Electrode, secondary battery including the same, and method for manufacturing the same

Abstract

The present invention provides an electrode comprising: an electrode current collector; and an electrode layer positioned on the electrode current collector and including an active material, a conductive material, and a binder, wherein the binder includes a fluorine-based polymer and a modified polyolefin, the fluorine-based binder being polytetrafluoroethylene (PTFE), the modified polyolefin including a functional group derived from a carboxylic acid anhydride, and a content of the modified polyolefin being 2 to 40 parts by weight based on 100 parts by weight of the binder; a secondary battery including the electrode; and an energy storage device.

Description

[Technical Field]

[0001] The present invention relates to an electrode, a secondary battery including the same, and a manufacturing method thereof, and more particularly to an electrode with improved flexibility, a secondary battery including the same, and a manufacturing method thereof.

[0002] This application claims priority based on Korean Patent Application No. 10-2022-0188383, filed on December 29, 2022, the entire contents of which are incorporated herein by reference in their entirety in the specification and drawings of that application. [Background technology]

[0003] The rapid increase in fossil fuel use has led to an increasing demand for alternative and clean energy sources, and one of the most actively researched fields is the field of electrochemical power generation and storage. Currently, secondary batteries are a representative example of electrochemical devices that use electrochemical energy, and their applications are gradually expanding. Lithium secondary batteries, a representative example of such secondary batteries, are not only used as an energy source for mobile devices, but are also increasingly being used as a power source for electric vehicles and hybrid electric vehicles, which can replace fossil fuel-powered vehicles such as gasoline and diesel vehicles, which are one of the main causes of air pollution. Their applications are also expanding to include auxiliary power sources for grid-connected vehicles.

[0004] The manufacturing process of such a lithium secondary battery can be roughly divided into three steps: an electrode manufacturing process, an electrode assembly manufacturing process, and a chemical formation process. The electrode manufacturing process can be further divided into an electrode mixture mixing process, an electrode coating process, a drying process, a rolling process, a slitting process, and a winding process.

[0005] Among these, the electrode mixture mixing process is a process of blending components for forming an electrode active layer where an electrochemical reaction actually occurs in the electrode. More specifically, it is a process of mixing an electrode active material, which is an essential element of an electrode, other additives such as a conductive material and a filler, a binder for binding the powder particles together and adhering them to the current collector, and a solvent for imparting viscosity and dispersing the powder, to produce a fluid slurry.

[0006] This slurry is applied to an electrically conductive current collector in an electrode application process, followed by a drying process to remove the solvent contained in the electrode mixture slurry. The electrode is then rolled to produce an electrode with a predetermined thickness.

[0007] Meanwhile, evaporation of the solvent contained in the electrode mixture during the drying process can cause defects such as pinholes and cracks in the already formed electrode active layer. Furthermore, since the inside and outside of the active layer are not dried uniformly, differences in solvent evaporation rates can cause powder floating, i.e., powder in the first-dried area floats up and forms gaps with the later-dried area, resulting in a deterioration in electrode quality.

[0008] In order to solve the above problems, drying devices that can adjust the evaporation rate of the solvent while uniformly drying the inside and outside of the active layer have been considered. However, such drying devices are very expensive and require considerable cost and time for operation, which is disadvantageous in the manufacturing process.

[0009] Therefore, recently, much research has been conducted into the production of dry electrodes that do not use solvents.

[0010] The dry electrode is generally produced by laminating a free-standing film containing an active material, a binder, a conductive material, etc., on a current collector.

[0011] Conventional dry electrodes involve mixing an active material, a carbon material as a conductive material, and a fiberizable binder together in a blender, etc., and then fiberizing the binder through a high-shear mixing process such as jet milling. The mixture is then calendered to form a film to produce a free-standing film. The free-standing film produced after calendering is then laminated onto a current collector to produce a dry electrode.

[0012] Meanwhile, in the conventional dry electrode manufacturing process, a primer-coated current collector is used to ensure adhesion when joining the dry film and current collector, but this poses the problem of incurring additional costs. Therefore, there is an urgent need to develop a dry electrode manufacturing technology that can solve these problems. Summary of the Invention [Problem to be solved by the invention]

[0013] The present invention has been made to solve the above problems, and an object of the present invention is to provide an electrode having improved electrode adhesion, a secondary battery including the same, and a method for manufacturing the same. [Means for solving the problem]

[0014] In order to solve the problems of the present invention, according to one aspect of the present invention, there is provided an electrode having the following embodiment.

[0015] According to the first embodiment, an electrode current collector; an electrode layer located on the electrode current collector and including an active material, a conductive material, and a binder; the binder comprises a fluorine-based polymer and a modified polyolefin, the fluorine-based polymer is polytetrafluoroethylene (PTFE), the modified polyolefin contains a functional group derived from a carboxylic acid anhydride, The electrode has a content of the modified polyolefin of 2 to 40 parts by weight based on 100 parts by weight of the binder.

[0016] According to the second embodiment, in the first embodiment, The content of the modified polyolefin may be 3 to 40 parts by weight based on 100 parts by weight of the binder.

[0017] According to the third embodiment, in the first or second embodiment, The modified polyolefin may have a melt index (MI) of 50 g / 10 min or less.

[0018] According to the fourth embodiment, in any one of the first to third embodiments, The modified polyolefin may have a melting point of 175°C or less.

[0019] According to the fifth embodiment, in any one of the first to fourth embodiments, The modified polyolefin may include one or more of modified polyethylene and modified polypropylene.

[0020] According to the sixth embodiment, in any one of the first to fifth embodiments, The olefin of the modified polyolefin contains at least one of ethylene and propylene, The functional group derived from a carboxylic acid anhydride may be derived from maleic anhydride, glutaric anhydride, phthalic anhydride, trimellitic anhydride, pyromellitic monoanhydride, pyromellitic dianhydride, 1,8-naphthalenedicarboxylic anhydride, 2,3-naphthalenedicarboxylic anhydride, 1,4,5,8-naphthalenetetracarboxylic monoanhydride, 1,4,5,8-naphthalenetetracarboxylic dianhydride, 2,3,6,7-naphthalenetetracarboxylic monoanhydride, 2,3,6,7-naphthalenetetracarboxylic dianhydride, or a carboxylic acid anhydride including two or more of these.

[0021] According to the seventh embodiment, in any one of the first to sixth embodiments, The modified polyolefin may be a modified polyethylene.

[0022] According to the eighth embodiment, in any one of the first to seventh embodiments, The modified polyolefin may be one or more of polyethylene containing functional groups derived from maleic anhydride and polypropylene containing functional groups derived from maleic anhydride.

[0023] According to the ninth embodiment, in any one of the first to eighth embodiments, The content of functional groups derived from carboxylic acid anhydrides in the modified polyolefin may be 0.5 mol % to 20 mol %.

[0024] According to the tenth embodiment, in any one of the first to ninth embodiments, The binder is fibrous and can bind the active material, the conductive material, and the modified polyolefin.

[0025] According to the eleventh embodiment, in any one of the first to tenth embodiments, The active material may be a positive electrode active material or a negative electrode active material.

[0026] According to the twelfth embodiment, in any one of the first to eleventh embodiments, The content of the active material may be 80 to 98 parts by weight, the content of the conductive material may be 0.5 to 10 parts by weight, the content of the fluorine-based polymer may be 0.5 to 5 parts by weight, and the content of the modified polyolefin may be 0.02 to 3.3 parts by weight.

[0027] According to the thirteenth embodiment, in any one of the first to twelfth embodiments, The electrode current collector may not include a conductive primer layer on at least one surface.

[0028] According to the fourteenth embodiment, in any one of the first to thirteenth embodiments, The electrode layer may be derived from a dry electrode film.

[0029] According to a fifteenth embodiment, the method includes the steps of preparing a mixture including an active material, a conductive material, and a binder, the binder including a fluorine-based polymer and a modified polyolefin, and the fluorine-based polymer being polytetrafluoroethylene (PTFE); kneading the mixture at a temperature in the range of 70°C to 200°C under a pressure equal to or higher than atmospheric pressure to produce a mixture mass; pulverizing the mixture mass to obtain a mixed powder for an electrode; The electrode mixed powder is placed between a plurality of rolls and calendered to form an electrode film; and laminating the electrode film on a metal current collector.

[0030] According to the 16th embodiment, in the 15th embodiment, The step of kneading to produce the mixture mass can be carried out in a kneader under atmospheric pressure or higher.

[0031] According to the seventeenth embodiment, in the fifteenth or sixteenth embodiment, The rolling ratio of the electrode film may be 20% or less.

[0032] According to the 18th embodiment, There is provided a secondary battery comprising a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode, wherein at least one of the positive electrode and the negative electrode is an electrode according to any one of the first to fourteenth embodiments.

[0033] According to the 19th embodiment, An energy storage device including the secondary battery according to the eighteenth embodiment as a unit battery is provided. [Effects of the Invention]

[0034] According to one embodiment of the present invention, the film for a dry electrode further contains, in addition to an existing binder, a modified polyolefin, which is a copolymer including a repeating unit derived from an olefin and a repeating unit derived from a carboxylic acid or a carboxylic acid anhydride, in a predetermined content range, thereby ensuring adhesion to a current collector that is not coated with a primer. This makes it possible to provide a dry electrode that has a simple manufacturing process, excellent adhesion to a current collector both before and after immersion in an electrolyte solution, and does not experience a significant increase in interfacial resistance both before and after immersion in an electrolyte solution.

[0035] The following drawings attached to this specification illustrate preferred embodiments of the present invention and, together with the detailed description of the invention, serve to further understand the technical concepts of the present invention. Therefore, the present invention should not be interpreted as being limited to only the matters described in the drawings. [Brief explanation of the drawings]

[0036] [Figure 1a] 3A to 3C are schematic diagrams illustrating a manufacturing process of an electrode film for an electrode applied to an electrode assembly according to an embodiment of the present invention. [Figure 1b] 3A to 3C are schematic diagrams illustrating a manufacturing process of an electrode film for an electrode applied to an electrode assembly according to an embodiment of the present invention. [Figure 2] FIG. 2 is a schematic diagram of an electrode lamination step according to one embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0037] The present invention will now be described in more detail to facilitate understanding of the present invention. The terms and words used in this specification and claims should not be interpreted as being limited to their ordinary and dictionary meanings, but should be interpreted as having meanings and concepts that correspond to the technical ideas of the present invention, in accordance with the principle that the inventor himself can appropriately define the concepts of terms in order to best explain the invention.

[0038] The terms used in this specification are used only to describe exemplary embodiments and are not intended to limit the present invention. The singular expressions include the plural expressions unless the context clearly dictates otherwise.

[0039] Also, throughout the specification, when a part is said to "comprise" a certain element, this does not mean that it excludes other elements, but that it may further include other elements, unless specifically stated to the contrary.

[0040] According to one aspect of the present invention, an electrode current collector; an electrode layer located on the electrode current collector and including an active material, a conductive material, and a binder; the binder comprises a fluorine-based polymer and a modified polyolefin, the fluorine-based polymer is polytetrafluoroethylene (PTFE), the modified polyolefin contains a functional group derived from a carboxylic acid anhydride, The electrode has a content of the modified polyolefin of 2 to 40 parts by weight based on 100 parts by weight of the binder.

[0041] According to one embodiment of the present invention, the electrode may be a positive electrode or a negative electrode, and the active material may be a positive electrode active material or a negative electrode active material.

[0042] The positive electrode active material may include, but is not limited to, a lithium transition metal oxide, a lithium metal iron phosphate, a lithium nickel-manganese-cobalt oxide, an oxide in which a portion of the lithium nickel-manganese-cobalt oxide is substituted with another transition metal, or two or more of these. Specifically, the positive electrode active material may include, for example, a layered compound such as lithium cobalt oxide (LiCoO2) or lithium nickel oxide (LiNiO2), or a compound substituted with one or more transition metals, and a compound represented by the chemical formula Li 1+x Mn 2-x Lithium manganese oxides such as LiMnO4 (where x is 0 to 0.33), LiMnO3, LiMn2O3, and LiMnO2, lithium copper oxide (Li2CuO2), vanadium oxides such as LiV3O8, LiV3O4, V2O5, and Cu2V2O7, and oxides with the chemical formula LiNi 1-x M x O2 (where M=Co, Mn, Al, Cu, Fe, Mg, B, or Ga, and x=0.01 to 0.3), and Ni-site lithium nickel oxide represented by the chemical formula LiMn 2-x M x Lithium manganese composite oxides represented by Li2Mn3MO8 (where M = Co, Ni, Fe, Cr, Zn, or Ta, and x = 0.01 to 0.1) or Li2Mn3MO8 (where M = Fe, Co, Ni, Cu, or Zn), lithium metal phosphate LiMPO4 (where M = Fe, CO, Ni, or Mn), and lithium nickel-manganese-cobalt oxide Li 1+x (Ni a Co b Mn c ) 1-x O2 (x = 0-0.03, a = 0.3-0.95, b = 0.01-0.35, c = 0.01-0.5, a + b + c = 1) and lithium nickel-manganese-cobalt oxide, in which some of the oxide is substituted with aluminum (lithium nickel-manganese-cobalt-aluminum oxide) Li a [Ni b Co c Mn d Al e ] 1-f M 1f O2 (where M 1 is one or more selected from the group consisting of Zr, B, W, Mg, Ce, Hf, Ta, La, Ti, Sr, Ba, F, P, and S, and 0.8 ≦ a ≦ 1.2, 0.5 ≦ b ≦ 0.99, 0 < c < 0.5, 0 < d < 0.5, 0.01 ≦ e ≦ 0.1, 0 ≦ f ≦ 0.1), a disulfide compound, and Fe2(MoO4)3, etc. are included, but not limited thereto. Specifically, the lithium nickel-manganese-cobalt-aluminum oxide is Li[Ni 0.88 Co 0.07 Mn 0.04 Al 0.01 O2), etc.

[0043] Also, as the negative electrode active material, carbon such as graphitizable carbon and graphite-based carbon, and 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, Group 2, Group 3 elements of the periodic table, halogen, 0 ≦ x ≦ 1, 1 ≦ y ≦ 3, 1 ≦ z ≦ 8), etc. metal composite oxides, lithium metal, lithium alloy, silicon-based alloy, tin-based alloy, silicon-based oxides such as SiO, SiO / C, SiO2, metal oxides such as SnO, SnO2, PbO, PbO2, Pb2O3, Pb3O4, Sb2O3, Sb2O4, Sb2O5, GeO, GeO2, Bi2O3, Bi2O4, and Bi2O5, conductive polymers such as polyacetylene, and Li-Co-Ni-based materials can be used.

[0044] According to one embodiment of the present invention, the electrode is a positive electrode. Therefore, the active material is, specifically, a positive electrode active material, and more specifically, a lithium transition metal oxide, a lithium nickel-manganese-cobalt oxide, an oxide in which part of the lithium nickel-manganese-cobalt oxide is substituted with Al or other transition metals, a lithium iron phosphate, etc.

[0045] The conductive material is not particularly limited as long as it is conductive and does not cause a chemical change in the battery. Examples of the conductive material include graphite such as natural graphite and artificial graphite; carbon-based materials such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, and carbon fiber; metal powder or metal fiber such as copper, nickel, aluminum, and silver; needle-like or branch-like conductive whiskers such as zinc oxide whiskers, calcium carbonate whiskers, titanium dioxide whiskers, silicon oxide whiskers, silicon carbide whiskers, aluminum borate whiskers, magnesium borate whiskers, potassium titanate whiskers, silicon nitride whiskers, silicon carbide whiskers, and alumina whiskers; conductive metal oxides such as titanium oxide; and conductive polymers such as polyphenylene derivatives. These may be used alone or in combination. Specifically, in order to uniformly mix the conductive material and improve conductivity, the conductive material may contain one or more selected from the group consisting of activated carbon, graphite, carbon black, and carbon nanotubes, and more specifically, activated carbon.

[0046] The binder includes a fluorine-based polymer and a modified polyolefin, and the fluorine-based polymer is polytetrafluoroethylene (PTFE).

[0047] According to an embodiment of the present invention, the binder may further include a non-fluorine-based polymer in addition to the fluorine-based polymer and modified polyolefin. The non-fluorine-based polymer may include polyolefin, polyethylene oxide (PEO), etc.

[0048] The modified polyolefin contains a functional group derived from a carboxylic acid anhydride. According to one embodiment of the present invention, the modified polyolefin containing a functional group derived from a carboxylic acid anhydride is a copolymer containing a repeating unit derived from an olefin and a repeating unit derived from a carboxylic acid anhydride, or a modified polyolefin containing a functional group derived from a carboxylic acid anhydride not as a repeating unit but as a side chain functional group, or a copolymer containing a repeating unit derived from an olefin and a repeating unit derived from a carboxylic acid anhydride and also containing a functional group derived from a carboxylic acid anhydride as a side chain functional group, or it can contain two or more of these.

[0049] When the modified polyolefin containing a functional group derived from a carboxylic acid anhydride is a copolymer containing a repeating unit derived from an olefin and a repeating unit derived from a carboxylic acid anhydride, the copolymer may be a block copolymer, a random copolymer, or an alternating copolymer in which the repeating unit derived from an olefin and the repeating unit derived from a carboxylic acid or a carboxylic acid anhydride are all linked in the main chain. Furthermore, the modified polyolefin containing a functional group derived from a carboxylic acid anhydride may be a graft copolymer containing a repeating unit derived from a carboxylic acid anhydride in a side chain of a polyolefin.

[0050] Furthermore, according to one embodiment of the present invention, when the modified polyolefin containing a functional group derived from a carboxylic acid anhydride is a modified polyolefin containing the functional group derived from a carboxylic acid anhydride not as a repeating unit but as a side chain functional group, the modified polyolefin may be a compound in which at least one hydrogen atom of a polyolefin has been substituted with the functional group derived from a carboxylic acid anhydride.

[0051] The modified polyolefin may include one or more of modified polyethylene and modified polypropylene. The modified polyolefin may be modified polyethylene.

[0052] According to one embodiment of the present invention, the modified polyolefin is a polymer containing repeating units derived from the olefin, and in this case, the repeating units derived from the olefin may be derived from an olefin including at least one of ethylene and propylene.

[0053] According to one embodiment of the present invention, the modified polyolefin may further include a repeating unit derived from an olefin elastomer, a repeating unit derived from a styrene-based compound, a repeating unit derived from an unsaturated hydrocarbon, or two or more of these.

[0054] The repeating units derived from the olefin elastomer may be repeating units derived from 1-butene, 1-octene, or the like.

[0055] The styrenic-derived repeating unit may be a repeating unit derived from styrene, a substituted styrene, etc. The unsaturated hydrocarbon-derived repeating unit may be a repeating unit derived from 1,2-butadiene, 1,3-butadiene, etc.

[0056] Specifically, the modified polyolefin may be a poly(ethylene)-(1-butene) copolymer, a poly(ethylene)-(1-octene) copolymer, a poly(ethylene)-(1-propylene) copolymer, a poly(ethylene)-(styrene)-(butadiene) copolymer, or the like, which contains a functional group derived from a carboxylic acid anhydride.

[0057] According to one embodiment of the present invention, when the modified polyolefin containing a functional group derived from a carboxylic acid anhydride is a copolymer containing a repeating unit derived from an olefin and a repeating unit derived from a carboxylic acid anhydride, the functional group derived from the carboxylic acid anhydride may be derived from maleic anhydride, glutaric anhydride, phthalic anhydride, trimellitic anhydride, pyromellitic monoanhydride, pyromellitic dianhydride, 1,8-naphthalenedicarboxylic anhydride, 2,3-naphthalenedicarboxylic anhydride, 1,4,5,8-naphthalenetetracarboxylic monoanhydride, 1,4,5,8-naphthalenetetracarboxylic dianhydride, 2,3,6,7-naphthalenetetracarboxylic monoanhydride, 2,3,6,7-naphthalenetetracarboxylic dianhydride, or a carboxylic acid anhydride containing two or more of these.

[0058] The modified polyolefin may be one or more of polyethylene containing functional groups derived from maleic anhydride and polypropylene containing functional groups derived from maleic anhydride.

[0059] According to one embodiment of the present invention, the content of functional groups derived from carboxylic acid anhydrides in the modified polyolefin may be 0.5 mol % to 20 mol %, or 0.5 mol % to 15 mol %. When the content of repeating units derived from carboxylic acid anhydrides in the modified polyolefin satisfies this range, the modified polyolefin can have excellent reactivity with carboxylic acid anhydrides, ensuring hydrophilicity, and the electrode layer containing such modified polyolefin has significantly improved adhesive strength at the bonding surface with a current collector (e.g., a metal current collector).

[0060] In this case, the mole % content of the carboxylic acid anhydride-derived functional groups in the modified polyolefin can be defined as the percentage of the moles of the carboxylic acid anhydride-derived functional groups (including all the cases of repeating units and simple side chain functional groups) relative to the total moles of all repeating units and functional groups (e.g., olefin-derived repeating units, carboxylic acid anhydride-derived functional groups (including all the carboxylic acid anhydride-derived repeating units, and carboxylic acid anhydride-derived functional groups (bonded to simple side chains rather than repeating units of copolymers))) contained in the modified polyolefin.

[0061] In the electrode according to the present invention, in addition to the active material, conductive material, and fluoropolymer binder, a modified polyolefin is added to the electrode layer as a binder that has high adhesive properties with the current collector. This eliminates the need for a step of providing a primer layer on the current collector, and makes it possible to improve the adhesive strength between the electrode layer and an uncoated current collector that does not have any primer layer.

[0062] According to one embodiment of the present invention, the electrode layer includes a fiberized binder as a means for binding the active material and the conductive material. This fiberized binder exhibits less breakage and superior longitudinal extensibility compared to conventional non-fiberized binders, thereby improving the flexibility of the electrode layer and the electrode itself. That is, the binder can be fiberized to bind the active material and the conductive material. Specifically, the fluoropolymer in the binder is fiberized to bind the active material and the conductive material together with the modified polyolefin, thereby improving the adhesive strength with the current collector. The fiberization process of the binder will be specifically discussed in the electrode manufacturing method described below.

[0063] The content of the modified polyolefin is 2 to 40 parts by weight based on 100 parts by weight of the binder.

[0064] According to one embodiment of the present invention, the content of the modified polyolefin may be 3 to 40 parts by weight, 3.5 to 40 parts by weight, 4 to 40 parts by weight, 4.2 to 38.5 parts by weight, 4.2 to 8.3 parts by weight, 4.2 to 16.7 parts by weight, or 8.3 to 16.7 parts by weight, based on 100 parts by weight of the binder.

[0065] If the content of the modified polyolefin is less than 2 parts by weight based on 100 parts by weight of the binder, it will not be effective in improving the adhesive strength between the electrode layer and the current collector. If the content exceeds 40 parts by weight, the proportion of the fluorine-based polymer in the total binder content will decrease, weakening the mechanical properties of the electrode film that forms the electrode layer, making it difficult to form the film itself, which is undesirable.

[0066] According to one embodiment of the present invention, the melt index (MI) of the modified polyolefin may be 50 g / 10 min or less, or 0.5 to 50 g / 10 min, or 1 to 30 g / 10 min, or 1 to 10 g / 10 min, or 3 to 50 g / 10 min, or 3 to 30 g / 10 min, or 3 to 10 g / 10 min, or 0.5 to 3 g / 10 min, or 2 to 50 g / 10 min, or 2 to 30 g / 10 min, or 2 to 10 g / 10 min, or 0.5 to 2 g / 10 min, or 2 to 3 g / 10 min.

[0067] When the melt index (MI) of the modified polyolefin satisfies 50 g / 10 min or less, the appropriate molecular weight of the modified polyolefin is ensured, and the adhesive strength between the electrode layer and the current collector can be further improved.

[0068] The melt index, also known as the melt flow index, is one of the rheological properties of polymers. For example, the melt index can be calculated as the weight of a polymer sample that flows for 10 minutes, and its unit is g / 10 min.

[0069] According to one embodiment of the present invention, the melt index (MI) can be measured according to ASTM D-1238 (condition E, 190°C, 2.16 kg load) or can be measured under the conditions of 230°C, 2.16 kg load. Specifically, of the above measurement conditions, the former condition (190°C, 2.16 kg load) can be applied to the melt index measurement of modified polyethylene, and the latter condition (230°C, 2.16 kg load) can be applied to the melt index measurement of modified polypropylene.

[0070] According to one embodiment of the present invention, the melting point of the modified polyolefin is 175° C. or lower, or 110° C. to 175° C., or 110° C. to 128° C., or 128° C. to 175° C., or 110° C. to 122° C., or 122° C. to 175° C., or 122° C. to 128° C., or 110° C. to 165° C., or 165° C. to 175° C., or 122° C. to 165° C., or 128° C. to 165° C. When the melting point of the modified polyolefin is 175° C. or lower, the modified polyolefin can be more uniformly mixed with the active material, conductive material, and binder in the kneading step during production of the electrode film, which will be described later.

[0071] The melting point of the modified polyolefin can be measured using a differential scanning calorimeter (DSC, DSC 2920, TA Instruments). Specifically, the polymer is heated to 220°C, maintained at that temperature for 5 minutes, cooled to 20°C, and then the temperature is increased again, with the temperature increasing and decreasing rates being controlled at 10°C / min.

[0072] According to one embodiment of the present invention, the content of the active material is 80 to 98 parts by weight, the content of the conductive material is 0.5 to 10 parts by weight, the content of the fluorine-based polymer is 0.5 to 5 parts by weight, and the content of the modified polyolefin is 0.02 to 3.3 parts by weight.

[0073] The content of the active material is 90 to 98 parts by weight, or 90 to 96 parts by weight, or 90 to 96.6 parts by weight, the content of the conductive material is 0.5 to 7 parts by weight, or 0.5 to 1 part by weight, or 1 to 7 parts by weight, and the content of the fluorine-based polymer is 0.5 to 4.5 parts by weight, or 0.5 to 2 parts by weight, or 2 to 4.5 parts by weight, or 0.5 to 2.3 parts by weight, or 2 to 2.3 parts by weight, or 2.3 to 4.5 parts by weight, or 0.5 to 2.2 parts by weight, or 2 to 2 0.2 parts by weight, or 2.2 parts by weight to 4.5 parts by weight, or 2.2 parts by weight to 2.3 parts by weight, or 0.5 parts by weight to 1.6 parts by weight, or 1.6 parts by weight to 2.2 parts by weight, or 1.6 parts by weight to 4.5 parts by weight, or 1.6 parts by weight to 2.3 parts by weight, and the content of the modified polyolefin is 0.02 parts by weight to 3 parts by weight, or 0.02 parts by weight to 2.5 parts by weight, 0.02 parts by weight to 1 part by weight, or 0.03 parts by weight to 2 parts by weight, or 0.1 parts by weight to 3 parts by weight, or 0.2 parts by weight to 3 parts by weight, or 0.4 parts by weight to 3 parts by weight, or 1 part by weight to 3 parts by weight.

[0074] When the contents of the active material, conductive material, binder, and modified polyolefin satisfy these ranges, the binder can be sufficiently fiberized in the subsequent kneading process to form a mixture mass, and the mixed powder formed in the pulverization process can be easily molded into an electrode film, ensuring the physical properties of the electrode film, ensuring the content of the active material to prevent the problem of capacity reduction, and ensuring sufficient conductivity.

[0075] On the other hand, in some cases, a filler, which is a component that suppresses expansion of the electrode, can be further added to the electrode layer. The filler is not particularly limited as long as it is a fibrous material that does not cause chemical changes in the battery, and for example, olefin polymers such as polyethylene and polypropylene, and fibrous substances such as glass fiber and carbon fiber are used.

[0076] The current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery, and examples thereof include stainless steel, aluminum, nickel, titanium, calcined carbon, copper, or aluminum or stainless steel whose surface has been surface-treated with carbon, nickel, titanium, silver, etc. The current collector can also be formed with fine irregularities on its surface to improve the adhesive strength of the positive electrode active material, and can be in various forms such as a film, sheet, foil, net, porous material, foam, or nonwoven fabric.

[0077] As described above, the electrode layer of the electrode of the present invention contains a modified polyolefin, which is a copolymer containing a repeating unit derived from an olefin and a repeating unit derived from a carboxylic acid or a carboxylic acid anhydride. The repeating unit derived from the carboxylic acid anhydride of such a modified polyolefin has excellent reactivity, so that the electrode layer containing the modified polyolefin has significantly improved adhesion to the current collector. Therefore, the current collector used in the electrode of one embodiment of the present invention does not need to be provided with a separate primer layer, and excellent adhesion and interfacial resistance characteristics between the electrode layer and the current collector can be ensured.

[0078] The porosity of the electrode layer of the electrode is 20% to 50%, or 20% to 45%, or 20% to 40%, or 20% to 35%, or 22% to 30%, or 20% to 28%, or 20% to 26%, or 23.1% to 27.4%, or 23.1% to 24.8%, or 23% to 26%, or 24.8% to 27.4%. Such porosity may vary slightly depending on which effect is being focused on.

[0079] However, when the porosity of the electrode layer is within this range, the electrolyte impregnation property is improved, resulting in excellent life characteristics and output characteristics, and since there is no need to increase the volume to achieve the same capacity, it is also advantageous in terms of energy density per volume.

[0080] The porosity of the electrode layer can be determined by the following relational expression, using the actual density calculated based on the actual density and composition of each constituent component, after measuring the apparent density of only the composite film by subtracting the volume and weight of the current collector from the volume and weight of the electrode. Porosity (%) = {1-(apparent density / actual density)} x 100

[0081] In one embodiment of the present invention, the crystallinity of the binder in the electrode layer may be 10% or less.

[0082] In the present invention, the crystallinity (Xc) can be measured using a differential scanning calorimetry (DSC) and is based on the temperature (peak temperature) at which the highest enthalpy is observed during crystallization. Specifically, the crystallinity can be calculated based on the melting enthalpy (ΔH m ) value was calculated from the enthalpy of fusion (ΔH m 0 ) (heat of equilibrium fusion) and expressed as a percentage, and can be calculated using the following relational expression 1. Here, the theoretical enthalpy of fusion of a perfect crystal can be found in a polymer handbook for known polymers, and for unknown or newly synthesized substances, it can be calculated by extrapolation, which involves extending the crystallinity of two or more points. [Equation 1] Xc(%)=(ΔH m / ΔH m 0 ) x 100

[0083] The electrode layer may be derived from a dry electrode film. The dry electrode film refers to a film manufactured by a dry manufacturing method that does not use a dispersant, as opposed to a conventional wet electrode manufacturing method in which an active material, a conductive material, and a binder are dissolved and / or dispersed in a dispersant such as water or an organic solvent, to form a slurry, which is then coated on a current collector and dried. The electrode film manufactured in this manner is laminated on a current collector to finally manufacture an electrode. Specific methods for manufacturing the electrode film and electrode will be described later.

[0084] According to one aspect of the present invention, preparing a mixture including an active material, a conductive material, a binder, and a modified polyolefin; kneading the mixture at a temperature in the range of 70°C to 200°C under a pressure equal to or higher than atmospheric pressure to produce a mixture mass; pulverizing the mixture mass to obtain a mixed powder for an electrode; The electrode mixed powder is placed between a plurality of rolls and calendered to form an electrode film; and laminating the electrode film on a metal current collector.

[0085] The method for producing an electrode according to one embodiment of the present invention will be described in more detail below. First, a mixture containing an active material, a conductive material, a binder, and a modified polyolefin is prepared.

[0086] In this case, the mixing for preparing the mixture is performed so that the active material, conductive material, binder, and modified polyolefin are uniformly distributed and mixed in a powder form, and therefore, various methods can be used as long as they enable simple mixing. However, since the electrode of the present invention is produced by a dry production method that does not use a dispersion medium, the mixing can be performed by dry mixing, which can be performed by putting the materials into a device such as a blender.

[0087] To ensure uniformity, the mixture can be produced by mixing in a mixer at 5,000 rpm to 20,000 rpm for 30 seconds to 2 minutes, more specifically, at 10,000 rpm to 15,000 rpm for 30 seconds to 1 minute.

[0088] According to one embodiment of the present invention, a super mixer or the like may be used in the mixing step of preparing the mixture. Specifically, a method of mixing using a super mixer at 1,000 to 2,000 rpm for 2 to 10 minutes may be applied.

[0089] The binder can be made into fine fibers by the step of preparing the mixed powder. The term "fine fiber" refers to a process of finely dividing a high molecular weight polymer, and can be performed using, for example, mechanical shear force. Specific examples of such binders are as described above.

[0090] Next, the mixture is kneaded at a temperature in the range of 70°C to 200°C under a pressure equal to or higher than atmospheric pressure to produce a mixture mass.

[0091] In conventional techniques, high-shear kneading using a jet mill or the like is performed to fiberize the binder, but this kneading causes problems such as the active material being pulverized and the formed fibers being cut. Therefore, in the present invention, the above problems are solved by using a low-shear kneading method instead of high-shear kneading.

[0092] The kneading method is not limited to a specific method. In a specific embodiment of the present invention, the kneading can be performed using a kneading machine such as a kneader.

[0093] This kneading step is a step in which the binder is fiberized to bond or link the active material, conductive material, and modified polyolefin, thereby forming a mixture mass with a solid content of 100%. In addition, in this kneading step, by raising the temperature above the melting point of the modified polyolefin, the modified olefin melts, thereby improving the dispersibility of the kneaded material.

[0094] Specifically, the kneading can be controlled at a speed of 10 rpm to 100 rpm. For example, the kneading can be controlled at a speed of 20 rpm or more or 70 rpm or less within the above range. The kneading can be carried out for 1 minute to 30 minutes.

[0095] For example, the kneading can be carried out for 3 to 30 minutes at a speed of 20 to 50 rpm within the above range. Meanwhile, the shear rate during the kneading can be controlled within a range of 10 / s to 500 / s. In one specific embodiment of the present invention, the kneading can be carried out for 1 to 30 minutes, and the shear rate can be controlled within a range of 30 / s to 100 / s.

[0096] Furthermore, such a kneading step can be carried out under conditions of high temperature and pressure equal to or higher than atmospheric pressure, and more specifically, under conditions of pressure higher than atmospheric pressure.

[0097] More specifically, the kneading can be carried out by heating the mixture in the range of 70°C to 200°C, specifically 90°C to 180°C.

[0098] If the temperature is lower than the above range, the binder will not be fibrous during kneading and will not form a mass due to the kneading, making it difficult to form a film during calendering. If the temperature is too high, the binder will be fibrous rapidly, and then the already formed fibers will be cut by excessive shear force, which is undesirable.

[0099] The reaction can also be carried out at atmospheric pressure or higher, or under a pressure of 1 atm (atmospheric pressure) to 60 atm, or under a pressure of 1 atm to 30 atm, or under a pressure of 1 atm to 10 atm, or under a pressure of 1 atm to 8 atm, or under a pressure of 1.1 atm to 7 atm, or under a pressure of 1.1 atm to 6 atm.

[0100] When the pressure range is satisfied, problems such as cutting of the formed fibers due to application of excessive shear force and pressure, or excessively high density of the mixture mass can be prevented. That is, according to the present invention, the intended effect of the present invention can be achieved by performing a low shear kneading step under high temperature and pressure conditions equal to or higher than atmospheric pressure, instead of high shear kneading.

[0101] Furthermore, according to one embodiment of the present invention, in order to improve the dispersibility of the modified polyolefin, a part of the active material or a part of the conductive material may be pre-mixed and kneaded with the modified polyolefin, and the pre-mixed and kneaded product may be mixed and kneaded with the remaining electrode material.

[0102] Next, the mixture mass is pulverized to obtain a mixed powder for an electrode. Specifically, the mixture mass produced by the kneading process can be immediately subjected to a calendering process, but in this case, the mixture mass may need to be compressed to produce a thin film, which may result in a non-uniform film. Therefore, according to the present invention, the produced mixture mass is subjected to the pulverization step. That is, if the electrode powder mixture obtained by pulverization is excessively large or agglomerated, bridges may form during the calendering process, resulting in poor film appearance such as pinholes, or the film may have non-uniform surface properties. Therefore, the electrode powder mixture is obtained by pulverization to obtain a powder mixture of uniform size, and then the calendering process is performed.

[0103] In this case, the pulverization step can be performed using a device such as a blender or grinder, but is not limited thereto. Specifically, the pulverization step can be performed at a speed of 5,000 rpm to 20,000 rpm for 30 seconds to 10 minutes, more specifically, at a speed of 10,000 rpm to 18,000 rpm for 30 seconds to 2 minutes.

[0104] When the above-mentioned grinding speed and time are satisfied, sufficient grinding can be achieved to form powder of a size suitable for film formation, and the problem of a large amount of fine powder being generated from the mixture mass can be prevented. If necessary, a classification step can be performed to filter out powders above or below a certain size.

[0105] According to an embodiment of the present invention, the pulverization step can be performed using a cutter mill, a fine mill, or the like. The cutter mill can be used to roughly pulverize the kneaded mixture mass to a few mm size at 400 rpm to 500 rpm for several minutes. The fine mill can be used to uniformly pulverize the coarsely pulverized powder to a certain size or less at 3,000 rpm to 8,000 rpm.

[0106] Next, the electrode powder mixture is placed between a plurality of rolls and calendered to form an electrode film.

[0107] 1a and 1b, in the process 100 for forming an electrode film, a plurality of rolls 110 are arranged at a distance from each other, and the electrode powder mixture 120 obtained in the previous step is placed between adjacent rolls 110. The rolls 110 are rotated in opposite directions to roll out the electrode powder mixture 120, and the mixed powder 120 is formed into a sheet or film through a powder sheeting step. After that, a final electrode film having a target thickness can be obtained through multiple calendering steps.

[0108] According to one embodiment of the present invention, in the process of forming an electrode film, the gap between multiple rolls can be appropriately controlled in consideration of the specifications and physical properties of the electrode film to be manufactured. For example, compared to Figure 1a, in Figure 1b, the gap between the second and third rolls and the gap between the fourth and fifth rolls can be controlled to be larger.

[0109] Specifically, such a calendering treatment is a step of processing the mixed powder for an electrode into a film shape, and can be, for example, a step of producing a film shape having an average thickness of 50 μm to 300 μm.

[0110] In this case, the calendering treatment can be carried out, for example, by using rolls facing each other. According to one embodiment of the present invention, the calendering treatment can be repeated one or more times, for example, 1 to 5 times, or 3 to 4 times, or 4 times.

[0111] At this time, the roll temperature may be 50°C to 200°C. The rotation speed ratio of the rolls can be appropriately controlled depending on the size of the rolls, the number of times of calendaring, and the thickness of the electrode film, and can be controlled, for example, within the range of 1 to 10 times, 1 to 8 times, 1 to 7 times, or 1.2 to 5 times.

[0112] The distance between the opposing rolls can be variably adjusted depending on the thickness and density of the film to be obtained.

[0113] By carrying out the calendering step, a film for a dry electrode that serves as an electrode mixture can be produced. Such a film for a dry electrode is also conventionally called a free-standing film.

[0114] The electrode film produced in this manner does not contain a solvent, so it has almost no fluidity and is easy to handle, and can be processed into a desired shape to be used in the production of electrodes of various shapes. Furthermore, when the electrode film of the present invention is used in the production of an electrode, the drying step for removing the solvent can be omitted, which not only significantly improves the efficiency of the electrode production process but also solves problems that have been encountered in the production of existing dry electrodes, such as damage to the active material and cutting of the fibrous binder contained therein.

[0115] Meanwhile, in the present invention, the porosity of the electrode film is 20% to 50%, and preferably can be controlled to a value of 40% or less or 30% or less within the above range. When the porosity satisfies this range, electrolyte impregnation is easy, life characteristics and output characteristics can be improved, and since there is no need to increase the volume to achieve the same capacity, the energy density per volume can be improved. In one embodiment of the present invention, the porosity can be calculated by the following formula, using the actual density calculated based on the actual density and composition of each component, after measuring the apparent density of the dry electrode film. Porosity (%) = {1-(apparent density / actual density)} x 100

[0116] Next, the electrode film is laminated onto a metal current collector. The laminating step may be a step of rolling and attaching the electrode film obtained in the previous step to a predetermined thickness on a current collector. The laminating step may also be performed using a laminating roll, and the laminating roll may be maintained at a temperature of 25°C to 250°C.

[0117] As described above, the electrode layer of the electrode of the present invention contains a modified polyolefin, which is a copolymer containing a repeating unit derived from an olefin and a repeating unit derived from a carboxylic acid or a carboxylic acid anhydride. The repeating unit derived from the carboxylic acid anhydride of such a modified polyolefin has excellent reactivity, so that the electrode layer containing the modified polyolefin can have significantly improved adhesion to the current collector. Therefore, the current collector used in the electrode of one embodiment of the present invention can be applied without the need to provide a separate primer layer.

[0118] According to one embodiment of the present invention, the compression ratio of the electrode film may be 30% to 50%, or 35% to 50%, or 40% to 50%.

[0119] The compression ratio of the electrode film can be defined as the ratio of the thickness to which the electrode film is compressed during lamination, and can be expressed by the following formula 1. [Formula 1] Compression ratio (%) = T p / T1×100 In Equation 1, T p means the pressed thickness of the electrode film in the lamination step, T1 refers to the thickness of the electrode film before the lamination step.

[0120] In the present invention, by adjusting the compression ratio in the lamination step to satisfy a specific range, it is possible to provide an electrode film with an appropriate density and porosity, as well as excellent adhesion between the electrode film and the current collector.

[0121] When the compression ratio of the electrode film is within the range of 30% to 50%, the pressure applied to the electrode film is sufficient, improving the adhesive strength between the electrode film and the current collector, preventing the electrode film from peeling off from the current collector after the lamination process, and eliminating the problem of the electrode film having an excessively high density, resulting in a porosity lower than the target porosity, or damage to the current collector.

[0122] In one embodiment of the present invention, when an electrode film is laminated on both sides of the current collector, the compression ratio (%) in the above formula 1 can be expressed by the following formula 2. [Formula 2] 30≦(T1+0.5T c -0.5T gap ) / T1×100≦50 In Equation 2, T1 means the thickness of the electrode film before the lamination step, and T c means the thickness of the current collector, and T gap means the gap between the first and second rolls.

[0123] Furthermore, the rolling ratio of the electrode film after the lamination step is 20% or less, or 18% or less, or 15% or less, or in the range of 5% to 15%, or 6% to 15%, or 7% to 15%, or 9% to 13%.

[0124] Here, the rolling ratio can be defined as the ratio of the thickness of the electrode film after the lamination step to the thickness of the electrode film before the lamination step, and can be expressed by the following formula 3. [Formula 3] Rolling ratio (%) = (T1-T2) / T1 x 100 In the above formula 3, T1 means the thickness of the electrode film before the lamination step, T2 refers to the thickness of the electrode film after the lamination step.

[0125] When the rolling ratio satisfies the above range, it is possible to achieve an appropriate density and porosity of the electrode film, as well as adhesive strength between the electrode film and the current collector.

[0126] The increase rate of the apparent density of the electrode film before and after lamination with the current collector can be expressed by the following formula 4. [Formula 4] Apparent density increase rate (%) = (D2 - D1) / D1 x 100 D1 is the apparent density (g / cm) of the electrode film before the lamination step. 3 ), D2 is the apparent density (g / cm) of the electrode film after the lamination step. 3 ) means

[0127] The increase rate of the apparent density of the electrode film before and after lamination with the current collector is 5% to 30%, or 7% to 25%, or 10% to 20%.

[0128] The apparent densities D1 and D2 of the electrode film may vary depending on the type of active material. According to one embodiment of the present invention, the active material is lithium nickel-manganese-cobalt oxide Li 1+x (Ni a Co b Mn c ) 1-xO2 (where x = 0 to 0.03, a = 0.3 to 0.95, b = 0.01 to 0.35, c = 0.01 to 0.5, a + b + c = 1), or an oxide in which part of lithium nickel - manganese - cobalt oxide is substituted with aluminum (lithium nickel - manganese - cobalt - aluminum oxide) Li a [Ni b Co c Mn d Al e 1-f M 1 f O2 (where the M 1 is one or more selected from the group consisting of Zr, B, W, Mg, Ce, Hf, Ta, La, Ti, Sr, Ba, F, P and S, and 0.8 ≤ a ≤ 1.2, 0.5 ≤ b ≤ 0.99, 0 < c < 0.5, 0 < d < 0.5, 0.01 ≤ e ≤ 0.1, 0 ≤ f ≤ 0.1), etc., when the D1 and D2 are in the range of 2.75 g / cm 3 ~3.75 g / cm 3 .

[0129] On the other hand, when the apparent density increase rate of the electrode film satisfies the above range, the adhesion between the electrode film and the current collector can be improved, and problems such as the porosity deviating from the target range or damage to the positive electrode active material or the current collector can be prevented.

[0130] The apparent density of the electrode film before and after lamination with the current collector can be calculated by measuring the weight and thickness of the electrode film before lamination, measuring the weight and thickness of the electrode after lamination, and subtracting the weight and thickness of the current collector to obtain the weight and thickness of the film.

[0131] Also, the active material loading of the dry - type electrode film is 3 mAh / cm 2 ~15 mAh / cm 2 , and specifically, it is 4 mAh / cm 2 ~10 mAh / cm 2 . Here, the active material loading is the value calculated by the following formula 5. [Formula 5] Active material loading (mAh / cm​2 ) = Capacity of active material (mAh / g) × Weight content ratio of active material in dry electrode film (wt%) × Weight per unit area of ​​dry electrode film (g / cm 2 )

[0132] The interface resistance between the electrode film and the current collector (resistance before immersion in the electrolyte, initial resistance) is 1 Ω cm 2 or less, or 0.8Ω·cm 2 or less, or 0.7Ω·cm 2 or less, or 0.5Ω·cm 2 or less, or 0.29 Ω·cm 2 or less, or 0.20 Ω·cm 2 ~1Ω·cm 2 , or 0.20 Ω·cm 2 ~0.29 Ω·cm 2 It could be.

[0133] Here, the interfacial resistance can be calculated by applying a current of 100 μA to the electrode using a multi-probe (MP) resistance measurement method, and measuring the resistance between the film for a dry electrode and the current collector layer based on the potential difference measured between multiple probes. If the interfacial resistance satisfies the range, the battery performance of a subsequently manufactured secondary battery can be improved.

[0134] According to one embodiment of the present invention, the interface resistance between the electrode film and the current collector after the electrode is immersed in the electrolyte is 1.0 Ω cm. 2 or less, or 0.8Ω·cm 2 or less, or 0.7Ω·cm 2 or less, or 0.3Ω·cm 2 ~1.0Ω·cm 2 , or 0.32 Ω·cm 2 ~1.0Ω·cm 2 , or 0.32 Ω·cm 2 ~0.69 Ω·cm 2 is.

[0135] In this case, the interfacial resistance between the electrode film and the current collector after immersion in the electrolyte can be calculated by preparing a liquid electrolyte in which LiPF6 is dissolved at 1M in a solvent made by mixing ethylene carbonate, dimethyl carbonate, and diethyl carbonate in a 1:2:1 (volume ratio), immersing the electrode in the electrolyte for one week, removing it, and measuring the resistance between the dry electrode film and the current collector layer based on the potential difference measured between the multiple probes using the MP (Multi-Probe) resistance measurement method.

[0136] According to one embodiment of the present invention, the adhesive strength of the electrode (initial adhesive strength, adhesive strength before immersion in the electrolyte) is 38 gf / 2 cm or more, or 50 gf / 2 cm or more, or 50 gf / 2 cm to 500 gf / 2 cm, or 150 gf / 2 cm to 250 gf / 2 cm, or 162 gf / 2 cm to 212 gf / 2 cm.

[0137] The adhesive strength of the electrode can be measured by attaching double-sided tape to a glass slide, placing an electrode sample cut to a predetermined size (e.g., 20 mm x 100 mm) on the tape, and then rolling it back and forth with a 2 kg roller 10 times to adhere the electrode. Air bubbles are removed using a laminator with a gap of 5 mm and a speed of 5 mpm, and the adhesive strength can be measured by pulling the electrode from the glass slide at 100 mm / min using a UTM (TA, Universal Testing Machine) instrument. The measurement angle between the glass slide and the electrode can be 90°.

[0138] According to one embodiment of the present invention, the adhesive strength of the electrode after immersion in the electrolyte is 38 gf / 2 cm or more, or 50 gf / 2 cm or more, or 150 gf / 2 cm or more, or 50 gf / 2 cm to 500 gf / 2 cm, or 150 gf / 2 cm to 300 gf / 2 cm, or 170 gf / 2 cm to 250 gf / 2 cm, or 174 gf / 2 cm to 233 gf / 2 cm.

[0139] The adhesive strength of the electrode after immersion in the electrolyte was measured by preparing a liquid electrolyte containing 1M LiPF6 dissolved in a 1:2:1 (volume ratio) mixture of ethylene carbonate, dimethyl carbonate, and diethyl carbonate, immersing the electrode for one week, removing it, rinsing it with DMC solution, and drying it. A cathode sample cut to a predetermined size (e.g., 20 mm x 100 mm) was placed on the electrode, and the electrode was bonded by rolling it back and forth 10 times with a 2 kg roller. Air bubbles were removed using a laminator with a gap of 5 mm and a speed of 5 mpm. The adhesive strength was measured by pulling the electrode from the glass slide at 100 mm / min using a UTM (TA) device. The measurement angle between the glass slide and the electrode may be 90°.

[0140] When the adhesive strength of the electrode after immersion in the electrolyte solution satisfies this range, the electrode layer does not appear to be lifted even after the electrode is immersed in the electrolyte solution, and there is no detachment of the electrode layer or generation of bubbles, so the adhesive strength can be maintained even after immersion in the electrolyte solution.

[0141] 2 is a schematic diagram illustrating a step of laminating electrode films on both sides of a current collector according to an embodiment of the present invention. That is, in the laminating step 200, the electrode film 230 obtained in the previous step is rolled to a predetermined thickness and attached to the current collector 220 using a pair of laminating rolls 210, thereby finally obtaining an electrode 240.

[0142] According to another embodiment of the present invention, there is provided an electrode manufactured by the above-described electrode manufacturing method, a secondary battery including the electrode, wherein the electrode is a positive electrode, and an electrode assembly including the positive electrode, a negative electrode, and a separator is incorporated into a battery case (cylindrical case, prismatic case, pouch, etc.) together with a lithium-containing non-aqueous electrolyte, and an energy storage device including the same as a unit battery.

[0143] At this time, the specific structures of the secondary battery and the energy storage device are well known and will not be described in this specification.

[0144] Meanwhile, according to one embodiment of the present invention, there is provided an apparatus for manufacturing an electrode, the apparatus including: a blender that mixes raw materials for a composite including an active material, a conductive material, a binder, and a modified polyolefin; a kneader that kneads the mixture to prepare a mixture mass; a pulverizer that pulverizes the mixture mass to form a mixed powder for an electrode; a calender that forms the mixed powder for an electrode into a film for a dry electrode; and a lamination roll that places the film for a dry electrode on at least one surface of a current collector and laminates it.

[0145] The blender is a mixer for mixing raw materials, and as described above, can mix the raw materials for the combination at a speed of 5000 rpm to 20000 rpm. A super mixer or the like can be used as the mixer.

[0146] The kneader is a device for fiberizing the binder and dispersing the raw materials for the composite in the present invention, and the mixture is obtained as a mass of the mixture by kneading with the kneader. In this case, the kneading to obtain the results of the present invention can be performed at a temperature range of 70 to 200°C, or 90 to 180°C, and at a pressure of above atmospheric pressure, or 1 to 60 atm (atmospheric pressure), or 1 to 30 atm, or 1 to 10 atm, or 1 to 8 atm, or 1.1 to 7 atm, or 1.1 to 6 atm.

[0147] The pulverizer is a device for pulverizing the mixture mass to form a mixed powder for an electrode, and a blender or grinder can be used for this as well. Examples of the grinder include a cutter mill and a fine mill.

[0148] The calender is a device for forming the electrode powder mixture into a film, and is, for example, a pair of rollers facing each other, and the thickness of the film can be adjusted by adjusting the gap between them.

[0149] The laminating roll serves to attach the film for a dry electrode formed by the calendar onto at least one surface of a current collector and roll it.

[0150] By using such a calendar and laminating roll, the porosity of the film for a dry electrode according to the present invention can be determined.

[0151] That is, the dry electrode manufacturing apparatus according to the present invention includes a kneader and a pulverizer.

[0152] The specific structures of the blender, kneader, calendar, and laminating roll are well known, and therefore will not be described in detail in this specification.

[0153] Hereinafter, the present invention will be described in detail with reference to examples. However, the embodiments of the present invention can be modified into various different forms, and the scope of the present invention should not be construed as being limited to the examples described below. The examples of the present invention are provided to more completely explain the present invention to those skilled in the art.

[0154] Example 1 Lithium nickel cobalt manganese aluminum oxide (NCMA:Li[Ni 0.88 Co 0.07 Mn 0.04 ]Al 0.01 96.6g of O2, 1g of carbon black as a conductive material, 2g of polytetrafluoroethylene (PTFE) as a binder, and 0.4g of a polyethylene copolymer containing functional groups derived from maleic anhydride as a modified polyolefin (Woosung Chemical, SP1750) (Tm 128°C, Melt Index 3g / 10min (measured at 190°C, 2.16kg)) were added to a blender and mixed at 10,000 rpm for 1 minute to produce a mixture, which was then added to a kneader.

[0155] The kneader temperature was stabilized at 150°C, and the mixture was placed in a pressure kneader and operated at 40 rpm for 5 minutes under approximately 1.1 atmospheres (atm) to obtain a mixture mass. The mixture mass was then placed in a blender, pulverized at 10,000 rpm for 30 seconds, and sieved through a 1 mm mesh sieve to obtain an electrode mixture powder. The electrode mixture powder was then placed in a wrap calender (roll diameter: 160 mm, roll temperature: 100°C) to produce a film, which was then calendered twice to produce a final electrode film. Two electrode films thus produced were placed on both sides of aluminum foil (thickness: 19 μm) without a primer layer and laminated through a compression roll maintained at 150°C to produce an electrode (cathode).

[0156] The total thickness of the finally manufactured electrode was 169 μm, and the thickness of the active material layer formed on one surface of the active material layers formed on both surfaces of the current collector was 75 μm.

[0157] Example 2 Lithium nickel cobalt manganese aluminum oxide (NCMA:Li[Ni 0.88 Co 0.07 Mn 0.04 ]Al 0.01 An electrode film and an electrode (cathode) were produced in the same manner as in Example 1, except that 96.6 g of O2, 1 g of carbon black as a conductive material, 2.3 g of polytetrafluoroethylene (PTFE) as a binder, and 0.1 g of a polyethylene copolymer containing a functional group derived from maleic anhydride (Woosung Chemical, SP1300) as a modified polyolefin (Tm 122°C, Melt Index 2 g / 10 min (measured at 190°C, 2.16 kg)) were added to a blender and mixed at 10,000 rpm for 1 minute to produce a mixture, and the resultant mixture was added to a kneader.

[0158] The total thickness of the finally manufactured electrode was 171 μm, and the thickness of the active material layer formed on one surface of the active material layers formed on both surfaces of the current collector was 76 μm.

[0159] Example 3 Lithium nickel cobalt manganese aluminum oxide (NCMA:Li[Ni 0.88 Co 0.07 Mn 0.04 ]Al 0.01 96.6 g of O2), 1 g of carbon black as a conductive material, 2.2 g of polytetrafluoroethylene (PTFE) as a binder, and 0.2 g of a polypropylene copolymer containing a functional group derived from maleic anhydride (Woosung Chemical, SP3789) as a modified polyolefin (Tm 165°C, Melt Index (3 g / 10 min (measured at 230°C, 2.16 kg)) were added to a blender and mixed at 10,000 rpm for 1 minute to prepare a mixture. The resultant mixture was then added to a kneader at 170°C, and an electrode film and an electrode (cathode) were prepared in the same manner as in Example 1, except that the rolling mill was maintained at 170°C.

[0160] The total thickness of the finally manufactured electrode was 173 μm, and the thickness of the active material layer formed on one surface of the active material layers formed on both surfaces of the current collector was 77 μm.

[0161] Example 4 Lithium nickel cobalt manganese aluminum oxide (NCMA:Li[Ni 0.88 Co 0.07 Mn 0.04 ]Al 0.01 An electrode film and an electrode (cathode) were produced in the same manner as in Example 1, except that 96.0 g of O2), 1 g of carbon black as a conductive material, 1.6 g of polytetrafluoroethylene (PTFE) as a binder, and 1.0 g of a polyethylene copolymer containing a functional group derived from maleic anhydride (Woosung Chemical, SP1300) as a modified polyolefin (Tm 122°C, Melt Index 2 g / 10 min (measured at 190°C, 2.16 kg)) were added to a blender and mixed at 10,000 rpm for 1 minute to produce a mixture, and the resultant mixture was added to a kneader.

[0162] The total thickness of the finally manufactured electrode was 179 μm, and the thickness of the active material layer formed on one surface of the active material layers formed on both surfaces of the current collector was 80 μm.

[0163] Comparative Example 1 Lithium nickel cobalt manganese aluminum oxide (NCMA:Li[Ni 0.88 Co 0.07 Mn 0.04 ]Al 0.01 An electrode film and an electrode (cathode) were manufactured in the same manner as in Example 1, except that 96.6 g of O2), 1 g of carbon black as a conductive material, and 2.4 g of polytetrafluoroethylene (PTFE) as a binder were added to a blender and mixed at 10,000 rpm for 1 minute to prepare a mixture, and the resultant mixture was then added to a kneader.

[0164] The total thickness of the finally manufactured electrode was 171 μm, and the thickness of the active material layer formed on one surface of the active material layers formed on both surfaces of the current collector was 76 μm.

[0165] Comparative Example 2 Lithium nickel cobalt manganese aluminum oxide (NCMA:Li[Ni 0.88 Co 0.07 Mn 0.04 ]Al 0.01 An electrode film and an electrode (cathode) were manufactured in the same manner as in Example 1, except that 96.6 g of O2), 1 g of carbon black as a conductive material, 2 g of polytetrafluoroethylene (PTFE) as a binder, and 0.4 g of polyethylene were added to a blender and mixed at 10,000 rpm for 1 minute to prepare a mixture, and the resultant mixture was then added to a kneader.

[0166] The total thickness of the finally manufactured electrode was 169 μm, and the thickness of the active material layer formed on one surface of the active material layers formed on both surfaces of the current collector was 75 μm.

[0167] Comparative Example 3 Lithium nickel cobalt manganese aluminum oxide (NCMA:Li[Ni 0.88 Co 0.07 Mn 0.04 ]Al 0.01 An electrode was manufactured in the same manner as in Example 1, except that 96.6 g of O2), 1 g of carbon black as a conductive material, 2.36 g of polytetrafluoroethylene (PTFE) as a binder, and 0.04 g of a polyethylene copolymer containing a functional group derived from maleic anhydride (Woosung Chemical, SP1300) as a modified polyolefin (Tm 122°C, Melt Index 2 g / 10 min (measured at 190°C, 2.16 kg)) were added to a blender and mixed at 10,000 rpm for 1 minute to prepare a mixture, and the resultant mixture was then added to a kneader.

[0168] The total thickness of the finally manufactured electrode was 173 μm, and the thickness of the active material layer formed on one surface of the active material layers formed on both surfaces of the current collector was 77 μm.

[0169] Comparative Example 4 Lithium nickel cobalt manganese aluminum oxide (NCMA:Li[Ni 0.88 Co 0.07 Mn 0.04 ]Al 0.01 An attempt was made to produce an electrode film in the same manner as in Example 1, except that 96.0 g of O2), 1 g of carbon black as a conductive material, 1.5 g of polytetrafluoroethylene (PTFE) as a binder, and 1.5 g of a polyethylene copolymer containing a functional group derived from maleic anhydride (Woosung Chemical, SP1300) as a modified polyolefin (Tm 122°C, Melt Index 2 g / 10 min (measured at 190°C, 2.16 kg)) were placed in a blender and mixed at 10,000 rpm for 1 minute to produce a mixture, and the resultant mixture was placed in a kneader. However, the electrode film was easily torn, and an intact film could not be obtained.

[0170] Comparative Example 5 Lithium nickel cobalt manganese aluminum oxide (NCMA:Li[Ni 0.88 Co 0.07 Mn 0.04 ]Al 0.01 96.0 g of O2, 1 g of carbon black as a conductive material, 1.0 g of polytetrafluoroethylene (PTFE) as a binder, and 2.0 g of a modified polyolefin polyethylene copolymer containing maleic anhydride-derived functional groups (Woosung Chemical, SP1300) (Tm 122°C, Melt Index 2 g / 10 min (measured at 190°C, 2.16 kg)) were added to a blender and mixed at 10,000 rpm for 1 minute to produce a mixture. The kneader temperature was stabilized at 150°C, and the mixture was placed in a pressure kneader and operated at 40 rpm for 5 minutes under approximately 1.1 atmospheres (atm) to obtain a mixture mass. The mixture mass was added to the blender, pulverized at 10,000 rpm for 30 seconds, and sieved through a 1 mm mesh sieve to obtain a mixed powder for electrodes. The electrode powder mixture was then placed in a wrap calendar (roll diameter: 160 mm, roll temperature: 100°C) to produce a film, but the film was torn and an intact film could not be obtained.

[0171] Comparative Example 6 Lithium nickel cobalt manganese aluminum oxide (NCMA:Li[Ni 0.88 Co 0.07 Mn 0.04 ]Al 0.0196.6 g of O2, 1 g of carbon black as a conductive material, 2 g of PVDF as a binder, and 0.4 g of a modified polyolefin polyethylene copolymer containing maleic anhydride-derived functional groups (Woosung Chemical, SP1300) (Tm 122°C, Melt Index 2 g / 10 min (measured at 190°C, 2.16 kg)) were added to a blender and mixed at 10,000 rpm for 1 minute to produce a mixture. The kneader temperature was stabilized at 150°C, and the mixture was placed in a pressure kneader and operated at 40 rpm for 5 minutes under approximately 1.1 atmospheres (atm) to obtain a mixture mass. The mixture mass was added to the blender, pulverized at 10,000 rpm for 30 seconds, and sieved through a 1 mm mesh sieve to obtain a mixed powder for electrodes. The electrode powder mixture was then placed in a wrap calendar (roll diameter: 160 mm, roll temperature: 100°C) to produce a film, but the film was torn and an intact film could not be obtained.

[0172] Performance evaluation The electrodes (positive electrodes) produced in Examples 1 to 4 and Comparative Examples 1 to 3 were evaluated as follows, and the results are shown in Table 1. In the cases of Comparative Examples 4 to 6, as described above, it was not possible to produce an electrode film itself.

[0173] Adhesion strength (initial adhesion strength, adhesion strength before immersion in electrolyte) evaluation Double-sided tape was attached to a glass slide, and electrode samples cut into 20 mm x 100 mm from the electrodes prepared in Examples 1 to 4 and Comparative Examples 1 to 3 were placed on the tape and rolled back and forth 10 times with a 2 kg roller to adhere the electrodes. Air bubbles were removed using a laminator with a gap of 5 mm and a speed of 5 mpm, and the adhesive strength was measured by pulling the electrode from the glass slide at 100 mm / min using a UTM (TA) device. The measurement angle between the glass slide and the electrode was 90°.

[0174] Adhesion strength after immersion in electrolyte A liquid electrolyte containing 1M LiPF6 dissolved in a 1:2:1 (volume ratio) mixture of ethylene carbonate, dimethyl carbonate, and diethyl carbonate was prepared, and the electrodes manufactured in Examples 1 to 4 and Comparative Examples 1 to 3 were immersed in the electrolyte for one week. After immersion in the electrolyte, the electrodes were removed, washed with DMC solution, and dried. A 20 mm x 100 mm electrode sample was placed on the electrode and bonded by rolling it back and forth 10 times with a 2 kg roller. Air bubbles were removed using a laminator with a gap of 5 mm and a speed of 5 mpm. The adhesive strength after immersion in the electrolyte was measured by pulling the electrode from the glass slide at 100 mm / min using a UTM (TA) instrument. The measurement angle between the glass slide and the electrode was 90°.

[0175] Interface resistance (initial interface resistance, resistance before immersion in electrolyte) The interfacial resistance was calculated by applying a current of 100 μA to the electrodes prepared in Examples 1 to 4 and Comparative Examples 1 to 3 using a multi-probe (MP) resistance measurement method, and measuring the resistance between the film for dry electrodes and the current collector layer based on the potential difference measured between multiple probes.

[0176] Interface resistance after immersion in electrolyte A liquid electrolyte was prepared by dissolving 1M LiPF6 in a solvent containing a 1:2:1 (volume ratio) mixture of ethylene carbonate, dimethyl carbonate, and diethyl carbonate, and the electrodes manufactured in Examples 1 to 4 and Comparative Examples 1 to 3 were immersed in the electrolyte for one week. The electrodes were then removed from the electrolyte and the interfacial resistance was calculated by applying a current of 100 μA using a multi-probe (MP) resistance measurement method and measuring the resistance between the dry electrode film and the current collector layer based on the potential difference measured between the multiple probes.

[0177] [Table 1]

[0178] Referring to Table 1, it can be seen that the electrodes prepared in Examples 1 to 4 containing modified polyethylene exhibited significantly improved adhesive strength and adhesive strength after immersion in an electrolyte solution, and also exhibited very low interfacial resistance and interfacial resistance after immersion in an electrolyte solution, compared to the electrodes prepared in Comparative Examples 1 to 3 which did not contain modified polyethylene, contained general polyethylene, or had a modified polyolefin content outside the range of 2 to 40 parts by weight (based on 100 parts by weight of binder).

Claims

1. an electrode current collector; an electrode layer located on the electrode current collector and including an active material, a conductive material, and a binder; the binder comprises a fluorine-based polymer and a modified polyolefin, the fluorine-based polymer is polytetrafluoroethylene (PTFE), the modified polyolefin contains a functional group derived from a carboxylic acid anhydride, The electrode has a content of the modified polyolefin of 2 to 40 parts by weight based on 100 parts by weight of the binder.

2. 2. The electrode according to claim 1, wherein the content of the modified polyolefin is 3 to 40 parts by weight based on 100 parts by weight of the binder.

3. 2. The electrode according to claim 1, wherein the modified polyolefin has a melt index (MI) of 50 g / 10 min or less.

4. 2. The electrode according to claim 1, wherein the melting point of the modified polyolefin is 175°C or less.

5. The electrode of claim 1 , wherein the modified polyolefin comprises one or more of a modified polyethylene and a modified polypropylene.

6. the olefin of the modified polyolefin contains at least one of ethylene and propylene; 2. The electrode according to claim 1, wherein the functional group derived from a carboxylic acid anhydride is derived from maleic anhydride, glutaric anhydride, phthalic anhydride, trimellitic anhydride, pyromellitic monoanhydride, pyromellitic dianhydride, 1,8-naphthalenedicarboxylic anhydride, 2,3-naphthalenedicarboxylic anhydride, 1,4,5,8-naphthalenetetracarboxylic monoanhydride, 1,4,5,8-naphthalenetetracarboxylic dianhydride, 2,3,6,7-naphthalenetetracarboxylic monoanhydride, 2,3,6,7-naphthalenetetracarboxylic dianhydride, or a carboxylic acid anhydride including two or more of these.

7. The electrode of claim 1 , wherein the modified polyolefin is a modified polyethylene.

8. 2. The electrode of claim 1, wherein the modified polyolefin is one or more of polyethylene containing functional groups derived from maleic anhydride and polypropylene containing functional groups derived from maleic anhydride.

9. 2. The electrode according to claim 1, wherein the content of functional groups derived from carboxylic acid anhydrides in the modified polyolefin is 0.5 mol % to 20 mol %.

10. The electrode according to claim 1 , wherein the binder is fibrous to bind the active material and the conductive material.

11. The electrode according to claim 1 , wherein the active material is a positive electrode active material or a negative electrode active material.

12. 2. The electrode according to claim 1, wherein the content of the active material is 80 parts by weight to 98 parts by weight, the content of the conductive material is 0.5 parts by weight to 10 parts by weight, the content of the fluorine-based polymer is 0.5 parts by weight to 5 parts by weight, and the content of the modified polyolefin is 0.02 parts by weight to 3.3 parts by weight.

13. The electrode of claim 1 , wherein the electrode current collector does not include a conductive primer layer on at least one surface.

14. 10. The electrode of claim 1, wherein the electrode layer is derived from a dry electrode film.

15. preparing a mixture containing an active material, a conductive material, and a binder, the binder containing a fluorine-based polymer and a modified polyolefin, the fluorine-based polymer being polytetrafluoroethylene (PTFE); kneading the mixture at a temperature in the range of 70°C to 200°C under a pressure equal to or higher than atmospheric pressure to produce a mixture mass; pulverizing the mixture mass to obtain a mixed powder for an electrode; The electrode mixed powder is placed between a plurality of rolls and calendered to form an electrode film; The method for manufacturing an electrode according to claim 1 , further comprising the step of: laminating the electrode film onto a metal current collector.

16. The method for producing an electrode according to claim 15 , wherein the step of kneading to produce the mass of mixture is carried out in a kneader under a pressure equal to or higher than atmospheric pressure.

17. The method for producing an electrode according to claim 15 or 16, wherein the rolling ratio of the electrode film is 20% or less.

18. A secondary battery comprising a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode, wherein at least one of the positive electrode and the negative electrode is the electrode according to any one of claims 1 to 14.

19. An energy storage device comprising the secondary battery according to claim 18 as a unit battery.

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