KR20170084453A - Non-Aqueous Slurry Composition, Cathode Thereof, And Lithium Sulfur Batteries Comprising The Same - Google Patents

Abstract

The present invention relates to a nonaqueous positive electrode slurry composition for a lithium-sulfur battery, a positive electrode and a lithium-sulfur battery manufactured using the same, and more particularly to a nonaqueous positive electrode slurry composition using a nonaqueous binder based on an organic solvent A positive electrode and a lithium-sulfur battery. The lithium-sulfur barrier according to the present invention has a low water content in the electrode due to the preparation of the positive electrode slurry on the basis of an organic solvent rather than water, thereby preventing the phenomenon of swelling of the battery, The deterioration phenomenon can be improved. Also, compared with an aqueous slurry-based battery, the initial charge / discharge characteristics, discharge cycle characteristics, and charge / discharge efficiency of the lithium-sulfur battery are improved.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-aqueous slurry composition for a lithium-sulfur battery, a positive electrode and a lithium-sulfur battery produced therefrom,

The present invention relates to a nonaqueous cathode slurry composition for a lithium-sulfur battery, a cathode and a lithium-sulfur battery produced therefrom, and more particularly to a nonaqueous cathode slurry composition using a nonaqueous binder based on an organic solvent, And a lithium-sulfur battery.

In recent years, miniaturization and weight reduction of electronic products, electronic devices, and communication devices are rapidly proceeding. As the necessity of electric automobiles has been greatly increased with respect to environmental problems, there has been an increase in demand for performance improvement of secondary batteries used as power sources for these products . Among them, lithium secondary batteries are attracting considerable attention as high performance batteries due to high energy density and high standard electrode potential.

In particular, a lithium-sulfur (Li-S) battery is a secondary battery in which a sulfur-based material having a sulfur-sulfur bond is used as a cathode active material and lithium metal is used as an anode active material. Sulfur, the main material of the cathode active material, is very rich in resources, has no toxicity, and has a low atomic weight. The theoretical energy density of the lithium-sulfur battery is 1672 mAh / g-sulfur and the theoretical energy density is 2,600 Wh / kg. The theoretical energy density (Ni-MH battery: 450 Wh / , Which is the most promising among the batteries that have been developed to date, because it is much higher than the FeS battery (480Wh / kg), Li-MnO ₂ battery (1,000Wh / kg) and Na-S battery (800Wh / kg).

During the discharge reaction of the lithium-sulfur battery, an oxidation reaction of lithium occurs at the anode and a sulfur reduction reaction occurs at the cathode. Sulfur before discharging has an annular S ₈ structure. When the SS bond is cut off during the reduction reaction (discharging), the oxidation number of S decreases, and when the oxidation reaction (charging) The reduction reaction is used to store and generate electrical energy. During this reaction, the sulfur is converted to a linear polysulfide (Li ₂ S _x , x = 8, 6, 4, 2) by a reduction reaction at the cyclic S ₈ and consequently the lithium polysulfide is completely reduced Lithium sulfide (Li ₂ S) is finally produced. Unlike the lithium ion battery, the discharge behavior of the lithium-sulfur battery is characterized by showing the discharge voltage stepwise by the process of being reduced to each lithium polysulfide.

Generally, a method for producing a positive electrode of a lithium-sulfur battery includes preparing a positive electrode slurry composition prepared by using water as a solvent and a material such as carboxymethylcellulose (CMC) and styrene-butadiene rubber (SBR) To the whole. For this reason, residual water is present in the anode at about 700 to 1000 ppm, and when moisture is present in the battery, water reacts with the electrolytic solution due to potential energy provided in the charging process. As a result, The cell swells around.

In addition, due to the residual moisture, the electrolyte is decomposed, the active material is deteriorated, and the internal resistance of the battery is increased. As a result, the initial discharge capacity is 900 to 1100 mAh / g which is far below the theoretical discharge capacity. There is a problem that the lifetime is shortened due to a sudden decrease in charge / discharge capacity.

Korean Patent Laid-Open Publication No. 2015-0061874 "A cathode for a lithium-sulfur battery and a method for producing the same"

As described above, the positive electrode slurry composition for a lithium-sulfur battery produced using water as a solvent causes the battery to swell and deteriorate due to the residual water.

Accordingly, an object of the present invention is to provide a non-aqueous liquid anode slurry composition for improving the phenomenon due to moisture.

It is another object of the present invention to provide a positive electrode for a lithium-sulfur battery manufactured using the non-aqueous positive electrode slurry composition.

Still another object of the present invention is to provide a lithium-sulfur battery including a positive electrode for a lithium-sulfur battery manufactured using the non-aqueous positive electrode slurry composition.

In order to accomplish the above object, the present invention provides a positive electrode slurry composition for a lithium-sulfur battery including a carbon-sulfur (S) composite, a dispersant, a binder and a non-aqueous solvent, wherein the dispersant is a polyvinyl butyral Wherein the binder is selected from the group consisting of N, N-bis [3- (triethoxysilyl) propyl] urea, polyethylene oxide (PEO), polyvinylidene fluoride (PVDF), poly (vinylidene fluoride- A positive electrode slurry composition for a lithium-sulfur battery, characterized by containing one selected from the group consisting of styrene-butadiene rubber (co-hexafluoropropylene) (PVDF-HFP), styrene butadiene rubber (SBR) and a combination thereof.

The lithium-sulfur barrier according to the present invention has a low water content in the electrode due to the preparation of the positive electrode slurry on the basis of an organic solvent rather than water, thereby preventing the phenomenon of swelling of the battery, The deterioration phenomenon can be improved.

Also, compared with an aqueous slurry-based battery, the initial charge / discharge characteristics, discharge cycle characteristics, and charge / discharge efficiency of the lithium-sulfur battery are improved.

FIG. 1 is a graph showing initial charging / discharging curves of lithium-sulfur batteries according to Examples and Comparative Examples of the present invention.
2 is a graph showing discharge cycle characteristics of a lithium-sulfur battery according to Examples and Comparative Examples of the present invention.
3 is a graph showing the charge and discharge efficiency of a lithium-sulfur battery according to Examples and Comparative Examples of the present invention.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art can easily carry out the present invention. The present invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein.

The positive electrode slurry composition for a lithium-sulfur battery according to the present invention comprises a carbon-sulfur (S) composite, a dispersant, a binder and a non-aqueous solvent, wherein the dispersant comprises polyvinyl butyral (PVB) (N-bis [3- (triethoxysilyl) propyl] Urea), polyethylene oxide (PEO), poly (vinylidene fluoride (PVDF), poly (vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP), styrene butadiene rubber (SBR), and combinations thereof.

The carbon-sulfur complex of the present invention is a combination of carbon (C) particles and sulfur (S) particles, and the carbon constituting the carbon-sulfur complex may be crystalline or amorphous carbon. The conductive carbon is not limited as long as it is natural graphite, Graphite, Activated carbon, Channel black, Denka black, Furnace black, Thermal black, Expanded graphite, Graphene, Thermal black, Carbon black such as contact black, lamp black, and acetylene black; Carbon nanotubes such as carbon fiber, carbon nanotube (CNT), and fullerene, and a combination thereof. The sulfur may also include elemental sulfur (S ₈ ), a sulfur-based compound, or a mixture thereof. 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?

Preferably, the carbon-sulfur (S) complex is a complex of sulfur (S) with a carbon nanotube (CNT) (S / CNT) or a complex of sulfur (S) and super- And more preferably, a mixture obtained by mixing them at a predetermined blending ratio can be applied. For example, a composite in which sulfur (S) and carbon nanotubes (CNT) are mixed at a weight ratio of 7: 3, a mixture of sulfur (S) and super-P (SP) at a weight ratio of 9: By weight.

The content ratio of the dispersant and the binder is preferably 5 to 20 parts by weight based on 100 parts by weight of the total positive electrode slurry composition. If the amount is less than 5 parts by weight, the physical properties of the positive electrode may deteriorate and the active material and the conductive material may fall off. When the amount exceeds 20 parts by weight, the ratio of the active material and the conductive material may be relatively decreased, not.

The weight ratio of the dispersant to the binder is preferably 1: 5 to 5: 1 in order to secure the dispersing effect of the slurry composition and the effect of bonding to the positive electrode collector.

The nonaqueous solvent according to the present invention can be made of materials known in the art. More specifically, the organic solvent is not particularly limited as long as it is an organic solvent capable of uniformly dispersing the cathode active material and the conductive material, and being easily evaporated. Specific examples thereof include alcohols such as ethanol, isopropanol, acetonitrile, toluene, benzene, N-methylpyrrolidone (NMP), dimethylsulfoxide (DMSO), acetone, chloroform, dimethylformamide, cyclohexane, tetrahydrofuran , Polyethylene glycol, and methylene chloride. Preferably a mixed solvent containing acetonitrile, toluene and isopropanol, and more preferably a weight ratio of 4: 2: 4.

The composition may further comprise a conductive material to impart additional conductivity to the carbon-sulfur (S) complex. As the conductive material, any conductive material may be used without limitation, and for example, a carbon-based material having porosity may be used. Examples of such carbon-based materials include natural graphite, artificial graphite, expanded graphite, graphite such as graphene, active carbon, channel black, furnace black, A carbon black system such as thermal black, contact black, lamp black, and acetylene black; A carbon nano structure such as a carbon fiber, a carbon nanotube (CNT), and a fullerene, and a combination thereof may be used. Further, metallic fibers such as metal mesh; Metallic powder such as copper (Cu), silver (Ag), nickel (Ni) and aluminum (Al); Or an organic conductive material such as a polyphenylene derivative can also be used. The conductive materials may be used alone or in combination.

The slurry may be mixed by a conventional method using a conventional mixer such as a paste mixer, a high-speed shear mixer, a homomixer, or the like.

The positive electrode slurry is applied to a current collector and vacuum dried to form a positive electrode for a lithium-sulfur battery. The slurry may be coated on the current collector with an appropriate thickness according to the viscosity of the slurry and the thickness of the anode to be formed, and may be suitably selected within the range of 10 nm to 1 mu m.

The slurry may be coated by a method such as doctor blade coating, dip coating, gravure coating, slit die coating, spin coating, Spin coating, comma coating, bar coating, reverse roll coating, screen coating, cap coating and the like.

The current collector generally has a thickness of 3 to 500 μm and is not particularly limited as long as it has high conductivity without causing chemical change in the battery. Specifically, a conductive material such as stainless steel, aluminum, copper, or titanium can be used, and more specifically, a carbon-coated aluminum current collector can be used. The use of a carbon-coated aluminum substrate is advantageous in that it has an excellent adhesion to an active material, has a low contact resistance, and can prevent corrosion caused by aluminum polysulfide, as compared with a carbon-coated aluminum substrate. The current collector may be in various forms such as a film, a sheet, a foil, a net, a porous body, a foam or a nonwoven fabric.

The positive electrode prepared using the above-described slurry composition is preferably applicable as a separator for a lithium-sulfur battery, and the positive electrode for the lithium-sulfur battery; A negative electrode comprising lithium metal or a lithium alloy as a negative electrode active material; A separation membrane positioned between the anode and the cathode; And an electrolyte impregnated with the negative electrode, the positive electrode and the separator, and including a lithium salt and an organic solvent. Such a lithium-sulfur battery can be produced by a conventional method known to those skilled in the art.

The negative electrode is a negative electrode active material, which is capable of reversibly intercalating or deintercalating lithium ions (Li ⁺ ), a material capable of reversibly forming a lithium-containing compound by reacting with lithium ions, a lithium metal or lithium Alloys may be used. The material capable of reversibly storing or releasing lithium ions (Li ^< ^{+ &} gt ^; ) may be, for example, crystalline carbon, amorphous carbon, or a mixture thereof. The material capable of reacting with the lithium ion (Li ^< ^{+ &} gt ^; ) to reversibly form a lithium-containing compound may be, for example, tin oxide, titanium nitride or silicon. The lithium alloy includes, for example, lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), francium (Fr), beryllium (Be), magnesium (Mg) Ca, strontium (Sr), barium (Ba), radium (Ra), aluminum (Al), and tin (Sn).

In addition, in the course of charging / discharging the lithium-sulfur battery, sulfur used as a cathode active material is changed to an inactive material and can be attached to the surface of the lithium anode. Inactive sulfur means sulfur in which sulfur can no longer participate in the electrochemical reaction of the anode through various electrochemical or chemical reactions. Inert sulfur formed on the surface of the lithium negative electrode is a protective layer of the lithium negative electrode It is also an advantage to serve as

The electrolyte impregnated in the positive electrode, the negative electrode and the separator is a non-aqueous electrolyte containing a lithium salt and is composed of a lithium salt and an electrolyte. In addition, organic solid electrolytes and inorganic solid electrolytes are used.

The lithium salt of the present invention can be dissolved in a non-aqueous organic solvent, for example, LiCl, LiBr, LiI, LiClO ₄ , LiBF ₄ , LiB ₁₀ Cl ₁₀ , LiB (Ph) _{4 ,} LiPF ₆ , LiCF ₃ SO ₃ , _{LiCF 3 CO 2, LiAsF 6,} LiSbF 6, LiAlCl 4, LiSO 3 CH 3, LiSO 3 CF 3, LiSCN, LiC (CF 3 SO 2) 3, LiN (CF 3 SO 2) 2, chloroborane lithium, lower aliphatic Lithium tetraborate, lithium tetraborate, lithium tetraborate, lithium tetraborate, lithium tetraborate, lithium tetraborate, and lithium imide.

The concentration of the lithium salt may be 0.2 to 2 M according to various factors such as the precise composition of the electrolyte mixture, the solubility of the salt, the conductivity of the dissolved salt, the charging and discharging conditions of the battery, the working temperature and other factors known to the lithium battery May be 0.6 to 2M, more specifically 0.7 to 1.7M. If it is used at less than 0.2 M, the conductivity of the electrolyte may be lowered and the performance of the electrolyte may be deteriorated. If it is used in excess of 2 M, the viscosity of the electrolyte may increase and the mobility of lithium ions (Li ⁺ ) may be reduced.

Examples of the non-aqueous organic solvent of the present invention include N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, di Ethyl carbonate, ethyl methyl carbonate, gamma-butylolactone, 1,2-dimethoxyethane, 1,2-diethoxyethane, tetrahydroxyfuran, 2-methyltetrahydrofuran, dimethylsulfoxide, Diethyl ether, formamide, dimethyl formamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, phosphoric acid triester, trimethoxymethane , Dioxolane derivatives, sulfone, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ether, methyl propionate, ethyl propionate and the like May be used, and the organic solvent may be one or a mixture of two or more organic solvents.

Examples of the organic solid electrolyte include organic polymers such as polyethylene derivatives, polyethylene oxide derivatives, polypropylene oxide derivatives, phosphate ester polymers, agitation lysine, polyester sulfides, polyvinyl alcohols, polyvinylidene fluoride, A polymer including a group can be used.

Examples of the inorganic solid electrolyte of the present invention include Li ₃ N, LiI, Li ₅ NI ₂ , Li ₃ N-LiI-LiOH, LiSiO ₄ , LiSiO ₄ -LiI-LiOH, Li ₂ SiS ₃ , Li ₄ SiO ₄ , Nitrides, halides and sulfates of Li such as Li ₄ SiO ₄ -LiI-LiOH and Li ₃ PO ₄ -Li ₂ S-SiS ₂ can be used.

The electrolyte of the present invention may be added to the electrolyte for the purpose of improving charge / discharge characteristics, flame retardancy, etc., for example, pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylenediamine, glyme, hexaphosphoric triamide, Benzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N, N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, . In some cases, a halogen-containing solvent such as carbon tetrachloride, ethylene trifluoride or the like may be further added to impart nonflammability. In order to improve the high-temperature storage characteristics, carbon dioxide gas may be further added. carbonate, PRS (propene sultone), FPC (fluoro-propylene carbonate) and the like.

The electrolyte can be used either as a liquid electrolyte or as a solid electrolyte separator. When used as a liquid electrolyte, the separator further includes a separation membrane made of porous glass, plastic, ceramic, or polymer as a physical separation membrane having a function of physically separating the electrode.

The stacked electrode assembly can be manufactured by interposing a separation membrane having a predetermined size corresponding to the positive electrode plate and the negative electrode plate sandwiched between the positive electrode plate and the negative electrode plate obtained by cutting the positive electrode and the negative electrode to a predetermined size.

Or two or more unit cells in which two or more positive plates and negative plates are stacked on a separator sheet so that the positive and negative electrodes face each other with a separator sheet therebetween, And the stacked and folded electrode assembly can be manufactured by winding the separator sheet or by bending the separator sheet to the size of the electrode plate or the unit cell.

The battery pack including the lithium-sulfur battery includes an electric vehicle (EV), a hybrid electric vehicle (HEV), a plug-in hybrid electric vehicle (PHEV) Airplanes, and power storage devices.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail with reference to examples. However, the embodiments according to the present invention can be modified into various other forms, and the scope of the present invention should not be construed as being limited to the embodiments described below. The embodiments of the present invention are provided to enable those skilled in the art to more fully understand the present invention.

<Examples>

(1) Production of positive electrode slurry composition

Step 1. 8.4 g of a solvent mixture of acetonitrile, toluene and iso-propanol in a weight ratio of 4: 2: 4, 2 g of 10% by weight of polyvinyl butyral, 0.2 g of black (Denka Black) was mixed with ZrO ₂ Balls in a PDM paste mixer (1000/1500 RPM) three times for 10 minutes.

Step 2. 1.7 g of S / SP composite with a weight ratio of sulfur (S) and super P (SP) of 9: 1 and S / CNT composite 1.7 with a weight ratio of sulfur (S) and carbon nanotube (CNT) g was added to the mixture of 1 and mixed with PDM paste mixer (1000/1500 RPM) three times for 10 minutes.

Step 3. 2 g of 10 wt% N, N-bis [3- (triethoxysilyl) propyl] urea (N, N-bis [3- And mixed with a paste mixer (1000/1500 RPM) once for 5 minutes to prepare a positive electrode slurry composition.

(2) Manufacture of anode and manufacture of lithium-sulfur battery

The prepared positive electrode slurry composition was coated on one side of an aluminum foil to a thickness of 150 μm and then dried at room temperature for 24 hours to prepare a positive electrode having a loading of 1.9 mAh / cm ² . A lithium-sulfur battery including the positive electrode, the negative electrode, the separator interposed therebetween, and the electrolyte was produced by using a commonly known manufacturing method.

<Comparative Example>

(1) Preparation of positive electrode slurry composition

step 1. 0.4 g of Denka Black was mixed with 10 g of 1.2% by weight of Carboxymethyl Cellulose (CMC) dissolved in distilled water (DI water) and mixed once with PDM paste mixer (1000/1500 RPM) for 5 minutes .

Step 2. Add 3.2 g of S / SP composite with sulfur (S) and Super P (SP) in a weight ratio of 9: 1 together with ZrO ₂ Balls to the mixture of 1 above and mix with ₅ g of PDM paste mixer (1000/1500 rpm) Min.

Step 3. 0.67 g of a 42 wt% styrene-butadiene rubber (SBR) dispersed in a distilled water solvent was added to the mixture of the above 2 and mixed with PDM paste mixer (1000/1500 RPM) for 5 minutes once To prepare a positive electrode slurry composition.

(2) Manufacture of anode and manufacture of lithium-sulfur battery

The positive electrode slurry compositions of the prepared examples and comparative examples were coated on one side of aluminum foil to a thickness of 150 μm and dried at room temperature for 24 hours to prepare a positive electrode having a loading of 2.3 mAh / cm ² . A lithium-sulfur battery including the positive electrode, the negative electrode, the separator interposed therebetween, and the electrolyte was produced by using a commonly known manufacturing method.

<Experimental Example>

The lithium-sulfur batteries of the prepared examples and comparative examples were charged and discharged at a rate of 0.1 C after impregnation with an electrolyte for 10 hours, and data on the sulfur activity rate, charge / discharge capacity, and charge / discharge efficiency were recorded. The results are shown in Fig. 1 to Fig.

FIG. 1 shows the initial charging / discharging curve. As a result, the initial charging / discharging amount was improved to 1100 mAh / g in comparison with 1000 mAh / g in the comparative example. 2 is a graph showing the characteristics of the discharge cycle. It is confirmed that the discharge amount is maintained until the 70th cycle of the embodiment is compared with the comparative example in which the discharge amount abruptly drops after 50 cycles. FIG. 3 shows the charge / discharge efficiency , And it was confirmed that the embodiment shows improved charge / discharge efficiency as compared with the comparative example.

While the invention has been shown and described with reference to certain preferred embodiments thereof, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims. And falls within the scope of the invention.

Claims (9)

A positive electrode slurry composition for a lithium-sulfur battery comprising a carbon-sulfur (S) complex, a dispersant, a binder and a non-aqueous solvent,
The dispersant may include polyvinyl butyral (PVB)
The binder may be selected from the group consisting of N, N-bis [3- (triethoxysilyl) propyl] urea, polyethylene oxide (PEO), poly (vinylidene fluoride) (PVDF), poly (vinylidene fluoride-co-hexafluoro Propylene) (PVDF-co-HFP), styrene butadiene rubber (SBR), and a combination thereof.
The method according to claim 1,
Wherein the carbon-sulfur (S) composite is a mixture of a composite of sulfur and carbon nanotubes (S / CNT) and a composite of sulfur and super-P (S / SP) .
The method according to claim 1,
Wherein the weight ratio of the polyvinyl butyral to the dispersant is 1: 5 to 5: 1.
The method according to claim 1,
Wherein the content of the dispersant and the binder is 5 to 20 parts by weight based on 100 parts by weight of the total positive electrode slurry composition.
The method according to claim 1,
Wherein the non-aqueous solvent is a mixed solvent comprising acetonitrile, toluene, and isopropanol.
6. The method of claim 5,
Wherein the weight ratio of the mixed solvent of acetonitrile, toluene and isopropanol is 4: 2: 4.
The method according to claim 1,
Wherein the positive electrode slurry composition further comprises a conductive material.
A positive electrode for a lithium-sulfur battery, which is formed using the positive electrode slurry composition of any one of claims 1 to 7.
anode; cathode; A lithium-sulfur battery including a separator interposed therebetween and an electrolyte,
Wherein the positive electrode is formed using the positive electrode slurry composition according to any one of claims 1 to 7.

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