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CN113690437A - Graphite-phase carbon nitride/graphene lithium-sulfur battery positive electrode material and preparation method thereof - Google Patents

Graphite-phase carbon nitride/graphene lithium-sulfur battery positive electrode material and preparation method thereof Download PDF

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CN113690437A
CN113690437A CN202110785451.0A CN202110785451A CN113690437A CN 113690437 A CN113690437 A CN 113690437A CN 202110785451 A CN202110785451 A CN 202110785451A CN 113690437 A CN113690437 A CN 113690437A
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graphene
carbon nitride
graphite
phase carbon
lithium
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邢飞
田敬坤
姬广民
韩雪
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Shandong University of Technology
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Abstract

本发明属于电化学应用技术领域，公开了一种石墨相氮化碳/石墨烯锂硫电池正极材料及其制备方法。该材料以三聚氰胺和尿素作为石墨相氮化碳的前驱体，使用改进的Hummers法制备氧化石墨烯气凝胶，将石墨烯气凝胶在三聚氰胺/尿素溶液充分吸收，最终得到石墨相氮化碳/石墨烯杂化材料。再通过熔融扩散法制备石墨相氮化碳/石墨烯/硫复合材料，然后按比例混合石墨相氮化碳/石墨烯/硫复合材料、导电炭黑、PVDF，边滴加NMP边研磨以获得正极浆料，最后通过涂膜，真空干燥，压片，冲片并在手套箱里组装成CR2032扣式电池。本发明结合了石墨相氮化碳高氮含量和石墨烯高电导率的优势协同限制多硫化锂的扩散，提高锂硫电池的存储能力，大大提升了锂硫电池的循环稳定性。

Figure 202110785451

The invention belongs to the technical field of electrochemical application, and discloses a graphite phase carbon nitride/graphene lithium-sulfur battery cathode material and a preparation method thereof. The material uses melamine and urea as the precursors of graphitic carbon nitride, and uses the improved Hummers method to prepare graphene oxide aerogels. The graphene aerogels are fully absorbed in melamine/urea solution, and finally graphitic carbon nitride is obtained. /Graphene Hybrid Materials. Then prepare graphitic carbon nitride/graphene/sulfur composite material by melt diffusion method, then mix graphitic carbon nitride/graphene/sulfur composite material, conductive carbon black, PVDF in proportion, and grind while adding NMP to obtain The positive electrode slurry is finally coated, vacuum dried, pressed, punched and assembled into a CR2032 button cell in a glove box. The invention combines the advantages of high nitrogen content of graphitic carbon nitride and high electrical conductivity of graphene to synergistically limit the diffusion of lithium polysulfide, improve the storage capacity of lithium-sulfur batteries, and greatly improve the cycle stability of lithium-sulfur batteries.

Figure 202110785451

Description

Graphite-phase carbon nitride/graphene lithium-sulfur battery positive electrode material and preparation method thereof
Technical Field
The invention belongs to the field of preparation of lithium-sulfur battery positive electrode materials, and particularly relates to a graphite-phase carbon nitride/graphene lithium-sulfur battery positive electrode material and a preparation method thereof.
Background
The information in this background section is only for enhancement of understanding of the general background of the invention and is not necessarily to be construed as an admission or any form of suggestion that this information forms the prior art that is already known to a person of ordinary skill in the art.
Has high theoretical energy density (2600 Wh kg)-1) Have become potential energy storage devices for electric vehicles and large-scale electrical storage. However, practical application of lithium-sulfur batteries presents numerous challenges due to low sulfur utilization and poor cycle stability resulting from low conductivity of sulfur intermediates and dissolution of lithium polysulfide.
To address these problems, carbon is widely introduced to sulfur cathodes to facilitate electron transport. Carbon materials are often designed as multifunctional frameworks that improve lithium ion diffusion, especially in thick electrodes. Although the micropores of the porous carbon provide physical constraints for the soluble lithium polysulphides, the kinetics of the redox reaction are also much reduced during the discharge/charge process due to the constraints of the penetration of sulphur into the pores as an active species.
The structure of graphite-phase carbon nitride is similar to that of layered graphite, and is an emerging ordered polymeric material that has been used as an important catalyst in the field of photocatalysis due to its superior optical and electronic properties. First-principles calculations also indicate that lipopolysaccharides tend to anchor at sites with intrinsically high-charge polar functional groups, such as pyridine nitrogens. Thus, when used in a carbon matrix-based sulfur cathode, carbon nitride can be considered a carbon material doped with the highest level of nitrogen, which provides more active sites for anchoring lithium polysulfides, than conventional nitrogen-doped carbon materials with limited nitrogen doping content. In addition, the polymeric nature imparts excellent structural flexibility to the graphite phase carbon nitride, providing a cushion support for volume expansion as lithium sulfide is formed at lower densities during discharge. In addition, the graphitic carbon nitride can catalytically capture the molecular configuration of lithium polysulfides and improve their redox reaction kinetics during discharge/charge. However, the accessible surface of most graphite phase carbon nitrides is very limited and there are fewer active sites for the adsorption and conversion of lithium polysulfides. Worse still, the poor conductivity of graphite phase carbon nitride severely reduces the sulfur utilization and leads to greater polarization during discharge/charge, limiting its application in sulfur cathodes. Graphene assembled carbons, particularly carbons having a three-dimensional graphene network structure, are considered promising carbon hosts in lithium sulfur batteries due to their continuous conductive scaffold, interpenetrating ion transport pathways, and readily accessible pores. These properties greatly contribute to the kinetics of the redox reaction of the lithium lead battery during discharge/charge. Therefore, the patent proposes a new strategy, graphite phase carbon nitride is introduced into a three-dimensional graphene framework to serve as a host of a sulfur cathode, so as to realize the synergistic combination of space limitation, chemical anchoring and rapid catalytic conversion of the sulfur cathode, and the method combines the advantages of the two, so that the carbon nitride can serve as a very promising lithium-sulfur cathode material.
Therefore, a method for improving the capacity retention rate of the lithium-sulfur battery by using the graphite-phase carbon nitride/graphene hybrid material as the positive electrode is provided.
Disclosure of Invention
The invention aims to provide a graphite-phase carbon nitride/graphene lithium-sulfur battery positive electrode material and a preparation method thereof, and provides a sulfur cathode host material which is high in sulfur load, high in active substance sulfur utilization rate, high in energy density, high in nitrogen content and obvious in shuttle inhibition effect and is used for improving poor cycle performance of a lithium-sulfur battery, aiming at the problems that a sulfur composite positive electrode material in the prior art is low in sulfur load, small in specific capacity of a sulfur electrode, low in energy density, poor in cycle stability and the like.
The technical scheme of the invention is as follows:
a graphite phase carbon nitride/graphene lithium sulfur battery positive electrode material and a preparation method thereof comprise the following steps:
1) preparing 10mol/L melamine/urea mixed solution by taking melamine and urea as precursors;
2) preparing graphene oxide by adopting an improved Hummers method, placing graphite powder into a beaker, adding distilled water, performing ultrasound by using an ultrasonic machine to obtain uniformly dispersed graphene oxide dispersion liquid, transferring the obtained graphene oxide dispersion liquid into a polytetrafluoroethylene hydrothermal kettle, and reacting for 6 hours at 180 ℃ to obtain reduced graphene oxide hydrogel with a three-dimensional structure;
3) completely immersing the reduced graphene oxide hydrogel obtained in the step 2) in the melamine/urea mixed solution prepared in the step 1) at room temperature, repeatedly washing with distilled water, drying in an oven, placing the obtained material in a crucible after drying, heating to 550 ℃ in a tubular furnace at a heating rate of 5 ℃/min under the atmosphere of nitrogen, and maintaining for 2 hours to finally obtain the graphite-phase carbon nitride/graphene hybrid material;
4) mixing and grinding the graphite-phase carbon nitride/graphene hybrid material obtained in the step 3) with sublimed sulfur, placing the mixture in a polytetrafluoroethylene reaction kettle, heating to 155 ℃, keeping the temperature for 12 hours, and obtaining a graphite-phase carbon nitride/graphene/sulfur composite material by a melting diffusion method;
5) mixing the graphite-phase carbon nitride/graphene/sulfur composite material obtained in the step 4) with PVDF and acetylene black, and grinding the mixture into positive slurry;
6) coating the positive electrode slurry obtained in the step 5) on an aluminum foil current collector, and performing coating, drying, tabletting and punching to finally obtain the lithium-sulfur battery positive electrode material.
According to the invention, the mass mixing ratio of melamine and urea in step 1) is preferably 3: 4, mixing and grinding the two materials for half an hour before preparing the solution, and cleaning the grinding bowl by using deionized water and absolute ethyl alcohol in advance.
According to the invention, preferably, the graphene oxide dispersion liquid obtained by the ultrasonic treatment in the step 2) is 2mg/mL, and the ultrasonic temperature is lower than 40 ℃ to prevent the reduction of the graphene.
According to the invention, preferably, the reduced graphene oxide aerogel in the step 3) needs to be soaked in a melamine/urea solution for 24 hours, the temperature of the reduced graphene oxide aerogel in the oven is 80 ℃, and the time is 24 hours.
According to the invention, preferably, the graphite phase carbon nitride/graphene/sulfur composite material obtained in the step 4) is fully ground for half an hour before being subjected to the step 5).
According to the present invention, preferably, the mixing ratio of the graphite phase carbon nitride/graphene/sulfur composite material in the step 5) to the conductive carbon black and the polyvinylidene fluoride binder (PVDF) is 8: 1: 1, dropwise adding an N-methyl pyrrolidone solvent while grinding.
According to the present invention, preferably, the positive electrode slurry in the step 6) is coated on an aluminum foil current collector at one time by a coater, the precision of a coating scraper is 100 microns, and then the coated material is dried in a vacuum drying oven at 60 ℃ for 24 hours.
According to the invention, the punched piece in the step 6) is preferably cut into a 12mm circular piece by a punching machine, and the punched piece cannot have wrinkles and burrs.
According to the invention, the grinding mode of the graphite phase carbon nitride/graphene/sulfur composite material, the conductive carbon black and the PVDF is preferably uniform in direction, clockwise or anticlockwise, and the direction cannot be changed in the midway.
A button electrode is characterized in that: the cathode comprises a cathode shell, a lithium plate, electrolyte, a diaphragm, electrolyte, an anode plate, a gasket, an elastic sheet and an anode shell which are assembled in sequence, wherein the anode plate is a graphite-phase carbon nitride/graphene/sulfur cathode composite anode plate of the lithium-sulfur battery.
The invention has the beneficial effects that:
the method takes the melamine and the urea as precursors for preparing the graphite-phase carbon nitride material, has the advantages of cheap and easily-obtained raw materials, low production cost and simple and convenient preparation method. The carbon nitride has high nitrogen content and high specific surface area, the graphene has very high conductivity, the carbon nitride and the graphene supplement each other, the high nitrogen content chemically limits the diffusion of lithium polysulfide, the excellent electron mobility of the graphene makes up the defect of low conductivity of the carbon nitride, the graphite-phase carbon nitride/graphene sulfur host material has 70wt% of sulfur loading capacity, the utilization rate of sulfur is also improved, and the cycle stability of the lithium-sulfur battery is integrally improved.
Drawings
Fig. 1 is a scanning electron microscope image of graphite-phase carbon nitride/graphene prepared in example 1;
fig. 2 is a scanning electron microscope image of the graphite phase carbon nitride/graphene/sulfur composite prepared in example 1;
FIG. 3 is a graph of electrochemical performance of example 1, comparative example 2, and comparative example 3 tested at a current of 0.1A/g.
Detailed Description
It is to be noted that the following detailed description is exemplary and is intended to provide further explanation of the invention, unless otherwise specified, and all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.
Example 1
160mg of graphite oxide powder prepared by an improved Hummers method is weighed in a plastic beaker, 80mL of deionized water is added, the mixture is placed in an ultrasonic machine for ultrasonic crushing, graphene oxide dispersion liquid with uniform dispersion and concentration of 2mg/mL is obtained, the obtained dispersion liquid is placed in a 100mL polytetrafluoroethylene reaction kettle and reacts in an oven at 180 ℃ for 6 hours, and graphene hydrogel with a three-dimensional columnar structure is obtained.
Completely immersing the obtained graphene hydrogel in 10mol/L melamine/urea solution at room temperature for 24h, taking out the treated graphene hydrogel after complete adsorption, repeatedly cleaning the graphene hydrogel with distilled water, and drying the graphene hydrogel in an oven at 80 ℃ for 24 h; then putting the mixture into a crucible and putting the crucible into a tube furnace for heating, and heating the mixture in N2Heating to 550 ℃ at a speed of 5 ℃/min and keeping for 2 hours to obtain the graphite phase carbon nitride/graphene hybrid material. Fig. 1 is a scanning electron microscope image of the graphite phase carbon nitride/graphene hybrid material prepared in this example, which shows that the network structure of the material is fluffy, the gap size is large, and the graphite phase carbon nitride/three-dimensional graphene network has developed pores.
And fully grinding the obtained graphite-phase carbon nitride/graphene hybrid material until no obvious blocky body exists. And (3) putting 3g of the prepared graphite-phase carbon nitride/graphene hybrid material and 7g of the sublimed sulfur simple substance into a cleaned grinding bowl, fully grinding for 30min, and keeping the same direction (clockwise or anticlockwise). Transferring the ground material into a reaction kettle, placing the reaction kettle in a blast drying oven, raising the temperature to 155 ℃, and then keeping the temperature at 155 ℃ for 12 hours to obtain the graphite phase carbon nitride/sulfur composite material. Fig. 2 is a scanning electron microscope image of the graphite-phase carbon nitride/graphene/sulfur composite material prepared in this example, and it can be seen that the shape did not change much from the previous one, and still had a lamellar structure, but some sulfide and a small amount of sulfur-aggregated curls were present on the surface, indicating that sulfur was successfully compounded with graphite-phase carbon nitride.
Respectively weighing 0.8g of graphite-phase carbon nitride/graphene/sulfur composite material, 0.1g of acetylene black and 0.1g of PVDF, putting the materials into a cleaned grinding pot, taking 100 microliters of NMP by using a liquid transfer gun with a 100 microliter range, dropwise adding the NMP into the mixed material, slowly grinding, and grinding for 5min in one-step manner to obtain the anode slurry of the carbon nitride/sulfur composite material.
And adjusting the thickness of a scraper to be 100 micrometers, coating the positive electrode slurry on an aluminum foil without wrinkles, coating by using a coater, placing the coated material in a culture dish to ensure the smoothness of the aluminum foil, and drying in a vacuum drying oven at 60 ℃ for 24 hours to obtain the positive electrode plate.
And cooling to room temperature, taking out, slicing, tabletting and punching to obtain the lithium-sulfur battery button cell. And sequentially assembling the positive plate, the elastic sheet, the gasket, the positive plate, the electrolyte, the diaphragm, the electrolyte, the lithium plate and the negative plate in the glove box, and sealing the battery by using a sealing machine to obtain the CR2032 type button battery. The charge-discharge voltage range of the prepared button battery is 1.8V-2.8V, the charge-discharge current is 0.1A/g, the button battery is circulated for 600 times, the coulomb efficiency is not obviously attenuated, and the reversible discharge capacity is 1163 mAh g-1Corresponding to a decay rate of 0.087% per cycle.
Comparative example 1
The difference from the embodiment 1 lies in that: the absorption is carried out without soaking the graphene in a melamine/urea solutionThe other steps and parameters were the same. The prepared button cell is tested with the charge-discharge voltage range of 1.8-2.8V and the charge-discharge current of 0.1A/g, and the reversible charge-discharge capacity of the button cell is 715.6mAh g-1The cycle was 600 times, and the capacity decayed 0.146% per cycle.
Comparative example 2
The difference from the embodiment 1 lies in that: and soaking the graphene in a melamine/urea saturated solution for adsorption and absorption, wherein other steps and parameters are the same. The prepared button cell is tested with the charge-discharge voltage range of 1.8-2.8V and the charge-discharge current of 0.1A/g, and the reversible charge-discharge capacity of 826mAh g-1The cycle was 600 times, with a capacity fade of 0.116% per cycle.
Comparative example 3
The difference from the embodiment 1 lies in that: the method has no graphene doping, belongs to a pure graphite phase carbon nitride electrode, and has the same other steps and parameters. The prepared button cell is tested with the charge-discharge voltage range of 1.8-2.8V and the charge-discharge current of 0.1A/g, and the reversible charge-discharge capacity of the button cell is 571.3 mAh.g-1The cycle was 600 times, with a capacity fade of 0.136% per cycle.
FIG. 3 is a long cycle performance test chart of example 1, comparative example 2 and comparative example 3 at a current rate of 0.1A/g, all of which have coulombic efficiencies of 95% or more, and it is apparent that the difference is that the concentration of melamine/urea solution has a great influence on the electrochemical performance, wherein the cycle stability of the electrode of comparative example 1 is significantly worse because of no chemisorption of nitrogen element on lithium polysulfide; the melamine/urea saturated solution in the comparative example 2 also affects the cycling stability of the electrode, the electrode in the comparative example 3 has no high conductivity of graphene, the overall sulfur utilization rate is obviously reduced, and the best is the embodiment 1 with 10mol/L of melamine/urea, and the concentration of the melamine/urea solution just can express the performance of the motor to the utmost.
Finally, it is noted that the disclosed embodiments are intended to aid in further understanding of the invention, but those skilled in the art will appreciate that: various substitutions and modifications are possible without departing from the spirit and scope of the invention and the appended claims. Therefore, the invention should not be limited to the embodiments disclosed, but the scope of the invention is defined by the appended claims.

Claims (10)

1. The graphite phase carbon nitride/graphene lithium-sulfur battery positive electrode material is prepared by adsorbing a dissolved carbon nitride precursor solution through graphene aerogel and then carrying out heat treatment, and is characterized by comprising the following steps of:
1) preparing 10mol/L melamine/urea mixed solution by taking melamine and urea as precursors;
2) preparing graphene oxide by adopting an improved Hummers method, placing graphite powder into a beaker, adding distilled water, performing ultrasound by using an ultrasonic machine to obtain uniformly dispersed graphene oxide dispersion liquid, transferring the obtained graphene oxide dispersion liquid into a polytetrafluoroethylene hydrothermal kettle, and reacting for 6 hours at 180 ℃ to obtain reduced graphene oxide hydrogel with a three-dimensional structure;
3) completely immersing the reduced graphene oxide hydrogel obtained in the step 2) in the melamine/urea mixed solution prepared in the step 1) at room temperature, repeatedly washing with distilled water, drying in an oven, placing the obtained material in a crucible after drying, heating to 550 ℃ in a tubular furnace at a heating rate of 5 ℃/min under the atmosphere of nitrogen, and maintaining for 2 hours to finally obtain the graphite-phase carbon nitride/graphene hybrid material;
4) mixing and grinding the graphite-phase carbon nitride/graphene hybrid material obtained in the step 3) with sublimed sulfur, placing the mixture in a polytetrafluoroethylene reaction kettle, heating to 155 ℃, keeping the temperature for 12 hours, and obtaining a graphite-phase carbon nitride/graphene/sulfur composite material by a melting diffusion method;
5) mixing the graphite-phase carbon nitride/graphene/sulfur composite material obtained in the step 4) with PVDF and acetylene black, and grinding the mixture into positive slurry;
6) coating the positive electrode slurry obtained in the step 5) on an aluminum foil current collector, and performing coating, drying, tabletting and punching to finally obtain the lithium-sulfur battery positive electrode material.
2. The positive electrode material of the graphite-phase carbon nitride/graphene lithium-sulfur battery and the preparation method thereof according to claim 1, wherein the mass mixing ratio of melamine and urea in step 1) is 3: 4, mixing and grinding the two materials for half an hour before preparing the solution, and cleaning the grinding bowl by using deionized water and absolute ethyl alcohol in advance.
3. The positive electrode material of the graphite-phase carbon nitride/graphene lithium-sulfur battery as claimed in claim 1, wherein the graphene oxide dispersion obtained by the ultrasonic treatment in step 2) is 2mg/mL, and the ultrasonic temperature is lower than 40 ℃ to prevent the reduction of graphene.
4. The positive electrode material of the graphite-phase carbon nitride/graphene lithium-sulfur battery as claimed in claim 1, wherein the reduced graphene oxide aerogel in step 3) is soaked in a melamine/urea solution for 24 hours at 80 ℃ in an oven for 24 hours.
5. The positive electrode material of the graphite-phase carbon nitride/graphene lithium sulfur battery and the preparation method thereof according to claim 1, wherein the graphite-phase carbon nitride/graphene/sulfur composite material obtained in the step 4) is ground for half an hour sufficiently before the step 5).
6. The positive electrode material of the graphite-phase carbon nitride/graphene lithium-sulfur battery as claimed in claim 1, wherein the mixing ratio of the graphite-phase carbon nitride/graphene/sulfur composite material in the step 5) to the conductive carbon black and the polyvinylidene fluoride binder (PVDF) is 8: 1: 1, dropwise adding an N-methyl pyrrolidone solvent while grinding.
7. The positive electrode material of the graphite-phase carbon nitride/graphene lithium-sulfur battery and the preparation method thereof according to claim 1, wherein the positive electrode slurry in the step 6) is coated on an aluminum foil current collector at one time by a coater, the coating precision of a coating scraper is 100 microns, and then the coated material is dried in a vacuum drying oven at 60 ℃ for 24 hours.
8. The positive electrode material of the graphite-phase carbon nitride/graphene lithium-sulfur battery as claimed in claim 1, wherein the punched piece in step 6) is cut into a 12mm circular piece by a punching machine, and the punched piece is free from wrinkles and burrs.
9. The positive electrode material of a graphite-phase carbon nitride/graphene lithium-sulfur battery as claimed in claim 6, wherein the graphite-phase carbon nitride/graphene/sulfur composite material, the conductive carbon black and the PVDF are ground in a uniform direction, clockwise or counterclockwise, and the direction is not changeable in the middle.
10. A button electrode is characterized in that: the lithium-sulfur battery positive plate is a graphite-phase carbon nitride/graphene/sulfur cathode composite positive plate of the lithium-sulfur battery prepared according to claims 6-9.
CN202110785451.0A 2021-07-12 2021-07-12 Graphite-phase carbon nitride/graphene lithium-sulfur battery positive electrode material and preparation method thereof Pending CN113690437A (en)

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CN115744842A (en) * 2022-10-11 2023-03-07 山西大学 Method for preparing graphite-phase carbon nitride from coal gasification ash

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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN115744842A (en) * 2022-10-11 2023-03-07 山西大学 Method for preparing graphite-phase carbon nitride from coal gasification ash

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