CN114792797A - Preparation method of sulfydryl modified MXene-sulfur composite material and lithium-sulfur battery thereof - Google Patents
Preparation method of sulfydryl modified MXene-sulfur composite material and lithium-sulfur battery thereof Download PDFInfo
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Abstract
The invention relates to a preparation method of a sulfydryl modified MXene-sulfur composite material and a lithium-sulfur battery thereof, belonging to the technical field of material chemistry. With MAX-Ti 3 AlC 2 The two-dimensional MXene material is used as a raw material and is obtained by a chemical etching method. And dissolving low-cost cysteamine hydrochloride into the MXene water dispersion, and preparing the MXene modified by sulfydryl by adopting a one-step hydrothermal reaction method. And finally, bonding sulfur molecules with the modified sulfydryl on MXene at high temperature to obtain the sulfydryl modified MXene-sulfur composite material serving as the positive electrode of the lithium-sulfur battery. The sulfydryl modified MXene and the original MXene have excellent conductivity, but the interlayer spacing of the MXene is increased, so that more active sites and functional groups are exposed, and capture of polysulfide is facilitated. In addition, the sulfur atoms forming chemical bonds tend to form low-order polysulfides during charge and discharge, which is more beneficial to reduce the dissolution of polysulfides in the electrolyte and reduce the dissolution of polysulfides in the electrolyteLess loss of the active substance sulfur. Therefore, the battery has high specific discharge capacity and good cycle performance.
Description
Technical Field
The invention relates to a preparation method of a sulfydryl modified MXene-sulfur composite material and a lithium-sulfur battery thereof, belonging to the technical field of material chemistry.
Background
The lithium ion secondary battery is the first choice for various electronic product power sources because of its characteristics of high energy density, high operating voltage, long cycle performance and no memory effect. Nowadays, due to the high popularity of electric vehicles and the rapid growth of consumer electronics in daily life, energy storage devices with higher and higher energy densities are required. The conventional lithium ion secondary battery is increasingly difficult to meet the requirements due to the theoretical specific capacity limitation. The theoretical specific capacity of the lithium-sulfur battery is up to 1675mAh/g, and the lithium-sulfur battery has high energy density 2600 Wh/kg. In addition, the sulfur with abundant resources, low price, environmental protection and low toxicity make the secondary battery system with high energy density popular.
However, the positive electrode material of the lithium-sulfur battery has some disadvantages. Firstly, elemental sulfur and lithium sulfide, a discharge product, have poor conductivity, so that the reaction efficiency of the electrode is low, and the utilization rate of sulfur, an active material, is low. Second, the charging and discharging processes of lithium-sulfur batteries are different from those of lithium-ion batteries in that the cyclic S8 molecules form soluble and insoluble lithium polysulfides, which dissolve and migrate in the electrolyte solution to form a "shuttle" effect. This results in a loss of sulfur as an active material, resulting in a short battery life. Finally, during the conversion of sulfur to lithium sulfide, the electrode expands by about 80% in volume, and repeated volume scaling during charging and discharging collapses the electrode, resulting in a reduction in capacity. These have limited commercial applications of lithium sulfur batteries.
Therefore, researchers have devised a number of solutions to overcome these drawbacks. A two-dimensional crystal material MXene with a layered graphene-like structure is concerned by most students in recent years. The main component of the material is titanium carbide, which is obtained by etching off IIIA/IVA elements in MAX phase of a precursor by using strong acid by using a chemical liquid phase method, and has excellent conductivity and capability of capturing lithium polysulfide. However, due to strong surface functional group interaction, the prepared MXene still cannot be uniformly dispersed in a form of a single-layer sheet, and the MXene is easy to stack and agglomerate, so that the specific surface area is greatly reduced, and the application of the MXene to the electrode material of the lithium-sulfur battery is limited.
Therefore, it is an object of the present invention to solve the above-mentioned drawbacks of the prior art and to solve the MXene modification method.
Disclosure of Invention
The invention aims to provide a preparation method of a sulfydryl modified MXene-sulfur composite material.
The invention also aims to provide a lithium-sulfur battery applying the mercapto-modified MXene-sulfur composite material.
In order to achieve the purpose, the invention provides the following technical scheme: a preparation method of a sulfydryl modified MXene-sulfur composite material comprises the following steps:
preparing sheet MXene, preparing sulfydryl modified Mxene and preparing a sulfydryl modified MXene-sulfur composite material;
the preparation method of the flaky MXene comprises the following steps:
s1, adding lithium fluoride into 20-37 wt% hydrochloric acid, and adding 1.5-3.5g of lithium fluoride into every 40mL of hydrochloric acid; stirring at the rotation speed of 250-600rpm for 20-45min to obtain a reaction solution A, wherein the lithium fluoride and the hydrochloric acid generate hydrogen fluoride;
s2, mixing MAX-Ti 3 AlC 2 Slowly adding the MAX-Ti into the reaction solution A 3 AlC 2 And the lithium fluoride in a mass ratio of 1: 0.5-2; continuously stirring for 12-36h at 30-45 ℃ to obtain a reaction solution B, wherein the MAX-Ti is 3 AlC 2 Etching with the reaction solution A to form Ti 3 C 2 ；
S3, centrifuging the reaction solution B at the rotation speed of 3500-9000rpm, removing the supernatant, retaining the precipitate A, adding deionized water into the precipitate A, fully shaking up, performing ultrasonic treatment for 15-25min to uniformly disperse the precipitate A, repeating the operation for 4-6 times, and collecting the cleaned precipitate B; wherein, in the step S1, 25-100mL of the deionized water is required to be added for every 40mL of hydrochloric acid used;
s4, adding ethanol into the precipitate B, fully shaking up, performing ultrasonic treatment for 1-3h, centrifuging at the rotation speed of 8000-10000rpm, and collecting the precipitate C, wherein 25-100mL of ethanol is required to be added when 40mL of hydrochloric acid is used in the step S1; freeze-drying the precipitate C at-40 to-60 ℃ for 24 to 48 hours to obtain flake MXene;
the preparation method of the mercapto-modified MXene comprises the following steps:
s5, preparing the flaky MXene into MXene dispersion liquid with the concentration of 0.5-2 mg/mL;
s6, taking 100mL of MXene dispersion liquid, adding 0.4-2g of cysteamine hydrochloride, simultaneously adding 0.4-2mL of ammonia water, and stirring to form a mixed solution A;
s7, placing the mixed solution A in a muffle furnace, and carrying out hydrothermal reaction at 90 ℃ for 3-12h to form a mixed solution B;
s8, filtering, washing and freeze-drying the mixed solution B to obtain sulfydryl modified MXene;
the preparation method of the sulfydryl modified MXene-sulfur composite material comprises the following steps:
s9, grinding and mixing the mercapto-modified MXene and the elemental sulfur in a mass ratio of 1:2-4 to obtain a reactant A; then placing the reactant A into a reaction kettle and filling argon, heating the reactant A to 160-200 ℃ in a muffle furnace and keeping the temperature for 7-12h, heating the reactant A to 230-250 ℃ and keeping the temperature for 1-3h, and naturally cooling the reactant A to room temperature to obtain a reactant B;
s10, heating the reactant B to 160 ℃ at a heating rate of 10 ℃/min under an argon atmosphere, and keeping the temperature for 2-5h to obtain the mercapto-modified MXene-sulfur composite material.
Further, the ultrasonic treatment in the step S7 and the step S8 uses 35-50KHz of frequency and 600-800W of ultrasonic power.
Further, the flaky MXene prepared in the step S4 is flaky MXene fluffy powder with few layers.
Further, the freeze-drying process in step S8 is drying for 12-48h at-40 to-60 ℃ in a freeze dryer.
Further, the number of water washes in step S8 is 2 to 5.
The invention also provides a lithium-sulfur battery using the sulfhydryl-modified MXene-sulfur composite material prepared by any one of the preparation methods. The technical scheme is as follows: the thiol-modified MXene-sulfur composite material prepared by the preparation method of the thiol-modified MXene-sulfur composite material is used as a positive electrode material for a lithium-sulfur battery, and the positive electrode is prepared by the following steps:
and (3) preparing the cathode material: acetylene black: and mixing the binder at a mass ratio of 8:1:1, adding N-methylpyrrolidone as a solvent, grinding into slurry, uniformly coating on an aluminum foil current collector to prepare an electrode, and drying in a vacuum environment at 50-75 ℃ for 8-24 hours to prepare the anode.
Further, the lithium sulfur battery also comprises a cathode, and the preparation of the cathode comprises the following steps:
a lithium sheet is used as a negative electrode material, wherein 1M lithium bistrifluoromethanesulfonylimide electrolyte is dissolved in 1, 3-dioxolane and ethylene glycol dimethyl ether according to the volume ratio of 1:1, and the mass ratio of the 1, 3-dioxolane to the ethylene glycol dimethyl ether is 1: 0.4-2.
Further, the positive electrode and the negative electrode were assembled in a glove box in an inert gas atmosphere to obtain the lithium sulfur battery.
Further, the sulfur carrying amount of the coating film is 1-2mg/cm 2 。
The technical scheme I of the invention has the beneficial effects that:
1. according to the invention, the cysteamine hydrochloride is selected as a raw material, is dissolved in MXene aqueous dispersion, and is prepared into the mercapto-modified MXene by adopting a one-step hydrothermal reaction method, so that the experimental steps are simple and easy to operate. Both the mercapto-modified MXene and the original MXene have good conductivity and strong polysulfide trapping capacity. Compared with the prior art, the mercapto-modified MXene has a fluffy porous structure and a high specific surface area, is not easy to stack and can better exert the advantages of the mercapto-modified MXene. The sulfydryl modified MXene has high specific surface area, and is favorable for improving the utilization rate of active substance sulfur and improving the specific capacity after being compounded with sulfur.
2. According to the technical scheme, in the melting step, a heating process different from the traditional direct melting at 155 ℃ is adopted, and the temperature is higher, so that the bonding reaction between the broken bonds of sulfur molecules and MXene functional groups occurs. Different from the traditional melting process, sulfur particles with the size of 1-5 microns can be formed when the elemental sulfur and MXene are melted and mixed, the full utilization of active substance sulfur is not facilitated, and the performance of the battery is poor. In the patent, sulfydryl modified MXene and sulfur complex cannot be agglomerated into large particles after being melted, so that the generated composite material also has higher specific surface area.
The second technical scheme of the invention has the beneficial effects that:
1. the invention adopts the sulfydryl modified MXene-sulfur composite material as the anode of the lithium-sulfur battery, can increase the interlayer spacing of MXene, improve the specific surface area and increase the porosity, thereby exposing more surface active sites and functional groups, increasing the ion transmission channel and realizing Li + The effective de-intercalation. Meanwhile, the mercapto-modified MXene is in a porous and fluffy structure after being freeze-dried, and is not easy to stack compared with the original MXene. The lithium-sulfur ion battery anode material is used as a lithium-sulfur ion battery anode material, so that the utilization rate of active substance sulfur is increased, the specific capacity of the battery is improved, and the cycling stability of the battery is kept.
2. In this patent, sulfur (S) is formed after bonding of sulfur to mercapto-modified MXene 8 ) The chemical bond of the molecule to the thiol group in a way that bonds the sulfur to MXene more fully than the physical contact of simple conventional melt techniques. The sulfur element forming chemical bond with MXene is not easy to generate high-order polysulfide (Li) in the process of charging and discharging the battery 2 S n ,n>4) Tend to form low-order polysulfides (Li) 2 S n N is less than or equal to 4). And the high-order polysulfide which is dissolved in the electrolyte and easily causes the loss of active substances is high-order polysulfide, so the composite material can also greatly reduce the loss of the active substances sulfur by controlling the generated species besides capturing the polysulfide per se, thereby greatly improving the cycle performance. This also allows a higher utilization of the active substance sulfur.
The foregoing description is only an overview of the technical solutions of the present invention, and in order to make the technical solutions of the present invention more clearly understood and to make the technical solutions of the present invention practical in accordance with the contents of the specification, the following detailed description is given of preferred embodiments of the present invention with reference to the accompanying drawings.
Drawings
FIG. 1 is a SEM image of various materials of example one, wherein (a, d) is MXene, (b, e) is mercapto-modified MXene, and (c, f) is mercapto-modified MXene-sulfur.
FIG. 2 is an FE-SEM image and element scan image of thiol-modified MXene of example one, wherein (a) is thiol-modified MXene, and (b-f) is element scan image.
Fig. 3 is a graph of cycle performance of different composite electrode batteries according to different embodiments of the present invention, where (a) is 0.1C low current density, and (b) is rate performance.
Detailed Description
The following detailed description of the present invention is provided in connection with the accompanying drawings and examples. The following examples are intended to illustrate the invention, but are not intended to limit the scope of the invention.
The present disclosure will be described in detail and with reference to the drawings, and it is to be understood that various changes and modifications can be made by those skilled in the art without departing from the spirit and scope of the present disclosure.
As used herein, the terms "comprising," "including," "having," and the like are open-ended terms that mean including but not limited to.
As used herein, the term (terms), unless otherwise indicated, shall generally have the ordinary meaning as commonly understood by one of ordinary skill in the art, in this application, and in the special art. Certain terms used to describe the disclosure are discussed below or elsewhere in this specification to provide additional guidance to those skilled in the art in describing the disclosure.
Example one (a): a preparation method of a mercapto-modified MXene-sulfur composite material comprises the following steps of preparation of flaky MXene, preparation of mercapto-modified MXene and preparation of the mercapto-modified MXene-sulfur composite material:
preparation of mono-sheet MXene
1-1, adding 2g of lithium fluoride into 40mL of 12M hydrochloric acid, and stirring at the rotation speed of 400rpm for 30min to obtain a reaction liquid A, so that the lithium fluoride and the hydrochloric acid are fully reacted to generate HF;
1-2 g of MAX-Ti 3 AlC 2 Slowly adding into the reaction solution A, wherein MAX-Ti is 3 AlC 2 The mass of (2 g); then adjusting the reaction temperature to 35 ℃, and continuously stirring for 24 hours to obtain reaction liquid B, so that MAX-Ti is obtained 3 AlC 2 Al in the Ti is fully etched to obtain Ti 3 C 2 ；
1-3, centrifuging the reaction solution B at the rotating speed of 5000rpm, removing a supernatant after centrifugation, retaining the precipitate A, adding 20mL of deionized water into the precipitate A, and fully shaking up to uniformly mix the precipitate and the deionized water; then ultrasonic treatment is carried out for 25 minutes, so that the precipitate is uniformly dispersed in the solution again; finally, continuously centrifuging the solution, repeating the step for 6 times to clean the hydrogen fluoride, and collecting the last precipitate B;
1-4, adding 20mL of ethanol into the precipitate B, and fully shaking up; carrying out ultrasonic treatment for 1.5h to realize intercalation operation of MXene (namely, fully dispersing the MXene into a single-layer sheet structure), and further obtaining a few-layer MXene dispersion liquid; then centrifuging at 10000rpm, fully collecting precipitate B, and finally freeze-drying at-40 to-60 ℃ for 36h to obtain flake MXene.
In this example, MXene was obtained as a flake-like MXene fluffy powder with few layers.
It should be noted that, every time 40mL of hydrochloric acid is used in the step 1-1, 20-120mL of deionized water is needed in the step 1-3, and the proper dosage of deionized water is added according to the dosage of the hydrochloric acid actually used; in the steps 1-4, 20-120mL of ethanol needs to be added, and the proper ethanol dosage is added according to the actually used hydrochloric acid dosage.
As mentioned above, the frequency used for the ultrasonic treatment in the steps 1-3 and 1-4 is 35-50KHz, and the ultrasonic power is 600- & gt 800W.
Preparation of bis-mercapto modified MXene
2-1, adding the flaky MXene prepared in the step 1-4 into deionized water to prepare 1mg/mL MXene dispersion liquid;
2-2, taking 100mL of MXene dispersion liquid obtained in the step 2-1, adding 500mg of cysteamine hydrochloride and 0.5mL of ammonia water, and uniformly stirring to obtain a mixed solution A;
2-3, placing the mixed solution A in a muffle furnace, and carrying out hydrothermal reaction at 90 ℃ for 6 hours to obtain a mixed solution B;
2-4, filtering the mixed solution B, washing with water for 5 times, and drying in a freeze dryer at the temperature of-40 ℃ for 12 hours to obtain the porous sulfydryl modified MXene.
It should be noted that the freeze-drying process in step 2-4 is drying in a freeze-dryer at-40 to-60 deg.C for 12-48h, and the number of water washes in step 2-4 is 2-5.
Preparation of tri-mercapto modified MXene-sulfur composite material
3-1, mixing the freeze-dried powder of the sulfydryl modified MXene prepared in the step 2-4 with a sulfur simple substance in a mass ratio of 1: 3 grinding and mixing to obtain a reactant A;
3-2, filling argon into the reactant A, putting the reactant A into a reaction kettle, heating the reactant A in a muffle furnace at 185 ℃ for 10 hours, and heating the reactant A to 245 ℃ for 2 hours to excite elemental sulfur (S) 8 ) The ring-opening polymerization reaction of (3) bonds elementary sulfur to the functional group of MXene to form a chemical bond. After heating, naturally cooling to room temperature to obtain a reactant B;
3-3, heating the reactant B to 155 ℃ at a heating rate of 10 ℃/min in an argon introducing environment, and keeping for 3h to remove residual elemental sulfur, thereby obtaining the mercapto-modified MXene-sulfur composite material.
Please refer to fig. 1, which is a SEM image of various materials of the first embodiment, wherein (a, d) is flake MXene, (b, e) is mercapto-modified MXene, and (c, f) is mercapto-modified MXene-sulfur composite.
As can be seen from the figures (a, d), simple MXene has a lamellar shape, and the lamellar shape is smooth, and the size of the lamellar structure is large and is about several micrometers.
As can be seen from the graphs (b, e), the mercapto-modified MXene still maintains the original lamellar shape, but the lamellar shape is wrinkled, and a lamellar structure with small size is partially formed. This is because a great deal of mercapto functional groups are introduced in the process of modifying MXene, and element doping is also carried out. Thus forming a porous pleated morphology, obtaining a high specific surface area.
Unlike the conventional physical melting method of growing elemental sulfur at 155 degrees, the high temperature melting process mentioned in the patent in preparation step 3-2 forms chemical bonds. Therefore, as can be seen from the graphs (c, f), unlike the conventional physical melting method which can form agglomerated large particles of several micrometers, a certain flake-like morphology of the mercapto-modified MXene layer can be observed in the mercapto-modified MXene-sulfur composite material, but not a completely agglomerated large particle morphology. The form also has a certain porosity, and the specific surface area is kept high. This is beneficial to the high utilization rate of the active substance sulfur and the exertion of the sulfydryl modified MXene conductivity.
As shown in fig. 2, it is the FE-SEM images and the mapping images of the corresponding elements of the thiol-modified MXene in example one, wherein (a) is the FE-SEM image of the thiol-modified MXene (b-f) is the mapping image of the S, N, C, Ti and O elements, respectively.
As can be seen from FIG. (a), the thiol-modified MXene has a more clear platelet-layered structure. As can be seen from the graphs (b, c), the existence of the thiol S element doped by cysteamine hydrochloride and the N element uniformly distributed on the molecule indicates that the doping is successful, but the signal is weak because the content is not much. As can be seen from the graphs (d, e, f), the uniform distribution signals of the main components C and Ti of MXene are strong, and the existence of the O element is due to the existence of other oxygen-containing functional groups.
Example one (B): lithium-sulfur battery applying sulfydryl modified Xmene-sulfur composite material
The sulfydryl modified MXene-sulfur composite material prepared in the step 3-3 is applied to a positive electrode as a positive electrode material, and the positive electrode manufacturing step comprises the following steps:
according to the positive electrode material: acetylene black (super-P): binder (PVDF) 8:1:1 to form a mixture, adding N-methylpyrrolidone (NMP) as a solvent, wherein the mass ratio of the solvent to the mixture is (10-25): 1, grinding into slurry, then uniformly coating to prepare an electrode, and drying for 12 hours in a vacuum environment at the temperature of 60 ℃ to prepare the anode.
Taking a lithium sheet as a negative electrode, wherein electrolyte is 1M lithium bistrifluoromethanesulfonylimide which is dissolved in 1, 3-dioxolane and ethylene glycol dimethyl ether according to the volume ratio of 1:1, wherein the mass ratio of 1, 3-dioxolane to ethylene glycol dimethyl ether is 1: 0.4 to 2.
Preferably, the sulfur carrying amount of the coating film is 1-2mg/cm 2 。
Preferably, the respective components of the positive electrode and the negative electrode are assembled in a glove box with an inert gas (e.g., argon) atmosphere to obtain a lithium sulfur battery.
The invention adopts the sulfydryl modified MXene-sulfur composite material as the anode of the lithium-sulfur battery, can increase the interlayer spacing of MXene, improve the specific surface area and increase the porosity, thereby exposing more surface active sites and functional groups, increasing the ion transmission channel and realizing Li + The effective de-intercalation. Meanwhile, the mercapto-modified MXene is in a porous and fluffy structure after being freeze-dried, and is not easy to stack compared with the original MXene. The lithium-sulfur ion battery anode material is used as a lithium-sulfur ion battery anode material, so that the utilization rate of active substance sulfur is increased, the specific capacity of the battery is improved, and the cycling stability of the battery is kept.
In order to illustrate the advantages and effects of the technical solutions of the present invention, in addition to the first embodiment, the applicant makes second, third and fourth embodiments different from the first embodiment, thereby intuitively reflecting the effect differences among different solutions through different experimental data.
Example two (a):
after the preparation of flaky MXene is finished, the preparation of sulfydryl modified MXene is carried out by different preparation methods which comprise the following steps: and (3) taking 100ml of MXene dispersion liquid in the step 2-1, adding 1000mg of cysteamine hydrochloride and 1ml of ammonia water at the same time, and uniformly stirring.
Example three (a):
after the preparation of flaky MXene is finished, the preparation of sulfydryl modified MXene is carried out by different preparation methods which comprise the following steps: and (3) taking 100ml of MXene dispersion liquid in the step 2-1, adding 1500mg of cysteamine hydrochloride and simultaneously adding 1.5ml of ammonia water, and uniformly stirring.
Example four (a):
after the preparation of flaky MXene is finished, the preparation of sulfydryl modified MXene is carried out by different preparation methods which comprise the following steps: and (3) taking 100ml of MXene dispersion liquid in the step 2-1, adding 2000mg of cysteamine hydrochloride and simultaneously adding 2ml of ammonia water, and uniformly stirring.
Results referring to fig. 3, a graph of cycling performance of different composite electrode cells for lithium sulfur cells using mercapto-modified MXene-sulfur composites prepared in examples one (a) to four (a) where (a) is 0.1C low current density and (b) is rate capability.
Wherein, the S-MXene SH 5, the S-MXene SH 10, the S-MXene SH 15 and the S-MXene SH 20 are sulfhydryl modified MXene-sulfur composite materials, and the mass of the added cysteamine hydrochloride is 5, 10, 15 and 20 times of that of MXene.
As can be seen from the graph (a), the batteries of four different mercapto-modified MXene-sulfur electrode materials have high coulombic efficiencies of more than 98% basically in the cyclic charge-discharge test at a low current density of 0.1C, but have different specific capacities. S-MXene SH 15, namely adding 15 times of cysteamine hydrochloride when modifying MXene, shows the highest initial discharge specific capacity of 1387.8mAh/g, and still maintains 810.4mAh/g after 100 cycles, which shows that the addition amount of the cysteamine hydrochloride plays the best role in modifying and doping the MXene, and the final composite material has the highest utilization rate of active substance sulfur and stronger capability of capturing polysulfide, so that the cycle stability is good. As can be seen from the graph (b), the rate performance of the MXene-sulfur electrode material is optimized for four different thiol-modified MXene-S electrode materials, wherein S-MXene SH 15 has the best performance due to excellent conductivity. The specific discharge capacity of 457.8mAh/g is still maintained during 4C high current density charging and discharging. The electrode material has a channel for fast transmission of electrons and is suitable for fast charge and discharge.
In summary, the invention relates to a preparation method of a sulfydryl modified MXene-sulfur composite material and a lithium-sulfur battery thereof, and MAX phase Ti is used 3 AlC 2 The material is a laminar two-dimensional MXene material obtained by a chemical etching method. Then dissolving low-cost cysteamine hydrochloride into MXene water dispersion, and preparing the sulfydryl by adopting a one-step hydrothermal reaction methodModified MXene. And finally, bonding sulfur molecules with the modified sulfydryl on the MXene at high temperature by adopting a process different from the traditional melting process to obtain the sulfydryl modified MXene-sulfur composite material serving as the anode of the lithium-sulfur battery. The sulfydryl modified MXene has excellent conductivity as the original MXene, and meanwhile, the interlayer spacing of the MXene is increased, more active sites and functional groups are exposed, and capture of polysulfide is facilitated. In addition, the sulfur atoms forming chemical bonds tend to form low-order polysulfides rather than high-order polysulfides during charge and discharge, which is more beneficial to reduce the dissolution of polysulfides in the electrolyte and the loss of active material sulfur. Therefore, the battery has high specific discharge capacity and good cycle performance.
The technical features and the detection items of the above-described embodiments may be arbitrarily combined, and for the sake of brevity, all possible combinations of the technical features in the above-described embodiments are not described, but should be considered as being within the scope of the present specification as long as there is no contradiction between the combinations of the technical features.
The above-mentioned embodiments only express several embodiments of the present invention, and the description thereof is more specific and detailed, but not construed as limiting the scope of the invention. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the inventive concept, which falls within the scope of the present invention. Therefore, the protection scope of the present patent should be subject to the appended claims.
Claims (9)
1. The preparation method of the mercapto-modified MXene-sulfur composite material is characterized by comprising the following steps of: preparing sheet MXene, preparing mercapto-modified MXene and preparing a mercapto-modified MXene-sulfur composite material;
the preparation method of the flaky MXene comprises the following steps:
s1, adding lithium fluoride into 20-37 wt% hydrochloric acid, and adding 1.5-3.5g of lithium fluoride into each 40mL of hydrochloric acid; stirring at the rotation speed of 250-600rpm for 20-45min to obtain a reaction solution A, wherein the lithium fluoride and the hydrochloric acid generate hydrogen fluoride;
s2, mixing MAX-Ti 3 AlC 2 Slowly adding the MAX-Ti into the reaction solution A 3 AlC 2 And the mass ratio of the lithium fluoride is 1: 0.5-2; continuously stirring for 12-36h at 30-45 deg.C to obtain reaction solution B, the MAX-Ti 3 AlC 2 Etching with the reaction solution A to form Ti 3 C 2 ；
S3, centrifuging the reaction solution B at the rotation speed of 3500-9000rpm, removing the supernatant, retaining the precipitate A, adding deionized water into the precipitate A, fully shaking up, performing ultrasonic treatment for 15-25min to uniformly disperse the precipitate A, repeating the operation for 4-6 times, and collecting the cleaned precipitate B; wherein 25-100mL of the deionized water is required to be added for every 40mL of hydrochloric acid used in the step S1;
s4, adding ethanol into the precipitate B, fully shaking up, performing ultrasonic treatment for 1-3h, centrifuging at the rotation speed of 8000-10000rpm, and collecting the precipitate C, wherein 25-100mL of ethanol is required to be added when 40mL of hydrochloric acid is used in the step S1; freeze-drying the precipitate C at-40 to-60 ℃ for 24-48h to obtain flake MXene;
the preparation method of the mercapto-modified MXene comprises the following steps:
s5, preparing the flaky MXene into MXene dispersion liquid with the concentration of 0.5-2 mg/mL;
s6, taking 100mL of the MXene dispersion liquid, adding 0.4-2g of cysteamine hydrochloride, simultaneously adding 0.4-2mL of ammonia water, and stirring to form a mixed solution A;
s7, placing the mixed solution A in a muffle furnace, and carrying out hydrothermal reaction for 3-12h at 90 ℃ to form a mixed solution B;
s8, filtering, washing and freeze-drying the mixed solution B to obtain sulfydryl modified MXene;
the preparation method of the sulfydryl modified MXene-sulfur composite material comprises the following steps:
s9, grinding and mixing the mercapto-modified MXene and the elemental sulfur in a mass ratio of 1:2-4 to obtain a reactant A; putting the reactant A into a reaction kettle, filling argon, heating to 160-;
s10, heating the reactant B to 160 ℃ at a heating rate of 10 ℃/min under an argon atmosphere, and keeping the temperature for 2-5h to obtain the mercapto-modified MXene-sulfur composite material.
2. The method for preparing the mercapto-modified MXene-sulfur composite material of claim 1, wherein the ultrasonic treatment in step S1 and step S2 is performed at a frequency of 35-50KHz and an ultrasonic power of 600-800W.
3. The method for preparing the mercapto-modified MXene-sulfur composite material of claim 1, wherein the flake MXene prepared in step S4 is a low flake MXene fluffy powder.
4. The method for preparing the mercapto-modified MXene-sulfur composite material of claim 1, wherein the lyophilization process in step S8 is drying in a lyophilizer at-40 to-60 ℃ for 12-48 h.
5. The method for preparing the mercapto-modified MXene-sulfur composite material of claim 1, wherein the number of water washes in step S8 is 2-5.
6. A lithium-sulfur battery using the mercapto-modified MXene-sulfur composite material, wherein the mercapto-modified MXene-sulfur composite material prepared by the method for preparing the mercapto-modified MXene-sulfur composite material according to any one of claims 1 to 5 is used as a positive electrode material in a positive electrode, and the positive electrode is prepared by the following steps:
and (3) preparing the cathode material: acetylene black: and mixing the binder in a mass ratio of 8:1:1, adding N-methyl pyrrolidone serving as a solvent, grinding into slurry, uniformly coating on an aluminum foil current collector to prepare an electrode, and drying for 8-24 hours in a vacuum environment at the temperature of 50-75 ℃ to prepare the anode.
7. The lithium sulfur battery with mercapto-modified MXene-sulfur composite material of claim 6, wherein said lithium sulfur battery further comprises a cathode, said cathode is prepared by the steps of:
a lithium sheet is used as a negative electrode material, wherein electrolyte is 1M lithium bistrifluoromethanesulfonimide which is dissolved in 1, 3-dioxolane and ethylene glycol dimethyl ether according to the volume ratio of 1:1, and the mass ratio of the 1, 3-dioxolane to the ethylene glycol dimethyl ether is 1: 0.4-2.
8. The lithium sulfur battery using mercapto-modified MXene-sulfur composite material of claim 7, wherein the lithium sulfur battery is obtained by assembling the positive electrode and the negative electrode in a glove box under inert gas atmosphere.
9. The lithium-sulfur battery using the mercapto-modified MXene-sulfur composite material of claim 6, wherein the sulfur loading amount of the coating film is 1-2mg/cm 2 。
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