CN115275096A - Self-repairing flexible electrode, preparation method thereof and lithium-sulfur battery - Google Patents

Self-repairing flexible electrode, preparation method thereof and lithium-sulfur battery Download PDF

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CN115275096A
CN115275096A CN202210990658.6A CN202210990658A CN115275096A CN 115275096 A CN115275096 A CN 115275096A CN 202210990658 A CN202210990658 A CN 202210990658A CN 115275096 A CN115275096 A CN 115275096A
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self
repairing
flexible electrode
binder
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刘洋
许文成
黄苗
彭燕秋
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Eve Energy 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
    • H01M4/13—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
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • 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
    • 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
    • H01M4/362—Composites
    • H01M4/366—Composites as layered products
    • 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
    • H01M4/621—Binders
    • 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
    • H01M4/621—Binders
    • H01M4/622—Binders being polymers
    • 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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Abstract

The invention provides a self-repairing flexible electrode, a preparation method thereof and a lithium-sulfur battery, wherein the self-repairing flexible electrode comprises a current collector and a flexible electrode coating arranged on at least one side surface of the current collector, the flexible electrode coating comprises a self-repairing binder and a positive electrode active material, the self-repairing binder comprises a high molecular polymer containing amino and a high molecular polymer containing carbonyl, and the high molecular polymer containing amino and the high molecular polymer containing carbonyl are not the same. According to the invention, a specific amino-containing high molecular polymer and a carbonyl-containing high molecular polymer are used as self-repairing binders, and the self-repairing capability of the binders is endowed through a dynamic hydrogen bond 3D cross-linked network formed by the carbonyl and the amino, so that the integrity of the electrode is ensured; meanwhile, polysulfide is fixed by a large number of polar groups, namely carbonyl and amino, redox conversion kinetics of the polysulfide is promoted, a shuttle effect is inhibited, and the self-repairing flexible electrode with excellent cycle performance is prepared.

Description

Self-repairing flexible electrode, preparation method thereof and lithium-sulfur battery
Technical Field
The invention belongs to the technical field of batteries, and relates to a self-repairing flexible electrode, a preparation method thereof and a lithium-sulfur battery.
Background
The advent of flexible electronic devices such as foldable touch screens, flexible biosensors, and artificial skin has seen the need for high performance flexible batteries in recent years. The nature of wearable devices requires that the flexible battery be foldable, lightweight, thin, and lightweight, which necessarily sacrifices the energy density of the battery to some extent.
At present, the energy density of the lithium ion battery is close to the theoretical limit and is challenged by the ever-increasing demand of the energy storage market. In this regard, flexible lithium-sulfur batteries (Li-S) are considered to be one of the most promising candidates due to their overwhelming advantages of high energy density and low sulfur cost. CN106374113A discloses a method for preparing a lithium-sulfur battery by using a graphitized carbon nanotube flexible membrane as a lithium-sulfur battery current collector, which comprises the steps of taking sulfur as an active substance, adding a conductive agent, an adhesive and a solvent, mixing slurry, and coating the slurry on the graphitized carbon nanotube flexible membrane to obtain a flexible lithium-sulfur battery positive plate. CN111864190A discloses a flexible sulfur positive electrode of a lithium sulfur battery, which comprises flexible multifunctional carbon foam and a sulfur-containing active substance loaded in the flexible multifunctional carbon foam, and the overall flexibility of a positive electrode sheet is realized through the action of the flexible carbon foam. CN109103439A discloses a flexible self-supporting lithium-sulfur battery positive electrode material and a preparation method thereof, the patent prepares graphene/tin oxide nanocomposite through hydrothermal reaction of nitrogen-doped graphene and a tin salt solution, then adds elemental sulfur for mixing and vacuum melting diffusion, and adds a graphene oxide solution for hydrothermal reaction again to obtain the flexible self-supporting lithium-sulfur battery positive electrode material.
In the prior art, a flexible positive electrode of the lithium-sulfur battery is prepared by doping and modifying a positive electrode material of the lithium-sulfur battery or adopting a flexible current collector as a base material to load a positive electrode active material, so that the flexible positive electrode has the flexibility characteristic and has the advantage of high energy density of the lithium-sulfur battery; however, commercialization of the lithium-sulfur battery is still hindered by some troublesome problems, including insulation of sulfur, shuttling of high-order lithium polysulfide (LiPS) substances, and large volume change during charging and discharging, and the above methods using flexible current collectors or doping modification of the positive electrode material cannot effectively inhibit shuttling of lithium polysulfide, nor inhibit volume change of the active material during charging and discharging, and small cracks of the electrode plate caused by bending or volume change of the active material on the flexible sulfur positive electrode can further expand during long-term cycling, which eventually leads to poor cycling performance of the lithium-sulfur battery, and even battery failure.
In conclusion, the adhesive which can fix polysulfide, inhibit the shuttle effect of lithium polysulfide and has higher adhesion and self-repairing performance is provided from the internal consideration of the pole piece of the lithium-sulfur battery, and the adhesive has important significance for preparing the flexible pole piece of the lithium-sulfur battery and fundamentally improving the cycle performance of the lithium-sulfur battery from the internal part of the pole piece.
Disclosure of Invention
Aiming at the problems in the prior art, the invention aims to provide a self-repairing flexible electrode, a preparation method thereof and a lithium-sulfur battery. According to the invention, a specific amino-containing high molecular polymer and a carbonyl-containing high molecular polymer are used as self-repairing binders, and the self-repairing capability of the binders is endowed through a dynamic hydrogen bond 3D cross-linked network formed by the carbonyl and the amino, so that the integrity of the electrode is ensured; meanwhile, polysulfide is fixed by a large number of polar groups, namely carbonyl and amino, redox conversion kinetics of the polysulfide is promoted, a shuttle effect is inhibited, and the self-repairing flexible electrode with excellent cycle performance is prepared.
In order to achieve the purpose, the invention adopts the following technical scheme:
in a first aspect, the invention provides a self-repairing flexible electrode, which comprises a current collector and a flexible electrode coating arranged on at least one side surface of the current collector, wherein the flexible electrode coating comprises a self-repairing binder and a positive electrode active material, the self-repairing binder comprises a high molecular polymer containing amino and a high molecular polymer containing carbonyl, and the high molecular polymer containing amino and the high molecular polymer containing carbonyl are not the same high molecular polymer.
As an indispensable component of the entire battery system, the binder not only can bind the active material and the conductive agent together to improve the electronic conductivity, but also can cause the active material to adhere tightly to the collector electrode, thereby ensuring the integrity of the electrode. The traditional polyvinylidene fluoride (PVDF) binder is widely applied to various batteries due to good adhesion capacity and a wide electrochemical window, but the combination energy between nonpolar groups in the PVDF and polysulfide is weak, so that shuttling of the polysulfide cannot be effectively inhibited, large volume change cannot be inhibited, and microcracks on a pole piece cannot be effectively prevented. Therefore, the development of Li-S batteries requires a binder capable of self-healing, high adhesion, and capturing polysulfides.
The invention adopts a specific self-repairing adhesive to replace the traditional adhesive, the self-repairing adhesive comprises a macromolecular polymer containing amino and a macromolecular polymer containing carbonyl, on one hand, the amino (-NH) 2 ) The group can form a dynamic hydrogen bond 3D cross-linked network with a carbonyl (C = O) group, the hydrogen bond self-repairing polymer is one of self-repairing polymers based on supramolecular chemistry, when a pole piece has a crack, the dynamic hydrogen bond can be broken, but due to the high directionality of thermal motion and the hydrogen bond, the hydrogen bond can be spontaneously recombined, so that the healing of the crack is promoted; therefore, the self-repairing adhesive containing the dynamic hydrogen bond 3D cross-linked network can repair damage caused by frequent bending and volume change of the pole piece, and the integrity of the electrode is ensured. On the other hand, a large number of polar groups, namely carbonyl and amino, can fix polysulfide and promote redox conversion kinetics of the polysulfide, so that a shuttle effect is inhibited, and the cycle performance of the lithium-sulfur battery is further improved.
In the present invention, the phrase "the amino group-containing polymer and the carbonyl group-containing polymer are not the same polymer" means that the amino group-containing polymer and the carbonyl group-containing polymer are different from each other; for example, polyacrylamide contains both amino and carbonyl groups, but cannot be used as both an amino-containing polymer and a carbonyl-containing polymer, that is, only polyacrylamide contained in the self-repairing adhesive satisfies the condition of containing both amino and carbonyl groups, but due to the polarity of the polymer itself, the carbonyl and amino groups in polyacrylamide itself cannot be crosslinked to form dynamic hydrogen bonds, and thus cannot be used alone as a self-repairing adhesive, and it is necessary to add a different kind of amino-containing polymer or carbonyl-containing polymer to be used in combination.
Preferably, the amino group-containing high molecular polymer includes Polyethyleneimine (PEI) and/or Polyacrylamide (PAM).
Preferably, the carbonyl group-containing high molecular polymer includes polyvinylpyrrolidone (PVP) and/or polyacrylamide, and the amino group-containing polymer and the carbonyl group-containing polymer are not polyacrylamide at the same time.
In the invention, PVP contains carbonyl, PEI contains amino, PAM contains amino and carbonyl, any two of three high molecular polymers are selected as self-repairing binders, polar groups and a hydrogen bond 3D cross-linking network can be fully utilized to anchor polysulfide, damage caused by frequent bending and volume change of the pole piece is repaired, and the cycle performance of the pole piece is improved. Meanwhile, the preferable PVP, PEI and PAM of the invention are water-soluble high molecular polymers, and compared with PVDF only dissolved in expensive and toxic organic solvents (such as NMP and DMF), the PVP, PEI and PAM have the advantages of lower cost and environmental pollution prevention.
In the present invention, polyacrylamide cannot be selected from the amino group-containing polymer and the carbonyl group-containing polymer at the same time, and although polyacrylamide contains both an amino group and a carbonyl group, the amino group-containing polymer and the carbonyl group-containing polymer are not the same polymer, and polyacrylamide should be used in combination with other amino group-containing polymer or carbonyl group-containing polymer.
As a preferred embodiment of the production method of the present invention, the mass ratio of the amino group-containing polymer to the carbonyl group-containing polymer is (1 to 3) to (1 to 3), wherein the range of choice (1 to 3) for the amino group-containing polymer may be, for example, 1, 1.5, 2, 2.5, or 3, and the range of choice (1 to 3) for the carbonyl group-containing polymer may be, for example, 1, 1.5, 2, 2.5, or 3.
Preferably, the self-healing adhesive comprises polyvinylpyrrolidone, polyethyleneimine and polyacrylamide.
Preferably, the mass ratio of polyvinylpyrrolidone, polyethyleneimine and polyacrylamide in the self-repairing binder is (2-5): (2-5), wherein the selection range of polyvinylpyrrolidone (2-5) can be, for example, 2, 2.5, 3, 3.5, 4, 4.5 or 5, the selection range of polyethyleneimine (2-5) can be, for example, 2, 2.5, 3, 3.5, 4, 4.5 or 5, the selection range of polyacrylamide (2-5) can be, for example, 2, 2.5, 3, 3.5, 4, 4.5 or 5, and the most preferred mass ratio of polyvinylpyrrolidone, polyethyleneimine and polyacrylamide is 3.5.
According to the invention, by limiting the proportion of PVP, PEI and PAM or the proportion of amino and carbonyl in the self-repairing binder, the formation of dynamic hydrogen bonds and a 3D cross-linked network structure can be more fully promoted, and the cycle performance of the self-repairing flexible electrode is further improved.
Preferably, the polyvinylpyrrolidone has a molecular weight of 24000 to 1300000, and may be, for example, 24000, 25000, 100000, 300000, 500000, 1000000, 1300000, or the like.
Preferably, the polyethyleneimine has a molecular weight of 1000 to 10000, which may be, for example, 1000, 2000, 5000, 8000, 10000, or the like.
Preferably, the molecular weight of the polyacrylamide is 2000000 to 14000000, and for example, 2000000, 4000000, 6000000, 8000000, 10000000, 12000000 or 14000000 can be used.
In the invention, PVP, PEI and PAM with proper molecular weight are selected, and sufficient dynamic hydrogen bonds can be formed to ensure adhesion and improve cycle performance.
In a preferred embodiment of the self-healing flexible electrode according to the present invention, the mass ratio of the positive electrode active material to the self-healing binder is (8 to 9): (0.5 to 1.5), wherein the selection range of the positive electrode active material (8 to 9) may be, for example, 8, 8.2, 8.4, 8.6, 8.8, or 9, and the selection range of the self-healing binder (0.5 to 1.5) may be, for example, 0.5, 0.7, 0.9, 1, 1.2, or 1.5.
Preferably, the flexible electrode coating further comprises a conductive agent.
Preferably, the mass ratio of the positive electrode active material, the conductive agent and the self-repairing binder is (8-9): (0.5-1.5): 0.5-1.5), wherein the selection range of the positive electrode active material (8-9) can be, for example, 8, 8.2, 8.4, 8.6, 8.8 or 9, etc., the selection range of the conductive agent (0.5-1.5) can be, for example, 0.5, 0.7, 0.9, 1, 1.2 or 1.5, etc., and the selection range of the self-repairing binder (0.5-1.5) can be, for example, 0.5, 0.7, 0.9, 1, 1.2 or 1.5, etc.
According to the invention, through the synergistic cooperation of the positive active material, the conductive agent and the self-repairing binder with appropriate contents, the effects of promoting the healing of microcracks and inhibiting the shuttling effect of the self-repairing binder are fully exerted, and meanwhile, the high energy density of the sulfur battery is utilized, and the energy density and the cycle performance of the self-repairing flexible electrode are improved.
Preferably, the positive electrode active material includes a sulfur/carbon composite material.
Preferably, the conductive agent includes any one or a combination of at least two of conductive carbon black, carbon nanotubes and graphene, and may be, for example, a combination of conductive carbon black and carbon nanotubes, a combination of carbon nanotubes and graphene, a combination of conductive carbon black, carbon nanotubes and graphene, or the like.
In a second aspect, the present invention provides a method for preparing the self-repairing flexible electrode according to the first aspect, the method comprising:
and mixing the self-repairing binder with the positive active material to obtain flexible electrode slurry, and coating the flexible electrode slurry on the surface of at least one side of the current collector to obtain the self-repairing flexible electrode.
The raw materials of the invention have been industrialized, the preparation method is simple, the operability is strong, and the invention is convenient for large-scale production.
Preferably, the mixing of the self-repairing binder and the positive electrode active material is performed as follows:
dissolving the self-repairing binder in a solvent and stirring to obtain a binder solution, mixing the binder solution and the positive active material, and stirring.
Preferably, during the process of dissolving the self-repairing adhesive in the solvent and stirring, the rotation speed of the stirring is 300-1000 rpm/min, such as 300rpm/min, 400rpm/min, 500rpm/min, 600rpm/min, 800rpm/min, or 1000 rpm/min.
Preferably, in the process of dissolving the self-repairing binder in the solvent and stirring, the stirring time is 2 to 12 hours, for example, 2 hours, 4 hours, 6 hours, 8 hours, 10 hours or 12 hours, etc.
Preferably, the self-repairing binder is dissolved in the solvent and stirred at a temperature of 25 to 35 ℃, for example, 25 ℃, 26 ℃, 28 ℃, 30 ℃, 32 ℃ or 35 ℃.
Preferably, the solvent comprises water.
Illustratively, the self-healing adhesive is dissolved in a solvent, and the stirring manner can be magnetic stirring or mechanical stirring.
Illustratively, the binder solution and the positive active material are mixed, the stirring manner may be ball milling or double planetary stirring, and the stirring time may be 5 to 12 hours, for example, 5 hours, 6 hours, 7 hours, 8 hours, 10 hours, 12 hours, or the like.
Preferably, after the flexible electrode slurry is coated on the surface of at least one side of the current collector, a drying step is further included.
Preferably, the drying temperature is 60 to 70 ℃, for example, 60 ℃, 61 ℃, 62 ℃, 63 ℃, 64 ℃, 65 ℃, 66 ℃, 67 ℃, 68 ℃, 69 ℃ or 70 ℃.
Preferably, the drying time is 0.5 to 6 hours, for example, 0.5 hour, 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, or the like.
In a third aspect, the invention provides a lithium-sulfur battery, and the positive electrode of the lithium-sulfur battery adopts the self-repairing flexible electrode according to the first aspect.
The lithium-sulfur battery provided by the invention adopts the self-repairing flexible electrode as the positive electrode, the positive electrode can anchor polysulfide in a circulating process, and damage caused by pole pieces in frequent bending and volume change processes can be repaired by the positive electrode, so that the prepared lithium-sulfur battery has excellent circulating stability.
Compared with the prior art, the invention has the following beneficial effects:
the invention adopts a specific self-repairing adhesive to replace the traditional adhesive, the self-repairing adhesive comprises a macromolecular polymer containing amino and a macromolecular polymer containing carbonyl, on one hand, the amino (-NH) 2 ) The group and a carbonyl (C = O) group can form a dynamic hydrogen bond 3D cross-linked network, when the pole piece has cracks, the dynamic hydrogen bond can be broken, but due to thermal motion and high orientation of the hydrogen bond, the hydrogen bond can be spontaneously recombined, so that the healing of the cracks is promoted; therefore, the self-repairing adhesive containing the dynamic hydrogen bond 3D cross-linked network can repair the damage caused by frequent bending and volume change of the pole piece, and the integrity of the electrode is ensured. On the other hand, a large number of polar groups, namely carbonyl and amino, can fix polysulfide and promote redox conversion kinetics of the polysulfide, so that a shuttle effect is inhibited, and the cycle performance of the lithium-sulfur battery is further improved.
Drawings
Fig. 1 is a graph of cycle performance of lithium sulfur batteries of example 1 of the present invention and comparative example 1.
Detailed Description
The technical solution of the present invention is further explained by the following embodiments. It should be understood by those skilled in the art that the examples are only for the understanding of the present invention and should not be construed as the specific limitations of the present invention.
Example 1
The embodiment provides a self-repairing flexible electrode, which comprises a current collector aluminum foil and a flexible electrode coating arranged on the surface of one side of a current collector, wherein the flexible electrode coating comprises a sulfur/carbon composite material, conductive carbon black and a self-repairing binder, the mass ratio of the sulfur/carbon composite material to the conductive carbon black is 8;
the self-repairing adhesive comprises polyvinylpyrrolidone (PVP, molecular weight of 1300000), polyethyleneimine (PEI, molecular weight of 10000) and polyacrylamide (PAM, molecular weight of 2000000) in a mass ratio of 3.5; the sulfur/carbon composite consisted of sulfur and carbon in a mass ratio of 7:3.
The embodiment also provides a preparation method of the self-repairing flexible electrode, which comprises the following steps:
(1) Dissolving PVP, PEI and PAM in a mass ratio of 3.5;
(2) Ball-milling and mixing the sublimed sulfur and the Ketjen black for 30min according to the mass ratio of 7:3, transferring the mixed powder into an argon tube furnace, and preserving heat for 12h at 155 ℃ to obtain a sulfur/carbon composite material;
(3) Adding the sulfur/carbon composite material obtained in the step (2), conductive carbon black and the binder solution obtained in the step (1) into a certain amount of ultrapure water according to the mass ratio of 8.
PVP with molecular weight in the range of 24000-1300000 adopted in the embodiments 1-8 of the invention is derived from Aladdin, PEI with molecular weight in the range of 1000-10000 is derived from Maclin Macklin, and PAM with molecular weight in the range of 2000000-14000000 is derived from Maclin Macklin.
Example 2
The embodiment provides a self-repairing flexible electrode, which comprises a current collector aluminum foil and a flexible electrode coating arranged on the surface of one side of a current collector, wherein the flexible electrode coating comprises a sulfur/carbon composite material, conductive carbon black, a carbon nanotube and a self-repairing binder, the mass ratio of which is 8;
the self-repairing binder comprises polyvinylpyrrolidone (PVP, molecular weight of 58000), polyethyleneimine (PEI, molecular weight of 10000) and polyacrylamide (PAM, molecular weight of 2000000) in a mass ratio of 4; the sulfur/carbon composite material is composed of sulfur and carbon in a mass ratio of 6:4.
The embodiment also provides a preparation method of the self-repairing flexible electrode, which comprises the following steps:
(1) Dissolving PVP, PEI and PAM in a mass ratio of 4;
(2) Ball-milling and mixing the sublimed sulfur and the Ketjen black for 30min according to the mass ratio of 6:4, transferring the mixed powder into an argon tube furnace, and preserving heat for 12h at 155 ℃ to obtain a sulfur/carbon composite material;
(3) Adding the sulfur/carbon composite material obtained in the step (2), the conductive carbon black, the carbon nano tube and the binder solution obtained in the step (1) into a certain amount of ultrapure water according to the mass ratio of 8.25.
Example 3
The embodiment provides a self-repairing flexible electrode, which comprises a current collector aluminum foil and a flexible electrode coating arranged on the surface of one side of a current collector, wherein the flexible electrode coating comprises a sulfur/carbon composite material, conductive carbon black and a self-repairing binder, the mass ratio of the sulfur/carbon composite material to the conductive carbon black is 9;
the self-repairing adhesive comprises 3 mass ratios of polyvinylpyrrolidone (PVP, molecular weight of 1300000), polyethyleneimine (PEI, molecular weight of 1800) and polyacrylamide (PAM, molecular weight of 12000000) to 3; the sulfur/carbon composite consisted of sulfur and carbon in a mass ratio of 5:5.
The embodiment also provides a preparation method of the self-repairing flexible electrode, which comprises the following steps:
(1) Dissolving PVP, PEI and PAM in a mass ratio of 3;
(2) Ball-milling and mixing the sublimed sulfur and the Ketjen black for 30min according to the mass ratio of 5:5, transferring the mixed powder into an argon tube furnace, and preserving heat for 12h at 155 ℃ to obtain a sulfur/carbon composite material;
(3) Adding the sulfur/carbon composite material obtained in the step (2), the conductive carbon black and the binder solution obtained in the step (1) into a certain amount of ultrapure water according to the mass ratio of 9.5 (the binder solution is calculated according to the mass of the self-repairing binder), stirring and mixing for 9 hours by double planets to obtain flexible electrode slurry, uniformly coating the flexible electrode slurry on one side surface of an aluminum foil, and drying for 5 hours in a vacuum oven at 70 ℃ to obtain the self-repairing flexible electrode.
Example 4
The process was the same as example 1 except that the self-healing adhesive was replaced with PVP and PEI in a mass ratio of 1:2.
Example 5
Except that the mass ratio of PVP, PEI and PAM in the self-repairing binder is replaced by PVP: PEI: the examples were the same as in example 1 except for PAM = 1.
Example 6
Except that the mass ratio of PVP, PEI and PAM in the self-repairing binder is replaced by PVP: PEI: the examples were the same as in example 1 except for PAM = 8.
Example 7
The same as example 1 except that the mass ratio of the sulfur/carbon composite material, the conductive carbon black and the self-repairing binder is 7.
Example 8
The composite material is the same as the composite material in example 1 except that the mass ratio of the sulfur/carbon composite material to the conductive carbon black to the self-repairing binder is 8.6.
Example 9
The procedure was as in example 1 except that the molecular weight of PVP was changed to 10000 (TCI/TP 047125G), the molecular weight of PEI was changed to 600 (Wolk/XW 90029866), and the molecular weight of PAM was changed to 100000 (Acros/448530050).
Comparative example 1
The same as example 1 except that the self-healing adhesive was replaced with polyvinylidene fluoride (PVDF) of the same mass, and the deionization in step (1) was replaced with NMP to dissolve the PVDF.
Comparative example 2
The same procedure as in example 1 was followed except that the self-healing binder was replaced with the same mass of PVP.
Comparative example 3
The same as example 1 except that the self-healing adhesive was replaced with PEI of the same quality.
Comparative example 4
The procedure was as in example 1 except that the self-healing adhesive was replaced with PAM of the same mass.
1. Preparation of lithium-sulfur battery
The electrodes prepared in examples 1 to 9 and comparative examples 1 to 4 of the present invention were used as positive electrodes, and the areal density of the flexible electrode coating in the electrodes was 90g/m 2 And assembling the lithium-sulfur battery with a cathode made of metal lithium, a diaphragm made of double-sided ceramic and an electrolyte made of commercial ether electrolyte.
2. Testing of cycle Performance
And (3) carrying out a charge-discharge test on the prepared lithium-sulfur battery at a multiplying power of 0.1C, wherein the voltage interval is 1.8-2.6V, the cycle charge-discharge period is 120 weeks, recording the discharge capacity of the battery in the first circle, recording the discharge capacity of the battery in the 120 th circle, and dividing the discharge capacity of the battery in the 120 th circle by the discharge capacity of the battery in the first circle to obtain the capacity retention rate, wherein the records are shown in Table 1.
TABLE 1
Figure BDA0003803787180000121
Figure BDA0003803787180000131
To sum up, the embodiments 1 to 9 show that the self-repairing capability of the binder is provided by adopting the specific high molecular polymer containing amino and the high molecular polymer containing carbonyl as the self-repairing binder and the dynamic hydrogen bond 3D cross-linked network formed by the carbonyl and the amino, so that the integrity of the electrode is ensured; meanwhile, polysulfide is fixed by a large number of polar groups, namely carbonyl and amino, redox conversion kinetics of the polysulfide is promoted, a shuttle effect is inhibited, and the self-repairing flexible electrode with excellent cycle performance is prepared.
It is clear from the comparison between example 1 and examples 5-6 that the cycling performance of the lithium-sulfur battery can be further improved when the PVP, PEI and PAM are synergistic in a proper ratio in the self-healing binder. The higher amino content in example 5 results in the presence of a highly branched structure alone, with insufficient carbonyl groups to form hydrogen bonds; in example 6, excessive carbonyl content can cause excessive carbonyl, and insufficient amino groups can form dynamic hydrogen bonds; therefore, the capacity retention ratio of example 1 was higher.
It can be seen from comparison between example 1 and examples 7-8 that when the self-healing binder is mixed with the positive electrode active material and the conductive agent in a proper ratio, the self-healing binder can exert the capacities of fixing lithium polysulfide and repairing electrode damage, and a lithium-sulfur battery with better comprehensive electrochemical performance can be obtained. The self-repairing binder in the embodiment 7 has a high content, which affects the ratio of main materials and reduces the capacity performance, thereby affecting the cycle performance, and the self-repairing binder in the embodiment 8 has a low content, which reduces the self-repairing capability of the self-repairing binder, affects the integrity of the electrode, and reduces the cycle performance of the lithium-sulfur battery; thus, the overall electrochemical performance of example 1 is better compared to examples 7-8.
It can be seen from a comparison of example 1 and example 9 that the molecular weights of PVP, PEI and PAM in the self-healing binder affect the cycling performance of the lithium sulfur battery. The molecular weights of the three water-soluble high molecular polymers in example 9 are lower, so that the hydrogen bond ratio is reduced, sulfur cannot be effectively limited in a hydrogen bond network, and the cycle performance of the lithium-sulfur battery is reduced, so that the cycle stability of example 1 is better.
Fig. 1 is a graph of cycle performance of the lithium-sulfur batteries in example 1 and comparative example 1, and it can be known from comparison between example 1 and comparative example 1 that, when the same amount of binder is added, after 120 cycles, the conventional PVDF binder can only exert a basic binding effect, the binding between the nonpolar group in the molecule and the polysulfide is weak, shuttle of the polysulfide cannot be effectively inhibited, and microcracks generated by bending or volume change in the pole piece cycle process cannot be improved, so that the capacity response of the lithium-sulfur battery prepared in comparative example 1 is reduced along with the cycle progress, and the capacity retention rate after 120 cycles is lower than 80%; in the embodiment 1, the self-repairing flexible electrode is prepared by using the specific self-repairing binder, so that not only can polysulfide be anchored, but also damage caused by frequent bending and volume change of the electrode can be repaired, and the battery still has high capacity retention rate after 120 cycles.
As is clear from comparison of example 1 with comparative examples 2 to 4, the amino group-containing polymer and the carbonyl group-containing polymer of the present invention are not indispensable, and the amino group-containing polymer and the carbonyl group-containing polymer cannot be the same polymer. The high molecular polymers in comparative examples 2 and 3 only contain one group and cannot generate a dynamic hydrogen bond 3D cross-linked network, and in comparative example 4, although the high molecular polymer PAM has both amino and carbonyl groups, the amino and carbonyl groups cannot be bonded to generate dynamic hydrogen bonds and cannot be self-healed when the pole piece is damaged due to the polarity of the molecules and no electronegativity among the polymers, so the cycling stability of comparative examples 2-4 is obviously inferior to that of example 1.
The above description is only for the specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto, and it should be understood by those skilled in the art that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present invention are within the protection scope and the disclosure of the present invention.

Claims (10)

1. The self-repairing flexible electrode is characterized by comprising a current collector and a flexible electrode coating arranged on at least one side surface of the current collector, wherein the flexible electrode coating comprises a self-repairing binder and a positive electrode active material, the self-repairing binder comprises a high molecular polymer containing amino and a high molecular polymer containing carbonyl, and the high molecular polymer containing amino and the high molecular polymer containing carbonyl are not the same high molecular polymer.
2. The self-healing flexible electrode according to claim 1, wherein the amino group-containing high molecular polymer comprises polyethyleneimine and/or polyacrylamide;
preferably, the carbonyl group-containing high molecular polymer includes polyvinylpyrrolidone and/or polyacrylamide, and the amino group-containing polymer and the carbonyl group-containing polymer are not polyacrylamide at the same time.
3. The self-repairing flexible electrode according to claim 1 or 2, wherein the mass ratio of the amino group-containing high molecular polymer to the carbonyl group-containing high molecular polymer is (1-3) to (1-3).
4. The self-healing flexible electrode of claim 2 or 3, wherein the self-healing adhesive comprises polyvinylpyrrolidone, polyethyleneimine, and polyacrylamide;
preferably, the mass ratio of the polyvinylpyrrolidone to the polyethyleneimine to the polyacrylamide in the self-repairing binder is (2-5) to (2-5).
5. The self-healing flexible electrode according to any one of claims 2 to 4, wherein the polyvinylpyrrolidone has a molecular weight of 24000 to 1300000;
preferably, the molecular weight of the polyethyleneimine is 1000 to 10000;
preferably, the molecular weight of the polyacrylamide is 2000000-14000000.
6. The self-repairing flexible electrode according to any one of claims 1 to 5, wherein the mass ratio of the positive electrode active material to the self-repairing binder is (8-9) to (0.5-1.5).
7. The self-healing flexible electrode of any one of claims 1 to 6, further comprising a conductive agent in the flexible electrode coating;
preferably, the mass ratio of the positive electrode active material to the conductive agent to the self-repairing binder is (8-9) to (0.5-1.5);
preferably, the positive electrode active material includes a sulfur/carbon composite;
preferably, the conductive agent includes any one of conductive carbon black, carbon nanotubes, and graphene or a combination of at least two thereof.
8. A preparation method of the self-repairing flexible electrode according to any one of claims 1 to 7, wherein the preparation method comprises the following steps:
and mixing the self-repairing binder with the positive electrode active material to obtain flexible electrode slurry, and coating the flexible electrode slurry on the surface of at least one side of the current collector to obtain the self-repairing flexible electrode.
9. The preparation method according to claim 8, wherein the self-repairing binder and the positive electrode active material are mixed as follows:
dissolving a self-repairing binder in a solvent and stirring to obtain a binder solution, mixing the binder solution and a positive active material, and stirring;
preferably, the self-repairing binder is dissolved in the solvent and stirred at the rotating speed of 300-1000 rpm/min;
preferably, in the process of dissolving the self-repairing binder in the solvent and stirring, the stirring time is 2-12 h;
preferably, the self-repairing binder is dissolved in a solvent and stirred at the temperature of 25-35 ℃;
preferably, the solvent comprises water.
10. A lithium-sulfur battery, wherein the positive electrode of the lithium-sulfur battery adopts the self-repairing flexible electrode according to any one of claims 1 to 7.
CN202210990658.6A 2022-08-18 2022-08-18 Self-repairing flexible electrode, preparation method thereof and lithium-sulfur battery Pending CN115275096A (en)

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN115425226A (en) * 2022-08-18 2022-12-02 楚能新能源股份有限公司 Ternary material flexible positive electrode and preparation method thereof

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN115425226A (en) * 2022-08-18 2022-12-02 楚能新能源股份有限公司 Ternary material flexible positive electrode and preparation method thereof
CN115425226B (en) * 2022-08-18 2023-04-14 楚能新能源股份有限公司 Ternary material flexible positive electrode and preparation method thereof

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