KR100354229B1 - Low impedance lithium-sulfur batteries - Google Patents

Abstract

The present invention relates to a lithium-sulfur battery exhibiting low impedance, comprising a cathode, a sulfur element, Li ₂ S _n (n ≥1), an organic sulfur compound, and a carbon- Sulfur polymer and an electrolyte comprising an electrolyte comprising a lithium salt and a weak polar solvent and an organic solvent of a strong polar solvent, and a cathode comprising an electrically conductive material. When the lithium-sulfur battery is completely discharged for the first time, the lithium-sulfur battery has a standard impedance value of a region where a mass transfer process occurs _mt (f = 10 mHz) is less than 500 OMEGA, and the solution impedance component is the standard impedance value of the region _left (f = 100 kHz) is less than 100 Ω. here _mt (f = 10 mHz) shows that when the opposite surface of the anode and the cathode is 2 cm 2, Lt; / RTI > _sol (f = 100 kHz) shows the case where the opposing face of the cathode and the anode is 2 cm 2, .

Description

[0001] LOW IMPEDANCE LITHIUM-SULFUR BATTERIES WITH LOW IMPEDANCE [0002]

[Industrial Applications]

The present invention relates to a lithium-sulfur battery, and more particularly, to a lithium-sulfur battery exhibiting a low impedance.

BACKGROUND ART [0002]

The lithium-sulfur battery uses a sulfur-based compound having a sulfur-sulfur combination as a cathode active material and a carbon-based material in which metal ions such as lithium or lithium ions are intercalated or deintercalated A secondary battery used as an anode active material is a secondary battery in which a reduction in the number of S oxidation occurs during the reduction reaction (discharge) and a reduction in the oxidation number of S during charging (charging) The reaction is used to store and generate electrical energy.

As the electrolyte solution in the lithium-sulfur battery, a material capable of dissolving polysulfide is used.

U.S. Patent No. 6,030,720 (PolyPlus Battery) discloses an electrolyte solution for a lithium-sulfur battery in which R ₁ (CH ₂ CH ₂ O) _n R ₂ (n is 2 to 10 and R ₁ and R ₂ are alkyl or alkoxy groups) A compound as a main solvent and a solvent having a donor number of 15 or more as a co-solvent. Also disclosed is a liquid electrolyte comprising a solvent having at least one of a crown ether, a cryptand, and a donor solvent. Further, an electrolytic solution which becomes a catholyte after discharging the lithium-sulfur battery is described.

It is an object of the present invention to provide a lithium-sulfur battery exhibiting low impedance.

1 is a graph showing impedance results of the lithium-sulfur battery of the present invention.

In order to achieve the above object, the present invention provides a negative electrode comprising a negative electrode active material of lithium metal or lithium alloy; A cathode comprising an anode active material, a cathode active material comprising at least one sulfur-based material selected from the group consisting of Li ₂ S _n (n ≥ 1), an organic sulfur compound and a carbon-sulfur polymer, and an electrically conductive material; And an electrolyte comprising a lithium salt and a weak polar solvent and an organic solvent of a strong polar solvent. When the lithium-sulfur battery is completely discharged for the first time, the lithium-sulfur battery has a standard impedance value of a region where a mass transfer process occurs _mt (f = 10 mHz) is less than 500 OMEGA, and the solution impedance component is the standard impedance value of the region _left (f = 100 kHz) is less than 100 Ω. here _mt (f = 10 mHz) shows that when the opposite surface of the anode and the cathode is 2 cm 2, Lt; / RTI > _sol (f = 100 kHz) shows the case where the opposing face of the cathode and the anode is 2 cm 2, .

The anode may further comprise at least one additive selected from transition metals, Group IIIA, Group IVA metals, sulfur compounds thereof, and alloys thereof.

Wherein the electrolyte is selected from the group consisting of an aryl compound, a cyclic compound, a heterocyclic compound containing N, O and S, a weakly polar solvent selected from the group consisting of a solvent having a dielectric constant of less than 15 and a dipole moment less than 1 debye, ₁ (CO) _n R ₂ , R ₁ (CO) _n R ₂ OR ₃ , R ₁ (CO ₂ ) _n R ₂ , R ₁ (CO ₂ ) _n R ₂ OR ₃ and R ₁ (CH ₂ CH ₂ O) a solvent having a structure of _n R ₂ (n ≥1, R ₁ , R ₂ and R ₃ are alkyl, aryl, allyl, alkenyl, alkynyl and alkoxy groups), a solvent having a dielectric constant of more than 15 and a dipole moment of 1 and a stronger polar solvent selected from the group consisting of solvents larger than the debye.

When the lithium-sulfur battery is discharged, polysulfide (S _n ^-1 , S _n ^-2 , where n ≥2) or sulfide (S ^-2 ) is generated in the anode and dissolved in the electrolyte. However, precipitation may occur if these concentrations are local to the solubility of the electrolyte. The positive electrode active material of the lithium-sulfur battery comprises at least one of a sulfur element, Li ₂ S _n (n ≥ 1), an organic sulfur compound and a carbon-sulfur polymer, and the active material is solid or electrolyte- It exists in a dissolved state.

When the lithium-sulfur battery is reduced, the first reduction (charging) peak of the cyclic voltammetry during the first reduction reaction appears at a voltage of 2.4 to 2.0 V at a scan rate of less than 0.1 mV / s, The second reduction peak appears at 2.2 to 1.7 V voltage.

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

The present invention relates to a lithium-sulfur battery exhibiting low impedance. The major components of the impedance of the battery are contact resistance, solution resistance, charge transfer resistance, mass transfer process (diffusion, migration, ), Convection], electric double layer capacitance, and the like. When the impedance of the battery is lowered, the voltage drop (iR drop) and the overvoltage (polarization) are lowered, so that the voltage of the battery is increased, and as a result, the performance is improved. Proper electrolyte and cell design are essential to lower the impedance due to battery impedance, especially solution resistance, electron transfer resistance, and mass transfer phenomena (diffusion, migration, convection). In the present invention, a suitable electrolytic solution is used to lower the battery impedance.

In the lithium-sulfur battery, the electrolyte includes a lithium salt, which is a supporting electrolyte, and an organic solvent. This organic solvent should dissolve the sulfur element (S ₈ ) and the polysulfide (S _n ^-1 , S _n ^-2 , where n ≥ 2) well and have good affinity with the lithium anode. Theoretically, the sulfur element, which is fully oxidized state, is a nonpolar material and therefore dissolves in a nonpolar solvent or a weakly polar solvent. The sulfur oxidation number of the polysulfide (S _n ^-1 , S _n ^-2 , where n ≥ 2) or the sulfide (S ^-2 ) of the sulfur element is greater than 0 and less than -2 (in this case, It is expected that polysulfides with a sulfur oxidation number near zero are expected to be soluble in weakly polar solvents, but a strong polar solvent is necessarily required to dissolve polysulfides having an oxidation number of sulfur of at least -1. Therefore, in order to dissolve a polysulfide having a wide oxidation range, it is basically required to use a mixed solvent containing a weak polar solvent and a strong polar solvent as an electrolyte. Generally, the higher the solubility of the polysulfide, the larger the discharge capacity of the battery. In order for the lithium-sulfur battery to have high capacity and good lifetime characteristics, the precipitated polysulfide (S _n ^-1 , S _n ^-2 , Where n ≥ 2) or sulfide (S ^-2 ) can participate in the electrochemical reaction upon charging.

In the present invention, a mixed organic solvent containing a weak polar solvent and a strong polar solvent is used as a solvent for the electrolyte. Weak polar solvents include aryl compounds, cyclic compounds and heterocyclic compounds containing N, O and S, solvents with a dielectric constant less than 15, solvents with dipole moments less than 1 debye . Specific examples of the weak polar solvent include xylene, dioxolane, tetrahydrofuran, dimethoxyethane, 2-methyltetrahydrofuran, 2,5-dimethyltetrahydrofuran, diethylcarbonate, dimethylcarbonate, toluene, etc. . A strong polar solvent is _{R 1 (CO) n R 2} , R 1 (CO) n R 2 OR 3, R 1 (CO 2) n R 2, R 1 (CO 2) n R 2 OR 3, R 1 ( CH ₂ CH ₂ O) _n R ₂ wherein n is 1 and R ₁ , R ₂ and R ₃ are alkyl, aryl, allyl, alkenyl, alkoxy groups, cyclic carbonates having a dielectric constant of 15 or more A large solvent, and an aprotic solvent capable of dissolving lithium polysulfide or lithium sulfide. Specific examples of the strong polar solvent include hexamethyl phosphoric triamide,? -Butyrolactone, acetonitrile, ethylene carbonate, propylene carbonate, N-methylpyrrolidone, 3-methyl-2-oxazolidone , Dimethylformamide, sulfolane, dimethylacetamide, dimethylsulfoxide, and the like.

Further, a solvent serving as a Lewis acid or a Lewis base may be further used as a co-solvent. Specific examples of the co-solvent Lewis acid include methanol, ethylene glycol, polyethylene glycol, nitromethane, trifluoroacetic acid, trifluoromethanesulfonic acid, sulfur dioxide or boron trifluoride. Specific examples of Lewis bases include Lewis Specific examples of the base include hexamethylphosphoric amide, pyridine, N, N-diethylacetamide, N, N-diethylformamide, dimethylsulfoxide, tetramethylurea, N, -Dimethylformamide, tributyl phosphate, trimethyl phosphate N, N, N ', N'-tetraethylsulfamide, tetramethylenediamine, tetramethylpropylenediamine or pentamethyldiethylenetriamine.

Lithium trifluoromethanesulfonimide, lithium triflate, lithium perchlorate, LiPF ₆ , LiBF ₄ or the like is used as the lithium salt as the supporting electrolyte.

In the electrolyte, electricity is transferred by the movement of ions. Ultimately, to lower the solution resistance, the gap between the anode and the cathode should be minimized, the facing area should be widened, and the electrolytic solution with high ion conductivity should be used. In order to lower the impedance due to the mass transfer phenomenon, it is important to reduce the diffusion distance of the active material. Therefore, the thickness of the cathode plate must be made thin. In particular, the conductivity is related to the number of dissociated ions and the viscosity of the medium. Therefore, it is necessary to select an electrolyte having a low viscosity while dissolving the lithium salt well.

In the lithium-sulfur battery of the present invention, the cathode active material is a sulfur element such as a sulfur element, Li ₂ S _n (n ≥ 1), an organosulfur compound or a carbon-sulfur polymer [(C ₂ S _x ) _n , Here, x = 2.5-50, n ≥ 2] can be used. The anode may further comprise one or more additives selected from transition metals, Group IIIA, Group IVA metals, sulfur compounds thereof, and alloys thereof. The transition metal may be at least one selected from the group consisting of Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Cd, , Os, Ir, Pt, Au, and Hg. The Group IIIA metal includes Al, Ga, In, and Tl, and the Group IVA metal includes Si, Ge, Sn, and Pb.

The positive electrode of the present invention further includes an electrically conductive conductive material for allowing electrons to move smoothly in the positive electrode active material together with a sulfur compound or, optionally, an additive. The conductive material is not particularly limited, but conductive materials such as carbon (e.g., Super-P) and carbon black or conductive polymers such as polyaniline, polythiophene, polyacetylene, and polypyrrole may be used alone or in combination .

The positive electrode active material may further include a binder capable of adhering the positive electrode active material to the current collector. Examples of the binder include poly (vinyl acetate), polyvinyl alcohol, polyethylene oxide, polyvinylpyrrolidone, alkylated polyethylene oxide, (Trade name: Kynar), poly (ethyl acrylate), poly (vinylidene fluoride), poly (vinylidene fluoride), poly (vinylidene fluoride) , Polytetrafluoroethylene, polyvinyl chloride, polyacrylonitrile, polyvinylpyridine, polystyrene, derivatives thereof, blends, copolymers and the like can be used.

In order to produce the positive electrode of the present invention, a binder is first dissolved in a solvent for preparing a slurry, and then the conductive material is dispersed. As the solvent for preparing the slurry, sulfur-compound, binder and conductive material can be uniformly dispersed, and it is preferable to use one that is easily evaporated. Representative examples include acetonitrile, methanol, ethanol, tetrahydrofuran, water, Isopropyl alcohol and the like can be used. Next, at least one of the sulfur element, Li ₂ S _n (n ≥ 1), the organic-sulfur compound, the carbon-sulfur polymer is selected, or alternatively, with the additive, To prepare a positive electrode slurry. The amount of the solvent, the sulfur compound or optionally the additive contained in the slurry is not particularly important in the present invention, and it is sufficient if the slurry has an appropriate viscosity to facilitate the coating of the slurry.

The slurry thus prepared is applied to a current collector and vacuum dried to form a positive electrode plate, which is then used for battery assembly. The slurry may be coated on the current collector with an appropriate thickness according to the viscosity of the slurry and the thickness of the anode plate to be formed. The current collector is not particularly limited, but a conductive material such as stainless steel, aluminum, copper, , And it is more preferable to use a carbon-coated aluminum current collector. The use of a carbon-coated Al substrate is advantageous in that it has excellent adhesion to active materials, low contact resistance, and corrosion resistance due to aluminum polysulfide, compared to a carbon-free coating.

The lithium-sulfur battery of the present invention uses a lithium alloy electrode such as lithium metal or lithium / aluminum alloy as a cathode. Further, in the course of charging / discharging the lithium-sulfur battery, lithium and polysulfide react with each other and eventually the sulfur is changed to an inactive material (for example, Li ₂ S) and can be attached to the surface of the lithium negative electrode. Inactive sulfur is sulfur in which sulfur can no longer participate in the electrochemical reaction of the anode through various electrochemical or chemical reactions, and the inert sulfur formed on the surface of the lithium negative electrode is a protective layer of the lithium negative electrode There is also an advantage to play a role. Therefore, a composite electrode of a lithium metal and an inert sulfur formed on the lithium metal, for example, lithium and lithium sulfide, may be used as a negative electrode.

The electrochemical characteristics of the lithium-sulfur battery having the above-described structure were measured by electrochemical impedance analysis and cyclic voltammetry analysis. The following two important criteria impedance values are defined as a measure for evaluating the impedance characteristics of a battery.

As a result of measurement of the redox peak, the lithium-sulfur battery of the present invention exhibited a standard impedance value of a region where a mass transfer process occurred _mt (f = 10 mHz), and the standard impedance value of the region where the solution resistance component appears _left (f = 100 kHz). here _mtmt (f = 10 mHz) is a characteristic of the case where the opposite surface of the cathode and the anode is 2 cm 2, _mt , _mt (f = 100 kHz) shows that when the opposing face of the cathode and the anode is 2 cm 2, . At this time, = (Z _re ² + Z _im ² ) ^1/2 , where Z = Z _re + i Z _im (where i = ). The lithium-sulfur battery of the present invention is characterized in that | Z | _{When mt} (f = 10 mHz) is smaller than 500 Ω and | Z | _left (f = 100 kHz) is less than 100 Ω.

The electrochemical behavior of the lithium-sulfur battery of the present invention was also measured by cyclic voltammetry analysis. The cyclic voltammetry scans the voltage in a negative direction from 1.5 to 1.8 V at open circuit voltage (OCV) and then scans the voltage in a positive direction from 1.5 to 1.8 V to 2.4 to 3.0 V Then, the voltage is scanned again in the negative direction from 2.4 to 3.0 V to the first OCV. At this time, a cyclic voltammogram was obtained at various scan rates between 2 V / sec and 0.0001 mV / sec. The lithium-sulfur battery of the present invention exhibits a first reduction peak at a voltage of 2.4 to 2.0 V and a second reduction peak at a voltage of 2.2 to 1.7 V at a scan rate as low as 0.1 mV / s or less.

When the lithium-sulfur battery of the present invention is scanned in a negative direction from 1.5 to 1.8 V at an open circuit voltage (OCV), polysulfide (S _n ^-1 , S _n ^-2 , where n ≥2) Or sulfide (S < ^{2 &} gt ^; ) is generated and dissolved in the electrolyte solution. However, precipitation may occur if these concentrations are local to the solubility of the electrolyte.

Hereinafter, preferred embodiments of the present invention will be described. However, the following embodiments are merely preferred embodiments of the present invention, and the present invention is not limited to the following embodiments.

(Example 1)

A cathode mix slurry for a lithium-sulfur battery was prepared by mixing 60 wt% sulfur element, 20 wt% Super-P as a conductive material, and 20 wt% poly (vinyl acetate) as a binder in an acetonitrile solvent. The slurry was coated on a carbon-coated Al current collector, and the slurry-coated current collector was dried under vacuum for 12 hours or more to prepare a positive electrode plate. The positive electrode plate and the vacuum-dried separator were transferred to a glove box, and 1 M LiSO ₃ CF ₃ dissolved in dioxolane (DOL), dimethoxyethane, diglyme (DG) and sulfolane (SL) 1 volume ratio) The mixed electrolyte was dropped in an appropriate amount. A separator was placed on the positive electrode plate, and a little more electrolyte was added. A lithium electrode was placed thereon as a cathode, and the cell was charged and discharged at a rate of 0.1 C. At this time, the cut-off voltage was set to 1.5 to 2.5 V.

Impedance was measured when the assembled battery was first discharged. The frequency range was 100 kHz-10 mHz, and the AC amplitude was 7 mV. The measured impedance results are shown in Fig.

The lithium-sulfur battery of the present invention exhibits low impedance.

Claims (22)

A negative electrode comprising a negative active material of lithium metal or lithium alloy; And at least one sulfur series selected from the group consisting of sulfur elements, Li ₂ S _n (n ≥ 1), organic sulfur compounds and carbon-sulfur polymers ((C ₂ S _x ) _n : x = 2.5 to 50, A cathode comprising a cathode active material and an electrically conductive material; An electrolyte comprising a lithium salt and a mixed polar solvent and a strong polar solvent A lithium-sulfur battery having a low impedance, When the lithium-sulfur battery is completely discharged for the first time, the lithium-sulfur battery has a standard impedance value of a region where a mass transfer process occurs _mt (f = 10 mHz) is less than 500 OMEGA, and the solution impedance component is the standard impedance value of the region _sol (f = 100 kHz) appears to be less than 100 Ω, where _mt (f = 10 mHz) shows that the material movement at 10 mHz when the opposite surface of the cathode and anode is 2 cm 2 Lt; / RTI > _sol (f = 100 kHz) shows the case where the solution resistance component appears when the opposite surface of the cathode and the anode is 2 cm 2. Which means A lithium-sulfur battery exhibiting low impedance. The lithium-sulfur battery of claim 1, wherein the anode further comprises at least one additive selected from transition metals, Group IIIA, Group IVA metals, sulfur compounds thereof, and alloys thereof. The lithium-sulfur battery of claim 1, wherein the positive electrode active material exhibits a low impedance in a state of being dissolved in a solid or an electrolytic solution. The method of claim 1, wherein the electrolyte is selected from the group consisting of an aryl compound, a cyclic compound, a heterocyclic compound containing N, O and S, a solvent having a dielectric constant of less than 15, and a solvent having a dipole moment less than 1 debye weak polar solvent with R ₁ (CO) that is _{n R 2, R 1 (CO} ) n R 2 OR 3, R 1 (CO 2) n R 2, R 1 (CO 2) n R 2 OR 3 , and R ₁ ( CH ₂ CH ₂ O) _n R ₂ wherein n is 1, R ₁ , R ₂ and R ₃ are alkyl, aryl, allyl, alkenyl, alkynyl and alkoxy groups, A solvent and a strong polar solvent selected from the group consisting of a solvent having a dipole moment greater than 1 debye. The lithium-sulfur battery of claim 1, wherein the electrolyte further comprises a co-solvent that is a Lewis acid or Lewis base. The lithium-sulfur battery according to claim 1, wherein the lithium salt is selected from the group consisting of lithium trifluoromethane sulfonimide, lithium triflate, lithium perchlorate, LiPF _6, and LiBF ₄ . A negative electrode comprising a negative active material of lithium metal or lithium alloy; And at least one sulfur series selected from the group consisting of sulfur elements, Li ₂ S _n (n ≥ 1), organic sulfur compounds and carbon-sulfur polymers ((C ₂ S _x ) _n : x = 2.5 to 50, A cathode comprising a cathode active material and an electrically conductive material; And An electrolyte in which a polysulfide (S _n ^-1 , S _n ^-2 , where n ≥ 2) or a sulfide (S ^-2 ) is produced at the anode when discharged, A lithium-sulfur battery having a low impedance, When the lithium-sulfur battery is completely discharged for the first time, the lithium-sulfur battery has a standard impedance value of a region where a mass transfer process occurs _mt (f = 10 mHz) is less than 500 OMEGA, and the solution impedance component is the standard impedance value of the region _sol (f = 100 kHz) appears to be less than 100 Ω, where _mt (f = 10 mHz) shows that the material movement at 10 mHz when the opposite surface of the cathode and anode is 2 cm 2 Lt; / RTI > _sol (f = 100 kHz) shows the case where the solution resistance component appears when the opposite surface of the cathode and the anode is 2 cm 2. Which means A lithium-sulfur battery exhibiting low impedance. 8. The lithium-sulfur battery of claim 7, wherein the positive electrode further comprises at least one additive selected from transition metals, Group IIIA, Group IVA metals, sulfur compounds thereof, and alloys thereof. The method of claim 7, wherein the electrolyte is selected from the group consisting of an aryl compound, a cyclic compound, a heterocyclic compound containing N, O and S, a solvent having a dielectric constant of less than 15, and a solvent having a dipole moment less than 1 debye weak polar solvent with R ₁ (CO) that is _{n R 2, R 1 (CO} ) n R 2 OR 3, R 1 (CO 2) n R 2, R 1 (CO 2) n R 2 OR 3 , and R ₁ ( CH ₂ CH ₂ O) _n R ₂ (n ≧ 1, R ₁ , R ₂ and R ₃ are alkyl, aryl, allyl, alkenyl, alkynyl and alkoxy groups) A solvent and a strong polar solvent selected from the group consisting of a solvent having a dipole moment greater than 1 debye. 8. The lithium-sulfur battery as claimed in claim 7, wherein the electrolyte further comprises a co-solvent which is a Lewis acid or a Lewis base. The method of claim 7, wherein the lithium salt is lithium trifluoromethane sulfonimide, lithium triflate, lithium perchlorate, LiPF ₆ and Li indicating a low impedance is selected from the group consisting of LiBF ₄ - sulfur battery. A negative electrode comprising a negative active material of lithium metal or lithium alloy; And at least one sulfur series selected from the group consisting of sulfur elements, Li ₂ S _n (n ≥ 1), organic sulfur compounds and carbon-sulfur polymers ((C ₂ S _x ) _n : x = 2.5 to 50, A cathode comprising a cathode active material and an electrically conductive material; And An electrolyte comprising a lithium salt and a weak polar solvent and an organic solvent of a strong polar solvent A lithium-sulfur battery having a low impedance, Wherein the electrolyte is selected from the group consisting of an aryl compound, a cyclic compound, a heterocyclic compound containing N, O and S, R ₁ OR ₂ (R ₁ and R ₂ are alkyl), a solvent having a dielectric constant of less than 15 and a dipole moment of 1 debye weaker polar solvent with R ₁ (CO) is selected from the group consisting of small solvent _{n R 2, R 1 (CO} ) n R 2 OR 3, R 1 (CO 2) n R 2, R 1 (CO 2) n R ₂ OR ₃ and R ₁ (CH ₂ CH ₂ O) _n R ₂ wherein n ≧ 1 and R ₁ , R ₂ and R ₃ are alkyl, aryl, allyl, alkenyl, alkynyl and alkoxy groups A solvent, a solvent having a dielectric constant greater than 15, and a solvent having a dipole moment greater than 1 debye, Wherein when the lithium-sulfur battery is discharged (reduced), the first reduction peak of cyclic voltammetry appears at a voltage of 2.4 to 2.0 V at a scan rate of 0.1 mV / s or less. 13. The lithium-sulfur battery of claim 12, wherein the anode further comprises at least one additive selected from transition metals, Group IIIA, Group IVA metals, sulfur compounds thereof, and alloys thereof. 13. The lithium-sulfur battery of claim 12, wherein the electrolyte further comprises a co-solvent that is a Lewis acid or a Lewis base. The method of claim 12, wherein the lithium salt is lithium trifluoromethane sulfonimide, lithium triflate, lithium perchlorate, LiPF ₆ and Li indicating a low impedance is selected from the group consisting of LiBF ₄ - sulfur battery. A negative electrode comprising a negative active material of lithium metal or lithium alloy; And at least one sulfur series selected from the group consisting of sulfur elements, Li ₂ S _n (n ≥ 1), organic sulfur compounds and carbon-sulfur polymers ((C ₂ S _x ) _n : x = 2.5 to 50, A positive electrode comprising a positive electrode active material composition comprising a material and a positive electrode active material composition comprising an electrically conductive material; And An electrolyte in which a polysulfide (S _n ^-1 , S _n ^-2 , where n ≥ 2) or a sulfide (S ^-2 ) is produced at the anode when discharged, A lithium-sulfur battery having a low impedance, Wherein the lithium-sulfur battery exhibits a low impedance when the second reduction peak of cyclic voltammetry appears at a voltage of 2.2-1.7 V at a scan rate of 0.1 mV / s or less. 17. The lithium-sulfur battery of claim 16, wherein the anode further comprises at least one additive selected from transition metals, Group IIIA, Group IVA metals, sulfur compounds thereof, and alloys thereof. 18. The method of claim 16, wherein the electrolyte is selected from the group consisting of aryl compounds, cyclic compounds, heterocyclic compounds containing N, O and S, R ₁ OR ₂ where R ₁ and R ₂ are alkyl, And a solvent having a dipole moment of less than 1 debye and a polar solvent selected from the group consisting of R ₁ (CO) _n R ₂ , R ₁ (CO) _n R ₂ OR ₃ , R ₁ (CO ₂ ) _n R ₂ , R _{1 (CO 2) n R 2} OR 3 , and _{R 1 (CH 2 CH 2 O} ) n R 2 (n ≥1, R 1, R 2 and R ₃ are alkyl, aryl, allyl, alkenyl, alkynyl and alkoxy And a strong polar solvent selected from the group consisting of a solvent having a structure of the following formula (I), a solvent having a dielectric constant of more than 15, and a solvent having a dipole moment of more than 1 debye. 17. The lithium-sulfur battery of claim 16, wherein the electrolyte further comprises a co-solvent that is a Lewis acid or a Lewis base. 17. The method of claim 16 wherein the lithium salt is lithium trifluoromethane sulfonimide, lithium triflate, lithium perchlorate, LiPF ₆ and Li indicating a low impedance is selected from the group consisting of LiBF ₄ - sulfur battery. 18. The method of claim 17, wherein the transition metal is selected from the group consisting of Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Ta, W, Re, Os, Ir, Pt, Au, and Hg. 18. The method of claim 17, wherein the Group IIIA metal is selected from the group consisting of Al, Ga, In, and Tl, and wherein the Group IVA metal is selected from the group consisting of Si, Ge, Sn, and Pb. - Yellow cells.