CN110890532A

CN110890532A - Lithium-sulfur battery positive electrode material and preparation method thereof

Info

Publication number: CN110890532A
Application number: CN201911131263.5A
Authority: CN
Inventors: 王鹏; 季山
Original assignee: Jiaxing University
Current assignee: Jiaxing University
Priority date: 2019-11-19
Filing date: 2019-11-19
Publication date: 2020-03-17

Abstract

The invention relates to the technical field of lithium batteries, in particular to a lithium-sulfur battery positive electrode material and a preparation method thereof. After the prepared material is prepared into a battery, the capacitance of the first charge and discharge at 0.1 ℃ can reach 1212 mA/g. Through reasonable amount of research on DIB and SHG, we found that cp (S) was observed in comparison to other materials_90％‑r‑DIB_9.53％)‑SHG_0.4％The stability is more excellent under the high current of 5C, and in the charging cycle of 800 circles under the current of 0.1C, the capacitance retention rate is 52.3%, and the average decay rate of each cycle is only 0.06%.

Description

Lithium-sulfur battery positive electrode material and preparation method thereof

Technical Field

The invention relates to the technical field of lithium batteries, in particular to a lithium-sulfur battery positive electrode material and a preparation method thereof.

Background

The Lithium Sulfur Battery (LSB) is considered as a next generation battery having high energy density, and is one of lithium batteries, which is a lithium battery having elemental sulfur as a battery positive electrode and metallic lithium as a negative electrode. The elemental sulfur has rich reserves in the earth, and has the characteristics of low price, environmental friendliness and the like. The lithium-sulfur battery utilizes sulfur as a positive electrode material, the theoretical specific capacity of the material and the theoretical specific energy of the battery are higher and respectively reach 1675mAh/g and 2600Wh/kg, the capacity of the lithium-sulfur battery is far higher than that of a cobalt acid lithium battery widely applied commercially (less than 150mAh/g), and the capacity is about 3-5 times higher than that of a current most advanced commercial cathode material of a lithium ion battery. .

However, the lithium-sulfur battery positive electrode material still faces some critical problems to be solved urgently, and the commercial application of the lithium-sulfur battery positive electrode material is severely limited. For example, during battery charge-discharge cycles, Li₂S_xLithium polysulfide intermediate products such as (X ═ 4-8) are easily soluble in the electrolyte, resulting in loss of active sulfur in the positive electrode and causing polysulfide "shuttle effect", resulting in reduction in battery capacity and occurrence of safety problems. In addition, the positive electrode material sulfur and its reduction product Li₂S(5×10^-3S/cm), which seriously affects the utilization rate of sulfur and the rate capability of the battery. At the same time, due to sulfur atoms and Li₂The S density has a large difference, and the volume of the electrode can be greatly changed (the change range is about 80%) in the charging and discharging process, so that the sulfur of the active substance physically adsorbed on the current collector falls off, and the cycle performance of the battery is further influenced. In order to solve these problems, sulfur is generally intercalated into a polymer, a metal-organic framework, a carbon-based material, or a composite material to form a core-shell, yolk, layered, sandwich-type, or the like structure, thereby increasing the conductivity of the positive electrode material and reducing the loss of active sulfur. However, it is difficult to form a strong chemical bond force constraint between the surface of these electrode materials and sulfur, and the active material inevitably falls off from the current collector due to the change in the volume of the electrode during the charge and discharge processes, thereby resulting in a decrease in the battery capacity. Intermediate to the limitation of physical adsorption, research and development of sulfur-based composite materials based on chemical constraints are necessary. For this reason, extensive research has been carried out on the free-radical polymerization of sulfur with polymerizable monomers or polymers containing reactive groups. However, since most sulfur-rich copolymers have low or insulating conductivity, this results in an active sulfur loading of only 1 mg/cm²Even lower. The specific capacity of the lithium-sulfur battery cannot be effectively improved based on the method. Therefore, sulfur, modified conductive graphene and cross-linking molecules DIB are directly copolymerized to form the sulfur cross-linking catalystElectropolymers are an effective means to solve the problem.

Disclosure of Invention

The invention aims to: the performance of the battery is improved by introducing a cross-linking agent DIB and a conductive carbon material which are cooperatively optimized, specifically, the introduction of the DIB can fix active sulfur in a chemical bond form and inhibit shuttle of polysulfide in the charge-discharge process; the introduction of the sulfhydrylation graphene material (SHG) can optimize the conductivity of the material, and in addition, sulfhydryls widely existing on the SHG can react with active sulfur, so that S and graphene are connected by chemical bonds, the resistance is further reduced, and the performance of the material is further improved.

In order to achieve the purpose, the invention adopts the following technical scheme:

a lithium-sulfur battery positive electrode material and a preparation method thereof, the process is divided into the following steps;

preparing materials:

1) synthesis of SHG Graphene Oxide (GO) is prepared by a traditional Hummers method and dispersed in secondary distilled water to prepare a solution with a certain concentration. 1g of 2-mercaptoethylamine hydrochloride, 1mL of ammonia water and 1mg/mL of GO90mL (1mg/mL) are mixed in a 250mL flask, the temperature is set to be 90 ℃, and the mixture is heated for 6 hours. After the reaction is completed, filtering and rinsing the mixture by using secondary distilled water to obtain an SHG material with high porosity;

2) synthesis of cp (S-r-DIB) -SHG

Firstly, accurately weighing sulfur and DIB and SHG materials with different proportions according to a mass ratio of 9: 1. Subsequently, sublimed sulfur (4g, 0.125mol) was added under an argon atmosphere in a round bottom flask equipped with a magnetic stirrer, then the flask was placed in an oil bath preheated to 185 ℃, when the sublimed sulfur melted to a liquid state exhibiting cherry red color, a calculated amount of 1, 3-Diisopropylbenzene (DIB) was added, stirring was continued for about 5-10min until the product exhibited a vitrified state, then a calculated amount of SHG was added thereto and stirring was continued for 2 hours, finally, the flask was immediately taken out and placed in liquid nitrogen to be cooled to quench the reaction, and finally, a brownish black transparent crystalline material, PolyS-AS, was obtained;

assembling the lithium-sulfur battery:

1) preparing an electrode: mixing an active substance to be detected, a conductive agent (SuperP) and a binder (PVDF) according to a mass ratio of 7:2:1, adding a proper amount of N-methylpyrrolidone (NMP) as a solvent, uniformly stirring, uniformly rolling by using a roller press to form a film, cutting a circular film with the diameter of 12mm, coating the circular film on a clean aluminum (Al) foil, and drying in an oven at the temperature of 80 ℃ for 24 hours to obtain a working electrode;

2) assembling the battery: dissolving LiTFSI with 1M electrolyte in EC/DMC solution according to the volume ratio of 1: 1; the test of the bimodal sulfur-based composite also used electrolyte 1MLiTFSI in DOL/DME (1: 1 by volume) solution (containing 0.1M additive LiNO)₃) A button cell (CR2032) was assembled in an argon-filled glove box (MB-10compact, MBRAUN) with a lithium metal sheet as the negative electrode and Celgard2400 as the separator.

The positive electrode material of the lithium-sulfur battery and the preparation method thereof have the beneficial effects that: by introducing DIB and SHG into a sulfur system, the construction of a high-crosslinking sulfur-rich network is realized, and the conductivity of the material is optimized. After the prepared material is prepared into a battery, the first charge and discharge capacity at 0.1 ℃ is up to 1212 mA/g. Through reasonable amount of research on DIB and SHG, we found that cp (S) was observed in comparison to other materials_90％-r-DIB_9.53％)-SHG_0.4％The stability is more excellent under the high current of 5C, and in the charging cycle of 800 circles under the current of 0.1C, the capacitance retention rate is 52.3%, and the average decay rate of each cycle is only 0.06%.

Drawings

FIG. 1 is a schematic diagram of the synthetic route for cp (S-r-DIB) -SHG;

FIG. 2 is a 1H NMR chart of cp (S-r-DIB) -SHG and cp (S-r-DIB);

FIG. 3 is an XRD pattern of various materials;

FIG. 4 is an infrared plot of various substances;

FIG. 5 is a TGA;

FIG. 6 is an SEM scan of (a) SHG and (b) cp (S-r-DIB) -SHG of FIG. 6;

FIG. 7 is a graph of CV testing performed at 0.1 mV;

FIG. 8 is an EIS plot of cp (S-r-DIB) -SHG electrode material at different scales;

FIG. 9 is a graph of lithium ion mobility versus different ratios of cp (S-r-DIB) -SHG electrode material;

FIG. 10 is a charge point charge curve;

FIG. 11 is a graph comparing the rate charge and discharge performance of different materials;

FIG. 12 is a graph of discharge capacitance for different materials cycled 900 cycles at 1C

FIG. 13(a)1C Current at cp (S)_90％-r-DIB_9.53％)-SHG_0.47％Charging and discharging curves under different turns;

FIG. 13(b) retained capacitance for different materials at different turns at 1C current.

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments.

The experimental steps are as follows:

experimental procedure

Synthesis of SHG Graphene Oxide (GO) is prepared by a traditional Hummers method and dispersed in secondary distilled water to prepare a solution with a certain concentration. 2-mercaptoethylamine hydrochloride (1g), ammonia (1mL), GO (90mL, 1mg/mL) was mixed well in a 250mL flask, set at 90 ℃ and heated for 6 h. And after the reaction is completed, filtering and rinsing the mixture by using secondary distilled water to obtain the high-porosity SHG material.

Synthesis of cp (S-r-DIB) -SHG

Sublimed sulfur (4g, 0.125mol) was added under an argon atmosphere in a round-bottomed flask equipped with a magnetic stir bar, and 1, 3-Diisopropylbenzene (DIB) and SHG were accurately weighed in a mass ratio of 9: 1. The flask was then placed in a preheated 185 ℃ oil bath and a calculated amount of 1, 3-Diisopropylbenzene (DIB) was added as the sublimed sulfur melted to a liquid state exhibiting a cherry red color. Stirring was continued for about 5-10min until the product appeared to be vitrified. A calculated amount of SHG was then added to it and stirring was continued for 2 hours (in the experiment, we selected 1, 3-diisopropyl ether separately)The mass ratio of phenyl to SHG is 5:1, 10:1, 20: 1 and 40: 1). Finally, the flask was immediately taken out and placed in liquid nitrogen to cool to quench the reaction. Finally, a brownish black transparent crystalline material, Poly S-AS, was obtained. Respectively denoted cp (S) according to the added mass_90％-r-DIB_9.76％)-SHG_0.24％，cp(S_90％-r-DIB_9.53％)- SHG_0.47％,cp(S_90％-r-DIB_9.10％)-SHG_0.9％And cp (S)_90％-r-DIB_8.34％)-SHG_1.66％。

2.2 characterization of the principal physical Properties

2.2.1X-ray diffraction

X-ray diffraction (XRD) is used for testing the crystalline structure of raw materials and prepared composite materials, and the structural state of the materials is analyzed according to the change of XRD data of samples. The testing instrument is a Rigaku D/max-2200/PC type X-ray diffractometer, the target Cu (Ka), the tube voltage is 40kV, the current is 30 mA, the diffraction angle range is 5-80 degrees, and the scanning speed is 5-1 min. The sample was mounted flat against the surface in a quartz cell for testing.

2.2.2 scanning Electron microscope

Scanning Electron Microscope (SEM) is used to examine the microscopic morphology change of the raw material and the product, study the surface structure composition of the composite material, and analyze the composite effect. The test instrument is a JEOLJSM-7401F type scanning electron microscope, and the excitation voltage is 5 kV. The sample powder is ultrasonically dispersed in water or ethanol and then dripped on a smooth silicon chip, or is directly adhered on a conductive adhesive of a sample table, and the test is carried out after gold plating.

2.2.5 Infrared Spectroscopy

Infrared spectroscopic analysis (IR) is mainly used to analyze the radical composition of graphene oxide and the change of graphene oxide after being compounded with polyacrylonitrile. The testing instrument is a BrukerVECTOR22 type infrared analyzer, and the sample and KBr are ground, mixed and tabletted to carry out testing.

2.2.6 Raman Spectroscopy

Raman spectroscopy is mainly used to analyze the composition and carbonization status of composite materials. The testing instrument is a Bruker OpticsSenterRaR200-L type Raman scattering instrument, an Ar ion laser is used as a light source, the excitation wavelength is 633nm, and the data acquisition time is 10 s. The sample powder was spread on a glass slide and tested after flattening.

2.2.7 thermogravimetric and differential scanning calorimetry (TG/DSC) test

As the temperature increases, some components in the sample decompose and remove or chemically react with the test atmosphere as the temperature changes, causing the mass of the sample to change. The thermogravimetric analysis method is a testing technique for accurately measuring the change of the sample mass along with the temperature change under the operation of a set temperature. The thermogravimetric analysis curve reflects the intrinsic characteristics of the substance, so that some physical and chemical properties of the substance can be obtained through the thermogravimetric analysis. Differential Scanning Calorimetry (DSC) can be used with a thermogravimetric instrument, and by setting a temperature program, in order to obtain the same temperature as the program temperature, and inputting heat under different powers to a test material and a reference material, a relation curve chart of the input heat and the temperature is always kept without temperature difference among the set program temperature, the test sample temperature and the reference temperature. The thermogravimetric analysis curves of various samples were tested herein using TGA-DSC of mettler, switzerland, further demonstrating the temperature of synthesis; meanwhile, by analyzing a thermogravimetric analysis curve of the polysulfide polymer, the content of the prepared sulfur element in a sample, an endothermic peak of the material in the temperature rising process and the like are determined to determine whether the material is polymerized.

2.3 electrochemical Performance Studies

2.3.1 Assembly of the Battery

Preparing an electrode: mixing an active substance to be detected, a conductive agent (SuperP) and a binder (PVDF) according to a certain mass ratio (7:2:1), adding a proper amount of N-methyl pyrrolidone (NMP) as a solvent, uniformly stirring, uniformly rolling by using a roller press to form a film, cutting a circular film with the diameter of 12mm, coating the circular film on a clean aluminum (Al) foil, and drying in an oven at 80 ℃ for 24 hours to obtain the working electrode.

Assembling the battery: the electrolyte is 1MLiTFSI dissolved in EC/DMC (volume ratio 1:1) solution; the dual-mode sulfur-based composite was also tested using electrolyte 1MLiTFSI in solution in DOL/DME (1: 1 by volume) with 0.1M additive LiNO 3. The metal lithium sheet is used as a negative electrode. Celgard2400 is a septum. The button cell (CR2032) was assembled in an argon-filled glove box (MB-10compact, MBRAUN).

2.3.2 Charge/discharge test

The charge and discharge test was performed on a LandCT model 2007A battery test system manufactured by wuhan jinuo electronics ltd. The ambient temperature of charging and discharging of the battery is 25 ℃, and the cut-off voltage range is 1.7-2.6 VV. Two calculation methods are employed herein in calculating the specific capacity of the sulfur-based composite material: if the unit of mass calculation of sulfur in the composite material is mAhg^-1 _sulfur(ii) a If the unit of the overall mass calculation based on the sulfur-based composite material is m Ahg^-1 _compositeOr mAhg^-1。

3.3 Cyclic voltammetry test

The cyclic voltammetry scans electrode potential back and forth in a certain range at a constant change speed in a cyclic mode, records the change of current along with the potential to detect the electrochemical activity of a substance, measure the oxidation-reduction potential of the substance, investigate the reversibility of electrochemical reaction, reaction mechanism and the like, and can provide rich information for electrode process research. It can also be used for semi-quantitative analysis of reaction rate. The electrochemical properties of the electrode active material are tested herein to determine the sulfur recombination type of the material. The test is carried out on a CHI650C electrochemical workstation, the test environment temperature is 25 ℃, and the scanning voltage range is 1.5-2.8V. The scanning speed was 0.1mVs^-1。

2.3.4 AC impedance test

The ac impedance method studies the dynamics of the electrode process by applying a small amplitude ac voltage or current signal to perturb the electrode around the equilibrium electrode potential and measuring the relationship between its response current or potential signal after reaching steady state. Because the amplitude of the alternating signal is extremely small and is near the equilibrium potential, the relationship between the electrode process dynamics and the electrode state can be accurately researched. The method is used for testing the impedance of electrodes made of different materials, the change of the electrochemical performance caused by the modification of the materials is determined, and the test is carried out on a CHI650C electrochemical workstation, the ambient temperature is 25 ℃, and the frequency range is 0.01-100 kHz.

DIB and sulfhydrylation graphene (SHG) are successfully introduced into a ring-opening sulfur chain through a simple high-temperature solid-phase reaction at 180 ℃ in a nitrogen atmosphere to obtain a series of polymers cp (S-r-DIB) -SHG. The reaction was also evidenced by a color change during which the product changed from an initial bright yellow to a reddish brown and then to a final tan. The specific synthetic procedure is that of cp (S-r-DIB) -SHG and cp (S-r-DIB) with S content of 90% as shown in FIG. 2¹HNMR spectrogram. It is shown that according to previous reports, the peak of the cp (S-r-DIB) signal between 1.5ppm and 2.5ppm can be attributed to the signal near the methylene group of the polysulfide chain, indicating the presence of alkyl protons in the system, probably due to the copolymerization of vinyl groups with other vinyl groups. Multiple signal peaks between 7.2ppm and 8.0ppm, indicating the presence of benzene ring protons on DIB. When nuclear magnetic spectra of cp (S-r-DIB) -SHG and cp (S-r-DIB) were compared, it was found that some peak shape changes occurred between 7.0 and 8.0ppm, which may be caused by the introduced SHG.

As can be seen from FIG. 3, the XRD of sublimed sulfur is in the range of 20-30, the sublimed sulfur shows a plurality of high intensity peaks, and cp (S-r-DIB) -SHG in this region, although a plurality of high intensity peaks are also present, has a significant protrusion in the bottom region, which may be caused by the presence of SHG inside the material, which indicates that the sulfur has both crystalline and amorphous states in the composite material.

As can be seen from the IR chart (FIG. 4), S-SHG, cp (S-r-DIB) and cp (S-r-DIB) -SHG all showed a characteristic C-S peak at 648 cm-1. Furthermore, at 827 and 501cm^-1Is the S-S vibration peak. At 2989cm^-1The occurrence of amide bond indicates that SHG exists inside the material. The above results indicate that SHG is widely present in cp (S-r-DIB) -SHG and that part of sulfur is fixed in the form of C-S.

As shown in FIG. 5, samples of the cp (S-r-DIB) -SHG series, prepared at different DIB and SHG loadings, were subjected to thermogravimetric analysis (TGA) in a nitrogen atmosphere to determine sulfur content. It can be seen from the figure that all samples show a weight loss starting at approximately 180 ℃ and ending around 310 ℃, a characteristic consistent with the thermogravimetric properties of elemental sulfur. This indicates that this weight loss is due to evaporation of the sulfur nanocrystals in the copolymer. From the SEM image (FIG. 6), it can be seen that the SHG is uniformly distributed on the surface of the cp (S-r-DIB) -SHG material; s is immobilized by DIB and exists in cp (S-r-DIB) -SHG in a cross-linked form.

Button cells were prepared as shown in fig. 7 with different loadings of cp (S-r-DIB) -SHG series material as the positive electrode and subjected to Cyclic Voltammetry (CV) testing. As shown, the cp (S-r-DIB) -SHG cell exhibited two distinct reduction peaks in potential sweeps from +3.0V to +1.5V, the first of which was around +2.25V, which was probably caused by the conversion of the polymeric sulfur in cp (S-r-DIB) -SHG to polysulfide (Li2Sn, 4. ltoreq. n.ltoreq.8); while the second peak at +1.93V is due to further reduction of lithium polysulfide to lithium sulfide (Li 2S). In the charged state, an oxidation peak at 2.53V occurs, which is caused by the oxidation of Li2S to polysulfides.

To further understand the electrochemical stability of the electrode material, different loadings of cp (S-r-DIB) -SHG material were subjected to EIS testing as shown in fig. 8 and 9. The equivalent circuit of the recorded Electrochemical Impedance Spectroscopy (EIS) plot and the Nyquist plot used for the fitting are shown. The intersection of the semicircle with the x-axis represents the ohmic resistance Re between the electrode and the electrolyte, and the semicircle of the Nyquist plot is the overlap (RSL) of two semicircles consisting of the charge transfer resistance (Rct) and the interface layer resistance. As can be seen from the figure, all cp (S-r-DIB) -SHG materials show a semicircle in the high frequency region and a radial slant line in the low frequency region. Form a semicircle, cp (S)_90％-r-DIB_9.76％)-SHG_0.24％And cp (S)_90％-r-DIB_9.53％)-SHG_0.47％The Rct of the positive electrode is only 12 omega and 18 omega respectively, and excellent low-resistance performance is shown. These observations clearly show that the copolymerization of sulfur with DIB to form crosslinked copolymers significantly facilitates the transfer of electrons and protons.

Further, according to the lithium ion transfer calculation formula:

calculated cp (S)_90％-r-DIB_9.53％)-SHG_0.47％The lithium ion mobility of the lithium ion battery is only 9.27E-13cm²s^-1And cp (S)_90％-r-DIB_9.76％)-SHG_0.24％Has a lithium ion mobility of 2.96E-14cm²s^-1This may be due to the optimization of the conductivity inside the material by the more introduced SHG.

Referring to FIGS. 10 and 11, the charge and discharge curves of the cp (S-r-DIB) -SHG positive electrode at a rate current of 0.1C and different DIB and SHG loading amounts show that cp (S)_90％-r-DIB_9.53％)-SHG_0.47％The highest first discharge specific capacity is 1212mAh/g, and the first charge-discharge capacity of other cp (S-r-DIB) -SHG materials is also larger than 1000mAh/g, which indicates that the SHG is doped into the cp (S-r-DIB) materials, and the CP (S-r-DIB) -SHG materials can be used for facilitating the release of battery energy after being formed into a battery.

Subsequently, cp (S-r-DIB) -SHG materials with different DIB and SHG loading amounts are subjected to a rate capability test, and as a result, the cp (S-r-DIB) -SHG series electrode materials all show excellent rate capability as shown in FIGS. 12 and 13. Wherein based on cp (S)_90％-r-DIB_9.53％)-SHG_0.47％The specific discharge capacity of the battery made of the material is 1236, 1108, 1044, 952 and 797mAh/g at the multiplying power of 0.1C, 0.2C, 0.5C, 1C and 2C respectively. Meanwhile, cp (S) is obtained after uninterrupted multiplying power charge-discharge circulation_90％-r-DIB_9.53％)-SHG_0.47％The discharge capacity of the material does not substantially change significantly from the previous capacity at this rate. Compared with other proportions of cp (S-r-DIB) -SHG materials, the discharge capacity is obviously improved, which is probably caused by the synergy between the fixation of active sulfur by the introduced DIB and the optimization of positive electrode conductivity by the SHG. In addition, these materials are cp (S) at high magnification of 5C_90％-r-DIB_9.53％)-SHG_0.47％The discharge capacity (498 mAh/g) of the material is far better than that of materials (71-400mAh/g) in other proportions, and the synergistic effect of DIB and SHG in the proportions can greatly reduce the damage of large current to a polymer electrode in the charging and discharging processes of the battery.

Fig. 13 is a charge-discharge curve of cp (S-r-DIB) -SHG series material under different cycle times at 0.1C rate, and it can be found that the specific discharge capacity of the material gradually decreases as the cycle times increase, but the discharge voltage remains substantially unchanged. In addition, cp (S)_90％-r-DIB_9.53％)-SHG_0.47％In the material, after 800 charge and discharge cycles, the capacity of the material is reduced from initial 1233mAh/g to 646mAh/g, compared with the initial capacity, 52.3% is retained, and the average decay rate of each cycle is only 0.06%.

cp(S_90％-r-DIB_9.53％)-SHG_0.47％The higher cycling stability of the material is likely due to the combination of the highly crosslinked sulfur copolymer formed and the excellent conductivity of the SHG.

The above description is only for the preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any person skilled in the art should be considered to be within the technical scope of the present invention, and the technical solutions and the inventive concepts thereof according to the present invention should be equivalent or changed within the scope of the present invention.

Claims

1. A lithium-sulfur battery positive electrode material and a preparation method thereof are characterized in that: comprises the following steps;

preparing materials:

1) synthesis of SHG

Graphene Oxide (GO) is prepared by a traditional Hummers method and dispersed in secondary distilled water to prepare a solution with a certain concentration. Taking 1g of 2-mercaptoethylamine hydrochloride, 1mL of ammonia water and 90mL (1mg/mL) of GO (graphene oxide) to be fully mixed in a 250mL flask, setting the temperature to be 90 ℃, heating for 6 hours, and after the reaction is completed, filtering and rinsing the mixture by using secondary distilled water to obtain an SHG material with high porosity;

2) synthesis of cp (S-r-DIB) -SHG

In a round bottom flask equipped with a magnetic stir bar, sublimed sulphur (4g, 0.125mol) was added under argon atmosphere and the mixture was cooled to room temperature in the form of sublimed sulphur: accurately weighing 1, 3-Diisopropylbenzene (DIB) and SHG according to the mass ratio of 9:1, then placing the flask in an oil bath preheated to 185 ℃, adding a calculated amount of 1, 3-Diisopropylbenzene (DIB) when sublimed sulfur melts into a liquid state which is cherry red, continuously stirring for about 5-10min until the product is in a vitrified state, then adding a calculated amount of SHG, continuously stirring for 2 hours, finally, immediately taking out the flask, placing the flask in liquid nitrogen for cooling, quenching the reaction, and finally obtaining a brownish black transparent crystal cp (S-r-DIB) -SHG; assembling the lithium-sulfur battery:

2) assembling the battery: dissolving LiTFSI with 1M electrolyte in EC/DMC solution according to the volume ratio of 1: 1; the test of the bimodal sulfur-based composite also used an electrolyte of 1M LiTFSI in a solution of DOL/DME (1: 1 by volume) containing 0.1M of the additive Li NO3, a metallic lithium sheet as negative electrode, Celgard2400 as separator, and a button cell (CR2032) assembled in an argon-filled glove box (MB-10compact, MBRAUN).