Preparation method of electrode slurry for secondary battery

Abstract

According to the present disclosure, provided is a method for preparing an electrode slurry for a secondary battery, comprising: a step a) of feeding raw materials including an electrode active material, a conductive agent, and a thickener into a mixer; and a step b) of adding a solvent into the mixer and kneading the raw materials, in which the thickener in the step a) is in a solid state.

Description

Technical Field

[0001] The present disclosure relates to a method for preparing an electrode slurry for a secondary battery and a secondary battery electrode manufactured thereby. Background Art

[0002] With the global warming problem existing in modern society, the demand for environmental protection technology is increasing rapidly as a measure to deal with the problem. In particular, with the increase in technical requirements for electric vehicles and energy storage systems (ESS), the demand for lithium secondary batteries, which have attracted much attention as energy storage devices, has also exploded. Therefore, research is being conducted to improve the life characteristics of lithium secondary batteries.

[0003] The electrode slurry for lithium secondary batteries is prepared by mixing and dispersing an electrode active material, a conductive agent, a thickener and a binder with a solvent for a certain period of time using a mixer. Generally, when the solid content in the electrode slurry is low, the migration of the binder occurs when the electrode slurry is coated on the current collector and dried, thereby adversely affecting the quality of the electrode, such as cracks. Therefore, efforts are being made to suppress the migration of the binder by increasing the content of the solids in the electrode slurry. However, if the content of the solids in the electrode slurry increases, the viscosity will increase, so there are difficulties in carrying out processes such as transportation and coating.

[0004] Therefore, efforts are needed to increase the solids content of the slurry while ensuring a coatable viscosity.

[0005] In addition, research is needed to continuously prepare electrode slurry without being limited by factors such as the capacity of a mixing tank or the load of an equipment, while improving the quality of the slurry. Summary of the invention

[0006] Technical issues

[0007] According to one aspect of the present disclosure, the quality of a coated electrode may be improved by increasing the solid content of an electrode slurry for a secondary battery while ensuring a coatable slurry viscosity.

[0008] According to another aspect of the present disclosure, a method of continuously preparing electrode slurry for a secondary battery may be provided.

[0009] Technical Solution

[0010] The method for preparing electrode slurry for secondary batteries according to the present disclosure may include: step a), adding raw materials including an electrode active material, a conductive agent and a thickener into a mixer; and step b), adding a solvent into the mixer and kneading the raw materials.

[0011] According to one embodiment of the method for preparing an electrode slurry for a secondary battery disclosed herein, the mixer may be an extruder.

[0012] According to another embodiment of the method for preparing electrode slurry for secondary battery disclosed herein, the step b) may be performed simultaneously by a conveying part including a conveying screw and a mixing part including a kneading block in an extruder.

[0013] According to another embodiment of the method for preparing electrode slurry for a secondary battery disclosed herein, the conveying part and the mixing part in the extruder may be repeatedly disposed in sequence along the conveying direction.

[0014] According to another embodiment of the method for preparing the electrode slurry for a secondary battery disclosed herein, the method may further include a step of adjusting the viscosity by adding a solvent into the extruder.

[0015] According to another embodiment of the method for preparing electrode slurry for secondary batteries disclosed herein, the method further includes a step of adjusting the viscosity by adding a solvent into the extruder, but the solvent may be added at a position of 40 to 70% based on the total length of the extruder in the conveying direction.

[0016] According to another embodiment of the method for preparing electrode slurry for a secondary battery of the present disclosure, the internal temperature of the extruder may be 25°C to 60°C.

[0017] According to another embodiment of the method for preparing an electrode slurry for a secondary battery disclosed herein, the electrode may be a negative electrode.

[0018] According to another embodiment of the method for preparing electrode slurry for a secondary battery disclosed herein, the solid content of the prepared slurry may be 50% to 65%.

[0019] According to another embodiment of the method for preparing electrode slurry for a secondary battery disclosed herein, the viscosity of the prepared slurry may be 20,000 cp or less.

[0020] According to the present disclosure, a system for preparing electrode slurry for secondary batteries may include: a raw material input section, comprising an electrode active material, a conductive agent and a thickener; an extrusion section, conveying the raw materials while kneading the raw materials; a first solvent input section, arranged on one side of the extrusion section in the length direction; and a second solvent input section, arranged on the other side of the extrusion section in the length direction.

[0021] In the system for preparing electrode slurry for a secondary battery according to the present disclosure, the second solvent input part may be provided at a rear end of the first solvent input part based on a conveying direction.

[0022] In the system for preparing an electrode slurry for a secondary battery according to the present disclosure, the second solvent input part may be provided at a position of 40 to 70% based on a total length of the extruder in a conveying direction.

[0023] The method for preparing an electrode according to the present disclosure may include the step of coating the electrode slurry prepared according to the embodiment on a current collector.

[0024] A secondary battery according to the present disclosure may include the manufactured electrode.

[0025] Effects of the Invention

[0026] The method for preparing the electrode slurry for a secondary battery according to the present disclosure can coat a high content of solids, thereby suppressing the migration of the binder, and thus has the effect of improving the quality of the electrode.

[0027] In addition, as the solid content of the slurry increases, the amount of solvent required for drying decreases, the length of the drying furnace can be reduced, thereby reducing investment costs, and productivity can be improved by increasing the coating speed within the same drying furnace.

[0028] Furthermore, in the method for preparing the electrode slurry for a secondary battery according to the present disclosure, continuous preparation is possible without being limited by factors such as the capacity of a mixing tank or the load of equipment, thus having the effect of significantly improving the production volume. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 This is a schematic diagram of a sample selected at 5 points with a predetermined interval in the longitudinal direction of the negative electrode active material layer and punched into a circular shape with a diameter of 38 mm in order to evaluate the homogeneity of the negative electrode active material layer;

[0030] Figure 2 is a graph showing life characteristics of secondary batteries including electrodes manufactured according to Example 1, Comparative Example 1, and Comparative Example 2 of the present disclosure. DETAILED DESCRIPTION

[0031] The present disclosure is described in detail below. However, this is merely an illustrative example, and the present disclosure is not limited to the specific embodiments described illustratively. The specific contents for implementing the present disclosure are described in detail with reference to the accompanying drawings. Regardless of the accompanying drawings, the same reference numerals refer to the same constituent elements, and "and / or" includes all combinations of each and more than one of the items mentioned.

[0032] Throughout the specification, unless otherwise specifically stated to the contrary, when describing a part as "including" a certain constituent element, it means that other constituent elements may also be included, rather than excluding other constituent elements. In addition, unless otherwise specifically stated, the singular form also includes the plural form.

[0033] In this specification, when a layer, film, region, plate or the like is described as being “on” or “over” another part, this includes not only the case of being “directly” “on” another part but also the case of having other parts in between.

[0034] According to the present disclosure, a method for preparing electrode slurry for secondary batteries is provided, which comprises: step a), adding raw materials including electrode active material, conductive agent and thickener into a mixer; and step b), adding a solvent into the mixer and kneading the added raw materials, wherein the thickener in step a) is solid.

[0035] The mixer may be in the form of an extruder capable of simultaneously performing kneading and conveying, but is not limited thereto.

[0036] In the above step a), a raw material including an electrode active material, a conductive agent and a thickener is fed into a raw material feeding part of an extruder.

[0037] The thickener is used to increase the dispersibility of the electrode active material, and also acts as a partial binder, and is usually used in a solution state dispersed in a solvent. In the existing slurry preparation process, the thickener is pre-dissolved in the solvent and then put into the mixer, but due to the low solubility of the thickener, it is difficult to reduce the amount of solvent, so there are limitations in increasing the solid content of the final slurry. In contrast, in the present disclosure, a solid thickener is directly added and mixed, so that the solid content in the electrode slurry can be increased. In addition, the stability of the slurry viscosity that may be caused when the thickener is mixed in a solid state is achieved by kneading and conveying using an extruder. That is, a slurry that ensures a coatable slurry viscosity and increases the solid content can be prepared, thereby greatly improving the coating quality of the electrode.

[0038] The thickener may be a cellulose compound, specifically, a mixture of carboxymethyl cellulose, hydroxypropyl methyl cellulose, methyl cellulose or one or more of their alkali metal salts. The alkali metal may be Na, K or Li.

[0039] The electrode active material can be used without limitation as long as it is an electrode active material commonly used in secondary batteries. As an example of the negative electrode active material, it can be a carbon-based negative electrode active material, a silicon-based negative electrode active material, or a mixture thereof, but is not limited thereto. The carbon-based negative electrode active material can be one or more selected from artificial graphite, natural graphite, and hard carbon. The silicon-based negative electrode active material can be Si, SiO x(0 < x < 2), an Si-Q alloy (wherein Q is an element selected from alkali metals, alkaline earth metals, Group 13 elements, Group 14 elements, Group 15 elements, Group 16 elements, transition metals, rare earth elements, and combinations thereof, and is not Si), an Si-carbon composite, or a mixture of at least one of them and SiO2. In the case of the positive electrode active material, it can be a composite oxide of a metal selected from cobalt, manganese, nickel, and combinations thereof and lithium, but is not limited thereto.

[0040] The raw materials may contain a binder, and in order to improve conductivity, a conductive agent may be further included.

[0041] The binder is not particularly limited as long as it is an existing binder that can function to well adhere the electrode active material particles to each other and well adhere the electrode active material to the current collector. As an example, the binder can be a water-based binder, specifically styrene-butadiene rubber, acrylated styrene-butadiene rubber, polyvinyl alcohol, sodium polyacrylate, a copolymer of propylene and an olefin having 2 to 8 carbon atoms, a copolymer of (meth)acrylic acid and an alkyl (meth)acrylate, or a combination thereof. At this time, the binder may be added in a solution state with a solids content of 20 to 60% by weight, for example, 30 to 50% by weight, but is not limited thereto.

[0042] The solvent can be used without limitation as long as it is a solvent commonly used in electrode slurries. Specifically, as the solvent for the negative electrode, it can be at least one selected from water, pure water, deionized water, distilled water, ethanol, isopropyl alcohol, methanol, acetone, n-propanol, and tert-butanol, but is not limited thereto. The solvent for the positive electrode can be at least one selected from amines such as N,N-dimethylaminopropylamine and diethylenetriamine; ethers such as ethylene oxide and tetrahydrofuran; ketones such as methyl ethyl ketone; esters such as methyl acetate; and aprotic polar solvents such as dimethylacetamide and N-methyl-2-pyrrolidone, but is not limited thereto.

[0043] The conductive agent can be one or more selected from carbon nanotubes, acetylene black, carbon black, natural graphite, artificial graphite, Ketjen black, and carbon fibers. The conductive agent may be added in a solution state with a solids content of 0.5 to 2% by weight, for example, 0.5 to 1.8% by weight, but is not limited thereto. The solvent used at this time is the same as described above.

[0044] Step b) is a step of putting the solvent into a mixer and kneading the input raw materials. Specifically, the mixer can be in the form of an extruder. Through the extruder, the input raw materials are continuously kneaded and conveyed, and extruded to the outer surface of the substrate so that continuous coating can be performed. Specifically, the raw materials are mixed by rotating the screw of the extruder, and the mixed product is pushed out and passed through a die head installed in front of the barrel of the extruder, so that it can be coated on the outside of the substrate.

[0045] The step of adding the solvent in step b) may be at a position of 5% to 30% based on the total length of the extruder in the conveying direction, for example, at a position of 7% to 27%. The solvent may be the same as described above, preferably, water, but is not limited thereto.

[0046] The kneading and conveying can be performed simultaneously by a plurality of conveying sections and mixing sections in the extruder. Specifically, the raw materials fed into the raw material feeding section of the extruder can be conveyed to the mixing section by the conveying section for kneading, and then can be conveyed again to the die head direction of the extruder by the conveying section. The conveying section and the mixing section can be repeatedly arranged in sequence according to the conveying direction.

[0047] The conveying portion may include a conveying screw having a continuous pitch.

[0048] The mixing section may include a kneading block.

[0049] The kneading block has a structure in which oval disks are arranged at a certain angle, and can be divided into a forward kneading block, a reverse kneading block and a neutral kneading block according to the direction of the raw material. Specifically, the forward kneading block means that the raw material moves downstream toward the die head of the screw as the kneading block rotates, while the reverse kneading block moves in the opposite direction to the direction of the raw material, that is, upstream. The neutral kneading block means that the raw material does not move forward or backward due to the rotation of the screw.

[0050] In terms of ensuring the residence time of the input raw materials in the extruder to achieve a sufficient kneading process, the screws in the extruder are assembled in the middle of forward / reverse, forward / neutral / reverse, etc. to apply sufficient kneading.

[0051] The conveying screw at the end of the mixing section along the advancing direction of the raw material can be a reverse conveying screw. In addition, the advancing direction of the raw material itself will not be changed to the reverse direction by the reverse conveying screw, and most of the raw material is conveyed toward the die head direction of the extruder.

[0052] The combination of kneading blocks contained in the mixing section may be constituted in various combinations without limitation as long as a reverse kneading block is provided at the end along the running direction of the raw material, but the kneading block provided continuously with the reverse kneading block among the plurality of kneading blocks is preferably a forward kneading block.

[0053] The combination ratio of the mixing part and the conveying part in the extruder can be 55:45 to 80:20, specifically 60:40 to 75:25. Therefore, the input raw materials can be uniformly mixed during the residence period of the extruder, and the adsorption amount of the binder and the conductive agent on the electrode active material can be increased.

[0054] In the process of performing the step b), a step of further adding a solvent to the extruder to adjust the viscosity may be further included. Specifically, the solvent may be added at a position of 50% to 75% based on the total length of the screw of the extruder, and the solvent is the same as described above. By further adding the solvent, the solid content of the mixing step can be adjusted, which affects the viscosity of the slurry. When the solid content of the mixing step is higher than the appropriate range, the slurry viscosity decreases, which increases the adsorption force between the thickener and the electrode active material, resulting in a decrease in the final slurry viscosity. When the solid content of the mixing step is lower than the appropriate range, the adsorption force between the thickener and the electrode active material decreases in turn, resulting in an increase in the final slurry viscosity. Therefore, it is necessary to select a solid content of the mixing step in an appropriate range that does not reduce the electrode adhesion and battery performance, and the solid content of the mixing step may be 55% to 80%, for example, 60% to 75% or 65% to 70%.

[0055] The final solid content of the electrode slurry after the mixing and conveying steps may be 40% to 65%, for example, 45% to 60% or 46% to 57%.

[0056] In order to prepare the electrode slurry in which the input raw materials are uniformly dispersed during the residence time, the internal temperature of the extruder may be 25°C to 60°C, for example, 25°C to 35°C.

[0057] The present disclosure also provides a method for preparing an electrode, which includes the step of coating the electrode slurry prepared according to one embodiment of the present disclosure on a current collector.

[0058] The coating may be any coating method commonly used for coating liquid to form a film, such as spray coating, dip coating, spin coating, gravure coating, slot extrusion coating, doctor blade coating, roller coating, inkjet printing, slot extrusion coating, flexographic printing, screen printing, electrohydrodynamic printing, microcontact printing, embossing, reverse offset printing, rod coating, gravure offset printing, etc., but the invention is not limited thereto.

[0059] The current collector may be selected from copper foil, nickel foil, stainless steel foil, titanium foil, foamed nickel, foamed copper, a polymer substrate coated with a conductive metal, and a combination thereof, but is not limited thereto.

[0060] The current collector coated with the electrode slurry may be subjected to a drying process at 100 to 300° C., for example, 100 to 250° C., to form an electrode active material layer on the current collector. At this time, the current collector coated with the electrode slurry may be subjected to a calendering process before the drying step to increase the adhesion between the electrode active material in the electrode slurry and the current collector. Specifically, the current collector coated with the electrode slurry may be subjected to a calendering process before the drying step to increase the adhesion between the electrode active material in the electrode slurry and the current collector. Specifically, the current collector coated with the electrode slurry may be subjected to a calendering process to pass between two or more rotating rollers, but is not limited thereto.

[0061] The present disclosure also provides a secondary battery including the electrode manufactured according to one embodiment of the present disclosure.

[0062] In detail, the electrode according to the present disclosure may have improved substrate adhesion and thickness uniformity. Therefore, a secondary battery including the electrode may have further improved long-term stability, and is therefore preferred.

[0063] The electrode may become a positive electrode or a negative electrode according to the kind of electrode active material contained in the electrode active material layer. The electrode active material is the same as described above.

[0064] The secondary battery may further include a separator between the positive electrode and the negative electrode, and an electrolyte.

[0065] The separator can be selected from, for example, glass fiber, polyester, polyethylene, polypropylene, polytetrafluoroethylene or a combination thereof, and can be in the form of a non-woven fabric or a woven fabric. For example, polyolefin-based polymer separators such as polyethylene and polypropylene can be mainly used in lithium secondary batteries, and in order to ensure heat resistance or mechanical strength, a separator coated with a ceramic component or a composition containing a polymer substance can also be used, and can be selectively used in a single-layer or multi-layer structure, and a known separator in the technical field can be used, but the present disclosure is not limited thereto.

[0066] The electrolyte may include an organic solvent and a lithium salt.

[0067] The organic solvent acts as a medium through which ions participating in the electrochemical reaction of the battery can move. For example, the organic solvent can use a carbonate-based solvent, an ester-based solvent, an ether-based solvent, a ketone-based solvent, an alcohol-based solvent or an aprotic solvent. The organic solvent can be used alone or in combination of two or more. The mixing ratio when two or more organic solvents are mixed can be appropriately adjusted according to the desired battery performance. In addition, a well-known organic solvent in the technical field can be used, but the present disclosure is not limited thereto.

[0068] The lithium salt is a substance that is dissolved in an organic solvent and used as a supply source of lithium ions in a battery so that a lithium secondary battery can basically operate and promote the movement of lithium ions between the positive electrode and the negative electrode. Examples of the lithium salt include LiPF6, LiBF4, LiSbF6, LiAsF6, LiN(SO3C2F5)2, LiN(CF3SO2)2, LiC4F9SO3, LiClO4, LiAlO2, LiAlCl4, LiN(C x F 2x+1 SO2)(C y F 2y+1 SO2) (x and y are natural numbers), LiCl, LiI, LiB(C2O4)2 or a combination thereof, but the present disclosure is not limited thereto.

[0069] The concentration of the lithium salt may be used in the range of 0.1 M to 2.0 M. When the concentration of the lithium salt is within the above range, the electrolyte has appropriate conductivity and viscosity, and thus may exhibit excellent electrolyte performance, and may allow lithium ions to move efficiently.

[0070] In addition, in order to improve the charge and discharge characteristics, flame retardant properties, etc., the electrolyte may further contain pyridine, triethyl phosphate, triethanolamine, cyclic ether, ethylenediamine, n-glyme, hexamethylphosphoric acid triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, aluminum chloride, etc. According to circumstances, in order to impart non-flammability, halogen-containing solvents such as carbon tetrachloride and trifluoroethylene may be further included, and in order to improve high-temperature storage characteristics, fluoro-ethylene carbonate (FEC), propene sultone (PRS), fluoro-propylene carbonate (FPC), etc. may be further included.

[0071] In the manufacturing method of the secondary battery according to the present disclosure for achieving the above-mentioned purpose, the manufactured negative electrode, separator and positive electrode can be stacked in sequence to form an electrode assembly, and the manufactured electrode assembly is placed in a cylindrical battery case or a prismatic battery case and then injected with an electrolyte to manufacture a battery. Alternatively, the electrode assembly can be stacked and then immersed in an electrolyte, and the obtained product can be placed in a battery case and sealed for manufacturing.

[0072] The battery case used in the present disclosure may adopt a battery case commonly used in the art and is not limited by the shape according to the use of the battery, for example, it may be cylindrical, prismatic, pouch or coin-shaped using a can.

[0073] The secondary battery disclosed herein can be used not only as a cell for a power source of a small device, but also preferably as a unit cell of a medium-to-large battery module including a plurality of cells. Preferred examples of the medium-to-large device include electric vehicles, hybrid vehicles, plug-in hybrid vehicles, power storage systems, etc., but are not limited thereto.

[0074] Mode for carrying out the invention

[0075] The embodiments of the present invention are further described below with reference to specific experimental examples. The embodiments and comparative examples included in the experimental examples are only used to illustrate the present invention, rather than to limit the scope of rights. Various changes and modifications can be made to the embodiments within the scope of the present invention and the technical concept, which is obvious to those skilled in the art, and such variations and modifications also belong to the scope of rights.

[0076] {Example}

[0077] (Example 1)

[0078] Step 1: Preparation of negative electrode slurry

[0079] The raw materials listed in Table 1 below were respectively fed into the raw material feeding part of the extruder. At this time, the conductive agent and the SBR binder were fed in a liquid state, and the CMC was fed in a powder state.

[0080] The conveying screw and the kneading block in the extruder are composed of a 3:7 combination.

[0081] Next, the kneading and conveying process is carried out under the conditions of a screw speed of 1200 rpm and an internal temperature of 25-30°C, and 30-35% by weight of distilled water is added relative to 100 parts by weight of the solid raw material through the liquid input part located at 8-14% of the total length of the extruder screw, and then after sufficient kneading, residual distilled water is added at 42-56% to prepare a negative electrode slurry with a final solid content of 55%.

[0082] [Table 1]

[0083]

[0084] Step 2: Fabrication of the negative electrode

[0085] The negative electrode slurry prepared in step 1 was coated on a copper current collector (copper foil with a thickness of 6 μm) using a coating machine. Then, the negative electrode active material layer was dried in a drying furnace heated with hot air at 120° C. for 1 minute to complete the negative electrode active material layer. At this time, the thickness of the negative electrode active material layer was 50 μm.

[0086] Step 3: Secondary battery manufacturing

[0087] The negative electrode and the positive electrode are notched into predetermined sizes and stacked, and a separator (polyethylene, 13 μm thick) is inserted between the negative electrode and the positive electrode to form a battery cell, and then the tabs of the positive and negative electrodes are welded respectively. The welded positive electrode / separator / negative electrode assembly is placed in a soft pack, and the three surfaces except the electrolyte injection surface are sealed, and the electrolyte is injected through the remaining surfaces except the sealing part and the remaining surfaces are sealed, and then immersed for more than 12 hours to manufacture a 1Ah-level soft pack battery.

[0088] The positive electrode used a Li[Ni 0.6 Co 0.2 Mn 0.2 The positive electrode was manufactured by coating a slurry of 100% O 2 , 2 wt % carbon black and 2 wt % PVDF binder on an aluminum current collector (aluminum foil with a thickness of 12 μm).

[0089] The electrolyte used was a solution prepared by dissolving 1M LiPF6 in a mixed solvent of EC / EMC / DEC (25 / 45 / 30; volume ratio), followed by adding 1 wt% vinylene carbonate (VC), 0.5 wt% 1,3-propylene sultone (PRS) and 0.5 wt% lithium bis(oxalatoborate) (LiBOB).

[0090] (Comparative Example 1)

[0091] The same method is used except that a conventional mixer (Planetary Despa Mixer, PD Mixer) is used to prepare the negative electrode slurry instead of the method of preparing the slurry using an extruder in step 1 of Example 1. Specifically, the raw materials recorded in Table 1 and 30-35% by weight of distilled water based on 100 parts by weight of the raw materials are kneaded for 60 minutes using a PD mixer to prepare the negative electrode slurry.

[0092] (Comparative Example 2)

[0093] The same procedure was followed except that a thickener solution (same thickener content) was added instead of the solid thickener in Comparative Example 1.

[0094] {Evaluation Example}

[0095] Evaluation Example 1: Evaluation of viscosity and binding force of negative electrode slurry according to slurry preparation method

[0096] The shear rate of each slurry was 0.1s using a rotational viscometer. -1 The viscosity of each negative electrode slurry prepared in Example 1, Comparative Example 1 and Comparative Example 2 was measured below.

[0097] The negative electrode manufactured in Example 1, Comparative Example 1 and Comparative Example 2 was cut into 18 mm in the horizontal direction and 150 mm in the vertical direction, and a tape with a width of 18 mm was pasted on the foil layer of the negative electrode, and then a roller with a load of 2 kg was used to enable sufficient adhesion. The active material layer of the negative electrode was pasted with a double-sided tape on one side of the tensile tester. The tape pasted on the foil was fastened on the other side of the tensile tester to measure the adhesion.

[0098] The evaluation results of the viscosity and adhesive force of Example 1, Comparative Example 1 and Comparative Example 2 are shown in Table 2 below.

[0099] [Table 2]

[0100]

[0101] As shown in Table 2, since the thickener is added in solid form in Example 1 and Comparative Example 1, the solid content is higher than that in Comparative Example 2. However, in Comparative Example 1, although the solid content is high, the viscosity and electrode adhesion decrease. In contrast, in Example 1, although a high content of solids is included to prepare the slurry composition, the viscosity is maintained and the adhesion is excellent.

[0102] In addition, since the thickener is dissolved in advance in Comparative Example 2, the viscosity and adhesive force are not reduced, but an additional solvent is required, and the solid content in the final slurry is also lower than that in Example 1.

[0103] Evaluation Example 2: Coating uniformity and life span of the negative electrode active material layer in the width direction according to the slurry preparation method Evaluation of life characteristics

[0104] In order to analyze the coating uniformity in the width direction of the negative electrode active material layer manufactured in Example 1, Comparative Example 1 and Comparative Example 2, as shown in FIG. Figure 1 As shown in FIG. 1 , five points with predetermined intervals are selected in the length direction of the negative electrode active material layer and punched out into a circle with a diameter of 38 mm, and then the weight of the negative electrode active material layer in the punched sample (the loading amount of the negative electrode active material layer composition) is measured. Then, the maximum value (W ) of the loading of the negative electrode active material layer measured at the point is calculated. max ) and the minimum load (W min ) to the average value (W) of the negative electrode active material layer at the five points (W) max-W min ) / W*100, %) are shown in the following Table 3.

[0105] In addition, the charge and discharge performance of the secondary batteries manufactured in Example 1, Comparative Example 1 and Comparative Example 2 was evaluated under the conditions of charge 1C / discharge 1C, and the capacity change according to the number of cycles is shown in FIG. Figure 2 The capacity retention results during 300 cycles are shown in Table 3 below.

[0106] [Table 3]

[0107]

[0108] Referring to Table 3, for Example 1, the difference in the load value of the negative electrode active material layer is 2.49% depending on whether an extruder is used when preparing the negative electrode slurry and the state of the thickener added, which is equal to or higher than the levels of 2.51% and 2.50% of Comparative Examples 1 and 2 using a PD mixer. That is, it can be seen that when the negative electrode slurry is prepared using the extruder of Example 1, the load amount in the center and the load amount in the periphery are evenly distributed.

[0109] It is believed that when the negative electrode slurry is prepared using the extruder of Example 1, the dispersibility of the active material in the slurry is improved, and the adsorption amount of the binder and the conductive agent on the active material particles is increased, thereby increasing the coating uniformity and the capacity retention rate. In Comparative Example 1, it can be seen that it is difficult to produce a slurry with improved dispersibility when the thickener is mixed in a solid state in a PD mixer, so the capacity retention rate is greatly reduced.

[0110] In addition, in the case of Comparative Example 2 in which the thickener is added in the form of a solution pre-dissolved in a solvent, although the capacity retention rate is maintained at a similar level to that of Example 1, the solid content is low, so there is a problem of binder migration that may occur in the drying step after coating. In addition, not only is it necessary to increase the process of dissolving the thickener, but the use of an additional solvent also increases the drying time, etc. On the other hand, in Example 1, the solid thickener raw material can be directly added without the need for a dissolution step, so there is no need for a preparation process of the thickener solution, which improves the continuous productivity of the slurry, and because the slurry has a high solid content, the drying efficiency is improved, thereby having the effect of improving the performance of the battery cell.

[0111] The above contents are merely examples of applying the principles of the present disclosure, and other configurations may be included without departing from the scope of the present invention.

Claims

1. A method for preparing an electrode slurry for a secondary battery, comprising: Step a), putting raw materials including electrode active material, conductive agent and thickener into a mixer; as well as Step b), adding a solvent into the mixer and kneading the raw materials, Wherein, the thickener in step a) is solid.

2. The method for preparing an electrode slurry for a secondary battery according to claim 1, wherein: The mixer is an extruder.

3. The method for preparing an electrode slurry for a secondary battery according to claim 2, wherein: The step b) is simultaneously performed by a conveying part including a conveying screw and a mixing part including a kneading block in the extruder.

4. The method for preparing an electrode slurry for a secondary battery according to claim 3, wherein: The conveying part and the mixing part in the extruder are repeatedly arranged in sequence along the conveying direction.

5. The method for preparing an electrode slurry for a secondary battery according to claim 2, wherein: The method further comprises the step of adjusting the viscosity by adding a solvent into the extruder.

6. The method for preparing an electrode slurry for a secondary battery according to claim 5, wherein: The solvent is added at a position of 40 to 70% based on the total length of the extruder in the conveying direction.

7. The method for preparing an electrode slurry for a secondary battery according to claim 2, wherein: The internal temperature of the extruder was 25°C to 60°C.

8. The method for preparing an electrode slurry for a secondary battery according to claim 1, wherein: The electrode is a negative electrode.

9. The method for preparing an electrode slurry for a secondary battery according to claim 8, wherein: The slurry is prepared with a solid content of 50% to 65%.

10. The method for preparing an electrode slurry for a secondary battery according to claim 8, wherein: The viscosity of the prepared slurry is less than 20000 cp.

11. A system for preparing electrode slurry for secondary batteries, comprising: The raw material input part includes electrode active material, conductive agent and thickener; An extrusion section for conveying the raw material while kneading the raw material; A first solvent input portion is provided on one side of the extrusion portion in the longitudinal direction; and The second solvent introduction portion is provided on the other side of the extrusion portion in the longitudinal direction.

12. The system for preparing electrode slurry for secondary battery according to claim 11, wherein: The second solvent input portion is provided at the rear end of the first solvent input portion based on the conveying direction.

13. The system for preparing electrode slurry for secondary battery according to claim 11, wherein: The second solvent introduction portion is provided at a position of 40 to 70% based on the total length of the extruder in the conveying direction.

14. A method for manufacturing an electrode, comprising the step of coating the electrode slurry prepared according to any one of claims 1 to 10 on a current collector.

15. A secondary battery comprising the electrode manufactured according to claim 14.

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