KR102207522B1 - Electrolyte for lithium-sulfur battery and lithium-sulfur battery comprising thereof - Google Patents

Abstract

The present invention relates to a lithium-sulfur battery electrolyte and a lithium-sulfur battery comprising the same. When applied to a lithium-sulfur battery, the electrolytic solution of the present invention has less discharge overvoltage, exhibits an energy density improvement effect, and thus improves battery life characteristics. Therefore, it is desirable to improve the performance of the lithium-sulfur battery.

Description

Electrolyte for lithium-sulfur battery and lithium-sulfur battery containing the same {ELECTROLYTE FOR LITHIUM-SULFUR BATTERY AND LITHIUM-SULFUR BATTERY COMPRISING THEREOF}

The present invention relates to a lithium-sulfur battery electrolyte and a lithium-sulfur battery comprising the same.

Recently, as portable electronic devices, electric vehicles, and large-capacity power storage systems have been developed, the need for large-capacity batteries has emerged. Lithium-sulfur battery is a secondary battery that uses a sulfur-based material having an SS bond (Sulfur-sulfur bond) as a positive electrode active material and lithium metal as a negative electrode active material. Sulfur, the main material of the positive electrode active material, is very rich in resources and is toxic. It has the advantage of having a low weight per atom.

In addition, the theoretical discharge capacity of the lithium-sulfur battery is 1672mAh/g-sulfur, and the theoretical energy density is 2,600Wh/kg, and the theoretical energy density of other battery systems currently being studied (Ni-MH battery: 450Wh/kg, Li- FeS battery: 480Wh/kg, Li-MnO ₂ battery: 1,000Wh/kg, Na-S battery: 800Wh/kg), which is very high compared to), thus attracting attention as a battery having high energy density characteristics.

However, lithium-sulfur batteries have not yet been commercialized. This is because when sulfur is used as an active material, the ratio used in the electrochemical reaction (sulfur utilization rate) is low, so that sufficient capacity as the theoretical capacity is not secured, and lifespan characteristics are poor.

Various attempts have been made to overcome this problem. That is, a method of increasing the specific surface area by complexing sulfur with carbon, a method of using an electrolytic solution having a high solubility of polysulfide, a method of improving the reactivity of sulfur and polysulfide by applying an additive to the electrolytic solution, etc. are being studied.

For example, Korean Patent No. 1511206 discloses a technology for improving sulfur utilization and lifespan characteristics by suppressing elution of a sulfur compound from a positive electrode agent by including lithium polysulfide in an electrolyte.

However, these conventional techniques have a problem in that the capacity characteristics and life characteristics of the lithium-sulfur battery are not significantly improved.

Korean Patent Registration No. 1511206, "Lithium Sulfur Battery"

In order to solve the above problem, the present inventors studied the composition of an electrolyte solvent of a lithium-sulfur battery, and as a result, the present invention was completed.

Accordingly, an object of the present invention is to provide an electrolyte for a lithium-sulfur battery that improves the energy density of the battery by increasing the utilization rate of sulfur to improve discharge overvoltage.

In addition, another object of the present invention is to provide a lithium-sulfur battery comprising the electrolyte.

In order to solve the above problems, the present invention,

An ionic liquid containing sulfonium ions; And a non-aqueous solvent; It provides an electrolyte for a lithium-sulfur battery comprising a.

The ionic liquid may be included in an amount of 0.01 to 10% by weight based on 100% by weight of the electrolyte.

The sulfonium ion may be at least one selected from the group consisting of diethylmethylsulfonium and triethylsulfonium.

The non-aqueous solvent may be an ether solvent, and the ether solvent may be a linear ether, a cyclic ether, or a combination thereof.

The linear ethers are dimethyl ether, diethyl ether, dipropyl ether, dibutyl ether, diisobutyl ether, ethylmethyl ether, ethylpropyl ether, ethyl tertbutyl ether, dimethoxymethane, trimethoxymethane, dimethoxyethane, Diethoxyethane, dimethoxypropane, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, ethylene glycol divinyl ether, diethylene glycol divinyl ether, triethylene glycol di Vinyl ether, dipropylene glycol dimethylene ether, butylene glycol ether, diethylene glycol ethyl methyl ether, diethylene glycol isopropyl methyl ether, diethylene glycol butyl methyl ether, diethylene glycol tertbutyl ethyl ether, and ethylene glycol ethyl methyl It may be one or more selected from the group consisting of ether.

The cyclic ethers are dioxolane, methyldioxolane, dimethyldioxolane, vinyldioxolane, methoxydioxolane, ethylmethyldioxolane, oxane, dioxane, trioxane, tetrahydrofuran, methyltetrahydrofuran, dimethyltetra It may be one or more selected from the group consisting of hydrofuran, dimethoxytetrahydrofuran, ethoxytetrahydrofuran, dihydropyran, tetrahydropyran, furan, and methylfuran.

The electrolyte is LiCl, LiBr, LiI, LiClO ₄ , LiBF ₄ , LiB ₁₀ Cl ₁₀ , LiPF ₆ , LiCF ₃ SO ₃ , LiCF ₃ CO ₂ , LiC ₄ BO ₈ , LiAsF ₆ , LiSbF ₆ , LiAlCl ₄ , CH ₃ SO ₃ Li, CF ₃ SO ₃ Li, (CF ₃ SO ₂ ) ₂ NLi, (C ₂ F ₅ SO ₂ ) ₂ NLi, (SO ₂ F) ₂ NLi, (CF ₃ SO ₂ ) ₃ CLi, lithium bis(jade Salato)borate, lithium-oxalyldifluoroborate, lithium 4,5-dicyano-2-(trifluoromethyl)imidazole, lithium dicyanotriazolate, lithium thiocyanate, chloroborane lithium, lower grade It may further include one kind of lithium salt selected from the group consisting of aliphatic lithium carboxylic acid, lithium tetraphenylborate, lithium imide, and combinations thereof.

The lithium salt may be contained in a concentration of 0.1 to 8.0 M.

The electrolyte may further include a compound having an intramolecular N-O bond.

Compounds having NO bonds in the molecule include lithium nitrate, potassium nitrate, cesium nitrate, barium nitrate, ammonium nitrate, lithium nitrite, potassium nitrite, cesium nitrite, ammonium nitrite, methyl nitrate, dialkyl imidazolium nitrate, guanidine nitrate Rate, imidazolium nitrate, pyridinium nitrate, ethyl nitrite, propyl nitrite, butyl nitrite, pentyl nitrite, octyl nitrite, nitromethane, nitropropane, nitrobutane, nitrobenzene, dinitrobenzene, nitro It may be one or more selected from the group consisting of pyridine, dinitropyridine, nitrotoluene, dinitrotoluene, pyridine N-oxide, alkylpyridine N-oxide, and tetramethyl piperidinyloxyl.

The compound having an intramolecular N-O bond may be included in an amount of 0.01 to 10% by weight based on 100% by weight of the electrolyte.

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

When applied to a lithium-sulfur battery, the electrolytic solution of the present invention has less discharge overvoltage, exhibits an energy density improvement effect, and thus improves battery life characteristics. Therefore, it is desirable to improve the performance of the lithium-sulfur battery.

1 is an initial discharge curve of Example 1 and Comparative Example 5.
2 is a discharge curve of Examples 1 to 2 and Comparative Examples 1 to 4.
3 is a graph comparing the energy density of Examples 1 to 2 and Comparative Examples 1 to 5.
4 is a graph showing specific discharge capacity according to the number of cycles of Examples 1 to 2 and Comparative Examples 1 to 5;

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

Lithium-sulfur battery electrolyte

The present invention is an ionic liquid containing sulfonium ions; And a non-aqueous solvent; It provides an electrolyte for a lithium-sulfur battery comprising a.

The ionic liquid refers to a liquid salt, and the ionic liquid of the present invention may exist as a liquid in a wide temperature range. In particular, it is preferred to exist primarily in liquid form at the operating temperature of the battery. Specifically, the ionic liquid of the present invention exists as a liquid at a temperature of 100 °C or less, preferably 50 °C or less, more preferably 25 °C or less.

The present inventors studied the composition of an electrolyte solution capable of improving the reactivity of sulfur, a positive electrode active material of a lithium-sulfur battery, and as a result, improved energy density and lifespan when a predetermined amount of an ionic liquid containing sulfonium ions as a cation is added to the electrolyte. It was confirmed that the characteristics and discharge overvoltage improvement effect was exhibited.

This effect is not at all when an ionic liquid containing cations other than sulfonium ions, i.e., imidazolium, pyrrolidinium, pyridinium, piperidinium series, which are widely known as ionic liquids in the past, is used. It did not appear, and when the ionic liquid was added, the reactivity was rather lowered, resulting in lower energy density and lifespan characteristics.

The ionic liquid contained in the electrolytic solution of the present invention includes a sulfonium ion represented by the following formula (1) as a cation, and is not particularly limited as long as it exists as a liquid in the above-described temperature range.

[Formula 1]

At this time, the R ₁ to R ₃ are the same as or different from each other, and each may be a C1 to C5 alkyl group, such as a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, an isobutyl group, or a pentyl group, but is limited thereto. It does not become.

Preferably, each of R ₁ to R ₃ may be a methyl group, an ethyl group, or a propyl group. More preferably, the sulfonium ion may be at least one selected from the group consisting of diethylmethylsulfonium and triethylsulfonium.

On the other hand, the anion of the ionic liquid contained in the electrolytic solution of the present invention is bis (perfluoroethyl sulfonyl) imide _{(N (C 2 F 5 SO} 2) 2 -), methylsulfonyl meth as tris (trifluoromethyl Id _{(C (CF 3 SO 2)} 2 -), bis (sulfonyl fluorophenyl) imide _{(N (SO 2 F) 2} -), bis (trifluoromethyl sulfonimide) (N (CF ₃ SO _{2) 2} ^-), trifluoromethane sulfonate (CF ₃ SO ₃ ^-), AsF ₆ ^-, ClO ₄ ^-, PF ₆ ^-, BF ₄ ^-, SCN ^-, NO ₃ ^-, I ^-, Br ^-, Cl ^-, N(CN ₂ ) ^- , CH ₃ SO ₃ ^- may be one or more of, but is not limited thereto.

For example, the ionic liquid contained in the electrolytic solution of the present invention is diethylmethylsulfonium bis(trifluoromethylsulfonyl)imide, diethylmethylsulfonium trifluoromethanesulfonate, diethylmethylsulfonium bis( Fluorosulfonyl)imide, diethylmethylsulfonium bis(perfluoroethylsulfonyl)imide, diethylmethylsulfonium nitrate, diethylmethylsulfonium iodide, diethylmethylsulfonium bromide and/ Or it may be triethylsulfonium bis(trifluoromethylsulfonyl)imide. Such an ionic liquid can be used by purchasing a commercially available liquid, or can be directly prepared and used by substituting various anions.

The content of the ionic liquid containing sulfonium ions in the electrolyte is not particularly limited, but may be included in an amount of 0.01 to 10% by weight based on 100% by weight of the electrolyte, preferably 0.1 to 5% by weight, more preferably It may be included in the following 0.5 to 3% by weight. If the content of the ionic liquid is less than 0.01% by weight, the effect of preventing overvoltage, improving the energy density and improving the life characteristics due to the addition of the ionic liquid cannot be obtained. If it exceeds 10% by weight, side reactions may occur in the electrolyte. , It is appropriately adjusted within the above range.

The electrolyte for a lithium-sulfur battery of the present invention includes a non-aqueous solvent, and the non-aqueous solvent is not particularly limited as long as it is used as a solvent of the electrolyte in the art. Specifically, the non-aqueous solvent may be one or more selected from the group consisting of carbonate-based, ester-based, ether-based, ketone-based, alcohol-based, and aprotic solvents.

The carbonate-based solvents include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (MEC), ethylene carbonate ( EC), propylene carbonate (PC), or butylene carbonate (BC) may be used, but is not limited thereto.

As the ester solvent, methyl acetate, ethyl acetate, n-propyl acetate, 1,1-dimethylethyl acetate, methyl propionate, ethyl propionate, γ-butyrolactone, decanolide, valero Lactone, mevalonolactone, caprolactone, and the like may be used, but are not limited thereto.

As the ether solvent, diethyl ether, dipropyl ether, dibutyl ether, dimethoxymethane (DMM), trimethoxymethane (TMM), dimethoxyethane (DME), diethoxyethane (DEE), diglyme, Triglyme, tetraglyme, tetrahydrofuran, 2-methyltetrahydrofuran, polyethylene glycol dimethyl ether, and the like may be used, but are not limited thereto.

As the ketone solvent, for example, cyclohexanone may be used. In addition, ethyl alcohol, isopropyl alcohol, etc. may be used as the alcohol-based solvent, and nitriles such as acetonitrile, amides such as dimethylformamide, and 1,3-dioxolane (DOL) as the aprotic solvent Dioxolanes such as, or sulfolane, or the like may be used.

In addition, ethyl alcohol, isopropyl alcohol, etc. may be used as the alcohol-based solvent, and R-CN (R is a C2 to C20 linear, branched, or cyclic hydrocarbon group, wherein Nitriles such as a bonded aromatic ring or an ether bond), amides such as dimethylformamide, dioxolanes such as 1,3-dioxolane, sulfolane, and the like may be used.

The non-aqueous solvent may be used alone or in combination of one or more, and the mixing ratio in the case of using one or more mixtures may be appropriately adjusted according to the desired battery performance.

Preferably, the non-aqueous solvent is an ether solvent. The ether-based solvent is preferable because it has excellent compatibility with lithium metal, which is a negative electrode of a lithium-sulfur battery, and can increase the efficiency, cycle life, and safety of the battery. In addition, since the ether-based solvent has a high donor number, it is possible to increase the dissociation degree of lithium salts by chelation of lithium cations, and to increase the solubility of lithium polysulfide, making it easy to secure sulfur reactivity. In addition, since the viscosity is low, the movement of ions is free, and the ionic conductivity of the electrolyte can be greatly improved.

The ether-based solvent may be linear ether, cyclic ether, or a mixed solvent thereof.

Non-limiting examples of the linear ether include dimethyl ether, diethyl ether, dipropyl ether, dibutyl ether, diisobutyl ether, ethylmethyl ether, ethylpropyl ether, ethyl tertbutyl ether, dimethoxymethane, trimethoxymethane , Dimethoxyethane, diethoxyethane, dimethoxypropane, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, ethylene glycol divinyl ether, diethylene glycol divinyl ether , Triethylene glycol divinyl ether, dipropylene glycol dimethylene ether, butylene glycol ether, diethylene glycol ethyl methyl ether, diethylene glycol isopropyl methyl ether, diethylene glycol butyl methyl ether, diethylene glycol tertbutyl ethyl ether, And at least one selected from the group consisting of ethylene glycol ethylmethyl ether.

Non-limiting examples of the cyclic ether include dioxolane, methyldioxolane, dimethyldioxolane, vinyldioxolane, methoxydioxolane, ethylmethyldioxolane, oxane, dioxane, trioxane, tetrahydrofuran, methyltetra Hydrofuran, dimethyltetrahydrofuran, dimethoxytetrahydrofuran, ethoxytetrahydrofuran, dihydropyran, tetrahydropyran, furan, and one or more selected from the group consisting of methylfuran.

Preferably, the ether solvent is 1,3-dioxolane, 1,2-dimethoxyethane, tetrahydrofuran, 2,5-dimethylfuran, furan, 2-methyl furan, 1,4-oxane, 4 -Methyl-1,3-dioxolane, tetraethylene glycol dimethyl ether, or a mixed solvent thereof.

More specifically, the ether-based solvent may be a mixed solvent obtained by selecting and mixing one type of linear ether and cyclic ether, respectively, and the mixing ratio may be 5:95 to 95:5 by volume.

According to an embodiment of the present invention, the mixed solvent may be a mixed solvent of 1,3-dioxolane (1,3-Dioxolane: DOL) and 1,2-dimethoxyethane (DME). have. At this time, the DOL and DME may be a solvent mixed in a volume ratio of 5:95 to 95:5, preferably 30:70 to 70:30, more preferably a mixed solvent in a volume ratio of 40:60 to 60:40 Can be every day.

Meanwhile, the electrolyte for a lithium-sulfur battery of the present invention may additionally contain a lithium salt to increase ionic conductivity. 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 secondary battery.

Specifically, the lithium salt is LiCl, LiBr, LiI, LiClO ₄ , LiBF ₄ , LiB ₁₀ Cl ₁₀ , LiPF ₆ , LiCF ₃ SO ₃ , LiCF ₃ CO ₂ , LiC ₄ BO ₈ , LiAsF ₆ , LiSbF ₆ , LiAlCl ₄ , CH ₃ SO ₃ Li, CF ₃ SO ₃ Li, (CF ₃ SO ₂ ) ₂ NLi, (C ₂ F ₅ SO ₂ ) ₂ NLi, (SO ₂ F) ₂ NLi, (CF ₃ SO ₂ ) ₃ CLi, Lithium bis (oxalato) borate, lithium-oxalyldifluoroborate, lithium 4,5-dicyano-2- (trifluoromethyl) imidazole ( Lithium 4,5-dicyano-2-(trifluoromethyl)imidazole), lithium dicyanotriazolate, lithium thiocyanate, lithium chloroborane, lithium lower aliphatic carboxylic acid (at this time, lower aliphatic is For example, it may mean an aliphatic having 1 to 5 carbon atoms.), tetraphenyl borate lithium, lithium imide, and one selected from the group consisting of a combination thereof, and preferably (CF ₃ SO ₂ ) ₂ NLi, (C ₂ F ₅ SO ₂ ) ₂ NLi, (SO ₂ F) ₂ NLi, etc. may be used.

The concentration of the lithium salt may be determined in consideration of ionic conductivity, and the like, and may be, for example, 0.1 to 8.0 M (mol/L), preferably 0.1 to 4.0 M, and more preferably 0.5 to 2.0 M. If the concentration of the lithium salt is less than the above range, it is difficult to secure the ion conductivity suitable for driving the battery.If the concentration of the lithium salt is exceeded, the viscosity of the electrolyte may increase and the mobility of lithium ions may decrease, and the decomposition reaction of the lithium salt itself increases. Since the performance of may be deteriorated, it is appropriately adjusted within the above range.

In addition, the electrolyte for a lithium-sulfur battery of the present invention may further include a compound having an intramolecular N-O bond. The compound has an effect of forming a stable film on the lithium electrode and greatly improving charging and discharging efficiency.

These compounds may be specifically nitric or nitrous compounds, nitro compounds, and the like. For example, lithium nitrate, potassium nitrate, cesium nitrate, barium nitrate, ammonium nitrate, lithium nitrite, potassium nitrate, cesium nitrite, ammonium nitrite, methyl nitrate, dialkyl imidazolium nitrate, guanidine nitrate, imidazolium nitrate , Pyridinium nitrate, ethyl nitrite, propyl nitrite, butyl nitrite, pentyl nitrite, octyl nitrite, nitromethane, nitropropane, nitrobutane, nitrobenzene, dinitrobenzene, nitropyridine, dinitropyridine, nitro At least one member selected from the group consisting of toluene, dinitrotoluene, pyridine N-oxide, alkylpyridine N-oxide, and tetramethyl piperidinyloxyl may be used. According to an embodiment of the present invention, lithium nitrate (LiNO ₃ ) may be used.

The compound having an intramolecular N-O bond is used within the range of 0.01 to 10% by weight, preferably 0.1 to 5% by weight, based on 100% by weight of the total electrolyte composition. If the content is less than the above range, the above-described effect cannot be secured. On the contrary, if the content exceeds the above range, the resistance may increase due to the coating of the lithium electrode. Therefore, the above range is appropriately adjusted.

In the present invention, the combination of the ionic liquid, the non-aqueous solvent, the lithium salt, and the compound having an intramolecular N-O bond is not particularly limited and may be various.

For example, the electrolyte for a lithium-sulfur battery of the present invention is a solvent in which 1,3-dioxolane (DOL) and 1,2-dimethoxyethane (DME) are mixed in a volume ratio of 40:60 to 60:40, and ionic Diethylmethylsulfonium bis(trifluoromethylsulfonyl)imide and/or triethylsulfonium bis(trifluoromethylsulfonyl)imide as a liquid is contained in an amount of 0.01 to 10% by weight based on 100% by weight of the electrolyte And, as a lithium salt (CF ₃ SO ₂ ) ₂ NLi, (C ₂ F ₅ SO ₂ ) ₂ NLi, or (SO ₂ F) ₂ NLi at a concentration of 0.1 to 8.0 M, lithium nitrate based on 100% by weight of the electrolyte It may be included in an amount of 0.01 to 10% by weight.

The electrolyte for a lithium-sulfur battery of the present invention includes an ionic liquid containing sulfonium ions as a cation, and exhibits high energy density by improving the reactivity of sulfur, which is a positive electrode active material, has less discharge overvoltage, and is less than a conventional electrolyte. Remarkably improved battery life. Therefore, it is preferable to improve the capacity characteristics and life characteristics of the lithium-sulfur battery.

The method for preparing the electrolyte is not particularly limited in the present invention, and may be prepared by a conventional method known in the art.

Lithium-sulfur battery

The lithium-sulfur battery according to the present invention uses the electrolyte for a lithium-sulfur battery according to the present invention as an electrolyte, and exhibits improved capacity characteristics and lifespan characteristics. The lithium-sulfur battery includes a positive electrode and a negative electrode containing sulfur, and may further include a separator interposed between the positive electrode and the negative electrode.

The configuration of the positive electrode, the negative electrode, and the separator of the lithium-sulfur battery is not particularly limited in the present invention, and follows what is known in the art.

anode

The positive electrode according to the present invention includes a positive electrode active material formed on a positive electrode current collector.

As the positive electrode current collector, any material that can be used as a current collector in the technical field may be used. Specifically, it may be preferable to use foamed aluminum, foamed nickel, etc. having excellent conductivity.

The positive electrode active material may include elemental sulfur (S8), a sulfur-based compound, or a mixture thereof. Specifically, the sulfur-based compound may be Li ₂ S _n (n≥1), an organosulfur compound or a carbon-sulfur polymer ((C ₂ S _x ) _n : x=2.5 to 50, n≥2). These can be applied in combination with a conductive material because the sulfur material alone has no electrical conductivity.

The conductive material may be porous. Accordingly, the conductive material may be used without limitation as long as it has porosity and conductivity, and for example, a carbon-based material having porosity may be used. Carbon black, graphite, graphene, activated carbon, carbon fiber, etc. may be used as such a carbon-based material. Further, metallic fibers such as metal mesh; Metallic powders such as copper, silver, nickel, and aluminum; Alternatively, an organic conductive material such as a polyphenylene derivative can also be used. The conductive materials may be used alone or in combination.

The positive electrode may further include a binder for bonding a positive electrode active material and a conductive material and bonding to a current collector. The binder may include a thermoplastic resin or a thermosetting resin. For example, polyethylene, polyethylene oxide, polypropylene, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), styrene-butadiene rubber, tetrafluoroethylene-perfluoro alkyl vinyl ether copolymer, vinyl fluoride Liden-hexafluoropropylene copolymer, vinylidene fluoride-chlorotrifluoroethylene copolymer, ethylene-tetrafluoroethylene copolymer, polychlorotrifluoroethylene, vinylidene fluoride-pentafluoropropylene copolymer, propylene -Tetrafluoroethylene copolymer, ethylene-chlorotrifluoroethylene copolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer, vinylidene fluoride-perfluoromethylvinylether-tetrafluoroethylene copolymer A mixture, an ethylene-acrylic acid copolymer, and the like may be used alone or in combination, but are not necessarily limited thereto, and any one that can be used as a binder in the art may be used.

The positive electrode as described above may be manufactured according to a conventional method, and specifically, a composition for forming a positive electrode active material layer prepared by mixing a positive electrode active material, a conductive material, and a binder in an organic solvent is applied and dried on a current collector, and optionally In order to improve the electrode density, it can be manufactured by compression molding on a current collector. In this case, as the organic solvent, a positive electrode active material, a binder, and a conductive material may be uniformly dispersed, and it is preferable to use an easily evaporated one. Specifically, acetonitrile, methanol, ethanol, tetrahydrofuran, water, and isopropyl alcohol are exemplified.

cathode

The negative electrode according to the present invention includes a negative active material formed on the negative electrode current collector.

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

As the negative active material, a material capable of reversibly intercalating or deintercalating lithium ions (Li ⁺ ), a material capable of reversibly forming a lithium-containing compound by reacting with lithium ions, lithium metal or lithium alloy You can use The material capable of reversibly occluding or releasing lithium ions (Li ⁺ ) may be, for example, crystalline carbon, amorphous carbon, or a mixture thereof. A material capable of reversibly forming a lithium-containing compound by reacting with the lithium 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 ( It may be an alloy of a metal selected from the group consisting of Ca), strontium (Sr), barium (Ba), radium (Ra), aluminum (Al), and tin (Sn).

The negative electrode may further include a binder for bonding of the negative active material and the conductive material to the current collector, and specifically, the binder is the same as described above for the binder of the positive electrode.

Separator

A conventional separator may be interposed between the anode and the cathode. The separator is a physical separator having a function of physically separating an electrode, and if it is used as a conventional separator, it can be used without particular limitation. In particular, it is preferable that the separator has low resistance against ion migration of the electrolyte and has excellent electrolyte-moisturizing ability.

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

Specifically, a porous polymer film, for example, an ethylene homopolymer, a propylene homopolymer, an ethylene/butene copolymer, an ethylene/hexene copolymer, and an ethylene/methacrylate copolymer, etc. Or it may be used by laminating them, or a conventional porous nonwoven fabric, for example, a nonwoven fabric made of a high melting point glass fiber, polyethylene terephthalate fiber, etc. may be used, but is not limited thereto.

The positive electrode, negative electrode, and separator included in the lithium-sulfur battery may be prepared according to conventional components and manufacturing methods, respectively, and the appearance of the lithium-sulfur battery is not particularly limited, but cylindrical, rectangular, and pouch using cans It can be a (Pouch) type or a coin type.

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

[Example]

Examples 1 to 2 and Comparative Examples 1 to 5

(1) Preparation of electrolyte

1,3-dioxolane (1,3-Dioxolane) and 1,2-dimethoxyethane (1,2-Dimethoxyethane) in a 1: 1 volume ratio of a mixed solvent, 1.0 M concentration of LiTFSI ((CF ₃ SO ₂ ) ₂ NLi) was added, and 1% by weight of LiNO ₃ was added based on 100% by weight of the electrolyte to prepare an electrolyte. Then, as shown in Table 1 below, ionic liquids having different cations were added in an amount of 1 to 3% by weight of the total weight of the electrolyte, respectively, to prepare the electrolyte solutions of Examples 1 to 2 and Comparative Examples 1 to 5.

Ionic liquid Cation Negative ions Content (% by weight) Example 1 Diethylmethylsulfonium _{N (CF 3 SO 2) 2} - 3 Example 2 Diethylmethylsulfonium One Comparative Example 1 1-hexyl-3-methylimidazolium 3 Comparative Example 2 1-butyl-1-methylpyrrolidinium 3 Comparative Example 3 1-ethylpyridinium 3 Comparative Example 4 1-butyl-1-methylpiperidinium 3 Comparative Example 5 No additives

(2) Preparation of lithium-sulfur battery

65% by weight of sulfur, 25% by weight of carbon black, and 10% by weight of polyethylene oxide were mixed with acetonitrile to prepare a positive electrode active material slurry. The positive electrode active material slurry was coated on an aluminum current collector and dried to prepare a positive electrode having a size of 30 × 50 mm ² and a loading amount of 5 mAh/cm ² . Further, a lithium metal having a thickness of 150 µm was used as a negative electrode.

The prepared positive electrode and the negative electrode were positioned so as to face each other, and a polyethylene separator having a thickness of 20 μm was interposed therebetween, and then filled with the electrolyte solutions of the prepared Examples and Comparative Examples.

Experimental Example 1: Battery performance evaluation

For each of the lithium-sulfur batteries of Examples 1 to 2 and Comparative Examples 1 to 5, discharge capacity and voltage were measured while cycling under the following conditions, and energy density and specific discharge capacity Was measured.

Charging: rate 0.1C, voltage 2.8V, CC/CV (5% current cut at 0.1C)

Discharge: rate 0.1C, voltage 1.5V, CC

(1) Comparison of discharge characteristics

1 is an initial discharge curve of Example 1 and Comparative Example 5, and FIG. 2 is a discharge curve of Examples 1 to 2 and Comparative Examples 1 to 4;

1 and 2, in the case of Examples 1 and 2 to which the electrolytic solution of the present invention is applied, Comparative Examples 1 to 5 including ionic liquids containing no ionic liquid or containing cations other than sulfonium, and By comparison, it can be seen that the discharge overvoltage is significantly improved. From this, it can be seen that when the electrolyte solution of the present invention is used, the output characteristics of a lithium-sulfur battery can be improved.

(2) energy density comparison

Tables 2 and 3 below show the energy density of each battery of Example 1 and Comparative Examples 2 to 5. At this time, the energy density was calculated by multiplying the discharge nominal voltage (unit V) and the capacity (capacity, unit mAh/g _s ).

Energy density (Wh/g _s ) Example 1 2.48 Example 2 2.47 Comparative Example 1 2.28 Comparative Example 2 2.24 Comparative Example 3 2.21 Comparative Example 4 2.30 Comparative Example 5 2.34

As a result of the experiment, the energy density of Example 1 was 2.48 Wh/g _s , the energy density of Example 2 was 2.47 Wh/g _s , and the energy density was significantly improved compared to the case of Comparative Example 5 that did not contain an ionic liquid. I can confirm.

In addition, the effect of the type of ionic liquid on the energy density of the battery was also confirmed. In the case of Comparative Examples 1 to 4 containing ions other than sulfonium ions as cations of the ionic liquid, the energy density was lower than that of Comparative Example 5 not containing the ionic liquid.

(3) Comparison of cycle characteristics

The cycle characteristics of the batteries of the Examples and Comparative Examples were compared, and the results are shown in FIG. 4. 4, it can be seen that the batteries of Examples 1 and 2 stably maintain the discharge capacity for 15 cycles or more.

On the other hand, when an electrolyte solution containing an ionic liquid containing a cation other than sulfonium ions was used (Comparative Examples 1 to 4), the cycle characteristics were rather poor than when the ionic liquid was not included (Comparative Example 1). appear.

From the above results, it can be seen that the effect of improving the energy density and improving the cycle characteristics of the lithium-sulfur battery can be secured only when the ionic liquid is included in the electrolyte, and the cation of the ionic liquid is sulfonium ions.

The lithium-sulfur battery electrolyte of the present invention contains an ionic liquid containing a sulfonium cation to improve the reactivity of sulfur, which is a positive electrode active material. Therefore, when the electrolyte solution of the present invention is applied to a lithium-sulfur battery, discharge overvoltage is improved and energy density is improved, and excellent battery performance can be expected.

Claims (13)

As a lithium-sulfur battery comprising an electrolyte solution containing an ionic liquid and a non-aqueous solvent,
The ionic liquid is diethylmethylsulfonium bis(trifluoromethylsulfonyl)imide, diethylmethylsulfonium trifluoromethanesulfonate, diethylmethylsulfonium bis(fluorosulfonyl)imide, Ethylmethylsulfonium bis(perfluoroethylsulfonyl)imide, diethylmethylsulfonium nitrate, diethylmethylsulfonium iodide, diethylmethylsulfonium bromide or triethylsulfonium bis(trifluoromethyl Sulfonyl)imide,
The non-aqueous solvent is 1,3-dioxolane, 1,2-dimethoxyethane, tetrahydrofuran, 2,5-dimethylfuran, furan, 2-methyl furan, 1,4-oxane, 4-methyl-1 ,3-dioxolane, tetraethylene glycol dimethyl ether, or a mixed solvent thereof, a lithium-sulfur battery. The method of claim 1,
The ionic liquid is contained in an amount of 0.01 to 10% by weight based on 100% by weight of the electrolyte, lithium-sulfur battery. delete delete delete delete delete The method of claim 1,
The electrolyte is LiCl, LiBr, LiI, LiClO ₄ , LiBF ₄ , LiB ₁₀ Cl ₁₀ , LiPF ₆ , LiCF ₃ SO ₃ , LiCF ₃ CO ₂ , LiC ₄ BO ₈ , LiAsF ₆ , LiSbF ₆ , LiAlCl ₄ , CH ₃ SO ₃ Li, CF ₃ SO ₃ Li, (CF ₃ SO ₂ ) ₂ NLi, (C ₂ F ₅ SO ₂ ) ₂ NLi, (SO ₂ F) ₂ NLi, (CF ₃ SO ₂ ) ₃ CLi, lithium bis(jade Salato)borate, lithium-oxalyldifluoroborate, lithium 4,5-dicyano-2-(trifluoromethyl)imidazole, lithium dicyanotriazolate, lithium thiocyanate, chloroborane lithium, lower grade Lithium-sulfur battery, further comprising one kind of lithium salt selected from the group consisting of lithium aliphatic carboxylic acid, lithium tetraphenylborate, lithium imide, and combinations thereof. The method of claim 8,
The lithium salt is contained in a concentration of 0.1 to 8.0 M, lithium-sulfur battery. The method of claim 1,
The electrolyte solution further comprises a compound having an intramolecular NO bond, lithium-sulfur battery. The method of claim 10,
Compounds having NO bonds in the molecule include lithium nitrate, potassium nitrate, cesium nitrate, barium nitrate, ammonium nitrate, lithium nitrite, potassium nitrite, cesium nitrite, ammonium nitrite, methyl nitrate, dialkyl imidazolium nitrate, guanidine nitrate. Rate, imidazolium nitrate, pyridinium nitrate, ethyl nitrite, propyl nitrite, butyl nitrite, pentyl nitrite, octyl nitrite, nitromethane, nitropropane, nitrobutane, nitrobenzene, dinitrobenzene, nitro At least one selected from the group consisting of pyridine, dinitropyridine, nitrotoluene, dinitrotoluene, pyridine N-oxide, alkylpyridine N-oxide, and tetramethyl piperidinyloxyl, lithium-sulfur battery. The method of claim 10,
The compound having an intramolecular NO bond is contained in an amount of 0.01 to 10% by weight based on 100% by weight of an electrolyte solution, a lithium-sulfur battery. delete

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