Electrode for secondary battery and method for manufacturing the same

Abstract

An electrode for a secondary battery according to an embodiment of the present disclosure includes: an electrode current collector; and an active material layer disposed on the electrode current collector, wherein the active material layer is formed by coating an electrode paste prepared from an aqueous solution containing an anode active material, a conductive material, a surfactant, and a binder onto the electrode current collector, and wherein the binder includes a water-soluble polymer.

Description

Technical Field

[0001] Cross - reference to related applications

[0002] This application claims the benefit of Korean Patent Application Nos. 10-2020-0113648, filed with the Korean Intellectual Property Office on September 7, 2020, and 10-2021-0110158, filed with the Korean Intellectual Property Office on August 28, 2021, the disclosures of which are incorporated herein by reference in their entirety.

[0003] The present disclosure relates to an electrode for a secondary battery and a method of manufacturing an electrode for a secondary battery, and more particularly, to an electrode for a secondary battery having improved dispersibility and viscosity and a method of manufacturing an electrode for a secondary battery. Background Art

[0004] As the technology development and demand for mobile devices increase, the demand for secondary batteries as an energy source has rapidly increased. Among these secondary batteries, lithium secondary batteries having high energy density, high voltage, long cycle life, and low self-discharge rate are commercially available and widely used.

[0005] In particular, secondary batteries are attracting attention as an energy source for power-driven devices such as electric bicycles, electric vehicles, and hybrid electric vehicles, and as an energy source for mobile devices such as mobile phones, digital cameras, laptop computers, and wearable devices.

[0006] In addition, as the attention to environmental problems increases, research on electric vehicles, hybrid electric vehicles, etc., which can replace fossil fuel-powered vehicles such as gasoline vehicles and diesel vehicles, which are one of the main causes of air pollution, is becoming more frequent. Although nickel-metal hydride secondary batteries are mainly used as power sources for electric vehicles and hybrid electric vehicles, research on using lithium secondary batteries having high energy density and discharge voltage is being actively conducted, and some of them are in the commercialization stage.

[0007] When manufacturing an anode in a conventional secondary battery electrode, the electrode paste applied to the electrode current collector is divided into an organic-based and a water-based. At this time, in terms of cost, such as manufacturing cost and management cost, the water-based electrode paste is more advantageous than the organic-based electrode paste, and thus conventional anodes for secondary batteries have been manufactured using the water-based electrode paste.

[0008] In addition, generally, graphite, which is an anode active material contained in an anode for a secondary battery, is a material that cannot be dispersed in water. Therefore, a conventional anode for a secondary battery includes carboxymethyl cellulose (CMC) in an aqueous electrode paste to ensure the dispersibility of graphite and the viscosity of the electrode paste.

[0009] However, the solubility of carboxymethyl cellulose in water is relatively low. Therefore, there is a limitation in increasing the content of the anode active material that can be contained in the aqueous electrode paste. In addition, since the solubility of carboxymethyl cellulose in water is low, undissolved substances or insoluble substances (micro-gel) may be generated. As a result, problems such as gelation, defects on the electrode surface, and clogging of filters in pipelines occur, and thus the electrode quality deteriorates.

[0010] In addition, considering the low solubility of carboxymethyl cellulose in water, in the case of a conventional aqueous electrode paste, in order to improve the dispersibility of graphite, further separate high-viscosity kneading is required. Here, high-viscosity kneading applies a uniform shear force to the solid components in a high-viscosity dough to improve the dispersibility of the solid components. However, it is limited to improve the dispersibility of the solid components only by high-viscosity kneading. When the shear force cannot be sufficiently applied in high-viscosity kneading, there is a problem that the dispersibility and phase stability of the electrode paste deteriorate.

[0011] In addition, when the viscosity of the electrode paste is determined by the solvent added after high-viscosity kneading, the solid components inevitably decrease, and there are problems of reduced process efficiency and increased process complexity.

[0012] Therefore, it is necessary to develop an electrode including an aqueous electrode paste that can overcome the limitations of carboxymethyl cellulose and a method for manufacturing the electrode. Specifically, there is an increasing need to develop an electrode including an aqueous electrode paste having a high solid content while improving the dispersibility and viscosity of the solid components contained in the electrode paste. SUMMARY OF THE INVENTION

[0013] TECHNICAL PROBLEM

[0014] An object of the present disclosure is to provide an electrode for a secondary battery having improved dispersibility and viscosity, and a method for manufacturing the electrode for a secondary battery.

[0015] The object of the present disclosure is not limited to the above object, and those skilled in the art should clearly understand other objects not described herein through the following detailed description and the drawings.

[0016] Technical solution

[0017] According to an embodiment of the present disclosure, there is provided an electrode for a secondary battery, comprising: an electrode current collector; and an active material layer located on the electrode current collector, wherein the active material layer is formed such that an electrode paste prepared from an aqueous solution containing an anode active material, a conductive material, a surfactant, and a binder is coated onto the electrode current collector, and wherein the binder comprises a water-soluble polymer.

[0018] The electrode paste may have a solid content of 50 wt% to 90 wt% based on the total weight of the electrode paste.

[0019] The viscosity of the electrode paste may be 1000 cps to 50000 cps.

[0020] The content of the surfactant may be 0.01 wt% to 10 wt% based on the total weight of the electrode paste.

[0021] The surfactant may include at least one of tert-octylphenoxy polyethoxyethanol, octylphenoxy polyethoxyethanol, and polysorbate 20.

[0022] The viscosity of the binder may be 3000 cps to 50000 cps.

[0023] The binder may include at least one of polyvinylpyrrolidone, polyimide, polyacrylonitrile, and polyamide.

[0024] The anode active material may include graphite, a silicon oxide-based material (SiO x ) or a mixture thereof.

[0025] The conductive material may include a carbon-based material, CNT (carbon nanotube), graphene, or a mixture thereof.

[0026] According to another embodiment of the present disclosure, there is provided a secondary battery including the above electrode for a secondary battery.

[0027] According to still another embodiment of the present disclosure, there is provided a method for manufacturing an electrode for a secondary battery, comprising the steps of: mixing an anode active material and a conductive material with an aqueous surfactant solution to prepare a first solution; mixing a binder with the first solution to prepare an electrode paste; and applying and coating the electrode paste onto an electrode current collector, wherein the binder may include a water-soluble polymer.

[0028] The electrode paste may have a solids content of 50 wt% to 90 wt% based on the total weight of the electrode paste.

[0029] The viscosity of the electrode paste may be from 1000 cps to 50000 cps.

[0030] The content of the surfactant may be from 0.01 wt% to 10 wt% based on the total weight of the electrode paste.

[0031] The viscosity of the binder may be from 3000 cps to 50000 cps.

[0032] Advantageous Effects

[0033] According to various embodiments of the present disclosure, there is provided an electrode for a secondary battery and a method of manufacturing the same, in which the electrode is formed by coating an electrode paste including a surfactant and a binder including a water-soluble polymer onto an electrode current collector, and thus the dispersibility of the active material in the electrode paste can be improved and the viscosity of the electrode paste can be improved.

[0034] The effects of the present disclosure are not limited to the above effects, and those skilled in the art will clearly understand other additional effects not described above from the specification and the appended claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 is a magnified image of the dispersion according to the comparative example; and

[0036] Figure 2 is a magnified image of the dispersion according to an embodiment of the present disclosure. DETAILED DESCRIPTION

[0037] Hereinafter, various embodiments of the present disclosure will be described in detail with reference to the drawings so that those skilled in the art can easily implement them. The present disclosure can be modified in various different ways and is not limited to the embodiments set forth herein.

[0038] Now, an electrode for a secondary battery and a method of manufacturing the same according to an embodiment of the present disclosure will be described.

[0039] An electrode for a secondary battery according to an embodiment of the present disclosure includes: an electrode current collector; and an active material layer located on the electrode current collector, wherein the active material layer is formed by coating an electrode paste prepared from an aqueous solution including an anode active material, a conductive material, a surfactant, and a binder onto the electrode current collector, and wherein the binder includes a water-soluble polymer.

[0040] In addition, the electrode paste may have a solid component of 30 wt% to 90 wt% based on the total weight of the electrode paste. More preferably, the electrode paste may have a solid component of 30 wt% to 80 wt% based on the total weight of the electrode paste. As an example, the electrode paste may have a solid component of 50 wt% to 90 wt% based on the total weight of the electrode paste.

[0041] When the content of the solid contained in the electrode paste satisfies the above range, the electrode paste may contain a sufficient amount of the anode active material, which may be advantageous in terms of electrode quality, manufacturing cost, and process control. When the solid component of the electrode paste is less than 30 wt%, the electrode paste contains a relatively small amount of the anode active material, so the battery performance deteriorates, which may be disadvantageous in terms of time and cost depending on the manufacturing process. In addition, when the solid component of the electrode paste exceeds 90 wt%, the electrode paste has no fluidity, so it cannot be coated on the current collector, and the phase stability of the electrode paste is very unstable, the solid component is difficult to disperse in the electrode paste, and the quality of the electrode, such as surface defects of the electrode, deteriorates.

[0042] In addition, the viscosity of the electrode paste may be 1000 cps to 50000 cps. More preferably, the viscosity of the electrode paste may be 3000 cps to 30000 cps. In one example, the viscosity of the electrode paste may be 4000 cps to 20000 cps.

[0043] When the viscosity of the electrode paste satisfies the above range, sedimentation of the solid component contained in the electrode paste can be suppressed, and the dispersed state of the active material may not be maintained evenly for a long time. When the viscosity of the electrode paste is less than 1000 cps, it is difficult to suppress sedimentation of the solid component in the electrode paste, so the dispersed state of the active material may not be maintained evenly for a long time. In addition, when the viscosity of the electrode paste is greater than 50000 cps, it may be difficult to stir the electrode paste, so the degree of dispersion of the solid component may be greatly reduced.

[0044] Hereinafter, each component included in the electrode for a secondary battery according to an embodiment of the present disclosure will be described in detail.

[0045] The active material may be an anode active material. The anode active material may be an anode active material commonly used in the art for lithium secondary batteries. As an example, materials such as lithium metal, lithium alloy, petroleum coke, activated carbon, graphite, silicon, tin, metal oxide, or other carbon may be used. More preferably, the anode active material may be Graphite, silicon oxide-based material (SiO x ) or a mixture thereof.

[0046] More specifically, most anode active materials can be hydrophobic and have low reactivity with water. Thus, in the electrode for a secondary battery according to the present embodiment, even if the electrode paste further includes an aqueous solvent matrix such as distilled water (Di water) as a solvent together with the anode active material, no reaction occurs between the anode active material and the solvent, and thus the capacity of the electrode can be easily achieved and the resistance can be small.

[0047] However, general cathode active materials are metal oxide-based materials including lithium (Li) and have high reactivity with water due to their hydrophilicity. Thus, when an aqueous solvent matrix such as distilled water (Di water) as a solvent is included together with the cathode active material as the electrode paste, reaction often occurs between the cathode active material and water, making it difficult to achieve the capacity of the electrode and correspondingly presenting technical limitations such as a very large resistance. In addition, considering the reactivity between the cathode active material and water, there is a problem that it is very difficult to manage moisture in the process.

[0048] Therefore, in the case of a water-based electrode paste using an aqueous solvent matrix such as distilled water (Di water) as a solvent, similar to the electrode for a secondary battery according to the present embodiment, the active material is preferably an anode active material.

[0049] The content of the anode active material can be 40 wt% to 80 wt% based on the total weight of the electrode paste. More preferably, the content of the anode active material can be 45 wt% to 70 wt% based on the total weight of the electrode paste. As an example, the content of the anode active material can be 50 wt% to 65 wt% based on the total weight of the electrode paste.

[0050] When the content of the anode active material contained in the electrode paste satisfies the above range, the electrode paste can contain a sufficient amount of the anode active material, which is advantageous in terms of electrode quality, manufacturing cost, and process control. When the electrode paste contains less than 40 wt% of the anode active material, the electrode paste contains a relatively small amount of the anode active material, so the battery performance will decline, which is disadvantageous in terms of time and cost depending on the manufacturing process. In addition, when the electrode paste contains more than 80 wt% of the anode active material, there may be anode active materials that are not dispersed in the electrode paste, and the electrode quality such as surface defects of the electrode will deteriorate.

[0051] The surfactant can be a non-ionic surfactant. In one example, the surfactant can include t-Octylphenoxypolyethoxyethanol (Triton X-100), octylphenoxypolyethoxyethanol (Nonidet P40 or IGEPAL CA-630), Polyoxyethylene(20), sorbitan monolaurate (Tween20), and the like, and one of them can be used alone or a mixture of two or more of them can be used. However, the surfactant is not limited to the above materials, and any surfactant that can disperse the anode active material in an aqueous solvent matrix such as distilled water (Di water) can be included in the surfactant of the present disclosure.

[0052] The surfactant can act as a dispersant in the electrode paste. Specifically, the surfactant can disperse the anode active material contained in the electrode paste. More specifically, from the perspective that most of the anode active materials are hydrophobic, the surfactant can improve the dispersibility of the anode active material in an aqueous solvent matrix such as distilled water (Di water) as a solvent.

[0053] Therefore, different from the conventional water-based electrode paste, in the case of the present embodiment, the anode active material is easily dispersed in the solvent by the surfactant, so that the solid content of the electrode paste can be further increased. In addition, in the case of the present embodiment, a separate high-viscosity kneading for improving the dispersibility of graphite may not be performed additionally, which has the advantages of not only improving the process efficiency but also simplifying the process.

[0054] The content of the surfactant can be 0.01 wt% to 10 wt% based on the total weight of the electrode paste. More preferably, the content of the surfactant can be 0.01 wt% to 5 wt% based on the total weight of the electrode paste. In one example, the content of the surfactant can be 0.1 wt% to 1 wt% based on the total weight of the electrode paste.

[0055] When the content of the surfactant satisfies the above range, the dispersibility of the active material contained in the electrode paste can be improved, and the content of the active material that can be contained in the electrode paste can also be increased. When the content of the surfactant is less than 0.01% by weight, it is difficult to disperse a sufficient amount of the active material and the conductive material in the electrode paste, and the quality of the electrode paste may deteriorate. In addition, when the content of the surfactant exceeds 10% by weight, there are problems such as excessive generation of bubbles caused by the surfactant, difficulty in handling the electrode paste, and side reactions of the surfactant with the electrolyte, thereby reducing the battery performance.

[0056] The conductive material is used to impart conductivity to the electrode, and the conductive material can be used without particular limitation as long as it has electronic conductivity and does not cause chemical changes to the constructed battery. Specific examples of the conductive material include: carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal carbon black, carbon graphene, and carbon fiber; graphite such as natural graphite and artificial graphite; metal powders or metal fibers such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives, and one of them can be used alone or a mixture of two or more of them can be used. More preferably, the conductive material can be a carbon-based material, CNT (Carbon nanotube), Graphene, or a mixture thereof.

[0057] The content of the conductive material can be 0.01% by weight to 20% by weight based on the total weight of the electrode paste.

[0058] The binder serves to improve the adhesion between the anode active material particles and the adhesion between the anode active material and the current collector. In addition, the binder has a high viscosity and is used to improve the viscosity of the electrode paste.

[0059] In one example, the binder can generally include polyvinylidene fluoride (PVDF), vinylidene fluoride-co-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, or various copolymers thereof, and one of them can be used alone or a mixture of two or more of them can be used.

[0060] More preferably, the binder may include a water-soluble polymer. The binder containing the water-soluble polymer may include polyvinyl acetate (PVA), polyacrylic acid (PAA), polyacrylate, ethylene-vinyl acetate, styrene-acrylate resin, styrene-butadiene resin (SBR), polyvinyl alcohol (PVA), carboxymethyl cellulose (CMC), starch, cellulose resin, alginate, polyurethane, polyethylene oxide (PEO), polyvinyl pyrrolidone (PVP), polyimide (PI), polyacrylonitrile (PAN), polyamide (PA), and the like. One of them can be used alone or a mixture of two or more of them can be used.

[0061] As the binder according to the present embodiment, in addition to carboxymethyl cellulose (CMC) and styrene-butadiene resin (SBR) among the water-soluble polymers listed above, polyvinyl acetate (PVA), polyacrylic acid (PAA), polyacrylate, ethylene-vinyl acetate, styrene-acrylate resin, polyvinyl alcohol (PVA), starch, cellulose resin, alginate, polyurethane, polyethylene oxide (PEO), polyvinyl pyrrolidone (PVP), polyimide (PI), polyacrylonitrile (PAN), polyamide (PA), or various copolymers thereof, and the like can be used. One of them can be used alone or a mixture of two or more of them can be used.

[0062] The content of the binder may be 1 wt% to 30 wt% based on the total weight of the electrode paste. More preferably, the content of the binder may be 1 wt% to 20 wt% based on the total weight of the electrode paste. In one example, the content of the binder may be 1 wt% to 10 wt% based on the total weight of the electrode paste.

[0063] In addition, the viscosity of the binder may be 3000 cps to 50000 cps. More preferably, the viscosity of the binder may be 4000 cps to 50000 cps. In one example, the viscosity of the binder may be 5000 cps to 50000 cps.

[0064] When the viscosity of the binder satisfies the above range, the binder can sufficiently ensure the adhesiveness and viscosity of the electrode paste. When the viscosity of the binder is less than 3000 cps, it may be difficult to ensure that the viscosity of the electrode paste reaches the expected value, which will make it difficult to maintain the uniform dispersion state of the active material for a long time. In addition, when the viscosity of the binder exceeds 50000 cps, it may be difficult to stir the binder, and the degree of dispersion of the solid components may be greatly reduced.

[0065] A secondary battery according to another embodiment of the present disclosure may include an anode for the secondary battery. More specifically, the secondary battery may include an electrode assembly and an electrolyte, the electrode assembly including an anode for the secondary battery, a cathode, and a separator interposed between the anode and the cathode for the secondary battery.

[0066] Similar to the anode for the secondary battery, the cathode may be manufactured by applying a cathode paste including a cathode active material, a binder, a conductive material, etc. to a cathode current collector.

[0067] In addition, the cathode may be manufactured in a form in which a cathode paste including a cathode active material is applied to a cathode current collector, and the cathode paste may further include the conductive material and the binder as described above together with the cathode active material.

[0068] The cathode active material may include, for example: layered compounds such as lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), or a compound substituted by one or more transition metals; lithium manganese oxides such as the chemical formula Li 1+x Mn 2-x O4 (where x is 0 or more and 0.33 or less), LiMnO3, LiMn2O3, LiMnO2; lithium copper oxide (Li2CuO2); vanadium oxides such as LiV3O8, LiV3O4, V2O5, and Cu2V2O7; Ni-site type lithium nickel oxides represented by the chemical formula LiNi 1-x M x O2 (where M is Co, Mn, Al, Cu, Fe, Mg, B, or Ga, and x is 0.01 or more and 0.3 or less); lithium manganese composite oxides represented by the chemical formula LiMn 2-x M x O2 (where M is Co, Ni, Fe, Cr, Zn, or Ta, and x is 0.01 or more and 0.1 or less) or Li2Mn3MO8 (where M is Fe, Co, Ni, Cu, or Zn); lithium manganese composite oxides having a spinel structure represented by LiNi x Mn 2-x O4; LiMn2O4, in which the Li part in the chemical formula is partially substituted by alkaline earth metal ions; disulfide compounds; Fe2(MoO4)3; and the like, but not limited thereto.

[0069] The cathode current collector is not particularly limited as long as it has high electrical conductivity and does not cause chemical changes to the battery. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel with a surface treated with carbon, nickel, titanium, silver, etc. can be used. In addition, the cathode current collector can have a thickness of 3 μm to 500 μm and can have fine irregularities formed on the surface of the current collector to enhance the adhesion of the cathode active material. For example, it can be used in various forms such as films, sheets, foils, meshes, porous bodies, foams, and non-woven fabrics.

[0070] The separator separates the anode and the cathode and provides a channel for the migration of lithium ions. Any separator can be used without particular limitation as long as it is commonly used as a separator in lithium secondary batteries. In particular, a separator having excellent moisture retention ability for the electrolyte and low resistance to the migration of electrolyte ions is preferred. Specifically, a porous polymer membrane can be used, for example, a porous polymer membrane made of a polyolefin-based polymer such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer, or a laminated structure having two or more layers thereof. In addition, a conventional porous non-woven fabric can be used, for example, a non-woven fabric made of high melting point glass fiber, polyethylene terephthalate fiber, or the like. In addition, to ensure heat resistance or mechanical strength, a coated separator containing a ceramic component or a polymer material can be used, and optionally, a single-layer or multi-layer structure can be used.

[0071] In addition, the electrolyte solution used in the present disclosure may include, but is not limited to, organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, molten inorganic electrolytes, or the like that can be used in the preparation of lithium secondary batteries.

[0072] Specifically, the electrolyte solution may include an organic solvent and a lithium salt.

[0073] As the organic solvent, any solvent can be used without particular limitation as long as it can serve as a medium through which ions participating in the electrochemical reaction of the battery can migrate. Specifically, as the organic solvent, ester group solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, or ε-caprolactone can be used; ether group solvents such as dibutyl ether or tetrahydrofuran; ketone group solvents such as cyclohexanone; aromatic hydrocarbon group solvents such as benzene or fluorobenzene; carbonate group solvents such as dimethylcarbonate (DMC), diethylcarbonate (DEC), methylethylcarbonate (MEC), ethylmethylcarbonate (EMC), ethylene carbonate (EC) or propylene carbonate (PC); alcohol group solvents such as ethanol or isopropanol; nitriles such as R-CN (where R is a linear, branched or cyclic C2-C20 hydrocarbon group and may include double bonds, aromatic rings or ether bonds); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; or sulfolane. Among them, carbonate group solvents are preferred, and more preferably a mixture composed of cyclic carbonates (e.g., ethylene carbonate, propylene carbonate, etc.) having high ionic conductivity and high dielectric constant and chain-like carbonate group compounds (e.g., ethylmethylcarbonate, dimethylcarbonate, diethylcarbonate, etc.) with low viscosity, which can improve the charge and discharge performance of the battery, is used. In this case, when the cyclic carbonate and the chain-like carbonate are mixed and used at a volume ratio of about 1:1 to about 1:9, the performance of the electrolyte can be excellently exhibited.

[0074] The lithium salt can be used without particular limitation as long as it is a compound capable of providing lithium ions used in a lithium secondary battery. Specifically, LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, LiB(C2O4)2, or the like can be used as the lithium salt. The lithium salt is preferably used in a concentration range of 0.1 M to 2.0 M. If the concentration of the lithium salt is within the above range, the electrolyte has appropriate conductivity and viscosity, and thus can exhibit excellent electrolyte performance, and lithium ions can migrate effectively.

[0075] To improve the life characteristics of the battery, suppress the reduction of the battery capacity, and increase the discharge capacity of the battery, in addition to the above electrolyte components, the electrolyte solution may further include, for example, one or more additives such as a halogenated alkylene carbonate group compound (such as ethylene carbonate difluoride), pyridine, triethyl phosphite, triethanolamine, cyclic ether, ethylenediamine, ethylene glycol dimethyl ether (glyme), hexaphosphoric triamide, nitrobenzene derivative, sulfur, quinone imine dye, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxyethanol, or aluminum trichloride. In this case, the content of the additive may be 0.1% by weight to 5% by weight based on the total weight of the electrolyte solution.

[0076] A method of manufacturing an electrode for a secondary battery according to another embodiment of the present disclosure includes the steps of: mixing an anode active material and a conductive material with an aqueous surfactant solution to prepare a first solution; mixing a binder with the first solution to prepare an electrode paste; and applying and coating the electrode paste onto an electrode current collector.

[0077] Thus, the method of manufacturing an electrode for a secondary battery according to the present embodiment does not require additional high-viscosity kneading in order to improve the dispersion of graphite in conventional carboxymethyl cellulose, and therefore, has the advantages of improving the efficiency of the process and simplifying the process.

[0078] In addition, as in the above-described electrodes for secondary batteries, even in the case of the manufacturing method according to the present embodiment, the binder may include a water-soluble polymer. In addition, the electrode paste may have a solid content of 50 wt% to 90 wt% based on the total weight of the electrode paste. In addition, the viscosity of the electrode paste may be 1000 cps to 50000 cps. In addition, the content of the surfactant may be 0.01 wt% to 10 wt% based on the total weight of the electrode paste. In addition, the viscosity of the binder may be 3000 cps to 50000 cps.

[0079] Thus, the manufacturing method according to the present embodiment can manufacture an electrode including an aqueous electrode paste having a high solid content while improving the dispersibility and viscosity of the solid content contained in the electrode paste.

[0080] Hereinafter, the content of the present disclosure will be described by way of examples. However, the following examples are for illustrative purposes only, and the scope of the present disclosure is not limited thereto.

[0081] <Example 1>

[0082] Example 1 is a dispersion obtained by mixing 0.02 g of graphite and 0.001 wt% to 0.01 wt% of a surfactant with 10 mL of distilled water.

[0083] <Comparative Example 1>

[0084] Example 1 is a dispersion obtained by mixing 0.02 g of graphite and 1 wt% of carboxymethyl cellulose with 10 mL of distilled water.

[0085] <Test Example 1 (Confirmation of layer separation)>

[0086] Figure 1 is an enlarged image of the dispersion according to the comparative example. Figure 2 is an enlarged image of the dispersion according to the embodiment of the present disclosure.

[0087] Refer to Figure 1 , it can be confirmed that the dispersion according to Comparative Example 1 causes the phenomenon of layer separation of graphite in the aqueous solution. From this, it can be confirmed that graphite has the property of not dispersing in water, but the carboxymethyl cellulose of Comparative Example 1 also cannot sufficiently disperse graphite in water.

[0088] Therefore, in order to improve the dispersibility of graphite, the carboxymethyl cellulose of Comparative Example 1 needs to be further subjected to separate high-viscosity kneading. That is, when the water-based electrode paste contains carboxymethyl cellulose as in Comparative Example 1, the layer separation phenomenon is extremely likely to occur (as Figure 1as shown), and since separate high-viscosity kneading should be additionally performed, there are problems of reduced process efficiency and increased process complexity.

[0089] On the other hand, referring to Figure 2 , it can be confirmed that the graphite according to Example 1 does not stratify in the aqueous solution phase but is uniformly dispersed. Thus, it can be confirmed that graphite has the property of not dispersing in water, but the tert-octylphenoxy polyethoxyethanol of Example 1 enables the graphite to be sufficiently dispersed in water. Therefore, different from Comparative Example 1, the tert-octylphenoxy polyethoxyethanol of Example 1 does not require separate high-viscosity kneading, and the possibility of occurrence of the layer separation phenomenon is very low (as Figure 2 shown), which is advantageous in terms of increased process efficiency and simplification.

[0090] <Example 2>

[0091] Graphite and Super-C65 as a conductive material were added to an aqueous solution of tert-octylphenoxy polyethoxyethanol and mixed. Polyvinylpyrrolidone was added to the mixed aqueous solution and mixed again to prepare an electrode paste. At this time, the total mixing time was 40 minutes.

[0092] At this time, the content of graphite contained in the electrode paste was 55.99 wt%, the content of the conductive material was 1 wt%, the content of tert-octylphenoxy polyethoxyethanol was 0.01 wt%, and the content of polyvinylpyrrolidone was 3 wt%. At this time, the electrode paste of Example 2 had a solid content of 60 wt% based on the total weight.

[0093] <Example 3>

[0094] Different from Example 2, the content of graphite contained in the electrode paste was 55.95 wt%, and the content of tert-octylphenoxy polyethoxyethanol was 0.05 wt%. Except for these, the electrode paste was prepared in the same manner as in Example 2.

[0095] <Example 4>

[0096] Different from Example 2, the content of graphite contained in the electrode paste was 60.95 wt%, and the content of tert-octylphenoxy polyethoxyethanol was 0.05 wt%. At this time, the electrode paste of Example 3 had a solid content of 65 wt% based on the total weight. Except for these, the electrode paste was prepared in the same manner as in Example 2.

[0097] <Example 5>

[0098] Different from Example 2, the content of graphite contained in the electrode paste is 60.9% by weight, and the content of tert-octylphenoxypolyethoxyethanol is 0.1% by weight. At this time, the electrode paste of Example 4 has a solid content of 65% by weight based on the total weight. Except for these, the electrode paste is prepared in the same manner as in Example 2.

[0099] <Comparative Example 2>

[0100] Super-C65 as a conductive material was dispersed in an aqueous solution of carboxymethyl cellulose (CMC), and graphite was added to the aqueous solution of carboxymethyl cellulose in which the conductive material was dispersed, and hard mixing was performed. Carboxymethyl cellulose was additionally added to the aqueous solution subjected to hard mixing, and then mixing was performed. Styrene-butadiene rubber (SBR) was added to the mixed aqueous solution, and then mixing was performed again to prepare an electrode paste. At this time, the total mixing time was 80 minutes.

[0101] At this time, the content of graphite contained in the electrode paste is 35% by weight, the content of the conductive material is 1.0% by weight, the content of carboxymethyl cellulose is 1.0% by weight, and the content of styrene-butadiene rubber is 3.0% by weight. At this time, the electrode paste of Comparative Example 2 has a solid content of 40% by weight based on the total weight.

[0102] <Comparative Example 3>

[0103] Different from Comparative Example 2, the content of graphite contained in the electrode paste is 42% by weight. At this time, the electrode paste of Comparative Example 2 has a solid content of 47% by weight based on the total weight. Except for these, the electrode paste is prepared in the same manner as in Example 2.

[0104] <Comparative Example 4>

[0105] Different from Comparative Example 2, the content of graphite contained in the electrode paste is 34.5% by weight, and the content of carboxymethyl cellulose is 1.5% by weight. Except for these, the electrode paste is prepared in the same manner as in Example 2.

[0106] <Comparative Example 5>

[0107] Different from Comparative Example 2, the content of graphite contained in the electrode paste is 39.5% by weight, and the content of carboxymethyl cellulose is 1.5% by weight. At this time, the electrode paste of Comparative Example 5 has a solid content of 45% by weight based on the total weight. Except for these, the electrode paste is prepared in the same manner as in Example 2.

[0108] <Test Example 2 (Viscosity measurement)>

[0109] The viscosities of Examples 2 to 5 and Comparative Examples 2 to 5 were measured based on a B-type viscometer, and the results are shown in Table 1 below.

[0110] [Table 1]

[0111] Brookfield viscosity (cps) Brookfield viscosity (cps) after 48 hours Example 2 7,000 5,000 Example 3 7,000 7,000 Example 4 12,000 12,000 Example 5 12,000 12,000 Comparative Example 2 4,000 2,000 Comparative Example 3 10,000 6,000 Comparative Example 4 9,000 7,000 Comparative Example 5 15,000 13,000

[0112] Referring to Table 1, it can be confirmed that in the case of Examples 2 to 5, the viscosity is similar to or relatively higher than that of Comparative Examples 2 to 5. From this, it can be confirmed that the viscosity of the polyvinylpyrrolidone contained in Examples 2 to 5 is equivalent to 3000 cps to 50000 cps. Therefore, in addition to acting as a binder between the anode active materials, polyvinylpyrrolidone also acts as a thickener to increase the viscosity of the electrode paste.

[0113] In contrast, it can be confirmed that in the case of Comparative Examples 2 to 5, some of the comparative examples have a high viscosity, but the B-type viscosity of the electrode paste decreases over time. In addition, it can be confirmed that in Comparative Examples 2 to 5, the solid content of the electrode paste is 40 wt% to 47 wt%. Therefore, although the solid content is lower than that of Examples 2 to 5 (60 wt% to 65 wt%), a large change in viscosity is shown. From this, it can be known that when the solid components contained in the electrode paste of Comparative Examples 2 to 5 are dispersed in the solvent of the electrode paste, layer separation occurs.

[0114] From this, it can be confirmed that the carboxymethyl cellulose in Comparative Examples 2 to 5 did not sufficiently disperse the graphite in water. More specifically, the viscosity of the styrene-butadiene rubber (SBR) included in Comparative Examples 2 to 5 is equivalent to 500 cps to 1000 cps. Therefore, it can be confirmed that carboxymethyl cellulose acts as a thickener in addition to the role of a dispersant, but there are limitations in maintaining the viscosity due to the low solubility of carboxymethyl cellulose in water.

[0115] On the other hand, in the case of Examples 2 to 5, it can be confirmed that although time has passed, the B-type viscosity of the electrode paste remains mostly equal. From this, it can be confirmed that the electrode paste of Examples 2 to 5 has high phase stability. In addition, it can be confirmed that in Examples 2 to 5, the content of the solid components contained in the electrode paste is 60 wt% to 65 wt%. Therefore, although the solid content is higher than that of Comparative Examples 2 to 5 (40 wt% to 47 wt%), the change in viscosity is mostly equal. Thus, Examples 2 to 5 have an electrode paste with high phase stability, and the tert-octylphenoxypolyethoxyethanol contained in the electrode paste sufficiently disperses a considerable amount of solid components.

[0116] <Test Example 3 (Coin half - cell test)>

[0117] The electrode slurries prepared in each of Examples 2 to 5 and Comparative Examples 2 to 5 were coated on a copper foil electrode current collector to prepare anodes.

[0118] Each of the anodes prepared above was used as a working electrode, and a circular Li metal thin film cut to 1.7671 cm 2 was used as a counter electrode. A polyethylene separator was inserted between the working electrode and the counter electrode to prepare an electrode assembly. Ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed at a volume ratio of 7:3. 0.5 wt% of vinylene carbonate (VC) and 1 M LiPF6 were added to the mixed solvent as non-aqueous electrolyte additives to prepare a non-aqueous electrolyte solution. The electrode assembly was placed inside a coin-type case, and the prepared non-aqueous electrolyte solution was injected to fabricate a coin-type secondary half-cell battery.

[0119] In a state where each of the secondary batteries manufactured in this way had a discharge capacity of 350 mAh / g and an initial efficiency of 93%, the discharge resistance and the 2C (rate) discharge cycle capacity retention rate were measured respectively, and the results are shown in Table 2 below.

[0120] [Table 2]

[0121]

[0122] Referring to Table 2, in the case of Comparative Examples 2 to 5, a relatively high discharge resistance was measured, and a relatively low 2C discharge cycle capacity retention rate was measured.

[0123] It can be confirmed therefrom that since Comparative Examples 2 to 5 contain carboxymethyl cellulose, the solid components of the electrode slurry are relatively less dispersed. Therefore, the dispersion amounts of the active material and the conductive material in Comparative Examples 2 to 5 are also relatively reduced, which is disadvantageous for the resistance and the cycle characteristics.

[0124] On the other hand, it can be confirmed that since Examples 2 to 5 include tert-octylphenoxy polyethoxyethanol, the solid components of the electrode slurry are relatively more dispersed. Therefore, in Examples 2 to 5, the amounts of the active material and the conductive material are relatively increased, and thus the discharge resistance and the cycle characteristics are favorable.

[0125] Although the present invention has been shown and described with reference to preferred embodiments, the scope of the present disclosure is not limited thereto, and various modifications and improvements made by those skilled in the art using the basic concepts of the present disclosure defined in the appended claims also fall within the scope of the present disclosure.

Claims

1. An electrode for a secondary battery, comprising: Electrode current collector; and an active material layer located on the electrode current collector, wherein the active material layer is formed such that an electrode paste prepared from an aqueous solution containing an anode active material, a conductive material, a surfactant, and a binder is coated onto the electrode current collector, and wherein the binder includes a water-soluble polymer, wherein: the electrode paste has a solid content of 50 wt% to 90 wt% based on the total weight of the electrode paste, wherein the surfactant includes at least one of tert-octylphenoxypolyethoxyethanol, octylphenoxypolyethoxyethanol, and polysorbate 20, wherein the content of the surfactant is 0.01 wt% to 10 wt% based on the total weight of the electrode paste, wherein the binder includes at least one of polyvinylpyrrolidone, polyimide, polyacrylonitrile, and polyamide, and the viscosity of the binder is 3000 cps to 50000 cps, wherein the viscosity of the electrode paste is 4000 cps to 50000 cps, and wherein the content of the anode active material is 40 wt% to 80 wt% based on the total weight of the electrode paste.

2. The electrode for a secondary battery according to claim 1, wherein: The anode active material includes graphite, silicon oxide-based material (SiO x ), or a mixture thereof.

3. The electrode for a secondary battery according to claim 1, wherein: The conductive material includes a carbon-based material, CNT (Carbon nanotube), Graphene, or a mixture thereof.

4. A secondary battery, comprising the electrode for a secondary battery according to claim 1.

5. A method for manufacturing an electrode for a secondary battery, comprising the following steps: Mix the anode active material and the conductive material with an aqueous surfactant solution to prepare a first solution; Mix the binder with the first solution to prepare an electrode paste; and Apply and coat the electrode paste onto the electrode current collector, wherein the binder includes a water-soluble polymer, wherein the electrode paste has a solid content of 50 wt% to 90 wt% based on the total weight of the electrode paste, wherein the surfactant includes at least one of tert-octylphenoxypolyethoxyethanol, octylphenoxypolyethoxyethanol, and polysorbate 20, wherein the content of the surfactant is 0.01 wt% to 10 wt% based on the total weight of the electrode paste, wherein the binder includes at least one of polyvinylpyrrolidone, polyimide, polyacrylonitrile, and polyamide, and the viscosity of the binder is 3000 cps to 50000 cps, wherein the viscosity of the electrode paste is 4000 cps to 50000 cps, and wherein the content of the anode active material is 40 wt% to 80 wt% based on the total weight of the electrode paste.

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