KR100382302B1 - Positive active material composition for lithium-sulfur battery and lithium-sulfur battery manufactured using same - Google Patents

Abstract

The present invention is a lithium-sulfur battery positive electrode active material composition and a lithium-sulfur battery prepared using the same, the positive electrode active material composition is a positive electrode active material containing a sulfur compound, polyvinylidene fluoride, polyvinyl acetate and polyvinyl pyrrolidone It includes a binder, a conductive material and at least one organic solvent selected from the group consisting of dimethylformamide, isopropyl alcohol and acetonitrile.

Lithium-sulfur battery prepared using the active material composition can be seen that not only the initial discharge capacity but also the cycle life characteristics are significantly improved compared to the conventional lithium-sulfur battery.

Description

A positive electrode active material composition for a lithium-sulfur battery, and a lithium-sulfur battery manufactured using the same, the present invention relates to a lithium-sulfur battery.

[Industrial use]

The present invention relates to a positive electrode active material composition for a lithium-sulfur battery and a lithium-sulfur battery manufactured using the same, and more particularly, a positive electrode active material composition for a lithium-sulfur battery having excellent positive electrode active material binding ability and excellent cycle life characteristics, and use thereof It relates to a lithium-sulfur battery prepared by.

[Prior art]

With the rapid development of portable electronic devices, the demand for secondary batteries is increasing. In particular, there is a continuous demand for the emergence of high energy density batteries that can meet the trend toward smaller, lighter, thinner and smaller portable electronic devices. In addition, there is a need for a battery that must satisfy inexpensive, safe and environmentally friendly aspects.

Lithium-Sulfur battery is an inexpensive and environmentally friendly material, the energy density of lithium in terms of energy density is 3830 mAh / g, the energy density of sulfur is expected to be 1675 mAh / g high energy density It is emerging as the most promising battery which satisfies the above conditions.

The lithium-sulfur battery uses a sulfur-based compound having a sulfur-sulfur combination as a positive electrode active material, and an alkali metal such as lithium or a carbon-based material in which insertion and deintercalation of metal ions such as lithium ions occur. 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.

In the lithium-sulfur battery, the positive electrode is prepared by mixing a positive electrode active material, a binder, a conductive material, and an organic solvent to prepare a positive electrode active material slurry composition, and coating the slurry composition on a current collector. The binder serves to prevent the active material or the conductive material from falling off from the current collector. Examples of the binder used in the lithium-sulfur battery include polytetrafluoroethylene, polyvinylidene fluoride or polyethylene oxide. However, even when such a binder is used, there is a problem in that a positive electrode active material easily falls from the current collector in a lithium-sulfur battery.

Therefore, in order to prevent dropping of the positive electrode active material, US Patent No. 5,919,587 (Moltech) discloses an electroactive sulfur-containing material including -SSS- moiety and an electroactive transition metal chalcogenide surrounding the same. A cathode active material consisting of (electroactive transition metal chalcogenide) is described. The method used in the above-mentioned US patent is a method of adding an electroactive sulfur-containing material to an electroactive transition metal chalcogenide solution and then adding a conductive material to prepare a cathode active material slurry composition, and coating the cathode active material slurry composition on a current collector. . In this U.S. patent, the electroactive transition metal chalcogenides used effectively wrap and hold the electroactive sulfur-containing negative electrode material. This method is a method in which the transition metal chalcogenide catches the positive electrode active material by chemical electrostatic attraction to prevent dropping from the current collector, but its effect is not great.

U.S. Patent No. 5,961,672 (Moltech) discloses a polymer film coated on a lithium metal anode to improve its life and safety. TEFLON ^™ (PTFE-K30, DuPont) was used as the positive electrode binder, but there is no mention of improvement in performance due to the binder.

The present invention has been made to solve the above problems, and an object of the present invention is to provide a cathode active material composition for a lithium-sulfur battery capable of firmly attaching a cathode active material to a current collector.

The present invention is to solve the above problems, an object of the present invention is to attach the positive electrode active material to the current collector firmly, exhibiting excellent ion conductivity can increase the life of the battery positive electrode active material for lithium-sulfur battery It is to provide a composition.

Another object of the present invention to provide a lithium-sulfur battery prepared using the positive electrode active material composition.

1 is a graph showing the cycle life of the lithium-sulfur battery of Examples 1 to 5 of the present invention.

2 is a graph showing the cycle life of the lithium-sulfur battery of Examples 1 to 3 and Examples 6 to 8 of the present invention.

In order to achieve the above object, the present invention is a positive electrode active material containing a sulfur compound; A binder comprising at least one polymer selected from the group consisting of polyvinylidene fluoride, polyvinyl acetate and polyvinyl pyrrolidone; Conductive material; And dimethylformamide, isopropyl alcohol, and acetonitrile. The present invention provides an anode active material composition for a lithium-sulfur battery, including an organic solvent. The binder further includes at least one ion conductive polymer selected from the group consisting of polyethylene oxide and polypropylene oxide, and may further include a solvent selected from the group consisting of 1,3-dioxolane and acetonitrile.

The present invention also provides a positive electrode active material comprising a sulfur compound, a positive electrode comprising a binder and a conductive material comprising at least one polymer selected from the group consisting of polyvinylidene fluoride, polyvinyl acetate and polyvinyl pyrrolidone; A negative electrode including a negative electrode active material selected from the group consisting of a material capable of reversibly intercalating or deintercalating lithium ions, a material capable of forming a compound reversibly with lithium, a lithium metal and a lithium alloy; And it provides a lithium-sulfur battery comprising an electrolyte comprising a lithium salt and an organic solvent.

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

The present invention relates to a binder used in a positive electrode active material composition for producing a positive electrode plate of a lithium-sulfur battery.

The positive electrode active material composition is composed of a positive electrode active material, a conductive material, a binder, and a solvent. The composition is coated on a current collector and dried to produce a positive electrode plate. The important thing at this time is the choice of binder and solvent. The binder must first be well dissolved in the solvent, and must form a conductive network of sulfur and a conductive material, and must also have an impregnation property of the electrolyte. The solvent must be able to dissolve the binder well and dry easily. Also, the solvent should not dissolve sulfur. When the solvent dissolves sulfur, the sulfur of the slurry has a high specific gravity (D = 2.07), so that the sulfur sinks in the slurry, so that the current is concentrated in the current collector during coating, causing problems in the conductive network, and thus, the battery does not operate well.

In the present invention, at least one of polyvinylidene fluoride, polyvinyl acetate or polyvinyl pyrrolidone is used as a binder to satisfy these conditions, and an organic solvent including dimethylformamide, isopropyl alcohol or acetonitrile as an organic solvent. Was used.

The polyvinylidene fluoride is a binder that has excellent adhesive strength so that the active material or the conductive material does not fall from the current collector, does not react electrochemically even when charging and discharging continues, and has an advantage in dispersion when mixing. In addition, the polyvinylidene fluoride is a binder that does not dissolve in the organic solvent of the electrolyte generally used in lithium-sulfur batteries having physical properties of dissolving the polymer well. In addition, the polyvinyl acetate is excellent in the impregnation of the electrolyte solution, polyvinyl pyrrolidone is a binder having a suitable impregnation ability to dissolve only a part of the solvent of the electrolyte solution.

As such, the three binders have all the physical properties required for the binder in the lithium-sulfur battery. In particular, polyvinylidene fluoride has been attempted as a binder in the lithium-sulfur battery. However, polyvinylidene fluoride was actually used in lithium-sulfur batteries, which resulted in very deteriorated battery characteristics, making it difficult to use in practice. The reason is that in order to manufacture a positive electrode in a battery, first, a positive electrode active material composition in the form of a slurry in which a positive electrode active material, a conductive material and a binder are mixed in an organic solvent should be prepared. The organic solvent used at this time is most preferably capable of dissolving a binder and maintaining it in a dispersed state without dissolving the positive electrode active material and the conductive material. Considering these physical properties, the most suitable organic solvent for the polyvinylidene fluoride binder is N-methylpyrrolidone. However, in the case of manufacturing a lithium-sulfur battery using N-methylpyrrolidone, N-methylpyrrolidone not only dissolves the sulfur compound which is a positive electrode active material, but also has a problem that the charge and discharge cycle does not proceed. Due to these problems, polyvinylidene fluoride binders having many properties suitable for batteries have not been available in lithium-sulfur batteries.

The present inventors continue to study to solve this problem, when using dimethylformamide, isopropyl alcohol or acetonitrile as an organic solvent, polyvinylidene fluoride without the problem that occurs when using N-methylpyrrolidone The present invention has been completed by knowing that the ride, in addition, polyvinyl acetate and polyvinyl pyrrolidone may be used as a binder in lithium-sulfur batteries.

In the present invention, two or more of polyvinylidene fluoride, polyvinyl acetate or polyvinyl pyrrolidone is more preferably used as the binder. This is preferable because the adhesive force and the electrolyte impregnation property is better than when only one binder is used.

In addition, in order to further increase the cycle life characteristics by increasing the ion conductivity of the binder, an ion conductive polymer of polyethylene oxide or polypropylene oxide may be further used. In this case, in addition to dimethylformamide, isopropyl alcohol or acetonitrile which can dissolve polyvinylidene fluoride, polyvinyl acetate, and polyvinyl pyrrolidone (hereinafter referred to as "basic binder") used as a basic binder, Solvents of 1,3-dioxolane or acetonitrile that can dissolve the conductive polymer should be further used. Preferably, dimethylformamide and 1,3-dioxolane are used as the organic solvent.

Polyvinylidene fluoride, polyvinyl acetate, polyvinyl pyrrolidone, polyethylene oxide or polypropylene oxide used in the present invention uses those having a molecular weight of 10,000 to 5,000,000.

The positive electrode active material composition of the present invention includes 5 to 30% by weight of the base binder, and when using an ion conductive polymer binder, 5 to 30% by weight of the base binder and 2 to 20% by weight of the ion conductive polymer binder. When the content of the basic binder and the ion conductive polymer binder is smaller than the above-mentioned range, the effect of using the binder is less, and when the content of the above-mentioned range is exceeded, the amount of the positive electrode active material is relatively small and the capacity is reduced, which is not preferable. . In addition, when using two or more types of polyvinylidene fluoride, polyvinyl acetate, or polyvinyl pyrrolidone as the base binder, the mixing ratio thereof may be appropriately adjusted according to the desired physical properties, and there is no particular limitation.

In the cathode active material composition of the present invention, the cathode active material is a cathode, an organic sulfur compound, and carbon in which sulfur (elemental sulfur, S ₈ ) solid Li ₂ S _n (n ≧ 1), Li ₂ S _n (n ≧ 1) is dissolved One or more sulfur compounds selected from the group consisting of -sulfur polymers [(C ₂ S _x ) _n , x = 2.5 to 50, n> 2] can be used.

In addition, the positive electrode active material composition of the present invention includes an electrically conductive conductive material for allowing electrons to move smoothly in the positive electrode active material together with the positive electrode active material, and the conductive material is not particularly limited, but may be carbon (trade name: Super P ), Conductive materials such as carbon black or conductive polymers such as polyaniline, polythiophene, polyacetylene, polypyrrole may be used alone or in combination.

In order to manufacture the positive electrode of the present invention, first, a basic binder is dissolved in an organic solvent to prepare a binder solution. When further using an ion conductive polymer binder, the basic binder and the ion conductive polymer binder are added to a mixed solvent of N, N-dimethylformamide, acetonitrile or isopropyl alcohol, and 1,3-dioxolane or acetonitrile and mixed to binder Prepare a solution.

After adding and dispersing a conductive material for securing electrical conductivity thereto, a positive electrode active material is added to the product to prepare a positive electrode active material composition, for example, a composition in the form of a slurry. This positive electrode active material composition is applied to a current collector to prepare a positive electrode. The current collector is not particularly limited, but conductive materials such as stainless steel, aluminum, copper, and titanium are preferably used, and more preferably, a carbon-coated aluminum current collector is used. 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.

As the negative electrode used together with the positive electrode, a material capable of reversibly intercalating lithium ions, a material capable of reversibly forming a compound with lithium metal, and a material made of a negative electrode active material including lithium metal or a lithium alloy are used. do. As the lithium alloy, a lithium / aluminum alloy or a lithium / tin alloy may be used. 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 such, inactive sulfur refers to sulfur in a state in which sulfur can no longer participate in the electrochemical reaction of the anode through various electrochemical or chemical reactions, and inactive sulfur formed on the surface of the lithium anode is a protective layer of the lithium cathode. It also has the advantage of playing a role. Therefore, lithium metal and inert sulfur formed on the lithium metal, for example lithium sulfide, may be used as the negative electrode.

As a material capable of reversibly intercalating lithium ions, any carbon negative active material generally used in a lithium ion secondary battery may be used, and representative examples thereof include crystalline carbon, amorphous carbon, or a combination thereof. Can be used. In addition, a representative example of a material capable of reversibly forming a compound with the lithium metal may include titanium nitrate, but is not limited thereto.

The electrolyte used with the positive electrode of the present invention includes a lithium salt as a supporting electrolytic salt and a non-aqueous organic solvent. The organic solvent of the electrolyte used in the lithium-sulfur battery is suitably the elemental sulfur (S ₈ ), lithium sulfide (Li ₂ S), lithium polysulfide (Li ₂ S _n , n = 2, 4, 6, 8 ...) Dissolve well. The organic solvent may be benzene, fluorobenzene, toluene, trifluorotoluene, xylene, cyclohexane, tetrahydrofuran, 2-methyl tetrahydrofuran, cyclohexanone, ethanol, isopropyl alcohol, dimethyl carbonate, ethyl Methyl carbonate, diethyl carbonate, methylpropyl carbonate, methylpropionate, ethylpropionate, methyl acetate, ethyl acetate, propyl acetate, dimethoxy ethane, 1,3-dioxolane, diglyme, tetraglyme, ethylene carbonate At least one solvent selected from the group consisting of propylene carbonate, γ-butyrolactone and sulfolane.

The lithium salts include lithium hexafluorophosphate (LiPF ₆ ), lithium tetrafluoroborate (LiBF ₄ ), lithium hexafluoroazate (LiAsF ₆ ), lithium perchlorateLiClO ₄ , and lithium trifluoromethanesulfonate ( CF ₃ SO ₃ Li)) is used at least one compound selected from the group consisting of. The electrolyte contains a lithium salt in a concentration of 0.5 to 2.0M.

The electrolyte may be used as a liquid electrolyte, or may be used in the form of a solid electrolyte separator. When used as a liquid electrolyte, a physical separator having a function of physically separating an electrode further includes a separator made of porous glass, plastic, ceramic, or polymer.

The electrolyte separator functions as a physical separation of the electrode and a transfer medium for moving metal ions, and both electrochemically stable electric and ion conductive materials may be used. As such an electrically and ion conductive material, a glass electrolyte, a polymer electrolyte, or a ceramic electrolyte may be used. As a particularly preferred solid electrolyte, the supported electrolyte salt is mixed with a polymer electrolyte such as polyether, polyimine, polythioether, or the like. The solid electrolyte separator may include less than about 20% by weight of the non-aqueous organic solvent, and in this case, may further include a suitable gelling agent to reduce the fluidity of the organic solvent.

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)

Dimethylformamide (DMF) positive electrode active material slurry A polyvinylidene fluoride (PVdF) binder was dissolved in an organic solvent to prepare a binder solution. After dispersing by adding a carbon powder (super P) conductive material to the binder solution, a powder of sulfur (S ₈ ) pulverized to an average particle size of 20 μm, which is a positive electrode active material, was added and stirred with a ball mill for at least one day to prepare a positive electrode active material slurry composition. Prepared. At this time, the mixing ratio of the positive electrode active material (S ₈ ): binder: conductive material was 60: 20: 20 wt%.

The prepared positive electrode active material slurry composition was coated on a carbon-coated Al current collector, and then dried in an 80 ° C. drying furnace for 1 hour. The dried electrode plate was rolled using a roll press so that the electrode plate had a thickness of 50 μm to prepare a positive electrode.

As the negative electrode, an unoxidized lithium metal foil (thickness 50 mu m) was used.

After the prepared positive electrode was left in a vacuum oven (60 ° C.) for at least 1 hour, it was transferred to a glove box in which moisture and oxygen were controlled, and a coin cell was prepared in a conventional method using the positive electrode and the negative electrode in the glove box. In this case, a 1,3-dioxolane, diglyme, sulfolane and dimethoxyethane mixture (50: 20: 10: 20 by volume) in which 1M LiSO ₃ CF ₃ was dissolved was used.

(Comparative Example 1)

N-methylpyrrolidone (NMP) positive electrode active material slurry A polyvinylidene fluoride (PVdF) binder was dissolved in an organic solvent to prepare a binder solution. After dispersing by adding a carbon powder (super P) conductive material to the binder solution, a powder (S ₈ ) pulverized to an average particle size of 20㎛ as a positive electrode active material was added and stirred with a ball mill for at least one day to prepare a positive electrode active material slurry composition It was. At this time, the mixing ratio of the positive electrode active material (S ₈ ): binder: conductive material was 60: 20: 20 wt%.

The prepared positive electrode active material slurry composition was coated on a carbon-coated Al current collector and then dried in an 80 ° C. drying furnace for at least 12 hours. The dried electrode plate was rolled using a roll press so that the electrode plate had a thickness of 50 μm to prepare a positive electrode.

As the negative electrode, an unoxidized lithium metal foil (thickness 50 mu m) was used.

The prepared anode was left in a vacuum oven (60 ° C.) for at least 1 hour and then transferred to a glove box in which moisture and oxygen were controlled. In the glove box, a coin cell was manufactured by a conventional method using the anode and the cathode. In this case, a mixture of 1,3-dioxolane, diglyme, sulfolane and dimethoxyethane (50: 20: 10: 20 by volume) in which 1M LiSO ₃ CF ₃ was dissolved was used.

Aging of the lithium-sulfur batteries of Example 1 and Comparative Example 1 at room temperature for 24 hours and then 110% of the cut-off charge calculation capacity, 0.1C once charging and discharging under the conditions of discharge 1.8V, 0.2C three times charging, discharging, Charge and discharge of 0.5C five times and charge and discharge of 1.0C 100 times were performed. 100 charge and discharge cycle life characteristics and initial discharge capacity are shown in Table 1 below.

Remarks Organic solvent / binder Life characteristic (100 times) [mAhg] Initial Discharge Capacity [mAh / g] Example 1 Use DMF / PVdF 60 550 Comparative Example 1 NMP / PVdF Battery - 10

As shown in Table 1, it can be seen that the initial discharge capacity of the lithium-sulfur battery of Example 1 is much higher than that of Comparative Example 1. In addition, although the battery of Comparative Example 1 cannot be used because the capacity is not measured after 100 charge / discharge cycles, it can be seen that the battery of Example 1 is a usable battery.

(Example 2)

Except for using polyvinyl pyrrolidone (PVP) as a binder and isopropyl alcohol (IPA) as a positive electrode active material slurry organic solvent was carried out in the same manner as in Example 1.

(Example 3)

Except for using polyvinyl acetate (PVAc) as a binder and acetonitrile (Acetonitrile) as the positive electrode active material slurry organic solvent was carried out in the same manner as in Example 1.

(Example 4)

Polyvinylidene fluoride and polyvinyl acetate were dissolved in N, N-dimethylformamide positive electrode active material slurry organic solvent to prepare a binder solution. At this time, the mixing ratio of polyvinylidene fluoride and polyvinyl acetate was 1: 1. The prepared binder solution was mixed with 60 wt% of sulfur element, 20 wt% of Super-P, and mixed until the slurry was completely mixed to prepare a positive electrode active material slurry. At this time, the amount of the binder was 20% by weight of the total weight of the slurry. The positive electrode active material slurry was coated on a carbon-coated Al current collector.

The coated positive electrode plate was dried and then dried under vacuum for at least 12 hours to prepare a positive electrode plate. The prepared positive electrode plate and the vacuum dried separator were transferred to a glove box. On the positive electrode plate, an appropriate amount of 1,3-dioxolane / diglyme / sulforan / dimethoxyethane (50/20/10/20 volume ratio) electrolyte using 1M LiSO ₃ CF ₃ as a salt was dropped. Subsequently, the separator was placed thereon and a little more electrolyte was added. The lithium electrode was put on it.

(Example 5)

It carried out similarly to Example 4 except having used the mixed binder (1: 1: 1 weight ratio) of polyvinylidene fluoride, polyvinyl acetate, and polyvinyl pyrrolidone as a binder.

In order to determine the change in life characteristics and initial discharge capacity according to the binder type, the life characteristics and initial discharge capacity of the lithium-sulfur battery manufactured by the method of Example 1-5 were measured. After measuring the battery of Example 1-5 at room temperature for 24 hours, the measurement conditions were 0.1C once charge / discharge, 0.2C three charge / discharge, 0.5C five times under the condition of 1.5-2.8V voltage with cut-off voltage. Charge and discharge, 1.0C Charge and discharge were performed 100 times. The results are shown in Table 2 below.

Anode Binder / Solvent Lifetime Characteristics (100 Times) / Initial% Initial Discharge Capacity [mAh / g] Example 1 PVdF / DMF 11 550 Example 2 PVAc / ACN 44 571 Example 3 PVP / IPA 52 600 Example 4 PVdF / PVAc (1: 1) / DMF 50 585 Example 5 PVdF / PVAc / PVP (1: 1: 1) / DMF 58 594

PVdF: polyvinylidene fluoride

* PVAc: Polyvinyl Acetate

* PVP: Polyvinyl Pyrrolidone

* DMF: N, N-dimethyl formamide

* ACN: acetonitrile

* IPA: Isopropyl Alcohol

As shown in Table 2, the lithium-sulfur batteries of Examples 4 and 5 have much better life characteristics than Example 1, better initial discharge capacity, and better life characteristics and initial discharge capacity than Example 2. Able to know. In addition, it can be seen that the battery of Examples 4 and 5 showed the same or better life characteristics and initial discharge capacity than Example 3.

In addition, when comparing Example 1 and Example 2, the discharge capacity does not have a large difference, but it can be seen that the lifespan is greatly increased according to the type of binder (11% to 44%). It is thought that the impregnation of the polyvinyl acetate in the electrolyte solution is superior to that of polyvinylidene fluoride, so that the oxidation / reduction reaction of sulfur proceeds smoothly and the service life is increased.

In addition, when comparing Example 2 and Example 3, the initial capacity is also improved by about 5% or more (571 → 600), and the lifespan characteristics are also improved by 44% to 52%. This result also seems to be due to the polyvinyl pyrrolidone having the best impregnation with the electrolyte.

In addition, the capacity (cycle life characteristic) according to the charge / discharge cycles of the lithium-sulfur batteries of Examples 1 to 5 is shown in FIG. 1, and the results show that the cycle life characteristics of Example 5 were the best. Except for Example 1, it can be seen that the results of Example 2-5 were almost the same. This result is thought to have appeared as the battery of Example 1 used polyvinylidene fluoride having the lowest impregnation with the electrolyte solution among the three basic binders.

(Example 6)

Polyvinylidene fluoride and polyethylene oxide were dissolved in a mixed solvent of N, N-dimethylformamide and 1,3-dioxolane to prepare a binder solution. At this time, the mixing ratio of polyvinylidene fluoride and polyvinyl acetate was 1: 1. Sulfur element, Super-P was added to the prepared binder solution and mixed until it was thoroughly mixed to prepare a cathode active material slurry. At this time, the mixing ratio of the mixed weight of the elemental sulfur: super-P: polyvinylidene fluoride and polyethylene oxide was 60% by weight: 20% by weight: 20% by weight. The positive electrode active material slurry was coated on a carbon-coated Al current collector.

The coated positive electrode plate was dried and then dried under vacuum for at least 12 hours to prepare a positive electrode plate. The prepared positive electrode plate and the vacuum dried separator were transferred to a glove box. Dropwise an appropriate amount of 1,3-dioxolane diglyme / sulfolane / dimethoxy ethane (50/20/10/20 volume ratio) electrolyte solution used in the salt 1M LiSO ₃ CF ₃ on the positive electrode plate. Subsequently, the separator was placed thereon and a little more electrolyte was added. The lithium electrode was put on it.

(Example 7)

Polyvinyl acetate and polyethylene oxide were used as the binder, and acetonitrile and 1,3-dioxolane were used as the solvent, and the same procedure as in Example 6 was carried out.

(Example 8)

Polyvinyl pyrrolidone and polyethylene oxide were used as the binder and isopropyl alcohol and 1,3-dioxolane were used as the solvent, and the same procedure as in Example 6 was carried out.

In order to investigate the electrochemical characteristics of the battery further using the ion conductive polymer binder, the battery assembled by the method of Examples 1 to 3 and Examples 6 to 8 was aged at room temperature for 24 hours, and then the voltage was cut-off voltage. 0.1C one time charge and discharge, 0.2C three times charge and discharge, 0.5C five times charge and discharge, 1.0C 100 times charge and discharge under 1.5-2.8V conditions. The life characteristics and initial discharge capacity were measured and the results are shown in Table 3 below.

Anode Binder / Solvent Lifetime Characteristics (100 Times) / Initial% Initial Discharge Capacity [mAh / g] Example 1 PVdF / DMF 11 550 Example 6 PVdF / PEO / DMF / DOX 20 576 Example 2 PVAc / ACN 44 571 Example 7 PVAc / PEO / ACN / DOX 54 590 Example 3 PVP / IPA 52 600 Example 8 PVP / PEO / IPA / DOX 60 650

PVdF: polyvinylidene fluoride

* PVAc: Polyvinyl Acetate

* PVP: Polyvinyl Pyrrolidone

* PEO: polyethylene oxide

* DMF: N, N-dimethyl formamide

* ACN: acetonitrile

* IPA: Isopropyl Alcohol

* DOX: 1,3-dioxolane

As shown in Table 3, the batteries of Examples 6 to 8, each using polyethylene oxide as the positive electrode binder more than Examples 1 to 3, slightly increased the discharge capacity (19-50 mAh / g), and the lifetime was 8-10. It can be seen that the percent increase. This is because polyethylene oxide, an ion conductive polymer, acts as a binder and plays a role in activating the movement of lithium ions in the positive electrode plate.

In addition, the capacity (cycle life characteristic) according to the charge / discharge cycles of the lithium-sulfur batteries of Examples 1 to 3 and Examples 6 to 8 is shown in FIG. 2, and as a result, Example 2 except Example 6 It can be seen that the results of -3 and Examples 7-8 are almost similar. This result is thought to have come from the use of polyvinylidene fluoride having the lowest impregnation with the electrolyte solution among the three basic binders in Example 6.

As described above, the lithium-sulfur battery prepared according to the present invention can be seen that the cycle life characteristics as well as the initial discharge capacity is greatly improved compared to the conventional lithium-sulfur battery.

Claims (11)

A positive electrode active material containing a sulfur compound; A binder comprising at least one polymer selected from the group consisting of polyvinylidene fluoride, polyvinyl acetate and polyvinyl pyrrolidone; Conductive material; And Organic solvent selected from the group consisting of dimethylformamide, isopropyl alcohol and acetonitrile A positive electrode active material composition for a lithium-sulfur battery comprising a. The method of claim 1, wherein the binder further comprises at least one ion conductive polymer selected from the group consisting of polyethylene oxide and polypropylene oxide, A positive electrode active material composition for a lithium-sulfur battery, further comprising a solvent selected from the group consisting of 1,3-dioxolane and acetonitrile. (delete) The cathode active material of claim 1, wherein the cathode active material is a cathode, an organic sulfur compound, and carbon in which elemental sulfur (S ₈ ), solid Li ₂ S _n (n ≧ 1), and Li ₂ S _n (n ≧ 1) are dissolved -Sulfur polymer [(C ₂ S _x ) _n , x = 2.5 to 50, n ≥ 2] positive electrode active material composition for a lithium-sulfur battery comprising at least one sulfur compound selected from the group consisting of. The cathode active material composition of claim 1, wherein the cathode active material composition comprises the binder in an amount of 5 to 30% by weight. A positive electrode comprising a positive electrode active material comprising a sulfur compound, a binder and a conductive material comprising at least one polymer selected from the group consisting of polyvinylidene fluoride, polyvinyl acetate and polyvinyl pyrrolidone; A negative electrode including a negative electrode active material selected from the group consisting of a material capable of reversibly intercalating or deintercalating lithium ions, a material capable of forming a compound reversibly with lithium, a lithium metal and a lithium alloy; And Electrolyte Containing Lithium Salt And Organic Solvent Lithium-sulfur battery comprising a. The method of claim 6, wherein the binder further comprises at least one ion conductive polymer selected from the group consisting of polyethylene oxide and polypropylene oxide, A lithium-sulfur battery further comprising a solvent selected from the group consisting of 1,3-dioxolane and acetonitrile. 7. The cathode active material of claim 6, wherein the cathode active material is a 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? ₂ S _x ) _n , x = 2.5 to 50, n ≥ 2) containing at least one sulfur compound selected from the group consisting of lithium-sulfur battery. The method of claim 6, wherein the organic solvent is benzene, fluorobenzene, toluene, trifluorotoluene, xylene, cyclohexane, tetrahydrofuran, 2-methyl tetrahydrofuran, cyclohexanone, ethanol, isopropyl alcohol , Dimethyl carbonate, ethylmethyl carbonate, diethyl carbonate, methylpropyl carbonate, methylpropionate, ethylpropionate, methyl acetate, ethyl acetate, propyl acetate, dimethoxy ethane, 1,3-dioxolane, diglyme, tetra A lithium-sulfur battery, which is at least one solvent selected from the group consisting of glyme, ethylene carbonate, propylene carbonate, γ-butyrolactone and sulfolane. The lithium salt of claim 6, wherein the lithium salt is lithium hexafluorophosphate (LiPF ₆ ), lithium tetrafluoroborate (LiBF ₄ ), lithium hexafluoroazate (LiAsF ₆ ), lithium perchlorate (LiClO ₄ ), and lithium tri Lithium-sulfur battery that is at least one compound selected from the group consisting of fluoromethanesulfonate (CF ₃ SO ₃ Li). The lithium-sulfur battery of claim 6, wherein the electrolyte comprises lithium salt at a concentration of 0.5 to 2.0 M. 8.