KR100485092B1 - Lithium-suflur battery - Google Patents

Abstract

The present invention relates to a lithium-sulfur battery, comprising: a positive electrode comprising a sulfur powder positive electrode active material having a purity of 98% or more; A material capable of reversibly intercalating or deintercalating lithium ions, a material capable of reacting with lithium ions to form a lithium-containing compound reversibly, and a negative electrode active material selected from the group consisting of lithium metals and lithium alloys Cathode; A separator interposed between the positive electrode and the negative electrode; And an electrolyte solution impregnated in the positive electrode, the negative electrode, and the separator.

As described above, the lithium-sulfur battery of the present invention using high purity sulfur powder has a high initial capacity and excellent cycle life characteristics.

Description

Lithium-sulfur battery {LITHIUM-SUFLUR BATTERY}

[Industrial use]

The present invention relates to a lithium-sulfur battery, and more particularly, to a lithium-sulfur battery having excellent capacity characteristics and cycle life characteristics.

[Prior art]

With the development of portable electronic devices, the demand for light and high capacity batteries is increasing. As a secondary battery that satisfies these demands, 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

The lithium-sulfur battery has an energy density of 3830 mAh / g when using lithium metal used as a negative electrode active material, and an energy density of 1675 mAh / g when using sulfur (S ₈ ) used as a positive electrode active material. Among the most promising cells in terms of energy density. In addition, the sulfur-based material used as the positive electrode active material has the advantage that it is cheap and environmentally friendly material.

However, there are no examples of successful commercialization with lithium-sulfur battery systems. The reason why the lithium-sulfur battery is not commercialized is that when sulfur is used as an active material, the utilization rate indicating the amount of sulfur participating in the electrochemical redox reaction in the battery relative to the amount of sulfur input is low. Because it represents.

Therefore, studies to increase the capacity by increasing the electrochemical redox reaction are ongoing, but the satisfactory effect has not yet been obtained.

The present invention has been made to solve the above problems, and an object of the present invention is to provide a lithium-sulfur battery having excellent capacity.

Another object of the present invention is to provide a lithium-sulfur battery having excellent cycle life characteristics.

In order to achieve the above object, the present invention is a positive electrode comprising a sulfur powder positive electrode active material having a purity of 98% or more; A material capable of reversibly intercalating or deintercalating lithium ions, a material capable of reacting with lithium ions to form a lithium-containing compound reversibly, and a negative electrode active material selected from the group consisting of lithium metals and lithium alloys Cathode; A separator interposed between the positive electrode and the negative electrode; And it provides a lithium-sulfur battery comprising an electrolyte solution impregnated in the positive electrode, the negative electrode and the separator.

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

The present invention relates to a lithium-sulfur battery having improved capacity characteristics and cycle life characteristics by using high purity sulfur powder as a sulfur powder used as a cathode active material in a lithium-sulfur battery.

The sulfur powder used as the cathode active material in the present invention is at least 98%, preferably at least 99% high purity powder. The sulfur powder is more preferably free of impurities, but may contain impurities up to 2%. Such impurities may include Ca, Cd, Co, Cu, Fe, K, Na, Pb, or Zn. . As in the present invention, when the sulfur powder having a purity of 98% or more is used as the positive electrode active material, it is preferable to provide a lithium-sulfur battery having a high initial capacity and excellent cycle life characteristics.

In addition to the positive electrode active material, the positive electrode of the present invention further includes an electrically conductive conductive material for smoothly moving electrons in the positive electrode active material. The conductive material is not particularly limited, but conductive materials such as carbon (eg, Super-P), carbon black, or conductive polymers such as polyaniline, polythiophene, polyacetylene, and polypyrrole may be used alone or in combination. .

In addition, the positive electrode active material may further include a binder capable of adhering well to the current collector, the binder may be poly (vinyl acetate), polyvinyl alcohol, polyethylene oxide, polyvinyl pyrrolidone, alkylated polyethylene oxide, Crosslinked polyethylene oxide, polyvinyl ether, poly (methyl methacrylate), polyvinylidene fluoride, copolymers 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 order to manufacture the positive electrode of the present invention, first, the binder is dissolved in a solvent for preparing the active material composition, and then the conductive material is dispersed. As a solvent for preparing the composition, it is possible to uniformly disperse the positive electrode active material, the binder and the conductive material, and it is preferable to use an easily evaporated material. Typically, acetonitrile, methanol, ethanol, tetrahydrofuran, water and iso Propyl alcohol and the like. Next, high purity sulfur powder, which is a positive electrode active material, is uniformly dispersed again in the composition in which the binder and the conductive material are dispersed to prepare a positive electrode active material composition. The amount of the solvent, the positive electrode active material, the binder, and the conductive material included in the positive electrode active material composition does not have a particularly important meaning in the present invention, and merely has an appropriate viscosity to facilitate coating of the composition.

The composition thus prepared is applied to a current collector, and vacuum dried to form a positive electrode plate, which is then used for battery assembly. The composition is sufficient to coat the current collector to an appropriate thickness according to the viscosity of the composition and the thickness of the positive electrode plate to be formed, and is not particularly limited as the current collector, but using a conductive material such as stainless steel, aluminum, copper, titanium, etc. Preference is given to using carbon-coated aluminum current collectors. The use of an Al substrate coated with carbon has an advantage in that the adhesion to the active material is excellent, the contact resistance is low, and the corrosion by polysulfide of aluminum can be prevented, compared with the non-carbon coated Al substrate.

The negative electrode of the lithium-sulfur battery of the present invention is 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, lithium metal and lithium alloy It includes a negative electrode active material selected from the group consisting of.

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. The inorganic protective film is Li, P, O, S, N, B, Al, F, Cl, Br, I, As, Sb, Bi, C, Si, Ge, In, Tl, Mg, Ca, Sr and Ba It includes one or more elements selected from the group consisting of. The organic protective film comprises polyethylene oxide or polypropylene oxide, or polyethylene glycol diacrylate, polypropylene glycol diacrylate, ethoxylated neopentyl glycol diacrylate, ethoxylated bisphenol A diacrylate, ethoxy At least one acrylate monomer selected from the group consisting of toxylated aliphatic urethane acrylates, ethoxylated alkylphenol acrylates and alkylacrylates. Or the organic protective film is a copolymer of polyvinylidene fluoride, polyvinylidene fluoride and hexafluoropropylene, poly (vinylacetate), poly (vinyl butyral-co-vinyl alcohol-co-vinyl acetate), poly ( Methyl methacrylate-co-ethyl acrylate), polyacrylonitrile, polyvinyl chloride co-vinyl acetate, polyvinyl alcohol, poly (1-vinylpyrrolidone-co-vinyl acetate), cellulose acetate, polyvinyl py Ralidone, Polyacrylate, Polymethacrylate, Polyolefin, Polyurethane, Polyvinyl ether, Acrylonitrile-butadiene rubber, Styrene-butadiene rubber, Acrylonitrile-butadiene-styrene, Sulfonated styrene / ethylene-butylene Triblock copolymers, polyethylene oxides, and mixtures thereof.

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 inert sulfur formed on the surface of the lithium cathode is a protective layer of the lithium cathode. There is also an advantage to act as. Therefore, lithium metal and inert sulfur formed on the lithium metal, for example lithium sulfide, may be used as the negative electrode.

As the separator present in the positive electrode and the negative electrode, a polymer film such as polyethylene or polypropylene or a multilayer thereof is used.

The electrolyte solution used in the lithium-sulfur battery of the present invention contains an organic solvent and an electrolyte salt. As the organic solvent, benzene, fluorobenzene, toluene, dimethylformamide, dimethyl acetate, trifluorotoluene, xylene, cyclohexane, tetrahydrofuran, 2-methyltetrahydrofuran, cyclohexanone, ethanol, isopropyl alcohol , Dimethyl carbonate, ethylmethyl carbonate, diethyl carbonate, methylpropyl carbonate, methylpropionate, ethylpropionate, methyl acetate, ethyl acetate, propyl acetate, dimethoxyethane, 1,3-dioxolane, diglyme, tetra One or more solvents selected from the group consisting of glyme, ethyl carbonate, propyl carbonate, γ-butyrolactone and sulfolane can be used.

The electrolytic salts include lithium hexafluorophosphate (LiPF ₆ ), lithium tetrafluoroborate (LiBF ₄ ), lithium hexafluoroazate (LiAsF ₆ ), lithium perchlorate (LiClO ₄ ), and lithium trifluoromethanesulfonate (LiSO ₃ CF ₃ ), lithium bis (trifluoromethyl) sulfonimide (LiN (SO ₂ CF ₃ ) ₂ ), lithium bis (perfluoroethylsulfonyl) imide (LiN (SO ₂ C ₂ F ₅ One or more lithium salts selected from the group consisting of ₂ ) may be used.

In the electrolyte solution, the concentration of the electrolytic salt is used at 0.1 to 2.0M.

Hereinafter, preferred examples and comparative examples of the present invention are described.

(Example 1)

A positive electrode active material slurry was prepared by stirring 60% by weight of a sulfur powder positive electrode active material having a purity of 99.95% or more, 20% by weight of carbon conductive material, and 20% by weight of polyvinyl pyrrolidone binder until completely mixed in an isopropyl alcohol solvent. The resulting well mixed slurry was coated on a carbon-coated Al 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 plate. This positive electrode plate was punched out to a size of 25 mm x 50 mm, and a pouch-type lithium-sulfur battery was produced using this positive electrode plate and lithium foil negative electrode. At this time, a dimethoxyethane / 1,3-dioxolane (80/20) solution in which 1M LiN (SO ₂ CF ₃ ) ₂ was dissolved was used as an electrolyte.

(Example 2)

The same procedure as in Example 1 was carried out except that sulfur powder having a purity of 98.9% was used.

(Example 3)

The same procedure as in Example 1 was carried out except that sulfur powder having a purity of 98% was used.

The sulfur powders used in Examples 1 to 3 were quantitatively analyzed using ICP-MS and ICP-AES. In Table 1 below, the amount of impurities is in ppm. The lowest purity shown in Table 1 below, Example 3 is 97.9634% purity of about 98%.

division Ca CD Co Cu Fe K Na Pb Zn Minimum purity Example 1 <50 <1.0 <1.0 <10.0 <50 <100 <100 <5.0 <50 99.9633 Example 2 <50 <1.0 <10.0 <50 10000 <100 <100 <5.0 <50 98.9634 Example 3 <50 <1.0 <10.0 <50 20000 <100 <100 <5.0 <50 97.9634

As shown in Table 1, the impurity contained in the sulfur powder is Ca, Cd, Co, Cu, Fe, K, Na, Pb and Zn, among which iron makes up most of the impurities.

After charging and discharging the lithium-sulfur batteries of Examples 1 to 3 with 0.2C charge and 0.5C discharge, the capacity at one cycle, the capacity at ten cycles, and the ten cycle life characteristics were measured, and the results are as follows. Table 2 shows. In Table 2 below, the ten cycle life represents the capacity retention rate after the battery was charged and discharged ten times.

One time capacity (mAh / g) 10 times capacity (mAh / g) 10 cycle life (%) Example 1 605 600 99 Example 2 548 530 97 Example 3 473 315 67

As shown in Table 2, it can be seen that as the purity is improved, the capacity of one, the capacity of ten and the cycle life are improved. In addition, in Example 3, in which the purity of sulfur was 97.9634% and about 98%, the 10 cycle life was 67%, indicating a very deteriorated cycle life characteristic. Thus, a battery using sulfur powder having sulfur purity lower than 98% as the positive electrode active material was used. Can predict little availability.

As described above, the lithium-sulfur battery of the present invention using high purity sulfur powder has a high initial capacity and excellent cycle life characteristics.

Claims (10)

delete delete delete delete Sulfur having a purity of 98% or more and containing less than 2% of impurities selected from the group consisting of Ca, Cd, Co, Cu, Fe, K, Na, Pb, and Zn, and the Fe content of the impurities is 10,000 ppm or less A positive electrode including a powder positive electrode active material; A material capable of reversibly intercalating or deintercalating lithium ions, a material capable of reacting with lithium ions to form a lithium-containing compound reversibly, and a negative electrode active material selected from the group consisting of lithium metals and lithium alloys A cathode including an inorganic protective film or an organic protective film; A separator interposed between the positive electrode and the negative electrode; And Electrolyte impregnated in the positive electrode, the negative electrode and the separator Lithium-sulfur battery comprising a. The method of claim 5, wherein the inorganic protective film is Li, P, O, S, N, B, Al, F, Cl, Br, I, As, Sb, Bi, C, Si, Ge, In, Tl, Mg, Li-sulfur battery comprising at least one element selected from the group consisting of Ca, Sr and Ba. The lithium-sulfur battery of claim 5, wherein the organic protective layer comprises polyethylene oxide or polypropylene oxide. The method of claim 5, wherein the organic protective film is polyethylene glycol diacrylate, polypropylene glycol diacrylate, ethoxylated neopentyl glycol diacrylate, ethoxylated bisphenol A diacrylate, ethoxylated aliphatic urethane A lithium-sulfur battery which is at least one acrylate monomer selected from the group consisting of acrylates, ethoxylated alkylphenol acrylates and alkylacrylates. The method of claim 5, wherein the organic protective film is a copolymer of polyvinylidene fluoride, polyvinylidene fluoride and hexafluoropropylene, poly (vinylacetate), 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, polyvinyl pyrrolidone, polyacrylate, polymethacrylate, polyolefin, polyurethane, polyvinyl ether, acrylonitrile-butadiene rubber, styrene-butadiene rubber, acrylonitrile-butadiene-styrene, sulfonated styrene A lithium-sulfur battery which is a polymer selected from the group consisting of ethylene-butylene triblock copolymers, polyethylene oxides and mixtures thereof. The lithium-sulfur battery of claim 5, wherein the sulfur powder has a purity of 99% or more.