KR20200137091A - A positive electrode for lithium secondary battery including a sulfur-kaolin complex, method for preparing the same and lithium secondary battery including the positive electrode - Google Patents

Abstract

Disclosed are a positive electrode for a lithium secondary battery including a sulfur-kaolin composite that can improve the capacity and energy of the battery by replacing a conventional sulfur-carbon composite being applied as a positive electrode active material with a sulfur-clay composite and increasing the sulfur content in the positive electrode, a method of manufacturing the same, and a lithium secondary battery including the positive electrode. The positive electrode for a lithium secondary battery includes sulfur-kaolin composite which includes kaolin which is a kaolin-based clay; and sulfur immerged in the kaolin.

Description

A positive electrode for lithium secondary battery including a sulfur-kaolin complex, method for preparing the same and lithium secondary battery including the positive electrode for lithium secondary battery including the sulfur-kaolin complex positive electrode}

The present invention relates to a positive electrode for a lithium secondary battery including a sulfur-kaolin complex, a method for manufacturing the same, and a lithium secondary battery including the positive electrode, and more particularly, a general sulfur-carbon composite that is applied as a positive electrode active material is sulfur- A positive electrode for a lithium secondary battery including a sulfur-kaolin complex, which can be replaced with a clay composite and improve the capacity and energy of the battery by increasing the content of sulfur in the positive electrode, a manufacturing method thereof, and a lithium secondary battery including the positive electrode About.

In recent years, interest in energy storage technology is increasing, and as the fields of application to mobile phones, camcorders and notebook PCs, and even electric vehicles are expanded, efforts for research and development of electrochemical devices are being materialized. Electrochemical devices are the field that is receiving the most attention in this respect, and among them, the development of secondary batteries such as lithium-sulfur batteries capable of charging and discharging has become the focus of interest, and in recent years, capacity density and In order to improve the specific energy, research and development on the design of new electrodes and batteries are being conducted.

Among these electrochemical devices, a lithium-sulfur (Li-S) battery has a high energy density and can replace a lithium ion battery having a low energy density, and thus a next-generation secondary battery that can implement an electric vehicle and a large-capacity energy storage system. It is in the limelight as one of them. The lithium-the sulfur battery, the discharge when occurs the oxidation reaction of the reducing reaction with the lithium metal of sulfur, at this time, the sulfur lithium poly linear structure from the S ₈ of the ring structure sulfide _{(Li 2 S 2, Li 2} S 4, Li ₂ S ₆ and Li ₂ S ₈ ) are formed, and such a lithium-sulfur battery is characterized by a stepwise discharge voltage until polysulfide (PS) is completely reduced to Li ₂ S.

Sulfur, which is applied as a positive active material for lithium-sulfur batteries, has low electrical conductivity and is generally used in combination with a carbon material (ie, sulfur-carbon composite), and supports a large amount of active material (sulfur). To do this, the carbon material must have a high specific surface area. However, carbon materials such as graphene and carbon nanotubes (CNT) have a high unit cost, making it difficult to reduce the cost of manufacturing the positive electrode, and side reactions on the surface of the carbon material prevent electrolyte decomposition within the battery. There is a problem such as accelerating and causing deterioration of the battery. Accordingly, there is a need to develop a novel sulfur-containing composite for lithium secondary battery electrodes that can lower the manufacturing cost of the positive electrode and solve the problems arising from applying the above carbon material to the positive electrode.

Accordingly, it is an object of the present invention to replace a conventional sulfur-carbon composite being applied as a positive electrode active material with a sulfur-clay composite, and increase the amount of sulfur in the positive electrode, thereby improving the capacity and energy amount of the battery, sulfur-kaolin. It is to provide a positive electrode for a lithium secondary battery including a composite, a method of manufacturing the same, and a lithium secondary battery including the positive electrode.

In order to achieve the above object, the present invention, kaolin-based clay kaolin; And it provides a positive electrode for a lithium secondary battery comprising a sulfur-kaolin complex containing; sulfur supported on the kaolin.

In addition, the present invention comprises the steps of: a) mixing the kaolin powder and the solvent and then pulverizing; b) adding and mixing sulfur powder to the pulverized mixture, followed by pulverizing; c) drying the pulverized sulfur-containing mixed solution; d) further pulverizing the sulfur-kaolin powder formed through drying and then heat-treating to prepare a sulfur-kaolin complex; And e) dispersing the prepared sulfur-kaolin complex in a solvent to prepare a slurry, and then applying the slurry to a current collector; and a method of manufacturing a positive electrode for a lithium secondary battery is provided.

In addition, the present invention, the positive electrode for the lithium secondary battery; cathode; A separator interposed between the anode and the cathode; It provides a lithium secondary battery comprising; and an electrolyte.

A positive electrode for a lithium secondary battery comprising a sulfur-kaolin composite according to the present invention, a method of manufacturing the same, and a lithium secondary battery including the positive electrode, replace a conventional sulfur-carbon composite being applied as a positive electrode active material with a sulfur-clay composite, It has the advantage of improving the capacity and energy amount of the battery by increasing the sulfur content in the positive electrode.

1 is a graph evaluating the pores of kaolin applied to the positive electrode of a lithium secondary battery of the present invention.
2 is an image obtained by observing the surface of a kaolin and sulfur-kaolin complex according to an embodiment of the present invention with a scanning electron microscope.
3 is a graph measuring changes in open circuit voltage (OCV) of a lithium secondary battery according to an embodiment and a comparative example of the present invention.
4 is a graph showing the discharge capacity of a lithium secondary battery according to the present invention.
5 is a graph showing the discharge capacity of a lithium secondary battery according to an embodiment and a comparative example of the present invention.
6 is a graph showing life characteristics of a lithium secondary battery manufactured according to an embodiment and a comparative example of the present invention.

Hereinafter, it will be described in detail so that those of ordinary skill in the art may easily implement the present invention. The present invention may be implemented in various different forms, and is not limited to this specification.

The terms or words used in the specification and claims should not be construed as being limited to their usual or dictionary meanings, and the inventor shall appropriately define the concept of terms in order to explain his own invention in the best way. It should be interpreted as a meaning and concept consistent with the technical idea of the present invention based on the principle that it can be.

The term'composite' as used herein refers to a material that exhibits a more effective function while forming a different phase physically and chemically by combining two or more materials.

The present invention provides a positive electrode for a lithium secondary battery including a positive electrode active material having a novel structure capable of stably driving the battery while reducing the total carbon content applied to the electrode by supplementing the disadvantages of the conventional positive electrode for a lithium secondary battery, a method of manufacturing the same, and It provides a lithium secondary battery including the positive electrode. More specifically, the positive electrode for a lithium secondary battery provided by the present invention includes a positive electrode active material, a conductive material, and a binder, and the positive electrode active material is a sulfur-kaolin composite.

Positive electrode for lithium secondary battery

In the case of a lithium-sulfur battery, which is a kind of lithium secondary battery, the electrical conductivity of sulfur, which is a positive electrode active material, is about 5.0 × 10 ^-14 S/cm. 'Sulfur-carbon composite' was mainly used, in which a conductive material, carbon material was applied together. The sulfur-carbon composite is a combination of a carbon-based material and sulfur particles, and generally forms a shape in which sulfur particles are supported on a porous carbon-based material.

The positive electrode of such a lithium-sulfur battery uses a porous carbon material as a carrier to support sulfur, and contains a significant amount of carbon in the electrode, such as including a conductive material, a separate carbon component, to secure the conductivity of the electrode. . However, carbon-based materials have a much higher specific surface area than ordinary inorganic materials, which causes a problem of impairing the physical properties of the electrode slurry by adsorbing a binder in the electrode slurry process. Accordingly, a solvent is added to sufficiently secure the viscosity of the electrode slurry. There is a disadvantage in that the solid content of the slurry is reduced when added to.

The present invention has been devised to solve the above problems, and is a material capable of stably supporting sulfur, which is a positive electrode active material, and reducing the carbon content in the electrode, and can be obtained from nature and is a relatively inexpensive kaolin-based clay. Kaolin was introduced to solve the above problems.

That is, the positive electrode for a lithium secondary battery according to the present invention is (as a positive electrode for a lithium secondary battery including a sulfur-kaolin composite positive electrode active material, a conductive material, and a binder) kaolin, a kaolin-based clay, and sulfur-containing sulfur supported on the kaolin- It contains kaolin complex.

Kaolin has a layered structure in which a plurality of plates are stacked, so that the specific surface area and pore volume are larger than those of other inorganic materials or materials, and the density is low, making it suitable for supporting a large amount of sulfur. In addition, the kaolin allows for insertion of cations into its layered structure, so that the ion conductivity is high, so it is easy to transfer lithium ions between the electrolyte and the active material, and also has the advantage of rapid wetting due to excellent absorption properties. have. Accordingly, the applicant applied the kaolin to a positive electrode of a lithium secondary battery (in particular, a lithium-sulfur battery) according to the present invention, and more specifically, the kaolin served as a support for sulfur in the positive electrode.

The kaolin is a silicate clay mineral in which the ratio of aluminum and silicon is 1:1, and has a chemical composition of Al ₂ Si ₂ O ₅ (OH) ₄ . When the stacked length of the kaolin is defined as the thickness and the length of one layer, that is, the single side is defined as the diameter, the kaolin of the present invention may have a particle size of 1 to 10 nm in thickness and 100 to 1,000 nm in average diameter. have. Therefore, when the thickness and average diameter of the kaolin are out of the above range, basic physical properties of the kaolin may not be implemented. In addition, the kaolin has a specific surface area (SSA) of 100 m ² /g or more, has a low density and develops internal pores, and thus has a high level of specific surface area even though it is an inorganic material.

In the sulfur-kaolin complex, the sulfur content may be 60 to 80% by weight, preferably 70 to 75% by weight, based on the total weight of the sulfur-kaolin complex. If the content of sulfur is less than 60% by weight based on the total weight of the sulfur-kaolin complex, there is a problem that the content of sulfur participating in the reaction decreases and the energy density is lowered. If it exceeds 80% by weight, it is not combined with kaolin. The unstable sulfur or sulfur compound may clump between them or re-elute to the surface, making it difficult to receive electrons, and thus it may be difficult to directly participate in the electrode reaction.

Meanwhile, the sulfur content based on the total weight of the positive electrode is, for example, the mixed weight ratio of the sulfur-kaolin composite, the conductive material, and the binder is 85:10:5, and the sulfur content in the sulfur-kaolin composite is 80% by weight. In this case, it may have a higher sulfur content compared to the positive electrode to which the existing sulfur-carbon composite is applied, such as which may be up to 68% by weight (85 × 0.8% by weight) based on the total weight of the positive electrode, and accordingly, a battery such as capacity and overvoltage Performance improvement can be achieved.

The average particle diameter of the sulfur-kaolin composite may be 1 to 100 µm, preferably 5 to 20 µm. If the average particle diameter of the sulfur-kaolin composite is less than 1 μm, water dispersibility may be lowered, and if it exceeds 100 μm, the electrode roughness deviation increases, resulting in poor uniformity of the electrode surface, and penetration of the electrolyte into the active material is difficult. The ability to transfer ions may be reduced.

Sulfur, which is an active material supported on the kaolin, may be elemental sulfur (S8), a sulfur-based compound, or a mixture thereof, and the sulfur-based compound is specifically, Li ₂ S _n (n=1), an organic sulfur compound, or It may be a sulfur-carbon complex ((C2Sx)n: x=2.5 ~ 50, n=2), and the like, and even if such sulfur is uniformly impregnated on the surface of kaolin, kaolin can maintain its own structure.

The sulfur-kaolin composite may further include a carbon material to further secure conductivity. The addition of such a carbon material does not affect the maintenance of the sulfur-kaolin complex structure. The carbon material may be a graphite system such as natural graphite, artificial graphite, expanded graphite, graphene, Super-P, and Super-C; Activated carbon (Active carbon) system; Denka black, Ketjen black, Channel black, Furnace black, Thermal black, Contact black, Lamp black, Acetylene Carbon black system such as black (Acetylene black); Carbon nanostructures such as carbon fiber, carbon nanotube (CNT), and fullerene; And it may be one or more selected from the group consisting of a combination thereof, and considering the dispersibility and conductivity in the electrode, carbon nanotubes may be the most appropriate carbon material.

When such a carbon material is additionally included in the sulfur-kaolin composite, the content of the carbon material is 1 to 13 parts by weight, preferably based on 100 parts by weight of the content of kaolin (powder) included in the sulfur-kaolin composite. It may be 5 to 12 parts by weight, more preferably 7 to 12 parts by weight. If the content of the carbon material is less than 1 part by weight based on 100 parts by weight of the kaolin (powder) contained in the sulfur-kaolin composite, the effect obtained by additionally including the carbon material may be insignificant, and 13 parts by weight If it exceeds, the ratio of the carbon material contained in the sulfur-kaolin composite or the positive electrode is relatively high, and the spirit of the present invention may be impaired.

The positive electrode for a lithium secondary battery according to the present invention includes a positive electrode current collector and an electrode active material layer formed on at least one surface of the current collector, and the electrode active material layer includes an active material including the sulfur-kaolin composite, a conductive material, and a binder. It may contain a base solid. As the current collector, it may be preferable to use aluminum or nickel having excellent conductivity. The content of the active material may be 50 to 95 parts by weight, preferably about 85 parts by weight, based on 100 parts by weight of the base solid content. If the active material is contained in an amount of less than 50 parts by weight based on 100 parts by weight of the base solid content, the amount of energy of the battery may decrease, and if it exceeds 95 parts by weight, the content of other conductive materials and binders is relatively insufficient, and thus sufficient electrode reaction Can be difficult to exert.

Among the base solids constituting the positive electrode of the present invention, the conductive material is a material that acts as a path for electrons to move from the current collector to sulfur by electrically connecting the electrolyte and the positive electrode active material, causing a chemical change in the battery. It is not particularly limited as long as it does not have porosity and conductivity. Examples of such a conductive material include graphite-based materials such as KS6; Carbon blacks such as Super-P, carbon black, denka black, acetylene black, ketjen black, channel black, furnace black, lamp black, and summer black; Carbon derivatives such as fullerene; Conductive fibers such as carbon fibers and metal fibers; Metal powders such as carbon fluoride, aluminum, and nickel powder; Conductive polymers such as polyaniline, polythiophene, polyacetylene, and polypyrrole; And mixtures thereof.

The content of the conductive material may be 1 to 10 parts by weight, preferably 5 parts by weight, based on 100 parts by weight of the base solid content. If the content of the conductive material is less than 1 part by weight based on 100 parts by weight of the base solid, the electron transfer capacity inside the electrode decreases, thereby reducing the oxidation/reduction reaction of sulfur, thereby reducing the capacity of the battery and increasing the overvoltage. When it exceeds a part by weight, the high rate discharge characteristic is improved, but the amount of the active material is relatively reduced, so that the amount of electrode energy may decrease.

Among the base solids constituting the positive electrode of the present invention, the binder is a material used to adhere well the slurry composition of the base solids forming the positive electrode to the current collector, and is well soluble in a solvent, and conducts conduction between the positive electrode active material and the conductive material. Any material that can construct a network well is good. Unless otherwise specified, all binders known in the art can be used, for example, poly(vinyl)acetate, polyvinyl alcohol, polyethylene oxide, polyvinyl pyrrolidone, alkylated polyethylene oxide, crosslinked Polyethylene oxide, polyvinyl ether, poly(methyl methacrylate), polyvinylidene fluoride (PVdF), polyhexafluoropropylene, polyvinylidene fluoride copolymer (trade name: Kynar), poly(ethyl acrylate) , Polytetrafluoroethylene polyvinyl chloride, polytetrafluoroethylene, polyacrylonitrile, polyvinylpyridine, polystyrene, carboxymethyl cellulose, siloxanes such as polydimethylsiloxane, styrene-butadiene rubber, acrylonitrile- Examples thereof include a rubber-based binder including butadiene rubber, styrene-isoprene rubber, ethylene glycol-based such as polyethylene glycol diacrylate, and derivatives thereof, blends thereof, and copolymers thereof.

The content of the binder may be 1 to 10 parts by weight, preferably about 5 parts by weight based on 100 parts by weight of the base solid content. If the content of the binder is less than 1 part by weight based on 100 parts by weight of the base solid content, the physical properties of the positive electrode may be deteriorated, so that the positive electrode active material and the conductive material may fall off. If it exceeds 10 parts by weight, the ratio of the active material and the conductive material in the positive electrode is It is relatively reduced so that the battery capacity can be reduced.

Method of manufacturing positive electrode for lithium secondary battery

Next, a method of manufacturing a positive electrode for a lithium secondary battery according to the present invention will be described. The manufacturing method of the positive electrode for a lithium secondary battery includes: a) mixing and pulverizing kaolin powder and a solvent, b) adding sulfur powder to the pulverized mixture, mixing and pulverizing, c) the pulverized sulfur Drying the containing mixed solution, d) further pulverizing the sulfur-kaolin powder formed through the drying, followed by heat treatment to prepare a sulfur-kaolin complex, and e) dispersing the prepared sulfur-kaolin complex in a solvent to obtain a slurry After manufacturing, it includes the step of applying the slurry to the current collector, and at the time of mixing in step a), a carbon material to further secure conductivity may be additionally added (the description of the carbon material is described above. Bar mutatis mutandis).

The solvent in step a) may be an alcohol-based compound such as ethanol or a conventional solvent such as water. The grinding of steps a), b) and d) may be performed by a conventional grinding method such as a ball milling method, but the grinding of step a) may be performed for 30 minutes to 3 hours, and , The pulverization of step b) may be performed for 10 to 36 hours, and the pulverization of step d) may be performed for 10 minutes to 5 hours. In addition, the drying in step c) may be performed under a temperature of 60 to 90 °C, and the heat treatment in step d) may be performed under a temperature of 100 to 200 °C.

In addition, the sulfur-kaolin complex (positive electrode active material) of step e) is dispersed in a solvent to prepare a slurry (composition), and the process of applying the prepared slurry to a current collector may be performed by a conventional positive electrode manufacturing method, If necessary, in addition to the sulfur-kaolin composite, any one or more of a binder, a conductive material, and a dispersant can be dispersed in a solvent, and after applying the slurry to the current collector, the current collector is compression-molded to improve the electrode density, And the drying process may be additionally performed.

There is no particular limitation on the method of applying (coating) the slurry in step e), for example, Doctor blade coating, Dip coating, Gravure coating, Slit die coating coating), spin coating, comma coating, bar coating, reverse roll coating, screen coating or cap coating method, etc. I can.

As the solvent in step e), one capable of uniformly dispersing a positive electrode active material or the like is used. As such a solvent, water is most preferable as an aqueous solvent, and in this case, the water may be secondary distilled DW (Distilled Water) or tertiary distilled DIW (Deionzied Water). However, it is not necessarily limited thereto, and if necessary, a lower alcohol that can be easily mixed with water may be used. Examples of the lower alcohol include methanol, ethanol, propanol, isopropanol and butanol, and may be used by mixing with water.

The porosity of the positive electrode active material layer including the sulfur-kaolin composite may be 30 to 90%, preferably 40 to 80%, and more preferably 50 to 70%. When the porosity of the positive electrode active material layer is less than 30%, the filling degree of the base solid content including the active material, the conductive material, and the binder becomes too high to maintain a sufficient electrolyte solution capable of showing ionic conduction and/or electrical conduction between the active materials. As a result, output characteristics or cycle characteristics of the battery may be deteriorated, and overvoltage and discharge capacity of the battery may decrease. In addition, when the porosity of the positive electrode active material layer exceeds 90% and has an excessively high porosity, the physical/electrical connection with the current collector is lowered, resulting in a decrease in adhesion and difficulty in reaction. The energy density per weight can decrease as the density decreases and the electrolyte required to fill the pores increases. Meanwhile, the porosity may be performed by a hot press method, a roll press method, a plate press method, or a roll lamination method.

In addition, the content of carbon in the positive electrode for a lithium secondary battery according to the present invention may be 1 to 15% by weight based on the total weight of the positive electrode active material layer. When the content of carbon is less than 1% by weight based on the total weight of the positive electrode active material layer, it may be difficult to stably drive the battery because the conductivity of the electrode is not sufficiently secured, and when the content of carbon exceeds 15% by weight, The decomposition of the electrolyte solution is accelerated, and the solvent or salt contained in the electrolyte is decomposed to generate by-products that reduce the life of the lithium secondary battery. Meanwhile, the carbon content refers to the total amount of the total carbon-based material contained in the lithium secondary battery positive electrode, and may be, for example, the sum of the content of the carbon material and the content of the conductive material that may be additionally included in the sulfur-kaolin composite. have.

On the other hand, as the content of the carbon material in the electrode increases, the reaction surface area increases in proportion to the specific surface area and mass of the carbon material, and eventually the life of the battery decreases. In addition, when carbon with a low density is included, the volume of the electrode increases and the thickness of the electrode increases as the content increases, which causes a decrease in the energy density per volume of the battery. To solve this problem, a rolling process such as a roll press can be performed, but the elastic force of the electrode increases due to carbon contained in and a spring-back phenomenon occurs after rolling, or during the rolling process, the electrode Problems such as deformation of the structure and disconnection of a conductive path due to this also occur.

Accordingly, in order to solve the above problems caused by the carbon material, the applicant of the present invention reduced the carbon content of the electrode by applying kaolin, which is a kaolin-based clay, instead of a carbon material as a sulfur carrier of the positive electrode of a lithium secondary battery. It is the most commonly used sulfur carrier and can exclude expensive carbon nanotubes that require separate synthesis.

Lithium secondary battery

Finally, a lithium secondary battery according to the present invention will be described. The lithium secondary battery includes the above-described positive electrode for a lithium secondary battery, a negative electrode, a separator and an electrolyte interposed between the positive electrode and the negative electrode, and all known in the art, such as a lithium-sulfur battery, a lithium air battery, and a lithium metal battery. Lithium-based secondary batteries may be exemplified, and among them, lithium-sulfur batteries are preferred. In addition to the positive electrode, the remaining negative electrode, separator, and electrolyte applied to the lithium secondary battery may be conventional ones used in the art, and a detailed description thereof will be described later.

After manufacturing an electrode assembly in which such a positive electrode, a separator, and a negative electrode are sequentially stacked, it is put in a battery case, and then an electrolyte is injected into the upper part of the case, and then assembled by sealing with a cap plate and a gasket to manufacture a lithium secondary battery. . The shape of the lithium secondary battery is not particularly limited, and may be, for example, a jelly-roll type, a stack type, a stack-folding type (including a stack-Z-folding type) or a lamination-stack type, of which the stack-folding type is It may be desirable. The lithium secondary battery may be classified into a cylindrical type, a square type, a coin type, a pouch type, etc. according to the shape, and may be divided into a bulk type and a thin film type according to the size. The structure and manufacturing method of these batteries are well known in this field, and thus detailed descriptions are omitted.

In addition, the lithium secondary battery of the present invention is not only applied to a battery cell used as a power source of a small device, but also can be suitably used as a unit cell of a battery module that is a power source of a medium-large device. In this aspect, the present invention also provides a battery module including two or more lithium secondary batteries electrically connected (series or parallel). It goes without saying that the number of lithium secondary batteries included in the battery module may be variously adjusted in consideration of the use and capacity of the battery module.

Furthermore, the present invention provides a battery pack in which the battery modules are electrically connected according to conventional techniques in the art. The battery module and the battery pack may include a power tool; Electric vehicles including electric vehicles (EV), hybrid electric vehicles (HEVs), and plug-in hybrid electric vehicles (PHEVs); Electric truck; Electric commercial vehicles; Alternatively, it can be used as a power supply for any one or more medium and large devices among the power storage systems, but is not limited thereto.

Hereinafter, a description of the negative electrode, the separator, and the electrolyte applied to the lithium secondary battery according to the present invention will be added.

cathode

As the negative electrode, any one capable of occluding and releasing lithium ions can be used, and examples thereof include metal materials such as lithium metal and lithium alloys, and carbon materials such as low crystalline carbon and high crystalline carbon. Soft carbon and hard carbon are typical examples of low-crystalline carbon, and natural graphite, kish graphite, pyrolytic carbon, and liquid crystal pitch-based carbon fiber are high-crystalline carbon. (Mesophase pitch based carbon fiber), carbon microspheres (Meso-carbon microbeads), liquid crystal pitches (Mesophase pitches), and high-temperature calcined carbon such as Petroleum or coal tar pitch derived cokes are typical. In addition, silicon-containing alloys or oxides such as Li ₄ Ti ₅ O ₁₂ are also well-known cathodes.

At this time, the negative electrode may include a binder, and as the binder, polyvinylidenefluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), and polyacrylonitrile (Polyacrylonitrile), polymethylmethacrylate (Polymethylmethacrylate), styrene-butadiene rubber (SBR), and various kinds of binder polymers can be used.

The negative electrode may optionally further include a negative electrode current collector for supporting the negative electrode active layer including the negative electrode active material and the binder. The negative electrode current collector may be specifically selected from the group consisting of copper, stainless steel, titanium, silver, palladium, nickel, alloys thereof, and combinations thereof. The stainless steel may be surface-treated with carbon, nickel, titanium, or silver, and an aluminum-cadmium alloy may be used as the alloy. In addition, calcined carbon, a non-conductive polymer surface-treated with a conductive agent, or a conductive polymer may be used.

The binder serves as a paste of the negative active material, mutual adhesion between the active materials, adhesion between the active material and the current collector, and a buffering effect on expansion and contraction of the active material. Specifically, the binder is the same as described above for the binder of the positive electrode. In addition, the negative electrode may be a lithium metal or a lithium alloy. As a non-limiting example, the negative electrode may be a thin film of lithium metal, and lithium and one selected from the group consisting of Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Ba, Ra, Al, and Sn It may be an alloy with the above metals.

Separator

The separator is interposed between the anode and the cathode to prevent a short circuit therebetween and serves to provide a passage for lithium ions to move. As the separator, olefin-based polymers such as polyethylene and polypropylene, glass fibers, etc. may be used in the form of sheets, multi-membrane, microporous films, woven fabrics and non-woven fabrics, but are not limited thereto. Meanwhile, when a solid electrolyte such as a polymer (eg, organic solid electrolyte, inorganic solid electrolyte, etc.) is used as the electrolyte, the solid electrolyte may also serve as a separator. Specifically, an insulating thin film having high ion permeability and mechanical strength is used. Meanwhile, pores through which lithium ions move are formed in the separator, and the pores may have a diameter of 0.01 to 10 μm and a thickness of 5 to 300 μm, but are not limited thereto.

Electrolyte

The electrolyte is a non-aqueous electrolyte containing a lithium salt, and is composed of a lithium salt and an electrolytic solution. As the electrolyte, a non-aqueous organic solvent, an organic solid electrolyte, an inorganic solid electrolyte, and the like are used. The lithium salt is a material that can be easily dissolved in a non-aqueous organic solvent, for example, LiCl, LiBr, LiI, LiClO ₄ , LiBF ₄ , LiB ₁₀ Cl ₁₀ , LiB(Ph) ₄ , LiPF ₆ , LiCF ₃ SO ₃ , _{LiCF 3 CO 2, LiAsF 6,} LiSbF 6, LiAlCl 4, LiSO 3 CH 3, LiSO 3 CF 3, LiSCN, LiC (CF 3 SO 2) 3, LiN (CF 3 SO 2) 2, chloroborane lithium, lower aliphatic It may be one or more from the group consisting of lithium carboxylate, lithium 4-phenyl borate, and lithium imide.

The concentration of the lithium salt is 0.2 to 2 M, depending on several factors, such as the exact composition of the electrolyte mixture, the solubility of the salt, the conductivity of the dissolved salt, the charging and discharging conditions of the battery, the working temperature and other factors known in the lithium battery field, It may be preferably 0.6 to 2 M, more preferably 0.7 to 1.7 M. If the concentration of the lithium salt is less than the above range, the conductivity of the electrolyte may be lowered and the electrolyte performance may be deteriorated.If the concentration of the lithium salt is greater than the above range, the viscosity of the electrolyte may increase and the mobility of lithium ions (Li+) may decrease. It is desirable to choose the concentration.

The non-aqueous organic solvent is a material capable of dissolving a lithium salt well, preferably 1,2-dimethoxyethane, 1,2-diethoxyethane, 1,2-dibutoxyethane, dioxolane (DOL ), 1,4-dioxane, tetrahydrofuran, 2-methyltetrahydrofuran, dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), methyl propyl carbonate (MPC), ethyl propyl carbonate , Dipropyl carbonate, butyl ethyl carbonate, ethyl propanoate (EP), toluene, xylene, dimethyl ether (dimethyl ether, DME), diethyl ether, triethylene glycol monomethyl ether (Triethylene glycol monomethyl ether, TEGME), Diglyme, tetraglyme, hexamethyl phosphoric triamide, gamma butyrolactone (GBL), acetonitrile, propionitrile, ethylene carbonate (EC), propylene carbonate (PC), N-methylpi Rolidone, 3-methyl-2-oxazolidone, acetic acid ester, butyric acid ester and propionic acid ester, dimethylformamide, sulfolane (SL), methylsulfolane, dimethylacetamide, dimethyl sulfoxide, dimethyl sulfate, ethylene glycol di An aprotic organic solvent such as acetate, dimethyl sulfite, or ethylene glycol sulfite may be used, and one or two or more of them may be used in the form of a mixed solvent.

The organic solid electrolyte includes a polyethylene derivative, a polyethylene oxide derivative, a polypropylene oxide derivative, a phosphate ester polymer, a poly etch lysine, a polyester sulfide, a polyvinyl alcohol, a polyvinylidene fluoride, an ionic dissociation group. Polymers and the like can be used. The inorganic solid electrolyte of the present invention includes Li ₃ N, LiI, Li ₅ NI ₂ , Li ₃ N-LiI-LiOH, LiSiO ₄ , LiSiO ₄ -LiI-LiOH, Li ₂ SiS ₃ , Li ₄ SiO ₄ , Li ₄ SiO Nitrides, halides and sulfates of Li such as ₄ -LiI-LiOH and Li ₃ PO ₄ -Li ₂ S-SiS ₂ can be exemplified.

Hereinafter, preferred embodiments are presented to aid in the understanding of the present invention, but the following examples are only illustrative of the present invention, and it is obvious to those skilled in the art that various changes and modifications are possible within the scope and spirit of the present invention, It is natural that such changes and modifications fall within the scope of the appended claims.

[Preparation Example 1] Preparation of sulfur-kaolin complex

First, 200 mL of ethanol (solvent), 5.6 g of kaolin powder (Kaolin nanoclay, SIGMA-ALDRICH) and 0.4 g of carbon nanotube (CNT) powder were mixed, and then pulverized for about 2 hours using a zirconia ball, and the pulverization 14 g of sulfur powder was added to the resulting mixture, mixed, and further pulverized for about 24 hours. Subsequently, the mixture in the form of a dough that had been pulverized twice was sifted to remove zirconia balls, and the filtered mixture was put in an oven at 80° C. and dried for several hours. Finally, the dried and hardened sulfur-kaolin powder was pulverized with a mortar, and then a sulfur-kaolin composite was prepared through heat treatment in an oven at 155° C. for 30 minutes (sulfur content in the composite: 70 wt%).

[Production Example 2] Preparation of sulfur-kaolin complex

The total amount of kaolin powder and CNT powder added was changed from 6 g to 5 g (kaolin: 4.6 g, CNT: 0.4 g) and sulfur powder added from 14 g to 15 g so that the sulfur content in the composite was 75% by weight. Except for the one, a sulfur-kaolin complex was prepared in the same manner as in Preparation Example 1.

[Preparation Example 3] Preparation of sulfur-kaolin complex

Change the total amount of kaolin powder and CNT powder added from 6 g to 4 g (kaolin: 3.6 g, CNT: 0.4 g) and sulfur powder added from 14 g to 16 g so that the sulfur content in the composite is 80% by weight. Except for the one, a sulfur-kaolin complex was prepared in the same manner as in Preparation Example 1.

[Comparative Preparation Example 1] Preparation of sulfur-carbon composite

After mixing 20 g of carbon nanotubes (CNT) and 80 g of sulfur, they were pulverized for about 2 hours using a zirconia ball, and then a sulfur-carbon composite was prepared through heat treatment in an oven at 155° C. for 30 minutes (in the composite Sulfur content: 80 wt%).

[Experimental Example 1] Pore evaluation of kaolin

In order to evaluate the pores of kaolin commonly used in Preparation Examples 1 to 3, BET analysis was performed. FIG. 1 is a graph evaluating the pores of kaolin applied to the positive electrode of a lithium secondary battery of the present invention. FIG. 1A is an adsorption/desorption curve, and FIG. 1B is a BJH plot.

As described above, as a result of performing BET analysis to evaluate the pores of kaolin, as shown in FIG. 1, it is predicted that the pore structure in kaolin is mostly composed of large pores of mesopore/macropore, so that the access of the electrolyte solution will be easy. Could

In addition, the kaolin was subjected to BET analysis to measure the specific surface area, pore volume, and pore size of kaolin. As a result of the measurement, the specific surface area (SSA) of kaolin was about 190 m ² /g, the pore volume (Pore V) was about 1.48 cm ³ /g, and the mean pore diameter was 31.3 nm, from which kaolin was in density. Is low and internal pores are developed, indicating a high level of specific surface area and pore volume even though it is an inorganic material.

[Experimental Example 2] Surface evaluation of kaolin and sulfur-kaolin complex

In order to evaluate the surfaces of the kaolin commonly used in Preparation Examples 1 to 3 and the sulfur-kaolin complex prepared in Preparation Example 1, each surface was observed with a scanning electron microscope (SEM). FIG. 2 is an image obtained by observing the surface of the kaolin and sulfur-kaolin complex according to an embodiment of the present invention with a scanning electron microscope, and FIG. 2A is an observation of the surface of kaolin commonly used in Preparation Examples 1 to 3 It is an SEM image, and FIG. 2B is an SEM image observing the surface of the sulfur-kaolin composite prepared in Preparation Example 1.

As a result of observing the respective surfaces of the kaolin and sulfur-kaolin complexes, it was confirmed that kaolin was in a plate shape through a of FIG. 2, and the plate shape of kaolin was relatively well maintained through b of FIG. It was confirmed that sulfur was supported on the surface of kaolin.

[Example 1] Preparation of a lithium secondary battery using a sulfur-kaolin composite as a positive electrode

First, the sulfur-kaolin complex prepared in Preparation Example 1 in water as a solvent is 85 parts by weight based on 100 parts by weight of the solvent, Denka Black as a conductive material is 10 parts by weight, and styrene butadiene rubber/carboxymethyl cellulose (SBR/CMC 7) as a binder. :3) was added in 7 parts by weight and mixed to prepare a positive electrode slurry composition, and then the prepared positive electrode slurry composition was coated on a current collector (Al Foil) and dried at 50° C. for 12 hours to prepare a positive electrode (at this time , The loading amount was 4-5 mAh/cm ² , and the porosity of the positive electrode was 70%).

Subsequently, an electrode assembly in which the prepared positive electrode (punched with a 14 phi circular electrode), a polyethylene separator (punched with 19 phi), and a lithium metal negative electrode having a thickness of 45 um (punched with 16 phi) are sequentially stacked After manufacturing, it was put into a battery case, and then an electrolyte was injected into the upper portion of the case, sealed with a cap plate and a gasket, and assembled to prepare a coin cell type lithium secondary battery.

[Example 2] Preparation of a lithium secondary battery using a sulfur-kaolin composite as a positive electrode

A coin cell type lithium secondary battery was manufactured in the same manner as in Example 1, except that the sulfur-kaolin complex prepared in Preparation Example 1 was changed to the sulfur-kaolin complex prepared in Preparation Example 2. .

[Example 3] Preparation of a lithium secondary battery using a sulfur-kaolin composite as a positive electrode

A coin cell type lithium secondary battery was manufactured in the same manner as in Example 1, except that the sulfur-kaolin composite prepared in Preparation Example 3 was used instead of the sulfur-kaolin composite prepared in Preparation Example 1.

[Comparative Example 1] Preparation of a lithium secondary battery using a sulfur-carbon composite as a positive electrode

A coin cell type lithium secondary battery was manufactured in the same manner as in Example 1, except that the sulfur-carbon composite prepared in Comparative Preparation Example 1 was used instead of the sulfur-kaolin composite prepared in Preparation Example 1. .

[Experimental Example 3] OCV evaluation of lithium secondary battery

Changes in open circuit voltage (OCV) of the lithium secondary batteries prepared in Example 3 and Comparative Example 1 were measured. 3 is a graph measuring changes in open circuit voltage (OCV) of a lithium secondary battery according to an embodiment and a comparative example of the present invention. As a result of measuring the open circuit voltage of the lithium secondary batteries prepared in Example 3 and Comparative Example 1 as described above, as shown in FIG. 3, the lithium secondary battery of Example 3 in which the sulfur-kaolin composite was applied as a positive electrode, Compared to the lithium secondary battery of Comparative Example 1 in which the sulfur-carbon composite was applied as a positive electrode, it was confirmed that the electrolyte solution penetrated into the electrode faster, so that the initial OCV was low and the stabilization time was fast.

[Experimental Example 4] Evaluation of discharge capacity of lithium secondary battery

First, the lithium secondary batteries prepared in Examples 1 to 3 were discharged (@0.1C) to evaluate the initial discharge capacity of the battery. FIG. 4 is a graph showing the discharge capacity of the lithium secondary battery according to the present invention, and as shown in FIG. 4, even if the sulfur content in the positive electrode is increased, the discharge capacity is not significantly reduced and it can be confirmed that the discharge capacity is at a similar level.

Next, the lithium secondary batteries prepared in Example 3 and Comparative Example 1 having the same sulfur content (sulfur content in the composite: 80 wt%) were discharged (@0.1C) to evaluate the initial discharge capacity of the battery. 5 is a graph showing the discharge capacity of a lithium secondary battery according to an embodiment and a comparative example of the present invention. As shown in FIG. 5, the battery of Example 3 in which kaolin is applied to the composite is a composite of carbon nanotubes. Compared to the battery of Comparative Example 1 applied to, it was found that the utilization rate of the composite active material with a high sulfur content was high and the resistance was small due to the improvement of the surface ion transfer ability.

Finally, the lithium secondary batteries prepared in Examples 1 to 3 and Comparative Example 1 were discharged (@0.1C) to compare and contrast the initial discharge capacity of each battery, and the results are shown in Table 1 below.

In the positive active material composite
Sulfur content (wt%) Within the anode
Sulfur content (wt%) Discharge capacity
(mAh/g) Example 1 70 (sulfur/kaolin complex) 59.5 1014 Example 2 75 (sulfur/kaolin complex) 63.8 1019 Example 3 80 (sulfur/kaolin complex) 68 1011 Comparative Example 1 80 (sulfur/carbon complex) 68 918

As described above, it was confirmed that even if the sulfur content in the positive electrode increased, the discharge capacity was not significantly affected, and even if the positive electrode active material composite had the same sulfur content, the discharge capacity was excellent when kaolin was included in the positive electrode active material composite.

[Experimental Example 5] Evaluation of life characteristics of lithium secondary battery

In order to evaluate the life characteristics of the lithium secondary batteries prepared in Examples 1 to 3 and Comparative Example 1, the discharge capacity according to the cycle was measured. At this time, the measurement was repeated at 0.1C/0.1C (charge/discharge) 3 cycles, 0.2C/0.2C 3 cycles and then 0.3C/0.5C.

6 is a graph showing the life characteristics of a lithium secondary battery manufactured according to an embodiment and a comparative example of the present invention. As shown in FIG. 6, the conductivity of the composite decreases as the sulfur content in the positive electrode increases, resulting in a high rate capacity. Is somewhat lower, but it was confirmed that it was superior to the case of applying a sulfur-carbon composite having the same sulfur content (Comparative Example 1).

Claims (10)

Kaolin, a kaolin based clay; And
A positive electrode for a lithium secondary battery comprising a sulfur-kaolin complex comprising; sulfur supported on the kaolin. The method of claim 1, wherein the sulfur content is 60 to 80% by weight based on the total weight of the sulfur-kaolin complex, and 68% by weight or less based on the total weight of the positive electrode, the sulfur-kaolin complex containing lithium secondary Battery positive electrode. The method according to claim 1, characterized in that the average particle diameter of the sulfur-kaolin composite is 1 to 100 ㎛, the positive electrode for a lithium secondary battery comprising a sulfur-kaolin composite. The cathode for a lithium secondary battery according to claim 1, wherein the sulfur-kaolin composite further comprises a carbon material. a) mixing and pulverizing kaolin powder and a solvent;
b) adding and mixing sulfur powder to the pulverized mixture, followed by pulverizing;
c) drying the pulverized sulfur-containing mixed solution;
d) further pulverizing the sulfur-kaolin powder formed through drying and then heat-treating to prepare a sulfur-kaolin complex; And
e) dispersing the prepared sulfur-kaolin complex in a solvent to prepare a slurry, and then applying the slurry to a current collector; a method for producing a positive electrode for a lithium secondary battery comprising: The method of claim 5, wherein the pulverization of step a) is performed for 30 minutes to 3 hours, the pulverization of step b) is performed for 10 to 36 hours, and the pulverization of step d) is performed for 10 minutes to 5 hours. It characterized in that the method of manufacturing a positive electrode for a lithium secondary battery. The method according to claim 5, wherein the solvent in step e) further comprises at least one of a binder, a conductive material, and a dispersant in addition to the sulfur-kaolin composite, and the content of carbon in the prepared positive electrode is 1 based on the total weight of the positive electrode active material layer. A method for producing a positive electrode for a lithium secondary battery, characterized in that to 15% by weight. The method of claim 5, wherein a carbon material is additionally added during mixing in step a). The positive electrode for a lithium secondary battery according to any one of claims 1 to 4; cathode; A separator interposed between the anode and the cathode; And an electrolyte; a lithium secondary battery containing. The lithium secondary battery according to claim 9, wherein the lithium secondary battery is a lithium-sulfur battery.

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