CN115465870A - Preparation method of magnesium boride nanosheet and application of magnesium boride nanosheet in Li-S battery diaphragm - Google Patents
Preparation method of magnesium boride nanosheet and application of magnesium boride nanosheet in Li-S battery diaphragm Download PDFInfo
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- PZKRHHZKOQZHIO-UHFFFAOYSA-N [B].[B].[Mg] Chemical compound [B].[B].[Mg] PZKRHHZKOQZHIO-UHFFFAOYSA-N 0.000 title claims abstract description 143
- 239000002135 nanosheet Substances 0.000 title claims abstract description 73
- 238000002360 preparation method Methods 0.000 title claims abstract description 19
- 229910003003 Li-S Inorganic materials 0.000 title abstract 2
- JDZCKJOXGCMJGS-UHFFFAOYSA-N [Li].[S] Chemical compound [Li].[S] JDZCKJOXGCMJGS-UHFFFAOYSA-N 0.000 claims abstract description 44
- 238000000034 method Methods 0.000 claims abstract description 18
- 229920001155 polypropylene Polymers 0.000 claims description 54
- 239000004743 Polypropylene Substances 0.000 claims description 37
- 239000011259 mixed solution Substances 0.000 claims description 31
- 239000007788 liquid Substances 0.000 claims description 19
- 239000006185 dispersion Substances 0.000 claims description 18
- -1 polypropylene Polymers 0.000 claims description 17
- XKRFYHLGVUSROY-UHFFFAOYSA-N Argon Chemical compound [Ar] XKRFYHLGVUSROY-UHFFFAOYSA-N 0.000 claims description 14
- SECXISVLQFMRJM-UHFFFAOYSA-N N-Methylpyrrolidone Chemical compound CN1CCCC1=O SECXISVLQFMRJM-UHFFFAOYSA-N 0.000 claims description 14
- 238000005119 centrifugation Methods 0.000 claims description 14
- 239000006228 supernatant Substances 0.000 claims description 14
- 238000003756 stirring Methods 0.000 claims description 12
- 239000000843 powder Substances 0.000 claims description 11
- 238000005303 weighing Methods 0.000 claims description 8
- 229910052786 argon Inorganic materials 0.000 claims description 7
- 238000001035 drying Methods 0.000 claims description 6
- 239000002055 nanoplate Substances 0.000 claims description 6
- LFQSCWFLJHTTHZ-UHFFFAOYSA-N Ethanol Chemical compound CCO LFQSCWFLJHTTHZ-UHFFFAOYSA-N 0.000 claims description 5
- ZMXDDKWLCZADIW-UHFFFAOYSA-N N,N-Dimethylformamide Chemical compound CN(C)C=O ZMXDDKWLCZADIW-UHFFFAOYSA-N 0.000 claims description 5
- 239000002244 precipitate Substances 0.000 claims description 5
- 239000003960 organic solvent Substances 0.000 claims description 4
- 239000000523 sample Substances 0.000 claims description 4
- 238000000967 suction filtration Methods 0.000 claims description 3
- 239000007789 gas Substances 0.000 claims 1
- WHXSMMKQMYFTQS-UHFFFAOYSA-N Lithium Chemical compound [Li] WHXSMMKQMYFTQS-UHFFFAOYSA-N 0.000 abstract description 15
- 229910052744 lithium Inorganic materials 0.000 abstract description 15
- 230000000694 effects Effects 0.000 abstract description 13
- 229920001021 polysulfide Polymers 0.000 abstract description 12
- 239000005077 polysulfide Substances 0.000 abstract description 12
- 150000008117 polysulfides Polymers 0.000 abstract description 12
- 239000010410 layer Substances 0.000 abstract description 8
- 229910052751 metal Inorganic materials 0.000 abstract description 8
- 239000002184 metal Substances 0.000 abstract description 8
- 230000004048 modification Effects 0.000 abstract description 7
- 238000012986 modification Methods 0.000 abstract description 7
- 230000003197 catalytic effect Effects 0.000 abstract description 5
- 239000000463 material Substances 0.000 abstract description 5
- 238000001179 sorption measurement Methods 0.000 abstract description 4
- 230000007246 mechanism Effects 0.000 abstract description 3
- 239000002356 single layer Substances 0.000 abstract description 3
- 239000003575 carbonaceous material Substances 0.000 abstract description 2
- 239000007791 liquid phase Substances 0.000 abstract description 2
- NINIDFKCEFEMDL-UHFFFAOYSA-N Sulfur Chemical compound [S] NINIDFKCEFEMDL-UHFFFAOYSA-N 0.000 description 11
- 229910052717 sulfur Inorganic materials 0.000 description 9
- 239000011593 sulfur Substances 0.000 description 9
- 239000003792 electrolyte Substances 0.000 description 8
- XTHFKEDIFFGKHM-UHFFFAOYSA-N Dimethoxyethane Chemical compound COCCOC XTHFKEDIFFGKHM-UHFFFAOYSA-N 0.000 description 6
- 239000012528 membrane Substances 0.000 description 6
- WNXJIVFYUVYPPR-UHFFFAOYSA-N 1,3-dioxolane Chemical compound C1COCO1 WNXJIVFYUVYPPR-UHFFFAOYSA-N 0.000 description 4
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 4
- 229910052799 carbon Inorganic materials 0.000 description 4
- 238000006243 chemical reaction Methods 0.000 description 4
- 239000003795 chemical substances by application Substances 0.000 description 4
- 230000001351 cycling effect Effects 0.000 description 4
- 230000008569 process Effects 0.000 description 4
- 230000002441 reversible effect Effects 0.000 description 4
- 238000007789 sealing Methods 0.000 description 4
- 238000004513 sizing Methods 0.000 description 4
- 239000000243 solution Substances 0.000 description 4
- 239000000126 substance Substances 0.000 description 4
- 229910018091 Li 2 S Inorganic materials 0.000 description 3
- 230000005540 biological transmission Effects 0.000 description 3
- 230000000052 comparative effect Effects 0.000 description 3
- 238000007599 discharging Methods 0.000 description 3
- 239000002994 raw material Substances 0.000 description 3
- 239000002904 solvent Substances 0.000 description 3
- 238000012360 testing method Methods 0.000 description 3
- 230000004913 activation Effects 0.000 description 2
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 2
- 238000006555 catalytic reaction Methods 0.000 description 2
- 239000011248 coating agent Substances 0.000 description 2
- 238000000576 coating method Methods 0.000 description 2
- 238000010277 constant-current charging Methods 0.000 description 2
- 239000013078 crystal Substances 0.000 description 2
- 238000011161 development Methods 0.000 description 2
- 238000009792 diffusion process Methods 0.000 description 2
- 238000003487 electrochemical reaction Methods 0.000 description 2
- 238000011156 evaluation Methods 0.000 description 2
- 238000002173 high-resolution transmission electron microscopy Methods 0.000 description 2
- 230000002401 inhibitory effect Effects 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
- 229910052760 oxygen Inorganic materials 0.000 description 2
- 239000001301 oxygen Substances 0.000 description 2
- 239000012071 phase Substances 0.000 description 2
- 150000003839 salts Chemical class 0.000 description 2
- 238000001228 spectrum Methods 0.000 description 2
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 2
- 239000013543 active substance Substances 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- QYHKLBKLFBZGAI-UHFFFAOYSA-N boron magnesium Chemical compound [B].[Mg] QYHKLBKLFBZGAI-UHFFFAOYSA-N 0.000 description 1
- 230000008859 change Effects 0.000 description 1
- 238000007600 charging Methods 0.000 description 1
- 238000004146 energy storage Methods 0.000 description 1
- 230000007613 environmental effect Effects 0.000 description 1
- 230000003993 interaction Effects 0.000 description 1
- 239000013067 intermediate product Substances 0.000 description 1
- 230000001788 irregular Effects 0.000 description 1
- 230000002427 irreversible effect Effects 0.000 description 1
- 239000011777 magnesium Substances 0.000 description 1
- 239000002245 particle Substances 0.000 description 1
- 239000007774 positive electrode material Substances 0.000 description 1
- 230000001737 promoting effect Effects 0.000 description 1
- 238000011160 research Methods 0.000 description 1
- 239000012798 spherical particle Substances 0.000 description 1
- 238000003860 storage Methods 0.000 description 1
- 230000014233 sulfur utilization Effects 0.000 description 1
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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
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B82—NANOTECHNOLOGY
- B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
- B82Y30/00—Nanotechnology for materials or surface science, e.g. nanocomposites
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B82—NANOTECHNOLOGY
- B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
- B82Y40/00—Manufacture or treatment of nanostructures
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
- C01B35/00—Boron; Compounds thereof
- C01B35/02—Boron; Borides
- C01B35/04—Metal borides
-
- 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
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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
- H01M50/409—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
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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
- H01M50/409—Separators, membranes or diaphragms characterised by the material
- H01M50/446—Composite material consisting of a mixture of organic and inorganic materials
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- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
- C01P2002/00—Crystal-structural characteristics
- C01P2002/70—Crystal-structural characteristics defined by measured X-ray, neutron or electron diffraction data
- C01P2002/72—Crystal-structural characteristics defined by measured X-ray, neutron or electron diffraction data by d-values or two theta-values, e.g. as X-ray diagram
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- C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
- C01P2004/00—Particle morphology
- C01P2004/01—Particle morphology depicted by an image
- C01P2004/04—Particle morphology depicted by an image obtained by TEM, STEM, STM or AFM
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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
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Abstract
The invention relates to a preparation method of magnesium boride nanosheets and application of the magnesium boride nanosheets in a Li-S battery diaphragm. The method adopts a normal-temperature liquid-phase stripping method, can rapidly obtain single-layer or few-layer magnesium boride in a pollution-free manner at low cost under mild conditions, has relatively large specific surface area, not only has theoretical density close to a carbon material and conductivity comparable to metal, but also shows the characteristics of unique lithium polysulfide surface adsorption and catalytic mechanism, and uses the magnesium boride nanosheet as a lithium-sulfur battery diaphragm modification material to well relieve the shuttle effect of a lithium-sulfur battery and improve the cycle stability of the lithium-sulfur battery.
Description
Technical Field
The invention relates to the technical field of diaphragms for Li-S batteries, in particular to a preparation method of magnesium boride nano-sheets and application of the magnesium boride nano-sheets in diaphragms for Li-S batteries.
Background
The lithium-sulfur (Li-S) battery system adopts elemental sulfur as a positive electrode material, the theoretical specific capacity of the lithium-sulfur (Li-S) battery system is 1675mAh/g, when the lithium-sulfur (Li-S) battery system is assembled with metal lithium in a matching mode, the theoretical mass energy density can reach 2600Wh/kg, the volume energy density can reach 2800Wh/h, the lithium-sulfur (Li-S) battery system is far higher than that of the existing commercial secondary battery, the storage capacity of elemental sulfur in the earth is very rich, the price of the elemental sulfur is low, and the lithium-sulfur (Li-S) battery system is environment-friendly, so that the elemental sulfur is considered to be a next-generation energy storage system. With the increasing environmental and energy problems, the development and utilization of new energy is increasingly gaining attention from countries around the world, and therefore, the development of high energy density lithium sulfur batteries is imminent. However, the current lithium-sulfur battery cannot meet the requirements of new electronic devices such as rapidly developed electric vehicles.
Although the lithium-sulfur battery has the advantages, the current research still faces some problems: lithium polysulfide, an intermediate product generated by electrochemical reaction, is dissolved in the electrolyte, and can migrate and diffuse to react with lithium of the negative electrode, and finally irreversible loss of effective substances in the battery is caused, and the process is called 'shuttle effect'. The shuttle effect reduces sulfur utilization and can lead to rapid decay of cell capacity and permanent failure of the cell. This problem has severely hampered the commercial use of the lithium sulfur battery industry.
Most of the currently used lithium-sulfur battery separators are polypropylene (PP) separators, which have good ionic conductivity, but are easily deformed at high temperature, lithium polysulfide (Li) 2 S n ) Shuttle easily and eventually cause short circuits inside the battery. Separator modification is an effective method to suppress the "shuttling effect" of lithium polysulfides in lithium sulfur batteries. Typically, membrane finishingThere are two main types: (1) modifying the separator with a coating that inhibits diffusion of lithium polysulfide; (2) novel membranes were made that inhibited shuttling of polysulfides by chemisorption. The coating for inhibiting the diffusion of the lithium polysulfide is used for modifying the diaphragm, so that the problem of poor conductivity of the positive electrode can be solved, and the shuttle effect of the lithium polysulfide in the electrolyte can be effectively relieved. The mode of improving the battery performance by modifying the diaphragm has the advantages of high yield, simple operation, uniform surface and the like, and provides possibility for realizing commercialization of the lithium-sulfur battery.
Metal borides of chemical polarity can be used to modify PP separators with Li 2 S n Has strong chemical interaction with each other, can effectively fix Li 2 S n In addition, the metal borides also have catalytic Li 2 S n To Li 2 The role of S conversion, which is a surface catalytic conversion mechanism, is greatly influenced by the specific surface area of the material. However, most of the metal borides applied to the lithium-sulfur battery at present are spherical particles with larger particle sizes, and compared with a nanosheet structure, the metal borides have relatively smaller active specific surface area, and can not fully exert stronger chemical polarity adsorption effect and surface catalytic conversion effect of the metal borides so as to relieve the shuttle effect. Therefore, it is urgently needed to develop a preparation method of a magnesium boride nanosheet, and further modify a diaphragm by using the magnesium boride nanosheet so as to well relieve the shuttle effect of the lithium-sulfur battery, improve the cycle stability of the lithium-sulfur battery, and make the lithium-sulfur battery easier to be applied industrially, thereby promoting the commercialization of the lithium-sulfur battery.
Disclosure of Invention
In order to solve the problems, the invention provides a preparation method of a magnesium boride nanosheet and application of the magnesium boride nanosheet in a Li-S battery diaphragm. The method for preparing the magnesium boride nanosheet by the physical stripping method can rapidly obtain single-layer or few-layer magnesium boride with low cost and no pollution under mild conditions, and can well relieve the shuttle effect of the lithium-sulfur battery due to the unique surface adsorption and catalysis characteristics of the magnesium boride nanosheet.
One of the purposes of the invention is to provide a method for preparing a magnesium boride nanosheet by a physical stripping method, which specifically comprises the following steps:
weighing magnesium boride with a certain mass of 50-200 meshes, adding the magnesium boride into a beaker filled with an organic solvent to obtain a mixed solution A, magnetically stirring the mixed solution A for 15-60 min at the stirring speed of 2000-3000 rpm to obtain a magnesium boride dispersion liquid, then ultrasonically stripping the magnesium boride dispersion liquid at 0-20 ℃ for 40-60 min by using a cell disruptor, wherein the ultrasonic power is 100-250W, firstly centrifuging the ultrasonically stripped magnesium boride dispersion liquid for 8min at the rotating speed of 4000rpm, and then centrifuging the supernatant obtained after the first centrifugation for the second time at the rotating speed of 10000rpm, wherein the time of the second centrifugation is 10min. And adding the precipitate obtained by the second centrifugation into 10mL of absolute ethyl alcohol, fully and uniformly stirring to obtain a mixed solution B, and drying the mixed solution B in an oven at 40 ℃ for 12h to finally obtain the magnesium boride nanosheet powder.
Further, the concentration of the magnesium boride dispersion is 5mg/mL.
Further, the organic solvent includes at least one of N-methylpyrrolidone (NMP) and N, N-Dimethylformamide (DMF).
Further, the ultrasonically peeled magnesium boride dispersion was first centrifuged at 4000rpm for 8min to remove the thick layer of magnesium boride.
Further, according to the method for preparing the magnesium boride nanosheet by the physical stripping method, the obtained magnesium boride nanosheet is a high-conductivity magnesium boride nanosheet, the thickness of the high-conductivity magnesium boride nanosheet is less than or equal to 5nm, and the size of the nanosheet is 0.1-5 microns.
The invention also aims to provide a preparation method of the polypropylene diaphragm modified by the magnesium boride nanosheet, which specifically comprises the following steps: weighing 0.5g of magnesium boride nanosheet, adding the magnesium boride nanosheet into 100mL of NMP solvent to obtain mixed liquid C, then inserting an ultrasonic probe of a cell disruptor into the mixed liquid C, adjusting the power of the cell disruptor to 200W, carrying out ultrasonic operation on the mixed liquid C for 1h under the protection of argon, and obtaining mixed liquid D after the ultrasonic operation is finished. Transferring the mixed solution D into a centrifuge tube, centrifuging for 8min at the rotating speed of 8000rpm, and collecting the obtained supernatant. And repeating the steps for multiple times to obtain 500mL of supernatant, and performing suction filtration on the supernatant to obtain the PP diaphragm modified by the magnesium boride nanosheet.
Further, the magnesium boride nanosheet is prepared by the preparation method.
The invention also aims to provide the polypropylene diaphragm modified by the magnesium boride nanosheet prepared by the preparation method.
The invention also aims to provide application of the polypropylene diaphragm modified by the magnesium boride nanosheet prepared by the method in a lithium-sulfur battery.
Compared with the prior art, the invention has the following beneficial effects:
(1) The invention adopts a normal temperature liquid phase stripping method, and can obtain single-layer or few-layer magnesium boride rapidly at low cost and without pollution under mild conditions;
(2) Based on the fact that magnesium boride not only has theoretical density close to a carbon material and conductivity comparable to metal, but also has relatively large specific surface area, the magnesium boride nanosheet displays the characteristics of unique lithium polysulfide surface adsorption and catalysis mechanism, and is used as a good diaphragm modification material for inhibiting polysulfide shuttle effect, so that the shuttle effect of a lithium-sulfur battery is well relieved, and the cycle stability of the lithium-sulfur battery is improved.
Drawings
FIG. 1 is an atomic force microscope photomicrograph of magnesium boride nanoplates prepared in example 1 of the present invention;
FIG. 2 is a thickness data curve of the magnesium boride nanosheet prepared in example 1 of the present invention measured by an atomic force microscope;
FIG. 3 is a high resolution TEM image of a nano-sheet of magnesium boride prepared in example 1 of the present invention;
FIG. 4 is an XRD spectrum of a magnesium boride nanosheet prepared in example 1 of the present invention;
FIG. 5 shows Mg in example 1 of the present inventionB 2 @ PP modified diaphragm lithium sulfur battery prepared using the diaphragm and the lithium sulfur battery prepared using the PP diaphragm of comparative example 1 were respectively subjected to cycling performance curves at current densities of 0.1C, 0.2C, 0.5C, 1C, and 2C (the previous two cycles were 0.05C activation cycles);
FIG. 6 shows MgB in example 1 of the present invention 2 The cycling performance curves of the lithium sulfur battery prepared by using the @ PP modified diaphragm and the lithium sulfur battery prepared by using the PP diaphragm in the comparative example 1 under the current density of 0.5C for the charge-discharge cycling test are respectively shown.
Detailed Description
To make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below with reference to specific embodiments and accompanying drawings. The embodiments generally described and illustrated in the figures herein can be implemented in a variety of different configurations. Thus, the following detailed description of the embodiments of the present invention, as presented in the figures, is not intended to limit the scope of the claims, but is merely representative of selected embodiments of the invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments of the present invention without any inventive step, are within the scope of the present invention.
The invention has no special limitation on the sources of all the raw materials, and the raw materials can be commercially or self-made, and the purity of the raw materials is not specially limited.
Example 1:
(1) Preparing magnesium boride nanosheets: weighing 500mg 100-mesh magnesium boride powder, adding the magnesium boride powder into a beaker containing 100mL of N-methylpyrrolidone (NMP) to obtain a mixed solution A, magnetically stirring the mixed solution A for 60min at the stirring speed of 2000rpm to obtain a magnesium boride dispersion liquid with the concentration of 5mg/mL, then carrying out ultrasonic stripping on the magnesium boride dispersion liquid for 1h at the temperature of 0 ℃ by using a cell disrupter, wherein the ultrasonic power is 150W, firstly centrifuging the magnesium boride dispersion liquid subjected to ultrasonic stripping for 8min at the rotating speed of 4000rpm to remove thick magnesium boride layers, and then carrying out secondary centrifugation on supernatant obtained after the primary centrifugation at the rotating speed of 10000rpm, wherein the time for the secondary centrifugation is 10min. And adding the precipitate obtained by the second centrifugation into 10mL of absolute ethyl alcohol to obtain a mixed solution B, and drying the mixed solution B in an oven at 40 ℃ for 12h to finally obtain the magnesium boride nanosheet powder.
(2) Magnesium boride (MgB) 2 ) Preparing a nanosheet modified polypropylene (PP) diaphragm: weighing 0.5g of the magnesium boride nanosheet obtained in the step (1) of the embodiment, adding the magnesium boride nanosheet into 100mL of NMP to obtain a mixed solution C, then inserting an ultrasonic probe of a cell disruptor into the mixed solution C, adjusting the power of the cell disruptor to 200W, carrying out ultrasonic operation on the mixed solution C for 1h under the protection of argon, and obtaining a mixed solution D after the ultrasonic operation is finished. And transferring the mixed solution D into a centrifuge tube, centrifuging for 8min at the rotating speed of 8000rpm, and collecting the obtained supernatant.
Repeating the steps for multiple times to obtain 500mL of supernatant, and performing suction filtration on the supernatant to obtain the PP diaphragm modified by the magnesium boride nanosheet, namely MgB 2 @ PP modifies the diaphragm.
The PP separator used in this example was Celgard 2400.
(3) The obtained MgB 2 The @ PP modified membrane is used for preparing a lithium-sulfur battery: the CR2025 button cell was used, and the concentration of water and oxygen in the argon glove box of the assembled cell was less than 0.01ppm. The electrolyte is composed of 1.0M lithium bistrifluoromethanesulfonimide (LiTFSI) as electrolyte salt and solvent of 1,3-Dioxolane (DOL) and 1,2-Dimethoxyethane (DME) in a volume ratio of 1:1. The positive electrode is a prepared carbon/sulfur positive plate, the negative electrode is a pure lithium plate, and the preparation of the carbon/sulfur positive plate is the prior art.
Firstly, assembling a positive and negative battery shell for the button battery and MgB obtained in the step (2) 2 The @ PP modified diaphragm, the positive pole piece, the elastic sheet and the gasket are placed in an oven to dry the surface moisture of the diaphragm and then transferred into an argon glove box;
then the positive electrode battery shell is flatly laid in a glove box, the side of the positive electrode pole piece coated with the sizing agent is upwards placed in the middle of the positive electrode battery shell, and 15 mu L of the sizing agent is added -1 Adding electrolyte according to the liquid-sulfur ratio;
then MgB is added 2 Place the @ PP modified diaphragm inPlacing the modification layer of the modification diaphragm upwards above the positive pole piece;
then, placing a lithium sheet above the diaphragm, and then sequentially placing the gasket and the elastic sheet;
and finally, buckling a cathode battery shell, sealing the button battery by using a sealing machine, and taking out the button battery from the glove box to obtain MgB 2 The @ PP modified diaphragm is used for preparing the lithium-sulfur battery.
Evaluation of battery cycle stability: mgB obtained in the step (3) 2 The @ PP modified diaphragm is placed in a constant temperature box at 25 ℃, and the rate performance of the lithium-sulfur battery is tested by constant current charging and discharging for 10 circles under the conditions of rates of 0.1C, 0.2C, 0.5C, 1C and 2C.
Comparative example 1:
magnesium boride (MgB) will not be present 2 ) The PP diaphragm modified by the nanosheets is used for preparing a lithium-sulfur battery: the CR2025 button cell was used, and the concentration of water and oxygen in the argon glove box of the assembled cell was less than 0.01ppm. The PP diaphragm model is Celgard 2400, and the electrolyte is formed by adding a solvent of 1,3-Dioxolane (DOL) and 1,2-Dimethoxyethane (DME) in a volume ratio of 1:1 by taking 1.0M lithium bistrifluoromethanesulfonimide (Li TFSI) as an electrolyte salt. The positive electrode is a prepared carbon/sulfur positive plate, the negative electrode is a pure lithium plate, and the preparation of the carbon/sulfur positive plate is the prior art.
Firstly, placing a positive and negative battery shell, a polypropylene diaphragm, a positive pole piece, an elastic sheet and a gasket used for assembling the button battery in an oven to dry the surface moisture of the positive and negative battery shell, and then transferring the positive and negative battery shell, the polypropylene diaphragm, the positive pole piece, the elastic sheet and the gasket into an argon glove box;
then the positive electrode battery shell is laid in a glove box, the side of the positive electrode plate coated with the sizing agent is placed in the middle of the positive electrode battery shell upwards, and 15 mu L of the sizing agent is added -1 Adding electrolyte according to the liquid-sulfur ratio;
then placing a polypropylene diaphragm above the positive pole piece;
then, placing a lithium sheet above the diaphragm, and then sequentially placing the gasket and the elastic sheet;
finally, buckling a negative battery shell, sealing the button battery by using a sealing machine, and taking out the button battery from the glove box to obtain magnesium boride (MgB) 2 ) Nano-sheet trimmingA decorated polypropylene (PP) separator was used to prepare the lithium sulfur battery.
Evaluation of battery cycle stability: the obtained magnesium boride (MgB) 2 ) The lithium-sulfur battery prepared by the nanosheet-modified polypropylene (PP) diaphragm is placed in a thermostat at 25 ℃, and the multiplying power performance of the lithium-sulfur battery is tested by constant-current charging and discharging for 10 circles under the multiplying power conditions of 0.1C, 0.2C, 0.5C, 1C and 2C respectively.
Fig. 1 is an atomic force microscope photograph of the magnesium boride nanosheet prepared in this example, showing that the magnesium boride has a flat lamellar structure, with the nanosheet size being about 2 μm.
Fig. 2 is a thickness data curve measured by an atomic force microscope of the magnesium boride nanosheet prepared in this embodiment, the thickness of the magnesium boride nanosheet sample in this embodiment is measured by a MULTIMODE8 atomic force microscope, and it can be seen from fig. 2 that the thickness of the magnesium boride nanosheet is below 3 nm.
Fig. 3 is a high-resolution transmission electron microscope photograph of the magnesium boride nanosheet prepared in this embodiment, and the high-resolution transmission electron microscope lattice calibration in the inset determines that the lattice spacing obtained by the magnesium boride nanosheet is 0.26nm, which corresponds to the (100) crystal face of magnesium boride, indicating that the magnesium boride nanosheet obtained by ultrasonic stripping in NMP solution is still a pure phase.
As shown in FIG. 3, microscopic morphology of the magnesium boride nanosheet ultrasonically stripped in an NMP solution is observed by using a high-resolution TEM (transmission electron microscope), the stripped magnesium boride is almost transparent irregular nanosheet morphology, the nanosheet size is between 100 and 500nm, the specific surface area of the material can be increased by the ultrathin nanosheet structure, and the unique surface sulfur fixation and catalytic capability of the magnesium boride can be fully exerted.
Fig. 4 is an XRD spectrum of the magnesium boride nanosheet prepared in this embodiment, and compared with data of a magnesium boride standard PDF card (JCPDS: 38-1369), each diffraction peak can be assigned to peaks of (001), (100), (101), (002), (110), (102), (111), (200), (201), (003), (112) crystal planes of the magnesium boride standard PDF card, and meets standard data, which indicates that the material does not undergo a chemical reaction during the peeling process, and the nanosheet obtained is still pure-phase magnesium boride.
FIG. 5 shows MgB of this example 2 @ PP modified diaphragm for preparing lithium-sulfur battery and magnesium boride (MgB) free diaphragm 2 ) Cycle performance curves (the first two cycles are 0.05C activation cycles) of lithium-sulfur batteries prepared by using nanosheet-modified PP membranes under current densities of 0.1C, 0.2C, 0.5C, 1C and 2C, and MgB is used 2 When the @ PP is used for modifying the diaphragm, the reversible specific capacity of the adopted sulfur anode is 1184mA h g under the multiplying power of 0.1C, 0.2C, 0.5C, 1C and 2C respectively -1 、1041mA h g -1 、920mA h g -1 、815mA h g -1 、732mA h g -1 While magnesium boride (MgB) is not used 2 ) When the PP diaphragm is modified by the nano-sheets, the initial discharge specific capacity of the adopted sulfur anode is 880mA h g under the current density of 0.1C -1 When the current density was increased to 0.2C, 0.5C, 1.0C and 2.0C, the discharge capacity was 616mA hr g, respectively -1 、448mA h g -1 、307mA h g -1 And 208mA h g -1 . Using magnesium boride (MgB) 2 ) The rate capability of the lithium-sulfur battery is obviously poor when the PP diaphragm is modified by the nanosheets, which indicates that the electrode is slow in the electrochemical reaction kinetic process under high current density, and lithium polysulfide shuttles to cause serious active substance loss in the test process, so that the electrode has low reversible specific capacity under high current density, and MgB (magnesium boron) is low 2 The @ PP modified diaphragm has good reversibility and stability.
FIG. 6 shows MgB of this example 2 @ PP modified diaphragm for preparing lithium-sulfur battery and magnesium boride (MgB) free diaphragm 2 ) The cycle performance curve of the lithium-sulfur battery prepared by the nanosheet-modified PP membrane and subjected to charge-discharge cycle test at the current density of 0.5C can be seen from the figure, and MgB is used 2 The initial discharge capacity of the lithium-sulfur battery prepared by the @ PP modified diaphragm is 923mA h g -1 Still has 840mA h g after 200 charging and discharging cycles -1 The reversible specific capacity of (2) has an average capacity attenuation rate per cycle of 0.0465%. Using magnesium boride (MgB) 2 ) The initial discharge capacity of the nanosheet-modified PP membrane in the battery is 560mA h g -1 The reversible specific capacity after 200 times of charge-discharge cycles is 486mA h g -1 The average capacity attenuation rate per cycle is 0.053%, and under the current density circulation of 0.5C, theWith MgB 2 The coulombic efficiency of the battery with the @ PP modified diaphragm is obviously higher than that of the battery without magnesium boride (MgB) 2 ) The battery with the PP diaphragm modified by the nanosheets proves that the shuttle effect of polysulfide is effectively inhibited, and the result shows that MgB is used 2 The battery with the @ PP modified diaphragm has better cycling stability.
Example 2:
(1) Preparing magnesium boride nanosheets: weighing 500mg magnesium boride powder of 50 meshes, adding the powder into a beaker containing 100mL of N-methylpyrrolidone (NMP) to obtain a mixed solution A, magnetically stirring the mixed solution A for 60min at the stirring speed of 2500rpm to obtain a magnesium boride dispersion liquid with the concentration of 5mg/mL, ultrasonically stripping the magnesium boride dispersion liquid for 1h at the temperature of 0 ℃ by using a cell disruptor, wherein the ultrasonic power is 100W, firstly centrifuging the ultrasonically stripped magnesium boride dispersion liquid for 8min at the rotating speed of 4000rpm to remove thick magnesium boride layers, and secondly centrifuging the supernatant obtained after the first centrifugation at the rotating speed of 10000rpm for 10min. And adding the precipitate obtained by the second centrifugation into 10mL of absolute ethyl alcohol to obtain a mixed solution B, and drying the mixed solution B in an oven at 40 ℃ for 12h to finally obtain the magnesium boride nanosheet powder.
(2) Magnesium boride (MgB) 2 ) Preparation process of nanosheet modified polypropylene (PP) diaphragm and MgB obtained by preparation process 2 The process for preparing the @ PP modified separator for the lithium sulfur battery was the same as that of example 1.
Example 3:
(1) Preparing magnesium boride nanosheets: weighing 500mg magnesium boride powder of 200 meshes, adding the powder into a beaker containing 100mL of N-methylpyrrolidone (NMP) to obtain a mixed solution A, magnetically stirring the mixed solution A for 60min at the stirring speed of 3000rpm to obtain a magnesium boride dispersion liquid with the concentration of 5mg/mL, ultrasonically stripping the magnesium boride dispersion liquid at 0 ℃ for 1h by using a cell disruptor, wherein the ultrasonic power is 250W, firstly centrifuging the ultrasonically stripped magnesium boride dispersion liquid for 8min at the rotating speed of 4000rpm to remove thick magnesium boride layers, and secondly centrifuging the supernatant obtained after the first centrifugation at the rotating speed of 10000rpm for 10min. And adding the precipitate obtained by the second centrifugation into 10mL of absolute ethyl alcohol to obtain a mixed solution B, and drying the mixed solution B in an oven at 40 ℃ for 12h to finally obtain the magnesium boride nanosheet powder.
(2) Magnesium boride (MgB) 2 ) Preparation process of nanosheet modified polypropylene (PP) diaphragm and MgB obtained through preparation process 2 The process for preparing the @ PP modified separator for the lithium sulfur battery was the same as that of example 1.
The above description is only an embodiment of the present invention, and is not intended to limit the present invention in any way, and the present invention may also have other embodiments according to the above structures and functions, and are not listed. Therefore, any simple modification, equivalent change and modification of the above embodiments according to the technical essence of the present invention by those skilled in the art can be made within the technical scope of the present invention.
Claims (7)
1. A preparation method of a magnesium boride nanosheet is characterized by comprising the following steps:
weighing magnesium boride with a certain mass of 50-200 meshes, adding the magnesium boride into a beaker filled with an organic solvent to obtain a mixed solution A, magnetically stirring the mixed solution A for 15-60 min at the stirring speed of 2000-3000 rpm to obtain a magnesium boride dispersion liquid, carrying out ultrasonic stripping on the magnesium boride dispersion liquid for 40-60 min at the temperature of 0-20 ℃ by using a cell disruptor, wherein the ultrasonic power is 100-250W, firstly centrifuging the ultrasonically stripped magnesium boride dispersion liquid for 8min at the rotation speed of 4000rpm, then carrying out secondary centrifugation on a supernatant obtained after the primary centrifugation at the rotation speed of 10000rpm for 10min, adding a precipitate obtained by the secondary centrifugation into 10mL of anhydrous ethanol, fully and uniformly stirring to obtain a mixed solution B, and drying the mixed solution B in a drying oven for 12h at the temperature of 40 ℃ to finally obtain magnesium boride nanosheet powder.
2. A method of producing magnesium boride nanoplates as recited in claim 1 wherein the organic solvent includes at least one of N-methylpyrrolidone, N-dimethylformamide.
3. A method of preparing magnesium boride nanoplates as defined in claim 1, characterised in that the concentration of the magnesium boride dispersion is 5mg/mL.
4. Magnesium boride nanoplate prepared by the method of preparing magnesium boride nanoplate of claim 1, having a thickness of 5nm or less and nanoplate size of 0.1 to 5 μm.
5. A preparation method of a polypropylene diaphragm modified by magnesium boride nanosheets is characterized by comprising the following steps: weighing 0.5g of magnesium boride nanosheet prepared according to the preparation method of any one of claims 1 to 3, adding the magnesium boride nanosheet into 100mL of N-methylpyrrolidone to obtain a mixed solution C, inserting an ultrasonic probe of a cell disruptor into the mixed solution C, adjusting the power of the cell disruptor to 200W, carrying out ultrasonic operation on the mixed solution C for 1h under the protection of argon gas, and obtaining a mixed solution D after the ultrasonic operation is finished; transferring the mixed solution D into a centrifuge tube, centrifuging for 8min at the rotating speed of 8000rpm, and collecting the obtained supernatant; and repeating the steps for multiple times to obtain 500mL of supernatant, and performing suction filtration on the supernatant on the polypropylene diaphragm to obtain the polypropylene diaphragm modified by the magnesium boride nanosheet.
6. A polypropylene separator modified by magnesium boride nanosheets prepared by the preparation method as claimed in claim 5.
7. The application of the polypropylene separator modified by the magnesium boride nanosheet in a lithium-sulfur battery.
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