Electrode, method for preparing same, and secondary battery comprising same

Abstract

Provided are an electrode with an improved sliding portion, a method for preparing same, and a secondary battery comprising same, the electrode provided with a current collector and an active material layer located on at least one surface of the current collector, wherein the current collector is provided with at least one first surface portion which is in surface contact with the active material layer and a second surface portion on which the active material layer is not located and which is located on both sides of the first surface, wherein a water drop contact angle of the first surface portion is smaller than the water drop contact angle of the second surface portion.

Description

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

[0001] The present invention relates to an electrode, a method for manufacturing the same, and a secondary battery including the same, and more particularly, to an electrode having improved sliding portions at both ends of an active material layer, a method for manufacturing the same, and a secondary battery including the same.

[0002] This application claims priority to Korean Application No. 10-2023-0093423, filed July 18, 2023, the entire disclosure of which is incorporated herein by reference.

[0003] As technological development and demand for mobile devices increase, the demand for secondary batteries as an energy source is rapidly increasing, and accordingly, extensive research is being conducted on batteries that can meet various needs.

[0004] These secondary batteries can be broadly categorized into anode, cathode, separator, and electrolyte. Upon initial charging, lithium ions released from the cathode active material are inserted into the cathode active material. Upon subsequent discharge, they are released and shuttled back and forth between the two electrodes. This process converts energy, enabling charging and discharging.

[0005] In general, the electrode of a lithium secondary battery is manufactured by dispersing an active material and a binder to prepare an active material slurry, and then coating an active material layer on one surface of a current collector. When coating the active material slurry on one surface of a current collector, a sliding phenomenon occurs in which the active material slurry spreads. As a result, a sliding portion is formed at the ends of the active material layer that is thinner than the central portion. Specifically, the sliding portion may refer to a portion that extends from both ends of the central portion and gradually becomes thinner as it goes toward the ends of the active material layer, that is, from the central portion of the active material layer toward the uncoated portion where the active material layer is not formed. Due to this sliding phenomenon, the loading amount at both ends of the active material layer is formed to be lower than the loading amount at the center, which causes a problem in that the capacity of the secondary battery is lower than the designed capacity.

[0006] Furthermore, due to the sliding portion occurring on the non-conductive side of the electrode end as described above, the ratio of positive and negative electrodes in the non-conductive part (tab part) of the electrode may be reversed, a physical separation may occur, and furthermore, it may be difficult to control the sliding portion, making it difficult to maintain stable electrode quality.

[0007] In order to solve these problems, various core shapes were applied to increase the flow rate of the slurry for forming the active material layer supplied to both ends of the active material layer, i.e., the side portion, but the increase in the flow rate of the slurry to the side portion resulted in the formation of a ring, and thus there was still a limit to improving the sliding.

[0008] Therefore, the problem to be solved by the present invention is to provide an electrode having improved sliding portions at both ends of an active material layer, a method for manufacturing the same, and a secondary battery including the same.

[0009] In order to solve the above problem, the present invention provides the electrodes and methods for manufacturing the electrodes of the following embodiments.

[0010] According to the first implementation example,

[0011] The entire house; and

[0012] An active material layer positioned on at least one surface of the above-mentioned collector;

[0013] The above-mentioned collector has at least one first surface portion that contacts the active material layer, and a second surface portion located on both sides of the first surface, where the active material layer is not located,

[0014] An electrode is provided, characterized in that the water droplet contact angle of the first surface portion is smaller than the water droplet contact angle of the second surface portion.

[0015] According to the second embodiment, in the first embodiment,

[0016] The difference (BA) between the water droplet contact angle (A) of the first surface portion and the water droplet contact angle (B) of the second surface portion may be 10° or more.

[0017] According to the third embodiment, in the first embodiment or the second embodiment,

[0018] The water droplet contact angle of the first surface portion may be 19.9 degrees to 39.9 degrees, and the water droplet contact angle of the second surface portion may be 50.8 degrees to 70.8 degrees.

[0019] According to the fourth embodiment, in any one of the first to third embodiments,

[0020] The above first surface portion can be surface treated.

[0021] According to the fifth embodiment, in any one of the first to fourth embodiments,

[0022] Surface protrusions are formed on a second surface portion located spaced apart from both sides of the first surface portion of the above-mentioned collector, and the active material layer can be located between the spaced-apart surface protrusions.

[0023] According to the sixth implementation example,

[0024] Steps to prepare the entire house;

[0025] A step of forming a first surface portion and a second surface portion located on both sides of the first surface portion in the longitudinal direction of the above-described collector, and controlling a water droplet contact angle of the first surface portion to be smaller than a water droplet contact angle of the second surface portion;

[0026] A step of applying a slurry for an active material layer to the first surface portion; and

[0027] A method for manufacturing an electrode is provided, including a step of drying a slurry for the above active material layer.

[0028] According to the seventh embodiment, in the sixth embodiment,

[0029] A surface treatment can be applied to at least one of the first surface portion and the second surface portion of the above-mentioned collector.

[0030] According to the eighth embodiment, in the sixth embodiment or the seventh embodiment,

[0031] Surface treatment can be performed only on the first surface of the above-mentioned collector.

[0032] According to the ninth embodiment, in the eighth embodiment,

[0033] Immediately after surface-treating the first surface portion, a slurry for an active material layer can be applied to the same location of the surface-treated first surface portion.

[0034] According to the tenth embodiment, in any one of the seventh to ninth embodiments,

[0035] The above surface treatment may be performed by plasma, corona, ultraviolet (UV) treatment, extreme ultraviolet (EUV) treatment, or two or more of these.

[0036] According to the eleventh embodiment, in any one of the sixth to tenth embodiments,

[0037] The difference (BA) between the water droplet contact angle (A) of the first surface portion and the water droplet contact angle (B) of the second surface portion may be 10° or more.

[0038] According to the 12th embodiment, in any one of the 6th to 11th embodiments,

[0039] The water droplet contact angle of the first surface portion may be 19.9° to 39.9°, and the water droplet contact angle of the second surface portion may be 50.8° to 70.8°.

[0040] According to the 13th embodiment, in any one of the 6th to 12th embodiments,

[0041] Surface protrusions on the second surface portion located on both sides of the first surface portion of the above-described collector are spaced apart at a predetermined interval, and the surface protrusions can act as dams on both sides of the slurry for the active material layer applied to prevent the slurry for the active material layer from flowing down.

[0042] According to the 14th implementation example,

[0043] A secondary battery is provided, characterized by including an electrode of any one of the first to fifth embodiments.

[0044] According to the 15th embodiment, in the 14th embodiment,

[0045] The above secondary battery may be a lithium secondary battery.

[0046] According to one embodiment of the present invention, only the first surface portion of the current collector on which the slurry for the active material layer is to be applied is surface-treated, and the second surface portion on which the slurry for the active material layer is not to be applied is not surface-treated, so that the water droplet contact angle of the first surface portion is controlled to be smaller than the water droplet contact angle of the second surface portion, and at this time, the second surface portions are respectively positioned on both sides of the first surface portion, so that the sliding portion of the electrode that occurs on the non-coated portion, which is the both ends of the electrode, due to the spreading phenomenon of the slurry for the active material layer by wet coating can be improved, and as a result, the reversal phenomenon of the capacity balance (N / P balance) between the positive and negative electrodes can be prevented. In addition, the Li precipitation phenomenon that occurs in the conventional sliding portion can be suppressed, and the cycle characteristics of a secondary battery employing such an electrode can be improved. In addition, according to one embodiment of the present invention, the physical distance between the positive and negative electrode layers is reduced, so that the concentration gradient of lithium ions between the positive and negative electrodes, i.e., the electrolyte concentration polarization phenomenon, can be prevented, and the overvoltage field can be reduced.

[0047] The following drawings attached to this specification illustrate preferred embodiments of the present invention and, together with the contents of the invention described above, serve to further understand the technical idea of ​​the present invention, and therefore, the present invention should not be interpreted as being limited to matters described in such drawings.

[0048] Figure 1 is a schematic diagram showing a cross-section of a collector according to a prior art.

[0049] Figure 2 is a schematic diagram showing a process of applying slurry for an active material layer to one surface of a current collector according to a conventional technology.

[0050] Figure 3 is a schematic diagram showing slurry applied to one surface of a collector according to a conventional technique.

[0051] Figure 4 is a schematic diagram comparing hydrophilicity and hydrophobicity according to the water droplet contact angle.

[0052] Figure 5 is a schematic diagram showing a cross-section of a collector according to one embodiment of the present invention.

[0053] Figure 6 is a schematic diagram showing the upper surface of a collector according to one embodiment of the present invention.

[0054] Figure 7 is a schematic diagram showing a process of applying slurry for an active material layer to one surface of a current collector according to one embodiment of the present invention.

[0055] Figure 8 is a schematic diagram showing slurry applied to one surface of a collector according to one embodiment of the present invention.

[0056] Figure 9 is a schematic diagram showing a sliding part of an electrode according to one embodiment of the present invention.

[0057] Figure 10 is a graph showing the results of evaluating the sliding part length of the electrodes manufactured in Example 1 and Comparative Example 1.

[0058] Hereinafter, the present invention will be described in detail with reference to the drawings. Terms and words used in this specification and claims should not be construed as limited to their conventional or dictionary meanings. Based on the principle that the inventor can appropriately define the concept of a term to best explain his or her invention, they should be interpreted in the sense and concept consistent with the technical spirit of the present invention.

[0059] In the case of conventional electrodes, since wet coating is performed on the current collector, sliding parts inevitably occur at both ends of the wet-coated active material layer due to the spreading phenomenon of the slurry, and this entails a reversal of the capacity balance (N / P balance) between the positive and negative electrodes in an electrochemical device employing an electrode having such a sliding part formed, which can cause Li to precipitate and deterioration of the electrochemical device.

[0060] Fig. 1 is a schematic diagram showing a cross-section of a current collector (10) according to a prior art. Since no treatment process is performed on the surface (10A) of the current collector (10), fine surface protrusions may exist.

[0061] FIG. 2 is a schematic diagram showing a process of forming a slurry layer (20) by applying slurry for an active material layer to one surface of a current collector (10) according to a conventional technology using a slurry coating device (30) (e.g., a slot die, etc.). At this time, as described above, fine surface protrusions may exist on the surface (10A) of the current collector (10) according to the conventional technology.

[0062] Referring to FIG. 3, a slurry for an active material layer in a liquid state is applied on a surface protrusion (10A) on one surface of a current collector (10) according to the prior art, and at this time, the slurry has a property of spreading in all directions due to the influence of gravity, so that as a result, the slurry in a state of spreading in all directions is dried as is, and a sliding portion having a thinner thickness at both ends than at the center is formed in the active material layer of the final electrode manufactured. Due to the sliding portions present at both ends of the active material layer, the loading amount at both ends of the active material layer is formed to be lower than the loading amount at the center, which may cause various performance degradations of the secondary battery, such as realizing a lower capacity than the designed capacity of the secondary battery.

[0063]

[0064] The present invention aims to solve these problems of conventional electrodes,

[0065] The entire house; and

[0066] An active material layer positioned on at least one surface of the above-mentioned collector;

[0067] The above-mentioned collector has at least one first surface portion that contacts the active material layer, and a second surface portion located on both sides of the first surface, where the active material layer is not located,

[0068] An electrode is provided, characterized in that the water droplet contact angle of the first surface portion is smaller than the water droplet contact angle of the second surface portion.

[0069] That is, in the present invention, by forming two surface areas with different water droplet contact angles through surface treatment on a predetermined area of ​​the surface area of ​​the current collector, the problem of forming a sliding area at both ends of the active material layer is improved by controlling the property of the slurry spreading in all directions on the current collector of the prior art.

[0070] In general, the surfaces of solids such as metals and polymers have their own surface energy, and this surface energy can be evaluated by measuring the water droplet contact angle. On the surface of a solid, when a straight line is drawn from the point where a stationary water droplet makes contact with the solid, the angle between the water droplet surface and the surface of the solid is called the water droplet contact angle. Referring to Fig. 4, the smaller the water droplet contact angle (θ), the more the spherical water droplet loses its shape on the solid surface and wets the surface of the solid, and in this case, the surface of the solid is said to be hydrophilic. Conversely, if the contact angle is large, the water droplet maintains its spherical shape and does not wet the surface of the solid, and is therefore said to be hydrophobic.

[0071] In the present application, the water droplet contact angle refers to the angle formed between the surface of the current collector and the contact surface of the current collector. A small water droplet contact angle on the first surface of the current collector means that the first surface of the current collector has high wettability (hydrophilicity) and high surface energy, and conversely, a large water droplet contact angle on the second surface of the current collector means that the second surface of the current collector has low wettability (hydrophobicity) and low surface energy.

[0072] In the present invention, the water droplet contact angle can be measured by dropping a distilled water droplet on the surface of the corresponding current collector and measuring the contact angle formed under the conditions of 23°C and 50% RH using a contact angle measuring device (e.g., Model CA-DT-A (mfd. manufactured by Kyowa Kaimen Kagaku KK)). Specifically, the contact angle is measured at two points (left point and right point) of each of three current collector samples, and the average value of six measurements can be expressed as the water droplet contact value. The diameter of the distilled water droplet can be 2 mm, and the contact angle value indicated by the measuring device can be a value measured 1 minute after dropping the distilled water droplet.

[0073]

[0074] Referring to FIGS. 5 and 6, a current collector (10) according to one embodiment of the present invention has at least one first surface portion (10B) on its surface and second surface portions (10A) located on both sides of the first surface. At this time, the water droplet contact angle of the first surface portion is characterized by being smaller than the water droplet contact angle of the second surface portion.

[0075] Referring to FIGS. 7 and 8, a slurry for an active material layer is applied only to a first surface portion (10B) located between second surface portions (10A) using a slurry coating device (30) (e.g., a slot die, etc.) on one surface of a current collector (10) according to one embodiment of the present invention, thereby forming a slurry layer (20).

[0076] At this time, the slurry layer (20) positioned on the first surface portion (10B) in FIG. 8 is suppressed from spreading in both directions further because the surface protrusions of the second surface portions (10A) positioned on both sides of the first surface portion (10B) serve as a kind of dam (barrier), and the thickness difference between the central portion of the slurry layer and the ends extending to both sides of the central portion can be minimized. As a result, in the active material layer obtained by drying the slurry layer later, the phenomenon of a sliding portion in which the thickness of both ends is greatly reduced compared to the thickness of the central portion of the active material layer can be prevented.

[0077] Accordingly, an electrode according to one embodiment of the present invention may have surface protrusions formed on a second surface portion spaced apart from both sides of a first surface portion of the current collector, and the active material layer may be positioned between the spaced-apart surface protrusions.

[0078] At this time, the above 'surface protrusion' refers to a bumpy part that protrudes convexly on the surface, i.e., an uneven part.

[0079] The degree of unevenness of the surface protrusions of the above-mentioned collector can be analyzed by measuring the surface roughness.

[0080] According to one embodiment of the present invention, the method for measuring the surface roughness of the surface protrusion can be performed using an optical measuring device. For example, the optical measuring device (SRN2515 from SHINREIN) is a device that measures the surface roughness while taking an enlarged photograph of the surface of a measurement target. Specifically, the optical measuring device moves from one end to the other in the width direction of the surface of the measurement target, takes an enlarged photograph of the surface, and then calculates the difference in height between the highest peak and the lowest peak within the movement distance to calculate the surface roughness value (Rz) of the measurement target.

[0081] In the specification of the present invention, the sliding portion of the electrode can be defined as a portion that extends from both ends of the central portion of the active material layer and gradually becomes thinner as it goes toward the ends of the active material layer, that is, from the central portion of the active material layer toward the non-conductive portion where the active material layer is not formed.

[0082] Referring to FIG. 9, an electrode (50) of one embodiment of the present invention includes a current collector (51); and an electrode layer (52) positioned on at least one surface of the current collector (51) and a non-coated portion (53) without an electrode layer, and a vertical cross-section of the electrode layer (52) includes a central portion (52a) of the electrode layer and an end portion (sliding portion) (52b, 52c) that extends from both sides of the central portion (52a) of the electrode layer so that the height of the electrode layer in the central portion of the electrode layer decreases and comes into contact with the current collector.

[0083] At this time, the end length (d) of the electrode layer means the distance between the vertically opposite point (B) of the inclination starting point (A) to the current collector (51) and the boundary point (C) where the end of the electrode layer comes into contact with the current collector, and the inclination starting point (A) is the position on the end where the acute angle (α) formed by the extension line (X) of the central part of the electrode layer and the tangent line (Y) on the end along the end extended from the central part first becomes 10° or more. That is, from any position on the end where the height of the electrode layer in the central part of the electrode layer begins to decrease along the direction of the boundary point (C), the acute angle (α) formed by the extension line (X) of the central part of the electrode layer and the tangent line (Y) at any position on the end can mean the position on the end where the acute angle (α) first becomes 10° or more. When the outer line of the vertical cross-section of the above end portion has a curved shape and the electrode layer height decreases to contact the current collector, the position on the end portion where the acute angle (α) first becomes 10° or more can be confirmed by continuously changing any position on the end portion. On the other hand, when the outer line of the vertical cross-section of the above end portion has a diagonal or vertical line shape having a constant angle of 10° or more and the electrode layer height decreases to contact the current collector, the point where the diagonal or vertical line shape starts can be the position on the end portion where the acute angle (α) first becomes 10° or more.

[0084] In addition, according to one embodiment of the present invention, the sliding portion length (end length) of the electrode layer can be defined as the length of a portion having a thickness of 90% or less of the average thickness of the active material layer.

[0085] At this time, the sliding part length can be measured using a laser thickness measuring device (SNU). Compared to an electrode according to a conventional method that uses a current collector without any surface treatment, an electrode according to an embodiment of the present invention manufactured using a current collector subjected to surface treatment on the first surface can have a sliding part length reduced by 30% or less, or by 5 to 30%, or by 5 to 23%.

[0086] The end length (sliding portion length) of the electrode layer of the present invention is 10 mm or less, and according to one embodiment of the present invention, the end length of the electrode layer may be 1 to 10 mm, or 1.2 to 7 mm, or 1.7 to 7 mm, or 1.7 to 10 mm.

[0087] In this way, when the end portion of the electrode layer satisfies this range, the reversal phenomenon of the capacity balance (N / P balance) between the positive and negative electrodes can be prevented, the electrolyte concentration occurring in the sliding portion can be calculated to suppress the Li precipitation phenomenon, the overvoltage and cycle characteristics of a secondary battery employing such an electrode can be improved, and the adhesion between the end electrode and the separator can be improved.

[0088] According to one embodiment of the present invention, the difference (BA) between the water droplet contact angle (A) of the first surface portion and the water droplet contact angle (B) of the second surface portion may be 10° or more, or 10° to 30°, or 30° to 50°. When the difference (BA) between the water droplet contact angle (A) of the first surface portion and the water droplet contact angle (B) of the second surface portion satisfies this range, the second surface portion can effectively function as a dam that prevents the slurry applied to the first surface portion from spreading on both sides of the first surface portion, and can suppress the slurry spreading phenomenon.

[0089] Specifically, the water droplet contact angle of the first surface portion may be 19.9° to 39.9°, or 30° to 50°, and the water droplet contact angle of the second surface portion may be 50.8° to 70.8°, or 80° to 90°.

[0090] According to one embodiment of the present invention, the first surface portion of the current collector may be surface-treated. In this case, any treatment process that reduces the water droplet contact angle compared to the second surface portion that is not surface-treated may be applied without limitation, and examples thereof include corona treatment, plasma treatment, ultraviolet (UV) treatment, extreme ultraviolet (EUV), etc., and the treatment may be performed using one of these processes, or two or more of these processes may be used in combination.

[0091] In the present invention, the electrode may be a positive electrode or a negative electrode, and the active material layer may be a positive electrode active material layer or a negative electrode active material layer.

[0092] For example, if the electrode is a positive electrode, the active material included in the positive electrode active material layer may be a lithium-containing oxide as a positive electrode active material, and a lithium-containing transition metal oxide may be preferably used. For example, the lithium-containing transition metal oxide may be Li x (Ni a Co b Mn c )O2(0.5 <x<1.3, 0<a<1, 0<b<1, 0<c<1, a+b+c=1), Li x FePO4(0.5 <x<1.3), Li x CoO2(0.5 <x<1.3), Li x NiO2(0.5 <x<1.3), Li x MnO2(0.5 <x<1.3), Li x Mn2O4(0.5 <x<1.3), Li x Ni 1-y Co y O2(0.5 <x<1.3, 0<y<1), Lix Co 1-y Mn y O2(0.5 <x<1.3, 0≤y<1), Li x Ni 1-y Mn y O2(0.5 <x<1.3, O≤y<1), Li x (Ni a Co b Mn c )O4(0.5 <x<1.3, 0<a<2, 0<b<2, 0<c<2, a+b+c=2), Li x Mn 2-z Ni z O4(0.5 <x<1.3, 0<z<2), Li x Mn 2-z Co z O4(0.5 <x<1.3, 0<z<2) 및 Li x CoPO4(0.5 <x<1.3)로 이루어진 군으로부터 선택되는 어느 하나 또는 이들 중 2종 이상의 혼합물일 수 있으며, 상기 리튬 함유 전이금속 산화물은 알루미늄(Al) 등의 금속이나 금속산화물로 코팅될 수 도 있다. 또한, 상기 리튬 함유 전이금속 산화물 외에 황화물(sulfide), 셀렌화물(selenide) 및 할로겐화물(halide) 등도 사용될 수 있다.

[0093] For example, if the above electrode is a cathode, the cathode active material included in the active material layer may include carbon such as non-graphitizable carbon and graphite carbon; 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, elements of group 1, 2, and 3 of the periodic table, halogens; 0 <x≤1; 1≤y≤3; 1≤z≤8) 등의 금속 복합산화물; 리튬 금속; 리튬 합금; 규소계 합금; 주석계 합금; SiO, SiO / C, SiO2등의 실리콘계 산화물; SnO, SnO2, PbO, PbO2, Pb2O3, Pb3O4, Sb2O3, Sb2O4, Sb2O5, GeO, GeO2, Bi2O3, Bi2O4및 Bi2O5등의 금속 산화물; 폴리아세틸렌 등의 도전성 고분자; Li-Co-Ni 계 재료 등을 사용할 수 있다.

[0094] An electrode according to one embodiment of the present invention may include a current collector; and an active material layer, which is a region formed by laminating an active material slurry including an active material, a conductive material, and a binder, and which is located on at least one surface of the current collector; and a non-laminated region, which is a region where the active material layer is not laminated.

[0095] According to one embodiment of the present invention, the electrode may be a positive electrode, and the active material may be a positive electrode active material. In this case, the positive electrode current collector may be generally made to have a thickness of about 3 to 50 ㎛. The positive electrode current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery, and for example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc. may be used. The positive electrode current collector may form fine irregularities on its surface to increase the adhesiveness of the positive electrode active material, and may be in various forms such as a film, sheet, foil, net, porous body, foam, or non-woven fabric. In addition, the conductive material included in the first active material layer and the second active material layer in the present invention is typically added in an amount of 0.2 to 5 wt% based on the total weight of the mixture including the positive electrode active material. The conductive material is not particularly limited as long as it is conductive and does not cause a chemical change in the battery, and examples thereof include graphite such as natural graphite or artificial graphite; carbon black such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, and summer black; conductive fibers such as carbon fiber or metal fiber; metal powders such as fluorinated carbon, aluminum, and nickel powder; conductive whiskey such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives. In addition, the binder included in the active material layer in the present invention is a component that assists in the bonding of the active material and the conductive material and the bonding to the current collector, and is typically added in an amount of 0.2 to 5 wt% based on the total weight of the slurry including the positive electrode active material.Examples of such binders include polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene butylene rubber, fluoroelastomer, and various copolymers.

[0096] For example, when the electrode is a negative electrode, 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. can be used. In addition, the negative electrode current collector can typically have a thickness of 3 to 50 ㎛, and like the positive electrode current collector, fine unevenness can be formed on the surface of the current collector to strengthen the bonding strength of the negative electrode active material. For example, it can be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, a non-woven fabric, etc. In addition, the conductive material and binder included in the active material layer can be the same as those described above for the positive electrode.

[0097]

[0098] According to one aspect of the present invention,

[0099] Steps to prepare the entire house;

[0100] A step of forming a first surface portion and a second surface portion located on both sides of the first surface portion in the longitudinal direction of the above-described collector, and controlling a water droplet contact angle of the first surface portion to be smaller than a water droplet contact angle of the second surface portion;

[0101] A step of applying a slurry for an active material layer to the first surface portion; and

[0102] A method for manufacturing an electrode is provided, including a step of drying a slurry for the above active material layer.

[0103]

[0104] First, prepare the entire house.

[0105] For details on the entire house, please refer to the above.

[0106] Next, a first surface portion and a second surface portion located on both sides of the first surface portion are formed in the longitudinal direction of the entire body, and the water droplet contact angle of the first surface portion is controlled to be smaller than the water droplet contact angle of the second surface portion.

[0107] The surface treatment described above can be applied without limitation as long as it is a treatment process that makes the water droplet contact angle smaller compared to the second surface portion that is not surface treated, and for example, it can be performed by corona treatment, plasma treatment, ultraviolet (UV) treatment, extreme ultraviolet (EUV) treatment, or two or more of these. In this case, the treatment can be performed by one of these treatment processes, or two or more of these processes can be used in combination.

[0108] According to one embodiment of the present invention, in order to control the water droplet contact angle of the first surface portion to be smaller than the water droplet contact angle of the second surface portion, surface treatment may be performed on at least one of the first surface portion and the second surface portion. The surface treatment may be performed only on the first surface portion of the current collector.

[0109] Afterwards, a slurry for the active material layer is applied to the first surface portion.

[0110] According to one embodiment of the present invention, in the case where only the first surface portion of the collector is surface-treated, a step of applying a slurry for an active material layer to the same position of the surface-treated first surface portion may be performed immediately after surface-treating the first surface portion.

[0111] For example, a surface treatment device (plasma, corona device, etc.) that performs surface treatment on a predetermined area of ​​the surface of a current collector is installed immediately before the position where the device for applying slurry for the active material layer is arranged, so that the surface is treated in the same shape and position as the area to which the slurry is to be applied, thereby controlling the contact angle of the predetermined area of ​​the surface of the current collector, and then applying the slurry to the same position, thereby improving sliding of the active material layer due to the spreading phenomenon of the slurry.

[0112] The method for applying the above slurry may be, for example, roll-to-roll coating, spin coating, nozzle printing, inkjet printing, slot coating, etc.

[0113] According to one embodiment of the present invention, after applying the slurry for the active material layer to the first surface portion, surface protrusions present on the second surface portion located on both sides of the first surface portion of the current collector are spaced apart at a predetermined interval, and the surface protrusions act as dams on both sides of the applied slurry for the active material layer, thereby preventing the slurry for the active material layer from flowing down. (See Fig. 8)

[0114] Next, the slurry for the active material layer is dried.

[0115] Through the above drying, the solvent included in the slurry for the active material layer may evaporate, thereby forming an active material layer. The drying temperature may be, for example, 30°C or higher, 40°C or higher, or 45°C or higher, 200°C or lower, 180°C or lower, or 160°C or lower, or 80°C to 170°C, or 80°C to 160°C. In addition, the drying may be performed in a drying device controlled at a single temperature, or may be performed in a drying device controlled by two or more multi-stage drying sections of different temperatures. For example, the multi-stage drying sections may include a first drying section controlled at 80°C to 100°C, a second drying section controlled at 100°C to 150°C, and a third drying section controlled at 150°C to 160°C.

[0116] In addition, the drying may be performed by leaving the current collector coated with the slurry for the active material layer in a drying device, or by passing the current collector through the drying device at a predetermined speed. When the drying is performed through a multi-stage drying section, the time for which the current collector coated with the slurry for the active material layer passes through each drying section at a predetermined speed may be controlled to be the same or different.

[0117] Additionally, after forming the above active material layer, the rolling step may be further performed.

[0118] This rolling process can be applied without limitation to conventional electrode processes. Through this rolling process, the electrode layer thickness can be controlled to a desired level.

[0119]

[0120] According to one aspect of the present invention, a secondary battery is provided, which comprises 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 one embodiment of the present invention described above.

[0121] There is no particular limitation on the separator to be applied together with the electrode of the present invention. The separator is interposed between the positive and negative electrodes to separate them, and a thin insulating film with high ion permeability and mechanical strength is used. Anything commonly used as a separator in secondary batteries can be used without particular limitation. Specifically, a porous polymer film, for example, a porous polymer film made of a polyolefin polymer such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer, or a laminated structure of two or more layers thereof, can 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. can also be used.

[0122] Additionally, a separator coated with inorganic particles, a binder polymer, or a mixture of inorganic particles and a binder polymer may be used to secure heat resistance or mechanical strength, and may optionally be used in a single-layer or multi-layer structure. Furthermore, when a solid electrolyte such as a polymer is used as the electrolyte, the solid electrolyte may also function as a separator.

[0123] In the present invention, the secondary battery may be a lithium secondary battery including a lithium metal secondary battery, a lithium ion secondary battery, a lithium polymer secondary battery, or a lithium ion polymer secondary battery.

[0124]

[0125] Hereinafter, the present invention will be described in detail with examples to specifically illustrate it. However, the examples according to the present invention may be modified in various ways, and the scope of the present invention should not be construed as being limited to the examples described below. These examples are provided to more fully explain the present invention to those of average skill in the art.

[0126]

[0127] Example 1

[0128] (1) Surface treatment of the entire body

[0129] Through a roll-to-roll process, a 10 ㎛ thick copper current collector was moved, and the surface of the current collector (first surface) at the position where the electrode slurry was to be applied was treated once using a plasma device at 800 W and 100 mm / s to remove surface protrusions formed on the surface of the current collector. As a result, the contact angle of the current collector surface before surface treatment was 60.8°, but the contact angle of the first surface after surface treatment was 29.9°. Therefore, the difference (BA) between the water droplet contact angle (A) (29.9°) of the first surface and the water droplet contact angle (B) (60.8°) of the second surface (current collector surface before surface treatment) was 30.9°.

[0130]

[0131] (2) Preparation of slurry for active material layer

[0132] Lithium nickel cobalt manganese aluminum oxide (NCMA, Li[Ni)) as the cathode active material 0.87 Co 0.05 Mn 0.07 Al 0.01 ]O2)) 300 parts by weight, 0.7 parts by weight of carbon black as a conductive agent, and 1.56 g of polyvinylidene fluoride (PVDF) as a binder were placed in a mixer with N-methylpyrrolidone (NMP) as a dispersion medium and mixed at 30,000 rpm for 60 minutes to prepare a slurry for the active material layer. (The solid content of the prepared slurry was 70%)

[0133]

[0134] (3) Manufacturing of electrode (anode)

[0135] The slurry for the active material layer prepared previously was applied onto the first surface of the current collector from which surface protrusions were removed by plasma surface treatment using a slot die coating device.

[0136] An electrode having an active material layer on a first surface of a current collector was manufactured by passing the current collector coated with the slurry for the active material layer through an oven controlled in multiple sections at a temperature of 80°C to 160°C, thereby drying the solvent in the slurry. Specifically, the oven had a first drying section controlled at 80°C to 100°C, a second drying section controlled at 100°C to 150°C, and a third drying section controlled at 150°C to 160°C. The passage time of the current collector coated with the slurry for the active material layer through each drying section was 0 sec for the first drying section, 60 sec for the second drying section, and 30 sec for the third drying section, and the passage speed was 40 m / min. At this time, the thickness of the active material layer formed on the current collector was 200 μm.

[0137]

[0138] Comparative Example 1

[0139] An electrode was manufactured in the same manner as in Example 1, except that a collector without surface treatment was used.

[0140]

[0141] Evaluation experiment

[0142] The sliding part length of the electrodes manufactured in Example 1 and Comparative Example 1 was measured using a laser thickness measuring device (SNU), and the results are shown in Fig. 10.

[0143] At this time, the sliding part length was defined as the length of the part with a thickness less than 90% of the average thickness of the active material layer.

[0144] Referring to Fig. 10, compared to the electrode of Comparative Example 1 according to the conventional method of using a current collector without any surface treatment, the electrode of Example 1 manufactured using a current collector with surface treatment applied only to the first surface portion exhibited a sliding portion length reduced by about 23%.

Claims

1. The entire house; and An active material layer positioned on at least one surface of the above-mentioned collector; The above-mentioned collector has at least one first surface portion that contacts the active material layer, and a second surface portion located on both sides of the first surface, where the active material layer is not located, An electrode characterized in that the water droplet contact angle of the first surface portion is smaller than the water droplet contact angle of the second surface portion.

2. In paragraph 1, An electrode characterized in that the difference (BA) between the water droplet contact angle (A) of the first surface portion and the water droplet contact angle (B) of the second surface portion is 10° or more.

3. In paragraph 1, An electrode characterized in that the water droplet contact angle of the first surface portion is 19.9 degrees to 39.9 degrees, and the water droplet contact angle of the second surface portion is 50.8 degrees to 70.8 degrees.

4. In paragraph 1, An electrode characterized in that the first surface portion is surface-treated.

5. In paragraph 1, An electrode characterized in that surface protrusions are formed on a second surface portion located spaced apart from both sides of a first surface portion of the above-mentioned collector, and the active material layer is located between the spaced-apart surface protrusions.

6. Step to prepare the entire house; A step of forming a first surface portion and a second surface portion located on both sides of the first surface portion in the longitudinal direction of the above-described collector, and controlling a water droplet contact angle of the first surface portion to be smaller than a water droplet contact angle of the second surface portion; A step of applying a slurry for an active material layer to the first surface portion; and A method for manufacturing an electrode, comprising: a step of drying the slurry for the active material layer.

7. In paragraph 6, A method for manufacturing an electrode, characterized in that a surface treatment is performed on at least one of the first surface portion and the second surface portion of the above-mentioned collector.

8. In paragraph 6, A method for manufacturing an electrode characterized in that only the first surface portion of the above-mentioned collector is subjected to surface treatment.

9. In paragraph 8, A method for manufacturing an electrode, characterized in that immediately after surface-treating the first surface portion, a slurry for an active material layer is applied to the same location of the surface-treated first surface portion.

10. In paragraph 7, A method for manufacturing an electrode, characterized in that the surface treatment is performed by plasma, corona, ultraviolet (UV) treatment, extreme ultraviolet (EUV), or two or more of these methods.

11. In paragraph 6, A method for manufacturing an electrode, characterized in that the difference (BA) between the water droplet contact angle (A) of the first surface portion and the water droplet contact angle (B) of the second surface portion is 10° or more.

12. In paragraph 6, A method for manufacturing an electrode, characterized in that the water droplet contact angle of the first surface portion is 19.9° to 39.9°, and the water droplet contact angle of the second surface portion is 50.8° to 70.8°.

13. In paragraph 6, A method for manufacturing an electrode, characterized in that surface protrusions on a second surface portion located on both sides of a first surface portion of the above-described collector are spaced apart at a predetermined interval, and the surface protrusions act as dams on both sides of the applied slurry for the active material layer to prevent the slurry for the active material layer from flowing down.

14. A secondary battery characterized by including an electrode according to any one of claims 1 to 5.

15. In paragraph 14, A secondary battery characterized in that the secondary battery is a lithium secondary battery.

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