Method for manufacturing electrodes for lithium secondary batteries, transfer laminate, and lithium secondary battery including electrodes

Abstract

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

Description

Technical Field

[0001] This application claims the benefit of the filing date of Korean Patent Application No. 10-2022-0175729, filed with the Korean Intellectual Property Office on December 15, 2022, and all of its contents are incorporated herein by reference.

[0002] This application relates to a method for manufacturing an electrode for a lithium secondary battery, a transfer laminate, and a lithium secondary battery including the 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, a typical example of an electrochemical device using such electrochemical energy is a secondary battery, and its usage areas are showing a trend of increasing more and more.

[0005] With the development of technologies related to mobile devices and the increase in demand, 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 conducted.

[0006] Generally, a secondary battery includes 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 may 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, which can be alloyed with lithium, are being considered as negative electrode materials. Among these, silicon-based materials have attracted attention due to their low cost and high capacity (4200 mAh / g).

[0008] However, when using silicon-based negative electrode active materials, a problem arises: a large initial irreversible capacity. In the charge-discharge reaction of lithium secondary batteries, lithium released from the positive electrode is inserted into the negative electrode during charging, and desorbed from the negative electrode and returned to the positive electrode during discharge. However, in the case of silicon-based negative electrode active materials, volume changes and surface side reactions are significant, and much of the lithium inserted into the negative electrode during initial charging cannot return to the positive electrode. Therefore, a problem arises in which the initial irreversible capacity is large. A large initial irreversible capacity leads to a rapid decrease in battery capacity and cycle characteristics.

[0009] To solve the aforementioned problems, methods for pre-lithifying silicon anodes containing silicon-based anode active materials are known. Known pre-lithification methods include manufacturing electrodes after lithification by physical / chemical methods such as electroplating, lithium metal transfer, and lithium metal deposition, as well as electrochemically pre-lithifying the anode.

[0010] Conventional electrochemical methods require a wet process within the electrolyte, which inherently carries risks such as fire and explosion, necessitating the creation of an inert environment. However, creating this environment is difficult due to the need to control moisture levels and other conditions using the inert gas in the room where the electrochemical process is performed. Furthermore, uniformly controlling the initial irreversible capacity requires maximizing the slow rate of pre-lithification using electrochemical methods, which increases production costs.

[0011] Furthermore, in the lithium metal transfer process in the pre-lithium process, it is difficult to transfer lithium metal safely and easily. 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, causing 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, with lithium uniformly pre-lithified 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] The lithium metal transfer step in the pre-lithiation process includes a step of transferring a lithium metal layer from a transfer laminate to the upper part of the electrode active material layer. Research has shown that forming a transfer initiation portion in the lithium metal layer facilitates the transfer of the lithium metal layer from the transfer laminate to the upper part of the electrode active material layer. Therefore, this application relates to a method for manufacturing electrodes for lithium secondary batteries, a transfer laminate, and a lithium secondary battery including these electrodes. [Means for solving the problem]

[0015] One embodiment of this specification provides a method for manufacturing an electrode for a lithium secondary battery, comprising the steps of: forming an electrode current collector layer and an electrode active material layer on one or both sides of the electrode current collector layer; preparing a transfer laminate in which a base film, a transfer force improving layer, and a lithium metal layer are sequentially laminated; removing the lithium metal layer in the TD (Transverse direction) direction to form a transfer initiation portion; transferring the lithium metal layer on which the transfer initiation portion is formed to the upper part of the electrode active material layer; and removing the base film.

[0016] In another embodiment, the present invention provides a transfer laminate comprising a base film; a transfer strength improving layer formed on one surface of the base film; and a lithium metal layer formed on the opposite side of the transfer strength improving layer from the surface in contact with the base film, wherein the lithium metal layer includes a portion where lithium metal has not been deposited.

[0017] Finally, in one embodiment of the present application, a lithium secondary battery is provided comprising a positive electrode for a lithium secondary battery; a negative electrode for a lithium secondary battery; a separator membrane provided between the positive electrode and the negative electrode; and an electrolyte, wherein at least one of the positive electrode and the negative electrode for a lithium secondary battery is an electrode for a lithium secondary battery manufactured by the method of the present application. [Effects of the Invention]

[0018] A method for manufacturing an electrode for a lithium secondary battery according to one embodiment of the present invention utilizes a lithium metal transfer process, and specifically includes the aforementioned transfer initiation section for which the lithium metal layer to be transferred is easily transferred to the upper part of the electrode active material layer, characterized by excellent surface uniformity and the ability to suppress the generation of by-products.

[0019] In other words, one embodiment of this application includes a step of preparing a transfer laminate in which a base film, a transfer strength improving layer, and a lithium metal layer are sequentially laminated, followed by a step of removing the lithium metal layer in the TD (Transverse direction) direction to form a transfer initiation section, and includes a transfer initiation section from which the lithium metal layer has been removed. When this is included, the transferability to the upper part of the electrode active material layer can be improved even when the transfer speed is fast, and the base film can be directly peeled off from the transfer laminate. As a result, the heat generated during pre-lithiation is released smoothly, and the generation of by-products can be suppressed compared to when a base film is laminated during pre-lithiation. [Brief explanation of the drawing]

[0020] [Figure 1] This figure shows a process for transferring lithium metal to an electrode for a lithium secondary battery according to one embodiment of the present application. [Figure 2] This figure shows the experimental results according to Example 1 of this application. [Figure 3] This figure shows the experimental results obtained using Comparative Example 1 of this application. [Modes for carrying out the invention]

[0021] Before describing the present invention, let us first define some terms.

[0022] In this specification, when a part "includes" a component, this means that, unless otherwise stated, it may include other components rather than excluding them.

[0023] In this specification, "p~q" means "p or greater and q or less".

[0024] 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 a BELSORP-mini II manufactured by BEL Japan. In other words, in this application, BET specific surface area can mean the specific surface area measured by the above measurement method.

[0025] 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. Alternatively, the particle size distribution may be measured using the laser diffraction method. Specifically, after dispersing the powder to be measured in a dispersion medium, it is introduced into a commercially available laser diffraction particle size analyzer (e.g., Microtrac S3500), and the difference in diffraction patterns due to particle size is measured as the particles pass through the laser beam to calculate the particle size distribution.

[0026] In this specification, the statement that a polymer contains a monomer as a monomer unit 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 is said to contain a monomer, this is interpreted as being equivalent to the polymer containing a monomer as a monomer unit.

[0027] In this specification, the term "polymer" is understood to be used in a broad sense, including copolymers, unless otherwise explicitly stated as "homopolymer."

[0028] 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.

[0029] 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 embodied in various different forms and is not limited to the following description.

[0030] One embodiment of this specification provides a method for manufacturing an electrode for a lithium secondary battery, comprising the steps of: forming an electrode current collector layer and an electrode active material layer on one or both sides of the electrode current collector layer; preparing a transfer laminate in which a base film, a transfer force improving layer, and a lithium metal layer are sequentially laminated; removing the lithium metal layer in the TD (Transverse direction) direction to form a transfer initiation portion; transferring the lithium metal layer on which the transfer initiation portion is formed to the upper part of the electrode active material layer; and removing the base film.

[0031] Figure 1 shows the structure of the transfer laminate and the transfer process in the method for manufacturing electrodes for lithium secondary batteries according to this application.

[0032] In one embodiment of this application, removing the lithium metal layer in the TD (Transverse direction) direction may mean forming a transfer initiation portion perpendicular to the MD (Machine direction) direction in a roll-to-roll process.

[0033] In other words, the base film 10, the transfer strength improving layer 35, and the lithium metal layer 20 can be continuously laminated by a roll-to-roll (R2R) process to form a transfer laminate. In this process, the direction in which the roll-to-roll (R2R) process proceeds can be defined as the MD direction, and the direction perpendicular to the process proceeding direction can be defined as the TD direction. In this process, the lithium metal layer can be removed in the TD (Transverse direction) direction to form the transfer start section 300.

[0034] Ultimately, in a transfer laminate, the MD direction can represent the width of the transfer laminate, and the TD direction can represent the length of the transfer laminate.

[0035] In one embodiment of this application, the electrode may be a negative electrode or a positive electrode.

[0036] A method for manufacturing electrodes for lithium secondary batteries according to one embodiment of the present invention utilizes a lithium metal transfer process. Specifically, the present invention relates to a method for pre-lithifying electrodes for lithium secondary batteries that satisfies the conditions for the transfer of the lithium metal layer to be easily transferred to the upper part of the electrode active material layer, exhibits excellent surface uniformity, and suppresses the generation of by-products.

[0037] Figure 2 shows a step of transferring a lithium metal layer to an electrode for a lithium secondary battery according to one embodiment of this application. Specifically, it shows a step of laminating a transfer laminate 100, which is formed by sequentially laminating a base film 10, a transfer strength improving layer 35, and a lithium metal layer 20 onto an electrode 200 for a lithium secondary battery formed from an electrode current collector layer 40 and an electrode active material layer 30, and then removing the base film 10 from the transfer laminate 100. At this time, it can be confirmed that a transfer start section (lithium-unladen section) 300 is included.

[0038] In other words, the problems related to transfer force, such as reverse transfer, in the conventional lithium metal layer transfer process were solved by forming the transfer initiation section as described above.

[0039] Hereinafter, specific details of the method for manufacturing an electrode for a lithium secondary battery according to the invention of the present application will be described.

[0040] The method for manufacturing an electrode for a lithium secondary battery according to an embodiment of the present application may include a step of forming an electrode current collector layer and an electrode active material layer on one or both surfaces of the electrode current collector layer.

[0041] In one embodiment of the present application, the step of forming an electrode current collector layer and an electrode active material layer on one or both surfaces of the electrode current collector layer includes a step of coating an electrode slurry containing an electrode active material layer composition on one or both surfaces of the electrode current collector layer, and the electrode active material layer composition includes one or more selected from the group consisting of an electrode active material, an electrode conductive material, and an electrode binder, and provides a method for manufacturing an electrode for a lithium secondary battery.

[0042] At this time, the electrode active material includes a silicon-based active material, and the silicon-based active material includes one or more selected from the group consisting of SiOx (x = 0), SiOx (0 < x < 2), SiC, and Si alloy, and provides a method for manufacturing an electrode for a lithium secondary battery.

[0043] In one embodiment of the present application, the electrode may be a negative electrode, and hereinafter, an explanation of the method for manufacturing a negative electrode for a lithium secondary battery will be described.

[0044] The method for manufacturing an electrode for a lithium secondary battery according to an embodiment of the present application may include a step of forming a negative electrode current collector layer and a negative electrode active material layer on one or both surfaces of the negative electrode current collector layer.

[0045] In one embodiment of this application, the negative electrode current collector layer typically 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 may be made of materials such as copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., or aluminum-cadmium alloy. Furthermore, fine irregularities may be formed on the surface to strengthen the bonding force of the negative electrode active material, and it may be used in various forms such as film, sheet, foil, net, porous body, foam, or nonwoven fabric.

[0046] 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.

[0047] However, the thickness may vary depending on the type and application of the negative electrode used, and is not limited thereto.

[0048] In one embodiment of this application, the step 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 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, wherein the negative electrode active material layer composition contains one or more selected from the group consisting of a negative electrode active material, a negative electrode conductive material, and a negative electrode binder, thereby providing a method for manufacturing an electrode for a lithium secondary battery.

[0049] In one embodiment of this application, the negative electrode slurry may include a negative electrode active material layer composition and a slurry solvent.

[0050] In one embodiment of this application, the solid content of the negative electrode slurry may be 5% or more and 40% or less.

[0051] In another embodiment, the solid content of the negative electrode slurry may be in the range of 5% to 40%, preferably 7% to 35%, and more preferably 10% to 30%.

[0052] In another embodiment, the solid content of the negative electrode slurry can satisfy the range of 5% or more and 55% or less, preferably 7% or more and 35% or less, and more preferably 10% or more and 30% or less.

[0053] The solid content of the negative electrode slurry refers to the content of the negative electrode active material layer composition contained in the negative electrode slurry, and may refer to the content of the negative electrode active material layer composition based on 100 parts by weight of the negative electrode slurry.

[0054] When the solid content of the negative electrode slurry satisfies the aforementioned range, the viscosity is appropriate during the formation of the negative electrode active material layer, minimizing the caking phenomenon of the particles in the negative electrode active material layer composition, and enabling efficient formation of the negative electrode active material layer.

[0055] In one embodiment of this application, the slurry solvent is not limited as long as it can dissolve the negative electrode active material layer composition, but specifically, distilled water may be used.

[0056] In one embodiment of this application, the negative electrode may be formed by coating and drying the negative electrode slurry on a negative electrode current collector layer.

[0057] The aforementioned drying step can dry the slurry solvent in the negative electrode slurry.

[0058] In one embodiment of this application, the negative electrode active material layer composition may include one or more selected from the group consisting of a negative electrode active material, a negative electrode conductive material, and a negative electrode binder.

[0059] In one embodiment of the present application, a silicon-based active material may be used as the negative electrode active material, or a negative electrode containing a silicon-based active material and a carbon-based active material together may be used. In this case, a lithium secondary battery with improved various performances such as cycle life characteristics can be manufactured.

[0060] In one embodiment of the present application, the silicon-based active material may include one or more selected from the group consisting of Si particles, SiOx (0 < x < 2), SiC, and Si alloys.

[0061] 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 based on 100 parts by weight of the silicon-based active material, the SiOx (x = 0) may be included in an amount of 70 parts by weight or more.

[0062] In another embodiment, based on 100 parts by weight of the silicon-based active material, the SiOx (x = 0) may be included 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 included 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.

[0063] In one embodiment of the present application, particularly pure silicon (Si) may be used as the silicon-based active material. Using pure silicon (Si) as the silicon-based active material may mean, as described above, that when the entire silicon-based active material is based on 100 parts by weight, pure Si particles (SiOx (x = 0)) not combined with other particles or elements are included within the above range.

[0064] In the charge-discharge reaction of lithium secondary batteries, lithium released from the positive electrode is inserted into the negative electrode during charging, and desorbed from the negative electrode and returned to the positive electrode during discharging. However, in the case of silicon-based negative electrode active materials, volume changes and surface side reactions are significant, resulting in a small amount of lithium being inserted into the negative electrode during initial charging and returning to the positive electrode. This leads to a problem of a large initial irreversible capacity. A large initial irreversible capacity leads to a rapid decrease in battery capacity and cycle life.

[0065] 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 process for suppressing the generation of by-products so that when the lithium transfer process is performed in the pre-lithification process, the lithium metal layer can be easily transferred from the transfer laminate and lithium can be uniformly pre-lithified within the negative electrode active material layer.

[0066] On the other hand, the average particle size (D50) of the silicon-based active material in the present invention may be 5 μm to 10 μm, more 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 is 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 range, the contact area between the silicon particles and the conductive material is excellent due to the composite of the conductive material and the binder in the negative electrode slurry, increasing the likelihood of the conductive network being maintained and increasing the capacity retention rate. In addition, when the average particle size satisfies the above range, excessively large silicon particles are excluded, and the surface of the negative electrode is formed smoothly, thereby preventing the phenomenon of uneven current density during charging and discharging.

[0067] In one embodiment of this application, the silicon-based active material typically 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 preferably, 0.1 m 2 / g to 100.0 m 2 / g, particularly preferably, 0.2 m 2 / g to 80.0 m 2 / g, most preferably, 0.2 m 2 / g to 18.0 m 2 / g. The BET specific surface area is measured according to DIN 66131 (using nitrogen).

[0068] In one embodiment of the present application, the silicon-based active material may exist, for example, in a crystalline form or an amorphous form, and is preferably not porous. The silicon particles are preferably spherical or multi-piece particles. Alternatively, the silicon particles may have a fibrous structure or may exist in the form of a silicon-containing film or coating, but this is not as preferred.

[0069] In one embodiment of the present application, the silicon-based active material may be 60 parts by weight or more based on 100 parts by weight of the negative electrode active material layer composition.

[0070] In another embodiment, the silicon-based active material may be contained 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 contained 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.

[0071] The negative electrode active material layer composition according to the present application contains, together, a negative electrode conductive material and a negative electrode binder that can control the volume expansion rate during the charge and discharge process even when using a silicon-based active material with a significantly high capacity within the above range. Even when containing the silicon-based active material within the above range, the performance of the negative electrode is not deteriorated, and it has the characteristic of excellent output characteristics during charging and discharging.

[0072] In one embodiment of this application, the silicon-based active material may have a non-spherical shape, and its degree of 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.

[0073] In this application, the circularity is determined by the following formula A, where A is the area and P is the boundary line. [Formula A] 4πA / P 2

[0074] Traditionally, graphite-based compounds were commonly used as the negative electrode active material. However, with the increasing demand for high-capacity batteries, 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.

[0075] In one embodiment of this application, the negative electrode conductive material may include one or more selected from the group consisting of point conductive materials, planar conductive materials, and linear conductive materials.

[0076] In one embodiment of this application, the point-like conductive material can be used to improve conductivity in 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 fiber, fluorocarbon, aluminum powder, nickel powder, zinc oxide, potassium titanate, titanium oxide, and polyphenylene derivatives, and preferably contains carbon black in terms of embodying high conductivity and having excellent dispersibility.

[0077] 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 It may be less than or equal to / g, preferably 45m 2 / g or more 65m 2 / g or less, more comfortably, 50m 2 / g or more 60m 2 It may be less than / g.

[0078] In one embodiment of this application, the particle size of the dot-like conductive material may be 10 nm to 100 nm, preferably 20 nm to 90 nm, and more preferably 40 nm to 60 nm.

[0079] In one embodiment of this application, the negative electrode conductive material may include a planar conductive material.

[0080] The aforementioned planar conductive material can improve conductivity by increasing surface contact between silicon particles within the negative electrode, while simultaneously suppressing the disruption of the conductive path due to volume expansion. It is used in concepts that include bulk-type conductive materials or plate-type conductive materials.

[0081] In one embodiment of this application, the planar conductive material may include at least one selected from the group consisting of plate-type graphite, graphene, graphene oxide, and graphite flakes, and preferably plate-type graphite.

[0082] In one embodiment of this application, the average particle size (D50) of the planar conductive material may be 2 μm to 7 μm, more specifically 3 μm to 6 μm, and more specifically 4 μm to 5 μm. When this range is satisfied, the particle size is sufficient, so the viscosity of the negative electrode slurry does not increase excessively, and dispersion becomes easy. Therefore, when dispersion is performed using the same apparatus and time, the dispersion effect is excellent.

[0083] In one embodiment of this application, a negative electrode active material layer 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.

[0084] In one embodiment of this application, the planar conductive material may be a high specific surface area planar conductive material with a high BET specific surface area, or a low specific surface area planar conductive material.

[0085] In one embodiment of this application, the planar conductive material may be a high specific surface area planar conductive material or a low specific surface area planar conductive material without limitation. However, since the electrode performance of the planar conductive material according to this application may be affected to some extent by dispersion, it is particularly preferable to use a low specific surface area planar conductive material that does not cause dispersion problems.

[0086] 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.

[0087] In another embodiment, the planar conductive material has a BET specific surface area of ​​5 m². 2 / g or more 500m 2 It may be less than / g, 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.

[0088] 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 Less than or equal to / g, preferably 80m 2 / g or more 300m 2 Less than / g, more comfortably, 100m 2 / g or more 300m 2 The range of / g or less may also be satisfied.

[0089] 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.

[0090] In addition, linear conductive materials such as carbon nanotubes can be used as the negative electrode conductive material. The carbon nanotubes may be bundle-type carbon nanotubes. The bundle-type carbon nanotubes may contain multiple carbon nanotube units. Specifically, here, "bundle type" refers to a secondary shape in the form of a bundle or rope, where multiple carbon nanotube units are arranged in parallel with substantially the same orientation in the longitudinal direction of the carbon nanotube units, or are intertwined. The carbon nanotube units have a graphite sheet with a nanoscale diameter in a cylindrical shape and have an sp2 bond structure. In this case, depending on the angle and structure in which the graphite sheet is wound, it can exhibit conductive or semiconductor properties. The bundle-type carbon nanotubes can be dispersed more uniformly during the manufacturing of the negative electrode compared to entangled type carbon nanotubes, and a conductive network can be smoothly formed within the negative electrode, thereby improving the conductivity of the negative electrode.

[0091] 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.

[0092] 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 15 to 25 parts by weight, based on 100 parts by weight of the negative electrode active material layer composition.

[0093] The negative electrode conductive material of this application has a completely different configuration from the conductive material applied to the positive electrode. Specifically, the negative electrode conductive material of this application plays a role in controlling the contact points between silicon-based active materials, which experience very large volume expansion due to charging and discharging. The positive electrode conductive material, on the other hand, acts as a buffer during rolling while partially imparting conductivity. Its configuration and role are completely different from the negative electrode conductive material of the present invention.

[0094] 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. That is, conductive materials used in electrodes with graphite-based active materials simply have particles that are smaller than the active material, and therefore have the properties of improving output characteristics and imparting some conductivity. Thus, their structure and role are completely different from negative electrode conductive materials applied together with silicon-based active materials, as in the present invention.

[0095] In one embodiment of this application, the planar conductive material used as the anode conductive material has a structure and role different from that of carbon-based active materials generally used as anode active materials. Specifically, the carbon-based active material used as the anode active material may be artificial graphite or natural graphite, and refers to a material that is processed into a spherical or point-like form to facilitate the storage and release of lithium ions.

[0096] 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 represented as plate-type 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.

[0097] 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-shaped 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.

[0098] 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 substance that plays a role in storing or releasing lithium.

[0099] 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 form and a BET specific surface area of ​​5m². 2 It may be more than / g.

[0100] 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 are substituted with Li, Na, or Ca, or may contain a variety of copolymers thereof.

[0101] A binder according to one embodiment of this application plays a role in controlling the negative electrode active material and negative electrode conductive material in order to prevent twisting and structural deformation of the negative electrode structure during volume expansion and relaxation of the silicon-based active material. Any ordinary negative electrode binder can be applied as long as it fulfills the above role. Specifically, an aqueous binder may be used, and more specifically, a PAM-based binder may be used.

[0102] In one embodiment of this application, the negative electrode binder may be included in a quantity of 30 parts by weight or less, preferably 25 parts by weight or less, more preferably 20 parts by weight or less, based on 100 parts by weight of the negative electrode active material layer composition, and may also be included in a quantity of 1 part by weight or more, or 3 parts by weight or more.

[0103] In one embodiment of this application, the electrode may be a positive electrode, and the following describes a method for manufacturing a positive electrode for a lithium secondary battery. In this case, the same description as the method for manufacturing a negative electrode for a lithium secondary battery described above may apply, the only difference being that it is a positive electrode.

[0104] A method for manufacturing an electrode for a lithium secondary battery according to one embodiment of this application may include the step of forming a positive electrode current collector layer and a positive electrode active material layer on one or both sides of the positive electrode current collector layer.

[0105] In one embodiment of this application, the positive electrode current collector is not particularly limited as long as it is conductive without inducing a chemical change in the battery. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surfaces treated with carbon, nickel, titanium, silver, etc. may be used. The positive electrode current collector may also have a thickness of 3 μm to 500 μm, and fine irregularities can be formed on the surface of the positive electrode current collector layer to enhance the adhesion of the positive electrode active material. For example, it may be used in various forms such as films, sheets, foils, nets, porous materials, foams, and nonwoven fabrics.

[0106] The thickness of the positive electrode current collector layer may vary depending on the type and application of the negative electrode used, and is not limited thereto.

[0107] In one embodiment of this application, the step of forming a positive electrode current collector layer and a positive electrode active material layer on one or both sides of the positive electrode current collector layer includes the step of coating one or both sides of the positive electrode current collector layer with a positive electrode slurry containing a positive electrode active material layer composition, wherein the positive electrode active material layer composition contains one or more selected from the group consisting of a positive electrode active material, a positive electrode conductive material, and a positive electrode binder, thereby providing a method for manufacturing an electrode for a lithium secondary battery.

[0108] In one embodiment of this application, the contents for the positive electrode slurry may be the same as those for the negative electrode slurry described above, the only difference being that it is the positive electrode.

[0109] In one embodiment of this application, the positive electrode active material layer composition may include one or more selected from the group consisting of a positive electrode active material, a positive electrode conductive material, and a positive electrode binder.

[0110] 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 c3Lithium 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 be Li metal.

[0111] In one embodiment of this application, a method for manufacturing an electrode for a lithium secondary battery is provided, wherein the electrode active material includes a positive electrode active material, and the positive electrode active material includes one or more selected from the group consisting of Ni, Co, Mn, LTO, LFP, RuO2, Nb2O5, Mn3O4, Fe2O3, and Co3O4.

[0112] The positive electrode may include a sacrificial positive electrode material, and any type of material used in the industry may be used without limitation.

[0113] 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 in the battery without causing chemical changes. 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. One of these alone or a mixture of two or more may be used.

[0114] Furthermore, the positive electrode binder plays a role in improving 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), polyvinylidene 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 or more of these may be used.

[0115] Furthermore, the content of the positive electrode active material, positive electrode conductive material, and positive electrode binder contained in the positive electrode active material layer composition can be similarly determined to those applied to the negative electrode active material layer composition described above.

[0116] Generally, the pre-lithiation process involves chemically or physically pre-lithifying a lithium metal layer onto an electrode, and may be carried out by a lithium metal transfer process, lithium metal powder deposition, electrochemical process, or lithium metal deposition process. The pre-lithiation process according to this application may include a lithium metal transfer process.

[0117] In the lithium metal layer transfer process, the highly reactive lithium metal can be transferred more stably to the top of the electrode active material layer. In this process, a step is needed to easily transfer the lithium metal layer from the transfer laminate to the top of the electrode active material layer.

[0118] One embodiment of this application includes the steps of: preparing a transfer laminate in which a base film, a transfer strength improving layer, and a lithium metal layer are sequentially laminated; transferring the lithium metal layer on which the transfer start portion is formed to the upper part of the electrode active material layer; and removing the base film.

[0119] In this process, the step of removing the lithium metal layer in the TD (Transverse direction) direction to form a transfer initiation section includes, after the step of preparing a transfer laminate in which the base film, the transfer strength improving layer, and the lithium metal layer are sequentially laminated, the step of removing the lithium metal layer using a tape or knife.

[0120] Specifically, the transfer initiation portion can be formed as a line by removing the lithium metal layer in the TD (Transverse direction) direction using a knife, and the width of the transfer initiation portion may be 30 μm or more.

[0121] In another embodiment, the width of the transfer initiation portion may be 30 μm or more, preferably 35 μm or more, more preferably 40 μm or more, and 100 μm or less, preferably 90 μm or less, and more preferably 80 μm or less.

[0122] As described above, when the transfer initiation portion is formed with the aforementioned width, the transferability to the upper part of the electrode active material layer can be improved even at high transfer speeds, and the base film can be immediately peeled off from the transfer laminate. This allows for smoother release of heat generated during pre-lithiation, resulting in a characteristic that suppresses the generation of by-products compared to when the base film is laminated during pre-lithiation.

[0123] In one embodiment of this application, the transfer start portion may include one or more line shapes.

[0124] In one embodiment of this application, after forming a lithium metal layer, the lithium metal layer is removed first from the portion where the transfer is to be initiated to form a transfer initiation portion, but its form is not limited.

[0125] In one embodiment of this application, the deposition method for depositing the lithium metal layer onto the substrate film on which the transferability-enhancing layer is formed may be selected from among, 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 may be used.

[0126] In this case, the electrode for the lithium secondary battery on which the transfer laminate is stacked is subjected to a load of 5 kgf / cm². 2 ~500 kgf / cm² 2 The lamination process may be carried out via roll pressing by applying a load. This is followed by a step of removing the base film.

[0127] In one embodiment of this application, the base film can be used without limitation as long as it has the characteristics of being able to withstand process conditions such as high temperature during the stage of depositing lithium metal, and being able to prevent the reverse peeling problem in which the lithium metal is transferred onto the base film during the winding step for transferring the deposited lithium metal.

[0128] Specifically, in one embodiment of this application, the base film may be one or more selected from the group consisting of polyethylene terephthalate (PET), polyimide (PI), poly(methyl methacrylate) (PMMA), polypropylene, polyethylene, and polycarbonate.

[0129] In one embodiment of this application, the thickness of the base film 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 less, or 10 μm or more and 100 μm or less.

[0130] In one embodiment of this application, the thickness of the lithium metal layer may be 1 μm or more and 10 μm or less, and preferably 3 μm or more and 10 μm or less.

[0131] By ensuring that the thickness of the base film and the lithium metal layer meets the specified range, the lithium metal layer can be efficiently transferred to the electrode active material layer and reverse transfer can be prevented.

[0132] In one embodiment of this application, a method for manufacturing an electrode for a lithium secondary battery is provided, which includes a transferability-enhancing layer on the surface of the transfer laminate in contact with the substrate film and the lithium metal layer in order to improve the peelability of the lithium metal layer, ensure transferability to the electrode active material layer, and serve as a protective layer after the transfer of the lithium metal layer.

[0133] In other words, the base film may have a transfer-enhancing layer formed on at least one surface, or it may have a transfer-enhancing layer formed on both surfaces. The transfer-enhancing layer prevents the reverse delamination problem in which the lithium metal layer is transferred onto the base film during the winding process for transferring the deposited lithium metal layer to the electrode, and also allows for easy separation of the base film after the lithium metal has been transferred onto the electrode active material layer.

[0134] The transfer strength improving 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.

[0135] In one embodiment of this application, the transferability-enhancing layer may include poly(methyl methacrylate) (PMMA).

[0136] In one embodiment of this application, the transfer strength improving layer may 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 that can be used in the industry to form a coating layer may be employed.

[0137] In one embodiment of this application, the present invention provides a step of laminating the transfer laminate onto the electrode active material layer such that the opposite surface of the lithium metal layer that contacts the transfer power improving layer contacts the opposite surface of the electrode active material layer that contacts the electrode current collector layer.

[0138] In this process, the lamination step is carried out under temperature conditions of 20°C to 90°C and a load of 5 kgf / cm². 2 ~500 kgf / cm² 2 Lamination may be performed under these pressure conditions.

[0139] In one embodiment of this application, the lamination step may satisfy pressurizing conditions of 5 kgf / cm to 500 kgf / cm, preferably 10 kgf / cm to 150 kgf / cm.

[0140] However, temperature conditions may be omitted during the lamination stage. In particular, if the lamination stage satisfies the aforementioned pressurization conditions, the pre-lithiation rate of the lithium metal layer can be smoothly adjusted, thereby suppressing the generation of large amounts of oxides and nitrides during the transfer process. Furthermore, by satisfying the aforementioned pressurization range, the lithium metal is smoothly transferred to the upper part of the electrode active material layer, and the problem of reverse transfer does not occur.

[0141] After the lamination step, pre-lithiation of the electrode active material layer with a highly reactive lithium metal may be performed, or the reaction may not proceed and pre-lithiation may be performed during battery assembly.

[0142] One embodiment of this application provides a method for manufacturing an electrode for a lithium secondary battery, comprising the step of pre-lithifying the electrode active material layer after the step of removing the substrate film, wherein the pre-lithification step of the electrode active material layer is performed within 30 minutes to 7 days after transferring lithium metal.

[0143] In conventional lithium metal layer transfer processes, there was a problem in that it was difficult to peel off the base film during the pre-lithiation process after the transfer laminate was laminated. As a result, pre-lithiation was performed with the base film not removed, and the heat generated during pre-lithiation was blocked by the base film and not released, leading to the formation of by-products on the surface during the pre-lithiation of lithium metal. The pre-lithiation method for lithium secondary battery electrodes according to this application has the advantage that, by forming the transfer initiation portion as described above, the base film can be easily peeled off immediately after laminating the transfer laminate, and the generation of by-products during pre-lithiation can be suppressed.

[0144] In one embodiment of this application, the lithium metal layer is not transferred alone, but the transfer-enhancing layer and the lithium metal are transferred together to the upper part of the electrode active material layer. In this case, the transfer-enhancing layer can also serve as a protective layer that can prevent the highly reactive lithium metal layer from reacting in air.

[0145] In one embodiment of this application, the step of pre-lithifying the electrode active material layer may be included.

[0146] The invention provides a method for manufacturing electrodes for lithium secondary batteries, wherein the step of pre-lithifying the electrode active material layer is performed within 30 minutes to 24 hours under conditions of 25°C and 1 atm.

[0147] The aforementioned pre-lithiation step is a step in which conditions are set for the diffusion of lithium metal into the 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 electrode active material layer has completely disappeared.

[0148] In one embodiment of this application, the activation reaction time may be 30 minutes to 7 days, preferably 1 hour to 6 hours.

[0149] One embodiment of this application provides a transfer laminate comprising a base film; a transfer strength improving layer formed on one surface of the base film; and a lithium metal layer formed on the surface of the transfer strength improving layer opposite to the surface in contact with the base film, wherein the lithium metal layer includes a portion where lithium metal has not been deposited.

[0150] In one embodiment of this application, a transfer laminate is provided in which the width of the lithium metal undeposited portion is 30 μm or more. In this case, the undeposited portion may have the same meaning as the transfer initiation portion described above.

[0151] In the aforementioned transfer laminate, the above-described components may be applied to each component.

[0152] In one embodiment of this application, a lithium secondary battery is provided, comprising a positive electrode for a lithium secondary battery; a negative electrode for a lithium secondary battery; a separator membrane provided between the positive electrode and the negative electrode; and an electrolyte, wherein at least one of the positive electrode and the negative electrode for a lithium secondary battery is an electrode for a lithium secondary battery manufactured by the method of this application.

[0153] In this case, the transfer power improving layer 35 used during pre-lithiation may be removed as described above, thereby preventing unnecessary increases in resistance by not remaining on the top of the electrode. That is, the transfer power improving layer may be used to improve transfer power and to protect the lithium metal layer before pre-lithiation, and may be removed before the electrolyte is injected.

[0154] In one embodiment of this application, the electrolyte can be an organic liquid electrolyte, an inorganic liquid electrolyte, a solid polymer electrolyte, a gel-type polymer electrolyte, a solid inorganic electrolyte, or a molten inorganic electrolyte, which can be used in the manufacture of lithium secondary batteries, and is not limited to these.

[0155] Specifically, the electrolyte may contain a non-aqueous organic solvent and a metal salt.

[0156] 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, gamma-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.

[0157] In particular, among the carbonate-based organic solvents, ethylene carbonate and propylene carbonate, which are cyclic carbonates, are suitable for use because they are high-viscosity organic solvents, have high dielectric constants, and dissociate lithium salts well. Furthermore, by mixing such cyclic carbonates with linear carbonates with low viscosity and low dielectric constant, such as dimethyl carbonate and diethyl carbonate, in appropriate ratios, electrolytes with high electrical conductivity can be produced, making them even more suitable for use.

[0158] The metal salt may be a lithium salt, and the lithium salt is a substance that is easily soluble in the non-aqueous electrolyte, for example, the anion of the lithium salt may be 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 may use one or more selected from the group consisting of the following:

[0159] In addition to the components of the electrolyte, the electrolyte may further contain one or more additives for the purpose of improving the battery's lifespan, suppressing the decrease in battery capacity, and improving the battery's discharge capacity, such as haloalkylene carbonate compounds like difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glyme, hexalic acid 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.

[0160] One embodiment of the present invention provides a battery module including the secondary battery as a unit cell, and a battery pack including the same. Since the battery module and battery pack include the secondary battery having high capacity, high rate characteristics and cycle characteristics, they may 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]

[0161] The following are preferred embodiments to aid in understanding the present invention. However, these embodiments are merely illustrative of the present description, and it will be obvious to those skilled in the art that various changes and modifications are possible within the scope of the present description and the technical concept, and such variations and modifications naturally fall within the scope of the claims.

[0162] (Manufacturing example) <Manufacturing of Transfer Layers> <Example 1> A release layer capable of improving transfer strength was coated onto the top of the PET layer to form a transfer laminate. Next, lithium metal was deposited onto the top of the PET substrate at a thickness of 6 μm using a PVD method to form a lithium metal layer, thereby producing a transfer laminate.

[0163] In this process, a transfer start line (line) approximately 40 μm in size was constructed on the upper end of the transfer laminate using a knife. The transfer start line is a state in which only the Li portion of the PET film on which lithium has been deposited has been removed.

[0164] <Example 2> In the above-described embodiment, the transfer laminate was manufactured in the same manner as in embodiment 1, except that a transfer start section (line) with a size of approximately 60 μm was constructed at the upper end of the transfer laminate using a knife.

[0165] <Example 3> In the above-described embodiment 1, the transfer laminate was manufactured in the same manner as in embodiment 1, except that a transfer start section (line) with a size of approximately 120 μm was constructed at the upper end of the transfer laminate using a knife.

[0166] <Comparative Example 1> A release layer capable of improving transfer strength was coated onto the top of the PET layer to form a lithium metal layer. Next, lithium metal was deposited onto the top of the PET substrate at a level of 6 μm using a PVD method to form a lithium metal layer, thereby manufacturing a transfer laminate.

[0167] In other words, it was formed in the same manner as in Example 1, except that a transfer initiation portion was not formed.

[0168] <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 as a solvent for negative electrode slurry formation (solid content concentration 25% by weight).

[0169] As a mixing method, the conductive material, binder, and thickener were dispersed with water using a homo mixer at 2500 rpm for 30 minutes, and then the active material was added. After that, the mixture was dispersed at 2500 rpm for another 30 minutes to produce a slurry.

[0170] 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: 15 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%).

[0171] Subsequently, in order to transfer the transfer laminate to the negative electrode active material layer, the lithium metal of the transfer laminate was positioned on top of the negative electrode active material layer, and then external pressure conditions were applied and roll pressing was performed to bond the lithium metal and the negative electrode active material layer. Immediately after lamination, the PET layer of the transfer laminate was removed to pre-lithify the negative electrode.

[0172] In this application, for the experiments in Examples 1 to 3 and Comparative Example 1, the effect was confirmed by applying Nitto 31b tape to the upper front surface of the lithium metal layer and then removing it. That is, the transferability was confirmed in the pre-lithification process of the electrode by using Nitto 31b tape as described above.

[0173] Figure 2 shows the case where the transfer laminate according to Example 1 of this application is transferred using Nitto 31b tape. Specifically, in Example 1 in which the transfer start portion is formed, it can be confirmed that the entire Li metal layer is transferred onto the Nitto 31b tape, and similarly, it can be confirmed that the lithium metal is completely transferred to the transfer start portion as well.

[0174] On the other hand, Figure 3 shows the case where the transfer laminate according to Comparative Example 1 of this application is transferred using Nitto 31b tape. Specifically, in the case of Comparative Example 1, in which no transfer start portion is formed, it was confirmed that the Li metal layer was not completely transferred onto the Nitto 31b tape, and the Li metal fell off from the middle portion.

[0175] From the results described above, it was confirmed that in the case of the transfer laminates of Examples 1 to 3 of this application, when transferring to the upper part of the electrode active material layer, the lithium metal layer can be easily transferred to the upper part of the electrode active material layer by forming a transfer initiation section, and that this can solve problems such as by-products on the upper part of the electrode active material layer. Comparative Example 1 is a case in which no transfer initiation section is formed, and corresponds to a case in which the lithium metal is transferred to the upper part of the electrode active material layer unevenly. It was confirmed that the reaction does not occur uniformly, by-products are formed on the upper part of the electrode active material layer, and problems such as increased battery resistance occur.

[0176] For reference, in Example 3, the transfer initiation area is 120 μm, which is larger than that formed in Examples 1 and 2. If the transfer initiation area is too small, the effectiveness may be partially reduced. Conversely, if the transfer initiation area is large, as in Example 3, lithium consumption is greater than in Examples 1 and 2, which can lead to disposal problems. However, even in this case, it was confirmed that the lithium metal layer was completely transferred compared to Comparative Example 1. [Explanation of symbols]

[0177] 10 ···Base film 20 ···Lithium metal layer 30...electrode active material layer 35... Transfer force improvement layer 40 ···Electrode current collector layer 100 ···Transfer laminate 200 ···Electrodes for lithium secondary batteries 300 ···Transfer start section

Claims

1. A step of forming an electrode current collector layer and an electrode active material layer on one or both sides of the electrode current collector layer; A step of preparing a transfer laminate in which a base film, a transfer strength improving layer, and a lithium metal layer are sequentially laminated; The lithium metal layer is removed in the TD (Transverse direction) direction to form a transfer initiation area (where the TD direction refers to the direction perpendicular to the direction of travel in the roll-to-roll process); A step of transferring the lithium metal layer on which the transfer initiation portion is formed to the upper part of the electrode active material layer; and Steps to remove the aforementioned base film; A method for manufacturing electrodes for lithium secondary batteries, including the method described above.

2. The method for manufacturing an electrode for a lithium secondary battery according to claim 1, wherein the width of the transfer start portion (where the width refers to the width in the MD direction, which is the direction of progress of the roll-to-roll process) is 30 μm or more.

3. The method for manufacturing an 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.

4. The method for manufacturing an electrode for a lithium secondary battery according to claim 1, wherein the transferability-enhancing layer comprises 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.

5. The step of removing the substrate film is followed by a step of pre-lithifying the electrode active material layer. The method for manufacturing an electrode for a lithium secondary battery according to claim 1, wherein the step of pre-lithifying the electrode active material layer is performed within 30 minutes to 7 days after transferring the lithium metal layer.

6. The step of forming an electrode current collector layer and an electrode active material layer on one or both sides of the electrode current collector layer includes the step of coating one or both sides of the electrode current collector layer with an electrode slurry containing an electrode active material layer composition. The method for manufacturing an electrode for a lithium secondary battery according to claim 1, wherein the composition of the electrode active material layer comprises one or more selected from the group consisting of an electrode active material, an electrode conductive material, and an electrode binder.

7. The electrode active material includes a silicon-based active material. The method for manufacturing an electrode for a lithium secondary battery according to claim 6, wherein the silicon-based active material comprises one or more selected from the group consisting of SiOx (x=0), SiOx (0<x<2), SiC, and Si alloys.

8. The electrode active material includes a positive electrode active material. The positive electrode active material is Ni, Co, Mn, LTO, LFP, RuO ２ , Nb ２ O ５ , Mn ３ O ４ , Fe ２ O ３ , and Co ３ O ４ The method for manufacturing an electrode for a lithium secondary battery according to claim 6, comprising one or more selected from the group consisting of.

9. The step of removing the lithium metal layer in the TD (Transverse direction) direction to form a transfer initiation area is: A method for manufacturing an electrode for a lithium secondary battery according to claim 1, comprising the step of preparing a transfer laminate in which a base film, a transfer strength improving layer, and a lithium metal layer are sequentially laminated, followed by the step of removing the lithium metal layer using a tape or knife.

10. The method for manufacturing an electrode for a lithium secondary battery according to claim 1, wherein the transfer initiation portion includes one or more line shapes.

11. Base film; A transfer strength improving layer formed on one surface of the base film; and A lithium metal layer formed on the side opposite to the surface of the transferability-enhancing layer that is in contact with the substrate film; A transfer laminate containing, The transfer laminate includes a lithium metal undeposited portion having a width (wherein width refers to the width in the MD direction, which is the direction of progress in the roll-to-roll process) of 30 μm or more.

Images