Lithium-sulfur battery positive electrode catalyst iodine-doped graphene material and rapid preparation method thereof

Abstract

The rapid preparation method comprises the following steps: mechanically ball-milling and uniformly mixing elemental iodine and reduced graphene oxide, tabletting, packaging into a quartz bottle in an argon glove box, carrying out microwave synthesis for a few times in a microwave synthesizer, and removing the elemental iodine physically deposited on the surface of the reduced graphene oxide to obtain the iodine-doped graphene material for the positive electrode catalyst of the lithium-sulfur battery. The iodine-doped graphene material is obtained; according to the invention, iodine atoms with high content and low price are selected as a catalyst, and the iodine-doped reduced graphene oxide material can be rapidly and efficiently prepared within 100 seconds by utilizing the wave-absorbing characteristic of the reduced graphene oxide material and the characteristic that iodine elementary substance is easy to sublimate and utilizing a microwave gas-phase synthesis method without high-temperature reaction or long-time hydrothermal synthesis; the material is applied to the sulfur positive electrode side of the lithium-sulfur battery; the positive electrode material of the battery is prepared by adding a catalyst, so that the reaction energy barrier of sulfur reduction is reduced, the electrochemical reaction polarization is reduced, the redox reaction kinetics is accelerated, the shuttle effect of polysulfide is inhibited, and the cycling stability of the battery is improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of transition metal catalyst preparation, and particularly relates to a lithium-sulfur battery positive electrode catalyst iodine-doped graphene material and a rapid preparation method. BACKGROUND

[0002] With the growing demand for energy in the world, electrochemical energy storage systems are developing towards large capacity and low cost. Lithium-sulfur batteries are considered to be the most promising next-generation product beyond lithium-ion battery technology due to their high theoretical energy density (2600 Wh / kg) and excellent theoretical capacity (1675 mAh / g). However, the positive electrode of lithium-sulfur batteries faces problems such as poor electrical conductivity, volume expansion, and the shuttle effect of soluble polysulfides, which seriously hinder the practical development and industrial application of lithium-sulfur batteries.

[0003] In view of the above problems, many current works focus on loading elemental sulfur on conductive carbon black, carbon nanotubes and other carbon materials, and using the porous or layered structure to adsorb polysulfides through van der Waals force, but such physical adsorption capacity is limited and temporary. Therefore, the prior art often uses transition metal nanocatalysts or catalytic components containing transition metals, such as metal oxides, metal nitrides, metal sulfides, and metal selenides, as sulfur positive electrode catalysts to accelerate the sulfur reduction reaction process, inhibit the shuttle of intermediate product lithium polysulfide, and reduce the reaction energy barrier of sulfur reduction. However, the preparation of transition metal catalysts is complex, requires high preparation conditions, and the material itself is expensive and has low storage content.

[0004] A patent application for a lithium-sulfur battery composite positive electrode material based on a high-entropy rare earth metal oxide carrier and a preparation method thereof (CN120261553A) uses a high-entropy sintering technique to convert polar lithium polysulfide by analogy with transition metal atoms, inhibit the dissolution of lithium polysulfide in ether-based electrolyte, and slow down the shuttle effect, but the content of rare earth metal is low, the price is high, which is not conducive to the commercialization and industrialization of lithium-sulfur batteries, and the preparation method is complex, energy-consuming, and has other defects.

[0005] The document "Iodine-doped carbon nanotubes boosting the adsorption effect and conversion kinetics of lithium-sulfur batteries (Journal of Colloid And Interface Science 672 (2024) 287-298)" can significantly improve the polarity and conductivity of I-CNTs by high-temperature vacuum synthesis of iodine-doped carbon nanotubes, accelerate reaction kinetics and improve electrocatalytic activity, but the synthesis temperature required for high-temperature vacuum synthesis of iodine-doped carbon nanotubes is high (750℃), the synthesis time is long (12h+), and there are still defects of high energy consumption and low thermal efficiency. SUMMARY

[0006] In order to overcome the defects of the prior art described above, the purpose of the present application is to provide a lithium-sulfur battery positive electrode catalyst iodine-doped graphene material and a rapid preparation method. The iodine-doped graphene catalyst formed by reduced graphene oxide and iodine can effectively load sulfur, limit its volume expansion, improve the conductivity of the positive electrode side of the lithium-sulfur battery, adsorb and catalyze polysulfides, and significantly improve the electrochemical performance of the lithium-sulfur battery. After the prepared iodine-doped graphene positive electrode catalyst is used for the positive electrode side of the lithium-sulfur battery, it has stronger polysulfide adsorption and catalytic conversion capacity compared with traditional carbon materials. In addition, the preparation method of the present application is simple and fast, and the microwave directly transmits heat through dielectric loss, without high-temperature synthesis. The reaction only takes 100s, greatly shortening the reaction time and improving the utilization rate of thermal reaction.

[0007] In order to achieve the above-mentioned purpose, the specific technical scheme adopted by the present application is as follows:

[0008] A lithium-sulfur battery positive electrode catalyst iodine-doped graphene material, the raw materials comprising: reduced graphene oxide and iodine element in a mass ratio of (1-3):1.

[0009] A preparation method of an iodine-doped graphene positive electrode catalyst material for a lithium-sulfur battery positive electrode, the specific steps being as follows:

[0010] Step 1, mechanically grinding 1-2g of iodine element for 10-15 minutes to obtain iodine element powder with a fineness of 150-250 mesh, then uniformly mixing 2-6g of reduced graphene oxide with the ground iodine element powder, and mechanically ball milling for 20-30 minutes to obtain iodine graphene mixed powder with a fineness of 700-1000 mesh;

[0011] Step 2, taking 49-51mg of the iodine graphene mixed powder obtained in step 1, pressing it into a thin sheet, and then transferring it to a quartz bottle and packaging in an argon environment;

[0012] Step 3, the quartz bottle packaged in step 2 is placed in a microwave synthesis instrument, and the surface of the sheet is free of purple gas under the conditions of power 700-900W and temperature 200-300℃ for 80-100s;

[0013] Step 4, after the quartz bottle is taken out and cooled to room temperature, the sheet material is dissolved in 40-60mL of anhydrous ethanol solution and centrifuged multiple times until the ethanol solution is clear and transparent. After suction filtration, vacuum drying at 60-80℃ for 24-30h, iodine-doped graphene material is obtained.

[0014] The specific tabletting method of step 2 is: tabletting under a pressure of 10-15MP for 5-8 minutes to obtain a sheet with a diameter of 10-12mm.

[0015] The alternative method of step 4 is: after the quartz bottle is taken out and cooled to room temperature, the sheet material is dissolved in 40-60mL of anhydrous ethanol solution and centrifuged multiple times until the ethanol solution is clear and transparent. After suction filtration, under an argon atmosphere, first aeration for 30-50min, then heating to 200-300℃ at a heating rate of 2-5℃ / min for 2-3h and then cooling to room temperature, annealing treatment to obtain iodine-doped graphene material.

[0016] The preparation method of the sulfur positive electrode sheet based on the lithium-sulfur battery positive electrode catalyst iodine-doped graphene material, specifically includes the following steps:

[0017] Step 1, the sulfur battery positive electrode catalyst iodine-doped graphene material is mixed and ground with sulfur element according to a mass ratio of 1:4-2:3 to obtain a sulfur positive electrode composite material powder with a fineness of 50-150mesh; then 49-51mg of the sulfur positive electrode composite material powder is pressed into a disc with a diameter of 10-12mm and a thickness of 0.8-1.2mm; then the disc is packaged in a quartz bottle filled with argon, and placed in a microwave solid-phase synthesis instrument, with the microwave power set to 300-400W and the time set to 20-30s;

[0018] Step 2, then the sulfur positive electrode composite material obtained in step 1, Super P conductive carbon black (conductive agent) and binder PVDF (polyvinylidene fluoride) are mixed and ground uniformly according to a mass ratio of 6:2:2-8:1:1 to obtain a powder with a fineness of 150-250mesh. 150-170mg of the mixed and ground powder material is added to NMP (N-methyl pyrrolidone) 200-300μl for further grinding to form a viscous fluid slurry, which is coated on a carbon-coated aluminum foil with a coating thickness of 200-250μm. The coated carbon-coated aluminum foil is placed in a 60-80℃ air oven for drying for 1-2h, and then transferred to a 60-80℃ vacuum oven for drying for 12-16h to obtain a positive electrode sheet.

[0019] The application discloses an iodine-doped graphene material used as a positive electrode catalyst of a lithium-sulfur battery.

[0020] The application discloses a sulfur positive electrode sheet based on the iodine-doped graphene material used as a positive electrode catalyst of a lithium-sulfur battery.

[0021] Compared with the prior art, the application has the following beneficial effects:

[0022] 1. The traditional iodine-doped graphene synthesis method is a multi-step process and needs high temperature (750 DEG C and above) and long time (12h+) reaction, the application greatly shortens the reaction time and improves the heat reaction utilization rate by a simple and fast preparation method, microwave direct heat transfer through dielectric loss, no high-temperature synthesis, and reaction only needs 100s; the formed iodine-doped graphene catalyst can effectively load sulfur to limit the volume expansion, improve the positive electrode side conductivity of the lithium-sulfur battery, adsorb and catalyze polysulfides, and thus significantly improve the electrochemical performance of the lithium-sulfur battery.

[0023] 2. The raw material iodine element used in the application is cheap and easy to obtain, and no unsafe dopant and harmful organic reagent is used, so that the application is more green and environmentally friendly and meets the new development concept; the preparation method is simple, more economical and effective, and has the potential for large-scale use.

[0024] 3. The iodine-doped graphene catalyst formed by the reduced graphene oxide and the iodine element can effectively load sulfur to limit the volume expansion, improve the positive electrode side conductivity of the lithium-sulfur battery, adsorb and catalyze polysulfides, and thus significantly improve the electrochemical performance of the lithium-sulfur battery; compared with the traditional carbon material, the prepared iodine-doped graphene positive electrode catalyst has stronger polysulfide adsorption and catalytic conversion capacity after being used for the positive electrode side of the lithium-sulfur battery; under the condition of 1C current, the initial capacity is about 1036.8 mAh g -1 , and the capacity attenuation rate is about 0.13% after 200 cycles, and the capacity of the ordinary lithium-sulfur battery is improved by 436.2 mAh g -1 .

[0025] In summary, first, iodine atoms are doped into the rGO sheet structure by p-type doping, forming stable iodine anions with electronegativity on the surface of rGO, the electrochemical performance of rGO is improved, at the same time, the defect structure is produced inside rGO, the lattice distance is expanded, and the structural stability is improved, so that high capacity and enhanced cycle stability are obtained; at the same time, the electronegativity (2.66) of iodine atom is greater than that (2.55) of carbon atom, when iodine is embedded in rGO, C-I covalent bond is formed, the iodine atom with lone pair electrons (Lewis base) can interact with lithium cation (Lewis acid) in lithium polysulfide (LiPSs), anchor and capture lithium polysulfide, and can inhibit the serious shuttle effect of existing lithium-sulfur battery, and solve the problem of slow reaction kinetics; the material is prepared by using a simple microwave gas phase synthesis method, without high temperature reaction or long time hydrothermal synthesis, with the characteristics of the material itself, iodine element is uniformly doped into the damaged edge of rGO material under the action of high power microwave, and the iodine-doped reduced graphene oxide material can be quickly and efficiently prepared in 100 seconds, and is used for the sulfur positive electrode side of lithium-sulfur battery; the positive electrode material is prepared by adding a catalyst, the reaction energy barrier of sulfur reduction is reduced, the electrochemical reaction polarization is reduced, the redox reaction kinetics is accelerated, the polysulfide shuttle effect is inhibited, and the cycle stability of the battery is improved.

[0026] The prepared positive electrode catalyst has low cost, short time consumption and excellent cycle rate performance, solves the problem of high cost of excessive metal compounds and rare earth metals at present, and provides a new idea for the application of iodine element in lithium-sulfur batteries. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 The preparation flow chart of I-rGO of the embodiment 1 of the application.

[0028] Figure 2 The scanning electron microscope (SEM) image of I-rGO of the embodiment 1 of the application.

[0029] Figure 3 The Raman spectrum of I-rGO of the embodiment 1 of the application.

[0030] Figure 4 The scanning electron microscope (SEM) and X-ray energy spectrum (EDS) images of I-rGO loaded with sulfur of the embodiment 1 of the application; wherein, Figure 4 (a) is a scanning electron microscope image of an iodine-doped graphene composite sulfur positive electrode, and the image shows that sulfur element is dispersed between the layers of the iodine-doped graphene material by the microwave synthesis method; Figure 4 (b) is an X-ray energy spectrum of an iodine-doped graphene composite sulfur positive electrode, which shows that C, S and I elements exist in the composite positive electrode material, further proving that iodine is uniformly doped into graphene, and the iodine-doped graphene material successfully uniformly loads sulfur element.

[0031] Figure 5 Charge-discharge cycle diagram of lithium-sulfur full battery assembled with I-rGO loaded sulfur positive electrode plate prepared in the present application examples 1-3 and comparative examples 1-2 at 1C current.

[0032] Figure 6 Rate performance diagram of lithium-sulfur full battery assembled with I-rGO loaded sulfur positive electrode plate prepared in the present application examples 1-3 and comparative examples 1-2.

[0033] Figure 7 Schematic diagram for assembling button cell. DETAILED DESCRIPTION

[0034] In order to clarify the content of the present application, the present application will be further specifically and in detail described below in conjunction with examples, but the scope of protection of the present application is not limited to the content described, and the chemical reagents used in the examples are all of analytical purity.

[0035] Example 1

[0036] Reference Figure 1 A preparation method of iodine-doped graphene positive electrode catalyst material for lithium-sulfur battery positive electrode, the specific steps are as follows:

[0037] (1) Take 90 mg of iodine element (I2) and mechanically ball mill for 10 min at room temperature to obtain iodine powder with a fineness of 200 mesh; according to a mass ratio of 2:1, take 180 mg of reduced graphene oxide (rGO) powder and 90 mg of milled iodine element, mechanically grind for 20 min, and prepare iodine graphene mixed powder with a uniform fineness of 800 mesh;

[0038] (2) Take 50 mg of the iodine graphene mixed powder prepared in step (1), and press it into a uniform sheet with a diameter of 10 mm and a thickness of 1 mm in a 10 mm diameter tablet press mold at a pressure of 10 MP for 5 min; and package it in a quartz bottle filled with argon;

[0039] (3) Place the sealed quartz bottle in step (2) in a microwave solid-phase synthesis instrument, set the microwave power to 800 W, the temperature to 300℃, and the time to 100 s until no purple-red gas is precipitated from the surface of the material;

[0040] (4) After taking out the quartz bottle and naturally cooling it to room temperature, dissolve the sheet material in 60 mL of anhydrous ethanol solution and centrifuge it 5 times until the anhydrous ethanol solution is clear and transparent, then filter it and transfer it to a ceramic crucible, and place it in a tube furnace for annealing treatment: previously introduce argon into the tube furnace for 30 min, then heat it to 200℃ at a heating rate of 2℃ / min and keep it for 2 h, then naturally cool it to room temperature to obtain the iodine-doped graphene material, i.e. the catalyst of I-rGO.

[0041] Figure 2 This is a scanning electron microscope (SEM) image of I-rGO from Example 1.

[0042] Figure 3 The image shows the Raman spectrum of I-rGO from Example 1.

[0043] Figure 4 The images show scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) images of sulfur loaded with I-rGO in Example 1.

[0044] Depend on Figures 2-4 As can be seen, the EDS spectrum shows that iodine is relatively uniformly doped into the graphene material, and the Raman spectrum shows characteristic peaks of carbon-iodine bonding, proving that carbon and iodine form chemical bonds; at the same time, the Raman spectrum shows that the introduction of elemental iodine increases the degree of defects in graphene, thereby increasing the adsorption and conversion of polysulfides in the material.

[0045] The preparation method of sulfur cathode sheet based on iodine-doped graphene material as a cathode catalyst for lithium-sulfur batteries specifically includes the following steps:

[0046] (1) The sulfur battery cathode catalyst iodine-doped graphene material and elemental sulfur were mixed and ground evenly at a mass ratio of 1:4 to a fineness of 100 mesh. The mixed powder was then pressed into 10 mm thick discs with a thickness of 0.8 mm and a mass of 50 mg per disc. The discs were then sealed in a quartz bottle filled with argon gas and placed in a microwave solid phase synthesizer with a microwave power of 300 W and a time of 20 s.

[0047] (2) Then, the sulfur positive electrode composite material obtained in step (1) is mixed with 136 mg of Super P conductive carbon black (conductive agent) and 17 mg of PVDF (polyvinylidene fluoride) binder and ground evenly to a fineness of 200 mesh. After mixing and grinding, 300 μl of NMP (N-methylpyrrolidone) is added to the mixed and ground material and the grinding is continued to be thorough to form a viscous fluid slurry. This slurry is coated on carbon-coated aluminum foil with a coating thickness of 200 μm. The coated electrode is placed in a 60°C forced-air oven to dry for 2 h, and then transferred to an 80°C vacuum oven to dry for 12 h to obtain the positive electrode.

[0048] like Figure 5 As shown, the initial specific capacity of the composite sulfur cathode material obtained in Example 1 at a 1C rate is 1036.8 mAh g. -1 After 200 cycles, the battery capacity is approximately 750.0 mAh g. -1 The capacity retention rate was 72.34%; Figure 6 As shown, the composite sulfur cathode material obtained in Example 1 has a discharge specific capacity of 1296 mAh g at 0.2C and 3C rates. -1 and 709.7mAh g-1 .

[0049] Example 2

[0050] A preparation method of an iodine-doped graphene positive electrode catalyst material for a lithium-sulfur battery positive electrode, the specific steps are as follows:

[0051] (1) Take 1 g of iodine element (I2) and mechanically ball mill for 12 min at room temperature to obtain iodine powder with a fineness of 150 mesh; mix 2 g of reduced graphene oxide (rGO) powder and the ground iodine powder uniformly, and mechanically grind for 20 min to obtain uniformly mixed iodine graphene powder with a fineness of 700 mesh;

[0052] (2) Take 50 mg of the iodine graphene mixed powder prepared in step (1), and press it into a tablet in a 12 mm diameter tablet press mold with a pressure of 12 MP for 6 min to form a uniform tablet with a diameter of 12 mm and a thickness of 1.2 mm; and package it in a quartz bottle filled with argon;

[0053] (3) Place the sealed quartz bottle in step (2) in a microwave solid-phase synthesis instrument, set the microwave power to 800 W, the temperature to 250°C, and the time to 80 s until no purple-red gas is precipitated from the surface of the material;

[0054] (4) After taking out the quartz bottle and naturally cooling it to room temperature, dissolve the tablet material in 60 mL of anhydrous ethanol solution and centrifuge it 5 times until the anhydrous ethanol solution is clear and transparent; then, after suction filtration, dry it at 80°C under vacuum for 30 h to obtain the iodine-doped graphene material, i.e., the catalyst I-rGO.

[0055] As shown in Figure 5 , the initial specific capacity of the composite sulfur positive electrode material obtained in Example 2 at 1C rate is 1032.2 mAh g -1 , and the capacity of the battery after 200 cycles is about 635.4 mAh g -1 , with a capacity retention rate of 61.56%; as shown in Figure 6 , the discharge specific capacities of the composite sulfur positive electrode material obtained in Example 2 at 0.2C and 3C rates are 1203.8 mAh g -1 and 673.3 mAh g -1 , respectively.

[0056] A preparation method of a sulfur positive electrode sheet based on the iodine-doped graphene material as a lithium-sulfur battery positive electrode catalyst, specifically including the following steps:

[0057] (1) The iodine-doped graphene material of the positive electrode catalyst of the sulfur battery is mixed with sulfur element according to a mass ratio of 2:3, uniformly ground, and the fineness is 80 meshes. Then, 50 mg of the mixed powder is pressed into a 10 mm diameter and 1.2 mm thick disc, which is then packaged in a quartz bottle filled with argon, and placed in a microwave solid-phase synthesis instrument. The microwave power is set to 350 W, and the time is 25 s;

[0058] (2) Then, 90 mg of the sulfur positive electrode composite material obtained in step (1) and 30 mg of Super P conductive carbon black (conductive agent) and 30 mg of binder PVDF (polyvinylidene fluoride) are mixed and uniformly ground, and the fineness is 150 meshes. The mixed and ground material is added to 200 μl of NMP (N-methyl pyrrolidone) and further ground to form a viscous fluid slurry, which is coated on a carbon-coated aluminum foil with a coating thickness of 200 μm. The coated electrode sheet is placed in a 70°C air oven for drying for 2 h, and then transferred to a 80°C vacuum oven for drying for 14 h to obtain a positive electrode sheet.

[0059] Example 3

[0060] A preparation method of an iodine-doped graphene positive electrode catalyst material for a lithium-sulfur battery positive electrode, the specific steps are as follows:

[0061] (1) 2 g of iodine element (I2) is mechanically ball milled at room temperature for 15 min to obtain iodine powder with a fineness of 250 meshes. 4 g of reduced graphene oxide (rGO) powder and 2 g of the ground iodine powder are mechanically ground for 20 min to obtain uniformly mixed iodine graphene mixed powder with a fineness of 900 meshes;

[0062] (2) 50 mg of the iodine graphene mixed powder prepared in step (1) is pressed into a thin sheet with a diameter of 10 mm and a thickness of 0.8 mm in a 10 mm diameter tablet press die at a pressure of 15 MP for 8 min. The thin sheet is then packaged in a quartz bottle filled with argon;

[0063] (3) The sealed quartz bottle in step (2) is placed in a microwave solid-phase synthesis instrument, the microwave power is set to 900 W, the temperature is 200°C, and the time is 100 s until no purple-red gas is precipitated from the surface of the material;

[0064] (4) After the quartz bottle is taken out and naturally cooled to room temperature, the thin sheet material is dissolved in 50 mL of anhydrous ethanol solution and centrifuged 5 times until the anhydrous ethanol solution is clear and transparent. After suction filtration, the material is transferred to a ceramic crucible and placed in a tube furnace for annealing treatment. The tube furnace is pre-filled with argon for 30 min, then heated to 300°C at a heating rate of 3°C / min and kept for 3 h. After natural cooling to room temperature, the iodine-doped graphene material, i.e. the catalyst of I-rGO, is obtained.

[0065] As Figure 5As shown, the initial specific capacity of the composite sulfur cathode material obtained in Example 3 at a 1C rate is 942.9 mAh g. -1 After 200 cycles, the battery capacity is approximately 586.6 mAh g. -1 The capacity retention rate was 62.21%; Figure 6 As shown, the composite sulfur cathode material obtained in Example 3 has a discharge specific capacity of 1042.8 mAh g at 0.2C and 3C rates, respectively. -1 and 620.5mAh g -1 .

[0066] The preparation method of sulfur cathode sheet based on iodine-doped graphene material as a cathode catalyst for lithium-sulfur batteries specifically includes the following steps:

[0067] (1) The sulfur battery cathode catalyst iodine-doped graphene material and sulfur element were mixed and ground evenly at a mass ratio of 1:4 to a fineness of 100 mesh. Then, 50 mg of the mixed powder was pressed into a disc with a diameter of 10 mm and a thickness of 1 mm. The disc was then sealed in a quartz bottle filled with argon gas and placed in a microwave solid phase synthesizer. The microwave power was set to 400 W and the time was 30 s.

[0068] (2) Then, the sulfur positive electrode composite material obtained in step (1) is mixed with 136 mg of Super P conductive carbon black (conductive agent) and 17 mg of PVDF (polyvinylidene fluoride) binder and ground evenly to a fineness of 200 mesh. After mixing and grinding, 300 μl of NMP (N-methylpyrrolidone) is added to the mixed and ground material and the grinding is continued to be thorough to form a viscous fluid slurry. This slurry is coated on carbon-coated aluminum foil with a coating thickness of 200 μm. The coated electrode is placed in an 80°C forced-air oven to dry for 2 h, and then transferred to an 80°C vacuum oven to dry for 16 h to obtain the positive electrode.

[0069] Example 4

[0070] A method for preparing an iodine-doped graphene cathode catalyst material for lithium-sulfur batteries, comprising the following specific steps:

[0071] (1) Take 2g of iodine (I2) and mechanically ball mill it for 15min at room temperature to obtain iodine powder with a fineness of 250 mesh; weigh 4g of reduced graphene oxide (rGO) powder and 2g of ground iodine powder, and mechanically grind them for 20min to obtain a uniformly mixed iodine-graphene powder with a fineness of 900 mesh.

[0072] (2) Weigh 50mg of the iodine-graphene mixed powder prepared in step (1), press it in a 10mm diameter tablet press at a pressure of 15MP for 8min to form a uniform sheet with a diameter of 10mm and a thickness of 0.8mm; and encapsulate it in a quartz bottle filled with argon gas.

[0073] (3) Put the sealed quartz bottle in step (2) into the microwave solid-phase synthesis instrument, set the microwave power to 900 W, the temperature to 200 ℃, and the time to 100 s until no purple-red gas is precipitated on the surface of the material;

[0074] (4) After taking out the quartz bottle and naturally cooling it to room temperature, dissolve the thin sheet material in 50 mL of anhydrous ethanol solution and centrifuge it 5 times until the anhydrous ethanol solution is clear and transparent. After suction filtration, transfer it to a ceramic crucible and place it in a tube furnace for annealing treatment: pre-blow argon for 30 min in the tube furnace, then heat it to 225 ℃ at a heating rate of 3 ℃ / min, keep it for 3 h, then naturally cool it to room temperature to obtain the iodine-doped graphene material, namely the I-rGO catalyst.

[0075] Example 5

[0076] A preparation method of an iodine-doped graphene positive electrode catalyst material for a lithium-sulfur battery positive electrode, the specific steps are as follows:

[0077] (1) Take 2 g of iodine element (I2) and mechanically ball mill it for 15 min at room temperature to obtain iodine powder with a fineness of 250 mesh; weigh 4 g of reduced graphene oxide (rGO) powder and 2 g of the ground iodine powder, mechanically grind them for 20 min to obtain uniformly mixed iodine graphene powder with a fineness of 900 mesh;

[0078] (2) Weigh 50 mg of the iodine graphene mixed powder prepared in step (1), press it into a uniform sheet with a diameter of 10 mm and a thickness of 0.8 mm in a 10 mm diameter tablet press die at a pressure of 15 MP for 8 min, and then seal it in an argon-filled quartz bottle;

[0079] (3) Put the sealed quartz bottle in step (2) into the microwave solid-phase synthesis instrument, set the microwave power to 900 W, the temperature to 200 ℃, and the time to 100 s until no purple-red gas is precipitated on the surface of the material;

[0080] (4) After taking out the quartz bottle and naturally cooling it to room temperature, dissolve the thin sheet material in 50 mL of anhydrous ethanol solution and centrifuge it 5 times until the anhydrous ethanol solution is clear and transparent. After suction filtration, transfer it to a ceramic crucible and place it in a tube furnace for annealing treatment: pre-blow argon for 30 min in the tube furnace, then heat it to 225 ℃ at a heating rate of 3 ℃ / min, keep it for 3 h, then naturally cool it to room temperature to obtain the iodine-doped graphene material, namely the I-rGO catalyst.

[0081] Comparative Example 1

[0082] The preparation process and conditions of Comparative Example 1 are the same as those of Example 1, except that the step of grinding the mixed iodine element in S1 (1) is omitted, and the rGO after microwave treatment is used to prepare the sulfur composite cathode in S2.

[0083] As shown in Figure 5 , the initial specific capacity of the composite sulfur cathode material obtained in Comparative Example 1 is 861.5 mAh g -1 at 1C rate, and the capacity of the battery is about 556.4 mAh g -1 after 200 cycles, with a capacity retention rate of 64.54%; as shown in Figure 6 , the discharge specific capacities of the composite sulfur cathode material obtained in Comparative Example 1 are 997.1 mAh g -1 and 536 mAh g -1 at 0.2C and 3C rates, respectively.

[0084] Comparative Example 2

[0085] The rGO without microwave treatment is directly used to prepare the sulfur composite cathode in S2.

[0086] As shown in Figure 5 , the initial specific capacity of the composite cathode material obtained in Comparative Example 2 is 828.1 mAh g -1 at 1C rate, and the capacity of the battery is 312.7 mAh g -1 after 200 cycles, with a capacity retention rate of 37.80%; as shown in Figure 6 , the discharge specific capacities of the composite sulfur cathode material obtained in Comparative Example 2 are 889.1 mAh g -1 and 498.1 mAh g -1 at 0.2C and 3C rates, respectively.

[0087] Test Example 1

[0088] The composite cathode materials prepared in Examples 1-3 and Comparative Examples 1-2 are used to make electrode sheets, and batteries are assembled, with the process described as follows:

[0089] S1 Battery assembly

[0090] The batteries are assembled using button cells (2025) and the performance is tested, with the assembly sequence being negative shell - lithium sheet - electrolyte - separator - positive sheet - spring - gasket - electrolyte - positive shell, and the battery is then packaged; the entire process is completed in an argon-filled glove box, as shown in Figure 7 .

[0091] The obtained 2025 button cell is placed on a battery test system, and after standing for 8 h, the voltage cutoff range is set to 1.7-2.8 V, and the charge-discharge cycle test is carried out at 1C rate, with the results shown in Figure 5The results are shown in the following table. Figure 6 The results are shown in the following table.

[0092]

[0093]

[0094] As shown in the above table, the material obtained in Example 1 has the highest initial specific capacity and capacity retention rate compared with other materials. Meanwhile, the composite positive electrode material obtained in Example 1 has discharge specific capacities of 1296 mAh g -1 and 709.7 mAh g -1 at 0.2 C and 3 C rates, respectively, which are obviously superior to the composite positive electrode materials obtained in Comparative Example 1, Comparative Example 2 and the rest of the examples.

Claims

1. A lithium-sulfur battery cathode catalyst iodine-doped graphene material, characterized in that, The raw materials include: reduced graphene oxide and iodine element in a mass ratio of (1-3):

1.

2. A method for preparing a lithium-sulfur battery cathode catalyst iodine-doped graphene material, characterized in that, The specific steps are as follows: Step 1: 1-2 g of iodine element is mechanically ground for 10-15 minutes to obtain iodine element powder with a fineness of 150-250 mesh, then 2-6 g of reduced graphene oxide is uniformly mixed with the ground iodine element powder, and mechanical ball milling is performed for 20-30 minutes to obtain iodine graphene mixed powder with a fineness of 700-1000 mesh; Step 2: 49-51 mg of the iodine graphene mixed powder obtained in step 1 is pressed into a thin sheet, and then transferred to a quartz bottle and sealed in an argon environment; Step 3: The sealed quartz bottle in step 2 is placed in a microwave synthesis instrument, and the sheet surface is free of purple red gas under the conditions of a power of 700-900 W and a temperature of 200-300 ℃ for 80-100 s; Step 4: After the quartz bottle is removed and cooled to room temperature, the sheet material is dissolved in 40-60 mL of anhydrous ethanol solution, centrifuged multiple times until the anhydrous ethanol solution is clear and transparent, and then vacuum dried at 60-80 ℃ for 24-30 h after suction filtration to obtain iodine-doped graphene material.

3. The method for preparing a lithium-sulfur battery cathode catalyst iodine-doped graphene material according to claim 2, characterized in that, The specific tablet pressing method in step 2 is: tablet pressing under a pressure of 10-15 MP for 5-8 minutes to obtain a sheet with a diameter of 10-12 mm and a thickness of 0.8-1.2 mm.

4. The method for preparing the iodine-doped graphene material of the lithium-sulfur battery positive electrode catalyst according to claim 2, characterized in that, The alternative method of step 4 is: after the quartz bottle is removed and cooled to room temperature, the sheet material is dissolved in 40-60 mL of anhydrous ethanol solution, centrifuged multiple times until the anhydrous ethanol solution is clear and transparent, and then suction filtered under an argon atmosphere, first aerated for 30-50 min, then heated to 200-300 ℃ at a heating rate of 2-5 ℃ / min for 2-3 h, and then cooled to room temperature to obtain iodine-doped graphene material after annealing treatment.

5. The preparation method of the lithium-sulfur battery positive electrode catalyst iodine-doped graphene material according to claim 2, and the specific steps are as follows: Step 1: 90 mg of iodine element I2 is mechanically ball milled for 10 min at room temperature to obtain iodine powder with a fineness of 200 mesh; 180 mg of reduced graphene oxide rGO powder and 90 mg of ground iodine element are weighed according to a mass ratio of 2:1, mechanically ground for 20 min, and iodine graphene mixed powder with a fineness of 800 mesh is prepared; Step 2: 50 mg of the iodine graphene mixed powder prepared in step 1 is weighed, pressed into a sheet with a diameter of 10 mm in a tablet press die, and pressed into a sheet with a diameter of 10 mm and a thickness of 1 mm under a pressure of 10 MP for 5 min; and the sheet is sealed in a quartz bottle filled with argon; Step 3: The sealed quartz bottle in step 2 is placed in a microwave solid-phase synthesis instrument, the microwave power is set to 800 W, the temperature is 300 ℃, and the time is 100 s until the material surface is free of purple red gas; Step 4: After the quartz bottle is removed and cooled to room temperature, the sheet material is dissolved in 40-60 mL of anhydrous ethanol solution, centrifuged multiple times until the anhydrous ethanol solution is clear and transparent, and then vacuum dried at 60-80 ℃ for 24-30 h after suction filtration to obtain iodine-doped graphene material. Step 4, after the quartz bottle is taken out and naturally cooled to room temperature, the flake material is dissolved in 60 mL of anhydrous ethanol solution and centrifuged 5 times until the anhydrous ethanol solution is clear and transparent, then filtered and transferred to a ceramic crucible, and placed in a tube furnace for annealing treatment: 30 min of argon is introduced in advance in the tube furnace, then heated to 200℃ at a heating rate of 2℃ / min, kept for 2h, then naturally cooled to room temperature, and the iodine-doped graphene material, namely I-rGO, is obtained.

6. The preparation method of the lithium-sulfur battery positive electrode catalyst iodine-doped graphene material according to claim 2, and the specific steps are as follows: Step 1, 1g of iodine I2 is mechanically ball milled for 12 min at room temperature to obtain iodine powder with a fineness of 150 mesh; 2g of reduced graphene oxide (rGO) powder and the ground iodine powder are mixed uniformly, and then mechanically ground for 20 min to obtain uniformly mixed iodine graphene powder with a fineness of 700 mesh; Step 2, 50mg of the iodine graphene mixed powder prepared in step 1 is pressed into a flake with a diameter of 12mm and a thickness of 1.2mm in a 12mm-diameter tablet press mold at a pressure of 12MP for 6min; and the flake is packaged in a quartz bottle filled with argon; Step 3, the sealed quartz bottle in step 2 is placed in a microwave solid-phase synthesis instrument, the microwave power is set to 800W, the temperature is 250℃, and the time is 80s until no purple-red gas is precipitated on the surface of the material; Step 4, after the quartz bottle is taken out and naturally cooled to room temperature, the flake material is dissolved in 60 mL of anhydrous ethanol solution and centrifuged 5 times until the anhydrous ethanol solution is clear and transparent, then filtered and transferred to a ceramic crucible, and placed in a tube furnace for annealing treatment: 30 min of argon is introduced in advance in the tube furnace, then heated to 200℃ at a heating rate of 2℃ / min, kept for 2h, then naturally cooled to room temperature, and the iodine-doped graphene material, namely I-rGO, is obtained.

7. The preparation method of the lithium-sulfur battery positive electrode catalyst iodine-doped graphene material according to claim 2, and the specific steps are as follows: Step 1, 2g of iodine I2 is mechanically ball milled for 15 min at room temperature to obtain iodine powder with a fineness of 250 mesh; 4g of reduced graphene oxide (rGO) powder and 2g of the ground iodine powder are mechanically ground for 20 min to obtain uniformly mixed iodine graphene powder with a fineness of 900 mesh; Step 2, 50mg of the iodine graphene mixed powder prepared in step 1 is pressed into a flake with a diameter of 10mm and a thickness of 0.8mm in a 10mm-diameter tablet press mold at a pressure of 15MP for 8min; and the flake is packaged in a quartz bottle filled with argon; Step 3, the sealed quartz bottle in step 2 is placed in a microwave solid-phase synthesis instrument, the microwave power is set to 900W, the temperature is 200℃, and the time is 100s until no purple-red gas is precipitated on the surface of the material; Step 4, after the quartz bottle is taken out and naturally cooled to room temperature, the flake material is dissolved in 50 mL of anhydrous ethanol solution and centrifuged 5 times until the anhydrous ethanol solution is clear and transparent, then filtered and transferred to a ceramic crucible, placed in a tube furnace for annealing treatment: the tube furnace is pre-filled with argon for 30 min, then heated to 300℃ at a rate of 3℃ / min, kept for 3 h, then naturally cooled to room temperature to obtain the iodine-doped graphene material, i.e. I-rGO, as a catalyst.

8. A method for preparing a sulfur positive electrode sheet based on a lithium-sulfur battery positive electrode catalyst iodine-doped graphene material, characterized in that, Specifically comprising the following steps: Step 1, the iodine-doped graphene material as a sulfur battery positive electrode catalyst is mixed and ground with elemental sulfur according to a mass ratio of 1:4-2:3 to obtain a sulfur positive electrode composite material powder with a fineness of 50-150 mesh; then 49-51 mg of the sulfur positive electrode composite material powder is pressed into a disc with a diameter of 10-12 mm and a thickness of 0.8-1.2 mm; then the disc is packaged in a quartz bottle filled with argon and placed in a microwave solid-phase synthesis instrument, with the microwave power set to 300-400 W and the time set to 20-30 s; Step 2, then the sulfur positive electrode composite material obtained in step 1 is mixed and ground with Super P conductive carbon black (a conductive agent) and a binder PVDF (polyvinylidene fluoride) according to a mass ratio of 6:2:2-8:1:1 to obtain a powder with a fineness of 150-250 mesh, 150-170 mg of the mixed and ground powder material is added to 200-300 μl of NMP (N-methyl pyrrolidone) for further grinding to form a viscous fluid slurry, which is coated on a carbon-coated aluminum foil with a coating thickness of 200-250 μm, the coated carbon-coated aluminum foil is placed in a 60-80℃ air oven for drying for 1-2 h, then transferred to a 60-80℃ vacuum oven for drying for 12-16 h to obtain a positive electrode sheet.

9. An iodine-doped graphene material as a lithium-sulfur battery positive electrode catalyst, prepared by any of the methods of claims 2-7.

10. A sulfur positive electrode sheet based on the iodine-doped graphene material as a lithium-sulfur battery positive electrode catalyst, prepared by claim 8.

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