CN110649251A - Porous carbon-sulfur composite cathode material for lithium-sulfur battery and preparation method thereof - Google Patents

Abstract

The invention discloses a porous carbon-sulfur composite positive electrode material for lithium-sulfur batteries, which is prepared from the following parts by weight of raw materials: 35-50 parts of modified graphene porous carbon material, 200-230 parts of ethylene glycol, 10-15 parts of mixed Miscellaneous agents, 2-6 parts of carbon black, 15-25 parts of elemental sulfur, and 225-250 parts of N-methylpyrrolidone; the invention also discloses a preparation method of a porous carbon-sulfur composite positive electrode material for lithium-sulfur batteries; modification The graphene porous carbon material has a porous structure and a wrinkled morphology, and does not generate aggregation, has an ultra-high specific surface area and porosity, and can support more sulfur elements. The positive electrode material prepared by the present invention is in use. , the ultra-high specific surface area enables the modified graphene porous carbon material to fully contact the electrolyte and form a double electron layer, and its high porosity can provide a channel for the rapid transfer of electrons, which is convenient for charge transport. More excellent electrical conductivity.

Description

Porous carbon-sulfur composite cathode material for lithium-sulfur battery and preparation method thereof

technical field

The invention belongs to the field of electrochemistry, in particular to a porous carbon-sulfur composite positive electrode material for lithium-sulfur batteries and a preparation method thereof.

Background technique

Lithium-sulfur batteries use elemental sulfur as the positive electrode reaction material, and elemental lithium or lithium alloy as the negative electrode material. During discharge, the negative electrode reaction is that lithium loses electrons to become lithium ions, and the positive electrode reaction is that sulfur reacts with lithium ions and electrons to form sulfides. The potential difference between the positive and negative electrodes is the discharge voltage of the lithium-sulfur battery. The theoretical discharge voltage of the lithium-sulfur battery is 2.287V. When the sulfur and lithium are completely reacted to form lithium sulfide (Li ₂ S), the overall theoretical energy density of the lithium-sulfur battery reaches 2600 Wh/kg. Much larger than the commercial secondary batteries used at this stage. In addition, as a positive electrode material, elemental sulfur has abundant raw material sources and low cost. Therefore, it is most promising to surpass ordinary lithium-ion batteries in large-capacity batteries. Moreover, sulfur is an environmentally friendly element that is basically non-polluting to the environment. It is a kind of Very promising battery electrode material. However, since elemental sulfur is an insulator, it needs to be recombined with a conductive material to effectively transport ions and charges.

Chinese invention patent CN105390665B discloses an aqueous polyaniline lithium-sulfur battery cathode material and a preparation method thereof, belonging to the field of electrochemistry. Solve the problem that the existing lithium-sulfur battery electrode materials cannot be dispersed in water. In the method, graphene oxide and aqueous polyaniline are first mixed to obtain a mixed solution A; then an aqueous solution of sodium thiosulfate is added to the mixed solution A, and hydrochloric acid is added to react to obtain a mixed solution B; hydriodic acid is added to the mixed solution B reacts to obtain an aqueous polyaniline lithium-sulfur battery positive electrode material.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a porous carbon-sulfur composite positive electrode material for lithium-sulfur batteries and a preparation method thereof.

The technical problem that the present invention needs to solve is:

There are super strong van der Waals forces and conjugation forces between graphenes, and it is easy to form a three-dimensional structure, making it less dispersable in organic phase and aqueous phase solvents, and prone to agglomeration; carbon dioxide in the prior art When the sheet is etched, it is affected by the structure of graphene itself, resulting in an incomplete etching effect during etching.

The object of the present invention can be realized through the following technical solutions:

The porous carbon-sulfur composite positive electrode material for lithium-sulfur batteries is prepared from the following raw materials in parts by weight: 35-50 parts of modified graphene porous carbon material, 200-230 parts of ethylene glycol, 10-15 parts of dopant, 2-6 parts of parts of carbon black, 15-25 parts of elemental sulfur, 225-250 parts of N-methylpyrrolidone;

The porous carbon-sulfur composite positive electrode material for the lithium-sulfur battery is made by the following method:

Step S1, adding the modified graphene porous carbon material into ethylene glycol and ultrasonically to form a suspension A, then adding a dopant, transferring it to a hydrothermal kettle, heating in a 45°C water bath, and stirring at a rotational speed of 120 r/min 15min, then filtered, washed three times with absolute ethanol, and dried to obtain the doped modified graphene porous carbon material;

Step S2, adding carbon black and elemental sulfur into N-methylpyrrolidone, heating in a water bath at 40°C, and sonicating until the elemental sulfur dissolves to obtain suspension B;

Step S3, adding suspension B into suspension A, stirring at a speed of 150 r/min for 30 min, adding deionized water, centrifuging, washing with deionized water three times, and drying to obtain the porous carbon-sulfur battery for lithium-sulfur batteries. Composite cathode material.

Further, the modified graphene porous carbon material is made from the following raw materials in parts by weight: 10-15 parts of graphene, 5-8 parts of sodium nitrate, 150-200 parts of 98% concentrated sulfuric acid by mass, and 1-1.5 parts of potassium chlorate , 40-60 parts by volume of 20% hydrogen peroxide solution, 20-30 parts of xylene, 20-30 parts of absolute ethanol, 20-30 parts of deionized water, 2-3 parts of dodecylbenzene sulfonic acid, 25 -40 parts of aniline, 5-8 parts of p-phenylenediamine, 3.5-6 parts of sodium persulfate.

Further, the modified graphene porous carbon material is made by the following method:

(1) Put graphene into a round-bottomed flask, add sodium nitrate and 98% concentrated sulfuric acid, stir in an ice bath at 3°C for 15 minutes, add potassium chlorate, continue stirring for 30 minutes, then heat in a water bath at 40°C, react for 3 hours, and add deionized water and placed in an oil bath at 80 °C for 30 min, adding 20% aqueous hydrogen peroxide solution to continue the reaction for 10 min, and then suction filtration, washing and drying to obtain graphene oxide;

(2) Add xylene, absolute ethanol and deionized water to the beaker and mix, stir magnetically for 15min, add dodecylbenzenesulfonic acid, then add the obtained graphene oxide, ultrasonically and magnetically stir for 30min, add aniline and p-phenylenediamine, heated in a water bath at 55°C and continued magnetic stirring for 30min, added sodium persulfate, stirred at a speed of 240r/min for 5h, after the reaction was completed, filtered and washed three times with deionized water to obtain modified graphene;

(3) Put the modified graphene into the tube furnace, feed nitrogen to discharge air, heat up to 800°C at a speed of 8°C/min, feed carbon dioxide, react at this temperature for 2.5h, then feed nitrogen, The temperature was lowered to 30° C. to prepare the modified graphene porous carbon material.

There are super strong van der Waals force and conjugation force between graphenes, and it is easy to form a three-dimensional structure, which makes it less dispersable in organic phase and aqueous phase solvent. A kind of graphene oxide is prepared under the action of hydrogen oxide aqueous solution etc., and this graphene oxide can be dispersed in water also can be dispersed in organic solvent, and this graphene oxide surface has increased abundant oxygen-containing functional groups, and is not easy to produce agglomeration; Step ( 2) By mixing aniline and p-phenylenediamine with graphene oxide in solution, aniline and p-phenylenediamine can polymerize in solution to form a polymer, and then the polymer can shuttle between graphene oxide sheets, and then The graphene oxide sheet is wrapped, and then in step (3), the separated graphene oxide sheet is etched by carbon dioxide to obtain the modified graphene porous carbon material, and the porous carbon material has a porous structure and a wrinkled shape. It has high specific surface area and porosity without aggregation.

Further, the dopant is one or both of phosphate and sulfonate.

A preparation method of a porous carbon-sulfur composite positive electrode material for a lithium-sulfur battery, comprising the following steps:

Step S1, adding the modified graphene porous carbon material into ethylene glycol and ultrasonically to form a suspension A, then adding a dopant, transferring it to a hydrothermal kettle, heating in a 45°C water bath, and stirring at a rotational speed of 120 r/min 15min, then filtered, washed three times with absolute ethanol, and dried to obtain the doped modified graphene porous carbon material;

Step S2, adding carbon black and elemental sulfur into N-methylpyrrolidone, heating in a water bath at 40°C, and sonicating until the elemental sulfur dissolves to obtain suspension B;

Step S3, adding suspension B into suspension A, stirring at a speed of 150 r/min for 30 min, adding deionized water, centrifuging, washing with deionized water three times, and drying to obtain the porous carbon-sulfur battery for lithium-sulfur batteries. Composite cathode material.

Beneficial effects of the present invention:

(1) porous carbon-sulfur composite positive electrode material for lithium-sulfur battery of the present invention, with modified graphene porous carbon material and elemental sulfur etc. as raw materials, with modified graphene porous carbon material as matrix material, the modified graphene porous carbon material In the preparation process step (1), graphene is prepared under the action of potassium chlorate and 20% hydrogen peroxide solution to prepare a kind of graphene oxide, and the graphene oxide can be dispersed in water or in an organic solvent, and Abundant oxygen-containing functional groups are added on the surface of the graphene oxide, and it is not easy to agglomerate; in step (2), aniline and p-phenylenediamine are mixed with graphene oxide in a solution, and aniline and p-phenylenediamine can be polymerized in the solution to form polymer, and then the polymer can shuttle between the graphene oxide sheets, then wrap the graphene oxide sheets, and then in step (3), the separated graphene oxide sheets are etched by carbon dioxide to obtain the obtained polymer. The modified graphene porous carbon material, the porous carbon material has a porous structure and a wrinkled morphology, and does not produce aggregation, has an ultra-high specific surface area and porosity, can support more sulfur element, and can improve The utilization of sulfur in the electrochemical reaction solves the existence of super strong van der Waals force and conjugation force between graphenes, and it is easy to form a three-dimensional structure, making it less dispersable in organic phase and aqueous phase solvent, and easy to occur. Reunion; in the prior art, when carbon dioxide etched the graphene oxide sheet, it was affected by the structure of graphene itself, resulting in a technical problem of incomplete etching effect during etching;

(2) During the use process of the positive electrode material prepared by the present invention, the ultra-high specific surface area enables the modified graphene porous carbon material to fully contact the electrolyte and form a double electron layer, and its high porosity can It provides a channel for the rapid transfer of electrons, which is convenient for charge transport, and thus has more excellent electrical conductivity.

Detailed ways

The technical solutions in the embodiments of the present invention will be described clearly and completely below. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

Example 1

The porous carbon-sulfur composite positive electrode material for lithium-sulfur batteries is made from the following raw materials in parts by weight: 35 parts of modified graphene porous carbon material, 200 parts of ethylene glycol, 10 parts of phosphate ester, 2 parts of carbon black, 15 parts of elemental sulfur, 225 parts of N-methylpyrrolidone;

The porous carbon-sulfur composite positive electrode material for the lithium-sulfur battery is made by the following method:

Step S1, adding the modified graphene porous carbon material into ethylene glycol and ultrasonically to form suspension A, then adding phosphate ester, transferring to a hydrothermal kettle, heating in a water bath at 45°C, and stirring at a speed of 120r/min for 15min , then filter, wash three times with absolute ethanol, and dry to obtain doped modified graphene porous carbon material;

Step S2, adding carbon black and elemental sulfur into N-methylpyrrolidone, heating in a water bath at 40°C, and sonicating until the elemental sulfur dissolves to obtain suspension B;

Step S3, adding suspension B into suspension A, stirring at a speed of 150 r/min for 30 min, adding deionized water, centrifuging, washing with deionized water three times, and drying to obtain the porous carbon-sulfur battery for lithium-sulfur batteries. Composite cathode material.

The modified graphene porous carbon material is made by the following method:

(1) Put graphene into a round-bottomed flask, add sodium nitrate and 98% concentrated sulfuric acid, stir in an ice bath at 3°C for 15 minutes, add potassium chlorate, continue stirring for 30 minutes, then heat in a water bath at 40°C, react for 3 hours, and add deionized water and placed in an oil bath at 80 °C for 30 min, adding 20% aqueous hydrogen peroxide solution to continue the reaction for 10 min, and then suction filtration, washing and drying to obtain graphene oxide;

(2) Add xylene, absolute ethanol and deionized water to the beaker and mix, stir magnetically for 15min, add dodecylbenzenesulfonic acid, then add the obtained graphene oxide, ultrasonically and magnetically stir for 30min, add aniline and p-phenylenediamine, heated in a water bath at 55°C and continued magnetic stirring for 30min, added sodium persulfate, stirred at a speed of 240r/min for 5h, after the reaction was completed, filtered and washed three times with deionized water to obtain modified graphene;

(3) Put the modified graphene into the tube furnace, feed nitrogen to discharge air, heat up to 800°C at a speed of 8°C/min, feed carbon dioxide, react at this temperature for 2.5h, then feed nitrogen, The temperature was lowered to 30° C. to prepare the modified graphene porous carbon material.

Example 2

The porous carbon-sulfur composite positive electrode material for lithium-sulfur batteries is made from the following raw materials in parts by weight: 40 parts of modified graphene porous carbon material, 210 parts of ethylene glycol, 12 parts of phosphate ester, 4 parts of carbon black, 18 parts of elemental sulfur, 230 parts of N-methylpyrrolidone;

The porous carbon-sulfur composite positive electrode material for the lithium-sulfur battery is made by the following method:

Step S1, adding the modified graphene porous carbon material into ethylene glycol and ultrasonically to form suspension A, then adding phosphate ester, transferring to a hydrothermal kettle, heating in a water bath at 45°C, and stirring at a speed of 120r/min for 15min , then filter, wash three times with absolute ethanol, and dry to obtain doped modified graphene porous carbon material;

Step S2, adding carbon black and elemental sulfur into N-methylpyrrolidone, heating in a water bath at 40°C, and sonicating until the elemental sulfur dissolves to obtain suspension B;

Step S3, adding suspension B into suspension A, stirring at a speed of 150 r/min for 30 min, adding deionized water, centrifuging, washing with deionized water three times, and drying to obtain the porous carbon-sulfur battery for lithium-sulfur batteries. Composite cathode material.

Example 3

The porous carbon-sulfur composite positive electrode material for lithium-sulfur batteries is made from the following raw materials in parts by weight: 45 parts of modified graphene porous carbon material, 220 parts of ethylene glycol, 14 parts of phosphate ester, 5 parts of carbon black, 22 parts of elemental sulfur, 240 parts of N-methylpyrrolidone;

The porous carbon-sulfur composite positive electrode material for the lithium-sulfur battery is made by the following method:

Step S1, adding the modified graphene porous carbon material into ethylene glycol and ultrasonically to form suspension A, then adding phosphate ester, transferring to a hydrothermal kettle, heating in a water bath at 45°C, and stirring at a speed of 120r/min for 15min , then filter, wash three times with absolute ethanol, and dry to obtain doped modified graphene porous carbon material;

Step S2, adding carbon black and elemental sulfur into N-methylpyrrolidone, heating in a water bath at 40°C, and sonicating until the elemental sulfur dissolves to obtain suspension B;

Step S3, adding suspension B into suspension A, stirring at a speed of 150 r/min for 30 min, adding deionized water, centrifuging, washing with deionized water three times, and drying to obtain the porous carbon-sulfur battery for lithium-sulfur batteries. Composite cathode material.

Example 4

The porous carbon-sulfur composite positive electrode material for lithium-sulfur batteries is made from the following raw materials in parts by weight: 50 parts of modified graphene porous carbon material, 230 parts of ethylene glycol, 15 parts of phosphate ester, 6 parts of carbon black, 25 parts of elemental sulfur, 250 parts of N-methylpyrrolidone;

The porous carbon-sulfur composite positive electrode material for the lithium-sulfur battery is made by the following method:

Step S1, adding the modified graphene porous carbon material into ethylene glycol and ultrasonically to form suspension A, then adding phosphate ester, transferring to a hydrothermal kettle, heating in a water bath at 45°C, and stirring at a speed of 120r/min for 15min , then filter, wash three times with absolute ethanol, and dry to obtain doped modified graphene porous carbon material;

Step S2, adding carbon black and elemental sulfur into N-methylpyrrolidone, heating in a water bath at 40°C, and sonicating until the elemental sulfur dissolves to obtain suspension B;

Step S3, adding suspension B into suspension A, stirring at a speed of 150 r/min for 30 min, adding deionized water, centrifuging, washing with deionized water three times, and drying to obtain the porous carbon-sulfur battery for lithium-sulfur batteries. Composite cathode material.

Comparative Example 1

Compared with Example 1, this comparative example uses graphene to replace the modified graphene porous carbon material, and the preparation method is as follows:

Step S1, adding graphene to ethylene glycol and ultrasonication to form suspension A, then adding phosphate ester, transferring to a hydrothermal kettle, heating in a water bath at 45°C, and stirring for 15min at a rotating speed of 120r/min, then filtering, using Washing with anhydrous ethanol three times and drying to obtain the doped modified graphene porous carbon material;

Step S2, adding carbon black and elemental sulfur into N-methylpyrrolidone, heating in a water bath at 40°C, and sonicating until the elemental sulfur dissolves to obtain suspension B;

Step S3, adding suspension B into suspension A, stirring at a speed of 150 r/min for 30 min, adding deionized water, centrifuging, washing with deionized water three times, and drying to obtain the porous carbon-sulfur battery for lithium-sulfur batteries. Composite cathode material.

Comparative Example 2

This comparative example is a cathode material for lithium-sulfur batteries in the market.

The specific surface area and pore volume of the modified graphene porous carbon material prepared in Example 1 are calculated. The modified graphene porous carbon material has a specific surface area of 3350m ² ·g ^-1 and a pore volume of 1.98m ³ ·g ^-1 ;

Embodiment 1-4 and comparative example 1-2 are detected, and the results are shown in the following table;

It can be seen from the above table that the first discharge specific capacity of Examples 1-4 is 756-801mAh/g, the first efficiency is 78-81%, the discharge specific capacity after 100 cycles is 667-682mAh/g, and the ring capacity retention rate is 84.0 -88.2%, the first discharge specific capacity of Comparative Example 1-2 is 496-568mAh/g, the first efficiency is 60-65%, the discharge specific capacity after 100 cycles is 387-422mAh/g, and the ring capacity retention rate is 74.3-78.0%; Therefore, the positive electrode material prepared by the present invention has an ultra-high specific surface area, so that the modified graphene porous carbon material can fully contact the electrolyte and form a double electron layer, and its high porosity can be used for the rapid transfer of electrons Provide channels to facilitate charge transport, which in turn has better electrical conductivity.

The above content is only an example and description of the structure of the present invention, and those skilled in the art can make various modifications or supplements to the specific embodiments described or replace them in similar ways, as long as they do not deviate from the structure of the invention or Anything beyond the scope defined by the claims shall belong to the protection scope of the present invention.

Claims (5)

1. The porous carbon-sulfur composite cathode material for the lithium-sulfur battery is characterized by being prepared from the following raw materials in parts by weight: 35-50 parts of modified graphene porous carbon material, 230 parts of ethylene glycol, 10-15 parts of doping agent, 2-6 parts of carbon black, 15-25 parts of elemental sulfur and 250 parts of N-methylpyrrolidone through 225;

the porous carbon-sulfur composite positive electrode material for the lithium-sulfur battery is prepared by the following method:

step S1, adding the modified graphene porous carbon material into ethylene glycol for ultrasonic treatment to form a suspension A, then adding a doping agent, transferring the suspension A into a hydrothermal kettle, heating in a water bath at 45 ℃, stirring for 15min at a rotating speed of 120r/min, then filtering, washing with absolute ethyl alcohol for three times, and drying to obtain the doped modified graphene porous carbon material;

step S2, adding carbon black and elemental sulfur into N-methyl pyrrolidone, heating in a water bath at 40 ℃, and performing ultrasonic treatment until the elemental sulfur is dissolved to obtain a suspension B;

and step S3, adding the suspension B into the suspension A, stirring for 30min at the rotating speed of 150r/min, adding deionized water, centrifuging, washing with the deionized water for three times, and drying to obtain the porous carbon-sulfur composite cathode material for the lithium-sulfur battery.

2. The porous carbon-sulfur composite positive electrode material for the lithium-sulfur battery according to claim 1, wherein the modified graphene porous carbon material is prepared from the following raw materials in parts by weight: 10-15 parts of graphene, 5-8 parts of sodium nitrate, 150-200 parts of 98% concentrated sulfuric acid, 1-1.5 parts of potassium chlorate, 40-60 parts of 20% aqueous hydrogen peroxide, 20-30 parts of xylene, 20-30 parts of absolute ethyl alcohol, 20-30 parts of deionized water, 2-3 parts of dodecylbenzenesulfonic acid, 25-40 parts of aniline, 5-8 parts of p-phenylenediamine and 3.5-6 parts of sodium persulfate.

3. The porous carbon-sulfur composite positive electrode material for a lithium-sulfur battery according to claim 2, wherein the modified graphene porous carbon material is prepared by a method comprising:

(1) adding graphene into a round-bottom flask, adding sodium nitrate and 98% concentrated sulfuric acid, stirring for 15min in an ice bath at 3 ℃, adding potassium chlorate, continuously stirring for 30min, then heating in a water bath at 40 ℃, reacting for 3h, adding deionized water, placing under an oil bath at 80 ℃, reacting for 30min, adding 20% aqueous hydrogen peroxide, continuously reacting for 10min, then performing suction filtration, washing and drying to obtain graphene oxide;

(2) adding dimethylbenzene, absolute ethyl alcohol and deionized water into a beaker, mixing, magnetically stirring for 15min, adding dodecylbenzene sulfonic acid, then adding the prepared graphene oxide, ultrasonically stirring for 30min, magnetically stirring, adding aniline and p-phenylenediamine, heating in a water bath at 55 ℃, continuously magnetically stirring for 30min, adding sodium persulfate, stirring for 5h at the rotating speed of 240r/min, filtering after the reaction is finished, and washing with the deionized water for three times to obtain the modified graphene;

(3) and putting the modified graphene into a tubular furnace, introducing nitrogen to discharge air, heating to 800 ℃ at the speed of 8 ℃/min, introducing carbon dioxide, reacting for 2.5 hours at the temperature, introducing nitrogen, and cooling to 30 ℃ to obtain the modified graphene porous carbon material.

4. The porous carbon-sulfur composite positive electrode material for a lithium-sulfur battery according to claim 1, wherein the dopant is one or both of phosphate and sulfonate.

5. The preparation method of the porous carbon-sulfur composite cathode material for the lithium-sulfur battery is characterized by comprising the following steps of:

step S1, adding the modified graphene porous carbon material into ethylene glycol for ultrasonic treatment to form a suspension A, then adding a doping agent, transferring the suspension A into a hydrothermal kettle, heating in a water bath at 45 ℃, stirring for 15min at a rotating speed of 120r/min, then filtering, washing with absolute ethyl alcohol for three times, and drying to obtain the doped modified graphene porous carbon material;

step S2, adding carbon black and elemental sulfur into N-methyl pyrrolidone, heating in a water bath at 40 ℃, and performing ultrasonic treatment until the elemental sulfur is dissolved to obtain a suspension B;

and step S3, adding the suspension B into the suspension A, stirring for 30min at the rotating speed of 150r/min, adding deionized water, centrifuging, washing with the deionized water for three times, and drying to obtain the porous carbon-sulfur composite cathode material for the lithium-sulfur battery.