Secondary battery electrode comprising highly adhesive electron conductive layer, manufacturing method therefor, and secondary battery

Abstract

Provided is a secondary battery electrode, which includes a highly adhesive electron conductive layer coupled to an electrode assembly, so as to have improved physical and electrochemical performances. One embodiment of the present invention provides a secondary battery electrode, which includes an electrode assembly and a highly adhesive electron conductive layer coupled to the electrode assembly, wherein the highly adhesive electron conductive layer comprises a substrate and a poly (ethylenedioxythiophene): poly (styrenesulfonate) (PEDOT:PSS).

Description

Electrode for secondary battery including high-adhesion electron-conducting layer, method for manufacturing same, and secondary battery

[0001] The present invention relates to an electrode for a secondary battery, and more specifically, to an electrode for a secondary battery having improved electrochemical performance including a high-adhesion electronic conductive layer, a method for manufacturing the same, and a secondary battery.

[0002] Secondary batteries, which can be repeatedly charged and discharged, are gaining attention as an alternative to fossil fuels. Secondary batteries have been primarily used in traditional handheld devices such as cell phones, video cameras, and power tools. However, their applications are increasingly expanding, encompassing electric vehicles (EVs, HEVs, PHEVs), large-capacity energy storage systems (ESSs), and uninterruptible power supply systems (UPSs).

[0003] Among these secondary batteries, lithium secondary batteries are representative not only as an energy source for mobile devices, but recently, they are being realized as a power source for electric vehicles and hybrid electric vehicles that can replace vehicles that use fossil fuels such as gasoline and diesel vehicles, which are one of the main causes of air pollution. Their use areas are also expanding to purposes such as auxiliary power sources through grid integration. However, electric vehicles currently lack competitiveness compared to existing internal combustion engines due to technological limitations such as short driving range and low energy density. To solve these problems, next-generation battery systems with high energy density are attracting attention, and in particular, efforts are being made to utilize NCM (Lithium nickel manganese cobalt oxides)-based lithium secondary batteries due to their high theoretical capacity.

[0004] The manufacturing process of lithium secondary batteries is largely divided into three stages: electrode process, assembly process, and formation process. The electrode process is further divided into active material mixing process, electrode coating process, drying process, rolling process, slitting process, and winding process. In the existing electrode manufacturing process, during the active material mixing process, a large amount of solvent is used for solvent and / or dispersion of various components such as electrode active materials or conductive materials, and in the electrode coating, an electrode is formed through a wet process in which a slurry-type electrode mixture composition is applied on a current collector and then the solvent is removed through drying.

[0005] However, when forming electrodes by this wet process, defects such as pinholes or cracks may be induced in the electrode active material layer during the process of evaporating and removing the solvent. In addition, a significant amount of energy is required to remove a large amount of solvent during the drying process, and a large and expensive drying device is required, which has the disadvantage of significantly reducing the processability of the overall secondary battery. In order to develop a high energy density battery, there is a continuous demand for manufacturing high loading electrodes, but high loading electrodes have a thick thickness, which limits their energy density. In this case, electrodes manufactured by the existing wet thick film process have the problem of the binder moving to the electrode surface during drying, which increases the surface resistance, and the binder moving to the surface weakens the adhesion at the bottom of the electrode, which reduces the life characteristics.

[0006] To address the shortcomings of these wet electrode manufacturing processes, active research has recently been conducted on methods for manufacturing dry electrodes for secondary batteries through a dry process that does not use solvents. Previously proposed methods for manufacturing dry electrodes mainly involved mixing electrode active material particles, conductive materials, and fiberizable organic binders in a solid state and applying shear force to obtain dry electrode powder, which was then calendered to produce a dry electrode composite film. However, existing dry electrodes suffer from low adhesion between the manufactured electrode and current collector, which leads to increased resistance and a shortened long-term lifespan. Therefore, there is a continuous need for technological development for a high-adhesion electronically conductive layer that not only improves the adhesion between the dry electrode and the current collector but also has high electronic conductivity.

[0007] The purpose of the present invention is to provide an electrode for a secondary battery and a method for manufacturing the same, which can prevent capacity reduction by reducing interfacial resistance by introducing a highly adhesive electronic conductive layer having high electronic conductivity and strong adhesive properties.

[0008] The purpose of the present invention is to provide an electrode for a secondary battery and a method for manufacturing the same, which can solve the limitations of high interfacial resistance, low electronic conductivity, and low adhesive strength with a current collector when manufacturing an electrode through a conventional dry process.

[0009] Another object of the present invention is to provide an electrode for a secondary battery and a method for manufacturing the same, which can simultaneously improve electrochemical performance, such as life performance and rate performance.

[0010] Another object of the present invention is to provide an electrode for a secondary battery and a method for manufacturing the same, which improves the charge / discharge capacity retention rate of the battery by reducing the decrease in battery capacity due to a decrease in interfacial resistance.

[0011] Another object of the present invention is to provide a high-adhesion electronically conductive layer that improves the physical and electrochemical performance of an electrode by combining with an electrode assembly, and a method for manufacturing the same.

[0012] Another object of the present invention is to provide a secondary battery including the electrode.

[0013] The purposes of the present invention are not limited to those mentioned above, and other unmentioned purposes and advantages of the present invention can be understood through the following description and will be more clearly understood through the embodiments of the present invention. Furthermore, it will be readily apparent that the purposes and advantages of the present invention can be realized by the means and combinations thereof set forth in the claims.

[0014] One embodiment of the present invention for achieving the above object provides an electrode for a secondary battery, which includes an electrode assembly and a high-adhesion electron-conducting layer combined with the electrode assembly, wherein the high-adhesion electron-conducting layer includes a substrate and a conductive polymer.

[0015] In one embodiment of the present invention, the conductive polymer may include at least one conductive polymer selected from the group consisting of polyfluorine polymers, polyphenylene polymers, polypyrene polymers, polyazulenes, polynaphthalenes, polyacetylenes, poly(p-phenylene vinylene), polypyrrole polymers, polycarbazole polymers, polyindoles, polyazepines, polyanilines, polythiophene polymers, and polyacrylic acid polymers.

[0016] In one embodiment of the present invention, the electrode assembly may include a current collector, an electrode active material, a dry conductive material, and a dry binder.

[0017] In one embodiment of the present invention, the collector may include at least one selected from the group consisting of stainless steel, aluminum, nickel, titanium, and silver (Ag).

[0018] In one embodiment of the present invention, the entire body may be carbon coated.

[0019] In one embodiment of the present invention, the electrode active material may be a lithium composite metal oxide including lithium and at least one metal selected from the group consisting of nickel (Ni), cobalt (Co), manganese (Mn), iron (Fe), and aluminum (Al).

[0020] Another embodiment of the present invention for achieving the above object can provide a method for manufacturing an electrode for a secondary battery, including the steps of mixing an electrode active material, a dry conductive material, and a dry binder and then performing a first fiberization, performing a second fiberization on the mixed powder subjected to the first fiberization using a cotton swab, performing a first rolling on the mixed powder subjected to the second fiberization, applying the mixed powder subjected to the first rolling on a current collector and performing a second rolling to manufacture an electrode assembly, mixing a conductive polymer and a solvent to manufacture a polymer solution, applying the polymer solution on a substrate to manufacture a high-adhesion electron-conducting layer, and laminating the electrode assembly on the high-adhesion electron-conducting layer and performing rolling.

[0021] In one embodiment of the present invention, the electrode active material, the dry conductive material, and the dry binder may be dry mixed.

[0022] In one embodiment of the present invention, the thickness of the electrode assembly may be 50 to 600 μm.

[0023] In one embodiment of the present invention, a step of heat-treating the electrode assembly laminated with the high-adhesion electron-conducting layer at 50 to 200°C for 5 minutes to 2 hours may be further included.

[0024] Another embodiment of the present invention for achieving the above object can provide a method for producing a high-adhesion electron-conducting layer, including the steps of preparing a polymer solution by mixing poly(ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) and a solvent, applying the polymer solution on a substrate to produce a high-adhesion electron-conducting layer, and performing a heat treatment at 50 to 200°C for 5 minutes to 2 hours.

[0025] In one embodiment of the present invention, the solvent may be an alcohol.

[0026] In one embodiment of the present invention, the alcohol may include at least one selected from the group consisting of ethylene glycol and methanol.

[0027] Another embodiment of the present invention for achieving the above purpose can provide a secondary battery including the electrode separator and electrolyte.

[0028] The solutions to the above problems do not enumerate all features of the present invention. The various features of the present invention, along with their corresponding advantages and effects, can be understood in more detail by referring to the specific examples below.

[0029] According to one embodiment of the present invention, a secondary battery electrode can be provided that can prevent capacity reduction by reducing interfacial resistance by introducing a high-adhesion electronic conductive layer having excellent electronic conductivity, strong adhesive properties, and flexibility.

[0030] According to another embodiment of the present invention, a high-adhesion electronic conductive layer having excellent electronic conductivity, strong adhesive properties, and flexibility is introduced, thereby providing an electrode for a secondary battery capable of resolving the limitations of low electronic conductivity and low adhesive strength with a current collector when manufacturing an electrode through a conventional dry process.

[0031] When manufacturing a secondary battery using these electrodes, electrochemical performance, such as life performance and rate performance, can be improved simultaneously.

[0032] Additionally, according to one embodiment of the present invention, a high-energy-density battery can be manufactured without applying a wet process, so that an electrode having excellent overall physical properties can be easily manufactured while taking advantage of the dry process that omits the use of a large amount of solvent or a drying process / device.

[0033] In addition to the effects described above, specific effects of the present invention are described below while explaining specific details for carrying out the invention.

[0034] Figures 1a to 1f are photographs of electrodes after a peel strength test (peel test) of electrodes for secondary batteries according to Example 2 and Comparative Examples 1 to 5.

[0035] Figure 2 is a graph showing the adhesive strength (N) in a peel test of the electrode for a secondary battery according to Example 2 and Comparative Examples 1 to 5.

[0036] Figure 3 shows the results of evaluating the cycle stability of a secondary battery (coin cell) including an electrode according to Examples 1 to 2 and Comparative Examples 1 to 5.

[0037] FIG. 4a is a Nyquist plot of a secondary battery cell after evaluating the cycle stability of the secondary battery (coin cell) including the electrode according to Examples 1 to 2 and Comparative Examples 1 to 5.

[0038] Figure 4b is an enlarged version of the Nyquist plot of Figure 4a, showing the frequency range from 1.0 MHz to 20 MHz.

[0039] Figure 5 shows the cycle stability and Coulombic Efficiency (CE) at 0.1 C for secondary batteries (coin cells) including electrodes according to Example 2 and Comparative Example 2.

[0040] The present invention will be described in more detail below with reference to the attached drawings. However, the attached drawings are merely examples intended to facilitate the description and scope of the technical concept of the present invention and are in no way intended to limit or alter the technical scope of the present invention. Furthermore, it will be apparent to those skilled in the art that various modifications and variations are possible within the scope of the technical concept of the present invention based on these examples.

[0041] In addition, terms or words used in this specification and claims should not be interpreted as limited to their usual or dictionary meanings, but should be interpreted as meanings and concepts that conform to the technical idea of ​​the present invention based on the principle that the inventor can appropriately define the concept of the term to explain his or her own invention in the best way. Therefore, it should be understood that the embodiments described in this specification are merely the most preferred embodiments of the present invention and do not represent all of the technical idea of ​​the present invention, and that there may be various equivalents and modified examples that can replace them at the time of this application.

[0042] One embodiment of the present invention provides an electrode for a secondary battery, comprising an electrode assembly and a high-adhesion electron-conducting layer coupled to the electrode assembly, wherein the high-adhesion electron-conducting layer includes a substrate and a conductive polymer.

[0043] When electrodes are manufactured using a conventional wet process, the solvent (e.g., NMP, distilled water) in the slurry used for electrode manufacturing is evaporated and removed, and the binder migrates to the electrode surface, which increases the electrode surface resistance and causes defects such as pinholes and cracks in the electrode active material layer. In addition, the binder that migrates to the surface may cause an insufficient binder content at the electrode-current collector interface, which may weaken the adhesive strength between the electrode and current collector, and this may result in a deterioration in the life characteristics of the secondary battery.

[0044] In addition, there was a problem that a considerable amount of energy was consumed to remove a large amount of solvent during the solvent drying process, which significantly lowered the manufacturing process of the secondary battery. The conventional dry electrode manufacturing technology developed to solve this problem has the advantage of being able to manufacture a thin battery while increasing the energy density, but there was a problem that the interfacial resistance increased and the life performance was deteriorated due to the low adhesive force between the electrode and the current collector. According to one embodiment of the present invention, by introducing a high-adhesion electron conductive layer having excellent electrical conductivity, strong adhesive properties, and flexibility, the peeling phenomenon can be prevented due to the excellent adhesive force between the electrode active material layer and the current collector.

[0045] When manufacturing a secondary battery using such an electrode, the interfacial resistance can be reduced to prevent a decrease in battery capacity, and as a result, electrochemical performance such as rate performance and life performance can be effectively improved.

[0046] Below, the configuration of the present invention is described in more detail.

[0047] 1. Electrode for secondary batteries

[0048] An electrode for a secondary battery according to the present invention includes an electrode assembly and a high-adhesion electron-conducting layer combined with the electrode assembly, wherein the high-adhesion electron-conducting layer includes a substrate and a conductive polymer.

[0049] The above electrode assembly includes a current collector, an electrode active material, a conductive material, and a binder. Here, the current collector can serve as a passage for transferring electrons from the outside to cause an electrochemical reaction in the active material, or for receiving electrons from the active material and sending them to the outside.

[0050] The current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery. Specifically, stainless steel, aluminum, nickel, titanium, silver (Ag), etc. can be used as the electrode current collector, and those surface-treated with carbon, nickel, titanium, silver, etc. can also be used. For example, those surface-treated with carbon, nickel, titanium, silver, etc. on the surface of stainless steel or aluminum can be used, and specifically, aluminum foil (Al foil) or aluminum foil coated with carbon can be used. The positive electrode current collector can typically have a thickness of 6 to 20 μm.

[0051] The above electrode active material may be a positive electrode active material, and the positive electrode active material is a compound capable of reversible absorption and release of lithium, and specifically, may include a lithium composite metal oxide containing lithium and at least one metal selected from the group consisting of nickel (Ni), cobalt (Co), manganese (Mn), iron (Fe), and aluminum (Al).

[0052] More specifically, the lithium composite metal oxide is a lithium-manganese oxide (e.g., LiMnO2, LiMn2O4, etc.), a lithium-cobalt oxide (e.g., LiCoO2, etc.), a lithium-nickel oxide (e.g., LiNiO2, etc.), a lithium-nickel-manganese oxide (e.g., LiNi 1-y1 Mn y1 O2 (where 0<y1<1), LiMn 2-z1 Ni z O4 (wherein, 0<Z1<2) etc.), lithium-nickel-cobalt oxides (e.g., LiNi 1-y2 Co y2 O2 (where 0<y2<1), etc.), lithium-manganese-cobalt oxides (e.g., LiCo 1-y3 Mn y3 O2 (where 0<y3<1), LiMn 2-z2 Co z2O4 (wherein, 0<Z2<2) etc.), lithium-nickel-manganese-cobalt oxides (e.g., Li(Ni p1 Co q1 Mn r1 )O2(wherein, 0<p1<1, 0<q1<1, 0<r1<1, p1+q1+r1=1), lithium-nickel-manganese-aluminum oxide Li(Ni p2 Co q2 Al r2 )O2 (wherein, 0<p2<2, 0<q2<2, 0<r2<2, p2+q2+r2=1), etc.), or lithium-nickel-cobalt-transition metal (M) oxide (e.g., Li(Ni p3 Co q3 Mn r3 M S3 )O2 (wherein, M is selected from the group consisting of Al, Fe, V, Cr, Ti, Ta, Mg, and Mo, and p3, q3, r3, and s3 are each independently an atomic fraction of an element, and 0<p3<1, 0<q3<1, 0<r3<1, 0<s3<1, p3+q3+r3+s3=1)), etc., and these may be included alone or may include two or more thereof.

[0053] Meanwhile, the electrode active material may be a negative electrode active material, and the negative electrode active material may be a silicon-based negative electrode active material, a graphite-based negative electrode active material, or a lithium metal oxide-based negative electrode active material.

[0054] The conductive material can improve conductivity between active material particles in the electrode or with the metal current collector and prevent the binder from acting as an insulator. The conductive material can be, for example, a mixture of one or two or more conductive materials selected from the group consisting of graphite, carbon black, carbon fiber, metal fiber, metal powder, conductive whisker, conductive metal oxide, activated carbon, and polyphenylene derivatives, and more specifically, a mixture of one or two or more conductive materials selected from the group consisting of natural graphite, artificial graphite, Super-p, acetylene black, Ketjen black, channel black, furnace black, lamp black, summer black, Denka black, aluminum powder, nickel powder, zinc oxide, potassium titanate, and titanium oxide.

[0055] The above binder can suppress separation between electrode active material particles, or between the electrode active material layer and the current collector. A polymer commonly used in electrodes in the relevant technical field can be used as the binder. Such binders include, but are not limited to, polyvinylidene fluoride, poly(vinylidene fluorideco-hexafluoropropylene), poly(vinylidene fluoride-co-trichloroethylene), poly(methylmethacrylate), poly(ethylhexylacrylate), poly(butylacrylate), poly(acrylonitrile), poly(vinylpyrrolidone), poly(vinyl acetate), poly(ethylene-co-vinyl acetate), poly(ethylene oxide), polyacrylate, cellulose acetate, cellulose It may include at least one selected from the group consisting of cellulose acetate butyrate, cellulose acetate propionate, cyano ethyl pullulan, cyano ethyl poly(vinylalcohol), cyanoethylcellulose, cyano ethylsucrose, pullulan, and carboxyl methyl cellulose.In particular, when a polymer capable of being fibrillated as the binder is used in the manufacture of a dry electrode, when a high shear force is applied during the mixing process of the active material, the binder, and the conductive material, the polymer capable of being fibrillated is physically stretched, and the stretched polymer can serve to capture the active material, thereby forming a web-like fiber network. In addition, when the adhesive force between the used binder and the conductive material is stronger than the adhesive force between the binder and the active material, the binder and the conductive material can be mixed to form conductive bond aggregates between the active material particles, which fill the space between the active material particles without wrapping them, thereby forming a conductive path, thereby facilitating the insertion and de-insertion of lithium ions from the active material.

[0056] The high-adhesion electron-conducting layer according to the present invention includes a substrate and a conductive polymer and is combined with the electrode assembly. The conductive polymer may include at least one conductive polymer selected from the group consisting of polyfluorine polymers, polyphenylene polymers, polypyrene polymers, polyazulenes, polynaphthalenes, polyacetylenes, poly(p-phenylene vinylene), polypyrrole polymers, polycarbazole polymers, polyindoles, polyazepines, polyanilines, polythiophene polymers, and polyacrylic acid polymers, and among them, polythiophene polymers are preferable. Poly(ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) is most preferred.

[0057] Poly(ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) is the most representative high-conductivity polymer material, and has excellent electrical conductivity and light transmittance, excellent flexibility, and strong adhesive properties. The high-adhesion electron-conducting layer can prevent the peeling phenomenon of the electrode when adhered to the electrode assembly by including poly(ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS), and thus, when a secondary battery is manufactured using the electrode of the present invention, the interfacial resistance is reduced, thereby preventing a decrease in the capacity of the battery, and as a result, the electrochemical performance such as rate performance and life performance can be effectively improved.

[0058] The above-mentioned substrate has high conductivity without causing chemical changes in the battery, and can use the same material as the current collector. Preferably, it is aluminum (Al) or nickel (Ni), and the current collector surface may be treated with carbon, nickel, titanium, silver, etc. Specifically, aluminum foil (Al foil) or aluminum foil coated with carbon, similar to the current collector, may be used.

[0059] 2. Manufacturing method of electrode for secondary battery

[0060] Another embodiment of the present invention can provide a method for manufacturing the electrode for the secondary battery. The above-described portions and repeated descriptions are briefly described or omitted.

[0061] A method for manufacturing an electrode for a secondary battery according to the present invention may include a step of mixing an electrode active material, a conductive material, and a binder and then performing a first fiberization, a step of performing a second fiberization on the mixed powder subjected to the first fiberization using a surface mill, a step of performing a first rolling on the mixed powder subjected to the second fiberization, a step of applying the mixed powder subjected to the first rolling onto a current collector and performing a second rolling to manufacture an electrode assembly, a step of mixing a conductive polymer and a solvent to produce a polymer solution, a step of applying the polymer solution onto a substrate to produce a high-adhesion electron-conducting layer, and a step of laminating the electrode assembly on the high-adhesion electron-conducting layer and performing rolling.

[0062] The current collector, the electrode active material, the conductive material, and the binder can be manufactured using a dry method that mixes the active material, the binder, and the conductive material without using a solvent, that is, a method in which each dry powder of the active material, the binder, and the conductive material is mixed, rolled, and applied to the current collector. Dry electrode processing can significantly reduce the cost of battery manufacturing by omitting the use of solvents and related equipment for solvent drying, and reducing processing costs. A high-intensity or high-energy mixer can be used to uniformly mix the dry powders of the electrode active material, the binder, and the conductive material, and a dry fiberization step can be performed using a jet mill using a high shear technique. In addition, a high-voltage electrostatic spray deposition method can be used to supply the dry mixture to the current collector. Preferably, the electrode active material, the binder, and the conductive material are mixed and then spun into a first fiberization process, and then a second fiberization process is performed using a cotton mill, thereby more uniformly dispersing each powder of the mixture. If step-by-step fiberization is not performed, the binder and conductive agent are not sufficiently dispersed while being mixed with the electrode active material, and if the rolling process is performed in this state, the binder and conductive agent are distributed only on a part of the surface of the active material particles, which is undesirable.

[0063] The method for manufacturing an electrode for a secondary battery according to the present invention can perform a first rolling process to form a fiberized mixed powder through a rolling roll into a target thickness. Thereafter, the mixed powder can be applied onto the current collector and a second rolling process can be performed to manufacture an electrode assembly. The thickness of the electrode assembly is preferably 300 to 900 μm. If the thickness is less than 300 μm, the energy density may be low, which may lower the target performance of the battery. If the thickness is more than 900 μm, the weight and volume of the battery may increase, and the charge / discharge efficiency may be lowered.

[0064] The method for manufacturing the high-adhesion electron-conducting layer may include a step of mixing poly(ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) and a solvent to prepare a polymer solution, and a step of applying the polymer solution onto a substrate. According to one embodiment of the present invention, the high-adhesion conductive layer may be laminated on the electrode assembly and rolled to bond the high-adhesion conductive layer to the electrode assembly. Preferably, the high-adhesion electron-conducting layer and the electrode assembly may be rolled and heat-treated at 50 to 200°C for 5 minutes to 2 hours to harden the polymer and strengthen the bonding strength between the electrode assembly and the high-adhesion electron-conducting layer. Specifically, by heat-treating the high-adhesion electron-conducting layer within the temperature and time ranges, the connection strength between a plurality of high-conductive polymers may be improved, and thus the durability of the electrode may be significantly improved.

[0065] Meanwhile, the method for manufacturing a secondary battery electrode according to the present invention can be used not only for manufacturing a small-area electrode at the coin cell level, but also for manufacturing a large-area electrode.

[0066] 3. Cathode

[0067] The secondary battery electrode of the present invention is preferably used as a positive electrode, but may also be used as a negative electrode. When the secondary battery electrode of the present invention is used as a positive electrode, the negative electrode of the present invention or a negative electrode manufactured by a conventional method known in the art may be used. The aforementioned portions and repeated descriptions will be briefly described or omitted.

[0068] A negative electrode manufactured by a conventional method known in the art can be manufactured by applying a negative electrode active material slurry containing a negative electrode active material, optionally a conductive material, a binder, a solvent, etc., onto a negative electrode current collector, followed by drying and rolling. Alternatively, the negative electrode can be manufactured by a dry method in which the negative electrode active material, a binder, and a conductive material are mixed without using a solvent.

[0069] The above negative electrode current collector is generally made with a thickness of 3 ㎛ to 500 ㎛. The negative electrode current collector is not particularly limited as long as it is conductive and does not cause a chemical change in the battery. For example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., aluminum-cadmium alloy, etc. can be used. In addition, like the positive electrode current collector, the bonding strength of the negative electrode active material can be strengthened by forming fine unevenness on the surface, and can be used in various forms such as a film, sheet, foil, net, porous body, foam, non-woven fabric, etc.

[0070] The above negative active material may be lithium metal, a lithium alloy, or a lithium metal oxide such as lithium titanium oxide, carbon such as non-graphitizable carbon, graphite carbon, etc. together. The lithium alloy may be an alloy composed of lithium and at least one metal selected from Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Ba, Ra, Al, and Sn. The conductive material is not particularly limited as long as it has conductivity and does not cause side reactions with other elements of the secondary battery, and for example, a single material selected from the group consisting of natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, carbon nanotubes, fullerene, carbon fiber, metal fiber, fluorocarbon, aluminum, nickel powder, zinc oxide, potassium titanate, titanium oxide, and polyphenylene derivatives, or a mixture of two or more thereof may be used.

[0071] The above binder is used to bind active material particles and maintain the molded body, and may be a single material selected from the group consisting of acrylonitrile-butadiene rubber, styrene-butadiene rubber (SBR), hydroxyethyl cellulose, vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyvinyl alcohol, starch, polyacrylonitrile, hydroxypropyl cellulose, regenerated cellulose, polymethyl methacrylate, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, and polytetrafluoroethylene (PTFE), or a mixture of two or more thereof.

[0072] 4. Secondary batteries

[0073] Another embodiment of the present invention can provide a secondary battery comprising the electrode, separator, and electrolyte. The above-described portions and repeated descriptions are briefly described or omitted.

[0074] The separation membrane according to the present invention may be, for example, a conventional porous polymer film, for example, a porous polymer film made of a polyolefin polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, and an ethylene / methacrylate copolymer, or the like, used alone or in a laminated manner, or a conventional porous nonwoven fabric, for example, a nonwoven fabric made of high-melting-point glass fiber, polyethylene terephthalate fiber, or the like, but is not limited thereto.

[0075] The electrolyte according to the present invention may include a solvent and a lithium salt.

[0076] The solvent according to the present invention may be, for example, one or a mixture of two or more selected from the group consisting of propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), dimethyl sulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, tetrahydrofuran, N-methyl-2-pyrrolidone (NMP), ethyl methyl carbonate (EMC), gamma butyrolactone (GBL), fluoroethylene carbonate (FEC), methyl formate, ethyl formate, propyl formate, methyl acetate, ethyl acetate, propyl acetate, pentyl acetate, methyl propionate, ethyl propionate, ethyl propionate, and butyl propionate.

[0077] Lithium salt according to the present invention is, for example, NO 3- , F - , Cl - , Br - , I - , PF6 - , FSI - , TFSI - It may contain anions such as, where FSI is bis(fluorosulfonyl)imide and TFSI is bis(trifluoromethylsulfonyl)imide.

[0078] If necessary, the electrolyte according to the present invention may further include an additive that contributes to protecting the surface of the electrode so that charge and discharge can be performed more stably when lithium ions move. For example, the additive may be one or a mixture of two or more selected from the group consisting of fluoroethylene carbonate (FEC), cyclohexylbenzene, biphenyl, vinylene carbonate, succinic anhydride, ethylene sulfite, propylene sulfite, dimethyl sulfite, propane sultone, butane sultone, methyl methane sulfonate, methyl toluene sulfonate, dimethyl sulfate, ethylene sulfate, sulfolane, dimethyl sulfone, diethyl sulfone, dimethyl sulfoxide, diethyl sulfoxide, tetramethylene sulfoxide, diphenyl sulfide, thioanisole, diphenyl disulfide, and dipyridinium disulfide.

[0079] According to another embodiment of the present invention, any one of a battery module including the secondary battery as a unit battery, a battery pack including the battery module, and a device including the battery pack as a power source may be provided. Specific examples of the device include, but are not limited to, a power tool that is powered by an electric motor; an electric vehicle including an electric vehicle (EV), a hybrid electric vehicle (HEV), a plug-in hybrid electric vehicle (PHEV), etc.; an electric two-wheeled vehicle including an electric bicycle (E-bike) and an electric scooter (E-scooter); an electric golf cart; and a power storage system.

[0080] Hereinafter, embodiments of the present invention will be described in detail so that those skilled in the art can easily implement the present invention. However, this is merely an example, and the scope of the present invention is not limited by the following contents.

[0081] [Manufacturing Example 1: Manufacturing of a Dry Anode]

[0082] Cathode active material (Li(Ni) 0.8 Mn 0.1 Co 0.1 )O2), the conductive agent (Super P), and the binder (PTFE (polytetrafluoroethylene)) were mixed in the first stage at a weight of 9.6 g, 0.2 g, and 0.2 g, respectively, and then the first fiberization was performed using a mortar.

[0083] After completing the first fiberization, a second fiberization and second dispersion were performed using a noodle machine, and a dry electrode of approximately 600 μm was manufactured. The dry electrode after the second fiberization was rolled into a dry electrode with a thickness of 500 μm using a roll pressing method.

[0084] [Manufacturing Example 2: Preparation of a Polymer Solution]

[0085] PEDOT:PSS, ethylene glycol, and methanol were mixed in weights of 1 g, 1.113 g, and 3.95 g, respectively, and stirred for more than 6 hours to prepare a polymer solution.

[0086] [Manufacturing Example 3: Manufacturing of a Dry Anode]

[0087] <Example 1>

[0088] The polymer solution prepared in Manufacturing Example 2 was applied to an aluminum (Al) current collector cut to a size of 20 mm X 20 mm using a spin coating device at 2000 rpm for 30 seconds. The applied aluminum current collector was laminated with the dry electrode prepared in Manufacturing Example 1 and rolled together. Thereafter, the polymer was hardened by heating at 150°C for 5 minutes, and the final positive electrode was prepared.

[0089] <Example 2>

[0090] The polymer solution prepared in Manufacturing Example 2 was applied to a carbon-coated aluminum current collector cut to a size of 20 mm X 20 mm using a spin coating device at 2000 rpm for 30 seconds. The applied carbon-coated aluminum current collector was rolled together with the dry electrode prepared in Manufacturing Example 1. Thereafter, the polymer solution was heated at 150°C for 5 minutes to harden the polymer and prepare a final positive electrode.

[0091] <Comparative Example 1>

[0092] An aluminum (Al) current collector cut to a size of 20 mm X 20 mm was rolled together with the dry electrode manufactured in Manufacturing Example 1 to manufacture a positive electrode.

[0093] <Comparative Example 2>

[0094] Carbon coated aluminum (Carbon coated Al) cut to a size of 20 mm X 20 mm was rolled together with the dry electrode manufactured in Manufacturing Example 1 to manufacture an anode.

[0095] <Comparative Example 3>

[0096] Poly(ethylene oxide) and NMP (1-Methyl-2-Pyrrolidone) were mixed in weights of 1 g and 500 g, respectively, and stirred for more than 6 hours to prepare a solution. This solution was applied to a carbon-coated aluminum current collector cut to a size of 20 mm X 20 mm using a spin coating device at 2000 rpm for 30 seconds. The applied carbon-coated aluminum current collector was rolled together with the dry electrode manufactured in Manufacturing Example 1. Thereafter, the polymer was cured by heating to 100°C, and the final positive electrode was manufactured.

[0097] Comparative Example 4

[0098] An anode was manufactured in the same manner as in Comparative Example 3 above, except that PVdF-HFP (Poly(vinylidene fluoride-co-hexafluoropropylene)) was used instead of poly(ethylene oxide).

[0099] Comparative Example 5

[0100] Ethyl cellulose and isopropyl alcohol were mixed in weights of 1 g and 500 g, respectively, and stirred for more than 6 hours to prepare a solution. This solution was applied to a carbon-coated aluminum current collector cut to a size of 20 mm X 20 mm using a spin coating device at 2000 rpm for 30 seconds. The applied carbon-coated aluminum current collector was rolled together with the dry electrode manufactured in Manufacturing Example 1. Thereafter, the polymer was cured by heating to 100°C, and the final positive electrode was manufactured.

[0101] [Experimental Example 1: Peel test]

[0102] A peel strength test (Peel test) was performed on the electrodes (positive electrodes) manufactured in Example 2 and Comparative Examples 1 to 5. FIGS. 1a to 1f are photographs of electrodes after the peel strength test (Peel test) of the electrodes according to Example 2 and Comparative Examples 1 to 5. FIG. 2 is a graph showing the adhesive strength (N) in the peel strength test (Peel test) of the electrodes for secondary batteries according to Example 2 and Comparative Examples 1 to 5.

[0103] Referring to FIGS. 1A to 1F, it can be confirmed with the naked eye that the electrode constituent materials of Example 2 are not peeled off from the tape, confirming that the adhesive force between the electrode and the current collector is very strong.

[0104] In addition, it was confirmed that some of the electrode constituent materials of the electrode of Comparative Example 4 were peeled off from the tape, and although the adhesive strength was not as strong as that of Example 2, it was confirmed that the electrode had a higher adhesive strength than the other experimental groups.

[0105] Referring to FIG. 2, the electrode of Example 2 has the highest adhesive strength with a peel strength of 1.25972 N, and the electrode of Comparative Example 4 using PVdF-HFP as the polymer has a peel strength of 0.73001 N, confirming that the adhesive strength is about 60% or less than that of the electrode of Example 2. The remaining comparative examples have adhesive strengths of about 15% or less than that of the electrode of Example 2. Therefore, it can be confirmed that the adhesive strength of the electrode according to one embodiment of the present invention is very excellent.

[0106] [Manufacturing Example 4: Manufacturing of a secondary battery including a dry cathode]

[0107] The electrodes manufactured in Examples 1 to 2 and Comparative Examples 1 to 5 were assembled into a 2032 coin cell type.

[0108] [Experimental Example 2: Electrochemical Performance Experiment]

[0109] An electrochemical performance test was performed using the secondary battery manufactured in the above Manufacturing Example 4, and specifically, a rate evaluation test was performed for a total of 35 cycles, with 5 cycles each at 0.1 C, 0.2 C, 0.5 C, 1.0 C, 2.0 C, 3.0 C, and 0.1 C.

[0110] Figure 3 shows the results of rate evaluation of secondary batteries (coin cells) including electrodes according to Examples 1 to 2 and Comparative Examples 1 to 5.

[0111] Referring to Figure 3, the discharge capacity of Example 2 is 128.69 mAh g at 2.0 C and 3.0 C, respectively. -1 , 55.35 mAh g -1It can be confirmed that it exhibits the best rate characteristics. In addition, the discharge capacities of Comparative Examples 1, 3 to 5 are 80 mAh g at 2.0 C and 3.0 C, respectively. -1 Below, about 50 mAh g -1 As shown below, it can be seen that the rate performance is significantly reduced.

[0112] [Experimental Example 3: Electrochemical Impedance Spectrum (EIS) Analysis]

[0113] Fig. 4a shows a Nyquist plot of a secondary battery (coin cell) after rate evaluation of the secondary battery including the electrode according to Examples 1 and 2 and Comparative Examples 1 to 5. Fig. 4b shows data in the frequency range from 1.0 MHz to 20 MHz by enlarging the Nyquist plot of Fig. 4a.

[0114] Referring to Figures 4a and 4b, it can be confirmed that the EIS semicircle of Comparative Example 1 is the largest, and thus the resistance of the secondary battery including the electrode according to Comparative Example 1 has the largest value.

[0115] Meanwhile, the resistance of the secondary battery including the electrode according to Example 1 is the second highest after that of Comparative Example 1, and the resistance of the secondary battery including the electrode according to Example 2 and Comparative Example 2 is the lowest, so it can be confirmed that the resistance of the secondary battery is lowered when a carbon-coated aluminum current collector is used.

[0116] In the case of Example 2 using the conductive polymer PEDOT:PSS, it can be confirmed that a lower resistance is measured than in Comparative Examples 3 to 5 using non-conductive polymers. Therefore, it can be confirmed that the secondary battery according to one embodiment of the present invention has improved electrochemical performance while reducing the decrease in battery capacity through suppression of resistance increase.

[0117] [Experimental Example 4: Evaluation of Lifespan and Coulombic Efficiency]

[0118] Figure 5 shows the results of evaluating the life performance and Coulombic Efficiency (CE) of a secondary battery (coin cell) including an electrode according to Example 2 and Comparative Example 2. In this experimental example, the battery was charged and discharged at 0.1 C.

[0119] Referring to FIG. 5, it can be confirmed that the life performance of the secondary battery including the electrode according to Example 2 is superior to that of the secondary battery including the electrode according to Comparative Example 2.

[0120] It was confirmed that the capacity retention rate of the secondary battery including the electrode according to Comparative Example 2 was about 3.51% around 160 cycles, and the coulombic efficiency was reduced to about 65%, whereas the capacity retention rate of the secondary battery including the electrode according to Example 2 was about 67%, and the coulombic efficiency was close to 100%.

[0121] Considering the above experimental results comprehensively, it can be inferred that by introducing a high-adhesion electronic conductive layer with excellent electrical conductivity, strong adhesive properties, and flexibility, the interfacial resistance is reduced, thereby preventing a decrease in battery capacity, effectively improving rate performance and life performance, and exhibiting high stability and long life effects.

[0122] Although the preferred embodiments of the present invention have been described in detail above, the scope of the present invention is not limited thereto, and various modifications and improvements made by those skilled in the art using the basic concept of the present invention defined in the following claims also fall within the scope of the present invention.

Claims

1. Electrode assembly; and A highly adhesive conductive layer coupled to the above electrode assembly, The above high-adhesion electron-conducting layer is an electrode for a secondary battery including a substrate and a conductive polymer.

2. In paragraph 1, The conductive polymer is an electrode for a secondary battery comprising at least one conductive polymer selected from the group consisting of polyfluorine polymers, polyphenylene polymers, polypyrene polymers, polyazulenes, polynaphthalenes, polyacetylenes, poly(p-phenylene vinylene), polypyrrole polymers, polycarbazole polymers, polyindoles, polyazepines, polyanilines, polythiophene polymers, and polyacrylic acid polymers.

3. In paragraph 1, The above electrode assembly is an electrode for a secondary battery including a current collector, an electrode active material, a dry conductive material, and a dry binder.

4. In paragraph 3, The above electrode for a secondary battery comprises at least one selected from the group consisting of stainless steel, aluminum, nickel, titanium and silver (Ag).

5. In paragraph 4, The above electrode for a secondary battery is a carbon-coated electrode.

6. In paragraph 3, The electrode active material is a lithium composite metal oxide electrode for a secondary battery containing lithium and at least one metal selected from the group consisting of nickel (Ni), cobalt (Co), manganese (Mn), iron (Fe), and aluminum (Al).

7. A step of performing first fiberization after mixing the electrode active material, dry conductive agent, and dry binder; A step of performing a second fiberization using a noodle machine on the mixed powder that has undergone the first fiberization; A step of performing first rolling on the mixed powder that has undergone the second fiberization; A step of manufacturing an electrode assembly by applying the mixed powder subjected to the first rolling on the entire body and performing a second rolling; A step of preparing a polymer solution by mixing a conductive polymer and a solvent; A step of manufacturing a high-adhesion electronic conductive layer by applying the polymer solution on a substrate; and A method for manufacturing an electrode for a secondary battery, comprising the step of laminating the electrode assembly on the high-adhesion electron-conducting layer and performing rolling.

8. In paragraph 7, A method for manufacturing an electrode for a secondary battery, wherein the above electrode active material, the dry conductive material, and the dry binder are dry mixed.

9. In paragraph 7, A method for manufacturing an electrode for a secondary battery, wherein the thickness of the electrode assembly is 50 to 600㎛.

10. In paragraph 7, A method for manufacturing an electrode for a secondary battery, further comprising a step of heat-treating the electrode assembly laminated with the high-adhesion electron-conducting layer at 50 to 200°C for 5 minutes to 2 hours.

11. It is laminated with an electrode assembly for a secondary battery, Poly(ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT:PSS) and a substrate, The above-described material is a high-adhesion electronic conductive layer comprising at least one selected from the group consisting of aluminum (Al) and nickel (Ni).

12. A step of preparing a polymer solution by mixing poly(ethylenedioxythiophene):poly(styrenesulfonate)(PEDOT:PSS) and a solvent; A step of manufacturing a high-adhesion electronic conductive layer by applying the polymer solution on a substrate; A method for manufacturing a high-adhesion electronic conductive layer, comprising a step of heat treating at 50 to 200°C for 5 minutes to 2 hours.

13. In paragraph 12, A method for manufacturing a high-adhesion electronic conductive layer, wherein the solvent is an alcohol.

14. In paragraph 13, A method for manufacturing a high-adhesion electronic conductive layer, wherein the alcohol comprises at least one selected from the group consisting of ethylene glycol and methanol.

15. In paragraph 12, A method for manufacturing a high-adhesion electronic conductive layer in which the above polymer solution is applied onto the substrate using a spin coating device.

16. Electrode according to paragraph 1; membrane; and A secondary battery containing an electrolyte.

17. Electronic devices including secondary batteries according to Article 16

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