KR20190062969A - Positive electrode for lithium-sulfur battery and method for manufacturing the same - Google Patents

Abstract

The present invention relates to a positive electrode for a lithium-sulfur battery and a method for manufacturing the same. The positive electrode for a lithium-sulfur battery comprises: a current collector; and a positive electrode active material layer formed on at least one surface of the current collector. The positive electrode active material layer comprises a sulfur-carbon composite and an inorganic additive, and the porosity of the positive electrode is 50-70%. According to the present invention, a positive electrode for a lithium-sulfur battery which can enhance cycle life characteristics can be provided.

Description

TECHNICAL FIELD [0001] The present invention relates to a positive electrode for a lithium-sulfur battery, and a method for manufacturing the positive electrode.

The present invention relates to a positive electrode for a lithium-sulfur battery and a method of manufacturing the same.

Recently, interest in energy storage technology is increasing. As the application fields of cell phones, camcorders, notebook PCs and even electric vehicles are expanding, efforts for research and development of electrochemical devices are becoming more and more specified.

Electrochemical devices have attracted the greatest attention in this respect. Among them, the development of rechargeable secondary batteries has become a focus of attention. In recent years, in order to improve capacity density and energy efficiency in developing such batteries, Research and development on the design of new electrodes and batteries are underway.

 Among the currently applied secondary batteries, the lithium secondary battery developed in the early 1990s has advantages such as higher operating voltage and higher energy density than conventional batteries such as Ni-MH, Ni-Cd and sulfuric acid-lead batteries using an aqueous electrolyte solution .

In particular, a lithium-sulfur (Li-S) battery is a secondary battery using a sulfur-based material having a sulfur-sulfur bond as a cathode active material and using lithium metal as an anode active material. Sulfur, the main material of the cathode active material, is very rich in resources, has no toxicity, and has a low atomic weight. The theoretical energy density of the lithium-sulfur battery is 1675 mAh / g-sulfur and the theoretical energy density is 2,600 Wh / kg. The theoretical energy density (Ni-MH battery: 450 Wh / , Which is the most promising among the batteries that have been developed to date, because it is much higher than the FeS battery (480Wh / kg), Li-MnO ₂ battery (1,000Wh / kg) and Na-S battery (800Wh / kg).

During the discharge reaction of the lithium-sulfur battery, an oxidation reaction of lithium occurs at the anode and a sulfur reduction reaction occurs at the cathode. Sulfur before discharging has an annular S ₈ structure. When the SS bond is cut off during the reduction reaction (discharging), the oxidation number of S decreases, and when the oxidation reaction (charging) The reduction reaction is used to store and generate electrical energy. During this reaction, the sulfur is converted to a linear polysulfide (Li ₂ S _x , x = 8, 6, 4, 2) by the reduction reaction at the cyclic S ₈ , When it is reduced, lithium sulfide (Li ₂ S) is finally produced. The discharge behavior of the lithium-sulfur battery by the process of reducing to each lithium polysulfide characterizes the discharge voltage stepwise unlike the lithium ion battery.

However, in the case of such a lithium-sulfur battery, it is necessary to solve the problems of low electric conductivity of sulfur, dissolution and volumetric expansion of lithium polysulfide during charging and discharging, low Coulomb efficiency and rapid capacity reduction due to charging and discharging.

In such a lithium sulfur battery system, when a sulfur-based compound is used as a cathode active material and an alkali metal such as lithium is used as a negative electrode active material, lithium-polysulfide generated during charging and discharging of the battery is transferred to a cathode, The lifetime is reduced and the reactivity is decreased due to a large amount of lithium-polysulfide.

To solve this problem, studies are under way to control the electrode porosity of the anode. However, as the electrode porosity decreases, the initial reactivity of the electrode decreases and the overvoltage phenomenon occurs. Also, the electrolyte concentration is increased due to poly-sulfide dissolution, Degeneration occurs.

In addition, if the porosity of the electrode is increased, the effect of increasing the initial reactivity of the electrode is exhibited. However, there arises a problem that the cycle life is degraded preferentially as the charge and discharge proceeds.

Korean Patent Publication No. KR 2015-0046861 "Lithium-sulfur battery anode and method for manufacturing the same"

The inventors of the present invention have conducted extensive research and have found that the use of an inorganic additive (CoS ₂ , CeO ₂ ) as an electrode component in the form of an extra-electrode additive in an environment where the reactivity of the electrode is somewhat low , The reactivity of the electrode due to the rapid reaction of the redox-mediator (RM) is increased, and excellent long-life cycle life can be achieved, thereby completing the present invention.

Accordingly, an object of the present invention is to provide a positive electrode for a lithium-sulfur battery capable of improving the overvoltage generated as the porosity of an electrode for a Li-S battery is lowered, thereby improving cycle life characteristics.

In order to achieve the above object,

Collecting house; And a positive electrode active material layer formed on at least one surface of the current collector, wherein the positive electrode active material layer includes a sulfur-carbon composite material and an inorganic additive, and the porosity of the positive electrode is in a range of 50 - 70% by weight of the positive electrode for a lithium-sulfur battery.

In addition,

Preparing a slurry for forming a cathode active material comprising a sulfur-carbon composite and an inorganic additive; And coating the slurry on at least one surface of the current collector to produce a positive electrode having a porosity of 50 to 70%. The present invention also provides a method for manufacturing a positive electrode for a lithium-sulfur battery.

The present invention also provides a lithium-sulfur battery comprising the positive electrode for a lithium-sulfur battery.

According to the present invention, it is possible to provide a positive electrode for a lithium-sulfur battery capable of improving an overvoltage caused by lowering the porosity of an electrode for a Li-S battery, thereby improving cycle life characteristics.

1 is a 0.1 / 0.1 charge / discharge graph of the lithium-sulfur battery produced in Examples 1 and 2 and Comparative Example 1. FIG.
FIG. 2 is a 0.3 / 0.5 charge / discharge graph of the lithium-sulfur battery produced in Examples 1 and 2 and Comparative Example 1. FIG.
FIG. 3 is a graph showing lifetime characteristics of the lithium-sulfur battery produced in Examples 1 and 2 and Comparative Example 1. FIG.
FIG. 4 is a graph showing charge and discharge efficiency characteristics of the lithium-sulfur battery manufactured in Comparative Examples 2 to 4. FIG.
FIG. 5 is a graph showing lifetime characteristics of the lithium-sulfur battery prepared in Comparative Examples 2 to 4. FIG.

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art can easily carry out the present invention. The present invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein.

In the drawings, the same reference numerals are used for similar parts throughout the specification. In addition, the size and relative size of the components shown in the figures are independent of the actual scale and may be reduced or exaggerated for clarity of description.

The terms and words used in the present specification and claims should not be construed as limited to ordinary or dictionary terms and the inventor may appropriately define the concept of the term in order to best describe its invention It should be construed as meaning and concept consistent with the technical idea of the present invention.

As used herein, the term " composite " refers to a material that combines two or more materials to form a phase that is physically and chemically distinct, and that exhibits more effective functions.

The lithium-sulfur battery uses sulfur as the cathode active material and lithium metal as the anode active material. At the discharge of the lithium-sulfur battery, the oxidation reaction of lithium occurs at the cathode and the reduction reaction of sulfur occurs at the anode. At this time, the reduced sulfur is converted to lithium polysulfide by binding with lithium ions that have been moved from the cathode, and finally involves a reaction to form lithium sulfide.

The lithium-sulfur battery has a much higher theoretical energy density than the conventional lithium secondary battery, and the sulfur used as the cathode active material is inexpensive because of its abundant resources, so it can be used as a next-generation battery have.

Despite these advantages, it is difficult to realize all the theoretical energy densities in actual operation due to the low electric conductivity and the lithium ion conductivity of the cathode active material sulfur.

In order to improve the electrical conductivity of sulfur, a method of forming a composite with a conductive material such as carbon, a polymer, and coating is used. Among the various methods, the sulfur-carbon composite is most widely used as the cathode active material because it is effective in improving the electrical conductivity of the anode, but it is still not sufficient in terms of charge / discharge capacity and efficiency.

To solve this problem, studies are under way to control the electrode porosity of the anode. However, as the electrode porosity decreases, the initial reactivity of the electrode decreases and the overvoltage phenomenon occurs. Also, the electrolyte concentration is increased due to poly-sulfide dissolution, Degeneration occurs.

In addition, if the porosity of the electrode is increased, the effect of increasing the initial reactivity of the electrode is exhibited. However, there arises a problem that the cycle life is degraded preferentially as the charge and discharge proceeds.

Anode for lithium-sulfur battery

Lithium-sulfur battery has much higher discharging capacity and theoretical energy density than existing lithium secondary batteries, and sulfur, which is used as a cathode active material, is attracting attention as a next-generation battery because of its abundant reserves, low cost, and environment friendliness.

Despite these advantages, the theoretical capacity and the energy density are not realized in actual operation. This is because the low lithium ion conductivity of sulfur, the cathode active material, is very low in the proportion of sulfur participating in the actual electrochemical redox reaction. The capacity and efficiency of the lithium-sulfur battery may vary depending on the amount of lithium ions delivered to the anode. Therefore, it is important to increase the lithium ion conductivity of the positive electrode to increase the capacity and high efficiency of the lithium-sulfur battery.

In addition, in the lithium-sulfur battery, the lithium polysulfide formed in the anode during the charge and discharge reactions is lost outside the anode reaction region, and a shuttle phenomenon occurs in which it moves between the anode and the cathode. At this time, lithium sulfide is fixed on the surface of the lithium metal due to the side reaction between the lithium polysulfide eluted from the anode and the lithium metal as the negative electrode, so that the reaction activity is lowered and the lithium ion is unnecessarily consumed, A problem arises.

In the prior art, in order to improve the lithium ion conductivity, a method of increasing the lithium salt concentration of the electrolyte or introducing an additive into the electrolyte has been used, but the performance and lifetime of the lithium-sulfur battery have not been effectively improved.

Accordingly, the present invention provides a positive electrode for a lithium-sulfur battery capable of improving an overvoltage caused by lowering the porosity of an electrode for a Li-S battery and thereby improving cycle life characteristics.

The positive electrode for a lithium-sulfur battery according to the present invention

Collecting house; And a positive electrode active material layer formed on at least one surface of the current collector,

Wherein the cathode active material layer comprises a sulfur-carbon composite and an inorganic additive,

And the porosity of the anode is 50 to 70%.

The current collector for a lithium-sulfur battery for a lithium-sulfur battery according to the present invention is not particularly limited as long as it has a thickness of 3 to 500 占 퐉 and has high conductivity without causing chemical change in the battery. For example, a conductive metal such as stainless steel, aluminum, copper, or titanium can be used, and an aluminum current collector can be preferably used. Such a positive electrode current collector may have various forms such as a film, a sheet, a foil, a net, a porous body, a foam or a nonwoven fabric.

The positive electrode active material layer of the positive electrode for a lithium-sulfur battery according to the present invention includes a sulfur-carbon composite material and an inorganic additive.

Lithium-sulfur batteries contain sulfur as a cathode active material, which has the problem of elution of lithium polysulfide during charging and discharging. By using the carbon - sulfur complex, the sulfur in the structure is uniformly distributed, and pores of various sizes and three - dimensionally interconnected and regularly arranged pores can carry sulfur in a high content. Therefore, even when the lithium polysulfide is eluted, the structure entangled in three dimensions is maintained and the phenomenon that the anode structure is collapsed can be suppressed. As a result, the lithium-sulfur battery including the carbon-sulfur complex has an advantage that a high capacity can be realized even at high loading. For this purpose, the sulfur-carbon composite used in the lithium-sulfur battery of the present invention may contain sulfur in an amount of 50 to 90% by weight based on the total weight of the composite.

Further, the positive electrode for a lithium-sulfur battery according to the present invention includes an inorganic additive.

In the present invention, even when the electrode has a low reactivity, the inorganic additive, which is well known as a redox-mediator, is included as an electrode component in the form of an electrode, The reaction can increase the reactivity of the electrode and can exhibit an excellent long life cycle life. Examples of the inorganic additive include CoS ₂ and CeO ₂ , And the inorganic additive may be included in an amount of 1 to 10% by weight based on the total weight of the cathode active material layer.

If the content of the inorganic additive is less than 1% by weight, the effect of improving the electrochemical performance due to the addition of the inorganic additive is insignificant and the effect of improving the overvoltage and improving the reactivity of the electrode may be somewhat reduced. On the other hand, There is a problem that degradation occurs.

In addition, the positive electrode for a lithium-sulfur battery according to the present invention may have a porosity of 50 to 70%, and preferably 60 to 65%.

The positive electrode for a lithium-sulfur battery according to the present invention is characterized in that it can increase the reactivity of the electrode even in a low / high rate charge / discharge environment where the reactivity of the electrode is somewhat lacking, and exhibits an excellent long life cycle life. The cycle life is rapidly degraded as the charge and discharge proceeds, and the porosity is limited to 50 to 70%, preferably 60 to 65%.

The porosity in the present invention is defined as the ratio of the volume excluding the volume considering the true density of the cathode active material to the total actual volume of the cathode material as the porosity. Can be determined.

The positive electrode active material layer of the positive electrode for a lithium-sulfur battery according to the present invention may further include at least one selected from the group consisting of a binder and a conductive material.

First, the cathode active material layer may further include a conductive material to impart additional conductivity. The conductive material plays a role in allowing electrons to move smoothly in the anode. The conductive material is not particularly limited as long as the conductive material does not cause a chemical change in the battery and can provide a large surface area. Materials are used.

Examples of the carbon-based material include natural graphite, artificial graphite, expanded graphite, graphite such as Graphene, active carbon, channel black, furnace black, Carbon black such as black, thermal black, contact black, lamp black, and acetylene black; A carbon nano structure such as a carbon fiber, a carbon nanotube (CNT), and a fullerene, and a combination thereof may be used.

In addition to the carbon-based materials, metallic fibers such as metal mesh may be used depending on the purpose. Metallic powder such as copper (Cu), silver (Ag), nickel (Ni) and aluminum (Al); Or an organic conductive material such as a polyphenylene derivative can also be used. The conductive materials may be used alone or in combination.

Further, the cathode active material layer may further include a binder to provide an adhesive force to the current collector. The binder must be well dissolved in a solvent, and it should not only constitute a conductive network between the cathode active material and the conductive material, but also have an ability to impregnate the electrolyte appropriately.

The binder applicable to the present invention may be any binder known in the art and specifically includes a fluororesin binder containing polyvinylidene fluoride (PVdF) or polytetrafluoroethylene (PTFE) ; Rubber-based binders including styrene-butadiene rubber, acrylonitrile-butadiene rubber, and styrene-isoprene rubber; Cellulosic binders including carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, and regenerated cellulose; Polyalcohol-based binders; Polyolefin binders including polyethylene and polypropylene; But are not limited to, polyimide-based binders, polyester-based binders, and silane-based binders, or a mixture or copolymer of two or more thereof.

The content of the binder resin may be 0.5-30 wt% based on the total weight of the positive electrode for a lithium-sulfur battery, but is not limited thereto. If the content of the binder resin is less than 0.5% by weight, the physical properties of the positive electrode may deteriorate and the positive electrode active material and the conductive material may fall off. When the amount of the binder resin is more than 30% by weight, the ratio of the active material and the conductive material is relatively decreased The battery capacity can be reduced.

Method for manufacturing positive electrode for lithium-sulfur battery

The method for producing a positive electrode for a lithium-sulfur battery of the present invention comprises the steps of: preparing a slurry for forming a positive electrode active material comprising a sulfur-carbon composite and an inorganic additive; And coating the slurry on at least one surface of the current collector to produce a cathode having a porosity of 50 to 70%.

a) preparing a slurry for forming a cathode active material

The composition for forming the cathode active material layer is prepared by mixing a sulfur-carbon composite and an inorganic additive. At this time, the composition for forming the positive electrode active material layer may further include at least one selected from the group consisting of a binder and a conductive material.

A solvent is used to prepare the composition for forming the positive electrode active material layer in a slurry state. At this time, it is most preferable that the solvent should be easy to dry and dissolve the binder well, while the cathode active material and the conductive material can be maintained in a dispersed state without dissolving. When the solvent dissolves the cathode active material, the specific gravity (D = 2.07) of the sulfur in the slurry is high, so that the sulfur is submerged in the slurry, which causes sulfur in the current collector in the coating, have.

The solvent according to the present invention may be water or an organic solvent, and the organic solvent may be an organic solvent containing at least one selected from the group consisting of dimethylformamide, isopropyl alcohol, acetonitrile, methanol, ethanol and tetrahydrofuran It is possible.

The mixing of the cathode composition may be carried out by a conventional method using a conventional mixer such as a latex mixer, a high-speed shear mixer, a homomixer, and the like.

The contents of the sulfur-carbon composite and the inorganic additive are the same as those of the anode for a lithium-sulfur battery as described above.

b) Whole-house  Coated on at least one side, The porosity is  Step of preparing an anode having 50 to 70%

The positive electrode composition may be applied to a current collector and dried to form a positive electrode for a lithium-sulfur battery. The slurry may be coated on the current collector with an appropriate thickness according to the viscosity of the slurry and the thickness of the anode to be formed, and may be suitably selected within the range of 10 to 300 mu m.

The slurry may be coated by a method such as doctor blade coating, dip coating, gravure coating, slit die coating, spin coating, Spin coating, comma coating, bar coating, reverse roll coating, screen coating, cap coating and the like.

The drying of the slurry is not particularly limited as long as it is a drying method in the art, and for example, drying can be performed at 40 to 70 ° C for 4 to 12 hours.

Thus, the method for producing a positive electrode for a lithium-sulfur battery of the present invention comprises:

During the coating of the positive electrode, a positive electrode having a porosity of 50 to 70%, preferably 60 to 65%, can be prepared through roll-pressing control.

The current collector generally has a thickness of 3 to 500 占 퐉 and is not particularly limited as long as it has high conductivity without causing chemical change in the battery. For example, a conductive metal such as stainless steel, aluminum, copper, or titanium can be used, and an aluminum current collector can be preferably used. Such a positive electrode current collector may have various forms such as a film, a sheet, a foil, a net, a porous body, a foam or a nonwoven fabric.

Lithium-sulfur battery

In one embodiment of the present invention, the lithium-sulfur battery includes the positive electrode for the lithium-sulfur battery described above; A negative electrode comprising lithium metal or a lithium alloy as a negative electrode active material; A separator interposed between the anode and the cathode; And an electrolyte impregnated with the negative electrode, the positive electrode and the separator, and including a lithium salt and an organic solvent.

The negative electrode is a negative active material that can reversibly intercalate or deintercalate lithium ions (Li ⁺ ), a material capable of reversibly reacting with lithium ions to form a lithium-containing compound , A lithium metal or a lithium alloy can be used. The material capable of reversibly intercalating or deintercalating lithium ions may be, for example, crystalline carbon, amorphous carbon, or a mixture thereof. The material capable of reacting with the lithium ion to form a lithium-containing compound reversibly may be, for example, tin oxide, titanium nitrate or silicon. The lithium alloy may be, for example, an alloy of lithium and a metal selected from the group consisting of Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Ba, Ra, Al and Sn.

Further, in the process of charging / discharging the lithium-sulfur battery, sulfur used as the positive electrode active material is changed to an inactive material and can be attached to the surface of the lithium negative electrode. Inactive sulfur is sulfur in which sulfur can not participate in the electrochemical reaction of the anode after various electrochemical or chemical reactions. Inactive sulfur formed on the surface of the lithium anode is a protective film of the lithium anode layer as well. Therefore, a lithium metal and an inert sulfur formed on the lithium metal, such as lithium sulfide, may be used as the cathode.

The negative electrode of the present invention may further include a pretreatment layer made of a lithium ion conductive material in addition to the negative electrode active material, and a lithium metal protective layer formed on the pretreatment layer.

The separator interposed between the anode and the cathode separates or insulates the anode and the cathode from each other and allows transport of lithium ions between the anode and the cathode, and may be made of a porous nonconductive or insulating material. Such a separator may be an independent member such as a thin film or a film as an insulator having high ion permeability and mechanical strength, or may be a coating layer added to the anode and / or the cathode. When a solid electrolyte such as a polymer is used as the electrolyte, the solid electrolyte may also serve as a separation membrane.

The separator preferably has a pore diameter of 0.01 to 10 μm and a thickness of 5 to 300 μm. The separator may be a glass electrolyte, a polymer electrolyte, a ceramic electrolyte, or the like. For example, olefin-based polymers such as polypropylene having chemical resistance and hydrophobicity, sheets or nonwoven fabrics made of glass fibers or polyethylene, kraft paper, and the like are used. Representative examples currently on the market include the Celgard ^R 2400 (2300 Hoechest Celanese Corp.), polypropylene separator (Ube Industries Ltd. or Pall RAI), and polyethylene (Tonen or Entek).

The solid electrolyte separation membrane may contain less than about 20% by weight of a non-aqueous organic solvent, in which case it may further comprise a suitable gelling agent to reduce the fluidity of the organic solvent. Representative examples of such gel-forming compounds include polyethylene oxide, polyvinylidene fluoride, and polyacrylonitrile.

The electrolyte impregnated in the negative electrode, the positive electrode and the separator is a non-aqueous electrolyte containing a lithium salt. The non-aqueous electrolyte is composed of a lithium salt and an electrolyte. Non-aqueous organic solvents, organic solid electrolytes and inorganic solid electrolytes are used as the electrolyte.

The lithium salt of the present invention can be dissolved in a non-aqueous organic solvent, for example, LiSCN, LiCl, LiBr, LiI, LiPF ₆ , LiBF ₄ , LiSbF ₆ , LiAsF ₆ , LiB ₁₀ Cl ₁₀ , LiCH ₃ SO ₃ , LiCF _{3 SO 3, LiCF 3 CO 2} , LiClO 4, LiAlCl 4, Li (Ph) 4, LiC (CF 3 SO 2) 3, LiN (FSO 2) 2, LiN (CF 3 SO 2) 2, LiN (C 2 (F ₃ SO ₂ ) ₂ , LiN (SFO ₂ ) ₂ , LiN (CF ₃ CF ₂ SO ₂ ) ₂ , chloroborane lithium, lower aliphatic carboxylate lithium, lithium tetraphenylborate, lithium imide and combinations thereof May be included.

The concentration of the lithium salt may be in the range of 0.2 to 2 M, preferably 1 to 2 M, depending on various factors such as the precise composition of the electrolyte mixture, the solubility of the salt, the conductivity of the dissolved salt, the charging and discharging conditions of the battery, Specifically, it may be 0.6 to 2 M, more specifically 0.7 to 1.7 M. If it is used at less than 0.2 M, the conductivity of the electrolyte may be lowered and the performance of the electrolyte may be deteriorated. If it is used in excess of 2 M, the viscosity of the electrolyte may increase and the mobility of lithium ions (Li ⁺ ) may be reduced.

Examples of the non-aqueous organic solvent of the present invention include N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, di Ethyl carbonate, ethyl methyl carbonate, gamma-butyrolactone, 1,2-dimethoxyethane, 1,2-diethoxyethane, tetrahydroxyfuran, 2-methyltetrahydrofuran, dimethylsulfoxide, 3-dioxolane, diethyl ether, formamide, dimethyl formamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, phosphoric acid triester, trimethylene Ethers such as ethoxymethane, dioxolane derivatives, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ether, methyl pyrophosphate, ethyl propionate Organic solvent And the organic solvent may be one or a mixture of two or more organic solvents.

Examples of the organic solid electrolyte include a polymer electrolyte such as a polyethylene derivative, a polyethylene oxide derivative, a polypropylene oxide derivative, a phosphate ester polymer, an agitation lysine, a polyester sulfide, a polyvinyl alcohol, a polyvinylidene fluoride, A polymer including a group can be used.

Examples of the inorganic solid electrolyte include 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 Nitrides, halides, sulfates and the like of Li such as SiO ₄ -LiI-LiOH and Li ₃ PO ₄ -Li ₂ S-SiS ₂ can be used.

The electrolyte of the present invention may contain at least one selected from the group consisting of pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylenediamine, glyme, hexa-phosphoric triamide, Benzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N, N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, . In some cases, a halogen-containing solvent such as carbon tetrachloride, ethylene trifluoride or the like may be further added to impart nonflammability. In order to improve the high-temperature storage characteristics, carbon dioxide gas may be further added. carbonate, PRS (propene sultone), FPC (fluoro-propylene carbonate) and the like.

The electrolyte may be used as a liquid electrolyte or as a solid electrolyte separator. When used as a liquid electrolyte, the separator further includes a separation membrane made of porous glass, plastic, ceramic, or polymer as a physical separation membrane having a function of physically separating the electrode.

It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the present invention. Such variations and modifications are intended to be within the scope of the appended claims.

[Example]

Preparation of sulfur-carbon composites

[Example 1]

Sulfur-carbon composite material: binder: dispersant: conductive material: additive = 82.86: 6.25: 0.89: 4.76: 4.76 to prepare a slurry.

The sulfur-carbon composite was prepared by adding sulfur to FT9111 (manufactured by CNT, CNano) and having a sulfur content of 70% by weight. LiPAA (Lithiated Polyacrylic Acid) was used as a binder. PVA (Polyvinyl alcohol) was used, VGCF (Vapor Grown Carbon Fibers) was used as a conductive material, and CoS ₂ was used as an additive.

The slurry was coated on a current collector made of aluminum foil having a thickness of 20 탆, and then a collector electrode was prepared. The prepared electrode was dried overnight in a 50 ° C oven to prepare a positive electrode for a lithium-sulfur battery, and the loading amount of sulfur was 5.5 mAh / cm ² .

Further, at the time of preparing the electrode, the porosity was controlled to be 62% by adjusting the thickness through electrode rolling.

The porosity was defined as the ratio of the volume excluding the volume considering the true density of the electrode active material to the total actual volume of the electrode material. The thickness of the electrode was measured using an electrode thickness measuring instrument (TESA u-hite) , And porosity were calculated.

 [Example 2]

As an additive, CoS ₂ A positive electrode for a lithium-sulfur battery was prepared in the same manner as in Example 1 except that CeO ₂ was used instead, and the loading amount of sulfur was 5.4 mAh / cm ² .

During the preparation of the electrode, the porosity was adjusted to 60% by adjusting the thickness through electrode rolling.

[Comparative Example 1]

Sulfur battery was prepared in the same manner as in Example 1, except that an additive was not used, and a slurry was prepared in a weight ratio of sulfur-carbon composite: binder: dispersant: conductive material = 87: 7: 1: And the loading amount of sulfur was 5.7 mAh / cm ² .

During the preparation of the electrode, the porosity was adjusted to 60% by adjusting the thickness through electrode rolling.

[Comparative Example 2]

A positive electrode for a lithium-sulfur battery was prepared in the same manner as in Comparative Example 1, except that the electrode was adjusted to have a porosity of 72% by controlling the thickness through electrode rolling. The loading amount of sulfur was 5.8 mAh / cm ² Respectively.

[Comparative Example 3]

The positive electrode for a lithium-sulfur battery was prepared in the same manner as in Example 1, except that the porosity was adjusted to 73% by controlling the thickness of the electrode during the electrode rolling. The loading amount of sulfur was 5.6 mAh / cm ² Respectively.

[Comparative Example 4]

A positive electrode for a lithium-sulfur battery was prepared in the same manner as in Example 2, except that the electrode was adjusted to have a porosity of 72% through thickness adjustment through electrode rolling. The loading amount of sulfur was 5.6 mAh / cm ² Respectively.

Experimental Example  1: Battery performance evaluation

The lithium-sulfur battery coin cell manufactured in Examples 1 to 2 and Comparative Examples 1 to 4 was used as a positive electrode, polyethylene was used as a separator, and lithium foil having a thickness of 45 탆 was used as a negative electrode. . At this time, the coin cell was prepared by dissolving 0.75 M LiFSI and 3 wt% LiNO ₃ in an organic solvent composed of methyltetrahydrofuran and ethylene glycol ethyl methyl ether (2-ME THF: EGEME = 1: 2 by volume) Used.

(Evaluation of charge / discharge characteristics)

The coin cell manufactured above was tested for charge / discharge characteristics change using a charge / discharge measuring apparatus. Using the obtained battery, the initial discharge / charging proceeded to 0.1 C / 0.1 C during the initial 2.5 cycles, followed by 0.2 C / 0.2 C for 3 cycles, and then the cycle progressed to 0.5 C / 0.3 C. The above results were measured and shown in Figs. 1 to 4. Fig.

FIG. 1 is a graph showing the initial charge / discharge characteristics of the lithium-sulfur battery prepared in Examples 1 to 2 and Comparative Example 1, and FIG. 2 is a graph showing the charge / discharge characteristics of Examples 1 to 2 and Comparative Example 1 FIG. 3 is a graph showing the charge-discharge efficiency of the lithium-sulfur battery of the lithium-sulfur battery manufactured in Examples 1 to 2 and Comparative Example 1, and FIG. And FIG. 4 is a graph showing initial charging and discharging characteristics of the lithium-sulfur battery prepared in Comparative Examples 2 to 4. FIG. 5 is a graph showing the initial charging and discharging characteristics of the lithium-sulfur battery prepared in Comparative Examples 2 to 4 It is a graph showing discharge efficiency.

4 and 5, in the case of the electrodes of Comparative Examples 2 to 4 in which the porosity of the electrode was 72 to 73%, the electrode of Comparative Example 2 containing no inorganic additive had poor reactivity of the electrode, It was found that the cell gradually degraded (started to deteriorate) cycle life after the charge and discharge, and the electrode of Comparative Examples 3 to 4 containing the inorganic additive in the electrode had an effect of improving the reactivity of the electrode. However, The cell gradually degraded (started to deteriorate) after charging and discharging, and the cycle life characteristics were rather lower than that of Comparative Example 2. [

1 and 2, in the case of the electrodes of Examples 1 and 2 and Comparative Example 1 in which the porosity of the electrode was 60 to 62%, the electrode of Comparative Example 1, which did not contain the inorganic additive, As the temperature decreased from 72% to 60%, the overvoltage of the cell deepened during the initial discharge (0.1 C charge / 0.1 C discharge), and the reactivity of the electrode was decreased. However, the electrodes of Examples 1 and 2 including the inorganic additive in the electrode showed a tendency that the overvoltage of the cell was somewhat improved and the reactivity of the electrode was somewhat restored. In the high rate charge / discharge (0.3 C charge / 0.5 C discharge) The effect was more pronounced and the reactivity of the electrode was improved.

Referring to FIG. 3, as the charge and discharge proceeded, it was confirmed that the electrode of Comparative Example 1 containing no inorganic additive deteriorated (started to deteriorate) after about 40 charge / discharge cycles after recovery of the discharge capacity. However, in the electrodes of Examples 1 and 2 including the inorganic additive, it was confirmed that the cell was gradually degraded (started to deteriorate) after about 100 times of charging and discharging. When the inorganic additive was included, The improvement of cycle life characteristics was confirmed.

Claims (13)

Collecting house; And
A positive electrode active material layer formed on at least one surface of the current collector;
A positive electrode for a lithium-sulfur battery comprising:
Wherein the cathode active material layer comprises a sulfur-carbon composite and an inorganic additive,
Wherein the anode has a porosity of 50 to 70%. The method according to claim 1,
The inorganic additives include CoS ₂ and CeO ₂ A positive electrode for a lithium-sulfur battery. The method according to claim 1,
Wherein the anode has a porosity of 60 to 65%. The method according to claim 1,
Wherein the inorganic additive is contained in an amount of 1 to 10 wt% based on the total weight of the positive electrode active material layer. The method according to claim 1,
Wherein the sulfur-carbon composite comprises sulfur in an amount of 50 to 90% by weight based on the total weight of the composite. The method according to claim 1,
Wherein the positive electrode active material layer further comprises at least one selected from the group consisting of a binder and a conductive material, Preparing a slurry for forming a cathode active material comprising a sulfur-carbon composite and an inorganic additive; And
And coating the slurry on at least one surface of the current collector to produce a positive electrode having a porosity of 50 to 70%. 8. The method of claim 7,
The inorganic additives include CoS ₂ and CeO ₂ Wherein the positive electrode is a positive electrode. 8. The method of claim 7,
Wherein the anode has a porosity of 60 to 65%. 8. The method of claim 7,
Wherein the inorganic additive is contained in an amount of 1 to 10% by weight based on the total weight of the slurry for forming a cathode active material. 8. The method of claim 7,
Wherein the sulfur-carbon composite comprises sulfur in an amount of 50 to 90% by weight based on the total weight of the composite. 8. The method of claim 7,
Wherein the slurry for forming a cathode active material further comprises at least one selected from the group consisting of a binder and a conductive material. A lithium-sulfur battery comprising the positive electrode for the lithium-sulfur battery of claim 1.

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