CN114914446A - Composite electrode, preparation method of composite electrode and battery - Google Patents

Composite electrode, preparation method of composite electrode and battery Download PDF

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CN114914446A
CN114914446A CN202210447927.4A CN202210447927A CN114914446A CN 114914446 A CN114914446 A CN 114914446A CN 202210447927 A CN202210447927 A CN 202210447927A CN 114914446 A CN114914446 A CN 114914446A
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electrode
buffer layer
layer
composite electrode
aperture
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CN114914446B (en
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董琛
鲁晓峰
廖晓东
侯丽伟
张玉西
张禹佳
侯戌琪
杨宗烨
周家宇
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China Wuzhou Engineering Group Co ltd
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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
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H01M4/628—Inhibitors, e.g. gassing inhibitors, corrosion inhibitors
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M12/00—Hybrid cells; Manufacture thereof
    • H01M12/08—Hybrid cells; Manufacture thereof composed of a half-cell of a fuel-cell type and a half-cell of the secondary-cell type
    • 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
    • H01M4/134—Electrodes based on metals, Si or alloys
    • 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
    • H01M4/139—Processes of manufacture
    • H01M4/1395—Processes of manufacture of electrodes based on metals, Si or alloys
    • 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
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/38—Selection of substances as active materials, active masses, active liquids of elements or alloys
    • 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
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/38—Selection of substances as active materials, active masses, active liquids of elements or alloys
    • H01M4/381—Alkaline or alkaline earth metals elements
    • 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
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/38—Selection of substances as active materials, active masses, active liquids of elements or alloys
    • H01M4/381—Alkaline or alkaline earth metals elements
    • H01M4/382—Lithium
    • 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
    • H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
    • H01M2004/027—Negative electrodes
    • 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

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  • Electrochemistry (AREA)
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  • Engineering & Computer Science (AREA)
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  • Manufacturing & Machinery (AREA)
  • Battery Electrode And Active Subsutance (AREA)

Abstract

The present invention provides a composite electrode comprising: the electrode comprises an electrode body and a buffer layer, wherein the buffer layer is coated on the electrode body; the buffer layer is provided with buffer holes which are distributed in a continuous gradient manner, the aperture is 0.5nm-3 mu m, and the aperture of the buffer holes is sequentially increased along the direction far away from the electrode body. The composite electrode can inhibit the generation of dendritic crystals, has good performance and can prolong the service life.

Description

Composite electrode, preparation method of composite electrode and battery
Technical Field
The invention relates to the technical field of battery electrodes, in particular to a composite electrode, a preparation method of the composite electrode and a battery.
Background
Metal batteries have received much attention because of their ultra-high energy density. The most representative lithium-air battery among the metal batteries has a volumetric energy density of 1100Wh/l, which is similar to that of gasoline. Therefore, the development of the metal battery has important significance for improving the endurance mileage of the electric automobile, promoting the popularization of the electric automobile and solving the environmental pollution caused by the scattered emission of automobile exhaust.
However, the development of metal batteries at this stage is limited by the interfacial stability of the metal electrodes. During cell cycling, metal ions at the metal electrode/electrolyte interface are unevenly deposited, which causes dendrite growth. The dendrites can pierce the separator causing a short circuit in the battery. Meanwhile, the metal electrode is a "hostless" electrode. During the charging and discharging process of the battery, repeated volume changes easily cause the internal stress of the battery to be uneven, and further the service life of the battery is influenced.
In view of the above, the present invention is particularly proposed.
Disclosure of Invention
The first purpose of the invention is to provide a composite electrode, which can reduce uneven deposition of metal ions on the surface of the electrode by coating a buffer layer on the electrode, thereby effectively inhibiting dendritic crystal growth and prolonging the service life of the electrode.
The second purpose of the invention is to provide a preparation method of the composite electrode, the method is simple to operate and high in efficiency, and the prepared composite electrode has good stability.
A third object of the present invention is to provide a battery having good cycle stability, using the above-described composite electrode as a negative electrode.
In order to achieve the above purpose of the present invention, the following technical solutions are adopted:
the present invention provides a composite electrode comprising: the electrode comprises an electrode body and a buffer layer, wherein the buffer layer is coated on the electrode body; the buffer layer is provided with buffer holes; the aperture of the buffer hole is distributed in a continuous gradient manner, and the apertures are sequentially increased along the direction far away from the electrode body; the aperture of the buffer hole is 0.5nm-3 μm.
In the prior art, the development of metal batteries is limited by the interfacial stability of metal electrodes. During cell cycling, metal ions at the metal electrode/electrolyte interface are unevenly deposited, which causes dendrite growth. The dendrites can pierce the separator causing a short circuit in the battery. Meanwhile, the metal electrode is a "hostless" electrode. During the charging and discharging process of the battery, repeated volume changes easily cause the internal stress of the battery to be uneven, and further the service life of the battery is influenced.
In order to solve the problems, the invention provides a composite electrode, which combines a buffer layer and an electrode body for use, and utilizes a hierarchical pore structure which is distributed on the buffer layer in a continuous gradient manner, so that the migration of metal ions at an interface can be limited, the uneven deposition of the metal ions can be prevented, and the generation of dendritic crystals can be inhibited; meanwhile, the buffer layer can relieve pressure change generated in the battery due to volume change of the electrode, so that the service life is prolonged.
Preferably, the buffer layer comprises a surface layer and a supporting layer which are sequentially arranged along the direction of keeping away from the electrode body, the buffer hole comprises micropores, mesopores and macropores which are sequentially arranged along the direction of keeping away from the electrode body, the micropores are arranged on the surface layer, and the mesopores and the macropores are arranged on the supporting layer. The epidermal layer is close to the electrode body, and the micron-level migration channel formed by the microporous structure on the epidermal layer can only accommodate the migration of a limited number of metal ions, so that the 'limited area' effect is achieved, the resistance of the transverse diffusion of the metal ions is increased, the metal ions can only carry mass in the direction vertical to the surface of the electrode body, the uneven deposition of the metal ions on the surface of the electrode body is reduced, and the growth of lithium dendrites is inhibited; the supporting layer is positioned on the outer side and is provided with a mesoporous structure and a macroporous structure, the gradient pore structures determine that the epidermal layer and the supporting layer in the buffer layer have different mechanical properties, and when the volume of the metal electrode changes, the supporting layer preferentially deforms elastically due to the fact that the supporting layer has a smaller elastic modulus, so that the pressure change inside the battery is relieved, and the service life of the battery is prolonged.
Preferably, the aperture of the micropores is 0.5-2nm, the diameter of the mesopores is 5-50nm, and the diameter of the macropores is 0.1-3 μm;
furthermore, the aperture of the micropores is 0.6-1nm, the aperture of the mesopores is 10-30nm, and the aperture of the macropores is 0.5-2 μm;
furthermore, the aperture of the micropores is 0.75nm, the aperture of the mesopores is 23.6nm, and the aperture of the macropores is 1.4 μm.
Preferably, the thickness of the buffer layer is 1nm-500 μm; further, the thickness of the buffer layer is 10nm-300 μm; further, the thickness of the buffer layer is 1-50 μm; further, the thickness of the buffer layer is 28 μm. Through setting up suitable buffer layer thickness, can enough play the effect of restraining dendritic crystal, can prevent again that the buffer layer from causing the influence to the mass transfer of electrode body.
Preferably, the buffer layer is one or more of a nanofiltration membrane or an ultrafiltration membrane.
Preferably, the electrode body is any one or more of a metal lithium electrode, a metal sodium electrode, a metal zinc electrode, a metal aluminum electrode or a metal magnesium electrode.
The invention also provides a preparation method of the composite electrode, which is characterized by comprising the following steps: and covering the buffer layer on the surface of the electrode body.
The preparation method provided by the invention is simple to operate, high in preparation efficiency and capable of preparing the electrode with good stability.
Preferably, the buffer layer is prepared by the following method:
(A) preparing a base film;
(B) sequentially immersing the base membrane into a polycation electrolyte solution and a polyanion electrolyte solution, taking out, washing off redundant solution on the surface, drying in the shade, immersing into a trimesoyl chloride solution, taking out, drying in the shade, and carrying out heat treatment to obtain a supporting layer;
(C) coating the surface layer membrane-forming liquid on the supporting layer, drying in the shade, and performing heat treatment.
Preferably, the step (a) includes: according to the mass parts, 20-30 parts of high polymer material A, 45-52 parts of N, N-dimethylacetamide, 10-15 parts of pore-forming agent and 3-5 parts of modifier are uniformly mixed, and the base membrane is prepared by a solution spinning method;
preferably, the skin layer membrane-forming solution in the step (C) is prepared by the following method: uniformly mixing 15-20 parts of high polymer material B, 30-40 parts of N, N-dimethylacetamide and 3-5 parts of a micropore regulator in parts by weight, heating for 1h at 45-75 ℃, and carrying out ultrasonic treatment after fully stirring;
preferably, the polymer material A and the polymer material B are any one or more of polyurethane, polysulfone, polyethersulfone, polyvinylidene fluoride and polyimide;
preferably, the heat treatment temperature in the step (B) is 45-100 ℃, and the heat treatment time is 15-45 min;
preferably, the heat treatment temperature in the step (C) is 70-80 ℃, and the time is 80-100 min;
preferably, the concentration of the trimesoyl chloride solution is 0.01-0.3 wt%, and the immersion time is 10-120 s.
Preferably, the preparation method of the polycation electrolyte solution is as follows: and dissolving the polycation electrolyte in water to prepare an aqueous solution with the concentration of 2-10 wt%, and standing and defoaming for later use. The polycation electrolyte is an allylated polycation electrolyte.
Preferably, the polyanionic electrolyte solution is prepared by the following method: dissolving polyanionic electrolyte in water to prepare aqueous solution with the concentration of 2-10 wt%, standing and defoaming for later use. The polyanionic electrolyte is an allylated polyanionic electrolyte.
Preferably, the porous base membrane is soaked in the polycation electrolyte solution for 1-45min and soaked in the polyanion electrolyte solution for 1-45 min.
Preferably, the solution spinning method comprises: forming spinning trickle by a spinneret plate, immersing the spinning trickle in a coagulating bath through an air bath, immersing the film in purified water at the temperature of 60-70 ℃ after the coagulation is finished, and drying the surface moisture by blowing to form a base film; further, the temperature of the coagulation bath is 20-50 ℃, and the distance of the air bath is 1-10 cm; the temperature of the air bath is 25-30 ℃, and the humidity is 40-70% RH.
When the buffer layer is prepared, the selection and the proportion of raw materials and various process parameters in the preparation process are strictly limited. When the base film of the supporting layer is prepared, the ratio of the high polymer material A to the pore-foaming agent is 2:1, the addition amount of the pore-foaming agent cannot be excessive, and excessive pore-foaming agent can increase the most probable pore diameter, so that the strength of the supporting layer is too low, and the service life of the supporting layer is further influenced; the too little then can lead to the elastic modulus of supporting layer too big of pore-forming agent dosage, can't alleviate the change of battery internal volume, only guarantee this proportion can guarantee that the aperture of base film pore-forming reaches the requirement, and then guarantee that the intensity of supporting layer reaches the requirement. The ratio of the high molecular material B to the pore-forming agent of the epidermal layer membrane-forming liquid is only 5:1 during preparation, because micropores are required to be formed on the epidermal layer, and the micropores capable of limiting the metal ions can be formed only by ensuring the ratio, so that the inhibition effect of the epidermal layer membrane-forming liquid on the generation of dendrites is ensured.
After the preparation of the base film is finished, the base film is sequentially immersed into a polycation electrolyte solution and a polyanion electrolyte solution, so that a polycation electrolyte layer and a polyanion electrolyte layer are alternately deposited on the surface of the base film through electrostatic action to form a composite layer, the support layer has good stability under the conditions of acid electrolyte and alkaline electrolyte, and a composite layer can be formed on the surface of the support layer after the subsequent immersion into a trimesoyl chloride solution, so that the mechanical property of the support layer is ensured.
The invention also provides a battery which comprises a shell, wherein the shell is internally provided with a positive electrode, electrolyte, a battery core and a negative electrode, and the negative electrode is the composite electrode and the composite electrode prepared by the preparation method.
Wherein, the material of the positive electrode is any one of elemental sulfur, pure oxygen, air and transition metal oxide.
Compared with the prior art, the invention has the beneficial effects that:
the composite electrode provided by the invention can limit the migration of metal ions at the interface by arranging the buffer layer, and prevent the uneven deposition of the metal ions, thereby inhibiting the generation of dendritic crystals; meanwhile, the buffer layer can relieve pressure change generated in the battery due to volume change of the electrode, so that the service life is prolonged.
Drawings
Various other advantages and benefits will become apparent to those of ordinary skill in the art upon reading the following detailed description of the preferred embodiments. The drawings are only for purposes of illustrating the preferred embodiments and are not to be construed as limiting the invention. Also, like reference numerals are used to refer to like parts throughout the drawings. In the drawings:
FIG. 1 is a surface deposition lithium topography of buffer layer modified electrodes and blank control electrodes of example 1 and comparative example 1;
FIG. 2 is a surface deposition lithium topography of buffer layer modified electrodes and blank control electrodes of example 1 and comparative example 1;
fig. 3 is a graph showing the cycle count-coulombic efficiency and cycle count-positive electrode capacity of lithium iron phosphate full cells of example 2 and comparative example 2.
Detailed Description
The technical solutions of the present invention will be clearly and completely described below in conjunction with the accompanying drawings and the detailed description, but those skilled in the art will understand that the following described embodiments are a part of the embodiments of the present invention, rather than all of the embodiments, and are only used for illustrating the present invention, and should not be construed as limiting the scope of the present invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention. The examples, in which specific conditions are not specified, were conducted under conventional conditions or conditions recommended by the manufacturer. The reagents or instruments used are not indicated by the manufacturer, and are all conventional products available commercially.
In order to more clearly illustrate the technical solution of the present invention, the following description is made in the form of specific embodiments.
Example 1
The embodiment provides a composite electrode, and a preparation method of the composite electrode comprises the following steps: the buffer layer is covered on the electrode body. Wherein, the electrode body is a metal lithium electrode.
The buffer layer of this example was prepared using the following method:
firstly, uniformly mixing 20g of polyurethane, 45g of N, N-dimethylacetamide, 10g of a pore-forming agent and 3g of a modifying agent, forming a spinning trickle through a spinneret plate, immersing the spinning trickle into a coagulating bath through an air bath, soaking a base film in purified water at 60 ℃ after the coagulation is finished, taking out the base film, and drying the surface water to form the base film;
meanwhile, uniformly mixing 15g of polyether sulfone, 30g of N, N-dimethylacetamide and 3g of a micropore regulator, heating for 1h at 45 ℃, fully stirring, and performing ultrasonic treatment to obtain a surface layer membrane-forming solution;
then, immersing the prepared base membrane into a polycation electrolyte solution with the concentration of 10 wt% for 1min, taking out, washing away the redundant solution on the surface by using deionized water, immersing into a polyanion electrolyte solution with the concentration of 10 wt% for 1min, taking out, washing away the redundant solution on the surface by using deionized water, drying in the shade, immersing into a trimesoyl chloride solution with the concentration of 0.01 wt% for 120s, taking out, drying in the shade, and carrying out heat treatment for 45min at the temperature of 5 ℃ to obtain a supporting layer;
and finally, coating the epidermal layer membrane-forming solution on the supporting layer, drying in the shade, and carrying out heat treatment for 80min at the temperature of 70 ℃.
In this example, the thickness of the buffer layer was 1 nm. The aperture of the macropores on the formed buffer layer supporting layer is 0.1 μm, the aperture of the mesopores is 5nm, and the aperture of the micropores on the surface layer is 0.5nm through the observation of a transmission electron microscope.
The embodiment also provides a battery, which comprises a shell, wherein the shell is internally provided with a positive electrode, electrolyte, a battery core and a negative electrode, and the negative electrode adopts the composite electrode prepared by the embodiment.
Example 2
The embodiment provides a composite electrode, and a preparation method of the composite electrode comprises the following steps: the buffer layer is covered on the electrode body. Wherein, the electrode body is a metal sodium electrode.
The buffer layer of this example was prepared using the following method:
firstly, uniformly mixing 24g of polyether sulfone, 47g of N, N-dimethylacetamide, 12g of a pore-forming agent and 3g of a modifying agent, forming a spinning trickle through a spinneret plate, immersing the spinning trickle into a coagulating bath through an air bath, soaking a base film in purified water at 65 ℃ after the coagulation is finished, taking out the base film, and drying the surface water to form the base film;
meanwhile, 16g of polysulfone, 32g of N, N-dimethylacetamide and 3g of micropore regulator are uniformly mixed, heated for 1h at 50 ℃, fully stirred and subjected to ultrasonic treatment to prepare a skin layer membrane forming solution;
then, immersing the prepared base membrane into 5 wt% of polycation electrolyte solution for 30min, taking out, washing off the redundant solution on the surface by using deionized water, immersing into 5 wt% of polyanion electrolyte solution for 30min, taking out, washing off the redundant solution on the surface by using deionized water, drying in the shade, immersing into 0.1 wt% of trimesoyl chloride solution for 60s, taking out, drying in the shade, and carrying out heat treatment at 50 ℃ for 20min to obtain a supporting layer;
and finally, coating the epidermal layer membrane-forming solution on the supporting layer, drying in the shade, and carrying out heat treatment at 75 ℃ for 90 min.
In this example, the thickness of the buffer layer was 10 nm. The aperture of the macropores on the formed buffer layer supporting layer is 0.5 μm, the aperture of the mesopores is 10nm, and the aperture of the micropores on the surface layer is 0.6nm through the observation of a transmission electron microscope.
The embodiment also provides a battery, which comprises a shell, wherein the shell is internally provided with a positive electrode, electrolyte, a battery core and a negative electrode, and the negative electrode adopts the composite electrode prepared by the embodiment.
Example 3
The embodiment provides a composite electrode, and a preparation method of the composite electrode comprises the following steps: the buffer layer is covered on the electrode body. Wherein, the electrode body is a metal lithium electrode.
The buffer layer of this example was prepared using the following method:
firstly, uniformly mixing 25g of polyether sulfone, 48g of N, N-dimethylacetamide, 13g of a pore-forming agent and 4g of a modifying agent, forming a spinning trickle through a spinneret plate, immersing the spinning trickle into a coagulating bath through an air bath, soaking a base film in purified water at 65 ℃ after the coagulation is finished, taking out the base film, and drying the surface water to form the base film;
meanwhile, uniformly mixing the high polymer material B17g, 35g of N, N-dimethylacetamide and 4g of micropore regulator, heating for 1h at the temperature of 60 ℃, fully stirring, and performing ultrasonic treatment to obtain a skin layer membrane-forming solution; wherein the high polymer material B is obtained by mixing polyurethane and polyether sulfone according to the mass ratio of 1: 1.
Then, immersing the prepared base membrane into a polycation electrolyte solution with the concentration of 6 wt% for 30min, taking out, washing away the redundant solution on the surface by using deionized water, immersing into a polyanion electrolyte solution with the concentration of 6 wt% for 30min, taking out, washing away the redundant solution on the surface by using deionized water, drying in the shade, immersing into a trimesoyl chloride solution with the concentration of 0.2 wt% for 70s, taking out, drying in the shade, and carrying out heat treatment at 70 ℃ for 30min to obtain a supporting layer;
and finally, coating the epidermal layer membrane-forming solution on the supporting layer, drying in the shade, and carrying out heat treatment at 75 ℃ for 90 min.
In this example, the buffer layer had a thickness of 28 μm. The aperture of the macropores on the formed buffer layer supporting layer is 1.4 mu m, the aperture of the mesopores is 23.6nm, and the aperture of the micropores on the surface layer is 0.75nm through the observation of a transmission electron microscope.
The embodiment also provides a battery, which comprises a shell, wherein the shell is internally provided with a positive electrode, electrolyte, a battery core and a negative electrode, and the negative electrode adopts the composite electrode prepared by the embodiment.
Example 4
The embodiment provides a composite electrode, and a preparation method of the composite electrode comprises the following steps: the buffer layer is covered on the electrode body. Wherein, the electrode body is a metal zinc electrode.
The buffer layer of this example was prepared using the following method:
firstly, uniformly mixing 28g of polyimide, 50g of N, N-dimethylacetamide, 14g of a pore-forming agent and 4g of a modifying agent, forming a spinning trickle through a spinneret plate, immersing the spinning trickle in a coagulating bath through an air bath, soaking a base film in purified water at the temperature of 60-70 ℃ after the coagulation is finished, taking out the base film, and drying the surface water to form the base film;
meanwhile, uniformly mixing 18g of polyvinylidene fluoride, 37g of N, N-dimethylacetamide and 4g of micropore regulator, heating for 1h at 70 ℃, fully stirring, and performing ultrasonic treatment to obtain a skin layer membrane-forming solution;
then, immersing the prepared base membrane into a polycation electrolyte solution with the concentration of 6 wt% for 30min, taking out, washing away the redundant solution on the surface by using deionized water, immersing into a polyanion electrolyte solution with the concentration of 6 wt% for 30min, taking out, washing away the redundant solution on the surface by using deionized water, drying in the shade, immersing into a trimesoyl chloride solution with the concentration of 0.2 wt% for 80s, taking out, drying in the shade, and carrying out heat treatment at 80 ℃ for 40min to obtain a supporting layer;
and finally, coating the epidermal layer membrane-forming solution on the support layer, drying in the shade, and carrying out heat treatment at 75 ℃ for 100 min.
In this example, the buffer layer had a thickness of 300 μm. The aperture of the macropores on the formed buffer layer supporting layer is 2 μm, the aperture of the mesopores is 30nm, and the aperture of the micropores on the surface layer is 1nm through observation of a transmission electron microscope.
The embodiment also provides a battery, which comprises a shell, wherein the shell is internally provided with a positive electrode, electrolyte, a battery core and a negative electrode, and the negative electrode adopts the composite electrode prepared by the embodiment.
Example 5
The embodiment provides a composite electrode, and a preparation method of the composite electrode comprises the following steps: the buffer layer is covered on the electrode body. Wherein, the electrode body is a metal aluminum electrode.
The buffer layer of this example was prepared using the following method:
firstly, uniformly mixing 30g of polyurethane, 52g of N, N-dimethylacetamide, 15g of a pore-forming agent and 5g of a modifying agent, forming a spinning trickle through a spinneret plate, immersing the spinning trickle into a coagulating bath through an air bath, soaking a base film in purified water at 70 ℃ after the coagulation is finished, taking out the base film, and drying the surface water to form the base film;
meanwhile, uniformly mixing 20g of polyurethane, 40g of N, N-dimethylacetamide and 5g of a micropore regulator, heating for 1h at 75 ℃, fully stirring, and performing ultrasonic treatment to obtain a skin layer membrane-forming liquid;
then, immersing the prepared base membrane into a polycation electrolyte solution with the concentration of 10 wt% for 1min, taking out, washing away the redundant solution on the surface by using deionized water, immersing into a polyanion electrolyte solution with the concentration of 10 wt% for 1min, taking out, washing away the redundant solution on the surface by using deionized water, drying in the shade, immersing into a trimesoyl chloride solution with the concentration of 0.3 wt% for 10s, taking out, drying in the shade, and carrying out heat treatment for 15min at the temperature of 100 ℃ to obtain a supporting layer;
and finally, coating the epidermal layer membrane-forming solution on the supporting layer, drying in the shade, and carrying out heat treatment at 80 ℃ for 80 min.
In this example, the buffer layer had a thickness of 500 μm. The aperture of the macropores on the formed buffer layer supporting layer is 3 μm, the aperture of the mesopores is 50nm, and the aperture of the micropores on the surface layer is 2nm through observation of a transmission electron microscope.
The embodiment also provides a battery, which comprises a shell, wherein the shell is internally provided with a positive electrode, electrolyte, a battery core and a negative electrode, and the negative electrode adopts the composite electrode prepared by the embodiment.
Example 6
This example differs from example 3 only in that the polymeric material B used is polyether sulfone.
The aperture of the micropores on the surface layer is 1.0nm by the observation of a transmission electron microscope.
Example 7
This example differs from example 3 only in that the polymeric material B used was polyether sulfone and polysulfone in a mass ratio of 1: 1.
The aperture of the micropores on the epidermal layer is 0.8nm by observation of a transmission electron microscope.
Example 8
This example differs from example 3 only in that a support layer is used as the final buffer layer.
Example 9
The difference between this example and example 3 is only that 10g of the porogen was used in the preparation of the skin layer deposition solution.
The aperture of the holes on the epidermal layer is 13.6nm by observation of a transmission electron microscope.
Example 10
The difference between this example and example 3 is only that 1g of porogen was used in the preparation of the skin layer deposition solution.
The aperture of the micropores on the epidermal layer is 0.2nm by observation of a transmission electron microscope.
Comparative example 1
The surface of the copper foil current collector was covered with the buffer layer of example 3.
Comparative example 2
Only copper foil current collectors were used.
Comparative example 3
This example differs from example 3 in that no buffer layer is used.
Experimental example 1
The electrodes of comparative example 1 and comparative example 2 were applied as working electrodes to a system using copper foil as a working electrode and metallic lithium as a reference electrode, and a copper-lithium half-cell performance test was performed to observe the deposition of lithium ions on the surface of the working electrode. As can be seen from (a), (b), and (c) of FIG. 1, the working electrode of the comparative example had a large amount of lithium dendrite growth on the surface. In the process of repeated charging and discharging of the battery, the lithium dendrite continuously grows and finally pierces the diaphragm to cause short circuit of the battery, and potential safety hazards such as fire, explosion and the like can be caused in serious cases. It can be seen from fig. 1(d), (e) and (f) that no lithium dendrites are generated on the surface of the composite electrode of the example. The deposited metal lithium is completely wrapped under the hierarchical pore structure of the buffer layer, and the buffer layer is elastically compressed along with the volume change of the surface of the working electrode, so that on one hand, the strength of the buffer layer is enhanced, the service life of the buffer layer is prolonged, and the cycle life of the battery is prolonged; on the other hand, lithium ions are limited between the electrode body and the buffer layer to be deposited, so that micro short circuit of the battery caused by extrusion of the deposited lithium to the diaphragm is avoided.
And carrying out electrochemical test on the copper-lithium half-cell, and exploring the influence of the buffer layer on the cycling stability of the cell under different current densities. Electrochemical test parameters were set as follows: the discharge capacity is 1.0mAh/cm 2 The charging voltage was 0.5V and the current density was set to 0.5mA/cm, respectively 2 ，1.0mA/cm 2 ，2.0mA/cm 2 ，5.0mA/cm 2 . The test results are shown in fig. 2. At a low current density of 0.5mA/cm 2 Under the condition, the cell of the comparative example 1 can only keep the coulombic efficiency of more than 90 percent stably circulating for 150 circles. However, the cell modified by the buffer layer can keep the coulombic efficiency of more than 97% for stable circulation of 450 circles, and the coulombic efficiency is reduced to less than 90% after 480 circles of circulation. When the current density increased to 1.0mA/cm 2 ，2.0mA/cm 2 ，5.0mA/cm 2 And in the process, the battery modified by the buffer layer can still keep coulombic efficiency of more than 90% for stable circulation for 270 circles, 210 circles and 100 circles. But at the same current density, the coulombic efficiency of the cell of comparative example 1 started to fluctuate in the beginning of the cycle and rapidly decreased to below 90%. The cycle stability of the buffer layer modified electrode is obviously improved.
Experimental example 2
The electrodes of example 3 and comparative example 3 were applied as a negative electrode to a full cell system in which metal lithium was used as a negative electrode and a lithium iron phosphate electrode was used as a positive electrode, to observe the practicality of the composite electrode. The cell test conditions were as follows: the current density is 1.0C, and the charge-discharge voltage plateau is 2.0-4.2V. The test results are shown in fig. 3. The first discharge capacity of example 3 was 158mAh/g, while the first discharge capacity of the electrode of comparative example 2 was 150 mAh/g. It can be seen that in example 3, the buffer layer and the electrode body are used in a combined manner, so that the cycling stability of the full cell is significantly improved, and the discharge capacity of the cell decays to 90% of the initial capacity when the cell cycles to 700 cycles. While the discharge capacity of the battery of comparative example 3 decayed to 90% of the initial capacity when it was cycled to 60 cycles. Capacity retention, either initial capacity or capacity retention example 3 cell performance was much higher than comparative example 3 cell performance.
Experimental example 3
The electrodes of examples 1-12 were applied as negative electrodes to a full cell system with lithium metal as the negative electrode and lithium iron phosphate as the positive electrode, and the first-cycle discharge capacity and the number of cycles of the cell cycle when it decayed to 90% of the initial capacity were tested. The cell test conditions were as follows: the current density is 1.0C, and the charge-discharge voltage plateau is 2.0-4.2V. The test results are shown in table 1:
TABLE 1 test results
Figure BDA0003616148480000121
Figure BDA0003616148480000131
As can be seen from the above table, the electrodes shown in examples 1 to 10 are all capable of improving the performance of the battery. Among them, the battery prepared using the electrode prepared in example 3 exhibited the best performance.
Comparing example 3 with examples 6-7, it is found that the full cell system using the electrode of example 3 has higher initial capacity and capacity retention rate than those of examples 6-7, which indicates that the composite electrode prepared by mixing the polyurethane and the polyethersulfone is most effective when the polymer material B is formed into a film, probably because the distribution of micropores is more uniform when the two polymer materials are used for forming the film, and the generated micropores are more restricted to lithium ions.
Comparing the data of example 3 with the data of comparative example 3 measured in example 8 and experimental example 2, it is found that the use of the support layer as the buffer layer can significantly improve the performance of the electrode and the battery using the electrode, but the improvement effect is limited and is significantly lower than that of the full-cell system using the composite electrode of example 3. The mesoporous and macroporous structures on the supporting layer have certain confinement effect on the migration of lithium ions, and can inhibit the generation of dendrites to a certain extent. But has limited utility due to its relatively large pore size. The composite electrode of example 3 employs a buffer layer having a skin layer, which has a microporous structure, and thus has a more significant confinement effect on lithium ions, and can suppress the generation of dendrites for a long time, thereby ensuring that the battery has good performance.
Comparing example 3 with examples 9-10, it can be seen that the full cell system obtained in examples 9-10 is significantly inferior to example 3 in performance, because the pore-forming diameter is too large due to the excessive amount of the porogen used in example 9, and cannot perform a good confinement effect on lithium ion migration; in example 10, the pore-forming agent is too small, the number of pores formed on the surface layer is small, and the diameter is too small, which affects the mass transfer of lithium ions, thereby affecting the performance of the full cell system. Therefore, only by adopting the proper amount of the pore-foaming agent, the prepared electrode can be ensured to have the optimal performance.
In conclusion, the composite electrode can inhibit the generation of dendrites, has good performance and can prolong the service life.
Finally, it should be noted that: the above embodiments are only used to illustrate the technical solution of the present invention, and not to limit the same; while the invention has been described in detail and with reference to the foregoing embodiments, it will be understood by those skilled in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some or all of the technical features may be equivalently replaced; and the modifications or the substitutions do not make the essence of the corresponding technical solutions depart from the scope of the technical solutions of the embodiments of the present invention.

Claims (10)

1. A composite electrode, comprising: the electrode comprises an electrode body and a buffer layer, wherein the buffer layer is coated on the electrode body; the buffer layer is provided with buffer holes which are distributed in a continuous gradient manner, the aperture is 0.5nm-3 mu m, and the aperture of the buffer holes is sequentially increased along the direction far away from the electrode body.
2. The composite electrode of claim 1, wherein the buffer layer comprises a skin layer and a support layer sequentially disposed in a direction away from the electrode body, and the buffer hole comprises micropores, mesopores, and macropores sequentially disposed in a direction away from the electrode body, wherein the micropores are disposed on the skin layer, and the mesopores and the macropores are disposed on the support layer.
3. The composite electrode according to claim 2, wherein the pore size of the micropores is 0.5 to 2nm, the diameter of the mesopores is 5 to 50nm, and the diameter of the macropores is 0.1 to 3 μm;
preferably, the aperture of the micropores is 0.6-1nm, the aperture of the mesopores is 10-30nm, and the aperture of the macropores is 0.5-2 μm;
preferably, the pore diameter of the micropores is 0.75nm, the pore diameter of the mesopores is 23.6nm, and the pore diameter of the macropores is 1.4 μm.
4. The composite electrode of claim 3, wherein the buffer layer has a thickness of 1nm to 500 μ ι η; preferably, the thickness of the buffer layer is 10nm-300 μm; preferably, the thickness of the buffer layer is 1-50 μm; preferably, the thickness of the buffer layer is 28 μm.
5. The composite electrode according to any one of claims 1 to 4, wherein the buffer layer is one or a combination of nanofiltration membrane and ultrafiltration membrane.
6. The composite electrode according to any one of claims 1 to 4, wherein the electrode body is any one or a combination of a metal lithium electrode, a metal sodium electrode, a metal zinc electrode, a metal aluminum electrode or a metal magnesium electrode.
7. A method of making a composite electrode according to any one of claims 1 to 4, comprising the steps of: and covering the buffer layer on the surface of the electrode body.
8. The method according to claim 7, wherein the buffer layer is prepared by:
(A) preparing a base film;
(B) sequentially immersing the base membrane into a polycation electrolyte solution and a polyanion electrolyte solution, taking out, washing off redundant solution on the surface, drying in the shade, immersing into a trimesoyl chloride solution, taking out, drying in the shade, and carrying out heat treatment to obtain a supporting layer;
(C) coating the surface layer membrane-forming liquid on the supporting layer, drying in the shade, and performing heat treatment.
9. The method according to claim 8, wherein the step (A) comprises: according to the mass parts, 20-30 parts of high polymer material A, 45-52 parts of N, N-dimethylacetamide, 10-15 parts of pore-foaming agent and 3-5 parts of modifier are uniformly mixed, and the base film is prepared by a solution spinning method;
preferably, the skin layer membrane forming solution in the step (C) is prepared by the following method: uniformly mixing 15-20 parts of high polymer material B, 30-40 parts of N, N-dimethylacetamide and 3-5 parts of a micropore regulator in parts by weight, heating for 1h at 45-75 ℃, and carrying out ultrasonic treatment after fully stirring;
preferably, the polymer material A and the polymer material B are any one or more of polyurethane, polysulfone, polyethersulfone, polyvinylidene fluoride and polyimide;
preferably, the heat treatment temperature in the step (B) is 45-100 ℃, and the heat treatment time is 15-45 min;
preferably, the heat treatment temperature in the step (C) is 70-80 ℃, and the time is 80-100 min;
preferably, the concentration of the trimesoyl chloride solution is 0.01-0.3 wt%, and the immersion time is 10-120 s.
10. A battery, which is characterized by comprising a shell, wherein a positive electrode, an electrolyte, a battery core and a negative electrode are arranged in the shell, and the negative electrode is the composite electrode of any one of claims 1 to 6 and the composite electrode prepared by the preparation method of any one of claims 7 to 9.
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