Composite current collector and preparation method thereof, negative pole piece and lithium ion battery

Abstract

The invention relates to a composite current collector and a preparation method thereof, a negative pole piece and a lithium ion battery. The composite current collector comprises a polymer layer; the first metal layers are arranged on the upper and lower surfaces of the polymer layer; the through hole penetrates through the polymer layer and the first metal layer; the second metal layer is arranged on the inner side wall of the through hole; and the lithium metal layer is filled in the through hole. The lithium metal is selectively filled in the through hole, so that the comprehensive advantages of the hole wall metal layer and the lithium layer in the hole are combined in the through hole.

Description

Technical Field

[0001] The present application relates to the field of battery technology, and in particular to a composite current collector and a preparation method thereof, a negative electrode sheet, and a lithium-ion battery. Background Art

[0002] With the continuous advancement and rapid development of science and technology, the requirements for lithium-ion batteries in various fields are also constantly increasing, especially with higher energy density and better cycle performance.

[0003] However, in traditional lithium-ion battery (LIB) structures, pure metal current collectors are typically used to support the positive and negative active materials. However, pure metal current collectors not only account for a high proportion of the mass of the lithium-ion battery, but also do not contribute to the battery capacity, which greatly hinders the improvement of the overall energy density of lithium-ion batteries. In addition, during the formation and aging stages of the battery, trace amounts of electrolyte components will continue to decompose on the surface of the negative electrode, continuously consuming active lithium to form new SEI film components, which in turn causes a decline in battery cycle performance.

[0004] Therefore, there is an urgent need to develop a new current collector to solve the problems of battery energy density and cycle performance. Summary of the Invention

[0005] Based on this, the present application provides a composite current collector and its preparation method, a negative electrode sheet, and a lithium-ion battery to solve the above technical problems.

[0006] A first aspect of the present application provides a composite current collector, comprising:

[0007] polymer layer;

[0008] a first metal layer, the first metal layer being disposed on the upper and lower surfaces of the polymer layer;

[0009] a through hole, the through hole penetrating the polymer layer and the first metal layer;

[0010] a second metal layer disposed on an inner sidewall of the through hole; and

[0011] The lithium metal layer is filled in the through hole.

[0012] In some embodiments, the thickness of the polymer layer is 1 μm to 50 μm, preferably 5 μm to 10 μm.

[0013] In some embodiments, the aspect ratio of the thickness of the polymer layer to the diameter of the through hole is 1:100 to 50:1;

[0014] Preferably, the aspect ratio of the thickness of the polymer layer to the diameter of the through hole is 1:30 to 1:1.

[0015] In some embodiments, the through-hole has a pore size of 1 μm to 100 μm, preferably 35 μm to 80 μm;

[0016] and / or the hole spacing between any adjacent through holes is 1 μm to 50 μm, preferably 8 μm to 32 μm;

[0017] and / or the hole density of through holes is 10 5 pieces / cm 2 ~10 8 pieces / cm 2 , preferably 10 6 pieces / cm 2 ~3×10 7 pieces / cm 2 .

[0018] In some embodiments, the thickness of the first metal layer and the second metal layer is 0.1-1 μm, preferably 0.2-0.8 μm.

[0019] A second aspect of the present application provides a method for preparing a composite current collector, comprising the following steps:

[0020] S1. Providing a composite layer, the composite layer comprising a polymer layer, a first metal layer, and a through hole, wherein the first metal layer is provided on the upper and lower surfaces of the polymer layer, and the through hole penetrates the polymer layer and the first metal layer;

[0021] S2, forming a second metal layer on the inner sidewall of the through hole;

[0022] S3, forming an insulating coating on the surface of the first metal layer facing away from the polymer layer to obtain a first composite structure;

[0023] S4, soaking the first composite structure in a lithium-containing electrolyte for a preset time, and then filling the through-holes with lithium metal to obtain a second composite structure;

[0024] S5. The second composite structure is placed in a first organic solvent for cleaning to remove the insulating coating, and then dried to obtain a composite current collector.

[0025] In some embodiments, the thickness of the insulating coating is 0.1 mm to 1 mm.

[0026] In some embodiments, S1 specifically comprises: punching holes at predetermined positions of the polymer layer to obtain a porous polymer layer including a plurality of through holes; forming a first metal layer on the upper and lower surfaces of the porous polymer layer to obtain a composite layer; or

[0027] A first metal layer is formed on the upper and lower surfaces of the polymer layer to obtain an intermediate composite layer; and holes are punched at preset positions of the intermediate composite layer to obtain a composite layer.

[0028] The third aspect of the present application provides a negative electrode plate, which includes the composite current collector provided in the first aspect of the present application, or a composite current collector prepared by the preparation method of the composite current collector provided in the second aspect of the present application.

[0029] A fourth aspect of the present application provides a lithium-ion battery, which includes the negative electrode sheet provided in the third aspect of the present application.

[0030] Compared with the existing technology, this application has the following beneficial effects:

[0031] The present application arranges a second metal layer on the inner wall of the through hole and fills a lithium metal layer inside the through hole, so that the through hole combines the comprehensive advantages of the hole wall metal layer and the lithium layer inside the hole. The hole wall metal layer provides a flow channel for electrons, transforming the traditional lateral surface flow of electrons into lateral surface and longitudinal flow, diversifying the flow path and enhancing the conductivity of the composite current collector; the lithium layer inside the hole provides a lithium source for the consumption of active lithium, thereby improving the energy density and cycle performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] In order to more clearly illustrate the technical solutions in the embodiments of the present application or related technologies, the following briefly introduces the drawings required for use in the embodiments or related technical descriptions. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0033] Figure 1 Schematic diagram of the structure of the composite current collector in some embodiments of the present application.

[0034] Figure 2 This is a process flow chart of the preparation method of the composite current collector in some embodiments of the present application.

[0035] Reference numerals

[0036] 1. Polymer layer; 21. First metal layer; 22. Second metal layer; 3. Through hole; 4. Lithium metal layer. DETAILED DESCRIPTION

[0037] Reference will now be made to embodiments of the present application in detail, one or more examples of which are described below. Each example is provided to illustrate, but not to limit, the present application. Indeed, it will be apparent to those skilled in the art that various modifications and variations may be made to the present application without departing from the scope or spirit of the present application. For example, features illustrated or described as part of one embodiment may be used in another embodiment to produce further embodiments.

[0038] Therefore, it is intended that this application covers such modifications and variations that fall within the scope of the appended claims and their equivalents. Other objects, features, and aspects of the present application are disclosed in or are apparent from the following detailed description. Those skilled in the art will appreciate that this discussion is merely a description of exemplary embodiments and is not intended to limit the broader aspects of the present application.

[0039] In this application, the technical features described in an open manner include closed technical solutions composed of the listed features, and also include open technical solutions containing the listed features.

[0040] In this application, when referring to numerical ranges, unless otherwise specified, the numerical ranges are considered continuous and include the minimum and maximum values of the range, as well as every value between such minimum and maximum values. Further, when a range refers to an integer, every integer between the minimum and maximum values of the range is included. In addition, when multiple ranges are provided to describe a feature or characteristic, the ranges can be combined. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges subsumed therein.

[0041] In this document, when referring to a range, if the unit is followed only by the right endpoint, it means that the units of the left and right endpoints are the same. For example, 100~150 nm means that the units of the left endpoint "100" and the right endpoint "150" are both nm (nanometers).

[0042] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0043] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0044] Unless otherwise specified, all steps of the present application may be performed sequentially or randomly, preferably sequentially. For example, a statement that a method includes steps (a) and (b) indicates that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, a statement that a method may also include step (c) indicates that step (c) may be added to the method in any order, for example, the method may include steps (a), (b), and (c), or may include steps (a), (c), and (b), or may include steps (c), (a), and (b), etc.

[0045] Unless otherwise specified, the terms "include" and "comprising" used in this application may be open-ended or closed-ended. For example, "include" and "comprising" may indicate that other components not listed may also be included or that only the listed components are included.

[0046] Unless otherwise specified, the term "or" is used in this application to be inclusive. For example, the phrase "A or B" means "A, B, or both A and B." More specifically, the condition "A or B" is satisfied if any of the following conditions are met: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0047] like Figure 1 As shown, one aspect of the present application provides a composite current collector, comprising:

[0048] polymer layer 1;

[0049] A first metal layer 21 is provided on the upper and lower surfaces of the polymer layer 1;

[0050] a through hole 3, the through hole 3 passing through the polymer layer 1 and the first metal layer 21;

[0051] A second metal layer 22 , the second metal layer 22 being disposed on the inner sidewall of the through hole 3 ; and

[0052] The lithium metal layer 4 is filled in the through hole 3 .

[0053] In some embodiments, the thickness of polymer layer 1 is 1 μm to 50 μm, including but not limited to 1 μm, 10 μm, 20 μm, 30 μm, 40 μm, and 50 μm. Furthermore, the thickness of polymer layer 1 is 5 μm to 10 μm. If the thickness of polymer layer 1 is too thin, the support strength of the composite current collector will be insufficient. If the thickness of polymer layer 1 is too thick, it will not be conducive to improving the energy density of the battery and will not conform to the development trend of lightweight batteries.

[0054] In some embodiments, the aspect ratio of the thickness of the polymer layer 1 to the diameter of the through hole 3 is (1:100) to (50:1). Furthermore, the aspect ratio of the thickness of the polymer layer 1 to the diameter of the through hole 3 is (1:30) to (1:1).

[0055] In some embodiments, the diameter of the through hole 3 is 1 μm to 100 μm, including but not limited to 1 μm, 10 μm, 20 μm, 30 μm, 40 μm, 50 μm, 80 μm, and 100 μm. Further, the diameter of the through hole 3 is 35 μm to 80 μm.

[0056] In some embodiments, the distance between any two adjacent through holes 3 is 1 μm to 50 μm, including but not limited to 1 μm, 10 μm, 20 μm, 30 μm, 40 μm, and 50 μm. Further, the distance between the through holes is 8 μm to 32 μm.

[0057] In some embodiments, the hole density of the through holes 3 is 10 5 pieces / cm 2 ~10 8 pieces / cm 2 , including but not limited to 10 5 pieces / cm 2 , 10 6 pieces / cm 2 , 10 7 pieces / cm 2 , 10 8 pieces / cm 2 Furthermore, the hole density of the through hole 3 is 10 6 pieces / cm 2 ~3×10 7 pieces / cm 2 .

[0058] In some embodiments, the thickness of the first metal layer 21 and the second metal layer 22 is 0.1 μm to 1 μm, including but not limited to 0.1 μm, 0.2 μm, 0.4 μm, 0.6 μm, 0.8 μm, and 1 μm. Further, the thickness of the first metal layer 21 and the second metal layer 22 is 0.2 μm to 0.8 μm.

[0059] In some embodiments, the first metal layer and the second metal layer have equal or different thicknesses.

[0060] In some embodiments, the thickness of the first metal layer 21 on the upper surface and the lower surface of the polymer layer 1 is equal or different.

[0061] In some embodiments, the materials of the first metal layer 21 and the second metal layer 22 are independently selected from one or more of copper, nickel, silver, zinc, titanium, alloys thereof, and stainless steel. Further, the materials of the first metal layer 21 and the second metal layer 22 are copper or nickel.

[0062] It is understandable that the present application does not particularly limit the coating method of the first metal layer 21 and the second metal layer 22. By way of example, the coating method includes but is not limited to one or more of physical vapor deposition (PVD), chemical vapor deposition (CVD), vacuum evaporation, hot dip plating, ion plating, and spray plating.

[0063] like Figure 2 As shown, the first aspect of the present application provides a method for preparing a composite current collector, comprising the following steps:

[0064] S1. Providing a composite layer; wherein the composite layer includes a polymer layer 1, a first metal layer 21, and a through hole 3, wherein the first metal layer 21 is provided on the upper and lower surfaces of the polymer layer 1, and the through hole 3 penetrates the polymer layer 1 and the first metal layer 21;

[0065] S2, forming a second metal layer 22 on the inner sidewall of the through hole 3;

[0066] S3, forming an insulating coating on the surface of the first metal layer 21 on the side facing away from the polymer layer 1 to obtain a first composite structure;

[0067] S4, soaking the first composite structure in a lithium-containing electrolyte for a preset time, and then filling the through hole 3 with lithium metal to obtain a second composite structure;

[0068] S5. The second composite structure is placed in a first organic solvent for cleaning to remove the insulating coating, and then dried to obtain a composite current collector.

[0069] In some embodiments, the material of the polymer layer 1 includes but is not limited to one or more of polyethylene (PE), polypropylene (PP), polyethylene terephthalate (PET), polyimide (PI), polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polycarbonate (PC), polyethylene naphthalate (PEN), polyphenylene sulfide (PPS), and polyetheretherketone (PEEK).

[0070] In some embodiments, step S1 is specifically:

[0071] Punching holes at predetermined positions of the polymer layer 1 to obtain a porous polymer layer including a plurality of through holes 3;

[0072] A first metal layer 21 is formed on the upper and lower surfaces of the porous polymer layer to produce a composite layer.

[0073] In some embodiments, step S1 is specifically:

[0074] forming a first metal layer 21 on the upper and lower surfaces of the polymer layer 1 to obtain an intermediate composite layer;

[0075] Punching is performed at preset positions of the middle composite layer to obtain the composite layer.

[0076] It is understood that the present application does not specifically limit the punching method and shape of the through hole 3 in step S1. The following is merely exemplary:

[0077] The punching methods include but are not limited to at least one of laser punching, chemical etching, ion beam etching, plasma etching, mechanical punching, electrochemical punching, ultrasonic punching, water jet punching, thermal punching, and photolithography punching.

[0078] The shapes of the through holes 3 include, but are not limited to, circular, rectangular, elliptical, sector-shaped, polygonal or irregular shapes, etc. The shapes of the through holes 3 can be the same or different.

[0079] It should be noted that, when the through hole 3 is non-circular in shape, the “aperture diameter” refers to the area equivalent diameter, that is, based on the area occupied by the through hole 3 , it is converted into the diameter of a circle with the same area.

[0080] It is understood that the present application does not particularly limit the specific form of the through hole 3, as long as the through hole 3 penetrates the polymer layer 1 and the first metal layer 21 so that the lithium metal can be filled throughout the entire thickness direction of the polymer layer 1 and the first metal layer 21. The following is merely an example, and the through hole penetrates the polymer layer 1 and the first metal layer 21 in an oblique, vertical, or curved manner.

[0081] In some embodiments, a femtosecond laser is used to control the aperture size by adjusting the wavelength and focus spot of the laser. Within a certain wavelength range, the smaller the laser focus spot, the smaller the aperture.

[0082] In some embodiments, the wavelength range of the femtosecond laser is 150 nm to 350 nm, and the focal length range of the focused spot is 1 mm to 500 mm. The aperture size of the through hole can be adjusted by adjusting the wavelength range and the focal length range.

[0083] It is understandable that the present application does not impose any particular limitation on the material of the insulating coating. Any existing insulating coating material can be applied to the present application as long as the overall inventive concept of the present application is met. The following is merely an illustrative description.

[0084] In some embodiments, the insulating coating is a silicone oil coating, a polyvinylidene fluoride coating, a polytetrafluoroethylene coating, or an epoxy resin coating.

[0085] In some embodiments, a silicone oil coating is formed on the surface of the first metal layer 21 facing away from the polymer layer 1 by spraying or printing.

[0086] In some embodiments, the thickness of the insulating coating is 0.1 mm to 1 mm, including but not limited to 0.1 mm, 0.2 mm, 0.4 mm, 0.6 mm, 0.8 mm, and 1 mm. Further, the thickness of the insulating coating is 0.2 mm to 0.5 mm.

[0087] In some embodiments, step S4 is specifically as follows: the first composite structure is immersed in a lithium-containing electrolyte for 3h~6h, so that the electrolyte fully infiltrates each through hole 3, and then the first metal layer 21 and the second metal layer 22 are connected to a power supply to form a circuit, and the current is controlled to be 1μA~10μA, and the electroplating time is 10 -4 s~10 4 s, so as to confine and uniformly deposit the lithium ions in the lithium-containing electrolyte on the surface of the second metal layer 22 on the inner side wall of the through hole 3 until the through hole 3 is completely filled.

[0088] Because an insulating coating is formed on the surface of the first metal layer 21, lithium metal does not grow on the surface of the first metal layer 21. Since a second metal layer 22 is formed on the inner wall of the through hole 3, the lithium metal will grow in a confined area within the through hole 3. The electroplating time is subject to the current size and the thickness of the polymer layer 1. Under a certain current, the thicker the lithium metal deposition thickness, the longer the electroplating time, until the entire through hole 3 is filled with lithium metal.

[0089] It is understandable that the present application does not specifically limit the composition of the lithium-containing electrolyte. Any existing lithium-containing electrolyte can be applied to the present application as long as it meets the overall inventive concept of the present application. The following is only used as an example.

[0090] In some embodiments, the lithium-containing electrolyte includes a lithium salt and a second organic solvent. The lithium salt includes one or more of LiPF6, LiBF4, LiClO4, LiAsF6, Li2SiF6, LiB(C6H5)4, LiCH3SO3, LiCF3SO3, LiC(SO2CF3)3, and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI).

[0091] The second organic solvent includes, but is not limited to, one or more of ethylene carbonate (EC), ethylene glycol methyl ether (EMC), dimethyl carbonate (DMC), and diethyl carbonate (DEC).

[0092] In some embodiments, the first organic solvent includes one or more of benzene, toluene, xylene, diethyl ether, and chloroalkane.

[0093] The present application selectively fills lithium metal in the through-hole 3 through the setting of a regional insulating coating, through the coordinated cooperation of the second metal layer 22, electroplating and a lithium-containing electrolyte, so that the through-hole 3 combines the comprehensive advantages of the hole wall metal layer and the lithium layer in the hole. Specifically, the hole wall metal layer provides a flow channel for electrons, transforming the traditional lateral surface flow of electrons into lateral surface and longitudinal flow, thereby diversifying the flow path and enhancing the conductivity of the composite current collector; the lithium layer in the hole provides a lithium source for the consumption of active lithium, thereby improving the energy density and cycle performance.

[0094] The third aspect of the present application provides a negative electrode plate, which includes the composite current collector provided in the first aspect of the present application, or a composite current collector prepared by the preparation method of the composite current collector provided in the second aspect of the present application.

[0095] In some embodiments, the negative electrode sheet includes a negative electrode active layer disposed on the surface of the composite current collector, and the negative electrode active layer includes a negative electrode active material, a negative electrode conductive agent, and a negative electrode binder.

[0096] The present application does not particularly limit the types of negative electrode active materials, negative electrode conductors and negative electrode binders. Without violating the inventive concept of the present application, any known negative electrode active materials, negative electrode conductors and negative electrode binders can be used in the present application.

[0097] The negative electrode active material includes but is not limited to at least one of artificial graphite, natural graphite, soft carbon, hard carbon, silicon, silicon-carbon, and silicon-oxygen.

[0098] Negative electrode conductive agents include, but are not limited to, carbon-based materials, powdered nickel or other metal particles, or conductive polymers. Carbon-based materials may include, for example, carbon black, graphite, super-P, acetylene black (such as KETCHEN™ black or DENKA™ black), carbon fibers and nanotubes, graphene, and the like. Examples of conductive polymers include polyaniline, polythiophene, polyacetylene, polypyrrole, poly(3,4-ethylenedioxythiophene) polystyrene sulfonate, and the like.

[0099] The negative electrode binder includes but is not limited to any one or a combination of at least two of polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polypropylene (PP), polyvinyl chloride (PVC), polystyrene (PS), polyoxymethylene (POM), polycarbonate (PC), polyamide (PA), acrylic plastics, other polyolefins and their copolymers, polysulfone, polyphenylene ether (PPO), styrene-butadiene rubber (SBR) and carboxymethyl cellulose (CMC).

[0100] A fourth aspect of the present application provides a lithium-ion battery, which includes the negative electrode sheet provided in the third aspect of the present application.

[0101] In some embodiments, a lithium-ion battery includes a positive electrode sheet, which includes a positive electrode current collector and a positive electrode active layer disposed thereon, and the positive electrode active layer includes a positive electrode active material, a positive electrode conductive agent, and a positive electrode binder.

[0102] The present application does not particularly limit the types of positive electrode active materials, positive electrode conductors and positive electrode binders. Any known positive electrode active materials, positive electrode conductors and positive electrode binders can be used in the present application without violating the inventive concept of the present application.

[0103] The positive electrode active material includes, but is not limited to, one of a layered oxide cathode, a spinel cathode, or a polyanion cathode; for example, the layered oxide positive electrode active material (e.g., a rock salt layered oxide) comprises one or more lithium-based positive electrode electroactive materials selected from the group consisting of LiCoO2 (LCO), LiNi x Mn y Co 1-x-y O2 (where 0≤x≤1 and 0≤y≤1), LiNi 1-x- y Cox Al y O2 (where 0≤x≤1 and 0≤y≤1), LiNi x Mn 1-x O2 (where 0≤x≤1), and Li 1+x MO2 (wherein M is one of Mn, Ni, Co and Al and 0≤x≤1); the spinel positive electrode active material comprises one or more lithium-based positive electrode active materials selected from the group consisting of LiMn2O4 (LMO) and LiNi x Mn 1.5 O4. The olivine-type positive electrode active material includes one or more lithium-based positive electrode active materials LiMPO4 (wherein M is at least one of Fe, Ni, Co and Mn).

[0104] Positive electrode conductive agents include, but are not limited to, carbon-based materials, powdered nickel or other metal particles, or conductive polymers. Carbon-based materials may include, for example, carbon black, graphite, acetylene black (e.g., KETCHEN™ black or DENKA™ black), carbon fibers and nanotubes, graphene, and other particles. Examples of conductive polymers include polyaniline, polythiophene, polyacetylene, polypyrrole, and the like.

[0105] Positive electrode binders include but are not limited to polytetrafluoroethylene (PTFE), sodium carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), polyvinylidene fluoride (PVDF), nitrile rubber (NBR), styrene-ethylene-butylene-styrene copolymer (SEBS), styrene-butadiene-styrene copolymer (SBS), lithium polyacrylate (LiPAA), sodium polyacrylate (NaPAA), sodium alginate, lithium alginate and combinations thereof.

[0106] In some embodiments, the lithium-ion battery further includes a separator for separating the positive electrode sheet from the negative electrode sheet and providing a migration path for lithium ions.

[0107] It will be appreciated that the separator of the present application can use any separator without particular limitation, as long as it is a separator commonly used in lithium ion batteries. In particular, a separator having excellent wettability to an electrolyte and low resistance to ion movement in an electrolyte is preferred. Specifically, a porous polymer film can be used, for example, a porous polymer film made of a polyolefin polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer and an ethylene / methacrylate copolymer, or a laminated structure having two or more layers thereof. Furthermore, 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.

[0108] It is understandable that the present application does not specifically limit the method for preparing the battery. Without violating the inventive concept of the present application, any known process method for preparing the battery can be applied to the present application.

[0109] The fifth aspect of the present application provides an electrical device, comprising the lithium-ion battery provided in the fourth aspect of the present application, wherein the lithium-ion battery is used to provide electrical energy to the electrical device.

[0110] The present application will be further described below with reference to specific embodiments and comparative examples.

[0111] Example 1

[0112] Preparation of composite current collector:

[0113] S1. Punch the PET polymer layer 1 under laser irradiation to obtain through holes 3 penetrating the polymer layer 1. The thickness of the polymer layer 1 is 5 μm. A femtosecond laser with a wavelength of 265 nm and a focal length of 10 mm is used. The aperture of the through holes 3 is 35 μm, the hole spacing is 10 μm, and the hole density is 10. 6 pieces / cm 2 , aspect ratio is 1:7.

[0114] S2. Form a first copper layer on the upper and lower surfaces of the polymer layer 1 and a second copper layer on the inner sidewall of the through hole 3 by physical evaporation. The thickness of the first copper layer and the second copper layer is 0.8 μm.

[0115] S3. Spray a silicone oil coating on the surface of the first copper layer facing away from the polymer layer 1 to produce a first composite structure. The thickness of the silicone oil coating is 0.5 mm.

[0116] S4. After soaking the first composite structure in a lithium-containing electrolyte for 5 hours, lithium metal is filled into the through-hole 3 by electroplating to produce a second composite structure. The lithium-containing electrolyte comprises: a lithium hexafluorophosphate (LiPF6) concentration of 1 mol / L, a solvent ratio of EC:EMC:DMC (1:1:1), an electroplating current of 1 μA, and an electroplating time of 35.7 seconds.

[0117] S5. The second composite structure is placed in toluene for cleaning to remove the silicone oil coating, and then dried to obtain a composite current collector.

[0118] Preparation of negative electrode sheet:

[0119] Based on the total weight of silicon carbon & graphite, SP, SWCNTs, MWCNTs, and PVDF, a negative electrode active layer slurry was prepared according to the ratio of silicon carbon & graphite: SP: SWCNTs: MWCNTs: PVDF = 95.1%: 0.5%: 0.2%: 0.2%: 4% (mass percentage). The solid content of the negative electrode active layer slurry was 32%, the viscosity was 5500 mPa·s, and the fineness was 33 μm.

[0120] The negative electrode active layer slurry is coated on the surface of the composite current collector through a coating die of a coating machine to form a negative electrode active layer on the surface of the composite current collector, and then baked to obtain a negative electrode sheet, wherein the double-sided surface density of the negative electrode sheet is 150 g / m 2 The compaction density of the negative electrode active layer is 1.1 g / cm 3 .

[0121] Preparation of positive electrode sheet:

[0122] A positive electrode active layer slurry was prepared by mixing NCM811, SWCNTs, MWCNTs, and PVDF in a mass ratio of 97.3%:0.2%:0.8%:1.7%. The positive electrode active layer slurry had a solid content of 66%, a viscosity of 6200 mPa·s, and a fineness of 30 μm.

[0123] The positive electrode sheet is prepared by coating the positive electrode active layer slurry on the surface of aluminum foil and baking it. The double-sided surface density of the positive electrode sheet is 550 g / m 2 The compaction density of the positive electrode active layer is 3.45 g / cm 3 .

[0124] Diaphragm: PE film.

[0125] The electrolyte is lithium hexafluorophosphate (LiPF6) with a concentration of 1 mol / L, and the solvent is EC, EMC and DMC with a molar ratio of 1:1:1.

[0126] Preparation of lithium-ion batteries

[0127] The positive electrode sheet, the negative electrode sheet and the separator are wound / stacked to form a battery cell, the electrolyte is injected into the battery cell, and the battery cell is vacuum packaged, allowed to stand, and subjected to a formation process to prepare a lithium-ion battery.

[0128] Example 2

[0129] The difference between this embodiment and embodiment 1 is that the pore size of the polymer layer 1 is 1 μm, and the aspect ratio of the thickness of the polymer layer 1 to the pore size of the through hole 3 is 5:1.

[0130] Example 3

[0131] The difference between this embodiment and embodiment 1 is that the pore size of the polymer layer 1 is 50 μm, and the aspect ratio of the thickness of the polymer layer 1 to the pore size of the through hole 3 is 1:10.

[0132] Example 4

[0133] The difference between this embodiment and embodiment 1 is that the pore size of the polymer layer 1 is 80 μm, and the aspect ratio of the thickness of the polymer layer 1 to the pore size of the through hole 3 is 1:16.

[0134] Example 5

[0135] The difference between this embodiment and embodiment 1 is that the pore size of the polymer layer 1 is 100 μm, and the aspect ratio of the thickness of the polymer layer 1 to the pore size of the through hole 3 is 1:20.

[0136] Example 6

[0137] The difference between this embodiment and embodiment 1 is that the thickness of the polymer layer 1 is 1 μm, and the aspect ratio of the thickness of the polymer layer 1 to the diameter of the through hole 3 is 1:35.

[0138] Example 7

[0139] The difference between this embodiment and embodiment 1 is that the thickness of the polymer layer 1 is 10 μm, and the aspect ratio of the thickness of the polymer layer 1 to the diameter of the through hole 3 is 2:7.

[0140] Example 8

[0141] The difference between this embodiment and embodiment 1 is that the thickness of the polymer layer 1 is 20 μm, and the aspect ratio of the thickness of the polymer layer 1 to the diameter of the through hole 3 is 4:7.

[0142] Example 9

[0143] The difference between this embodiment and embodiment 1 is that the thickness of the polymer layer 1 is 40 μm, and the aspect ratio of the thickness of the polymer layer 1 to the diameter of the through hole 3 is 8:7.

[0144] Example 10

[0145] The difference between this embodiment and embodiment 1 is that the thickness of the polymer layer 1 is 50 μm, and the aspect ratio of the thickness of the polymer layer 1 to the diameter of the through hole 3 is 10:7.

[0146] Example 11

[0147] The difference between this embodiment and embodiment 1 is that the pore size of the polymer layer 1 is 0.1 μm, and the aspect ratio of the thickness of the polymer layer 1 to the pore size of the through hole 3 is 50:1.

[0148] Example 12

[0149] The difference between this embodiment and embodiment 1 is that the pore size of the polymer layer 1 is 200 μm, and the aspect ratio of the thickness of the polymer layer 1 to the pore size of the through hole 3 is 1:40.

[0150] Example 13

[0151] The difference between this embodiment and embodiment 1 is that the thickness of the polymer layer 1 is 0.1 μm, and the aspect ratio of the thickness of the polymer layer 1 to the diameter of the through hole 3 is 1:350.

[0152] Example 14

[0153] The difference between this embodiment and embodiment 1 is that the thickness of the polymer layer 1 is 150 μm, and the aspect ratio of the thickness of the polymer layer 1 to the diameter of the through hole 3 is 30:7.

[0154] Comparative Example 1

[0155] The difference between this comparative example and Example 1 is that the polymer layer 1 is not punched, and the thickness of the copper layer on the surface of the polymer layer 1 is 0.8 μm.

[0156] Comparative Example 2

[0157] The difference between this comparative example and Example 1 is that the through hole 3 is not filled, and the thickness of the copper layer on the surface of the polymer layer 1 and the inner wall of the through hole 3 is 0.8 μm.

[0158] Comparative Example 3

[0159] The difference between this comparative example and Example 1 is that the through hole 3 is filled with metal copper (the inner sidewall and the inside of the through hole 3 are both copper).

[0160] Comparative Example 4

[0161] The difference between this comparative example and Example 1 is that the through hole 3 is filled with metal nickel (the inner sidewall of the through hole 3 is copper and the hole is filled with nickel.

[0162] Test Case

[0163] (1) Energy density test:

[0164] The battery after filling and standing is subjected to the formation process: charged to 3V at 0.05C, charged to 3.4V at 0.1C, and charged to 3.9V at 0.2C, and then charged to 4.3V at 0.33C constant current and constant voltage. The battery is then subjected to the capacity separation process: discharged at a constant current of 0.33C to a cut-off voltage of 2.5V, and the average voltage and capacity of the battery are read from the capacity separation device.

[0165]

[0166] Where, Em is the mass energy density of the battery, Wh / kg; Qd is the discharge capacity of the battery, mAh; --The average discharge voltage of the battery, V; m--the mass of the battery after secondary sealing, g.

[0167] (2) Capacity retention test (800 cycles)

[0168] The battery was subjected to a cycle performance test in a biochemical incubator at a temperature of 25±3°C, with constant current and constant voltage charging at a charging rate of 0.5C, constant current discharge at a discharge rate of 1C, and a charge and discharge cut-off voltage of 2.500-4.300V. The discharge capacity was recorded each time.

[0169]

[0170] Where Q r --Battery capacity retention rate,%;Q n --The discharge capacity of the battery in a certain cycle, mAh; Q 1st --Discharge capacity of the battery during the first cycle, in mAh. See Table 1 below for the results.

[0171] Table 1

[0172]

[0173] From the comparison of Examples 1-14, it can be seen that when the thickness of the polymer layer and the pore size are relatively moderate, the battery performance is the best. Since the density of lithium is lower than that of PET (lithium density is 0.534 g / cm 3 PET density 1.38g / cm 3 PET is more than twice as heavy as lithium. The composite current collector will be lighter and have higher energy density. At the same time, more active lithium will be available for the SEI film during the formation phase and consumed by side reactions during the aging phase, contributing to improved battery energy density and cycle life.

[0174] Compared with Example 1, Example 2 reduces the pore size. As the pore size becomes smaller, the energy density and cycle capacity retention rate both decrease to varying degrees. This may be related to the weight of the composite current collector and the reduction in active lithium consumed by the SEI film in the formation stage and the side reactions in the aging stage.

[0175] Compared with Example 1, Examples 3 to 5 have increased pore size. As the pore size becomes larger, the energy density and cycle capacity retention rate decrease to varying degrees. This may be related to the side reaction between excessive lithium metal and battery moisture and the instability of the composite current collector structure.

[0176] Compared with Example 1, Example 6 reduces the thickness of the polymer layer, that is, the lithium metal layer in the pore becomes thinner, and the energy density and cycle capacity retention rate are reduced to varying degrees. This may be related to the thinning of the lithium metal layer, which results in less active lithium consumed by the SEI film in the formation stage and the side reactions in the aging stage, and is not conducive to improving the initial coulombic efficiency and cycle life of the battery.

[0177] Compared with Example 1, Examples 7 to 10 increase the thickness of the polymer layer, that is, the lithium metal layer in the pore becomes thicker, and the energy density and cycle capacity retention rate are reduced to varying degrees. This may be related to the lengthening of the longitudinal conduction diffusion path of electrons, the increase in internal resistance, and the fact that the thick polymer layer is not conducive to rolling processing.

[0178] Compared with Example 1, in Examples 11-12, the pore diameter exceeds the range of 1μm~100μm, and the energy density and cycle capacity retention rate both decrease to a large extent. When the pore diameter is too large, the specific gravity of the PET skeleton is too small, which may cause the composite current collector structure to be unstable. When the pore diameter is too small, the longitudinal electron conduction area becomes smaller, which will cause the internal resistance of the composite current collector to increase.

[0179] Compared with Example 1, in Examples 13-14, the thickness of the polymer layer exceeds the range of 1μm~50μm, and the energy density and cycle capacity retention rate are greatly reduced. When the polymer layer is too thick, the internal resistance increases significantly, and it is not conducive to processing during electrode rolling; when the polymer layer is too thin, the bonding reliability between the surface copper layer and the polymer layer will decrease, and even some areas will fall off, which directly leads to a decrease in the battery cycle life.

[0180] Compared with Example 1, Comparative Example 1 is a composite current collector in which the polymer layer is not perforated, and has the lowest energy density and cycle capacity retention rate.

[0181] Compared with Example 1, Comparative Examples 2 to 4 are composite current collectors with porous structures in which the pores are not filled or filled with non-lithium metal (copper metal, nickel metal), respectively. The energy density and cycle capacity retention rate are greatly reduced. This is mainly because there is no active lithium to be used for the SEI film in the formation stage and the active lithium consumption in the side reactions in the aging stage.

[0182] Among them, when the through hole is filled with copper metal, in the case of a large pore size, the density of copper is higher than that of lithium (copper density is 8.96g / cm 3 , lithium density 0.534g / cm 3 ,), the weight of the composite current collector will increase significantly, which will cause the energy density to decrease. Therefore, the lithium filled in Example 1 has a higher energy density than copper.

[0183] When the through-hole is not filled with copper metal or is not filled, if active particles enter the through-hole and the surface of the hole is covered by other active particles or other substances, the ion diffusion rate of the active particles in the hole will be greatly reduced (although the electronic conduction is not affected by the metal layer on the hole wall). At this time, the active particles in the hole are approximately "islands", which will increase polarization and even inactivation (no contact with the electrolyte). At the same time, the active particles in the hole may deposit lithium in the hole due to uneven ion diffusion, and the formed lithium dendrites have the risk of piercing the diaphragm and forming a short circuit. In addition, the negative electrode expands and contracts during charging and discharging, especially the silicon-containing system, which may crush the thin copper layer on the hole wall, resulting in a decrease in the ability to conduct electrons. Moreover, the polymer support layer may deform after repeated expansion and contraction, which will cause the contact internal resistance to increase. Therefore, lithium has a better ion transmission path than copper, reducing the risk of lithium deposition and cycle life reduction.

[0184] The technical features of the above embodiments can be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0185] The above embodiments merely illustrate several implementation methods of the present application. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent application. It should be noted that a person of ordinary skill in the art may make various modifications and improvements without departing from the spirit of the present application, all of which fall within the scope of protection of the present application. Therefore, the scope of protection of the present patent application shall be determined by the appended claims.

Claims

1. A composite current collector, characterized in that: include: polymer layer; a first metal layer, the first metal layer being disposed on the upper and lower surfaces of the polymer layer; a through hole, the through hole penetrating the polymer layer and the first metal layer; a second metal layer, the second metal layer being disposed on an inner sidewall of the through hole; as well as A lithium metal layer is filled in the through hole.

2. The composite current collector according to claim 1, characterized in that The thickness of the polymer layer is 1 μm to 50 μm, preferably 5 μm to 10 μm.

3. The composite current collector according to claim 1, wherein: The aspect ratio of the thickness of the polymer layer to the aperture of the through hole is 1:100 to 50:1; Preferably, the aspect ratio of the thickness of the polymer layer to the aperture of the through hole is 1:30 to 1:

1.

4. The composite current collector according to claim 1, characterized in that The through hole has a pore diameter of 1 μm to 100 μm, preferably 35 μm to 80 μm; and / or the hole spacing between any adjacent through holes is 1 μm to 50 μm, preferably 8 μm to 32 μm; And / or the hole density of the through hole is 10 5 pieces / cm 2 ~10 8 pieces / cm 2 , preferably 10 6 pieces / cm 2 ~3×10 7 pieces / cm 2 .

5. The composite current collector according to claim 1, characterized in that The thickness of the first metal layer and the second metal layer is 0.1-1 μm, preferably 0.2-0.8 μm.

6. A method for preparing a composite current collector, characterized in that: The following steps are involved: S1. Providing a composite layer; wherein the composite layer includes a polymer layer, a first metal layer, and a through hole, wherein the first metal layer is provided on the upper and lower surfaces of the polymer layer, and the through hole penetrates the polymer layer and the first metal layer; S2, forming a second metal layer on the inner sidewall of the through hole; S3, forming an insulating coating on a surface of the first metal layer facing away from the polymer layer to obtain a first composite structure; S4, soaking the first composite structure in a lithium-containing electrolyte for a preset time, and then filling the through-hole with lithium metal to obtain a second composite structure; S5. The second composite structure is placed in a first organic solvent for cleaning to remove the insulating coating, and then dried to obtain a composite current collector.

7. The method for preparing a composite current collector according to claim 6, wherein: The thickness of the insulating coating is 0.1 mm to 1 mm.

8. The method for preparing a composite current collector according to claim 6, wherein: The step S1 specifically comprises: punching holes at predetermined positions of the polymer layer to obtain a porous polymer layer including a plurality of through holes; forming a first metal layer on the upper and lower surfaces of the porous polymer layer to obtain a composite layer; or, A first metal layer is formed on the upper and lower surfaces of the polymer layer to obtain an intermediate composite layer; and holes are punched at preset positions of the intermediate composite layer to obtain a composite layer.

9. A negative electrode plate, characterized in that: The negative electrode plate comprises the composite current collector according to any one of claims 1 to 5, or a composite current collector prepared by the method for preparing the composite current collector according to any one of claims 6 to 8.

10. A lithium ion battery, characterized in that: The lithium-ion battery comprises the negative electrode sheet according to claim 9.

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