KR20200046634A - Manufacturing method for asymmetric electrode and asymmetric electrode, secondary battery prepared by the same - Google Patents

Abstract

The present invention provides a method for manufacturing an asymmetric electrode, in which the thickness of a lower coating layer is greater than that of an upper coating layer or a binder or a volume expansion inducement additive is added to the lower coating layer to increase bendability of an electrode, and an asymmetric electrode thereof. According to the present invention, the method comprises the following steps: coating electrode slurry on both surfaces of a collector to form the upper and lower coating layers; and winding the collector while the lower coating layer of the collector coated with an active material faces the inside of a winding roll and drying the collector by applying heat. Accordingly, the asymmetric electrode can alleviate a bending phenomenon of an electrode generated during an electrode manufacturing process and the bendability-increased asymmetric electrode is used, thereby increasing power of a secondary battery.

Description

Manufacturing method of asymmetric electrode and asymmetric electrode and secondary battery prepared therefrom {Manufacturing method for asymmetric electrode and asymmetric electrode, secondary battery prepared by the same}

The present invention relates to a method for manufacturing an asymmetric electrode, and an asymmetric electrode and a secondary battery prepared therefrom, which produce electrode bending during the manufacturing process of a pouch type secondary battery and to improve the output of the secondary battery. It's about how.

As the price of energy sources increases due to the exhaustion of fossil fuels, and interest in environmental pollution is amplified, the demand for eco-friendly alternative energy sources has become an indispensable factor for future life, and in particular, technology development for mobile devices Demand for secondary batteries as an energy source is rapidly increasing as the demand for electricity increases.

Typically, the shape of the battery has a high demand for prismatic secondary batteries and pouch-type secondary batteries that can be applied to products such as mobile phones with a thin thickness, and in terms of materials, lithium ion batteries with high energy density, discharge voltage, and output stability, There is a high demand for lithium secondary batteries such as lithium ion polymer batteries.

The lithium secondary battery is manufactured by using a material capable of intercalating and deintercalating lithium ions as a negative electrode and a positive electrode, and filling an organic electrolyte or a polymer electrolyte between the positive electrode and the negative electrode. Electrical energy is generated by the oxidation and reduction reaction of.

The negative electrode and the positive electrode include an electrode active material on the current collector of each electrode. Specifically, after mixing and stirring the electrode active material and a binder, a solvent, and a conductive material, a dispersing material, if necessary, to prepare a slurry, and then After coating and rolling on the current collector, the electrode can be prepared by drying and winding.

The electrode of the existing secondary battery is manufactured through a method of manufacturing by coating the electrode active material of the same weight on the upper and lower parts of the electrode current collector. As shown in Figure 1, by coating the active material of the same weight on both sides of the electrode current collector 101 (102, 103), there is an advantage that the electrode 110 is easy to manufacture and manage. In addition, the characteristics of the electrode produced due to the uniform coating also have the same advantage.

However, the electrode manufacturing method as described above, after coating the slurry containing the electrode active material, undergoes a rolling and drying process, depending on the characteristics of the binder and the active material in the slurry, the electrode is placed on a cylindrical winding roll 220 as shown in FIG. 2. After winding and drying, there is a disadvantage in that the electrode is bent when the assembly process is released from the roll again. In addition, there is a problem of deepening the bending phenomenon of the electrode due to the difference in the stretching of the external electrode in the winding roll.

This bending phenomenon of the electrode not only causes defects in electrode production, but also has a limitation in that it is difficult to produce an optimized output of a manufactured secondary battery.

Japanese Patent Application Publication No. 2014-099317 Japanese Patent Application Publication No. 2006-173138 Japanese Patent Application Publication No. 1997-161768 Korean Patent Publication No. 2009-0051381

Therefore, the present invention was devised to solve the above problems, and a method of manufacturing an asymmetric electrode to provide a secondary battery with improved bending and improved output of an electrode, and an asymmetric electrode and a secondary battery prepared accordingly It is aimed at.

Other objects and advantages of the present invention can be understood by the following description, and will be more clearly understood by examples of the present invention. In addition, it will be readily appreciated that the objects and advantages of the present invention can be realized by means of the appended claims and combinations thereof.

According to an embodiment of the present invention, the step of manufacturing an electrode slurry; Preparing an upper coating layer and a lower coating layer by coating the electrode slurry on both sides of the electrode current collector, respectively; Rolling; And winding and drying the lower coating layer of the current collector coated with the active material toward the inside of the winding roll, wherein the lower coating layer provides a method of manufacturing an asymmetric electrode, characterized in that the upper coating layer has a thicker thickness than the upper coating layer. You can.

The electrode may be an anode or a cathode.

In addition, the thickness of the lower coating layer may be 101 to 200% of the thickness of the upper coating layer.

According to an embodiment of the present invention, it is possible to provide an asymmetric electrode manufactured by the above manufacturing method.

According to an embodiment of the present invention, the step of manufacturing an electrode slurry; Preparing an upper coating layer and a lower coating layer by coating the electrode slurry on both sides of the electrode current collector, respectively; Rolling; And winding and drying the lower coating layer of the current collector coated with the active material toward the inside of the winding roll, wherein the coating thickness of the upper coating layer and the lower coating layer is the same, and the composition of the electrode slurry for preparing the lower coating layer is included. And the composition of the electrode slurry for manufacturing the upper coating layer may provide a method for manufacturing an asymmetric electrode, characterized in that different.

The binder content in the electrode slurry for manufacturing the lower coating layer may be higher than the binder content in the electrode slurry for preparing the upper coating layer.

At this time, the binder content in the lower coating layer may be 101 to 200% by weight compared to the binder content in the upper coating layer.

In addition, the electrode slurry for manufacturing the lower coating layer may include a volume expansion-inducing additive, wherein the content of the volume expansion-inducing additive may be 0.01 to 1% by weight compared to the electrode slurry.

The bulk expansion inducing additives include polyethylene, polypropylene, polyethylene oxide, polypropylene oxide, polyvinylidene fluoride, polytetrafluoroethylene, polyvinylfluoride, polyacrylonitrile, polyvinyl chloride, polyvinyl chloride Liden, polymethyl methacrylate, polymethyl acrylate, polyvinyl alcohol, polymethacrylonitrile, polyvinyl acetate, polyvinyl pyrrolidone, polycarbonate, polyethylene terephthalate, polycaprolactam, polyurethane, polyethyleneimine, It may be one or two or more selected from the group consisting of polybutadiene, polystyrene and polyisoprene.

In addition, the electrode may be an anode or a cathode.

According to an embodiment of the present invention, it is possible to provide an asymmetric electrode manufactured by the above manufacturing method.

According to an embodiment of the present invention, it is possible to provide a secondary battery including the asymmetric electrode.

Asymmetric electrode according to the present invention, to prevent the electrode bending phenomenon that occurs during the manufacturing process of the secondary battery, the thickness of the lower coating layer of the electrode toward the inside of the winding roll during electrode manufacturing is thicker than the thickness of the upper coating layer, or lower The composition of the coating layer further includes a binder or an additive that expands in volume when heated, thereby providing a method for manufacturing an electrode having improved bending and an asymmetric electrode.

According to another aspect of the present invention, it is possible to provide a secondary battery with improved output by using an asymmetric electrode with improved bending.

1 and 2 are perspective views showing a general electrode coating and winding shape according to the prior art.
3 to 5 are perspective views showing an asymmetric electrode coating and winding shape according to an embodiment of the present invention.

The terms used in the present specification and claims should not be interpreted as being limited to ordinary or dictionary meanings, and the inventor can appropriately define the concept of terms to describe his or her invention in the best way. Based on the principle, it should be interpreted as meanings and concepts consistent with the technical idea of the invention. Therefore, the configuration shown in the embodiments described herein is only one of the most preferred embodiments of the present invention and does not represent all of the technical spirit of the present invention, and various equivalents that can replace them at the time of this application And it should be understood that there may be variations.

Throughout this specification, when a part is "connected" to another part, this includes not only "directly connected" but also "electrically connected" with another element in between. .

Throughout the present specification, when a part “includes” a certain component, it means that the component may further include other components, not to exclude other components, unless otherwise stated.

The terms "about", "substantially", and the like used throughout this specification are used as or in close proximity to the numerical values when manufacturing and material tolerances specific to the stated meaning are used, and are used to help understand the present application. Or, an absolute value is used to prevent unscrupulous use of the disclosed content by unscrupulous intruders.

Throughout the present specification, the term "combination (s)" included in the expression of the marki form means one or more mixtures or combinations selected from the group consisting of elements described in the expression of the marki form, It means to include one or more selected from the group consisting of the above components.

The present invention relates to an electrode for an electrochemical device and an electrochemical device comprising the same. In the present invention, the electrochemical device includes all devices that undergo an electrochemical reaction, and specific examples include all types of primary, secondary cells, fuel cells, solar cells, or capacitors. In particular, 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 among the secondary batteries.

The description of "A and / or B" in the present specification means "A or B or both".

Hereinafter, the present invention will be described in more detail.

First, a method of manufacturing an asymmetric electrode of the present invention comprises the steps of preparing an electrode slurry; Coating on the electrode current collector; Rolling; And winding and drying on a winding roll.

The step of preparing the electrode slurry is a step of preparing a slurry for coating on the surface of the electrode current collector by mixing an electrode active material, a conductive material, a binder, and a solvent.

At this time, the electrode may be an anode or a cathode.

More specifically, when the electrode is a positive electrode, for example, it is prepared by applying a mixture of a positive electrode active material, a conductive material, and a binder on a positive electrode current collector, followed by drying. If necessary, a filler is further added to the mixture.

The positive electrode active material may be a layered compound such as lithium cobalt oxide (LiCoO ₂ ) or lithium nickel oxide (LiNiO ₂ ) or a compound substituted with one or more transition metals; Lithium manganese oxides such as the formula Li _{1 + x} Mn _2-x O ₄ (where x is 0 to 0.33), LiMnO ₃ , LiMn ₂ O ₃ , LiMnO ₂ ; Lithium copper oxide (Li2CuO ₂ ); Vanadium oxides such as LiV ₃ O ₈ , LiFe ₃ O ₄ , V ₂ O 5 and Cu ₂ V ₂ O ₇ ; A Ni-site 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); Formula LiMn _2-x M _x O ₂ (where M = Co, Ni, Fe, Cr, Zn or Ta, x = 0.01 to 0.1) or Li ₂ Mn ₃ MO ₈ (where M = Fe, Co, Lithium manganese composite oxide represented by Ni, Cu or Zn); LiMn ₂ O _{4 in} which part of Li in the formula is substituted with alkaline earth metal ions; Disulfide compounds; Fe ₂ (MoO ₄ ) ₃ and the like, but are not limited to these.

The conductive material is usually added in 1 to 20% by weight based on the total weight of the positive electrode slurry containing the positive electrode active material. The conductive material is not particularly limited as long as it has conductivity without causing a chemical change in the battery. For example, graphite such as natural graphite or 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 fibers and metal fibers; Metal powders such as carbon fluoride powder, aluminum powder, and nickel powder; Conductive whiskey such as zinc oxide and potassium titanate; Conductive metal oxides such as titanium oxide; Conductive materials such as polyphenylene derivatives may be used.

The binder is a component that assists in bonding the active material and the conductive material and the like to the current collector, and is usually added in an amount of 1 to 30% by weight based on the total weight of the positive electrode slurry containing the positive electrode active material. Examples of such binders include polyvinylidene fluoride, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropyl cellulose, recycled cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene , Polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene styrene rubber, fluorine rubber, and various copolymers.

The filler is optionally used as a component that inhibits the expansion of the positive electrode, and is not particularly limited as long as it is a fibrous material without causing chemical changes in the battery, and includes, for example, an olefinic polymer such as polyethylene and polypropylene; Fibrous materials such as glass fibers and carbon fibers are used. The filler is usually added at 1 to 20% by weight based on the total weight of the positive electrode slurry containing the positive electrode active material.

The positive electrode current collector may have a thickness of about 3 to 500 μm, for example. The positive electrode current collector is not particularly limited as long as it does not cause a chemical change in the battery and has conductivity. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, or carbon on the surface of aluminum or stainless steel, Surface treatment with nickel, titanium, silver, or the like can be used. The positive electrode current collector can increase the adhesion of the positive electrode active material by forming fine irregularities on its surface, and various forms such as a film, sheet, foil, net, porous body, foam, and nonwoven fabric are possible.

On the other hand, when the electrode is a negative electrode, for example, it is produced by applying and drying a negative electrode active material on a negative electrode current collector. If necessary, components as described above may be optionally further included.

Examples of the negative electrode active material include carbons such as non-graphitized carbon and graphite-based 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 ': Al, B, P, Si, Group 1, 2, 3 element of the periodic table, halogen; metal such as 0 <x = 1; 1≤ = y≤ = 3; 1≤ = z≤ = 8) Composite oxides; Lithium metal; Lithium alloys; Silicon-based alloys; Tin-based alloys; 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 , And metal oxides such as Bi ₂ O ₅ ; Conductive polymers such as polyacetylene; Li-Co-Ni based materials and the like can be used.

The negative electrode current collector may have a thickness of about 3 to 500 μm, for example. The negative electrode current collector is not particularly limited as long as it has conductivity without causing chemical changes in the battery. For example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, or copper or stainless steel surfaces Carbon, nickel, titanium, silver, or the like, aluminum-cadmium alloy, or the like may be used. Like the positive electrode current collector, the negative electrode current collector can form fine irregularities on its surface to increase the adhesion of the negative electrode active material, and various forms such as films, sheets, foils, nets, porous bodies, foams, and nonwoven fabrics are possible. .

On the other hand, as the solvent, the electrode active material, the conductive material, and the binder do not dissolve without causing a chemical change in the art, and then having a low boiling point for easy removal can be used without limitation, and these solvents Examples include acetone, tetrahydrofuran, methylene chloride, chloroform, and dimethylformamide.

Thereafter, the step of coating the slurry on the current collector is to coat the slurry prepared through the step of preparing the electrode slurry on the surface of the electrode current collector, the coating method is not limited to the method commonly used in the art. Various methods such as dip coating, die coating, roll coating, comma coating, or a mixing method thereof may be used as examples of the coating method.

In addition, since the coating method is preferably performed individually or continuously in terms of productivity, for example, a die having one or more slots can be utilized for coating of the slurry. That is, the electrode slurry is supplied onto the electrode current collector through the die, and the current collector corresponding to this is supplied from the supply roll. The slurry is coated on both sides of the electrode current collector, which is advanced by a roller.

By coating the slurry on both sides of the electrode current collector, an upper coating layer coated on the upper surface of the electrode current collector and a lower coating layer coated on the lower surface of the electrode current collector are prepared.

In the present invention, each slurry coated on both surfaces of the electrode current collector may have the same composition, or may be composed of different compositions.

In addition, the conductive material or the binder in each coating layer may be uniformly distributed in the thickness direction of the coating layer.

Here, the lower coating layer means a coating layer directed to the inside of the winding roll in the winding and drying process of the electrode to be described later.

In one embodiment of the present invention, in the process of coating the slurry, the thickness of the lower coating layer is thicker than the thickness of the upper coating layer. When the thickness of the lower coating layer located inside the winding roll is made thicker, the slurry composition of the upper coating layer and the lower coating layer is the same.

As shown in FIG. 3, by increasing the coating loading amount of the lower coating layer 303, the thickness is increased, and after winding and drying on a cylindrical winding roll, which has been a problem in the prior art, when the assembly process is released from the roll again, the electrode is wound. The bending phenomenon in which the electrode is bent due to curvature and stress caused by pressure may be alleviated.

As can be seen from FIG. 5, when the lower coating layer 503 having a thick thickness is used for assembling by unwinding the electrode from the winding roll 520 after winding, with respect to the bending phenomenon of the electrode occurring in the rolling and drying process of the electrode described later. Bending phenomenon is alleviated by reversely bending the bending.

In the present invention, the (cross-section) thickness of the upper coating layer is preferably 1 to 100 μm, preferably 50 to 80 μm. When the thickness of the upper coating layer satisfies this thickness range, the amount of the active material in the coating layer is sufficiently secured to prevent the battery capacity from being reduced, and the cycle characteristics and output of the battery can be improved.

In addition, in the present invention, the (cross-section) thickness of the lower coating layer is characterized in that 101 to 200%, preferably 110 to 150% of the thickness of the upper coating layer. If the thickness ratio of the lower coating layer is less than 101%, the relaxation of the bending phenomenon does not appear sufficiently, and if it exceeds 200%, the processability of the electrode is lowered and sufficient drying does not occur, resulting in a problem that the solvent is not easily removed.

In the present invention, by increasing the thickness of the lower coating layer as described above, the secondary battery output, which is additionally manufactured, may be improved and the effect of reducing battery resistance may be obtained. That is, the portion where the upper coating layer, which is thinly coated, is located has good output and resistance characteristics as the distance from the electrode current collector to the outer edge of the coating is shortened, and the lower coating layer portion, which has a thick coating, has characteristics opposite to the upper coating layer. do. In this case, when the initial current flows strongly, the output of the battery is improved by rapidly moving lithium in the portion of the upper coating layer where the coating is thin, and an effect of decreasing the initial resistance can be exhibited, and the current continuously flowing in the thick lower coating layer It is exhausted and the dose is expressed. That is, the thin portion of the coating is responsible for the initial output, and the lower thick portion can exert an effect of acting as a capacity expression.

On the other hand, in another embodiment of the present invention, in the process of coating the slurry, the slurry composition of the lower coating layer is different from the slurry composition of the upper coating layer. That is, the composition is different by further including a binder or an additive in the composition of the lower coating layer located inside the winding roll. In this case, the slurry thickness of the upper coating layer 402 and the lower coating layer 403 is the same.

When the slurry composition of the lower coating layer is different, the following two cases are included.

(i) When increasing the binder content in the slurry of the lower coating layer

(ii) When the volume expansion inducing additive in the corresponding slurry of the lower coating layer is included

In the present invention, by increasing the binder content of the lower coating layer facing the inside of the winding roll or by further including a volume expansion inducing additive, the electrode is released from the winding roll and subjected to assembly after passing through the rolling and drying process described below. It restores the volume, thereby alleviating the bending phenomenon of the electrode.

First, (i) when the binder content in the corresponding slurry of the lower coating layer is increased, it is characterized by being higher than the binder content in the slurry constituting the upper coating layer.

Generally, the binder in the slurry may contain 1 to 3% by weight, preferably 1.5 to 2.5% by weight, relative to 100% by weight of the electrode slurry. When the content of the binder is less than 1% by weight, a problem of insufficient binding strength of the electrode occurs, and when it exceeds 3% by weight, charging and discharging performance and capacity of the secondary battery may be deteriorated.

In the present invention, while the content of the binder in the lower coating layer and the upper coating layer is maintained within the content of 1 to 3% by weight described above, the binder content of the lower coating layer is 101 to 200% compared to the binder content of the upper coating layer, preferably 110 to 150% It is characterized by being. When the binder content is less than 101%, the relief of the electrode bending phenomenon is not effective, and when it exceeds 200%, the capacity of the secondary battery is lowered, resulting in a problem that the output is lowered.

The binder may use the material of the above-described binder.

Second, as shown in FIG. 4, (ii) when the volume expansion-inducing additive 404 is further included in the slurry of the lower coating layer 403, the volume expansion-inducing additive is not included in the slurry of the upper coating layer.

The volume expansion inducing additives are polyethylene, polypropylene, polyethylene oxide, polypropylene oxide, polyvinylidene fluoride, polytetrafluoroethylene, polyvinylfluoride, polyacrylonitrile, polyvinyl chloride, polyvinylidene chloride , Polymethyl methacrylate, polymethyl acrylate, polyvinyl alcohol, polymethacrylonitrile, polyvinyl acetate, polyvinyl pyrrolidone, polycarbonate, polyethylene terephthalate, polycaprolactam, polyurethane, polyethyleneimine, poly Preference is given to one or two or more selected from the group consisting of butadiene, polystyrene and polyisoprene.

The content of the volume expansion inducing additive may be 0.01 to 1% by weight, preferably 0.05 to 0.5% by weight, relative to 100% by weight of the electrode slurry of the lower coating layer. When the content of the volume expansion inducing additive is less than 0.01% by weight, the effect of alleviating the electrode bending is not sufficient, and when it exceeds 1% by weight, the capacity of the secondary battery is lowered, resulting in a problem that the output falls.

In addition, the volume expansion inducing additive in the lower coating layer may be uniformly distributed in the thickness direction of the coating layer.

In conclusion, as can be seen in FIG. 5 according to (i) and (ii), the lower coating layer 503 undergoes a winding and drying process, and thus the thickness of the lower coating layer 503 becomes thicker than that of the upper coating layer 502. Regarding the bending phenomenon of the case, when the electrode is released from the winding roll 520 after winding and used for assembly, the bending phenomenon of the bending is reversely relaxed to relieve the bending phenomenon. That is, when the upper and lower coating layers are subjected to the same pressure during rolling by making the thickness of the lower coating layer and the upper coating layer different, a difference in the rolling rate occurs. Due to this, the lower coating layer having a thicker coating layer later has a larger springback (a phenomenon of returning to the state before external pressure is applied) compared to the upper coating layer, thereby naturally improving the bending phenomenon. The electrode bending tends to be exacerbated mainly in the drying process, particularly in the vacuum drying (VD) process, and springback occurs mainly in the drying process. In the present invention, as the springback of the thick lower coating layer becomes larger, the bending phenomenon is relieved. will be.

On the other hand, after the step of coating the slurry to the current collector as described above, it may include the step of removing the solvent additionally. This serves to fix the electrode slurry on the surface of the electrode current collector by removing the solvent in the electrode slurry in a step of firing or curing the electrode slurry, and may be performed by drying the solvent by applying a temperature above the boiling point of the solvent. have. At this time, the step of removing the solvent may proceed within 10 minutes, and preferably proceed within 5 minutes. In addition, the solvent is sufficient if it is removed to such an extent that the fluidity of the electrode slurry can be eliminated, and it is not necessary to completely remove it.

Thereafter, the step of rolling is a step of manufacturing a slurry layer by rolling the electrode slurry coated on the electrode current collector. In the rolling step, the electrode slurry is adhered to the electrode current collector by passing the electrode current collector coated with the slurry containing the electrode active material between two or more rotating rolls. At this time, the rotating roll may be in a high temperature state, thereby further improving the adhesion between the electrode active material and the electrode current collector.

Thereafter, the step of winding and drying the wound roll is a step of removing the solvent by preparing the rolled electrode current collector and the electrode active material layer in a wound form and then drying. The slurry layer coated on the electrode current collector can be dried at the same time or separately by using a dryer or the like to remove the solvent. Specifically, when passing through a dryer or the like, it is affected by heat or hot air, and thus, solvent or moisture is removed as it is dried in sequence from a portion directly contacting the hot or hot air to the inside or vice versa. In the present invention, preferably, drying under vacuum (Vacuum Drying; VD) may be performed. Removing the solvent under vacuum can be effective to prevent moisture from being present in the electrode or moisture from entering the outside. This removal of water is essential because it may cause problems in the performance and stability of the final secondary battery by side reactions with components in the electrode according to the presence of water. Vacuum drying time in the present invention may vary depending on the solvent used.

Preferably, the vacuum drying may be performed by heating under vacuum at a temperature of 150 to 300 ° C. for 1 to 15 hours, but the present invention is not necessarily limited to such a drying method.

Hereinafter, a method of manufacturing a secondary battery including the asymmetric electrode of the present invention will be described in more detail.

When the asymmetric electrode is manufactured as described above, an electrode assembly is manufactured by interposing a separator between both electrodes (positive and negative electrodes) and winding them. At this time, at least one of the positive electrode or the negative electrode is characterized in that the electrode manufactured by the method of manufacturing an asymmetric electrode of the present invention.

Here, an insulating thin film having high ion permeability and mechanical strength is used as the separator. The pore diameter of the separator is generally 0.01 to 10 μm, and the thickness is generally 5 to 300 μm. Examples of the separator include a polyolefin porous substrate; Or a group consisting of polyethylene terephthalate, polybutylene terephthalate, polyester, polyacetal, polyamide, polycarbonate, polyimide, polyether ether ketone, polyethersulfone, polyphenylene oxide, polyphenylene sulfite, and polyethylene naphthalene. It is preferably a porous substrate formed of any one or a mixture of two or more selected from them. The polyolefin-based porous substrate may be any polyolefin-based porous substrate, and more specifically, polyethylene such as high-density polyethylene, linear low-density polyethylene, low-density polyethylene, and ultra-high molecular weight polyethylene, polypropylene, polybutylene, poly A film, sheet, or non-woven fabric formed of polyolefin-based polymers such as pentene alone or of a polymer obtained by mixing them may be used.

When the electrode current collector is formed by winding the positive electrode, the negative electrode, and the separator as described above, the electrode current collector is dried.

After the electrode current collector is dried, the secondary battery can be manufactured by storing it in a battery case and injecting an electrolyte solution.

Specifically, the electrolyte solution is composed of a polar organic electrolyte solution and a lithium salt. Non-aqueous liquid electrolyte, organic solid electrolyte, inorganic solid electrolyte, and the like are used as the electrolyte.

Examples of the non-aqueous liquid electrolyte include N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, and gamma. -Butyl lactone, 1,2-dimethoxy ethane, tetrahydroxy franc, 2-methyl tetrahydrofuran, dimethyl sulfoxide, 1,3-dioxorun, formamide, dimethylformamide, dioxol , Acetonitrile, nitromethane, methyl formate, methyl acetate, phosphoric acid triester, trimethoxy methane, dioxon derivative, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbohydrate Aprotic organic solvents such as nate derivatives, tetrahydrofuran derivatives, ethers, methyl pyropionate and ethyl propionate can be used.

Examples of the organic solid electrolyte include polyethylene derivatives, polyethylene oxide derivatives, polypropylene oxide derivatives, phosphate ester polymers, poly agitation lysine, polyester sulfide, polyvinyl alcohol, polyvinylidene fluoride, Polymers including ionic dissociative groups and the like can be used.

Examples of the inorganic solid electrolyte include Li ₃ N, LiI, Li ₅ NI ₂ , Li ₃ N-LiI-LiOH, LiSiO ₄ , LiSiO ₄ -LiI-LiOH, Li ₂ SiS ₃ , Li ₄ SiO ₄ , Li ₄ nitrides such as Li ₄ SiO ₄ -LiI-LiOH, Li ₃ PO ₄ -Li ₂ S-SiS ₂ , halides, sulfates, and the like can be used.

The lithium salt is a material soluble in the non-aqueous electrolyte, for example, LiCl, LiBr, LiI, LiClO ₄ , LiBF ₄ , LiB ₁₀ Cl ₁₀ , LiPF ₆ , LiCF ₃ SO ₃ , LiCF ₃ CO ₂ , LiAsF _{6, LiSbF 6, LiAlCl 4,} CH 3 SO 3 Li, CF 3 SO 3 Li, (CF 3 SO 2) 2 NLi, chloroborane lithium, lower aliphatic carboxylic acid lithium, lithium tetraphenyl borate and imide have.

In addition, the non-aqueous electrolyte solution has the purpose of improving charge / discharge characteristics, flame retardancy, etc., for example, pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylene diamine, n-glyme, hexaphosphate triamide , Nitrobenzene derivative, sulfur, quinone imine dye, N-substituted oxazolidinone, N, N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxy ethanol, aluminum trichloride, etc. can be added It might be. In some cases, in order to impart non-flammability, a halogen-containing solvent such as carbon tetrachloride or ethylene trifluoride may be further included, or carbon dioxide gas may be further included to improve high temperature storage characteristics.

On the other hand, when a solid electrolyte such as a polymer is used as the electrolyte solution, the solid electrolyte may also serve as the separation membrane described above.

Hereinafter, the secondary battery of the present invention will be described in detail.

Specifically, the pouch-type secondary battery includes an electrode assembly including an anode and a cathode in a state in which an electrode active material is charged in a grid, and an electrode assembly in which a separator having an electrolyte interposed therebetween is alternately stacked and stacked. It consists of a molded or stacked / folded structure. At this time, an anode tab is formed on one side of the anode, and a cathode tab is formed on one side of the cathode, and the anode tab and the cathode tab are arranged side by side at regular intervals. The tabs are connected to an external circuit by being electrically connected to a positive electrode lead and a negative electrode lead, respectively. The electrode assembly and the positive electrode lead and the negative electrode lead are sealed by an insulating battery case having a cover. At this time, a part of the positive electrode lead and the negative electrode lead are sealed by the battery case while exposed to the outside for electrical connection to the outside of the electrode assembly. In addition, an insulating film may be attached to a portion of the upper and lower surfaces of the positive electrode lead and the negative electrode lead to increase the sealing degree with the pouch and secure an electrical insulation state.

The battery case is usually made of an aluminum laminate sheet, provides a space for accommodating the electrode assembly, and has a pouch shape as a whole. The pouch-type secondary battery is manufactured through a process of heat-sealing an outer circumferential surface in which the upper laminate sheet and the lower laminate sheet of the battery case are embedded after the electrode assembly is embedded in the storage portion of the battery case and the electrolyte is injected.

Looking in more detail about the battery case of the laminate sheet structure, it is composed of an inner sealant layer for sealing, a metal layer for preventing material penetration, and an outer resin layer forming the outermost portion of the case. Among them, the internal sealant layer is heat-sealed to each other by heat and pressure applied in a state in which the electrode assembly is embedded, and serves to provide sealing properties, and is mainly composed of CPP (non-stretched polypropylene film). The metal layer serves to prevent air, moisture, etc. from entering the inside of the battery, and aluminum (Al) is mainly used. In addition, since the outer resin layer serves to protect the battery from the outside, excellent tensile strength and weather resistance to thickness are required, and ONy (stretched nylon film) is frequently used.

Hereinafter, examples will be described in detail to help understanding of the present invention. However, the embodiments according to the present invention can be modified in many different forms, and the scope of the present invention should not be construed as being limited by the following examples. The embodiments of the present invention are provided to more fully describe the present invention to those skilled in the art.

[Example 1]

An electrode slurry was prepared so that the electrode active material, the conductive material, and the binder were 96.5 wt%, 1.5 wt%, and 2.0 wt%, respectively, in a solvent, and an upper coating layer was prepared with a thickness of 60 μm on one side of the electrode current collector using a die coater. Did. A lower coating layer was prepared to a thickness of 80 μm by using a die coater on the other surface of the electrode current collector using the same electrode slurry.

After rolling the electrode current collector coated with the electrode slurry prepared as above, the lower coating layer was wound so that it was directed to the inside of the winding roll, and then the electrode was manufactured by vacuum drying.

[Example 2]

A first electrode slurry was prepared so that the electrode active material, the conductive material, and the binder in the solvent were 96.5% by weight, 1.5% by weight, and 2.0% by weight, respectively.

A second electrode slurry was prepared so that the electrode active material, the conductive material, and the binder in the solvent were 95.5 wt%, 1.5 wt%, and 3.0 wt%, respectively.

An upper coating layer was prepared by coating a first electrode slurry with a thickness of 60 μm on one surface of the electrode current collector using a die coater. Thereafter, a second electrode slurry was coated on the other surface of the electrode current collector to a thickness of 60 μm to prepare a lower coating layer.

After rolling the electrode current collector coated with the electrode slurry prepared as above, the lower coating layer was wound so that the inside of the winding roll faced, and then the electrode was manufactured by vacuum drying.

[Example 3]

A first electrode slurry was prepared so that the electrode active material, the conductive material, and the binder in the solvent were 96.5% by weight, 1.5% by weight, and 2.0% by weight, respectively.

Example 2 except that the second electrode slurry was prepared so that polyethylene was 96.0 wt%, 1.5 wt%, 2.0 wt%, and 0.5 wt%, respectively, as an electrode active material, a conductive material, a binder, and a volume expansion-inducing additive in a solvent. Electrodes were prepared in the same way.

[Comparative Example 1]

An electrode slurry was prepared so that the electrode active material, the conductive material, and the binder in the solvent were 96.5 wt%, 1.5 wt%, and 2.0 wt%, respectively, and the upper and lower coating layers were coated with a thickness of 60 μm on both sides of the electrode current collector using a die coater. An electrode was prepared in the same manner as in Example 1, except that was prepared.

(Comparison experiment of electrode bending)

Thereafter, the electrodes wound on the winding rolls of Examples 1 to 3 and Comparative Example 1 were unwound from the rolls to check the degree of bending (bending) of the electrodes when the assembly process was performed to manufacture the electrode assembly.

As a result of the experiment, it was visually confirmed that the bending angles of Examples 1 to 3 were larger than the bending angles of the electrodes according to Comparative Example 1, whereby the electrode produced by the embodiment according to the present invention has an effect of reducing bending. It was confirmed to exhibit.

101, 201, 301, 401, 501: electrode current collector,
102, 202, 302, 402, 502: upper coating layer,
103, 203, 303, 403, 503: lower coating layer,
110, 210, 310, 410, 510: electrode,
220, 520: winding roll,
404: volume expansion additive.

Claims (13)

Preparing an electrode slurry;
Preparing an upper coating layer and a lower coating layer by coating the electrode slurry on both sides of the electrode current collector, respectively;
Rolling; And
Winding and drying the lower coating layer of the current collector coated with the active material toward the inside of the winding roll;
It includes,
The lower coating layer is a method of manufacturing an asymmetric electrode, characterized in that the thickness is thicker than the upper coating layer.
According to claim 1,
The electrode is a method of manufacturing an asymmetric electrode, characterized in that the anode or the cathode.
According to claim 1,
Method of manufacturing an asymmetric electrode, characterized in that the thickness of the lower coating layer is 101 to 200% of the thickness of the upper coating layer.
An asymmetric electrode manufactured by the method of claim 1.
Preparing an electrode slurry;
Preparing an upper coating layer and a lower coating layer by coating the electrode slurry on both sides of the electrode current collector, respectively;
Rolling; And
Winding and drying the lower coating layer of the current collector coated with the active material toward the inside of the winding roll;
It includes,
The coating thickness of the upper coating layer and the lower coating layer is the same,
The asymmetric electrode manufacturing method characterized in that the composition of the electrode slurry for manufacturing the lower coating layer and the composition of the electrode slurry for manufacturing the upper coating layer are different from each other.
The method of claim 5,
The method of manufacturing an asymmetric electrode, characterized in that the binder content in the electrode slurry for manufacturing the lower coating layer is higher than the binder content in the electrode slurry for preparing the upper coating layer.
The method of claim 5,
The method of manufacturing an asymmetric electrode, characterized in that the binder content in the lower coating layer is 101 to 200% by weight compared to the binder content in the upper coating layer.
The method of claim 5,
The electrode slurry for manufacturing the lower coating layer is a method of manufacturing an asymmetric electrode, characterized in that it comprises an additive for inducing volume expansion.
The method of claim 8,
The content of the volume expansion inducing additive is a method of manufacturing an asymmetric electrode, characterized in that 0.01 to 1% by weight compared to the electrode slurry.
The method of claim 8,
The volume expansion inducing additives are polyethylene, polypropylene, polyethylene oxide, polypropylene oxide, polyvinylidene fluoride, polytetrafluoroethylene, polyvinylfluoride, polyacrylonitrile, polyvinyl chloride, polyvinylidene chloride , Polymethyl methacrylate, polymethyl acrylate, polyvinyl alcohol, polymethacrylonitrile, polyvinyl acetate, polyvinyl pyrrolidone, polycarbonate, polyethylene terephthalate, polycaprolactam, polyurethane, polyethyleneimine, poly A method of manufacturing an asymmetric electrode, characterized in that it is one or two or more selected from the group consisting of butadiene, polystyrene and polyisoprene.
The method of claim 5, wherein the electrode is an anode or a cathode.
An asymmetric electrode manufactured by the method of claim 5.
A secondary battery comprising the asymmetric electrode of claim 4 or 12.

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