Method for evaluating the dispersion state of a slurry and method for producing a slurry using the same

Abstract

A method for evaluating the dispersion state of a slurry according to one embodiment of the present invention measures the SMD value of a slurry, which is expressed by Equation 1. [Formula 1] SMD=G'1 / G'2 (In Equation 1, G'1 is the elastic modulus measured after stirring the slurry at a shear rate of 1000 / s, and G'2 is the elastic modulus measured after stirring the slurry at a shear rate of 10 / s.)

Description

[Technical Field]

[0001] [CROSS-REFERENCE TO RELATED APPLICATIONS] This application claims the benefit of priority based on Korean Patent Application No. 10-2023-0101241 filed August 2, 2023 and Korean Patent Application No. 10-2024-0101477 filed July 31, 2024, and all contents disclosed in the documents of said Korean patent applications are incorporated herein by reference.

[0002] The present invention relates to a method for evaluating a slurry for an electrode of a secondary battery and a method for producing a slurry using the same. [Background technology]

[0003] In modern society, as the use of portable devices such as mobile phones, laptops, camcorders, and digital cameras has become commonplace, the development of technologies related to these mobile devices has become active. Furthermore, rechargeable secondary batteries are being used as power sources for electric vehicles (EVs), hybrid electric vehicles (HEVs), and plug-in hybrid electric vehicles (P-HEVs) as a solution to address air pollution caused by existing gasoline-powered vehicles that use fossil fuels, and the need for development of secondary batteries is increasing.

[0004] Currently commercially available secondary batteries include nickel-cadmium batteries, nickel-metal hydride batteries, nickel-zinc batteries, and lithium secondary batteries. Of these, lithium secondary batteries are attracting attention due to their advantages over nickel-based secondary batteries, such as almost no memory effect, freedom in charging and discharging, a very low self-discharge rate, and high energy density.

[0005] Such lithium secondary batteries mainly use lithium-based oxides and carbon materials as positive and negative electrode active materials, respectively, and may include an electrode assembly including a positive electrode and a negative electrode coated with the positive and negative electrode active materials, and a separator disposed between the positive and negative electrodes.

[0006] Meanwhile, slurries can be used to manufacture electrodes and separators for lithium secondary batteries. Slurries can be manufactured by mixing and processing active material particles, binders, conductive agents, solvents, etc. The dispersion state of the slurry varies depending on the processing conditions and composition, and the dispersion state of the slurry is an important factor that significantly affects whether or not defects occur during the process.

[0007] Therefore, it is necessary to predict electrode processability by quantifying the dispersion state of the slurry. Conventional evaluation of the dispersion state of a slurry has been carried out using a variety of methods and tools, such as using a microscope to observe the dispersion state of particles and measure their size and morphology, optical methods such as observing particle size distribution using imaging technology, laser technology, and sensor technology, and mechanical methods that quantify the slurry structure through viscosity measurement of the slurry.

[0008] However, optical methods are difficult to apply to opaque slurries and suffer from variations in quantification methods and application equipment.Mechanical methods provide limited information on the slurry structure, so there is essentially no correlation between the viscosity of the slurry and issues related to the actual dispersion state, such as sedimentation, aging, filter clogging, and coating defects.

[0009] Therefore, there is a pressing need for a method for evaluating the dispersion state of a slurry that can quickly and accurately evaluate changes in the slurry structure and that can be applied to a wide range of slurries regardless of the slurry characteristics, such as transparency or opacity. Summary of the Invention [Problem to be solved by the invention]

[0010] The problem to be solved by the present invention is to provide a method for evaluating the dispersion state of a slurry, which can predict electrode processability in advance depending on the slurry composition at the development stage, quickly evaluate changes in the structure of the slurry when a processability issue occurs at the slurry production stage, and predict changes over time depending on the storage period of the slurry in advance.

[0011] Another object of the present invention is to provide a method for producing a slurry with improved reliability by utilizing a method for evaluating the dispersion state of the slurry.

[0012] However, the problems to be solved by the embodiments of the present invention are not limited to the above problems, and can be variously expanded within the scope of the technical ideas included in the present invention. [Means for solving the problem]

[0013] In a method for evaluating the dispersion state of a slurry according to an embodiment of the present invention, the SMD value of a slurry is measured using the following equation 1.

[0014] [Formula 1] SMD=G'1 / G'2 (The G'1 is the elastic modulus measured after stirring the slurry at a shear rate of 1000 / s, and the G'2 is the elastic modulus measured after stirring the slurry at a shear rate of 10 / s.)

[0015] In one embodiment, the slurry may include active material particles.

[0016] In one embodiment, the slurry may be in a state where the flow history is removed by stirring at a shear rate of 1000 / s.

[0017] In one embodiment, each of G'1 and G'2 may be an elastic modulus measured by stirring the slurry at the shear rate and then applying vibration of 0.1 Hz to 1 Hz in a stationary state.

[0018] In one embodiment, the vibration may be between 0.1 Hz and 0.5 Hz.

[0019] In one embodiment, the vibration may be 0.215 Hz.

[0020] In one embodiment, the vibration may be applied for a period of at least 10 seconds and not more than 30 seconds.

[0021] In one embodiment, the larger the SMD value, the more unstable the dispersion state of the slurry may be.

[0022] In one embodiment, when the SMD value is 0.1 or more and less than 5, it can be determined that the dispersion state of the slurry is good.

[0023] In one embodiment, if the SMD value is 5 or more, it can be determined that the dispersion state of the slurry is poor.

[0024] A method for preparing a slurry according to one embodiment of the present invention includes the steps of preparing a slurry by mixing an active material, a binder, and optionally a conductive agent in a solvent; and measuring the SMD value of the slurry, which is represented by the following Equation 1:

[0025] [Formula 1] SMD=G'1 / G'2 (The G'1 is the elastic modulus measured after stirring the slurry at a shear rate of 1000 / s, and the G'2 is the elastic modulus measured after stirring the slurry at a shear rate of 10 / s.)

[0026] In one embodiment, if the SMD value is 0.1 or more and less than 5, it is determined that the dispersion state of the slurry is good, and the method may further include applying the slurry.

[0027] In one embodiment, if the SMD value is 5 or more, the method may further include determining that the dispersion state of the slurry is poor and re-manufacturing the slurry. [Effects of the Invention]

[0028] The method for evaluating the dispersion state of a slurry according to the present invention makes it possible to predict in advance the processability of an electrode according to the composition at the stage of slurry production.

[0029] In addition, it is possible to predict process issues such as coating defects, filter clogging, and mixing defects that may occur on the production line during the slurry manufacturing stage.

[0030] It is also possible to predict the change over time due to storage of the slurry.

[0031] The method for producing a slurry of the present invention allows the dispersion state of the produced slurry to be evaluated, making it easy to develop a slurry with improved stability, and as a result, product quality can be improved. [Brief explanation of the drawings]

[0032] [Figure 1] 1 is a photograph showing an evaluation of the storage stability of slurry A. [Figure 2] 10 is a photograph showing an evaluation of the storage stability of Slurry C. [Figure 3] 10 is a photograph showing the evaluation of the change over time of Slurry B. [Figure 4] 10 is a photograph showing the evaluation of the change over time of Slurry C. DETAILED DESCRIPTION OF THE INVENTION

[0033] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will now be described in detail with reference to the accompanying drawings, so that those skilled in the art can easily understand and practice the present invention. As those skilled in the art may realize various different forms, the present invention is not limited to the embodiments set forth herein.

[0034] Furthermore, throughout the specification, when a part is said to "comprise" a certain element, this means that it may further include other elements, not excluding other elements, unless otherwise specified.

[0035] In this embodiment, terms indicating directions such as front, back, left, right, up, and down are used, but these terms are merely for convenience of explanation and may change depending on the position of the object of interest, the position of the observer, etc.

[0036] In addition, in this specification, "elastic modulus (G')" means bulk modulus.

[0037] A method for evaluating the dispersion state of a slurry according to one embodiment of the present invention provides a method for measuring the SMD value of a slurry, which is represented by the following Equation 1.

[0038] [Formula 1] SMD=G'1 / G'2

[0039] The inventors of the present application have confirmed that slurries containing particles used in organic-inorganic composite materials exhibit thixotropy, which has sol-gel transition characteristics, and have developed an index that can evaluate the dispersion state of a slurry from the elastic modulus (G') based on this characteristic. Specifically, the index is expressed as shown in Equation 1 above.

[0040] That is, the inventors of the present application measured the elastic modulus after stirring the slurry at a shear rate of 1000 / s to obtain the G'1 value, and measured the elastic modulus after stirring the slurry at a shear rate of 10 / s to obtain the G'2 value. They then confirmed that the larger the (G'1 / G'2) value, the greater the thixotropy, which increases the instability of the slurry dispersion state due to flow, which may cause problems in actual processes. They therefore confirmed that the SMD index represented by Equation 1 above can be an objective index.

[0041] This evaluation method can be applied to a slurry form of an organic-inorganic composite material, and is not limited thereto. Specifically, the slurry can be applied to an electrode slurry containing active material particles, more specifically, an electrode slurry for a lithium secondary battery.

[0042] The electrode slurry of one embodiment can be produced by mixing an active material, a binder, and optionally a conductive agent in a solvent. An electrode of a positive electrode or a negative electrode can be produced by coating and drying the electrode slurry on a current collector to form an electrode composite layer.

[0043] The active material can be a positive electrode active material or a negative electrode active material.

[0044] As the positive electrode active material, a compound capable of reversible intercalation and deintercalation of lithium can be used without limitation among compounds known in the art. Specifically, the positive electrode active material can be a lithium composite metal oxide containing one or more metals such as cobalt, manganese, nickel, or aluminum and lithium.

[0045] Examples of the lithium composite metal oxide include lithium-manganese-based oxides (such as LiMnO2, LiMn2O4, etc.), lithium-cobalt-based oxides (such as LiCoO2, etc.), lithium-nickel-based oxides (such as LiNiO2, etc.), lithium-nickel-manganese-based oxides (such as LiNi 1-Y Mn Y O2 (where 0 < Y < 1), LiMn 2-z Ni z O4 (where 0 < Z < 2), etc.), lithium-nickel-cobalt-based oxides (such as LiNi 1-Y1 Co Y1 O2 (where 0 < Y1 < 1), etc.), lithium-manganese-cobalt-based oxides (such as LiCo 1-Y2 Mn Y2 O2 (where 0 < Y2 < 1), LiMn 2-Z1 Co Z1 O4 (where 0 < Z1 < 2), etc.), lithium-nickel-manganese-cobalt-based oxides (such as Li(Ni p Co q Mn r1 )O2 (where 0 < p < 1, 0 < q < 1, 0 < r1 < 1, p + q + r1 = 1) or Li(Ni p1Co q1 Mn r2 )O4 (where 0 < p1 < 2, 0 < q1 < 2, 0 < r2 < 2, p1 + q1 + r2 = 2), etc.), or lithium-nickel-cobalt-transition metal (M) oxide (e.g., Li(Ni p2 Co q2 Mn r3 M S2 )O2 (where M is one or more selected from the group consisting of Al, Fe, V, Cr, Ti, Ta, Mg, and Mo, and p2, q2, r3, and s2 are atomic fractions of independent elements, 0 < p2 < 1, 0 < q2 < 1, 0 < r3 < 1, 0 < s2 < 1, and p2 + q2 + r3 + s2 = 1), etc.), etc. may be mentioned, and any one or two or more of these compounds may be included.

[0046] The binder is used for binding the active material and the conductive agent and for binding to the current collector. Non-limiting examples of such binders include polyvinylidene fluoride (PVDF), polyvinyl alcohol (PVA), polyacrylic acid (PAA), polymethacrylic acid (PMA), polymethyl methacrylate (PMMA), polyacrylamide (PAM), polymethacrylamide, polyacrylonitrile (PAN), polymethacrylonitrile, polyimide (PI), alginic acid, alginate, chitosan, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene-butadiene rubber (SBR), fluorine rubber, and various copolymers thereof, etc. The binder may be included at 1 wt% to 30 wt%, specifically 1 wt% to 10 wt%, more specifically 1 wt% to 5 wt% based on the total weight of the slurry.

[0047] Conductive agents are used to further improve the conductivity of the electrode active material. Such conductive agents are not particularly limited as long as they do not induce chemical changes in the battery and have electrical conductivity. Examples include graphite such as natural graphite and artificial graphite; carbon black such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black; conductive fibers such as carbon fiber and metal fiber; metal powders such as carbon fluoride, aluminum, and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and polyphenylene derivatives. The conductive agent may be included in an amount of 1 wt % to 30 wt %, specifically 1 wt % to 10 wt %, and more specifically 1 wt % to 5 wt %, based on the total weight of the slurry.

[0048] The solvent may generally be an organic solvent or an aqueous solvent. For example, the organic solvent may be one or a mixture of two or more selected from the group consisting of N-methyl-2-pyrrolidone (NMP), methoxypropyl acetate, butyl acetate, glycolic acid, butyl ester, butyl glycol, methylalkylpolysiloxane, alkylbenzene, propylene glycol, xylene, monophenyl glycol, aralkyl-modified methylalkylpolysiloxane, polyether-modified dimethylpolysiloxane copolymer, polyether-modified dimethylpolysiloxane copolymer, polyacrylate solution, alkylbenzene, diisobutyl ketone, organically modified polysiloxane, butanol, isobutanol, modified polyacrylate, modified polyurethane, and polysiloxane-modified polymer.

[0049] As the aqueous solvent, water can be used.

[0050] Hereinafter, a method for evaluating the dispersion state of a slurry, which measures the SMD value represented by the above formula 1, will be described.

[0051] In Equation 1, G'1 is the elastic modulus measured after stirring the slurry at a shear rate of 1000 / s. Specifically, it is the elastic modulus measured by applying vibration of 0.1 Hz to 1 Hz to the slurry while the slurry is stopped after stirring at a shear rate of 1000 / s.

[0052] In Equation 1, G'2 is the elastic modulus measured after stirring the slurry at a shear rate of 10 / s. Specifically, it is the elastic modulus measured by applying vibration of 0.1 Hz to 1 Hz to the slurry while the slurry is stopped after stirring at a shear rate of 10 / s.

[0053] The slurry may be stirred for 30 seconds or more at each shear rate, for example, 60 seconds. If the slurry is stirred for less than 30 seconds, the slurry may not reach a steady state or the driving / measurement reliability of the equipment may be reduced.

[0054] The stirring may be carried out using any device capable of stirring a thixotropic slurry, for example, a rheometer, more specifically, a Couette cell of a rheometer.

[0055] After stirring the slurry under the above conditions, vibration is applied while the slurry is stopped to measure the elastic modulus. For example, the elastic modulus can be measured through an oscillatory frequency sweep test.

[0056] The vibration applied to the slurry may be in the range of 0.1 to 1 Hz. If the vibration is less than 0.1 Hz, the measurement error of the instrument may increase, reducing reliability. Furthermore, if the vibration exceeds 1 Hz, the structure of the slurry may be destroyed, which is undesirable.

[0057] Therefore, the frequency at which the change in the slurry structure is most pronounced can be selected from the above range, and the elastic modulus (G') value at this specific frequency can be set as the target for incorporation into Equation 1.

[0058] The inventors of the present application have confirmed that, although the selection of such a value is not limited and is influenced by factors such as the composition of the slurry being measured, generally, a larger change is observed at lower Hz values. For example, the vibration applied to the slurry may be specifically 0.1 Hz to 0.5 Hz, more specifically 0.1 Hz to 0.3 Hz, and most specifically 0.215 Hz.

[0059] At this time, the vibration may be applied for 10 to 30 seconds, more particularly, 10 to 20 seconds, and even more particularly, 10 to 15 seconds.

[0060] The elastic modulus of the slurry can be measured for a slurry in the range of 20 degrees Celsius or more and 30 degrees Celsius or less, for example, for a slurry at 23 degrees Celsius.

[0061] The elastic modulus of the slurry can be affected by temperature, and is preferably measured for the slurry at the same temperature. At this time, if the temperature is too high, the viscosity of the slurry decreases, and if the temperature is too low, the viscosity increases. Therefore, it is preferable to measure the elastic modulus at room temperature (23°C), which is the temperature at which the slurry is actually used in the process.

[0062] The G'1 and G'2 values ​​are obtained for the elastic modulus measured as described above, and the SMD value can be obtained by substituting these values ​​into Equation 1.

[0063] On the other hand, in the method for evaluating a slurry of the present invention, the slurry is stirred before measuring the elastic modulus to remove and initialize the flow history in order to improve measurement accuracy and reproducibility.

[0064] The stirring for the initialization can be carried out at a shear rate of 500 / s to 1000 / s for 30 to 100 seconds, more specifically, at a shear rate of 1000 / s to 1500 / s for 50 to 80 seconds, for example, at a shear rate of 1000 / s for 60 seconds.

[0065] If the stirring speed is too low or for too short a time, outside the above range, initialization such as removal of flow history may not be performed well. However, if the stirring speed is too high or for too long a time, uniform stirring may be difficult and slippage may occur, which is undesirable.

[0066] The stirring may be performed using any device capable of stirring a thixotropic slurry as described above, but may be performed using, for example, a rheometer, more specifically, a Couette cell of a rheometer.

[0067] The larger the SMD value of Equation 1 obtained through this process, the more unstable the slurry dispersion state is. Specifically, when the SMD value is 0.1 or more and less than 5, the slurry dispersion state is determined to be good. On the other hand, when the SMD value is 5 or more, the slurry dispersion state is determined to be poor. When the slurry dispersion state is determined to be good, the slurry is expected to have excellent reliability. When the slurry dispersion state is determined to be poor, the slurry is expected to cause problems such as slurry precipitation, deterioration over time, and filter clogging when applied to actual processes.

[0068] Therefore, through the slurry evaluation method, process issues depending on the composition and mixing conditions can be predicted in advance from the slurry production stage and production line, and appropriate composition and mixing conditions can be derived, and the appropriateness of slurry storage can also be considered.

[0069] Furthermore, this method is not limited by optical properties, and according to the results of the research conducted by the inventors of the present application, it has been confirmed that the information obtained from this method has an effect on the changes over time and precipitation that actually appear in the slurry, and therefore the dispersion state of the slurry can be accurately evaluated.

[0070] The method for producing a slurry according to an embodiment of the present invention may utilize the above-described method for evaluating the dispersion state of a slurry.

[0071] The method for producing a slurry of the present invention includes the steps of: mixing an active material, a binder, and optionally a conductive agent in a solvent to form a slurry; and The step of measuring the SMD value of the slurry is represented by the following formula 1:

[0072] [Formula 1] SMD=G'1 / G'2 (The G'1 is the elastic modulus measured after stirring the slurry at a shear rate of 1000 / s, The G'2 is the elastic modulus measured after stirring the slurry at a shear rate of 10 / s.

[0073] In one embodiment, the slurry is a slurry for an electrode, and the step of preparing the slurry is a step of mixing an active material, a binder, and optionally a conductive agent in a solvent. The above-described contents of each component of the slurry are equally applicable, and detailed description thereof will be omitted.

[0074] The step of measuring the SMD value is a step of measuring the SMD value represented by the following Equation 1 for the prepared slurry.

[0075] [Formula 1] SMD=G'1 / G'2 G'1 is the elastic modulus measured after stirring the slurry at a shear rate of 1000 / s, The G'2 is the elastic modulus measured after stirring the slurry at a shear rate of 10 / s.

[0076] The specific explanation for Equation 1 is the same as that described above.

[0077] Meanwhile, a method for preparing a slurry according to an embodiment includes the steps of preparing a slurry and measuring an SMD value of the prepared slurry, and may further include the following steps.

[0078] In one embodiment, the method for preparing a slurry may further include determining that the dispersion state of the slurry is good when the measured SMD value is greater than or equal to 0.1 and less than 5, and applying the prepared slurry. The slurry may be applied to a current collector to form a coating, and then dried and rolled to form an electrode.

[0079] Alternatively, in one embodiment, the method for preparing a slurry may further include determining that the dispersion state of the slurry is poor if the measured SMD value is 5 or greater, and re-preparing the slurry. For example, poor dispersion of the slurry may occur due to the inclusion of moisture or foreign matter during the slurry preparation process. Alternatively, poor dispersion may occur due to an error in mixing the components by weight during the slurry preparation process. The present invention measures the SMD of the prepared slurry, and then predicts poor dispersion of the slurry in advance based on the SMD value.

[0080] As described above, a method for preparing a slurry according to one embodiment includes preparing a slurry and measuring the SMD value of the prepared slurry, thereby enabling the dispersion state of the slurry to be predicted in advance before the process is performed, thereby minimizing process defects.

[0081] Therefore, the present invention can provide a method for producing a slurry with improved reliability, and facilitates the development of slurries with improved stability, resulting in improved product quality.

[0082] Example Hereinafter, with reference to examples and comparative examples, it will be explained that the evaluation method of the present invention and the index represented by Equation 1 obtained thereby have a highly reliable correlation with the slurry stability that appears in an actual process, such as precipitation, changes over time, filter clogging, etc.

[0083] Example 1: Preparation of Slurry A Active material (Li(Ni) 1 / 3 Co 1 / 3 Mn 1 / 3) O2), a conductive agent (carbon nanotubes), and a binder (polyvinylidene fluoride) were mixed in a weight ratio of 96.4:1.8:1.8 in NMP solvent at a solids concentration of 75%.

[0084] Example 2: Preparation of Slurry B Active material (Li(Ni) 1 / 3 Co 1 / 3 Mn 1 / 3) O2), conductive agent (carbon black), and binder (polyvinylidene fluoride) were mixed in a weight ratio of 96.4:1.8:1.8 in NMP solvent at a solids concentration of 75%.

[0085] <Comparative Example 1: Production of Slurry C> The active material (LFP), conductive agent (carbon nanotubes), and binder (polyvinylidene fluoride) were mixed in a weight ratio of 96.4:1.8:1.8 in NMP solvent at a solid content of 60%.

[0086] <Experimental Example 1> The slurry A was subjected to the following steps, and G'1 was measured.

[0087] First, Slurry A at room temperature (23°C) was placed in a Couette cell of a rheometer and stirred at a shear rate of 1000 / s for 60 seconds to remove the flow history of the slurry.

[0088] Then, the slurry A was stirred at a shear rate of 1000 / s for 60 seconds, and then, in the stopped state, vibration of 0.215 Hz was applied to perform an oscillatory frequency sweep test. However, before applying the vibration of 0.215 Hz, various vibration frequencies in the range of 0.1 Hz to 1 Hz were applied for 15 seconds to measure the elastic modulus in order to determine the vibration value that shows the greatest characteristic change in the slurry structure.

[0089] Here, for the test, the shear rate was set to 1000 / s, the amplitude (Strain): 0.5%, and the frequency: 0.1 to 1 Hz.

[0090] The same process was carried out for slurry B and slurry C, and G'1 for each was measured.

[0091] <Experimental Example 2> The slurry A was subjected to the following steps, and G'2 was measured.

[0092] First, Slurry A at room temperature (23°C) was placed in a Couette cell of a rheometer and stirred at a shear rate of 1000 / s for 60 seconds to remove the flow history of the slurry.

[0093] Thereafter, the slurry A was stirred at a shear rate of 10 / s for 60 seconds, and then, in the stopped state, vibration of 0.215 Hz was applied as in Experimental Example 1 to perform an oscillatory frequency sweep test.

[0094] Here, for the test, the shear rate was set to 10 / s, the amplitude (Strain): 0.5%, and the frequency: 0.1 to 1 Hz.

[0095] The same process was carried out for slurry B and slurry C, and G'2 for each was measured.

[0096] The elastic modulus values ​​measured in Experimental Examples 1 and 2 are shown in Table 1 below. [Table 1]

[0097] <Experimental Example 3> The SMD values ​​of Slurry A, Slurry B, and Slurry C were measured with reference to Table 1 and Equation 1 and are shown in Table 2 below. In Table 2, the SMD values ​​are rounded to two decimal places. [Table 2]

[0098] Referring to Table 2, Slurry A and Slurry B, which have an SMD value of less than 5, were judged to have a good slurry dispersion state. Slurry C, which has an SMD value of more than 5, was judged to have a poor slurry dispersion state, that is, it can be predicted that the structure is highly unstable.

[0099] <Experimental Example 4> To confirm the storage stability of the prepared slurries A and C, each slurry at room temperature (23°C) was poured into a glass substrate and left at 23°C for 7 days. The presence or absence of precipitates was then confirmed, and the results are shown in Figures 1 and 2.

[0100] Referring to FIG. 1, it can be seen that no precipitate was generated in slurry A, whereas referring to FIG. 2, it can be seen that a large amount of precipitate was generated in slurry C.

[0101] <Experimental Example 5> To check for filter clogging for the prepared slurries B and C, slurries B and C at room temperature (23°C) were respectively introduced into a 150 mesh filter, and the pressure applied to the filter over time was measured using a pressure sensor.

[0102] The measurement results showed that the pressure increased slowly over time for Slurry B, whereas the pressure rose rapidly from the beginning for Slurry C. In other words, it was predicted that filter clogging would occur when Slurry C was used.

[0103] <Experimental Example 6> To confirm the changes over time of the prepared slurries A and C, 100 ml of each slurry at room temperature (23°C) was poured onto a glass substrate and left in an environment of 23°C for 5 days. The results are shown in Figures 3 and 4.

[0104] Referring to FIG. 3, it can be seen that Slurry B maintains a slurry state, whereas referring to FIG. 4, it can be seen that Slurry C solidifies and changes into a phase close to a solid state.

[0105] From the results of Experimental Examples 3 to 6, the dispersion state of the slurry was judged to be good or bad by the evaluation method of the present invention, and the results of the evaluation of precipitation, filter clogging, and change over time were also obtained. Therefore, it can be confirmed that the method of evaluating the dispersion state of the slurry according to the present invention can be an indicator of the dispersion state of the actual slurry.

[0106] 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 claims also fall within the scope of the present invention.

Claims

1. A method for evaluating the dispersion state of a slurry by measuring the SMD value of the slurry, which is expressed by the following formula 1. [Formula 1] SMD=G’ １ / G’ ２ (The above G' １ is the elastic modulus measured after stirring the slurry at a shear rate of 1000 / s, The G' ２ is the elastic modulus measured after stirring the slurry at a shear rate of 10 / s.

2. The method for evaluating a dispersion state of a slurry according to claim 1 , wherein the slurry contains active material particles.

3. The method for evaluating a dispersion state of a slurry according to claim 1 , wherein the slurry is in a state in which a flow history has been removed by stirring the slurry at a shear rate of 1000 / s.

4. The G' １ and G' ２ 2. The method for evaluating a dispersion state of a slurry according to claim 1, wherein each of the elastic moduli is measured by stirring the slurry at the shear rate and then applying vibration of 0.1 Hz to 1 Hz in a stationary state.

5. The method for evaluating a dispersion state of a slurry according to claim 4 , wherein the vibration is 0.1 Hz or more and 0.5 Hz or less.

6. The method for evaluating a dispersion state of a slurry according to claim 4 , wherein the vibration is 0.215 Hz.

7. The method for evaluating a dispersion state of a slurry according to claim 4 , wherein the vibration is applied for a period of 10 seconds or more and 30 seconds or less.

8. The method for evaluating a dispersion state of a slurry according to claim 1 , wherein the larger the SMD value, the more unstable the dispersion state of the slurry becomes.

9. The method for evaluating a dispersion state of a slurry according to claim 1 , wherein the dispersion state of the slurry is determined to be good when the SMD value is 0.1 or more and less than 5.

10. 2. The method for evaluating a slurry dispersion state according to claim 1, wherein the slurry dispersion state is determined to be poor when the SMD value is 5 or more.

11. mixing an active material, a binder, and optionally a conductive agent in a solvent to form a slurry; and A method for preparing a slurry, comprising: measuring an SMD value of the slurry, which is represented by the following equation 1: [Formula 1] SMD=G’ １ / G’ ２ (The above G' １ is the elastic modulus measured after stirring the slurry at a shear rate of 1000 / s, The G' ２ is the elastic modulus measured after stirring the slurry at a shear rate of 10 / s.

12. The method of claim 11 , further comprising: determining that the dispersion state of the slurry is good when the SMD value is 0.1 or more and less than 5, and applying the slurry.

13. The method of claim 11, further comprising the step of determining that the dispersion state of the slurry is poor if the SMD value is 5 or more, and reproducing the slurry.

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