KR20220136099A - Lithium secondary battery - Google Patents

Abstract

The present invention relates to a lithium secondary battery including tellurium as a positive electrode additive and bis(2,2,2-trifluoroethyl) ether as an electrolyte additive, and has an effect of improving lifespan characteristics of the lithium secondary battery. The present invention includes: a positive electrode; a negative electrode; a separator interposed therebetween; and an electrolyte.

Description

Lithium secondary battery {LITHIUM SECONDARY BATTERY}

The present invention relates to a lithium secondary battery, and more particularly, to a lithium secondary battery containing tellurium as a positive electrode additive and bis(2,2,2-trifluoroethyl) ether as an electrolyte additive.

Recently, miniaturization and weight reduction of electronic products, electronic devices, communication devices, etc. is rapidly progressing, and as the need for electric vehicles is greatly raised in relation to environmental problems, the demand for performance improvement of secondary batteries used as power sources for these products also increases. the situation is. Among them, the lithium secondary battery has been in the spotlight as a high-performance battery because of its high energy density and high standard electrode potential.

In particular, a lithium-sulfur (Li-S) battery is a secondary battery that uses a sulfur-based material having an SS bond as a positive electrode active material and lithium metal as a negative electrode active material. Sulfur, the main material of the cathode active material, has the advantage of being very abundant in resources, non-toxic, and having a low weight per atom. In addition, the theoretical discharge capacity of the lithium-sulfur battery is 1675 mAh/g-sulfur, and the theoretical energy density is 2,600 Wh/kg. FeS battery: 480 Wh/kg, Li-MnO ₂ battery: 1,000 Wh/kg, Na-S battery: 800 Wh/kg), it is the most promising battery among the batteries being developed so far.

During the discharge reaction of a lithium-sulfur battery, an oxidation reaction of lithium occurs at the negative electrode, and a reduction reaction of sulfur occurs at the positive electrode. Sulfur before discharging has a cyclic S ₈ structure. During the reduction reaction (discharge), the oxidation number of S decreases as the SS bond is broken, and during the oxidation reaction (charge), the oxidation number of S increases as the SS bond is re-formed. Reduction reactions are used to store and generate electrical energy. During this reaction, sulfur is converted from cyclic S ₈ into a linear lithium polysulfide (Lithium polysulfide, Li ₂ S _x , x=8, 6, 4, 2) by a reduction reaction, and eventually this lithium polysulfide is completely When reduced, lithium sulfide (Li ₂ S) is finally produced. The discharge behavior of the lithium-sulfur battery by the process of reduction to each lithium polysulfide is characterized in that it shows the discharge voltage in stages, unlike a general lithium ion battery.

However, the biggest problem in the commercialization of lithium-sulfur batteries is the lifespan, and the charging/discharging efficiency decreases during the charging/discharging process, and the lifespan of the battery deteriorates. The causes of such deterioration of the lifespan of lithium-sulfur batteries include side reactions of the electrolyte (deposition of by-products due to the decomposition of the electrolyte), instability of lithium metal (short occurs due to dendrites growing on the lithium anode), and by-products of the positive electrode. deposition (elution of lithium polysulfide from the anode), etc.

That is, in a battery using a sulfur-based compound as a positive electrode active material and an alkali metal such as lithium as a negative electrode active material, dissolution and shuttle phenomena of lithium polysulfide occur during charging and discharging, and lithium polysulfide is transferred to the negative electrode. The capacity of the lithium-sulfur battery is reduced, and accordingly, the lithium-sulfur battery has a major problem in that the lifespan is reduced and the reactivity is reduced. That is, since lithium polysulfide eluted from the positive electrode has high solubility in the organic electrolyte, an unwanted movement (PS shuttling) may occur toward the negative electrode through the electrolyte, thereby reducing capacity due to irreversible loss of the positive electrode active material and A decrease in battery life occurs due to the deposition of sulfur particles on the lithium metal surface due to side reactions.

In addition, as lithium metal easily reacts with an electrolyte due to its high chemical/electrochemical reactivity, a passivation layer is formed on the surface of the anode. Since this passivation film has weak mechanical strength, the structure collapses as the charging and discharging of the battery progresses, causing a difference in local current density and forming a dendritic lithium dendrite on the surface of the lithium metal. In addition, the lithium dendrite formed in this way causes a short circuit inside the battery and dead lithium, which not only increases the physical and chemical instability of the lithium-sulfur battery, but also reduces the capacity of the battery and shortens the cycle life.

In order to solve these problems and improve the lifespan characteristics of lithium-sulfur batteries, a coating layer capable of preventing dissolution of lithium polysulfide is formed on the surface of the positive electrode particle, use of a positive electrode additive capable of absorbing lithium polysulfide, and shuttle reaction control Efforts have been made to form an oxide film of the lithium anode for lithium ion anode and to use a functional electrolyte of a novel composition to suppress dissolution of polysulfide into the electrolyte, but the method is somewhat complicated. Therefore, it is necessary to develop a new technology capable of solving these problems and improving the lifespan characteristics of a lithium-sulfur battery.

Republic of Korea Patent Publication No. 10-2017-0121047

Accordingly, the present inventors have conducted multifaceted research to solve the above problem, and as a result, tellurium (Te) is included as a positive electrode additive for a lithium secondary battery, and bis (2,2,2-trifluoroethyl) is included as an electrolyte additive. ) In the case of including ether (Bis(2,2,2-trifluoroethyl)ether, BTFE), it was confirmed that the lifespan characteristics of the lithium secondary battery were improved, and the present invention was completed.

Accordingly, an object of the present invention is to provide a lithium secondary battery capable of implementing excellent lifespan characteristics.

In order to achieve the above object,

The present invention is a positive electrode; cathode; a separation membrane interposed therebetween; And a lithium secondary battery comprising an electrolyte,

The positive electrode includes a positive electrode active material and a positive electrode additive,

The positive electrode additive includes tellurium,

The electrolyte includes a lithium salt, an organic solvent and an electrolyte additive,

The electrolyte solution additive aims to provide a lithium secondary battery containing bis (2,2,2-trifluoroethyl) ether.

The positive electrode may include a current collector and a positive active material layer disposed on at least one surface of the current collector, and the positive active material layer may include a positive active material and tellurium.

The tellurium may be included in an amount of 1 to 10% by weight based on 100% by weight of the total weight of the positive electrode active material layer.

The positive active material may include at least one selected from the group consisting of elemental sulfur and sulfur compounds.

The bis(2,2,2-trifluoroethyl)ether may be included in an amount of 1 to 20% by volume based on 100% by volume of the total electrolyte.

The organic solvent may include a cyclic ether and an acyclic ether.

The cyclic ether is furan, 2-methylfuran, 3-methylfuran, 2-ethylfuran, 2-propylfuran, 2-butylfuran, 2,3-dimethylfuran, 2,4-dimethylfuran, 2,5-dimethyl Furan, pyran, 2-methylpyran, 3-methylpyran, 4-methylpyran, benzofuran, 2-(2-nitrovinyl)furan, tetrahydrofuran, 2-methyl tetrahydrofuran, 2,5-dimethyl tetrahydro group consisting of furan, 2,5-dimethoxy tetrahydrofuran, 2-ethoxy tetrahydrofuran, tetrahydropyran, 1,2-dimethoxy benzene, 1,3-dimethoxy benzene and 1,4-dimethoxy benzene It may include one or more selected from.

The acyclic ether is dimethyl ether, diethyl ether, dipropyl ether, methylethyl ether, methylpropyl ether, ethylpropyl ether, dimethoxyethane, diethoxyethane, methoxyethoxyethane, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol methylethyl ether, triethylene glycol dimethyl ether, triethylene glycol diethyl ether, triethylene glycol methylethyl ether, tetraethylene glycol dimethyl ether, tetraethylene glycol diethyl ether, tetraethylene glycol methylethyl It may include at least one selected from the group consisting of ether, polyethylene glycol dimethyl ether, ethylene glycol diethyl ether, and ethylene glycol ethyl methyl ether.

The electrolyte may include lithium salt, 2-methylfuran, dimethoxyethane, and bis(2,2,2-trifluoroethyl)ether.

The lithium salt is LiCl, LiBr, LiI, LiClO ₄ , LiBF ₄ , LiB ₁₀ Cl ₁₀ , LiB(Ph) ₄ , LiC ₄ BO ₈ , 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 , LiN(C ₂ F ₅ SO ₂ ) ₂ , LiN(SO ₂ F ) ) ₂ , it may include at least one selected from the group consisting of lithium chloroborane, lithium lower aliphatic carboxylate, lithium tetraphenyl borate, and lithium imide.

The lithium secondary battery may be a lithium-sulfur battery.

The lithium secondary battery of the present invention includes tellurium as a positive electrode additive and bis (2,2,2-trifluoroethyl) ether as an electrolyte additive to improve the efficiency of a negative electrode including lithium metal, and lithium It inhibits the dissolution of polysulfide and can form a protective layer on the surface of the anode, which is lithium metal, to suppress the generation of lithium dendrites, and side reactions with the electrolyte or lithium polysulfide on the surface of the anode and decomposition of the electrolyte can reduce As a result, it is possible to extend the cycle of reaching 80% of the initial discharge capacity of the lithium secondary battery, thereby improving the lifespan characteristics of the lithium secondary battery.

1 is a graph of measuring the lifespan characteristics of lithium-sulfur batteries of Examples 1 to 3 and Comparative Examples 1 to 3;
2 is a graph evaluating the lifespan characteristics of the lithium-sulfur battery of Example 4.
3 is a graph of measuring the cycle voltage of the lithium-sulfur battery of Example 1.
4 is a graph of measuring the cycle voltage of the lithium-sulfur battery of Example 4.
5 is a graph measuring the lifespan characteristics of the lithium-sulfur battery of Example 5;
6 is a graph measuring the initial coulombic efficiency of the lithium-sulfur battery of Example 3.
7 is a graph of measuring initial coulombic efficiencies of lithium-sulfur batteries of Examples 1 to 3 and Comparative Example 3. FIG.

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

The terms or words used in the present specification and claims should not be construed in their ordinary or dictionary meanings, and the principle that the inventor may appropriately define the concept of the term in order to best describe his invention. It should be interpreted as meaning and concept consistent with the technical idea of the present invention based on the

The terms used in the present invention are only used to describe specific embodiments, and are not intended to limit the present invention. The singular expression includes the plural expression unless the context clearly dictates otherwise. In the present invention, terms such as 'comprising' or 'having' are intended to designate the existence of features, numbers, steps, operations, components, parts, or combinations thereof described in the specification, but one or more other features It is to be understood that it does not preclude the possibility of the presence or addition of figures, numbers, steps, operations, components, parts, or combinations thereof.

As used herein, the term “composite” refers to a material in which two or more materials are combined to form different phases physically and chemically, while exhibiting more effective functions.

As used herein, the term “polysulfide” refers to “polysulfide ions (S _x ^2- , x = 8, 6, 4, 2))” and “lithium polysulfide (Li ₂ S _x or LiS _x ⁻ , x = 8, 6, 4, 2)" is a concept inclusive of all.

Among lithium secondary batteries, lithium-sulfur batteries have high theoretical discharge capacity and theoretical energy density among various secondary batteries, and sulfur, which is used as the main material of the positive electrode active material, is in the spotlight as a next-generation secondary battery due to its abundant reserves, low cost, and environmental friendliness. are receiving

Lithium-sulfur batteries exhibit high theoretical discharge capacity and theoretical energy density among various secondary batteries, and lithium metal, which is mainly used as an anode active material, has a very small atomic weight (6.94 g/a.u.) and density (0.534 g/cm 3 ). And it is easy to reduce the weight, so it is spotlighted as a next-generation battery.

However, as described above, lithium metal has high reactivity, and as it easily reacts with the electrolyte, a passivation film is formed on the surface of the lithium metal due to the spontaneous decomposition of the electrolyte, which causes a non-uniform electrochemical reaction on the surface of the lithium metal. and lithium dendrites to reduce the efficiency and stability of the negative electrode. In addition, in a lithium-sulfur battery using a sulfur-based material as a positive electrode active material, the oxidation number of sulfur in lithium polysulfide (Li ₂ S _x , x = 8, 6, 4, 2) formed in the positive electrode when the battery is driven High lithium polysulfide (Li ₂ S _x , usually x≥4) has high solubility in the electrolyte, so it continuously melts, elutes out of the positive electrode reaction region and moves to the negative electrode. At this time, lithium polysulfide eluted from the positive electrode causes a side reaction with lithium metal, which causes lithium sulfide to adhere to the surface of the lithium metal, causing passivation of the electrode. % can be implemented, and as the cycle progresses, the capacity and charge/discharge efficiency decrease rapidly, resulting in low battery lifespan characteristics.

To this end, in the prior art, a method of forming a protective layer on the surface of the lithium metal or changing the composition of the electrolyte in order to secure the uniform reactivity of the surface of the lithium metal and suppress the growth of lithium dendrites has been attempted. However, in the case of a protective layer introduced to the surface of lithium metal, high mechanical strength for suppressing lithium dendrite and high ionic conductivity for lithium ion transport are required at the same time, but the mechanical strength and ionic conductivity are in a trade-off ), it is difficult to simultaneously improve the mechanical strength and ionic conductivity, so the lithium stability improvement effect of the lithium metal protective layer proposed so far is not excellent. In addition, the practical application is not easy because it causes serious problems in the performance and driving stability of the battery due to the compatibility problem with other elements constituting the battery.

Accordingly, in the present invention, tellurium is included as a positive electrode additive and bis (2,2,2-trifluoroethyl) ether is included as an electrolyte additive to suppress the elution of lithium polysulfide, and lithium metal as a negative electrode in the initial discharge stage An attempt was made to improve the lifespan characteristics of a lithium secondary battery, preferably a lithium-sulfur battery, by forming a protective film (solid electrolyte interface, SEI layer) on the surface to solve the above problems.

The present invention is a positive electrode; cathode; a separation membrane interposed therebetween; And to a lithium secondary battery comprising an electrolyte,

The positive electrode includes a positive electrode active material and a positive electrode additive,

The positive electrode additive includes tellurium (Te),

The electrolyte includes a lithium salt, an organic solvent and an electrolyte additive,

The electrolyte additive includes bis(2,2,2-trifluoroethyl)ether (Bis(2,2,2-trifluoroethyl)ether, BTFE).

The positive electrode may include a positive electrode current collector and a positive electrode active material layer disposed on at least one surface of the positive electrode current collector, and the positive electrode active material layer includes a positive electrode active material and a positive electrode additive.

The positive electrode additive of the present invention includes tellurium (Te).

The tellurium reacts with lithium polysulfide to form polytellurosulfide ions (S _x Te _y ^2- ), and the polytellurosulfide ions are dissolved in an electrolyte and move to lithium metal, which is the negative electrode, to form lithium thiotelluride or It contributes to the formation of a protective layer of the negative electrode made of lithium telluride. Accordingly, an improved stripping/plating process may be performed on the surface of the lithium metal, which is an anode. The protective layer allows the lithium metal to be plated at a higher density, and has an effect of suppressing unnecessary decomposition of the electrolyte or loss of lithium. Accordingly, the efficiency and stability of the negative electrode are improved, and the lifespan characteristics of a lithium secondary battery including the same, preferably a lithium-sulfur battery, can be increased.

In the positive electrode of the lithium secondary battery of the present invention, the positive electrode additive, tellurium, may be included in an amount of 1 to 10% by weight, preferably 3 to 7% by weight, based on 100% by weight of the total weight of the positive electrode active material layer. In the case of tellurium, the initial coulombic efficiency may decrease as the content of tellurium increases in the range of 1 to 10% by weight, but even if the initial coulombic efficiency decreases, the lifespan characteristics of the lithium-sulfur battery may be improved. If the tellurium content is less than 1% by weight, the effect of improving the life characteristics of the lithium secondary battery is insignificant. have.

The positive electrode current collector is not particularly limited as long as it supports the positive electrode active material and has high conductivity without causing a chemical change in the battery. For example, copper, stainless steel, aluminum, nickel, titanium, palladium, fired carbon, a copper or stainless steel surface treated with carbon, nickel, silver, etc., an aluminum-cadmium alloy, etc. may be used.

The positive electrode current collector may form fine irregularities on its surface to enhance bonding strength with the positive electrode active material, and various forms such as films, sheets, foils, meshes, nets, porous bodies, foams, and nonwovens may be used.

The positive active material may include at least one selected from the group consisting of elemental sulfur (S ₈ ) and sulfur compounds. preferably from the group consisting of inorganic sulfur, Li ₂ S _n (n≧1), disulfide compounds, organosulfur compounds and carbon-sulfur polymers ((C ₂ S _x ) _n , x=2.5 to 50, n≧2). It may include one or more selected from, and most preferably, the positive active material may include inorganic sulfur.

Accordingly, the lithium secondary battery of the present invention may be a lithium-sulfur battery.

In the case of sulfur contained in the positive electrode active material, since it does not have electrical conductivity alone, it is used in combination with a conductive material such as carbon material. Accordingly, the sulfur is included in the form of a sulfur-carbon composite, and preferably, the cathode active material may be a sulfur-carbon composite.

The sulfur-carbon composite includes a porous carbon material that not only provides a framework in which the above-described sulfur can be uniformly and stably fixed, but also compensates for the low electrical conductivity of sulfur so that the electrochemical reaction can proceed smoothly.

The porous carbon material may be generally prepared by carbonizing precursors of various carbon materials. The porous carbon material includes non-uniform pores therein, and the average diameter of the pores is in the range of 1 to 200 nm, and the porosity or porosity may be in the range of 10 to 90% of the total volume of the porous carbon material. If the average diameter of the pores is less than the above range, impregnation of sulfur is impossible because the pore size is only at the molecular level. Not desirable.

The shape of the porous carbon material is spherical, rod-shaped, needle-shaped, plate-shaped, tube-shaped or bulk-shaped, as long as it is commonly used in lithium-sulfur batteries, and may be used without limitation.

The porous carbon material may have a porous structure or a high specific surface area, so long as it is commonly used in the art. For example, the porous carbon material may include graphite; graphene; carbon black such as denka black, acetylene black, ketjen black, channel black, furnace black, lamp black, and summer black; carbon nanotubes (CNTs) such as single-walled carbon nanotubes (SWCNTs) and multi-walled carbon nanotubes (MWCNTs); carbon fibers such as graphite nanofibers (GNF), carbon nanofibers (CNF), and activated carbon fibers (ACF); It may be at least one selected from the group consisting of graphite and activated carbon, such as natural graphite, artificial graphite, and expanded graphite, but is not limited thereto. Preferably, the porous carbon material may be carbon nanotubes.

In the sulfur-carbon composite, the sulfur is located on at least one of the inner and outer surfaces of the porous carbon material, for example, less than 100%, preferably 1 to 95%, of the entire inner and outer surfaces of the porous carbon material, More preferably, it may be present in the region of 40 to 96%. When the sulfur is present on the inner and outer surfaces of the porous carbon material within the above range, the maximum effect may be exhibited in terms of electron transport area and wettability with the electrolyte. Specifically, since the sulfur is thinly and evenly impregnated on the inner and outer surfaces of the porous carbon material in the above-mentioned range region, it is possible to increase the electron transport contact area in the charge/discharge process. If the sulfur is located in 100% of the entire inner and outer surfaces of the porous carbon material, the porous carbon material is completely covered with sulfur, so the wettability to the electrolyte is lowered and the contact property is lowered, so that the electron transfer is not received and the electrochemical reaction will not be able to participate in

The sulfur-carbon composite may include 65 to 90% by weight of the sulfur, preferably 70 to 85% by weight, more preferably 72 to 80% by weight based on 100% by weight of the sulfur-carbon composite. When the sulfur content is less than the above-mentioned range, the specific surface area increases as the content of the porous carbon material in the sulfur-carbon composite is relatively increased, so that the content of the binder increases when the positive electrode is manufactured. An increase in the amount of the binder used may eventually increase the sheet resistance of the positive electrode and act as an insulator to prevent electron pass, thereby degrading the performance of the battery. Conversely, when the sulfur content exceeds the above-mentioned range, the sulfur, which cannot be combined with the porous carbon material, aggregates with each other or re-elutes to the surface of the porous carbon material, making it difficult to receive electrons and thus not participating in the electrochemical reaction of the battery. Capacity loss may occur.

The method for preparing the sulfur-carbon composite of the present invention is not particularly limited in the present invention, and methods commonly used in the art may be used. As an example, a method of simply mixing the sulfur and the porous carbon material and then heat-treating the compound may be used.

The positive active material may further include one or more selected from transition metal elements, ² elements, ₃ elements, sulfur compounds of these elements, and alloys of these elements and sulfur in addition to the above-described composition.

Examples of the transition metal element include Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Os, Ir, Pt, Au or Hg and the like are included, and the ² group element includes Al, Ga, In, Ti, and the like, and the ₃ group element may include Ge, Sn, Pb, and the like.

In the positive electrode of the lithium secondary battery of the present invention, the positive active material may be included in an amount of 50 to 95% by weight based on 100% by weight of the total of the positive active material layer constituting the positive electrode of the lithium secondary battery. The content of the positive active material may be, based on 100% by weight of the total of the positive active material layer, a lower limit of 70% by weight or more or 85% by weight or more, and an upper limit of 99% by weight or less or 90% by weight or less. The content of the positive active material may be set as a combination of the lower limit and the upper limit. When the content of the positive active material is less than the above range, it is difficult to sufficiently exhibit the electrochemical reaction of the electrode. On the contrary, when the content of the positive active material exceeds the above range, there is a problem in that the physical properties of the electrode are deteriorated because the content of the binder is relatively insufficient.

In addition, the positive active material layer may further include a binder and a conductive material in addition to the positive active material and tellurium.

The binder may be additionally used to adhere the positive electrode active material and tellurium well to the positive electrode current collector.

The binder maintains the positive electrode active material on the positive electrode current collector and organically connects the positive electrode active materials to increase the binding force therebetween, and any binder known in the art may be used.

For example, the binder is polyvinylidene fluoride (PVDF), polyvinyl alcohol (PVA), polyacrylic acid (PAA), polyacrylic acid metal salt (Metal-PAA), polymethacrylic acid (PMA), polymethyl methacrylate ( PMMA) polyacrylamide (PAM), polymethacrylamide, polyacrylonitrile (PAN), polymethacrylonitrile, polyimide (PI), chitosan, starch, polyvinylpyrrolidone, tetrafluoro ethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene-butadiene rubber (SBR), fluororubber, hydroxypropyl cellulose, regenerated cellulose, and various copolymers thereof. However, the present invention is not limited thereto.

The content of the binder may be 1 to 10% by weight based on 100% by weight of the total of the positive active material layer constituting the positive electrode for a lithium secondary battery. If the content of the binder is less than the above range, the physical properties of the positive electrode may be deteriorated and the positive electrode active material may fall off, and if it exceeds the above range, the ratio of the positive electrode active material in the positive electrode may be relatively decreased to reduce the battery capacity. It is desirable to determine the appropriate content in

In addition, the conductive material may be additionally used to further improve the conductivity of the positive electrode active material.

The conductive material electrically connects the electrolyte and the positive electrode active material to serve as a path for electrons to move from the current collector to the positive electrode active material, and may be used without limitation as long as it has conductivity.

For example, the conductive material may include graphite such as natural graphite and artificial graphite; carbon black such as Super-P (Super-P), Denka Black, Acetylene Black, Ketjen Black, Channel Black, Furnace Black, Lamp Black, and Summer Black; carbon derivatives such as carbon nanotubes and fullerenes; conductive fibers such as carbon fibers and metal fibers; carbon fluoride; A metal powder such as aluminum or nickel powder or a conductive polymer such as polyaniline, polythiophene, polyacetylene, or polypyrrole may be used alone or in combination.

The conductive material may be included in an amount of 1 to 10% by weight, preferably 4 to 7% by weight, based on 100% by weight of the total weight of the positive electrode active material layer constituting the positive electrode. When the content of the conductive material is less than the above range, electron transfer between the positive active material and the current collector is not easy, so that the voltage and capacity decrease. Conversely, when the amount exceeds the above range, the proportion of the positive electrode active material is relatively reduced, and thus the total energy (charge amount) of the battery may decrease. Therefore, it is preferable to determine an appropriate content within the above-described range.

In the present invention, the method for manufacturing the positive electrode is not particularly limited, and a method known by those skilled in the art or various methods for modifying it may be used.

For example, the positive electrode may be prepared by preparing a positive electrode slurry composition including the composition as described above and then applying it on at least one surface of the positive electrode current collector.

The positive electrode slurry composition includes the positive electrode active material and tellurium as described above, and may further include a binder, a conductive material, and a solvent.

As the solvent, one capable of uniformly dispersing the positive electrode active material, tellurium, a conductive material, and a binder is used. As such a solvent, water is most preferable as an aqueous solvent, and in this case, the water may be distilled water or deionzied water. However, the present invention 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 preferably, these may be used by mixing with water.

The content of the solvent may be contained at a level having a concentration capable of facilitating coating, and the specific content varies depending on the application method and apparatus.

The positive electrode slurry composition may additionally include, if necessary, a material commonly used in the relevant technical field for the purpose of improving its function. For example, a viscosity modifier, a fluidizing agent, a filler, etc. are mentioned.

The method of applying the positive electrode slurry composition is not particularly limited in the present invention, and for example, methods such as doctor blade, die casting, comma coating, screen printing, etc. can In addition, after forming on a separate substrate, the positive electrode slurry may be applied on the positive electrode current collector by pressing or lamination.

After the application, a drying process for removing the solvent may be performed. The drying process is performed at a temperature and time at a level sufficient to remove the solvent, and the conditions may vary depending on the type of the solvent, so the present invention is not particularly limited. As an example, drying by hot air, hot air, low-humidity air, vacuum drying, (far) infrared rays and a drying method by irradiation with an electron beam, etc. are mentioned. The drying rate is usually adjusted to remove the solvent as quickly as possible within a speed range such that the positive electrode active material layer is not cracked or the positive electrode active material layer is not peeled off from the positive electrode current collector due to stress concentration.

Additionally, the density of the positive electrode active material in the positive electrode may be increased by pressing the current collector after drying. Methods, such as a die press and roll press, are mentioned as a press method.

The electrolyte includes a lithium salt, an organic solvent, and an electrolyte additive.

The electrolyte additive includes bis(2,2,2-trifluoroethyl)ether (Bis(2,2,2-trifluoroethyl)ether, BTFE).

The bis(2,2,2-trifluoroethyl)ether has low solubility in lithium polysulfide. Accordingly, the elution of lithium polysulfide is suppressed, and a protective layer can be formed on the surface of the negative electrode in the initial discharge stage of a lithium secondary battery, specifically, a lithium-sulfur battery. Accordingly, a side reaction between lithium polysulfide and lithium metal as an anode can be effectively suppressed, thereby reducing the shuttle phenomenon caused by lithium polysulfide, thereby improving the lifespan characteristics of a lithium-sulfur battery.

The bis (2,2,2-trifluoroethyl) ether is included in an amount of 1 to 20% by volume, preferably 5 to 15% by volume, more preferably 7 to 12% by volume based on 100% by volume of the total electrolyte. can

When the bis (2,2,2-trifluoroethyl) ether is contained in an amount of less than 1% by volume, the effect of improving the life characteristics of the lithium-sulfur battery is insignificant, and when it exceeds 20% by volume, an overvoltage is formed, resulting in high rate discharge capacity and There may be a problem that the output characteristics are reduced.

The total 100% by volume of the electrolyte means the volume of the liquid excluding the lithium salt.

The lithium salt is included as an electrolyte salt of the electrolyte, and the type of the lithium salt is not particularly limited in the present invention, and may be used without limitation as long as it is commonly used in a lithium-sulfur battery.

For example, the lithium salt is LiCl, LiBr, LiI, LiClO ₄ , LiBF ₄ , LiB ₁₀ Cl ₁₀ , LiB(Ph) ₄ , LiC ₄ BO ₈ , 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 , LiN(C ₂ F ₅ SO ₂ ) ₂ , LiN (SO ₂ F) ₂ , chloroborane lithium, lower aliphatic lithium carboxylate, lithium tetraphenyl borate and at least one selected from the group consisting of lithium imide, preferably (SO ₂ F) ₂ NLi ( lithium bis(fluorosulfonyl)imide; LiFSI).

The concentration of the lithium salt may be appropriately determined in consideration of ionic conductivity, solubility, and the like, and may be, for example, 0.1 to 4.0 M, preferably 0.5 to 2.0 M. When the concentration of the lithium salt is less than the above range, it is difficult to secure ionic conductivity suitable for battery driving. Since the performance of the battery may be deteriorated, it is appropriately adjusted within the above range.

The organic solvent is a medium through which ions involved in the electrochemical reaction of the lithium secondary battery can move and includes the organic solvent.

The organic solvent includes cyclic ethers and acyclic ethers.

The ether-based compound maintains solubility in sulfur or a sulfur-based compound while ensuring electrochemical stability within the driving voltage range of the battery, and relatively less occurrence of side reactions with intermediate products according to the driving of the battery.

The cyclic ether is furan, 2-methylfuran, 3-methylfuran, 2-ethylfuran, 2-propylfuran, 2-butylfuran, 2,3-dimethylfuran, 2,4-dimethylfuran, 2,5-dimethyl Furan, pyran, 2-methylpyran, 3-methylpyran, 4-methylpyran, benzofuran, 2-(2-nitrovinyl)furan, tetrahydrofuran, 2-methyl tetrahydrofuran, 2,5-dimethyl tetrahydro group consisting of furan, 2,5-dimethoxy tetrahydrofuran, 2-ethoxy tetrahydrofuran, tetrahydropyran, 1,2-dimethoxy benzene, 1,3-dimethoxy benzene and 1,4-dimethoxy benzene It may include one or more selected from. Preferably, it may contain 2-methylfuran.

The dioxolane-based compound mainly used in the cyclic ether has an excessively high solubility in lithium polysulfide, which is very likely to cause a shuttle phenomenon, and accelerates the loss of sulfur, which is a positive electrode active material, thereby reducing the lifespan performance of a lithium secondary battery. . Therefore, the dioxolane-based compound is not preferable for use as an organic solvent of the lithium secondary battery electrolyte of the present invention.

The acyclic ether is dimethyl ether, diethyl ether, dipropyl ether, methylethyl ether, methylpropyl ether, ethylpropyl ether, dimethoxyethane, diethoxyethane, methoxyethoxyethane, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol methylethyl ether, triethylene glycol dimethyl ether, triethylene glycol diethyl ether, triethylene glycol methylethyl ether, tetraethylene glycol dimethyl ether, tetraethylene glycol diethyl ether, tetraethylene glycol methylethyl It may include one or more selected from the group consisting of ether, polyethylene glycol dimethyl ether, ethylene glycol diethyl ether, and ethylene glycol ethyl methyl ether, preferably dimethyl ether.

The cyclic ether and the acyclic ether may be mixed and used in a volume ratio of 1:9 to 9:1, preferably 1:2 to 1:5.

The electrolyte of the lithium secondary battery of the present invention may preferably include lithium salt, 2-methylfuran, dimethoxyethane and bis(2,2,2-trifluoroethyl)ether.

In addition, the electrolyte of the lithium secondary battery of the present invention may further include an organic solvent commonly used in the electrolyte of a lithium secondary battery. For example, it may further include one or more selected from the group consisting of an ester compound, an amide compound, a linear carbonate compound, and a cyclic carbonate compound.

The ester compounds include methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, γ-valerolactone, γ-caprolactone, σ-valero At least one selected from the group consisting of lactone and ε-caprolactone may be used, but is not limited thereto.

The linear carbonate compound may include at least one selected from the group consisting of dimethyl carbonate, diethyl carbonate, dipropyl carbonate, ethylmethyl carbonate, methylpropyl carbonate, and ethylpropyl carbonate, but is not limited thereto.

Examples of the cyclic carbonate compound include ethylene carbonate, propylene carbonate, 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2-pentylene carbonate, 2,3-pentylene carbonate, vinylene carbonate, vinylethylene It may include one or more selected from the group consisting of carbonates and halides thereof, but is not limited thereto.

The electrolyte of the lithium secondary battery of the present invention may further include nitric acid or a nitrite-based compound in addition to the above-described composition. The nitric acid or nitrite-based compound has the effect of forming a stable film on the lithium metal electrode, which is the negative electrode, and improving the charge/discharge efficiency.

The nitric acid or nitrite-based compound is not particularly limited in the present invention, but lithium nitrate (LiNO ₃ ), potassium nitrate (KNO ₃ ), cesium nitrate (CsNO ₃ ), barium nitrate (Ba(NO ₃ ) ₂ ), ammonium nitrate (NH ₄ NO ₃ ), lithium nitrite (LiNO ₂ ), potassium nitrite (KNO ₂ ), cesium nitrite (CsNO ₂ ), ammonium nitrite (NH ₄ NO ₂ ), such as inorganic nitric acid or nitrite compounds; Organic nitric acids such as methyl nitrate, dialkyl imidazolium nitrate, guanidine nitrate, imidazolium nitrate, pyridinium nitrate, ethyl nitrite, propyl nitrite, butyl nitrite, pentyl nitrite, and octyl nitrite or a nitrite compound; One selected from the group consisting of organic nitro compounds such as nitromethane, nitropropane, nitrobutane, nitrobenzene, dinitrobenzene, nitropyridine, dinitropyridine, nitrotoluene, dinitrotoluene, and combinations thereof is possible, preferably uses lithium nitrate.

In addition, the electrolyte of the present invention may further include other additives for the purpose of improving charge/discharge characteristics, flame retardancy, and the like. Examples of the additive include pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylene diamine, n-glyme, hexaphosphoric acid triamide, nitrobenzene derivative, sulfur, quinone imine dye, N-substituted oxazoli Dinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxy ethanol, aluminum trichloride, fluoroethylene carbonate (FEC), propene sultone (PRS), vinylene carbonate ( VC) and the like.

The injection of the electrolyte may be performed at an appropriate stage during the manufacturing process of the electrochemical device according to the manufacturing process and required properties of the final product. That is, it may be applied before assembling the electrochemical device or in the final stage of assembling the electrochemical device.

The negative electrode of the lithium secondary battery of the present invention may include a negative electrode current collector and a negative electrode active material layer coated on one or both surfaces of the negative electrode current collector. Alternatively, the negative electrode may be a lithium metal plate.

The negative electrode current collector is for supporting the negative electrode active material layer, as described in the positive electrode current collector.

The anode active material layer may include a conductive material, a binder, etc. in addition to the anode active material. In this case, the conductive material and the binder are as described above.

The negative active material is a material capable of reversibly intercalating or deintercalating lithium (Li ⁺ ), a material capable of reversibly forming a lithium-containing compound by reacting with lithium ions, lithium metal or a lithium alloy. may include

The material capable of reversibly intercalating or deintercalating lithium ions (Li ⁺ ) may be, for example, crystalline carbon, amorphous carbon, or a mixture thereof. The material capable of reversibly forming a lithium-containing compound by reacting with the lithium ions (Li ⁺ ) may be, for example, tin oxide, titanium nitrate, or silicon. The lithium alloy is, for example, lithium (Li) and sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), francium (Fr), beryllium (Be), magnesium (Mg), calcium ( Ca), strontium (Sr), barium (Ba), radium (Ra), aluminum (Al), and may be an alloy of a metal selected from the group consisting of tin (Sn).

Preferably, the anode active material may be lithium metal, and specifically may be in the form of a lithium metal thin film or lithium metal powder.

The method of forming the negative active material is not particularly limited, and a method of forming a layer or a film commonly used in the art may be used. For example, a method such as pressing, coating, or vapor deposition may be used. In addition, a case in which a metal lithium thin film is formed on a metal plate by initial charging after assembling the battery in a state in which there is no lithium thin film in the current collector is also included in the negative electrode of the present invention.

The separator may be positioned between the anode and the cathode.

The separator separates or insulates the positive electrode and the negative electrode from each other, and enables lithium ion transport between the positive electrode and the negative electrode, and may be made of a porous non-conductive or insulating material. can be used without The separator may be an independent member such as a film, or may be a coating layer added to the positive electrode and/or the negative electrode.

As the separation membrane, it is preferable that the electrolyte has a low resistance to ion movement and has excellent moisture content to the electrolyte.

The separator may be made of a porous substrate. The porous substrate can be used as long as it is a porous substrate commonly used in secondary batteries, and a porous polymer film can be used alone or by laminating them, for example, a high melting point. A nonwoven fabric made of glass fiber, polyethylene terephthalate fiber, or the like, or a polyolefin-based porous membrane may be used, but the present invention is not limited thereto.

The material of the porous substrate is not particularly limited in the present invention, and any porous substrate commonly used in electrochemical devices may be used. For example, the porous substrate may include polyolefin such as polyethylene and polypropylene, polyester such as polyethyleneterephthalate, and polybutyleneterephthalate, and poly amide, polyacetal, polycarbonate, polyimide, polyetheretherketone, polyethersulfone, polyphenyleneoxide, polyphenylenesulfide (polyphenylenesulfide), polyethylenenaphthalate (polyethylenenaphthalate), polytetrafluoroethylene (polytetrafluoroethylene), polyvinylidene fluoride (polyvinylidenefluoride), polyvinyl chloride (polyvinyl chloride), polyacrylonitrile, cellulose (cellulose), nylon (nylon), polyparaphenylenebenzobisoxazole (poly(p-phenylene benzobisoxazole) and polyarylate (polyarylate) may include at least one material selected from the group consisting of.

The thickness of the porous substrate is not particularly limited, but may be 1 to 100 μm, preferably 5 to 50 μm. Although the thickness range of the porous substrate is not limited to the above-mentioned range, when the thickness is too thin than the above-described lower limit, mechanical properties are deteriorated and the separator may be easily damaged during use of the battery.

The average diameter and pore size of the pores present in the porous substrate are also not particularly limited, but may be 0.001 to 50 μm and 10 to 95%, respectively.

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

The shape of the lithium secondary battery is not particularly limited, and may have various shapes such as a cylindrical shape, a stacked type, and a coin type.

The lithium secondary battery of the present invention, specifically, the lithium-sulfur battery includes tellurium as a positive electrode additive. The tellurium contributes to the formation of a protective layer on the surface of the anode in the initial discharging stage of the lithium-sulfur battery, so that an improved stripping/plating process can be performed on the surface of the anode. As a result, the efficiency and stability of the negative electrode may be improved, thereby improving the lifespan characteristics of the lithium-sulfur battery.

In addition, the lithium-sulfur battery of the present invention includes bis(2,2,2-trifluoroethyl)ether as an electrolyte additive. The bis(2,2,2-trifluoroethyl) ether inhibits the elution of lithium polysulfide, and forms a protective layer on the surface of the negative electrode in the initial discharging stage of the lithium-sulfur battery to form a protective layer on the negative electrode surface with lithium polysulfide and lithium metal as the negative electrode. It is possible to effectively suppress side reactions between the lithium-sulfur batteries, thereby improving the lifespan characteristics of the lithium-sulfur battery.

Accordingly, the lithium secondary battery of the present invention has an effect of improving lifespan characteristics, and specifically, it is possible to extend the number of cycles in which the discharge capacity reaches 80% of the initial discharge capacity.

Hereinafter, preferred examples are presented to help the understanding of the present invention, but the following examples are merely illustrative of the present invention, and it will be apparent to those skilled in the art that various changes and modifications are possible within the scope and spirit of the present invention, It goes without saying that such variations and modifications fall within the scope of the appended claims.

<Production of lithium-sulfur battery>

Example 1.

A mixed solution was prepared by mixing a sulfur-carbon (CNT) composite (S:C=75:25 (weight ratio)) and 3 wt% lithium-polyacrylic acid (Li-PAA) aqueous solution as a cathode active material. Then, tellurium (Te) powder was added to the mixed solution. At this time, the weight ratio of the sulfur-carbon composite, the lithium-polyacrylic acid solid content and the tellurium was 90:5:5. Water was further added thereto and mixed to prepare a positive electrode slurry having a solid content of 32 wt%.

The positive electrode slurry was applied on an aluminum foil current collector and then coated to a predetermined thickness using a Mathis coater (Mathis Switzerland, SV-M). Thereafter, the cathode was prepared by drying at a temperature of 50° C. for 2 hours.

The loading amount of the positive electrode was 3.3 mAh/cm ² , and the porosity was 73%.

0.75 M LiFSI and 4 wt% of lithium nitrate (LiNO ₃ ) were mixed with 2-methylfuran (2-methylfuran, 2-MeF), bis (2,2,2-trifluoroethyl) ether (Bis (2,2, An electrolyte solution was prepared by dissolving 2-trifluoroethyl)ether, BTFE) and 1,2-dimethoxyethane (1,2-dimethoxyethane, DME) in an organic solvent mixed in a volume of 2:1:7. At this time, the bis (2,2,2-trifluoroethyl) ether is included in an amount of 10% by volume based on the total volume of the electrolyte.

A lithium-sulfur battery is prepared by placing the prepared positive electrode and the negative electrode to face each other, interposing a polyethylene separator having a thickness of 16 μm and a porosity of 45% between them, putting it in an aluminum pouch, injecting the electrolyte and sealing it did.

In this case, a lithium metal thin film having a thickness of 30 μm was used as the negative electrode.

Example 2.

A lithium-sulfur battery was prepared in the same manner as in Example 1, except that the weight ratio of the sulfur-carbon composite, lithium-polyacrylic acid, and tellurium was 85:5:10.

Example 3.

A lithium-sulfur battery was manufactured in the same manner as in Example 1, except that the weight ratio of the sulfur-carbon composite, lithium-polyacrylic acid and tellurium was 80:5:15.

Example 4.

2-methylfuran (2-MeF), bis(2,2,2-trifluoroethyl)ether (Bis(2,2,2-trifluoroethyl)ether, BTFE) and 1,2-dimethoxy A lithium-sulfur battery was prepared in the same manner as in Example 1, except that ethane (1,2-dimethoxyethane, DME) was mixed in a volume of 20:25:55.

Example 5.

1,3-dioxolane (DOL), bis(2,2,2-trifluoroethyl)ether (Bis(2,2,2-trifluoroethyl)ether, BTFE) and 1,2- A lithium-sulfur battery was prepared in the same manner as in Example 1, except that dimethoxyethane (1,2-dimethoxyethane, DME) was mixed in a volume of 40:10:50.

Comparative Example 1.

A mixed solution was prepared by mixing a sulfur-carbon (CNT) composite (S:C=75:25 (weight ratio)) and 3 wt% lithium-polyacrylic acid (Li-PAA) aqueous solution as a cathode active material. At this time, the weight ratio of the solid content of the sulfur-carbon composite and lithium-polyacrylic acid was 95:5. Water was further added thereto and mixed to prepare a positive electrode slurry having a solid content of 32 wt%.

The positive electrode slurry was applied on an aluminum foil current collector and then coated to a predetermined thickness using a Mathis coater (Mathis Switzerland, SV-M). Thereafter, the cathode was prepared by drying at a temperature of 50° C. for 2 hours.

The loading amount of the positive electrode was 3.3 mAh/cm ² , and the porosity was 73%.

0.75 M LiFSI and 4 wt% of lithium nitrate (LiNO ₃ ) were mixed with 2-methylfuran (2-methylfuran, 2-MeF) and 1,2-dimethoxyethane (DME) in a 1:4 ratio An electrolyte solution was prepared by dissolving in an organic solvent mixed by volume.

A lithium-sulfur battery was prepared by placing the prepared positive electrode and the negative electrode to face each other and interposing a polyethylene separator having a thickness of 16 μm and a porosity of 45% therebetween, and then injecting the electrolyte.

In this case, a lithium metal thin film having a thickness of 30 μm was used as the negative electrode.

Comparative Example 2.

0.75 M LiFSI and 4 wt% of lithium nitrate (LiNO ₃ ) were mixed with 2-methylfuran (2-methylfuran, 2-MeF) and 1,2-dimethoxyethane (DME) in a 1:4 ratio A lithium-sulfur battery was prepared in the same manner as in Example 1, except that an electrolyte was prepared by dissolving it in an organic solvent mixed by volume.

Comparative Example 3.

A mixed solution was prepared by mixing a sulfur-carbon (CNT) composite (S:C=75:25 (weight ratio)) and 3 wt% lithium-polyacrylic acid (Li-PAA) aqueous solution as a cathode active material. At this time, the weight ratio of the solid content of the sulfur-carbon composite and lithium-polyacrylic acid was 95:5. Water was further added thereto and mixed to prepare a positive electrode slurry having a solid content of 32 wt%.

Except for this, a lithium-sulfur battery was prepared in the same manner as in Example 1.

Experimental Example 1. Evaluation of lifetime characteristics of lithium-sulfur batteries

For the batteries prepared in Examples 1 to 3 and Comparative Examples 1 to 3, performance was evaluated using a charge/discharge measuring device (PESCO5-0.01, PNE solution Korea).

In the first 3 cycles, the charge/discharge capacity from 2.5 to 1.8V was measured at 0.1C current density, and from the fourth cycle, the charge/discharge capacity was measured by discharging at 0.3C and charging at 0.2C. Capacity retention results were calculated using the discharge capacity of the fourth cycle of the lithium-sulfur battery of Comparative Example 1 as 100%, and the relative capacity of subsequent cycles was calculated, and was measured until the discharge capacity reached 80% (cycle@80%). .

The results are shown in Table 1 and FIG. 1 below.

cycle@80% Improvement (%) Comparative Example 1 164 cycle - Comparative Example 2 174 cycle 6.1% Comparative Example 3 163 cycle - Example 1 202 cycle 23.2% Example 2 198 cycle 20.7% Example 3 147 cycle -

From the above results, the lithium-sulfur battery of Example 1 containing tellurium in an amount of 5% by weight based on 100% by weight of the total positive active material layer, and including bis(2,2,2-trifluoroethyl)ether, has a lifespan Characteristics were greatly improved. In addition, the lithium-sulfur battery of Example 2 containing tellurium in an amount of 10% by weight based on 100% by weight of the total positive active material layer, and including bis(2,2,2-trifluoroethyl)ether, also had a lifespan characteristic. showed improved results.

On the other hand, the lithium-sulfur battery of Example 3 containing tellurium in an amount of 15% by weight based on 100% by weight of the total weight of the positive active material layer and including bis(2,2,2-trifluoroethyl)ether As the amount of tellurium exceeded the preferred content range of 1 to 10% by weight, the lifespan characteristics decreased. In addition, the lithium-sulfur battery of Comparative Example 2 containing only tellurium showed slight improvement in lifespan characteristics, and the lithium-sulfur battery of Comparative Example 3 containing only bis(2,2,2-trifluoroethyl)ether The battery did not show the effect of improving the lifespan characteristics.

Accordingly, tellurium is included as a positive electrode additive, bis (2,2,2-trifluoroethyl) ether is included as an electrolyte additive, and the amount of tellurium is 1 to 10 weight percent based on 100 weight% of the total weight of the positive electrode active material layer. %, it can be seen that the lifetime characteristics of the lithium-sulfur battery can be improved.

In addition, lifespan characteristics of the lithium-sulfur batteries of Examples 4 and 5 were measured in the same manner as above.

Example 4 is a lithium-sulfur battery using an electrolyte containing bis (2,2,2-trifluoroethyl) ether in an amount of 25% by volume, and the deterioration of life was accelerated ( FIG. 2 ). In addition, the voltages of the 5th, 15th, 25th and 35th cycles of the lithium-sulfur batteries of Examples 1 and 4 were measured. The lithium-sulfur battery of Example 1 maintains a constant cycle capacity ( FIG. 3 ), while the lithium-sulfur battery of Example 4 has a capacity that decreases as the cycle progresses, and the overvoltage at the end gradually worsens, resulting in capacity degradation. Accelerated results were shown (FIG. 4).

From the above results, including tellurium as anode additive, bis(2,2,2-trifluoroethyl)ether as electrolyte additive, and bis(2,2,2-trifluoroethyl)ether as It can be seen that when 1 to 20% by volume is included based on 100% by volume of the total electrolyte, the lifespan characteristics can be further improved.

Example 5 is a lithium-sulfur battery using 1,3-dioxolane (DOL) instead of 2-methylfuran as an electrolyte, in which 1,3-dioxolane/1,2-dimethoxyethane is used as an electrolyte solution. As a result of the lifespan characteristics of the lithium-sulfur battery of Example 5, it was seen that deterioration appeared rapidly (FIG. 5).

From the above results, even if tellurium is included as a positive electrode additive and bis(2,2,2-trifluoroethyl) ether is included as an electrolyte additive, the use of 1,3-dioxolane as an electrolyte improves the lifespan characteristics. You can see what you can't see

That is, the positive electrode additive contains tellurium in an amount of 1 to 10% by weight based on 100% by weight of the total positive electrode active material layer, and bis(2,2,2-trifluoroethyl)ether is used as an electrolyte additive in 100% by volume of the total electrolyte. When it contains 1 to 20% by volume based on and does not use a dioxolane-based compound as an electrolyte, the effect of improving the lifespan characteristics of a lithium-sulfur battery may be exhibited.

Experimental Example 2. Evaluation of initial coulombic efficiency of lithium-sulfur batteries

For the batteries prepared in Examples 1 to 3 and Comparative Example 3, the initial coulombic efficiency according to the tellurium content was evaluated using a charge/discharge measuring device (PESCO5-0.01, PNE solution Korea).

In the initial 3 cycles, the charging and discharging capacities from 2.5 to 1.8V were measured at 0.1C current density, and from the fourth cycle, the initial coulombic efficiency was measured by discharging at 0.3C and charging at 0.2C, and the results are shown in FIG. 6 and 7 shows.

The lithium-sulfur battery of Comparative Example 3 not containing tellurium showed no decrease in initial coulombic efficiency. However, the lithium-sulfur batteries of Examples 1 to 3 containing tellurium showed a decrease in initial coulombic efficiency. The lithium-sulfur batteries of Examples 1 and 2 contained tellurium in an amount of 5 and 10% by weight, respectively, based on 100% by weight of the total of the positive active material layer, and although the initial coulombic efficiency decreased, the Experimental Example 1 As shown in the results, the lifespan characteristics of the lithium-sulfur battery were improved. The lithium-sulfur battery of Example 3 contains tellurium in an amount of 15% by weight based on 100% by weight of the total amount of the positive active material layer, exceeding the tellurium content range of 1 to 10% by weight. Accordingly, the lithium-sulfur battery of Example 3 showed an excessive decrease in the initial coulombic efficiency, and the lifespan characteristics of the lithium-sulfur battery were not improved as in the result of Experimental Example 1 due to the excessive decrease in the coulombic efficiency. showed results.

From this, it can be seen that when the amount of tellurium exceeds 10% by weight based on 100% by weight of the total weight of the positive electrode active material layer, the coulombic efficiency decreases, and it can be seen that it is preferable to include tellurium in an amount of 1 to 10% by weight. there was.

Claims (11)

anode; cathode; a separation membrane interposed therebetween; And a lithium secondary battery comprising an electrolyte,
The positive electrode includes a positive electrode active material and a positive electrode additive,
The positive electrode additive includes tellurium,
The electrolyte includes a lithium salt, an organic solvent and an electrolyte additive,
The electrolyte additive is a lithium secondary battery comprising bis (2,2,2-trifluoroethyl) ether.
According to claim 1,
The positive electrode includes a positive electrode current collector and a positive electrode active material layer disposed on at least one surface of the positive electrode current collector,
The cathode active material layer is a lithium secondary battery, characterized in that it comprises a cathode active material and tellurium.
3. The method of claim 2,
The lithium secondary battery, characterized in that the tellurium is contained in 1 to 10% by weight based on 100% by weight of the total weight of the positive electrode active material layer.
According to claim 1,
The cathode active material is a lithium secondary battery, characterized in that it comprises at least one selected from the group consisting of elemental sulfur and sulfur compounds.
According to claim 1,
The bis (2,2,2-trifluoroethyl) ether is a lithium secondary battery, characterized in that it is contained in an amount of 1 to 20% by volume based on 100% by volume of the total electrolyte.
According to claim 1,
The organic solvent is a lithium secondary battery, characterized in that it comprises a cyclic ether and an acyclic ether.
7. The method of claim 6,
The cyclic ether is furan, 2-methylfuran, 3-methylfuran, 2-ethylfuran, 2-propylfuran, 2-butylfuran, 2,3-dimethylfuran, 2,4-dimethylfuran, 2,5-dimethyl Furan, pyran, 2-methylpyran, 3-methylpyran, 4-methylpyran, benzofuran, 2-(2-nitrovinyl)furan, tetrahydrofuran, 2-methyl tetrahydrofuran, 2,5-dimethyl tetrahydro group consisting of furan, 2,5-dimethoxy tetrahydrofuran, 2-ethoxy tetrahydrofuran, tetrahydropyran, 1,2-dimethoxy benzene, 1,3-dimethoxy benzene and 1,4-dimethoxy benzene A lithium secondary battery comprising at least one selected from
7. The method of claim 6,
The acyclic ether is dimethyl ether, diethyl ether, dipropyl ether, methylethyl ether, methylpropyl ether, ethylpropyl ether, dimethoxyethane, diethoxyethane, methoxyethoxyethane, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol methylethyl ether, triethylene glycol dimethyl ether, triethylene glycol diethyl ether, triethylene glycol methylethyl ether, tetraethylene glycol dimethyl ether, tetraethylene glycol diethyl ether, tetraethylene glycol methylethyl A lithium secondary battery comprising at least one selected from the group consisting of ether, polyethylene glycol dimethyl ether, ethylene glycol diethyl ether, and ethylene glycol ethyl methyl ether.
According to claim 1,
The electrolyte solution is a lithium secondary battery, characterized in that it comprises a lithium salt, 2-methylfuran, dimethoxyethane and bis (2,2,2-trifluoroethyl) ether.
According to claim 1,
The lithium salt is LiCl, LiBr, LiI, LiClO ₄ , LiBF ₄ , LiB ₁₀ Cl ₁₀ , LiB(Ph) ₄ , LiC ₄ BO ₈ , 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 , LiN(C ₂ F ₅ SO ₂ ) ₂ , LiN(SO ₂ F ) ) ₂ , Lithium secondary battery comprising at least one selected from the group consisting of lithium chloroborane, lithium lower aliphatic carboxylate, lithium tetraphenyl borate, and lithium imide.
According to claim 1,
The lithium secondary battery is a lithium secondary battery, characterized in that the lithium-sulfur battery.

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