Method for manufacturing a negative electrode for a lithium secondary battery, a negative electrode for a lithium secondary battery, and a lithium secondary battery containing a negative electrode

Abstract

The present application relates to a method for producing a negative electrode for a lithium secondary battery, a negative electrode for a lithium secondary battery, and a lithium secondary battery including the negative electrode.

Description

Technical Field

[0001] This application claims the benefit of the filing date of Korean Patent Application No. 10-2022-0014548, filed with the Korean Intellectual Property Office on February 4, 2022, and all of its contents are incorporated herein by reference.

[0002] This application relates to a method for manufacturing a negative electrode for a lithium secondary battery, a negative electrode for a lithium secondary battery, and a lithium secondary battery including the negative electrode.

Background Art

[0003] Due to the rapid increase in the use of fossil fuels, the demand for alternative and clean energy has been increasing. As part of this, the fields of power generation and energy storage using electrochemical reactions are the most actively studied.

[0004] Currently, secondary batteries are representative examples of electrochemical devices that utilize such electrochemical energy, and their usage areas are increasingly expanding.

[0005] As the technology development and demand for mobile devices increase, the demand for secondary batteries as an energy source has been rapidly increasing. Among such secondary batteries, lithium secondary batteries having a high energy density, voltage, long cycle life, and low self-discharge rate have been commercialized and widely used. In addition, research on methods for manufacturing high-density electrodes with a higher energy density per unit volume as electrodes for such high-capacity lithium secondary batteries has been actively underway.

[0006] Generally, a secondary battery is composed of a positive electrode, a negative electrode, an electrolyte, and a separator. The negative electrode includes a negative electrode active material that inserts and desorbs lithium ions emitted from the positive electrode, and silicon-based particles having a large discharge capacity can be used as the negative electrode active material.

[0007] Generally, carbon materials such as graphite are used for the negative electrode of a lithium secondary battery, but the theoretical capacity density of carbon is 372 mAh / g (833 mAh / cm3 ) Therefore, in order to improve the energy density of the negative electrode, silicon (Si), tin (Sn), and their oxides and alloys that alloy with lithium are being considered as negative electrode materials. Among them, silicon-based materials have attracted attention due to their low price and high capacity (4200 mAh / g).

[0008] However, when using a silicon-based negative electrode active material, there is a problem of a large initial irreversible capacity. In the charge-discharge reaction of a lithium secondary battery, lithium released from the positive electrode during charging is inserted into the negative electrode, and during discharging, it desorbs from the negative electrode and returns to the positive electrode again. In the case of a silicon-based negative electrode active material, however, volume change and surface side reactions are intense, and a large amount of the lithium inserted into the negative electrode during the initial charging cannot return to the positive electrode again, thus causing a problem of a large initial irreversible capacity. When the initial irreversible capacity increases, problems such as a sharp decrease in battery capacity and cycle performance occur.

[0009] In order to solve the above problems, a method of pre-lithiating a silicon negative electrode containing a silicon-based negative electrode active material is known. As the pre-lithiation method, there are methods of manufacturing an electrode after lithiating by physical / chemical methods such as electrolytic plating, lithium metal transfer, and lithium metal evaporation, and methods of electrochemically pre-lithiating a negative electrode.

[0010] However, in order to use the conventional electrochemical method, it is necessary to proceed with a wet process in an electrolyte, which involves risks such as fire and explosion, so it was necessary to properly control an inert environment. That is, in order to create the above environment, it is necessary to adjust conditions such as moisture adjustment using an inert gas in the room where the electrochemical method is carried out, and the adjustment of conditions is complicated. Also, in order to uniformly control the initial irreversible capacity, it is necessary to proceed with the pre-lithiation using the electrochemical method as slowly as possible, so there is a problem of an increase in production cost in the application of the electrochemical method.

[0011] Furthermore, in the pre-lithiation process, specifically the lithium metal transfer process, it is difficult to safely and easily transfer the lithium metal. As a result, either lithium is not transferred from the transfer laminate, or even if it is transferred, the highly reactive lithium metal immediately begins to react with the electrode active material, leading to problems such as particle cracking on the surface of the electrode active material layer.

[0012] Therefore, research is needed on process conditions and materials that allow for easy transfer of lithium metal to the upper part of the electrode active material layer during the lithium metal transfer process, and that enable safer and more efficient pre-lithification of the electrode, while uniformly pre-lithifying lithium within the electrode active material layer. [Prior art documents] [Patent Documents]

[0013] [Patent Document 1] Japanese Patent Publication No. 2009-080971 [Overview of the project] [Problems that the invention aims to solve]

[0014] In the pre-lithiation process, the lithium metal transfer process includes transferring the lithium metal layer from the transfer stack to the upper part of the electrode active material layer. Through research, we have found that by adjusting the surface characteristics of the negative electrode, the degree of lithium metal transfer can be adjusted in order to easily transfer the lithium metal layer on the transfer stack to the upper part of the negative electrode active material layer (or the negative electrode active material layer with a buffer layer stacked on top of it).

[0015] Therefore, this application relates to a method for manufacturing a negative electrode for a lithium secondary battery, a negative electrode for a lithium secondary battery, and a lithium secondary battery including a negative electrode. [Means for solving the problem]

[0016] One embodiment of this specification provides a method for manufacturing a negative electrode for a lithium secondary battery, comprising the steps of: forming a negative electrode by laminating a negative electrode current collector layer and a negative electrode active material layer on one or both sides of the negative electrode current collector layer; pre-treating the negative electrode; transferring a lithium metal layer to the pre-treated negative electrode; and activating the lithium metal layer, wherein the pre-treating step is plasma treatment or corona treatment.

[0017] In another embodiment, a negative electrode for a lithium secondary battery is provided, comprising a negative electrode current collector layer and a negative electrode active material layer provided on one or both sides of the negative electrode current collector layer, wherein the negative electrode for a lithium secondary battery satisfies the following formula 1.

[0018] [Formula 1] 10°≦AB≦60° In the above formula 1, A represents the water contact angle of the negative electrode surface before pretreatment of the negative electrode. B represents the water contact angle of the negative electrode surface after pretreatment of the negative electrode.

[0019] Another embodiment provides a lithium secondary battery comprising a positive electrode; a negative electrode for a lithium secondary battery according to this application; a separation membrane provided between the positive electrode and the negative electrode; and an electrolyte. [Effects of the Invention]

[0020] A method for manufacturing a negative electrode for a lithium secondary battery according to one embodiment of the present invention is characterized in that, in the step of prelithification by transferring a lithium metal layer onto the upper part of a negative electrode active material layer having a negative electrode active material layer or a buffer layer laminated thereon, the method includes a step of pre-treating the negative electrode surface in order to ensure that the lithium metal layer adheres uniformly to the upper part of the negative electrode active material layer having a negative electrode active material layer or a buffer layer laminated thereon.

[0021] As described above, pre-treating the negative electrode surface (specifically, indirect atmospheric pressure plasma treatment) changes the negative electrode surface properties (increased hydrophilicity), which increases the interfacial adhesion between the lithium metal layer and the negative electrode during lithium metal layer transfer, and prevents the formation of by-products at the interface.

[0022] Furthermore, as described above, the interfacial adhesion between the negative electrode and the lithium metal layer is excellent, improving the peelability of the transfer laminate for transfer. This makes it easier to release the heat generated during pre-lithiation to the outside, suppressing the generation of by-products in the pre-lithiation process, and enabling a relatively uniform pre-lithiation process within the negative electrode active material layer. [Brief explanation of the drawing]

[0023] [Figure 1] This figure shows a method for pre-lithifying a negative electrode for a lithium secondary battery according to one embodiment of this application. [Figure 2] This figure shows a stacked structure of a lithium secondary battery according to one embodiment of the present application. [Modes for carrying out the invention]

[0024] Before describing the present invention, let us first define some terms. In this specification, when a part "includes" a component, this means, unless otherwise stated, that it may include other components rather than excluding them.

[0025] In this specification, "p~q" means the range "p or greater and q or less". In this specification, "specific surface area" is measured by the BET method, specifically calculated from the amount of nitrogen gas adsorbed at liquid nitrogen temperature (77K) using BELSORP-mino II from BEL Japan. In other words, in this application, BET specific surface area may mean the specific surface area measured by the above measurement method.

[0026] In this specification, "Dn" refers to the particle size distribution, specifically the particle size at the n% point of the cumulative particle number distribution by particle size. That is, D50 is the particle size (average particle size, median particle size) at the 50% point of the cumulative particle number distribution by particle size, D90 is the particle size at the 90% point of the cumulative particle number distribution by particle size, and D10 is the particle size at the 10% point of the cumulative particle number distribution by particle size. On the other hand, the particle size distribution can be measured using the laser diffraction method. Specifically, the powder to be measured is dispersed in a dispersion medium, then introduced into a commercially available laser diffraction particle size analyzer (e.g., Microtrac S3500), and the difference in diffraction patterns due to particle size as the particles pass through the laser beam is measured to calculate the particle size distribution.

[0027] In this specification, when a polymer contains a monomer as a monomer unit, it means that the monomer participates in the polymerization reaction and is included as a repeating unit within the polymer. In this specification, when a polymer contains a monomer, this is interpreted as meaning that the polymer contains monomers as monomer units.

[0028] In this specification, the term "polymer" is understood to be used in a broad sense, including copolymers, unless otherwise specified as "homopolymer."

[0029] In this specification, weight-average molecular weight (Mw) and number-average molecular weight (Mn) are polystyrene-equivalent molecular weights measured by gel permeation chromatography (GPC) using monodisperse polystyrene polymers of various degrees of polymerization (standard samples) commercially available for molecular weight measurement as standard substances. In this specification, molecular weight refers to weight-average molecular weight unless otherwise specified.

[0030] The present invention will be described in detail below with reference to the drawings so that a person with ordinary skill in the art to which the present invention pertains can easily implement it. However, the present invention can be implemented in various different forms and is not limited to the following description.

[0031] One embodiment of this specification provides a method for manufacturing a negative electrode for a lithium secondary battery, comprising the steps of: forming a negative electrode current collector layer and a negative electrode active material layer on one or both sides of the negative electrode current collector layer; pre-treating the negative electrode active material layer; transferring a lithium metal layer to the side of the pre-treated negative electrode active material layer opposite to the side in contact with the negative electrode current collector layer; and activating the lithium metal layer, wherein the pre-treatment step is plasma treatment or corona treatment.

[0032] A method for manufacturing a negative electrode for a lithium secondary battery according to one embodiment of the present invention is characterized in that, in the step of transferring a lithium metal layer to the upper part of the negative electrode active material layer to prelithify it, the upper part of the negative electrode active material layer is pretreated in order to ensure that the lithium metal layer is uniformly adhered to the upper part of the negative electrode active material layer.

[0033] As described above, pre-treating the upper part of the negative electrode active material layer (specifically, indirect atmospheric pressure plasma treatment) changes the surface properties of the negative electrode active material layer, increasing the interfacial adhesion between the lithium metal layer and the negative electrode active material layer during lithium metal layer transfer, and preventing the formation of by-products at the interface. Furthermore, the increased interfacial adhesion also improves the transferability of the lithium metal layer.

[0034] In this application, in order to effectively adhere (transfer) a lithium metal layer to the electrode surface, hydrophilicity must be imparted to the surface to be transferred, which can be achieved through plasma treatment or corona treatment according to this application.

[0035] The method for manufacturing a negative electrode for a lithium secondary battery described in this application will be explained in detail below. One embodiment of this application provides a step of forming a negative electrode by laminating a negative electrode current collector layer and a negative electrode active material layer on one or both sides of the negative electrode current collector layer.

[0036] The present invention provides a method for manufacturing a negative electrode for a lithium secondary battery, wherein the aforementioned step is a step of laminating a negative electrode for a lithium secondary battery, and the step of laminating a negative electrode current collector layer and a negative electrode active material layer on one or both sides of the negative electrode current collector layer includes a step of coating one or both sides of the negative electrode current collector layer with a negative electrode slurry containing a negative electrode active material layer composition, and the negative electrode active material layer composition comprises at least one selected from the group consisting of silicon-based active material; negative electrode conductive material; and negative electrode binder.

[0037] In one embodiment of this application, the negative electrode current collector layer generally has a thickness of 1 μm to 100 μm. Such a negative electrode current collector layer is not particularly limited as long as it has high conductivity without inducing chemical changes in the battery, and for example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., and aluminum-cadmium alloy can be used. Furthermore, fine irregularities can be formed on the surface to strengthen the bonding force of the negative electrode active material, and it can be used in various forms such as film, sheet, foil, net, porous body, foam, and nonwoven fabric.

[0038] In one embodiment of this application, the thickness of the negative electrode current collector layer may be 1 μm or more and 100 μm or less, and the thickness of the negative electrode active material layer may be 20 μm or more and 500 μm or less.

[0039] However, the thickness can vary depending on the type and application of the negative electrode used, and is not limited to this.

[0040] In one embodiment of this application, the negative electrode slurry may include a negative electrode active material layer composition and a slurry solvent.

[0041] In one embodiment of this application, the solid content of the negative electrode slurry may be 5% or more and 40% or less.

[0042] In another embodiment, the solid content of the negative electrode slurry may satisfy the range of 5% or more and 40% or less, preferably 7% or more and 35% or less, and more preferably 10% or more and 30% or less.

[0043] The solid content of the negative electrode slurry can mean the content of the negative electrode active material layer composition contained in the negative electrode slurry, and can mean the content of the negative electrode active material composition based on 100 parts by weight of the negative electrode slurry.

[0044] When the solid content of the negative electrode slurry satisfies the above range, the viscosity during the formation of the negative electrode active material layer is appropriate, and it has the characteristic that the particle aggregation phenomenon of the negative electrode active material layer composition can be minimized and the negative electrode active material layer can be efficiently formed.

[0045] In one embodiment of the present application, the slurry solvent is not limited as long as it can dissolve the negative electrode active material layer composition. Specifically, distilled water can be used.

[0046] The negative electrode according to one embodiment of the present application can be formed by coating and drying the negative electrode slurry on the negative electrode current collector layer.

[0047] Through the drying process, the slurry solvent in the negative electrode slurry can be dried.

[0048] In one embodiment of the present application, the negative electrode active material layer composition may include at least one selected from the group consisting of a silicon-based active material; a negative electrode conductive material; and a negative electrode binder.

[0049] In one embodiment of the present application, the silicon-based active material may include at least one selected from the group consisting of SiOx (x = 0), SiOx (0 <x <2), SiC, and Si alloys.

[0050] In one embodiment of the present application, the silicon-based active material includes one or more selected from the group consisting of SiOx (x = 0) and SiOx (0 < x < 2), and may contain 70 parts by weight or more of the SiOx (x = 0) based on 100 parts by weight of the silicon-based active material.

[0051] In another embodiment, based on 100 parts by weight of the silicon-based active material, the SiOx (x = 0) may be contained in an amount of 70 parts by weight or more, preferably 80 parts by weight or more, more preferably 90 parts by weight or more, and may be contained in an amount of 100 parts by weight or less, preferably 99 parts by weight or less, more preferably 95 parts by weight or less.

[0052] In one embodiment of the present application, the silicon-based active material may contain metal impurities. The metal impurities are impurities that can be contained in silicon, and the content can satisfy the range of 0.1 part by weight or less based on 100 parts by weight of the total silicon-based active material.

[0053] In one embodiment of the present application, particularly, pure silicon (Si) can be used as the silicon-based active material. Using pure silicon (Si) as the silicon-based active material may mean that, as described above, when based on 100 parts by weight of the total silicon-based active material, pure Si particles (SiOx (x = 0)) not bonded to other particles or elements are included within the above range.

[0054] In the charge-discharge reaction of a lithium secondary battery, during charging, lithium released from the positive electrode is inserted into the negative electrode, and during discharging, it desorbs from the negative electrode and returns to the positive electrode again. However, in the case of a silicon-based negative electrode active material, volume change and surface side reactions are intense, and a large amount of the lithium inserted into the negative electrode during the initial charging cannot return to the positive electrode again, thus causing a problem that the initial irreversible capacity increases. When the initial irreversible capacity increases, problems such as a sharp decrease in battery capacity and cycle performance occur.

[0055] In the present invention, in order to solve the above-mentioned problems, the initial irreversible capacity problem is solved by pre-lithifying the negative electrode of a lithium secondary battery. Specifically, the present invention relates to a step of pre-treating the negative electrode before the pre-lithification step so that when the lithium transfer step is carried out, the lithium metal is easily transferred from the transfer laminate and the lithium in the negative electrode active material layer is uniformly pre-lithified.

[0056] Furthermore, in the present invention, in order to improve capacity performance, while using only silicon-based active materials as the negative electrode active material, the problems of maintaining the conductive path due to volume expansion and maintaining the bonding between the conductive material, binder, and active material were resolved by using a binder under specific conditions and a conductive material composite bonded to the binder.

[0057] On the other hand, the average particle size (D50) of the silicon-based active material of the present invention is 5 μm to 10 μm, specifically 5.5 μm to 8 μm, and more specifically 6 μm to 7 μm. When the average particle size falls within the above range, the specific surface area of ​​the particles falls within an appropriate range, and the viscosity of the negative electrode slurry is formed within an appropriate range. This allows for smooth dispersion of the particles constituting the negative electrode slurry. Furthermore, when the size of the silicon-based active material is greater than or equal to the lower limit of the above range, the composite material consisting of the conductive material and binder in the negative electrode slurry provides excellent contact area between the silicon particles and the conductive material, increasing the likelihood of a sustained conductive network and increasing the capacity retention rate. On the other hand, when the average particle size satisfies the above range, excessively large silicon particles are eliminated, and the surface of the negative electrode is formed smoothly, thereby preventing the phenomenon of non-uniform current density during charging and discharging.

[0058] In one embodiment of this application, the silicon-based active material generally has a characteristic BET specific surface area. The BET specific surface area of ​​the silicon-based active material is preferably 0.01 m². 2 / g~150.0m 2 / g, more comfortably 0.1m 2 / g~100.0m 2 / g, particularly preferably 0.2m 2 / g~80.0m2 / g, most preferably 0.2 m 2 / g to 18.0 m 2 / g. The BET specific surface area is measured in accordance with DIN 66131 (using nitrogen).

[0059] In one embodiment of the present application, the silicon-based active material can exist, for example, in crystalline or amorphous form and is preferably not porous. The silicon particles are preferably spherical or flaky particles. As an alternative, but less preferably, the silicon particles may also have a fibrous structure or exist in the form of a silicon-containing film or coating.

[0060] In one embodiment of the present application, the silicon-based active material may be included in an amount of 60 parts by weight or more based on 100 parts by weight of the negative electrode active material layer composition.

[0061] In another embodiment, the silicon-based active material may be included in an amount of 60 parts by weight or more, preferably 65 parts by weight or more, more preferably 70 parts by weight or more, and may be included in an amount of 95 parts by weight or less, preferably 90 parts by weight or less, more preferably 80 parts by weight or less, based on 100 parts by weight of the negative electrode active material layer composition.

[0062] Even when the silicon-based active material with a significantly high capacity is used within the above range, the negative electrode composition according to the present application uses a specific conductive material and binder that can suppress the volume expansion rate during the charge and discharge process, and does not deteriorate the performance of the negative electrode even when including the above range, and has excellent output characteristics during charging and discharging.

[0063] In one embodiment of the present application, the silicon-based active material can have a non-spherical shape, and its sphericity is, for example, 0.9 or less, for example, 0.7 to 0.9, for example, 0.8 to 0.9, for example, 0.85 to 0.9.

[0064] In the present application, the sphericity is determined by the following formula A-1, where A is the area and P is the boundary line. [Formula A-1] 4πA / P 2

[0065] Traditionally, graphite-based compounds were the only active materials used for the negative electrode. However, with the increasing demand for high-capacity batteries in recent years, there has been a growing trend to mix in silicon-based compounds to increase capacity. However, silicon-based compounds have a limitation: their volume expands rapidly during the charge / discharge process, damaging the conductive paths formed within the negative electrode active material layer and actually degrading battery performance. Therefore, the type of negative electrode conductive material used in combination with the silicon-based active material is crucial.

[0066] Accordingly, in one embodiment of this application, the negative electrode conductive material may include at least one selected from the group consisting of point conductive material; linear conductive material; and planar conductive material.

[0067] In one embodiment of this application, the point-like conductive material can be used to improve the conductivity of the negative electrode and means a conductive material that has conductivity without inducing chemical changes. Specifically, the point-like conductive material may be at least one selected from the group consisting of natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, conductive fibers, fluorocarbon, aluminum powder, nickel powder, zinc oxide, potassium titanate, titanium oxide, and polyphenylene derivatives, and may preferably include carbon black in that it embodies high conductivity and has excellent dispersibility.

[0068] In one embodiment of this application, the point conductive material has a BET specific surface area of ​​40 m². 2 / g or more 70m 2 / g or less, preferably 45m 2 / g or more 65m 2 / g or less, more preferably 50m 2 / g or more 60m 2 It may be less than / g.

[0069] In one embodiment of this application, the particle size of the dot-like conductive material is 10 nm to 100 nm, preferably 20 nm to 90 nm, and more preferably 20 nm to 60 nm.

[0070] In one embodiment of this application, the conductive material may include a planar conductive material. The aforementioned planar conductive material can improve conductivity by increasing surface contact between silicon particles within the negative electrode, and at the same time suppress the disruption of the conductive path due to volume expansion. It can be described as a plate-shaped conductive material or a bulk-type conductive material.

[0071] In one embodiment of this application, the planar conductive material may include at least one selected from the group consisting of plate graphite, graphene, graphene oxide, and graphite flakes, and preferably plate graphite.

[0072] In one embodiment of this application, the average particle size (D50) of the planar conductive material is 2 μm to 7 μm, specifically 3 μm to 6 μm, and more specifically 4 μm to 5 μm. When this range is met, the particle size is sufficient to facilitate dispersion without causing an excessive increase in the viscosity of the negative electrode slurry. Therefore, when dispersion is performed using the same equipment and time, the dispersion effect is superior.

[0073] In one embodiment of this application, a negative electrode composition is provided in which the planar conductive material has a D10 of 0.5 μm or more and 1.5 μm or less, a D50 of 2.5 μm or more and 3.5 μm or less, and a D90 of 7.0 μm or more and 15.0 μm or less.

[0074] In one embodiment of this application, a high specific surface area planar conductive material with a high BET specific surface area, or a low specific surface area planar conductive material, may be used as the planar conductive material.

[0075] In one embodiment of this application, a high specific surface area planar conductive material or a low specific surface area planar conductive material can be used without limitation as the planar conductive material. In particular, the planar conductive material according to this application may be affected to some extent by dispersion in terms of electrode performance, and it may be particularly preferable to use a low specific surface area planar conductive material that does not cause dispersion problems.

[0076] In one embodiment of this application, the planar conductive material has a BET specific surface area of ​​5 m². 2 It may be more than / g.

[0077] In another embodiment, the planar conductive material has a BET specific surface area of ​​5 m². 2 / g or more 500m 2 / g or less, preferably 5m 2 / g or more 300m 2 / g or less, more preferably 5m 2 / g or more 250m 2 It may be less than / g.

[0078] In another embodiment, the planar conductive material is a high specific surface area planar conductive material with a BET specific surface area of ​​50 m². 2 / g or more 500m 2 / g or less, preferably 80mg 2 / g or more 300m 2 / g or less, more preferably 100m 2 / g or more 300m 2 The range of / g or less may also be satisfied.

[0079] In another embodiment, the planar conductive material is a low specific surface area planar conductive material with a BET specific surface area of ​​5 m². 2 / g or more 40m 2 / g or less, preferably 5m 2 / g or more 30m 2 / g or less, more preferably 5m 2 / g or more 25m 2 The range of / g or less may also be satisfied.

[0080] Other conductive materials may include linear conductive materials such as carbon nanotubes. The carbon nanotubes may be bundle-type carbon nanotubes. The bundle-type carbon nanotubes may contain multiple carbon nanotube units. Specifically, unless otherwise specified, "bundle type" here refers to a secondary shape in the form of a bundle or rope, in which multiple carbon nanotube units are arranged in substantially the same orientation along their longitudinal axes, or are intertwined. The carbon nanotube units have a graphite sheet that is cylindrical with a nanoscale diameter and has an sp2 bond structure. In this case, the properties of a conductor or semiconductor can be determined by the angle and structure in which the graphite sheet is wound. Compared to entangled-type carbon nanotubes, the bundle-type carbon nanotubes can be uniformly dispersed during anode manufacturing, smoothly form a conductive network within the anode, and improve the conductivity of the anode.

[0081] In one embodiment of this application, the negative electrode conductive material may be 10 to 40 parts by weight, based on 100 parts by weight of the negative electrode active material layer composition.

[0082] In another embodiment, the negative electrode conductive material may be included in an amount of 10 to 40 parts by weight, preferably 10 to 30 parts by weight, and more preferably 10 to 20 parts by weight, based on 100 parts by weight of the negative electrode active material layer composition.

[0083] The negative electrode conductive material of this application has a completely different structure from the conductive material applied to the positive electrode. Specifically, the negative electrode conductive material of this application plays the role of capturing the contact points between silicon-based active materials, where the volume expansion of the electrodes is very large due to charging and discharging, while the positive electrode conductive material plays the role of a buffer during rolling while partially imparting conductivity, and its structure and role are completely different from the negative electrode conductive material of the present invention.

[0084] Furthermore, the negative electrode conductive material described in this application is applied to silicon-based active materials and has a completely different structure from conductive materials applied to graphite-based active materials. In other words, conductive materials used in electrodes with graphite-based active materials simply have smaller particles compared to the active material, thus improving output characteristics and imparting some conductivity. This is completely different in structure and role from negative electrode conductive materials applied together with silicon-based active materials, as in the present invention.

[0085] In one embodiment of this application, the planar conductive material used as the negative electrode conductive material described above has a different structure and role from carbon-based active materials generally used as negative electrode active materials. Specifically, the carbon-based active material used as the negative electrode active material may be artificial graphite or natural graphite, and refers to a material that is processed into a spherical or point-like form for use in order to facilitate the storage and release of lithium ions.

[0086] On the other hand, planar conductive materials used as negative electrode conductive materials are substances having a planar or plate-like form, and can be described as plate-like graphite. In other words, they are substances included to maintain conductive pathways within the negative electrode active material layer, and do not play a role in lithium storage and release, but rather refer to substances that secure conductive pathways in a planar manner within the negative electrode active material layer.

[0087] In other words, in this application, the use of plate-shaped graphite as a conductive material means that it was processed into a planar or plate-like form and used not to store or release lithium, but as a material to secure a conductive path. In this case, the negative electrode active material included together has high capacity characteristics for lithium storage and release, and plays a role in storing and releasing all lithium ions transmitted from the positive electrode.

[0088] On the other hand, in this application, the use of a carbon-based active material as the active material means that it was processed into a point-like or spherical shape and used as a material to store or release lithium.

[0089] In other words, in one embodiment of this application, the carbon-based active material, artificial graphite or natural graphite, has a BET specific surface area of ​​0.1 m². 2 / g or more 4.5m 2 The range of less than or equal to / g may also be satisfied. In addition, plate-type graphite, which is a planar conductive material, has a planar BET specific surface area of ​​5m². 2 It may be more than / g.

[0090] In one embodiment of this application, the negative electrode binder may contain at least one selected from the group consisting of polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile, polymethyl methacrylate, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, polyacrylic acid, and substances in which the hydrogens of these substances are substituted with Li, Na, or Ca, and may also contain various copolymers thereof.

[0091] The negative electrode binder according to one embodiment of this application plays a role in holding the active material and conductive material in order to prevent distortion and structural deformation of the negative electrode structure during the volume expansion and relaxation of the silicon-based active material. Any general binder can be applied as long as it satisfies the above role, and specifically, an aqueous binder can be used, and more specifically, a PAM-based binder may be used.

[0092] In one embodiment of this application, a method for manufacturing a negative electrode for a lithium secondary battery may include a step of pre-treating the negative electrode.

[0093] In this case, pre-treating the negative electrode may include the steps of pre-treating the surface of the negative electrode active material layer as described above; or, if a buffer layer described later is formed on the surface of the negative electrode active material layer, the step of pre-treating the buffer layer.

[0094] In other words, in the case of a negative electrode for a lithium secondary battery, a buffer layer, described later, can be formed on top of the negative electrode active material layer for smoother pre-lithiation, and the concept of pre-treating the negative electrode may encompass both pre-treating the surface of the negative electrode active material layer where the buffer layer is not formed, and pre-treating the surface of the buffer layer in the negative electrode active material layer where the buffer layer is formed.

[0095] The method for manufacturing a negative electrode for a lithium secondary battery according to this application may include a step of pre-treating the negative electrode surface before the lithium metal layer transfer step, as described above. This increases the adhesion between the negative electrode and the lithium metal layer, allowing the substrate layer used as the transfer laminate to be easily removed after lamination of the lithium metal layer, thereby suppressing the defect phenomenon of separation of the negative electrode portion. Furthermore, through the above-described pre-treatment process, the uniformity of the upper interface between the lithium metal layer and the negative electrode is increased, the generation of lithium by-products during pre-lithification is suppressed, and the amount of lithium loss is also reduced.

[0096] In one embodiment of this application, the invention provides a method for manufacturing a negative electrode for a lithium secondary battery, wherein the pretreatment step is plasma treatment or corona treatment.

[0097] In one embodiment of this application, the pretreatment step is plasma treatment, which provides a method for manufacturing a negative electrode for a lithium secondary battery.

[0098] In one embodiment of this application, the pretreatment step provides a method for manufacturing a negative electrode for a lithium secondary battery using an indirect atmospheric pressure plasma method.

[0099] The aforementioned plasma surface treatment method can be defined as a surface treatment method that alters the chemical bonding of a material by utilizing the high energy of ions and electrons in the plasma state. Generally, plasma treatment includes vacuum plasma and atmospheric pressure plasma. Of these, atmospheric pressure plasma uses a discharge system that does not require a vacuum system and can operate appropriately even in non-vacuum environments. Methods for atmospheric pressure plasma include dielectric barrier discharge (DBD), corona discharge, and arc discharge.

[0100] Plasma processing conditions vary greatly depending on the plasma equipment. Specifically, the indirect atmospheric pressure plasma described in this application is carried out under atmospheric pressure conditions, not vacuum conditions, so adjusting the difference in plasma intensity is not very significant. Generally, in the case of vacuum plasma, the processing effect tends to change greatly depending on the amount of gas injected, the frequency, and the power. Conversely, the indirect atmospheric pressure plasma method is performed under atmospheric pressure conditions, so it is less affected, and in such cases, the processing time has an even greater impact, and as the processing time increases, the surface hydrophilicity of the object being plasma-treated increases.

[0101] In one embodiment of this application, the dielectric barrier discharge (DBD) method includes a direct method and an indirect method. The direct method involves directly irradiating the treatment surface with plasma, while the indirect method involves generating plasma and then treating the surface with ions generated from the plasma using a carrier gas. Since such methods do not cause arcing during plasma treatment, the indirect method may be more preferable as a pretreatment method for electrodes using a metal negative electrode current collector layer.

[0102] In this case, the difference between the direct and indirect methods lies in the power used during plasma generation. The direct method uses a power level of approximately 50W to 200W, while the indirect method uses a power level of approximately 1kW to 10kW.

[0103] Specifically, in one embodiment of this application, the pretreatment step is an atmospheric pressure plasma method, which provides a method for manufacturing a negative electrode for a lithium secondary battery. More specifically, the pretreatment step may be an indirect atmospheric pressure plasma method, and more specifically, an indirect dielectric barrier discharge (DBD) method.

[0104] In one embodiment of this application, the plasma treatment can mean a process in which a manufactured negative electrode for a lithium secondary battery is passed through a plasma generating unit at a frequency of 50 kHz to 250 kHz, with the power adjusted to a range of 1 kW to 10 kW, and N2 (700 slm) and CDA (28 slm) are flowed to generate plasma, and the negative electrode is passed through at a processing speed of 1 m / min to 40 m / min to treat the surface of the negative electrode.

[0105] When the plasma processing conditions described above are met, the water contact angle can be changed by ensuring appropriate hydrophilicity on the negative electrode surface, thereby facilitating the transfer of the lithium metal layer.

[0106] Furthermore, in one embodiment of this application, the pretreatment step is preferably performed using an indirect atmospheric pressure plasma method. In the case of this application using a metal negative electrode current collector layer, the above effects can also be obtained by using a direct atmospheric pressure plasma method, but when the electrode surface is treated with direct plasma, arcing may occur, causing damage to the negative electrode surface and resulting in only a portion of the lithium metal layer being transferred.

[0107] In one embodiment of this application, the indirect atmospheric pressure plasma method provides a method for manufacturing a negative electrode for a lithium secondary battery, wherein the plasma processing gas transports plasma using a plasma processing gas, the plasma processing gas contains nitrogen gas, and the plasma processing gas contains 3% to 10% oxygen gas relative to the nitrogen gas.

[0108] The processing method according to this application may use plasma processing. In this case, the plasma processing is carried out using a plasma processing gas. That is, in the indirect plasma method, the plasma is transferred via a plasma processing gas, and it is preferable that nitrogen and oxygen (or cleaned dry air) are used as the plasma processing gas.

[0109] In one embodiment of this application, the plasma processing gas comprises nitrogen gas and oxygen gas, preferably containing 3% to 10% oxygen gas relative to the nitrogen gas.

[0110] Although the plasma treatment gas can be driven by atmospheric oxygen even if it does not contain oxygen, including oxygen gas within the aforementioned range improves the effectiveness and reproducibility of the treatment. Furthermore, the radicals of oxygen and ozone generated during plasma generation adsorb to the treatment area, increasing its hydrophilicity, or form hydrophilic functional groups such as hydroxyl groups on the surface of the treated object, further increasing the surface hydrophilicity.

[0111] In other words, the manufacturing method according to this application is characterized by using a plasma treatment method to form a surface having hydrophilic groups on the negative electrode surface so as to be suitable for transferring a lithium metal layer, and specifically by applying a dielectric barrier type indirect atmospheric pressure plasma treatment method to reduce damage to the electrode. For the minimum amount of treatment required for the attachment of the lithium metal layer, the frequency of the dielectric barrier type indirect atmospheric pressure plasma treatment method can be 50 kHz to 250 kHz, the power can be adjusted in the range of 1 kW to 10 kW, and the processing can be performed at a speed of 1 m / min to 40 m / min.

[0112] In this case, as mentioned above, if the processing time is long, the surface hydrophilicity of the object to be plasma-treated increases, so specifically, it may be preferable to process at a speed of 1 m / min.

[0113] One embodiment of this application provides a method for manufacturing a negative electrode for a lithium secondary battery in which a difference of 10° or more is formed in the water contact angle of the negative electrode surface before and after the pretreatment.

[0114] In another embodiment, a difference of 10° or more and 15° or more may be formed in the water contact angle of the negative electrode surface before and after the pretreatment, and a difference of 65° or less, preferably 60° or less, may be formed.

[0115] Here, the water contact angle difference can mean the water contact angle difference on the surface of the negative electrode active material layer or the water contact angle difference on the surface of the buffer layer.

[0116] As described above, by pre-treating the negative electrode surface, it is possible to create a difference of 10° or more in the water contact angle of the negative electrode surface compared to before pre-treatment. By changing the water contact angle through the above process, it is possible to improve the interfacial adhesion with the lithium metal layer later.

[0117] In other words, the main feature of the present invention is that, according to one embodiment of this application, the method for manufacturing a negative electrode for a lithium secondary battery does not involve forming a separate layer on top of the negative electrode active material layer or changing the composition of the surface portion of the negative electrode active material layer, but rather only changes the interfacial properties by treating the surface portion of the negative electrode active material layer.

[0118] The water contact angle of the negative electrode active material layer surface or the buffer layer surface cannot be generally defined because the surface energy value differs depending on the composition. However, the water contact angle of the negative electrode active material layer surface before pretreatment (water contact angle A before pretreatment of the negative electrode active material layer surface) can satisfy 40° to 50°, and the water contact angle after pretreatment (water contact angle B after pretreatment of the negative electrode active material layer surface) can satisfy 5° to 30°.

[0119] Furthermore, the water contact angle with respect to the buffer layer surface before pretreatment (water contact angle A of the buffer layer surface before pretreatment) may be 110° to 130°, and the water contact angle after pretreatment (water contact angle B of the buffer layer surface after pretreatment) may be 60° to 110°.

[0120] One embodiment of this application provides a method for manufacturing a negative electrode for a lithium secondary battery, further comprising the steps of forming a negative electrode current collector layer and a negative electrode active material layer on one or both sides of the negative electrode current collector layer, and then coating the side of the negative electrode active material layer opposite to the side in contact with the negative electrode current collector layer with a buffer layer composition to form a buffer layer.

[0121] When the buffer layer is further included, even if lithium metal is transferred to the upper part of the negative electrode active material layer, direct contact with the highly reactive silicon-based active material is prevented, a rapid reaction can be suppressed, and the rate of pre-lithification can be adjusted to uniformly pre-lithify the lithium in the negative electrode active material layer.

[0122] In one embodiment of this application, the thickness of the buffer layer can be in the range of 0.1 μm to 2 μm.

[0123] In another embodiment, the thickness of the buffer layer may be in the range of 0.1 μm or more and 2 μm or less, preferably 0.2 μm or more and 1.5 μm or less, and more preferably 0.5 μm or more and 1 μm or less.

[0124] The buffer layer according to this application has the aforementioned thickness range, which allows the pre-lithiation rate to be adjusted to an appropriate range, suppressing the generation of by-products and ensuring uniform pre-lithiation within the negative electrode active material layer.

[0125] In one embodiment of this application, the buffer layer composition may include at least one substance selected from the group consisting of acrylic polymers and binders.

[0126] In one embodiment of this application, a negative electrode for a lithium secondary battery is provided in which the acrylic polymer comprises at least one selected from the group consisting of polyethylene (PE); polypropylene (PP); polyacrylic acid (PAA); and polyester.

[0127] One embodiment of this application provides a negative electrode for a lithium secondary battery in which the binder contained in the buffer layer composition contains a binder copolymer containing a monomer containing a fluorogroup, and the monomer contains a perfluoroolefin.

[0128] In one embodiment of this application, the binder copolymer may include at least one diverse copolymer selected from the group consisting of polyvinylidene fluoride, polyacrylonitrile, polymethyl methacrylate, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, and polyacrylic acid.

[0129] In this case, one embodiment of the present application is characterized in that the binder copolymer contains a monomer containing a fluoro group.

[0130] In one embodiment of this application, the statement that the binder copolymer contains monomers containing fluorogroups means that monomer units containing fluorogroups may be included in the copolymer in random, alternating, or blocky monomer units.

[0131] In one embodiment of this application, the monomer containing the fluorogroup may include C2-C8 fluoroolefins or perfluoroolefins such as tetrafluoroethylene (TFE), hexafluoropropylene (HFP), pentafluoropropylene, and hexafluoroisobutylene.

[0132] Specifically, in one embodiment of this application, the monomer containing the fluoro group may be hexafluoropropylene (HFP).

[0133] The binder copolymer according to this application may contain 5 to 20 parts by weight of the monomer based on 100 parts by weight of the binder copolymer.

[0134] In another embodiment, the monomer may be included in an amount of 5 to 20 parts by weight, preferably 8 to 15 parts by weight, based on 100 parts by weight of the binder copolymer.

[0135] "Containing the monomer in the amount described above relative to the binder copolymer" can mean the amount of the monomer when the total binder copolymer formed by the reaction of two or more monomers is used as a reference.

[0136] The binder according to this application has the characteristic of having the above composition, which allows for an appropriate pre-lithiation rate of lithium metal during subsequent pre-lithiation, suppression of side reaction generation, and prevention of cracking of negative electrode active material particles.

[0137] In one embodiment of this application, the binder copolymer may be a polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP).

[0138] In one embodiment of this application, the buffer layer composition may include the binder.

[0139] In one embodiment of this application, the method for manufacturing the negative electrode for a lithium secondary battery may include a step of transferring a lithium metal layer to the pre-treated negative electrode.

[0140] The aforementioned step corresponds to the step of transferring the lithium metal layer to the upper part of the negative electrode to pre-lithify the negative electrode.

[0141] In one embodiment of this application, the step of transferring a lithium metal layer to the opposite side of the surface of the pre-treated negative electrode that is in contact with the negative electrode current collector layer includes the steps of: preparing a transfer laminate including a base layer and a lithium metal layer provided on the base layer; laminating the transfer laminate on the negative electrode active material layer such that the opposite side of the lithium metal layer that is in contact with the base layer is in contact with the opposite side of the negative electrode active material layer that is in contact with the negative electrode current collector layer; and removing the base layer; thereby providing a method for manufacturing a negative electrode for a lithium secondary battery.

[0142] In one embodiment of this application, the deposition method for depositing the lithium metal layer onto the substrate layer can be selected from, but is not limited to, vacuum deposition, chemical vapor deposition, chemical vapor deposition (CVD), and physical vapor deposition. Various deposition methods used in the industry can be used.

[0143] Figure 1 shows a method for pre-lithifying a negative electrode for a lithium secondary battery according to one embodiment of the present application. Specifically, it shows the process of preparing a transfer laminate 100 including a base layer 10 and a lithium metal layer 20, laminating it so that the negative electrode active material layer 30 and lithium metal 20 of a negative electrode 200 for a lithium secondary battery, on which a negative electrode active material layer 30 is formed on a negative electrode current collector layer 40, are in contact, and then removing the base layer 10 to transfer only the lithium metal layer 20 onto the upper part of the negative electrode active material layer 30. Figure 1 shows the transfer of the lithium metal layer onto the upper part of the negative electrode active material layer where no buffer layer is formed, and the same applies when a buffer layer is further laminated.

[0144] At this time, the transfer process can be carried out by applying a load of 100 kgf to 800 kgf to the negative electrode for the lithium secondary battery on which the transfer laminate is stacked via a roll press. Subsequently, a step of removing the base layer is included, and during removal, the upper part of the negative electrode according to this application is pre-treated, thereby improving the interfacial properties between the pre-treated negative electrode and the lithium metal layer, and enabling easy transfer of the lithium metal layer.

[0145] In one embodiment of this application, the substrate layer can be used without limitation as long as it can withstand process conditions such as high temperature during the stage of depositing the lithium metal layer and has the characteristic of preventing the problem of reverse delamination in which the lithium metal layer is transferred onto the substrate layer during the winding process for transferring the deposited lithium metal layer.

[0146] Specifically, in one embodiment of this application, the substrate layer may be at least one selected from the group consisting of polyethylene terephthalate (PET), polyimide (PI), poly(methylmethacrylate) (PMMA), polypropylene, polyethylene, and polycarbonate.

[0147] In one embodiment of this application, the thickness of the substrate layer may be 1 μm or more and 300 μm or less, and may satisfy the range of 5 μm or more and 200 μm or 10 μm or more and 100 μm or less.

[0148] In one embodiment of this application, the thickness of the lithium metal layer is 1 μm or more and 10 μm or less, preferably 3 μm or more and 10 μm or less.

[0149] By ensuring that the thickness of the substrate layer and the lithium metal layer meets the specified range, the lithium metal can be efficiently transferred to the negative electrode active material layer, and reverse transfer can be prevented.

[0150] In one embodiment of this application, a method for manufacturing a negative electrode for a lithium secondary battery is provided, which further includes a release layer on the surface of the transfer laminate in contact with the substrate layer and the lithium metal layer in order to improve the peelability of the lithium metal layer and ensure transferability to the negative electrode active material layer.

[0151] In this embodiment of the present application, the release force between the substrate layer and the release layer can satisfy the range of 50 gf / inch or more and 1,000 gf / inch or less, more specifically the range of 60 gf / inch or more and 900 gf / inch or less, and more specifically the range of 70 gf / inch or more and 800 gf / inch or less.

[0152] In other words, the base material layer may have a release layer formed on at least one surface, or it may have a release layer formed on both surfaces. The release layer prevents the reverse delamination problem in which the lithium metal layer is transferred onto the base material layer during the winding process for transferring the deposited lithium metal layer to the negative electrode, and furthermore, the base material layer can be easily separated after the lithium metal layer has been transferred onto the negative electrode active material layer.

[0153] In particular, the plasma treatment effect of the negative electrode active material layer described above improves the interfacial adhesion between the negative electrode active material layer and the lithium metal layer. Therefore, the release layer according to this application has the characteristic of being able to be used without limitation whether the release force is low or high, as described above.

[0154] The release layer may contain one or more selected from the group consisting of silicon-modified polyester in which silicon chains are grafted onto a polyester main chain, acrylic resin, Si, melamine, and fluorine.

[0155] In one embodiment of this application, the release layer can be formed by a coating method, for example, the coating method may be selected from the group consisting of dip coating, spray coating, spin coating, die coating, gravure coating, micro-gravure coating, comma coating, and roll coating, but is not limited thereto, and a variety of coating methods used in the industry to form a coating layer can be used.

[0156] In one embodiment of this application, the pre-lithiation step can be carried out from the step of laminating and transferring the lithium metal layer onto the negative electrode, and this can be referred to as a pre-lithiation reaction due to the high reactivity of the lithium metal layer before the activation step.

[0157] In one embodiment of this application, the step of activating the transferred lithium metal layer may be included.

[0158] As described above, due to the high reactivity of the lithium metal layer, the reaction of the lithium metal can proceed the moment it comes into contact with the upper part of the negative electrode. This is a reaction before the activation stage, and the subsequent step of removing the substrate layer and activating the lithium to pre-lithify it can be defined as the activation stage.

[0159] The present invention provides a method for manufacturing a negative electrode for a lithium secondary battery, wherein the step of activating the lithium metal involves an activation reaction occurring within 30 minutes to 3 hours under conditions of 25°C and 1 atm.

[0160] The aforementioned activation step is a step in which conditions are set for the diffusion of lithium metal into the negative electrode active material layer, and whether or not pre-lithiation is complete can be determined by whether or not the lithium on the upper part of the metal layer has been completely removed.

[0161] In one embodiment of this application, the activation reaction time may be 30 minutes to 3 hours, preferably 1 to 2 hours. That is, unlike existing technologies, the negative electrode active material layer according to this application is pretreated, thereby enabling uniform lithium transfer throughout the entire negative electrode active material layer.

[0162] In one embodiment of this application, a negative electrode for a lithium secondary battery is provided, comprising a negative electrode current collector layer and a negative electrode active material layer provided on one or both sides of the negative electrode current collector layer, wherein the negative electrode for a lithium secondary battery satisfies the following formula 1.

[0163] [Formula 1] 10°≦AB≦60° In the above formula 1, A represents the water contact angle of the negative electrode surface before pretreatment, and B represents the water contact angle of the negative electrode surface after pretreatment.

[0164] In the case of a negative electrode for a lithium secondary battery as described above, the negative electrode is characterized by being pre-treated, and the water contact angle before and after pre-treatment is characterized by satisfying the above range.

[0165] One embodiment of this application provides a negative electrode for a lithium secondary battery manufactured by the method for manufacturing a negative electrode for a lithium secondary battery according to this application.

[0166] One embodiment of this application provides a lithium secondary battery comprising: a positive electrode; a negative electrode for a lithium secondary battery according to this application; a separation membrane provided between the positive electrode and the negative electrode; and an electrolyte.

[0167] Figure 2 shows a stacked structure of a lithium secondary battery according to one embodiment of the present application. Specifically, a negative electrode 200 for a lithium secondary battery, including a negative electrode active material layer 30, can be seen on one side of a negative electrode current collector layer 40, and a positive electrode 300 for a lithium secondary battery, including a positive electrode active material layer 70, can be seen on one side of a positive electrode current collector layer 60. The negative electrode 200 and the positive electrode 100 for a lithium secondary battery are formed in a stacked structure with a separation membrane 50 in between.

[0168] The negative electrode for lithium secondary batteries according to this application is characterized by transferring a lithium metal layer onto the upper part of the negative electrode that has been pre-treated as described above, thereby proceeding with pre-lithiation.

[0169] In this case, the pre-lithified negative electrodes can be compared using SEM images, and specifically, the degree of particle fracture in the SEM images can be expressed as a ratio through image analysis.

[0170] A secondary battery according to one embodiment of this specification may include, in particular, the negative electrode for a lithium secondary battery described above. Specifically, the secondary battery may include a negative electrode, a positive electrode, a separator membrane interposed between the positive electrode and the negative electrode, and an electrolyte, wherein the negative electrode is the same as the negative electrode described above. Since the negative electrode has been described above, a detailed explanation will be omitted.

[0171] The positive electrode may include a positive electrode current collector layer and a positive electrode active material layer formed on the positive electrode current collector layer, which contains the positive electrode active material.

[0172] In the positive electrode, the positive electrode current collector layer is not particularly limited as long as it does not induce chemical changes in the battery and is conductive. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel with a surface treatment of carbon, nickel, titanium, silver, etc. can be used. The positive electrode current collector layer can usually have a thickness of 3 to 500 μm, and fine irregularities can be formed on the surface of the current collector layer to increase the adhesion strength of the positive electrode active material. For example, it may be used in various forms such as film, sheet, foil, net, porous material, foam, or nonwoven fabric.

[0173] The positive electrode active material may be a commonly used positive electrode active material. Specifically, the positive electrode active material may be a layered compound such as lithium cobalt oxide (LiCoO2) or lithium nickel oxide (LiNiO2), or a compound substituted with one or more transition metals; lithium iron oxide such as LiFe3O4; or a compound with the chemical formula Li 1+c1 Mn 2-c1 Lithium manganese oxides such as O4 (0 ≤ c1 ≤ 0.33), LiMnO3, LiMn2O3, LiMnO2; lithium copper oxide (Li2CuO2); vanadium oxides such as LiV3O8, V2O5, Cu2V2O7; chemical formula LiNi 1-c2 M c2 Ni-site type lithium nickel oxide represented as O2 (where M is at least one selected from the group consisting of Co, Mn, Al, Cu, Fe, Mg, B, and Ga, satisfying 0.01 ≤ c2 ≤ 0.3); chemical formula LiMn 2-c3 M c3 Lithium manganese composite oxides represented as O2 (where M is at least one selected from the group consisting of Co, Ni, Fe, Cr, Zn, and Ta, satisfying 0.01 ≤ c3 ≤ 0.1) or Li2Mn3MO8 (where M is at least one selected from the group consisting of Fe, Co, Ni, Cu, and Zn); LiMn2O4 in which part of the Li in the chemical formula is substituted with an alkaline earth metal ion, etc., are examples, but are not limited to these. The positive electrode may also be metallic lithium (Li-metal).

[0174] The positive electrode active material layer may also include a positive electrode conductive material and a positive electrode binder, along with the positive electrode active material described above.

[0175] In this case, the positive electrode conductive material is used to impart conductivity to the electrode, and can be used without particular limitations as long as it has electronic conductivity without undergoing chemical changes in the battery that is constructed. Specific examples include graphite such as natural graphite or artificial graphite; carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, and carbon fiber; metal powders or metal fibers such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives, and one of these alone or a mixture of two or more can be used.

[0176] Furthermore, the positive electrode binder plays a role in improving the adhesion between positive electrode active material particles and the adhesion between the positive electrode active material and the positive electrode current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene-butadiene rubber (SBR), fluororubber, or various copolymers thereof, and one of these alone or a mixture of two or more may be used.

[0177] The separation membrane separates the negative and positive electrodes and provides a pathway for lithium ions to move. Any membrane commonly used as a separation membrane in secondary batteries is generally acceptable, but those with low resistance to electrolyte ion movement while exhibiting excellent electrolyte moisture absorption capacity are particularly preferred. Specifically, porous polymer films, such as ethylene homopolymers, propylene homopolymers, ethylene / butene copolymers, ethylene / hexene copolymers, and ethylene / methacrylate copolymers, or laminated structures of two or more layers thereof, may be used. Alternatively, ordinary porous nonwoven fabrics, such as nonwoven fabrics made from high-melting-point glass fibers or polyethylene terephthalate fibers, can also be used. Furthermore, coated separation membranes containing ceramic components or polymeric substances may be used to ensure heat resistance or mechanical strength, and may be selectively used in single-layer or multi-layer structures.

[0178] Examples of the aforementioned electrolytes include, but are not limited to, organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used in the manufacture of lithium secondary batteries. Specifically, the electrolyte may include a non-aqueous organic solvent and a metal salt.

[0179] As the non-aqueous organic solvent, for example, aprotic organic solvents such as N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, γ-butyrolactone, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, triester phosphate, trimethoxymethane, dioxolane derivatives, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethers, methyl propionate, and ethyl propionate may be used.

[0180] In particular, among the carbonate-based organic solvents, ethylene carbonate and propylene carbonate, which are cyclic carbonates, are preferred because they are high-viscosity organic solvents with high dielectric constants that effectively dissociate lithium salts. When such cyclic carbonates are mixed with linear carbonates with low viscosity and low dielectric constant, such as dimethyl carbonate and diethyl carbonate, in appropriate proportions, an electrolyte with high electrical conductivity can be created, and this mixture is even more preferable.

[0181] The metal salt can be a lithium salt, which is a substance that dissolves easily in the non-aqueous electrolyte, for example, the anion of the lithium salt is F - Cl - , I - NO3 - , N(CN)2 - BF4 - ClO4 - PF6 - (CF3)2PF4 - (CF3)3PF3 - (CF3)4PF2 - (CF3)5PF - (CF3)6P - CF3SO3 - CF3CF2SO3 - (CF3SO2)2N - , (FSO2)2N - CF3CF2(CF3)2CO - (CF3SO2) 2CH - (SF5)3C - (CF3SO2)3C - CF3(CF2)7SO3 - CF3CO2 - CH3CO2 - SCN - and (CF3CF2SO2)2N - You can use one or more selected from the group consisting of the following.

[0182] In addition to the electrolyte components, the electrolyte may further contain one or more additives for purposes such as improving battery life characteristics, suppressing battery capacity reduction, and improving battery discharge capacity, such as haloalkylene carbonate compounds like difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glyme, hexaphosphate triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride.

[0183] One embodiment of the present invention provides a battery module and a battery pack containing the secondary battery as a unit cell. Since the battery module and battery pack include a secondary battery having high capacity, high rate characteristics and cycle characteristics, they can be used as a power source for medium to large devices selected from the group consisting of electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles and power storage systems. [Examples]

[0184] The following are preferred embodiments to aid in understanding the present invention. These embodiments are for illustrative purposes only, and it will be apparent to those skilled in the art that various changes and modifications are possible within the scope of the present invention and the technical concept, and that such variations and modifications fall within the scope of the appended claims.

[0185] <Examples> <Manufacturing of Transfer Layers> A laminate (I-One Film Co., Ltd.) was prepared in which an acrylic resin was coated at a thickness of 1 μm as a release layer on a polyethylene terephthalate substrate layer. A lithium metal layer with a thickness of 6 μm was deposited on the release layer of the laminate using a thermal evaporation method to produce a transfer laminate. At this time, the deposition equipment was an EWK-050 from ULVAC, and the deposition process was carried out with a speed of 2.5 m / min, a lithium supply temperature of 500°C, and a main roll temperature of -25°C.

[0186] <Example 1> <Manufacturing of negative electrodes> A negative electrode slurry was prepared by adding Si (average particle size (D50): 3.5 μm) as a silicon-based active material, Denka Black as a conductive material, SBR as a binder, and CMC as a thickener, in a weight ratio of 80:15.8:3:1.2 to distilled water used as a solvent for negative electrode slurry formation (solid content concentration 25% by weight).

[0187] As a mixing method, the conductive material, binder, and thickener were dispersed with water using a homomixer at 2500 rpm for 30 minutes, after which the active material was added, and the mixture was dispersed again at 2500 rpm for 30 minutes to prepare a slurry.

[0188] As the negative electrode current collector, 85 mg / 25 cm of the negative electrode slurry was applied to both sides of a copper current collector (thickness: 8 μm). 2 The material was coated with the specified loading amount, rolled (roll press), and dried in a vacuum oven at 130°C for 10 hours to form a negative electrode active material layer (thickness: 33 μm), which was used as the negative electrode (negative electrode thickness: 41 μm, negative electrode porosity: 40.0%).

[0189] <Example 1> Using the manufactured electrode, the negative electrode was subjected to indirect plasma treatment on the surface of the negative electrode active material layer by flowing N2 (700 slm) and CDA (28 slm) into the plasma generation unit at a frequency of 250 kHz (7.2 kW (4.3 kV)). The negative electrode was then passed through the plasma at a speed of 1 m / min. In this process, N2 was used to generate the plasma and also acted as a carrier gas to transfer ions generated from the plasma to the electrode. In other words, because the indirect plasma method requires the plasma to be transferred by a carrier gas, a larger amount of N2 was used compared to the direct plasma method.

[0190] Subsequently, in order to transfer the transfer laminate to the negative electrode active material layer, the lithium metal layer of the transfer laminate was positioned above the negative electrode active material layer, and then a load of 40 kgf / cm was applied and rolling (roll pressing) was carried out. The transfer laminate used had a lithium release force of approximately 70-80 gf / inch. The temperature at this time was room temperature (25°C), and immediately after lamination, the PET layer of the transfer laminate was removed to pre-lithify the negative electrode.

[0191] <Example 2> In the above-described embodiment 1, the negative electrode was pre-lithified in the same manner as in embodiment 1, except that the plasma treatment speed of the negative electrode surface was 20 m / min.

[0192] <Example 3> In the above-described embodiment 1, the negative electrode was pre-lithified in the same manner as in embodiment 1, except that the plasma treatment speed of the negative electrode surface was 40 m / min.

[0193] <Example 4> In the above-described embodiment 1, the negative electrode was pre-lithified in the same manner as in embodiment 1, except that the plasma treatment conditions for the negative electrode surface were set to 60 kHz (3.1 kW (5.5 kV)) and N2 (700 slm) and CDA (28 slm) were flowed to generate plasma, and the negative electrode was treated by passing it through at a speed of 1 m / min.

[0194] <Example 5> In the above-described embodiment 4, the negative electrode was pre-lithified in the same manner as in embodiment 4, except that the plasma treatment speed of the negative electrode surface was 20 m / min.

[0195] <Example 6> In the above-described embodiment 4, the negative electrode was pre-lithified in the same manner as in embodiment 4, except that the plasma treatment speed of the negative electrode surface was 40 m / min.

[0196] <Example 7> In Example 1, the negative electrode was pre-lithified in the same manner as in Example 1, except that the lithium release force of the transfer laminate was adjusted to approximately 700-800 gf / inch.

[0197] <Example 8> For the negative electrode manufactured in the above-mentioned manufacturing example, a buffer layer composition slurry was bar-coated onto the upper part of the negative electrode active material layer and dried to form a buffer layer with a thickness of 0.5 μm to 2 μm. In this case, the buffer layer composition used was a composition containing PVDF-HFP.

[0198] Subsequently, under conditions of a frequency of 250 kHz (7.2 kW (4.3 kV)), N2 (700 slm) and CDA (28 slm) were flowed into the plasma generation section to generate plasma, which was then passed over the negative electrode at a speed of 1 m / min to perform indirect plasma treatment on the surface. In this process, N2 was used to generate the plasma and also acted as a carrier gas to transfer the ions generated from the plasma to the electrode section. In other words, because the indirect plasma method requires the plasma to be transferred to the carrier gas, a larger amount of N2 was used compared to the direct plasma method.

[0199] Subsequently, in order to transfer the transfer laminate to the negative electrode active material layer, the lithium metal layer of the transfer laminate was positioned above the negative electrode active material layer, and then a load of 40 kgf / cm was applied and rolling (roll pressing) was carried out. The transfer laminate used had a lithium release force of approximately 70-80 gf / inch. At this time, the temperature was kept at room temperature (25°C), and immediately after lamination, the PET layer of the transfer laminate was removed to pre-lithify the negative electrode.

[0200] <Example 9> In the above-described embodiment 8, the negative electrode was pre-lithified in the same manner as in embodiment 8, except that the plasma treatment speed of the negative electrode surface was 20 m / min.

[0201] <Example 10> In Example 8, the negative electrode was pre-lithified in the same manner as in Example 8, except that the plasma treatment speed of the negative electrode surface was 40 m / min.

[0202] <Example 11> In the above-described embodiment 8, the negative electrode was pre-lithified in the same manner as in embodiment 8, except that the plasma treatment conditions for the negative electrode surface were set to 60 kHz (3.1 kW (5.5 kV)) and N2 (700 slm) and CDA (28 slm) were flowed to generate plasma, and the negative electrode was treated by passing it through at a speed of 1 m / min.

[0203] <Example 12> The negative electrode was pre-lithified in the same manner as in Example 11, except that the plasma treatment speed of the negative electrode surface was 20 m / min.

[0204] <Example 13> The negative electrode was pre-lithified in the same manner as in Example 11, except that the plasma treatment speed of the negative electrode surface was 40 m / min.

[0205] <Example 14> In Example 8, the negative electrode was pre-lithified in the same manner as in Example 8, except that the lithium release force of the transfer laminate was adjusted to approximately 700-800 gf / inch.

[0206] <Comparative Example 1> In the above-described Example 1, the negative electrode was pre-lithified in the same manner as in Example 1, except that the negative electrode surface was not plasma-treated.

[0207] <Comparative Example 2> In Example 7, the negative electrode was pre-lithified in the same manner as in Example 7, except that the negative electrode surface was not plasma-treated.

[0208] <Comparative Example 3> In Comparative Example 1, the negative electrode was pre-lithified in the same manner as in Comparative Example 1, except that the lithium release force of the transfer laminate was adjusted to approximately 700-800 gf / inch.

[0209] In Examples 1-14 and Comparative Examples 1-3, the surface water contact angles before and after pretreatment were as shown in Table 1 below. The water contact angles below were measured using a POENIX-MT (SEO Corporation) instrument, and the results shown in Table 1 below represent the average value after three repeated measurements using the sample under each condition.

[0210] [Table 1]

[0211] In Table 1, Examples 1 to 7 show the water contact angles obtained by plasma treatment of the negative electrode active material layer surface, and Examples 8 to 14 show the water contact angles obtained by plasma treatment of the buffer layer surface.

[0212] From the experimental results in Table 1, it was confirmed that there is a difference in the transfer force characteristics of the lithium metal layer depending on whether or not plasma treatment is performed on the upper part of the negative electrode active material layer. It was confirmed that the transfer force is maintained even when the plasma treatment speed is greatly increased and the change in contact angle is less than 20°.

[0213] Specifically, this can be confirmed by comparing Examples 1-3, 4-6, 8-10, and 11-13. In each case, it was confirmed that the difference in water contact angle increased as the plasma treatment speed changed, resulting in a longer treatment time as the plasma treatment was performed more slowly and the surface hydrophilicity of the plasma-treated object increased.

[0214] For example, when comparing Example 1 and Example 3, the plasma processing speed (40 m / min) in Example 3 increased significantly, and the change in water contact angle was relatively small. However, even in this case, it was confirmed that the lithium metal layer exhibited excellent transfer characteristics.

[0215] Furthermore, while Examples 1 and 4 involve changing the frequency conditions of the plasma treatment, resulting in some differences in the water contact angle, it can be confirmed that differences due to the plasma treatment speed are a major factor in the water contact angle.

[0216] Furthermore, when comparing Example 1 and Example 7, it was confirmed that lithium transfer after plasma treatment was successful in both cases: when the release force of the release layer was low (70-80 gf / inch) and when the release force was high (700-800 gf / inch). This is a result of improved adhesion due to the plasma treatment effect at the interface between the negative electrode active material layer and the lithium metal layer, and it was confirmed that transfer is performed well regardless of the presence or absence of release force in the transfer laminate.

[0217] <Calculation experiment of lithium loss after pre-lithification> To confirm the amount of lithium lost after pre-lithification, a half-bisell type battery was fabricated using the negative electrode (pre-lithification process progressing) prepared in Table 1 above and a lithium metal foil (10 μm) as the counter electrode. The electrolyte used in this battery was fluoroethylene carbonate (FEC) / ethyl methyl carbonate (EMC) = 3 / 7 (volume ratio) in which 1 M LiPF6 was dissolved.

[0218] To measure lithium loss, the amount of pre-lithified lithium was determined by the difference in the initial charge capacity values ​​of the unpre-lithified electrode and the electrode after pre-lithification. The amount of lithium loss was calculated as the ratio of the pre-lithified lithium capacity to the theoretical lithium capacity. This can be expressed as the same formula as equation A-2 below, and the results are shown in Table 2 below.

[0219] [Formula A-2] Lithium loss (%) = 1 - {("Pre-lithification electrode charge capacity" - "Pre-lithification electrode charge capacity") / Theoretical capacity of lithium used during pre-lithification}

[0220] [Table 2]

[0221] In Examples 1-14, the lithium metal layer was fully transferred to the upper part of the negative electrode active material layer, and the measured lithium loss was found to be at a good level of less than 20%. In Comparative Examples 1-3, where only partial transfer was performed, the lithium loss was found to be very high.

[0222] In other words, as can be seen from Tables 1 and 2, by pre-treating the upper part of the negative electrode as in Examples 1 to 14, the interfacial adhesion between the negative electrode active material layer and the lithium metal layer is excellent, and the peelability of the transfer laminate for transfer is good. As a result, the heat generated during pre-lithiation is easily released to the outside, the generation of by-products in the pre-lithiation process is suppressed, and a relatively uniform pre-lithiation process can be carried out inside the negative electrode active material layer. [Explanation of Symbols]

[0223] 10...Base material layer 20 ···Lithium metal layer 30...Negative electrode active material layer 40 ···Negative electrode current collector layer 50...Separation membrane 60 ···Positive electrode current collector layer 70...Cathode active material layer 100 ···Transfer laminate 200 ···Negative electrode for lithium secondary batteries 300 ···Positive electrode for lithium secondary batteries

Claims

1. A step of forming a negative electrode by laminating a negative electrode current collector layer and a negative electrode active material layer on one or both sides of the negative electrode current collector layer. In the step of pre-treating the negative electrode, The steps include transferring a lithium metal layer to the pre-treated negative electrode, and Steps to activate the lithium metal layer, A method for manufacturing a negative electrode for a lithium secondary battery, including, The aforementioned pretreatment step is plasma treatment or corona treatment. The negative electrode for a lithium secondary battery satisfies the following equation 1: [Formula 1] 10° ≤ A - B ≤ 60° In the above formula 1, A represents the water contact angle of the negative electrode surface before the pretreatment, A method for manufacturing a negative electrode for a lithium secondary battery, wherein B represents the water contact angle of the negative electrode surface after the pretreatment of the negative electrode.

2. The step of laminating a negative electrode current collector layer and a negative electrode active material layer on one or both sides of the negative electrode current collector layer includes the step of coating one or both sides of the negative electrode current collector layer with a negative electrode slurry containing a negative electrode active material layer composition. The method for manufacturing a negative electrode for a lithium secondary battery according to claim 1, wherein the negative electrode active material layer composition comprises a silicon-based active material.

3. The method for manufacturing a negative electrode for a lithium secondary battery according to claim 1, wherein the aforementioned pretreatment step is performed using an indirect atmospheric pressure plasma method.

4. In the indirect atmospheric pressure plasma method, the plasma is transported using a plasma processing gas. The method for manufacturing a negative electrode for a lithium secondary battery according to claim 3, wherein the plasma processing gas comprises nitrogen gas and 3% to 10% oxygen gas relative to the nitrogen gas.

5. The method for manufacturing a negative electrode for a lithium secondary battery according to claim 3, wherein the frequency of the indirect atmospheric pressure plasma method is 50 kHz to 250 kHz, the power is 1 kW to 10 kW, and the processing speed range is 1 m / min to 40 m / min.

6. A method for manufacturing a negative electrode for a lithium secondary battery according to claim 1, further comprising the step of laminating a negative electrode current collector layer and a negative electrode active material layer on one or both sides of the negative electrode current collector layer, and then coating the side of the negative electrode active material layer opposite to the side in contact with the negative electrode current collector layer with a buffer layer composition to form a buffer layer.

7. The method for manufacturing a negative electrode for a lithium secondary battery according to claim 1, wherein, in the step of activating the lithium metal layer, the activation reaction occurs within 30 minutes to 3 hours under conditions of 25°C and 1 atm.

8. The step of transferring the lithium metal layer to the pre-treated negative electrode is as follows: A step of preparing a transfer laminate including a substrate layer and a lithium metal layer provided on the substrate layer, The steps of laminating the transfer laminate onto the negative electrode active material layer such that the opposite side of the lithium metal layer that contacts the substrate layer contacts the opposite side of the negative electrode active material layer that contacts the negative electrode current collector layer, and Steps to remove the aforementioned substrate layer, A method for manufacturing a negative electrode for a lithium secondary battery according to claim 1, including the method described in claim 1.

9. The method for manufacturing a negative electrode for a lithium secondary battery according to claim 8, further comprising a release layer on the surface of the transfer laminate in contact with the substrate layer and the lithium metal layer.

10. The method for manufacturing a negative electrode for a lithium secondary battery according to claim 2, wherein the silicon-based active material comprises at least one selected from the group consisting of SiOx (x=0), SiOx (0<x<2), SiC, and Si alloys.

11. The method for manufacturing a negative electrode for a lithium secondary battery according to claim 2, wherein the silicon-based active material comprises at least one selected from the group consisting of SiOx (x = 0) and SiOx (0 < x ≤ 2), and comprises 70 parts by weight or more of SiOx (x = 0) based on 100 parts by weight of the silicon-based active material.

12. The method for manufacturing a negative electrode for a lithium secondary battery according to claim 1, wherein the thickness of the lithium metal layer is 1 μm or more and 10 μm or less.

Images