Self-supporting film for dry electrode, method of manufacturing the same, dry electrode comprising the same, and secondary battery

Abstract

According to one embodiment of the present application, a self-supporting film for a dry electrode includes: a binder, an active material, and a conductive material, wherein the self-supporting film has a tensile strength of 2000 gf / cm 2 or more, based on a thickness of 200 μm.

Description

TECHNICAL FIELD

[0001] Cross Reference to Related Applications

[0002] This application claims priority to Korean Patent Application No. 10-2021-0011773, filed on January 27, 2021, and Korean Patent Application No. 10-2022-0005069, filed on January 13, 2022, in the Korean Intellectual Property Office, the entire contents of which are incorporated herein by reference.

[0003] The present application relates to a self-supporting film for a dry electrode, a manufacturing apparatus thereof, a dry electrode comprising the same, and a secondary battery. BACKGROUND

[0004] Due to the rapid increase in the use of fossil fuels, there is an increasing demand for the use of alternative or clean energy, and the field in which research is most active is the field of utilizing electrochemical power generation and power storage.

[0005] Currently, a secondary battery is a representative example of an electrochemical device that utilizes such electrochemical energy, and its range of use tends to gradually expand.

[0006] Among these secondary batteries, a typical lithium secondary battery is not only used as a power source for mobile devices, but also used as a power source for electric vehicles and hybrid electric vehicles, which can replace fossil fuel-using vehicles such as gasoline vehicles and diesel vehicles, which are one of the main causes of air pollution. Even in applications such as power-assisted power sources formed through a grid, the range of use is expanding.

[0007] The manufacturing process of such a lithium secondary battery is mainly divided into three processes: an electrode process, an assembly process, and a forming process. The electrode process is further divided into an active material mixing process, an electrode coating process, a drying process, a rolling process, a slitting process, a winding process, etc.

[0008] Among them, the active material mixing process is a process of mixing a coating material for forming an electrode active layer in which an actual electrochemical reaction occurs in the electrode. Specifically, by mixing an electrode active material, which is an essential component of an electrode, a conductive material and a filler, which are other additives, an adhesive for adhesion between particles and attachment to a current collector, a solvent for imparting viscosity and dispersing particles, etc.

[0009] The composition mixed in this way to form an electrode active layer is also referred to as an electrode mixture in a broad sense.

[0010] After that, an electrode coating process of coating the electrode mixture on a conductive current collector and a drying process of removing a solvent contained in the electrode mixture are performed, and in addition, the electrode is rolled and manufactured to a prescribed thickness.

[0011] Meanwhile, since the solvent contained in the electrode mixture is evaporated during the drying process, defects such as pinholes or cracks can occur in the pre-formed electrode active layer. Further, due to the non-uniform drying inside and outside the active layer, the particles in the first dried portion can float up and form gaps with the later dried portion due to the difference in the evaporation speed of the solvent, thereby reducing the quality of the electrode. In particular, in the case of thick film coating, the floating up of the relatively light conductive material and the binder is aggravated due to the long evaporation time of the solvent during the drying of the electrode, and thus there is a fatal disadvantage in that it is difficult to manufacture a high-quality electrode.

[0012] Accordingly, in order to solve the above problems, a drying apparatus capable of adjusting the evaporation speed of the solvent while uniformly drying the inside and outside of the active layer is being researched, but such a drying apparatus is very expensive and requires considerable cost and time to operate, which is disadvantageous in terms of manufacturing processability.

[0013] Accordingly, recently, active research has been conducted on the manufacturing of dry electrodes that do not use a solvent.

[0014] The dry electrode is generally manufactured by laminating a separate film manufactured in the form of a film containing an active material, a binder, a conductive material, etc. on a current collector.

[0015] Accordingly, it is highly anticipated as an innovative technology capable of manufacturing a high-quality thick film electrode without the use of an organic solvent harmful to the human body, while solving the high process cost caused by long drying time.

[0016] Meanwhile, in the manufacturing of such a dry electrode, polytetrafluoroethylene (PTFE) powder is mainly used as a binder. In such PTFE, long fiber structures having an atomic arrangement of (-CFε-CFε-)n are sequentially arranged inside primary particles having a diameter of several hundred nm or less. When a shear force is applied under certain conditions, they are elongated into a fiber shape, and such PTFE nanofibers play a role in connecting the active material and the conductive material like a rope to maintain the electrode form.

[0017] Meanwhile, since the mixture of the active material and the conductive material fiberized by the PTFE greatly reduces the flowability in the same state as chewing gum, it is difficult to provide a uniform amount for rolling and calendering, and it is difficult to uniformly control the rolling density during rolling and calendering in order to manufacture in the form of a self-supporting film.

[0018] Accordingly, there is an urgent need to develop a self-supporting film technology for manufacturing a dry electrode capable of solving these problems. SUMMARY

[0019] Technical Problem

[0020] The present application is intended to solve the above problems, and an object of the present application is to provide a self-supporting film having improved tensile strength.

[0021] Another object of the present application is to provide an apparatus for manufacturing a self-supporting film, in which when a fiberized composition is prepared by an extruder and then extruded from a main body to the outside, quantitative extrusion can be performed by making the self-supporting film have a uniform density while minimizing load, thereby satisfying the above conditions.

[0022] Still another object of the present application is to provide a dry electrode including the self-supporting film, and a secondary battery including the dry electrode.

[0023] Technical Solution

[0024] According to one embodiment of the present application, there is provided a self-supporting film for a dry electrode, including:

[0025] a binder, an active material, and a conductive material,

[0026] wherein, based on a thickness of 200 μm, the self-supporting film has a tensile strength of 2000 gf / cm2or more.

[0027] At this time, the binder includes a fiberizable polymer, which can be polytetrafluoroethylene (PTFE).

[0028] More specifically, based on a thickness of 200 μm, the self-supporting film can have a tensile strength of 2000 gf / cm2to 4000 gf / cm2.

[0029] Further, based on a thickness of 200 μm, the self-supporting film can have a thickness deviation of 0.5% or less.

[0030] The thickness of the self-supporting film can be 10 to 1000 μm.

[0031] Meanwhile, according to another embodiment of the present application, there is provided an apparatus for manufacturing the self-supporting film, the apparatus including:

[0032] a main body storing a solvent-free mixture containing a binder, an active material, and a conductive material,

[0033] at least one extruder mixing the solvent-free mixture to prepare a fiberized composition and extruding the same from the main body, and

[0034] a pair of preforming rollers rotating in opposite directions in a state of facing each other and discharging the fiberized composition.

[0035] At this time, the binder can include a fibrillatable polymer, and the fibrillatable polymer is polytetrafluoroethylene (PTFE).

[0036] Meanwhile, the extruder can perform grinding by rotation or mixing by blending, and apply a shearing force to the solvent-free mixture to prepare the fibrillated composition.

[0037] At this time, the extruder is not limited as long as it can mix the materials stored in the main body as described above, apply pressure thereto, and discharge the materials from the main body to the outside, and even an extruder having any structure can be used, but specifically, it can be a screw.

[0038] The pair of pre-forming rollers can be located at the end of the main body, and specifically, below the discharge port of the main body, so that the extruder can extrude the fibrillated composition while forming it into a film shape.

[0039] Meanwhile, the self-supporting film manufacturing apparatus can further include a pre-mixer for mixing the binder, the active material, and the conductive material to form a solvent-free mixture, and a calender for calendering the fibrillated composition formed into a thin film form by the pair of pre-forming rollers.

[0040] Meanwhile, according to another embodiment of the present application, there is provided a dry electrode in which a self-supporting film is laminated on a current collector coated with a primer layer, and specifically, there is provided a dry electrode in which a self-supporting film manufactured using the self-supporting film manufacturing apparatus is laminated on a current collector coated with a primer layer.

[0041] According to still another embodiment of the present application, there is provided a secondary battery including the dry electrode. BRIEF DESCRIPTION OF DRAWINGS

[0042] Figure 1 FIG. 1 is a schematic view of a self-supporting film manufacturing apparatus according to an embodiment of the present application. DETAILED DESCRIPTION

[0043] Hereinafter, the present application will be described in greater detail for a better understanding of the present application.

[0044] The terms or words used in the present specification and claims should not be interpreted as being limited to commonly used meanings or meanings in dictionaries, but should be interpreted based on the meanings and concepts consistent with the technical idea of the present application on the basis of the principle that the inventor can properly define the concepts of the terms to best describe his own disclosure.

[0045] The technical and scientific terms used herein are intended to refer to terms as commonly understood by one of ordinary skill in the art unless otherwise explicitly indicated herein. The singular forms "a," "an," and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise.

[0046] Further, throughout the specification, when a part is referred to as "including" a certain component, unless otherwise specified, it means that the part can further include another component, not excluding the other component.

[0047] According to one embodiment of the present application, there is provided a self-supporting film for a dry electrode, comprising:

[0048] a binder, an active material, and a conductive material,

[0049] wherein the self-supporting film has a tensile strength of 2000 gf / cm 2 or more, based on a thickness of 200 μm.

[0050] At this time, the binder includes a fibrillatable polymer, which can be polytetrafluoroethylene (PTFE).

[0051] The self-supporting film can have a tensile strength of 2000 gf / cm 2 to 4000 gf / cm 2 , based on a thickness of 200 μm. Specifically, 2000 gf / cm 2 to 3000 gf / cm 2 , most specifically, 2200 gf / cm 2 to 2700 gf / cm 2 .

[0052] Here, the self-supporting film can be cut into a sample of 20 mm in width x 20 mm in length x 200 μm in thickness, and its tensile strength is measured, and the tensile strength (the maximum value of force at the point of time at which the sample is not broken) is measured using a UTM device (LLOYD Instruments Ltd.) at an angle of 180 degrees and a speed of 50 mm / min.

[0053] If the tensile strength is too low outside the above range, there is a problem of deterioration in processability in which the electrode is too easily cut in a continuous roll-to-roll process.

[0054] Further, the self-supporting film can have a thickness deviation of 0.5% or less, based on a thickness of 200 μm.

[0055] The thickness deviation can be obtained by measuring the thickness of 20 points at intervals of 1 cm using an automatic thickness measuring device (Mahr, Millimar).

[0056] If the thickness deviation is excessively large outside the above range, it cannot have a uniform density, and thus the defect rate increases, which leads to a problem of deterioration in the life characteristics, and thus is not preferable.

[0057] The thickness of the self-supporting film can be in the range of 10 μm to 1000 μm. Specifically, it can be 50 ~ 500 μm, and more specifically, it can be 100 ~ 500 μm.

[0058] That is, the self-supporting film for dry electrode according to the present application can be manufactured to be thick, and is suitable for the manufacture of thick film electrodes.

[0059] Meanwhile, the self-supporting film can be manufactured using a specific manufacturing apparatus as follows.

[0060] Specifically, according to another embodiment of the present application, there is provided an apparatus for manufacturing the self-supporting film, the apparatus including:

[0061] a main body storing a solvent-free mixture containing a binder, an active material, and a conductive material,

[0062] at least one extruder mixing the solvent-free mixture to prepare a fiberized composition and extruding the same from the main body, and

[0063] a pair of preforming rollers rotating in opposite directions in a state of facing each other and discharging the fiberized composition.

[0064] Figure 1 A part of the self-supporting film manufacturing apparatus 100 according to the present application is schematically shown.

[0065] Then, referring to Figure 1 , the self-supporting film manufacturing apparatus and the specific manufacturing method according to the present application are described.

[0066] The self-supporting film manufacturing apparatus 100 according to the present application includes a main body 110 storing a solvent-free mixture containing a binder, an active material, and a conductive material, an extruder 120 mixing the solvent-free mixture to prepare a fiberized composition 111, applying pressure to the fiberized composition 111 and extruding the fiberized composition 111 from the main body to the outside, and a pair of preforming rollers 130 rotating in opposite directions in a state of facing each other and discharging the fiberized composition 111.

[0067] Further, the solvent-free mixture including the binder, the active material, and the conductive material can be formed by mixing the materials in a mixer.

[0068] Therefore, although Figure 1The mixing device 100 according to the present application can further include a mixer, although not shown. At this time, the mixer can be configured to batch load each material, or can be configured to batch load, thereby allowing control of the loading order.

[0069] Mixing for preparing a mixture is performed in the mixer so that the active material, the conductive material, and the binder are uniformly distributed and mixed in powder form. Thus, there is no limitation as long as mixing can be simply performed, and mixing can be performed by various methods. However, since the present application is to manufacture a dry electrode that does not use a solvent, mixing can be performed by a dry mixing method, and can be performed by loading the materials into a mixer such as a blender or a mill.

[0070] Mixing can be performed in the mixer at 5,000 rpm to 20,000 rpm for 30 seconds to 2 minutes, and specifically, at 10,000 rpm to 15,000 rpm for 30 seconds to 1 minute to secure uniformity. In addition, if it is necessary to secure a heating problem of the device and durability of the applicable material, the above mixing step can be repeated one or more times to improve dispersibility in dry mixing.

[0071] Meanwhile, the binder can include a fibrillatable polymer, which can be polytetrafluoroethylene (PTFE). The fibrillatable polymer can be included in an amount of 50% by weight or more, based on the total weight of the binder, or can be 100% by weight.

[0072] Further, the binder can include polyethylene oxide (PEO), polyvinylidene fluoride (PVdF), polyvinylidene fluoride-co-hexafluoropropylene (PVdF-HFP), an acrylic binder, or the like, in addition to polytetrafluoroethylene. In addition, it can further include other binders known in the art

[0073] At this time, the binder composition can vary depending on whether the dry electrode is a positive electrode or a negative electrode.

[0074] In addition, the type and composition of the active material can also differ depending on whether the dry electrode is a positive electrode or a negative electrode.

[0075] For the manufacture of a self-supporting film for forming a dry positive electrode, the active material is not limited as long as it is in the form of a lithium transition metal oxide, lithium metal iron phosphate, or a metal oxide. For example, the active material can be a layered compound such as lithium cobaltate (LiCoO2) or lithium nickelate (LiNiO2), or a compound substituted with one or more transition metals; a lithium manganese oxide such as Li 1+x Mn 2-x O4(wherein x is 0 to 0.33), LiMnO3, Li2MnO3, LiMn2O3, LiMnO2; a lithium copper oxide (Li2CuO2); vanadium oxides such as LiV3O8, LiV3O4, V2O5, Cu2V2O7; a lithium nickel oxide represented by the chemical formula LiNi 1-x M x O2(wherein M = Co, Mn, Al, Cu, Fe, Mg, Ca, Zr, Ti, B, P, W, Si, Na, K, Mo, V, Nb, Ru, 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(wherein M = Co, Ni, Fe, Cr, Zn, or Ta, x = 0.01 to 0.1) or Li2Mn3MO8(wherein M = Fe, Co, Ni, Cu, or Zn); LiMn2O4, in which the Li portion in the chemical formula is substituted with an alkaline earth metal ion; a disulfide; a lithium metal phosphate LiMPO4(wherein M = Fe, Co, Ni, or Mn), a disulfide; Fe2(MoO4)3, etc., but is not limited thereto.

[0076] For the manufacture of a self-supporting film for forming a dry negative electrode, the active material can include carbon such as non-graphitizable carbon and graphite-based carbon, a metal composite oxide such as Li x Fe2O3(0≤x≤1), Li x WO2(0≤x≤1), Sn x Me 1-x Me' y O z (Me: Mn, Fe, Pb, Ge; Me': Al, B, P, Si, Group 1, 2, 3 elements of the Periodic Table, halogen; 0 < x ≤ 1; 1 ≤ y ≤ 3; 1 ≤ z ≤ 8); lithium metal; lithium alloy; silicon-based alloy; tin-based alloy; SiO, SiO / C, SiO x (1 < x < 2), SiO2, etc.; metal oxides such as SnO, SnO2, PbO, PbO2, Pb2O3, Pb3O4, Sb2O3, Sb2O4, Sb2O5, GeO, GeO2Bi2O3, Bi2O4, and Bi2O5; a conductive polymer such as polyacetylene; a Li-Co-Ni-based material, etc.

[0077] However, the dry electrode can specifically be a cathode, whereby the active material for manufacturing the self-supporting film can be a cathode active material, more specifically, a lithium transition metal oxide, a lithium nickel-manganese-cobalt oxide, an oxide in which the lithium nickel-manganese-cobalt oxide is substituted with a different transition metal, a lithium iron phosphate, etc.

[0078] Meanwhile, in the case of a negative electrode using graphite as a main active material, compared to the application of a cathode active material, a conductive material having a large specific surface area is not required to be used, or the amount thereof can be greatly reduced. Therefore, compared to a cathode, it is easy to implement the PTFE binder fiberization of the dry electrode. However, generally, since the negative electrode material using the silicon-based active material has a higher capacity compared to the cathode material, the thickness of the negative electrode is implemented to be thinner than that of the cathode in the electrode design, and thus, the process difficulty in manufacturing the self-supporting film can increase.

[0079] The conductive material is not particularly limited as long as it has high conductivity and does not cause chemical changes in the corresponding battery, and for example, graphite such as natural graphite and artificial graphite; graphene; activated carbon; activated carbon fiber; carbon black such as acetylene black, ketjen black, channel black, slot black, furnace black, lamp black, thermal black, etc.; conductive fiber such as carbon fiber and metal fiber; metal powder such as fluorinated carbon, aluminum, nickel; conductive whisker such as zinc oxide and potassium titanate; conductive metal oxide such as titanium oxide; conductive material of polystyrene derivative can be used. Specifically, the conductive material can include at least one selected from activated carbon, graphite, carbon black, graphene, and single-walled or multi-walled carbon nanotube for uniform mixing and improvement of conductivity, and more specifically, it can include carbon black or activated carbon.

[0080] The weight ratio of the active material, the conductive material, and the binder can include 60 to 99.8 wt%: 0.1 to 20 wt%: 0.1 to 20 wt%, and specifically, 80 to 99 wt%: 0.5 to 10 wt%: 0.5 to 10 wt%.

[0081] If the content of the binder is excessively high beyond the above range, the fibrous polymer of the binder becomes stiff, and at the same time, is excessively fiberized thereafter, whereby the load applied to the process equipment and the resistance of the electrode itself can greatly increase. Meanwhile, if the content of the binder is excessively small, it is not sufficiently fiberized, and there is a problem in that it is difficult to manufacture a self-supporting film or the electrode properties such as electrode peeling are deteriorated.

[0082] If the content of the conductive material is too high and exceeds the above range, the content of the active material will be relatively reduced, which can cause a problem of volume reduction, and can hinder the fiberization of the PTFE. In contrast, if the content of the conductive material is too small, sufficient conductivity can not be ensured, or the physical properties of the electrode of the self-supporting film can be deteriorated, which is not preferable.

[0083] Meanwhile, in some cases, a filler as a component for suppressing the expansion of the electrode can be further added to the mixture. The filler is not particularly limited as long as it is a fibrous material and does not cause a chemical change in the corresponding battery. For example, an olefin-based polymer such as polyethylene and polypropylene; a fibrous material such as glass fiber or carbon fiber is used.

[0084] When the solvent-free mixture is prepared in this way, the solvent-free mixture is loaded into the main body 110 and stored.

[0085] After that, the extruder 120 rotates and grinds the solvent-free mixture, or mixes the mixture by blending, and applies a shearing force to the solvent-free mixture to form the fiberized composition 111.

[0086] At this time, the extruder 120 can be rotated at a speed of 10 rpm to 500 rpm for 1 minute to 30 minutes.

[0087] In addition, the temperature at which the fiberized composition is prepared can be performed at 20 to 120°C, specifically, 40 to 120°C, more specifically, 60 to 120°C.

[0088] The type of the extruder 120 is not limited, but can be exemplified by a screw.

[0089] Although the extruder 120 is shown as a single extruder in the drawing, in order to improve the mixing efficiency, it is more preferable that a pair of extruders, i.e., in which two extruders are applied as a double screw arranged in parallel to each other.

[0090] The configuration in which the PTFE as a binder fiberizes the active material and the conductive material when subjected to a shearing force is known in the art.

[0091] After that, the extruder 120 moves in the up-and-down direction of the main body 110, applies pressure to the fiberized composition 111, and extrudes it through the discharge port formed at the lower end of the main body 110.

[0092] At this time, the extrusion speed of the fiberized composition 111 can be 100 ml / min to 5000 ml / min.

[0093] The extrusion speed is related to the circumferential speed of the preforming roll, which will be described later.

[0094] If the extrusion speed is too low outside the above range, the processing time is long and the efficiency is not high. If the extrusion speed is too high, the extrusion portion can have an overload problem, which is not preferred.

[0095] The fiberized composition 111 extruded in this way is used in a process for manufacturing a self-supporting film. The process can be generally performed by calendering, i.e., rolling, with a calender.

[0096] However, according to the present application, by removing the slit guide located below the discharge port formed at the end of the main body 110, i.e., the lower end of the main body 110, and positioning the pre-forming roller 130, the extruder 120 independently extrudes the fiberized composition 111 by calendering while being shaped into a film shape.

[0097] At this time, as a configuration in which the discharge port is formed at the lower end of the main body 110, only a configuration in which the pre-forming roller 130 is positioned at the lower end is illustrated in the drawing, but the main body 110 can be a form in which the fiberized composition 111 is extruded to the side, in which the discharge portion can be positioned at the side end of the main body, and the pre-forming roller 130 can be positioned at the side of the main body 110. In addition, the extrusion direction can also be a form in which the extruder 120 moves in the left-right direction and extrudes the composition.

[0098] When the pre-forming roller 130 is applied in this way instead of the slit guide, the load applied to the portion from which the fiberized composition 111 is extruded from the main body 110 can be minimized. Even if the content of the binder increases and the fiberization is performed a lot, it can easily form a thin film, thereby enabling the manufacture of a self-supporting film having excellent physical properties.

[0099] The diameter of the pre-forming roller 130 is not limited, but can be 10 to 500 mm, specifically 10 to 300 mm, more specifically 10 to 150 mm.

[0100] If the diameter is too small outside the above range, the pressure applied to the fiberized composition 111 is small, which is not preferred, and if the diameter is too large, the efficiency is low in terms of space and cost.

[0101] The surface temperature of the pre-forming roller 130 can be, for example, 20 to 120°C, specifically 40 to 120°C, more specifically 60 to 120°C.

[0102] If the surface temperature is too low outside the above range, there is a problem that the fiberizable polymer is not activated. If the surface temperature is too high, the fiberization of the fiberizable polymer is rapidly performed, such that the diameter of the fiber becomes thin, and a part is cut off, such that the active material cannot be combined, thereby causing a quality problem. The performance of the self-supporting film is deteriorated, which is not preferred.

[0103] At this time, the circumferential speed of the preforming roller 130 is related to the speed at which the fibrous composition is extruded from the main body, and is affected by the thickness of the self-supporting film that is required. For example, the circumferential speed of the preforming roller 130 can be 10 rpm to 500 rpm.

[0104] If the circumferential speed is too fast outside the above range, the fibrous composition can be lumped between the preforming roller and the end of the main body, and if the circumferential speed is too slow, the thickness of the self-supporting film can be greatly deviated, which is not desirable.

[0105] Meanwhile, a process of calendering the fibrous composition 111 shaped into the form of a film by the preforming roller 130 as described above can be further included.

[0106] That is, in the present application, the fibrous composition 111 can be prepared into the form of a film by the preforming roller 130, thereby manufacturing a self-supporting film, but in addition, a calendering process can be further included.

[0107] Therefore, although Figure 1 The self-supporting film manufacturing apparatus according to the present application can further include a calendering machine for performing calendering, although not shown in the drawings.

[0108] At this time, calendering can also be performed by a calendering roller. At this time, the diameter of the roller can be greater than the diameter of the preforming roller 130, thereby applying a greater pressure than the preforming roller 130. In such a range, for example, it can be 50 to 1000 mm, specifically 100 to 1000 mm, more specifically 100 to 500 mm.

[0109] In addition, the surface temperature of the calendering roller can be 20 to 200℃, specifically 40 to 150℃, more specifically 60 to 150℃.

[0110] The circumferential speed of the calendering roller can be 10 rpm to 500 rpm.

[0111] By applying a shearing pressure through such a calendering roller, a self-supporting film can be finally manufactured.

[0112] In addition, specifically, a dry electrode is provided in which a self-supporting film manufactured by using the self-supporting film manufacturing apparatus is laminated on a current collector coated with a primer layer.

[0113] That is, the dry electrode can have a structure in which a self-supporting film is formed on a current collector coated with a primer layer.

[0114] A polytetrafluoroethylene (PTFE) polymer for manufacturing a self-supporting film binds an active material and a conductive material together through fiberization, and can be made in the form of a thin film. However, since it does not have adhesion to a current collector, by using a current collector coated with a primer layer, it is possible to secure the adhesion of the current collector to the self-supporting film.

[0115] The current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery. For example, stainless steel, aluminum, nickel, titanium, sintered carbon, and a material formed by surface treatment of the surface of aluminum or stainless steel with carbon, nickel, titanium, silver, or the like can be used. The current collector can have fine irregularities formed on the surface thereof, or can be processed into a mesh shape to improve the bonding strength of the positive active material, and various forms such as a thin film, a sheet, a foil, an aluminum foil, a mesh, a porous body, a foamed body, and a nonwoven fabric structure can be used.

[0116] The primer layer can be entirely or partially coated on the current collector, and specifically, can be entirely coated.

[0117] Such a primer layer can include a conductive material and a binder. The conductive material is not limited as long as it is a conductive material, and for example, can be a carbon-based material such as carbon black, a carbon nanotube, graphene, graphite, or the like. The binder can include a fluorine-based binder (including PVDF and a PVDF copolymer), an acrylic binder, and a water-based binder that can be dissolved in a solvent.

[0118] The combination of the self-supporting film and the current collector coated with the primer layer can be performed by lamination.

[0119] The lamination can also be performed by a lamination roll, which can be maintained at a temperature of 80 to 200°C.

[0120] Meanwhile, according to another embodiment of the present application, a secondary battery including a dry electrode is provided.

[0121] Specifically, the electrode assembly including the dry electrode, the separator, and the counter electrode can have a structure that is incorporated into a battery case together with an electrolyte. Since other configurations of the secondary battery are well known in the art, a description thereof will be omitted.

[0122] Hereinafter, the present application will be described in detail through examples, comparative examples, and experimental examples so that those skilled in the art can easily understand the present application.

[0123] <Example 1>

[0124] LiMn2O4, 1.5 g of Ketjen black as a conductive material, and 1.5 g of polytetrafluoroethylene (PTFE) as a binder were mixed for 5 minutes at 5°C and 10,000 rpm using a powder mixer device (KMTech). A pair of preforming rollers having a diameter of 100 mm were installed in an extruder formed at the lower end of the extruder at a temperature of 90°C at 100 rpm, and the mixture was charged at a rate of 5 g / sec. The mixture was extruded while applying a shearing force, and was simultaneously rolled using preforming rollers (roller diameter: 100 mm, roller temperature: 100°C, circumferential speed: 100 rpm, roller gap: 400 μm).

[0125] The rolled film was repeatedly charged into an experimental calender (roller diameter: 200 mm, roller temperature: 100°C, 20 rpm) twice, and a self-supporting film having a thickness of 200 μm was finally produced by adjusting the roller gap.

[0126] <Example 2>

[0127] Except that 95.5 g of LiMn2O4, 1.5 g of activated carbon as a conductive material, and 3.0 g of polytetrafluoroethylene (PTFE) as a binder were mixed using a powder mixer device (KMTech) and charged into the extruder in Example 1, a self-supporting film having a thickness of 200 μm was produced in the same manner as in Example 1.

[0128] <Comparative Example 1>

[0129] Except that a T-die slit was used in the extruder in Example 1 and no preforming rollers were used in Example 1, a self-supporting film was produced in the same manner as in Example 1.

[0130] <Comparative Example 2>

[0131] In Example 2, a mixture of 95.5 g of LiMn2O4, 1.5 g of activated carbon as a conductive material, and 3.0 g of polytetrafluoroethylene (PTFE) as a binder was charged into the extruder without preforming rollers and was extruded, but no rolling was performed, so that a self-supporting film could not be produced.

[0132] <Comparative Example 3>

[0133] LiMn2O4, 1.5 g of activated carbon as a conductive material, and 3.0 g of polytetrafluoroethylene (PTFE) as a binder were mixed at 5°C and 10,000 rpm for 5 minutes using a powder mixer device (KM Tech). The mixed mixture was put into a twin-screw kneader (Irie Shokai, PBV-0.1L) and mixed at a temperature of 90°C at 100 rpm for about 3 minutes to prepare a fiberized composition. The fiberized composition was manufactured into a thin film having a thickness of 400 μm by roll-pressing.

[0134] The manufactured thin film was loaded into an experimental calender (roll diameter: 200 mm, roll temperature: 100°C, 20 rpm) to adjust the distance between the rolls, and a self-supporting film having a thickness of 200 μm was finally manufactured.

[0135] <Comparative Example 4>

[0136] Except that the mixture was loaded into a twin-screw kneader and a fiberized composition was prepared at a temperature of 25°C in Comparative Example 3, a self-supporting film was manufactured in the same manner as in Comparative Example 3.

[0137] <Comparative Example 5>

[0138] Except that the mixture was loaded into a paste mixer (Thinky, ARE-400) and mixed at a temperature of 25°C at 1,000 rpm for about 5 minutes to prepare a fiberized composition in Comparative Example 3, a self-supporting film was manufactured in the same manner as in Comparative Example 3.

[0139] <Comparative Example 6>

[0140] Except that 95.5 g of LiMn2O4as a cathode active material, 1.5 g of activated carbon as a conductive material, and 3.0 g of polytetrafluoroethylene (PTFE) as a binder were mixed at 5°C and 10,000 rpm for 5 minutes using a powder mixer device (KM Tech) in Comparative Example 3, after the mixture was readjusted to a temperature of 25°C in the same device, the mixture was mixed at a speed of 10,000 rpm for about 5 minutes, and a self-supporting film was manufactured in the same manner as in Comparative Example 3.

[0141] <Experimental Example 1>

[0142] The thickness deviation of the self-supporting films of Examples 1 to 2 and Comparative Examples 1 to 6 was measured and shown in Table 1 below.

[0143] The thickness deviation was obtained by measuring the thickness of 20 points at intervals of 1 cm using an automatic thickness gauge (Mahr, Millimar).

[0144] <Experimental Example 2>

[0145] The tensile strength of the self-supporting films of Examples 1 to 2 and Comparative Examples 1 to 6 was measured and is shown in Table 1 below.

[0146] The tensile strength was measured by cutting the self-supporting film into a sample of 20 mm in width x 20 mm in length x 200 μm in thickness, and using a UTM device of LLOYD to measure the tensile strength.

[0147] The tensile strength was measured by cutting the self-supporting film into a sample of 20 mm in width x 20 mm in length x 200 μm in thickness, and using a UTM device (LLOYD Instruments Ltd.) to measure the tensile strength (the maximum value of the force applied to the sample at the point of no breakage) of the sample at an angle of 180 degrees and a speed of 50 mm / min.

[0148] <Experimental Example 3>

[0149] The self-supporting films of Examples 1 to 2 and Comparative Examples 1 to 6 were placed on one side of an aluminum foil (20 μm, Primer Coated Al Foil, Dongwon Systems) coated with a primer layer mixed with carbon black: PVDF binder, and an electrode was prepared by lamination using a lamination roll maintained at 120°C.

[0150] A coin-type half cell was manufactured using the electrode and lithium metal as a counter electrode, and an electrolyte solution containing 1 M LiPF6 in a solvent of EC:DMC:DEC = 1:2:1.

[0151] The coin-type half cell manufactured above was charged and discharged 100 times at a 0.33C rate current condition in a voltage range of 3.0 to 4.30 V at 25°C, and then the discharge capacity over time was calculated with respect to the 100 times capacity retention rate, and the results are shown in Table 1 below.

[0152] [Table 1]

[0153]

[0154] As can be seen from Table 1, when manufactured using the device of the present application, not only is the thickness deviation of the self-supporting film small, but the tensile strength and life characteristics are also good.

[0155] However, when an extruder in which a T-die slit is formed is used, there is no great problem with this configuration when the content of the binder is small. However, in terms of thickness variation or particularly the tensile strength and life characteristics, it is more preferable to use the configuration of the present application. This is believed to be because the unevenness in the amount of supply is eliminated by the quantitative extrusion through the extruder, and at the same time, the load on the extrusion site is small, and further thickness deviation does not occur.

[0156] On the other hand, if the content of the binder is increased and the fiberization is performed a lot, it can be confirmed that, when an extruder in which a T-die slit is formed is used, the load of the extrusion site is increased and the extrusion cannot be performed, which is not preferable.

[0157] On the other hand, in the case of simple rolling using a kneader other than the extruder, it can be confirmed that even if the mixing time is increased or the temperature is increased, the uniformity of the electrode mixture used for the PTFE fiberization is not easily improved, as a result, the thickness deviation of the electrode becomes serious, and the tensile strength and the life characteristics are also deteriorated.

[0158] On the other hand, the self-supporting film and the dry electrode according to the present application can uniformly maintain the electrode quality, thereby obtaining excellent tensile strength and capacity retention effects while reducing the electrode thickness deviation.

[0159] Industrial applicability

[0160] According to the present application, the extruder is used as a device for manufacturing a self-supporting film, and can uniformly and quantitatively feed.

[0161] Further, by removing the slit guide and applying a pre-forming roll to a portion through which the fiberized composition is discharged from the conventional extruder, a self-supporting film having a uniform density and improved tensile strength and life characteristics can be manufactured while minimizing the load at the discharge portion.

Claims

1. An apparatus for manufacturing a self-supporting film for a dry electrode, the apparatus comprising: a main body storing a solvent-free mixture containing a binder including a fiberizable polymer, an active material, and a conductive material, at least one extruder that mixes the solvent-free mixture to prepare a fiberized composition and extrudes it from the main body, and a pair of preforming rollers that rotate in opposite directions in a state of facing each other and discharge the fiberized composition, wherein the pair of preforming rollers are located at the end of the main body, the extruder grinds by rotation or mixes by blending and applies a shear force to the solvent-free mixture to prepare the fiberized composition.

2. The apparatus according to claim 1, wherein: the fiberizable polymer is polytetrafluoroethylene.

3. The apparatus according to claim 1, wherein: the main body has a discharge port formed at the lower end, the extruder moves in the up-and-down direction of the main body, and extrudes the fiberized composition from the discharge port by pressure.

4. The apparatus according to claim 1, wherein: the extruder is a screw.

5. The apparatus according to claim 1, wherein: the main body has a discharge port formed at the lower end, the pair of preforming rollers are located below the discharge port of the main body, so that the extruder extrudes the fiberized composition while being formed into a thin film shape.

6. The apparatus according to claim 1, wherein: the apparatus further comprises a premixer for mixing the binder, the active material, and the conductive material to form a solvent-free mixture, and a calender for calendering the fiberized composition formed into a thin film shape by the pair of preforming rollers.

7. A self-supporting film manufactured by the apparatus of any one of claims 1-6, comprising: a binder, an active material, and a conductive material, the active material, the conductive material, and the binder being included in a weight ratio of 60 to 99.8 wt%: 0.1 to 20 wt%: 0.1 to 20 wt%, wherein the self-supporting film has a tensile strength of 2000 gf / cm 2 to 4000 gf / cm 2 based on a thickness of 200 μm, and wherein the self-supporting film has a thickness deviation of 0.5% or less based on a thickness of 200 pm.

8. The self-supporting film according to claim 7, wherein: the thickness of the self-supporting film is 10-1000 pm.

9. A dry electrode in which the self-supporting film of any one of claims 7 to 8 is laminated on a current collector coated with a primer layer.

10. A dry electrode in which a self-supporting film manufactured using the self-supporting film manufacturing apparatus of any one of claims 1 to 6 is laminated on a current collector coated with a primer layer.

11. A secondary battery comprising the dry electrode of claim 9.

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