Current collector, electrode and lithium secondary battery

Abstract

The present invention relates to a current collector, an electrode comprising same, and a secondary battery, the current collector comprising a primer layer that includes a conductive material, a binder and a thickener, wherein the conductive material is a multi-walled carbon nanotubes having a BET specific surface area of at least 170 m2 / g, and thus the present invention has excellent adhesion with an electrode active material layer, low interfacial resistance, and excellent scratch resistance.

Description

Current collector, electrode, and lithium secondary battery

[0001] Cross-citation with related applications

[0002] This application claims the benefit of priority from Korean Patent Application No. 10-2023-0174768, filed December 5, 2023, the entire contents of which are incorporated herein by reference.

[0003]

[0004] Technology field

[0005] The present invention relates to a current collector including a primer layer, an electrode including the same, and a lithium secondary battery.

[0006]

[0007] Recently, as the application areas of lithium secondary batteries have rapidly expanded to include not only power supply for electronic devices such as electric, electronic, communication, and computer devices, but also power storage for large-area devices such as automobiles and power storage devices, the demand for lithium secondary batteries with high capacity, high output, and high stability is increasing.

[0008] Lithium secondary batteries are generally manufactured by applying a slurry containing a positive electrode active material capable of inserting and de-inserting lithium ions, or a negative electrode active material capable of absorbing and releasing lithium ions, and optionally a binder and a conductive material, to a positive electrode current collector and a negative electrode current collector, respectively, and removing the solvent using heat, etc., and then laminating these on both sides of a separator to form an electrode current collector of a predetermined shape, and then inserting this electrode current collector and a non-aqueous electrolyte into a battery case. However, when manufacturing the positive and negative electrodes in this way, there is a problem that the solvent contained in the slurry needs to be removed through an additional process, which increases the cost of the manufacturing process and lowers productivity. Therefore, a dry manufacturing method has been proposed in which each active material is positioned in the form of a film on a current collector and passed through a rolling roll.

[0009] Meanwhile, electrodes manufactured by a dry manufacturing method that coats electrode active materials on a current collector without a solvent have a problem in that the electrode active material layer is detached from the current collector due to shrinkage and expansion of the electrode that occurs during charging and discharging of the secondary battery, because the adhesive strength between the current collector and the electrode active material layer is weak. Therefore, a method of providing a primer layer on the surface of the current collector that can strengthen the adhesive strength between the current collector and the electrode active material layer has been proposed.

[0010] The above primer layer is typically composed of a binder and a conductive agent. The binder melts during high-temperature rolling to ensure adhesion, while the conductive agent can play a role in reducing interfacial resistance with the electrode active material layer. However, conventional primer layers composed solely of a binder and a conductive agent have poor scratch resistance, leading to the problem of easy scratching during rolling. Therefore, there is a need to develop a current collector coated with a primer layer that exhibits excellent adhesive strength, low interfacial resistance, and excellent scratch resistance.

[0011]

[0012] The present invention has been devised to solve the problems of the above-mentioned prior art, and aims to provide a current collector having excellent scratch resistance along with excellent adhesive strength and low interfacial resistance characteristics.

[0013] In addition, the present invention aims to provide an electrode having an electrode active material layer on the current collector.

[0014] In addition, the present invention aims to provide a lithium secondary battery including the above electrode.

[0015]

[0016] To solve the above problems, the present invention provides a separator and an electrochemical cell including the same.

[0017] (1) The present invention comprises a metal layer and a primer layer coated on at least one surface of the metal layer, wherein the primer layer comprises a conductive material, a binder, and a thickener, and the conductive material has a BET specific surface area of ​​170 m 2 / g or more, and a current collector is provided in which the weight ratio of the conductive material and the binder is 1:1 or more and 10 or less.

[0018] (2) The present invention provides a current collector in which, in the above (1), the content of the thickener is 5 parts by weight or more and 20 parts by weight or less, based on 100 parts by weight of the total weight of the conductive material, binder, and thickener.

[0019] (3) The present invention provides a current collector in which, in the above (1) or (2), the content of the conductive material is 10 parts by weight or more and 50 parts by weight or less, based on 100 parts by weight of the total weight of the conductive material, binder, and thickener.

[0020] (4) The present invention provides a current collector in which the content of the binder is 35 parts by weight or more and 75 parts by weight or less, based on 100 parts by weight of the total weight of the conductive material, binder, and thickener in any one of the above (1) to (3).

[0021] (5) The present invention provides a current collector according to any one of the above (1) to (4), wherein the binder is at least one selected from the group consisting of polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, hydrogenated nitrile butadiene rubber, styrene butadiene rubber, polyacrylonitrile, polymethyl methacrylate, polyethylene, tetrafluoroethylene, and polyacrylic acid.

[0022] (6) The present invention provides a collector according to any one of the above (1) to (5), wherein the thickener is at least one selected from the group consisting of carboxymethylcellulose, polyvinylpyrrolidone, and polyvinyl alcohol.

[0023] (7) The present invention provides a current collector in any one of the above (1) to (6), wherein the thickness of the primer layer is 0.2 ㎛ or more and 2 ㎛ or less.

[0024] (8) The present invention provides a collector having a surface roughness of the primer layer of any one of (1) to (7) above of 1.1 ㎛ or less.

[0025] (9) The present invention provides an electrode comprising a current collector and an electrode active material layer of any one of (1) to (8), wherein the electrode active material layer is attached on a primer layer of the current collector.

[0026] (10) The present invention provides an electrode in which, in the above (9), the adhesive strength between the electrode active material layer and the primer layer, measured at a peeling speed of 100 mm / min in a 90° peel test, is 40 gf / 2cm or more.

[0027] (11) The present invention, in the above (9) or (10), has an interface resistance between the electrode active material layer and the current collector of 0.6 Ω·cm. 2 An electrode is provided as follows.

[0028] (12) The present invention provides a lithium secondary battery including any one of the electrodes (9) to (11).

[0029]

[0030] The current collector of the present invention comprises a conductive material, a binder and a thickener, and the conductive material has a BET specific surface area of ​​170 m 2 By including a primer layer containing multi-walled carbon nanotubes having a mass of / g or more, it has excellent adhesion to the electrode active material layer, low interfacial resistance, and excellent scratch resistance.

[0031] In addition, the electrode of the present invention can exhibit excellent battery characteristics by having an electrode active material layer attached on the primer layer of the current collector, thereby having excellent adhesive strength and low interfacial resistance.

[0032] In addition, the lithium secondary battery of the present invention includes the electrode, thereby preventing the problem of the electrode active material layer being peeled off during charging and discharging, and thus enabling the secondary battery to be operated stably.

[0033]

[0034] Figure 1 is a scanning electron microscope (SEM) photograph of the primer layer of the collector manufactured in Example 1 of the present invention.

[0035] Figure 2 is a scanning electron microscope (SEM) photograph of the primer layer of the collector manufactured in Comparative Example 3 of the present invention.

[0036] Figure 3 is a photograph of the collectors manufactured in Example 1 and Comparative Example 3 of the present invention after a friction test in a scratch resistance evaluation. The collector on the left is the collector of Comparative Example 3, and the collector on the right is the collector of Example 1.

[0037]

[0038] Hereinafter, the present invention will be described in more detail to help understand the present invention.

[0039] The terms and words used in this specification should not be interpreted as limited to their usual or dictionary meanings, but should be interpreted as meanings and concepts that conform to the technical idea of ​​the present invention, based on the principle that the inventor can appropriately define the concept of the term to explain his or her own invention in the best way.

[0040] The terms used herein are for the purpose of describing exemplary embodiments only and are not intended to limit the present invention. Singular expressions include plural expressions unless the context clearly dictates otherwise.

[0041] In this specification, it should be understood that the terms “include,” “comprising,” or “having” are intended to specify the presence of a feature, number, step, component, or combination thereof, but do not preclude the possibility of the presence or addition of one or more other features, numbers, steps, components, or combinations thereof.

[0042]

[0043] Whole house

[0044] The present invention provides a current collector in which a primer layer is coated on at least one surface of a metal layer.

[0045] According to one embodiment of the present invention, the current collector includes a metal layer and a primer layer coated on at least one surface of the metal layer, the primer layer includes a conductive material, a binder, and a thickener, and the conductive material has a BET specific surface area of ​​170 m 2 / g or more multi-walled carbon nanotubes, and the weight ratio of the conductive material and the binder may be 1:1 or more and 10 or less.

[0046] The above current collector may have the primer layer coated on at least one surface of the metal layer, and for example, the primer layer may be coated on both surfaces of the metal layer. In addition, the metal layer may be copper, stainless steel, aluminum, nickel, titanium, sintered carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, or the like, or may include an aluminum-cadmium alloy, and for example, may be at least one selected from the group consisting of aluminum foil, aluminum mesh, stainless steel foil, and copper foil.

[0047] The primer layer of the current collector may have significantly high peeling resistance and low interfacial resistance by including multi-walled carbon nanotubes as a conductive material. Specifically, the multi-walled carbon nanotubes have higher strength than conductive materials such as carbon black, and thus can significantly improve the peeling resistance of the primer layer. As a result, the primer layer including the multi-walled carbon nanotubes can have excellent scratch resistance. In addition, the multi-walled carbon nanotubes have excellent electrical conductivity, and thus can also reduce the interfacial resistance of the current collector.

[0048] In addition, the multi-walled carbon nanotube has a specific surface area of ​​170 m 2 / g or more, and specifically, the specific surface area of ​​the multi-walled carbon nanotube is 170 m 2 / g or more, 180 m 2 / g or more, 190 m 2 / g or more, 200 m 2 / g or more, 210 m 2 / g or more, 220 m 2 / g or more, or 230 m 2 / g or more, and also, 300 m 2 / g or less, 290 m 2 / g or less, 280 m 2 / g or less, 270 m 2 / g or less, 260 m 2 / g or less, or 250 m 2 / g or less. When the specific surface area of ​​the multi-walled carbon nanotube satisfies the above range, the dispersibility of the multi-walled carbon nanotube, which is a conductive material, can be excellent, and since the conductive material is evenly distributed within the primer layer and strongly bonds with the binder, the adhesive strength and peeling resistance of the primer layer can be significantly improved.

[0049] In addition, the multi-walled carbon nanotube may have an average diameter of 5 nm or more and 20 nm or less, and specifically, the average diameter may be 5 nm or more, 6 nm or more, 7 nm or more, 8 nm or more, 9 nm or more, or 10 nm or more, and may also be 20 nm or less, 19 nm or less, 18 nm or less, 17 nm or less, 16 nm or less, or 15 nm or less.

[0050] Conventionally, a primer layer composed only of a conductive material and a binder has poor peeling resistance due to weak bonding between the conductive material and the binder, resulting in a problem of layer separation between the conductive material and the binder due to friction. Therefore, the primer layer of the current collector of the present invention includes a thickener, so that the binder and the conductive material can be strongly bonded to each other by the thickener, and as a result, layer separation between the conductive material and the binder is suppressed, so that the peeling resistance of the primer layer and the adhesion to the electrode active material layer are excellent, and the interfacial resistance can also be low.

[0051] In addition, the weight ratio of the conductive material and the binder in the primer layer may be 1:1 or more and 10 or less, specifically 1:1 or more, 1:2 or more, 1:3 or more, 1:4 or more, or 1:5 or more, and also 1:10 or less, 1:9 or less, 1:8 or less, 1:7 or less, 1:6 or less, or 1:5 or less. When the weight ratio of the conductive material and the binder in the primer layer satisfies the above range, an appropriate electron transfer path can be introduced into the primer layer, and the adhesive strength between the primer layer and the electrode active material layer can be excellent. On the other hand, when the content of the conductive material in the primer layer is relatively high and the weight ratio of the conductive material and the binder exceeds 1:10, the electron movement path is reduced due to the decrease in the conductive material in the primer layer, and at the same time, the content of the binder that impedes the flow of electrons is relatively increased, so that the interfacial resistance of the current collector may increase. In addition, when the content of the conductive material in the primer layer is relatively reduced and the weight ratio of the conductive material and the binder is less than 1:1, the adhesive ability of the primer layer is significantly reduced as the amount of binder is relatively decreased, so that the primer layer may lose its function as a primer layer that improves the adhesive strength with the active material layer.

[0052]

[0053] According to one embodiment of the present invention, with respect to the total weight of 100 parts by weight of the conductive material, the binder, and the thickener, the content of the thickener may be 5 parts by weight or more and 20 parts by weight or less, and specifically, the content of the thickener may be 5 parts by weight or more, 6 parts by weight or more, 7 parts by weight or more, 8 parts by weight or more, 9 parts by weight or more, 10 parts by weight or more, or 11 parts by weight or more, and may also be 20 parts by weight or less, 19 parts by weight or less, 18 parts by weight or less, 17 parts by weight or less, 16 parts by weight or less, or 15 parts by weight or less. When the content of the thickener in the primer layer satisfies the above range, the thickener is sufficiently present in the primer layer, so that the conductive material and the binder can be more strongly bonded by the thickener. In addition, since the conductive material and the binder are sufficiently present in the primer layer, compared to when the thickener is excessively large, the primer layer can also have excellent adhesion to the electrode active material layer.

[0054]

[0055] According to one embodiment of the present invention, with respect to 100 parts by weight of the total weight of the conductive material, the binder, and the thickener, the content of the conductive material may be 10 parts by weight or more and 50 parts by weight or less, and specifically, the content of the conductive material may be 10 parts by weight or more, 15 parts by weight or more, 20 parts by weight or more, 25 parts by weight or more, 30 parts by weight or more, or 35 parts by weight or more, and may also be 50 parts by weight or less, 45 parts by weight or less, 40 parts by weight or less, 35 parts by weight or less, 30 parts by weight or less, or 25 parts by weight or less. When the content of the conductive material in the primer layer satisfies the above range, since there is sufficient conductive material capable of bonding with the binder in the primer layer, the adhesive strength of the primer layer may be high and the interface resistance may be low. In addition, since the current collector sufficiently contains a conductive material having high electrical conductivity, an appropriate electron movement path can be introduced to the primer layer, and the battery performance of the electrode including the current collector can be improved.

[0056]

[0057] According to one embodiment of the present invention, with respect to 100 parts by weight of the total weight of the conductive material, the binder, and the thickener, the content of the binder may be 35 parts by weight or more and 75 parts by weight or less, and specifically, the content of the binder may be 35 parts by weight or more, 40 parts by weight or more, 45 parts by weight or more, 50 parts by weight or more, or 55 parts by weight or more, and may also be 75 parts by weight or less, 70 parts by weight or less, 65 parts by weight or less, 60 parts by weight or less, or 55 parts by weight or less. When the content of the binder in the primer layer satisfies the above range, the adhesive strength of the primer layer is improved due to the high binder content, so that the current collector can be more strongly adhered to the electrode active material layer.

[0058]

[0059] According to one embodiment of the present invention, the binder may be at least one selected from the group consisting of polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, hydrogenated nitrile butadiene rubber, styrene butadiene rubber, polyacrylonitrile, polymethyl methacrylate, polyethylene, tetrafluoroethylene, and polyacrylic acid, and specifically, may be polyvinylidene fluoride, hydrogenated nitrile butadiene rubber, or styrene butadiene rubber. The binder has excellent dispersibility for multi-walled carbon nanotubes and adhesion to a current collector, and thus can improve the adhesion of a primer layer including the binder.

[0060]

[0061] According to one embodiment of the present invention, the thickener may be at least one selected from the group consisting of carboxymethylcellulose, polyvinylpyrrolidone, and polyvinyl alcohol, and specifically, may be carboxymethylcellulose. Since the thickener has excellent dispersibility for multi-walled carbon nanotubes, the conductive material and the binder can be more strongly bonded, and the primer layer including the thickener has improved adhesive strength and peeling resistance, so that it can have excellent scratch resistance and adhesive strength to the electrode active material layer, and low interfacial resistance.

[0062]

[0063] According to one embodiment of the present invention, the thickness of the primer layer may be 0.2 ㎛ or more and 2 ㎛ or less, and specifically, the thickness of the primer layer may be 0.2 ㎛ or more, 0.3 ㎛ or more, 0.4 ㎛ or more, 0.5 ㎛ or more, 0.6 ㎛ or more, 0.7 ㎛ or more, 0.8 ㎛ or more, 0.9 ㎛ or more, or 1 ㎛ or more, and also 2 ㎛ or less, 1.9 ㎛ or less, 1.8 ㎛ or less, 1.7 ㎛ or less, 1.6 ㎛ or less, 1.5 ㎛ or less, 1.4 ㎛ or less, 1.3 ㎛ or less, 1.2 ㎛ or less, 1.1 ㎛ or less, 1 ㎛ or less, 0.9 ㎛ or less, 0.8 ㎛ or less, 0.7 ㎛ or less, or 0.6 ㎛ or less. When the thickness of the primer layer satisfies the above range, sufficient adhesive strength between the primer layer and the electrode active material layer can be achieved compared to when the thickness of the primer layer is excessively thin, scratch resistance can be excellent, and the interface resistance can be lower compared to when the thickness of the primer layer is excessively thick.

[0064]

[0065] According to one embodiment of the present invention, the surface roughness (Ra) of the primer layer may be 1.1 ㎛ or less, specifically 1.1 ㎛ or less, 1 ㎛ or less, 0.9 ㎛ or less, or 0.8 ㎛ or less, and further may be 0.1 ㎛ or more, 0.2 ㎛ or more, 0.3 ㎛ or more, 0.4 ㎛ or more, 0.5 ㎛ or more, 0.6 ㎛ or more, or 0.7 ㎛ or more. The surface roughness of the primer layer refers to the surface roughness of one side of the primer layer that is not in contact with the metal layer, and when the surface roughness of the primer layer satisfies the above range, the adhesion of the primer layer to the electrode active material layer may be excellent.

[0066]

[0067] electrode

[0068] The present invention provides an electrode including the above-described collector.

[0069] According to one embodiment of the present invention, the current collector and the electrode active material layer are included, and the electrode active material layer may be attached on a primer layer of the current collector. For example, when a primer layer is coated on both sides of an aluminum metal layer of the current collector, the electrode active material layer may also be attached on both sides of the current collector, and specifically, may be attached on the primer layer.

[0070] Specifically, the electrode active material layer may be a positive electrode active material layer including a positive electrode active material, and the positive electrode active material may be LiCoO2, LiCoPO4, LiNiO2, Li x Ni a Co b M 1 c M 2 d O2(M 1 and M 2is independently one kind selected from the group consisting of Al, Mn, Cu, Fe, V, Cr, Mo, Ga, B, W, Mo, Nb, Mg, Hf, Ta, La, Ti, Sr, Ba, Ce, F, P, S and Y, and 0.9≤x≤1.1, 0 <a<1.0, 0<b<1.0, 0≤c<0.5, 0≤d<0.5, a+b+c+d=1이다.), LiMnO2, LiMnO3, LiMn2O3, LiMn2O4, LiMn 2-e M 3 e O2(M 3 is at least one selected from the group consisting of Co, Ni, Fe, Cr, Zn and Ta, and 0.01≤e≤0.1), Li2Mn3M 4 O8(M 4 is at least one selected from the group consisting of Ci, Ni, Fe, Cu and Zn), LiFePO4, Li2CuO2, LiV3O8, V2O5, Cu2V2O7 and lithium metal. The electrode active material layer may include lithium iron phosphate oxide, and the lithium iron phosphate oxide may be LiFePO4.

[0071] Meanwhile, the electrode active material layer may be an anode active material layer including an anode active material, and a compound capable of reversible intercalation and deintercalation of lithium may be used as the anode active material. Specifically, the anode active material may include a carbonaceous material such as artificial graphite, natural graphite, graphitized carbon fiber, or amorphous carbon; a metallic compound capable of alloying with lithium such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, a Si alloy, a Sn alloy, or an Al alloy; a metal oxide capable of doping and dedoping lithium such as SiOβ (0<β<2), SnO2, vanadium oxide, or lithium vanadium oxide; or a composite including the metallic compound and a carbonaceous material such as a Si-C composite or a Sn-C composite, and any one or a mixture of two or more thereof may be used. In addition, a metallic lithium thin film may be used as the anode active material. In addition, both low-crystalline carbon and high-crystalline carbon can be used as carbon materials. Representative examples of low-crystalline carbon include soft carbon and hard carbon, and representative examples of high-crystalline carbon include amorphous, plate-like, flaky, spherical or fibrous natural or artificial graphite, Kish graphite, pyrolytic carbon, mesophase pitch-based carbon fiber, meso-carbon microbeads, mesophase pitches, and high-temperature calcined carbon such as petroleum or coal tar pitch derived cokes. The negative electrode active material may be included in an amount of 80 to 99 wt% based on the total weight of the negative electrode active material layer.

[0072]

[0073] Since the electrode of the present invention includes the current collector, the electrode active material layer is strongly adhered to the primer layer of the current collector, and thus, when applied to a secondary battery, the long-term stability of the secondary battery can be improved. In addition, since the interfacial resistance of the electrode active material layer and the primer layer is low, when applied to a secondary battery, the battery characteristics of the secondary battery can also be excellent.

[0074]

[0075] According to one embodiment of the present invention, the electrode may have an adhesive strength between the electrode active material layer and the primer layer of 40 gf / 2cm or more, as measured at a peeling speed of 100 mm / min in a 90° peel test, and specifically, the adhesive strength may be 40 gf / 2cm or more, 50 gf / 2cm or more, or 60 gf / 2cm or more. The electrode of the present invention, in which the adhesive strength between the electrode active material layer and the primer layer as measured in the 90° peel test satisfies the above range, has an advantage in that the electrode active material layer and the primer layer can be strongly adhered to each other, and as a result, when applied to a secondary battery, detachment between the current collector and the electrode active material layer is suppressed, so that the battery can be stably operated.

[0076]

[0077] According to one embodiment of the present invention, the electrode has an interface resistance between the electrode active material layer and the current collector of 0.6 Ω·cm. 2 It may be less than or equal to, and specifically, the interface resistance is 0.6 Ω·cm 2 Below, 0.55 Ω·cm 2 Below 0.5 Ω·cm 2 Below, 0.45 Ω·cm 2 Below, 0.4 Ω·cm 2 Below, 0.35 Ω·cm 2 or less, or 0.3 Ω·cm 2 The electrode of the present invention, in which the interfacial resistance between the electrode active material layer and the current collector satisfies the above range, may have excellent electrode characteristics due to low interfacial resistance.

[0078]

[0079] Meanwhile, according to one embodiment of the present invention, the electrode may be manufactured by a commonly known wet electrode manufacturing method or a dry electrode manufacturing method. Specifically, the dry electrode manufacturing method may be manufactured by positioning and rolling a dry electrode film for forming an electrode active material layer on a current collector. At this time, the film for forming the electrode active material layer does not contain a solvent, and may further include a conductive material and a binder together with the electrode active material, and may further include a dispersant, an additive, an aqueous binder, etc., as needed. In addition, the film used in the dry electrode manufacturing method that does not contain such a solvent is called a free-standing dry electrode film, and such a free-standing dry electrode film can be manufactured by a commonly known method as described in International Publication Nos. WO2019 / 103874 and WO2019 / 191397.

[0080] Here, the dry electrode film means an electrode film manufactured by a dry manufacturing method without using a solvent, unlike a wet electrode film, and does not contain a detectable processing solvent, residue of the processing solvent, or impurities of the processing solvent, and the dry manufacturing method means a process that does not use or substantially use a solvent in the manufacturing of the electrode film, that is, a process that manufactures the electrode film in the form of a film using a mixture of a dry electrode active material and a dry binder, rather than manufacturing it as a slurry using a solvent.

[0081]

[0082] lithium secondary battery

[0083] The present invention provides a lithium secondary battery including the above electrode.

[0084] According to one embodiment of the present invention, the lithium secondary battery may include the electrode. Since the secondary battery includes the electrode of the present invention in which the current collector and the electrode active material layer are strongly bonded, the problem of detachment of the electrode active material layer and the current collector is suppressed even during long-term operation of the secondary battery, thereby improving the long-term stability of the secondary battery.

[0085] The lithium secondary battery of the present invention may be a lithium ion battery comprising a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte, or an all-solid-state battery comprising a positive electrode, a negative electrode, and a solid electrolyte present between the positive electrode and the negative electrode, and at least one of the positive electrode and the negative electrode may be the electrode of the present invention, and specifically, the positive electrode may be the electrode of the present invention.

[0086] In addition, the lithium secondary battery may optionally further include a battery container that houses the electrode assembly of the positive electrode, the negative electrode, and the separator, and a sealing member that seals the battery container.

[0087] Meanwhile, when the positive electrode is the electrode of the present invention, the negative electrode may include a negative electrode current collector and a negative electrode active material layer positioned on the negative electrode current collector. The negative electrode current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery, and for example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., aluminum-cadmium alloy, etc. may be used. In addition, the negative electrode current collector may typically have a thickness of 3 to 500 ㎛, and like the positive electrode current collector, fine unevenness may be formed on the surface of the current collector to strengthen the bonding strength of the negative electrode active material. For example, various forms such as a film, a sheet, a foil, a net, a porous body, a foam, and a non-woven fabric may be used as the negative electrode current collector.

[0088] The above-described negative electrode active material layer may optionally include a binder and a conductive material together with the above-described negative electrode active material.

[0089] The binder of the negative electrode active material layer is a component that assists in bonding between the conductive material, the active material, and the current collector, and may typically be added in an amount of 0.1 to 10 wt% based on the total weight of the negative electrode active material layer. Examples of the binder include polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose, starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer, sulfonated-ethylene-propylene-diene polymer, styrene-butadiene rubber, nitrile-butadiene rubber, fluororubber, and various copolymers thereof.

[0090] The conductive material of the above-described negative electrode active material layer is a component for further improving the conductivity of the negative electrode active material, and may be added in an amount of 10 wt% or less, preferably 5 wt% or less, based on the total weight of the negative electrode active material layer. The conductive material is not particularly limited as long as it has conductivity without causing a chemical change in the battery, and examples thereof include graphite such as natural graphite or artificial graphite; carbon black such as acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermal black; conductive fibers such as carbon fiber or metal fiber; fluorinated carbon; metal powder such as aluminum or nickel powder; conductive whiskers such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives.

[0091] The above negative electrode can be manufactured by applying and drying a composition for forming a negative electrode active material layer, which is prepared by dissolving or dispersing a negative electrode active material, and optionally a binder and a conductive material in a solvent, on a negative electrode current collector, or by casting the composition for forming a negative electrode active material layer on a separate support, and then laminating the resulting film on a negative electrode current collector by peeling it off from the support. As another example, the above negative electrode can be manufactured through the conventional dry electrode manufacturing method described above.

[0092] The above separator separates the negative electrode and the positive electrode and provides a passage for lithium ions to move. Any separator commonly used in lithium secondary batteries can be used without any particular restrictions, and in particular, one having low resistance to ion movement of the electrolyte and excellent electrolyte moisture retention capacity is preferable. Specifically, a porous polymer film, for example, a porous polymer film made of a polyolefin polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, and an ethylene / methacrylate copolymer, or a laminated structure of two or more layers thereof, may be used. In addition, a conventional porous nonwoven fabric, for example, a nonwoven fabric made of high-melting-point glass fiber, polyethylene terephthalate fiber, etc. may also be used. In addition, a coated separator containing a ceramic component or a polymer material to secure heat resistance or mechanical strength may be used, and may optionally be used in a single-layer or multi-layer structure.

[0093] Examples of the electrolyte include, but are not limited to, organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used in the manufacture of lithium secondary batteries. As a specific example, the electrolyte may include an organic solvent and a lithium salt.

[0094] The organic solvent may be used without any particular limitation as long as it can serve as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, the organic solvent may include ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether solvents such as dibutyl ether or tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic hydrocarbon solvents such as benzene and fluorobenzene; Carbonate solvents such as dimethylcarbonate (DMC), diethylcarbonate (DEC), methylethylcarbonate (MEC), ethylmethylcarbonate (EMC), ethylenecarbonate (EC), and propylene carbonate (PC); alcohol solvents such as ethyl alcohol and isopropyl alcohol; nitriles such as R-CN (where R is a linear, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms and may include a double-bonded aromatic ring or an ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; or sulfolanes can be used. Among these, a carbonate solvent is preferable, and a mixture of a cyclic carbonate (e.g., ethylene carbonate or propylene carbonate, etc.) having high ionic conductivity and high dielectric constant that can improve the charge / discharge performance of the battery and a linear carbonate compound having low viscosity (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate, etc.) is more preferable.

[0095] The above lithium salt can be used without any special limitation as long as it is a compound that can provide lithium ions used in a lithium secondary battery. Specifically, the anion of the above lithium salt is F - , Cl - , Br - , I - , NO3 - , N(CN)2 - , BF4 - , CF3CF2SO3 - , (CF3SO2)2N - , (FSO2)2N - , CF3CF2(CF3)2CO - , (CF3SO2)2CH - , (SF5)3C - , (CF3SO2)3C - , CF3(CF2)7SO3 - , CF3CO2 - , CH3CO2 - , SCN - and (CF3CF2SO2)2N - At least one selected from the group consisting of may be used, and the lithium salt may be LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAl04, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, or LiB(C2O4)2. It is preferable to use the concentration of the lithium salt within the range of 0.1 to 2.0 M. When the concentration of the lithium salt is within the above range, the electrolyte can exhibit excellent electrolyte performance because it has appropriate conductivity and viscosity, and lithium ions can move effectively.

[0096] In addition to the electrolyte components, the electrolyte may also contain, for example, vinylene carbonate (VC), vinyl ethylene carbonate (VEC), fluoro ethylene carbonate (FEC), propane sultone (PS), 1,3-propane sultone (PRS), ethylene sulfate (Esa), succinonitrile (SN), adiponitrile (AN), hexane tricarbonitrile (HTCN), γ-butyrolactone, biphenyl (BP), cyclohexyl benzene (CHB), t-amyl ester, etc. for the purpose of improving the life characteristics of the battery, suppressing the decrease in battery capacity, and improving the discharge capacity of the battery. One or more additives selected from the group consisting of tert-amyl benzene (TAB), haloalkylene carbonate compounds such as difluoroethylene carbonate, pyridine, triethylphosphite, triethanolamine, cyclic ethers, ethylene diamine, n-glyme, hexaphosphoric acid triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride may be further included. At this time, the additives may be included in an amount of 0.1 to 5 wt% based on the total weight of the electrolyte.

[0097]

[0098] A lithium secondary battery including the electrode of the present invention stably exhibits excellent capacity characteristics, output characteristics, and life characteristics, and is therefore useful in portable devices such as mobile phones, laptop computers, and digital cameras, and electric vehicles such as hybrid electric vehicles (HEVs) and electric vehicles (EVs).

[0099] There is no particular limitation on the external shape of the lithium secondary battery of the present invention, but it may be a cylindrical shape using a can, a square shape, a pouch shape, or a coin shape.

[0100] The lithium secondary battery according to the present invention can be used not only as a battery cell used as a power source for a small device, but can also be preferably used as a unit battery in a medium- to large-sized battery module including a plurality of battery cells. Accordingly, a battery module including the lithium secondary battery as a unit cell and a battery pack including the same can be provided. The battery module or battery pack can be used as a power source for any one or more medium- to large-sized devices selected from the group consisting of a power tool; an electric vehicle (EV), a hybrid electric vehicle, and a plug-in hybrid electric vehicle (PHEV); or a power storage system.

[0101]

[0102] Hereinafter, embodiments of the present invention will be described in detail so that those skilled in the art can easily implement them. However, the present invention may be implemented in various different forms and is not limited to the embodiments described herein.

[0103]

[0104] Example

[0105] Example 1

[0106]

[0107] *(1) Manufacturing of the entire body

[0108] Multi-walled carbon nanotubes (LG Chem, product name: BT1004M, BET=180 m) as a challenge material 2 / g, average diameter 13 nm) was dispersed in water to a concentration of 4 wt%, and polyvinylidene fluoride (Solvey, product name: Solef 2042) as a binder was added to the solution in which the conductive material was dispersed in an amount twice the weight of the conductive material. Next, a carboxymethylcellulose solution dispersed in water to a concentration of 1.5 wt% was added as a thickener so that the weight of the carboxymethylcellulose was 0.4 times the weight of the conductive material, thereby preparing an aqueous slurry for forming a primer layer with a solid content of 7%.

[0109] Next, the aqueous slurry for forming the primer layer was applied to one side of an aluminum foil having a thickness of 20 μm using a bar coater, and dried at 100°C for 2 minutes to manufacture a current collector having a primer layer having a thickness of 0.5 μm coated on each side of the aluminum foil.

[0110]

[0111] (2) Manufacturing of the anode

[0112] Afterwards, an LFP film was laminated on each of the primer layers on both sides of the current collector so that it was in contact with the primer layer, and then rolled at room temperature and vacuum-dried at 170°C for 10 hours to manufacture a positive electrode having a positive electrode active material layer attached to one side of the current collector.

[0113]

[0114] Examples 2 to 7 and Comparative Examples 1 to 5

[0115] In Example 1, the current collectors and positive electrodes of Examples 2 to 7 and Comparative Examples 1, 2, 4 and 5 were manufactured in the same manner as in Example 1, except that the contents of multi-walled carbon nanotubes, polyvinylidene fluoride and carboxymethylcellulose were changed as shown in Table 1 below.

[0116] In Example 1, instead of multi-walled carbon nanotubes, carbon black (Denka Co., Ltd., product name: Li250, BET=60 m) was used. 2 / g) was dispersed in water to a concentration of 20 wt% to prepare an aqueous slurry for forming a primer layer, and the current collector and positive electrode of Comparative Example 3 were manufactured in the same manner as in Example 1, except that the aqueous slurry for forming a primer layer was prepared.

[0117]

[0118] Classification Implementation Preliminary Comparative Example 123456712345 Primer layer thickness (㎛) 0.5 ... 1) MWCNT 1) MWCNT 1) MWCNT 1) MWCNT 1) MWCNT 1) MWCNT 1) MWCNT 1) MWNCT 1) CB 2) MWCNT 1) MWCNT 1) Content (parts by weight)Challenge agent29.2739.2714.2524.2731.4228.1726.5529.274.24.29.2732.1825.13Binder59.1449.1474.1659.1463.4856.9353.6570.7384.1759.1465.0250.78Thickener11.5911.5911.5916.595.114.919.8011.5911.592.824.1

[0119] 1) MWCNT: Multi-walled carbon nanotube 2) CB: Carbon black

[0120] Experimental example

[0121] Experimental Example 1: Scratch resistance evaluation and surface roughness measurement

[0122] For the entire body of the examples and comparative examples, scratch resistance was evaluated and surface roughness was measured.

[0123]

[0124] (1) Scratch resistance evaluation

[0125] For the collectors manufactured in the examples and comparative examples, scratch resistance was evaluated, and the results are shown in Table 2 below.

[0126]

[0127] Aluminum foil coated with a primer layer was punched into 3 cm X 20 cm (width X height) to prepare a current collector specimen. After wrapping the ball of an abrasion friction tester (Ocean Science, product name: COAD.105) with a wiper (Kimtech Science), a 300 gf weight was placed on it, and the surface of the current collector specimen coated with a primer layer was rubbed back and forth three times in the vertical direction in a 10 cm section at a speed of 27 cpm (cycles per minute), and then the surface area of ​​the exposed aluminum foil was measured. The surface area of ​​the exposed aluminum foil can be measured by a method of quantifying color information using RGB color space or HSV color space, and the surface area was measured specifically in the following manner.

[0128] An image was obtained from the center of the specimen on which the wear and friction test was performed using a 5x magnification lens of an Optical Microscope (Olympus, product name: BX51), and then the color information of each pixel of the obtained image was quantified using the RGB color space. The color range of the metal layer of the aluminum foil to be measured was defined, and a binary image was created in which pixels belonging to this color range were marked in white and other areas were marked in black. Then, the number of areas marked in white was A, the total number of areas marked in white and black was B, and the K value was calculated by applying this to the following equation (1). The lower the K value, the better the scratch resistance of the current collector.

[0129] (1) K=A / BΥ100

[0130] In the above equation (1), A is the surface area of ​​the metal layer exposed as a result of rubbing the surface of a primer layer having a width of 3 cm, a length of 20 cm, and a thickness of 0.5 ㎛ three times in a 10 cm section in the vertical direction at a force of 300 gf, a speed of 27 cpm, using a wear friction tester (Ocean Science, product name: COAD.105), and B is the surface area of ​​the primer layer, and A and B are measured by a method of quantifying color information using the RGB color space.

[0131]

[0132] (2) Surface roughness measurement

[0133] For the collectors manufactured in the examples and comparative examples, the surface roughness of the primer layer was measured.

[0134]

[0135] Using a shape measurement laser microscope (KEYENCE, product name: VK-X100K), laser scanning was performed in Auto measure mode with a focus on the surface of the primer layer of each collector manufactured in the examples and comparative examples at a magnification of 10 to 50.

[0136] After selecting the JIS B0601:2001 standard for all areas, the surface roughness (Ra) of the entire primer layer was measured, and 3 points were measured by moving 1 mm at a time, and the average value of the surface roughness was obtained as follows.

[0137]

[0138] Classification Preliminary Comparison Example 1 2 3 4 5 6 7 1 2 3 4 5 K Value 1.8 3.9 0.5 1.6 3.8 0.8 2.5 8 5.3 0.3 9 3.1 9.7 4.2 Surface Roughness (㎛) 0.96 1.1 0.7 2 0.8 8 0.8 5 0.9 9 0.9 8 1.3 3 0.6 9 1.1 7 0.8 1 1.0 7

[0139] As shown in Table 2 above, the current collectors of the examples all showed small K values ​​of less than 5, which confirms that the current collectors of the examples have considerably excellent scratch resistance. On the other hand, the current collector of Comparative Example 1, which does not include a thickener in the primer layer, and the current collector of Comparative Example 3, which uses carbon black as a conductive material, both showed poor scratch resistance with K values ​​exceeding 80. Meanwhile, the current collectors of the examples all showed surface roughness of the primer layer of 1.1 or less, which indicates that the low surface roughness will result in excellent adhesion to the positive electrode active material layer.

[0140]

[0141] Experimental Example 2: Evaluation of Adhesion and Interface Resistance

[0142]

[0143] For the positive electrodes manufactured in the examples and comparative examples, the adhesion and interfacial resistance between the current collector and the positive electrode active material layer were measured, and the results are shown in Table 3 below.

[0144]

[0145] (1) Adhesion measurement according to 90° peel test

[0146] Adhesion was measured using a Texture Analyzer (TA Analyzer, Lloyd). The measurement mode was set to 90° peel test reciprocating mode, the moving speed during measurement was set to 100 mm / min, the measuring length was set to 50 mm, and the returning speed to the original position after measurement was set to 300 mm / min.

[0147] Each anode was punched out to 2 cm X 10 cm (width X length) to prepare a specimen. Glass was used as a base plate (2.5 cm X 7.5 cm X 1 mm) (width X length X thickness), and double-sided tape (3M) was attached to the glass. The short side of the specimen was positioned so that it matched the end of the short side of the glass substrate, and one side of the specimen was adhered to the double-sided tape. At this time, the specimen attached to the other short side of the glass substrate was prepared by separating it by about 5 mm, and the glass side of the glass substrate to which the specimen was not attached was fixed to the TA specimen stage so that it faced the floor, and one end of the specimen that was not attached to the double-sided tape was fixed to the TA specimen holder so that it was perpendicular to the glass substrate. When measuring the adhesive strength, a pulley was connected so that the angle of the vertically erected specimen could be maintained at 90° with respect to the glass substrate (floor surface), and then the adhesive strength was measured.

[0148]

[0149] (2) Interfacial resistance measurement

[0150] The interfacial resistance was measured using an MP Tester (XF-057, Hioki EE Corporation, Japan). Each positive electrode was punched out to 5 cm X 5 cm (width X height) to prepare a specimen, and the positive electrode active material layer was fixed on the specimen measurement section so that it was facing upward. The thickness of the specimen (positive electrode), the thickness of the aluminum foil, and the resistivity value of the current collector (2.82 X 10 -6 Ωcm) were input for each, and the measurement was performed by setting 100 μA, Speed: slow, 0.5 V, and Max iteration number to 30 times. Each measurement was performed three times, and the average value was calculated to present the results.

[0151]

[0152] Classification Preliminary Comparative Example 123456712345 Adhesive strength (gf / 2cm) 56.248.167.357.449.751.143.81778.34128.935.1 Interfacial resistance (Ω cm) 2)0.440.350.530.280.580.310.262.671.630.641.870.24

[0153] As shown in Table 3 above, the positive electrode of the example showed excellent adhesion between the positive electrode active material layer and the current collector, and also low interfacial resistance. In contrast, in the case of the positive electrode of Comparative Example 1, which did not include a thickener in the primer layer, the adhesion was significantly lower than in the example, and the interfacial resistance was considerably higher. In addition, in the case of the positive electrode of Comparative Example 2, in which the content of the conductive agent was excessively low, and the weight ratio of the conductive agent and the binder was approximately 1:20, the interfacial resistance was considerably high, and in the case of the positive electrode of Comparative Example 3, in which carbon black was used as the conductive agent, the adhesion was lower and the interfacial resistance was higher than in the example. In addition, Comparative Example 4, in which the content of the thickener was less than 5 parts by weight based on 100 parts by weight of the total of the conductive agent, binder, and thickener, the adhesion was lower and the interfacial resistance was higher than in the example. In Comparative Example 5, in which the content of the thickener exceeded 20 parts by weight, the adhesion was also lower than in the example.

Claims

1. Metal layer; and Comprising a primer layer coated on at least one surface of the metal layer, The above primer layer comprises a conductive agent, a binder and a thickener, The above challenge material has a BET surface area of ​​170 m 2 / g or more multi-walled carbon nanotubes, A current collector wherein the weight ratio of the above-mentioned challenge agent and binder is 1:1 or more and 10 or less.

2. In paragraph 1, A current collector, wherein the content of the thickener is 5 parts by weight or more and 20 parts by weight or less, based on 100 parts by weight of the total weight of the above-mentioned challenge agent, binder, and thickener.

3. In paragraph 1, A current collector, wherein the content of the conductive material is 10 parts by weight or more and 50 parts by weight or less, based on 100 parts by weight of the total weight of the conductive material, binder, and thickener.

4. In paragraph 1, A current collector, wherein the content of the binder is 35 parts by weight or more and 75 parts by weight or less, based on 100 parts by weight of the total weight of the above-mentioned challenge agent, binder, and thickener.

5. In paragraph 1, A current collector wherein the above binder is at least one selected from the group consisting of polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, hydrogenated nitrile butadiene rubber, styrene butadiene rubber, polyacrylonitrile, polymethyl methacrylate, polyethylene, tetrafluoroethylene, and polyacrylic acid.

6. In paragraph 1, A collector wherein the thickener is at least one selected from the group consisting of carboxymethylcellulose, polyvinylpyrrolidone, and polyvinyl alcohol.

7. In paragraph 1, A collector having a thickness of the primer layer of 0.2 ㎛ or more and 2 ㎛ or less.

8. In paragraph 1, A collector having a surface roughness of the above primer layer of 1.1 ㎛ or less.

9. The entire collection of paragraph 1; and Containing an electrode active material layer, An electrode in which the electrode active material layer is attached on a primer layer of the current collector.

10. In paragraph 9, In a 90° peel test, the adhesion between the electrode active material layer and the primer layer was 40 gf / 2cm measured at a peeling speed of 100 mm / min. An electrode that is ideal.

11. In paragraph 9, The interfacial resistance between the electrode active material layer and the current collector is 0.6 Ω cm. 2 Electrodes that are as follows.

12. A lithium secondary battery comprising the electrode of clause 9.

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