CN113948816B - MXene composite material modified diaphragm for lithium-sulfur battery and preparation method thereof - Google Patents
MXene composite material modified diaphragm for lithium-sulfur battery and preparation method thereof Download PDFInfo
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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
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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
- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/05—Accumulators with non-aqueous electrolyte
- H01M10/052—Li-accumulators
- H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
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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
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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
- H01M50/431—Inorganic material
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- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/10—Energy storage using batteries
Abstract
The invention discloses an MXene composite material modified diaphragm for a lithium-sulfur battery and a preparation method thereof. The preparation method of the diaphragm comprises the following steps: step 1: dispersing the MXene composite material in an ethanol water solution to form a modified solution with the concentration of 0.05-0.5 mg/mL; step 2: taking the basement membrane as a filter membrane, adding the modification solution into a suction filtration device, and carrying out vacuum suction filtration; and (5) drying in vacuum to obtain the diaphragm. Has the beneficial effects that: (1) using MXene @ SnS 2 The synergistic effect of three substances in ZnO enhances the conductivity of lithium ion, effectively fixes polysulfide, inhibits the shuttle effect of polysulfide, accelerates the electrochemical redox kinetics of polysulfide, greatly improves the utilization rate of active sulfur, and further improves the electrochemical performance of the lithium-sulfur battery. (2) The modification liquid concentration is limited, and a polyethylene glycol-lignin compound is added, so that MXene @ SnS is ensured 2 The dispersibility of ZnO, the adhesiveness of the modification layer is increased, and the performance of the lithium-sulfur battery is further improved.
Description
Technical Field
The invention relates to the technical field of battery diaphragms, in particular to an MXene composite material modified diaphragm for a lithium-sulfur battery and a preparation method thereof.
Background
The increase of the resource usage amount by people increases the energy dependence, and the limitation of resources causes the renewable energy to be widely concerned. Among them, energy storage elements such as lithium ion batteries are widely used in electric vehicles, wearable electronic devices, and the like due to their cleanliness and recyclability. However, the matching between low energy density and high demand of lithium ion batteries has been a problem, and therefore, the development of new energy storage elements having high energy density is urgently needed.
In the existing research, a lithium-sulfur battery is one of lithium ion batteries, and a battery using elemental sulfur as a positive electrode and lithium as a negative electrode has the advantages of high energy density, low cost, and the like, so that the lithium-sulfur battery is considered to be one of the most promising battery technologies. The lithium-sulfur battery diaphragm, which is an important component in the lithium-sulfur battery, has great influence on the performance and the service life of the battery, and the commercial popularization of the lithium-sulfur battery is seriously restricted. The reason is that: in a liquid lithium-sulfur battery, polysulfide is continuously generated in the battery during the charging and discharging processes, and the porosity of a general commercial diaphragm provides possibility for the diffusion of the polysulfide, so that the polysulfide finally causes a serious shuttle effect, and the specific capacity of the lithium-sulfur battery is rapidly attenuated, and the service life of the lithium-sulfur battery is reduced.
In conclusion, the MXene composite material modified diaphragm for the lithium-sulfur battery is of great significance in solving the problems.
Disclosure of Invention
The invention aims to provide an MXene composite material modified diaphragm for a lithium-sulfur battery and a preparation method thereof, so as to solve the problems in the background technology.
In order to solve the technical problems, the invention provides the following technical scheme:
a preparation method of an MXene composite material modified diaphragm for a lithium-sulfur battery comprises the following steps: step 1: dispersing the MXene composite material in an ethanol water solution to form a modified solution with the concentration of 0.05-0.5 mg/mL; step 2: taking the basement membrane as a filter membrane, adding the modification solution into a suction filtration device, and carrying out vacuum suction filtration; and (5) drying in vacuum to obtain the diaphragm.
Wherein the water-alcohol ratio of the ethanol water solution is 3: 7.
Preferably, in the step 1, the MXene composite material is folded MXene @ SnS 2 /ZnO; the concentration of the modifying solution is 0.1-0.3 mg/mL.
Preferably, the fold MXene @ SnS 2 The preparation method of the/ZnO comprises the following steps: (1) folding MXene @ SnS 2 Ultrasonically dispersing in a methanol solution to obtain a solution A; reacting Zn (COOH) 2 Ultrasonically dissolving the mixture in a methanol solution to obtain a solution B; dissolving KOH in a methanol solution to obtain a solution C; (2) adding the solution A into the solution B, setting the temperature to be 55-65 ℃, and stirring for 60-100 min uniformly; slowly dripping the solution C, and continuously stirring for 120-180 min; centrifuging, washing and drying to obtain folded MXene @ SnS 2 /ZnOMXene。
Preferably, the fold MXene @ SnS 2 The preparation method comprises the following steps: ultrasonically dispersing folded MXene nanosheets in water; adding SnCl in sequence 4 ·5H 2 O, L-cysteine, and ultrasonically mixing uniformly to obtain a suspension; transferring the suspension into a stainless steel autoclave with a PTFE lining, heating for 12h at the set temperature of 200 ℃, and naturally cooling; centrifuging, washing and drying to obtain powder; it is at 600 ℃Annealing at 700 ℃ for 2-3 h to obtain a folded MXene @ SnS 2 。
Preferably, the preparation method of the folded MXene nanosheet comprises the following steps: (1) ball-milling titanium hydride, titanium carbide and aluminum powder, uniformly mixing, and calcining in inert gas at 1450 ℃ for 2 hours to obtain massive MAX; (2) placing the blocky MAX into a ball mill for ball milling to obtain powdery MAX; sieving the MXene powder, uniformly mixing the MXene powder with lithium fluoride and hydrochloric acid according to the proportion of 1g to 20m, setting the temperature to be 30 ℃, stirring for 24 hours, centrifugally washing until the pH value is more than 6, and freeze-drying to obtain three-dimensional MXene; (3) ultrasonically dispersing three-dimensional MXene in water under the inert gas atmosphere, wherein the solid-liquid ratio is 1g to 25 mL; freeze drying to obtain peeled MXene nano sheet; (4) uniformly mixing the stripped MXene nanosheet with hydrazine hydrate according to the volume ratio of 1:20, transferring the MXene nanosheet to a stainless steel autoclave with a PTFE liner, setting the temperature to be 95 ℃, reacting for 5 hours, and naturally cooling; and filtering, washing and drying to obtain the folded MXene nanosheet.
Optimally, in the step 2, in the vacuum filtration process, the vacuum degree is 0.03-0.08 Mpa; in the vacuum drying process, the vacuum degree is 0.03-0.08 Mpa, the drying temperature is 40-80 ℃, and the drying time is 8-24 hours.
Preferably, the specific steps of step 1 are: dispersing the MXene composite material in an ethanol water solution to form a modified solution with the concentration of 0.05-0.5 mg/mL, adding the polyethylene glycol-lignin composite, and uniformly stirring to obtain a modified solution B; step 2: taking the basement membrane as a filter membrane, adding the modification solution B into a suction filtration device, and carrying out vacuum suction filtration; and (5) drying in vacuum to obtain the diaphragm.
Preferably, the addition amount of the polyethylene glycol-lignin compound accounts for 10-20% of the mass of the MXene composite material.
Preferably, the preparation method of the polyethylene glycol-lignin compound comprises the following steps: (1) dissolving poly (ethylene glycol) methyl ether p-toluenesulfonate in acetone, adding triethylamine and methanesulfonic anhydride, and stirring to react for 10-12 hours to obtain a mixed solution A; (2) ultrasonically dispersing sulfonated lignin in water, adding the solution A, uniformly mixing, adjusting the pH value to 10.8-11.2 by using sodium hydroxide, heating to 65-72 ℃, reacting for 2-3 days, purifying, and freeze-drying to obtain the polyethylene glycol-lignin compound.
The diaphragm in the technical scheme comprises a base film and MXene @ SnS 2 the/ZnO modified layer is prepared by adding MXene @ SnS 2 And depositing the repair solution of/ZnO on the surface of the base film in a low-speed vacuum filtration mode, and drying to obtain the diaphragm. When the modified layer is used for the lithium-sulfur battery, the side with the modified layer faces the positive electrode of the battery.
The prepared diaphragm has excellent lithium ion conductivity, can effectively fix polysulfide, inhibit shuttle effect of polysulfide, accelerate electrochemical redox kinetics of polysulfide, greatly improve the utilization rate of active sulfur, and further improve the electrochemical performance of the lithium-sulfur battery.
Compared with the prior art, the invention has the following beneficial effects:
(1) the MXene material has better mechanical property, and on one hand, the high conductivity of the material greatly enhances the electronic conductivity of the lithium-sulfur battery; on the other hand, early transition metal atoms in MXene have a good adsorption effect on polysulfide intermediates in the lithium-sulfur battery, and ultrathin folded MXene nanosheets (1.0nm) in the scheme have extremely large surface areas and highly exposed active edge positions, so that the shuttle effect can be effectively inhibited, and the cycle stability of the lithium-sulfur battery is greatly improved. Meanwhile, the folded MXene is used in the scheme, so that the coverage area of the membrane holes by the sheet layer can be reduced.
(2)SnS 2 The introduction of the nano-sheets improves the polarity of the material on one hand, and a polysulfide intermediate can be effectively fixed through a chemical mode; on the other hand, the electrochemical oxidation-reduction kinetics of polysulfide intermediates can be accelerated, and further the electrochemical performance of the lithium-sulfur battery is improved. The reason is that: SnS 2 Covalent bonds are generated with titanium in MXene and penetrate into an MXene sheet layer, so that the interlayer distance between two substance sheets is widened, and the migration rate of ions and electrons is increased. And the substance interaction increases the structural integrity and inhibits the dissolution of sulfur.
(3) In SnS 2 ZnO grows in situ on the surface of the nano-sheet and can form chemical bondsEnhancing binding energy and affinity to sulfur and polysulfide intermediates, thereby further inhibiting polysulfide shuttling. And the embedding of the MXene composite material further enhances the distance between the sheets and increases the electron mobility.
(4) The concentration of the modification solution is limited to be 0.05-0.5 mg/mL, and the optimized condition is 0.1-0.3 mg/mL. The reason is that: MXene has strong charges on the surface, has excellent hydrophilicity, has certain viscosity at very low concentration, and can increase the adhesion of the MXene to the surface of a basement membrane.
Meanwhile, adding a polyethylene glycol-lignin compound into the modification solution to form a modification solution B; the polyethylene glycol-lignin compound is obtained by grafting polyethylene glycol by utilizing nucleophilic substitution between phenolic hydroxyl and acid anhydride in sulfonated lignin. Because the sulfonated lignin is an anionic surfactant, the sulfonated lignin is changed into a nonionic surfactant after being grafted with polyethylene glycol chain, and the sulfonated lignin is added into a modifier to enhance MXene @ SnS 2 The dispersibility of ZnO, thereby increasing the uniformity of suction filtration deposition.
In addition, the polyethylene glycol-lignin complex can be mixed with MXene @ SnS 2 Hydroxyl on the surface of the/ZnO forms hydrogen bonds to effectively protect the structure and the performance of MXene. Meanwhile, on one hand, the polyethylene glycol block of the compound increases the viscosity of the solution due to larger molecular weight, thereby enhancing MXene @ SnS 2 The adhesion of/ZnO can effectively trap lithium ions, thereby improving the migration efficiency of ions and electrons, and further improving the performance and the service life of the lithium-sulfur battery. On the other hand, the sulfonated lignin itself has a sulfonic acid group which can effectively block the passage of polysulfide compounds having negative charges without impairing the transport of positively charged lithium ions.
(5) Compared with the existing commercial polypropylene diaphragm, the diaphragm of the invention can obviously improve the capacity of the lithium-sulfur battery and the rate capability of the battery under the same rate condition, and well solve the problems caused by the shuttle effect.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
(1) Preparation of folded MXene nanosheets:
7.1321g of titanium hydride, 17.3623g of titanium carbide and 4.6916g of aluminum powder are taken to be ball-milled in a ball-milling pot for 4 hours, so that the titanium hydride, the titanium carbide and the aluminum powder are uniformly mixed, and are calcined for 2 hours at 1450 ℃ in an argon atmosphere to obtain a block MAX. And placing the blocky MAX into a ball mill for ball milling for 2h to obtain powdery MAX. The powdered MAX was sieved, then magnetically stirred with lithium fluoride and 9M hydrochloric acid at 1g:1g:20mL for 24h at 30 ℃ and washed with water by centrifugation to a pH > 6. The three-dimensional product MXene obtained was freeze-dried. Adding the three-dimensional MXene and water into a beaker according to the proportion of 1g to 25mL, performing ultrasonic treatment for 180min under the atmosphere of argon, and centrifuging to obtain a supernatant to obtain a stripped MXene dispersion liquid. And then, freeze-drying the stripped MXene dispersion liquid again to obtain the stripped MXene nanosheet. The obtained stripped MXene nanoplatelets were reacted with hydrazine hydrate (80%) in a 1:20, sealing the obtained mixed solution in a stainless steel high-pressure kettle with a PTFE liner, keeping the mixed solution at 95 ℃ for 5 hours, naturally cooling to room temperature after the completion, filtering and collecting precipitates after cooling, fully washing the precipitates by absolute ethyl alcohol and deionized water, finally drying the obtained precipitates in a vacuum drying box at 80 ℃ for 24 hours, controlling the vacuum degree of vacuum drying to be 0.08Mpa, and obtaining the folded MXene nanosheet to be prepared after the vacuum drying is finished.
(2) Folded MXene @ SnS 2 Preparing the nano-sheet composite material:
dissolving 0.17g of the obtained folded MXene nanosheet in 45mL of ultrapure water under the condition of continuous stirring, and then performing ultrasonic dispersion for 1.5 h; then 1.13mmol SnCl 4 ·5H 2 O was added to the mixed solution, and ultrasonic dispersion was continued for 15 minutes. Then, 6.78mmol of L-cysteine was added to the above solution and sonicated for 30 minutes. Finally, the suspension obtained was sealed in a stainless steel autoclave with a PTFE liner and heated at 200 ℃ for 12 h. Naturally cooling the autoclave to room temperature, centrifuging to collect precipitate, washing with deionized water and absolute ethyl alcohol for several times, drying in vacuum for 12 hours after washing, annealing the obtained powder after drying, controlling the annealing temperature to be 650 ℃ and the annealing time to be 3 hours to obtain folded MXene @ SnS 2 。
(3) Folded MXene @ SnS 2 Preparation of ZnO:
weighing 55mg of folded MXene @ SnS 2 Adding the nano-sheet composite material into 60mL of methanol, and placing the mixture into an ultrasonic machine to perform ultrasonic treatment for 45min at 60 ℃. Weighing 125mg of Zn (COOH) 2 Then, the mixture was added to 100mL of methanol and stirred at 60 ℃ for 60 min. 78mg of KOH were weighed, added to 90mL of methanol, and stirred at 60 ℃ for 60 min. Dispersing folded MXene @ SnS 2 Adding the nano-sheet composite material suspension into Zn (COOH) 2 Stirring the methanol solution at 60 ℃ for 90min, slowly dripping the KOH methanol solution into the methanol solution by using a dropper, and continuously stirring the solution at 60 ℃ for 150min after the dripping is finished. Centrifuging and collecting precipitates after the reaction is finished, alternately washing the precipitates for several times by using deionized water and absolute ethyl alcohol, drying the precipitates in vacuum for 12 hours after washing, and obtaining the folded MXene @ SnS to be prepared after the vacuum drying is finished 2 /ZnOMXene。
In the following examples and comparative examples, a polypropylene separator (Celgard2500) was used as a base film, and a tsumadam suction filtration apparatus was used as a vacuum suction filtration apparatus.
Example 1:
step 1: folding MXene @ SnS 2 Dispersing ZnO in ethanol water solution with water-alcohol ratio of 3:7, stirring for 60min to form modified solution;
and 2, step: adding the modified solution into a suction filtration device by taking a polyolefin diaphragm as a filter membrane, and performing vacuum filtration under the vacuum degree of 0.06 Mpa; setting the vacuum degree at 0.08Mpa and the drying temperature at 60 ℃, and drying for 12 hours to obtain the diaphragm.
Example 2:
step 1: (1) 10.035g of poly (ethylene glycol) methyl ether p-toluenesulfonate were dissolved in 100mL of acetone, andadding 2mL of triethylamine and 1.058g of methanesulfonic anhydride, stirring and reacting for 12 hours to obtain a mixed solution A; (2) ultrasonically dispersing 6.068g of sulfonated lignin in 30mL of water, adding the solution A, uniformly mixing, adjusting the pH value to 11 by using sodium hydroxide, heating to 70 ℃, reacting for 3 days, purifying, and freeze-drying to obtain the polyethylene glycol-lignin compound. (2) Folding MXene @ SnS 2 Dispersing ZnO in ethanol water solution with the ratio of water to alcohol of 3:7, and stirring for 30min to obtain a modified solution; adding polyethylene glycol-lignin complex, and stirring for 60 min; forming a modification solution B;
step 2: taking a polyolefin diaphragm as a filter membrane, adding the modification solution B into a suction filtration device, and performing vacuum filtration under the vacuum degree of 0.06 Mpa; setting the vacuum degree at 0.08Mpa and the drying temperature at 60 ℃, and drying for 18 hours to obtain the diaphragm.
In the technical scheme, the molecular weight of the poly (ethylene glycol) methyl ether p-toluenesulfonate is 2000; the addition amount of the polyethylene glycol-lignin compound accounts for the folded MXene @ SnS 2 18% of the ZnO content.
Example 3:
step 1: (1) 10.042g of poly (ethylene glycol) methyl ether p-toluenesulfonate is dissolved in 100mL of acetone, 2mL of triethylamine and 1.062g of methanesulfonic anhydride are added, and the mixture is stirred and reacted for 12 hours to obtain a mixed solution A; (2) dispersing 6.053g sulfonated lignin in 30mL water by ultrasonic, adding the solution A, mixing uniformly, adjusting the pH value to 10.8 by using sodium hydroxide, heating to 68 ℃, reacting for 3 days, purifying, and freeze-drying to obtain the polyethylene glycol-lignin compound. (2) Folding MXene @ SnS 2 Dispersing ZnO in ethanol water solution with water-alcohol ratio of 3:7, and stirring for 30min to obtain modified solution; adding polyethylene glycol-lignin complex, and stirring for 60 min; forming a modification solution B;
step 2: taking a polyolefin diaphragm as a filter membrane, adding the modification solution B into a suction filtration device, and performing vacuum filtration under the vacuum degree of 0.03 Mpa; setting the vacuum degree at 0.03Mpa and the drying temperature at 40 ℃, and drying for 24 hours to obtain the diaphragm.
In the technical scheme, the molecular weight of the poly (ethylene glycol) methyl ether p-toluenesulfonate is 2000; the addition amount of the polyethylene glycol-lignin compound accounts for the folds MXene@SnS 2 20% of the ZnO content.
Example 4:
step 1: (1) 10.023g of poly (ethylene glycol) methyl ether p-toluenesulfonate is dissolved in 100mL of acetone, 2mL of triethylamine and 1.038g of methanesulfonic anhydride are added, and stirring reaction is carried out for 10-12 hours to obtain a mixed solution A; (2) dispersing 6.058g sulfonated lignin in 30mL water by ultrasonic, adding the solution A, mixing uniformly, adjusting the pH value to 11.2 by using sodium hydroxide, heating to 72 ℃, reacting for 2 days, purifying, and freeze-drying to obtain the polyethylene glycol-lignin compound. (2) Folding MXene @ SnS 2 Dispersing ZnO in ethanol water solution with water-alcohol ratio of 3:7, and stirring for 30min to obtain modified solution; adding polyethylene glycol-lignin complex, and stirring for 60 min; forming a modification solution B;
step 2: taking a polyolefin diaphragm as a filter membrane, adding the modification solution B into a suction filtration device, and performing vacuum suction filtration at a vacuum degree of 0.08 Mpa; setting the vacuum degree at 0.06Mpa and the drying temperature at 80 ℃, and drying for 8 hours to obtain the diaphragm.
In the technical scheme, the molecular weight of the poly (ethylene glycol) methyl ether p-toluenesulfonate is 2000; the addition amount of the polyethylene glycol-lignin compound accounts for the wrinkle MXene @ SnS 2 10% of the ZnO content.
Comparative example 1:
step 1: dispersing folded MXene in an ethanol water solution with the water-alcohol ratio of 3:7, and stirring for 60min to form a modified solution;
step 2: adding the modified solution into a suction filtration device by taking a polyolefin diaphragm as a filter membrane, and performing vacuum filtration under the vacuum degree of 0.06 Mpa; setting the vacuum degree at 0.08Mpa and the drying temperature at 60 ℃, and drying for 12 hours to obtain the diaphragm.
Comparative example 2:
step 1: folding MXene @ SnS 2 Dispersing in ethanol water solution with water-alcohol ratio of 3:7, stirring for 60min to form modified solution;
step 2: adding the modified solution into a suction filtration device by taking a polyolefin diaphragm as a filter membrane, and performing vacuum filtration under the vacuum degree of 0.06 Mpa; setting the vacuum degree at 0.08Mpa and the drying temperature at 60 ℃, and drying for 12 hours to obtain the diaphragm.
Comparative example 3: unmodified commercial polypropylene separators were used.
Comparative example 4: the polyethylene glycol-lignin complex was replaced with sulfonated lignin.
Step 1: folding MXene @ SnS 2 Dispersing ZnO in ethanol water solution with water-alcohol ratio of 3:7, and stirring for 30min to obtain modified solution; adding sulfonated lignin, and stirring for 60 min; forming a modification solution B;
and 2, step: taking a polyolefin diaphragm as a filter membrane, adding the modification solution B into a suction filtration device, and performing vacuum filtration under the vacuum degree of 0.06 Mpa; setting the vacuum degree at 0.08Mpa and the drying temperature at 60 ℃, and drying for 18 hours to obtain the diaphragm.
In the technical scheme, the addition of the sulfonated lignin accounts for the folded MXene @ SnS 2 18% of the ZnO content.
Experiment: the separators prepared in examples and comparative examples were used for lithium sulfur batteries and tested for performance.
Assembling the lithium-sulfur battery: fully mixing conductive carbon black SuperP and sublimed sulfur in a mass ratio of 1:3, and treating the mixture at the high temperature of 155 ℃ for 12 hours to obtain a product recorded as CB/S. Fully mixing CB/S, SuperP and LA133 in a mass ratio of 8:1:1 in a ball mill to obtain slurry, coating the slurry on an aluminum foil by using a blade coater, and controlling the thickness to ensure that the area sulfur loading is about 2mg/cm 2 Drying to obtain a positive electrode; the negative electrode was a commercial lithium plate and the electrolyte was 1M lithium bistrifluoromethanesulfonimide +2 wt% lithium nitrate +1M1, 2-dimethoxyethane +1M1, 3-dioxolane (1, 2-dimethoxyethane: 1, 3-dioxolane mixed in equal volume). In addition, the whole battery assembly process is carried out in an argon atmosphere.
Testing the voltage on a Wuhan blue electricity testing system, wherein the charging and discharging voltage range is 1.7-2.8V, and the initial capacity is under the current density of 0.2C, 0.5C, 1C, 2C and 3C; at the same time, the capacity after 100 cycles of circulation at 0.2C (1C 1675mAh g) -1 ). In addition, the concentration of the modification solution in the table is the concentration of the MXene composite material.
The data obtained are shown in the following table:
and (4) conclusion: comparing the data of example 1 and comparative examples 1 to 3, it can be found that: unmodified polypropylene membranes, membranes modified solely with pleated MXene nanosheets, and membranes modified with pleated MXene @ SnS 2 In the practical application of the nanosheet-modified diaphragm in the lithium-sulfur battery, the capacity retention rate, rate capability and cycle stability of the battery are all lower than those of folded MXene @ SnS 2 A ZnO modified diaphragm. The diaphragm prepared by the method has excellent lithium ion conductivity, can effectively fix polysulfide, inhibit shuttle effect of polysulfide, accelerate polysulfide electrochemical redox kinetics, greatly improve the utilization rate of active sulfur, well solve the problem caused by the shuttle effect, and further improve the electrochemical performance of the lithium-sulfur battery. Has good application prospect in the field of diaphragms.
Comparing the data of examples 2-4 with example 1, it can be found that: after the polyethylene glycol-lignin compound is added, the thickness of the modification layer is increased after the diaphragm is used for the lithium-sulfur battery, but the capacity retention rate and the rate performance of the battery are not reduced, and the cycle stability is enhanced. The reason is that: MXene @ SnS is enhanced by polyethylene glycol-lignin compound 2 The dispersibility of ZnO, thereby increasing the uniformity of suction filtration deposition; meanwhile, the hydroxyl groups and the sulfonic acid groups added to the polyethylene glycol-lignin increase the migration efficiency of electrons and effectively prevent polysulfide compounds from passing through; and the addition of the compound effectively enhances MXene @ SnS 2 adhesion/ZnO, thereby increasing the service life. Further comparison with the data of comparative example 4, it can be found that: the capacity retention rate, rate capability and cycle stability of the battery were all reduced compared to example 2 because: the abundance of hydroxyl in the polyethylene glycol block in the polyethylene glycol-lignin compound is high, and a hydrogen bond can be formed with the MXene surface, so that the structure and performance of the MXene are effectively protected; the increase of the abundance of the hydroxyl groups can effectively trap lithium ions, so that the migration efficiency of the ions and electrons is improved, and the performance of the lithium-sulfur battery is improved; at the same time, the molecular weight is lowerGreatly and effectively enhances MXene @ SnS 2 The adhesion of/ZnO can further improve the service life.
Finally, it should be noted that: although the present invention has been described in detail with reference to the foregoing embodiments, it will be apparent to those skilled in the art that changes may be made in the embodiments and/or equivalents thereof without departing from the spirit and scope of the invention. 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 (6)
1. A preparation method of an MXene composite material modified diaphragm for a lithium-sulfur battery is characterized by comprising the following steps: the method comprises the following steps: step 1: dispersing the MXene composite material in an ethanol water solution to form a modified solution with the concentration of 0.1-0.3 mg/mL; step 2: adding the modification solution into a suction filtration device by taking the basement membrane as a filter membrane, and carrying out vacuum suction filtration; vacuum drying to obtain a diaphragm;
the MXene composite material is a fold MXene @ SnS 2 /ZnO；
The fold MXene @ SnS 2 The preparation method of the/ZnO comprises the following steps: (1) folding MXene @ SnS 2 Ultrasonically dispersing in a methanol solution to obtain a solution A; reacting Zn (COOH) 2 Ultrasonically dissolving the mixture in a methanol solution to obtain a solution B; dissolving KOH in a methanol solution to obtain a solution C; (2) adding the solution A into the solution B, setting the temperature to be 55-65 ℃, and stirring for 60-100 min uniformly; slowly dripping the solution C, and continuously stirring for 120-180 min; centrifuging, washing and drying to obtain folded MXene @ SnS 2 /ZnO；
The fold MXene @ SnS 2 The preparation method comprises the following steps: ultrasonically dispersing folded MXene nanosheets in water; adding SnCl in sequence 4 ·5H 2 O, L-cysteine, and ultrasonically mixing uniformly to obtain a suspension; transferring the suspension into a stainless steel autoclave with a PTFE lining, heating for 12h at the set temperature of 200 ℃, and naturally cooling; centrifuging, washing and drying to obtain powder; annealing at 600-700 deg.CHeating for 2-3 h to obtain a folded MXene @ SnS 2 ；
The preparation method of the folded MXene nanosheet comprises the following steps: (1) ball-milling titanium hydride, titanium carbide and aluminum powder, uniformly mixing, and calcining in inert gas at 1450 ℃ for 2 hours to obtain massive MAX; (2) placing the blocky MAX into a ball mill for ball milling to obtain powdery MAX; sieving the MXene powder, uniformly mixing the MXene powder with lithium fluoride and hydrochloric acid according to a ratio of 1g:1g:20mL, setting the temperature at 30 ℃, stirring for 24 hours, centrifugally washing until the pH value is more than 6, and freeze-drying to obtain three-dimensional MXene; (3) ultrasonically dispersing three-dimensional MXene in water under the inert gas atmosphere, wherein the solid-liquid ratio is 1g:25 mL; freeze drying to obtain peeled MXene nano sheet; (4) uniformly mixing the stripped MXene nanosheets and hydrazine hydrate according to the volume ratio of 1:20, transferring the MXene nanosheets and the hydrazine hydrate into a stainless steel high-pressure kettle with a PTFE liner, setting the temperature to be 95 ℃ for reaction for 5 hours, and naturally cooling; and filtering, washing and drying to obtain the folded MXene nanosheet.
2. The method for preparing the MXene composite material modified diaphragm for the lithium-sulfur battery according to claim 1, wherein the MXene composite material modified diaphragm comprises: in the step 2, in the vacuum filtration process, the vacuum degree is 0.03-0.08 Mpa; in the vacuum drying process, the vacuum degree is 0.03-0.08 Mpa, the drying temperature is 40-80 ℃, and the drying time is 8-24 hours.
3. The method for preparing the MXene composite material modified diaphragm for the lithium-sulfur battery according to claim 1, wherein the MXene composite material modified diaphragm comprises: the specific steps of the step 1 are as follows: dispersing the MXene composite material in an ethanol water solution to form a modified solution with the concentration of 0.1-0.3 mg/mL, adding a polyethylene glycol-lignin compound, and uniformly stirring to obtain a modified solution B; step 2: taking the basement membrane as a filter membrane, adding the modification solution B into a suction filtration device, and carrying out vacuum suction filtration; and (5) drying in vacuum to obtain the diaphragm.
4. The method for preparing the MXene composite material modified diaphragm for the lithium-sulfur battery according to claim 3, wherein the MXene composite material modified diaphragm comprises the following steps: the addition amount of the polyethylene glycol-lignin compound accounts for 10-20% of the mass of the MXene composite material.
5. The method for preparing the MXene composite material modified diaphragm for the lithium-sulfur battery according to claim 3, wherein the MXene composite material modified diaphragm comprises the following steps: the preparation method of the polyethylene glycol-lignin compound comprises the following steps: (1) dissolving poly (ethylene glycol) methyl ether p-toluenesulfonate in acetone, adding triethylamine and methanesulfonic anhydride, stirring and reacting for 10-12 hours to obtain a mixed solution A; (2) ultrasonically dispersing sulfonated lignin in water, adding the solution A, uniformly mixing, adjusting the pH value to 10.8-11.2 by using sodium hydroxide, heating to 65-72 ℃, reacting for 2-3 days, purifying, and freeze-drying to obtain the polyethylene glycol-lignin compound.
6. The separator prepared by the preparation method of the MXene composite material modified separator for the lithium-sulfur battery according to any one of claims 1 to 5.
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