KR20230067005A - Anode and lithium ion secondary battery comprising same - Google Patents

Abstract

current collector; and a negative electrode active material layer located on at least one surface of the current collector and containing a negative electrode active material, a conductive material, and a binder polymer, and a glossiness of the surface of the negative electrode active material layer measured at an incident light angle of 85° of 10 to 37 In addition, a cathode characterized in that the glossiness means the intensity of light when the reflected light is received at the same angle as the incident light is presented.

Description

Negative electrode and lithium ion secondary battery including the same {ANODE AND LITHIUM ION SECONDARY BATTERY COMPRISING SAME}

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 negative electrode.

Recently, interest in energy storage technology is increasing. Efforts in the research and development of electrochemical devices are becoming more and more specific as the fields of application are expanded to mobile phones, camcorders, notebook PCs, and even the energy of electric vehicles.

The electrochemical device is the field that is attracting the most attention in this respect, and among them, the development of a secondary battery capable of charging and discharging has become the focus of attention. In recent years, research and development on the design of new electrodes and batteries have been actively conducted in order to improve capacity density and specific energy in the development of secondary batteries.

Among the currently applied secondary batteries, the lithium secondary battery developed in the early 1990s has the advantage of higher operating voltage and significantly higher energy density than conventional batteries such as Ni-MH, Ni-Cd, and sulfuric acid-lead batteries using aqueous electrolytes. is gaining popularity as

These secondary batteries can be broadly classified into positive electrodes, negative electrodes, separators, and electrolytes. Lithium ions from the positive electrode active material are inserted into the negative electrode active material by the first charge and then desorbed again during discharging to reciprocate between the two electrodes. By transferring energy through this process, charging and discharging are possible.

For example, a lithium secondary battery has a structure in which an electrode assembly composed of a positive electrode including a lithium transition metal oxide as an electrode active material, a negative electrode including a carbon-based active material, and a separator including a porous polymer substrate is impregnated with an electrolyte solution. there is.

In such a battery, the distribution of the binder polymer in the battery electrode active material layer is one factor that determines the performance of the electrode. As the content of the binder polymer in the electrode active material layer increases, it can affect the improvement of the adhesion between the active material layer and the current collector. However, since the content of the binder and the battery capacity are inversely proportional, the distribution of the polymer binder within the electrode active material layer at the same binder content. is important. The distribution of the binder polymer generally tends to decrease from the surface of the electrode active material layer to the inside. As the position of the minimum content of the binder polymer is further away from the current collector, the adhesive strength of the electrode layer is lowered and there is a problem in that it is peeled off. Therefore, it is important in terms of improving electrode adhesion to control the position where the content of the binder polymer is minimum in the electrode layer as close to the current collector as possible and to lower the content of the binder polymer on the surface of the electrode layer.

The present invention has been devised to solve the problems of the prior art as described above, and is intended to provide a cathode that simultaneously satisfies high adhesion and low resistance.

However, the technical problem to be achieved by the present invention is not limited to the above-mentioned problem, and other problems not mentioned will be clearly understood by those skilled in the art from the description of the invention described below.

In order to solve the problems of the present invention, the following embodiments of the negative electrode and its manufacturing method are provided.

According to the first embodiment,

current collector;

A negative active material layer located on at least one surface of the current collector and containing a negative active material, a conductive material, and a binder polymer;

The glossiness of the surface of the negative electrode active material layer measured at an incident light angle of 85 ° is 10 to 37,

The glossiness is provided to the cathode, characterized in that it means the intensity of light when the reflected light is received at the same angle as the incident light.

According to the second embodiment, in the first embodiment,

The glossiness may be a relative ratio when the surface gloss of glass having a refractive index of 1.567 is 100.

According to the third embodiment, in the first embodiment or the second embodiment,

The glossiness of the surface of the negative electrode active material layer may be 11 to 36.5.

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

The content of the binder polymer may be 1 to 4 parts by weight based on 100 parts by weight of the negative electrode active material layer.

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

The content of the binder polymer may be 1.5 parts by weight to 3.5 parts by weight based on 100 parts by weight of the negative electrode active material layer.

According to the sixth embodiment, in any one of the first to fifth embodiments,

The binder polymer may include a rubber-based binder polymer and a water-soluble polymer-based binder polymer.

According to the seventh embodiment, in the sixth embodiment,

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

According to the eighth embodiment, in the sixth embodiment,

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

According to the ninth embodiment,

preparing a slurry for an anode in which an anode active material, a conductive material, and a binder polymer are mixed in a solvent; and

A method for manufacturing a negative electrode according to the first embodiment is provided, including applying the slurry for the negative electrode to at least one surface of the negative electrode current collector and then drying the slurry.

According to the tenth embodiment, in the ninth embodiment,

The drying step may be performed a plurality of times.

According to the eleventh embodiment, in the ninth embodiment or the tenth embodiment,

As the number of times of the drying step increases, the drying temperature may increase.

According to the twelfth embodiment, in any one of the ninth to eleventh embodiments,

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. It can be carried out at a temperature of ° C.

According to the thirteenth embodiment,

It includes a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode,

The negative electrode is a lithium secondary battery, characterized in that the negative electrode according to any one of the first to eighth embodiments is provided.

In the negative electrode according to an embodiment of the present invention, while including a predetermined content of the binder polymer in the negative electrode active material layer, the position where the content of the binder polymer is minimized in the negative electrode active material layer is controlled as close to the current collector as possible, and the negative electrode active material By lowering the content of the binder polymer on the surface of the layer, the binder polymer in the negative electrode active material layer can be relatively uniformly distributed without being biased on the surface. Therefore, in the negative electrode according to one embodiment of the present invention, the surface roughness of the negative electrode active material layer is implemented at an appropriate level, and the glossiness of the surface of the negative electrode active material layer measured at an incident light angle of 85 ° satisfies the range of 10 to 37, , The adhesive strength between the negative electrode active material layer and the current collector is higher than 10 gf/20 mm, so that the problem of separation of the negative electrode active material layer from the current collector can be prevented in advance, thereby providing a stable negative electrode.

In addition, in the negative electrode according to one embodiment of the present invention, the distribution and content of the binder polymer in the negative electrode active material layer are controlled together, thereby providing a negative electrode with relatively low resistance.

1 is a schematic diagram schematically showing a gloss measurement method according to an embodiment of the present invention.

Hereinafter, the present invention will be described in detail with reference to the drawings. The terms or words used in this specification and claims should not be construed as being limited to ordinary or dictionary meanings, and the inventors may appropriately define the concept of terms in order to explain their invention in the best way. It should be interpreted as a meaning and concept consistent with the technical idea of the present invention based on the principle that there is.

Hereinafter, the embodiments described in this specification and the configurations shown in the drawings are only one of the most preferred embodiments of the present invention and do not represent all of the technical ideas of the present invention, so various equivalents that can replace them at the time of the present application. It should be understood that there may be waters and variations.

A negative electrode of a secondary battery may be manufactured by applying a slurry obtained by mixing a negative electrode active material, a conductive material, and a binder polymer in a solvent to a current collector. At this time, in the process of evaporating the solvent, the binder polymer may move to the surface of the active material layer together with the solvent, so the distribution of the binder polymer according to the thickness of the negative electrode may not be uniform. However, in a lithium secondary battery, the distribution of the binder polymer in the battery negative electrode active material layer is a factor determining the performance of the negative electrode.

As the distribution of the binder polymer is constant over the entire thickness of the negative electrode active material layer, the adhesive strength is improved. In general, the distribution of the binder polymer tends to decrease as it goes from the surface of the negative electrode active material layer to the inside. As the position, which is the minimum content of the binder polymer, is further away from the current collector, the adhesive strength between the negative electrode active material layer and the current collector is lowered, resulting in peeling. Therefore, it is important in terms of improving the adhesion of the negative electrode to control the position where the content of the binder polymer is minimum in the negative active material layer as close as possible to the current collector and to lower the content of the binder polymer on the surface of the negative active material layer.

Since the negative electrode active material layer can be formed by coating and drying the negative electrode slurry on the negative electrode current collector, when the negative electrode slurry containing the same amount of the binder polymer is applied, the smaller the content of the binder polymer on the surface of the negative electrode active material layer, the better. It can be said that the distribution of the binder polymer inside the negative electrode active material layer is more uniform. A negative electrode according to one aspect of the present invention is conceived from the above trends.

A negative electrode according to an aspect of the present invention,

current collector;

A negative active material layer located on at least one surface of the current collector and containing a negative active material, a conductive material, and a binder polymer;

The glossiness of the surface of the negative electrode active material layer measured at an incident light angle of 85 ° is 10 to 37,

It is characterized in that the gloss means the intensity of light when the reflected light is received at the same angle as the incident light.

Considering that the adhesion of the negative electrode varies according to the distribution of the binder polymer in the negative electrode active material layer, the present inventors confirmed the distribution of the binder polymer through the glossiness of the surface of the negative electrode active material layer.

In particular, the inventors of the present invention confirmed that when the glossiness of the surface of the negative electrode active material layer measured at an incident light angle of 85° was 10 to 37, the resistance was low and the adhesive strength was improved.

In the present invention, 'glossiness' is a measure of the glossiness of a surface, and means the intensity of light when reflected light is received at the same angle as incident light. This can be confirmed in Figure 1.

The gloss unit (GU) may mean a relative ratio when the gloss of a glass surface having a refractive index of 1.567 is 100.

The gloss measurement method is not particularly limited, and may be measured using a gloss measurement method used in the art. However, in the gloss measurement method used in one embodiment of the present invention, the reference material is fixed as an absolute value, and the reference value does not change. Accordingly, there is no hassle of setting a new reference according to the material to be measured, and highly reliable results can be obtained.

For example, the gloss measurement method may be measured according to ASTM D528 at a predetermined angle with a gloss meter.

Referring to FIG. 1 , the glossiness of the negative electrode 10 having the negative electrode active material layer 12 located on one surface of the electrode current collector 11 is the angle of incident light (θ of the light irradiation unit 20 in the glossiness measuring device). _in ) and the angle (θ _re ) of the reflected light of the light sensing unit 30 is measured by setting it to 85°. In addition, in the step (S2), the glossiness of the electrode is selected by randomly selecting the glossiness measurement part of the negative electrode active material layer to measure the glossiness, measuring the glossiness a predetermined number of times, and obtaining the average of the measured glossiness. figure can be determined.

In general, glossiness is affected by the roughness and refractive index of the material surface. The higher the surface roughness (roughness), the greater the scattering of the incident light, resulting in lower gloss, and the lower the surface roughness, the higher the gloss. On the other hand, the lower the refractive index of the material surface, the less scattering of light occurs and the lower the gloss. The higher the refractive index, the higher the gloss.

The inventors of the present invention, using the fact that the above-described gloss characteristics change according to the content of the polymer binder on the surface of the negative electrode active material layer, can implement a negative electrode active material layer with excellent adhesive strength by adjusting the glossiness of the surface of the negative electrode active material layer in an appropriate range. could

For example, as the content of the binder polymer on the surface of the negative electrode active material layer increases, the roughness of the surface decreases and the glossiness increases.

When the glossiness of the surface of the negative active material layer, measured at an incident light angle of 85 °, satisfies 10 to 37, the adhesive strength of the negative active material layer is higher than 10 gf / 20 mm to prevent the negative active material layer from peeling off. can When the gloss exceeds 37, the binder polymer is located too much on the surface of the negative active material layer, and the stability of the negative active material layer may deteriorate due to a decrease in adhesive strength.

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

At this time, the negative electrode may be prepared by applying a negative electrode slurry prepared by mixing a negative electrode mixture including a negative electrode active material, a conductive material, and a binder with an organic solvent on a negative electrode current collector, followed by drying and rolling.

The anode current collector is not particularly limited as long as it does not cause chemical change in the battery and has high conductivity. For example, it is formed on the surface of copper, stainless steel, aluminum, nickel, titanium, fired carbon, copper or stainless steel. A surface treated with carbon, nickel, titanium, silver, or the like, an aluminum-cadmium alloy, or the like may be used. In addition, the negative electrode current collector may have a thickness of typically 3 to 500 μm, and, like the positive electrode current collector, fine irregularities may be formed on the surface of the current collector to enhance bonding strength of the negative electrode active material. For example, it may be used in various forms such as films, sheets, foils, nets, porous materials, foams, and non-woven fabrics.

As the anode active material, a carbon material, lithium metal, silicon, tin, or the like, which can occlude and release lithium ions, may be used. The negative electrode active material may be used by mixing at least one of graphite, non-graphite, and silicon oxide. The graphite-based material may be, for example, artificial graphite or natural graphite. Representative examples of the non-graphite-based material include soft carbon and hard carbon. As the silicon oxide, silicon dioxide or the like can be used.

The conductive material is not particularly limited as long as it has conductivity without causing chemical change in the battery, and examples include graphite such as natural graphite or artificial graphite; carbon black such as carbon black, acetylene black, ketjen black, channel black, farnes black, lamp black, and thermal black; conductive fibers such as carbon fibers and metal fibers; conductive tubes such as carbon nanotubes; metal powders such as fluorocarbon, aluminum, and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; polyphenylene derivatives; graphene; A conductive material such as may be used.

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

According to one embodiment of the present invention, the content of the binder polymer is 1 part by weight to 4 parts by weight, 1.5 parts by weight to 3.5 parts by weight, or 2.5 parts by weight to 4 parts by weight based on 100 parts by weight of the negative electrode active material layer, or It may be 1 to 2.5 parts by weight. When the content of the binder polymer satisfies this range, the binding property of the electrode active material, that is, the adhesion between the current collector and the active material layer is improved, and the movement of electrons and lithium ions in the battery is smooth, resulting in an increase in cell resistance. can be prevented

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

The negative electrode may be manufactured by the following method, but is not limited thereto.

First, a slurry for a negative electrode is prepared by mixing a negative electrode 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 negative electrode 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 slurry for the coating layer for the negative electrode active material. A method of mixing the materials is not particularly limited, and a method commonly used in the art may be used.

Next, the prepared slurry for a negative electrode is applied to at least one surface of the negative electrode current collector, and then dried.

The method of coating the negative electrode slurry on the negative electrode current collector is not particularly limited, but, for example, bar coating method, knife coating method, roll coating method, blade coating method, die coating method, micro gravure coating method, comma coating method, a slot die coating method, a lip coating method, or a solution casting method may be used.

At this time, the drying step may be performed a plurality of times. For example, it may be performed 2 to 5 times, or 2 to 3 times, and the higher the order, the higher the drying temperature.

According to one embodiment of the present invention, the drying step may be performed three times, and the primary drying of the three drying steps may be performed at a temperature of 25 to 40 ° C. or 30 to 40 ° C., Secondary drying may be performed at a temperature of 120 to 140 ° C, or 125 to 130 ° C, or 130 to 140 ° C, and third drying may be performed at a temperature of 140 to 160 ° C, or 140 to 155 ° C, or 150 to 155 ° C. It can be carried out at a temperature of ° C. More specifically, the drying step is performed three times, and among the three drying steps, the primary drying may be performed at a temperature of 25 to 40 ° C. for 10 to 60 seconds, and the secondary drying is performed at 120 to 140 ° C. It may be performed for 120 to 150 seconds at a temperature of ℃, and the tertiary drying may be performed for 90 to 160 seconds at a temperature of 140 to 160 ℃.

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

The positive electrode is a slurry prepared by mixing a positive electrode active material, a conductive material, a binder and a solvent, and then directly coated on a metal current collector, or cast on a separate support, and the positive electrode active material film peeled from the support is laminated on the metal current collector Thus, an anode can be prepared.

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.Active materials used in the cathode include LiCoO ₂ , LiNiO ₂ , LiMn ₂ O ₄ , LiCoPO ₄ , LiFePO ₄ and LiNi _1-xyz Co _x M1 _y M2 _z O ₂ (M1 and M2 are independently Al, Ni, Co, Any one selected from the group consisting of Fe, Mn, V, Cr, Ti, W, Ta, Mg, and Mo, and x, y, and z are, independently of each other, the atomic fractions of oxide composition elements, which are 0

x<0.5, 0≤y<0.5, 0≤z<0.5, 0<x+y+z≤1), and may include any one active material particle selected from the group consisting of or a mixture of two or more of them.

Meanwhile, the conductive material, binder, and solvent may be used the same as those used in preparing the negative electrode.

The separator is a conventional porous polymer film used as a conventional separator, for example, a polyolefin polymer such as ethylene homopolymer, propylene homopolymer, ethylene/butene copolymer, ethylene/hexene copolymer, and ethylene/methacrylate copolymer. The prepared porous polymer film may be used alone or in a laminated manner. In addition, an insulating thin film having high ion permeability and mechanical strength may be used. The separator may include a safety reinforced separator (SRS) in which a ceramic material is thinly coated on a surface of the separator. In addition, conventional porous non-woven fabrics, for example, non-woven fabrics made of high melting point glass fibers, polyethylene terephthalate fibers, etc. may be used, but are not limited thereto.

The electrolyte solution includes a lithium salt as an electrolyte and an organic solvent for dissolving the lithium salt.

The lithium salt may be used without limitation as long as it is commonly used in an electrolyte solution for a secondary battery. For example, as an anion of the lithium salt, F ^- , Cl ^- , I ^- , NO ₃ ^- , N(CN) ₂ ^- , BF ₄ ^- , ClO ₄ ^- , PF ₆ ^- , (CF ₃ ) ₂ PF ₄ ^- , (CF ₃ ) ₃ PF ₃ ^- , (CF ₃ ) ₄ PF ₂ ^- , (CF ₃ ) ₅ PF ^- , (CF ₃ ) ₆ P ^- , CF ₃ SO ₃ ^- , CF ₃ CF ₂ SO ₃ ^- , (CF ₃ SO ₂ ) ₂ N ^- , (FSO ₂ ) ₂ N ^- , CF ₃ CF ₂ (CF ₃ ) ₂ CO ^- , ( CF ₃ SO ₂ ) ₂ CH ^- , (SF ₅ ) ₃ C ^- , (CF ₃ SO ₂ ) ₃ C ^- , CF ₃ (CF ₂ ) ₇ SO ₃ ^- , CF ₃ CO ₂ ^- , CH ₃ CO ₂ ^- , One selected from the group consisting of SCN ^- and (CF ₃ CF ₂ SO ₂ ) ₂ N ^- may be used.

Any organic solvent included in the electrolyte may be used without limitation as long as it is commonly used, and representative examples include propylene carbonate, ethylene carbonate, diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, dipropyl carbonate, and dimethyl sulfoxide. At least one selected from the group consisting of side, acetonitrile, dimethoxyethane, diethoxyethane, vinylene carbonate, sulfolane, gamma-butyrolactone, propylene sulfite, and tetrahydrofuran may be used.

In particular, among the carbonate-based organic solvents, ethylene carbonate and propylene carbonate, which are cyclic carbonates, are high-viscosity organic solvents and have a high dielectric constant, so they can be preferably used because they dissociate lithium salts in the electrolyte well. When a low-viscosity, low-dielectric constant linear carbonate such as carbonate is mixed and used in an appropriate ratio, an electrolyte solution having high electrical conductivity can be prepared and can be more preferably used.

Optionally, the electrolyte solution stored according to the present invention may further include additives such as an overcharge inhibitor included in conventional electrolyte solutions.

In the lithium secondary battery according to one embodiment of the present invention, an electrode assembly is formed by disposing a separator between a positive electrode and a negative electrode, the electrode assembly is placed in, for example, a pouch, a cylindrical battery case, or a prismatic battery case, and then the electrolyte is After injection, the secondary battery can be completed. Alternatively, a lithium secondary battery may be completed by laminating the electrode assembly, impregnating it with an electrolyte, and sealing the resulting product in a battery case.

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

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 also can be preferably used as a unit cell in a medium-large battery module including a plurality of battery cells. Preferable examples of the medium-to-large-sized device include an electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, and a power storage system. In particular, it is useful for hybrid electric vehicles and batteries for renewable energy storage, which are areas where high power is required. can be used

Hereinafter, examples will be described in detail to aid understanding of the present invention. However, the embodiments according to the present invention can be modified in many different forms, and the scope of the present invention should not be construed as being limited to the following examples. Embodiments of the present invention are provided to more completely explain the present invention to those skilled in the art.

Example 1 - Preparation of negative electrode

Anode slurry by mixing artificial graphite, natural graphite, carbon black, Carboxy Methyl Cellulose (CMC), and Styrene-Butadiene Rubber (SBR) with water in a weight ratio of 30 : 66.5 : 1.0 : 1.0 : 1.5 was manufactured.

The anode slurry was coated on a copper foil (Cu-foil) with a capacity of 3.5 mAh/cm ² to form a thin electrode plate, followed by primary drying at 40° C. for 30 seconds, secondary drying at 130° C. for 120 seconds, and drying at 150° C. After tertiary drying for 150 seconds, a negative electrode was prepared by pressing.

<Manufacture of positive electrode>

96wt% of Li[Ni _0.6 Mn _0.2 Co _0.2 ]O ₂ as a cathode active material, 1wt% of a carbon nanotube (bundle type) with a diameter of 10 nm and a length of 50 μm as a conductive material, and polyvinylidene fluoride as a binder polymer ( A slurry was prepared by mixing 3 wt% of polyvinylidene fluoride) in a solvent of N-Methyl-2-Pyrrolidinone (NMP) to have a solid content of 45 wt%. Mixing was performed at 1800 rpm for 25 minutes using a nobilta machine (Hosokawa Co.). Thereafter, a shear force of 250 N was applied to the mixture (Nobilta (Hosokawa micron)) to prepare a slurry (positive electrode slurry) for forming a positive electrode active material layer.

After coating the slurry for forming the positive electrode active material layer on one surface of an aluminum current collector having a thickness of 15 μm, it was dried at 100° C. for 5 minutes to prepare a positive electrode.

<Manufacture of lithium secondary battery>

LiPF ₆ was dissolved in an organic solvent in which ethylene carbonate (EC), dimethyl carbonate (DMC) and diethyl carbonate (DEC) were mixed in a composition of 1:2:1 (volume ratio) to a concentration of 1.0 M to form a non-aqueous electrolyte solution. manufactured.

A lithium secondary battery was prepared by interposing a polyethylene porous film as a separator between the positive electrode and the negative electrode prepared above, inserting the film into a pouch cell, and then injecting the electrolyte solution.

Examples 2 to 3

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

Comparative Examples 1 to 3

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

Experimental Example 1 - Gloss measurement

In the present invention, the glossiness is a measure of the glossiness of the surface, and means the intensity of light when reflected light is received at the same angle as incident light.

The gloss unit (GU) means a relative ratio when the surface gloss of a reference glass (a glass having a refractive index of 1.567) is set to 100.

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

Specifically, Dark Calibration made the surface gloss of 92 at 20°, 95 at 60°, and 99 at 85° using a reference glass. Then, the surface gloss of the active material layer of the negative electrode prepared in Examples 1 to 3 and Comparative Examples 1 to 3 was measured. For gloss measurement, the measurement part was randomly selected and the average was obtained after measuring 5 times at 85° each.

Experimental Example 2 - Adhesion (Peel Test)

The negative electrodes prepared in Examples 1 to 3 and Comparative Examples 1 to 3 were adhered to the slide glass using a double-sided tape for removal. After this, TA. A 90° Peel Test was performed at a speed of 5 mm/sec using XT plusC (Stable Micro Systems) equipment. The results are shown in Table 2.

Experimental Example 3 - Resistance measurement of cathode

The interface resistance between the electrode layer and the current collector is measured using a multi-probe tester. Interfacial resistances of the negative electrodes prepared in Examples 1 to 3 and Comparative Examples 1 to 3 were cut into 5 cm x 5 cm using a punching machine, and the interfacial resistance was measured under the following conditions. The results are shown in Table 2.

Current: 100μA (positive), 10mA (negative)

Speed: low

Voltage range: 0.5V

Current collector resistivity: 8.28*10 _-6 Ωㆍcm (positive), 1.68*10 ^-6 Ωㆍcm (negative)

Experimental Example 4 - Calculation of the content of the binder polymer on the surface of the negative electrode active material layer

The negative electrodes prepared in Examples 1 to 3 and Comparative Examples 1 to 3 were prepared in a size of 1 cm X 1 cm and put in a container containing OsO4 (Osmium tetraoxide) to be sealed. After 3 hours, the negative electrode was taken out, put in a vacuum oven and dried for 48 hours, and the binder polymer included in the negative electrode active material layer was dyed using OsO ₄ .

The content of the binder polymer on the surface of the dyed cathode was analyzed using energy dispersive X-ray spectroscopy. The atomic ratio of osmium on the surface of the negative electrode active material layer was measured under the conditions shown in Table 1 using X-Max80 and an Extreme detector (Oxford Co.). The results are shown in Table 2.

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

Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Comparative Example 3 dry condition 1st drying 40℃ 30 seconds 30℃ 30 seconds 40℃ 60 seconds 90℃
300 seconds 150℃
300 seconds 80℃
300 seconds 2nd 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 on the surface of the negative electrode active material layer (wt%) 0.5 0.6 0.8 1.1 1.2 0.3

Referring to Table 2, the negative electrodes of Examples 1 to 3 in which the glossiness of the surface of the negative electrode active material layer, measured at an incident light angle of 85 °, satisfies the range of 10 to 37, the Os content dyed on the surface of the negative electrode active material layer It can be seen that the content of the binder polymer distributed on the surface is small and uniformly distributed in the active material layer, and as a result, it can be confirmed that excellent adhesive strength and low resistance characteristics are exhibited.

Although the present invention has been described above with limited examples and drawings, the present invention is not limited thereto and will be described below along with the technical spirit of the present invention by those skilled in the art to which the present invention belongs. Of course, various modifications and variations are possible within the scope of equivalence of the claims.

Claims (13)

current collector;
A negative active material layer located on at least one surface of the current collector and containing a negative active material, a conductive material, and a binder polymer;
The glossiness of the surface of the negative electrode active material layer measured at an incident light angle of 85 ° is 10 to 37,
The cathode, characterized in that the gloss means the intensity of light when the reflected light is received at the same angle as the incident light. According to claim 1,
The negative electrode, characterized in that the relative ratio of the glossiness when the surface gloss of glass having a refractive index of 1.567 is 100. According to claim 1,
A negative electrode, characterized in that the glossiness of the surface of the negative electrode active material layer is 11 to 36.5. According to claim 1,
A negative electrode, characterized in that the content of the binder polymer is 1 part by weight to 4 parts by weight based on 100 parts by weight of the negative electrode active material layer. According to claim 4,
A negative electrode, characterized in that the content of the binder polymer is 1.5 parts by weight to 3.5 parts by weight based on 100 parts by weight of the negative electrode active material layer. According to claim 1,
The negative electrode, characterized in that the binder polymer comprises a rubber-based binder polymer and a water-soluble polymer-based binder polymer. According to claim 6,
The negative electrode, characterized in that the rubber-based binder polymer comprises styrene-butadiene rubber (SBR), fluorine-based rubber, ethylene propylene rubber, butadiene rubber, isoprene rubber, acrylic rubber, silane-based rubber, or two or more of these. According to claim 6,
The negative electrode, characterized in that the water-soluble polymer-based binder polymer includes carboxymethyl cellulose (CMC), cellulose, polyvinyl alcohol, polyacrylic acid, or two or more of these. preparing a slurry for an anode in which an anode active material, a conductive material, and a binder polymer are mixed in a solvent; and
The manufacturing method of claim 1 including the step of drying the slurry for the negative electrode on at least one surface of the negative electrode current collector. According to claim 9,
Method for producing a negative electrode, characterized in that the drying step is performed a plurality of times. According to claim 10,
A method for producing a negative electrode, characterized in that the drying temperature increases as the number of times of the drying step increases. According to claim 10,
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. Method for producing a negative electrode, characterized in that carried out at ℃ temperature. It includes a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode,
The negative electrode is a lithium secondary battery, characterized in that the negative electrode according to any one of claims 1 to 8.

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