CN112510170B - Nitrogen and sulfur double-doped porous carbon lithium sulfur battery positive electrode material and preparation method and application thereof - Google Patents

Nitrogen and sulfur double-doped porous carbon lithium sulfur battery positive electrode material and preparation method and application thereof Download PDF

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CN112510170B
CN112510170B CN201910872473.3A CN201910872473A CN112510170B CN 112510170 B CN112510170 B CN 112510170B CN 201910872473 A CN201910872473 A CN 201910872473A CN 112510170 B CN112510170 B CN 112510170B
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甄蒙蒙
沈伯雄
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Hebei University of Technology
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Abstract

The invention discloses a nitrogen and sulfur double-doped porous carbon lithium sulfur battery anode material and a preparation method and application thereof, wherein the nitrogen and sulfur double-doped porous carbon material consists of 5.0-7.0% of nitrogen, 4.5-6.0% of sulfur and 87-90.5% of carbon in atomic percentage. Mixing a nitrogen and sulfur double-doped porous carbon material with sulfur, infiltrating by adopting a wet method to obtain a sulfur positive electrode active material, mixing the sulfur positive electrode active material, conductive carbon, a binder and N-methyl pyrrolidone to obtain a first slurry, coating the first slurry on an aluminum foil, and drying at 60-80 ℃ for 12-16 hours in a vacuum environment to obtain the nitrogen and sulfur double-doped porous carbon lithium sulfur battery positive electrode material. The invention utilizes the nitrogen and sulfur double-doped porous carbon material as a sulfur host and a modified diaphragm material at the same time, realizes the strong cycling stability and excellent rate capability of the battery, and the nitrogen and sulfur double-doped porous carbon material has simple preparation process and is suitable for large-scale synthesis.

Description

Nitrogen and sulfur double-doped porous carbon lithium sulfur battery positive electrode material and preparation method and application thereof
Technical Field
The invention belongs to the technical field of battery materials, and particularly relates to a nitrogen and sulfur double-doped porous carbon lithium sulfur battery positive electrode material and a preparation method and application thereof.
Background
The energy is the basis for human survival and development and is an important material guarantee for realizing the sustainable development of society and economy. China is in the period of high-speed economic development, the energy demand is greatly increased, and the problems of energy shortage and environmental pollution are increasingly highlighted. Therefore, how to effectively utilize renewable clean energy is a great problem related to the national civilization. Most renewable energy sources are intermittent and need high-efficiency energy storage technology to be stored, so that energy can be released according to requirements, and excessive energy sources are avoided. Energy storage technology is the core power to promote the development of renewable energy. Therefore, the development of an efficient energy storage technology can realize the utilization of renewable energy to the maximum extent, and has become one of the research hotspots in the field of energy development nowadays.
The advantages of high theoretical capacity, ultrahigh energy density and the like of the lithium-sulfur battery make the lithium-sulfur battery become a high-efficiency energy storage technology with the greatest application prospect. However, several disadvantages of lithium-sulfur batteries severely hinder the large-scale application of lithium-sulfur batteries: (1) poor electronic conductivity of sulfur and the product lithium sulfide; (2) large volume expansion during charging and discharging; (3) the shuttle effect generated by the diffusion of the soluble intermediate high-order lithium polysulfide between two poles of the battery is also the most serious problem faced by the lithium-sulfur battery at present. The method for improving the cycle performance of the lithium-sulfur battery mainly focuses on three aspects, namely (1) encapsulating sulfur into a conductive material to improve the electronic conductivity of an electrode; (2) constructing a modified membrane to mitigate shuttling of soluble lithium polysulfides; (3) the addition of the catalyst accelerates the conversion of lithium polysulphides and thus suppresses the shuttling effect. The methods effectively improve the cycle performance of the lithium-sulfur battery and provide important theoretical and technical references, which have advantages, but have some defects in practical application. The general conductive material has poor adsorbability to lithium polysulfide and cannot effectively inhibit the shuttle effect. The construction of a modified separator can temporarily alleviate shuttling of lithium polysulfides, but has poor long-term cycling stability. The construction method of the catalyst is generally complex, the yield is low, and the method is not beneficial to practical application. Therefore, a single method to improve the cycle performance of lithium sulfur batteries is not ideal.
Disclosure of Invention
Aiming at the defects of the prior art, the invention aims to provide a nitrogen and sulfur double-doped porous carbon material. The nitrogen and sulfur double-doped porous carbon material utilizes a carbon network framework to improve the conductivity of the battery, and utilizes the strong bond energy of Li-N and S-S to fix liquid lithium polysulfide. In addition, the catalytic action of the nitrogen and sulfur double-doped porous carbon material on lithium polysulfide can accelerate the conversion of the lithium polysulfide, thereby effectively inhibiting the shuttle effect in the lithium-sulfur battery and improving the specific capacity and the cycling stability of the lithium-sulfur battery.
The invention also aims to provide a preparation method of the nitrogen and sulfur double-doped porous carbon material, which is simple and suitable for large-scale production.
The invention aims to provide a preparation method of a nitrogen and sulfur double-doped porous carbon lithium-sulfur battery positive electrode material.
The invention also aims to provide the positive electrode material of the nitrogen and sulfur double-doped porous carbon lithium sulfur battery obtained by the preparation method, the positive electrode material of the nitrogen and sulfur double-doped porous carbon lithium sulfur battery has high conductivity and catalytic performance, and can be used as a host material of sulfur and a modification material of a diaphragm, so that the cycle performance of the lithium sulfur battery can be effectively improved, and the energy consumption can be reduced.
The purpose of the invention is realized by the following technical scheme.
The nitrogen and sulfur double-doped porous carbon material (NSC) consists of 5.0-7.0% of nitrogen, 4.5-6.0% of sulfur and 87-90.5% of carbon in atomic percentage.
The preparation method of the nitrogen and sulfur double-doped porous carbon material comprises the following steps:
1) dissolving citric acid and urea in a mixed solvent, stirring at 60-80 ℃ to form gel, heating the gel at 100-120 ℃ for 12-16 hours to obtain a carbon material precursor, wherein the mixed solvent is a mixture of distilled water and ethanol, and the ratio of the distilled water to the ethanol in the mixed solvent is (1-2): (2-4), wherein the ratio of the citric acid to the urea is (20-40) according to the parts by weight of the substances;
in the step 1), the ratio of the parts by weight of the citric acid to the parts by volume of the mixed solvent is 1 (30-40), and when the parts by weight of the citric acid is millimole, the parts by volume is milliliter.
2) Grinding the carbon material precursor, calcining for 4-6 hours at 300-350 ℃ under inert gas after grinding, and calcining for 8-10 hours at 650-950 ℃ to obtain a nitrogen-doped porous carbon material;
in the step 2), the grinding time is 30-60 minutes.
3) And calcining the nitrogen-doped porous carbon material for 4-6 hours at 650-950 ℃ in a mixed atmosphere to obtain the nitrogen-sulfur double-doped porous carbon material, wherein the mixed atmosphere is a mixture of hydrogen sulfide and inert gas.
In the step 3), the ratio of hydrogen sulfide to inert gas in the mixed atmosphere is (18-19) to (2-1) in parts by volume, and the inert gas is argon.
A preparation method of a nitrogen and sulfur double-doped porous carbon lithium-sulfur battery positive electrode material comprises the following steps:
a) mixing the nitrogen and sulfur double-doped porous carbon material with sulfur, and wetting by a wet method to obtain a sulfur anode active material, wherein the ratio of the nitrogen and sulfur double-doped porous carbon material to the sulfur is (2-4) according to parts by mass;
b) the method comprises the steps of mixing the sulfur positive electrode active material, conductive carbon, a binder and N-methyl pyrrolidone (NMP) to obtain a first slurry, coating the first slurry on an aluminum foil, and drying at 60-80 ℃ for 12-16 hours in a vacuum environment to obtain the nitrogen and sulfur double-doped porous carbon lithium sulfur battery positive electrode material (S-NSC @ Al), wherein the ratio of the sulfur positive electrode active material, the conductive carbon and the binder is (8-7): 1-2): 1 in parts by mass.
In the step b), the binder is polyvinylidene fluoride (PVDF).
In the step b), the ratio of the mass part of the binder to the volume part of the N-methylpyrrolidone in the first slurry is 1 (5-6).
In the step b), the thickness of the aluminum foil is 0.25-0.5 mm.
The nitrogen and sulfur double-doped porous carbon lithium sulfur battery positive electrode material obtained by the preparation method.
In the technical scheme, the sulfur content of the nitrogen-sulfur double-doped porous carbon lithium-sulfur battery positive electrode material is 1.5-2.0 mg/cm2。
The positive electrode of the battery is a nitrogen and sulfur double-doped porous carbon lithium sulfur battery positive electrode material, the negative electrode of the battery is a lithium sheet, and the diaphragm is a base membrane coated with the nitrogen and sulfur double-doped porous carbon material.
In the technical scheme, the loading capacity of the nitrogen and sulfur double-doped porous carbon material on the base membrane is 0.5-1 mg/cm2。
In the above technical solution, the preparation method of the separator of the battery comprises:
mixing the nitrogen-sulfur double-doped porous carbon material, a binder and N-methylpyrrolidone (NMP) to obtain a second slurry, wherein the ratio of the nitrogen-sulfur double-doped porous carbon material to the binder is (3-4): 1,
in the first step, the ratio of the mass part of the binder to the volume part of the N-methylpyrrolidone in the second slurry is 1 (6-8). The unit of the mass part is milligram, and the unit of the volume part is milliliter.
In the step (i), the binder is polyvinylidene fluoride (PVDF).
And secondly, coating the second slurry on a base film, and drying to obtain the diaphragm.
In the second step, the second slurry is coated on the base film, which is a PP film, using a wet film maker.
In the second step, the drying is: drying for 12-16 hours at 60-80 ℃ in a vacuum environment.
In the second step, the thickness of the second slurry coated on the base film is 50-80 microns.
In the technical scheme, the capacity of the battery is kept at 980mAh/g after 100 times of circulation at the rate of 0.2C, and the capacity of the battery is kept at 393.6mAh/g after 500 times of circulation at the rate of 5C.
The invention discloses a nitrogen and sulfur double-doped porous carbon material which has a multifunctional effect when applied to a lithium battery. The carbon network structure of the nitrogen and sulfur double-doped porous carbon material forms a conductive matrix, and the transfer of electrons is accelerated. The large pore volume and the mesoporous structure can provide enough space for carrying sulfur and effectively relieve volume expansion. The nitrogen and sulfur double-doped carbon material has a strong chemical adsorption effect on lithium polysulfide, and can accelerate the conversion of the lithium polysulfide, so that the shuttle effect is effectively inhibited, and the cycle performance of the lithium-sulfur battery is improved. The method solves the problems of complex preparation process, high energy consumption, low material yield, poor stability and the like of electrode materials brought by the traditional method for improving the performance of the lithium-sulfur battery, realizes strong cycling stability and excellent rate performance of the battery by using the nitrogen-sulfur double-doped porous carbon material as a sulfur host and a modified diaphragm material, and is simple in preparation process and suitable for large-scale synthesis.
Drawings
FIG. 1a is a scanning electron microscope image of the nitrogen and sulfur double-doped porous carbon material obtained in example 1;
FIG. 1b is a scanning electron micrograph of the nitrogen-doped porous carbon material obtained in comparative example 1;
FIG. 2a is a transmission electron microscope image of the nitrogen and sulfur double-doped porous carbon material obtained in example 1;
FIG. 2b is a transmission electron micrograph of the nitrogen-doped porous carbon material obtained in comparative example 1;
FIG. 3 is a graph of the cycling performance of a 2025 button cell assembled from the nitrogen and sulfur double-doped porous carbon materials obtained in examples 1-5 at a current density of 0.2C;
fig. 4a is a charge and discharge performance diagram of a 2025 button cell assembled by the nitrogen and sulfur double-doped porous carbon material obtained in example 1 under different current multiplying powers;
FIG. 4b is a graph showing the charge and discharge performance of a 2025 button cell assembled by the nitrogen-doped porous carbon material obtained in comparative example 1 at different current rates;
FIG. 5a is a graph of the cycling performance at 0.2C current density for a 2025 button cell assembled from the nitrogen and sulfur double doped porous carbon material from example 1 (S-NSC @ Al + NSC @ PP) and the nitrogen doped porous carbon material from comparative example 1 (S-NC @ Al + NC @ PP);
FIG. 5b is a graph of rate capability of a 2025 button cell assembled from the nitrogen and sulfur double-doped porous carbon material (S-NSC @ Al + NSC @ PP) obtained in example 1 and the nitrogen-doped porous carbon material (S-NC @ Al + NC @ PP) obtained in comparative example 1 at different current densities;
FIG. 6 is a graph of long cycle performance at 5C current density for a 2025 button cell assembled from the nitrogen and sulfur double doped porous carbon material from example 1 (S-NSC @ Al + NSC @ PP) and the nitrogen doped porous carbon material from comparative example 1 (S-NC @ Al + NC @ PP).
Detailed Description
TABLE 1 Chemicals used in the experiments
Figure BDA0002203253340000051
TABLE 2 Instrument Equipment for the experiments
Figure BDA0002203253340000052
The technical scheme of the invention is further explained by combining specific examples.
Example 1
A preparation method of a nitrogen and sulfur double-doped porous carbon material (NSC) comprises the following steps:
1) dissolving 5 millimole of citric acid and 160 millimole of urea in a mixed solvent, stirring at 80 ℃ to form gel, heating the gel in an oven at 110 ℃ for 16 hours to obtain a carbon material precursor, wherein the mixed solvent is a mixture of distilled water and ethanol, and the ratio of the distilled water to the ethanol in the mixed solvent is 1:3 in parts by volume; the ratio of the mass fraction of citric acid to the volume fraction of the mixed solvent is 1:30, the unit of the mass fraction is millimole, and the unit of the volume fraction is milliliter.
2) Grinding the carbon material precursor for 40min, placing the carbon material precursor in a furnace body under argon after grinding, heating from the room temperature of 20-25 ℃ to 350 ℃ and calcining at 350 ℃ for 5 hours, then heating from 350 ℃ to 950 ℃ and calcining at 950 ℃ for 10 hours to obtain the nitrogen-doped porous carbon material; wherein the temperature rise speed is 5 ℃/min.
3) And calcining the nitrogen-doped porous carbon material at 950 ℃ for 5 hours in a mixed atmosphere to obtain the nitrogen-sulfur double-doped porous carbon material, wherein the mixed atmosphere is a mixture of hydrogen sulfide and argon, and the ratio of the hydrogen sulfide to inert gas in the mixed atmosphere is 19:1 in parts by volume.
Example 2
A preparation method of a nitrogen and sulfur double-doped porous carbon material (NSC) comprises the following steps:
1) dissolving 5 millimole of citric acid and 160 millimole of urea in a mixed solvent, stirring at 80 ℃ to form gel, heating the gel in an oven at 110 ℃ for 16 hours to obtain a carbon material precursor, wherein the mixed solvent is a mixture of distilled water and ethanol, and the ratio of the distilled water to the ethanol in the mixed solvent is 1:3 in parts by volume; the ratio of the mass fraction of citric acid to the volume fraction of the mixed solvent is 1:30, the unit of the mass fraction is millimole, and the unit of the volume fraction is milliliter.
2) Grinding the carbon material precursor for 40min, placing the carbon material precursor in a furnace body under argon after grinding, heating from the room temperature of 20-25 ℃ to 350 ℃ and calcining at 350 ℃ for 5 hours, then heating from 350 ℃ to 850 ℃ and calcining at 850 ℃ for 10 hours to obtain the nitrogen-doped porous carbon material; wherein the temperature rise speed is 5 ℃/min.
3) And calcining the nitrogen-doped porous carbon material at 850 ℃ for 5 hours under a mixed atmosphere to obtain the nitrogen-sulfur double-doped porous carbon material, wherein the mixed atmosphere is a mixture of hydrogen sulfide and argon, and the ratio of the hydrogen sulfide to inert gas in the mixed atmosphere is 19:1 in parts by volume.
Example 3
A preparation method of a nitrogen and sulfur double-doped porous carbon material (NSC) comprises the following steps:
1) dissolving 5 millimole of citric acid and 160 millimole of urea in a mixed solvent, stirring at 80 ℃ to form gel, heating the gel in an oven at 110 ℃ for 16 hours to obtain a carbon material precursor, wherein the mixed solvent is a mixture of distilled water and ethanol, and the ratio of the distilled water to the ethanol in the mixed solvent is 1:3 in parts by volume; the ratio of the mass fraction of citric acid to the volume fraction of the mixed solvent is 1:30, the unit of the mass fraction is millimole, and the unit of the volume fraction is milliliter.
2) Grinding the carbon material precursor for 40min, placing the carbon material precursor in a furnace body under argon after grinding, heating from the room temperature of 20-25 ℃ to 350 ℃ and calcining at 350 ℃ for 5 hours, then heating from 350 ℃ to 750 ℃ and calcining at 750 ℃ for 10 hours to obtain the nitrogen-doped porous carbon material; wherein the temperature rise speed is 5 ℃/min.
3) And calcining the nitrogen-doped porous carbon material at 750 ℃ for 5 hours under a mixed atmosphere to obtain the nitrogen-sulfur double-doped porous carbon material, wherein the mixed atmosphere is a mixture of hydrogen sulfide and argon, and the ratio of the hydrogen sulfide to inert gas in the mixed atmosphere is 19:1 in parts by volume.
Example 4
A preparation method of a nitrogen and sulfur double-doped porous carbon material (NSC) comprises the following steps:
1) dissolving 5 millimole of citric acid and 120 millimole of urea in a mixed solvent, stirring at 80 ℃ to form gel, heating the gel in an oven at 110 ℃ for 16 hours to obtain a carbon material precursor, wherein the mixed solvent is a mixture of distilled water and ethanol, and the ratio of the distilled water to the ethanol in the mixed solvent is 1:3 in parts by volume; the ratio of the mass fraction of citric acid to the volume fraction of the mixed solvent is 1:30, the unit of the mass fraction is millimole, and the unit of the volume fraction is milliliter.
2) Grinding the carbon material precursor for 40min, placing the carbon material precursor in a furnace body under argon after grinding, heating from the room temperature of 20-25 ℃ to 350 ℃ and calcining at 350 ℃ for 5 hours, then heating from 350 ℃ to 950 ℃ and calcining at 950 ℃ for 10 hours to obtain the nitrogen-doped porous carbon material; wherein the temperature rise speed is 5 ℃/min.
3) And calcining the nitrogen-doped porous carbon material at 950 ℃ for 5 hours in a mixed atmosphere to obtain the nitrogen-sulfur double-doped porous carbon material, wherein the mixed atmosphere is a mixture of hydrogen sulfide and argon, and the ratio of the hydrogen sulfide to inert gas in the mixed atmosphere is 19:1 in parts by volume.
Example 5
A preparation method of a nitrogen and sulfur double-doped porous carbon material (NSC) comprises the following steps:
1) dissolving 5 millimole of citric acid and 200 millimole of urea in a mixed solvent, stirring at 80 ℃ to form gel, heating the gel in an oven at 110 ℃ for 16 hours to obtain a carbon material precursor, wherein the mixed solvent is a mixture of distilled water and ethanol, and the ratio of the distilled water to the ethanol in the mixed solvent is 1:3 in parts by volume; the ratio of the mass fraction of citric acid to the volume fraction of the mixed solvent is 1:30, the unit of the mass fraction is millimole, and the unit of the volume fraction is milliliter.
2) Grinding the carbon material precursor for 40min, placing the carbon material precursor in a furnace body under argon after grinding, heating from the room temperature of 20-25 ℃ to 350 ℃ and calcining at 350 ℃ for 5 hours, then heating from 350 ℃ to 950 ℃ and calcining at 950 ℃ for 10 hours to obtain the nitrogen-doped porous carbon material; wherein the temperature rise speed is 5 ℃/min.
3) And calcining the nitrogen-doped porous carbon material at 950 ℃ for 5 hours in a mixed atmosphere to obtain the nitrogen-sulfur double-doped porous carbon material, wherein the mixed atmosphere is a mixture of hydrogen sulfide and argon, and the ratio of the hydrogen sulfide to inert gas in the mixed atmosphere is 19:1 in parts by volume.
The preparation method of the nitrogen and sulfur double-doped porous carbon lithium-sulfur battery positive electrode material comprises the following steps:
a) the nitrogen-sulfur double-doped porous carbon material obtained in any one of examples 1 to 5 was mixed with sulfur, and wet infiltrated (Yuanyuan Li, Qifa Cai, Lei Wang, Qingwei Li, Xiaong Peng, Biao Gao, Kaifu Huo and Paul K.Chu, Mesoporous TiO)2nanocrystalline/Graphene as an Efficient Sulfur Host Material for High-Performance Lithium-Sulfur Batteries, ACS appl.mater.interfaces,2016,8(36), 23784-;
b) mixing a sulfur positive electrode active material, conductive carbon, polyvinylidene fluoride (PVDF) and N-methylpyrrolidone (NMP) to obtain a first slurry, coating the first slurry on an aluminum foil with the thickness of 0.3mm by using a wet film preparation device, and drying the aluminum foil at 60 ℃ for 16 hours in a vacuum environment to obtain a nitrogen and sulfur double-doped porous carbon lithium sulfur battery positive electrode material (S-NSC @ Al), wherein the ratio of the sulfur positive electrode active material, the conductive carbon and the polyvinylidene fluoride (binder) is 8:1:1 in parts by mass; in the first slurry, the ratio of the mass part of polyvinylidene fluoride to the volume part of N-methylpyrrolidone is 1: 5. Parts by mass are in milligrams, parts by volume are in milliliters.
The sulfur content of the positive electrode material of the nitrogen and sulfur double-doped porous carbon lithium-sulfur battery obtained in example 1 is measured to be 1.6mg/cm2。
A battery (S-NSC @ Al + NSC @ PP) is characterized in that the positive electrode of the battery is a nitrogen and sulfur double-doped porous carbon lithium sulfur battery positive electrode material, the negative electrode of the battery is a lithium sheet (the diameter is 12mm), a diaphragm is a base membrane coated with a nitrogen and sulfur double-doped porous carbon material, and the loading capacity of the nitrogen and sulfur double-doped porous carbon material on the base membrane is 0.8mg/cm2. The preparation method of the battery diaphragm comprises the following steps:
mixing a nitrogen and sulfur double-doped porous carbon material, a binder and N-methylpyrrolidone (NMP) to obtain a second slurry, wherein the ratio of the nitrogen and sulfur double-doped porous carbon material to the binder is 4:1 in parts by mass; the ratio of the mass part of the binder to the volume part of the N-methylpyrrolidone in the second slurry is 1:6, wherein the unit of the mass part is milligram, and the unit of the volume part is milliliter. The binder is polyvinylidene fluoride (PVDF).
Secondly, the second slurry was coated on a base film (the base film is a PP film) with a thickness of 50 μm using a wet film maker, and dried at 60 ℃ for 16 hours in a vacuum environment, to obtain a separator (NSC @ PP).
The positive and separator and negative electrodes were assembled into 2025 button cells in a glove box.
The nitrogen and sulfur double-doped porous carbon materials obtained in examples 1-5 were prepared into 2025 button cells, respectively.
Comparative example 1
A method for preparing a nitrogen-doped porous carbon material (NC) comprising the steps of:
1) dissolving 5 millimole of citric acid and 160 millimole of urea in a mixed solvent, stirring at 80 ℃ to form gel, heating the gel in an oven at 110 ℃ for 16 hours to obtain a carbon material precursor, wherein the mixed solvent is a mixture of distilled water and ethanol, and the ratio of the distilled water to the ethanol in the mixed solvent is 1:3 in parts by volume; the ratio of the mass fraction of citric acid to the volume fraction of the mixed solvent is 1:30, the unit of the mass fraction is millimole, and the unit of the volume fraction is milliliter.
2) Grinding the carbon material precursor for 40min, placing the carbon material precursor in a furnace body under argon after grinding, heating from the room temperature of 20-25 ℃ to 350 ℃ and calcining at 350 ℃ for 5 hours, then heating from 350 ℃ to 950 ℃ and calcining at 950 ℃ for 10 hours to obtain the nitrogen-doped porous carbon material; wherein the temperature rise speed is 5 ℃/min.
3) And calcining the nitrogen-doped porous carbon material in the air at 950 ℃ for 5 hours to obtain the nitrogen-doped porous carbon material, wherein the mixed atmosphere is a mixture of hydrogen sulfide and argon, and the ratio of the hydrogen sulfide to inert gas in the mixed atmosphere is 19:1 in parts by volume.
The preparation method of the nitrogen-doped porous carbon lithium-sulfur battery positive electrode material comprises the following steps:
a) nitrogen-doped porous carbon materials were mixed with sulfur and wet infiltrated (Yuanyuanan Li, Qifa Cai, Lei Wang, Qingwei Li, Xiang Peng, Biao Gao, Kaifu Huo and Paul K.Chu, Mesoporous TiO)2nanocrystalline/Graphene as an Efficient Sulfur Host Material for High-Performance Lithium-Sulfur Batteries, ACS appl.mater.interfaces,2016,8(36), 23784-;
b) mixing a sulfur positive electrode active material (single nitrogen-doped), conductive carbon, polyvinylidene fluoride (PVDF) and N-methylpyrrolidone (NMP) to obtain a third slurry, coating the third slurry on an aluminum foil with the thickness of 0.3mm by using a wet film preparation device, and drying for 16 hours at 60 ℃ in a vacuum environment to obtain a nitrogen-doped porous carbon lithium sulfur battery positive electrode material (NSC @ Al), wherein the ratio of the sulfur positive electrode active material (single nitrogen-doped), the conductive carbon and the polyvinylidene fluoride (binder) is 8:1:1 in parts by mass; in the third slurry, the ratio of the mass part of polyvinylidene fluoride to the volume part of N-methylpyrrolidone is 1: 5. Parts by mass are in milligrams, parts by volume are in milliliters.
A battery (S-NC @ Al + NC @ PP) is characterized in that the positive electrode of the battery is a nitrogen-doped porous carbon lithium sulfur battery positive electrode material, the negative electrode of the battery is a lithium sheet (the diameter is 12mm), a diaphragm is a base film coated with a nitrogen-doped porous carbon material, and the loading capacity of the nitrogen-doped porous carbon material on the base film is 0.8mg/cm2. The preparation method of the battery diaphragm comprises the following steps:
mixing a nitrogen-doped porous carbon material, a binder and N-methylpyrrolidone (NMP) to obtain a fourth slurry, wherein the ratio of the nitrogen-doped porous carbon material to the binder is 4:1 in parts by mass; the ratio of the mass part of the binder to the volume part of the N-methylpyrrolidone in the fourth slurry is 1:6, wherein the unit of the mass part is milligram, and the unit of the volume part is milliliter. The binder is polyvinylidene fluoride (PVDF).
Secondly, the fourth slurry was coated on a base film (the base film was a PP film) with a thickness of 50 μm using a wet film maker, and dried at 60 ℃ for 16 hours in a vacuum environment, to obtain a separator (NSC @ PP).
The positive and separator and negative electrodes were assembled into 2025 button cells in a glove box.
Performance testing
As a result of testing, as shown in table 3, the nitrogen, sulfur double-doped porous carbon material obtained in example 1 included 6.710 at% of nitrogen, 4.589 at% of sulfur and 88.550 at% of carbon in atomic percentage, and the nitrogen-doped porous carbon material obtained in comparative example 1 consisted of 10.06 at% of nitrogen and 89.940 at% of carbon in atomic percentage.
TABLE 3
Figure BDA0002203253340000101
The morphology of the nitrogen-and sulfur-double-doped porous carbon material obtained in example 1 and the nitrogen-doped porous carbon material obtained in comparative example 1 was tested. FIG. 1a is a scanning electron microscope image of a nitrogen and sulfur double-doped porous carbon material, FIG. 1b is a scanning electron microscope image of a nitrogen-doped porous carbon material, and it can be seen from FIGS. 1a and 1b that the two obtained carbon materials have a layered network structure and a plurality of pores, and the loose and porous nanosheets are connected with each other to form a channel. Fig. 2a is a transmission electron microscope image of a nitrogen and sulfur double-doped porous carbon material, and fig. 2b is a transmission electron microscope image of a nitrogen-doped porous carbon material, and it can be clearly observed from fig. 2a and 2b that the nanosheet structures of the two carbon materials are similar to graphene and have more wrinkles.
Electrochemical performance tests of the positive electrode material of the 2025 button cells assembled by the nitrogen-and sulfur-double-doped porous carbon materials obtained in examples 1 to 5 and the nitrogen-doped porous carbon material obtained in comparative example 1 were performed. The results are shown in FIGS. 3, 4a, 4b, 5a and 5 b.
As can be seen from fig. 3, the cycle performance graphs of the nitrogen and sulfur double-doped porous carbon materials obtained in examples 1 to 5 at a current density of 0.2C show that the nitrogen and sulfur double-doped porous carbon material obtained in example 1 has more excellent cycle stability and higher specific capacity.
From the charge and discharge performance graphs of the two carbon materials (the nitrogen and sulfur double-doped porous carbon material obtained in example 1 and the nitrogen-doped porous carbon material obtained in comparative example 1) under different current multiplying factors, the nitrogen and sulfur double-doped porous carbon material can show remarkable voltage platforms at about 2.3 and 2.0V, and a long discharge platform is still maintained under the currents of 1 and 2C under large multiplying factors. In contrast, the voltage plateau of nitrogen-doped porous carbon material has disappeared at 1C current rate.
As can be seen from the cycle performance diagram of the two carbon materials in fig. 5a at the current density of 0.2C, the nitrogen and sulfur double-doped porous carbon material has more excellent cycle stability than the pure nitrogen-doped porous carbon material, and the specific capacity is still maintained at about 980mAh/g after 100 cycles. In addition, as shown in fig. 5b, the high specific capacity of the nitrogen and sulfur double-doped porous carbon material is also shown in the aspect of the rate capability, and the specific capacity is respectively maintained at 1302.9,1140.1,1033.6,971.9and 910.5mAh/g under the current densities of 0.1,0.2,0.5,1 and 2C. In contrast, the specific capacity of the pure nitrogen-doped porous carbon material is lower, and particularly, the specific capacity is only 335mAh/g under the current density of 2C.
From the long cycle performance diagram of two carbon materials of fig. 6 under the large current density of 5C, it can be clearly observed that the nitrogen and sulfur double-doped porous carbon material has 500 cycles and still maintains high specific capacity (393.6 mAh/g). The excellent electrochemical properties of the nitrogen and sulfur double-doped porous carbon material prove that the material can effectively inhibit the diffusion of soluble polysulfide and can effectively improve the cycle stability of the battery.
The data show that the specific capacity of the pure nitrogen-doped porous carbon material is attenuated too fast, the cycle life is short, and the specific capacity, the cycle life and the cycle stability of the nitrogen-sulfur double-doped porous carbon material are obviously superior to those of the pure nitrogen-doped porous carbon material, especially under the condition of high current density. In addition, the nitrogen and sulfur double-doped porous carbon material can effectively inhibit the diffusion of lithium polysulfide and can also obviously promote the catalytic conversion of the lithium polysulfide, and the multifunctional effect effectively improves the cycle performance of the lithium-sulfur battery.
The invention has been described in an illustrative manner, and it is to be understood that any simple variations, modifications or other equivalent changes which can be made by one skilled in the art without departing from the spirit of the invention fall within the scope of the invention.

Claims (10)

1. A preparation method of a nitrogen and sulfur double-doped porous carbon material is characterized by comprising the following steps:
1) dissolving citric acid and urea in a mixed solvent, stirring at 60-80 ℃ to form gel, heating the gel at 100-120 ℃ for 12-16 hours to obtain a carbon material precursor, wherein the mixed solvent is a mixture of distilled water and ethanol, and the ratio of the distilled water to the ethanol in the mixed solvent is (1-2): (2-4), wherein the ratio of the citric acid to the urea is (20-40) according to the parts by weight of the substances;
2) grinding the carbon material precursor, calcining for 4-6 hours at 300-350 ℃ under inert gas after grinding, and calcining for 8-10 hours at 650-950 ℃ to obtain a nitrogen-doped porous carbon material;
3) calcining the nitrogen-doped porous carbon material for 4-6 hours at 650-950 ℃ in a mixed atmosphere to obtain a nitrogen-sulfur double-doped porous carbon material, wherein the mixed atmosphere is a mixture of hydrogen sulfide and inert gas;
the nitrogen and sulfur double-doped porous carbon material consists of 5.0-7.0% of nitrogen, 4.5-6.0% of sulfur and 87-90.5% of carbon in percentage by atom.
2. The preparation method according to claim 1, wherein in the step 1), the ratio of the amount part of the citric acid to the volume part of the mixed solvent is 1 (30-40), and when the amount part of the citric acid is millimole, the volume part is milliliter;
in the step 2), the grinding time is 30-60 minutes;
in the step 3), the ratio of hydrogen sulfide to inert gas in the mixed atmosphere is (18-19) to (2-1) in parts by volume, and the inert gas is argon.
3. A preparation method of a nitrogen and sulfur double-doped porous carbon lithium-sulfur battery positive electrode material is characterized by comprising the following steps:
a) mixing the nitrogen and sulfur double-doped porous carbon material of claim 1 with sulfur, and wetting by a wet method to obtain a sulfur positive electrode active material, wherein the ratio of the nitrogen and sulfur double-doped porous carbon material to the sulfur is 1 (2-4);
b) the method comprises the steps of mixing the sulfur positive electrode active material, conductive carbon, a binder and N-methyl pyrrolidone to obtain first slurry, coating the first slurry on an aluminum foil, and drying the aluminum foil in a vacuum environment at the temperature of 60-80 ℃ for 12-16 hours to obtain the nitrogen and sulfur double-doped porous carbon lithium sulfur battery positive electrode material, wherein the ratio of the sulfur positive electrode active material to the conductive carbon to the binder is (8-7): 1-2): 1 in parts by mass.
4. The method of claim 3, wherein in the step b), the binder is polyvinylidene fluoride;
in the step b), the ratio of the mass part of the binder to the volume part of the N-methylpyrrolidone in the first slurry is 1 (5-6);
in the step b), the thickness of the aluminum foil is 0.25-0.5 mm.
5. The positive electrode material of the nitrogen-sulfur double-doped porous carbon lithium-sulfur battery obtained by the preparation method of claim 4.
6. A battery, characterized in that the positive electrode of the battery is the positive electrode material of the nitrogen and sulfur double-doped porous carbon lithium sulfur battery as defined in claim 5, the negative electrode of the battery is a lithium sheet, and the separator is a base film coated with the nitrogen and sulfur double-doped porous carbon material.
7. The battery according to claim 6, wherein the loading amount of the nitrogen and sulfur double-doped porous carbon material on the base film is 0.5-1 mg/cm2。
8. The battery according to claim 6 or 7, wherein the separator of the battery is prepared by:
mixing the nitrogen-sulfur double-doped porous carbon material, a binder and N-methylpyrrolidone (NMP) to obtain a second slurry, wherein the ratio of the nitrogen-sulfur double-doped porous carbon material to the binder is (3-4): 1,
and secondly, coating the second slurry on a base film, and drying to obtain the diaphragm.
9. The battery according to claim 8, wherein in the step (r), the ratio of the mass part of the binder to the volume part of the N-methylpyrrolidone in the second slurry is 1 (6-8); the unit of the mass part is milligram, and the unit of the volume part is milliliter;
in the step (i), the binder is polyvinylidene fluoride.
10. The battery of claim 9, wherein in step two, the second slurry is coated on the base film using a wet film maker, the base film being a PP film;
in the second step, the drying is: drying for 12-16 hours at 60-80 ℃ in a vacuum environment;
in the second step, the thickness of the second slurry coated on the base film is 50-80 microns.
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