CN113036087B - Ultrahigh-sulfur-content two-dimensional molecular brush and preparation method and application thereof - Google Patents
Ultrahigh-sulfur-content two-dimensional molecular brush and preparation method and application thereof Download PDFInfo
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Abstract
The invention provides a two-dimensional molecular brush with ultrahigh sulfur content, a preparation method and application thereof, wherein the preparation method comprises the following steps: (1) modifying graphene and grafting bromine group to obtain graphene containing bromine functional groups; (2) uniformly mixing graphene containing bromine functional groups with a high-molecular monomer, a ligand and a solvent, and preparing a two-dimensional molecular brush by adopting a surface polymerization grafting technology; (3) and uniformly mixing the two-dimensional molecular brush and sulfur powder, and carrying out heat treatment in an inert gas atmosphere to obtain the ultrahigh sulfur content two-dimensional molecular brush. The two-dimensional molecular brush contains the graphene substrate and the functional polymer hair, so that the conductivity of the active substance is improved, the internal impedance of the battery is reduced, the polarization is reduced, a large amount of sulfur active substance can be fixed through the vulcanization crosslinking reaction between the polymer hair and sulfur powder, the utilization rate of the active substance is improved, and the electrochemical reaction between deposited lithium polysulfide and a sulfur positive electrode can be promoted, so that the performance of the battery is improved.
Description
Technical Field
The invention relates to a preparation method of a two-dimensional molecular brush with ultrahigh sulfur content, and the material can be applied to a high-performance lithium-sulfur battery. The present invention relates to the field of nanomaterials and lithium sulphur batteries.
Background
Lithium-sulfur battery has ultrahigh theoretical capacity (1675mAh g)-1) High natural sulfur storage capacity, and environmentally friendly sulfur cathode material, etc., have attracted considerable attention in next-generation energy storage systems. However, lithium sulfur batteries face some key issues that limit their commercial applications. First, sulfur and its discharge products (Li)2S2/Li2S) results in low utilization of the active species, slow reaction kinetics and low rate performance. Secondly, lithium polysulfide generated from the positive electrode during charging and discharging is easily dissolved into the electrolyte, resulting in severe capacity fade, poor cycling stability and low coulombic effectAnd (4) rate. In addition, sulfur and Li during charge-discharge cycling2The interconversion between S may cause the collapse of the microstructure of the positive electrode material, destroying the conductive network, and further deteriorating the performance of the lithium-sulfur battery.
In order to solve the above problems, researchers have made a lot of work on the composition and structure of the sulfur positive electrode. Currently, the research on the positive electrode material of lithium-sulfur batteries mainly focuses on porous carbon materials having a physical confinement effect on polysulfides, metal oxides, nitrides and other materials having a chemical adsorption effect on polysulfides, organic sulfur materials chemically reacting with sulfur, and lithium-sulfur catalytic materials capable of promoting the conversion rate between lithium polysulfides and sulfur. However, the sulfur content in most of the lithium-sulfur battery positive electrode materials is less than 80% at present, which is not favorable for the commercial application. It is well known that increasing the sulfur content is beneficial to increase the density of the sulfur cathode material, thereby increasing the volumetric energy density of the lithium sulfur battery. In addition, higher sulfur content or sulfur loading means more active species in the cell, which undoubtedly increases the energy density of the cell. However, some of the key issues (e.g., polysulfide shuttling effect, volume expansion, capacity fade, etc.) present in low sulfur content positive electrode materials will be further magnified in high sulfur content positive electrode materials. Therefore, the development of a high-performance lithium-sulfur battery cathode material with ultrahigh sulfur content is of great significance.
Disclosure of Invention
Aiming at the defects in the prior art, the invention aims to provide a preparation method of a two-dimensional molecular brush with ultrahigh sulfur content and application of the two-dimensional molecular brush in a lithium-sulfur battery. According to the invention, a two-dimensional molecular brush with ultrahigh sulfur content is designed on the surface of two-dimensional graphene by utilizing a functional molecular brush concept and by means of a vulcanization crosslinking reaction of sulfur and the two-dimensional functional molecular brush. Firstly, the introduction of the graphene substrate can improve the conductivity of the electrode material; and secondly, the uniformly grafted polymer chains are beneficial to uniformly distributing sulfur active substances in the induced vulcanization crosslinking reaction, and the cycling stability of the battery is improved.
In order to achieve the purpose, the technical scheme adopted by the application is as follows:
the first purpose of the invention is to provide a preparation method of a two-dimensional molecular brush with ultrahigh sulfur content, wherein the material is prepared by grafting functional polymers on graphene through a surface grafting technology and then carrying out a vulcanization crosslinking reaction with sulfur powder.
A preparation method of a two-dimensional molecular brush with ultrahigh sulfur content comprises the following steps:
(1) modifying graphene and grafting bromine group to obtain graphene containing bromine functional groups;
(2) uniformly mixing the graphene containing the bromine functional groups prepared in the step (1) with a high-molecular monomer, a ligand and a solvent, introducing inert gas for deoxygenation, adding a catalyst, introducing inert gas for deoxygenation, then heating for reaction, filtering, washing and drying to obtain a two-dimensional molecular brush;
(3) and (3) uniformly mixing the two-dimensional molecular brush prepared in the step (2) with sulfur powder, and carrying out heat treatment in an inert gas atmosphere to obtain the ultrahigh sulfur content two-dimensional molecular brush.
Preferably, the monomer in the step (2) is one or more of styrene, acrylic acid, tert-butyl acrylate, polyacrylonitrile and acrylamide; the ligand is N, N, N ', N ', N ' -pentamethyl diethylenetriamine.
Preferably, the mass ratio of the graphene containing a bromine functional group to the polymer monomer, the solvent, the ligand and the catalyst in the step (2) is 1: (50-200): (20-200): (0.2-1): (0.2 to 1).
Preferably, the solvent in step (2) comprises one or more of N, N-dimethylformamide, N-dimethylacetamide and tetrahydrofuran; the catalyst is one or two of cupric bromide, cuprous bromide, cupric chloride and cuprous chloride; the inert gas in the step (2) and (3) comprises one or more of nitrogen, helium and argon.
Preferably, the reaction temperature in the step (2) is 60-100 ℃, and the reaction time is 12-72 h.
Preferably, the mass ratio of the two-dimensional molecular brush to the sulfur powder in the step (3) is 1 (5-35).
Preferably, the heat treatment temperature in the step (3) is 200-400 ℃, and the heat treatment time is 4-12 h.
Preferably, the step of modifying graphene to be grafted with bromine group in the step (1) is as follows: adding a certain amount of hydrazine hydrate into the water dispersion containing the graphene oxide, and heating and reducing for a period of time. And then adding 2- (4 aminophenyl) ethanol and isoamyl nitrite into the mixed solution, heating and reacting for a period of time, carrying out suction filtration, washing and drying to obtain the modified hydroxyl graphene. Dispersing the graphene containing hydroxyl modification into tetrahydrofuran, adding a certain amount of triethanolamine under the protection of ice water bath and inert gas, then slowly dropwise adding 2-bromo-isobutyryl bromide, stirring at normal temperature for reaction for a period of time, and performing post-treatment to obtain the graphene containing bromine functional groups.
Preferably, the step of modifying graphene to be grafted with bromine group in the step (1) is as follows: 0.5-2.0mL of hydrazine hydrate is added into 350mg of graphene oxide aqueous dispersion for heating and reducing for a period of time. And then adding 1-3g of 2- (4-aminophenyl) ethanol and 0.5-2.0mL of isoamyl nitrite into the mixed solution, heating to react for 8-20h, performing suction filtration, washing and drying to obtain the modified hydroxyl graphene. Dispersing 0.3-0.6g of graphene containing hydroxyl group modification into 10-20mL of tetrahydrofuran, adding 0.5-2mL of triethanolamine under the protection of ice water bath and inert gas, then slowly dropwise adding 0.2-0.5g of 2-bromo-isobutyryl bromide, stirring at normal temperature for reaction for a period of time, and carrying out aftertreatment to obtain the graphene containing a bromine functional group.
Preferably, the step of modifying graphene to be grafted with bromine group in the step (1) is as follows: 1.25mL of hydrazine hydrate was added to an aqueous dispersion of 350mg of graphene oxide, and the mixture was reduced by heating at 80 ℃ for 4 hours. And then adding 1.5g of 2- (4-aminophenyl) ethanol and 1.25mL of isoamyl nitrite into the mixed solution, heating at 80 ℃ for reaction for 12 hours, carrying out suction filtration, washing and drying to obtain the modified hydroxyl graphene. Dispersing 0.5g of graphene containing hydroxyl group modification into 10mL of tetrahydrofuran, adding a certain amount of triethanolamine of 0.9mL under the protection of ice water bath and inert gas, then slowly dropwise adding 0.43g of 2-bromo-isobutyryl bromide, stirring at normal temperature for reaction for 24h, and carrying out post-treatment to obtain the graphene containing a bromine functional group.
The second purpose of the invention is to provide the application of the ultrahigh sulfur content two-dimensional molecular brush material prepared by the method, and the material can be applied to a lithium-sulfur battery cathode material.
The application of the ultra-high sulfur content two-dimensional molecular brush in the preparation of the sulfur electrode slice comprises the following steps:
and mixing the ultrahigh-sulfur-content two-dimensional molecular brush, a conductive agent and a binder in a mortar, fully grinding by using an N-methylpyrrolidone (NMP) solution as a dispersing agent to enable the mixed materials to be uniform, and coating the surface of the carbon cloth with the obtained coating slurry to prepare the sulfur electrode slice.
The sulfur electrode plate is used as the positive electrode in the lithium sulfur battery, and comprises the following steps:
dissolving the commercial Celgard 2325 serving as a battery diaphragm, a metal lithium sheet serving as a cathode and 1.0M lithium bis (trichloromethylsulfonyl) imide in a mixed solution prepared from 1,3 dioxolane and tetraglyme in a volume ratio of 1:1 by taking the sulfur electrode sheet as an anode, adding 1wt% of anhydrous LiNO3And assembling the CR2032 type button cell in a waterless and anaerobic glove box according to the corresponding sequence.
Preferably, the conductive agent is one or more than two of conductive carbon black, carbon nano tube, graphene and ketjen black; the binder is one or more than two of PVDF, SBR and CMC; the mass ratio of the ultrahigh sulfur content two-dimensional molecular brush polymer to the conductive agent to the binder is (6-8): (3-1): 1, more preferably 7: 2: 1.
the principle of the invention is as follows: firstly, grafting functional polymers on the surface of graphene by using a surface graft polymerization technology, then mixing the functional polymers with sulfur powder, vulcanizing and crosslinking to obtain the two-dimensional molecular brush with ultrahigh sulfur content, and then using the two-dimensional molecular brush as a lithium-sulfur battery anode material. It is worth pointing out that the introduction of the graphene substrate in the two-dimensional graphene molecular brush can improve the conductivity of the electrode material; and secondly, the uniformly grafted polymer chains are beneficial to uniformly distributing sulfur active substances in the induced vulcanization crosslinking reaction, and the cycling stability of the battery is improved.
Compared with the prior art, the invention has the following beneficial effects:
(1) the lithium-sulfur battery cathode material disclosed by the invention has an ultra-high sulfur content (96.35 wt%), the graphene two-dimensional molecular brush can fix a large amount of sulfur active substances, and the uniformly grafted polymer chains are beneficial to uniformly distributing the active substances in the induced vulcanization crosslinking reaction, so that the circulation stability of the lithium-sulfur battery is improved.
(2) The ultrahigh-sulfur-content two-dimensional molecular brush disclosed by the invention contains the conductive graphene substrate and the functional polymer hair for inducing the sulfur active substances to be uniformly distributed, so that the conductivity of the active substances is improved, the internal impedance of a battery is reduced, the polarization is reduced, a large amount of sulfur active substances can be fixed through a vulcanization crosslinking reaction between the polymer hair and sulfur powder, and the utilization rate of the active substances is improved.
(3) The lithium-sulfur battery assembled by adopting the two-dimensional molecular brush with ultrahigh sulfur content as the anode material can promote the electrochemical reaction between deposited lithium polysulfide and the sulfur anode, greatly improves the cycle stability and rate capability, has simple preparation process and is beneficial to industrial production.
Drawings
To more clearly and clearly explain the objects, technical solutions and advantages of the present application, the present invention will be described in further detail below with reference to the accompanying drawings, which are used for describing embodiments and prior arts. It should be understood that the drawings in the following description are only a few embodiments of the present invention, are only used for explaining the present invention, and are not limited to the present invention, and those skilled in the art can also obtain other drawings based on the drawings under the premise of inventive work. In addition, the technical features involved in the embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.
Fig. 1 (a) and (B) are scanning electron micrographs of Graphene Oxide (GO) and two-dimensional graphene molecular brush (G-PS) before grafting provided in embodiment 1 of the present invention.
Fig. 2 is a thermogravimetric analysis diagram of bromine-based modified graphene (G-Br), a linear polystyrene molecular chain (PS), and a two-dimensional graphene molecular brush (G-PS) provided in embodiment 1 of the present invention.
Fig. 3 is a scanning electron micrograph (a) of the ultra-high sulfur two-dimensional molecular brush provided in example 1 of the present invention, a thermogravimetric analysis graph (B), and X-ray photoelectron spectra of (C) C1S and (D) S2 p.
Fig. 4 is an electrochemical impedance spectrum of the lithium-sulfur battery according to the present invention manufactured using example 1, comparative example 1, and comparative example 2 at 100kHz to 0.01Hz, respectively.
Fig. 5 is a graph showing rate performance at 0.2C to 2C of the lithium sulfur battery prepared in the present invention using example 1, comparative example 1, and comparative example 2, respectively.
Detailed Description
The following detailed description of embodiments of the invention refers to the accompanying drawings. The embodiment is implemented on the premise of the technical scheme of the invention, and a detailed implementation scheme and a specific operation process are given, but the protection scope of the invention is not limited to the following embodiment.
Various modifications to the precise description of the invention will be readily apparent to those skilled in the art from the information contained herein without departing from the spirit and scope of the appended claims. It should be understood that the embodiments described herein are presently preferred, and not all embodiments of the invention. Other embodiments, which may be devised by those skilled in the art without departing from the obvious innovations herein, are within the scope of the claims.
For a better understanding of the invention, and not as a limitation on the scope thereof, all numbers expressing quantities, percentages, and other numerical values used in this application are to be understood as being modified in all instances by the term "about". Accordingly, unless expressly indicated otherwise, the numerical parameters set forth in the specification and attached claims are approximations that may vary depending upon the desired properties sought to be obtained. At the very least, each numerical parameter should at least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques.
The reagents and materials used in the examples described below are all commercially available.
Example 1
Preparing a high-sulfur-content lithium-sulfur battery based on a two-dimensional molecular brush:
(1) 1.25mL of hydrazine hydrate was added to an aqueous dispersion of 350mg of graphene oxide, and the mixture was reduced by heating at 80 ℃ for 4 hours. And then adding 1.5g of 2- (4-aminophenyl) ethanol and 1.25mL of isoamyl nitrite into the mixed solution, heating at 80 ℃ for reaction for 12 hours, carrying out suction filtration, washing and drying to obtain the modified hydroxyl graphene. Dispersing 0.5g of graphene containing hydroxyl group modification into 10mL of tetrahydrofuran, adding a certain amount of triethanolamine of 0.9mL under the protection of ice water bath and inert gas, then slowly dropwise adding 0.43g of 2-bromo-isobutyryl bromide, stirring at normal temperature for reaction for 24h, and carrying out post-treatment to obtain the graphene containing a bromine functional group.
(2) Dispersing 0.2g of graphene containing bromine functional groups obtained in the step (1) in 20mL of styrene monomer and 10mL of N, N-dimethylformamide, adding 0.084mL of N, N, N ', N ', N ' -pentamethyldiethylenetriamine ligand into the mixed solution, and introducing N2And (4) deoxidizing for 30 min. 0.056g of cupric bromide was added to the system, and then deoxygenated with nitrogen for 30 min. And then placing the graphene brush into an oil bath kettle at 90 ℃ for reaction for 60 hours, centrifuging, and washing with tetrahydrofuran for several times to obtain the two-dimensional graphene molecular brush.
(3) Fully grinding and uniformly mixing 0.1g of the two-dimensional graphene molecular brush in the step (2) and 3g of sulfur powder, keeping the obtained mixture at 200 ℃ for 2h in a nitrogen atmosphere, heating to 280 ℃ and keeping for 4h to obtain the two-dimensional molecular brush with ultrahigh sulfur content.
(4) Mixing the prepared two-dimensional molecular brush material with the ultra-high sulfur content, conductive carbon black (Super P), Ketjen black (EPC-600JD) and a binder (PVDF) in a mortar according to the mass ratio of 7:1:1:1, fully grinding the mixture to be uniform by taking an N-methyl pyrrolidone (NMP) solution as a dispersing agent, coating the surface of carbon cloth cut in advance with the coating slurry to prepare a sulfur electrode plate, and drying the sulfur electrode plate in a constant-temperature drying phase at 80 ℃ for 12 hours for later use.
(5) Dissolving lithium bis (trichloromethylsulfonyl) imide with the prepared sulfur electrode plate as a positive electrode, a commercial Celgard 2325 as a battery diaphragm, a metal lithium plate as a negative electrode and 1.0M electrolyteAdding 1wt% of anhydrous LiNO into a mixed solution prepared from 1, 3-dioxolane and tetraglyme in a volume ratio of 1:13In the absence of water and anaerobic (H)2O＜0.1ppm，O2Less than 0.1ppm) and assembling a CR2032 type button cell in a glove box according to a corresponding sequence, and naming the prepared button cell as a G-G-PS @ S button cell.
(6) And testing the charge and discharge performance of the assembled G-G-PS @ S button cell at room temperature by using a LandCT2001A cell testing system and a CHI660C electrochemical workstation, wherein the charge and discharge termination range is 1.7-2.8V.
As can be seen from fig. 1, the prepared graphene molecular brush inherits the two-dimensional sheet structure of graphene oxide.
The mass fraction of the grafted polystyrene polymer can be determined by the formula: x is calculated as (C-B)/(a-B). A, B, C respectively represents the residual mass percentage of linear polystyrene, graphene initiator (G-Br) and two-dimensional graphene molecular brush (G-G-PS) after thermal weight loss analysis. As can be seen from fig. 2, a is 0.5 wt%, B is 67.9 wt%, and C is 29.7 wt%, and X is 56.7 wt% by calculation, so that the prepared two-dimensional graphene molecular brush has a polystyrene grafting rate of 56.7 wt%.
As can be seen from FIG. 3, the prepared ultrahigh sulfur content two-dimensional molecular brush (G-G-PS @ S) still maintains the two-dimensional sheet structure morphology, the thermal weight loss curve of the material shows that the material has ultrahigh sulfur content, and the sulfur content in the G-G-PS @ S is 96.35 wt% as determined by elemental analysis (Table 1). X-ray photoelectric energy spectrum analysis of C1S and S2p of the ultrahigh sulfur content two-dimensional molecular brush proves that the vulcanization crosslinking reaction between the grafted polystyrene molecular chain and sulfur powder occurs.
TABLE 1 elemental analysis of ultra-high sulfur content two-dimensional molecular brushes (G-G-PS @ S)
Comparative example 1
Preparation of graphene-based high-sulfur-content lithium-sulfur battery
(1) Fully grinding and uniformly mixing 0.1G of graphene powder and 3G of sulfur powder, keeping the obtained mixture at 200 ℃ for 2h in a nitrogen atmosphere, heating to 280 ℃ and keeping for 4h to obtain the high-sulfur-content graphene @ sulfur composite material (G @ S).
(2) Mixing the prepared G @ S with conductive carbon black (Super P), Ketjen black (EPC-600JD) and a binder (PVDF) in a mortar according to the mass ratio of 7:1:1:1, fully grinding the mixture to be uniform by taking an N-methylpyrrolidone (NMP) solution as a dispersing agent, coating the coating slurry on the surface of carbon cloth cut in advance by using a stainless steel spoon to prepare a sulfur electrode sheet, and drying the sulfur electrode sheet in a constant-temperature drying phase at 80 ℃ for 12 hours for later use.
(3) Dissolving the prepared sulfur electrode slice as a positive electrode, a commercial Celgard 2325 as a battery diaphragm, a metal lithium slice as a negative electrode and 1.0M lithium bis (trichloromethylsulfonyl) imide as an electrolyte in a mixed solution prepared by 1:1 of 1,3 dioxolane and tetraglyme in volume ratio, and adding 1wt% of anhydrous LiNO3In the absence of water and anaerobic (H)2O＜0.1ppm，O2Less than 0.1ppm) and assembling a CR2032 type button cell in a corresponding sequence in a glove box, and naming the prepared button cell as a G @ S button cell.
(4) The G @ S button cell assembled above was tested for charge and discharge performance at room temperature using a LandCT2001A battery test system and CHI660C electrochemical workstation with a charge and discharge end range of 1.7-2.8V.
Comparative example 2
Preparation of high-sulfur lithium-sulfur battery based on graphene and polystyrene mixture
(1) Fully grinding and uniformly mixing 0.04G of graphene powder, 0.06G of linear polystyrene polymer powder and 3G of sulfur powder, keeping the obtained mixture at 200 ℃ for 2h under a nitrogen atmosphere, heating to 280 ℃ and keeping for 4h to obtain the high-sulfur-content graphene and polystyrene mixture @ sulfur (G/PS @ S) composite material.
(2) Mixing the prepared G/PS @ S with conductive carbon black (Super P), Ketjen black (EPC-600JD) and a binder (PVDF) in a mortar according to the mass ratio of 7:1:1:1, fully grinding the mixture to be uniform by using an N-methylpyrrolidone (NMP) solution as a dispersing agent, coating the surface of carbon cloth cut in advance with the coating slurry to prepare a sulfur electrode sheet, and drying the sulfur electrode sheet in a constant-temperature drying phase at 80 ℃ for 12 hours for later use.
(3) Dissolving the prepared sulfur electrode slice as a positive electrode, a commercial Celgard 2325 as a battery diaphragm, a metal lithium slice as a negative electrode and 1.0M lithium bis (trichloromethylsulfonyl) imide as an electrolyte in a mixed solution prepared by 1:1 of 1,3 dioxolane and tetraglyme in volume ratio, and adding 1wt% of anhydrous LiNO3In the absence of water and anaerobic (H)2O＜0.1ppm，O2Less than 0.1ppm) and assembling a CR2032 type button cell in a corresponding sequence in the glove box, and naming the prepared button cell as a G/PS @ S button cell.
(4) The G/PS @ S button cell assembled above was tested for charge and discharge performance at room temperature using a LandCT2001A cell testing system and CHI660C electrochemical workstation with a charge and discharge end range of 1.7-2.8V.
Fig. 4 is an electrochemical impedance spectrum of the lithium-sulfur battery according to the present invention manufactured using example 1, comparative example 1, and comparative example 2 at 100kHz to 0.01Hz, respectively. The ac impedance curve of the lithium-sulfur battery is composed of a semicircular arc in the high frequency region and a straight line in the low frequency region. The smaller the semicircular arc diameter of the high frequency region is, the lower the resistance of the lithium sulfur battery is, and conversely, the larger the semicircular arc diameter of the high frequency region is, the higher the resistance is. The impedance of the G-G-PS @ S battery is obviously lower than that of the G @ S battery and the G/PS @ S battery, which shows that the G-G-PS @ S battery can improve the conductivity of the active substance as the positive electrode material of the lithium sulfur battery without influencing Li+The transmission of (2) can play the role of a current collector, and the electron transmission speed is improved.
Fig. 5 is a graph showing rate performance at 0.2C to 2C of the lithium sulfur battery prepared in the present invention using example 1, comparative example 1, and comparative example 2, respectively. The discharge specific capacities of the G-G-PS @ S battery at 0.2C, 0.5C, 1C and 2C are 930mA h G-1，865mA h g-1，722mA h g-1And 559mA h g-1. When the current density returns to 0.2C, the specific discharge capacity still exceeds 890mA h g-1And excellent rate performance is shown. The specific discharge capacity of the G @ S and G/PS @ S cells prepared in comparative examples 1 and 2 was lower than that of the G-PS @ S cell in example 1 at the same current density. Shows that G-G-PS @ S can not only reduce the charge-discharge processThe loss of active material and the promotion of electrochemical reaction between deposited lithium polysulfide and active material, so as to raise the specific discharge capacity of the battery.
In conclusion, the invention provides a preparation method of a two-dimensional molecular brush with ultrahigh sulfur content and application of the two-dimensional molecular brush in a lithium-sulfur battery. The ultrahigh-sulfur-content two-dimensional molecular brush provided by the invention contains the conductive graphene substrate and the functional polymer hair for inducing the sulfur active substances to be uniformly distributed, so that the conductivity of the active substances is improved, the internal impedance of the battery is reduced, the polarization is reduced, the utilization rate of the active substances is improved, a large amount of sulfur active substances can be effectively fixed, and the electrochemical reaction between deposited lithium polysulfide and a sulfur positive electrode can be promoted, thereby improving the performance of the battery.
Finally, it should be noted that: the above description is only for the preferred embodiment of the present invention, and is not intended to limit the present invention in any way. It will be apparent to those skilled in the art that various changes and modifications can be made therein without departing from the spirit and scope thereof, and it is intended that the present invention encompass such changes and modifications.
Claims (7)
1. The preparation method of the ultrahigh sulfur content two-dimensional molecular brush is characterized by comprising the following steps:
(1) modifying graphene and grafting bromine group to obtain graphene containing bromine functional groups;
(2) uniformly mixing the graphene containing the bromine functional groups prepared in the step (1) with a high-molecular monomer, a ligand and a solvent, introducing inert gas to remove oxygen, adding a catalyst, introducing nitrogen or inert gas to remove oxygen, then heating for reaction, and filtering, washing and drying to obtain a two-dimensional molecular brush;
(3) uniformly mixing the two-dimensional molecular brush prepared in the step (2) with sulfur powder, and carrying out heat treatment in an inert gas atmosphere to obtain the two-dimensional molecular brush with ultrahigh sulfur content;
the monomer in the step (2) is one or more of styrene, acrylic acid, tert-butyl acrylate, acrylonitrile and acrylamide; the ligand is N, N, N ', N', N '' -pentamethyl diethylenetriamine;
the mass ratio of the two-dimensional molecular brush to the sulfur powder in the step (3) is 1 (5-35);
the heat treatment temperature in the step (3) is 200-400 ℃, and the heat treatment time is 4-12 h;
in the step (2), the mass ratio of the graphene containing the bromine functional groups to the high-molecular monomer, the solvent, the ligand and the catalyst is 1: (50-200): (20-200): (0.2-1): (0.2 to 1);
the step (1) of modifying and grafting the graphene with bromine groups comprises the following steps: adding 0.5-2.0mL of hydrazine hydrate into 350mg of graphene oxide aqueous dispersion, and heating and reducing for a period of time; then adding 1-3g of 2- (4-aminophenyl) ethanol and 0.5-2.0mL of isoamyl nitrite into the mixed solution, heating to react for 8-20h, carrying out suction filtration, washing and drying to obtain modified hydroxyl graphene; dispersing 0.3-0.6g of graphene containing hydroxyl group modification into 10-20mL of tetrahydrofuran, adding 0.5-2mL of triethanolamine under the protection of ice water bath and inert gas, then slowly dropwise adding 0.2-0.5g of 2-bromo-isobutyryl bromide, stirring at normal temperature for reaction for a period of time, and carrying out aftertreatment to obtain the graphene containing a bromine functional group.
2. The preparation method according to claim 1, wherein the solvent in step (2) comprises one or more of N, N-dimethylformamide, N, N-dimethylacetamide and tetrahydrofuran; the catalyst is one or two of cupric bromide, cuprous bromide, cupric chloride and cuprous chloride; the inert gas in the step (2) and (3) comprises one or more of helium and argon.
3. The preparation method according to claim 2, wherein the reaction temperature in the step (2) is 60-100 ℃ and the reaction time is 12-72 hours.
4. The two-dimensional molecular brush with ultrahigh sulfur content prepared by the method of any one of claims 1 to 3.
5. The application of the ultra-high sulfur content two-dimensional molecular brush in the preparation of sulfur electrode slices, which is characterized by comprising the following steps:
and mixing the ultrahigh-sulfur-content two-dimensional molecular brush, a conductive agent and a binder in a mortar, fully grinding by using an N-methylpyrrolidone (NMP) solution as a dispersing agent to enable the mixed materials to be uniform, and coating the surface of the carbon cloth with the obtained coating slurry to prepare the sulfur electrode slice.
6. Use of the sulfur electrode sheet of claim 5 as a positive electrode in a lithium sulfur battery,
dissolving the commercial Celgard 2325 serving as a battery diaphragm, a metal lithium sheet serving as a cathode and 1.0M lithium bis (trichloromethylsulfonyl) imide in a mixed solution prepared from 1,3 dioxolane and tetraglyme in a volume ratio of 1:1 by taking the sulfur electrode sheet as an anode, adding 1wt% of anhydrous LiNO3And assembling the CR2032 type button cell in a waterless anaerobic glove box according to the corresponding sequence.
7. The use of claim 6, wherein the conductive agent is one or more of conductive carbon black, carbon nanotubes and graphene; the binder is one or more than two of PVDF, SBR and CMC; the mass ratio of the ultrahigh sulfur content two-dimensional molecular brush to the conductive agent to the binder is (6-8): (3-1): 1.
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