KR101499196B1 - Manufacturing method of active cathode materials using network structured hydrogels and active cathode materials coated with carbon - Google Patents

Abstract

The present invention relates to a method for producing a cathode active material coated with a carbon layer on a surface thereof, specifically, a method for producing a cathode active material using a hydrogel, a cathode active material coated with a carbon layer on the surface thereof, and a secondary battery comprising the cathode active material.
More particularly, the present invention relates to a method for preparing a hydrogel having a network structure, A second step of preparing an aqueous solution of a precursor of a cathode active material; A third step of swelling the hydrogel in the aqueous solution of the precursor of the cathode active material; And a fourth step of firing the hydrogel having absorbed the aqueous solution of the cathode active material to obtain a cathode active material coated with a carbon layer, and a method of manufacturing the cathode active material using the hydrogel.
The process for preparing a cathode active material using the hydrogel according to the present invention reduces the process of forming a carbon layer on the surface of a cathode active material using a hydrated gel having a network structure and facilitates the control of fine nanostructures and chemical components, .

Description

Technical Field [0001] The present invention relates to a method for producing a cathode active material using a hydrogel having a network structure and a cathode active material coated with a carbon layer,

The present invention relates to a method for preparing a cathode active material for a secondary battery using a hydrogel, and more particularly, to a method for producing a cathode active material coated with a carbon layer on a surface thereof using a hydrated gel having a network structure, To a cathode active material and a secondary battery including the same.

The secondary battery is a product that can be repeatedly charged and discharged as it can convert between chemical energy and electric energy. As the environment issues and reuse are possible, the market is growing rapidly based on the home appliance market.

Typically, lithium-ion batteries are characterized by high capacitance and energy density. They are used not only as power sources for mobile communication devices, information communication devices, and portable video devices, but also for use in hybrid vehicles, plug-in hybrid vehicles Electric vehicles, and non-IT power sources such as industrial tools and robots. Future automobiles, such as plug-in hybrid vehicles and electric vehicles, are expected to expand their use as high-capacity, high-capacity energy storage devices with long life and high stability characteristics.

Here, the core components of the lithium ion battery are mainly an anode, a cathode, an electrolyte, and a separator. The anode refers to an electrode that receives electrons from an external conductor when discharging and causes a reduction reaction, and the cathode refers to an electrode that discharges electrons to a conductor while oxidizing the anode active material.

Particularly, the cathode active material, which is a layered material applied to the anode, is a core part that has the greatest influence on the potential difference, capacity, and operating speed of the battery. The cathode active material is a material that affects the performance of the electrode. As shown in FIG. That is, each of the raw materials is mixed with the raw materials uniformly and uniformly in accordance with the chemical composition of the material to be finally produced, and then the carbonate and the hydroxide are removed by calcination. The calcined material is pulverized to a desired particle size and classified and packed to complete the product.

However, in order to develop a stable large-capacity lithium ion battery system, it is necessary to control the compound forming the cathode active material to maintain a high output of the cathode active material. For this purpose, various methods such as nano- . As a related art, Korean Patent Laid-Open Publication No. 10-2012-0058311 (published on Jun. 07, 2012) discloses a method for producing a positive electrode active material for a lithium secondary battery in which a carbon layer is formed on the surface to improve electric conductivity, However, the above-mentioned prior art is complicated in manufacturing process by mixing, stirring and pulverizing a carbon compound, a solvent and a cathode active material, followed by drying and heat-treating processes, resulting in poor economical efficiency, There is a problem that it is not suitable for the following.

Accordingly, the inventors of the present invention have made efforts to develop a cathode active material having a complicated manufacturing process of a cathode active material having a carbon coating layer, and capable of stabilizing a fine nanostructure and controlling a chemical composition. As a result, By manufacturing the active material, the manufacturing process of the present invention, which exhibits excellent electrical conductivity characteristics, has been completed.

In order to solve the above problems, the present invention provides a method for manufacturing a cathode active material, which comprises using a hydrogel having a network structure to reduce the process of forming a carbon layer on the surface of a cathode active material, It is an object of the present invention to provide a method for producing a positive electrode active material.

It is another object of the present invention to provide a cathode active material having a surface coated with a carbon layer.

Finally, the present invention provides a secondary battery including the cathode active material.

In order to solve the above problems, the present invention provides, as one aspect,

A first step of preparing a hydrogel having a network structure; A second step of preparing an aqueous solution of a precursor of a cathode active material; A third step of swelling the hydrogel in the aqueous solution of the precursor of the cathode active material; And a fourth step of firing the hydrogel having absorbed the aqueous solution of the cathode active material to obtain a cathode active material coated with a carbon layer. The method of manufacturing a cathode active material using the hydrogel according to claim 1,

Also preferably, the hydrogel is composed of hydrogen, carbon, nitrogen and oxygen.

Preferably, the hydrogel is crosslinked by copolymerizing one or more selected from among an amide-based monomer, an acrylamide-based monomer, an acrylate-based monomer and an ester-based monomer.

Also preferably, the hydrogel has a degree of crosslinking of 0.01% to 10%.

Preferably, the cathode active material precursor is one or a mixture of two or more selected from the group consisting of Li, Zn, Fe, Co, Ni, Mn, Cu, V, Ti and Cr metal salts.

Preferably, the firing is performed at a temperature of 150 to 400 ° C.

Also preferably, the carbon layer has a thickness of 2 to 30 nm.

According to another aspect of the present invention,

A carbon layer is coated on the surface of the positive electrode active material, and the carbon layer is formed by copolymerizing a mixture of one or more kinds selected from an amide monomer, an acrylamide monomer, an acrylate monomer and an ester monomer, Wherein the carbon layer is coated on the surface of the positive electrode active material. Preferably, it is produced by the above method.

According to another aspect of the present invention, there is provided a secondary battery including the positive electrode active material.

As described above, the method of producing a cathode active material using a hydrogel according to the present invention is a method of synthesizing a cathode active material by a firing process from a cathode active material precursor by using a hydrated gel having a network structure, So that the manufacturing process can be reduced and mass production can be facilitated.

In addition, since the carbon layer can be coated on the surface of the cathode active material by using a hydrogel, it is possible to control the micro-nano structure and the chemical composition easily, thereby improving the electrical conductivity and the structure stability during battery operation, .

1 shows a process for producing a cathode active material using a hydrogel according to the present invention.
2 is a schematic representation of the formation of a cathode active material coated with a carbon layer on its surface.
FIG. 3 shows a structural formula of the hydrogel prepared in an embodiment of the present invention.
4 is a pattern graph showing the results of X-ray diffraction (XRD) analysis of a cathode active material using the hydrogel prepared according to an embodiment of the present invention.
FIG. 5 is a graph showing an initial capacity discharge curve of a cathode active material using a hydrogel manufactured according to an embodiment of the present invention.

Hereinafter, the present invention will be described in detail.

FIG. 1 is a view showing a process for producing a cathode active material using a hydrogel according to an embodiment of the present invention, FIG. 2 is a schematic view showing a carbon layer coated on a cathode active material,

1 and 2, the present invention provides a method for preparing a hydrogel having a network structure, A second step of preparing an aqueous solution of a precursor of a cathode active material; A third step of swelling the hydrogel in the aqueous solution of the precursor of the cathode active material; And a fourth step of firing the hydrogel having absorbed the aqueous solution of the positive electrode active material to obtain a cathode active material coated with a carbon layer, and a method for producing the positive electrode active material using the hydrogel.

More specifically, in the present invention, the first step is a step of producing a hydrogel having a network structure, wherein the hydrophilic monomer is crosslinked to prepare a hydrogel.

At this time, the hydrogel is a material having a property that the hydrophilic polymer is crosslinked by chemical bonding such as physical bonding or covalent bonding to have a three-dimensional network structure, thereby absorbing and swelling the aqueous solution. The amide monomer, the acrylamide monomer , An acrylate monomer and an ester monomer, and more preferably an acrylate-based monomer having an anionic group on its side chain and capable of increasing its volume when swelled It is preferable to copolymerize the monomers. In a specific embodiment of the present invention, a hydrogel of a network structure was prepared by copolymerization using an acrylamide-based monomer and an acrylate-based monomer (see FIG. 3).

The hydrogel preferably has a degree of crosslinking of 0.01% to 10%. Here, the degree of crosslinking refers to the ratio of the number of moles of monomer to the number of moles of crosslinking agent, which is directly related to the volume of increase when the hydrogel absorbs the aqueous solution. In the present invention, when the degree of crosslinking of the hydrogels is less than 0.01%, it is not possible to effectively form a three-dimensional network structure. When the degree of crosslinking is more than 10%, the water absorption rate of the cathode active material precursor is lowered. In the present invention, the above range of the degree of crosslinking of the hydrogen gel is suitable, more preferably 0.01% to 5%.

In the present invention, the second step is a step of preparing the aqueous solution of the positive electrode active material precursor capable of being calcined and processed, and the positive electrode active material precursor is not limited if it is water-soluble. However, Lt; / RTI > Therefore, the cathode active material precursor is preferably a mixture of at least one selected from the group consisting of metal salts of Li, Zn, Fe, Co, Ni, Mn, Cu, V, Ti and Cr, Vanadium oxide and iron fluoride which do not cause phase separation are more preferable.

In the present invention, the third step is a step of swelling the hydrogel in the aqueous solution of the precursor of the cathode active material. That is, the third step is a step of using the hydrogel as a mold for synthesizing a cathode active material. As the mixing of the hydrogel and the precursor of the polarizing material is performed in a liquid phase, it is easy to control the particle size, shape and composition The resulting positive electrode active material is synthesized. At this time, the hydrogels absorb the aqueous solution of the precursor of the cathode well so as not to dissolve or decompose, so as to be used as a mold for synthesis of the cathode active material, and do not contain other heteroatoms in the molecule , Carbon, nitrogen and oxygen, and more preferably one obtained by copolymerizing and crosslinking one kind or a mixture of two or more kinds selected from an amide type monomer, an acrylamide type monomer, an acrylate type monomer and an ester type monomer Do.

In the fourth step of the present invention, the swollen hydrogel having the three-dimensional structure absorbing the aqueous solution of the precursor of the cathode active material formed in the third step is fired to obtain a cathode active material, The cathode active material precursor absorbed therein is reacted to obtain a cathode active material. In this process, the hydrogel is pyrolyzed and coated with carbon on the surface of the cathode active material to form a carbon layer. That is, the cathode active material is synthesized by a single firing, and a carbon layer is formed on the surface of the cathode active material, thereby forming a network, so that a cathode active material capable of remarkably improving the electric conductivity can be obtained.

At this time, it is preferable that the firing is performed in a temperature range of 150 to 400 ° C under an inert gas atmosphere so that the hydrolysis of the hydrogel of the network can be performed well. When the firing is performed at a temperature lower than 150 ° C., the hydrogel is not thermally decomposed. If the firing is performed at a temperature higher than 400 ° C., the carbon is also decomposed to form a carbon layer on the surface of the cathode active material Can not do it. As the inert gas, nitrogen or argon may be used.

The carbon layer formed on the surface of the cathode active material preferably has a thickness of 2 to 30 nm. When the thickness of the carbon layer is less than 2 nm, satisfactory electrical conductivity improvement is not obtained. When the thickness exceeds 30 nm, the carbon layer is not uniformly formed and the electrode density is decreased.

Specifically, the content of carbon formed on the surface of the positive electrode active material is 0.1 wt% or more and 30 wt% or less, preferably 0.5 wt% or more and 20 wt% or less, more preferably 1 wt% or more and 15 wt% % Or less, and most preferably 1 wt% or more and 10 wt% or less. When the cathode active material for a secondary battery is used in which the content of the conductive carbon is less than 0.1 wt%, it may be difficult to obtain sufficient conductivity, the internal resistance of the anode may be improved, When the positive electrode active material for a lithium secondary battery having a carbon content of more than 30% by weight is used, sufficient conductivity is obtained, but the content of the transition metal complex oxide in the positive electrode is decreased, , It is difficult to use the battery as a highly practical battery.

As described above, the method for producing a cathode active material using the hydrogel according to the present invention is characterized in that the hydrogel and the aqueous solution of the precursor of the cathode active material are mixed and fired to prepare a cathode active material having a carbon layer on its surface, Layer formation is easy and the process is significantly reduced compared to the conventional carbon layer formation process, which makes mass production easy.

In another aspect, the present invention relates to a cathode active material coated with a carbon layer on a surface thereof, which is prepared by the above method, and a carbonaceous layer provided on the surface of the cathode active material, thereby improving the electric conductivity.

According to another aspect of the present invention, there is provided a secondary battery including the positive electrode active material, wherein the positive electrode active material has improved electroconductivity, thereby improving the stability of the structure during battery operation, will be.

Hereinafter, the present invention will be described in detail with reference to examples, but these examples should not be construed as limiting the scope of the present invention.

≪ Preparation of vanadium oxide precursor aqueous solution >

3.78 g of oxalic acid was stirred in 10 mL of distilled water at room temperature. After all the oxalic acid was dissolved, 2.46 g of ammonium metavanadate was added by heating at 80 DEG C, and the mixture was stirred to obtain a vanadium oxide precursor aqueous solution.

Example 1 Production of a cathode active material using a hydrogel 1

1-1. Synthesis of polyisopropylacrylamide-co-polyacrylate having a network structure

After dissolving 410 mg of isopropyl acrylamide, 3.5 mg of methylene bisacrylamide and 86 mg of sodium acrylate in 4500 uL of distilled water, the mixture was vacuumed using a pressure reducer and then nitrogen was added thereto. 5.8 mg of tetramethylethylenediamine and 2.5 mg of ammonium phosphate were added in a nitrogen atmosphere, and the mixture was gelled for one hour to obtain a crosslinked network-shaped hydrated gel. The structural formula of the hydrogel obtained in FIG. 3 is shown.

1-2. Cathode active material manufacturing

First, the hydrogel prepared in 1-1 was immersed in secondary distilled water for 24 hours, and secondary distilled water was changed several times to remove unreacted monomers. The hydrogel was swelled in an aqueous vanadium oxide precursor solution for 24 hours. The hydrogel swollen in the vanadium oxide precursor aqueous solution was heat-treated in an oven at 80 ° C for 12 hours and then heated in a muffle furnace at 300 ° C for 6 hours to be fired to obtain 0.392 g of a cathode active material as a dark black solid .

≪ Example 2 > Preparation of a cathode active material using a hydrogel 2

2-1. Synthesis of polyacrylamide-co-polyacrylate having network structure

317 mg of acrylamide, 5.1 mg of methylenebisacrylamide, and 124 mg of sodium acrylate were dissolved in 4500 uL of distilled water, and the solution was vacuumed using a pressure reducer and then nitrogen was added thereto. 5.8 mg of tetramethylethylenediamine and 2.5 mg of ammonium phosphate were added in a nitrogen atmosphere, and the mixture was gelled for one hour to obtain a crosslinked network-shaped hydrated gel. The structural formula of the hydrogel obtained in FIG. 3 is shown.

2-2. Cathode active material manufacturing

First, the hydrogel prepared in 2-1 was immersed in secondary distilled water for 24 hours, and secondary distilled water was changed several times to remove unreacted monomers. The hydrogel was swelled in an aqueous vanadium oxide precursor solution for 24 hours. The hydrogel swollen in the vanadium oxide precursor aqueous solution was heat-treated in an oven at 80 ° C. for 12 hours, and then heated in a muffle furnace at 300 ° C. for 6 hours to be fired to obtain 0.669 g of a cathode active material as a dark black solid .

≪ Example 3 > Preparation of a cathode active material using a hydrogel 3

3-1. Synthesis of polyhydroxyethylmethacrylate-co-polyacrylate having a network structure

At room temperature, 420 mg of 2-hydroxyethyl methacrylate, 3.1 mg of methylene bisacrylamide, and 76 mg of sodium acrylamide were dissolved in 4500 uL of distilled water, vacuumed using a pressure reducer, and then nitrogen was added. 5.8 mg of tetramethylethylenediamine and 2.5 mg of ammonium phosphate were added in a nitrogen atmosphere, and the mixture was gelled for one hour to obtain a crosslinked network-shaped hydrated gel. The structural formula of the hydrogel obtained in FIG. 3 is shown.

3-2. Cathode active material manufacturing

First, the hydrogel prepared in 3-1 was immersed in the secondary distilled water for 24 hours, and the secondary distilled water was changed several times to remove the unreacted monomer. The hydrogel was swelled in an aqueous vanadium oxide precursor solution for 24 hours. The hydrogel swollen in the vanadium oxide precursor aqueous solution was heat-treated in an oven at 80 ° C. for 12 hours, and then heated in a muffle furnace at 300 ° C. for 6 hours to be fired to obtain 0.328 g of a cathode active material as a dark black solid .

<Comparative Example> Production of vanadium oxide cathode active material

The vanadium oxide precursor aqueous solution prepared above was heat treated in an oven at 80 ° C for 12 hours without using a hydrogel, and then heated in a muffle furnace at 300 ° C for 6 hours to obtain a final vanadium oxide cathode active material .

X-ray diffraction (XRD) analysis of the cathode active material using the hydrogel produced in Example 1 of the present invention and the vanadium oxide cathode active material produced in Comparative Example was performed and the graph is shown in FIG.

As shown in FIG. 4, it can be confirmed that the cathode active material using the hydrogel has the same crystal structure as the vanadium oxide cathode active material immediately fired in the precursor. Therefore, it can be confirmed that the method of preparing the cathode active material using the hydrogel of the present invention does not modify the crystal structure of the cathode active material, and can synthesize the cathode active material coated with the carbon layer on the surface by the simplified manufacturing process.

A charge / discharge test was conducted to examine the electrochemical performance of the positive electrode active material using the hydrogel produced through Example 1 of the present invention, and the graph is shown in FIG.

As shown in FIG. 5, the positive electrode active material using the hydrogel according to the present invention exhibited a flat interval indicating a period in which lithium moved, and the discharge tended to be discharged. The initial discharge capacity increased to 331 mAh / g And the charge / discharge capacity of the positive electrode active material using the hydrogel according to the present invention was remarkably improved.

Therefore, the initial capacity of the cathode active material using the hydrogel according to the present invention is not only a numerical value comparable to the initial discharge capacity of the cathode active material synthesized in the conventional nanostructured or nanosized form, but also remarkably reduced the manufacturing process It can be confirmed that it is a cathode active material.

Claims (10)

A first step of preparing a hydrogel having a network structure;
A second step of preparing an aqueous solution of a precursor of a cathode active material;
A third step of swelling the hydrogel in the aqueous solution of the precursor of the cathode active material; And
And a fourth step of firing the hydrogel having absorbed the aqueous solution of the cathode active material to obtain a cathode active material coated with a carbon layer on the surface thereof. The method according to claim 1,
Wherein the hydrogel is composed of hydrogen, carbon, nitrogen, and oxygen. The method according to claim 1,
Wherein the hydrogel is crosslinked by copolymerizing one or more selected from among an amide-based monomer, an acrylamide-based monomer, an acrylate-based monomer and an ester-based monomer. The method according to claim 1,
Wherein the hydrogel has a degree of crosslinking of 0.01% to 10%. The method according to claim 1,
Wherein the positive electrode active material precursor is one or a mixture of two or more selected from the group consisting of Li, Zn, Fe, Co, Ni, Mn, Cu, V, Ti, Cr and metal salts thereof. A method for producing a cathode active material. The method according to claim 1,
Wherein the firing is performed at a temperature of 150 to 400 ° C. The method according to claim 1,
Wherein the carbon layer has a thickness of 2 to 30 nm. A carbon layer is coated on the surface of the positive electrode active material,
Wherein the carbon layer is a heated hydrolyzate of a hydrogel formed by copolymerizing one or more selected from among an amide-based monomer, an acrylamide-based monomer, an acrylate-based monomer and an ester-based monomer,
The cathode active material according to any one of claims 1 to 7, wherein the cathode active material is coated with a carbon layer on the surface. delete A secondary battery comprising the cathode active material according to claim 8.

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