KR100433001B1 - Method for manufacturing cathode electrode, cathode electrode manufactured using the same, and lithium battery containing the same - Google Patents

Abstract

(a) a slurry of the sulfur, sulfur-containing organic compounds or mixtures thereof is prepared by mixing and ball milling the sulfur, the sulfur-containing organic compound, or a mixture thereof and a conductive material together in a solvent exhibiting solubility with respect to the sulfur or the sulfur-containing organic compound. Manufacturing; And (b) mixing the binder solution with the slurry to produce a homogeneous cathode active material slurry, wherein the cathode electrode prepared according to the method of the present invention has a low swelling phenomenon due to the electrolyte solution and excellent binding force. Can be used as it is as a binder can stabilize the performance of the lithium sulfur battery.

Description

Method for manufacturing cathode electrode, cathode electrode manufactured using the same, and a lithium battery employing the same

The present invention relates to a method for producing a cathode electrode using sulfur as an active material, a cathode electrode produced thereby, and a lithium battery employing the same, and more particularly, a cathode active material layer using an electrolyte in a cathode electrode using sulfur as an active material. The present invention relates to a method of manufacturing a cathode electrode having a minimal swelling of the cathode, a cathode electrode manufactured thereby, and a lithium battery employing the same.

The monomeric sulfur theoretically has a very large electrochemical reaction capacity of 1680 mAh / g and exhibits an average voltage flat region of 2 V for lithium metal at room temperature. Therefore, the anode using the sulfur is capable of manufacturing a high-capacity electrode as compared to the conventional cathode for secondary batteries has recently been a new research target as a cathode active material for the next-generation secondary batteries.

However, since the sulfur used as the cathode active material is an electrical insulator, it cannot transmit electrons, which is one of the essential elements of the electrochemical reaction, and thus the composition for forming the cathode active material layer must include a conductive agent having excellent electrical conductivity in addition to the sulfur. need. The binder allows the particles of the active material layer components to maintain their shape in a state where they are aggregated with each other and maintains physical contact with the current collector, thereby enabling the movement of electrons and ions, thereby ultimately providing desired electrochemistry. It serves to facilitate the reaction.

By the way, in manufacturing a lithium-sulfur secondary battery, PEO binder is generally used as a binder for a cathode active material layer. However, when the PEO binder is impregnated with the electrolyte, excessive swelling occurs, causing physical changes such as an increase in the thickness of the cathode active material layer and a weakening of the aggregated state of the components, resulting in a decrease in active material utilization and an increase in electrical resistance. This causes a decrease.

Therefore, in order to minimize this phenomenon, the selection of a binder without swelling during electrolyte impregnation is very important in securing the performance of a lithium sulfur battery, and at the same time, it is appropriate to consider the reactivity between a solvent and a sulfur active material required for dissolving the binder. The manufacturing process of the cathode electrode has to be developed.

An object of the present invention is to provide a method of manufacturing a cathode electrode in which the swelling of the cathode active material layer by the electrolyte is minimized in the cathode electrode using a sulfur active material.

Another object of the present invention is to provide a method of manufacturing a cathode electrode in which the swelling of the cathode active material layer by the electrolyte is minimized.

Another object of the present invention is to provide a lithium battery employing the cathode electrode.

1 shows a flowchart of a manufacturing process of a cathode electrode according to the present invention.

FIG. 2 is a SEM photograph of a sulfur slurry obtained by ball milling in NMP solvent for 24 hours using only sulfur according to Comparative Example 1. FIG.

FIG. 3 is an SEM image of a sulfur slurry obtained by ball milling a mixture of sulfur and carbon in NMP solvent for 24 hours according to Example 1. FIG.

4 is a graph showing charge / discharge cycle characteristics of a lithium battery employing a cathode electrode prepared according to the method of Example 2. FIG.

5 is a graph showing charge and discharge cycle characteristics of a lithium battery employing a cathode electrode manufactured according to the method of Example 3. FIG.

FIG. 6 is a graph showing charge and discharge cycle characteristics of a lithium battery employing a cathode electrode manufactured using a PEO binder according to Comparative Example 2. FIG.

The present invention to achieve the above technical problem,

(a) a slurry of the sulfur, sulfur-containing organic compounds or mixtures thereof is prepared by mixing and grinding together sulfur, sulfur-containing organic compounds or mixtures thereof and conductive materials in a solvent which shows solubility with respect to the sulfur or sulfur-containing organic compounds. Making; And

(b) mixing the binder solution with the slurry to produce a homogeneous cathode active material slurry.

In the method of manufacturing a cathode electrode according to the present invention, the binder solution of step (b) may further comprise a conductive material.

In the method for producing a cathode electrode according to the invention, the amount of the solvent showing solubility with respect to the sulfur or sulfur-containing organic compound in the step (a) is 40 to 80 parts by weight, the sulfur, sulfur-containing organic compound or these The amount of the mixture is 5 to 10 parts by weight, the amount of the conductive material is 1 to 3 parts by weight, and the particle size of the slurry of the sulfur, sulfur-containing organic compound or a mixture thereof is adjusted to 0.5 to 2 µm,

In the step (b), the binder solution is preferably used at a concentration of 0.1 to 1.7 parts by weight of the binder dissolved in 0.9 to 20 parts by weight of the solvent, in which case the binder solution may further include 1 to 3 parts by weight of the conductive material. Can be.

In the method of manufacturing a cathode electrode according to the present invention, after the step (b) may further comprise the step of coating the cathode active material slurry on the current collector to a thickness of 10 ~ 100㎛.

In the method of manufacturing a cathode electrode according to the present invention, the conductive material is preferably a carbon powder having a particle size of 30nm ~ 100nm.

In the method for producing a cathode electrode according to the invention, the binder is a group consisting of polyvinylidene fluoride, a copolymer of vinylidene fluoride and hexafluoropropylene, and a mixture of polyvinylidene fluoride and styrene-butadiene rubber It is preferable that at least one selected from.

In the method of manufacturing a cathode electrode according to the present invention, the solvent of step (a) is preferably at least one selected from the group consisting of NMP, THF and DMF.

In the method of manufacturing a cathode electrode according to the present invention, the binder solvent of the step (b) is preferably the same as the solvent of the step (a).

The present invention to achieve the above other technical problem,

In a cathode electrode in which a cathode active material layer is laminated on a current collector,

The cathode active material layer provides a cathode, characterized in that it comprises a sulfur, a sulfur-containing organic compound or a mixture thereof having a particle diameter of 0.5 ~ 2㎛.

In order to achieve the above another technical problem, the present invention also provides a cathode electrode manufactured according to the method of the present invention.

In order to achieve the above another technical problem, the present invention provides a lithium battery comprising a cathode electrode manufactured according to the method of the present invention.

In order to achieve the above another technical problem, the present invention also provides a lithium battery comprising a cathode electrode, an anode electrode and a separator interposed therebetween, wherein the cathode electrode has a particle size of 0.5 ~ 2㎛ on the current collector Provided is a lithium electrode, wherein a cathode active material layer comprising a sulfur, a sulfur-containing organic compound, or a mixture thereof is laminated.

Next, a cathode electrode according to the present invention and a method of manufacturing a lithium battery employing the same will be described.

1 is a flowchart illustrating a procedure of a method of manufacturing a cathode electrode according to the present invention.

Referring to FIG. 1, first, 5 to 10 parts by weight of sulfur and 1 to 3 parts by weight of a conductive material are mixed together with 40 to 80 parts by weight of a solvent showing solubility with respect to sulfur. Subsequently, an appropriate ball such as a zirconia ball is put therein, followed by ball milling to prepare a sulfur slurry in which the particle size of the sulfur is adjusted to 0.5 to 2 μm.

The process of grinding the sulfur under a conventional solvent was a method of mixing only the sulfur and the ball in the solvent and ball milling. The ball milling energy used in such a grinding method is sufficient to refine the sulfur particles to a size of several micrometers or less, but the sulfur dissolved in a supersaturated state in the solvent is rapidly re-grown using the ground fine particles as nuclei. . If this reaction is repeated and the distribution of the sulfur particles grown above a certain size increases, the particle size increases on average, and thus fine sulfur powder cannot be obtained.

However, in the pulverization of the sulfur according to the present invention, the solvent is not mixed with only the sulfur and the ball in the solvent, but is characterized by mixing the appropriate amount of the carbon conductive agent at the same time. Then, the mixed carbon in the grinding process such as ball milling adheres to the surface of the heavy sulfur particles, preventing the regrowth of the sulfur particles. That is, the carbon conductive agent adheres to the surface of the finely ground sulfur particles, which are momentarily crushed by ball milling, thereby forming a kind of coating layer, which further blocks the contact between the sulfur particles and the sulfur particles, thus preventing the regrowth of the sulfur particles. Thus, as shown in FIG. 3 to be described below, it is possible to obtain a sulfur slurry composed of fine sulfur particles on the order of 0.5 to 2 μm. In this case, the conductive material used to prevent regrowth of the pulverized sulfur particles is preferably a carbon powder having a particle diameter of 30 to 100 nm.

Subsequently, a binder solution in which 0.1 to 1.7 parts by weight of the binder is dissolved in 0.9 to 20 parts by weight of the solvent is mixed and homogenized into the sulfur slurry to prepare a cathode active material slurry. In this case, 1 to 3 parts by weight of the conductive material may be further included in the binder solution added to the sulfur slurry.

Meanwhile, as the binder, polyvinylidene fluoride and vinylidene fluoride, which can minimize swelling during electrolyte impregnation, which is commonly used to assemble lithium batteries instead of polyethylene oxide which is conventionally used in the manufacture of conventional lithium sulfur batteries. Preference is given to using fluorine-containing resins such as copolymers of lide and hexafluoropropylene, or mixtures of polyvinylidene fluoride and styrene-butadiene rubber, among which polyvinylidene fluoride is more preferred. This is because fluorine-containing resins, in particular polyvinylidene fluoride, have excellent binding properties, and organic solvents such as carbonate-based compounds, dioxolane, sulfolane, diglyme, dimethyl ether, etc. may be appropriately combined according to the purpose. This is because the lithium salts such as LiSO 3 CF 3, PF 6 LiPF 6, and the like are not easily swollen by the organic electrolyte composition which is widely used in the production of a conventional lithium secondary battery in which a lithium salt, such as LiSO 3 CF 3, PF 6 LiPF 6, is dissolved in a mixture solvent.

However, in the present invention, PVDF having almost no swelling phenomenon due to the electrolyte and having excellent binding strength can be applied to the cathode active material for the following reasons.

That is, when using PVDF as a binder, it is preferable to use NMP as a solvent, but this solvent also has solubility with respect to a sulfur active material. Therefore, considering that NMP is used to prepare the subsequent binder solution, when NMP is selected as the solvent in the sulfur grinding process, the size of the sulfur particles grows to several tens of micrometers as described above when simple grinding of the sulfur in the NMP solvent. This makes it impossible to produce fine active material powders of 0.5 to 2 micrometers or less.

On the other hand, in the case of using a solvent having no solubility with respect to the sulfur during the grinding of the sulfur, the mixing process with the subsequent PVDF binder causes the gelation phenomenon of the PVDF, making uniform mixing impossible.

Therefore, in order to use a PVDF binder, it is essential to develop a process for refining the sulfur powder in an NMP solvent. Unlike the conventional method, the present invention does not mix the conductive particles with the binder solution to be mixed in the subsequent process, and pulverizes the sulfur particles. Ball milling is performed by simultaneously mixing the sulfur particles with the carbon powder from the step so that the size of the sulfur particles can be pulverized to about 0.5 to 2 μm even using NMP solvent in the sulfur grinding process. The cathode active material layer can be formed.

As described above, the solvent used in the sulfur grinding process of the present invention is preferably NMP. THF or DMF may also be used. In addition, the solvent used to prepare the PVDF binder solution is preferably the same as the solvent used in the sulfur grinding process.

Subsequently, when the production of the homogeneous cathode active material slurry is completed, it is coated with a thickness of 10 to 100 μm on the current collector, followed by drying, rolling, and cutting to a predetermined dimension to complete the manufacture of the cathode electrode.

Subsequently, the assembly of the lithium secondary battery is completed by assembling the anode electrode through the separator, impregnating the electrolyte, and sealing the electrolyte, which can be achieved by a conventional method.

Hereinafter, a method of manufacturing a cathode electrode and a lithium battery according to the present invention will be described in more detail with reference to the following examples. However, the present invention may be modified and implemented in an equivalent range by those skilled in the art, and thus the protection scope of the present invention is limited thereto. Of course not.

Comparative Example 1

340 g of a 5 mm diameter zirconia (ZrO ₂ ) ball was charged to a 250 ml HDPE container, followed by mixing 7 g of sulfur and 40 g of NMP solvent. The mixture was ball milled for 24 hours to prepare a sulfur slurry.

FIG. 2 is a scanning electron microscope (SEM) photograph of a sulfur slurry obtained by ball milling only sulfur in a NMP solvent for 24 hours. FIG. Referring to Figure 2, it can be seen that the sulfur slurry obtained by the simple milling by ball milling using only sulfur, the size of the sulfur particles is very large as 5 ~ 20㎛.

Example 1

400 g of zirconia (ZrO ₂ ) balls having a diameter of 5 mm were charged in a 250 ml HDPE container, followed by mixing 7 g of sulfur, 1.46 g of carbon (Super-P), and 50 g of NMP solvent. The mixture was ball milled for 24 hours to prepare a sulfur slurry.

FIG. 3 is a SEM photograph of the sulfur slurry obtained by ball milling the mixture of sulfur and carbon in NMP solvent for 24 hours. Referring to FIG. 3, a sulfur slurry obtained by ball milling using a mixture of sulfur and carbon is prevented from regrowth of sulfur particles by carbon particles, and thus, a slurry obtained by ball milling using only sulfur as in Comparative Example (FIG. 2). Unlike the sulfur particles of 0.5 ~ 2㎛ size can be seen that very fine.

Example 2

The sulfur slurry obtained in Example 1 was mixed with 5.83 g of a 10% by weight PVDF binder solution in which polyvinylidene fluoride (PVDF) was dissolved in an NMP solvent, and 1.46 g of additional carbon, followed by homogenization treatment for 1 hour. A cathode active material slurry having a composition of / carbon / PVDF binder = 66.7 / 28.3 / 5 wt% was prepared.

It was coated on a Al substrate having a thickness of 18 μm using a doctor blade at a thickness of 60 μm (thickness after drying), and then dried at a temperature of 80 ° C. for 24 hours. After rolling this, a cathode was manufactured by cutting to a predetermined dimension.

In addition, a lithium metal plate was cut separately to a predetermined dimension to prepare a lithium metal anode electrode.

A polyethylene separator (manufactured by Asahi) having a thickness of 25 µm was disposed between the cathode electrode and the anode electrode thus prepared, and assembled into a pouch-type lithium battery cell. The lithium secondary battery was completed by inject | pouring and sealing an organic electrolyte solution in this pouch. Herein, as the organic electrolyte, 1.0 M in a mixed solvent mixed with dioxolane (DOX): diglyme (DGM): dimethyl ether (DME): sulfolane (SUL) = 5: 2: 2: 1. 80 to 150 mg of an electrolyte in which LiSO 3 CF 3 was dissolved was used.

After leaving the finished lithium battery cell in this manner for 3 hours, 0.25C discharge and charge were performed once each in a 2.8-1.5V section, and then a cycling test was performed under the condition of 0.5C. During charging, an additional 150% cut-off condition of the design capacity was set.

The result of the cycle test obtained from this is shown in FIG. Referring to FIG. 4, it can be seen that the initial discharge capacity is preserved even after about 100 cycles, and the cycle stability is improved as compared with the case of using the PEO binder.

Example 3

Sulfur slurry was prepared in the same manner as in Example 1 except that the amount of the solvent NMP was 110 g and the conductive carbon was K / B (Ketjenblack) carbon.

The sulfur slurry thus obtained was mixed with 5.83 g of a 10 wt% PVDF binder solution in which PVDF was dissolved in an NMP solvent and homogenized for 1 hour to give a sulfur / carbon / PVDF binder = 77.4 / 17.6 / 5 wt% composition. A cathode active material slurry was prepared. The mixture was homogenized for 1 hour and a final mixture slurry of Sulfur / Carbon / Binder = 77.4 / 17.6 / 5 wt% composition was prepared.

It was coated on a Al substrate having a thickness of 18 μm using a doctor blade to a thickness of 50 μm (thickness after drying), and then dried at a temperature of 80 ° C. for 24 hours. After rolling this, a cathode was manufactured by cutting to a predetermined dimension.

In addition, a lithium metal plate was cut separately to a predetermined dimension to prepare a lithium metal anode electrode.

A polyethylene separator (manufactured by Asahi) having a thickness of 25 µm was disposed between the cathode electrode and the anode electrode thus prepared, and assembled into a pouch-type lithium battery cell. The lithium secondary battery was completed by inject | pouring and sealing an organic electrolyte solution in this pouch. Here, as an organic electrolyte solution, dioxolane (DOX): diglyme (DGM): dimethyl ether (DME): sulfolane (SUL) = 5: 2; 80-150 mg of electrolyte solution in which 1.0 M LiSO 3 CF 3 was dissolved in a mixed solvent mixed at a volume ratio of 2: 1 was used.

After leaving the finished lithium battery cell in this manner for 3 hours, 0.25C discharge and charge were performed once each in a 2.8-1.5V section, and then a cycling test was performed under the condition of 0.5C. During charging, an additional 150% cut-off condition of the design capacity was set.

The result of the cycle test obtained from this is shown in FIG. Referring to FIG. 5, it can be seen that the capacity decreases as the cycle increases, but the discharge capacity of the initial 10 cycles is greatly improved to 700mAh. As mentioned, the discharge capacity decreases as the number of cycles increases, but the cycle characteristics are slightly improved compared to the case of using the PEO binder.

Comparative Example 2

340 g of 5 mm diameter zirconia (ZrO ₂ ) balls were charged to a 250 ml HDPE container, followed by mixing 7 g of sulfur and 50 g of AN solvent. The mixture was ball milled for 24 hours to prepare a sulfur slurry.

Separately, 150 g of binder solution prepared at 4 wt% concentration of PEO (molecular weight 400 million) in AN solvent, 3 g of K / B (Ketjenblack) conductive agent, 340 g of zirconia ball having a diameter of 5 mm, and 70 g of AN were mixed at 200 rpm at room temperature. A homogeneous treatment was performed for 24 hours to prepare a conductive slurry.

The sulfur slurry and the conductive slurry thus prepared were mixed and homogenized at 50 rpm for 1 hour to prepare a cathode active material slurry.

It was coated on a Al substrate having a thickness of 18 μm using a doctor blade at a thickness of 50 μm (thickness after drying) and then dried at a temperature of 70 ° C. for 24 hours. After rolling this, a cathode was manufactured by cutting to a predetermined dimension.

In addition, a lithium metal plate was cut separately to a predetermined dimension to prepare a lithium metal anode electrode.

A polyethylene separator (manufactured by Asahi) having a thickness of 25 µm was disposed between the cathode electrode and the anode electrode thus prepared, and assembled into a pouch-type lithium battery cell. The lithium secondary battery was completed by inject | pouring and sealing an organic electrolyte solution in this pouch. Herein, as the organic electrolyte, 1.0 M in a mixed solvent mixed at a volume ratio of dioxolane (DOX): diglyme (DGM): dimethyl ether (DME): sulfolane (SUL) = 5: 2: 2: 1. 80 to 150 mg of an electrolyte in which LiSO 3 CF 3 was dissolved was used.

After leaving the finished lithium battery cell in this manner for 3 hours, 0.25C discharge and charge were performed once each in a 2.8-1.5V section, and then a cycling test was performed under the condition of 0.5C. During charging, an additional 150% cut-off condition of the design capacity was set.

Thus, the result of the cycle test obtained from the lithium battery which employ | adopted the cathode electrode using a PEO binder was shown in FIG. Comparing FIG. 6 with FIG. 5, it can be seen that the storage capacity of the capacity is significantly lowered as the cycle progresses as compared with the electrode (FIG. 6) using the PEO binder (FIG. 5).

As described above, the cathode electrode having a sulfur prepared according to the method of the present invention as an active material can use a fluorine-containing binder containing PVDF as it is, and thus has a low swelling phenomenon due to electrolyte and excellent binding ability. Has the advantage of stable battery performance. In addition, since the chemically stable PVDF binder used in the conventional lithium ion battery can be used as it is, a wide range of electrolyte choices may enable more various attempts in the future development of lithium-sulfur batteries.

Claims (13)

(a) preparing a sulfur slurry by mixing and ball milling only the sulfur and a carbon powder conductive material having a particle size of 30 nm to 100 nm together with a solvent showing solubility with respect to sulfur; And (b) mixing and homogenizing a binder solution into the slurry to prepare a cathode active material slurry. The method of claim 1, wherein the binder solution of step (b) further comprises a conductive material. According to claim 1, wherein the amount of the solvent showing the solubility with respect to the sulfur in the step (a) is 40 to 80 parts by weight, the amount of the sulfur is 5 to 10 parts by weight, the amount of the conductive material is 1 to 3 parts by weight, and the particle size of the sulfur slurry is adjusted to 0.5 ~ 2㎛, The method of claim 1, wherein the binder solution is used in a concentration of 0.1 to 1.7 parts by weight of the binder dissolved in 0.9 to 20 parts by weight of the solvent. The method of claim 3, wherein the binder solution of step (b) further comprises 1-3 parts by weight of the conductive material. The method of claim 1, further comprising coating the cathode active material slurry on a current collector to a thickness of 10 μm to 100 μm after the step (b). delete The method of claim 1, wherein the binder is at least one selected from the group consisting of polyvinylidene fluoride, a copolymer of vinylidene fluoride and hexafluoropropylene, and a mixture of polyvinylidene fluoride and styrene-butadiene rubber. The manufacturing method to make. The method of claim 1, wherein the solvent of step (a) is at least one selected from the group consisting of NMP, THF and DMF. The method of claim 1, wherein the binder solvent of step (b) is the same as the solvent of step (a). In a cathode electrode in which a cathode active material layer is laminated on a current collector, The cathode active material layer comprises a cathode having a particle size of 0.5 ~ 2㎛ cathode. A cathode electrode prepared according to any one of claims 1 to 5 and 7 to 9. A lithium battery comprising a cathode electrode prepared according to any one of claims 1 to 5 and 7 to 9. In a lithium battery comprising a cathode electrode, an anode electrode and a separator interposed therebetween, the cathode electrode, Lithium electrode, characterized in that the cathode active material layer comprising a sulfur having a particle diameter of 0.5 ~ 2㎛ laminated on the current collector.