Composite electrode sheet, method for preparing same, and secondary battery

Abstract

The present invention discloses a composite electrode sheet, a preparation method thereof and a secondary battery. The composite electrode sheet includes a composite current collector, an electrode material layer formed on the composite current collector, and a tab. The composite current collector includes a polymer layer, and metal transition layers are disposed on both side surfaces of the polymer layer for tab welding. The metal transition layer partially overlaps with the polymer layer inside the edge of the polymer layer and extends outside the edge of the polymer layer. The composite current collector further includes a metal film layer, and the metal film layer covers the polymer layer and the metal transition layer in the overlapping area. An electrode material coating is further disposed on one side of the metal film layer away from the overlapping area of the metal transition layer and the polymer layer. The present invention effectively solves the technical problems in the prior art, such as the reduction of the current conduction area caused by welding, the increase of the internal resistance of the battery, poor overcurrent capacity, poor welding quality, and unstable connection state of the weld seam.

Description

Technical Field

[0001] The present invention relates to the field of secondary batteries, and particularly to a composite electrode sheet, a preparation method thereof, and a secondary battery. Background Art

[0002] With the large-scale commercial use of lithium-ion batteries, frequent safety accidents have attracted wide attention. Among them, the problem of thermal runaway fire and explosion caused by short circuits and the like is an urgent problem that battery manufacturers need to solve. At present, researchers have tried to use composite foil current collectors to replace traditional metal foil current collectors as the current collectors for the positive and negative electrodes. The composite foil usually has a polymer layer added between two metal film layers on both sides. Using a current collector with a metal-polymer-metal structure can effectively improve the performance of the battery against needle puncture, extrusion, and heavy object impact. At the same time, the polymer material is lighter, which can reduce the weight of the current collector and improve the energy density of the battery.

[0003] However, in order for the battery to have relatively excellent electrochemical performance, the metal film layers on both sides of the composite foil are often relatively thin. And due to the presence of the middle polymer layer, the tab cannot be directly welded to the battery electrode sheet. Therefore, a metal adapter piece needs to be spliced for welding. Under the pressure of the welding head, the polymer layer gives way, and it is easy to form a weld seam with a cavity in the middle, reducing the current conduction area and resulting in poor overcurrent capacity, which leads to an increase in the internal resistance of the electrode sheet. Moreover, the welding pressure is not easy to control. With a small welding pressure, the welding states on the front and back sides are not stable, and it is easy to fall off during subsequent handling and use, resulting in poor battery performance. With a large welding pressure, the welding head is easily damaged, increasing the production cost. Summary of the Invention

[0004] Aiming at the above problems existing in the prior art, the purpose of the present invention is to provide a composite electrode sheet, a preparation method thereof, and a secondary battery. It can effectively solve the technical problems that when welding the tab in the prior art, due to the pressure of the welding head, the polymer layer gives way, resulting in the formation of cavities, reducing the current conduction area, and thus increasing the internal resistance of the battery and poor overcurrent capacity. It can also strengthen the quality of the weld seam and is beneficial to improving the connection strength of the weld seam.

[0005] To achieve the above object, the present invention adopts the following technical solutions:

[0006] In a first aspect, the present invention provides a composite electrode sheet, including a composite current collector, an electrode material layer formed on the composite current collector, and a tab;

[0007] Wherein, the composite current collector includes a polymer layer, a metal adapter layer stacked with the polymer layer in a partially overlapping manner, and a metal film layer formed on the polymer layer and the metal adapter layer;

[0008] The tab is connected to the metal adapter layer.

[0009] In some embodiments of the present application, the metal film layer is formed on the polymer layer and the first region where the polymer layer overlaps with the metal transition layer.

[0010] Preferably, the thickness of the metal transition layer is 12 - 16 μm.

[0011] In one embodiment, the metal film layer can extend to the metal transition layer.

[0012] Preferably, the thickness of the polymer layer is 2 - 10 μm, preferably 3 - 5 μm.

[0013] Preferably, the width of the overlapping region between the polymer layer and the metal transition layer is 3 mm - 6 mm.

[0014] As a preferred technical solution of the composite electrode sheet of the present invention, the thickness of the metal film layer is 100 nm - 5 μm.

[0015] Preferably, the metal film layer is a metal film layer with a carbon coating on its surface.

[0016] Preferably, the distance between the electrode material coating and the metal transition layer is 5 mm - 40 mm.

[0017] In the present invention, the electrode material coating is located on at least one side of the composite current collector;

[0018] Preferably, when only one side of the metal transition layer is connected to the tab, the electrode material coating and the tab are located on the same surface of the composite current collector.

[0019] Preferably, the electrode material coating and the tab are located on the same surface of the composite current collector.

[0020] In order to facilitate the welding of the tab, metal transition layers are provided on both surfaces of the polymer layer, namely the first metal transition layer and the second metal transition layer.

[0021] The thicknesses of the first metal transition layer and the second metal transition layer can be the same or different;

[0022] Preferably, the metal film layer includes a first metal film layer and a second metal film layer.

[0023] Second, the present invention provides a method for preparing the composite electrode sheet as described in the first aspect, and the method includes the following steps:

[0024] S1: Splice the metal transition layer on both surfaces of the polymer layer;

[0025] S2: Form a metal film layer on the surfaces of the polymer layer and the metal transition layer;

[0026] S3: Weld the splicing area;

[0027] S4: Form an electrode material coating on one side away from the splicing area;

[0028] It can be understood that any method that can form a metal film layer on the surface of the polymer layer and the metal transfer layer can be used in the present invention.

[0029] Exemplarily, in step S2, the metal film layer is formed by evaporation, deposition or sputtering.

[0030] Optionally, after step S4, step S5 is carried out: After drying, tab welding is carried out on the metal transfer layer.

[0031] The present invention does not limit the formation method of the electrode material coating. For example, the method of coating electrode paste can be adopted.

[0032] In a third aspect, the present invention provides a secondary battery, and the secondary battery includes the composite electrode sheet described in the first aspect.

[0033] The present invention does not limit the preparation method of the secondary battery. For example, the above composite electrode sheets can be wound or laminated to form an electric core.

[0034] Compared with the prior art, the present invention has the following beneficial effects:

[0035] By improving the structure of the composite electrode sheet, especially changing the position of the metal film layer in the composite electrode sheet, the present invention increases the current conduction area, effectively avoids the problems of increased resistance and poor over-current capacity caused by welding. By using the structure of the composite electrode sheet of the present application, the welding quality can also be effectively improved, and the shedding of the metal sheet and the tab during handling and other processes can be effectively prevented, resulting in poor use of the battery. Description of the Drawings

[0036] Figure 1 and Figure 2 is a schematic structural diagram of a composite electrode sheet in an embodiment of the present invention, where Figure 1 is a front view, Figure 2 is a top view.

[0037] Among them, 110 - polymer layer, 121 - first metal transfer layer, 1222 - second metal transfer layer, 130 - metal film layer, 140 - welding structure, 200 - electrode material coating, 300 - tab. Detailed Embodiments

[0038] The technical solution of the present invention will be further described below with reference to the drawings and through specific embodiments.

[0039] In an embodiment, the present invention provides a composite electrode sheet, such asFigure 1 and Figure 2 As shown in Figure 2 , it can be used in secondary batteries, including a composite current collector 100, an electrode material layer 200 formed on the composite current collector, and a tab 300.

[0040] The composite current collector includes a polymer layer 110, a metal transfer layer 120 spliced with the polymer layer in a partially overlapping manner, and a metal film layer 130 formed on the polymer layer and the metal transfer layer;

[0041] The metal transfer layer partially overlaps with the polymer layer 110 inside the edge of the polymer layer and extends outside the edge of the polymer layer 110.

[0042] In some embodiments of the present application, the metal film layer is formed on the polymer layer and the first region where the polymer layer overlaps with the metal transfer layer.

[0043] In one embodiment, the thickness of the metal transfer layer is 12 - 16 μm, such as 12 μm, 13 μm, 13 μm, 14 μm, 15 μm or 16 μm, etc.

[0044] As a preferred embodiment of the present invention, in the present invention, the electrode material coating and the tab are located on the same side of the composite electrode.

[0045] The composite electrode provided by an embodiment of the present invention increases the current conduction area by setting a layered electrode, effectively reducing the internal resistance of the battery. It effectively solves the problems of increased internal resistance of the battery and poor overcurrent capacity caused by the reduction of the current conduction area due to avoiding welding the polymer layer.

[0046] In the present invention, the functions of the polymer layer 110 are mainly as follows: on the one hand, when the temperature inside the battery cell rises sharply, it melts, thereby cutting off the current and improving the safety of the battery; on the other hand, when being punctured, due to its own extensibility, it prevents the sharp part from piercing the separator or other parts to cause a short circuit. If the polymer substrate is too thin, it is easily punctured when encountering puncture or impact, and cannot effectively solve the problem of battery short circuit caused by puncture, etc. If the polymer substrate is too thick, it will increase the internal resistance of the battery and deteriorate the battery performance.

[0047] The tab 300 is connected to the metal transfer layer 120.

[0048] In one embodiment, the thickness of the polymer layer 110 is 2 - 10 μm, such as 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm or 10 μm, etc., and preferably 3 - 5 μm.

[0049] In some embodiments, the material of the polymer layer 110 may be one or more of polyethylene terephthalate, polybutylene terephthalate, polyethylene terephthalate, polypropylene, polyamide, polyimide, polyethylene, polyethylene oxide, polyvinyl chloride, polycarbonate, polymethyl methacrylate, polytetrafluoroethylene, polyvinyl alcohol, styrene-butadiene rubber, fluororubber, etc.

[0050] In one embodiment, the width of the overlap between the metal transfer layer and the polymer layer 110 is 3 mm - 6 mm, such as 3 mm, 3.5 mm, 4 mm, 4.5 mm, 5 mm, 5.5 mm, or 6 mm, etc.

[0051] In one embodiment, the material of the metal transfer layer is one or several of aluminum, copper, stainless steel, nickel, titanium, etc.

[0052] To achieve the welding of the tab and the composite electrode, as Figure 1 and Figure 2 shown, metal transfer layers 120 are provided on both side surfaces of the polymer layer 110, namely a first metal transfer layer 121 and a second metal transfer layer 122 respectively. The materials of the first metal transfer layer 121 and the second metal transfer layer 122 may be the same or different.

[0053] In one embodiment, the first metal transfer layer 121 and the second metal transfer layer 122 have the same thickness.

[0054] In one embodiment, the thickness of the metal film layer 130 is 100 nm - 15 μm, such as 100 nm, 500 nm, 1 μm, 3 μm, or 5 μm, etc. Although thickening the metal film layer is beneficial to increasing the current conduction area, improving the overcurrent capacity and reducing the resistance, an overly thick metal layer is not conducive to improving the battery energy density.

[0055] In one embodiment, the material of the metal film layer 130 is one or several of aluminum, copper, stainless steel, nickel, titanium, etc.

[0056] In one embodiment, the material of the metal film layer 130 is the same as or different from the material of the metal transfer layer.

[0057] In one embodiment, the metal film layer 130 is a metal film layer with a carbon coating on its surface.

[0058] In one embodiment, the metal film layer 130 can be divided into a first metal film layer and a second metal film layer located on both sides of the polymer layer.

[0059] In one embodiment, the distance between the electrode material coating 200 and the metal adapter layer is 5 mm - 40 mm, such as 5 mm, 8 mm, 10 mm, 12.5 mm, 15 mm, 20 mm, 25 mm, 28 mm, 30 mm, 35 mm, 37 mm or 40 mm, etc. The distance herein refers to the distance between the electrode material coating and the metal adapter layer on the same side, specifically, the minimum distance from the edge of the electrode coating to the edge of the metal adapter layer.

[0060] The present invention does not limit the specific type of the electrode material coating 200. According to actual needs, it can be divided into a positive electrode active material layer and a negative electrode active material layer.

[0061] In one embodiment, the positive electrode active material layer includes a positive electrode active material. The positive electrode active material is a compound that can reversibly intercalate and deintercalate lithium. Specifically, it may include a lithium transition metal composite oxide containing lithium and at least one transition metal selected from the group consisting of nickel, cobalt, manganese, and aluminum; preferably, it may include lithium and transition metals such as nickel, cobalt, or manganese.

[0062] In some embodiments, the positive electrode material may also be sulfur and sulfur-containing compounds.

[0063] In one embodiment, the amount of the positive electrode active material contained in the positive electrode active material layer may be 80 wt% to 99 wt%, such as 80 wt%, 82.5 wt%, 85 wt%, 87 wt%, 90 wt%, 92 wt%, 94 wt%, 95 wt%, 97 wt% or 99 wt%, etc., preferably 92 wt% to 98.5 wt%.

[0064] In one embodiment, in addition to the positive electrode active material, the positive electrode active material layer may further include a positive electrode binder and / or a positive electrode conductive material.

[0065] The positive electrode binder is used to bond components such as the positive electrode active material, the positive electrode conductive material, and the current collector together. Specifically, it may include at least one selected from the group consisting of polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer, styrene-butadiene rubber, and fluororubber, preferably polyvinylidene fluoride.

[0066] In one embodiment, the amount of the positive electrode binder contained in the positive electrode active material layer may be 1 wt% to 20 wt%, such as 1 wt%, 3 wt%, 5 wt%, 7 wt%, 10 wt%, 12.5 wt%, 15 wt%, 16 wt%, 18 wt% or 20 wt%, etc., preferably 1.2 wt% to 10 wt%.

[0067] The positive electrode conductive material is mainly used to assist and improve the conductivity in secondary batteries and is not particularly limited as long as it has conductivity without causing chemical changes. Specifically, the positive electrode conductive material may include graphite, such as natural graphite or artificial graphite; carbon materials, such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermal cracking carbon black; conductive fibers, such as carbon fibers and metal fibers; conductive tubes, such as carbon nanotubes; metal powders, such as carbon fluoride powder, aluminum powder, and nickel powder; conductive whiskers, such as zinc oxide and potassium titanate; conductive metal oxides, such as titanium oxide; and polyphenylene derivatives. From the aspect of improving conductivity, carbon black is preferably included.

[0068] In one embodiment, the specific surface area of the positive electrode conductive material may be 80 m 2 / g to 200 m 2 / g, such as 80 m 2 / g, 90 m 2 / g, 100 m 2 / g, 110 m 2 / g, 125 m 2 / g, 150 m 2 / g, 160 m 2 / g, 170 m 2 / g, 180 m 2 / g, 190 m 2 / g or 200 m 2 / g, etc., and preferably 100 m 2 / g to 150 m 2 / g.

[0069] In one embodiment, the amount of the positive electrode conductive material contained in the positive electrode active material layer may be 1 wt% to 20 wt%, such as 1 wt%, 3 wt%, 5 wt%, 7 wt%, 10 wt%, 12.5 wt%, 15 wt%, 16 wt%, 18 wt% or 20 wt%, etc., and preferably 1.2 wt% to 10 wt%.

[0070] In one embodiment, the thickness of the positive electrode active material layer may be 30 μm to 400 μm, such as 30 μm, 40 μm, 50 μm, 60 μm, 70 μm, 80 μm, 100 μm, 110 μm, 120 μm, 130 μm, 150 μm, 160 μm, 170 μm, 180 μm, 200 μm, 220 μm, 240 μm, 260 μm, 300 μm, 325 μm, 350 μm, 370 μm or 400 μm, etc., and preferably 50 μm to 110 μm.

[0071] In one embodiment, the positive electrode active material layer is obtained by coating a positive electrode slurry containing a positive electrode active material and optionally a positive electrode binder, a positive electrode conductive material and a solvent, followed by drying and roll pressing.

[0072] In one embodiment, the solvent for forming the positive electrode slurry may include an organic solvent, such as N-methyl-2-pyrrolidone (NMP), and the amount may be such that a preferred viscosity is obtained when the positive electrode active material is included and the positive electrode binder, the positive electrode conductive material, etc. are selectively included. For example, the amount of the positive electrode slurry-forming solvent included in the positive electrode slurry may be such that the concentration of the solid containing the positive electrode active material and the positive electrode binder and the positive electrode conductive material is 50wt% to 95wt%, such as 50wt%, 55wt%, 60wt%, 65wt%, 70wt%, 75wt%, 80wt%, 85wt%, 90wt% or 95wt%, etc., preferably 70wt% to 90wt%.

[0073] In one embodiment, the negative electrode active material layer includes a negative electrode active material. As the negative electrode active material, there is no particular limitation as long as it is a material that can electrochemically absorb and release S-zone metal ions such as lithium ions, sodium ions, potassium ions, and magnesium ions. As specific examples thereof, there can be listed: carbonaceous materials, metal compound materials, or their oxides, carbides, nitrides, silicides, sulfides, phosphides, etc. These substances can be used alone, or two or more can be used in combination. The embodiments of the present invention do not particularly limit the negative electrode active material.

[0074] In some embodiments, a carbon material can be selected as the negative electrode active material, and specifically one or more of the following can be selected, such as: graphite, needle coke, amorphous carbon, a carbon-containing mesophase, carbon fiber, and a carbon material with a low degree of graphitization. Among them, graphite can include natural graphite, artificial graphite, etc. In addition, materials obtained by coating them with carbon materials, such as amorphous carbon and graphitized materials, can also be used. As amorphous carbon, for example: particles obtained by firing the entire mesophase, particles obtained by infusible treatment and firing of a carbon precursor. As carbonaceous particles with a low degree of graphitization, particles obtained by firing organic matter at a temperature generally below 2500°C can be listed.

[0075] In addition, non-metallic materials that can be used as negative electrode active materials include silicon and its compounds, such as Si, SiO x (0≤x<2), since silicon-containing materials are prone to expansion, easy to fall off from the negative electrode current collector, and have poor conductivity, they are often mixed with carbon materials, such as a core-shell structure containing a carbon coating layer.

[0076] In some embodiments, metallic elements and metal compounds can be selected as the negative electrode active material, and specific examples are as follows: compounds containing metals or metalloids such as Li, Ag, Al, Bi, Cu, Ga, Ge, In, Ni, Pb, Sb, Si, Sn, Sr, Zn, etc.

[0077] In one embodiment, the amount of the negative electrode active material contained in the negative electrode active material layer can be 80 wt% to 99 wt%, such as 80 wt%, 82 wt%, 83 wt%, 85 wt%, 88 wt%, 90 wt%, 92.5 wt%, 95 wt%, 96 wt% or 98 wt%, etc., and preferably 95 wt% to 97 wt%.

[0078] In one embodiment, in addition to the negative electrode active material, the negative electrode active material layer may further contain a negative electrode binder.

[0079] In one embodiment, the negative electrode active material is a non-metallic material such as a carbon material, and one or more of aqueous binders such as sodium carboxymethyl cellulose, styrene-butadiene latex, polyacrylic acid, acrylic acid copolymers, cyclodextrin, etc. are used. When an aqueous solvent is used as the liquid medium for forming the slurry, it is preferable to use a thickener for slurrying. Thickeners are generally used to adjust the viscosity of the slurry.

[0080] In one embodiment, the thickener can be one or more of the following: carboxymethyl cellulose, methyl cellulose, hydroxymethyl cellulose, ethyl cellulose, polyvinyl alcohol, oxidized starch, phosphorylated starch, casein and their salts, etc.

[0081] In one embodiment, the amount of the thickener in the negative electrode active material layer is 0.1 wt% - 5 wt%, such as 0.1 wt%, 0.3 wt%, 0.5 wt%, 0.7 wt%, 1 wt%, 1.2 wt%, 1.5 wt%, 2 wt%, 2.5 wt%, 3 wt%, 3.5 wt%, 4 wt%, 4.5 wt% or 5 wt%, etc., preferably 0.5 wt% - 3 wt%, and more preferably 0.6 wt% - 2 wt%.

[0082] In yet another embodiment of the present invention, a method for preparing the composite electrode sheet as described above is provided, and the method includes the following steps:

[0083] S1: Splice metal transition layers on both side surfaces of the polymer layer;

[0084] S2: Form a metal film layer on the surfaces of the polymer layer and the metal transition layers;

[0085] S3: Weld the splicing area;

[0086] S4: Form an electrode material coating on one side away from the splicing area.

[0087] It is understood that any method capable of forming a metal film layer on the surface of the polymer layer and the metal transfer layer can be used in this application.

[0088] Exemplarily, in step S2, the metal film layer is formed by evaporation coating, deposition or sputtering.

[0089] In one embodiment of the present invention, a secondary battery is provided, and the secondary battery includes the above-mentioned composite electrode sheet.

[0090] The present invention does not specifically limit the preparation method of the secondary battery, and those skilled in the art can refer to the methods disclosed in the prior art for the preparation of the secondary battery.

[0091] In one embodiment, the secondary battery contains an electrolyte. The present invention does not particularly limit the type of the electrolyte, and any known electrolyte material can be used in this application on the basis of not violating the inventive concept of this application. As a schematic example, the electrolyte can be a liquid electrolyte, a solid electrolyte, or a mixed form of a solid electrolyte and a liquid electrolyte.

[0092] When the electrolyte is a liquid electrolyte, a separator should also be provided in the battery system.

[0093] The main function of the separator is to separate the negative electrode and the positive electrode and provide a moving path for lithium ions. Any separator can be used without particular limitation as long as it is a commonly used separator in secondary batteries. In particular, a separator having excellent electrolyte wettability and low ion movement resistance in the electrolyte is preferably used. Specifically, a porous polymer film can be used. For example, a porous polymer film made of polyolefin polymers such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer, or a laminated structure having two or more layers thereof can be used. And, typical porous non-woven fabrics can be used. For example, non-woven fabrics formed of glass fibers with a high melting point, polyethylene terephthalate fibers, etc. can be used. In addition, a coated separator containing a ceramic component or a polymer material can be used to ensure heat resistance or mechanical strength, and it can be selectively used in a single-layer or multi-layer structure.

[0094] In one embodiment, the electrolyte used in the present invention can be an organic liquid electrolyte, an inorganic liquid electrolyte, a solid polymer electrolyte, a gel-type polymer electrolyte, a solid inorganic electrolyte, a molten-type inorganic electrolyte, etc. that can be used in the manufacture of secondary batteries, but is not limited thereto.

[0095] Specifically, the electrolyte may include an organic solvent and a lithium salt. Any organic solvent can be used without particular limitation as long as it can serve as a medium through which ions participating in the electrochemical reaction of the battery can move. Specifically, as the organic solvent, ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone can be used; ether solvents such as dibutyl ether or tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic hydrocarbon solvents such as benzene and fluorobenzene; carbonate solvents such as dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (MEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC); alcohol solvents such as ethanol and isopropanol; nitriles such as R-CN (where R is a linear, branched, or cyclic C2-C20 hydrocarbon group and may contain a double bond, an aromatic ring, or an ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; or sulfolane. Among the above solvents, carbonate solvents are preferred, and a mixture of a cyclic carbonate (such as ethylene carbonate or propylene carbonate) having high ionic conductivity and high dielectric constant and a low-viscosity linear carbonate compound (such as ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate) that can improve the charge / discharge performance of the battery is more preferred. In this case, when the cyclic carbonate and the linear carbonate are mixed in a volume ratio of about 1:1 to about 1:9, the performance of the electrolyte may be excellent.

[0096] Any compound can be used as the lithium salt without particular limitation as long as it can provide lithium ions used in the lithium secondary battery. Specifically, LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, LiB(C2O4)2, etc. can be used as the lithium salt. The use concentration range of the lithium salt can be 0.1 - 2.0 M, such as 0.1 M, 0.3 M, 0.5 M, 0.7 M, 0.8 M, 1 M, 1.2 M, 1.3 M, 1.5 M, 1.6 M, 1.8 M, or 2.0 M, etc. When the concentration of the lithium salt is within the above range, the electrolyte has appropriate conductivity and viscosity, thus showing excellent performance, and lithium ions can move effectively.

[0097] In one embodiment, the electrolyte can be a solid-state electrolyte. The solid-state electrolyte particles can include one or more polymer components, oxide solid electrolytes, sulfide solid electrolytes, halide solid electrolytes, borate solid electrolytes, nitride solid electrolytes, or hydride solid electrolytes. When polymer particles are used, they should be doped with a lithium salt. As an implementation, the polymer-based components can include one or more polymer materials selected from the group consisting of polyethylene glycol, polyethylene oxide (PEO), poly(phenylene oxide) (PPO), poly(methyl methacrylate) (PMMA), polyacrylonitrile (PAN), polyvinylidene fluoride (PVDF), polyvinylidene fluoride-co-hexafluoropropylene (PVDF-HFP), polyvinyl chloride (PVC), and combinations thereof. It can be understood that a high ionic conductivity of the polymer material is beneficial to the performance of the overall solid-state electrolyte material. Preferably, the polymer material should have an ionic conductivity greater than or equal to 10 -4 S / cm.

[0098] Example 1

[0099] This example provides a composite electrode structure, as shown in Figure 1 and Figure 2 Based on the composite electrode provided in a specific embodiment above, on both the front and back surfaces of the polymer layer 110, there are metal transfer layers, specifically divided into a first metal transfer layer 121 and a second metal transfer layer 122. The tab 300 is disposed on the first metal transfer layer 121;

[0100] The width of the overlap between the first metal transfer layer 121 and the polymer layer 110 is 4 mm, the width of the overlap between the second metal transfer layer 122 and the polymer layer 110 is 4 mm, the thickness of the polymer layer 110 is 4 μm, and the thicknesses of the transfer layers of the first metal transfer layer 121 and the second metal transfer layer 122 are equal, both being 12 μm; the thickness of the metal film layer is 800 nm;

[0101] The electrode material coating 200 is located on one side of the composite electrode, on the same side as the tab, and the distances from the metal transfer layer are both 20 mm;

[0102] The materials of the metal film layer 130, the first metal transfer layer 121, and the second metal transfer layer 122 are all aluminum metal. The positive electrode active material is NCM523, and the negative electrode is graphite;

[0103] In this example, the metal film layer 130, the first metal transfer layer 121, the polymer layer 110, and the second metal transfer layer 122 are welded to form a welded structure 140.

[0104] This embodiment also provides a method for preparing the above composite electrode structure, including the following steps:

[0105] S1: Splice metal transition layers on both side surfaces of the polymer layer;

[0106] S2: Form a metal film layer on the surfaces of the polymer layer and the metal transition layers, and the method for forming the metal film layer is evaporation coating;

[0107] S3: Weld the splicing area;

[0108] S4: Coat electrode paste on one side far from the splicing area, dry to obtain an electrode material coating, and obtain a composite electrode after rolling;

[0109] Adopt the above composite electrode, weld the tab 2 on the first metal transition layer 121, and wind or stack the electrodes to form an electric core.

[0110] Embodiment 2

[0111] The difference between this embodiment and Embodiment 1 is that the thickness of the metal film layer is 1 μm;

[0112] Embodiment 3

[0113] The difference between this embodiment and Embodiment 1 is that the thickness of the metal film layer is 3 μm;

[0114] Embodiment 4

[0115] The difference between this embodiment and Embodiment 1 is that the thickness of the metal film layer is 5 μm;

[0116] Comparative Example 1

[0117] The difference between this comparative example and Embodiment 1 is that a composite foil (i.e., directly evaporate and coat a metal film layer on the polymer layer) is used, and metal transition layers (the material, splicing position and size of the metal transition layers are the same as those in Embodiment 1) are spliced and welded on the front and back sides on the same side as in Embodiment 1, and the other features are the same as those in Embodiment 1.

[0118] Comparative Example 2

[0119] The difference between this comparative example and Embodiment 1 is that a metal current collector with the same thickness as the composite current collector in Embodiment 1 is used, and the other features are the same as those in Embodiment 1.

[0120] Needle penetration test:

[0121] The battery is fully charged. At 25 °C, use a 3 - 8 mm steel needle to penetrate the battery at a speed of 25 mm / s, and observe for 10 min. Check whether there is fire or explosion, and the results are shown in Table 1.

[0122] Resistance test:

[0123] The prepared battery can be measured for its internal resistance by a voltage and internal resistance meter, and the results are shown in Table 1.

[0124] Current conduction test:

[0125] Fix the battery cell with tape, pull the tab with a tensile force of 600 N / mm respectively, connect the battery after pulling to an ammeter, and test the current conduction situation. The results are shown in Table 1.

[0126] Overcurrent capacity test

[0127] Conduct a charging test at a high-rate current of 5C at room temperature, and test the surface temperatures of the empty foil area of the electrode plate and the tab; if it is greater than 60 °C, the overcurrent capacity fails. The results are shown in Table 1.

[0128] Table 1

[0129]

[0130] As can be seen from the above, the composite electrode plates of Examples 1-4 can effectively reduce the internal resistance of the battery, and at the same time, the overcurrent capacity is also greatly improved. Compared with Comparative Example 1, current can still pass through after the large tensile force pulling in Examples 1-4. This may be because the presence of the metal film layer increases the connection strength of the weld, making the tab not easy to come off.

[0131] Although thickening the metal film layer is beneficial to increasing the current conduction area, improving the overcurrent capacity and reducing the resistance, too thick a metal layer is not conducive to improving the energy density of the battery.

[0132] When Examples 1-4 use large-current charge and discharge, the battery surface gets slightly hot, while the battery in Comparative Document 1 gets severely hot. This may be because in Comparative Document 1, the current is only conducted through the contact area of the weld, and the overcurrent capacity is poor. When using large current for charge and discharge, the heat generation will be severe. In fact, the battery cell needs to work within a suitable temperature range (generally 20-45 °C), and too high a temperature will cause irreversible chemical side reactions inside it, thus reducing the lifespan.

[0133] As can be seen from the above, the present invention improves the structure of the composite electrode plate, and by changing the position of the metal film layer in the composite electrode plate, effectively increases the current conduction area from the electrode material coating to the tab, reduces the internal resistance of the battery, and can effectively improve the connection quality of the conductive structure, which is beneficial to stabilizing the process flow and production.

[0134] The applicant declares that the present invention illustrates the detailed method of the present invention through the above embodiments, but the present invention is not limited to the above detailed method, that is, it does not mean that the present invention must rely on the above detailed method to be implemented. Those skilled in the art should understand that any improvement to the present invention, the equivalent substitution of each raw material of the product of the present invention, the addition of auxiliary components, the selection of specific methods, etc. all fall within the protection scope and the disclosure scope of the present invention.

Claims

1. A composite electrode sheet, comprising a composite current collector, an electrode material layer formed on the composite current collector, and a tab, characterized in that, The composite current collector includes a polymer layer, a metal transfer layer, and a metal film layer, and the metal transfer layer is used for tab welding; The metal transfer layer partially overlaps with the polymer layer inside the edge of the polymer layer and extends outside the edge of the polymer layer; The metal film layer is formed on the polymer layer and the first region where the polymer layer overlaps with the metal transfer layer; An electrode material coating is further provided on one side of the metal film layer away from the overlapping region of the metal transfer layer and the polymer layer; Both the front and back surfaces of the polymer layer are provided with metal transfer layers, namely a first metal transfer layer and a second metal transfer layer; The metal film layer, the metal transfer layer, and the polymer layer are connected by welding; The metal film layer, the first metal transfer layer, the polymer layer, and the second metal transfer layer form a welded structure by welding; 2. The composite electrode sheet according to claim 1, wherein, The thickness of the polymer layer is 2 - 10 μm.

3. The composite electrode sheet according to claim 2, wherein, The thickness of the polymer layer is 3 - 5 μm.

4. The composite electrode sheet according to claim 2, wherein The width of the overlap between the metal transfer layer and the polymer layer is 3 mm - 6 mm.

5. The composite electrode sheet according to claim 4, wherein The single-sided thickness of the metal transfer layer is 12 - 16 μm.

6. The composite electrode sheet according to claim 5, characterized in that, The first metal transfer layer and the second metal transfer layer have the same length.

7. The composite electrode sheet according to claim 5, wherein, The first metal transfer layer and the second metal transfer layer have different lengths.

8. The composite electrode sheet according to claim 5, wherein, When only one side of the metal transfer layer is connected to the tab, the electrode material coating and the tab are on the same side surface of the composite current collector.

9. The composite electrode sheet according to claim 5, wherein The thickness of the metal film layer is 100 nm - 5 μm.

10. The composite electrode sheet according to claim 9, characterized in that, The metal film layer is a metal film layer with a carbon coating on its surface.

11. The composite electrode sheet according to claim 9, wherein, The metal film layer can be divided into a first metal film layer and a second metal film layer located on both sides of the polymer layer.

12. The composite electrode sheet according to claim 9, wherein, The distance between the electrode material coating and the metal transfer layer is 5 mm - 40 mm.

13. A method for preparing a composite electrode tab according to claim 1, characterized in that, The method includes the following steps: S1: Splice the metal transfer layers on both side surfaces of the polymer layer; S2: Form a metal film layer on the surfaces of the polymer layer and the metal transfer layer; S3: Weld the splicing area; S4: Form an electrode material coating on one side away from the splicing area.

14. A secondary battery, characterized in that, The secondary battery includes the composite electrode sheet described in claim 1.

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