Composite current collector, method for manufacturing the same, composite electrode tab, and secondary battery

Abstract

The application discloses a kind of composite current collector, its preparation method, composite pole piece, and secondary battery, the composite current collector includes polymer base material, the two side surfaces of polymer base material are provided with metal foil material, and are divided into first metal foil material and second metal foil material, only the second metal foil material is used for tab welding;The metal foil material is partially overlapped with the polymer base material inside the edge of the polymer base material, and extends outside the edge of the polymer base material;The composite current collector further includes metal layer, and is divided into first metal layer and second metal layer, the first metal layer covers polymer base material layer, first metal foil material and part of second metal foil material, forms conductive path.The application effectively solves the technical problems that the prior art passes through weld joint to conduct current, due to the small contact area of weld joint, the battery resistance increases, the overcurrent capacity is poor, and the cycle performance is deteriorated.

Description

Technical Field

[0001] The present invention relates to the field of secondary batteries, and in particular to a composite current collector, a preparation method thereof, a composite pole piece and a secondary battery. Background Art

[0002] With the large-scale commercial use of lithium-ion batteries, frequent safety incidents have attracted widespread attention. Among them, thermal runaway fires and explosions caused by short circuits are a problem that battery manufacturers urgently need to solve. Currently, researchers are trying to use composite foils to replace traditional metal foils as current collectors for positive and negative electrodes. Composite current collectors are usually made by adding a polymer substrate layer to the metal layers on both sides. The use of this metal-polymer-metal structure can effectively improve the battery's resistance to needle puncture, extrusion, and heavy object impact. At the same time, the polymer substrate is lighter, which can reduce the weight of the current collector and increase the battery's energy density.

[0003] In order to further reduce the weight of the current collector and increase the energy density of the battery, the metal layers on both sides of the composite current collector are often relatively thin. However, this makes it impossible to weld the composite current collector to the tabs. Metal foil is needed for welding, and the current conduction on both sides of the current collector is achieved through the weld. On the other hand, in order to further improve the utilization rate of the electrode sheet, the electrode material layer is coated on both sides of the current collector, and the tabs need to be led out on both sides of the metal foil. This makes it difficult to align the tabs during subsequent packaging and requires a large amount of tab glue. If the tabs are too thick, it will not be conducive to packaging and will easily lead to leakage. Summary of the Invention

[0004] To address the aforementioned problems in the prior art, the present invention aims to provide a composite current collector, a method for preparing the same, a composite pole piece, and a secondary battery. These effectively address the existing technical issues of increased battery internal resistance, poor current capacity, and unstable welding conditions resulting from tab detachment caused by the small contact area of ​​the weld when using tab welding. Furthermore, they address the packaging difficulties caused by the multiple tabs when double-sided coating is used.

[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 current collector comprising

[0007] polymer substrate layer,

[0008] The metal foil provided on at least one side of the polymer substrate layer can be divided into a first metal foil and a second metal foil, wherein the second metal foil is connected to the tab;

[0009] a first metal layer formed on the polymer substrate layer, the first metal foil and part of the second metal foil; and a second metal layer formed on the other side of the polymer substrate opposite to the first metal layer;

[0010] At least one side length of the second metal foil is greater than the side length of the first metal foil in the direction.

[0011] In one embodiment of the present application, the length of the second metal foil is greater than the length of the first metal foil.

[0012] In one embodiment of the present application, the width of the second metal foil is greater than the width of the first metal foil.

[0013] In one embodiment of the present application, the length of the second metal foil is greater than the length of the first metal foil.

[0014] In one embodiment, the length and width of the second metal foil are both greater than the length and width of the first metal foil.

[0015] In the present application, the metal foil partially overlaps the polymer substrate layer inside the edge of the polymer substrate layer and extends outside the edge of the polymer substrate layer, and when the metal foil is located on the side of the metal layer away from the polymer substrate layer, the metal foil partially overlaps the metal layer inside the edge of the metal layer and extends outside the edge of the metal layer 110.

[0016] In some embodiments of the present application, the second metal layer is formed on the polymer substrate, and the second metal foil is arranged on the surface of the side of the second metal layer away from the polymer substrate.

[0017] In other embodiments of the present application, the second metal layer is formed on the outside of the polymer substrate and the second metal foil.

[0018] As a preferred embodiment of the present application, the relationship between the length L1 of the first metal foil and the length L2 of the second metal foil is L2 / L1 = n1 (1 < n1 ≤ 8), the width of the first metal foil is L3, and the width of the second metal foil is L4, L4 / L3 = n2 (1 ≤ n2 ≤ 5),

[0019] The length L5 of the first metal layer on the second metal foil is L5 = n3 * (L2 - L1), 0 < n3 ≤ 0.85, preferably 0.4 ≤ n3 ≤ 0.85.

[0020] The extension direction of the polymer substrate layer to the tab is the length direction of the first and second metal foils, and the direction perpendicular thereto is the width direction of the first and second metal foils.

[0021] It can be understood that when the length of the first metal layer formed on the second metal foil is too short, the connection and the stability of the current conduction are not good, and when the length of the first metal layer formed on the second metal foil is too long, the current conduction is good, but the cost is high.

[0022] Preferably, the thickness of the polymer substrate layer is 2-10 μm, preferably 3-5 μm.

[0023] Preferably, the width of the overlapping area of the polymer substrate layer and the metal foil layer is 3-6 mm.

[0024] Preferably, the thickness of the first metal foil and the second metal foil is 10-15 μm. The thickness of the first metal foil and the second metal foil can be the same or different.

[0025] Preferably, the thickness of the metal layer is 100 nm-30 μm, and the thickness of the first metal layer and the second metal layer can be the same or different.

[0026] Preferably, the thickness of the first metal layer on the surface of the polymer substrate, the first metal foil and the second metal foil can be the same or different.

[0027] Preferably, the metal layer is a metal layer coated with a carbon coating on the surface.

[0028] As a preferred embodiment of the present application, the side length of the first metal foil along the length direction of the polymer substrate is equal to the side length of the overlapping area of the first metal foil and the polymer substrate in the direction.

[0029] In a third aspect, the present application provides a preparation method of the composite current collector as described in the first aspect, and the method comprises the following steps:

[0030] S1: splicing the first metal foil and the second metal foil on both sides of the surface of the polymer substrate;

[0031] S2: forming the first metal layer on the side surface of the first metal foil spliced on the polymer substrate layer, the surface of the first metal foil and part of the surface of the second metal foil;

[0032] S3: forming the second metal layer on the side surface of the second metal foil spliced on the polymer substrate layer and the splicing area of the second metal foil;

[0033] S4: welding the overlapping area of the polymer substrate layer and the first metal foil, the second metal foil, the first metal layer and the second metal layer;

[0034] Alternatively, the method comprises the following steps:

[0035] S100: forming a second metal layer on one surface of the polymer substrate;

[0036] S200: splicing a first metal foil on the other side of the polymer substrate, and splicing a second metal foil on the second metal layer;

[0037] S300: forming a first metal layer by splicing one side surface of the first metal foil, the first metal foil, and a portion of the second metal foil surface on the polymer substrate layer;

[0038] S400: welding the polymer substrate layer to the first metal foil, the second metal foil, and the overlapping areas of the first metal layer and the second metal layer;

[0039] It is understood that any method that can form a metal layer on the surface of a polymer substrate layer and a metal foil can be used in the present invention.

[0040] Illustratively, in steps S2, S3, S100, and S300, the metal layer is formed by evaporation, deposition, or sputtering.

[0041] In a third aspect, the present invention provides a composite electrode sheet comprising the composite current collector, an electrode material layer formed on the composite current collector, and a tab.

[0042] Specifically, the electrode material layer is formed on the side of the first metal layer and the second metal layer respectively away from the polymer substrate.

[0043] In the present invention, a tab is provided only on one side of the current collector, and the electrode material layer, the first metal foil, the second metal foil and the tab are connected together through a metal layer to form a conductive path, thereby increasing the current conduction area from both sides of the composite current collector to the tab, effectively improving the current flow capacity of the composite electrode, and effectively avoiding the technical problem of increased internal resistance caused by relying solely on the welding area for current conduction due to too small a contact area.

[0044] Preferably, the distance between the electrode material layer and the metal foil is 5 mm-40 mm.

[0045] Preferably, the metal layer includes a first metal layer and a second metal layer.

[0046] As an embodiment of the present application, the first metal layer includes a first portion formed on the polymer substrate layer, a second portion formed on the overlapping area of ​​the polymer substrate layer and the first metal foil layer, and a third portion formed on the second metal foil, and the first portion, the second portion and the third portion are integrally formed;

[0047] The polymer substrate layer, the metal foil layer and the metal layer are connected to form a whole through the extension of the metal layer;

[0048] In other embodiments of the present application, the first part, the second part, and the third part may be different conductive layers that are interconnected or conductive to each other.

[0049] Preferably, the polymer substrate layer, metal foil layer and metal layer are connected by welding, which can effectively further increase the stability of the composite electrode structure, ensure the quality of the welded structure, and prevent the metal sheets and tabs from falling off during subsequent transportation and use.

[0050] In a fourth aspect, the present invention provides a secondary battery comprising the composite electrode described in the first aspect.

[0051] The present invention does not limit the preparation method of the secondary battery. For example, the composite electrode sheets mentioned above can be wound or stacked to form a battery core.

[0052] Compared with the prior art, the present invention has the following beneficial effects:

[0053] The present invention improves the structure of the composite pole piece, especially changes the position of the metal layer in the composite pole piece structure, thereby increasing the current conduction area and realizing the transfer of current from the metal layer to the metal foil, effectively avoiding the problems of increased resistance and poor current capacity caused by the small contact area of ​​the weld. It can also avoid the problem of current failure due to unstable welding structure or poor welding quality, and achieve stable battery performance. At the same time, by using the composite pole piece structure of the present application, the welding quality can also be effectively improved, which can effectively prevent the metal sheet and the pole ear from falling off during transportation and other processes, resulting in poor battery performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] Figure 1 Schematic diagram of the structure of a composite electrode in one embodiment of the present invention;

[0055] Figure 2 is a top view of a composite pole piece in one embodiment of the present invention;

[0056] Among them, 110 is a polymer substrate, 121 is a first metal foil, 122 is a second metal foil, 131 is a first metal layer, 132 is a second metal layer, 140 is a welding area, 200 is a tab, and 300 is an electrode material layer. DETAILED DESCRIPTION

[0057] The technical solution of the present invention will be further described below with reference to the accompanying drawings and through specific implementation methods.

[0058] In the present invention, the extending direction from the polymer substrate layer to the tab is the length direction of the first and second metal foils, and the direction perpendicular thereto is the width direction of the first and second metal foils.

[0059] The present application provides a composite current collector 100 in one embodiment, as shown in the figure, comprising a polymer substrate layer 110; Figure 1 A metal foil layer is arranged on at least one side of the polymer substrate layer, which can be divided into a first metal foil layer 121 and a second metal foil layer 122, and the second metal foil layer 122 is connected to the tab 200.

[0060] A first metal layer 131 is formed on the polymer substrate layer 110, the first metal foil layer 121 and part of the second metal foil layer 122; and a second metal layer 132 is further included on the other side of the polymer substrate 110 opposite to the first metal layer 131.

[0061] At least one side length of the second metal foil layer is greater than the side length of the first metal foil layer in that direction.

[0062] In one embodiment of the present application, the length of the second metal foil layer is greater than the length of the first metal foil layer.

[0063] In one embodiment of the present application, the width of the second metal foil layer is greater than the width of the first metal foil layer.

[0064] In one embodiment of the present application, the length of the second metal foil layer is greater than the length of the first metal foil layer.

[0065] In one embodiment of the present application, the length of the second metal foil layer is greater than the length of the first metal foil layer.

[0066] In one embodiment, the length and width of the second metal foil layer are both greater than the length and width of the first metal foil layer.

[0067] In some embodiments of the present application, the second metal layer 132 is formed on the polymer substrate 110, and the second metal foil 122 is arranged on the surface of the second metal layer 132 away from the polymer substrate 110.

[0068] In other embodiments of the present application, the second metal layer 132 is formed on the outer surface of the polymer substrate 110 and the second metal foil 122.

[0069] In some embodiments of the present application, the length L1 of the first metal foil and the length L2 of the second metal foil satisfy the relationship L2 / L1=n1 (1

[0070] The length L5 of the first metal layer on the second metal foil is n3*(L2-L1), 0

[0071] The metal foil partially overlaps the polymer substrate layer 110 on the inner side of the edge of the polymer substrate and extends outward from the edge of the polymer substrate layer 110;

[0072] When the metal foil is located on the side of the metal layer away from the polymer substrate layer, the metal foil partially overlaps the metal layer on the inner side of the edge of the metal layer and extends outward from the edge of the metal layer 110 .

[0073] The composite electrode provided in one embodiment of the present invention utilizes a layered electrode structure to increase the current conduction area, eliminating the need for current conduction solely through the weld teeth. This effectively reduces the battery's internal resistance, effectively resolving the issues of increased internal resistance and poor current handling caused by a small weld contact area.

[0074] In the present invention, the polymer substrate layer 110 primarily functions as follows: First, it melts when the internal temperature of the battery cell rises sharply, thereby cutting off the current and improving battery safety; second, it utilizes its inherent elongation to prevent the sharp edge from piercing the separator or other parts, causing a short circuit, in the event of a needle puncture. If the polymer substrate is too thin, it will easily be punctured by a needle puncture or impact, failing to effectively address the problem of battery short circuits caused by needle punctures. If the polymer substrate is too thick, the battery's internal resistance increases, degrading battery performance.

[0075] In one embodiment, the polymer substrate layer 110 has a thickness of 2-10 μm, such as 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm or 10 μm, and preferably 3-5 μm.

[0076] In some embodiments, the material of the polymer substrate 110 can 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, fluorinated rubber, etc.

[0077] In one embodiment, the overlapping width of the first metal foil, the second metal foil and the polymer substrate 1 is 3 mm to 6 mm, for example, 3 mm, 3.5 mm, 4 mm, 4.5 mm, 5 mm, 5.5 mm or 6 mm.

[0078] In one embodiment, the metal foil is made of one or more of aluminum, copper, stainless steel, nickel, titanium, etc.

[0079] In some embodiments of the present application, the materials of the first metal foil 121 and the second metal foil 122 may be the same or different.

[0080] In one embodiment, the thickness of the first metal foil 121 and the second metal foil 122 is 10-15 μm, such as 10 μm, 11 μm, 12 μm, 13 μm, 14 μm or 15 μm, etc. The thickness of the first metal foil 121 and the thickness of the second metal foil 122 can be the same or different.

[0081] In one embodiment, the first metal foil 121 and the second metal foil 122 have the same thickness.

[0082] In one embodiment, the width of the overlapping portion between the first metal foil 121 and the polymer substrate layer 110 is a, and the width of the overlapping portion between the second metal foil 122 and the polymer substrate layer 110 is b. a and b may be the same or different, preferably a=b.

[0083] In one embodiment, the side length of the overlapping portion of the first metal foil 121 and the polymer substrate layer 110 is a, and the side length of the first metal foil 121 along the length direction of the polymer substrate 110 is c, where a=c.

[0084] In one embodiment, the thickness of the first metal layer 131 and the second metal layer 132 is 100 nm-30 μm, for example, 100 nm, 400 nm, 800 nm, 1.5 μm, 3.5 μm, 5 μm, 10 μm, 16 μm, 25 μm, or 30 μm. It is understood that if the thickness of the metal layer on the polymer substrate layer is too high, it will not be conducive to improving the energy density of the battery.

[0085] In one embodiment, the first metal layer 131 has the same thickness on the polymer substrate layer, the first metal foil, and the second metal foil.

[0086] In one embodiment, the thickness of the first metal layer 131 on the polymer substrate layer, the first metal foil, and the second metal foil are different.

[0087] In one embodiment, the first metal layer 131 and the second metal layer 132 are made of one or more of aluminum, copper, stainless steel, nickel, titanium, etc.

[0088] In one embodiment, the material of the first metal layer 131 and the second metal layer 132 is the same as or different from the material of the metal foil.

[0089] In one embodiment, the first metal layer 131 and the second metal layer 132 are metal layers coated with a carbon coating.

[0090] In one embodiment, the present invention provides a method for preparing the composite current collector as described above, the method comprising the following steps:

[0091] S1: splicing a first metal foil and a second metal foil on both sides of the polymer substrate;

[0092] S2: forming a first metal layer by splicing the surface of the first metal foil, the first metal foil and a portion of the surface of the second metal foil on the polymer substrate layer;

[0093] S3: forming a second metal layer on the surface of the polymer base material layer spliced ​​with the second metal foil and on the splicing area with the second metal foil;

[0094] S4: welding the polymer substrate layer to the first metal foil, the second metal foil, and the overlapping areas of the first metal layer and the second metal layer;

[0095] In another embodiment, the present invention provides a method for preparing the composite electrode as described above, the method comprising the following steps:

[0096] S100: forming a second metal layer on one surface of the polymer substrate;

[0097] S200: splicing a first metal foil on the other side of the polymer substrate, and splicing a second metal foil on the second metal layer;

[0098] S300: forming a first metal layer by splicing the surface of the first metal foil, the first metal foil and a portion of the surface of the second metal foil on the polymer substrate layer;

[0099] S400: welding the polymer substrate layer to the first metal foil, the second metal foil, and the overlapping areas of the first metal layer and the second metal layer;

[0100] It is understood that any method that can form a metal layer on the surface of a polymer substrate layer and a metal foil can be used in the present invention.

[0101] In one embodiment, in step S2 , the metal layer is formed by evaporation, deposition or sputtering.

[0102] In one embodiment, steps S4 and S400 further include coating an electrode material layer on the composite current collector.

[0103] As a preferred embodiment, an electrode material layer is formed on a side of the composite current collector away from the overlapping area between the polymer substrate and the metal foil.

[0104] In some embodiments of the present invention, steps S5 and S500 are performed after steps S4 and S400: tab welding is performed on the metal foil after drying.

[0105] Furthermore, the present invention provides a composite electrode sheet, comprising the composite current collector 100 , an electrode material layer 300 formed on the composite current collector, and a tab 200 .

[0106] In one embodiment, the first metal layer 131 is formed on the polymer substrate layer 110 and the first metal foil layer 121, and the length of the first metal foil layer 121 is less than the length of the second metal foil layer 122. The first metal layer 131 includes a first portion formed on the polymer substrate layer 110, a second portion formed on the overlapping area of ​​the polymer substrate layer and the first metal foil layer 121, and a third portion formed on the second metal foil 122, and the first portion, the second portion and the third portion are a whole.

[0107] In the present invention, the polymer substrate layer 110 , the metal foil layer 120 , and the metal layer are connected to form a whole through the extension of the metal layer 130 .

[0108] In one embodiment, the polymer substrate layer 110, the first metal foil 121, the second metal foil 121 and the first metal layer 131 and the second metal layer 132 are connected by welding. Welding can effectively further increase the stability of the composite electrode structure, ensure the quality of the welding structure, and prevent the metal sheets and the pole ears from falling off during subsequent transportation, use, etc.

[0109] In one embodiment, the distance between the electrode material layer 300 and the metal foil is 5 mm to 40 mm, for example, 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. The distance here refers to the distance between the electrode material layer and the metal foil on the same side, specifically, the minimum distance from the edge of the electrode material layer to the edge of the metal foil.

[0110] The present invention does not limit the specific type of the electrode material layer 300 , and according to actual needs, it can be divided into a positive electrode active material layer and a negative electrode active material layer.

[0111] In one embodiment, the positive electrode active material layer includes a positive electrode active material. The positive electrode active material is a compound capable of reversibly intercalating and deintercalating lithium. Specifically, it may include a lithium transition metal composite oxide containing lithium and at least one other transition metal selected from the group consisting of nickel, cobalt, manganese, and aluminum. Preferably, it may include lithium and a transition metal such as nickel, cobalt, or manganese.

[0112] In some embodiments, the positive electrode material may also be elemental sulfur and sulfur-containing compounds.

[0113] In one embodiment, the amount of the positive electrode active material contained in the positive electrode active material layer can be 80wt% to 99wt%, for example, 80wt%, 82.5wt%, 85wt%, 87wt%, 90wt%, 92wt%, 94wt%, 95wt%, 97wt% or 99wt%, etc., preferably 92wt% to 98.5wt%.

[0114] In one embodiment, the positive electrode active material layer may further include a positive electrode binder and / or a positive electrode conductive material in addition to the positive electrode active material.

[0115] The positive electrode binder is used to bind the positive electrode active material, positive electrode conductive material and current collector components together. Specifically, it can include at least one selected from the group consisting of polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, polyvinyl pyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer, styrene-butadiene rubber and fluororubber, preferably polyvinylidene fluoride.

[0116] In one embodiment, the amount of the positive electrode binder contained in the positive electrode active material layer can be 1wt% to 20wt%, for example, 1wt%, 3wt%, 5wt%, 7wt%, 10wt%, 12.5wt%, 15wt%, 16wt%, 18wt% or 20wt%, etc., preferably 1.2wt% to 10wt%.

[0117] The positive electrode conductive material is mainly used to assist and improve the conductivity of the secondary battery and is not particularly limited as long as it has conductivity and does not cause chemical changes. Specifically, the positive electrode conductive material can 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 black; conductive fibers, such as carbon fibers and metal fibers; conductive tubes, such as carbon nanotubes; metal powders, such as fluorocarbon 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. In terms of improving conductivity, carbon black is preferably included.

[0118] In one embodiment, the specific surface area of ​​the positive electrode conductive material can be 80m 2 / g to 200m 2 / g, for example 80m 2 / g、90m 2 / g、100m 2 / g、110m 2 / g, 125m 2 / g, 150m 2 / g, 160m 2 / g, 170m 2 / g, 180m 2 / g, 190m 2 / g or 200m 2 / g, etc., preferably 100m 2 / g to 150m 2 / g.

[0119] In one embodiment, the amount of the positive electrode conductive material contained in the positive electrode active material layer can be 1 wt% to 20 wt%, for example, 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%.

[0120] In one embodiment, the thickness of the positive electrode active material layer can be 30μm to 400μm, for example, 30μm, 40μm, 50μm, 60μm, 70μm, 80μm, 100μm, 110μm, 120μm, 130μm, 150μm, 160μm, 170μm, 180μm, 200μm, 220μm, 240μm, 260μm, 300μm, 325μm, 350μm, 370μm or 400μm, preferably 50μm to 110μm.

[0121] In one embodiment, the positive electrode active material layer is obtained by coating a positive electrode slurry comprising 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.

[0122] 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 used may be such that a preferred viscosity is obtained when the positive electrode active material is included and optionally includes a positive electrode binder, a positive electrode conductive material, etc. 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 solids including the positive electrode active material and optionally including the positive electrode binder and the positive electrode conductive material is 50 wt % to 95 wt %, such as 50 wt %, 55 wt %, 60 wt %, 65 wt %, 70 wt %, 75 wt %, 80 wt %, 85 wt %, 90 wt % or 95 wt %, and preferably 70 wt % to 90 wt %.

[0123] 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 substance that can electrochemically absorb and release S-block metal ions such as lithium ions, sodium ions, potassium ions, and magnesium ions. Specific examples thereof include: 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.

[0124] 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, and particles obtained by infusible treatment and firing of a carbon precursor can be listed. 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.

[0125] 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 core-shell structures containing carbon coating layers.

[0126] In some embodiments, metal elements and metal compounds can be selected as negative electrode active materials, and specific examples include compounds containing metals or metalloids such as Li, Ag, Al, Bi, Cu, Ga, Ge, In, Ni, Pb, Sb, Si, Sn, Sr, and Zn.

[0127] In one embodiment, the amount of the negative electrode active material contained in the negative electrode active material layer can be 80wt% to 99wt%, for example, 80wt%, 82wt%, 83wt%, 85wt%, 88wt%, 90wt%, 92.5wt%, 95wt%, 96wt% or 98wt%, etc., preferably 95wt% to 97wt%.

[0128] In one embodiment, the negative electrode active material layer may further include a negative electrode binder in addition to the negative electrode active material.

[0129] In one embodiment, the negative electrode active material is a non-metallic material such as a carbon material, and an aqueous binder such as one or more of sodium hydroxymethyl cellulose, styrene-butadiene latex, polyacrylic acid, acrylic copolymer, and cyclodextrin is used. When an aqueous solvent is used as the liquid medium for forming the slurry, a thickener is preferably used for slurry formation. Thickeners are generally used to adjust the viscosity of the slurry.

[0130] In one embodiment, the viscosity increasing agent may be one or more of the following: carboxymethyl cellulose, methyl cellulose, hydroxymethyl cellulose, ethyl cellulose, polyvinyl alcohol, oxidized starch, phosphorylated starch, casein, and salts thereof.

[0131] In one embodiment, the amount of the thickener in the negative electrode active material layer is 0.1wt%-5wt%, for example, 0.1wt%, 0.3wt%, 0.5wt%, 0.7wt%, 1wt%, 1.2wt%, 1.5wt%, 2wt%, 2.5wt%, 3wt%, 3.5wt%, 4wt%, 4.5wt% or 5wt%, etc., preferably 0.5wt%-3wt%, more preferably 0.6wt%-2wt%.

[0132] In one embodiment, the present invention provides a secondary battery, which includes the composite electrode sheet described above.

[0133] The present invention does not specifically limit the method for preparing the secondary battery, and those skilled in the art may prepare the secondary battery by referring to the methods disclosed in the prior art.

[0134] In one embodiment, the secondary battery includes an electrolyte. The present invention does not particularly limit the type of electrolyte; any known electrolyte material may be used in the present invention without violating the inventive concept of the present application. As illustrative examples, the electrolyte may be a liquid electrolyte, a solid electrolyte, or a mixture of a solid electrolyte and a liquid electrolyte.

[0135] When a liquid electrolyte is used as the electrolyte, a diaphragm should also be provided in the battery system.

[0136] The main function of the separator is to separate the negative electrode and the positive electrode and provide a path for the movement of lithium ions. Any separator can be used without particular limitation, as long as it is a separator commonly used in secondary batteries. In particular, a separator with excellent wettability to the electrolyte and low resistance to the movement of ions in the electrolyte is preferred. Specifically, a porous polymer film can be used, for example, a porous polymer film made of a polyolefin polymer 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. In addition, a typical porous non-woven fabric can be used, for example, a non-woven fabric formed of glass fiber, polyethylene terephthalate fiber, etc. having a high melting point. In addition, a coated separator comprising a ceramic component or a polymer material can be used to ensure heat resistance or mechanical strength, and can be selectively used in a single-layer or multilayer structure.

[0137] 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 polymer electrolyte, a solid inorganic electrolyte, a molten inorganic electrolyte, etc. that can be used in the manufacture of secondary batteries, but is not limited thereto.

[0138] Specifically, the electrolyte may include an organic solvent and a lithium salt. Any organic solvent may be used without particular limitation, as long as it can act 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 may 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), ethyl methyl carbonate (MEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC) and propylene carbonate (PC); alcohol solvents such as ethanol and isopropanol; nitrile such as R-CN (wherein R is a linear, branched or cyclic C2-C20 hydrocarbon group, and may contain a double bond aromatic ring or ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolanes; or sulfolane. Among the above-mentioned solvents, carbonate solvents are preferred, and a mixture of a cyclic carbonate (such as ethylene carbonate or propylene carbonate) with 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 increase the charge / discharge performance of the battery is more preferred. In this case, when the cyclic carbonate and the chain carbonate are mixed with a volume ratio of about 1:1 to about 1:9, the performance of the electrolyte may be excellent.

[0139] Any compound can be used as the lithium salt without particular limitation, as long as it can provide the 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 lithium salt can be used in a concentration range of 0.1-2.0M, such as 0.1M, 0.3M, 0.5M, 0.7M, 0.8M, 1M, 1.2M, 1.3M, 1.5M, 1.6M, 1.8M or 2.0M, etc. When the concentration of the lithium salt is within the above range, the electrolyte has suitable conductivity and viscosity, thereby exhibiting excellent performance, and lithium ions can be effectively moved.

[0140] In one embodiment, the electrolyte can be a solid electrolyte, and the solid 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, lithium salts should be used for review. As an embodiment, the polymer-based component can include one or more polymer materials selected from the group consisting of: polyethylene glycol, polyethylene oxide (PEO), poly(p-phenylene ether) (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 the high ionic conductivity of the polymer material is beneficial to the performance of the overall solid electrolyte material. Preferably, the polymer material should have a carbon content greater than or equal to 10 -4 S / cm ionic conductivity.

[0141] Example 1

[0142] This embodiment provides a composite electrode structure, such as Figure 1 and Figure 2As shown, based on the composite current collector provided in one specific embodiment described above, metal foils are provided on both the front and back surfaces of the polymer substrate layer 110, specifically a first metal foil 121 and a second metal foil 122. The first metal foil 121 is longer than the second metal foil 122, and the tab 200 is provided on the second metal foil 122. The length L1 of the first metal foil is 4 mm, and the length L2 of the second metal foil is 16 mm. The widths of the first and second metal foils are the same as the width of the polymer substrate layer. The length of the first metal layer deposited on the second metal foil is 8 mm, and the width is the same as the width of the second metal foil, which is 60 mm.

[0143] The overlapping width of the first metal foil 121 and the polymer substrate layer 110 is 4 mm, the overlapping width of the second metal foil 122 and the polymer substrate layer 110 is 4 mm, the thickness of the polymer substrate layer 110 is 5 μm, and the thickness of the first metal foil 121 and the second metal foil 122 are equal, both 12 μm;

[0144] The distance between the electrode material layer 200 on each side and the metal foil on the same side is 20 mm;

[0145] The metal layer 130, the first metal foil 121, and the second metal foil 122 are all made of aluminum metal, the positive electrode active material is NCM523, and the negative electrode is graphite;

[0146] In this embodiment, the metal layer 130 , the first metal foil 121 , the polymer base material layer 110 , and the second metal foil 122 are welded to form a welded structure.

[0147] This embodiment also provides a method for preparing the composite electrode structure, comprising the following steps:

[0148] S1: splicing a first metal foil and a second metal foil on both sides of the polymer substrate;

[0149] S2: forming a first metal layer on one side of the polymer substrate layer joined to the first metal foil, the first metal foil, and a portion of the second metal foil, wherein the metal layer is formed by vapor deposition;

[0150] S3: forming a second metal layer on one side of the polymer base material layer spliced ​​with the second metal foil and on the splicing area with the second metal foil;

[0151] S4: Welding the polymer substrate layer to the first metal foil, the second metal foil, and the overlapping areas of the first metal layer and the second metal layer. Figure 2 The middle welding area is 140;

[0152] S5: coating the electrode slurry on the side away from the splicing area, drying it to obtain an electrode material layer, and rolling it to obtain a composite electrode sheet;

[0153] The composite electrode sheet is used, and the electrode tab 200 is welded to the second metal foil 122 , and the electrode sheet is wound or stacked to form a battery cell.

[0154] Example 2

[0155] The difference between this embodiment and embodiment 1 is that the length of the first metal foil is 4 mm, the length of the second metal foil is 28 mm, and the length of the first metal layer deposited on the second metal foil is 16 mm. The remaining features are the same as those of embodiment 1.

[0156] Example 3

[0157] The difference between this embodiment and embodiment 1 is that the width of the polymer substrate layer is 60 mm, the width of the first metal foil is 48 mm, and the width of the second metal foil is 72 mm. The remaining features are the same as those of embodiment 1.

[0158] Example 4

[0159] The difference between this embodiment and embodiment 1 is that the first metal layer 131 is formed on the polymer substrate layer and the first metal foil, but not on the second metal foil. The remaining features are the same as those of embodiment 1.

[0160] Example 5

[0161] The difference between this embodiment and embodiment 1 is that the polymer substrate layer is not welded to the first metal foil, the second metal foil, and the overlapping area between the first metal layer and the second metal layer. The remaining features are the same as those of embodiment 1.

[0162] Comparative Example 1

[0163] This embodiment differs from Example 1 in that a composite foil (i.e., metal layers are deposited on both sides of a polymer substrate layer, with the parameters of the polymer and metal layers being the same as those in Example 1) is used as the current collector, and metal foils are spliced ​​on the front and back sides of the same side as in Example 1 (the material, splicing position, and size of the metal foils are the same as those in Example 1) for welding, using the same welding process parameters as in Example 1. The remaining features are the same as in Example 1.

[0164] Comparative Example 2

[0165] The difference from Example 1 is that a metal foil having the same thickness as the composite foil is used as the current collector to form the battery cell. The remaining features are the same as those of Example 1.

[0166] Acupuncture test

[0167] Fully charge the battery. At 25°C, penetrate the battery with a 3-8 mm steel needle at a speed of 25 mm / s for 10 minutes. Observe for any fire or explosion.

[0168] Resistance test:

[0169] The internal resistance of the prepared battery can be measured using a voltage internal resistance meter. The results are shown in Table 1.

[0170] Welding condition test:

[0171] Fix the battery cell with tape and pull the tabs at a force of 400N / mm to observe whether the tabs are well welded. The results are shown in Table 1.

[0172] Overcurrent capability test

[0173] The charging test is carried out at room temperature with a high rate current of 5C to test the surface temperature of the electrode blank foil area and the electrode ear; if it is greater than 60℃, the overcurrent capability fails.

[0174] Table 1

[0175]

[0176] As can be seen from the above embodiments, the structure of the present invention can effectively prevent batteries from short circuiting, fire, etc. due to needle puncture. By comparing Example 1 with Examples 2 and 3, the formation of a larger vapor-deposited area of ​​the first metal layer on the second foil is beneficial for reducing the internal resistance of the battery and increasing the current conduction area and flow capacity from the electrode material layer on the first metal layer to the tab. In Example 4, the first metal layer is not formed on the second metal foil. Although the internal resistance is reduced compared to Comparative Document 1, the flow capacity is still poor. In Example 5, when only relying on the first metal layer to connect the metal layer, metal foil, and polymer layer, although the current conduction area is large and the flow capacity is good, the connection strength between the metal foil, tab, and electrode sheet is low. When there is a large pressure, the metal foil, tab, and electrode sheet are easily separated, which is not conducive to the transportation and long-term use of the battery.

[0177] When using large current for charging and discharging in Examples 1-3, the surface of the battery becomes slightly heated, while the battery in Comparative Document 1 becomes severely heated. This may be because the current in Comparative Document 1 is conducted only by relying on the contact area of ​​the weld, and the overcurrent capacity is poor. When using large current for charging and discharging, the heating will be severe. In fact, the battery cell needs to operate within a suitable temperature range (generally 20-45°C). Excessively high temperatures will cause irreversible chemical side reactions inside it, thereby reducing its lifespan.

[0178] As can be seen from the above, by improving the structure of the composite electrode sheet and changing the position of the metal layer within the composite electrode sheet, the present invention effectively increases the current conduction area on the upper and lower surfaces of the electrode sheet, reduces the internal resistance of the battery, and enhances the current carrying capacity of the electrode sheet after adopting the composite current collector. By combining welding with the second metal layer, the welding quality is effectively improved, which is conducive to stabilizing the process flow and stable production.

[0179] The applicant states that the present invention is intended to illustrate the detailed methods of the present invention through the above-described embodiments, but the present invention is not limited to the above-described detailed methods, that is, it does not mean that the present invention must rely on the above-described detailed methods in order to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent substitutions for various raw materials in the products of the present invention, addition of auxiliary ingredients, and selection of specific methods, etc., are all within the scope of protection and disclosure of the present invention.

Claims

1. A composite current collector, characterized in that: include polymer substrate layer; The metal foils provided on both sides of the polymer substrate layer can be divided into a first metal foil and a second metal foil, wherein the second metal foil is connected to the tab; A first metal layer is formed on the polymer substrate layer, the first metal foil and a portion of the second metal foil; and a second metal layer is further included on the other side of the polymer substrate opposite to the first metal layer; At least one side of the second metal foil is longer than the side of the first metal foil in the same direction; The first metal layer, the first metal foil layer, the polymer substrate layer, the second metal foil layer, and the second metal layer are connected together by welding; The second metal layer is formed on the polymer substrate, and the second metal foil is arranged on a side of the second metal layer away from the polymer substrate.

2. The composite current collector according to claim 1, characterized in that The first metal foil is located inside the edge of the polymer substrate layer, partially overlaps with the polymer substrate layer, and extends outside the edge of the polymer substrate layer; The second metal foil is located inside the edge of the second metal layer, partially overlaps with the second metal layer, and extends outside the edge of the second metal layer.

3. The composite current collector according to claim 1, characterized in that Welding is performed in the overlapping area of ​​the polymer substrate layer and the metal foil.

4. The composite current collector according to claim 1, characterized in that The relationship between the length L1 of the first metal foil and the length L2 of the second metal foil is L2 / L1=n1, 1<n1≤8; The width of the first metal foil is L3, the width of the second metal foil is L4, L4 / L3=n2, 1≤n2≤5; The length of the first metal layer on the second metal foil is L5 = n3*(L2-L1), 0<n3≤0.

85.

5. The composite current collector according to claim 4, characterized in that: The length of the first metal layer on the second metal foil is L5 = n3*(L2-L1), 0.4≤n3≤0.

85.

6. The composite current collector according to claim 3, characterized in that: The overlapping width of the metal foil and the polymer substrate is 3 mm to 6 mm.

7. A method for preparing a composite current collector according to any one of claims 1 to 6, characterized in that: The method comprises the following steps: S1: splicing a first metal foil and a second metal foil on both sides of the polymer substrate; S2: forming a first metal layer by splicing one side surface of the first metal foil, the first metal foil, and a portion of the second metal foil surface on the polymer substrate layer; S3: forming a second metal layer on a surface of the polymer base material layer on which the second metal foil is spliced ​​and on a splicing area with the second metal foil; S4: welding the polymer substrate layer to the first metal foil, the second metal foil, and the overlapping areas of the first metal layer and the second metal layer; Alternatively, the method comprises the following steps: S100: forming a second metal layer on one surface of the polymer substrate; S200: splicing a first metal foil on the other side of the polymer substrate, and splicing a second metal foil on the second metal layer; S300: forming a first metal layer by splicing one side surface of the first metal foil, the first metal foil, and a portion of the second metal foil surface on the polymer substrate layer; S400: welding the polymer substrate layer to the first metal foil, the second metal foil, and the overlapping areas of the first metal layer and the second metal layer.

8. A composite pole piece, characterized in that: The composite current collector comprises the composite current collector according to any one of claims 1 to 6, and an electrode material layer and a tab formed on the current collector.

9. The composite pole piece according to claim 8, characterized in that: The distance between the electrode material layer on each side and the metal foil on the same side is 5 mm to 40 mm.

10. A secondary battery, characterized in that: The secondary battery includes the composite electrode according to claim 8 or 9.

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