CN116995242A - Metal-free current collector and preparation method and application thereof - Google Patents

Metal-free current collector and preparation method and application thereof Download PDF

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Publication number
CN116995242A
CN116995242A CN202310466796.9A CN202310466796A CN116995242A CN 116995242 A CN116995242 A CN 116995242A CN 202310466796 A CN202310466796 A CN 202310466796A CN 116995242 A CN116995242 A CN 116995242A
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China
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current collector
metal
layer
graphene
free current
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王亚雄
万远鑫
孔令涌
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Shenzhen Dynanonic Co ltd
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Shenzhen Dynanonic Co ltd
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Priority to CN202310466796.9A priority Critical patent/CN116995242A/en
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/64—Carriers or collectors
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/64—Carriers or collectors
    • H01M4/66—Selection of materials
    • H01M4/665—Composites
    • H01M4/667—Composites in the form of layers, e.g. coatings
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

Abstract

The application provides a metal-free current collector, a preparation method and application thereof. The metal-free current collector comprises a substrate layer and a conductive layer, wherein the conductive layer is made of a non-metal material and is positioned on two rough surfaces opposite to each other of the substrate layer. According to the preparation method, after roughening treatment is carried out on the surface of the substrate layer, the binding force between the substrate layer and the conductive layer is improved through a hot pressing process, and the obtained current collector has good mechanical property and conductive property, is light and safe, and is low in cost.

Description

Metal-free current collector and preparation method and application thereof
Technical Field
The application relates to the technical field of lithium ion batteries, in particular to a metal-free current collector, a preparation method and application thereof.
Background
The current collector is one of important components of electrode plates in lithium ion batteries, is a carrier for carrying electrode active materials, and is mainly used for collecting current generated by battery active materials so as to form larger current for transmission. The current collector has important influence on the aspects of energy density, safety, cost and the like of the lithium ion battery.
Current collectors are commonly made from metal foil such as aluminum or copper foil, but suffer from the following three-point drawbacks: 1, the aluminum foil or copper foil material has larger mass, and is taken as a current collector to occupy a small mass proportion of the lithium ion secondary battery, so that the improvement of the energy density and the reduction of the cost of the lithium ion battery are not facilitated; 2, the aluminum foil material or the copper foil material has the characteristics of low brittleness and toughness, so that the anode and cathode materials can be broken, broken edges, burrs and the like in the production process, and the consistency of products is poor and safety problems possibly occur; 3, when the battery is subjected to external impact such as needling, the internal short circuit of the battery is extremely easily caused, thereby causing safety accidents such as ignition, explosion, etc. of the battery.
Therefore, current collectors are generally thinned to achieve light weight of the current collector so as to optimize performance, but copper foil and aluminum foil need to maintain certain mechanical properties, and infinite thinning is impossible. For this reason, researchers have now devised composite current collectors to further improve the safety and energy density of the battery and reduce the cost. The composite current collector has a structure mainly comprising three layers, wherein an upper layer and a lower layer are respectively copper layers or aluminum layers with the thickness of a few nanometers, and a middle layer is a high polymer layer with the thickness of a few nanometers. The base material of the polymer layer can be PI/PET/PP, etc. From the viewpoints of comprehensive performance and cost, PET (high temperature resistant polyester film) is mainly selected in the industry at present. However, the composite current collector still uses the metal layer as the conductive layer, so that the problems of metal corrosion and burrs generated in the manufacturing process may exist, the bonding force of the interface between the metal material and the high polymer material is weak, the requirement on the preparation process of the composite current collector is high, and the cost is relatively high.
Disclosure of Invention
In order to solve the technical problems in the prior art, the application provides the current collector without metal materials, and the surface of the substrate layer is roughened to enhance the binding force between the substrate layer and the conductive layer, so that the current collector has good mechanical property and conductive property, is light and safe, has low cost, and can better meet the requirements of a lithium ion battery on the current collector.
In order to achieve the above purpose, the application adopts the following technical scheme:
in a first aspect, the present application provides a metal-free current collector comprising a base layer and a conductive layer, the conductive layer being of non-metallic material and being located on two roughened surfaces opposite the base layer.
In the present application, the roughened surface of the base layer may be obtained by treating the surface of the base layer by a method conventional in the art, for example, plasma treatment or treatment using a corona machine.
In some embodiments, the roughened surface of the substrate layer is obtained by plasma treating the surface of the substrate layer. In some embodiments, the power of the plasma treatment is 0.5-10W, e.g., 0.5W, 1W, 2W, 3W, 4W, 5W, 6W, 7W, 8W, 9W, 10W, or any value therebetween, preferably 1-6W. When the power is too high during plasma treatment, the roughness of the substrate surface is too high, which is unfavorable for coating and adhesion of the slurry, and therefore, the power needs to be controlled in a proper range. In some embodiments, the plasma treatment is for a period of time ranging from 5 to 20 minutes.
According to some embodiments of the application, the roughness Ra of the roughened surface is 0.03 μm-0.5 μm, e.g. 0.03 μm, 0.05 μm, 0.08 μm, 0.1 μm, 0.15 μm, 0.2 μm, 0.25 μm, 0.3 μm, 0.35 μm, 0.4 μm, 0.45 μm, 0.5 μm or any value in between, preferably 0.05 μm-0.3 μm.
According to some embodiments of the application, the surface tension of the roughened surface is 0.03-0.5N/m, e.g. 0.03N/m, 0.05N/m, 0.08N/m, 0.1N/m, 0.15N/m, 0.2N/m, 0.25N/m, 0.3N/m, 0.35N/m, 0.4N/m, 0.45N/m, 0.5N/m or any value in between, preferably 0.05-0.2N/m.
According to some embodiments of the application, the roughened surface has an NMP (N-methylpyrrolidone) contact angle of 10 ° -40 °, for example 10 °, 15 °, 20 °, 25 °, 30 °, 35 °, 40 °, or any value therebetween. The contact angle is an indicator that characterizes the wettability of a liquid on the surface of an object. If the contact angle is too small, the liquid is easy to spread on the surface, the slurry is poured on the substrate, and the slurry is automatically spread without being scraped by a tool such as a scraper, thereby being not beneficial to the coating control of the conductive slurry on the polymer substrate; if the contact angle is too large, the wettability is not good enough, and after the doctor-blading, the slurry is not good in contact with the substrate, and the binding force is not strong.
According to some embodiments of the application, the base layer comprises a high molecular polymer, preferably at least one of Polyimide (PI), polypropylene (PP), polyethylene terephthalate (PET). Among the high molecular polymers selected by the application, PI has good mechanical, electrical, chemical and radiation resistance, high temperature resistance and low temperature resistance. PP has good optical properties, good transparency, and no release of toxic substances at high temperatures. PET has good high temperature resistance, low temperature resistance and excellent mechanical properties, and toughness is the best of all thermoplastic materials. The binding force between the three high molecular polymers and the conductive layer is not very different, and the technical effect of the application can be realized.
According to some embodiments of the application, the conductive layer comprises at least one of carbon nanotubes, graphene, graphite, carbon fibers, carbon black, preferably carbon nanotubes and/or graphene. The diameter and length of the carbon nanotubes affect the ease of dispersion in a solvent and the mechanical flexibility of the resulting conductive layer, and therefore, the diameter of the carbon nanotubes is preferably 2 to 50nm and/or the length is preferably 10 to 1000 μm in the present application. The G/D ratio is an important indicator for characterizing defects of the carbon material, and the higher the G/D ratio is, the fewer the defects of the carbon material are, the higher the corresponding conductivity is, so the G/D ratio in the raman spectrum of the carbon nanotube according to the present application is preferably greater than 2, and/or the purity is preferably greater than 99.5%. The thickness and the number of layers of the graphene are also related to the conductivity and the mechanical flexibility of the graphene, so that the thickness of the graphene is preferably 0.5-5nm, and/or the number of layers is preferably less than 10. The G/D ratio in the raman spectrum of the graphene is preferably greater than 3, and/or the purity is preferably greater than 99.5%.
The polymer material is used as the substrate layer, and the nonmetallic conductive material with good interface compatibility with the polymer material, especially carbon nano tubes, graphene and the like, are used as the conductive layer, so that the weight of the current collector can be greatly reduced, the mechanical property, especially the flexibility, of the material can be improved, and the cost is reduced.
The thicknesses of the base layer and the conductive layer are not particularly limited in the present application, and may be selected in accordance with a moderate principle. If the thickness of the substrate layer is too thin, the strength of the substrate is low, the corresponding external force cannot be borne, and if the thickness is too large, the mass fraction occupied by the substrate is larger, so that the aim of weight reduction is not facilitated, meanwhile, more volume is occupied, and the volume energy density of the battery core is reduced. In some preferred embodiments, the base layer has a thickness of 3-10 μm. In some preferred embodiments, the conductive layer has a thickness of 1-5 μm.
According to some embodiments of the application, the conductive layer has a compacted density of 1-2g/cm 3 . If the compaction density of the conductive layer is too low, the carbon nanotubes or graphene may be too loose, so that a complete and well-connected conductive network is difficult to form, which is not beneficial to the improvement of the conductivity of the conductive layer; if the compaction density is too high, serious agglomeration phenomenon of the carbon nano tube or the graphene may occur, which is unfavorable for the construction of a conductive network, and the specific surface area of the nano material is large, the density is generally low, the high compaction density is realized, enough pressure needs to be applied, the high polymer substrate is difficult to bear the large pressure, and the difficulty of operation implementation is increased.
According to some embodiments of the application, the conductive layer further comprises a binder. The specific kind of the binder is not particularly limited, and conventional binders in the art can be used, for example, the binder can be one or more of polyvinylidene fluoride, polyacrylic acid, polyvinyl alcohol, polyvinylpyrrolidone, methylcellulose, sodium carboxymethylcellulose and styrene butadiene rubber. In some embodiments, the binder is present in the conductive layer at a mass ratio of 0.5% to 10%.
In some embodiments, the conductive layer is coated and hot pressed to bond with the roughened surface of the base layer. Preferably, the pressure of the hot pressing is 0.5-5MPa, for example 0.5MPa, 0.8MPa, 1MPa, 1.5MPa, 2MPa, 2.5MPa, 3MPa, 3.5MPa, 4MPa, 4.5MPa, 5MPa or any value in between, preferably 0.5-3MPa. Preferably, the temperature of the hot pressing is 90-120 ℃, for example 90 ℃, 95 ℃, 100 ℃, 105 ℃,110 ℃, 115 ℃, 120 ℃ or any value therebetween, preferably 100-110 ℃.
In a second aspect, the present application provides a method for preparing a metal-free current collector, comprising the steps of:
s1, preprocessing a basal layer to obtain a basal layer with at least two rough surfaces;
s2, mixing a non-metal conductive material with a binder to obtain conductive slurry, coating the conductive slurry on two rough surfaces of the substrate layer, and hot-pressing to obtain the metal-free current collector.
According to some embodiments of the application, in step S1, the substrate layer comprises a high molecular polymer, preferably at least one of polyimide, polypropylene, polyethylene terephthalate.
According to some embodiments of the application, in step S1, the preprocessing comprises: the substrate surface is treated with a plasma, preferably at a power of 0.5-10W, such as 0.5W, 1W, 2W, 3W, 4W, 5W, 6W, 7W, 8W, 9W, 10W or any value in between, preferably 1-6W. Preferably, the plasma treatment is carried out for a period of time ranging from 5 to 20 minutes.
According to some embodiments of the application, in step S2, the non-metallic conductive material comprises at least one of carbon nanotubes, graphene, graphite, carbon fibers, carbon black, preferably carbon nanotubes and/or graphene.
According to some embodiments of the application, in step S2, the binder is at least one selected from polyvinylidene fluoride, polyacrylic acid, polyvinyl alcohol, polyvinylpyrrolidone, methylcellulose, sodium carboxymethylcellulose, and styrene butadiene rubber.
According to some embodiments of the application, the binder is present in the conductive layer at a mass ratio of 0.5% to 10%.
According to some embodiments of the application, in step S2, the coating is spin coating, slot coating or doctor blade coating.
According to some embodiments of the application, in step S2, the pressure of the hot pressing is 0.5-5MPa, e.g. 0.5MPa, 0.8MPa, 1MPa, 1.5MPa, 2MPa, 2.5MPa, 3MPa, 3.5MPa, 4MPa, 4.5MPa, 5MPa or any value in between.
According to some embodiments of the application, in step S2, the hot pressing is performed at a temperature of 90-120 ℃, e.g. 90 ℃, 95 ℃, 100 ℃, 105 ℃,110 ℃, 115 ℃, 120 ℃ or any value in between.
In a third aspect, the application provides an electrode slice, which comprises the metal-free current collector in the first aspect or the metal-free current collector obtained by the preparation method in the second aspect.
Preferably, the electrode tab further comprises a material layer containing an active material disposed on the metal-free current collector. The material layer containing the active substance preferably comprises at least one of positive active materials such as lithium iron phosphate, nickel cobalt manganese ternary composite material, nickel cobalt aluminum ternary composite material, lithium manganese iron phosphate, lithium nickel manganese oxide, lithium cobalt oxide and the like.
In a fourth aspect, the present application provides a lithium ion battery, which comprises the electrode slice according to the third aspect of the present application.
The electrode plate is preferably used as a positive electrode plate in a lithium ion battery.
In a fifth aspect, the present application provides an application of the metal-free current collector described in the first aspect or the metal-free current collector obtained by the preparation method described in the second aspect in a lithium ion battery.
The beneficial effects of the application are as follows: the current collector does not contain metal materials, and the binding force between the substrate layer and the nonmetallic conductive layer is improved by using the macromolecule substrate layer with certain roughness on the surface, so that the mechanical properties, particularly the flexibility and the conductive property, of the material are improved, and the current collector is light and safe and low in cost, and can better meet the requirements of a lithium ion battery on the current collector.
Drawings
In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings that are needed in the embodiments will be briefly described below, it being understood that the following drawings only illustrate some embodiments of the present application and therefore should not be considered as limiting the scope, and other related drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.
Fig. 1 is a schematic structural view of a metal-free current collector prepared in example 1 of the present application.
The reference numerals are as follows:
1-a substrate layer; 2-conductive layer.
Detailed Description
The present application will be described in further detail with reference to the following examples and the accompanying drawings, in order to make the objects, technical solutions and advantages of the present application more apparent. The specific embodiments described herein are for purposes of illustration only and are not to be construed as limiting the application in any way.
Example 1
The embodiment provides a graphene/PET composite current collector, which comprises a PET polymer substrate layer and graphene conductive layers positioned on the upper surface and the lower surface of the PET polymer substrate layer, wherein the thickness of the PET polymer substrate is 5 mu m, and the thicknesses of the two graphene conductive layers are 2 mu m, as shown in figure 1. The roughness of the upper and lower surfaces of the PET substrate layer was 0.08 μm, and the surface tension was 0.05N/m.
The preparation process of the composite current collector comprises the following steps:
step 1: adding graphene and binder polyvinyl alcohol into a certain amount of NMP (N-methyl pyrrolidone) solvent according to a mass ratio of 15:1, and carrying out ultrasonic stirring treatment for 1h to obtain uniformly dispersed graphene dispersion liquid.
Step 2: the PET substrate was cleaned with water, dried, and then treated with plasma at a power of 1W for 10min to have a roughness of 0.08 μm on both the upper and lower surfaces and a surface tension of 0.05N/m.
Step 3: and (2) coating the graphene dispersion liquid obtained in the step (1) on the upper surface and the lower surface of the PET substrate obtained in the step (2) by adopting a spin coating method, wherein the spin coating rotating speed is 250r/min, the time is 20min, and then drying the PET substrate at room temperature for 1h, and then drying the PET substrate in a vacuum drying oven.
Step 4: and carrying out hot pressing treatment on the dried composite current collector, wherein the pressure is 1MPa, the temperature is 100 ℃, the hot pressing time is 1min, and then naturally cooling to obtain the graphene/PET composite current collector.
Example 2
The difference between the graphene/PET composite current collector provided in this embodiment and the embodiment 1 is that the roughness of the upper and lower surfaces of the PET substrate layer is 0.18 μm, and the surface tension is 0.1N/m.
The process for preparing the composite current collector differs from example 1 only in that the power of the plasma treatment in step 2 is 3W.
Example 3
The difference between the graphene/PET composite current collector provided in this embodiment and the embodiment 1 is that the roughness of the upper and lower surfaces of the PET substrate layer is 0.25 μm, and the surface tension is 0.18N/m.
The process for preparing the composite current collector differs from example 1 only in that the power of the plasma treatment in step 2 is 5W.
Example 4
The present embodiment provides a single-walled carbon nanotube/PET composite current collector differing from embodiment 1 only in that graphene is replaced with single-walled carbon nanotubes.
The preparation process of the composite current collector is the same as in example 1.
Example 5
The present example provides a single-walled carbon nanotube/PET composite current collector, which is different from example 4 in that the roughness of the upper and lower surfaces of the PET substrate layer is 0.18 μm, and the surface tension is 0.1N/m.
The process for preparing the composite current collector is different from that of example 4 in that the power of the plasma treatment in step 2 is 3W.
Example 6
The present example provides a single-walled carbon nanotube/PET composite current collector, which is different from example 4 in that the roughness of the upper and lower surfaces of the PET substrate layer is 0.25 μm, and the surface tension is 0.18N/m.
The process for preparing the composite current collector differs from example 4 only in that the power of the plasma treatment in step 2 is 5W.
Example 7
The difference between the graphene/PET composite current collector provided in this embodiment and the embodiment 1 is that the roughness of the upper and lower surfaces of the PET substrate layer is 0.5 μm, and the surface tension is 0.5N/m.
The process for preparing the composite current collector differs from example 1 only in that the power of the plasma treatment in step 2 is 10W.
Example 8
The present embodiment provides a graphene/PI composite current collector and a method for preparing the same, which are different from embodiment 1 only in that the substrate layer material is PI.
Example 9
The difference between the graphene/PET composite current collector and the preparation method thereof provided in the embodiment and the embodiment 1 is that the hot pressing condition in the step 4 in the preparation process is different:
step 4: and (3) carrying out hot pressing on the dried composite current collector, wherein the pressure is 3MPa, the temperature is 100 ℃, the hot pressing time is 1min, and then naturally cooling to obtain the graphene/PET composite current collector.
Example 10
The difference between the graphene/PET composite current collector and the preparation method thereof provided in the embodiment and the embodiment 1 is that the hot pressing condition in the step 4 in the preparation process is different:
step 4: and (3) carrying out hot pressing on the dried composite current collector, wherein the pressure is 5MPa, the temperature is 100 ℃, the hot pressing time is 1min, and then naturally cooling to obtain the graphene/PET composite current collector.
Example 11
The difference between the graphene/PET composite current collector and the preparation method thereof provided in the embodiment and the embodiment 1 is that the hot pressing condition in the step 4 in the preparation process is different:
step 4: and (3) carrying out hot pressing on the dried composite current collector, wherein the pressure is 1MPa, the temperature is 110 ℃, the hot pressing time is 1min, and then naturally cooling to obtain the graphene/PET composite current collector.
Comparative example 1
This comparative example provides a graphene layer/PET composite current collector, which is different from example 1 in that the PET substrate is not subjected to surface treatment, has a surface roughness of 0.01 μm, has a surface tension of 0.01N/m, and is not subjected to heat pressing treatment.
The preparation process of the composite current collector specifically comprises the following steps:
step 1: as in example 1.
Step 2: and (3) coating the graphene dispersion liquid obtained in the step (1) on the cleaned PET substrate which is not subjected to surface treatment by adopting a spin coating method (the surface roughness of the substrate is 0.01 mu m, the surface tension is 0.01N/m), the spin coating rotating speed is 250r/min, the time is 20min, and then drying the graphene dispersion liquid at room temperature for 1h, and then drying the graphene dispersion liquid in a vacuum drying oven to obtain the graphene/PET composite current collector.
Comparative example 2
The comparative example provides a graphene layer/PET composite current collector and a preparation method thereof, which are different from example 1 only in that the hot pressing treatment of step 4 is not performed in the preparation process.
Comparative example 3
This comparative example provides a single-walled carbon nanotube layer/PET composite current collector and a method for preparing the same, which is different from example 4 in that the PET substrate is not subjected to surface treatment, has a surface roughness of 0.01 μm, has a surface tension of 0.01N/m, and is not subjected to hot pressing treatment.
The preparation process of the composite current collector specifically comprises the following steps:
step 1: same as in example 4.
Step 2: and (2) coating the single-walled carbon nanotube dispersion liquid obtained in the step (1) on the cleaned PET substrate which is not subjected to surface treatment by adopting a spin coating method (the surface roughness of the substrate is 0.01 mu m, the surface tension is 0.01N/m), wherein the spin coating rotating speed is 250r/min, the time is 20min, and then drying the single-walled carbon nanotube dispersion liquid at room temperature for 1h, and then drying the single-walled carbon nanotube dispersion liquid in a vacuum drying oven to obtain the single-walled carbon nanotube/PET composite current collector.
Comparative example 4
This comparative example provides a single-walled carbon nanotube layer/PET composite current collector and a method for preparing the same, which are different from example 4 only in that the hot pressing treatment of step 4 is not performed in the preparation process.
Comparative example 5
This comparative example provides a graphene/PET composite current collector differing from example 1 only in that the PET substrate was not surface treated, had a surface roughness of 0.01 μm and a surface tension of 0.01N/m.
The preparation process of the composite current collector is different from that of the embodiment 1 in that no plasma treatment is performed, and specifically comprises the following steps:
step 1: adding graphene and a binder (any one of polyvinyl alcohol, polyvinylpyrrolidone or methyl cellulose) into a certain amount of NMP (N-methyl pyrrolidone) solvent according to a mass ratio of 1:5, and carrying out ultrasonic stirring treatment for 1h to obtain a uniformly dispersed graphene dispersion liquid.
Step 2: and (2) coating the graphene dispersion liquid obtained in the step (1) on the upper and lower surfaces of a PET substrate with the surface roughness of 0.01 mu m and the surface tension of 0.01N/m by adopting a spin coating method, wherein the spin coating rotating speed is 250r/min, the time is 20min, and then drying the substrate at room temperature for 1h, and then drying the substrate in a vacuum drying oven.
Step 3: and (3) carrying out hot pressing on the dried composite current collector, wherein the pressure is 1MPa, the temperature is 100 ℃, the hot pressing time is 1min, and then naturally cooling to obtain the graphene/PET composite current collector.
Comparative example 6
This comparative example provides a current collector differing from example 1 in that the conductive layer material is aluminum.
Comparative example 7
This comparative example provides a current collector differing from example 1 in that graphene in the conductive layer is replaced with carbon black.
Performance testing
And conducting conductivity test and peel strength test on the current collector, and applying the obtained current collector to a lithium ion battery to conduct battery related performance test.
And (3) assembling and testing of power buckling:
(1) Lithium iron phosphate positive electrode material was combined with polyvinylidene fluoride (PVDF) and SP at 95:3:2, mixing, ball milling and stirring to obtain positive electrode slurry, coating the positive electrode slurry in the current collectors obtained in the examples 1-6 and the comparative examples 1-2, rolling, and vacuum drying at 110 ℃ overnight to obtain corresponding positive electrode plates respectively;
and (3) a negative electrode: lithium metal sheet;
electrolyte solution: mixing ethylene carbonate and ethylmethyl carbonate in a volume ratio of 3:7, and adding LiPF 6 Electrolyte is formed, liPF 6 The concentration of (C) was 1mol/L.
A diaphragm: a polypropylene microporous separator;
and (3) assembling a lithium ion battery: and assembling the lithium ion battery in an inert atmosphere glove box according to the assembling sequence of the lithium metal sheet, the diaphragm, the electrolyte and the positive electrode sheet.
(2) The electrochemical performance of each lithium ion battery assembled as described above and comprising the examples or comparative examples was tested under the following conditions: constant-current and constant-voltage charging is carried out to 4.2V at the rate of 0.055C, and the cut-off current is 0.02C; and standing for 10min, and discharging the constant current to 2.0V at the rate of 0.055C. And charging to 4.2V with constant current and constant voltage of 1C multiplying power, and the cut-off current is 0.02C; standing for 10min, discharging to 2.0V at 1C constant current, and circulating for 100 circles.
The results of the current collector conductivity, current collector peel strength, and gram capacity after 100 cycles of the corresponding positive electrode tab for each example and comparative example are shown in table 1 below.
TABLE 1
Comparison of hot press effect: from comparative example 1 and comparative example 2, it can be seen that the conductivity of the heat-pressed graphene/PET current collector of example 1 (5.1×10 5 S/m) and peel strength (291N/m) were both much higher than the corresponding conductivities (2X 10) in comparative example 2 (not autoclaved) 5 S/m) and peel strength (170N/m), possible reasons are that the autoclave treatment is favorable for better adhesion of the graphene conductive layer to the PET current collector, and also promotes the connection between graphene sheets inside the graphene conductive layer, so that the whole conductive network is better in contact, and the conductivity of the finally obtained current collector is relatively high. As is clear from comparison of examples 1, 9 and 10, the conductivity and peel strength of the current collector can be improved by appropriately increasing the hot pressing pressure.
Comparison of the surface treatment effect of the polymer substrate: by comparing examples 1, 2, 3, 7 and comparative example 5, it can be seen that the conductivity and peel strength of the current collector subjected to the plasma surface treatment were higher in the case of the soaking pressure treatment. The PET has larger roughness due to plasma treatment, so that the graphene dispersion liquid is convenient to attach, the adhesion of the conductive layer on the PET substrate can be improved, and meanwhile, the construction of a graphene conductive network is facilitated. Properly increasing the plasma treatment power can increase the roughness of the PET as well as the conductivity and peel strength of the final current collector. In addition, in both comparative examples 1 and 2, the current collector subjected to the PET plasma surface treatment was also higher in conductivity and peel strength than the current collector not treated in both cases.
Effect contrast with respect to conductive layer material selection: as can be seen from comparing examples 1, 4 and comparative example 7, the current collector conductivity and the peel strength of graphene or single-walled carbon nanotubes as the conductive layer material are much higher than that of carbon black as the conductive layer material, and the corresponding pole piece battery performance is better. This is probably because graphene and single-walled carbon nanotubes themselves have higher conductivity and because they are two-dimensional and one-dimensional structures, respectively, good electronic contacts and conductive networks are more easily formed, whereas carbon black belongs to particles of zero dimension, and the connection of conductive networks is relatively poor.
Effect contrast with respect to polymeric substrate material selection: by comparing example 1 with example 8, it can be seen that the effect of using PI as the substrate is close to that of PET substrate, but the cost of PET is lower, so PET is preferred.
There are similar phenomena and laws in battery performance. Regarding the gram capacity of the battery after 100 cycles, the gram capacity of example 1 was higher than that of comparative example 2, and the gram capacity of comparative example 2 was higher than that of comparative example 1. This is because the cycle performance of the battery has a certain relationship with the impedance of the battery, while the conductivity diameter of the current collector affects the impedance of the battery. The current collector has high conductivity, the battery impedance is small, and the corresponding circulation capacity is kept better.
From the results of examples 1 to 11, it can be seen that the metal-free current collector provided by the present application is equivalent to the current collector obtained by using metallic aluminum as the conductive layer in comparative example 6 in terms of conductivity, peel strength and gram capacity after 100 cycles of the battery, and in particular, the peel strength is superior to that of comparative example 6. Therefore, the current collector still has excellent conductive performance on the premise of not using the metal conductive layer, can meet the use requirement, and can solve the problems of high cost, potential safety hazard and relatively low energy density caused by using the metal conductive layer.
Summarizing: in summary, the current collector provided by the application improves the conductivity and the peeling strength of the carbon material/PET nonmetallic current collector by adopting the PET surface plasma treatment process and the subsequent hot pressing process, and is also beneficial to improving the electrochemical performance of the battery.
The technical scheme of the application is not limited to the specific embodiment, and all technical modifications made according to the technical scheme of the application fall within the protection scope of the application.

Claims (10)

1. A metal-free current collector comprising a base layer and a conductive layer, the conductive layer being of a non-metallic material and being located on two roughened surfaces opposite the base layer.
2. A metal-free current collector according to claim 1, wherein the roughness Ra of the roughened surface is 0.03-0.5 μm, preferably 0.05-0.3 μm;
and/or the surface tension of the roughened surface is 0.03-0.5N/m, preferably 0.05-0.2N/m;
preferably, the roughened surface is obtained by plasma treatment of the substrate layer surface, the power of the plasma treatment being 0.5-10W, preferably 1-6W; the plasma treatment time is 5-20min.
3. The metal-free current collector of claim 1 or 2, wherein the base layer comprises a high molecular polymer, preferably at least one of polyimide, polypropylene, polyethylene terephthalate;
and/or the conductive layer comprises at least one of carbon nanotubes, graphene, graphite, carbon fibers, carbon black, preferably carbon nanotubes and/or graphene;
and/or the thickness of the basal layer is 3-10 mu m;
and/or the thickness of the conductive layer is 1-5 μm.
4. A metal-free current collector according to any one of claims 1-3, wherein the conductive layer is coated and hot pressed to bond with the roughened surface of the base layer;
preferably, the pressure of the hot pressing is 0.5-5MPa;
preferably, the temperature of the hot pressing is 90-120 ℃.
5. A preparation method of a metal-free current collector comprises the following steps:
pretreating the substrate layer to obtain a substrate layer with at least two rough surfaces;
mixing a non-metal conductive material with a binder to obtain conductive slurry, coating the conductive slurry on two rough surfaces of the substrate layer, and hot-pressing to obtain the metal-free current collector.
6. The method of manufacturing according to claim 5, wherein the substrate layer comprises a high molecular polymer, preferably at least one of polyimide, polypropylene, polyethylene terephthalate;
and/or, the preprocessing comprises: the substrate surface is treated with a plasma, preferably at a power of 0.5-10W, more preferably 1-6W, and preferably for a time of 5-20min.
7. The method of claim 5 or 6, wherein the non-metallic conductive material comprises at least one of carbon nanotubes, graphene, graphite, carbon fibers, carbon black, preferably carbon nanotubes and/or graphene;
and/or the adhesive is at least one selected from polyvinylidene fluoride, polyacrylic acid, polyvinyl alcohol, polyvinylpyrrolidone, methyl cellulose, sodium carboxymethyl cellulose and styrene-butadiene rubber, and preferably, the mass ratio of the adhesive in the conductive layer is 0.5-10%;
and/or, the coating includes at least one of spin coating, slot coating, and blade coating;
and/or the pressure of the hot pressing is 0.5-5MPa, and the temperature is 90-120 ℃.
8. An electrode sheet comprising the metal-free current collector of any one of claims 1 to 4 or obtained according to the production method of any one of claims 5 to 7;
preferably, the electrode tab further comprises a material layer containing an active material disposed on the metal-free current collector.
9. A lithium ion battery comprising the electrode sheet of claim 8, preferably the electrode sheet is a positive electrode sheet.
10. Use of the metal-free current collector of any one of claims 1 to 4 or the metal-free current collector obtained by the preparation method of any one of claims 5 to 7 in a lithium ion battery.
CN202310466796.9A 2023-04-23 2023-04-23 Metal-free current collector and preparation method and application thereof Pending CN116995242A (en)

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CN116995242A true CN116995242A (en) 2023-11-03

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