KR101955122B1 - Electrode having microstructure, preparation method thereof and secondary battery including the same - Google Patents

Abstract

An electrode having a fine structure and a method of manufacturing the same are provided. According to the present invention, there is provided a process for producing an electrode active material slurry, comprising: preparing an electrode active material slurry containing active material particles, sulfur particles, a binder and a solvent; applying a slurry on a current collector and then drying the electrode active material layer; And then heat-treating to form a plurality of pores in the active material layer by sublimating the sulfur particles from within the active material layer. According to the present invention, by preparing an anode active material layer containing micropores using sulfur as a pore forming agent, the electrolyte can penetrate into the anode active material layer, thereby further improving the reactivity of the battery. Thus, high output characteristics and life of the battery, specifically, the secondary battery, can be improved. Furthermore, by introducing inexpensive sulfur into the slurry for electrode formation, a high output cell can be produced while maintaining the existing process, and advantages in commercialization of a cell having a fine structure can be exhibited.

Description

TECHNICAL FIELD The present invention relates to an electrode having a microstructure, a method of manufacturing the electrode, and a secondary battery including the electrode.

The present invention relates to an electrode, and more particularly, to an electrode having a fine structure and a method for manufacturing the same.

Recently, a large capacity battery capable of rapidly storing and discharging a large amount of energy as well as a high energy density battery that supplies a small amount of power over a long period of time, such as a battery used in a mobile phone or a notebook computer, is under development. For example, a large-capacity battery may be an energy storage system (ESS) used for an electric vehicle, a hybrid electric vehicle, or a building, or an energy stored in a power peak time And is used in a power supply and demand management system corresponding to a power peak without needing an additional generator.

On the other hand, the power that we use will be supplied to a specific frequency, and electric utilities will be manufactured and used accordingly. However, in the power system using the above-described large-capacity battery, the power frequency is reduced and increased due to an instantaneous increase in power consumption in the electrical grid, sudden accidents, etc., and this causes problems such as power failure do. Therefore, it is necessary to manage and maintain the power frequency by using a high output cell capable of coping with such a sudden change in the power frequency.

Further, output characteristics are very important for a lithium secondary battery to be used as an electric vehicle or a battery for a hybrid electric vehicle, for example. Particularly, considering the mountability in an electric vehicle, a high energy density is required to minimize the volume and weight of the battery, and a hybrid electric vehicle also requires a high output density battery that supplies a large amount of electric power in a short time. As a result, there is a limitation in that a conventional small-sized battery can not satisfy a hybrid electric vehicle requiring a high output density.

In other words, a high-power battery capable of managing power supply and demand, that is, a large-capacity battery, must be able to store a large amount of energy and emit a large amount of electric power. Conventional batteries can not easily penetrate into the active material in the electrode Ions on the surface of the electrode cause side reactions, energy can not be stored in the active material, and the life of the battery is reduced.

Korean Patent Registration No. 10-1134122

Disclosure of Invention Technical Problem [8] The present invention provides an electrode capable of improving the reactivity, high output characteristics, and service life of a battery and a method for producing the same.

According to an aspect of the present invention, there is provided a method of manufacturing an electrode having a fine structure. The method for manufacturing an electrode having a fine structure includes the steps of: preparing an electrode active material slurry containing active material particles, sulfur particles, a binder and a solvent; applying the slurry on a current collector and then drying to form an electrode active material layer And rolling the electrode active material layer, followed by heat treatment to sublimate the sulfur particles from the active material layer to form a plurality of pores in the active material layer.

The active material particles may have a plurality of pores in the particles, and the average particle diameter of the sulfur particles may be larger than the pore size of the active material particles and smaller than or equal to the average particle size of the active material particles. The heat treatment may be conducted at a pressure lower than atmospheric pressure. Some of the plurality of pores may be connected to each other to form a channel structure.

The binder may be an aqueous binder. The binder may be any one selected from the group consisting of styrene-butadiene rubber (SBR), carboxymethyl cellulose, and combinations thereof. The solvent may be aqueous or non-aqueous. The binder may be contained in an amount of 1 to 5 parts by weight based on 100 parts by weight of the active material particles.

According to another aspect of the present invention, there is provided an electrode having a microstructure. The electrode having the fine structure may include a current collector and an electrode active material layer disposed on the current collector and containing active material particles and having a plurality of pores between the active material particles.

The active material particle has a plurality of pores in the particle, and the size of the pores between the active material particles may be larger than the size of the pores in the active material particle, and may be equal to or smaller than the size of the active material particle. The size of the pores between the active material particles may be 50% to 100% of the average particle diameter of the active material particles. Some of the plurality of pores may be connected to each other to form a channel structure.

According to another aspect of the present invention, there is provided a secondary battery. Wherein the secondary battery comprises a current collector and an electrode active material layer on the current collector, the electrode active material layer containing active material particles and having a plurality of pores between the active material particles, a negative electrode having a fine structure, And an electrolyte between the anode and the cathode.

The active material particle has a plurality of pores in the particle, and the size of the pores between the active material particles may be larger than the size of the pores in the active material particle, and may be equal to or smaller than the size of the active material particle.

According to the present invention, by preparing an anode active material layer containing micropores using sulfur as a pore forming agent, the electrolyte can penetrate into the anode active material layer, thereby further improving the reactivity of the battery. Thus, high output characteristics and life of the battery, specifically, the secondary battery, can be improved.

Furthermore, by introducing inexpensive sulfur into the slurry for electrode formation, a high output cell can be produced while maintaining the existing process, and advantages in commercialization of a cell having a fine structure can be exhibited.

The technical effects of the present invention are not limited to those mentioned above, and other technical effects not mentioned can be clearly understood by those skilled in the art from the following description.

1 is a flowchart illustrating a method of manufacturing an electrode having a fine structure according to an embodiment of the present invention.
2 is a schematic view showing an electrode having a microstructure according to an embodiment of the present invention.
Fig. 3 is a photograph of the outer surface of the electrode according to the electrode production example and the electrode comparison example.
4 is a scanning electron microscope (SEM) photograph of a surface of an electrode according to a comparative electrode.
5A and 5B are scanning electron microscope (SEM) photographs of a surface of an electrode according to an electrode production example.
6 is a graph showing the degree of penetration of the electrolyte into the electrode according to the electrode production example and the electrode comparison example.
7 is a graph showing the charge / discharge characteristics of a lithium secondary battery according to Comparative Example of Cell and Production Example of Battery.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings and will herein be described in detail. Rather, the intention is not to limit the invention to the particular forms disclosed, but rather, the invention includes all modifications, equivalents and substitutions that are consistent with the spirit of the invention as defined by the claims.

It will be appreciated that when an element such as a layer, region or substrate is referred to as being present on another element "on," it may be directly on the other element or there may be an intermediate element in between .

1 is a flowchart illustrating a method of manufacturing an electrode having a fine structure according to an embodiment of the present invention.

Referring to FIG. 1, an electrode active material slurry can be prepared (S100). The slurry may be a secondary battery, specifically, an electrode of a lithium ion battery, more specifically, a negative electrode active material slurry of a lithium ion battery. The slurry may contain active material particles, sulfur particles, a solvent and a binder.

The active material particles may be carbon particles that are carbon-based materials. The carbon-based material may be at least one selected from the group consisting of graphite carbon, coke carbon and hard carbon, and may be graphite carbon. The graphite carbon may include, but is not limited to, natural graphite, artificial graphite and expanded graphite. The carbon particles may be crystalline artificial graphite.

In some cases, the active material particles may further include silicon oxide / carbon (SiO x / C, 0 <x <2) composite particles in addition to the carbon particles. At this time, the silicon oxide / carbon composite particles may be particles coated with carbon on the surface of silicon oxide, and may be mixed with 5 to 15 parts by weight, for example, 10 parts by weight, based on the carbon particles.

For example, the average particle size of the active material particles may be 1 탆 to 50 탆, specifically, 10 탆 to 40 탆, more specifically, 10 탆 to 30 탆. The active material particles, specifically, the carbon particles may have a plurality of pores in the particles. The size of the pores (212 in FIG. 2) in the active material particles may be nanometer size.

The sulfur particles may form a microstructure, specifically, a porous structure within the electrode active material layer to be described later. The sulfur particles are in the form of a powder of elemental sulfur (S ₈ ), and the size of the sulfur particles is in micrometer size, which is larger than the size of the pores in the active material particles and smaller than or equal to the size of the carbon particles. For example, the average particle diameter of the sulfur particles may be 1 탆 to 50 탆, specifically 10 탆 to 40 탆, more specifically, 10 탆 to 30 탆, more specifically, 10 탆 to 20 탆.

The size of the sulfur particles can form a microstructure, specifically, a porous structure and a channel structure between the active material particles in the electrode active material layer to be described later, and may not impregnate pores in the active material particles. Lt; / RTI &gt; The formation of the microstructure in the electrode active material layer by the sulfur particles will be described in more detail in step S300 described later.

The sulfur particles may be contained in an amount of 5 to 20 parts by weight, specifically 5 to 15 parts by weight, for example, 10 parts by weight, based on 100 parts by weight of the active material particles.

The solvent may be aqueous or non-aqueous. For example, the aqueous solvent may be water, an alcohol, or a combination thereof. In one example, the solvent may be water. Accordingly, the sulfur particles are not dissolved in the aqueous solvent and can be inserted between the active material particles in the form of particles.

The binder may be an aqueous binder. For example, the binder may be styrene-butadiene rubber (SBR), carboxymethyl cellulose, or a combination thereof. For example, the binder may be a combination of styrene butadiene rubber and carboxymethyl cellulose. For example, the binder may be a mixture of styrene butadiene rubber and carboxymethyl cellulose in a weight ratio of 1: 0.1 to 1: 5, for example, 1: 1.5.

The aqueous binder can disperse the active material particles in the solvent more uniformly. Specifically, when the styrene butadiene rubber and carboxymethyl cellulose are used in combination as a binder, the solvent and the active material particles, for example, water and graphite particles can be prevented from being separated from each other.

The binder may be contained in an amount of 1 to 5 parts by weight, specifically 2 to 3 parts by weight, based on 100 parts by weight of the active material particles. As described above, in the present embodiment, the content of the binder is very small as compared with the content of the active material. In the anode active material layer, a small amount of the binder exists between the active material particles and binds them. And the active material particles are dispersedly arranged in the matrix. The weight ratio of the binder to the active material particles may be such that the fine structure in the electrode active material layer to be described later, that is, micropores, is mainly formed between the active particles rather than in the binder.

The slurry may be coated on the current collector to form an electrode active material layer (S200). The current collector may be a material that has conductivity but does not cause a chemical change. For example, the current collector may include copper, stainless steel, aluminum, nickel, titanium or sintered carbon, and may be in the form of a film, a sheet, a foil, a net, a porous body, . &Lt; / RTI &gt; For example, the current collector may use a steal use stainless foil (SUS) or a copper foil, for example, a sulfo foil. For example, the current collector may have a thickness of 3 탆 to 500 탆.

Specifically, the slurry can be applied on a current collector and dried. By the drying, the solvent can be almost removed. The application may be carried out by a conventional method such as drop casting or doctor blade. The first drying is performed in an air atmosphere at atmospheric pressure using an oven or the like at a temperature of 100 ° C to 120 ° C, for example, 110 ° C for 10 minutes to 1 hour, specifically 10 minutes to 30 minutes, more specifically 10 minutes to 20 minutes Min. &Lt; / RTI &gt;

The electrode active material layer may be pressed and heat treated to form a microstructure, that is, a porous structure in the active material layer (S300). The rolling may be performed by a conventional method such as a roll press.

The heat treatment is preferably carried out at a pressure lower than the atmospheric pressure, for example, in a vacuum condition, at a relatively low temperature, specifically 40 ° C to 100 ° C, more specifically 50 ° C to 90 ° C, more specifically 60 ° C to 80 ° C, Hour to 24 hours. The heat treatment can form pores in the place where the sulfur particles exist by sublimating the sulfur particles dispersed in the electrode active material layer. Specifically, by using a principle in which sulfur particles having relatively weak intermolecular attraction are sublimated by low pressure, sulfur particles dispersed in the electrode active material layer, specifically between the active material particles are removed to form a plurality of pores And the plurality of pores are connected to each other to form a channel structure penetrating the inside of the electrode active material layer.

In this case, the size of the sulfur particles, for example, 10 μm to 20 μm may be smaller than or equal to the size of the active material particles and larger than the size of the pores (212 of FIG. 2) in the active material particles. Accordingly, the sulfur particles form pores (211a in FIG. 2) as large as the size of the sulfur particles between the active material particles, but are not impregnated or impregnated with the pores (212 in FIG. 2) Can be reduced. Sulfur sublimation by the heat treatment can be almost completely performed, and there may be no sulfur particles remaining in the electrode active material layer.

In other words, it is possible to secure a pore structure and a channel structure in the active material layer by using sulfur having low conductivity as a pore-forming agent, and there is almost no sulfur particles remaining in the final structure, so that the effect of improving the conductivity of the electrode can be exerted.

The above-described temperature range in which the heat treatment is performed may exhibit an effect of preventing side reactions with the current collector during the sulfur sublimation and a phenomenon in which the binder may be damaged.

On the other hand, by the heat treatment, the solvent may be completely removed from the active material layer.

2 is a schematic view showing an electrode having a microstructure according to an embodiment of the present invention.

2, an electrode 300 having a fine structure includes a current collector 100, an electrode active material layer 200 having a microstructure, that is, a porous structure, which is disposed on the current collector 100 . The current collector 100 may be formed of the same material as described with reference to FIG.

The electrode active material layer 200 includes active material particles 210 and a binder 213. The electrode active material layer 200 has a microstructure formed between the active material particles 210 and specifically a plurality of pore structures 211a, Lt; RTI ID = 0.0 &gt; 211b. &Lt; / RTI &gt; The pore structure 211a and channel structure 211b may be due to the sublimation of sulfur particles (not shown) as described above in FIG.

Accordingly, the size of the pores 211a or the width of the channel can be determined by the size of sulfur particles (not shown). Specifically, the size of the pores 211a or the width of the channel may be smaller than or equal to an average particle diameter of the active material particles 210. [ More specifically, the pore size or the width of the channel may have a size ranging from 50% to 100% of the average particle size of the active material particles. For example, the size of the pores 211a may be 1 占 퐉 to 50 占 퐉, specifically, 10 占 퐉 to 40 占 퐉, more specifically, 10 占 퐉 to 30 占 퐉, and more specifically, 10 占 퐉 to 20 占 퐉. The size of the pores 211a may be in a range that is suitable for electrolyte impregnation and may increase the unit volume capacity of the electrode.

The channel 211b may be formed by connecting a part of a plurality of pores 211a disposed in the active material layer 200 with each other. The pores 211a and the channels 211b may serve to impregnate the electrolyte or electrolyte disposed on the electrode active material layer 200 into the electrode active material layer 200 well. That is, the microstructure increases the penetration rate of the electrolyte and prevents a phenomenon in which ions of the electrolyte on the electrode surface cause a side reaction when the electrolyte can not penetrate into the internal active material of the electrode, thereby improving the reactivity of the electrode, The storage rate and the life of the battery can be improved.

The electrode 300 may be used as an electrode of a secondary battery, for example, a lithium ion secondary battery, a lithium ion polymer battery, a nickel-cadmium battery, a nickel metal hydride battery, or a lead acid battery. For example, the electrode 300 may be used as an electrode of a lithium ion secondary battery, for example, a cathode of a lithium ion secondary battery. Although the embodiment according to the present invention described below has described a lithium ion secondary battery having a negative electrode having a fine structure, the kind of the secondary battery to which the electrode is applied is not limited thereto.

Specifically, the lithium ion secondary battery (not shown) may include a negative electrode having a fine structure, a positive electrode, and an electrolyte between the negative electrode and the positive electrode. The negative electrode can be manufactured in the same manner as the description of Fig. 1 described above.

The anode may include a cathode active material. For example, the cathode active material may be lithium metal or lithium oxide. The lithium oxide may be, but is not limited to, lithium cobalt oxide (LiCoO ₂ ), lithium iron phosphate (LiFePO ₄ ), or lithium manganese oxide (LiMn ₂ O ₄ ) .

And a separator disposed between the cathode and the anode for transferring lithium ions between the cathode and the anode. For example, the separator may be a polyolefin-based porous film such as polyethylene or polypropylene.

The electrolyte, which is a transfer medium of lithium ions, may be filled between the cathode and the anode. The electrolyte may be an aqueous or non-aqueous electrolyte solution, but a non-aqueous electrolyte solution is preferred to increase the operating voltage of the device. However, the electrolyte is not limited thereto and may be a solid electrolyte. The non-aqueous electrolyte solution has an electrolyte and a medium, and the electrolyte may be a lithium salt. The lithium salt is selected from the group consisting of lithium perchlorate (LiClO ₄ ), lithium tetrafluoroborate (LiBF ₄ ), lithium hexafluorophosphate (LiPF ₆ ), lithium trifluoromethane sulfonate (LiCF ₃ SO ₃ ), lithium hexafluoroacetate _6), or lithium trifluoromethanesulfonate sulfonyl imide _{(Li (CF 3 SO 2)} 2 N) may be. The medium is ethylene carbonate, propylene carbonate. Dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, acrylonitrile,? -Caprolactone, or a combination thereof.

The electrode 300 is applied to a battery module including the unit cell and a battery pack including the battery module, and thus can be used as a power source for small, medium and large devices having the same. For example, the electrode is expected to improve the capacity and high output characteristics by being applied to a portable communication device, an electric vehicle, a hybrid electric vehicle, a medical device, and an energy storage system (ESS).

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. However, the present invention is not limited to the embodiments described herein but may be embodied in other forms.

&Lt; Example of electrode production &

, 9.75 g of a SiOx / carbon composite powder (average particle diameter 5 占 퐉 to 10 占 퐉), 9.75 g of a sulfur element powder (average particle diameter 10 占 퐉), 0.75 g of carboxymethyl cellulose and styrene butadiene An electrode active material slurry was prepared by mixing 2.5 g of a binder mixed with rubber at a weight ratio of 1: 1.5 in 54.875 g of water. The slurry was drop-cast on a 50 占 퐉 SUS foil and then dried in an oven at 110 占 폚 to prepare an electrode active material layer. The electrode active material layer was rolled by a roll press and then heat-treated at 65 DEG C under a vacuum condition for 15 hours to prepare a negative electrode having a size of 15 pi.

<Electrode Comparative Example>

An electrode was prepared in the same manner as in the electrode preparation example except that a slurry not containing a sulfur element powder was used.

&Lt; Example of battery cell production &

The electrode prepared in Preparation Example 1 was prepared as a negative electrode. A nonaqueous electrolyte solution in which LiPF ₆ was dissolved in a solvent (containing EC / EMC having a volume ratio of 3: 7 and VC of 3 wt%) at a concentration of 1M was injected between the positive electrode of lithium foil and the negative electrode to form a lithium ion secondary battery unit cell .

&Lt; Comparative Example of Battery Cell &

A lithium ion secondary battery unit cell was manufactured in the same manner as in the battery cell preparation example except that the negative electrode prepared by the electrode comparison example was used in place of the negative electrode prepared by the electrode production example.

Fig. 3 is a photograph of the outer surface of the electrode according to the electrode production example and the electrode comparison example.

Referring to FIG. 3, it can be visually confirmed that all of the electrodes according to the electrode preparation example and the electrode comparison example form a smooth outer surface. In other words, it has been confirmed that the electrode according to the electrode preparation example of the present invention, that is, the electrode having the pore structure formed by the sublimation of sulfur also forms a uniform surface with the naked eye.

4 is a scanning electron microscope (SEM) photograph of a surface of an electrode according to a comparative electrode. Here, (a) and (b) are photographs taken at a low magnification and a high magnification of the surface of the electrode according to the electrode comparison example, respectively.

Referring to FIG. 4, it can be seen that the pore structure was not formed even after the rolling and the vacuum heat treatment proceeded in the electrode comparison example, that is, the electrode in which sulfur was not introduced.

5A and 5B are scanning electron microscope (SEM) photographs of a surface of an electrode according to an electrode production example. In the case of the photograph of FIG. 5A, the film was taken before the vacuum heat treatment after rolling during the progress of the electrode production example, and the case of FIG. 5B was taken after the vacuum heat treatment was completed.

Referring to FIGS. 5A and 5B, it can be confirmed that sulfur particles (a portion denoted by a circle in FIG. 5A) are dispersed and present in the active material layer before the vacuum heat treatment. On the other hand, when the vacuum heat treatment is performed, it can be confirmed that a large number of pore structures (a portion denoted by a circle in FIG. 5B) are formed in the active material layer. At this time, it can be seen that the pores have a size of about 10 탆 to 20 탆. These pores were understood as a phenomenon caused by the sublimation and removal of sulfur particles in the vacuum heat treatment process.

6 is a graph showing the degree of penetration of the electrolyte into the electrode according to the electrode production example and the electrode comparison example. Specifically, 6 占 퐇 of the electrolyte solution was added to each electrode according to the electrode preparation example and the electrode comparison example, and then the time when the electrolyte was absorbed into the electrode was measured. At this time, the electrolyte used was one in which LiPF ₆ was dissolved in a solvent (containing EC / EMC having a volume ratio of 3: 7 and containing 3 wt% of VC) at a concentration of 1M.

Referring to FIG. 6, it can be seen that the electrode according to the electrode preparation example has an electrolyte permeability about 2.3 times higher than the electrode according to the electrode comparison example. It was understood that the electrode according to the electrode production example was formed by forming a plurality of pores and a channel formed by connecting the plurality of pores to each other due to the sublimation of sulfur particles in the active material layer, thereby improving the electrolyte penetration effect.

7 is a graph showing the charge / discharge characteristics of a lithium secondary battery according to Comparative Example of Cell and Production Example of Battery. At this time, constant current charging was performed at 10 mA / g up to 0.01 V and constant voltage charging was performed until the current reached 5 mA / g. The discharge was carried out up to 2 V with constant current discharge at the same rate as the charging rate. The graphs show charge / discharge characteristics in the first cycle.

Referring to FIG. 7, it can be seen that the reversed cell according to the cell preparation example exhibits a capacity of 620 mAh / g at the time of charging and a capacity of 523 mAh / g at the time of discharging. On the other hand, the reversed cell according to the comparative example of the battery shows a capacity of 503 mAh / g when charged and a capacity of 430 mAh / g when discharged. As described above, it can be seen that, in the case of Comparative Example of Batteries, that is, when a plurality of pores formed by vaporization of sulfur are formed in the anode active material layer, the discharge capacity is improved in addition to the charging capacity.

It should be noted that the embodiments of the present invention disclosed in the present specification and drawings are only illustrative of specific examples for the purpose of understanding and are not intended to limit the scope of the present invention. It will be apparent to those skilled in the art that other modifications based on the technical idea of the present invention are possible in addition to the embodiments disclosed herein.

100: collector 200: electrode active material layer
210: active material particle 211a: pore structure
211b: channel structure 212: porosity in carbon particles
213: binder 300: electrode

Claims (14)

Preparing an electrode active material slurry containing active material particles, sulfur particles, a binder and a solvent;
Coating the slurry on a current collector, and drying the slurry to form an electrode active material layer; And
Wherein the electrode active material layer is rolled and then heat treated to sublimate the sulfur particles from the active material layer to form a plurality of pores in the active material layer. The method according to claim 1,
Wherein the active material particle has a plurality of pores in the particle,
Wherein an average particle size of the sulfur particles is larger than a size of pores in the active material particle and smaller than or equal to an average particle size of the active material particles. The method according to claim 1,
Wherein the heat treatment proceeds at a pressure lower than atmospheric pressure. The method according to claim 1,
Wherein some of the plurality of pores are connected to each other to form a channel structure. The method according to claim 1,
Wherein the binder is an aqueous binder. 6. The method of claim 5,
Wherein the binder is any one selected from the group consisting of styrene-butadiene rubber (SBR), carboxymethyl cellulose, and combinations thereof. The method according to claim 1,
Wherein the solvent is an aqueous solvent. The method according to claim 1,
Wherein the binder is contained in an amount of 1 to 5 parts by weight based on 100 parts by weight of the active material particles. delete delete delete delete delete delete

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