Negative electrode for lithium secondary battery and method for manufacturing the same

Abstract

The present technology relates to a negative electrode for a lithium secondary battery and a manufacturing method thereof, by treating the surface of a negative electrode current collector with normal pressure plasma, thereby controlling the static water contact angle of the surface of the negative electrode current collector and the angle (e.g., contact angle) formed by the end portion of the negative electrode mixture layer and the negative electrode current collector within a certain range, the adhesion between the negative electrode current collector and the negative electrode mixture layer can be improved, and the N / P ratio reversal between the positive electrode and the negative electrode at the end portion of the electrode assembly and the occurrence of uncalendering in the negative electrode mixture layer can be prevented, so that the effects of improving the safety and performance reduction of a lithium secondary battery containing the negative electrode are excellent.

Description

TECHNICAL FIELD

[0001] The present application relates to a negative electrode for a lithium secondary battery and a manufacturing method thereof.

[0002] This application claims the benefit of priority from Korean Patent Application No. 10-2021-0106413, filed on August 12, 2021, the entire contents of which are incorporated herein by reference. BACKGROUND

[0003] A lithium secondary battery is used as a battery while repeating intercalation and deintercalation of lithium ions in a positive electrode and a negative electrode. Between these electrodes, a lithium ion-containing salt electrolyte in which lithium ions move but electrons cannot move, and a separator that separates the positive electrode and the negative electrode so that the positive electrode and the negative electrode do not come into contact to prevent short circuiting between the electrodes due to contact are provided.

[0004] In a lithium secondary battery, much research has been conducted in terms of high capacity and high density, and recently, various research has been conducted to improve lifespan and safety. Specifically, an electrode used in a lithium secondary battery is generally manufactured by coating an electrode slurry on a current collector to a predetermined thickness and drying the coated electrode to form a mixture layer, the mixture layer thus formed becomes a solid phase while the liquid binder solvent is dried to become a gas phase at the time of slurry drying, and exists as a solid binder between the particles and between the current collector and the particles to have adhesion. In this case, when the adhesion between the particles and the current collector is reduced, the electron conduction speed is reduced due to the resistance to movement of electrons from the particles to the current collector, and thus, there is a problem in that the charge / discharge speed characteristics and the cycle characteristics of the battery are reduced. In addition, because the current collector is easily separated from the mixture layer when an external force is applied to the battery, there is also a limitation in that the safety is reduced.

[0005] To improve such problems, a technology of increasing the binder content of the mixture layer to improve the adhesion between the electrode mixture layer and the current collector, or forming a primer layer to modify the surface structure of the current collector or improve the adhesion has been developed. However, when the binder content of the electrode mixture layer is increased, because the content of the electrode active material and the conductive material in the mixture layer is relatively reduced to thereby increase the electrode resistance and reduce the conductivity, there is a limitation in that the battery performance is reduced. In addition, when the surface structure of the current collector is modified or a primer layer is formed, because the contact angle formed by the end portion of the negative electrode mixture layer and the current collector is reduced when the electrode is a negative electrode, the N / P ratio between the positive electrode and the negative electrode can be reversed, and thus, safety problems such as internal short circuiting and waste of battery capacity can occur. Therefore, there is a need to develop a technology capable of improving both the safety and the performance of the battery by increasing the adhesion between the electrode mixture layer and the current collector.

[0006] [Related Art Documents]

[0007] [Patent Literature]

[0008] Korean Patent Application Publication No. 10-2016-0033482. Summary of the Invention

[0009] Technical issues

[0010] Therefore, one object of the present invention is to provide an electrode, particularly a negative electrode for lithium secondary batteries, which can improve the adhesion between the electrode mixture layer and the electrode current collector, while improving the safety or performance degradation of the battery caused by the reversal of the N / P ratio between the positive and negative electrodes.

[0011] Technical solution

[0012] To address the aforementioned problems, one embodiment of the present invention provides a negative electrode for a lithium secondary battery, the negative electrode for a lithium secondary battery comprising a negative electrode current collector and a negative electrode mixture layer, the negative electrode mixture layer comprising a negative electrode active material on at least one surface of the negative electrode current collector, and wherein the static water contact angle of the negative electrode current collector is 60° to 100°.

[0013] In this case, at least one surface of the negative electrode current collector may be surface-treated with an alkyl group having 1 to 6 carbon atoms.

[0014] Furthermore, the angle formed between the end of the negative electrode mixture layer and the negative electrode current collector can be 60° or more, and in the negative electrode, the peel strength of the negative electrode mixture layer relative to the negative electrode current collector according to ASTM D903 can be in the range of 10 gf / cm to 50 gf / cm.

[0015] Furthermore, one embodiment of the present invention provides a method for manufacturing a negative electrode for a lithium secondary battery, the method comprising: surface treating a negative electrode current collector with atmospheric pressure plasma; and forming a negative electrode mixture layer by applying and drying a slurry containing a negative electrode active material on at least one surface of the surface-treated negative electrode current collector, wherein the negative electrode current collector is surface treated by atmospheric pressure plasma treatment under conditions containing a mixture of inert gas and hydrocarbon gas.

[0016] Here, in the surface treatment, the atmospheric pressure plasma treatment can be performed for 0.05 seconds to 1 hour using radio frequency (RF) power with a frequency of 0.1 MHz to 50 MHz.

[0017] Furthermore, the atmospheric pressure plasma treatment can be performed under conditions of a mixture of inert gas and hydrocarbon gas, and the mixture can contain the hydrocarbon gas at a partial pressure of 0.1% to 10%.

[0018] In addition, the hydrocarbon gas may include one or more of methane (CH4) gas and ethane (C2H6) gas.

[0019] In addition, the negative electrode current collector may contain any of stainless steel, copper, nickel, carbon, calcined carbon, titanium, or aluminum-cadmium alloy.

[0020] Beneficial effects

[0021] In the negative electrode for lithium secondary batteries according to the present invention, by treating the surface of the negative electrode current collector with atmospheric pressure plasma, the static water contact angle of the surface of the negative electrode current collector and the angle (e.g., contact angle) formed by the end of the negative electrode mixture layer and the negative electrode current collector are controlled within a specific range. This improves the adhesion between the negative electrode current collector and the negative electrode mixture layer. Furthermore, it prevents the N / P ratio reversal induced at the end of the electrode assembly and the occurrence of unrolling in the negative electrode mixture layer. This results in excellent improvement in the safety and performance degradation of the lithium secondary battery containing the negative electrode. Attached Figure Description

[0022] Figure 1 This is an image showing the measurement results of the static water contact angle of the negative current collector.

[0023] Figure 2 This is an image showing the measured contact angle of the negative electrode slurry relative to the negative electrode current collector. Detailed Implementation

[0024] Although the present invention is susceptible to various variations and substitutions, its specific implementation will be described in detail herein.

[0025] However, it should be understood that the invention is not intended to be limited to the specific forms disclosed; rather, the invention covers all variations, equivalents, and substitutions that fall within the spirit and scope of the invention.

[0026] It should be further understood that, when used herein, the terms “comprising,” “including,” “containing,” and / or “comprising” specify the presence of the described features, figures, steps, operations, elements, components, and / or groups thereof, but do not exclude the presence or addition of more than one other feature, figure, step, operation, element, component, and / or group thereof.

[0027] Furthermore, when this document describes a portion of a layer, membrane, region, plate, etc., "on" another portion, the description includes the meaning that the portion is "directly on" the other portion, and also includes the meaning that another portion is located in between. Conversely, when this document describes a portion of a layer, membrane, region, plate, etc., "below" another portion, the description includes the meaning that the portion is "directly below" the other portion, and also includes the meaning that another portion is located in between. Moreover, when this document describes an element being positioned "on" another element, it means not only that the element is positioned above the other element, but also that the element is positioned below the other element.

[0028] Furthermore, in this invention, the term "major component" may refer to a component whose content relative to the total weight of the composition or a specific component is 50% by weight or more, 60% by weight or more, 70% by weight or more, 80% by weight or more, 90% by weight or more, 95% by weight or more, or 97.5% by weight or more. In some cases, the term "major component" may also refer to a component whose content is 100% by weight when the component constitutes the entire composition or a specific component.

[0029] Furthermore, in this invention, the term "solids of the mixture layer" can refer to the remaining components of the negative electrode slurry from which the solvent has been removed, used in the manufacture of the mixture layer.

[0030] The invention will be described in more detail below.

[0031] Negative electrode for lithium secondary battery

[0032] One embodiment of the present invention provides

[0033] A negative electrode for a lithium secondary battery, the negative electrode comprising a negative electrode current collector and a negative electrode mixture layer, the negative electrode mixture layer comprising a negative electrode active material on at least one surface of the negative electrode current collector, and...

[0034] The static water contact angle of the negative current collector is 60° to 100°.

[0035] The negative electrode for a lithium secondary battery according to the present invention has the following structure: wherein a negative electrode mixture layer containing a negative electrode active material is disposed on the negative electrode current collector.

[0036] In this case, there are no particular limitations on the negative electrode current collector, as long as it is conductive and does not cause chemical changes in the battery. Specifically, a negative electrode current collector containing any of stainless steel, copper, nickel, carbon, calcined carbon, titanium, or an aluminum-cadmium alloy can be used. As an example, a copper current collector can be used.

[0037] Furthermore, the surface of the negative electrode current collector on which the negative electrode mixture layer is formed is surface treated, thereby allowing the negative electrode current collector to exhibit high adhesion to the negative electrode mixture layer while having low affinity for water. To improve adhesion to the electrode mixture layer by hydrophilizing the surface of the current collector, conventional surface treatment methods used for electrode current collectors, such as plasma treatment and electrolytic treatment, are employed. However, when the above methods are applied to the negative electrode current collector for lithium secondary batteries, while adhesion to the negative electrode mixture layer is improved, the contact angle (e.g., the "slip angle" of the negative electrode mixture layer) of the end of the negative electrode mixture layer relative to the negative electrode current collector decreases, thus potentially reversing the N / P ratio at the ends of the positive and negative electrodes. Furthermore, when the contact angle of the negative electrode end relative to the negative electrode current collector decreases, unrolling may occur at the ends of the negative electrode mixture layer, which could cause deintercalation of the mixture layer.

[0038] Therefore, the present invention may include a configuration in which at least one surface of the negative electrode current collector is introduced into the at least one surface of the negative electrode current collector by treating it with atmospheric pressure plasma in the presence of a mixture of inert gas and hydrocarbon gas. In this case, the alkyl group having 1 to 6 carbon atoms may include one or more of methyl (CH3-), ethyl (CH3CH2-), n-propyl (CH3CH2CH2-), and n-butyl (CH3CH2CH2CH2-).

[0039] As an example, at least one surface of the negative electrode current collector can be treated with one or more alkyl groups selected from methyl (CH3-) and ethyl (CH3CH2-).

[0040] Furthermore, the alkyl group can be introduced into the surface of the negative electrode current collector in a predetermined proportion, and when carbon atom mapping on the negative electrode current collector is analyzed by field emission scanning electron microscopy (FE-SEM), it can be confirmed that the amount of carbon atoms relative to the total atoms is 1 atomic% to 40 atomic%. Specifically, it can be confirmed that the amount of carbon atoms relative to the total atoms is 1 atomic% to 30 atomic%, 1 atomic% to 20 atomic%, 1 atomic% to 15 atomic%, 10 atomic% to 40 atomic%, 20 atomic% to 40 atomic%, 10 atomic% to 30 atomic%, 20 atomic% to 30 atomic%, 10 atomic% to 20 atomic%, or 5 atomic% to 15 atoms.

[0041] Furthermore, by introducing alkyl groups onto the surface of the negative electrode current collector, the repulsion of the solvent contained in the slurry can be increased during the manufacturing of the negative electrode mixture layer, thereby achieving a large contact angle with the end of the negative electrode mixture layer and simultaneously imparting high adhesion to the negative electrode mixture layer.

[0042] Specifically, in the negative electrode current collector according to the present invention, a predetermined amount of alkyl groups is introduced to the surface of the negative electrode current collector, and the repulsive force against the solvent contained in the negative electrode slurry is increased. Therefore, when the negative electrode slurry is applied to the current collector, a large angle (i.e., the contact angle of the negative electrode slurry relative to the negative electrode current collector) can be achieved by the end of the applied negative electrode slurry relative to the current collector. Furthermore, the contact angle of the negative electrode slurry relative to the current collector can be equal to the angle (e.g., the sliding angle of the negative electrode mixture layer) formed by removing the solvent only from the negative electrode slurry and the current collector, and in some cases, the deviation of the angle can be within ±5%.

[0043] As an example, in the negative electrode according to the present invention, the contact angle of the negative electrode slurry relative to the negative electrode current collector can be 60° or more, more specifically, 70° or more, 80° or more, 90° or more, 100° or more, within the range of 60° to 100°, within the range of 60° to 80°, within the range of 60° to 75°, within the range of 65° to 95°, within the range of 60° to 95°, within the range of 70° to 99°, within the range of 65° to 89°, within the range of 65° to 84°, or within the range of 65° to 78°.

[0044] According to the present invention, by controlling the static water contact angle of the negative electrode current collector and the angle formed between the end of the negative electrode mixture layer formed on the negative electrode current collector and the negative electrode current collector to meet the above range, it is possible to prevent the negative electrode mixture layer from being unrolled, and at the same time prevent the N / P ratio from reversing at the end between the positive electrode mixture layer and the negative electrode mixture layer.

[0045] Furthermore, in the negative electrode current collector according to the present invention, a predetermined amount of alkyl groups is introduced to the surface to increase the surface energy, thereby adjusting the static water contact angle of the negative electrode current collector to meet the above-mentioned specific range, and achieving high adhesion to the components constituting the negative electrode mixture layer, such as solids of the mixture layer including negative electrode active materials, adhesives, and conductive agents.

[0046] As an example, the negative electrode according to the present invention may comprise a negative electrode current collector with a static water contact angle of 60° to 100°. Specifically, the negative electrode may comprise a negative electrode current collector with a static water contact angle of 60° to 90°, 60° to 80°, 65° to 95°, 65° to 80°, 60° to 70°, 70° to 80°, or 64° to 79°.

[0047] As another example, in the negative electrode according to the invention, the peel strength of the negative electrode mixture layer relative to the negative electrode current collector, as measured according to ASTM D903, can be in the range of 10 gf / cm to 50 gf / cm. Specifically, the peel strength of the negative electrode mixture layer relative to the negative electrode current collector can be in the range of 10 gf / cm to 40 gf / cm, 10 gf / cm to 30 gf / cm, 10 gf / cm to 20 gf / cm, 20 gf / cm to 50 gf / cm, 30 gf / cm to 50 gf / cm, 20 gf / cm to 40 gf / cm, or 15 gf / cm to 43 gf / cm.

[0048] On the other hand, the negative electrode mixture layer is a layer containing a negative electrode active material and imparting electrical activity to the battery, and may contain the negative electrode active material, conductive material, binder, additives, etc.

[0049] The negative electrode active material may include, for example, carbon materials and silicon materials. The carbon material refers to a carbon material containing carbon atoms as its main component, and may include graphite with a fully layered crystal structure, such as natural graphite; soft carbon with a low-crystallinity layered crystal structure (graphene structure in which hexagonal carbon units are arranged in a honeycomb layered form); hard carbon with a structure in which such a structure is mixed with an amorphous portion; artificial graphite; expanded graphite; carbon fiber; non-graphitized carbon; carbon black; acetylene black; Ketjen black; carbon nanotubes; fullerenes; activated carbon; graphene, etc., and the carbon material may preferably include one or more selected from the group consisting of natural graphite, artificial graphite, graphene, and carbon nanotubes.

[0050] Furthermore, as a metallic component, the silicon material may include silicon (Si) particles and silicon oxide (e.g., SiO2). x The silicon material comprises one or more of the following particles (0.8 ≤ x ≤ 2.2) as particles containing silicon (Si) as the main component. As an example, the silicon material may include silicon (Si) particles, silicon monoxide (SiO) particles, silicon dioxide (SiO2) particles, or mixtures thereof.

[0051] Furthermore, the silicon material may be in the form of a mixture of crystalline and amorphous particles, and the proportion of amorphous particles relative to 100 parts by weight of total silicon material may be 50 to 100 parts by weight, specifically 50 to 90 parts by weight, 60 to 80 parts by weight, or 85 to 100 parts by weight. In this invention, by controlling the proportion of amorphous particles contained in the silicon material within the above-mentioned range, thermal stability and flexibility can be improved without reducing the electrical performance of the electrode.

[0052] Furthermore, the negative electrode active material may comprise carbon and silicon materials, and the content of carbon and silicon materials may be 1 to 20 parts by weight relative to 100 parts by weight of the negative electrode mixture layer. Specifically, the content of carbon and silicon materials may be 5 to 20 parts by weight, 3 to 10 parts by weight, 8 to 15 parts by weight, 13 to 18 parts by weight, or 2 to 7 parts by weight relative to 100 parts by weight of the negative electrode mixture layer.

[0053] According to the present invention, during the initial charging and discharging of the battery, by adjusting the content of carbon and silicon materials contained in the negative electrode active material to the above-mentioned range, lithium consumption and irreversible capacity loss can be reduced, and the charging capacity per unit mass can be improved.

[0054] Furthermore, the adhesive may include polyvinyl alcohol (PVA), carboxymethyl cellulose (CMC), hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride (PVC), carboxylated polyvinyl chloride (C-PVC), polyvinyl fluoride, ethylene oxide-containing polymers, polyvinylpyrrolidone, polyurethane (PU), polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), polyethylene (PE), polypropylene (PP), styrene-butadiene rubber (SBR), acrylated styrene-butadiene rubber, epoxy resin, nylon, etc. As an example, the adhesive may use one or more of carboxymethyl cellulose (CMC) and styrene-butadiene rubber (SBR).

[0055] Furthermore, relative to 100 parts by weight of the total negative electrode mixture layer, the content of the adhesive can be 1 to 10 parts by weight, specifically 2 to 8 parts by weight, or the content of the conductive material can be 1 to 5 parts by weight.

[0056] Furthermore, the average thickness of the negative electrode mixture layer can be from 100 μm to 200 μm, specifically from 100 μm to 180 μm, 100 μm to 150 μm, 120 μm to 200 μm, 140 μm to 200 μm, or 140 μm to 160 μm.

[0057] Since the negative electrode for lithium secondary batteries according to the present invention has the structure described above, the adhesion between the negative electrode current collector and the negative electrode mixture layer can be increased, and a large contact angle of the end of the mixture layer relative to the negative electrode current collector can be achieved in balance with adhesion, thereby exhibiting better battery safety and superior performance.

[0058] Method for manufacturing negative electrode for lithium secondary battery

[0059] Furthermore, one embodiment of the present invention provides a method for manufacturing a negative electrode for a lithium secondary battery, the method comprising:

[0060] Surface treatment of the negative electrode current collector using atmospheric pressure plasma; and

[0061] A negative electrode mixture layer is formed by applying and drying a slurry containing a negative electrode active material onto at least one surface of a surface-treated negative electrode current collector.

[0062] The negative electrode current collector is surface-treated by atmospheric pressure plasma treatment under conditions containing a mixture of inert gas and hydrocarbon gas.

[0063] In the method for manufacturing a negative electrode for a lithium secondary battery according to the present invention, before applying the negative electrode mixture layer with a slurry to the surface of the negative electrode current collector, the area on which the negative electrode slurry is applied is surface treated with atmospheric pressure plasma, and then a negative electrode mixture layer is formed by applying and drying a negative electrode slurry containing a negative electrode active material to the surface-treated area, thereby manufacturing a negative electrode for a lithium secondary battery.

[0064] Here, surface treatment can be performed by treating the entire surface of the negative electrode current collector with atmospheric pressure plasma, or by treating only a portion of the area where the negative electrode mixture layer is formed with atmospheric pressure plasma. Furthermore, in the manufacturing method, during atmospheric pressure plasma treatment, alkyl groups having 1 to 6 carbon atoms can be introduced to the surface of the negative electrode current collector using a mixed gas containing hydrocarbon gases in addition to an inert gas.

[0065] Specifically, atmospheric pressure plasma is generated as follows: An alternating electric field is applied between electrodes facing each other, accelerating electrons to high energies within the reactor. These accelerated electrons collide with a gas supplied to the reactor (e.g., a mixture of inert and hydrocarbon gases) and separate into atomic ions. The separated ions combine with surrounding electrons to form free radicals, which then collide with electrons again and decompose into free radicals. The free radicals generated by repeating this process are ejected onto the surface of a negative electrode current collector to be treated, thereby removing organic matter and causing alkyl groups to bind to the surface of the current collector, thus altering its surface properties.

[0066] Here, hydrocarbon gases can be used without restriction, as long as they are gases that can provide alkyl groups with 1 to 6 carbon atoms. Specifically, methane (CH4), ethane (CH3CH3), n-propane (CH3CH2CH3), n-butane (CH3CH2CH2CH3), etc., can be used.

[0067] In addition, accordingly, an alkyl group having 1 to 6 carbon atoms can be introduced into the surface of the surface-treated negative electrode current collector, and the alkyl group having 1 to 6 carbon atoms may include one or more of methyl (CH3-), ethyl (CH3CH2-), n-propyl (CH3CH2CH2-) and n-butyl (CH3CH2CH2CH2-).

[0068] As an example, during atmospheric pressure plasma treatment, one or more gases, namely methane (CH4) and ethane (CH3CH3), can be used to perform surface treatment on the negative electrode current collector via one or more alkyl groups, namely methyl (CH3-) and ethyl (CH3CH2-).

[0069] According to the present invention, as described above, by limiting the type of alkyl group introduced to the surface of the negative electrode current collector, the hydrophobicity of the current collector surface can be prevented from increasing significantly due to the increase in hydrocarbon chain length.

[0070] Furthermore, a predetermined proportion of alkyl groups can be introduced into the surface of the negative electrode current collector. For this purpose, when performing atmospheric pressure plasma treatment, the partial pressure of hydrocarbon gases contained in the mixed gas, the flow rate of the mixed gas, the frequency conditions of the power supply, etc., can be controlled within a specific range.

[0071] Specifically, in the method for manufacturing a negative electrode for a lithium secondary battery according to the present invention, during atmospheric pressure plasma treatment, the partial pressure of the hydrocarbon gas contained in the mixed gas can be adjusted to 0.1% to 10%, more specifically, the partial pressure of the hydrocarbon gas can be adjusted to 0.1% to 8%, 0.1% to 5%, 0.1% to 3%, 0.5% to 5%, 1% to 7%, 5% to 9%, 3% to 7%, 2% to 8%, or 1% to 5%.

[0072] As an example, in the method for manufacturing a negative electrode for a lithium secondary battery according to the present invention, a gas containing an inert gas and a hydrocarbon gas can be used as the mixed gas during atmospheric pressure plasma treatment, and the partial pressure of the hydrocarbon gas can be 3% to 5% of the total gas.

[0073] Furthermore, in atmospheric pressure plasma processing, the aforementioned mixed gas is introduced at a flow rate of 0.1 L / min to 40 L / min, preferably 1 L / min to 10 L / min. When the flow rate is less than 0.1 L / min, the process time increases, and when the flow rate exceeds 40 L / min, stability decreases.

[0074] In addition, atmospheric pressure plasma treatment for 0.05 seconds to 1 hour can be performed using radio frequency (RF) power with a frequency of 0.1 MHz to 50 MHz. Specifically, atmospheric pressure plasma treatment for 0.05 seconds to 30 minutes, 0.05 seconds to 20 minutes, 0.05 seconds to 10 minutes, 0.05 seconds to 5 minutes, 0.05 seconds to 1 minute, 0.05 seconds to 10 seconds, or 0.05 seconds to 2 seconds can be performed using RF power with frequencies of 0.1 MHz to 20 MHz, 0.1 MHz to 10 MHz, 1 MHz to 50 MHz, 5 MHz to 30 MHz, 10 MHz to 30 MHz, 20 MHz to 40 MHz, or 1 MHz to 10 MHz.

[0075] On the other hand, there are no particular limitations on the negative electrode current collector, as long as it is conductive and does not cause chemical changes in the battery. Specifically, a negative electrode current collector containing any of stainless steel, copper, nickel, carbon, calcined carbon, titanium, or aluminum-cadmium alloy can be used. As an example, a copper current collector can be used.

[0076] Preferred implementation scheme

[0077] The invention will be described in more detail below with reference to examples and experimental cases.

[0078] However, the embodiments and experimental examples described below are for illustrative purposes only, and the scope of the invention is not limited thereto.

[0079] Examples 1 to 3 and Comparative Examples 1 to 7. Manufacturing of negative electrodes for lithium secondary batteries.

[0080] The entire surface of a copper (Cu) current collector supplied via a transfer path was treated for 0.05 to 1 second using atmospheric pressure plasma generated with RF power. During this atmospheric pressure plasma treatment, a mixed gas was supplied at a flow rate of 5 ± 0.1 L / min, and the composition and partial pressure of the mixed gas, as well as the frequency of the RF power, were adjusted as shown in Table 1 below.

[0081] In addition, carbon atom mapping was performed on each surface-treated negative electrode current collector by FE-SEM analysis to measure the ratio of carbon atoms to total atoms on the surface of the negative electrode current collector. The results are shown in Table 1 below.

[0082] Subsequently, a negative electrode slurry (solvent: water) comprising 83 wt% graphite and 15 wt% silicon dioxide (SiO2) (based on solids) as negative electrode active materials and 2 wt% SBR as a binder was applied to the surface of a copper current collector that had undergone plasma treatment. The slurry was dried at 100°C and then calendered to manufacture a negative electrode for lithium-ion batteries. Here, it was determined whether the ends of the negative electrode mixture layer were not calendered due to the small angle between the ends of the negative electrode mixture layer and the negative electrode current collector during calendering; the results are shown in Table 1 below.

[0083] [Table 1]

[0084]

[0085] Experimental example.

[0086] To evaluate the negative electrode for lithium secondary batteries according to the present invention, the following experiments were conducted.

[0087] A) Measurement of static water contact angle of negative electrode current collector

[0088] The surfaces of the negative electrode current collectors were subjected to atmospheric pressure plasma treatment in the same manner as in Examples 1 to 3 and Comparative Examples 1 to 7. Static water contact angle (static WCA) measurements were performed on each atmospheric pressure plasma-treated negative electrode current collector using a contact angle measuring device (model name: SmartDrop, manufactured by Femtofab Ltd.). Each measurement was performed by dripping 10 μl of water or oil onto each surface, and the measurements were repeated three times to obtain the average value. The results are shown below. Figure 1 And in Table 2 below.

[0089] B) Measurement of contact angle of negative electrode slurry with respect to negative electrode current collector

[0090] The surfaces of the negative electrode current collectors were subjected to atmospheric pressure plasma treatment in the same manner as in Examples 1 to 3 and Comparative Examples 1 to 7. Subsequently, three drops of negative electrode slurry were dropped onto the surface of each atmospheric pressure plasma-treated negative electrode current collector, and the angle (i.e., contact angle) formed between the negative electrode slurry with droplets formed on the surface and the negative electrode current collector was measured using a contact angle measuring device (model name: SmartDrop, manufactured by Femtofab Ltd.).

[0091] At this point, the negative electrode slurry comprises 83 wt% graphite and 15 wt% silicon dioxide (SiO2) (based on solids) as the negative electrode active material, 2 wt% SBR as the binder, and water as the solvent at an amount of 10 wt% relative to the total solids. Measurement results are shown in... Figure 2 And in Table 2 below.

[0092] C) Measurement of adhesion between negative electrode current collector and negative electrode mixture layer

[0093] For the negative electrodes manufactured in Examples 1 to 3 and Comparative Examples 1 to 7, the 180° peel strength of the negative electrode mixture layer was measured according to ASTM D903, and the results are shown in Table 2 below.

[0094] [Table 2]

[0095]

[0096] like Figure 1 and Figure 2 As can be seen from Table 2, in the negative electrode for lithium secondary batteries according to the present invention, the adhesion between the negative electrode current collector and the negative electrode mixture layer is excellent, and the end of the negative electrode mixture layer has a large contact angle relative to the negative electrode current collector.

[0097] Specifically, the negative electrode for the lithium secondary battery in the embodiment exhibits a static water contact angle of 66° to 95°, and the contact angle formed by the end of the negative electrode mixture layer and the negative electrode current collector is 60° to 90°. This means that alkyl groups are introduced to the surface of the negative electrode current collector in a predetermined ratio (specifically, a predetermined atomic ratio), so that when the negative electrode mixture layer is manufactured, a repulsive force is induced against the solvent contained in the negative electrode slurry, specifically water, thereby achieving a large contact angle between the end of the negative electrode current collector and the negative electrode mixture layer.

[0098] Furthermore, in the negative electrode for lithium secondary batteries of the embodiments, it was confirmed that the peel strength between the negative electrode current collector and the negative electrode mixture layer was in the range of 10 gf / cm to 40 gf / cm. This means that the adhesion between the negative electrode current collector and the negative electrode mixture layer is improved.

[0099] Based on these results, it can be seen that in the negative electrode for lithium secondary batteries according to the present invention, the static water contact angle of the negative electrode current collector surface and the angle (e.g., contact angle) formed by the end of the negative electrode mixture layer and the negative electrode current collector can be controlled within a specific range by treating the surface of the negative electrode current collector with atmospheric pressure plasma. This can improve the adhesion between the negative electrode current collector and the negative electrode mixture layer, and prevent the N / P ratio of the positive and negative electrodes from being induced to reverse and the negative electrode mixture layer from becoming unrolled.

[0100] Although the invention has been described with reference to exemplary embodiments thereof, those skilled in the art will understand that various changes in form and detail may be made herein without departing from the spirit and scope of the invention as defined by the appended claims.

[0101] Therefore, the technical scope of the present invention should not be limited to what is described in the detailed description of the specification, but should be determined by the scope of the appended claims.

Claims

1. A negative electrode for a lithium secondary battery, the negative electrode comprising: Negative current collector; and A negative electrode mixture layer, the negative electrode mixture layer comprising a negative electrode active material, on at least one surface of the negative electrode current collector. The static water contact angle of the negative current collector is 60° to 100°, and The angle formed between the end of the negative electrode mixture layer and the negative electrode current collector is 60° or more.

2. The negative electrode according to claim 1, wherein the at least one surface of the negative electrode current collector is surface-treated with an alkyl group having 1 to 6 carbon atoms.

3. The negative electrode according to claim 1, wherein the peel strength of the negative electrode mixture layer relative to the negative electrode current collector according to ASTM D903 is in the range of 10 gf / cm to 50 gf / cm.

4. A method for manufacturing a negative electrode for a lithium secondary battery according to claim 1, the method comprising: Surface treatment of negative electrode current collector using atmospheric pressure plasma; and A negative electrode mixture layer is formed by applying and drying a slurry containing a negative electrode active material onto at least one surface of a surface-treated negative electrode current collector. The negative electrode current collector is surface-treated by atmospheric pressure plasma treatment under conditions containing a mixture of inert gas and hydrocarbon gas, thereby introducing alkyl groups onto the surface of the negative electrode current collector, such that when carbon atom mapping is performed on the negative electrode current collector by field emission scanning electron microscopy, the amount of carbon atoms is 1 atomic% to 40 atoms relative to the total atoms.

5. The method of claim 4, wherein the mixed gas contains the hydrocarbon gas at a partial pressure of 0.1% to 10%.

6. The method according to claim 4, wherein the hydrocarbon gas comprises one or more of methane gas and ethane gas.

7. The method of claim 4, wherein the atmospheric pressure plasma treatment uses radio frequency power with a frequency of 0.1 MHz to 50 MHz.

8. The method of claim 4, wherein the atmospheric pressure plasma treatment is performed for 0.05 seconds to 1 hour.

9. The method of claim 4, wherein the negative current collector comprises any one of stainless steel, copper, nickel, carbon, calcined carbon, titanium, or an aluminum-cadmium alloy.

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