KR101198672B1 - Method for synthesizing electrode for secondary cell, electrode synthesized by the method, and secondary cell comprising the electrode - Google Patents

Abstract

The present invention relates to a secondary battery, while using a conventional electrode constituent material as it is, while reducing the amount of the binder and reducing the amount of the active material and increasing the content of the active material without inhibiting the stability of the electrode, that is, binding and adhesion It is related with the method which can manufacture a battery electrode. In the present invention, it is possible to increase the content of the electrode active material and to increase the energy by only a partial change and addition of the conventional process, and to improve the electrode and battery performance by reducing the content of the binder that inhibits the electrical conductivity. . In addition, in the phase inversion step, solvent extraction, phase separation of the polymer binder and the nonsolvent occurs, and after the nonsolvent is removed in the drying process, voids are formed at the nonsolvent site, so that the effect of the binder content is reduced as well. The effect of improving the porosity of the plate or obtaining a more effective porous structure can also be expected.

Description

A method for manufacturing a secondary battery electrode, a secondary battery electrode produced thereby, and a secondary battery comprising the same {Method for synthesizing electrode for secondary cell, electrode synthesized by the method, and secondary cell comprising the electrode}

The present invention relates to a secondary battery, and more particularly, to a method for manufacturing a secondary battery electrode having excellent performance by reducing the amount of binder and increasing the content of the active material without impairing the stability of the electrode. will be.

In response to the rapid development of the communication industry such as the electronics industry and various information and communication including mobile communication, in response to the demand for thin and short electronic devices, notebooks, netbooks, tablet PCs, mobile phones, smartphones, PDAs, digital cameras, camcorders, etc. BACKGROUND ART Portable electronic products and communication terminals have been widely used. Accordingly, interest in development of batteries which are driving power sources for these devices has been increasing.

In addition, according to the development of electric vehicles such as pure electric vehicles, hybrid vehicles, fuel cell vehicles, a great deal of attention is focused on the development of high performance, large capacity, high density, high output, high stability, and a battery having a fast charge and discharge characteristics Development is also a big issue.

Batteries, a device that converts chemical energy into electrical energy, are classified into primary cells, secondary batteries, fuel cells, and solar cells, depending on the types and characteristics of basic materials.

Among them, primary batteries produce energy through irreversible reactions such as manganese batteries, alkaline batteries, and mercury batteries, and thus have a disadvantage in that they have a large capacity but are not recycled, and thus have various problems such as energy inefficiency and environmental pollution.

Secondary batteries include lead-acid batteries, nickel-metal hydride batteries, nickel-cadmium batteries, lithium-ion batteries, lithium polymer batteries, and lithium metal batteries, and the charging and discharging are repeated using a reversible interconversion between chemical and electrical energy. As a chemical battery that can be, it operates by a reversible reaction has the advantages of recycling and environmentally friendly.

The secondary battery has four basic components: a positive electrode, a negative electrode, a separator, and an electrolyte.

The anode and the cathode are electrodes in which energy is converted and stored, such as oxidation / reduction, and have positive and negative potentials, respectively. The separator is positioned between the positive electrode and the negative electrode to maintain electrical insulation and provide a path for charge movement. The electrolyte also serves as a medium for charge transfer.

Among the constituent materials of the respective electrodes, a material that actually causes a reaction is called an active material, and the constituent material of the electrode and the constituent material of the secondary battery will be described as examples of the lithium secondary battery.

Most of the positive electrode active material is a material capable of intercalating lithium ions, and lithium cobalt oxide (Li _x CoO ₂ ), lithium nickel oxide (Li _x NiO ₂ ), lithium nickel cobalt oxide (Li _x (NiCo) O ₂ ), Oxides such as lithium nickel cobalt manganese oxide (Li _x (NiCoMn) O ₂ ), spinel-type lithium manganese oxide (Li _x Mn ₂ O ₄ ), manganese dioxide (MnO ₂ ), or lithium iron phosphate (Li _x FePO ₄ ), lithium Olivine type, such as manganese phosphate (Li _x MnPO ₄ ), NASICON type phosphates, silicates (silicates), sulfates (sulfates), or polymer materials may be used.

As the negative electrode active material, a lithium metal, an alloy thereof, or a compound in which lithium ions may be intercalated may be used. A polymer material or a carbon material may be used, and a graphite or egg such as artificial or natural graphite may be used. (I) non-graphitizable carbon, hard-carbon, or graphitizable carbon (soft-carbon), carbon nanotube (CNT), carbon nanofiber (carbon nanofiber) , CNF), carbon nanowall (carbon nanowall, CNW) and the like can be used.

Separation membranes are generally porous polymer membranes such as polyolefin-based, polyester-based, and natural polymers such as pulp, cellulose, and cork, such as polyethylene and polypropylene. Alternatively, a nonwoven form may be used, and a structure of a single layer film or a multi layer film may be preferably used.

Alternatively, a thermoplastic polyolefin polymer porous multilayer membrane (T _m 100 to 150 ° C.) such as polyethylene or polypropylene, or a high molecular weight to ultra high molecular weight thermoplastic heat resistant polyolefin polymer porous membrane (T _m 150 to 200 ° C.) may be more preferably used.

The introduction of a liquid electrolyte composed of an organic solvent and a salt may provide a movement path for ions moving between the positive electrode and the negative electrode during the charge and discharge of the battery.

The organic solvent can be used to increase the polarity of the electrolyte to improve the dissociation of the ions, and to facilitate the conduction of the ions by lowering the local viscosity around the ions.

Examples of organic solvents include ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, gamma-butyrolactone, Dimethylsulfoxide, sulforane, ethyl acetate, 1,3-dioxane, tetrahydrofuran, 2-methyltetrahydrofuran (2- methyltetrahydrofuran, N, N-dimethylformamide, diglyme, triglyme, tetraglyme and the like. In particular, it is preferable to use two or more mixed solutions composed of a high viscosity solvent and a low viscosity solvent as the organic solvent.

Lithium salts preferably have a small dissociation degree due to their lattice energy. LiClO ₄ , LiBF ₄ , LiPF ₆ , LiAsF ₆ , LiCF ₃ SO ₃ , LiC (CF ₃ SO ₂ ) ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiSCN and the like can be used more preferably, and optional mixtures thereof can also be used.

Conventionally known electrode manufacturing processes generally proceed in five steps: material weighing, mixing, coating, drying, pressing, and the like.

Material metering is a step of measuring the electrode constituent material including the active material and the binder according to a predetermined composition ratio, mixing is a step of dissolving, dispersing and kneading by introducing the electrode constituent material in a certain order. In general, after the mixing process is completed in the form of a slurry (slurry) to be put into the coating process. That is, the mixed slurry (electrode slurry, i.e., negative electrode slurry, positive electrode slurry) is composed of an electrode component and a dispersion medium, and the electrode component is composed of the above-described active material, conductive material, binder, and other additives.

The conducting agent is a material for improving the electrical conductivity of the electrode. Specific surface area such as graphite, carbon black, activated carbon, carbon nanotubes and carbon nanofibers, electrical conductivity, and liquid electrolyte absorption This excellent carbon system can be preferably used.

A binder is a material for improving binding force between electrode constituent materials such as an electrode active material and a conductive material and adhesion between the electrode constituent material and the electrode current collector, and a polymer may be used, and a vinylidene fluoride-based, Vinyl chloride series, vinyl alcohol series, acrylate series, ether series, acrylonitrile series, imide series, rubber series, siloxane ( siloxane series, silicone polymer, and the like may be preferably used.

The dispersion medium is a material capable of dissolving or dispersing the above-described binders, and includes pyrolidinone-based, furan-based, amide-based, nitrile-based, ketone-based, and alcohol ( alcohol series, water, etc. may be used.

The mixing step is a process of dissolving, dispersing, and kneading the electrode constituent material, and dryly mixing the powdery electrode constituent material, that is, the active material, the conductive material, the polymer binder, and the like in a closed container, and then using a solvent or a dispersion medium of the polymer binder. Dissolved in and dispersed.

In order to facilitate the dissolution of the polymer binder and to prevent the electrode components from agglomerating with each other, stirring using a magnetic stirrer, a mechanical stirrer, a planetary mixer, an ultrasonic agitator, and the like is performed. You may.

The coating and drying step is a step of coating the slurry obtained by mixing the above materials on the electrode current collector and drying to obtain an electrode consisting of only solid content, in the coating step it is preferable to use a method that can be produced in the form of a film, comma method, slit-die method, gravure method, doctor blade method, silk screen method, offset method, spray method, dip method ) May be used.

The drying step is a step of removing the dispersion medium by volatilization, hot air method, direct heating method, induction heating method and the like can be used.

A current collector is a component that collects electrons obtained from an oxidation / reduction reaction of an active material and flows to an external conductive line, and includes a metal foil, a foam, a grid, and an expanded metal ( expanded metal) and the like, and an anode in the case of an anode, and an aluminum or copper current collector in the case of a cathode may be preferably used.

Rolling step is to adjust the thickness, surface condition, density, binding force, adhesive strength, etc. to a desired level by pressing the electrode in a completely dry or semi-dry state obtained by applying and drying to a certain thickness and pressure, plate Method, roll method can be used, cold or hot roll method can be used more preferably.

As described above, the electrode is finally completed through the material metering, mixing, coating, drying, and rolling steps.

In the case of the conventional electrode manufacturing, in particular the negative electrode manufacturing, the composition and the content ratio of about 90% by weight of the negative electrode active material, about 5 to 10% by weight of the binder, and other constituent materials, etc., the content of the negative electrode active material is increased in capacity and energy It is more preferable because it is directly connected, and the binder is less preferable because it may interfere with the material or electrical conductivity necessary for the stability of the electrode, that is, the binding force, the adhesion.

Since the negative electrode active material and other constituent materials have a tradeoff relationship, the lower the content of the binder and the higher the content of the negative electrode active material, the better the electrical performance. In this case, since the role of the binder, that is, the binding force between the electrode components and the adhesion between the electrode components and the electrode current collector may be lowered, adjustment is made at an appropriate level.

For this reason, the binder content is generally set at 5 to 10% by weight based on the total weight, but in order to obtain higher energy and performance, there is a demand to reduce the content of the binder as much as possible without impairing the binding force and the adhesive force. It is true.

Accordingly, the present invention has been invented in view of the above, and while using a conventional electrode component as it is, while reducing the amount of the binder that inhibits the performance, such as electrical conductivity without impairing the stability of the electrode, that is, binding and adhesion It is an object of the present invention to provide a method for manufacturing a secondary battery electrode having excellent performance by allowing the content of the active material to be increased.

In order to achieve the above object, the present invention comprises the steps of dissolving, dispersing and mixing an electrode component material containing an active material and a polymer binder in a solvent of the polymer binder to prepare a mixed slurry; Applying the mixed slurry to an electrode current collector in the form of a film; The electrode current collector to which the mixed slurry is applied is immersed in a non-solvent that does not dissolve the polymer binder, thereby changing the composition of the mixed slurry due to the exchange of the solvent and the non-solvent of the polymer binder and the mutual diffusion of the solvent and the non-solvent. Causing a phase inversion to cause solidification of the polymer including the liquid-liquid phase separation phenomenon while causing a; Drying the combination of the electrode layer and the electrode current collector formed from the mixed slurry after the phase inversion in a drying furnace; It provides a method for producing a secondary battery electrode comprising a; after the drying and rolling the electrode layer having pores to complete the electrode laminated on the electrode current collector.

Here, the solvent of the polymer binder is N-methylpyrrolidinone (N-methylpyrolidinone), dimethylformamide (dimethylformamide), dimethylacetamide, hexamethylphosphoramide (hexamethylphosphoramide), acetonitrile (acetonitrile), acetone one or two selected from the group consisting of (acetone), cyclohexanone, dimethylsulfoxide, tetrahydrofuran, dioxane, chloroform, chloroform, dichloromethane and water It is characterized by the above mixture.

In addition, the non-solvent is N-methylpyrrolidinone, water, ethanol (ethanol), propanol, butanol, butanol, pentanol, hexanol, ethylene glycol, glycerol ), Acetone, dimethylether (dimethylether), diethylether (diethylether), ethyl acetate (ethylacetate) and dichloromethane is characterized in that one or two or more mixtures selected from the group consisting of.

In addition, the active material is a negative electrode active material, characterized in that to produce a negative electrode for secondary batteries by sequentially performing the above steps using the negative electrode active material.

In addition, the active material is a positive electrode active material, it characterized in that the production of a positive electrode for a secondary battery by sequentially performing each step using the positive electrode active material.

In addition, the time to be immersed in the non-solvent is 1 minute to 1 hour, characterized in that the temperature at this time is maintained at 10 ℃ to 70 ℃.

In addition, the drying step is characterized in that the drying at 50 ℃ ~ 200 ℃ so that the non-solvent in the electrode layer exchanged with the solvent of the polymer binder is completely removed.

In addition, the present invention includes a secondary battery electrode manufactured by the above-described manufacturing method, and further includes a secondary battery having a secondary battery electrode manufactured by the above-described manufacturing method.

Accordingly, in the electrode and manufacturing method for a secondary battery according to the present invention, by applying a more improved coating process using a mixing and coating process, in particular a phase inversion method based on solvent-non-solvent interaction, the amount of binder active material instead of reducing the amount of binder active material The content of can be significantly increased.

In the conventional case, in the preparation of the negative electrode, about 90 wt% of the negative electrode active material, 5 to 10 wt% of the binder, and the composition and content ratio of other constituent materials could be prepared, but in the present invention, 95 to 98 wt% of the negative electrode active material, and the binder Since it can manufacture using 2 to 4 weight%, it becomes possible to significantly increase content of a negative electrode active material.

That is, only a partial change and addition of the conventional process may increase the content of the electrode active material and increase energy. In addition, by reducing the amount of the binder that inhibits the electrical conductivity, it is possible to expect additional advantages such as improvement of electrode and battery performance.

In addition, even if the content of the binder is significantly reduced, it is possible to maintain the structural stability of the electrode, that is, the binding force and the adhesive force, by the process of modification and addition according to the present invention.

In addition, in the phase inversion step, solvent extraction, phase separation of the polymer binder and the nonsolvent occurs, and after the nonsolvent is removed in the drying process, voids are formed at the nonsolvent site, so that the effect of the binder content is reduced as well. Compared with the prior art, the porosity of the electrode plate may be improved or an effect of obtaining a more effective porous structure may be expected.

1 is a schematic diagram illustrating a manufacturing process of an electrode, (a) shows a process according to the prior art, and (b) shows a process according to an embodiment of the present invention.
2 is a schematic view of a secondary battery using the electrode according to the present invention, a cross-sectional view showing a structure in which a negative electrode and a negative electrode current collector, a separator, a positive electrode and a positive electrode current collector are stacked.
Figure 3 is a SEM photograph of the negative electrode, (a) is a negative electrode of the embodiment according to the present invention, (b) shows a negative electrode of the comparative example according to the prior art.
4 is a view showing the results of the capacity retention and life characteristics test according to the charge-discharge iteration for the secondary battery using the negative electrode of Example 1 and Example 2 and the comparative example according to the prior art according to the present invention.
5 is a view showing the results of the capacity expression experiment according to the discharge current applied value for the secondary battery using the negative electrode of Example 1 and Example 2 according to the present invention and the comparative example according to the prior art.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings, which will be readily apparent to those skilled in the art to which the present invention pertains.

The present invention relates to a method for manufacturing a secondary battery electrode that can reduce the content of the binder without impairing the stability of the electrode, that is, binding and adhesion while using the conventional electrode constituent material, in particular by improving the mixing and coating process The present invention relates to a method for manufacturing a secondary battery electrode to solve the problems.

Such a manufacturing method of the present invention can be applied to both manufacturing a negative electrode and a positive electrode for a secondary battery, and to prepare a negative electrode for a secondary battery, a negative electrode active material, a conductive material, a binder and other additives are required as in the prior art, and in addition to the preparation of a negative electrode slurry There is a need for a dispersion medium and a negative electrode current collector.

In the manufacturing process, the electrode is finally completed through the steps of material metering, mixing, and application of a slurry (cathode slurry and cathode slurry), drying, and rolling as in the prior art.

However, in order to reduce the content of the binder and to increase the content of the active material while maintaining the composition of the conventional electrode components, some modifications or additions to the existing processes are required. A more advanced application process using a phase inversion method is used.

In the present invention as described above, there are various advantages in that the amount of the active material can be greatly increased instead of greatly reducing the content of the binder in preparing the electrode.

Hereinafter, the manufacturing process of the present invention will be described in more detail with reference to the negative electrode.

In the process of manufacturing the negative electrode according to the present invention, the electrode constituent material is composed of a negative electrode active material, a conductive material, a binder, and other additives. After mixing with and applied to the negative electrode current collector (electrode current collector, in the case of a positive electrode current collector), the electrode is finally completed through the drying and rolling steps.

The phase inversion method can be used in this process. Preferably, a negative electrode slurry is prepared by dissolving, dispersing, and mixing a negative electrode active material, a conductive material, a polymer binder, and other additives in a solvent of the polymer binder, and applying the negative electrode slurry to a negative electrode current collector in the form of a film, followed by A wet process can be used in which the solvent of the binder is exchanged with a non-solvent that does not dissolve the polymer binder.

Alternatively, the negative electrode slurry may be prepared by dispersing a negative electrode active material, a conductive material, a polymer binder, and other additives in a mixture of a volatile solvent that dissolves the polymer binder, a nonvolatile non-solvent that does not dissolve the polymer binder, and a pore former. Then, the negative electrode slurry may be applied to the negative electrode current collector in the form of a film, and then a dry process may be used in which the solvent and the nonsolvent are dried to completely remove the negative electrode slurry.

That is, a wet method for applying a negative electrode slurry to the microporous microporous polymer matrix in a drying step, or a dry method for adding a non-solvent and a pore-forming agent capable of introducing porosity into the negative electrode slurry before casting the polymer membrane.

The phase inversion method can induce the solidification of a polymer by the exchange of a solvent and a non-solvent. The polymer material is dissolved in an appropriate solvent to prepare a uniform solution, and the polymer solution is immersed in the non-solvent. The non-solvent cross-diffusion leads to a change in the composition of the polymer solution, which leads to solidification of the polymer including a liquid-liquid phase separation phenomenon. As a result, a part of the portion occupied by the solvent and the non-solvent is formed into pores to form a membrane. Shape.

Accordingly, when the mixing and coating processes are carried out using a phase inversion method using a non-solvent in which a polymer binder is not dissolved in the preparation of the negative electrode, porosity can be improved, and crystallinity of the polymer binder is suppressed to disperse and bond. It is possible to increase the properties and binding properties, while maintaining the stability of the electrode while increasing the content of the polymer binder can be improved performance.

Any material may be used as the negative electrode active material as long as it is a material commonly used in secondary batteries, particularly lithium secondary batteries, for the same purpose. Lithium metal, alloys thereof, or compounds in which lithium ions may be intercalated may be used, and polymer materials or carbon materials may be used. Preferably, graphite-based, such as artificial or natural graphite, non-graphitizable carbon (hard-carbon), or graphitizable carbon (soft-carbon), Carbon systems such as carbon nanotubes (CNT), carbon nanofibers (CNF), carbon nanowalls (carbon nanowall, CNW), and the like may be used.

The conductive material may be any material commonly used for secondary batteries, particularly lithium secondary batteries, for the same purpose. Carbon-based materials such as graphite, carbon black, activated carbon, carbon nanotubes, and carbon nanofibers are preferred. It may not be added.

Almost all ordinary polymers can be used as the polymer binder, including polyvinylidene fluoride, a copolymer of polyvinylidene fluoride and hexafluoropropylene, vinylidene fluoride and hexafluoro Copolymers of low-propylene, copolymers of vinylidene fluoride and maleic anhydride, polyvinylchloride, polyvinylalcohol, polyvinyl formal, polymethylmethacrylate (polymethylmethacrylate), polymethacrylate, tetra (ethylene glycol) diacrylate, cellulose triacetate, polyurethane, polysulfone, polyether polyolefins such as polyether, polyethylene and polypropylene, Lithium oxide, polyisobutylene, polybutyldiene, polyacrylonitrile, polyimide, acrylonitrile-butadiene rubber, styrene-butadiene One or more mixtures or copolymers thereof selected from the group consisting of styrene-butadiene rubber, ethylene-propylene-diene monomer, polydimethylsiloxane, and polysilicone Is preferred.

The solvent for the polymer binder may be N-methylpyrolidinone, dimethylformamide, dimethylacetamide, hexamethylphosphoramide, acetonitrile, acetone ), Cyclohexanone, dimethylsulfoxide, tetrahydrofuran, dioxane, dioformane, chloroform, dichloromethane and water or mixtures of two or more selected from the group consisting of This is preferred.

Non-solvents for polymer binders include N-methylpyrrolidinone, water, ethanol, propanol, butanol, pentanol, hexanol, ethylene glycol, One or more mixtures selected from the group consisting of glycerol, acetone, dimethylether, diethylether, ethylacetate and dichloromethane are preferred.

Pore formers include methanol, trifluoroethanol, 2-propanol, cyclohexanol, resorcinol, hexafluoroisopropanol, and maleic acid. one or two or more mixtures selected from the group consisting of hemiacetal obtained by the reaction of acid) with hexafluoroacetone.

In addition, the present invention includes an electrode manufactured through the manufacturing process, that is, a positive electrode or a negative electrode, or a positive electrode and a negative electrode, and a secondary battery using the electrode, wherein the secondary battery may be a lithium secondary battery.

After the coating and drying, the rolling step may be used as a negative electrode. The secondary battery may be manufactured by assembling a positive electrode and a separator separately prepared together with the negative electrode thus prepared and absorbing an ion conductive liquid electrolyte thereto. have.

The material of the positive electrode is composed of a positive electrode active material, a conductive material, a binder, and other additives similarly to the negative electrode. In addition, a dispersion medium and a positive electrode current collector are required for slurry production. Like the cathode, the material is finally weighed, mixed, slurry coated, dried, and rolled into a cathode.

In preparing the positive electrode, a process of preparing the positive electrode slurry and then applying the positive electrode slurry to the positive electrode current collector may be performed by a wet method or a dry method similarly to the negative electrode.

The positive electrode active material may be any material commonly used for secondary batteries, particularly lithium secondary batteries, for the same purpose, and may be transition metal-oxide type, transition metal-phosphate type, transition metal-silicate type, transition metal-sulfate type or Polymeric materials and the like are preferable.

For example, as a material capable of intercalating lithium ions, lithium cobalt oxide (Li _x CoO ₂ ), lithium nickel oxide (Li _x NiO ₂ ), lithium nickel cobalt oxide (Li _x (NiCo) O ₂ ), lithium nickel cobalt manganese Oxides such as oxides (Li _x (NiCoMn) O ₂ ), spinel type lithium manganese oxide (Li _x Mn ₂ O ₄ ), manganese dioxide (MnO ₂ ), or lithium iron phosphate (Li _x FePO ₄ ), lithium manganese phosphate (Li Olivine type or NASICON type phosphates, silicates, sulfates, or polymer materials such as _x MnPO ₄ ) may be used.

The conductive material, binder and slurry dispersion medium for producing the positive electrode can be selected from the same material group as the negative electrode, and selecting the same material as the negative electrode is advantageous in terms of process and material management, but it is not necessarily identical. .

In the present invention, the conductive material or other additives or all of the conductive material and other additives in the electrode components of the cathode and the anode may not be added in some cases.

The electrode current collector may be any one commonly used in a secondary battery, especially a lithium secondary battery, for the same purpose, and the negative electrode current collector and the positive electrode current collector may be any metal foil, foam, grid, expanded metal, and the like. It can be used and more preferred if it is a foil. In the case of the positive electrode, an electrode current collector made of aluminum or copper may be preferably used in the case of the negative electrode.

Membrane if a material commonly used in the secondary battery, particularly a lithium secondary battery with the same purpose mubang if any, and polyethylene, polypropylene, thermoplastic polyolefin polymer porous multi-layer film (T _m 100 ~ 150 ℃) or high molecular weight to ultra high molecular weight thermoplastic Heat resistant polyolefin polymer porous membranes (T _m 150-200 ° C.) are preferred.

The liquid electrolyte may be any material commonly used for secondary batteries, particularly lithium secondary batteries, for the same purpose. As the organic solvent, two or more mixed solutions composed of a high viscosity solvent and a low viscosity solvent are used, and a carbonate type or the like is preferable. The lithium salt is preferably one selected from LiClO ₄ , LiBF ₄ , LiPF ₆ , LiAsF ₆ , LiCF ₃ SO ₃ , LiC (CF ₃ SO ₂ ) ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiSCN, or an optional mixture thereof. . The concentration of lithium salt in the liquid electrolyte is preferably 0.5 M to 2 M.

Hereinafter, a wet method prepared through the steps of metering, dissolving, dispersing and mixing, coating, phase inversion and drying, and rolling of an active material, a conductive material, a polymer binder, and other additives in order to manufacture electrodes according to the present invention. and; The dry method of manufacturing through the steps of metering, dissolving, dispersing and mixing the active material, conductive material, polymeric binder and other additives, adding non-solvent and pore former, applying and drying and rolling will be described in more detail.

1) Wet method

Figure 1 schematically shows the electrode manufacturing process according to the present invention compared with the prior art, Figure 1 (a) is a prior art process, (b) shows a process according to the wet method of the present invention. Reference numeral 1 denotes a supply roll to which the electrode current collector 21 is supplied, reference numeral 2 denotes a guide roller, and reference numeral 3 denotes an application roller 3 for applying the mixed slurry 22 to the electrode current collector 21. ) And 4 denote winding rolls, respectively.

When the mixed slurry (cathode or positive electrode slurry) 22 is introduced into the application roller 3 and the electrode current collector 21 is pulled by the winding roll 4 to pass through the application roller in which the mixed slurry is introduced, the electrode current collector As the negative electrode or the positive electrode current collector passes through the mixed slurry, the mixed slurry is applied to the electrode current collector to a predetermined thickness. In the process of the related art, the electrode current collector in which the mixed slurry is applied is directly transferred to the drying furnace 10. It is transferred and goes through a drying step.

On the other hand, in the present invention, the non-solvent which does not dissolve the polymer binder for phase inversion is passed through the stored non-solvent bath (9) and then transferred to the drying furnace 10, and thus undergoes a drying step after phase inversion.

First, in the wet method, a powdery electrode material, that is, an active material, a conductive material, and a polymer binder are dry mixed in a sealed container, and then dissolved and dispersed in a solvent of the polymer binder to prepare a mixed slurry. In this process, a magnetic stirrer, a mechanical stirrer, a planetary stirrer, an ultrasonic stirrer, or the like may be used to facilitate the dissolution of the polymer binder and prevent the electrode component materials from agglomerating with each other.

When the polymer binder is completely dissolved and the electrode constituent materials are uniformly dispersed and mixed, the mixed slurry is supplied onto the foil, which is the electrode current collector, and adjusted to have a constant thickness, and then applied in the form of a film. It is possible to apply by passing through a coating roller of.

Of course, any method that can be produced in the form of a film may be used as the coating process, and a comma method, a slit die method, a gravure method, a doctor blade method, a silk screen method, an offset method, a spray method, and a dip method are used. Can be.

Thereafter, the electrode current collector 21 in which the mixed slurry 22 is applied is immersed in the non-solvent tank 9 containing the non-solvent (non-solvent in which the polymer binder does not melt) of the polymer binder, thereby extracting the solvent of the polymer binder. . Immersion time soaked in the nonsolvent is preferably about 1 minute to 1 hour depending on the type of solvent and nonsolvent. If the time is short, sufficient exchange between the solvent and the non-solvent may not be achieved. On the contrary, if the time is long, the productivity is lowered, which is not preferable. 10 degreeC-70 degreeC is preferable at this time, More preferably, it is good to maintain at 20 degreeC-50 degreeC. If the temperature is too low, sufficient exchange is not achieved, and if the temperature is too high, the mechanical strength of the electrode layer formed from the mixed slurry falls, which is undesirable.

After the extraction of the solvent, the binder of the electrode layer formed from the electrode, that is, the electrode current collector and the mixed slurry, was removed from the nonsolvent 9 and transferred to a drying furnace. The electrode layer was completely dried to remove the nonsolvent in the electrode layer exchanged with the solvent of the polymer binder. Remove it completely. Drying is applied to hot air method, direct heating method, induction heating method, etc. according to the situation at non-solvent temperature. At this time, the drying temperature is preferably 50 ℃ ~ 200 ℃, if it is too low may take a long time or incomplete to dry the non-solvent, if too high may damage the electrode component material, the electrode current collector.

2) dry method

First, the powdery active material, the conductive material, and the polymer binder are dry mixed in an airtight container, and then dissolved and dispersed in the solvent of the polymer binder. The above mixing process is the same as the said wet method.

After the polymer binder is completely dissolved and uniformly dispersed and mixed with the electrode constituent material, a nonsolvent which does not dissolve the polymer binder is gradually added within the range where coagulation and precipitation of the polymer binder do not occur. At this time, it may be desirable to add a pore-forming agent, etc. in order to smoothly create a porous structure.

After these additives are uniformly dispersed and mixed, the slurry is supplied onto the foil, which is an electrode current collector, and adjusted to a constant thickness to be applied in the form of a film. The application step is the same as the wet method.

Then transfer to a drying furnace to completely dry the electrode layer on the electrode current collector to remove the solvent and non-solvent. The drying process is the same as the wet method.

Drying the negative electrode of the dry state prepared by the above-described method, together with a positive electrode and a separator separately prepared in the order of a negative electrode-membrane-anode, assembled in the form of a battery, absorbing the liquid electrolyte, and the usual packaging step Finish the secondary battery through.

The cross-sectional schematic diagram of the secondary battery using the electrode of this invention is shown in FIG. With the negative electrode 101 obtained from the above process below, the separator 105 and the positive electrode 104 are laminated in this order to constitute a battery. The electrode layer 101a of the negative electrode 101 is electrically connected to the negative electrode current collector 102, and the electrode layer 104a of the positive electrode 104 is electrically connected to the positive electrode current collector 103. After the step of absorbing the liquid electrolyte in the assembly thus configured is a state capable of operating as a battery.

In the following, the method for producing an electrode, in particular a cathode according to the present invention will be described in detail. However, these examples do not limit the content of the present invention, and modifications may be made without departing from the basic spirit of the present invention. For example, it is possible to apply to the positive electrode instead of the negative electrode, it is also possible to apply to both the positive electrode and the negative electrode.

Example

Example 1 Preparation of Negative Electrode-Wet Method Application

N-methylpyrrolidone, a solvent of the binder, was added to a mixture consisting of 97% by weight of graphite powder as a negative electrode active material and 3% by weight of polyvinylidene fluoride as a binder, followed by mixing for 4 hours in an oil-based stirrer to obtain a solid slurry of 50% solids. Was prepared. The negative electrode slurry was applied to a copper foil having a thickness of 10 μm, which is a negative electrode current collector, by a doctor blade method to a thickness of 150 μm to prepare a negative electrode in a wet state. The wet cathode was then immersed in a bath containing ultrapure water, the nonsolvent of the binder, to allow for a solvent-nonsolvent exchange. At this time, water temperature was 30 degreeC and immersion time was 10 minutes. After it was judged that sufficient exchange occurred, such as solidification of the slurry, the negative electrode was taken out of the water bath, dried in a hot air drying furnace at 120 ° C. for 5 minutes, and then roll-pressed to prepare a negative electrode.

Example 2 Preparation of Cathode-Dry Method Application

A mixture of 96.5 wt% graphite powder as the negative electrode active material, 0.5 wt% carbon black as the conductive material, and 3 wt% polyvinylidene fluoride-hexafluoropropylene copolymer (PVdF-HFP) as the binder was placed in a magnetic stirrer for about 5 minutes. Dry mix. Acetone, which is a solvent of the binder, was added thereto and mixed in an oil stirrer for 4 hours to prepare a negative electrode slurry having a solid content of 50%. In addition to this negative electrode slurry, 10% by weight of ultrapure water, which is a non-solvent of the polymer binder, was carefully added dropwise so that the polymer binder did not coagulate and settle, and mixed for an additional 1 hour in a planetary stirrer to sufficiently disperse. The negative electrode slurry was applied to a copper foil having a thickness of 10 μm, which is a negative electrode current collector, by a doctor blade method to a thickness of 150 μm to prepare a negative electrode in a wet state. Then, the resultant was dried for 2 hours in an air at 80 ° C., followed by drying for 5 minutes in a hot air drying furnace at 120 ° C., and then subjected to roll press to prepare a negative electrode.

Comparative Example -Cathode Preparation

N-methylpyrrolidone, a solvent of the binder, was added to the mixture consisting of 91 wt% graphite powder as the negative electrode active material, 1 wt% carbon black as the conductive material, and 8 wt% polyvinylidene fluoride as the binder. A negative electrode slurry having 50% solids was prepared by mixing for a while. The negative electrode slurry was applied to a copper foil having a thickness of 10 μm, which is a negative electrode current collector, by a doctor blade method at a thickness of 150 μm, dried in a hot air drying furnace at 120 ° C. for 5 minutes, and then roll-pressed to prepare a negative electrode.

The difference from Example 1 is that the phase inversion process of immersing in the non-solvent after applying the negative electrode slurry is not performed, and the difference from Example 2 is that no non-solvent or the like is added to the negative electrode slurry.

Figure 3 is a SEM photograph of the negative electrode, (a) is a negative electrode of Example 1 prepared by the present invention, (b) shows a negative electrode of a comparative example according to the prior art. As shown in FIG. 3, the negative electrode manufactured by the present invention was found to have fine pores uniformly formed by the phase change effect. On the other hand, the negative electrode according to the prior art was volatilized by the hot air drying, it was found that the surface of the surface is very uneven because the local active material particles are aggregated and non-uniform pores are formed.

Manufacturing example  And Comparative Production Example

Preparation Example 1 Preparation of Secondary Battery-Use of Negative Electrode of Example 1

Preparation Example 2 Preparation of Secondary Battery-Use of Negative Electrode of Example 2

-Comparative Production Example: Secondary Battery Manufacturing-Comparative Example

Lithium as a cathode active material-nickel-cobalt-manganese composite oxide _{(LiNi 1/3 Co 1/} 3 Mn 1/3 O 2) 94 wt%, 3 wt% of carbon black as a conductive material, a binder polyvinylidene fluoride 3 parts by weight A positive electrode slurry having a solid content of 50% was prepared by adding N-methylpyrrolidone as a solvent of the binder to the mixture composed of% and mixing for 4 hours in the planetary stirrer in the same manner as the negative electrode of the comparative example. The positive electrode slurry was applied to an aluminum thin film having a thickness of 20 μm, which is a positive electrode current collector, by a doctor blade method at a thickness of 100 μm, dried in a hot air drying furnace at 120 ° C. for 5 minutes, and rolled to prepare a positive electrode.

The negative electrode manufactured by Example 1, Example 2, and Comparative Example, and the positive electrode produced by the above process were cut to predetermined dimensions to obtain respective negative electrode plates and positive electrode plates, and the negative electrode plates, positive electrode plates, and general The secondary battery separators were assembled by sequentially stacking the cathode-separator-anode. The laminate was placed in an aluminum pouch, an exterior material, and organic in which LiPF ₆ lithium salt was dissolved at a concentration of 1.1 M in an organic solvent mixed with ethylene carbonate (EC) and diethyl carbonate (DEC) (volume ratio 3: 7). A secondary battery of Preparation Example 1 (using the negative electrode of Example 1), Preparation Example 2 (using the negative electrode of Example 2), and Comparative Production Example (using the negative electrode of Comparative Example) were prepared by injecting and sealing a general electrolyte solution composed of a solution. It was.

The main points according to Example 1, Example 2, Comparative Example, Preparation Example 1, Preparation Example 2, Comparative Preparation Example are summarized as shown in Table 1 below.

Experimental Example

Experimental Example 1

<Capacity maintenance rate and life characteristics test by repeated charge-discharge cycle of secondary battery>

The life characteristics of the secondary batteries prepared in Preparation Example 1, Preparation Example 2, and Comparative Preparation Example were tested by the following conditions and methods, and the results are shown graphically in FIG. 4.

ㆍ Charging: Charge at constant current 1.0C speed until voltage rises to 4.2V, then apply constant voltage 4.2V until current value drops to 0.1C value

ㆍ Discharge: Discharge until it drops to 3.0V at constant current 1.0C

Secondary batteries (Preparation Example 1, Preparation Example 2) prepared using the negative electrodes of Examples 1 to 2 according to the present invention through FIG. 4 were manufactured using the negative electrode of the comparative example according to the prior art (comparatively Compared with the preparation example), it can be seen that the equivalent or more than equivalent performance is expressed.

Experimental Example 2

<Capacity expression according to the discharge current applied value of the secondary battery>

The high rate discharge characteristics of the secondary batteries prepared in Preparation Example 1, Preparation Example 2, and Comparative Preparation Example were tested by the following conditions and methods, and the results are shown in the graph of FIG. 5.

ㆍ Charging: Charge at constant current 1.0C speed until voltage rises to 4.2V, then apply constant voltage 4.2V until current value drops to 0.1C value

ㆍ Discharge: Discharge until it drops to 3.0V at constant speed of 0.5C, 1.0C, 2C, 5C

Secondary batteries (Manufacture Example 1, Preparation Example 2) prepared using the negative electrode of Example 1 to Example 2 according to the present invention through Figure 5, the secondary battery produced using a negative electrode of the comparison according to the prior art (comparative Compared with the preparation example), it can be seen that the equivalent or more than equivalent performance is expressed.

As described above, the negative electrode for the secondary battery of the present invention through Experimental Examples 1 to 2 exhibited the same or more equivalents in terms of performance compared to the prior art even with a low binder content and a high negative electrode active material content, and the stability of the binding force and adhesion of the electrode, etc. It was confirmed that no inhibition.

Thus, in the present invention, by applying a more improved application process using a mixing and application process, in particular a phase inversion method based on solvent-non-solvent interaction, the content of the electrode active material can be greatly increased instead of reducing the content of the binder. Will be.

In the conventional case, in the preparation of the negative electrode, about 90 wt% of the negative electrode active material, 5 to 10 wt% of the binder, and the composition and content ratio of other constituent materials could be prepared, but in the present invention, 95 to 98 wt% of the negative electrode active material, and the binder It can be produced using 2 to 4% by weight, it is possible to significantly increase the content of the negative electrode active material.

That is, only a partial change and addition of the conventional process may increase the content of the electrode active material and increase energy. In addition, by reducing the amount of the binder that inhibits the electrical conductivity, it is possible to expect additional advantages such as improvement of electrode and battery performance.

In addition, even if the amount of the binder is drastically reduced, the structural stability of the electrode, that is, the binding force and the adhesive force, can be maintained by the modified and added process according to the present invention.

In the present invention, the reason why it is possible to maintain the performance and stability of the electrode and the battery even with a low content of the binder is equal or higher than that, the binder is crystallized through the phase inversion (solvent-non-solvent exchange) step proposed in the present invention Presumably because it is suppressed and solidified in an amorphous form, or better dispersed, bound or adhered to other electrode components.

In addition, in the phase inversion step, solvent extraction, phase separation of the polymer binder and the nonsolvent occurs, and after the nonsolvent is removed in the drying process, voids are formed at the nonsolvent site, so that the effect of the binder content is reduced as well. Compared with the prior art, the porosity of the electrode plate may be improved or an effect of obtaining a more effective porous structure may be expected.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the scope of the present invention is not limited to the disclosed exemplary embodiments. Modified forms are also included within the scope of the present invention.

1: supply roll 2: guide roller
3: coating roller 4: winding roll
9: cost selling 10: drying furnace
21 electrode collector 22 mixed slurry
101: cathode 101a: electrode layer
102: negative electrode current collector 103: positive electrode current collector
104: anode 104a: electrode layer
105: separator

Claims (16)

Preparing a mixed slurry by dissolving, dispersing and mixing an electrode component material including an active material and a polymer binder in a solvent of the polymer binder;
Applying the mixed slurry to an electrode current collector in the form of a film;
The electrode current collector to which the mixed slurry is applied is immersed in a non-solvent that does not dissolve the polymer binder, thereby changing the composition of the mixed slurry due to the exchange of the solvent and the non-solvent of the polymer binder and the mutual diffusion of the solvent and the non-solvent. Causing a phase inversion to cause solidification of the polymer including the liquid-liquid phase separation phenomenon while causing a;
Drying the combination of the electrode layer and the electrode current collector formed from the mixed slurry after the phase inversion in a drying furnace;
Rolling after the drying to complete an electrode in which an electrode layer having pores is laminated on an electrode current collector;
Method of manufacturing an electrode for a secondary battery comprising a.
The method according to claim 1,
The solvent of the polymer binder is N-methylpyrrolidinone (N-methylpyrolidinone), dimethylformamide (dimethylformamide), dimethylacetamide (dimethylacetamide), hexamethylphosphoramide (hexamethylphosphoramide), acetonitrile (acetonitrile), acetone (acetone) ), Cyclohexanone, dimethylsulfoxide, tetrahydrofuran, dioxane, dioformane, chloroform, dichloromethane and water or mixtures of two or more selected from the group consisting of Method for producing a secondary battery electrode, characterized in that.
The method according to claim 1,
The non-solvent is N-methylpyrrolidinone, water, ethanol, propanol, butanol, butanol, pentanol, hexanol, ethylene glycol, glycerol Acetone, dimethyl ether (dimethylether), diethyl ether (diethylether), ethyl acetate (ethylacetate) and dichloromethane a method for producing a secondary battery electrode, characterized in that at least one mixture selected from the group consisting of.
The method according to claim 1,
The active material is a negative electrode active material, the secondary battery electrode manufacturing method, characterized in that to produce a secondary battery negative electrode by sequentially performing the above steps using the negative electrode active material.
The method according to claim 1,
The active material is a positive electrode active material, the method of manufacturing a secondary battery electrode, characterized in that to produce a positive electrode for a secondary battery by sequentially performing each step using the positive electrode active material.
The method according to claim 1,
The time for the immersion in the non-solvent is 1 minute to 1 hour, the temperature of the manufacturing method of the secondary battery electrode, characterized in that maintained at 10 ℃ ~ 70 ℃.
The method according to claim 1,
The drying method of the secondary battery electrode, characterized in that for drying at a drying temperature 50 ℃ ~ 200 ℃ to completely remove the non-solvent in the electrode layer exchanged with the solvent of the polymer binder in the drying step.
After dissolving, dispersing and mixing the electrode constituent material including the active material and the polymer binder in the solvent of the polymer binder, adding, dispersing and mixing the non-solvent which does not dissolve the polymer binder and the pore former for producing the porous structure. Preparing a slurry;
Applying the mixed slurry to an electrode current collector in the form of a film;
Drying the electrode current collector to which the mixed slurry is applied in a drying furnace;
Rolling after the drying to complete an electrode in which an electrode layer having pores is laminated on an electrode current collector;
Method of manufacturing an electrode for a secondary battery comprising a.
The method according to claim 8,
The solvent of the polymer binder is N-methylpyrrolidinone (N-methylpyrolidinone), dimethylformamide (dimethylformamide), dimethylacetamide (dimethylacetamide), hexamethylphosphoramide (hexamethylphosphoramide), acetonitrile (acetonitrile), acetone (acetone) ), Cyclohexanone, dimethylsulfoxide, tetrahydrofuran, dioxane, dioformane, chloroform, dichloromethane and water or mixtures of two or more selected from the group consisting of Method for producing a secondary battery electrode, characterized in that.
The method according to claim 8,
The pore formers are methanol, trifluoroethanol, 2-propanol, cyclohexanol, cyclohexanol, resorcinol, hexafluoroisopropanol, and maleic acid ( A method for manufacturing a secondary battery electrode, characterized in that one or more mixtures selected from the group consisting of hemiacetal (hemiacetal) obtained by the reaction of maleic acid) and hexafluoroacetone.
The method according to claim 8,
The non-solvent is N-methylpyrrolidinone, water, ethanol, propanol, butanol, butanol, pentanol, hexanol, ethylene glycol, glycerol Acetone, dimethyl ether (dimethylether), diethyl ether (diethylether), ethyl acetate (ethylacetate) and dichloromethane a method for producing a secondary battery electrode, characterized in that at least one mixture selected from the group consisting of.
The method according to claim 8,
The active material is a negative electrode active material, the secondary battery electrode manufacturing method, characterized in that to produce a secondary battery negative electrode by sequentially performing the above steps using the negative electrode active material.
The method according to claim 8,
The active material is a positive electrode active material, the method of manufacturing a secondary battery electrode, characterized in that to produce a positive electrode for a secondary battery by sequentially performing each step using the positive electrode active material.
The method according to claim 8,
Method of manufacturing a secondary battery electrode, characterized in that for drying at 50 ℃ ~ 200 ℃ drying temperature so that the solvent and non-solvent in the electrode layer is completely removed in the drying step.
A secondary battery electrode manufactured by any one of claims 1 to 14.
A secondary battery prepared by using the electrode produced by any one of claims 1 to 14.

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