CN110828810A

CN110828810A - Iron-doped porous carbon-sulfur material based on polypyrrole and preparation method and application thereof

Info

Publication number: CN110828810A
Application number: CN201911169478.6A
Authority: CN
Inventors: 孙立贤; 管彦洵; 徐芬; 程日光; 袁元芝; 韩成习; 李�昊; 林祺
Original assignee: Guilin University of Electronic Technology
Current assignee: Guilin University of Electronic Technology
Priority date: 2019-11-26
Filing date: 2019-11-26
Publication date: 2020-02-21
Anticipated expiration: 2039-11-26
Also published as: CN110828810B

Abstract

The invention discloses an iron-doped porous carbon-sulfur composite material based on polypyrrole, which takes inorganic ferric salt, pyrrole and sulfur as raw materials and prepares the polypyrrole as a porous carbon precursor through a low-temperature polymerization method; introducing iron element by a liquid phase method, and preparing polypyrrole-based iron-doped porous carbon by a high-temperature sintering method; and finally, introducing sulfur element by a melting method to obtain the activated iron-doped porous carbon-sulfur composite material based on the polypyrrole, wherein the sulfur content is 45-55%. When the lithium sulfur battery positive electrode is applied, the initial discharge specific capacity reaches 1000-plus-one 1100mAh/g, the specific capacity after circulation is 500-plus-one 600mAh/g, and the average attenuation rate per time is 0.5%. The invention has the following advantages: 1. the porous shape of the carbon carrier is stable, and the loss of active substance sulfur in the circulation process is reduced; 2. the distribution of sulfur in the carrier is more uniform; 3. the sulfur content is high; 4. the method is simple and effective and is suitable for large-scale commercial production.

Description

Iron-doped porous carbon-sulfur material based on polypyrrole and preparation method and application thereof

Technical Field

The invention belongs to the technical field of batteries, and particularly relates to an iron-doped porous carbon-sulfur material based on polypyrrole and a preparation method and application thereof.

Background

As society continues to grow, the demand for energy from humans also increases. However, as fossil fuel resources are continuously exploited for nearly 200 years, the fossil fuel resources have tended to be exhausted, and environmental pollution due to the combustion of fossil fuels has become a major challenge for human survival. Therefore, energy problems and environmental safety problems become global concerns and are urgently needed to be solved. The development of secondary batteries with high energy, high density, high safety, environmental protection and low cost has great significance in the field of new energy. The lithium-sulfur battery is a secondary battery with higher energy density, adopts elemental sulfur or a sulfur-containing material as a positive electrode active substance, has the theoretical energy density of 2600Wh/kg, and has the advantages of rich resources, environmental friendliness, low price and the like. The lithium-sulfur battery with high sulfur content has high capacity density and energy density, and can solve the technical problem that the lithium-ion battery cannot meet the requirements of electric vehicles due to insufficient energy density.

Porous carbon is a sulfur-carrying material widely used in lithium-sulfur batteries, and as early as 2002, Wang et al melted sulfur and distributed and infiltrated into the porous structure of activated carbon (document 1: Wang J, Liu L, Ling Z, et al, polymeric lithium cells with sulfur compounds as materials [ J ]. electrochemica acta, 2003, 48(13): 1861-1867.), thereby applied to the positive electrode of a lithium-sulfur battery, its specific first discharge capacity is 30% at a current density of 0.3A/cm2, its specific first discharge capacity is 800mAh/g, its specific capacity is 440mAh/g after 25 cycles, and its specific first discharge capacity is only 180mAh/g when its sulfur-carrying capacity is increased to 60.9%, and the material has the following disadvantages: (1) the activated carbon has difficulty in limiting the dissolution of polysulfide, so that the sulfur-carrying amount of the material is low and the cycle number is too low; (2) with the increase of the sulfur carrying capacity, the utilization rate of the active substance sulfur is greatly reduced, and the specific capacity is sharply reduced.

To inhibit polysulfide dissolution by doping with metallic elements, Jeon et al incorporate iron powder into a sulfur positive electrode to form a positive electrode composite (Jeon B H, Yeon J H, Chung I J. Preparation and electric properties of lithium-sulfur-composite polymer batteries [ J ]. Journal of materials Processing Technology, 2003, 143. 144(none): 93-97.), having a sulfur content of 50%, a current density of 0.1mA/cm2, a first discharge specific capacity of about 520 mAh/g, and a specific capacity of about 380mAh/g after 10 cycles, which has the disadvantages of: although the addition of iron improves the cycle performance of the lithium-sulfur battery, the material has irregular appearance, sulfur is unevenly dispersed in the composite material, the use efficiency of active substances is influenced, and meanwhile, the direct addition of iron powder enables the contact area of the active substance sulfur and electrolyte to be insufficient, so that the overall capacity of the battery is very low, the cycle current is small, and the number of cycle turns is insufficient.

In order to improve the cycle performance of the lithium-sulfur battery by modifying the morphology of the carrier so that the active substance sulfur can be stably dispersed in the carrier, Liang et al prepare tubular polypyrrole by a self-degradation template method, melt and load the sulfur and apply the tubular polypyrrole to the lithium-sulfur battery (document 3: Liang X, Liu Y, Wen Z, et al, A nano-structured and high-chlorinated polypyrole-sulfur for lithium-sulfur batteries [ J ]. Journarof Power Source, 2011, 196(16): 6955 695.), wherein the material has a sulfur carrying amount of 30% and a specific capacity of 650 mAh/g after 80 cycles, and when the sulfur carrying amount is 50%, the specific capacity is only 140mAh/g after 80 cycles, and the material has the following disadvantages: (1) the material has low sulfur carrying capacity; (2) after the sulfur carrying amount is increased, the utilization rate of the sulfur active substance is reduced, and the cycle performance is sharply reduced.

Disclosure of Invention

The invention aims to provide an iron-doped porous carbon-sulfur material based on polypyrrole, which enables active substance sulfur to be uniformly and stably loaded on a carbon carrier through a porous structure, and simultaneously iron element is doped into the carrier by virtue of a complexation reaction of pyrrole and iron ions, so that the influence of doping on the contact area of the active substance and an electrolyte is reduced, and an intermediate product lithium polysulfide is anchored by metal doping, so that the dissolution of the intermediate product lithium polysulfide in the electrolyte is inhibited, and the following technical problems of a lithium-sulfur battery are solved:

firstly, the problem of uneven dispersion of active substance sulfur in the anode material;

secondly, the sulfur carrying amount is improved, and the cycle performance is sharply reduced;

and thirdly, the specific capacity of the lithium-sulfur battery is sharply reduced due to the shuttle effect caused by the dissolution of the intermediate product lithium polysulfide into the electrolyte.

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

the polypyrrole-based iron-doped porous carbon-sulfur material is prepared by taking inorganic iron salt, pyrrole and sulfur in a certain mass ratio as raw materials, obtaining a porous carbon precursor through low-temperature polymerization, preparing the iron-doped porous carbon precursor through a liquid phase method, preparing the iron-doped porous carbon through a high-temperature sintering method, and finally preparing the activated polypyrrole-based iron-doped porous carbon-sulfur composite material through a melting method. Wherein the inorganic iron salt is FeCl3 ∙ 6H2O, and the sulfur content of the obtained material is 45-55%.

The preparation method of the iron-doped porous carbon-sulfur material based on polypyrrole comprises the following steps:

step 1) preparing a porous carbon precursor by a low-temperature liquid-phase polymerization method, uniformly dispersing pyrrole in dilute hydrochloric acid to obtain a solution A, adding ammonium persulfate into the solution A at the temperature of 0 ℃ according to the mass ratio of the pyrrole to the ammonium persulfate being 1:1, stirring for reacting for 6-8h, washing and drying to obtain the porous carbon precursor;

step 2) preparing iron-doped porous carbon based on polypyrrole by a high-temperature sintering method, dissolving a certain mass of inorganic iron salt in water to form an iron ion solution, then adding the porous carbon precursor obtained in the step 1) into the solution, wherein the mass ratio of the added porous carbon precursor to the inorganic iron salt is 5:1, stirring and reacting for 18-24h, obtaining uniformly dispersed suspension after the reaction is completed, and then filtering and drying to obtain the iron-doped porous carbon precursor. Keeping the obtained iron-doped porous carbon precursor at 500 ℃ for 1.5-2h in a nitrogen atmosphere, continuously heating to 800 ℃, and keeping the temperature for 1-2h to obtain polypyrrole-based iron-doped porous carbon;

step 3) preparing an activated polypyrrole-based iron-doped porous carbon-sulfur composite material by a fusion method, wherein the iron-doped porous carbon obtained in the step 2) and sulfur are mixed according to a mass ratio of 1: (3-3.5), uniformly mixing, keeping the temperature at 155 ℃ for 10-12h in the nitrogen atmosphere, continuously heating to 270 ℃, and keeping the temperature for 30-40min to obtain the activated polypyrrole-based iron-doped porous carbon-sulfur composite material.

The polypyrrole-based iron-doped porous carbon-sulfur material is applied as the anode of the lithium-sulfur battery, when the current density is 167.5mA/cm2, the first discharge specific capacity is 1000-plus-1100 mAh/g, after 100 times of circulation, the specific capacity is attenuated to 500-plus-600 mAh/g, when the current density is 1675mA/cm2, the first discharge specific capacity is 800-plus-900 mAh/g, and after 100 times of circulation, the specific capacity is attenuated to 400-plus-500 mAh/g.

Compared with the prior art, the invention has the following advantages:

1. the porous carbon-sulfur composite material doped with iron prepared by the invention has stable porous morphology of the carbon carrier, can effectively allow molten sulfur to enter the porous carbon, reduces the loss of active substance sulfur in the circulation process, and simultaneously, the existence of the porous structure and iron well limits the dissolution of intermediate product lithium polysulfide, and the negative corrosion caused by the lithium polysulfide penetrating through a diaphragm to reach a negative lithium plate of a battery and the shuttle effect of increasing the internal resistance of the battery are improved, thereby improving the electrochemical circulation performance of the battery;

2. the iron-doped porous carbon-sulfur composite material prepared by the invention has a special porous shape, so that the sulfur is uniformly distributed in the carrier, and the lithium-sulfur battery still keeps high specific capacity and electrochemical cycle performance under high current;

3. the sulfur content is greatly improved and can reach 45-55%, and the specific discharge capacity is also greatly improved;

4. the invention has the advantages of easy reaction condition, good safety, simple and effective synthesis method, and suitability for large-scale commercial production.

Drawings

FIG. 1 is a thermogravimetric plot of an iron-doped porous carbon-sulfur material;

fig. 2 is an SEM image of an iron-doped porous carbon-sulfur material;

FIG. 3 is an XRD image of iron-doped porous carbon and iron-doped porous carbon-sulfur material;

FIG. 4 is a graph of the cycle performance of the lithium sulfur battery prepared in example 1 at a current density of 167.5mA/cm 2;

FIG. 5 is a graph of the cycling capacity of the lithium-sulfur cell prepared in example 1 at current densities of 167.5mA/cm2, 335 mA/cm2, 1675mA/cm 2;

FIG. 6 is a graph showing cycle performance at a current density of 335 mA/cm2 for the lithium sulfur battery prepared in comparative example 1;

FIG. 7 is a graph of the cycle performance of the lithium sulfur battery prepared in example 2 at a current density of 335 mA/cm 2;

FIG. 8 is a graph of the cycle performance of the lithium sulfur battery prepared in example 3 at a current density of 335 mA/cm 2;

FIG. 9 is a graph showing cycle performance at a current density of 335 mA/cm2 for the lithium sulfur battery prepared in comparative example 2.

Detailed Description

The present invention will be described in further detail with reference to the accompanying drawings, which are given by way of examples, but are not intended to limit the present invention.

Example 1

A preparation method of an iron-doped sulfur composite material based on polypyrrole comprises the following steps:

step 1) preparing a porous carbon precursor by a low-temperature liquid-phase polymerization method. Putting 200ml of 0.05mol/L diluted hydrochloric acid into a beaker, putting the beaker under an ice bath condition, adding 4ml of pyrrole into the diluted hydrochloric acid after the temperature is stable, stirring for 30min, adding 2.74g of ammonium persulfate into the beaker, reacting for 6h, washing and drying a product by using distilled water and an organic solvent to obtain a porous carbon precursor;

and step 2) preparing the iron-doped porous carbon by a high-temperature sintering method. Weighing 0.5g of the porous carbon precursor obtained in the step 1) and 0.1g of FeCl3 ∙ 6H2O, placing the mixture in a beaker, adding 50ml of distilled water, reacting for 24 hours under magnetic stirring to obtain uniformly dispersed suspension, and then filtering and drying to obtain the iron-doped porous carbon precursor. Keeping the obtained iron-doped porous carbon precursor at 500 ℃ for 2h in a nitrogen atmosphere, continuously heating to 800 ℃ and keeping the temperature for 1h to obtain iron-doped porous carbon;

and 3) preparing the activated iron-doped porous carbon-sulfur composite material by a melting method. Weighing 0.1g of the iron-doped porous carbon obtained in the step 2) and 0.35g of sublimed sulfur, placing the weighed materials in a mortar for uniform grinding, keeping the temperature for 10 hours at 155 ℃ in a nitrogen atmosphere, continuously heating to 270 ℃, and keeping the temperature for 30 minutes to obtain the activated iron-doped porous carbon-sulfur composite material.

The positive electrode material (accounting for 80% of the positive electrode of the lithium-sulfur battery), the carbon black conductive agent (accounting for 10% of the positive electrode of the lithium-sulfur battery), and the binder (accounting for 10% of the positive electrode of the lithium-sulfur battery, and the binder is 15wt% of polyvinylidene fluoride solution) of the lithium-sulfur battery of the embodiment are fully dispersed and uniformly ground to obtain positive electrode slurry, the prepared positive electrode slurry is coated on an aluminum foil current collector to prepare an electrode plate, and the electrode plate is dried to obtain the positive electrode of the lithium-sulfur battery.

The lithium-sulfur battery prepared in this example was assembled with the positive electrode, negative electrode (lithium metal sheet) and separator (polyethylene film) together, and the electrolyte solution filled in the battery was a mixed solution of 1, 3-dioxolane, ethylene glycol dimethyl ether, and lithium trifluoromethanesulfonate.

In order to verify the content of sulfur element in the iron-doped porous carbon-sulfur anode material, thermogravimetric analysis is carried out on the iron-doped porous carbon-sulfur to determine that the content of sublimed sulfur is 54.54%, and the composite material contains more active material sulfur;

in order to verify the micro morphology of the iron-doped porous carbon material, SEM test is carried out on the material, and as shown in figure 2, the material has a remarkable porous structure;

in order to verify the compounding condition of the iron-doped porous carbon and the sublimed sulfur, XRD (X-ray diffraction) tests are carried out on the iron-doped porous carbon and the iron-doped porous carbon-sulfur composite material, and XRD images show that the iron-doped porous carbon and the sublimed sulfur are better melted and mixed;

FIG. 4 is a graph of cycle performance of the lithium sulfur battery prepared in example 1 at a current density of 167.5mA/cm 2. The first discharge specific capacity of the lithium-sulfur battery of the embodiment is 1031mAh/g, and after 100 cycles, the specific capacity is attenuated to 554 mAh/g. The coulombic efficiency of the lithium-sulfur battery is also close to 100 percent, and the lithium-sulfur battery of the embodiment has higher specific capacity and better cycle performance;

FIG. 5 is a graph of the cycling capacity of the lithium-sulfur cell prepared in example 1 at current densities of 167.5mA/cm2, 335 mA/cm2, 1675mA/cm 2. The first discharge specific capacity is 1031mAh/g, 949 mAh/g and 812 mAh/g respectively, and after 100 times of circulation, the specific capacity is attenuated to 554mAh/g, 409 mAh/g and 410 mAh/g. The lithium-sulfur battery of the embodiment still maintains good cycle performance under high current.

In order to verify the effect of the addition of Fe on the cycle performance of the lithium sulfur battery, a porous carbon-sulfur composite material without the addition of iron was prepared by comparative example 1.

Comparative example 1

A method for producing a porous carbon-sulfur composite material without adding iron, the steps not specifically described being the same as those in example 1, except that: in the step 1), FeCl3 ∙ 6H2O is not added.

FIG. 6 is a graph showing cycle performance at a current density of 335 mA/cm2 for the lithium sulfur battery prepared in comparative example 1. The first discharge specific capacity of the lithium-sulfur battery of the comparative example is 677 mAh/g, after 100 times of circulation, the specific capacity is attenuated to 245 mAh/g, and the first-turn capacity and the cycle performance of the lithium-sulfur battery are greatly reduced compared with those of the lithium-sulfur battery of the example 1.

The results of comparative example 1 show that doping with iron can anchor the intermediate lithium polysulfide inside the carbon support, resulting in an increase in the electrochemical performance of the lithium sulfur battery.

In order to verify the influence of the addition amount of Fe on the cycle performance of the lithium-sulfur battery, composite materials having mass ratios of the porous carbon precursor to the inorganic iron salt of 1:1 and 10:1 were prepared by examples 2 and 3.

Example 2

A method for preparing an iron-doped sulfur composite material based on polypyrrole (the mass ratio of a porous carbon precursor to an inorganic iron salt is 1: 1), wherein the steps which are not particularly described are the same as those in example 1, except that: in the step 1), the addition amount of FeCl3 ∙ 6H2O was 0.5 g.

FIG. 7 is a graph showing cycle performance of the lithium sulfur battery prepared in example 2 at a current density of 335 mA/cm 2. The first discharge specific capacity of the lithium-sulfur battery of the comparative example is 213mAh/g, after 100 cycles, the specific capacity is attenuated to 140mAh/g, and the first-cycle capacity and the cycle performance of the lithium-sulfur battery are greatly reduced compared with those of the lithium-sulfur battery of the example 1.

Example 3

A method for preparing an iron-doped sulfur composite material based on polypyrrole (the mass ratio of a porous carbon precursor to an inorganic iron salt is 10: 1), wherein the steps which are not particularly described are the same as those in example 1, except that: in the step 1), the addition amount of FeCl3 ∙ 6H2O was 0.05 g.

FIG. 8 is a graph showing cycle performance of the lithium sulfur battery prepared in example 3 at a current density of 335 mA/cm 2. The first discharge specific capacity of the lithium-sulfur battery of the comparative example is 1072mAh/g, after 100 cycles, the specific capacity is attenuated to 334mAh/g, and the cycle performance is greatly reduced compared with that of the example 1.

The results of examples 2 and 3 show that, when the iron content is too high, part of the pore structure is occupied, so that the utilization rate of the active material sulfur is decreased; at lower iron levels, however, the effect of anchoring polysulfides is poor, resulting in a faster decrease in cycle performance.

In order to verify the influence of the kind of Fe as an adsorbent on the cycle performance of the lithium sulfur battery, a composite material having a mass ratio of porous carbon precursor powder to inorganic manganese salt of 5:1 was prepared by comparative example 2.

Comparative example 2

A preparation method of a polypyrrole-based manganese-doped porous carbon-sulfur composite material (the mass ratio of a porous carbon precursor to an inorganic manganese salt is 1: 1), which has the same steps as those in example 1 except that: in the step 1), the added FeCl3 ∙ 6H2O was changed to MnCO3, and the addition amount was 0.1 g.

FIG. 9 is a graph showing cycle performance at a current density of 335 mA/cm2 for the lithium sulfur battery prepared in comparative example 2. The first discharge specific capacity of the lithium-sulfur battery of the comparative example is 691mAh/g, after 100 times of circulation, the specific capacity is attenuated to 159mAh/g, and the first circle capacity and the cycle performance of the lithium-sulfur battery are greatly reduced compared with the example 1.

The results of comparative example 2 show that when the doping element is manganese, its anchoring effect to polysulfides is inferior to that of iron element, and the problem of loss of sulfur, which is an active material, during the cycle cannot be effectively solved.

Meanwhile, experimental results also show that the difference of the physical and chemical properties of the metal elements and the transition elements results in great difference of technical effects generated when the material is applied; the technical effect of the invention can be obviously improved only if the composition morphology of the metal element and the carbon material is effectively matched.

Claims

1. An iron-doped porous carbon-sulfur composite material based on polypyrrole is characterized in that: preparing polypyrrole as a porous carbon precursor by using inorganic ferric salt, pyrrole and sulfur as raw materials through a low-temperature polymerization method; introducing iron element by a liquid phase method, and preparing polypyrrole-based iron-doped porous carbon by a high-temperature sintering method; and finally, introducing sulfur element by a melting method to obtain the activated iron-doped porous carbon-sulfur composite material based on the polypyrrole.

2. The polypyrrole-based iron-doped porous carbon-sulfur composite material according to claim 1, wherein: the inorganic ferric salt is FeCl₃∙6H₂O。

3. The polypyrrole-based iron-doped porous carbon-sulfur composite material according to claim 1, wherein: the sulfur content of the iron-doped porous carbon-sulfur composite material is 45-55%.

4. The preparation method of the polypyrrole-based iron-doped porous carbon-sulfur composite material according to claim 1, characterized by comprising the following steps:

step 1) preparing polypyrrole as a porous carbon precursor by a low-temperature polymerization method, uniformly dispersing the pyrrole in dilute hydrochloric acid to obtain a solution A, adding ammonium persulfate into the solution A at a low temperature by using the pyrrole and ammonium persulfate to meet the certain mass ratio, stirring for reacting for a certain time, washing and drying to obtain the porous carbon precursor;

step 2) preparing iron-doped porous carbon based on polypyrrole by a high-temperature sintering method, dissolving inorganic ferric salt in water to form an iron ion solution, adding the porous carbon precursor obtained in the step 1) into the iron ion solution with the porous carbon precursor and the inorganic ferric salt satisfying a certain mass ratio, stirring and reacting for a certain time, obtaining a uniformly dispersed suspension after complete reaction, filtering, drying, and performing heat treatment under certain conditions to obtain the iron-doped porous carbon based on polypyrrole;

and 3) preparing the activated iron-doped porous carbon-sulfur composite material based on the polypyrrole by a fusion method, uniformly mixing the iron-doped porous carbon based on the polypyrrole obtained in the step 2) with sulfur, and carrying out heat treatment under a certain condition to obtain the activated iron-doped porous carbon-sulfur composite material based on the polypyrrole.

5. The method of claim 4, wherein: the mass ratio of the pyrrole to the ammonium persulfate in the step 1) is 1:1, and the low-temperature reaction in the step 1) is carried out under the conditions that the reaction temperature is 0 ℃ and the reaction time is 6-8 h.

6. The method of claim 4, wherein: the mass ratio of the porous carbon precursor to the inorganic ferric salt in the step 2) is 5:1, the stirring reaction time in the step 2) is 18-24h, and the heat treatment condition in the step 2) is that the temperature is kept for 1.5-2h at 500 ℃ in a nitrogen atmosphere, the temperature is continuously increased to 800 ℃, and then the temperature is kept for 1-2 h.

7. The method of claim 4, wherein: the mass ratio of the iron-doped porous carbon based on polypyrrole to sulfur in the step 3) is 1: (3-3.5), the heat treatment condition in the step 3) is heat preservation for 10-12h at 155 ℃ under the nitrogen atmosphere, and the temperature is continuously raised to 260-280 ℃ and then is preserved for 30-40 min.

8. Use of a polypyrrole based iron doped porous carbon-sulfur composite as claimed in claim 1 as lithium sulfur battery positive electrode, characterized in that: when the current density is 167.5mA/cm²When the discharge specific capacity is 1000-1100mAh/g for the first time; after 100 times of circulation, the specific capacity is attenuated to 500-600mAh/g, which is 50 percent of the first discharge, and the average attenuation rate per time is 0.5 percent.

9. Use of a polypyrrole based iron doped porous carbon-sulfur composite as claimed in claim 1 as lithium sulfur battery positive electrode, characterized in that: when the current density is 1675mA/cm²When the discharge specific capacity is 800-900mAh/g for the first time; after 100 times of circulation, the specific capacity is attenuated to 400-500mAh/g, which is 50 percent of the first discharge, and the average attenuation rate per time is 0.5 percent.