KR20200058920A - Sulfur-carbon composite, preparation method thereof and lithium-sulfur battery comprising the same - Google Patents

Abstract

The present invention relates to a sulfur-carbon composite, a manufacturing method thereof, and a lithium-sulfur battery comprising the same. According to the present invention, the sulfur-carbon composite contains a porous carbon material having a specific range of electrical conductivity. Therefore, when used as a positive electrode active material for a lithium-sulfur battery, the sulfur-carbon composite exhibits excellent electrical conductivity, thereby improving the capacity and life characteristics of a battery.

Description

Sulfur-carbon composite, manufacturing method thereof, and lithium-sulfur battery including the same {SULFUR-CARBON COMPOSITE, PREPARATION METHOD THEREOF AND LITHIUM-SULFUR BATTERY COMPRISING THE SAME}

The present invention relates to a sulfur-carbon composite, a method for manufacturing the same, and a lithium-sulfur battery comprising the same.

Recently, with the development of portable electronic devices, electric vehicles, and large-capacity power storage systems, the need for large-capacity batteries has emerged.

The lithium-sulfur battery uses a sulfur-sulfur bond-containing sulfur-sulfur-based material as a positive electrode active material, and lithium metal, a carbon-based material in which lithium ions are inserted / de-inserted, or silicon that forms an alloy with lithium As a secondary battery that uses inert tin or the like as a negative electrode active material, the main material of the positive electrode active material, sulfur, is very rich in resources, non-toxic, and has the advantage of having a low weight per atom.

In addition, the theoretical discharge capacity of the lithium-sulfur battery is 1,672 mAh / g-sulfur, and the theoretical energy density is 2,600 Wh / kg, which is the theoretical energy density of other battery systems currently being studied (Ni-MH battery: 450 Wh / kg, Li-FeS battery: 480Wh / kg, Li-MnO ₂ battery: 1,000Wh / kg, Na-S battery: 800Wh / kg), so it is attracting attention as a battery having high energy density characteristics.

Sulfur, which is used as a positive electrode active material in a lithium-sulfur battery, has an electrical conductivity of 5 × 10 ^-30 S / cm, so it is difficult to move electrons generated by an electrochemical reaction because it is a non-conductor without electrical conductivity. Accordingly, it is used in combination with a conductive material such as carbon that can provide an electrochemical reaction site.

In addition, sulfur used as a positive electrode active material in a lithium-sulfur battery is converted to a lithium polysulfide (lithium polysulfide, Li ₂ S _x , x = 8, 6, 4, 2) having a linear structure in a cyclic form by a reduction reaction. When lithium polysulfide is completely reduced, finally, lithium sulfide (Li ₂ S) is generated. Among the lithium polysulfides, which are intermediate products according to the reduction reaction of sulfur, lithium polysulfide (Li ₂ S _x , usually x> 4) having a high sulfur oxidation number is a highly polar substance and is easily dissolved in an electrolyte containing a hydrophilic organic solvent to form a positive electrode. There is a problem that not only causes sulfur loss due to elution outside the reaction region, but also diffuses to the cathode and causes various side reactions.

Since the elution of lithium polysulfide adversely affects the capacity and life characteristics of the battery, various techniques for suppressing the elution of lithium polysulfide have been proposed.

As an example, Republic of Korea Patent Publication No. 2016-0037084 is to prevent the melting of lithium polysulfide by using a carbon nanotube aggregate of a three-dimensional structure coated with graphene with a carbon material, the conductivity of the sulfur-carbon nanotube composite It is disclosed that it can be improved.

In addition, Korean Patent Registration No. 1379716 treats hydrofluoric acid on graphene to form pores on the graphene surface, and uses a graphene composite containing sulfur produced through a method of growing sulfur particles in the pores as a positive electrode active material. It is disclosed that it is possible to minimize the capacity decrease of the battery by suppressing the dissolution of lithium polysulfide through.

These patents prevented the loss of sulfur by varying the structure or material, such as introducing a coating layer or forming pores in the carbon material constituting the sulfur-carbon composite, thereby improving the capacity or lifespan of the lithium-sulfur battery to some extent, but its effect Is not enough. In addition, in the case of such a carbon material, there is a difficulty in securing performance due to a large deviation in terms of electrical conductivity, which is a basic property required. In addition, the method proposed in these patents has a problem that it is not suitable for commercialization due to the high cost of the material and the complicated process. Therefore, it is necessary to develop a sulfur-carbon composite having excellent electrical conductivity while being able to solve the elution problem of lithium polysulfide.

Republic of Korea Patent Publication No. 2016-0037084 (2016.04.05), sulfur-carbon nanotube composite, a manufacturing method thereof, a cathode active material for a lithium-sulfur battery containing the same, and a lithium-sulfur battery including the same Republic of Korea Registered Patent No. 1379716 (2014.03.25), a lithium-sulfur secondary battery comprising a graphene composite anode containing sulfur and a manufacturing method thereof

Accordingly, the present inventors conducted various studies to solve the above problem, and introduced a porous carbon material having a certain range of electrical conductivity to produce a sulfur-carbon composite, and the thus prepared sulfur-carbon composite was a lithium-sulfur battery The present invention was completed by confirming that the electrical conductivity and the suppression effect of lithium polysulfide dissolution were improved when used as a positive electrode active material.

Accordingly, an object of the present invention is to provide a sulfur-carbon composite excellent in electrical conductivity.

In addition, another object of the present invention is to provide a method for producing the sulfur-carbon composite.

In addition, another object of the present invention to provide a positive electrode comprising the sulfur-carbon composite and a lithium-sulfur battery comprising the same.

In order to achieve the above object, the present invention is a sulfur-carbon composite comprising a porous carbon material and sulfur, wherein the porous carbon material is subjected to primary heat treatment of starch at 100 to 1200 ° C and secondary heat treatment at 1150 to 1800 ° C. As prepared, a sulfur-carbon composite having electrical conductivity of 3 to 50 S / cm is provided.

The porous carbon material may include mesopores and micropores.

The mesopores may have an average diameter of 10 to 200 nm.

The micro pores may have an average diameter of 1 to 10 nm.

The volume ratio of mesopores and micropores in the porous carbon material may be 40:60 to 100: 0.

The porous carbon material may have a specific surface area of 50 to 800 m 2 / g.

The sulfur may include at least one selected from the group consisting of inorganic sulfur, Li ₂ S _n (n = 1), disulfide compounds, organic sulfur compounds, and carbon-sulfur polymers.

The weight ratio of the porous carbon material and sulfur may be 1: 1 to 1: 9.

In addition, the present invention comprises the steps of (S1) carbonizing the first heat treatment; (S2) preparing a porous carbon material by secondary heat treatment of the carbonized starch; And (S3) provides a method for producing a sulfur-carbon composite comprising the step of complexing the porous carbon material and sulfur.

The primary heat treatment may be performed in a temperature range of 100 to 1200 ℃.

The second heat treatment may be performed in a temperature range of 1150 to 1800 ℃.

In addition, the present invention provides a positive electrode for a lithium-sulfur battery comprising the sulfur-carbon composite.

In addition, the present invention provides a lithium-sulfur battery comprising the positive electrode.

The sulfur-carbon composite according to the present invention improves electrical conductivity when used as a positive electrode active material of a lithium-sulfur battery by heat-treating starch twice to include a porous carbon material having a certain range of electrical conductivity, a problem caused by lithium polysulfide elution To improve. Accordingly, the lithium-sulfur battery including the sulfur-carbon composite as a positive electrode active material has an advantage of excellent capacity and performance characteristics.

1 is a graph showing electrical conductivity evaluation results according to Experimental Example 1 of the present invention.
2 is a scanning electron microscope image according to Experimental Example 2 of the present invention.
3 is a graph showing the charge and discharge capacity of Example 1 according to Experimental Example 3 of the present invention.
4 is a graph showing the discharge characteristics of Example 1 according to Experimental Example 3 of the present invention.
5 is a graph showing the charge and discharge capacity of Comparative Example 1 according to Experimental Example 3 of the present invention.
6 is a graph showing the discharge characteristics of Comparative Example 1 according to Experimental Example 3 of the present invention.

Hereinafter, the present invention will be described in more detail.

The terms or words used in the present specification and claims should not be interpreted as being limited to ordinary or dictionary meanings, and the inventor can appropriately define the concept of terms in order to best describe his or her invention. Based on the principle that it should be interpreted as meanings and concepts consistent with the technical spirit of the present invention.

The terms used in the present invention are only used to describe specific embodiments, and are not intended to limit the present invention. Singular expressions include plural expressions unless the context clearly indicates otherwise. In the present invention, terms such as 'include' or 'have' are intended to designate the existence of features, numbers, steps, operations, components, parts, or combinations thereof described in the specification, and one or more other features. It should be understood that the existence or addition possibilities of fields or numbers, steps, operations, components, parts or combinations thereof are not excluded in advance.

As used herein, the term “composite” refers to a substance that combines two or more materials to form physically and chemically different phases and express more effective functions.

As used herein, the terms “polysulfide” are “polysulfide ions (S _x ^2- , x = 8, 6, 4, 2)” and “lithium polysulfide (Li ₂ S _x. Or LiS _x ^- x = 8, 6, 4, 2) ”.

In the lithium-sulfur battery, the oxidation-reduction of sulfur decreases when the sulfur-sulfur bond of the sulfur-based compound is broken during discharge, which is a reduction reaction, and the sulfur-sulfur bond is generated again during charging, which is an oxidation reaction, and the oxidation-reduction of sulfur increases Reaction is used to generate electrical energy.

Lithium-sulfur batteries have a high discharge capacity and energy density among various secondary batteries, and sulfur used as a positive electrode active material has a large amount of reserves and is inexpensive, so it is possible to lower the manufacturing cost of the battery, and it is a next-generation secondary battery due to its environmentally friendly advantages. It is in the limelight.

Despite these advantages, since the positive electrode active material, sulfur, is a non-conductor, a sulfur-carbon composite compounded with a conductive carbon material is generally used to compensate for this.

However, in the case of the existing sulfur-carbon composite, the loss of sulfur occurs because it cannot suppress the elution of lithium polysulfide as described above, and as a result, the amount of sulfur participating in the electrochemical reaction is rapidly reduced, and thus the theoretical discharge capacity and theory in actual driving Not all energy densities are realized. In addition, in addition to being suspended or precipitated in the electrolyte, the eluted lithium polysulfide reacts directly with lithium and adheres to the surface of the cathode in the form of Li ₂ S, thereby causing a problem of corrosion of the lithium metal anode.

In the prior art, carbon materials of various structures or materials, such as introducing a coating layer or forming pores in the carbon material to suppress the dissolution of lithium polysulfide, have not been effectively improved. In addition, in the case of a carbon material having a different structure or material, there is a disadvantage in that performance variation occurs due to a difference in physical properties such as electrical conductivity or is inefficient in terms of process.

Accordingly, in the present invention, the starch is heat-treated twice to secure the effect of improving the capacity and life characteristics of the lithium-sulfur battery by suppressing the elution of lithium polysulfide while the sulfur-carbon composite has excellent electrical conductivity, but the secondary heat treatment is high temperature. Proceeding from to provide a sulfur-carbon composite comprising a porous carbon material having a range of electrical conductivity.

Specifically, the sulfur-carbon composite according to the present invention includes a porous carbon material and sulfur, and the porous carbon material has electrical conductivity in a range of 3 to 50 S / cm through two heat treatments performed at different temperature ranges.

In the present invention, the porous carbon material is used to provide a skeleton capable of uniformly and stably immobilizing the positive electrode active material sulfur, and having an electrical conductivity in the above-described range so that the electrochemical reaction of sulfur can proceed smoothly.

The porous carbon material of the present invention is derived from starch, and may be prepared by specifically heat-treating starch and extracting elements other than carbon in starch. At this time, the heat treatment method is not particularly limited, and a known method may be used, but it is preferably performed by the method for producing a sulfur-carbon composite according to the present invention, which will be described later. According to the method for producing a sulfur-carbon composite according to the present invention, the porous carbon material according to the present invention is manufactured without a templating agent and forms a porous structure by self-assembly of the starch chain. In addition, the porous carbon material of the present invention is graphitized by two heat treatments, and thus has improved electrical conductivity compared to the carbon material used as a conventional sulfur-carbon composite material.

Specifically, the electrical conductivity of the porous carbon material may be 3 to 50 S / cm, preferably 5 to 40 S / cm. When the electrical conductivity of the porous carbon material is less than the above range, there is a problem of an increase in electrode resistance due to low electrical conductivity, and conversely, when it exceeds the above range, battery performance may be deteriorated.

The porous carbon material includes a plurality of pores on the surface and inside, wherein the pores include both mesopores and micropore. In the porous carbon material, the total porosity or porosity including both mesopores and micropores may range from 10 to 90%.

In the present invention, mesopores mean pores having an average diameter of 10 to 200 nm, and micropores mean pores having an average diameter of 1 to 10 nm. When the average diameter of the mesopores and micropores is less than the above range, the pore size is only at the molecular level, so impregnation of sulfur is impossible. On the contrary, when the above-mentioned range is exceeded, the mechanical strength of the porous carbon material is weakened or polysulfide elution is suppressed. The effect is lowered, which is undesirable for application in the electrode manufacturing process.

As described above, the present invention can improve the electrical conductivity of the carbon material including both mesopores and micropores.

The volume ratio of mesopores and micropores in the porous carbon material may be 40:60 to 100: 0, preferably 50:50 to 100: 0. When the volume ratio of the pores contained in the porous carbon material exceeds the above range, the electrolyte performance in the pore structure is limited and battery performance may be deteriorated.

The porous carbon material may have a specific surface area of 50 to 800 m 2 / g, preferably 50 to 650 m 2 / g. At this time, the specific surface area can be measured by a conventional BET method. When the specific surface area of the porous carbon material is less than the above range, there is a problem of deterioration of reactivity due to a decrease in the contact area with sulfur. There may be a problem that the required amount of binder addition increases.

The porous carbon material has a spherical shape, a rod shape, a needle shape, a plate shape, a fiber shape, a tube shape, or a bulk shape, and is commonly used in lithium-sulfur batteries, and may be used without limitation.

The porous carbon material as described above is used as a sulfur-carbon composite by mixing with sulfur.

In the present invention, the sulfur is inorganic sulfur (S ₈ ), Li ₂ S _n (n = 1), 2,5-dimercapto-1,3,4-thiadiazole (2,5-dimercapto-1,3 Disulfide compounds such as, 4-thiadiazole), 1,3,5-trithiocyanuic acid, organosulfur compounds and carbon-sulfur polymers ((C ₂ S _x ) _n , x = 2.5 to 50, n = 2). Preferably, inorganic sulfur (S ₈ ) can be used.

In the sulfur-carbon composite according to the present invention, the weight ratio of the porous carbon material and sulfur may be 1: 1 to 1: 9, preferably 1: 1.2 to 1: 4, and more preferably 1: 1.5 to 1: 3. . If it is less than the above weight ratio range, as the content of the porous carbon material increases, the amount of binder addition required in preparing the positive electrode slurry increases. The increase in the amount of the binder added eventually increases the sheet resistance of the electrode and acts as an insulator preventing electron pass, which can degrade cell performance. Conversely, when the weight ratio range is exceeded, sulfur may be aggregated between them, and it may be difficult to directly participate in the electrode reaction due to difficulty receiving electrons.

The sulfur-carbon composite of the present invention may further include a conductive material.

The conductive material is not particularly limited as long as it has conductivity without causing a chemical change in the battery. For example, the conductive material is carbon black such as Super P (Super-P), Denka Black, Acetylene Black, Ketjen Black, Channel Black, Furnace Black, Lamp Black, Summer Black; Carbon derivatives such as carbon nanotubes and fullerenes; Conductive fibers such as carbon fibers and metal fibers; Metal powders such as carbon fluoride, aluminum, and nickel powders; Alternatively, conductive polymers such as polyaniline, polythiophene, polyacetylene, and polypyrrole may be used alone or in combination.

The sulfur-carbon composite presented in the present invention may be complexed by simply mixing sulfur and the above-mentioned porous carbon material, or may have a core-shell structured coating form or a supported form. The core-shell structure is coated with a material of which one of the sulfur or porous carbon materials is different, for example, the surface of the porous carbon material may be wrapped with sulfur or vice versa. In addition, the supported form may be a form in which sulfur is supported inside the porous carbon. The form of the sulfur-carbon composite may be any form as long as it satisfies the content ratio of the sulfur and the porous carbon material, and is not limited in the present invention.

The average diameter of the sulfur-carbon composite according to the present invention is not particularly limited in the present invention and may vary, but is 0.1 to 100 μm, preferably 1 to 50 μm. When the above range is satisfied, there is an advantage that a high loading electrode can be manufactured.

In addition, the present invention provides a method for producing the sulfur-carbon composite.

The method for producing a sulfur-carbon composite according to the present invention comprises: (S1) carbonizing the starch by primary heat treatment; (S2) preparing a porous carbon material by secondary heat treatment of the carbonized starch; And (S3) complexing the porous carbon material with sulfur.

In particular, in the method of manufacturing the sulfur-carbon composite of the present invention, the starch is heat-treated twice to prepare a porous carbon material. The porous carbon material prepared as described above has a certain range of electrical conductivity, thereby improving the electrical conductivity when preparing a sulfur-carbon composite using the same, and it is possible to suppress the dissolution of lithium polysulfide without additional additives. This large lithium-sulfur battery electrode can be produced.

Hereinafter, each step will be described.

First, in step (S1), the starch is first heat treated and carbonized to form a porous structure made of carbon.

In the present invention, the starch is a natural polymer, and is a carbonaceous starting material for forming a porous carbon material. The starch has a great advantage in that it is a non-toxic natural raw material that can be supplied indefinitely as long as green plants exist on the earth compared to the oil resources in danger of depletion.

The starch may include one or more selected from the group consisting of natural starch and modified starch.

The natural starch may be a starch derived from a plant, and the type is not particularly limited, but is preferably corn starch, sweet potato starch, potato starch, rice starch, barley starch, soybean starch, amaranth starch, wheat starch, sago ) Starch, sorghum starch, kuzukiri starch, Dongdu starch, mung bean starch, and banana starch may be used.

The modified starch refers to any molecule produced by a modification or modification series to a natural starch-physical, chemical and / or genetic. Thus, the modified starch is an enzyme or acid hydrolyzed starch (maltodextrin, glucose syrup and hydrolysis product); Degraded starch (eg, starch degraded by heat, oxidation, catalysts or oxidizing agents such as roast dextrin and weak-boiled starch); Pre-gelatinized starch; Starch ester (n-octenyl succinate); Starch ether; Cross-linked starch; Retrograded starch; Bleached starch; Cationsied or anionised starch; Amophoteric starch; Starch phosphate; Hydrogenated starch and alkali treated starch.

The starch may include a polysaccharide in which a large amount of D-glucose (glucose) is condensed and linked. For example, the starch is amylose, amylopectin, fructan, gellan, glucan, glycogen, pullulan, dextran, cellulose, met, xylan, lignin, arban, galactan, galacturonan, alginate-based compounds , Chitin, chitosan, glucuronozylan, arabinoxyllan, xyloglucan, glucomannan, pectic acid, pectin, arabinogalactan, carrageenan, agar, glycosaminoglycan, gum arabic, traga Kant gum, gati gum, karaya gum, locust bean gum and galactomannan may include one or more polysaccharides selected from the group consisting of, but is not limited thereto.

In order to include a large amount of pores of the porous carbon material produced from the starch, expansion of the starch, that is, a gelatinization process is required. For example, it may be to use the expanded starch (expanded starch) to advance the gel (gel) while heating the starch at a temperature of 60 to 150 ℃ and cooled to room temperature.

The primary heat treatment step may be performed with or without an oxidizing agent, for example oxygen, provided that the oxidizing agent does not completely oxidize the carbon present in the carbonaceous starting material. In order to very effectively suppress the oxidation of carbon present in the carbonaceous starting material, heat treatment can be carried out under substantial or complete exclusion of oxygen, preferably in the presence of an inert gas.

Further, the primary heat treatment can be carried out basically under reduced pressure, for example under vacuum, under standard pressure, or under elevated pressure, for example in a pressurized autoclave. Generally, the heat treatment is performed at a pressure in the range of 0.01 to 100 bar, preferably 0.1 to 10 bar, in particular 0.5 to 5 bar or 0.7 to 2 bar. The heat treatment can be carried out in a closed system or an open system (where the volatile components produced are removed with a gas stream, an inert gas or a reducing gas).

In the present invention, the primary heat treatment may be performed in a temperature range of 100 to 1200 ° C, preferably 200 to 1000 ° C. If the primary heat treatment temperature is less than the above range, there is a problem that the pore structure is not formed due to insufficient carbonization, and conversely, if the temperature exceeds the above range, there may be a collapse of the pore structure due to rapid heat treatment.

In addition, the first heat treatment time may vary depending on the carbonaceous starting material and the first heat treatment temperature. In one example, the primary heat treatment time may be 0.5 to 48 hours, preferably 0.5 to 24 hours.

The starch carbonized through the first heat treatment as described above can be directly manufactured or purchased and used. An example of a commercially available product is Starbon ^® (from Sigma Aldrich). In addition, the (S1) step can use, for example, the manufacturing method disclosed in European Patent Registration No. 2,007,675.

Next, in the step (S2), the carbonized starch in the step (S1) is subjected to secondary heat treatment to graphitize to prepare a porous carbon material.

The carbonized starch through the primary heat treatment obtained from the step (S1) is subjected to a secondary heat treatment in a temperature range of 1150 to 1800 ° C, preferably 1200 to 1600 ° C. In the present invention, by further heat treatment in addition to the above temperature range to reinforce the carbonization proceeded in the preceding (S1) step, and thereby graphitizing a porous carbon material having an electrical conductivity in the range of 3 to 50 S / cm can be produced . On the other hand, if the secondary heat treatment temperature is less than the above range, there is a problem that graphitization for improving electrical conductivity may not be sufficient. Conversely, if the temperature exceeds the above range, there may be a structure collapse due to excessive carbonization.

The second heat treatment time may vary depending on the carbonaceous starting material, the first heat treatment temperature and the second heat treatment temperature. In one example, the secondary heat treatment time may be 0.5 to 48 hours, preferably 0.5 to 24 hours.

The heat treatment method in the second heat treatment step is as described in step (S1).

Next, in the step (S3), the porous carbon material prepared in the step (S2) is combined with sulfur to prepare a sulfur-carbon composite.

The sulfur used at this time is as described in the sulfur-carbon composite.

At this time, it is preferable that the porous carbon material and sulfur are compounded in the above-described weight ratio. If the sulfur content is less than the above range, the amount of the active material is insufficient to be used as the positive electrode active material, and if the carbon-based material is less than the above range, the electrical conductivity of the sulfur-carbon composite becomes insufficient, so it is appropriately adjusted within the above range.

The complexing method is not particularly limited in the present invention, and a method commonly used in the art may be used. For example, a method commonly used in the art, such as wet complexing such as dry compounding or spray coating, may be used. Specifically, the method for allowing the sulfur powder and the porous carbon material to be milled by ball milling and then placed in an oven at 120 to 160 ° C. for 20 minutes to 1 hour so that the molten sulfur is evenly coated on the inner and outer surfaces of the porous carbon material. Can be used.

The method of manufacturing the sulfur-carbon composite according to the present invention is simple and economical because expensive raw materials are unnecessary, and in particular, a porous carbon material having a certain level of electrical conductivity can be produced through a two-step heat treatment without a separate process. There is an advantage. The sulfur-carbon composite prepared by the above-described manufacturing method shows excellent electrical conductivity and ability to inhibit lithium polysulfide elution, and thus can be used as a positive electrode active material for a lithium-sulfur battery.

In addition, the present invention provides a positive electrode for a lithium-sulfur battery comprising the sulfur-carbon composite.

The sulfur-carbon composite may be included as a positive electrode active material in the positive electrode.

The positive electrode may further include at least one additive selected from transition metal elements, group IIIA elements, group IVA elements, sulfur compounds of these elements, and alloys of these elements with sulfur in addition to the positive electrode active material.

The transition metal elements include Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Os, Ir, Pt, Au or Hg, etc. are included, and the group IIIA elements include Al, Ga, In, and Ti, and the group IVA elements may include Ge, Sn, and Pb.

The positive electrode may further include a positive electrode active material or, optionally, an additive, an electrically conductive conductive material for smoothly moving electrons within the positive electrode, and a binder for well attaching the positive electrode active material to the current collector.

The conductive material is not particularly limited as long as it has conductivity without causing a chemical change in the battery, but Super P (Super-P), Denka Black, Acetylene Black, Ketjen Black, Channel Black, Furnace Black, Lamp Black, Carbon blacks such as summer black and carbon black; Carbon derivatives such as carbon nanotubes and fullerenes; Conductive fibers such as carbon fibers and metal fibers; Metal powders such as carbon fluoride, aluminum, and nickel powders; Alternatively, conductive polymers such as polyaniline, polythiophene, polyacetylene, and polypyrrole may be used alone or in combination.

The content of the conductive material may be added in an amount of 0.01 to 30% by weight based on the total weight of the mixture containing the positive electrode active material.

The binder has a function of maintaining the positive electrode active material in the positive electrode current collector and organically connecting the positive electrode active materials, such as polyvinylidene fluoride, polyvinyl alcohol, carboxymethylcellulose, starch, hydroxypropyl cellulose, Regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene propylene diene rubber (EPDM), sulfonated-EPDM, styrene-butadiene rubber, fluorine rubber, various of these And copolymers.

The content of the binder may be added in 0.5 to 30% by weight based on the total weight of the mixture containing the positive electrode active material. If the content of the binder is less than 0.5% by weight, the physical properties of the positive electrode may deteriorate, and the active material and the conductive material in the positive electrode may drop off. If the content exceeds 30% by weight, the ratio of the active material and the conductive material in the positive electrode is relatively reduced to decrease the battery capacity. can do.

Looking specifically at the method for manufacturing the positive electrode of the present invention, first, the binder is dissolved in a solvent for preparing a slurry, and then the conductive material is dispersed. As a solvent for preparing the slurry, a positive electrode active material, a binder, and a conductive material can be uniformly dispersed, and it is preferable to use one that is easily evaporated. Representatively, acetonitrile, methanol, ethanol, tetrahydrofuran, water, iso Profile alcohol, etc. can be used. Next, the positive electrode active material, or optionally with an additive, is uniformly dispersed again in a solvent in which the conductive material is dispersed to prepare a positive electrode slurry. The amount of the solvent, positive electrode active material, or optionally additive contained in the slurry does not have any particular significance in the present application, and it is sufficient to have an appropriate viscosity to facilitate coating of the slurry.

The slurry thus prepared is applied to a current collector and vacuum dried to form an anode. The slurry may be coated on the current collector to an appropriate thickness according to the viscosity of the slurry and the thickness of the anode to be formed.

The current collector may generally be made to a thickness of 3 to 500 μm, and is not particularly limited as long as it has high conductivity without causing chemical changes in the battery. Specifically, a conductive material such as stainless steel, aluminum, copper, and titanium may be used, and more specifically, a carbon-coated aluminum current collector may be used. The use of a carbon-coated aluminum substrate has advantages in that adhesion to an active material is excellent, contact resistance is low, and corrosion of aluminum by polysulfide can be prevented as compared with that in which carbon is not coated. In addition, the current collector may be in various forms such as a film, sheet, foil, net, porous body, foam, or nonwoven fabric.

In addition, the present invention is an anode comprising the above-mentioned sulfur-carbon composite; cathode; And an electrolyte solution interposed between the positive electrode and the negative electrode.

The positive electrode is according to the present invention and follows the foregoing.

The negative electrode may be composed of a current collector and a negative electrode active material layer formed on one or both sides thereof. Alternatively, the negative electrode may be a lithium metal plate.

The current collector is for supporting the negative electrode active material, and is not particularly limited as long as it has excellent conductivity and is electrochemically stable in the voltage range of the lithium secondary battery. For example, copper, stainless steel, aluminum, nickel, titanium, and palladium , Surface-treated with carbon, nickel, silver, etc. on the surface of calcined carbon, copper or stainless steel, aluminum-cadmium alloy, and the like can be used.

The negative electrode current collector can form a fine unevenness on its surface to enhance the bonding force with the negative electrode active material, and various forms such as a film, sheet, foil, mesh, net, porous body, foam, and nonwoven fabric can be used.

The negative active material is a material capable of reversibly intercalating or deintercalating lithium ions, a material capable of reacting with lithium ions to reversibly form a lithium-containing compound, lithium metal or lithium alloy Can be used.

The material capable of reversibly intercalating or deintercalating the lithium ions may be, for example, crystalline carbon, amorphous carbon, or a mixture thereof.

A material capable of reversibly forming a lithium-containing compound by reacting with the lithium ion may be, for example, tin oxide, titanium nitrate, or silicon.

The lithium alloy is, for example, lithium (Li) and sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), francium (Fr), beryllium (Be), magnesium (Mg), calcium (Mg) Ca), strontium (Sr), barium (Ba), radium (Ra), aluminum (Al), and tin (Sn).

A separator may be additionally included between the aforementioned positive electrode and negative electrode. The separator separates or insulates the positive electrode and the negative electrode from each other and enables transport of lithium ions between the positive electrode and the negative electrode, and may be made of a porous non-conductive or insulating material. The separator may be an independent member such as a film, or may be a coating layer added to the anode and / or cathode.

The material constituting the separator includes, for example, polyolefin such as polyethylene and polypropylene, glass fiber filter paper, and ceramic material, but is not limited thereto, and the thickness is about 5 to about 50 μm, preferably about 5 to about 25 Μm.

The electrolyte is located between the positive electrode and the negative electrode and includes a lithium salt and a non-aqueous organic solvent.

The concentration of the lithium salt is 0.2 to 2 M, specifically, depending on several factors such as the exact composition of the electrolyte, the solubility of the salt, the conductivity of the dissolved salt, the conditions for charging and discharging the cell, the working temperature and other factors known in the field of lithium batteries. 0.6 to 2 M, more specifically 0.7 to 1.7 M. When the concentration of the lithium salt is used less than 0.2 M, the conductivity of the electrolyte may be lowered and the performance of the electrolyte may be deteriorated. When the concentration is more than 2 M, the viscosity of the electrolyte may increase and mobility of lithium ions may be reduced.

The lithium salt may be used without limitation as long as it is commonly used in the electrolyte solution for lithium-sulfur batteries. For example, LiSCN, LiBr, LiI, LiPF ₆ , LiBF ₄ , LiB ₁₀ Cl ₁₀ , LiSO ₃ CF ₃ , LiCl, LiClO ₄ , LiSO ₃ CH ₃ , LiB (Ph) ₄ , LiC (SO ₂ CF ₃ ) _{3 , LiN (SO 2 CF 3)} 2, LiCF 3 CO 2, LiAsF 6, LiSbF 6, LiAlCl 4, may be included are one or more from LiFSI, chloro group consisting of borane lithium, lower aliphatic carboxylic acid lithium or the like.

As the non-aqueous organic solvent, those that are commonly used in lithium secondary battery electrolytes can be used without limitation. For example, the organic solvent may be used alone or in combination of two or more of ether, ester, amide, linear carbonate, cyclic carbonate, and the like. Among them, representatively may include ether-based compounds.

In one example, the ether-based compound is dimethyl ether, diethyl ether, dipropyl ether, methylethyl ether, methylpropyl ether, ethylpropyl ether, dimethoxyethane, diethoxyethane, methoxyethoxyethane, diethylene glycol dimethyl ether , Diethylene glycol diethyl ether, diethylene glycol methylethyl ether, triethylene glycol dimethyl ether, triethylene glycol diethyl ether, triethylene glycol methylethyl ether, tetraethylene glycol dimethyl ether, tetraethylene glycol diethyl ether, tetraethylene At least one selected from the group consisting of glycol methyl ethyl ether, polyethylene glycol dimethyl ether, polyethylene glycol diethyl ether, polyethylene glycol methyl ethyl ether, 1,3-dioxolane, tetrahydrofuran, and 2-methyltetrahydrofuran may be used. However, it is not limited thereto.

Esters in the organic solvent include methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, γ-valerolactone, γ-caprolactone, σ- Any one selected from the group consisting of valerolactone and ε-caprolactone or a mixture of two or more of them may be used, but is not limited thereto.

Specific examples of the linear carbonate compound include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate, ethylmethyl carbonate (EMC), methylpropyl carbonate, and ethylpropyl carbonate. Mixtures of two or more types may be used, but are not limited thereto.

In addition, specific examples of the cyclic carbonate compound include ethylene carbonate (EC), propylene carbonate (PC), 1,2-butylene carbonate, 2,3-butylene carbonate, and 1,2-pentylene carbonate. , 2,3-pentylene carbonate, vinylene carbonate, vinyl ethylene carbonate, and any one selected from the group consisting of halides or mixtures of two or more of them.

Examples of these halides include, but are not limited to, fluoroethylene carbonate (FEC).

In addition, N-methylpyrrolidone, dimethyl sulfoxide, sulfolane, etc. may be used in addition to the above-described organic solvent.

The electrolyte solution may further include a nitric acid-based compound commonly used in the art in addition to the above-described composition. For example, lithium nitrate (LiNO ₃ ), potassium nitrate (KNO ₃ ), cesium nitrate (CsNO ₃ ), magnesium nitrate (MgNO ₃ ), barium nitrate (BaNO ₃ ), lithium nitrite (LiNO ₂ ), potassium nitrite (KNO ₂₎ ), Cesium nitrite (CsNO ₂ ), and the like.

The injection of the electrolytic solution may be performed at an appropriate stage during the manufacturing process of the electrochemical device, depending on the manufacturing process of the final product and the required physical properties. That is, it can be applied before the assembly of the electrochemical device or at the final stage of the assembly of the electrochemical device.

The lithium-sulfur battery according to the present invention is capable of lamination, stacking, and folding processes of a separator and an electrode in addition to the general process of winding.

The shape of the lithium-sulfur battery is not particularly limited and may be various shapes such as a cylindrical shape, a stacked shape, and a coin shape.

In addition, the present invention provides a battery module including the lithium-sulfur battery as a unit cell.

The battery module can be used as a power source for medium to large-sized devices that require high temperature stability, long cycle characteristics, and high capacity characteristics.

Examples of the medium-to-large-sized device include a power tool that moves under power by an all-electric motor; Electric vehicles including electric vehicles (EVs), hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), and the like; Electric two-wheeled vehicles including electric bicycles (E-bikes) and electric scooters (E-scooters); Electric golf carts; And a power storage system, but is not limited thereto.

Hereinafter, a preferred embodiment is provided to help the understanding of the present invention, but the following examples are only illustrative of the present invention, and it is apparent to those skilled in the art that various changes and modifications are possible within the scope and technical scope of the present invention. It is natural that such modifications and corrections fall within the scope of the appended claims.

Examples and comparative examples

[Example 1]

To the reactor, 5 g of Starbon-300 (manufactured by Sigma Aldrich) was added, followed by secondary heat treatment at 1500 ° C. for 1 hour in an argon atmosphere to graphitize to obtain a porous carbon material.

Sulfur-carbon composites were mixed evenly in a weight ratio of 3: 7 by mixing 0.6 g of the obtained porous carbon material and 1.4 g of sulfur (S ₈ ), and then crushed by mortar mixing for 30 minutes in an oven at 155 ° C. Was prepared.

Using the sulfur-carbon composite prepared above, a slurry was prepared in a weight ratio of sulfur-carbon composite: conductive material: binder = 90: 5: 5, and then coated on a current collector of 20 μm thick aluminum foil to prepare an electrode. At this time, carbon black was used as the conductive material, and styrene-butadiene rubber and carboxymethyl cellulose were used as the binder.

[Comparative Example 1]

An electrode was manufactured in the same manner as in Example 1, except that Starbon-800 (a product of Sigma Aldrich), which was not subjected to secondary heat treatment, was used as a porous carbon material.

[Comparative Example 2]

An electrode was manufactured in the same manner as in Example 1, except that a porous carbon material graphitized by secondary heat treatment of Starbon-300 at 1100 ° C. for 1 hour was used.

Experimental Example 1. Evaluation of electrical conductivity

The electrical conductivity was measured using the porous carbon material prepared in the above Examples and Comparative Examples using a powder resistance meter (model name: HPRM-FA2, manufactured by Hantech). The results obtained at this time are shown in Figure 1 below.

Referring to FIG. 1, it can be seen that in the case of the porous carbon material prepared according to Example 1, the electrical conductivity is increased by 10 times or more compared to the porous carbon material of the comparative example.

Experimental Example 2. Scanning electron microscope analysis

The surface shape of the porous carbon material and the sulfur-carbon composite prepared in Example 1 and Comparative Example 1 was observed using a scanning electron microscope (SEM). The results obtained at this time are shown in Figure 2 below.

Referring to Figure 2, the surface of the porous carbon material prepared according to Example 1 is the same as the porous carbon material of Comparative Example 1, through which it can be confirmed that there is no change in the surface shape of the porous carbon material during the second stage heat treatment. .

Experimental Example 3. Battery performance evaluation

An electrode prepared in Example 1 and Comparative Example 1 was used as an anode, polyethylene was used as a separator, and a lithium-sulfur battery coin cell was manufactured using a lithium foil having a thickness of 150 μm as a cathode. At this time, the coin cell used an electrolyte prepared by dissolving 1 M LiTFSI and 1% LiNO ₃ in an ether-based organic solvent.

The produced coin cell was measured for a capacity from 1.8 to 2.5 V using a charge / discharge measuring device. In addition, the discharge capacity was measured by performing a cycle of sequentially discharging at 0.1C, 0.2C and 0.5C rate CC (CC: Constant Current). The results obtained at this time are shown in FIGS. 3 to 6 below.

3 to 6, it can be seen that the charge and discharge characteristics of the coin cell including the positive electrode according to the present invention are superior to the comparative example.

Specifically, since the discharge capacity of the coin cell including the positive electrode of Example 1 is higher than that of Comparative Example 1 throughout the cycle, it can be confirmed that the discharge capacity retention rate is improved. From the above results, it can be confirmed that the performance of the battery including the sulfur-carbon composite of the present invention is excellent.

Claims (15)

In the sulfur-carbon composite comprising a porous carbon material and sulfur,
The porous carbon material is prepared by primary heat treatment of starch at 100 to 1200 ° C and secondary heat treatment at 1150 to 1800 ° C, and is a sulfur-carbon composite having electrical conductivity of 3 to 50 S / cm. According to claim 1,
The porous carbon material includes mesopores and micropores, a sulfur-carbon composite. According to claim 2,
The mesopores have an average diameter of 10 to 200 nm, a sulfur-carbon composite. According to claim 2,
The micro pores have an average diameter of 1 to 10 nm, sulfur-carbon composite. According to claim 2,
The volume ratio of mesopores and micropores in the porous carbon material is 40:60 to 100: 0, sulfur-carbon composite. According to claim 1,
The porous carbon material has a specific surface area of 50 to 800 m 2 / g, a sulfur-carbon composite. According to claim 1,
The sulfur includes at least one selected from the group consisting of inorganic sulfur, Li ₂ S _n (n = 1), disulfide compound, organic sulfur compound, and carbon-sulfur polymer, sulfur-carbon composite. According to claim 1,
The weight ratio of the porous carbon material and sulfur is 1: 1 to 1: 9, sulfur-carbon composite. According to claim 1,
The weight ratio of the porous carbon material and sulfur is 1: 1.2 to 1: 4, sulfur-carbon composite. According to claim 1,
The weight ratio of the porous carbon material and sulfur is 1: 1.5 to 1: 3, sulfur-carbon composite. (S1) carbonizing the starch by primary heat treatment;
(S2) preparing a porous carbon material by secondary heat treatment of the carbonized starch; And
(S3) a method for producing a sulfur-carbon composite comprising the step of complexing the porous carbon material and sulfur. The method of claim 11,
The primary heat treatment is carried out in a temperature range of 100 to 1200 ℃, sulfur-carbon composite manufacturing method. The method of claim 11,
The secondary heat treatment is performed in a temperature range of 1150 to 1800 ℃, sulfur-carbon composite manufacturing method. A positive electrode for a lithium-sulfur battery comprising the sulfur-carbon composite according to any one of claims 1 to 10. A lithium-sulfur battery comprising the positive electrode according to claim 14.

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