP, PI, etc. with a thickness of 4-8 μm). On the upper and lower surfaces of the intermediate base film 12, a very thin first metal layer 11 and a second metal layer 13 are formed by magnetron sputtering, evaporation and other processes, for example, with a thickness of about 1 μm.

[0060] Further, the first metal strip 2 and the second metal strip 3 are provided with a composite coating for enhancing the welding performance, such as a NiP-SiC coating, to change the physical and chemical properties of the surface of the first metal strip 2 and the second metal strip 3, which can enhance its hardness, wear resistance, and significantly improve its laser welding compatibility with the thinner first metal layer 11 and second metal layer 13 of the composite current collector 1, to promote the formation of a firm metallurgical bond between the two, rather than a simple adhesion, to improve the strength and reliability of the welding interface.

[0061] Further, a part of the composite current collector 1 in the length direction is reserved as a “blank area” without composite coating, i.e. the tab forming area.

[0062] Please refer to Figure 1 , the thickness of the first metal strip 2 and the second metal strip 3 (for example, 0.08-0.15 mm) is much greater than the thickness of the metal layer of the composite current collector 1. The first metal strip 2 and the second metal strip 3 are designed to be placed on both sides of the tab blank area of the composite current collector 1.

[0063] Further, in the present embodiment, the first metal strips 2 are firmly welded with their adjacent first metal layers 11 of the composite current collector 1 in the plane (X-Y plane) by one or more laser welds. Similarly, the second metal strips 3 are welded with the second metal layers 13. This ensures that the metal strips are fixed on the surface of the current collector. The first metal strips 2 and the second metal strips 3 are welded to each other on the side of the edge end surface of the composite current collector 1, connecting the two originally independent first metal strips 2 and second metal strips 3 in the Z direction.

[0064] Please refer to Figure 1 By the combination of the above-mentioned "lateral welding" and "edge mutual welding", the first metal strips 2, the second metal strips 3 and the edge of the composite current collector 1 together form a "U"-shaped integrated all-metal edge covering structure that wraps around the edge of the composite current collector 1.

[0065] Further, please refer to Figure 1 The to-be-welded regions of the first metal strips 2 and the second metal strips 3 are distributed with a plurality of pre-pressing lines 4. In the present embodiment, the pre-pressing lines 4 can be diamond knurls formed on the to-be-welded regions of the first metal strips 2 and the second metal strips 3, with a depth of 0.5 μm-2 μm, thereby creating micro mechanical interlocking points and molten pool guiding structures. On the one hand, the increased surface area improves the bonding force; on the other hand, these micro pits can accurately capture and position the molten metal during laser welding, preventing it from flowing randomly, thereby forming more uniform and more secure welds.

[0066] Further, please refer to Figure 1 The to-be-welded regions of the first metal layers 11 and the second metal layers 13 are distributed with a plurality of marking points 14 for positioning marks. In the present embodiment, the marking points 14 are an array of micro pits precisely marked by ultraviolet laser (wavelength 355 nm) as precise positioning marks for subsequent welding.

[0067] In the present embodiment, the metal edge covering structure is not a simple covering, but a continuous metal frame formed by welding. It provides a thick, pure and all-metal welding terminal; when it needs to be welded with the current collector plate, the laser directly acts on the metal edge covering structure, just like welding two traditional metal pieces, completely avoiding the problem of heat damage to the polymer layer, improving the welding strength. At the same time, the metal edge covering structure forms a low-resistance metal bridge across the upper and lower surfaces of the composite current collector 1. The current can pass through the first metal layers 11, the first metal strips 2, the edge mutual welding points, the second metal strips 3 and the second metal layers 13 in turn, forming an efficient Z-direction conductive path, solving the problem of insulation blockage of the polymer layer, and significantly reducing the contact resistance of the tab itself and the overall internal resistance of the battery.

[0068] In the present embodiment, please refer to Figure 3, stable low resistance connection effectively reduces the internal resistance of the battery (about 12%), improves the rate and cycle performance, fully develops the lightweight advantage of the composite current collector 1, and helps to improve the energy density of the battery.

[0069] Embodiment two: a battery.

[0070] The present embodiment provides a battery, for example, a cylindrical full-tab battery. The battery comprises a shell, an electrode core located in the shell, and a positive current collector disc and a negative current collector disc (or the shell itself as one pole) closing the open ends of the shell. Among them, the tab structure of the electrode core is the full-tab structure of the composite current collector with full-metal wrapping structure in embodiment one.

[0071] In the present embodiment, the positive current collector disc inside the battery is connected in series with the full-metal wrapping of all positive tabs through laser welding; the negative current collector disc is connected in series with the full-metal wrapping of all negative tabs through laser welding. The full-metal wrapping structure provides a high-strength, low-impedance connection interface, so that the battery of the present embodiment exhibits significantly reduced internal resistance, excellent rate performance, high safety, and long cycle life.

[0072] Embodiment three: a method for preparing a battery with a full-tab structure of a composite current collector.

[0073] Before preparation, a composite aluminum current collector for the positive electrode and a composite copper current collector for the negative electrode are provided, both of which comprise an intermediate base film 12 and a first metal layer 11 and a second metal layer 13 formed on both sides of the intermediate base film 12. It is generally a plastic film such as PET, PP, PI as the base material, and a very thin copper / aluminum is plated on both sides by vacuum sputtering plus electroplating or chemical plating, forming a sandwich structure.

[0074] A first metal strip 2 and a second metal strip 3 are provided, the first metal strip 2 is generally a metal aluminum strip coiled material, and the second metal strip 3 is generally a metal copper strip coiled material.

[0075] In the present embodiment, the thickness of the composite aluminum current collector used is 8μm, and the thickness of the composite copper current collector used is 6μm. The thickness of the metal aluminum strip coiled material used is 0.1mm, and the thickness of the metal copper strip coiled material used is 0.08mm.

[0076] S1: Pre-treatment of composite current collector 1.

[0077] S11: Wrinkle removal;

[0078] The coiled composite aluminum current collector (for the positive electrode) and the composite copper current collector (for the negative electrode) are respectively passed through a set of rubber-coated flattening rollers. Under controlled environmental temperature (about 40℃±1℃) and walking speed (such as 10m / min), the gradient tension (center tension 8N→edge tension 6N) control method is used to prevent material curling.

[0079] The wrinkle-removing step of the composite current collector 1 can eliminate the wrinkles and residual stress of the foil generated during slitting and transportation, ensure the absolute flatness of the welding area, and avoid false welding or welding stress concentration caused by uneven material.

[0080] S12: Plasma cleaning;

[0081] The flattened composite current collector 1 is sent into a plasma cleaning chamber. Under the excitation of a radio frequency power source (such as 13.56 MHz, 800 W), a mixed gas of argon and oxygen (for example, the ratio of argon to oxygen is 4:1) is introduced, and the metal layer contact angle is <5° under low pressure (such as 0.3 mbar) for 90 seconds to generate plasma and impact clean the metal layer on the surface of the composite current collector 1.

[0082] The cleaning of the composite current collector 1 can deeply physically impact and chemically activate, completely remove the natural oxide layer and organic contaminants on the surface of aluminum or copper, make the metal surface reach high cleanliness and high activity, significantly reduce the contact angle, and greatly reduce the contact resistance of subsequent welding, which is a necessary prerequisite for obtaining high-strength welding.

[0083] S13: Laser marking;

[0084] An ultraviolet laser (wavelength 355 nm) is used to accurately ablate a micro-pit array (for example, pit points with a diameter of Φ20 μm and a spacing of 50 μm±1 μm) on the predetermined welding area (i.e., the margin area) of the composite current collector 1, which is used as a mark point 14 for subsequent welding positioning.

[0085] The mark point 14 provides a high-precision visual positioning reference mark, which provides an absolute coordinate reference for the subsequent robot or precision mechanism to grab and place the metal strip, and is the key to realizing automatic and high-precision production, further reducing welding errors.

[0086] S2: Metal strip pretreatment.

[0087] S21: Coating of composite coating;

[0088] The metal aluminum and copper strip coils are unwound with a micro-tension. A NiP-SiC composite coating (for example, the composition is Ni85P10SiC5, and the thickness is 1.5 μm) is uniformly deposited on the surface of the metal strip by a 5N micro-tension uncoiling magnetic control sputtering or similar process.

[0089] By forming a modified layer with special properties on the surface of the metal strip, not only the hardness and wear resistance of the metal strip surface are enhanced, but more importantly, the composition design makes it have good metallurgical compatibility with aluminum or copper, which can promote interface alloying during laser welding and form a connection with higher strength and lower resistance.

[0090] S22: Pre-embossed 4 processing;

[0091] A precise embossing machine is used to emboss a specific pattern (such as diamond pattern) on the area to be welded of the coated metal strip, with the embossing depth controlled at 1.2 μm ± 0.3 μm and the density at 200 pits / mm².

[0092] Through the pre-embossed 4, the real contact area is increased to improve the bonding force, and it serves as an ideal nucleation point of the molten pool during welding, thereby restricting the flow of liquid metal, so as to obtain a regular-shaped, internally dense and defect-free welding spot, greatly improving the welding process window and reliability.

[0093] S3: Metal edge welding to form the pole piece;

[0094] S31: Positioning and alignment;

[0095] The machine vision system (such as CCD vision system) is used to identify the laser-marked mark points 14 on the composite current collector 1, while the corresponding metal strip after pretreatment is grabbed, and the corresponding metal strip is accurately placed on both sides of the blank area of the tab of the composite current collector 1, so as to realize the precise alignment of the metal strip and the ultrathin welding area.

[0096] S32: Welding;

[0097] The fiber pulse laser is used to focus the laser beam on the contact interface between the first metal strip 2 and the first metal layer 11 of the composite current collector 1 for welding, so as to ensure that the heat is sufficient to melt the metal strip coating and the thin metal layer of the current collector, but not to penetrate too much. The laser penetrates the first metal strip 2 to melt and weld the first metal layer 11 of the composite current collector 1, and forms a Φ80 μm welding spot, firmly connecting the first metal strip 2 and the first metal layer 11.

[0098] The second metal strip 3 is welded to the second metal layer 13 of the composite current collector 1 by the same or symmetrical process as above.

[0099] The laser beam is focused on the edge of the composite current collector 1, i.e. the end of the first metal strip 2 and the second metal strip 3 away from the welding point with the composite current collector 1, at which point they are adjacent. The laser simultaneously acts on the end of the first metal strip 2 and the second metal strip 3, causing them to locally melt and fuse together to form a 150 μm deep overall edge structure. The two metal strips, which are respectively fixed on the first metal layer 11 and the second metal layer 13, are connected into one whole on the side, thereby forming an integrated all-metal edge structure.

[0100] In the present embodiment, the welding parameters are selected in the range of: laser wavelength 800-1200 nm (wavelength 1064 nm can be selected), power 60-180 W (power 120 W can be selected), pulse width 0.6-1 ms (pulse width 0.8 ms can be selected), frequency 300-700 Hz (frequency 500 Hz can be selected), and the welding process is carried out in an inert gas (such as Ar) protection environment to prevent high-temperature oxidation of the metal.

[0101] S33: coating;

[0102] After the completion of the metal edge-welding structure welding, the composite current collector 1 substrate with "full metal edge-welding" is obtained. The composite current collector 1 substrate obtained by the above-mentioned metal edge-welding structure welding (i.e., the composite aluminum current collector and the composite copper current collector with the metal edge-welding structure) is used as the substrate of the positive electrode and the negative electrode, respectively, and the positive electrode active paste (such as LiNi0.8Co0.1Mn0.1O2) and the negative electrode active paste (such as graphite) are coated, respectively, to obtain the composite current collector 1 positive and negative electrode sheet with the metal edge-welding structure.

[0103] S4: slitting, die cutting, winding, and welding of the electrode sheet.

[0104] S41: rolling and slitting;

[0105] The coated electrode sheet is rolled to the required compaction density (positive electrode compaction density 3.4 g / cm3, negative electrode 1.6 g / cm3), and then slitted into electrode sheets of a predetermined width (for example, 58 mm).

[0106] S42: tab die cutting;

[0107] The reserved blank area of the welded metal strip is die cut to form multiple independent tab units. Specifically, the positive electrode sheet is die cut into multiple tab units, each tab unit having a width of 2-6 mm and a length of 6-10 mm, for example, 4.0 x 8.0 mm ± 0.1 mm. The negative electrode sheet is die cut into multiple tab units, each tab unit having a width of 2-6 mm and a length of 5-9 mm, for example, 3.5 x 7.0 mm ± 0.1 mm.

[0108] In this step, the edge of each tab unit is composed of the above-mentioned metal edge-welding structure, and the composite current collector 1 is covered by the first metal strip 2 and the second metal strip 3, and the edge mutual welding area forms a continuous conductive interface.

[0109] In the present embodiment, the key process design of "welding the metal strip first and then coating and die cutting" significantly avoids the thermal damage and pollution of the active material layer by the subsequent welding, greatly improving the production yield (expected to be more than 15%).

[0110] S43: winding;

[0111] The positive electrode sheet, the separator, and the negative electrode sheet are sequentially wound into a Φ18 mm battery cell containing 48 pairs of tabs. The separator can use Celgard 2400 separator.

[0112] S44: tab folding and current collector welding;

[0113] The full tab group at both ends of the battery cell is folded and arranged.

[0114] The aluminum metal edge structure on the positive tab is welded to the aluminum positive current collector using laser welding. The copper metal edge structure on the negative tab is welded to the copper or nickel-plated copper negative current collector.

[0115] In particular, the positive end directly flattens the tab group, the negative end covers the negative current collector upper surface with a 5° copper tape to form an isolation layer, and 300W laser welding is used to weld the positive aluminum tape edge layer to the aluminum alloy current collector (welding point spacing 0.5mm), and 250W laser welding is used to weld the negative copper tape metal edge structure to the nickel-plated copper current collector (welding depth 100pm). Ultimately, the high-performance lithium-ion battery is obtained, with tab resistance reduced to 3.8±0.3mΩ (traditional structure 12.5±1.2mΩ), welding peel strength increased to 4.8N / mm (traditional structure 1.2N / mm), cycle 500 times expansion rate only 15% (traditional 38%) and tab oxidation rate <1% (traditional 27%).

[0116] Reference is made to Figure 4 , which is a comparison chart of the cycle performance of the composite current collector 1 and the ordinary current collector under the same test conditions. As can be seen from the chart, under the test conditions of 25℃, 1C / 1C, with the increase of cycle number, the capacity retention of the composite current collector 1 and the ordinary current collector both show a downward trend. But the capacity retention of the composite current collector 1 is higher than that of the ordinary current collector in each cycle stage. This performance difference is of great significance to the actual application of the battery. In scenarios that require long-life batteries, such as electric vehicles, energy storage systems, etc., the application of the composite current collector 1 can improve the overall performance and service life of the battery, and reduce the replacement cost.

[0117] Comparative Example 1:

[0118] The difference between this comparative example and Example Three is that no special metal tape is used for edge covering, laser spot welding is directly performed on the upper and lower metal layers of the composite current collector 1, and after the tab folding, the composite current collector 1 tab and the current collector are directly welded by laser welding. Other steps (such as metal tape pretreatment, precision welding, coating, etc.) remain consistent.

[0119] Comparative Example 2:

[0120] The difference between this comparative example and Example Three is that a metal strip is used, but only the metal layer adjacent to the composite current collector 1 is welded and the step of welding the two metal strips to each other at the edge is omitted. Other steps (such as current collector pretreatment, precision welding parameters, coating, etc.) remain consistent with the example.

[0121] Comparative Example 3:

[0122] The difference between this comparative example and Example Three is that the step of plasma cleaning of the metal layer of the composite current collector 1 is omitted. Other steps (such as current collector pretreatment, metal strip pretreatment, coating, etc.) remain consistent with the example.

[0123] Comparative Example 4:

[0124] The difference between this comparative example and Example Three is that the step of coating the NiP-SiC composite coating on the surface of the metal strip is omitted. Other steps (such as pretreatment, coating, die cutting, winding, etc.) remain consistent with the example.

[0125] Comparative Example 5:

[0126] The difference between this comparative example and Example Three is that the width of the metal strip and the corresponding tab width after die cutting are changed. Other steps (such as metal strip pretreatment, precision welding, etc.) remain consistent with the example.

[0127] Please refer to Figure 3 , the battery prepared by the preparation method of Example Three has a composite current collector full-tab structure with a full-metal edge-wrapped structure; the performance of the battery is compared with that prepared by the preparation method of each of Comparative Examples 1-5, wherein:

[0128] When no special metal strip is used for edge wrapping in Comparative Example 1, the success rate of welding the current collector disc is 0, indicating that the metal edge-wrapped structure is crucial for successful welding of the current collector disc. Omitting the welding of the metal strip at the edge in Comparative Example 2 will result in poor conductivity and high internal resistance; omitting the plasma cleaning of the metal layer in Comparative Example 3 will result in low welding yield, indicating that the plasma cleaning of the metal layer is an important step to ensure welding quality. Omitting the coating of the composite coating on the surface of the metal strip in Comparative Example 4 results in low welding yield and high internal resistance. This shows that edge welding of the metal strip and coating of the composite coating on the surface help to improve conductivity and reduce internal resistance. Changing the width of the metal strip and the corresponding tab width after die cutting in Comparative Example 5 results in low internal resistance, indicating that this process adjustment has a positive effect on improving conductivity.

[0129] In summary, the steps and designs of edge wrapping, edge welding, plasma cleaning, coating, size matching, etc. in Example Three are all key processes to ensure the welding quality, low internal resistance and high conductivity of the tabs of the composite current collector 1. Omitting or simplifying any step may result in welding failure, poor conductivity, high internal resistance, etc., indicating that the tabs of the composite current collector 1 have very high requirements for process integrity and material matching.

[0130] The above application of specific examples to illustrate the present application, is only used to help understand the present application, and not to limit the present application. For the skilled in the art to which the present application belongs, according to the idea of the present application, can make a number of simple deduction, deformation or replacement.

Claims

1. A composite current collector omnipolar structure, characterized in that, include The composite current collector (1) includes an intermediate base film (12) and a first metal layer (11) and a second metal layer (13) formed on both sides of the intermediate base film (12). The first metal strip (2) is fixed to the first metal layer (11) by welding; and, The second metal strip (3) is fixed to the second metal layer (13) by welding. Wherein, the first metal strip (2) and the second metal strip (3) are welded to each other at the edge of the composite current collector (1) to form a metal edging structure that wraps around the edge of the composite current collector (1), and the metal edging structure constitutes a continuous metal interface for welding with the current collector plate; The composite current collector (1) has multiple tab units formed on its edge, and each tab unit has the metal edging structure.

2. The composite current collector omnipolar structure according to claim 1, characterized in that, The surfaces of the first metal strip (2) and the second metal strip (3) are provided with a composite coating to enhance welding performance.

3. The composite current collector omnipolar structure according to any one of claims 1 or 2, characterized in that, The areas to be welded of the first metal strip (2) and the second metal strip (3) have multiple pre-pressed patterns (4).

4. The composite current collector omnipolar structure according to claim 1, characterized in that, The areas to be welded in the first metal layer (11) and the second metal layer (13) have multiple marking points (14) for positioning marking.

5. The composite current collector omnipolar structure according to claim 1, characterized in that, The first metal strip (2) is made of the same material as the first metal layer (11), and the second metal strip (3) is made of the same material as the second metal layer (13).

6. A battery, characterized in that, include: case; A battery cell disposed within the housing, the battery cell comprising electrodes having a composite current collector full-tab structure as described in any one of claims 1 to 5; Collector disk; The metal edging structure of the electrode is electrically connected to the current collector by welding.

7. A method for preparing a battery with a composite current collector omni-tab structure, characterized in that, Includes the following steps: A composite current collector (1) is provided, comprising an intermediate base film (12) and a first metal layer (11) and a second metal layer (13) formed on both sides of the intermediate base film (12). Provide a first metal strip (2) and a second metal strip (3); The composite current collector (1) is pretreated; Pre-pressing is performed on the first metal strip (2) and the second metal strip (3) to form pre-pressed patterns (4) for improving welding strength. Metal edge welding to form an electrode: The first metal strip (2) and the second metal strip (3) are respectively positioned to the welding area of ​​the composite current collector (1); the first metal strip (2) is welded to the first metal layer (11); the second metal strip (3) is welded to the second metal layer (13); the first metal strip (2) and the second metal strip (3) are welded to each other at the edge of the composite current collector (1) to form a metal edge structure that wraps around the edge of the composite current collector (1) and bridges the first metal layer (11) and the second metal layer (13); Electrode slitting, die cutting, winding, and welding.

8. The preparation method according to claim 7, characterized in that, The pretreatment of the composite current collector (1) includes the following steps: The composite current collector (1) is subjected to wrinkle removal; The composite current collector (1) is cleaned to remove oxides from the first metal layer (11) and the second metal layer (13); Laser is used to precisely mark micro-pit arrays at predetermined welding positions on the first metal layer (11) and the second metal layer (13), which serve as marker points (14) for subsequent welding positioning.

9. The preparation method according to claim 7, characterized in that, After the metal edging structure is welded, the composite current collector (1) is coated to obtain a composite current collector (1) electrode with a metal edging structure.

10. The preparation method according to claim 7, characterized in that, In the electrode slitting, die-cutting, winding and welding steps, the area of ​​the composite current collector (1) where the first metal strip (2) and the second metal strip (3) have been welded is die-cut to form multiple electrode units, and each electrode unit has the metal edging structure.

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