CN110540204A - Self-supporting three-dimensional porous MXene foam material and preparation method and application thereof - Google Patents
Self-supporting three-dimensional porous MXene foam material and preparation method and application thereof Download PDFInfo
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- C01B17/00—Sulfur; Compounds thereof
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Abstract
The invention relates to the field of porous materials, and provides a self-supporting three-dimensional porous MXene foam material, a preparation method and application thereof, wherein the preparation method of the self-supporting three-dimensional porous MXene foam material comprises the following steps: mixing a sulfur-containing compound, a dispersant and water to obtain a sulfur-containing compound aqueous solution; adding acid into the aqueous solution of the sulfur-containing compound to react to obtain nano sulfur particle dispersion liquid; adjusting the pH value of the nano sulfur particle dispersion liquid to be neutral, and then stirring and mixing the nano sulfur particle dispersion liquid and the aqueous dispersion liquid of the two-dimensional layered MXene material to obtain mixed feed liquid; carrying out reduced pressure suction filtration on the mixed feed liquid to obtain a two-dimensional layered MXene/sulfur composite membrane; and removing sulfur in the composite membrane to obtain the self-supporting three-dimensional porous MXene foam material. The three-dimensional porous MXene foam material prepared by the method provided by the invention has better electrochemical performance when being used in the fields of electrochemical energy storage and pressure sensing.
Description
Technical Field
The invention relates to the field of porous materials, in particular to a self-supporting three-dimensional porous MXene foam material and a preparation method and application thereof.
Background
MXene is a novel layered transition metal carbide/nitride, has high specific surface area, excellent conductivity and abundant surface functional groups, is a hotspot of the current research in the field of electrochemical energy storage, and is increasingly widely researched in the fields of lithium/sodium ion batteries, super capacitors and lithium-sulfur batteries. However, as with other two-dimensional materials, the two-dimensional layered structure of MXene enables spontaneous stacking during the assembly process, and the formed compact structure can affect the permeation of electrolyte and the ion transmission, and finally affect the effective utilization of MXene surface active sites, thereby limiting the expression of the electrochemical performance of MXene.
Disclosure of Invention
in view of the above, in order to inhibit the dense stacking of the two-dimensional layered MXene nanosheets and exert the advantages of the two-dimensional MXene nanosheets to the greatest extent, the sulfur simple substance is used as the template, and the two-dimensional layered MXene material is constructed into the self-supporting three-dimensional porous MXene foam material. The invention provides a self-supporting three-dimensional porous MXene foam material, a preparation method and application thereof, the porous material fully exposes active sites on the surface of a two-dimensional MXene material, and when the porous material is used as an electrode material, the porous material can promote the permeation of electrolyte and the transmission of ions, and the excellent performance of the layered MXene material is exerted to the greatest extent.
the invention provides a preparation method of a self-supporting three-dimensional porous MXene foam material, which comprises the following steps:
(1) mixing a sulfur-containing compound, a dispersant and water to obtain a sulfur-containing compound aqueous solution;
(2) Adding acid into the aqueous solution of the sulfur-containing compound to react to obtain nano sulfur particle dispersion liquid;
(3) Adjusting the pH value of the nano sulfur particle dispersion liquid to be neutral, and then stirring and mixing the nano sulfur particle dispersion liquid and the aqueous dispersion liquid of the two-dimensional layered MXene material to obtain mixed feed liquid;
(4) Carrying out reduced pressure suction filtration on the mixed feed liquid to obtain an MXene/sulfur composite material;
(5) And removing sulfur in the MXene/sulfur composite membrane to obtain the self-supporting three-dimensional porous MXene foam material.
preferably, the dispersing agent in step (1) includes one or a mixture of two or more of polyvinylpyrrolidone, polyoxyethylene type nonionic surfactant, polyol type nonionic surfactant, alkanolamide type nonionic surfactant, polyether type nonionic surfactant, amine oxide type nonionic surfactant, amine salt type cationic surfactant, quaternary ammonium salt type cationic surfactant, heterocyclic type cationic surfactant and xanthate type cationic surfactant; the mass concentration of the dispersing agent in the sulfur-containing compound aqueous solution is 0.01-1 per mill.
preferably, the sulfur-containing compounds in step (1) include thiosulfate and/or polysulfide; the mass concentration of the sulfur-containing compound in the sulfur-containing compound aqueous solution is 0.01-2 g/mL.
Preferably, the pH regulator for regulating the pH of the nano sulfur particle dispersion liquid to be neutral in step (3) is a base, and the base includes one or more of sodium hydroxide, potassium hydroxide and ammonia water.
Preferably, the mass ratio of the nano sulfur particles in the mixed feed liquid in the step (3) to the two-dimensional layered MXene material is 1: 20-20: 1.
Preferably, the two-dimensional layered MXene material comprises one or more of Ti3C2Tx, Ti2CTx, V2CTx, Mo2CTx, Nb4C3Tx, Mo2TiC2Tx and Mo2Ti2C3 Tx.
Preferably, the filter membrane used in the reduced-pressure suction filtration in the step (4) is an aqueous microporous filter membrane, an organic microporous filter membrane or a battery diaphragm.
Preferably, the method for removing sulfur in step (5) comprises: heating under protective atmosphere to remove sulfur or adopting a solvent dissolving method to remove sulfur; when the removing is carried out by adopting a heating method, the heating temperature is 300-700 ℃; when sulfur is removed by solvent dissolution, the solvent comprises one or more of carbon disulfide, carbon tetrachloride, chloroform, benzene, and toluene.
The invention also provides the self-supporting three-dimensional porous MXene foam material prepared by the preparation method of the technical scheme, wherein the pore volume of the self-supporting three-dimensional porous MXene foam material is 0.15-6 cm3/g, and the pore diameter is 0.05-3 μm.
The invention also provides application of the self-supporting three-dimensional porous MXene foam material in the technical scheme as an electrode in the fields of electrochemistry and pressure sensing.
the invention provides a preparation method of a self-supporting three-dimensional porous MXene foam material, which comprises the following steps: mixing a sulfur-containing compound, a dispersant and water to obtain a sulfur-containing compound aqueous solution; adding acid into the aqueous solution of the sulfur-containing compound to react to obtain nano sulfur particle dispersion liquid; adjusting the pH value of the nano sulfur particle dispersion liquid to be neutral, and then stirring and mixing the nano sulfur particle dispersion liquid and the aqueous dispersion liquid of the two-dimensional layered MXene material to obtain mixed feed liquid; the stirring and mixing time is 5-120 min, and the stirring and mixing rotating speed is 100-600 r/min; carrying out reduced pressure suction filtration on the mixed feed liquid to obtain a two-dimensional layered MXene/sulfur composite membrane; and removing sulfur in the MXene/sulfur composite membrane to obtain the self-supporting three-dimensional porous MXene foam material. The method provided by the invention can construct the two-dimensional layered MXene material into the three-dimensional porous MXene foam material, effectively inhibits the compact stacking of layers among the two-dimensional layered material, enables active sites in the layered material to be fully exposed and exerts the performance of the layered material to the maximum extent; meanwhile, the foam structure of the three-dimensional porous material provided by the invention provides enough buffer volume, can generate compression deformation along with the change of pressure, and can be used as a pressure sensor material. In addition, the method provided by the invention takes sulfur as a template, and the sulfur is low in price and easy to remove, so that the method provided by the invention is low in cost, mild in condition and easy to operate.
drawings
FIG. 1 is a scanning electron microscope image of a three-dimensional porous MXene foam material prepared in example 1;
FIG. 2 is a constant current charge and discharge diagram of the three-dimensional porous MXene foam prepared in example 1;
FIG. 3 is a graph of rate capability of the three-dimensional porous MXene foam prepared in example 1;
FIG. 4 is a scanning electron microscope image of the three-dimensional porous MXene foam material prepared in example 2;
FIG. 5 is a constant current charge and discharge diagram of the three-dimensional porous MXene foam prepared in example 2;
FIG. 6 is a graph of rate capability of three-dimensional porous MXene foam prepared in example 2;
FIG. 7 is a scanning electron microscope image of a three-dimensional porous MXene foam material prepared in example 3;
FIG. 8 is a scanning electron microscope image of a three-dimensional porous MXene foam material prepared in example 3;
FIG. 9 is a constant current charge and discharge diagram of the three-dimensional porous MXene foam prepared in example 3;
FIG. 10 is a constant current charge and discharge diagram of the three-dimensional porous MXene foam material prepared in example 3 at 1A/g;
FIG. 11 is a graph of rate capability of three-dimensional porous MXene foam prepared in example 3;
FIG. 12 is a graph of pressure versus current for the three dimensional porous MXene foam prepared in example 3.
Detailed Description
The invention provides a preparation method of a self-supporting three-dimensional porous foam material, which comprises the following steps:
(1) Mixing a sulfur-containing compound, a dispersant and water to obtain a sulfur-containing compound aqueous solution;
(2) Adding acid into the aqueous solution of the sulfur-containing compound to react to obtain nano sulfur particle dispersion liquid;
(3) Adjusting the pH value of the nano sulfur particle dispersion liquid to be neutral, and then stirring and mixing the nano sulfur particle dispersion liquid and the aqueous dispersion liquid of the two-dimensional layered MXene material to obtain mixed feed liquid; the stirring and mixing time is 5-120 min, and the stirring and mixing rotating speed is 100-600 r/mim;
(4) Carrying out reduced pressure suction filtration on the mixed feed liquid to obtain an MXene/sulfur composite material;
(5) and removing sulfur in the MXene/sulfur composite membrane to obtain the self-supporting three-dimensional porous MXene foam material.
The invention mixes the sulfur-containing compound, the dispersant and the water to obtain the sulfur-containing compound aqueous solution.
In the present invention, the sulfur-containing compound preferably includes thiosulfate and/or polysulfide, and further preferably includes sodium thiosulfate and/or sodium polysulfide; the mass concentration of the sulfur-containing compound in the sulfur-containing compound aqueous solution is preferably 0.01-2 g/mL, more preferably 0.1-1.5 g/mL, and even more preferably 0.1 g/mL. In the present invention, the dispersant preferably includes one or a mixture of two or more of polyvinylpyrrolidone, polyoxyethylene type nonionic surfactant, polyol type nonionic surfactant, alkanolamide type nonionic surfactant, polyether type nonionic surfactant, amine oxide type nonionic surfactant, amine salt type cationic surfactant, quaternary ammonium salt type cationic surfactant, heterocyclic type cationic surfactant, and xanthate type cationic surfactant; the polyoxyethylene type nonionic surfactant preferably comprises long-chain fatty alcohol polyoxyethylene ether or fatty amine polyoxyethylene ether; the quaternary ammonium salt cationic surfactant preferably comprises cetyl trimethyl ammonium bromide or stearyl trimethyl ammonium chloride; the mass concentration of the dispersing agent in the sulfur-containing compound aqueous solution is preferably 0.01-1 per mill, the invention preferably uses the substances as the dispersing agent, and controls the concentration of the dispersing agent in the range, so that the sulfur generated in situ is fully dispersed in the solution, the preparation of the two-dimensional layered material/sulfur composite membrane with uniform sulfur dispersion is facilitated, the preparation of the three-dimensional porous material with uniform pore structure is facilitated, and the electrochemical performance of the three-dimensional porous material is improved.
After the sulfur compound aqueous solution is obtained, acid is added into the sulfur compound aqueous solution for reaction, and the nano sulfur particle dispersion liquid is obtained. In the present invention, taking a sulfur-containing compound as an example, the reaction formula of the sodium thiosulfate and the acid is shown in formula 1:
Na2S2O3+2H + ═ 2Na + + S ↓ + SO2 ↓ + H2O formula 1;
in the case of a sulfur-containing compound as sodium polysulfide, the reaction formula of the sodium polysulfide and acid is shown in formula 2:
na2Sx +2H + (2 Na + + H2S ↓ + (x-1) S ↓2.
In the invention, the acid is preferably hydrochloric acid or sulfuric acid, and the mass concentration of the hydrochloric acid or the sulfuric acid is preferably 0.1-6 mol/L, more preferably 1-5 mol/L, and more preferably 2-4 mol/L; according to the invention, the acid is preferably added dropwise, so that sulfur can be slowly and uniformly generated, and the pore structure of the prepared three-dimensional porous material is uniformly distributed, so that the electrochemical performance of the three-dimensional porous material is improved; the dripping speed of the acid is preferably 2-120 drops/min; the present invention preferably adds an excess of acid to enable sufficient reaction of the sulfur-containing compounds; the "excess" is relative to the amount of acid required to completely react the sulfur-containing compounds of formula 1 and formula 2. In the present invention, the time for the reaction of the sulfur-containing compound and the acid is preferably 2 to 120min, and the reaction time is calculated from the time of starting the dropwise addition of the acid.
In the invention, the particle size of the sulfur simple substance in the nano sulfur particle dispersion liquid is preferably 0.1-3 μm, more preferably 0.5-2.5 μm, and even more preferably 0.5-1.5 μm. According to the invention, the size of the pores of the self-supporting three-dimensional porous MXene foam material prepared by controlling the size of the sulfur simple substance is further controlled.
After the nano sulfur particle dispersion liquid is obtained, the pH value of the nano sulfur particle dispersion liquid is adjusted to be neutral, and then the nano sulfur particle dispersion liquid is stirred and mixed with the water dispersion liquid of the two-dimensional layered MXene material to obtain mixed feed liquid.
In the invention, the pH value regulator for regulating the pH value of the nano sulfur particle dispersion liquid to be neutral is preferably alkali, the alkali preferably comprises one or more of sodium hydroxide, potassium hydroxide and ammonia water, and by regulating the pH value of the nano sulfur particle dispersion liquid to be neutral, on one hand, the reaction of a sulfur-containing compound and acid to generate sulfur can be stopped, and on the other hand, the appearance change of the two-dimensional layered MXene material in an acidic solution or the reaction of functional groups in the two-dimensional layered MXene material in the acidic solution can be avoided. In the invention, the mass ratio of the nano sulfur particles to the two-dimensional layered MXene material in the mixed feed liquid is preferably 1: 20-20: 1, more preferably 1: 15-15: 1, more preferably 1: 10-10: 1, and most preferably 1: 4-4: 1. In the invention, the time for stirring and mixing is preferably 5-120 min, more preferably 10-100 min, more preferably 20-80 min, and most preferably 40-60 min, and the rotation speed for stirring and mixing is preferably 100-600 r/min, more preferably 200-500 r/min, and more preferably 300-400 r/min.
In the present invention, the two-dimensional layered MXene material preferably includes one or more of Ti3C2Tx, Ti2CTx, V2CTx, Mo2CTx, Nb4C3Tx, Mo2TiC2Tx, and Mo2Ti2C3 Tx. In the invention, when the two-dimensional layered MXene material is Ti3C2Tx, the preparation method of the Ti3C2Tx is preferably as follows: mixing LiF and concentrated hydrochloric acid, and then mixing with Ti3AlC2 to obtain a mixed solution; and etching the mixed solution at 30-40 ℃ for 20-30 h, washing and centrifuging the product in sequence after the etching is finished, and collecting supernatant to obtain the Ti3C2Tx MXene aqueous solution. The invention has no special requirements on the preparation methods of other two-dimensional layered materials Ti2CTx, V2CTx, Mo2CTx, Nb4C3Tx, Mo2TiC2Tx and Mo2Ti2C3Tx, and the method is known by the technical personnel in the field.
After the mixed material liquid is obtained, the invention carries out reduced pressure suction filtration on the mixed material liquid to obtain the two-dimensional layered material/sulfur composite membrane. In the present invention, the filtration membrane for reduced-pressure filtration is preferably an aqueous microfiltration membrane, an organic microfiltration membrane or a battery separator; the water-based microporous filter membrane preferably comprises a polypropylene filter membrane; the organic microporous filter membrane preferably comprises a polyamide filter membrane, and the battery separator preferably comprises a polypropylene separator, and further preferably comprises a celgard3501 separator. In the two-dimensional layered MXene material/sulfur composite film obtained by the invention, sulfur is distributed in the sheet layer of the two-dimensional layered MXene material. In the invention, the mass ratio of the sulfur particles in the two-dimensional layered MXene/sulfur composite film to the two-dimensional layered MXene is preferably 1: 4-4: 1, and more preferably 1: 3-3: 1.
After the two-dimensional layered MXene/sulfur composite membrane is obtained, the sulfur in the two-dimensional layered MXene/sulfur composite membrane is removed, and the self-supporting three-dimensional porous MXene foam material is obtained.
in the present invention, the method for removing sulfur preferably comprises: heating under protective atmosphere to remove sulfur or removing sulfur by solvent dissolution. In the invention, when the sulfur is removed by a heating method, the heating temperature is preferably 300-700 ℃, more preferably 300-600 ℃, more preferably 300-500 ℃, and most preferably 300-400 ℃; the heating rate for heating to the target temperature is preferably 1-20 ℃/min, more preferably 5-15 ℃/min, and even more preferably 5-10 ℃/min; the heating time is preferably 1-5 h, and more preferably 2-4 h; the protective atmosphere is preferably argon or inert gas, and the gas flux of the protective atmosphere is preferably 50-500 mL/min, more preferably 100-400 mL/min, and even more preferably 200-300 mL/min. According to the invention, sulfur is evaporated through heating treatment, and after the sulfur is removed, the material structure cannot collapse, so that a self-supporting three-dimensional MXene porous structure is formed.
In the present invention, when sulfur is removed by dissolution in a solvent, the solvent preferably includes one or more of carbon disulfide, carbon tetrachloride, chloroform, benzene, and toluene. In the invention, the solvent can dissolve sulfur, but the porous material structure does not collapse, and then a self-supporting three-dimensional porous MXene structure is formed. In the invention, when the sulfur is removed by adopting a solvent dissolving method, the specific process is as follows: and (2) immersing the two-dimensional layered MXene/sulfur composite membrane in a solvent, replacing the solvent after a period of time, repeating the operation of replacing the solvent until the color of the solvent does not turn yellow after the two-dimensional layered MXene/sulfur composite membrane is immersed, taking out the composite material, and freeze-drying to obtain the self-supporting three-dimensional porous MXene foam material. In the invention, the dosage ratio of the two-dimensional layered material/sulfur composite membrane and the solvent is preferably 0.1mg/mL to 20mg/mL, more preferably 0.1mg/mL to 15mg/mL, even more preferably 0.5mg/mL to 10mg/mL, and most preferably 0.5mg/mL to 5mg/mL independently in each immersion process; the temperature of the immersed solvent is preferably 20-60 ℃, more preferably 20-50 ℃, and even more preferably 30-40 ℃; in each immersion process, the immersion time is preferably 10min to 180min, more preferably 10min to 100min, even more preferably 10min to 60min, and most preferably 20min to 40 min. In the invention, when the two-dimensional layered MXene/sulfur composite membrane is immersed in a solvent, sulfur in the composite material can be dissolved in the solvent to turn yellow, the sulfur in the composite material is gradually removed by continuously replacing the solvent, and when the color of the solvent is not turned yellow any more, the sulfur in the composite material is completely removed.
The invention also provides the self-supporting three-dimensional porous MXene foam material prepared by the preparation method in the technical scheme, wherein the pore volume of the self-supporting three-dimensional porous MXene foam material is 0.15-6 cm3/g, the volume density is 0.15-3 g/cm3, and the pore size is 0.05-3 mu m.
The invention also provides application of the self-supporting three-dimensional porous MXene foam material in the technical scheme as an electrode in the electrochemical field and pressure sensors. In the invention, the self-supporting three-dimensional porous MXene foam material can be used as an electrode in lithium ion batteries, sodium ion batteries, potassium ion batteries and super capacitors, and the self-supporting three-dimensional porous MXene foam material can be used as an electrode in pressure sensors. The self-supporting three-dimensional porous MXene foam material provided by the invention has higher capacity and cycle performance as a lithium ion battery cathode material, as shown in an example, after the self-supporting three-dimensional porous MXene foam material is cycled for 300 times under a current density of 50mA/g, the battery capacity is still as high as 314.9mAh/g, and the self-supporting three-dimensional porous MXene foam material can be stably cycled for 3500 times under a capacity of 220mAh/g even under a current density of 1A/g.
The technical solution of the present invention will be clearly and completely described below with reference to the embodiments of the present invention.
Example 1
(1) Synthesis of MXene
0.99g LiF is added into a plastic bottle filled with 10mL concentrated hydrochloric acid, stirred for 5min to dissolve the LiF, then 1g Ti3AlC2 is added, and stirred uniformly. And placing the obtained mixed solution into a constant-temperature water bath kettle at 35 ℃, and stirring and etching for 24 hours. And after the etching reaction, adding water into the product, centrifuging for repeated operation until the pH value of the supernatant is approximately equal to 6, pouring out the supernatant, adding water again, performing ultrasonic treatment for 30min, centrifuging for 1h, and collecting the supernatant to obtain an etched Ti3C2Tx MXene solution, wherein the concentration of the solution is 2.6 mg/mL.
(2) Preparation of porous MXene
The sulfur template is prepared by in-situ reaction of sodium thiosulfate (Na2S2O3 & 5H2O) and hydrochloric acid (HCl), and the specific preparation method comprises the following steps: 0.1g/mL of Na2S2O3 & 5H2O aqueous solution 10mL is prepared, polyvinylpyrrolidone (PVP) is added as a dispersing agent, and the mass concentration of PVP in the sodium thiosulfate aqueous solution is 0.012 per mill. Then, an excess of HCl (3mol/L) was added dropwise to form nano-sulfur particles. After reacting for 40min, NaOH is added to neutralize unreacted HCl, so as to generate stable sulfur dispersion solution, and the size of the sulfur template is about 1.8 mu m. Slowly adding 12.56mg of Ti3C2Tx MXene, uniformly stirring for 10min, vacuum filtering with Celgard3501 membrane (effective radius of filter membrane is 2cm) to obtain self-supporting MXene/sulfur composite membrane, vacuum drying, and weighing. The composite membrane is placed in a tube furnace, the composite membrane is treated for 3 hours under the protection of argon gas at the temperature of 300 ℃ (the temperature rise speed is 5 ℃/min, the Ar flux is 200 mL/min), the sulfur template is removed, the obtained flexible self-supporting membrane is three-dimensional porous Ti3C2Tx MXene foam, the mass ratio of the sulfur template to the two-dimensional layered MXene material is 1:2 according to the mass of the materials before and after the sulfur template is removed through testing, and the three-dimensional porous MXene foam is named as PMF-33.
the shape test is carried out on the three-dimensional porous MXene foam material PMF-33 prepared in example 1, a scanning electron microscope image is shown in figure 1, and as shown in figure 1, the PMF-33 is a developed porous layered membrane structure and has an independent self-supporting foam structure, so that dense stacking of MXene nanosheets is well inhibited, and lithium storage active sites on the MXene surface are improved. Mercury intrusion test example 1 three-dimensional porous MXene foam PMF-50 had a pore volume of 1.91cm 3/g.
the electrochemical performance of the three-dimensional porous MXene foam material PMF-33 prepared in example 1 was tested. A three-dimensional porous MXene foam material PMF-33 is used as a negative electrode material of a lithium ion battery, a glass fiber diaphragm is adopted, an electrolyte is an Ethylene Carbonate (EC)/diethyl carbonate (DEC) (V/V is 1:1) solution added with 1mol/L lithium hexafluorophosphate (LiPF6), and the battery is assembled in a glove box filled with high-purity argon. The result of constant current charge and discharge test (voltage range 0.01-3V) is shown in FIG. 2, and it can be seen from FIG. 2 that after the battery is cycled for 300 times under the current density of 50mA/g, the battery capacity is still as high as 182.8 mAh/g; as shown in FIG. 3, the results of the rate capability test show that FIG. 3 shows a capacity of 106.8mAh/g at a current density of 1A/g, and the capacity still remains 31.6mAh/g at a current density of 18A/g.
Example 2
(1) Synthesis of MXene
0.99g LiF is added into a plastic bottle filled with 10mL concentrated hydrochloric acid, stirred for 5min to dissolve the LiF, then 1g Ti3AlC2 is added, and stirred uniformly. And placing the obtained mixed solution into a constant-temperature water bath kettle at 35 ℃, and stirring and etching for 24 hours. And after the etching reaction, adding water into the product, centrifuging for repeated operation until the pH value of the supernatant is approximately equal to 6, pouring out the supernatant, adding water again, performing ultrasonic treatment for 30min, centrifuging for 1h, and collecting the supernatant to obtain an etched Ti3C2Tx MXene solution, wherein the concentration of the solution is 2.6 mg/mL.
(2) Preparation of porous MXene
The sulfur template is prepared by in-situ reaction of sodium thiosulfate (Na2S2O3 & 5H2O) and hydrochloric acid (HCl), and the specific preparation method comprises the following steps: preparing 24mL of Na2S2O3 & 5H2O aqueous solution with the concentration of 0.1g/mL, adding PVP as a dispersing agent, and controlling the mass concentration of PVP in the sodium thiosulfate aqueous solution to be 0.012 per thousand. Then, an excess of HCl (3mol/L) was added dropwise to form nano-sulfur particles. After reacting for 40min, NaOH is added to neutralize unreacted HCl, so as to generate stable sulfur dispersion solution, and the size of the sulfur template is about 1.8 mu m. Slowly adding 12.56mg of Ti3C2Tx MXene, uniformly stirring for 10min, vacuum filtering with Celgard3501 membrane (effective radius of filter membrane is 2cm) to obtain self-supporting MXene/sulfur composite membrane, vacuum drying, and weighing. The composite membrane is placed in a tube furnace, the composite membrane is treated for 3 hours under the protection of argon at the temperature of 300 ℃ (the temperature rise speed is 5 ℃/min, the Ar flux is 200 mL/min), the sulfur template is removed, the obtained flexible self-supporting membrane is three-dimensional porous Ti3C2Tx MXene foam, the mass ratio of the sulfur template to the two-dimensional layered MXene material is 1:1 according to the mass of the materials before and after the sulfur template is removed through testing, and the three-dimensional porous MXene foam is named as PMF-50.
The shape test is carried out on the three-dimensional porous MXene foam material PMF-50 prepared in the embodiment 2, a scanning electron microscope image is shown in fig. 4, and as shown in fig. 4, the PMF-50 is a developed porous layered membrane structure and has an independent self-supporting foam structure, so that dense stacking of MXene nanosheets is well inhibited, and lithium storage active sites on the MXene surface are improved. Mercury intrusion test example 2 three-dimensional porous MXene foam PMF-50 had a pore volume of 2.53cm 3/g.
the electrochemical performance of the three-dimensional porous MXene foam material PMF-50 prepared in example 2 was tested. A three-dimensional porous MXene foam material PMF-50 is used as a lithium ion battery cathode material, a glass fiber diaphragm is adopted, an electrolyte is an Ethylene Carbonate (EC)/diethyl carbonate (DEC) (V/V is 1:1) solution added with 1mol/L lithium hexafluorophosphate (LiPF6), and the battery is assembled in a glove box filled with high-purity argon. The result of constant current charge and discharge test (voltage range 0.01-3V) is shown in FIG. 5, and it can be seen from FIG. 5 that the battery capacity is still 209.7mAh/g after circulating 300 times under the current density of 50 mA/g; as shown in FIG. 6, it can be seen from FIG. 6 that the capacity of 133.5mAh/g was exhibited at a current density of 1A/g, and the capacity of 33.6mAh/g was maintained at a current density of 18A/g.
Example 3
(1) synthesis of MXene
0.99g LiF is added into a plastic bottle filled with 10mL concentrated hydrochloric acid, stirred for 5min to dissolve the LiF, then 1g Ti3AlC2 is added, and stirred uniformly. And placing the obtained mixed solution into a constant-temperature water bath kettle at 35 ℃, and stirring and etching for 24 hours. And after the etching reaction, adding water into the product, centrifuging for repeated operation until the pH value of the supernatant is approximately equal to 6, pouring out the supernatant, adding water again, performing ultrasonic treatment for 30min, centrifuging for 1h, and collecting the supernatant to obtain an etched Ti3C2Tx MXene solution, wherein the concentration of the solution is 2.6 mg/mL.
(2) Preparation of porous MXene
The sulfur template is prepared by in-situ reaction of Na2S2O3 & 5H2O and HCl, and the preparation method specifically comprises the following steps: 0.1g/mL of Na2S2O3 & 5H2O aqueous solution 64mL is prepared, PVP is added as a dispersing agent, and the mass concentration of the PVP in the sodium thiosulfate aqueous solution is 0.012 per thousand. Then, an excess of HCl (3mol/L) was added dropwise to form nano-sulfur particles. After reacting for 40min, NaOH is added to neutralize unreacted HCl, so as to generate a stable sulfur dispersion solution, and the size of sulfur particles is about 1.5 mu m. Slowly adding 12.56mg MXene, uniformly stirring for 10min, vacuum filtering with Celgard3501 membrane (effective radius of filter membrane is 2cm) to obtain self-supporting MXene/sulfur composite membrane, vacuum drying, and weighing. The composite membrane is placed in a tube furnace, the composite membrane is treated for 3 hours under the protection of argon gas at the temperature of 300 ℃ (the temperature rise speed is 5 ℃/min, the heating flux is 200 mL/minAr), the sulfur template is removed, the obtained flexible self-supporting membrane is three-dimensional porous Ti3C2Tx MXene foam, the mass ratio of the sulfur template to the two-dimensional layered MXene material is 7:3 according to the mass of the material before and after the sulfur template is removed through testing, and the three-dimensional porous MXene foam is named as PMF-70.
The three-dimensional porous MXene foam material PMF-70 prepared in example 3 is subjected to morphology test, a scanning electron microscope image is shown in fig. 7 and fig. 8, as can be seen from fig. 1, fig. 4 and fig. 7, the porous structure becomes developed along with the increase of the sulfur template content, and the pore volume of the three-dimensional porous MXene foam material in example 3 is 4.34cm3/g and is higher than that of the foam materials in examples 1 and 2 through mercury intrusion method test, meanwhile, the flexible self-supporting foam structure is maintained, the dense stacking of MXene nanosheets is inhibited, and the specific surface area and lithium storage active sites of MXene are improved.
The electrochemical performance of the three-dimensional porous MXene foam material PMF-70 prepared in example 3 was tested. A three-dimensional porous MXene foam PMF-70 is used as a negative electrode material, a glass fiber diaphragm is adopted, an electrolyte is an EC/DEC (V/V is 1:1) solution added with 1mol/L LiPF6, and the battery is assembled in a glove box filled with high-purity argon. The results of constant current charge and discharge tests (voltage range of 0.01-3V vs Li/Li +) are shown in FIG. 9, and it can be seen from FIG. 9 that after the battery is cycled for 300 times under a current density of 50mA/g, the battery capacity is as high as 314.9 mAh/g; the cycle performance is shown in FIG. 10. from FIG. 10, it can be seen that the battery capacity is up to 220mAh/g after 3500 cycles at a current density of 1A/g; as shown in FIG. 11, it can be seen from FIG. 11 that the capacity is still as high as 101mAh/g at a current density of 18A/g.
The pressure sensing performance of the three-dimensional porous MXene foam material PMF-70 prepared in example 3 is tested by the following test method: fixing the three-dimensional porous MXene foam material PMF-70 between two polylactic acid films by using double faced adhesive tape to ensure the flexibility of the electrode, connecting the PMF-70 with an electrochemical workstation through a copper wire, and placing the prepared electrode on a force measuring platform for measuring and carrying out real-time sensing recording. The current change curves of the sensor under different pressures are shown in FIG. 12, and it can be seen from FIG. 12 that the three-dimensional porous MXene foam material shows stable pressure response under the pressures of 70Pa to 9200Pa, the value of delta I/I0 is gradually increased along with the increase of the pressure, and the value of delta I/I0 is 9.2 at 9200 Pa.
Comparative example 1
The experiment was performed in the manner of example 1, except that no dispersant was added during the preparation of sulfur, sulfur particles in the prepared sulfur dispersion gradually grow up and agglomerate, the size of sulfur is not uniform, and the pore size distribution of the obtained three-dimensional porous MXene material is not uniform.
In conclusion, the invention provides a method for converting a two-dimensional layered material into a three-dimensional porous material, which is simple and easy to operate. The method provided by the invention effectively inhibits the stacking of two-dimensional layered materials and promotes the transmission of interlayer ions; the method provided by the invention can fully expose the active sites in the layered material, and is favorable for improving the activity of the material.
The foregoing is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, various modifications and decorations can be made without departing from the principle of the present invention, and these modifications and decorations should also be regarded as the protection scope of the present invention.
Claims (10)
1. the preparation method of the self-supporting three-dimensional porous MXene foam material is characterized by comprising the following steps of:
(1) mixing a sulfur-containing compound, a dispersant and water to obtain a sulfur-containing compound aqueous solution;
(2) Adding acid into the aqueous solution of the sulfur-containing compound to react to obtain nano sulfur particle dispersion liquid;
(3) adjusting the pH value of the nano sulfur particle dispersion liquid to be neutral, and then stirring and mixing the nano sulfur particle dispersion liquid and the aqueous dispersion liquid of the two-dimensional layered MXene material to obtain mixed feed liquid;
(4) Carrying out reduced pressure suction filtration on the mixed feed liquid to obtain a two-dimensional layered MXene/sulfur composite membrane;
(5) and removing sulfur in the two-dimensional layered MXene/sulfur composite membrane to obtain the self-supporting three-dimensional porous MXene foam material.
2. the preparation method according to claim 1, wherein the dispersing agent in step (1) comprises one or a mixture of two or more of polyvinylpyrrolidone, polyoxyethylene type nonionic surfactant, polyol type nonionic surfactant, alkanolamide type nonionic surfactant, polyether type nonionic surfactant, amine oxide type nonionic surfactant, amine salt type cationic surfactant, quaternary ammonium salt type cationic surfactant, heterocyclic type cationic surfactant and xanthate type cationic surfactant; the mass concentration of the dispersing agent in the sulfur-containing compound aqueous solution is 0.01-1 per mill.
3. the method according to claim 1, wherein the sulfur-containing compound in the step (1) comprises thiosulfate and/or polysulfide; the mass concentration of the sulfur-containing compound in the sulfur-containing compound aqueous solution is 0.01-2 g/mL.
4. the preparation method according to claim 1, wherein the pH adjusting agent for adjusting the pH of the nano-sulfur particle dispersion to neutral in the step (3) is a base, and the base comprises one or more of sodium hydroxide, potassium hydroxide and ammonia water.
5. The preparation method according to claim 1, wherein the mass ratio of the nano sulfur particles in the mixed feed liquid in the step (3) to the two-dimensional layered MXene material is 1: 20-20: 1.
6. The preparation method according to claim 1 or 5, wherein the two-dimensional layered MXene material comprises one or more of Ti3C2Tx, Ti2CTx, V2CTx, Mo2CTx, Nb4C3Tx, Mo2TiC2Tx and Mo2Ti2C3 Tx.
7. The production method according to claim 1, wherein the filter membrane used in the reduced-pressure suction filtration in the step (4) is an aqueous microporous filter membrane, an organic microporous filter membrane, or a battery separator.
8. the method of claim 1, wherein the step (5) of removing sulfur comprises: heating under protective atmosphere to remove sulfur or adopting a solvent dissolving method to remove sulfur; when the removing is carried out by adopting a heating method, the heating temperature is 300-700 ℃; when sulfur is removed by solvent dissolution, the solvent comprises one or more of carbon disulfide, carbon tetrachloride, chloroform, benzene, and toluene.
9. The self-supporting three-dimensional porous MXene foam material prepared by the preparation method of any one of claims 1 to 8, wherein the self-supporting three-dimensional porous MXene foam material is of a self-supporting structure, the pore volume is 0.15-6 cm3/g, and the pore diameter is 0.05-3 μm.
10. Use of the self-supporting three-dimensional porous MXene foam material of claim 9 as an electrode in the electrochemical field and in the pressure sensing field.
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