CN114204214A - Functionalized modified diaphragm and preparation method and application thereof - Google Patents
Functionalized modified diaphragm and preparation method and application thereof Download PDFInfo
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- CN114204214A CN114204214A CN202111508062.XA CN202111508062A CN114204214A CN 114204214 A CN114204214 A CN 114204214A CN 202111508062 A CN202111508062 A CN 202111508062A CN 114204214 A CN114204214 A CN 114204214A
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- vanadium carbide
- diaphragm
- ketjen black
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- 238000002360 preparation method Methods 0.000 title claims abstract description 11
- INZDTEICWPZYJM-UHFFFAOYSA-N 1-(chloromethyl)-4-[4-(chloromethyl)phenyl]benzene Chemical compound C1=CC(CCl)=CC=C1C1=CC=C(CCl)C=C1 INZDTEICWPZYJM-UHFFFAOYSA-N 0.000 claims abstract description 105
- 239000002127 nanobelt Substances 0.000 claims abstract description 84
- 239000004743 Polypropylene Substances 0.000 claims abstract description 82
- 229920001155 polypropylene Polymers 0.000 claims abstract description 81
- 239000003273 ketjen black Substances 0.000 claims abstract description 69
- -1 polypropylene Polymers 0.000 claims abstract description 53
- 239000002121 nanofiber Substances 0.000 claims abstract description 49
- JDZCKJOXGCMJGS-UHFFFAOYSA-N [Li].[S] Chemical compound [Li].[S] JDZCKJOXGCMJGS-UHFFFAOYSA-N 0.000 claims abstract description 43
- 238000000034 method Methods 0.000 claims abstract description 18
- 239000002074 nanoribbon Substances 0.000 claims abstract description 16
- 238000013329 compounding Methods 0.000 claims abstract description 6
- BNOODXBBXFZASF-UHFFFAOYSA-N [Na].[S] Chemical compound [Na].[S] BNOODXBBXFZASF-UHFFFAOYSA-N 0.000 claims abstract description 5
- 230000002194 synthesizing effect Effects 0.000 claims abstract description 5
- LFZAXBDWELNSEE-UHFFFAOYSA-N [S].[K] Chemical compound [S].[K] LFZAXBDWELNSEE-UHFFFAOYSA-N 0.000 claims abstract description 4
- VEXZGXHMUGYJMC-UHFFFAOYSA-N Hydrochloric acid Chemical compound Cl VEXZGXHMUGYJMC-UHFFFAOYSA-N 0.000 claims description 51
- 239000000243 solution Substances 0.000 claims description 44
- KWGKDLIKAYFUFQ-UHFFFAOYSA-M lithium chloride Chemical compound [Li+].[Cl-] KWGKDLIKAYFUFQ-UHFFFAOYSA-M 0.000 claims description 24
- 239000000203 mixture Substances 0.000 claims description 24
- 239000011259 mixed solution Substances 0.000 claims description 15
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- 238000001035 drying Methods 0.000 claims description 12
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- 238000001291 vacuum drying Methods 0.000 claims description 12
- 238000009210 therapy by ultrasound Methods 0.000 claims description 10
- 239000000126 substance Substances 0.000 claims description 9
- 239000000725 suspension Substances 0.000 claims description 9
- SECXISVLQFMRJM-UHFFFAOYSA-N N-Methylpyrrolidone Chemical compound CN1CCCC1=O SECXISVLQFMRJM-UHFFFAOYSA-N 0.000 claims description 8
- 239000002033 PVDF binder Substances 0.000 claims description 8
- 239000007795 chemical reaction product Substances 0.000 claims description 8
- 238000004140 cleaning Methods 0.000 claims description 8
- 239000012459 cleaning agent Substances 0.000 claims description 8
- 229920002981 polyvinylidene fluoride Polymers 0.000 claims description 8
- 229910001220 stainless steel Inorganic materials 0.000 claims description 8
- 239000010935 stainless steel Substances 0.000 claims description 8
- 239000006228 supernatant Substances 0.000 claims description 8
- 239000007864 aqueous solution Substances 0.000 claims description 7
- 239000012528 membrane Substances 0.000 claims description 7
- 238000005086 pumping Methods 0.000 claims description 7
- 239000008367 deionised water Substances 0.000 claims description 6
- 229910021641 deionized water Inorganic materials 0.000 claims description 6
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Chemical compound O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 6
- 238000011068 loading method Methods 0.000 claims description 4
- 238000000926 separation method Methods 0.000 claims description 4
- 239000007787 solid Substances 0.000 claims description 4
- 238000003828 vacuum filtration Methods 0.000 claims description 4
- DKAGJZJALZXOOV-UHFFFAOYSA-N hydrate;hydrochloride Chemical compound O.Cl DKAGJZJALZXOOV-UHFFFAOYSA-N 0.000 claims description 3
- 229920001021 polysulfide Polymers 0.000 abstract description 24
- 239000005077 polysulfide Substances 0.000 abstract description 24
- 150000008117 polysulfides Polymers 0.000 abstract description 24
- WHXSMMKQMYFTQS-UHFFFAOYSA-N Lithium Chemical compound [Li] WHXSMMKQMYFTQS-UHFFFAOYSA-N 0.000 abstract description 22
- 229910052744 lithium Inorganic materials 0.000 abstract description 22
- 230000000694 effects Effects 0.000 abstract description 20
- 230000000670 limiting effect Effects 0.000 abstract description 5
- 238000011161 development Methods 0.000 abstract description 3
- 239000002131 composite material Substances 0.000 description 29
- 239000003792 electrolyte Substances 0.000 description 21
- SPEUIVXLLWOEMJ-UHFFFAOYSA-N 1,1-dimethoxyethane Chemical compound COC(C)OC SPEUIVXLLWOEMJ-UHFFFAOYSA-N 0.000 description 12
- XTHFKEDIFFGKHM-UHFFFAOYSA-N Dimethoxyethane Chemical compound COCCOC XTHFKEDIFFGKHM-UHFFFAOYSA-N 0.000 description 12
- NINIDFKCEFEMDL-UHFFFAOYSA-N Sulfur Chemical compound [S] NINIDFKCEFEMDL-UHFFFAOYSA-N 0.000 description 11
- 229910052717 sulfur Inorganic materials 0.000 description 11
- 238000006243 chemical reaction Methods 0.000 description 10
- 238000002484 cyclic voltammetry Methods 0.000 description 9
- 239000011593 sulfur Substances 0.000 description 9
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 8
- 229910052799 carbon Inorganic materials 0.000 description 8
- VDFVNEFVBPFDSB-UHFFFAOYSA-N 1,3-dioxane Chemical compound C1COCOC1 VDFVNEFVBPFDSB-UHFFFAOYSA-N 0.000 description 6
- 230000005540 biological transmission Effects 0.000 description 6
- 239000000463 material Substances 0.000 description 6
- 238000001000 micrograph Methods 0.000 description 6
- HBBGRARXTFLTSG-UHFFFAOYSA-N Lithium ion Chemical compound [Li+] HBBGRARXTFLTSG-UHFFFAOYSA-N 0.000 description 5
- 229910001416 lithium ion Inorganic materials 0.000 description 5
- 238000001556 precipitation Methods 0.000 description 5
- 230000008569 process Effects 0.000 description 5
- 238000012360 testing method Methods 0.000 description 5
- XKRFYHLGVUSROY-UHFFFAOYSA-N Argon Chemical compound [Ar] XKRFYHLGVUSROY-UHFFFAOYSA-N 0.000 description 4
- 101100317222 Borrelia hermsii vsp3 gene Proteins 0.000 description 4
- 230000008901 benefit Effects 0.000 description 4
- 239000011248 coating agent Substances 0.000 description 4
- 238000000576 coating method Methods 0.000 description 4
- 238000002474 experimental method Methods 0.000 description 4
- GLNWILHOFOBOFD-UHFFFAOYSA-N lithium sulfide Chemical compound [Li+].[Li+].[S-2] GLNWILHOFOBOFD-UHFFFAOYSA-N 0.000 description 4
- 230000004048 modification Effects 0.000 description 4
- 238000012986 modification Methods 0.000 description 4
- 238000010899 nucleation Methods 0.000 description 4
- 238000001179 sorption measurement Methods 0.000 description 4
- LFQSCWFLJHTTHZ-UHFFFAOYSA-N Ethanol Chemical compound CCO LFQSCWFLJHTTHZ-UHFFFAOYSA-N 0.000 description 3
- 230000004913 activation Effects 0.000 description 3
- 238000004873 anchoring Methods 0.000 description 3
- 230000009286 beneficial effect Effects 0.000 description 3
- 239000013078 crystal Substances 0.000 description 3
- 150000002500 ions Chemical class 0.000 description 3
- 239000010410 layer Substances 0.000 description 3
- 230000007246 mechanism Effects 0.000 description 3
- 230000006911 nucleation Effects 0.000 description 3
- XOFYZVNMUHMLCC-ZPOLXVRWSA-N prednisone Chemical compound O=C1C=C[C@]2(C)[C@H]3C(=O)C[C@](C)([C@@](CC4)(O)C(=O)CO)[C@@H]4[C@@H]3CCC2=C1 XOFYZVNMUHMLCC-ZPOLXVRWSA-N 0.000 description 3
- 238000012546 transfer Methods 0.000 description 3
- 229910013553 LiNO Inorganic materials 0.000 description 2
- 238000002441 X-ray diffraction Methods 0.000 description 2
- PTXMVOUNAHFTFC-UHFFFAOYSA-N alumane;vanadium Chemical compound [AlH3].[V] PTXMVOUNAHFTFC-UHFFFAOYSA-N 0.000 description 2
- 229910052786 argon Inorganic materials 0.000 description 2
- 230000004888 barrier function Effects 0.000 description 2
- 230000003197 catalytic effect Effects 0.000 description 2
- 238000006555 catalytic reaction Methods 0.000 description 2
- 239000013256 coordination polymer Substances 0.000 description 2
- 238000009792 diffusion process Methods 0.000 description 2
- 238000001453 impedance spectrum Methods 0.000 description 2
- 230000006872 improvement Effects 0.000 description 2
- IIPYXGDZVMZOAP-UHFFFAOYSA-N lithium nitrate Inorganic materials [Li+].[O-][N+]([O-])=O IIPYXGDZVMZOAP-UHFFFAOYSA-N 0.000 description 2
- QSZMZKBZAYQGRS-UHFFFAOYSA-N lithium;bis(trifluoromethylsulfonyl)azanide Chemical compound [Li+].FC(F)(F)S(=O)(=O)[N-]S(=O)(=O)C(F)(F)F QSZMZKBZAYQGRS-UHFFFAOYSA-N 0.000 description 2
- 238000004519 manufacturing process Methods 0.000 description 2
- 230000010287 polarization Effects 0.000 description 2
- 229920001343 polytetrafluoroethylene Polymers 0.000 description 2
- 239000004810 polytetrafluoroethylene Substances 0.000 description 2
- 239000011148 porous material Substances 0.000 description 2
- 230000004044 response Effects 0.000 description 2
- 239000002002 slurry Substances 0.000 description 2
- 238000001228 spectrum Methods 0.000 description 2
- ZUHZGEOKBKGPSW-UHFFFAOYSA-N tetraglyme Chemical compound COCCOCCOCCOCCOC ZUHZGEOKBKGPSW-UHFFFAOYSA-N 0.000 description 2
- 229910052720 vanadium Inorganic materials 0.000 description 2
- LEONUFNNVUYDNQ-UHFFFAOYSA-N vanadium atom Chemical compound [V] LEONUFNNVUYDNQ-UHFFFAOYSA-N 0.000 description 2
- 239000002841 Lewis acid Substances 0.000 description 1
- UCKMPCXJQFINFW-UHFFFAOYSA-N Sulphide Chemical compound [S-2] UCKMPCXJQFINFW-UHFFFAOYSA-N 0.000 description 1
- 239000013543 active substance Substances 0.000 description 1
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 description 1
- 229910052782 aluminium Inorganic materials 0.000 description 1
- 239000010405 anode material Substances 0.000 description 1
- 230000008859 change Effects 0.000 description 1
- 239000003086 colorant Substances 0.000 description 1
- 150000001875 compounds Chemical class 0.000 description 1
- 238000001816 cooling Methods 0.000 description 1
- 230000001351 cycling effect Effects 0.000 description 1
- 238000009831 deintercalation Methods 0.000 description 1
- 230000008021 deposition Effects 0.000 description 1
- 238000013461 design Methods 0.000 description 1
- 238000007599 discharging Methods 0.000 description 1
- 230000009881 electrostatic interaction Effects 0.000 description 1
- 238000004146 energy storage Methods 0.000 description 1
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- 125000000524 functional group Chemical group 0.000 description 1
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- 230000014759 maintenance of location Effects 0.000 description 1
- 238000005259 measurement Methods 0.000 description 1
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- 230000008018 melting Effects 0.000 description 1
- VNWKTOKETHGBQD-UHFFFAOYSA-N methane Chemical compound C VNWKTOKETHGBQD-UHFFFAOYSA-N 0.000 description 1
- 239000011268 mixed slurry Substances 0.000 description 1
- 239000005486 organic electrolyte Substances 0.000 description 1
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Classifications
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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
- H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
- H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
- H01M50/403—Manufacturing processes of separators, membranes or diaphragms
-
- 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
- H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
- H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
- H01M50/409—Separators, membranes or diaphragms characterised by the material
- H01M50/411—Organic material
- H01M50/414—Synthetic resins, e.g. thermoplastics or thermosetting resins
- H01M50/417—Polyolefins
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
- H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
- H01M50/409—Separators, membranes or diaphragms characterised by the material
- H01M50/44—Fibrous material
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
- H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
- H01M50/409—Separators, membranes or diaphragms characterised by the material
- H01M50/449—Separators, membranes or diaphragms characterised by the material having a layered structure
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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
- H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
- H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
- H01M50/489—Separators, membranes, diaphragms or spacing elements inside the cells, characterised by their physical properties, e.g. swelling degree, hydrophilicity or shut down properties
- H01M50/491—Porosity
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- 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
A functionalized modified diaphragm and a preparation method and application thereof relate to a diaphragm and a preparation method and application thereof. The invention aims to solve the problem of shuttle effect of lithium polysulfide in a lithium-sulfur battery, namely the problem of limiting the development and practical application of the lithium-sulfur battery. The functionalized modified diaphragm is a polypropylene diaphragm which is modified by compounding vanadium carbide nanobelts and Ketjen black nanofibers; the vanadium carbide nanobelt and the Ketjen black nanofiber are of a three-dimensional network structure, and the mass ratio of the vanadium carbide nanobelt to the Ketjen black nanofiber is (2-10): 1; wherein the width of the vanadium carbide nanoribbon is 10-50nm, the length is 100nm-20 μm, the number of layers is 1-30, and the (002) interplanar spacing is 0.2-0.9 nm. The method comprises the following steps: firstly, synthesizing vanadium carbide nanobelts; secondly, compounding and modifying the polypropylene diaphragm by the vanadium carbide nanobelt and the Ketjen black nanofiber. The functionalized modified diaphragm is used as a diaphragm of a lithium-sulfur battery, a potassium-sulfur battery or a sodium-sulfur battery.
Description
Technical Field
The invention relates to a diaphragm and a preparation method and application thereof.
Background
Lithium sulfur batteries are one type of lithium battery. Typical lithium sulfur batteries generally employ elemental sulfur as the positive electrode and a metallic lithium plate as the negative electrode. The elemental sulfur has rich reserves in the earth, and has the characteristics of low price, environmental friendliness and the like. The lithium-sulfur battery using sulfur as the anode material has higher material theoretical specific capacity and battery theoretical specific energy which respectively reach 1675mAh/g and 2600Wh/kg, which are far higher than the capacity of lithium cobaltate battery widely used commercially (<150 mAh/g). And the sulfur is an element which is friendly to the environment, basically has no pollution to the environment, and is a lithium battery with very prospect. The reaction mechanism of lithium-sulfur batteries is different from the ion deintercalation mechanism of lithium-ion batteries, but is an electrochemical mechanism. During discharge, the negative electrode reacts to lose electrons of lithium and change the lithium into lithium ions, and the positive electrode reacts to generate sulfide through the reaction of sulfur, the lithium ions and the electrons. Lithium polysulfide as intermediate product of reaction2SnThe (n-3-8) can be dissolved in the organic electrolyte and can migrate between the positive electrode and the negative electrode, so that a shuttle effect is caused, and the main reason for limiting the development and practical application of the lithium-sulfur battery is provided. The present invention is an improvement over the diaphragm in many options to address this problem.
Currently, lithium sulfur batteries generally employ a commercially available microporous polypropylene (PP) membrane as a separator, which has advantages of good mechanical properties and chemical stability. But the disadvantages are: low wettability, poor electrolyte liquid retention, low ionic conductivity, no anchoring polysulfide effect and the like.
Disclosure of Invention
The invention aims to solve the problem of shuttle effect of lithium polysulfide in a lithium-sulfur battery, namely the problem of limiting the development and practical application of the lithium-sulfur battery, and provides a functionalized modified diaphragm, a preparation method and application.
A functional modified diaphragm is a polypropylene diaphragm which is compositely modified by vanadium carbide nanobelts and Ketjen black nanofibers; the vanadium carbide nanobelt and the Ketjen black nanofiber are of a three-dimensional network structure, and the mass ratio of the vanadium carbide nanobelt to the Ketjen black nanofiber is (2-10): 1; wherein the width of the vanadium carbide nanoribbon is 10-50nm, the length is 100nm-20 μm, the number of layers is 1-30, and the (002) interplanar spacing is 0.2-0.9 nm.
A preparation method of a functionalized modified diaphragm comprises the following steps:
firstly, synthesizing vanadium carbide nanobelts:
adding LiF into HCl water solution, and adding V2AlC is evenly stirred to obtain a mixed solution;
secondly, transferring the mixed solution into a polytetrafluoroethylene-lined stainless steel high-pressure autoclave, and then preserving the polytetrafluoroethylene-lined stainless steel high-pressure autoclave for 100-130 h at the temperature of 85-90 ℃ to obtain black precipitates;
centrifugally cleaning the black solid substance for 5-6 times by using a hydrochloric acid solution as a cleaning agent, and removing the hydrochloric acid solution to obtain a precipitate cleaned by the hydrochloric acid solution; centrifuging and cleaning the precipitate cleaned by the hydrochloric acid solution for 5-6 times by taking LiCl solution as a cleaning agent, collecting supernatant, and centrifuging the supernatant for 40-45 min at a centrifugal speed of 9000 r/min to obtain a reaction product; drying the reaction product in a vacuum drying oven to obtain a vanadium carbide nanobelt;
secondly, compounding and modifying the polypropylene diaphragm by the vanadium carbide nanobelt and the Ketjen black nanofiber:
mixing Ketjen black and vanadium carbide nanobelts to obtain a Ketjen black/vanadium carbide nanobelt mixture;
secondly, mixing the Ketjen black/vanadium carbide nano-belt mixture with polyvinylidene fluoride to obtain a solute; adding the solute into N-methylpyrrolidone, and carrying out ultrasonic treatment to obtain a suspension;
and thirdly, pumping the suspension onto a polypropylene diaphragm by vacuum filtration through vacuum pumping separation, and then putting the polypropylene diaphragm into a vacuum drying oven for drying to obtain the functional modified diaphragm.
A functionalized modified diaphragm is used as a diaphragm of a lithium-sulfur battery or a sodium-sulfur battery.
The invention has the advantages that:
firstly, the functional modified diaphragm prepared by the invention is a polypropylene diaphragm modified by a vanadium carbide nanobelt and Keqin black nanofiber composite; the vanadium carbide nanobelt and the Ketjen black nanofiber are of a three-dimensional network structure, and can generate a physical barrier effect on lithium polysulfide dissolved in electrolyte, so that shuttle benefits are effectively reduced; moreover, the Ketjen black nano-fibers are used as a conductive framework to form a mutually communicated network structure, which is beneficial to the permeation of electrolyte and the rapid conduction of ions/electrons; meanwhile, the wettability of the diaphragm is improved due to the multi-size pores in the structure, and better electrochemical performance can be obtained;
secondly, the functional modified diaphragm prepared by the invention is a polypropylene diaphragm modified by a vanadium carbide nanobelt and Keqin black nanofiber composite; vanadium carbide is a typical two-dimensional layered material, has stronger chemical adsorption effect on lithium polysulfide due to the special lattice structure, energy band structure and the like, can provide faster charge transfer, and catalyzes and accelerates the lithium polysulfide to Li2The dynamic redox reaction of S conversion effectively inhibits polysulfide shuttling, promotes polysulfide phase conversion, recovers shuttered polysulfide and increases the cycle number of the battery;
thirdly, the functional modified diaphragm prepared by the invention is a polypropylene diaphragm modified by a vanadium carbide nanobelt and Keqin black nanofiber composite; the vanadium carbide is in a nano-belt shape, has the width of 10-50nm and the length of 100nm-20 mu m, and provides higher specific surface area and more edge active sites compared with the conventional flaky shape of MXene materials; moreover, the number of the vanadium carbide nanobelts is 1-30, and the (002) crystal face spacing is 0.2-0.9 nm, so that charge transfer is facilitated, and conditions are created for better anchoring lithium polysulfide dissolved in the electrolyte;
fourthly, the functional modified diaphragm prepared by the method is a polypropylene diaphragm modified by the vanadium carbide nanobelt and the Keqin black nanofiber composite; the performance can be optimized by adjusting the number of layers and the interlayer spacing of the vanadium carbide nanobelts, so that the reasonable design and the accurate control of materials are facilitated, and a theoretical basis and a technical support are provided for the research and the practical application of the lithium-sulfur battery;
fifthly, the prepared functional modified diaphragm is a polypropylene diaphragm modified by a vanadium carbide nanobelt and Keqin black nanofiber composite; the surface of the vanadium carbide nanobelt contains functional groups such as-O, -Cl, -F, -OH and the like, the binding energy of polysulfide and the surface of the diaphragm can be obviously improved through Lewis acid reaction, so that the surface of the diaphragm is polarized to generate dipoles, dipole-dipole electrostatic interaction is formed with polar polysulfide, and finally sufficient surface binding force and limiting effect are provided for the polar polysulfide, the loss of active substances and the attenuation of capacity are improved, and the performance of the battery is improved;
sixthly, the functional modified diaphragm prepared by the invention is a polypropylene diaphragm modified by a vanadium carbide nanobelt and Keqin black nanofiber composite; coating the vanadium carbide nanobelt and the Ketjen black nanofiber composite on carbon paper, and adding Li2S6When the vanadium carbide nanobelt is used as an electrolyte to manufacture a symmetrical battery, a volt-ampere characteristic curve has an obvious redox peak and a higher response current, which shows that the vanadium carbide nanobelt and the ketjen black nanofiber composite polysulfide have an obvious chemical adsorption effect and can effectively inhibit a shuttle effect;
seventhly, the functional modified diaphragm prepared by the invention is a polypropylene diaphragm modified by a vanadium carbide nanobelt and Keqin black nanofiber composite; coating the vanadium carbide nanobelt and the Ketjen black nanofiber composite on carbon paper, and adding Li2S6Symmetric cell is made by using the electrolyte, and the exchange current density is 1.608mA cm–2Almost ten times the exchange current density of pure carbon paper (j 0.177mA cm)–2) The vanadium carbide nanobelt and Ketjen black nanofiber composite for Li is illustrated2Sn-to-Li2The process of S has good catalysis effect, can accelerate reaction kinetics and inhibit shuttle effect;
eighthly, the functional modified diaphragm prepared by the invention is a polypropylene diaphragm modified by a vanadium carbide nanobelt and Ketjen black nanofiber composite; the modification process of the diaphragm is ingenious, simple and feasible to operate, excellent in performance and beneficial to commercial production;
ninth, the functional modified diaphragm prepared by the invention is a polypropylene diaphragm modified by a vanadium carbide nanobelt and Keqin black nanofiber composite; application thereof to lithium-sulfur batteries, S8To Li2S4The Tafel slope of (1) is 93mVdec–1The activation energy is 28.63kJmol lower than that of a commercial polypropylene diaphragm–1，Li2S4To Li2The Tafel slope of S is 86mVdec–1The activation energy is lower than that of a commercial polypropylene diaphragm by 24.82kJmol–1The interface transmission resistance is obviously smaller than that of a commercial polypropylene diaphragm, so that good battery performance is obtained;
tenth, the functional modified diaphragm prepared by the invention is a polypropylene diaphragm modified by a vanadium carbide nanobelt and Keqin black nanofiber composite; it is applied to lithium-sulfur batteries, consisting of8To Li2S4And from Li2S4To Li2Diffusion coefficients of lithium ions in the S process were 5.18X 10, respectively–8And 3.27X 10–7cm2 s–1Nearly ten times (8.25X 10) that of commercial polypropylene separators–9And 1.03X 10–8cm2s–1)；
Eleven, the functional modified diaphragm prepared by the invention is a polypropylene diaphragm modified by a vanadium carbide nanobelt and Keqin black nanofiber composite; in Li2In the S precipitation experiment, the precipitation time of the vanadium carbide nanobelt and the Ketjen black nanofiber composite is increased from 6000S to 1901S, and Li is added2The precipitation capacity of S was 194.0mAh g–1Is raised to 345.5mAhg–1The vanadium carbide nanobelt and Ketjen black nanofiber composite is illustrated for polysulfide to Li2The transformation of S has good catalysis effect;
twelfth, the functional modified diaphragm prepared by the method is a polypropylene diaphragm modified by the vanadium carbide nanobelt and the Keqin black nanofiber composite; when the composite material is applied to a lithium-sulfur battery, the shuttling effect is well inhibited, and the specific capacity (at 0.2 ℃ C.) is improved compared with that of a commercial polypropylene diaphragm，1236.1mAh g-1(ii) a The commercial polypropylene membrane is 876.2mAhg-1) Polarization overpotential (at 0.2C, Δ E ═ 156.3 mV; the commercial polypropylene diaphragm is 269.7mV (Delta E), the rate capability is 851.5mAhg at 2C-1(ii) a The commercial polypropylene separator was 141.4mAhg-1) And cycle stability (0.2C cycle 150 cycles after each cycle decay rate of 0.16%; 1C initial discharge capacity of 1069mAhg-1The attenuation per cycle of 1000 cycles was 0.049% and the coulombic efficiency was 98%. The attenuation rate of each ring of the commercial polypropylene diaphragm after 200 rings is 0.27%; the initial discharge capacity at 1C was 643.2mAh g-1The attenuation of 600 cycles per cycle is 0.113%, and the coulombic efficiency is 93%;
the functional modified diaphragm prepared by the invention is a polypropylene diaphragm modified by the composite of the vanadium carbide nanobelt and the Ketjen black nanofiber, and has wide application prospects in the energy storage fields of lithium-sulfur batteries, potassium-sulfur batteries, sodium-sulfur batteries and the like.
Drawings
FIG. 1 is an X-ray diffraction spectrum, in which V2CTXVanadium carbide nanoribbons prepared for one step one of the examples, V2AlC is vanadium aluminum carbide;
FIG. 2 is a low power transmission electron microscope image of vanadium carbide nanoribbons prepared in one step one of the example;
FIG. 3 is a high power transmission electron microscope image of vanadium carbide nanoribbons prepared in one step one of the example;
FIG. 4 is Li2S6Solution and Ketjen black/vanadium carbide nanoribbon mixture/Li2S6Standing the solutions for 3 hours respectively to obtain digital images;
FIG. 5 is a CV curve of a symmetrical cell, in which 1 is a CP symmetrical cell and 2 is KB/V2CTX-a CP symmetric cell;
FIG. 6 shows the exchange current density of a symmetrical cell, where 1 is CP symmetrical cell and 2 is KB/V2CTX-a CP symmetric cell;
FIG. 7 is Li2The constant voltage discharge curve of S nucleation experiment is shown in figure 1 as CP cell and 2 as KB/V2CTX-a CP battery;
FIG. 8 is a scanning electron microscope image of a functionalized modified diaphragm prepared in the second step of the example;
fig. 9 is CV curves of a lithium sulfur battery in which the separators are respectively PP and the functionalized modified separator prepared in example one, wherein the separator 2 is PP, and the separator 1 is the functionalized modified separator prepared in example one;
fig. 10 is an impedance spectrum of a lithium sulfur battery with a separator of PP and a functionalized modified separator prepared in example one, wherein the separator 1 is PP and the separator 2 is the functionalized modified separator prepared in example one;
fig. 11 is a charge-discharge curve of a lithium-sulfur battery whose separator is a functionalized modified separator prepared in example one, in which 1 is the 1 st turn, 2 is the 10 th turn, 3 is the 20 th turn, 4 is the 50 th turn, 5 is the 100 th turn, and 6 is the 150 th turn;
fig. 12 is a charge-discharge curve of a lithium-sulfur battery having a PP separator, in which 1 is the 1 st turn, 2 is the 10 th turn, 3 is the 20 th turn, 4 is the 50 th turn, 5 is the 100 th turn, and 6 is the 150 th turn;
fig. 13 is a first cycle characteristic of a lithium sulfur battery in which the separator is PP and the functionalized modified separator prepared in example one, respectively, in which fig. 1 shows PP and fig. 2 shows the separator is the functionalized modified separator prepared in example one;
fig. 14 shows the first cycle characteristics of a lithium sulfur battery with a separator of PP and a functionalized modified separator prepared in example one, wherein the separator 1 is PP and the separator 2 is the functionalized modified separator prepared in example one;
fig. 15 is a digital image of the lithium negative electrode side of a lithium sulfur battery cycled 150 cycles at 0.2C with PP as the separator of (a) and the functionalized modified separator of example one, respectively, where the separator of (b) is the functionalized modified separator of example one;
fig. 16 shows the rate characteristics of a lithium-sulfur battery in which the separator is PP and the functionalized modified separator prepared in example one, wherein the separator 1 is PP and the separator 2 is the functionalized modified separator prepared in example one.
Detailed Description
The following examples further illustrate the present invention but are not to be construed as limiting the invention. Modifications and substitutions to methods, procedures, or conditions of the invention may be made without departing from the spirit of the invention.
The first embodiment is as follows: the functionalized modified diaphragm is a polypropylene diaphragm compositely modified by vanadium carbide nanobelts and Ketjen black nanofibers; the vanadium carbide nanobelt and the Ketjen black nanofiber are of a three-dimensional network structure, and the mass ratio of the vanadium carbide nanobelt to the Ketjen black nanofiber is (2-10): 1; wherein the width of the vanadium carbide nanoribbon is 10-50nm, the length is 100nm-20 μm, the number of layers is 1-30, and the (002) interplanar spacing is 0.2-0.9 nm.
The second embodiment is as follows: the present embodiment differs from the present embodiment in that: the loading capacity of the vanadium carbide nanobelt and the Ketjen black nanofiber on the polypropylene diaphragm is 0.1-5 mg/cm2. Other steps are the same as in the first embodiment.
The third concrete implementation mode: the present embodiment differs from the first or second embodiment in that: the preparation method of the functionalized modified diaphragm comprises the following steps:
firstly, synthesizing vanadium carbide nanobelts:
adding LiF into HCl water solution, and adding V2AlC is evenly stirred to obtain a mixed solution;
secondly, transferring the mixed solution into a polytetrafluoroethylene-lined stainless steel high-pressure autoclave, and then preserving the polytetrafluoroethylene-lined stainless steel high-pressure autoclave for 100-130 h at the temperature of 85-90 ℃ to obtain black precipitates;
centrifugally cleaning the black solid substance for 5-6 times by using a hydrochloric acid solution as a cleaning agent, and removing the hydrochloric acid solution to obtain a precipitate cleaned by the hydrochloric acid solution; centrifuging and cleaning the precipitate cleaned by the hydrochloric acid solution for 5-6 times by taking LiCl solution as a cleaning agent, collecting supernatant, and centrifuging the supernatant for 40-45 min at a centrifugal speed of 9000 r/min to obtain a reaction product; drying the reaction product in a vacuum drying oven to obtain a vanadium carbide nanobelt;
secondly, compounding and modifying the polypropylene diaphragm by the vanadium carbide nanobelt and the Ketjen black nanofiber:
mixing Ketjen black and vanadium carbide nanobelts to obtain a Ketjen black/vanadium carbide nanobelt mixture;
secondly, mixing the Ketjen black/vanadium carbide nano-belt mixture with polyvinylidene fluoride to obtain a solute; adding the solute into N-methylpyrrolidone, and carrying out ultrasonic treatment to obtain a suspension;
and thirdly, pumping the suspension onto a polypropylene diaphragm by vacuum filtration through vacuum pumping separation, and then putting the polypropylene diaphragm into a vacuum drying oven for drying to obtain the functional modified diaphragm. The other steps are the same as in the first or second embodiment.
The fourth concrete implementation mode: the difference between this embodiment and one of the first to third embodiments is as follows: the ratio of the mass of the LiF to the volume of the HCl aqueous solution in the first step (2 g-4 g) is 20 mL; the mass fraction of the HCl aqueous solution in the first step is 5-38%. The other steps are the same as those in the first to third embodiments.
The fifth concrete implementation mode: the difference between this embodiment and one of the first to fourth embodiments is: v described in step one2The ratio of the mass of AlC to the volume of HCl aqueous solution (0.6 g-1 g) was 20 mL. The other steps are the same as those in the first to fourth embodiments.
The sixth specific implementation mode: the difference between this embodiment and one of the first to fifth embodiments is as follows: the hydrochloric acid solution in the step one is formed by mixing 20mL of hydrochloric acid with the mass fraction of 37% and 180mL of deionized water. The other steps are the same as those in the first to fifth embodiments.
The seventh embodiment: the difference between this embodiment and one of the first to sixth embodiments is: dissolving the LiCl solution in the step one to 180mL of deionized water, wherein the LiCl solution is 7.63-8 g of LiCl; the temperature of the vacuum drying oven in the step one is 60 ℃, and the drying time is 10-12 h. The other steps are the same as those in the first to sixth embodiments.
The specific implementation mode is eight: the difference between this embodiment and one of the first to seventh embodiments is: the mass ratio of the Ketjen black to the vanadium carbide nanobelt in the second step is 2: 8; and the mass ratio of the Ketjen black/vanadium carbide nano-belt mixture to the polyvinylidene fluoride in the second step is 9: 1. The other steps are the same as those in the first to seventh embodiments.
The specific implementation method nine: the difference between this embodiment and the first to eighth embodiments is: in the second step, the volume ratio of the mass of the solute to the volume of the N-methylpyrrolidone is (0.5 g-1.2 g) 10 mL; the power of ultrasonic treatment in the second step is 100W-500W, and the time of ultrasonic treatment is 2 h-3 h; the temperature of the vacuum drying oven in the second step is 60 ℃, and the drying time is 10-12 h. The other steps are the same as those in the first to eighth embodiments.
The detailed implementation mode is ten: in the present embodiment, the functionalized modified separator is used as a separator for a lithium-sulfur battery, a potassium-sulfur battery, or a sodium-sulfur battery.
The first embodiment is as follows: a preparation method of a functionalized modified diaphragm comprises the following steps:
firstly, synthesizing vanadium carbide nanobelts:
adding 3g LiF into 20mL of HCl aqueous solution with the mass fraction of 18.5%, and then adding 0.8g V2AlC is evenly stirred to obtain a mixed solution;
transferring the mixed solution into a 50mL stainless steel autoclave with a polytetrafluoroethylene lining, and preserving the stainless steel autoclave with the polytetrafluoroethylene lining at the temperature of 85 ℃ for 120h to obtain black precipitates;
centrifugally cleaning the black solid substance for 6 times by using a hydrochloric acid solution as a cleaning agent, and removing the hydrochloric acid solution to obtain a precipitate cleaned by the hydrochloric acid solution; centrifuging and cleaning the precipitate cleaned by the hydrochloric acid solution for 6 times by using LiCl solution as a cleaning agent, collecting supernatant, and centrifuging the supernatant at a centrifugal speed of 9000 r/min for 45min to obtain a reaction product; drying the reaction product in a vacuum drying oven at 60 ℃ for 12h to obtain a vanadium carbide nanobelt;
the hydrochloric acid solution in the step one is formed by mixing 20mL of hydrochloric acid with the mass fraction of 37% and 180mL of deionized water;
dissolving the LiCl solution in the step one to 180mL of deionized water, wherein the LiCl solution is 7.63-8 g of LiCl;
secondly, compounding and modifying the polypropylene diaphragm by the vanadium carbide nanobelt and the Ketjen black nanofiber:
mixing Ketjen black and vanadium carbide nanobelts to obtain a Ketjen black/vanadium carbide nanobelt mixture;
the mass ratio of the Ketjen black to the vanadium carbide nanobelt in the second step is 2: 8;
secondly, mixing the Ketjen black/vanadium carbide nano-belt mixture with polyvinylidene fluoride to obtain a solute; adding the solute into N-methylpyrrolidone, and carrying out ultrasonic treatment for 2h under the ultrasonic treatment power of 180W to obtain a suspension;
the mass ratio of the Ketjen black/vanadium carbide nanobelt mixture to the polyvinylidene fluoride in the second step is 9: 1;
the volume ratio of the mass of the solute to the N-methylpyrrolidone in the second step is 0.8g to 10 mL;
thirdly, the suspension is pumped to a polypropylene diaphragm through vacuum filtration by adopting vacuum pumping separation, and then the polypropylene diaphragm is dried in a vacuum drying oven at the temperature of 60 ℃ for 12 hours to obtain the polypropylene diaphragm (KB/V) functionally modified by the vanadium carbide nanobelt and the Ketjen black nanofiber composite2CTX-PP) with a mass load of 0.5 to 5mgcm-2(ii) a In addition, the suspension is filtered and dried to obtain the composite (KB/V) of the vanadium carbide nanobelt and the Ketjen black nanofiber2CTX)；
And the polypropylene diaphragm in the second step III is a commercial polypropylene diaphragm (Celgard 2400).
FIG. 1 is an X-ray diffraction spectrum, in which V2CTXVanadium carbide nanoribbons prepared for one step one of the examples, V2AlC is vanadium aluminum carbide;
all diffraction peaks in fig. 1 belong to vanadium carbide, and therefore, the product synthesized by the present example is a vanadium carbide crystal material.
FIG. 2 is a low power transmission electron microscope image of vanadium carbide nanoribbons prepared in one step one of the example;
FIG. 3 is a high power transmission electron microscope image of vanadium carbide nanoribbons prepared in one step one of the example;
as can be seen from fig. 2 and 3, the vanadium carbide has a nano-ribbon shape, a width of 10-20nm and a length of more than 100nm, and provides a higher specific surface area and more edge active sites compared with the conventional flake shape of the MXene material. Moreover, the number of the vanadium carbide nanobelts is 5-8, and the (002) crystal face spacing is 0.76nm, so that charge transfer is facilitated, and conditions are created for better anchoring lithium polysulfide dissolved in the electrolyte.
Visible adsorption test:
(1) lithium sulfide (Li) in a mass ratio of 1:52S) and sulfur are mixed and added into a mixed solution of 1, 2-Dimethoxyethane (DME) and 1, 3-Dioxane (DOL), and then the mixture is stirred for 24 hours at the temperature of 60 ℃ to obtain Li2S6A solution;
the volume ratio of the 1, 2-Dimethoxyethane (DME) to the 1, 3-Dioxane (DOL) in the mixed solution of the 1, 2-Dimethoxyethane (DME) and the 1, 3-Dioxane (DOL) is 1: 1;
the volume ratio of the lithium sulfide substance to the mixed solution of 1, 2-Dimethoxyethane (DME) and 1, 3-Dioxane (DOL) is 0.01mol: 1L.
(2) 20mg of Ketjen black/vanadium carbide nanoribbon mixture was added to 3mL of Li2S6Standing in the solution for 3h to obtain Ketjen black/vanadium carbide nanobelt mixture/Li2S6A solution;
the mass ratio of the Ketjen black to the vanadium carbide nanobelts in the mixture of the Ketjen black/vanadium carbide nanobelts in the step (2) is 2: 8.
FIG. 4 is Li2S6Solution and Ketjen black/vanadium carbide nanoribbon mixture/Li2S6Standing the solutions for 3 hours respectively to obtain digital images;
as can be seen from FIG. 4, Li added to the Ketjen black/vanadium carbide nanoribbon mixture2S6The color of the solution has changed from brown yellow to transparent, which indicates that the mixture of Ketjen black/vanadium carbide nanoribbon is mixed with Li2S6Has strong chemical adsorption effect.
Assembling the symmetrical battery:
in the assembly of Ketjen black/vanadium carbide symmetrical battery (KB/V)2CTX-CP) in symmetric cells, dispersing ketjen black and vanadium carbide nanobelts in absolute ethanol at a mass ratio of 2:8, the mass ratio of ketjen black to absolute ethanol being 1g:50mL, to obtain a slurry; the slurry was applied to a Carbon Paper (CP) 15 mm in diameter by a pipette gun, thoroughly dried, and used as a working electrode and a counter electrode, respectively, with a mass loading of 1.0mgcm for the active material-2The electrolyte was 30. mu.L DOL/DME (30. mu.L DOL and DME in 1:1 volume) to a concentration of 0.5mol L-1Li of (2)2S6In the solution, a Ketjen black/vanadium carbide symmetrical battery (KB/V) is obtained2CTX-CP)；
When assembling CP symmetrical cell, Carbon Paper (CP) with diameter of 15 mm is used as working electrode and counter electrode respectively, and electrolyte of 30 μ L DOL/DME (30 μ L, volume of DOL and DME is 1:1) is added to concentration of 0.5mol L-1Li of (2)2S6Obtaining a CP symmetrical battery in the solution;
as a control, the assembled Ketjen black/vanadium carbide symmetric cells and the assembled CP symmetric cells were subjected to Cyclic Voltammetry (CV) tests on a VMP3 electrochemical workstation (BioLogic, France) with a CV scan rate ranging from 10mV-1The voltage window is between-0.8V and 0.8V.
FIG. 5 is a CV curve of a symmetrical cell, in which 1 is a CP symmetrical cell and 2 is KB/V2CTX-a CP symmetric cell;
as can be seen from FIG. 5, the CV curve has an obvious redox peak and a higher response current, which indicates that the vanadium carbide nanobelt has an obvious chemisorption effect with the Ketjen black nanofiber composite polysulfide, and can effectively inhibit the shuttle effect.
FIG. 6 shows the exchange current density of a symmetrical cell, where 1 is CP symmetrical cell and 2 is KB/V2CTX-a CP symmetric cell;
as can be seen from FIG. 6, the exchange current density is 1.608mA cm–2Almost ten times the exchange current density of pure carbon paper (j 0.177mA cm)–2) The vanadium carbide nanobelt and Ketjen black nanofiber composite for Li is illustrated2Sn-to-Li2The process of S has a good catalytic effect,the reaction kinetics can be accelerated, and the shuttle effect can be inhibited.
Li on vanadium carbide surface2Nucleation and deposition of S:
mixing Li with the mass ratio of 1:72The mixture of S and S was added to 1.0M LiTFSI in tetraglyme (tetraglyme) and stirred at 60 ℃ for 24h to give 0.25MLi2S8A catholyte;
in this experiment, 0.8mg of the vanadium carbide nanobelt prepared in example 1 and Ketjen black nanofiber composite (KB/V)2CTX) Dispersing into 8 μ L absolute ethyl alcohol to obtain solution; the resulting solution was coated on Carbon Paper (CP) having a diameter of 10mm and dried at 60 ℃ for 2 hours to obtain KB/V2CTXA working electrode. KB/V2CTXThe mass load of (A) is 1.0mg cm-2. At KB/V2CTXAdding 20 mu L of Li on the working electrode2S8Electrolyte, adding 20 μ L LiNO containing 2 wt% on the counter electrode3Li of (2)2S8And (3) an electrolyte. The cell was discharged at a constant current of 0.112mA using VMP3 electrochemical workstation (BioLogic, France) until the voltage reached 2.06V consuming higher order polysulfides, then discharged at a constant current to 2.05V, allowing Li to precipitate2S nucleation, as shown in FIG. 7.
Li2S8The electrolyte is prepared by the following steps:
mixing lithium sulfide (Li) with the mass ratio of 1:72S) and sulfur are mixed and added into a mixed solution of 1, 2-Dimethoxyethane (DME) and 1, 3-Dioxane (DOL), and then the mixture is stirred for 24 hours at the temperature of 60 ℃ to obtain Li2S8A solution; lithium sulfide (Li)2S) and the volume ratio of the mass of the 1, 2-Dimethoxyethane (DME) to the mixed solution of 1, 3-Dioxane (DOL) are 11.5mg:1 mL;
as a control, 20. mu.L of Li was added to a Carbon Paper (CP) working electrode2S8Electrolyte, adding 20 μ L LiNO containing 2 wt% on the counter electrode3Li of (2)2S8And (3) an electrolyte. The cells were discharged at a constant current of 0.112mA using VMP3 electrochemical workstation (BioLogic, France) until the voltage reached 2.06V, and then discharged at a constant current to 2.05V, as shown in fig. 7.
FIG. 7 is Li2The constant voltage discharge curve of S nucleation experiment is shown in figure 1 as CP cell and 2 as KB/V2CTX-a CP battery;
as can be seen from FIG. 7, the vanadium carbide nanobelt and Ketjen black nanofiber composite (KB/V)2CTX) The precipitation time is accelerated from 6000s to 1901s, and Li is added2The precipitation capacity of S was 194.0mAh g–1Is raised to 345.5mAh g–1The vanadium carbide nanobelt and Ketjen black nanofiber composite is illustrated for polysulfide to Li2The conversion of S has good catalytic action.
FIG. 8 is a scanning electron microscope image of a functionalized modified diaphragm prepared in the second step of the example;
as can be seen from fig. 8, the thickness of the functionalized modified separator was 15.5 μm. The vanadium carbide nanobelt and the Ketjen black nanofiber are of three-dimensional network structures, and can generate a physical barrier effect on lithium polysulfide dissolved in electrolyte, so that shuttle benefits are effectively reduced. Moreover, the Ketjen black nano-fiber is used as a conductive framework to form a mutually communicated network structure, which is beneficial to the permeation of electrolyte and the rapid conduction of ions/electrons. Meanwhile, the wettability of the diaphragm is improved due to the multi-size pores in the structure, and better electrochemical performance can be obtained.
Assembly and electrochemical testing of lithium sulfur batteries:
a) preparation of C/S positive electrode
And (3) filling protective gas into the uniformly mixed C/S (mass ratio of 1:3), putting the mixture into a reaction kettle, and heating the mixture for 12 hours at the temperature of 155 ℃ by adopting a melting method. After cooling to room temperature, uniformly grinding the obtained C/S mixture, conductive carbon black and PVDF according to the mass ratio of 8:1:1, carrying out ultrasonic treatment for 30min by using NMP as a solvent, coating the mixed slurry on an aluminum foil as a positive electrode by using an automatic coating machine, and drying the prepared electrode in a vacuum oven at 60 ℃ for 12 h. Finally, the electrode slice is cut into a circular slice with the diameter of 13mm, and the sulfur loading capacity is 1.3mg/cm2。
b) Assembling the lithium-sulfur battery:
electrochemical performance was tested using a model 2025 cell, assembled in a glove box filled with argon. C/S complexesAs a positive electrode, a lithium sheet is used as a negative electrode, and the separator is the functional modified separator KB/V prepared in the first example2CTX-a PP; the electrolyte used was 1.0M lithium bis (trifluoromethane) sulfonimide (LiTFSI) containing 2 wt% LiNO3In a mixed solution of DOL and DME (volume ratio of 1: 1). The ratio of the amount of electrolyte to the amount of sulfur was 15 μ Lmg-1。
c) As a control, the electrochemical performance was tested with a model 2025 cell, assembled in a glove box filled with argon. The C/S compound is used as a positive electrode, a lithium sheet is used as a negative electrode, the diaphragm is PP (commercial polypropylene diaphragm Celgard 2400), the electrolyte used by the diaphragm is 1.0M lithium bis (trifluoromethane) sulfonimide (LiTFSI), and the electrolyte contains 2 wt% of LiNO3In a mixed solution of DOL and DME (volume ratio of 1: 1). The ratio of the amount of electrolyte to the amount of sulfur was 15 μ Lmg-1。
d) Electrochemical testing
The charging and discharging performance test of the lithium-sulfur battery is carried out on a LAND battery test system (CT 2001A, Wuhan, China) and the voltage range is 1.7-2.8V under the room temperature condition. Specific capacities of 0.1C,0.2C,0.5C,1C, and 2C (1C — 1675mA/g) were measured under constant current charge and discharge, respectively. Cyclic Voltammograms (CV) were tested on a VMP3 electrochemical workstation (BioLogic, France) at a scan rate of 0.1mV/s and a voltage range of 1.7-2.8V. The measurement frequency of Electrochemical Impedance (EIS) ranges from 0.01Hz to 100kHz, see fig. 9 and 10.
Fig. 9 is CV curves of a lithium sulfur battery in which the separators are respectively PP and the functionalized modified separator prepared in example one, wherein the separator 2 is PP, and the separator 1 is the functionalized modified separator prepared in example one;
fig. 10 is an impedance spectrum of a lithium sulfur battery with a separator of PP and a functionalized modified separator prepared in example one, wherein the separator 1 is PP and the separator 2 is the functionalized modified separator prepared in example one;
as can be seen from FIGS. 9 and 10, S is8To Li2S4The Tafel slope of (1) is 93mV dec–1The activation energy is 28.63kJ mol lower than that of a commercial polypropylene diaphragm–1，Li2S4To Li2The Tafel slope of S was 86mV dec–1Activation energy ratio of commercialPolypropylene diaphragm is 24.82kJ mol lower–1. Example one functionalized modified separator prepared from S8To Li2S4And from Li2S4To Li2Diffusion coefficients of lithium ions in the S process were 5.18X 10, respectively–8And 3.27X 10–7cm2 s–1Nearly ten times (8.25X 10) that of commercial polypropylene separators–9And 1.03X 10–8cm2 s–1) And the interface transmission resistance is obviously smaller than that of a commercial polypropylene diaphragm, so that good battery performance is obtained.
Fig. 11 is a charge-discharge curve of a lithium-sulfur battery whose separator is a functionalized modified separator prepared in example one, in which 1 is the 1 st turn, 2 is the 10 th turn, 3 is the 20 th turn, 4 is the 50 th turn, 5 is the 100 th turn, and 6 is the 150 th turn;
fig. 12 is a charge-discharge curve of a lithium-sulfur battery having a PP separator, in which 1 is the 1 st turn, 2 is the 10 th turn, 3 is the 20 th turn, 4 is the 50 th turn, 5 is the 100 th turn, and 6 is the 150 th turn;
as can be seen from fig. 11 and 12, the initial capacity of the lithium-sulfur battery with the separator being the functionalized modified separator prepared in example one at 0.2C is 1236.1mAhg-1Polarization overpotential Δ E ═ 156.3 mV; the initial capacity of the commercial polypropylene diaphragm is 876.2mAhg-1The polarization overpotential Δ E ═ 269.7 illustrates that the functionalized modified separator prepared in example one can anchor lithium polysulfide well, reduce shuttle effect, and improve battery performance.
Fig. 13 is a first cycle characteristic of a lithium sulfur battery in which the separator is PP and the functionalized modified separator prepared in example one, respectively, in which fig. 1 shows PP and fig. 2 shows the separator is the functionalized modified separator prepared in example one;
fig. 14 shows the first cycle characteristics of a lithium sulfur battery with a separator of PP and a functionalized modified separator prepared in example one, wherein the separator 1 is PP and the separator 2 is the functionalized modified separator prepared in example one;
as can be seen from fig. 13 and 14, the decay rate per cycle of the lithium sulfur battery with the separator being the functionalized modified separator prepared in example one is 0.16% after 150 cycles of 0.2C cycle; 1C initial discharge capacity of 1069mAh g-1The attenuation per cycle of 1000 cycles was 0.049% and the coulombic efficiency was 98%. The attenuation rate of each ring of the commercial polypropylene diaphragm after 200 rings is 0.27%; the initial discharge capacity at 1C was 643.2mAh g-1The attenuation per cycle of 600 cycles was 0.113% and the coulombic efficiency was 93%. Therefore, the functionalized modified separator prepared in the first embodiment can well improve the cycle performance of the lithium-sulfur battery.
Fig. 15 is a digital image of the lithium negative electrode side of a lithium sulfur battery cycled 150 cycles at 0.2C with PP as the separator of (a) and the functionalized modified separator of example one, respectively, where the separator of (b) is the functionalized modified separator of example one;
as can be seen in fig. 15, the two diaphragms are of different colors. The surface had significant brownish yellow sulfur deposits after cycling of the PP separator, indicating that the PP separator did not prevent the shuttling effect of lithium polysulfides well. In contrast, the cycle back surface of the composite separator prepared in example one was much cleaner, indicating that the composite separator prepared in example one can anchor lithium polysulfide well, preventing the occurrence of shuttle effect.
Fig. 16 shows the rate characteristics of a lithium-sulfur battery in which the separator is PP and the functionalized modified separator prepared in example one, wherein the separator 1 is PP and the separator 2 is the functionalized modified separator prepared in example one.
As can be seen from fig. 16, the capacity of the lithium-sulfur battery having PP as the separator and the functionalized and modified separator prepared in example one was 141.4mAhg as the separator at 2C-1And 851.5mAhg-1It is demonstrated that the lithium sulfur battery using the functionalized modified separator prepared in example one has better rate capability.
The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention, and various modifications and changes may be made by those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (10)
1. A functional modified diaphragm is characterized in that the functional modified diaphragm is a polypropylene diaphragm compositely modified by vanadium carbide nanobelts and Ketjen black nanofibers; the vanadium carbide nanobelt and the Ketjen black nanofiber are of a three-dimensional network structure, and the mass ratio of the vanadium carbide nanobelt to the Ketjen black nanofiber is (2-10): 1; wherein the width of the vanadium carbide nanoribbon is 10-50nm, the length is 100nm-20 μm, the number of layers is 1-30, and the (002) interplanar spacing is 0.2-0.9 nm.
2. The functionalized and modified membrane as claimed in claim 1, wherein the loading amount of the vanadium carbide nanobelt and the Ketjen black nanofiber on the polypropylene membrane is 0.1-5 mg/cm2。
3. The method for preparing a functionalized modified membrane according to claim 1, wherein a functionalized modified membrane is prepared by the following steps:
firstly, synthesizing vanadium carbide nanobelts:
adding LiF into HCl water solution, and adding V2AlC is evenly stirred to obtain a mixed solution;
secondly, transferring the mixed solution into a polytetrafluoroethylene-lined stainless steel high-pressure autoclave, and then preserving the polytetrafluoroethylene-lined stainless steel high-pressure autoclave for 100-130 h at the temperature of 85-90 ℃ to obtain black precipitates;
centrifugally cleaning the black solid substance for 5-6 times by using a hydrochloric acid solution as a cleaning agent, and removing the hydrochloric acid solution to obtain a precipitate cleaned by the hydrochloric acid solution; centrifuging and cleaning the precipitate cleaned by the hydrochloric acid solution for 5-6 times by taking LiCl solution as a cleaning agent, collecting supernatant, and centrifuging the supernatant for 40-45 min at a centrifugal speed of 9000 r/min to obtain a reaction product; drying the reaction product in a vacuum drying oven to obtain a vanadium carbide nanobelt;
secondly, compounding and modifying the polypropylene diaphragm by the vanadium carbide nanobelt and the Ketjen black nanofiber:
mixing Ketjen black and vanadium carbide nanobelts to obtain a Ketjen black/vanadium carbide nanobelt mixture;
secondly, mixing the Ketjen black/vanadium carbide nano-belt mixture with polyvinylidene fluoride to obtain a solute; adding the solute into N-methylpyrrolidone, and carrying out ultrasonic treatment to obtain a suspension;
and thirdly, pumping the suspension onto a polypropylene diaphragm by vacuum filtration through vacuum pumping separation, and then putting the polypropylene diaphragm into a vacuum drying oven for drying to obtain the functional modified diaphragm.
4. The preparation method of the functionalized modified diaphragm according to claim 3, wherein the volume ratio of the mass of LiF to the volume of the HCl aqueous solution in the first step (2 g-4 g) is 20 mL; the mass fraction of the HCl aqueous solution in the first step is 5-38%.
5. The method for preparing a functionalized and modified membrane according to claim 3, wherein V is the same as V in the first step2The ratio of the mass of AlC to the volume of HCl aqueous solution (0.6 g-1 g) was 20 mL.
6. The method for preparing a functionalized modified diaphragm according to claim 3, wherein the hydrochloric acid solution in the first step is prepared by mixing 20mL of hydrochloric acid with a mass fraction of 37% and 180mL of deionized water.
7. The method for preparing a functionalized modified diaphragm according to claim 3, wherein the LiCl solution in the first step is obtained by dissolving 7.63-8 g LiCl into 180mL of deionized water; the temperature of the vacuum drying oven in the step one is 60 ℃, and the drying time is 10-12 h.
8. The method for preparing the functionalized modified diaphragm according to claim 3, wherein the mass ratio of the Ketjen black to the vanadium carbide nanobelts in the second (r) step is 2: 8; and the mass ratio of the Ketjen black/vanadium carbide nano-belt mixture to the polyvinylidene fluoride in the second step is 9: 1.
9. The method for preparing the functionalized modified diaphragm according to claim 3, wherein the volume ratio of the mass of the solute to the volume of the N-methylpyrrolidone in the second step (0.5 g-1.2 g) is 10 mL; the power of ultrasonic treatment in the second step is 100W-500W, and the time of ultrasonic treatment is 2 h-3 h; the temperature of the vacuum drying oven in the second step is 60 ℃, and the drying time is 10-12 h.
10. The use of a functionally modified separator as claimed in claim 1, wherein a functionally modified separator is used as a separator for a lithium-sulfur battery, a potassium-sulfur battery or a sodium-sulfur battery.
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