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

Abstract

The present invention relates to a negative electrode for a lithium secondary battery and a manufacturing method thereof. In the negative electrode for a lithium secondary battery, the surface of the negative electrode current collector is treated with atmospheric pressure plasma to control the static contact angle of water on the surface of the negative electrode current collector and the angle formed by the edge of the negative electrode composite layer with the negative electrode current collector (i.e., the contact angle) within a specific range. This not only improves the adhesion between the negative electrode current collector and the negative electrode composite layer, but also prevents the N / P ratio of the positive and negative electrodes from being reversed at the edge of the electrode assembly and prevents the negative electrode composite layer from being unrolled. This effectively improves the safety and performance degradation of a lithium secondary battery including the negative electrode current collector.

Description

Technical Field

[0001] The present invention relates to a negative electrode for a lithium secondary battery and a method for manufacturing the same.

[0002] This application claims the benefit of priority based on Korean Patent Application No. 10-2021-0106413 filed on August 12, 2021, and all contents disclosed in the literature of the Korean patent application are included as part of this specification.

Background Art

[0003] A lithium secondary battery operates by repeating the insertion and desorption of lithium ions at the positive electrode and the negative electrode. Between these electrodes, lithium ions move, but electrons do not move. A lithium salt-containing electrolyte and a separator that separates the positive electrode and the negative electrode so as not to contact each other and functions to prevent a short circuit between the electrodes due to such contact are provided.

[0004] Such lithium secondary batteries have been studied extensively from the viewpoints of high capacity and high density, and recently, research for improving the lifespan and safety has been conducted in various ways. Specifically, the electrodes used in lithium secondary batteries are generally manufactured by coating an electrode slurry on a current collector with a certain thickness, drying it, and forming a composite layer. However, in the composite layer formed in this way, when the slurry dries, the liquid binder solvent dries in the gas phase and changes to a solid state, and exists as a solid binder between particles and between the current collector and the particles and has an adhesive force. At this time, if the adhesive force between the particles and the current collector is reduced, resistance is received in the electron transfer from the particles to the current collector, and the electron conduction speed decreases, so there is a problem that the charge / discharge speed characteristics and cycle characteristics of the battery deteriorate. In addition, when an external force is applied to the battery, separation between the current collector and the composite layer is likely to occur, so there is also a limit to the reduction in safety.

[0005] In order to improve such problems, technologies have been developed to increase the binder content of the composite material layer, modify the surface structure of the current collector, or form a primer layer to improve the adhesive force between the composite material layer and the current collector. However, when the binder content of the electrode composite material layer increases, the content of the electrode active material and the conductive material in the composite material layer relatively decreases, the electrode resistance increases, the conductivity decreases, and there is a limit to the reduction of the battery performance. In addition, when modifying the surface structure of the current collector or forming a primer layer or the like, when the electrode is a negative electrode, the contact angle formed between the end portion of the negative electrode composite material layer and the current collector may become low and the N / P ratio of the positive electrode and the negative electrode may be reversed, so that safety problems such as internal short circuits and waste of battery capacity may occur. Therefore, there is a demand for the development of a technology that can increase the adhesive force between the electrode composite material layer and the current collector and improve both the safety and performance of the battery.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0007] Therefore, an object of the present invention is to provide an electrode, particularly a negative electrode for a lithium secondary battery, which can improve the adhesive force between the electrode composite material layer and the electrode current collector and can improve problems such as a decrease in battery safety and performance due to a reversal of the N / P ratio between the positive electrode and the negative electrode.

Means for Solving the Problems

[0008] In order to solve the above-described problems, In one embodiment, the present invention includes a negative electrode current collector and a negative electrode composite material layer formed on the negative electrode current collector and containing a negative electrode active material. The above negative electrode current collector provides a negative electrode for a lithium secondary battery having a static contact angle with water of 60° to 100°.

[0009] At this time, the negative electrode current collector may be surface-treated with an alkyl group having 1 to 6 carbon atoms.

[0010] Further, the angle formed by the end portion of the negative electrode composite material layer with respect to the negative electrode current collector may be 60° or more, and the peel strength of the negative electrode composite material layer with respect to the negative electrode current collector (based on ASTM D903) may be 10 gf / cm to 50 gf / cm.

[0011] Further, in one embodiment of the present invention, a surface treatment step of subjecting the negative electrode current collector to atmospheric pressure plasma treatment; a step of applying and drying a slurry containing a negative electrode active material on the surface of the surface-treated negative electrode current collector to form a negative electrode composite material layer, and the above atmospheric pressure plasma treatment provides a method for manufacturing a negative electrode for a lithium secondary battery, which is performed under a mixed gas condition of an inert gas and a hydrocarbon gas.

[0012] Here, in the above surface treatment step, the atmospheric pressure plasma treatment can be performed for 0.05 seconds to 1 hour using an RF power source having a frequency of 0.1 MHz to 50 MHz.

[0013] Further, the above atmospheric pressure plasma treatment is performed under a mixed gas condition of an inert gas and a hydrocarbon gas, and the above mixed gas may contain a hydrocarbon gas at a partial pressure of 0.1 to 10%.

[0014] Further, the above hydrocarbon gas may contain any one or more of methane (CH 4 ) gas and ethane (C 2 H 6 ) gas.

[0015] Further, the negative electrode current collector may be formed of any one of stainless steel, copper, nickel, carbon, fired carbon, titanium, or an aluminum-cadmium alloy.

Advantages of the Invention

[0016] The negative electrode for a lithium secondary battery according to the present invention improves the adhesion between the negative electrode current collector and the negative electrode composite material layer by subjecting the surface of the negative electrode current collector to atmospheric pressure plasma treatment to control the static contact angle of the surface of the negative electrode current collector with respect to water and the angle formed by the end of the negative electrode composite material layer with respect to the negative electrode current collector (i.e., the contact angle) within a specific range. Moreover, it can prevent the induction of, for example, the reversal of the N / P ratio between the positive electrode and the negative electrode at the end of the electrode assembly and prevent the occurrence of unrolling of the negative electrode composite material layer. Therefore, it is excellent in the effect of improving the safety and performance degradation of the lithium secondary battery including this.

Brief Description of the Drawings

[0017]

Figure 1

Figure 2

Embodiments for Carrying Out the Invention

[0018] The present invention can be subjected to various modifications and may have various embodiments. However, specific embodiments will be described in detail.

[0019] However, this is not intended to limit the present invention to specific embodiments, and it should be understood to include all modifications, equivalents, or alternatives included in the spirit and technical scope of the present invention.

[0020] In the present invention, terms such as "including" or "having" are intended to specify the presence of features, numbers, steps, operations, components, parts, or combinations thereof described in the specification, and it should be understood that the presence or addition possibility of one or more other features, numbers, steps, operations, components, parts, or combinations thereof are not precluded in advance.

[0021] In the present invention, when a part such as a layer, a film, a region, a plate, etc. is described as being "on" another part, this includes not only the case where it is directly "above" the other part, but also the case where there are other parts in between. Conversely, when a part such as a layer, a film, a region, a plate, etc. is described as being "under" another part, this includes not only the case where it is directly "below" the other part, but also the case where there are other parts in between. Also, in the present application, being "disposed on" may include not only the upper part but also the case of being disposed in the lower part.

[0022] In the present invention, "main component" means 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 with respect to the total weight of the composition or a specific component. In some cases, when it constitutes the entire composition or specific component, that is, it means 100% by weight.

[0023] In the present invention, "the solid content of the composite material layer" means the residual component obtained by removing the solvent from the negative electrode slurry used in the production of the composite material layer.

[0024] Hereinafter, the present invention will be described in more detail.

[0025] <Negative electrode for lithium secondary battery> In one embodiment, the present invention comprises a negative electrode current collector and a negative electrode composite material layer formed on the negative electrode current collector and containing a negative electrode active material. The negative electrode current collector provides a negative electrode for a lithium secondary battery having a static contact angle with water of 60° to 100°.

[0026] The negative electrode for a lithium secondary battery according to the present invention has a configuration including a negative electrode composite material layer containing a negative electrode active material on a negative electrode current collector.

[0027] At this time, the negative electrode current collector is not particularly limited as long as it has conductivity without inducing chemical changes in the battery. Specifically, it can be formed of any one of stainless steel, copper, nickel, carbon, fired carbon, titanium, or an aluminum-cadmium alloy. As an example, a copper current collector can be used as the negative electrode current collector.

[0028] In addition, the surface of the negative electrode current collector where the negative electrode composite material layer is formed can be surface-treated so that it has a low affinity for water but shows a high adhesive force to the negative electrode composite material layer. Conventionally, surface treatment methods such as plasma treatment and electrolytic treatment generally applied to electrode current collectors have been carried out for the purpose of hydrophilizing the surface of the current collector to improve the adhesive force to the electrode composite material layer. However, when such a method is applied to the negative electrode current collector of a lithium secondary battery, although the adhesive force to the negative electrode composite material layer is improved, the contact angle (for example, the "sliding angle" of the negative electrode composite material layer) at the end of the negative electrode composite material layer with respect to the negative electrode current collector becomes low, and the N / P ratio at the ends of the positive and negative electrodes may be reversed. Moreover, if the contact angle of the negative electrode end with respect to the negative electrode current collector is low, unrolling may occur at the end of the negative electrode composite material layer, which may induce detachment of the composite material layer.

[0029] Therefore, the present invention may include a structure in which an alkyl group having 1 to 6 carbon atoms is introduced onto the surface of the negative electrode current collector by treating the surface of the negative electrode current collector with atmospheric pressure plasma in the presence of a mixed gas of an inert gas and a hydrocarbon gas. At this time, as the alkyl group having 1 to 6 carbon atoms, it may include one or more of a methyl group (CH 3- ), an ethyl group (CH 3 CH 2- ), an n-propyl group (CH 3 CH 2 CH 2- ), and an n-butyl group (CH 3 CH 2 CH 2 CH 2- ).

[0030] As an example, the negative electrode current collector has a methyl group (CH 3-) and an ethyl group (CH 3 CH 2- ) or may be those whose surfaces are treated with one or more alkyl groups of.

[0031] Further, the alkyl group is introduced at a certain ratio on the surface of the negative electrode current collector, and when performing carbon atom mapping through field emission scanning electron microscope (FE-SEM) analysis on the negative electrode current collector, it can be confirmed that the carbon atoms are 1 to 40 atomic% of all atoms. Specifically, it can be confirmed that the carbon atoms are 1 to 30 atomic%, 1 to 20 atomic%, 1 to 15 atomic%, 10 to 40 atomic%, 20 to 40 atomic%, 10 to 30 atomic%, 20 to 30 atomic%, 10 to 20 atomic%, or 5 to 15 atomic% of all atoms.

[0032] Further, when the alkyl group is introduced on the surface of the negative electrode current collector, the repulsive force against the solvent contained in the slurry during the production of the negative electrode composite material layer is increased, and the contact angle formed with the end portion of the negative electrode composite material layer can be made high. At the same time, the adhesive force to the negative electrode composite material layer can be increased.

[0033] Specifically, in the negative electrode current collector according to the present invention, a certain amount of alkyl group is introduced on the surface, and since the repulsive force against the solvent contained in the negative electrode slurry increases, when the negative electrode slurry is applied on the current collector, the angle formed by the end portion of the applied negative electrode slurry with the negative electrode current collector (that is, the contact angle of the negative electrode current collector with respect to the negative electrode slurry) can be made high. Further, the contact angle of the negative electrode slurry with respect to the negative electrode current collector may be the same as the angle formed by the negative electrode composite material layer formed by removing only the solvent from the negative electrode slurry with the negative electrode current collector (for example, the sliding angle of the negative electrode composite material layer), and in some cases, it may have a deviation within ±5%.

[0034] As an example, in the negative electrode according to the present invention, the contact angle of the negative electrode slurry with respect to the negative electrode current collector may be 60° or more, and more specifically, 70° or more, 80° or more, 90° or more, 100° or more, 60 to 100°, 60 to 80°, 60 to 75°, 65 to 95°, 60 to 95°, 70 to 99°, 65 to 89°, 65 to 84°, or 65 to 78°.

[0035] The present invention controls the static water contact angle of the negative electrode current collector and the angle formed by the end of the negative electrode composite layer formed on the negative electrode current collector with the negative electrode current collector so as to satisfy the above-mentioned range, thereby preventing unrolling of the negative electrode composite layer and preventing reversal of the N / P ratio between the positive electrode composite layer and the negative electrode composite layer at the end.

[0036] In addition, in the negative electrode current collector according to the present invention, a certain amount of alkyl groups is introduced on the surface, increasing the surface energy. Therefore, as described above, not only is the static water contact angle of the negative electrode current collector adjusted to satisfy a specific range, but also a high adhesive force with respect to the solid content of the composite layer components constituting the negative electrode composite layer, such as negative electrode active material, binder, conductive agent, etc., can be realized.

[0037] As an example, the negative electrode according to the present invention may include a negative electrode current collector having a static water contact angle of 60° to 100°. Specifically, the negative electrode may include a negative electrode current collector having 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°.

[0038] As another example, in the negative electrode according to the present invention, the peel strength of the negative electrode composite layer with respect to the negative electrode current collector based on ASTM D903 may be 10 gf / cm to 50 gf / cm, and specifically, the peel strength of the negative electrode composite layer with respect to the negative electrode current collector may be 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.

[0039] On the one hand, the negative electrode composite layer contains a negative electrode active material and is a layer that imparts electrical activity to the battery, and may contain a negative electrode active material, a conductive material, a binder, an additive, and the like.

[0040] The negative electrode active material may include, for example, a carbon material and a silicon material. The carbon material means a carbon material mainly composed of carbon atoms. Such carbon materials include graphite having a perfect layered crystal structure like natural graphite, soft carbon having a low crystalline layered crystal structure (graphene structure; a structure in which hexagonal honeycomb-shaped planes of carbon are arranged in layers), and hard carbon in which such a structure is mixed with an amorphous part, artificial graphite, expanded graphite, carbon fiber, graphitization-resistant carbon, carbon black, acetylene black, ketjen black, carbon nanotube, fullerene, activated carbon, graphene, carbon nanotube, etc. may be included, and preferably, one or more selected from the group consisting of natural graphite, artificial graphite, graphene, and carbon nanotube may be included.

[0041] In addition, the silicon material is particles mainly containing silicon (Si) as a metal component, and may contain one or more of silicon (Si) particles and silicon oxide (SiO X , 0.8 ≦ X ≦ 2.2) particles. As an example, the silicon material may include silicon (Si) particles, silicon monoxide (SiO) particles, silicon dioxide (SiO 2 ) particles, or a mixture of these particles.

[0042] In addition, the silicon material may have a form in which crystalline particles and amorphous particles are mixed, and the proportion of the amorphous particles 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 with respect to 100 parts by weight of the entire silicon material. The present invention can improve the thermal stability and flexibility without degrading the electrical physical properties of the electrode by controlling the proportion of the amorphous particles contained in the silicon material within the above range.

[0043] Further, the negative electrode active material contains a carbon material and a silicon material, and the silicon material may be contained in an amount of 1 to 20 parts by weight, specifically, 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 with respect to 100 parts by weight of the negative electrode composite material layer.

[0044] According to the present invention, by adjusting the contents of the carbon material and the silicon material contained in the negative electrode active material to the above ranges, the lithium consumption amount and the irreversible capacity loss during the initial charge and discharge of the battery can be reduced, and the charge capacity per unit mass can be improved.

[0045] Further, as the binder, polyvinyl alcohol (PVA), carboxymethyl cellulose (CMC), hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride (PVC), carboxylated polyvinyl chloride (C-PVC), polyvinyl fluoride, a polymer containing ethylene oxide, polyvinyl pyrrolidone, polyurethane (PU), polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polyethylene (PE), polypropylene (PP), styrene butadiene rubber (SBR), acrylate styrene-butadiene rubber, epoxy resin, nylon, etc. can be used. As an example, the binder can use one or more of carboxymethyl cellulose (CMC) and styrene butadiene rubber (SBR).

[0046] Further, the binder may be contained in an amount of 1 to 10 parts by weight, specifically, 2 to 8 parts by weight, or 1 to 5 parts by weight with respect to 100 parts by weight of the entire negative electrode composite material layer.

[0047] Further, the negative electrode composite material layer may have an average thickness of 100 μm to 200 μm, specifically, an average thickness of 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.

[0048] By having the configuration as described above, the negative electrode for a lithium secondary battery according to the present invention can not only increase the adhesive force between the negative electrode current collector and the negative electrode composite material layer, but also can highly embody the contact angle of the end portion of the composite material layer with respect to the negative electrode current collector, which has a trade-off relationship with the above adhesive force. Therefore, the battery has further excellent safety and can exhibit excellent performance.

[0049] <Method for manufacturing a negative electrode for a lithium secondary battery> Further, in one embodiment, the present invention includes a surface treatment step of subjecting the negative electrode current collector to atmospheric pressure plasma treatment, and a step of applying and drying a slurry containing a negative electrode active material on the surface of the surface-treated negative electrode current collector to form a negative electrode composite material layer. The atmospheric pressure plasma treatment provides a method for manufacturing a negative electrode for a lithium secondary battery, which is performed under a mixed gas condition of an inert gas and a hydrocarbon gas.

[0050] The method for manufacturing a negative electrode for a lithium secondary battery according to the present invention includes a step of surface-treating a region where the negative electrode slurry is to be applied with atmospheric pressure plasma before applying the slurry for the negative electrode composite material layer on the surface of the negative electrode current collector, and then performing a step of applying and drying a negative electrode slurry containing a negative electrode active material on the surface-treated region to form a negative electrode composite material layer, thereby manufacturing a negative electrode for a lithium secondary battery.

[0051] Here, the surface treatment step can be performed by subjecting the entire surface of the negative electrode current collector or only the region where the negative electrode composite material layer is to be formed to atmospheric pressure plasma treatment. Further, in the manufacturing method, by using a mixed gas containing a hydrocarbon gas together with an inert gas during the atmospheric pressure plasma treatment, an alkyl group having 1 to 6 carbon atoms can be introduced onto the surface of the negative electrode current collector.

[0052] Specifically, in atmospheric pressure plasma, an alternating electric field is applied between electrodes facing each other, and electrons are accelerated with high energy inside the reactor by the electric field. The electrons thus accelerated collide with the gas supplied to the reactor (for example, a mixed gas of an inert gas and a hydrocarbon gas) and are separated into atomic ions. The ions thus separated combine with surrounding electrons to form radicals, and the radicals collide with electrons again and are decomposed into radicals. The radicals generated by repeating such a process are ejected onto the surface of the negative electrode current collector, which is the object to be treated, to remove organic substances, and an alkyl group can be bonded to the surface of the current collector to change the surface characteristics.

[0053] Here, the hydrocarbon gas can be used without particular limitation as long as it can provide an alkyl group having 1 to 6 carbon atoms. Specifically, methane gas (CH 4 ), ethane gas (CH 3 CH 3 ), n-propane gas (CH 3 CH 2 CH 3 ), n-butane gas (CH 3 CH 2 CH 2 CH 3 ) and the like can be used.

[0054] Also, thereby, an alkyl group having 1 to 6 carbon atoms can be introduced onto the surface of the surface-treated negative electrode current collector. Examples of the alkyl group having 1 to 6 carbon atoms include a methyl group (CH 3- ), an ethyl group (CH 3 CH 2- ), an n-propyl group (CH 3 CH 2 CH 2- ) and an n-butyl group (CH 3 CH 2 CH 2 CH 2- ), and may contain one or more of them.

[0055] As an example, the negative electrode current collector is methane gas (CH 4 ) and ethane gas (CH 3 CH3 ) using one or more of the gases, a methyl group (CH 3- ) and an ethyl group (CH 3 CH 2- ) may be those having a surface treated with one or more alkyl groups.

[0056] By limiting the types of alkyl groups introduced on the surface of the negative electrode current collector as described above, the present invention can prevent the chain length of the hydrocarbon from becoming long and the hydrophobicity of the surface of the current collector from increasing significantly.

[0057] In addition, in the above negative electrode current collector, a certain proportion of alkyl groups can be introduced on the surface. Therefore, when performing atmospheric pressure plasma, the partial pressure of the hydrocarbon gas contained in the mixed gas, the flow rate of the mixed gas, the frequency condition of the power supply, etc. can be controlled within a specific range.

[0058] Specifically, in the method for manufacturing a negative electrode for a lithium secondary battery according to the present invention, the partial pressure of the hydrocarbon gas contained in the mixed gas can be adjusted to 0.1 to 10% during atmospheric pressure plasma treatment. 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%.

[0059] As an example, in the method for manufacturing a negative electrode for a lithium secondary battery according to the present invention, during atmospheric pressure plasma treatment, a gas obtained by mixing an inert gas and a hydrocarbon gas is used as the mixed gas, and the partial pressure of the hydrocarbon gas may be 3 to 5% of the total gas.

[0060] In addition, the above atmospheric pressure plasma treatment supplies the above mixed gas at a flow rate of 0.1 to 40 L / min, preferably at a flow rate of 1 to 10 L / min. When the flow rate is less than 0.1 L / min, there is a problem that the process time increases, and when it exceeds 40 L / min, there is a problem that the stability decreases.

[0061] Further, the above atmospheric pressure plasma treatment can be performed for 0.05 seconds to 1 hour using an RF power source with a frequency of 0.1 MHz to 50 MHz. Specifically, the above atmospheric pressure plasma treatment can be performed 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 using an RF power source with a frequency 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.

[0062] On the other hand, the above negative electrode current collector is not particularly limited as long as it has conductivity without inducing chemical changes in the battery. Specifically, it can be formed of any one of stainless steel, copper, nickel, carbon, fired carbon, titanium, or an aluminum-cadmium alloy. As an example, a copper current collector can be used as the above negative electrode current collector.

[0063] Hereinafter, the present invention will be described in more detail with reference to Examples and Experimental Examples.

[0064] However, the following Examples and Experimental Examples are illustrative of the present invention, and the content of the present invention is not limited to the following Examples and Experimental Examples.

[0065] <Manufacture of negative electrodes for lithium secondary batteries in Examples 1 to 3 and Comparative Examples 1 to 7.> The entire surface of the copper (Cu) current collector provided through the transfer path was treated with atmospheric pressure plasma formed using an RF power source for 0.05 to 1 second. At this time, during the treatment of the atmospheric pressure plasma, the mixed gas was supplied at a flow rate of 5 ± 0.1 L / min, and the composition and partial pressure of the above mixed gas and the frequency of the RF power source were adjusted as shown in Table 1 below.

[0066] In addition, carbon atom mapping was performed through field emission scanning electron microscope (FE-SEM) analysis on each surface-treated negative electrode current collector, and the ratio of carbon atoms to all atoms on the surface of the negative electrode current collector was measured and shown in Table 1 below.

[0067] Next, on the surface of the copper current collector treated with atmospheric pressure plasma, a negative electrode slurry (solvent: water) containing 83% by weight of graphite and 15% by weight of silicon oxide (SiO 2 2) as a negative electrode active material based on the solid content and 2% by weight of SBR as a binder was applied, dried at 100 °C, and then rolled to produce a negative electrode for a lithium secondary battery. Here, when rolling the negative electrode composite layer, it was confirmed whether the angle formed by the end of the negative electrode composite layer and the negative electrode current collector was low and unrolled, and the results are shown in Table 1 below.

[0068]

Table 1

[0069] <Experimental Example> In order to evaluate the negative electrode for a lithium secondary battery according to the present invention, the following experiments were conducted.

[0070] i) Measurement of the static water contact angle of the negative electrode current collector The surface of the negative electrode current collector was treated with atmospheric pressure plasma in the same manner as the methods presented in Examples 1 to 3 and Comparative Examples 1 to 7. For each of the negative electrode current collectors treated with atmospheric pressure plasma, the static water contact angle (static WCA) was measured using a contact angle measuring instrument (model name: SmartDrop, manufacturer: Femtofab Co., Ltd). At this time, each measurement was performed by dropping a 10 μl drop of water or oil onto the surface each time during measurement and repeating it three times to derive the average value. The results are shown in FIG. 1 and Table 2.

[0071] ii) Measurement of the contact angle of the negative electrode slurry with respect to the negative electrode current collector In the same manner as the methods presented in Examples 1 to 3 and Comparative Examples 1 to 7, the surface of the negative electrode current collector was treated with atmospheric pressure plasma. Then, three drops of the negative electrode slurry were dropped onto the surface of each negatively charged current collector that had been treated with atmospheric pressure plasma, and the angle (i.e., the contact angle) formed by the negative electrode slurry droplets on the surface with the negative electrode current collector was measured using a contact angle measuring instrument (model name: SmartDrop, manufacturer: Femtofab Co., Ltd).

[0072] At this time, the above-mentioned negative electrode slurry contained 83% by weight of graphite and 15% by weight of silicon oxide (SiO 2 ) as negative electrode active materials based on the solid content, and 2% by weight of SBR as a binder. Water, which is a solvent, was mixed at 10% by weight with respect to the weight of the total solid content. The measurement results are shown in FIG. 2 and Table 2.

[0073] (c) Measurement of the adhesion between the negative electrode current collector and the negative electrode composite material layer For the negative electrodes manufactured in Examples 1 to 3 and Comparative Examples 1 to 7, the 180° peel strength with respect to the negative electrode composite material layer was measured in accordance with ASTM D903, and the results are shown in Table 2 below.

[0074]

Table 2

[0075] As shown in FIGS. 1 and 2 and Table 2, it can be seen that the negative electrode for a lithium secondary battery according to the present invention has excellent adhesion between the negative electrode current collector and the negative electrode composite material layer, and a high contact angle at the end of the negative electrode composite material layer with respect to the negative electrode current collector.

[0076] Specifically, the negative electrode for a lithium secondary battery in the examples was shown to have a static water contact angle of 66 to 95°, and the contact angle formed by the end of the negative electrode composite layer with respect to the negative electrode current collector was 60 to 90°. This means that an alkyl group is introduced at a certain ratio (specifically, a certain atomic ratio) on the surface of the negative electrode current collector, and during the production of the negative electrode composite layer, a repulsive force against the solvent contained in the negative electrode slurry, specifically water, is induced, resulting in a high contact angle formed between the negative electrode current collector and the end of the negative electrode composite layer.

[0077] Also, it was confirmed that the peeling strength between the negative electrode current collector and the negative electrode composite layer of the negative electrode for a lithium secondary battery in the examples was 10 to 40 gf / cm. This means that the adhesive force between the negative electrode current collector and the negative electrode composite layer is improved together.

[0078] From such results, it can be seen that the negative electrode for a lithium secondary battery according to the present invention can control the static contact angle of the surface of the negative electrode current collector with respect to water and the angle (i.e., the contact angle) formed by the end of the negative electrode composite layer with respect to the negative electrode current collector within a specific range by subjecting the surface of the negative electrode current collector to atmospheric pressure plasma treatment. Through this, not only can the adhesive force between the negative electrode current collector and the negative electrode composite layer be improved, but it can also be induced that the N / P ratio of the positive electrode and the negative electrode is reversed at the end of the electrode assembly, and it can be prevented that the unrolling of the negative electrode composite layer occurs.

[0079] In the above, the preferred embodiments of the present invention have been described with reference to the examples. However, it can be understood that those skilled in the art or those with ordinary knowledge in the technical field can make various modifications and changes to the present invention without departing from the spirit and technical scope of the present invention described in the claims below.

[0080] Therefore, the technical scope of the present invention should not be limited to the content described in the detailed description of the specification, but should be determined by the claims.

Claims

1. A negative electrode current collector, and a negative electrode composite material layer formed on the negative electrode current collector and containing a negative electrode active material. The negative electrode current collector has a static contact angle with respect to water of 60° to 100°. The negative electrode current collector is surface-treated with an alkyl group having 1 to 6 carbon atoms. A negative electrode for a lithium secondary battery, wherein an angle formed by an end portion of the negative electrode composite material layer with respect to the negative electrode current collector is 60° to 100°.

2. The negative electrode for a lithium secondary battery according to Claim 1, wherein the peeling strength of the negative electrode composite material layer with respect to the negative electrode current collector based on ASTM D903 is 10 gf / cm to 50 gf / cm.

3. A surface treatment step of subjecting a negative electrode current collector to atmospheric pressure plasma treatment; A step of applying and drying a slurry containing a negative electrode active material on the surface of the surface-treated negative electrode current collector to form a negative electrode composite material layer. The atmospheric pressure plasma treatment is performed under a mixed gas condition of an inert gas and a hydrocarbon gas. The negative electrode current collector after the surface treatment step has a static contact angle with respect to water of 60° to 100°. A method for manufacturing a negative electrode for a lithium secondary battery, wherein the slurry is an aqueous slurry.

4. The method for manufacturing a negative electrode for a lithium secondary battery according to Claim 3, wherein the mixed gas contains a hydrocarbon gas at a partial pressure of 0.1 to 10%.

5. The hydrocarbon gas is methane (CH ４ ), ethane (C ２ H ６ ), or any one or more thereof, and the method for manufacturing a negative electrode for a lithium secondary battery according to claim 3 or 4.

6. The method for manufacturing a negative electrode for a lithium secondary battery according to Claim 3, wherein the atmospheric pressure plasma treatment uses an RF power source having a frequency of 0.1 MHz to 50 MHz.

7. The method for manufacturing a negative electrode for a lithium secondary battery according to Claim 3, wherein the atmospheric pressure plasma treatment is performed for 0.05 seconds to 1 hour.

8. The negative electrode current collector is formed of any one of stainless steel, copper, nickel, carbon, fired carbon, titanium, or an aluminum-cadmium alloy. The method for manufacturing a negative electrode for a lithium secondary battery according to Claim 3.

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