JP2003123840A - Electrolyte for lithium-sulfur battery and lithium - sulfur battery containing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lithium - sulfur battery having a large capacity and excellent life characteristics, large current discharging characteristics and low temperature characteristics. SOLUTION: The lithium - sulfur battery comprises a positive electrode containing at least one positive electrode active material selected from the group consisting of a sulfur element, Li2 Sn (n>=1), Li2 Sn (n>=1) dissolved in a catholyte, organic sulfur compounds and carbon - sulfur polymers ((C2 Sx )n ; x=2.5 to 50, n>=2); an electrolyte containing a salt having a cation; and a negative electrode containing a negative electrode active material selected from the group consisting of a substance capable of reversibly introducing or eliminating a lithium ion, a substance capable of reacting with a lithium ion to reversibly form a lithium-containing compound, lithium metal and lithium alloys.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrolyte for lithium-sulfur batteries and a lithium-sulfur battery containing the same, and more particularly to excellent electrochemical properties such as battery capacity, high rate, life and low temperature characteristics. The present invention relates to an electrolytic solution for a lithium-sulfur battery and a lithium-sulfur battery including the electrolytic solution.

[0002]

2. Description of the Related Art With the development of portable electronic devices, the demand for light and high capacity secondary batteries is increasing. Among various secondary batteries satisfying such requirements, development of a lithium-sulfur battery using a sulfur-based material as a positive electrode material has been actively conducted.

Lithium-sulfur batteries are S--S bonded (Sul).
A sulfur-based material having a fur-Sulfur linkage) is used as a positive electrode active material, and a carbon-based material that causes insertion / deinsertion of an alkali metal such as lithium or a metal ion such as lithium ion is used as a negative electrode active material. It is the next battery. In a lithium-sulfur battery, the S-S bond decreases during the reduction reaction (during discharge) and the S oxidation number decreases, and the S-S bond forms again while the S oxidation number increases during the oxidation reaction (charge). The electric energy is stored and generated by utilizing the oxidation-reduction reaction.

Lithium-sulfur batteries are the most promising in terms of energy density among batteries developed to date. When using lithium metal used as the negative electrode active material, the energy density is 3830 mAh / g, and when using sulfur (S ₈ ) used as the positive electrode active material,
This is because the energy density is 1675 mAh / g. In addition, the sulfur-based material used as the positive electrode active material has the advantage that it is inexpensive and environmentally friendly.

[0005]

However, the fact is that there is no example of successful commercialization of a lithium-sulfur battery system yet. The reason why a lithium-sulfur battery cannot be commercialized is that it is very low when the sulfur is used as an active material, because the utilization factor indicating the amount of sulfur involved in the electrochemical redox reaction in the battery is low relative to the amount of sulfur that is input. It means to indicate the battery capacity.

[0006] Further, when sulfur is eluted into the electrolyte during the redox reaction and the battery life is deteriorated and an appropriate electrolyte cannot be selected, lithium sulfide (Li ₂ S) which is a sulfur reducing substance is deposited. However, there is a problem that it is no longer possible to participate in the electrochemical reaction.

In US Pat. No. 6,030,720, the main solvent is R ₁ (CH ₂ CH ₂ O) _n R ₂ (where n is 2 to 10 and R ₁ and R ₂ are alkyl or alkoxy groups). , The cosolvent is the donor number (donor n
A mixed solvent having a umber of 15 or more is used. Also, a liquid electrolyte containing at least one of a crown ether, a cryptand, and a donor solvent is used, and after the electrolyte is discharged, as a result, a catholyte is formed.
It is an electrolytic solution that becomes e). However, even if such an electrolytic solution is used, the capacity, high rate characteristics or life characteristics of the lithium-sulfur battery do not reach a satisfactory level.

[0008] At present, as an electrolyte solution component for use in a lithium-ion battery, active research is being carried out on an electrolyte salt and an organic solvent exhibiting a high ionic conductivity and a high oxidation potential. Li-ion batteries are mainly Li
Lithium salts such as ClO ₄ , LiBF ₄ , LiPF ₆ have been used. US Pat. No. 5,827,602
No. is a triflate, imide (i
A non-aqueous battery using a lithium salt containing a middle) and a methide-based anion is described.

However, although the above-mentioned lithium-ion battery electrolyte exhibits excellent performance in lithium-ion batteries, lithium-sulfur batteries have problems such as deterioration of battery characteristics. Is not used as it is as an electrolyte of a lithium-sulfur battery. This is because the carbonate-based electrolytic solution is mainly used for lithium-ion batteries, and the electrochemical reaction of polysulfide is extremely unstable. In order to be used as an electrolyte for lithium-sulfur batteries, the electrochemical reaction of polysulfide occurs stably, and there is a continuous demand for the development of an electrolyte that can dissolve the produced high-concentration polysulfide. .

Recently, for application to electric storage devices such as high-capacity capacitors and batteries, ionic liquids (Ionic Liquids (trademark)) based on imidazolium cations have been made into a liquid state at room temperature. The existing salt is attracting attention as a non-aqueous electrolyte salt for various electrochemical devices (K
och, et al. , J. Electroche
m. Soc. , Vol. 143, p155,
1996). US Pat. No. 5,965,054 (Cov
alent Associates, Inc. ), An electrolyte containing a liquid salt such as 1-ethyl-3-methylimidazolium hexafluorophosphate (EMIPF ₆ ) has a high conductivity (> 13 mS / c).
m), excellent electrochemical stability (> 2.5V), high salt concentration (> 1M), high thermal stability (> 100 ° C), and high when it is a double layer capacitor using an activated carbon electrode. Capacitance (> 100 F / g) is shown.

Recently published papers (AB M
cEwen et al. , J. Electroch
em. Soc. , Vol. 146, p168
7, 1999), the characteristics of a liquid salt and an electrolyte prepared by mixing it with various carbonate-based organic solvents were presented.
Such an electrolyte has further improved characteristics such as ionic conductivity (60 mS / cm) and excellent electrochemical stability (20 u).
> 4V at A / cm ² and high salt concentration (> 3M) values. US Pat. No. 5,973,913 describes that an electrolyte containing such a liquid salt can be applied to an electric storage device such as an electrochemical capacitor or a battery to obtain a high capacitance and a high energy density. There is.

Battery characteristics of a lithium-sulfur battery vary greatly depending on the type and composition of salt and organic solvent used as an electrolyte. Nevertheless, the above patents and papers do not specifically describe the type and composition of the optimum salt and organic solvent suitable for lithium-sulfur batteries that exhibit high capacity and excellent high rate characteristics and low temperature characteristics. . In particular, there has been no development in which the liquid salt is applied to a lithium-sulfur battery.

The present invention is to solve the above-mentioned problems, and an object of the present invention is to provide a lithium-sulfur battery having high capacity and excellent life characteristics, high rate discharge characteristics and low temperature characteristics. Especially.

[0014]

To SUMMARY OF THE INVENTION To achieve the above object, the present invention is elemental _{sulfur, Li 2 S n (n ≧} 1), Li was dissolved in catholyte _{2 S n (n ≧ 1)} , organic sulfur compounds, and carbon - sulfur polymer _{((C 2 S x) n} : x =
2.5 to 50, n ≧ 2) and a positive electrode containing at least one positive electrode active material selected from the group consisting of: an electrolytic solution containing a salt having an organic cation; and reversible lithium ion insertion or desorption. Provided is a lithium-sulfur battery including a negative electrode including a negative electrode active material selected from the group consisting of a substance, a substance capable of reacting with lithium ions to reversibly form a lithium-containing compound, a lithium metal and a lithium alloy.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in more detail below.

When a lithium-sulfur battery is discharged, elemental sulfur is reduced at the positive electrode and sulfide (S ²⁻ ) or polysulfide (S _n ⁻ , S _n ²⁻ , where n ≧ 2).
Is generated. Therefore, a lithium - sulfur batteries elemental sulfur, using lithium sulfide _(Li 2 S), or a lithium polysulfide _{(Li 2 S n, n =} 2,4,6,8) as a positive electrode active material. Double sulfur has a small polarity, and lithium sulfide and lithium polysulfide are ionic compounds with a large polarity.Lithium sulfide exists in an organic solvent in a precipitated state, but lithium polysulfide exists in an almost dissolved state. To do. In order for the sulfur-based substances having such various characteristics to smoothly carry out the electrochemical reaction, it is important to select an electrolytic solution in which these sulfur-based substances are well dissolved. As an electrolyte of a conventional lithium-sulfur battery, lithium salt in a solid state is added to an organic solvent for use.

In the lithium-sulfur battery of the present invention, a salt having an organic cation, which has excellent solubility in a sulfur-based positive electrode active material and exhibits high ionic conductivity, is used as an electrolytic solution.

The salt having the organic cation does not contain Li ion. In addition, since the vapor pressure is low, the flash point is very high, and the non-combustibility is provided, the stability of the battery can be improved, and the non-corrosive and mechanically stable film is formed. Has the advantage of being manufacturable. The salt preferably used in the present invention has a van der Waals volume of 100Å
Contains ³ or more large organic cations. The larger the van der Waals volume of such cations, the lower the lattice energy of the molecule and the better the ionic conductivity. The electrolytic solution containing the salt of the present invention can improve the sulfur utilization rate of a lithium-sulfur battery.

The salt can exist in a liquid state in a wide temperature range, and particularly in a liquid state at the operating temperature of the battery, the salt itself can be used as an electrolytic solution. The salt used in the present invention is preferably in a liquid state at a temperature of 100 ° C. or lower, more preferably in a liquid state at a temperature of 50 ° C. or lower, and most preferably in a liquid state at a temperature of 25 ° C. or lower. . As a matter of course, it is also possible to use the liquid state at different temperatures depending on the application method.

The organic cation of the salt is preferably a cation of a heterocyclic compound. The heteroatoms of the heterocyclic compound are selected from N, O, S or combinations thereof, and the number of heteroatoms is preferably 1 to 4,
One or two is more preferable. The cation of such a heterocyclic compound is pyridinium (Pyridine).
ium), Pyridazinium (Pyridaziniu)
m), Pyrimidinium,
Pyrazinium, Imidazolium, Pyrazolium
azolium), thiazolium (Thiazoliu)
m), oxazolium (Oxazolium), and triazolium (Triazolium), or a cation of a substituted compound thereof. Among such compounds, 1-ethyl-3
It is preferable to use a cation of an imidazolium compound such as -methylimidazolium (EMI), 1,2-dimethyl-3-propylimidazolium (DMPI) and 1-butyl-3-methylimidazolium (BMI). it can.

The anion bound to the cation is bis (perfluoroethylsulfonyl) imide (N (C ₂ F _{2
^{5 SO 2) 2 -, Beti}} ), bis (trifluoromethylsulfonyl) _{imide) (N (CF 3 SO 2} ) 2 -, I
m), tris (trifluoromethylsulfonyl) methide ^{_{(C (CF 3 SO 2)}} 2 -, Me), trifluoromethane sulfonimide, trifluoromethyl sulfonimide, trifluoromethylsulfonate, _AsF ⁶ -, C
^{_{lO 4 -, PF 6 -,}} BF 4 - is one of.

As an example of the salt which can be preferably used in the present invention, 1-ethyl-3-methylimidazolium bis (perfluoroethylsulfonyl) imide (EM
IBeti), 1,2-dimethyl-3-propylimidazolium bis (trifluoromethylsulfonyl) imide (DMPIIm), 1-butyl-3-methylimidazolium hexafluorophosphate (BMIPF ₆ ) and the like.

The salt is preferably contained in an amount of 80% by volume or less, more preferably 0.001 to 60% by volume, and 0.01 to 40% by total electrolyte.
More preferably, the content is 0.01% to 20% by volume.
More preferably, the content is 5% to 20% by volume.
It is more preferably contained, and most preferably 5 to 10% by volume. In addition, the salt is preferably contained in an amount of 90% by weight or less based on the total electrolyte,
It is more preferable that the content is 01 to 70% by weight,
More preferably, it is contained in an amount of 0.01 to 50% by weight.

In the present invention, the solute having the above organic cation is used.
Can be used as an electrolyte for lithium-sulfur batteries.
However, the solid state lithium
It is also possible to use a mixed solution containing salt as an electrolyte.
Wear. As the lithium salt, a conventional battery electrolytic
It is possible to use all the lithium salt added to the solution.
Wear. Examples of these include LiPF₆, LiBF_Four,
LiSbF₆, LiAsF₆, LiClO_Four, LiCF
_ThreeSO_Three, Li (CF_ThreeSO_Two)_TwoN, LiC _FourF₉S
O_Three, LiSbF₆, LiAlO_Four, LiAlCl_Four,
LiN (C_xF _{2x + 1}SO_Two) (C_yF_{2y + 1}S
O_Two) (Where x and y are natural numbers), LiC
1 and LiI. In this, lithium hexaflu
Orophosphate (LiPF₆), Lithium tetraful
Oroborate (LiBF_Four), Lithium hexafluoro
Arsenate (LiAsF₆), Lithium perchlorate (L
iClO _Four), Lithium bis (trifluoromethylsulfur)
Honyl) imide (LiN (CF_ThreeSO_Two)_Two,lithium
Bis (perfluoroethylsulfonyl) imide (LiN
(C_TwoF₅SO_Two)_Two, Lithium trifluorosulfone
Acid salt (CF_ThreeSO_ThreeLi) or the like is preferably used
it can. The concentration of the lithium salt is in the range of 0 to 4M.
Preferably in the range of 0.05 to 1.5M.
More preferably.

The electrolyte solution of the present invention may further include an organic solvent in the salt having the organic cation. As the organic solvent, all organic solvents used in conventional lithium-sulfur batteries can be used. Preferred examples of such organic solvents include dimethoxyethane and dioxolane. Dimethoxyethane is 0 in the total electrolyte
To 90% by volume, more preferably 0 to 80% by volume. Dioxolane is 0 out of all electrolytes
To 60% by volume, preferably 0 to 30% by volume.

As the organic solvent used in the electrolytic solution of the present invention, a single solvent may be used or a mixed organic solvent of two or more may be used. When two or more mixed organic solvents are used, it is preferable to select and use one or more solvents from two or more groups of a weak polar solvent group, a strong polar solvent group, and a lithium metal protective solvent group.

A weak polar solvent is defined as a solvent having a dielectric constant of less than 15 capable of dissolving elemental sulfur among aryl compounds, bicyclic ethers, and acyclic carbonates, and a strong polar solvent is a bicyclic carbonate, A sulfoxide compound, a lactone compound, a ketone compound, an ester compound, a sulfate compound, a sulfuric acid compound is defined as a solvent having a dielectric constant of more than 15 capable of dissolving lithium polysulfide, and a lithium protective solvent is a saturated ether compound, Saturated ether compound, N, O,
SEI (Solid Solid) stable to lithium metal such as a heterocyclic compound containing S or a combination thereof.
Charge / discharge cycle efficiency (cycle ef) for forming an Electrolyte Interface film
ficinity) is defined as a solvent having a ficity of 50% or more.

Specific examples of the weak polar solvent include xylene, dimethoxyethane, 2-methyltetrahydrofuran, diethyl carbonate, dimethyl carbonate, toluene, dimethyl ether, diethyl ether, diglyme and tetraglyme.

As a specific example of the strong polar solvent, hexamethylphosphoric triamide (hexamethyl p
phosporic triamide), gamma-butyrolactone, acetonitrile, ethylene carbonate, propylene carbonate, N-methylpyrrolidone,
3-methyl-2-oxazolidone (3-methyl-
2-oxazolidene), dimethylformamide, sulfolane, dimethylacetamide or dimethylsulfoxide, dimethylsulfate, ethylene glycol diacetate, dimethylsulfite, ethyleneglycolsulfite and the like.

Specific examples of the lithium protective solvent include:
There are tetrahydrofuran, ethylene oxide, dioxolane, 3,5-dimethylisoxazole, 2,5-dimethylfuran, furan, 2-methylfuran, 1,4-dioxane, 4-methyldioxolane and the like.

The lithium-sulfur battery 1 according to the present invention is shown in FIG.
As shown in FIG. 3, the positive electrode 3, the negative electrode 4, and the positive electrode 3 and the negative electrode 4
And a battery can 5 including a separator positioned between and. A salt electrolyte containing organic cations is injected between the positive electrode 3 and the negative electrode 4.

The positive electrode 3 of the lithium sulfur battery of the present invention is elemental _{sulfur, Li 2 S n (n ≧} 1), Li was dissolved in catholyte _{2 S n (n ≧ 1)} , organic sulfur compounds, and carbon - sulfur Polymer ((C ₂ S _x ) _n : x = 2.5 to 50, n
It contains at least one positive electrode active material selected from the group consisting of ≧ 2).

The positive electrode 3 may further include one or more additives selected from the group consisting of transition metals, Group IIIA metals, Group IVA metals, alloys thereof, and sulfur compounds containing these metals. The transition metals are Sc, Ti, V, C
r, Mn, Fe, Co, Ni, Cu, Zn, Y, Zr,
Nb, Mo, Tc, Ru, Rh, Pd, Ag, Cd, T
It is preferably selected from the group consisting of a, W, Re, Os, Ir, Pt, Au and Hg. The Group IIIA metal is preferably selected from the group consisting of Al, Ga, In and Tl. The group IVA metals are Si, Ge, Sn and P.
It is preferably selected from the group consisting of b.

Further, an electrically conductive agent may be further included to allow electrons to move smoothly in the positive electrode plate 3. The conductive agent is not particularly limited, but a conductive material such as a graphite-based material or a carbon-based material or a conductive polymer can be preferably used. The graphite-based material includes KS 6 (a product of Timcal), and the carbon-based material includes Super P (a product of MMM), Ketchenblack, and Denka Black (d).
Enka black), acetylene black, carbon black and the like. Examples of the conductive polymer include polyaniline, polythiophene, polyacetylene, and polypyrrole. These conductive agents may be used alone or in combination of two or more.

The positive electrode active material is attached to the current collector by a binder. Examples of the binder include poly (vinyl acetate), polyvinyl alcohol, polyethylene oxide, polyvinyl pyrrolidone, alkylated polyethylene oxide, cross-linked polyethylene oxide, polyvinyl ether, poly (methyl methacrylate), polyvinylidene fluoride, polyhexafluoropropylene. Polyvinylidene fluoride copolymer (trade name: Kynar), poly (ethyl acrylate), polytetrafluoroethylene, polyvinyl chloride, polyacrylonitrile, polyvinyl pyridine, polystyrene, their derivatives, mixtures, and copolymers can be used. it can.

In order to manufacture the positive electrode of the present invention, first,
After the binder is dissolved in the solvent for producing the slurry, the conductive agent is dispersed. As the solvent for producing the slurry, it is preferable to use a solvent that can uniformly disperse a sulfur compound, a binder and a conductive agent, and that is easily evaporated, typically acetonitrile, methanol, ethanol, tetrahydrofuran, water. , Isopropyl alcohol, dimethylformamide, etc. Next, the sulfur-based active material and the additive are uniformly dispersed again in the slurry in which the conductive agent is dispersed to produce a positive electrode active material slurry. The amount of solvent, sulfur compound or selectively added additive contained in the slurry is not particularly important in the present invention, and it suffices that the slurry has a proper viscosity so as to facilitate coating of the slurry. .

The thus prepared slurry is applied to a current collector and vacuum dried to form a positive electrode plate 3, which is then used for assembling the battery 1. The slurry may be coated on the current collector with an appropriate thickness depending on the viscosity and the thickness of the positive electrode plate to be formed. The current collector is not particularly limited, but a conductive material such as stainless steel, aluminum, copper, or titanium is preferably used, and a carbon-coated aluminum current collector is more preferably used. The carbon-coated aluminum substrate has better adhesion to the active material than the carbon-uncoated aluminum substrate, lower contact resistance, and can prevent aluminum from being corroded by polysulfide. There are advantages.

The negative electrode 4 of the lithium-sulfur battery 1 of the present invention is a substance capable of reversibly inserting or releasing lithium ions, and a substance capable of reacting with lithium ions to reversibly form a lithium-containing compound. , A negative electrode active material selected from the group consisting of lithium metal and lithium alloy.

The material capable of reversibly inserting / releasing lithium ions is a carbon material, and any of the carbon-based negative electrode active materials generally used in lithium-ion secondary batteries can be used. As a specific example, crystalline carbon, amorphous carbon, or these can be used together. In addition, typical examples of the substance capable of reversibly forming a lithium-containing compound by reacting with the lithium ion include tin oxide (SnO ₂ ), titanium nitrate, and silicon, but are not limited thereto. Absent. As a lithium alloy, lithium and Na, K, Rb, Cs,
An alloy of a metal selected from the group consisting of Fr, Be, Mg, Ca, Sr, Ba, Ra, Al and Sn can be used.

An inorganic protective film (pro
A negative layer may also be formed of a luminescent layer, an organic protective film, or a material in which these are stacked. As the inorganic protective film, Mg, Al, B,
C, Sn, Pb, Cd, Si, In, Ga, lithium silicate, lithium borate, lithium phosphate,
Lithium Phosphor Nitride (lithium ph
osphonnitride), lithium silicosulfid (lithium silicosulfid)
e), a material selected from the group consisting of lithium borosulfide, lithium aluminosulfide, and lithium phosphosulfide. Examples of the organic protective film include poly (p-phenylene), polyacetylene, poly (p-phenylene vinylene), polyaniline, polypyrrole, polythiophene, poly (2,5-ethylene vinylene), acetylene, poly (ferrinaphthalene), polyacene, And a conductive monomer, oligomer or polymer selected from the group consisting of poly (naphthalene-2,6-diyl).

Further, in the process of charging / discharging the lithium-sulfur battery, the sulfur used as the positive electrode active material may change to an inactive material and be attached to the surface of the lithium negative electrode. Thus, inactive sulfur (inactive sulfur)
r) refers to sulfur in a state where it cannot contribute to the electrochemical reaction of the positive electrode through various electrochemical or chemical reactions, and the inert sulfur formed on the surface of the lithium negative electrode is a protective film of the lithium negative electrode. (Protective la
It also has the advantage of acting as a yer). Therefore, lithium metal and inert sulfur formed on this lithium metal, such as lithium sulfide, can also be used as the negative electrode.

In the lithium-sulfur battery, the porosity of the electrode plate is very important because it is related to the impregnated amount of the electrolytic solution. If the porosity is too low, a local discharge will occur and the concentration of lithium polysulfide will be very high, and it is very likely that the sulfur utilization rate will be reduced due to the extremely easy formation of a precipitate. If it is too high, the mixture density will be low and it will be difficult to manufacture a high capacity battery. The porosity of the positive electrode plate is preferably 5% or more, more preferably 10% or more, and most preferably 15 to 5 of the total volume of the positive electrode plate.
It is 0%.

As the separator existing on the positive electrode and the negative electrode, a polymer film such as polyethylene or polypropylene or a multi-layer film of these is used.

[0044]

EXAMPLES Preferred examples and comparative examples of the present invention will be described below. However, the following embodiment is only one preferred embodiment of the present invention, and the present invention is not limited to this.

(Example 1) 67.5% by weight of elemental sulfur, 11.4% by weight of Ketjen black as a conductive agent, and 21.1% by weight of polyethylene oxide as a binder were mixed with an acetonitrile solvent to prepare a positive electrode for a lithium-sulfur battery. An active material slurry was produced. The slurry was coated on a carbon-coated aluminum current collector, and the slurry-coated current collector was dried in a vacuum oven at 60 ° C. for 12 hours or more to obtain 25 × 50 mm ^2.
A positive electrode plate of ² mAh / cm ² having a size of ² mm was manufactured. A positive electrode plate, a vacuum-dried separator, and a negative electrode were stacked on a lithium electrode in this order, and then inserted into a pouch. 0.5M
LiSO ₃ CF ₃ dissolved dimethoxyethane / 1
An electrolytic solution prepared by mixing -ethyl-3-methylimidazolium bis (perfluoroethylsulfonyl) imide (EMIBeti) / dioxolane in a volume ratio of 75: 5: 20 was injected into the pouch. After injecting the electrolyte, the pouch type test cell was assembled by sealing.

Example 2 0.5M LiSO ₃ CF ₃
A test cell was assembled in the same manner as in Example 1 except that a solution prepared by mixing dimethoxyethane / EMIBeti / dioxolane in a volume ratio of 70:10:20 was used as an electrolyte.

Example 3 Example 3 except that a solution of 0.5M LiPF ₆ dissolved in dimethoxyethane / EMIPF ₆ / dioxolane at a volume ratio of 75: 5: 20 was used as an electrolytic solution. A test cell was assembled in the same manner as in 1.

Example 4 Example 4 except that a solution prepared by mixing 0.5M LiPF ₆ dissolved in dimethoxyethane / EMIPF ₆ / dioxolane in a volume ratio of 70:10:20 was used as an electrolytic solution. A test cell was assembled in the same manner as in 1.

Example 5 A test cell was assembled in the same manner as in Example 1 except that EMIBeti was used as the electrolytic solution.

Example 6 0.5M LiSO ₃ CF ₃
A test cell was assembled in the same manner as in Example 1 except that EMIBeti in which was dissolved was used as an electrolytic solution.

Comparative Example 1 1.0M LiSO ₃ CF ₃
Was dissolved in dimethoxyethane / dioxolane 80:
A test cell was assembled in the same manner as in Example 1 except that an electrolytic solution mixed in a volume ratio of 20 was used.

Comparative Example 2 A test was conducted in the same manner as in Example 1 except that an electrolyte solution prepared by mixing dimethoxyethane / dioxolane in which 1.0M LiPF ₆ was dissolved at a volume ratio of 80:20 was used. The cell was assembled.

Comparative Example 3 1.0M LiSO ₃ CF ₃
A test cell was assembled in the same manner as in Example 1 except that an electrolyte solution prepared by mixing dimethoxyethane / diglyme / sulfolane / dioxolane in a volume ratio of 20: 20: 10: 50 was used.

Evaluation of Life Characteristics The life characteristics of the test cells of Examples 1 to 6 and Comparative Examples 1 to 3 were evaluated at room temperature. In the case of the lithium-sulfur battery, since it was in a charged state when the test cell was manufactured, it was first discharged for one cycle at a discharge current density of 0.2 mA / cm ² . In order to investigate the change in capacity according to the change in discharge current, the current density during charging was fixed at 0.4 mA / cm ² and the discharge current was 0.2, 0.4, 1.0, 2.0 mA / cm ^{2. 2} (each C-rate is 0.1C, 0.2C, 0.5C,
1C) and then 1 cycle at a time, 1.
The discharge current was fixed at 0 mA / cm ² (0.5 C), and the battery was charged and discharged for 50 cycles. During charge and discharge, the cut-off voltage was set to 1.5 to 2.8V.

The life characteristics of the cells manufactured in Examples 1 and 2 and Comparative Example 1 depending on the number of cycles are shown in FIG. As shown in FIG. 2, the cells of Examples 1 and 2 including the electrolyte solution containing EMIBeti salt had a discharge capacity value slightly lower than that of the cell of Comparative Example 1 in the initial cycle, but after 30 cycles, The capacity of the cells decreased sharply, but the capacity of the cells of Examples 1 and 2 did not decrease until 50 cycles. The life characteristics of the cells manufactured in Examples 3 and 4 and Comparative Example 2 are shown in FIG. As shown in FIG. 3, the capacity of the cell of Comparative Example 2 dropped sharply after 30 cycles, but the capacity of the cells of Examples 3 and 4 was excellent up to 100 cycles. Therefore, it can be seen that the cells of Examples according to the present invention have an excellent sulfur utilization rate and exhibit stable life characteristics.

Evaluation of Discharge Characteristics The same method as in the evaluation of life characteristics was applied to the cells of Examples 1 to 6 and Comparative Examples 1 to 3 except that the cut-off voltage was set to 1.8 to 2.8V. It was charged and discharged. When the discharge current is 1.0 mA / cm ² (0.5 C), the test results of Examples 1 and 2 and Comparative Example 1 are shown in FIG. 4, and the discharge current is 2.0 mA / cm ² (1 C). The test results at one time are shown in FIG. Cell energy density (spe
(Cific energy, mWh / g) was calculated by measuring the average discharge voltage and discharge capacity. 4 and 5, the x-axis represents the energy density (average discharge voltage x discharge capacity) and the y-axis represents the voltage.

As shown in FIGS. 4 and 5, the cells of Examples 1 and 2 were far superior to the cells of Comparative Example 1 in average discharge voltage and energy density. The difference between the average discharge voltage and the energy density is low (1.0 mA / cm
² ) (0.5C)) Higher rate than discharge (2.0mA / cm)
² ) 1C)) It was shown to be even greater during discharge. Therefore, it can be confirmed that the cells of Examples 1 and 2 according to the present invention have excellent discharge characteristics not only at a low rate but also at a high rate.

In addition, 10% by volume of EMI was obtained from the cell of Example 1 using an electrolytic solution containing 5% by volume of EMIBeti.
The discharge average voltage was increased in the cell of Example 2 using the electrolyte solution containing Beti. 1.0 mA / cm ² (0.5 C)
The energy densities of Example 1 and Example 2 are similar to each other when discharged at 2, but when discharged at 2.0 mA / cm ² (1 C), Example 2 has a higher energy density than Example 1. did.

EMIBe with the electrolyte used in Example 1
The average discharge voltage and the discharge capacity were measured while changing the content of ti from 0 to 30% by volume with respect to the electrolytic solution, and are shown in FIGS. 6 and 7, respectively. As shown in FIG. 6 and FIG.
The content of eti salt is 5 to 10% by volume with respect to the electrolyte.
It can be confirmed that the average discharge voltage and the discharge capacity are excellent in the case of.

Evaluation of low temperature characteristics The low temperature characteristics of the test cells of Examples 1 and 2 and Comparative Example 1 were evaluated. The cell was first discharged at a discharge current density of 0.2 mA / cm ² for one cycle, and then the current density during charging was 0.4 mA.
/ Cm ² fixed to the same, discharge current 0.2, 0.4,
1.0, 2.0 mA / cm ² (each C-rate
Was changed to 0.1 C, 0.2 C, 0.5 C, 1 C), and each cycle was performed. After that, charging / discharging was carried out at 0.4 mA / cm ² to obtain the discharge capacity at room temperature. Then, the battery was charged at room temperature at 0.4 mA / cm ² , transferred to a device having a low temperature atmosphere of −10 ° C. and −20 ° C., left for about 2 hours, and then discharged to 0.4 mA / cm ² . The discharge capacity at this time was converted into a percentage based on the discharge capacity at room temperature and shown in Table 1 below. The cut-off voltage during charge / discharge was set to 1.5 to 2.8V.

[0061]

[Table 1]

In Table 1, it can be seen that the cell of Example 1 exhibits a better discharge capacity at a lower temperature than Comparative Example 1.

In the following reference examples, the electrochemical characteristics when the electrolytic solution of the lithium-sulfur battery of the present invention was applied to a lithium ion battery were evaluated.

Reference Example 1 A binder solution prepared by adding a binder (polyvinylidene fluoride) to N-methylpyrrolidone (NMP) was added with a conductive agent (Super P) and a LiCoO ₂ positive electrode active material having an average particle size of 10 μm. Was added to produce a positive electrode active material slurry. The weight ratio of the positive electrode active material / conductive agent / binder was 96/2/2. The slurry was coated on a carbon-coated Al foil, and the slurry-coated Al foil was dried in a vacuum oven at 60 ° C. for 12 hours or more and then dried at 25 × 5.
A positive electrode plate of ² mAh / cm ² having a size of 0 mm ² was manufactured. A positive electrode plate, a vacuum-dried separator, and a lithium electrode as a negative electrode were sequentially stacked and then inserted into a pouch. A pouch type lithium ion cell was manufactured using a mixed solution of ethylene carbonate and dimethyl carbonate (volume ratio: 1/1) in which 1.0 M LiSO ₃ CF ₃ was dissolved as an electrolytic solution.

Reference Example 2 EMIBeti as an electrolyte
A lithium ion cell was manufactured in the same manner as in Reference Example 1 except that the above was used.

Reference Example 3 1.0 M Li as an electrolyte
A lithium ion cell was manufactured in the same manner as in Reference Example 1 except that EMIBeti in which SO ₃ CF ₃ was dissolved was used.

Reference Example 4 1.0 M Li as an electrolyte
SO ₃ dimethoxyethane CF ₃ was dissolved / EMIB
A lithium ion cell was manufactured in the same manner as in Reference Example 1 except that a solution in which eti / dioxolane was mixed at a volume ratio of 70:10:20 was used.

It is shown that the lithium ion cells according to Reference Examples 2 to 4 are less than 20% of the discharge capacity of the lithium ion cell according to Reference Example 1 using a carbonate-based solvent as an electrolytic solution. It was shown to be less than about 10% of capacity. That is, lithium-
It can be confirmed that the electrolytic solution for improving the characteristics of the sulfur battery does not show such characteristics in the lithium ion battery. Therefore, it is understood that the lithium-ion battery and the lithium-sulfur battery require different electrolytic solution characteristics because the active materials contributing to the electrochemical reaction are different from each other.

[0069]

INDUSTRIAL APPLICABILITY The lithium-sulfur battery of the present invention has an organic cation that is not a lithium ion and uses a salt having an excellent ionic conductivity at room temperature as an electrolytic solution, which has an excellent sulfur utilization factor and a long life and discharge characteristics. (Discharge capacity and average discharge voltage)
In addition, the low temperature characteristics are extremely superior to the batteries using the existing electrolyte.

[Brief description of drawings]

FIG. 1 is a perspective view of a lithium-sulfur battery manufactured according to a preferred embodiment of the present invention.

FIG. 2 is a graph showing life characteristics of cells manufactured in Example 1, Example 2 and Comparative Example 1.

FIG. 3 is a graph showing life characteristics of cells manufactured in Example 3, Example 4, and Comparative Example 2.

FIG. 4 is a graph showing low rate discharge characteristics of cells manufactured according to Example 1, Example 2 and Comparative Example 1.

FIG. 5 is a graph showing high rate discharge characteristics of cells manufactured in Example 1, Example 2 and Comparative Example 1.

FIG. 6 is a drawing showing the average discharge voltage of a lithium-sulfur battery according to the content of salt in the electrolyte of the present invention.

FIG. 7 is a diagram showing a discharge capacity of a lithium-sulfur battery according to a content of a salt in an electrolyte of the present invention.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Yong-Joo Jun             Republic of Korea Daejeon City Yousung               Song Gun-Dong Song Gamma Ul Aper             To 202-602 (72) Inventor Choi Yu Sui             Chungcheongnam-do, Cheonan-do, South Korea             507 building 401 (72) Inventor Zandy Kim             South Korea Seoul June Run-Kumi             Jongmok 5-Don 153-4 (72) Inventor Choi Suishi             191-3 Shiraishi-dong, Cheonan-si, Chungcheongnam-do, South Korea             Local modern apartment 105, 1002 F term (reference) 5H029 AJ03 AJ05 AK05 AK15 AK19                       AL02 AL12 AL18 AM02 AM03                       AM04 AM07 AM09 BJ04 BJ12                       DJ08 EJ07 EJ12 HJ02 HJ07                       HJ10 HJ14                 5H050 AA06 AA07 AA08 BA16 CA11                       CA26 CA29 CB02 CB12 CB29                       DA02 DA09 DA11 EA15 EA24                       FA02 HA02 HA07 HA10 HA14

Claims (49)

[Claims] 1. An electrolytic solution for a lithium-sulfur battery, which contains a salt having an organic cation having high ionic conductivity by dissolving a sulfur-based positive electrode active material of a lithium-sulfur battery. 2. The electrolytic solution for a lithium-sulfur battery according to claim 1, wherein the salt exists in a liquid state at a temperature of 100 ° C. or lower. 3. The electrolyte solution for a lithium-sulfur battery according to claim 2, wherein the salt exists in a liquid state at a temperature of 50 ° C. or lower. 4. The electrolytic solution for a lithium-sulfur battery according to claim 3, wherein the salt exists in a liquid state at a temperature of 25 ° C. or lower. 5. The electrolyte solution for a lithium-sulfur battery according to claim 1, wherein the salt contains an organic cation having a van der Waals volume of 100Å ³ or more. 6. The electrolytic solution for a lithium-sulfur battery according to claim 1, wherein the salt contains a cation of a heterocyclic compound. 7. The electrolyte solution for a lithium-sulfur battery according to claim 6, wherein the heterocyclic compound contains a hetero atom selected from the group consisting of N, O, S and combinations thereof. . 8. The electrolytic solution for a lithium-sulfur battery according to claim 6, wherein the heterocyclic compound contains 1 to 4 heteroatoms. 9. The electrolyte solution for a lithium-sulfur battery according to claim 8, wherein the heterocyclic compound contains one or two heteroatoms. 10. The cation of the heterocyclic compound is
The lithium-sulfur battery according to claim 7, which is a compound selected from the group consisting of pyridinium, pyridazinium, pyrimidinium, pyrazinium, imidazolium, pyrazolium, thiazolium, oxazolium, and triazolium or a cation of these substituted compounds. Electrolyte. 11. The electrolytic solution for a lithium-sulfur battery according to claim 1, wherein the salt contains a cation of an imidazolium compound. 12. The imidazolium compound is 1-ethyl-3-methylimidazolium (EMI), 1,2-dimethyl-3-propylimidazolium (DPMI), and 1-butyl-3-methylimidazolium (BMI). The lithium-sulfur battery electrolyte according to claim 11, which is a compound selected from the group consisting of: 13. The salt binds to an organic cation
Further comprising an anion, wherein the anion is bis (perffluent
Oroethylsulfonyl) imide (N (C_TwoF ₅SO_Two)
_Two ⁻, Beti), bis (trifluoromethylsulfoni)
) Imide (N (CF_ThreeSO_Two)_Two ⁻, Im), Tris
(Trifluoromethylsulfonyl) methide (C (CF_Three
SO_Two)_Two ⁻, Me), trifluoromethanesulfone
Mido, trifluoromethylsulfonimide, trifluor
Romethyl sulfonate, AsF ₆ ⁻, ClO_Four ⁻, PF
₆ ⁻, And BF_Four ⁻At least selected from the group consisting of
The lithium-sulfur battery according to claim 1, which is also one.
Electrolyte. 14. The salt is 1-ethyl-3-methylimidazolium bis (perfluoroethylsulfonyl).
Imide (EMIBeti), 1,2-dimethyl-3-propylimidazolium bis (trifluoromethylsulfonyl) imide (DMPIIm), 1-butyl-3methylimidazolium hexafluorophosphate (BMIP)
The electrolytic solution for a lithium-sulfur battery according to claim 1, which is a salt selected from the group consisting of F ₆ ) and combinations thereof. 15. The electrolyte of claim 1, wherein the electrolyte further comprises an organic solvent mixed with a salt having an organic cation. 16. The electrolytic solution for a lithium-sulfur battery according to claim 15, wherein the salt is present at 80% by volume or less. 17. The electrolytic solution for a lithium-sulfur battery according to claim 15, wherein the salt is present in an amount of 5 to 10% by volume. 18. The organic solvent is dimethoxyethane, dioxolane or a mixed solvent thereof.
The lithium-sulfur battery electrolyte solution according to. 19. The electrolytic solution for a lithium-sulfur battery according to claim 18, wherein the organic solvent is dimethoxyethane, and the dimethoxyethane is used in an amount of 90% by volume or less of the total electrolytic solution. . 20. The organic solvent is dioxolane,
The electrolytic solution for a lithium-sulfur battery according to claim 18, wherein dioxolane is used in an amount of 60% by volume or less of the total electrolytic solution. 21. The organic solvent is a solvent in which one or more solvents are selected and mixed from two or more groups of a weak polar solvent group, a strong polar solvent group, and a lithium metal protective solvent group. 15. The lithium-sulfur battery electrolyte solution according to 15. 22. The weakly polar solvent is an aryl compound,
Selected from the group consisting of bicyclic ethers, and acyclic carbonates, the strong polar solvent is a bicyclic carbonate,
Sulfoxide compound, lactone compound, ketone compound,
The compound selected from the group consisting of an ester compound, a sulfate compound, and a sulfuric acid compound, wherein the lithium protecting solvent is a group consisting of a saturated ether compound, an unsaturated ether compound, N, O, S, or a heterocyclic compound containing a combination thereof. 22. It is further selected,
The lithium-sulfur battery electrolyte solution according to. 23. The electrolyte solution for a lithium-sulfur battery according to claim 21, wherein the electrolyte solution further comprises a lithium solid salt. 24. The solid lithium salt is LiP.
F₆, LiBF_Four, LiSbF₆, LiAsF₆, Li
ClO_Four, LiCF_ThreeSO_Three, Li (CF_ThreeSO _Two)_Two
N, LiC_FourF₉SO_Three, LiSbF₆, LiAl
O_Four, LiAlCl_Four, LiN (CxF_{2x + 1}S
O_Two) (C_yF_{2y + 1}SO_Two) (Where x and y are
A natural number), LiCl, and LiI
24. At least one selected, according to claim 23.
Electrolyte for lithium-sulfur batteries. 25. The electrolyte solution for a lithium-sulfur battery according to claim 23, wherein the concentration of the lithium solid salt is in the range of 0 to 4M. 26. The concentration of lithium salt is 0.05.
26. The electrolyte solution for a lithium-sulfur battery according to claim 25, which is in the range of 1 to 1.5M. 27. A positive electrode containing at least one positive electrode active material selected from the group consisting of elemental sulfur, a sulfur-based compound and a mixture thereof; an electrolytic solution containing a salt having an organic cation; and reversibly inserting lithium ions. Alternatively, a lithium-sulfur battery including a negative electrode including a desorbable substance, a substance capable of reversibly forming a lithium-containing compound by reacting with lithium ions, and a negative electrode active material selected from the group consisting of lithium metal and lithium alloy. 28. The positive electrode active material is elemental sulfur, Li ₂ S
_n (n ≧ 1), Li ₂ Sn (n
≧ 1), an organic sulfur compound, and a carbon-sulfur polymer ((C ₂ S _x ) _n : x = 2.5 to 50, n ≧ 2), which is at least one positive electrode active material selected from the group consisting of: The lithium-sulfur battery of claim 27. 29. The positive electrode is a transition metal, Group IIIA or IVA.
28. The lithium-sulfur battery of claim 27, further comprising one or more additives selected from the group consisting of group metals, alloys thereof, or sulfur compounds containing these metals. 30. The transition metal is Sc, Ti, V, C
r, Mn, Fe, Co, Ni, Cu, Zn, Y, Zr,
Nb, Mo, Tc, Ru, Rh, Pd, Ag, Cd, T
at least one element selected from the group consisting of a, W, Re, Os, Ir, Pt, Au and Hg, and
The Group IIIA metal is at least one element selected from the group consisting of Al, Ga, In, and Tl, and the Group IVA metal is at least one element selected from the group consisting of Si, Ge, Sn, and Pb. 30. The lithium-sulfur battery of claim 29. 31. The lithium-sulfur battery of claim 27, wherein the positive electrode further comprises an electrically conductive agent that facilitates smooth movement of electrons. 32. The positive electrode further comprises a current collector and a binder for attaching a positive electrode active material to the current collector, the binder being poly (vinyl acetate), polyvinyl alcohol, polyethylene oxide, polyvinylpyrrolidone, alkylated. Polyethylene oxide,
Cross-linked polyethylene oxide, polyvinyl ether, poly (methyl methacrylate), polyvinylidene fluoride, copolymer of polyhexafluoropropylene and polyvinylidene fluoride (trade name: Kynar), poly (ethyl acrylate), polytetrafluoroethylene,
Polyvinyl chloride, polyacrylonitrile, polyvinyl pyridine, polystyrene, and their derivatives, mixtures,
28. The lithium-sulfur battery according to claim 27, which is at least one selected from the group consisting of copolymers. 33. The electrolytic solution further contains an organic solvent,
The lithium-sulfur battery according to claim 27, wherein the content of the salt is 5 to 10% by volume based on the total amount of the electrolytic solution. 34. The lithium-sulfur battery according to claim 27, wherein the salt exists in a liquid state at a temperature of 100 ° C. or lower. 35. The lithium-sulfur battery of claim 27, wherein the salt comprises an organic cation having a van der Waals volume of 100Å ³ or more. 36. The lithium-sulfur battery of claim 27, wherein the salt comprises a cation of a heterocyclic compound. 37. The cation of the heterocyclic compound is a compound selected from the group consisting of pyridinium, pyridazinium, pyrimidinium, pyrazinium, imidazolium, pyrazolium, thiazolium, oxazolium, and triazolium, or a substituted compound thereof. 37. The lithium-sulfur battery of claim 36, which is a cation. 38. The salt further comprises an anion bonded to an organic cation, the anion being bis (perfluoroethylsulfonyl) imide (N (C ₂ F ₅ S
^{_{O 2) 2 -, Beti)}} , bis (trifluoromethylsulfonyl) imide ^{_{(N (CF 3 SO 2)}} 2 -, Im),
Tris (trifluoromethylsulfonyl) methide (C
^{_{(CF 3 SO 2) 2 -}} , Me), trifluoromethane sulfonimide, trifluoromethyl sulfonimide, _{trifluoromethylsulfonate,} ^AsF 6 -, ClO ₄
^-, PF ₆ ^-, and BF ₄ ^- is at least one selected from the group consisting of lithium according to claim 37 -
Sulfur battery. 39. The salt is 1-ethyl-3-methylimidazolium bis (perfluoroethylsulfonyl).
Imide (EMIBeti), 1,2-dimethyl-3-propylimidazolium bis (trifluoromethylsulfonyl) imide (DMPIIm), 1-butyl-3methylimidazolium hexafluorophosphate (BMIP)
F ₆₎ and a salt selected from the group consisting of lithium according to claim 27 - sulfur battery. 40. The electrolytic solution further comprises at least one organic solvent selected from the group consisting of dimethoxyethane, dioxolane, and a mixture thereof, which is mixed with a salt having an organic cation. Item 1. The electrolytic solution for a lithium-sulfur battery according to Item 1. 41. An electrolytic solution for a lithium-sulfur battery, which comprises a salt that exists in a liquid state at a temperature of 100 ° C. or lower. 42. The salt comprises a cation of a heterocyclic compound, the cation being a compound selected from the group consisting of pyridinium, pyridazinium, pyrimidinium, pyrazinium, imidazolium, pyrazolium, thiazolium, oxazolium, and triazolium, or 5. The yangine of these substituted compounds, 5.
The electrolytic solution for a lithium-sulfur battery according to 1. 43. The salt further comprises an anion bound to an organic cation, the anion being bis (perfluoroethylsulfonyl) imide (N (C ₂ F ₅ S
^{_{O 2) 2 -, Beti)}} , bis (trifluoromethylsulfonyl) _{imide) (N (CF 3 SO 2} ) 2 -, I
m), tris (trifluoromethylsulfonylmethide)
^{_{(C (CF 3 SO 2)}} 2 -, Me), trifluoromethane sulfonimide, trifluoromethyl sulfonimide, trifluoromethylsulfonate, _AsF ⁶ -, C
lO ₄ ^-, PF ₆ ^-, and BF ₄ ^- is at least one selected from the group consisting of lithium according to claim 41 - sulfur battery electrolyte solution. 44. The salt is 1-ethyl-3-methylimidazolium bis (perfluoroethylsulfonyl).
Imide (EMIBeti), 1,2-dimethyl-3-propylimidazolium bis (trifluoromethylsulfonyl) imide (DMPIIm), 1-butyl-3methylimidazolium hexafluorophosphate (EMIP)
F ₆₎ and a salt selected from the group consisting of lithium according to claim 41 - sulfur battery electrolyte solution. 45. The electrolyte solution for a lithium-sulfur battery according to claim 41, wherein the salt exists in a liquid state at a temperature of 50 ° C. or lower. 46. The electrolyte solution for a lithium-sulfur battery according to claim 41, wherein the salt exists in a liquid state at a temperature of 25 ° C. or lower. 47. The electrolyte solution for a lithium-sulfur battery according to claim 41, wherein the electrolyte solution further contains a solid lithium salt. 48. The solid lithium salt is LiP.
F₆, LiBF_Four, LiSbF₆, LiAsF₆, Li
ClO_Four, LiCF_ThreeSO_Three, Li (CF_ThreeSO _Two)_Two
N, LiC_FourF₉SO_Three, LiSbF₆, LiAl
O_Four, LiAlCl_Four, LiN (C_xF_{2x + 1}S
O_Two) (C_yF_{2y + 1}SO_Two) (Where x and y are
A natural number), LiCl, and LiI
48. At least one selected, according to claim 47.
Electrolyte for lithium-sulfur batteries. 49. 1-Ethyl-3-methylimidazolium bis (perfluoroethylsulfonyl) imide (EM
IBeti), 1,2-dimethyl-3-propylimidazolium bis (trifluoromethylsulfonyl) imide (DMPIIm), 1-butyl-3-methylimidazolium hexafluorophosphate (BMIPF ₆ ) and combinations thereof. And a LiP having a high ionic conductivity by dissolving a sulfur-based positive electrode active material of a lithium-sulfur battery;
F ₆ , LiBF ₄ , LiSbF ₆ , LiAsF ₆ , Li
ClO ₄ , LiCF ₃ SO ₃ , Li (CF ₃ SO ₂ ) ₂
N, LiC ₄ F ₉ SO ₃ , LiSbF ₆ , LiAl
O ₄ , LiAlCl ₄ , LiN (C _x F _{2x + 1} S
O ₂ ) (C _y F _{2 y + 1} SO ₂ ), where x and y are natural numbers, LiCl, and lithium containing at least one lithium solid salt selected from the group consisting of LiI. Electrolyte for sulfur batteries.