KR102273894B1 - Electrode using porous polymer composite scaffold and Li battery comprising the same - Google Patents

Abstract

The present invention provides an electrode improved so that lithium ions move to an active material smoothly, a lithium secondary battery including the same, and a method for rapidly manufacturing such an electrode. An electrode according to the present invention, a current collector; and a porous polymer structure formed on the current collector, wherein the porous polymer structure comprises a porous PVDF-HFP (vinylidene fluoride-co-hexafluoropropylene) film; and an active material and a conductive material contained in the porous PVDF-HFP film. According to the present invention, by minimizing the physical adhesion of the active material and the binder, the area where lithium ions can react with the active material is maximized.Therefore, the lithium secondary battery including such an electrode can be charged/discharged quickly performance, such as capacity conservation, can be improved.

Description

Electrode using porous polymer composite scaffold and Li battery comprising the same

The present invention relates to a lithium secondary battery and a manufacturing method thereof, and more particularly, to a lithium secondary battery having an improved electrode and a manufacturing method thereof.

As technology development and demand for mobile devices increase, the demand for secondary batteries as an energy source is rapidly increasing. Among these secondary batteries, a lithium secondary battery having a high energy density and voltage, a long cycle life, and a low self-discharge rate has been commercialized and widely used.

A typical lithium secondary battery has a positive electrode, a negative electrode, and a separator interposed therebetween, and is manufactured by being sealed in a battery case together with an electrolyte. The positive electrode and the negative electrode include an active material layer applied on a current collector. During the discharging process of a lithium secondary battery, lithium ions (Li ⁺ ) are formed by ionizing lithium stored in the negative active material. The lithium ions thus formed move through the electrolyte, enter the cathode active material, and are reduced back to lithium. In this process, as the surface area of the active material and the electrolyte increases, many reactions can be performed at once, which realizes a fast charge/discharge rate and high capacity.

Conventionally, electrodes of lithium secondary batteries are manufactured by coating a slurry in which an active material, a conductive material, and a binder are mixed in an NMP (1-Methyl-2-pyrrolidinone) solution on a current collector and then drying. The binder binds the active material and the conductive material on the current collector and is necessary to mechanically stabilize the electrode, and a polymer such as PVDF is usually used. The conductive material is added for the purpose of improving the electronic conductivity between the particles of the active material or with the current collector. In particular, it is necessary to prevent the binder region from acting as an electronic insulator and to compensate for insufficient electronic conductivity of the active material.

1 shows a conventional binding model of an active material and a binder.

Referring to FIG. 1 , the binder 10 is attached to the surface of the active material 20 like a rubber band to bind the active material 20 , and point binding as shown in (a) or surface binding as shown in (b) may be performed. When the amount of the binder 10 is excessively large, conduction inhibition occurs when a binder region is formed between the current collector 30 and the current collector 30 as in (c).

However, in the case of the electrode manufactured by the conventional slurry method, there is a problem in that the smooth movement of lithium ions to the active material is prevented through physical attachment between the binder and the active material. In addition, the NMP solution used has a high boiling point, so it has a disadvantage that the drying time is long.

The present invention was devised in recognition of the above-described problems of the prior art, and an object of the present invention is to provide an improved electrode and a lithium secondary battery including the same so that lithium ions move to an active material smoothly.

Another problem to be solved by the present invention is to provide a method for rapidly manufacturing such an electrode.

An electrode according to the present invention for solving the above technical problem, a current collector; and a porous polymer structure formed on the current collector, wherein the porous polymer structure includes a porous PVDF-HFP (Poly (vinylidene fluoride-co-hexafluoropropylene) film formed on the current collector; and in the porous PVDF-HFP film) Includes active material and conductive material included.

The active material may be Co ₃ O ₄ and the conductive material may be graphite.

The present invention also provides a lithium secondary battery comprising an electrode and a separator or a polymer electrolyte according to the present invention.

The electrode manufacturing method according to the present invention comprises the steps of preparing a mixed solution by mixing a solvent that does not dissolve PVDF-HFP and a non-solvent that does not dissolve; forming an electrode solution by adding and dissolving PVDF-HFP in the mixed solution and further mixing a conductive material and an active material; and drying the electrode solution after coating on the current collector.

Preferably, the solvent is acetone and the non-solvent is methanol.

It is preferable to mix less methanol than the acetone.

The conductive material may be graphite, and the active material may be Co ₃ O ₄ , and a weight ratio of the PVDF-HFP:active material:conductive material may be 2.0:6.4:1.6.

According to the present invention, an electrode including a porous polymer structure including an active material in a porous PVDF-HFP film is provided. The porous PVDF-HFP film can maximize the contact area between the active material and the electrolyte. In addition, the porous PVDF-HFP film minimizes the physical adhesion of the active material and the binder, so that even after the electrode is manufactured, lithium ions are directly transferred to the surface of the active material of the electrode through the electrolyte, thereby maximizing the area where lithium ions can react with the active material. Accordingly, a lithium secondary battery including such an electrode can be charged/discharged quickly and performance such as capacity preservation is improved.

According to the present invention, a porous film is formed using PVDF-HFP, and the porous PVDF-HFP film can form a support serving as a conventional binder. Such a porous film can be formed by using a mixed solution of acetone and methanol without using the high boiling point NMP solution used in the conventional slurry. Thereby, an electrode can be manufactured easily and quickly. Therefore, it is possible to reduce the manufacturing time of the electrode of the lithium secondary battery can reduce the process cost.

The following drawings attached to this specification illustrate preferred embodiments of the present invention, and together with the detailed description of the present invention serve to further understand the technical spirit of the present invention, the present invention is should not be construed as limited to
1 shows a conventional binding model of an active material and a binder.
2 is a schematic diagram of an electrode according to the present invention;
3 is a schematic diagram of a lithium secondary battery according to the present invention.
4 is a schematic diagram for comparing the electrode formed by the conventional slurry method and the electrode formed by the method according to the present invention.
5 is an image of a film in which the electrode solution formed in Experimental Example of the present invention is deposited on a copper foil using a spin coating method.
6 shows the capacity measured at a charge/discharge rate of 0.1 C-rate for electrodes formed in different ratios.
7 shows the capacity measured at a charge/discharge rate of 0.1 C-rate for the electrode according to the present invention and the electrode deposited by the conventional slurry method.

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings. The drawings introduced below are provided as examples so that the spirit of the present invention can be sufficiently conveyed. Accordingly, the present invention is not limited to the drawings presented below and may be embodied in other forms. Unless otherwise defined in technical terms and scientific terms used in this specification, it is apparent that those of ordinary skill in the art to which this invention pertains have the meaning commonly understood. In addition, in the following description and accompanying drawings, descriptions of well-known functions and configurations that may unnecessarily obscure the gist of the present invention will be omitted.

The present invention particularly relates to an electrode manufacturing process for attaching an active material to an electrode in a lithium secondary battery. Through this, it is possible to increase the amount of lithium ions generated on the surface of the active material and the electrolyte by minimizing the reduction of the surface of the active material formed by the physical attachment of the active material and the binder in the electrode. In addition, by replacing the existing NMP solution with a mixed solution of acetone and methanol, it is possible to dramatically reduce the drying time required for electrode manufacturing.

2 is a schematic diagram of an electrode according to the present invention;

2, in the electrode 100 according to the present invention, a porous PVDF-HFP (Poly (vinylidene fluoride-co-hexafluoropropylene) film 110 is formed on the current collector 130. And, the porous PVDF- The HFP film 110 includes an active material 120 and a conductive material 140. Al ₂ O ₃ , SiO ₂ , TiO _2, etc., which can improve lithium ion transport properties or improve the mechanical strength of the electrode Nanoparticles (not shown) may be further included.

The porous PVDF-HFP film 110 , the active material 120 , a conductive material, and nanoparticles that may be further included therein constitute a porous polymer structure. The porous polymer structure may be understood as a concept similar to a bulk heterojunction known in a solar cell or a light receiving device, which will be described in detail below.

When manufacturing the negative electrode, the current collector 130 may be copper. Alternatively, the current collector of the negative electrode may be a stainless steel, aluminum, nickel, titanium, copper or a stainless steel surface treated with carbon, nickel, titanium, silver, etc., and an aluminum-cadmium alloy may be used. have.

The active material 120 may vary according to the type of the secondary battery. For example, the negative active material is a carbon-based active material, and a carbon material such as crystalline carbon, amorphous carbon, carbon composite material, or carbon fiber, lithium metal, lithium alloy, or the like may be used. For example, carbon; Li _x Fe ₂ O ₃ (0≤x≤1), Li _x WO ₂ (0≤x≤1), Au _x Me _{1 - x} Me' _y O _z (Me: Mn, Fe, Pb, Ge; Me' : metal composite oxides such as Al, B, P, Si, elements of Groups 1, 2, and 3 of the periodic table, halogen; 0 < x ≤ 1; 1 ≤ y ≤ 3; 1 ≤ z ≤ 8); lithium metal; lithium alloy; silicon-based alloys; tin-based alloys; AuO, SnO ₂ , PbO, PbO ₂ , Pb ₂ O ₃ , Pb ₃ O ₄ , Sb ₂ O ₃ , Sb ₂ O ₄ , Sb ₂ O ₅ , GeO, GeO ₂ , Bi ₂ O ₃ , Bi ₂ O ₄ , and metal oxides such as _{Bi 2} O _{5 ;} conductive polymers such as polyacetylene; Li-Co-Ni-based materials; titanium oxide; Lithium titanium oxide and the like can be used. However, it should be understood that the specific examples listed above are merely examples.

The conductive material 140 is used to impart conductivity to the electrode 100, and in the battery configured, any electronic conductive material without causing chemical change can be used, for example, natural graphite or artificial graphite. graphite such as; carbon black, such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, and summer black; conductive fibers such as carbon fibers and metal fibers; metal powders such as carbon fluoride, aluminum, and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; polyphenylene derivatives; Alternatively, a conductive material including a mixture of two or more thereof may be used. It should be understood that the examples listed herein are merely exemplary.

In the case of a lithium secondary battery formed by the conventional slurry method, as shown in FIG. 1 , there is a problem in that the smooth movement of lithium ions to the active material 20 is prevented through physical attachment between the binder 10 and the active material 20 . In the electrode 100 according to the present invention, the porous PVDF-HFP film 110 serves as a binder to hold the active material 120 during electrode manufacturing, while minimizing the physical adhesion of the active material 120 and the binder to a porous medium or porous film. It can serve as a matrix or porous support. Since the physical adhesion of the active material 120 and the binder is minimized, even after the electrode 100 is formed, lithium ions are directly transferred to the surface of the active material 120 of the electrode 100 through the porous PVDF-HFP film 110 and the electrolyte. can

When the lithium secondary battery including the electrode 100 according to the present invention is driven, the porous PVDF-HFP film 110 including the active material 120 and the conductive material 140, that is, the porous polymer structure, forms a bulk heterojunction. It is similar to forming In general, bulk heterojunctions are a state in which polymer compounds that act as electron acceptors and donors are mixed in a bulk state, and since electron acceptors and electron donors form an interpenetrating network structure at intervals of about 10 to 20 nm, numerous interfaces are difficult for excitons to separate. It is located within a short distance suitable for , so it can effectively separate electrons and holes, and has a structure with countless reaction sites. In the porous polymer structure included in the electrode 100 of the present invention, since the active material 120, the conductive material 140, and PVDF-HFP are mixed in a bulk state, a large reaction surface area is formed as in the concept of a bulk heterojunction to form a lithium secondary battery can increase the performance of

A method of manufacturing such an electrode 100 is as follows.

A mixed solution is prepared by mixing a solvent capable of dissolving PVDF-HFP and a non-solvent that cannot dissolve PVDF-HFP. Preferably, a mixed solution of acetone and methanol is prepared. Acetone is a solvent and methanol is a non-solvent. The nonsolvent is mixed in a small amount compared to the solvent only enough to form a porous membrane upon vaporization. For example, mix less methanol than acetone in a mixed solution. For example, acetone : methanol in the mixed solution may be in a ratio of 5:1 Vol %. Since the ratio of acetone and methanol and the ambient temperature during film formation can determine the microstructure of the porous PVDF-HFP film 110, carefully control it.

Next, put PVDF-HPF in this mixed solution and melt it. It is not necessary to use a specific molecular weight range for the PVDF-HFP used.

Thereafter, the conductive material and the active material are further mixed to form an electrode solution. The concentration of the electrode solution may be determined in consideration of the appropriate degree for subsequent coating, the degree of easy handling, the loading amount of the active material after electrode formation, and the like according to the selected coating method, and may be, for example, 0.25 mg/ml. Al ₂ O ₃ , SiO ₂ , TiO _{2 ,} etc., may be prepared by further including nanoparticles capable of improving the transport properties of lithium ions or improving the mechanical strength of the electrode in the electrode solution.

When graphite is used as a conductive material and Co ₃ O ₄ is used as an active material, an anode can be manufactured. The weight ratio of PVDF-HFP:active material:conductive material may be selected for appropriate capacity characteristics. For example, 2.0 : 6.4 : 1.6. As the amount of PVDF-HFP increases, the electrical conductivity decreases. If the amount of PVDF-HFP is reduced, it may be difficult to expect binder properties. Increasing the amount of the active material is preferable in terms of capacity. However, there is a physical limit to increasing the amount of the active material without limitation, such as the loading density. Increasing the amount of the conductive material increases the electrical conductivity. However, if the amount of the conductive material is greatly increased, it is not preferable because the amount of the active material must be decreased by that much. The 2.0:6.4:1.6 weight ratio exemplified above is a preferable weight ratio selected in consideration of these points.

This electrode solution is coated on the current collector by a method such as application, spin coating, painting, doctor blade, die casting, comma coating, screen printing, etc. and then dried, including the active material 120 and the conductive material 140 A porous PVDF-HPF film 110 can be obtained. The method of evenly coating the electrode solution on the current collector may be selected from known methods in consideration of the characteristics of the material or may be performed by a new appropriate method. Alternatively, after molding on a separate substrate, it may be bonded to the current collector by pressing or lamination.

PVDF-HFP is soluble in acetone and insoluble in methanol. That is, for PVDF-HFP, acetone is a solvent and methanol is a non-solvent. In the present invention, using this point, a mixed solution of acetone and methanol is mixed with PVDF-HFP to form a porous film. When the mixed solution and the mixed solution of PVDF-HFP are coated and dried, pores are formed as acetone and methanol are vaporized at different rates. In the case of acetone, PVDF-HFP is dissolved and vaporized, and PVDF-HFP is formed in the form of a film. Methanol does not contain PVDF-HFP, so it vaporizes and forms only empty spaces (porous pores).

The NMP solution used in the conventional slurry method has a high boiling point, and thus has a disadvantage in that the drying time is long. According to the present invention, since a mixed solution of acetone and methanol is used instead of using an NMP solution, there is an advantage in that the drying time is fast.

3 is a schematic diagram of a lithium secondary battery according to the present invention.

The electrode 100 as shown in FIG. 2 may be implemented as a negative electrode or a positive electrode depending on the type of active material. In this embodiment, an example implemented as a cathode is shown.

In (a) of FIG. 3, the lithium secondary battery 1000 includes a negative electrode which is the electrode 100 according to the present invention, a separator 200 stacked on the negative electrode, and a positive electrode 300 stacked on the separator 200. including an electrode assembly. The electrode assembly is sealed in the battery case together with the liquid electrolyte.

The positive electrode 300 may be manufactured by another known method. According to a conventional method, a cathode active material slurry including a cathode active material, a conductive material, a binder, and a solvent may be prepared by coating, drying, and rolling the cathode current collector. However, the method according to the present invention may be prepared using only the active material as the positive electrode active material. The positive active material is, for example, a lithium-based active material, and representative examples include LiCoO ₂ , LiNiO ₂ , LiMnO ₂ , LiMn ₂ O ₄ , LiFePO ₄ or Li _{1 + z} Ni _{1 -x- y} Co _x M _y O ₂ (0≤x A metal oxide such as ≤1, 0≤y≤1, 0≤x+y≤1, 0≤z≤1, M is a metal such as Al, Sr, Mg, La, Mn) may be used. The positive electrode 300 may be made of lithium metal without a separate positive electrode current collector.

The separator 200 is not particularly limited as long as it has a porous material. Separation membrane 200 is a porous polymer membrane, such as a porous polyolefin membrane, polyvinylidene fluoride-hexafluoropropylene, polyvinylidene fluoride-trichloroethylene, polymethyl methacrylate, polyacrylonitrile, Polyvinylpyrrolidone, polyvinyl acetate, ethylene vinyl acetate copolymer, polyethylene oxide, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cyanoethyl pullulan, cyanoethyl polyvinyl alcohol, cyanoethyl cellulose , cyanoethyl sucrose, pullulan, carboxyl methyl cellulose, acrylonitrile styrene butadiene copolymer, polyimide, polyethylene terephthalate, polybutylene terephthalate, polyester, polyacetal, polyamide, polyether ether ketone, poly It may be made of ether sulfone, polyphenylene oxide, polyphenylene sulfide, polyethylene naphthalene, a non-woven fabric membrane, a membrane having a porous web structure, or a mixture thereof. Inorganic particles may be bound to one or both surfaces of the separation membrane 200 .

The electrolyte may include an organic solvent and a lithium salt as a representative electrolyte. The organic solvent is not limited as long as it can minimize decomposition due to oxidation reaction during charging and discharging of the battery and exhibit desired properties, for example, it may be a cyclic carbonate, a linear carbonate, an ester, an ether or a ketone. These may be used alone, or two or more of them may be used in combination. Among the organic solvents, a carbonate-based organic solvent may be preferably used. Examples of the cyclic carbonate include ethylene carbonate (EC), propylene carbonate (PC) and butylene carbonate (BC), and the linear carbonate includes dimethyl carbonate (DMC). ), diethyl carbonate (DEC), dipropyl carbonate (DPC), ethylmethyl carbonate (EMC), methylpropyl carbonate (MPC) and ethylpropyl carbonate (EPC) are representative. Lithium salt is LiPF ₆ , LiAsF ₆ , LiCF ₃ SO ₃ , LiN(CF ₃ SO ₂ ) ₂ , LiBF ₄ , LiBF ₆ , LiSbF ₆ , LiN(C ₂ F5SO ₂ ) ₂ , LiAlO ₄ , LiAlCl ₄ , LiSO ₃ CF ₃ and LiClO ₄ Lithium salts commonly used in the electrolyte of a lithium secondary battery may be used without limitation, and these may be used alone, or two or more kinds may be used in combination. The step of preparing such an electrolyte is not particularly limited and may be performed according to a known method.

The battery case may be a pouch made of an aluminum laminate sheet or a metal can. The step of preparing such a battery case is not particularly limited and may be performed according to a known method.

In (b) of FIG. 3 , the lithium secondary battery 1000 ′ has a negative electrode as the electrode 100 according to the present invention, a polymer electrolyte 200 ′ stacked on the negative electrode, and a positive electrode stacked on the polymer electrolyte 200 ′ ( 200 ′). 300) including an electrode assembly comprising the. The lithium secondary battery 1000 ′ can be manufactured by additionally forming a porous PDVF-HFP film on the electrode 100 according to the present invention without using the separator 200 separately. In addition, the polymer electrolyte 200' is, for example, a polyethylene derivative, a polyethylene oxide derivative, a polypropylene oxide derivative, a phosphoric acid ester polymer, poly agitation lysine, polyester sulfide, polyvinyl alcohol, polyvinylidene fluoride. , a polymerization agent containing an ionic dissociation group, etc. may be used. Of course, it is not limited only to these.

4 is a schematic diagram of an electrode formed by a conventional slurry method and an active material portion of an electrode formed by a method according to the present invention. The arrows in FIG. 4 indicate the diffusion path of lithium.

4 (a) is a conventional electrode 1, in which an active material 20' and a conductive material 40 are bound by a binder 10', and a liquid electrolyte 50 is formed between the active material 20'. contained in the interface. Due to the physical bonding between the binder 10 ′ and the active material 20 ′, the surface area of the active material 20 ′ capable of participating in the reaction decreases, indicating that the movement of lithium ions is small.

4B is an electrode 100 according to the present invention, in which an active material 120 and a conductive material 140 are included in a porous PDVF-HFP film 110 . Movement of lithium ions occurs in all surface areas of the active material 120 so that a relatively large amount of lithium ions may migrate.

In the case of a lithium secondary battery, particularly, a lithium ion secondary battery, the battery is driven by movement of lithium ions dissolved in an electrolyte between a negative electrode and a positive electrode inside the battery. Electrons are generated and annihilated through a reaction with lithium ions on the surface of the active material, and the larger the surface area of the active material, the greater the reaction amount.

Conventionally, the electrode is formed using a slurry. In the case of PVDF used as a binder included in the slurry, it adheres to the surface of the active material and inhibits the reaction, and since NMP having a high boiling point is used in manufacturing the electrode, a long drying process is used.

In contrast, the method of the present invention uses PVDF-HFP to form a porous polymer support. Direct reaction with the electrolyte occurs on the surface of the active material formed with the porous polymer support, and even when PVDF-HFP is attached to the active material on the surface of the active material, there is an advantage that the electrolyte can directly react on the surface of the active material through pores. In addition, by using a mixed solution of acetone and methanol, the drying time required for manufacturing the electrode is reduced, so that the electrode can be manufactured more easily.

Hereinafter, experimental examples including examples in which a negative electrode according to the present invention was manufactured and a lithium secondary battery was manufactured using the negative electrode and performance was tested will be described. The present invention may be more specifically described by way of experimental examples, but the examples described herein are merely illustrative of the present invention, and the present invention is not limited thereto.

Experimental example

A mixed solution obtained by mixing acetone: methanol in a ratio of 5:1 Vol % was used as a solvent. Dissolve PVDF-HPF (Sigma Aldrich, average mW ~400,000, pellets) in 0.2 g and 4 ml of solvent. Melt by rotating the magnet at a speed of 400 rpm at 40 °C for 1 hour. Then, 0.16 g of Carbon black (Graphene supermarket) is added as a conductive material and mixed at 400 rpm for 30 minutes. As an active material, 0.64 g of Cobalt(II,III) oxide (Sigma Aldrich, nanopowder, <50 nm particle size) was added and mixed at 400 rpm for one day to form an electrode solution. PVDF-HFP: Cobalt (II, III) oxide: Carbon black in Example 1 in a ratio of 6.0: 3.6: 0.4 and Example 2 in a ratio of 2.0: 6.4: 1.6 were prepared. In all cases, the concentration of the electrode solution was prepared to be 0.25 mg/ml.

Although the manufacturing process of the electrode solution was the same, a comparative example containing only an active material without a conductive material was also tested. PVDF-HFP: Comparative Example 1 prepared in a ratio of 6.0: 4.0 Cobalt (II, III) oxide, and Comparative Example 2 prepared in a ratio of 2.0: 8.0 were prepared. In all cases, the concentration of the electrode solution was prepared to be 0.25 mg/ml.

A comparative example using a conventional slurry system using PVDF as a binder was also tested. In Comparative Example 3, a slurry prepared by PVDF:Cobalt(II,III) oxide:Carbon black in a ratio of 1.0:8.9:1.0 was used.

5 is an image of a film in which the electrode solution formed in Experimental Example of the present invention is deposited on a copper foil using a spin coating method. In the left and right sides of FIG. 5 , electrodes of different composition ratios were formed to compare capacities according to films. 5, a) is Example 1, b) is Comparative Example 1, c) is Example 2, d) is according to Comparative Example 2.

6 shows the capacity measured at a charge/discharge rate of 0.1 C-rate for electrodes formed in different ratios. 6, a) is a charge and discharge curve of Example 1 and Comparative Example 1, b) is a charge and discharge curve of Example 2 and Comparative Example 2.

As a result of charging/discharging, it is confirmed that in Example 1 and Comparative Example 1, charging/discharging was not performed properly, and low charging/discharging of 200 mAh/g or less after the first discharge was confirmed. It is understood that this occurs because electrons formed after the reaction of the active material within the electrode are not well transferred to the outside of the electrode. Therefore, the content of PVDF-HFP, which is a non-conductor, is preferably reduced compared to Example 1.

In Example 2, the PVDF-HFP content is lower and the active material content is higher than in Example 1. Comparative Example 2 has no conductive material compared to Example 2. Comparing Example 2 and Comparative Example 2, the capacity of Example 2 is high, which is considered to be because electrons are easily moved and the capacity is increased depending on whether or not a conductive material is added.

It is confirmed that the highest capacity was observed in Example 2 when 64 wt% of the active material, 16 wt% of the conductive material, and 20 wt% of the binder were used. In particular, in Example 2, except for the first discharge capable of forming a solid electrolyte interface (SEI) layer, in the second cycle, it showed a capacity of 920 mAh/g, which exceeds the theoretical value of 890 mAh/g capacity of _{Co 3} O _{4 .} has been confirmed Therefore, according to the present invention, it is supported that capacity close to the theoretical value can be exhibited through the concept of bulk heterojunction, and the performance of the lithium secondary battery can be improved.

7 shows the capacity measured at a charge/discharge rate of 0.1 C-rate for the electrode according to the present invention and the electrode deposited by the conventional slurry method. PVDF-HFP: Co ₃ O ₄ : Example 2 and Comparative Example 3, which are electrodes in which the ratio of Carbon Black is 2.0: 6.4: 1.6, is shown.

Referring to FIG. 7 , it can be confirmed that the capacity is better maintained even when the cycle increases according to the present invention.

As described above, according to the present invention, when PVDF-HFP is used as an electrode material and a porous PVDF-HFP film is used as a support for the electrode, the surface area between the electrolyte and the active material can be increased to increase the lithium secondary battery performance.

In the above, the present invention has been illustrated and described with reference to specific preferred embodiments, but the present invention is not limited to the above-described embodiments, and those of ordinary skill in the art to which the invention pertains within the scope not departing from the spirit of the present invention have Various changes and modifications will be possible by the person.

100: electrode
110: porous PVDF-HFP film
120: active material
130: current collector
140: conductive material
200: separator
200': Polyelectrolyte
300: positive
1000, 1000': lithium secondary battery

Claims (3)

current collector; and
It includes a porous polymer structure formed on the current collector,
The porous polymer structure,
A mixed solution is prepared by mixing a solvent that dissolves PVDF-HFP and a non-solvent that does not dissolve, and PVDF-HFP is added to the mixed solution to dissolve, and an electrode solution formed by further mixing a conductive material and an active material is coated and dried. As that,
Porous PVDF-HFP (Poly (vinylidene fluoride-co-hexafluoropropylene) film as a porous support; and
Including the active material and the conductive material contained in the porous PVDF-HFP film,
The active material, the conductive material, and PVDF-HFP are mixed in a bulk state,
The conductive material is graphite and the active material is Co ₃ O ₄ The weight ratio of the PVDF-HFP:active material:conductive material is 2.0:6.4:1.6. A lithium secondary battery comprising the electrode of claim 1 and a separator or a polymer electrolyte. preparing a mixed solution by mixing acetone, which is a solvent for dissolving PVDF-HFP, and methanol, which is a non-solvent, which does not dissolve;
forming an electrode solution by adding and dissolving PVDF-HFP in the mixed solution and further mixing a conductive material and an active material; and
After coating the electrode solution on the current collector, comprising the step of drying,
The solvent has a lower boiling point than NMP and is vaporized to form PVDF-HFP in the form of a film, and the non-solvent forms an empty space during vaporization,
The conductive material is graphite and the active material is Co ₃ O ₄ The weight ratio of the PVDF-HFP:active material:conductive material is 2.0:6.4:1.6.

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