CN118943377A

CN118943377A - Composite current collector, pole piece and secondary battery using the same

Info

Publication number: CN118943377A
Application number: CN202410970943.0A
Authority: CN
Inventors: 朱中亚; 夏建中; 韩梦婕; 曾来源; 李学法; 张国平
Original assignee: Jiangyin Nali New Material Technology Co Ltd
Current assignee: Jiangyin Nali New Material Technology Co Ltd
Priority date: 2024-07-18
Filing date: 2024-07-18
Publication date: 2024-11-12
Anticipated expiration: 2044-07-18
Also published as: CN118943377B

Abstract

The invention provides a composite current collector, which comprises a base layer and a conductive layer, wherein the conductive layer is arranged on at least one surface of the base layer, the conductive layer comprises n ₁ transition layers and n ₂ metal layers, n ₁ is a positive integer greater than 1, n ₂ is a positive integer greater than 1, and the metal layers and the transition layers are alternately laminated in the conductive layer; the transition layer is composed of a fluorocarbon compound having a chemical formula of C _xF_yH_z, and x, y, and z satisfy: x/(x+y+z) is less than or equal to 0.25 and less than or equal to 0.95, and x is not equal to 0, y is not equal to 0, and z is not equal to 0. In the composite current collector provided by the invention, the arrangement of the transition layer can have a good protection effect on the metal layer, so that the cyclic charge and discharge performance of an electrochemical device applying the composite current collector is promoted, and meanwhile, the existence of the transition layer can be beneficial to generating non-penetrating grains with smaller size in the metal layer, so that the closed loop formed by conducting positive and negative current collectors in the needling process of a battery applying the composite current collector and the thermal runaway of the battery generated by the closed loop can be avoided, and the safety performance of the battery is promoted.

Description

Composite current collector and pole piece and secondary battery applying same

Technical Field

The invention belongs to the technical field of secondary batteries, and particularly relates to a composite current collector, a pole piece applying the composite current collector and a secondary battery.

Background

The current collector is one of indispensable component parts in the lithium ion battery, is used as a current collecting structure or part, and is used for collecting electrons generated by electrochemical reaction and conducting the electrons to an external circuit, so that the process of converting chemical energy into electric energy is realized. The current collector comprises a metal foil and a composite current collector, wherein the composite current collector has a multi-layer structure, a high polymer film is used as a base material in the middle of the composite current collector, and metal layers are plated on two sides of the base material. Compared with the traditional metal foil current collector (aluminum foil or copper foil), the composite current collector has the characteristics of low cost, light weight, good internal insulation property and the like, is favorable for improving the energy density and the safety of an electrochemical device, and has been widely focused and applied in new energy industry at present

However, regarding the composite current collector which has been put into use in the field of secondary batteries at present, there are mainly two problems: ① The metal layer of the composite current collector applied by the battery is continuously eroded by the electrolyte in the process of battery cyclic charge and discharge, so that the battery performance attenuation is obvious, and the battery charge and discharge cyclic performance is poor; ② The current composite current collector mainly improves the safety of the battery by means of the insulation and flame retardance of the middle layer, namely the polymer film layer, and the improvement on the safety of the battery is limited although the safety of the battery is improved. Therefore, in order to further improve the charge-discharge cycle and safety performance of the secondary battery based on the composite current collector, it is necessary to develop a new composite current collector, thereby promoting the application and popularization of the composite current collector in the secondary battery.

Disclosure of Invention

The invention provides a composite current collector, a pole piece and a secondary battery using the same, and the composite current collector can improve the cycle charge and discharge performance and the safety performance of the secondary battery on the premise of keeping good mechanical properties.

According to a first aspect of the present invention, there is provided a composite current collector comprising a base layer and a conductive layer provided on at least one surface of the base layer, the conductive layer comprising n ₁ transition layers and n ₂ metal layers, n ₁ being a positive integer greater than 1, n ₂ being a positive integer greater than 1, in which the metal layers and the transition layers are alternately laminated; the transition layer is composed of a fluorocarbon compound having a chemical formula of C _xF_yH_z, and x, y, and z satisfy: x/(x+y+z) is less than or equal to 0.25 and less than or equal to 0.95, and x is not equal to 0, y is not equal to 0, and z is not equal to 0.

In the composite current collector provided by the scheme, the applicable base layer is not limited, and can be used as a current collector base layer, for example, a textile layer, a polymer base film or a polymer base film mixed with conductive particles.

In the composite current collector, the carbon content of the fluorocarbon used for constructing the transition layer is sufficient, so that the composite current collector has good conductivity, and meanwhile, the fluorocarbon has good corrosion resistance and can generate certain binding force with the metal layer. In the composite current collector provided by the invention, the arrangement of the transition layer has the following effects: ① The transition layer has good barrier and tolerance to electrolyte, and can realize layer-by-layer protection to the metal layer, thereby promoting the improvement of the cyclic charge and discharge performance of the battery based on the composite copper current collector; ② The transition layer can obstruct the penetration of the crystal grains of the adjacent metal layers and promote the re-nucleation growth of the crystal grains, so as to generate non-penetration crystal grains with smaller size, the generated metal layer formed by the non-penetration crystal grains with smaller size can generate microcracks after certain deformation in the battery needling process and rapidly spread to the periphery, and the metal layer is broken and fragmented in a large area, thereby realizing the separation of the metal layer and the steel needle, avoiding the conduction of the positive and negative current collector to form a closed loop and the thermal runaway of the battery generated thereby, and further improving the safety performance of the battery; ③ The strain hardening of the composite current collector can be enhanced, and the local stress concentration is reduced, so that the transmission of cracks generated by the deformation of the metal layer of the composite current collector to the periphery in the needling process of the battery is promoted, the large-area fracture and fragmentation of the metal layer are continuously promoted, the closed loop formed by the conduction of the positive and negative current collectors and the thermal runaway of the battery generated by the closed loop are avoided, and the safety performance of the battery is improved.

Preferably, in the formula of the fluorocarbon, x, y and z satisfy: x/(x+y+z) is more than or equal to 0.3 and less than or equal to 0.9,0.05 and y/(x+y+z) is more than or equal to 0.5,0.05 and z/(x+y+z) is more than or equal to 0.2. The chemical composition of the fluorocarbon used for constructing the transition layer meets the characteristics, so that the corrosion resistance of the fluorocarbon and the bonding force of the fluorocarbon to the metal layer can be further improved on the premise of keeping good conductivity, and the flexibility of the transition layer formed by the fluorocarbon is also improved.

In the above scheme: the transition layer may be composed of a plurality of sub-transition layers; the metal layer may be composed of a plurality of sub-metal layers; in the case that the base layer is provided with more than one transition layer, the materials of the transition layers can be the same or different; in the case that the base layer is provided with more than one metal layer, the materials of the metal layers may be the same or different.

Preferably, the composite current collector satisfies at least one of the conditions (a), (b), and (c): the thickness of each transition layer is d1, d1 is more than or equal to 2nm and less than or equal to 50nm; (b) The thickness of the conductive layer is D, D is more than or equal to 500nm and less than or equal to 2000nm, preferably, D is more than or equal to 800nm and less than or equal to 1800nm; (c) the thickness of the base layer is d3, d3 is more than or equal to 1 μm and less than or equal to 10 μm.

When the thickness of each transition layer is d1, d1 is more than or equal to 2nm and less than or equal to 50nm. By controlling the thickness of the transition layer within the range, the safety performance of the composite current collector can be obviously improved by means of the arrangement of the transition layer on the premise that the composite current collector keeps good conductive performance, and the electrochemical device applying the composite current collector has good safety performance and cycle performance.

Preferably, d1 is 5 nm.ltoreq.d1 is.ltoreq.20nm.

Alternatively, the transition layer is prepared by a magnetron sputtering method or a chemical vapor deposition method.

Preferably, the transition layer is prepared by a magnetron sputtering method, and the related process for preparing the transition layer comprises the following steps: graphite with purity more than or equal to 99.9% is used as a target material, and the target power is set to be 1 kW-8 kW; the vacuum degree of the vacuum cabin body for magnetron sputtering is less than or equal to 0.1Pa; the gas source of the film coating comprises argon, methane and carbon tetrafluoride, and the gas flow is 10 mL/min-500 mL/min; the coating time is 0.1 s-30 s each time.

When the thickness of the conductive layer is D, D is more than or equal to 500nm and less than or equal to 2000nm. The thickness of the conductive layer is controlled within the above range, and both maintaining good conductivity of the composite current collector and providing good energy density to the electrochemical device to which the composite current collector is applied can be achieved.

Preferably, D is more than or equal to 800nm and less than or equal to 1800nm; further preferably, 800 nm.ltoreq.D.ltoreq.1200 nm.

When the thickness of the base layer is d3, d3 is more than or equal to 1 mu m and less than or equal to 10 mu m. The preferred thickness range of the base layer is determined based on the difficulty and cost of the manufacturing process.

Preferably, the material constituting the base layer includes at least one of polyethylene terephthalate (PET), polypropylene (PP), polybutylene terephthalate (PBT), polyethylene naphthalate (PEN), polyethylene (PE), polypropylene, polyvinyl chloride (PVC), polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyphenylene Sulfide (PPs), polyphenylene oxide (PPO), polystyrene (PS), polyimide (PI).

Alternatively, the above-described base layer is prepared using a melt-extrusion-biaxially stretching method.

Preferably, the material constituting the metal layer includes at least one of copper, aluminum, copper alloy, and aluminum alloy; the thickness of each metal layer is d2, d2 is more than 0 and less than or equal to 200nm. The thickness of the metal layer is controlled within the range, so that the preparation efficiency of the composite current collector is considered on the premise that the safety performance of the current collector can be obviously improved by the arrangement of the transition layer. If the metal layer is arranged too thin, the preparation efficiency of the composite current collector is lower, and if the metal layer is arranged too thick, the degree of improving the safety performance of the composite current collector by the arrangement of the transition layer is reduced.

Preferably, 50 nm.ltoreq.d2.ltoreq.150 nm.

Preferably, the composite current collector satisfies the condition (e) and/or (f): (e) The number of the metal layers n ₂ meets that n ₂ is more than or equal to 2, preferably, n ₂ is more than or equal to 5 and less than or equal to 15; (f) The number of transition layers n ₁ satisfies n ₁.gtoreq.2, preferably 5.ltoreq.n ₁.ltoreq.15. The metal layers and the transition layers are alternately laminated, and when the composite current collector meets the conditions (e) and/or (f), the preparation efficiency of the composite current collector is considered on the premise that the safety performance of the current collector can be obviously improved by the arrangement of the transition layers. If the number of the metal layers is too large, the preparation efficiency of the composite current collector is lower, and if the number of the metal layers is too small, the number of the transition layers is correspondingly reduced because the metal layers and the transition layers are alternately laminated, so that the safety performance improvement degree of the composite current collector by the arrangement of the transition layers is reduced.

Alternatively, the metal layer is prepared by one or a combination of physical vapor deposition, electroplating and electroless plating.

Preferably, the composite current collector further comprises a protective layer, the protective layer is arranged on the surface of the conductive layer, and the material constituting the protective layer comprises at least one of nickel, chromium, nickel-based alloy, copper oxide, aluminum oxide, silicon oxide, nickel oxide, chromium oxide, cobalt oxide, graphite, carbon black, copper chromate, copper chromite, carbon nano quantum dots, carbon nano tubes, carbon nano fibers, graphene and hydrocarbon. The method is suitable for constructing the hydrocarbon compound of the transition layer and is also suitable for constructing the hydrocarbon compound of the protective layer. The protective layer is provided to better protect the conductive layer from chemical corrosion or physical damage.

Optionally, the protective layer is prepared by one or a combination of physical vapor deposition, chemical vapor deposition, in-situ forming, and coating.

When the protective layer is prepared by physical vapor deposition, it is preferably prepared by vacuum evaporation and/or magnetron sputtering. When the protective layer is prepared by chemical vapor deposition, it is preferable to use atmospheric pressure chemical vapor deposition and/or plasma enhanced chemical vapor deposition. When the protective layer is prepared by an in-situ forming method, a method of forming a metal oxide passivation layer in-situ on the surface of the metal layer is preferably used. When the above protective layer is prepared by a coating method, it is preferable to use one or a combination of processes of die coating, blade coating, extrusion coating.

Preferably, the thickness of the protective layer is d4, and d4 is more than or equal to 5nm and less than or equal to 100nm.

Preferably, 10 nm.ltoreq.d4.ltoreq.80 nm.

According to a second aspect of the present invention, there is provided a method of preparing a composite current collector as above: the preparation method comprises the following operations: alternately forming a transition layer and a metal layer on at least one surface of the base layer; the forming mode of the transition layer is a magnetron sputtering forming process and/or a chemical vapor deposition forming process; the forming conditions of the magnetron sputtering forming process comprise: adopting a carbon-containing target material, and setting the target power to be 1-8kW; providing a gas containing fluorine and hydrogen as a coating gas source, and setting the flow rate of the coating gas source to be 10-500mL/min; in the film plating process, a vacuum environment with the vacuum degree less than or equal to 0.1Pa is provided, and the film plating time is 0.1-30s each time.

According to a third aspect of the present invention, there is provided a pole piece comprising a composite current collector as described above and an active material layer disposed on the surface of the composite current collector.

According to a fourth aspect of the present invention, there is provided a secondary battery comprising the electrode sheet as described above. The secondary battery has good cycle charge and discharge characteristics and good safety performance due to the application of the composite pole piece provided by the invention.

Detailed Description

In order that those skilled in the art will better understand the present invention, a technical solution of the embodiments of the present invention will be clearly and completely described below, and it is apparent that the described embodiments are only some embodiments of the present invention, not all embodiments.

Example 1

The embodiment adopts a magnetron sputtering method to prepare the composite current collector according to the following steps:

S1, a biaxially oriented PET film with the thickness of 4.5 mu m is adopted as a base layer, and the base layer is placed in a magnetron sputtering machine.

S2, depositing a transition layer on the surface of the base layer, and setting materials and operation parameters related to preparation of the transition layer as follows: graphite target (purity is 99.99%) is used as target material, and target power is 2kW; carbon tetrafluoride (CF ₄), methane (CH ₄) and argon are used as air sources, wherein the flow rate of CF ₄ is 180mL/min, the flow rate of CH ₄ is 60mL/min and the flow rate of argon is 50mL/min; the vacuum degree of the coating is 0.08Pa, the coating time is 1s, and the temperature of the main roller in the coating process is 0 ℃; the transition layer thus produced is composed of a fluorocarbon compound having the formula C _xF_yH_z, and x, y and z satisfy: x/(x+y+z) =0.6, y/(x+y+z) =0.3, z/(x+y+z) =0.1, and the thickness of the transition layer is 5nm.

S3, depositing a metal layer on the surface of the transition layer formed in the step S2, wherein materials and operation parameters related to the preparation of the metal layer are set as follows: copper targets (purity: 99.99%) are used as targets, and target power is 12kW; taking argon as an origin, wherein the flow of the argon is 50mL/min, the vacuum degree of the coating is 0.08Pa, the coating time is 5s, and the temperature of a main roller in the coating process is 2 ℃; the metal layer thus obtained consisted of elemental copper and had a thickness of 50nm.

S4, sequentially and circularly repeating the steps S2 and S3 until 10 transition layers and 10 metal layers are formed on the two side surfaces of the base layer respectively, and alternately laminating the 10 transition layers and the 10 metal layers on any side surface of the base layer to form a conductive layer, wherein the total thickness of the conductive layer is 550nm, so that a composite current collector semi-finished product is obtained.

S5, placing the semi-finished product of the composite current collector obtained after the completion of the step S4 in coating equipment, taking a graphene solution (a solvent is nitrogen methyl pyrrolidone) with the solid content of 0.10wt.% as a coating liquid, uniformly coating the coating liquid on the surfaces of conductive layers on two sides of the semi-finished product of the composite current collector (the conductive layers on each side are all made of metal layers serving as the surface layers thereof) through a die head coating process, and finally drying at 70 ℃ to obtain a protective layer with the thickness of 10nm on the surface of the conductive layer, thereby obtaining the composite current collector of the embodiment, wherein the total thickness of the composite current collector is 5.62 mu m.

Example 2

This example the fabrication of the composite current collector of this example was accomplished with reference to the method for preparing a composite current collector of example 1. The difference from example 1 is that the coating time for preparing the metal layer in S3 of the process of preparing the composite current collector is adjusted to 10S, and the thickness of the metal layer prepared by the method is 100nm, and materials and other specific operations adopted in the process of preparing the composite current collector in this example are strictly consistent with those in example 1 except the above differences.

Example 3

This example the fabrication of the composite current collector of this example was accomplished with reference to the method for preparing a composite current collector of example 1. The difference from example 1 is that the coating time for preparing the metal layer in S3 of the process of preparing the composite current collector is adjusted to 15S, and the thickness of the metal layer prepared by the method is 150nm, and materials and other specific operations adopted in the process of preparing the composite current collector are strictly consistent with those of example 1 except the difference.

Example 4

This example the fabrication of the composite current collector of this example was accomplished with reference to the method for preparing a composite current collector of example 1. The difference from example 1 is that the coating time for preparing the metal layer in S3 of the process of preparing the composite current collector is adjusted to 20S, and the thickness of the metal layer prepared thereby is 200nm, and the materials and other specific operations adopted in the process of preparing the composite current collector in this example are strictly consistent with those in example 1 except the above differences.

Example 5

This example the method for preparing a composite current collector according to example 2 completes the fabrication of the composite current collector according to this example. The difference from example 2 is that the coating time for preparing the transition layer is adjusted to 0.4S in S2 of the process of preparing the composite current collector, and the thickness of the prepared transition layer is 2nm, and materials and other specific operations adopted in the process of preparing the composite current collector are strictly consistent with those of example 2 except the difference.

Example 6

This example the method for preparing a composite current collector according to example 2 completes the fabrication of the composite current collector according to this example. The difference from example 2 is that the coating time for preparing the transition layer is adjusted to 4S in S2 of the process of preparing the composite current collector, and the thickness of the prepared transition layer is 20nm, and materials and other specific operations adopted in the process of preparing the composite current collector in this example are strictly consistent with those in example 2 except the above differences.

Example 7

This example the method for preparing a composite current collector according to example 2 completes the fabrication of the composite current collector according to this example. The difference from example 2 is that the coating time for preparing the transition layer is adjusted to 10S in S2 of the process of preparing the composite current collector, and the thickness of the prepared transition layer is 50nm, and materials and other specific operations adopted in the process of preparing the composite current collector in this example are strictly consistent with those in example 2 except the above differences.

Example 8

This example the method for preparing a composite current collector according to example 2 completes the fabrication of the composite current collector according to this example. The difference from the constitution of example 2 is that the process of preparing a composite current collector is adjusted to "the above-mentioned S2, S3 are repeated in turn and cyclically until 3 transition layers and 3 metal layers are formed on each of both side surfaces of the base layer, and on either side surface of the base layer, 3 transition layers and 3 metal layers are alternately laminated to constitute a conductive layer having a total thickness of 315nm, whereby a composite current collector semi-finished product is obtained," except the above-mentioned difference, the materials and other specific operations adopted in the process of preparing a composite current collector in this example are strictly consistent with those of example 2.

Example 9

This example the method for preparing a composite current collector according to example 2 completes the fabrication of the composite current collector according to this example. The difference from the constitution of example 2 is that the process of preparing a composite current collector is adjusted to "the above-mentioned S2, S3 are sequentially and cyclically repeated until 5 transition layers and 5 metal layers are formed on each of both side surfaces of the base layer, and on either side surface of the base layer, 5 transition layers and 5 metal layers are alternately laminated to constitute a conductive layer having a total thickness of 525nm, whereby a composite current collector semi-finished product is obtained, and materials and other specific operations adopted in the process of preparing a composite current collector in this example are strictly consistent with those of example 2 except the above-mentioned difference.

Example 10

This example the method for preparing a composite current collector according to example 2 completes the fabrication of the composite current collector according to this example. The difference from example 2 is that the process of preparing the composite current collector is adjusted to "the steps of sequentially repeating the steps of S2 and S3 in a cyclic manner until 15 transition layers and 15 metal layers are formed on both side surfaces of the base layer, and the 15 transition layers and the 15 metal layers are alternately laminated on either side surface of the base layer to form a conductive layer, and the total thickness of the conductive layer is 1575nm, so that a semi-finished product of the composite current collector is obtained.

Example 11

This example the fabrication of the composite current collector of this example was accomplished with reference to the method for preparing a composite current collector of example 1. The difference from example 1 is that the process of preparing the composite current collector is S3 adjusted to "depositing a metal layer on the surface of the transition layer formed in S2, and the materials and operating parameters involved in the preparation of the metal layer are set as follows: taking an aluminum target (purity: 99.99%) as a target material, wherein the target power is 10kW; the metal layer prepared by taking argon as an origin, wherein the argon flow is 50mL/min, the vacuum degree of the coating is 0.07Pa, the coating time is 5s, the temperature of the main roller in the coating process is 2 ℃, the metal layer is composed of an aluminum simple substance, and the thickness of the metal layer is 50nm, and except the difference, materials and other specific operations adopted in the process of preparing the composite current collector in the embodiment are strictly consistent with those in the embodiment 1.

Example 12

This example the fabrication of the composite current collector of this example was accomplished with reference to the method for preparing a composite current collector of example 1. The difference from example 1 is that the film material used as the base layer was replaced with a polypropylene (PP) film having a thickness of 4.5 μm in S1 of the process of preparing the composite current collector, and the materials and other specific operations used in the process of preparing the composite current collector in this example were strictly consistent with those in example 1 except the above differences.

Example 13

This example the fabrication of the composite current collector of this example was accomplished with reference to the method for preparing a composite current collector of example 1. The difference from example 1 is that the S2 of the process of preparing the composite current collector is adjusted to "deposit a transition layer on the surface of the base layer, the materials involved in the preparation of the transition layer and the operating parameters are set as follows: graphite target (purity is 99.99%) is used as target material, and target power is 1.8kW; carbon tetrafluoride (CF ₄), methane (CH ₄) and argon are used as air sources, wherein the flow rate of CF ₄ is 200mL/min, the flow rate of CH ₄ is 120mL/min and the flow rate of argon is 50mL/min; the vacuum degree of the coating is 0.08Pa, the coating time is 1.2s, the temperature of the main roller in the coating process is 0 ℃, the prepared transition layer is composed of fluorocarbon, the chemical formula of the fluorocarbon is C _xF_yH_z, and x, y and z satisfy the following conditions: except for the above differences, the materials used in the process of preparing the composite current collector in this example and other specific operations were exactly the same as those in example 1, except for the differences described above, x/(x+y+z) =0.3, y/(x+y+z) =0.5, and z/(x+y+z) =0.2.

Example 14

This example the fabrication of the composite current collector of this example was accomplished with reference to the method for preparing a composite current collector of example 1. The difference from example 1 is that the S2 of the process of preparing the composite current collector is adjusted to "deposit a transition layer on the surface of the base layer, the materials involved in the preparation of the transition layer and the operating parameters are set as follows: graphite target (purity is 99.99%) is used as target material, and target power is 2.4kW; carbon tetrafluoride (CF ₄), methane (CH ₄) and argon are used as air sources, wherein the flow rate of CF ₄ is 200mL/min, the flow rate of CH ₄ is 120mL/min and the flow rate of argon is 50mL/min; the vacuum degree of the coating is 0.08Pa, the coating time is 0.8s, the temperature of the main roller in the coating process is 0 ℃, the prepared transition layer is composed of fluorocarbon, the chemical formula of the fluorocarbon is C _xF_yH_z, and x, y and z satisfy the following conditions: except for the above differences, the materials used in the process of preparing the composite current collector in this example and other specific operations were exactly the same as those in example 1, except for the differences that x/(x+y+z) =0.9, y/(x+y+z) =0.05, and z/(x+y+z) =0.05.

Example 15

This example the fabrication of the composite current collector of this example was accomplished with reference to the method for preparing a composite current collector of example 1. The difference from example 1 is that the coating time of S3 in the process of preparing the composite current collector is adjusted to 22S, and the thickness of the metal layer prepared by the method is 220nm, and the materials and other specific operations adopted in the process of preparing the composite current collector are strictly consistent with those of example 1 except the difference.

Example 16

This example the method for preparing a composite current collector according to example 2 completes the fabrication of the composite current collector according to this example. The difference from example 2 is that the coating time for preparing the transition layer is adjusted to 11S in S2 of the process of preparing the composite current collector, and the thickness of the prepared transition layer is 55nm, and materials and other specific operations adopted in the process of preparing the composite current collector in this example are strictly consistent with those in example 2 except the above differences.

Example 17

This example the method for preparing a composite current collector according to example 2 completes the fabrication of the composite current collector according to this example. The difference from example 2 is that the coating time for preparing the transition layer is adjusted to 0.2S in the process of preparing the composite current collector in S2, and the thickness of the prepared transition layer is 1nm, and materials and other specific operations adopted in the process of preparing the composite current collector in this example are strictly consistent with those in example 2 except the difference.

Example 18

This example the method for preparing a composite current collector according to example 2 completes the fabrication of the composite current collector according to this example. The difference from example 2 is that the process of preparing the composite current collector is adjusted to "the steps of sequentially repeating the steps of S2 and S3 in a cyclic manner until 16 transition layers and 16 metal layers are formed on both side surfaces of the base layer, and the 16 transition layers and the 16 metal layers are alternately laminated on either side surface of the base layer to form a conductive layer having a total thickness of 1680nm, thereby obtaining a semi-finished product of the composite current collector", and materials and other specific operations adopted in the process of preparing the composite current collector are strictly consistent with those of example 2 except the difference.

Example 19

This example the method for preparing a composite current collector according to example 2 completes the fabrication of the composite current collector according to this example. The difference from the constitution of example 2 is that the process of preparing a composite current collector is adjusted to "the above-mentioned S2, S3 are sequentially and cyclically repeated until 2 transition layers and 2 metal layers are formed on each of both side surfaces of the base layer, and on either side surface of the base layer, 2 transition layers and 2 metal layers are alternately laminated to constitute a conductive layer having a total thickness of 210nm, thereby obtaining a composite current collector semi-finished product", and materials and other specific operations adopted in the process of preparing a composite current collector in this example are strictly consistent with those of example 2 except the above-mentioned difference.

Example 20

This example the fabrication of the composite current collector of this example was accomplished with reference to the method for preparing a composite current collector of example 1. The difference from example 1 is that the S2 of the process of preparing the composite current collector is adjusted to "deposit a transition layer on the surface of the base layer, the materials involved in the preparation of the transition layer and the operating parameters are set as follows: graphite target (purity is 99.99%) is used as target material, and target power is 1.6kW; carbon tetrafluoride (CF ₄), methane (CH ₄) and argon are used as air sources, wherein the flow rate of CF ₄ is 318mL/min, the flow rate of CH ₄ is 132mL/min and the flow rate of argon is 50mL/min; the vacuum degree of the coating is 0.08Pa, the coating time is 1.5s, the temperature of the main roller in the coating process is 0 ℃, the prepared transition layer is composed of fluorocarbon, the chemical formula of the fluorocarbon is C _xF_yH_z, and x, y and z satisfy the following conditions: except for the above differences, the materials used in the process of preparing the composite current collector in this example and other specific operations were exactly the same as those in example 1, except for the differences described above, x/(x+y+z) =0.25, y/(x+y+z) =0.53, and z/(x+y+z) =0.22.

Example 21

This example the fabrication of the composite current collector of this example was accomplished with reference to the method for preparing a composite current collector of example 1. The difference from example 1 is that the S2 of the process of preparing the composite current collector is adjusted to "deposit a transition layer on the surface of the base layer, the materials involved in the preparation of the transition layer and the operating parameters are set as follows: graphite target (purity is 99.99%) is used as target material, and target power is 2.6kW; carbon tetrafluoride (CF ₄), methane (CH ₄) and argon are used as air sources, wherein the flow rate of CF ₄ is 18mL/min, the flow rate of CH ₄ is 12mL/min and the flow rate of argon is 50mL/min; the vacuum degree of the coating is 0.08Pa, the coating time is 0.7s, the temperature of the main roller in the coating process is 0 ℃, the prepared transition layer is composed of fluorocarbon, the chemical formula of the fluorocarbon is C _xF_yH_z, and x, y and z satisfy the following conditions: except for the above differences, the materials and other specific operations used in the process of preparing the composite current collector in this example were exactly the same as those in example 1, except for the differences that x/(x+y+z) =0.95, y/(x+y+z) =0.03, and z/(x+y+z) =0.02.

Comparative example 1

This comparative example uses example 1 as a control, and a magnetron sputtering method is used to prepare a composite current collector, and the steps for preparing the composite current collector in this comparative example are specifically as follows:

S2, depositing a metal layer on the surface of the base layer, and setting the materials and operation parameters related to the preparation of the metal layer as follows: copper targets (purity: 99.99%) are used as targets, and target power is 12kW; taking argon as an origin, wherein the flow of the argon is 50mL/min, the vacuum degree of the coating is 0.08Pa, the coating time is 50s, and the temperature of a main roller in the coating process is 2 ℃; the metal layer thus produced consisted of elemental copper and the thickness of the metal layer was 500nm, thereby obtaining a composite current collector semi-finished product.

S3, placing the semi-finished product of the composite current collector obtained after the S2 is completed in coating equipment, taking a graphene solution (a solvent is nitrogen methyl pyrrolidone) with the solid content of 0.10wt.% as a coating liquid, uniformly coating the coating liquid on the surfaces of conductive layers on two sides of the semi-finished product of the composite current collector through a die head coating process (the conductive layers on each side are all made of metal layers as the surface layers), and finally drying at 70 ℃ to obtain a protective layer with the thickness of 10nm on the surface of the conductive layer, thereby obtaining the composite current collector of the comparative example, wherein the total thickness of the composite current collector is 5.52 mu m.

Comparative example 2

This comparative example the preparation of the composite current collector of this example was completed with reference to the method for preparing a composite current collector of example 1. The difference from example 1 is that S2 of the process of preparing the composite current collector is adjusted to "deposit a carbon layer on the surface of the base layer, the materials involved in the preparation of the carbon layer and the operating parameters are set as follows: graphite targets (purity 99.99%) are used as targets, the target power is 3kW, the argon flow is 50mL/min, the vacuum degree of the coating is 0.08Pa, the coating time is 1s, the temperature of a main roller in the coating process is 0 ℃, the thickness of a prepared carbon layer is 5nm, and materials and other specific operations adopted in the process of preparing the composite current collector in the comparative example are strictly consistent with those in the embodiment 1 except the differences.

Preparation example

Preparation of a class A lithium ion battery:

S1, preparing a composite negative plate, wherein the metal layers of the composite current collectors prepared in the examples 1-10, 12-21 and the comparative examples 1 and 2 are all copper simple substances, and the composite current collectors are respectively used as the negative current collectors; according to graphite: conductive carbon (Super P): carbon nanotubes: carboxymethyl cellulose = 96:1.0:0.5:2.5, adding the materials into deionized water according to the mass ratio to prepare negative electrode slurry with the solid content of 70%; and coating the negative electrode slurry on the surface of the negative electrode current collector, and drying to form a negative electrode active material layer.

S2, preparing a conventional positive plate, wherein an aluminum foil with the thickness of 13 mu m is adopted as a positive current collector; according to NCM622: conductive carbon (Super P): carbon nanotubes: polyvinylidene fluoride=96: 1.8:0.5:1.7, adding the materials into N-methyl pyrrolidone to prepare anode slurry with the solid content of 70%; and coating the positive electrode slurry on the surface of the positive electrode current collector, and drying to form a positive electrode active material layer.

S3, selecting a diaphragm, namely adopting an alumina ceramic coated polyethylene diaphragm (with the thickness of 25 mu m) as the diaphragm for assembling the lithium ion battery.

S4, preparing electrolyte, namely taking propylene carbonate, ethylene carbonate and methyl ethyl carbonate, fully mixing the materials according to the mass ratio of 1:1:1 to obtain a carbonate solvent, adding LiPF ₆ into the carbonate solvent to prepare a carbonate solution of 1 mol.L ^-1LiPF₆, and taking the carbonate solution as the electrolyte of the lithium ion battery.

S5, assembling the lithium ion battery, namely enabling different composite negative plates to be matched with the conventional positive plates respectively based on different types of included composite current collectors, and stacking the conventional positive plates, the isolation film and the composite negative plates in sequence to prepare a bare cell; and placing the bare cell in an outer packaging shell of the lithium battery, drying, injecting electrolyte, and performing procedures such as vacuum packaging, standing, formation, shaping and the like to obtain the class A lithium ion battery.

Preparation of a B-type lithium ion battery:

S1, preparing a composite positive plate, wherein the metal layers included in the composite current collector prepared in the embodiment 11 are all made of aluminum simple substances, the composite current collector is respectively used as a positive current collector, and a positive active material layer using LiNi _0.6Mn_0.2Co_0.2O₂ (NCM 622) as a positive active material is prepared on the surface of the positive current collector.

S2, preparing a conventional negative plate, namely preparing a negative active material layer taking artificial graphite as a negative active material on the surface of a negative current collector by taking copper foil with the thickness of 6 mu m as the negative current collector.

S3, selecting a diaphragm, wherein the diaphragm is the same as the diaphragm used for assembling the I-type lithium ion battery.

S4, preparing electrolyte, wherein the electrolyte is the same as the electrolyte prepared by assembling the class I lithium ion battery.

S5, assembling the lithium ion battery, namely, enabling different composite positive plates to be matched with the conventional negative plates respectively based on different types of included composite current collectors, and sequentially stacking the composite positive plates, the isolation films and the conventional negative plates to prepare a bare cell; and placing the bare cell in an outer packaging shell of the lithium battery, drying, injecting electrolyte, and performing procedures such as vacuum packaging, standing, formation, shaping and the like to obtain the B-class lithium ion battery.

In the preparation operation of the A-type lithium ion battery and the B-type lithium ion battery, the following steps are carried out: the slurry composition for forming the anode active material layers on the surfaces of different anode current collectors is kept completely the same, and the specific operation for forming the anode active material layers is also kept completely the same, thereby keeping the anode active material layers uniform in each lithium ion battery; the slurry composition for forming the positive electrode active material layers on the surfaces of different positive electrode current collectors is kept identical, and the specific operation for forming the positive electrode active material layers is also kept identical, so that the positive electrode active material layers in each lithium ion battery are kept identical; except for the difference between the positive electrode plate and the negative electrode plate, other parts and related operations adopted for assembling the lithium ion battery are strictly consistent.

Preparation of control lithium ion battery:

S1, preparing a conventional positive plate, wherein a conventional aluminum current collector with the thickness of 13 mu m (which is consistent with that of a conventional aluminum current collector applied to a class A lithium ion battery) is used as a positive current collector, and a positive active material layer with LiNi _0.6Mn_0.2Co_0.2O₂ (NCM 622) as a positive active material is prepared on the surface of the positive current collector.

S2, preparing a conventional negative plate, wherein a traditional copper current collector (consistent with a traditional copper current collector applied to a B-type lithium ion battery) with the thickness of 6 μm is used as a negative current collector, and a negative active material layer using artificial graphite as a negative active material is prepared on the surface of the negative current collector.

S5, assembling the lithium ion battery, namely, enabling different composite positive plates to be matched with the conventional negative plates respectively based on different types of included composite current collectors, and sequentially stacking the composite positive plates, the isolation films and the conventional negative plates to prepare a bare cell; and placing the bare cell in an outer packaging shell of the lithium battery, drying, injecting electrolyte, and performing procedures such as vacuum packaging, standing, formation, shaping and the like to obtain the control lithium ion battery.

The lithium ion batteries prepared in this preparation example are numbered, and the current collector used for assembling the lithium ion batteries is shown in table 1 corresponding to the specific lithium ion battery number, as shown in table 1.

TABLE 1 lithium ion Battery prepared in this preparation example

Test case

1. Elongation at break test of current collector

(1) Test object

The composite current collectors prepared in examples 1 to 21 and comparative examples 1 and 2 were used as test subjects.

(2) Test item and test method

Elongation at break test: the elongation at break of the test object is tested according to national standard GB/T1040.3-2006.

2. Battery performance test

(1) Test object

The composite current collector adopted in the preparation example and the lithium ion battery prepared by the composite current collector are used as test objects.

(2) Test item and test method

Charge-discharge cycle performance: the lithium ion battery was charged and discharged for 2000 cycles at a charge/discharge rate of 1C, and the battery capacity retention after 2000 cycles of charging and discharging of the lithium ion battery was calculated as battery capacity retention after 2000 cycles of charging and discharging = battery capacity after 2000 cycles of charging and discharging/initial capacity of the battery x 100%.

Safety performance test: the safety performance of the lithium ion battery is verified by adopting a needling experiment, which is concretely characterized in that the lithium ion battery is placed in a needling experiment device, the diameter of a steel needle in the needling experiment device is 3mm, the needling speed is set to be 10mm/s, the needling experiment is carried out on the lithium ion battery, wherein each lithium ion battery is provided with 100 repetitions, each repetition is 1 lithium ion battery, in the needling experiment process, a test object is not exploded, does not fire and does not smoke, and is marked as passing, otherwise, the test object is marked as passing, the quantity of the lithium ion batteries marked as passing and marked as not passing in 100 repeated experiments set for each lithium ion battery is recorded and counted, the needling passing rate of each lithium ion battery is calculated, the quantity of the lithium ion batteries marked as passing in each lithium ion battery is = the total quantity of the lithium ion batteries/the test object is provided with the repeated experiment multiplied by 100%.3. Analysis of results

The test results of this test example are shown in table 2. As is apparent from the data shown in table 2, in the test examples, the battery capacity retention and the battery penetration rate measured by the batteries D1 and D2 were significantly lower, and the batteries 1 to 21 each had a higher battery capacity retention and a higher battery penetration rate than the above-mentioned lithium ion batteries. In the class a lithium ion battery, transition layers made of hydrocarbon are provided in the negative electrode current collectors used in the batteries 1 to 10 and the batteries 12 to 21, and the provision of the transition layers has the effect of: ① The transition layer can resist electrolyte and can be attached to the surface of the metal layer, so that a certain barrier effect can be achieved on the contact between the electrolyte and the metal layer, a good protection effect is achieved on the metal layer, and the cycle charge and discharge performance of the batteries 1-21 is obviously improved relative to the batteries D1 and D2; ② The transition layer can obstruct the penetration of the crystal grains of the adjacent metal layers and promote the re-nucleation growth of the crystal grains, so as to generate non-penetration crystal grains with smaller size, the generated metal layer formed by the non-penetration crystal grains with smaller size can generate microcracks after certain deformation in the battery needling process and rapidly spread to the periphery, and the metal layer is broken and fragmented in a large area, thereby realizing the separation of the metal layer and the steel needle, avoiding the conduction of the positive and negative current collector to form a closed loop and the thermal runaway of the battery generated thereby, and further improving the safety performance of the battery; ③ The strain hardening of the composite current collector can be enhanced, and the local stress concentration is reduced, so that the transmission of cracks generated by the deformation of the metal layer of the composite current collector to the periphery in the needling process of the battery is promoted, the large-area fracture and fragmentation of the metal layer are continuously promoted, the closed loop formed by the conduction of the positive and negative current collectors and the thermal runaway of the battery generated by the closed loop are avoided, and the safety performance of the battery is improved. The above-mentioned effects are favorable to avoiding the positive and negative electrode current collectors of the batteries 1-21 from being conducted to form a closed loop and the battery thermal runaway caused by the closed loop, so that the safety performance of the batteries 1-21 is obviously improved relative to the batteries D1 and D2.

The test results of the batteries 1, 13, 14, 20 and 21 in the test example are compared, and compared with the batteries 20 and 21, the batteries 1, 13 and 14 have higher battery capacity retention rate and higher battery needling passing rate, and have better cycle charge and discharge performance and safety. In the above test objects, the difference is that the chemical composition of the hydrocarbon compound forming the transition layer of the composite current collector, the carbon content, fluorine content and hydrogen content in the hydrocarbon compound affect the properties of the transition layer, so that the lithium ion battery applying the composite current collector forms a certain difference in the cyclic charge-discharge performance and the safety performance. Wherein, as the hydrocarbon carbon content in the composition transition layer increases, the conductivity of the composite current collector tends to increase and the flexibility tends to decrease, when the hydrocarbon carbon content of the composition transition layer satisfies 0.3 < x/(x+y+z) < 0.9, the composition transition layer can be made to have good conductivity and flexibility, and when the hydrocarbon carbon content of the composition transition layer is low, the conductivity of the composition transition layer is deteriorated to some extent, thereby causing the conductivity of the composite current collector to decrease, causing the cycle performance of the battery to decrease, and when the hydrocarbon carbon content of the composition transition layer is high, the flexibility of the transition layer is decreased, and the probability of forming defects relative to the transition layer is increased, causing the cycle performance of the battery to decrease. The fluorine content and the hydrogen content in the hydrocarbon comprehensively influence the corrosion resistance of the transition layer and the polarity of the transition layer, when the fluorine content of the hydrocarbon meets 0.05-0.5 y/(x+y+z) and the hydrogen content meets 0.05-0.2 z/(x+y+z), the transition layer has excellent corrosion resistance, the polarity of the transition layer can be controlled within a preferred range, so that the transition layer can be stably compounded with the metal layer, and compared with the hydrocarbon with the fluorine content and the hydrogen content which can reach the preferred range, the corrosion resistance of the transition layer is reduced, so that the cycle performance of the battery is reduced, and when the fluorine content of the hydrocarbon is higher or the hydrogen content is lower, the binding force of the transition layer and the metal layer is reduced, so that the cycle performance and the safety performance of the battery are reduced. In general, regarding the hydrocarbon compound constituting the transition layer, the chemical composition C _xF_yH_z of the hydrocarbon compound satisfies 0.3.ltoreq.x/(x+y+z). Ltoreq. 0.9,0.05.ltoreq.y/(x+y+z). Ltoreq. 0.5,0.05.ltoreq.z/(x+y+z). Ltoreq.0.2, and the transition layer can be provided with more excellent comprehensive properties, and the corrosion resistance of the transition layer and the binding force thereof to the metal layer can be further improved on the basis of ensuring good conductivity and flexibility of the transition layer, so that the lithium ion battery using the composite current collector provided with the transition layer exhibits excellent cyclic charge-discharge performance and safety.

The difference between the composite current collectors prepared in examples 2, 5 to 7, 16 and 17 is that the thicknesses of the transition layers are different, and it can be seen from comparison of test results of lithium ion batteries (batteries 2, 5 to 7, 16 and 17) using the composite current collector as a negative electrode current collector: along with the increase of the thickness of the transition layer of the applied composite current collector, the cyclic capacity retention rate of the lithium ion battery shows a change trend of increasing firstly and then decreasing, and on the other hand, the battery needling passing rate measured by the lithium ion battery shows a change rule of increasing obviously firstly and then tending to keep stable. The reason for the rule of variation of the test results may be that a transition layer is provided based on the application of the lithium ion battery: the thickness of the transition layer is increased, so that the blocking and tolerance of the transition layer to electrolyte can be improved, the cyclic charge and discharge performance of the battery based on the composite copper current collector is promoted, but when the thickness of the transition layer exceeds a certain range, the conductive performance of the conductive layer is reduced, and the cyclic charge and discharge performance of the lithium ion battery applying the composite current collector is deteriorated; on the other hand, the thickness of the transition layer is increased, large-area fission of the conductive layer in the needling process can be promoted, so that the conductive layer is easier to break away from the steel needle, the needling passing rate of the battery measured by a test object is obviously increased, namely, the safety performance of the lithium ion battery is obviously improved, but when the thickness of the transition layer exceeds a certain range, the further increase of the thickness of the transition layer is difficult to obviously increase the needling passing rate of the battery, and the safety performance of the lithium ion battery basically tends to be stable. Based on the analysis of the test results of the batteries 2, 5-7, 16 and 17, the preferred value range of the thickness d1 of the transition layer is 2-50 nm, and the more preferred value range is 5-20 nm by comprehensively considering the cycle charge-discharge performance and the safety performance of the lithium ion battery.

The difference between the composite current collectors prepared in examples 1 to 4 and 15 is that the thicknesses of the metal layers are different, and it can be seen that the test results of the test objects (batteries 1 to 4 and 15) using the composite current collector as the negative electrode current collector are compared with each other: as the thickness of the metal layer of the applied composite current collector increases, both the capacity retention rate measured by the lithium ion battery and the battery needling pass rate show a tendency to increase and then decrease. The reason for the variation rule of the test result may be that the conductive layer of the composite current collector applied on the basis of the lithium ion battery is formed by alternately laminating the metal layer and the transition layer, the variation of the thickness of the metal layer can influence the grain size distribution condition of the metal layer along the thickness direction of the metal layer, and further influence the breaking behavior of the metal layer in the needling experiment process, so that the safety performance of the lithium ion battery is changed, and meanwhile, the variation of the grain size along the thickness direction of the metal layer can influence the conduction resistance of electrons in the charging and discharging processes of the lithium ion battery, so that the cyclic charging and discharging performances of the battery are influenced. Based on the analysis of the test results of the batteries 1 to 4 and 15, the metal layer thickness d2 is preferably controlled within a value range of not more than 200nm, and the more preferred value range of d2 is 50nm to 150nm by comprehensively considering the cycle charge-discharge performance and the safety performance of the lithium ion battery.

In the process of preparing the composite current collector in examples 2, 8 to 10, 18 and 19, the difference is that the number of transition layers n1 and the number of metal layers n2 are different, and the composite current collector prepared in the above examples is applied to the preparation of the batteries 2, 8 to 10, 18 and 19 respectively, and by comparing the test results of the batteries 2, 8 to 10, 18 and 19, it can be seen that: with the increase of the number of metal layers and the number of transition layers of the composite current collector, the thickness of the composite current collector is increased, and the capacity retention rate and the battery needling pass rate measured by the lithium ion battery are all in a change rule that the increase is obvious and then tends to keep stable. The reason for the test results is probably that by improving the multilayer alternating structure of the transition layer and the metal layer, on one hand, the layer-by-layer protection of the transition layer to the metal layer can be enhanced, the inhibition effect of the electrolyte on corroding the metal layer is enhanced, thereby promoting the improvement of the battery cycle charge and discharge performance, on the other hand, the conductive layer of the lithium ion battery is easier to break in a large area in the needling experiment process, thereby leading the conductive layer to be easier to disconnect with a steel needle, further promoting the safety performance of the lithium ion battery, but after the number of layers of the transition layer and the metal layer exceeds 15 layers, the number of layers of the transition layer and the metal layer is increased continuously, so that the lithium ion battery performance based on the application of the composite current collector is difficult to be obviously improved, and however, the number of layers of the transition layer and the metal layer is increased, so that the manufacturing procedure and the manufacturing cost of the composite current collector are correspondingly increased. By combining the analysis of the results, the cyclic charge and discharge performance and the safety performance of the lithium ion battery based on the application of the composite current collector and the preparation efficiency and the cost of the composite current collector are comprehensively considered, and the number of transition layers and metal layers is preferably 5-15.

TABLE 2 statistics of the test results of the battery performance of the reference lithium ion batteries of the test examples

Among the lithium ion batteries to be tested, the differences among the battery 1, the battery 13, the battery 14, the battery 20, the battery 21 and the battery D2 are the materials of the transition layers included in the composite current collector used in the lithium ion battery, wherein the transition layers included in the composite current collector used in the battery 1 (corresponding to example 1), the battery 13 (corresponding to example 13), the battery 14 (corresponding to example 14), the battery 20 (corresponding to example 20) and the battery 21 (corresponding to example 21) are each composed of a fluorocarbon compound, and the transition layers included in the composite current collector used in the battery D2 (corresponding to example 2) are only composed of a simple substance of carbon. In order to fully reflect the influence of the material composition of the transition layer on the performance of the composite current collector and the lithium ion battery, the elongation at break test of the composite current collector applied to the lithium ion battery is further carried out, and the test results are shown in table 3. As can be seen from the data shown in table 3, the measured elongation at break of the composite current collector prepared in comparative example 2 is significantly lower than that of the other composite current collectors tested, thus demonstrating that the application rate of fracture of the composite current collector is significantly reduced by using the transition layer composed of elemental carbon compared with the transition layer structure composed of hydrocarbon, and thus the mechanical properties of the composite current collector are significantly deteriorated. Although the test results shown in table 2 show that in the battery capacity retention test performed on the lithium ion battery in the present test example, the battery capacity retention of the battery D2 is higher than the battery capacity retention of the battery 13, the battery 14, the battery 20, and the battery 21, considering the elongation at break test results in the present test example, the elongation at break of the composite current collector decreases and the mechanical properties of the composite current collector become worse as the carbon content of the transition layer increases, and thus, in the practical application process, as the number of cycles of the lithium ion battery increases gradually, the external stress to which the composite current collector is subjected accumulates, so that the mechanical properties of the composite current collector have an increasingly significant effect on the structural stability of the composite current collector and the cycle performance of the lithium ion battery, and as the number of cycles increases, the degradation of the cycle stability of the battery D2 will become increasingly significant, as the battery performance of the battery D2 decreases.

TABLE 3 statistical test results of elongation at break of composite current collectors

The above embodiments are only for illustrating the technical solution of the present invention and not for limiting the scope of the present invention, and although the present invention has been described in detail with reference to the above embodiments, it should be understood by those skilled in the art that modifications or equivalent substitutions can be made to the technical solution of the present invention, but these modifications or substitutions are all within the scope of the present invention.

Claims

1. A composite current collector, characterized by:

The composite current collector comprises a base layer and a conductive layer, wherein the conductive layer is arranged on at least one surface of the base layer, the conductive layer comprises n ₁ transition layers and n ₂ metal layers, n ₁ is a positive integer greater than 1, n ₂ is a positive integer greater than 1, and the metal layers and the transition layers are alternately laminated in the conductive layer;

the transition layer is composed of a fluorocarbon having a chemical formula of C _xF_yH_z:

and x, y and z satisfy: x/(x+y+z) is less than or equal to 0.25 and less than or equal to 0.95, and x is not equal to 0, y is not equal to 0, and z is not equal to 0.

2. The composite current collector of claim 1, wherein: in the formula of the hydrocarbon compound, x, y and z satisfy: x/(x+y+z) is more than or equal to 0.3 and less than or equal to 0.9,0.05 and y/(x+y+z) is more than or equal to 0.5,0.05 and z/(x+y+z) is more than or equal to 0.2.

3. The composite current collector of claim 1, wherein said composite current collector satisfies at least one of conditions (a), (b), and (c):

(a) The thickness of each transition layer is d1, d1 is more than or equal to 2nm and less than or equal to 50nm;

(b) The thickness of the conductive layer is D, D is more than or equal to 500nm and less than or equal to 2000nm, preferably, D is more than or equal to 800nm and less than or equal to 1800nm;

(c) The thickness of the base layer is d3, d3 is more than or equal to 1 mu m and less than or equal to 10 mu m.

4. The composite current collector of claim 1, wherein: the material constituting the metal layer comprises at least one of copper, aluminum, copper alloy and aluminum alloy; the thickness of each metal layer is d2, d2 is more than 0 and less than or equal to 200nm, preferably, d2 is more than or equal to 50nm and less than or equal to 150nm.

5. A composite current collector according to claim 4, wherein the composite current collector satisfies conditions (e) and/or (f):

(e) The number of the metal layers n ₂ meets that n ₂ is more than or equal to 2, preferably, n ₂ is more than or equal to 5 and less than or equal to 15;

(f) The number of transition layers n ₁ satisfies n ₁ not less than 2, preferably 5 not less than ₁ not more than 15.

6. The composite current collector of claim 1, wherein: the material constituting the base layer comprises at least one of polyethylene terephthalate, polypropylene, polybutylene terephthalate, polyethylene naphthalate, polyethylene, polypropylene, polyvinyl chloride, polyvinylidene fluoride, polytetrafluoroethylene, polyphenylene sulfide, polyphenylene oxide, polystyrene and polyimide.

7. A composite current collector according to any one of claims 1 to 6, wherein: the composite current collector further comprises a protective layer, wherein the protective layer is arranged on the surface of the conductive layer, and the material for forming the protective layer comprises at least one of nickel, chromium, nickel-based alloy, copper oxide, aluminum oxide, silicon oxide, nickel oxide, chromium oxide, cobalt oxide, graphite, carbon black, copper chromate, copper chromite, carbon nano quantum dots, carbon nano tubes, carbon nano fibers, graphene and hydrocarbon; preferably, the thickness of the protective layer is d4, and d4 is more than or equal to 5nm and less than or equal to 100nm.

8. A method of producing a composite current collector according to any one of claims 1 to 9, characterized in that:

The preparation method comprises the following operations: alternately molding the transition layer and the metal layer on at least one surface of the base layer;

the forming mode of the transition layer is a magnetron sputtering forming process and/or a chemical vapor deposition forming process;

The forming conditions of the magnetron sputtering forming process comprise: adopting a carbon-containing target material, and setting the target power to be 1-8kW; providing a gas containing fluorine and hydrogen as a film plating gas source, wherein the flow rate of the film plating gas source is set to be 10-500mL/min; in the film plating process, a vacuum environment with the vacuum degree less than or equal to 0.1Pa is provided, and the film plating time is 0.1-30s each time.

9. A pole piece, characterized in that: the pole piece comprises the composite current collector as claimed in any one of claims 1 to 7 and an active material layer arranged on the surface of the composite current collector.

10. A secondary battery characterized in that: the secondary battery comprises the pole piece of claim 9.