Bipolar current collector, electrochemical device and electronic device

Abstract

The present invention provides a bipolar current collector, an electrochemical device, and an electronic device. The bipolar current collector comprises a porous matrix, a first metal, and a second metal. The first metal is present on one surface of the porous matrix, the second metal is present on the other surface, and at least one of the first metal and the second metal is present within the porous matrix. The porous matrix exhibits oxidation resistance, reduction resistance, and ion insulation, providing a certain degree of mechanical strength. The metal layer of the bipolar current collector exhibits excellent electronic conductivity and ion insulation, high mechanical strength, and good thermal stability. Furthermore, the roughness of both surfaces of the bipolar current collector optimizes the interface between the positive and negative electrode membranes on both sides and the composite bipolar current collector, enhancing membrane adhesion.

Description

Technical Field

[0001] The present invention relates to the field of batteries, and in particular to a bipolar current collector, an electrochemical device and an electronic device comprising the bipolar current collector. Background Art

[0002] Lithium-ion batteries are widely used in consumer electronics due to their numerous advantages, including high volumetric and mass energy density, long cycle life, high nominal voltage, low self-discharge rate, compact size, and light weight. With the rapid development of electric vehicles and mobile electronic devices in recent years, people have increasingly demanded higher requirements for battery energy density, safety performance, and cycle performance, necessitating the development of new lithium-ion batteries with comprehensively improved performance.

[0003] To increase the output voltage of lithium-ion batteries, a series connection is currently being adopted. In this approach, two electrode assemblies are placed in a sealed chamber, with tabs extending from each assembly. These tabs are then connected in series to increase the output voltage. Another approach is to place a separator between the two electrode assemblies, with tabs extending from each assembly, and connect them in series to increase the output voltage. Summary of the Invention

[0004] The object of the present invention is to provide a bipolar current collector, an electrochemical device and an electronic device to increase the output voltage of the electrochemical device.

[0005] A first aspect of the present invention provides a bipolar current collector comprising a porous substrate, a first metal M, and a second metal N, wherein the first metal M is present on one surface of the porous substrate, the second metal N is present on the other surface, and at least one of the first metal M and the second metal N is present inside the porous substrate;

[0006] The material of the porous matrix includes at least one of a carbon material, a polymer material or a third metal;

[0007] The porosity of the porous matrix is ​​20% to 90%.

[0008] In one embodiment of the present invention, the carbon material comprises at least one of single-walled carbon nanotube film, multi-walled carbon nanotube film, carbon felt, porous carbon film, carbon black, acetylene black, fullerene, conductive graphite or graphene.

[0009] In one embodiment of the present invention, the polymer material includes polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polyetheretherketone, polyimide, polyamide, polyethylene glycol, polyamideimide, polycarbonate, cyclic polyolefin, polyphenylene sulfide, polyvinyl acetate, polytetrafluoroethylene, polymethylene naphthalene, polyvinylidene fluoride, polyethylene naphthalate, polypropylene carbonate, poly(vinylidene fluoride-hexafluoropropylene), poly(vinylidene fluoride-co-chlorotrifluoroethylene), silicone, vinylon, polypropylene, polyethylene, polyvinyl chloride, polystyrene, polyether nitrile, polyurethane, polyphenylene ether, polyester, polysulfone or at least one of their derivatives.

[0010] In one embodiment of the present invention, the third metal, the first metal M, and the second metal N used for the porous matrix independently include at least one of Cu, Al, Ni, Ti, Ag, Au, Pt, stainless steel, or alloys thereof.

[0011] In one embodiment of the present invention, the thickness of the layer formed by the first metal M on the surface of the porous substrate is 0.95 μm to 900 μm; the thickness of the layer formed by the second metal N on the surface of the porous substrate is 0.95 μm to 900 μm.

[0012] In one embodiment of the present invention, the bipolar current collector has a thickness of 2 μm to 1000 μm.

[0013] In one embodiment of the present invention, the surface roughness of the bipolar current collector is 0.05 μm to 10 μm.

[0014] In one embodiment of the present invention, the thickness ratio of the layer formed by the first metal M on the surface of the porous substrate to the layer formed by the second metal N on the surface of the porous substrate is 0.05 to 20.

[0015] In one embodiment of the present invention, the electronic resistivity in the Z direction of the bipolar current collector is 2.00×10 -10 Ω·cm to 2.00×10 -4 Ω·cm.

[0016] In one embodiment of the present invention, the bipolar current collector satisfies at least one of the following characteristics:

[0017] (a) the bipolar current collector has a thickness of 5 μm to 50 μm;

[0018] (b) the surface roughness of the bipolar current collector is 0.2 μm to 5 μm;

[0019] (c) a thickness ratio of the layer formed by the first metal M on the surface of the porous substrate to the layer formed by the second metal N on the surface of the porous substrate is 0.2 to 5;

[0020] (d) The electronic resistivity of the bipolar current collector in the Z direction is 2.00×10 -10 Ω·cm to 2.00×10 -6 Ω·cm;

[0021] (e) The porosity of the porous matrix is ​​40% to 70%.

[0022] In one embodiment of the present invention, the bipolar current collector satisfies at least one of the following characteristics:

[0023] (a) the thickness of the layer formed by the first metal M on the surface of the porous substrate is 0.40 μm to 13.33 μm; the thickness of the layer formed by the second metal N on the surface of the porous substrate is 0.40 μm to 13.33 μm;

[0024] (b) the bipolar current collector has a thickness of 5 μm to 20 μm;

[0025] (c) the surface roughness of the bipolar current collector is 0.5 μm to 2 μm;

[0026] (d) The electronic resistivity of the bipolar current collector in the Z direction is 2.00×10 -10 Ω·cm to 2.00×10 -8 Ω·cm.

[0027] A second aspect of the present invention provides an electrochemical device comprising at least two electrode assemblies and the bipolar current collector described in any one of the above embodiments, wherein the bipolar current collector is located between the two electrode assemblies.

[0028] A third aspect of the present invention provides an electronic device, comprising the electrochemical device according to the second aspect.

[0029] The present invention provides a bipolar current collector, which includes a porous matrix, a first metal, and a second metal. The first metal is present on one surface of the porous matrix, the second metal is present on the other surface, and at least one of the first metal and the second metal is present inside the porous matrix. Since the porous material has oxidation resistance, reduction resistance, and ion insulation, it has the advantage of certain mechanical strength; the metal layer of the bipolar current collector has the advantages of good electron conduction and ion insulation, high mechanical strength, and good thermal stability. In addition, since the surfaces on both sides of the bipolar current collector have a certain roughness, the interface bonding between the positive and negative electrode membranes on both sides and the composite bipolar current collector can be optimized, thereby improving the membrane adhesion. The bipolar current collector of the present invention can be coated with positive and negative active materials on both sides, respectively, to form an electrochemical unit with adjacent battery components, thereby improving the energy density and output voltage of the electrochemical device. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In order to more clearly illustrate the technical solutions of the present invention and the prior art, the following briefly introduces the drawings required for use in the embodiments and the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other technical solutions can be obtained based on these drawings without paying any creative work.

[0031] Figure 1 is a schematic diagram of a current collector in one embodiment of the present invention;

[0032] Figure 2 is a schematic diagram of an electrochemical device in one embodiment of the present invention;

[0033] Figure 3 Schematic diagram of the preparation process of a composite current collector in one embodiment of the present invention. DETAILED DESCRIPTION

[0034] To make the objectives, technical solutions, and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and embodiments. It is apparent that the embodiments described are only a portion of the embodiments of the present invention, not all of them. All other embodiments derived by persons of ordinary skill in the art based on the embodiments of the present invention without inventive effort are intended to fall within the scope of protection of the present invention.

[0035] As a new type of lithium-ion battery, bipolar lithium-ion batteries utilize multiple cells connected in series to form a single lithium-ion battery, thereby increasing the output voltage of the lithium-ion battery. The current collector used in this type of lithium-ion battery is a bipolar current collector, in which one side of the bipolar current collector contacts the positive electrode active material and the other side contacts the negative electrode active material. This requires the current collector to be resistant to oxidation and reduction, and is therefore typically made of metal foil such as aluminum / copper composite foil. However, existing bipolar lithium-ion batteries often suffer from the following problems: Firstly, the poor intermetallic bonding between the aluminum / copper composite foil compromises the cycling stability of bipolar lithium-ion batteries; secondly, metal foil is relatively expensive, increasing the manufacturing cost of bipolar lithium-ion batteries.

[0036] In addition, the existing bipolar current collector can also include a multilayer metal composite current collector, which is usually obtained by directly compounding Cu foil and Al foil. Although it has certain anti-oxidation and anti-reduction capabilities, it has problems such as poor interface bonding between metals and difficulty in thinning the current collector.

[0037] In view of this, if Figure 1 As shown, the present invention provides a bipolar current collector, which includes a porous matrix 1, a first metal M, and a second metal N. The first metal M exists on one surface of the porous matrix, the second metal N exists on the other surface, and at least one of the first metal M or the second metal N exists inside the porous matrix; the material of the porous matrix includes at least one of a carbon material, a polymer material or a third metal; the porosity of the porous matrix is ​​20% to 90%, preferably 40% to 70%.

[0038] The porous matrix material has the advantages of high oxidation resistance, high reduction resistance, high ion insulation, high mechanical strength, thin thickness and high thermal stability. When the thermal stability is greater than 300°C, a metal layer can be prepared on its surface by the PVD (Physical Vapor Deposition) method. Since the porous matrix material has pores, the metal material can penetrate into the porous matrix material and contact with the metal material deposited on the other side, providing electronic conductivity. The metal layer surface obtained by the PVD method on both sides of the bipolar current collector has a certain roughness, which can improve the interface bonding between the bipolar current collector and the positive active material and the negative active material coated on its two side surfaces respectively, and improve the bonding force between the bipolar current collector and the positive and negative electrode membranes. In the present invention, the porous matrix can be in a network shape.

[0039] In the present invention, the first metal and the second metal may be located on both side surfaces of the porous substrate, or may be infiltrated into the pores of the porous substrate. Furthermore, the first metal and the second metal may be in contact with each other after infiltration.

[0040] The first and second metals described above have the advantages of high oxidation resistance, high reduction resistance, high ion insulation, high mechanical strength, high thermal stability, and thin thickness. Because the first and second metals will contact the positive and negative active materials, respectively, they should be compatible with the positive and negative active materials, respectively.

[0041] The bipolar current collector of the present invention has a thickness less than or equal to that of the existing Cu / Al foil current collector material and can be manufactured on a large scale industrially. Compared with the existing mature stainless steel foil and Ti foil, it has the advantage of low cost; compared with the lower-cost conductive material / polymer composite, it has the advantages of high electronic conductivity, good rate performance and thin thickness.

[0042] In one embodiment of the present invention, the carbon material comprises at least one of single-walled carbon nanotube film, multi-walled carbon nanotube film, carbon felt, porous carbon film, carbon black, acetylene black, fullerene, conductive graphite or graphene.

[0043] In one embodiment of the present invention, the polymer material includes polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polyetheretherketone, polyimide, polyamide, polyethylene glycol, polyamideimide, polycarbonate, cyclic polyolefin, polyphenylene sulfide, polyvinyl acetate, polytetrafluoroethylene, polymethylene naphthalene, polyvinylidene fluoride, polyethylene naphthalate, polypropylene carbonate, poly(vinylidene fluoride-hexafluoropropylene), poly(vinylidene fluoride-co-chlorotrifluoroethylene), silicone, vinylon, polypropylene, polyethylene, polyvinyl chloride, polystyrene, polyether nitrile, polyurethane, polyphenylene ether, polyester, polysulfone or at least one of their derivatives.

[0044] When the matrix of the bipolar current collector is a polymer material, since the density of the polymer material is lower than that of the commonly used metal current collector material, the weight of the inactive material can be reduced and the mass energy density of the battery cell can be improved.

[0045] In one embodiment of the present invention, the third metal, the first metal M, and the second metal N each independently include at least one of Cu, Al, Ni, Ti, Ag, Au, Pt, stainless steel, or alloys thereof.

[0046] The first metal M and the second metal N may be the same or different, but should be compatible with the positive electrode active material or the negative electrode active material coated on the surface thereof and have corresponding anti-oxidation or anti-reduction properties.

[0047] In one embodiment of the present invention, the thickness of the layer formed by the first metal M on the surface of the porous substrate is 0.95 μm to 900 μm, preferably 0.40 μm to 13.33 μm; the thickness of the layer formed by the second metal N on the surface of the porous substrate is 0.95 μm to 900 μm, preferably 0.40 μm to 13.33 μm.

[0048] In one embodiment of the present invention, the bipolar current collector has a thickness of 2 μm to 1000 μm, preferably 5 μm to 50 μm, and more preferably 5 to 20 μm. If the bipolar current collector is too thick, the proportion of inactive material in the electrochemical device increases, reducing the energy density. If the thickness is too thin, the mechanical strength is insufficient and it is easily damaged.

[0049] In one embodiment of the present invention, the surface roughness of the bipolar current collector is 0.05 μm to 10 μm, preferably 0.2 μm to 5 μm, and more preferably 0.5 μm to 2 μm. When the surface roughness of the bipolar current collector is too low, the adhesion to the electrode active material coated on its surface is insufficient; when the surface roughness of the bipolar current collector is too high, not only will the adhesion effect not be further improved, but it may also cause fluctuations in the weight distribution of the active material, increasing the risk of local lithium deposition.

[0050] In one embodiment of the present invention, the thickness ratio of the layer formed by the first metal M on the surface of the porous substrate to the layer formed by the second metal N on the surface of the porous substrate is 0.05 to 20, preferably 0.2 to 5. This thickness ratio varies with the types of materials selected for M and N. Generally speaking, metal layers with low density, low cost, and high production efficiency are thicker, while metal layers with low density, low cost, and high production efficiency are thinner, thereby improving ED (Energy Density) and reducing costs.

[0051] In one embodiment of the present invention, the electronic resistivity in the Z direction of the bipolar current collector is 2.00×10 -10 Ω·cm to 2.00×10 -4 Ω·cm, preferably 2.00×10 -10 Ω·cm to 2.00×10 -6 Ω·cm, more preferably 2.00×10 --10 Ω·cm to 2.00×10 --8 Ω·cm. The Z direction refers to the thickness direction of the bipolar current collector, that is, the direction with the smallest dimension. In the present invention, it is desired that the electronic resistivity in the Z direction of the bipolar current collector is small to provide good electronic conductivity.

[0052] The present invention also provides an electrochemical device comprising at least one bipolar current collector according to the present invention, the bipolar current collector being sealed to the outer packaging of the electrochemical device, forming two independent sealed chambers on either side of the bipolar current collector, each containing an electrode assembly and an electrolyte, forming an independent electrochemical unit, wherein the bipolar current collector is coated on both sides with electrode active materials of opposite polarity. Adjacent electrochemical units are connected in series via bipolar electrodes containing the bipolar current collector of the present invention, forming a bipolar lithium-ion battery with a higher operating voltage.

[0053] In one embodiment of the present invention, two adjacent electrode assemblies may each have a tab extending therefrom, and the tabs of the two electrode assemblies have opposite polarities. For example, when the side of the bipolar current collector adjacent to electrode assembly A is coated with a positive electrode active material, and the side adjacent to electrode assembly B is coated with a negative electrode active material, the negative electrode tab is extended from electrode assembly A, and the positive electrode tab is extended from electrode assembly B. In this case, the output voltage between the two tabs is the sum of the output voltages of the two electrochemical units.

[0054] In one embodiment of the present invention, two adjacent electrode assemblies can each have two tabs. For example, when the bipolar current collector is coated with a positive electrode active material on the side adjacent to electrode assembly A and a negative electrode active material on the side adjacent to electrode assembly B, the positive electrode tab of electrode assembly A and the positive electrode tab of electrode assembly B are connected in series, the negative electrode tab of electrode assembly A and the positive electrode tab of electrode assembly B serve as output tabs, and the output voltage is the sum of the output voltages of the two electrochemical units. In this case, both internal series connection through the bipolar current collector and external series connection through the tabs exist between the two adjacent electrochemical units.

[0055] In one embodiment of the present invention, the bipolar current collector may lead out a tab for monitoring the operating status of the lithium-ion battery.

[0056] In one embodiment of the present invention, the electrochemical device of the present invention comprises at least one bipolar current collector, which is sealed to the outer packaging, forming independent sealed chambers on both sides of the bipolar current collector, each of which contains an electrode assembly and an electrolyte, forming an electrochemical unit. The bipolar current collector is coated with an electrode active material on one side, and directly contacts and electrically connects to the current collector of the electrode assembly on the other side. For example, the bipolar current collector is coated with a positive electrode active material on the side near electrode assembly A, and directly contacts and electrically connects to the negative electrode current collector of electrode assembly B on the side near electrode assembly B. In this case, electrode assembly A can have a negative electrode tab, and electrode assembly B can have a positive electrode tab, with the two electrochemical units connected in series via the bipolar current collector; or electrode assemblies A and B can each have two tabs, with the positive electrode tab of electrode assembly A connected in series with the negative electrode tab of electrode assembly B. In this case, the two electrochemical units are connected in series via the bipolar current collector and externally via the tabs. In addition, the bipolar current collector can lead out a tab for monitoring the battery operating status.

[0057] In one embodiment of the present invention, the electrochemical device of the present invention comprises at least one bipolar current collector, which is sealed to the outer packaging, and separate sealed chambers are formed on both sides of the bipolar current collector, each of which contains an electrode assembly and an electrolyte, forming an electrochemical unit, wherein one side of the bipolar current collector is coated with an electrode active material, and the other side is in contact with the separator of the electrode assembly to form electrical insulation. For example, the side of the bipolar current collector close to electrode assembly A is coated with a positive electrode active material, and the side close to electrode assembly B is in contact with the separator of electrode assembly B to form electrical insulation from electrode assembly B. In this case, the two electrode assemblies each lead out two tabs, and the bipolar current collector leads out one tab, which is connected in parallel with the positive electrode tab of electrode assembly A and then in series with the negative electrode tab of electrode assembly B.

[0058] In one embodiment of the present invention, the electrochemical device comprises at least one bipolar current collector, which is sealed to the outer packaging. Separate, independent sealed chambers are formed on either side of the bipolar current collector. Each sealed chamber contains an electrode assembly and an electrolyte, forming an electrochemical cell. The two sides of the bipolar current collector are in direct contact with and electrically insulated from the separator of an adjacent electrode assembly. In this case, the two electrode assemblies each have two tabs extending therefrom, and the two electrode assemblies are connected in series via the tabs.

[0059] In one embodiment of the present invention, a primer layer may be included between the bipolar current collector and the electrode active material. The primer layer serves to improve the bonding performance between the bipolar current collector and the active material and to enhance the electronic conductivity between the bipolar current collector and the active material. The primer layer is typically obtained by coating a slurry formed by mixing conductive carbon black, styrene-butadiene rubber, and deionized water onto the bipolar current collector and drying the mixture. The primer layers on both sides of the bipolar current collector may be the same or different. The preparation process of the positive active material layer, the negative active material layer, the positive primer layer, and the negative primer layer will be described below.

[0060] Figure 2 A schematic diagram of an electrochemical device in one embodiment of the present invention is shown in FIG. Figure 2 As shown, the bipolar current collector 300 separates the electrochemical device into two electrode assemblies, namely a first electrode assembly 100 and a second electrode assembly 200. Figure 2 The negative electrode 101, the first negative electrode active material layer 102, the first separator 103, the first positive electrode active material layer 104, and a portion of the bipolar current collector 300 are sequentially included from top to bottom; the second electrode assembly 200 is Figure 2 From bottom to top, the electrochemical device includes a positive electrode 201, a second positive electrode active material layer 202, a second separator 203, a second negative electrode active material layer 204, and another portion of the bipolar current collector 300. Furthermore, the electrochemical device can be sealed by a seal 400, so that the electrochemical device forms two independent cavity structures, corresponding to the first electrode assembly 100 and the second electrode assembly 200, respectively.

[0061] The present invention also provides an electronic device comprising the electrochemical device according to the above embodiment.

[0062] The electrode assembly of the present invention is not particularly limited and any electrode assembly of the prior art can be used as long as it can achieve the purpose of the present invention. For example, a laminated electrode assembly or a wound electrode assembly can be used. The electrode assembly generally includes a positive electrode sheet, a negative electrode sheet, and a separator.

[0063] There are no particular limitations on the negative electrode sheet in the present invention, as long as the purpose of the present invention can be achieved. For example, the negative electrode sheet generally comprises a negative electrode current collector and a negative electrode active material layer. Among them, there are no particular limitations on the negative electrode current collector, and any negative electrode current collector known in the art can be used, such as copper foil, aluminum foil, aluminum alloy foil, and composite current collector. The negative electrode active material layer includes a negative electrode active material, and the negative electrode active material is not particularly limited, and any negative electrode active material known in the art can be used. For example, it can include at least one of artificial graphite, natural graphite, mesophase carbon microbeads, soft carbon, hard carbon, silicon, silicon carbon, lithium titanate, and the like.

[0064] There is no particular limitation on the positive electrode sheet in the present invention, as long as the purpose of the present invention can be achieved. For example, the positive electrode sheet generally comprises a positive electrode current collector and a positive electrode active material. Among them, the positive electrode current collector is not particularly limited and can be any positive electrode current collector known in the art, such as aluminum foil, aluminum alloy foil or composite current collector. The positive electrode active material is not particularly limited and can be any positive electrode active material in the prior art, and the active material includes at least one of NCM811, NCM622, NCM523, NCM111, NCA, lithium iron phosphate, lithium cobalt oxide, lithium manganese oxide, lithium iron manganese phosphate or lithium titanate.

[0065] The electrolyte in the present invention is not particularly limited and any electrolyte known in the art can be used, for example, it can be any of gel, solid and liquid. For example, the liquid electrolyte can include lithium salt and non-aqueous solvent.

[0066] The lithium salt is not particularly limited, and any lithium salt known in the art can be used, as long as the purpose of the present invention can be achieved. For example, the lithium salt can include at least one of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium difluorophosphate (LiPO2F2), lithium bis(trifluoromethanesulfonyl)imide LiN(CF3SO2)2 (LiTFSI), lithium bis(fluorosulfonyl)imide Li(N(SO2F)2) (LiFSI), lithium bis(oxalatoborate) LiB(C2O4)2 (LiBOB), or lithium difluorooxalatoborate LiBF2(C2O4) (LiDFOB). For example, the lithium salt can be selected from LiPF6.

[0067] The non-aqueous solvent is not particularly limited as long as the purpose of the present invention can be achieved. For example, the non-aqueous solvent may include at least one of a carbonate compound, a carboxylate compound, an ether compound, a nitrile compound, or other organic solvents.

[0068] For example, the carbonate compound may include at least one of diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC), ethyl methyl carbonate (MEC), ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), vinyl ethylene carbonate (VEC), fluoroethylene carbonate (FEC), 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate, 1,1,2,2-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1,2-difluoro-1-methylethylene carbonate, 1,1,2-trifluoro-2-methylethylene carbonate, or trifluoromethylethylene carbonate.

[0069] The separator in the present invention is not particularly limited. For example, the separator includes a polymer or an inorganic substance formed of a material stable to the electrolyte of the present invention. The separator should generally have ion conductivity and electronic insulation.

[0070] For example, the diaphragm may include a substrate layer and a surface treatment layer. The substrate layer may be a non-woven fabric, a film, or a composite film having a porous structure, and the material of the substrate layer may be selected from at least one of polyethylene, polypropylene, polyethylene terephthalate, and polyimide. Optionally, a polypropylene porous film, a polyethylene porous film, a polypropylene non-woven fabric, a polyethylene non-woven fabric, or a polypropylene-polyethylene-polypropylene porous composite film may be used. Optionally, a surface treatment layer is provided on at least one surface of the substrate layer, and the surface treatment layer may be a polymer layer or an inorganic layer, or a layer formed by a mixed polymer and an inorganic material.

[0071] For example, the inorganic layer includes inorganic particles and a binder, and the inorganic particles are not particularly limited, for example, can be selected from at least one of aluminum oxide, silicon oxide, magnesium oxide, titanium oxide, hafnium dioxide, tin oxide, cerium dioxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide and barium sulfate. The binder is not particularly limited, for example, can be selected from one or more combinations of polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylic acid salt, polyvinyl pyrrolidone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene and polyhexafluoropropylene. Polymer is included in the polymer layer, and the material of the polymer includes at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylic acid salt, polyvinyl pyrrolidone, polyvinyl ether, polyvinylidene fluoride or poly (vinylidene fluoride-hexafluoropropylene).

[0072] like Figure 3 As shown, the present invention also provides a method for preparing the composite bipolar current collector in any of the above embodiments, comprising the following steps:

[0073] 1) Preparing a layer of polymer material particle coating 2 on the surface of a stainless steel substrate 3 by electrostatic spraying;

[0074] 2) high temperature heat treatment to make the polymer material particle coating 2 reach the softening temperature;

[0075] 3) Laminating the A surface of the heat-resistant porous network substrate 1 to the surface of the polymer material coating;

[0076] 4) Superheated pressure roller to ensure effective and consistent bonding between the heat-resistant porous network matrix and the polymer material coating;

[0077] 5) After cooling to room temperature, the heat-resistant porous network matrix / polymer coating composite membrane is removed from the stainless steel substrate with a scraper;

[0078] 6) Preparing a second metal N of a certain thickness on the B side of the heat-resistant porous network matrix / polymer coating composite membrane by a PVD method;

[0079] 7) Using an organic solvent to dissolve and clean the polymer coating on surface A, so that the heat-resistant porous network matrix on surface A is completely exposed;

[0080] 8) On the A surface of the porous network substrate, a first metal M of a certain thickness is prepared by a PVD method;

[0081] 9) Overheat the roller to ensure that the metal M and N on both sides of the A and B surfaces fit closely with them;

[0082] 10) Collect the paper.

[0083] Those skilled in the art will appreciate that the bipolar current collector according to the present invention can be prepared by any other method, not limited to the above-described methods. For example, the PVD method can be performed by CVD (Chemical Vapor Deposition), electroplating, or other methods.

[0084] PVD (Physical Vapor Deposition) uses low-voltage, high-current arc discharge technology under vacuum conditions to vaporize the target material and ionize both the evaporated material and the gas. The electric field accelerates the vaporized material and its reaction products, depositing them on the workpiece. Compared to CVD, PVD processes operate at lower temperatures, resulting in compressive stress within the film. PVD has no adverse environmental impact and aligns with the development of modern green manufacturing.

[0085] It should be noted that, in the specific embodiment of the present invention, a lithium ion battery is used as an example of an electrochemical device to implement the electrochemical device, but the electrochemical device is not limited to the lithium ion battery.

[0086] The following examples and comparative examples are provided to more specifically illustrate the embodiments of the present invention. Various tests and evaluations were performed according to the following methods. In addition, unless otherwise specified, "parts" and "%" are by weight.

[0087] Example 1

[0088] <Preparation of bipolar pole piece>

[0089] <Preparation of Bipolar Current Collector>

[0090] 1) A layer of PVDF (polyvinylidene fluoride) particle coating with a thickness of 45 μm was prepared on the surface of a stainless steel substrate by electrostatic spraying;

[0091] 2) Heat treatment at 180°C to make the PVDF layer reach the softening temperature;

[0092] 3) Laminating the A side of a 140 μm thick PI (polyimide) porous film to the surface of the PVDF coating, where the porosity of the polyimide porous film is 60%;

[0093] 4) Superheat the roller to 180°C to ensure effective and consistent bonding of the PI porous film and the PVDF coating;

[0094] 5) After cooling to room temperature, remove the PI porous film and PVDF coating composite membrane from the stainless steel substrate with a scraper;

[0095] 6) On the B side of the PI porous film and PVDF coating composite membrane, Al with a thickness (L2') of 95 μm was prepared by PVD method;

[0096] 7) Use DMF (N,N-dimethylformamide) to dissolve and clean the PVDF on surface A, so that the PI porous film matrix on surface A is completely exposed;

[0097] 8) On the A side of the PI porous film, a Cu layer with a thickness (L1') of 45 μm was prepared by PVD method;

[0098] 9) Using a superheated press roller at 200°C, the metal Al and Cu on both sides of the A and B surfaces are tightly bonded to them, and the total thickness of the composite current collector is thinned to 100 μm, where the thickness of the Al layer is about 66.66 μm and the thickness of the Cu layer is about 33.33 μm;

[0099] 10) Collect the paper.

[0100] <Preparation of the Negative Active Material Layer in the Bipolar Pole Sheet>

[0101] The negative electrode active materials, graphite, Super P (conductive carbon black), and SBR (styrene-butadiene rubber), were mixed in a mass ratio of 96:1.5:2.5. Deionized water was then added as a solvent to create a slurry with a solids content of 70%, which was then stirred evenly. The slurry was evenly coated on one side of a bipolar current collector and dried at 110°C to form a negative electrode active material layer with a thickness of 130μm.

[0102] <Preparation of the positive electrode active material layer in the bipolar electrode>

[0103] The positive electrode active material, LiCoO2 (lithium cobalt oxide), conductive carbon black, and PVDF were mixed in a mass ratio of 97.5:1.0:1.5. NMP (N-methylpyrrolidone) was then added as a solvent to form a slurry with a solid content of 75%, which was then stirred evenly. The slurry was evenly coated on the other side of the bipolar current collector and dried at 90°C to obtain a positive electrode active material layer with a thickness of 110 μm.

[0104] After the above steps are completed, a bipolar pole piece is obtained, and the pole piece is cut into a size of 41 mm × 61 mm for use.

[0105] <Preparation of negative electrode sheet>

[0106] The negative electrode active materials graphite, conductive carbon black, and styrene-butadiene rubber were mixed in a mass ratio of 96:1.5:2.5. Deionized water was added as a solvent to create a slurry with a solids content of 70%, and the mixture was stirred evenly. The slurry was evenly coated on one surface of a 10μm-thick copper foil and dried at 110°C to produce a negative electrode sheet coated on one side with a 150μm-thick layer of negative electrode active material. The coating process was repeated on the other surface of the negative electrode sheet. After coating, the sheet was cut into 41mm x 61mm dimensions and the tabs were welded before use.

[0107] <Preparation of positive electrode sheet>

[0108] The positive electrode active material, LiCoO2, conductive carbon black, and PVDF, were mixed in a mass ratio of 97.5:1.0:1.5. NMP was added as a solvent to create a slurry with a solids content of 75%, and stirred evenly. The slurry was evenly coated on one surface of a 12μm-thick aluminum foil and dried at 90°C to produce a single-sided positive electrode sheet coated with the positive electrode active material layer, with a thickness of 100μm. The above steps were repeated on the other surface of the positive electrode sheet. After coating, the sheet was cut into 38mm x 58mm squares and the tabs were welded for later use.

[0109] <Preparation of Electrolyte>

[0110] In a dry argon atmosphere, organic solvents EC (ethylene carbonate), EMC (ethyl methyl carbonate) and DEC (diethyl carbonate) are first mixed in a mass ratio of EC:EMC:DEC=30:50:20, and then LiPF6 (lithium hexafluorophosphate) is added to the organic solvent to dissolve and mix evenly to obtain an electrolyte with a lithium salt concentration of 1.15M.

[0111] <Preparation of Electrode Assembly>

[0112] A PE (polyethylene) film with a thickness of 15 μm is selected as the isolation membrane. A positive electrode sheet is placed on each side of the negative electrode sheet, and a layer of isolation membrane is placed between the positive electrode sheet and the negative electrode sheet to form a laminate. Then, the four corners of the entire laminate structure are fixed to obtain electrode assembly A.

[0113] A PE film with a thickness of 15 μm is selected as the isolation membrane. A negative electrode sheet is placed on each side of the positive electrode sheet, and a layer of isolation membrane is placed between the positive electrode sheet and the negative electrode sheet to form a laminate. Then, the four corners of the entire laminate structure are fixed to obtain electrode assembly B.

[0114] <Preparation of bipolar lithium-ion batteries>

[0115] <Preparation of Bipolar Electrode Assembly>

[0116] Place the punched packaging film (aluminum-plastic film) with a thickness of 90 μm in the assembly fixture with the pit side facing up, then place the electrode assembly A in the pit with the positive pole piece of the electrode assembly A facing up, and then place the double-sided bipolar pole piece with the negative coating facing down on the electrode assembly A, so that the positive pole piece of the electrode assembly A corresponds to the negative active material coating area of ​​the bipolar pole piece, and apply external force to compress it.

[0117] The semi-finished assembly is placed in another assembly fixture with the positive electrode of the bipolar pole piece facing upward. Electrode assembly B is placed on the bipolar current collector, with the negative electrode of electrode assembly B corresponding to the positive active material layer of the bipolar pole piece. Then, another 90μm thick aluminum-plastic film with a dented shape is placed on top of electrode assembly B with the dented surface facing downward. The two aluminum-plastic films are then heat-sealed using hot pressing to separate electrode assembly A and electrode assembly B by the bipolar pole piece, thereby obtaining a bipolar electrode assembly. The bipolar electrode assembly has two independent cavities, wherein electrode assembly A corresponds to the first cavity and electrode assembly B corresponds to the second cavity.

[0118] <Electrode Assembly Liquid Injection Packaging>

[0119] The electrolyte is injected into the two cavities of the bipolar electrode assembly respectively and then packaged. A tab is led out from each electrode assembly. The electrode assembly in the first cavity and the electrode assembly in the second cavity are connected in series through a bipolar current collector to obtain a bipolar lithium-ion battery. There is no ion exchange between the two cavities of the bipolar lithium-ion battery.

[0120] Example 2

[0121] In addition to the preparation of bipolar current collectors,

[0122] <Preparation of Bipolar Current Collector>

[0123] 1) A layer of PVDF (polyvinylidene fluoride) particle coating was prepared on the surface of a stainless steel substrate by electrostatic spraying; the thickness was 9 μm:

[0124] 2) Heat treatment at 180°C to make the PVDF layer reach the softening temperature;

[0125] 3) Laminating the A side of a 28 μm thick PI (polyimide) porous film to the surface of the PVDF coating, where the porosity of the polyimide porous film is 60%;

[0126] 4) Superheat the roller to 180°C to ensure effective and consistent bonding of the PI porous film and the PVDF coating;

[0127] 5) After cooling to room temperature, remove the PI porous film and PVDF coating composite membrane from the stainless steel substrate with a scraper;

[0128] 6) On the B side of the PI porous film and PVDF coating composite membrane, Al with a thickness of 19 μm was prepared by PVD method;

[0129] 7) Use DMF (N,N-dimethylformamide) to dissolve and clean the PVDF on surface A, so that the PI porous film matrix on surface A is completely exposed;

[0130] 8) On the A side of the PI porous film, a Cu film with a thickness of 9.00 μm was prepared by PVD method;

[0131] 9) Using a superheated press roller at 200°C, the metal Al and Cu on both sides of the A and B surfaces are tightly bonded to them, and the total thickness of the composite current collector is thinned to 20 μm, where the thickness of the Al layer is about 13.33 μm and the thickness of the Cu layer is about 6.67 μm;

[0132] 10) Collect the paper.

[0133] The rest is the same as Example 1.

[0134] Example 3

[0135] The process was the same as in Example 2 except that the temperature of the superheated pressure roller in step 9) was adjusted to 220° C. to make the surface roughness of the bipolar current collector 0.2 μm.

[0136] Example 4

[0137] The process was the same as in Example 2 except that the temperature of the superheated pressure roller in step 9) was adjusted to 230° C. to make the surface roughness of the bipolar current collector 0.05 μm.

[0138] Example 5

[0139] The process was the same as in Example 2, except that during the preparation of the bipolar current collector, Al with a thickness of 26.67 μm and Cu with a thickness of 1.33 μm were prepared by PVD, the thickness of Al after the hot roller was reduced to 19.05 μm, and the thickness of Cu was changed to 0.95 μm.

[0140] Example 6

[0141] The process was the same as in Example 2, except that during the preparation of the bipolar current collector, Al with a thickness of 5.60 μm and Cu with a thickness of 22.40 μm were prepared by PVD, the thickness of Al after the hot roller was reduced to 4.00 μm, and the thickness of Cu was changed to 16.00 μm.

[0142] Example 7

[0143] The process was the same as in Example 2, except that during the preparation of the bipolar current collector, Al with a thickness of 1.33 μm and Cu with a thickness of 26.67 μm were prepared by PVD, the thickness of Al after the hot roller was reduced to 0.95 μm, and the thickness of Cu was changed to 19.05 μm.

[0144] Example 8

[0145] The process is the same as Example 5 except that Ti is prepared on the B side and Ti is prepared on the A side in the process of <Preparation of Bipolar Current Collector>, and the porosity of the PI porous film is 20%.

[0146] Example 9

[0147] In addition to the preparation of the bipolar current collector, the porosity of the PI porous film was 40%, and the Z-direction electronic resistivity was adjusted to 2.00×10 -7 Except for Ω·cm, the rest is the same as that of Example 6.

[0148] Example 10

[0149] Except for the process of <Preparation of Bipolar Current Collector>, the PI porous film was replaced with a Ni porous substrate with a porosity of 90%; 6) On the B side of the Ni porous substrate and PVDF coating composite membrane, Ag with a thickness of 14.00 μm was prepared by PVD method;

[0150] 8) On the A surface of the Ni porous substrate, Ag with a thickness of 14.00 μm was deposited by PVD. Other than that, the same procedures as in Example 2 were followed.

[0151] Example 11

[0152] Except that the PI porous film was replaced with a carbon felt porous matrix in the process of <Preparation of Bipolar Current Collector>, the rest was the same as Example 6.

[0153] Example 12

[0154] Except that in the process of <Preparation of Bipolar Current Collector>, the PI porous film was replaced with a PET (polyethylene terephthalate) porous matrix, the rest was the same as Example 6.

[0155] Example 13

[0156] Except that the PI porous film was replaced with a stainless steel porous substrate in the process of <Preparation of Bipolar Current Collector>, the rest was the same as Example 6.

[0157] Example 14

[0158] Except for preparing Ni on the A side during the process of <Preparation of Bipolar Current Collector>, the rest is the same as Example 6.

[0159] Example 15

[0160] Except for the preparation of Ti on the A surface during the preparation of the bipolar current collector, the rest is the same as in Example 6.

[0161] Example 16

[0162] Except for preparing Ni on the B surface during the process of <Preparation of Bipolar Current Collector>, the rest is the same as Example 6.

[0163] Example 17

[0164] Except for the preparation of Ti on the B surface during the preparation of the bipolar current collector, the rest is the same as in Example 6.

[0165] Example 18

[0166] In addition to the preparation of bipolar current collectors,

[0167] <Preparation of Bipolar Current Collector>

[0168] 1) A layer of PVDF (polyvinylidene fluoride) particle coating was prepared on the surface of a stainless steel substrate by electrostatic spraying; the thickness was 450 μm:

[0169] 2) Heat treatment at 180°C to make the PVDF layer reach the softening temperature;

[0170] 3) Laminating the A side of a 1400 μm thick PI (polyimide) porous film to the surface of the PVDF coating, where the porosity of the polyimide porous film is 60%;

[0171] 4) Superheat the roller to 180°C to ensure effective and consistent bonding of the PI porous film and the PVDF coating;

[0172] 5) After cooling to room temperature, remove the PI porous film and PVDF coating composite membrane from the stainless steel substrate with a scraper;

[0173] 6) On the B side of the PI porous film and PVDF coating composite membrane, Al with a thickness of 280 μm was prepared by PVD method;

[0174] 7) Use DMF (N,N-dimethylformamide) to dissolve and clean the PVDF on surface A, so that the PI porous film matrix on surface A is completely exposed;

[0175] 8) On the A side of the PI porous film, a Cu layer with a thickness of 1120 μm was prepared by PVD method;

[0176] 9) Using a superheated press roller at 200°C, the metal Al and Cu on both sides of the A and B surfaces are closely attached to them, and the total thickness of the composite current collector is pressed to 1000 μm, where the thickness of the Al layer is about 200.00 μm and the thickness of the Cu layer is about 800.00 μm;

[0177] 10) Collect the paper.

[0178] The rest is the same as Example 1.

[0179] Example 19

[0180] In addition to the preparation of bipolar current collectors,

[0181] <Preparation of Bipolar Current Collector>

[0182] 1) A layer of PVDF (polyvinylidene fluoride) particle coating was prepared on the surface of a stainless steel substrate by electrostatic spraying; the thickness was 4.5 μm:

[0183] 2) Heat treatment at 180°C to make the PVDF layer reach the softening temperature;

[0184] 3) Laminating the A side of a 14 μm thick PI (polyimide) porous film to the surface of the PVDF coating, where the porosity of the polyimide porous film is 60%;

[0185] 4) Superheat the roller to 180°C to ensure effective and consistent bonding of the PI porous film and the PVDF coating;

[0186] 5) After cooling to room temperature, remove the PI porous film and PVDF coating composite membrane from the stainless steel substrate with a scraper;

[0187] 6) On the B side of the PI porous film and PVDF coating composite membrane, Al with a thickness of 2.80 μm was prepared by PVD method;

[0188] 7) Use DMF (N,N-dimethylformamide) to dissolve and clean the PVDF on surface A, so that the PI porous film matrix on surface A is completely exposed;

[0189] 8) On the A side of the PI porous film, a Cu layer with a thickness of 11.20 μm was prepared by PVD method;

[0190] 9) Using a superheated press roller at 200°C, the metal Al and Cu on both sides of the A and B surfaces are closely attached to them, and the total thickness of the composite current collector is thinned to 10 μm, where the thickness of the Al layer is about 2.00 μm and the thickness of the Cu layer is about 8.00 μm;

[0191] 10) Collect the paper.

[0192] The rest is the same as Example 1.

[0193] Example 20

[0194] In addition to the preparation of bipolar current collectors,

[0195] <Preparation of Bipolar Current Collector>

[0196] 1) A layer of PVDF (polyvinylidene fluoride) particle coating was prepared on the surface of a stainless steel substrate by electrostatic spraying; the thickness was 0.9 μm:

[0197] 2) Heat treatment at 180°C to make the PVDF layer reach the softening temperature;

[0198] 3) Laminating the A side of a 0.28 μm thick PI (polyimide) porous film to the surface of the PVDF coating, where the porosity of the polyimide porous film is 60%;

[0199] 4) Superheat the roller to 180°C to ensure effective and consistent bonding of the PI porous film and the PVDF coating;

[0200] 5) After cooling to room temperature, remove the PI porous film and PVDF coating composite membrane from the stainless steel substrate with a scraper;

[0201] 6) On the B side of the PI porous film and PVDF coating composite membrane, Al with a thickness of 0.56 μm was prepared by PVD method;

[0202] 7) Use DMF (N,N-dimethylformamide) to dissolve and clean the PVDF on surface A, so that the PI porous film matrix on surface A is completely exposed;

[0203] 8) On the A side of the PI porous film, a Cu layer with a thickness of 2.24 μm was prepared by PVD method;

[0204] 9) Using a superheated press roller at 200°C, the metal Al and Cu on both sides of the A and B surfaces are tightly bonded to them, and the total thickness of the composite current collector is thinned to 2 μm, where the thickness of the Al layer is about 0.40 μm and the thickness of the Cu layer is about 1.60 μm;

[0205] 10) Collect the paper.

[0206] The rest is the same as Example 1.

[0207] Example 21

[0208] A negative electrode base coating and a positive electrode base coating are added to the bipolar electrode sheet. Specific data are shown in Table 1. The rest is the same as Example 19.

[0209] <Preparation of negative electrode undercoating in bipolar pole pieces>

[0210] Conductive carbon black and styrene-butadiene rubber were mixed in a mass ratio of 95:5, and deionized water was added as a solvent to prepare a slurry with an 80% solids content. The mixture was then stirred evenly. The slurry was evenly coated on the surface A of the composite bipolar current collector and dried at 110°C to obtain a negative electrode undercoat with a thickness of 5 μm.

[0211] <Preparation of the Negative Active Material Layer in the Bipolar Pole Sheet>

[0212] The negative electrode active materials, graphite, conductive carbon black, and styrene-butadiene rubber, were mixed in a mass ratio of 96:1.5:2.5. Deionized water was added as a solvent to create a slurry with a solid content of 70%. The mixture was stirred evenly. The slurry was evenly coated on the negative electrode undercoat layer and dried at 110°C to obtain a negative electrode sheet with a thickness of 120μm.

[0213] <Preparation of positive electrode bottom coating in bipolar pole piece>

[0214] Conductive carbon black and styrene-butadiene rubber were mixed in a mass ratio of 97:3, and deionized water was added as a solvent to prepare a slurry with a solid content of 85%. The mixture was stirred evenly. The slurry was evenly coated on the B surface of the composite bipolar current collector and dried at 110°C to obtain a positive electrode primer with a thickness of 3μm.

[0215] <Preparation of the positive electrode active material layer in the bipolar electrode>

[0216] The positive electrode active material, LiCoO2, conductive carbon black, and PVDF were mixed in a mass ratio of 97.5:1.0:1.5. NMP was added as a solvent to prepare a slurry with a solid content of 75%, and stirred evenly. The slurry was evenly coated on the positive electrode base coating and dried at 90°C to obtain a positive electrode sheet with a thickness of 100μm.

[0217] Example 22

[0218] In the preparation of the negative electrode undercoat for the bipolar electrode, polypyrrole (PPY) and styrene-butadiene rubber (SBR) were mixed in a mass ratio of 95:5, deionized water was added as a solvent, and a slurry with a solid content of 80% was prepared. The mixture was then stirred evenly. The slurry was evenly coated on the surface A of the composite bipolar current collector and dried at 110°C to obtain the negative electrode undercoat. The thickness of the negative electrode undercoat was 3μm.

[0219] Preparation of the Positive Electrode Primer in the Bipolar Pole Sheet: Polypyrrole (PPY) and styrene-butadiene rubber were mixed in a weight ratio of 97:3. Deionized water was added as a solvent to form a slurry with an 85% solids content, which was then stirred evenly. The slurry was evenly coated on the B surface of the composite bipolar current collector and dried at 110°C to obtain a positive electrode primer coating with a thickness of 3 μm. The remaining steps were the same as in Example 21.

[0220] Example 23

[0221] <Preparation of Electrode Assembly>

[0222] The double-sided coated negative electrode sheet, separator, and double-sided coated positive electrode sheet are stacked in sequence to form a laminate, and then the entire laminate is wound, with the negative electrode sheet placed on the outermost side. Among them, the separator is a polyethylene (PE) film with a thickness of 15μm. The double-sided coated negative electrode sheet, separator, and double-sided coated positive electrode sheet are stacked in sequence to form a laminate, and then the entire laminate is wound, with the positive electrode sheet placed on the outermost side. Among them, the separator is a polyethylene (PE) film with a thickness of 15μm.

[0223] <Preparation of bipolar lithium-ion batteries>

[0224] <Preparation of Bipolar Electrode Assembly>

[0225] Place the aluminum-plastic film with holes punched and formed in the assembly fixture with the holes facing up, place the electrode assembly A in the holes, and then place the bipolar current collector with the side containing the positive electrode active material facing down on the electrode assembly A so that the active material coating areas correspond, and apply external force to compact it to obtain the assembled semi-finished product.

[0226] The semi-finished assembly was placed in another assembly fixture, with the bipolar current collector facing upwards, and the electrode assembly B was placed on the bipolar current collector so that the active material-coated areas aligned. External pressure was applied to tighten the assembly. The punched aluminum-plastic film was then placed over the electrode assembly B with the pitted surface facing downwards, and heat-sealed around the edges using hot pressing to obtain the assembled electrode assembly. The remainder of the process was the same as in Example 19.

[0227] Comparative Example 1

[0228] Except that the bipolar current collector is a Cu / Al composite foil current collector, the rest is the same as in Example 1.

[0229] The thickness of the Cu / Al composite current collector is 20 μm.

[0230] Comparative Example 2

[0231] Except that a stainless steel foil current collector is selected as the bipolar current collector, the rest is the same as Example 1.

[0232] The thickness of the stainless steel foil current collector is 20 μm.

[0233] Comparative Example 3

[0234] Except that the bipolar current collector is a composite of a zero-dimensional structure conductive material and a polymer matrix, the rest is the same as in Example 1.

[0235] In the bipolar current collector, the zero-dimensional structure conductive material is point-shaped carbon black particles, the polymer substrate is a PET substrate, the point-shaped carbon black particles are uniformly and non-orientedly dispersed in the three-dimensionally distributed matrix, and the thickness of the bipolar current collector is about 50 μm.

[0236] Comparative Example 4

[0237] Except that the bipolar current collector is a composite of a one-dimensional structure conductive material and a polymer matrix, the rest is the same as Example 1.

[0238] In the bipolar current collector, the one-dimensional structural conductive material is MWCNT, the polymer substrate is a PET substrate, the MWCNT is uniformly and non-orientedly dispersed in the three-dimensionally distributed matrix, and the thickness of the bipolar current collector is about 50 μm.

[0239] Comparative Example 5

[0240] Except that the bipolar current collector is a composite of a two-dimensional structure conductive material and a polymer substrate, the rest is the same as Example 1.

[0241] In the bipolar current collector, the two-dimensional structural conductive material is graphene, the polymer substrate is a PET substrate, the graphene is uniformly and non-orientedly dispersed in the three-dimensionally distributed matrix, and the thickness of the bipolar current collector is about 50 μm.

[0242] <Performance Test>

[0243] The bipolar current collectors and bipolar lithium-ion batteries prepared in each embodiment and each comparative example were tested using the following method:

[0244] Material surface roughness testing

[0245] This is a contact measurement method that uses the instrument's stylus to contact the surface being measured and gently slide it along it to measure surface roughness. A sharp stylus is placed vertically on the surface being measured and moved laterally. Due to the roughness of the working surface, the stylus moves vertically and follows the contour of the surface being measured. This tiny displacement is converted into an electrical signal through an electronic circuit, amplified, and processed to obtain the surface roughness parameter value. Alternatively, a recorder can be used to draw a graphical image of the surface profile, and then data processing can be performed to obtain the surface roughness parameter value.

[0246] The specific test method is: the difference between the average of the five largest profile peak heights and the average of the five largest profile valley depths within the sampling length (10cm). This method is suitable for measuring surface roughness Rz in the range of 0.02μm to 160μm.

[0247] Composite bipolar current collector M, N layer thickness direction ratio test

[0248] Prepare a cross-sectional sample of the sample, measure SEM (Scanning Electron Microscope) and perform elemental analysis to find the interface between M and N. The distance from the interface to the outer edge of the M layer is L1, and the distance from the interface to the outer edge of the N layer is L2. The ratio of L1 to L2 is the value.

[0249] The thickness of the bipolar current collector layer is denoted as H.

[0250] Z-direction electronic resistivity R test

[0251] The composite bipolar current collector is clamped on both sides with fixed-area clamps, and the resistance value is measured, which is then divided by the thickness and multiplied by the plate area.

[0252] Diaphragm and bipolar current collector adhesion test

[0253] 1) The electrode sheet is removed from an electrode assembly that has not undergone a charge-discharge cycle, i.e., a fresh electrode assembly, and cut into strips with a width of 3 cm and a length of 10-16 cm;

[0254] 2) Apply a special strong double-sided tape with a width of 2 cm and a length of 9-15 cm to the surface of the steel plate;

[0255] 3) Stick the cut electrode sample on the double-sided tape with the test side facing down; insert a paper tape with a width equal to the electrode width and a length 8-20 cm greater than the length of the electrode sample under the electrode and fix it with wrinkle glue;

[0256] 4) Fix the end of the steel plate that is not attached to the electrode with a clamp, place the steel plate vertically, fold the paper tape upwards, and fix it with the clamp;

[0257] 5) Pull the paper tape vertically upward at a speed of 5 cm / min to separate the tape from the adhered membrane coating area and the current collector. Measure the force obtained when pulling them apart. Calculate the ratio of the measured force to the width of the upper electrode. Take the average value of multiple measurements to obtain the bonding force.

[0258] The bonding force with the positive electrode is F + , the bonding force with the negative electrode is F - .

[0259] Discharge energy density ED test

[0260] The lithium-ion battery was left at room temperature for 30 minutes, then charged at a constant current of 0.05C to a voltage of 8.8V (rated voltage), and then discharged at a rate of 0.05C to 6.0V. The charge / discharge steps were repeated for three cycles to complete the formation of the electrochemical device to be tested. After the formation of the electrochemical device was completed, the battery was charged at a constant current of 0.1C to a voltage of 8.8V, and then discharged at a rate of 0.1C to 6.0V. The discharge capacity was recorded, and the energy density at 0.1C discharge was calculated:

[0261] Mass energy density (Wh / kg) = discharge energy (Wh) / lithium-ion battery weight (kg)

[0262] Discharge capacity after 50 cycles / initial discharge capacity Q50 / Q0 (%)

[0263] The test temperature is 25°C. Charge to 8.8V at a constant current of 0.5C, charge to 0.025C at a constant voltage, let it stand for 5 minutes, and then discharge to 6.0V at 0.5C. The capacity obtained in this step is taken as the initial capacity. After 50 cycles of 0.5C charge / 0.5C discharge, calculate the ratio of the lithium-ion battery capacity to the initial capacity.

[0264] Table 1 Test parameters and corresponding experimental results of each embodiment and comparative example

[0265]

[0266]

[0267] As shown in Table 1, compared with Comparative Example 1 and Comparative Example 2, that is, compared with the lithium ion batteries with ordinary Cu / Al composite foil current collector and ordinary stainless steel foil current collector, the energy density, the ratio of the discharge capacity after 50 cycles to the initial discharge capacity, and the bonding force between the diaphragm and the bipolar current collector of the lithium ion battery in the embodiment of the present invention are increased.

[0268] Compared with Comparative Examples 3-5, the energy density of the lithium-ion batteries provided in the embodiments of the present invention is basically unchanged, the ratio of the discharge capacity after 50 cycles to the initial discharge capacity of Examples 1-2, 6, and 9-23 of the present invention increases, and the bonding force between the diaphragm and the bipolar current collector of the embodiments of the present invention increases.

[0269] It can be seen from Examples 1-4 that as the surface roughness of the bipolar current collector increases, the bonding force between the bipolar current collector and the positive and negative electrode sheets tends to increase; it can be seen from Examples 5-7 that as the ratio of the bipolar current collector in the thickness direction increases, the mass energy density of the lithium-ion battery tends to decrease, and the ratio of the discharge capacity after 50 charge and discharge cycles to the initial discharge capacity first increases and then decreases. Taking all factors into consideration, the ratio in the thickness direction should not be too large or too small; it can be seen from Examples 17-20 that as the thickness of the bipolar current collector increases, the mass energy density of the lithium-ion battery decreases, and the ratio of the capacity after 50 charge and discharge cycles to the initial discharge capacity first increases and then decreases. Taking all factors into consideration, the thickness of the bipolar current collector should not be too thick or too thin.

[0270] In summary, the performance of the lithium-ion battery of the embodiment of the present invention is better than that of the comparative example.

[0271] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A bipolar current collector comprising a porous matrix, a first metal M, and a second metal N, wherein the first metal M is present on one surface of the porous matrix, the second metal N is present on the other surface, and at least one of the first metal M and the second metal N is present inside the porous matrix; The material of the porous matrix includes at least one of a carbon material, a polymer material or a third metal; The porosity of the porous matrix is ​​20% to 90%; The electronic resistivity of the bipolar current collector in the Z direction is 2.00×10 -10 Ω·cm to 2.00×10 -4 Ω·cm, the Z-direction electronic resistivity is tested as follows: clamp the two sides of the bipolar current collector with fixed-area clamps, measure the resistance value, and then divide it by the thickness and multiply it by the plate area to obtain the value.

2. The bipolar current collector according to claim 1, wherein The carbon material includes at least one of single-walled carbon nanotube film, multi-walled carbon nanotube film, carbon felt, porous carbon film, carbon black, acetylene black, fullerene, conductive graphite or graphene.

3. The bipolar current collector according to claim 1, wherein: The polymer material includes at least one of polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polyetheretherketone, polyimide, polyamide, polyethylene glycol, polyamideimide, polycarbonate, cyclic polyolefin, polyphenylene sulfide, polyvinyl acetate, polytetrafluoroethylene, polymethylene naphthalene, polyvinylidene fluoride, polyethylene naphthalate, polypropylene carbonate, poly(vinylidene fluoride-hexafluoropropylene), poly(vinylidene fluoride-co-chlorotrifluoroethylene), silicone, vinylon, polypropylene, polyethylene, polyvinyl chloride, polystyrene, polyether nitrile, polyurethane, polyphenylene oxide, polyester, polysulfone or its derivatives.

4. The bipolar current collector according to claim 1, wherein The third metal, the first metal M, and the second metal N each independently include at least one of Cu, Al, Ni, Ti, Ag, Au, Pt, or stainless steel.

5. The bipolar current collector according to claim 1, wherein The thickness of the layer formed by the first metal M on the surface of the porous substrate is 0.95 μm to 900 μm; the thickness of the layer formed by the second metal N on the surface of the porous substrate is 0.95 μm to 900 μm.

6. The bipolar current collector according to claim 1, wherein: The bipolar current collector has a thickness of 2 μm to 1000 μm.

7. The bipolar current collector according to claim 1, wherein: The surface roughness of the bipolar current collector is 0.05 μm to 10 μm.

8. The bipolar current collector according to claim 1, wherein: The thickness ratio of the layer formed by the first metal M on the surface of the porous substrate to the layer formed by the second metal N on the surface of the porous substrate is 0.05 to 20.

9. The bipolar current collector according to claim 1, wherein: The bipolar current collector satisfies at least one of the following characteristics: (a) the bipolar current collector has a thickness of 5 μm to 50 μm; (b) the surface roughness of the bipolar current collector is 0.2 μm to 5 μm; (c) a thickness ratio of the layer formed by the first metal M on the surface of the porous substrate to the layer formed by the second metal N on the surface of the porous substrate is 0.2 to 5; (d) The electronic resistivity of the bipolar current collector in the Z direction is 2.00×10 -10 Ω·cm to 2.00×10 -6 Ω·cm; (e) The porosity of the porous matrix is ​​40% to 70%.

10. The bipolar current collector according to claim 1, wherein The bipolar current collector satisfies at least one of the following characteristics: (a) the thickness of the layer formed by the first metal M on the surface of the porous substrate is 0.40 μm to 13.33 μm; the thickness of the layer formed by the second metal N on the surface of the porous substrate is 0.40 μm to 13.33 μm; (b) the bipolar current collector has a thickness of 5 μm to 20 μm; (c) the surface roughness of the bipolar current collector is 0.5 μm to 2 μm; (d) The electronic resistivity of the bipolar current collector in the Z direction is 2.00×10 -10 Ω·cm to 2.00×10 -8 Ω·cm.

11. An electrochemical device comprising at least two electrode assemblies and the bipolar current collector according to any one of claims 1 to 10, wherein the bipolar current collector is located between the two electrode assemblies. 12 . An electronic device comprising the electrochemical device according to claim 11 .

Images