Anode and lithium ion secondary battery comprising same

Abstract

A cathode is provided, comprising: a current collector; a cathode active material layer located on at least one surface of the current collector and comprising a cathode active material, a conductive material, and a binder polymer; wherein the glossiness of the surface of the cathode active material layer measured at an incident light angle of 85° is 10 to 37, and the glossiness refers to the intensity of light when reflected light is received at the same angle as the incident light.

Description

Technology Field

[0001] The present invention relates to a negative electrode that can be used in an electrochemical device such as a lithium secondary battery, and a lithium-ion secondary battery including the same. Background Technology

[0002] Recently, interest in energy storage technology has been steadily increasing. As application fields expand to include energy for mobile phones, camcorders, laptop PCs, and even electric vehicles, efforts in the research and development of electrochemical devices are becoming increasingly concrete.

[0003] Electrochemical devices are the most 주목받는 field in this regard, and among them, the development of rechargeable secondary batteries is the focus of interest. Recently, active research and development on new electrode and battery designs is being conducted to improve capacity density and specific energy in the development of secondary batteries.

[0004] Among the secondary batteries currently in use, lithium secondary batteries developed in the early 1990s are gaining attention for their advantages of having a higher operating voltage and significantly higher energy density compared to conventional batteries such as Ni-MH, Ni-Cd, and lead-acid batteries that use aqueous electrolytes.

[0005] These secondary batteries can be broadly classified into a positive electrode, a negative electrode, a separator, and an electrolyte. During the first charge, lithium ions released from the positive electrode active material are inserted into the negative electrode active material, and subsequently, during discharge, they are released again, circulating back and forth between the two electrodes. This process transfers energy, thereby enabling charging and discharging.

[0006] For example, a lithium secondary battery is structured such that an electrode assembly comprising a positive electrode containing a lithium transition metal oxide as an electrode active material, a negative electrode containing a carbon-based active material, and a separator containing a porous polymer substrate is impregnated with an electrolyte.

[0007] In such batteries, the distribution of binder polymers within the electrode active material layer is a determining factor in electrode performance. While increasing the content of binder polymers within the electrode active material layer can influence the improvement of adhesion between the active material layer and the current collector, the distribution of binder polymers within the electrode active material layer is critical at the same binder content, as binder content and battery capacity are inversely proportional. Generally, the distribution of binder polymers tends to decrease from the surface of the electrode active material layer inward. As the location of the minimum binder polymer content moves further away from the current collector, the adhesion of the electrode layer deteriorates, leading to the problem of delamination. Therefore, controlling the location of the minimum binder polymer content within the electrode layer to be as close as possible to the current collector and reducing the binder polymer content on the electrode layer surface is important for improving electrode adhesion. The problem to be solved

[0008] The present invention was devised to solve the problems of the prior art described above, and aims to provide a cathode that simultaneously satisfies high adhesion and low resistance.

[0009] However, the technical problems that the present invention aims to solve are not limited to those described above, and other unmentioned problems will be clearly understood by those skilled in the art from the description of the invention below. means of solving the problem

[0010] To solve the problem of the present invention, the following embodiments of a cathode and a method for manufacturing the same are provided.

[0011] According to the first embodiment,

[0012] The whole house;

[0013] A negative electrode active material layer is positioned on at least one surface of the above-mentioned current collector and comprises a negative electrode active material, a conductive material, and a binder polymer; and

[0014] The glossiness of the surface of the cathode active material layer measured at an incident light angle of 85° is 10 to 37, and

[0015] The above glossiness is provided in a cathode characterized by meaning the intensity of light when reflected light is received at the same angle as the incident light.

[0016] According to the second embodiment, in the first embodiment,

[0017] The above glossiness may be a relative ratio when the surface glossiness of glass with a refractive index of 1.567 is set to 100.

[0018] According to the third embodiment, in the first embodiment or the second embodiment,

[0019] The glossiness of the surface of the above-mentioned cathode active material layer may be 11 to 36.5.

[0020] According to the fourth embodiment, in any one of the first to third embodiments,

[0021] The content of the binder polymer may be 1 to 4 parts by weight based on 100 parts by weight of the cathode active material layer.

[0022] According to the fifth embodiment, in any one of the first to fourth embodiments,

[0023] The content of the binder polymer may be 1.5 to 3.5 parts by weight based on 100 parts by weight of the cathode active material layer.

[0024] According to the 6th embodiment, in any one of the 1st to 5th embodiments,

[0025] The above binder polymer may include a rubber-based binder polymer and a water-soluble polymer-based binder polymer.

[0026] According to the seventh embodiment, in the sixth embodiment,

[0027] The above rubber-based binder polymer may include styrene butadiene rubber (SBR), fluororubber, ethylene propylene rubber, butadiene rubber, isoprene rubber, acrylic rubber, silane rubber, or two or more of these.

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

[0029] The above water-soluble polymer-based binder polymer may include carboxymethylcellulose (CMC), cellulose, polyvinyl alcohol, polyacrylic acid, or two or more of these.

[0030] According to the ninth embodiment,

[0031] A step of preparing a cathode slurry by mixing a cathode active material, a conductive material, and a binder polymer in a solvent; and

[0032] A method for manufacturing a cathode of a first embodiment is provided, comprising the step of applying the above cathode slurry to at least one surface of a cathode current collector and then drying it.

[0033] According to the 10th embodiment, in the 9th embodiment,

[0034] The above drying step can be performed multiple times.

[0035] According to the 11th embodiment, in the 9th embodiment or the 10th embodiment,

[0036] As the number of drying steps increases, the drying temperature may increase.

[0037] According to the 12th embodiment, in any one of the 9th to 11th embodiments,

[0038] The above drying step may be performed three times, and among the three drying steps, the first drying may be performed at a temperature of 25 to 40 ℃, the second drying may be performed at a temperature of 120 to 140 ℃, and the third drying may be performed at a temperature of 140 to 160 ℃.

[0039] According to the 13th embodiment,

[0040] It includes an anode, a cathode, and a separator interposed between the anode and the cathode,

[0041] A lithium secondary battery is provided, characterized in that the above-mentioned cathode is a cathode according to any one of the first to eighth embodiments. Effects of the invention

[0042] A cathode according to one embodiment of the present invention contains a predetermined amount of binder polymer within a cathode active material layer, and controls the position where the amount of binder polymer within the cathode active material layer is minimized to be as close as possible to the current collector, thereby lowering the amount of binder polymer on the surface of the cathode active material layer so that the binder polymer within the cathode active material layer is not concentrated on the surface area but is distributed relatively uniformly. Accordingly, the cathode according to one embodiment of the present invention has a surface roughness of the cathode active material layer at an appropriate level, so that the glossiness of the surface of the cathode active material layer measured at an incident light angle of 85° satisfies the range of 10 to 37, and the adhesion force between the cathode active material layer and the current collector is high at 10 gf / 20mm or higher, thereby preventing the problem of the cathode active material layer peeling off from the current collector and providing a stable cathode.

[0043] In addition, the cathode according to one embodiment of the present invention can provide a cathode with relatively low resistance by controlling the distribution and content of the binder polymer within the cathode active material layer. Brief explanation of the drawing

[0044] FIG. 1 is a schematic diagram illustrating a method for measuring glossiness according to one embodiment of the present invention. Specific details for implementing the invention

[0045] 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 interpreted as being limited to their ordinary or dictionary meanings, and should be interpreted in a meaning and concept consistent with the technical spirit of the present invention, based on the principle that the inventor can appropriately define the concept of the terms to best describe his invention.

[0046] The embodiments described in the specification below and the configurations illustrated in the drawings are merely the most preferred embodiments of the present invention and do not represent all technical concepts of the present invention; therefore, it should be understood that various equivalents and modifications that can replace them may exist at the time of filing this application.

[0048] The negative electrode of a secondary battery can be manufactured by applying a slurry, in which a negative electrode active material, a conductive material, and a binder polymer are mixed in a solvent, to a current collector. At this time, during the process of evaporating the solvent, the binder polymer may move to the surface of the active material layer along with the solvent, so the distribution of the binder polymer according to the thickness of the negative electrode may not be uniform. However, in lithium secondary batteries, the distribution of the binder polymer within the negative electrode active material layer is a factor that determines the performance of the negative electrode.

[0050] Adhesion improves as the distribution of binder polymers becomes more uniform across the entire thickness of the cathode active material layer; however, the distribution of these binder polymers generally tends to decrease from the surface of the cathode active material layer inward. As the location with the minimum binder polymer content moves further away from the current collector, the adhesion between the cathode active material layer and the current collector deteriorates, leading to delamination. Therefore, controlling the location within the cathode active material layer where the binder polymer content is minimum to be as close as possible to the current collector, and reducing the binder polymer content on the surface of the cathode active material layer, is important for improving cathode adhesion.

[0051] Since the negative active material layer can be formed by applying and drying a negative slurry onto a negative current collector, when a negative slurry containing the same amount of binder polymer is applied, the lower the binder polymer content on the surface of the negative active material layer, the more uniform the distribution of the binder polymer inside the negative active material layer can be said to be. A negative electrode according to one aspect of the present invention is conceived from the above trend.

[0053] A cathode according to one aspect of the present invention is,

[0054] The whole house;

[0055] A negative electrode active material layer located on at least one surface of the above-mentioned current collector and comprising a negative electrode active material, a conductive material, and a binder polymer; and

[0056] The glossiness of the surface of the cathode active material layer measured at an incident light angle of 85° is 10 to 37, and

[0057] The above glossiness is characterized by representing the intensity of light when reflected light is received at the same angle as the incident light.

[0059] Considering that the adhesion of the cathode varies depending on the distribution of the binder polymer within the cathode active material layer, the inventors confirmed the distribution of such binder polymer through the glossiness of the surface of the cathode active material layer.

[0060] In particular, the inventors confirmed that when the glossiness of the surface of the cathode active material layer measured at an incident light angle of 85° is 10 to 37, the resistance is low and the adhesion is improved.

[0062] In the present invention, 'glossiness' is a measure indicating the gloss of a surface, and refers to the intensity of light when reflected light is received at the same angle as incident light. This can be confirmed in FIG. 1.

[0063] The gloss unit (GU) mentioned above may represent a relative ratio when the gloss of a glass surface with a refractive index of 1.567 is set to 100.

[0064] The glossiness measurement method described above is not particularly limited and can be measured using glossiness measurement methods used in the industry. However, in the glossiness measurement method used in one embodiment of the present invention, the reference material is fixed as an absolute value, so the reference value does not change. Accordingly, there is no inconvenience of having to set a new reference depending on the material to be measured, and highly reliable results can be obtained.

[0065] For example, the above gloss measurement method can be measured using a gloss meter at a predetermined angle in accordance with ASTM D528.

[0066] Referring to FIG. 1, the glossiness of a cathode (10) having a cathode active material layer (12) located on one side of an electrode current collector (11) is the angle (θ) of incident light from a light irradiation unit (20) in a glossiness measuring device. in ) and the angle (θ) of the reflected light of the light sensor (30) re ) is measured by setting it to 85°. In addition, the glossiness of the electrode can be determined by selecting a glossiness measurement portion of the cathode active material layer to measure the glossiness randomly in step (S2), measuring the glossiness a predetermined number of times, and calculating the average of the measured glossiness.

[0068] Generally, glossiness is influenced by the surface roughness and refractive index of the material. As surface roughness (roughness) increases, incident light scattering occurs more significantly, resulting in lower glossiness; conversely, as surface roughness decreases, glossiness appears relatively higher. Meanwhile, as the refractive index of the material surface decreases, light scattering occurs less, leading to lower glossiness; conversely, as the refractive index increases, glossiness appears higher.

[0069] The inventors utilized the fact that the glossiness characteristics described above change depending on the content of the polymer binder on the surface of the cathode active material layer, and were able to realize a cathode active material layer with excellent adhesion by controlling the glossiness of the surface of the cathode active material layer to an appropriate range.

[0070] For example, as the binder polymer content on the surface of the above-mentioned cathode active material layer increases, the surface roughness decreases and the glossiness increases.

[0071] When the glossiness of the surface of the cathode active material layer measured at an incident light angle of 85° satisfies 10 to 37, the adhesion strength of the cathode active material layer is higher than 10 gf / 20mm, thereby preventing the problem of the cathode active material layer peeling off. If the glossiness exceeds 37, the binder polymer is located excessively on the surface of the cathode active material layer, which may reduce the stability of the cathode active material layer due to a decrease in adhesion strength.

[0072] According to one embodiment of the present invention, the glossiness of the surface of the cathode active material layer measured at an incident light angle of 85° may be 11 to 36.5, or 11.4 to 36.5.

[0073] At this time, the above cathode can be manufactured by mixing a cathode composite containing a cathode active material, a conductive material, and a binder in an organic solvent to produce a cathode slurry, applying it onto a cathode current collector, and then drying and rolling.

[0074] The above-mentioned negative 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., and aluminum-cadmium alloy may be used. In addition, the above-mentioned negative current collector may typically have a thickness of 3 to 500 μm, and, similar to the positive current collector, fine irregularities may be formed on the surface of the current collector to strengthen the bonding strength of the negative active material. For example, it may be used in various forms such as a film, sheet, foil, net, porous body, foam, nonwoven fabric, etc.

[0075] The above-mentioned negative electrode active material may typically be a carbon material capable of absorbing and releasing lithium ions, lithium metal, silicon, or tin. The above-mentioned negative electrode active material may be used by mixing at least one of graphite-based, non-graphite-based, and silicon oxides. The above-mentioned graphite-based material may be, for example, artificial graphite or natural graphite. Representative examples of the above-mentioned non-graphite-based material are soft carbon and hard carbon. Silicon dioxide may be used as the silicon oxide.

[0076] The above conductive material is not particularly limited as long as it is conductive without causing chemical changes in the battery, and for example, graphite such as natural graphite or artificial graphite; carbon black such as carbon black, acetylene black, Ketjen black, channel black, Farnes black, lamp black, thermal black; conductive fibers such as carbon fibers or metal fibers; conductive tubes such as carbon nanotubes; metal powders such as fluorocarbon, aluminum, or nickel powder; conductive whiskers such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; polyphenylene derivatives; graphene; and other conductive materials may be used.

[0077] The above binder polymers may include rubber-based binder polymers and water-soluble polymer-based binder polymers. For example, the rubber-based binder polymer may include styrene butadiene rubber (SBR), fluororubber, ethylene propylene rubber, butadiene rubber, isoprene rubber, acrylic rubber (butyl acrylate rubber, acrylonitrile rubber, acrylonitrile butadiene rubber, etc.), silane rubber, or two or more of these. For example, the water-soluble polymer-based binder polymer may include at least one of carboxymethylcellulose (CMC), cellulose, polyvinyl alcohol, and polyacrylic acid.

[0078] According to one embodiment of the present invention, the content of the binder polymer may be 1 to 4 parts by weight, 1.5 to 3.5 parts by weight, 2.5 to 4 parts by weight, or 1 to 2.5 parts by weight based on 100 parts by weight of the negative electrode active material layer. When the content of the binder polymer satisfies these ranges, the bonding properties of the electrode active material, that is, the adhesion between the current collector and the active material layer, are improved, and the movement of electrons and lithium ions within the battery is smooth, thereby preventing the problem of increased cell resistance.

[0079] According to one embodiment of the present invention, the cathode may have a structure of a single layer or a plurality of layers (double layer, triple layer, etc.) of two or more layers.

[0081] The above cathode may be manufactured in the following ways, but is not limited thereto.

[0082] First, a cathode slurry is prepared by mixing a cathode active material, a conductive material, and a binder polymer in a solvent. The solvent may be a solvent for the binder polymer and a dispersion medium for the cathode active material and the conductive material. At this time, the content of the binder polymer may be 1 to 4 parts by weight based on 100 parts by weight of the solid content of the coating layer slurry for the cathode active material. The method of mixing the materials is not particularly limited and may use methods commonly used in the industry.

[0083] Next, the prepared cathode slurry is applied to at least one surface of the cathode current collector and then dried.

[0084] The method of coating the above cathode slurry onto the above cathode current collector is not particularly limited, but, for example, a bar coating method, knife coating method, roll coating method, blade coating method, die coating method, microgravure coating method, comma coating method, slot die coating method, lip coating method, or solution casting method may be used.

[0085] At this time, the drying step may be performed multiple times. For example, it may be performed 2 to 5 times, or 2 to 3 times, and the drying temperature may be higher as the number of times increases.

[0086] According to one embodiment of the present invention, the drying step may be performed three times, and among the three drying steps, the first drying may be performed at a temperature of 25 to 40 ℃ or at a temperature of 30 to 40 ℃, the second drying may be performed at a temperature of 120 to 140 ℃ or at a temperature of 125 to 130 ℃ or at a temperature of 130 to 140 ℃, and the third drying may be performed at a temperature of 140 to 160 ℃ or at a temperature of 140 to 155 ℃ or at a temperature of 150 to 155 ℃. More specifically, the drying step is performed three times, and among the three drying steps, the first drying can be performed at a temperature of 25 to 40 ℃ for 10 to 60 seconds, the second drying can be performed at a temperature of 120 to 140 ℃ for 120 to 150 seconds, and the third drying can be performed at a temperature of 140 to 160 ℃ for 90 to 160 seconds.

[0088] Another embodiment of the present invention relates to a lithium secondary battery comprising a negative electrode manufactured as described above. Specifically, the lithium secondary battery may be manufactured by injecting a lithium salt-containing electrolyte into an electrode assembly comprising a positive electrode, a negative electrode as described above, and a separator interposed therebetween.

[0089] The above anode can be manufactured by mixing an anode active material, a conductive material, a binder, and a solvent to prepare a slurry, then directly coating it onto a metal current collector, or by casting it onto a separate support and laminating the anode active material film peeled off from the support onto a metal current collector.

[0090] Active materials used in the anode include LiCoO2, LiNiO2, LiMn2O4, LiCoPO4, LiFePO4, and LiNi 1-x-y-z Co x M1 y M2 zO2(M1 and M2 are independently selected from the group consisting of Al, Ni, Co, Fe, Mn, V, Cr, Ti, W, Ta, Mg, and Mo, and x, y, and z are independently atomic fractions of oxide composition elements as 0 x<0.5, 0≤y<0.5, 0≤z<0.5, 0 <x+y+z≤1임)로 이루어진 군으로부터 선택된 어느 하나의 활물질 입자 또는 이들 중 2종 이상의 혼합물을 포함할 수 있다.

[0091] Meanwhile, the conductive material, binder, and solvent can be used in the same way as those used in the manufacture of the cathode above.

[0092] The above separator may be used alone or in a laminated form, using a conventional porous polymer film used as a separator, such as a polyolefin-based polymer film made of ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer. Additionally, an insulating thin film having high ion permeability and mechanical strength may be used. The above separator may include a safety reinforced separator (SRS) in which a ceramic material is thinly coated on the surface of the separator. Furthermore, a conventional porous nonwoven fabric, such as a nonwoven fabric made of high-melting-point glass fibers or polyethylene terephthalate fibers, may be used, but is not limited thereto.

[0093] The above electrolyte comprises a lithium salt as an electrolyte and an organic solvent for dissolving it.

[0094] The above lithium salt may be used without limitation as long as it is one commonly used in electrolytes for secondary batteries, for example, as the anion of the above lithium salt, F - , Cl - , I - , NO3 - , N(CN)2- , BF4 - , ClO4 - , PF6 - , (CF3)2PF4 - , (CF3)3PF3 - , (CF3)4PF2 - , (CF3)5PF - , (CF3)6P - , CF3SO3 - , CF3CF2SO3 - , (CF3SO2)2N - , (FSO2)2N - , CF3CF2(CF3)2CO - , (CF3SO2)2CH - , (SF5)3C - , (CF3SO2)3C - , CF3(CF2)7SO3 - , CF3CO2 - , CH3CO2 - , SCN - and (CF3CF2SO2)2N - One type selected from the group consisting of can be used.

[0095] The organic solvent included in the above electrolyte may be any commonly used solvent without limitation, and one or more selected from the group consisting of propylene carbonate, ethylene carbonate, diethyl carbonate, dimethyl carbonate, ethylmethyl carbonate, methylpropyl carbonate, dipropyl carbonate, dimethyl sulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, vinylene carbonate, sulfolane, gamma-butyrolactone, propylene sulfite, and tetrahydrofuran may be used.

[0096] In particular, among the above carbonate-based organic solvents, ethylene carbonate and propylene carbonate, which are cyclic carbonates, are high-viscosity organic solvents with high dielectric constants that effectively dissociate lithium salts in the electrolyte, so they can be used preferably. Furthermore, if low-viscosity, low-dielectric constant linear carbonates such as dimethyl carbonate and diethyl carbonate are mixed with these cyclic carbonates in appropriate proportions, an electrolyte with high electrical conductivity can be produced, making it even more preferable to use.

[0097] Optionally, the electrolyte stored according to the present invention may further include additives such as an overcharge prevention agent included in conventional electrolytes.

[0098] A lithium secondary battery according to one embodiment of the present invention may be completed by forming an electrode assembly by placing a separator between a positive electrode and a negative electrode, placing the electrode assembly in, for example, a pouch, a cylindrical battery case, or a prismatic battery case, and then injecting an electrolyte. Alternatively, a lithium secondary battery may be completed by stacking the electrode assemblies, impregnating them with an electrolyte, and placing the resulting product into a battery case and sealing it.

[0099] According to one embodiment of the present invention, the lithium secondary battery may be a stack type, a wound type, a stack and folding type, or a cable type.

[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 small devices, but can also preferably be used as a unit cell in a medium-to-large battery module comprising a plurality of battery cells. Preferred examples of the medium-to-large devices include electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, and power storage systems, and can be particularly usefully applied in areas requiring high output, such as hybrid electric vehicles and batteries for storing new and renewable energy.

[0102] Hereinafter, the present invention will be described in detail with reference to examples to aid in understanding. However, the embodiments according to the present invention may be modified in various different forms, and the scope of the present invention should not be interpreted as being limited to the following embodiments. The embodiments of the present invention are provided to more completely explain the present invention to those with average knowledge in the art.

[0104] Example 1 - Preparation of the cathode

[0105] A cathode slurry was prepared by mixing artificial graphite, natural graphite, carbon black, carboxymethylcellulose (CMC), and styrene-butadiene rubber (SBR) with water in a weight ratio of 30:66.5:1.0:1.0:1.5.

[0106] The above cathode slurry at 3.5 mAh / cm 2 A cathode was manufactured by coating a copper foil (Cu-foil) with a certain amount to form a thin electrode plate, then drying it once at 40°C for 30 seconds, drying it twice at 130°C for 120 seconds, drying it three times at 150°C for 150 seconds, and then pressing it.

[0108] Manufacturing of the anode

[0109] Li[Ni as positive electrode active material 0.6 Mn 0.2 Co 0.2A slurry was prepared by mixing 296 wt% O2, 1 wt% of carbon nanotubes (bundled type) with a diameter of 10 nm and a length of 50 μm as a conductive material, and 3 wt% of polyvinylidene fluoride as a binder polymer in N-methyl-2-pyrrolidinone (NMP) solvent to achieve a solid content of 45 wt%. The mixture was mixed at 1800 rpm for 25 minutes using a Nobilta instrument (Hosokawa). Subsequently, a shear force of 250 N was applied to the mixture (Nobilta (Hosokawa Micron)) to prepare a slurry for forming an anode active material layer (anode slurry).

[0110] The above slurry for forming the positive electrode active material layer was coated onto one side of an aluminum current collector with a thickness of 15 μm, and then dried at 100°C for 5 minutes to produce a positive electrode.

[0112] Manufacture of Lithium Secondary Batteries

[0113] A non-aqueous electrolyte was prepared by dissolving LiPF6 to a concentration of 1.0 M in an organic solvent mixed with ethylene carbonate (EC), dimethyl carbonate (DMC), and diethyl carbonate (DEC) in a composition of 1:2:1 (volume ratio).

[0114] A lithium secondary battery was manufactured by interposing a polyethylene porous film as a separator between the anode and cathode prepared above, embedding this in a pouch cell, and then injecting the electrolyte.

[0116] Examples 2 to 3

[0117] A cathode and a secondary battery were manufactured in the same manner as in Example 1, except that the drying temperature and drying time of the cathode slurry were controlled as shown in Table 2 below.

[0119] Comparative Examples 1 to 3

[0120] A cathode and a secondary battery were manufactured in the same manner as in Example 1, except that the drying temperature and drying time of the cathode slurry were controlled as shown in Table 2 below.

[0122] Experimental Example 1 - Glossiness Measurement

[0123] In the present invention, glossiness is a measure indicating the gloss of a surface, and refers to the intensity of light when reflected light is received at the same angle as the incident light.

[0124] The gloss unit (GU) mentioned above refers to a relative ratio when the surface gloss of a reference glass (glass with a refractive index of 1.567) is set to 100.

[0125] The surface gloss of the cathodes prepared in Examples 1 to 3 and Comparative Examples 1 to 3 was measured using the Dark Calibration of the micro-TRI-gloss equipment from BYK Gardner in the following manner. The results are shown in Table 2.

[0126] Specifically, Dark Calibration was performed using a reference glass to achieve a surface gloss of 92 at 20°, 95 at 60°, and 99 at 85°. Subsequently, the surface gloss of the active material layer of the cathode prepared in Examples 1 to 3 and Comparative Examples 1 to 3 was measured. For the gloss measurement, a measurement area was randomly selected, and the average was calculated after measuring each five times at 85°.

[0128] Experimental Example 2 - Adhesion (Peel Test)

[0129] The cathodes prepared in Examples 1 to 3 and Comparative Examples 1 to 3 were attached to a slide glass using double-sided tape, which is a removal tape. Subsequently, a 90° Peel Test was performed at a speed of 5 mm / sec using a TA. XT plusC (Stable Micro Systems) instrument. The results are shown in Table 2.

[0131] Experimental Example 3 - Measurement of Cathode Resistance

[0132] The interfacial resistance between the electrode layer and the current collector is measured using a multi-probe tester. The interfacial resistance of the cathodes prepared in Examples 1 to 3 and Comparative Examples 1 to 3, which were cut to a size of 5 cm x 5 cm using a die cutter, was measured under the following conditions. The results are shown in Table 2.

[0133] Current: 100μA (anode), 10mA (cathode)

[0134] Speed: low

[0135] Voltage range: 0.5V

[0136] Current collector resistivity: 8.28*10 -6 Ω·cm (anode), 1.68*10⁻⁶ -6 Ω·cm (negative electrode)

[0138] Experimental Example 4 - Calculation of Binder Polymer Content on the Surface of the Cathode Active Material Layer

[0139] The cathodes prepared in Examples 1 to 3 and Comparative Examples 1 to 3 were prepared in a size of 1 cm X 1 cm and placed in a container containing OsO4 (Osmium tetraoxide) and sealed. After 3 hours, the cathodes were removed and placed in a vacuum oven to dry for 48 hours, and the binder polymer contained in the cathode active material layer was dyed using OsO4.

[0140] The content of the binder polymer on the surface of the stained cathode was analyzed using Energy Dispersive X-ray Spectroscopy. The osmium atomic ratio on the surface of the cathode active material layer was measured under the conditions shown in Table 1 below using an X-Max80 and an Extreme detector (Oxford). The results are shown in Table 2.

[0141] item condition Secondary Electron Microscopy equipment JEOL JSM-7200F Acceleration voltage (kV) 5 Magnification (X) 1000 Dwell Time (μs) 100

[0142] Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Comparative Example 3 Drying conditions 1st drying 40℃ 30 seconds 30℃ 30 seconds 40℃ 60 seconds 90℃ 300 seconds 150℃ 300 seconds 80℃ 300 seconds Secondary drying 130℃ 120 seconds 140℃ 150 seconds 120℃ 150 seconds 3rd drying 150℃ 150 seconds 140℃ 120 seconds 160℃ 90 seconds 85° gloss 11.48 24.84 36.42 37.89 38.88 9.83 Adhesion (gf / 20mm) 25 15 13 6 4 5 Cathode resistance (ohm*cm) 2 ) 0.451 0.415 0.395 0.729 0.682 0.31 Os content (wt%) on the surface of the cathode active material layer 0.5 0.6 0.8 1.1 1.2 0.3

[0144] Referring to Table 2, the cathodes of Examples 1 to 3, in which the glossiness of the surface of the cathode active material layer measured at an incident light angle of 85° satisfies the range of 10 to 37, can be seen to have a small Os content dyed on the surface of the cathode active material layer, so the content of the binder polymer distributed on the surface is small and uniformly distributed within the active material layer, and as a result, it was confirmed that they exhibit excellent adhesion and low resistance characteristics.

[0145] Although the present invention has been described above with reference to limited embodiments and drawings, the present invention is not limited thereto, and it is obvious that various modifications and variations are possible within the scope of the technical spirit of the present invention and the equivalent scope of the claims described below by those skilled in the art to which the present invention belongs.

Claims

Claim 1 The whole house; The present invention comprises a negative electrode active material layer located on at least one surface of the present collector and comprising a negative electrode active material, a conductive material, and a binder polymer; wherein the binder polymer comprises a rubber-based binder polymer and a water-soluble polymer-based binder polymer, wherein the rubber-based binder polymer comprises styrene butadiene rubber (SBR), fluororubber, ethylene propylene rubber, butadiene rubber, isoprene rubber, acrylic rubber, silane rubber, or two or more of these, and the water-soluble polymer-based binder polymer comprises carboxymethylcellulose (CMC), cellulose, polyvinyl alcohol, polyacrylic acid, or two or more of these, wherein the glossiness of the surface of the negative electrode active material layer measured at an incident light angle of 85° is 10 to 37, wherein the glossiness refers to the intensity of light when reflected light is received at the same angle as the incident light, and wherein the adhesion strength between the negative electrode active material layer and the present collector is 10 gf / 20mm or more. Cathode. Claim 2 A cathode according to claim 1, characterized in that the glossiness is a relative ratio when the surface glossiness of glass with a refractive index of 1.567 is set to 100. Claim 3 A cathode according to claim 1, characterized in that the glossiness of the surface of the cathode active material layer is 11 to 36.

5. Claim 4 A cathode according to claim 1, characterized in that the content of the binder polymer is 1 to 4 parts by weight based on 100 parts by weight of the cathode active material layer. Claim 5 A cathode according to claim 4, characterized in that the content of the binder polymer is 1.5 to 3.5 parts by weight based on 100 parts by weight of the cathode active material layer. Claim 6 delete Claim 7 delete Claim 8 delete Claim 9 A method for manufacturing a cathode according to claim 1, comprising: a step of preparing a cathode slurry by mixing a cathode active material, a conductive material, and a binder polymer in a solvent; and a step of applying the cathode slurry to at least one surface of a cathode current collector and then drying; wherein the drying step is performed three times, and among the three drying steps, the first drying is performed at a temperature of 25 to 40°C, the second drying is performed at a temperature of 120 to 140°C, and the third drying is performed at a temperature of 140 to 160°C. Claim 10 delete Claim 11 delete Claim 12 delete Claim 13 A lithium secondary battery comprising a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode, wherein the negative electrode is a negative electrode according to any one of claims 1 to 5.

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