Method for producing polymer solutions for electrode slurries

Abstract

The present invention relates to a method for producing a polymer solution for electrode slurry, and according to the present invention, there is provided a method for producing a polymer solution for electrode slurry, comprising the steps of mixing a water-soluble polymer and an aqueous solvent to obtain a mixed solution, and irradiating the mixed solution with ultraviolet (UV) light for a predetermined period of time.

Description

[Technical Field]

[0001] The present invention relates to a method for producing a polymer solution for electrode slurry used in secondary batteries, and to an electrode slurry for secondary batteries produced thereby.

[0002] This application claims priority based on Korean Patent Application No. 2022-0026843, filed on March 2, 2022, and all contents disclosed in the specification and drawings of said application are incorporated herein by reference. [Background technology]

[0003] As technological development and demand for mobile devices increase, the demand for rechargeable batteries as an energy source is rapidly growing. Among these rechargeable batteries, lithium-ion batteries, which have high energy density and operating potential, long cycle life, and low self-discharge rate, have been commercialized and are widely used.

[0004] The electrodes of a lithium secondary battery are manufactured by mixing a positive electrode active material or a negative electrode active material with a binder resin component, dispersing it in a solvent to produce a slurry, applying this slurry to the surface of the electrode current collector, drying it, and then forming a composite layer.

[0005] Of these, considering the case of anode slurry, anode slurries are generally classified into aqueous and organic types. Since aqueous slurries are advantageous in terms of cost, aqueous slurries are commonly used in the battery industry. In this case, the graphite-based active material, which makes up the majority of the anode slurry, is mainly dispersed in water.

[0006] However, since graphite-based active materials are generally hydrophobic, they are not easily dispersed in water and tend to settle in the slurry over time, sometimes leading to problems with the storage stability of the slurry. Specifically, attempts have been made to increase the solid content in the negative electrode slurry for reasons such as increasing the load amount of the negative electrode during negative electrode manufacturing, improving efficiency during the drying process, and improving binder migration. As a result, the problems of dispersibility of the graphite-based active material due to the increased solid content, and the problems of non-uniformity of the solid content in the slurry due to problems with the storage stability of the slurry, become even more pronounced. The dispersibility problem causes filter clogging during the transfer of the negative electrode slurry in the negative electrode manufacturing process, which reduces the overall efficiency of the lithium secondary battery manufacturing process. Furthermore, the problem of reduced storage stability of the slurry is a major issue because it leads to the formation of a non-uniform coating layer during negative electrode manufacturing, resulting in problems due to the different compositions of each part of the negative electrode. To solve the aforementioned problems of dispersibility and storage stability of graphite-based active materials, attempts have been made to use thickeners.

[0007] As an example, attempts have been made to ensure the viscosity of a slurry by dispersing graphite-based active material in an aqueous negative electrode slurry using a thickening agent. However, if the solubility of the thickening agent itself in water is low, a method has been adopted in which the thickening agent is dissolved in distilled water beforehand to produce a thickened solution, which is then used in the production of the slurry. However, under mass production conditions, such thickened solutions may be stored for up to a week, and during this time, changes occur over time, such as a decrease in the viscosity of the thickened solution itself. This not only reduces the workability in the electrode coating process but also degrades the quality of the electrode itself.

[0008] Therefore, there is still a need to develop electrode slurries that can improve the dispersibility and storage stability of graphite-based active materials and enhance the quality of electrodes. [Overview of the project] [Problems that the invention aims to solve]

[0009] Therefore, in one embodiment, the problem that the present invention aims to solve is to provide a polymer solution that can improve the dispersibility and storage stability of graphite-based active material in an electrode slurry when manufacturing electrodes for use in secondary batteries, and a method for producing the same.

[0010] In another embodiment, the aim is to provide a polymer solution having appropriate viscosity and improved stability over time, as a polymer solution for the production of the electrode slurry described above, and a method for producing the same.

[0011] In another embodiment, we aim to provide an electrode slurry in which the dispersibility and storage stability of the graphite-based active material are improved using the polymer solution described above, an electrode manufactured using the slurry, and a lithium secondary battery containing the manufactured electrode. [Means for solving the problem]

[0012] To solve the above problems, according to one aspect of the present invention, a method for producing a polymer solution for electrode slurry is provided as described below.

[0013] According to the first embodiment, a method for producing a polymer solution for electrode slurry is provided, characterized by comprising the steps of: mixing a water-soluble polymer and an aqueous solvent to obtain a mixed solution; and irradiating the mixed solution with ultraviolet light (UV) for a predetermined time.

[0014] According to the second embodiment, in the first embodiment, the water-soluble polymer may include polyvinylidene fluoride (PVDF), polyvinyl alcohol (PVA), starch, polyvinylpyrrolidone (PVP), polytetrafluoroethylene (PTFE), polyethylene (PE), polypropylene (PP), ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, fluororubber, methylcellulose (MC), ethylcellulose (EC), carboxymethylcellulose (CMC), carboxyethylcellulose (CEC), hydroxyethylcellulose, benzylcellulose, tritylcellulose, cyanoethylcellulose, aminoethylcellulose, nitrocellulose, cellulose ether, regenerated cellulose, hydroxypropylcellulose (HPC), a copolymer of two or more of these, or a mixture of two or more of these.

[0015] According to the third embodiment, in the first embodiment or the second embodiment, the water-soluble polymer may include carboxymethylcellulose (CMC).

[0016] According to the fourth embodiment, in any one of the first to third embodiments, the water-soluble polymer may have a weight average molecular weight (Mw) of 500,000 g / mol to 5,000,000 g / mol.

[0017] According to the fifth embodiment, in any one of the first to fourth embodiments, the water-soluble polymer may include a powdery one.

[0018] According to the sixth embodiment, in any one of the first to fifth embodiments, the water-soluble polymer may be mixed at a content of 0.1% by weight to 5% by weight based on the total weight of the aqueous solvent.

[0019] According to the seventh embodiment, in any one of the first to sixth embodiments, the wavelength of the ultraviolet ray to be irradiated may be 240 nm to 400 nm.

[0020] According to the eighth embodiment, in any one of the first to seventh embodiments, the wavelength of the irradiated ultraviolet ray can be from 240 nm to 260 nm.

[0021] According to the ninth embodiment, in any one of the first to eighth embodiments, the ultraviolet ray can be irradiated during the production of the mixed solution.

[0022] According to the tenth embodiment, in any one of the first to ninth embodiments, the ratio of the irradiation time of the ultraviolet ray to the total mixing time can be from 1% to 100%.

[0023] According to the eleventh embodiment, in any one of the first to tenth embodiments, the mixing step can be performed while irradiating ultraviolet rays throughout the entire time, or while irradiating ultraviolet rays only for a part of the time including a predetermined time of mixing without irradiating ultraviolet rays.

[0024] According to another aspect of the present invention, there is provided a polymer solution for an electrode slurry according to the following embodiment.

[0025] According to the twelfth embodiment, there is provided a polymer solution for an electrode slurry, which is produced by any one of the first to eleventh embodiments and has a viscosity change rate according to the following [Formula 1] in the range of -20% to 5% when stored at 23°C for 7 days. [Formula 1] Viscosity change rate (%) = (Vis(d) - Vis(i)) / Vis(i) × 100 In Formula 1, Vis(i) is the initial viscosity value of the electrode slurry, Vis(d) is the viscosity value measured after storing for d days out of 1 to 7 days, and the viscosity value represents a value measured using a Brookfield viscometer (DV2T viscometer, 12 rpm, spindle 24) at 23°C.

[0026] According to another aspect of the present invention, there is provided a production apparatus for a polymer solution according to the following embodiment. According to the 13th embodiment, an apparatus for producing a polymer solution for electrode slurry is provided, characterized by including a mixing section and an ultraviolet irradiation section mounted in the mixing section for irradiating the object to be mixed with ultraviolet light. [Effects of the Invention]

[0027] A method for producing a polymer solution for electrode slurry according to one embodiment of the present invention has the effect of improving the dispersibility and storage stability of graphite-based active material in electrode slurry when manufacturing electrodes for use in secondary batteries.

[0028] A method for producing a polymer solution for electrode slurry according to one embodiment of the present invention not only improves workability during the production of electrode slurry by having an appropriate viscosity and improving stability over time, but also has the effect of improving the quality of the electrode slurry, electrode, and secondary battery.

[0029] The following drawings accompanying this specification illustrate preferred embodiments of the invention and, together with the detailed description of the invention, serve to further illustrate the technical idea of ​​the invention; therefore, the invention should not be construed as being limited solely to what is shown in the drawings. [Brief explanation of the drawing]

[0030] [Figure 1] This graph shows the results of measuring the viscosity of a polymer solution produced by one embodiment of the present invention over time during storage. [Figure 2] This is a photograph of the surface immediately after preparing an electrode slurry in which a graphite-based active material was dispersed using the polymer solution for electrode slurry prepared in Comparative Example 1. [Figure 3] This is a photograph of the surface immediately after preparing an electrode slurry in which a graphite-based active material was dispersed using the polymer solution for electrode slurry prepared in Comparative Example 2. [Figure 4] This is a photograph of an electrode slurry in which a graphite-based active material was dispersed using the polymer solution for electrode slurry prepared in Comparative Example 1, after being passed through a filtration filter. [Figure 5]This is a photograph of the electrode slurry after passing it through a filtration filter, in which a graphite-based active material was dispersed using the polymer solution for electrode slurry prepared in Comparative Example 2. [Modes for carrying out the invention]

[0031] The present invention will be described in detail below. A method for producing a polymer solution for electrode slurry according to one aspect of the present invention includes the steps of mixing a water-soluble polymer and an aqueous solvent to obtain a mixed solution, and irradiating the mixed solution with ultraviolet light (UV) for a predetermined time.

[0032] In this specification, the polymer solution may be used to disperse solid components such as active material when manufacturing an electrode slurry for use in the manufacture of electrodes for secondary batteries, but the use of the polymer solution is not limited to this.

[0033] The step of obtaining the mixed solution involves mixing the water-soluble polymer with an aqueous solvent, ensuring that the water-soluble polymer is uniformly dispersed.

[0034] The mixing to obtain the aforementioned mixed solution can be carried out by various methods of mixing the water-soluble polymer with an aqueous solvent, and is not particularly limited.

[0035] In one embodiment of the present invention, the water-soluble polymer can be used without particular limitation as long as it functions as a thickener in the electrode slurry. The thickening function of the water-soluble polymer provides advantageous effects, particularly in ensuring the dispersibility of active materials, such as graphite, silicon compounds, silicon oxide / carbide composites, or mixtures of two or more of these, in the electrode slurry.

[0036] In one embodiment of the present invention, the water-soluble polymer may include a biodegradable polymer. For example, when the manufactured polymer solution is used in the manufacture of an electrode slurry, the water-soluble polymer may include a type that is biodegradable, meaning it is decomposed by bacteria present in the stirring tank or raw material input hopper when stored in the stirring tank or hopper.

[0037] In other embodiments of the present invention, the water-soluble polymer may include, but is not limited to, polyvinylidene fluoride (PVDF), polyvinyl alcohol (PVA), starch, polyvinylpyrrolidone (PVP), polytetrafluoroethylene (PTFE), polyethylene (PE), polypropylene (PP), ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, fluororubber, methylcellulose (MC), ethylcellulose (EC), carboxymethylcellulose (CMC), carboxyethylcellulose (CEC), hydroxyethylcellulose, benzylcellulose, tritylcellulose, cyanoethylcellulose, aminoethylcellulose, nitrocellulose, cellulose ether, regenerated cellulose, hydroxypropylcellulose (HPC), copolymers of two or more of these, or mixtures of two or more of these.

[0038] In one embodiment of the present invention, the water-soluble polymer may include carboxymethylcellulose (CMC). When the water-soluble polymer includes carboxymethylcellulose, advantageous effects are obtained in terms of dispersion and maintaining phase stability of the electrode slurry, specifically the aqueous negative electrode slurry for lithium-ion secondary batteries, but the present invention is not limited thereto. More specifically, when the water-soluble polymer includes carboxymethylcellulose, not only is the dispersibility of the active material in the electrode slurry excellent, but the carboxymethylcellulose also has excellent solubility in aqueous electrode slurries, and by imparting an appropriate viscosity to the electrode slurry, advantageous effects are obtained in that the degree of re-aggregation or sedimentation of the active material dispersed in the electrode slurry is suppressed.

[0039] In other embodiments of the present invention, the water-soluble polymer may have, for example, a weight-average molecular weight (Mw) ranging from 500,000 g / mol to 5,000,000 g / mol. Specifically, the weight-average molecular weight (Mw) of the water-soluble polymer may be 750,000 g / mol or more, 1,000,000 g / mol or more, 1,500,000 g / mol or more, 4,000,000 g / mol or less, 3,000,000 g / mol or less, or 2,500,000 g / mol or less. When the weight-average molecular weight (Mw) of the water-soluble polymer is within the above range, advantageous effects are obtained in terms of dispersion and thickening of electrode slurries, specifically aqueous negative electrode slurries for lithium-ion secondary batteries, but the present invention is not limited thereto. The weight-average molecular weight (Mw) may represent a value measured using gel permeation chromatography (GPC).

[0040] In one embodiment of the present invention, the water-soluble polymer may include a powder. In one embodiment of the present invention, the aqueous solvent can be used without particular limitation as long as it is capable of dissolving the water-soluble polymer. The aqueous solvent may include, for example, water.

[0041] In another embodiment of the present invention, the aqueous solvent may be water alone. In one embodiment of the present invention, the water-soluble polymer may be mixed in an amount ranging from 0.1% to 5% by weight based on the total weight of the aqueous solvent. Specifically, the water-soluble polymer may be included in amounts of 0.1% or more, 0.5% or more, 1% or more, 5% or less, 4.5% or less, 4% or less, 3.5% or less, and 3% or less by weight based on the total weight of the aqueous solvent. When the content of the water-soluble polymer is within the above range, advantageous effects can be obtained in terms of convenience in the manufacturing process of the electrode slurry, specifically the negative electrode slurry, and improvement of the solid content in the negative electrode slurry, but the present invention is not limited thereto.

[0042] In one embodiment of the present invention, the step of mixing the water-soluble polymer and the aqueous solvent to obtain a mixed solution can be performed by simultaneously introducing the water-soluble polymer and the aqueous solvent into a mixer and mixing them, or by introducing the water-soluble polymer and the aqueous solvent sequentially and mixing them, and the introduction procedure and method are not particularly limited.

[0043] In another embodiment of the present invention, the step of mixing the water-soluble polymer with an aqueous solvent to obtain a mixed solution can be performed by first introducing the aqueous solvent into the mixer, followed by introducing a predetermined amount of the water-soluble polymer and mixing. This may be advantageous in improving the scattering of fine powder in the mass production process and ultimately improving the quality of the polymer solution for electrode slurry produced.

[0044] The present invention provides a method for producing a polymer solution for electrode slurry, which includes the step of irradiating the mixed solution produced above with ultraviolet light (UV) for a predetermined time.

[0045] In one embodiment of the present invention, irradiating a mixed solution of the water-soluble polymer and an aqueous solvent with ultraviolet light can have a bactericidal effect against bacteria that proliferate in the mixer. This prevents or reduces the degree of decomposition of the water-soluble polymer by bacteria proliferating in the mixer, thereby maintaining the appropriate viscosity of the polymer solution for electrode slurry and improving its stability over time. However, the mechanism of the present invention is not limited to these effects.

[0046] In particular, as mentioned above, water-soluble polymers such as carboxymethylcellulose, which are excellent at improving the dispersibility of active materials and suppressing the re-aggregation or sedimentation of dispersed active materials, may have the problem that, despite their excellent properties as described above, their effect when used in the production of electrode slurries is minimal due to their biodegradability. Therefore, when the mixed solution contains a biodegradable polymer such as carboxymethylcellulose as the water-soluble polymer, the ultraviolet irradiation step can be used to significantly improve its effectiveness.

[0047] The step of irradiating the mixed solution with ultraviolet light can be performed by irradiating the mixed solution with ultraviolet light after it has been manufactured, during its manufacture, or from the time of manufacture until after it has been manufactured, but the procedure for irradiating with ultraviolet light is not particularly limited.

[0048] In another embodiment of the present invention, the step of irradiating with ultraviolet light may be performed in a shielded container in order to prevent or minimize human exposure to ultraviolet light.

[0049] In one embodiment of the present invention, the wavelength of the irradiated ultraviolet light may be, for example, 240 nm to 400 nm. Generally, the wavelength of ultraviolet light may be 10 nm to 400 nm, but in one embodiment of the present invention, if the wavelength of the irradiated ultraviolet light is less than 240 nm, problems may arise such as a decrease in not only the stability of the polymer solution but also the operational stability during the production of the polymer solution due to the generation of ozone. Therefore, the wavelength of ultraviolet light can be limited to 240 nm.

[0050] In another embodiment of the present invention, when means are provided to suppress or prevent the generation of ozone generated by the irradiated ultraviolet light, the wavelength of the irradiated ultraviolet light may also include a range of less than 240 nm, as long as it does not hinder the above-mentioned sterilization effect.

[0051] In yet another embodiment of the present invention, the wavelength of the irradiated ultraviolet light may be specifically 240 nm or more, 245 nm or more, 250 nm or more, 254 nm or more, 280 nm or more, 400 nm or less, 380 nm or less, 370 nm or less, 360 nm or less, 350 nm or less, 340 nm or less, 320 nm or less, 310 nm or less, 300 nm or less, 290 nm or less, 280 nm or less, or 260 nm or less. More specifically, the wavelength of the irradiated ultraviolet light may be 240 nm to 300 nm or 240 nm to 260 nm, and even more specifically, the wavelength of the irradiated ultraviolet light may be 250 nm to 260 nm. When the wavelength of the irradiated ultraviolet light is within the above range, advantageous effects can be obtained in terms of sterilization of water-soluble polymers in the mixed solution and suppression of decomposition by biodegradable bacteria, but the present invention is not limited thereto.

[0052] For this reason, the predetermined time for irradiation with ultraviolet light can be determined by considering the wavelength of the irradiated ultraviolet light, and is not particularly limited.

[0053] In another embodiment of the present invention, the predetermined time for irradiation with ultraviolet light is, for example, 1 minute to 300 minutes, specifically 10 minutes to 180 minutes, when the total weight of the water-soluble polymer and the aqueous solvent is 100 g, and the irradiation time can be increased in proportion to the total weight of the water-soluble polymer and the aqueous solvent.

[0054] In one embodiment of the present invention, the ratio of ultraviolet irradiation time to the total mixing time may be, for example, 1% to 100%. Specifically, the ratio of ultraviolet irradiation time to the total mixing time may be 30% to 90%, 50% to 90%, 50% to 80%, or 60% to 70%. When the ratio of ultraviolet irradiation time to the total mixing time falls within the above range, there are advantageous effects in terms of the stability of the water-soluble polymer and process efficiency, but the present invention is not limited thereto.

[0055] In yet another embodiment of the present invention, the water-soluble polymer and the aqueous solvent can be mixed, and ultraviolet light can be irradiated after a predetermined time has elapsed.

[0056] For example, the process may include a step of mixing the water-soluble polymer and an aqueous solvent to obtain a mixed solution, and then storing the mixed solution in a storage container until the electrode slurry is manufactured. In this case, after storing the mixed solution in the storage container, the polymer solution for the electrode slurry can be manufactured by irradiating the stored mixed solution with ultraviolet light when manufacturing the electrode slurry.

[0057] In one embodiment of the present invention, the step of mixing the water-soluble polymer and the aqueous solvent can be performed together with stirring.

[0058] In one embodiment of the present invention, the method for producing the polymer solution for electrode slurry may include producing the polymer solution for electrode slurry by stirring and mixing a water-soluble polymer and an aqueous solvent in a mixer while simultaneously irradiating them with ultraviolet light.

[0059] In one embodiment of the present invention, the step of mixing the water-soluble polymer and the aqueous solvent may include mixing while irradiating with ultraviolet light for a portion of the time, such that a predetermined time is spent mixing the water-soluble polymer and the aqueous solvent in the mixer without irradiating with ultraviolet light.

[0060] In another embodiment of the present invention, the method for producing the polymer solution for electrode slurry may include the steps of stirring and mixing a water-soluble polymer and an aqueous solvent in a mixer, and irradiating with ultraviolet light, each of which may be performed alternately one or more times in any order.

[0061] In yet another embodiment of the present invention, the method for producing the polymer solution for electrode slurry may include stirring the water-soluble polymer and aqueous solvent in a mixer for a certain period of time, followed by simultaneous irradiation with ultraviolet light and stirring.

[0062] According to the above method, a polymer solution can be produced for the purpose of dispersing solid components such as active materials when manufacturing electrode slurries for use in secondary batteries.

[0063] According to one embodiment of the present invention, the polymer solution for electrode slurry produced by the above-described method has a viscosity useful for producing electrode slurry and exhibits excellent stability over time due to storage.

[0064] According to one embodiment of the present invention, the electrode manufacturing process can be carried out by first manufacturing a large quantity of the polymer solution for the electrode slurry at once, and then adding these to the electrode slurry manufacturing process in several batches, in order to improve process efficiency. This provides an advantage in terms of the efficiency of the electrode manufacturing process because the polymer solution for the electrode slurry, once manufactured, has excellent stability over time. For example, if the polymer solution for the electrode slurry, once manufactured, maintains stability over time for at least 7 days after manufacturing, it has the advantage of maximizing the efficiency of the electrode manufacturing process.

[0065] A polymer solution for electrode slurry according to another aspect of the present invention is manufactured by the method described above, and when stored at 23°C for 7 days, the viscosity change rate according to the following [Formula 1] is in the range of -20% to 5%. [Formula 1] Viscosity change rate (%)=(Vis(d)-Vis(i)) / Vis(i)×100 In Equation 1, Vis(i) is the initial viscosity value of the electrode slurry, and Vis(d) is the viscosity value measured after storage for d days between 1 and 7 days, where the viscosity value is measured at 23°C using a Brookfield viscometer (DV2T viscometer, 12 rpm, spindle 24).

[0066] In one embodiment of the present invention, the viscosity of the polymer solution for electrode slurry after storage for 7 days may be, for example, 5,000 cps to 50,000 cps at 23°C. Specifically, the viscosity of the polymer solution for electrode slurry after storage for 7 days may be 7,000 cps to 30,000 cps or 7,500 cps to 10,000 cps at 23°C. While the viscosity of the polymer solution for electrode slurry after storage for 7 days within the above range may offer advantages in terms of quality control of the electrode slurry on a mass production scale, the present invention is not limited to these values.

[0067] In another embodiment of the present invention, the viscosity of the polymer solution for electrode slurry can be maintained to an excellent viscosity maintenance effect by keeping the viscosity change over 7 days due to storage within ±20%, specifically within the range of -20% to +5%. The viscosity change may be within ±5%, ±4.5%, ±4%, ±3.5%, ±3%, ±2%, ±1%, ±0.8%, ±0.7%, ±0.6%, ±0.5%, ±0.3%, or ±0.2%.

[0068] In yet another embodiment of the present invention, an increase in the viscosity of the polymer solution for electrode slurry may mean that the water-soluble polymer present in the polymer solution for electrode slurry remains stable and swells without decomposition. Therefore, it is preferable that the viscosity change of the polymer solution for electrode slurry over 7 days due to storage is within +5%, +4%, +3%, +2%, +1%, +0.8%, +0.7%, +0.6%, +0.5%, +0.3%, or +0.2%, but the present invention is not limited to these.

[0069] Another embodiment of the present invention provides a polymer solution manufacturing apparatus that includes a mixing unit and an ultraviolet irradiation unit mounted in the mixing unit for irradiating the material to be mixed with ultraviolet light, for manufacturing the polymer solution for electrode slurry described above.

[0070] In one embodiment of the present invention, the mixing unit can be a conventional mixer for producing polymer solutions, and the type of mixer is not particularly limited. For example, the mixing unit can include various mixers such as a PD mixer, BTM mixer, Soken mixer, Corona mixer, etc.

[0071] In another embodiment of the present invention, the ultraviolet irradiation unit may include any device capable of irradiating ultraviolet light having wavelengths within the range described above, and its type is not particularly limited.

[0072] The polymer solution for electrode slurry described above can be used as a dispersion solution or thickening solution to disperse solid components such as active material in the electrode slurry when manufacturing electrodes used in secondary batteries.

[0073] In this specification, the electrode may refer to the positive or negative electrode included in a secondary battery. In this specification, the active material may refer to a negative electrode active material or a positive electrode active material.

[0074] In one embodiment of the present invention, the negative electrode active material can be, for example, graphite such as natural graphite or artificial graphite, carbon black such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, or thermal black, conductive fibers such as carbon fibers or metal fibers, metal powders such as carbon fluoride, aluminum, or nickel powder, conductive whiskers such as zinc oxide or potassium titanate, conductive metal oxides such as titanium oxide, or conductive materials such as polyphenylene derivatives. In another embodiment of the present invention, the negative electrode active material may include a graphite material.

[0075] In other embodiments of the present invention, examples of the positive electrode active material include, but are not limited to, lithium transition metal oxides, lithium metal iron phosphate, lithium nickel-manganese-cobalt oxide, oxides in which a part of the lithium nickel-manganese-cobalt oxide is substituted with another transition metal, and two or more of these. Specifically, the positive electrode active material is, for example, a layered compound such as lithium cobalt oxide (LiCoO2) or lithium nickel oxide (LiNiO2), a compound substituted with one or more transition metals, and a chemical formula Li 1+x Mn 2-x O4 (where x is 0 to 0.33), lithium manganese oxides such as LiMnO3, LiMn2O3, LiMnO2, lithium copper oxide (Li2CuO2), vanadium oxides such as LiV3O8, LiV3O4, V2O5, Cu2V2O7, and a Ni-site type lithium nickel oxide 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 = 0.01 to 0.3), a lithium manganese composite oxide represented by the chemical formula LiMn 2-x M x O2 (where M is Co, Ni, Fe, Cr, Zn or Ta, and x = 0.01 to 0.1), or Li2Mn3MO8 (where M is Fe, Co, Ni, Cu or Zn), a lithium metal phosphate LiMPO4 (where M is Fe, CO, Ni, or Mn), a lithium nickel-manganese-cobalt oxide Li 1+x (Ni a Co b Mn c ) 1-x O2 (x = 0 to 0.03, a = 0.3 to 0.95, b = 0.01 to 0.35, c = 0.01 to 0.5, a + b + c = 1), and an oxide in which a part of the lithium nickel-manganese-cobalt oxide is substituted with aluminum, Li a [Ni b Co c Mn d Al e 1-f M1 f ​O2 (M1 is one or more selected from the group consisting of Zr, B, W, Mg, Ce, Hf, Ta, La, Ti, Sr, Ba, F, P, and S, 0.8 ≦ a ≦ 1.2, 0.5 ≦ b ≦ 0.99, 0 < c < 0.5, 0 < d < 0.5, 0.01 ≦ e ≦ 0.1, 0 ≦ f ≦ 0.1), and a part of the lithium nickel-manganese-cobalt oxide is replaced with another transition metal oxide Li 1+x (Ni a Co b Mn c M d ) 1-x O2 (x = 0 to 0.03, a = 0.3 to 0.95, b = 0.01 to 0.35, c = 0.01 to 0.5, d = 0.001 to 0.03, a + b + c + d = 1, M is any one selected from the group consisting of Fe, V, Cr, Ti, W, Ta, Mg, and Mo), a disulfide compound, and Fe2(MoO4)3, etc. are mentioned, but not limited thereto. Further, in addition to the above types, sulfides, selenides, halides, etc. can also be used as the positive electrode active material.

[0076] In this specification, the secondary battery can be a lithium secondary battery including a lithium metal secondary battery, a lithium ion secondary battery, a lithium polymer secondary battery, or a lithium ion polymer secondary battery, etc.

[0077] Hereinafter, the present invention will be described in more detail by way of examples. However, the following examples are for illustrative purposes of the present invention, and the scope of the present invention is not limited thereto.

[0078] [Manufacture of Polymer Solution for Electrode Slurry] Comparative Example 1 0.7 kg of spherical carboxymethyl cellulose (CMC) powder with a weight average molecular weight (Mw) of 2,000,000 g / mol and 34.3 kg of distilled water were charged into a 50 L tank and stirred for 3 hours to produce a polymer solution. The stirring was carried out using a BTM mixer under the conditions of Anchor disper 50 rpm and Homo disper 1,000 rpm.

[0079] Comparative Example 2 A polymer solution was prepared in the same manner as in Comparative Example 1, except that polyvinylidene propylene (PVP) with a weight-average molecular weight (Mw) of 2,000,000 g / mol was used instead of carboxymethylcellulose (CMC).

[0080] Example 1 A polymer solution was prepared in the same manner as in Comparative Example 1, except that after stirring for 1 hour, ultraviolet light with a wavelength of 254 nm was irradiated from two UV lamps (20W each) located on top of the BTM mixer, and then stirring and ultraviolet irradiation were performed simultaneously for the remaining 2 hours.

[0081] Example 2 A polymer solution was prepared in the same manner as in Example 1, except that it was irradiated with ultraviolet light at a wavelength of 280 nm.

[0082] Example 3 A polymer solution was prepared in the same manner as in Example 1, except that it was irradiated with ultraviolet light at a wavelength of 300 nm.

[0083] Example 4 A polymer solution was prepared in the same manner as in Example 1, except that it was irradiated with ultraviolet light at a wavelength of 360 nm.

[0084] [Evaluation of the physical properties of polymer solutions] Measurement of initial viscosity The polymer solutions of Comparative Example 1 and Examples 1 to 4, manufactured as described above, were stored in PE containers immediately after production, and the PE containers containing the polymer solutions were stored in an open system.

[0085] The viscosity of each polymer solution immediately after manufacturing was measured at 23°C using a Brookfield viscometer (DV2T viscometer, 12 rpm, spindle 24), and the results are shown in Table 1 below.

[0086] Evaluation of viscosity changes The viscosity of the polymer solutions of Comparative Example 1 and Examples 1 to 4 prepared above was measured every 24 hours at 23°C using the same viscometer, and the results are shown in Table 1 and Figure 1 below.

[0087] Table 1 below shows the viscosity change rate after 7 days compared to immediately after manufacturing, calculated using Equation 2 below. [Formula 2] Viscosity change rate (%)=(Vis(7)-Vis(0)) / Vis(0)×100 In Equation 2, Vis(0) represents the viscosity value immediately after manufacturing, and Vis(7) represents the viscosity value after 7 days.

[0088] Evaluation of dispersibility based on the type of water-soluble polymer. To evaluate the dispersibility of the active material depending on the type of water-soluble polymer, 100 g of graphite (POSCO Corporation) was added as the negative electrode active material to 105 mL of the polymer solutions for electrode slurries of Comparative Example 1 and Comparative Example 2 in a mixer, and then stirred to produce electrode slurries. Photographs of each electrode slurry immediately after production are shown in Figure 2 (Comparative Example 1) and Figure 3 (Comparative Example 2).

[0089] Furthermore, photographs showing the properties of the electrode slurry after passing it through a filtration filter (ROKI TECHNO HCB filter cartridge) are shown in Figures 4 (Comparative Example 1) and 5 (Comparative Example 2).

[0090] [Table 1]

[0091] According to the results in Table 1 and Figure 1 above, in the case of Comparative Example 1, in which the polymer solution was manufactured without irradiation with ultraviolet light, the viscosity of the polymer solution immediately after manufacture was at the same level as in the Examples, but it was confirmed that the stability over time decreased significantly as storage time progressed.

[0092] On the other hand, as can be seen from Figures 2 and 3, when the active material was dispersed using the CMC solution for electrode slurries, the surface of the electrode slurry was smooth and no clumps of undispersed active material were observed. In contrast, when the active material was dispersed using the PVP solution for electrode slurries, clumps of undispersed active material were visually observed on the surface of the electrode slurry.

[0093] Furthermore, as can be seen from Figures 4 and 5, when the manufactured electrode slurry was passed through a filtration filter, the electrode slurry using the CMC solution for electrode slurry (Comparative Example 1) passed through well without any undispersed active material being observed, while the electrode slurry using the PVP solution for electrode slurry (Comparative Example 2) had poor dispersion of active material and could not pass through the filtration filter, resulting in clogging of the filtration filter.

[0094] This demonstrated that using CMC as a polymer solution for electrode slurries allows for excellent dispersibility of active materials. In particular, irradiating the polymer solution for electrode slurries with ultraviolet light during its production ensures its stability over time, resulting in the production of electrode slurries with superior active material dispersibility, and furthermore, providing advantageous effects for improving the performance of electrodes and batteries using these slurries.

[0095] As described above with reference to embodiments and drawings of the present invention, any person with ordinary skill in the art to which the present invention belongs will be able to make various applications and modifications within the scope of the present invention based on the above description.

Claims

1. The steps include: mixing a water-soluble polymer and an aqueous solvent to obtain a mixed solution; The process includes the step of irradiating the mixed solution with ultraviolet (UV) light ranging from 240 nm to 340 nm for a predetermined time. The aforementioned mixed solution does not contain electrode active material. The ultraviolet light is irradiated during the production of the mixed solution, The water-soluble polymer comprises carboxymethylcellulose (CMC), A method for producing a polymer solution for electrode slurry, characterized in that the water-soluble polymer has a weight-average molecular weight (Mw) of 500,000 g / mol to 5,000,000 g / mol.

2. The method for producing a polymer solution for electrode slurry according to claim 1, characterized in that the water-soluble polymer includes a powder.

3. The method for producing a polymer solution for an electrode slurry according to claim 1, characterized in that the water-soluble polymer is mixed in an amount of 0.1% to 5% by weight based on the total weight of the aqueous solvent.

4. The method for producing a polymer solution for electrode slurry according to claim 1, characterized in that the wavelength of the irradiated ultraviolet light is from 240 nm to 260 nm.

5. A method for producing a polymer solution for an electrode slurry according to claim 1, characterized in that the ratio of ultraviolet irradiation time to total mixing time is from 1% to 100%.

6. The mixing step described above is: Mix while irradiating with ultraviolet light for the entire duration, or A method for producing a polymer solution for an electrode slurry according to claim 1, characterized in that the mixture is mixed while irradiating it with ultraviolet light for a portion of the time, including a predetermined time for mixing without irradiation with ultraviolet light.

7. It contains water-soluble polymers and aqueous solvents, and does not contain electrode active materials. When stored at 23°C for 7 days, the viscosity change rate calculated by the following [Formula 1] is in the range of -5% to 5%. The water-soluble polymer comprises carboxymethylcellulose (CMC), The aforementioned water-soluble polymer is characterized by having a weight-average molecular weight (Mw) of 500,000 g / mol to 5,000,000 g / mol, and is a polymer solution for electrode slurry. [Formula 1] Viscosity change rate (%) = (Vis(d)-Vis(i)) / Vis(i)×100 In Equation 1, Vis(i) is the initial viscosity value of the polymer solution for electrode slurry. Vis(d) is the viscosity value measured after storage for d days out of 1 to 7 days. The viscosity values ​​mentioned above represent the values ​​measured at 23°C using a Brookfield viscometer (DV2T viscometer, 12 rpm, spindle 24).

8. Mixing section, A manufacturing apparatus for carrying out the method for producing a polymer solution for electrode slurry according to claim 1, characterized in that it includes an ultraviolet irradiation unit mounted in the mixing unit for irradiating the object to be mixed with ultraviolet light in the range of 240 nm to 340 nm.

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