WO2016068534A1 - Lithium sulfur battery - Google Patents

Abstract

The present invention relates to a lithium sulfur battery, the battery comprising an anode and a cathode arranged facing each other, a separator interposed between the anode and cathode, and electrolyte, and additionally comprising: a lithium ion conductive polymer membrane positioned between the cathode and separator, and having a sulfonic acid group (-SO3H); and at least one membrane, from among metal oxide membranes, positioned between the anode and separator, and thus damage to electrode active material is reduced, and as the spread of lithium polysulfide to the anode is blocked, enhanced lifespan characteristic can be attained, and additionally, as dendritic growth in the anode is suppressed, improved safety can be attained.

Description

Lithium sulfur battery

The present invention relates to a lithium sulfur battery having reduced safety of the electrode active material, preventing diffusion of lithium polysulfide into the negative electrode, showing improved life characteristics, and having improved safety by suppressing dendrite growth at the negative electrode. will be.

As the demand for light and high capacity batteries increases with the development of portable electronic devices, the development of lithium-sulfur batteries using sulfur-based materials as positive electrode active materials as secondary batteries capable of meeting these demands is actively progressing.

Lithium-sulfur battery uses a sulfur-based compound having a sulfur-sulfur bond as a positive electrode active material, and an alkali metal such as lithium, or a carbon-based material in which insertion / deintercalation of metal ions such as lithium ions occurs As a negative electrode active material, wherein the oxidation number of S decreases as the SS bond is broken during the reduction reaction (discharge), and the oxidation of the SS bond is formed again when the oxidation number of S increases during the oxidation reaction (charging). Reduction reactions are used to store and generate electrical energy.

Specifically, the redox reaction of lithium and sulfur in a lithium sulfur battery may be represented by the following reaction formula.

2Li + S ₈ (solid) ↔ Li ₂ S ₈ (solution)

2Li + Li ₂ S ₈ (solution) ↔ 2Li ₂ S ₄ (solution)

2Li + Li ₂ S ₄ (solution) ↔ 2Li ₂ S ₂ (solution)

2Li + Li ₂ S ₂ (solution) ↔ 2Li ₂ S (solid precipitate)

Referring to the reaction scheme, it can be seen that during the redox reaction of sulfur and lithium, a new reaction product, lithium polysulfide, is produced. The reaction capacity of sulfur available in the actual lithium sulfur battery is very low, about 840 mAh / g, which is about half of the theoretical capacity due to the irreversible reaction characteristic of some polysulfides. As a result, lithium sulfur batteries using sulfur as a cathode active material have a problem of low battery capacity.

In addition, lithium metal as an anode has the advantage of being light in weight and excellent in energy density, but has a problem in that cycle life characteristics are deteriorated because of its high reactivity. In order to solve such a problem, researches on forming a protective film capable of protecting a lithium metal surface have recently been conducted. Such protective films include inorganic protective films and polymer protective films. Among them, LiPON (Lithium Phosphorus Oxy-Nitride), which is a lithium ion conductor, has been studied. However, the LiPON passivation layer is formed by sputtering under a nitrogen gas atmosphere. When the LiPON protective layer is formed directly on the lithium metal surface, the black porous lithium composite compound having a very poor binding force on the lithium metal surface is reacted with nitrogen gas and lithium metal. There was a problem formed by. Moreover, even when forming a polymer protective film, reaction between the organic solvent and lithium metal used at the time of protective film formation may generate | occur | produce.

Therefore, development of a material for increasing capacity by increasing the electrochemical redox reaction in lithium sulfur batteries is required.

[Preceding technical literature]

[Patent Documents]

Korea Registered Patent No. 10-0385357 (2003.05.14 registration)

It is an object of the present invention to reduce the loss of electrode active material, to prevent the diffusion of lithium polysulfide to the negative electrode, which can exhibit improved life characteristics, and lithium sulfur which can exhibit improved safety by suppressing dendrite growth at the negative electrode. It is to provide a battery.

Lithium sulfur battery according to an embodiment of the present invention, the positive electrode and the negative electrode disposed opposite each other; A separator interposed between the positive electrode and the negative electrode; And an electrolyte and further comprising at least one of a film of a lithium ion conductive polymer having a sulfonic acid group (-SO ₃ H) and a metal oxide film positioned between the cathode and the separator, positioned between the anode and the separator. Contains,

In the lithium sulfur battery, the membrane of the lithium ion conductive polymer having the sulfonic acid group is a copolymer of poly (perfluorosulfonic acid), poly (perfluorocarboxylic acid), sulfonated tetrafluoroethylene and fluorovinyl ether. , Sulfonated polyarylene ether, sulfonated polyarylene ether ether ketone, sulfonated polyarylene ether ether sulfone, sulfonated polyazole, sulfonated polyvinyl alcohol, sulfonated polyphenylene oxide, sulfonated polyphenylene sulfide , Sulfonated polysulfones, sulfonated polycarbonates, sulfonated polystyrenes, sulfonated polyimides, sulfonated polyamides, sulfonated polyquinoxalines, sulfonated (phosphated) polyphosphazenes, sulfonated polybenzimidazoles and these It may be to include one or more polymers selected from the group consisting of a copolymer.

In addition, the lithium ion conductive polymer having a sulfonic acid group may be one having a lithium ion conductivity of 1 × 10 ⁻⁴ S / cm or more.

In addition, the membrane of the lithium ion conductive polymer having a sulfonic acid group may have a thickness of 0.1 to 10㎛.

In addition, the metal oxide film may be colloidal silica, amorphous silica, surface treated silica, colloidal alumina, amorphous alumina, tin oxide, titanium oxide, titanium sulfide, vanadium oxide, zirconium oxide, iron oxide, iron sulfide, iron titanate, barium titanate and It may be one containing a metal oxide selected from the group consisting of a mixture thereof.

In addition, the metal oxide film may have a thickness of 0.1 to 10㎛.

In addition, the electrolyte may include a supersaturated lithium polysulfide (lithium polysulfide).

In addition, the positive electrode may include a positive electrode active material consisting of an elemental sulfur, a sulfur-based compound, and a mixture thereof.

In addition, the positive electrode may include carbon paper coated with a carbon-based conductive agent, and the carbon paper may be impregnated with an electrolyte including lithium polysulfide.

In addition, the anode may be positioned on the carbon paper and the carbon paper, and include a conductive layer including a carbon-based conductive agent, and the carbon paper and the conductive layer may include lithium polysulfide.

Other specific details of the embodiments of the present invention are included in the following detailed description.

The lithium sulfur battery according to the present invention exhibits reduced lifespan of the electrode active material, prevents diffusion of lithium polysulfide into the negative electrode, thereby improving life characteristics, and further improves safety by inhibiting dendrite growth in the negative electrode.

1 is an exploded perspective view of a lithium sulfur battery according to an embodiment of the present invention.

2 is an exploded perspective view of a lithium sulfur battery according to another embodiment of the present invention.

3 is a graph showing the cycle characteristics of Li ₂ S ₆ concentration of the battery according to an embodiment of the present invention.

FIG. 4 is a graph normalized to FIG. 3.

FIG. 5 is a schematic diagram illustrating a test procedure of voltage characteristics for each chain of Li ₂ S _n in Experimental Example 4 of the present invention. FIG.

6 is a graph showing the battery voltage according to the capacity characteristics of the battery according to Experimental Example 4 of the present invention.

7 is a graph showing the discharge capacity characteristics according to the number of cycles of the battery according to Experimental Example 4 of the present invention.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art may easily implement the present invention. As those skilled in the art would realize, the described embodiments may be modified in various different ways, all without departing from the spirit or scope of the present invention.

The terminology used herein is for the purpose of describing particular example embodiments only and is not intended to be limiting of the present invention. Singular expressions include plural expressions unless the context clearly indicates otherwise. In the present invention, the terms 'comprise' or 'have' are intended to indicate that there is a feature, number, step, operation, component, part, or combination thereof described in the specification, and one or more other features. It is to be understood that the present invention does not exclude the possibility of the presence or the addition of numbers, steps, operations, components, components, or a combination thereof.

The present invention forms a film of a lithium ion conductive polymer having a sulfonic acid end group between a positive electrode and a separator in manufacturing a lithium sulfur battery, thereby preventing lithium polysulfide from diffusing to the negative electrode, thereby improving the life characteristics of the battery. Or by forming a metal oxide film between lithium and the separator to suppress dendrite growth at the negative electrode, thereby improving the safety of the battery, and additionally, the loss of the electrode active material due to the use of an electrolyte saturated with lithium polysulfide. Characterized in that to prevent.

That is, the lithium sulfur battery according to an embodiment of the present invention, the positive electrode and the negative electrode which are disposed facing each other; A separator interposed between the positive electrode and the negative electrode; And an electrolyte and further comprising at least one of a film of a lithium ion conductive polymer having a sulfonic acid group (-SO ₃ H) and a metal oxide film positioned between the cathode and the separator, positioned between the anode and the separator. Include.

1 is a schematic diagram schematically showing the structure of a lithium sulfur battery according to an embodiment of the present invention. 1 is only an example for describing the present invention and the present invention is not limited thereto.

Referring to FIG. 1, a lithium sulfur battery according to an embodiment of the present invention includes a positive electrode 1 and a negative electrode 2 disposed opposite to each other, a separator 3 interposed between the positive electrode and the negative electrode, And a membrane of a lithium ion conductive polymer having an electrolyte and having a sulfonic acid group (-SO ₃ H) between the positive electrode 1 and the separator 3 and between the negative electrode 2 and the separator 3, respectively. 5) and at least one film of the metal oxide film 6 optionally further.

As that in the above lithium-sulfur battery (100), the sulfonic acid group membrane 5 of the lithium ion conductive polymer having a (-SO ₃ H) comprises a sulfonic acid group (-SO ₃ H) at the terminal of the polymer chain, wherein Located between the positive electrode 1 and the separator 3 to block the diffusion of lithium polysulfide to the negative electrode 2 to improve battery life characteristics.

Specifically, the membrane 5 of the lithium ion conductive polymer having the sulfonic acid group (-SO ₃ H) is tetrafluoro containing a poly (perfluorosulfonic acid), a poly (perfluorocarboxylic acid), and a sulfonic acid group. Sulfonated fluorine hydrocarbon polymers such as ethylene and fluorovinyl ether copolymers; Or sulfonated polyaryleneether (PAE), sulfonated polyaryleneetheretherketone (PAEEK), sulfonated polyaryleneetherethersulfone (PAEES), sulfonated polyazole, sulfonated Polyvinylalcohol (PVA), sulfonated polyphenylene oxide, sulfonated polyphenylene sulfide, sulfonated polysulfone, sulfonated polycarbonate, sulfonated polystyrene, sulfonated polyimide And sulfonated non-fluorinated hydrocarbon polymers such as sulfonated polyamide, sulfonated polyquinoxaline, sulfonated (phosphated) polyphosphazene, or sulfonated polybenzimidazole, and the like. It may be a block copolymer, a multiblock copolymer, or a grafting copolymer. One kind or a mixture of two or more kinds of the lithium ion conductive polymer may be included.

In addition, the lithium ion conductive polymer having a sulfonic acid group (-SO ₃ H) may be preferably a weight average molecular weight of 90,000 to 1,000,000 g / mol. When the weight average molecular weight of the lithium ion conductive polymer is less than 90,000 g / mol or more than 1,000,000 g / mol, the improvement effect of using the lithium ion conductive polymer may be insignificant.

In addition, the lithium ion conductive polymer having a sulfonic acid group preferably has a lithium ion conductivity of 1 × 10 ⁻⁴ S / cm or more. If the lithium ion conductivity is less than 1 × 10 ⁻⁴ S / cm, the lithium ion may not move smoothly, and thus an improvement effect due to the film formation of the lithium ion conductive polymer may be insignificant.

In addition, the membrane 5 of the lithium ion conductive polymer having a sulfonic acid group may have a thickness of 0.1 to 10㎛. When the thickness is less than 0.1 μm, it is difficult to completely block the contact between the active material and the organic solvent. When the thickness is more than 10 μm, the lithium ion conductivity is low, so that the overvoltage is large, and thus battery characteristics are deteriorated. More preferably, it may be 0.5 to 5㎛.

On the other hand, the metal oxide film 6 is located between the negative electrode 2 and the separator 3 to suppress the growth of the dendrite in the negative electrode 2 to improve the safety of the battery.

Specifically, the metal oxide film 6 is colloidal silica, amorphous silica, surface-treated silica, colloidal alumina, amorphous alumina, tin oxide, titanium oxide, titanium sulfide (TiS ₂ ), vanadium oxide, zirconium oxide (ZrO ₂ ), Iron oxide (Iron Oxide), iron sulfide (Iron Sulfide, FeS), iron titanate (Iron titanate, FeTiO ₃ ), barium titanate (Vanadium titanate, BaTiO ₃ ) and mixtures thereof. Can be.

The metal oxide film 6 may have a thickness of 0.1 to 10㎛. If the thickness is less than 0.1 μm or more than 10 μm, the improvement effect of forming the metal oxide film 6 may be insignificant.

On the other hand, in the lithium sulfur battery 100, the positive electrode 1, for example, is located on the positive electrode current collector and the positive electrode current collector, and includes a positive electrode active material layer including a positive electrode active material and optionally a conductive agent and a binder. can do.

As the cathode current collector, it may be preferable to use foamed aluminum, foamed nickel, and the like, which have excellent conductivity.

In addition, the cathode active material layer may include elemental sulfur (S8), a sulfur-based compound, or a mixture thereof as the cathode active material. Specifically, the sulfur-based compound may be Li ₂ S _n (n ≧ 1), an organic sulfur compound or a carbon-sulfur polymer ((C ₂ S _x ) _n : x = 2.5 to 50, n ≧ 2), or the like.

In addition, the positive electrode active material layer further includes a conductive agent for allowing electrons to move smoothly in the positive electrode 1 together with the positive electrode active material, and a binder for increasing the binding force between the positive electrode active material or between the positive electrode active material and the current collector. can do.

The conductive agent may be a carbon-based material such as carbon black, acetylene black or Ketjen black; Or it may be a conductive polymer such as polyaniline, polythiophene, polyacetylene, polypyrrole, it may be preferably included in 5 to 20% by weight relative to the total weight of the positive electrode active material layer. If the content of the conductive agent is less than 5% by weight, the conductivity improvement effect according to the use of the conductive agent is insignificant, whereas if it exceeds 20% by weight, the content of the positive electrode active material is relatively small, there is a fear that the capacity characteristics.

The binder may be poly (vinyl acetate), polyvinyl alcohol, polyethylene oxide, polyvinylpyrrolidone, alkylated polyethylene oxide, crosslinked polyethylene oxide, polyvinyl ether, poly (methyl methacrylate), poly Vinylidene fluoride, copolymer of polyhexafluoropropylene and polyvinylidene fluoride (trade name: Kynar), poly (ethyl acrylate), polytetrafluoroethylene, polyvinylchloride, polyacrylonitrile, polyvinylpyridine , Polystyrene, derivatives thereof, blends, copolymers and the like can be used. In addition, the binder may be preferably contained in 5 to 20% by weight based on the total weight of the positive electrode active material layer. When the content of the binder is less than 5% by weight, the effect of improving the binding strength between the positive electrode active material or between the positive electrode active material and the current collector according to the use of the binder is insignificant.However, when the content of the binder exceeds 20% by weight, the content of the positive electrode active material is relatively small, thereby decreasing the capacity characteristics. There is a concern.

The positive electrode 1 as described above may be prepared according to a conventional method. Specifically, after the positive electrode active material layer-forming composition prepared by mixing a positive electrode active material, a conductive agent and a binder on an organic solvent, is applied onto a current collector It can be prepared by drying and optionally rolling.

In this case, the organic solvent may uniformly disperse the positive electrode active material, the binder, and the conductive agent, and it is preferable to use one that is easily evaporated. Specifically, acetonitrile, methanol, ethanol, tetrahydrofuran, water, isopropyl alcohol, etc. are mentioned.

As another example of the positive electrode (1), the positive electrode (1) is a positive electrode current collector; And a conductive layer positioned on the positive electrode current collector and including a conductive agent and optionally a binder, wherein the positive electrode current collector and the conductive layer may include lithium polysulfide as a liquid positive electrode active material.

Specifically, the positive electrode 1 is prepared by coating a mixture of a conductive agent and a binder selectively on the positive electrode current collector to prepare a positive electrode material, and then to prepare an electrode assembly using the electrolyte, and includes an electrolyte containing supersaturated lithium polysulfide It can be prepared by adding. In this case, lithium polysulfide may be inserted between the pores of the cathode material to serve as a cathode.

In this case, the positive electrode current collector and the conductive agent may be the same as described above, and the positive electrode current collector may be carbon paper, and the conductive agent may be a carbon-based conductive agent such as carbon black.

2 is a schematic diagram schematically showing the structure of a lithium sulfur battery 200 including the positive electrode 10 having the above configuration. 2 is only an example for describing the present invention and the present invention is not limited thereto.

Hereinafter, referring to FIG. 2, a lithium sulfur battery 200 according to another exemplary embodiment of the present invention includes a positive electrode 10 and a negative electrode 20 disposed opposite to each other, and the positive electrode 10 and the negative electrode 20. A membrane of a lithium ion conductive polymer including a separator 30 interposed between the separator 30 and an electrolyte, and positioned between the anode 10 and the separator 30 and having a sulfonic acid group (-SO ₃ H). 50 and a metal oxide film 60 positioned between the cathode 30 and the separator 30. In this case, the positive electrode 10 includes a carbon paper 11 and a conductive agent 12 including a carbon-based conductive agent such as carbon black, positioned on the carbon paper 11 and the carbon paper 11 as a positive electrode current collector. 11) and lithium polysulfide 13 as a liquid positive electrode active material in the conductive agent 12 may be included.

As described above, the electrolyte containing lithium polysulfide is poured into the carbon paper 11 coated with the conductive agent 12 such as carbon black without using the sulfur electrode as the positive electrode 10 as in the conventional lithium sulfur battery. By using the prepared positive electrode 10, the production of the positive electrode 10 is simple and easy, there is no influence by the proportion of the electrode constituents, the final production of the lithium sulfur battery 200 by producing a uniform active material composition This can reduce the deviation from.

Meanwhile, in the lithium sulfur battery 200, the negative electrode 20 reacts with a material capable of reversibly intercalating or deintercalating lithium ions and lithium ions as a negative electrode active material, and reversibly reacts with a lithium-containing compound. It may include a material selected from the group consisting of a lithium metal and a lithium alloy.

As a material capable of reversibly intercalating / deintercalating the lithium ion, any carbon-based negative electrode active material generally used in lithium sulfur batteries may be used, and specific examples thereof include crystalline carbon and amorphous materials. Carbon or these can be used together. In addition, a representative example of a material capable of reacting with lithium ions to reversibly form a lithium-containing compound may include, but is not limited to, tin oxide (SnO ₂ ), titanium nitrate, silicon (Si), and the like. Specifically, the alloy of the lithium metal may be an alloy of lithium with a metal of Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, or Cd.

In addition, the negative electrode 20 may optionally further include a binder together with the negative electrode active material.

The binder serves to paste the negative electrode active material, mutual adhesion between the active materials, adhesion between the active material and the current collector, and buffer effect on the expansion and contraction of the active material. Specifically, the binder is the same as described above.

In addition, the negative electrode 20 may further include a negative electrode current collector for supporting the negative electrode active layer including the negative electrode active material and the binder.

The negative electrode current collector may be specifically selected from the group consisting of copper, aluminum, 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 nonconductive polymer surface-treated with a conductive agent, or a conductive polymer may be used.

In addition, the cathode 30 may be a thin film of lithium metal.

Typically, in the process of charging and discharging the lithium sulfur battery 200, sulfur used as the cathode active material may be converted into an inert material and attached to the surface of the lithium anode. Such inactive sulfur is sulfur in a state in which sulfur can no longer participate in the electrochemical reaction of the anode through various electrochemical or chemical reactions. However, inert sulfur formed on the surface of the lithium negative electrode may serve as a protective layer of the lithium negative electrode. As a result, the lithium metal and inert sulfur formed on the lithium metal, for example lithium sulfide, may be used as the negative electrode 30.

In addition, in the lithium sulfur battery 200, the separator 30 is a physical separator having a function of physically separating the electrode, and can be used without particular limitation as long as it is usually used as a separator in a lithium sulfur battery. It is desirable to have low resistance to ion migration of the electrolyte and excellent electrolyte-wetting ability. Specifically, a porous polymer film made of a polyolefin-based polymer such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer and ethylene / methacrylate copolymer may be used alone. It may be used as a lamination or or a conventional porous non-woven fabric, for example, a non-woven fabric made of glass fibers, polyethylene terephthalate fibers of high melting point, etc. may be used, but is not limited thereto.

In addition, in the lithium sulfur battery 200, the electrolyte may include supersaturation lithium polysulfide. In this case, the supersaturation means a state in which the concentration of the solute dissolved in the solvent exceeds the equilibrium value.

When the lithium polysulfide is not dissolved in the electrolyte, sulfur alone becomes polysulfide from the positive electrode and dissolves in the electrolyte at the time of discharge, thereby reducing the battery capacity due to the decrease in the positive electrode active material. However, when the lithium polysulfide is dissolved in the electrolyte in a supersaturated state, the lithium polysulfide (Li ₂ S _x ) (1 ≦ _x ≦ ₈ ) dissolved in the electrolyte is S ₈ ^2- , S ₆ ^2- , there are uniformly dispersed in the electrolyte in the form of ^{_{- S 4 2-, S 2 2-}} , polysulfide ions (S _x ^2), such as S ^2-. As a result, diffusion of the polysulfide ions dissolved from the electrode can be suppressed to reduce the active material loss, and charge / discharge efficiency and cycle performance can be improved because the polysulfide ions near the electrode are involved in the discharge reaction. In addition, since there is a kinetic synergy effect by the solid-liquid reaction, it can exhibit a high reaction activity compared to the solid surface (solid surface).

The lithium polysulfide may be prepared by adding and mixing a lithium sulfur compound such as Li ₂ S and elemental sulfur in an electrolyte.

In addition, the electrolyte further includes a non-aqueous organic solvent and a lithium salt.

Specifically, the non-aqueous organic solvent may be a polar solvent such as an aryl compound, bicyclic ether, acyclic carbonate, sulfoxide compound, lactone compound, ketone compound, ester compound, sulfate compound, sulfite compound, and the like.

More specifically, the non-aqueous organic solvent may be 1,2-dimethoxyethane, 1,2-diethoxyethane, 1,2-dibutoxyethane, dioxolane (Dioxolane, DOL), 1,4-dioxane, tetra Hydrofuran, 2-methyltetrahydrofuran, dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), methyl propyl carbonate (MPC), ethyl propyl carbonate, dipropyl carbonate, butyl ethyl carbonate, ethyl Propanoate (EP), toluene, xylene, dimethyl ether (dimethyl ether, DME), diethyl ether, triethylene glycol monomethyl ether (TEGME), diglyme, tetraglyme, hexamethyl phosph Hexamethyl phosphoric triamide, gamma butyrolactone (GBL), acetonitrile, propionitrile, ethylene carbonate (EC), propylene carbonate (PC), N-methylpyrrolidone, 3-methyl-2-oxa Zolidone, Acetate Ester, Buty Leric acid ester and propionic acid ester, dimethylformamide, sulfolane (SL), methyl sulfolane, dimethylacetamide, dimethyl sulfoxide, dimethyl sulfate, ethylene glycol diacetate, dimethyl sulfite, ethylene glycol sulfite, etc. are mentioned. .

Of these, a mixed solvent of triethylene glycol monomethyl ether / dioxolane / dimethyl ether may be more preferable.

The lithium salt may be used without particular limitation as long as it is a compound capable of providing lithium ions used in lithium sulfur batteries. Specifically, the lithium salt is LiPF ₆ , LiClO ₄ , LiAsF ₆ , LiBF ₄ , LiSbF ₆ , LiAl0 ₄ , LiAlCl ₄ , LiCF ₃ SO ₃ , LiC ₄ F ₉ SO ₃ , LiN (C ₂ F ₅ SO ₃ ) ₂ LiN (C ₂ F ₅ SO ₂ ) ₂ (Lithium bis (perfluoroethylsulfonyl) imide, BETI), LiN (CF ₃ SO ₂ ) ₂ (Lithium bis (Trifluoromethanesulfonyl) imide, LiTFSI), LiN (C _a F _{2a + 1} SO ₂ ) (C _b F _{2b + 1} SO ₂ ) (where a and b are natural numbers, preferably 1 ≦ a ≦ 20 and 1 ≦ b ≦ 20), lithium poly [4,4 ′-(hexafluoro Lysopropylidene) diphenoxy] sulfonylimide (lithium poly [4,4 '-(hexafluoroisopropylidene) diphenoxy] sulfonylimide, LiPHFIPSI) LiCl, LiI, LiB (C ₂ O ₄ ) _2, etc. may be used, and In the above, sulfonyl group-containing imide lithium compounds such as LiTFSI, BETI or LiPHFIPSI may be more preferable.

In addition, the lithium salt may be included at a concentration of 0.6 to 2M in the electrolyte. If the concentration of the lithium salt is less than 0.6M, the conductivity of the electrolyte is lowered and the performance of the electrolyte is lowered. If the concentration of the lithium salt is higher than 2M, the viscosity of the electrolyte is increased to reduce the mobility of lithium ions.

In addition to the electrolyte components, the electrolyte further includes additives (hereinafter, referred to as 'other additives') that can be generally used in the electrolyte for the purpose of improving the life characteristics of the battery, suppressing the reduction of the battery capacity, and improving the discharge capacity of the battery. can do.

As described above, the lithium sulfur batteries 100 and 200 according to the present invention may reduce the loss of the electrode active material, block diffusion of lithium polysulfide into the negative electrode, and exhibit improved life characteristics, and dendrites at the negative electrode. Increased safety due to growth inhibition, portable devices such as mobile phones, notebook computers, digital cameras, camcorders, hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (plug-in) HEV, PHEV) and electric vehicles, and medium to large energy storage system.

Hereinafter, embodiments of the present invention will be described in detail so that those skilled in the art can easily practice the present invention. As those skilled in the art would realize, the described embodiments may be modified in various different ways, all without departing from the spirit or scope of the present invention.

Experimental Example 1: Determination of the Effect of Supersaturated Lithium Polysulfide

A symmetric cell was fabricated using lithium metal (bulk Li: 150 μm) as an anode, and a lithium thin film-copper thin film (Li foil (40 μm) —Cu foil (20 μm)) as a cathode. The effect of the supersaturated lithium polysulfide was indirectly measured by adding as an additive while changing the content of lithium polysulfide to confirm the increase in utilization efficiency of the symmetric battery.

( Reference Example  One)

Lithium bis (1 M) in an organic solvent composed of triethylene glycol monomethyl ether (TEGDME) / dioxolane (DOL) / dimethyl ether (DME) (mixed volume ratio = 1/1/1) as an electrolyte in the symmetric battery. An electrolyte prepared by dissolving trifluoromethanesulfonyl) imide (LiTFSI) and LiNO ₃ at a concentration of 0.1 M was used.

( Reference Example  2)

In the electrolyte of Reference Example 1, 0.05 M Li ₂ S ₆ was further added.

( Reference Example  3)

In the electrolyte of Reference Example 1, Li ₂ S ₆ at a concentration of 0.5 M was further added.

For the symmetric battery prepared in Reference Examples 1 to 3, C-rate 0.1C, DOD 10 from the positive electrode (bulk Li: 150㎛) to the negative electrode (Li foil (40㎛) -Cu foil (20㎛)) After 15 cycles of charging after% discharge, the Li content on the copper thin film was pulled out at the maximum charge to confirm the capacity. Residual amount and residual capacity of Li on the negative electrode side were confirmed by the measured Li content. Using this, the battery utilization efficiency was calculated according to Formula 1 below, and the results are shown in Table 1 below.

[Calculation 1]

X = [(q _c- (q ₁ -q _r ) / N) / q _c ]

q _c : Progressive Li content (DOD 10%: 1.32mA)

q ₁ : Li content on Cu thin film (40㎛: 13.2mA)

q _r : Li content measured by fully stripping after cycle

-N: 15 times

In addition, the contents of Li ₂ S and S according to the concentration of Li ₂ S ₆ in the symmetric cells prepared in Reference Examples 2 and 3 are shown in Table 2 below.

division	Electrolyte	Cyclic efficiency	Deviation
Reference Example 1	TEGDME / DOL / DME (1: 1: 1) + LiTFSI (1M) + LiNO 3 (0.1M)	85.38%	1.06%
Reference Example 2	TEGDME / DOL / DME (1: 1: 1) + LiTFSI (1M) + LiNO 3 (0.1M) + Li 2 S 6 (0.05M)	88.1%	0.98%
Reference Example 3	TEGDME / DOL / DME (1: 1: 1) + LiTFSI (1M) + LiNO 3 (0.1M) + Li 2 S 6 (0.5M)	92.12%	0.04%

division	Li 2 S 6 concentration	Content per mg of electrolyte (mg)
		Li 2 S	S
Reference Example 2	0.05M	2.2973	8.0165
Reference Example 3	0.5M	22.973	80.165

Referring to Table 1 and Table 2, it can be seen that as the amount of lithium polysulfide added increases, the content of Li ₂ S and S increases, and the utilization efficiency of the battery increases. Therefore, it can be seen that the efficiency of the battery will be further improved if the electrolyte contains supersaturated lithium polysulfide.

[ Example  1: Preparation of Battery]

Sulfur (average particle size: 5 µm) was mixed in acetonitrile using a conductive agent, a binder, and a ball mill to prepare a composition for forming a cathode active material layer. In this case, carbon black was used as the conductive agent and polyethylene oxide (molecular weight 5,000,000 g / mol) was used as the binder, and the mixing ratio was 60:20:20 in the weight ratio of sulfur: conductor: binder. The prepared positive electrode active material layer-forming composition was applied to an aluminum current collector and dried to prepare a positive electrode (energy density of the positive electrode: 1.0 mAh / cm 2).

On the active material layer of the positive electrode, a film (thickness: 0.5 μm, ion conductivity: 1 × 10 ⁻⁴ S / cm) of a lithium ion conductive polymer of poly (perfluorosulfonic acid) was formed.

In addition, a metal oxide film (thickness: 0.5 µm) containing colloidal silica was formed on a cathode of lithium metal having a thickness of 150 µm.

The prepared anode and the cathode are positioned so that the lithium ion conductive polymer film and the metal oxide film face each other, and then, an electrode assembly is manufactured through a separator of porous polyethylene, the electrode assembly is placed inside the case, and then lithium is inserted into the case. An electrolyte containing polysulfide was injected to prepare a lithium sulfur battery. At this time, the electrolyte containing lithium polysulfide, 1M concentration in an organic solvent consisting of triethylene glycol monomethyl ether (TEGDME) / dioxolane (DOL) / dimethyl ether (DME) (mixed volume ratio = 1/1/1) In an electrolyte prepared by dissolving lithium bis (trifluoromethanesulfonyl) imide (LiTFSI), dilithium sulfide (Li ₂ S) and elemental sulfur were added, followed by a magnetic stirrer at 90 ° C. The reaction was performed for 48 hours to synthesize lithium polysulfide (Li ₂ S _n ) in the electrolyte.

[ Example  2: Fabrication of Battery]

A lithium sulfur battery was manufactured in the same manner as in Example 1, except that the metal oxide film was not formed on the cathode.

[ Example  3: Fabrication of Battery

A lithium sulfur battery was manufactured in the same manner as in Example 1, except that a film of the lithium ion conductive polymer was not formed on the cathode.

[ Example  4: Fabrication of Battery]

A positive electrode material was prepared by dip coating carbon black on carbon paper (thickness: 142 mu m, fiber diameter: 7 to 7.5 mu m) (82% porosity). A film (thickness: 0.5 mu m, ionic conductivity: 1 × 10 ^-4 S / cm) of a lithium ion conductive polymer of poly (perfluorosulfonic acid) was formed on the cathode material.

In addition, a metal oxide film (thickness: 0.5 µm) containing colloidal silica was formed on a cathode of lithium metal having a thickness of 150 µm.

The prepared anode and cathode were positioned so that the lithium ion conductive polymer film and the metal oxide film faced each other, and then, an electrode assembly was manufactured through a separator of porous polyethylene, and the electrode assembly was placed inside the case. The lithium sulfur battery was manufactured by injecting an electrolyte including lithium polysulfide into the case. At this time, the electrolyte containing lithium polysulfide, 1M concentration in an organic solvent consisting of triethylene glycol monomethyl ether (TEGDME) / dioxolane (DOL) / dimethyl ether (DME) (mixed volume ratio = 1/1/1) Lithium bis (trifluoromethanesulfonyl) imide (LiTFSI) was dissolved in an electrolyte prepared by adding dilithium sulfide (Li ₂ S) and elemental sulfur (elemental sulfur) and then using a magnetic stirrer at 90 ° C. The reaction was carried out for 48 hours at to prepare lithium polysulfide (Li ₂ S _n ) in the electrolyte.

[ Comparative example  1: Preparation of Battery]

Sulfur (average particle size: 5 µm) was mixed in acetonitrile using a conductive agent, a binder, and a ball mill to prepare a composition for forming a cathode active material layer. In this case, carbon black was used as the conductive agent and polyethylene oxide (molecular weight 5,000,000 g / mol) was used as the binder, and the mixing ratio was 60:20:20 in the weight ratio of sulfur: conductor: binder. The resulting positive electrode active material layer-forming composition was applied to an aluminum current collector and then dried to prepare a positive electrode (energy density of the positive electrode: 1.0 mAh / cm 2).

In addition, lithium metal having a thickness of 150 µm was used as the negative electrode.

An electrode assembly was manufactured between the prepared positive electrode and the negative electrode through a separator of porous polyethylene, the electrode assembly was placed in a case, and an electrolyte was injected into the case to prepare a lithium sulfur battery. In this case, the electrolyte is lithium bis (trifluorine) at a concentration of 1M in an organic solvent composed of triethylene glycol monomethyl ether (TEGDME) / dioxolane (DOL) / dimethyl ether (DME) (mixed volume ratio = 1/1/1). An electrolyte prepared by dissolving romethanesulfonyl) imide (LiTFSI) was used.

Experimental Example 2: Observation of Anode

The positive electrode prepared in Example 4 was observed using a scanning electron microscope. The result is shown in FIG. 3 of Korean Patent Application No. 2015-0115013 (Application Date: August 14, 2015) which is the original application of the present invention.

As shown in FIG. 3 of Korean Patent Application No. 2015-0115013, carbon black is dispersed and present on the carbon paper, and lithium polysulfide is filled between the carbon paper and the pores in the carbon black.

Experimental Example 3 Measurement of Cycle Characteristics According to Li ₂ S ₆ Concentration of Electrolyte

Li ₂ S ₆ of the electrolyte of the lithium sulfur battery according to Example 1 Cycle characteristics according to the concentration was measured and shown in FIG. 3 and FIG. 4, and the capacity retention ratio was calculated therefrom and shown in Table 3 (@ 50CYC.).

division	Electrolyte	Capacity maintenance rate (@ 50cyc.)
Comparative Example 1	TEGDME / DOL / DME (1: 1: 1) + LiTFSI (1M) + LiNO 3 (0.1M)	51.78%
Example 1: Li 2 S 6 (0.1M)	TEGDME / DOL / DME (1: 1: 1) + LiTFSI (1M) + LiNO 3 (0.1M) + Li 2 S 6 (0.1M)	66.07%
Example 1: Li 2 S 6 (0.2M)	TEGDME / DOL / DME (1: 1: 1) + LiTFSI (1M) + LiNO 3 (0.1M) + Li 2 S 6 (0.2M)	73.37%
Example 1: Li 2 S 6 (0.5M)	TEGDME / DOL / DME (1: 1: 1) + LiTFSI (1M) + LiNO 3 (0.1M) + Li 2 S 6 (0.5M)	75.96%

Referring to Figures 3, 4 and Table 3, the discharge capacity characteristics and capacity retention rate of Example 1 are generally good, and the higher the Li ₂ S ₆ concentration of the electrolyte, the higher the discharge capacity characteristics and capacity retention rate can be confirmed. there was.

Experimental Example 4: Voltage characteristic for each chain of Li ₂ S _n ]

In order to investigate the voltage characteristics of Li ₂ S _n for each chain, the experiment was carried out with a catholyte system having less influence of the sulfur electrode. The experimental procedure is shown in FIG. 5 and Table 4.

Referring to FIG. 5, as in Example 4, a cathode material (GDL) prepared by deep coating carbon black on carbon paper (thickness: 142 μm, fiber diameter: 7 to 7.5 μm) is used as a cathode. Using a lithium metal having a thickness of 150 μm, the positive electrode and the negative electrode were positioned to face each other, and then a test cell was prepared through a separator of porous polyethylene. Thereafter, 40 μl of polysulfide (Li ₂ S _n ) catholyte was dropped into the cathode material, and the voltage characteristics of each chain of Li ₂ S _n were measured. In this case, the type of polysulfide and the amount of sulfur (mg) added in 40 μl of the polysulfide cathode are shown in Table 4 below.

	Input S (mg)
Li 2 S 6 (0.2M)	0.688
Li 2 S 8 (0.2M)	0.917
Li 2 S 6 (0.5M)	1.72
Li 2 S 8 (0.5M)	2.29
Ref. (Li / S)	0.986

* JNT-E: Thickness: 142㎛, Porosity 82%

The battery voltage according to the capacity-specific capacity characteristics of lithium polysulfide of the cathode system is shown in FIG. 6, and the discharge capacity characteristics of the lithium polysulfide concentration-dependent cycle number of the cathode system are shown in FIG. 7.

6 and 7, it was confirmed that the higher the lithium polysulfide concentration of the electrolyte, the higher the capacity characteristic and the battery voltage were maintained.

When the electrolyte contains supersaturated lithium polysulfide, diffusion of polysulfide ions dissolved from the electrode can be suppressed to reduce active material loss, and polysulfide ions in the vicinity of the electrode are involved in the discharge reaction, thereby improving charge and discharge efficiency and cycle performance. In addition, since the kinetic synergy effect can be improved by the solid-liquid reaction, it was confirmed by Experimental Examples 3 and 4 that the reaction activity was higher than that of the solid surface. .

Although the preferred embodiments of the present invention have been described in detail above, the scope of the present invention is not limited thereto, and various modifications and improvements of those skilled in the art using the basic concepts of the present invention defined in the following claims are also provided. It belongs to the scope of rights.

[Description of the code]

1, 10: anode

2, 20: cathode

3, 30: separator

5, 50: membrane of lithium ion conductive polymer having sulfonic acid group

6, 60: metal oxide film

11: carbon paper

12: Challenger

13: lithium polysulfide solution

100, 200: lithium sulfur battery

The present invention relates to a lithium sulfur battery, the battery comprising a positive electrode and a negative electrode disposed opposite each other; A separator interposed between the positive electrode and the negative electrode; And an electrolyte and further comprising at least one of a film of a lithium ion conductive polymer having a sulfonic acid group (-SO ₃ H) and a metal oxide film positioned between the cathode and the separator, positioned between the anode and the separator. By including, the loss of the electrode active material is reduced, the diffusion of the lithium polysulfide to the negative electrode can be blocked to exhibit improved life characteristics, and can also exhibit improved safety by suppressing dendrite growth at the negative electrode.

Claims (10)

1. An anode and a cathode disposed to face each other;

   A separator interposed between the positive electrode and the negative electrode; And

   Contains an electrolyte, and

   Lithium sulfur battery further comprising at least one of a membrane of a lithium ion conductive polymer having a sulfonic acid group (-SO ₃ H) and a metal oxide film positioned between the cathode and the separator, positioned between the anode and the separator.
2. The method of claim 1,

   The membrane of the lithium ion conductive polymer having the sulfonic acid group is poly (perfluorosulfonic acid), poly (perfluorocarboxylic acid), copolymer of sulfonated tetrafluoroethylene and fluorovinyl ether, sulfonated polyarylene ether , Sulfonated polyarylene ether ether ketone, sulfonated polyarylene ether ether sulfone, sulfonated polyazole, sulfonated polyvinyl alcohol, sulfonated polyphenylene oxide, sulfonated polyphenylene sulfide, sulfonated polysulfone, sulfonated Sulfonated polycarbonate, sulfonated polystyrene, sulfonated polyimide, sulfonated polyamide, sulfonated polyquinoxaline, sulfonated (phosphated) polyphosphazene, sulfonated polybenzimidazole and copolymers thereof Lithium sulfur battery comprising one or more selected polymers.
3. The method of claim 1,

   Lithium ion conductive polymer having a sulfonic acid group will have a lithium ion conductivity of 1X10 ^-4 S / cm or more.
4. The method of claim 1.

   A lithium sulfur battery, wherein the film of the lithium ion conductive polymer having a sulfonic acid group has a thickness of 0.1 to 10㎛.
5. The method of claim 1.

   The metal oxide film is colloidal silica, amorphous silica, surface treated silica, colloidal alumina, amorphous alumina, tin oxide, titanium oxide, titanium sulfide, vanadium oxide, zirconium oxide, iron oxide, iron sulfide, iron titanate, barium titanate, and these Lithium sulfur battery comprising a metal oxide selected from the group consisting of a mixture.
6. The method of claim 1.

   Lithium sulfur battery that the metal oxide film has a thickness of 0.1 to 10㎛.
7. The method of claim 1,

   Lithium sulfur battery that the electrolyte comprises a supersaturated lithium polysulfide (lithium polysulfide).
8. The method of claim 1,

   Lithium sulfur battery wherein the positive electrode comprises a positive electrode active material consisting of elemental sulfur, sulfur-based compounds and mixtures thereof.
9. The method of claim 1,

   The positive electrode comprises a carbon paper coated with a carbon-based conductive agent, the lithium sulfur battery in which the electrolyte containing lithium polysulfide is impregnated in the carbon paper.
10. The method of claim 1,

    Wherein the positive electrode is positioned on the carbon paper and the carbon paper, and includes a conductive layer including a carbon-based conductive agent, and the carbon paper and the conductive layer include lithium polysulfide.

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