KR20180074902A - Sulfur-carbon composite and method for preparing thereof - Google Patents

Abstract

Provided are: a crystalline or paracrystalline carbonaceous conductive material having a three-dimensional framework structure formed by aggregating a plurality of primary particles having pores; sulfur existing in the pores of the primary particles and on the surface of the three-dimensional framework structure; and a sulfur-carbon composite comprising the carbonaceous conductive material and an outermost carbonaceous coating layer surrounding the sulfur. It is an object of the present invention to provide the sulfur-carbon composite having a structure capable of improving the utilization ratio of sulfur in an electrochemical oxidation-reduction reaction and inhibiting dissolution of sulfur into a non-aqueous solvent.

Description

FIELD OF THE INVENTION [0001] The present invention relates to a sulfur-

The present invention relates to a sulfur-carbon composite material and a method of manufacturing the same, and more particularly, to a sulfur-carbon composite material which is applied to a cathode material of a secondary battery and exhibits excellent performance.

BACKGROUND ART [0002] A secondary battery is used as a high-performance energy source for a large-capacity power storage battery such as an electric car or a battery power storage system, and a portable electronic device such as a mobile phone, a camcorder, and a notebook.

As a secondary battery, a lithium ion battery has a higher energy density and a larger capacity per unit area than a nickel-manganese battery or a nickel-cadmium battery, but has various disadvantages such as low stability due to overheating, low energy density and low output characteristics.

In order to improve the disadvantages of such lithium ion batteries, research and development on lithium sulfur secondary batteries and lithium secondary batteries having high output and high energy density are actively under way.

Of these, the lithium sulfur secondary battery uses sulfur as a cathode active material and uses lithium metal as a cathode. It exhibits 2500 Wh / kg, which is five times higher than the theoretical energy density of a conventional lithium ion battery and requires high output and high energy density It is suitable as battery for electric vehicles.

Despite the above advantages, when sulfur is used as the active material, the utilization rate of sulfur participating in the electrochemical oxidation-reduction reaction in the cell is lower than the total amount of sulfur added, which actually results in a cell capacity lower than the theoretical capacity.

In addition, during the oxidation-reduction reaction occurring during the operation of the battery, the sulfur is discharged to the electrolyte, which is a non-aqueous solvent, and the lifetime of the battery deteriorates. Due to the shuttle phenomenon that lithium- polysulfide, which is a reducing material of sulfur, is eluted and moves between the anode and the cathode, There is a problem that the capacity and the service life are deteriorated.

In addition, most of the cathode active materials for lithium sulfur secondary batteries known so far are related to a composite of a conductive mesophase and a sulfur-doped microporous material used as a support for sulfur, but the composites according to the prior art do not contain sulfur - Aggregates are present or the sulfur is not uniformly dispersed in the composite, and the elution of sulfur components during the operation of the battery can not be prevented, resulting in a shuttle phenomenon.

Disclosure of the Invention The present invention has been made to solve the above-mentioned problems, and it is an object of the present invention to provide a sulfur-carbon composite having a structure capable of improving the utilization ratio of sulfur in an electrochemical oxidation-reduction reaction and inhibiting dissolution of sulfur into non- The purpose.

It is also an object of the present invention to provide a sulfur-carbon composite having mechanical properties similar to those of sulfur as sulfur is not uniformly dispersed and coated in some regions of the composite.

It is another object of the present invention to provide a process for producing a sulfur-carbon composite having the above advantages.

In one embodiment of the present invention, a crystalline or pseudocratic carbonaceous conductive material having a three-dimensional framework structure formed by aggregating a plurality of primary particles having pores; Sulfur existing in the pores of the plurality of primary particles and on the surface of the three-dimensional framework structure; And an outermost carbonaceous coating layer surrounding the carbonaceous conductive material and the sulfur.

The pores may include mesopores having a diameter of 2 nm to 50 nm and micropores having a diameter of more than 0 nm and less than 2 nm, and the sulfur may be filled in the mesopores and the micropores.

The filling ratio of the mesopores and the sulfur in the micropores may be 90% to 100% by area.

The carbon of the outermost carbonaceous coating layer and the sulfur may form a covalent bond.

The outermost carbonaceous coating layer may be derived from a low crystalline carbon material comprising one selected from the group consisting of petroleum pitch, coal pitch, chemical pitch and combinations thereof.

The outermost carbonaceous coating layer may be less than about 50% by weight in the composite, for example, greater than about 0% by weight, and less than about 50% by weight.

In another embodiment of the present invention, there is provided a method for preparing a mixture of a) a carbonaceous conductive material having a three-dimensional skeleton structure formed by aggregating a plurality of primary particles having pores and a crystalline or pseudocratic carbonaceous conductive material, Producing; b) subjecting the mixture to a first heat treatment to melt the sulfur powder in the mixture to fill the pores of the plurality of primary particles and coat the surface of the three-dimensional framework structure; c) mixing the low-crystalline carbon material with the mixture to form the carbonaceous conductive material and the outermost carbonaceous coating layer surrounding the sulfur; d) subjecting the mixture having the outermost carbonaceous coating layer formed to a second heat treatment; And e) subjecting the mixture having the outermost carbonaceous coating layer formed to a third heat treatment to carbonize the outermost carbonaceous coating layer.

In the step a), the mixture may be prepared by mixing the carbonaceous conductive material and the sulfur powder so that the weight ratio of the carbonaceous conductive material: the sulfur powder is 1: 15 to 1:30.

In the step b), the first heat treatment temperature may be 120 ° C to 180 ° C. In addition, in the step d), the second heat treatment temperature may be 200 ° C to 350 ° C. In the step e), the third heat treatment temperature may be 500 ° C to 1000 ° C. In the step d), the second heat treatment may be performed under a pressure of 1 bar to 10 bar.

The sulfur-carbon composite according to one embodiment of the present invention has a structure capable of improving the utilization ratio of sulfur in an electrochemical oxidation-reduction reaction and inhibiting dissolution of sulfur into a non-aqueous solvent.

In addition, the sulfur-carbon composite may exhibit a mechanical property similar to sulfur as sulfur is not aggregated in a part of the composite and uniformly dispersed and coated as a whole.

In addition, the sulfur-carbon composite having the above-described advantages can be obtained through the method for producing the sulfur-carbon composite according to another embodiment of the present invention.

1 schematically shows a sulfur-carbon composite of the present invention.
2 shows a graph of a result of Experimental Example 2 of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS The above and other features and advantages of the present invention will become more apparent by describing in detail exemplary embodiments thereof with reference to the attached drawings in which: These embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art to which the invention pertains. Only.

In the drawings, the thickness or area is enlarged to clearly indicate layers and regions. In the drawings, for purposes of explanation, some layers and regions are exaggerated. Like reference numerals refer to like elements throughout the specification.

Hereinafter, a sulfur-carbon composite according to embodiments of the present invention and a method of manufacturing the same will be described in detail.

One embodiment of the present invention relates to a carbonaceous conductive material of a crystalline or pseudocrystalline having a three-dimensional framework structure formed by aggregating a plurality of primary particles having pores; Sulfur existing in the pores of the plurality of primary particles and on the surface of the three-dimensional framework structure; And an outermost carbonaceous coating layer surrounding the carbonaceous conductive material and the sulfur.

1 schematically illustrates the sulfur-carbon composite 100 according to an embodiment of the present invention. Referring to FIG. 1, the sulfur-carbon composite 100 includes a carbonaceous conductive material 10, a sulfur 20, and an outermost carbonaceous coating layer 30.

Referring to FIG. 1, the carbonaceous conductive material 10 has a structure in which a plurality of primary particles having pores are aggregated to form a branch-like structure, and the branch-like structure is irregularly formed And has a three-dimensional skeletal structure. Through the three-dimensional framework structure, the carbonaceous conductive material has a large specific surface area relative to volume.

Specifically, the BET specific surface area of the carbonaceous conductive material can be from about 50 m 2 / g to about 1300 m 2 / g, for example from about 50 m 2 / g to about 1000 m 2 / g, G may be from about 50 m 2 / g to about 100 m 2 / g, for example from about 50 m 2 / g to about 500 m 2 / g, G to about 80 m < 2 > / g. The BET specific surface area means the BET surface area of the carbonaceous conductive material itself before the presence of sulfur in the pores of the plurality of primary particles of the carbonaceous conductive material and on the surface of the three-dimensional framework structure. Through the BET specific surface area in the above range, the sulfur-carbon composite can contain a high content of sulfur, and the desired sulfur utilization can be ensured.

The plurality of primary particles of the carbonaceous conductive material may each have a particle diameter of about 30 nm to about 100 nm. At this time, the particle diameter can be measured using an optical microscope or an electron microscope, and is regarded as an arithmetic average value of each particle.

In addition, the plurality of primary particles constituting the carbonaceous conductive material may be a porous structure in which each particle has pores, and may specifically include mesopores, micropores, or both. The mesopore is a pore having a diameter of about 2 nm to about 50 nm, and the micropore is a pore having a pore diameter of less than about 2 nm, i.e., more than about 0 nm and less than about 2 nm.

The carbonaceous conductive material is made of a highly crystalline carbon material, that is, a carbon material of a crsyalline or a similar paracrystalline. For example, the carbonaceous conductive material may include carbon black, ketjen black, lamp black, channel black, acetylene black, fines black, summer black, graphene, fullerene, carbon nanotubes, carbon nanofibers, . ≪ / RTI >

Also, the weight of the carbonaceous conductive material in the total weight of the sulfur-carbon composite material may be about 1 wt% to about 10 wt%.

Referring to FIG. 1, the sulfur 20 of the sulfur-carbon composite 100 is injected into the pores of a plurality of primary particles of the carbonaceous conductive material 10, The surface of the structure, or both.

Specifically, the sulfur 20 is in the form of a sulfur atom or a sulfur compound, wherein the sulfur compound is not a sulfur-containing polymer. That is, the sulfur 20 is in the form of a sulfur atom or a non-polymeric sulfur compound.

Sulfur present in the pores of the plurality of primary particles is present in a state filled with the mesopores and the micropores, more specifically, the mesopores and the micropores are coated on the inner wall.

Here, the filling rate of the sulfur in the mesopores and the micropores may be about 90% to about 100%, for example, about 90% to about 98.5%. That is, about 90% to about 100%, for example, about 90% to about 98.5% of the total area of the pore inner wall. As a result, the sulfur content of the sulfur-carbon composite is increased and the presence of sulfur in the pores reduces the possibility of sulfur leaching. The filling rate of the sulfur in the pores can be derived by comparing the specific surface area of the carbonaceous conductive material before the sulfur is filled with the specific surface area of the carbonaceous conductive material after the sulfur is filled. At this time, the specific surface area can be measured using a BET measuring instrument

Sulfur present on the surface of the three-dimensional framework structure of the carbonaceous conductive material 10 may exist in a space between branch-shaped structures formed by aggregation of the plurality of primary particles. Due to the presence of sulfur at such locations, a sufficient reaction surface area of sulfur with low electrical conductivity can be secured.

In addition, in the sulfur-carbon composite, the sulfur present on the surface of the three-dimensional framework structure may not exist in the space between the branched structures as a whole, but may occupy only a part of the space. As a result, the spaces not occupied by sulfur can be used as a path for diffusion or migration of the electrolyte for the electrochemical oxidation-reduction reaction, and the electrolyte easily reaches the sulfur, and the utilization rate of sulfur in the electrochemical oxidation- Can be improved.

In addition, the weight of the sulfur in the total weight of the sulfur-carbon composite may be about 10 wt% to about 50 wt%.

Referring to FIG. 1, the outermost carbonaceous coating layer 30 of the sulfur-carbon composite 100 is a covering layer surrounding the carbonaceous conductive material 10 and the sulfur 20.

The performance of preventing the leaching of the sulfur 20 to the non-aqueous solvent is greatly improved by including the outermost carbonaceous coating layer 30 on the sulfur-carbon composite 100, Can be improved.

Specifically, the outermost carbonaceous coating layer 30 may be less than about 50 wt%, for example, greater than about 0 wt% and less than about 50 wt% of the total weight of the sulfur-carbon composite 100.

Further, the outermost carbonaceous coating layer may be derived from a low-crystalline carbon material. Specifically, the low-crystalline carbon material may include one selected from the group consisting of a petroleum pitch, a coal pitch, a chemical pitch, and combinations thereof.

Since the outermost carbonaceous coating layer is derived from a low-crystalline carbon material, there is an advantage that the crystalline phase is variable as compared with the case where it is produced using a high-crystalline carbon material, that is, a crystalline material or a carbon material having a similar crystal phase, It may be advantageous in that the crystal phase of the vaginal coating layer can be processed to the desired level through heat treatment conditions.

Referring to FIG. 1, the outermost carbonaceous coating layer can directly contact sulfur coated on the surface of the three-dimensional framework structure of the carbonaceous conductive material, and in some cases, a plurality of primary particles of the carbonaceous conductive material It can also come in contact with sulfur present inside the pores.

At this time, the carbon atom (C) of the outermost carbonaceous coating layer can form a covalent bond with the sulfur atom (S) of the sulfur. As a result, the effect of inhibiting dissolution of sulfur in the non-aqueous solvent is maximized, which contributes to the improvement of battery capacity and lifetime.

Also, as noted above, the sulfur 20 is in the form of a sulfur atom or a sulfur compound, wherein the sulfur compound is not a sulfur containing polymer. That is, the sulfur 20 is in the form of a sulfur atom or a non-polymeric sulfur compound.

Generally, sulfur-containing polymer materials have been used to inhibit the elution of sulfur. Here, the sulfur-containing polymer material is a polymer material having a carbon-sulfur (C-S) bond or a sulfur-sulfur (S-S) bond in its chemical structure. However, the polymer material containing sulfur has a disadvantage that the reversibility of the reaction is lost as the polymer is cleaved by the binding of lithium (Li) ion and sulfur atom (S) at the time of discharge of the battery, there was.

Accordingly, the sulfur-carbon composite according to one embodiment of the present invention has the effect of suppressing the elution of sulfur and improving the lifetime of the battery by using the sulfur (20) in the form of a sulfur atom or a non-polymeric sulfur compound .

The nonpolymeric sulfur compound is not particularly limited and includes, for example, diphenyl disulfide, dibenzothiophene, thioethers, thioesters, thioacetals, ), And a combination thereof.

Another embodiment of the present invention provides a process for producing the sulfur-carbon composite. At this time, the method for producing the sulfur-carbon composite may include the following steps.

a) preparing a mixture by mixing a carbonaceous conductive material of a crystalline or pseudocratic paratrystalline structure having a three-dimensional skeleton structure formed by collecting a plurality of primary particles having pores and sulfur powder;

b) subjecting the mixture to a first heat treatment to melt the sulfur powder in the mixture to fill the pores of the plurality of primary particles and coat the surface of the three-dimensional framework structure;

c) mixing the low-crystalline carbon material with the mixture to form the carbonaceous conductive material and the outermost carbonaceous coating layer surrounding the sulfur;

d) subjecting the mixture having the outermost carbonaceous coating layer formed to a second heat treatment; And

e) subjecting the mixture having the outermost carbonaceous coating layer formed to a third heat treatment to carbonize the outermost carbonaceous coating layer.

Through the above steps a) to d), a sulfur-carbon composite having the above-described structure and characteristics can be produced. The matters relating to the carbonaceous conductive material, the sulfur and the outermost carbonaceous coating layer are as described above.

In the step a), the mixture is prepared by mixing the carbonaceous conductive material and the sulfur powder, wherein the weight ratio of the carbonaceous conductive material: sulfur powder may be 1:15 to 1:30.

The carbonaceous conductive material and the sulfur powder may be physically processed for mixing and may be processed by a method of grinding or milling and mixed uniformly.

Step b) is a step for impregnating sulfur into the surface or pores of the three-dimensional framework structure of the carbonaceous conductive material, wherein the first heat treatment temperature may be about 120 ° C to about 180 ° C. By the heat treatment in this temperature range, the sulfur powder can be melted and flowability can be easily ensured to penetrate into the surface or pores of the three-dimensional framework structure.

At this time, step b) may be carried out under pressurized conditions of about 1 bar to about 10 bar to more efficiently penetrate the molten sulfur.

The step b) is a step for melting the sulfur raw material and penetrating the carbonaceous conductive material into the inside of the carbonaceous conductive material, and immediately after the completion of the step b), the sulfur forms a state of physical contact with the carbonaceous conductive material at each position And may exist in a coagulated state in some regions.

Next, in the step c), a low-crystalline carbon material is mixed with the mixture to form the carbonaceous conductive material and the outermost carbonaceous coating layer surrounding the sulfur. At this time, the step c) may be performed at about 90 ° C to about 110 ° C.

Wherein the step c) comprises the step of bringing the low-crystalline carbon material into contact with the carbonaceous conductive material and the sulfur, and immediately after completing the step c), the low- They are physically in contact with each other and do not form any chemical bonds.

Next, in the step d), the mixture in which the outermost carbonaceous coating layer is formed is subjected to a second heat treatment. At this time, the second heat treatment temperature may be about 200 ° C to about 350 ° C. Wherein the second heat treatment temperature is a temperature higher than the performance temperature of step b) or step c), and refolding the sulfur present in the aggregated state in a part of the step b) through the step d) It can be uniformly dispersed in the conductive material. At the same time, carbon-sulfur (C-S) covalent bonds can be formed between the outermost carbonaceous coating layer and the sulfur, which are in physical contact with each other in the step c).

Also, step d) may be carried out under pressurized conditions of from about 1 bar to about 10 bar. As a result, the carbon-sulfur (CS) covalent bond can be well formed, and as a result, leakage of sulfur to the non-aqueous electrolyte can be prevented and sulfur release can be prevented at high temperature to improve the utilization ratio of sulfur and the lifetime stability of the battery .

Next, in the step e), the second heat-treated mixture is subjected to a third heat treatment to carbonize the outermost carbonaceous coating layer. At this time, the third heat treatment temperature may be about 500 ° C to about 1000 ° C. As a result, the outermost carbonaceous coating layer is formed as a final shell of the sulfur-carbon composite, and functions to prevent sulfur from leaking or escaping.

For example, step e) may be carried out at a temperature in the above range for about 1 hour.

The method for producing the sulfur-carbon composite can improve the three-dimensional skeleton structure of the carbonaceous conductive material and the sulfur-loading amount and the sulfur-filling amount of the pores of the primary particles by so-called high temperature / pressure coating and processing, Atoms can be uniformly dispersed and coated without aggregation.

Further, the outermost carbonaceous coating layer is formed through the steps of forming the outermost carbonaceous coating layer and heat-treated, and the outermost carbonaceous coating layer has a degree of crystallinity which contributes to securing a good electrical conductivity, and the sulfur- Or < / RTI > chemical structure capable of functioning to prevent sulphation and escape of sulfur within the body.

As a result, the sulfur-carbon composite material is applied to a secondary battery to realize a superior function, and more specifically, it can exhibit improved physical properties as a cathode material of a secondary battery.

Hereinafter, specific embodiments of the present invention will be described. However, the embodiments described below are only intended to illustrate or explain the present invention, and thus the present invention is not limited thereto.

< Example  And Comparative Example >

Example  One

1 g of carbon black (Ketjenblack EC, AKZO-NOBEL) powder as an aggregate of a plurality of primary particles having mesopores and micropores was mixed with 60 g of sulfur powder, followed by grinding to prepare a mixture. The mixture was then heat treated at 150 ° C to melt the sulfur powder and the molten sulfur was charged into the mesopores and micropores and coated on the outer surface of the carbon black powder. Subsequently, 15.25 g of coal-based pitch (OCI) as a low-crystalline carbon material was mixed at 100 ° C to form a carbon coating material and a pitch coating layer surrounding the sulfur. Subsequently, the pitch-coated carbonaceous conductive material and sulfur were heat-treated at 300 DEG C under an inert gas condition at 7 bar. Subsequently, heat treatment was performed at 500 캜 for 1 hour under an inert gas atmosphere to prepare a final sulfur-carbon composite.

Comparative Example  One

Using the mixture of carbon black powder and sulfur powder of the same kind and content as in Example 1, but without forming a pitch coating layer, the mixture was heat-treated at 150 ° C to melt the sulfur powder, Pores and micropores, coated on the outer surface of the carbon black powder, and then heat treated at 300 DEG C under a pressure of 7 bar to prepare a composite.

<Evaluation>

Experimental Example  1: Sulfur content in the sulfur-carbon composite

The content of sulfur (S) in each of the composites prepared in Example 1 and Comparative Example 1 was measured by an elementary analyzer (EA, Eager 300 elemental analyzer). The results are shown in Table 1 below.

Experimental Example  2: Sulfur release and release prevention performance evaluation

For each of the composites finally prepared in Example 1 and Comparative Example 1, the elution and prevention performance of sulfur was evaluated by thermal gravimetric analysis (TGA, thermogravimetric analysis) up to 500 ° C. The results are shown in the following Table 1 and the graph of Fig. The thermogravimetric results in Table 1 below are percentages of the weight of the composite reduced during the heat treatment compared to the weight of the composite before heat treatment.

Sulfur Content [wt%]  Thermogravimetric analysis [%] Example 1 47% 1.4% Comparative Example 1 3% 98.1%

Referring to the results of Table 1 above, it can be seen that the composite of Example 1 has a significantly higher sulfur content than that of the composite of Comparative Example 1, and has an advantage of effectively preventing elution and desorption of sulfur during use of the battery .

100: sulfur-carbon complex
10: carbonaceous conductive material
20: sulfur
30: Outermost carbonaceous coating layer

Claims (10)

A crystalline or pseudocratic carbonaceous conductive material having a three-dimensional framework structure formed by aggregating a plurality of primary particles having pores;
Sulfur existing in the pores of the plurality of primary particles and on the surface of the three-dimensional framework structure; And
A carbonaceous conductive material and an outermost carbonaceous coating layer surrounding said sulfur.
The method according to claim 1,
Wherein the pores include mesopores having a diameter of 2 nm to 50 nm and micropores having a diameter of more than 0 nm and less than 2 nm,
Wherein said sulfur is present in said mesopore and in said micropores
Sulfur - carbon complex.
3. The method of claim 2,
The filling ratio of the mesopores and the sulfur in the micropores is 90% to 100%
Sulfur - carbon complex.
The method according to claim 1,
Wherein the carbon atom (C) of the outermost carbonaceous coating layer and the sulfur atom (S) of the sulfur are covalently bonded
Sulfur - carbon complex.
The method according to claim 1,
Wherein said outermost carbonaceous coating layer is a layer of carbonaceous material derived from a low crystalline carbon material comprising one selected from the group consisting of a petroleum pitch, a coal pitch, a chemical pitch,
Sulfur - carbon complex.
The method according to claim 1,
Wherein the outermost carbonaceous coating layer comprises greater than 0 wt%, less than 50 wt%
Sulfur - carbon complex.
a) preparing a mixture by mixing a carbonaceous conductive material of a crystalline or pseudocratic paratrystalline structure having a three-dimensional skeleton structure formed by collecting a plurality of primary particles having pores and sulfur powder;
b) subjecting the mixture to a first heat treatment to melt the sulfur powder in the mixture to fill the pores of the plurality of primary particles and coat the surface of the three-dimensional framework structure;
c) mixing the low-crystalline carbon material with the mixture to form the carbonaceous conductive material and the outermost carbonaceous coating layer surrounding the sulfur;
d) subjecting the mixture having the outermost carbonaceous coating layer formed to a second heat treatment; And
and e) subjecting the mixture having the outermost carbonaceous coating layer formed to a third heat treatment to carbonize the outermost carbonaceous coating layer
Sulfur - carbon composite.
8. The method of claim 7,
In the step a), the mixture is prepared by mixing the carbonaceous conductive material and the sulfur powder so that the weight ratio of the carbonaceous conductive material: sulfur powder is 1: 15 to 1:30
Sulfur - carbon composite.
8. The method of claim 7,
In the step b), the first heat treatment temperature is 120 ° C to 180 ° C,
In the step d), the second heat treatment temperature is 200 ° C to 350 ° C,
Wherein the third heat treatment temperature in step e) is in the range of 500 &lt; 0 &gt;
Sulfur - carbon composite.
8. The method of claim 7,
The second heat treatment in step d) is carried out under pressure conditions of 1 bar to 10 bar
Sulfur - carbon composite.

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