KR20150080745A - An electrode with enhanced electrode conductivity for electrochemical device and a method for manufacturing the same - Google Patents

Abstract

The present invention relates to an electrode for an electrochemical device and a manufacturing method thereof and, more specifically, to an electrode with improved conductivity as well as with increased density and binding strength, and a manufacturing method thereof. A binder contained in an electrode compound, an electrode active material, a particle of a conductive agent, etc., are manufactured in contact form in comparison with the conventional electrode, thus manufacturing an electrode with improved contact force and conductivity. In addition, electrode resistance is decreased with respect to the improved electrical conductivity of an electrode, and having effects in reducing swelling of an electrode during charging and discharging of a battery.

Description

TECHNICAL FIELD [0001] The present invention relates to an electrode for an electrochemical device having improved electrode conductivity and a method for manufacturing the electrode. [0002]

The present invention relates to an electrode for an electrochemical device and a method for manufacturing the same. More particularly, the present invention relates to an electrode having improved conductivity and density as well as an increased density and a binding force, and a method for producing the electrode.

2. Description of the Related Art [0002] In recent years, demand for secondary batteries which can be recharged due to the spread of portable electronic devices such as mobile phones, notebooks, and PDAs has been rapidly increasing, and the performance of secondary batteries has been gradually improved. Examples of the secondary battery include a nickel-cadmium battery, a nickel-metal hydride battery, a nickel-hydrogen battery, and a lithium secondary battery. Among them, the lithium secondary battery has a working voltage of 3.6 V or higher and is used as a power source for portable electronic devices, or several series are connected to a high-output hybrid vehicle. Compared with a nickel-cadmium battery or a nickel-metal hydride battery The operating voltage is three times higher and the energy density per unit weight is also excellent.

Electrode (anode or cathode) As a method of forming the active material layer on the current collector, the electrode active material particles, the conductive agent particles and the binder resin are dispersed in a solvent and mixed and stirred to prepare an active material slurry. Then, this is coated on both sides of the current collector, followed by drying and roll pressing, directly applying the electrode active material slurry to the current collector, and drying or by applying the electrode active material slurry to the top of another support and drying, And a film peeled off from the support is laminated on the current collector.

In order to improve the performance of the lithium ion battery, many studies have been made to improve the electrode conductivity properties by changing materials such as a cathode active material, an anode active material, a binder, and a conductive material inside the electrode. However, there are problems with the price and the manufacturing process. In the case of the electrode, charging / discharging of the battery repeatedly progresses, so that the expansion and contraction of the electrode due to the insertion and the elimination reaction of the lithium ion cause the coupling between the active material and the conductive material And the contact resistance between the particles increases. As a result, the electrode conductivity is lowered and the battery characteristics are deteriorated. In particular, the problem is expected to be even more serious in high-power hybrid electric vehicles that require fast charging and discharging, ESS applications that require frequent charge and discharge for frequency regulation and voltage maintenance.

SUMMARY OF THE INVENTION The present invention is directed to providing an electrode for an electrochemical device having improved electrode contact force and conductivity. Other objects and advantages of the present invention will become apparent from the following description. It is also to be easily understood that the objects and advantages of the present invention can be realized by the means or method described in the claims, and the combination thereof.

The present invention provides a novel electrode manufacturing method for solving the above problems. The method includes the steps of: preparing an electrode slurry including an electrode active material, a conductive material, and a polymeric binder resin; Applying the electrode slurry prepared above to a current collector; Heating the current collector coated with the slurry; Pressing the applied current collector with the heated slurry; And cooling the current collector coated with the pressurized slurry.

The method may further include drying the slurry applied to the current collector before, after, or simultaneously with the heating step.

The heating step may be performed at a temperature higher than the melting temperature of the polymeric binder resin contained in the electrode slurry.

The pressing step may be performed by a rolling roller part composed of a pair of rollers.

The pressing step may be performed under heating conditions.

The heating and pressurizing steps may be carried out simultaneously by a hot rolling method by a roller part composed of a pair of rollers.

The cooling step may be performed by a cooling roller part composed of a pair of rollers.

The cooling step may be performed at a rate of 10 DEG C / minute.

Further, the present invention provides an electrode for an electrochemical device manufactured by the above method.

The present invention also provides an electrode assembly for an electrochemical device including the electrode.

Since the binder, the electrode active material, the conductive agent particles, and the like included in the electrode mixture are manufactured in a close contact with the conventional electrode, an electrode having improved contact force and conductivity can be manufactured. Also, as the electrical conductivity of the electrode is improved, the electrode resistance is reduced and the swelling of the electrode is reduced when the battery is charged / discharged.

FIG. 1 is a view illustrating an electrode manufacturing process according to an embodiment of the present invention, in which a rolling process and a cooling process are sequentially performed.
Fig. 2 schematically shows a cross-section of an electrode according to one embodiment of the present invention. Fig. 2 (a) shows a cross-section of an electrode in a state where a rolling process is not performed, Sectional view of the electrode.
3 is a schematic process flow diagram of an electrode manufacturing process according to one embodiment of the present invention.

Hereinafter, the present invention will be described in detail. Prior to this, terms and words used in the present specification and claims should not be construed as limited to ordinary or dictionary terms, and the inventor may designate the concept of a term appropriately in order to describe its own invention in the best way possible. It should be interpreted as meaning and concept consistent with the technical idea of the present invention. Therefore, the embodiments described in this specification and the configurations shown in the drawings are merely the most preferred embodiments of the present invention and do not represent all the technical ideas of the present invention. Therefore, It is to be understood that equivalents and modifications are possible.

The present invention provides a method of manufacturing an electrode including a step of recrystallizing the polymer resin by heating / rolling / cooling the polymer binder resin contained in the electrode slurry to melt, and an electrode manufactured by the method do.

The electrode is an electrode for an electrochemical device. In one specific embodiment of the present invention, the electrochemical device includes all devices that perform an electrochemical reaction, and specific examples thereof include all kinds of primary, secondary, fuel cell, solar cell, or super- Capacitors and the like. Particularly, a lithium secondary battery including a lithium metal secondary battery, a lithium ion secondary battery, a lithium polymer secondary battery, or a lithium ion polymer secondary battery is preferable.

3 is a process flow chart schematically showing a method of manufacturing an electrode for an electrochemical device according to the present invention. Hereinafter, the electrode manufacturing method of the present invention and the electrode manufactured by the method will be described in detail with reference to FIG.

First, an electrode slurry is prepared by mixing an electrode active material, a conductive material, and a polymer binder resin (S100).

In the present specification, the electrode may be a cathode or an anode. When the electrode is a negative electrode, the negative electrode active material may include carbon such as non-graphitized carbon and graphite carbon; _{Li x Fe 2 O 3 (0} = x = 1), Li x WO 2 (0 = x = 1), Sn x Me 1 -x Me 'y O z (Me: Mn, Fe, Pb, Ge; Me' : A metal complex oxide of Al, B, P, Si, group 1, group 2, group 3 elements of the periodic table, halogen, 0? X = 1; y = 3; Lithium metal; Lithium alloy; Silicon-based alloys; Tin alloy; _{SnO, 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, Bi ₂ O ₅ and the like; Conductive polymers such as polyacetylene; Li-Co-Ni-based materials and the like can be used. However, this is only a non-limiting example of the negative electrode active material, and it is obvious that the negative electrode active material used in the present invention is not limited thereto and other types of negative electrode active materials can be selected depending on the end use purpose.

If the electrode is an anode, the cathode active material particle may be a layered compound such as lithium cobalt oxide (LiCoO ₂ ), lithium nickel oxide (LiNiO ₂ ), or a compound substituted with at least one transition metal; A lithium manganese oxide (LiMnO ₂ ) such as LiMnO ₃ , LiMn ₂ O ₃ , LiMnO _2, etc. represented by the formula Li _{1 + x} Mn _{2 - x} O ₄ (where x is 0 to 0.33); Lithium copper oxide (Li ₂ CuO ₂ ); LiV ₃ O ₈ , LiFe ₃ O ₄ , V ₂ O ₅ , Cu ₂ V ₂ O ₇ Vanadium oxide; Nickel type lithium nickel oxide represented by the formula LiNi _{1 - x} M _x O ₂ (where M = Co, Mn, Al, Cu, Fe, Mg, B or Ga and x = 0.01 to 0.3) oxide); Formula _{LiMn 2 - x M x O 2} ( where, M = Co, Ni, Fe , Cr, and Zn, or Ta, x = 0.01 to 0.1 Im) or Li ₂ Mn ₃ MO ₈ (where, M = Fe, Co, Ni, Cu, or Zn); LiMn ₂ O _{4 in} which part of the lithium in the formula is substituted with an alkaline earth metal ion; Disulfide compounds; Fe ₂ (MoO ₄ ) _3, or a composite oxide formed by a combination of these materials, and the like. However, this is only a non-limiting example of the cathode active material, and it is obvious that the cathode active material used in the present invention is not limited thereto and other kinds of cathode active materials can be selected depending on the end use purpose.

The binder is a component which assists in bonding of the electrode active material particles and the conductive material to the current collector, for example, about 1 to about 50 wt% based on the total weight of the electrode slurry. Examples of such binders include polyvinylidene fluoride, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene , Polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene butylene rubber, fluorine rubber, various copolymers and the like.

The electrode slurry includes a conductive material. The conductive material is added, for example, at about 1 to about 50 weight percent based on 100 weight percent of the electrode slurry. Such a conductive material is not particularly limited as long as it has high conductivity without causing chemical changes in the battery, and examples thereof include graphite such as natural graphite and artificial graphite; Carbon black such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, and summer black; Conductive fibers such as carbon fiber and metal fiber; Metal powders such as carbon fluoride, aluminum, and nickel powder; Conductive whiskey such as zinc oxide and potassium titanate; Conductive oxides such as titanium oxide; Conductive materials such as polyphenylene derivatives and the like can be used.

The electrode slurry can be produced by dispersing an electrode active material, a polymer resin binder, and a conductive material in a suitable solvent. Specifically, a binder suitable for a predetermined electrode is put into a solvent and is dissolved to produce a binder solution. Then, the electrode active material particles and the conductive material for the desired electrode are added to the resulting binder solution to form a mixture. The mixture is further mixed with the binder active material particles by a method such as stirring using a mixer, And finally dispersed uniformly in a solution to prepare a slurry for the electrode.

Non-limiting examples of the solvent include acetone, tetrahydrofuran, methylene chloride, chloroform, dimethylformamide, N-methyl-2-pyrrolidone (N -methyl-2-pyrrolidone, NMP), cyclohexane, water, or a mixture thereof. These solvents provide an appropriate level of viscosity so that a slurry coating layer can be formed at a desired level on the current collector surface.

On the other hand, the negative electrode is manufactured by applying and drying negative electrode active material particles on a negative electrode current collector, and may further include components such as the above-described conductive material, binder, solvent and the like, if necessary. If necessary, the slurry may further contain other additives such as a thickener.

Next, the electrode slurry prepared above is applied on the current collector (S200).

The electrode slurry prepared above is applied to at least one surface of the selected current collector to form a slurry layer. The application of the slurry can be carried out continuously or discontinuously by various methods such as slot die coating, slide coating, curtain coating and the like. Particularly, in terms of productivity, it is preferable that the application is carried out continuously or simultaneously at the same time. For example, a die having one or more slots may be used to perform the application of the slurry. That is, the slurry is supplied through the slot of the die, and the corresponding current collector corresponding to the slurry is supplied to the rotating roller. A slurry layer is formed by applying a slurry corresponding to one side or both sides of the current collector progressed by these rollers.

The cathode current collector has a thickness of, for example, about 3 to about 500 mu m. The negative electrode current collector is not particularly limited as long as it has conductivity without causing a chemical change in the battery, and examples thereof include copper, stainless steel, aluminum, nickel, titanium, sintered carbon, copper or stainless steel Surface-treated with carbon, nickel, titanium, silver or the like, aluminum-cadmium alloy, or the like can be used. In addition, like the positive electrode current collector, fine unevenness may be formed on the surface to enhance the binding force of the negative electrode active material particles, and it may be used in various forms such as films, sheets, foils, nets, porous bodies, foams and nonwoven fabrics.

The cathode current collector has a thickness of, for example, about 3 to about 500 mu m. Such a positive electrode current collector is not particularly limited as long as it has electrical conductivity without causing chemical changes in the battery. For example, the positive electrode current collector may be formed on the surface of stainless steel, aluminum, nickel, titanium, sintered carbon or aluminum or stainless steel Carbon, nickel, titanium, silver, or the like may be used. The current collector may have fine irregularities on the surface thereof to increase the adhesive force of the cathode active material, and various forms such as a film, a sheet, a foil, a net, a porous body, a foam, and a nonwoven fabric are possible.

In the manufacturing method according to one aspect of the present invention, the electrode active material (i.e., the positive electrode active material and the negative electrode active material) (or particles thereof) and the current collector (i.e., the positive electrode current collector and the negative electrode current collector) And they can be prepared according to a conventional method known in the art or a modified method thereof.

Next, the current collector coated with the slurry is heated (S300). According to a specific embodiment of the present invention, the heating step is performed at a temperature equal to or higher than the melting temperature of the polymeric binder resin contained in the electrode slurry. Preferably, the heating step is controlled so that the melting temperature of the polymeric binder resin + 20 DEG C or less. If the heating step is performed at an excessively high temperature, problems such as electrode damage and contamination of the roll press apparatus due to the binder may occur.

1 schematically shows a heating, rolling and cooling process as a part of the electrode manufacturing method according to a specific embodiment of the present invention. The heating step may be performed by passing through a heating unit having external heating means as shown in FIG. The external heating means or the heating portion may further include a temperature control device (not shown) so that the applied heating temperature is maintained near the binder melting temperature. According to another embodiment, the heating step may allow the electrode to be run through a set of heating rollers. Here, the heating roller may be integrated with the heating member so as to have a heating member at the inner center of the roller, for example. The heating step is carried out for a time sufficient for the polymeric binder resin to melt at 90% or more, preferably all. The heating time at this stage may vary depending on the polymer resin used and the temperature conditions of the electrode.

Next, the heated slurry-applied current collector is rolled (S400). According to a specific embodiment of the present invention, the rolling step may be performed by a rolling roller composed of a pair of rollers. As the rolling step is performed, the electrode active material in the electrode and the conductive material particles are closely adhered to each other and densely distributed. As the particles are narrowed, the size of the voids distributed between the mouths is reduced. However, the polymer binder resin melts in the heating step, and the viscosity is lowered to penetrate into the voids, thereby increasing the adhesion between the particles.

According to a specific embodiment of the present invention, the heating step and the rolling step may be simultaneously performed in a hot rolling manner by a rolling roller having a heating member.

Next, the current collector coated with the rolled slurry is cooled (S500). The cooling may be performed by an externally installed cooler. According to another embodiment, the cooling step may be carried out by a cooling roller composed of a set. According to the present invention, the cooling is carried out at a rate of 10 캜 / min, preferably at a rate of 5 캜 / min until the temperature reaches the room temperature.

Figure 2 schematically shows the shape of the electrode before and after the heating / rolling / cooling step is performed. The polymer binder resin in the electrode slurry is not uniformly distributed between the active material and / or the conductive material before the heating / rolling / cooling step is performed and the electrode active material 1, the polymer binder resin 2 and the conductive material 3 are in close contact with each other It is not. On the contrary, after the heating / rolling / cooling step is performed, the polymer binder resin penetrates into the particles, and the active material particles and the conductive material closely adhere to each other and are distributed in a compact state.

The electrode manufactured by the above-described method according to the present invention can be moved and distributed to a fine space of several micrometers in size such as a gap formed between the electrode active material and / or conductive material particles by the polymer binder resin melted by heating, Is increased. Thus, the distance between the active material and / or the conductive material is shortened to form a dense structure, so that the expansion phenomenon of the electrode can be remarkably reduced upon charge / discharge of the battery. Further, since the contact area between the current collector and the binder is increased, the binding force between the electrode mixture and the current collector is improved. On the other hand, since conductive particles are more densely distributed in the electrode, the distance between the particles is shortened, so that the movement speed of the electrons is increased, thereby improving the electric conductivity and resistance characteristics. In addition, the polymer binder resin is recrystallized by the heating and cooling. Through the recrystallization, the physical and / or chemical properties of the polymer binder resin may be changed to produce an electrode having improved battery characteristics.

According to a specific embodiment of the present invention, the step of removing the solvent included in the electrode slurry may be further performed before or after the heating step (S600). The at least one slurry layer applied over the current collector is dried simultaneously or separately with the heating step by using a drier or the like to remove the solvent. Specifically, when it is passed through a dryer or the like, it is affected by heat or hot air, so that the solvent or moisture will be removed by drying in succession from the part directly contacting with heat or hot air to the inside or the opposite part.

A secondary battery such as an electrochemical device such as a lithium secondary battery is manufactured by winding or laminating the electrodes of different kinds manufactured according to the manufacturing method of the present invention described above, that is, the positive electrode and the negative electrode with a separator interposed therebetween .

As the porous substrate of the separator for insulating the electrodes between the anode and the cathode, any porous substrate used for electrochemical devices such as a porous membrane or nonwoven fabric formed of various polymers can be used. For example, a polyolefin porous film used as a separator for an electrochemical device, particularly, a lithium secondary battery, or a nonwoven fabric made of polyethylene terephthalate fiber may be used. The material and the shape may be variously selected depending on the purpose. For example, the polyolefin-based porous membrane may be formed of a polymer such as polyethylene, polypropylene, polybutylene, or polypentene, such as high-density polyethylene, linear low-density polyethylene, low-density polyethylene, ultra-high molecular weight polyethylene, And the nonwoven fabric may also be made of a polyolefin-based polymer or a fiber using a polymer having higher heat resistance. The thickness of the porous substrate is not particularly limited, but is preferably about 1 to about 100 mu m, more preferably about 5 to about 50 mu m, and the pore size and porosity existing in the porous substrate are also not particularly limited, To about 50 [mu] m and from about 10 to about 95%.

The electrolytic solution which can be used in the electrochemical device of the present invention is a salt having a structure such as A ⁺ B ^- , wherein A ⁺ includes an alkali metal cation such as Li ⁺ , Na ⁺ , K ^{+ -} it is _{^{PF 6 -, BF 4 -,}} Cl -, Br -, I -, ClO 4 -, AsF 6 -, CH 3 CO 2 -, CF 3 SO 3 -, N (CF 3 SO 2) 2 -, C (CF ₂ SO _{2) 3} ^- anion, or a salt containing an ion composed of a combination of propylene carbonate (PC) such as, ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl (DMP), dimethyl sulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, tetrahydrofuran, N-methyl-2-pyrrolidone (NMP), ethylmethyl carbonate (EMC), gamma butyrolactone -Butyrolactone), or a mixture thereof, but the present invention is not limited thereto.

The electrolyte may be injected at an appropriate stage of the battery manufacturing process, depending on the manufacturing process and required properties of the final product. That is, it can be applied before assembling the cell or at the final stage of assembling the cell.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not to be limited to the details thereof and that various changes and modifications will be apparent to those skilled in the art. And various modifications and variations are possible within the scope of the appended claims.

Example

LiCoO ₂ as a cathode active material, polyvinylidene fluoride (PVDF) as a binder and carbon as a conductive agent were mixed at a weight ratio of 92: 4: 4, and then dispersed in N-methyl-2-pyrrolidone to prepare a cathode slurry Respectively. This slurry was coated on an aluminum foil having a thickness of 20 탆 and dried. Next, it was heated at 160 ° C for 10 minutes and then rolled. Thereafter, it was cooled to 25 DEG C at a rate of 10 DEG C / minute to prepare a positive electrode. Styrene-butadiene rubber as a binder and carboxymethylcellulose as a thickener were mixed in a weight ratio of 96: 2: 2 and then dispersed in water to prepare a negative electrode active material slurry. This slurry was coated on a copper foil having a thickness of 15 mu m and then dried. Next, it was heated at 125 ° C for 10 minutes and then rolled. Thereafter, it was cooled to 25 DEG C at a rate of 10 DEG C / minute to prepare a negative electrode. The separator was interposed between the electrodes thus prepared, and was wound and compressed to be inserted into a cylindrical can. At this time, the separation membrane is formed by sequentially laminating a porous membrane layer and an ion conductive glass formed by bonding of a ceramic material and a binder on a negative electrode active material layer, respectively. An electrolyte was injected into the cylindrical can to prepare a lithium secondary battery.

Comparative Example

LiCoO ₂ as a cathode active material, polyvinylidene fluoride (PVDF) as a binder and carbon as a conductive agent were mixed at a weight ratio of 92: 4: 4, and then dispersed in N-methyl-2-pyrrolidone to prepare a cathode slurry Respectively. This slurry was coated on an aluminum foil having a thickness of 20 mu m, followed by drying and rolling to prepare a positive electrode. Styrene-butadiene rubber as a binder and carboxymethylcellulose as a thickener were mixed in a weight ratio of 96: 2: 2 and then dispersed in water to prepare a negative electrode active material slurry. This slurry was coated on a copper foil having a thickness of 15 mu m, followed by drying and rolling to prepare a negative electrode. The separator was interposed between the electrodes thus prepared, and was wound and compressed to be inserted into a cylindrical can. At this time, the separation membrane is formed by sequentially laminating a porous membrane layer and an ion conductive glass formed by bonding of a ceramic material and a binder on a negative electrode active material layer, respectively. An electrolyte was injected into the cylindrical can to prepare a lithium secondary battery.

Claims (10)

(S100) preparing an electrode slurry including an electrode active material, a conductive material, and a polymeric binder resin;
(S200) applying the electrode slurry to the current collector;
(S300) heating the current collector coated with the slurry;
(S400) pressurizing the current collector to which the heated slurry is applied; And
(S500) cooling the current collector coated with the pressurized slurry;
And an electrode for electrochemical device.
The method according to claim 1,
The method for manufacturing an electrode for an electrochemical device according to claim 1, further comprising a step (S600) of drying the slurry applied to the current collector before, after or after the step (S300).
The method according to claim 1,
Wherein the step (S300) is performed at a temperature higher than the melting temperature of the polymeric binder resin contained in the electrode slurry.
The method according to claim 1,
Wherein the step (S400) is carried out by a rolling roller part composed of a pair of rollers.
5. The method of claim 4,
Wherein the step (S400) is performed under heating conditions.
The method according to claim 1,
Wherein the steps (S300) and (S400) are simultaneously performed in a hot rolling manner by a roller part composed of a pair of rollers.
The method according to claim 1,
Wherein the step (S500) is carried out by a cooling roller part composed of a pair of rollers.
The method according to claim 1,
Wherein cooling in the step (S500) is performed at a rate of 10 DEG C / minute.
An electrode for an electrochemical device produced by the method according to any one of claims 1 to 8.
An electrode assembly for an electrochemical device, comprising the electrode according to claim 9.

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