KR20050030441A - Current collector for lithium-sulfur battery and lithium-sulfur battery comprising same - Google Patents

Abstract

Provided are a current collector for a lithium-sulfur battery which inhibits the reactivity with a sulfur-based positive electrode active material, and a lithium-sulfur battery containing the current collector which is improved in discharge characteristics. The current collector comprises an aluminum foil; and an aluminum oxide coat formed on the surface of the aluminum foil. Preferably the aluminum oxide coat is formed by naturally oxidizing aluminum by using chemical or electrochemical etching method. Preferably the aluminum foil has a surface roughness to give a capacity of 10 muF/cm2 or more. Preferably a transition metal, a metal oxide or a metal sulfide is added in the pore of the aluminum foil; the transition metal is at least one selected from the group consisting of Ti, Ni, Sn, Zn, Cu, Mo, Mn, Fe, V, Co, W, Cd, Au and Ag; the metal oxide is at least one selected from the group consisting of TiO2, MoOx (2<x<8), MnO2 and Al2O3; and the metal sulfide is at least one selected from the group consisting of Cu2S, FeS, NiS, Ag2S and MoS2.

Description

Current collector for lithium-sulfur battery and lithium-sulfur battery comprising same TECHNICAL FIELD

[Industrial use]

The present invention relates to a current collector for a lithium-sulfur battery and a lithium-sulfur battery including the same, and more particularly, to a current collector for a lithium-sulfur battery having an aluminum oxide film and a lithium-sulfur battery including the same.

[Prior art]

With the development of portable electronic devices, there is an increasing demand for light and high capacity batteries. As a secondary battery that satisfies these requirements, development of a lithium-sulfur battery using a sulfur-based material as a cathode active material is being actively conducted.

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 It is a secondary battery using as a negative electrode active material. In the reduction reaction (discharged), the SS bond is broken and the oxidation number of S decreases. In the oxidation reaction (charged), the oxidation-reduction reaction of the SS bond is formed by increasing the oxidation number of S and the electrical energy is stored and stored. Create

Lithium-sulfur battery is a cathode active material in the group consisting of cathode, an organic-sulfur compound and a carbon-sulfur polymer in which elemental sulfur, solid Li ₂ S _n (n≥1), Li ₂ S _n (n≥1) are dissolved At least one selected sulfur-based material is used as a positive electrode active material, a material capable of reversibly intercalating or deintercalating lithium ions, a material capable of forming a compound reversibly with lithium, and a lithium metal and a lithium alloy. A material selected from the group is used as the negative electrode active material.

In a lithium-sulfur battery, a positive electrode is prepared by dispersing a binder and a conductive material in an organic solvent, adding the positive electrode active material to the obtained dispersion, preparing a slurry, and then applying and drying the current collector. As the current collector, generally, a conductive metal foil such as stainless steel, aluminum, titanium, nickel, or a carbon-coated aluminum current collector is used. Among them, aluminum is inexpensive and can be economically used as a current collector for a lithium-sulfur battery, but there is a problem in that it does not function as a current collector, such as being severely damaged by reacting with a sulfur-based positive electrode active material during charge and discharge.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide a current collector for a lithium-sulfur battery, in which a film for suppressing reactivity with a sulfur-based cathode active material is formed.

Another object of the present invention is to provide a lithium-sulfur battery with improved discharge characteristics, including the current collector for lithium-sulfur batteries.

In order to achieve the above object, the present invention provides a current collector for a lithium-sulfur battery comprising an aluminum foil and an aluminum oxide film formed on the surface of the aluminum foil.

The invention also relates to one or more selected from the group consisting of elemental sulfur, solid Li ₂ S _n (n ≧ 1), catholyte in which Li ₂ S _n (n ≧ 1) is dissolved, organo-sulfur compounds and carbon-sulfur polymers An anode comprising a sulfur-based material, the anode including a current collector comprising an aluminum foil and an aluminum oxide film formed on the surface of the aluminum foil; A negative electrode including a negative electrode active material selected from the group consisting of a material capable of reversibly intercalating lithium ions, a material capable of reacting with lithium ions to form a lithium-containing compound reversibly, and a lithium metal and a lithium alloy; And it provides a lithium-sulfur battery comprising an electrolyte solution.

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

The current collector for lithium-sulfur batteries of the present invention is an aluminum foil in which an aluminum oxide film is formed on an aluminum foil. The aluminum oxide film can suppress the reactivity of the aluminum current collector and the positive electrode active material. The aluminum oxide film may be formed by naturally oxidizing aluminum by chemical or electrochemical etching, may be formed through chemical conversion treatment, or may be formed by aluminum oxide deposition.

The chemical etching is a method of naturally oxidizing the aluminum foil by immersing the aluminum foil in a certain concentration of acid solution, and the acid may be an acid capable of forming hydrogen ions such as sulfuric acid, nitric acid, phosphoric acid, and the like. Electrochemical etching is a method of oxidizing an aluminum surface by flowing a direct current or alternating current power, and the current density is preferably in the range of 0.1 to 500 mA / cm ² . The degree of etching can be controlled by adjusting the current density and the etching process time. In other words, when the current density is high, the etching process time is reduced, and when the current density is low, the etching degree can be controlled by increasing the etching process time. After performing the etching process, the natural oxide film forming process is generally performed by leaving the aluminum foil in the air. At this time, the leaving time is sufficient to be less than 5 minutes.

The chemical conversion treatment for forming the aluminum oxide film is preferably performed at a current density of 0.2 to 1 mA / cm ² using a direct current or alternating current power source. In addition, the chemical conversion treatment is preferably carried out for 30 seconds to 10 minutes. If the conversion current density or the conversion treatment time is lower than the above range, it is not preferable to form a film having a desired thickness. If the conversion current density or conversion processing time is higher than the above range, the coating becomes thick and the insulation property is high, which is not preferable.

Although the chemical conversion treatment may be performed on aluminum foil, an aluminum foil having a natural oxide film formed by etching-natural oxidation may be used. Etching-natural oxidation pretreatment before the chemical conversion treatment is preferred because it can secure the surface cleaning effect and uniformity.

The aluminum foil on which the aluminum oxide film of the present invention is formed has a degree of surface roughness. When converted to capacity and has a surface roughness having a 10μF / cm ² or more, the capacity of preferably from 10 μF / cm ² to 800 μF / cm ² range. In the case of having the surface roughness in the above range is preferable because the binding force between the coating layer is strong. When the surface roughness of the aluminum foil is less than 10 μF / cm ^2, there is a problem that the binding force is insufficient when the active material is applied, which is not preferable.

By the etching-natural oxidation process, the chemical conversion treatment, or the etching-natural oxidation-chemical treatment process, the aluminum oxide film has a surface roughness, whereby pores are formed. A transition metal, a metal oxide, or a metal sulfide may be added to the pores of the aluminum foil current collector on which the aluminum oxide film is formed to improve electronic conductivity. These materials allow the solid lithium sulfide formed during the discharge of the lithium-sulfur cell to grow more finely and facilitate the transfer of electrons and lithium ions to the lithium sulfide. It is preferable to control the pores of the aluminum oxide film through the chemical conversion process and stably exist when the transition metal, metal oxide or metal sulfide is injected into the controlled pores.

Preferred examples of the transition metal include Ti, Ni, Sn. Zn. Cu, Mo, Mn, Fe, V, Co, W, Cd, Au, Ag, and the like, among which Ni, Ti, Mo, mixtures thereof, and the like can be preferably used. Preferred examples of the metal oxide include TiO ₂ , MoO _x (2 <x <8), MnO ₂ , Al ₂ O ₃ , mixtures thereof, and the like, and the metal sulfide may be Cu ₂ S, FeS, NiS, Ag _2. S, MoS ₂ , mixtures thereof, and the like.

The aluminum oxide film is formed to a thickness of 1nm to 5㎛, preferably 20nm to 100nm. If the thickness of the aluminum oxide film is less than 1 nm, there is almost no effect of forming the aluminum oxide film, and if it exceeds 5 µm, electron transfer is not easy, which is not preferable.

In the present invention, the aluminum oxide film has a breakdown voltage of 1 V or more. The break down voltage is a voltage at which the oxide film is destroyed. If the voltage is lower than 1V, the oxide film on the surface of the aluminum is destroyed during the charge and discharge process.

The present invention provides a lithium-sulfur battery including a positive electrode prepared by applying a positive electrode active material slurry to an aluminum foil current collector having an aluminum oxide film formed as described above. The lithium sulfur battery 1 according to the present invention includes a battery can 5 including a positive electrode 3, a negative electrode 4, and a separator positioned between the positive electrode 3 and the negative electrode 4 as shown in FIG. 1. ). A salt electrolyte containing an organic cation is injected between the anode 3 and the cathode 4. Cathorite, organic sulfur compound, and carbon-sulfur polymer ((C ₂ S) in which the elemental sulfur (S ₈ ), Li ₂ S _n (n ≧ 1), Li ₂ S _n (n ≧ 1) is dissolved _x ) _n : it can be used selected from the group consisting of x = 2.5 to 50, n≥2).

The anode of the present invention may also further comprise a coating layer composed of a polymer, an inorganic substance or a mixture thereof.

The polymers are polyvinylidene fluoride, copolymers of polyvinylidene fluoride and hexafluoropropylene, poly (vinyl acetate), poly (vinyl butyral-co-vinyl alcohol-co-vinyl acetate), poly (methylmetha) Acrylate-co-ethyl acrylate), polyacrylonitrile, polyvinyl chloride-co-vinyl acetate, polyvinyl alcohol, poly (1-vinylpyrrolidone-co-vinyl acetate), cellulose acetate, polyvinylpyrroly Don, polyacrylate, polymethacrylate, polyolefin, polyurethane, polyvinyl ether, acrylonitrile-butadiene rubber, styrene-butadiene rubber, acrylonitrile-butadiene styrene, sulfonated styrene / ethylene-butylene / styrene Triblock copolymers, polyethylene oxides and mixtures thereof can be used.

The inorganic material may be selected from the group consisting of colloidal silica, amorphous silica, surface treated silica, colloidal alumina, amorphous alumina, conductive carbon, tin oxide, titanium oxide, vanadium oxide, and mixtures thereof.

In the lithium-sulfur battery including the positive electrode, as a negative electrode, a material capable of reversibly intercalating or deintercalating lithium ions, a material capable of reacting with lithium ions to reversibly form a lithium-containing compound, and lithium metal And a negative electrode active material selected from the group consisting of lithium alloys.

As a material capable of reversibly intercalating / deintercalating the lithium ions, any carbon-based negative electrode active material generally used in a lithium ion secondary battery may be used, and representative examples thereof include crystalline carbon. , Amorphous 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. As the lithium alloy, an alloy of a metal selected from the group consisting of lithium and Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Ba, Ra, Al, and Sn may be used.

An inorganic protective layer, an organic protective layer, or a material in which these layers are stacked on a lithium metal surface may also be used as a cathode. As the inorganic protective film, Mg, Al, B, C, Sn, Pb, Cd, Si, In, Ga, lithium silicate, lithium borate, lithium phosphate, lithium phosphoride nitride, lithium silicosulfide, lithium borosulfide, lithium aluminium It consists of a material selected from the group consisting of nosulfide and lithium phosphosulfide. The organic protective film is poly (p-phenylene), polyacetylene, poly (p-phenylene vinylene), polyaniline, polypyrrole, polythiophene, poly (2,5-ethylene vinylene), acetylene, poly (ferry) Naphthalene), polyacene, and poly (naphthalene-2,6-diyl), and a monomer, oligomer or polymer having conductivity selected from the group consisting of.

In addition, in the process of charging and discharging the lithium-sulfur battery, sulfur used as the positive electrode active material may be changed into an inert material and adhered to the surface of the lithium negative electrode. As described above, inactive sulfur refers to sulfur in which sulfur is no longer able to participate in the electrochemical reaction of the anode through various electrochemical or chemical reactions, and the inactive sulfur formed on the surface of the lithium anode is a protective layer of the lithium cathode. It also has the advantage of acting as). Therefore, inert sulfur formed on the lithium metal, for example, lithium metal including lithium sulfide as a protective film may be used as the negative electrode.

As electrolyte solution of the lithium-sulfur battery of this invention, the thing containing an electrolyte salt and an organic solvent can be used.

As the organic solvent, a single solvent may be used, or two or more mixed organic solvents may be used. When using two or more mixed organic solvents, it is preferable to select one or more solvents from two or more groups among the weak polar solvent group, the strong polar solvent group, and the lithium metal protective solvent group.

Weak polar solvents are defined as those having a dielectric constant of less than 15 that can dissolve elemental sulfur among aryl compounds, bicyclic ethers, and acyclic carbonates; strong polar solvents include acyclic carbonates, sulfoxide compounds, lactone compounds, Among ketone compounds, ester compounds, sulfate compounds, and sulfite compounds, a dielectric constant capable of dissolving lithium polysulfide is defined as greater than 15, and lithium protective solvents are saturated ether compounds, unsaturated ether compounds, N, O, It is defined as a solvent having a charge and discharge cycle efficiency (cycle efficiency) of 50% or more to form a SEI (Solid Electrolyte Interface) film stable on a lithium metal, such as a heterocyclic compound containing S or a combination thereof.

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

Specific examples of strong polar solvents include hexamethyl phosphoric triamide, gamma-butyrolactone, acetonitrile, ethylene carbonate, propylene carbonate, N-methylpyrrolidone, 3-methyl-2-oxazolidone , Dimethyl formamide, sulfolane, dimethyl acetamide, dimethyl sulfoxide, dimethyl sulfate, ethylene glycol diacetate, dimethyl sulfite, or ethylene glycol sulfite.

Specific examples of the lithium protective solvent include tetrahydrofuran, ethylene oxide, dioxolane, 3,5-dimethyl isoxazole, 2,5-dimethyl furan, furan, 2-methyl furan, 1,4-oxane, 4-methyldioxolane Etc.

The electrolytic salt lithium salt is lithium trifluoromethansulfonimide (lithium trifluoromethansulfonimide), lithium triflate (lithium triflate), lithium perchlorate (lithium perclorate), LiPF ₆ , LiBF ₄ or tetraalkylammonium, for example tetra One or more butylammonium tetrafluoroborate, or liquid salts at room temperature, such as imidazolium salts such as 1-ethyl-3-methylimidazolium bis- (perfluoroethyl sulfonyl) imide and the like Can be.

Hereinafter, preferred examples and comparative examples of the present invention are described. However, the following examples are only one preferred embodiment of the present invention and the present invention is not limited to the following examples.

(Example 1)

The aluminum foil was immersed in 5% sulfuric acid solution for 2 minutes to etch the surface, and then left in the air for 5 minutes to prepare a current collector having a natural aluminum oxide film having a thickness of 10 nm.

60% by weight of elemental sulfur (S ₈ ) powder, 20% by weight of carbon conductive material and 20% by weight of polyvinylpyrrolidone binder were mixed in an isopropyl alcohol solvent and stirred until the slurry was thoroughly mixed.

The well mixed slurry was coated on the current collector. The coated current collector was dried at room temperature for at least 2 hours, and then dried at 50 ° C. for at least 12 hours to prepare a positive electrode for a lithium-sulfur battery.

The tab-welded anode was placed inside the pouch cut to specifications, and the separator was covered on the anode, and then the lithium foil with the tab was covered on the separator, and the pouch was sealed, leaving only the electrolyte injection hole. An appropriate amount of dimethoxyethane / 1.3-dioxolane (80/20) electrolyte in which 1M LiN (SO ₂ CF ₃ ) ₂ was dissolved was injected into the pouch. One side of the remaining pouch was vacuum sealed to prepare a lithium-sulfur pouch battery.

(Example 2)

The aluminum foil was immersed in 5% sulfuric acid solution for 2 minutes to etch the surface, and then left in the air for 5 minutes to form a 10 nm thick natural aluminum oxide film. Then, a current collector was formed by forming an aluminum oxide film having a thickness of 50 nm by chemical conversion treatment at 0.2% AC / cm ² for 5 minutes in a 5% sulfuric acid solution.

A lithium-sulfur pouch battery was manufactured in the same manner as in Example 1 using the current collector.

(Example 3)

The aluminum foil was immersed in 5% sulfuric acid solution for 2 minutes to etch the surface, and then left in the air for 5 minutes to form a 10 nm thick natural aluminum oxide film. Then, a 5 nm sulfuric acid solution was converted to 0.2 A / cm ² for 5 minutes to form an aluminum oxide film having a thickness of 50 nm. The aluminum foil on which the aluminum oxide film was formed was supported on an acid solution containing Ni. A current collector was manufactured by applying a 0.2 A / cm ² power source using the aluminum foil as a cathode to impregnate the transition metal with pores of the aluminum oxide film.

A lithium-sulfur pouch battery was manufactured in the same manner as in Example 1 using the current collector.

(Comparative Example 1)

A lithium-sulfur pouch battery was manufactured in the same manner as in Example 1, except that an aluminum foil, on which an aluminum oxide film was not formed, was used as a current collector for the positive electrode.

The batteries of Examples 1 and 2 and Comparative Example 1 were discharged at a voltage of 0.4 mA / cm ² and 1.5 V cut off to evaluate discharge characteristics, and are described in FIG. 2. As shown in FIG. 2, the batteries of Examples 1 and 2 showed excellent sulfur utilization as compared to Comparative Example 1.

The aluminum oxide film is formed on the aluminum foil used as the positive electrode current collector of the lithium-sulfur battery, and the discharge performance of the lithium-sulfur battery can be greatly improved.

1 is a perspective view of a lithium-sulfur battery.

2 is a view showing the discharge characteristics of the battery according to Examples 1, 2 and Comparative Example 1 according to the present invention.

Claims (21)

A current collector for a lithium-sulfur battery, comprising an aluminum foil and an aluminum oxide film formed on a surface of the aluminum foil. The current collector of claim 1, wherein the aluminum oxide film is formed by natural oxidation of aluminum by chemical or electrochemical etching. The current collector of claim 1, wherein the aluminum oxide film is formed through a chemical conversion treatment. The current collector of claim 1, wherein the aluminum foil on which the aluminum oxide film is formed has a surface roughness to have a capacity of 10 µF / cm ² or more. The current collector for a lithium-sulfur battery according to claim 4, wherein the aluminum foil having the surface roughness formed aluminum oxide film has a transition metal, metal oxide, or metal sulfide added to pores. The method of claim 5, wherein the transition metal is Ti, Ni, Sn. Zn. At least one selected from the group consisting of Cu, Mo, Mn, Fe, V, Co, W, Cd, Au, and Ag, the metal oxide is TiO ₂ , MoO _x (2 <x <8), MnO ₂ , And at least one selected from the group consisting of Al ₂ O ₃ , and the metal sulfide is at least one selected from the group consisting of Cu ₂ S, FeS, NiS, Ag ₂ S, and MoS ₂ . The current collector of claim 1, wherein the aluminum oxide film has a thickness of 1 nm to 5 μm. 8. The current collector of claim 7, wherein the aluminum oxide film has a thickness of 20 nm to 100 nm. The current collector for a lithium-sulfur battery according to claim 1, wherein the breakdown voltage of the aluminum oxide film is 1 V or more. At least one sulfur-based material selected from the group consisting of elemental sulfur, solid Li ₂ S _n (n ≧ 1), catholyte in which Li ₂ S _n (n ≧ 1) is dissolved, an organo-sulfur compound and a carbon-sulfur polymer An anode comprising a current collector comprising an aluminum foil and an aluminum oxide film formed on a surface of the aluminum foil; A negative electrode including a negative electrode active material selected from the group consisting of a material capable of reversibly intercalating lithium ions, a material capable of reacting with lithium ions to form a lithium-containing compound reversibly, and a lithium metal and a lithium alloy; And Electrolyte Lithium-sulfur battery comprising a. The lithium-sulfur battery of claim 10, wherein the aluminum oxide film is formed by natural oxidation of aluminum by chemical or electrochemical etching. The lithium-sulfur battery of claim 10, wherein the aluminum oxide film is formed through a chemical conversion treatment. The lithium-sulfur battery of claim 10, wherein the aluminum foil on which the aluminum oxide film is formed has a surface roughness to have a capacity of 10 μF / cm ² or more. The lithium-sulfur battery of claim 13, wherein the aluminum foil having the surface roughness-formed aluminum oxide film is formed by adding transition metal, transition metal oxide, or metal sulfide to pores. The method of claim 14, wherein the transition metal is Ti, Ni, Sn. Zn. At least one selected from the group consisting of Cu, Mo, Mn, Fe, V, Co, W, Cd, Au, and Ag, the metal oxide is TiO ₂ , MoO _x (2 <x <8), MnO ₂ , And at least one selected from the group consisting of Al ₂ O ₃ , and the metal sulfide is at least one selected from the group consisting of Cu ₂ S, FeS, NiS, Ag ₂ S, and MoS ₂ . The lithium-sulfur battery of claim 10, wherein the aluminum oxide film has a thickness of 1 nm to 5 μm. The lithium-sulfur battery of claim 16, wherein the aluminum oxide film has a thickness of 20 nm to 100 nm. The lithium-sulfur battery according to claim 10, wherein the breakdown voltage of the aluminum oxide film is 1 V or more. The lithium-sulfur battery of claim 10, wherein the positive electrode further comprises a coating layer made of a polymer, an inorganic material, or a mixture thereof. The method of claim 19, wherein the polymer is polyvinylidene fluoride, copolymer of polyvinylidene fluoride and hexafluoropropylene, poly (vinyl acetate), poly (vinyl butyral-co-vinyl alcohol-co-vinyl acetate ), Poly (methylmethacrylate-co-ethyl acrylate), polyacrylonitrile, polyvinyl chloride-co-vinyl acetate, polyvinyl alcohol, poly (1-vinylpyrrolidone-co-vinyl acetate), cellulose Acetate, polyvinylpyrrolidone, polyacrylate, polymethacrylate, polyolefin, polyurethane, polyvinyl ether, acrylonitrile-butadiene rubber, styrene-butadiene rubber, acrylonitrile-butadiene styrene, sulfonated styrene / Lithium-sulfur former selected from the group consisting of ethylene-butylene / styrene triblock copolymers, polyethylene oxides and mixtures thereof . The method of claim 19, wherein the inorganic material is selected from the group consisting of colloidal silica, amorphous silica, surface treated silica, colloidal alumina, amorphous alumina, conductive carbon, tin oxide, titanium oxide, vanadium oxide, and mixtures thereof. Phosphorus lithium-sulfur battery.