KR20200137816A - Positive electrode for lithium secondary battery, method for preparing the same and lithium secondary battery including the positive electrode - Google Patents

Abstract

The present invention relates to a positive electrode for a lithium secondary battery, which implements a double layer electrode of carbon/metal oxide by selectively depositing metal oxide only on a surface of carbon, to a production method thereof, and to a lithium secondary battery comprising the positive electrode. The positive electrode for a lithium secondary battery comprises: a carbon layer; a metal oxide layer formed by depositing on the surface of the carbon layer; and sulfur applied to the surface of the metal oxide layer.

Description

Positive electrode for lithium secondary battery, method for preparing the same and lithium secondary battery including the positive electrode}

The present invention relates to a positive electrode for a lithium secondary battery, a method of manufacturing the same, and a lithium secondary battery including the positive electrode, and more particularly, a double layer electrode of carbon/metal oxide is realized by selectively depositing a metal oxide only on the surface of a carbon material. One, it relates to a positive electrode for a lithium secondary battery, a method of manufacturing the same, and a lithium secondary battery including the positive electrode.

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.

However, in the case of a lithium-sulfur battery, there is a problem of low electrical conductivity of sulfur, elution of lithium polysulfide (LiPSs) during charging and discharging, and problems of ~80% volume expansion, low coulomb efficiency and rapid capacity reduction due to charging and discharging. have. To solve this problem, conventionally, a composite material in which a metal oxide is coated on a porous carbon substrate by most chemical methods (ex: sol-gel method) was applied, and the introduction of a chemically adsorbable metal oxide-porous carbon composite material It was effective in improving the capacity and life characteristics of the battery to some extent by preventing the elution of lithium polysulfide and improving the electrical conductivity.

However, when the above chemical method is followed, since metal oxides are generated or formed on the entire carbon substrate, resistance is increased, which leads to an increase in resistance in the electrode and interfacial resistance, and sulfur utilization and electrochemical properties (rate characteristics and lifetime There is a limit to improving the characteristics). Accordingly, there is a need for a method capable of improving electrochemical properties such as rate-limiting characteristics and lifespan characteristics compared to conventional electrodes by improving the internal resistance and interfacial resistance.

Korean Patent Publication No. 10-2016-0141615

Accordingly, an object of the present invention is to selectively deposit a metal oxide only on the surface of a carbon material to realize a double layer electrode of carbon/metal oxide, thereby improving the electrochemical properties of a battery, a positive electrode for a lithium secondary battery, a method of manufacturing the same, and It is to provide a lithium secondary battery including the positive electrode.

In order to achieve the above object, the present invention, a carbon layer; A metal oxide layer formed by depositing on the surface of the carbon layer; It provides a positive electrode for a lithium secondary battery comprising; and sulfur applied to the surface of the metal oxide layer.

In addition, the present invention, (a) preparing a carbon film containing a carbon material; (b) depositing a metal oxide on the surface of the prepared carbon film to prepare a carbon layer/metal oxide layer bilayer electrode; (c) heat-treating the prepared electrode; And (d) applying sulfur to the heat-treated electrode and then heat-treating the heat-treated electrode. It provides a method of manufacturing a positive electrode for a lithium secondary battery comprising a.

In addition, the present invention, the positive electrode for the lithium secondary battery; Lithium-based negative electrode; An electrolyte interposed between the positive electrode and the negative electrode; It provides a lithium secondary battery comprising; and a separator.

According to the positive electrode for a lithium secondary battery according to the present invention, a method of manufacturing the same, and a lithium secondary battery including the positive electrode, a double layer electrode of carbon/metal oxide is realized by selectively depositing a metal oxide only on the surface of a carbon material. The properties can be improved.

1 is a schematic diagram of a process of depositing a metal oxide on a carbon film according to an embodiment of the present invention.
2 is a visual observation image of a double-layer electrode of a carbon layer/metal oxide layer according to an embodiment of the present invention.
3 is an image obtained by observing a double-layer electrode of a carbon layer/metal oxide layer according to an embodiment of the present invention with a scanning electron microscope.
4 is an XRD peak image of a double layer electrode subjected to heat treatment according to an embodiment of the present invention.
5 is an image evaluating the lithium polysulfide adsorption capacity of a heat-treated double-layer electrode according to an embodiment of the present invention.
6 is a graph comparing discharge capacity by C-rate of a lithium secondary battery manufactured according to an embodiment and a comparative example of the present invention.
7 is a graph comparing and comparing life characteristics of lithium secondary batteries manufactured according to an embodiment and a comparative example of the present invention.

Hereinafter, the present invention will be described in detail.

The cathode for a lithium secondary battery according to the present invention includes a carbon layer, a metal oxide layer formed by depositing on the surface of the carbon layer, and sulfur applied to the surface of the metal oxide layer.

Lithium secondary batteries, especially lithium-sulfur batteries, have low electrical conductivity of sulfur, elution of lithium polysulfide (LiPSs) during charging and discharging, and volume expansion of ~80% as described above, and low coulomb efficiency and charge/discharge. Accordingly, there is a problem of rapid capacity reduction, and in order to solve this problem, a metal oxide was coated on a porous carbon substrate by a chemical method such as a sol-gel method. However, when the above chemical method is followed, the resistance is increased because the metal oxide is formed on the entire carbon substrate, which leads to an increase in the resistance of the electrode and the interfacial resistance, and the utilization of sulfur and the electrochemical characteristics (rate characteristics and life characteristics, etc. There is a limit to improving ). Accordingly, the applicant of the present application introduced a vapor deposition method to selectively form metal oxides only on the surface of the carbon substrate, and through this, internal resistance and interfacial resistance are improved, thereby improving electrochemical properties such as rate-limiting characteristics and lifetime characteristics compared to conventional electrodes. It was possible to make it.

First, referring to the carbon layer, the carbon layer as a deposition target of the metal oxide constituting the metal oxide layer is a layer containing a carbon material (or carbon source) capable of supplementing the low electrical conductivity of sulfur in the anode. The carbon material may be in the form of a cylinder. Here, the cylindrical carbon material refers to a carbon material having a rod type grown in one direction or a cylindrical structure with an empty inside, not in the form of spherical particles or flakes. Through this cylindrical structure, not spherical particles, pores aligned in one direction can be easily formed, and when a spherical carbon material (ex: carbon black, etc.) is applied instead of a cylindrical carbon material, it is three-dimensionally It may not be easy to form the pores that are interconnected and aligned.

The cylindrical carbon material is preferably a spherical or elliptical particle consisting of a net structure by crosslinking or entangled with a number of cylindrical carbon materials, and preferably has a nano structure, carbon nanotube (CNT), carbon nanotube paper (CNT paper), graphite Nanofibers (GNF), carbon nanofibers (CNF), activated carbon fibers (ACF), and mixtures of two or more of them may be exemplified. In addition, among the carbon materials, carbon nanotubes (or carbon nanotube paper) may be classified as single-walled carbon nanotubes (SWCNT, or SWCNT paper) or multi-walled carbon nanotubes (MWCNT, or MWCNT paper), and manufactured Depending on the method, it may be classified into a spherical type, an entangled type, and a bundle type, and any one or a mixture of two or more types may be used.

In the present invention, among such carbon materials, in consideration of the fact that space can be effectively utilized when a structure is formed from carbon having a relatively large diameter and a structure is filled with carbon having a relatively small diameter, carbon nanofibers ( It is recommended to use carbon nanofiber-single-walled carbon nanotube paper (CNF-SWCNT paper) that is a mixture of CNF, a carbon source with a relatively large diameter) and a single-walled carbon nanotube paper (SWCNT paper, a carbon source with a relatively small diameter). It may be desirable. In addition, the carbon material used in the present invention is not particularly limited if it is a conventional one having conductivity, and graphene, reduced graphene oxide (rGO), and thermally exfoliated reduced graphene oxide (TErGO), etc. are also available. Can be illustrated. Meanwhile, the cross-sectional diameter of each of the cylindrical carbon materials may be 1 to 100 nm, preferably 1 to 50 nm, more preferably 1 to 10 nm.

In addition, pores are formed in the carbon material constituting the carbon layer, and the porosity of the pores is 40 to 90%, preferably 60 to 80%, and if the porosity of the pores is less than 40%, lithium ion transfer is normally Since it is not made, it may act as a resistance component and cause a problem, and if it exceeds 90%, a problem of lowering the mechanical strength may occur. In addition, the pore size of the carbon material is 10 nm to 5 μm, preferably 50 nm to 5 μm, and if the pore size is less than 10 nm, there may be a problem in which lithium ion penetration is impossible, and the pore size exceeding 5 μm In this case, a battery short circuit and safety problems may occur due to contact between electrodes.

Subsequently, a metal oxide layer formed by vapor deposition on the surface of the carbon layer will be described. Metal oxide constituting the metal oxide layer is deposited on the surface of the carbon layer, suppressing the elution of lithium polysulfide, and promoting the reduction of the eluted lithium polysulfide (redox mediator). ) And supplements the low electrical conductivity of sulfur. The metal oxide includes inorganic metal particles (or inorganic particles), inorganic metal and oxygen are combined, and the inorganic metal particles may have a nanometer size to a micrometer size. More specifically, the particle diameter of the inorganic metal particles is 10 nm to 1 μm, preferably 10 to 40 nm, more preferably 10 to 20 nm, and when the particle diameter of the inorganic metal particles is less than 10 nm, self-aggregation ( Self-aggregation) may cause a problem in that the activity for lithium polysulfide decreases, and when it exceeds 1 μm, the specific surface area decreases and thus the activity decreases.

As the inorganic metal included in the metal oxide (or metal oxide layer), titanium, manganese, tin, nickel, cobalt, magnesium, aluminum, cerium, iron, vanadium, and mixtures thereof may be exemplified. It may be preferable to apply it as a metal in terms of securing chemical stability. Therefore, when the metal oxide of the present invention is also titanium oxide, the effect may be the most excellent. As such titanium oxide, titanium oxide such as titanium dioxide (TiO ₂ ), TiO, Ti ₂ O ₃ , and Ti ₄ O ₇ may be exemplified, and it may be preferable to apply titanium dioxide as a metal oxide layer. . In addition, as manganese oxides, manganese dioxide (MnO ₂ ), manganese trioxide (MnO ₃ ), dimanganese trioxide (Mn ₂ O ₃ ), and trimanganese tetraoxide (Mn ₃ O ₄ ) can be exemplified (manganese dioxide is applied as a metal oxide. It is preferable to do), tin dioxide (SnO ₂ ), etc. may be exemplified as the tin oxide, and NiCo ₂ O ₄ may be exemplified as the nickel-cobalt oxide. That is, the metal oxide layer includes a metal oxide selected from the group consisting of metal dioxide, metal trioxide, and metal tetraoxide.

The thickness of the metal oxide layer is 10 to 500 nm, preferably 50 to 200 nm, and the metal oxide layer is formed to have a thin thickness of tens nanometers to hundreds of nanometers as described above. Characteristics can be dramatically improved. If the thickness of the metal oxide layer is less than 10 nm, the effect obtained by applying the metal oxide to the positive electrode may be insignificant, and if it exceeds 500 nm, the metal oxide acts as a resistance and degrades the performance of the battery. There is concern.

In addition, since the metal oxide layer can be selectively formed on a part or all of the surface of the carbon layer, the resistance due to the formation of the metal oxide can be lowered, and accordingly, the resistance in the electrode and the interface resistance can be lowered. It is possible to improve or improve the electrochemical properties such as the rate-limiting properties and the life properties of the.

Meanwhile, as described above, the metal oxide layer may be selectively formed on a part or all of the surface of the carbon layer (here,'part' means not 100% of the total surface area of the carbon layer), but the electrochemical of the battery In order to maximize the properties, it is preferable that the carbon layer is deposited on a large area as much as possible, and it may be most preferable to be formed on the entire surface of the carbon layer.

The content of the metal oxide layer may vary depending on the surface area of the carbon layer to which the metal oxide is deposited, but when the metal oxide is deposited on the entire surface of the carbon layer, the total weight of the carbon layer is 100 parts by weight. Based on 0.1 to 10 parts by weight, preferably 0.1 to 5 parts by weight, more preferably 1 to 3 parts by weight may be. At this time, when the content of the metal oxide layer is less than 0.1 parts by weight based on 100 parts by weight of the total weight of the carbon layer, the effect of inhibiting the dissolution of lithium polysulfide may be insignificant, and when it exceeds 10 parts by weight, the reaction of the battery Can reduce the overall efficiency.

In addition, pores may be formed in the metal oxide (or metal oxide layer), and the porosity of the pores may be 40 to 90%, preferably 60 to 80%. When pores are formed in the metal oxide, sulfur may be adsorbed to at least one of pores of the metal oxide layer or pores of the carbon material. Meanwhile, when the lithium secondary battery of the present invention is a lithium-sulfur battery, sulfur is included in the positive electrode, and the sulfur may be a conventional sulfur or sulfur compound applied to a lithium-sulfur battery.

On the other hand, in the anode for lithium secondary batteries to which a conventional metal oxide is applied, a binder must be used because the metal oxide is introduced through a chemical method, and as the binder is used, the binder covers the surface of the metal oxide, thereby oxidizing lithium polysulfide. It has a drawback that a problem that does not promote the reduction reaction occurs. However, since the anode for a lithium secondary battery according to the present invention introduces a metal oxide using a deposition method, it is possible to implement an electrode without a binder.

Next, a method of manufacturing a positive electrode for a lithium secondary battery according to the present invention will be described. The method of manufacturing a positive electrode for a lithium secondary battery includes (a) preparing a carbon film containing a carbon material, (b) depositing a metal oxide on the surface of the prepared carbon film to form a carbon layer/metal oxide layer bilayer electrode And (c) heat-treating the prepared electrode, and (d) applying sulfur to the heat-treated electrode and then heat-treating.

The biggest feature of the anode manufacturing method of the present invention is that a metal oxide is introduced on the surface of a carbon material (or carbon layer) by a deposition method. In other words, there are cases in which metal oxides have been introduced into carbon materials in the past, but since all of them are chemically used, metal oxides are generated on the entire carbon substrate, and accordingly, resistance and interfacial resistance in the electrode are increased, resulting in electrochemical properties and sulfur utilization. Showed low problem. However, the applicant has improved the existing problem by introducing the deposition method as described above.

In addition, by applying a deposition method to the introduction of metal oxides, metal oxides can be deposited on the surface of the carbon layer in a single process. Also, it is possible to easily control the thickness so that the metal oxides are deposited on the surface of the carbon layer in a uniform and thin thickness. Can be formed. Therefore, it has the advantage of dramatically improving the electrochemical properties of the battery while forming the metal oxide in the form of a thin film. In addition, the conventional anode incorporating a metal oxide is one using a particulate composite material of porous carbon/metal oxide, whereas the anode of the present invention is also large in applying a double-layer electrode material of a porous carbon layer/metal oxide layer. There is a difference.

Step (a) is a process of manufacturing a carbon film (or carbon layer) using a carbon material, for example, a carbon material is titrated in a solution in which a surfactant is dissolved in a solvent such as water (DI water, etc.) After preparing the dispersion by mixing in a ratio, the dispersion may be vacuum filtered (Vacuum Filtration, or reduced pressure filtration) using a separator such as PVDF Membrane to prepare a carbon film (at this time, the prepared carbon film is separated to Drying process may be involved).

The step (b) is a process of depositing a metal oxide (or metal oxide precursor) on the surface of the carbon film prepared in step (a) to prepare a double layer electrode of the carbon layer/metal oxide layer, wherein the deposition is performed by heat A method such as Thermal Evaporation, Pulsed Laser Deposition, or Chemical Vapor Deposition may be used. Here, the deposited metal oxide is in the form of a metal monoxide such as TiO, MnO, or SnO, or a source (metal oxide precursor) capable of providing a metal monoxide. 1 is a schematic diagram of a process of depositing a metal oxide on a carbon film according to an embodiment of the present invention, and the step (b) may be performed through a process as illustrated in FIG. 1.

In addition, the electrode heat treatment in step (c) may be performed for 10 minutes to 5 hours in an inert gas atmosphere and 150 to 900° C., through which the metal oxides subjected to (deposition and) heat treatment are TiO ₂ , MnO ₂ , SnO ₂ will take the form of metal dioxide, metal trioxide or metal tetraoxide. In other words, the metal oxide in step (b) is a metal monoxide, and is converted into one of metal dioxide, metal trioxide, and metal tetraoxide through the heat treatment in step (c).

The step (d) is a process of heat treatment after applying sulfur to the heat-treated electrode.For example, sulfur is dissolved in carbon disulfide (CS ₂ ), applied to the heat-treated electrode, dried, and then 100 Heat treatment may be performed at a temperature of from to 200° C. for about 30 minutes to 5 hours, through which the positive electrode for a lithium secondary battery according to the present invention is manufactured.

Finally, when describing a lithium secondary battery including a positive electrode for a lithium secondary battery, the lithium secondary battery includes a positive electrode for a lithium secondary battery, a lithium-based negative electrode, an electrolyte interposed between the positive electrode and the negative electrode, and a separator. . The lithium secondary battery may be a lithium-based secondary battery such as a lithium-sulfur battery, a lithium metal battery, and a lithium air battery, but a lithium-sulfur battery may best meet the spirit of the present invention.

Meanwhile, all configurations included in the positive electrode, and the negative electrode, the electrolyte, and the separator may be conventional ones used in the art, and a detailed description thereof will be given below.

The positive electrode included in the lithium secondary battery of the present invention further includes a binder and a conductive material. The binder is a component that aids in bonding of a positive electrode active material and a conductive material and bonding to a current collector, for example, polyvinylidene fluoride (PVdF), polyvinylidene fluoride-polyhexafluoropropylene copolymer (PVdF/ HFP), polyvinyl acetate, polyvinyl alcohol, polyvinyl ether, polyethylene, polyethylene oxide, alkylated polyethylene oxide, polypropylene, polymethyl (meth) acrylate, polyethyl (meth) acrylate, polytetrafluoroethylene (PTFE) ), polyvinyl chloride, polyacrylonitrile, polyvinylpyridine, polyvinylpyrrolidone, styrene-butadiene rubber, acrylonitrile-butadiene rubber, ethylene-propylene-diene monomer (EPDM) rubber, sulfonated EPDM rubber, styrene -One or more selected from the group consisting of butylene rubber, fluorine rubber, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, and mixtures thereof may be used, but must be It is not limited thereto.

The binder is typically added in an amount of 1 to 50 parts by weight, preferably 3 to 15 parts by weight, based on 100 parts by weight of the total weight of the positive electrode. If the content of the binder is less than 1 part by weight, adhesion between the positive electrode active material and the current collector may be insufficient, and if it exceeds 50 parts by weight, the adhesion is improved, but the amount of the positive electrode active material decreases so that the battery capacity may be lowered.

The conductive material included in the positive electrode is not particularly limited as long as it does not induce side reactions in the internal environment of the lithium secondary battery, does not cause chemical changes in the battery, and has excellent electrical conductivity. Typically, graphite or conductive carbon may be used. Examples thereof include graphite such as natural graphite and artificial graphite; Carbon blacks such as carbon black, acetylene black, ketjen black, denka black, thermal black, channel black, furnace black, lamp black, and thermal black; A carbon-based material having a crystal structure of graphene or graphite; Conductive fibers such as carbon fibers and metal fibers; Carbon fluoride; Metal powders such as aluminum and nickel powder; Conductive whiskey such as zinc oxide and potassium titanate; Conductive oxides such as titanium oxide; And a conductive polymer such as a polyphenylene derivative, but may be used alone or in combination of two or more, but is not limited thereto.

The conductive material is typically added in an amount of 0.5 to 50 parts by weight, preferably 1 to 30 parts by weight, based on 100 parts by weight of the total weight of the positive electrode. If the content of the conductive material is too small, such as less than 0.5 parts by weight, it is difficult to expect an effect of improving the electrical conductivity or the electrochemical properties of the battery may be deteriorated.If the content of the conductive material exceeds 50 parts by weight and is too large, the amount of the positive electrode active material is relatively high. It becomes less, and the capacity and energy density may be lowered. The method of including the conductive material in the positive electrode is not particularly limited, and a conventional method known in the art such as coating on a positive electrode active material may be used. In addition, if necessary, since the second conductive coating layer is added to the positive electrode active material, the addition of the conductive material as described above may be substituted.

In addition, a filler may be optionally added to the positive electrode of the present invention as a component that suppresses its expansion. Such a filler is not particularly limited as long as it can suppress the expansion of the electrode without causing a chemical change in the battery, and examples thereof include olivine polymers such as polyethylene and polypropylene; Fibrous substances such as glass fibers and carbon fibers; Etc. can be used.

A positive electrode active material, a binder, a conductive material, and the like are dispersed and mixed in a dispersion medium (solvent) to form a slurry, and the positive electrode of the present invention can be completely manufactured by applying it on a positive electrode current collector and then drying and rolling. As the dispersion medium, NMP (N-methyl-2-pyrrolidone), DMF (dimethyl formamide), DMSO (dimethyl sulfoxide), ethanol, isopropanol, water, and mixtures thereof may be used, but are not limited thereto.

The positive electrode current collector includes platinum (Pt), gold (Au), palladium (Pd), iridium (Ir), silver (Ag), ruthenium (Ru), nickel (Ni), stainless steel (STS), aluminum (Al ), molybdenum (Mo), chromium (Cr), carbon (C), titanium (Ti), tungsten (W), ITO (In doped SnO ₂ ), FTO (F doped SnO ₂ ), and alloys thereof , Carbon (C), nickel (Ni), titanium (Ti), or silver (Ag) surface-treated on the surface of aluminum (Al) or stainless steel may be used, but the present invention is not limited thereto. The shape of the positive electrode current collector may be in the form of a foil, film, sheet, punched, porous body, foam, or the like.

The negative electrode may be manufactured according to a conventional method known in the art. For example, a negative electrode active material, a conductive material, a binder, and if necessary, a filler, etc., are dispersed and mixed in a dispersion medium (solvent) to make a slurry, which is coated on the negative electrode current collector, and then dried and rolled to prepare a negative electrode. . As the negative active material, lithium metal or a lithium alloy (eg, an alloy of lithium and a metal such as aluminum, zinc, bismuth, cadmium, antimony, silicon, lead, tin, gallium, or indium) may be used. The anode current collector includes platinum (Pt), gold (Au), palladium (Pd), iridium (Ir), silver (Ag), ruthenium (Ru), nickel (Ni), stainless steel (STS), copper (Cu). ), molybdenum (Mo), chromium (Cr), carbon (C), titanium (Ti), tungsten (W), ITO (In doped SnO ₂ ), FTO (F doped SnO ₂ ), and alloys thereof , Copper (Cu) or stainless steel may be surface-treated with carbon (C), nickel (Ni), titanium (Ti), or silver (Ag), but is not limited thereto. The negative electrode current collector may be in the form of a foil, a film, a sheet, a punched one, a porous body, or a foam.

The separator is interposed between the positive electrode and the negative electrode 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. On the other hand, 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. The separator may have a pore diameter of generally 0.01 to 10 μm, and a thickness of 5 to 300 μm.

As the electrolyte or electrolyte, carbonate, ester, ether, or ketone may be used alone or in combination of two or more as a non-aqueous electrolyte (non-aqueous organic solvent), but is not limited thereto. For example, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, methylpropyl carbonate, ethylpropyl carbonate, methylethyl carbonate, ethylene carbonate, propylene carbonate, butylene carbonate, γ-butyrolactone, n-methyl acetate, n- Such as ethyl acetate, n-propyl acetate, phosphoric acid tryster, dibutyl ether, N-methyl-2-pyrrolidinone, 1,2-dimethoxy ethane, tetrahydroxy franc (Franc), 2-methyl tetrahydrofuran Tetrahydrofuran derivatives, dimethylsulfoxide, formamide, dimethylformamide, dioxolone and derivatives thereof, acetonitrile, nitromethane, methyl formate, methyl acetate, trimethoxy methane, sulfolane, methyl sulfolane, 1,3 -An aprotic organic solvent such as dimethyl-2-imidazolidinone, methyl propionate, and ethyl propionate may be used, but is not limited thereto.

A lithium salt may be further added to the electrolyte solution (so-called lithium salt-containing non-aqueous electrolyte solution), and the lithium salt is a well-known one that is soluble in a non-aqueous electrolyte solution, such as LiCl, LiBr, LiI, LiClO ₄ , LiBF ₄ , LiB ₁₀ Cl ₁₀ , LiPF ₆ , LiCF ₃ SO ₃ , LiCF ₃ CO ₂ , LiAsF ₆ , LiSbF ₆ , LiPF ₃ (CF ₂ CF ₃ ) ₃ , LiAlCl ₄ , CH ₃ SO ₃ Li, CF ₃ SO ₃ Li, (CF ₃ SO ₂ ) ₂ NLi, lithium chloroborane, lithium lower aliphatic carboxylic acid, lithium 4 phenyl borate, and imide, but are not limited thereto. In the (non-aqueous) electrolyte solution, for the purpose of improving charge/discharge properties and flame retardancy, for example, pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylene diamine, n-glyme, hexaphosphate triamide , Nitrobenzene derivative, sulfur, quinone imine dye, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxy ethanol, aluminum trichloride, etc. May be. If necessary, a halogen-containing solvent such as carbon tetrachloride or ethylene trifluoride may be further included in order to impart non-flammability, and carbon dioxide gas may be further included in order to improve high-temperature storage characteristics.

On the other hand, the lithium secondary battery of the present invention can be manufactured according to a conventional method in the art. For example, it can be prepared by putting a porous separator between the positive electrode and the negative electrode, and adding a non-aqueous electrolyte. The lithium secondary battery according to the present invention can be particularly suitably used as a unit cell of a battery module, which is a power source for medium and large devices, as well as applied to a battery cell used as a power source for a small device. In this respect, 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, preferred embodiments are presented to aid in the understanding of the present invention, but this is 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 the modifications belong to the appended claims.

[Production Example 1] Fabrication of double-layer electrode of carbon layer/metal oxide layer

First, in a solution obtained by dissolving CTAB (Cetyltrimethylammonium bromide, Alfa Aesar) as a surfactant in DI water at 1 to 5 wt%, the outer diameter is 100 to 200 nm, the inner diameter is 50 to 100 nm, and the specific surface area is 10 to 100 m. ² /g carbon nanofibers (CNF, Sigma Aldrich) and single-walled carbon nanotubes (SWCNT, Xiamen Tob New Energy Technology) with a length of 0.1 to 5 nm and a total length of 1 to 100 nm were 10 : 1 to 10: The mixed carbon material was dispersed in a weight ratio of 5 (Sonication). Subsequently, the carbon material dispersion was vacuum-filtered with PVDF Membrane (Durapore, Sigma-Aldrich) to prepare a carbon film, which was separated and dried at a temperature of 60° C. for 2 hours, and finally, the prepared carbon film TiO (1~3 mm Granule Type, Tiffaine) was deposited on the surface of the surface by a thermal evaporator system (Thermal evaporator system, Daedong Hitech, Solar-Bridge), and TiO was formed with a thickness of 70 nm. A double layer electrode was prepared.

[Production Example 2] Fabrication of double-layer electrode of carbon layer/metal oxide layer

Except for changing the thickness of TiO to be formed to be 250 nm, the same procedure as in Preparation Example 1 was carried out to prepare a carbon layer/metal oxide layer bilayer electrode.

[Production Example 3] Manufacture of heat-treated carbon layer/metal oxide layer double-layer electrode

The bilayer electrode of the carbon layer/metal oxide layer prepared in Preparation Example 1 was heat-treated while heating in an argon atmosphere and 500° C. for 2 hours.

[Experimental Example 1] Surface evaluation of a double layer electrode

The surfaces (front/rear) of the bilayer electrodes prepared in Preparation Examples 1 and 2 were observed and evaluated with the naked eye and a scanning electron microscope (SEM). 2 is a visual observation image of a double-layer electrode of a carbon layer/metal oxide layer according to an embodiment of the present invention, and FIG. 3 is a scanning electron diagram of a double-layer electrode of a carbon layer/metal oxide layer according to an embodiment of the present invention. It is an image observed with a microscope (left view of FIG. 3: TiO formed to a thickness of 70 nm, right view of FIG. 3: TiO formed to a thickness of 250 nm).

As shown in Fig. 2, the front surface of the electrode was black and it could be seen that the carbon material was located, and the back side of the electrode was brown, indicating that the metal oxide was located.Through this, it was prepared in Preparation Examples 1 and 2 It was found that the electrode was made of a double layer of a carbon layer and a metal oxide layer. In addition, through the SEM image of FIG. 3, it was confirmed that a layer was formed by coating a metal oxide in the form of particles on the carbon surface.

[Experimental Example 2] XRD analysis evaluation of heat-treated double-layer electrode

The double-layer electrode of Preparation Example 3, which was performed up to the heat treatment process, was subjected to XRD analysis. 4 is an XRD peak image of a double-layer electrode heat-treated according to an embodiment of the present invention. As shown in FIG. 4, the crystallinity of TiO ₂ in the double-layer electrode generated through heat treatment, and a wide peak at 26 degrees are shown. It was confirmed that the amorphous carbon was composited.

[Experimental Example 3] Evaluation of lithium polysulfide adsorption of heat-treated double-layer electrode

The lithium polysulfide adsorption ability of the heat-treated double layer electrode of Preparation Example 3 was evaluated. 5 is an image evaluating the lithium polysulfide adsorption ability of a heat-treated double-layer electrode according to an embodiment of the present invention. The left view of FIG. 5 is an image containing only a yellow lithium polysulfide solution, and the right view of FIG. 5 is an image of lithium polysulfide. This is an image after adding the heat-treated double-layer electrode of Preparation Example 3 to the sulfide solution and leaving it for 12 hours. As shown in FIG. 5, it was confirmed that the heat-treated carbon layer/metal oxide layer double-layer electrode of the present invention had a lithium polysulfide adsorption ability, so that the color was pale.

[Example 1] Preparation of positive electrode for lithium secondary battery

To the (heat-treated) double-layer electrode prepared in Preparation Example 3, a solution in which sulfur was dissolved in carbon disulfide (CS ₂ ) in 5 to 30 wt% was added dropwise (Drop) and then dried, for lithium secondary battery according to the present invention. A positive electrode was prepared (sulfur content in the positive electrode: 5-20% by weight).

[Comparative Example 1] Preparation of positive electrode for lithium secondary battery

First, in a solution in which the surfactant CTAB (Cetyltrimethylammonium bromide) is dissolved in DI water at 1-5 wt%, the outer diameter is 100 to 200 nm, the inner diameter is 50 to 100 nm, and the specific surface area is 10 to 100 m ² /g. Carbon nanofibers (CNF, Sigma Aldrich) and CNT single-walled carbon nanotubes (SWCNT, Xiamen Tob New Energy Technology) with a length of 0.1 to 5 nm and a total length of 1 to 100 nm were 10:1 to 10 : The mixed carbon material was dispersed in a weight ratio of 5 (Sonication). Subsequently, the carbon material dispersion was vacuum-filtered with PVDF Membrane (Durapore, Sigma-Aldrich) to prepare a carbon film, which was separated and dried at a temperature of 60° C. for 2 hours, and finally, the prepared carbon film A solution in which sulfur was dissolved in carbon disulfide at 5-30 wt% was added dropwise to the surface of and dried to prepare a positive electrode for a lithium secondary battery (ie, excluding the deposition process of metal oxide).

[Example 2, Comparative Example 2] Preparation of lithium secondary battery

After preparing each positive electrode and lithium metal negative electrode prepared in Example 1 and Comparative Example 1, an electrode assembly was manufactured by interposing a separator of porous polyethylene between the positive electrode and the negative electrode, and the electrode assembly was placed inside the case. An electrolyte solution (DOL:DME=1:1 (v/v%), 1M LiTFSi, 0.2M LiNO ₃ ) was injected at about 2.2 times the weight of sulfur, and a pouch-type lithium-sulfur battery of 0.45 Ah (450 Wh/kg) was prepared. Was prepared.

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

The lithium secondary battery (precisely, a lithium-sulfur battery) prepared in Example 2 and Comparative Example 2 was discharged at 0.2/0.5/1/2/4C (5 cycles each) to evaluate the discharge capacity of the battery. (Charge-discharge potential range (potential window): 1.7-2.8 V). 6 is a graph comparing discharge capacity by C-rate of a lithium secondary battery manufactured according to an embodiment and a comparative example of the present invention.

As a result of evaluating the discharge capacity by C-rate of the lithium secondary batteries prepared in Example 2 and Comparative Example 2, as shown in FIG. 6, the battery of Comparative Example 2 to which the positive electrode from which the metal oxide was deposited was applied was The specific specific capacity per C-rate was 894/702/634/591/555 mAh/g, and the battery of Example 2 to which a positive electrode deposited with a metal oxide was applied has a specific specific capacity per C-rate of 995/759/682/633/594 mAh /g, and through this result, it was found that it was due to the improvement of the electrochemical reaction on the electrode surface due to the lithium polysulfide adsorption characteristics due to metal oxide deposition.

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

Life characteristics of the lithium secondary batteries (precisely, lithium-sulfur batteries) prepared in Example 2 and Comparative Example 2 were evaluated under 1 C-rate conditions (charge and discharge potential range: 1.7-2.8 V). 7 is a graph comparing and comparing life characteristics of lithium secondary batteries manufactured according to an embodiment and a comparative example of the present invention.

As a result of evaluating the life characteristics of the lithium secondary batteries prepared in Example 2 and Comparative Example 2, as shown in FIG. 7, the battery of Comparative Example 2 to which the anode from which the metal oxide was deposited was applied has an initial capacity of 661. mAh/g, after 100 charging and discharging, showed 360 mAh/g, and the battery of Example 2 to which a positive electrode deposited with metal oxide was applied had an initial capacity of 876 mAh/g, and 803 mAh/g after 100 charging and discharging. Through these results, it was confirmed that stable lifespan characteristics can be realized by the lithium polysulfide adsorption characteristics according to metal oxide deposition.

Claims (15)

Carbon layer;
A metal oxide layer formed by depositing on the surface of the carbon layer; And
A positive electrode for a lithium secondary battery comprising; sulfur applied to the surface of the metal oxide layer. The method of claim 1, wherein the metal oxide layer includes an inorganic metal, and the inorganic metal is selected from the group consisting of titanium, manganese, tin, nickel, cobalt, magnesium, aluminum, cerium, iron, vanadium, and mixtures thereof. Characterized in that, a positive electrode for a lithium secondary battery. The cathode for a lithium secondary battery according to claim 1, wherein the metal oxide layer comprises a metal oxide selected from the group consisting of metal dioxide, metal trioxide, and metal tetraoxide. The cathode for a lithium secondary battery according to claim 3, wherein the metal oxide is selected from the group consisting of titanium dioxide (TiO ₂ ), manganese dioxide (MnO ₂ ), and tin dioxide (SnO ₂ ). The cathode for a lithium secondary battery according to claim 1, wherein the metal oxide layer has a thickness of 10 to 500 nm. The cathode for a lithium secondary battery according to claim 1, wherein the metal oxide layer is selectively deposited on a part or the entire surface of the carbon layer. The cathode for a lithium secondary battery according to claim 1, wherein the content of the metal oxide layer is 0.1 to 10 parts by weight based on 100 parts by weight of the total weight of the carbon layer. The method according to claim 1, wherein pores are formed in the metal oxide layer, the porosity of the pores is 40 to 90%, and the sulfur is adsorbed to at least one of pores of the metal oxide layer or pores of the carbon material. A positive electrode for a lithium secondary battery. The method according to claim 1, wherein the carbon layer includes a carbon material, and the carbon material is carbon nanotubes (CNT), carbon nanotubes paper (CNT paper), graphite nanofibers (GNF), carbon nanofibers (CNF), activated carbon A positive electrode for a lithium secondary battery, characterized in that selected from the group consisting of fibers (ACF) and a mixture of two or more of them. The cathode for a lithium secondary battery according to claim 9, wherein the carbon material is a carbon nanofiber-single-walled carbon nanotube paper (CNF-SWCNT paper). (a) preparing a carbon film containing a carbon material;
(b) depositing a metal oxide on the surface of the prepared carbon film to prepare a carbon layer/metal oxide layer bilayer electrode;
(c) heat-treating the prepared electrode; And
(d) applying sulfur to the heat-treated electrode and then performing heat treatment. The method of claim 11, wherein the deposition in step (b) is performed by a method selected from the group consisting of thermal deposition, laser pulse deposition, and chemical vapor deposition. The lithium secondary of claim 11, wherein the metal oxide in step (b) is a metal monoxide, and is converted to one of metal dioxide, metal trioxide, and metal tetraoxide through the heat treatment in step (c). Method of manufacturing a battery positive electrode. The method of claim 11, wherein the heat treatment in step (c) is performed for 10 minutes to 5 hours under an inert gas atmosphere and 150 to 900 °C, and the heat treatment in step (d) is performed at a temperature of 100 to 200 °C for about 30 minutes to A method of manufacturing a positive electrode for a lithium secondary battery, characterized in that performed for 5 hours. The positive electrode for a lithium secondary battery of claim 1; Lithium-based negative electrode; An electrolyte interposed between the positive electrode and the negative electrode; And a separator; lithium secondary battery comprising a.

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