CN115966704A

CN115966704A - Composite current collector and preparation method thereof, lithium battery and power utilization device

Info

Publication number: CN115966704A
Application number: CN202310006602.7A
Authority: CN
Inventors: 朱中亚; 王帅; 夏建中; 李学法; 张国平
Original assignee: Yangzhou Nanopore Innovative Materials Technology Ltd
Current assignee: Yangzhou Nanopore Innovative Materials Technology Ltd
Priority date: 2023-01-04
Filing date: 2023-01-04
Publication date: 2023-04-14

Abstract

The application relates to the technical field of lithium batteries, in particular to a composite current collector, a preparation method thereof, a lithium battery and an electric device. The problem that a polymer film and a metal layer of a composite current collector in the related technology are easy to separate and are not beneficial to normal use of the composite current collector is solved. A composite current collector, comprising: the base layer comprises a first surface and a second surface which are arranged oppositely along the thickness direction of the base layer, and the material of the base layer comprises a polymer material; the first modification layer is arranged on the first surface of the substrate layer, and the material of the first modification layer comprises one or more of silicon oxycarbide, titanium oxycarbide and aluminum oxycarbide nano materials; the first metal layer is arranged on the surface, far away from the base layer, of the first modified layer. The method is used for preparing the lithium battery.

Description

Composite current collector and preparation method thereof, lithium battery and power utilization device

Technical Field

The application relates to the technical field of lithium batteries, in particular to a composite current collector, a preparation method thereof, a lithium battery and an electric device.

Background

At present, lithium batteries are increasingly developed towards high energy density, high volume utilization and high safety.

Compare with traditional pure metal mass flow body, polymer membrane in the compound mass flow body has tensile strength height, soft texture, cladding material are thin, the quality is light, the good advantage of internal insulation, on the one hand, the burr is difficult to appear in the compound mass flow body, even if the burr also can be because soft texture, cladding material are thin pierces through the possibility of diaphragm less, and can prevent the inside short circuit of battery well, promote the security of battery. On the other hand, the energy density per unit weight of the composite current collector is higher under the same thickness. In yet another aspect, the thickness of the composite current collector may be reduced, thereby allowing for higher volumetric energy density.

However, the difference between the surface structures and the chemical environments of the polymer film and the metal layer used in the current composite current collector results in a weak adhesion force after the two are combined, and further the separation of the polymer film and the metal layer is easy to occur in the use process of the composite current collector, which affects the normal use of the composite current collector.

Therefore, there is a need to develop a composite current collector capable of effectively improving the adhesion property of the polymer film and the metal layer.

Disclosure of Invention

Based on this, the application provides a composite current collector, a preparation method thereof, a lithium battery and an electric device, and is used for solving the problems that in the related art, a polymer film and a metal layer of the composite current collector are easy to separate and are not beneficial to normal use of the composite current collector.

In a first aspect, there is provided a composite current collector comprising:

the substrate layer comprises a first surface and a second surface which are arranged oppositely along the thickness direction of the substrate layer, and the material of the substrate layer comprises a polymer material;

the first modification layer is arranged on the first surface of the substrate layer, and the material of the first modification layer comprises one or more of silicon oxycarbide, titanium oxycarbide and aluminum oxycarbide nano materials;

the first metal layer is arranged on the surface, far away from the base layer, of the first modified layer.

In one possible embodiment of the first aspect, the lattice structure of the crystal of the first modification layer near the surface of the first metal layer is doped with metal atoms contained in the first metal layer.

In one possible embodiment of the first aspect, the atoms of the first modified layer near the surface of the substrate layer are covalently bonded to the substrate layer.

In one possible embodiment of the first aspect, the molar content of oxygen atoms of the surface of the first modified layer facing away from the substrate layer is 10% to 50%.

In one possible embodiment of the first aspect, the average size of the grains of the surface of the first modified layer facing away from the base layer is 50 to 88nm.

In one possible embodiment of the first aspect, the surface tension of the first modified layer away from the surface of the base layer is 42 to 57mN/m.

In one possible embodiment of the first aspect, the surface roughness of the first modified layer away from the surface of the base layer is 75 to 125nm.

In one possible embodiment of the first aspect, the first modified layer has a thickness of 100 to 200nm.

In one possible embodiment of the first aspect, the base layer has a thickness of 2 to 20 μm.

In one possible embodiment of the first aspect, the polymeric material comprises one or more of polypropylene, polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polyimide, polypropylene, polyvinyl chloride, polyvinylidene fluoride, polytetrafluoroethylene, polyphenylene sulfide, polyphenylene oxide, polystyrene, and polyamide.

In a possible implementation manner of the first aspect, the method further includes: a second metal layer and a second modified layer;

the second modified layer is arranged on the second surface of the substrate layer, the second metal layer is arranged on the surface, far away from the substrate layer, of the second modified layer, and the material and/or the surface structure of the second modified layer are defined as the first modified layer.

In a possible implementation manner of the first aspect, the method further includes: a first protective layer and/or a second protective layer;

the first protective layer is arranged on the surface of the first metal layer far away from the basal layer, and the second protective layer is arranged on the surface of the second metal layer far away from the basal layer.

In one possible embodiment of the first aspect, the thickness of the first protective layer is not more than 1/10 of the thickness of the first metal layer; the thickness of the second protective layer is not more than 1/10 of the thickness of the second metal layer.

In one possible embodiment of the first aspect, the first protective layer and the second protective layer have the same or different thicknesses and are each independently 10 to 150nm.

In one possible embodiment of the first aspect, the first metal layer has a thickness of 500 to 2000nm.

In a second aspect, there is provided a lithium battery comprising:

is a composite current collector as described in the first aspect.

In a third aspect, an electric device is provided, which comprises the lithium battery of the second aspect.

In a fourth aspect, a method for preparing a composite current collector is provided, including:

providing a substrate layer, wherein the material of the substrate layer comprises a polymer material;

forming a first modification layer on a first surface of the substrate layer along the thickness direction of the substrate layer, wherein the material of the first modification layer comprises one or more of silicon oxycarbide, titanium oxycarbide and aluminum oxycarbide nano materials;

and forming a first metal layer on the surface of the first modified layer far away from the substrate layer.

In one possible embodiment of the fourth aspect, the first modified layer is formed on the first surface of the base layer in the thickness direction thereof by a plasma-assisted chemical vapor deposition method.

In one possible embodiment of the fourth aspect, the plasma-assisted chemical vapor deposition process uses a RF generator with a frequency of 10-15 MHz and a power of 100-300W.

In one possible embodiment of the fourth aspect, the reactive gas used in the plasma-assisted chemical vapor deposition process comprises: the gas source comprises an oxygen source, a carbon source and an X element gas source, wherein X comprises one or more of silicon, titanium and aluminum, and the carbon source is small molecular alkane such as methane, ethane, propane and the like.

In a possible implementation manner of the fourth aspect, during the reaction process, a plasma gas source is firstly introduced into the plasma-assisted chemical vapor deposition apparatus, and then a reaction gas is introduced into the plasma-assisted chemical vapor deposition apparatus;

wherein, the input of the plasma gas source makes the pressure in the plasma auxiliary chemical vapor deposition device be 10-30 mTorr, the input of the reaction gas makes the pressure in the plasma auxiliary chemical vapor deposition device be 35-50 mTorr, the flow ratio of the oxygen element gas source, the carbon element gas source and the X element gas source satisfies: the ratio of the total molar amount of oxygen element and carbon element contained in the oxygen element gas source and the carbon element gas source to the total molar amount of the X element is 2.

In one possible embodiment of the fourth aspect, the reaction time is 2 to 20min.

Compared with the prior art, this application has following beneficial effect:

by arranging the first modification layer on the first surface of the base layer, because the material of the first modification layer comprises one or more of silicon oxycarbide, titanium oxycarbide and aluminum oxycarbide nano materials, compared with the prior art in which separation between the base layer and the first metal layer is easy to occur due to the difference of the surface structure, the chemical environment and the like between the base layer and the first metal layer, on one hand, atoms in the first modification layer can form covalent bonds with the polymer material in the base layer for bonding, for example, the silicon oxycarbide nano materials form C-O-Si bonds with the polymer material, so that the bonding firmness of the first modification layer and the base layer can be improved; on the other hand, the surface of the first modified layer, which is far away from the base layer, can be connected with the first metal layer in a physical and/or chemical mode, so that the connection firmness of the first metal layer and the base layer can be improved, and the problems that the base layer and the first metal layer are easy to separate and are not beneficial to normal use of the composite current collector in the related technology are solved.

In addition, one or more of silicon oxycarbide, titanium oxycarbide and aluminum oxycarbide nano materials are used as the first modified layer, the first modified layer has conductivity, and when the first metal layer is formed on the surface of the first modified layer, the formation of hole defects in the composite current collector (such as the first metal layer, the first modified layer and the substrate layer) caused by static electricity generated on the surface of the first modified layer can be prevented, so that the product yield is improved, the compactness of the first metal layer can be further improved by reducing the hole defects, and the combination firmness of the first metal layer and the first modified layer is further improved.

Drawings

Fig. 1 is a schematic cross-sectional structural view of a composite current collector provided in an embodiment of the present application;

FIG. 2 is a cross-sectional infrared spectrum of the polymer films and modification layers of example 1 and comparative example 1 provided in the examples herein;

fig. 3 is a schematic flow chart of a method for manufacturing a composite current collector according to an embodiment of the present disclosure;

FIG. 4 is an XPS spectrum of cross sections of polymer films of example 1 and comparative example 1 as provided in the examples herein;

fig. 5 is an EDS test chart of a cross section of the composite current collector of example 1 provided in an example of the present application.

Detailed Description

The present application will be described in further detail with reference to specific examples. This application may be embodied in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete.

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein in the description of the present application is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. As used herein, the term "and/or" includes any and all combinations of one or more of the associated listed items.

Based on the above technical problem, some embodiments of the present application provide a composite current collector 10, as shown in fig. 1, including: a base layer 1, a first metal layer 2 and a first modified layer 3. The substrate layer 1 comprises a first surface 11 and a second surface 12 which are arranged oppositely along the thickness direction, and the material of the substrate layer 1 comprises a polymer material. The first metal layer 2 is disposed on the first surface 11 of the base layer 1. The first modification layer 3 is arranged on the first surface of the substrate layer 1, and the material of the first modification layer 3 comprises one or more of silicon oxycarbide, titanium oxycarbide and aluminum oxycarbide nano materials; the first metal layer 2 is disposed on a surface of the first modified layer 3 away from the base layer 1.

In some embodiments, as shown in fig. 1, the composite current collector 10 further comprises: a second metal layer 4 and a second modified layer 5. The second modified layer 5 is disposed on the second surface 12 of the substrate layer 1, the second metal layer 4 is disposed on the surface of the second modified layer 5 away from the substrate layer 1, and the material and/or surface structure of the second modified layer 5 is defined as the first modified layer 3. In this way, the same material and/or surface structure as the first modified layer 3 can be obtained. For example, in some embodiments, the materials of the first modification layer 3 and the second modification layer 5 each include one or more of silicon oxycarbide, titanium oxycarbide, and aluminum oxycarbide nanomaterials, and the average size of crystal grains and the surface roughness of the surfaces of the first modification layer 3 and the second modification layer 5 away from the substrate layer 1 are the same. The first modified layer 3 and the second modified layer 5 can be prepared by the same process conditions. In the following embodiments, the present application will be described in detail by taking the first metal layer 2 and the first modified layer 3 as examples, and the description of the second metal layer 4 may refer to the description of the first metal layer 2 below.

The silicon oxycarbide nano material, the titanium oxycarbide nano material and the aluminum oxycarbide nano material refer to silicon oxycarbide, titanium oxycarbide and aluminum oxycarbide compounds with the size of nanometer magnitude. Thus, on the one hand, the first modification layer 3 comprising silicon oxycarbide nanomaterial, titanium oxycarbide nanomaterial, and aluminum oxycarbide nanomaterial is able to bond well with the polymer material because: the atoms (e.g., oxygen atoms) in the first modified layer 3 can form covalent bonds with the polymer material to bond, so that the bonding strength of the first modified layer 3 to the substrate layer 1 can be improved. On the other hand, the first modified layer 3 may be a nano-film, the surface of the first modified layer, which is far away from the substrate layer 1, is formed by combining nano-particles (or crystal grains), and has a certain roughness, and the surface roughness of the first modified layer 3 can be adjusted by adjusting the size of the nano-particles, so that the bonding firmness of the first modified layer 3 and the first metal layer 2 can be adjusted. On the other hand, under the condition that the lattice structure of the crystal of the first modification layer 3 on the surface far away from the substrate layer 1 is similar to the metal lattice structure of the first metal layer 2, for example, the silicon oxycarbide lattice structure and the metal lattice structure are both face-centered cubic lattice structures, which is beneficial for the metal lattice of the first metal layer 2 to be embedded in the lattice of the first modification layer 3 on the surface far away from the substrate layer 1, so that the combining firmness of the first modification layer 3 and the first metal layer can be further improved, and the bonding capacity of the first metal layer 2 and the substrate layer 1 can be further improved. On the other hand, for the silicon oxycarbide nanomaterial, the titanium oxycarbide nanomaterial, and the aluminum oxycarbide nanomaterial, by controlling the number of oxygen atoms on the surface of the first modification layer 3 away from the substrate layer 1, the surface tension of the surface of the first modification layer 3 away from the substrate layer 1 can be adjusted, and the metal atoms and the oxygen atoms on the surface of the first modification layer 3 can generate interaction force, such as forming metal-O bonds, so that the bonding capability of the first modification layer 3 and the first metal layer 2 can be improved, the bonding capability of the first metal layer 2 and the substrate layer 1 can be further improved, and finally, the bonding firmness of the first metal layer 2 and the substrate layer 1 can be improved.

In summary, by forming the first modification layer 3 on the first surface of the substrate layer 1, since the material of the first modification layer 3 includes one or more of silicon oxycarbide, titanium oxycarbide, and aluminum oxycarbide nanomaterials, on one hand, atoms in the first modification layer 3 can form covalent bonds with the polymer material in the substrate layer 1 to bond, for example, the silicon oxycarbide nanomaterials form C-O-Si bonds with the polymer material, and the bonding firmness of the first modification layer 3 and the substrate layer 1 can be improved, compared with the related art in which the substrate layer 1 and the first metal layer 2 are easily separated due to the difference between the surface structure, the chemical environment, and the like between the substrate layer 1 and the first metal layer 2; on the other hand, the surface of the first modified layer 3, which is far away from the substrate layer 1, can be connected with the first metal layer 2 in a physical and/or chemical manner, so that the connection firmness of the first metal layer 2 and the substrate layer 1 can be improved, and the problems that the substrate layer 1 and the first metal layer 2 are easily separated and are not beneficial to the normal use of the composite current collector in the related art are solved.

In addition, one or more of silicon oxycarbide, titanium oxycarbide and aluminum oxycarbide nano materials are used as the first modified layer 3, the first modified layer 3 has conductivity, when the first metal layer 2 is formed on the surface of the first modified layer 3, static electricity generated on the surface of the first modified layer 3 can be prevented from forming a hole defect in a composite current collector (such as the first metal layer, the first modified layer and the substrate layer), the product yield is improved, the compactness of the first metal layer 2 can be further improved due to the reduction of the hole defect, and the combination firmness of the first metal layer 2 and the first modified layer 3 is further improved.

In some embodiments, the lattice structure of the crystal of the first modification layer 3 near the surface of the first metal layer 2 is doped with metal atoms included in the first metal layer 2.

In these embodiments, the material of the first modification layer 3 may include silicon oxycarbide nanomaterial, the lattice structure of the silicon oxycarbide nanomaterial may be a face-centered cubic lattice structure, and the lattice structures of metals such as aluminum and copper used in the first metal layer 2 are all face-centered cubic structures, so that the lattice structure of the crystal of the first modification layer 3 on the surface far away from the substrate layer 1 and the lattice structure of the first metal layer 2 are easily engaged with each other, so that the lattice structure of the crystal of the first modification layer 3 on the surface near the first metal layer 2 is doped with metal atoms included in the first metal layer 2, and the above characteristics can be characterized by performing metal element line scanning on the cross section of the first modification layer 3 and the first metal layer 2 by using EDS (Energy Dispersive X-ray spectroscopy).

In some embodiments, the silicon oxycarbide nanomaterial may be SiO _x C _y ，x+y＝2，3:17≤x:y≤3:1。

In some embodiments, a metal-oxygen chemical bond is also formed between the first metal layer 2 and the first modified layer 3. The bonding firmness of the first metal layer 2 and the first modified layer 3 can be further improved. This feature can be characterized by XPS (X-ray photoelectron spectroscopy).

In some embodiments, the molar content of oxygen atoms of the surface of the first modification layer 3 away from the substrate layer 1 is 10% to 50%. The molar oxygen content is the percentage of the number of oxygen atoms to the total number of atoms.

In these embodiments, by controlling the molar content of oxygen atoms within the above range, on the one hand, a suitable surface tension can be imparted to the surface of the first modified layer 3 remote from the substrate layer 1, and on the other hand, a certain number of metal-oxygen bonds can be formed between the oxygen atoms and the metal atoms contained in the first metal layer 2, so that the bonding firmness between the first metal layer 2 and the first modified layer 3 can be maximally improved.

Here, it should be noted that the molar content of oxygen atoms can be obtained by using XPS (X-ray photoelectron spectroscopy), and in the test, the X-ray is excited on the surface of the first modified layer 3, and the kinetic energy of electrons emitted from the surface of the first modified layer 3 within a thickness range of 30nm is measured to obtain an XPS spectrum.

In some embodiments, atoms of the first modification layer 3 near the surface of the substrate layer 1 are bound to the substrate layer 1 by covalent bonds.

In these embodiments, the bonding strength between the first modified layer 3 and the base layer 1 can be improved, and the bonding strength between the first metal layer 2 and the base layer 1 can be further improved.

This feature can be obtained by infrared spectroscopy characterization of the cross section of the modified substrate layer 1 (e.g. the first modified layer 3 and the substrate layer 1).

As an example, in the case that the material of the base layer 1 is a PP (Polypropylene) film, the first modified layer 3 and the PP film are bonded through a C-O-Si bond, and an infrared spectrum is obtained as shown in fig. 2.

While the above-mentioned bonding between the surface of the first modification layer 3 away from the substrate layer 1 and the first metal layer 2 is performed through chemical bonds, those skilled in the art can understand that the bonding firmness of the surface of the first modification layer 3 away from the substrate layer 1 and the first metal layer 2 is also related to the physical properties of the surface of the first modification layer 3 away from the substrate layer 1, such as surface tension, surface roughness, and the like. Based on this, in some embodiments, the surface tension of the surface of the first modification layer 3 away from the base layer 1 is 42 to 57mN/m.

In these examples, the surface tension of the first modified layer 3 on the surface remote from the base layer 1 was controlled to be in the range of 42 to 57mN/m, whereby the bonding strength between the first metal layer 2 and the first modified layer 3 could be improved to the maximum extent.

In some embodiments, the average size of the grains of the nanomaterial of the surface of the first modification layer 3 remote from the substrate layer 1 is 50 to 88nm, and the surface roughness of the surface of the first modification layer 3 remote from the substrate layer 1 is 75 to 125nm.

In these embodiments, the bonding firmness of the first modified layer 3 and the first metal layer 2 can be improved to the greatest extent.

Based on the above, it should be noted that the first modified layer 3 is to improve the surface structure and properties of the base layer 1, and if the modification is uniform, the bonding strength between the first modified layer 3 and the first metal layer 2 cannot be further improved by increasing the thickness of the first modified layer 3, and the raw material cost is also increased.

Based on this, in some embodiments, the thickness of the first modification layer 3 is 100 to 200nm.

In these embodiments, by controlling the thickness of the first modification layer 3 within the above range, the base layer 1 can be regarded as a result of subjecting the surface of the polymer film to the surface modification treatment of silicon oxide, and the bonding strength between the polymer film and the metal layer can be improved without affecting the flexibility of the base layer 1.

In some embodiments, the modulus of elasticity of the modified substrate layer 1 is less than or equal to 3660MPa.

In these embodiments, the flexibility of the composite current collector may be maintained to the greatest extent.

In some embodiments, the thickness of the base layer 1 is 2 to 20 μm.

The base layer 1 functions to promote the increase of the energy density of the composite current collector, and it has been found through experiments that the thinner the thickness of the base layer 1 is, the better the energy density of the composite current collector can be further promoted, but the thinner the thickness of the base layer 1 is, because the base layer 1 also functions as a carrier for supporting the first metal layer 2, the first modified layer 3, and the like in the process of preparing the composite current collector, and therefore, it is most appropriate to control the thickness of the base layer 1 within a range of 2 to 20 μm.

The material of the polymer material of the base layer 1 is not particularly limited. As long as the polymer material can play a role in promoting the energy density of the composite current collector to be improved, and has better flexibility.

In some embodiments, the polymeric material comprises one or more of polypropylene, polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polyimide, polypropylene, polyvinyl chloride, polyvinylidene fluoride, polytetrafluoroethylene, polyphenylene sulfide, polyphenylene oxide, polystyrene, and polyamide.

Polypropylene (PP) is a semi-crystalline thermoplastic with high impact resistance, strong mechanical properties, and resistance to corrosion by various organic solvents and acids and bases. Polyethylene (PE) is a thermoplastic resin prepared by polymerizing ethylene, has no odor and toxicity, has excellent low-temperature resistance, good chemical stability, resistance to corrosion of most acids and alkalis, small water absorption and excellent electrical insulation performance. Polyethylene terephthalate (PET) has excellent physical and mechanical properties in a wide temperature range, can reach 120 ℃ in long-term use, has excellent electrical insulation, has good electrical properties even at high temperature and high frequency, and has good creep resistance, fatigue resistance, friction resistance and dimensional stability. Polybutylene terephthalate (PBT) is a translucent or opaque crystalline thermoplastic polyester resin prepared by condensing 1, 4-butanediol and terephthalic acid or terephthalate and by a mixing procedure, and has excellent molding processability, high cost performance and comprehensive performance. Polyethylene naphthalate (PEN) has a chemical structure similar to PET, except that PEN in the molecular chain is replaced by a naphthalene ring having higher rigidity. Compared with PET, PEN has higher physical and mechanical properties, gas barrier property, chemical stability, heat resistance, ultraviolet resistance, radiation resistance and the like due to the naphthalene ring structure. Polyimide (PI) refers to a polymer having an imide ring (-CO-NR-CO-) in the main chain, and is one of organic polymer materials with the best overall performance. Polypropylene (PPE), a composite material of PPE material mixed with other thermoplastic materials such as PS (styrene), PA (polyamide, commonly known as nylon), etc., all have good geometric stability, chemical stability, electrical insulation and low thermal expansion coefficient after processing and molding. Polyvinyl chloride (PVC) has good mechanical properties and excellent dielectric properties. Polyvinylidene fluoride (PVDF) has excellent properties such as aging resistance, chemical resistance, weather resistance, ultraviolet radiation resistance and the like. Polytetra fluoroethylene (PTFE) has excellent chemical stability, corrosion resistance, sealing property, high lubrication non-stick property, electrical insulation property and good ageing resistance. Polyphenylene Sulfide (PPS) is a novel high-performance thermoplastic resin, and has the advantages of high mechanical strength, high temperature resistance, chemical resistance, flame retardancy, good thermal stability, excellent electrical property and the like. Polyphenylene Oxide (PPO) is transparent, has low relative density, and has excellent mechanical strength, stress relaxation resistance, creep resistance, heat resistance, water vapor resistance and dimensional stability. Polystyrene (PS) products have extremely high transparency, light transmittance of over 90 percent, good electrical insulation performance, easy coloring, good processing fluidity, good rigidity and good chemical corrosion resistance. Polyamide (PA) has good comprehensive properties including mechanical property, heat resistance, abrasion resistance, chemical resistance and self-lubricity, has low friction coefficient and certain flame retardance, is easy to process, is suitable for being filled, reinforced and modified by glass fiber and other fillers, and can improve the performance and expand the application range of the Polyamide.

In some embodiments, the material of the first metal layer 2 and the second metal layer 4 may be any metal having a flow conductivity. For example, the material of the first metal layer 2 and the second metal layer 4 may be selected from one or more of copper, aluminum, nickel, titanium, and silver.

Among the metal materials, copper foil and aluminum foil are the most conductive and inexpensive. In addition, for the wound battery, the pole piece used for preparing the battery has certain flexibility so as to ensure that the pole piece is not brittle when wound, and the copper foil and the aluminum foil are soft metal materials. In addition, the copper foil and the aluminum foil are relatively stable in air. The aluminum is easy to generate chemical reaction with oxygen in the air to generate a layer of compact aluminum oxide film on the surface of the aluminum to prevent the aluminum from further reacting, and the thin aluminum oxide film has a certain protection effect on the aluminum in the electrolyte. Copper is inherently stable in air and undergoes substantially no chemical reaction in dry air.

For the lithium battery, the positive electrode potential is high, the copper foil is easily oxidized at the high potential, the oxidation potential of aluminum is high, and the surface of the aluminum foil is provided with a compact oxidized foil, so that the internal aluminum is well protected, therefore, in some embodiments, the first metal layer 2 and the second metal layer 4 may be both aluminum or aluminum alloy in the case that the composite current collector is the positive electrode current collector, and the first metal layer 2 and the second metal layer 4 may be both copper or copper alloy in the case that the composite current collector is the negative electrode current collector.

In some embodiments, as shown in fig. 1, the composite current collector 10 described above further comprises: a first protective layer 6 and/or a second protective layer 7. The first protective layer 6 is disposed on the surface of the first metal layer 2 away from the substrate layer 1, and the second protective layer 7 is disposed on the surface of the second metal layer 4 away from the substrate layer 1.

In these embodiments, by providing the first protective layer 6 and the second protective layer 7, the first metal layer and the second metal layer 4 can be protected, and the first metal layer 2 and the second metal layer 4 can be prevented from being exposed to chemical corrosion or physical damage.

The materials of the first protective layer 6 and the second protective layer 7 may be the same or different, and the thicknesses may also be the same or different, which are not specifically limited herein, as long as the first protective layer 6 and the second protective layer 7 can protect the first metal layer 2 and the second metal layer 4.

In some embodiments, the materials of the first protective layer 6 and the second protective layer 7 are both selected from oxidation resistant materials.

The oxidation resistant material may be a metallic material or a non-metallic material.

Examples of the metallic material may be a material that is not easily oxidized in air, such as nickel, chromium, nickel-based alloy, copper-based alloy, and the like, and examples of the non-metallic material may be a metal oxide material, a non-metallic simple substance, and the like.

Examples of the metal oxide material may include one or more of copper oxide, aluminum oxide, nickel oxide, chromium oxide, and cobalt oxide, and examples of the non-metallic element may include one or more of graphite, carbon black, acetylene black, ketjen black, carbon nano quantum dots, carbon nanotubes, carbon nanofibers, and graphene.

In some embodiments, the thickness of the first protective layer 6 is no more than 1/10 of the thickness of the first metal layer, and the thickness of the second protective layer 7 is no more than 1/10 of the thickness of the second metal layer 4.

In these embodiments, by making the thickness of the first protective layer 6 not more than 1/10 of the thickness of the first metal layer and the thickness of the second protective layer 7 not more than 1/10 of the thickness of the second metal layer 4, it is possible to prevent the resistivity of the composite current collector from increasing due to the first protective layer 6 and the second protective layer 7 being too thick, thereby causing a problem of deterioration in the conductivity of the composite current collector.

In some embodiments, the first protective layer 6 and the second protective layer 7 have the same or different thicknesses, and are each independently 10 to 150nm.

In these embodiments, by controlling the thicknesses of the first protective layer 6 and the second protective layer 7 in the range of 10 to 150nm, the thicknesses of the first protective layer 6 and the second protective layer 7 can be reduced to the maximum extent and the energy density of the composite current collector can be improved while ensuring good protection of the first metal layer 6 and the second metal layer 7.

Alternatively, the thicknesses of the first protective layer 6 and the second protective layer 7 may each be 20 to 100nm.

In some embodiments, the thickness of the first metal layer 2 is 500 to 2000nm.

In these embodiments, by controlling the thickness of the first metal layer 2 within the range of 500 to 2000nm, it is possible to prevent the first metal layer 2 from being excessively thick and causing a problem of material waste while securing high conductive performance of the first metal layer 2.

Optionally, the thickness of the first metal layer 2 is 700 to 1200nm.

Some embodiments of the present application provide a lithium battery including a composite current collector as described above.

In some embodiments, the lithium battery may include a positive electrode tab and a negative electrode tab. The positive electrode tab may include a positive current collector and a positive active material, and the negative electrode tab may include a negative current collector and a negative active material.

In some embodiments, the positive and/or negative current collectors may be the composite current collectors described above.

In the case that the positive current collector is the composite current collector, the first metal layer and the second metal layer included in the composite current collector may be both aluminum foils, and then, the lithium battery further includes a positive active material formed on at least one surface (for example, two opposite surfaces of the composite current collector in the thickness direction) of the composite current collector. In the case that the negative current collector is the composite current collector, the first metal layer and the second metal layer included in the composite current collector may be both copper foils, and in this case, the lithium battery further includes a negative active material formed on at least one surface of the composite current collector.

In the case of a lithium ion battery, the positive electrode active material may be a lithium alloy metal oxide material, and the negative electrode active material may be a carbon material, a silicon-based material, a titanium oxide material, a tin-based composite material, or the like. In the case where the lithium battery is a lithium metal battery, unlike a lithium ion battery, the negative active material may be metal lithium or an alloy metal thereof.

Of course, in some embodiments, in the case where the lithium battery is a lithium ion battery, the positive active material may also be a sodium alloy metal oxide material, in which case the lithium ion battery may also be referred to as a sodium ion battery. In the case where the lithium battery is a lithium metal battery, the negative active material may be metallic sodium or an alloy metal thereof, and in this case, the lithium metal battery may also be referred to as a sodium metal battery. In other embodiments, the negative active material is in the case where the lithium battery is a lithium metal battery. The slurry can be prepared to be coated on the negative electrode current collector, and a negative electrode material layer (such as a lithium metal layer) can also be formed on the negative electrode current collector in an electroplating way.

Some embodiments of the present application provide an electrical device comprising a lithium battery as described above.

In some embodiments, the powered device may be exemplified by an electric car, a mobile phone, a tablet computer, a notebook computer, or a digital camera.

Some embodiments of the present application provide a method of manufacturing a composite current collector, as shown in fig. 3, including:

s31, providing a substrate layer 1, wherein the material of the substrate layer 1 comprises a polymer material.

The substrate layer 1 may be obtained commercially or may be obtained by the user.

In some embodiments, the substrate layer 1 may be prepared by a melt, extrusion and stretching process using a polymer material.

Wherein the stretching may be unidirectional stretching or bidirectional stretching.

And S32, forming a first modification layer 3 on the first surface of the substrate layer 1 along the thickness direction of the substrate layer, wherein the material of the first modification layer 3 comprises one or more of silicon oxide nano-materials and titanium oxide nano-materials.

Here, the first modified layer 3 may be formed on the first surface 11 of the base layer 1 in the thickness direction thereof by a plasma-assisted chemical vapor deposition method.

Plasma is a fourth state of matter existence, a macroscopic system of unbound states consisting of equal amounts of free electrons and charged ions.

Chemical Vapor Deposition (CVD) is a process that utilizes gaseous substances to chemically react on a solid surface to produce a solid deposit.

The plasma may be generated by means of electrical breakdown, radio frequency discharge, microwave excitation, shock waves, energetic particle flux, high temperature heating, and the like.

The plasma-assisted chemical vapor deposition is a solid-state deposition method in which, in a low-pressure chemical vapor deposition process, plasma generated by glow discharge is used to control reaction gas pressure, gas flow rate, substrate (referred to as a base layer herein) material temperature, deposition time, and the like in the deposition process, so as to control a nanomaterial nucleation growth process and a crystallization process of the first modified layer 3.

In the plasma-assisted chemical vapor deposition process, the microscopic process is as follows:

the gas molecules collide with electrons in the plasma to generate active groups and ions, the active groups can be directly diffused to the substrate layer 1, the active groups can also interact with other gas molecules or active groups to form chemical groups required by deposition, the chemical groups required by deposition are diffused to the surface of the substrate layer 1, the gas molecules can also be directly diffused to the vicinity of the substrate layer 1 without the activation process, various chemical groups reaching the surface of the substrate layer perform various deposition reactions and release reaction products, and the reaction products are discharged out of the system under the drive of the unreacted gas molecules.

In some embodiments, the reaction gas used in the plasma-assisted chemical vapor deposition may include: the gas source comprises an oxygen element gas source, a carbon element gas source and an X element gas source, wherein X comprises one or more of silicon, titanium and aluminum. Exemplary sources of elemental carbon may be short chain alkanes such as methane, ethane, propane, and the like.

The inert gas is used as a plasma gas source, the reaction gas is the gas molecules, and the gas molecules collide with electrons in the plasma to generate active groups containing one or more of silicon atoms, titanium atoms and aluminum atoms and oxygen atoms, wherein the active groups containing one or more of silicon atoms, titanium atoms and aluminum atoms and oxygen atoms are diffused to the substrate layer 1 to form the nano material film on the substrate layer 1.

In the process, the nucleation process of the nanomaterial in the first modification layer 3 can be controlled by controlling the gas flow of the plasma gas source, the oxygen and the reaction gas, so that the size, the molar content of oxygen atoms (hereinafter referred to as oxygen atom content) and the like of the crystal grains of the nanomaterial in the first modification layer 3 can be controlled, the size, the oxygen atom content, the surface roughness, the surface tension and the like of the crystal grains on the surface of the first modification layer 3 far away from the substrate layer can be controlled, and preparation is made for subsequently improving the bonding capability between the first modification layer 3 and the first metal layer 2.

In some embodiments, before the reaction starts, the pressure in the plasma-assisted chemical vapor deposition device is reduced to below 10mTorr by vacuumizing, and during the reaction, a plasma gas source is firstly introduced into the plasma-assisted chemical vapor deposition device, and then reaction gas is introduced into the plasma-assisted chemical vapor deposition device. Wherein, the input of the plasma gas source makes the pressure in the plasma auxiliary chemical vapor deposition device be 10-30 mTorr, the total input of the reaction gas makes the pressure in the plasma auxiliary chemical vapor deposition device be 35-50 mTorr, the flow ratio of the oxygen element gas source, the carbon element gas source and the X element gas source satisfies: the ratio of the total molar amount of oxygen element and carbon element contained in the oxygen element gas source and the carbon element gas source to the total molar amount of the X element is 2.

In these embodiments, the plasma gas source is introduced first, the plasma gas source generates plasma under the action of glow power generation, and then the reaction gas is introduced, so that the reaction gas can be activated by the plasma, the plasma and the reaction gas react, and one or more of silicon atoms, titanium atoms and aluminum atoms, and oxygen atoms are deposited on the surface of the substrate layer 1, thereby forming the first modification layer 3.

In the process, the surface structure and properties of the first modification layer 3 can be adjusted by controlling the pressure introduced by the plasma gas source, the pressure introduced by the reaction gas, the flow ratio of the oxygen element gas source, the carbon element gas source and the X element gas source, and the like, so that the grain size, the surface tension, the surface roughness, the sheet resistance and the like of the surface of the first modification layer 3 far away from the substrate layer 1 meet the application requirements. In addition, if the molar content of the oxygen element is too high or too low, the uniformity of the distribution of oxygen atoms on the surface of the first modified layer 3 is not favorable, and the subsequent bonding between the first metal layer and the first modified layer 3 is not favorable. The carbon element molar content is too low, which is not beneficial to the promotion of the surface conductivity of the first modified layer 3, thereby being not beneficial to the reduction of the surface hole defects, and the carbon element molar content is too high, and the oxygen element content is too low, which is not beneficial to the promotion of the bonding firmness between the subsequent first metal layer and the first modified layer 3.

In some embodiments, the plasma gas source may include: one or more of argon, helium and neon. The elemental silicon source gas may be an alkoxysilane which may be selected from one or more of hexamethyloxysilane, tetraethoxysilane, dimethyldiethoxysilane, ethyltriethoxysilane, and vinyltriethoxysilane.

The source of the titanium element can be titanate, and the titanate can be one or more selected from isopropyl titanate, n-propyl titanate, ethyl titanate and methyl titanate.

The aluminum source gas can be alkyl aluminum, and the alkyl aluminum can be one or more of trimethyl aluminum, triethyl aluminum and triisobutyl aluminum.

The carbon element gas source is short-chain alkane which can be one or more selected from methane, ethane and propane.

The source of elemental oxygen may be oxygen.

In some embodiments, plasma-assisted chemical vapor deposition may employ a radio frequency generator to generate the plasma, which may enable low temperature deposition. In this case, the frequency of the RF generator may be 10-15 MHz, and the power may be 100-300W.

By limiting the frequency and power of the rf generator within the above ranges, the deposition yield can be improved and the uniformity of the distribution of oxygen atoms in the first modified layer 3 can be improved. The power is too low, the deposition effect is poor, the power is too high, and the distribution of oxygen atoms in the first modified layer is not uniform.

In some embodiments, the time for the above reaction may be 2 to 20min.

In these embodiments, the thickness and surface properties of the first modification layer 3 can be well controlled. The reaction time is too short, which causes the incomplete formation of the first modified layer 3, and the better effect cannot be achieved, and the reaction time is too long, which increases the thickness of the first modified layer 3 cumulatively, and is not favorable for controlling the cost of raw materials.

Here, the plasma-assisted chemical vapor deposition apparatus may be a roll-to-roll type plasma-assisted chemical vapor deposition apparatus in which a take-up roll is provided, so that chemical vapor deposition can be performed on both front and back surfaces of the polymer film. That is, the first modified layer 3 is formed on the first surface of the foundation layer 1, and the second modified layer 5 is formed on the second surface of the foundation layer 1. The value ranges of the parameters formed by the second modified layer 5 are the same as those of the parameters formed by the first modified layer 3, and the description of the parameters may be specifically referred to, and will not be repeated herein.

And S33, forming a first metal layer 2 on the surface of the first modified layer 3 far away from the base layer 1.

The first metal layer 2 may be formed on the surface of the first modified layer 3 away from the substrate layer 1 by one or more of physical vapor deposition (e.g., resistance heating vacuum evaporation, electron beam heating vacuum evaporation, laser heating vacuum evaporation, magnetron sputtering, etc.), electroplating, chemical plating, etc.

Similar to the second modified layer 5, the preparation method of the second metal layer 4 may be the same as the preparation method of the first metal layer 2, and is not described herein again.

And S34, forming a first protective layer 6 on the surface of the first metal layer 2 far away from the base layer 1.

The first protective layer 6 may be formed on the surface of the first metal layer 2 away from the base layer 1 by one or more of physical vapor deposition, chemical vapor deposition, in-situ forming, coating, and the like.

Wherein, the vapor deposition method can comprise one or more of vacuum evaporation and magnetron sputtering; the chemical vapor deposition may include one or more of atmospheric pressure chemical vapor deposition and plasma-assisted chemical vapor deposition; the in-situ forming may be a method of forming a metal oxide (one or more of copper oxide, aluminum oxide, nickel oxide, chromium oxide, and cobalt oxide as described above) in situ on the surface of the first metal layer 2, so as to obtain a first protective layer 6 containing the metal oxide; the coating process may include one or more of die coating, blade coating, and extrusion coating.

In some embodiments, the method further comprises: as shown in fig. 3, a second protective layer 7 is formed on the surface of the second metal layer 4 away from the base layer 1.

The preparation method of the second passivation layer 7 may be the same as the preparation method of the first passivation layer 6, and is not described herein again.

The embodiments of the present application are introduced above, and in order to objectively explain the technical effects produced by the present application, next, description will be made by the following examples and comparative examples.

In the following examples and comparative examples, all the raw materials were commercially available, and in order to maintain the reliability of the experiment, the raw materials used in the following examples and comparative examples all had the same physical and chemical parameters or were subjected to the same treatment.

Example 1

Preparing a surface-modified polymer film (i.e., forming a first modified layer and a second modified layer on the upper and lower surfaces of the polymer film):

placing a commercially available biaxially oriented Polypropylene (PP) film with a thickness of 6 μm in a Plasma Enhanced Chemical Vapor Deposition (PECVD) apparatus, setting the frequency of a radio frequency generator of the PECVD apparatus to 13.45MHz and the power to 100W, and evacuating by using a vacuum pump until the pressure in the chamber is 10mTorr, and then opening an argon pipeline control valve, slowly introducing argon into the PECVD apparatus, and adjusting the flow of the argon gas so that the pressure in the chamber of the PECVD apparatus is maintained at 20mTorr; then, opening pipeline valves of oxygen, ethane and hexamethyldisiloxane, slowly introducing the oxygen, the ethane and the hexamethyldisiloxane into the pipeline valves, wherein the flow ratio of the total flow of the oxygen and the ethane to the flow of the hexamethyldisiloxane is 2; after 2min of treatment, stopping introducing gas, turning off the vacuum pump, and relieving pressure; and after pressure relief is finished, taking out the polymer film to obtain the PP film with the modified surface.

Preparing a composite current collector:

preparation of the metal layer (preparation of the first metal layer and the second metal layer): placing the prepared surface modified PP film in a vacuum evaporation cabin, melting and evaporating high-purity copper wires (the purity is more than 99.99%) in a metal evaporation chamber at the high temperature of 1400-2000 ℃, and depositing evaporated metal atoms on two surfaces of the surface modified polymer film through a cooling system in a vacuum coating chamber to form a copper metal layer with the thickness of 1 mu m.

Preparation of protective layer (preparation of first protective layer and second protective layer): uniformly dispersing 1g of graphene into 999g of N-methyl pyrrolidone (NMP) solution by an ultrasonic dispersion method to prepare a coating liquid with the solid content of 0.1wt%, uniformly coating the coating liquid on the surface of a metal layer by a die head coating process, wherein the coating thickness is controlled at 80 mu m, and drying at 80 ℃ to prepare the protective layer.

Example 2

Essentially the same as in example 1, except that: the power of the RF generator is 200W.

Example 3

Essentially the same as in example 1, except that: the power of the radio frequency generator was 300W.

Example 4

Essentially the same as in example 1, except that: the flow ratio of oxygen to ethane was 1.

Example 5

Essentially the same as in example 1, except that: the flow ratio of oxygen to ethane was 3.

Example 6

Essentially the same as in example 1, except that: the modification treatment time was 5min.

Example 7

Essentially the same as in example 1, except that: the modification treatment time was 10min.

Example 8

Essentially the same as in example 1, except that: the modification treatment time was 15min.

Example 9

Essentially the same as in example 1, except that: the modification treatment time is 20min.

Example 10

Essentially the same as in example 1, except that: the polymer film is a PET film.

Comparative example 1

Essentially the same as in example 1, except that: the power of the rf generator was 95W.

Comparative example 2

Essentially the same as in example 1, except that: the power of the rf generator was 305W.

Comparative example 3

Comparative example 4

Essentially the same as in example 1, except that: the flow ratio of oxygen to ethane was 4.

Comparative example 5

Essentially the same as in example 1, except that: the modification treatment time was 1min.

Comparative example 6

Essentially the same as in example 1, except that: the modification treatment time was 21min.

Comparative example 7

Essentially the same as in example 1, except that: the polymer film is not subjected to surface modification treatment.

And (3) test evaluation:

as described above, a covalent bond of C — O — Si exists between the modified layer (i.e., the first modified layer and the second modified layer) and the polymer film, thereby improving the bonding strength between the polymer film and the modified layer; a metal-O chemical bond exists between the modified layer and the metal layer, and the metal-O chemical bond and parameters such as the surface structure and the property of the modified layer promote the adhesive force between the modified layer and the metal layer. To confirm this, infrared spectrum scans were performed on the cross-sections of the polymer films and the modified layers of the above example 1 and comparative example 1, XPS scans were performed on the modified layer and metal layer interface vicinity of the example 1 and comparative example 1, and EDS line scans were performed on the modified layer and metal layer interface vicinity of the example 1. The specific test method and test results are as follows:

1. infrared spectrum scanning characterization: the modified polymer film prepared in example 1 was subjected to section sampling using an argon ion polisher (Fischione 1061), and then the section sample was placed in a fourier transform attenuated total reflection infrared spectrometer (Thermo Nicolet 6700) to perform infrared spectrum scanning on the section, thereby obtaining an infrared spectrum as shown in fig. 2. The polymer film provided in comparative example 1 was sampled in the same cross section as in example 1, and the above operation was repeated to perform infrared spectrum scanning, and an infrared spectrum was obtained as shown in FIG. 2.

As can be seen from FIG. 2, compared with the unmodified PP film, the infrared spectrum of the modified PP film is increased by 1250cm ^-1 、1199cm ^-1 、1077cm ^-1 、956cm ^-1 、783cm ^-1 Characteristic absorption peaks at equal positions, which respectively correspond to characteristic absorption peaks of C-O-Si symmetric stretching vibration, C-Si symmetric stretching vibration, si-O-Si symmetric stretching vibration, C-O-Si bending stretching vibration and Si-O-Si asymmetric stretching vibration. This indicates that the formation of the modified layer and the formation of a covalent bond of C-O-Si between the modified layer and the PP based film.

2. XPS characterization: polishing the surface of the prepared composite current collector by using an argon ion polisher (Fischione 1061), removing the protective layer and the oxidized metal layer on the surface, then preparing a section sample, placing the prepared section sample in XPS (PHI Versaprobe 4) after completing the sample preparation, and scanning the section of the sample to obtain an XPS spectrogram as shown in fig. 4. The polymer film provided in comparative example 1 was sampled in the same cross section as in example 1, and infrared spectrum scanning was repeated to obtain an XPS spectrum as shown in FIG. 4.

As can be seen from fig. 4, compared with the composite current collector prepared by using an unmodified PP film as a base film, characteristic peaks of Cu (i) and Cu (ii) appear in an XPS spectrum of a cross section of the composite current collector prepared by using the modified PP film as the base film, and generation of a Cu-O chemical bond between the modified PP film and the metal layer is demonstrated, wherein Cu (i) represents monovalent copper ions, and Cu (ii) represents divalent copper ions.

3. EDS (Energy Dispersive Spectrometer, energy Dispersive X-ray spectroscopy) characterization: performing section sampling on the prepared composite current collector by using an argon ion polisher (Fischinone 1061), and placing the prepared section sample in an X-ray energy spectrometer (Bruker QUANTAX EDS)

7) Namely the interface of modified layer and metal layer in EDS (energy spectrometer)An EDS test chart obtained by performing X-ray scanning in the near (30 nm upward and downward with the interface as the origin) is shown in FIG. 5.

As shown in fig. 5, the origin of coordinates is the interface position of the modified layer and the metal layer, the negative coordinates represent the position on the metal layer side, and the positive coordinates represent the position on the modified layer side, and it can be seen that: from the interface to a position 30nm deeper inside the modified layer, the presence of metallic Cu was detected, indicating that copper crystals are embedded into the modified layer, because: in the process of forming the metal layer, the surface temperature of the modified layer is higher, crystals in the modified layer are rearranged and moved, the lattice structures of the generated Cu crystals and the silicon oxycarbide crystals in the modified layer belong to face-centered cubic structures, and the structures are similar, so that the copper crystals and the silicon oxycarbide crystals are embedded.

As described above, one of the purposes of the prepared surface-modified polymer film is to improve the bonding property between the polymer film and the metal layer, and further to solve the problem of weak adhesion between the base film and the metal layer of the composite current collector prepared by using the polymer film as the base film. The surface structure and properties of the polymer films of the examples and comparative examples provided herein can be characterized by the effect of the surface structure and properties of the polymer film on the bonding performance of the polymer film to the metal layer by subjecting the polymer film to a silicon oxide surface modification treatment and testing the average grain size, surface oxygen atom content, surface tension and surface roughness of the surface-modified polymer film provided herein and the polymer film of the related art that has not been subjected to the surface modification treatment, and the adhesion between the polymer film and the metal layer. The prepared surface modified polymer film has another purpose of improving the surface conductivity of the prepared polymer film so as to reduce the number of hole defects caused by static electricity in the physical vapor deposition process, and the sheet resistance of the prepared surface modified polymer film and the number of holes on the prepared composite current collector film surface are characterized. In addition, in order to objectively evaluate the modification effect of the embodiment of the present application, the present application also characterizes the thickness of the modified layer (i.e., the silicon oxycarbide layer), and characterizes the elastic modulus of the polymer film forming the modified layers with different thicknesses, so as to objectively evaluate the flexibility of the polymer film after modification. The specific test method and test results are as follows:

1. testing of average grain size of surface grains: the polymer films prepared in the above examples 1 to 16 and comparative example 1 were placed in a field emission scanning electron microscope for surface morphology testing, and the average particle size of the surface grains corresponding to the above examples 1 to 16 and comparative example 1 was analyzed by means of image processing software, and the specific test results are shown in table 1 below.

2. Surface oxygen atom content test: the surface elements of the polymer films were characterized by X-ray photoelectron spectroscopy (XPS), and the relative content of surface oxygen atoms of the polymer films corresponding to examples 1 to 16 and comparative example 1 was analyzed, and the specific test results are shown in table 1 below.

3. And (3) testing the surface tension: the test is carried out according to the national standard GB/T14216-2008, and the specific test results are shown in the following table 1.

4. And (3) testing surface roughness: the test is carried out according to the national standard GB/T31227-2014, and the specific test results are shown in the following table 1.

5. Adhesion of polymer film to metal layer: adhering a Permacel P-94 double-sided adhesive tape on a 1mm thick aluminum foil, adhering a composite current collector on the double-sided adhesive tape, covering a layer of ethylene acrylic acid copolymer film (Dupont Nurcel0903, thickness 50 μm) on the composite current collector, and covering the film on the aluminum foil at 1.3 × 105N/m ² Hot pressing at 120 deg.C for 10s, cooling to room temperature, and cutting into small strips of 150mm × 15 mm. And finally, fixing the small sample strip of the ethylene acrylic acid copolymer film on an upper fixture of a tensile machine, fixing the rest part of the small sample strip of the ethylene acrylic acid copolymer film on a lower fixture, moving the upper fixture and the lower fixture at a speed of 100mm/min according to an angle of 180 degrees after the small sample strip of the ethylene acrylic acid copolymer film is fixed, stripping the polymer film and the metal layer, and testing the tensile force applied when the polymer film and the metal layer are stripped, so that the adhesive force between the polymer film and the metal layer can be obtained, and the specific test results are shown in the following table 1.

6. Thickness of the modified layer: placing the prepared modified polymer film sample in an argon ion polisher (Fischione 1061) to cut the sample by using an argon ion beam (the diameter of the argon ion beam is 1 mm), and after the cutting is finished, carrying out gold spraying treatment on the sample so as to prepare a section sample; placing the prepared cross section sample in a field emission scanning electron microscope (Zeiss Gemini Sigma 300VP SEM), amplifying by 5 ten thousand times, and observing the cross section morphology of the sample; and marking the thickness of the modified layer in the section morphology by using measurement software carried by an electron microscope, so as to obtain the thickness of the modified layer.

7. Modulus of elasticity of modified polymer film: refer to the national standard GB/T1040.3-2006.

8. Square resistance: and (3) placing the prepared surface-modified polymer film on a sample table, and testing the sheet resistance of the sample by using a four-probe sheet resistance tester.

9. Hole drilling: and (2) placing the composite current collector finished product in a surface quality detection system (a micro-vision Charge Coupled Device (CCD)), scanning the surface, converting an optical signal into an electrical signal, transmitting the electrical signal to a computer, and counting the number of surface holes with the unit area (per square meter) of the composite aluminum current collector finished product, wherein the pore diameter of the composite aluminum current collector finished product is less than 100 micrometers (generally, the finished product cannot have holes with the diameter of more than 100 micrometers).

TABLE 1

As can be seen from table 1, the adhesion between the polymer film and the metal layer after surface modification is effectively improved, and the surface void defects of the prepared composite current collector are effectively controlled, particularly, the power of the radio frequency generator is controlled within the range of 100 to 300W, the flow ratio of oxygen to ethane is controlled within the range of 3.

Comparing examples 1 to 3 with comparative examples 1 to 2, it can be seen that as the power of the rf generator is increased, the average size and surface roughness of the silicon oxycarbide nanocrystals on the surface of the modified polymer film gradually increase, while the surface oxygen content and surface tension do not change, and the changes in the surface structure and properties result in the increase and decrease of the adhesion between the polymer film and the metal layer. In addition, along with the power increase of the radio frequency generator, the deposition efficiency is improved, the thickness of the modified layer is gradually increased, the surface sheet resistance is reduced due to the increase of the thickness of the modified layer, the elastic modulus is slightly increased, and along with the gradual increase of the thickness, the elastic modulus is in an acceptable range, so that the flexibility of the composite current collector is not greatly influenced. From this, it can be seen that when the power of the rf generator is controlled in the range of 100 to 300W, the surface structure and properties of the obtained polymer film are optimized, and the adhesion between the polymer film and the metal layer can be maximally improved.

Comparing examples 1,4, 5 and comparative examples 3 to 4, it can be seen that: with the increasing flow ratio of the introduced oxygen to the ethane, the grain size and the surface roughness of the silicon oxycarbide on the polymer film surface are basically unchanged, the surface oxygen atom content and the surface tension are increased, and the change of the surface structure and the properties leads to the tendency that the adhesive force between the polymer film and the metal layer is increased. In addition, the thickness of the modified layer is basically unchanged along with the increasing of the flow ratio of the introduced oxygen to the ethane, but the carbon content of the modified layer is reduced and the conductivity is reduced due to the increasing of the flow ratio of the introduced oxygen to the ethane, so that the sheet resistance is increased. When the proportion of the surface sheet resistance and the surface sheet resistance is too high, the surface sheet resistance is too low, the conductivity is poor, and the prepared composite current collector has a hole defect on the membrane surface. When the ratio of the two is too low, the surface oxygen content is low, resulting in low surface tension, thereby causing low adhesion of the base film to the metal layer of the prepared composite current collector. Therefore, when the flow ratio of oxygen to ethane is in the range of 3.

By comparing examples 1, 6 to 9 and comparative examples 5 to 6, it can be seen that: with the continuous increase of the treatment time, the average size and the surface roughness of silicon oxycarbide nano-crystal grains on the polymer film surface are gradually increased, the surface oxygen atom content and the surface tension are unchanged, and the change of the surface structure and the properties causes the adhesive force between the polymer film and the metal layer to be increased and then reduced. In addition, as the treatment time is increased continuously, the thickness of the modified layer is increased, the sheet resistance is reduced, the elastic modulus is slightly increased, but the elastic modulus is in an acceptable range, and the flexibility of the composite current collector is not greatly influenced. This indicates that: the longer the treatment time is, the higher the adhesion capability between the polymer film and the metal layer, and the treatment time is controlled within 2-20 min, so that the adhesion between the polymer film and the metal layer can be improved to the greatest extent.

Comparing examples 1 and 10, it can be concluded that: under the same modification condition, the modification effect of the PP film is close to that of the PET film.

Comparing examples 1-9 with comparative example 7, it can be seen that: compared with an unmodified PP film, the adhesion force between the base film and the metal layer of the composite current collector prepared by using the modified PP film as the base film is obviously improved, and the surface hole defect is obviously reduced.

In summary, by forming the first modified layer and the second modified layer on the upper and lower surfaces of the polymer film and controlling the process conditions for forming the first modified layer and the second modified layer, the microstructure and properties of the surfaces of the first modified layer and the second modified layer away from the polymer film can be adjusted, and thus, when the metal layer is deposited on the obtained polymer film, the bonding firmness between the metal layer and the polymer film can be effectively improved. Through experiments, the parameters in the process conditions for forming the first modification layer and the second modification layer are not as large as possible, but are related to the microstructure and the property of the surfaces of the first modification layer and the second modification layer far away from the polymer film, so that the interaction relationship between the microstructure and the property of the surfaces of the first modification layer and the second modification layer far away from the polymer film and the bonding force between the polymer film and the metal layer is obtained, and research basis is provided for the influence of the surface structure and the property of the polymer film on the bonding firmness between the polymer film and the metal layer.

The technical features of the embodiments described above may be arbitrarily combined, and for the sake of brevity, all possible combinations of the technical features in the embodiments described above are not described, but should be considered as being within the scope of the present specification as long as there is no contradiction between the combinations of the technical features.

The above-mentioned embodiments only express several implementation modes of the present application, and the description thereof is specific and detailed, but not construed as limiting the scope of the claims. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the concept of the present application, which falls within the scope of protection of the present application. Therefore, the protection scope of the present patent application shall be subject to the appended claims.

Claims

1. A composite current collector, comprising:

a base layer comprising first and second surfaces disposed opposite one another along a thickness thereof, the material of the base layer comprising a polymeric material;

the first metal layer is arranged on the surface, far away from the substrate layer, of the first modified layer.

2. The composite current collector of claim 1,

the lattice structure of the crystal of the first modification layer close to the surface of the first metal layer is doped with metal atoms contained in the first metal layer.

3. The composite current collector of claim 1,

atoms of the first modified layer near the surface of the substrate layer are covalently bonded to the substrate layer.

4. The composite current collector of claim 1,

the molar content of oxygen atoms on the surface of the first modified layer far away from the substrate layer is 10-50%.

5. The composite current collector of claim 1,

the average size of crystal grains of the surface of the first modified layer far away from the substrate layer is 50-88 nm.

6. The composite current collector of claim 1,

the surface tension of the surface of the first modified layer far away from the substrate layer is 42-57 mN/m.

7. The composite current collector of claim 1,

the surface roughness of the surface of the first modified layer far away from the substrate layer is 75-125 nm.

8. The composite current collector of claim 1,

the thickness of the first modified layer is 100-200 nm.

9. The composite current collector of any one of claims 1 to 8,

the thickness of the substrate layer is 2-20 μm.

10. The composite current collector of any one of claims 1 to 8,

the polymer material comprises one or more of polypropylene, polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polyimide, polypropylene, polyvinyl chloride, polyvinylidene fluoride, polytetrafluoroethylene, polyphenylene sulfide, polyphenylene oxide, polystyrene and polyamide.

11. The composite current collector of any one of claims 1 to 8, further comprising: a second metal layer and a second modified layer;

the second modification layer is arranged on the second surface of the substrate layer, the second metal layer is arranged on the surface, far away from the substrate layer, of the second modification layer, and the material and/or the surface structure of the second modification layer are defined as those of the first modification layer.

12. The composite current collector of claim 11, further comprising: a first protective layer and/or a second protective layer;

the first protective layer is arranged on the surface of the first metal layer far away from the substrate layer, and the second protective layer is arranged on the surface of the second metal layer far away from the substrate layer.

13. The composite current collector of claim 12,

the thickness of the first protective layer is not more than 1/10 of the thickness of the first metal layer;

the thickness of the second protective layer is not more than 1/10 of the thickness of the second metal layer.

14. The composite current collector of claim 12 or 13,

the first protective layer and the second protective layer have the same or different thicknesses and are respectively and independently 10-150 nm.

15. The composite current collector of any one of claims 1 to 8,

the thickness of the first metal layer is 500-2000 nm.

16. A lithium battery, comprising:

a composite current collector as claimed in any one of claims 1 to 15.

17. An electric device, comprising:

a lithium battery as in claim 16.

18. A method of making a composite current collector, comprising:

providing a substrate layer, the material of the substrate layer comprising a polymeric material;

and forming a first metal layer on the surface of the first modified layer far away from the base layer.

19. The method of claim 18,

and forming the first modified layer on the first surface of the substrate layer along the thickness direction of the substrate layer by adopting a plasma-assisted chemical vapor deposition method.

20. The method of claim 19,

the frequency of a radio frequency generator adopted by the plasma-assisted chemical vapor deposition method is 10-15 MHz, and the power is 100-300W.

21. The method of claim 19,

the reaction gas adopted by the plasma-assisted chemical vapor deposition method comprises the following steps: the gas source comprises an oxygen element gas source, a carbon element gas source and an X element gas source, wherein X comprises one or more of silicon, titanium and aluminum.

22. The method of claim 21,

in the reaction process, firstly introducing a plasma gas source into a plasma-assisted chemical vapor deposition device, and then introducing reaction gas into the plasma-assisted chemical vapor deposition device;

wherein the introduction amount of the plasma gas source enables the pressure in the plasma-assisted chemical vapor deposition device to be 10-30 mTorr, the introduction amount of the reaction gas enables the pressure in the plasma-assisted chemical vapor deposition device to be 35-50 mTorr, and the flow ratio of the oxygen element gas source, the carbon element gas source and the X element gas source meets the following requirements: the ratio of the total molar amount of oxygen element and carbon element contained in the oxygen element gas source and the carbon element gas source to the total molar amount of the X element is 2.

23. The method of claim 22,

the reaction time is 2-20 min.